Robotic Grasp Force Distribution And Uncertainty Analysis

This thesis addresses the issue on prediction of the contact force in robotic grasping. The contact force has a great influence on the grasping performance of the object-hand system, such as the stability,robustness. In enveloping grasp, not only the fingertip can contact with the grasped object, but also the finger link and palm, which will lead to passive constraints and some new problems.In this paper, we will focus on:(1) When the actuator forces and the external forces are given, the contact forces analysis problem is indeterminate. Using the Hertz contact model and the complementary energy minimal principle, the grasping forces analysis problem can be transformed into a nonlinear constraint optimization problem, which can be solved efficiently using the Augmented Lagrangian Method(ALM).(2) When the external force is given, we want to calculate the minimal actuator force to keep the stability of the grasping. Here, we use the rigid body contact model and consider the uncertainty of the contact location. Then the problem can be transformed into a robust optimization problem, together with the exterior penalty method, which can be eventually formulated an unconstrained least-squares problem.(3) Considering the similarity between robotic grasping and fixture system, we optimize the clamping force and location in large scale fixture system, which will take the workpiece geometry, contact model and friction into consideration. A numerical example is given to illustrate the method.