Manipulation And Active Sensing By Pushing Using Tactile Feedback

Abstract

We investigate manipulation and active sensing by a pushing control system using only tactile feedback. The equations of motion of a pushed object are derived using a model of the object's limit surface, and we design a control system to translate and orient objects. The effectiveness of the proposed controller is confirmed through simulation and experiments. Active sensing of the object's center of mass is described. I. INTRODUCTTON Pushing is a useful robotic capability for positioning and orienting parts. Several researchers have demonstrated the utility of pushing operations by planning open-loop pushing sequences to position and orient polygonal objects despite the presence of uncertainty in the initial state (l, 2, 3, 4, 5, 6, 71. These operations typically plan for a known object shape and center of mass (CM) and a flat pushing fence or specially designed pusher geomehy to exploit the mechanics of pushing. Others have proposed pushing control systems based on visual feedback (8,9). The pusher makes point contact with the object, and the position and orientation of the object is determined by a vision system. The goal is to push the object along a desired trajectory. Uncertainty in the frictional forces governing the object's motion is compensated for by the appropriate design of a feedback controller. The purpose of this work is to investigate the possibility of useful manipulation by a pushing control system using only tactile feedback. Try closing your eyes and controlling the motion of an object on a table by pushing it with a finger. This is the type of capability we would like to give a robot. In contrast to vision, tactile sensing requires very little data processing. The tactile sensor is mounted directly on the manipulator and the robot requires no peripheral sensors. The primary difficulty arises from the fact that tactile sensing can only give local contactinformation. Theconfigurationof theobjecthas three degrees-of-freedom: two position coordinates and an orientation. When the pusher is in contact with the object, these three degrees-of- freedom may be equivalently expressed by the location of the pushing contact, the contact point on the perimeter of the object, and the orientation of the object. The tactile sensor we use is capable of sensing the contact location and the object orientation at the contact, but not the contact point on the object. With vision, all three degrees- of-freedom are directly sensed. Despite this missing information, we demonstrate that simple manipulation is possible by pushing using only tactile feedback. Specifically, we implement a controller to translate the object and regulate its orientation.