Two-Mode Transmission

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Multi-Chamber Programmable Air Cushion (MC-PAC)
Joli-A Kabamba Masahiro Ohno Scott Paik Joe Suarez
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Pressure Ulcer (Bedsore)

• Tissue damage caused by restricted blood flow,
  friction, and shear force.
• Affect 500,000 people in US hospitals. When
  combined with other conditions, mortality is two
  to five times higher than patients without
  pressure ulcers.
• Prolonged hospital stay up to 5 times longer than
  patients without pressure sores.

Stage 2 Pressure Ulcer
Stage 4 Pressure Ulcer
1 http//www.hcup-us.ahrq.gov/reports/statbriefs
/sb64.jsp
Picture courtesy of the National Pressure Ulcer
Advisory Panel (NPUAP)
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Pressure Ulcer (Bedsore)
Christopher Reeve died in 2004 from heart failure
due to the septicemia caused by the pressure
ulcer. 2
Septicemia A condition in which the bloodstream
is overwhelmed by bacteria. Symptoms include
organ failure and blood pressure drop.
2 http//www.apparelyzed.com/pressuresores.html
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Project Summary

• The cushion with automatic distribution of
  individual air cell pressure
• Based on the suggestion from Shepherd Spinal
  Center to reduce occurrence of pressure ulcers on
  paraplegic patients in wheelchairs
• Sponsored by Texas Instruments Analog University
  Design Competition
• Expected cost of 2,000.00

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Technical Objectives
Proposed Developed
25 Air cushions for even pressure distribution 25 Air cushions with individual cell control
Remap contact pressure distribution on cushion periodically, (25min) as suggested by NPUAP Timer used to re-adjust pressure every 10 minutes
Portable for use on wheelchair 60 hr battery life using 100Ah lead-acid battery Small enough to be installed on motorized or unmotorized wheelchair
Easy to Use UI for manual override and data logging
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Example System Packaging

• System is compact enough to be packaged on
  motorized and unmotorized wheelchairs

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Project Photo
Air control block
Pressure Cushion
Power Supply
Air Pump
UI Board
Pump Driver
Pressure Sensing Amplifier
Display Module
Switch Board
Debug Interface
MSP430F1612 MCU
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MSP430 CPU Peripherals
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Valve Selection and Description
Valve cartridge
Manifold and fitting
Servo motor
Original Valve NOT used

• Integrated Air control and Sensor Manifold saves
  space and reduces number of electrical components

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Pump Selection
Ryobi portable air compressor
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Pressure Cushion Sealing
We welded the channels shut using a re-flow
station from the lab
Original cushion had passages Interconnecting
cells
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Sealing Improvisation
Reflow station was used with small tip _at_ 200C
and then passage was clamped shut until bonded
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Pressure Cushion Intakes
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Pressure Sensing

• Freescale MPX2202 Sensors are used to monitor
  pressure readings from the individual cushions
• Typical air cell pressure is shown to be about
  10-20 psi.
• Set Gain 100 to read up to 50psi using Texas
  Instruments INA333 Precision Instrumentation
  Amplifiers
• At 10 psi, /- 20 reading accuracy
• High inaccuracy possibly caused by sensor
• grounding issue. Currently troubleshooting to
• obtain higher accuracy

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Algorithm Description

• Two main state Manual and Autopilot
• Manual mode
• Enable control buttons
• Allowing to Inflate /deflate on each cell
• Autopilot mode
• Disable control buttons
• Load Configuration every period

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Control System Flow
START
Toggle SW?
H
Manual Mode
SW Read
L
Open valves
Autopilot
Pressure read
Pump ON
Open valves
Pump ON
Pressure Read
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User Interface Implementation

• Debug and tracking purpose
• TeraTerm Terminal emulator
• Log and track instructions and data
• ASCII data TxD from MSP430
• AVR 8-bit MCU controlled16x2 LCD
• Same function as TeraTerm
• But simpler for user

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User Interface in Prototype

• TeraTerm
• Console
• 16x2 LCD
• AVR controlled

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Portability and Battery Life

• Portability
• Cushion can be installed on the wheelchair seat,
  with control elements mounted on the frame
• Device weight is under 20lbs without the 12V
  battery
• 12V car battery weighs approximately 40 lbs.
• Battery Life
• Current draw with pump ON 2 5 Amps
• Current draw with pump OFF 40 mA
• Using 100Ah battery, Usage life is expected to be
  60 hours

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Portability and Battery Life
5 A
40mA
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System Performance Testing

• Short Term Testing
• Individual components tested and functioning
• User comfort testing, to be done
• Long Term Testing
• Pressure mapping to test performance of different
  operating modes
• Long term efficacy in pressure sore reduction /
  prevention

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Manual/ Auto Demo
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Problems and Solutions
Challenges Solutions
Isolating each cushion cell Use glue, and heat gun
Solenoids cost out of budget Team made our own valves using servos from senior labs
Pressure sensors reading Use INA333 to amplify signal
Material limitation to build prototype Use available wood and parts from lab to build cushion support
Intake air units for each cell Use tire air intake piece and glue it at the bottom of cells
PWM control for servos Use external servo controller
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Development Cost
Parts ordered Price Total amount sponsored Total without sponsor
MSP430F1612 (Controller) (18.87)
MSP-FET43OU64 (Debug) (149.00)
INA333AIDGKR (Amplifier) (5.40 x 25)
TMP75 (Temperature) (1.34)
TLC2558IDW (12bit ADC) 8.38
ROHO Mosaic cushion 97 x 2
Pressure sensors MPX-2202 GP 8.36 x 30
Other Purchased Components 318.44
Other Sponsored Components (21.03)
Total 926.57 1096.86
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Production Run Cost

• 5,000 units for 5 years

Production Item Cost
Development Cost per Unit 35.00
Assembly Labor (2 hr) 40.00
Testing Labor (1 hr) 20.00
Customer Support (5 hr) 100.00
Fringe Benefits (30 of Labor) 48.00
Production Equipment (500,000) 100.00
Material Cost 411.00
Overhead and Sales Expense 943.00
Selling Price 2000.00
Profit Per Unit 303.00
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• Recommended Future Work
• Pump Select low noise pump, and small in size
  that can fit in the cushion package
• Improve UI display, use touch / tongue control or
  eye track
• Cushion material resilient to damage
• Add moisture and temperature sensors to increase
  device capability
• Select light material when designing cushion to
  reduce weight
• Add air cooler to the system to keep the skin
  dry

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Questions?
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Appendix 1
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(No Transcript)
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Appendix 2