Modeling and Optimization of Contact Forces for Heavy Duty Robot Grippers

Different from dexterous robotic hands, the contact status of a two-finger heavy duty gripper between the two tongs and the object are much complex during forging operation, and the contact forces are difficult to be controlled in real-time, because the tong usually is designed to rotate freely around the arm to some extent, and the contact area is usually a surface or a line. Based on the force-closure condition to meet the force and the torque equilibrium equations, this paper presents a real-time calculation model considering the gripping contact areas as equivalent friction points for N robot fingers including four contact points for the heavy gripper gripping a cylinder object. Then the contact force optimization method for multi-fingered hand researches can be used for the gripping forces' calculation between gripper tongs and the forged object, and the task is formulated as an optimization problem on the smooth manifold of linearly constrained positive definite matrices, which has globally exponentially convergent solutions via gradient flows. This is a new approach to optimize the gripping forces in real-time for the gripper's design and control of heavy forging manipulators. Simulation and experimental results are analyzed.