DC motor-harmonic drive torque control with application to robot joints

The permanent magnet DC motor and the harmonic drive transmission are common components for actuation of small robot joints. This thesis examines torque control of these components as applied to robot joints. Joint torque control is an important aspect in the development of a robot capable of force control. Joint torque control can also improve robustness of a joint position controller to parametric variations. Models of the DC motor and the harmonic drive are developed. Analysis and simulation of the combined models lead a design of a torque controller for these components. Verification of the model analysis results through experimentation is accomplished by the use of the experimental facility developed within the Laboratory for Nonlinear Systems Control. Experiments validating increased robustness of a robot joint position controller with added torque control have been performed. The joint torque controller has also been implemented onto the base joint of the CRS Plus Inc., A-460 robot. Joint torque sensing, for feedback to the torque controller, is facilitated through the use of a strain gauge torque sensor placed onto the flexspline of the harmonic drive. Torque control is shown to be beneficial for joint positional control and will lead to the development of a robot capable of force control.