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Auto focus laser encoder having three light beams and a reflective grating

Authors Cai, Li-Long
Zhang, Jihua
Issue Date 1998-10-20
Source US Patent , 5,825,023. Washington, DC: US Patent and Trademark Office, 1998.
Summary An auto-focus laser incremental encoder for measuring linear or rotary motion or position of an object is described. An optical read head focuses three laser beams on the surface of a scaling grating. The grating is a reflection type grating where the height difference between adjacent pixels is one quarter of the wavelength of the laser light whereby the pitch of the grating can be detected by interferometric reflection. There are two sections of grating displaced with respect to each other so that a direction of movement can be readily determined. The third beam acts to provide an autofocus and is reflected from a smooth part of the grating between the two sections of reflective grating.
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Language English
Format Patent
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