Overload Forging Manipulator Gripping Device Gripping Contact Force Modeling And Optimization Studies

Mechanization and automation is becoming more and more important in modernized industry. The application of forging manipulators to improve productivity has been very effective, especially in case of large-heavy work piece's forging. Stably and safely gripping work-piece during the forging process is very important to large-scale heavy manipulators, and whether the gripper of a forging manipulator can achieve stable gripping depends mainly on the position and constraint pattern of contact points.After elaborate analysis of stably gripping principle and complete understanding of the structure of gripping mechanism, a three-dimension gripping-contact model based on the assumption of point contact with friction is presented to calculate closed-form solutions of contact forces. Friction force limit constraints and force balancing constraints are equivalent to the positive definiteness of a certain matrix subject to linear constraints, then formulate the task of grasping force optimization as an optimization problem on the smooth manifold of linearly constrained positive definite matrices for which there are known globally exponentially convergent solutions via gradient flows according to the achievement of BUSS. The problem of critical contact force related to gripping mechanism of manipulator is solved this way. Compared with methods that ever used to calculate holding force while designing gripping mechanism the contact model presented in the paper is direct, easily calculate and more general by which the contact force could be calculated at optional position of the gripper rather than two special position of horizontal and vertical.The primary work and research results introduced in this thesis are as follows.(1) The point contact model with friction of jaw and work piece is created based on the equivalence principle of force and the theory of screws. The contact force could be calculated at optional position of the gripper rather than two special position of horizontal and vertical.(2) The position of contact force is searched on condition that the sum of all normal contact force and the power of driving are minimal with the majorized function constructed by lagrangian multiplier method. (3) The optimized minimum contact force is solved by means of equivalent the friction force limit constraints and force balancing constraints to the positive definiteness of a certain matrix subject to linear constraints. The method of linearly constrained positive definite matrices via gradient flows is used to solve the optimization problem.(4) The dynamical equation subject to contact constraints of gripping mechanism is derived while product exponentials formula is used to construct the spatial manipulator Jacobian. Results of different structure achieved by the numerical model are verified by the dynamic simulation and experimental data.