A Mechatronic Platform for Calibration and Performance Test of Extrinsic Tactile Sensor on Prosthesis Hand

Abstract

This paper presents a mechatronic platform consists of a stimulator and a prosthesis hand holder, which aims at extrinsic flexible tactile sensor calibration and performance test for prosthesis hand application. The former is driven by a linear motor and the latter is driven by the combination of one 3 dimensions of freedom (DoF) motion stage and two rotation stages. A procedure is developed to calibrate flexible tactile sensors attached on the anthropomorphic prosthetic hand, whose surface is curved. Although the flexible tactile sensors can be easily integrated on to the mentioned curved surface due to its flexibility and compliance, they are usually flat fabricated and characterized under the working of flat situation. Curved surface sensor characterization is not directly available from the manufacturer. Furthermore, when tactile sensors are applied, there would be an elastic layer covered on top for protection and improvement of grasping ability. This elastic material essentially deteriorates the characteristics of the sensor under it, which is another important reason for establishing a platform to re-calibrate tactile sensor mounted on prosthetic hand. In this paper, two kinds of commercial tactile sensors are involved which are force sensing resistor (FSR) representing static measurement sensor and polyvinylidene fluoride (PVDF) sensor representing dynamic measurement sensor where a rigid rod with polydimethylsiloxane (PDMS) covered imitates prosthetic finger. The methodology of calibration compares the measured data obtained from tactile sensor with the one from a load cell fixed on the stimulator. The procedure of receptive-field measurement for tactile sensor on the prosthetic hand is shown and the equation for estimating the position and amplitude of surface load on top of elastic cover is established. Different combinations of tactile sensors are implemented on the rigid substance and two motion patterns of stimulator are performed on them, which are indentation and sliding. The performance of developed platform is also analyzed and it shows the ability of testing flexible tactile sensor for prosthesis hand.