Shadi A.K ShiraziJamie Westell

Arash Jamalian

Background Motivation System Overview Implementation Results Future Develpoment Business Case Finances Final thoughts

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

Ian Denison, PhysiotherapistG.F. Strong Rehabilitaion Centre

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

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

Modes of OperationModes of Operation

PressureRelief

Wheelchair

Stability

Joystick Control

BACK

Motor Controller

AVR Butterfly Microcontroller

BACK

Motor Controller

AVR Butterfly Microcontroller

BACK

Motor Controller

AVR Butterfly

User Interface◦ Mode Switches◦ Emergency Stop◦ Power LED

Switching Between Modes◦ Priorities

1. Emergency Stop2. Joystick3. Wheelchair Stability4. Pressure Relief

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

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

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

Additional Cost = 598.54 ◦ Unused parts◦ Tools and Equipment◦ Restocking Fee◦ Long distance calls and Travel

Funding:Engineering Science Student Endowment Fund: $890

Whighton Fund: $900

Funding -Actual Budget =126.59

Proposed Budget $1,603 Actual Budget $1,663.41

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

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

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

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

Ian Denison, PhysiotherapistG.F. Strong Rehabilitaion Centre

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

Questions?

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

Challenges◦ Integral Wind Up◦ Proportionality Constants for WSM◦ A/D Converter◦ Signal Filtering

(Images and Data c/o amequipment.com)

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

Desired Speed = 1 cm/sec

Maximum linear force required : 100 lbs= 444.82 N

Required operating current 13 Amps

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

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

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)

VTI Technologies SCA-61T◦ Single Axis◦ Analog Output

(Images and Data c/o vti.fi)

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)

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

35 Amp-Hour Sealed Lead-Acid Battery◦ Used for prototype purposes◦ Supplied by Brunette Battery

(Image and Data c/o batterymart.com)

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

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

Wheelchair Stability & Pressure Relief System