Comparison of motion control loops for industrial applications

High-performance AC and DC industrial servomotor drives use standardized motion control algorithms. The algorithms are based on common feedback sensing methods (digital position measurement via encoders or resolvers) and a common assumption that the electromagnetic torque dynamics are substantially faster than the motion control dynamics desired. The vast majority of these motion control algorithms close the motion control loops in one of two ways: (1) an average velocity loop is cascaded with a position loop; or (2) multiple state variable loops are closed in parallel. If the state variable form is properly configured, the command tracking properties are virtually independent of the disturbance rejection properties. However, this controller would require a command for acceleration which is frequently not available. In this case some modified form of cascaded loop controller topology is often used. In this paper,the alternative methods for this case are explored and tuning guidelines developed based on both simulation and laboratory results