Low-speed high-torque drive system applying vernier motor torque

Abstract

The application of the direct drive system is increasing in the field of robot and factory automation because of controllability with high accuracy. However, it requires the motor high torque at low speed. Although the vernier motor presented by Lee in 1963 could produce the reluctance torque in low speed, it involved many problems to be solved. This paper studies the reluctance torque of the vernier motor using the finite-element field analysis. Since the increase of rotor slot number is effective in producing high torque, in the model here, there are not only winding slots but also small slots on the stator teeth surfaces. Also, the rotor slots are provided in the periphery of the core more than the total number of stator slots by the pole number. The calculated torques have agreed very well with the experimental results. A prominent feature of the control scheme is to control the armature current phase based on the detected rotor slot position. Thus there is no problem such as pull-in or pull-out in Lee's vernier motor. Then the instantaneous torque is controlled by the amplitude of armature current. The experimental results on both the speed control and the position control also are shown in this paper.