Speed control of two-mass mechanical loads in electric drives

This paper deals with model-based two-degrees-of-freedom (2DOF) speed control of two-mass systems. An analytic gain selection of a proportional integral (PI) type feedback controller is proposed. The gains are given as functions of system parameters and desired dominant closed-loop poles. An analytic design of a prefilter is given to complete the 2DOF structure, using the pole-zero distribution of the feedback loop. The prefilter design covers step, ramp, and parabolic reference tracking. The proposed 2DOF controller is evaluated by means of simulations and experiments. The experimental setup consists of two 4-kW servo motors coupled together with a toothed belt. It was found that the proposed controller gives good reference tracking for step and dynamic commands as well as robust and fast load-torque rejection.