JP5007922B2 - Magnetic encoder device - Google Patents

Description

  The present invention relates to a magnetic encoder device that detects a rotational position of a rotating body, and more particularly to a magnetic encoder device that can obtain a stable detection signal with respect to fluctuations in the axial direction of the rotating body.

  Conventionally, in order to detect the rotation angle of a rotating body such as a motor shaft, a disk-shaped permanent magnet magnetized with two poles is fixed to the rotating body, and the magnetic field from the disk-shaped permanent magnet is fixed to the fixed body. A magnetic encoder device that is detected by a magnetic field detection element and detects the absolute position of a rotating body is disclosed (for example, see Patent Document 1).

FIG. 7 is a perspective view showing a configuration of a conventional magnetic encoder. FIG. 8 is a side sectional view of the detection unit.
In FIG. 7, 11 is a rotating body (shaft), 12 is a disk-shaped permanent magnet fixed to the rotating body 11 so that the rotation axis is the same, and is in one direction parallel to the axis of the rotating body 11 in a direction perpendicular to the axis. Is magnetized. Reference numeral 13 denotes a ring-shaped fixed body provided on the outer peripheral side of the permanent magnet 12 and is made of a magnetic block material. Four magnetic field detecting elements 14 are attached to the fixed body 13 at intervals of 90 degrees in the circumferential direction, and are arranged to face the outer peripheral surface of the permanent magnet 12 with a gap. Further, as shown in FIG. 8, in the detection unit including the permanent magnet 12, the fixed body 13, and the magnetic field detection element 14, the cross section of the fixed body 13 is rectangular, and the surfaces of the permanent magnet 12 and the fixed body 13 that face each other. Are configured to be parallel.

Next, an angle signal detection operation will be described.
In FIG. 7, when the rotating body 11 rotates, the permanent magnet 12 also rotates. Due to the change in the magnetic field of the permanent magnet 12, a sinusoidal signal of one cycle is output from the magnetic field detection element 14 for one rotation of the rotating body 11. .
FIG. 9 is a block diagram of a signal processing circuit, which processes a signal from the magnetic field detection element 14 and converts it into an angle signal θ.
In FIG. 9, 51 and 52 are differential amplifiers, and 53 is an angle calculation circuit. The detection signals Va1 and Va2 from the A1 phase magnetic field detection element 141 and the A2 phase magnetic field detection element 143, which are arranged at positions opposite to each other by 180 degrees, are input to the differential amplifier 51, and the A phase which is a differential signal of both signals A signal Va is obtained. Similarly, the detection signals Vb1 and Vb2 from the B1 phase magnetic field detection element 142 and the B2 phase magnetic field detection element 144 arranged at positions opposite to each other by 180 degrees are input to the differential amplifier 52, and the differential signals of both signals are obtained. A certain B-phase signal Vb is obtained.

FIG. 10 is a waveform diagram showing the output of the magnetic field detection element, and shows a waveform diagram of the A-phase signal Va and the B-phase signal Vb which are differential signals of the magnetic field detection element 14. The A-phase signal Va and the B-phase signal Vb are signals that are 90 degrees out of phase from the corresponding arrangement of detection elements.
The A-phase signal Va and the B-phase signal Vb are input to the angle calculation circuit 53. An angle signal θ that linearly changes with respect to the rotation angle is obtained by the arithmetic processing of arctan (Va / Vb).

Thus, in the conventional magnetic encoder device, the gap between the permanent magnet and the fixed body is formed so that the gap is constant, and the magnetic field from the permanent magnet is detected by the magnetic field detection element fixed to the fixed body and rotated. The absolute position of the body was detected.
WO99 / 013296

  However, in the conventional magnetic encoder, the gap between the permanent magnet and the fixed body is formed so that the gap is constant, and the magnetic flux density distribution having a peak at the center in the rotation axis direction (magnet width direction) of the gap is present. Although formed, the region where the magnetic flux density is constant near the peak is small. For this reason, when the permanent magnet fluctuates in the axial direction, there is a problem that the magnetic field detected by the magnetic field detecting element fluctuates and the accuracy of the encoder is lowered.

  The position change in the axial direction of the permanent magnet occurs when the rotor shaft vibrates due to the influence of the load connected to the motor and the rotor unbalance. In addition, when the permanent magnet and the stator are attached, if the permanent magnet and the stator are misaligned, they are easily affected by the fluctuation.

The conventional problem will be described in detail with reference to FIGS.
FIG. 11 is a side sectional view showing a positional relationship between a permanent magnet and a fixed body in a conventional magnetic encoder, and shows a case where the center of the permanent magnet 12 in the magnet width direction coincides with the center of the gap.
FIG. 12 is a graph showing the magnetic field distribution in the gap in the positional relationship of FIG.
The distribution is such that the magnetic flux density has a peak at the center, and the region where the magnetic flux density is constant is small. Thus, the magnetic flux density distribution has a peak at the center and the region where the magnetic flux density is constant is small because the leakage magnetic field at the end of the permanent magnet is large.

FIG. 13 is a side sectional view showing a positional relationship between a permanent magnet and a fixed body in a conventional magnetic encoder, and shows a case where the center of the permanent magnet 12 in the magnet width direction is shifted from the center of the gap.
FIG. 14 is a graph showing the magnetic field distribution in the gap in the positional relationship of FIG.
As shown in FIG. 13, when the permanent magnet 12 and the fixed body are displaced in the axial direction, the magnetic flux density distribution in the gap moves in the axial direction as shown in FIG. 14, and the peak of the magnetic flux density is the center of the fixed body 13 in the axial direction. It will deviate from. Since the magnetic field detection element is arranged at the center of the fixed body, the magnetic field detected by the magnetic detection element fluctuates when a positional shift occurs. Therefore, the output voltage of the magnetic field detection element fluctuates and the rotation angle detection accuracy deteriorates.

  The present invention has been made in view of such problems, and suppresses the influence caused by the positional deviation between the permanent magnet and the fixed body in the rotation axis direction, and can detect the rotation angle with high accuracy. An object is to provide an encoder device.

In order to solve the above problems, the present invention is configured as follows.
According to the first aspect of the present invention, a magnetic encoder device is attached to a rotating body, is magnetized in one direction perpendicular to the rotation axis direction of the rotating body, and has a disk-like permanent shape having a predetermined magnet width. In a magnetic encoder device comprising: a magnet; a stationary body opposed to the permanent magnet through a gap; and a signal processing circuit that processes a signal from the magnetic field detection element. The fixed body is characterized in that the gap length of the gap portion changes in the magnet width direction, and the gap length at the end of the permanent magnet is shorter than the gap length at the center portion.
Further, the magnetic encoder apparatus, a surface opposed to the gap portion of the fixed body may be I arcuate der.
Further, the magnetic encoder apparatus, a surface opposed to the gap portion of the fixed body may be I-shaped der having a taper toward both ends from the central portion of the width of the magnets.
Further, in this magnetic encoder device, the surface of the fixed body that faces the gap portion has a parallel portion having a predetermined width with respect to the rotation axis direction at the center portion of the magnet width, and both ends of the magnet width. may it shape der provided with a taper in parts.

According to the above magnetic encoder device , since the gap length of the surface of the fixed body facing the permanent magnet is longer at the center of the magnet width and shorter at the end of the magnet width, the region where the magnetic field is uniform is expanded. Thus, a magnetic encoder device can be realized in which fluctuations in the detection voltage of the magnetic field detection element due to fluctuations in the position of the permanent magnet in the rotation axis direction are suppressed.
In addition, according to this magnetic encoder device , if the surface of the fixed body facing the gap is made into an arc shape, the region where the magnetic field becomes uniform can be expanded. A magnetic encoder device that suppresses fluctuations in the detection voltage of the detection element can be realized.
Also, according to this magnetic encoder device , if the surface of the fixed body facing the gap is tapered from the center of the gap toward the left and right in the rotational axis direction, the magnetic field becomes uniform. Since the area can be expanded, it is possible to realize a magnetic encoder device in which fluctuations in the detection voltage of the magnetic field detection element due to fluctuations in the position of the permanent magnet in the rotation axis direction are suppressed.
Further, according to this magnetic encoder device , the surface of the fixed body that faces the gap portion has a parallel portion having a predetermined width in the magnet width direction at the center portion of the gap portion, and is tapered at both ends of the fixed body. Since the region where the magnetic field is uniform can be widened, it is possible to realize a magnetic encoder device that suppresses variation in the detection voltage of the magnetic field detection element due to variation in the position of the permanent magnet in the rotation axis direction.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of a detection unit in the magnetic encoder device of the present invention, FIG. 1 (a) is a plan view, and FIG. 1 (b) is a side view. FIG. 2 is a side sectional view of the detection unit.
In FIG. 1, reference numeral 12 denotes a disk-like permanent magnet fixed to the rotating body 11 so that the rotation axis is the same, and is magnetized in one direction parallel to the axis of the rotating body 11 in a direction perpendicular to the axis. Reference numeral 13 denotes a ring-shaped fixed body that is provided on the outer peripheral side of the permanent magnet 12 and is composed of the soft magnetic body 13. Reference numeral 14 denotes four magnetic field detecting elements attached to the fixed body 13, which are opposed to the outer peripheral surface of the permanent magnet 12 through the air gap 20, and are arranged 90 degrees out of phase with each other at a mechanical angle. .
In addition, as shown in FIG. 2, in the detection unit composed of the permanent magnet 12, the fixed body 13, and the magnetic field detection element 14, the surface of the fixed body 13 that faces the gap 20 is arcuate, The gap length 22 at the end is smaller than the gap length 21.
The difference between this embodiment and the prior art is that the gap length of the gap changes with respect to the magnet width direction (rotational axis direction), and the gap length at the end of the permanent magnet is shorter than the gap length at the center. This is the point that the surface of the fixed body that faces the gap is arcuate. Note that the angle signal detection operation is the same as that of the prior art, and the description thereof is omitted.

FIG. 3 is a graph showing the magnetic field distribution in the gap of the magnetic encoder device according to this embodiment.
In the figure, the horizontal axis is the position in the rotation axis direction, and the vertical axis is the magnetic flux density. A solid line is a magnetic flux density distribution in the gap portion in the present embodiment, and shows a magnetic flux distribution at a position on the AB line indicated by a dotted line in FIG. In this embodiment, the region where the magnetic flux density is constant is widened. This is because the gap between the fixed body 13 and the permanent magnet 12 is narrowed at the end of the magnet width, so that the leakage magnetic field at the end of the permanent magnet is reduced. The broken line shows the magnetic flux density distribution in the conventional structure for comparison.

  FIG. 4 is a graph schematically showing the magnetic flux density distribution when the positions of the permanent magnet 12 and the fixed body 13 are relatively displaced in the rotation axis direction. In this embodiment, since the region where the magnetic flux density is constant is widened, the influence on the magnetic field detection element due to the position fluctuation of the permanent magnet 12 in the rotation axis direction can be reduced.

  As described above, in this embodiment, the surface of the fixed body 13 is formed in an arc shape, whereby the gap at the end of the permanent magnet is reduced, and the region where the magnetic flux density is constant can be widened. For this reason, fluctuations in the output voltage of the magnetic field detection element due to positional deviation in the direction of the rotation axis between the permanent magnet and the fixed body can be reduced, and the detection accuracy of the rotation angle can be improved.

FIG. 5 is a side sectional view of a detection unit of a magnetic encoder device showing a second embodiment of the present invention.
The surface of the fixed body 13 with respect to the gap portion 20 has a shape in which a taper is provided from the central portion of the magnet width toward both end portions. With this shape, the gap at the end of the permanent magnet can be reduced, so that the region where the magnetic flux density is constant can be expanded as in the first embodiment.

FIG. 6 is a side sectional view of a detecting portion of a magnetic encoder device showing a third embodiment of the present invention.
The surface of the fixed body 13 that faces the air gap 20 has a parallel portion having a predetermined width with respect to the rotation axis direction at the center of the magnet width, and is tapered at both ends of the magnet width. . In this shape, the gap at the end of the permanent magnet can be reduced by providing the taper at both ends, so that the region where the magnetic flux density is constant can be expanded. In addition, since the parallel portion is provided at the center, the position of the magnetic field detection element is stabilized.

In this way, by making the gap length of the surface facing the permanent magnet of the fixed body longer at the center of the magnet width and shorter at the end of the magnet width, it is less affected by displacement in the rotation axis direction and stable. Therefore, it is possible to realize a magnetic encoder device with high accuracy from which the detected signal is obtained.
The detailed shape of the fixed body, that is, the arcuate radius of curvature and the inclination of the taper can be determined using a numerical analysis technique such as a finite element method.
In addition, the fixed body is made of block-shaped soft magnetic material, magnetic steel plate, molded powder magnetic material,
A soft magnetic material such as a wire core can be used.

  The present invention can be applied to a magnetic encoder device that detects a rotation angle of a servo motor used as an actuator of a machine tool, a robot, or the like.

It is a perspective view which shows the structure of the magnetic encoder which shows the 1st Example of this invention. It is sectional drawing of the magnetic encoder which shows the 1st Example of this invention. It is a figure which shows the magnetic flux density distribution of the space | gap in the magnetic encoder of this invention. It is a figure which shows the magnetic flux density distribution of a space | gap when the position shift of the permanent magnet and fixed body of the magnetic encoder of this invention has occurred. It is a sectional side view of the detection part of the magnetic encoder apparatus which shows the 2nd Example of this invention. It is a sectional side view of the detection part of the magnetic encoder apparatus which shows the 3rd Example of this invention. It is a perspective view which shows the structure of the conventional magnetic encoder apparatus. It is a sectional side view of the detection part of the conventional magnetic encoder apparatus. It is a block diagram of a signal processing circuit. It is a wave form diagram which shows the output of a magnetic field detection element. It is a sectional side view which shows the positional relationship of the permanent magnet and fixed body in the conventional magnetic encoder (when there is no position shift). It is a graph which shows the magnetic field distribution of the space | gap part in the positional relationship of FIG. It is a sectional side view which shows the positional relationship of the permanent magnet and fixed body in the conventional magnetic encoder (when there exists a position shift). It is a graph which shows the magnetic field distribution of the space | gap part in the positional relationship of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Rotating body 12 Permanent magnet 13 Fixed body 14 Magnetic field detection element 141 A1 phase magnetic field detection element 142 B1 phase magnetic field detection element 143 A2 phase magnetic field detection element 144 B2 phase magnetic field detection element 20 Cavity 21 Cavity length 22 at the end Air gap length 50 Signal processing circuit 51, 52 Differential amplifier 53 Angle calculation circuit

Claims (4)

A disk-shaped permanent magnet attached to the rotating body on the rotating shaft, magnetized in one direction perpendicular to the rotating shaft direction of the rotating body, and having a predetermined magnet width;
A fixed body in which the permanent magnet is formed in a ring shape inserted into a hole, and a plurality of magnetic field detection elements facing the permanent magnet via a gap portion are disposed on the inner surface of the ring shape ,
A signal processing circuit for processing a signal from the magnetic field detection element ;
Equipped with a,
The fixed body, so that the gap length of the gap portion is changed by the magnet width direction, the gap length at the end of the permanent magnet is shorter than the length of the gap in the central portion of the permanent magnet, facing the air gap The surface to be concaved at the center of the magnet width direction,
Each of the plurality of magnetic field detection elements is disposed on the inner surface of the recessed central portion in the magnet width direction .   The magnetic encoder device according to claim 1, wherein a surface of the fixed body facing the gap is arcuate.   2. The magnetic encoder device according to claim 1, wherein a surface of the fixed body facing the gap is tapered from the center of the magnet width toward both ends. The surface of the fixed body that faces the gap portion has a parallel portion having a predetermined width with respect to the rotation axis direction at the center portion of the magnet width, and is tapered at both ends of the magnet width. 4. The magnetic encoder device according to claim 1, wherein the magnetic encoder device is a magnetic encoder device.

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