JPH08145718A - Magneto-resistive sensor - Google Patents

Abstract

PURPOSE: To eliminate third higher harmonic noise and improve resolution by identifying the element number of MR elements constituting MR(magnetic resistance effect) elements and the arrangement intervals of the MR elements. CONSTITUTION: A magnetic memory 6, for example, is wire-shaped and is formed by using a Fe-Cr-Co material. In addition, an MR sensor 5, four MR elements 1 to 4 are connected, and a differential movement circuit is constituted. And, MR elements R1 to R3 are formed in the linear shape with line width of 20μm from Permalloy tin film, intervals of the elements R1 to R3 is M=1 in a formula λ*M+ΔL (in the formula, λ is wavelength corresponding to 1/2 of an arrival magnetic pitch of a body to be detected, M is integer of 1 or more, and ΔL expresses the conventional interval), and in ΔL=λ(3*K), λis determined as 30μm of 1/2 of an arrival magnetic pitch of 60μm and the number of elements K is determined as 3. Thus, MR sensor can be easily constituted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetoresistive (hereinafter abbreviated as MR) sensor used in a magnetic encoder for detecting the number of revolutions, the position and the like.

[0002]

2. Description of the Related Art A magnetic encoder used for rotation and position detection in a field of industrial machines using a servomotor has become smaller and higher in density because an MR sensor unit and a circuit unit are integrated with the development of a microcomputer in recent years. There is. In particular, high-precision resolution is required, and various MR element patterns and circuit configurations have been proposed. In this case, what is important is that the output from the MR sensor is a clean sine wave. This is because the output of the MR sensor is divided by the circuit portion, and when the calculation is performed by dividing one wavelength λ, the calculation is based on the sine wave.

Conventionally, the configuration as shown in FIG. 1 has eliminated even-order harmonic components and third-order harmonic components.

In FIG. 1, reference numeral 6 denotes a magnetic memory as an object to be detected which constitutes a magnetic encoder. Specifically, it is constituted by a straight wire or a magnetic tape, for example.
It is magnetized at a predetermined magnetizing pitch (pitch between N poles or S poles), and in this case, 1/2 of the magnetizing pitch
Can be regarded as the wavelength λ of the leakage magnetic field.

Reference numeral 5 is an M which constitutes a magnetic encoder.
The R sensor is provided on a substrate (not shown) and is moved along the magnetic memory 6 to detect the magnitude (absolute value) of the magnetic field of the magnetic memory 6.

The MR sensor 5 is configured as the differential circuit shown in FIG. 2 by connecting four MR elements 1 to 4. That is, two MR elements 1, 2, 3 and 4 connected in series are connected in parallel.

Each of the MR elements 1 to 4 is constructed by connecting MR element elements R1 to R3 in series. The MR element elements R1 to R3 are formed in a linear pattern as a ferromagnetic thin-film resistor that detects a magnetic field and exhibits a change in electric resistance value. The MR element elements R1 to R3 face the magnetic memory 6 and are magnetized in a magnetic direction (from the magnetic poles). They are arranged at intervals of ΔL in the direction toward the magnetic poles and in the longitudinal direction of the magnetic memory 6.

The phases of the MR elements 1, 2, 3 and 4 are reversed, and a differential output voltage is generated at a midpoint e1 between the MR elements 1 and 2 and a midpoint e2 between the MR elements 3 and 4. . Midpoint e1, e
The output of 2 is guided to an amplifier (not shown), and its differential output is amplified and taken out.

Next, the removal of harmonic components in the above configuration will be described.

In FIG. 1, the magnetic element 6 is magnetized at the wavelength λ, and the head MR element element R1 of the MR element 1 coincides with the position of the code P, that is, the position of the N pole.
The respective positions of the MR element elements R1 at the head of the MR elements 2 to 4 coincide with the positions from the N pole to 1 / 2λ, the S pole, and the S pole to 1 / 2λ, respectively.

In this case, when a plurality of MR element elements are connected in series and the output waveform is converted to a sine wave, the elements may be arranged with a distance of ΔL = λ / (3 * K). Here, K is the number of MR element elements connected in series which constitute each MR element, and 3 is the order of the harmonic wave to be eliminated. Since the lower harmonics are larger, the second and third harmonics are generally problematic, but the even harmonics have three terminals and the MR elements 1 and 2 or the MR elements 3 and 4 are out of phase by 180 °. Therefore, it does not occur. Therefore,
In the case of the circuit (1), the odd-order harmonic noise is a problem, and the purpose is to eliminate the third-order harmonic having the largest absolute value.

The reason why the above equation ΔL = λ / (3 * K) is set will be described with reference to FIGS. FIG. 4 shows a simplified circuit of the MR elements 1 and 2 in FIG. As described above, the MR element elements R1 to R of the MR elements 1 and 2
Three 3 are arranged in series.

MR element elements R1, R2 and R3 3
When the third harmonic is extinguished with a book, the magnetoresistive component ΔR of the element R1 within 2π of one wavelength of the third harmonic as shown in FIG.
1, R2 magnetic resistance ΔR2, R3 magnetic resistance ΔR3
May be set at an angle of 2π / 3 so that the combined waveform becomes zero. This time, the case where three MR element elements are connected in series is shown, but if it is set to four, for example, 2π (1
If the angle is shifted by (wavelength) / 4 = π / 2, the combined waveform of the third harmonic becomes zero.

Next, when the third harmonic wave is converted into the fundamental wave phase, the phase of the fundamental wave is 1/3 times the phase of the third harmonic wave, so when divided by 3, it is between ΔR1 and ΔR2 and between ΔR2 and ΔR3.
The angle between them is 2π / 9, as shown in FIG. When four MR element elements are connected in series, the angle is π / 6.

Therefore, in order to eliminate the third harmonic component, one wavelength λ corresponding to the phase 2π of the fundamental wave is divided by the harmonic order 3, and further divided by the number of MR element elements to obtain the fundamental phase. The size of the interval ΔL by which the arrangement of the MR element elements is shifted is determined. In the configuration of FIG. 1, the arrangement of the MR element elements is determined in this way.

[0016]

In the conventional magnetic encoder, since the wavelength λ of the magnetic field described above can be set relatively long, a plurality of MRs are arranged in one wavelength λ as shown in FIG.
By arranging the element elements at intervals of ΔL and connecting them in series, the third harmonic noise could be eliminated.

However, in recent years, the resolution of magnetic encoders has become higher in density, and it has been required to shorten the magnetization pitch of the magnetic memory to shorten the wavelength λ, or to divide the output of the MR sensor into high-divided circuits. Has been done. If the wavelength λ is shortened, it becomes difficult to form an MR sensor by forming a plurality of MR element elements within one wavelength λ as shown in FIG. Further, when the output of the MR sensor is highly divided by a circuit, there is a problem that the higher the division, the larger the circuit becomes and the more expensive, and the absolute value accuracy of the resolution is not good.

Therefore, an object of the present invention is to provide an MR sensor capable of eliminating third-order harmonic noise with a configuration in which MR element elements are arranged at intervals larger than the wavelength λ of the magnetic field to be detected, and a magnetic encoder using the MR sensor. An object of the present invention is to provide an MR sensor that can shorten the magnetization pitch and improve the resolution.

[0019]

In order to solve the above problems, according to the present invention, a plurality of MR element elements made of ferromagnetic thin film resistors are arranged at a predetermined interval and connected in series. In an MR sensor that is configured by connecting two in series and detects the magnitude of the leakage magnetic field of wavelength λ corresponding to 1/2 of the magnetization pitch of the object to be detected, M is an arbitrary integer of 1 or more, K Is the MR that constitutes each of the MR elements
Assuming that the number of element elements is ΔL = λ / (3 * K), the arrangement interval of the MR element elements is λ * M +
A configuration that is ΔL was adopted.

[0020]

According to this structure, since the MR element element spacing is λ * M + ΔL, the positional deviation of each element corresponds to ΔL = λ / (3 * K) as in the conventional example. The combined waveform of the magnetoresistive component of each element with respect to the third harmonic becomes 0, and the third harmonic can be erased. Moreover, the interval λ * M + ΔL is λ * M, that is, M wavelengths are larger than the conventional interval ΔL, and the interval λ * M + ΔL is 1 between M wavelengths.
Since it is sufficient to form the MR element of the book, the MR sensor can be easily configured and the magnetization pitch can be shortened even if the magnetization pitch of the object to be detected is short and the wavelength λ is short.

It should be noted that the noise can be eliminated more accurately as the number K of elements increases. For example, in the case of erasing with K = 2, if the position of the second element is displaced, the third harmonic component remains due to the displacement. On the other hand, if the number of lines is increased, the deviation of one line is alleviated by the remaining number of lines, and the remaining noise for the third harmonic is reduced. Further, in terms of the ratio of the fundamental wave to the third harmonic, that is, the distortion factor, the more the number is, the stronger the displacement of the element or the variation of the output of each element becomes. However, as the number of sensors increases, the size of the entire sensor increases, so it is necessary to make a decision at a certain compromise.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows the configuration of an embodiment of the present invention. In FIG. 3, the magnetic memory 6 is formed, for example, in the shape of a wire using a Fe—Cr—Co material. The reason is that as the magnetization pitch becomes finer, the smaller the linear expansion coefficient of the magnetic memory, the higher the reliability of the absolute value under various temperature environments. For that purpose, a ferrite magnet made of ceramics having a small linear expansion coefficient but having a weak mechanical strength is ideal, and a plastic magnet or a coating medium coated with magnetic powder is not preferable. Metal is better than plastic. The magnetic memory 6 made of the Fe—Cr—Co material was magnetized at a pitch of 60 μm, which is higher in density than the conventional example shown in FIG.

Further, in FIG. 3, the MR sensor 5 is formed by connecting four MR elements 1 to 4 so as to form the differential circuit of FIG. 2 as in the conventional example of FIG. Also, M
Each of the R elements 1 to 4 is configured by connecting three MR element elements R1 to R3 as ferromagnetic thin film resistors in series, as in the conventional example.

The MR element elements R1 to R3 are formed from a permalloy thin film in a linear shape with a line width of 20 μm, and are opposed to the magnetic memory 6 and are arranged at predetermined intervals in the magnetizing direction of the magnetic memory 6.

Here, the interval of the arrangement of the MR element elements R1 to R3 is ΔL = λ / (3, where M is 1 in the formula λ * M + ΔL described in the section for solving the problem.
* K) is 30 which is ½ of the magnetizing pitch of 60 μm
μm and the number of elements K were determined to be 3.

That is, ΔL = 30/3 * 3 = 3.33
Since it is μm, the distance between elements is 1 wavelength λ30μ.
m + 3.33 μm. As a result, as shown in FIG. 3, in each of the MR elements 1 to 4, the head (left end) is
The second element R2 with respect to the MR element element R1 is located at a distance of one wavelength λ + ΔL1 to the right, and Δ
L1 is 3.3 μm. Also the third element R3
Is located at a distance of 2λ + ΔL2 to the right from the leading element R1, and ΔL2 is 6.6 μm.

According to this structure, the third harmonic noise can be eliminated due to the phase shift caused by ΔL as described in the section of the operation. Further, since it is sufficient to form one MR element element within one wavelength λ, the magnetizing pitch is as short as 60 μm, and even if the wavelength λ is short, the MR sensor can be easily constructed and the magnetizing pitch can be made smaller than the conventional one. It can be shortened significantly to improve the detection resolution. Also, to improve resolution, M
It is not necessary to divide the output of the R sensor into high divisions, and the division may be about two or three divisions, and the division circuit can be a small scale and inexpensive one.

Incidentally, the output of the MR sensor 5 of this embodiment was divided into three by a dividing circuit, and finally an encoder having a position accuracy of 10 μm was produced. Observing the output of this final stage, almost no harmonic components were detected.

In the above embodiment, M is set to 1 in the equation λ * M + ΔL which determines the spacing between MR element elements, but it is needless to say that M may be an integer of 2 or more.

Although the MR sensor is constructed by connecting the series connection of the MR elements 1 and 2 and the series connection of the MR elements 3 and 4 in parallel, only the series connection of the MR elements 1 and 2 or the MR The MR sensor can be configured only by connecting the elements 3 and 4 in series.

[0032]

As is apparent from the above description, according to the present invention, a plurality of MR element elements made of ferromagnetic thin film resistors are arranged at a predetermined interval and connected in series.
In an MR sensor that is configured by connecting two elements in series and detects the magnitude of a leakage magnetic field having a wavelength λ corresponding to ½ of the magnetization pitch of the object to be detected, M is an arbitrary integer of 1 or more,
K is the number of MR element elements forming each of the MR elements, and ΔL = λ / (3 * K)
Since the arrangement interval of the element elements is λ * M + ΔL, the third harmonic noise can be eliminated by the arrangement of the MR element elements at an interval larger than the wavelength λ, and a magnetic encoder using an MR sensor can be used. The magnetization pitch of the object to be detected can be significantly shortened compared to the conventional one, and the resolution can be improved. Further, it is not necessary to divide the output of the MR sensor into a large amount for improving the resolution, and the excellent effect that a small dividing circuit and an inexpensive one can be used can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a conventional MR sensor and a magnetic memory.

FIG. 2 is a circuit diagram showing a differential circuit formed by an MR sensor.

FIG. 3 is an explanatory diagram showing a configuration of an MR sensor according to an embodiment of the present invention.

4 is a circuit diagram of MR elements 1 and 2 in FIG.

FIG. 5 is an explanatory diagram of a phase for eliminating a third harmonic in the MR element.

FIG. 6 is an explanatory diagram showing a case where the phase of FIG. 5 is converted into the phase of a fundamental wave.

[Explanation of symbols]

 1 to 4 MR element 5 MR sensor 6 magnetic memory R1 to R3 MR element element Vcc power supply voltage G ground

Claims (1)

[Claims] 1. An object to be detected, wherein a plurality of magnetoresistive effect element elements made of a ferromagnetic thin film resistor are arranged at a predetermined interval, and two magnetoresistive effect elements connected in series are connected in series. In the magnetoresistive effect sensor for detecting the magnitude of the leakage magnetic field of wavelength λ corresponding to ½ of the magnetizing pitch of M, M is an arbitrary integer of 1 or more, and K is the magnetic field of each of the magnetoresistive elements. Assuming that the number of resistance effect element elements is ΔL = λ / (3 * K), the arrangement interval of the magnetoresistive effect element elements is λ *
A magnetoresistive effect sensor characterized by being M + ΔL.