Thick-film force and slip sensors for a prosthetic hand

In an attempt to improve the functionality of a prosthetic hand device, a new fingertip has been developed that incorporates sensors to measure temperature and grip force and to detect the onset of object slip from the hand. The sensors have been implemented using thick-film printing technology and exploit the piezoresistive characteristics of commercially available screen printing resistor pastes and the piezoelectric properties of proprietary lead-zirconate-titanate (PZT) formulated pastes. The force sensor exhibits a highly linear response to forces up to 50 N with a maximum hysteresis of less than 1.4% of full scale. When configured as a pseudo half-bridge measurement circuit, the force sensor demonstrates superior insensitivity to the position of the force on the fingertip than when configured as a classic half-bridge circuit. The force sensor response is also extremely stable with temperature, typically showing variation in the output response of less than ±0.04% over the temperature range −10 °C to +35 °C when loaded with forces up to 10.8 N. The ability of the piezoelectric PZT vibration sensor to detect small vibrations of the cantilever, indicative of object slip, has also been demonstrated.