JPH08118496A - Synthetic resin polygon mirror, and injection mold therefor - Google Patents

Abstract

PURPOSE: To provide a polygon mirror made of a synthetic resin in which the focused position of an optical beam on a photosensitive member by a reflected surface is not deviated in a main scanning direction and pixels for forming main scanning are aligned at an equal interval or pixels for forming the main scanning becomes uniform density and an injection mold therefor. CONSTITUTION: A synthetic resin polygon mirror is formed in a polygonal shape in which a plurality of reflecting surfaces 3 for reflecting an optical beam are connected and a central hole 4 conforming a rotary drive shaft is formed in such a manner that the inner diameter of the hole 4 is formed larger than the profile of the shaft, and a plurality of protrusions 5 in contact with the shaft are disposed at each split angle of the surface 3. An injection mold comprises grooves corresponding to the protrusions 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synthetic resin polygon mirror used in an image forming apparatus such as a laser printer or a copying machine, and an injection molding die for the same. The present invention relates to a synthetic resin polygon mirror used in an optical scanning device that forms a desired electrostatic latent image on the surface of a photoconductor by exposure according to the above, and an injection molding die thereof.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 10, a polygon mirror 1 is formed in a polygonal prism shape, and has a cylindrical central hole 4 penetrating from the center of its upper surface to the center of its lower surface, and its outer surface. And a plurality of reflecting surfaces 3.

Then, for example, as shown in FIG. 9, the polygon mirror 1 has a pedestal 11 attached to a rotary shaft.
It is fixed to the rotary shaft 2 by being sandwiched by the plate spring 12 and the plate spring 12, and is rotated together with the rotary shaft by the drive of the motor 13. Further, for example, as shown in FIG. 9, the optical scanning device includes a semiconductor laser 14 that emits a light beam, a collimator lens 15 that converts the light beam into a parallel light beam, and a light beam of the parallel light beam that is deflected while rotating. Then, the polygon mirror 1 for converting the parallel light flux of uniform angular velocity and the fθ lens 16 for converting the parallel light flux of constant angular velocity into the uniform linear velocity and converging
And a plane mirror 17 that reflects the focused light beam toward the photoconductor drum 18. In addition,
The broken line in the figure indicates the path of the light beam. Further, a light receiving element (not shown) is arranged on the upstream side in the rotation direction of the polygon mirror 1 with respect to the photosensitive drum 18, and image information for one scanning is obtained after a certain time from the timing when the light beam is incident on the light receiving element. Is superimposed on the light beam to perform scanning in the rotation axis direction of the photosensitive drum 18 (hereinafter referred to as main scanning). Then, for example, in the case of the polygon mirror 1 having the four reflecting surfaces 3 shown in FIG. 11A, four main scans are performed while the polygon mirror makes one rotation, and the polygon mirror 1 rotates a plurality of times. As a result, a desired electrostatic latent image is formed on the photosensitive drum 18 (see FIG. 11B). The image information is superposed on the light beam in time series for each main scanning, and the light beam is deflected while the polygon mirror 1 is rotating to deflect the light beam to form a plurality of pixels arranged in the main scanning direction. An image is formed on the body drum 18.

Conventionally, an aluminum material is used for such a polygon mirror, and the outer surface and the like are turned by a diamond tool to form the above-mentioned shape, and a reflective film and a protective film or only a protective film is formed on each outer surface. It was applied to form a reflective surface. However, in the polygon mirror, the roundness and inner diameter of the central hole, or the surface roughness and flatness of each reflecting surface,
High accuracy is required for the inclination with respect to the rotation axis, the distance with respect to the rotation axis, the error between the reflecting surfaces of those parameters, and the central angle formed by the perpendiculars of the adjacent reflecting surfaces. It took a very long time to turn aluminum.

Therefore, a polygon mirror is formed by an injection molding method or an injection compression molding method using a thermoplastic resin such as polycarbonate, polymethylmethacrylate or acrylic resin, and a metal such as aluminum, gold or copper is vacuumed on the outer surface thereof. Japanese Patent Application Laid-Open No. 4-176622 proposes a method of manufacturing a polygon mirror which is coated by a vapor deposition method to form a reflecting surface. In this method, since the surface roughness of the die is transferred to the polygon mirror, the die surface of the molding die corresponding to the reflecting surface of the polygon mirror is made into a mirror surface having a surface roughness accuracy higher than that required for the reflecting surface. If finished, it is possible to easily form a reflecting surface having a required surface roughness accuracy on the polygon mirror without performing a turning process.

[0006]

However, the synthetic resin polygon mirror contracts due to cooling after being taken out from the molding die. Therefore, it is difficult to form a molding die in consideration of the amount of shrinkage and finish the roundness and inner diameter of the central hole with the same accuracy as that of the aluminum material.
Therefore, as shown in FIG. 12A, a gap is likely to be formed between the central hole 4 and the rotary shaft 2 of the motor. Further, since the synthetic resin has a larger linear expansion coefficient than metal, when the heat generated by the motor is transmitted to the polygon mirror 1 through the rotary shaft, the central hole 4 expands more than the rotary shaft 2 and the center The gap between the hole 4 and the rotary shaft 2 of the motor is widened. Then, when a gap is formed between the center hole 4 and the rotation shaft 3 of the motor, the polygon mirror 1 rotates in an eccentric state and rotates with vibration, so that the light beam on which the image information is superimposed is generated. The angle formed with respect to the light beam at the timing of incidence on the polygon mirror 1 differs for each reflecting surface 3. As a result, as shown in FIG. 12B, the image forming position of the light beam on the photoconductor 18 is displaced in the main scanning direction for each reflecting surface 3, and the electrostatic latent image formed on the photoconductor 18 is displaced. Will be disturbed.

Therefore, when the center hole is not simply formed in a cylindrical shape but a large number of projections are arranged in series in the cylindrical center hole and the rotary shaft of the drive motor is conventionally press-fitted into the center hole. Japanese Patent Application Laid-Open No. 1-128320 discloses a polygonal mirror made of synthetic resin in which a rotary shaft is press-fitted into a central hole while preventing elastic deformation of the reflecting surface which has occurred in the above.

However, when the polygon mirror is viewed from above, a plurality of projections connected to each other are located in a triangle which is supposed to connect each reflecting surface and the center of rotation (hereinafter, referred to as a projection).
These projections are called the projections corresponding to the reflective surface). Also, when the synthetic resin is cooled, it contracts in the direction of the thick part by pulling the thin part, so when multiple projections are connected to correspond to the reflective surface, each reflective surface is cooled. Then, a local curve corresponding to the arrangement of the protrusions is continuously formed, and the entire reflecting surface has a wavy surface shape. Then, the wavy surface-shaped anti-slope reflects the light beam in a different direction from the case where the anti-slope is a plane,
Further, the difference is also different depending on the part where the light beam is deflected, so that the arrangement in the main scanning direction of the pixels forming an image on the photoconductor becomes sparse or dense depending on the corrugation of the above-mentioned surface shape, or is not formed on the photoconductor. Density unevenness occurs in the imaged pixels, and the electrostatic latent image formed on the photoconductor is disturbed.

Further, since the number of protrusions corresponding to the reflecting surface is different for each reflecting surface, the surface shape of each reflecting surface has a different corrugation for each reflecting surface, and the image information is superimposed. The angle formed by the reflecting surface with respect to the light beam when the light beam is incident on the polygon mirror is different for each reflecting surface. As a result, the image forming position of the light beam on the photoconductor is displaced in the main scanning direction for each reflecting surface, and the electrostatic latent image formed on the photoconductor is disturbed.

Therefore, an object of the present invention is to provide a polygonal mirror made of synthetic resin and an injection molding die for the same, which fits together with a rotary drive shaft without forming a gap, and whose reflecting surfaces have the same surface shape. It is in.

[0011]

That is, the present invention is made of a synthetic resin which is formed in a polygonal shape in which a plurality of reflecting surfaces for reflecting a light beam are connected and in which a central hole to which a rotary drive shaft is fitted is formed. In the polygon mirror, the inner diameter of the center hole is formed to be larger than the outer shape of the rotary drive shaft, and a plurality of protrusions abutting against the rotary drive shaft are formed on the inner peripheral surface of the center hole at the dividing angle of the reflecting surface. It is a polygon mirror made of synthetic resin arranged for each.

An injection molding die for manufacturing the synthetic resin polygon mirror of the present invention has a fixed die having a sprue of molten resin formed therein and a cavity in combination with the fixed die when the die is clamped. A movable die to be formed, a gate is formed so as to face the sprue and project into the cavity from the movable die, and a groove corresponding to a protrusion formed in the center hole of the polygon mirror is formed on the outer peripheral surface, and , A core pin which is arranged so as to be able to advance and retreat toward the fixed mold and which, when advanced, is fitted with the sprue of the fixed mold and cuts the gate.

In the present invention, it is sufficient that the projection has a height such that the tip end portion thereof comes into contact with the drive rotation shaft. For example, even if the tip end portion is formed with a concave surface that comes into contact with the rotation drive shaft, The tip may be sharply pointed. The width of the protrusion in the drive rotation axis direction may be formed over the entire width of the inner peripheral surface of the central hole, or the vicinity of the upper surface and / or the vicinity of the lower surface of the polygon mirror may be chamfered.

The plurality of protrusions are the division angles of the reflecting surface,
That is, 360 ° may be arranged side by side on the inner peripheral surface of the central hole at each angle obtained by dividing the number of the reflective surfaces. For example, a plane orthogonal to the reflective surface and including the center of rotation may be the inner peripheral surface of the central hole. Even if each of the protrusions is disposed at a portion that intersects with, the protrusions are disposed at a portion where a plane including a line of intersection of two adjacent reflecting surfaces and a rotation center intersects with the inner peripheral surface of the central hole. May be. In the former case, the protrusions are formed only at the portion where the reflecting surface intersects with the flat surface, that is, at the position corresponding to the central portion of the reflecting surface. Therefore, when the polygon mirror contracts after injection molding, even if the reflecting surface is curved due to the influence of the projection, each anti-slope surface is formed in a symmetrical left-right surface shape around the center thereof. Also, in the latter case, since the protrusions are formed only at the corners and not at the positions corresponding to the reflection surfaces, even if the polygon mirror contracts after injection molding, compared to the former case. The reflection surface is unlikely to be curved due to the influence of the protrusion.

It is sufficient that the inner diameter of the central hole is larger than the outer circumference of the rotary drive shaft. Even if the central hole is formed in a cylindrical shape, it is formed in a polygonal shape similar to the outer shape of the polygon mirror. In addition, the corners of the center hole and the corners of the outer shape of the polygon mirror that correspond to each other may be formed in a shape that is located on the same plane including the center of rotation. In the latter case, the thickness between the reflecting surface and the inner peripheral surface of the central hole facing it becomes uniform, so when the polygon mirror contracts after injection molding, the parts of uniform thickness contract equally. The curvature of the entire slope can be suppressed.

[0016]

In the polygon mirror of the present invention, the inner diameter of the central hole is made larger than the outer shape of the rotary drive shaft, and a plurality of projections that are in contact with the rotary drive shaft are provided on the inner peripheral surface of the central hole. Therefore, the tip end of the protrusion is brought into contact with the rotary drive shaft so as to be firmly fitted to the drive shaft. Further, the respective protrusions are arranged at each division angle of the reflecting surface, that is, the protrusions are arranged so as to have the same positional relationship with respect to the respective reflecting surfaces. Therefore, even if the polygon mirror contracts after injection molding and the influence of the protrusions is exerted on the reflecting surface, the influences of the protrusions act on the anti-slope surfaces in the same manner, so that the reflecting surfaces are formed in the same surface shape. .

Further, according to the injection molding die of the present invention, since the concave groove corresponding to the projection of the polygon mirror is formed on the outer peripheral surface of the core pin, the polygon mirror of the present invention can be easily formed by integral molding. .

[0018]

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

Embodiment 1 As shown in FIG. 1A, a polygon mirror 1 according to this embodiment is made of a polycarbonate resin containing no inorganic substance filler, and has four reflecting surfaces 3 for reflecting a light beam. A central hole 4 formed in a continuous quadrangular shape and having an inner diameter larger than the outer shape of the rotating shaft of the motor, and provided on the inner peripheral surface 6 of the central hole at intervals of 90 °. And four projections 5 that abut. Further, specifically, the polygon mirror 1 has a height of 4 m in the direction of the rotation axis of the motor.
m, circumscribed circle diameter is 32 mm, and the shape is a quadrangular prism.
It has a cylindrical central hole 4 of 0 mm and projections 5 arranged at respective portions of the inner peripheral surface 6 of the central hole 4 where the plane orthogonal to the reflecting surface 3 and including the center of the rotation axis intersects.

The diameter of the inscribed circle 7 (see the chain line in FIG. 1A) formed by connecting the four projections 5 at their tip ends is larger than the outer diameter of the rotary shaft of the motor. The polygon mirror 1 was fitted to the rotary shaft of the motor without a gap by forming the height to be small and pressing the rotary shaft into the center hole 4. Further, since the inscribed circle 7 is formed so as to be smaller than the outer diameter of the rotary shaft of the motor by about 10 to 15 μm, it can be continuously used for a long time or the ambient temperature can be reduced to −10 to −10 μm.
Even if the size of the center hole was changed by changing the temperature to 70 ° C., the polygon mirror 1 was fitted to the rotating shaft of the motor without any gap. Further, each protrusion 5 is formed in a curved surface shape in which the contact area with the rotating shaft 2 is reduced so that the reflecting surface 3 is not distorted when the rotating shaft is press-fitted. Further, as shown in FIG. 1B, one end of each protrusion 5 in the rotation axis direction is chamfered so as to be easily press-fitted.

The polygon mirror 1 is formed by an injection compression molding method, and in order to improve the reflection efficiency of the reflecting surface 3, an undercoat film, a Cu film, or a SiO film is formed on each reflecting surface 3.
Two films were sequentially laminated.

In the injection compression molding method, as shown in FIG. 5, a heating cylinder 22 having a screw 21 for holding the molten polycarbonate resin in an internal space 20 and injecting the molten polycarbonate resin, a molding die, An injection compression molding machine having The molding die is a quadrangular prism-shaped cavity 23 for molding the resin injected from the heating cylinder 22, a movable core die 26 having a compression core 24 and a core pin 25 that move forward and backward in the cavity 23, and a space between them. And a fixed-side mold 29 having a sprue bush 28 having a hole 27 serving as a gate in the center. Here, as shown in FIG. 6, the core pins 25 include four U's extending in the column axis direction on the side surface of the columnar shape.
It has a shape in which four grooves 25a are formed every 90 °. Also,
The sprue bush 28 has a cylindrical hole on one side surface and four protrusions 28a for each 90 ° of the side surface, and the tip of the core pin 25 is fitted to that portion. (See FIG. 7).

The steps of the injection compression molding method will be further described. First, as shown in FIG. 8, after the cavity 23 side of the movable mold 26 is brought into close contact with the fixed mold 29 (FIG. 8).
(See (a)), the above-mentioned polycarbonate resin in a molten state in the heating cylinder 22 is injected to fill the cavity 23 from the gate 27. At this time, the core pin 25
Has a state in which its tip projects into the cavity 23 in order to form a gate having a width of 8 mm and a thickness of 0.2 mm (see FIG. 8B). Next, the core pin 25 is moved until it is fitted into the sprue bush 28, and the gate 27 is shut off (see FIG. 8C). Further, the compression core 24 is moved by a predetermined amount to compress the molten synthetic resin filled in the cavity 23, and the mirror surface applied to the surface of the movable mold 26 is transferred to the synthetic resin surface (see FIG. 8 ( See d)). Finally, after waiting for the polycarbonate resin to cool, the movable side mold 26 is separated from the fixed side mold 2, the compression core 25 is further moved, and the molded body is separated from the cavity 23 to remove the polygonal mirror 1. The molding process of is finished. As a result, the polygon mirror 1 having the central hole 4 in which the protrusion 5 corresponding to the U groove of the core pin was formed could be formed. The shapes of the core pin 25 and the sprue bushing 28 can be changed to form the shape of the central hole 4 and the shape of the protrusion 5.

In the polygon mirror 1 thus molded, even if the polygon mirror 1 contracts after injection molding,
Each reflecting surface was formed into a curved surface shape with left and right symmetrically centered on the central portion thereof, and the reflecting surfaces also had a uniform surface shape.

When an image is formed by using the polygon mirror 1, it is possible to align the image forming positions on the photosensitive member in the main scanning direction by the respective reflecting surfaces 3 and form a good electrostatic latent image. We were able to.

Embodiment 2 As shown in FIG. 2, except that the above-mentioned four protrusions 5 are arranged at a portion where a plane including the intersection line and the rotation center of two adjacent reflecting surfaces 3 intersects with each other. The same as 1. Further, in the polygon mirror of the present embodiment, since the protrusions 5 are arranged corresponding to the corners, in addition to the above-described effects of the polygon mirror of the first embodiment, even if the polygon mirror contracts after injection molding, The curvature of the reflecting surface due to the influence of the protrusion was smaller than that of Example 1. In addition, the polygon mirror 1
When an image is formed using, it is possible to align the image forming positions in the main scanning direction on the photoconductor by the reflecting surfaces 3,
A good electrostatic latent image could be formed.

Embodiment 3 As shown in FIG. 3, the center hole 4 is formed in a rectangular shape similar to the outer shape of the polygon mirror 1, and the corner portions of the center hole 4 and the outer shape of the polygon mirror 1 correspond to each other. The second embodiment is the same as the second embodiment except that it is formed so that the corners thereof are located on the same plane including the center of rotation. Since the polygon mirror of the present embodiment has a uniform thickness between the reflecting surface and the inner peripheral surface of the central hole facing the reflecting surface, in addition to the above effects of the polygon mirror of the second embodiment, Even when the polygon mirror contracted after molding, the portion having the uniform thickness contracted equally, and the curvature of the entire anti-slope surface was smaller than that of Example 2. Further, when the polygon mirror 1 is used to form an image, the image forming positions of the reflecting surfaces 3 on the photoconductor in the main scanning direction can be aligned, and a good electrostatic latent image can be formed. did it.

Incidentally, for example, as shown in FIG.
The polygon mirror 1 is formed into a hexagonal prism shape, or the center hole 4
Is formed in a hexagonal shape, or the projection 5 is formed in a triangular shape having a sharp tip as shown in FIG.
Alternatively, as shown in FIG. 4C, even if the projections 5 are formed in a square shape or the projections 5 are not chamfered, these results are the same.

[0029]

As described above, in the polygon mirror made of synthetic resin of the present invention, since the projection is provided on the inner peripheral surface of the central hole, the polygon mirror can be fitted to the rotary drive shaft without forming a gap.
Also, because the projections are arranged so that they have the same positional relationship with each reflecting surface, even if the polygon mirror contracts after injection molding and the projections have an effect on the reflecting surface, the effect on each anti-slope will be that of the projection. Have the same effect, the shapes of the reflecting surfaces can be made uniform.

Further, according to the injection molding die of the present invention, since the concave groove corresponding to the projection of the polygon mirror is formed on the outer peripheral surface of the core pin, the polygon mirror of the present invention can be easily formed by integral molding. .

[Brief description of drawings]

FIG. 1 is a top view (a) and a side view (b) of a polygon mirror according to a first embodiment of the present invention.

FIG. 2 is a top view of a polygon mirror according to a second embodiment of the present invention.

FIG. 3 is a top view of a polygon mirror according to a third embodiment of the present invention.

FIG. 4 is a top view of a polygon mirror obtained by modifying an embodiment of the present invention.

FIG. 5 is a cross-sectional view of essential parts of an injection compression molding die and a heating cylinder of the present invention.

FIG. 6 is a perspective view of a core pin incorporated in the injection compression mold of the present invention.

FIG. 7 is a perspective view of a sprue bush incorporated in the injection compression mold of the present invention.

FIG. 8 is an injection compression molding process diagram by the injection compression molding die of the present invention.

FIG. 9 is a perspective view of a conventional polygon mirror.

FIG. 10 is a schematic diagram of an optical scanning device.

11A is a top view of an ideal polygon mirror, and FIG. 11B is an image forming position on the photosensitive drum in main scanning by the polygon mirror.

FIG. 12A is a top view of a polygon mirror in which a gap is formed between a center hole and a rotation shaft, and FIG. 12B is an image forming position on the photosensitive drum in main scanning by the polygon mirror.

[Explanation of symbols]

1: polygon mirror, 3: reflective surface, 4: central hole, 5: protrusion, 6: inner peripheral surface.

Claims (5)

[Claims] 1. A synthetic resin polygon mirror, which is formed in a polygonal shape in which a plurality of reflecting surfaces for reflecting a light beam are connected to each other, and in which a central hole to which a rotation drive shaft is fitted is formed. It is characterized in that it is formed to be larger than the outer shape of the rotary drive shaft, and that a plurality of protrusions, which are in contact with the rotary drive shaft, are provided on the inner peripheral surface of the central hole for each division angle of the reflecting surface. Polygon mirror made of synthetic resin. 2. The projections are located on a plane that is orthogonal to the reflecting surface and that includes the center of rotation.
The polygon mirror made of synthetic resin described. 3. The synthetic resin polygon mirror according to claim 1, wherein each of the protrusions is located on a plane including a line of intersection of two reflecting surfaces adjacent to each other and a rotation center. 4. The center hole is formed in a polygonal shape similar to the outer shape of the polygon mirror, and the corner portion of the center hole and the corner portion of the outer shape of the polygon mirror which correspond to each other are located on the same plane including the center of rotation. The synthetic resin polygon mirror according to claim 1, wherein the polygon mirror is made of synthetic resin. 5. An injection molding die for manufacturing the synthetic resin polygon mirror according to claim 1, wherein the fixed die has a sprue of molten resin formed thereon, and the fixed die cooperates when the die is clamped. And a movable die that forms a cavity, and a gate is formed so as to project from the movable die into the cavity so as to face the sprue, and a groove corresponding to the protrusion formed in the center hole of the polygon mirror is formed on the outer peripheral surface. Formed and
An injection molding die, which is arranged so as to be capable of advancing and retracting toward the fixed die, and is configured to include a core pin that engages with the sprue of the fixed die and cuts the gate when advanced.