For Wheelchair Propulsion Assessment. 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. Data recorded in LabVIEW. 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