Wright State University - Engineering Senior Design Projects to Aid

Transcription

CHAPTER 21
WRIGHT STATE UNIVERSITY
College of Engineering and Computer Science
Department of Biomedical and Human Factors Engineering
Dayton, Ohio 45435-0001
Principal Investigator:
Chandler A. Phillips (937) 775-5044
[email protected]
David B. Reynolds (937) 775-5045
323
324 NSF 1999 Engineering Senior Design Projects to Aid Persons with Disabilities
LEARNING AUDIO DEVICE
Designers: Benjamin R. Lucas, Anthony J. Ewald, and Russel A. Clark
Supervising Professor: Dr. Thomas N. Hangartner
Wright State University
Dayton, OH 45435-0001
INTRODUCTION
A teacher at a school for children with disabilities
requested a modification of a toy to help foster
learning of shape recognition.
The students
previously used a cylindrical plastic toy with three
holes in its lid. The holes were square, triangular,
and circular. The child dropped red, yellow, and
blue plastic blocks corresponding to the holes in the
cylinder as they learned to recognize different
shapes and colors. Children frequently placed a
shape at the opening of the correct hole but moved
the block to another hole when it did not
immediately fit. This was because the child was not
holding the block in the correct orientation and did
not have enough affirmation that the block was near
the correct hole.
The teacher requested a similar toy that would emit
a beeping sound when a block was above its
corresponding hole. With this proximity feedback
the child knows that the hole was correct and that
the block must be rotated to the correct position.
This process would encourage the child to
concentrate on the configuration of the shape of the
Figure 21.2. Children Safely Interacting With The
Learning Audio Device.
block and the hole.
The teacher also requested an audio reward for the
child when a block is successfully placed inside the
toy. The success feedback was to be independent of
the proximity sensing method.
Additional
specifications were that the toy be:
•
Portable,
•
Small enough to enable small children
seated at a desk or table to see the whole lid,
•
Battery powered to eliminate cords that
might pose a tripping hazard, and
•
Safe for use with small children, having no
sharp edges, exposed electrical components,
or small pieces that can be swallowed.
The learning audio device is illustrated in Figure
21.1, and shown in use in Figure 21.2.
SUMMARY OF IMPACT
Figure 21.1. Learning Audio Device.
The learning audio device is safe and fun. There are
a few recommendations for further work that would
make this product more enjoyable and practical.
Battery life is less than an hour, meaning frequent
replacement by the user. Supplying the user with a
9-volt battery charger would reduce maintenance
cost. For future development one could find ways
Chapter 21: Wright State University 325
to reduce the overall power consumption to get
more life out of the battery.
Another
recommendation would be to institute a means of
audio volume control on the device. According to
the evaluator, the design is thoughtful, as are the
switch options. The easy-access collection box
eliminates the need to open the box itself. The
battery is easy to change. The instruction manual
was reportedly very helpful.
TECHNICAL DESCRIPTION
For proximity sensing, the method implemented is
mutual inductive coupling. The basic physical
concept behind this method is Faraday’s Law, which
states that if an alternating current is sent through a
(primary) wire, an electromagnetic field will be
induced around the wire. The magnitude of this
field is proportional to the frequency of the current
(i.e. the derivative of the current with respect to
time). If another (secondary) wire is brought within
proximity of this field, energy will be transferred to
it, and a current will be induced.
Winding both of the wires into coils capitalizes on
this phenomenon while keeping the system
compact. Each coil acts as a large inductor, with an
inductance value (L) that depends on both the
geometry of the coil and the number of windings. If
a coil is then placed in parallel with a capacitor, the
transfer of energy back and forth between the two
components results in an oscillating system. The
magnitude of energy transfer is maximized at a
particular frequency, known as the resonant
frequency. By varying the capacitor, the circuit can
be “tuned” to any desired frequency. The circuitry
is depicted in Figure 21.3.
Application of this method to the design involves
attaching an active (power supplied) coil around
each of the holes in the lid. A passive coil is placed
inside the block. Each shape (in both the block and
the lid) is tuned to a specific frequency so that when
the coils are brought together, energy is transferred
from the active coil to the passive one. Shapes can
be differentiated by frequency modulation (e.g. the
squares are tuned to 600 kHz, circles to 455 kHz, and
triangles to 300kHz). The voltage change associated
with the active coil is then used to trigger audio
feedback. This means that the passive circuit (in the
block) is only absorbing and dissipating power, and
therefore requires no power supply in the blocks.
Implementing this circuitry is inexpensive since wire
coils and passive components are readily available
and inexpensive.
The proximity sensor relies on three different
components:
•
A measuring resistor,
•
A half-wave rectifier, and
•
A comparator.
The measuring resistor is placed in series with the
RLC circuit, and when the coils are tuned, the
voltage across the resistor is at its minimum because
the voltage across the coils is at its maximum
(Ohm’s Law).
When a tuned passive coil comes close to the active,
it draws current from the active coil, which in turn
increases the current in the circuit. By Ohm’s Law,
this increases the voltage across the measuring
resistor. This increase in AC voltage is then rectified
and smoothed before it is sent to a comparator. An
appropriate threshold voltage is input to the
comparator also. This is done by constructing a
voltage divider from the power source. When the
input from the rectifier exceeds this threshold (i.e.
when a block is brought near the correct hole), a
high output pulse is sent to a piezoelectric beeper,
producing the required feedback.
For the success sound, three different microswitches
are mounted on the underside of the ramp inside the
toy. The lever arms of these switches extend up
through the holes in the ramp under each of the
differently shaped holes. As the blocks fall through
the lid of the toy, they strike the switches before
hitting the ramp and sliding down into the
collection bin. When the switches are thrown, they
complete a circuit connecting the voltage supply to
an audio chip that was extracted from a children’s
book. Each momentary switch is connected to a
different location on the chip, causing a different
jingle for each shape. The schematic of these
components is illustrated in Figure 21.3.
The finished toy is a small box constructed with
poplar wood, stained with a red oak finish and
sealed with polyurethane. All of the electrical
components were connected using standard
soldering techniques and IC sockets wherever
possible. A computer-generated diagram of the
circuitry is shown in Figure 21.4.
The master switch is a red, three-position switch
located on the side of the toy. When this switch is in
the center position, the toy is off. When the switch is
thrown toward the collection bin of the toy, only the
success feedback is activated. When the switch is
thrown in the other direction, both the proximity
and success feedback systems are activated. When
the toy is not in use, it is important that the switch
be in the “off” (center) position. Leaving the toy on,
especially when both success and proximity
feedback are activated (i.e. the switch is away from
the collection bin) will rapidly decrease the life of
the batteries inside the toy.
In order to change the battery, the lid of the toy must
be opened, exposing the inner success slope. After
carefully lifting this slope (making sure the large
wires to the lid area out of the way), the underlying
circuitry can be seen. The battery holder is mounted
on the same side as the switch. The battery is placed
so that the large terminal slides onto the small
terminal on the holder. Finally, the battery is firmly
put in place in full contact with the terminals of the
holder.
The base can be rotated from side to side to vary the
positions of the holes, but the collection bin should
not be oriented toward the child. Giving the child a
block with the indentation (grip) directed upward
helps ensure correct vertical orientation and a good
signal for proximity sensing. After the block has
been put in the correct hole, it slides to the collection
bin. The collection bin lid can be kept open to clear
the ramp.
The overall cost of the learning audio device is
$890.00.
2.2k
2.2k
2.2k
5k
5k
5k
-5/5V
22k
6.4nF
.8nF
50nF
22k
300kHz
1k
22k
78L05
7.2V
10nF
IN OUT
+
COM
-5/5V
18
22k
6.4nF
.8nF
50nF
22k
300kHz
1k
22k
10nF
DC/DC Converter
+
IN
+15v
COM
-15v
22k
6.4nF
.8nF
50nF
22k
300kHz
-5/5V
8
1k
22k
10nF
+
Figure 21.3. Circuit Schematic.
Battery
Oscillators (3)
Speaker
Raised Circuit Board
Voltage
Regulator
Trimming
Capacitors (3)
EPROM
Variable
Resistors (3)
Comparators
(2)
Circuitry for
On/Off switch
Figure 21.4. Circuitry Diagram.
Proximity
Beeper
WHEELCHAIR ADAPTED BARCODE SCANNER
SYSTEM
Designers: Angeles Seibert and Mary Yinger
Supervising Professor: Dr. Blair Rowley
Dayton, Ohio 45435-0001
INTRODUCTION
A fifty-year old man with spastic cerebral palsy is
employed at a home improvement warehouse. His
employer would like him to scan barcodes on the
shelves to check for incorrect prices. The client’s
movement and posture disorder is characterized by
increased muscle tone that results in movement
difficulty. He uses a wheelchair and has moderate
ataxia (shaking).
The client’s ataxia makes it
difficult to hold the bar code scanner steadily
enough to scan a barcode. The client uses a Ranger
X Storm Series wheelchair and his steering
mechanism is located on the left side of his
wheelchair. The barcode scanner is a Symbol
Technology LRT 3800.
The purpose of this design was to create a system
that securely attaches a barcode scanner to the
client’s wheelchair without inhibiting use of the
scanner or wheelchair. The system, depicted in
Figure 21.5, must allow raising and lowering of the
scanner as well as triggering of the scanner and data
entry.
SUMMARY OF IMPACT
The client was a very active part of the design
process. The current system requires some physical
exertion from the client. The repetitiveness of the
exercise will increase his muscle tone and will
improve his ability to use the system.
Unfortunately, the design is not as easy for the client
to operate as originally intended.
It is
recommended that further work involving the
scanner be achieved. Additionally, the scanner
should be internally wired to a stereo jack located at
the back of the scanner, allowing for a push button
to be plugged into the jack to eliminate one rope
from the system, which in turn would reduce some
of the physical exertion required.
Figure 21.5. Bar Code Adapter System.
With a securely mounted scanner, the client is able
to raise and lower the scanner, trigger the scanner
and press the enter button, thus allowing him to
perform his job duties successfully. The whole
system can be easily removed from the wheelchair
and the scanner can be easily removed from the
system.
The barcode system is constructed of ¾ inch PVC
pipe. It measures 5 feet high, 10 inches across, and 5
inches deep. The entire system weight is less than 7
pounds without the scanner attached. There is a 4½foot steel rod inserted into the PVC pipe to help
keep the system from bending. The scanner is
attached to a ½ inch thick wood backboard by
Velcro straps. The scanner is raised and lowered by
ropes and six 1” rigidly mounted pulleys. The
scanner’s operating range is 14 to 55 inches from the
floor. The system is not designed to lift more than
20 pounds.
To operate this system, the scanner is positioned into
the upper cutout on the backboard. It is necessary
that the handle slide down through the triggering
mechanism and that the rubber strip be secured over
the trigger. Once the handle is secured tightly to the
backboard with two Velcro straps, the scanner is
securely mounted to the system.
The system is attached to the wheelchair by hooking
the metal base over the lower wheelchair bar. The
middle portion of the scanner is secured with a
Velcro strap wrapped around the vertical arm bar of
the wheelchair. All colored handles are placed in
the user’s lap for easy access as well as to keep them
from getting caught in the wheels.
The yellow handle, as shown in Figure 21.6, can be
pulled to raise the scanner. The green handle is
used to lower the backboard when the scanner is not
mounted, so it can be secured out of the way at the
bottom of the system with a nylon buckle strap.
There is no need for it when the scanner is mounted
because the additional weight will pull the system
down naturally. The scanner is secured at the
correct height by wrapping the yellow handled cord
around the gold hook located on the back of the
system.
Pulling on the blue handle triggers the scanner. The
handle pulls the trigger mechanism on the scanner.
The entire system shifts slightly when this occurs,
but the weight of the scanner reduces this greatly.
When a correct price is scanned, the scanner will
beep once and the client can simply go on to scan
the next barcode. However, when an incorrect price
is scanned, the scanner beeps twice and the client
will have to press the enter key located on the top of
the scanner. Pulling the red handle will press the
enter button. This action has to be completed twice
before proceeding onto the next barcode.
The total cost of this bar code adapter system is
$550.00.
Eye Screws
Pulleys
Enter Key
Activator
Trigger Gun
Activator
Enter Key Activator
Handle
Velcro Straps
Raising Handle
Pulley
Trigger Gun
Activator Handle
Lowering
Handle
Eye Screws
Nipple
Hook
Plate
Figure 21.6. Side View of System.
ERGONOMIC ANALYSIS OF THE BLOOD
MANUFACTURING PROCESS
Designers: Brian Bautsch, Nora Buzek, P. Joseph Gilkerson, and Kristianne Liebel
Supervising Professor: Dr. Richard Koubek
Dayton, OH 45435-0001
INTRODUCTION
An ergonomic analysis of the current blood
collection process utilized by the American Red
Cross (ARC) indicates that the current hand tools
used during this process are predisposing
employees to repetitive motion injuries, or
cumulative trauma disorders (CTDs), due to
inadequate design considerations and improper
technique. From January 1990 to December 1995, it
is reported the ARC spent over $2.75 million for
workers’ compensation claims related to repetitive
injuries. This basic fact has led them to seek out
possible methods of eliminating such injuries and
subsequent claims. The current hand tools require
repetitive bent-wrist motions and require the wrist
to be in an ulnar deviation posture.
These
combinations of repetitive motions that are
completed in a non-neutral wrist posture increase
the chances of CTDs.
While the repetitive nature of the task cannot be cost
efficiently reduced, the redesign of the current hand
tool can help to eliminate the problem. The hand
tools should incorporate ergonomic advantages,
including:
•
Neutral wrist posture,
•
Curved handles,
•
Longer handles,
•
Reduction in required grip strength to
perform the stripping task, and
•
Cushioned gripped handles.
This redesigned hand tool, along with proper
training techniques, will be the proposed as a viable
solution to the costly CTD problem.
There are several additional design specifications.
The tool must incorporate both the crimper and the
stripper into one tool, to allow the user to work
Figure 21.7. Newly Designed Hand Tool.
continuously without stopping to switch tools
during the process. Employees may be left or right
handed, thus necessitating a tool that can be used
easily by both. The wrist must be placed in a neutral
position, promoting neutral hand and wrist posture
so as to reduce the risk of CTDs. The weight of the
hand tool should not exceed 0.5 kg. The tool must be
intuitive to use such that the training time is
minimal. It is also desired that the grip span be
between 2.5 and 3.5 inches and the handle grip
length be at least 5.5 inches.
SUMMARY OF IMPACT
The design goal was to reduce the likelihood of
CTDs by minimizing awkward wrist posture.
Following a through design process, excessive force
was determined not to be a significant factor and
repetition is a part of the job beyond the control of
the design team. It has been determined, through
preliminary user analysis, that an enhanced hand
tool design promoting a neutral wrist posture will
reduce wrist deviation. Based on statistical analysis,
the design goal is achieved. The design group was
unable to perform long-term follow-up testing,
given time constraints. Follow-up testing would
determine the true reduction of incidences related to
CTDs.
For the stripping process, a longer moment arm (in
the handle) is implemented in the new tool. The new
handle is approximately 3 inches longer. This
provides a greater mechanical advantage during the
task of stripping, thereby requiring less force to
operate the tool. For the crimping process, Instron
testing demonstrated that the round aluminum clip
required less compressive force than the square
aluminum clip. The final design of the new hand
tool is shown in Figure 21.8.
•
Functionality of the tool,
•
Intuitiveness of the tool,
•
Wrist deviation, and
•
Performance time.
Based upon the results, both tools are equally
functional; however, evidence suggested that the
new tool is more intuitive than the old. The angle of
wrist deviation on the new tool is consistently lower
than that on the old tool, such that the new tool
promotes a more neutral wrist posture than the old.
The old tool proved to have faster performance
times; however, the observed improvement times
suggests that the performance time of the new tool
will eventually converge with the performance time
of the old tool.
Once the tool had been designed and machined, the
next stage of the design process was to validate the
tool. The testing process consisted of having two
groups of ten subjects, each group responsible for
evaluating one of the two tools.
The total cost of this project, including labor and
materials, is $960.00.
The parameters of interest in the testing process
included:
+.005
.250 -.000 DIA
THRU
.750
NOTES:
.306 DIA
Ø.938
.265 DIA
1) Dimensions are in inches.
2) Material: 6061 T6 Aluminum Alloy
Wheel
Crimp Ring
3) Finish: Black Anodize
4) Finish Texture: 75
.938
Assembly
R5.000
10-24 UNC
THRU (3X)
8.00
2.313
Arm A
10-24 UNC THRU (2X)
1.438
1.468
.625
.250
.500
.625
Ø1.25
.250
.500
+.005
.250 -.000 DIA
THRU
Arm B
Full
Radius
Ø 1.25
.250
.185
.250
Notch shall be centered .125"
in from both edges.
.500
.625
.625
10-24 UNC THRU (3X)
1.438
.313
1.750
.750
1.125
Figure 21.8. AutoCAD Drawing of the Hand Tool Design.
.500
PHYSIOLOGICAL ACTIVITY MONITOR
Designers: Dean Acker, Lisa Carnes, Jere McLucas, and Tracy Rausch
Supervising Professors: Xudong Zhang, Ph. D. and D. Drew Pringle, Ed. D.
Dayton, OH 45435-0001
INTRODUCTION
Actigraphy, the long-term continuous measurement
of movement with a small solid-state recorder, is
being used in an increasing number of research
fields. Actigraphs are easy to wear because they are
small and lightweight and have been found to
effectively measure movement using a number of
different devices.
Devices used include
accelerometers, pizoelectric bimorphous beam
motion sensors, and electromagnetic systems.
Activity monitors currently on the market have
several limitations. First, they merely give an
indication of movement duration, causing
potentially valuable information about the
acceleration, velocity, and position amplitudes of the
movements to be lost.
In order to completely define actual movement and
the effects thereof, one must obtain more
information about the movements being performed,
including the direction of movement, range of
movement, or the force exerted by the muscles. The
goal of this project was to design a device, as
depicted in Figure 21.9, that will be able to define
specific movements as well as collect information
about an individual’s heart rate and skin
temperature.
Based upon available funding and time constraints,
a device was built for one limb. If one limb can be
analyzed, then theoretically, the other three that
would need to be analyzed would be identical. The
objective of this project was to utilize
accelerometers, contraction sensors, a polar heart
rate monitor, and a thermistor to obtain specific limb
movement direction, heart rate, muscle group
contraction, and skin temperature. These devices
were chosen based on availability, budget
requirements, and time constraints.
There were several design requirements for the
physiological activity monitor (PAM), including that
it measure heart rate, skin temperature, movement
direction, movement acceleration, and contraction.
Figure 21.9. Physiological Activity Monitor.
The PAM must not restrict movement of the subject
and must be easily attached to the subject.
Additionally, the PAM must dissipate heat
adequately, be operable in multiple environments,
have high thresholds for muscle contractions, use
standard parts, be portable, and comply with AAMI.
SUMMARY OF IMPACT
Human body movement has become increasingly
popular when studying neuromuscular diseases,
sleep patterns, and sports rehabilitation. A device
that can monitor human movement outside of a
laboratory setting can provide researchers useful
insights.
This device utilizes two triaxial accelerometers, two
contraction sensors, a heart rate monitor and a
temperature probe.
The accelerometers enable
location of limb position. The contraction sensors,
constructed of strain gauges and epoxy resin board,
aid in the determination of changes in limb segment
diameter, possibly signifying a muscle group
contraction.
When coupled together, the
accelerometers and contraction sensors can assist in
determining limb movement.
The device proved to be accurate in all
measurements so long as the accelerometer
remained in the same orientation as the stance file.
Should any tilt or rotation occur, it is impossible to
separate the effects of gravity and the actual inertial
accelerations. These results warrant further study.
The physiological activity monitor consists of two
contraction sensors, two triaxial accelerometers, a
heart rate monitor and a thermistor. Data are
collected on a laptop computer using Labview. The
data is then analyzed using Matlab. The block
diagram for the PAM is shown in Figure 21.6. Two
contraction sensors are used in the PAM. One is
placed on the forearm directly over the extensor
muscle group and the other is placed over the biceps
brachii. This maximizes any limb volume change,
which can be assumed to be a muscle contraction.
The sensors are composed of two strain gauges
mounted on a glass epoxy resin board with
precision resistors. This board is then attached to a
strap made of headliner material, which is
breathable but does not slide easily. The distal strap
is decreased in size for better comfort. The strain
gauges and resistors are delicate. A black rubber
protective coating is placed over the gauges and
resistors for protection. Overstrain of the gauges
will cause them to fatigue, which in turn
permanently deforms the gauges.
It was
determined that normal human movement would
not cause the strain gauges to fatigue.
The accelerometers are ADXL150EM-3 triaxial
accelerometers, which are pre-assembled mountable
modules, comprised of a silicon micromachined
Figure 21.10. Block Diagram for PAM.
capacitive beam accelerometer. They have a range
of +10g. They are fragile and may be damaged if
dropped or abused. Each accelerometer is placed on
the distal end of a limb segment. They are attached
with a cotton-belting strap, which is fit snuggly
around the arm and attached with Velcro. Each is
situated so that when the body is in anatomical
position, the z-plane is parallel to the transverse
plane with positive facing towards the posterior of
the body. The x-pane is parallel with the frontal
plane with positive in the medialateral direction.
The y-plane is parallel with the midsagittal plane
with positive being superior to the hand. The major
problem with the accelerometers is that they also
measure gravity; therefore, to pick up inertial
acceleration of the human body, gravity must be
corrected for with two accelerometers.
Heart rate is measured from the R-R wave using a
Polar Heart Rate Monitor. The heart rate monitor
sends to a belt worn receiver, which is tethered to
the laptop computer and it attached around the
chest of the subject. When applying it, it is best to
dampen the monitor with water and place across the
chest. The signal is viewed in the LED on the
receiver worn on the belt. Total cost of project is
$640.00.
PEDESTRIAN KNEE LEGFORM
Designers: Matt Freyhoff, Thor Castillo, Gilbert Bandry, and Jonathan Geist
Supervising Professor: Dr. David Reynolds
Dayton, OH 45435-0001
INTRODUCTION
The National Highway Traffic Safety Administration
(NHTSA) has historically tried to reduce the amount
of pedestrian injuries and fatalities through injury
reduction and collision prevention programs.
Education and enforcement programs have been
used in efforts to increase the level of collision
prevention. These programs focus on behavior
modification. To date, lower extremity and knee
injuries account for the most frequent pedestrian
injuries. These injuries result in significant financial
and personal loss due to the occurrence of long-term
damage to the affected area(s). Although most fatal
injuries are in the head and thorax region, most nonfatal injuries occur in the lower extremities of the
body.
International automobile research facilities have
developed legform impactors for biofidelic research.
However, these legforms have all utilized a
frangible part approach to represent the
anthropometry correctly. In our approach to the
problem, we are designing a non-frangible legform
for testing, which requires more consideration for
the part selection. In the current design, the static
bending testing proposed by the European
Experimental Vehicles Committee (EEVC) is being
addressed. The current problem with the friction
plates that currently are used in the legform is nonuniformity of testing. More specifically, the friction
facings do not always perform similarly during the
first testing as they do during the last test due to the
nature of the plates. The plates initially must be
bent a few times in order to prepare them for data
requisition. It is inconvenient and time consuming
to perform testing and certification. Therefore, the
legform should meet the current static-testing
corridors specified by the EEVC certification
documentation. Prior failed attempts at solving this
problem have included the use of springs,
dashpot/shock absorbers, and cables and pulleys.
Figure 21.11. Pedestrian Knee Legform.
SUMMARY OF IMPACT
Solving the problem of static testing allows the
legform to be certified for testing on automobiles.
Once the testing can be started on automobiles,
recommendations can be made to automobile
manufacturers about the improvement of their
designs. Data will enable the car manufacturer’s to
build better and safer automobiles. In 1996 alone,
there were approximately 5400 fatal vehiclepedestrian accidents, and thousands more causing
injuries that could have been less severe with design
improvement.
The focus of this design is on the knee joint of the
legform, and specifically the mechanisms provided
to impede angular displacement, in this case
bending. The current legform uses friction plates to
resist bending. The proposed design uses a cam
mechanism to resist bending. The cams measure 50
mm in diameter and from 2 mm thick, at the
makes it easier to fit the bending pin. Once the knee
joint is together the cams are tightened.
shallowest point, to 3 mm thick at its thickest pint.
The cams are made of A-2 steel and have been
treated with carbon-nitride to harden the surfaces.
This is a means of insuring that no premature wear
is experienced by the components.
The operational range of the legform is from 0 to 16
degrees but this range may be exceeded to
accommodate other tests, such as dynamic bending
tests. The range of the corridors specifies 250
Newtons as the upper limit of the force. Again this
limit may be exceeded, but it is not advised since it
may cause some of the components to go beyond
their region of elasticity.
The cams are sloped so that the legform bends from
0 to 4 degrees; the thickness increases at an angle of
16 degrees. At this point the angle changes to 1.375
degrees until the thickness of the cam reaches 3 mm.
The significance of difference in thickness is that it
causes deflection between the cams and the key
elements. It is this deflection that enables the
legform to resist bending. The amount of force
required at each bend is determined from the force
vs. bend curve, as depicted in Figure 21.12, and
mandated by EEVC. In turn, the deflection can be
calculated from its mathematical relationship to the
force.
Safety considerations in the context of this device
mostly apply to the safety of the device during
testing. The testing apparatus should not apply
extreme stresses or strain rates to the knee joint. For
static testing, strain rates will necessarily be low, so
only extreme stresses need be considered. The knee
design calls for both aluminum and steel parts. The
steel parts lend strength and stability to the bending
clamp and shear casing. The steel also exhibits the
elastic behavior required for the deflection cycles the
bending clamps will go through. The aluminum is
used primarily because it is lightweight while
providing reasonable strength. The maximum stress
on the flanges was found to be 38 MPa and the yield
strength of A36 steel is approximately 260 MPa.
This means the factor of safety for the flange
deflection is roughly 6.
Installation of the cams is a two-step process. The
first part deals with the insertion of the key
elements. These are simply slid into the grooves
located on each side of the shear element casing.
They are oriented so that the sloped portion is facing
outward. The next step involves the mounting of
the cams. Each cam is screwed onto a bending
clamp so that the cams are facing one another,
specifically the sloped portions of the cams. The
cams are not tightened down until the bending pin
in inserted through the assembled knee joint. This
The total cost of this project is $600.00.
300
Upper
Limit
250
200
Lower
Limit
150
100
50
0
4
Figure 21.12. EECV Corridors for Static Bending.
8
12
16
ADJUSTABLE WHEELCHAIR TRAY
Designers: Latisha Long, Larita Jo’ Martin, and Janell Thomas
Supervising Professor: Dr. Chandler Phillips
Dayton, OH 45435-0001
INTRODUCTION
An adjustable lap tray was designed for a small
child with cerebral palsy. He is unable to walk or
crawl and uses to a wheelchair. He usually holds
his arms close to his chest due to muscle spasms.
His head is secured backward and strapped to his
chair because he is unable to control it. The
adjustable wheelchair, as shown in Figure 21.13, was
designed to assist in bringing objects on the tray into
view and reach of the user.
The child’s previous tray was wooden and was fixed
at a 45-degree angle. He was unable to view objects
on the tray. The angle of the tray allowed objects to
slide and fall from the surface. The child has limited
hand and arm mobility, so he is unable to grasp
objects. Although gains have been made with his
am mobility, the current tray allows no arm or
elbow room or adjustability for improvement.
Manual raise and tilt mechanisms were use instead
of hydraulic mechanisms due to budget restrictions.
The tray clamps onto the right and left arms of the
wheelchair, and it raises and lowers along
lightweight telescoping aluminum tubes, which are
held in position by pins on each side. It pivots about
a joint on each side and the angle position is held by
pins and telescoping tubes. The tube is made of
wood, with cork on its surface for traction, and holes
around the perimeter for the tying of toys. There is
an additional, attachable wooden surface for writing
and eating.
SUMMARY OF IMPACT
This adjustable wheelchair tray improves the child’s
interaction with objects in an educational setting,
such that brings objects into the view and reach of
the child.
Figure 21.13. Adjustable Wheelchair Tray.
The material of the desk is wood, as shown in Figure
21.10, and its dimensions are 59 x 32 x 2 cm. The
material of the attachment and tilt elements is
aluminum. There are three telescoping poles, from
largest to smallest, the diameters of which are 2 ¼”,
1 ¾”, and 1” respectively.
The attachment
dimensions are 2” x 6 ¼”. The minimum height for
vertical adjustment is 4 ¼” and the maximum height
is 9”. The minimum tilt angle is 0 degrees and the
maximum is 45 degrees.
Figure 21.14. Adjustable Wooden Desk.
AUTOMATIC CAN OPENER
Designers: James Klosterboer, Charles Platt, and Stephanie Taylor
Supervising Professor: Dr. David B. Reynolds
Dayton, OH 45435-0001
INTRODUCTION
The objective of this design project was to assist an
individual in opening cans through the use of an
automated can opener. The individual has partial
paraplegia due to a fracture of the C5 and C6
vertebrae. The fracture has left the individual with
little to no finger dexterity and limited hand motion.
He has found it difficult to position cans for a can
opener while simultaneously trying to control the
device.
The client does not have movement of the lower
muscles below the point where he was injured. He
does have the ability to move his hands by
contracting his forearms, thus moving his hands up
and down. The client uses a wheelchair with his
back strapped to the vertical backing of the chair.
His reach from this position from shoulder to hand
is 25 inches. He is able to reach only 14 inches
beyond his knees. Sitting in his wheelchair his
height comes to 36 inches. He is not able to exert
control over the movement of his fingers, but he can
force a can into his hand. He cannot release the can
on his own.
The automatic can opener, as depicted in Figure
21.15, has been designed such that the client can
open cans without additional human assistance.
This device allows the client to place a can of food in
any spot he chooses on a surface, and press a button
to automatically position the can under a
mechanism that will open it. The can opener returns
to its original position to allow for easy access for
the user to remove the can.
SUMMARY OF IMPACT
By using this opener the client is able to cook meals
without any additional assistance, greatly increasing
his overall independence, as shown in Figure 21.16.
The biggest shortcoming of the device to this point is
the lack of covering of the height adjustment motor
in the rear of the device. The goal of passing
Figure 21.15. Automatic Can Opener.
Figure 21.16. Client Operating Automatic Can
Opener.
mechanical safety testing would most likely not be
fulfilled because of this.
The basic concept of the positioning mechanism is to
move the can forward to a precise position directly
under the opening mechanism’s blade without
deviation every time. This is accomplished using a
threaded rod (threaded at 16 threads per inch)
connected to a 13- by 2-inch aluminum plate with
two dowel pins on either end. This assembly is
attached directly under the aluminum platform
upon which the can is placed when the device is in
operation. The primary reason for this was for
safety purposes so that the user cannot come into
contact with the moving parts.
The threaded rod spins powered by a reversible 60
Hz AC motor, and the aluminum plate, centrally
threaded through the rod, advances forward and
backward depending on the direction that the motor
is rotating. The two dowel pins on either side of the
aluminum plate rise above the platform on which
the can is placed. A block of plastic cutting board
material with a centrally placed V, placed on the
dowel pins and extending across the width of the
platform, catches the can and advances it to a
position directly under the opening mechanism.
For the opening mechanism, a commercial device
make by Krups was chosen so that the user could
easily replace a faulty opening mechanism. The
Krups Open Master is a device that does not cut a
can in a conventional way. Instead, it decrimps the
edges of the can and removes the top of the can
without producing sharp edges. The top of the can
is then easily replaceable to cover the remaining
contents for refrigeration.
Master. This is accomplished using an aluminum
plate, through which three rods are attached. The
outer two rods are made of unthreaded aluminum,
while the central rod is threaded at 16 threads per
inch.
The two outer rods provide stability for the
aluminum plate while it is advancing either up or
down, and a common aluminum bar at the top of all
three rods provides additional stability and safety.
The threaded rod also spins powered by an AC
motor. The operation of the motor is aided by a slip
clutch, providing torque to lift the opening
mechanism/plate combination in addition to acting
as a sort of brake for the height adjustment.
When the can is in position and the opening
mechanism has been lowered until the blade
contacts the edge of the can, the remainder of the
operation of the device requires operation of the
Krups Open Master. Figure 21.17 depicts the
circuitry schematic for the automatic can opener.
The height adjustment mechanism is designed to
include an attachment site for the Krups Open
Motor 1
1/2 CS2
2A
2.3 uF
CS1
Motor 2
Opener
Socket
1/2 CS2
S3
2.3 uF
S1
Figure 21.17. Circuitry Schematic.
S2
VISUAL TRACKING DEVICE
Designers: Ken Imhoff, Barb Scheide, and Stephanie Ives
Supervising Professor: Dr. Chandler Phillips
Dayton, OH 45435-0001
INTRODUCTION
A ball drop toy was in use by children with
disabilities in an elementary school. The purpose of
the toy was to enhance motion tracking abilities and
attention span. The original toy consists of a series
of five wooden ramps down which a ball rolls. Each
ramp has a hole cut in the lower end to allow the
ball to drop to the next level. A ball is dropped
through a hole at the top of the toy by a student. The
ball then rolls down the series of ramps until it
reaches the holding tray at the bottom. Children
track the progression of the ball down the ramps. A
teacher requested that the device be redesigned so
that the majority of the children in her classroom
could use it.
The original device was approximately two feet tall
and one and a half feet wide. The size of the ball
drop prevented some of the children from using it
without assistance. When the toy was placed on a
table, most of the students, especially those in
wheelchairs, were not able to reach the top of the
device where the ball must be placed, four to five
feet off the ground. The other problem with the
original ball drop was the need for a wide range of
arm movement and motor skills on the part of the
user. Many of the children are not physically able to
pick up the ball.
The same design was attempted two years ago by a
design team at Wright State University. Their final
project did have motion, but failed to incorporate
lights and sound. Their device mainly consisted of a
series of multi-level ramps encased in see-through
acrylic. A ball was dropped into the device through
a hole in the top and then it traveled down the
ramps until it reached the bottom. Once at the
bottom, the ball exited into a small hole in the side of
the device. The elevator would then take the ball
back to the top where it would start over. However,
there were problems with the gears slipping on the
elevator and the device is now unusable. Therefore,
Figure 21.18. Visual Tracking Device.
a newer, more sophisticated mechanism was
constructed. The new device is toy now completely
automatic. Students easily activate it through the
use of a button, transporting the ball from the base
of the ball drop to the top, as shown in Figure 21.18.
SUMMARY OF IMPACT
The redesign of this toy eliminates the need for the
user to manually place the ball at the top of the ball
drop. The device can be used by all the children. It
allows students with limited dexterity to operate a
device and helps them to develop their motion
tracking abilities.
In addition, this device
incorporates lights and sound to enhance the user’s
enjoyment.
A microprocessor is used to control all of the ball
drop components. This greatly reduces the amount
of circuitry that is needed to control the system and
allows for design flexibility. If a problem occurs
with the microprocessor, it can be reprogrammed,
requiring minimal wiring reconfigurations. The
microprocessor is a BASIC Stamp II, which has
sixteen general-purpose input/output lines, 2048
bytes of program space (up to 600 instructions), a
20MHz clock, and a 5-volt regulator. The BASIC
Stamp II is inexpensive and easy to program.
The design of this project called for a retrieval and
drop-off system for the ball. In order to meet this
specification, an elevator was used to first travel
down an elevator shaft, retrieve the ball, ascend
back up the shaft and finally deposit the ball at the
top of the device. Attached to the top level of the
device is an angled platform that slightly protrudes
into the elevator shaft. This platform is angled to
facilitate rolling of the ball once it has left the
elevator car.
The driving force behind this system is a 12-volt
permanent magnet, reversible DC motor. Attached
to the shaft of the motor is a smaller shaft equipped
with two ¾ inch diameter spools. Fishing line is
wound around these spools in opposite directions.
As the motor rotates the shaft, one spool is taking up
line while the other spool is letting out slack, both
working at the same rate. This provides a pull in the
desired direction while at the same time winding the
opposite spool in preparation for pulling in the
opposite direction. Two guides are fixed to the
backside of the elevator car to prevent the car from
rotating off track.
The direction of the motor is controlled by a BASIC
STAMP II microprocessor, which receives input
from magnetic switches positioned at the top and
bottom of the elevator shaft and one on the back of
the elevator car. As the switch on the elevator car
comes into the proximity of either of the other
switches, a signal is sent to the microprocessor to
stop the motor and change its direction. Safety
switches are also positioned at the top and bottom of
the elevator shaft to stop the motor should the
magnetic switches fail.
Panel mount LEDs are used for additional tracking.
These are wired in series with current limiting
resistors directly to the output ports of the
microprocessor. The LEDs are attached to the ball
drop using Formic sample chips. A circuit diagram
is shown in Figure 21.19. Two mechanical bells were
used to create sound in the toy. The design is simple
and visually appealing to students.
The total cost of the visual tracking device is $650.00.
12V
+V
Connected to
Point A
On/Off Switch
A
Connected to
Point B
+12V
B
Microprocessor
Ports
Vin
VSS
VDD (+15V)
LED1
470
PO
LED2
470
P1
LED3
470
P2
LED4
470
P3
LED5
470
P4
LED6
470
P5
470
P6
Warning LED
8.7k
P7
P8
P9
P12
P13
8.7k
8.7k
8.7k
8.7k
Main Push Button
Bottom Safety
Top Mag. Reed
Bottom Mag. Reed
Top Safety
12V
+V
.015uF
P14
6.8k
P15
Figure21.19. Circuit Diagram.
.015uF
6.8k
12V
+V
ERGONOMIC ANALYSIS OF LUG/SHAFT
ASSEMBLY PROCESS
Designers: David Frederick, Chad Harshman-Smith, Jeff King, and Kristy Robeson
Supervising Professor: Xudong Zhang
Dayton, OH 45435-0001
INTRODUCTION
According to results from administration of the
IUE/GM Ergonomics Risk Factor Checklist, an
assembly process at a factory, involving manual
assembly of steel lugs to a shaft, posed twelve
different risk factors to workers. Three injury
reports had been filed regarding the job process. A
modification was implemented to ensure worker
safety and prevent CTDs.
The previous process involved getting a lug with
one hand from a lock-tight conveyor, positioning the
lug to the lughole on a V5 shaft, and screwing lugs
into the V5 shaft until they “seat.” Along with this
previous job process there were several irregular
tasks.
Given that the workers were half men and half
women, with varying body dimensions, the new
design was to be adjustable. Body dimension
information is important when designing or
modifying products, equipment, or the workplace,
as it allows more people of different sizes to be able
to use them safely and effectively.
Properly
designed work areas can also reduce or eliminate
risk factors that aggravate, contribute to, or cause
CTDs.
Previous administrative controls included:
•
Job rotation,
•
Warming exercises,
•
Controlling for pre-existing conditions, and
•
Removing time and pace pressures.
The factory had implemented a job rotation system
that required workers to rotate job duties every two
hours. This resulted in less exposure to the high
repetitiveness of the lug-to-shaft assembly process.
The job rotation program did minimize exposure to
the highly repetitive job process, but did not correct
the problem entirely. Workers were still being
exposed to high repetition for four hours during the
workday. It is suspected that this exposure is
enough to continue creating injuries. The goal of the
design solution was to eliminate injuries and
illnesses caused by repetitive motions by
administering Engineering controls.
SUMMARY OF IMPACT
Engineering controls include automation, job and
workspace redesign, tool redesign, and work/rest
cycle control. The ultimate goal was to prevent
injury by considering the worker and his/her
capabilities in the design solution. By eliminating
the ergonomic risk factors that cause CTDs, the
works will work without the risk of injury. This will
give the workers more confidence in their work and
higher morale, which will ultimately result in higher
production and quality.
A few additional improvements could be
implemented. One recommendation would be to
make the height of the table adjustable to decrease
the amount of pressure applied to the forearm. For
light work, it is recommended that the work surface
be at or above elbow height. In addition to table
height, the actual balancer-adjustment height could
prove to be slightly easier to operate and adjust.
Currently, the setting makes the gun hang from the
ceiling, and in order for the employee to bring it
down to a working height, he or she must stretch up
as high as possible to pull it down.
It is
recommended that the adjuster be lowered within
easier reach, preferably right above the tool rather
than at ceiling level.
Aligning Track
Aligning Arm
Slug Insertion Arm
Figure 20.20: DEPRAG Hand-Held Screw Driver.
The design of the DEPRAG hand-held screw driving
system, shown in Figure 21.20, incorporated several
key ergonomic principles. First, it was designed to
perform assemblies where depth is required
independently of torque. The purpose of the lugshaft assembly station is not to torque the lug down,
but rather to get the lug started so that the next
machining operation can be performed.
The depth-stop driver has an integrated and
adjustable finder that activates the depth shut-off
clutch and allows an exact and consistent screw
depth.
This system reduces guesswork while
performing the lug-shaft assembly and reduces the
likelihood that the wrist and forearm would be
subject to a force that would cause deviation of the
neutral wrist posture. Instead of using a standard
socket to holds the lug in place, the socket used
holds the lug in place with a strong magnet. The
magnet has enough force to hold the lug with little
or no force on the wrist.
The screw driving system’s outer shell is designed to
fit the shape of a right- or left-handed grip. Its oval
shape eliminates any abnormal hand position, such
as the use of a pinch grip. Its outer casing is also
comprised of a vibration-reducing (damping)
material that reduces the damage to the nerves and
smooth muscles of the blood vessels in the hand, a
risk associated with hand held pneumatic tools of
this type.
The new key design eliminates the use of the thumb
or index finger as a means of activating the screwing
mechanism. If the index finger is used excessively
for operating the trigger, a condition known as
trigger finger may develop. A person who suffers
Loading Arm
Unloading Arm
Figure 20.21: Top View of Redesigned Workstation.
from this typically can flex but cannot extend the
fingers actively. Normally, using either a thumb
switch or a recessed finger strip that allows all the
fingers to share the load has solved this problem.
However, the DEPRAG screw-driving system was
designed with an integrated switch that requires the
user to apply a small force to the end of the screwing
mechanism to start the rotating process. After
testing the gun with a pressure gauge, it was found
that it took approximately nine pounds to activate
the screwing mechanism. This pressure was applied
to the computer simulations that were used to
calculate and analyze different postures involved in
the assembly process.
A key rule in hand tool use is to avoid ulnar or
radial deviation. The design of this straight type
screw-driving system allows for a more natural
alignment of the wrist and forearm. When the wrist
is aligned with the forearm, the flexor tendons of the
fingers pass freely through the carpal tunnel of the
wrist, reducing such conditions as tenosynovitis and
carpal tunnel syndrome.
Figure 21.21 depicts the top view of the redesigned
workstation involving the lug/shaft assembly
process.

Wright State University - Engineering Senior Design Projects to Aid

Transcription

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