A novel 2-freedom-degrees brushless motor

In apparatus requiring articulated movements involving multiple freedom degrees, usually each one is managed by means of a conventional actuator charged to control the corresponding elementary motion, and the required comprehensive motion is obtained with the aid of suitable mechanisms. Nevertheless, weight, space and cost savings, besides structural simplifications, could be achieved by employing actuators able to simultaneously manage more freedom degrees. This paper proposes a novel rotary-linear 4-phase permanent magnets brushless motor. The machine structure and its basic principles are first described, obtaining then an approximated analytical model by means of a simplified electromagnetic anal based on the equivalent magnetic circuit approach. The machine regulation is then examined, demonstrating the ideal possibility to achieve a fully decoupled control of the electromagnetic force and torque, joined to the suppression of the potentially correlated ripple phenomena, by adopting a suitable yet simple supply logic. Several theoretical waveforms are finally reported.