Download Instrumented Wheel

Instrumented Wheel
For Wheelchair Propulsion
Assessment.
Jacob Connelly
Andrew Cramer
John Labiak

Dr. Mark Richter – Project Advisor
 Owner
and Director of R&D
 Stanford Graduate
 Wheelchair Propulsion Research

Handrim Biomechanics – Flexrim
 Product
design to maximize the mobility of
inidividuals with disability.
Problem Statement

Manual wheelchair users are at considerable risk
of developing upper extremity overuse injuries.
 Upper
extremities are primary means of mobility.
 Extensive upper extremity use in seating transfer.
 Upper extremity function is injury level dependent.

Need to quantify effect of propulsion biomechanics.
 Propulsion
assessment.
 Properly seat user.
 Train user.
Project Goals


Develop an inexpensive instrument capable of
measuring applied resultant force in order to
analyze propulsion techniques of manual
wheelchair users.
Costs less than alternatives: $5-6K
 SmartWheel (3rivers) ~ $25K
 Load cell propulsiometer > $10K
Market Outlook


Spinal Cord Injury Hospitals and Rehabilitation
Centers: 30 – 50 in U.S.
Seating and Training Clinics: 50 – 100
http://www.sci-info-pages.com/rehabs.html


Research Labs: ~50
Product will be sold as a pair of wheels
 Only
1 wheel will be instrumented.
 Same size diameter and same inertial effects.


Construction Cost: Below $2K
Price of Pair: $5K
Solution

Strain gauges used to measure resultant force.
ΔV  calculate strain  calculate resultant force.
 Create ΔV vs. Force standard curve.


6 push-rim attachments. This is variable.
Initial Solution – 1st Prototype

Voltage divider circuit.

1mV change with a 4V offset
result in 1.25mV sensitivity.

Contingencies involve
instrumentation amplifier design.


8-Pin DAQ unit.
Bluetooth wireless transceiver
(USB compatible)
T
C
Completed Work

1st prototype completed.




Strain gauges attached and wired to
DAQ.
Power supply active.
Connections Insulated in rubber coating.
Data recorded in LabVIEW.


Low CMRR.
 10 mV noise > signal
Low Pass Filter ineffective.
Completed Work

Adapt 1st Prototype.
 Decreased
from 6
attachments to 3.
 Handrim still too rigid; no
noticable difference.

Decided to redesign
attachments and implement
new bridge circuit.
Completed Work


Designed 1st Prototype
pushrim in SolidWorks.
Ran force simulation in
SolidWorks.
 Calculated
Safety Factor.
40 lb force : SF = 5.335
25 lb force : SF = 8.54
10 lb force : SF = 21.34
Completed Work

Designed new attachments.
Completed Work
Completed Work
Force Simulation in SolidWorks:
40 lb force : SF = 1.95
20 lb force : SF = 3.13
10 lb force : SF = 7.81
Completed Work.






Cut out 2 new tabs at 2 different thicknesses
(0.09 in. and 1/16th in.)
Attached strain gauges to top and bottom of
each.
Solder into a simple bridge circuit with
resistors and power supply.
Applied stress and measured voltage with
multimeter.
1/16th inch too weak.
0.09 inch gave 10mV changes in voltage.
Current Work
5.0 V
TENSION
DAQ
COMPRESSION
•Meeting with Dr. Baudenbacher to confirm circuit
design and help with getting components.
Current Work

Work on 2nd prototype:
 Drill
holes near push rim attachments to run wiring
through wheel.



Clean up appearance of wheel.
User cannot touch wiring when pushing.
Better organization.
 Run
all of the wiring for
the gauges before the
push rim is attached.
Won’t break any leads.
Future Work
Cut out 3 new push rim attachments (0.09’’
thickness)
 Have Russell weld tabs to push rim.
 Attach strain gauges to tabs.
 Connect wiring to gauges, power supply,
and DAQ.
 Test 2nd Prototype with LabView.

Future Work




Obtain acceptable change in voltage data
Analyze trends in the strain data
Calibrate the strain data to form a resultant force
curve
Design the hub to house the electronics of the
wheel