Grasp Modeling With Variable Constraints And Capability Analysis For Heavy-Duty Manipulator Gripper

The heavy-duty manipulators such as forging manipulators, which are the basic facilities of heavy manufacturing industry, play an important role in the manufacture of key-components for marine and nuclear power applications. The gripper, which is the end-effector of manipulator, clamps and locates the work-piece. The property of the gripper directly affects the loading capacity and operating performance of the manipulator equipment. For heavy-duty applications, a switching mechanism of 1DOF(Degree of Freedom) with large structural stiffness and simple driven model is adopted for gripper to clamp and release the work-piece. However, the switching mechanism is kinematically defective, which cannot achieve complex grasping motion. Variety gripper jaws with special shapes have been adopted for manipulator grippers to grasp the work-piece. Due to the size changes of work-piece and the inevitable manufacturing errors, adaptive joints are adopted to keep fine contact. The force-closure grasp analysis of gripper-workpiece system with the adaptive contact constraints is a major challenge of heavy-duty grasp.For the heavy-duty work-piece manipulation application, this paper studies the influence on grasp capacity with gripper structures, constraints of gripper jaw and contact deformation resulting from heavy-duty loads. Based on the modeling of variable contact constraints for adaptive gripper jaws, a new method for force-closure analysis is this proposed in this paper.Based on the topological analysis of gripper mechanism, the common grippers of heavy-duty manipulator can be classified into two sorts. The kinematics models of two typical grippers are proposed in this paper. Towards the need of approximate constant grip torque, series of index such as grip torque varying index are proposed to estimate the performance of gripper mechanism.According to the presence of adaptive joints, the kinematic constraint between gripper jaws and work-piece is adaptive. Based on the linearization of frictional cone, a grasp model of gripper-workpiece is proposed. Further, the theories of line geometry and screws are adopted to modeling and analysis the variable contact constraints. A new force-closure condition and analysis method is proposed for the heavy-duty grasp.In the heavy-duty grasp applications, large contact deformations resulting from large contact force can not be ignored. A surface contact model is proposed to describe the special constraints due to large contact deformations. Based on the quasi-rigid model and system stiffness model, a calculating method of indeterminate contact force is proposed. This method is a common method for heavy-duty manipulation.According to the characters of gripper mechanism, the external force applied on the work-piece is partly supported by the structure of gripper and partly supported by the joint torque. This paper proposes a method for loading capacity analysis of heavy-duty grippers. Towards the analysis and design requirement of forging manipulator gripper, a software platform is established for the loading capacity analysis.