| 摘要 |
<p>The displacement of a first object (6) relative to a second object (28) is measured by differential measurements from a photodetector (17) and an associated evaluation device (18). The photodetector (17) receives a measurement beam of radiation from a source (9) via a reflector (5) secured to object (6), and a reference beam of radiation from a source (10) via a reflector (26) secured to object (28). Sources (9, 10) are closely adjacent and in the focal plane of a collimating lens (13) through which both beams pass. Both beams are focused onto the detector (17) by a focusing lens (21). Because both beams pass through lenses (13, 21) movements thereof do not affect the displacement measurement. The remaining optical components which are used for beam steering and guidance are comparatively stable and so do not affect the displacement measurement.</p> |
