Slip compensation of grasped objects in robot gripper

Grasping in robot gripper is an operation that is inevitably performed by prosthetic hands or industrial robots. Meanwhile, slipping of the grasped object is considered as an undesirable phenomenon in any kind of grasping. Here, the computed torque control is used in order to slip control and also guarantee the desired behavior of the closed loop system. Nevertheless, any acceleration changes of the robot’s joints before completing the response time of the slip controller, influence directly on the object position relative to the robot and causes slip phenomenon. However, the applied computed torque controller is proper for tracking trajectory but this desired trajectory will be altered according to slip occurrence. This paper introduces a method to modify the desired trajectory during grasping an object. The modification is done according to the measured slip. These methods not only control the slip of the grasped object, but also compensate it. So the object could be handled and placed in its proper position in the task space. This approach guarantees the safe grasping and moving objects according to object position relative to the gripper.