JPS63206614A - Absolute magnetic encoder - Google Patents

Abstract

PURPOSE:To reduce a change in output in relation to a change in spacing by a method wherein an angle formed by the stripe length direction of a magnetoresistance (MR) element and the direction of the tangent of the surface of a substrate in a part wherein the MR element and the substrate are in the closest vicinity to each other is set to be within a specified range. CONSTITUTION:A plurality of magnetized pattern arrays n1... are written as shown by arrows on a magnetic recording medium 3 formed on the lateral side of a drum 2, and a magnetic field leaking from these magnetized patterns n1... acts on a corresponding MR element 5 formed on a substrate 4. It is found herein from an effect produced on an encoder output value by an angle alpha formed by the length (l) direction of the element 5 and the direction of the tangent of the surface of the recording medium 3, that the angle alpha needs only to be tan<-1> [(l+g)/p]<alpha<=90 deg. (g: a distance whereat the recording medium 3 and the element 5 are in the closest vicinity to each other, and p: a position reading unit). Since the stripe width direction of the element 5 is in the direction of the magnetized pattern arrays and the magnetic field is impressed in the direction of the stripe width, the element is made free from the effect of a diamagnetic field. In addition, the width of the magnetized pattern arrays can be narrowed without reducing resolving power, since a stripe can be turned back with the same pattern array.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an absolute position detector that detects the absolute position of a rotating body or a linearly moving body.

[Conventional technology]

There is a need for a detector that can instantaneously and accurately measure the position of an actuator that performs rotational or linear motion built into a robot or manipulator. Conventionally, photoelectric type detectors have often been used as such detectors. This photoelectric detector consists of an optical slit made by photolithography of a metal film deposited on a glass disk, a light emitting diode, and a photodiode as a light receiving element. The disadvantages are that it cannot be used at high temperatures and that it is impossible to make it thinner due to the arrangement of the light-emitting and light-receiving elements.

In recent years, with the miniaturization of robots and manipulators, the need for improved heat resistance and smaller size and higher resolution detectors has increased. In response to these demands, an angle detector was invented that combined a drum with a magnetization pattern written on it and a magnetoresistive element (hereinafter referred to as MR element) (Japanese Patent Laid-Open No. 54-11).
8259). This angle detector includes a magnetic recording medium that rotates in conjunction with a rotating shaft or an arrangement of a plurality of permanent magnets, and an MR element that detects magnetization information written on the magnetic recording medium or the arrangement of the permanent magnets. It consists of a drive detection circuit that detects the resistance change of this MR element and outputs it to the outside. In order to read the absolute value of the rotation angle, a large number of arrays of magnetization patterns or arrays of permanent magnets, that is, information tracks, are provided, and an MR element is provided in each of them.

[Problem that the invention seeks to solve]

FIG. 9(a) is a perspective view showing the structure, and FIG. 9(b) is an enlarged view of the MR element section. In these configurations, when the magnetic field Hex is applied from the magnetic recording medium 13 to the MR element 15, the magnetic field He, which enters the MR element 15, becomes Herf=Hex Hd, where Hd is the demagnetizing field (Japanese Patent Application Laid-Open No. 1983-1999). 197885).

Here, the pattern width of the MR element 15 is W, the film thickness is t, and M
R, and if the saturation magnetization of the MR element 15 is Is, then. In other words, when the pattern width W becomes smaller, the demagnetizing field H
As d increases and the magnetic field Haff decreases, the output of the MR element 15 decreases. Normally, twice the pattern width W is considered to be the position reading unit, so in this structure, considering the limit pattern width of 10 scales, the position reading unit is 20 μs, and the required number of scales cannot be achieved. Furthermore, M
The stripe length of the R elements 15 needs to be at least 2 mm in each row in order to suppress heat generation, so in the example shown in FIG. 9, the drum thickness becomes 10 mm or more. Of course, the stripes may be folded back, but the resolution will be reduced accordingly. In addition, since fluctuations in the distance g between the MR element 15 and the magnetic recording medium I3 are sensitive to output fluctuations, it is necessary to improve the mechanical finishing of the drum and the mounting of the MR element 15 in order to reduce fluctuations in the distance g. there were.

The purpose of the present invention is to achieve high resolution (smaller position reading unit)
The object of the present invention is to provide an absolute magnetic encoder that is thinner and has less output fluctuation even when the distance between an MR element and a magnetic medium changes.

[Means for solving problems]

The absolute magnetic encoder of the present invention has at least two rows of magnetization patterns depending on the required position reading accuracy.
An absolute magnetic encoder that reads out the absolute position of the base body, that is, the address, by a combination of a base body having a column and striped magnetoresistive elements arranged in each magnetization pattern column to detect the magnetic field leaking from the base body, When the stripe length of the magnetoresistive element is l, the closest distance between the substrate and the magnetoresistive element is g, and the position reading unit is P, the distance between the stripe length direction of the magnetoresistive element and the nearest part is The stripe width direction is parallel to the magnetization pattern row direction, and the magnetic field from the magnetization pattern is applied in the stripe width direction.

[Function] The influence of the angle θ between the magnetic recording medium surface and the length direction of the MR element pattern on the output value of the magnetic encoder was investigated, and the results shown in FIG. 7 were obtained. As the MR element pattern tilts, the output becomes smaller, and α becomes tan-'(-!!'-!
-) <a≦90°.

The pitch of the magnetization pattern is in the rotational direction, whereas the MR
The stripe width direction of the element is the magnetization pattern column direction, and since a magnetic field is applied in the stripe width direction, it is not affected by the demagnetizing field, the pattern width W can be made small, and the pitch P is not limited by the pattern width W. Furthermore, since the stripes may be folded back at the same bit position (same pattern row), the width of the magnetized pattern row can be narrowed without lowering the resolution.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of an embodiment of the absolute magnetic encoder of the present invention, and FIG. 2 is a diagram showing how the leakage magnetic field H from the magnetic field pattern in FIG. 1 is perpendicular to the sense current flowing through the MR element pattern. , FIG. 3 shows the magnetization pattern n1
．． n2. A diagram showing the output voltage for n3, Figure 4 is MR
FIG. 5 is a detailed diagram of the element 5, and FIG. 5 is a diagram showing the relationship between the output voltage and bit length in this embodiment in comparison with the conventional example. FIG. 6 is a diagram showing the relationship between the output voltage and spacing in this embodiment in comparison with the conventional example. It is a figure shown by comparison.

As shown in FIG. 1, this embodiment includes a drum 2 fixed to a rotating shaft 1, a magnetic recording medium 3 formed on the side surface of the drum 2, an MR element 5 and a conductor terminal 6 formed on a substrate 4. The drive detection circuit 8 has a lead wire 7 connected to a conductor terminal 6 and an output terminal to the outside. Five magnetization pattern arrays nl'''n5 are written on the magnetic recording medium 3 as shown by arrows in FIG. In other words, as shown in FIG. 2, the leakage magnetic field H from the magnetic recording medium 3 is orthogonal to the sense current flowing through the MR element pattern, and thereby acts on the magnetization pattern "+ + "2 + n3, respectively. Resistance changes, that is, output voltages, as shown in Figures 3(a), (b), and (c) are obtained.If the voltage near the center of the rising/falling portion of this signal is used as a threshold value and pulsed, the Figure 3 (d), (e), and (f) show the results, and from the combination table of these pulses (Figure 3 (g)), addresses are assigned in units of minimum reading angle Δθ, and the pulse output at each point is The absolute position can be determined from this.Here, if the number of magnetization pattern rows is n, the minimum reading angle θ is 380' Δθ=□ n .

Therefore, the minimum bit length p of the nth column is given by r, which is the radius of the drum 2.

A drum made of aluminum with a diameter of 2 (1 mm) and a height of 8 m IN+ was coated with a Ba-ferrite film to a thickness of 100 mm on the outer periphery, and was formed using a magnetizing head with magnetization patterns having various bit lengths p. The width of one row of magnetization pattern is 3
It was set as 00 tiles. This drum has a width of 20 mm as shown in Figure 4.
Scales, length 250μ pattern repeated 8 times, total length 2
, the relationship between the output voltage and the bit length p was investigated in combination with an MR sensor with a diameter of 2 mm. The sensor film thickness was set to 600 people. As shown in FIG. 5, in this embodiment, the limit of 20
Even below the scale, the output voltage is sufficiently higher than the nozzle level, indicating that high resolution is possible. Since the thickness of an MR sensor is normally 600 mm, in the structure of this embodiment, the minimum bit length is determined to be about twice this thickness. In addition, in this structure, the width of each row of MR element pattern stripes is 250 ul in this example compared to the conventional 211 Im.
This becomes approximately 178, which can be further reduced by narrowing the MR element pattern width. In other words, it can be made smaller.

Next, the influence of the distance g between the drum and the sensor on the output value was compared with that of the conventional example, and the results shown in FIG. 6 were obtained. Since the output fluctuation is small with respect to a change in the distance g, the tolerance range for the distance 111Jg is widened, and as a result, the finishing of the drum and the mounting of the MR sensor do not have to be very precise. FIG. 8 is a perspective view showing another embodiment of the present invention.

Figures (a) and (b) show Fe-Go-Cr magnets attached to the drum and disk, and figure (C) shows a non-magnetized part between the magnetized pattern rows, and further magnetization of adjacent comrades. The example in which the direction is reversed (FIG. 2(d)) uses Go and -Cr perpendicular magnetization films. It is clear that these have the same effect as the embodiment shown in FIG.

(Effects of the Invention) As explained above, the present invention provides an angle α between the length direction of the stripe of the magnetoresistive element and the surface line direction of the substrate at the closest point to the substrate by j a n −' (” By setting the stripe direction parallel to the magnetization pattern row direction and applying the magnetic field from the magnetization pattern in the width direction of the strip drive, the minimum position reading unit can be made small. Since the width of the magnetization pattern row can be made small, it is possible to manufacture a compact high-resolution encoder.Furthermore, since the output change with respect to the spacing variation is small, assembly and processing precision are not required, so the price can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the absolute magnetic encoder of the present invention, and FIG. 2 is a diagram showing how the leakage magnetic field H from the magnetic field pattern in FIG. 1 is perpendicular to the sense current flowing through the MR element pattern. , Figure 3 shows the magnetization pattern "I"
+”2 Diagram showing the output voltage for n3, 4th
The figure is a detailed diagram of the MR element 5, FIG. 5 is a diagram showing the relationship between the output voltage and bit', -1% p in this embodiment in comparison with the conventional example, and FIG. 6 is a diagram showing the relationship between the output voltage in this embodiment and A diagram showing the relationship between spacing g in comparison with a conventional example, FIG. 7 is a diagram showing the relationship between output voltage and θ in the present invention, FIG. 8 is a diagram showing another embodiment of the present invention, and FIG. 9 1 is a diagram showing a conventional example. 1...rotating shaft, 2...drum, 3...
・Magnetic recording medium, 4... Substrate, 5... MR element, 6... Conductor terminal, 7... Lead wire,
8... Drive detection circuit.

Claims (1)

[Scope of Claims] A base body having at least two rows of magnetization patterns corresponding to the required position reading accuracy, and a magnetic stripe arranged in each magnetization pattern row to detect magnetic fields leaking from the base body. In an absolute magnetic encoder that reads out the absolute position, that is, the address, of the base by a combination of resistive elements, the stripe length of the magnetoresistive element is l, the closest distance between the base and the magnetoresistive element is g, and the position is read. When the unit is p, the angle α between the stripe length direction of the magnetoresistive element and the substrate surface surface line direction at the nearest portion is ta.
The range is from n^-^1[(l+g)/p] degrees to 90 degrees, the stripe width direction is parallel to the magnetization pattern column direction, and the magnetic field from the magnetization pattern is applied in the stripe width direction. Features: Absolute position detector.