Magnetic detector

The invention provides a magnetic detector that exerts no influence on detection accuracy of a magnetic movable body, being a detected body, even if relative positions of magnetic resistance elements and a magnet are out of alignment due to variation occurred in manufacturing process. A magnetic detector includes: a magnetic field detection part constructed of at least two magnetic resistance elements; a magnet for applying a magnetic field to the magnetic resistance elements; a magnetic movable body for changing the magnetic field that is generated by the magnet; and a processing circuit part for outputting a signal based on the change in resistance values of the magnetic resistance elements due to the change in the magnetic field; and in which a shape of the magnetic resistance elements is symmetric with respect to a point.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic detector employing a giant magnetic resistance element (hereinafter, it is referred to as GMR element) acting as magnetoelectric transformation device.

2. Description of the Related Art

The GMR element is a laminate formed of alternately laminated magnetic layers and non-magnetic layers of a thickness of several angstroms to dozens of angstroms, being a so-called artificial grid film. (Fe/Cr)n, (Permalloy/Cu/Co/Cu)n, and (Co/Cu)n are known as this artificial grid film (n means the number of laminates).

It is a recent trend that the following magnetic detection method is employed for use in on-vehicle rotary sensor and the like. In this magnetic detection method, electrodes are formed at each terminal of a magnetic resistance segment constructed of the above-mentioned GMR element to constitute a bridge circuit, a power supply of a constant voltage and a constant current is connected between these two opposed electrodes of this bridge circuit, and a change in resistance values of the magnetic resistance segment is transformed into a change in voltages to detect a change in magnetic fields acting on this magnetic resistance element.

In the Japanese Patent Publication (unexamined) No. 69546/2004, such a conventional magnetic detector is disclosed, which is hereinafter described referring to the drawings.FIG. 1(a), (b), (c) and (d) show explanatory views of a constitution of a conventional magnetic detector disclosed in the Japanese Patent Publication (unexamined) No. 69546/2004. In the drawing,FIG. 1(a) is a perspective view,FIG. 1(b) is a top plan view, andFIG. 1(c) is an enlarged view of a magnetic resistance segment.

With reference toFIG. 1, reference numeral1designates a magnetic movable body, for example, a gear that includes protrusions on a circumference of a disk, and has a shape required for changing a magnetic field. Numeral2designates a processing circuit part in which a circuit is printed on the surface of a board. Numerals2aand2bdesignate magnetic resistance segments. Numeral3designates a magnet. Numeral4designates a rotary axis of the magnetic movable body1. When this rotary axis4rotates, the magnetic movable body1also rotates in synchronization. In addition, the magnetic resistance segments2aand2bare shown respectively in one black block inFIGS. 1(a) and (b), and a shape (pattern) of the magnetic resistance segment is shown in an enlarged manner inFIG. 1(c).

FIG. 2shows constitution of processing circuit part2of the above-mentioned conventional magnetic detector. With reference toFIG. 2, the processing circuit part2consists of a wheatstone bridge circuit11including two magnetic resistance segments (GMR elements)2aand2b, a differential amplifier circuit12, a comparator circuit13, and an output circuit14. In addition, numeral151designates a transistor, numeral152designates an output terminal, VCC designates a constant voltage, and Vref designates a reference voltage.

With reference toFIG. 2, a constant voltage VCC is applied to a bridge circuit constituted of the magnetic resistance segments2aand2bfixed resistors2cand2d, and a change in resistance values of the magnetic resistance segments2aand2bcaused by a change in magnetic fields is transformed into a change in voltages. The mentioned signals having been changed in voltage are amplified by the differential amplifier circuit12, and are inputted to the comparator circuit13. The signals having been compared with a predetermined reference voltage Vref by the comparator circuit13are transformed into a final output of “0” or “1” (=VCC) by the transistor151of the output circuit14, and are outputted from the output terminal152.

Now, operations of the conventional magnetic-detector are described referring to the drawings.FIG. 3is a timing chart showing the operations of the conventional magnetic detector. In this drawing, (a) shows positions of the magnetic movable body1; (b) shows resistance values of the magnetic resistance segments2aand2b; (c) shows outputs from the differential amplifier circuit12; and (d) shows final outputs respectively.

When the magnetic movable body1shown inFIG. 1rotates about the rotary axis4, magnetic fields to be applied to the magnetic resistance segments2aand2bchange. Further, as shown inFIGS. 3(a) and (b), the change in resistances corresponding to a magnetic field to be applied to the magnetic resistance segments2aand2bcomes out in accordance with a shape of the magnetic movable body1.

Furthermore, as shown inFIG. 3(c), outputs from the differential amplifier circuit12can be obtained due to the change in the above-mentioned resistance values. Then, as shown inFIG. 3(d), the output form of the differential amplifier circuit12is subject to a waveform shaping by the comparator circuit13, and final output signals of “1” or “0” can be obtained corresponding to a shape of the magnetic movable body1.

However, recently, there has been an increasing demand for higher detection accuracy in the above-described magnetic detector; whereas, there is a limit in achieving higher accuracy in detecting positions of the concave or convex parts of the magnetic movable body1due to variation in relative positions between the magnetic resistance segments2a,2band the magnet3that occurs in the manufacturing process.

FIGS. 4(a) and (b) schematically show cases where relative positions between the magnetic resistance segments2a,2band the magnet3are both arranged with high accuracy, andFIGS. 4(c) and (d) show cases where relative positions thereof are both out of alignment.FIGS. 4(a) and (b) are examples of a magnetic detector arranged with high accuracy, and in which (a) shows a case of the magnetic movable body1being close to the magnetic resistance segments2aand2band (b) shows a case of the magnetic movable body1being apart from the magnetic resistance segments2aand2b. In both cases, in-plane magnetic fields to be applied to the magnetic resistance segments2aand2bare equal. That is, a vertical magnetic field and a horizontal magnetic field with respect to the magnetic resistance segments are equivalent.

On the other hand, as shown inFIGS. 4(c) and (d), in the case where a positional relation between the magnetic resistance segments2a,2b, and the magnet3is misaligned, in-plane magnetic fields to be applied to the magnetic resistance fields21,2bare unequal. That is, as for the magnetic resistance segment2a, a horizontal magnetic field component comes to be more intense to a long side thereof. On the contrary, as for the magnetic resistance segment2b, a vertical magnetic field component comes to be more intense to a long side thereof. Therefore, a vertical magnetic field and a horizontal magnetic field with respect to the magnetic resistance segments2a,2bare unequal.

Now, features of a magnetic field to be applied and a change in resistance values of a GMR element, being a magnetic resistance element, are described. The GMR element is an element magnetic-sensitive in plane, and has a considerably large MR effect (rate of MR change) as compared with a magnetic resistance element (MR element); and with which element being dependent on only a relative angle between directions of magnetization of the adjacent magnetic layers, the same change in resistance values can be obtained even if a direction of an external magnetic field has any angular difference with respect to current.

FIGS. 5(a) and (b) show relations between the intensity of a magnetic field of a GMR element and a resistance value of a GMR element.FIG. 5(a) shows a case where relative positions between the magnetic resistance segments2a,2band the magnet3are arranged with high accuracy.FIG. 5(b) shows the case of the foregoing relative positions being out of alignment. In the GMR element, with respect to a magnetic field to be applied in plane, a difference is produced between resistance values of the GMR element due to the action of magnetic fields in vertical direction (direction indicated by the arrow A ofFIG. 4(a)) and a horizontal direction (direction indicated by the arrow B ofFIG. 4(a)) relative to a shape (pattern) of the GMR element. With reference toFIGS. 5(a) and (b), a thick line indicates a parallel magnetic field to be applied to a GMR pattern, and a thin line indicates a vertical magnetic field to be applied to a GMR pattern.

Arrows ofFIG. 5(a) indicate ranges of a resistance value and a magnetic field of a GMR element in the case where in-plane magnetic fields shown inFIG. 4are equal or even, and show that these ranges are located at the halfway point of the vertical magnetic field and the horizontal magnetic field. Furthermore, arrows ofFIG. 5(b) indicate ranges of a magnetic field and a resistance of a GMR element in the case where in-plane magnetic fields shown inFIGS. 4(c) and (d) are unequal or uneven, and show that the magnetic resistance segment2apossesses a larger horizontal magnetic field and the magnetic resistance segment2bpossesses a larger vertical magnetic field. In the case where in-plane magnetic fields are unequal or uneven as shown inFIG. 5(b), a difference in the range of resistance value change comes out between the magnetic resistance segment2aand the magnetic resistance segment2b. That is, the range of resistance change in the magnetic resistance segment2abecomes lower than the range of resistance change in the magnetic resistance segment2b.

Operations of a magnetic detector in the case where the magnetic resistance segments2a,2band the magnet3are out of alignment are described referring toFIG. 6. InFIG. 6, (a) shows positions of the magnetic movable body1, (b) shows resistance values of the magnetic resistance segments2a,2b, (c) shows outputs from the differential amplifier circuit12, and (d) shows final outputs, respectively.

As shown inFIGS. 6(c) and (d), a difference is generated in the changes of resistance value of the GMR element, and an output waveform from the differential amplifier circuit12shifts to one side. Since a voltage value of the comparator circuit13is not changed, displacement of output signals comes out as compared with the case where the magnetic resistance segments2a,2band the magnet3are in alignment, resulting in considerable reduction of detection accuracy.

SUMMARY OF THE INVENTION

The present invention was made to solve the above-described problems, and has an object of obtaining a magnetic detector having consistent detection accuracy of a magnetic movable body, being a detected body, even if relative position between magnetic resistance elements and a magnet is out of alignment due to variation occurred in manufacturing process.

A magnetic detector according to the invention includes: a magnetic field detecting part constituted of at least two magnetic resistance elements, a magnet for applying a magnetic field to the mentioned magnetic resistance elements, a magnetic movable body for changing a magnetic field that is generated by the mentioned magnet, and a processing circuit part for outputting a signal based on change in resistance values of the mentioned magnetic resistance elements due to change in the mentioned magnetic field; and in which a shape of the mentioned magnetic resistance elements is symmetric with respect to a point.

As a result, it is possible to eliminate the influence of variation in manufacturing on detection accuracy of the rotary movable body.

DETAILED DESCRIPTION OF THE INVENTION

A magnetic detector according to a first preferred embodiment of the present invention is described referring to the drawings.FIGS. 7(a), (b) and (c) are views showing constitution of a magnetic detector according to the first embodiment of this invention. In the drawings,FIG. 7(a) is a perspective view,FIG. 7(b) is a top plan view, andFIG. 7(c) is an enlarged view of a magnetic resistance segment. With reference to the drawings, reference numeral1designates a magnetic movable body having such a shape as to change a magnetic field, for example, protrusions on a circumference of a disk. Numeral2designates a processing circuit part in which a circuit is printed on the surface of aboard. Numerals2aand2bdesignate magnetic resistance segments. Numeral3designates a magnet. Numeral4designates a rotation axis of the magnetic movable body1. The movable body1also rotates in synchronization with the rotation of this rotation axis4, in addition, the magnetic resistance segments2aand2bare indicated in one black block inFIG. 7(b), because each segments are densely massed and one segment cannot be illustrated independently.FIG. 7(c) shows an enlarged view of each magnetic resistance segment.

A shape of the magnetic resistance segment is a polygon having n-numbers of angles symmetric with respect to a point. The “n” can be any value to such a degree as to have no anisotropic properties of a shape. Supposing that n=∞, a shape thereof will be a circle. In case where a magnetic resistance segment is of a symmetric shape in a plane, the magnetic resistance segment is subjected to the application of omni-directional magnetic fields in a plane from a leading end to a trailing end of the magnetic resistance segment. That is, an in-plane magnetic field to be applied to the magnetic resistance segment, has no directional properties with respect to an arbitrarily one-directional magnetic field, and has no anisotropy.

FIGS. 8(a), (b), (c) and (d) schematically show a change in magnetic fields simulating the variation in manufacturing process.FIGS. 8(a) and (b) are examples of a magnetic detector manufactured with high accuracy. In-plane magnetic fields to be applied to the magnetic resistance segments2a,2bare equal or even in both of the case where the magnetic movable body1comes close to the magnetic resistance segments2a,2band the case where the magnetic movable body1is apart from them. That is, a vertical magnetic field and a horizontal magnetic field in plane are equal or even. On the other hand, as shown inFIGS. 8(c) and (d), in the case where a positional relation between the magnetic resistance segments2a,2band the magnet3is out of alignment due to variation occurred in manufacturing process, in-plane magnetic fields to be applied to the magnetic resistance segments2a,2bcome to be as follows. That is, the magnetic resistance segment2ahas a larger horizontal magnetic field component, and the magnetic resistance segment2bhas a larger vertical magnetic field component.

However, since the magnetic resistance segment according to the first embodiment has no anisotropic properties of a shape, the magnetic resistance segments2a,2bare subjected to the application of omni-directional magnetic fields from a leading end to a trailing end. Therefore, there is no difference between a range of the change in resistance values of the magnetic resistance segment2aand a range of the change in resistance values of the magnetic resistance segment2b, resulting in no positional shift in output signals. Accordingly, in both of the case where a positional relation between the magnetic resistance segments2a,2band the magnet3is out of alignment and the case where the positional relation is in alignment with high accuracy, waveforms thereof is synchronous.