A non-linear control of robot manipulators driven by induction motors

The authors present in this paper a new asymptotically stable scheme for the motion control of rigid robots with induction motor drives. The result is established considering a model that includes the electrical and mechanical dynamics of the induction motors, as well as the full rigid body dynamics of the robot manipulator. The procedure they follow consists of four steps. First, they 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 crosscouplings are removed. Second, the torque required to track the desired joint trajectory is evaluated by a passivity approach. Third, they define a desired current behavior which reflects an objective of attaining field orientation. Four, they design a controller that insures the torques generated by the motors asymptotically track the desired torque. Parameters of both robot and motors are known. The local stability is obtained for a controller with a nonlinear observer of rotor motor currents. Simulation results are presented with a robot SCARA to illustrate the performance of the control law.