Manufacturing method for magnetic encoder

Abstract

Provided is a manufacturing method of an axial-type magnetic. The manufacturing method includes a press molding step and an injection molding step. The axial-type magnetic encoder includes a wrap-around binding part wrapping around from a sensor-opposed surface to a back surface of an inward flange part of an annular fixing member. A separated inner peripheral part separated from a rotating body is formed at an inner diameter-side portion of the inward flange part while an outer diameter-side portion of a back surface of the inward flange part is abutted against the rotating body. The inner peripheral part of the annular plastic magnet wraps around to a back surface of the separated inner peripheral part.

Claims

1. A manufacturing method of an axial-type magnetic encoder, comprising: a press molding step of fabricating by press molding an annular fixing member that has a cylindrical part attached to a rotating body and an inward flange part extended more radially inward than an end edge of the cylindrical part; and an injection molding step of, while the annular fixing member is placed in a metal mold, injecting a dissolved annular plastic magnet material into the metal mold to define a shape of an annular plastic magnet, wherein the manufacturing method includes a step of forming, by a press process or mechanical process, a separated inner peripheral part formed at an inner diameter-side portion of the inward flange part of the annular fixing member that is separated from the rotating body, the inward flange part of the annular fixing member having undergone the press molding step further includes an outer diameter-side portion of a back surface of the inward flange part that is abutted against the rotating body, the metal mold defining the shape of the annular plastic magnet to be attached to the annular fixing member at the injection molding step is shaped such that an inner peripheral part of the annular plastic magnet wraps around to a back surface of the separated inner peripheral part of the annular fixing member, and a wrap-around binding part of the annular plastic magnet that wraps around to the back surface of the separated inner peripheral part is flush with the outer diameter-side portion of the back surface of the inward flange part.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIGS. 1(a) and 1(b) show a magnetic encoder according to a first embodiment of the present invention: FIG. 1(a) is a vertical cross-sectional view and FIG. 1(b) is a partial vertical perspective view;

(2) FIG. 2 is an enlarged vertical cross-sectional view of major components of the magnetic encoder attached to an outer ring as a rotating body;

(3) FIGS. 3(a) and 3(b) represent enlarged vertical cross-sectional views of major components of the magnetic encoder: FIG. 3(a) shows an annular fixing member and FIG. 3(b) shows the magnetic encoder;

(4) FIGS. 4(a) and 4(b) represent enlarged vertical cross-sectional views of major components of a magnetic encoder according to a second embodiment: FIG. 4(a) shows an annular fixing member and FIG. 4(b) shows the magnetic encoder;

(5) FIGS. 5(a) and 5(b) represent enlarged vertical cross-sectional views of major components of a magnetic encoder according to a third embodiment: FIG. 5(a) shows an annular fixing member and FIG. 5(b) shows the magnetic encoder;

(6) FIGS. 6(a) and 6(b) represent enlarged vertical cross-sectional views of major components of a magnetic encoder according to a fourth embodiment: FIG. 6(a) shows an annular fixing member; and FIG. 6(b) shows the magnetic encoder;

(7) FIGS. 7(a) and 7(b) show a conventional inward flange-type magnetic encoder: FIG. 7(a) is a vertical cross-sectional view and FIG. 7(b) is a partial vertical perspective view; and

(8) FIG. 8(a) is an enlarged vertical cross-sectional view of major components of the conventional inward flange-type magnetic encoder attached to an inner ring as a rotating body, and FIG. 8(b) is an enlarged vertical cross-sectional view of major components of the conventional inward flange-type magnetic encoder for describing problems in attaching the magnetic encoder to an outer ring as a rotating body.

DESCRIPTION OF EMBODIMENTS

(9) Next, embodiments of the present invention will be described below in detail with reference to the attached drawings. The present invention is not limited to the embodiments shown in the attached drawings but includes all of embodiments satisfying the requirements described in the claims.

(10) First Embodiment

(11) As shown in the vertical cross-sectional view of FIG. 1(a), the partial vertical perspective view of FIG. 1(b), the enlarged vertical cross-sectional view of major components of FIG. 2, and the enlarged vertical cross-sectional view of major components of FIG. 3(b), an axial-type magnetic encoder 1 according to the first embodiment of the present invention is an inward flange type and includes an annular fixing member 2 and an annular plastic magnet 3 attached to the annular fixing member 2.

(12) The annular fixing member 2 shown in the enlarged vertical cross-sectional view of major components of FIG. 3(a) is composed of a cylindrical part 2A attached to an outer ring 10 as a rotating body (refer to FIG. 2) and an inward flange part 2B extended radially inward from an end edge of the cylindrical part 2A, and is fabricated from a stainless steel plate material at a press molding step.

(13) Specifically, the annular fixing member 2 is press-molded by a squeezing process into a general shape as shown in FIGS. 7(a), 7(b), 8(a) and 8(b), and then a stepwise pressing process is performed on an inner diameter-side portion of the inward flange part 2B to form a stepwise pressed portion 4 as a separated inner peripheral part D separated from the outer ring 10 while an outer diameter-side portion of a back surface B of the inward flange part 2B is abutted against the outer ring 10 as shown in FIG. 2.

(14) The annular plastic magnet 3 is attached to a surface A of the annular fixing member 2 opposed to a sensor 8 shown in FIG. 2 (hereinafter, referred to as sensor-opposed surface) at an injection molding step with the annular fixing member 2 shown in FIG. 3(a) as an insert. Specifically, the annular fixing member 2 and the annular plastic magnet 3 are integrated such that a thermoset resin adhesive is applied to the surface (sensor-opposed surface A) of the annular fixing member 2 to be joined to the annular plastic magnet 3, the annular fixing member 2 and the annular plastic magnet 3 are placed in a metal mold, and a dissolved annular plastic magnet material is injected into the metal mold.

(15) The thermoset resin adhesive may be any adhesive for use in general magnetic encoders and, for example, may be a phenolic resin adhesive, an epoxy resin adhesive, or the like. However, the adhesive is not necessarily used but may be omitted depending on the required specifications or the like.

(16) The annular plastic magnet 3 is made of a magnet material containing magnetic substance powder, a binder, and an additive. The magnetic substance powder is preferably ferrite-based magnetic powder such as strontium ferrite or barium ferrite, or neodymium- or samarium-based rare-earth magnetic powder.

(17) The binder is preferably a thermoplastic resin material such as polyamides (PA6, PA12, PA612, and the like) or polyphenylene sulfide (PPS). The additive is preferably an organic additive such as carbon fiber, or an inorganic additive such as glass beads, glass fiber, talk, mica, silicon nitride (ceramic), or crystalline (or non-crystalline) silica.

(18) A wrap-around binding part C is formed at the inner peripheral part of the annular plastic magnet 3 so as to wrap around from the sensor-opposed surface A to the back surface of the stepwise pressed portion 4 as the separated inner peripheral part D. The wrap-around binding part C does not come closer to the outer ring 10 than the outer diameter-side portion of the back surface B of the inward flange part 2B.

(19) For example, a portion of the wrap-around binding part C wrapping around to the back surface of the stepwise pressed portion 4 is formed flush with the outer diameter-side portion of the back surface B of the inward flange part 2B as shown in FIGS. 2 and 3(b).

(20) Specifically, the metal mold defining the shape of the annular plastic magnet 3 to be attached to the annular fixing member 2 at the injection molding step is shaped such that the inner peripheral part of the annular plastic magnet 3 wraps around to the back surface of the stepwise pressed portion 4 as the separated inner peripheral part D of the annular fixing member 2, and the wrap-around binding part C of the annular plastic magnet 3 wrapping around to the back surface of the stepwise pressed portion 4 is flush with the outer diameter-side portion of the back surface B of the inward flange part 2B.

(21) A step e in the stepwise pressed portion 4 as the separated inner peripheral part D formed at the annular fixing member 2 shown in FIG. 3(a) preferably falls within the range of 0.15 to 0.5 mm. When e is smaller than 0.15 mm, the resin does not flow. When e is larger than 0.5 mm, the inner diameter-side portion of the annular plastic magnet 3 at the sensor-opposed surface A side becomes thinner with reduction in strength.

(22) An outer diameter (diameter) d2 of the stepwise pressed portion 4 as the separated inner peripheral part D is preferably larger by the range of 0.3 to 2.0 mm than an inner diameter (diameter) d1 of the inward flange part 2B of the annular fixing member 2 ((d1+0.3 mm)d2(d1+2.0 mm)). When d2 is smaller than (d1+0.3 mm), no desired binding strength can be obtained due to molding shrinkage. When d2 is larger than (d1+2.0 mm), mechanical binding strength decreases due to lack of resin charging or the like.

(23) According to the thus configured magnetic encoder 1, the magnetic encoder 1 can be axially positioned relative to the reference surface of the outer ring 10 by abutting the outer diameter-side portion of the back surface B of the inward flange part 2B of the annular fixing member 2 against the outer ring 10 as a rotating body as shown in FIG. 2.

(24) In addition, even when the outer diameter-side portion of the back surface B of the inward flange part 2B of the annular fixing member 2 is abutted against the outer ring 10, the wrap-around binding part C of the annular plastic magnet 3 does not come closer to the outer ring 10 than the outer diameter-side portion of the back surface B of the inward flange part 2B, and thus the wrap-around binding part C is not broken.

(25) Further, since the wrap-around binding part C of the annular plastic magnet 3 wraps around to the back surface of the separated inner peripheral part D formed at the inner peripheral part of the annular plastic magnet 3, it is possible to improve reliability of binding of the annular fixing member 2 and the annular plastic magnet 3 by mechanical binding force of the wrap-around binding part C.

(26) As second to fourth embodiments, modifications of the separated inner peripheral part D formed by a pressing process or mechanical process at the inner diameter-side portion of the inward flange part 2B of the annular fixing member 2 will be described below.

(27) Second Embodiment

(28) The annular fixing member 2 is press-molded by a squeezing process into a general shape as shown in FIGS. 7(a), 7(b), 8(a) and 8(b), and then the inner diameter-side portion of the inward flange part 2B is subjected to a bending process to form a bent portion 5 with a larger separation distance from the outer ring 10 in a radially inward direction as the separated inner peripheral part D separated from the outer ring 10 while the outer diameter-side portion of the back surface B of the inward flange part 2B is abutted against the outer ring 10 (refer to FIG. 2), as shown in the enlarged vertical cross-sectional view of major components of FIG. 4(a).

(29) While the annular fixing member 2 shown in FIG. 4(a) as an insert is placed in the metal mold, injection molding is performed to form the wrap-around binding part C wrapping around from the sensor-opposed surface A to the back surface of the bent portion 5 as the separated inner peripheral part D at the inner peripheral part of the annular plastic magnet 3, as shown in enlarged vertical cross-sectional view of major components of FIG. 4(b). The wrap-around binding part C does not come closer to the outer ring 10 than the outer diameter-side portion of the back surface B of the inward flange part 2B. For example, a portion wrapping around to the back surface of the bent portion 5 as the separated inner peripheral part D is formed flush with the outer diameter-side portion of the back surface B of the inward flange part 2B as shown in FIG. 4(b).

(30) The magnetic encoder 1 of the second embodiment as described above provides the same advantages as those of the first embodiment.

(31) Third Embodiment

(32) The annular fixing member 2 is press-molded by a squeezing process into a general shape as shown in FIGS. 7(a), 7(b), 8(a) and 8(b), and then the inner diameter-side portion of the inward flange part 2B is subjected to surface pressing or turning to form a back surface inclined portion 6 inclined with a more increasing distance from the outer ring 10 in the radially inward direction as the separated inner peripheral part D separated from the outer ring 10 while the outer diameter-side portion of the back surface B of the inward flange part 2B is abutted against the outer ring 10 (refer to FIG. 2), as shown in the enlarged vertical cross-sectional view of major components of FIG. 5(a).

(33) While the annular fixing member 2 shown in FIG. 5(a) as an insert is placed in the metal mold, injection molding is performed to form the wrap-around binding part C wrapping around from the sensor-opposed surface A to the back surface of the back surface inclined portion 6 as the separated inner peripheral part D at the inner peripheral part of the annular plastic magnet 3, as shown in the enlarged vertical cross-sectional view of major components of FIG. 5(b). The wrap-around binding part C does not come closer to the outer ring 10 than the outer diameter-side portion of the back surface B of the inward flange part 2B. For example, a portion wrapping around to the back surface of the back surface inclined portion 6 as the separated inner peripheral part D is formed flush with the outer diameter-side portion of the back surface B of the inward flange part 2B as shown in FIG. 5(b).

(34) The magnetic encoder 1 of the third embodiment as described above provides the same advantages as those of the first embodiment.

(35) Fourth Embodiment

(36) The annular fixing member 2 is press-molded by a squeezing process into a general shape as shown in FIGS. 7(a), 7(b), 8(a) and 8(b), and then the inner diameter-side portion of the inward flange part 2B is subjected to coining or turning to form a thinned portion 7 as the separated inner peripheral part D separated from the outer ring 10 while the outer diameter-side portion of the back surface B of the inward flange part 2B is abutted against the outer ring 10 (refer to FIG. 2), as shown in the enlarged vertical cross-sectional view of major components of FIG. 6(a).

(37) While the annular fixing member 2 shown in FIG. 6(a) as an insert is placed in the metal mold, injection molding is performed to form the wrap-around binding part C wrapping around from the sensor-opposed surface A to the back surface of the thinned portion 7 as the separated inner peripheral part D at the inner peripheral part of the annular plastic magnet 3, as shown in enlarged vertical cross-sectional view of major components of FIG. 6(b). The wrap-around binding part C does not come closer to the outer ring 10 than the outer diameter-side portion of the back surface B of the inward flange part 2B. For example, a portion wrapping around to the back surface of the thinned portion 7 as the separated inner peripheral part D is formed flush with the outer diameter-side portion of the back surface B of the inward flange part 2B as shown in FIG. 6(b).

(38) The magnetic encoder 1 of the fourth embodiment as described above provides the same advantages as those of the first embodiment.

(39) In the foregoing description, the magnetic encoder is attached to an outer ring as a rotating body. Alternatively, the magnetic encoder may be attached to an inner ring as a rotating body.

(40) In the foregoing description, the annular fixing member of the magnetic encoder is composed of the cylindrical part and the inward flange part extended radially inward from the end edge of the cylindrical part. Alternatively, the annular fixing member may include the cylindrical part and an inward flange part extended more radially inward than the end edge of the cylindrical part.

REFERENCE SIGNS LIST

(41) 1, 1A Magnetic encoder 2 Annular fixing member 2A Cylindrical part 2B Inward flange part 3 Annular plastic magnet 4 Stepwise pressed portion 5 Bent portion 6 Back surface inclined portion 7 Thinned portion 8 Sensor 9 Inner ring at rotating side (rotating body) 10 Outer ring at rotating side (rotating body) A Sensor-opposed surface B Back surface C Wrap-around binding part D Separated inner peripheral part d1 Inner diameter d2 Outer diameter of step e Step