Optimal design of ironless permanent magnet planar motors for minimisation of force ripples

This study concerns the analysis and minimisation of the force ripples existing in ironless permanent magnet planar motors. The force ripples is one of the key factors for moving accuracy of the planar motors. One of the main sources of the force ripples, the neglected higher harmonics of the magnetic flux density distribution, is analysed for synthesis of real-time control model in this study. An analytical model of the planar motor is firstly developed, which illustrates that the force ripples part caused by some higher harmonics can cancel each other when the length of the coil is an even multiple of the pole pitch of the magnet array. As a result, the force ripples caused by the higher harmonics can be basically eliminated with a selected coil. Finally, the analysis results are both validated by comparative simulation and experiment of two partial motors.