Development of Direct Drive Motor for Machine Tools and its Performance in Machining

Abstract

This paper describes the development of a direct drive motor (DD motor) without a reduction gear for the rotary motion of machine tools and its performance. We investigate novel DD motors from a view of total performance on machine tools. Moreover, we estimate to employ the developed DD motors for 5-axis control machine tools and the multi-functional machine tools. The study proves the required performance of rotary motion is achieved on machine tools, and the developed DD motors are found to be effective as follows. First, designing a DD motor with quality engineering and FEM analysis of electro-magnetic field is found to be effective for a low cogging torque and a low torque ripple. It is demonstrated that the developed DD motor makes it feasible to generate the excellent surface roughness on the complex shape workpiece with a ball-nose endmill tool, compared with the machined surface roughness by a conventional rotary axis with a reduction gear. Second, a maximum angular velocity of the DD motor is balanced with a maximum velocity of the linear axis, but a maximum angular acceleration of the DD motor is not balanced enough with a maximum acceleration of the linear axis. Therefore, the angular acceleration is needed to be improved as a next step.