Minimum Tracking Error Control of Flexible Ball Screw Drives Using a Discrete-Time Sliding Mode Controller

This paper presents modeling, identification, and discrete-time sliding mode control of ball screw drives with structural flexibility. The mechanical system of the drive is modeled by a two degree-of-freedom system dominated by the coupled longitudinal and torsional dynamics of the drive assembly whose parameters are identified. A mode-compensating disturbance adaptive discrete-time sliding mode controller is then designed to actively suppress the vibrations of the drive. However, it is shown theoretically that, without using minimum tracking error filters, the tracking errors of the drive do not go to zero when sliding mode is reached. Therefore, a method for designing stable and robust minimum tracking error filters, irrespective of the identified open-loop behavior of the drive is proposed. The identification and control of flexible ball screw drives are experimentally tested, and the tracking accuracy of the drives is shown to improve considerably as a result of the designed minimum tracking error filters.