Profile tracking performance of a low ripple hybrid stepping motor servo drive

A control strategy to harness the torque ripple of a hybrid stepping motor at low speeds for precision profile tracking is proposed. The strategy uses a model-based control design that controls the phase current based on the direct quadrature transformation of the second-order nonlinear dynamics. An identification procedure based on a least-squares algorithm is applied to estimate the model parameters for calculation of the ripple dynamics. The method produces a more appropriate form of linear regression which avoids the problem of reconstructing important signals such as the rotor speed and the derivatives of the driving current, and rejects additional errors created by the quantisation of the measurements. This paves the way for an integrative process to obtain precise trajectory tracking by combining a reference trajectory, traditional PID control, and dynamic feedback linearising control coupled with feedforward compensation over a broad torque-ripple frequency band. Simulations and experiments are performed with a typical hybrid stepping motor to test its profile tracking accuracy. The results may be used to develop a commercial control scheme for tuning computer-controlled drives.