A magnetically suspended miniature spindle and its application for tool orbit control

TLDR: In this paper, the authors reported the design, analysis, and experimental results of a miniature spindle using magnetic bearings for very high-speed micromachining, which was designed such that the first flexible natural frequency was higher than 9 kHz.

Abstract: This paper reports the design, analysis, and experimental results of a miniature spindle using magnetic bearings for very high-speed micromachining. To ensure stable high-speed rotation, the shaft was designed such that the first flexible natural frequency was higher than 9 kHz. Four-pole radial magnetic bearings with a permanent magnet bias were located in front of and behind the spindle, and axial air bearings at the spindle covers were used to hold the shaft in the axial direction. Additionally, to ensure small tools were clamped effectively, a clamping mechanism with a shape memory alloy was added at the nose of the shaft. The designed miniature spindle has an outer diameter of 62 mm and a total length of 94 mm, including the housing. The spindle was controlled with a digital signal processor (DSP)-based control system and rotated at up to 200,000 rpm using a built-in air turbine. The stability and ability of the spindle to control the tool orbit to generate micro-features was evaluated.