A High-Precision Dual-Servo Stage Using Halbach Linear Active Magnetic Bearings

In this paper, a high-precision dual-servo stage with a magnetically levitated fine stage is described. For magnetic levitation, a Halbach linear active magnetic bearing (HLAMB) is used. The HLAMB has two functions: gravity compensation and actively control of vertical motion. To implement these functions, the HLAMB utilizes permanent magnet arrays and Lorentz coils. The fine stage has positioning capabilities with 6 DOF due to four HLAMBs and four voice coil motors (VCM). The HLAMBs control out-of-plane motions, and the VCM control in-plane motions. The fine stage achieves high-precision position feedback using laser interferometers and capacitive sensors. The coarse stage has an H-type structure that can carry the fine stage 300 mm by 300 mm along the x - and y-axes. Positioning and scanning performances are verified by the experimental results. It has ±10 and ±15 nm in-position stability in the x- and y-axes, respectively. At the scan with 10 mm/s constant velocity, ±1 nm mean tracking error and 4.7 nm jitter were obtained.