Vibration control of a redundant robot for grinding

Research on robotic grinding generally has emphasized grinding processes and methods for the control of process parameters. When an industrial robot is used to remove excess material from castings, grinding weld beads, or welded surfaces, excessive vibrations often occur. Methods based on force control can improve the response. In this paper, we present practical methods for vibration reduction, feed-speed/force control, and an optimal configuration of a 4-DOF redundant robotic manipulator for grinding welded surfaces. An optimal configuration of the robotic manipulator is derived to minimize the arm compliance. The proposed method maximizes the robotic arm stiffness to reduce vibrations. The robotic arm, grinding process parameters, feed-speed/force control, and the PID controller were modeled and simulated using ADAMS/view and ADAMS/controls under MATLAB. The grinding force was considered as an input to the dynamical system in addition to the torque/force inputs at each of the four joints. DC servomotors were modeled for actuation of each joint and the PID controller was tuned by the Ziegler-Nichols second rule. Simulation results demonstrate that feed speed/force control reduces vibrations, and provides the capability to use the robotic manipulator for profiling.