Abstract

Modern computer-controlled manufacturing machinery requires the absolute and highly accurate measurement of the linear position. Such an absolute, optical linear position encoder is described here. It is based on the transilluminance of a glass scale with an inexpensive light-emitting diode. The scale has two code tracks, one based on a pseudo-random binary sequence for the coarse determination of position and another periodic code for accurate fine-position measurement. A single-lens telecentric optical system images the code tracks in a mechanically insensitive way onto a custom photodetector. This special detector IC is capable of determining the components of the (complex) Fourier transform for the spatial frequency of the periodic code. The absolute optical position encoder shows a resolution of 10 nm and an absolute accuracy of better than 100 nm over short distances, verified with a commercial laser interferometer.

© 1996 Optical Society of America

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References

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  1. A. R. Luxmoore, ed., Optical Transducers and Techniques in Engineering Measurement (Applied Science Publishers, London, 1983), Chap. 3.
    [CrossRef]
  2. For example, Model LS 106, J. Heidenhain GmbH, Traunreut, Germany.
  3. For example, Model Magnescale GS (SR10-A), Sony Magne-scale Inc., Tokyo, Japan.
  4. N. Tanigushi, “Current status and future trends of ultraprecision machining,” CIRP Annals 32-2 (Hallwag, Bern, 1988), pp. 573–582.
  5. For example, Model LIP 101, J. Heidenhain GmbH, Traunreut, Germany.
  6. For example, Model L-104, Canon U.S.A. Inc., New York, N.Y. 11042.
  7. H. Kellner, “Verfahren zur Bestimmung der Lage eines Bezugspunktes eines Abtasters relativ zu einem Jnkremental-massstab sowie Bezugspunktgeber,” German patent DE3909856 (25March1989).
  8. W. L. Hassler, “Position sensing device,” European patent350,158 (31May1989).
  9. M. Durana, R. Gallay, P. Robert, “Absolute position detector for an apparatus for measuring linear angular values,” U.S. patent5,235,181 (10Aug.1993).
  10. LCI, RSF-Elektronik, Tarsdorf, Austria.
  11. C. J. Kennedy, A. T. Shepherd, G. I. Thomas, “Improvements relating to measuring apparatus,” U.K. patent1,284,641 (8Jan.1970).
  12. A. M. Lewis, C. L. Winkler, “Position measurement apparatus,” U.K. patent1,511,044 (7May1975).
  13. R. D. Elms, “Positioning determining method and apparatus,” U.S. patent4,009,377 (7Nov.1977).
  14. E. M. Petriu, “Absolute-type position transducers using a pseudo-random encoding,” IEEE Trans. Instrum. Meas. IM-36, 950–955 (1987).
  15. H. H. Hopkins, “The frequency response of a defocused optical system,” Proc. R. Soc. London Ser. A 231, 91–103 (1955).
    [CrossRef]
  16. K. Engelhardt, G. Häusler, “Acquisition of 3-D data by focus sensing,” Appl. Opt. 27, 4684–4689 (1988).
    [CrossRef] [PubMed]
  17. K. Engelhardt, “Acquisition of 3-D data by focus sensing utilizing the moiré effect of CCD cameras,” Appl. Opt. 30, 1401–1407 (1991).
    [CrossRef] [PubMed]
  18. M. T. Gale, M. Rossi, J. Pedersen, H. Schütz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng. 33, 3556–3566 (1994).
    [CrossRef]
  19. T. Stone, N. George, “Hybrid diffractive-refractive lenses and achromats,” Appl. Opt. 27, 2960–2971 (1988).
    [CrossRef] [PubMed]
  20. R. E. Kunz, M. Rossi, “Phase-matched Fresnel elements,” Opt. Commun. 97, 6–10 (1993).
    [CrossRef]
  21. Orbit Semiconductor Inc., 1230 Bordeaux Drive, Sunnyvale, Calif. 94089.
  22. SACMOS 3, Faselec AG, Binzstrasse 44, CH-8045 Zurich, Switzerland.
  23. HP 5528A Laser Measurement System, Hewlett-Packard Company, Santa Clara, Calif.
  24. LHKK 016B03S01.XXX Absolute Position Encoder, Baumer Electric AG, Frauenfeld, Switzerland.

1994 (1)

M. T. Gale, M. Rossi, J. Pedersen, H. Schütz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng. 33, 3556–3566 (1994).
[CrossRef]

1993 (1)

R. E. Kunz, M. Rossi, “Phase-matched Fresnel elements,” Opt. Commun. 97, 6–10 (1993).
[CrossRef]

1991 (1)

1988 (2)

1987 (1)

E. M. Petriu, “Absolute-type position transducers using a pseudo-random encoding,” IEEE Trans. Instrum. Meas. IM-36, 950–955 (1987).

1955 (1)

H. H. Hopkins, “The frequency response of a defocused optical system,” Proc. R. Soc. London Ser. A 231, 91–103 (1955).
[CrossRef]

Durana, M.

M. Durana, R. Gallay, P. Robert, “Absolute position detector for an apparatus for measuring linear angular values,” U.S. patent5,235,181 (10Aug.1993).

Elms, R. D.

R. D. Elms, “Positioning determining method and apparatus,” U.S. patent4,009,377 (7Nov.1977).

Engelhardt, K.

Gale, M. T.

M. T. Gale, M. Rossi, J. Pedersen, H. Schütz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng. 33, 3556–3566 (1994).
[CrossRef]

Gallay, R.

M. Durana, R. Gallay, P. Robert, “Absolute position detector for an apparatus for measuring linear angular values,” U.S. patent5,235,181 (10Aug.1993).

George, N.

Hassler, W. L.

W. L. Hassler, “Position sensing device,” European patent350,158 (31May1989).

Häusler, G.

Hopkins, H. H.

H. H. Hopkins, “The frequency response of a defocused optical system,” Proc. R. Soc. London Ser. A 231, 91–103 (1955).
[CrossRef]

Kellner, H.

H. Kellner, “Verfahren zur Bestimmung der Lage eines Bezugspunktes eines Abtasters relativ zu einem Jnkremental-massstab sowie Bezugspunktgeber,” German patent DE3909856 (25March1989).

Kennedy, C. J.

C. J. Kennedy, A. T. Shepherd, G. I. Thomas, “Improvements relating to measuring apparatus,” U.K. patent1,284,641 (8Jan.1970).

Kunz, R. E.

R. E. Kunz, M. Rossi, “Phase-matched Fresnel elements,” Opt. Commun. 97, 6–10 (1993).
[CrossRef]

Lewis, A. M.

A. M. Lewis, C. L. Winkler, “Position measurement apparatus,” U.K. patent1,511,044 (7May1975).

Pedersen, J.

M. T. Gale, M. Rossi, J. Pedersen, H. Schütz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng. 33, 3556–3566 (1994).
[CrossRef]

Petriu, E. M.

E. M. Petriu, “Absolute-type position transducers using a pseudo-random encoding,” IEEE Trans. Instrum. Meas. IM-36, 950–955 (1987).

Robert, P.

M. Durana, R. Gallay, P. Robert, “Absolute position detector for an apparatus for measuring linear angular values,” U.S. patent5,235,181 (10Aug.1993).

Rossi, M.

M. T. Gale, M. Rossi, J. Pedersen, H. Schütz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng. 33, 3556–3566 (1994).
[CrossRef]

R. E. Kunz, M. Rossi, “Phase-matched Fresnel elements,” Opt. Commun. 97, 6–10 (1993).
[CrossRef]

Schütz, H.

M. T. Gale, M. Rossi, J. Pedersen, H. Schütz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng. 33, 3556–3566 (1994).
[CrossRef]

Shepherd, A. T.

C. J. Kennedy, A. T. Shepherd, G. I. Thomas, “Improvements relating to measuring apparatus,” U.K. patent1,284,641 (8Jan.1970).

Stone, T.

Tanigushi, N.

N. Tanigushi, “Current status and future trends of ultraprecision machining,” CIRP Annals 32-2 (Hallwag, Bern, 1988), pp. 573–582.

Thomas, G. I.

C. J. Kennedy, A. T. Shepherd, G. I. Thomas, “Improvements relating to measuring apparatus,” U.K. patent1,284,641 (8Jan.1970).

Winkler, C. L.

A. M. Lewis, C. L. Winkler, “Position measurement apparatus,” U.K. patent1,511,044 (7May1975).

Appl. Opt. (3)

IEEE Trans. Instrum. Meas. (1)

E. M. Petriu, “Absolute-type position transducers using a pseudo-random encoding,” IEEE Trans. Instrum. Meas. IM-36, 950–955 (1987).

Opt. Commun. (1)

R. E. Kunz, M. Rossi, “Phase-matched Fresnel elements,” Opt. Commun. 97, 6–10 (1993).
[CrossRef]

Opt. Eng. (1)

M. T. Gale, M. Rossi, J. Pedersen, H. Schütz, “Fabrication of continuous-relief micro-optical elements by direct laser writing in photoresists,” Opt. Eng. 33, 3556–3566 (1994).
[CrossRef]

Proc. R. Soc. London Ser. A (1)

H. H. Hopkins, “The frequency response of a defocused optical system,” Proc. R. Soc. London Ser. A 231, 91–103 (1955).
[CrossRef]

Other (17)

Orbit Semiconductor Inc., 1230 Bordeaux Drive, Sunnyvale, Calif. 94089.

SACMOS 3, Faselec AG, Binzstrasse 44, CH-8045 Zurich, Switzerland.

HP 5528A Laser Measurement System, Hewlett-Packard Company, Santa Clara, Calif.

LHKK 016B03S01.XXX Absolute Position Encoder, Baumer Electric AG, Frauenfeld, Switzerland.

A. R. Luxmoore, ed., Optical Transducers and Techniques in Engineering Measurement (Applied Science Publishers, London, 1983), Chap. 3.
[CrossRef]

For example, Model LS 106, J. Heidenhain GmbH, Traunreut, Germany.

For example, Model Magnescale GS (SR10-A), Sony Magne-scale Inc., Tokyo, Japan.

N. Tanigushi, “Current status and future trends of ultraprecision machining,” CIRP Annals 32-2 (Hallwag, Bern, 1988), pp. 573–582.

For example, Model LIP 101, J. Heidenhain GmbH, Traunreut, Germany.

For example, Model L-104, Canon U.S.A. Inc., New York, N.Y. 11042.

H. Kellner, “Verfahren zur Bestimmung der Lage eines Bezugspunktes eines Abtasters relativ zu einem Jnkremental-massstab sowie Bezugspunktgeber,” German patent DE3909856 (25March1989).

W. L. Hassler, “Position sensing device,” European patent350,158 (31May1989).

M. Durana, R. Gallay, P. Robert, “Absolute position detector for an apparatus for measuring linear angular values,” U.S. patent5,235,181 (10Aug.1993).

LCI, RSF-Elektronik, Tarsdorf, Austria.

C. J. Kennedy, A. T. Shepherd, G. I. Thomas, “Improvements relating to measuring apparatus,” U.K. patent1,284,641 (8Jan.1970).

A. M. Lewis, C. L. Winkler, “Position measurement apparatus,” U.K. patent1,511,044 (7May1975).

R. D. Elms, “Positioning determining method and apparatus,” U.S. patent4,009,377 (7Nov.1977).

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Figures (12)

Fig. 1
Fig. 1

Schematic diagram of the high-resolution, absolute optical position encoder system.

Fig. 2
Fig. 2

Schematic diagram of the micro-optical telecentric imaging system: focal length, 1.5 mm; magnification factor, 4; numerical aperture, 0.09.

Fig. 3
Fig. 3

Synthesized defocus series of the central cross section of a grid image obtained with a diffractive lens at a spectral half-width of (a) 80 nm and (b) 30 nm.

Fig. 4
Fig. 4

Diffractive lens imaging in the encoder setup with broadband illumination: modulation of the signal from the phase detector at a spectral half-width of 80 and 30 nm as a function of defocus at the object side.

Fig. 5
Fig. 5

Layout of the position encoder's CMOS photo-ASIC. It consists of an array of sinusoidally shaped photodiodes for phase detection and a CCD line sensor for reading the absolute code pattern.

Fig. 6
Fig. 6

SEM image showing the sinusoidally shaped photodiodes of the phase detector.

Fig. 7
Fig. 7

SEM image showing a detail of a sinusoidally shaped photodiode fabricated in a CMOS process with 3-μm design rules. The minimum feature size is not a limit of the precision with which the ideal curve is approximated.

Fig. 8
Fig. 8

SEM image showing part of the CCD line sensor required for the acquisition of the absolute code pattern.

Fig. 9
Fig. 9

Example of the analog signal from the CCD line sensor when the absolute code track is imaged in the encoder system.

Fig. 10
Fig. 10

Photocurrents from the four diodes of the phase detector if a narrow slit is projected as a function of the slit's lateral position.

Fig. 11
Fig. 11

Graphic display of the quadrature output signals of the phase detector showing an almost perfectly circular Lissajous figure.

Fig. 12
Fig. 12

Position deviation of the values obtained with the laboratory encoder setup against the values obtained with a laser interferometer.

Equations (5)

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Δ z ( v G , T ) 1.2 γ ( T ) ( 2 sin u λ v G ) v G ,
Δ f f 0 Δ λ λ 0 .
U sin I PD 2 I PD 1 ,
U cos I PD 3 I PD 4 .
Φ = arctan U sin U cos .

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