Torque Limitation Control of Industrial Manipulators Based on General Weighted Least Norm method

Industrial manipulators are widely used in manufacturing process. With the help of off-line programming and CAM software, they are able to execute various processing tasks and ensure a high precision of the trajectory and processing effect. However, the capability of an industrial manipulator is constrained by many factors: the limitation on joint coordinates, the maximum speed of actuators, the range of output torques, etc. Kinematic or dynamic solutions without concern about these constraints may result in deviation from the planned joint trajectories and cause a crash in manipulation task through forward kinematics.In this paper, we solve the torque limitation control problem via Weighted-Least-Norm based method. An auxiliary variable is introduced to reformulate the control problem of torque limitation constrained manipulation task. Then the extended variable is solved by optimizing its weighted norm to keep the torque command for the planned joint acceleration in the actuators’ output ranges, which ensures a high precision trajectory tracking of the manipulator system.The validity of the algorithm is demonstrated by a mathematical proof, and a simulation of a PUMA-560 manipulator in the MATLAB ROBOTIC TOOLBOX. Comparison with the results generated by the null space torque optimization method and the existing weighted least norm method shows that the proposed method is more effective, accurate and stable and has superiority over these algorithms.

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