Overload Holding Mechanism Dynamic Clamping Force Modeling And Gripping Control Study

Few studies have been done on the load-carrying ability of the grippers for large-scale heavy duty forging manipulators. In previous studies, only the mechanical model of the tong force between the jaws and the workpiece was given under static conditions when the jaws are in the horizontal or vertical position. Then a simple moment formula was used to derive the driving force. The previous methods may lead to a large error in the engineering application, because the effects of the friction moment, the inertia force and the angular displacement were ignored. The main studies to solve such problems are as follows:The mechanical models of the dynamic tong force are built, in which the effects of the friction moment, the inertia force and the angular displacement are considered based on the push bar, long lever and short lever grippers and analyses the transfer of dynamic force in the grippers is analyzed. Then the dynamic mechanical model of the tong force between the jaws and the workpiece under different working conditions is built. Thus, the quantitative analysis of the load-carrying ability of the grippers can be done based on the built models.Dynamic simulations are performed by the dynamic simulation software ADAMS for the gripper mechanism. The computational results of the mechanical model are in agreement with the simulation results of ADAMS, proving that the mechanical model is reasonable. In addition, the test results of a short lever gripping mechanism fit the ADAMS simulation results and model computational results well.Based on the driving force obtained by the dynamic mechanical model of the gripper mechanism, the gripping hydraulic circuit is designed and the models of the proportional throttle valve and the valve controlled symmetric cylinder are built. The kinematics relation between the cylinder and the jaws is also established. According to the dynamic tong force models built, the load equation in the gripping process and the required tong force are determined. The displacement of the hydraulic cylinder's piston is controlled by using PID, which not only improves the gripping efficiency, but also reduces the effect of impact.