Magnetic length or angle measuring system having improved magnetic sensor arrangement

• US 4,612,502 A
• Filed: 04/04/1983
• Issued: 09/16/1986
• Est. Priority Date: 04/21/1982
• Status: Expired due to Fees

• Current Assignee: Dr. Johannes Heidenhain GmbH
• Original Assignee: Dr. Johannes Heidenhain GmbH
• Inventors: Spies, Alfons
• Primary Examiner(s): Karlsen, Ernest F.
• Assistant Examiner(s): Snow, Walter E.
• Application Number:
  US06/481,849
• Time in Patent Office: 1,261 Days
• Field of Search: 324/207, 324/208, 324/174, 324/173, 324/251, 324/252, 324/206, 338/32 H, 338/32 R
• US Class Current: 324/207.22
• CPC Class Codes: G01D 5/20 by varying inductance, e.g. by a movable armature

Abstract

A magnetic measuring instrument for measuring the relative position of two objects includes a scanning unit which incorporates a magnet positioned to scan a measuring division. The measuring division is provided with alternately magnetically conducting and magnetically non-conducting zones. Measuring signals of high signal quality are generated because the induction generated by the magnet in the measuring division runs only in planes perpendicular to the longitudinal extent of the measuring division (the measuring direction x). Magnetic field sensitive sensor elements in the air gap between the magnet and the measuring division scan the air gap induction to generate position dependent measuring signals.

Claims

1. In a magnetic measuring system for measuring the relative position of a first object with respect to a second object in a measuring direction, said system comprising means for defining a measuring division of alternating magnetically conducting and magnetically non-conducting zones, a scanning unit mounted to scan the division, and means for evaluating measuring signals to determine the position of the scanning unit with respect to the measuring division, the improvement comprising:

at least one magnet mounted to the scanning unit and oriented such that induction generated by the magnet in the measuring division extends only in planes perpendicular to the measuring direction and an air gap is created between the magnet and the measuring division;

at least one magnetic field sensitive element firmly secured adjacent the magnet to scan the measuring division, each of which elements generates a position dependent output signal as a function of measured magnetic induction in the air gap; and

means for supplying the output signals to the evaluating means;

wherein the measuring division defines a division period t;

wherein the at least one magnetic field sensitive element comprises first, second and third magnetic field sensitive elements;

wherein the length of the first and third elements in the measuring direction is less than t/2;

wherein the separation between the first and third elements is equal to (n+1/4)·

t (n=1, 2, 3, . . . );

wherein the length of the second element in the measuring direction is equal to n·

t (n=1, 2, 3 . . . );

wherein the supplying means operates to supply a first measuring signal, proportional to the difference between the signal of the first element and half the signal of the second element, and a second measuring signal, proportional to the difference between the signal of the third element and half the signal of the second element, to the evaluating means.

2. The invention of claim 1 wherein the means for defining the division comprises a carrier formed of a soft magnetic material which defines an alternating array of depressions and ridges.

4. The invention of claim 1 wherein the means for defining the division comprises a scale which defines an array of trough shaped depressions.

5. The invention of claim 1 wherein the means for defining the division comprises a scale which defines an array of truncated conical depressions.

6. The invention of claim 1 wherein the means for defining the division comprises;

a profile of a non-magnetic material which defines a groove; and

a thin band of soft magnetic material positioned in the groove, which band defines an array of recesses.

7. The invention of claim 1 further comprising a flux guide positioned partially to surround the magnet to direct the magnetic field of the magnet and to shield the magnet against interference.

8. The invention of claim 1 further comprising a plate of non-magnetic material secured to the magnet wherein the at least one magnetic field sensitive element is mounted on the plate.

9. The invention of claim 8 wherein the plate comprises an electrically non-conductive material, and wherein the plate supports at least one electrical supply conductor and at least one measurement signal conductor coupled to the element.

3. The invention of claim 3 wherein the alternating array of depressions and ridges is shaped in the form of a gear track.

10. In a magnetic measuring system for measuring the relative position of a first object with respect to a second object in a measuring direction, said system comprising means for defining a measuring division of alternating magnetically conducting and magnetically non-conducting zones, a scanning unit mounted to scan the division, and means for evaluating measuring signals to determine the position of the scanning unit with respect to the measuring division, the improvement comprising:

at least one magnet mounted to the scanning unit and oriented such that induction generated by the magnet in the measuring division extends only in planes perpendicular to the measuring direction and an air gap is created between the magnet and the measuring division;

at least one magnetic field sensitive element firmly secured adjacent the magnet to scan the measuring division, each of which elements generates a position dependent output signal as a function of measured magnetic induction in the air gap; and

means for supplying the output signals to the evaluating means;

wherein the measuring division defines a division period t;

wherein the at least one magnetic field sensitive element comprises first, second, third and fourth elements;

wherein the length of each of the four elements in the measuring direction is less than t/4;

wherein the separation between each pair of the four elements is equal to n·

t/4 (n=1, 2, 3 . . . ); and

wherein the supplying means comprises;

means for generating a first measuring signal as a function of the difference between the signals generated by the first and third elements, which are separated by a distance of k·

t/2 (k=1, 3, 5 . . . );

means for generating a second measuring signal as a function of the difference between the signals generated by the second and fourth elements, which are separated by a distance of k·

t/2 (k=1, 3, 5 . . . ); and

means for supplying the first and second measuring signals to the evaluating means.

11. The invention of claim 10 wherein the means for defining the division comprises a carrier formed of a soft magnetic material which defines an alternating array of depressions and ridges.

12. The invention of claim 11 wherein the alternating array of depressions and ridges is shaped in the form of a gear track.

13. The invention of claim 10 wherein the means for defining the division comprises a scale which defines an array of trough shaped depressions.

14. The invention of claim 10 wherein the means for defining the division comprises a scale which defines an array of truncated conical depressions.

15. The invention of claim 10 wherein the means for defining the division comprises:

a profile of non-magnetic material which defines a groove; and

a thin band of soft magnetic material positioned in the groove, which band defines an array of recesses.

16. The invention of claim 10 further comprising a flux guide positioned partially to surround the magnet to direct the magnetic field of the magnet and to shield the magnet against interference.

17. The invention of claim 10 further comprising a plate of non-magnetic material secured to the magnet wherein the at least one magnetic field sensitive element is mounted on the plate.

18. The invention of claim 17 wherein the plate comprises an electrically non-conductive material, and wherein the plate supports at least one electrical supply conductor and at least one measurement signal conductor coupled to the element.