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Shadi A.K ShiraziJamie Westell
Arash Jamalian
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Background Motivation System Overview Implementation Results Future Develpoment Business Case Finances Final thoughts
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What is pressure sore?-Also called decubiti, decubitus ulcer and bedsores.
What causes pressure sores after spinal cord injury?
oDecrease in blood circulationo Lower tolerance for pressureo lack of sensation
Bone
Subcutaneous Soft Tissue
Skin Layer
Stage 1
Stage 2
Stage 3
Stage 4
Images c/o www.spinal-injury.net
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Ian Denison, PhysiotherapistG.F. Strong Rehabilitaion Centre
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Pressure Relief Systemo The fast development of body soreso Side effects of sudden blood flow
Wheelchair Tipping Stabilityo Sudden Muscle Spasmo Navigating Over Sidewalk Curbso Meeting an Immovable Obstacleo Reaching awkwardly for something
In 2003,65-80% of 100000 wheelchair related injuries in US were due to tips and fall
Sitting Bone
Foot
Tail Bone
Shoulder Blade
Back of Knee
Image c/o www.spinal-injury.net
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Solution◦ A system which moves the upper body of the user
left and right in a controlled manner.
Goals1.Provide Pressure Relief to User2.Increase Stability of Wheelchair3.Provide Manual Control to the User
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Modes of OperationModes of Operation
PressureRelief
Wheelchair
Stability
Joystick Control
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BACK
Motor Controller
AVR Butterfly Microcontroller
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BACK
Motor Controller
AVR Butterfly Microcontroller
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BACK
Motor Controller
AVR Butterfly
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User Interface◦ Mode Switches◦ Emergency Stop◦ Power LED
Switching Between Modes◦ Priorities
1. Emergency Stop2. Joystick3. Wheelchair Stability4. Pressure Relief
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Lateral supports◦ Current limitation: vertical side bar◦ Placed on the rails◦ Chosen to fit the sides of each individual◦ Better Force Transfer◦ Aesthetically pleasing
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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
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Component Price
AVR Microcontroller 3 38.85
Rack and Pinion/DC Motor 303.62
H Bridge 160.15
Inclinometer 65.91
Linear Encoder 257.41
12V-Battery 50.40
Circuit Components 50.78
Hardware(Cases/Pulleys/Glue/etc)
55.65
Chest harness 44.1
Rope (Aluminum rope/Kite rope)
38
Total Product Cost $1064.87
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Additional Cost = 598.54 ◦ Unused parts◦ Tools and Equipment◦ Restocking Fee◦ Long distance calls and Travel
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Funding:Engineering Science Student Endowment Fund: $890
Whighton Fund: $900
Funding -Actual Budget =126.59
Proposed Budget $1,603 Actual Budget $1,663.41
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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
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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
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January February March April
6 | 13 | 20 | 27 | 3 | 10 |17 |24 | 2 | 9 | 16 | 23 | 30 |
ResearchProposalFunctional SpecificationDesign SpecificationAssembly of ModulesIntegrationDocumentation/websitePost Mortem
Task Name
Proposed TimelineActual Timeline
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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
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Ian Denison, PhysiotherapistG.F. Strong Rehabilitaion Centre
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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
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Questions?
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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
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Challenges◦ Integral Wind Up◦ Proportionality Constants for WSM◦ A/D Converter◦ Signal Filtering
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(Images and Data c/o amequipment.com)
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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
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Desired Speed = 1 cm/sec
Maximum linear force required : 100 lbs= 444.82 N
Required operating current 13 Amps
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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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Maximum Speed of the motor at 5 Amps : 85 RPM Maximum Speed of the rack
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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)
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VTI Technologies SCA-61T◦ Single Axis◦ Analog Output
(Images and Data c/o vti.fi)
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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)
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Devantech MD03 H Bridge (50V, 20A)Features:o Built in charge pumpo Supplying up to 20A of Current to the motoro Rapid motor current switching which allows PWM
controlo Over Temperature protectiono Over current shut down
Supply Voltageso 5v for the control logic o 12V motor voltage
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35 Amp-Hour Sealed Lead-Acid Battery◦ Used for prototype purposes◦ Supplied by Brunette Battery
(Image and Data c/o batterymart.com)
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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
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Rise Time Overshoot Settling Time
Steady State Error
Kp Decrease Increase Small Change
Decrease
Ki Decrease Increase Increase Eliminate
Kd Small Change
Decrease Decrease Small Change
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Wheelchair Stability & Pressure Relief System
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