The completed wheel design functions to produce resultant force as a function of voltage.

1
Instrumented Wheel for Wheelchair Propulsion
Assessment Jacob Connelly, Andrew Cramer, John
Labiak, Advisor Mark Richter, Ph.D. Vanderbilt
University Department of Biomedical Engineering,
Nashville, TN, USA Max Mobility LLC, Nashville,
TN, USA
INTRODUCTION
Description
Prototype 2
Prototype 1
Design Element

RESULTANT FORCE CURVE
A standard resultant force curve was constructed
from the output voltage data taken in LabView.
The three tabs measure individual voltage outputs
relating to applied force at that respective tab.
These measurements require a systemic integration
in order to produce an overall measurement of
total resultant force applied to the pushrim.
Decreased the number of push-rim attachments from
6 to 3 in order to decrease rigidity of push-rim.
Pushrim Attachments
Manual wheelchair users (MWUs) are living longer
and fuller lives due to innovative technological
and medical advances. While the progress has been
substantial, there are still areas of need in
this population. More than half of MWUs
experience upper extremity (UE) pain and injury
1,2,3. The UEs serve as the principle means for
mobility, therefore, any impeding factor, such as
pain or injury, can lead to a decreased quality
of life. The development of UE pain and injury
may be a result of improper propulsion
biomechanics or poor wheelchair seating
configurations. In order to quantitatively assess
a MWU's propulsion technique for training or
seating purposes, there is a need for an
instrumented assessment tool.
Changed tab dimensions in order to increase
sensitivity through increased flexibility.
Tab Design
Redesigned circuit to increase CMRR and amplify
the voltage output signal.
Circuit Design
The completed wheel design functions to produce
resultant force as a function of voltage.
Final Design
GOALS OBJECTIVES

• Develop an instrumented wheelchair wheel
  utilizing strain gauges.
• Quantitatively measure resultant force during
  wheelchair propulsion.
• Minimize costs in order to provide an affordable
  tool for wheelchair seating clinics.
• Production cost less than 2,000
• Market price 3,000 to 5,000
• Integrate universal compatibility into the design
  of the instrumented wheel.
• Capable of fitting all wheelchairs.
• Adaptable to different size wheels (24'', 25'',
  and 26'').
• Provide wireless capability with Bluetooth
  technology.

Figure 1. The initial prototype design changed
significantly during the course of the project.
Figure 3. Output voltage readings from each tab
were used to construct the Standard Curve above.
Each tab is routed to its respective bridge and
amplifier circuit.

• Connected printed circuit board to the DAQ.
• Developed LabView program to record, process,
  and display data.
• Recorded voltage data via Bluetooth in LabView.
• Recorded voltage data for each tab by applying
  known forces with a spring scale.
• Mounted the printed circuit board, DAQ, and
  power supply to the spokes of the wheel.
• Created a standard curve for the wheel.

CONCLUSIONS
The prototype wheel developed here demonstrates
the ability to assess wheel chair propulsion by
measuring strain created by resultant force.
Small changes in voltage created by flexion in
the pushrim can be sufficiently amplified in
order to gain the appropriate sensitivity to
clearly track the resultant force applied to the
system.
RESULTS AND DISCUSSION
FUTURE WORK
.
METHODS
OUTPUT VOLTAGE
Improvements to the current prototype include the
use of more precise circuit components, which can
cause imbalances in the bridge circuit creating
deviations in the output voltage of respective
tabs. Also, to more accurately gauge resultant
force over the entire pushrim, software or
hardware (angle sensor) additions are necessary
for determination of the applied force location.
Inclusion of more pushrim tabs around the wheel
to better track the applied propulsion forces is
another option for future modification.
The prototype was tested to determine the
sensitivity of the instrumented wheel. The output
voltage was recorded in LabView for each
individual tab, yielding high sensitivities for
each tab as seen in Figure 2. Voltage responses
were strongest when force was applied to the
pushrim directly above the tab. The two other
tabs, located 120 away, responded to a lesser
degree and oppositely to the previous tab as
expected.

• Pushrim tab redesign thickness (0.125?0.09)
  and width (0.50?0.40).
• Tested strain gauge response in a Wheatstone
  bridge circuit on breadboard.
• Designed the instrumentation amplifier based on
  the strain gauge response.
• Removed the old tabs and welded the three new
  tabs onto the pushrim.
• Designed printed circuit board.
• Wired the wheel.
• Attached the strain gauges to the tabs.
• Soldered all components onto the printed circuit
  board.
• Connected the strain gauges and power supply to
  printed circuit board.
• Measured theoutput voltages from printed circuit
  board.
• Must be between 0-5V.

References
1 Sie IH, Waters RL, Adkins RH, Gellman H. Upper
extremity pain in the postrehabilitation
spinal cord injured patient. Arch Phys Med
Rehabil. 1992734448. 2 Dalyan M, Cardenas DD,
Gerard B. Upper extremity pain after spinal cord
injury. Spinal Cord. 19993719195. 3
Gellman H, Sie IH, Waters RL. Late complications
of the weight-bearing upper extremity in the
paraplegic patient. Clin Orthop.
198823313235.
Acknowledgments
Paul King, Ph D. Faculty Advisor, VUSE
Department of Biomedical Engineering Russel
Rodriguez M.E. Project Engineer, Max Mobility
LLC Adam Karpinsky M.E. Project Engineer, Max
Mobility LLC Guo Liyon M.E. Project Engineer,
Max Mobility LLC Franz Baudenbacher, Ph D.
Consultant, VUSE Department of Biomedical
Engineering Tobias Meyer Consultant, VUSE
Department of Biomedical Engineering
Figure 2. The output voltage for tabs 1 (red), 2
(white), and 3 (green).