Optical position transmitter having a movable code element with optical path difference generating structure which is greater than the coherence length of the source
First Claim
1. An optical position transmitter comprising(a) a movable code element having a code track thereon, said code track comprising a pattern of optical path difference generating structure arranged to provide in a light beam impinging thereon, differences in optical path length of partial light beams falling on different elements of said pattern,(b) an optical scanning device for scanning said code track, said optical scanning device includinglight source means, emitting light the coherence length of which is smaller than the optical path differences generated by said optical path difference generating means between said partial light beams,means for directing a light beam from said light source means onto said pattern of optical path difference generating structure of said code track, whereby a modified beam with more than one partial beam with an optical path difference therebetween are provided, andan interferometer having photoelectric detector means and two optical paths of different lengths which receives aid modified beam, said interferometer responding to said path differences by providing optical interferences of said partial light beams as a function of said pattern, whereby said photoelectric detector means generate signals indicative of the movement of said code element.
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Abstract
An optical position transmitter comprises a movable code element (36). A light beam (44) is directed onto the code element. The coding of the code element (36) generates in the reflected light beam (44) sub-light beams having different optical path differences. This may be effected by stepped surface portions on the surface of the code element (36). The optical path differences are greater than the coherency length of the light of the light source (62). The reflected light beam is directed through a beam splitter (42) onto an interferometer for detection of the optical path differences. Interferences between sub-light beams are permitted by well-defined quick changes in the interferometer with determined path differences. Position signals can be obtained from the thus obtained "interference peaks".
22 Citations
16 Claims
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1. An optical position transmitter comprising
(a) a movable code element having a code track thereon, said code track comprising a pattern of optical path difference generating structure arranged to provide in a light beam impinging thereon, differences in optical path length of partial light beams falling on different elements of said pattern, (b) an optical scanning device for scanning said code track, said optical scanning device including light source means, emitting light the coherence length of which is smaller than the optical path differences generated by said optical path difference generating means between said partial light beams, means for directing a light beam from said light source means onto said pattern of optical path difference generating structure of said code track, whereby a modified beam with more than one partial beam with an optical path difference therebetween are provided, and an interferometer having photoelectric detector means and two optical paths of different lengths which receives aid modified beam, said interferometer responding to said path differences by providing optical interferences of said partial light beams as a function of said pattern, whereby said photoelectric detector means generate signals indicative of the movement of said code element.
Specification