Position measuring device including a scale having an integrated reference marking

• US 7,667,188 B2
• Filed: 05/13/2008
• Issued: 02/23/2010
• Est. Priority Date: 05/25/2007
• Status: Active Grant

• Current Assignee: Dr. Johannes Heidenhain GmbH
• Original Assignee: Dr. Johannes Heidenhain GmbH
• Inventors: Tovar, Heinz
• Primary Examiner(s): Luu; Thanh X
• Application Number:
  US12/120,126
• Publication Number:
  US 20080290262A1
• Time in Patent Office: 651 Days
• Field of Search: 25023113-23118, 250/237.G, 250/237.R, 356/616, 337/06, 337/07, 337/10, 324/207.24, 324/207.25, 341 9- 11, 341/13
• US Class Current: 250/231.13
• CPC Class Codes: G01D 5/2457 Incremental encoders having reference marks
• CPC Class Codes: G01D 5/366 Particular pulse shapes

Abstract

A scale and a position-measuring device include the shifting of reference markings in graduation tracks, offset transversely with respect to the measuring direction, by fractions of the interval of the reference markings within a graduation track. It is thus possible to eliminate, or at least to markedly reduce, negative effects of the disturbance of the periodicity of a graduation track by the reference markings.

Claims

1. A position-measuring device, comprising:

a scale including at least two graduation tracks, each track being P-periodic in a measuring direction and including an integrated reference marking in the form of an interruption of the P-periodicity at evenly spaced first intervals, the graduation tracks being offset transversely with respect to the measuring direction, and the integrated reference markings being staggered in the measuring direction; and

a patterned detector configured to scan the scale to generate electrical signals to form a position value, the detector including a plurality of detector tracks configured to scan the graduation tracks, the detector tracks being offset transversely to the measuring direction, each detector track, for a plurality of periods of the graduation tracks, including a plurality of m sensors per period arranged one after another in the measuring direction.

2. The position-measuring device according to claim 1, wherein, transversely to the measuring direction, the scale includes two P-periodic graduation tracks having reference markings staggered by half of the first interval in the measuring direction.

3. The position-measuring device according to claim 1, wherein the graduation tracks include light and dark regions alternating in the measuring direction, each period formed by one light region and one dark region, each nth light or dark region in each graduation track being replaced by an opposite dark or light region to form an integrated reference marking.

4. The position-measuring device according to claim 3, wherein n=8 and the first interval corresponds to an eightfold of the period.

5. The position-measuring device according to claim 1, wherein the graduation tracks include light and dark regions alternating in the measuring direction, each period formed by one light region and one dark region, each eighth light or dark region in each graduation track being replaced by an opposite dark or light region to form an integrated reference marking, the first interval corresponding to an eightfold of the period.

6. The position-measuring device according to claim 1, wherein, at a second interval different from the first interval, each detector track has a gap in which, in each case, m sensors are one of (a) missing and (b) not utilized to generate the electrical signals.

7. The position-measuring device according to claim 6, wherein the first interval and the second interval differ by one period.

8. The position-measuring device according to claim 6, wherein the gaps of the detector tracks are arranged next to one another.

9. The position-measuring device according to claim 1, wherein the sensors include photodetectors, each group of four photodetectors arranged one after another in the measuring direction is arranged to scan one period of a graduation track.

10. The position-measuring device according to claim 1, wherein light from a light source, after being collimated, passes through the scale onto the patterned detector.

11. The position-measuring device according to claim 10, wherein the sensors include photodetectors;

and

wherein photodetectors arranged adjacent each other are interconnected to detect the graduation tracks, and photodetectors arranged offset relative to each other in the measuring direction are interconnected to detect the integrated reference markings, the offset of the photodetectors corresponding to the offset of the integrated reference markings between the graduation tracks.

12. The position-measuring device according to claim 1, further comprising a light source and a collimator configured to collimate light from the light source and direct the collimate light through the scale on the patterned detector.

13. The position-measuring device according to claim 1, wherein m=4.