Overview of thrust ripple suppression technique for linear motors

Direct-drive actuators, linear motors are widely used in many industrial and military applications, particularly in high-end manufacturing due to advantages of high force density, rapid dynamic response, and low thermal losses. Permanent magnet linear synchronous motors (PMLSMs) can dramatically improve the dynamic and static performance of the motion system. However, as one of the most critical sources of error, the thrust ripple of linear motors can deteriorate performance and even excite the mechanical resonance. Thrust ripple suppression technology had received broad interest and has been researched extensively. Therefore, this paper summarizes different types of thrust ripple suppression methods and their principles are analyzed in detail. Firstly, structural optimization methods are introduced to suppress the thrust ripple and increase the precision of the thrust. Secondly, control methods are described to decrease the velocity fluctuation caused by the thrust ripple. Thirdly, a combination of structural design and control method is presented to compensate the ripple, meaning high order harmonic components are eliminated by permanent magnets (PM) skewing technology and low order harmonic are compensated by a linearization observer. Finally, conclusions are made regarding thrust ripple suppression technology and the future trend is proposed.