Wheelchair Stability

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
BACK
9
Wheelchair Stability Mode
BACK
10
Joystick Control
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
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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
• Safety improvements
• Pressure sensors on the harness/lateral
• Muscle Spasm detection
• User interface
• Sip-n-puff (ideal for quadriplegic people)
• Mechanical structure
• 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 Docu
mentation/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)
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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

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Stability Sample Calculations

• Maximum Speed of the motor at 5 Amps 85 RPM
• Maximum Speed of the rack

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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)
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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
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Demonstration

• Wheelchair Stability Pressure Relief System

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Pressure Relief
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Pressure Relief