JPH08285509A - Linear type magnetic sensor - Google Patents

Abstract

PURPOSE: To improve the output characteristic of a magnetoresistance effect (MR) sensor and also to enable miniaturization of the sensor by making the length of a stripe-shaped pattern of the sensor element smaller substantially than the dimensions of a rod-shaped magnetic scale. CONSTITUTION: In an MR sensor element 20, a stripe-shaped pattern being a part of which the electric resistance is changed by impression of a magnetic field is formed on a nonmagnetic base 21 and so disposed as to be opposite to a magnetized track of a magnetic scale 30. The magnetic scale 30 is prepared by machining an iron-chromium-cobalt series rolled magnet and by subjecting it then to heat treatment and position signals of N and S poles are written therein in the longitudinal direction. A flexible printed board 22 is connected electrically to terminal electrodes 24 and 26 and further to a connection terminal part 28. The length L of the stripe-shaped pattern of the MR sensor element 20 is made smaller than the dimensions of the magnetic scale 30. Thereby a part wherein the electric resistance due to a magnetoresistance effect does not change is eliminated and a sensor output can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic position detecting device utilizing the magnetoresistive effect of a ferromagnetic thin film, and more particularly to a structure of a linear magnetic sensor which has good sensitivity and is suitable for miniaturization. is there.

[0002]

2. Description of the Related Art A sensor that is used under severe environmental conditions such as a large amount of dust and high humidity and high temperature is required to have high reliability and excellent durability. For example, as a position detection method, there is an optical method in which a scale having glass slits is used, and intermittent light of a light emitting diode is detected by a phototransistor to obtain position information. In this optical method, since the light-emitting diode and the phototransistor are semiconductors, the operating temperature range on the high temperature side is limited by the junction temperature, and further dust and the like are likely to adhere to the glass scale and dew condensation at high humidity may occur. However, a special seal is required for the scale and the sensor element, which results in a complicated structure, resulting in problems in reliability and cost.

For this reason, the magnetic type has attracted attention as an alternative to the optical type, and various structural configurations have been developed and put into practical use. Conventionally, rotation angle detection has been the mainstream, but a magnetic linear sensor that can simplify the detection mechanism and can avoid the influence of backlash and the like for position detection of an object that moves linearly is an OA device. Is beginning to be used heavily in printer heads.

FIG. 4 shows a schematic structure of a magnetic linear sensor. On the rod-shaped magnetic scale 30, periodic position signals N and S poles are magnetized at a pitch λ in the length direction. The MR sensor element 20 is arranged to face this. In this figure, the MR sensor element 20 is fixed to a holding device (not shown) and has a mechanism (not shown) that moves parallel to the magnetic scale 30 while maintaining a constant gap. The magnetic position signal written on the magnetic scale 30 is converted into an electric signal by the MR sensor element 20, and the MR signal is converted using a flexible cable 22 or the like.
It can be taken out of the sensor element.

Next, the operating principle of the MR sensor element will be described with reference to FIGS. In FIG. 5, a ferromagnetic thin film such as Permalloy is formed on a non-magnetic substrate (not shown) such as glass to form a strip-shaped sensor pattern as shown in the figure. The magnetically sensitive portion, that is, the portion where the electric resistance changes due to the application of the magnetic field is the elongated portion L of the stripe pattern, which is represented by the equivalent resistances _Ra , _Ra ', _Rb and _Rb '. MR using ferromagnetic thin film made of permalloy
In the sensor element, when a magnetic field of about 100 Oersted is applied, the electric resistance changes by several percent.

[0006] Looking at the arrangement of the stripe pattern corresponding to the R _a and R _a 'The R _b and R _b', but away each interval magnetization pitch λ as shown in FIG, and R _a ' The array is separated from R _b by λ / 2. R _a and R _a ′ are connected in series by a connecting part 27, R _b and R _b ′ are connected in series by a connecting part 29, and the other ends of R _a ′ and R _b are electrically connected by a connecting part terminal 28. Has been done. Next, by connecting a constant DC voltage to the terminal electrodes 24 and 26, it operates as an MR sensor element. The equivalent circuit of this MR sensor element can be shown as in FIG.

As shown in FIG. 5, if R _a and R _a ′ move to the center of the N pole and R _b and R _b ′ move to the boundary between the N and S poles, then R _a and R _a Since the leakage magnetic flux as a position signal from the magnetic scale does not reach ('the magnetic field strength is zero), the electric resistance does not change, but conversely, R _b and R _b ' have a position signal as a position signal. The maximum magnetic field is applied, and as a result, the electric resistance is minimized, and the minimum potential is obtained at the connection terminal portion 28.

When the position of the MR sensor element moves and the positional relationship between R _a and R _a 'and R _b and R _b ' is reversed with respect to the position shown in FIG. 5, on the contrary, R _a and R _a ' Although the electric resistance is the minimum, the electric resistances of R _b and R _b ′ do not change, that is, have the maximum value, so that the connection terminal 28 is in the maximum potential state. The potential between this minimum and maximum changes in a substantially sinusoidal manner. The position signal of the magnetic scale can be detected as a pulse train signal by extracting the change in the potential from the connection unit 28 and guiding it to the amplifier and the waveform shaping circuit 1.

[0009]

The conventional linear magnetic sensor has low sensor efficiency, that is, sensor detection output, and
The configuration was not very suitable for miniaturization. This is M
Since the R sensor element is formed on the non-magnetic substrate, it has a flat plate shape. On the other hand, since the magnetic scale has a round bar shape, the track on the magnetic scale magnetized with the position signal has a curved surface, so that it is attached to the magnetic scale. The leakage flux of the magnetized position signal could not be used effectively. For example, the actual Kaihei 4-9
As disclosed in Japanese Patent No. 4514, it is proposed that the stripe pattern length is selected to be 1 to 1.5 times the magnetic scale, but it depends on many years of experience of the inventors of the present application and accumulated data. And with such a configuration, MR
The sensor element becomes large. Furthermore, when such a configuration is adopted, it is difficult to obtain a sufficiently large detection output because the leakage flux of the position signal does not reach over the entire stripe-shaped pattern that is the magnetic sensing section, and the range in which the sensor is used, There were restrictions on the conditions.

[0010]

In order to solve the problems of the conventional linear type magnetic sensor described above, it has been conceived to make the stripe pattern length of the MR sensor shorter than the outer dimension of the rod-shaped magnetic scale. To add further,
It has been found that the sensor efficiency is optimized if the position signal track width of the magnetic scale is equal to or less than the length projected on the MR sensor surface. Further, if the magnetic scale is composed of an iron-chromium-cobalt-based rolled magnet, the effect of the present invention can be brought out more.

[0011]

In a magnetic tape or magnetic disk device, the track width for recording / reproducing information is generally set wider than the track width of the magnetic head which is the detecting element. This is because the opposing portions of the magnetic recording medium and the magnetic head are planarly opposed to each other, so that the recording magnetic field has a two-dimensional distribution and the track deviation due to the error of the servo mechanism and the control circuit is prevented. . According to the present invention, when the position signals N and S poles are alternately magnetized in the longitudinal direction on a rod-shaped magnetic scale, the leakage magnetic flux as the position signal is three-dimensionally distributed, and the stripe pattern length is considered. This is the result of studying and finding a method for determining. As proposed in the present invention, by selecting the stripe pattern length of the MR sensor, it is possible to effectively and efficiently receive the leakage magnetic flux from the magnetic scale.

Further, when the effective magnetic flux distribution area in the magnetized track width direction of the magnetic scale on the MR sensor element surface is measured, if the track width is within the range of the length projected on the sensor element surface, the MR sensor element It was found that a stray magnetic field as a position signal was sufficiently added to the stripe pattern. In order to obtain the further effect of the present invention, the iron-chromium-cobalt-based rolled magnet material is applied to the magnetic scale. Compared to ferrite-based or rare earth-based magnets, iron-chromium-cobalt-based rolled magnets have appropriate coercive force, residual magnetic flux density, and demagnetization characteristics when magnetized as a position signal on the magnetic scale. This fact is confirmed experimentally.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment according to the present invention. In this figure, the same numbers are used for the same parts used in FIGS. The MR sensor element 20 has the sensor pattern described in the conventional example formed on the non-magnetic substrate 21, and is arranged so as to face the magnetized track of the magnetic scale 30. The magnetic scale 30 is made by rolling an iron-chromium-cobalt-based rolled magnet into a diameter of 4 mm, and then heat-treating it at an appropriate temperature to magnetize a longitudinal pitch λ = 200 μ.
Position signals of north and south poles were written in m. The flexible printed circuit board 22 is electrically coupled to the terminal electrodes 24 and 26 and the terminals of the connecting portion 28.

As shown in FIG. 1, the stripe pattern length L of the MR sensor element is shorter than the outer dimension D of the magnetic scale 30. M for the gap length in this case
The R sensor output characteristic is shown in FIG. It can be seen from the figure that the characteristic of the broken line is the conventional example, and the sensor output can be improved by the present invention shown by the solid line. With the conventional sensor configuration,
The ratio of the portion where the position signal magnetic field does not effectively reach was large in the lengthwise direction of the stripe pattern. For this reason,
Although the sensitivity of the MR sensor element is reduced by the stripe-shaped pattern portion that does not contribute to the magnetoresistive effect, the present invention can eliminate the portion where the electric resistance due to the magnetoresistive effect does not change, thereby increasing the sensor output. be able to.

Next, FIG. 2 shows the relationship between the magnetized track width T _W of the magnetic scale and the stripe pattern length L. The magnetized track width T _{W is set} to the MR sensor element 2
When projected onto the surface of 0, it is T _W '. If the relationship of T _W '> L is satisfied, a strong magnetic field from the magnetic scale can be received by the entire stripe pattern. On the contrary, if L is made longer than T _W ', L of the stripe pattern is
The portion of the -T _W 'difference of the magnetic field intensity from the magnetic scale is increased, resulting in the sensor output is reduced.

[0016]

As is clear from the detailed description of the above embodiments, according to the present invention, the output characteristics of the MR sensor can be improved as compared with the prior art, and the MR sensor element can have an optimum structural size. It is possible to achieve the effect of reducing the size of the sensor.

[Brief description of drawings]

FIG. 1 is a configuration of an MR sensor element and a magnetic scale according to the present invention.

FIG. 2 is another embodiment according to the present invention.

FIG. 3 is an output characteristic of the MR sensor.

FIG. 4 is a configuration of a conventional MR sensor.

FIG. 5 is a diagram showing the operating principle of the MR sensor.

FIG. 6 is a diagram showing an equivalent circuit of an MR sensor.

[Explanation of symbols]

1 amplifier and waveform shaping circuit, 20 MR sensor element,
21 non-magnetic substrate, 22 flexible cable, 24
Terminal electrode, 26 terminal electrode, 27 connecting part, 28 connecting terminal part, 29 connecting part, 30 magnetic scale

Claims (5)

[Claims] 1. A magnetoresistive effect sensor element (hereinafter abbreviated as MR sensor element) having a round bar-shaped magnetic scale in which a position signal is written in the longitudinal direction and a stripe pattern of a ferromagnetic thin film formed on a non-magnetic substrate. ) And the above M
In a linear magnetic sensor in which an R sensor element is arranged in contact with the magnetic scale in a non-contact manner to detect a position signal of the magnetic scale, the stripe pattern length of the MR sensor element is the outer dimension of the magnetic scale. A linear magnetic sensor characterized by being substantially shorter. 2. The linear magnetic scale according to claim 1, wherein the stripe-shaped pattern length of the MR sensor element is in the range of 0.5 to 0.9 times the outer dimension of the magnetic scale. And linear magnetic sensor. 3. The linear magnetic scale according to claim 1, wherein the stripe-shaped pattern length of the MR sensor element is equal to or larger than the radius of curvature on the facing surface side of the magnetic scale and is 2 or more.
A linear magnetic sensor characterized by being in a range of less than double. 4. The linear magnetic scale according to claim 1, wherein a stripe pattern length of the MR sensor element is a track width of a position signal magnetized on the magnetic scale on the MR sensor element surface. A linear magnetic sensor having a length equal to or less than the orthogonal projection length. 5. The linear magnetic sensor according to claim 1, wherein the magnetic scale is an iron-chromium-cobalt rolling magnet.