METHOD FOR INITIALIZING A POSITION-MEASURING SYSTEM

• US 20070227019A1
• Filed: 03/29/2007
• Published: 10/04/2007
• Est. Priority Date: 04/04/2006
• Status: Active Grant

• Current Assignee: Dr. Johannes Heidenhain GmbH
• Original Assignee: Dr. Johannes Heidenhain GmbH
• Inventors: HOLZAPFEL, Wolfgang, RASCHER, Kai
• Granted Patent: US 7,426,790 B2
• Time in Patent Office: Days
• US Class Current: 33/320
• CPC Class Codes: G01D 18/001 Calibrating encoders
• CPC Class Codes: G01D 5/24428 Error prevention

Abstract

A method is for initializing a position-measuring system for an object movable in at least two degrees of freedom relative to a measuring frame. The position-measuring system includes one position-measuring device per degree of freedom, including a scale having an incremental track for measuring relative positions and an absolute track for measuring absolute positions, as well as scanning heads, assigned to the scales, for reading the incremental tracks and absolute tracks. In an initialization step, the incremental tracks are evaluated using a first evaluation procedure having a large tolerance with respect to the alignment of scanning head and associated scale, and in so doing, approximate absolute positions are determined per degree of freedom. In an alignment step, the movable object is aligned relative to the measuring frame based on the approximate position. In an acquisition step, the absolute tracks are evaluated using a second evaluation procedure having a low tolerance with respect to the alignment of scanning head and associated scale, and precise absolute positions are determined for each degree of freedom.

Claims

1. A method for initializing a position-measuring system for an object movable in at least two degrees of freedom relative to a measuring frame, the position-measuring system including at least one position-measuring device per degree of freedom, each position-measuring device having a scale including an incremental track for measuring a relative position and an absolute track for measuring an absolute position and scanning heads, corresponding to the scales, for reading the incremental track and absolute track, comprising:

an initialization step in which at least one of the incremental tracks and the absolute tracks are evaluated with a first evaluation procedure to form an evaluation result;

an alignment step in which the movable object is aligned relative to the measuring frame based on the evaluation result; and

an acquisition step in which the absolute tracks are evaluated with a second evaluation procedure having a small tolerance with respect to alignment of scanning head and the corresponding scale to determine a precise absolute position for each degree of freedom.

2. The method according to claim 1, wherein in the initialization step, the absolute tracks are evaluated with the first evaluation procedure, and an approximate absolute position is determined as the evaluation result for each degree of freedom, the first evaluation procedure having a large tolerance with respect to the alignment of the scanning head and the corresponding scale.

3. The method according to claim 2, wherein, based on the approximate absolute positions ascertained in the initialization step, an alignment of the object relative to the measuring frame, and therefore of the scanning heads relative to the scales, is performed, so that the small tolerance is adhered to in the acquisition step.

4. The method according to claim 2, wherein the absolute track includes a reference mark that is evaluated in the first evaluation procedure and the second evaluation procedure.

5. The method according to claim 4, wherein the first evaluation procedure provides only an approximate assignment of the reference mark to the incremental track and the second evaluation procedure guarantees a precise assignment of the reference mark to the incremental track.

6. The method according to claim 2, wherein the absolute track includes a code in which a plurality of absolute positions are coded, and the code is evaluated in the first evaluation procedure and the second evaluation procedure.

7. The method according to claim 6, wherein the approximate absolute position is determined based only on the absolute track.

8. The method according to claim 1, wherein in the initialization step, the incremental tracks are evaluated with the first evaluation procedure, and, for each degree of freedom, a signal property of scanning signals of the incremental tracks is determined as the evaluation result.

9. The method according to claim 8, wherein based on the signal properties ascertained in the initialization step, an alignment of the object relative to the measuring frame, and therefore of the scanning heads relative to the scales, is performed so that the small tolerance is adhered to in the acquisition step.

10. The method according to claim 8, wherein the signal property of the scanning signals includes signal strength.

11. A method for initializing a position-measuring system for an object movable in at least two degrees of freedom relative to a measuring frame, the position-measuring system including at least one position-measuring device per degree of freedom, each position-measuring device having a scale including an incremental track for measuring a relative position and an absolute track for measuring an absolute position and scanning heads, corresponding to the scales, for reading the incremental track and absolute track, comprising:

evaluating, in an initialization step, at least one of (a) the incremental track and (b) the absolute track of each position-measuring device with a first evaluation procedure to form an evaluation result;

aligning, in an alignment step, the movable object relative to the measuring frame based on the evaluation result; and

evaluating, in an acquisition step, the absolute track of each position-measuring device with a second evaluation procedure having a small tolerance with respect to alignment of scanning head and the corresponding scale to determine a precise absolute position for each degree of freedom.

12. The method according to claim 11, wherein the initialization step includes:

evaluating the absolute track of each position-measuring device with the first evaluation procedure, the first evaluation procedure having a large tolerance with respect to the alignment of the scanning head and the corresponding scale; and

determining an approximate absolute position as the evaluation result for each degree of freedom.

13. The method according to claim 12, wherein the alignment step includes aligning the object relative to the measuring frame, and therefore the scanning heads relative to the scales, in accordance with the approximate absolute position determined in the initialization step to adhere to the small tolerance in the acquisition step.

14. The method according to claim 12, wherein the absolute track includes a reference mark evaluated in the first evaluation procedure and the second evaluation procedure.

15. The method according to claim 14, wherein the first evaluation procedure provides only an approximate assignment of the reference mark to the incremental track and the second evaluation procedure guarantees a precise assignment of the reference mark to the incremental track.

16. The method according to claim 12, wherein the absolute track includes a code, a plurality of absolute positions coded in the code, the first evaluation procedure and the second evaluation procedure including evaluation of the code.

17. The method according to claim 16, wherein the approximate absolute position is determined in the determining step based only on the absolute track.

18. The method according to claim 11, wherein the initialization step includes:

evaluating the incremental tracks in the first evaluation procedure; and

determining, for each degree of freedom, a signal property of scanning signals of the incremental tracks as the evaluation result.

19. The method according to claim 18, further comprising aligning the object relative to the measuring frame, and therefore the scanning heads relative to the scales, in accordance with the signal properties determined in the initialization step to adhere to the small tolerance in the acquisition step.

20. The method according to claim 18, wherein the signal property includes a signal strength.