JP5915289B2 - Optical scanning lens, manufacturing method thereof, and image forming apparatus - Google Patents

Description

  The present invention relates to an optical scanning lens, a manufacturing method thereof, and an image forming apparatus. The image forming apparatus can be implemented as a laser type digital copying machine, a laser printer, a facsimile, a plotter, and a complex machine thereof.

  A "rectangular lens" is often used in an optical scanning device used in an electrophotographic image forming apparatus known as a laser type digital copying machine, a printer, a facsimile machine or the like.

In recent years, this type of lens is often made of plastic in order to reduce the cost of the lens itself and the cost of the optical scanning device.
A plastic lens can be easily formed even if the lens surface shape is a “complex aspherical shape”, so that it is possible to achieve the necessary optical performance with a small number of lenses.

  Among the lenses used in the optical scanning device, the “lens to which the laser beam deflected by the optical deflector is incident” has a so-called “uneven shape” in which the thickness in the optical axis direction of the lens changes in the longitudinal direction. It is common.

  These plastic lenses can be mass-produced at low cost by injection-filling a material resin into a “cavity of a mold formed in accordance with the shape of the molded product” even in a special shape.

  In plastic molding, in the process of cooling and solidifying the molten material resin in the mold cavity, it is desirable to make the pressure and temperature of the material resin uniform in the cavity in order to achieve good shape accuracy. In the case of the above-mentioned “uneven-thickness lens”, the lens thickness varies depending on the lens part. Therefore, the “volume shrinkage amount inside the lens” varies during cooling and solidification, and the shape accuracy deteriorates. The so-called “sink (depression-like deformation in the lens surface shape)” may occur in the thick part of the lens.

  As a method of suppressing the “sink”, it is conceivable to increase the injection pressure by increasing the injection pressure of the material resin when the material resin in the molten state is injected and filled into the cavity. "Internal distortion" occurs in the lens.

  In particular, in the case of a thick and uneven-thickness lens, the internal distortion increases, resulting in non-uniform refractive index and birefringence, which adversely affects the optical performance of the lens itself.

  Conversely, if the injection filling amount of the molten material resin is reduced, the internal distortion is reduced, but “sinking” is likely to occur in the thick portion.

  In order to solve the problem of “sink marks”, incomplete transfer is intentionally performed on a part of the surface other than the “transfer surface on which the lens surface shape is transferred”, instead of preventing the occurrence of sink marks themselves. It is known to provide a surface and intentionally induce “sink marks” in the material resin in contact with the imperfect transfer surface so that a concave shape is formed on this surface.

  In this way, by intentionally inducing “sinks” in the resin part of the material that is in contact with the imperfect transfer surface, even if the lens is thick or uneven, it does not leave any internal distortion inside the lens. It is possible to form a plastic lens having an optical surface with good shape accuracy at the same cost as the above.

  Patent Document 1 discloses a technique for manufacturing a strip-shaped plastic lens while performing such “sink induction”.

  It is important that strip-shaped plastic lenses can be produced in large quantities efficiently. In order to reduce the manufacturing cost of lenses, “multi-piece mold devices” such as “four-piece” and “eight-piece” are generally used. ing.

  An example of a multi-cavity mold apparatus will be described with reference to FIG. The mold apparatus of this example is a “four-piece” one.

  As shown in the figure, two cavities CAV1, CAV2, CAV3, and CAV4 are arranged in the mold 1 two above each (displayed with the sky and below) (displayed with the ground).

  Each of the cavities CAV1 to CAV4 has the same cavity shape, and the cavity shape is set so that the longitudinal direction of the strip-shaped plastic lens to be molded is the vertical direction.

  Reference numeral 2 denotes a branch runner. Reference numeral 3 denotes a material flow channel pipe connecting the branch runner 2 and the cavities CAV1 to CAV4.

  The mold 1 in which each cavity is formed is maintained at a temperature “below the softening temperature of the material resin”, and the material resin that is heated to a temperature higher than the softening temperature and is in a molten state branches from the branch runner 2 to the material flow channel pipe 3. Then, the cavities CAV1 to CVA4 are injected and filled.

  When the material resin fills each cavity, the injected material resin is further pressurized, and the material resin in the cavity is in close contact with the inner wall of the cavity, and the transfer surface shape is transferred. Thereafter, when the surface temperature of the material resin falls below the softening temperature in the cavity, the surface of the material resin is solidified.

  In this state, the solidified plastic optical element 1 is taken out from the injection mold and allowed to cool naturally at room temperature.

  In recent years, electrophotographic image forming apparatuses such as digital copying machines have been colorized and speeded up, and a plurality (four mainstream) of photoconductive photoconductors (hereinafter simply referred to as “photoconductors”). )) Tandem image forming apparatuses are becoming widespread.

  In a typical tandem image forming apparatus, four photoconductors are arranged in the conveyance direction of the recording paper, a light source device is provided corresponding to each photoconductor, and light beams emitted from the plurality of light source devices are A common deflection means deflects and scans, and each photoconductor is simultaneously optically scanned by a different imaging optical system to create an electrostatic latent image. These electrostatic latent images are yellow, magenta, cyan, black, etc. After each image is individually visualized by a developing device using different color developers, the obtained color visible images are sequentially superimposed on the same recording paper and transferred and fixed to obtain a color image. It is configured.

  An optical scanning device used in a tandem image forming apparatus, pursuing low cost and compactness of the apparatus, and an optical deflector as an “optical scanning apparatus used in an image forming apparatus having four photosensitive members”. The polygon mirror is shared by the four photoconductors, two “optical scanning lenses of the same specification” are provided on both sides of the polygon mirror, and the light beam that passes through each optical scanning lens is “ There has been proposed one that conducts light scanning by guiding it to a “photosensitive member scanning section corresponding to an optical scanning lens” (Patent Document 2).

  In the optical scanning device disclosed in Patent Document 2, the two optical scanning lenses arranged on each side of the polygon mirror are “two-stage stacked in the sub-scanning direction”.

  In this way, the two optical scanning lenses provided on each side of the polygon mirror are used in a two-stage stack in the sub-scanning direction, so the two optical scanning lenses can be used in a minimum space, This is advantageous for making the optical scanning device compact.

  The inventors use a mold apparatus as described with reference to FIG. 1 by integrating two optical scanning lenses, which are provided on each side of the polygon mirror and used in two stages in the sub-scanning direction. I tried to manufacture it. As a result, the following facts were found.

  That is, an incomplete transfer surface for inducing sink marks is provided on the side surface in the sub-scanning direction of the optical scanning lens on the frame constituting the cavity, and when “sink” is induced, the surface is formed on the side surface of the optical scanning lens. The concave amount of the concave surface portion (the deepest portion of the concave surface in the virtual cross section parallel to the sub-scanning direction) has a concave amount (the depth in the deepest portion of the virtual cross section) in the main scanning direction corresponding to the longitudinal direction. Change irregularly.

  This irregular change tends to be different for different cavities.

  The “change in the concave amount in the main scanning direction” is preferably “a symmetric change that is maximized in the central portion in the main scanning direction”, but in the actually molded one, the “concave amount is maximum. The “position” is a position away from the center in the main scanning direction. That is, the maximum position of the concave amount is generated on the upper side (upper side) in the vertical direction of the cavity.

  The concave surface portion formed by “induction of sink marks” on the optical scanning lens is the lens surface of the optical scanning lens that is two-tiered (hereinafter also referred to as “two-stage integrated optical scanning lens”). “Inclined in the sub-scanning direction”. Therefore, the irregular amount of the concave portion changes in the main scanning direction when the “scan line” optically scanned using the optical scanning lens is irregularly bent (hereinafter referred to as “scan line bending”). Means.)

  When a color image is formed by superimposing two or more colors, if the scanning line is not bent in the formation of each color image, a phenomenon called “color shift” occurs in the superimposed color image, and the image quality of the color image This is a major cause of deterioration.

  In addition, when using a “two-stage integrated optical scanning lens” in which the “position at which the concave amount of the concave surface portion is maximum in the main scanning direction” deviates greatly from the central portion in the main scanning direction, Since the “curved portion” is deviated from the center in the scanning direction of the image, “distortion of the image due to bending of the scanning line” is easily noticeable in the obtained image.

  The present invention has been made in view of the above-described circumstances, and is manufactured by molding a strip-shaped two-stage integrated optical scanning lens that is long in the main scanning direction with a cavity whose longitudinal direction is the vertical direction. A manufacturing method capable of effectively reducing irregular changes in the main scanning direction of the concave amount of the concave surface portion and capable of positioning the maximum concave amount in the vicinity of the central portion in the main scanning direction. The challenge is to achieve this.

  Another object of the present invention is to effectively reduce irregularity in the main scanning direction of the concave amount of the concave surface portion by carrying out the manufacturing method, and position the maximum concave amount in the vicinity of the central portion in the main scanning direction. The present invention provides an optical scanning lens, and an optical scanning device and an image forming apparatus using the optical scanning lens.

  The manufacturing method of the optical scanning lens of the present invention is “a method of manufacturing an optical scanning lens made of plastic in which two strip-shaped lenses having the same specification long in the main scanning direction are integrated adjacent to each other in the sub scanning direction”. And has the following characteristics.

  That is, a transfer piece having the shape of the lens surface on the entrance side and the exit side of the optical scanning lens as a transfer surface, and incomplete for forming a concave surface portion due to incomplete transfer on the side surface portion in the sub-scanning direction of the optical scanning lens Using an incomplete transfer piece having a transfer surface, a cavity having a longitudinal direction in the vertical direction is formed, and the incomplete transfer piece is slidable in a direction perpendicular to the incomplete transfer surface. The transfer piece is formed with a vent hole communicating from the outside of the cavity to the cavity, the mold forming the cavity is heated and held below the softening temperature of the material resin, and the material heated and melted above the softening temperature in the cavity Injecting and filling the resin, pressurizing to bring the material resin into close contact with the transfer surface in the cavity, and after the temperature of the material resin has dropped below the softening temperature, the incomplete transfer piece is displaced to complete the process. A gap is forcibly formed between the transfer surface and the material resin, and compressed gas is applied to the gap through the vent hole, so that the amount of depression on the concave surface changes smoothly in a mountain shape in the main scanning direction. Then, the application of the compressed gas is controlled so as to be maximum above the center in the main scanning direction and in the vicinity of the center.

  As described above, the optical scanning lens manufactured by the manufacturing method of the present invention forms a concave surface portion in the “side surface in the sub-scanning direction” that induces sink marks and contacts the imperfect transfer surface. It is difficult for distortion to occur, and deterioration of optical characteristics due to internal distortion is effectively prevented.

  In addition, since the change in the concave amount of the concave surface changes to a “smooth mountain”, the shape of the “scan line curve” due to the change in the main scanning direction of the concave amount also becomes simple, and on different photoconductors. By aligning the “bending direction” with, the color shift can be effectively reduced or eliminated.

  Therefore, good optical scanning can be performed by the optical scanning device using such an optical scanning lens, and a high-quality image can be obtained by an image forming apparatus using such an optical scanning device.

It is a figure for demonstrating the metal mold | die apparatus for manufacturing the lens for optical scanning. It is a figure for demonstrating the example of an optical scanning device. It is a figure explaining the lens for optical scanning of 2 steps | paragraphs integrated type. It is a figure for demonstrating the shaping | molding process of the lens for optical scanning. It is a figure for demonstrating a solution subject. It is a figure for demonstrating the inclination of the lens surface resulting from shaping | molding. It is a figure for demonstrating one example of control of provision of compressed gas. It is a figure for demonstrating the effect of control of provision of compressed gas. It is a figure for demonstrating another example of control of provision of compressed gas. It is a figure for demonstrating one example of embodiment of an image forming apparatus.

Hereinafter, embodiments will be described.
First, an example of an optical scanning device will be briefly described with reference to FIG.
The optical scanning device described with reference to FIG. 2 is an example of an optical scanning device using a “strip-shaped two-stage integrated optical scanning lens that is long in the main scanning direction”.

  FIG. 2A shows a state where the optical scanning is viewed from the sub-scanning direction. Reference numerals 11A and 11B are light sources, reference numerals 12A and 12B are apertures, reference numerals 13A and 13B are coupling lenses, reference numerals 14A and 14B are cylindrical lenses, reference numeral 15 is an optical deflector, reference numeral 16 is an optical scanning lens, and reference numerals 17A and 17B. Denotes a mirror, and reference numerals 18A and 18B denote scanned surfaces.

  The light source 11A is a laser light source (such as LD) that emits a laser beam that optically scans the scanned surface 18A, and the light source 11B is a laser light source (such as LD that emits a laser beam that optically scans the scanned surface 18B).

  The apertures 12A and 12B are for performing beam shaping by controlling the amount of laser light emitted from the light sources 11A and 11B. The laser light beams emitted from the light sources 11A and 11B are divergent light beams, and the coupling lenses 13A and 13B use a light beam form (parallel light beam, weak divergent or Weakly convergent luminous flux).

  The “laser beam whose beam form has been converted” by the coupling lenses 13A and 13B is converged in the sub-scanning direction by the cylindrical lenses 14A and 14B, respectively, and is “a long line in the main scanning direction” in the vicinity of the deflection reflection surface of the optical deflector 15. An image is formed.

  The light sources 11A and 11B, the apertures 12A and 12B, the coupling lenses 13A and 13B, and the cylindrical lenses 14A and 14B described above are arranged so as to overlap each other in the sub-scanning direction as shown in FIG. Has been.

  The optical deflector 15 deflects the reflected laser light beam at a constant angular velocity by rotating at a constant speed.

  The deflected reflected laser beam becomes a “deflected laser beam” for each light source, and enters the optical scanning lens 16. The optical scanning lens 16 is a “two-stage integrated optical scanning lens”.

  The optical deflector 15 is of a “type of rotating a polygon mirror”, but has a type of deflecting two laser beams as shown in FIG. It is possible to use a method of deflecting by “each deflection reflection surface of a polygon mirror stacked in two stages” shown in FIG.

  In the system shown in FIG. 2B, the two laser light beams incident on the optical deflector 15 enter the deflecting reflection surface while approaching each other in the sub-scanning direction, and the deflected light beams are separated from each other in the sub-scanning direction. The light enters the optical scanning lens 16. In this system, the cylindrical lenses 14A and 14B can be made into a “single cylindrical lens” by sharing them.

  In the system shown in FIG. 2C, the two laser light beams incident on the optical deflector 15 are incident on the deflecting reflecting surface “parallel to each other” in the sub-scanning direction, and the deflected light beams are also mutually in the sub-scanning direction. The light enters the optical scanning lens 16 in parallel.

  The optical scanning lens 16 is a plastic optical scanning lens in which two strip-shaped lenses having the same specification long in the main scanning direction are integrated adjacent to each other in the sub scanning direction. The laser beam from the light source 11A is “upper stage”. And the laser beam from the light source 11B is incident on the “lower strip-shaped lens”.

  Each deflected laser beam travels while receiving the optical action of the corresponding strip-shaped lens, is reflected by the mirrors 17A and 17B, is guided to the scanned surfaces 18A and 18B, and is condensed on these scanned surfaces to be light. A spot is formed, and the surface to be scanned is optically scanned.

  The two strip-shaped lenses that are “superposed and integrated in the sub-scanning direction” constituting the optical scanning lens 16 are so-called “fθ lenses”, and make optical scanning on the scanned surfaces 18A and 18B at a constant speed. It has a function to do.

  Although the mirrors 11A and 17B are depicted as one sheet, the number of mirrors arranged on the optical path to different scanning surfaces may be different from each other.

  As in the case of the optical scanning lens 16, by sharing the laser beam toward the different scanned surfaces 18 </ b> A and 18 </ b> B, as compared with the case where “a plurality of plastic lenses are arranged in the sub-scanning direction”, Since the distance between the optical axes of the upper and lower light beams can be reduced, it is advantageous for downsizing and cost reduction of the optical scanning device, the number of parts is reduced, and the efficiency in terms of management other than the parts cost is also improved. Cost can be achieved.

  Although the light sources 11A and 11B are both assumed to be LDs and have been described on the assumption of single beam scanning, the light sources 11A and 11B are LD arrays, and the scanned surfaces 18A and 18B are optically scanned by a multi-beam method. Also good.

Next, the “two-stage optical scanning lens” will be described with reference to FIG.
FIG. 3A shows the external shape of the optical scanning lens LN. In this figure, the vertical direction is the “sub-scanning direction”, and the lens longitudinal direction is the “main scanning direction”.
The reference symbol LNS21 represents the lens surface on the exit side of the upper strip-shaped lens constituting the optical scanning lens LN, the symbol LNS22 represents the exit lens surface of the lower strip-shaped lens, and the symbol SF1 represents The side surface portion of the optical scanning lens LN in the sub-scanning direction is indicated, and the reference numeral H1 indicates a concave surface portion formed by “induction of sink due to incomplete transfer” on the side surface portion SF1.

  FIG. 3B is a cross-sectional view of the “imaginary cross section orthogonal to the longitudinal direction” at the central portion in the longitudinal direction of the optical scanning lens LN. In this figure, symbol LNS11 is the lens surface on the incident side of the upper strip-shaped lens, symbol LNS12 is the lens surface on the incident side of the lower strip-shaped lens, and symbol SF2 is the sub-scanning direction of the optical scanning lens LN. The other side surface part is shown, and the code | symbol H2 shows the concave-surface part formed by "induction of the sink by imperfect transfer" in side surface part SF2.

  In the example shown in FIG. 3B, the incident-side lens surface has two lens surfaces LNS11 and LNS12 formed in the sub-scanning direction, and the exit-side lens surface has two lens surfaces LNS21 and LNS22 in the sub-scanning direction. Is formed.

  The portion having the incident side lens surface LNS11 and the exit side lens surface LNS21 forms an “upper strip lens”, and the portion having the entrance side lens surface LNS21 and the exit side lens surface LNS22 is “lower strip shape”. A "lens".

  Each of the two upper and lower strip-shaped lenses has the same specification, and the design data is the same.

  In addition, the form of the optical scanning lens in the present invention is not limited to such a form. For example, in FIG. 3B, instead of forming the incident-side lens surface with the lens surfaces LNS11 and LNS12, the incident-side lens surface is configured by a single lens surface, and the single lens surface is formed in upper and lower stages. It may be shared by strip lenses.

  Similarly, instead of forming the lens surface on the exit side with the lens surfaces LNS21 and LNS22, the exit side lens surface is constituted by a single lens surface, and this single lens surface is shared by the upper and lower strip lenses. May be.

  In any case, the optical action of the laser beam passing through the upper strip-shaped lens and the laser beam passing through the lower strip-shaped lens may be the same in design (specification). The lens is “two rectangular lenses having the same specifications and integrated in the sub-scanning direction”.

  As the material resin constituting the optical scanning lens, since transparency is required, an amorphous material is used. For example, polymethacrylic resin, polycarbonate resin, alicyclic acrylic resin, cyclic olefin, Copolymers and cycloolefin polymers can be used.

Next, the “molding process” of the optical scanning lens will be described.
In FIG. 4, reference numerals 41, 42, 43, 44, 435, 436, 437, and 438 indicate a part of “pieces” that form the cavity CV in the mold. In FIG. 4, the direction orthogonal to the drawing is the vertical direction, and the cavity CV is combined with each frame so as to realize the shape of “a lens for optical scanning that is long in the direction orthogonal to the drawing”.

  In FIG. 4A, the “upper side in the drawing” surface T1 of the cavity CV is a transfer surface that transfers the shape of the lens surface on the incident side, and the lower surface T2 is a transfer surface that transfers the lens surface on the exit side. Indicates.

  Accordingly, the frames 41 and 42 are “transfer frames having a lens surface shape as a transfer surface”, and are hereinafter referred to as transfer frames 41 and 42.

  The pieces 43 and 44 are referred to as incomplete transfer pieces 43 and 44 in the following. However, the surfaces in contact with the cavity CV are “a concave surface portion due to incomplete transfer is formed on the side surface portion in the sub-scanning direction of the optical scanning lens. "Incomplete transfer surface".

  The pieces 435 to 438 are fixed pieces, and set the positions of the transfer pieces 41 and 42 and the incomplete transfer pieces 43 and 44.

  The incomplete transfer pieces 43 and 44 are movable by sliding in the left-right direction in FIG. Further, the incomplete transfer pieces 43 and 44 are formed with vent holes 431 and 441, respectively, so that compressed gas can be applied from the outside of the mold to the cavity CV side by a not-shown vent means (compressed gas supply device). ing.

  Molding is performed as follows. The mold with each piece forming the cavity CV is heated and held below the softening temperature of the material resin constituting the optical scanning lens, and the “material resin heated and melted above the softening temperature” is injected and filled into the cavity CV. The material resin is brought into close contact with the transfer surface in the cavity by applying pressure. This state is shown in FIG. In FIG.4 (b), the code | symbol PL shows the material resin with which the cavity was filled in the molten state.

  The temperature of the material resin PL injected and filled in the cavity is lowered due to a temperature difference from the pieces constituting the cavity. FIG. 4C shows a change in the cavity internal pressure in the “state in which the temperature of the material resin decreases” from the start of injection filling. The horizontal axis in FIG. 4C is “atmospheric pressure level”.

  Therefore, as shown in the figure, the imperfect transfer frames 43 and 44 are slid and displaced in the direction away from the cavity CV at the timing when the internal pressure of the cavity reaches the atmospheric pressure level. At this time, the surface of the material resin PL is lowered to “below the softening temperature”, and the resin surface is not in a fluid state, but the surface shape can be changed.

  When the imperfect transfer pieces 43 and 44 are displaced as described above, as shown in FIG. 4D, the imperfect transfer pieces 43 and 44 are forced between the imperfect transfer surface (the surface on the cavity side of the imperfect transfer pieces 43 and 44) and the material resin PL. Thus, voids V1 and V2 are formed.

  At the same time as or immediately after the formation of the gaps V1 and V2, compressed gas (which may be compressed air) AR1 and AR2 set to room temperature, for example, is applied to the cavity side through the vent holes 431 and 441. This state is shown in FIG.

  When the gaps V1 and V2 are forcibly formed between the material resin PL and the incomplete transfer surfaces of the incomplete transfer pieces 43 and 44, the material resin surface facing the gaps V1 and V2 becomes a “free surface”. It becomes easier to move than the surface in contact with the transfer surface.

  As a result, the thermal shrinkage caused by the further temperature drop of the material resin is absorbed by the movement of the material resin in this portion, the material resin surface facing the voids V1 and V2 is preferentially “sinked”, and the internal strain is reduced. Effectively mitigated. At the same time, the transfer surface shape is prevented from sinking in the transferred lens surface shape.

  Simultaneously with this “sink”, the wind pressures of the compressed gases AR1 and AR2 blown onto the free surface effectively promote the deformation of the free surface due to the sink, and the side surface in the sub-scanning direction of the optical scanning lens is shown in FIG. Concave surface portions H1 and H2 as described above are formed.

  FIG. 5 shows a change in the concave amount of the concave surface portion in the longitudinal direction (main scanning direction) of the optical scanning lens when the concave surface portion by the incomplete transfer surface is formed by the method described with reference to FIG. .

  FIG. 5B illustrates the state of the molded optical scanning lens LNE as viewed in the optical axis direction from the lens surface side. The longitudinal direction corresponds to the main scanning direction, “top” is the cavity upper side, and “ground” is the lower side. Reference numerals OL1 and OL2 indicate changes in the longitudinal direction of the “concave amount of the concave portion” formed by “induction of sink marks” on the side portion in the sub-scanning direction (hereinafter referred to as “concave amount line”). The concave amount lines OL1 and OL2 are generated substantially in contrast with each other in the left-right direction.

Fig.5 (a) has shown the concave curve when the said shaping | molding is performed changing conditions.
The size of the molded optical scanning lens LNE is 135 mm in the longitudinal direction (main scanning direction), 20 mm in the width direction (sub-scanning direction), and 15 mm in the maximum length in the optical axis direction.

  A cycloolefin polymer was used as the resin material.

  In the imperfect transfer pieces 43 and 44 shown in FIG. 4, slit-like air holes having a cross-sectional width of 0.003 mm were formed on each side from the center in the longitudinal direction by 50 mm. Therefore, the length of the vent hole is 10 mm in the main scanning direction, which is equal to the formation area of the lens surface in the main scanning direction.

  By the above-described method, “normal temperature compressed air” was applied as compressed gas from the 11 vent holes. At this time, the pressure of the compressed gas was set to Condition 1: 0.1 Mpa and Condition 2: 0.15 Mpa.

  In FIG. 5A, a curve 5-1 indicates a “concave line when condition 1” and a curve 5-2 indicates a “concave line when condition 2”. This concave amount line is shown by taking the concave amount line OL1 in FIG. 5B as an example.

  As shown in FIG. 5A, the concave curve lines 5-1 and 5-2 are both distorted and do not have a “smooth mountain shape”. Further, the position of the “maximum concave amount” of the concave amount line is shifted to the “top” side, that is, the upper side of the cavity from the center in the longitudinal direction.

  Here, the primary component and the high-order component in the concave curve will be briefly described.

  Consider a case where a concave curve (for example, a concave curve 5-1) is expanded into a Fourier series. Sometimes called high-frequency components).

  As will be described later, in the manufacturing method of the present invention, the change of the concave amount in the main scanning direction, that is, the “concave line” is “smooth mountain shape”. This means that it is extremely small.

  The concave amount lines 5-1 and 5-2 have a wavy shape on the negative side of the horizontal axis, that is, the “ground” side, and are not a smooth mountain shape. That is, in the concave quantity lines 5-1 and 5-2, the high-order component has a size that cannot be ignored with respect to the primary component.

  In each of the concave amount lines 5-1 and 5-2, the position of the maximum concave amount is shifted to “upper side than the central portion in the longitudinal direction”. The reason why the position of the maximum concave amount is shifted in this way is considered to be the influence of gravity acting on the material resin injected and filled in the cavity.

The material resin is affected by gravity (resin's own weight) in the process of shrinkage formed by the concave part on the material resin part in contact with the imperfect transfer surface. Since it is small, the “movement of the material resin” is easy, and for this reason, the amount of shrinkage becomes large on the top side, and the amount of recess of the concave surface portion formed becomes large.
This phenomenon is different from the “normal plastic optical element” in which the optical surfaces are not stacked in the sub-scanning direction. The two-stage integrated optical scanning lens is thicker in the sub-scanning direction, and the resin amount and the mold cavity volume increase. Therefore, it is easily affected by gravity and easily appears.

The effect of such a “concave line that does not form a smooth mountain shape (hereinafter referred to as“ complex concave line ”) will be described below.
The case where “the concave amount of the concave surface portion irregularly changes in the main scanning direction” described above is a case like the concave amount line 5-1 or 5-2 in the example in the description.

  In addition, as described above, the concave surface portion formed by the induction of sink marks “tilts in the sub-scanning direction” of the lens surface of the two-stage integrated optical scanning lens. This point will be described below.

  When the molded optical scanning lens LNE is as shown in FIG. 3, the concave lines 5-1 and 5-2 shown in FIG. 5A are formed by the concave surface portion H1 formed on the side surface portion SF1. FIG. 6A shows the inclination of the lens surface LNS11 shown in FIG.

  In the drawing, the “optical surface inclination” on the vertical axis indicates the position (horizontal scan direction) of the inclination of the lens surface LNS11 (in FIG. 3B, the inclination angle of the normal line at the center of the lens surface LNS11: min). The curve 6-1 is for the condition 1 and the curve 6-2 is for the condition 2.

  The optical surface tilt is “positive” when the lens surface LNS11 tilts clockwise.

FIG. 6B is a plot of the concave amount in the concave amount line and the optical surface inclination with two orthogonal axes. As shown in FIG. 6B, the correlation coefficient is R ² = 0.89. It can be seen that there is a correlation represented by “y = 0.65x−0.04” between the optical surface tilt: y and the concave amount: x. This relationship has been found by level experiments by the inventors.

  In view of this point, when the concave amount line in the optical scanning lens LNE “irregularly changes in the main scanning direction” as indicated by the curves 5-1 and 5-2 in FIG. "Irregularly changes in the longitudinal direction of the optical scanning lens, and this causes" a scanning line curve to be irregular "in the case of optical scanning, which causes a significant color shift.

  The concept of the correlation between the concave amount and the optical surface tilt is the same as that described above for each of the lens surfaces LNS11 to LNS22 shown in FIG. 3B, but the scanning line bending due to the optical surface tilt is an upper strip. It was confirmed that the lens and the lower rectangular lens occur “substantially mirror-symmetric with each other in the sub-scanning direction”.

  That is, the optical surface tilt is affected by the thermal contraction to the center of the lens and the shrinkage due to the induction of sink marks, so that the final optical surface tilt is determined, and when the concave surface is formed by the imperfect transfer surface, If a higher order component occurs, a higher order component also occurs in the final optical surface tilt.

  The “high-order component of the optical surface tilt” ultimately causes a scanning misalignment (scan line bending) having a high-order component. In particular, when the optical scanning device is applied to a color image forming apparatus, color misregistration in the image forming apparatus is deteriorated.

  In view of this point, in the present invention, as described above, “a void is forcibly formed between the imperfect transfer surface and the material resin, and a compressed gas is applied to the void through a vent hole”. When the compressed gas is applied, “the amount of depression of the concave surface portion smoothly changes in a mountain shape in the main scanning direction, and is maximum above and near the center in the main scanning direction”. The grant is controlled.

  Also in the case of the conditions 1 and 2 described with reference to FIG. 5, in forming, “forcibly forming a gap between the imperfect transfer surface and the material resin, and applying compressed gas to the gap through the vent hole. However, none of the formed concave quantity lines 5-1 and 5-2 of the concave surface portion “smoothly changes in a mountain shape in the main scanning direction”. That is, under conditions 1 and 2, the control of “applying compressed gas” is not sufficient.

  Here, “factors affecting the shape of the concave surface portion” in forming the concave surface portion will be described.

  The following three factors influence the formation of the concave surface portion.

1. Heat shrink
The temperature inside the lens is higher than that of the surface and is in a molten state. After the incomplete transfer piece slides, a concave amount (sink) corresponding to the amount of heat shrinkage inside the lens is generated until the lens surface solidifies. . Since the amount of heat shrinkage increases near the center of the lens where the resin temperature is high, the amount of concavity increases near the center in the longitudinal direction.

2. Resin density
The resin in the lens receives a force in the gravitational direction, and after the imperfect transfer piece moves, it moves in the gravitational direction until the lens surface solidifies, resulting in a resin density roughness, and a concave corresponding to the resin density. Yield amount. The top side where the resin density is sparse has a large concave amount, and the ground side where the resin density is dense has a small concave amount.

  Also, the shorter the time until the lens surface solidifies after the imperfect transfer piece moves, the less the resin moves in the direction of gravity. Therefore, the resin density is less likely to be uneven, and the concave amount is not likely to be uneven in the longitudinal direction.

3. Compressed gas pressure
Since the lens surface receives pressure by the compressed gas, a concave amount corresponding to the compressed gas pressure is generated after the imperfect transfer piece moves and until the lens surface solidifies. Since the lens surface is pushed harder in the portion where the compressed gas is stronger than in the weaker portion, the concave amount becomes larger.

Of these three factors, “1 and 2” are determined by the design conditions of the optical scanning lens and are difficult to control in the molding process.
In the present invention, by controlling the “applying compressed gas” in view of the above “3”, the concave curve is changed smoothly into a mountain shape in the main scanning direction as described above, and the center in the main scanning direction is changed. And the maximum near the center ”.

  Several methods are conceivable for controlling the application of the compressed gas.

  First, looking at the conditions 1 and 2 in FIG. 5A, as described above, the pressure of the compressed gas is condition 1: 0.1 Mpa, condition 2: 0.15 Mpa. Comparing the concave amount lines 5-1 and 5-2, the “peak of the concave amount line (maximum concave amount)” can be made smaller in the condition 2 where the pressure of the compressed gas is increased than in the case of the condition 1.

  Therefore, the inventors first tried to control the magnitude of the pressure of the compressed gas, and as a result of repeating the experiment, by controlling “the pressure of the compressed gas sufficiently large”, the desired “smoothly in the main scanning direction” was achieved. It has been found that it is possible to realize a concave line that changes in a mountain shape and the position of the maximum concave amount is near the center in the longitudinal direction and is located on the top side.

That is, as shown in FIG. 7B, the slit- shaped vent hole 431 having a width of 0.003 mm is symmetrical with respect to the center in the longitudinal direction as described above in the longitudinal direction (vertical direction) of the imperfect transfer piece. A concave curve when the pressure of the compressed gas applied by the vent 431 is defined as the above condition 1 (0.1 Mpa) is a curve 9-1 in FIG. 5 is the same as curve 5-1.
On the other hand, when the pressure of the compressed gas was set to “0.2 MPa” as a “measure plan”, the concave curve was as shown by a curve 9-2 in FIG.
As shown in the drawing, the concave amount line 9-2 is “smoothly changed in a mountain shape in the main scanning direction (longitudinal direction), and the position of the maximum concave amount is located on the top side in the vicinity of the center in the longitudinal direction” This is exactly the desired shape.

  Curves 9-1 and 9-2 shown in FIG. 7A are Fourier-expanded, and “higher order component” is extracted by subtracting “0th order component and first order component” from the result. FIG. 7C shows a plot in the direction. A curve 9-3 is for Condition 1, and a curve 9-4 is for a countermeasure (0.2 Mpa).

In the “measure plan”, “compressed air at normal temperature” is used as the compressed gas. Increasing the pressure of the compressed gas is equivalent to increasing the flow rate of the compressed gas. Cooling of the surface is promoted by compressed air at room temperature, which is lower than that of the surface of the surface where the concave portion is formed. After the complete transfer piece moves, the time until the concave surface is solidified is shortened.
As a result, the “unevenness of resin density due to gravity” is less likely to occur, and the unevenness of the concave curve in the longitudinal direction can be further reduced.
In addition, by increasing the pressure of the compressed gas, the proposed measure pushes the “surface-side concave surface projection with a small amount of concave” more strongly, so the ground-side concave amount can be increased. This effectively contributes to preventing the deviation in the longitudinal direction.

  FIG. 8A shows a high-order component of the concave amount curve of the formed concave portion (curve 9-3 (condition 1) and curve 9-4 (proposed measure) in FIG. 7C). PV (PEAK TO VALLEY) value of “high frequency component” is shown. Straight lines 8-1 and 8-2 are PV values, and straight lines 8-3 and 8-4 are target values of higher-order components.

  The "high-order component of the concave amount" of the concave surface portion formed by incomplete transfer is based on the recent "required specification for scanning position deviation", and the scanning position deviation due to the high-order component is "about 40 μm or less" In consideration of this, the PV value of the high frequency component of the optical surface tilt is preferably 0.5 min or less, and the PV value of the higher order component of the concave curve is preferably 0.8 mm or less.

  As described above, the concave amount of the incompletely transferred concave portion is represented by a smooth mountain-like curve in the longitudinal direction of the plastic optical scanning lens, and is concave in the vicinity of the central portion in the main scanning direction. By having the largest amount, it is possible to reduce the higher order component of the concave curve and to reduce the higher order component of the optical surface tilt.

  In addition, the color misregistration in the image forming apparatus can be improved without increasing the cost due to the design change of the mold.

  As the “control of application of compressed gas”, various methods other than the method of setting the compressed gas pressure high as described above can be considered.

That is, the vent hole formed in the imperfect transfer piece having the imperfect transfer surface is divided into two or more in the longitudinal direction of the cavity, and the action of the compressed gas is “strongest in the lowermost (ground side) vent hole”. A way to do this is considered.
In this case, the compressed gas is applied by increasing the injection pressure of the compressed gas “strongest at the lowest (ground side) vent hole” or “maximizing the width of the lowest (ground side) vent hole”. ”Method, and further, a method of“ the longest time in the lowermost (ground side) vent hole ”for the“ injection time of compressed gas ”through the vent hole formed by dividing into two or more in the longitudinal direction is possible. is there.

  Hereinafter, with reference to FIG. 9, three examples of a method of dividing the vent hole formed in the imperfect transfer piece into two in the longitudinal direction of the cavity and making the action of the compressed gas “strongest in the ground vent hole” will be described. To do.

FIG. 9A shows an incomplete transfer surface of the incomplete transfer frame 43. The incomplete transfer piece 43 is formed with a vent hole divided into two in the vertical direction. One is a vent region A (hereinafter simply referred to as “region A”), and the other is a vent region B (hereinafter simply referred to as “region B”).
Region A is the ground side vent hole region, and region B is the top side vent hole region. The reason why these are bent is that the shape of the optical scanning lens is curved in the longitudinal direction.

  Although the compressed gas is applied through these vent hole regions A and B, in the method shown in FIG. 9B, the pressure of the compressed gas applied between the region A and the region B is different. A high pressure (0.2 Mpa) compressed gas is injected, and in region B, a relatively low pressure (0.1 Mpa) compressed gas is injected.

  In this method, the pressure of the compressed gas acts strongly on the ground side portion of the resin surface that is imperfectly transferred (the action of gravity is strong). The ground side portion of the concave amount line of the portion can be enlarged, and the concave amount line can be made closer to a shape that is “more symmetrical with respect to the central portion” in the longitudinal direction.

  Moreover, in this method, the “pressure action of the compressed gas to the portion where the concave amount should be increased (the portion on the ground side)” of the concave portion due to incomplete transfer becomes strong, and the resin surface can be rapidly cooled by the compressed gas. The deterioration of internal distortion can be reduced.

  In the method shown in FIG. 9C, the amount of depression of the concave surface formed by incomplete transfer is controlled by changing the “injection time” of the compressed gas injected into the vent hole area A and the vent hole area B. Is doing.

  That is, in the upper diagram, the material resin is injected and filled into the cavity through the filling stage from the injection start, and then the pressure holding / cooling process is performed. The compressed gas injection is started, and after a certain time, the compressed gas injection into the region B is started. Then, after a predetermined time has elapsed, the injection is stopped in both areas A and B and the mold release is performed.

  Since the injection time of the compressed gas is made different and the injection is performed for a longer time in the ground side region A, the ground side material resin surface can be “pressed for a longer time”, and the concave amount on the ground side is increased. I can do it.

  In this way, the pressure of the compressed gas is strong against the ground side portion of the surface on which imperfect transfer is performed (the action of gravity is strong), that is, it acts for a long time, so that the ground side resin surface is relatively strong. By pressing, the ground side portion of the concave amount line of the concave surface portion can be enlarged, and the concave amount line can be brought close to a shape more “symmetrical with respect to the central portion” in the longitudinal direction.

  The total flow of compressed gas in the resin cooling (total flow of compressed gas from the start of compressed gas injection to mold opening) can be increased only on the ground side where the indented surface of the imperfect transfer surface should be increased. The resin surface can be rapidly cooled, and deterioration of internal strain can be reduced.

  In this case, not only the injection time into the regions A and B can be varied, but also the injection pressure into the region A can be increased at the same time.

  In the method shown in FIG. 9D, the concave amount of the concave surface portion formed by incomplete transfer is controlled by changing the vent hole width in the vent hole regions A and B.

  That is, the vent hole width is set to 0.002 mm in the top area B and 0.003 mm larger in the ground area A.

  In this way, by making the width of the vent hole large and small, “the flow rate of the compressed gas is relatively large” at the ground side portion where the concave amount of the concave surface portion formed by incomplete transfer should be increased. It is possible to “rapidly cool the resin surface at the ground side” by gas, and the deterioration of internal strain can be reduced.

In addition, since the control of the influence of compressed gas is controlled by the width of the vent, the application condition of compressed gas can be set to “single in the longitudinal direction of the lens”, and the control factor of the compressed gas supply device is reduced. Can be made easier.
In the above, four types of methods for controlling the application of compressed gas have been described. By these methods, the internal strain is satisfactorily reduced.

  Internal distortion increases the light spot diameter for optical scanning and decreases the resolution of the formed image. However, the optical scanning lens manufactured by the method of the present invention effectively reduces internal distortion. The increase in the light spot diameter (light spot diameter thickening) can be effectively reduced.

  In addition, the concave amount line of the concave surface has a “smooth mountain shape in the longitudinal direction”, and the position where the concave amount is maximized is also near the center of the main scanning direction. Therefore, the curve of the scanning line in the optical scanning becomes a "simple curve", and the writing direction of the scanning line can be easily aligned in writing each color image, and the phenomenon of "color shift" is effective in the formation of a color image. Can be reduced.

  In other words, the optical characteristics of the optical scanning lens deteriorate, in particular, high-quality image reproducibility with a small light spot diameter on the scanning surface can be ensured and manufactured easily, and the scanning position shift of high-order components is improved, and the image forming apparatus The color shift in can be improved satisfactorily.

Finally, referring to FIG. 10, “an embodiment of an image forming apparatus” will be described.
This image forming apparatus is a “tandem type full-color laser printer”, and a portion indicated by a symbol LS is an optical scanning device. The optical scanning device has a configuration in which laser beams from four light sources are deflected by a common optical deflector, and “two-stage integrated optical scanning lenses” are provided on both sides of the optical deflector. The lens for use is of the type shown in FIG.

  In addition, as described above, the lens surface inclination in the optical scanning lens occurs “mirror-symmetrically in the sub-scanning direction” in the two-tiered strip-shaped lens, and the scanning line curve direction is the upper strip shape. Since the lens and the lower strip lens are reversed, the laser beam passing through the upper strip lens is guided to the photosensitive member by one mirror, and the laser beam passing through the lower strip lens is two mirrors. The light is guided to the photoconductors so that the direction of the scanning line bending on each photoconductor is aligned.

In FIG. 10, a transport belt 17 that transports transfer paper (not shown) fed from a horizontal paper feed cassette 13 is provided on the lower side in the apparatus.
On the conveyor belt 17, a photosensitive body 7Y for yellow Y, a photosensitive body 7M for magenta M, a photosensitive body 7C for cyan C, and a photosensitive body 7K for black K are sequentially spaced from the upstream side in the transport direction of the transfer paper. It is arranged by.
Hereinafter, Y, M, C, and K attached to the reference numerals are appropriately added for distinction.
The photoreceptors 7Y, 7M, 7C, and 7K are all formed to have the same diameter, and process means for sequentially executing each process according to the electrophotographic process is disposed around the photoreceptors 7Y, 7M, 7C, and 7K.
Taking the photoconductor 7Y as an example, a charging charger 8Y, an optical scanning optical system 6Y, a developing device 10Y, a transfer charger 11Y, a cleaning device 12Y, and the like are arranged in order, and the other photoconductors 7M, 7C, and 7K are arranged. But the same is true.
That is, the surfaces of the photoconductors 7Y, 7M, 7C, and 7K are to be scanned surfaces set for each color, and an image is formed by using a light beam corresponding to each photoconductor from the optical scanning device as a light spot. The optical scanning is performed.
The optical scanning device LS is a counter scanning system, the optical deflector is single, the optical scanning lens is shared by M and Y, and is shared by K and C.
Around the conveyance belt 17, a registration roller 16 and a belt charging charger 20 are provided on the upstream side of the photoconductor 7Y, and are positioned on the downstream side in the rotation direction of the belt 17 with respect to the photoconductor 7K. A belt separation charger 21, a static elimination charger 22, a cleaning device 23, and the like are provided in this order.

  A fixing device 24 is provided downstream of the belt separation charger 21 in the transfer paper conveyance direction, and is connected to a paper discharge tray 26 by a paper discharge roller 25.

  In such a configuration, for example, in the full color mode (multiple color mode), each of the photoreceptors 7Y, 7M, 7C, and 7K is based on the image signals of each color for Y, M, C, and K. An electrostatic latent image corresponding to each color signal is formed on the surface of each photoconductor by optical scanning by the optical scanning device LS.

Each of these electrostatic latent images is developed with color toner by a corresponding developing device to become a toner image, and is superposed by being sequentially transferred onto a transfer sheet that is electrostatically attracted onto the transport belt 17 and transported. As a result, a full-color image is formed on the transfer paper.
The full-color image is fixed by the fixing device 24 and then discharged to a discharge tray 26 by a discharge roller 25.

  By using the optical scanning lens manufactured by the method of the present invention as the optical scanning lens used in the optical scanning device LS, the optical characteristics, particularly, the high-order component scanning position deviation is small, and the color deviation is high. An image forming apparatus that can ensure image reproducibility can be realized.

41, 42 Transfer piece 43 Incomplete transfer piece
431, 441 Vent
PL material resin
V1, V2 gap
AR1, AR2 Compressed gas
LN optical scanning lens

JP 2010-60962 A JP 2004-226864 A

Claims (12)

A method of manufacturing an optical scanning lens made of plastic in which two strip-shaped lenses of the same specification long in the main scanning direction are integrated adjacent to each other in the sub-scanning direction,
A transfer piece having the entrance and exit lens surface shapes of the optical scanning lens as transfer surfaces, and incomplete transfer for forming a concave surface by incomplete transfer on the side surface in the sub-scanning direction of the optical scanning lens Using an imperfect transfer piece having a surface, a cavity having a longitudinal direction as a longitudinal direction is formed,
The incomplete transfer piece is slidable in a direction perpendicular to the incomplete transfer surface, and a vent hole is formed in the incomplete transfer piece from the outside of the cavity to the cavity.
The mold for forming the cavity is heated and held below the softening temperature of the material resin,
Injecting and filling a material resin heated and melted above the softening temperature into the cavity, pressurizing it to make the material resin adhere to the transfer surface in the cavity,
After the temperature of the material resin falls below the softening temperature, the gap is forcibly formed between the incomplete transfer surface and the material resin by displacing the incomplete transfer piece, and the gap portion Apply compressed gas through the vents,
Applying the compressed gas so that the concave amount of the concave surface portion smoothly changes in a mountain shape in the main scanning direction, becomes maximum above the center in the main scanning direction and near the center. A method for manufacturing an optical scanning lens, comprising: controlling the optical scanning lens. In the manufacturing method of the optical scanning lens of Claim 1,
The vent hole formed in the imperfect transfer piece having the imperfect transfer surface is divided into two or more in the longitudinal direction of the cavity,
A method of manufacturing a lens for optical scanning, characterized in that the action of compressed gas is strongest in a lowermost air hole. In the manufacturing method of the optical scanning lens of Claim 2,
A method for manufacturing a lens for optical scanning, characterized in that an injection pressure of compressed gas is made strongest in a lowermost air hole. In the manufacturing method of the optical scanning lens of Claim 2,
In the vent hole formed by dividing the imperfect transfer piece having an imperfect transfer surface into two or more in the longitudinal direction of the cavity, the width of the lowermost vent hole is maximized and the compressed gas is applied. A manufacturing method of a characteristic lens for optical scanning. In the manufacturing method of the optical scanning lens of Claim 2,
The incomplete transfer piece having an incomplete transfer surface is characterized in that the compressed gas injection time through the vent hole formed by dividing it into two or more in the longitudinal direction of the cavity is the longest in the lowermost vent hole. Manufacturing method of optical scanning lens. An optical scanning lens made of plastic in which two strip-shaped lenses having the same specification long in the main scanning direction are integrated adjacent to each other in the sub-scanning direction,
A concave portion on the side surface in the sub-scanning direction;
An optical scanning lens in which the concave amount of the concave surface portion smoothly changes in a mountain shape in the main scanning direction, and is maximum on one side of the center in the main scanning direction and in the vicinity of the center. The optical scanning lens according to claim 6.
An optical scanning lens in which a higher-order component is smaller than a first-order component in a Fourier series expansion of a concave curve, which is a change in a concave amount in the main scanning direction of the concave surface portion . The optical scanning lens according to claim 7, wherein
An optical scanning lens in which a PV value of a higher-order component in the Fourier series expansion of the concave curve is 0.8 mm or less. The optical scanning lens according to any one of claims 6 to 8,
An optical scanning lens in which strip-shaped lenses having the same specifications have an fθ function. The optical scanning lens according to claim 9, wherein
An optical scanning lens characterized in that two strip-shaped lenses having the same specification condense two kinds of deflected light beams by an optical deflector onto different scanned surfaces. An optical scanning device in an image forming apparatus that forms an electrostatic ray image on a photoconductive photoconductor by writing by optical scanning, visualizes the electrostatic ray image, and transfers and fixes the image on a transfer paper to form an image, An optical scanning device comprising the optical scanning lens according to any one of claims 6 to 10 . 12. An image forming apparatus comprising two or more photoconductive photoconductors and the optical scanning device according to claim 11.

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