JP4543297B2 - Magnetic encoder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic encoder that detects a rotational position of a rotating body, and more particularly to a small-sized magnetic encoder.
[0002]
[Prior art]
Conventionally, there is a small magnetic encoder as shown in FIG. 3 that detects the rotational position of a rotating body. FIG. 3 is a side view showing a conventional magnetic encoder. In the figure, 1 is a yoke, 2 is a permanent magnet, 3 is a magnetic field detecting element, 4 is a rotating shaft, and 5 is a motor. This magnetic encoder includes a permanent magnet 2 that generates a magnetic field vertically and uniformly with respect to a rotating shaft 4, and a magnetic field detection element such as a Hall element having directivity and polarity with respect to the direction of the magnetic field between the yokes 1. The magnetic field detection element 3a is arranged in the magnetic field generated by the permanent magnet 2 so that the directivity is maximized in the direction perpendicular to the axis, and another magnetic field detection element 3b. Are rotated 90 degrees in the axial direction. Further, two magnetic field detecting means having the same axial angle but different polarities are arranged (not shown) with respect to two magnetic field detecting means having different axial angles.
Now, when the rotating shaft 4 is rotated by driving the motor 5, the yoke 1 fixed to the rotating shaft 4 is rotated. Since the direction of the magnetic field in the yoke 1 changes, a sine wave and a cosine wave can be obtained per rotation by the fixed magnetic field detection element 3. The rotational position can be detected by calculating these two signals using an angle calculator not shown. As for the calculation method, for example, when the voltage output of one magnetic detection element is Va and the voltage output of the other magnetic detection element is Vb, the rotational position θ can be calculated by θ = ARCTAN (Va / Vb).
Therefore, such a magnetic encoder can detect a position with high accuracy when the amplitude of the magnetic field is constant.
[0003]
[Problems to be solved by the invention]
However, the conventional permanent magnet has a large magnet and a complicated shape, and therefore the parallelism of the magnetic field is poor. If the parallelism of the magnetic field is poor, the waveform is distorted and the detection accuracy of minute angles is poor. Further, since the permanent magnet has a complicated shape, it is difficult to magnetize, making it difficult to put it into practical use. Furthermore, when manufacturing a small actuator, the above-mentioned magnetic encoder must also be miniaturized, but the permanent magnet that generates a magnetic field is difficult to process due to its complicated shape, making it difficult to miniaturize it. It was.
Accordingly, an object of the present invention is to provide a small magnetic encoder that is easy to manufacture, has high detection accuracy, and is small.
[0004]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention has a magnetic field generating means for generating a magnetic field vertically and uniformly with respect to a rotating shaft that rotates integrally with a detected object, and directivity and polarity with respect to the direction of the magnetic field. And at least one is arranged in the magnetic field generated by the magnetic field generating means so that directivity is maximized in the direction perpendicular to the rotation axis, and at least one is rotated around the rotation axis. In a magnetic encoder comprising a magnetic field detection means arranged at a position and a waveform processing circuit for converting a signal obtained from the magnetic field detection means into angle information and position information, the magnetic field detection means has at least three, In this configuration, the direction in which at least one magnetic field detection sensitivity of the magnetic field detection means is maximized is perpendicular to the directions of the two magnetic field detection means.
Further, the magnetic field generating means may be structured by a permanent magnet and a soft magnetic yoke, and the permanent magnet may be formed by a vapor phase growth method.
Further, the magnetic field detecting means may be a Hall element or a magnetoresistive effect element, or the Hall element may be formed in a substrate made of a semiconductor, and three elements may be formed to be orthogonal to each other.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
An embodiment of the present invention is shown in FIGS. FIG. 1 is a side view in which the magnetic encoder of the present invention is coupled to a small motor, and FIG. 2 is a front view of FIG. 1 viewed from the direction of the arrow. In the figure, 1 is a yoke, 2 is a permanent magnet, 3 is a magnetic field detecting element, 4 is a rotating shaft, and 5 is a motor.
The yoke 1 guides a magnetic field generated from the permanent magnet 2, and is formed by stacking U-shaped 3% Si—Fe soft magnetic silicon steel plates and forming them into two blocks. The permanent magnet 2 is formed by connecting a block-shaped ferrite magnet in the yoke 1.
The magnetic field detection element 3 is disposed in the opening of the yoke 1 using three Hall elements (3a, 3b, 3c). They are installed so that the directions in which the detection signals of the three Hall elements become maximum are perpendicular to each other. Therefore, the magnetic field generated from the permanent magnet 2 passes through the yoke 1 and forms a uniform magnetic field in the space where the magnetic field detection element 3 is installed.
Although not shown, a signal line for supplying drive power to the magnetic field detection element 3 and transmitting signals from the magnetic field detection means is connected to the waveform processing circuit. Although not shown, the rotating shaft 4 is supported on the casing by a bearing, and the magnetic field detection means is fixed to the casing via a frame.
[0006]
Next, the operation of this embodiment will be described.
Now, when the yoke 1 and the permanent magnet 2 are rotated by θ due to the rotation of the rotating shaft 4, the vector direction in which the directivity of the magnetic field detecting element 3a is maximum and the vector direction of the magnetic field generated by the permanent magnet are shifted by θ. Further, assuming that angles ψa and ψb are directed in the axial direction from the direction in which the detected magnetic fields of the magnetic field detecting elements 3a and 3b become maximum, respectively, the corrected output Va of each of the magnetic field detecting elements 3a and 3b. , Vb are expressed by equations (1) and (2), respectively.
Va = Bcos θ / cos ψa (1)
Vb = Bcos (θ + π / 2) / cosψb (2)
Furthermore, the absolute position Θ of the angle of the rotating shaft 2 is obtained as equation (3) using the output after each correction.
Θ = arctan (Va / Vb) (3)
From the above, if the values of ψa and ψb are known, it is possible to correct an output amplitude error due to a change in the magnetic field direction. Therefore, ψa and ψb are sequentially updated at positions where the magnetic field detection elements 3a and 3b are maximized, stored in the storage area included in the signal processing circuit, and used for correcting each magnetic field detection element. Specifically, if the output of the magnetic field detection element 3c is V _3c3amax when the output of the magnetic field detection element 3a is maximum, the maximum value of the magnetic field detection element 3c measured in advance is V _3cmax (4 ) Is given by
_ψa = sin ⁻¹ (V _3c3amax / V _3cmax ) (4)
Similarly, for the magnetic field detection element 3b, when the output of the magnetic field detection element 3b is maximized, _assuming that the output of the magnetic field detection element 3c is V _3c3bmax , (5) is given.
ψb = sin ⁻¹ (V _3c3bmax / V _3cmax ) (5)
Therefore, the values obtained by the equations (4) and (5) can be substituted into the equations (1) and (2), and Θ can be obtained by the equation (3).
In this embodiment, the three Hall elements of the magnetic field generating element 3 are arranged independently of each other. However, the present invention is not limited to this, and three Hall elements are formed on the semiconductor substrate so that the maximum magnetic field detection is orthogonal to each other. May be. Even with this configuration, the signal detection accuracy was as good as in the previous embodiment.
In the present embodiment, the Hall element is used as the magnetic field detection element, but a magnetoresistive element may be used. Further, although the block-shaped ferrite magnet is used as the permanent magnet, the present invention is not limited to this, and a rare earth magnet or the like may be attached to the end surface of the soft magnetic material using a sputtering method.
[0007]
【The invention's effect】
As described above, according to the present invention, at least three magnetic field detection means are provided, and the direction in which at least one magnetic field detection sensitivity of the magnetic field detection means is maximized is the direction of the other two magnetic field detection means. The output fluctuations of the magnetic field detection element can be easily corrected. Therefore, practical application is facilitated, and there is an effect of obtaining a small magnetic encoder with high detection accuracy.
[Brief description of the drawings]
FIG. 1 is a side view showing the overall configuration of a motor using a magnetic encoder of the present invention.
FIG. 2 is a front view seen from the direction of the arrow in FIG.
FIG. 3 is a side view showing a conventional magnetic encoder.
[Explanation of symbols]
1: Yoke 2: Permanent magnet 3: Magnetic field detection element 4: Rotating shaft 5: Motor

Claims (5)

A magnetic field generating means for generating a magnetic field perpendicularly and uniformly with respect to a rotating shaft that rotates integrally with the detected object;
It has directivity and polarity with respect to the direction of the magnetic field, and at least one is arranged in the magnetic field generated by the magnetic field generating means so that directivity is maximized in the direction perpendicular to the rotation axis, and a magnetic field detector at least one was placed at a position rotated around the rotary shaft,
A waveform processing circuit for converting a signal obtained from the magnetic field detection means into angle information representing an absolute position of the angle of the rotation axis ;
With
There are at least three magnetic field detection means, and the magnetic field detection means is arranged such that the direction in which at least one magnetic field detection sensitivity of the magnetic field detection means is maximized is perpendicular to the direction of the two magnetic field detection means. Magnetic encoder characterized by   2. The magnetic encoder according to claim 1, wherein the magnetic field generating means comprises a permanent magnet and a soft magnetic yoke.   The magnetic encoder according to claim 2, wherein the permanent magnet is formed by a vapor phase growth method.   The magnetic encoder according to any one of claims 1 to 3, wherein the magnetic field detection means is a Hall element or a magnetoresistive effect element.   5. The magnetic encoder according to claim 1, wherein the magnetic field detection unit is formed in a substrate made of a semiconductor, and three elements are formed so as to be orthogonal to each other.

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