JP2012245635A - Exposure head and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute an imaging optical system of three lenses and to correctly determine the lens distance between two lenses near the object while ensuring its large size.SOLUTION: The exposure head includes: light emitting elements which emit light; first convex lenses which allow the light emitted from the light emitting elements to pass; a first lens array having a first light-permeable base plate which supports the first lenses by its side facing the light emitting elements; second convex lenses which allow the light passing through the first lenses to pass; a second lens array having a second light-permeable base plate which supports the second lenses by its side other than that facing the light emitting elements; the third lenses having third lenses which allow the light passing through the second lenses to pass; a third lens array having a third light-permeable base plate which supports the lenses of the third; an aperture stop which focuses the light passing through the lenses of the first; and a spacer which is arranged between the first lens array and the second lens array.

Description

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

  Patent Document 1 describes an exposure head (line head) in which a plurality of imaging optical systems are arranged in the main scanning direction and a light emitting element group is arranged to face each imaging optical system. This light emitting element group is a plurality of light emitting elements arranged in the main scanning direction, and each imaging optical system forms an image of light emitted from the light emitting elements of the opposing light emitting element group, and the surface of the photosensitive drum To form a light spot.

JP 2010-1225836 A

  FIG. 12 of Patent Document 1 describes an exposure head in which an imaging optical system is configured by three lenses. Specifically, this imaging optical system has a configuration in which three convex lenses are arranged on the object side (light emitting element side). In such a configuration, it is advantageous for correcting the aberration to increase the distance between the two lenses on the object side. However, it may be difficult to accurately define the lens interval as it increases.

  The present invention has been made in view of the above problems, and in an exposure head in which an imaging optical system is configured by three lenses and an image forming apparatus using the exposure head, a lens interval between two lenses on the object side. The purpose of this technology is to provide a technology that can accurately define the above.

  In order to achieve the above object, an exposure head according to the present invention includes a light emitting element that emits light, a convex first lens that transmits light emitted from the light emitting element, and the first lens as a light emitting element. A first lens array having a first light-transmitting substrate supported by opposing surfaces, a convex second lens that transmits light transmitted through the first lens, and a second lens as a light-emitting element A second lens array having a second light-transmitting substrate supported by a surface opposite to the opposing surface, a third lens having a third lens through which light transmitted through the second lens is transmitted, and A third lens array having a third light-transmitting substrate that supports the third lens, an aperture stop for restricting light transmitted through the first lens, and the first lens array and the second lens array; A spacer disposed between and It is a symptom.

  In order to achieve the above object, an image forming apparatus according to the present invention includes a latent image carrier on which a latent image is formed, a light emitting element that emits light, and a convex shape that transmits light emitted from the light emitting element. A first lens array having a first light transmissive substrate that supports the first lens and a surface facing the light emitting element, and a convex shape through which light transmitted through the first lens is transmitted. The second lens and a second lens array having a second light-transmitting substrate that supports the second lens on a surface opposite to the surface facing the light emitting element, and light transmitted through the second lens are transmitted. A third lens array having a third lens having a third lens and a third light-transmitting substrate supporting the third lens; and an aperture stop for restricting light transmitted through the first lens. Arranged between the first lens array and the second lens array And a spacer provided with, and characterized by having an exposure head for forming a latent image on the image bearing member, a developing unit for developing a latent image formed on the latent image bearing member, a.

  In the invention thus configured (exposure head, image forming apparatus), the first, second and third lenses are arranged in this order from the light emitting element side. At this time, the first lens is convex to the light emitting element side, and is supported by the flat first light-transmitting substrate from the opposite side of the light emitting element. The second lens is convex on the opposite side of the light emitting element, and is supported from the light emitting element side by a flat second light-transmitting substrate. The present invention has a configuration in which a light transmissive spacer is sandwiched between a first light transmissive substrate and a second light transmissive substrate. Therefore, this spacer makes it possible to accurately define the surface distance between the first lens and the second lens with a large distance, and as a result, appropriate aberration correction can be realized. Moreover, since this spacer is provided with an aperture stop, this aberration correction can be performed more appropriately.

  At this time, the exposure head may be configured such that the spacer has a glass substrate and the aperture stop is bonded to the glass substrate.

  Various configurations of the light-transmitting substrate and the lens can be adopted. Therefore, the first light transmissive substrate, the second light transmissive substrate, and the third light transmissive substrate may be made of glass. The first lens, the second lens, and the third lens may be resin lenses. Therefore, the first light transmissive substrate, the second light transmissive substrate, and the third light transmissive substrate may be glass substrates. The first lens, the second lens, and the third lens may be resin lenses.

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. FIG. 6 is a ray diagram illustrating an image forming operation by an example of an image forming optical system. The figure which shows the lens data of the imaging optical system illustrated in FIG. 6 as a table | surface. The figure which shows the definition formula of an aspherical surface (XY polynomial surface). The figure which shows the coefficient which gives the lens surface shape of the imaging optical system illustrated in FIG. 6 as a table. The exploded view which showed typically the modification of the structure between lens array LA1, LA2. The exploded view which showed typically the modification of the structure between lens array LA1, LA2. The exploded view which showed typically the modification of the structure between lens array LA1, LA2.

  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 two-row staggered manner. In other words, this arrangement mode can be explained as follows. That is, the light emitting element groups EG are arranged at the distance of 2 × Dg in the longitudinal direction LGD, and one light emitting element group row GRa and the like are configured from the plurality of light emitting element groups EG linearly arranged in the longitudinal direction LGD. Further, the two light emitting element group rows GRa and GRb 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 two rows, A lens array LA2 in which a plurality of lenses LS2 are arranged in a staggered manner in two rows and a lens array LA3 in which a plurality of lenses LS3 are arranged in a staggered manner in two rows are provided. In other words, in the lens array LA1 (LA2, LA3), the lenses LS1 (LS2, LS3) are arranged at a distance of 2 × Dg in the longitudinal direction LGD and a plurality of lenses LS1 (LS2, LS3) linearly arranged in the longitudinal direction LGD. ) Constitutes one lens row. Further, the two 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 light-transmissive glass substrate SB having a flat plate shape.

  A spacer 294 and an aperture stop 295 are arranged between the lens arrays LA1 and LA2. The spacer 294 is glass (glass substrate) having a flat plate shape. On the other hand, the aperture stop 295 is formed of a thin flat plate in which a circular opening Ap having a diameter smaller than the diameters of the lenses LS1, LS2, and LS3 is formed. In the aperture stop 295, a plurality of apertures Ap are arranged in a two-row staggered manner so as to face each of the plurality of light emitting element groups EG arranged in a two-row staggered manner. The light emitted from each light emitting element E of the light emitting element group EG is imaged on the surface of the photosensitive drum 21 by the lenses LS1, LS2, and LS3 after the amount of light is defined by the aperture stop 295.

  Of the two 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. The lens array LA1, the spacer 294, the aperture stop 295, and the lens array in a state where the spacer 294 is disposed on the other surface of the glass substrate SB of the lens array LA1 and the aperture stop 295 is disposed on the other surface of the lens array LA2. LA2 are laminated in this order and bonded together. In this way, a plate-like optical member 298 is formed, in which the two lens arrays LA1 and LA2 are integrally bonded by way of the spacer 294 and 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.

  That is, 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 two-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 two-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, the symbol OSb is also written 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 GRb. That is, different signs OSa and OSb 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. Then, the imaging optical system OS forms incident light at an imaging magnification that forms a reverse image and an equal magnification image to form 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, bottom-up members 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 the bottom upper member 299 from the sub-scanning direction SD. As a result, a gap is provided between the lower peripheral portion of the light guide hole 2971 and the head substrate surface 293-h. It has been. 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. In this way, the light of the light emitting element group EG is imaged on the imaging optical system OS and bears exposure of a predetermined range of the surface of the photosensitive drum 21.

  Specifically, one imaging optical system OS takes charge of exposure of 2.667 [mm]. For example, in order to expose a width of 330 [mm], a lens array LA1 (LA2, LA3) in which 124 lenses LS1 (LS2, LS3) are formed is used. In each of the lenses LS1 (LS2, LS3), two rows of lens rows arranged at a pitch of 5.334 [mm] in the main scanning direction MD are arranged in a staggered manner, and the row interval Dt is 1.6 [mm]. It has become. On the other hand, the image side of the imaging optical system OS is telecentric. As a result, the lens LS3 closest to the image plane has a larger outer shape than the lenses LS1 and LS2, and their peripheral edges are connected (see FIG. 3). However, it is configured such that the peripheral edge thereof does not interfere with the light beam passage region of the lens LS3.

  In the above configuration, since one light emitting element group EG is responsible for exposure of an area of 2.667 [mm], the number of light emitting elements E constituting one light emitting element group EG has a resolution of 1200 dpi (dots per inch). In this case, 126 or more are required, and in the case of 2400 dpi, 252 or more are required. Since the magnification of the imaging optical system described later in FIG. 6 and the like is −1 (inverted equal magnification), the pitch of the imaging spots on the photosensitive drum 21 is equal to the pitch of the light emitting elements E in the light emitting element group EG.

  Since the imaging performance of the lenses LS1, LS2, and LS3 in this embodiment is very high, if the size of the light emitting element E is small, the imaging spot also becomes small. Therefore, if the light emitting elements E are arranged in a line, the size of the light emitting elements E is considerably smaller than the pitch. Therefore, the imaging spot on the surface of the photosensitive drum 21 is also smaller than the pitch. However, it is desirable that the spot diameter is slightly larger than the spot pitch. Therefore, in this embodiment, the light emitting elements E are arranged in two or more rows, and the size of the light emitting elements E is set to be equal to or slightly larger than the pitch of the light emitting elements E.

  Specific examples of the imaging optical system having the above-described configuration include the following. FIG. 6 is a ray diagram showing an image forming operation by an example of the image forming optical system. FIG. 7 is a table showing lens data of the imaging optical system illustrated in FIG. FIG. 8 is a diagram showing a definition formula of an aspheric surface (XY polynomial surface). FIG. 9 is a table showing coefficients giving the shapes of the lens surfaces of the imaging optical system illustrated in FIG.

  The light shown in the ray diagram of FIG. 6 has a wavelength of 620 [nm]. In the example shown in FIG. 6, each aberration can be corrected satisfactorily by using three anamorphic aspheric surfaces (lenses LS1, LS2, and LS3). In particular, the lens LS1 and the lens LS2 are arranged at an appropriate distance in front of and behind the aperture stop 295, the lens LS1 is convex on the object side (light source side), and the lens LS2 is convex on the image plane side (photosensitive drum side). Thus, it is possible to correct aberrations satisfactorily while suppressing the apertures of the lenses LS1 and LS2. Further, since the angle of view of the light beam corresponding to the maximum image height is also suppressed, the error sensitivity such as the on-axis position can be suppressed low, and at the same time, shading (difference in the amount of light between the center and the end) can be suppressed.

  Each lens array LA1, LA2, LA3 having lenses LS1, LS2, LS3 has a lens surface made of resin on the glass substrate SB in order to avoid expansion and contraction due to temperature fluctuation. The resin lens portion is molded by transferring and molding the lens shape onto the resin using a mold or a stamper. As the resin molding method, general injection molding, compression molding, light effect resin molding (2P = Photo Polymer), and the like are possible. In particular, 2P molding in which a resin is cured with ultraviolet rays can be supplied simply by applying the resin on a mold or a stamper, and the curing is fast, so that productivity is high.

  In this embodiment, a spacer 294 is interposed between the lens LS1 and the lens LS2, and a total of three glass substrates SB, SB, 294 are bonded to each other. Therefore, by managing the thickness of the glass, the surface distance between the lens LS1 and the lens LS2 can be accurately managed. Also, an alignment mark is formed on the two lenses LS1 and LS2, and they are positioned and bonded to each other with reference to the mark, or an alignment mark is also provided on the spacer 294, and the alignment marks of the lenses LS1 and LS2 By adjusting the position so as to match, the position in the in-plane direction can also be accurately adjusted. Thus, the two lenses LS1 and LS2 can be bonded with very high accuracy. In particular, double-side polished glass can be used for the substrate when the accuracy of the surface separation is required.

  The lenses LS1 and LS2 are molded on a glass substrate SB having a thickness of 0.5 [mm], and a surface interval of 1.5 [mm] can be secured by bonding the spacers 294 having the same thickness. . Further, if a thicker spacer 294 is used, it is possible to further widen the surface interval.

  As described above, in the embodiment configured as described above, the lenses LS1, LS2, and LS3 are arranged in this order from the light emitting element E side. At this time, the lens LS1 is convex on the light emitting element E side, and is supported on one surface of the flat glass substrate SB from the opposite side of the light emitting element E. The lens LS2 is convex on the opposite side of the light emitting element E, and is supported from one side of the flat glass substrate SB from the light emitting element E side. In this embodiment, a light transmissive spacer 294 is sandwiched between the other surface of the glass substrate SB that supports the lens LS1 and the other surface of the glass substrate SB that supports the lens LS2. Therefore, the spacer 294 can accurately define the distance between the lens LS1 and the lens LS2 with a large distance, and as a result, appropriate aberration correction can be realized. In addition, since this aperture 295 is provided in the spacer 294, this aberration correction can be executed more appropriately.

Others As described above, in the above embodiment, the line head 29 corresponds to the “exposure head” of the present invention, the light emitting element E corresponds to the “light emitting element” of the present invention, and the lens LS1 corresponds to the “first” of the present invention. The glass substrate SB that supports the lens LS1 corresponds to the “first light transmitting substrate” of the present invention, the lens array LA1 corresponds to the “first lens array” of the present invention, The lens LS2 corresponds to the “second lens” of the present invention, the glass substrate SB supporting the lens LS2 corresponds to the “second light transmitting substrate” of the present invention, and the lens array LA2 corresponds to the “second lens” of the present invention. 2, the lens LS3 corresponds to the “third lens” of the present invention, the glass substrate SB supporting the lens LS3 corresponds to the “third light transmissive substrate” of the present invention, The lens array LA3 is the “third lens array” of the present invention. It corresponds to.

  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 line head 29 of the above-described embodiment is configured by the aperture stop 295 and the spacer 294 configured by flat plates between the lens arrays LA1 and LA2. The configuration between the lens arrays LA1 and LA2 is not limited to this (FIGS. 10 to 12). Here, FIG. 10, FIG. 11 and FIG. 12 are exploded views schematically showing modifications of the configuration between the lens arrays LA1 and LA2. 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 FIG. 10, a light-shielding thin film formed on the spacer 294 by a technique such as metal vapor deposition or sputtering functions as the aperture stop 295. A spacer 294 and an aperture stop 295 made of a thin film are sandwiched between the lens arrays LA1 and LA2. 11 and 12, two spacers 294 are provided between the lens arrays LA1 and LA2, and an aperture stop 295 is provided between the two spacers 294. The lens array LA1, the spacer 294, the aperture stop 295, the spacer 294, and the lens array LA2 are stacked in this order and bonded to each other. In FIG. 11, the aperture stop 295 is a thin film formed on the spacer 294 on the lens array LA1 side by a technique such as metal vapor deposition or sputtering. On the other hand, in FIG. 12, the aperture stop 295 is formed of a thin flat plate. 11 and 12, the distances from the aperture stop 295 to the lenses LS1 and LS2 can be made equal. Incidentally, if an aperture stop 295 is provided on the other side of the lens array prior to lens formation by vapor deposition or the like, when the lens is formed by 2P molding in a later step, the aperture stop 295 is shielded from light. There was a possibility that the lens could not be cured. On the other hand, in this embodiment, by providing the aperture stop 295 in the spacer 294 which is a member different from the lens arrays LA1 and LA2, while forming the aperture stop 295 integrally on the glass substrate SB, a different substrate is provided. It is possible to mold the lens 2P freely.

  As described above, also in the modified examples shown in FIGS. 10 to 12, the light-transmitting spacer 294 is formed on the other surface of the glass substrate SB supporting the lens LS1 and the other surface of the glass substrate SB supporting the lens LS2. It has a sandwiched configuration. Therefore, the spacer 294 can accurately define the distance between the lens LS1 and the lens LS2 with a large distance, and as a result, appropriate aberration correction can be realized. In addition, since this aperture 295 is provided in the spacer 294, this aberration correction can be executed more appropriately.

  Incidentally, the glass substrates SB and the spacers 294 of the lens arrays LA1 and LA2 can be procured easily and cost can be reduced by using exactly the same material. Further, if the same material is used, there is an advantage that reflection at the interface after adhesion due to a difference in refractive index is eliminated. Further, by making the thickness of the spacer 294 different from the thickness of the glass substrate SB, the distance between the aperture stop 295 and the lenses LS1 and LS2 can be arbitrarily set.

  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 two and may be three 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, 294 ... Spacer, 295 ... Aperture stop, Ap ... Opening, 297 ... Light shielding member, 2971 ... Light guide hole, 298 ... Plate shape Optical member, E ... Light emitting element, EG ... Light emitting element group, LA1, LA2, LA3 ... Lens array, LS1, LS2, LS3 ... Lens, SB ... Glass substrate, LGD ... Longitudinal direction, LTD ... Width direction, MD ... Main scan Direction, SD ... sub-scanning direction

Claims (5)

A light emitting element that emits light;
A first lens array having a convex first lens that transmits light emitted by the light emitting element, and a first light-transmitting substrate that supports the first lens on a surface facing the light emitting element; ,
A convex second lens that transmits light transmitted through the first lens, and a second light-transmitting substrate that supports the second lens on a surface opposite to the surface facing the light emitting element. A second lens array;
A third lens having a third lens through which light transmitted through the second lens passes, and a third lens array having a third light-transmitting substrate that supports the third lens;
A spacer having an aperture stop for restricting light transmitted through the first lens, and disposed between the first lens array and the second lens array;
An exposure head comprising:   The exposure head according to claim 1, wherein the spacer includes a glass substrate, and the aperture stop is bonded to the glass substrate.   The exposure head according to claim 1, wherein the first light transmissive substrate, the second light transmissive substrate, and the third light transmissive substrate are made of glass.   4. The exposure head according to claim 1, wherein the first lens, the second lens, and the third lens are resin lenses. 5. A latent image carrier on which a latent image is formed;
A light emitting element that emits light, a convex first lens that transmits light emitted from the light emitting element, and a first light-transmissive substrate that supports the first lens on a surface facing the light emitting element. A first lens array having a convex second lens that transmits light transmitted through the first lens, and a second lens that supports the second lens on a surface opposite to the surface facing the light emitting element. A second lens array having a light transmissive substrate, a third lens having a third lens through which light transmitted through the second lens passes, and a third light transmissive supporting the third lens. A spacer disposed between the first lens array and the second lens array having a third lens array having a conductive substrate and an aperture stop for restricting light transmitted through the first lens The latent image is provided on the latent image carrier. And the exposure head to be formed,
A developing unit for developing the latent image formed on the latent image carrier;
An image forming apparatus comprising:

Images