A newly developed long range positioning table system with a sub-nanometer resolution
Introduction
Demands for nano-machining and nano-metrology over a relatively large range have recently increased in a variety of industries and sciences such as aerospace, electronics, energy, and astronomy [1], [2], [3]. In particular, such demands result in the development of innovative table systems which achieve long range positioning with a sub-nanometer resolution [4]. Although many studies on ultra-precision positioning table system have been performed so far, there were only few studies on table system which could achieve positioning with sub-nanometer resolution in a long travel range [5], [6], [7], [8], [9], [10].
This study aims at developing a long range positioning table system with a sub-nanometer resolution. The table system developed is designed based on a new concept and controlled with a new control scheme. In order to achieve a stable and accurate motion control in a long range, an improved homodyne interferometer with sub-nanometer resolution is used as the position feedback sensor. Performance evaluation results confirm that the developed table system in capable of providing a resolution of sub-nanometer in the 150 mm travel range.
Section snippets
Proposed design concept of a long range positioning table system with a sub-nanometer resolution
Fig. 1 shows a proposed design concept of a long range positioning table system with a sub-nanometer resolution. Based on the proposed design concept, an innovative table system can be realized, as shown in Fig. 2.
The table system proposed can be characterized by the following functions and structures:
- (1)
Long range positioning with a sub-nanometer resolution,
- (2)
A symmetrically designed structure with respect to the motion axis,
- (3)
Driving at the center of gravity of a moving table,
- (4)
Hybrid actuator
Structural configuration
Fig. 3 shows the structural configuration of the developed table system. Specifications of the table system are given in Table 1. The moving table is just a simple plate with a rectangular hole at the center to install a VCM. The table has porous air bearing pads on the bottom and both side surfaces. Neodymium magnets for preloading in the vertical direction are fixed on the bottom of the primary table. This structure can make eddy current loss minimum because the relative velocity between the
Performance evaluation results of the positioning table system
Sub-nanometer stepwise responses were investigated by using three kinds of laser interferometers; a double path heterodyne interferometer, a commercially available homodyne interferometer and the proposed homodyne interferometer. Fig. 7 shows typical examples of sub-nanometer stepwise responses. The stepwise response results show the effectiveness of the proposed interferometer, as shown in Fig. 8. Although the output signals include ±0.3 nm, both 0.5 nm and 0.3 nm stepwise responses can be
Conclusions
This paper presented a newly developed long range positioning table system with a sub-nanometer resolution. In addition, the performance was evaluated. As a result, the following conclusions could be drawn.
- (1)
The innovative table system was developed for achieving positioning with a 0.3 nm resolution in a 150 mm range.
- (2)
The performance evaluation results confirmed that the table system developed provides the positioning and tracking accuracy of a sub-nanometer order.
Acknowledgements
This project was financially supported by the Japan Society for the Promotion Science (JSPS) Grants-in-Aid for Scientific Research (A) No. 21246026 and Grants-in-Aid for Young Scientists (A) No. 20686011.
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