JPH05288569A - Magnetic encoder - Google Patents

Abstract

PURPOSE:To provide a magnetic encoder whose mechanism is simple and characteristics can be stabilized easily/highly accurately and which is suitable for mass-productivity at low cost. CONSTITUTION:A magnetic encoder is composed of a magnetic recording medium 1 and magnetic resistance effect elements 2 arranged oppositely on the magnetic recording medium 1. A magnetic resistance element 2 is divided into two or more parts, and patterns of the respective magnetic resistance effect elements 2 are approximately in parallel with the magnetic recording medium 1, and the respective magnetic resistance effect elements 2 are also approximately in parallel with each other, and are arranged at an interval (d) expressed by a formula.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic encoder for detecting a position by reading a magnetic signal recorded on a magnetic recording medium by a magnetoresistive effect element (hereinafter referred to as MR effect element).

[0002]

2. Description of the Related Art In recent years, an encoder, which is one of analog-digital (AD) converters for converting mechanical quantities such as rotation, position, displacement, movement, and angle into digital quantities, is a speed control for machine tools. , The positioning of cutting tools, the behavior control of robot arms, and the mechanical parts that require advanced positioning in combination with servo motors such as floppy disk drives, printers, and copiers.

This encoder is classified into an optical type and a magnetic type depending on a mechanical quantity detection method, and a magnetic type (magnetic encoder) excellent in frequency response and environment resistance gradually establishes its market due to its superiority. I am doing it.

A conventional magnetic encoder will be described below. FIG. 3 is a schematic diagram of a conventional magnetic encoder.

Reference numeral 3 denotes a magnetic recording medium which is multipolarly magnetized so that a leakage magnetic field is generated in the moving direction according to the position reading accuracy, and 4 is a position which is apart from the magnetic recording medium 3 by a certain distance (hereinafter referred to as a gap). The MR effect element is arranged such that the width direction of the pattern is parallel to the surface of the magnetic recording medium 3, and the arrow indicates the magnetization direction. The pattern of the MR effect element 4 is obtained by depositing a ferromagnetic MR effect thin film on a substrate such as glass,
It is produced by etching to a width of several to several tens of μm and a length of several mm.

The position detection of the conventional magnetic encoder configured as described above is performed by detecting the position fluctuation of the magnetic recording medium 3 as the resistance change of the MR effect element 4.

[0007]

However, in the above-mentioned conventional structure, the resistance change characteristic of the MR effect element largely depends on the gap between the magnetic recording medium and the MR effect element, and therefore a high level of technique is required for its adjustment. There was a problem that it was difficult to use. Also, the mechanism for adjusting the gap is complicated,
In addition, it is extremely difficult to stabilize the characteristics.

On the other hand, in order to overcome this problem, the contact type magnetic encoder which realizes no adjustment of the gap at the time of assembly by changing the conventional non-contact type to the contact type of the detecting portion constituted by the MR effect element. Has been partially developed, it is indispensable to adhere a protective layer such as a sintered alumina film to the surface of the contact portion with the magnetic recording medium for mechanical protection of the MR effect element. Since it is extremely difficult to control, the productivity is poor, and the characteristics fluctuate due to variations in the thickness of the adhesive layer, so that it is difficult to stabilize the characteristics and the accuracy is poor.

The present invention solves the above-mentioned conventional problems, and provides a magnetic encoder having a simple mechanism, capable of easily stabilizing the characteristics with high accuracy, at low cost, and suitable for mass production. The purpose is to

[0010]

In order to achieve this object, a magnetic encoder according to the present invention is a magnetic encoder comprising a magnetic recording medium and a magnetoresistive effect element arranged so as to face the magnetic recording medium. In addition, the magnetoresistive effect element is composed of two or more, the pattern of each magnetoresistive effect element is substantially parallel to the magnetic recording medium, and each magnetoresistive effect element is substantially parallel to each other. It has a configuration in which it is arranged at an interval d.

[0011]

With this structure, it is possible to arrange the MR effect element at an optimum position for stabilizing the MR effect element with respect to the magnetic field strength received from the magnetic recording medium. Can be stabilized. As a result, the position detection function can be stabilized with high accuracy.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view of a magnetic encoder which is an embodiment of the present invention. 1 is a magnetic recording medium, 2 is 2
It is an MR effect element which is divided into two parts and is arranged substantially parallel to each other at an arrangement distance d, and the pattern thereof is parallel to the magnetic recording medium 1 and arranged at a distance (gap) D from the magnetic recording medium 1. still,
Two different MR effect elements 2 may be prepared and arranged.

In this embodiment, a magnetic recording medium 1 and an MR effect element 2 having the characteristics shown in (Table 1) and (Table 2) were prepared.

[0015]

[Table 1]

[0016]

[Table 2]

A protective layer made of a sintered alumina thin plate is attached to the MR effect element 2 and slides in contact with the magnetic recording medium 1 through the protective layer. This MR effect element is divided into two, and they are arranged at an interval given by (Equation 1) described below, d≈20 μm (optimum value in the average thickness of the protective layer) in this embodiment.

In this embodiment, the magnetic recording medium 1 to MR
The optimization of the arrangement of the MR effect element 2 with respect to the magnetic field strength received by the effect element 2 is set by the following equation.

The resistance change characteristic (MR characteristic) of the MR effect element 2 can be expressed by the approximate expressions shown in (Equation 2) and (Equation 3).

[0020]

[Equation 2]

[0021]

[Equation 3]

Here, ρ / ρmax; resistance change rate H; magnetic field strength Hs received by MR effect element; split Hk of MR characteristic; coefficient x showing spread of MR characteristic; moving direction distance; and multipole attachment at equal intervals. The magnetic field strength H that the MR effect element 2 receives from the magnetized magnetic recording medium 1 can be approximated by the cosine wave (or sine wave) of (Equation 4).

[0023]

[Equation 4]

Here, Hm; maximum magnetic field strength λ; distance between magnetic poles (x direction) z; gap direction distance Therefore, M when the magnetic recording medium 1 moves in the x direction
It can be seen that the resistance change characteristic of the R effect element 2 is obtained by substituting (Equation 4) into (Equation 2) and (Equation 3), and is a function of λ / 4 period for x. Further, by partially differentiating this resistance change characteristic with z, the gap dependency can be obtained, and it was found that the characteristic is a monotonically decreasing characteristic with respect to z.

Next, the MR resistance change characteristics when the two MR effect elements 2 are arranged at the interval (d) so as to face the magnetic recording medium 1 are given by using (Equation 2) to (Equation 4). , (Equation 5)
You can see that is required.

[0026]

[Equation 5]

Therefore, the position (x =
The characteristic in (0) is (Equation 5), substituting x = 0,
It is represented by (Equation 6).

[0028]

[Equation 6]

Next, using the magnetic encoder of this embodiment,
The gap dependence of the maximum resistance change was confirmed. The result is shown in FIG. FIG. 2 is a diagram showing the gap dependence of the resistance change characteristic of the magnetic encoder of this embodiment.

As can be seen from this figure, the maximum value is recognized in the Z direction, and as is clear from (Equation 6), the resistance change characteristic is given by (Equation 7) in the z direction. At position D, it was found to be consistent with having an extremum.

[0031]

[Equation 7]

As is apparent from FIG. 2, it is understood that the variation of the characteristics is reduced within the range of the thickness variation (45 to 55 μm) of the protective layer. By rearranging this (Equation 7) for d, (Equation 8) is obtained.

[0033]

[Equation 8]

For the conventional product, the gap dependency of the maximum resistance change amount was confirmed. FIG. 4 is a diagram showing the gap dependence of the resistance change characteristic of the conventional magnetic encoder.

As is apparent from FIG. 4, in the conventional magnetic encoder, the maximum value was not recognized in the Z direction.

As described above, in this embodiment, the MR effect element 2 is divided into two, and the MR effect element 2 is arranged in parallel with each other at the same gap position with respect to the magnetic recording medium 1, whereby the above-mentioned gap dependence is obtained. Is controlled so that stabilization can be realized.

[0037]

As described above, according to the present invention, by dividing the magnetoresistive effect element into two and arranging them in parallel at a predetermined interval d, it is possible to easily stabilize the characteristics and improve the accuracy. It is possible to realize a magnetic encoder with a simple structure, low cost and excellent mass productivity.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a magnetic encoder according to an embodiment of the present invention.

FIG. 2 is a diagram showing gap dependence of resistance change characteristics of the magnetic encoder of the present embodiment.

FIG. 3 is a schematic diagram of a conventional magnetic encoder.

FIG. 4 is a diagram showing gap dependence of resistance change characteristics of a conventional magnetic encoder.

[Explanation of symbols]

 1 magnetic recording medium 2 magnetoresistive effect element 3 magnetic recording medium 4 magnetoresistive effect element

Claims (1)

[Claims] 1. A magnetic encoder comprising a magnetic recording medium and a magnetoresistive effect element arranged to face the magnetic recording medium, wherein the magnetoresistive effect element comprises two or more magnetoresistive elements. The effect elements are substantially parallel to each other, and A magnetic encoder characterized in that the magnetic encoders are arranged at an interval d shown by.