Multi-Chamber Programmable Air Cushion (MC-PAC)

Joli-A Kabamba

Masahiro Ohno

Scott Paik

Joe Suarez

The Pressure Ulcer Problem

• Tissue damage caused by restricted

blood flow, friction, and shear force

• Found on 12.3% of all hospitalized

patients. 4% of patients die from it

• Prolonged hospital stay up to 5

times longer than patients without

pressure sores Picture courtesy of the National Pressure Ulcer

Advisory Panel (NPUAP)

MC-PAC

• Programmed system to control distribution of

individual air cell pressure in the cushion

• Based on 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 price: $2,000.00

Design Objectives

• Provide automated means of pressure relief for

wheelchair bound

• Minimize risk of friction, shear force on skin

• Maximize user comfort

• Easy to use

• Operate on 12V battery

Technical Objectives

• Maintain pressure in air cells at set levels

• Remap contact pressure distribution on cushion

periodically, as suggested by NPUAP

• Use microcontroller to display status of each air

chamber

• Pressure configuration changeable by user via

intuitive user interface (UI)

MC-PAC Block Diagram

Microcontroller(TI MSP-430)

User Interface

Cell Pressure Sensors

Air Pump5x5 Air Valves

5x5 Air Cells

Air ReleaseAir Intake

Signal

Air

PRESS?HI LOW

OK

Pressure Regulation AlgorithmAlgorithm is programmed to maintain set pressure in individual air cells

CHECKSENSOR

(X,Y)

DELAYPRESS

HI LOW OK

DUMP SOME AIR

ADVANCE (X,Y)

COUNT

HI HI LOW

OK

OK

DONE

DONE

LOW

START

Sequential Control

Control Panel

• User Interface consists

of three switches and

one knob

• User can stop/switch

cycle, or change cycle

time

• Control panel displays

cell status

Display

Power Hold

Next Cycle

Timer

Parts Acquired for Project Build

Pressure sensors

5x5Air Cushion Air

Valve

Air Pump

MSP430LaunchpadMOSFET

Switches

Design Challenges / Alternatives

• Number of Cells

• More cells better for user comfort

• Up to 25 cells controllable by single MSP430

microcontroller

• Difficulty to construct custom cushion

• Cell sealing challenges

• Project time constraints

Development CostProject Component

Labor Hours

Labor CostsEquip. Costs

Total Cost

Algorithm Coding 160 $6,400.00   $6,400.00

Simulation 160 $6,400.00   $6,400.00

Code Debugging 80 $3,200.00   $3,200.00

Pressure Control Device Design 50 $2,000.00 $200.00 $2,200.00

Cushion Design 150 $6,000.00 $300.00 $6,300.00

Prototype Product Design (Tech Demo) 200 $8,000.00 $1,407.97 $9,407.97Final Product Design (Improved Prototype) 200 $8,000.00 $1,500.00 $9,500.00

Testing, Demo Preparation 160 $6,400.00   $6,400.00

Lecture / Group Meetings 300 $12,000.00   $12,000.00

Total Labor 1460 $58,400.00  

Fringe Benefits and Overhead   $113,324.00   $113,324.00

Total Parts Cost ($)     $3,907.97

Project Total       $175,621.97

Production Run Cost

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

• 5,000 units for 5 years

Components Selected, Tested, Integrated

• Semiconductor switches (TI)

• Air compressor (Ryobi)

• Pressure transducer (MSP-2202-ASX)

• Solenoid Valves (GEMS-M-SERIES)

• Air Cushion (ROHO MOSAIC)

• MCU (Texas Instruments MSP430)

Project Milestones

• March 25th : Modify ROHO seat cushion.

• March 28th : Mount the sensors and valves to the

air regulation block.

• April 4th : Complete circuits and wiring harnesses

• April 18th : Develop and calibrate the MCU

algorithm.– Control inflation and deflation of cells.

Future Improvement

• Graphical Display Touchscreen.

• More air cells, moisture control, and temperature

control.

• Custom user pressure mapping interface.

• MC-PAC for car seats and beds.

• Make profile smaller, quieter, lighter, and more

efficient.

Questions