Tactile Sensor Without Wire and Sensing Element in the Tactile Region Using New Rubber Material

Recently the idea of covering a robot's surface with a ‘skin’ of soft tactile sensors has attracted the attention of researchers, and some human-interactive robots covered with such sensors have actually been made (Tajima et al., 2002; Kanda et al., 2002). However, most conventional tactile sensors need a large number of sensing elements and wires because every detection point needs one sensing element and wiring to an A/D converter. There are some studies aiming to overcome this wiring problem by using 2D surface communication or wireless communication (Shinoda & Oasa, 2000; Ohmura et al., 2006), but these are very complicated and expensive solutions. We have developed a soft areal tactile sensor made of pressure-sensitive conductive rubber without any wire or sensing element in the tactile region. The distribution of applied pressure, relating to the resistivity change of the pressure-sensitive rubber, can be estimated by using inverse problem theory. We employed electrical impedance tomography (EIT) to reconstruct the resistivity distribution from information obtained by electrodes placed around the region. EIT is an established method in medical and industrial applications (Holder, 2005), but it has not been applied to tactile sensors until recently. Nagakubo and Alirezaei proposed a tactile sensor using an EIT algorithm operating with commonly used EIT software and commercially available pressure-sensitive rubber (Nagakubo & Kuniyoshi, 2006; Alirezaei et al., 2006). Their method is based on the same principle as ours, but their pressure-sensitive conductive rubber is not suitable for this method. We have newly developed special pressure-sensitive conductive rubber for this sensor, and adopted a new computation technique suitable for this rubber. We have also developed a prototype sensor system that can measure pressure distribution in real-time. In this paper, we describe basic structure and computation technique of our sensor system, as well as experimental results obtained using our prototype sensor system.