Thick-film force, slip and temperature sensors for a prosthetic hand

Abstract

Thick-film static and dynamic force sensors have been investigated for their suitability to measure the grip forces exerted upon an object held by a prosthetic hand, and to detect and correspondingly react to the possible slip of a gripped item. The static force sensors exploit the piezoresistive characteristics of commercially available thick-film pastes whilst the dynamic slip sensors utilize the piezoelectric behaviour of proprietary PZT (lead zirconate titanate) pastes. The sensors are located upon stainless steel cantilever type structures that will be placed at the fingertips of each digit of the prosthetic hand. Temperature sensors are also included to provide temperature compensation for the force sensors and to prevent accidental thermal damage to the prosthesis. Results have shown that the static force sensor is capable of measuring fingertip forces in excess of 100 N, with an electrical half-bridge configuration sensitivity approaching 10 µV V −1 N −1(with scope for improvement) and maximum hysteresis below 4% of full scale, depending on the manner in which the cantilever sensor array is attached to the finger. Failure in the bonding mechanism that secures the PZT layer to the stainless steel cantilever meant that the proposed dynamic force sensor could not be evaluated. However, investigations using the same sensor design fabricated on an alumina substrate have shown the potential of the PZT dynamic force sensor to measure the vibration and hence potentially operate as a slip sensor.

Object Manipulation Improvements Due to Single Session Training Outweigh the Differences Among Stimulation Sites During Vibrotactile Feedback

“…There is currently technology to detect contact force on prosthetic hands and fingers during object manipulation [6–12], with many groups successfully integrating these technologies into prosthetic hands, e.g., the cybernetic hand [8, 9]. However, these technologies have not been widely implemented in products.…”

Relative to direct haptic feedback, remote vibrotactile feedback improves but slows object manipulation

“…Multi-sensory feedback (such as visual and haptic) has been shown to mediate the self-attribution of body parts [4] in amputees, and to aid in object manipulation [e.g., 5,6] in unimpaired individuals. While it is currently possible to provide contact force feedback on prosthetic hand and fingers during object manipulation [e.g., 7,8], these technologies are not generally implemented in products.…”

Surface texture detection with artificial fingers

“…The sensor is mounted at the end of the finger link and held secure with small bolts. The sensor used for this work has been developed by Cranny [8] and Cotton [9]. Figure 2 illustrates the sensor with its finger link system.…”