Method of and apparatus for detecting an amount of displacement

• US 5,719,789 A
• Filed: 09/20/1995
• Issued: 02/17/1998
• Est. Priority Date: 09/22/1994
• Status: Expired due to Fees

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Kawamata, Naoki
• Primary Examiner(s): Voeltz, Emanuel T.
• Assistant Examiner(s): Bui, Bryan
• Application Number:
  US08/531,056
• Time in Patent Office: 881 Days
• Field of Search: 364/561, 364/577, 364/486, 364/487, 356/356, 356/358, 33/701, 33/702, 33/501
• US Class Current: 702/189
• CPC Class Codes: G01D 18/001 Calibrating encoders
• CPC Class Codes: G01D 5/24476 Signal processing G01D5/2448 - G01D5/24495 take precedence
• CPC Class Codes: G01D 5/2448 Correction of gain, threshold, offset or phase control
• CPC Class Codes: G01D 5/2449 using hard-stored calibration data
• CPC Class Codes: G01D 5/2451 Incremental encoders G01D5/2454 takes precedence

Abstract

This invention relates to a method of and an apparatus for detecting the amount of displacement of an object by the use of two periodic signals having a predetermined phase difference therebetween which are outputted in conformity with the displacement of the object. The apparatus has means for detecting the two periodic signals, means for calculating the ratio between the two periodic signals, and means for obtaining the amount of displacement of the object from the value of the ratio by reference to prestored data.

Claims

1. A displacement amount detecting method of detecting the amount of displacement of an object by the use of two periodic signals having a predetermined phase difference therebetween which are outputted in conformity with the displacement of said object comprising the steps of:

detecting said two periodic signals;

calculating the ratio between said two periodic signals; and

obtaining the amount of displacement of said object from the value of said ratio by reference to prestored data,

wherein said calculating step has the step of replacing denominator and numerator with each other so that said ratio may be less than 1 in conformity with the magnitudes of said periodic signals.

2. The method according to claim 1 wherein said prestored data have data corresponding to 1/8 period of said periodic signals.

3. The method according to claim 1, further comprising the step of making the amplitudes of said detected two periodic signals substantially equal to each other.

4. The method according to claims 1, further comprising the step of correcting the phases of said two periodic signals into said predetermined phase difference.

5. The method according to claim 1, wherein the number of said prestored data is a power of 2.

6. A displacement amount detecting method of detecting the amount of displacement of an object by the use of two periodic signals having a predetermined phase difference therebetween which are outputted in conformity with the displacement of said object comprising the steps of:

detecting said two periodic signals;

calculating the ratio between said two periodic signals; and

obtaining the amount of displacement of said object from the value of said ratio by reference to prestored data,

wherein the number of said prestored data is a power of 2.

7. The method according to claim 6, further comprising the step of making the amplitudes of said detected two periodic signals substantially equal to each other.

8. The method according to claim 6, further comprising the step of correcting the phases of said two periodic signals into said predetermined phase difference.

9. A displacement amount detecting apparatus for detecting the amount of displacement of an object by the use of two periodic signals having a predetermined phase difference therebetween which are outputted in conformity with the displacement of said object comprising:

means for detecting said two periodic signals;

means for calculating the ratio between said two periodic signals; and

means for obtaining the amount of displacement of said object from the value of said ratio by reference to prestored data,

wherein said calculating means has means for replacing denominator and numerator with each other so that said ratio may be less than 1 in conformity with the magnitudes of said periodic signals.

10. The apparatus according to claim 9, wherein said prestored data have data corresponding to 1/8 period of said periodic signals.

11. The apparatus according to claim 9, further having means for making the amplitudes of said detected two periodic signals substantially equal to each other.

12. The apparatus according to claim 9, further having means for correcting the phases of said two periodic signals into said predetermined phase difference.

13. The apparatus according to claim 9, wherein the number of said prestored data is a power of 2.

14. A displacement amount detecting apparatus for detecting the amount of displacement of an object by the use of two periodic signals having a predetermined phase difference therebetween which are outputted in conformity with the displacement of said object comprising:

means for detecting said two periodic signals;

means for calculating the ratio between said two periodic signals; and

means for obtaining the amount of displacement of said object from the value of said ratio by reference to prestored data,

wherein the number of said prestored data is a power of 2.

15. The apparatus according to claim 14, further having means for making the amplitudes of said detected two periodic signals substantially equal to each other.

16. The apparatus according to claim 14, further having means for correcting the phases of said two periodic signals into said predetermined phase difference.