JP2011185747A - Anomaly detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anomaly detector for detecting an anomaly in each magnetic detection element while reducing displacement of each magnetic detection element or variation in sensitivity, and preventing erroneous detection of an anomaly in a magnetic encoder owing to malfunction of each magnetic detection element. <P>SOLUTION: This anomaly detector 1 includes a rotary magnet 9 with its N poles and S poles alternately magnetized along its rotative direction, two magnetic detection elements 10a and 10b oppositely provided on the periphery of the rotary magnet 9, and an anomaly detection means 4 for detecting anomalies in the detection elements 10a and 10b based on output signals of the two detection elements 10a and 10b. The two detection elements 10a and 10b have the same sensitivity characteristics and are disposed close to each other on the same substrate. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an abnormality detection device that detects an abnormality of a magnetic detection element for a magnetic encoder.

  Conventionally, an abnormality detection circuit using two magnetic detection elements is known as one that detects an abnormality of this type of magnetic encoder (see Patent Document 1). This abnormality detection circuit includes a rotating magnet composed of a rotating body in which N poles and S poles are alternately magnetized, two magnetic detection elements provided in the circumferential direction of the rotating magnet, and outputs of the two magnetic detection elements. And an EXOR (Exclusive-OR) gate (circuit) to which a signal is input. The two magnetic sensing elements are arranged at positions where each output signal input to the EXOR circuit becomes a reverse phase signal. The output signal of the EXOR circuit is an “H” level signal if the magnetic encoder is normal so that the phase of each output signal is completely in reverse phase. However, if an abnormality occurs in the magnetic encoder due to missing magnets, etc. Becomes an “L” level signal because the phase relationship of each output signal is shifted. As described above, the abnormality detection circuit described in Patent Document 1 detects an abnormality of the magnetic encoder by taking the exclusive OR of the output signals of the magnetic detection elements.

JP 2001-201364 A

  By the way, in the conventional abnormality detection circuit, the abnormality of the magnetic encoder is detected based on the output signal of each magnetic detection element that is a reverse phase signal. However, in the conventional abnormality detection circuit, if a phase shift of the output signal of each magnetic detection element occurs due to a positional deviation or sensitivity variation of each magnetic detection element, it is determined that the magnetic encoder is abnormal. There was a problem that the abnormality of the element itself could not be detected and the abnormality of the magnetic encoder was erroneously detected.

  The present invention has been made in view of the above points, and can suppress the positional deviation and sensitivity variation of the magnetic detection element, detect an abnormality of the magnetic detection element, and cause a failure of the magnetic detection element. An object of the present invention is to provide an abnormality detection device that can prevent erroneous detection of an abnormality in a magnetic encoder.

  The abnormality detection device of the present invention includes a rotating magnet in which N poles and S poles are alternately magnetized along a rotating direction, two magnetic detecting elements provided facing the outer peripheral portion of the rotating magnet, An abnormality detection means for detecting an abnormality of the magnetic detection element based on output signals of the two magnetic detection elements, and the two magnetic detection elements have the same sensitivity characteristics and are on the same substrate. It is characterized by being arranged close to each other.

  According to this configuration, since two magnetic sensing elements having the same sensitivity characteristics are arranged close to each other on the same substrate, the sensitivity of the magnetic sensing elements does not vary and the positional deviation does not occur. Output the same signal. Therefore, the abnormality of the magnetic detection element can be detected, and the erroneous detection of the magnetic encoder abnormality due to the failure of the magnetic detection element can be prevented.

  In the abnormality detection device, it is preferable that the two magnetic detection elements are housed in a single package.

  In the abnormality detection apparatus, it is preferable that the two magnetic detection elements are stacked one above the other.

  In the abnormality detection device, the two magnetic detection elements are preferably magnetoresistive elements.

  According to this configuration, since each magnetic sensing element can be manufactured by the same process, it is possible to manufacture an element with less variation in sensitivity characteristics. In addition, since the two magnetoresistive elements can be arranged adjacent to each other, the sensor package can be reduced in size.

  In the abnormality detection device, the abnormality detection means is configured by a logic circuit that performs exclusive OR of output signals of the two magnetic detection elements.

  According to this configuration, it is possible to detect an abnormality of the magnetic detection element with a simple circuit configuration.

  In the abnormality detection apparatus, the abnormality detection means includes a first CMOS circuit in which an output signal of one magnetic detection element is a gate input, and a second CMOS circuit in which an output signal of the other magnetic detection element is a gate input. The gate outputs of the first and second CMOS circuits are connected in common.

  In this case, if the gate input of the first and second CMOS circuits becomes a signal whose phase is not aligned due to the failure of one of the magnetic sensing elements, the gate output is short-circuited and a large current flows, so that the magnetic sensing It can be determined that one of the elements is abnormal. On the other hand, when each gate input of the first and second CMOS circuits is a signal having the same phase, the gate output is not short-circuited (a large current does not flow), so that each magnetic sensing element is normal. It can be judged.

  According to the present invention, it is possible to suppress misalignment of each magnetic detection element and variation in sensitivity, detect abnormality of each magnetic detection element, and erroneously detect abnormality of a magnetic encoder caused by failure of each magnetic detection element. Can be prevented.

It is a figure which shows typically the abnormality detection apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the abnormality detection means of the abnormality detection apparatus which concerns on this Embodiment. It is a figure for demonstrating the effect | action of the abnormality detection apparatus which concerns on a comparative example and this invention. It is a figure which shows an example of the laminated structure of the magnetoresistive effect element which concerns on this Embodiment. It is a circuit diagram which shows the abnormality detection means of the abnormality detection apparatus which concerns on the 2nd Embodiment of this invention. It is a circuit diagram which shows the abnormality detection means of the abnormality detection apparatus which concerns on a modification.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. An abnormality detection device according to an embodiment of the present invention detects an abnormality of a magnetic detection element based on sensor outputs of a plurality of magnetic detection elements.

(First embodiment)
1A and 1B are diagrams schematically showing an abnormality detection device according to a first embodiment of the present invention. FIG. 1A shows the entire abnormality detection device, and FIG. A part of the apparatus is shown enlarged. As shown in FIG. 1A, the abnormality detection device 1 includes a magnetic encoder 2, a magnetic sensor 3 that senses the magnetic field of the magnetic encoder 2, and an abnormality detection means 4 that detects an abnormality of the magnetic sensor 3. ing.

  The magnetic encoder 2 includes a base 5 and a rotating body 6 provided on the base 5, and a rotating shaft 7 of the rotating body 6 is rotated by a bearing (not shown) fixed on the base 5. It is supported freely. The base 5, the bearing, and the rotary shaft 7 are made of a nonmagnetic material such as a synthetic resin material. The rotating body 6 is formed in a thin disc shape, and is composed of an inner peripheral portion 8 that is fixed to the rotating shaft 7 and formed of a nonmagnetic material, and a rotating magnet 9 provided on the outer periphery of the inner peripheral portion 8. Has been. The rotating magnet 9 is alternately magnetized with N and S poles in the rotational direction. That is, the rotating magnet 9 is magnetized with different polarities in adjacent magnetic poles in the circumferential direction.

  On the base 5, the magnetic sensor 3 is arranged close to the position facing the outer peripheral surface of the rotating magnet 9. As shown in FIG. 1B, the magnetic sensor 3 is mounted with a plurality of (for example, two) magnetic detection elements 10a and 10b in proximity to each other on the same substrate 12. It is accommodated in the sensor package 11. Each of the magnetic sensing elements 10 a and 10 b is composed of a magnetic sensing element having the same sensitivity characteristic, and the sensitivity axis is formed horizontally with the in-plane direction of the substrate 12. Here, as the magnetic sensing element 10, for example, a magnetoresistive effect element such as a GMR (Giant Magneto Resistive) element or a TMR (Tunnel Magneto Resistance) element can be used, and the GMR element is used in terms of high output and high sensitivity. It is preferable to use it. In this way, by configuring the magnetic sensing elements 10a and 10b with magnetoresistive elements having the same sensitivity characteristics, the magnetic sensing elements 10a and 10b can be manufactured under the same conditions (in the same process), and the sensitivity Magnetic sensing elements having no variation in characteristics can be produced.

  Each of the magnetic sensing elements 10a and 10b can be mounted on the substrate 12 with the distance L between the elements as short as possible (for example, 1 mm). Therefore, since the two-system sensor in which the two magnetic detection elements 10a and 10b are arranged adjacent to each other can be accommodated in the small sensor package 11, the entire magnetic sensor 3 can be reduced in size. In the following, a case where a GMR element is used as the magnetic sensing element 10 will be described as an example, and an output signal from the GMR element 10a will be described as sensor output 1 and an output signal from the GMR element 10b will be described as sensor output 2.

  Here, the GMR element will be briefly described. The GMR element is a magnetoresistive effect element utilizing a giant magnetoresistive effect (GMR effect), and is formed on the substrate from the bottom in an insulating layer, an underlayer, an antiferromagnetic layer, a fixed magnetic layer, a nonmagnetic intermediate layer, a free magnetic layer And a protective layer in this order using a thin film process. Since the antiferromagnetic layer and the pinned magnetic layer are formed in contact with each other, an exchange coupling magnetic field is generated at the interface between the two magnetic layers by heat treatment in a magnetic field, and the magnetization direction of the pinned magnetic layer is fixed in one direction. . On the other hand, unlike the pinned magnetic layer, the magnetization direction of the free magnetic layer is not fixed, and is configured to change in magnetization due to a change in the penetration direction of the external magnetic field. Therefore, when each GMR element 10a, 10b is affected by the magnetic field flowing from the north pole to the south pole of the rotating rotating magnet 9, the angle (magnetic field angle) of the magnetization direction of the free magnetic layer with respect to the magnetization direction of the fixed magnetic layer is changed. The electric resistance value changes based on the change in the magnetic field angle. The output signal based on the electric resistance value corresponding to the change in the magnetic field angle is used for detecting rotation of the rotating magnet 9 and for detecting abnormality of the GMR elements 10a and 10b in the abnormality detecting means 4. Note that the magnetization directions of the pinned magnetic layers of the GMR elements 10a and 10b are preferably aligned in the same direction.

  As shown in FIG. 2, the abnormality detection unit 4 includes an EXOR (Exclusive-OR) circuit 4. The EXOR circuit 4 detects an abnormality (failure) of the GMR elements 10a and 10b by taking an exclusive OR of the output signals output from the two GMR elements 10a and 10b. That is, the EXOR circuit 4 outputs an “L” level signal when the output signal of the GMR element 10a and the output signal of the GMR element 10b match, and each of the GMR elements 10a and 10b is normal. Judge. On the other hand, the EXOR circuit 4 outputs an “H” level signal when the output signal of the GMR element 10a and the output signal of the GMR element 10b do not match, and one of the GMR elements 10a and 10b is abnormal (failure). Judge that there is. Thereby, the failure of the GMR elements 10a and 10b can be detected with a simple circuit configuration.

  Next, the operation of the abnormality detection device 1 according to the present embodiment will be described using FIG. 3 while comparing with a comparative example. 3A and 3B are schematic diagrams for explaining the operation of the comparative example and the abnormality detection device according to the present embodiment. FIG. 3A shows the abnormality detection device according to the comparative example, and FIG. The abnormality detection apparatus 1 which concerns on the form of is shown. As a comparative example, a description will be given by taking as an example an abnormality detection device in which two magnetic sensors X and Y each having one Hall element as a magnetic detection element are arranged close to each other at a position facing the outer peripheral portion of the rotating body 6.

  In the abnormality detection apparatus according to the comparative example, the magnetic sensors X and Y packaged with a single Hall element are manufactured by separate processes, and the magnetic sensors X and Y manufactured by these separate processes are arranged close to each other. The positional deviation between the Hall elements of the magnetic sensors X and Y and the sensitivity characteristics tend to vary. When the positional deviation or sensitivity characteristic varies between the Hall elements, deviation occurs in the output signals (sensor outputs X, Y) from the Hall elements (dotted line portion shown in FIG. 3A). Therefore, when abnormality detection is performed based on this output signal, even if the magnetic encoder itself is normal, the output signal from each Hall element is not the same, so an abnormality detection signal indicating abnormality is output, and the magnetic An encoder error is erroneously detected. Therefore, in order to detect whether the cause of the abnormality detection signal is due to the abnormality of the magnetic encoder or the failure of the Hall element, it is necessary to further determine with a CPU or the like.

  On the other hand, in the abnormality detection device 1 according to the present embodiment, since two GMR elements 10a and 10b having the same sensitivity characteristic are manufactured on the same substrate 12 by the same process, the sensitivity characteristic does not vary and the position shift does not occur. Output signals from the GMR elements 10a and 10b are substantially the same signal (dotted line portion shown in FIG. 3B). Accordingly, since the sensitivity characteristics of the magnetic sensor 3 are not varied and the positional deviation is not generated, it is possible to detect the positional deviations of the GMR elements 10a and 10b and the variation of the sensitivity characteristics with a simple circuit configuration.

  Note that the GMR elements 10a and 10b may be formed side by side on the same substrate 12, or may be stacked on the same substrate 12 as shown in FIG. FIG. 4 is a diagram showing a laminated structure of the GMR elements 10a and 10b, and shows a case where the GMR element 10b is laminated on the GMR element 10a. 4, at least a pinned magnetic layer (Pin layer) 41, a nonmagnetic layer 42 provided on the pinned magnetic layer 41, and a free magnetic layer 43 provided on the nonmagnetic layer 42 are stacked. Then, the GMR element 10a is formed, and the same layer (the fixed magnetic layer 41, the nonmagnetic layer 42, and the free magnetic layer 43) as the GMR element 10a is laminated via the interlayer insulating layer 44 to form the GMR element 10b. The fixed magnetic layer 41 and the free magnetic layer 43 are formed of a magnetic material such as a CoFe alloy, a NiFe alloy, or a CoFeNi alloy. The nonmagnetic layer 42 is formed of Cu or the like.

  As described above, according to the present embodiment, the plurality of magnetic sensing elements 10a and 10b constituting the magnetic sensor 3 are configured by elements having the same sensitivity characteristic and are close to each other in the single sensor package 11. Since they are arranged, the sensitivity characteristics of the magnetic detection elements 10a and 10b do not vary or shift, and the same signals are output from the magnetic detection elements 10a and 10b. The EXOR circuit 4 detects an abnormality of the magnetic detection elements 10a and 10b by obtaining an exclusive OR of the output signals output from the magnetic detection elements 10a and 10b. That is, the abnormality detection device 1 according to the present embodiment detects the rotation of the rotating body 6 from the sensor outputs of the magnetic detection elements 10a and 10b, and matches or does not match the sensor outputs of the two magnetic detection elements 10a and 10b. Abnormality of the magnetic sensor 3 (magnetic detection elements 10a and 10b) is detected. Thereby, it is possible to prevent erroneous detection of abnormality of the magnetic encoder due to abnormality (failure) of each of the magnetic detection elements 10a and 10b.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. The abnormality detection device 20 according to the second embodiment of the present invention differs from the abnormality detection device 1 according to the first embodiment described above only in the configuration of the abnormality detection means. Therefore, only differences will be described in particular, and the same reference numerals are used for the same components, and repeated description is omitted.

  FIG. 5 is a circuit diagram showing the abnormality detection means 21 of the abnormality detection device 20 according to the second embodiment of the present invention. The abnormality detection means 21 shown in FIG. 5 includes a first CMOS circuit (transistor) 22 and a second CMOS circuit (transistor) 23. The gate input (terminal) T1 of the first CMOS circuit 22 is connected to the output (terminal) of the GMR element 10a, and the gate input (terminal) T2 of the second CMOS circuit 23 is the output (terminal) of the GMR element 10b. It is connected to the. The gate outputs (each totem pole output) T3 and T4 of the first CMOS circuit 22 and the second CMOS circuit 23 are commonly connected at a connection point P1. An ammeter 24 is provided on the output lines of the gate outputs T3 and T4 (abnormality detection line L2) connected in common at the connection point P1. Further, the PMOS source sides of the first and second CMOS circuits 22 and 23 are connected to the power supply Vdd via the detection resistor R, and the NMOS source side is connected to the ground GND. An abnormality detection line L1 is connected to a connection point between the source side of the PMOS and the detection resistor R. The abnormality detection line L1 is connected to the ground GND via a bypass capacitor C at high frequency.

  In this abnormality detection means 21, when the same “L” level signal is input from the GMR elements 10a, 10b to the gate inputs T1, T2 of the first and second CMOS circuits 22, 23, the PMOS side Conducted to Vdd, an “H” level signal having the same phase is output from the gate outputs T3 and T4, and the output signals from the gate outputs T3 and T4 are combined at the connection point P1. In this case, since a large current does not flow on the abnormality detection lines L1 and L2, it is determined that the GMR elements 10a and 10b are normal. Further, when the same “H” level signal is input from the GMR elements 10a and 10b to the gate inputs T1 and T2 of the first and second CMOS circuits 22 and 23, the NMOS side is made conductive to the ground GND, An “H” level signal having the same phase falls from the gate outputs T3 and T4 to the ground GND. Also in this case, since a large current does not flow on the abnormality detection line L2, it is determined that the GMR elements 10a and 10b are normal.

  On the other hand, an “L” level signal from the GMR element 10 a is input to the gate input T 1 of the first CMOS circuit 22, and an “H” level signal from the GMR element 10 b is input to the gate input T 2 of the second CMOS circuit 23. Is input, the PMOS side of the first CMOS circuit 22 is conducted to the power supply Vdd, and the NMOS side of the second CMOS circuit 23 is conducted to the ground GND. At this time, the gate outputs of the first and second CMOS circuits 22 and 23 are short-circuited and travel from the PMOS side of the first CMOS circuit 22 to the NMOS side of the second CMOS circuit 23 via the connection point P1. Since a large current flows through the path, by monitoring this large current with the ammeter 24 on the abnormality detection line L2, it can be determined that there is an abnormality in one of the GMR elements 10a and 10b.

  Further, the “H” level signal from the GMR element 10 a is input to the gate input T 1 of the first CMOS circuit 22, and the “L” level signal from the GMR element 10 b is input to the gate input T 2 of the second CMOS circuit 23. Is input, the NMOS side of the first CMOS circuit 22 is conducted to the ground GND, and the PMOS side of the second CMOS circuit 23 is conducted to the power source Vdd. At this time, the gate outputs of the first and second CMOS circuits 22 and 23 are short-circuited and travel from the PMOS side of the second CMOS circuit 23 to the NMOS side of the first CMOS circuit 22 via the connection point P1. Since a large current flows through the path, by monitoring this large current with the ammeter 24 on the abnormality detection line L2, it can be determined that there is an abnormality in one of the GMR elements 10a and 10b.

  As described above, when the gate inputs T1 and T2 of the first and second CMOS circuits 22 and 23 become signals whose phases are not aligned due to the failure of one of the magnetic sensing elements 10a and 10b, the gate outputs are short-circuited. Therefore, it can be determined that either one of the magnetic detection elements 10a and 10b is abnormal. On the other hand, when the gate inputs T1 and T2 of the first and second CMOS circuits 22 and 23 are signals having the same phase, the gate outputs are not short-circuited (no large current flows at the same potential). It can be determined that the detection elements 10a and 10b are both normal. Thereby, the abnormality of the magnetic detection elements 10a and 10b can be detected, and the erroneous detection of the magnetic encoder abnormality caused by the abnormality (failure) of the magnetic detection elements 10a and 10b can be prevented.

  Next, an abnormality detection apparatus according to a modification will be described. FIG. 6 is a circuit diagram showing the abnormality detection means 31 of the abnormality detection device 30 according to the modification. In the abnormality detection unit 31 of the abnormality detection apparatus 30 shown in FIG. 6, the detection resistor R, the abnormality detection line L1, and the bypass capacitor C are deleted from the abnormality detection unit 21 according to the second embodiment.

  In this abnormality detection means 31, an “L” level signal from the GMR element 10 a is input to the gate input T 1 of the first CMOS circuit 22, and the “input” from the GMR element 10 b to the gate input T 2 of the second CMOS circuit 23. When the “H” level signal is input, the PMOS side of the first CMOS circuit 22 is conducted to the power supply Vdd, and the NMOS side of the second CMOS circuit 23 is conducted to the ground GND. At this time, the gate outputs of the first and second CMOS circuits 22 and 23 are short-circuited and travel from the PMOS side of the first CMOS circuit 22 to the NMOS side of the second CMOS circuit 23 via the connection point P1. Since a large current flows through the path, it is possible to determine that there is an abnormality in one of the GMR elements 10a and 10b by monitoring the large current with the ammeter 24 on the abnormality detection line L2.

  On the other hand, an “H” level signal from the GMR element 10 a is input to the gate input T 1 of the first CMOS circuit 22, and an “L” level signal from the GMR element 10 b is input to the gate input T 2 of the second CMOS circuit 23. Is input, the NMOS side of the first CMOS circuit 22 is conducted to the ground GND, and the PMOS side of the second CMOS circuit 23 is conducted to the power source Vdd. At this time, the gate outputs of the first and second CMOS circuits 22 and 23 are short-circuited and travel from the PMOS side of the second CMOS circuit 23 to the NMOS side of the first CMOS circuit 22 via the connection point P1. Since a large current flows through the path, it is possible to determine that there is an abnormality in one of the GMR elements 10a and 10b by monitoring the large current with the ammeter 24 on the abnormality detection line L2.

  As described above, in the abnormality detection device 30 according to the modification, the gate inputs T1 and T2 of the first and second CMOS circuits 22 and 23 have the same phase due to the failure of one of the magnetic detection elements 10a and 10b. If there is no signal, the gate output is short-circuited and a large current flows to the abnormality detection line L2. Therefore, by detecting this large current with the ammeter 24, either one of the magnetic detection elements 10a and 10b has an abnormality. It can be judged. Thereby, the abnormality of the magnetic detection elements 10a and 10b can be detected, and the erroneous detection of the magnetic encoder abnormality caused by the abnormality (failure) of the magnetic detection elements 10a and 10b can be prevented.

  The embodiment disclosed this time is illustrative in all respects and is not limited to this embodiment. The scope of the present invention is shown not by the above description of the embodiments but by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

  The present invention is useful as an abnormality detection device that detects an abnormality of a magnetic sensor for a magnetic encoder.

DESCRIPTION OF SYMBOLS 1, 20, 30 Abnormality detection apparatus 2 Magnetic encoder 3 Magnetic sensor 4, 21, 31 Abnormality detection means 5 Base 6 Rotating body 7 Rotating shaft 8 Inner periphery 9 Rotating magnet (outer periphery)
10 (10a, 10b) Magnetic sensing element 11 Sensor package (package)
12 Substrate 22 First CMOS circuit 23 Second CMOS circuit 24 Ammeter T1, T2 Gate input (terminal)
T3, T4 Gate output (terminal)
P1 connection point

Claims (6)

A rotating magnet in which N and S poles are alternately magnetized along the direction of rotation;
Two magnetic sensing elements provided facing the outer periphery of the rotating magnet;
An abnormality detection means for detecting an abnormality of the detection element based on output signals of the two magnetic detection elements,
The abnormality detection apparatus, wherein the two magnetic detection elements have the same sensitivity characteristic and are arranged close to each other on the same substrate.   The abnormality detection apparatus according to claim 1, wherein the two magnetic detection elements are accommodated in a single package.   The abnormality detection device according to claim 1, wherein the two magnetic detection elements are formed to be stacked one above the other.   The abnormality detection device according to claim 1, wherein the two magnetic detection elements are magnetoresistance effect elements.   5. The abnormality detection device according to claim 1, wherein the abnormality detection unit is configured by a logic circuit that performs an exclusive OR of output signals of the two magnetic detection elements. The abnormality detection means includes a first CMOS circuit in which an output signal of one magnetic detection element is a gate input, and a second CMOS circuit in which an output signal of the other magnetic detection element is a gate input, 5. The abnormality detection device according to claim 1, wherein the gate outputs of the first and second CMOS circuits are connected in common.

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