Identification and compensation of force ripple in linear permanent magnet motors

The main problem in improving the tracking performance of linear permanent magnet motors is the presence of force ripple caused by the irregular magnetic field of the permanent magnets and inaccuracy in electronic commutation by the servo amplifier. This paper presents a method to identify and compensate the effect of the force ripple in servo control. A physical model of the linear motor and the force ripple is derived first. The identification of the model parameters is done in a closed position control loop by measurement of the control signal for movements with different load forces. No additional sensors (e.g. force sensors) are necessary. A comparison of the tracking performance with and without ripple compensation is given.