High Speed and High Sensitivity Slip Sensor Utilizing Characteristics of Conductive Rubber -Relationship Between Shear Deformation of Conductive Rubber and Resistance Change-

Humans can grasp an object without information such as a coefficient of friction or weight. To implement this grasping motion with the robot hand, sensors have been proposed that detect an incipient slip within the contact surface or stick-slip. A large number of slip sensors have been proposed, but small, flexible, and practical slip sensors are currently not available yet. We have been involved in research and development activities for a center of pressure (CoP) tactile sensor that is small and flexible. This sensor uses a pressure conductive rubber to detect the central position of the load distribution and total load. As a result of using the sensor to make experiments on slip detection, we found that a peculiar change appeared in the load output of the sensor immediately before the slip displacement of an object occurred. Based on this output change, we proposed a control method that was capable of setting a grasping force in accordance with the weight of an object. However, the principle was not made clear that caused the output change to occur. We hypothesized that the change was caused by the characteristics of the pressure conductive rubber used for the material of the sensor. As a result of making verification experiments based on this hypothesis, we found that the output change was due to a change in the resistance value when the pressure conductive rubber shear deformed. It was also found that the scale of a change in the resistance value was dependent largely upon the shear deformation speed of the pressure conductive rubber. This paper describes the principle that a peculiar change occurs in the CoP sensor immediately before the occurrence of an object slip. It also reports the characteristics of the pressure conductive rubber that have newly been made apparent.