Design of a double-stator magnetless vernier machine for direct-drive robotics

This paper proposes a new double-stator magnetless vernier (DSMV) machine for direct-drive robotics. By artfully incorporating the double-stator structure, vernier configuration and dc excitation together, this DSMV machine yields the merits of the flux control capability, low-speed operation, high torque output, free maintenance, and high cost-effectiveness. Also, the optimizations of the rotor-teeth arc angle, stator-teeth arc angle, and current phase angle are carried out for the improvement of torque performance. In this way, the torque ripple of the machine is significantly reduced up to a tiny value of 3.67%. Moreover, the rational dc current range and the rotational speed range are obtained through the performance analysis with flux regulation. In addition, the comparison is performed with the conventional surface-mounted permanent-magnet machine. Therefore, the proposed machine shows the distinct features and is fit for the special application. Finally, both theoretical derivation and simulation are given for the validation of the machine design.