A Robust Linear Design of an Uncertain Two-Mass System with Backlash

Abstract Backlash is a most important nonlinearity that limits the performance of speed control in industrial drives including automotive drives, and is an important impediment to position control as well. In earlier work a new backlash model was developed . In this paper we develop a method based on QFT techniques to design a linear robust performance controller for an uncertain two-mass system including our new backlash model. It is primarily assumed that only the motor axis position or speed is measured. The idea is to describe the effect of the backlash nonlinearity as a characteristic disturbance, added to the shaft torque, and then design a linear controller that works well not only for this disturbance, but also for reference steps and different load disturbances. The total performance of the system can now be described as a stun of the linear behavior of the system without backlash, and the effect of the introduced shaft torque disturbance. By using the QFT design method we can also take plant parameter uncertainty and unstructured uncertainty into account, and hence fulfill robust performance specifications for the closed loop.