Noncircular cutting on lathe using a discrete variable structure tracking control with optimal, rejected and enhanced robustness designs

In this paper, a discrete-time variable structure tracking control is applied to a noncircular cutting on lathe (NCL). In general, a noncircular cutting on lathe is subject to a time-varying cutting load whose period is the same as that of cutting profile. It is difficult to obtain a precise model when the voice coil motor (VCM) system is on a cutting condition. On the contrary, a linear discrete-time dynamic model with enough preciseness can be achieved under no cutting condition. However, a time-varying cutting load will force the cutting tool away from the desired trajectory; the cutting profile error then occurs. The proposed control rejects a periodic and constant cutting load and attenuates the effect of the output disturbance caused by the cutting load or uncertainties. The proposed scheme is effective and simple. Finally, the simulations for NCL are carried to evaluate the usefulness of the proposed method.