Sliding mode control of a permanent magnet direct drive under non-linear friction
Purpose - The purpose of this paper is to find a simple structure of motion controller for permanent magnet direct drive. Application of sliding mode controller theory and equivalent disturbance estimator creates proper non-linear characteristics, which ensures controller robustness against friction. Design/methodology/approach - The position and speed controller is based on robust design methodology introduced by a sliding mode technique. The paper proposes a combination of sliding mode controller and proportional integral (PI) equivalent disturbance estimator. The friction model is Coulomb friction with a large static friction effect. The double boundary layer is used to compensate the effect of stiction. The synthesis is performed using simulation techniques and subsequently the behaviour of a laboratory speed control system is validated in the experimental setup. The control algorithms of the system are performed by a microprocessor floating point DSP control system. Findings - The proposed sliding mode controller structure with equivalent disturbance estimator guarantees expected robustness against friction. Experimental results show that the control approach can decrease the tracking error, enhance the system's robustness and attenuate high-frequency chattering in the control signal. Research limitations/implications - The proposed controller was tested on a single machine under well-defined conditions. Further investigations are required before any industrial applications. Practical implications - The proposed controller synthesis and its results may be very helpful in robotic systems where non-linear friction is a characteristic for many industrial robots and manipulators. Originality/value - The method of sliding mode controller synthesis was proposed and validated by simulation and experimental investigations.
controllers friction motion electric motors