Spectrum characteristics of thrust in linear motor oriented to motion stability

Harmonic force of linear motor acts directly on the drive element, which reduces the motion stability of the feed system. The servo drive circuit and the nonlinear of motor structure are considering. With the equivalent magnetizing current method and Maxwell equations, the analytic expression of ripple force, cogging force, end effect force, coupling force and inductance asymmetry force are obtained. In the computation process, the coupling effect between multiple harmonic factor is considered, which makes up for the former single factor analysis of harmonic force. The results show that the thrust in the linear motor contains multiple harmonic force, influenced by the servo drive circuit and the nonlinear of motor structure, and each harmonic component gets mutually coupled. These harmonic force acts directly on the mechanical system to lead to the displacement wave of feed system. The effect of the harmonic force rises with the increasing speed. Near the speed of 5,20 and 33 m/min, the harmonic force results in system resonance to seriously weaken motion stability of the feed system. The amplitude of ripple force declines with the decreasing amplitude of the harmonic current. The ratio between pole pitch and tooth space pitch and ratio between tooth space opening and pitch exert an important influence on the harmonic frequency and amplitude of cogging force, especially, the cogging force disappears in the ratio of tooth space opening and pitch of 0.625.