Absolute encoder

• US 5,438,330 A
• Filed: 11/23/1994
• Issued: 08/01/1995
• Est. Priority Date: 10/28/1991
• Status: Expired due to Term

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Yamazaki, Yuji, Ohno, Koh
• Primary Examiner(s): Hoff, Marc S.
• Application Number:
  US08/347,227
• Time in Patent Office: 251 Days
• Field of Search: 341/1-4, 341/6-9, 341/11-14, 250/231.18
• US Class Current: 341/11
• CPC Class Codes: G01D 5/2492 Pulse stream
• CPC Class Codes: H03M 1/282 of the pattern-shifting type, e.g. pseudo-random chain code
• CPC Class Codes: H03M 1/308 with additional pattern means for determining the absolute position, e.g. reference marks

Abstract

An absolute encoder has a code plate formed with an absolute pattern and an incremental pattern. A first detector detects the absolute pattern, and outputs an absolute signal. A second detector detects the incremental pattern, and outputs an incremental signal. The absolute encoder stores the absolute signal according to an external input signal, and forms a corrected absolute signal on the basis of the incremental signal input after the absolute signal is stored.

Claims

1. An absolute encoder comprising:

a code plate formed with an absolute pattern and an incremental pattern;

first signal output means for detecting the absolute pattern by sequentially selecting the absolute pattern bit by bit, and outputting an absolute signal as serial data;

second signal output means for detecting the incremental pattern, and outputting two signals having a 90°

-phase difference therebetween;

a pattern generation circuit for generating an electrical signal pattern equivalent to the absolute pattern;

input means for inputting the absolute signal, obtained when a power supply is turned on or when a demand signal is input, to said pattern generation circuit as initial data; and

instruction means for operating said pattern generation circuit in synchronism with the outputs from said second signal output means after the initial data is input to said pattern generation circuit.

2. An absolute encoder according to claim 1, further comprising means for, when an absolute position moves during the input operation of the initial data to said pattern generation circuit, re-inputting the initial data.

3. An absolute encoder according to claim 1, wherein a predetermined pattern of an output from said pattern generation circuit is detected, and the detected pattern is output as an original position signal.

4. An absolute encoder comprising:

a code plate formed with a track of an absolute pattern and an incremental pattern;

absolute detection means for detecting the absolute pattern, and outputting an absolute signal;

incremental detection means for detecting the incremental pattern, and outputting an incremental signal;

absolute position detection means for outputting an incremental signal corresponding to the absolute pattern read by said absolute detection means when a power supply is turned on or when a demand signal is input, and thereafter, outputting the incremental signal read by said incremental detection means as an absolute position signal;

a pattern generation circuit for generating a code corresponding to a code detected by said absolute detection means on the basis of the incremental signal from said incremental detection means; and

comparison means for comparing the code detected by said absolute detection means with the code output from said pattern generation circuit.

5. An absolute encoder according to claim 4, wherein said pattern generation circuit sets, as an initial value, the code of the absolute track detected by said absolute detection means when the power supply is turned on or when the demand signal is input, and changes the initial value on the basis of the incremental signal detected by said incremental detection means so as to generate the code corresponding to the code detected by said absolute detection means.

6. An absolute encoder according to claim 4, wherein said pattern generation circuit sets, at an initial value, an arbitrary reference point when the power supply is turned on or when the demand signal is input, and changes the initial value on the basis of the incremental signal output from said absolute position detection means to an external circuit so as to generate the code corresponding to the code detected by said absolute detection means.

7. An absolute encoder according to claim 4, further comprising abnormality detection means for detecting whether or not the incremental signal detected by said incremental detection means is normal by causing said comparison means to compare the code of the absolute track detected by said absolute detection means with the code from said pattern generation circuit.

8. An absolute encoder according to claim 4, further comprising abnormality detection means for detecting whether or not the incremental signal from said absolute position detection means is normal by causing said comparison means to compare the code of the absolute track detected by said absolute detection means with the code from said pattern generation circuit.

9. An absolute encoder comprising:

a code plate formed with an absolute pattern and an incremental pattern;

a first detector which detects the absolute pattern and outputs an absolute signal;

a second detector which detects the incremental pattern and outputs an incremental signal; and

a pattern formation circuit which forms a pattern equivalent to the absolute pattern based on the incremental signal after the absolute signal is inputted thereto.

10. An absolute encoder according to claim 9, wherein said first detector has a plurality of detection elements to detect the absolute pattern, a converter which converts parallel signals from said plurality of detection elements into a serial signal, and a processor which processes the serial signal.

11. An absolute encoder comprising:

a code plate formed with an absolute pattern and an incremental pattern;

a first detector which detects the absolute pattern and outputs an absolute signal;

a second detector which detects the incremental pattern and outputs an incremental signal;

said code plate being movable relative to said first and second detectors; and

a pattern formation circuit which forms a pattern equivalent to the absolute pattern based on the incremental signal generated upon movement of said code plate relative to said second detector after the absolute signal is inputted to said circuit according to an external inputted signal.

12. An absolute encoder comprising:

a code plate formed with an absolute pattern and an incremental pattern;

an absolute detector which detects the absolute pattern and outputs an absolute signal;

an incremental detector which detects the incremental pattern and outputs an incremental signal;

an electrical signal generator which inputs the absolute signal according to an external input signal, and generates an electrical signal corresponding to the absolute pattern based on the incremental signal input after the absolute signal is inputted; and

a comparison circuit which compares the absolute signal with the electrical signal.

13. An absolute encoder comprising:

a code plate formed with a first pattern and a second pattern;

a first detector which detects the first pattern and outputs a first signal;

a second detector which detects the second pattern and outputs a second signal; and

an information generator which generates information equivalent to the first pattern based on the second signal after the first signal is inputted thereto.