JPH0617800B2 - Magnetic encoder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a speed and position detector of a drive control motor in products such as robots and manipulators.

(Prior Art) There is a demand for a detector capable of instantaneously and accurately measuring the position and velocity of an actuator that is incorporated in a robot or a manipulator and that performs rotary or linear motion.
Conventionally, photoelectric detectors have been widely used as such detectors. Since this photoelectric detector consists of an optical slit made by photolithography by depositing a metal film on a glass disk, a light emitting diode and a photodiode as a light receiving element, the glass disk is vulnerable to impact and emits light. Due to the arrangement of the light receiving element, it is impossible to reduce the wall thickness, and it has a drawback that it cannot be used at a high temperature of 80 ° C or higher.

In recent years, with the miniaturization of robots and manipulators, the need for improved heat resistance and smaller size and higher resolution of detectors has increased. In response to such demands, a magnetic encoder was invented in which a drum on which a magnetization pattern was written and a magnetoresistive effect element (hereinafter abbreviated as MR element) were combined (Japanese Patent Laid-Open No. 54-11).
5257).

(Problem to be Solved by the Invention) This detector rotates in conjunction with a rotation axis, and has a rotating body having a magnetic recording medium on which a magnetization pattern is written at a pitch p.
It is composed of an MR element that detects the periodic magnetic field distribution leaking from this magnetization pattern.
It looks like the figure. That is, the MR element stripe length direction is perpendicular to the magnetic field direction, and the stripe width direction is parallel to the rotor circumferential direction. Such magnetic field Hex from a magnetic recording medium in the construction field to enter the MR element when applied to the MR element H _eff is the demagnetizing field and H _d and H _eff = H _ex -H _d (JP 57-197885).

Here, the pattern width of the MR element W, film thickness t, when the saturation magnetic field of the MR element and I _s, the demagnetizing field H _d is So the magnetic field H _eff is Becomes That is, when the pattern width W becomes smaller, the demagnetizing field H
_{Since d} becomes large and the magnetic field H _eff becomes small, the output of the MR element decreases. Since it is possible to think that the position reading unit is two times the width of the pattern and the pattern width W, the MR pattern width of 10 μm is the limit in such a structure, and the position reading unit is 20 μm. Since the required resolution is a few μm, this structure is impossible. In addition, since the distance between the MR element and the magnetic recording medium must be several tens of μm, the MR element and the magnetic recording medium come into contact with each other when the magnetic encoder is assembled,
Sometimes the device was destroyed.

An object of the present invention is to provide a compact and high resolution magnetic encoder that is easy to assemble.

(Means for Solving the Problems) A magnetic encoder according to the present invention includes a magnetic recording medium in which at least one set of magnetization patterns that generate a periodic magnetic field at a pitch p according to required position reading accuracy is written. In a magnetic encoder for converting output of the periodic magnetic field by at least one stripe-shaped magnetoresistive effect element close to the magnetic recording medium, the magnetization intensity of the magnetic recording medium is different within one pitch p, and the magnetoresistive effect is The unit stripe length of the device is 1,
When the closest distance between the magnetic recording medium and the magnetoresistive effect element is g, the angle α formed between the stripe length direction and the surface of the magnetic recording medium at the closest portion is The stripe width direction is parallel to the magnetization pattern row direction (see Fig. 3).

(Operation) FIG. 7 is a view showing the influence of the angle α formed by the length direction of the MR element stripe and the tangential direction of the magnetic recording medium surface at the adjacent portion on the output value. The output becomes smaller as the MR element stripe tilts (the value of α deviates from 90 °), It turns out that it becomes a noise level.

Further, since the stripe width direction of the MR element is parallel to the magnetization pattern column direction and the magnetic field from the magnetization pattern is applied in the stripe width direction, it is the stripe width direction that is affected by the demagnetizing field H _d and the pitch. Since p is not limited by the stripe width and can be made small regardless of the stripe width, high resolution can be achieved.

(Example) Next, the Example of this invention is described with reference to drawings.

1 is a schematic view of a first embodiment of a magnetic encoder of the present invention, FIG. 2 is a view showing a method of forming a magnetization pattern in the embodiment of FIG. 1, and FIG. 3 is a view of the embodiment of FIG. Magnetization patterns and detailed views of the MR element, FIGS. 4 and 5 are output waveform diagrams in the embodiment of FIG.

In this embodiment, an aluminum alloy drum 2 fixed to a rotating shaft 1, a Co-γFe ₂ O ₃ magnetic recording medium 3 formed on the outer periphery of the drum 2, and an 81Ni-Fe film formed on a glass substrate 4. The detection head is composed of the MR element 5 and the terminal 6 formed of a Cu film, and the lead wire 7 and the drive detection circuit 8 connected to this terminal. The arrows shown on the magnetic recording medium 3 indicate the degree of magnetization, and a ring head 9 as shown in FIG. 2 was used to pass a current through the coil 10 for magnetization. The strength of magnetization changes within one pitch p. In such a structure, the resistance of the MR element 5 changes according to the strength of the magnetic field leaked from the magnetic recording medium 3, and an output signal having a triangular waveform as shown in FIG. 4 is obtained. When the median value of this signal is used as a threshold value and pulsed, it becomes as shown in FIG. 5, which can be used as a position detector.
In such a configuration, the influence of the demagnetizing field H _d is not limited by the pitch p in the stripe width direction.

FIG. 6 is a diagram showing the output signal with respect to the pitch p in the present embodiment in comparison with the conventional example.

It can be seen that even if the pitch is 20 μm pitch or less, which is the limit of the conventional example, the output voltage is sufficiently higher than the noise level, so that high resolution can be achieved. Further, since the MR element surface is perpendicular to the drum surface, the MR element does not touch the drum and break.

FIG. 8 is a diagram showing the outline of the second embodiment of the present invention. This is one in which the magnetic recording media 3 are magnetized in the opposite patterns in opposite directions, and by doing so, the output voltage can be made larger than in the first embodiment. The reason for this will be described below. When the MR element is located directly above the boundary b of the pitch where the magnetic field strength of the magnetic recording medium is zero, when the MR element is magnetized in the same direction as in Example 1, the pattern a is used. Since a magnetic field in the same direction is applied from the magnetic field and the pattern c, the magnetic field H entering the MR element does not actually become zero. On the other hand, in the case of the present embodiment (FIG. 8), since the directions of the magnetic fluxes entering the MR element are opposite in part b, they cancel each other and the intensity of the leakage magnetic flux becomes completely zero. That is, as shown in FIG. 9, the characteristic (b) in the case of the opposite direction magnetization shown in the example 2 has a larger magnetic field than the characteristic (a) in the case of the same direction magnetization shown in the example 1. As the amount of change increases, M
A place where the resistance change rate of the R element is large can be used. Therefore, the output voltage of this embodiment can be set higher than that of the first embodiment (Fig. 10A) as shown in Fig. 10B. Particularly, when the magnetizing pitch is 10 μm or less, it is sufficiently larger than the nozzle level, and its effect is remarkable.

In the above, the magnetization intensity distribution within one pitch has been described for a positive magnetic wave, but it is clear that the same effect can be obtained with a triangular wave.

11, 12 and 13 are perspective views showing another embodiment of the present invention. FIG. 11 shows an example in which a zero point and an incremental phase are formed by a sine wave current, FIG. 12 shows an example in which two rows of magnetization pattern having 90 ° phase difference are provided, and FIG. 13 shows two different phase differences. The same pattern as that shown in FIG. 6 was obtained in each case by forming a bridge by providing two rows of the magnetization pattern rows each having a Co—Cr perpendicular magnetization film and forming a bridge.

Although the drum is used in the above embodiment, it is clear that the same effect can be obtained by using a magnetic recording medium on the disk surface.

(Effect of the Invention) As described above, according to the present invention, the angle α formed by the stripe length direction and the tangential direction of the magnetic recording medium surface at the adjacent portion is By setting the range from 90 ° to 90 °, making the stripe width direction parallel to the magnetization pattern column direction, and applying the magnetic field from the magnetization pattern in the stripe width direction, it is possible to provide a high-resolution magnetic encoder.

[Brief description of drawings]

1 is a schematic view of a first embodiment of a magnetic encoder of the present invention, FIG. 2 is a view showing a method of forming a magnetization pattern in the embodiment of FIG. 1, and FIG. 3 is a view of the embodiment of FIG. Detailed views of the magnetization pattern and the MR element, FIGS. 4 and 5 are waveform diagrams of the output in the embodiment of FIG. 1, and FIG. 6 is a conventional example showing the relationship between the pitch p and the output voltage in the embodiment of FIG. FIG. 7 shows the effect of the angle α formed by the MR element pattern length direction and the magnetic recording medium surface in the vicinity on the output, and FIG. 8 shows the second embodiment of the present invention. FIG. 9 is a schematic diagram showing an example, FIG. 9 is a diagram showing a mechanism of output increase in the second embodiment, FIG. 10 is a diagram showing output voltage in the second embodiment, and FIGS. 11 to 13 are other embodiments of the present invention. FIG. 14 is a perspective view showing an example and its output waveform, and FIG.
It is a figure which shows arrangement | positioning of an element. 1 ... Rotation axis, 2 ... Drum, 3 ... Magnetic recording medium, 4 ... Glass substrate, 5 ... MR element, 6 ... Terminal, 7 ... Lead wire, 8 ... Drive detection circuit, 9 ... … Ring head, 10… coil.

Claims (4)

[Claims] 1. A pitch p according to a required position reading accuracy.
At least one magnetization pattern sequence that generates a periodic magnetic field in
In a magnetic encoder for converting the output of a periodic magnetic field from a written magnetic recording medium by at least one stripe-shaped magnetoresistive effect element close to the magnetic recording medium, the magnetic recording medium has a magnetization intensity of one pitch. the unit stripe length of the magnetoresistive effect element is l,
When the closest distance between the magnetic recording medium and the magnetoresistive effect element is g, the angle α formed between the stripe length direction and the surface of the magnetic recording medium at the closest portion is The magnetic encoder is characterized in that the stripe width direction is parallel to the magnetization pattern row direction. 2. The magnetic encoder according to claim 1, wherein the distribution of the magnetization intensity within one pitch of the magnetic recording medium is a sine wave. 3. The magnetic encoder according to claim 1, wherein the distribution of the magnetization intensity within one pitch of the magnetic recording medium is triangular. 4. The magnetic encoder according to claim 2, 3 or 4, wherein adjacent patterns in one magnetization pattern row of the magnetic recording medium are magnetized in the same direction or in opposite directions.