JP2010249719A - Minute angle detection sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple and inexpensive minute angle detection sensor detecting a minute displacement angle of a detection object with high accuracy. <P>SOLUTION: The minute angle detection sensor is provided with: a multipolar magnet 5 rotating in line with a displacement in a circumferential direction of a steering shaft 2, and having N- and S-pole alternately magnetized at equal pitches in the circumferential direction; a magnetic sensor 6 outputting an output signal according to a direction of a magnetic field to be generated from the multipolar magnet 5; an angle calculating section 13 calculating the displacement angle of the detection object based on the output signal; and a correcting section 14 correcting the displacement angle to be calculated by the angle calculating section 13 so that an ideal straight line conforms to an angle error to be expressed as a two-cycle sine wave with respect to the ideal straight line, within an angle corresponding to pitch intervals of the same pole of the multipolar magnet 5, the ideal straight line indicating ideal relations between the direction of the magnetic field and an actual displacement angle of the steering shaft 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a minute angle detection sensor, and more particularly to a minute angle detection sensor that magnetically detects a minute displacement angle of a detection target.

  2. Description of the Related Art Conventionally, as a minute angle detection sensor that detects a minute displacement angle of a detection target, a sensor that corrects an angle error of a rotation shaft that is a detection target is known (for example, see Patent Document 1). This minute angle detection sensor detects the direction of a magnetic field between one magnetic pole of a multipolar ring magnet fixed to a rotation axis by a magnetic sensor element, and calculates a minute rotation angle based on the detected direction of the magnetic field. . The minute angle detection sensor detects an actual rotation angle of the rotation shaft from an encoder fixed to the rotation shaft, and calculates an angle error from a difference between the detected actual rotation angle and the calculated rotation angle. Store in the storage unit. Then, the detection accuracy is improved by correcting the calculated rotation angle based on the direction of the magnetic field using the angle error stored in the storage unit.

JP 2006-234723 A

  However, in the conventional minute angle detection sensor as described above, an encoder is provided on the rotation shaft to detect an actual rotation angle, and an angle error must be calculated from the actual rotation angle and the calculated rotation angle. There is a problem that the calculation processing becomes complicated as the number increases.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a minute angle detection sensor capable of detecting a minute displacement angle of a detection target with high accuracy with a simple and inexpensive configuration. .

  The micro-angle detection sensor of the present invention rotates with the circumferential displacement of the detection target, and a multipolar magnet in which N poles and S poles are alternately magnetized at equal pitches in the circumferential direction or the axial direction, A magnetic sensor element that outputs an output signal corresponding to the direction of the magnetic field generated from the multipolar magnet; an angle calculating means that calculates a displacement angle of the detection target based on the output signal; and the same polarity of the multipolar magnet Within an angle corresponding to the pitch interval, an angle error that appears as a two-cycle sine wave with respect to an ideal straight line indicating an ideal relationship between the direction of the magnetic field and the actual actual displacement angle of the detection target is defined as the ideal straight line. The angle calculating means includes a correcting means for correcting the displacement angle so as to match.

  According to this configuration, when detecting a minute displacement angle within an angle corresponding to the pitch interval of the same poles of the multipolar magnet, the angle error appears as a sine wave having two cycles with respect to the ideal straight line. The correction process by can be made a simple configuration. Further, unlike the conventional case, it is not necessary to provide an encoder to detect the actual displacement angle to be detected, and it is not necessary to calculate an angle error from the difference between the actual displacement angle and the calculated displacement angle and store it for correction. Therefore, it is possible to detect a minute displacement angle of a detection target with high accuracy with a simple and inexpensive configuration.

  According to the present invention, in the minute angle detection sensor, the correction unit corrects the displacement angle with a correction signal having an opposite phase to the angle error.

  According to this configuration, the angle error can be removed by a simpler correction process.

  Further, the present invention provides, as an example of the minute angle detection sensor, the magnetic sensor element, a first element that outputs an output signal corresponding to the magnetic field component in the circumferential direction, and a magnetic field component in a direction orthogonal to the circumferential direction. And a second element that outputs an output signal according to the above.

  According to the present invention, in the minute angle detection sensor, the detection target is a steering shaft, and the displacement angle is a twist angle of the steering shaft.

  According to this configuration, a small torsion angle of the steering shaft can be detected with high accuracy with a simple and inexpensive configuration.

  According to the present invention, a minute displacement angle of a detection target can be detected with high accuracy with a simple and inexpensive configuration.

It is a figure which shows embodiment of the micro angle detection sensor which concerns on this invention, and is a whole block diagram of a micro angle detection sensor. It is a figure which shows embodiment of the micro angle detection sensor which concerns on this invention, and is explanatory drawing of the magnetic field which a multipolar magnet generate | occur | produces. It is a figure which shows embodiment of the micro angle detection sensor which concerns on this invention, and is a figure which shows the relationship between the actual rotation angle of a multipolar magnet, and the output voltage signal of a magnetic sensor. It is a figure which shows embodiment of the micro angle detection sensor which concerns on this invention, and is a figure which shows the relationship between the magnetic field angle before a correction process, and the actual rotation angle of a multipolar magnet. It is a figure which shows embodiment of the micro angle detection sensor which concerns on this invention, and is a figure which shows the relationship between an angle error and the actual rotation angle of a multipolar magnet. It is a figure which shows embodiment of the micro angle detection sensor which concerns on this invention, and is a figure which shows the relationship between the magnetic field angle after a correction process, and the actual rotation angle of a multipolar magnet.

  In a torque sensor or the like to which the present invention is applied, it is desired to magnetically detect a minute displacement angle to be detected, for example, about ± 5 degrees. In this case, in the method of detecting the displacement angle with the dipole magnet, the magnetic field direction (hereinafter referred to as the magnetic field angle) is rotated once by rotating the magnet once, so that detection is performed using only a part of the rotation of the magnet. In some cases, the resolution was low and sufficient detection accuracy could not be obtained. For this reason, a method has been devised in which a multipolar magnet is attached to a detection target instead of a dipole magnet so that the magnetic field angle rotates once by 1 / n rotation of the magnet.

  However, when the magnetic field angle when the multipolar magnet is rotated by a minute angle is calculated, linearity cannot be obtained between the magnetic field angle and the rotation angle of the multipolar magnet, and the displacement angle of the detection target can be detected with high accuracy. There wasn't. Therefore, as a result of investigating the relationship between the magnetic field angle and the rotation angle of the multipolar magnet, the present inventors have found that an angle error appears as a two-cycle sine wave with respect to the ideal linear characteristic. In other words, the gist of the present invention corrects a minute displacement angle of a detection target with high accuracy with a simple and inexpensive configuration by correcting by utilizing an angular error characteristic that regularly changes with respect to an ideal linear characteristic. Is to detect.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the case where the present invention is applied to a torque sensor used in a power steering system or the like will be described. However, the application target of the minute angle detection sensor according to the present embodiment is not limited to this and can be appropriately changed.

  With reference to FIG. 1, the overall configuration of the minute angle detection sensor will be described. FIG. 1 is an overall configuration diagram of a minute angle detection sensor according to an embodiment of the present invention.

  As shown in FIG. 1, a minute angle detection sensor 1 according to the present embodiment detects a twist angle of a steering shaft 2, a multipolar magnet 5 attached to the steering shaft 2, and a steering shaft 2. And a magnetic sensor 6 attached to a pinion gear (not shown) at the tip. Further, the minute angle detection sensor 1 has a calculation unit 7 connected to the magnetic sensor 6, and the calculation unit 7 calculates the twist angle of the steering shaft 2.

  The multipolar magnet 5 is formed in an annular shape and is fixed to the outer peripheral surface of the steering shaft 2 so as not to be relatively rotatable. The multipolar magnet 5 is a 12-pole axially magnetized magnet and is configured by alternately magnetizing N poles and S poles at equal pitches in the circumferential direction. An arc-shaped magnetic field from the N pole to the S pole is generated between adjacent different poles of the multipolar magnet 5, and the twist angle of the steering shaft 2 is obtained according to the magnetic field angle of the arc-shaped magnetic field. It is done.

  The magnetic sensor 6 is disposed on the pinion gear so as to face the multipolar magnet 5, and in the direction of the magnetic field generated from the multipolar magnet 5 by the two magnetoresistive elements (GMR elements) provided therein. A corresponding signal is output. Each magnetoresistive element is basically formed by laminating an antiferromagnetic layer, a pinned layer, an intermediate layer, and a free layer on a wafer (not shown). In the pinned layer, the magnetization direction is fixed in one direction by an antiferromagnetic layer, and in the free layer, the magnetization direction is changed in response to an external magnetic field. Then, the magnetization direction of the free layer is changed by the magnetic field formed by the multipolar magnet 5, and the resistance change rate is varied according to the angle formed with the magnetization direction of the pinned layer, so that an output signal reflecting this is output. .

  The pinned layers of the two magnetoresistive elements are magnetized so as to be orthogonal to each other. One magnetoresistive element is in the axial direction of the multipolar magnet 5, and the other magnetoresistive element is the multipolar magnet 5. The pinned layers are magnetized in accordance with the circumferential direction. One magnetoresistive element outputs a sine wave signal corresponding to the axial magnetic field component, and the other magnetoresistive element outputs a cosine wave signal corresponding to the circumferential magnetic field component.

  The calculation unit 7 calculates the rotation angle of the multipolar magnet 5 based on the amplifiers 11 and 12 that amplify the sine wave signal and the cosine wave signal output from the magnetic sensor 6 and the output signals amplified by the amplifiers 11 and 12. The angle calculation unit 13 and the correction unit 14 that corrects the calculated rotation angle calculated by the angle calculation unit 13 are configured. The angle calculation unit 13 calculates an arc tangent of the sine wave signal and the cosine wave signal input via the amplifiers 11 and 12 and calculates a magnetic field angle. From the calculated magnetic field angle, the rotation angle of the multipolar magnet 5, that is, The twist angle of the steering shaft 2 is calculated. At this time, the calculated rotation angle calculated by the angle calculation unit 13 includes an angle error due to the amplitude ratio between the magnetic field component in the axial direction and the magnetic field component in the circumferential direction.

  The correction unit 14 corrects the calculated rotation angle calculated by the angle calculation unit 13 so as to remove the angle error, and increases the detection accuracy of the twist angle of the steering shaft 2. In the calculation unit 7, a CPU (Central Processing Unit) incorporated therein performs calculations according to various programs such as a control program in a ROM (Read Only Memory), and executes calculation processing and correction processing.

  Before describing the correction process by the correction unit 14, the angle error included in the calculated rotation angle will be described. FIG. 2 is an explanatory diagram of a magnetic field generated by the multipolar magnet according to the embodiment of the present invention. FIG. 3 is a diagram showing the relationship between the rotation angle of the multipolar magnet according to the embodiment of the present invention and the output voltage signal of the magnetic sensor. 2 is a view of the multipolar magnet of FIG. 1 as viewed from the side, with the axial direction of the multipolar magnet being the Y-axis direction and the circumferential direction being the X-axis direction. In FIG. 3, the vertical axis is the output voltage, the horizontal axis is the rotation angle of the multipolar magnet, the solid line W1 is the output voltage signal of the magnetic field component in the Y-axis direction, and the broken line W2 is the output voltage signal of the magnetic field component in the X-axis direction. Respectively.

  As shown in FIG. 2, in the multipolar magnet 5, a magnetic field is generated from the N pole toward the S pole located on both sides, and the magnetic field rotates 180 degrees while moving from the N pole to the S pole. . Therefore, the magnetic field is rotated 360 degrees by NS2 corresponding to the pitch of the same polarity. In the present embodiment, since it is a 12-pole magnetized multipolar magnet, the magnetic field rotates 360 degrees when the multipolar magnet 5 rotates 60 degrees. The intensity of the magnetic field is maximum at the N-pole center and S-pole center, and is minimum at an intermediate position between the two magnetic poles.

  As shown in FIG. 3, the magnetic field angle at this time is such that the magnetic field component in the Y-axis direction and the magnetic field component in the X-axis direction are output as output voltage signals by the two magnetoresistive effect elements of the magnetic sensor 6. The magnetic field component in the Y-axis direction is output as a sine wave output voltage signal, and the magnetic field component in the X-axis direction is output as a cosine wave output voltage signal. In this case, the amplitude of the output voltage signal of the magnetic field component in the X axis direction is smaller than the output voltage signal of the magnetic field component in the Y axis direction, and the amplitude ratio is not 1. This is because, as described above, the strength of the magnetic field changes according to the rotation of the magnetic field.

  Here, the arc tangent is obtained from the output voltage signal corresponding to each magnetic field component shown in FIG. 3, the magnetic field angle is calculated, and the relationship between the magnetic field angle and the actual rotation angle of the multipolar magnet 5 is examined. As shown. FIG. 4 is a diagram showing the relationship between the magnetic field angle before the correction processing according to the present embodiment and the actual rotation angle of the multipolar magnet. In FIG. 4, the vertical axis represents the magnetic field angle, the horizontal axis represents the actual rotation angle of the multipolar magnet, the solid line W3 represents the actual actual linear characteristic, and the broken line W4 represents the ideal ideal linear characteristic (ideal straight line). Yes.

  As shown in FIG. 4, the actual linear characteristic matches the ideal linear characteristic only when the rotation angle of the multipolar magnet 5 is 0 degrees, 15 degrees, 30 degrees, 45 degrees, and 60 degrees, and particularly 7.5 degrees, 22 degrees. .5 degrees, 37.5 degrees, and 52.5 degrees greatly deviate from the ideal linear characteristics. That is, the calculated magnetic field angle includes an angular error deviating from the ideal value when the rotation angle of the multipolar magnet 5 is an angle other than 0 degrees, 15 degrees, 30 degrees, 45 degrees, and 60 degrees. Therefore, at angles other than 0 degrees, 15 degrees, 30 degrees, 45 degrees, and 60 degrees, the rotation angle of the multipolar magnet 5 cannot be accurately calculated based on the magnetic field angle.

  Examination of the angle error of the magnetic field angle at this time revealed that the angle error indicated by the solid line W5 regularly changes with respect to the ideal linear characteristic indicated by the broken line W6 as shown in FIG. That is, the angle error changes to a two-cycle sine wave with an amplitude of about 8 [degree] with respect to the ideal linear characteristic. Note that this angular error also changes to a two-cycle sine wave shape even if the number of magnetic poles of the multipolar magnet 5 is changed. However, the angle error increases as the number of magnetic poles decreases, and decreases as the number of magnetic poles increases.

  With reference to FIG. 6, the correction process by the correction unit will be described. FIG. 6 is a diagram showing the relationship between the magnetic field angle after the correction processing according to the present embodiment and the actual rotation angle of the multipolar magnet. In FIG. 6, the vertical axis represents the magnetic field angle, the horizontal axis represents the actual rotation angle of the multipolar magnet, the solid line W7 represents the actual actual linear characteristic, and the broken line W8 represents the ideal ideal linear characteristic (ideal straight line). Yes.

  When the regularity of the angle error is found, the correction unit 14 performs a correction process that cancels the angle error. In this case, the correction process by the correction unit 14 may be any process as long as it cancels the angular error that appears as a two-cycle sine wave. For example, two cycles with an amplitude of 8 [degrees] You may correct | amend by adding the sine wave of antiphase. By the correction process by the correction unit 14, the angle error included in the calculated rotation angle calculated by the angle calculation unit 13 is corrected to 0 degree.

  With this configuration, since the magnetic field angle is corrected to an ideal value so that the actual linear characteristic matches the ideal linear characteristic, the linearity between the magnetic field angle and the rotation angle of the multipolar magnet 5 is enhanced. Therefore, based on the magnetic field angle, the rotation angle of the multipolar magnet 5, that is, the twist angle of the steering shaft 2 can be detected easily and with high accuracy. Further, since the angle error of the magnetic field angle can be estimated according to the number of magnetic poles of the multipolar magnet, it is not necessary to calculate the angle error, and the correction process of the correction unit 14 can be set to a simple process setting. It becomes.

  As described above, according to the minute angle detection sensor 1 according to the present embodiment, when detecting the twist angle of the steering shaft 2 within an angle corresponding to the pitch interval of the same polarity of the multipolar magnet 5, the angle error is detected. Can be estimated to appear as a two-cycle sine wave with respect to the ideal linear characteristic, it is not necessary to calculate an angle error, and the correction process by the correction unit 14 can be simplified. Further, unlike the prior art, there is no need to provide an encoder to detect the twist angle of the steering shaft 2, and it is not necessary to calculate an angle error from the difference between the twist angle and the calculated angle and store it for correction. The twist angle of the steering shaft 2 can be detected with high accuracy with a simple and inexpensive configuration.

  In the above-described embodiment, after the magnetic field angle is obtained by the angle calculation unit, the magnetic field angle is corrected by the correction unit, and the rotation angle of the multipolar magnet is determined by the angle calculation unit from the corrected magnetic field angle. Although the calculation is performed to detect the twist angle of the steering shaft, the present invention is not limited to this configuration. Any configuration is possible as long as the angle error is excluded from the rotation angle of the multipolar magnet calculated by the angle calculation unit. For example, after calculating the rotation angle of the multipolar magnet by the angle calculation unit, the calculated rotation angle is corrected by the correction unit. And it is good also as a structure which detects the twist angle of a steering shaft.

  In the above-described embodiment, the angle calculation unit and the correction unit are configured. However, the correction process may be incorporated in the calculation process of the angle calculation unit without the correction unit.

  In the above-described embodiment, the configuration is such that the twist angle of the steering shaft is detected by the minute angle detection sensor, but the present invention is not limited to this configuration. The detection target may be anything that can be displaced at a minute angle. For example, the detection target may be configured to detect a minute rotation angle of a rotating body as a detection target.

  In the above embodiment, the magnetic sensor element is a magnetoresistive effect element such as a GMR element. However, the present invention is not limited to this structure. Any device may be used as long as it can output an output signal corresponding to the magnetic field angle by the magnetic field generated by the multipolar magnet.

  In the above-described embodiment, the configuration is such that the displacement angle of the detection target is detected using a 12-pole magnetized multipolar magnet. However, the present invention is not limited to this configuration. An arbitrary minute displacement angle can be detected by changing the number of magnetic poles, and a minute displacement angle can be detected with high accuracy by increasing the number of magnetic poles.

  In the above-described embodiment, the multipolar magnet is magnetized in the circumferential direction. However, the present invention is not limited to this configuration. It is sufficient that the displacement of the detection target can be detected. For example, a configuration in which the displacement is magnetized in the axial direction may be employed.

  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 claims for patent, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims for patent.

  As described above, the present invention has an effect that it is possible to detect a minute displacement angle of a detection target with high accuracy with a simple and inexpensive configuration. In particular, the minute displacement angle of the detection target is magnetically detected. This is useful for a minute angle detection sensor that detects the angle.

1 Minute angle detection sensor 2 Steering shaft (detection target)
5 Multi-Pole Magnet 6 Magnetic Sensor 7 Calculation Unit 11, 12 Amplifier 13 Angle Calculation Unit (Angle Calculation Unit)
14 Correction part (correction means)

Claims (4)

A multi-pole magnet that rotates in accordance with the circumferential displacement of the detection target, and whose N poles and S poles are alternately magnetized at equal pitches in the circumferential direction or the axial direction;
A magnetic sensor element that outputs an output signal according to the direction of the magnetic field generated from the multipolar magnet;
An angle calculating means for calculating a displacement angle of the detection target based on the output signal;
A sinusoidal wave having two cycles with respect to an ideal straight line indicating an ideal relationship between the direction of the magnetic field and the actual actual displacement angle of the detection target within an angle corresponding to the pitch interval of the same polarity of the multipolar magnet. A minute angle detection sensor comprising: a correction unit that corrects a displacement angle calculated by the angle calculation unit so that an angle error that appears may coincide with the ideal straight line.   The minute angle detection sensor according to claim 1, wherein the correction unit corrects the displacement angle by a correction signal having an opposite phase to the angle error.   The magnetic sensor element includes a first element that outputs an output signal corresponding to the magnetic field component in the circumferential direction, and a second element that outputs an output signal corresponding to the magnetic field component in a direction orthogonal to the circumferential direction. The minute angle detection sensor according to claim 1 or 2, characterized by comprising: The detection target is a steering shaft,
The minute angle detection sensor according to any one of claims 1 to 3, wherein the displacement angle is a twist angle of the steering shaft.

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