JP4223718B2 - Position detection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention, in the machine tool and industrial machines, etc., a digital scale, about the position detection equipment to be used for position detection, such as gauges and encoder.
[0002]
[Prior art]
Various types of position detection devices have been proposed as position detection devices that detect the amount and distance of movement of a movable part, which is a linearly moving part such as a machine tool or industrial machine.
[0003]
As such a position detection device, there is a position detection device 2 as shown in FIG. The position detection device 2 will be described below.
[0004]
The position detection device 2 includes a scale 30 that records a magnetic scale and a detector 31 that detects the magnetic scale recorded on the scale 30.
[0005]
The scale 30 is formed, for example, by recording a magnetic scale along the longitudinal direction on a recording medium having a flat plate shape. A detector 31 for detecting a magnetic scale recorded on the scale 30 is provided in the head slider. The detector 31 is provided, for example, at a position opposite to the magnetic scale so that the magnetic scale recorded on the scale 30 can be detected, and is translated in the longitudinal direction of the scale 30 as the head slider moves linearly. .
[0006]
Some detectors 31 use a magnetoresistive effect (hereinafter referred to as MR) element to detect a magnetic scale, for example. The MR element is formed by forming a thin film of a ferromagnetic material such as Fe-Ni or Ni-Co on a substrate such as glass, silicon or ceramic by a predetermined film forming method, and using the magnetoresistance effect of the thin film. The upper magnetic signal is detected.
[0007]
There is a gap (hereinafter referred to as a clearance) between the scale 30 and the detector 31, and foreign matter may be mixed into the clearance. Since the detector 31 may be damaged due to the mixing of foreign matter, a protective film is formed on the surface of the detector 31.
[0008]
[Problems to be solved by the invention]
However, in the conventional position detection device 2, when the size of the foreign matter to be mixed is smaller than the clearance, the protective film can cope with it. However, the size of the foreign matter to be mixed is equal to or larger than the clearance. In the case of the size, as shown in FIG. 3, since the protective film is thin, there is a problem that the protective film is peeled off by a foreign substance and the detector is damaged.
[0009]
In addition, conventionally, in order to prevent contamination of foreign matter having a size approximately equal to or larger than the clearance, it is necessary to install a foreign matter prevention portion such as a wiper or a scraper at both ends or around the detector. This was a cause of the expensive detection device.
[0010]
Therefore, the present invention has been proposed in view of the above-described circumstances, and foreign matter having a size equal to or larger than the clearance is included without installing a foreign matter mixing prevention unit such as a wiper or a scraper. It is an object of the present invention to provide a position detection device capable of preventing the above-described problem.
[0011]
[Means for Solving the Problems]
In order to solve the above-described problem, a position detection device according to the present invention is arranged to detect a signal from a scale on which a signal is recorded and a position where the signal is relatively movable facing the scale. A detector, an elastic layer for stress relaxation laminated on the detector surface, and a protective film laminated on the elastic layer, and when the clearance from the detector surface to the scale surface is 20 μm, When the protective film thickness is a and the distance from the protective film surface to the scale surface is b, a ≧ b ≧ 5 μm, and the protective film is composed of a diamond-like carbon thin film that is a nonmagnetic material. It is characterized by.
[0012]
That is, in the position detection device , a protective film is formed on the detector surface, and the film thickness from the detector surface to the protective film surface is formed to be thicker than the distance from the protective film surface to the scale surface .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0014]
The present invention is applied to, for example, a position detection apparatus 1 as shown in FIG.
[0015]
The position detection device 1 includes a scale 10 that records a magnetic scale and a detector 11 that detects the magnetic scale recorded on the scale 10.
[0016]
The scale 10 is formed, for example, by recording a magnetic scale along the longitudinal direction on a recording medium having a flat plate shape. Specifically, the position detection device 1 is configured by a scale 10, a housing 12, a head slider 13, and a carrier 14, for example, as shown in FIG.
[0017]
A detector 11 that detects a magnetic scale recorded on the scale 10 is provided in the head slider 13. The detector 11 is mounted, for example, at a position facing the magnetic scale so that the magnetic scale recorded on the scale 10 can be detected, and is translated in the longitudinal direction of the scale 10 as the head slider 13 moves linearly. To do.
[0018]
Here, the position detection by the position detection apparatus 1 will be described below.
[0019]
The position detection device 1 including the scale 10 and the detector 11 as described above is attached to a reference portion and a movable portion such as a machine tool that moves relatively linearly. In the position detection device 1, either the main body or the head slider 13 is fixed to a reference portion that does not move, and the other is fixed to a movable portion. At this time, the main body is attached so that the longitudinal direction of the scale 10 provided inside is parallel to the moving direction of the movable part. Therefore, in the position detection device 1, the relative position between the main body and the head slider 13 changes according to the linear movement of the movable part.
[0020]
Thus, in the position detection device 1, the detector 11 provided in the head slider 13 can detect a magnetic scale that changes in accordance with the change in the relative position, and can control the moving position of the movable portion.
[0021]
In such a position detection apparatus 1, a scale signal is recorded in the longitudinal direction of the scale 10 as a magnetic scale. In addition to the scale signal, the origin signal may be recorded on the scale 10 in the longitudinal direction.
[0022]
The scale signal is a signal in which pits, marks, and the like that are continuously repeated at a predetermined interval are recorded in the longitudinal direction of the scale 10. For example, a magnetic signal whose polarity is inverted at a predetermined recording wavelength is It is a signal recorded continuously in the longitudinal direction. By using the scale 10 on which such a scale signal is recorded, the position detection device 1 can linearly detect a change in the relative movement position between the main body portion and the head slider 13, and the reference portion and the movable portion. Can be continuously controlled.
[0023]
The origin signal is a signal in which at least one pit, mark, or the like is discretely recorded in the longitudinal direction of the scale 10. For example, a magnetic signal for one wavelength is a predetermined 1 in the longitudinal direction of the scale 10. It is a signal recorded in the place. By using the scale 10 in which such an origin signal is recorded, the position detection apparatus 1 can detect the reference position such as the initial setting position and the origin position of the main body and the head slider 13, The relative position with respect to the movable part can be set as the reference position.
[0024]
In the position detection device 1, there is a gap (hereinafter referred to as a clearance) between the scale 10 and the detector 11, and protection is provided to prevent the detection surface of the detector 11 from being damaged by foreign matter mixed in the clearance. A film 20 is formed. However, if the thickness of the protective film 20 is about 6 μm as in the prior art, as shown in FIG. 3, when foreign matter having a size equal to or larger than the clearance is mixed into the clearance, There is a problem that the protective film 20 is peeled off and the detector 11 may be physically damaged, and long-term reliability cannot be ensured. Further, in order to improve the detection sensitivity of the position detection device 1, the clearance needs to be narrowed. For example, in a system in which the clearance is narrowed to about 20 μm, the foreign matter mixed in the clearance must be a certain thickness as a protective film. Therefore, even if the detector 11 is not physically damaged, the stress due to the foreign matter deteriorates the characteristics of the detection element, and as a result, the detection signal may be adversely affected and the reading performance of the detector 11 may be lowered.
[0025]
Therefore, in the present invention, as shown in FIG. 4, when the clearance is 20 μm, the thickness of the protective film 20 is set to 10 to 12 μm to solve the above problem. Further, when the film thickness of the protective film 20 is a and the distance from the surface of the protective film 20 to the surface of the scale 10 is b, a ≧ b is established as in the above example, and a ≧ b ≧ 5 μm. If it is established, the thickness of the protective film 20 may be other than the above.
[0026]
Further, the protective film 20 may be a non-magnetic material such as copper, aluminum, or diamond-like carbon (hereinafter referred to as DLC) thin film.
[0027]
Here, the characteristics of the DLC thin film will be described. The DLC thin film has high hardness (Hv≈3000), and has a dense amorphous structure, so that its surface is very smooth and free from crystal grain boundaries. Due to such surface characteristics, the DLC thin film has a low friction coefficient (μ = 0.1 to 0.2) as compared with other hard thin films such as TiN and has characteristics such as wear resistance. In addition, DLC thin film is mainly composed of carbon and is widely used in cutting tools. It is not easily affected by water-soluble cutting fluid, and its hardness is so high that it is hardly affected by chips. Have.
[0028]
For example, the detector 11 may use an MR element including a magnetoresistive film (hereinafter referred to as an MR film) and an electrode. The MR film is made of a Ni—Fe alloy or the like and connected to an electrode connected to the outside. Further, the MR element changes in electric resistance in accordance with an external magnetic field, and detects a magnetic signal recorded on the magnetic recording medium.
[0029]
When the DLC thin film is directly formed on the MR film as described above, the magnetoresistive effect of the MR film may be deteriorated due to the stress of the DLC thin film. Therefore, in the present invention, an elastic layer for stress relaxation is formed between the DLC thin film and the MR element. The elastic layer also serves to adhere the protective film 20 to the detector 11. Further, when the protective film 20 is installed on the detector 11, an elastic adhesive is used so that the stress from the foreign matter entering the clearance applied to the protective film 20 is applied to the detector 11 by this elastic layer. It can be made difficult to transmit, and even better results are obtained. The thickness of the protective film 20 is from the surface of the detection element, but in the case of the MR element, the thickness of the element itself is about 30 to 100 nm, so that it is almost the same as the thickness of the surface of the detector 11 from the substrate. is there.
[0030]
Next, the shape of the end face of the protective film 20 will be described with reference to FIG. 5A to 5C are views of the protective film 20 as viewed from above. The shape of the protective film 20 is a parallelogram as shown in FIG. 5 (a), a hexagon as shown in FIG. 5 (b), and a circle as shown in FIG. 5 (c). As described above, the protective film 20 is formed in an inclined surface or a curved surface with respect to the traveling direction of the detector 11, thereby preventing foreign matter from accumulating on the end surface of the protective film 20. Any shape other than those described above may be used as long as it prevents the foreign matter from collecting on the end face of the protective film 20.
[0031]
Further, the shape of the detector 11 may be formed into an inclined surface or curved surface such as a parallelogram, hexagon, or circle with respect to the traveling direction, similarly to the shape of the protective film 20.
[0032]
In this way, in the position detection device 1, by forming the protective film 20 formed on the surface of the detector 11 to be thicker than the distance between the protective film 20 surface and the scale 10 surface, a wiper, a scraper, etc. Without providing the foreign matter mixing prevention part, it is possible to prevent the foreign matter having a size of the clearance between the scale 10 and the detector 11 from being mixed, so that the detector 11 can be prevented from being damaged. Further, in the position detection device 1, by forming an elastic layer between the detector 11 and the protective film 20, stress due to the protective film 20 is relieved, and foreign matter mixed between the protective film 20 and the scale 10 is caused. Since the influence can be mitigated, damage to the detector 11 can be prevented.
[0033]
As described above, the magnetic scale has been described as an embodiment of the present invention, but the present invention is not limited to this, and can be applied to an optical scale, a capacitance scale, an electromagnetic induction scale, or the like. It is.
[0034]
【The invention's effect】
The position detection device according to the present invention has a protective film formed on the detector surface with a thickness greater than that between the protective film surface and the scale, thereby providing a foreign matter prevention part such as a wiper or a scraper. It is possible to prevent foreign matter having a clearance of about the clearance between the scale and the detector from being installed, to prevent damage to the detector, and to provide an elastic layer between the detector and the protective film. This reduces the stress applied to the protective film even when foreign matter with a clearance of about the clearance between the scale and the detector is mixed , and the effect of foreign matter mixed between the protective film and the scale. Can be relaxed. Furthermore, a diamond-like carbon thin film is used as the protective film, and it has wear resistance and is hardly affected by the water-soluble cutting fluid. Therefore, the detector can be prevented from being damaged, and the overall resistance of the apparatus can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a position detection apparatus to which the present invention is applied.
FIG. 2 is a perspective view showing a specific example of a position detection apparatus to which the present invention is applied.
FIG. 3 is a diagram illustrating a state when a foreign substance having a clearance level is mixed in a conventional position detection device.
FIG. 4 is a side view of a position detection device to which the present invention is applied.
FIG. 5 is a diagram showing a shape of a protective film formed on a detector surface provided in a position detection device to which the present invention is applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Position detection apparatus, 2 Thin film formation apparatus, 10 Scale, 11 Magnetic head, 12 Housing, 13 Head slider, 14 Carrier, 20 Protective film

Claims (1)

The scale at which the signal is recorded,
A detector that is disposed at a position that is relatively movable facing the scale, and that detects a signal from the scale;
An elastic layer for stress relaxation laminated on the detector surface;
A protective film laminated on the elastic layer,
When the clearance from the detector surface to the scale surface is 20 μm, when the film thickness of the protective film is a and the distance from the protective film surface to the scale surface is b, a ≧ b ≧ 5 μm,
The position detecting device, wherein the protective film is made of a diamond-like carbon thin film which is a nonmagnetic material.

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