Reference mark selection arrangement for measuring instrument

• US 4,459,750 A
• Filed: 01/20/1983
• Issued: 07/17/1984
• Est. Priority Date: 02/05/1982
• Status: Expired due to Term

• Current Assignee: Dr. Johannes Heidenhain GmbH
• Original Assignee: Dr. Johannes Heidenhain GmbH
• Inventors: Affa, Alfred
• Primary Examiner(s): Stearns, Richard R.
• Application Number:
  US06/459,378
• Time in Patent Office: 544 Days
• Field of Search: 33/125 A, 33/125 C, 33/DIG. 3, 250/237 G, 250/578, 356/375
• US Class Current: 33/707
• CPC Class Codes: G01B 11/02 for measuring length, width or thickness G01B11/08 takes precedence
• CPC Class Codes: G01D 5/347 using displacement encoding scales

Abstract

An incremental measuring instrument having a series of reference marks extending alongside a division of a scale is provided with a selector element which is slideable along the length of the scale and can be aligned with a selected one of the reference marks in order to bring the selected reference mark into operation. The position of the selector element with respect to the selected reference mark is fixed by a plurality of filler elements which cooperate with a selector element to form a column of elements arranged end to end within a guide. Holding elements at the ends of the guides preclude undesired longitudinal movement of the column of elements.

Claims

1. In a measuring instrument of the type comprising a measuring scale which extends along a measuring direction and defines a measuring direction and plurality of reference marks, a scanning unit which includes means for detecting the reference marks and means for detecting at least one selector element positioned adjacent to the scale, and means for generating a reference pulse only when one of the reference marks and the selector element are simultaneously detected, such that only those reference marks which are associated with one of the selector elements are brought into action, the improvement comprising:

means for defining a guide which extends along the measuring direction adjacent the scale;

a column of elements coupled to the guide, said column of elements comprising the at least one selector element and a plurality of filler elements, positioned end to end, said guide, selector element, and filler elements shaped such that the column of elements is slideable along the guide yet is prevented from moving laterally out of contact with the guide;

and

holding elements positioned at two spaced locations of the guide, said holding elements movable between a first position, in which the column of elements is slideable along the guide, and a second position, in which the end elements in the column of elements are prevented from moving longitudinally past the holding elements;

said column of elements being of a length selected completely to fill the length of the guide between the holding elements in order to hold the at least one selector element in position, aligned with a selected one of the reference marks.

2. The invention of claim 1 wherein the reference marks are spaced in a periodic pattern with a predetermined distance between adjacent reference marks, wherein the length of each of the filler elements is equal to the predetermined distance, and wherein the length of the selector element is selected such that the length of the column of elements is equal to the length of the guide between the holding elements, the length of the selector element being no greater than the predetermined distance.

3. The invention of claim 1 wherein the length of at least some of the filler elements is equal to a whole number multiple of the separation between adjacent reference marks.

4. The invention of claim 1 wherein the length of at least some of the filler elements is equal to a whole number fraction of the separation between adjacent reference marks.

5. The invention of claim 1 wherein the selector element comprises a magnet.

6. The invention of claim 1 wherein the selector element comprises a light source.

7. The invention of claim 1 wherein the selector element comprises a mirror.

8. The invention of claim 1 wherein the selector element is inductively responsive.

9. The invention of claim 1 wherein the selector element is capacitively responsive.

10. The invention of claim 1 wherein the filler elements comprises a synthetic material.

11. The invention of claim 1 wherein the guide comprises a T-shaped groove.

12. The invention of claim 1 wherein the guide comprises a bore.

13. The invention of claim 1 wherein the means for detecting the selector element comprises a reed switch.

14. The invention of claim 1 wherein the means for detecting the selector element comprises a field plate.

15. The invention of claim 1 wherein the means for detecting the selector element comprises a photosensitive element.

16. The invention of claim 1 wherein at least some of the filler elements comprise resilient means for accommodating a selected amount of compression in the longitudinal direction.

17. The invention of claim 16 wherein the resilient means comprises a tongue resiliently mounted to one end of one of the filler elements to pivot about an axis perpendicular to the length of the filler element.

18. The invention of claim 17 wherein the tongue defines two protrusions of differing lengths at the end of the filler element, wherein the longer protrusion is farther from the axis than the shorter protrusion.