Position measuring device employing primary and auxiliary magnetic fields
First Claim
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1. A position measuring device for measuring the relative position of two objects which are movable with respect to each other wherein a periodic graduation formed by magnetizing a pattern on a scale is scanned in the measuring direction by a scanning unit, comprising:
- at least two magneto-resistive elements for generating position dependent output signals from which position measurement values can be determined in an evaluation device, the magneto-resistive element disposed in the scanning unit in a plane parallel to the periodic graduation and at an angle β
which ranges from about 0°
to about 90°
with respect to the measuring direction; and
said at least two magneto-resistive elements disposed in the scanning unit in a plane parallel to the graduation wherein the magneto-resistive elements are separated from each other by a fraction of a graduation period along the measuring direction, the plurality of magneto-resistive elements being interconnected to form an electrical bridge;
wherein each of the at least two magneto-resistive elements have a length measured in the measuring direction which is a fraction of the graduation period, wherein the fraction is determined by the reciprocal value of a harmonic to be eliminated;
means for generating an auxiliary magnetic field to magnetically bias the at least two magneto-resistive elements, said auxiliary magnetic field directed perpendicular with respect to a stray field generated by the magnetization of the scale.
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Abstract
A magnetic measuring system having a scale and a scanning unit, the scanning unit having a plurality of magneto-resistive elements which are disposed at an angle β with respect to the measuring direction. The scanning unit generates an auxiliary magnetic field which acts perpendicularly to the measuring direction so as to magnetically bias the magneto-resistive elements.
22 Citations
26 Claims
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1. A position measuring device for measuring the relative position of two objects which are movable with respect to each other wherein a periodic graduation formed by magnetizing a pattern on a scale is scanned in the measuring direction by a scanning unit, comprising:
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at least two magneto-resistive elements for generating position dependent output signals from which position measurement values can be determined in an evaluation device, the magneto-resistive element disposed in the scanning unit in a plane parallel to the periodic graduation and at an angle β
which ranges from about 0°
to about 90°
with respect to the measuring direction; andsaid at least two magneto-resistive elements disposed in the scanning unit in a plane parallel to the graduation wherein the magneto-resistive elements are separated from each other by a fraction of a graduation period along the measuring direction, the plurality of magneto-resistive elements being interconnected to form an electrical bridge; wherein each of the at least two magneto-resistive elements have a length measured in the measuring direction which is a fraction of the graduation period, wherein the fraction is determined by the reciprocal value of a harmonic to be eliminated; means for generating an auxiliary magnetic field to magnetically bias the at least two magneto-resistive elements, said auxiliary magnetic field directed perpendicular with respect to a stray field generated by the magnetization of the scale. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 21)
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13. A position measuring device for measuring the relative position of two objects which are movable with respect to each other in a measuring direction comprising:
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a scale having a periodic graduation formed by a plurality of magnetized strips of alternating field strength, the scale having a stray field generated by the magnetization of the scale; a scanning unit comprising; at least two magneto-resistive elements facing the periodic graduation and parallel thereto, the magneto-resistive element disposed at an angle β
which ranges from about 0°
to about 90°
with respect to the measuring direction;said at least two magneto-resistive elements disposed in the scanning unit in a plane parallel to the graduation wherein the magneto-resistive elements are separated from each other by a fraction of a graduation period along the measuring direction, the plurality of magneto-resistive elements being interconnected to form an electrical bridge circuit; wherein each of the at least two magneto-resistive elements have a length measured in the measuring direction which is a fraction of the graduation period, wherein the fraction is determined by the reciprocal value of a harmonic to be eliminated; means for generating an auxiliary magnetic field, the direction of the auxiliary magnetic field. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20)
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22. A method of measuring the relative position of two objects which are movable with respect to each other comprising the steps of:
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providing a scale on a first object, the scale having a periodic graduation formed by a magnetized pattern on the scale; providing a scanning unit on a second object, the scanning unit having at least two magneto-resistive elements for scanning the periodic graduation of the scale, the at least two magneto-resistive elements disposed in a plane parallel to the plane of the scale and at an angle β
ranging from about 0°
to about 90°
with respect to the measuring direction;disposing said at least two magneto-resistive elements in a plane parallel to the graduation wherein the magneto-resistive elements are separated from each other by a fraction of a graduation period along the measuring direction; interconnecting said two or more magneto-resistive elements to form an electrical bridge; choosing the length of each of the at least two magneto-resistive elements have a length measured in the measuring direction which is a fraction of the graduation period, wherein the fraction is determined by the reciprocal value of a harmonic to be eliminated; generating an auxiliary magnetic field for magnetically as the scanning unit scans the periodic graduation of the scale; generating a stray field from the magnetization of the scale, wherein said auxiliary magnetic field is directed perpendicular to said stray field; and generating at least one position dependent output signal.
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23. A position measuring device for measuring the relative position of two objects which are movable with respect to each other wherein a periodic graduation formed by magnetizing a pattern on a scale located on one of the two objects is scanned in a measuring direction by a scanning unit located on the other of the two objects, comprising:
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at least two magneto-resistive elements for generating position dependent output signals from which position measurement values can be determined in an evaluation device, the magneto-resistive element disposed in the scanning unit in a plane parallel to the periodic graduation and at an angle β
which ranges from about 0°
to about 90°
with respect to the measuring direction; andwherein the at least two magneto-resistive elements are separated from each other by a fraction of a graduation period along the measuring direction and are interconnected into electrical bridges; and wherein the length of each of the at least two magneto-resistive elements is graduated in correspondence to a displacement in the measuring direction according to a COS function so that the two or more magnetoresistive elements function to filter harmonics. - View Dependent Claims (24, 25, 26)
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Specification