Kinematics and statics of multifingered grasping

The problem of coordination of multiple robotic fingers grasping a passive object is studied. The general methodology is applicable to any robotic system in which multiple contacts occur between actively coordinated mechanisms and a passive object. The articulations are assumed to be massless and the problem is quasi-static. In other words, at every instant, the external load is balanced by forces generated at the contacts. In this work, two important subproblems are studied. First, the problem of completely restraining an object against arbitrary disturbances (forces & moments) is analyzed. Force distribution algorithms, that optimally allocate the external load between the different contacts, are developed. The field of contact forces is decomposed into two force fields. One consists of forces required to equilibrate the body, and the other consists of forces that squeeze the object in order to prevent slippage. This decomposition aids the characterization and determination of the contact forces. Based on this framework, a method to determine an admissible force distribution, which optimizes the contact conditions at the fingertips for any external load, is pursued. Efficient algorithms to compute the forces are developed. Secondly, the problem of fine manipulation is considered. By fine manipulation, we mean the positioning of the object relative to the palm as opposed to gross manipulation by the arm. The compliance in the fingers and the object is modeled by linear springs. It is shown that the motion of the fingers and object can be predicted by minimizing a quadratic objective function. A method for simulating position control algorithms is developed. In both cases, the algorithms are implemented and tested through computer simulation. Several examples are used to illustrate the methodology