Class 7 - personal.stevens.edu

EE/CpE322 Lecture 6
Bruce McNair
Based on
Engineering Design: A Project-Based Introduction
(the 3rd ed.), by C.L. Dym and P. Little
A Model of the Design Process
Design Space
!  A design space is a mental construct of an intellectual
space or framework that envelops or incorporates all
of the potential solutions to a design problem.
!  Large, or complex design spaces - ones for which the
number of potential designs is great or for which there
are many relevant design variables
!  Small, or bounded design spaces - ones for which there
are few design variables and few potential designs
Morphological Charts
!  Morphological charts are helpful development tools to
generate alternative designs.
!  They consist of a chart or matrix
!  Functions or key features are listed in the first
column,
!  Alternative means of realizing each function are
given in that function’s row.
!  Generating the means can be a highly creative process.
!  The means do not have to be words. They can be sketches
or thumbnails.
Morphological Charts
!  Beverage container example
Morphological Charts
!  Beverage container: two feasible designs
Morphological Charts
!  “Building block” analog computer example (1993)
Morphological Charts
!  Portable electric guitar
Morphological Charts
!  Morphological charts can be used to generate
complete alternatives.
!  Since the leftmost column lists all the functions, selecting a
means from each row guarantees that the solution will satisfy
all the required functionality.
!  Such an approach will not, however, guarantee that
the alternative will work, or even be internally
consistent. Judgment is still required.
!  This approach also can result in a huge number of
alternatives.
!  Morphological charts should contain all potential
alternatives. Infeasible ones must be pruned.
Complex Design Space
!  Complex design spaces may be very large and have
substantial interactions among the design variables.
!  Values of many design variables are highly dependent
!  A strategy for handling complex design spaces is
decomposition, or divide and conquer.
!  Morphological charts are suited to
!  Decomposing the overall functionality of a design into its
constituent sub-functions
!  Identifying the means for achieving each of those functions
!  Enabling the re-composition of possible design solutions
Expanding the Design Space
!  At early stages of the design process, it is desirable to
increase the size of the design space.
!  Design generation requires goal-directed creative
activity.
!  Two principle themes
!  There’s no sense of reinventing the wheel.
!  Group activities -- brainstorming
Brainstorming
!  True brainstorming occurs in two phases:
!  Free flowing idea generation without any analysis
!  THEN, analysis to weed out the useful ideas
Brainstorming
!  True brainstorming occurs in two phases:
!  Free flowing idea generation without any analysis
!  THEN, analysis to weed out the useful ideas
!  Ice build up on high tension wires in cold climates needs to be
removed to avoid damage due to excess weight/wind load on the
wires. How to remove ice?
Brainstorming
!  True brainstorming occurs in two phases:
!  Free flowing idea generation without any analysis
!  THEN, analysis to weed out the useful ideas
!  Ice build up on high tension wires in cold climates needs to be
removed to avoid damage due to excess weight/wind load on the
wires. How to remove ice?
!  Brainstorming led to a suggestion to train polar bears to climb
the towers to shake the wires, breaking the ice
Brainstorming
!  True brainstorming occurs in two phases:
!  Free flowing idea generation without any analysis
!  THEN, analysis to weed out the useful ideas
!  Ice build up on high tension wires in cold climates needs to be
removed to avoid damage due to excess weight/wind load on the
wires. How to remove ice?
!  Brainstorming led to a suggestion to train polar bears to climb
the towers to shake the wires, breaking the ice
!  While that idea is not a sensible suggestion, it led to the idea of
having helicopters fly over the wires to vibrate them, breaking the
ice free.
Expanding the Design Space
!  Sources of ideas for expanding the design space:
!  Taking advantage of design information that is readily
available, such as the Thomas Register or benchmarking
other products.
!  Patents: There are 2 basic kinds of patents, design patents
and utility patents. Patent information is now available on the
World Wide Web.
!  Group activities can be useful in expanding the design space,
and a number of techniques have been developed to
encourage such divergent thinking,
!  Other methods available include use of synectics, and other
analogy based tools. Analogical thinking of this sort has led to
a number of inventions, including velcro, and heart stents.
Group Activities
!  The 6-3-5 method
!  Six team members
!  Each writes an initial list of three design ideas, briefly
expressed in key words and phrases
!  Each list is circulated among five other team members
for annotation and comments.
!  No communication between team members during this
process
!  Collect all the annotated lists and discuss them in group
meeting
Group Activities
!  The C-sketch method
!  Six team members
!  Each provides an initial sketch of a single design
concept
!  Each sketch is circulated among five other team
members for annotation and comments.
!  Collect all annotated sketches and discuss them in
group meeting
Group Activities
!  C-sketch example
Group Activities
!  The gallery method
!  Each team member develops an initial design
!  All designs are collected and posted in a group meeting
!  All designs are discussed. Questions are asked,
critiques are offered and suggestions are made.
!  Each team member take the inputs and generate a
second generation design.
!  This process repeats until a consensus emerges.
Limiting the Design Space
!  After a thorough design generation process, limiting
the design space becomes necessary
!  Limiting the design space to a useful size is usually
based on a solid understanding of user needs,
available technologies, and external constraints.
!  Common sense considerations:
!  Invoke and apply constraints while assessing the
importance of user needs
!  Freeze the number of attributes being considered
!  Impose priority orders
!  Avoid infeasible ideas
Selecting the Preferred Design
!  Selecting the best alternatives can be done by many
different approaches.
!  The evaluation process usually begins, however, by
examining alternatives in terms of constraints,
!  This allows the design team to immediately reject any
designs that fail to satisfy constraints.
!  Different clients may have different values, they may
choose different designs for
!  Experience and judgment are needed in deciding how
complex an evaluation matrix to use, and how
detailed a set of calculations are appropriate.
Selecting the Preferred Design
!  Numerical evaluation matrices
!  Apply constraints to eliminate some design alternatives
!  Each design is assigned a score between 0~100 for each
objective
!  The design with the highest total score wins
!  The beverage container example
Selecting the Preferred Design
!  The priority checkmark method
!  The objectives are ranked with three priority levels (high,
medium, low)
!  If a design satisfy an objective, it scores points according to
the priority if that objective. If not satisfy, it scores nothing
!  The beverage container example
Selecting the Preferred Design
!  The best-of-class chart
!  For each objective, the best design alternative is
assigned a score of 1; the second-best design
alternative is assigned a score of 2, and so on.
!  The lowest summed score indicates the best design
alternative
Selecting the Preferred Design
!  Important reminder
!  The ordinal rankings of the objectives obtained
using PCCs can not be meaningfully scaled or
weighted.
!  Common sense must always be exercises.
Question the following:
!  Are the evaluations align with our expectations? Why or
why not?
!  Are designs with close scores really equivalent?
!  Are comparisons fair?
!  Are those constraints absolutely necessary?