Position measuring system

• US 6,018,881 A
• Filed: 12/15/1997
• Issued: 02/01/2000
• Est. Priority Date: 12/17/1996
• Status: Expired due to Term

• Current Assignee: Dr. Johannes Heidenhain GmbH
• Original Assignee: Dr. Johannes Heidenhain GmbH
• Inventors: Spies, Alfons
• Primary Examiner(s): Gibson, Randy W.
• Application Number:
  US08/990,825
• Time in Patent Office: 778 Days
• Field of Search: 33/702, 33/706, 33/708, 33/DIG. 1, 324/207.24, 324/207.11, 324/207.22
• US Class Current: 33/706
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06

Abstract

A position measuring system that includes a scale graduation and a scanning element, wherein the scanning element moves relative to the scale graduation along a measurement direction so as to generate position-dependent, intensity-modulated output signals. The scanning element includes a dynamic characteristic, which has saturation areas adjoining both sides of an at least partially approximately linear operating area, in which no significantly changed output signal results any more, even when the input signal changes. The scanning gap (d) between the scale graduation and the scanning element is selected in such a way that as the scanning element moves over its entire measurement range a modulation between maximum input signals, which are located in the saturation areas of the dynamic characteristic, takes place. In order to eliminate the distortions of the output signals which usually occur in this modulation area it is furthermore provided to perform signal filtering in order to remove, in particular, the third harmonic from the output signal.

Claims

1. A position measuring system comprising:

a scale graduation;

a scanning element, wherein said scanning element moves relative to said scale graduation along a measurement direction so as to generate position-dependent, intensity-modulated output signals;

said scanning element comprises a dynamic characteristic, which has saturation areas adjoining both sides of an at least partially approximately linear operating area, in which no significantly changed output signal results any more, even when the input signal changes;

the scanning gap (d) between said scale graduation and said scanning element is selected in such a way that said scanning element is operated in its saturation areas of the dynamic characteristic; and

wherein said scanning element is laid out in such a way, that at least filtering of the third harmonic from said output signal is assured.

2. The position measuring system of claim 1, comprising a evaluation unit that receives said output signals.

3. The position measuring system of claim 1, wherein said scanning element comprises a magneto-resistive element.

4. The position measuring system of claim 1, wherein said scale graduation comprises a magnetic scale graduation.

5. The position measuring system of claim 3, wherein said scale graduation comprises a magnetic scale graduation.

6. The position measuring system of claim 3, wherein said magneto-resistive element in the area of the scanned magnetic field strengths of said scale graduation comprises an essentially parabolic dynamic characteristic.

7. The position measuring system of claim 3, wherein said magneto-resistive element in the area of the scanned magnetic field strengths of said scale graduation comprises an essentially linearized dynamic characteristic.

8. The position measuring system of claim 1, wherein said scanning element comprises a plurality of strip-shaped magneto-resistive elements.

9. The position measuring system of claim 8, wherein said plurality of strip-shaped magneto resistive elements are arranged equidistantly from one another.

10. The position measuring system of claim 8, wherein said plurality of strip-shaped magneto-resistive elements are arranged at an acute angle (α

) with respect to a direction perpendicular to said measuring direction.

11. The position measuring system of claim 10, wherein arranging said plurality of strip shaped magneto resistive elements at said acute angle (α

) results in at least filtering of the third harmonic in said output signals.

12. The position measuring system of claim 8, wherein said plurality of strip magneto-resistive elements have a width as measured in said measuring direction such that at least filtering of the fifth harmonic in said output signals results.

13. The position measuring system of claim 10, wherein said plurality of strip magneto-resistive elements have a width as measured in said measuring direction such that at least filtering of the fifth harmonic in said output signals results.

14. The position measuring system of claim 12 wherein said width has a value equal to TP/5 wherein TP is the graduation period of said magnetic scale graduation.

15. The position measuring system of claim 8, wherein the length of said plurality of strip magneto-resistive elements in a direction perpendicular to said measuring direction is selected depending on a sine- or cosine function.

16. The position measuring system of claim 10, wherein the length of said plurality of strip magneto-resistive elements in a direction perpendicular to said measuring direction is selected depending on a sine- or cosine function.

17. The position measuring system of claim 10, wherein said acute angle (α

) has a value defined by the equation tan α

=TP/3l, wherein TP is the graduation period of said magnetic scale graduation and l is the length of said plurality of strip magneto-resistive elements in a direction perpendicular to said measuring direction.

18. The position measuring system of claim 8, wherein said plurality of strip-shaped magneto-resistive elements are V-shaped.

19. The position measuring system of claim 18, wherein said V-shaped strip-shaped magneto-resistive strips are arranged symmetrically with respect to a central axis, which is oriented parallel to said measuring direction.

20. The position measuring system of claim 18, wherein each of said V-shaped strip-shaped magneto-resistive elements have an edge that is arranged at an acute angle (α

) with respect to a direction perpendicular to said measuring direction.

21. The position measuring system of claim 20, wherein said acute angle (α

) has a value defined by the equation tan α

=TP/(3l/2), wherein TP is the graduation period of said magnetic scale graduation and l is the length of said plurality of strip magneto-resistive elements in a direction perpendicular to said measuring direction.

22. The position measuring system of claim 20, wherein arranging said plurality of strip shaped magneto resistive elements at said acute angle (α

) results in at least filtering of the third harmonic in said output signals.

23. The position measuring system of claim 18, wherein said plurality of strip magneto-resistive elements have a width as measured in said measuring direction such that at least filtering of the fifth harmonic in said output signals results.

24. The position measuring system of claim 23 wherein said width has a value equal to TP/5 wherein TP is the graduation period of said magnetic scale graduation.

25. The position measuring system of claim 8, wherein said plurality of strip-shaped magneto-resistive elements are sine-shaped.

26. The position measuring system of claim 9, wherein said plurality of strip-shaped magneto-resistive elements are sine-shaped.

27. The position measuring system of claim 25, wherein said sine-shaped strip-shaped magneto-resistive strips are arranged symmetrically with respect to a central axis, which is oriented parallel to said measuring direction.

28. A position measuring system comprising:

a scale graduation;

a scanning element, wherein said scanning element moves relative to said scale graduation along a measurement direction so as to generate position-dependent, intensity-modulated output signals;

an evaluation unit that receives said position-dependent, intensity modulated output signals that generates a dynamic characteristic which has respective saturation areas adjoining both sides of an at least partially approximately linear work area, in which no significantly changed output signal results, even when the input signal changes;

the scanning distance between said scale graduation and said scanning element is selected in such a way that is located in its saturation areas of the dynamic characteristic; and

wherein said evaluation unit is laid out in such a way, that at least filtering of the third harmonic from said output signal is assured.

29. The position measuring system of claim 28, wherein said scanning element comprises a Hall element.

30. The position measuring system of claim 29, wherein said Hall element has a largely linear dynamic characteristic.

31. The position measuring system of claim 28, wherein said evaluation unit comprises a component, having a non-linear characteristic, connected in parallel with an amplifier so that a dynamic characteristic with saturation areas of the amplifier results.

32. The position measuring system of claim 31, wherein said amplifier has a trapezoidal dynamic characteristic.

33. The position measuring system of claim 31, wherein said evaluation unit is laid out in such a way, that at least filtering of the third harmonic from said output signal is assured.

34. A position measuring system comprising:

a scale graduation;

a scanning element, wherein said scanning element comprises a plurality of V-shaped strip-shaped magneto-resistive elements and said scanning element moves relative to said scale graduation along a measurement direction so as to generate position-dependent, intensity-modulated output signals;

said scanning element comprises a dynamic characteristic, which has saturation areas adjoining both sides of an at least partially approximately linear operating area, in which no significantly changed output signal results any more, even when the input signal changes;

the scanning distance (d) between said scale graduation and said scanning element is selected in such a way that as said scanning element moves over its entire measurement range a modulation between maximum input signals, which are located in the saturation areas of the dynamic characteristic, takes place; and

wherein said scanning element is laid out in such a way, that at least filtering of the third harmonic from said output signal is assured.

35. A position measuring system comprising:

a scale graduation;

a scanning element, wherein said scanning element comprises a plurality of sine-shaped strip-shaped magneto-resistive elements and said scanning element moves relative to said scale graduation along a measurement direction so as to generate position-dependent, intensity-modulated output signals;

said scanning element comprises a dynamic characteristic, which has saturation areas adjoining both sides of an at least partially approximately linear operating area, in which no significantly changed output signal results any more, even when the input signal changes;

the scanning distance (d) between said scale graduation and said scanning element is selected in such a way that as said scanning element moves over its entire measurement range a modulation between maximum input signals, which are located in the saturation areas of the dynamic characteristic, takes place; and

wherein said scanning element is laid out in such a way, that at least filtering of the third harmonic from said output signal is assured.

36. A position measuring system comprising:

a scale graduation;

a scanning element, wherein said scanning element moves relative to said scale graduation along a measurement direction so as to generate position-dependent, intensity-modulated output signals;

said scanning element comprises a dynamic characteristic, which has saturation areas adjoining both sides of an at least partially approximately linear operating area, in which no significantly changed output signal results any more, even when the input signal changes;

the scanning gap (d) between said scale graduation and said scanning element is selected in such a way that as said scanning element is operated in its entire measurement range a maximum output signal does not occur when compared with other possible scanning gaps when the scanning element is operated in said at least partially approximately linear operating area; and

wherein said scanning element is laid out in such a way, that at least filtering of the third harmonic from said output signal is assured.

37. A position measuring system comprising:

a scale graduation;

a scanning element, wherein said scanning element moves relative to said scale graduation along a measurement direction so as to generate position-dependent, intensity-modulated output signals;

an evaluation unit that receives said position-dependent, intensity modulated output signals that generates a dynamic characteristic which has respective saturation areas adjoining both sides of an at least partially approximately linear work area, in which no significantly changed output signal results, even when the input signal changes;

the scanning distance between said scale graduation and said scanning element is selected in such a way that as said scanning element is operated in its entire measurement range a maximum output signal does not occur when compared with other possible scanning gaps when said scanning element is operated in said at least partially approximately linear working area; and

wherein said evaluation unit is laid out in such a way, that at least filtering of the third harmonic from said output signal is assured.