FEEDBACK LINEARIZED JOINT TORQUE CONTROL OF A GEARED, DC MOTOR DRIVENINDUSTRIAL ROBOT

Implementation of advanced model based robot control algorithms necess itates that joint actuators be capable of generating commanded joint t orques. This capability permits compensation of gravity torques, for e xample. Relatively recent work reported in the robotics literature has focused on development of load torque sensing and control of robots a ctuated with permanent magnet DC motors and harmonic drive gear reduce rs. This development introduces the possibility of the retrofit of a l arge class of small- to midsized industrial robots with advanced model based controllers, which require that the commanded torque signal be reproduced at each robot joint. In this paper; the authors establish t heoretically that the direct application of computed torque control to a geared, DC permanent magnet actuated robot with local joint load to rque controllers does nor lead to decoupled dynamics, as is the case w ith direct drive robots. The resultant dynamics are not decoupled due to the interaction of the computed torque control with the inner joint torque control loops. To achieve decoupled system behavior a modified computed torque control law is developed that leads to decoupled syst em dynamics. Experimental results are presented that compare the modif ied computed torque control with the standard computed torque control. The experiments are conducted on a commercial 6-DOF robot that has be en retrofitted with joint torque control on the first three joints. Te sts have been conducted at a control update rate of 1000 Hz The experi mental results illustrate that the modified computed torque controller performance is somewhat better than the conventional computed torque control approach.