Calibration and compensation of cogging effect in a permanent magnet linear motor

The cogging force significantly deteriorates positioning accuracy and tracking accuracy in the direct-drive system with a permanent magnet linear motor (PMLM) that has widely applied in electromechanical manufacturing industries. At present, the optimization design of motor construction and adequate control strategies are main measures to overcome the cogging force of PMLM. This paper proposes an experimental method with iterative process to calibrate the cogging compensation force that is used to counteract the cogging force effect. A compensation approach using linear interpolation is presented to make a real time feedforward compensation for the cogging force. The calibration of the cogging compensation force and the compensation of the cogging force are alternately executed. The experiments obtain gradually accurate cogging compensation force. The tracking errors of the motion system are compared with and without cogging force compensation. The results show that the positioning accuracy and tracking accuracy are improved greatly by applying the cogging compensation with the calibrated cogging compensation force. This demonstrates the effectiveness and feasibility of the proposed methods.