JP5026371B2 - Plastic optical element, optical scanning device, image forming apparatus - Google Patents

Description

  The present invention relates to a plastic optical element applied to an optical scanning system such as a laser-type digital copying machine, a laser printer, a facsimile machine, a plotter, and a complex machine thereof, and is particularly applicable to an optical apparatus such as a video camera. The present invention relates to a plastic optical element such as a long plastic scanning lens having a highly accurate optical mirror surface, an optical scanning device including the plastic optical element, and an image forming apparatus.

  In recent years, in order to cope with the high speed and high image quality of color image forming apparatuses, a plurality of light beams are simultaneously exposed to four photoreceptors arranged in the transport direction of the output paper, and different colors (yellow, magenta, cyan, Digital copiers and laser printers using a tandem optical system that sequentially transfer images developed by a black developing device and superimpose them to form a color image have been put into practical use.

  Such an image forming apparatus generally has a plurality of scanning units corresponding to the light beams. However, the plurality of light beams are incident on a single deflector and scanned to form an image on a corresponding photoconductor. An image unit is provided for each light beam, and the plastic optical element constituting the image forming unit includes the light source unit, an incident optical system on which a light beam emitted from the light source unit is incident, and a light beam emitted from the incident optical system. A method has been proposed in which a light deflector for deflecting the light is configured in a housing that houses the light deflector.

Conventionally, a processing method such as a gate seal molding method or a remelt molding method has been adopted as a processing method of the plastic optical element. These methods aim to process not only the shape accuracy but also the internal strain with high accuracy, and the temperature and pressure of the resin are uniform in the mold heated to the glass transition temperature or higher after filling the resin. Then, it is slowly cooled (slow cooling) until the temperature becomes equal to or lower than the heat distortion temperature, and then the mold is released.
However, while these methods can produce highly accurate molded products, it takes time to raise and lower the mold temperature, so the molding time is longer than the injection molding method with a constant mold temperature, and the productivity is inferior. .

  On the other hand, taking advantage of the high productivity of the injection molding method, low-pressure filling is performed on the mold below the glass transition temperature, and sink marks generated thereby do not adversely affect the shape accuracy of the optical function surface (transfer surface). In this way, the sink induction molding method is used. In this method, in order to prevent the occurrence of sink marks due to resin shrinkage on the transfer surface, the other surface is separated from the mold to form an incomplete transfer surface, and the resin shrinkage during cooling is concentrated on the incomplete transfer surface. .

  By this method, it is possible to reduce the shape accuracy and the internal distortion equivalent to the slow cooling molding method in a molding time equivalent to that of the conventional injection molding method without slow cooling the molded product having a thick and uneven thickness. Further, sink marks can be reliably induced only on the imperfect transfer surface, and high shape accuracy can be obtained on the transfer surface, and there is little pressure dependency during molding, and high molding stability can be obtained (see Patent Document 1). ).

However, the outer shape of the long plastic optical element is different from that of a thick plastic optical element such as an fθ lens, and its thickness in the light transmission direction (hereinafter sometimes referred to as “lens thickness”). Is thinner than the thickness in the sub-scanning direction (short direction) (hereinafter sometimes referred to as “lens thickness”). Therefore, in the cooling process, since the cooling rate in the lens thickness direction is high, the heat shrinkage force in the same direction increases, so that there is a problem that sink marks are likely to occur on the optical function surface as the transfer surface. In order to solve this problem, a method has been proposed in which a convex shape is formed on the transfer surface other than the optical function surface to increase the mold release resistance and prevent sink marks from entering the attachment reference surface (see Patent Document 2). ing.
As described above, in molding a long plastic optical element, a technique for efficiently sinking the imperfect transfer surface more than the fθ lens and transferring the optical functional surface with high accuracy is required.

Japanese Patent No. 3512595 JP 2007-133179 A

  In order to increase strength and prevent deformation due to external force, a thin plastic optical element having a thin wall thickness usually has a rib having a thickness of about several millimeters around the optical functional surface. As with the fθ lens, when an incomplete transfer surface is formed on the rib side surface, the distance between the incomplete transfer surface and the optical function surface is increased by the thickness of the rib. There is a problem that it is difficult to be transmitted to the optical function surface.

  Therefore, the present invention has been made in view of the above-described problems in the prior art, and the shape accuracy of the optical functional surface is improved by efficient sink induction to the non-transfer surface formed by incomplete transfer, and the optical An object of the present invention is to provide a compact and low-cost long plastic optical element with reduced deterioration of characteristics. Furthermore, it aims at providing the optical scanning device provided with this plastic optical element, and an image forming apparatus.

The present invention provided to solve the above problems is as follows.
[1] Provided in the imaging optical system of an optical scanning device having a light source means, an optical polarizer, and an imaging optical system for imaging a light beam deflected by the optical polarizer on a surface to be scanned. In an elongated plastic optical element whose thickness in the direction is thinner than the thickness in the sub-scanning direction,
A long optical functional surface formed by generating resin pressure on the resin in the cavity of the mold having the transferred surface and transferring the transferred surface, and a length in the longitudinal direction of the optical functional surface. An elongated rib adjacent in parallel,
A plastic optical element comprising: a concave portion in which at least one of the ribs is recessed toward the optical functional surface side; and a mold cavity-shaped incomplete transfer surface provided on a bottom surface of the concave portion.
[2] The plastic optical element according to [1], wherein the concave portion has a draft in a direction of releasing from the mold during molding.
[3] The plastic optical element according to any one of [1] to [2], which is made of a transparent resin material.
[4] An optical scanning device comprising the plastic optical element according to any one of [1] to [3].
[5] An image forming apparatus comprising the plastic optical element according to any one of [1] to [3].

  According to the present invention, a compact plastic low-cost long plastic optical element in which the shape accuracy of the optical functional surface is improved by the efficient sink induction to the imperfect transfer surface, and the deterioration of the optical characteristics is reduced, An optical scanning device and an image forming apparatus including the plastic optical element can be provided.

As an effect of the present invention, according to the first aspect of the present invention, an optical scanning device having a light source means, an optical polarizer, and an imaging optical system that forms an image of a light beam deflected by the optical polarizer on a surface to be scanned. In the image forming optical system, the resin pressure is generated in the resin in the cavity of the mold having the transfer surface in the long plastic optical element whose thickness in the light transmission direction is smaller than the thickness in the sub-scanning direction. An elongated optical functional surface formed by transferring the transferred surface, and an elongated rib adjacent to the longitudinal direction of the optical functional surface in parallel with the longitudinal direction,
Since the plastic optical element has a concave portion in which at least one of the ribs is recessed toward the optical function surface side and an incomplete transfer surface having a cavity shape of a mold provided on the bottom surface of the concave portion, As a result, the distance between the imperfect transfer surface and the optical function surface can be shortened, so that the effect caused by the occurrence of sink marks on the imperfect transfer surface is more likely to spread to the optical function surface. As a result, deterioration of optical characteristics can be reduced by improving the shape accuracy without causing sink marks.
According to the second aspect of the present invention, in the plastic optical element according to the first aspect, the concave portion has a draft in the direction of releasing from the mold at the time of molding. By providing the draft angle, it is possible to reduce the external force applied to the molded product at the time of mold release, and it is possible to reduce the deterioration of the optical characteristics by improving the shape accuracy of the optical function surface.
According to the invention of claim 3, since the plastic optical element according to any one of claims 1 to 2 is made of a transparent resin material, it is possible to reduce deterioration of optical characteristics.
According to the invention of claim 4, since the optical scanning device including the plastic optical element according to any one of claims 1 to 3 is provided, a highly accurate optical scanning device in which deterioration of optical characteristics is reduced is provided. Can do.
According to the invention of claim 5, since the image forming apparatus having the plastic optical element according to any one of claims 1 to 3 is provided, an image forming apparatus capable of achieving high speed image formation and high image quality is provided. can do.

Hereinafter, an embodiment of a plastic optical element of the present invention will be described with reference to the drawings.
The plastic optical element of the present invention is a long plastic optical element whose thickness in the light transmission direction is thinner than the thickness in the sub-scanning direction, and generates resin pressure on the resin in the cavity of the mold having the transfer surface. A long optical functional surface formed by transferring the transfer surface; and a long rib adjacent to the longitudinal direction of the optical functional surface in parallel with the longitudinal direction. At least one of which has a recess recessed toward the optical function surface, and an incomplete transfer surface having a cavity shape of a mold provided on the bottom surface of the recess. Alternatively, it has one or more transfer surfaces formed by generating a resin pressure on the resin in the cavity of the mold having the transfer surface and transferring the transfer surface, and at least one of the transfer surfaces is An optical functional surface having at least one rib projecting on both sides in a direction perpendicular to the optical functional surface, at least one of the ribs having a recess, and the bottom surface of the recess being a cavity of the mold An incomplete transfer surface (also referred to as a non-transfer surface) formed by incompletely transferring a shape. Alternatively, ribs that are parallel to the main scanning direction and perpendicular to the optical functional surface are provided, and at least one rib side surface is provided with a recess and an incomplete transfer surface on the bottom surface of the recess.

  FIG. 1 is a perspective view of a conventional general long plastic optical element, and FIG. 2 is a cross-sectional view (b) in the main scanning direction at a position indicated by A in FIG. When the thickness in the light transmission direction is a and the thickness in the sub-scanning direction is b, a <b. In the case of such a long shape, since the cooling rate in the light transmission direction is high in the cooling process, the heat shrinkage force in the same direction is increased, so that sink marks are likely to occur on the optical function surface as the transfer surface. Therefore, in molding, a technique for efficiently sinking the imperfect transfer surface more than the fθ lens and transferring the optical functional surface with high accuracy is required.

Next, with reference to FIGS. 3 and 4, the shrinkage force of the resin in the process of being cooled in the mold will be described focusing on the vicinity of the optical function surface in the conventional plastic optical element.
In the process in which the resin is cooled in the mold, contraction force acts in a region indicated by a circle in FIG. When the force (f1) at which the resin generated by this contraction is released from the mold exceeds the transfer force with the mold (force (f2) to keep in close contact with the mold), the resin is removed from the mold. It will peel off and cause sink marks.

  Here, the case where the sink induction method is used is shown in FIG. In this case, the resin near the imperfect transfer surface has a high temperature and a high fluidity. Therefore, when the contraction force starts to act on the resin in the vicinity of the optical function surface, the resin on the incomplete transfer surface side contracts preferentially (f3), so that the force that the resin tends to peel off from the mold is hardly generated. Therefore, sink marks are less likely to occur on the optical function surface.

  However, a thin plastic optical element having a small thickness usually has ribs with a thickness (c) of about several millimeters around the optical functional surface in order to increase strength and prevent deformation due to external force. The distance between the complete transfer surface and the optical functional surface is long. For this reason, the effect of sinking the imperfect transfer surface is not sufficiently transmitted to the optical functional surface, and it is difficult to transfer without causing the optical functional surface to sink and to reduce deterioration of the optical characteristics by improving the shape accuracy.

Therefore, as shown in FIG. 5, the plastic optical element of the present invention has a recess having a depth d on the rib side surface and a non-transfer surface formed by incomplete transfer on the bottom surface of the recess.
By providing such a recessed portion of depth d, the distance between the imperfect transfer surface and the optical function surface can be determined without reducing the thickness of the rib, that is, without being easily deformed by an external force. Compared to the case, it can be shortened by d. Thereby, the effect by sinking the non-transfer surface formed by incomplete transfer is easily transmitted to the optical function surface. Therefore, it is possible to transfer without causing the optical functional surface to sink, and it is possible to reduce deterioration of the optical characteristics by improving the shape accuracy of the optical functional surface.

In the plastic optical element of the present invention, it is preferable that the concave portion provided on the rib side surface has a draft in the direction of releasing from the mold during molding.
Since the resin molded with respect to the mold release direction has a gradient, the mold release resistance mainly due to friction is reduced, and the burden on the plastic optical element when taking out is reduced. Thereby, the distortion of the plastic optical element is reduced and the optical characteristics are improved. That is, since deformation is reduced, the shape accuracy of the transfer surface can be increased.

  Furthermore, the plastic optical element of the present invention is preferably made of a transparent resin material.

Hereinafter, an optical scanning device and an image forming apparatus equipped with the plastic optical element of the present invention will be described.
FIG. 9 is an explanatory diagram for explaining an optical scanning device 100 including a plastic optical element 10 according to an embodiment of the present invention.
An optical scanning device 100 that scans beams emitted from a plurality of light sources and forms an image according to image information includes a light source 30 that emits a plurality of beams according to image information, and a beam emitted from the light source 30. A deflecting means 20 for deflecting and a plastic optical element 10 of the present invention in which a plurality of the deflecting means 20 are disposed facing each other at a position facing the deflecting means 20 are provided.

  As shown in FIG. 9, a plurality of beams emitted from a plurality of laser light sources of the light source 30 are deflected by the same deflecting means 20 (for example, a polygon mirror), and are deflected corresponding to the plurality of laser light sources of the light source 30. Each plastic optical element 10 disposed at a position facing the means 20 forms an image on each photoconductor 40 and scans the photoconductor 40 to form an image according to image information.

FIG. 10 shows a configuration of a tandem type color copying machine as an embodiment of an image forming apparatus including the plastic optical element 10 and the optical scanning device 100 of the present invention.
The color copying machine 200 includes an image forming unit 200A positioned at the center of the apparatus main body, a paper feeding unit 200B positioned below the image forming unit 200A, and an image reading unit (not shown) positioned above the image forming unit 200A. The fixing device 220 is incorporated in the image forming unit 200A.

  The image forming unit 200A is provided with a transfer belt 202 having a transfer surface extending in the horizontal direction, and a configuration for forming an image of a color complementary to the color separation color on the upper surface of the transfer belt 202. Is provided. That is, photoconductors 203Y, 203M, 203C, and 203K as image carriers that can carry images of toners of complementary colors (yellow, magenta, cyan, and black) are juxtaposed along the transfer surface of the transfer belt 202. ing.

  Each of the photoconductors 203Y, 203M, 203C, and 203K is configured by a drum that can rotate in the same direction (counterclockwise direction). Around the drum, a charging device that performs image formation processing in the rotation process, and optical writing An apparatus, a primary transfer device, a developing device, and a cleaning device are arranged. In addition, each color toner is accommodated in each developing device.

  The transfer belt 202 is configured to be able to move in the same direction at the position facing the photoconductors 203Y, 203M, 203C, and 203K by being wound around a driving roller and a driven roller. A transfer roller 211 is provided at a position facing a roller 210 that is one of the driven rollers. Further, the conveyance path of the sheet P from the transfer roller 211 to the transfer device 220 is a horizontal path.

  The paper feed unit 200B separates the paper feed tray 215 for stacking and storing sheets P as recording media and the sheets P in the paper feed tray 215 one by one from the top to the position of the transfer roller 211. It has a transport mechanism for transporting.

  In image formation in the image forming apparatus 200 of the present invention, the surface of the photoreceptor 203Y is uniformly charged by the charging device, and an electrostatic latent image is formed on the photoreceptor 203Y based on image information from the image reading unit. The The electrostatic latent image is visualized as a toner image by a developing device containing yellow toner, and the toner image is primarily transferred onto the transfer belt 202 by a primary transfer device to which a predetermined bias is applied. . The other photoconductors 203M, 203C, and 203B also form similar images only with different toner colors, and the toner images of the respective colors are sequentially transferred and superimposed on the fixing belt by electrostatic force.

  Next, the toner image T primarily transferred from the photoconductors 203Y, 203M, 203C, and 203K onto the transfer belt 202 is transferred to the sheet P conveyed by the roller 210 and the transfer roller 211. The sheet P onto which the toner image T has been transferred is further conveyed to the fixing device 220 and is fixed at the nip portion between the fixing belt and the pressure roller.

  Next, the sheet P discharged from the nip portion is sent out along the discharge path. At this time, the sheet P that has been wound around the fixing belt is separated from the fixing belt at the tip of the fixing separation claw and returned to the discharge path.

  Although the present invention has been described with the embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and other embodiments, additions, modifications, deletions, etc. Can be changed within the range that can be conceived, and any embodiment is included in the scope of the present invention as long as the effects and advantages of the present invention are exhibited.

It is a perspective view which shows the prior art example of a general elongate plastic optical element. (A) is a perspective view which shows the conventional example of a general elongate plastic optical element, (b) is sectional drawing of the position shown to A in (a). It is explanatory drawing which shows the contraction force of resin at the time of shaping | molding in the conventional elongate plastic optical element. It is explanatory drawing which shows the shrinkage force of the resin at the time of shaping | molding in the conventional elongate plastic optical element which has the non-transfer surface by incomplete transfer. It is explanatory drawing which shows the shrinkage force of resin at the time of shaping | molding of the plastic optical element of this invention. It is sectional drawing which shows the example of the one aspect | mode of the plastic optical element of this invention. It is sectional drawing which shows the example of the other aspect of the plastic optical element of this invention. It is a perspective view which shows the example of the one aspect | mode of the plastic optical element of this invention. It is the schematic which shows the top view in one Embodiment of the optical scanning device carrying the plastic optical element of this invention. 1 is a schematic view showing a configuration in an embodiment of an image forming apparatus equipped with a plastic optical element and an optical scanning device of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Plastic optical element 11 Rib 12 Optical function surface 13 Non-transfer surface 20 Optical deflector 30 Light source 40 Photosensitive body 100 Optical scanning device 200 Image forming apparatus 200A Image forming part 200B Paper feed part 202 Transfer belt 203Y, 203M, 203C, 203B Photosensitive Body 210 Roller 211 Transfer roller 215 Paper feed tray 220 Fixing device

Claims (5)

Provided in the imaging optical system of an optical scanning device having a light source means, an optical polarizer, and an imaging optical system for imaging a light beam deflected by the optical polarizer on a surface to be scanned, and having a thickness in a light transmission direction In an elongated plastic optical element that is thinner than the thickness in the sub-scanning direction,
A long optical functional surface formed by generating resin pressure on the resin in the cavity of the mold having the transferred surface and transferring the transferred surface, and a length in the longitudinal direction of the optical functional surface. An elongated rib adjacent in parallel,
A plastic optical element comprising: a concave portion in which at least one of the ribs is recessed toward the optical functional surface side; and a mold cavity-shaped incomplete transfer surface provided on a bottom surface of the concave portion.   The plastic optical element according to claim 1, wherein the concave portion has a draft in a direction in which the concave portion is released from the mold during molding.   3. The plastic optical element according to claim 1, wherein the plastic optical element is made of a transparent resin material.   An optical scanning device comprising the plastic optical element according to claim 1.   An image forming apparatus comprising the plastic optical element according to claim 1.

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