JP2002303331A - Bearing holder and its injection molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a bearing holder which is a formed product used in a VTR capstan motor or the like easily and with accuracy. SOLUTION: The bearing holder 1 is provided with an axis hole 2 of an output rotation axis 7 and rotatably supports the output rotation axis 7 through bearing members 5 and 6 held on the inner circumferential face of the axis hole 2. An annular projection portion 4A is formed on an axis end 4 on the opposite output side of the bearing holder 1, and this annular projection portion 4A includes a thin portion 4B whose thickness is smaller in the axial direction and a thick portion 4C whose thickness is larger in the axial direction than the thin portion. On the side of the opposite output side axis end 4, an annular reduced thickness part 11 is formed. By this reduced thickness part 11, thickness of an axis hole outer circumferential wall part of an output side axis end 3 and an axis hole outer circumferential wall part of the opposite output side shaft end 4 can be made substantially equal, and then, a recess amount at the shaft end parts on both ends can be made almost equal in the process of hardening forming materials. As a result, accuracy drop of cylindrical degree and roundness of the axis hole of the obtained bearing holder can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing holder made of an injection-molded product that rotatably supports an output rotary shaft of a capstan motor such as a VTR via a bearing. The invention also relates to a method for injection molding such a bearing holder.

[0002]

2. Description of the Related Art There is known a VTR capstan motor or the like having a bearing holder which rotatably supports an output rotary shaft via a bearing member, and having a motor rotor mounted on an outer peripheral surface of the bearing holder. Have been. For example, Japanese Unexamined Utility Model Publication No. 2-41646 filed by the present applicant discloses a VTR capstan motor having such a bearing holder.

[0003] In the bearing holder disclosed in this publication, a flange portion formed at one shaft end portion and extending outward is formed by using a through-screw hole formed therein. The stator core of the motor is fixed by screws. A shaft is rotatably supported in the center hole of the bearing holder via a pair of bearing metals.

[0004] As a bearing holder of this type, a molded product by an injection molding method is often used. Such a bearing holder is formed by injecting a molding material into a cavity of a molding die from a plurality of gates arranged at portions defining an outer peripheral surface of the bearing holder in the cavity. For example, a molding material is injected using a three-point pin gate.

In order to form the shaft hole of the bearing holder, a mold core which can be divided into two in the axial direction is arranged in a molding die. After demolding, these mold cores are pulled out from the shaft ends on both sides of the bearing holder.

[0006]

In the bearing holder molded as described above, as disclosed in the above-mentioned published utility model publication, an outer peripheral wall defining a shaft hole at both shaft end portions is disclosed. Is usually different in wall thickness. If the thicknesses are different as described above, the sink amounts at the shaft end portions on both sides are different in the process of curing the injected molding material, and the molding accuracy may be insufficient. As a result, there is a possibility that the accuracy of the roundness or the cylindricity of the inner diameter of the shaft hole of the bearing holder after molding may not reach the target accuracy.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to propose a bearing holder having a structure that can be formed with higher precision than in the prior art. Another object of the present invention is to propose an injection molding method for a bearing holder that can mold a bearing holder with higher accuracy than in the past.

[0008]

In order to solve the above-mentioned problems, the present invention provides a shaft hole for an output rotary shaft, and the output rotary shaft is provided via a bearing member held on the inner peripheral surface of the shaft hole. In the bearing holder which is an injection-molded product rotatably supporting, has an output-side shaft end located at one end side in the axial direction of the bearing holder, and a non-output-side shaft end located at the other end side,
An annular protruding portion is formed at the non-output side shaft end, and the annular protruding portion has a thin portion having a small thickness in the axial direction and a thickness in the axial direction smaller than the thin portion. And a thick part, and the bearing member includes:
A first bearing member press-fitted from a shaft end opening on the output-side shaft end side of the shaft hole, and a second bearing member press-fitted from a shaft end opening on the non-output-side shaft end side are included. A ring-shaped robber is formed concentrically with the shaft hole on the side opposite to the output-side shaft end.

In the bearing holder of the present invention, since the annular projecting portion is formed, the thickness of the other output side shaft end portion is larger than that of the other output side shaft end portion. As a result, the wall thickness around the shaft hole of the output-side shaft end and the counter-output-side shaft end can be made substantially equal, and therefore, the amount of sink in the shaft end portions on both sides in the process of curing the molding material. Can be made substantially equal. As a result, it is possible to prevent the accuracy of the cylindricity and roundness of the shaft hole of the obtained bearing holder from lowering.

[0010] The thicker shaft end has a lower rigidity due to an annular thickness. Therefore, the press-fitting of the bearing member is not difficult, and can be performed similarly to the other thin output-side shaft end.

Here, the annular projecting portion formed on the side opposite to the shaft end on the non-output side is generally used for screwing a stator core or the like of a motor as in the bearing holder disclosed in the above-mentioned published utility model publication. Used as a part.
Therefore, in a typical example of the bearing holder of the present invention, a through hole extending parallel to the axial direction is formed in the thin portion of the annular projecting portion, and the thick portion is formed in the thick portion.
The blind hole extends parallel to the axial direction and is open to the output shaft end. In this case, the annular stealing may be formed at a position between the through hole and the blind hole and the shaft hole.

It is desirable that the depth of the annular thickness is equivalent to the depth in the axial direction into which the second bearing member is press-fitted.

Next, the present invention relates to an injection molding method for a bearing holder having the above-mentioned structure, wherein a tapered outer peripheral surface corresponding to the inner peripheral surface shape of the shaft hole is formed in a molding die cavity corresponding to the bearing holder. The present invention is characterized in that a molding core provided is disposed and a molding material is axially injected from a portion of the cavity that defines an axial end of the bearing holder into the cavity.

In the present invention, the molding material is injected into the mold cavity from the shaft end side. That is, the center gate method is adopted. When the molding material is injected in this way, the accuracy of the roundness and cylindricity of the shaft hole of the bearing holder obtained is improved as compared with the conventional case where the molding material is injected from the outer peripheral side of the cavity by the bin gate method. it can.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 show V to which the present invention is applied.
An example of a bearing holder for a TR capstan motor is shown. In these figures, FIG. 1 is a schematic sectional view showing a state in which the output rotary shaft is mounted on the bearing holder, and FIGS. 2A to 2D are views showing only the bearing holder.

The bearing holder 1 has a shaft hole 2 at its center, and has a cylindrical shape as a whole. This bearing holder 1
, One shaft end 3 is an output-side shaft end, and the other shaft end 4 is a non-output-side shaft end. Ring-shaped bearing members 5 and 6 having the same shape are press-fitted into the shaft hole 2 from the shaft end openings on both sides. The output rotary shaft 7 penetrates these bearing members 5 and 6 in a rotatable state.

Here, an annular protruding portion 4A is formed at the non-output side shaft end 4, so that the thickness is significantly larger than the thickness t13 of the outer peripheral wall of the shaft hole at the output side shaft end 3. I have. The annular protruding portion 4A is formed with a thin portion 4B having a small thickness in the axial direction and the thin portion 4B.
Three thick portions 4C having a greater thickness in the axial direction than B are formed at constant angular intervals in the circumferential direction. In the thin portion 4B, through holes 4D penetrating the thin portion 4B in the axial direction are formed at three locations at regular angular intervals.
Each thick portion 4C is formed with a blind hole 4E extending in the axial direction, which is open on the side of the output-side shaft end 3.

Next, the inner peripheral surface 21 of the shaft hole 2 is formed such that the inner diameter D4 of the shaft hole on the non-output side shaft end 4 is slightly smaller than the inner diameter D3 of the shaft hole on the side of the output side shaft end 3. It is formed in a slightly tapered shape in the axial direction. On the opposite side of the non-output side shaft end 4, a ring-shaped robber 11 is formed concentrically. This meat steal 11 is formed in the protruding portion 4A at a position inside the through hole 4D and the blind hole 4E. That is, it is located between these holes and the shaft hole 2. The thickness t12 of the shaft hole outer peripheral wall 12 of the non-output side shaft end 4 is thinner than the thickness t13 of the shaft hole outer peripheral wall 13 of the output side shaft end 3 due to the thickness thief 11.

FIG. 3A shows a longitudinal section of a molding die used for injection molding of the bearing holder 1 of this embodiment. A cavity 100 for molding the bearing holder 1 is formed by closing an upper mold 101 and a lower mold 102 which are split molds. The upper die 101 and the lower die 102 are fixed to dies 103 and 104, respectively. These dies 103 and 104 are driven by a mold clamping mechanism (not shown) to perform mold clamping and mold opening operations.

In this embodiment, a bearing holder 1 is provided on the upper mold 101 side.
A mold surface corresponding to the non-output side shaft end 4 is formed, and a mold surface of the other portion of the bearing holder 1 is formed on the other lower side 102. A center pin 110 as a molding die core for molding the shaft hole 2 of the bearing holder 1 is inserted into the cavity 100 in the axial direction thereof. A film gate 120 serving as a center gate is coaxially abutted on the shaft end face of the upper side of the center pin 110.

As shown in FIG. 3B, the film gate 120 has an exit 121 formed along a circular outer peripheral surface, and has a width of about 0.1 mm to about 1.5 mm. From the injection port 121, the molding material is injected toward the inside of the cavity 100 in the axial direction of the cavity.

Referring again to FIG. 3A,
On the outer peripheral side of the injection port 121 of the film gate 120, an annular projection 140 protruding in the axial direction is formed on the upper mold surface. The projection 140 is for forming the annular digging 11 in the portion of the bearing holder 1 opposite the output-side shaft end 4.

The distance between the outer peripheral surface 111 of the center pin 110 and the inner peripheral surface 141 of the projection 140 corresponds to the thickness t12 of the outer peripheral wall 12 of the shaft hole at the end of the bearing holder 1 opposite to the output side. Similarly, the interval between the center pin outer peripheral surface 111 corresponding to the outer peripheral wall 13 of the output side shaft end 3 of the bearing holder 1 on the lower die side and the lower die surface portion 113 is determined by the thickness t of the outer peripheral wall 13.
13 is supported.

Further, the center pin 110 is tapered along the axial direction so that the outer diameter increases from the upper die 101 toward the lower die 102 in correspondence with the inner peripheral surface 21 of the shaft hole. It is. That is, a draft is provided.

As described above, the upper die 101 and the lower die 102 are clamped while the center pin 110 is inserted, and the molding material is injected into the cavity 100 from the injection port 121 of the film gate 120. The molding material flows axially in the cavity and fills the interior.
Since the molding material is injected by the center gate method,
Compared to the conventional case of using the pin gate method,
The roundness and cylindricity of the shaft hole 2 of the formed bearing holder 1 can be improved.

After the molding material injected into the cavity is sufficiently hardened, a demolding operation is performed. In this work,
The center pin 110 that needs to be withdrawn from the molded article has a draft angle. Therefore, if the center pin 110 is pulled out in the direction indicated by the arrow in FIG. 3A, in other words, if the center pin 110 is pulled out from its thick shaft end side, the center pin 110 can be easily pulled out from the molded product. Further, since the draft is provided in this manner, the inner peripheral surface 21 of the shaft hole 2 of the molded product is not damaged at the time of drawing.

Next, as shown in FIG. 4A, the obtained molded product 1A is in a state where the gate portion 1B is integrally molded. For example, as shown in FIG. 4B, the molded product 1A is
Cut out by 2. As a result, a bearing holder 1 having the shape shown in FIG. 2 can be obtained.

Here, after such a gate cut, there is a possibility that some burrs remain in the cut portion. Therefore, in the present embodiment, the film gate 120 is provided on the side of the shaft end 4 opposite to the output side of the bearing holder 1 to be formed. The reason for this is that, in the bearing holder 1, the contribution to the bearing performance is smaller on the side of the non-output side shaft end 4 than on the side of the output side shaft end 3 of the bearing holder.

Further, in this example, as can be seen from FIG. 4A, the injection port 121 of the film gate 120 is arranged so as to face the inner peripheral edge of the outer wall portion 12 of the shaft end 4 opposite to the output side of the bearing holder 1. In, it is installed. With this configuration, at the time of gate cutting, the inner peripheral portion of the outer wall portion 12 is cut out together with the gate cutting. Therefore, burrs do not remain on the inner peripheral surface 21 of the shaft hole 2. On the other hand, for example, as shown in FIG.
When 21 is located on the inner peripheral surface 21 of the shaft hole 2, there is a possibility that burrs protruding inward on the inner peripheral surface 21 remain after the gate cut. If such burrs remain, the dimensional accuracy of the press-fitted portion of the bearing member 6 (see FIG. 1) cannot be ensured. In this case, it is necessary to perform another processing for deburring.

In the bearing holder 1 formed in this manner, the thickness of the annular hole 11 formed thereon is, for example, 0.5 mm or more, and the depth thereof is the bearing member 6 (see FIG. 1). ) Is required to have a length corresponding to the depth in the axial direction of the press-fitting, for example, 3 mm or more.

As shown in FIG. 1, bearing members 5 and 6 are press-fitted from both sides of the shaft end of the formed bearing holder 1,
The output rotary shaft 7 is installed so as to be rotatable.
Here, in the bearing holder 1, the inner peripheral surface 21 of the shaft hole is tapered in the axial direction. Therefore, the inside diameter D4 of the shaft hole 2 on the side opposite to the output side shaft end 4 is smaller than the inside diameter D3 of the other output side shaft end 3 side.

Therefore, the shaft ends 3, 4 on both sides are inserted into the shaft hole 2.
The press-fitting allowance of the ring-shaped bearing members 5 and 6 to be press-fitted from the shaft end 4 having a small inner diameter increases. However, the rigidity of the portion is reduced due to the ring-shaped meat steal 11 formed on the shaft end 4 side. Therefore, press-fitting of the bearing member 6 is not difficult and can be performed in the same manner as the other side. Further, the inner diameters of the shaft holes after the press-fitting of the bearing members 5 and 6 are almost the same at the shaft end portions on both sides.

Table 1 shows an example of a comparison result of the dimensional accuracy of the bearing holder 1 formed by the present invention and a bearing holder formed by a conventional forming method. As shown in this table, the errors in the coaxiality of the shaft hole and the roundness of the inner diameter were reduced to about half. It can also be seen that the cylindricity of the shaft hole has been improved.

[0035]

[Table 1]

[0036]

As described above, in the bearing holder according to the present invention, the annular protruding portion having a greater thickness than the output-side shaft end portion is formed. Since the thickness is formed, the thickness of the output side shaft end and the thickness of the shaft hole around the counter-output side shaft end can be made substantially equal,
Therefore, in the process of curing the molding material, the amount of shrinkage at both shaft end portions can be made substantially equal. As a result, it is possible to prevent the accuracy of the cylindricity and roundness of the shaft hole of the obtained bearing holder from lowering.

The rigidity of the outer peripheral wall of the shaft hole at the opposite end of the shaft on the opposite side of the output side, which is thickened, is reduced by the ring-shaped robbing. Therefore, the press-fitting of the bearing member can be easily performed similarly to the other thin output-side shaft end portion.

Next, in the injection molding method of the bearing holder of the present invention, the molding material is injected into the mold cavity from the shaft end side. That is, the center gate method is adopted. When the molding material is injected in this way,
The accuracy of the roundness and cylindricity of the shaft hole of the obtained bearing holder can be improved as compared with the conventional case where the molding material is injected from the outer peripheral side of the cavity by the bin gate method.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a bearing holder used for a VTR capstan motor or the like to which the present invention is applied.

2 (A) to 2 (D) are an end view, a side view, an end view and a longitudinal sectional view of an output-side shaft end showing the bearing holder of FIG. 1 respectively.

3 (A) is a schematic vertical sectional view of a molding die used for injection molding of the bearing holder of FIG. 1, and FIG. 3 (B) is an explanatory view showing a film gate portion taken out therefrom.

4A is an explanatory diagram showing a gate portion formed on a molded product, FIG. 4B is an explanatory diagram showing cutting of the gate portion,
(C) is an explanatory view to show a bad effect when the gate portion is formed on the inner peripheral surface of the shaft hole.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bearing holder 2 Shaft hole 21 Shaft hole inner peripheral surface 3 Output-side shaft end D3 Thickness of outer wall portion of output-side shaft end 4 Non-output-side shaft end 4A Annular protruding portion 4B Thin portion 4C Thick portion 4D Through hole 4E blind Hole D4 Thickness of outer wall portion at opposite output side shaft end 5, 6 Bearing member 7 Output rotating shaft 11 Annular robbery 12 Outer wall portion at opposite output side shaft end t12 Thickness of outer wall portion at opposite output side shaft end 13 Output side shaft Outer wall part of end part t13 Thickness of outer wall part of output side shaft end part 100 Mold 100 Center pin 120 Film gate

Claims (4)

[Claims] 1. A bearing holder, which is an injection-molded product provided with a shaft hole of an output rotary shaft and rotatably supporting the output rotary shaft via a bearing member held on an inner peripheral surface of the shaft hole, An output-side shaft end located on one end side in the axial direction of the bearing holder, and a non-output-side shaft end located on the other end side, and the anti-output-side shaft end is formed with an annular projecting portion. The annular protruding portion includes a thin portion having a smaller thickness in the axial direction and a thick portion having a larger thickness in the axial direction than the thin portion. A first bearing member press-fitted from a shaft end opening on the output-side shaft end side of the shaft hole, and a second bearing member press-fitted from a shaft end opening on the non-output-side shaft end side are included. A ring-shaped robber is formed concentrically with the shaft hole on the side of the non-output side shaft end. Bearing holder according to claim. 2. The annular projection according to claim 1, wherein the thin portion of the annular protruding portion has a through hole extending parallel to the axial direction, and the thick portion extends parallel to the axial direction. A blind hole that is open on the side of the output-side shaft end is formed, and the ring-shaped robbery is formed at a position between the through-hole and the blind hole and the shaft hole. Bearing holder. 3. The bearing holder according to claim 1, wherein a depth dimension of the ring-shaped robbery corresponds to an axial depth into which the second bearing member is press-fitted. 4. The injection molding method for a bearing holder according to claim 1, further comprising a tapered outer peripheral surface corresponding to an inner peripheral surface shape of the shaft hole in a molding die cavity corresponding to the bearing holder. A molding material is disposed in the cavity, and a molding material is axially injected into the cavity from a portion of the cavity that defines an axial end of the bearing holder.