JP4751184B2 - Plastic optical element, optical scanning device, and image forming apparatus equipped with the optical scanning device - Google Patents

Description

  The present invention relates to an optical scanning system of a laser type digital copying machine, a laser printer or a facsimile apparatus, a plastic optical element applied to an optical apparatus such as a video camera, an optical scanning apparatus equipped with the plastic optical element, and an optical scanning thereof. The present invention relates to an image forming apparatus equipped with the apparatus.

2. Description of the Related Art Conventionally, optical elements (lenses, mirrors) having laser beam imaging and correction functions have been used in optical units of scanning optical systems such as laser digital copying machines, printers, and facsimile machines.
In recent years, in these optical elements, the optical performance has been improved by adopting an aspheric surface, and the cost of the optical element itself has been reduced by adopting an injection molding method and an injection compression molding method capable of molding a complicated shape. .
In plastic molding including the above-described injection molding method and injection compression molding method, it is generally desired to uniformize the resin pressure and resin temperature in the cavity in the process of cooling and solidifying the molten resin in the mold cavity. It is known that it is desirable to accurately form the shape (for example, see Patent Documents 1 and 2).
These are disclosed in, for example, “Plastic molded product and molding of the plastic molded product” in Patent Document 1 and “Resin lens, scanning optical device, and image forming apparatus” in Patent Document 2.
In the disclosures of Patent Documents 1 and 2, if the resin pressure or the resin temperature is not uniform and there is a local distribution, the amount of thermal shrinkage varies depending on the site, and as a result, sink marks that are defective in appearance occur. In order to solve this problem, it is conceivable to increase the injection filling amount by increasing the injection pressure of the molten resin when the molten resin is injected and filled into the cavity of the mold.
However, in that case, the outer shape warpage of the plastic molded product increases. Further, when a transparent resin is used as the material, the optical performance is deteriorated due to an increase in internal strain, in particular, internal strain at a thin portion.
In addition, when the target is an elongated optical element, (1) the resin cooling rate, that is, the amount of heat shrinkage differs depending on the part due to the difference in the optical functional surface (for example, the lens thickness) in the longitudinal direction. Further, (2) since it is necessary to make the mold temperature distribution in the entire longitudinal direction uniform, the occurrence rate of sink marks, which are appearance defects, is increased.
In particular, for (1), not only the optical functional surface provided with the light beam effective portion but also the transfer surface adjacent to the optical functional surface causes sink marks in the longitudinal direction along the optical functional region which is a thick portion. To do.
In addition, on the transfer surface adjacent to the optical function surface of such a plastic molded product, an attachment reference surface for the optical unit is usually arranged outside the optical function region so as to avoid sink marks.
JP 2003-305754 A JP 2004-205875 A

However, once shrinkage occurs, that is, the thermal contraction of the released optical functional region is promoted, the adhesive force of the peripheral portion is reduced in a chained manner and enters the attachment reference surface. The above phenomenon causes deterioration of the surface accuracy of the attachment reference surface, resulting in a problem that the assembly accuracy of the plastic optical element to the optical unit is deteriorated.
This deterioration in assembly accuracy affects the imaging position of light transmitted or reflected by the plastic optical element. For example, when the plastic optical element is disposed in the optical unit of the scanning optical system, the scanning position of the laser beam, etc. This greatly affects the optical performance.
The present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide a plastic optical element that maintains the current optical performance and has improved mass productivity, an optical scanning device equipped with this plastic optical element, and An object of the present invention is to provide an image forming apparatus equipped with this optical scanning device.

In order to solve the above-mentioned problem, the invention according to claim 1 is an elongated plastic optical element having an optical functional surface having a light beam effective portion and a transfer surface adjacent to the optical functional surface. The transfer having at least one convex portion on the transfer surface in the longitudinal direction of the plastic optical element and outside the optical functional area including the light beam effective portion , and further outside the convex portion. A plastic optical element having a reference surface for mounting the plastic optical element on a surface is characterized.
According to a second aspect of the present invention, there is provided an optical scanning device including the plastic optical element according to the first aspect.
According to a third aspect of the present invention, there is provided an image forming apparatus equipped with the optical scanning device according to the second aspect.

According to the present invention, the plastic optical element increases the release resistance at the time of molding by the convex portion or the step, and the sink mark generated in the longitudinal direction reduces the adhesion of the peripheral portion in a chain and attaches it. Molded to prevent entry into the reference surface.
As a result, the assembly accuracy of the plastic optical element to the optical unit (optical scanning device) can be improved, and the improvement of the assembly accuracy stabilizes the imaging position of the light transmitted or reflected by the plastic optical element. Can do. It is possible to provide a plastic optical element that maintains the current optical performance and has improved mass productivity.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a top view showing a plastic optical element according to the first embodiment of the present invention. FIG. 2 is a front view of the plastic optical element of FIG.
With reference to FIG.1 and FIG.2, the plastic optical element as a long lens which is a component of the optical scanning device of a color laser beam printer is demonstrated. This plastic optical element A has an optical functional surface (lens surface) 2 provided with a light beam effective portion 1 and two transfer surfaces 3 adjacent to the optical functional surface 2.
The plastic optical element A is provided with convex portions 4 at both ends in the longitudinal direction outside the region of the light effective portion 1 on the transfer surface 3 adjacent to the optical function surface 2. Reference numeral 5 denotes an attachment reference plane.
This convex portion 4 increases the mold release resistance during molding, that is, increases the apparent adhesion force. As a result, sink marks generated in the longitudinal direction along the transfer surface 3 adjacent to the optical functional surface 2 and the light beam effective portion (optical functional region) 1 which is a thick portion reduce the adhesion of the peripheral portion in a chained manner. In addition, entry into the attachment reference plane 5 is prevented.
By using this measure, the surface accuracy of the attachment reference surface 5 can be improved, and as a result, the assembly accuracy of the plastic optical element A with respect to the optical unit (optical scanning device) can be improved.
FIG. 3 is a schematic view illustrating a mold and a insert for molding a plastic optical element. In addition, although the plastic optical element which has a convex-shaped part on the both sides mentioned later is shape | molded by the metal mold | die and nest | insert of FIG. Molding will be described.
As shown in FIG. 3, the mold includes a nesting 6 and a mirror piece 7. In molding, the optical surface of the plastic optical element A described above is formed by making the transfer surface 3 and the convex portion 4 the same nesting. The effect which improves the assembly | attachment precision with respect to can be acquired further.
The improvement of the assembly accuracy stabilizes the imaging position of the light transmitted or reflected by the plastic optical element A. For example, when the plastic optical element A is disposed in an optical unit (optical scanning device) of a scanning optical system. The optical performance such as the scanning position of the laser beam can be improved.

FIG. 4 is a top view showing a plastic optical element according to the second embodiment of the present invention. FIG. 5 is a front view of the plastic optical element of FIG. According to the second embodiment of FIG. 4 and FIG. 5, the mold release resistance is adjusted by making the convex portion 4 shown in the first embodiment into the tapered portion 8, and the optical at the time of mold release. The promotion of thermal shrinkage of the functional surface 2 can be reduced.
In the second embodiment shown in FIGS. 4 and 5, the configuration of the plastic optical element A is the same as that of the first embodiment except for the tapered portion 8, so that the same reference numerals are given and repeated description is given. Is omitted.
FIG. 6 is a top view showing a plastic optical element according to the third embodiment of the present invention. FIG. 7 is a front view of the plastic optical element of FIG. In the third embodiment shown in FIGS. 6 and 7, the plastic optical element A includes an optical functional surface 2 having a light beam effective portion 1, two transfer surfaces 3 adjacent to the optical functional surface 2, and an attachment reference surface. 5, at least one step 9 is provided at both ends in the longitudinal direction outside the optical function (light beam effective portion) region 1 on the transfer surface 3 adjacent to the optical function surface 2. In molding, a further effect can be obtained by making the transfer surface 3 and the step 9 into the same nesting of the mold.

FIG. 8 is a top view showing a plastic optical element according to the fourth embodiment of the present invention. FIG. 9 is a front view of the plastic optical element of FIG. In the fourth embodiment shown in FIGS. 8 and 9, the plastic optical element A includes an optical functional surface 2 having a light beam effective portion 1, two transfer surfaces 3 adjacent to the optical functional surface 2, and an attachment reference surface. The plastic optical element A is provided with convex portions 4 on both sides of both ends in the longitudinal direction outside the region of the light effective portion 1 on the transfer surface 3 adjacent to the optical function surface 2. Thereby, it is possible to cope with a case where the reference mounting surfaces 5 are required on both sides.
FIG. 10 is a top view showing a plastic optical element according to the fifth embodiment of the present invention. FIG. 11 is a front view of the plastic optical element of FIG. In the fifth embodiment shown in FIGS. 10 and 11, the plastic optical element A includes an optical functional surface 2 having a light beam effective portion 1, two transfer surfaces 3 adjacent to the optical functional surface 2, and an attachment reference surface. The plastic optical element A is provided with a step 9 on both sides of both ends in the longitudinal direction outside the region of the light effective portion 1 on the transfer surface 3 adjacent to the optical functional surface 2. Accordingly, it is possible to cope with the case where the optically effective portion has an asymmetrical shape and needs to be reversed and arranged.
That is, the plastic optical element A according to the fourth and fifth embodiments in FIGS. 8 and 10 has the convex portion 4 and the step 9 in FIGS. 1 and 4 showing the first and third embodiments as a transfer surface. 3 on both sides.
According to the above-described embodiment of the plastic optical element A according to the present invention, it is possible to provide a plastic optical element that maintains the current optical performance and has improved mass productivity. In addition, it is possible to provide a plastic molded product such as a thick-walled or uneven-shaped plastic scanning lens having a highly accurate optical mirror surface.
According to such a configuration, an optical scanning device that employs a tandem method using a multi-beam as disclosed in Japanese Patent Application Laid-Open No. 10-148777 requires mounting reference surfaces on both sides, or the optically effective portion has an asymmetric shape. However, it is possible to cope with the case where it is necessary to reverse the arrangement.
As the resin used for the molded article that is the plastic optical element described above, when molding an optical element that requires transparency, a transparent amorphous resin whose softening temperature is its glass transition temperature should be used. Can do.
The amorphous resin may be, for example, a polymethacrylic resin, a polycarbonate resin, an alicyclic acrylic resin, a cyclic polyolefin copolymer, or the like. Moreover, if it is used as an application other than the optical element, it is possible to use a crystalline resin whose softening temperature is the melting temperature.

FIG. 12 is a schematic top view showing an optical scanning device and an image forming apparatus on which the plastic optical element according to the present invention is mounted. FIG. 13 is a schematic side view of the optical scanning device and the image forming apparatus of FIG.
12 and 13, the image forming apparatus includes an optical scanning device 11 disposed on the housing above the photosensitive member 14. The optical scanning device 11 includes a plastic optical element A having a convex portion 4 according to the present invention, an optical deflector 12 that is a rotary polygon mirror, a laser light source 13, a photoconductor 14, and a reflection mirror 15.
As described above, the plastic optical element A according to the present invention increases the mold release resistance at the time of molding by the convex portion 4, and sink marks generated in the longitudinal direction reduce the adhesion of the peripheral portion in a chain manner. In addition, it is shaped so as to prevent entry into the mounting reference surface.
By using this measure, as a result, the assembly accuracy of the plastic optical element A with respect to the optical unit (optical scanning device) can be improved. This improvement in assembly accuracy can stabilize the imaging position of the light transmitted or reflected by the plastic optical element A.
Therefore, when the plastic optical element A is arranged in the optical unit (optical scanning device) 11 of the scanning optical system, the optical performance such as the scanning position of the laser beam can be improved. Furthermore, the image forming apparatus B can reduce the overall cost by mounting the optical scanning device 11 with improved optical performance.

The top view which shows the plastic optical element which is the 1st Embodiment of this invention. The front view of the plastic optical element shown in FIG. Schematic explaining the metal mold | die and nesting which shape | mold a plastic optical element. The top view which shows the plastic optical element which is the 2nd Embodiment of this invention. The front view of the plastic optical element shown in FIG. The top view which shows the plastic optical element which is the 3rd Embodiment of this invention. The front view of the plastic optical element shown in FIG. The top view which shows the plastic optical element which is the 4th Embodiment of this invention. The front view of the plastic optical element shown in FIG. The top view which shows the plastic optical element which is the 5th Embodiment of this invention. The front view of the plastic optical element shown in FIG. 1 is a schematic top view showing an optical scanning device and an image forming apparatus equipped with a plastic optical element according to the present invention. FIG. 13 is a schematic side view of the optical scanning device and the image forming apparatus in FIG. 12.

Explanation of symbols

A Plastic optical element (long lens)
B Image forming apparatus 1 Light beam effective portion 2 Optical functional surface 3 Transfer surface 4 Convex-shaped portion 5 Mounting reference surface 6 Nesting 8 Tapered-shaped portion 9 Step 11 Optical scanning device

Claims (3)

In a long plastic optical element having an optical functional surface having a light beam effective portion and a transfer surface adjacent to the optical functional surface,
The transfer having at least one convex portion on the transfer surface in the longitudinal direction of the plastic optical element and outside the optical functional area including the light beam effective portion , and further outside the convex portion. A plastic optical element comprising a reference surface for mounting the plastic optical element on a surface . An optical scanning device comprising the plastic optical element according to claim 1 . An image forming apparatus comprising the optical scanning device according to claim 2 .

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