JP4882278B2 - Magnetic encoder - Google Patents

Description

  The present invention relates to a magnetic encoder used in an apparatus for detecting the rotational speed, rotational position, etc. between two members that rotate relative to each other.

2. Description of the Related Art Conventionally, a device that uses a magnetic encoder as a device for detecting the rotational speed, rotational position, and the like between two members that rotate relatively is known.
JP 2003-344104 A

  For example, as shown in FIG. 2A, the magnetic encoder has an annular shape, and as shown in FIG. 2B, the bond magnet 2 is magnetized at equal intervals in the circumferential direction of the metal ring 1. Is used to detect the rotational speed of the shaft and the like by detecting the circular movement of the magnetic pole accompanying the shaft rotation with the fixed magnetic sensor 3. .

  Further, as the above-described bond magnet 2 for a magnetic encoder, a rubber magnet for a sensor in which a vulcanized rubber such as NBR and ethylene-methyl acrylate copolymer rubber is filled with magnetic powder such as ferrite is used.

By the way, as described above, magnetic encoders using rubber magnets can be reduced in weight compared to metal tone rings (tooth cutting plates), and are excellent in detecting the number of rotations at low speed. Has been. However, since the matrix material (rubber) used in this rubber magnet is a thermosetting material with a vulcanizing agent,
(1) Difficult to recycle (2) Low yield of materials due to molding with burrs (3) Long molding cycle due to vulcanization reaction (4) Post-processing such as removal of burrs and runners after molding is complicated Yes (5) There are few applicable molding directions and the molding processability is inferior (6) The maximum filling rate of fillers such as magnetic powder is lower than that of thermoplastic resins (7) Flow when magnetic powder is highly filled Low viscosity (high viscosity)
Such a problem occurred.

  On the other hand, as a bond magnet matrix material, a material using a thermoplastic resin such as nylon 6 or PPS (polyphenylene sulfide) is also used.

  In the case of such a material, although the above-mentioned trouble of the thermosetting material can be compensated, the product is easily cracked when the magnetic powder is highly filled (occurrence of a crack or the like) and is integrally formed with the metal ring 1. Is very difficult and unsuitable as a bonded magnet.

  Incidentally, when a crack or the like occurs in the product function part (magnetic detection part), it adversely affects the magnetic characteristics such as an increase in pitch error and so on, which is not preferable in terms of product function.

  Furthermore, in the case of the bond magnet 2 using a thermoplastic elastomer as a matrix material (a binder resin for magnetic powder), since it is necessary to use an adhesive for the adhesion between the bond magnet 2 and the metal ring 1, the material cost increases. In addition, there is a problem that a molding defect (weld portion) may be formed in the product function portion (magnetic detection portion).

  Incidentally, when molding defects such as welds occur in the magnetic detection unit, magnetic characteristics such as pitch errors are adversely affected. That is, since the orientation of the filled magnetic powder influences the sensor output (magnetic force), the partial variation in orientation leads to the variation in output intensity.

  In order to solve the above problems, the present invention provides a magnetic encoder capable of ensuring adhesion with a metal ring without using an adhesive, and further ensuring the adhesion and improving the anti-peeling property. The purpose is to do.

To achieve its purpose, the magnetic encoder of the present invention includes a metal ring of an annular and a bonded magnet was cured thermoplastic elastomer molten material impregnated with a magnetic powder on the outer surface of the metal ring, the In a magnetic encoder having a portion where the bonded magnet surrounds and wraps around the back surface at the outer peripheral edge of the metal ring , a plurality of slit-like holes are provided near the inner periphery of the metal ring so that the thermoplastic elastomer molten material wraps toward the inner surface The formed metal ring is used.

  In the magnetic encoder of the present invention, the slit-shaped hole extends along the circumferential direction of the metal ring and is formed in an elliptical shape or a shape similar to the elliptical shape in the longitudinal direction. And

  In the magnetic encoder of the present invention, the slit-shaped hole has a length along the longitudinal direction set to 1 to 3 times the product function width.

Furthermore, the magnetic encoder according to the present invention is such that a plurality of the slit-like holes are formed at regular intervals in the circumferential direction of the metal ring, and at least one of them is a gate for supplying a thermoplastic elastomer molten material. It is provided in the same position as the position.

Thermoplastic elastomer melt materials include styrene, polyurethane, polyester, polyamide, fluorine, vinyl chloride, polyolefin, polybutadiene, polyisoprene, polyethylene and other alloy types (block copolymers, grafts) Copolymers, polymer blends) or non-alloy (homopolymers, random copolymers) thermoplastic elastomer melt materials are used.

According to the magnetic encoder of the present invention, a plurality of slit-shaped holes for the thermoplastic elastomer molten material to wrap around the inner surface side are formed near the inner periphery of the metal ring, so that the bond magnet is on the back side of the metal ring. In addition to being able to improve the adhesion of the bonded magnet, it is possible to improve the adhesion of the bonded magnet by retracting it from the sensor detection position by forming a slit-like hole closer to the inner circumference of the metal ring. The occurrence of molding defects such as welds can be prevented, and the magnetic characteristics can be maintained satisfactorily.

Moreover, the magnetic encoder of this invention can make the thermoplastic elastomer molten material wrap around easily by making the slit-shaped hole into an elliptical shape along the circumferential direction of the metal ring.

  In addition, the magnetic encoder of the present invention prevents the peeling of the bonded magnet during rotation of the magnetic encoder by setting the length of the slit-shaped hole to 1 to 3 times the product functional width. Can do.

Furthermore, the magnetic encoder of the present invention, a slit-shaped hole by which the gate located at the same position for supplying a thermoplastic elastomer molten material, can be more easily sneak thermoplastic elastomer molten material.

  Next, the magnetic encoder of the present invention will be described with reference to the drawings. The overall configuration of the external appearance of the magnetic encoder is the same as that shown in FIG. 2A, and is not shown here.

  In FIG. 1 (A), 11 is a metal ring used for a magnetic encoder. Near the inner periphery of the metal ring 11, a plurality of slit-shaped holes 11a are formed at predetermined intervals in the circumferential direction. The metal ring 11 is covered with a bond magnet 12 on the surface side as shown in the cross-sectional view along the line AA in FIG.

The slit-shaped hole 11a extends along the circumferential direction of the metal ring 11, and is formed in an arc shape in the longitudinal direction and an elliptical shape or a shape similar to the elliptical shape. An elliptical shape or a shape conforming to it is a shape in which the major axis is set to a ratio of about 3 to 10 times, preferably about 3 to 7 times the minor axis, and the rectangular corners are rounded. It is . Further, the length L along the longitudinal direction of each slit-shaped hole 11a is 1 to 3 times the product function width W centering on the detection portion facing the sensor 13, as shown in FIG. , Preferably about twice as long.

The slit-shaped hole 11a is indicated by a gate (for example, shown by a chain line in FIG. 1A) when insert molding or the like of a thermoplastic elastomer molten material filled with magnetic powder as the bond magnet 12 to the metal ring 11. ) To make the thermoplastic elastomer molten material wrap around the metal ring 11 to the back side more easily.

As the material of the bond magnet 12, various thermoplastic elastomers as described above filled with magnetic powder, for example, TPE bond magnet molten material (100 parts by weight of AR750B manufactured by Aronkasei Co., Ltd. is used as TPE material , 700 parts by weight of Toda) Industrial-use FA-700 strontium ferrite powder) is used, but the material is not particularly limited. As the magnetic powder, ferrite magnetic powder or rare earth magnetic powder having a particle size of about 0.5 to 10 μm is generally used. The effect of various embodiments using such a TPE-based bonded magnet molten material will be described below.

  A plurality of such slit-shaped holes (with a length L doubled with respect to the product function part width) 11a are provided, and a part of the bond magnet 12 is made to wrap around the back surface of the metal ring 11 during injection molding. In the encoder, no peeling occurred even in the rotation test performed by fixing to the rotation tester. Further, there was no molding defect such as weld in the product function part, and the pitch error was 1.5% or less, and the magnetic characteristics could be maintained well.

  Here, when the same test as described above was performed using the metal ring 1 in which the slit-shaped hole 11a was not provided, the bond magnet 2 was peeled off. Further, defective molding (weld) was recognized in the product function part, and when the magnetic characteristics were measured, the pitch error was 3.0% or more.

  Further, when the slit-shaped hole 11a is circular (major axis / minor axis = 1.0), the adhesion of the bonded magnet 12 to the metal ring 11 after the injection molding can be kept good, but the product function Weld was observed in the part, and the magnetic characteristics (pitch error) were adversely affected.

  Furthermore, even when the length L of the slit-shaped hole 11a was made narrower than the width W of the product function part, generation of welds was observed in the product function part, and an adverse effect was observed on the magnetic characteristics (pitch error).

  Contrary to this, even when the length L of the slit-shaped hole 11a was 3 times the width W of the product function part, the adhesion was good and no weld was observed, but this magnification was The setting should be in accordance with the overall strength of the metal ring 11 and the usage environment.

Further, when injection was performed in a state where all of the slit-shaped holes 11a did not coincide with the gate of the injection molding machine, a phenomenon that the bond magnet 12 floated from the metal ring 11 occurred, and the back surface of the metal ring 11 of the thermoplastic elastomer molten material. Inadequate wraparound to the side was observed.

  As described above, according to the magnetic encoder of the present invention, the slit-shaped hole 11a is formed in the inner peripheral portion of the metal ring 11 excluding the center of the product function unit (magnetic detection unit). Smooth wrapping of the bond material 12 to the back surface side of the metal ring 11 is possible, and peeling from the metal ring 11 can be prevented.

  In addition, the slit-shaped hole 11a has an elliptical shape or a shape conforming to the elliptical shape, and its length L is 1 to 3 times the product function portion width W, thereby further preventing the bond material 12 from peeling. can do.

  Furthermore, by disposing the slit-shaped holes 11a in the runner part (gate part) of the injection mold, the peeling of the bond material 12 can be further prevented.

The magnetic encoder of this invention is shown, (A) is a front view of a metal ring, (B) is the AA line expanded sectional view. A conventional magnetic encoder is shown, (A) is a front view of the magnetic encoder, and (B) is an enlarged sectional view of a main part.

Explanation of symbols

11 ... Metal ring 11a ... Hole 12 ... Bond magnet 13 ... Sensor

Claims (3)

An annular metal ring and a bond magnet obtained by curing a magnetic powder-filled thermoplastic elastomer molten material on the outer surface of the metal ring , and the bond magnet surrounds and wraps around the back surface at the outer peripheral edge of the metal ring. In a magnetic encoder having
A plurality of slit-shaped holes are formed near the inner periphery of the metal ring to allow the thermoplastic elastomer molten material to go to the inner surface side, and the slit-shaped holes extend along the circumferential direction of the metal ring and A metal ring is used that is formed in an elliptical shape in the longitudinal direction or a shape similar thereto, and whose length along the longitudinal direction is set to 1 to 3 times the product functional width. Magnetic encoder. A plurality of the slit-like holes are formed at a constant interval in the circumferential direction of the metal ring, and at least one of them is provided at the same position as the gate position for supplying the thermoplastic elastomer molten material. The magnetic encoder according to claim 1. 3. The magnetic encoder according to claim 1, wherein the elliptical shape or a shape conforming thereto is a slit-like hole in which a ratio of a major axis to a minor axis is set to 3 to 10. 3.

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