Static friction coefficient determination by force sensing and its application

One of the essential parts of dextrous manipulation with fingers is the use of sliding motion. Sliding manipulation techniques can fulfil tasks, such as a change of contact point between fingers and objects, a change in the location of objects without losing contact under unknown object-fingertip surface conditions or the determination of an optimal grasp force in order to avoid losing grasped objects. These techniques require a knowledge of the friction coefficients between the finger and the object. A method of slip detection and static friction coefficient determination, requiring no additional sensors than the existing joint position and force sensors of a two fingered robot hand system, is proposed. This method is applicable to general use in multi-fingered robot hand systems. The authors describe the principle of slip detection using the stick-slip effect and the required control algorithm for grasp forces. The performance of the described method is demonstrated on a pick-up task application. Considerations due to experimental results are discussed