Application of Goertzel Algorithm to Piezoresistive Pressure Sensing Fabric for Custom Fitting of Wheelchair Cushions

Abstract

Pressure sores are a costly, painful problem for wheelchair users, caused by prolonged periods of mechanical loading. A common location of pressure sores in wheelchair users is the tissue between the ischial tuberosities and the seating surface. The pressure exerted on the tissue, or interface pressure, can be measured using piezoresistive fabric. This work demonstrates the use of the Goertzel algorithm for efficiently acquiring interface pressure data from a fabric assembly consisting of a layer of piezoresistive fabric between two layers of fabric with conducting and non-conducting stripes. The Goertzel algorithm was used to sample sums of sine waves from the conductive columns of the fabric assembly and calculate the amplitudes of each component sine wave corresponding to the local interface pressure. The Goertzel algorithm is more efficient for this application than a fast Fourier transform due to the limited number of calculated frequency bins needed for this application and more freedom in choice of sample size. The algorithm was successfully used to generate two-dimensional, 32 × 32 sensel interface pressure maps once per second. The Goertzel algorithm can be used in tandem with generated sine waves to measure interface pressure from piezoresistive fabric. Low-cost, accurate interface pressure measurements will help lessen the risk of pressure sores in wheelchair users.