Instrumented Wheel For Wheelchair Propulsion Assessment. Jacob Connelly Andrew Cramer John Labiak
n Dr. Mark Richter – Project Advisor ¨ Owner and Director of R&D ¨ Stanford Graduate ¨ Wheelchair Propulsion Research n Handrim Biomechanics – Flexrim ¨ Product design to maximize the mobility of inidividuals with disability.
Problem Statement n 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. n Need to quantify effect of propulsion biomechanics. ¨ Propulsion assessment. ¨ Properly seat user. ¨ Train user.
Project Goals n n 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 -6 K ¨ Smart. Wheel (3 rivers) ~ $25 K ¨ Load cell propulsiometer > $10 K
Market Outlook n n 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 n n 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. n n Construction Cost: Below $2 K Price of Pair: $5 K
Solution n Strain gauges used to measure resultant force. ΔV calculate strain calculate resultant force. n Create ΔV vs. Force standard curve. n n 6 push-rim attachments. This is variable.
Initial Solution – 1 st Prototype n Voltage divider circuit. ¨ 1 m. V change with a 4 V offset result in 1. 25 m. V sensitivity. n Contingencies involve instrumentation amplifier design. n n 8 -Pin DAQ unit. Bluetooth wireless transceiver (USB compatible) T C
Completed Work n 1 st prototype completed. Strain gauges attached and wired to DAQ. ¨ Power supply active. ¨ Connections Insulated in rubber coating. ¨ n Data recorded in Lab. VIEW. Low CMRR. n 10 m. V noise > signal ¨ Low Pass Filter ineffective. ¨
Completed Work n Adapt 1 st Prototype. ¨ Decreased from 6 attachments to 3. ¨ Handrim still too rigid; no noticable difference. n Decided to redesign attachments and implement new bridge circuit.
Completed Work n n Designed 1 st Prototype pushrim in Solid. Works. Ran force simulation in Solid. Works. ¨ Calculated Safety Factor. 40 lb force : SF = 5. 335 25 lb force : SF = 8. 54 10 lb force : SF = 21. 34
Completed Work n Designed new attachments.
Completed Work
Completed Work Force Simulation in Solid. Works: 40 lb force : SF = 1. 95 20 lb force : SF = 3. 13 10 lb force : SF = 7. 81
Completed Work. n n n Cut out 2 new tabs at 2 different thicknesses (0. 09 in. and 1/16 th 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. 1/16 th inch too weak. 0. 09 inch gave 10 m. V 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 n Work on 2 nd prototype: ¨ Drill holes near push rim attachments to run wiring through wheel. n n n 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) n Have Russell weld tabs to push rim. n Attach strain gauges to tabs. n Connect wiring to gauges, power supply, and DAQ. n Test 2 nd Prototype with Lab. View. n
Future Work n n 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
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