JPS60244812A - Magneto-resistance element for encoder - Google Patents

Abstract

PURPOSE:To easily adjust the positions of a moving body side and a fix side by covering the surface except above a magneto-resistance part with varies in electric resistance according to whether a magnetic field is present or not and covering the surface. CONSTITUTION:A protection film 2a made of metallic foil has a hole opened only above the magneto-resistance part 3 which detects a magnetic field with a magnetic pattern actually and generates heat. The protection film 2a has almost no rise in temperature even when the magneto-resistance part 3 heats up to high temperature, and the heat generation of the magneto-resistance part 3 causes no swelling. There is no metallic protection film provided above the magneto-resistance part 3 and the surface is recessed below the peripheral protection surface by tens of mum, so that a soft magnetic material film forming the magneto-resistance part is not damaged even if the moving body side contacts the fixed side.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention provides protection against accidental contact between the movable body side and the fixed side during installation or adjustment by means of a protective means made of a metal thin film installed on the surface. The soft ferromagnetic thin film of the magnetoresistive part that actually detects the porous pattern on the movable body side on the stationary side is not damaged, and furthermore, the thin metal film is prevented from blistering and problems such as difficulty in positioning due to the blistering occur. The present invention relates to a magnetoresistive element for an encoder.

[Background of the invention]

A drum or disk with a magnetic recording medium surface is attached to a moving object, such as a rotating body, and the magnetic pattern formed by magnetization on the surface is detected and read by a fixedly placed magnetoresistive element, which determines the rotational speed and stoppage of the rotating body. A magnetic encoder is used to measure position, etc.

In such applications, the magnetic field generated by the magnetic pattern on the moving body side is generally not strong. In particular, when the magnetic pattern is made finer in order to increase the resolution, it is difficult to increase the strength of the magnetic field. On the other hand, the rate of change in electrical resistance of the magnetoresistive element that detects the magnetic field of the magnetic pattern on the fixed side depending on the presence or absence of the magnetic field is not large. Therefore, in order to ensure measurement accuracy, it is difficult to create a large gap between the moving object side and the fixed side of the magnetic encoder, and usually,
Only a narrow gap of several tens to hundreds of micrometers can be created.

In this way, the gap size between the magnetic recording medium surface on the movable body side and the magnetoresistive element surface on the fixed side is originally under conditions that cannot be increased very much, and in general, as the movable body side moves, For example, due to a slight bend in the rotating shaft of a rotating body or slight eccentricity of a ball bearing, the position of the surface of a magnetic recording medium attached thereto will inevitably fluctuate slightly.

Due to the above-mentioned circumstances, during installation or adjustment of the magnetic encoder, an accident is likely to occur in which the movable body side and the fixed side come into contact with each other. As a measure against such accidents, the surface of the magnetoresistive element is covered with a thin metal film, such as stainless steel foil, about 10-odd micrometers thick, as shown in the plan view in Figure 1 and the side view in Figure 2. Protection has started to take place.

In these figures, 1 is a magnetoresistive element substrate, 2 is a protective film made of metal foil such as stainless steel, and 3 is a magnetoresistive part (the electrical resistance changes depending on the presence or absence of the magnetic field of the magnetic pattern).
(where the magnetic pattern is read), 4 is the adhesive (normally, the magnetic resistance part generates heat and becomes quite high temperature, so use polyimide with excellent heat resistance! Grease resistant etc.), 5 is the magnetic drum on the moving body side. be. In this way, it has become possible to prevent accidents during the setting of the magnetic encoder, but it has been found that this protective measure using a metal thin film has the following problems.

That is, during encoder operation, if the magnetoresistive element repeatedly performs an operation in which its electrical resistance changes depending on the presence or absence of a magnetic field, that portion generates heat. Moreover, as the resolution of magnetic encoders becomes higher, the integration of magnetoresistive elements becomes higher, and the pinch size becomes smaller, the above-mentioned heat generation points become localized in a small area, and the magnetoresistive part 3 that actually detects the magnetic field. started to rise to high temperatures. For substrate processing of magnetoresistive elements,
Usually, borosilicate glass is used, which has poor weather resistance and moisture resistance, and is free from alkali elution that eats away at the soft IA magnetic materials that form the magnetoresistive element, such as permanent LI. The coefficient is small.

On the other hand, as the protective film 2 made of metal foil on the surface of the magnetoresistive element, as mentioned above, stainless steel is relatively inexpensive and has relatively favorable properties in terms of magnetic permeability, electrical conductivity, and mechanical strength. Moreover, the coefficient of thermal expansion of stainless steel is large, reaching about three times that of borosilicate glass. Therefore, when the magnetoresistive element repeats temperature cycles of operation and non-operation, this protective metal foil plastically deforms and bulges.

In this way, when the bulge occurs, it becomes difficult to accurately position the movable body side (magnetic pattern) and the fixed side (magnetoresistive element) across the narrow gap. Furthermore, if the bulge is left as it is and the installation is forced, a subsequent contact accident may cause damage to the metal thin film or even damage to the magnetoresistive element body.

[Purpose of the invention]

The object of the present invention is to eliminate the problems of the conventional magnetoresistive element described above, and to use a metal that mechanically protects the surface during encoder operation. An object of the present invention is to provide a magnetoresistive element for an encoder in which troubles due to IN swelling do not occur.

[Summary of the Invention] In order to achieve the above object, the present invention is based on the present invention, in which the surface is made of metal foil, excluding only the area above the magnetic resistance part where the electrical resistance changes depending on the presence or absence of a magnetic field during encoder operation. It was decided to provide mechanical protection by coating it with a protective film. − In this way, a protective film against mechanical contact made of metal foil is provided on the magnetoresistive part used to actually detect the change in electrical resistance depending on the presence or absence of a magnetic field caused by the magnetic pattern on the moving body side. However, since the entire surface of the magnetoresistive element is coated with SiO2 film or a polyimide resin film, there is no problem in terms of moisture resistance and weather resistance. In addition, regarding mechanical protection, the surface of the magnetic resistance part is the first of its kind, and the thickness of the metal foil is smaller than the surface of the surrounding metal foil protective film. If it retracts by about μm,
Even if the movable body side and the stationary side come into contact, the contact will only occur at the area covered with the surrounding metal foil protective film, and the soft ferromagnetic thin film of the magnetoresistive part will be directly damaged. I don't do anything special. Moreover, since there is no blistering of the metal foil protective film on the surface of the nitric resistance part, the gap adjustment and positioning between the movable body side and the fixed side can be easily and accurately performed.

[Embodiments of the invention]

FIG. 3 is a plan view of one embodiment of the present invention, and FIG. 4 is a side view thereof. The protective film 2a made of metal foil according to the present invention actually detects the magnetic field of the magnetic pattern and generates heat using a magnetic resistor. There is a hole only above the part 3, so that even if the magnetic resistance part 3 generates heat and reaches a high temperature, the temperature of the protective IQ2a hardly rises, and no swelling occurs due to the heat generated by the magnetic resistance part 3. There is.

As mentioned above, the magnetoresistive element (the magnetoresistive part 3 is a part of the vapor-deposited thin film of a soft ferromagnetic material such as permalloy) is formed to be elongated and have a relatively large electrical resistance value. In addition, the surface of the element (which has a conductive terminal-like part whose width is wide relative to the length reaching the magnetoresistive part and whose electrical resistance can be virtually ignored) is covered entirely by S.
The film is coated with iO, IIQ and a film of a resin having good heat resistance, such as a polyimide resin, which is deposited thereon to compensate for cracks in the film, so as to provide moisture resistance and weather resistance. This resin film also serves as the adhesive 4.

With this structure, as mentioned above, there is no metal foil protective film on the magnetoresistive part 3, but instead, the surface of this part is recessed from the surrounding protective film surface by more than 10 μm. , even if a contact accident occurs between the moving object and the stationary side,
The soft ferromagnetic film forming the magnetoresistive part is not damaged. Further, since there is no protective film on the magnetoresistive part that generates heat during operation, there is no reason for the metal foil protective film to bulge as in the conventional example. Since no blistering occurs, it is easy to position the encoder when installing and adjusting it.
Gap length adjustment can be performed very easily and accurately. Note that, as shown in FIG. 3, if the magnetoresistive part 3 is divided into a plurality of parts and there is a part where the protective film is present in the middle of the part where the protective film is opened, the gap length adjustment and positioning will be easier. I can do it.

〔Effect of the invention〕

As explained above, according to the present invention, the metal foil protective film does not bulge due to heat generated by the magnetoresistive part during operation of the magnetic encoder, so position adjustment and gap adjustment between the movable body side and the fixed side can be easily performed. Moreover, even if a contact accident occurs during adjustment work, the magnetic resistance element will not be functionally damaged.

[Brief explanation of drawings]

Fig. 1 is a plan view of a conventional magnetoresistive element covered with a metal foil protective film, Fig. 2 is a side view of the same conventional example, Fig. 3 is a plan view of an embodiment of the present invention, and Fig. 4 is the same. FIG. 3 is a side sectional view of the embodiment.

Claims (1)

[Claims] Magnetoresistive elements for encoders detect and read the magnetic field generated by a magnetic pattern on the surface of a magnetic recording medium attached to a moving body at a fixed position separated by a small gap, and measure the moving state of a moving body. 1. A magnetoresistive element for an encoder, characterized in that the surface of the magnetoresistive part is protected by being covered with a thin metal film, excluding only the part above the magnetoresistive part whose electrical resistance changes depending on the presence or absence of the magnetoresistive part.