Wheelchair Stability & Pressure Relief System April 07,2008

1. Wheelchair Stability &Pressure Relief SystemApril 07,2008 Shadi A.K Shirazi Jamie Westell Arash Jamalian

2. Agenda • Background • Motivation • System Overview • Implementation • Results • Future Develpoment • Business Case • Finances • Final thoughts

3. Background • What is pressure sore? -Also called decubiti, decubitus ulcer and bedsores. • What causes pressure sores after spinal cord injury? • Decrease in blood circulation • Lower tolerance for pressure • lack of sensation Images c/o www.spinal-injury.net

4. Background Ian Denison, Physiotherapist G.F. Strong Rehabilitaion Centre

5. Design Motivation • Pressure Relief System • The fast development of body sores • Side effects of sudden blood flow • Wheelchair Tipping Stability • Sudden Muscle Spasm • Navigating Over Sidewalk Curbs • Meeting an Immovable Obstacle • Reaching awkwardly for something In 2003,65-80% of 100000 wheelchair related injuries in US were due to tips and fall Image c/o www.spinal-injury.net

6. System Overview • Solution • A system which moves the upper body of the user left and right in a controlled manner. • Goals • Provide Pressure Relief to User • Increase Stability of Wheelchair • Provide Manual Control to the User

7. System Overview Modes of Operation Pressure Relief Wheelchair Stability Joystick Control

8. Pressure Relief Mode AVR Butterfly Microcontroller BACK

9. Wheelchair Stability Mode AVR Butterfly Microcontroller BACK

10. Joystick Control AVR Butterfly BACK

11. Usability • User Interface • Mode Switches • Emergency Stop • Power LED • Switching Between Modes • Priorities • Emergency Stop • Joystick • Wheelchair Stability • Pressure Relief

12. Results: Pressure Relief

13. Results: Pressure Relief

14. Results: Gradual Tilt

15. Results: Gradual Tilt

16. Future Developments • Lateral supports • Current limitation: vertical side bar • Placed on the rails • Chosen to fit the sides of each individual • Better Force Transfer • Aesthetically pleasing

17. Future Developments • Customizing • Adjustable pressure relief timing • Manual speed control • Acceleration control • Centripetal acceleration • Acceleration dependant motor control • Safetyimprovements • Pressure sensors on the harness/lateral • Muscle Spasm detection • Userinterface • Sip-n-puff (ideal for quadriplegic people) • Mechanicalstructure • Appropriate casing

18. Finances: Product Cost

19. Finances: Actual Cost • Additional Cost = 598.54 • Unused parts • Tools and Equipment • Restocking Fee • Long distance calls and Travel

20. Finances: Funding Funding: Engineering Science Student Endowment Fund: $890 Whighton Fund: $900 • Funding -Actual Budget =126.59 Proposed Budget $1,603 Actual Budget $1,663.41 Total Funding: $1,790

21. Business Opportunities • Other uses for system • Manual posture adjustments • Correcting bent spine for eating/breathing • Incentive for insurance companies • Enhanced safety on sidewalks, trails • Incentive for physiotherapists • Optimizing the pressure relief to fit individual needs

22. Business Opportunities • Alternative products: • Pressure Relief System: • Pressure Reduction Cushion • Tipping Stability System: • Tilt Recliner • Manual. Not for Quadriplegic injuries • Can not be used throughout the day • Pneumatic actuators to move the seat • Very expensive • Requires a lot of power

23. Teamwork

24. Timeline January February March April Task Name 6 | 13 | 20 | 27 | 3 | 10 |17 |24 | 2 | 9 | 16 | 23 | 30 | Research Proposal Functional Specification Design Specification Assembly of Modules Integration Documentation/website Post Mortem Proposed Timeline Actual Timeline

25. Final Thoughts • Successful Team • Excellent Project Management • Excellent Communication • High Interest/Enthusiasm • Appropriate /Reliable Information Sources • Sufficient Technical Knowledge • Hard Work • What we learned • Technical details of each component • Integration • Implementation of our knowledge obtained from the past 5 years of education

26. Final Thoughts Ian Denison, Physiotherapist G.F. Strong Rehabilitaion Centre

27. Acknowledgements • GF Strong Rehabilitation Centre • Ian Denison (Physiotherapist and Equipment Evaluator) • Walt Lawrence (Spine Peer Mentor) • Doug Gayton ( Assistive Technology Practitioner) • Patrick Leung • Steve Whitmore • Andrew Rawicz • Shahram Payandeh • Carlo Menon • Brad Oldham • Jason Lee • ESSEF

28. Questions?

29. Technical Information • PI Controller • 12V DC Motor • Output Linear Force • Pressure Relief Operating Parameters • Stability Operating Parameters • Stability Sample Calculations • AVR Butterfly • Inclinometer • String Potentiometer • H Bridge • Power

30. PI Controller • Challenges • Integral Wind Up • Proportionality Constants for WSM • A/D Converter • Signal Filtering

31. 12V DC Motor (Images and Data c/o amequipment.com)

32. Output Linear Force • Recommended current rating from the supplier: 15 Amps • Radius of the pinion = 0.45 inches = 0.01143 m • Output torque at 15 Amps: 5.7 Nm • Linear output force required (neglecting internal resistance): • Maximum speed of the rack with no load is 11cm/sec (91.9 RPM) • Internal torque 0.5 Nm

33. Pressure Relief OperatingParameters Desired Speed = 1 cm/sec Maximum linear force required : 100 lbs= 444.82 N Required operating current 13 Amps

34. Stability Operating Parameters • The maximum current available for the motor 20 Amps (H-Bridge limitation) • Output torque at 10 Amps : 7.8 Nm • Maximum speed at 7.8 Nm : 40 RPM • The maximum output force: • limit on the controllable tipping accelerations depending on the weight of the user

35. Stability Sample Calculations • Maximum Speed of the motor at 5 Amps : 85 RPM • Maximum Speed of the rack

36. AVR Butterfly • Atmel AVR Microcontroller • Very Cheap (~$30) • Helpful Sample Code • RS-232 connection for data • Many peculiarities • Multiple use pins • Different versions • Startup Pin Levels (Images and Data c/o atmel.com)

37. Inclinometer • VTI Technologies SCA-61T • Single Axis • Analog Output (Images and Data c/o vti.fi)

38. String Potentiometer • Celesco SP1-25 • Absolute Encoder • Max. Extension 25in. (62.5 cm) • Analog Ratiometric Output • 0 to 5V Output • Application • Only used 12cm of extension • Output range 0 to 1V • ADC 1.1V internal reference (Images and Data c/o celesco.com)

39. H-Bridge • Devantech MD03 H Bridge (50V, 20A) Features: • Built in charge pump • Supplying up to 20A of Current to the motor • Rapid motor current switching which allows PWM control • Over Temperature protection • Over current shut down Supply Voltages • 5v for the control logic • 12V motor voltage

40. Power • 35 Amp-Hour Sealed Lead-Acid Battery • Used for prototype purposes • Supplied by Brunette Battery (Image and Data c/o batterymart.com)

41. Sampling • Response time • With 62.5 ms: Response time 0.25sec (loaded) • With 15.625 ms: Response time 0.15 sec • At 15.625 ms resolution drops by factor of 4, not enough memory to compensate for that • Speed resolution • Calculating speed by skipping 7 samples • Increases accuracy in the calculation • Better estimate of how fast the speed is changing • Slower velocity control

42. PID tuning

43. Results: Sudden Drop

44. Results: Sudden Drop

45. Demonstration Wheelchair Stability & Pressure Relief System

46. Pressure Relief

47. Pressure Relief