Engineering Senior Design Projects to Aid the Disabled
Arts and Crafts Work Station
A Work Station for Persons with Limited Arm
Movement
Designers: Mark Wysocki and Julia Jennings
Supervising Professor:
Dr. R. Conanf
Department of Mechanical Engineering
Montana State University
Bozeman, MT 59717
INTRODUCTION
This project arose from the need of a quadriplegic
requiring a table on which to do crafts. The woman
this work station was designed for has very limited
strength and range of motion in either arm and no
control of the muscles in her hands. A conventional
desk does not allow independent writing, painting,
or craft activities. A work station has been designed
and built to meet these needs after evaluating prod-
ucts currently on the market, constructing models of
possible design alternatives, and discussing the
probable value of each alternative with occupa-
tional therapists and possible end users. The sur-
face of the work station can be moved right and left
and tilted up and down by the user through a joy-
stick.
SUMMARY OF IMPACT
The work station allows the user to write a letter, tilt
the surface to paint a picture, and move the surface
to the right and left to reach the extremities of the
work piece. The major benefit of this design is that
it allows the user to do these things independently.
The work station provides a great deal of physical
as well as emotional therapy for the individual who
has reduced the handicap associated with her dis-
ability.
TECHNICAL DESCRIPTION
The design process began by trying to accurately
define the limits placed on our client by her recent
disability. The clients physical therapist was con-
tacted, medical muscle strength test results were
reviewed with rehabilitation specialists, and the
range of motion of each arm was measured to come
to a greater understanding of the specific disability.
The difficulties associated with using an ordinary
desk were discussed with the client in hopes of
gaining ideas for possible solutions. It was learned
that the client had difficulty moving her hands in an
area approximately twelve inches wide and eight
inches deep directly in front of her. This range of
motion did not allow her to access much of the table
surface. A solution that allowed the client to access
more of the table surface was determined to be
ideal.
After determining the physical abilities of our client,
a considerable effort was made to discover products
currently available that could help our client.
Rehabilitation professionals provided information
on products that were currently being used by cli-
ents as well as literature they had received from
adaptive equipment manufacturers.
The ABLE
DATA database was used to facilitate the search for
existing designs that addressed similar needs.
Several school desks, work desks, and drafting ta-
bles were found that would provide a partial solu-
tion. However, no one table or desk included all the
necessary features (right and left motion of the table
surface, tilting of the table surface, rotation of the
table surface, and most importantly, independent
use of the device). This market search supplied
several good ideas which were included in design
alternatives.
After defining functional abilities, and looking for a
commercially available device the process of com-
ing up with a unique design officially began. A de-
sirability matrix was formed to sort out the features
that were wanted in the design as shown in Figure
3.1. The matrix was comprised of the following
general areas: tasks that the client wished to inde-
pendently accomplish, features that would allow
these tasks to be accomplished, and overall qualities
of the design. The components of each general area
were ranked according to importance after compil-
ing the input from the client, rehabilitation profes-
sionals, and the designers. A great deal of time was Chanter 3: Montana State Universitv
15
spent involving the client in the design of the work
station. This made the hopes of developing a prod-
uct that would be used on a regular basis easier to
achieve. The user was directly involved with the
evolution of the design and felt some degree of con-
trol over the final shape and operation of the work
station.
The design specifications were next decided upon.
Specifications on weight and overall table
dimensions were set to allow portability and easy
access by the user. Specifications of range of motion
of the work station surface were set to give the user
as much increase of access to the surface as was
practical. Speed specifications were set to assure
that the motions of the table were fast enough that
the user did not get impatient waiting for the de-
sired positioning, and not so fast that the work
piece would topple over. Specifications for operat-
ing forces of the work station were set so that the
client could easily operate controls.
After determining what features the design must
have and setting the design specifications, a great
deal of time was spent generating ideas for possible
solutions. Brainstorming proved to be an excellent
source of creative design solutions. Brainstorming
groups targeted the overall table design as well as
the design of individual components. This method
of creative idea generation produced several unique
concepts such as suspending the table surface from
above to clear the under side of the table, or design-
ing a device that clamped to the edge of a kitchen
table. The three most promising combinations of
individual components were coupled with the three
most promising overall design concepts and were
then developed into three design alternatives.
The next step in the design process was to build
models of the design alternatives. The model build-
ing process allowed some of the major functional
problems of building a work station to be elimi-
nated before reaching the manufacturing stage of
the project. Building and evaluating the models
again gave the client a chance to see what the de-
signs we were considering looked like before we
built the actual work station. The client, as well as
professionals in rehabilitation fields, was able to of-
fer even more suggestions for improvements after
examining the models. The final design was se-
lected from one of the design alternatives and de-
tailed design of each attribute was completed. The
manufacturing of the work station then began.
The work station consists of a steel leg frame as-
sembly which adjusts for height (34 to 46) with
telescoping legs to allow a variety of working
heights and the possibility to use the table while in a
standing wheelchair. The feet of the leg frame have
locking casters to provide easy mobility for the 80
lb. work station and stability when in place. All
frame and leg members are made of square steel
tubing. The moving surface of the work station is
made of plywood covered by Formica on the top
and pine half round on the four edges. The surface
mounts with two ball bearing drawer glides to an
aluminum structural u channel U frame. This U
frame tilts with the table surface and supports the
drawer glides and a
HP induction gear motor
which powers the right and left motion of the
surface. The U frame is tilted by a power screw
which attaches to the leg frame and is powered by a
35 in-lb. induction gear motor. All motors are con-
trolled by a joystick and limit switches through re-
lays.
The electronic components (relays, circuit
breaker, capacitor, transformer, and voltage recti-
fier) are housed in an aluminum box mounted to
the leg frame at the rear of the table.
The mechanism that tilts the table surface consists
of a six link jack system powered by a
ACME
power screw. The stress in each link was mined by a computer program, and members were
sized to prevent possibility of buckling. The motor
was sized after determining the required energy of
the system provided by a power screw with known
efficiency. The tilting mechanism tilts the table
from 0 degrees to 60 degrees at a rate of 30 degrees
per minute.
The mechanism that moves the table surface right
and left is a chain and motor driven sprocket
arrangement which works like a rack and pinion.
The chain size and sprocket diameter were deter-
mined by anticipating the desired surface speed.
The motor was sized after determining the required
energy of the system and using known efficiency of
the drive mechanism. This mechanism moves the
table surface right and left at a rate of about 2 inches
per second.
All major structural components of the work station
were analyzed to determine maximum stress in
members, maximum stress at joints, and maximum
stress in welds. Generally the components were
designed with a factor of safety of three. The dan-
gerous moving parts are shielded from the user.
The electrical control system (joystick and limit
switches) is a low current six volt circuit which con-
trols a 120 volt circuit for the two motors through a
system of relays. The low voltage control system
adds to the safety of the design.
After completion, the work station was tested
against the design specifications. Speeds, ranges of
table motion, forces to operate the joystick that
controlled the motors, and weight were measured,
along with having the user fill out a usability
survey. The testing uncovered a few problem areas
that were corrected so that the user could make
better use of the work station. Through testing it
was determined that the minimum height of the
work station was too high.
This problem was
solved by cutting approximately two inches off each
leg.
The desi