Nonlinear H_infinity control with PID structure for robot manipualtors

In this paper the nonlinear H∞ control for robot manipulators introduced in (Feng, W., Postlethwaite, I., 1994) is extended. An additional integral term is included to cope with persistent disturbances, such as constant weights at the end-efecctor. The extended controller is interpreted like a computed torque control with and external PID, whose gain matrices vary with the position and velocity of the robot joints. A particular case of the cost variable weighting matrix is studied in which the resulting external nonlinear PID does not depend on the attenuation level γ of the H∞ formulation. Finally, experimental results are presented for the RM-10 industrial robot.