JP2960570B2 - Magnetic encoder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic encoder and a method for manufacturing the same, and more particularly, to a magnetic encoder having a function of detecting a linear displacement of a piston rod of a hydraulic cylinder, a cable of a cable cylinder, and a table of a slide table cylinder. The present invention relates to a magnetic linear encoder for a cylinder that performs a reciprocating operation, a magnetic rotary encoder such as a rotation sensor and an angle sensor of a DC motor, and a method of manufacturing the same. In addition, the present invention relates to a cylinder having a rod that reciprocates in a linear direction, and more particularly, to a cylinder having a rod having flexibility, flexibility, or rigidity and having a function of detecting a linear displacement amount of the rod. Pressure cylinder. INDUSTRIAL APPLICABILITY The present invention is particularly used in the field of industrial machinery for detecting and controlling a linear displacement of a piston rod or the like in an industrial robot.

[0002]

2. Description of the Related Art With the development of automation and labor saving, hydraulic and pneumatic cylinders provided with a position control function are used in various fields, particularly in industrial robots. As a position detection method in such position control of the hydraulic / pneumatic cylinder, a method of detecting a magnetic field is the cheapest, and thus various magnetic detection methods are used. The position of the rod by these magnetic detection methods is detected by, for example, forming a magnetic scale in the longitudinal direction of the rod and reading the movement of the rod from the magnetic scale by a magnetic sensor.

[0003] In the case of a magnetic scale for such a rod, for example, in the case of a rod made of a magnetic material, grooves are carved in at least one line at a constant pitch in the longitudinal direction, and the grooves are filled with a non-magnetic material to form a hard chrome. In the case of rods made of non-magnetic material, grooves are carved in at least one line in the longitudinal direction, and magnets magnetized at predetermined intervals along the grooves are fixed and formed. doing. In addition, a multipole-magnetized columnar magnet is directly connected to a rod and housed in a cylinder, for example, a magnetic scale is provided on a piston rod.

On the other hand, magnetic sensors include a method using a coil, a method using a Hall element, a method using a semiconductor magnetoresistive element, a method using a ferromagnetic magnetoresistive element (hereinafter referred to as an MR element), There are methods such as a method using a bias magnet type MR element, but since the change in output voltage with respect to the magnetic field in the weak magnetic field region is large and a small magnetization pitch can be detected, the displacement amount using the MR element is used. Has been detected.

[0005]

However, for example, in the case where the position of the piston rod in the conventional piston rod is detected by an MR element having an external bias magnet, a pattern is formed on the MR element substrate. Since the bias magnetic field is applied without knowing the position where the pattern is formed, it has been difficult to apply the pattern exactly in the direction of 45 ° to the pattern. In addition, since the MR element has a large temperature dependency, if the temperature of the MR element rises by an amount that the angle formed by the bias magnetic field and the pattern deviates from 45 °, the sensitivity decreases (for example, −0.2 to 0). 0.3% /
° C), a temperature change of the output voltage occurs, and a difference in the output of the N pole and the S pole occurs at the same magnetic field strength.

[0006] In addition, mechanical processing is indispensable for forming a groove for a rod, and the rod is expensive, and a single row of grooves cannot be detected due to rotation of the rod or the like. In addition, there is a problem that forming a plurality of grooves is more expensive and lowers productivity.
SUMMARY OF THE INVENTION It is an object of the present invention to solve the problems related to the price of the device and the accuracy of position control in the magnetic position detection of the conventional piston rod of the cylinder as described above.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic encoder capable of performing high-accuracy position control at relatively low cost. That is, the present invention
In a magnetic linear encoder in which a magnetoresistive element is provided close to the surface of a magnetic scale member, part or all of the surface of the magnetic scale member is magnetized at a constant pitch in the moving direction of the magnetic scale member. The magnetic encoder is characterized in that a high coercivity alloy plating film is formed, and the present invention provides a magnetic encoder in which a magnetoresistive element is provided in proximity to the surface of a magnetic scale member. In the manufacturing method, a high coercive force alloy plating film is formed on a part or all of the surface of the magnetic scale member by a plating method, and the alloy plating film is magnetized at a constant pitch in the moving direction of the magnetic scale member. A method for manufacturing a magnetic encoder, characterized in that:

In the present invention, the magnetic film having a high coercive force is
75 to 87% by weight of cobalt (Co), nickel (N
i) 8.5 to 22% by weight, phosphorus (P) 2.5 to 4.5
It is a hard magnetic alloy plating film having a composition of weight%, has a high coercive force of 600 Oersteds or more invented by the present inventors, and records a magnetic signal for controlling the position of a piston rod or the like. be able to. The magnetic film according to the present invention has a coercive force of 600 Oe or more. However, when the cobalt content is less than 75% by weight, the coercive force drops sharply. A coercive force higher than Steed cannot be achieved. If nickel is out of the range of 8.5 to 22% by weight, a high coercive force of 600 Oe or more cannot be obtained. Since the magnetic force is less than 600 Oersteds, it is necessary to control within this narrow range.

In the present invention, the alloy magnetic film having a high coercive force is easily and easily formed on the rod surface by applying a plating to the rod, so that not only the entire surface of the rod but also a plurality of rows on the surface of the rod. A magnetic film can be easily formed. The coercive force of the magnetic layer in the present invention is:
By changing the composition within the scope of the present invention, 60
Since the coercive force can be controlled within the range of 0 to 1000 Oersted and the coercive force does not change depending on the film thickness unlike the conventional plating film, the magnitude of the coercive force and the film thickness can be freely selected according to the application. Can be.

In the present invention, any material can be used as a base material by subjecting the base material to a base treatment, and there is no particular restriction on the material of the base material. However, a non-magnetic material is suitable when magnetizing the axis horizontally, and a ferromagnetic substrate or a non-magnetic substrate is used when magnetizing vertically to narrow the magnetizing pitch. In the case of magnetism, it is desirable to provide a ferromagnetic underlayer. Further, it is desirable to apply hard chrome plating or non-magnetic NiP plating as a protective film.

In the present invention, the bias magnet-integrated MR element includes a substrate made of a hard magnetic material (for example, a hard magnetic ferrite substrate) and a substrate (for example, a glass substrate, etc.) suitable for forming a thin film (by means such as vapor deposition). Are bonded in advance, a pattern is formed from thin film formation using the bonded substrate (hereinafter, referred to as a composite substrate), and necessary magnetization is performed later to form an MR element. The body type MR element is an element that linearly detects the magnitude of the magnetic field to be detected, and the output of the MR element of the present invention has a linear sine waveform until the bias magnetic field is up to 150 Oersteds. An accurate position can be detected with respect to the rod magnetization pitch λ. In the present invention, the magnetic sensor is of a type in which a magnetic signal is directly read by the MR element so that the output signal of the MR element can be sufficiently increased, and is a bias magnet-integrated MR element.

The bias magnet-integrated MR element can be provided by being supported on a holding member. In this case, it is preferable that the magnetic scale member is fixed at a position close to the magnetic plating film, for example, at a position which is １ ／ of the magnetization pitch λ of the magnetic scale member. Therefore, the bias magnet integrated type MR
The holding surface of the bias magnet-integrated MR element of the element holding member can be formed in an appropriate shape such as a plane, an arc, an annular shape, or a curved surface in accordance with the surface of the magnetic scale member. For example, when the magnetic scale member is a plate-shaped member, the holding surface of the bias-magnet-integrated MR element holding member can be formed in a planar shape corresponding to the plane of the member. When the magnetic scale member is a solid or hollow cylindrical member such as a piston rod or a member that rotates like a rotary encoder, for example, the holding surface of the bias magnet integrated MR element holding member is used. In a plane at a position corresponding to a part of the plating surface of the cylindrical member, or in an annular shape concentric with the cylindrical member or the rotating member, or corresponding to the shape of a cylinder or the like of these members, as appropriate. Can be formed into a curved shape.

[0013]

According to the present invention, a high-coercivity alloy plating film magnetized at a constant pitch in the moving direction of the magnetic scale member is formed on a part or the entire surface of the magnetic scale member. The magnetic alloy film formed on the surface has a high coercive force, and the magnetic signal recorded on the film is easily detected as a magnetic flux leaking from the alloy film to the outside by the bias magnet integrated type MR element. Therefore, it is possible to reduce the size and weight of the magnetic sensor unit.

Moreover, in the present invention, the desired high coercive force magnetic alloy film can be formed by plating.
Since it can be formed on the rod appropriately and easily, expensive work such as machining, embedding of a non-magnetic material, or addition of a multi-polar magnetized columnar magnet is not required as compared with a conventional rod. Further, in the present invention, the magnetic alloy film can be formed almost uniformly on the rod by plating, so that a magnetic signal for position control can be recorded on the entire circumference of the rod, and there is no need to stop the rod from rotating. Becomes

In the present invention, since the magnetic sensor is of a bias magnet integrated type, the angle between the magnetoresistive element pattern and the bias magnet can be made extremely close to, for example, 45 °, and the output voltage changes with temperature. Becomes extremely small, and highly accurate and stable signal processing becomes possible. Thus, in the present invention, since the magnetic signal is read directly by the MR element, the output signal of the element can be sufficiently increased.

[0016]

The embodiments of the present invention will be illustrated and described below, but the present invention is not limited by the following examples and descriptions. FIG. 1 is a schematic perspective view of a cylinder according to an embodiment of the present invention, showing an example in which a cylinder rod is magnetized. FIG. 2 is a schematic perspective view of a three-terminal type bias magnet-integrated MR element used in the case shown in FIG. 1, and FIG. 3 is a diagram showing a magnetized cylinder rod and a bias in the case of FIG. FIG. 3 is a front view showing an arrangement of a magnet-integrated MR element. FIG. 4 shows a state of the position detection signal in the case shown in FIG. FIG. 5 is a bridge circuit assembled with a bias magnet integrated type MR element and a resistor. FIG. 6 shows an example of output characteristics.

In the example of FIG. 1, the rod 1 has a diameter of 6 m.
SUS304 round bar is coated with a plating film 2 having a coercive force of 850 (Oe) composed of 86.5% Co, 9.5% Ni, and 4.0% P by weight. Are magnetized on the circumference so that magnetic poles appear alternately in the axial direction. To further protect this magnetized film,
A protective film of hard chrome plating is formed on the outside. The magnetization pitch λ (N pole-N pole) can be arbitrarily set, but is fixed at 4 mm here. This magnetized rod is incorporated in the piston cylinder 3.

In the example of FIG. 2, a bias magnet integrated type M for detecting a magnetic signal recorded on a magnetized rod is used.
The R element 14 is embedded in the holding member 37. The substrate of the bias magnet integrated type MR element 14 is made of a hard magnetic material 13.
And a glass material 12, and a Ni-Fe-Co-based material having an anisotropic magnetoresistance effect is formed on the glass surface by vacuum evaporation. In this example, the hard magnetic material 13 is magnetized, and the pattern portions 5, 6, 10
And 11, a bias magnetic field is applied. The pattern section includes power terminals 7 and 8, output terminals 4 and 9, and the magnetic field detection pattern section includes 5, 6, 10, and 11.
The pattern portion is made by etching the ferromagnetic thin film. The magnetic field detection patterns 5, 6 and 10, 11 are substantially orthogonal to each other, and the patterns 5, 10 are arranged at an angle of -π / 4 with respect to the bias magnetic field. The two sets of magnetic field detection patterns consisting of patterns 5, 6 and 10, 11 are arranged at a distance of (1/4 + n) λ (n is an integer), and the movement direction is detected together with the displacement of the magnetized rod. I can do it. The displacement amount is obtained by counting the output signal corresponding to the magnetized signal of the magnetized rod by a count circuit, and the moving direction is determined by using a phase discriminating circuit based on the difference in the phase of the output signals from the two sets of patterns. Obtained by

FIGS. 1 and 3 show the positional relationship between the magnetized rod 1 and the bias magnet integrated type MR element 14. FIG. Two sets of magnetic field detection patterns 5 and 6 of the bias magnet integrated type MR element 14
, 10 and 11 are arranged so as to be parallel to the axial direction of the magnetized rod 1. Bias magnet integrated type MR element 14
And the clearance between the magnetized rod 1 and the magnetized pitch λ are equal to or less than half.

FIG. 4 shows a state of a detection signal of the displacement of the magnetized rod in the embodiment. The vertical axis in FIG. 4 represents the output of the bias magnet-integrated ferromagnetic element and the horizontal axis represents the displacement of the magnetized rod. As can be seen from FIG.
It fluctuates at a cycle of mm and matches the magnetization pitch. Therefore, by counting the number of cycles of this output, the number of magnetized pitches that have passed through the element can be determined, and the displacement of the magnetized rod can be detected.

[0021] Now, as shown in FIG. 5, to form a bridge circuit composed of the bias magnet integrated MR element 14 of the 15, 16 a set of patterns and resistors 17 and 18 constructed in the above, the DC voltage _{V 0} Is applied. With respect to the signal magnetic field _{H s} is a bias magnetic field _{H B,} when that is applied from a substantially plane perpendicular, the combined magnetic field _{H com ^{is, H com = (H B 2}} + H s 2) ^1/2, a signal magnetic field Hs is the angle theta which forms with the bias magnetic field _{H B,} is expressed as ^{_{θ = tan -1 (H s /}} H B). For example, the bias magnetic field _{H B} is, 0.99 (O
e) The above saturation magnetic field was applied. Voltage change at this time Δ
As is well known, V is represented by ΔV = KV _o cos2 (θ−π / 4). Here, K is a constant determined by a material or the like, and -π / 4 is an angle between the combined magnetic field _Hcom and the pattern.

[0022] By the way, the signal magnetic field _{H s} is the magnetic field from the Chaku磁媒body. Since the MR element has sensitivity in the in-plane magnetic field direction and has an arrangement relationship with the magnetized medium as shown in FIGS. 1 and 3, the magnetic field detected by the MR element has a component parallel to the medium axis direction. Limited. Therefore, in general the signal magnetic field _{H s} in the case of multiple poles is definitive and _{H s = Hsin (2πx / λ} ). H is the magnitude (constant) of the magnetic field determined by the residual magnetic flux density, thickness and curvature of the magnetized medium, and the distance between the magnetized medium and the MR element pattern.

FIG. 6 shows a waveform represented by y = cos 2 {tan ⁻¹ {(H / H _B ) sin (2πx / λ)} − π / 4}. From this waveform, the signal magnetic field Hs can achieve high resolution by using the interpolation circuits so approximate to the more sinusoidal waveform less than the bias magnetic field H _B.

As a method of increasing the output voltage of the MR element, in addition to increasing the rate of change in magnetoresistance of the MR element, it is conceivable to increase the magnetization of a magnetically plated piston rod serving as a signal source. However, in the operating environment of the cylinder, magnetic powder can be sufficiently present, so that it is necessary to avoid increasing the magnetizing strength unnecessarily. Also, as is well known, there is a method of increasing the output voltage by making the three-terminal structure of the MR element a bridge structure. The bridge structure is constituted by two sets of patterns separated by a distance of (1/2 + n) λ. Is done. In the present example, the bias magnet integrated MR element holding surface of the bias magnet integrated MR element holding member 37 is formed flat, but may be formed to be curved along the surface of the piston rod. ,
Moreover, it can also be formed in a ring shape.

[0025]

As is apparent from the above description, the present invention provides a method of manufacturing a magnetic recording medium having a high coercive force applied to a part or the entire surface of a magnetic scale member at a constant pitch in the moving direction of the magnetic scale member. Because a gold-plated coating is formed, for example, compared to conventional magnetic scale members such as piston rods, high-precision position control is possible without the need for detent processing, and a magnetic type that is easy to handle An encoder such as a linear encoder can be manufactured at low cost. Therefore, the present invention enables high-precision position control without requiring high-level machining, as compared with the conventional encoder, and the cost is correspondingly reduced.

Further, in the encoder of the present invention, the formation of a magnetic scale for applying a magnetic signal can be easily obtained by plating, so that it is difficult to form a substantially uniform magnetic scale with a conventional encoder. It becomes easy to form the magnetic scale on the entire surface of the magnetic scale member,
Therefore, a magnetic signal for position control can be recorded on the entire surface of the magnetic scale member, for example, on the entire circumference of the rod, and the magnetic sensor can be arranged at an appropriate position.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a cylinder according to an embodiment of the present invention, showing a state where a cylinder rod is magnetized.

FIG. 2 is a perspective view of a bias terminal integrated MR element three-terminal type of the embodiment shown in FIG. 1;

FIG. 3 is a front view showing an arrangement relationship between a magnetized cylinder rod and a bias magnet integrated MR element.

FIG. 4 is a diagram showing a state of a position detection signal in the embodiment shown in FIG.

FIG. 5 is a circuit diagram showing a bridge circuit assembled with a bias magnet integrated MR element and a resistor.

FIG. 6 is a diagram showing an example of output characteristics of a bias magnet integrated MR element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Cylinder rod 2 Co, Ni, P system plating part 3 Cylinder main body 14 and 36 Bias magnet integrated MR element 4, 9, 21, 25, 28 and 33 Output terminal of bias magnet integrated MR element 5, 6, 10 , 11, 19, 20, 23, 24, 26,
27, 31 and 32 Magnetic field detection pattern of bias magnet integrated MR element 7, 8, 21, 22, 29 and 30 Applied voltage terminal of bias magnet integrated MR element 12, 34 Glass substrate 13, 35 Bias magnet 37 Bias magnet Integrated MR element holding member

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Matsuo Hino 30-4 Shimogawara, Oya, Okawara-machi, Shibata-gun, Miyagi Prefecture (56) References JP-A-59-164406 (JP, A) JP-A-60-209101 (JP) , A) Japanese Utility Model Application No. 1-160317 (JP, U) Japanese Utility Model Application No. 2-128519 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01B 7/00-7/34

Claims (4)

(57) [Claims] 1. A magnetic linear encoder in which a magnetoresistive element is provided near a surface of a magnetic scale member, wherein a part of or the entire surface of the magnetic scale member is fixed in a moving direction of the magnetic scale member. A magnetic encoder comprising a high coercivity alloy plating film magnetized at a pitch. 2. An alloy plating film having a high coercive force comprises cobalt of 75 to 87% by weight, nickel of 8.5 to 22% by weight,
2. The magnetic encoder according to claim 1, wherein said magnetic encoder is an alloy film having a composition of 2.5% to 4.5% by weight of phosphorus. 3. The magnetic encoder according to claim 1, wherein the magnetic scale member is a rod that reciprocates in a linear direction. 4. A method for manufacturing a magnetic encoder in which a magnetoresistive element is provided near a surface of a magnetic scale member, wherein a part or all of the surface of the magnetic scale member is plated with an alloy plating film having a high coercive force. A method of manufacturing a magnetic encoder, wherein the alloy plating film is magnetized at a constant pitch in a moving direction of the magnetic scale member.