JPH0739093A - Method of manufacturing rotor for stepping motor - Google Patents

Abstract

(57) [Summary] [Object] To provide a manufacturing method capable of improving the dimensional accuracy of a rotor for a permanent magnet type stepping motor. A rotor made of resin used for a permanent magnet type stepping motor includes a cylindrical portion 5 formed so as to wrap the permanent magnet 3 from the inside, a boss portion 7 formed so as to wrap the shaft 1, and a cylindrical portion 5. It is formed by connecting a disk-shaped middle flange 9 that connects with the boss 7 by resin injection molding. In the method of manufacturing a rotor according to the present invention, gates 11 for injecting resin into a molding die (not shown) are provided on the axial end surface of the boss portion 7 at three locations evenly in the circumferential direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a rotor for a stepping motor, and more particularly to a method of manufacturing a rotor used in a permanent magnet type stepping motor.

[0002]

2. Description of the Related Art A permanent magnet type stepping motor includes a rotor in which a permanent magnet is arranged and a stator yoke having magnetic pole teeth facing the rotor. As shown in FIG. 6, in the rotor, permanent magnets 3 are arranged in the circumferential direction around a central shaft 1, and the permanent magnet 3 and the shaft 1 are connected and fixed by a resin. This resin includes a cylindrical portion 5 that supports the permanent magnet 3 so as to wrap it from the inside, a boss portion 7 that wraps the shaft 1, and a disk-shaped middle collar portion 9 that connects the cylindrical portion 5 and the boss portion 7. To form.

This rotor is manufactured by injection molding a resin. That is, the shaft 1 and the permanent magnet 3 are arranged in a molding die (not shown), and resin is injected and filled into the inside from a resin injection port (hereinafter referred to as a gate) 11. At this time, as shown in FIGS. 6 (a) and 6 (b), the gate 11 was normally provided at three places in the middle collar portion 9. However, the following problems were encountered in the method of manufacturing such a rotor. There was a point.

[0004]

As shown in FIG. 6 (b), the resin filled from the gates 11 provided at the three positions of the middle collar 9 is circumferentially arranged inside the middle collar 9. The resin flows spread and collide with each other near the middle of the gates 11. Different gate 1 formed by this collision
The portion where the resins injected from No. 1 contact each other is called a weld line 13, and since the molding shrinkage ratio is different from the portion formed of other uniform resin, uneven shrinkage occurs in the middle flange portion 9. .

FIG. 7 is an explanatory view schematically showing a state in which the shrinkage unevenness has occurred. The shrinkage rate is small in the portion where the resin flow direction 15 is orthogonal to the circular periphery of the middle flange portion 9, and is large in the portion where the flow direction is substantially parallel to the circular periphery. Incidentally, in FIG.
The shorter the arrow 17, the larger the contraction rate. Therefore, the contraction does not occur much in the portion close to the gate 11 (arrow 17 is short), the contraction is large between the gates 11 (arrow 17 is long), and the circularity of the rotor is deteriorated.

Further, when unevenness in molding shrinkage occurs in the middle collar portion 9 in this way, the permanent magnet 3 and the cylindrical portion 5 supporting the permanent magnet 3 are formed.
A gap is created between the shaft 1 and the permanent magnet 3
There is a problem in that the coaxiality with is deteriorated, and the permanent magnet 3 is subjected to undesired stress due to the contraction of the cylindrical portion 5 in the radial direction and the contraction unevenness of the middle flange portion 9.

The present invention has been made to solve the above problems, and the molding shrinkage of the filled resin becomes uniform in the circumferential direction, and the dimensional accuracy of the rotor can be improved. It aims at providing the manufacturing method of.

[0008]

In order to achieve the above-mentioned object, one construction of the method of the present invention is that a cylindrical permanent magnet and a shaft concentrically arranged at the center of the permanent magnet are made of resin. The resin is a disk-shaped medium that connects the cylindrical portion and the boss portion, and the resin is a cylindrical portion that is formed so as to wrap the permanent magnet from the inside, a boss portion that wraps the shaft, In the method for manufacturing a stepping motor rotor having a collar portion, a gate is provided on the boss portion to inject the resin.

Preferably, a terrace portion having a smaller axial thickness than the boss portion and larger than the middle collar portion is formed in a part of the boss portion, and a gate is provided on the terrace portion.

Further, according to another structure of the method of the present invention, a ring-shaped thick portion is formed in the middle flange portion so as to surround the shaft and has a thickness in the axial direction, and the gate is formed in the ring-shaped thick portion. Is provided to inject the resin.

Further, in any of the above configurations, it is preferable to intermittently form slit portions that do not cover the permanent magnets in the circumferential direction of the cylindrical portion.

[0012]

According to the method of the present invention having the above-mentioned first structure, since the gate is provided in the boss portion to inject the resin, the resin injected from the gate first spreads into the wide boss portion, After filling the portion, it spreads radially to a narrower middle collar portion, and no weld line is formed in the middle collar portion and the cylindrical portion.

If a terrace portion having a smaller axial thickness than the boss portion and larger than the middle flange portion is formed on a part of the boss portion and a gate is provided on the terrace portion, the injected resin will be Since it once collides with the wall of the terrace and then spreads inside the boss, jetting (a phenomenon in which the resin injected into a wide space loses fluidity and solidifies one after another) is prevented.

Next, according to the second configuration of the above-mentioned method of the present invention, the injected resin first spreads in the wide ring-shaped thick portion, fills the ring-shaped thick portion, and then radially radiates to the narrow middle brim portion. As described above, the weld line is not formed in the middle brim portion (excluding the ring-shaped thick portion), the boss portion and the cylindrical portion.

In both of the first and second configurations described above, if the slits that do not cover the permanent magnets are formed intermittently in the circumferential direction of the cylindrical portion, the resin forming the cylindrical portion is not circumferentially formed. It becomes continuous and the molding shrinkage is non-uniformly distributed in the circumferential direction of the cylindrical portion, so that an inward external force in the permanent magnet is prevented from acting.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG. The rotor according to the present embodiment is a rotor of a permanent magnet (PM) type stepping motor, and includes a shaft 1 and a permanent magnet 3. That is, the shaft 1 is concentrically arranged at the center of the permanent magnets 3 arranged in the circumferential direction. The shaft 1 and the permanent magnet 3 are connected and fixed by resin. With this resin, the cylindrical portion 5 is formed so as to wrap the permanent magnet 3 from the inside, and the boss portion 7 is formed so as to wrap the shaft 1. The cylindrical portion 5 and the boss portion 7 are connected by a disc-shaped middle collar portion 9. The axial thickness of the boss portion 7 is larger than the axial thickness of the middle collar portion 9. Gates 11 as resin injection ports are formed at three locations on the boss portion 7 at equal intervals in the circumferential direction.

When forming the rotor, the shaft 1 and the permanent magnet 3 are placed in a molding die (not shown) for injection molding, and the resin is injected from the gate 11. The resin injected into the mold spreads into the boss portion 7 and first fills the boss portion 7. Then, the resin filling the boss portion 7 spreads radially into the middle collar portion 9. Further, the resin filling the middle collar portion 9 spreads to the cylindrical portion 5. Thus, the gate 1
The flow direction 15 of the resin which spreads from 1 → boss 7 → middle collar 9 → cylindrical 5 is indicated by an arrow in FIG. The double circles in FIG. 1 indicate the flow of resin in the direction orthogonal to the paper surface. (The same applies to FIGS. 2 and 4.) As described above, according to the first embodiment of the present invention, the boss portion 7 is provided with three gates 11 and the gates 11 are injected from the three locations. Since the filled and filled resin spreads radially into the inner collar 9 after filling the boss 7, the weld line is not formed in the middle collar 9 and the cylindrical portion 5 as in the conventional case, and the resin is radially filled. Oriented. Therefore, the molding shrinkage of the resin becomes more uniform than that of the conventional example, which improves the roundness of the rotor. Furthermore, since the weld line 13 is not formed in the middle collar portion 9 and the cylindrical portion 5, the weld line 1
It is also possible to prevent the strength of the rotor from being reduced due to No. 3 above.

In the above first embodiment, the gate 11 is connected to the shaft 1.
It is provided on the axial end surface of the boss portion 7 that encloses the boss portion 7. However, as shown in the second embodiment of the present invention in FIG. 2, the terrace portion 17 is formed on the boss portion 7 and the gate 11 is provided on the terrace portion 17. Good. That is, in this second embodiment, the terrace portion 17 is formed in the boss portion 7 so that the thickness in the axial direction is thinner than the thickness of the boss portion 7 and thicker than the thickness of the middle flange portion 9.

In this embodiment, the terrace 17 has three
3 provided on the boss 7 corresponding to the gate 11 at the location
It is formed as an arcuate depression at a location. When the resin is filled from the gate 11 formed on the terrace portion 17, the resin once collides with the inner wall surface of the terrace portion 17 facing the gate 11 and then flows to the surroundings. Therefore, when the resin is injected into a wide space, it is possible to prevent the phenomenon of jetting in which the resin loses fluidity and solidifies one after another.
That is, the resin once collides with the inner wall of the terrace portion 17 and then spreads to the entire inside of the boss portion 7 without losing fluidity to fill the boss portion 7. After that, the resin spreads radially into the middle collar portion 9 as in the first embodiment. Therefore,
The weld line 13 is not formed on the middle collar portion 9 and the cylindrical portion 5.

Next, the third embodiment of the present invention will be described with reference to FIG.
Will be described with reference to. In the first and second embodiments, the cylindrical portion 5 of the rotor is formed so as to wrap the permanent magnet 3 with resin from the inside, and the inner circumference and the end of the permanent magnet 3 are covered with resin on the entire circumference. There is. However, as shown in this embodiment, the slit portion 19 in which the permanent magnet 3 is not covered with the resin can be intermittently formed in the circumferential direction. By forming the slit portion 19 in this manner, the resin becomes discontinuous in the circumferential direction.

As described above, the resin has a flow direction of 15
Since the molding shrinkage along the direction is small, and the molding shrinkage is large in the direction orthogonal to the flow direction 15, the cylindrical portion 5 and the permanent magnet 3 are formed in the cylindrical portion 5 in the circumferential direction and the middle collar portion 9 is molded. Due to the non-uniform shrinkage, a part of the shrinkage may be deformed so as to be pulled inward in the radial direction. Therefore, as in this embodiment, if the slit portion 19 is provided in the cylindrical portion 5 and the resin is formed so as to be discontinuous in the circumferential direction,
It is possible to prevent the cylindrical portion 5 and the permanent magnet 3 from being unevenly deformed inward in the radial direction. Therefore, the finished dimensional accuracy of the rotor and the roundness of the rotor can be improved.
Furthermore, the resin forming the cylindrical portion 5 is deformed inward to generate a gap between the resin and the permanent magnet 3, and the backlash between the shaft 1 and the permanent magnet 3 is deteriorated. To prevent.

In the above first to third embodiments, the gate 11
Was provided in the boss portion 7, but as in the fourth embodiment of the present invention shown in FIG. 4, a ring-shaped thick portion 21 is provided in the middle collar portion 9,
The gate 11 may be formed on the ring-shaped thick portion 21. That is, a ring-shaped thick portion 21 that surrounds the shaft 1 in a circumferential direction is formed in a part of the middle brim portion 9 in the radial direction, the cross-section protruding in the axial direction. The gate 11 is provided on the axial end surface of the ring-shaped thick portion 21.

After filling the ring-shaped thick portion 21, the resin filled from the gate 11 spreads radially to the outside and the inside of the middle flange 9 in the radial direction. Since the resin spreads radially in this manner, the weld line 13 is not formed in the middle flange portion 9 (excluding the ring-shaped thick portion), the boss portion 7 and the cylindrical portion 5.

In particular, jetting can be prevented by making the axial dimension of the ring-shaped thick portion 21 substantially equal to the axial dimension of the terrace portion 17 of the second embodiment.

Also in the fourth embodiment, as shown in FIG. 5, a slit portion 19 can be formed in the cylindrical portion 5, and the same operation as that of the third embodiment is performed.

Here, the circularity of each of the rotor manufactured by the method of the second embodiment of the present invention and the rotor manufactured by the conventional method was measured to confirm the effect of the method of the present invention. The measurement comparison results are shown in Tables 1 and 2. Table 1
Is the measurement result for the rotor by the conventional manufacturing method shown in FIG. 6, and Table 2 is the measurement result for the rotor by the manufacturing method of the present invention.

In any case, as shown in FIG. 2, the roundness of the outer circumference of one permanent magnet (measurement point I) and the roundness of the outer circumference of the resin cylindrical portion between both permanent magnets (measurement point II). The roundness (measurement point III) of the outer circumference of the other permanent magnet was measured.
The measurement was performed for 12 conventional rotors and 3 rotors of the present invention, and the average value was obtained.

[0028]

[Table 1]

[Table 2] As shown in these tables, the average value at each measurement point is smaller in the rotor of the method of the present invention than in the rotor of the conventional method, and the roundness is improved by the present invention. it is obvious.

Although a plurality of cylindrical permanent magnets 3 are arranged at intervals in the axial direction in the above embodiments, the present invention uses a cylindrical permanent magnet 1 as a unit. It can also be applied to a rotor in which only individual pieces are arranged.

In the above embodiment, the gates 11 for filling the resin are provided at three places. However, if the gates are arranged at equal intervals in the circumferential direction of the rotor, even if there are four or more places. Alternatively, it may be provided at two locations. Further, as the gate 11, any type of gate may be adopted as long as it is a known gate.

Furthermore, in the third embodiment (FIG. 3) and the fifth embodiment (FIG. 5), the slit portion 19 is formed up to the axial end surface of the permanent magnet 3, but only in the central portion in the axial direction. The slit portion 19 may be formed so that the resin is continuously formed in the circumferential direction on the axial end surface.

[0032]

As described above in detail with reference to the embodiments, according to the method for manufacturing the stepping motor rotor having the first structure of the present invention, the resin is injected by providing the gate for injecting the resin in the boss portion. Therefore, the injected resin first spreads in the wide boss portion, fills the boss portion, and then radially spreads to the narrower middle brim portion, so that no weld line is formed in the middle brim portion and the cylindrical portion. The molding shrinkage of the middle flange portion is made uniform, the finished dimensional accuracy and roundness of the rotor are improved, and the strength is also improved.

In the method for manufacturing a rotor having the first structure according to the present invention, a terrace portion having a smaller axial thickness than the boss portion and larger than the middle flange portion is formed in a part of the boss portion, and the terrace portion is formed. If a resin is injected with a gate installed on the terrace, the injected resin will once hit the wall of the terrace and then spread inside the boss, preventing jetting and reducing the volume of the boss. Can be reduced and the manufacturing cost can be reduced accordingly.

According to the method of manufacturing the rotor for a stepping motor having the second structure of the present invention, the injected resin first spreads within the wide ring-shaped thick portion and then the ring-shaped thick portion is filled. Because it spreads radially to the narrow middle brim,
No weld lines are formed on the middle flange (excluding ring-shaped thick part), boss and cylinder, and uniform molding shrinkage of middle flange (excluding ring-shaped thick part), boss and cylinder As a result, the finished dimensional accuracy and roundness of the rotor are further improved.

Further, in any of the first and second configurations, if the slit portion which does not cover the permanent magnet is intermittently formed in the circumferential direction of the cylindrical portion, the resin forming the cylindrical portion is circumferentially formed. This prevents the inward external force from acting on the cylinder and the permanent magnet due to the non-uniformity of the molding shrinkage in the circumferential direction of the cylinder, which improves the finished dimensional accuracy of the rotor and the true circle of the rotor. It is possible to obtain various excellent effects such that the degree of rotation can be improved, and a play is generated due to a gap between the cylindrical portion and the permanent magnet, and the coaxiality between the shaft and the permanent magnet is prevented from being deteriorated.

[Brief description of drawings]

1A is a longitudinal sectional view of a rotor according to a first embodiment of the method of the present invention, and FIG. 1B is a transverse sectional view of FIG. 1A.

FIG. 2 (a) is a longitudinal sectional view of a second embodiment of the method of the present invention,
(B) is a cross-sectional view of (a).

FIG. 3 is a partially cutaway perspective view showing a third embodiment of the method of the present invention.

4A is a vertical sectional view showing a fourth embodiment of the method of the present invention, and FIG. 4B is a horizontal sectional view of FIG. 4A.

FIG. 5 is a partially cutaway perspective view showing a fifth embodiment of the method of the present invention.

6A is a vertical sectional view showing a rotor manufactured by a conventional manufacturing method, and FIG. 6B is a horizontal sectional view of FIG. 6A.

FIG. 7 is an explanatory view schematically showing a pattern of molding shrinkage in a conventional example.

[Explanation of symbols]

 1 Axis 3 Permanent magnet 5 Cylindrical part 7 Boss part 9 Middle collar part 11 Gate 13 Weld line 17 Terrace part 19 Slit part 21 Ring-shaped thick part

Claims (5)

[Claims] 1. A cylindrical permanent magnet and a shaft arranged concentrically at the center of the permanent magnet are connected and fixed by a resin, and the resin is formed so as to wrap the permanent magnet from the inside. In a method of manufacturing a stepping motor rotor, which comprises a cylindrical portion, a boss portion that encloses the shaft, and a disk-shaped middle brim portion that connects the cylindrical portion and the boss portion, a gate is provided on the boss portion. A method for manufacturing a stepping motor rotor, comprising: 2. A terrace portion having a thickness in the axial direction smaller than that of the boss portion and larger than that of the middle flange portion is formed in a part of the boss portion, and a gate is provided on the terrace portion. The method for manufacturing a stepping motor rotor according to claim 1. 3. The method for manufacturing a rotor for a stepping motor according to claim 1, wherein slit portions that do not cover the permanent magnets are intermittently formed in a circumferential direction of the cylindrical portion. 4. A cylindrical permanent magnet and a shaft concentrically arranged at the center of the permanent magnet are connected and fixed by a resin, and the resin is formed so as to wrap the permanent magnet from the inside. In a method for manufacturing a stepping motor rotor, which comprises a cylindrical portion, a boss portion that encloses the shaft, and a disk-shaped middle flange portion that connects the cylinder portion and the boss portion, the shaft is provided in the middle collar portion. A method for manufacturing a rotor for a stepping motor, characterized in that a ring-shaped thick portion that is thickly formed in the axial direction surrounding the is formed, a gate is provided in the ring-shaped thick portion, and the resin is injected. 5. The method for manufacturing a rotor for a stepping motor according to claim 4, wherein slit portions that do not cover the permanent magnets are intermittently formed in a circumferential direction of the cylindrical portion.