Abstract
This paper describes a positioning system for ultraprecision machine tools. This system has a hydrostatic slide table driven by a hydrostatic lead screw (36 mm diameter, pitch 10 mm) and a laser interferometric positioning system. This means that the table is supported by hydrostatic bearings in any direction absolutely without any mechanical contact. Quite high accuracy of straight motion and positioning is realized and maintained; straightness and angular deviation are better than 50 nm and 2 mu rad respectively, positioning accuracy is about 10 nm within a 200 mm stroke. In addition, the effect obtained by a self-controlled restrictor for screw and by a short-pitch (pitch 6 mm) lead screw is mentioned. The stiffness of the hydrostatic screw in the feed direction can be statically infinite with this restrictor. By the use of this lead screw, positioning accuracy is improved and a 0.1 nm positioning step is possible.
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