A Low Cost Instrumentation Based Sensor Array for Ankle Rehabilitation

Abstract

Tactile sensing technology has made significant progress towards the development of devices where robot fingers must have the ability of multi-dimensional tactile sensing in order to perform grasping and manipulating tasks (Chi & Shida, 2004); (Webster, 1998); (Nicholls & Lee, 1989); (Tarchanidis & Lygouras, 2001); (Da Silva et al., 2000). Therefore, many researchers have tried to develop various types of tactile sensors by applying MEMS technologies which usually rely on the measurement of pressure or force on a sensing element (Hasegawa et al, 2007). A variety of different types of sensors have been used, including resistive strain gauges, piezoelectric film, infrared displacement sensors, capacitive sensors, sensors detecting conductance, magnetic, magnetoelectric and ultrasonic sensors. Frequently large numbers of sensing elements are built into an array and the outputs of those sensors are processed, often in conjunction with a mathematical model, to give an assessment of the contacting object. Nowadays, force sensing becomes an important component for diver applications in biomedical applications and orthopedic rehabilitation. Thus, tactile sensors have been used in hand clinical evaluations and foot rehabilitation (Da Silva et al., 2000); (Mascaro & Asada, 2001); (Boukhenous & Attari, 2007); (Attari & Boukhenous, 2008). Human tactile sensing is achieved by means of at least four different types of receptor cells (Jayawant, 1989); (Cowie et al., 2007) and is used to feel, grasp and manipulate objects, and to assess attributes such as shape, size, texture, temperature, hardness, discontinuities such as holes or edges, and movement, including vibration. Reston and Kolesar (Reston et al., 1990) described a robotic tactile sensor manufactured from piezoelectric polyvinylidene fluoride (PVDF) film. It was not the best choice for finger mounted tactile sensors due to its limited load range and inability to measure static forces. Beebe and al (Beebe et al., 1989) developed a force sensor based on a silicon diaphragm structure instrumented with piezoresistors in Wheatstone bridge configuration. The applied force is distributed across the diaphragm via a grasping solid dome and mounted on rigid substrate with an excellent performance characteristic. In this paper a low cost tactile sensors array for the measurement of hand grasping forces is described in a first step. A second step is dedicated to the study of two-dimensional reaction forces distribution of foot during rehabilitation in the case of ankle sprain. The sensor element of the array is an easy structure based on the use of low cost Hall device and a general purpose polymer (polysiloxanes). First the elastic polymer is studied to show its ability in building such