JP3227883B2 - Injection molded product having a circular inner peripheral surface - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molded product having a circular inner peripheral surface as a dimensional surface for positioning with other parts, and in particular, can improve the positioning accuracy, and can be used for AV (Audio Visual) equipment and OA (Office) The present invention relates to an injection molded product having a circular inner peripheral surface which is advantageously applied to a bearing holder or the like of a small motor for equipment.

[0002]

2. Description of the Related Art Conventionally, there has been provided a positioning function between components, which is used for, for example, arranging one component coaxially with another component or arranging it at a predetermined relative position. As a kind of member, a member having a circular inner peripheral surface as a dimensional surface for positioning with another component is known, and is used for various devices.

For example, in a small motor used as a disk drive motor for a personal computer, a word processor, or the like, a function as such a positioning member is provided to a bearing holder for mounting a rotating shaft (spindle) to a chassis. That is, such a bearing holder has a substantially annular plate shape, and its outer peripheral surface is fitted into the mounting hole of the chassis and assembled, while the rotation of the disk drive motor rotates on the inner peripheral surface of the center hole as the positioning dimension surface. The shaft is mounted via a bearing, so that the rotating shaft of the disk drive motor is positioned and held at the center of the mounting hole of the chassis.

[0004] By the way, such a bearing holder for a small motor is conventionally formed of a metal die-cast product. In recent years, however, there has been a demand for smaller and lighter and lower cost AV and OA equipment. In order to cope with this, it has been considered to adopt an injection-molded resin bearing holder.

[0005] However, especially in small motors for AV equipment and OA equipment, extremely high positioning accuracy is required for the bearing holder in order to prevent the displacement between the disk and the reading device. Since the circular inner peripheral surface as the positioning dimension surface requires a roundness of 10 μm or less, it is extremely difficult to obtain the required roundness with a resin bearing holder. was there.

That is, as shown in FIG. 4, for example, a resin-made bearing holder is formed in a substantially annular plate-shaped molding cavity 6 formed between the mating surfaces of the fixed mold 4 and the movable mold 2. It is molded by injecting and filling a resin material through pinpoint gates 8 formed at a plurality of places (for example, three places) in the circumferential direction, and the bearing holder thus formed is formed. In FIG. 5, as shown in FIG. 5, a resin material filled in the molding cavity 6 is provided at a central portion in the circumferential direction between the pinpoint gates 8, 8.
A merges at a, and a weld line is generated there.

As a result, the flow direction of the resin is different from that of the other portions. In those portions where the weld lines exist, the molding shrinkage of the resin is different from the other portions, and the resin projects radially inward after cooling and solidification. Therefore, the roundness of the circular inner peripheral surface of the obtained bearing holder is significantly reduced, and it is extremely difficult to secure required dimensional accuracy. In addition, the protruding height inward in the radial direction in the portion where the weld line exists is about 10 μm,
In particular, when a resin containing a fibrous filler having a high aspect ratio is used, the size becomes larger.

[0008]

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an injection molded article having a circular inner peripheral surface.
A circular inner peripheral surface as a dimensional surface can be advantageously and stably obtained with roundness, and thereby, a circular inner peripheral surface that can be advantageously applied to a bearing holder for a small motor, and the like. An object of the present invention is to provide an injection molded product having the same.

[0009]

In order to solve such a problem, a feature of the present invention is to provide an injection molded product having a circular inner peripheral surface as a dimensional surface for positioning with other parts, and to be radially inward. A plurality of protruding positioning protrusions are formed in the circumferential direction, avoiding a portion where a weld line is generated, and the inner circumferential surface of the positioning protrusion forms a circular inner peripheral surface as the dimension surface.

[0010]

In the injection-molded article having such a circular inner peripheral surface, since the positioning projection is provided at the portion where the weld line is not formed, the weld line at the portion where the positioning projection is formed is provided. Is prevented.

In such an injection-molded product, the dimensional surface defined by the inner peripheral surfaces of the positioning projections is fitted to another component, thereby positioning the other component. Will be done.

Accordingly, in the injection-molded article having a structure as has been circularly shaped inner peripheral surface according to the present invention, the circularity of the circular inner peripheral surface thereof as the dimension plane, can be secured very advantageously and stably Therefore, excellent positioning accuracy can be exhibited, and it can be advantageously applied to a bearing holder of a small motor for AV equipment and OA equipment.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, in order to clarify the present invention more specifically, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a plan view of a bearing holder 20 of a spindle motor of an FDD (floppy disk drive) according to an embodiment of the present invention, and FIG. 20 is a cross-sectional view of the mounted state.

As shown in these figures, the bearing holder 20 has a circular center hole 22 in the center portion, and has a thin, generally annular plate shape as a whole. The bearing holder 20 injects a resin material through three pinpoint gates located on substantially the same circumference into a molding cavity formed between a fixed mold and a movable mold, as in the conventional case. It is formed by filling. The point corresponding to the pinpoint gate is indicated by G in FIG.
Indicated by

Here, in the circular center hole 22 of the bearing holder 20, three positioning projections 24 projecting inward in the radial direction are formed at a predetermined distance from each other in the circumferential direction. The tip portions of these positioning projections 24 are thickened in the plate thickness direction.
Their tip surfaces are located on a circumference centered on the central axis of the circular outer peripheral surface 26 of the bearing holder 20. Thereby, the boss portion 30 having the circular inner peripheral surface 28 is formed in cooperation with the distal end portions of the three positioning projections 24.

The center of the positioning projection 24, which forms the circular inner peripheral surface 28 of the boss 30, is slightly protruded at the center in the thickness direction. Accordingly, the circular inner peripheral surface 28 is formed to have a stepped inner peripheral shape including a small diameter portion at the axial center portion and a large diameter portion at both axial end portions.

These three positioning projections 24 are
Each of them is formed at a position corresponding to the portion where the pinpoint gate: G is located. As a result, these positioning projections 24 are positioned so as to avoid the portion where the weld line is generated.

That is, in the bearing holder 20, a pin point gate at which the flow of the resin material injected and filled into the molding cavity merges: G, a central portion between G: a
, A weld line is generated, and in those portions: a, the radial dimension is slightly increased due to the effect of the weld line. Where
Each of the positioning projections 24 is formed so as to avoid a portion where the radial dimension is not uniform due to the influence of the weld line.

The projecting height h of the positioning projection 24 is set to be at least larger than the projecting height of the portion a projected by the influence of the weld line.

As shown in FIG. 2, the bearing holder 20 having such a structure has its boss 3
At 0, the motor 38 is rotatably attached to a spindle 40 of the motor 38 via ball bearings 36, 36 press-fitted into the large diameter portion of the circular center hole 22, respectively. The lower surface 42 of the bearing holder 20 is
4 and are fixed. Thereby, the motor 38 is configured to include the bearing holder 20.

The basic structure of the motor 38 is the same as that of a conventionally known FDD spindle motor, and a coil 50 is arranged around an outer peripheral portion of a plate-shaped core 48 fixed on a substrate. While the spindle 40
A disk-shaped rotor 52 is fixed to the lower end of the rotor 52, and a rotor magnet 5 fixed to an outer peripheral portion of the rotor 52 is provided.
4 is arranged around the coil 50.

The motor 38 including the bearing holder 20 has the circular outer peripheral surface 26 of the bearing holder 20 and the circular mounting hole 5 formed in the chassis 56.
8, the FDD chassis 5
6 will be assembled. Thereby, the spindle 40 of the motor 38 is positioned and held so as to be located at the center of the mounting hole 58. A hub 62 supporting the floppy disk 60 is provided at the tip of the spindle 40.
Is attached.

In the bearing holder 20, a positioning surface for positioning the spindle 40 with respect to the chassis 56 is formed by the inner front end surface of the positioning projection 24 formed avoiding the weld line generating portion. Since the circular inner peripheral surface 28 is formed, the circular inner peripheral surface 28
Therefore, the mold accuracy can be reliably transferred, and the roundness on the dimensional surface can be secured with high accuracy and stability without being affected by the weld line.

Therefore, it is possible to position and hold the spindle 40 of the motor 38 with respect to the chassis 56 with high accuracy.

Incidentally, a polycarbonate resin containing 10% of glass fiber is used as a molding resin material, and the diameter of the dimensional surface (the large diameter portion on the circular inner peripheral surface 28) is φ10 ± 0.01 mm.
Injection molding of the bearing holder 20 of the structure of this embodiment was performed with the aim of obtaining a bearing holder having a roundness of 10 μm or less.
It was confirmed that a μm bearing holder could be obtained and that it could be sufficiently adopted as a product.

As a comparative example, a bearing holder having a conventional structure (see FIG. 5) having no positioning projection and injection-molded with a similar target has a diameter of φ9.
It was only 975 mm and had a roundness of only 19 μm, and the accuracy required for the product could not be obtained.

Next, a bearing holder 70 as another embodiment of the present invention is shown in FIG. In this embodiment, parts having the same structure as in the first embodiment are denoted by the same reference numerals in the drawings as those in the first embodiment, and detailed description thereof will be omitted. It shall be.

That is, the bearing holder 70 of the present embodiment
Formed by a mold having two pinpoint gates (located at points indicated by G in the figure),
Two locations located on both sides in the radial direction with respect to the central axis: a, a
, A weld line is formed.

And, those weld line generating parts:
The four positioning protrusions 24 are formed at predetermined intervals in the circumferential direction, avoiding a.

Accordingly, even in the bearing holder 70 having the structure of the present embodiment, the radial dimension of the positioning projection 24 is not affected by the weld line. The circularity of the circular inner peripheral surface 28 as the dimension surface constituted by the front end surface can be secured with high accuracy, and the same effect as in the first embodiment can be exhibited.

Incidentally, a polycarbonate resin containing 10% of glass fiber is used as a molding resin material, and the diameter of the dimensional surface is φ1.
With the aim of obtaining a bearing holder having a roundness of 0 μ ± 0.01 mm and a roundness of 10 μm or less, the bearing holder 7 of this embodiment
0 was injection molded, the diameter of the dimensional surface was φ9.997.
mm, a bearing holder with a roundness of 7 μm can be obtained.
It has been confirmed that it can be sufficiently adopted as a product.

As a comparative example, a bearing holder having a conventional structure and having no positioning projection, which is injection-molded with a similar target, has a dimensional surface diameter of φ9.983 mm,
A roundness of only 17 μm was obtained, and the accuracy required for the product could not be obtained.

Although the embodiments of the present invention have been described above in detail, these are literal examples, and the present invention is not construed as being limited to such specific examples.

For example, the positioning projection 24 is provided on the chassis 5
If at least three positioning points are located on the same circumference on the circular inner peripheral surface 28 so that the spindle 40 of the motor 38 can be positioned with respect to the bearing holder 20 mounted on the sixth holder 6. In addition, the number, circumferential length, interval, and the like of the positioning projections 24 are not limited to those in the above-described embodiment.

In the above-described embodiment, the circular inner peripheral surface as the dimensional surface is formed on the innermost peripheral portion of the component (bearing holder). A cylindrical portion protruding in the axial direction is formed, and a circular inner peripheral surface as a dimensional surface such as a member whose inner peripheral surface is a dimensional surface is formed on the innermost peripheral portion of the component. The present invention can be applied to parts that are not included.

Further, in the above-described embodiment, a specific example in which the present invention is applied to a bearing holder of an FDD spindle motor has been described. However, the present invention is also applicable to injection molding having a circular inner peripheral surface having various dimensions. It can be applied to goods. Specifically, for example, in a turntable that is fixedly mounted on a rotation shaft of a drive motor of an optical disk and supports the optical disk, in order to secure centering accuracy of the optical disk, a rotation hole of the rotation shaft of the motor is used. Since a high roundness is required for the peripheral surface, the present invention is advantageously applied with the inner peripheral surface of the fitting hole as a dimensional surface.

In addition, the injection-molded article having a circular inner peripheral surface to which the present invention is applied is not limited to a molded article obtained by injection molding of a thermoplastic, but may be injection-molded of a thermosetting plastic (transfer molding). Of course, it can also be advantageously applied to molded articles according to (1).

In addition, although not enumerated one by one, the present invention
Based on the knowledge of those skilled in the art, various changes, modifications, improvements and the like can be implemented in an embodiment,
It goes without saying that all such embodiments are included in the scope of the present invention without departing from the spirit of the present invention.

[Brief description of the drawings]

FIG. 1 is a plan view showing a bearing holder of an FDD spindle motor as one embodiment of the present invention.

FIG. 2 is an explanatory view showing a state in which the bearing holder shown in FIG. 1 is mounted on an FDD.

FIG. 3 is a plan view showing a bearing holder as another embodiment of the present invention.

FIG. 4 is an explanatory diagram for explaining a general manufacturing method of a bearing holder of an FDD spindle motor.

FIG. 5 is a plan view showing an example of a bearing holder of a conventional FDD spindle motor.

[Explanation of symbols]

 20, 70 Bearing holder 22 Circular center hole 24 Positioning projection 28 Circular inner peripheral surface 30 Boss 36 Ball bearing 38 Motor 40 Spindle 56 Chassis

Claims (1)

(57) [Claims] 1. A resin injection molded product having a circular inner peripheral surface as a dimensional surface for positioning with another part, wherein a circular center hole is provided at a central portion of the molded product, and
The positioning projection projecting from the periphery radially inward, in the so that avoid the generation portion of the weld line, as well as several forms in the circumferential direction, the plurality of positioning projections
The inner tip surface of the circular center hole with respect to the center axis of the circular center hole
Each is formed on the inner peripheral surface located on the circumference, and
Injection molded article having a circular inner peripheral surface, characterized in that in these the peripheral surface constitutes a circular inner peripheral surface as the dimension plane.