Slip detection by tactile sensors: algorithms and experimental results

Two techniques for slip detection with a rubber-based tactile matrix sensor are presented. The described results have been obtained within a common research activity between the Robotics and Automation Laboratory of the University of Bologna and the Control Laboratory of the Delft University of Technology. The first technique is based on a frequency analysis of the position of the center of force distribution. The main idea is that before a slip situation actually occurs, it is possible to detect a micro movement of the object due to the elasticity of the rubber. By implementing a FFT of the center of distribution and by testing the frequency components, the slip is identified before it practically occurs. The second approach is based on the principle that the normal forces measured by the tactile sensor fluctuate with a certain frequency during slip because of the rubber elasticity. This fluctuation is due to a 'catch and snap back' effect, which is present when an object is slipping over the sensor's surface. By testing the frequency domain of the normal force a slip condition can be detected. A comparison of the two approaches is presented and discussed on the basis of experimental results obtained in both laboratories.