JP5163518B2 - Optical scanning apparatus, image forming apparatus, and plastic lens manufacturing method - Google Patents

Description

  The present invention relates to an optical scanning device, an image forming apparatus, and a plastic lens manufacturing method.

  In general, an optical writing unit (optical scanning device) of an image forming apparatus such as a laser-type digital copying machine, a printer, or a facsimile machine uses a rectangular optical element having laser beam imaging and various correction functions. ing.

  In recent years, these optical elements have changed from glass to plastic due to demands for cost reduction of products, and in order to cover a plurality of functions with minimum elements, the mirror surface shape is not only spherical. It has come to be formed into a complex aspherical shape. Specifically, in the case where the optical element is a lens, the lens thickness is often increased, and in many cases, the lens is designed to have an uneven shape in which the lens thickness is not constant in the longitudinal direction.

  Such plastic molded products can be mass-produced at a low cost by inserting a resin base material into a mold cavity formed in the shape of the molded product or injection-filling a molten resin even if it is a special shape. be able to.

  However, in such conventional plastic molding, in the process of cooling and solidifying the molten resin material in the mold cavity, it is desirable to make the resin pressure and resin temperature uniform in the cavity. However, when the lens has an uneven shape, such as a long plastic lens disclosed in Patent Document 1, the volume shrinks depending on the thickness of the lens. When the amount is different, the shape accuracy is deteriorated, and there is a case where sink marks are generated at a thick lens.

  In order to solve this problem, in the injection molding method in which the molten resin is injected and filled into the mold cavity, if the injection pressure of the molten resin is increased to increase the injection filling amount, the internal strain of the plastic molded product increases, In particular, in the case of a thick or uneven shape, the internal strain increases, which may adversely affect optical performance and the like.

  In other words, if the injection pressure is lowered to reduce the internal strain and the injection filling amount is reduced, sinking occurs in the thick-walled portion, etc., while if the injection pressure is increased and the injection filling amount is increased, the internal strain increases. Become.

  Therefore, a plastic lens (specifically, for example, a long plastic lens disclosed in Patent Document 1) used in the imaging optical system of the optical scanning device is shown in FIG. 3 or FIG. 4 of Patent Document 2. As described above, it is possible to solve the above problem by providing an incomplete transfer portion which is a recess formed by incomplete transfer in a part other than the transfer surface.

  In particular, in the case of a long plastic lens in which the outer dimension a in the sub-scanning direction and the lens thickness b in the light transmission direction satisfy a / b> 1, the lens thickness b in the light transmission direction has an outer shape in the sub-scanning direction. Since it is thinner than the dimension a, the “in-mold cooling speed” of the lens portion, that is, “thermal shrinkage” is relatively faster than other parts, and the appearance of the lens surface is likely to cause sink marks.

  Here, the long plastic lens is basically configured as shown in FIG. That is, FIG. 1 shows a lens body 1 of the long plastic lens, and reference numerals 2 and 3 denote two transfer surfaces that function as a light incident surface and a light exit surface, respectively. When used in an optical scanning device, the long direction (longitudinal direction) of the long plastic lens is set as the main scanning direction. FIG. 2 shows the entire long plastic lens. That is, FIG. 2 shows the long plastic lens body 1 in which ribs 6 are provided on at least both side surfaces (opposite side surfaces other than the two transfer surfaces 2 and 3) 4 and 5. Yes. Although not shown in FIG. 2, ribs 6 are usually provided at both ends in the longitudinal direction (longitudinal direction) of the lens body 1 of the long plastic lens. Such ribs 6 can be formed integrally with the lens body 1 from the same material as the lens body 1.

  3A is a diagram (side view) of FIG. 2 viewed from the direction of the arrow S, and FIG. 3B is a diagram of FIG. 2 viewed from the direction of the arrow R (light incident direction) (front view). Figure). In FIG. 3A, reference numeral 7 denotes a light transmission region. 4 is a cross-sectional view taken along line AA in FIG. 2 (a cross-sectional view at an arbitrary position x in the main scanning direction).

  As for the long plastic lens as described above, for example, as shown in FIG. 3 or FIG. 4 of Patent Document 2, a part other than the transfer surfaces 2 and 3 (specifically, in FIG. By providing an incomplete transfer portion which is a recess formed by incomplete transfer on at least one of the left and right ribs 6 provided on the opposite side surfaces 4 and 5 other than the two transfer surfaces 2 and 3, the sub-scanning direction Even in a long plastic lens whose outer dimension a and the lens thickness b in the light transmission direction satisfy a / b> 1, even if the injection pressure is reduced to reduce the injection filling amount, Occurrence can be prevented.

  Incidentally, as described above, even in a long plastic lens in which the outer dimension a in the sub-scanning direction and the lens thickness b in the light transmission direction satisfy a / b> 1, for example, FIG. 3 or FIG. Even if the injection pressure is reduced and the injection filling amount is reduced by providing an incomplete transfer portion which is a recess formed by incomplete transfer in a part other than the transfer surface as shown in FIG. However, since the lens thickness b in the light transmission direction is thinner than the external dimension a in the sub-scanning direction, as will be described in detail later, Depending on the state, the lens surface shape is inclined in the sub-scanning direction (accuracy is deteriorated), and when the change is different between positions in the main scanning direction, the lens surface shape is twisted (lens distortion) in the sub-scanning direction. Scan direction That variability (scan positional deviation) is increased, the inventors have found.

  In particular, when this type of optical scanning apparatus is applied to a color image forming apparatus, the occurrence of a scanning position shift in the sub-scanning direction on the surface to be scanned, particularly a high-frequency component scanning position shift, is a color shift in the image forming apparatus. Will worsen. The scanning position shift of the high frequency component means a residual component obtained by subtracting the secondary component from the scanning position, and is an important characteristic for determining the color shift on the product.

  Such a problem is a problem that has become conspicuous with the trend toward higher image quality in image forming apparatuses.

  The present invention is a plastic lens used in an imaging optical system of an optical scanning device, and the outer dimension a in the sub-scanning direction and the lens thickness b in the light transmission direction of the plastic lens satisfy a / b> 1. In a plastic lens, when an incomplete transfer portion that is a recess is provided in a part other than the transfer surface, distortion of the plastic lens can be remarkably reduced, and variation in the sub-scanning direction (scanning position deviation) can be remarkably reduced. An object of the present invention is to provide an optical scanning device, an image forming apparatus, and a plastic lens manufacturing method.

In order to achieve the above object, an invention according to claim 1 is an optical scanning device comprising: an optical deflector; and an imaging optical system that forms an image of a light beam deflected by the optical deflector on a surface to be scanned. A plastic lens is used for the imaging optical system, and the plastic lens has two transfer surfaces including a light incident surface and an output surface, and is formed on opposite side surfaces other than the two transfer surfaces. , Along the main scanning direction of the transfer surface, and corresponding to the range of the light transmission region of the plastic lens, an incomplete transfer portion is provided as a recess,
When the position of the plastic lens in the main scanning direction is x and the outer dimension a of the plastic lens in the sub-scanning direction and the lens thickness b in the light transmission direction satisfy a / b> 1,
Deviations | d1 (x) −d2 (x) | of the depths d1 (x) and d2 (x) of the concave portions of the incomplete transfer portions provided on the opposite side surfaces are positions in the main scanning direction. x is set to be 5% or less of the outer dimension a in the sub-scanning direction.

  According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the plastic lens is formed of a transparent resin material.

  According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, the plastic lens has a rib on each of opposite sides on the outer side of the two transfer surfaces. In addition, a concave portion which is the incomplete transfer portion is formed.

  According to a fourth aspect of the invention, there is provided an image forming apparatus using the optical scanning device according to any one of the first to third aspects.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the image forming apparatus is a color image forming apparatus.

The invention according to claim 6 is used for the imaging optical system of an optical scanning device having an optical deflector and an imaging optical system that forms an image of a light beam deflected by the optical deflector on a surface to be scanned. A plastic lens manufacturing method, comprising:
The plastic lens has two transfer surfaces composed of a light incident surface and a light output surface, on opposite side surfaces other than the two transfer surfaces, along the main scanning direction of the transfer surface, and Corresponding to the range of the light transmission region of the plastic lens, the incomplete transfer portion that is a recess is formed by incomplete transfer of the cavity shape of the mold,
When the position of the plastic lens in the main scanning direction is x and the outer dimension a of the plastic lens in the sub-scanning direction and the lens thickness b in the light transmission direction satisfy a / b> 1,
Deviations | d1 (x) −d2 (x) | of the depths d1 (x) and d2 (x) of the concave portions of the incomplete transfer portions provided on the opposite side surfaces are positions in the main scanning direction. In x, each incomplete transfer portion is formed so as to be 5% or less of the outer dimension a in the sub-scanning direction.

According to the first to third and sixth aspects of the invention, the optical scanning includes the optical deflector and the imaging optical system that forms an image of the light beam deflected by the optical deflector on the surface to be scanned. In the apparatus, a plastic lens is used for the imaging optical system, and the plastic lens has two transfer surfaces including an incident surface and an output surface of a light beam, and is provided on both opposite sides other than the two transfer surfaces. On the side surface, along the main scanning direction of the transfer surface and corresponding to the range of the light transmission region of the plastic lens, an incomplete transfer portion that is a recess is provided,
When the position of the plastic lens in the main scanning direction is x and the outer dimension a of the plastic lens in the sub-scanning direction and the lens thickness b in the light transmission direction satisfy a / b> 1,
Deviations | d1 (x) −d2 (x) | of the depths d1 (x) and d2 (x) of the concave portions of the incomplete transfer portions provided on the opposite side surfaces are positions in the main scanning direction. Since x is set to be 5% or less of the outer dimension a in the sub-scanning direction,
The balance of the depths d1 (x) and d2 (x) of the concave portions of the incomplete transfer portions provided on the opposite side surfaces is improved, and thereby the difference in external dimension change (heat shrinkage) is reduced. As a result, the tilt component of the lens surface shape in the sub-scanning direction can be remarkably reduced at each position x in the main scanning direction, thereby reducing distortion of the plastic lens (twisting of the lens surface shape in the sub-scanning direction). This significantly reduces the variation in the sub-scanning direction (scanning position deviation). That is, it is possible to significantly reduce the scanning position deviation in the sub-scanning direction on the surface to be scanned, particularly the high-frequency component scanning position deviation.

  Further, according to the inventions according to claims 4 and 5, since the image forming apparatus uses the optical scanning device according to any one of claims 1 to 3, the image forming apparatus Is a color image forming apparatus, color misregistration in the image forming apparatus can be significantly reduced.

It is a figure which shows the lens main body of an elongate plastic lens. It is a figure which shows the whole elongate plastic lens. It is a figure which shows the whole elongate plastic lens. It is sectional drawing in the AA of FIG. In the long plastic lens as shown in FIGS. 2 to 4, incomplete transfer, which is a recess formed by incomplete transfer on one of the left and right ribs provided on opposite side surfaces other than the two transfer surfaces. It is a figure which shows the plastic lens provided with the part. In the long plastic lens as shown in FIGS. 2 to 4, incomplete transfer, which is a recess formed by incomplete transfer on one of the left and right ribs provided on opposite side surfaces other than the two transfer surfaces. It is a figure which shows the plastic lens provided with the part. It is sectional drawing in the AA of FIG. In the long plastic lens as shown in FIGS. 2 to 4, incomplete transfer, which is a recess formed by incomplete transfer on both the left and right ribs provided on the opposite side surfaces other than the two transfer surfaces. It is a figure which shows the plastic lens provided with the part. In the long plastic lens as shown in FIGS. 2 to 4, incomplete transfer, which is a recess formed by incomplete transfer on both the left and right ribs provided on the opposite side surfaces other than the two transfer surfaces. It is a figure which shows the plastic lens provided with the part. It is sectional drawing in the AA of FIG. In the elongated plastic lens of FIGS. 5 to 7 and the elongated plastic lens of FIGS. 8 to 10, compressed gas is applied to the molded product to form a recess (by imperfect transfer during molding). It is a figure for demonstrating the method of 1. FIG. In the elongated plastic lens of FIGS. 5 to 7 and the elongated plastic lens of FIGS. 8 to 10, compressed gas is applied to the molded product to form a recess (by imperfect transfer during molding). It is a figure for demonstrating the method of 2. FIG. 5 to 7, in the process of forming an incomplete transfer portion that is a recess in one of the left and right ribs, a change in external dimension (heat shrinkage) that occurs on the side of the incomplete transfer portion (left side) of the lens body is caused. FIG. It is a figure for demonstrating the dispersion | variation (scanning position shift | offset | difference) in the subscanning direction by the distortion (the twist of the lens surface shape to a subscanning direction) of a plastic lens. 8 to 10, the depth d1 (x) of the recess that is the left imperfect transfer portion is considerably larger than the depth d2 (x) of the recess that is the right imperfect transfer portion. In the process of forming an imperfect transfer portion that is a recess in both the left and right ribs, a difference in external dimension change (heat shrinkage) occurs, and this occurs on the incomplete transfer portion side (left side) of the lens body. It is a figure which shows an external dimension change (thermal contraction). 8 to 10, when the outer dimension a of the plastic lens in the sub-scanning direction and the lens thickness b in the light transmission direction satisfy a / b> 1, they are provided on the opposite side surfaces. The deviation | d1 (x) −d2 (x) | of the depths d1 (x) and d2 (x) of the recesses of each incomplete transfer portion is the outer dimension a in the sub-scanning direction at each main scanning direction position x. It is a figure which shows the state from which the balance of the external dimension change (thermal contraction) was taken in the process in which the imperfect transfer part which is a recessed part is formed in both the right and left ribs that it is 5% or less. FIG. 17 is a diagram illustrating a state in which variation in the sub-scanning direction (scan position deviation in the sub-scan direction on the surface to be scanned, in particular, high-frequency component scan position deviation) can be significantly reduced in the state of FIG. 16. It is a figure for demonstrating the method for forming the recessed part which is an incomplete transfer part in the side surface of the both sides which the plastic lens of this invention opposes. It is a figure for demonstrating the method for forming the recessed part which is an incomplete transfer part in the side surface of the both sides which the plastic lens of this invention opposes. It is a figure for demonstrating the method for forming the recessed part which is an incomplete transfer part in the side surface of the both sides which the plastic lens of this invention opposes. It is a figure which shows the structural example of the optical scanning device to which this invention was applied.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIGS. 5 to 7 correspond to FIGS. 2 to 4, respectively, and are long plastic lenses (external dimension a in the sub-scanning direction and lens in the light transmission direction) as shown in FIGS. In a long plastic lens with a thickness b satisfying a / b> 1, a part other than the transfer surfaces 2 and 3 (specifically, side surfaces 4 on opposite sides other than the two transfer surfaces 2 and 3). , 5 is a view showing a plastic lens provided with an incomplete transfer portion 10 which is a recess formed by incomplete transfer on one of the left and right ribs 6 provided in 5. 7 is a cross-sectional view taken along the line AA in FIG. 5 (a cross-sectional view at an arbitrary position x in the main scanning direction), and the imperfect transfer portion 10 that is a recess is provided on one of the left and right ribs 6. This corresponds to FIG. 3 of Patent Document 2.

  Here, as shown in FIG. 6, the incomplete transfer portion 10 is formed along the main scanning direction of the transfer surface and corresponding to the range of the light transmission region 7 of the plastic lens. Further, the concave portion that is the incomplete transfer portion 10 may extend from the rib 6 to the lens body 1, but should not extend to the light transmission region 7 in the lens body 1.

  FIGS. 8 to 10 correspond to FIGS. 2 to 4, respectively, and are long plastic lenses as shown in FIGS. 2 to 4 (the external dimension a in the sub-scanning direction and the light transmission direction). In a long plastic lens with a lens thickness b satisfying a / b> 1, a part other than the transfer surfaces 2 and 3 (specifically, on both opposing sides other than the two transfer surfaces 2 and 3) It is a figure which shows the plastic lens provided with the imperfect transfer parts 11 and 12 which are the recessed parts formed by the imperfect transfer in both the right-and-left rib 6 provided in the side surfaces 4 and 5. 10 is a cross-sectional view taken along the line AA in FIG. 8 (a cross-sectional view at an arbitrary position x in the main scanning direction), and is incomplete with recesses on opposite side surfaces (both the left and right ribs 6). This corresponds to FIG. 4 of Patent Document 2 in that the transfer portions 11 and 12 are provided.

  Here, as shown in FIG. 9, the incomplete transfer portions 11 and 12 are formed along the main scanning direction of the transfer surface and corresponding to the range of the light transmission region 7 of the plastic lens. Further, the concave portions that are the incomplete transfer portions 11 and 12 may extend from the rib 6 to the inside of the lens body 1, but should not extend to the light transmission region 7 in the lens body 1.

  11 (a) and 11 (b) show the shape of the long plastic lens in FIGS. 5 to 7 and the length of the plastic lens in FIGS. It is a figure for demonstrating the 1st method of forming a recessed part by the incomplete transfer of ().

  In the method of FIGS. 11A and 11B, at least one or more vent holes 54 are formed in a cavity piece 53 that forms a surface including a recess as an incomplete transfer portion, and the molded article is communicated with the vent holes 54. At least one communication port (not shown) for applying compressed gas is provided on the surface, and a compressed gas supply device (not shown) provided outside the mold is connected to the communication port to transfer the transfer surface 55 and the cavity. A pair of molds in which at least one cavity is defined by the piece 56 is prepared, the mold is heated and held below the softening temperature of the resin, and the molten resin 57 heated above the softening temperature in the cavity. Then, the resin pressure is generated on the transfer surface to bring the resin into close contact with the transfer surface, and then the resin is compressed from the vent into the resin in the cavity when the resin is cooled below the softening temperature. Give gas When the resin and the vent defines a forced air gap 58 between the cavity pieces provided, it is possible to form the air gap 58 as the recess.

  By forcibly defining the gap 58 between the resin and the cavity piece, the resin surface of the resin portion facing the gap 58 becomes a free surface, which is easier to move than the surface in contact with the other mold. As a result, the heat shrinkage caused by cooling is absorbed by the movement of the resin in this part, and the resin part facing the gap is preferentially attracted to relieve the internal strain. Can be prevented from occurring.

  12 (a) and 12 (b) show the shape of the elongated plastic lens of FIGS. 5 to 7 and the elongated plastic lens of FIGS. It is a figure for demonstrating the 2nd method of forming a recessed part by the incomplete transcription | transfer at the time of shaping | molding.

  In the method of FIGS. 12A and 12B, a part of a cavity piece that forms a surface including a recess as an incomplete transfer portion is slid to form a recess (by incomplete transfer at the time of molding).

  That is, in the method of FIGS. 12A and 12B, a part 59 of the cavity piece that forms a surface including a recess as an incomplete transfer portion is slidably provided, and at least by the transfer surface 60 and the cavity piece 61, A pair of molds (Fig. 12 (a)) in which one or more cavities were defined were prepared, the molds were heated and held below the softening temperature of the resin, and heated in the cavities above the softening temperature. After the molten resin 62 is injected and filled, and then the resin pressure is generated on the transfer surface to bring the resin into close contact with the transfer surface, the resin is slidably provided when the resin is cooled below the softening temperature. By sliding the cavity piece away from the resin and forcibly defining the gap 63 between the resin and the cavity piece, the gap 63 can be formed as a recess.

  By forcibly defining the gap 63 between the resin and the cavity piece, the resin surface of the resin portion facing the gap 63 becomes a free surface and is more movable than the surface in contact with the other mold. As a result, the heat shrinkage caused by cooling is absorbed by the movement of the resin in this part, and the resin part facing the gap is preferentially attracted to relieve the internal strain. Can be prevented from occurring.

  As described above, in the long plastic lens of FIGS. 5 to 7 and the long plastic lens of FIGS. 8 to 10, FIGS. 11 (a) and (b) or FIGS. 12 (a) and (b). By providing a concave portion which is an incomplete transfer portion in a part other than the transfer surface by this method, it is possible to improve the appearance defect of the plastic lens. Further, in the long plastic lens shown in FIGS. 8 to 10, the appearance defect of the plastic lens is improved by providing a concave portion as an incomplete transfer portion in the main scanning direction of the transfer surface and on the opposite side surfaces. To improve the effect.

  However, in the elongated plastic lens of FIGS. 5 to 7 and the elongated plastic lens of FIGS. 8 to 10, the lens thickness b in the light transmission direction is thinner than the outer dimension a in the sub-scanning direction. If the lens surface shape is inclined (decrease in accuracy) in the sub-scanning direction due to the state of the incomplete transfer portion (concave portion), and this change in inclination differs between the positions x in the main scanning direction, It will be twisted.

  As the mechanism of the occurrence, the inventors of the present application mean that the process of “formation of an incomplete transfer portion” means a process of “thermal shrinkage” (that is, the depth of the recess of the incomplete transfer portion ( (Recessed amount) ”is equivalent to“ heat shrinkage amount ”), and due to the state of the incomplete transfer portion (recessed portion), a difference in external dimension change (heat shrinkage) occurs, and the lens in the sub-scanning direction. If the surface shape is tilted (accuracy deteriorated) and the change in tilt differs between the positions x in the main scanning direction, the lens surface shape is twisted in the sub-scanning direction, and as a result, the sub-scanning direction on the surface to be scanned The present inventors have found that a scanning position shift to, particularly a high-frequency component scanning position shift, occurs and the color shift in the image forming apparatus deteriorates accordingly.

  The scanning position shift of the high frequency component means a residual component obtained by subtracting the secondary component from the scanning position, and is an important characteristic for determining the color shift on the product.

  Actually, in the configuration shown in FIGS. 5 to 7, since the imperfect transfer portion 10 that is a recess is provided only on one of the left and right ribs 6 (left rib 6), one of the left and right ribs 6 (left rib 6). ) In the process of forming the incomplete transfer portion 10 that is a concave portion, as shown by a broken line in FIG. 13, a change in outer dimension (thermal contraction) occurs on the incomplete transfer portion 10 side (left side) of the lens body 1, The inventors of the present application have confirmed that this causes distortion of the plastic lens (twisting of the lens surface shape in the sub-scanning direction) and variation in the sub-scanning direction (scanning position deviation) as shown in FIG. It was done. That is, it has been confirmed that a scanning position shift in the sub-scanning direction on the surface to be scanned, particularly a high-frequency component scanning position shift occurs.

  Further, in the configurations of FIGS. 8 to 10, although the imperfect transfer portions 11 and 12 that are concave portions are provided on the opposite side surfaces (both the left and right ribs 6), as shown by the broken lines in FIG. If the depths d1 (x) and d2 (x) of the recesses that are the imperfect transfer portions 11 and 12 are greatly different (for example, as shown in the example of FIG. The depth d1 (x) is considerably larger than the depth d2 (x) of the concave portion which is the incomplete transfer portion 12 on the right side), and the concave portions on the opposite side surfaces (both the left and right ribs 6). In the process of forming the imperfect transfer portions 11 and 12, the difference in external dimension change (heat shrinkage) occurs, which causes distortion of the plastic lens (twisting of the lens surface shape in the sub-scanning direction). 14, the variation in the sub-scanning direction (scanning position) Re) that occurs it is confirmed by the present inventor. That is, it has been confirmed that a scanning position shift in the sub-scanning direction on the surface to be scanned, particularly a high-frequency component scanning position shift occurs.

  In other words, in the configuration shown in FIGS. 5 to 7, since the imperfect transfer portion 10 which is a recess is provided only on one of the left and right ribs 6 (left rib 6), the plastic lens is distorted (in the sub-scanning direction). (Twisting of the lens surface shape) becomes remarkable, and variations in the sub-scanning direction (scanning position deviation) become remarkable. On the other hand, in the configurations of FIGS. 8 to 10, since the imperfect transfer portions 11 and 12 which are concave portions are provided on the opposite side surfaces (both the left and right ribs 6), the configuration of FIGS. In comparison, distortion of the plastic lens (lens surface shape torsion in the sub-scanning direction) is small, but the depths d1 (x) and d2 (x It has been confirmed by the inventors of the present application that the plastic lens is distorted (the lens surface shape is twisted in the sub-scanning direction) and the sub-scanning direction is uneven (scanning position deviation).

  Based on the past processing results, the inventor of the present application satisfies a / b> 1 in the outer dimension a in the sub-scanning direction and the lens thickness b in the light transmission direction of the plastic lens in the configurations of FIGS. The deviation | d1 (x) −d2 (x) | of the depths d1 (x) and d2 (x) of the recesses of the incomplete transfer portions 11 and 12 provided on the opposite side surfaces is If each outer scanning dimension x is less than 5% of the outer dimension a in the sub-scanning direction, as shown in FIG. 16, incomplete transfer that is a recess on both side surfaces (both the left and right ribs 6) facing each other. In the process of forming the portions 11 and 12, the balance of the external dimension change (thermal shrinkage) is balanced, thereby reducing the tilt component of the lens surface shape in the sub-scanning direction (improving accuracy), which is the position in each main scanning direction. If improved with x, distortion of plastic lens (side running) 17), the variation in the sub-scanning direction (scan position deviation in the sub-scan direction on the surface to be scanned, especially the scan position deviation of the high-frequency component) can be reduced. The present invention has been completed.

  Furthermore, the deviations | d1 (x) −d2 (x) | of the depths d1 (x) and d2 (x) of the recesses of the incomplete transfer portions 11 and 12 provided on the opposite side surfaces are respectively The above effect can be obtained when the external scanning dimension a in the sub-scanning direction is 5% or less at the main scanning direction position x, even when the external scanning dimension is changed. It was confirmed by the inventor of the present application that the outer dimension a and the lens thickness b in the light transmission direction are satisfied as long as a / b> 1 is satisfied.

As described above, the present invention provides an optical scanning device having an optical deflector and an imaging optical system that forms an image of a light beam deflected by the optical deflector on a surface to be scanned. A plastic lens is used, and the plastic lens has two transfer surfaces including a light incident surface and an output surface, and the main scanning direction of the transfer surface on opposite side surfaces other than the two transfer surfaces. And an incomplete transfer portion, which is a recess, is provided by incompletely transferring the cavity shape of the mold, corresponding to the range of the light transmission region of the plastic lens.
When the position of the plastic lens in the main scanning direction is x and the outer dimension a of the plastic lens in the sub-scanning direction and the lens thickness b in the light transmission direction satisfy a / b> 1,
Deviations | d1 (x) −d2 (x) | of the depths d1 (x) and d2 (x) of the concave portions of the incomplete transfer portions provided on the opposite side surfaces are positions in the main scanning direction. x is set to be 5% or less of the outer dimension a in the sub-scanning direction.

  Here, the plastic lens is formed of a transparent resin material. Specifically, an amorphous resin whose softening temperature is the glass transition temperature thereof (for example, polymethacrylic resin, polycarbonate resin, alicyclic acrylic resin, cyclic polyolefin copolymer, etc.) is used for the plastic lens. Can do.

  FIGS. 18, 19 and 20 are views for explaining a method for forming a concave portion which is an incomplete transfer portion on the opposite side surfaces of the plastic lens of the present invention.

  FIG. 18 shows a case where the method of FIGS. 11A and 11B in which a compressed gas is applied to a molded product to form a recess (by incomplete transfer at the time of molding) is applied to both side surfaces.

  Specific control methods in FIG. 18 include (1) slit position, (2) slit width, (3) air injection pressure, and (4) optimization of air injection timing.

  FIG. 19 shows a case where the method of FIGS. 12A and 12B in which a part of the cavity piece is slid to form a recess (by incomplete transfer at the time of molding) is applied to both side surfaces. Yes.

  Specific control methods in FIG. 19 include (1) the shape of a cavity piece provided slidably, (2) optimization of separation timing, and the like.

  FIG. 20 is a combination of the method shown in FIGS. 11A and 11B and the method shown in FIGS. 12A and 12B. For example, the method shown in FIGS. 11A and 11B is applied to the right side surface. 12 shows a case where the method shown in FIGS. 12A and 12B is applied to the left side surface.

  Moreover, in the method of FIG. 20 which employs the two methods of FIGS. 11A and 11B and the methods of FIGS. 12A and 12B, the molding conditions including the resin filling amount are optimized. Must be carried out simultaneously.

  FIGS. 21A and 21B are diagrams showing a configuration example of an optical scanning device to which the present invention is applied. FIG. 21A is a schematic top view, and FIG. 21B is a schematic side view. Here, 71, 72, 73, and 74 are light sources (semiconductor lasers) of C, M, Y, and K, respectively, and 75 and 76 deflect light beams emitted from the light sources 71, 72, 73, and 74, respectively. Optical deflectors (polygon mirrors), 81, 82, 83, and 84 are fθ lenses corresponding to C, M, Y, and K light beams, and 85, 86, 87, and 88 are C, M, Y, and K lenses, respectively. Long lenses 91, 92, 93, and 94 corresponding to light beams of respective colors are scanned surfaces (photoconductors) respectively corresponding to light beams of C, M, Y, and K colors. 21A and 21B, the fθ lenses 81, 82, 83, and 84 and the long lenses 85, 86, 87, and 88 constitute an imaging optical system.

  In the optical scanning device having such a configuration, light beams of C, M, Y, and K emitted from the light sources 71, 72, 73, and 74 are deflected by optical deflectors (polygon mirrors) 75 and 76, respectively. , Fθ lenses 81, 82, 83, 84, elongated lenses 85, 86, 87, 88, and the like. Then, the light beams of the respective colors from the imaging optical system are incident on the scanned surfaces (photosensitive members) 91, 92, 93, 94 through the mirrors, respectively, on the scanned surfaces (photosensitive members) 91, 92, 93, 94. Can be imaged.

  In the optical scanning device having such a configuration, the above-described long plastic lens of the present invention is more specifically used for the long lenses 85, 86, 87, and 88, and thus on the surface to be scanned. It is possible to improve the scanning position shift in the sub-scanning direction, particularly the high-frequency component scanning position shift.

  Further, when such an optical scanning device of the present invention is used in an image forming apparatus (particularly a color image forming apparatus), the optical scanning device of the present invention has a scanning position shift in the sub-scanning direction on the surface to be scanned, in particular, Since the scanning position shift of the high-frequency component is improved, the color misregistration in the image forming apparatus can be remarkably reduced accordingly, and a highly accurate image forming apparatus can be provided.

The present invention can be used for a copying machine, a printer, a facsimile machine, a plotter, and a multifunction machine including at least one of them.

DESCRIPTION OF SYMBOLS 1 Lens main body 2,3 Transfer surface 4,5 Opposite side surface 6 Rib 7 Light transmissive area | region 11,12 Incomplete transfer part 71,72,73,74 Light source (semiconductor laser) of each color
75,76 Optical deflector (polygon mirror)
81, 82, 83, 84 fθ lens 85, 86, 87, 88 Long lens 91, 92, 93, 94 Scanned surface (photosensitive member)

JP 2007-133179 A JP 2000-329908 A

Claims (6)

In an optical scanning device having an optical deflector and an imaging optical system that forms an image of a light beam deflected by the optical deflector on a surface to be scanned, a plastic lens is used for the imaging optical system. The lens has two transfer surfaces composed of a light incident surface and an output surface, and is disposed on opposite side surfaces other than the two transfer surfaces along the main scanning direction of the transfer surface, and the plastic lens. Corresponding to the range of the light transmission region of the incomplete transfer portion that is a recess is provided,
When the position of the plastic lens in the main scanning direction is x and the outer dimension a of the plastic lens in the sub-scanning direction and the lens thickness b in the light transmission direction satisfy a / b> 1,
Deviations | d1 (x) −d2 (x) | of the depths d1 (x) and d2 (x) of the concave portions of the incomplete transfer portions provided on the opposite side surfaces are positions in the main scanning direction. An optical scanning device, wherein x is set to be 5% or less of the outer dimension a in the sub-scanning direction.   2. The optical scanning device according to claim 1, wherein the plastic lens is made of a transparent resin material.   3. The optical scanning device according to claim 1, wherein the plastic lens has ribs on both opposing sides outside the two transfer surfaces, and each rib has a recess that is the imperfect transfer portion. An optical scanning device characterized by being formed.   An image forming apparatus using the optical scanning device according to any one of claims 1 to 3.   5. The image forming apparatus according to claim 4, wherein the image forming apparatus is a color image forming apparatus. A method of manufacturing a plastic lens used in the imaging optical system of an optical scanning device having an optical deflector and an imaging optical system that forms an image of a light beam deflected by the optical deflector on a scanned surface,
The plastic lens has two transfer surfaces composed of a light incident surface and a light output surface, on opposite side surfaces other than the two transfer surfaces, along the main scanning direction of the transfer surface, and Corresponding to the range of the light transmission region of the plastic lens, the incomplete transfer portion that is a recess is formed by incomplete transfer of the cavity shape of the mold,
When the position of the plastic lens in the main scanning direction is x and the outer dimension a of the plastic lens in the sub-scanning direction and the lens thickness b in the light transmission direction satisfy a / b> 1,
Deviations | d1 (x) −d2 (x) | of the depths d1 (x) and d2 (x) of the concave portions of the incomplete transfer portions provided on the opposite side surfaces are positions in the main scanning direction. A method for manufacturing a plastic lens, wherein each imperfect transfer portion is formed so that x is 5% or less of the outer dimension a in the sub-scanning direction at x.

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