A pneumatic bladder array for measuring dynamic interface pressure between seated users and their wheelchairs

An understanding of the dynamic pressure distribution changes that take place on the sitting surface of a wheelchair while one propels oneself on a level surface may influence the design of wheelchair seat cushions engineered to minimize pressure sores in wheelchair users. A pneumatic pressure transducer array and associated multiplexer were developed to permit measurement of dynamic interfacial pressure changes on the seated wheelchair user during short bursts of locomotion on a level surface. The system design, calibration and interface to an IBM PC computer are described. Each transducer element consists of a 0.7" thick x 1.25" diameter bladder innervated by a miniature piezoresistive pressure transducer. Fifty elements make up the array covering a 7.5" x 15" area. The 50 differential outputs were multiplexed with six 16 to one CMOS analog switches and one 4-channel differential CMOS analog switch. A Keithley 570 data acquisition system was utilized. Frequency response, effect of normal loading and effect of shear loading on a single transducer element are discussed.