Position measuring device

• US 5,651,187 A
• Filed: 08/11/1995
• Issued: 07/29/1997
• Est. Priority Date: 08/12/1994
• Status: Expired due to Fees

• Current Assignee: Dr. Johannes Heidenhain GmbH
• Original Assignee: Dr. Johannes Heidenhain GmbH
• Inventors: Affa, Alfred
• Primary Examiner(s): Bennett, G. Bradley
• Application Number:
  US08/514,259
• Time in Patent Office: 718 Days
• Field of Search: 33/706, 33/708, 33/707, 250/237 G
• US Class Current: 33/706
• CPC Class Codes: G01D 5/2457 Incremental encoders having reference marks
• CPC Class Codes: G01D 5/34792 with only digital scales or both digital and incremental scales
• CPC Class Codes: H03M 1/28 with non-weighted coding
• CPC Class Codes: H03M 1/308 with additional pattern means for determining the absolute position, e.g. reference marks

Abstract

A position measuring system in which a scale has a reference mark track with two different sequences of reference marks are provided adjacent to an incremental division track. A first sequence of reference marks are disposed at successively different intervals and a second sequence of reference marks are disposed at equal intervals. Two modes of operation are available where either the absolute position is determined by scanning either the first sequence of reference marks or the second sequence of reference marks.

Claims

1. A position measuring instrument comprising:

a scale having at least one incremental division track and one reference mark track, wherein the reference mark track has a sequence of identical first reference marks located at different intervals along the scale and the reference mark track has a second reference mark track of evenly spaced second reference marks which differ from the sequence of first reference marks; and

either a first scanner unit that can be positioned to scan the incremental division track and generate counting signals and to scan the reference mark track and generate reference mark pulses, the first scanner unit having a first scanning field which is designed so that in the course of scanning the sequence of first reference marks, a first reference mark pulse is generated at each of the first reference marks, and in the course of scanning the second reference mark, no reference mark pulse is generated wherein an absolute position is assigned to the respective reference mark pulses in that the different characteristic intervals between the first reference marks are determined by an evaluation of the counting signals of the incremental division track between the reference mark pulses;

or

a second scanner unit that can be positioned to scan the incremental division track, the second scanner unit having a second scanning field which is designed so that in the course of scanning the sequence of second reference marks a second reference mark pulse is generated at each one of the second reference marks, and in the course of scanning the first reference mark no reference mark pulses are generated.

2. A position measuring instrument according to claim 1 further comprising a selector assigned to at least one of the second reference marks wherein the selector is scanned and an absolute position of the position measuring instrument is determined with respect to the selector.

3. A position measuring instrument according to claim 1, wherein the first and second reference marks are differently designed.

4. A position measuring instrument according to claim 1, wherein each first reference mark and each second reference mark consists of a pattern of lines disposed next to each other in the measuring direction, the pattern of the lines of the first reference marks differs from the pattern of the lines of the second reference marks and the first scanning field of the scanner unit has a pattern of lines which is identical with the pattern of the first reference marks and the second scanning field has a pattern of lines which is identical with the pattern of the second reference marks.

5. A position measuring instrument according to claim 2, wherein the selector is a magnet which is scanned by a Hall generator of the scanner unit.

6. A position measuring instrument comprising:

a scanner unit having a first scanning field and a second scanning field; and

either a first scale having at least one incremental division track which is scanned by the scanner unit to form counting signals and a first reference mark track with a sequence of identical first reference marks spaced at different intervals from each other which is also scanned by the scanner unit, whereby the first scanning field is designed so that scanning the sequence of first reference marks, a first reference mark pulse is generated at each of the first reference marks and the second scanning field is designed so that scanning the sequence of first reference marks, no reference mark pulses are generated and an absolute position is assigned to the reference mark pulses in that the different characteristic intervals between the first reference marks are determined by an evaluation of the counting signals of the incremental division track between the reference mark pulses;

or

a second scale having at least one incremental division track which is scanned by the scanner unit to form counting signals and a second reference mark track with a sequence of identical second reference marks spaced at identical intervals which is also scanned by the scanner unit, whereby the first scanning field is designed so that scanning the sequence of second reference marks no reference mark pulses are generated and the second scanning field is designed so that scanning the sequence of second reference marks, a second reference mark pulse is generated at each of the second reference marks.

7. A position measuring instrument according to claim 6, wherein each first reference mark and each second reference mark consists of a pattern of lines disposed next to each other in the measuring direction;

the pattern of the lines of the first reference marks differs from the pattern of the lines of the second reference marks, the first scanning field has a pattern of lines which is identical with the pattern of the first reference mark, and the second scanning field has a pattern of lines which is identical with the pattern of the second reference mark.

8. A position measuring instrument comprising:

at least one incremental division track which is scanned by a scanner unit for forming counting signals and one reference mark track, the reference mark track having a first sequence of identical first reference marks which are disposed at different intervals in the first reference track so that these reference marks can be distinguished by characteristic intervals between a plurality of reference marks of this sequence, the same reference track also having a second sequence of identical second reference marks disposed in successive identical intervals, the reference marks of the first sequence being different than the reference marks of the second sequence;

the scanner unit having a first scanning field which is designed such that in the course of scanning the sequence of first reference marks a reference mark pulse is generated at each of these reference marks, and in the course of scanning the second reference mark no reference mark pulse is generated, the scanner unit also having a second scanning field which is designed such that in the course of scanning the sequence of second reference marks a reference mark pulse is generated at each of these reference marks and in the course of scanning the first reference mark no reference mark pulse is generated; and

means for selecting whether the position measuring instrument is operated in a first or second mode of operation wherein in the first mode the first scanning field scans the scale and the reference pulses from the first sequence of first reference marks are supplied to an evaluation unit which ascertains the absolute position of one first reference mark from the characteristic intervals obtained by counting signals between first reference marks and in the second mode the second scanning field scans the scale and reference mark pulses from the second sequence of second reference marks are supplied to the evaluation unit which ascertains the absolute position of one of the second reference mark.

9. A position measuring instrument according to claim 8 wherein the first and second sequence of reference marks are formed by a like gap distribution of a row of successive opaque lines and transparent gaps which are scanned photoelectrically by the scanner unit, the scanner unit further comprising a first scanning field with a line-gap distribution identical to the first sequence of reference marks and a second scanning field with a line-gap distribution identical to the second scanning field, the line-gap distribution of the second sequence of reference marks being different from the line-gap distribution of the first sequence of reference marks so that when the first sequence of reference marks is scanned by the second scanning field and the second sequence of reference marks is scanned by the first scanning field, no reference pulse is generated.

10. A position measuring instrument according to claim 8, wherein said means for selecting is an electric reversing switch mounted on the position measuring instrument.

11. A position measuring instrument according to claim 8, wherein said means for selecting is a covering, which is provided in the beam path between said light source and a first receiving field assigned to said first scanning field, or in the beam path between said light source and a second receiving field assigned to said scanning field.