Abstract

A laser incremental encoder with autofocus operation is proposed. In the encoder, an optical read head focuses three laser beams upon a disk with a scaling grating. The scaling grating is a reflection grating for which the height difference between adjacent pixels is one quarter of the wavelength of the laser. Each of the two laser beams is focused onto one of the two sections of the reflective grating, whereby the pitch of the grating can be detected by interferometric reflection. The third beam acts to provide autofocus and is reflected from a smooth part between the two sections of the reflective grating. Therefore the encoder is less sensitive to the gap between the optical read head and the scaling grating, and no precision adjustment is required. Also, the reading data are free from the vibration and waviness of the grating surface. In the experiments an encoder disk was fabricated from a wafer by lithographic techniques. The encoder with an 18-mm radius of the disk can reach a resolution of 216 = 65,536 pulses per revolution without electronic interpolation.

© 1998 Optical Society of America

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References

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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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  5. Catalog , Incremental Angle Encoders (Heidenhain GMBH, Traunreut, Germany).
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    [CrossRef]
  7. K. Ishizuka, M. Tsukiji, Y. Kubota, S. Ishii, T. Nishimura, “Diffracted beam encoder,” U.S. patent5,017,777 (21May1991).
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    [CrossRef]

1997 (1)

J. H. Zhang, L. Cai, “Profilometry using an optical stylus with interferometric readout,” Meas. Sci. Technol. 8, 546–549 (1997).
[CrossRef]

1996 (1)

1993 (1)

1992 (1)

H. Epstein, “Incremental optical angle encoder of high resolution,” Elektronikpraxis 27, 88–90, 92–93 (1992).

1989 (1)

T. Wigmore, “Optical shaft encoder from Sharp,” Elektor Electron. 15, 60–62 (1989).

Akedo, J.

Baba, N.

K. Kudo, H. Maeda, N. Baba, H. Funato, “High resolution encoder using double gratings,” in International Conference on Applications of Optical Holography, T. Honda, ed., Proc. SPIE2577, 138–145 (1995).
[CrossRef]

Beccue, S.

B. G. Kolloff, J. S. Schoenwaldet, S. Beccue, M. Khoshnevisan, “High resolution optical hybrid digital-analog linear position encoder,” U.S. patent5,451,776 (19September1995).

M. Khoshnevisan, J. S. Schoenwaldet, J. P. Rode, R. J. D. Smith, B. G. Kolloff, S. Beccue, “High resolution optical hybrid absolute incremental position encoder,” U.S. patent5,336,884 (9August1994).

Cai, L.

J. H. Zhang, L. Cai, “Profilometry using an optical stylus with interferometric readout,” Meas. Sci. Technol. 8, 546–549 (1997).
[CrossRef]

Dirk, C.

C. Dirk, B. Jan, U. Kristof, “Encoder element,” European patent application; publication 0638810 A1 (15February1995).

Engelhardt, K.

Epstein, H.

H. Epstein, “Incremental optical angle encoder of high resolution,” Elektronikpraxis 27, 88–90, 92–93 (1992).

Funato, H.

K. Kudo, H. Maeda, N. Baba, H. Funato, “High resolution encoder using double gratings,” in International Conference on Applications of Optical Holography, T. Honda, ed., Proc. SPIE2577, 138–145 (1995).
[CrossRef]

Ishii, S.

K. Ishizuka, M. Tsukiji, Y. Kubota, S. Ishii, T. Nishimura, “Diffracted beam encoder,” U.S. patent5,017,777 (21May1991).

Ishizuka, K.

T. Nishimura, K. Ishizuka, “Rotary encoder having a plurality of beams emitted by a diffraction grating,” U.S. patent5,101,102 (31March1992).

K. Ishizuka, M. Tsukiji, Y. Kubota, S. Ishii, T. Nishimura, “Diffracted beam encoder,” U.S. patent5,017,777 (21May1991).

Jan, B.

C. Dirk, B. Jan, U. Kristof, “Encoder element,” European patent application; publication 0638810 A1 (15February1995).

Kato, Y.

Khoshnevisan, M.

B. G. Kolloff, J. S. Schoenwaldet, S. Beccue, M. Khoshnevisan, “High resolution optical hybrid digital-analog linear position encoder,” U.S. patent5,451,776 (19September1995).

M. Khoshnevisan, J. S. Schoenwaldet, J. P. Rode, R. J. D. Smith, B. G. Kolloff, S. Beccue, “High resolution optical hybrid absolute incremental position encoder,” U.S. patent5,336,884 (9August1994).

Kobayashi, H.

Kolloff, B. G.

B. G. Kolloff, J. S. Schoenwaldet, S. Beccue, M. Khoshnevisan, “High resolution optical hybrid digital-analog linear position encoder,” U.S. patent5,451,776 (19September1995).

M. Khoshnevisan, J. S. Schoenwaldet, J. P. Rode, R. J. D. Smith, B. G. Kolloff, S. Beccue, “High resolution optical hybrid absolute incremental position encoder,” U.S. patent5,336,884 (9August1994).

Kristof, U.

C. Dirk, B. Jan, U. Kristof, “Encoder element,” European patent application; publication 0638810 A1 (15February1995).

Kubota, Y.

K. Ishizuka, M. Tsukiji, Y. Kubota, S. Ishii, T. Nishimura, “Diffracted beam encoder,” U.S. patent5,017,777 (21May1991).

Kudo, K.

K. Kudo, H. Maeda, N. Baba, H. Funato, “High resolution encoder using double gratings,” in International Conference on Applications of Optical Holography, T. Honda, ed., Proc. SPIE2577, 138–145 (1995).
[CrossRef]

Maeda, H.

K. Kudo, H. Maeda, N. Baba, H. Funato, “High resolution encoder using double gratings,” in International Conference on Applications of Optical Holography, T. Honda, ed., Proc. SPIE2577, 138–145 (1995).
[CrossRef]

Nishimura, T.

K. Ishizuka, M. Tsukiji, Y. Kubota, S. Ishii, T. Nishimura, “Diffracted beam encoder,” U.S. patent5,017,777 (21May1991).

T. Nishimura, K. Ishizuka, “Rotary encoder having a plurality of beams emitted by a diffraction grating,” U.S. patent5,101,102 (31March1992).

Rode, J. P.

M. Khoshnevisan, J. S. Schoenwaldet, J. P. Rode, R. J. D. Smith, B. G. Kolloff, S. Beccue, “High resolution optical hybrid absolute incremental position encoder,” U.S. patent5,336,884 (9August1994).

Schoenwaldet, J. S.

M. Khoshnevisan, J. S. Schoenwaldet, J. P. Rode, R. J. D. Smith, B. G. Kolloff, S. Beccue, “High resolution optical hybrid absolute incremental position encoder,” U.S. patent5,336,884 (9August1994).

B. G. Kolloff, J. S. Schoenwaldet, S. Beccue, M. Khoshnevisan, “High resolution optical hybrid digital-analog linear position encoder,” U.S. patent5,451,776 (19September1995).

Seitz, P.

Smith, R. J. D.

M. Khoshnevisan, J. S. Schoenwaldet, J. P. Rode, R. J. D. Smith, B. G. Kolloff, S. Beccue, “High resolution optical hybrid absolute incremental position encoder,” U.S. patent5,336,884 (9August1994).

Tsukiji, M.

K. Ishizuka, M. Tsukiji, Y. Kubota, S. Ishii, T. Nishimura, “Diffracted beam encoder,” U.S. patent5,017,777 (21May1991).

Wigmore, T.

T. Wigmore, “Optical shaft encoder from Sharp,” Elektor Electron. 15, 60–62 (1989).

Zhang, J. H.

J. H. Zhang, L. Cai, “Profilometry using an optical stylus with interferometric readout,” Meas. Sci. Technol. 8, 546–549 (1997).
[CrossRef]

Appl. Opt. (2)

Elektor Electron. (1)

T. Wigmore, “Optical shaft encoder from Sharp,” Elektor Electron. 15, 60–62 (1989).

Elektronikpraxis (1)

H. Epstein, “Incremental optical angle encoder of high resolution,” Elektronikpraxis 27, 88–90, 92–93 (1992).

Meas. Sci. Technol. (1)

J. H. Zhang, L. Cai, “Profilometry using an optical stylus with interferometric readout,” Meas. Sci. Technol. 8, 546–549 (1997).
[CrossRef]

Other (8)

Catalog , Incremental Angle Encoders (Heidenhain GMBH, Traunreut, Germany).

K. Kudo, H. Maeda, N. Baba, H. Funato, “High resolution encoder using double gratings,” in International Conference on Applications of Optical Holography, T. Honda, ed., Proc. SPIE2577, 138–145 (1995).
[CrossRef]

K. Ishizuka, M. Tsukiji, Y. Kubota, S. Ishii, T. Nishimura, “Diffracted beam encoder,” U.S. patent5,017,777 (21May1991).

T. Nishimura, K. Ishizuka, “Rotary encoder having a plurality of beams emitted by a diffraction grating,” U.S. patent5,101,102 (31March1992).

K. Ishizuka, T. Nishimura, “Encoder with high resolving power and accuracy,” U.S. patent5,146,085 (8September1992).

B. G. Kolloff, J. S. Schoenwaldet, S. Beccue, M. Khoshnevisan, “High resolution optical hybrid digital-analog linear position encoder,” U.S. patent5,451,776 (19September1995).

M. Khoshnevisan, J. S. Schoenwaldet, J. P. Rode, R. J. D. Smith, B. G. Kolloff, S. Beccue, “High resolution optical hybrid absolute incremental position encoder,” U.S. patent5,336,884 (9August1994).

C. Dirk, B. Jan, U. Kristof, “Encoder element,” European patent application; publication 0638810 A1 (15February1995).

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Figures (5)

Fig. 1
Fig. 1

Autofocus laser rotary encoder.

Fig. 2
Fig. 2

Relative positions of the three spots on the encoder disk.

Fig. 3
Fig. 3

Focus spot to scan the step of the grating.

Fig. 4
Fig. 4

Change of the spots on the six-segment photodetector.

Fig. 5
Fig. 5

Output waveform of the encoder.

Equations (3)

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s = 1.22 λ / NA ,
P   sin   θ = λ ,
w = L   tan   θ ,

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