MANIPULATING AND GRASPING FORCES IN MANIPULATION BY MULTIFINGERED ROBOT HANDS

Much research has been done recently on the analysis and design of multifingered robot hands. Several algorithms for determining the fingertip force for a given task have also been proposed. But, the grasping and manipulating forces involved in the manipulation of objects by robotic and human hands have not been defined in a physically reasonable way. The purpose of this paper is to propose a new definition of grasping and manipulating forces for multifingered robot hands. First, a short discussion of the grasping and manipulating forces for two-fingered hands with linear motion is given to explain the motivation more clearly and to give the basic idea of the new definition. Then, for three-fingered hands, based on a representation of the internal force, the grasping force is defined as an internal force that satisfies the static friction constraint. The concept of grasp mode is also introduced. The manipulating force is then defined as a fingertip force thatw satisfies the following three conditions: 1) It produces the specified resultant force. 2) It is not in the inverse direction of the grasping force. 3) It is orthogonal to the grasping force component. An algorithm for decomposing a given fingertip force into manipulating and grasping forces is presented. Extensions of the result to cases of two-fingered hands with planar motion and four-fingered hands are discussed. Finally, a simple example of synthesizing fingertip force for a given manipulation task is given to illustrate the usefulness of the proposed definition.