Gear tooth sensor (GTS) with magnetoresistive bridge
First Claim
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1. A method to determine position and rotational speed of a toothed wheel having a rim, an outer edge, and ferromagnetic teeth, comprising:
- providing a sensor that includes at least one permanent magnet that generates a gear field extending away from said outer edge in a direction parallel to said rim, said gear field having a maximum value when a ferromagnetic tooth is directly opposite said permanent magnet and a minimum value when a gap between two teeth is directly opposite said permanent magnet;
providing first, second, third, and fourth magneto-resistive (MR) elements, each having a long axis, a free layer, and a reference layer;
through a first node, connecting a first end of said first MR element to a first end of said second MR element and orienting said second MR element whereby the long axes of said first and second elements are at right angles to one another;
through a second node, connecting a first end of said third MR element to a first end of said fourth MR element and orienting said third and fourth MR elements whereby the long axes of said third and fourth elements are parallel to the long axes of said first and second MR elements, respectively;
through a third node, connecting a second end of said first MR element to a second end of said third MR element and connecting a second end of said second MR element to a second end of said fourth MR element through a fourth node, thereby serially connecting all four of said MR elements to form a closed loop;
positioning said sensor to overlie said rim at a first distance therefrom;
further positioning said sensor so that it is displaced a second distance from an edge of said toothed wheel whereby part of said sensor does not overlie said rim;
orienting said sensor so that said free layers are parallel to said rim and the long axes of said first and fourth MR elements are parallel to said edge;
for all MR elements, magnetically pinning said reference layers in a single direction that is neither parallel nor normal to that of any of said long axes;
applying an input voltage across said third and fourth nodes and extracting an output signal from between said first and third nodes, said output signal being proportional to the value of said gear field; and
thereby, enabling said gear wheel'"'"'s rotational status to be determined at any time, including when said gear wheel is not rotating.
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Abstract
The invention discloses a method and apparatus for determining the rotational status of a gear wheel whether or not it is actually turning. A key feature is the magnetic angle sensor that is used. Said sensor comprises a bridge structure of four MR devices in a square array. The direction of the pinned reference layer is the same for all four devices and lies along one of the diagonals of said square array. A single wafer process is used to manufacture the invented device.
93 Citations
29 Claims
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1. A method to determine position and rotational speed of a toothed wheel having a rim, an outer edge, and ferromagnetic teeth, comprising:
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providing a sensor that includes at least one permanent magnet that generates a gear field extending away from said outer edge in a direction parallel to said rim, said gear field having a maximum value when a ferromagnetic tooth is directly opposite said permanent magnet and a minimum value when a gap between two teeth is directly opposite said permanent magnet; providing first, second, third, and fourth magneto-resistive (MR) elements, each having a long axis, a free layer, and a reference layer; through a first node, connecting a first end of said first MR element to a first end of said second MR element and orienting said second MR element whereby the long axes of said first and second elements are at right angles to one another; through a second node, connecting a first end of said third MR element to a first end of said fourth MR element and orienting said third and fourth MR elements whereby the long axes of said third and fourth elements are parallel to the long axes of said first and second MR elements, respectively; through a third node, connecting a second end of said first MR element to a second end of said third MR element and connecting a second end of said second MR element to a second end of said fourth MR element through a fourth node, thereby serially connecting all four of said MR elements to form a closed loop; positioning said sensor to overlie said rim at a first distance therefrom; further positioning said sensor so that it is displaced a second distance from an edge of said toothed wheel whereby part of said sensor does not overlie said rim; orienting said sensor so that said free layers are parallel to said rim and the long axes of said first and fourth MR elements are parallel to said edge; for all MR elements, magnetically pinning said reference layers in a single direction that is neither parallel nor normal to that of any of said long axes; applying an input voltage across said third and fourth nodes and extracting an output signal from between said first and third nodes, said output signal being proportional to the value of said gear field; and thereby, enabling said gear wheel'"'"'s rotational status to be determined at any time, including when said gear wheel is not rotating. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An apparatus to determine position and rotational speed of a toothed wheel having a rim, an outer edge, and ferromagnetic teeth, comprising:
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a sensor that includes at least one permanent magnet that generates a gear field extending away from said outer edge in a direction parallel to said rim, said gear field having a maximum value when a ferromagnetic tooth is directly opposite said permanent magnet and a minimum value when a gap between two teeth is directly opposite said permanent magnet; first, second, third, and fourth magneto-resistive (MR) elements, each having a long axis, a free layer, and a reference layer; a first end of said first MR element being connected to a first end of said second MR element, said second MR element being oriented so that the long axes of said first and second elements are at right angles to one another; a first end of said third MR element being connected to a first end of said fourth MR element and said third and fourth MR elements being orienting so that their long axes are parallel to the long axes of said first and second MR elements, respectively; a second end of said first MR element being connected to a second end of said third MR element and a second end of said second MR element being connected to a second end of said fourth MR element, all four of said MR elements being thus serially connected in a closed loop; said sensor being positioned to overlie said rim at a first distance therefrom; said sensor being displaced a second distance from an edge of said toothed wheel whereby part of said sensor does not overlie said rim; said sensor being oriented so that said free layers are parallel to said rim and the long axes of said first and fourth MR elements are parallel to said edge; and all said reference layers being magnetically pinned in a direction that is the same for all of said MR elements, said direction being neither parallel nor normal to that of any of said long axes. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. A method to measure an amount of wobble of a rotating wheel having a rim and a ferromagnetic portion that extends inwards for a first distance from an outer edge, comprising:
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providing a magneto-resistive (MR) sensor and at least one permanent magnet to generates a bias field that extends away from said outer edge in a direction parallel to said rim; positioning said sensor to overlie said rim at a distance therefrom; further positioning said sensor so that it'"'"'s center is displaced a second distance from said outer edge whereby, as said wheel rotates, said second distance will vary in a cyclic manner that depends on how much wobble is exhibited by said wheel; and thereby measuring said amount of wobble by observing changes in said sensor'"'"'s output as said wheel rotates. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29)
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Specification