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Applied Optics

Applied Optics


  • Vol. 37, Iss. 13 — May. 1, 1998
  • pp: 2691–2695

Autofocus Laser Rotary Encoder

Ji-hua Zhang and Lilong Cai  »View Author Affiliations

Applied Optics, Vol. 37, Issue 13, pp. 2691-2695 (1998)

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A laser incremental encoder with autofocus operation isproposed. In the encoder, an optical read head focuses three laserbeams upon a disk with a scaling grating. The scaling grating is areflection grating for which the height difference between adjacentpixels is one quarter of the wavelength of the laser. Each of thetwo laser beams is focused onto one of the two sections of thereflective grating, whereby the pitch of the grating can be detected byinterferometric reflection. The third beam acts to provideautofocus and is reflected from a smooth part between the two sectionsof the reflective grating. Therefore the encoder is less sensitiveto the gap between the optical read head and the scaling grating, andno precision adjustment is required. Also, the reading data arefree from the vibration and waviness of the grating surface. In theexperiments an encoder disk was fabricated from a wafer by lithographictechniques. The encoder with an 18-mm radius of the disk can reacha resolution of 216 = 65,536 pulses per revolution withoutelectronic interpolation.

© 1998 Optical Society of America

OCIS Codes
(120.5700) Instrumentation, measurement, and metrology : Reflection
(140.3460) Lasers and laser optics : Lasers

Ji-hua Zhang and Lilong Cai, "Autofocus Laser Rotary Encoder," Appl. Opt. 37, 2691-2695 (1998)

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