Method for generating a synthetic reference signal for comparison with scanning signals of a position measuring device

• US 5,936,236 A
• Filed: 11/26/1997
• Issued: 08/10/1999
• Est. Priority Date: 11/26/1997
• Status: Expired due to Fees

• Current Assignee: HEIDENHAIN Corp. (Dr. Johannes Heidenhain GmbH)
• Original Assignee: Renco Encoders, Inc. (Dr. Johannes Heidenhain GmbH)
• Inventors: Setbacken, Robert, Barnett, Donald E.
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US08/980,047
• Time in Patent Office: 622 Days
• Field of Search: 250/231.13, 250/231.15, 250/231.16, 250/237 G, 250/214 R, 356/373, 356/374, 341/13
• US Class Current: 250/231.13
• CPC Class Codes: G01D 5/2451 Incremental encoders G01D5/2454 takes precedence

Abstract

A method and device for generating a reference signal for comparison with scanning signals generated by a position measuring device. The reference signal is generated using the same components used to scan a scale by averaging the scanning signals so that the reference signal is always less than the higher state of any scanning signal.

Claims

1. A measuring device comprising:

a scale with at least three graduation tracks;

a scanning unit having three sensors for scanning graduation tracks wherein the scale is displaceable relative to the scanning unit, the sensors generating scanning signals which have either a high or low state;

three comparator units coupled to the sensors wherein the comparator units generate digital signals from the scanning signals wherein each of the three comparator units has a first and a second input wherein the first input is coupled to a sensor and the second input receives a reference signal that is a combination of the output of each of the three sensors wherein the reference signal is always less than the higher state of any scanning signal.

2. A measuring device according to claim 1 wherein the sensors are optical sensors.

3. A measuring device according to claim 1 wherein the sensors are magnetic sensors.

4. A measuring device according to claim 1 wherein each graduation track comprises four opaque and four transparent areas sequentially disposed on the scale wherein each opaque and transport area covers an angular range of 45°

.

5. A measuring device according to claim 4 wherein each graduation track is shifted with respect to an adjacent track by 15°

.

6. A measuring device according to claim 1 wherein each of the three comparator units is an amplifier.

7. A measuring device according to claim 1 wherein the reference signal is an average of the output of the three sensors.

9. A method according to claim 7 further comprising the steps of generating a high state signal if the scanning signal is greater than the reference signal and generating a low state signal if the scanning signal is less than the reference signal.

11. A measuring device according to claim 9 wherein the means for comparing is a comparator.

12. A measuring device according to claim 9 wherein the reference signal is an average of the scanning signals.

8. A method for measuring the displacement of a scale relative to a scanning unit wherein the scale has at least three graduation tracks, the method comprising the steps of:

generating three scanning signals by scanning the three graduation tracks with three sensors wherein only two of the three scanning signals are in a same state;

generating a reference signal by averaging the three scanning signals wherein the reference signal is less than any one of the three scanning signals; and

comparing the reference signal with each scanning signal.

10. A measuring device comprising a scanning unit and a scale having at least three graduation tracks which is displaceable with respect to the scanning unit, the device comprising;

means for generating three scanning signals by scanning the three graduation tracks with three sensors wherein only two of the three scanning signals are in a same state;

means for generating a reference signal that is a combination of the scanning signals wherein the reference signal is less than any one of the three scanning signals; and

means for comparing the scanning signals with the reference signal.

13. A method for measuring the displacement of a scale relative to a scanning unit, wherein the scale has at least three graduation tracks, the method comprising the steps of:

generating three scanning signals by scanning the three graduation tracks with three sensors wherein only two of the three scanning signals are in a same state;

generating a reference signal that is a combination of a plurality of scanning signals wherein the reference signal is less than any one of the three scanning signals; and

comparing the reference signal with each scanning signal.

14. A method according to claim 13 further comprising the steps of generating a high state signal if the scanning signal is greater than the reference signal and generating a low state signal if the scanning signal is less than the reference signal.