Force ripple compensation in linear motors with application to a parallel kinematic machine

Permanent magnet linear synchronous motors are gaining increasing interest as direct-drive actuators for machine tools and production machines, whenever high dynamic performance are required. Control bandwidth limitations due to compliance in transmission elements are in fact eliminated. Like their rotational counterparts, these motors are however affected by a ripple, in the form of parasitic and undesired force pulsations. In this paper a force disturbance observer is used to compensate for force ripple in a two-head linear motor assembled to serve as the actuator for a two degrees of freedom parallel kinematic machine. Experimental and numerical results support the models and the analysis.