Thick-film piezoelectric slip sensors for automatic grip control in prosthetic hands

INTRODUCTION Piezoelectric sensors produce a charge when mechanically deformed (for example through the action of an applied force). This charge decays with time dependant upon the connected electronics. This makes piezoelectric sensors an ideal candidate for detecting the vibrations (change in surface forces) associated with object slip from a prosthetic hand. Most previous work undertaken with piezoelectric sensors to detect object slip from upper limb prosthetics has used polyvinylidene fluoride strips (PVDF) (Dario 1996) (Howe 1989). This type of sensor has a low sensitivity of around 20-30 pCN-1 and comes in a sheet format so would have to be adhered manually to a hand. Thick-film piezoelectric sensors offer a superior alternative for this application with a much higher sensitivity than PVDF of around 130pCN-1 (Torah et al 2005) and the thick-film fabrication technique allows the sensors to be accurately printed onto the flat surface of a prosthesis finger or fingertip