A nonlinear control of robot manipulators driven by induction motors

We present a new asymptotically stable scheme for motion control of rigid robots with induction motor drives. First, we design an inner control loop such that the overall system becomes a cascade connection of two nonlinear subsystems, i.e., the motor electrical dynamics and the robot mechanical system. The output of the first subsystem, that is the generated torque, drives the robot dynamics, and the other cross-coupling are removed. The torque required to track the desired joint trajectory is then evaluated by passivity approach. Next, we define a desired current behavior which reflects an objective of attaining field orientation. Finally, we design a controller that ensures the torques generated by the motors asymptotically track the desired torque. Parameters of robot and motors are known. The local stability is obtained for the controller with the nonlinear observer of rotor motor currents. Simulation results are presented for a SCARA robot to illustrate the performance of the control law