| 摘要 |
PCT No. PCT/GB88/00693 Sec. 371 Date Apr. 20, 1989 Sec. 102(e) Date Apr. 20, 1989 PCT Filed Aug. 24, 1988 PCT Pub. No. WO89/02059 PCT Pub. Date Mar. 9, 1989.The invention relates to a straightness interferometer system, for measuring transverse deviations in the relative movement of machine parts. The preferred embodiment comprises a laser (30) which directs a single frequency laser beam, polarized in two orthogonal modes, along a principal axis P onto a beam splitter (24) which splits the beam into its two modes to provide two secondary beams (26,28). One of the secondary beams (26) is undeviated from the principal axis, the other (28) is deviated through a small angle. A roof-top reflector-prism combination (30/40) is positioned in the paths of both secondary beams in a plane normal to the principal axis, the prism being arranged to deflect the deviated beam into a direction parallel to the principal axis so that both beams are reflected back to the beam splitter where they re-combine to form a combined beam. The combined beam is passed to a detector sytem (38) for detecting interference fringes reproduced from the combined beam caused by relative change in the path lengths of the two secondary beams as the reflector undergoes movements transverse to the principal axis. Three types of beam splitter are specificaly disclosed, two of which show a further preferred feature of displacing one of the beams transversely to solve the dead path problem of a prior art system. A variety of combinations of the varous elements of the preferred system are discussed but not all are illustrated.
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