Pulse counter circuit and displacement measuring device

• US 5,127,035 A
• Filed: 09/28/1990
• Issued: 06/30/1992
• Est. Priority Date: 09/29/1989
• Status: Expired due to Term

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Ishii, Satoshi
• Primary Examiner(s): Heyman, John S.
• Application Number:
  US07/589,264
• Time in Patent Office: 641 Days
• Field of Search: 377/17, 377/24, 377/10, 377/20, 377/44, 377/28, 324/78 D, 324/115, 250/231.13
• US Class Current: 377/24
• CPC Class Codes: G01D 5/24404 Interpolation using high frequency signals

Abstract

Disclosed is a pulse counting circuit for counting pulse signals comprising a first pulse signal generating means for generating a first pulse signal corresponding to an input signal, a counting means for counting at least either of said first pulse signal and a second pulse signal which differ from said first pulse signal corresponding to said input signal, said first pulse signal possessing a pitch set smaller than that of said second pulse signal, and a control means for selectively controlling the operation of said count means for counting said first and second pulse signal.

Claims

1. A pulse counting circuit for counting pulse signals, comprising:

a pulse signal generating means for generating first and second pulse signals by dividing an input periodic signal into first and second multiple pulse divisions, said first pulse signal having divisions greater than those of said second pulse signal;

a counting means for counting at least either of said first pulse signal and said second pulse signal; and

a control means for selectively controlling an operation of said counting means for effecting counting of said first and second pulse signals.

2. A circuit according to claim 1, wherein said input periodic signal comprises 2-phase sinusoidal wave signals.

3. A circuit according to claim 2, further comprising a frequency change detecting means for detecting changes of frequencies of said periodic signals.

4. A circuit according to claim 3, wherein said control means controls said counting operation based on detection results of said frequency change detecting means.

5. A circuit according to claim 4, wherein said control means directs said counting means to count said first pulse signals when frequencies of said periodic signals are lower than predetermined values, and switches pulse signals counted by said counting means from said first pulse signals to said second pulse signals when frequencies of said periodic signals are higher than predetermined values.

6. A circuit according to claim 1, wherein said control means directs said counting means to count either of said first and second pulse signals based on command signals received from the exterior.

7. A circuit according to claim 1, further comprising abnormality detecting means for detecting abnormality in counting of the first pulse signals by said counting means.

8. A circuit according to claim 7, wherein said control means directs said counting means to count said first pulse signals under the state where abnormality is not detected by said detecting means, and switches pulse signals counted by said counting means from said first pulse signals to said second pulse signals.

9. A displacement measuring device for measuring relative displacement of objects that undergo relative shift, comprising:

a scale provided on one side of two objects;

a scale reading means for reading said scale, said scale reading means being provided on the side differing from said one side;

a first pulse signal generating means for generating a first pulse signal of a first frequency corresponding to reading results of said scale reading means;

a second pulse signal generating means for generating a second pulse signal of a second frequency corresponding to reading results of said scale reading means, said second frequency is lower than said first frequency;

a counting means for counting at least either of said first and second pulse signals;

a control means for selectively controlling the counting operation of said first and second pulse signals by said counting means; and

a displacement detecting means for detecting relative displacement of two objects based on counting results of said counting means.

10. A device according to claim 9, further comprising a frequency change detecting means for detecting frequency changes of output signals by said scale reading means.

11. A device according to claim 10, wherein said control means controls said counting operation based on a detection results by said frequency change detecting means.

12. A device according to claim 11, wherein said control means directs said counting means to count said first pulse signals when frequencies of said output signals are lower than predetermined values, and switches pulse signals counted by said counting means from said first pulse signals to said second pulse signals when frequencies of said output signals become higher than predetermined values.

13. A device according to claim 9, wherein said control means directs said counting means to count either said first or second pulse signals based on the command signals received from exterior.

14. A device according to claim 9, further comprising an abnormality detecting means for detecting abnormality in counting the first pulse signals by said counting means.

15. A device according to claim 14, wherein said control means directs said counting means to count said first pulse signals when abnormality is not detected by said abnormality detecting means, and switches pulse signals counted by said counting means from said first pulse signals to said second signals when abnormality is detected by said abnormality detecting means.

16. A device according to claim 9, further comprising a speed detecting means for detecting changes of relative displacement speed of two objects.

17. A device according to claim 16, wherein said control means controls said counting operation based on the detection results of said speed change detecting means.

18. A device according to claim 17, wherein said control means directs said count means to count said first pulse signals when relative displacement speed of two objects is smaller than predetermined values, and switches pulse signals counted by counting means from said first pulse signals to said second pulse signals when the relative displacement speed of two objects becomes greater than predetermined values.

19. A device according to claim 9, wherein said scale has a diffraction grating.

20. A device according to claim 19, wherein said scale reading means includes a light source means for irradiating light beams to said diffraction grating, and a light detecting means for detecting interference light of diffraction light from the diffraction grating irradiated by said light source means.

21. A device according to claim 20, wherein said scale reading means further includes a beam splitter for splitting into two the beams emitted from said light source function, and a light deflecting means for directing two beams split by said beam splitter for irradiation to substantially the same position of said diffraction grating, said light detecting means detecting interference light of diffraction lights emitted to substantially the same direction from said a substantially the same location said two beams.

22. A device according to claim 9, wherein said reading results comprise 2-phase sinusoidal wave signals.

23. A device according to claim 22, further comprising, means for judging a direction of the relative displacement from said reading results.

24. A stage device, comprising:

a stage relatively displaceable to a main body of said device;

a scale provided on one side of either said stage or said main body of said device;

a scale reading means provided on a side differing from said one side of either said stage or said main body of said device;

a first pulse signal generating means for generating a first pulse signal of a first frequency corresponding to reading results of said scale reading means;

a second pulse signal generating means for generating a second pulse signal with a second frequency corresponding to reading results of said scale reading means, said second frequency being lower than said first frequency;

a counting means for counting at least either of said first and second pulse signals;

a counting control means for selectively controlling the counting operation of said first and second pulse signals by said counting means;

a displacement detecting means for detecting relative displacement of said stage and device main body based on the counting results of said counting means; and

a displacement control means for controlling relative displacement between said stage and device main body based on the detection results of said displacement detecting means.

25. A device according to claim 24, wherein said reading results comprise 2-phase sinusoidal wave signals.