Estimator/regulator performance at slow speeds [motors]

The design of a motor controller which uses a digital shaft encoder but does not directly measure the velocity is discussed. The controller incorporates estimates of the position, velocity, and load torque, using a steady-state Kalman filter. The load torque estimate is directly fed back to compensate for the load, eliminating the need for integral control, while removing steady-state errors. The other two states are fed back, in a control law of a very standard structure, which can be designed independently of the estimator. The feedback gains are the familiar position and velocity loop gains from analog design, and they are determined in the usual way. The estimator has virtually no effect on the risetimes and bandwidths which are set by the regulator for following position and velocity commands. The fundamental design trade-off for the estimator is the timely adjustment for load torque changes versus the smoothness of motion at slow speeds