JP4622487B2 - Magnetic encoder and motor equipped with the same - Google Patents

Description

  The present invention relates to a magnetic encoder that detects a rotational position of a rotating body, and more particularly to a magnetic encoder that detects a rotational position of a shaft of a servo motor and a motor including the same.

In the conventional magnetic encoder, a magnetic shield plate is installed on the bracket surface of the motor in order to reduce the influence of the magnetic flux leaking from the motor shaft.
In some cases, a magnetic shield is integrally formed with a bracket or a back yoke (see Patent Document 1).
JP-A-9-308171

FIG. 5 is a cross-sectional view when a conventional magnetic encoder is mounted on a motor (note that the illustration of the magnetic field sensor side is omitted).
In the figure, 1 is a sensor magnet, 2 is a back yoke, 4 is a motor shaft, and 6 is a hub for mounting the sensor magnet 1. The 50s are parts on the motor stator side, 51 is a frame, 52 is an electromagnetic part, 53 is a magnet, 54 is a bracket, 55 is a shield plate, and 56 is a bearing.
As can be seen from the figure, a magnet 53 is bonded and fixed to the surface of the shaft 4 rotatably held on the stator side via a bearing 56, and the tip of the shaft 4 reaches the inside of the back yoke 2. ing. A shield plate 55 serving as a magnetic shield is fixed to the magnet facing surface of the bracket 54 using fixing means such as insert molding or screws, and measures against leakage magnetic flux are taken as shown in FIG.

FIG. 6 shows the flow of leakage magnetic flux in a conventional magnetic encoder.
Since the main magnetic flux of the magnet 53 flows to the electromagnetic part 52, it is omitted.
On the other hand, the magnetic flux leakage of the magnet 53 is the magnetic flux (1) radiated directly from the corners of the magnet and the shaft to the shield plate 55, and passes through the inside of the magnet to the tip of the shaft 4 from there. A magnetic flux (2) is radiated into the interior. Since the magnetic flux (1) is shielded by the shield plate 55, there is no problem. However, since the magnetic flux (2) passes through the encoder section, it is affected by the leakage magnetic flux, which hinders accurate rotational position detection. There was a problem.
Moreover, although the motor with a magnetic encoder described in Patent Document 1 can omit the magnetic shield plate, certain results can be seen in terms of reduction in the number of parts, cost reduction, and effective magnetic shielding. The magnetic flux (2) described is also generated in this case and still passes through the encoder unit, so that it may be affected by the leakage magnetic flux and hinder accurate rotational position detection.

As described above, since the conventional magnetic encoder has a weak effect of shielding the leakage magnetic flux from the shaft, the magnetic encoder is affected by the leakage magnetic flux leaking into the back yoke through the shaft, and is detected by the magnetic sensor. There was a problem that the accuracy was lowered.
Further, although it was considered to change the shaft to a non-magnetic material such as stainless steel so that the magnetic flux does not pass therethrough, there is a problem that the shielding effect of the leakage magnetic flux is recognized but the cost becomes high.
The present invention has been made in view of such problems, and an object thereof is to provide a magnetic encoder that has a high magnetic shielding effect and can ensure high accuracy at low cost.

In order to solve the above problem, a magnetic encoder according to an aspect of the present invention includes a sensor magnet holding portion that holds a sensor magnet, and a concentric cylindrical shape that surrounds the sensor magnet holding portion to stabilize the magnetic flux of the sensor magnet. A magnetic encoder including a back yoke portion and a magnetic field detection element that detects a magnetic field formed by the sensor magnet, and shields magnetic flux leaking from the magnet of the motor from leaking to the magnetic field detection element side. The magnetic shield part is formed in a hollow disk shape, and the magnetic shield part disk is integrally formed concentrically inside the cylinder of the cylindrical back yoke.
In the magnetic encoder described above , the magnetic shield disk may have an H shape having an opening centered on a side sectional shape of a back yoke formed concentrically and integrally within a cylindrical back yoke .
Alternatively, the present invention is, in the magnetic encoder, as a concave of the magnetic shield portions disc has openings around the side sectional shape of the integrally formed back yoke concentrically cylindrical interior of the cylindrical back yoke Also good.
The present invention may also be a holding unit in which the fixed end of the sensor magnet is formed in a hollow cylindrical shape in the magnetic encoder .
A motor according to another aspect of the present invention is a motor on which the magnetic encoder is mounted, wherein the sensor magnet holding portion is fixed to an end portion of a motor shaft, and the concentric cylindrical back yoke is provided. Is fixed to the bracket of the motor.

According to the first aspect of the present invention, since the concentric disk of the concentric disk-shaped magnetic shield portion is integrated into the concentric cylinder of the concentric cylindrical back yoke, most of the leakage magnetic flux from the shaft is concentric disk-shaped magnetic shield. Therefore, a magnetic encoder that has a high magnetic shielding effect and can ensure high accuracy at low cost can be obtained.
According to the second aspect of the present invention, since the side cross-sectional shape of the integrated back yoke is the H-shaped opening at the center, it is easy to fix the back yoke to the bracket.
According to the third aspect of the invention, since the side cross-sectional shape of the integrated back yoke is a concave shape with an opening at the center, the shape of the back yoke is a shape in which the lower surface is removed from the magnetic shield portion, and the motor bracket surface is formed. This eliminates the need for inlay processing for positioning, which is advantageous in terms of processing costs.
According to the fourth aspect of the present invention, the sensor magnet can be used for fixing the hollow portion of the sensor magnet by fixing the fixed end of the sensor magnet into a hollow cylindrical shape. Can be reduced.
According to the fifth aspect of the present invention, the sensor magnet holding portion is fixed to the end portion of the motor shaft, and the concentric cylindrical back yoke is fixed to the bracket of the motor. A motor equipped with a magnetic encoder capable of ensuring accuracy can be easily obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an exploded perspective view showing a schematic structure of a magnetic encoder according to the present invention.
In the figure, reference numeral 10 denotes a magnetic encoder according to the present invention, which is largely composed of a sensor magnet 1, a back yoke 2, and a magnetic field sensor 3. Reference numeral 5 denotes a motor, and the motor shaft 4 on the rotor side faces the opening of the bracket 54 on the stator side.
The sensor magnet 1 of the magnetic encoder 10 is fixed to the motor shaft 4, and the back yoke 2 is fixed to the bracket 54. The back yoke 2 has a sensor magnet 1 disposed at the center of the space, and the magnetic field sensor 3 is inserted and disposed inside the back yoke 2 so that the magnetic field sensor 3 can detect the magnetic field formed by the sensor magnet 1. It has become. The magnetic field sensor 3 is omitted in the following illustration.

FIG. 2 is a cross-sectional view when the magnetic encoder of the present invention is mounted on the motor 5.
In the figure, 1 is a sensor magnet, 2 is a back yoke, 4 is a motor shaft, 5 is a motor, and 6 is a mounting hub for mounting the sensor magnet 1.
Reference numeral 51 denotes a frame, 52 denotes an electromagnetic part, 53 denotes a magnet, and 54 denotes a bracket.
The present invention differs from the prior art of FIG. 5 in that the magnetic shield 21 and the back yoke 2 are separated in the prior art, but here the magnetic shield 21 and the back yoke 2 are integrated. is there. By integrating in this way, higher leakage flux countermeasure effect and lower cost can be obtained.
The magnetic shield portion (21 in FIG. 2) of the back yoke 2 has a thickness t, and the tip portion of the shaft 4 is arranged up to the center (t / 2) of the thickness of the magnetic shield. It has been found that this arrangement is most effective in preventing leakage magnetic flux.

FIG. 3 is a component diagram for realizing the magnetic shield of the magnetic encoder according to the present invention.
In the figure, (a) is a plan view of the back yoke, and (b) is a front sectional view thereof. And (c) is a modification of the back yoke of (b).
In (a) and (b), the back yoke 2 is composed of a disk-shaped magnetic shield portion 21 and a cylindrical back yoke portion 22, and the disk of the disk-shaped magnetic shield portion 21 is a cylindrical back yoke. The lower end of the back yoke portion 22 extends further downward from the surface on which the magnetic shield portion 21 is formed so as to be concentrically integrated within the cylinder 22 and to have an H shape with the side cross-sectional shape of the back yoke 22 being open at the center. An extending portion 22a is formed.
As a result, the magnetic shielding effect is enhanced as will be described later, and it is not necessary to use a non-magnetic material for the motor shaft, so that the cost is reduced, and fixing the back yoke to the bracket 54 is possible at the lower end of the back yoke portion 22. Since the extended portion 22a is fitted into the stepped portion 54a (FIG. 2) of the bracket, the attachment and centering are extremely easy.
In the modified example of (c), the back yoke 2 ′ is composed of a disk-shaped magnetic shield part 21 and a cylindrical magnetic shield part 21, and the disk of the disk-shaped magnetic shield part 21 is a cylindrical back yoke. It is formed so as to be concentrically integrated within the cylinder 22 and to have a concave shape with the side sectional shape of the back yoke 2 'opened at the center. Thus, since the back yoke portion 22 has a shape in which the lower surface is removed from the magnetic shield portion 22, it is not necessary to process the positioning stepped portion 54a on the motor bracket 54, which is advantageous in terms of processing cost. It becomes. However, it is necessary to separately provide a mechanism for accurately positioning the back yoke 2 ′ on the motor bracket 54.

FIG. 4 illustrates the flow of leakage magnetic flux in the magnetic encoder according to the present invention.
In the figure, the main magnetic flux of the magnet is omitted because it flows to the electromagnetic part.
Although the return path of the magnetic flux is not shown in the figure, the rotor magnet is divided and magnetized in the circumferential direction, so that it travels before (or behind) the page, and then follows the reverse path of the leakage flux. Become.
As can be seen from the figure, the magnetic leakage flux of the magnet includes a magnetic flux (1) radiated directly from the corners of the magnet and the shaft to the encoder unit, and a magnetic flux (1) radiated from the inside of the magnet to the encoder unit through the shaft. 2).
Thus, in the structure of the present invention, the leakage fluxes of both the magnetic flux (1) and the magnetic flux (2) are directed to the magnetic shield part 21 of the back yoke 22, so that almost no leakage magnetic flux is present on the encoder part side. It is configured not to invade.
In addition, it is possible to absorb the influence of an external magnetic field by securing a sufficient thickness for the back yoke.
As described above, since the configuration is such that the influence of leakage magnetic flux and external magnetic field is eliminated, a magnetic encoder that is resistant to magnetic noise, highly accurate, and inexpensive can be realized.

In the above embodiment, the sensor magnet 1 is fixed to the shaft 4 via the hub 6. However, the shaft diameter of the end surface of the shaft 4 is reduced, while the lower end of the sensor magnet 1 is formed in a hollow cylindrical shape. Thus, by fixing the hollow cylindrical portion at the lower end of the sensor magnet 1 by fitting it to the shaft, the number of parts and the processing steps can be reduced.
At this time, the sensor magnet is preferably made of a material having a sufficiently large magnetic flux with respect to the leakage flux so that the magnetic field on the surface of the sensor magnet is not disturbed by the leakage flux.

1 is an exploded perspective view showing a schematic structure of a magnetic encoder according to the present invention. It is sectional drawing of the magnetic encoder which concerns on this invention. It is a component diagram which implement | achieves the magnetic shield of the magnetic encoder based on this invention. It is a figure which shows the flow of the leakage magnetic flux in the magnetic encoder which concerns on this invention. It is a cross-sectional view when a conventional magnetic encoder is mounted on a motor. It is a figure which shows the flow of the leakage magnetic flux in the conventional magnetic encoder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sensor magnet 2 Back yoke 21 Magnetic shield part 22 Back yoke part 3 Magnetic field sensor 4 Motor shaft 5 Motor 51 Frame 52 Electromagnetic part 53 Magnet 54 Bracket 55 Shield plate 56 Bearing 6 Hub 10 Magnetic encoder which concerns on this invention

Claims (6)

A sensor magnet holding portion that is formed to be connectable to the motor shaft and holds the sensor magnet;
A concentric cylindrical back yoke that surrounds the sensor magnet holder and stabilizes the magnetic flux of the sensor magnet;
A magnetic field detection element for detecting a magnetic field formed by the sensor magnet;
With
The magnetic shield part that shields the magnetic flux leaking from the magnet of the motor from leaking to the magnetic field detection element side has a hollow disk shape,
The magnetic shield disk is integrally formed concentrically inside the cylindrical back yoke ,
The magnetic encoder according to claim 1, wherein a tip end portion of the motor shaft is disposed within a thickness range of the magnetic shield portion disc .   The magnetic encoder according to claim 1, wherein a tip end portion of the motor shaft is disposed up to a center of a thickness of the magnetic shield portion disc. 3. The magnetism according to claim 1, wherein the magnetic shield disk is formed in an H shape having an opening centered on a side sectional shape of a back yoke formed concentrically and integrally within a cylindrical back yoke. Encoder. 3. The magnetism according to claim 1, wherein the magnetic shield disk has a concave shape with an opening centered on a side cross-sectional shape of a back yoke formed concentrically and integrally within a cylindrical back yoke. Encoder. The magnetic encoder according to any one of claims 1 to 4 , wherein the sensor magnet holding portion is omitted by using a holding portion formed in a hollow cylindrical shape as a fixed side end portion of the sensor magnet. A motor comprising the magnetic encoder according to any one of claims 1 to 5 , wherein the sensor magnet holding portion is fixed to an end portion of a motor shaft, and the concentric cylindrical back yoke is mounted on the motor. A motor with a magnetic encoder, wherein the motor is fixed to a bracket of the motor.

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