Design of a Reading Device Engenharia Mecânica

Transcription

Design of a Reading Device
Luís Miguel Ramos Fernandes
Dissertação para obtenção do Grau de Mestre em
Engenharia Mecânica
Júri
Presidente:
Prof. Luís Manuel Varejão Oliveira Faria
Orientador:
Prof. Arlindo José de Pinho Figueiredo e Silva
Vogal:
Prof. Mihail Fontul
Outubro de 2009
Know your enemy to know yourself,
in a hundred battles you will never peril.
Sun Tzu ( 500 BC)
Agradecimentos
Quero agradecer a todos os que sempre me apoiaram durante a realização desta dissertação, em
especial:
Ao meu orientador no Instituto Superior Técnico, Professor Arlindo Silva, por toda a disponibilidade,
conhecimentos e conselhos prestados, mesmo além fronteiras.
À Universidad de Huelva e ao meu orientador, Professor Sergio Goméz, pelo apoio e incentivo
demonstrados.
Ao Professor Mihail Fontul, pela sua disponibilidade no esclarecimento de qualquer dúvida.
Ao Virgílio Beatriz e à Rute Violante, fornecedores da ideia inicial, pela oportunidade de realização
deste trabalho.
Aos meus colegas, amigos e família, pelo apoio, incentivo e companhia.
À Dilan, pela atenção, carinho e compreensão demonstradas, especialmente nos momentos mais
difíceis da realização deste trabalho.
Aos meus pais pela oportunidade que me deram de tirar um curso superior, particularmente à minha
mãe pelo apoio incondicional durante toda a realização deste trabalho.
i
Resumo
A leitura de livros é frequentemente um processo incómodo devido ao seu peso, ao seu
formato ou à sua dificuldade de manobra. Com o intuito de agilizar todo esse processo, existem
alguns suportes de livros que permitem a sua utilização em diferentes situações, apresentando,
contudo, algumas limitações.
O presente trabalho tem como principal objectivo o desenvolvimento de um suporte de leitura
simples, de modo a que a sua utilização seja o mais flexível e prática possível e que melhore, de
algum modo, as limitações existentes como a falta de comodidade, a pouca flexibilidade na sua
utilização e a diferentes situações de leitura ou o difícil transporte, através de uma solução inovadora.
Será apresentada, inicialmente, uma primeira parte que inclui o desenvolvimento do produto
onde se fará um estudo sobre as necessidades dos utilizadores, uma análise a produtos que existem
actualmente no mercado, uma busca por patentes com possíveis sistemas inovadores a implementar
no produto, passando depois ao desenvolvimento dos primeiros esboços e respectiva avaliação
através de métodos conhecidos como o “concept scoring” ou o “concept screening” antes de chegar à
forma final do produto.
Após essa fase, prossegue-se para a selecção dos materiais bem como para o projecto de
detalhe e cálculo estrutural do dispositivo nas várias componentes. Para concluir, algumas
observações são efectuadas acerca do produto desenvolvido.
Palavras-chave: Dispositivos de leitura, Suporte simples e flexível, Comodidade, Solução
inovadora
ii
Abstract
Reading books is frequently an unpleasant process due to its weight, formats or manage
difficulties. However, in order to easier that process, there are some reading devices allowing one to
read in different situations, but still with some limitations.
The main purpose of the present work is the project and development of a book-holder, the
simplest, flexible and practical as possible that improves, somehow, the existing reading limitations
such as the lack of comfort, the lack flexibility in its usage and also for different reading or difficult
transportation situations, with an innovative solution.
In the first place, a part including the product development is presented, where one makes a
study about customers needs, an analysis of competitive products, a research for existent patents with
innovative systems to implement in the product, followed by the development of the first sketches and
respective evaluations using known methods like the concept screening and the concept scoring
before reaching the product’s final shape.
After this, follows the materials’ selection and the detailed mechanical design for the different
components of the support. Finally, some remarks are made about the developed product.
Keywords: Reading Device, Simple and flexible, Comfort, Innovative solution
iii
Table of contents
Agradecimentos __________________________________________________________ i
Resumo __________________________________________________________________ ii
Abstract_________________________________________________________________ iii
Table of contents ________________________________________________________ iv
List of tables ____________________________________________________________ vi
List of Figures ___________________________________________________________ vii
Abbreviations ____________________________________________________________ x
List of symbols ___________________________________________________________ x
CHAPTER 1
INTRODUCTION ____________________________________________ 1
CHAPTER 2
PRODUCT DESIGN AND DEVELOPMENT _____________________ 3
2.1
Identification and Interpretation of Customers Needs _____________________ 3
2.2
Organizing the Needs into a Hierarchy ___________________________________ 5
2.3
Product Specifications _________________________________________________ 6
2.4
List of Metrics _________________________________________________________ 8
2.5
Benchmarking Approach _______________________________________________ 9
2.5.1
2.5.2
2.5.3
2.5.4
2.6
Introduction _________________________________________________________________ 9
Competitive benchmarking chart based on perceived satisfaction of needs__________ 10
Competitive benchmarking chart based on metrics ______________________________ 11
Ideal and Marginally Acceptable Target Values _________________________________ 12
Concept Generation ___________________________________________________ 13
2.6.1
2.6.2
2.6.3
2.6.4
2.6.5
2.7
Introduction ________________________________________________________________
Patents ____________________________________________________________________
Concepts suggested in the inquiries ___________________________________________
Stand Supports _____________________________________________________________
Desk Supports______________________________________________________________
13
13
13
15
17
Concept Selection_____________________________________________________ 19
2.7.1
2.7.2
2.7.3
2.7.4
Concept screening – Stand supports __________________________________________
Concept scoring – Stand Supports ____________________________________________
Concept screening – Desk Supports ___________________________________________
Concept scoring – Desk Supports _____________________________________________
20
21
23
24
2.8
General Remarks______________________________________________________ 24
2.9
Product Architecture __________________________________________________ 25
2.9.1
2.9.2
2.9.3
Introduction ________________________________________________________________ 25
Concept Definition __________________________________________________________ 25
Schematic of the product_____________________________________________________ 26
2.10
Interaction between the different parts in the final concept _______________ 27
2.11
Materials _____________________________________________________________ 28
2.11.1
2.11.2
CHAPTER 3
3.1
Introduction ______________________________________________________________ 28
Selected materials ________________________________________________________ 29
DETAIL DESIGN ___________________________________________ 34
Introduction __________________________________________________________ 34
iv
3.2
Equations ____________________________________________________________ 34
3.3
Structural Calculations ________________________________________________ 41
3.3.1
3.3.2
3.3.3
3.3.4
3.3.5
3.3.6
3.3.7
3.3.8
3.3.9
3.3.10
Board, Side fixations and Bottom fixation _______________________________________
Board, locking system, lighting surface and rotary pieces _________________________
Rotary pieces, Connection-piece II, Bars and Connection-piece I __________________
Arm I and Clamp____________________________________________________________
Screws ____________________________________________________________________
Simulator surface, Top middle-component and M2 screws ________________________
Welding top middle-component and upper tube _________________________________
Upper tube and bottom tube __________________________________________________
Bottom tube, bottom middle-component and base _______________________________
Wheels selection _________________________________________________________
CHAPTER 4
41
46
49
57
64
70
73
74
76
80
CONCLUSIONS and FUTURE WORK ________________________ 81
4.1
Conclusions __________________________________________________________ 81
4.2
Future Work __________________________________________________________ 82
Bibliography ____________________________________________________________ 83
Appendix________________________________________________________________ 84
Appendix A - Questionary ____________________________________________________ 84
Appendix B - Needs-Metrics Matrix____________________________________________ 87
Appendix C - Benchmarking Information ______________________________________ 88
Appendix D - Patents ________________________________________________________ 90
Appendix E – Technical Drawings_____________________________________________ 93
v
List of tables
Tab. 2.1 - Customers statements and interpreted needs.
___________________________3 - 4
Tab. 2.2 - Customer needs importance. ________________________________________________ 5
Tab. 2.3 - Customer needs and relative importance.
_________________________________6 - 7
Tab. 2.4 - List of Metrics, relative importance and units.
_____________________________ 8
Tab. 2.5 - Competitive benchmarking chart based on perceived satisfaction of needs.
Tab. 2.6 - Competitive benchmarking chart based on metrics
_________ 10
____________________________ 11
Tab. 2.7 - Target Specifications.______________________________________________________12
Tab. 2.8 - Advantages and disadvantages from the inquiries’ concepts. ______________________14
Tab. 2.9 - Rating concepts scale._____________________________________________________19
Tab. 2.10 - Concept screening Matrix for Stand Supports._________________________________ 20
Tab. 2.11 - Concept scoring Matrix for Stand Supports. _______________________________21 - 22
Tab. 2.12 - Concept screening Matrix for Desk Supports.__________________________________23
Tab. 2.13 - Concept scoring Matrix for Desk Supports. __________________________________ 24
Tab. 2.14 - Hot Finished Steel Circular Hollow tubes._____________________________________ 31
Tab. 2.15 - Selected Material’s properties._____________________________________________ 33
Tab. 3.1 - Bending properties of a circle fillet weld.______________________________________ 40
Tab. 3.2 - Links’ type of stress in horizontal position._____________________________________ 54
Tab. 3.3 - Links’ type of stress in vertical position._______________________________________ 57
Tab. B1 - Needs – Metrics Matrix.___________________________________________________ 87
Tab, C1 - Atril de Lectura Lecco.____________________________________________________ 88
Tab. C2 - Levo Book Holder._______________________________________________________ 88
Tab. C3 - Soporte de lectura Tercera Estación._________________________________________ 89
Tab. C4 - Atril Monopié.___________________________________________________________ 89
vi
List of Figures
Fig. 1.1 - Example of a book-holder
________________________________________________ 1
Fig. 2.1 - Lecco Book Holder._________________________________________________________9
Fig. 2.2 - Levo - Stand Model.________________________________________________________9
Fig. 2.3 - Tercera Estación Book Holder.
__________________________________________9
Fig. 2.4 - Atril Monopié. _____________________________________________________________9
Fig. 2.5 - Concept A.
____________________________________________________________15
Fig. 2.6 - Concept B.
____________________________________________________________15
Fig. 2.7 - Concept C.
____________________________________________________________16
Fig. 2.8 - Concept D.
___________________________________________________________ 16
Fig. 2.9 - Concept E.
____________________________________________________________16
Fig. 2.10 - Concept F. ____________________________________________________________17
Fig. 2.11 - Concept G. ___________________________________________________________ 17
Fig. 2.12 - Concept H. ____________________________________________________________17
Fig. 2.13 - Concept I.
____________________________________________________________18
Fig. 2.14 - Concept J.
____________________________________________________________18
Fig. 2.15 - Concept K. ___________________________________________________________ 18
Fig. 2.16 - Concept L.
____________________________________________________________18
Fig. 2.17 - Reference product. _____________________________________________________ 19
Fig. 2.18 - Schematic of the product.
_______________________________________________ 26
Fig. 2.19 - Sketches of the base and middle part.
__________________________________ 27
Fig. 2.20 - Arm’s sketch – front and top views. ________________________________________ 27
Fig. 2.21 - Arm’s second part sketch.
Fig. 2.22 - Board’s sketch.
______________________________________________ 27
_____________________________________________________ 28
Fig. 2.23 - Board and transparent pieces.
Fig. 2.24 - Book holder’s arm.
________________________________________ 29
_____________________________________________________ 29
Fig. 2.25 - Graphic with settled parameters of density-price.
____________________________ 30
Fig. 2.26 - Book holder’s several middle parts. ________________________________________ 30
Fig. 2.27 - Tubes description.
_____________________________________________________ 31
Fig. 2.28 - Base’s material selection.
Fig. 2.29 - Base.
_______________________________________________32
____________________________________________________________32
Fig. 3.1 a) - Square section properties. _______________________________________________35
Fig. 3.1 b) - Circular section properties. _______________________________________________35
Fig. 3.1 c) - Hollow Circular section properties. _________________________________________36
Fig. 3.2 - Board and book fixations.
_______________________________________________ 41
Fig. 3.3 - Side fixation under maximum loading.
__________________________________ 42
Fig. 3.4 - Side fixation’s von Mises Stress in FEP Cosmos.
____________________________43
Fig. 3.5 - Bottom fixation under maximum loading – first case.
____________________________43
Fig. 3.6 - Bottom fixation under maximum loading on one side – second case.
_______________43
Fig. 3.7 - Bottom fixation’s von Mises Stress FEP Cosmos – first case. _____________________ 44
vii
Fig. 3.8 - Bottom Fixation’s von Mises Stress In FEP Cosmos – second case.
Fig. 3.9 - Board’s back side.
_______________ 45
_____________________________________________________ 46
Fig. 3.10 - Lightning Surface’s free body diagram.
Fig. 3.11 - Rotary Piece loadings.
__________________________________ 47
_______________________________________________ 47
Fig. 3.12 -Rotary Pieces, Connection-piece II, Bars and Connection-piece I.
Fig. 3.13 - Rotary Pieces, Connection-piece II and bars in detail.
_______________ 49
______________________49
Fig. 3.14 - Connection-piece II. _____________________________________________________ 49
Fig. 3.15 - 10cm bar and 5cm bar.
_______________________________________________49
Fig. 3.16 - Connection-piece II loading. _______________________________________________50
Fig. 3.17 - Arm completely stretched.
_______________________________________________51
Fig. 3.18 - Second part of the arm completely stretched under loading. _____________________ 51
Fig. 3.19 - Joint B as a free body diagram.
________________________________________ 51
Fig. 3.20 - Loadings at joint B. _____________________________________________________52
Fig. 3.21 - Section I – J of pin B.
______________________________________________ 52
Fig. 3.22 - Section I – K of pin B.
______________________________________________ 52
Fig. 3.23 - Member BD as a free body. ______________________________________________ 53
Fig. 3.24 - Joint H as a free body diagram.
________________________________________54
Fig. 3.25 - Connection-piece I. ____________________________________________________ 54
Fig. 3.26 - Connection-piece I loadings. ______________________________________________54
Fig. 3.27 - Section O – T of pin H.
______________________________________________55
Fig. 3.28 - Second part of the arm vertically.
Fig. 3.29 - Joint B free body.
_______________________________________ 56
____________________________________________________56
Fig. 3.30 - Arm I, Connection-piece I, Fixed-piece and Clamp.
__________________________ 57
Fig. 3.31 - First and second parts of the arm completely straight with each other.
Fig. 3.32 - Loadings at Arm I – first case.
_______________________________________ 58
Fig. 3.33 - Arm I’ von Mises Stress in Finite Element Cosmos – First case.
_____________ 59
Fig. 3.34 - First and second parts of the arm making a 90º angle with each other.
Fig. 3.35 - Loadings at Arm I – second case.
_______ 58
_______ 60
______________________________________ 60
Fig. 3.36 - Arm I’ von Mises Stress in Finite Element Cosmos – Second case.
_____________ 61
Fig. 3.37 - Clamp’s loadings.
___________________________________________________ 62
Fig. 3.38 - Clamp’s handle.
___________________________________________________ 63
Fig. 3.39 - Screws at the Arm I. ___________________________________________________ 64
Fig. 3.40 - Screw III.
__________________________________________________________ 65
Fig. 3.41 - Screw II.
__________________________________________________________ 66
Fig. 3.42 - Surface screw IV.
Fig. 3.43 - Screw IV.
__________________________________________________________ 68
Fig. 3.44 - Surface Screw V.
Fig. 3.45 - Screw V.
____________________________________________________69
__________________________________________________________ 69
Fig. 3.46 - Hinge of Screw V.
Fig. 3.47 - M2 screw.
____________________________________________________68
____________________________________________________70
__________________________________________________________ 71
viii
Fig. 3.48 - Simulator Surface, Top Middle-component, Upper Tube and M2 screws.
_________ 71
Fig. 3.49 - Loading and hinge. ______________________________________________________71
Fig. 3.50 - Top Middle-component, Upper Tub and Welding.
Fig. 3.51 - Welding loadings.
Fig. 3.52 - Tubes.
____________________________ 73
______________________________________________________73
____________________________________________________________75
Fig. 3.53 - Tubes’ loadings.
_____________________________________________________ 75
Fig. 3.54 - Friction Piece.
_____________________________________________________ 76
Fig. 3.55 - Base, Bottom Tube and Bottom Middle-component._____________________________ 76
Fig. 3.56 - Weld loadings.
_____________________________________________________ 77
Fig. 3.57 - Bottom Middle-component geometry_________________________________________78
Fig. 3.58 - Thread geometry.
_____________________________________________________ 78
Fig. 3.59 - Base’s loading.
_____________________________________________________ 79
Fig. 3.60 - Base’s Principal Stress in FEP Cosmos.
Fig. 3.61 - Base’s fixation space.
Fig. 3.62 - Selected Wheel.
__________________________________ 80
_______________________________________________80
_____________________________________________________ 80
Fig. D1- Patent A.
____________________________________________________________90
Fig. D2 - Patent B.
____________________________________________________________90
Fig. D3 - Patent C.
___________________________________________________________ 90
Fig. D4 - Patent D.
____________________________________________________________91
Fig. D5 - Patent E.
____________________________________________________________91
Fig. D6 - Patent F.
____________________________________________________________91
Fig. D7 - Patent G.
____________________________________________________________92
Fig. D8 - Patent H.
____________________________________________________________92
Fig. D9 - Patent I.
____________________________________________________________92
Fig. D10 - Patent J.
___________________________________________________________ 92
ix
Abbreviations
FE
– Finite Element
FEP
– Finite Element Analysis
FEP
– Finite Element Program
List of symbols
σ
- Normal Stress
τ
- Shear Stress
ε
- Strain
E
- Young’s modulus
n
- Factor of Safety
θ
- Angle
F
- Force
A
- Area
I
- Second Moment of Inertia
J
- Second Polar Moment of Area
M
- Bending Moment
T
- Torsional Moment
V
- Shear Force (Transverse Force)
m
- Mass
g
- Acceleration of Gravity
r
- Radius
t
- Thickness
b
- Width
D, d
- Diameter
f
- Coefficient of Friction
p
- Pitch
l
- Length
k
- Stiffness
C
- Stiffness’ Constant
x
CHAPTER 1 INTRODUCTION
Nowadays the development of new products has become a key process to the manufacturing
competitiveness. The increasing of competition, the decreasing of products life and the demand by
consumers requires business agility, productivity and quality.
The beginning of the Product Development Process starts when doubts arise from existing
products and as a reaction to this, other constructive solutions are chosen that need further
development. Alternative decisions in the beginning of the development process are responsible for
85% of the final costs. The changing costs during the development cycle increase because with each
change, a greater number of previous decisions can be eliminated.
Therefore it is necessary to get closer to customers and potential clients and know how to
implement their wishes, needs and difficulties. Each difficulty is one potential opportunity for the new
product and it is also very important bear in mind that the client will not elucidate us, in a research, of
what do clients think that is an obvious and obligatory characteristic. They also will not propose big
innovations.
In summary, client’s proposals have a tendency to be slightly conservative. Their wishes and
expectations are expressed but only the reasonable ones for the new product. The responsibility to
identify, according to benchmarking techniques, the primary characteristics of the product is relied on
those who generate the new concept. These, are also responsible for using creative ways, to achieve
certain innovation’s levels.
A book-holder (support) is an object designed to enhance the use of books while reading in
different situations such as in bed, on the sofa, or for those studying at a table. However it is believed
that the current designs of this product need more attention and work.
Problems like the lack of flexibility and difficult adaptation to several reading situations are
recognized and hence in need of further innovation.
There are several types of book-holders, with different characteristics or adds, but all have the
main goal of providing the reader the maximum comfort possible.
Fig. 1.1 illustrates an example of an existing book-holder.
Fig. 1.1 – Example of a book-holder.
1
The aim of this thesis is to develop an innovative solution for a book-holder, where some
disadvantages, in the existing products, can be improved. The new product can be used in more
places, situations and positions while offering high stability, user friendliness and is made for
robustness.
Besides this introductory chapter, where the structure of the present work is explained and the
objectives of this thesis are defined, this report is constituted by three additional chapters.
In Chapter 2, named “Product Design and Development”, an overview of all the steps of the
Product Development such as the identification, understanding and gathering of customers needs is
presented. This chapter also reports to a benchmarking approach and to the product specifications
and the generation of different concepts. After that the chapter focuses on the product architecture,
the establishment of product’s functions and the concept selection – conceptual formulation. This
chapter ends with a section regarding to the material selection for all components of the support.
In Chapter 3, named “Detail Design”, all the calculations made for the structure are presented.
This chapter includes dimension verifications for the different components of the structure, screws and
welding dimensioning and also a FE analysis performed in COSMOS for the critical components of the
support.
Finally, Chapter 4, entitled “Conclusions and future work”, briefly presents the conclusions derived
from this project and also some suggestions regarding possible future studies that can be made based
on this thesis’ development.
2
CHAPTER 2 PRODUCT DESIGN AND DEVELOPMENT
2.1 Identification and Interpretation of Customers Needs
In order to understand customer need and to specify the path of the product development, a
questionnaire was prepared to people that could be considered to be potential buyers.
Some questions, which in my point of view would be less relevant to the study, were not part of
the inquest in order not to make it too long and boring. That questionnaire can be seen in Appendix
A. Tab. 2.1 gathers all information collected from the questionnaire.
Tab. 2.1 - Customers statements and interpreted needs.
Topic
Customer Statement
Interpreted need
“Used with less regularity”;
Typical uses
“It has less publishing”;
• The average usage is too low;
“Used indoors, specially on bed, sofa or
• Low popularity;
table”;
• Used in and out doors where
“Used
in
the
kitchen,
bathroom,
lighting is or is not available;
garden”;
• Older people use it more often;
“Used while learning”;
• Easy assembly and disassembly;
“Using increases with older people”;
“It
Common Book
Holders
characteristics
doesn’t
satisfy
completely
the
customers needs”;
“Less stability”;
“It falls with heavier books”;
“Difficult handling with heavier books”;
• The book holder does not satisfy
the essential customer needs;
• The book holder is robust enough
to carry heavier books;
• Easy book fixing;
“Flexibility and comfort”;
Likes in Book
Holders
“It allows a convenient posture”;
• Easy reading;
“It allows a less tiring reading posture,
• The book holder is flexible, and
physically and visually”;
“Since its vertically, it occupies less
adjustable to several positions;
• Large room for the user;
space in the kitchen”;
3
Tab. 2.1 – Continued.
Topic
Customer Statement
Interpreted need
“Space for some books is insufficient
but sometimes it is also bothering
because it is exaggerated”;
Dislikes in
Book Holders
“It’s difficult to read on the sofa”;
• Suitable size for the most used
reading formats;
“Unpractical”;
• Easy carrying;
“Its weight difficult its transport to
• Cheap price;
different spaces”;
“Expensive”;
“Allows free hands to type in the
computer or to eat”;
“Advantageous and with big utility for
Several
Opinions
different reading situations”;
“Good for handicapped people”;
“It would allow me a bigger pleasure
and focus on reading”;
• Book Holder versatility provides a
simultaneous tasks at the same
time;
• Adaptable for handicapped people;
• It has lighting;
“Very positive if it allows lighting when
this is not available”;
“Different types of reading documents
and not only books”;
Suggested
improvements
• It is possible to read different
“Book Holder usage on the belly”;
document and not only books, in
“Design is important”;
several positions;
“Book Holder as a decoration piece
ready to be used”;
• Simple Design, pleasant, also used
for decoration;
“The Book Holder must be light”;
• Low weight;
“Books suspension and good handling”;
• Sufficient space to put other useful
“Useful when space is limited”;
objects used during reading;
“Compartment for cups”;
4
2.2 Organizing the Needs into a Hierarchy
Tab. 2.2 organizes needs into a hierarchical list with a relative importance, settled intuitively. A
level 5 importance indicates a critically important need while level 1 importance refers to a latent need.
Tab. 2.2 – Customer needs importance.
Needs
Importance
Ensure high comfort in different reading situations
5
The weight of the Book Holder is low
4
Price according to customers possibilities
5
Adaptability to several situations
4
Small size of the Book Holder
2
Easy to assembly and disassembly
4
Easy handling
4
High flexibility
4
Easy storage
2
Easy transport
3
Lighting possibility
4
High strength
2
Possibility of using all kinds of books
1
Possibility to put the Book Holder on the belly
1
Possibility of small compartment for pens, pencils and glasses placement
2
Ability do plug in different bases, according to the possible uses
3
Use at home (e.g.: beg, sofa, table)
5
Different adjustable types of fixing
5
Middle component has the possibility to have different sizes
4
Possibility to fix the Book Holder to a table
1
Possibility for the pages to be upside down
2
Possibility to put the book on the same level as the computer
3
Lighting adjustable to the size of the document
4
Simple and nice look
2
Big movement space for the user
3
Possible usage of different kinds of documents and not only books
3
Use outdoors
1
Possibility to have small bars on the back to support bigger documents
3
Be an innovative product
2
High stability of the Book Holder
5
The Book Holder has a big durability
1
5
2.3 Product Specifications
In Tab. 2.3 the relative importance of customers needs is established. Those aspects were
qualified using the inquiries that represent the hopes and aspirations before knowing what constraints
the product will actually have.
The different importance degrees are:
1- Not important
2- Slightly important
3- Important
4- Very important
5- Extremely important
Tab. 2.3 – Customer needs and relative importance.
Component (s)
Possibility to fix the Book Holder to a table using a
1
clamp system
2
Easy and efficient fixing in several directions
Existence of a small compartment or space to save
3
4
Upper
some objects
component
To have small bars on the back to support bigger
documents
5
To have adjustable lighting to the size of the document
It allows the use of different type of books and other
6
7
8
documents
Adjustable to different heights with an easy fixation of
Intermediate
component
the book
Possibility that in some situations this part won’t be used
Possibility of different bases usage: tripod, square base
9
10
Need
or others
Bottom
component
High flexibility, easy adaptation and high comfort for the
user
Importance
1
4
2
2
4
1
4
3
3
5
11
Applicability to other uses, with some changes
1
12
Physically pleasant
3
6
Component (s)
Need
Importance
13
Innovative and low cost product
3
14
The volume occupied in the users space is small
3
15
Small size and easy storage
2
Easy assembly and disassembly
4
High stability and security to the users
5
18
High strength with low weight
4
19
High resistance
2
20
High durability
1
21
Easy transport/carrying
4
16
17
Complete Book
Holder
7
2.4 List of Metrics
In Tab. 2.4, the different metrics, the correspondent importances and units are represented. With
this, different concepts can be compared. The most useful metrics are those which reflect as directly
as possible the degree to which the product satisfies the customer needs.
Tab. 2.4 – List of Metrics, relative importance and units.
Need (s)
Metric
Importance
1
1, 2, 7
Fixing
3
2
3
Compartments
2
Number
3
4, 6
2
Yes/No
4
5
Lighting
4
Watt
5
5, 10
Comfort
5
Subjective
6
7, 10
Flexibility
5
Massive, joints, malleable
7
9, 11
3
Yes/No
8
12, 13
Design
4
Industrial/ Graphic
9
13
Price
3
€
10
7, 14, 15
Dimensions
3
mm
11
15
Storage
1
m
12
16
Time to assembly
4
Second
13
16
Time to disassembly
4
Second
14
2, 17
Security
5
Yes/No
15
17, 18
Stability
4
Yes/No
16
18
Weight
4
kg
17
18, 19
Resistance
2
Pa
18
20
Durability (robustness)
1
Years
19
21
Transportation
4
Fixed. wheels, grip
Adaptable to several types of
books
Adaptability to different
situations
Units
Spring, suction cap, screw, rubber
anti-slip
3
As shown, in some cases, several metrics were necessary to reflect a single customer need.
The Needs – Metrics Matrix can be seen in Appendix B.
8
2.5 Benchmarking Approach
2.5.1 Introduction
A benchmarking process is a key factor in order to place the new product with competitive
products. It allows not only the understanding of what is truly important and essential but also what
really bothers customers, and might show potential openings in competitive products. Nowadays, the
benchmarking technique is considered to be as important as the interaction with customers.
Despite the fact that competitive products already exist in the market there are some innovations
that could be part of it. Achievement of improving key points like flexibility and transportation, without
ignoring innovation, will be used to adapt the product to the needs of potential users.
The next Benchmarking analysis will take over an evaluation of competitive products, their
services and characteristics, initially, based on perceived satisfaction of needs, and secondly, based
on metrics. Then, it is possible to know the relation between the new product and competitive products
in order to have commercial success. The following figures show the considered competitive products.
a) “Atril de Lectura Lecco”
Fig. 2.1 – Lecco Book Holder.
c) “Soporte de lectura Tercera Estación”
Fig. 2.3 - Tercera Estación Book Holder.
b) “Levo Book Holder”
Fig. 2.2 - Levo - Stand Model
d) “Atril Monopié”
Fig. 2.4 – Atril Monopié.
9
All the information about those products is gathered in Appendix C.
2.5.2 Competitive Benchmarking Chart Based on Perceived
Satisfaction of Needs
In Tab. 2.5, for each need, the relative importance settled in section 2.3 and the correspondent
perceived satisfaction of the need for each competitive product from 2.5.1 are shown. In this table,
scoring more “+” corresponds to greater perceived satisfaction of the need.
Tab. 2.5 – Competitive benchmarking chart based on perceived satisfaction of needs.
Need
Possibility to fix the Book Holder to a table
using a clamp system
Easy and efficient fixing in several
directions
Existence of a small compartment or space
to save some objects
To have small bars on the back to support
bigger documents
To have adjustable lighting to the size of
the document
It allows the use of different type of books
and other documents
Adjustable to different heights with an easy
fixation of the book
Possibility that in some situations this part
won’t be used
Possibility of different bases usage: tripod,
square base or others
High flexibility, easy adaptation and high
comfort for the user
Applicability to other uses, with some
changes
Imp.
a)
b)
c)
d)
1
+
+++++
+
+
4
+++
+++
++
+
2
+
+
+++
+++++
2
-
-
-
-
4
++++
+++
+
+
1
+++
+++
++
+++
4
+++++
+++++
+
+++
3
-
-
-
-
3
++++
+++++
+
+
5
++++
++++
+
+
1
-
-
-
-
12
Physically pleasant
3
+++
++++
++
+
13
3
+++
++
++++
++
3
+++
++
+++++
+
15
Innovative and low cost product
The volume occupied in the users space is
small
Small size and easy storage
2
+
++
++++
+
16
Easy assembly and disassembly
4
+++
+++
++++
+
17
High stability and security to the users
5
+++
++++
++
+++
18
High strength with low weight
4
+++
++
++
+
19
High resistance
2
+++
+++
+++
+++
20
High durability
1
+++
+++
++++
++
21
Easy transport/carrying
4
++
+++++
+++
+
1
2
3
4
5
6
7
8
9
10
11
14
.
10
2.5.3 Competitive Benchmarking Chart Based on Metrics
Tab. 2.6 presents the relative importances and units that were established in 2.4.
Tab. 2.6 – Competitive benchmarking chart based on metrics.
Metric
1
Fixing
3
2
2
2
Yes/No
Medium
Medium
Low
Low
4
5
Compartments
Adaptable to several
types of books
Lighting
Comfort
Units
Spring, suction cap,
screw, rubber anti-slip
Number
4
5
Watt
Subjective
Yes
High
Yes
High
No
Medium
No
Low
6
Flexibility
5
Massive, joints, malleable
Joints
Joints
Massive
Massive
7
Adaptability to different
situations
3
Yes/No
Medium/ High
Medium/ High
Low
Low
8
Design
4
Industrial/Graphic
Medium
Medium/ High
Low
Low
9
Price
3
€
195
249
6.75
29.81
10
Dimensions
3
mm
1200x450x450
1470x570x570
300x240x50
1500x550x550
11
Storage
1
m
410x340x125
300x350x850
300x240x50
1500x550x550
12
Time to assembly
4
Second
300
20
-
-
13
Time to disassembly
4
Second
180
10
-
-
14
Security
5
Yes/No
Medium
High
Medium
Medium
15
16
Stability
Weight
4
4
Yes/No
kg
Yes
4
Yes
15
No
0.520
Yes
12
17
Resistance
2
Pa
Medium
High
Low
Low/Medium
18
19
Durability (robustness)
Transportation
1
4
Years
Fixed. wheels, grip
Medium /High
Fixed
Medium/ High
Fixed or wheels
Medium/ High
Grip
Medium/High
Fixed
3
Imp.
3
a)
b)
c)
d)
High
High
Low/ Medium
Low
0
0
1
1
11
2.5.4 Ideal and Marginally Acceptable Target Values
After understanding how and which points are more important in the competitive products, at this
point, the target values for the metrics are set. There are two useful types of target values: an ideal
value and a marginally acceptable value. The ideal value is the best hoping result possible and the
marginally acceptable value is the value of the metric that would make the product feasible. Both of
these targets are useful and guide to the concept generation.
Tab. 2.7 shows the target specifications for the product in development.
Tab. 2.7 – Target Specifications.
Metric
Imp.
Units
Ideal value
Marginally
value
High
Low – High
1
0 to 2
1
Fixing
3
2
Compartments
Adaptable to
several types of
books
2
Spring, suction cap,
clamp, rubber antislip
Number
2
Yes/No
Medium
Low – High
4
Lighting
4
Watt
Yes
-
5
Comfort
5
Subjective
High
Low – High
6
Flexibility
5
Massive, joints,
malleable
High
Low – High
7
Adaptability to
different
situations
3
Yes/No
Medium
Low – High
8
Design
4
Industrial/ Graphic
High
Low – High
9
Price
3
€
75-125
10
Dimensions
3
mm
1450x450x450
11
Storage
1
m
12
Time to assembly
Time to
disassembly
4
Second
60
50 to 250
300x200x50 a
1700x750x750
300x200x50 a
300x350x850
20 to 300
4
Second
40
10 to 120
14
Security
5
Yes/No
High
Low – High
15
Stability
4
Yes/No
High
Low – High
16
Weight
4
kg
6
2.5 to 15
17
Resistance
2
Pa
High
Low – High
18
Durability
(robustness)
1
Years
Medium
Low – High
19
Transportation
4
Fixed, wheels, grip
Medium
Difficult/ Easy
3
13
3
750x250x250
12
2.6 Concept Generation
2.6.1 Introduction
After gathering and analyzing client’s needs and what exists in the market nowadays, it is time
now to establish goals for the new product, which must have the indispensable characteristics to
become practical and to guarantee a high comfort and stability. With this book-holder it is desired that
flaws like transportation, low flexibility and small adaptation to different reading situations are solved. A
solution that satisfies all needs mentioned with some innovations to benefit the final product will be
attempted to realize.
At this point, quantity of ideas is above quality, so, some wild – and practical, ideas are made.
After that it is time to shape those ideas and look at them with the purpose of implementing them as a
real solution.
Different types of concepts will be developed and mixed in order to have a rough approximation to
the final shape as well as all the required functions. Those concepts, with the initial ideas for the
product, were elaborated by hand drawings.
It was considered, apart from each other, two types of concepts. In a first place, the ones that
have a base that allows the book-holder to be placed on the floor – named Stand Supports, allowing
its use while reading on a sofa or a chair, and the ones whose fixation can be used in different places such as tables, shelves, ceilings or windows - without having a floor base, named Desk Supports.
With this, more reading options in different contexts are given to the user.
2.6.2 Patents
In order to have even more information about existing products and mechanisms a research for
already existing patents was made. Some of them have potentially concepts to be introduced in the
final product namely different types of book-holders, height adjusting mechanisms, transportations
systems or lighting systems. Those patents and abstracts were gathered from reference [10] and are
collected in Appendix D.
2.6.3 Concepts Suggested in the Inquiries
Using the answers of some of the inquired people it is verifiable that some innovations and
accessories might or not be part of the new product. A few essential aspects for the product are
verified, such as:
-
Nice Design;
-
Adjustable height system;
13
-
Several systems to hold the book;
-
Lighting system;
-
Space to save useful objects while reading;
-
Light weight and durable material;
-
Transport system – portability;
-
Applicable to several reading situations using different bases or fixing instruments;
As said before, the concepts suggested by the inquired people may or may not be part of the final
product. To know that it has to be studied advantages and disadvantages which are shown in Tab.
2.8.
Tab. 2.8 – Advantages and disadvantages from the inquiries’ concepts
Advantages
Disadvantages
Nice Design
Capacity to attract attention of
potential buyers;
Higher cost;
Product manufacturing more difficult;
Adjustable height system
Different height options;
Flexibility to different situations;
Instability;
Less handling;
Several systems to hold the book
Less handling;
Design limitations;
More expensive;
Security to the user;
Reading comfort;
Lighting system
More comfort;
Usage in places where illumination
is not available;
More expensive;
Space to save useful objects while reading
Better usage of the space;
Possibility to safe useful objects;
Design limitations;
Light weight and durable material
Better materials;
Less weight;
More durability;
More expensive;
Transport system
Easier transportation;
Less effort to transport;
Design limitations;
Applicable to several reading situations using different bases or fixing devices
More adaptability;
More stability;
More expensive;
Design limitations;
14
2.6.4 Stand Supports
In this section, several concepts for the stand support and their properties are presented followed
by the desk support concepts. For each concept, the respective figure is shown.
•
Concept A
-
Made of three distinct parts: base, middle part and arm;
-
Difficult transportation;
-
Simple book’s fixation;
-
Arm does not have adjustable length;
-
Simple square base;
-
Typical adjustable height;
-
The arm can rotate 360º;
Fig. 2.5 – Concept A.
•
Concept B
-
Design more attractive than Concept A;
-
Book’s fixation more accurate;
-
Base with four legs means less space to use the support;
-
Possibility to disassembly easily the support into the three
distinct parts;
-
Easy transportation but needs to be totally dismantled;
-
Arm’s length is adjustable by 3 concentric cylinders;
-
The middle part has a walking stick system: can be
easily dismantled;
-
The board for the book, in the extremity of the arm, is able
to rotate, and be in position just as the user wants it to be;
Fig. 2.6 – Concept B.
•
Concept C
-
This support has the possibility to fix illumination on it with a clamp system;
-
Design less attractive than Support 2, but more practical;
-
Books fixation allows the book to be upside down since
it has a fixation on the top of the board;
-
Light material;
15
-
Fragile structure;
-
Tripod requires less space;
-
Adjustable support’s height and length;
Fig. 2.7 – Concept C.
•
Concept D
-
This support has an attractive design;
-
Easy book handling.
-
Adjustable height has the system of some brooms, working by rotation to adjust at the desire
heigth;
-
Users security guarantee by a good fixation of the book, from the side and from the bottom;
-
Tripod base with wheels allow an easy transportation;
-
Stripes on the back of the board for bigger books or
other documents;
-
The arm has adjustable length and is able to rotate;
-
Little rubbers to stick the book against the support;
-
Fixation adapted to different thicknesses;
-
Possibility of a space to save objects on the board;
-
Flexible lighting;
Fig. 2.8 – Concept D.
•
Concept E
-
Design less attractive than Concept D;
-
Middle part system similar to the one of Concept D;
-
Space to save objects on the board;
-
Square base with wheels allows higher stability;
-
Arm’s system similar than the one of Concept C;
-
Easy assembly and disassembly systems;
Fig. 2.9 - Concept E.
16
•
Concept F
-
This concept is the wildest one;
-
Innovative design;
-
Possibility of a space to save a glass and another one
for other objects like pencils or glasses;
-
High malleability of the arm and security;
-
Square base with wheels with brakes;
-
Easy height fixation with a several concentric cylinders;
-
Pen incorporated in the support;
-
Adaptable to different book sizes;
-
Top fixation allows the book to be upside down with
a transparent material;
-
Lighting is with a little TL lamp;
Fig. 2.10 - Concept F.
2.6.5 Desk Supports
Concept G
-
This is the simplest desk support of all;
-
Distance from the user is easily changed;
-
Square base;
-
Adjustable height;
Fig. 2.11 - Concept G.
Concept H
-
Attractive design;
-
Possibility to set it on a bed or desks;
-
Easy adjustment of the height and distance from the user;
-
Must be used where a surface is available;
Fig. 2.12 - Concept H.
17
Concept I
-
Design less attractive;
-
Support is on the same level as the user only in some cases;
-
Higher fragility;
-
It can be easily set on shelves;
Fig. 2.13- Concept I.
Concept J
-
Attractive design;
-
The arms are provided of a malleable material;
-
Easy handling of the board;
-
Fixation requires surface to set the support on it;
-
Possibility to settle it on the bed, desks or tables;
Fig. 2.14 - Concept J.
Concept K
-
Fixation of the suction cap requires being close to a
window or to a smooth surface;
-
Simple design;
-
Simple arm;
-
Non adjustable length;
Fig. 2.15 - Concept K.
Concept L
-
Innovative design;
-
Easy change of the wanted height;
-
Pulley technique;
-
Suction cap applied on the ceiling;
-
The book might be more instable;
Fig. 2.16 - Concept L.
18
2.7 Concept Selection
This section is based on evaluating concepts in respect to customer needs, comparing
advantages and disadvantages between all those concepts. A choice, or choices, of concepts to
develop must be done and those will have further investigation.
An initially large number of concepts are winnowed down to a smaller number, although they can
be combined and improved. The concept screening (2.7.1 and 2.7.3) and concept scoring (2.7.2 and
2.7.4) methods help to refine and improve the concepts.
As said before, the concepts from 2.6.4 will be studied apart from the concepts from 2.6.5. Since
they represent two different types of concepts for book holders, and after comparisons, the concepts
selected for further investigation will be compared with the goal of finding a unique solution, including
both types of concepts.
In order to perform the concept selection and considering different combinations, concepts were
compared with the reference product existent in the market.
The reference product is depicted in Fig. 2.17:
“Atril de lectura Lecco”
Fig. 2.17 – Reference product.
To rate concepts in sections 2.7.2 and 2.7.4 the reference scale shown in Tab. 2.19 is used:
Tab. 2.9 – Rating concepts scale.
Relative Performance
Rating
Much worse than reference
1
Worse than reference
2
Same as reference
3
Better than reference
4
Much better than reference
5
19
2.7.1 Concept Screening – Stand Supports
To rate the concepts against the reference product, the code is: + for “better than the reference
product”, 0 for “same as” and – for “worse than”. Tab. 2.10 illustrates the screening matrix used.
Tab. 2.10 – Concept screening Matrix for Stand Supports.
Selection
Concepts
Ref.
Concept
Concept
Concept
Concept
Concept
Concept
A
B
C
D
E
F
Comfort
-
-
0
0
0
0
0
Security
-
-
0
0
0
0
0
Portability
0
0
0
+
+
+
0
0
+
+
+
+
0
0
Dimensions
-
0
+
0
+
+
0
Robustness
+
-
-
0
-
0
0
Weight
-
0
0
0
+
0
0
Design
-
0
0
+
0
+
0
0
+
+
+
+
+
0
Compartments
0
0
0
+
+
+
0
Storage
-
0
0
-
+
0
0
-
-
-
+
0
0
0
Flexibility
-
-
0
+
0
+
0
Lighting
-
-
0
0
0
+
Durability
+
+
-
-
-
-
0
Price
+
0
+
+
+
-
0
Sum +’s
3
3
4
8
8
7
Sum 0’s
4
7
9
6
6
7
Sum –‘s
9
6
3
2
2
2
Net Score
-6
-3
1
6
6
5
Rank
6
5
4
1
1
3
No
No
No
Yes
Yes
Yes
Criteria
Ease of setting
the book in
place and fixing
Assembly/
Disassembly
Use in different
situations
Continue?
The concepts for further investigation are Concept D, Concept E and Concept F.
20
2.7.2 Concept Scoring – Stand Supports
The next table refers to the weight score of each support against the selection criteria, using the reference scale in Tab. 2.9:
Tab. 2.11 – Concept scoring Matrix for Stand Supports.
Selection Criteria
Concept D
Weight (%)
Concept E
Concept F
Rating
Weight Score
Rating
Weight Score
Rating
Weight Score
Comfort
10
3
0,30
3
0,30
3
0,30
Security
10
3
0,30
3
0,30
3
0,30
Portability
7
5
0,35
4
0,28
4
0,28
Ease of setting the book in place and fixing
4
4
0,16
4
0,16
3
0,12
Dimensions
6
3
0,18
4
0,24
4
0,24
Robustness
6
3
0,18
2
0,12
3
0,18
Weight
5
3
0,15
3
0,15
3
0,15
Design
7
4
0,28
3
0,21
5
0,35
Assembly/Disassembly
4
3
0,12
3
0,12
3
0,12
Compartments
1
4
0,04
4
0,04
5
0,05
Storage
7
2
0,14
4
0,28
3
0,21
Use in different situations
6
5
0,30
3
0,18
3
0,18
21
Selection Criteria
Weight (%)
Flexibility
Concept D
Concept E
Concept F
Rating
Weight Score
Rating
Weight Score
Rating
Weight Score
7
4
0,28
3
0,21
5
0,35
Lighting
6
3
0,18
3
0,18
4
0,24
Durability
2
2
0,04
2
0,04
2
0,04
Price
12
4
0,48
5
0,60
1
0,12
Total Score
100
3,48
3,41
3,23
Rank
1
2
3
Continue?
Yes
Yes
No
The winning concepts will be part of a new analysis for a further combination between them.
22
2.7.3 Concept Screening – Desk Supports
Tab. 2.12 illustrates the screening matrix used.
Tab. 2.12 – Concept screening Matrix for Desk Supports.
Selection
Concepts
Ref.
Concept
Concept
Concept
Concept
Concept
Concept
G
H
I
J
K
L
Comfort
0
+
-
0
-
+
0
Portability
+
+
+
+
+
-
0
Dimensions
0
0
+
+
0
+
0
Robustness
0
0
-
+
-
-
0
Weight
0
0
+
0
0
+
0
Design
0
+
0
+
-
+
0
0
0
0
0
+
-
0
0
-
0
0
0
0
0
-
+
-
-
-
0
0
Flexibility
0
0
-
+
-
0
0
Price
0
0
0
-
0
0
0
Sum +’s
1
4
3
5
2
4
Sum 0’s
9
6
4
5
4
4
Sum –‘s
1
1
4
2
5
3
Net Score
0
3
-1
3
-3
1
Rank
3
2
5
1
6
4
Continue?
No
Yes
No
Yes
No
No
Criteria
Assembly/
Disassembly
Storage
Use in
different
situations
Concepts for further comparison, in this type of book holders are Concept H and Concept J.
23
2.7.4 Concept Scoring – Desk Supports
The next table refers to the weight score of each support against the selection criteria, using the
reference scale in Tab. 2.9.
Tab. 2.13 – Concept scoring Matrix for Desk Supports.
Selection Criteria
Concept H
Weight
Concept J
(%)
Rating
Weight Score
Rating
Weight Score
Comfort
12
4
0,48
3
0,36
Portability
12
4
0,48
4
0,48
Dimensions
8
3
0,24
4
0,32
Robustness
5
3
0,15
4
0,20
Weight
7
3
0,21
3
0,21
Design
9
4
0,36
5
0,45
Assembly/Disassembly
6
3
0,18
3
0,18
Storage
8
2
0,16
3
0,24
Use in different situations
9
5
0,45
2
0,18
Flexibility
9
3
0,27
4
0,36
Price
15
3
0,45
2
0,30
Total Score
100
3,43
3,28
Rank
1
2
Continue?
Yes
No
2.8 General Remarks
At this phase, and after knowing which potential buyers the product might have, concepts were
developed, concepts that already exist were analyzed and new alternatives for the product were
studied. Some alternatives between different components were matched in order to obtain the ones
who better satisfies, in my point of view, a potential client.
Analyzing the inquiry, some of the desired characteristics became obvious but most of them are
already patented, like some mobility systems, fixation or lighting.
The innovations to implement might be the rotary system that allows an easy adjustment of height
on the middle part, the stripes behind the support and some stretcher systems for the arm. Regarding
those aspects, no patent in book holders were found. It is also important to say that in case those
characteristics are implemented in the product, they will not make it more complex and can even turn
it more functional.
24
Using the concept scoring and the concept screening methods for Desk Supports it is clear that
the best option in this case is perfectly adaptable to any one of the Stand Supports with better
ranking. So, it will be reconsidered a new support that is able to join the best of the two stand winning
supports with the Desk Supports with the purpose of adapting the new support to all the necessary
situations in a better way.
The possibility of usage of a product with a nice and attractive design, flexible, with ease of
transportation, ease of storage and that can be used in several situations is the big goal for any
potential client.
2.9 Product Architecture
2.9.1 Introduction
In this part named Product Architecture, the product will be arranged into different physical parts
and the interaction between the main functional elements is explained. Without noticing, Product
Architecture already started developing while the sketches, diagrams and all concepts were being
done.
2.9.2 Concept Definition
As said before, in order to conciliate the best ideas of the supports that obtained the best marks in
the concept scoring and concept screening methods will be imagined, with some adjustments, a new
support.
It was also verified that it is important for the product, to have some important aspects, like:
-
Nice Design;
-
Adjustable height system;
-
Different systems to hold the book;
-
Lighting system;
-
Light weight and durable material;
-
Transport system – portability;
-
Applicable to several reading situations using different bases or fixing devices;
With this, the best aspects of all the supports were set together, and the final conceptual model for
the product was drawn.
25
2.9.3 Schematic of the Product
Board for the
book
- Classic Functionality;
- Hold books inverted to read lying down;
- Lighting system;
- Adapted to different book’s thicknesses;
- Rotation allows more reading positions;
Arm
- Adjustment to different positions and angles;
- Possibility to set it on a table or a desk;
Middle part
- Ease of height adjustment;
- Rotary fixation;
Wheel base
- Transportation system;
- Brings stability to the support;
Fig. 2.18 – Schematic of the product.
26
2.10 Interaction Between the Different Parts in the Final Concept
The sketch in Fig. 2.19 represents the three wheels base and the middle component, which are
connected by thread. It is visible the place where the fixation between those two is.
Fig. 2.19 – Sketches of the base and middle part.
The wheel base must be the heavier part of all the parts of the support. This need is because of
the arm’s length and its weight, counting, of course, with the book’s weight as well. A heavier base
intends to guarantee that the support does not fall down when a book is on the maximum distance
from its center.
The middle part height adjustment is very similar to a broom system. This system works by
rotation: in one way it binds and the other way it gets loosen so the height can be changed and
adjusted. The top of the middle part simulates a surface where the arm is attached to.
The base and the middle part might not be used if the user wants to set the arm directly on a
surface.
The element shown in Fig. 2.20 is the arm of the support, or superior component. It can be
attached to a surface using a screw-clamp system. The arm’s first part can rotate 360º on a horizontal
plane while for the second part the vertical angle can be easily changed. The first part’s size is not
adjustable and is approximately 6cm length. However, the second part length can be changed until
approximately 20cm – Fig. 2.21.
Fig. 2.20 – Arm’s sketch – front and top views.
Fig. 2.21 – Arm’s second part sketch.
27
In the middle of the arm there is a rotating system allowing both parts of the arm to make an angle
in the horizontal plane while at the end of the arm there is a rotating system allowing the board to
change position. This movement can also be seen in Fig. 2.20.
Fig. 2.22 shows the board for the book, the place where it is located. This part sustains
documents up to a weight of 2kg and is connected to the arm, as mentioned before, by a rotating
system. The board includes a place on which a little lamp can be attached to in order to have light
while reading. The materials used in pieces between the reader and the document should be
transparent, no to disturb the reading when those pieces are on the text.
Fig. 2.22 – Board’s sketch.
When totally assembled, the support is easily transportable with the help of the wheels. On the
other hand, if the option is to use the support only with the arm in the situations already demonstrated,
its portability is still easy but it must be carried manually.
The similarity and simplicity between designs was kept in mind when choosing the parts in order
to make product manufacturing less complicated. Furthermore making the product as attractive as
possible and adding security guarantees was considered. Basically, was tried to be innovative without
ignoring the realism inherent in a new product.
2.11 Materials
2.11.1 Introduction
An important aspect in the development of a new product is the definition of its constituted
materials. Concepts’ physical and mechanical properties are known only after those materials are
defined so they must be selected before the detail design.
28
In this way, the material selection for the book-holder was taken in consideration after primary
calculations were made for the basic support’s function. Once the materials were chosen the final
calculations were refined for each part of the support.
The material selections in this thesis have been performed in CES EduPack. It is also important to
take in consideration that the selected materials were connected to criteria used like weight,
resistance and transparency. Those materials were chosen but others could also be elected, due to
the search made.
2.11.2 Selected Materials
For the board, the component on which the book is put, the material selection criteria was based
essentially on the weight, material resistance and on the material cost.
In the case of the pieces whose function is to hold the book, the material selection respected not
only the previous aspects, but also the yield strength and transparency. This was taken in
consideration because these components are responsible for holding the book’s weight and allow the
pieces to be over the text so that the reader is able to read through them. Fig. 2.23 illustrates how the
board and the transparent pieces are and Fig. 2.24 shows the complete support’s arm.
Fig. 2.23 – Board and transparent pieces.
Fig. 2.24 – Book holder’s arm.
Yet, the book holder’s arm part is submitted to bigger extension due to the loadings putting
through it, and so the chosen elongation was bigger than the one from the board. This material
selected should have a ductile behaviour.
Using the referred software material selection, a first gap of parameters was studied followed by a
graphic - Fig. 2.25, including density and price parameters. The selected materials for the board are
ABS (Medium Impact) and ABS (Transparent) and for the arm of the support Pa (Type 6). As
mentioned before, these materials were selected because comply with the settled parameters but
other materials could have been chosen.
29
Fig. 2.25 – Graphic with settled parameters of density-price.
The middle part (or middle-component) of the book holder, is constituted, as will be seen in more
detail in Chapter 3, by five different parts (Fig. 2.26): the two tubes – upper tube and bottom tube, the
top middle-component and the bottom middle-component. The top middle-component is connected to
the upper tube by welding and to the “surface simulator” part by screws. In the same way, the bottom
middle-part is connected to the bottom tube by welding and to the base of the support by thread.
a)
b)
Fig. 2.26 – Book holder’s several middle parts.
30
The main function of the “surface simulator” component is, as the name says, to simulate a
surface where the arm can be attached to.
Using the referred software, the tubes were selected while considering four main aspects: length,
diameter, weight and yield strength. First calculations showed that these parts should be made of a
heavier material than plastic, because both arm’s length and book’s weight would make such a
bending moment on the structure that tube’s and base’s weight had to compensate those moments.
Using the software, the option stayed on a Hot Finished Steel (Y.S. 355MPa) Circular Hollow due
to its density and length. Fig. 2.27 shows both tubes characteristics. Total length is 0.5m for each one
of them. Tab. 2.14 shows some of the main properties of the tubes.
Tab. 2.14 – Hot Finished Steel Circular Hollow tubes.
Maximum depth, D
Maximum width, B
Inner thickness, t
Outer Thickness, T
(27 x 3.2)
(34 x 2.6)
0.0266m – 0.0272m
0.0334m – 0.034m
0.0028m – 0.0036m
0.0022m – 0.003m
Fig. 2.27 – Tubes description.
During the materials election for the “surface simulator”, the top middle-component and the bottom
middle-component, the fact that those pieces were connected by welding and screws were kept in
mind. Consequently, the top middle-component material should have a good weldability with the upper
tube as well as the bottom middle-component with the bottom tube.
With this, the material selected for the top and bottom middle-component was a Low Carbon
Steel, AISI 1015 (normalized) while the selection for the “surface simulator” was Cast Alluminum Alloy.
Intending to select the base’s material, initially, a search for eligible materials was made, based on
factors like weight, price and yield tensile. Despite the number of possibilities, the selected material is
Gray Cast Iron, since its properties accomplish the referred aim for the base.
As said before, the base (Fig. 2.29) is connected to the bottom middle-component by a thread and
should have such a weight that the bending moment made by the arm and book can be compensated,
avoiding the entire support to fall down. Fig. 2.28 shows the comparison graphic for the base’s
material.
31
Fig. 2.28 shows a graphic made during the base’s material selection.
Fig. 2.28 – Base’s material selection.
Fig. 2.29 illustrates the base’s shape.
Fig. 2.29 – Base.
32
Tab. 2.15 resumes information about the selected materials (from EduPack). Values marked * are estimates.
Tab. 2.15 – Selected Material’s properties.
Density, ρ
Young’s
Shear
Tensile
Compressive
modulus
Modulus
Strength
Strength
10
[GPa]
[GPa]
[MPa]
[MPa]
1.03 – 1.06
2.07 – 2.76
0.74 – 0.987
34.5 – 49.6
37.9 – 51.7
1.07 – 1.09
1.95 – 2.05
0.695 – 0.73
32* - 37
1.12 – 1.14
2.62 – 3.2
*0.97 – 1.19
7.8 – 7.9
195 - 205
2.67 – 2.7
Elongation
Recycle
%
[Yes / No]
39.2 – 86.2
5 - 60
Yes
40 - 46
55.2 - 61
18.6 – 21.5
Yes
86 – 94.8
90 - 165
89.6 - 110
30 - 100
Yes
-
350 - 360
-
-
-
-
71 – 74.6
27 – 28.4
103 – 114
152 - 172
103 – 114
0.7 - 1
Yes
7.8 – 7.9
205 – 215
79 – 84
300 – 355
380 – 470
300 – 355
29 - 45
Yes
6.9 – 7.1
80 – 100
31 – 40
65 – 98
100
130
0.5 – 0.7
Yes
3
[kg/m ] x
3
Yield Strength
[MPa]
1 - ABS (Medium –
Impact, Injection
Molding)
2 - ABS
(Transparent,
Injection Molding)
3 - PA (Type 6,
Molding and
Extrusion)
4 - Hot Finished
Steel, Circular
Hollow
5 - Cast Aluminum
Alloy
6 - Carbon Steel,
AISI 1015
(normalized)
7 - Gray (Flake
Graphite) Cast
Iron
33
CHAPTER 3 DETAIL DESIGN
3.1 Introduction
After defining the materials of the different components of the book holder in the previous chapter,
it is now time to proceed to calculations inherent to all the pieces part of the support in order to verify if
those components are well dimensioned. This dimensioning, such as diameters or lengths, depends
upon the load that each piece is putting through, therefore, for some pieces, different loadings are
going to be considered in order to perceive which one is the worst case. Thus, for all the calculations
made in this thesis the worst possible case is taken in consideration in each one of the pieces of the
structure.
It is important to have in consideration that, during the calculations procedure, the weight of the
structure – consequently all the component’s weight, is not neglected faced to the books weight. It is
considered that the maximum weight allowed for a book is 2kg. It is also important to refer previously
that in this thesis, all the dimensioning verification made refer to static problems for all components.
The first part of the chapter, “Equations”, presents a summary of the fundamental formulas used in
the structural calculations as well as the ones for the failure theory. Those formulas include the
respective reference used.
The second part of the chapter, explains how the different components are under loading and their
dimensioning will be verified. The calculations start at the board and end at the support’s base,
studying through all the pieces, one by one. Also in this part of the chapter, a study using the FE
program COSMOS is shown for some of the critical components.
3.2 Equations
• Failure Theory [4]
The Distortion-Energy Theory for Ductile Materials, also known as the von Mises Theory is the
theory used to determine the effective stress - usually called the von Mises stress, σ’.
σ '=
[
(
1
(σ x − σ y )2 + (σ y − σ z )2 + (σ z − σ x )2 + 6 τ xy2 + τ yz2 + τ zx2
2
)]
1/ 2
(3-1)
Where σx, σy and σz represent the normal stress for the xx, yy and zz axis respectively and σxy , σxz
and σyz represent the shear stress on zz, yy and xx axis respectively.
34
Normal Stress:
σ X = σ F + σ max
With:
Shear Stress:
τ XY = τ V + τ T
• Factor of Safety [4]
The von Mises stress – equation (3.1), can be compared against the yield strength of the material
using the following equation:
σ ' ≤ σ all =
Sy
n
,
(3-2)
Where σall is the allowed stress, Sy is the yield strength of the material and n is the factor of safety. In
this thesis, the chosen global factor of safety for all the dimensioning is n=3. If this equation is valid,
then the dimensioning made is also valid.
• Maximum Normal Strength [4]
The maximum normal strength can be calculated using the following equation:
σ max =
M max ⋅ c
,
I
(3.3)
Where, Mmax is the maximum bending moment on loading, I is the second moment of inertia and c is
the maximum distance to he neutral line.
Rectangle:
b ⋅ h3
12
A = b⋅h
Ix =
c = h/2
I xy = 0
Iy =
b3 ⋅ h
12
Fig. 3.1 a) – Square section properties.
Circle:
A=
π ⋅ D2
4
Ix = I y =
π ⋅ D4
64
I xy = 0
c = D/2
Fig. 3.1 b) – Circular section properties.
35
Hollow Circle:
A=
π ⋅ (D 2 − d 2 )
I xy = 0
4
Ix = Iy =
π ⋅ (D 4 − d 4 )
64
c = D/2
Fig. 3.1 c) – Hollow Circular section properties.
•
Maximum Normal Stress [4]
σF =
F
Amin
(3.4)
Where F is the normal force and Amin is the minimum area of the component.
•
Maximum Torsion Stress [4]
τT =
Tc
J
(3.5)
Where T is the torsion moment, c is the maximum distance to the neutral line and J is the second
polar moment of area.
•
Maximum Shear Stress [4]
Square Section: τ V
=
3V
2A
(3.6)
Circular Section: τ V
=
4V
3A
Where V is the transverse shear force at the considered section, and A is area of that section.
•
Links Crush Stress at Section B [4]
σB =
F
A
(3.7)
Where F and A are the force and the area, respectively, at section A.
36
•
Maximum Value of the Average Normal Stress in Link XY [4]
σA =
F
A
(3.8)
Where F is the normal force and A is the pin’s contact area, which depends if the link is under
compression or under tension:
Acompression = b ⋅ t
Atension = Amin = (b − d ) ⋅ t
Where t is the thickness, b the width and d the diameter of the pin.
• Threaded Fasteners [4]
The torque required to keep the load raised is given by:
TR =
 l + π ⋅ f ⋅ dm 


 π ⋅d − f ⋅l 
m


F ⋅ dm
2
(3.9)
Where: F is the required force
d m = d − 0.649619 ⋅ p , is the average diameter and p is the pitch
f is the coefficient of friction for threaded pairs
l = m ⋅ p , being m the type of pitch
The Stiffness of the Fastener, kb, can be calculated using:
kb =
Ad At E
Ad lt + At ld
(3.10)
Where: E = Young modulus of bolt’s material
At = tensile-stress area, taken from literature [4]
lt = length of threaded portion of grip
Ad = major-diameter area of fastener, given by
Ad =
πd 2
4
ld = length of unthreaded portion in grip
37
In order to find the Stiffness of the Members, km, the following expressions can be used:
i
1
1
= ∑ , if exists more than one member
km
1 ki
(3.11)
ki =
0.5774πEd
 (1.155t + D − d )(D + d ) 
ln 

 (1.1557t + D + d )(D − d ) 
Where: E = Young modulus of member’s material
t = thickness of the member
d = diameter of the bolt
D = 1 .5 d
D = diameter of bolt’s head, given by
The Stiffness Constant of the Joint, C, of a threaded fastener is obtained using the following
expression:
C=
kb
kb + k m
(3.12)
The Recommended Preload, Fi, in threaded fasteners is:
0.75 Fp
For nonpermanent connections
Fi =
(3.13)
0.90 Fp
Where Fp is the proof load, given by
For permanent connections
Fp = At S p and Sp is proof strength obtained from literature [4].
The Required Combined Preload, Fr, in threaded fasteners under shear and tension stresses, is
given by the following expression:
Fr = Frs + Fts
(3.14)
The Required Preload, Frs, in threaded fasteners under shear stresses, is given by the following
expression:
Frs =
Ps
fm
(3.15)
Where Ps is the shear load, fm is the friction coefficient.
38
The Required Preload, Frt, in threaded fasteners under tension stresses, is given by the following
expression:
Frt = (1 − C )P
(3.16)
Where P is a tension load.
The Factor of Safety Against Joint Separation – nt, in threaded fasteners is given by:
nt =
Fi
Frt
(3.17)
The Factor of Safety Against Joint Slippery – ns, in threaded fasteners is given by:
ns =
Fi
Frs
(3.18)
The Factor of Safety Against Joint Combination (Separation and Slippery – no), in threaded
fasteners is given by:
no = nt + ns
(3.19)
The Factor of Safety Guarding Against Fatigue – nf, is given by:
nf =
Su ⋅ At − Fi


S
C  k f Pm + u Pa 
Se 

(3.20)
Where kf is the fatigue stress-concentration factor for threaded elements and Se is the fully corrected
endurance strength. Both of these parameters come from reference [4].
• Welding of Permanent Joints [4]
The Nominal Throat Shear Stress, τ , is given by:
τM =
Where
M ⋅c
I
(3.21)
I = 0.707hI u , is the second moment of area, based on weld throat area.
39
Tab. 3.1 - Bending properties of a circle fillet weld.
Weld
Throat Area
Unit Second moment of Area
A = 1.414 ⋅ π ⋅ h ⋅ r
Iu = π ⋅ r3
• Member Under Compression and Bending Moment [4]
σ=
F M ⋅x
+
A
I
(3.22)
Where σ is the stress at the considered section, F is the compression load, A is the section area, M is
the bending moment, x is the maximum distance between the neutral line and the surroundings and I
is the second moment of inertia of the section.
• Principal Stresses for Plane Stress [4]
The Maximum-Normal-Stress for Brittle Materials, states that failure occurs whenever one of the
three principal stresses equals or exceeds the strength. For plane stress, the principal stresses are
given by:
σ A, B =
σ X + σY
2
 σ − σY 
2
±  X
 + τ XY
2


2
(3.23)
Where σx and σy represent the normal stress for the xx and yy axels respectively and σxy represents
the shear stress on zz axel, given in equation (3-1).
• Bending ( σ b ) and Transverse Shear (τ ) Stresses at the Root [4]
σb =
τ =
Where:
dr = d −
6⋅F
π ⋅ d r ⋅ nt ⋅ p
3⋅ F
π ⋅ d r ⋅ nt ⋅ p
(3-24)
1
⋅ p is the thread’s root diameter, nt is the number of engaged threads, p is the
2
thread’s pitch.
40
3.3 Structural Calculations
The structural analysis goes through all the connections, starting, as announced before, at the
board, component on which the book is set, and finishing at the base.
The 2D technical drawings of all the pieces – and respective tolerances and surface finishing, of
the support are collected in the CD in the end of this thesis while the 2D technical drawing of the final
assembly can be seen in Appendix E.
The weights determination procedure for all the components consists in multiplying the volume
taken from CAD 3D Program Solidworks with the respective densities from Tab. 2.15.
3.3.1 Board, Side Fixations and Bottom Fixation
3
The material selected for the board is ABS (Medium Impact), with a density of 1030kg/m , and a
weight of m1=691.7g. This component’s manufacturing process is the injection molding.
3
Yet, to the side and bottom fixations a ABS (Transparent), with 1070kg/m , is the chosen material.
The respective weights are m2=63.0g (the sum of both pieces) and m3=43.1g. These pieces
manufacturing process is also the injection molding process.
The side fixation connection with the board is possible through a locking system located at the
side linked to the board - section 3.3.2. Although the union between the bottom fixation and the board
is made by using a welding plastic process, the maximum loading at this component does not bring
problems to the critical area, due to its dimensions and material properties, as we can see further in
this section.
Fig. 3.2 illustrates how these components are positioned with each other.
Fig. 3.2 – Board and book fixations.
The side fixation for the book is under maximum loading (ideally) when it has to support the entire
book’s weight. Then, in Fig. 3.3, the force F=19.62N represents the bending load relatively to the
41
book’s weight and the critical section is in need of verification. Displacing the referred force and the
respective bending moment Mmax to the critical section - Fig. 3.3 b), we have:
M max = F ⋅ d = 0.834 N .m
In this case, the shear force will be considered not neglected and its value is the same as the
force F, and so, the shear stress has to be calculated.
a)
b)
c)
Fig. 3.3 – Side fixation under maximum loading.
Therefore, knowing that the critical section’s dimensions are b=20mm and h=5mm, and using
equations (3-3) and (3-6), we have:
σ max = 10.01MPa
< Tensile Strength modulus of the material
τ v = 0.29MPa
< Shear modulus of the material
Since this material’s elongation is considered ductile (ε > 5%) - Tab. 2.15, and assuming that for
this material’s yield strength value is needed Sy= 35MPa, using equations (3-1) and (3-2), it is finally
possible to determine the effective stress at the critical section. With this, it is obtained:
σ ' = 10.02MPa
Sy
n
= 11.67 MPa
Those results show a good side fixation dimensioning and that the shear stress could be, as a
matter of fact, neglected relative to the maximum normal strength.
42
Testing the critical area using the FEP Cosmos (Fig. 3.4), as expected for this simple component,
presents a great similarity of results using both computational (σ’ = 10.51MPa) and numerical
calculations is obvious.
Fig. 3.4 – Side fixation’s von Mises Stress in FEP Cosmos.
The case of the bottom fixation and support for the book is very similar to the side’s fixation
dimensioning verification. In this section two different loadings are going to be considered: a first one
when the board is on the vertical position and the piece has to hold the books’ weight (Fig. 3.5); and a
second case when one of the sides of this component holds the entire book’s weight – Fig 3.6. In both
cases, shear force F is considered to be F = 19.62N.
a)
b)
c)
Fig. 3.5 – Bottom fixation under maximum loading – first case.
a)
b)
c)
Fig. 3.6 – Bottom fixation under maximum loading on one side– second case.
43
In the first case, F is considered to be loading the critical section (rectangular section with
b=170mm and h=5mm) and M is the bending moment at this same section. Since this moment is
made by the force F for the maximum distance d=40mm, it is evaluated as:
M max = F ⋅ d = 0.785 N .m
In this case, the shear force (transverse force) will be, again, taken in consideration, knowing in
advance that it might not be necessary. Its value is the same as the force F and the maximum shear
stress as well as the maximum normal stress has to be calculated. Using equations (3-3) and (3-6), it
is obtained:
σ max = 1.11MPa
τ v = 0.04MPa
Considering this material’s elongation ductile and assuming again a necessary yield strength
value of Sy=35MPa, using equations (3-1) and (3-2), we find:
σ ' = 1.11MPa
Sy
n
= 11.67 MPa
Fig. 3.7 shows, for this first case, the analysis made using the FEP Cosmos.
Fig. 3.7 – Bottom fixation’s von Mises Stress FEP Cosmos – first case.
44
These results also show a good similarity between the numerical and computational methods and
a confirmation that this component is clearly safe due to the maximum loading at the critical section.
Instead, for the second case (Fig. 3.6), F is considered to be loading the critical section
(rectangular section with b=30mm and h=5mm) on one side of this component. The bending moment
M is also loading the same section and for the maximum distance c=30mm. This moment’s value is:
M max = F ⋅ c = 0.589 N .m
Considering also the maximum shear stress loading from the shear force F, using equations (3-3)
and (3-6), we have:
σ max = 4.71MPa
τ v = 0.20MPa
Lastly, comparing the effective stress using equations (3-1) and (3-2) it is obtained:
σ ' = 4.72MPa
Sy
n
= 11.67 MPa
Trying the FEA for this case (Fig. 3.8), the graphic also shows a good proximity of results,
demonstrating that the critical section dimensions are verified.
Fig. 3.8 – Bottom fixation’s von Mises Stress in FEP Cosmos – second case.
45
3.3.2 Board, Locking System, Lighting Surface and Rotary Pieces
The selected material for the locking systems pieces, rotary pieces and for the lighting surface is
3
ABS (Medium Impact), with a density of 1030kg/m , and the respective weights are m4=66.5g (sum of
both pieces), m5=10.8g and m6=26.9g. The manufacturing process for these components is the
injection molding.
The union between the lighting surface and the board is made by using a welding plastic process.
Instead, the rotary pieces and the board are linked by screws.
The locking system pieces connection with the board and with the side fixation as well as the
dimensional tolerances for the rotary pieces are explained in detail in Appendix E.
Fig. 3.9 shows how the components are positioned with each other,
Fig. 3.9 – Board’s back side.
This work will proceed now to the dimension verifications of the lighting surface at the union
section made with the board as well as the calculation of the maximum weight this component can
afford. On this surface it is intended to attach a lamp with a clamp system, or similar. Its dimensions
were previously set (35x30x10 mm) – Fig. 3.10, so are in need of verification.
In this case, the effective stress σ’ is unknown. Considering this material’s yield strength needs to
be Sy=49MPa, and using equation (3-2), the effective maximum stress can be determined:
σ ' = 16,33MPa
After this, and using the (3-1) equation it’s obtained:
σ '2 = σ M2 + 3 ⋅ τ V2
46
Since
V = Flamp = Fmax and M max = Flamp ⋅ d , being d the maximum distance for the bending
moment (d=30mm), and using equations (3.3) and (3.6), the maximum shear force allowed for this
section, is:
Flamp = 119.7 N
It is clear that this section due to the material’s yield strength condition is under dimensioned. In
order to guarantee security for all the components, the choice of selecting a material with the same
properties for different components was taken.
With the last result, we can conclude that in the market exist quite a lot of possibilities for lighter
lamps. The forthcoming calculations will be considered a lamp with the maximum weight of 100g.
Fig. 3.10 represents the free body diagram of the lighting surface.
Fig. 3.10 – Lighting surface’s free body diagram.
Relatively to the rotary pieces, the worst loading case is when each piece has to hold the entire
book’s weight, plus the weight of all the components attached to the board, namely fixations, locking
systems, lighting surface and lighting. As it is visible in Fig. 3.11 (rotary piece’s free body diagram),
the critical section is at the section where the area is minimal, d=15mm and di=6mm. For this
component a good surface finishing is predictable in advance, in order to have a lower friction
coefficient and allow them to rotate relatively to Connection-piece II – Fig. 3. 14.
Fig. 3.11 – Rotary piece loadings.
47
Thus, the shear F force is given by:
F = Fbook + Flight + F1 + F2 + F3 + F4 + F5
Each one of the F shear forces are associated to the respectively component weight multiplied by
2
the gravity acceleration constant g=9.81m/s . This is procedure used all through this thesis.
Consequently:
F = 29.298 N
The bending moment applied at the same section is given by:
M = M book + M light + M 1 + M 2 + M 3 + M 4 + M 5
In this formula, each bending moment is associated to the respective bending force F.
M = Fbook ⋅ zbook + Flight ⋅ zlight + F1 ⋅ z1 + F2 ⋅ z2 + F3 ⋅ z3 + F4 ⋅ z4 + F5 ⋅ z5
Here, each z value is the distance between the critical section and the center of mass of each
piece, on the “zz” axis, taken from Solidworks. All the similar bending moments’ calculation
procedures in this thesis is made like this one. Therefore:
M = 0.788 N .m
The maximum normal strength and the shear stress τ v for circular sections given by equations
(3.3) and (3.6), are:
σ max = 2.496MPa
τ yz = τ v = 0.26 MPa
Finally, a comparison between the effective stress and the maximum stress allowed for the
referred section can be made. Considering again that material’s yield strength is Sy=49MPa, and using
equations (3-1) and (3-2), the results are:
σ ' = 2.54 MPa <
Sy
n
= 16.33MPa
48
This shows that both rotary pieces are well dimensioned and able to sustain the other components
weight.
3.3.3 Rotary Pieces, Connection-piece II, Bars and Connection-piece I
In this section, the study will focus on links involving rotary pieces, connection-piece I and bars. As
we can see in Fig. 3.12 and Fig. 3.13, in between both rotary pieces and the connection-piece II,
there is a screw and a nut in one extremity. This is made with the intention of tightening the link, when
it gets loose. Despite the presence of a screw in this connection, all screws calculations are gathered
further in this work - section 3.3.5.
Before starting calculations, it is important to know the material these components are made of:
Connection-piece I, connection piece II (Fig. 3.14) and bars (Fig. 3.15) are all made of Polyamide –
3
PA (Type6), whose density is 1120kg/m . The weights are m9= 27.4g for the connection piece I,
m7=27.9g for the connection piece II and knowing the existence of eight 5cm bars and four 10cm bars,
the total weight is m8=107.0g. Injection molding is the process of manufacturing all of these
components, and a certain surface finishing is required. The considered yield tensile for those
components is 86MPa.
Fig. 3.12 –Rotary pieces, Connection-piece II,
bars and Connection-piece I.
Fig. 3.14 – Connection-piece II.
Fig. 3.13 – Rotary Pieces, Connection-piece II
and bars in detail.
Fig. 3.15 –10cm bar and 5cm bar.
49
It is now time to proceed to the dimension verification of the connection-piece II component in the
minimum section area, which is at pin (Fig.3.13). All the pins, as can be seen further in this section of
the work, have a diameter of 6mm,
The referred section area is not only under the book’s weight loading but also under the other
pieces weights. In this case, the weight inherent for the screws is considered.
As a consequence, it is obtained:
6
F = Fbook + Flight + ∑ Fi ⇒ F = 29.561N
1
The maximum crush stress this component is under occurs at the section where the area is
minimal. Here it is given b=15mm, d is the pin’s diameter (d = 6mm) and t=10mm is thickness of the
section.
Consequently:
Amin = (b − d ) ⋅ t = 9 × 10 −5 m 2
Fig. 3.16 shows how the connection-piece II is under loading.
Fig. 3.16 – Connection-piece II loading.
The link’s crush stress at the referred section is given by equation (3-7), and its result is:
σ = 0.328MPa
< Compressive Strength for the material (Tab. 2.15)
The arm of the support is made of two distinct parts: a first part whose length cannot be changed
(studied in section 3.3.4) and a second part whose most important attribute is to stretch and shrink, as
the user desires it to be.
Initially, is considered the case of the arm completely stretched (Fig. 3.17) on a horizontal
position, where the minimum angle between the bars’ axis and the horizontal plane (XZ plane) is
θ=11.79º, meaning that the maximum length for the second part of the arm is 195.58mm. For those
bars, a study of which links are in tension or compression is made as well as a study for the pins.
A second case will also be considered and the main difference is the first and second part of the
arm making a 90º angle – studied further in this section.
50
Fig. 3.17 –Arm completely stretched.
For this particular study, in a first place, the bars’ weight will not be considered. This
approximation will be verified at link H (Fig. 3.18), matching the difference of stresses those bars
suffer counting and not counting their weights.
Fig. 3.18 shows how the second part of the arm gets when it is completely stretched
Fig. 3.18 –Second part of the arm completely stretched under loading.
The force F in Fig. 3.18 and Fig. 3.19 represents the force earlier mentioned in this section. Using
the free body diagram in Fig. 3.19 for joint B, we have:
∑F
∑F
x
=0
y
=0
FCB ⋅ cos(θ ) + FDB ⋅ cos(θ ) = 0
(FCB − FDB ) ⋅ sen(θ ) = F
FCB = − FDB
2 ⋅ FCB ⋅ sen(θ ) = F ⇒ FCB = 72.34 N
FCB is in tension and FDB is in compression, and both forces have the same intensity.
Fig. 3.19 represents the free body diagram for joint B.
Fig. 3.19 –Joint B as a free body diagram.
51
Using equation (3.8), the maximum value of the average normal stress for the two links BC – that
are in tension, can be determined. This section dimensions are b=20mm, d=6mm and t=5mm, and it is
obtained:
A = 140mm 2 (for 2links), minimum section occurs at pin
σ = 0.517 MPa
< Tensile Strength of the material
Using the same equation, the tension in link BD (in compression) is:
A = 200mm 2 (for 2 links)
σ = 0.362 MPa
Using a global security factor of n=3, the last normal stress at link CB can be determined using the
following expressions, in which Fu and σu are respectively the last normal force and tensile strength
allowed:
Fu = FCB ⋅ n = 217.02 N , and σ u =
Fu
= 1.55MPa < Sy of the material.
A
Studying now the stresses pin B is under loaded, and dividing the pin into sections (Fig. 3.20, Fig.
3.21 and Fig. 3.22), we have:
Fig. 3.20 –Loadings at joint B.
Fig. 3.21 –Section I – J of pin B.
Fig. 3.22 –Section I – K of pin B.
52
In section I – J, it is obvious that:
In section I – K:
∑F
y
FJ =
FCB
= 36.17 N
2
F 
F
= 0 ⇒ FK = CB + DB  ⋅ sen(θ ) = 14.78 N
2 
 2
Once the loading at the pin is completely symmetric, the maximum shear force at pin B is given by
FJ, and the maximum shear stress, occurring at sections J and M, is:
τ max =
π
FJ
= 1.28MPa , given that Apin = d 2 = 28.27 mm 2 .
4
Apin
This maximum shear stress at pin B shows that a pin can be made of the same material than the
bars - Polyamide PA (Type 6) due to the material’s tensile strength (Tab. 2.15). This choice is based
on the fact that, if the material chosen for the pins would be a metal one, the erosion for the bars
would be much higher and displeasuring for the structure itself. That erosion, in these cases, is in a
more important level that the fatigue of those components so it has to be highly levelled.
Another thing to have in mind is that if some component of the arm breaks – as it might someday,
it is preferable for it to be a pin instead of a bar for obvious reasons.
In order to know if a link is under tension or compression, a free body diagram can be made. As
an example, member BD is taken for the following simple analysis.
Fig. 3.23 shows the free body diagram at member BD.
Fig. 3.23 – Member BD as a free body.
∑F = 0 ∑M = 0
x
D
=>
FCB = − FFD
F ⋅ 5 ⋅ cos(θ ) = FCB ⋅ sen(θ ) ⋅ 5 ⋅ cos(θ ) + FCB ⋅ cos(θ ) ⋅ 5 ⋅ sen(θ )
=>
FFD = −72.45 N
FCB = 72.34 N
This shows that link FD is in compression. It also confirms the value of FCB force.
53
Identical diagrams and studies could be made for all the other members, but it will only be
mentioned which ones are under tension or compression in Tab. 3.2. Notice that the considered value
of force for all those stresses is 72.34N.
Tab. 3.2 – Links’ type of stress in horizontal position.
Member
Type of stress
CB
Tension
DB
Compression
FD
Compression
GC
Tension
HG
Tension
FH
Compression
Using joint H as a free body (Fig. 3.24), the following figure is created:
Fig. 3.24 –Joint H as a free body diagram.
Fig. 3.25 shows connection-piece I and Fig. 3.26 shows how connection-piece I is under loading.
Fig. 3.25 – Connection-piece I.
Fig. 3.26 – Connection-piece I loadings.
Taking into account now the loadings at connection-piece I using the same methods as used for
connection-piece II and, importantly, considering the shown force F as the force associated to all the
components weight, including bar’s and connection-piece II weight, it is obtained:
F = (Fbook + Flight + F1 + F2 + F3 + F4 + F5 + F6 + F7 + F8 ) = 30.865 N
54
The maximum crush stress σ this component has is given by equation (3-7) and occurs at the
section where the area is minimal. As well as connection-piece I, b=15mm, d=6mm and t=10mm.
Consequently:
Amin = (b − d ) ⋅ t = 9 × 10 −5 m 2 and σ = 0.343MPa < Compressive Strength for the material.
Given that in a first place the bar’s weight was not considered, it is now time to study the stresses
at pin H. Using the free body diagram in Fig. 3.24 and the forces applied (Fig. 3.27) for joint H, we
have:
∑F
∑F
x
=0
y
=0
FHG ⋅ cos(θ ) − FFH ⋅ cos(θ ) = 0
F − (FFH + FHG ) ⋅ sen(θ ) = 0
FFH = FHG
F = 2 ⋅ FFH ⋅ sen(θ ) ⇒ FFH = 75.53 N
.
FFH is in compression and FHG is in tension like mentioned in Tab. 3.1.
Studying now the stresses at pin H, and dividing the pin into sections (Fig. 3.27), it is obtained:
Fig. 3.27 –Section O – T of pin H.
In section O – P, the shear force is:
FP =
FHG
= 37.77 N
2
Once the loading at the pin is, again, completely symmetric, the maximum shear force at pin H is
given by FP, and the maximum shear stress, occurring at sections P and S, is:
τ max =
FP
= 1.34 MPa
Apin
This shows that the approximation made of not counting with the bar’s weight in a first place was a
good approximation, since the maximum shear stress at pin H grew less than 5% over pin B.
55
As said earlier, a second case taken into reflection is when the arm’s second part is on a vertical
position and makes 90º with the first part of the arm (Fig. 3.28). For this potential case, θ is the angle
that would bring greater stress for the bars and is given by:
θ = 90º - 11.79º = 78.21º
Fig. 3.29 represents the free body diagram for joint B.
Fig. 3.28 – Second part of the arm vertically.
Fig. 3.29 –Joint B free body.
Using the free body diagram for joint B, we have:
.
If:
∑F
∑F
x
=0
y
=0
FCB ⋅ sen(θ ) − FCB ⋅ sen(θ ) = 0
F + (FFH + FHG ) ⋅ cos(θ ) = 0
FCB = FDB
FCB =
, with F=29.561N,
F
− 2 ⋅ cos(θ )
θ = 11.79º ⇒ FCB = 15.1N
.
θ = 90º −11.79º = 78.21º ⇒ FCB = 72.34 N
This shows, like it was expected, that links CB and DB are in compression.
Again, similar studies could be made for the all the other members but it will only be mentioned
the type of stress they are under in Tab. 3.3 Again the considered value of force for all those stresses
is 72.34N.
56
Tab. 3.3 – Links’ type of stress in vertical position.
Member
Type of stress
CB
Compression
DB
Compression
FD
Tension
GC
Tension
HG
Compression
FH
Compression
Particular studies for both joint B and H will not take place at this point. Those studies were
demonstrated in the previous case, when both parts of the arm were straight with each other. The only
difference between both cases is the mentioned angle θ that brings greater stress to the members and
pins (θ=11.79º in the first case and θ=78.21º in the second case). The final results, for both cases are
exactly the same.
3.3.4 Arm I and Clamp
This part of the work will focus on the Arm I diameter verification for two different cases: a first
one, when the second part of the arm is completely stretched and it is straight with Arm I (Fig. 3.31),
stressing the element only with a tensile bending stress; and a second one when they both make a 90º
angle in the horizontal plane adding a torsional stress into the Arm I (Fig. 3.34). Injection molding is its
manufacturing process.
After this, will take over verification in the clamp component, resultant from the intern forces
applied in it.
Fig. 3.30 shows how these components are connected.
Fig. 3.30 –Arm I, Connection-piece I, Fixed-piece and Clamp.
57
Despite the existence of two screws and one wing nut at the arm, with the intention of tightening
the connection when it gets loose, the calculations inherent to it are explained further in this work, in
section 3.3.5.
Both Arm I and Clamp’s material is Polyamide – PA (Type6) and the respective weights are:
m10=44.4g and m11=135.8g. Both of these components’ manufacturing process is injection molding
and a surface finishing is required in order to allow the arm to rotate relatively to the clamp.
Fig. 3.31 illustrates how the arm is when it is completely stretched.
Fig. 3.31 – First and second parts of the arm completely straight with each other.
A PA (Type 6) is a ductile material at normal temperatures, meaning that stress concentration
doesn’t need to be considered. Fig. 3.32 shows how Arm I is under stress at point A – which is the
weakest section and governs the strength of the assembly. The tensile load is subjected to a tensile
bending stress and to a shear stress.
The represented force F is the sum of all forces derivate from all pieces’ weight and M the sum of
the respective bending moments.
9
F = Fbook + Flight + ∑ Fi ⇒ F = 31.184 N
1
9
M = M book + M light + ∑ M i = 10.85 N .m
1
9
Fig. 3.32 –Loadings at Arm I – first case.
58
Using equations (3-3) and (3-6), the two stresses are:
σ x = σ M = 13.815MPa
τ zy = τ v = 0.132 MPa
Employing the distortion-energy theory, we find, from equation (3.1), that:
σ ' = 13.817 MPa
Since the considerate Yield Strength for this material is Sy = 86MPa and that the global factor of
safety is n=3:
Sy
n
= 28.667 MPa
These results show two things: the shear stress could have been disregarded; and the chosen
diameter for Arm I is well projected.
A simulation study using FEP was made (Fig. 3.33), and it is:
Fig. 3.33 – Arm I’ von Mises Stress in Finite Element Cosmos – First case.
This simulation shows that at the considered section, the von Mises Stress is approximately the
same as the one got from the numerical calculations. The highest stress shown in the figure above,
like in the previous case, respects to the stress at surface screw II, made of Alluminum-Bronze, as we
59
can see further in this work, and it doesn’t bring problems to the structure due to its yield strength
(275MPa).
Relatively to the second case studied for the Arm I, Fig. 3.35 shows how this component is under
stress. In this case, a bending loading F will be subjected to a tensile bending stress and a torsional
stress. The shear stress will be assumed as neglected. Similarly to the previous case, point A is the
weakest section so it governs the strength of the assembly. At this section it is represented the force
F, the bending moment M and the torsion moment T, and their values are:
Fig. 3.34 illustrates how the arm gets when it’s both parts make a 90º angle.
Fig. 3.34 – First and second parts of the arm
Fig. 3.35 - Loadings at Arm I – second case.
making a 90º angle with each other.
9
F = Fbook + Flight + ∑ Fi ⇒ F = 31.184 N
1


M =  Fbook + Flight + ∑ Fi  ⋅ (0.060 − 0.015) = 1.403 N .m
1


9
where (0.060-0-015) is the distance between all the forces and the point A.
9
T = Tbook + Tlight + ∑ Ti = 9.445 N .m
1
Using equations (3-3) and (3-5), the two stresses are:
σ x = σ M = 1.786MPa
τ zy = τ T = 6.013MPa
Employing the distortion-energy theory, we find, from equation (3.1), that:
σ ' = 10.567 MPa
60
Once that the considered yield strength for this material is Sy = 86MPa and that the global factor of
safety is n=3, it is obtained:
σ all =
Sy
n
= 28.667 MPa .
Fig. 3.36 shows the simulation study using FEP.
Fig.3.36 – Arm I’ von Mises Stress in Finite Element Cosmos – Second case.
This result shows that when the structure is under maximum torsional stress, the effective stress
σ’ continues lesser than in the previous case, consequently, the first case is the one that governs the
strength of the assembly. Also here, the highest stress respects to the stress at surface screw II.
Studying from now on the clamp, it is known that the bending moment Mc at section C proceeds,
as it has been all over the calculations in this work, from pieces weight. Thus, we have:
10
F = Fbook + Flight + ∑ Fi = 31.621N
1
10
M C = M book + M light + ∑ M i = 11.38 N .m
1
Fig. 3.37 shows how the clamp under loading.
61
Fig. 3.37 – Clamp’s loadings
Given that the screw clamp is perfectly collinear with the shown round part on the top of the
clamp, the bending moment MC at section C-C’ has to be compensated by the bending moment from
the tightening force Fclamp at the same section. This (internal) force is no more than a pressing force,
allowing the clamp to get tight against a surface. Therefore, we have:
M C = Fclamp ⋅ d ⇒ Fclamp = 379.33 N
Naturally, this is the case of the arm completely stretched, so the bending moment MC is the
greatest possible.
In order to verify section C-C’ for a Fclamp=379.33N, and considering the neutral axis to be between
sections A and B, the following analysis is made;
Since the dimensions are given as:
A = 0.01 ⋅ 0.045 = 4.5 ⋅ 10−4 m 2
1
⋅ 0.045 ⋅ 0.013 = 3.75 ⋅ 10− 9 m 4
12
c = 0.005m
I=
e = 0.025 + 0.005 = 0.030m
The bending couple can be calculated by:
M = Fclamp ⋅ e = 11.38 N .m
62
The stresses at point A and B can be determined as:
σA =
σB =
Fclamp
Fclamp
A
A
−
+
M ⋅c
= 16.01MPa < Tensile Strength from the material
I
M ⋅c
= −14.33MPa < Compressive Strength from the material
I
Verifying now if the location of neutral axis, we have:
σ =0⇒
Fclamp
A
−
M ⋅x
I
=0⇒ x=
= 0.28mm
I
A⋅e
This shows a minimal difference with the earlier considered neutral line.
Relatively to the screw clamp, it has a handle with a diameter of 5mm made of hot-rolled AISI
1006 steel (Sy = 170MPa [4]). This screw is M10 and is 10cm in long, overall. The clamp
accommodates parts up to 6cm in high.
Fig 3.38 illustrates the clamp’s handle dimensions.
Fig. 3.38 – Clamp’s handle.
The required torque TR needed to keep the Fclamp is given by equation (3.9). For this case, the
collar friction is neglected and the thread friction is 0.08, between the threaded surface made of
bronze and the screw clamp. Consulting bibliography [4], for M10 simple square threads, p=1.5. Using
the referred equation, the result is:
TR = 0.228 N .m
Given that the torque in the handle of the clamp is given by:
T = 0.04 ⋅ F
F is the required tightening force applied perpendicularly to the figure and it is given by equalizing
the last two torque moments’ equations. It is good to realize that this force is relative to the case in
63
which the arm is completely stretched, making a greater bending moment, like it was said before. With
this, we have:
TR = T ⇒ F = 5.7 N
It is also important to see if the self-locking relation is valid, with the intention of being sure that the
coefficient of thread friction ensures the thread to lock itself.
The self-locking relation is given by:
π ⋅ f ⋅ d m > l ⇒ 2.27 > 1.5
Subsequently, it is shown that the self-locking condition is valid.
3.3.5 Screws
This part of the work, as said before, will study screws, fasteners and joints in the structure of the
support. Those studies are gathered in this section with the purpose of having a better organization
and comparison. The screws’ aim is to tight the connections when they start to get loose.
Fig. 3.39 shows how the screws are connected with the arm.
a)
b)
Fig. 3.39 – Screws at the Arm I
To prevent the screws to erode the plastic pieces with the usage, the choice of putting threaded
surfaces made of bronze was taken. Since those surfaces do not have relative movements with the
components with which they have contact, and neither do the screws, the erosion is not significant.
Those bronze pieces’ young modulus is E = 110GPa and their length’s are respectively 20mm and
47mm for the surface screw III and surface screw II.
64
The selected steel M8x1.5 – CR4.6 screw (Fig. 3.40) has the following properties [4]:
E = 270GPa
Sp = 225MPa (minimum proof strength)
Su = 400MPa (minimum tensile strength)
Sy = 240MPa (minimum yield strength)
2
At = 36.6mm (tensile stress area)
A verification of the required preload is in need for this
connection. The factor of safety against joint separation also
needs to be calculated.
Fig. 3.40 – Screw III
Using the expressions (3.10), (3.11) and (3.12), the results for the stiffness of the fastener, for the
stiffness of the member and for the stiffness constant of the joint are, respectively:
kb = 0.21921GN/m
km = 1.19771GN/m
C = 0.155
The recommended preload, for a nonpermanent connection, given by equation (3.13), is:
Fi = 6176.25N
In order to determine the factor of safety against joint separation, the load P in tension from
equation (3.16) needs to be calculated. And so, we have:
P ≡ FM'' =
M ⋅ ri
∑ ri2
8
M = M book + M light + ∑ M t = 9.377 N .m
1
Where ri is the distance between the bolt’s axis and the hinge (Point H – Fig. 3.39-a)), point
around which the structure tends to rotate. The values refer to the radius of the connection piece I.
Since there is only one screw, P is given by:
P=
M 9.377
=
= 625.13 N
ri
0.015
65
Finally, using equation (3.16) and (3.17), it is obtained a factor of safety against joint separation of:
Frt = 528.23 N and nt = 11.69 > n p = 3
This results shows not only that the required preload verifies the specifications of not separation
(Frt < Fi) but also that the factor of safety against separation is accordingly to a good problem
dimensioning.
Relatively to the Wing Screw II, a similar analysis is made, as the following shows. The selected
steel M8x1.5 – CR4.6 screw (Fig. 3.41) has the following properties [4]:
E = 270GPa
2
Fig. 3.41 – Screw II.
Using the expressions (3.10), (3.11), (3.12) and (3.13), the results for the stiffness of the fastener,
for the stiffness of the member, for the stiffness constant of the joint and for the recommended preload
for a nonpermanent connection are, respectively:
kb = 0.21921GN/m
km = 1.19771GN/m
C = 0.155
Fi = 6176.25N
Using equation (3.16) the factor of safety against joint separation can be determined. The load P
in tension from the same equation needs to be calculated and so, we have:
P ≡ FM'' =
M ⋅ ri
∑ ri2
Where:
10
1
And ri is the distance between the bolt’s axis and the hinge (Point J – Fig. 3.39 a)), point around
which the structure tends to rotate. Again, the presence of a single screw brings to:
66
P=
M
= 758.67 N
ri
And using equation (3.16) and (3.17), we obtain the factor of safety against join separation:
Frt = 641.08 N and nt = 9.63 > n p = 3
With these results can be concluded that the required preload verifies the specifications of not
separation (Frt < Fi) and also that the factor of safety against separation is accordingly to a safe
problem dimensioning.
Considering that this screw II is under greater loading compared to screw III, a simple fatigue
study can be made for it. Consulting reference [4], the following parameters can be seen:
Se = 140MPa
kf = 2.2
Where kf is the fatigue stress-concentration factor for threaded elements and Se is the fully
corrected endurance strength. Ever since, using equation (3.20), the factor of safety guarding against
fatigue can be calculated. According to literature [4], considering Pmin = 0 => Pa = Pm = P .Thus, from
the referred equation, we have:
n f = 14.23
Like it was expected, this result shows that loadings from fatigue are not much important while
projecting these screws. Most importantly, is the erosion coming from the contact between the metal
and the plastic pieces.
Relatively to screw IV (Fig. 3.42), again, a similar analysis will be made. The difference to the
previous screws is that this one is only under shear stress. The length of the surface screw IV is
18mm, as we can understand from Fig. 3.43.
The selected steel M8x1.5 – CR4.6 screw IV has the following properties [4]:
E = 270GPa
2
67
Fig. 3.42 – Surface screw IV.
Fig. 3.43 – Screw IV.
In the same way, using the expressions (3.10), (3.11), (3.12) and (3.13), we have:
kb = 0.24357GN/m
km = 1.21987GN/m
C = 0.166
Fi = 6176.25N
In order to determine the factor of safety against joint slippery, the shear load Ps from equation
(3.15) is the sum of all the forces at this section. Thus, we have:
6


F =  Fbook + Flight + ∑ Ft  = 29.561N = Ps
1


Using equation (3.15) and (3.18), and collecting from [4] the friction coefficient between bronze
and steel fm = 0.08, we obtain a factor of safety against joint slippery of:
Fs = 369.51N and ns =
Fi
= 16.71 > n p = 3
Frs
This result shows that the factor of safety against slippery doesn’t bring problems for this screw in
particular.
Referring now case of screw V, again, a similar analysis can be made but with the particular
difference that this screw is under both shear stress and tensile stress. The length of the surface
screw V is 22mm.
In Fig. 3.44 is illustrated how the screw V is connected with the board by surface screw V. The
selected steel M3x0.4 – CR4.8 screw (Fig. 3.45) has the following properties [4].
68
E = 270GPa
2
Fig. 3.44 – Surface screw V.
Fig. 3.45 – Screw V.
Using the expressions (3.10), (3.11) and (3.12), the results for the stiffness of the fastener, for the
stiffness of the member and for the stiffness constant of the joint are, respectively:
kb = 0.07935N/m
km =0.43028 GN/m
C = 0.156
The recommended preload, for a permanent connection, given by equation (3.13), is:
Fi = 1403.37N
In order to determine the combined factor of safety against separation and slippery, the shear load
Ps and the P load in tension from equations (3.15) and (3.16) need to be calculated. And so, we have:
P ≡ FM'' =
M ⋅ ri
∑ ri2
5
1
Where ri (100mm) is the distance between the bolt’s axle and the hinge (Point J – Fig. 3.46), point
around which the screw tends to rotate. P and Ps are given by:
P=
M
= 7.88 N
ri
69
5


F =  Fbook + Flight + ∑ Ft  = 29.298 N = Ps
1


Fig. 3.46 – Hinge of Screw V.
Finally, using equation (3.14) and (3.19), and knowing from [4] that the friction coefficient between
bronze and steel is fm = 0.08 it is obtained a factor of safety against joint separation and slippery of:
Fr =
Ps
F
+ (1 − C )P = 372.88 N and no = i = 3.76 > n p = 3
fm
Fr
It is important to have in attention that the considered loadings are under estimated, since the
calculations were made only for one screw, consequently this result shows that the factor of safety
against separation is well estimated.
3.3.6 Simulator Surface, Top Middle-component and M2 screws
At this section of this thesis are studied the M2 screws, responsible for joining both simulator
surface and top middle component together – Fig. 3.48.
The material selected for the simulator surface is Cast Alluminum Alloy (E = 71GPa) and for the
top middle-component is Low Carbon Steel AISI 1015 (E = 205GPa) and their weights are:
m12=290.2gg, m13=175.3g.
The selected steel M2x0.4 – CR4.8 screw (Fig. 3.47) has the following properties [4]:
70
E = 270GPa
2
Fig. 3.47 – M2 screw.
Fig. 3.48 shows how these components are connected to each other.
Fig. 3.48 – Simulator Surface, Top Middle-component, Upper Tube and M2 screws.
A verification of the required preload for this connection is needed. The factor of safety against
joint separation also needs to be calculated.
With Fig. 3.49 is understandable the loading for this component as well as the place of the hinge.
Fig. 3.49 – Loading and hinge.
71
As usual, using the expressions (3.10), (3.11) and (3.12), the results for the stiffness of the
fastener, for the stiffness of the member and for the stiffness constant of the joint are, respectively:
kb = 0.03369GN/m
k1 = 0.27093GN/m
k2 =0.78225 GN/m
km =0.78223 GN/m
C = 0.04
The recommended preload, for a permanent connection, given by equation (3.13), is:
Fi = 481.28N
The load P in tension from equation (3.16) needs to be calculated in way to determine the factor of
safety against joint separation. Notice that this calculation is made relatively to the critical screw – the
screw under greater tension. Consequently, we have:
P ≡ FM'' =
M ⋅ ri
∑ ri2
Where ri is the distance between the bolt’s axle and the hinge (Fig. 3.49), ∑ ri
2
is the square sum
of all distances from all the screws to the hinge and M is the sum of all the bending moments from all
pieces weights.
For the critical screw, it is obtained:
11
1
And the load P is:
P=
12.89 ⋅ 97.5 ⋅ 10 −3
(97.5 ⋅ 10 ) + (90 ⋅ 10 ) + (90 ⋅ 10 ) + (82.5 ⋅ 10 )
−3 2
−3 2
−3 2
−3 2
+
= 38.66 N
Finally, using equation (3.16) and (3.17), we find the requires preload and factor of safety against
joint separation of:
Fr = 37.11N
nt = 12.98 > n p = 3
72
This result shows that these screw links are well projected.
3.3.7 Welding Top Middle-component and Upper Tube
In this section is studied the stress in the welded joint between the top middle-component and the
upper tube. Due to the loadings involved, only bending stress M inducing a throat shear stress
component in welds, this case is very simple. Fig. 3.50 illustrates how they are linked.
Fig. 3.50 – Top Middle-component, Upper Tube and Welding.
The selected material for the Top Middle-component is Low Carbon Steel AISI 1015 (Sy=300MPa)
3
and for the Upper Tube is a Steel Hot Finished (Y. S. 350MPa), both with densities of 7800kg/m . The
respective weights are: m13=175.3g and m14=951.3g.
Consulting reference [4], the yield strength for a hot rolled AISI 1015 is 190MPa, so this is the
yield strength value to have in account during calculations. Fig. 3.51 represents the weld’s free body
diagram.
Fig. 3.51 – Welding loadings.
73
The bending moment M in Fig. 3.51 Is given by:
12
M = M book + M light + ∑ M i ⇒ M = 13.05 N .m
1
For the corner weld shown in the same figure and using equation (3.17) and Tab. 3.1, we have:
h = 1mm
I u = 7729.5mm 3
I = 5464.8mm 4
c = 13.5mm
τ M = 32.24kPa
This low value of the nominal throat at shear stress is because of the low bending moments
loading. Thus, the welding solution guarantees that the top middle-component and the upper tube are
well linked.
This can be shown using the AISC Code for weld Metals [4], who shows the permitted stresses.
At this case, that code says that the nominal throat at shear stress doesn’t exceed
1.44 S sy ,being Ssy
the permissible stress. Calculating this parameter, given by the following expression, we have:
S sy = 0.577 S y = 109.63MPa
Where Sy is the lowest of the metal base’s yield strengths.
It is obvious that the welding throat is under dimensioned, because of the light loads inherent to
the problem.
3.3.8 Upper Tube and Bottom Tube
It is now time to study how tubes react when they are under the maximum loading. This loading
happens when the bending moment is the greater, again, when the arm of the support is completely
stretched.
The material selected for both tube is Steel Hot Finished and their properties are gathered in
section 2.11.2. The respective weights are: m14=951.3g, m15=1019.3g.
Fig. 3.52 shows the upper tube inside the bottom tube.
74
Fig. 3.52 – Tubes.
With the aim of calculating the maximum stress at the tubes, the following analysis is made:
The load F represented in the free body diagram in Fig. 3.53 represents the force respect to all
pieces weight, and M the respective bending moments. The figure on the right side represents an
approximation of the problem, with the free body diagram for the tube with smaller diameter. So we
have:
Fig. 3.53 – Tubes’ loadings.
14
F = Fbook + Flight + ∑ Fi = 37.66 N
1
12
1
Considering as an approximation that the compression force F and the bending moment M were
loading only the middle tube (tube with smaller diameter), the stress at the fixed section (point C) is
given by equation (3.22), and is:
(
)
13.05 ⋅ 27 ⋅ 10 −3
37.66
2
σ=
= 11.96 MPa
+
127.67 ⋅ 10 − 6
1.51 ⋅ 10 − 8
75
Since the material’s yield strength is Sy = 350MPa, using equation (3.2) it is clear that the allowed
stress, σall, for this section is highly above the stress at point C.
σ all = 116.67 MPa
The connection system between both tubes is comparable with the systems for common brooms
used nowadays.
Fig. 3.54 shows how the extremity of the upper tube is. Here, a friction piece
enlarged by rotating the upper tube, causes friction on the bottom tube. This eases the way of
choosing the desired height for the tubes, between approximately 50cm and 100cm. This component
can be obtained directly with the producer.
Fig. 3.54 – Friction Piece.
3.3.9 Bottom Tube, Bottom Middle-component and Base
Lastly, it is time to study the loads on the connection between the tubes and the base.
The bottom tube is connected to the bottom middle component by welding and this one is
connected to the base by a thread. The following figure illustrates the final assembly between them.
Fig. 3.55 demonstrates how these three pieces are connecting with each other.
Fig. 3.55 – Base, Bottom Tube and Bottom Middle-component.
The material selected for the Bottom Middle-component is a Low Carbon Steel AISI 1015
3
((Sy=300MPa) and for the Base is Gray Cast Iron (ρ = 7100kg/m ) and their weights are: m16=208.2g
76
and m17=4539.4g. The base requires a heavier weight comparing to all the other components because
its fundamental purpose is to bring stability to the support. Its weight and dimensions were studied
together in order to have a good relation between them, without exaggerating one of the parameters.
In order have the final shape of the base, a conventional machining process can be taken.
This case’s weld (Fig. 3.56) verification can be compared with the weld from section 3.3.7, since
they are under same loadings. Thus, we can conclude that, having this one a bigger section area
(d=34mm instead of 27mm), it is also well dimensioned. This welding also has a throat width of 1mm,
and the component’s material is the same. The following figure shows the free body diagram of the
weld.
Fig. 3.56 – Weld loadings.
Where the bending moment M in Fig. 3.56 is given by:
12
1
It is now time to verify if the thread’s geometry sustains the loading. This verification reports to the
root’s zone, section where the von Mises Stress σ’ is calculated.
Consulting reference [4], the chosen thread properties are d=30mm and pitch p=3.5mm, and
knowing that for a simple square type of thread the number of engaged threads is given by:
nt =
l2
p
The thread’s verification can now be taken. Fig. 3.57 and Fig. 3.58 show the bottom middle
component’s and the thread’s dimensions.
77
Fig. 3.57 – Bottom middle component geometry
Fig. 3.58 – Thread geometry
In Fig. 3.58 F is the force representative of all components’ weights, and it is:
15
F = Fbook + Flight + ∑ Fi = 56.97 N
1
using equation (3-24), the bending and transverse shear stresses are:
σ b = 0.154MPa
τ = 0.077 MPa
Using now equation (3-1), the respective effective stress σ’ at the top of the root plane, is given
by:
σ ' = 0.374MPa <<
Sy
n
= 100 MPa
This result shows that is clear that the number of engaged threads are more than enough to
support the force F, accordingly, this thread is under dimensioned.
Therefore, the resistant area of the threaded piece is:
Ar =
π ⋅ d r2
4
Since the case that rules the dimensioning is the case of the maximum bending moment (M =
13.05N.m), and that in this section there is no other loadings, using equation (3.3), it is obtained:
σ ' ≡ σ max = 5.9MPa <
Sy
n
= 100 MPa
78
It is now time to proceed to the base’s thread section verification. As we can see, the material of
the base is a brittle material; therefore, the failure theory used is the Maximum-Normal-Stress Theory
for Brittle Materials [4] that states that failure occurs whenever one of the three principal stresses
equals or exceeds the strength.
Considering the case of the support’s arm completely stretched, implying that the bending moment
(M = 13.05Nm) is maximum, the free body diagram in Fig. 3.59 shows that the base’s thread is only
under that same bending moment. Thus, from the inscription at equation (3.3) and equation (3.23), the
only stress applied at the base’s thread, and the principal stresses for plan stress, are:
σ X = σ max = 7.58MPa
σ A = 7.58MPa
σB = 0
For the base’s material, we have that the ultimate
tensile strength and the ultimate compressive stress,
are, respectively, given by:
Sut = 100 MPa and Suc = 130 MPa
Fig. 3.59 – Base’s loading
Employing the Maximum-Normal-Stress Theory, we find:
σ B Suc
≤
∧σA ≥ 0 ≥ σB
σ A Sut
Therefore, the failure equation to use is:
σA =
Sut
= 33.33MPa > 7.58MPa
n
This result shows that the effective stress applied at considered section is about four times lower
that the stress allowed for the same section. As a result, the base’s thread section is well dimensioned
and, despite being made of a brittle material, the weight of the book and structure doesn’t create any
problems to the base.
The base’s principal stress was also determined using the FEP Cosmos. As we can see in the
following picture, the principal stress is very similar to the one calculated before:
79
Fig.3.60 – Base’s Principal Stress in FEP Cosmos.
3.3.10 Wheels selection
The wheel’s selection for this support complies with parameters like the maximum weight they can
withstand as well as the necessary dimensions to attach the wheels on the bottom of the base (Fig.
3.61). The maximum weight of the support with the book and the lighting device is approximately
10.5kg. Using reference [7], the reference number of the chosen wheels is 918 708-87 (Fig.3.62), and
its primary characteristics – for each wheel, are:
-
Required dimensions for fixation: 11 x 22 mm;
-
Loading capacity: 30kg;
-
Construction height: 55mm;
-
Wheel diameter: 40mm;
-
Type of fixation: pin with tightening ring;
-
With locking system;
-
The wheels are made of black polyamide.
Fig. 3.61 – Base’s fixation space.
Fig. 3.62 – Selected Wheel.
80
CHAPTER 4 CONCLUSIONS and FUTURE WORK
4.1 Conclusions
The main goal for the execution of this work was to project and develop a solution for a bookholder where flaws like low flexibility, transportation and usage in different reading situations, besides
others, could be improved. A structure that could withstand documents with a range of sizes and
weights as well as a versatile solution, was also taken into consideration.
The beginning of the product generation started with a research for customers needs with a
questionnaire, followed by a benchmarking technique investigation and a study upon existent patents.
These analyses helped defining the basic product functions, targeting the main goals for the final
product and establishing the product specifications. After that, the developed product is, basically, a
multiple combination of different existing inventions that produce a new and improved product. It is
believed that a great number of the established target specifications were accomplished due to the
final product properties.
In this thesis, primary calculations and studies were made with the intention of analyzing the
general resistance, the dimensioning or the selection of different components for the support. After
this, the materials selection took over, having in mind the key functions of those components. That
selection complies with the desired properties for each component, but other materials (similar or not)
could have been elected. It is believed, supported by the calculations, that the chosen ones are a
good and reasonable solution for the product.
Looking at the several interaction systems between the different parts of the book holder, it is
believed that they bring something extra and positive to the product, namely: the wheels transportation
system which allows an ease of movement of the support; the height adjustment system, that
consents the user a greater number of reading situations; the clamp system of the arm, giving the
support a larger adaptability and easiness for different contexts; the rotational - in both extremities,
and the ”stretch/shrink” systems of the arm, allowing the support’s users a higher comfort and greater
reading positions; and the book’s side fixation, that allows vertically and horizontally adjustments,
dependent on size of the document.
Despite the relatively high weight of the base – approximately 4.5kg, derived from the maximum
length the arm can get, the wheel system guarantees a good transportability of the structure.
Due to the selected material for the bars - PA (Polyamide), the important decision of choosing the
same material for the pins was made while taking into account the loadings the structure is put under.
81
This decision complies with the fact that, if the chosen material for the pins was a metal one, the
erosion would be much higher and displeasuring for the bars.
4.2 Future Work
As mentioned in the work developed in this thesis, several components of the support requires
specific surfaces finishing, others requires specific geometric tolerances or particular manufacturing
processes. Despite the fact that a financial study was not an aim for this work, it was not completely
neglected due to the components characteristics. As a future work, it would be interesting to evaluate
the production costs for this book holder, regarding to the referred parameters as well as the
production volume. This would be helpful, for example, to understand which components are, or are
not, suitable to have a reduced cost design.
Again, the main objective of this thesis was to project and develop a solution for a reading device.
Hence, more and more innovations could be part of the support like, for instance, integrate lighting
and a switch on the board, provide the arm with more rotational movements, and allow the base to
occupy less space or allow the support to hold heavier and bigger books.
82
Bibliography
rd
[1]
Ulrich, K. T., Eppinger, S. D., Product Design and Development, 3 ed., McGraw- Hill, 2003.
[2]
Otto, K. and Wood, K., Product Design – Techniques in Reverse Engineering and New
Product Development, Pretince Hall, 2001.
rd
[3]
Dieter, G. E., Engineering Design, 3 ed., McGraw-Hill, 2000.
[4]
Shigley, J. E., Mischke, C. R., Budynas, R. G., Mechanicals Engineering Design, 7 ed.,
th
McGraw Hill, 2004.
[5]
rd
Beer, F. P., Johnston JR, E. R., Dewolf, J. T., Mechanical of Materials, 3 ed., McGraw-Hill,
2001.
[6]
th
Beer, F. P., Johnston JR, E. R, Vector Mechanics for Engineers, Statics, 6 ed., McGraw-Hill,
1998.
[7]
Kaiser + Kraft Catalogue, Julho 2004.
[8]
Silva, A., Dias, J., Sousa, L., Desenho Técnico Moderno, 3ª edição, Lidel, 2002.
[9]
www.surveymonkey.com
[10]
www.google.com/patents
[11]
www.lecturacomoda.com
[12]
www.bookholder.de
83
Appendix
Appendix A - Questionary
1- In which age group are you?
a) 0-12 years old
b) 13-17 years old
c) 18-24 years old
d) 25-34 years old
e) 35-54 years old
f)
55 years old or more
2- While reading, do you use a book-holder often?
a) Yes
b) No
2-1 If you answered Yes:
2-1-1
In which circumstances? (Eg: While reading in bed or outdoors, etc.. Specify situations.)
2-1-2
What is the range of books that your book-holder is able to carry?
a) Only small books, up to 400 grams approximately
b) Medium books up to 1.5kg approximately, but not for big books such as culinary
books
c) All kind of books
2-1-3
Does the book-holder completely satisfy your needs?
a) Yes
b) No
2-1-3-1 If your answer was No, explain why not.
3- Do you consider the design of a book-holder to be important?
a) Yes
b) No
84
4- Do you have mobility problems, back problems, vision problems or any other problem that
causes you discomfort while you are reading a book?
a) Yes
b) No
5- Which age group is most likely to use book-holder in your opinion?
a) 0-12 years old
b) 13-17 years old
c) 18-24 years old
d) 25-34 years old
e) 35-54 years old
f)
55 years old or more
6- Which of the following factors do you consider to be the most important for a new and better
book-holder? (You are able to chose up to 6 – put them in order of importance starting with
the most important)
a) Weight
b) Price
c) Comfort
d) Adaptability to different reading situations
e) Dimensions
f)
Assembly and disassembly
g) Handling, usage
h) Flexibility and easy storage
i)
Easy carrying
j)
Lighting
k) Design
l)
Robustness
m) Other(s) (Specify)
7- What is the average weight (approximate) of the books that you usually read?
a) Only small books, up to 0.5kg (Eg: thin reading books)
b) Médium books, between 0.5kg – 1kg (Eg: standard books)
c) Big books, between 1kg – 2kg (Eg: thick books, law books)
d) Very large books, with more than 2kg (Eg: cooking books, Encyclopedias)
e) All kind of books
85
8- In which places do you usually read books? (Put in order of highest use)
a) Bed
b) Sofa
c) Kitchen (Culinary or recipe books)
d) Car, bus
e) Beach
f)
On a table
g) Other (Specify)
9- In your opinion what are the main disadvantages of a book-holder? (Multiple answers
possible)
a) Difficult usage
b) Lack of adaptability for using in different places
c) Expensive
d) Transportation difficulties
e) Restrictions on the use of different type of books – in weight and size
f)
Not have lighting
g) Other(s). (Specify)
10- What do you think is the most important gained advantage of using a book-holder?
11- How much money [€] would you be willing to pay for a book’s holder reading support that is
comfortable, practical and adaptable in various situations? Be realistic.
a) 0 - 25
b) 25 – 50
c) 50 – 75
d) 75-100
e) Over 100
12- Would you consider using a product like this? Why (not)?
13- Make some comments, suggestions and observations that you consider relevant.
86
1- Fixing
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
19- Transportation
18- Durability
17- Resistance
16- Weight
+
15- Stability
14- Security
13- Time to
disassembly
12- Time to
assembly
11- Storage
10- Dimensions
9- Price
8- Design
7- Adaptability to
different
situations
6- Flexibility
5- Comfort
4- Lighting
3- Adaptable to
several types of
books
2- Compartments
Needs
Metrics
Appendix B - Needs-Metrics Matrix
Tab. B1 – Needs – Metrics Matrix.
+
+
+
+
87
Appendix C - Benchmarking Information
In this appendix, each table is relative to the correspondent product.
a) “Atril de Lectura Lecco”
-
Includes two substitutable bases.
-
Applicable to most kind of books.
-
Easy assembly. Doesn’t need tools.
-
Existence of three distinct models: sofa, wall and bed.
-
It has Lighting .
-
The material is stainless steel.
Tab. C1 - Atril de Lectura Lecco.
Model
Price [€]
Weight [kg]
Complete
195
4
Bed
146
1.5
Stand/Sofa
149
2.5
Wall
95
0.750
Lighting
16
0.200
b) “Levo Book Holder”
-
Existence of two different models: Stand Model and Desk Model.
-
Applicable to books until 2,25kg.
-
Easily clamps to a desk or table (up to 5cm thick).
-
It has lighting.
-
It is made of steel, nylon (super strong polymer), ABS (book board) and sturdy cast iron base.
Tab. C2 - Levo Book Holder.
Model
Price [€]
Weight [kg]
Stand
249
15
Desk
139
3.5
Lighting
9.90 to 49.90
0.221
88
c) “Soporte de lectura Tercera Estación”
-
Holds single copies, magazines.
-
Easy carrying.
-
It has a little space to store pens.
-
Its material is aluminum.
Tab. C3 - Soporte de lectura Tercera Estación.
Model
Price [€]
Weight [kg]
Portable
6.75
0.520
d) “Atril Monopié”
-
Adjustable height
-
High robustness.
-
It has a little compartment to store pens and glasses.
-
Made of wood and iron.
Tab. C4 – Atril Monopié.
Model
Price [€]
Weight [kg]
Fixed
29.81
12
89
Appendix D - Patents
All the figures in this appendix are relative to each considered patent.
a)
Patent number: 5884888
Inventors: Johnie Grimes, III, Hamilcar H. Candera, Timothy J.
Sweeney
Description: Portable reading material support, illuminated and a
goose-neck flexible permits the user to read more easily. The
platform is comprised of a linear deep recess for receiving the
binding (back) of the book.
Fig. D1 – Patent A.
b)
Patent number: US 2007/0090264 A1
Inventor: Paul J. MacLennan
Description: The book holding device is portable,
enjoyable and provides the user a greater freedom.
Fig. D2 – Patent B.
c)
Inventor: Matthew Lebar; Martin Lebar
Description: The support is stand and from the three cylindrical
legs, two are rotatably. It is possible to mount a support for a
book or a microphone.
Fig. D3 – Patent C.
90
d)
Patent number: US 2001/0035486 A1
Inventor: Allen C. Pryor
Description: The invention is a bedside book holding
apparatus. It includes a support frame for the document, a
lamp and angle adjusting.
Fig. D4 – Patent D.
e)
Inventor: Melvin H. Torme
Description: A book support used while reading
in bed including a suitable floor base or bedclamping base. It is adjustable to different book
sizes. It has lighting.
Fig. D5 – Patent E.
f)
Inventor: Richard J. Howell
Description: A book holder with an easy transportation system –
wheels. The book is hold between two plates, and one of them is
transparent.
Fig. D6 – Patent F.
91
g)
Inventor: Debra Haynes
Description: Support with a very flexible type of lighting.
Fig. D7 – Patent G.
h)
Patent number: US 2005/0132520
Inventor: Gabriel Navarro
Description: An adjustable broom with an easy locking
system.
Fig. D8 – Patent H.
i)
Inventor: Kohichi Yamaguchi
Description: This invention provides to an object to be set
horizontally without any difficulty.
Fig. D9 – Patent I.
j)
Patent number: US 6702482 B2
Inventor: Daniel Sherwin
Description: This invention provides a fast-deployable light weight
tripod with extended legs.
Fig. D10 – Patent J.
92
Appendix E – Technical Drawings
93

Design of a Reading Device Engenharia Mecânica

Transcription

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