JP2012240392A - Exposure head, and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve excellent exposure while suppressing the amount of stray light entering lenses by suppressing the size of the lenses in an exposure head to image light, emitted by a light-emitting element, with three lenses and an image forming device using the exposure head.SOLUTION: An exposure head includes: a first lens; an aperture stop having an opening to pass light transmitting through the first lens therethrough; a second lens into which the light passing through the opening enters; and a third lens into which the light transmitting through the second lens enters.

Description

  The present invention relates to an exposure head that performs exposure with light emitted from a light emitting element, and an image forming apparatus including the exposure head.

  Patent Document 1 describes an exposure head in which a plurality of light emitting elements are arranged in the main scanning direction to form a light emitting element group, and light from the light emitting element group is imaged by an imaging optical system. Further, Patent Document 1 describes an imaging optical system constituted by three lenses in addition to an imaging optical system constituted by two lenses (FIG. 32). Such a three-lens imaging optical system has an advantage that good imaging performance with small aberrations can be realized relatively easily.

JP 2008-152040 A

  By the way, in such an exposure head, it is preferable to reduce the lens constituting the imaging optical system. This is because the larger the lens, the higher the risk of stray light entering the lens. The risk of stray light entering the lens increases as the number of lenses increases. Therefore, in the imaging optical system constituted by the three lenses as described above, a problem such as incidence of stray light on the lens is likely to occur, and as a result, exposure failure due to stray light may become conspicuous. .

  The present invention has been made in view of the above problems, and suppresses the size of a lens in an exposure head that forms an image of light emitted from a light emitting element with three lenses and an image forming apparatus using the exposure head. Thus, it is an object to provide a technique capable of realizing good exposure while suppressing the amount of stray light incident on the lens.

  In order to achieve the above object, an exposure head according to the present invention provides a first light emitting element that emits light, and a second light emitting element that is disposed in a first direction of the first light emitting element and emits light. A light-emitting element substrate having an element; a first lens on which light emitted from the first light-emitting element and light emitted from the second light-emitting element are incident; and a first lens that emits light from the first light-emitting element An aperture stop having an aperture through which light transmitted through the first light-emitting element and light transmitted through the first lens are transmitted, and light transmitted from the first light-emitting element through the aperture stop and A second lens that emits light emitted from the second light emitting element and passes through an aperture of the aperture stop; a light that is emitted from the first light emitting element and transmitted through the second lens; and a second light emitting element. A third lens on which light that has been emitted and transmitted through the second lens enters, an image plane It is characterized by forming a latent image by emitting light latent image by emitting light from the first light emitting element and the first light-emitting element.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a first light emitting element that emits light and a second light emitting element that is disposed in a first direction of the first light emitting element. A light-emitting element substrate having the light-emitting element, a first lens on which light emitted from the first light-emitting element and light emitted from the second light-emitting element are incident, and the first lens emitting light from the first light-emitting element An aperture stop having an aperture through which the transmitted light and the second light emitting element emit light and pass through the first lens pass, and the first light emitting element emits light and passes through the aperture stop aperture and the second The second lens on which light emitted from the light emitting element emits light that has passed through the aperture stop, and the light emitted from the first light emitting element and transmitted through the second lens, and the second light emitting element emit light. And a third lens on which light transmitted through the second lens enters, and an image plane An exposure head for forming a latent image by light emitted from the first light emitting element and a latent image by light emitted from the first light emitting element; a latent image carrier on which a latent image is formed by the exposure head; And a developing unit that develops the latent image formed on the latent image carrier.

  In the invention configured as described above (exposure head, image forming apparatus), the light emitted from the light emitting elements (first and second light emitting elements) passes through the first lens, the second lens, and the third lens. An image is formed after transmitting in this order. And in this invention, the aperture stop which has an opening distribute | arranged between the 1st lens and the 2nd lens is provided. In other words, the first lens and the second lens are arranged near the position where the light is stopped by the aperture stop. Therefore, the effective areas of the first lens and the second lens are narrow, and the first lens and the second lens can be made small. Therefore, it is possible to realize good exposure while suppressing the amount of stray light incident on the first lens and the second lens.

  By the way, in the present invention, the first light emitting element and the second light emitting element are arranged in the first direction. The light emitted by the first and second light emitting elements is once stopped by the aperture stop, and then spreads again and enters the third lens. Therefore, the third lens needs a certain size in the first direction corresponding to the arrangement of the first and second light emitting elements. On the other hand, the second direction that is orthogonal or substantially orthogonal to the first direction is not so large. Therefore, the image plane of the third lens is calculated based on the radius of curvature in the second direction orthogonal to the first direction of the first area (effective area) that transmits light that forms a latent image on the image plane of the third lens. The exposure head may be configured such that the radius of curvature in the second direction of the second region through which light forming a latent image does not pass is small. In this way, in the second direction, the width of the region (second region) between the periphery of the effective region and the periphery of the third lens is reduced by reducing the radius of curvature outside the effective region. be able to. As a result, the size of the third lens in the second direction can be reduced, and the amount of stray light incident on the third lens can be suppressed to achieve good exposure.

  In addition, the exposure head is configured such that the radius of curvature of the first region of the third lens in the second direction is smaller than the radius of curvature of the first region of the third lens in the first direction. Also good. This also makes it possible to reduce the size of the third lens in the second direction, and to suppress the amount of stray light incident on the third lens, thereby realizing good exposure.

  The first and second lenses can be combined in various directions. For example, the first lens is convex on the light emitting element substrate side (first light emitting element and second light emitting element side). The second lens may be convex on the image plane side (image side).

  At this time, the exposure head may be configured to have a lens substrate on which the first lens, the second lens, and the aperture stop are disposed.

  Various specific configurations can be employed at this time. In view of this, a first substrate having a first lens disposed on one side and a second substrate having a second lens disposed on one side are provided, and the aperture stop is disposed on the other side of the first substrate. It may be configured such that the one surface of the first substrate and the one surface of the second substrate are adhered to each other between the other surface of the second substrate. Alternatively, a first substrate having a first lens disposed on one surface, a second substrate having a second lens disposed on one surface, and a third substrate having an aperture stop disposed thereon, The third substrate may be configured to be sandwiched between the first substrate and the second substrate and fixed to the first substrate and the second substrate.

1 is a diagram illustrating an example of an image forming apparatus to which the present invention can be applied. The block diagram which shows the electric constitution of the apparatus of FIG. The figure which shows an example of the line head which can apply this invention. The figure which shows an example of the line head which can apply this invention. The figure which shows an example of the line head which can apply this invention. The figure which showed the curvature radius of lens LS1, LS2 with the graph. The figure which showed the curvature radius of lens LS3 by the graph. The figure which looked at the lens LS3 on lens array LA3 clearly from the optical axis direction. The figure which shows the modification of lens LS3. The exploded view which showed typically the modification of the structure which supports an aperture stop. The exploded view which showed typically the modification of the structure which supports an aperture stop. The exploded view which showed typically the modification of the structure which supports an aperture stop. The exploded view which showed typically the modification of the structure which supports an aperture stop.

  FIG. 1 is a diagram showing an example of an image forming apparatus to which the present invention can be applied. FIG. 2 is a block diagram showing an electrical configuration of the apparatus of FIG. The image forming apparatus 1 includes four image forming stations 2Y (for yellow), 2M (for magenta), 2C (for cyan), and 2K (for black) that form images of different colors. The image forming apparatus 1 includes a color mode in which four color toners of yellow (Y), magenta (M), cyan (C), and black (K) are overlapped to form a color image, and black (K). A monochrome mode in which a monochrome image is formed using only toner can be selectively executed.

  In this image forming apparatus, when an image forming command is given from an external device such as a host computer to a main controller MC having a CPU, a memory, etc., the main controller MC provides a control signal to the engine controller EC and also supports the image forming command. The video data VD to be transmitted is supplied to the head controller HC. At this time, every time the main controller MC receives the horizontal request signal HREQ from the head controller HC, the main controller MC supplies video data VD for one line to the head controller HC in the main scanning direction MD. The head controller HC also sets the line heads 29 of the image forming stations 2Y, 2M, 2C, and 2K for each color based on the video data VD from the main controller MC, the vertical synchronization signal Vsync from the engine controller EC, and the parameter values. Control. Accordingly, the engine unit ENG executes a predetermined image forming operation, and forms an image corresponding to the image forming command on a sheet-like recording medium RM such as copy paper, transfer paper, paper, and an OHP transparent sheet.

  Each of the image forming stations 2Y, 2M, 2C, and 2K has the same structure and function except for the toner color. Therefore, in FIG. 1, in order to make the drawing easier to see, reference numerals are given only to the components constituting the image forming station 2 </ b> C, and description of reference numerals to be attached to the other image forming stations 2 </ b> Y, 2 </ b> M, and 2 </ b> K is omitted. In the following description, the structure and operation of the image forming station 2C will be described with reference to the reference numerals in FIG. 1, but the structure and operation of the other image forming stations 2Y, 2M, and 2K also differ in toner color. It is the same except that.

  The image forming station 2C is provided with a photosensitive drum 21 on which a cyan toner image is formed. The photosensitive drum 21 is arranged so that the rotation axis thereof is parallel or substantially parallel to the main scanning direction MD (direction perpendicular to the paper surface of FIG. 1), and is at a predetermined speed in the direction of arrow D21 in FIG. Is driven to rotate. As a result, the surface of the photosensitive drum 21 moves in the sub-scanning direction SD that is orthogonal or substantially orthogonal to the main scanning direction MD.

  Around the photosensitive drum 21, a charger 22 that is a corona charger that charges the surface of the photosensitive drum 21 to a predetermined potential, and an electrostatic latent image is formed by exposing the surface of the photosensitive drum 21 according to an image signal. A line head 29 for forming the electrostatic latent image, a developing device 24 for visualizing the electrostatic latent image as a toner image, a first squeeze unit 25, a second squeeze unit 26, and the surface of the photosensitive drum 21 after transfer. The cleaning units for cleaning are arranged along the rotation direction D21 (clockwise in FIG. 1) of the photosensitive drum 21 in the order of these.

  In this embodiment, the charger 22 includes two corona chargers 221 and 222, and the corona charger 221 is disposed upstream of the corona charger 222 in the rotation direction D 21 of the photosensitive drum 21. In addition, the two corona chargers 221 and 222 are configured to be charged in two stages. Each of the corona chargers 221 and 222 has the same configuration and does not contact the surface of the photosensitive drum 21 and is a scorotron charger.

  The line head 29 forms an electrostatic latent image on the surface of the photosensitive drum 21 charged by the corona chargers 221 and 222 based on the video data VD. That is, when the head controller HC transmits the video data VD to the line head 29, each light emitting element E emits light based on the video data VD. As a result, the surface of the photosensitive drum 21 is exposed to form an electrostatic latent image corresponding to the image signal. Details of the configuration and operation of the line head 29 will be described later.

  Toner is applied from the developing device 24 to the electrostatic latent image formed in this manner, and the electrostatic latent image is developed with the toner. The developing device 24 of the image forming apparatus 1 has a developing roller 241. The developing roller 241 is a cylindrical member, and is provided with an elastic layer such as polyurethane rubber, silicon rubber, NBR, or PFA tube on the outer periphery of an inner core made of metal such as iron. The developing roller 241 is connected to a developing motor, and is rotated counterclockwise on the paper surface of FIG. 1 to rotate with respect to the photosensitive drum 21. Further, the developing roller 241 is electrically connected to a developing bias generator (constant voltage power source) (not shown) so that the developing bias is applied at an appropriate timing.

  An anilox roller is provided to supply the liquid developer to the developing roller 241, and the liquid developer is supplied from the developer storage unit to the developing roller 241 via the anilox roller. As described above, the anilox roller has a function of supplying the liquid developer to the developing roller 241. This anilox roller is a roller in which a concave pattern is formed by spiral grooves or the like engraved finely and uniformly on the surface so as to easily carry the liquid developer. Similar to the developing roller 241, a metal cored bar wrapped with a rubber layer such as urethane or NBR, or a PFA tube is used. The anilox roller is connected to a developing motor and rotates.

  The liquid developer stored in the developer storage section is volatile at room temperature at a low concentration (1-2 wt%) and low viscosity using Isopar (trademark: Exon) as a liquid carrier, which is generally used conventionally. Not a volatile liquid developer having a solid particle having a mean particle size of 1 μm, in which a colorant such as a pigment is dispersed in a non-volatile resin having a high concentration and high viscosity at room temperature, an organic solvent, silicon oil, mineral oil or A liquid developer having a high viscosity (about 30 to 10,000 mPa · s) added to a liquid solvent such as edible oil together with a dispersant and having a toner solid content concentration of about 20% is used.

  As described above, the developing roller 241 supplied with the liquid developer rotates simultaneously with the anilox roller and rotates so as to move in the same direction as the surface of the photosensitive drum 21 and is carried on the surface of the developing roller 241. The liquid developer thus conveyed is conveyed to the development position. In order to form a toner image, the rotation direction of the developing roller 241 needs to be rotated so that the surface thereof moves in the same direction as the surface of the photosensitive drum 21, but is opposite to the anilox roller. It may be configured to move in either the direction or the same direction.

  In the developing device 24, a toner compression corona generator 242 is disposed opposite to the developing roller 241 immediately before the developing position in the rotation direction of the developing roller 241. The toner compression corona generator 242 is an electric field applying means for increasing the charging bias on the surface of the developing roller 241 and is electrically connected to a toner charge generator (not shown) configured with a constant current power source. When a toner charge bias is applied to the toner compression corona generator 242, an electric field is applied to the liquid developer toner conveyed by the developing roller 241 at a position close to the toner compression corona generator 242. Then, charging and compression are performed. For the toner charging and compression, a compaction roller that is charged by contact may be used instead of corona discharge by applying electrolysis.

  Further, the developing device 24 configured as described above can reciprocate between a developing position for developing the latent image on the photosensitive drum 21 and a retracted position away from the photosensitive drum 21. Therefore, when the developing device 24 is moved to the retracted position and positioned, supply of new liquid developer to the photosensitive drum 21 is stopped in the cyan image forming station 2C.

  A first squeeze portion 25 is disposed on the downstream side of the developing position in the rotation direction D <b> 21 of the photosensitive drum 21, and a second squeeze portion 26 is disposed on the downstream side of the first squeeze portion 25. These squeeze portions 25 and 26 are provided with squeeze rollers 251 and 261, respectively. Then, the squeeze roller 251 rotates in response to the rotational driving force from the main motor while contacting the surface of the photosensitive drum 21 at the first squeeze position to remove excess developer in the toner image. Further, in the rotation direction D21 of the photosensitive drum 21, the squeeze roller 261 rotates in response to the rotational driving force from the main motor while contacting the surface of the photosensitive drum 21 at the second squeeze position downstream of the first squeeze position. Then, excess liquid carrier and fog toner in the toner image are removed. In this embodiment, a squeeze bias generator (constant voltage power supply) (not shown) is electrically connected to the squeeze rollers 251 and 261 in order to increase the squeeze efficiency, and the squeeze bias is applied at an appropriate timing. It is configured to be. In this embodiment, the two squeeze portions 25 and 26 are provided. However, the number and arrangement of the squeeze portions are not limited to this, and for example, one squeeze portion may be disposed.

  The toner image that has passed through these squeeze positions is primarily transferred to the intermediate transfer member 31 of the transfer unit 3. The intermediate transfer member 31 is an endless belt as an image carrier that can temporarily carry a toner image on its surface, more specifically, on its outer peripheral surface. The intermediate transfer member 31 includes a plurality of rollers 32, 33, 34, 35, and 36. It is being handed over. Among these, the roller 32 is connected to a main motor, and functions as a belt driving roller for driving the intermediate transfer member 31 in the direction of the arrow D31 in FIG. In the present embodiment, an elastic layer is provided on the surface of the intermediate transfer body 31 in order to improve the adhesion with the recording paper RM and improve the transferability of the toner image onto the recording paper RM. A toner image is supported.

  Here, of the rollers 32 to 36 over which the intermediate transfer body 31 is stretched, only the belt driving roller 32 is driven by the main motor, and the other rollers 33 to 36 are driven without a driving source. It is a roller. Further, the belt driving roller 32 winds the intermediate transfer member 31 on the downstream side of the primary transfer position TR1 and the upstream side of the secondary transfer position TR2 described later in the belt moving direction D31.

  The transfer unit 3 includes a primary transfer backup roller 37, and the primary transfer backup roller 37 is disposed to face the photosensitive drum 21 with the intermediate transfer member 31 interposed therebetween. At the primary transfer position TR1 where the photosensitive drum 21 and the intermediate transfer member 31 are in contact, the outer peripheral surface of the photosensitive drum 21 is in contact with the intermediate transfer member 31 to form the primary transfer nip portion NP1c. Then, the toner image on the photosensitive drum 21 is transferred to the outer peripheral surface of the intermediate transfer member 31 (the lower surface at the primary transfer position TR1). Thus, the cyan toner image formed by the image forming station 2C is transferred to the intermediate transfer member 31. Similarly, the toner images are transferred at the other image forming stations 2Y, 2M, and 2K, so that the toner images of the respective colors are sequentially superimposed on the intermediate transfer member 31 to form a full-color toner image. On the other hand, when a monochrome toner image is formed, the toner image is transferred to the intermediate transfer member 31 only in the image forming station 2K corresponding to the black color.

  The toner image transferred to the intermediate transfer member 31 in this way is conveyed to the secondary transfer position TR2 via the winding position around the belt driving roller 32. At the secondary transfer position TR2, the secondary transfer roller 42 of the secondary transfer unit 4 is disposed opposite to the roller 34 around which the intermediate transfer body 31 is wound, with the intermediate transfer body 31 interposed therebetween. The surface 31 and the surface of the transfer roller 42 are in contact with each other to form the secondary transfer nip portion NP2. That is, the roller 34 functions as a secondary transfer backup roller. The rotation shaft of the backup roller 34 is supported elastically by a pressing portion 345 which is an elastic member such as a spring and can be moved toward and away from the intermediate transfer member 31.

  At the secondary transfer position TR2, the single-color or multi-color toner images formed on the intermediate transfer member 31 are transferred from the pair of gate rollers 51 to the recording medium RM conveyed along the conveyance path PT. Further, the recording medium RM on which the toner image is secondarily transferred is sent from the secondary transfer roller 42 to the fixing unit 7 provided on the transport path PT. In the fixing unit 7, heat or pressure is applied to the toner image transferred to the recording medium RM to fix the toner image on the recording medium RM. In this way, a desired image can be formed on the recording medium RM.

  The above is the schematic configuration of the image forming apparatus. Next, details of the line head 29 applicable to the image forming apparatus according to the present embodiment will be described. 3, 4 and 5 are diagrams showing an example of a line head to which the present invention can be applied. 3 is a plan view of a head substrate provided in the line head 29 as viewed from the optical axis direction Doa, FIG. 4 is a partial perspective view of the line head 29, and FIG. FIG. 4 is a partial step sectional view taken along line A (stepped two-dot chain line in FIG. 3), which corresponds to a case where the section is viewed from the longitudinal direction LGD of the line head 29. In FIG. 3, the aperture Ap of the aperture stop 295 is indicated by a broken line, and the lenses LS1 to LS3 are indicated by an alternate long and short dash line, but these are the light emitting element E on the head substrate 293 and the head substrate 293. It is described in order to show the positional relationship between the aperture Ap and the lenses LS1 to LS3.

  The line head 29 has an overall configuration that is long in the longitudinal direction LGD and short in the width direction LTD. Therefore, in FIGS. 3 to 5 and the following drawings, the longitudinal direction LGD and the width direction LTD of the line head 29 are shown as necessary. Further, the optical axis direction Doa of the imaging optical system formed by the lens is also appropriately shown in FIGS. 3 to 5 and the following drawings, and the arrow side of the optical axis direction Doa is indicated by “table” or “ It is expressed as “up”, and the side opposite to the arrow in the optical axis direction Doa is expressed as “back”, “down” or “bottom”. Note that these directions LGD, LTD, and Doa are orthogonal or substantially orthogonal to each other.

  As described above, when the line head 29 is applied to the image forming apparatus, the line head 29 moves relative to the surface of the photosensitive drum 21 that moves in the sub-scanning direction SD that is orthogonal to or substantially orthogonal to the main scanning direction MD. In addition, the main scanning direction MD of the surface of the photosensitive drum 21 is parallel or substantially parallel to the longitudinal direction LGD of the line head 29, and the sub-scanning direction SD of the surface of the photosensitive drum 21 is the sub-scanning direction SD of the line head 29. It is parallel or substantially parallel to the width direction LTD. Therefore, as necessary, the main scanning direction MD and the sub-scanning direction SD are also illustrated together with the longitudinal direction LGD and the width direction LTD.

  In the line head 29, a plurality of light emitting elements E (35 in the example of FIG. 1) are arranged in a zigzag pattern in the longitudinal direction LGD to form one light emitting element group EG. Further, in the line head 29, a plurality of light emitting element groups EG are arranged in the longitudinal direction LGD in a three-row zigzag pattern. In other words, this arrangement mode can be explained as follows. That is, a light emitting element group EG is arranged at a distance of 3 × Dg in the longitudinal direction LGD, and a plurality of light emitting element groups EG linearly arranged in the longitudinal direction LGD constitute one light emitting element group row GRa. Further, the three light emitting element group rows GRa, GRb, GRc are arranged with a distance Dt in the width direction LTD and are shifted from each other by a distance Dg in the longitudinal direction LGD.

  Each light emitting element E is a top emission type organic EL (Electro-Luminescence) element having the same emission spectrum. That is, the organic EL elements constituting each light emitting element E are formed on the surface 293-h of the head substrate 293 which is a glass plate that is long in the longitudinal direction LGD and short in the width direction LTD.

  One imaging optical system OS is opposed to each of the plurality of light emitting element groups EG arranged as described above. Specifically, the imaging optical system OS includes three lenses LS1, LS2, and LS3 arranged in the optical axis direction Doa. In plan view, these lenses LS1, LS2, and LS3 are arranged in this order from the side closer to the light emitting element group EG. The first lens LS1 is convex on the object side (light emitting element group EG side), the second lens LS2 is convex on the image side (photosensitive drum 21 side), and the third lens LS3 is convex on the object side. It has become. 4 and 5, a light shielding member 297 is shown between the light emitting element group EG and the lens LS1, which will be described after the description of the imaging optical system.

  In this line head 29, a lens array LA1 in which a plurality of lenses LS1 are arranged in a staggered manner in order to arrange the lenses LS1, LS2, and LS3 so as to face each of the plurality of light emitting element groups EG arranged in a staggered manner in three rows, A lens array LA2 in which a plurality of lenses LS2 are arranged in a staggered manner in three rows and a lens array LA3 in which a plurality of lenses LS3 are arranged in a staggered manner in three rows are provided. In other words, in the lens array LA1 (LA2, LA3), a plurality of lenses LS1 (LS2, LS3) linearly arranged in the longitudinal direction LGD are arranged by disposing the lenses LS1 (LS2, LS3) every 3 × Dg in the longitudinal direction LGD. ) Constitutes one lens row. Further, the three lens rows are arranged with a distance Dt in the width direction LTD and are shifted from each other by a distance Dg in the longitudinal direction LGD. Incidentally, the lens array LA1 (LA2, LA3) can be configured by forming resin lenses LS1 (LS2, LS3) on a glass substrate SB having a flat plate shape and made of light transmission.

  The thickness T1 of the glass substrate SB constituting the lens array LA1 and the thickness T2 of the glass substrate SB constituting the lens array LA2 are equal to each other (T1 = T2). The thickness T3 of the glass substrate SB constituting the lens array LA3 is thinner than the thicknesses T1 and T2 of the glass substrate SB constituting the lens arrays LA1 and LA2 (T3 <T1, T3 <T2). Thus, by thinning the glass substrate SB of the lens array LA3 facing the photoconductor drum 21, a work distance that is the distance from the glass substrate SB to the photoconductor drum 21 can be increased. As a result, it is easy to prevent the interference between the lens array LA3 and the photosensitive drum 21, and the design of the image forming apparatus can be facilitated.

  Further, between the lens arrays LA1 and LA2, there is provided a thin plate-shaped aperture stop 295 in which a circular aperture Ap having a diameter smaller than the diameter of the lenses LS1, LS2, and LS3 is formed. In the aperture stop 295, a plurality of apertures Ap are arranged in a three-row zigzag pattern so as to face each of the plurality of light emitting element groups EG arranged in a three-row zigzag pattern. The aperture stop 295 is sandwiched between two lens arrays LA1 and LA2. That is, out of both main surfaces of the glass substrates SB of the lens arrays LA1 and LA2, the main surface on which the lenses LS1 and LS2 are formed is one surface, and the main surface on which the lenses LS1 and LS2 are not formed is the other surface. When the aperture stop 295 is sandwiched between the other surface of the glass substrate SB (first substrate) of the lens array LA1 and the other surface of the glass substrate SB (second substrate) of the lens array LA2, The glass substrate SB (first and second substrates) is bonded to the other surface. In this way, a plate-like optical member 298 is formed, in which the two lens arrays LA1 and LA2 are integrally formed through the aperture stop 295.

  In this embodiment, it is difficult to produce a plate-like optical member 298 that is long in the longitudinal direction LGD and the lens array LA3 in an integrated configuration, and thus a relatively short plate-like optical member 298 is formed. In addition, the lens array LA3 is manufactured, and these are arranged in the longitudinal direction LGD to increase the length.

  More specifically, a plurality of spacers SP1 are linearly arranged in the longitudinal direction LGD at both ends in the width direction LTD of the head substrate surface 293-h. A plurality of plate-like optical members 298 (lens arrays LA1, LA2) are arranged in the longitudinal direction LGD in a state where they are installed on the spacers SP1, SP1 in the width direction LTD, thereby forming a long lens array. In addition, a plurality of spacers SP2 are linearly arranged in the longitudinal direction LGD at both ends of the surface of the plurality of plate-like optical members 298 in the width direction LTD. A plurality of lens arrays LA3 are arranged in the longitudinal direction LGD in a state where the spacers SP2 and SP2 are installed in the width direction LTD to form one long lens array.

  In other words, the plate-like optical member 298 and the lens array LA3 configured as described above are opposed to the head substrate 293, so that the lenses LS1 arranged in the optical axis direction Doa corresponding to the three-row staggered arrangement of the light emitting element group EG. The imaging optical system OS composed of the aperture Ap, the lens LS2, and the lens LS3 is arranged in the longitudinal direction LGD in a three-row staggered manner. Then, the light emitted from each light emitting element E of the light emitting element group EG passes through the imaging optical system OS and is irradiated onto the surface of the photosensitive drum 21. In FIG. 5, the symbol OSa is also shown for the imaging optical system OS that forms an image of light from the light emitting element group EG belonging to the light emitting element group row GRa. Similarly, symbols OSb and OSc are written together for the imaging optical system OS that forms an image of light from the light emitting element groups EG belonging to the light emitting element group rows GRb and GRc. That is, different signs OSa, OSb, and OSc are assigned to the imaging optical systems OS arranged at different positions in the width direction LTD.

  Thus, in the line head 29, the dedicated imaging optical system OS is arranged for each of the plurality of light emitting element groups EG. In such a line head 29, it is desirable that the light from the light emitting element group EG is incident only on the imaging optical system OS provided in the light emitting element group EG and not incident on the other imaging optical system OS. . Therefore, a light shielding member 297 is provided between the surface 293-h of the head substrate 293 and the lens array LA1. The light shielding member 297 functions to limit light traveling from the light emitting element group EG toward the imaging optical system OS facing the light emitting element group EG. Specifically, the light shielding member 297 is formed with a light guide hole 2971 extending from the light emitting element group EG to the imaging optical system OS facing the light emitting element group EG in the optical axis direction Doa. The light guide hole 2971 is a cylindrical hole having a diameter shorter than the width of the light emitting element group EG, and its central axis substantially coincides with the optical axis OA of the imaging optical system OS. Therefore, of the light emitted from the light emitting element group EG, the light that has passed through the light guide hole 2971 without being blocked by the bottom surface of the light shielding member 297 enters the imaging optical system OS. The imaging optical system OS forms incident light at an imaging magnification that forms a reverse image and a reduced image, and forms a light spot on the surface of the photosensitive drum 21.

  Incidentally, the upper side of the light guide hole 2971 of the light shielding member 297 faces the lens LS1, while the lower side of the light guide hole 2971 faces the light emitting element group EG composed of the top emission type light emitting elements E. In such a configuration, it is preferable to prevent the peripheral portion of the light guide hole 2971 from interfering with the lens LS1 and the light emitting element group EG.

  Therefore, in this embodiment, the intervals CL are provided between the plurality of lenses LS1 arranged in the lens array LA1 in each of the main scanning direction MD and the sub-scanning direction SD. At the interval CL, the back surface of the lens array LA1 is finished flat. The upper peripheral edge of the light guide hole 2971 finished with a diameter larger than the lens LS1 is provided so as to abut on the gap CL. Thus, interference between the peripheral edge portion of the light guide hole 2971 and the lens LS1 is prevented.

  On the other hand, on the surface 293-h of the head substrate 293, spacers 299 are provided on both outer sides in the sub-scanning direction SD of the region where the light emitting element E is formed. The light shielding member 297 is installed on these spacers 299 from the sub-scanning direction SD. As a result, a gap is provided between the lower peripheral edge of the light guide hole 2971 and the head substrate surface 293-h. Yes. As a result, the light emitting element group EG can be positioned in this gap, and interference between the lower peripheral portion of the light guide hole 2971 and the light emitting element group EG is prevented.

  As described above, in the line head 29, the lens LS1, the aperture Ap, the lens LS2, and the lens LS3 are arranged in this order in the optical axis direction Doa with respect to the light emitting element group EG. Therefore, the light emitted from the light emitting element group EG (each light emitting element E) passes through the lens LS1, the aperture Ap, the lenses LS2 and LS3 in this order, and forms an image on the surface of the photosensitive drum 21. Here, a region where light emitted from the light emitting element group EG and imaged on the surface of the photosensitive drum 21 is transmitted through each of the lenses LS1 to LS3 is referred to as an “effective region” of each of the lenses LS1 to LS3. Since the lenses LS2 and LS3 are provided on the image side (photoreceptor drum 21 side) with respect to the aperture Ap, the light that has passed through the aperture Ap passes through the lens in the effective area of each of the lenses LS2 and LS3. It becomes an area. In this embodiment, the radii of curvature of the lenses LS1 to LS3 are set as follows for the effective area of each lens.

  FIG. 6 is a graph showing the radii of curvature of the lenses LS1 and LS2. In the figure, the horizontal axis represents the image height, and the vertical axis represents the radius of curvature of the lens. In the figure, the main scanning effective area indicates an effective area in the main scanning direction MD (longitudinal direction LGD), and the sub scanning effective area indicates an effective area in the sub scanning direction SD (width direction LTD). The broken line with the characters “” indicates the radius of curvature of the lens in the main scanning direction MD (longitudinal direction LGD), and the solid line with the characters “sub” indicates the curvature of the lens in the sub scanning direction SD (width direction LTD). The radius is shown.

  As shown in FIG. 6, the lenses LS1 and LS2 have a curvature radius in the main scanning direction MD larger than that in the sub-scanning direction SD at any image height. The lenses LS1 and LS2 have a radius of curvature that increases with an increase in image height in both the main scanning direction MD and the sub-scanning direction SD, and are outside the effective region than within the effective region. The radius of curvature is large.

  In the configuration as described above, since the lenses LS1 and LS2 are disposed in the vicinity of the aperture Ap, the effective areas of the lenses LS1 and LS2 are relatively narrow. Accordingly, the lenses LS1 and LS2 can be easily narrowed in width (length in the width direction LTD) without impairing the effective area, and are narrower than the lens LS3 as shown in FIGS. It has a width (note that the lenses LS1, LS2 have a length smaller than the lens LS3 in the longitudinal direction LGD as well as in the width direction LTD). On the other hand, the lens LS2 is disposed between the lens LS3 and the aperture Ap, and the lens LS3 has a long distance from the aperture Ap, so that the effective area of the lens LS3 is relatively wide. Therefore, the width of the lens LS3 (length in the width direction LTD) is suppressed without impairing the effective area of the lens LS3, and the width of the lens array LA3 in which the lenses LS3 are arranged (length in the width direction LTD) is reduced. In order to suppress this, the lens LS3 has the following configuration (FIGS. 7 and 8).

  FIG. 7 is a graph showing the radius of curvature of the lens LS3. The notation in FIG. 7 is the same as the notation in FIG. As shown in FIG. 7, the lens LS3 has a curvature radius in the main scanning direction MD larger than that in the sub-scanning direction SD at any image height. Further, the radius of curvature of the lens LS3 in the main scanning direction MD increases as the image height increases, as in the lenses LS1 and LS2, and the radius of curvature is larger outside the effective area than within the effective area. Indicates the value. On the other hand, the radius of curvature of the lens LS3 in the sub-scanning direction SD decreases as the image height increases, and shows a smaller radius of curvature outside the effective area than within the effective area. The lenses LS3 having the curvature radii set in this way are connected to each other in the lens array LA3 (FIG. 8).

  FIG. 8 is a plan view of the lens LS3 on the lens array LA3 from the optical axis direction. As shown in FIG. 8 and FIG. 3 described above, the three lenses LS3 are arranged in the sub-scanning direction SD, and the two adjacent lenses LS3 are connected to each other between the effective areas ER. That is, the connection portion CP of the adjacent lenses LS3 is between the effective areas ER of the lenses LS3.

  As described above, in this embodiment, the light emitted from the light emitting element group EG (the light emitting element E) is imaged after passing through the lenses LS1, LS2, and LS3 in this order. In this embodiment, an aperture stop 295 having an aperture Ap is disposed between the lens LS1 and the lens LS2. In other words, the lens LS1 and the lens LS2 are arranged near the position where the light is stopped by the aperture stop 295. Therefore, the effective areas of the lenses LS1 and LS2 are narrow, and the lenses LS1 and LS2 can be made small. Therefore, it is possible to realize good exposure while suppressing the amount of stray light incident on the lenses LS1 and LS2.

  Moreover, the following effects can also be expected by reducing the lenses LS1 and LS2. That is, by making the lenses LS1 and LS2 small, it is possible to suppress the interference between adjacent lenses LS1 and LS2 on the lens arrays LA1 and LA2 and to facilitate the lens design. Furthermore, by designing the lenses LS1 and LS2 to be small, the lens manufacturing mold can be easily designed and manufactured. In addition, since the lenses LS1 and LS2 are small, the volume of the resin (resin constituting the lens) formed on the glass substrate SB is small, so that thermal expansion and contraction of the lens arrays LA1 and LA2 due to temperature fluctuations are suppressed. This makes it easy to maintain the optical characteristics of the lens arrays LA1 and LA2 regardless of temperature changes.

  By the way, in this embodiment, the light emitting element group EG is configured by arranging a plurality of light emitting elements in the main scanning direction MD. The light emitted from the light emitting element group EG is once stopped by the aperture stop 295 and then spreads again and enters the lens LS3. Therefore, the lens LS3 needs a certain size in the main scanning direction MD corresponding to the arrangement of the plurality of light emitting elements E in the light emitting element group EG. On the other hand, the size is not so large in the sub-scanning direction SD. Therefore, in this embodiment, the radius of curvature in the sub-scanning direction SD of the area outside the effective area of the lens LS3 (second area) is larger than the radius of curvature of the effective area (first area) of the lens LS3 in the sub-scanning direction SD. The line head 29 is configured to be small. Thus, by reducing the radius of curvature outside the effective area in the sub-scanning direction SD, the width Δ (FIG. 8) of the area (second area) between the periphery of the effective area and the periphery of the lens LS3 is reduced. Can be narrowed. As a result, the size of the lens LS3 in the sub-scanning direction SD can be reduced, and the amount of stray light incident on the lens LS3 can be suppressed to achieve good exposure.

  In this embodiment, the line head 29 is configured so that the curvature radius of the lens LS3 in the sub-scanning direction SD is smaller than the curvature radius of the lens LS3 in the main scanning direction MD. This also makes it possible to reduce the size of the lens LS3 in the sub-scanning direction SD, and to suppress the amount of stray light incident on the lens LS3, thereby realizing good exposure.

  In this embodiment, the lens LS1, the lens LS2, and the aperture stop 295 are integrally formed. Such a configuration can improve the relative positional accuracy of the lens LS1, the lens LS2, and the aperture stop 295, and appropriately forms an image of light from the light emitting element group to contribute to a good exposure operation.

  In this embodiment, the lens LS1 is convex on the light emitting element group EG side, and the lens LS2 is convex on the image side. Accordingly, the surfaces of the lens arrays LA1 and LA2 facing the aperture stop 295 are flat, and when assembling the lenses LS1 and LS2 and the aperture stop 295, they can be easily and accurately positioned.

  In this embodiment, the other surfaces (rear surfaces) of the lens arrays LA1 and LA2 are bonded together, and an aperture stop 295 is provided at the bonded portion. This makes it possible to correct aberrations satisfactorily while ensuring the assembly accuracy of the two lenses LS1 and LS2.

Others As described above, in the above embodiment, the line head 29 corresponds to the “exposure head” of the present invention, the photosensitive drum 21 corresponds to the “latent image carrier” of the present invention, and the main scanning direction MD or the longitudinal direction. The direction LGD corresponds to the “first direction” of the present invention, the sub-scanning direction SD or the width direction LTD corresponds to the “second direction” of the present invention, and the light emitting element E corresponds to the “first light emission” of the present invention. Element "," second light emitting element ", the head substrate 293 corresponds to" light emitting element substrate "of the present invention, the lens LS1 corresponds to" first lens "of the present invention, and the lens LS2 corresponds to this The lens LS3 corresponds to the “third lens” of the present invention, the glass substrate SB of the lens array LA1 corresponds to the “first substrate” of the present invention, and corresponds to the “second lens” of the present invention. The glass substrate SB of the array LA2 corresponds to the “second substrate” of the present invention. That. The effective area of the lens corresponds to the “first area” of the present invention, and the area from the periphery of the effective area to the periphery of the lens corresponds to the “second area” of the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications can be made to the above-described one without departing from the spirit of the present invention. For example, the setting mode of the curvature radii of the lenses LS1 to LS3 is not limited to the above, and various changes can be made.

  In the above embodiment, the radius of curvature of the lens LS3 continuously changes at the boundary between the effective area ER of the lens LS3 and the outside of the effective area ER of the lens LS3 (FIG. 7). However, the radius of curvature of the lens LS3 may be discontinuously changed at the boundary between the effective area ER of the lens LS3 and the outside of the effective area ER of the lens LS3 (FIG. 9). Here, FIG. 9 is a diagram showing a modified example of the lens LS3, and the notation in the same figure is the same as the notation in FIGS. Also in the modification shown in FIG. 9, the radius of curvature of the lens LS3 in the sub-scanning direction SD decreases as the image height increases, and the radius of curvature is smaller outside the effective area than within the effective area. Indicates. Therefore, similarly to the above-described embodiment, it is possible to secure the amount of light incident on the lens LS3 while suppressing the width of the line head 29.

  In the line head 29 of the above embodiment, the aperture stop 295 is supported between the lenses LS1 and LS2 by directly sandwiching the aperture stop 295 between the glass substrates SB of the lens arrays LA1 and LA2. However, the configuration for supporting the aperture stop 295 is not limited to this (FIGS. 10 to 13). Here, FIG. 10, FIG. 11, FIG. 12, and FIG. 13 are exploded views schematically showing modifications of the configuration that supports the aperture stop. Since these figures are exploded views, the constituent members in the figures are shown separately in the left-right direction, but actually they are configured to contact each other in the left-right direction. In these drawings, unlike the above-described embodiment, the case where the lenses LS1, LS2, LS3 and the aperture Ap are arranged in two rows in a staggered manner in the main scanning direction MD is shown.

  In FIG. 10, a light-shielding thin film formed on the glass substrate SBa (third substrate) by a technique such as metal vapor deposition or sputtering functions as the aperture stop 295. The aperture stop 295 is supported between the lenses LS1 and LS2 by sandwiching the glass substrate SBa on which the aperture stop 295 is formed between the glass substrates SB of the lens arrays LA1 and LA2. In FIG. 11, an aperture stop 295 having a flat thin plate with an aperture Ap is attached to a glass substrate SBa (third substrate). The aperture stop 295 is supported between the lenses LS1 and LS2 by sandwiching the glass substrate SBa on which the aperture stop 295 is attached between the glass substrates SB of the lens arrays LA1 and LA2.

  In FIG. 12, a light-shielding thin film formed on the glass substrate SBa (third substrate) by a technique such as metal vapor deposition or sputtering functions as the aperture stop 295. Then, the glass substrate SBb is bonded to the aperture stop 295 so as to sandwich the glass substrate SBa and the aperture stop 295. Thus, the glass substrate SBa, SBb sandwiching the aperture stop 295 is further sandwiched by the glass substrates SB of the lens arrays LA1, LA2, and the aperture stop 295 is supported between the lenses LS1, LS2. In FIG. 13, an aperture stop 295 having a flat thin plate with an aperture Ap is attached to a glass substrate SBa (third substrate). Then, the glass substrate SBb is bonded to the aperture stop 295 so as to sandwich the glass substrate SBa and the aperture stop 295. Thus, the glass substrate SBa, SBb sandwiching the aperture stop 295 is further sandwiched by the glass substrates SB of the lens arrays LA1, LA2, and the aperture stop 295 is supported between the lenses LS1, LS2.

  As described above, in the configuration shown in FIGS. 10 to 13, the glass substrate SBa and the glass substrate SBb function as spacers that define the distance between the lens arrays LA1 and LA2. As a result, it is possible to accurately define the distance between the surfaces of the lenses LS1 and LS2 and realize good imaging performance. In the configuration shown in FIGS. 10 to 13, it is preferable to fill the opening Ap with a light-transmitting adhesive to exclude air. Thereby, it can suppress that light is scattered by air in opening Ap.

  Further, the number of imaging optical systems OS (in other words, the number of lens rows) arranged at different positions in the sub-scanning direction SD is not limited to three, and may be two or four or more.

  Further, the shapes of the lenses LS1 to LS3 and the aperture Ap constituting the imaging optical system OS are not limited to those described above.

  In the above embodiment, various optical magnifications of the imaging optical system OS can be employed.

  In addition, the number and arrangement of the light emitting elements E constituting the light emitting element group EG can be variously changed.

  In addition to the organic EL element described above, a light source such as an LED (Light Emitting Diode) can also be used as the light emitting element E.

  The configuration of the light shielding member 297 is not limited to that described above, and for example, a light shielding member in which a plurality of light shielding plates are stacked while being spaced apart can be used as disclosed in Japanese Patent Application Laid-Open No. 2008-307885.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 21 ... Photosensitive drum, 29 ... Line head, 293 ... Head substrate, 295 ... Aperture stop, Ap ... Opening, 297 ... Light-shielding member, 2971 ... Light guide hole, 298 ... Plate-shaped optical member, E Light emitting element, EG ... Light emitting element group, LA1, LA2, LA3 ... Lens array, LS1, LS2, LS3 ... Lens, ER ... Effective area, LGD: Longitudinal direction, LTD ... Width direction, MD ... Main scanning direction, SD ... Sub-scan direction

Claims (8)

A light emitting element substrate having a first light emitting element that emits light, and a second light emitting element that is disposed in a first direction of the first light emitting element and emits light;
A first lens on which light emitted from the first light emitting element and light emitted from the second light emitting element are incident;
An aperture stop having an aperture through which the light emitted from the first light emitting element and transmitted through the first lens and the light emitted from the second light emitting element and transmitted through the first lens are passed;
A second lens on which the light emitted from the first light emitting element and passed through the opening of the aperture stop and the light emitted from the second light emitting element and passed through the opening of the aperture stop are incident;
A third lens on which the light emitted from the first light emitting element and transmitted through the second lens and the light emitted from the second light emitting element and transmitted through the second lens are incident;
With
An exposure head, wherein a latent image formed by light emitted from the first light emitting element and a latent image formed by light emitted from the first light emitting element are formed on an image surface.   Due to the radius of curvature in the second direction orthogonal to the first direction of the first region that transmits light that forms a latent image on the image plane of the third lens, the image plane of the third lens The exposure head according to claim 1, wherein a radius of curvature in the second direction of the second region through which light forming a latent image is not transmitted is small.   The radius of curvature of the first region of the third lens in the second direction is smaller than the radius of curvature of the first region of the third lens in the first direction. Exposure head.   4. The exposure head according to claim 1, wherein the first lens is convex toward the light emitting element substrate, and the second lens is convex toward the image plane. 5.   The exposure head according to claim 4, further comprising a lens substrate on which the first lens, the second lens, and the aperture stop are disposed. A first substrate having the first lens disposed on one surface, and a second substrate having the second lens disposed on one surface;
The aperture stop is sandwiched between the other surface of the first substrate and the other surface of the second substrate;
The exposure head according to claim 4, wherein one surface of the first substrate and one surface of the second substrate are bonded. A first substrate having the first lens disposed on one surface, a second substrate having the second lens disposed on one surface, and a third substrate having the aperture stop disposed; Prepared,
The exposure head according to claim 4, wherein the third substrate is sandwiched between the first substrate and the second substrate, and is fixed to the first substrate and the second substrate. . A light-emitting element substrate having a first light-emitting element that emits light and a second light-emitting element that is disposed in a first direction of the first light-emitting element, and the first light-emitting element emits light A first lens on which light and light emitted from the second light emitting element are incident; a light emitted from the first light emitting element and transmitted through the first lens; and a light emitted from the second light emitting element. An aperture stop having an aperture through which light transmitted through the first lens passes; the first light emitting element emits light; the light passing through the opening of the aperture stop; and the second light emitting element emits light, and The second lens on which light that has passed through the aperture of the aperture stop is incident, and the light emitted from the first light emitting element and transmitted through the second lens, and the second light emitting element emitted to emit the first lens. A third lens on which light transmitted through the second lens enters, An exposure head for forming a latent image of the latent image and by the first light emitted from the light emitting element to the surface by the light emitted from the first light emitting element,
A latent image carrier on which the latent image is formed by the exposure head;
A developing unit for developing the latent image formed on the latent image carrier;
An image forming apparatus comprising:

Images