Manipulating and grasping forces in manipulation by multifingered robot hands

A new definition of grasping and manipulating forces for multifingered robot hands is proposed. 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 that 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) and 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