Control of force distribution for power grasp in the DIGITS system

A linear programming approach is used to formulate and solve the force distribution problem in power grasps. The basic model used is taken from the DIGITS Grasping System, which consists of four three-degree-of-freedom fingers. The program solves for the required joint torques with limits imposed on their maximum value along with limits on contact normal reactions while optimizing an objective function. Friction constraints at the contacts are also included in the formulation to study their effects. The weight vector rotation method for analyzing power grasp stability is presented, which gives the maximum force the grasp can withstand in any given orientation. Power grasps with multiple contacts are found to be much more stable than fingertip grasps, with identical limits on the available applied torques. The load bearing and the torsional resistance capability of a wrap-type power grasp is studied for various size objects. Results show a significant increase in the maximum weight handling capability for completely enveloping type power grasps, and this improves even further with increasing friction at the contacts