JP5403127B2 - Exposure apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an exposure apparatus and an image forming apparatus.

  Conventionally, in a copying machine or printer that forms an image by electrophotography, a laser ROS (Raster Output Scanner) system that scans light emitted from a laser light source with a polygon mirror as an exposure device that writes a latent image on a photosensitive drum The exposure apparatus was used. Recently, an LED type exposure apparatus using a light emitting diode (LED) as a light source is becoming mainstream instead of a laser ROS type exposure apparatus. The LED type exposure apparatus is called an LED print head and is abbreviated as LPH.

  The LED print head includes an LED array in which a large number of LEDs are arranged on a long substrate, and a lens array in which a large number of gradient index rod lenses are arranged. Here, the array means an element array in which elements such as a plurality of LEDs and a plurality of lenses are arranged one-dimensionally or two-dimensionally. In the LED array, for example, 1200 pixels per inch (that is, 1200 dpi) and a large number of LEDs corresponding to the number of pixels in the main scanning direction are arranged. As the gradient index rod lens, a cylindrical rod lens represented by SELFOC (registered trademark) is used.

  In the LED print head, the light emitted from each LED is collected by a rod lens, and an erecting equal-magnification image is formed on the photosensitive drum. Therefore, a laser ROS scanning optical system is unnecessary, and the size can be greatly reduced as compared with the laser ROS system. In addition, a driving motor for driving the polygon mirror is unnecessary, and there is an advantage that no mechanical noise is generated.

  For LED print heads, several techniques using a hologram element array instead of a rod lens have been proposed (see Patent Documents 1 and 2).

  Note that, as an electrophotographic exposure apparatus, an LED print head using an LED array is generally used. Therefore, this exposure system is commonly referred to as an “LED system”. However, since it is not necessary to limit the light emitting elements to LEDs, the “LED method” will be appropriately referred to as “light emitting element array method” below.

Japanese Patent Laid-Open No. 4-201270 JP 2007-237576 A

  An object of the present invention is to provide a light-emitting element array system capable of condensing each light emitted from each of three or more light-emitting elements that are not positioned on a straight line to form a spot line arranged substantially on a straight line. An exposure apparatus and an image forming apparatus using the same are provided.

  In order to achieve the above object, the invention described in each claim has the following configuration.

According to a first aspect of the present invention, there is provided a light emitting element array in which three or more light emitting elements are arranged on the same substrate, and the three or more light emitting elements are not arranged on a straight line, and the substrate A hologram to which each light emitted from each of the three or more light emitting elements corresponds to a position corresponding to each of the three or more light emitting elements in a single hologram recording layer laminated adjacently on the hologram. An exposure apparatus comprising: a hologram element array in which a plurality of hologram elements are formed so that the elements are irradiated and condensed on a substantially straight line .

  The invention according to claim 2 is characterized in that the three or more light emitting elements are arranged at predetermined intervals in the length direction of the substrate, and the plurality of hologram elements have a diameter in the length direction of the substrate. The exposure apparatus according to claim 1, wherein the exposure apparatuses are formed so as to overlap each other larger than a predetermined interval.

  According to a third aspect of the present invention, the plurality of hologram elements are formed such that the plurality of condensing points formed on the imaging surface by condensing the respective lights are arranged in a predetermined direction. An exposure apparatus according to claim 1 or claim 2.

  According to a fourth aspect of the present invention, in any one of the first to third aspects, each of the plurality of condensing points is located outside an irradiation region of each light emitted from each of the corresponding light emitting elements. The exposure apparatus according to the item.

  A fifth aspect of the invention is the exposure apparatus according to any one of the first to fourth aspects, wherein each of the three or more light emitting elements is a non-coherent light source.

  According to a sixth aspect of the present invention, there is provided a light-shielding body that shields light passing through the outside of the plurality of hologram elements among the light emitted from each of the three or more light emitting elements. 5. The exposure apparatus according to any one of items 1 to 5.

  The invention of claim 7 is the exposure apparatus according to any one of claims 1 to 6, a photosensitive image recording medium on which an image is recorded by imagewise exposure by the exposure apparatus, and the image Based on the image data, the moving means for moving the recording medium relative to the exposure apparatus and the moving means are controlled so that the image recording medium is sub-scanned in a direction crossing the length direction of the substrate. In addition, the image forming apparatus includes a control unit that controls lighting of each of the three or more light emitting elements.

  According to the invention described in each claim of the present invention, the following effects are obtained.

  According to the first aspect of the present invention, it is possible to collect each light emitted from each of the three or more light emitting elements that are not positioned on a straight line, and to form a spot row that is arranged on a substantially straight line. There is an effect that a light emitting element array type exposure apparatus is provided.

  According to invention of Claim 2, there exists an effect that a working distance can be lengthened compared with the conventional LED print head.

  According to the third aspect of the invention, there is an effect that it is possible to form a spot row arranged in a predetermined direction on the imaging surface.

  According to the fourth aspect of the present invention, there is an effect that the background noise due to the 0th-order light can be reduced and a spot with high contrast can be formed.

  According to the fifth aspect of the present invention, there is an effect that a spot with high contrast can be formed even with incoherent light emitted from an incoherent light source.

  According to the sixth aspect of the invention, there is an effect that background noise can be further reduced by blocking stray light, in particular, zero-order light due to Lambertian orientation of a non-coherent light source.

  According to the seventh aspect of the present invention, it is possible to provide a light emitting element array type image forming apparatus capable of forming an image with a small size and high contrast as compared with an image forming apparatus equipped with a conventional LED print head. There is.

1 is a schematic diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the present invention. It is a schematic perspective view which shows an example of a structure of the LED print head as an exposure apparatus which concerns on a 1st reference example. (A) is a perspective view showing a schematic shape of a hologram element, (B) is a sectional view in the sub-scanning direction of the LED print head, and (C) is a sectional view in the main scanning direction of the LED print head. (A) And (B) is a figure which shows a mode that a hologram element is formed in a hologram recording layer. (A) And (B) is a figure which shows a mode that diffracted light is produced | generated from a hologram element. (A)-(E) is process drawing which shows the manufacturing process of an LED print head. It is sectional drawing which shows an example of the arrangement | positioning relationship between an LED print head and a photosensitive drum. It is a schematic perspective view which shows an example of a structure of the LED print head which concerns on the 1st Embodiment of this invention. (A) And (B) is a figure which shows a mode that diffracted light is produced | generated from a hologram element. It is a schematic perspective view which shows an example of a structure of the LED print head which concerns on the 2nd Embodiment of this invention. It is a schematic perspective view which shows an example of a structure of the LED print head which concerns on the modification of 2nd Embodiment. It is a schematic perspective view which shows an example of a structure of the LED print head which concerns on a 2nd reference example. It is sectional drawing of the subscanning direction of an LED print head. It is a conceptual diagram which shows the Lambertian light distribution of an incoherent light source. It is a schematic perspective view which shows an example of a structure of the LED print head which concerns on the 3rd Embodiment of this invention. It is sectional drawing which shows the other example of arrangement | positioning of a light-shielding body. It is sectional drawing which shows the other example of arrangement | positioning of a light-shielding body. It is sectional drawing which shows the other example of arrangement | positioning of a light-shielding body. It is sectional drawing which shows the other example of arrangement | positioning of a light-shielding body. It is sectional drawing which shows the other example of arrangement | positioning of a light-shielding body. It is sectional drawing which shows the other example of arrangement | positioning of a light-shielding body. It is sectional drawing which shows the other example of arrangement | positioning of a light-shielding body. It is sectional drawing which shows the other example of arrangement | positioning of a light-shielding body.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

<Image forming apparatus>
FIG. 1 is a schematic diagram showing an example of the configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus is a so-called tandem digital color printer, and includes an image forming process unit 10 as an image forming unit that forms an image corresponding to image data of each color, and a control unit 30 that controls the operation of the image forming apparatus. And an image processing unit 40 which is connected to the image reading device 3 and an external device such as a personal computer (PC) 2 and performs predetermined image processing on image data received from these devices.

  The image forming process unit 10 includes four image forming units 11Y, 11M, 11C, and 11K that are arranged in parallel at regular intervals. Each of the image forming units 11Y, 11M, 11C, and 11K forms yellow (Y), magenta (M), cyan (C), and black (K) toner images. The image forming units 11Y, 11M, 11C, and 11K are collectively referred to as “image forming unit 11” as appropriate.

  Each image forming unit 11 includes a photosensitive drum 12 as an image carrier that forms an electrostatic latent image and carries a toner image, a charger 13 that uniformly charges the surface of the photosensitive drum 12 at a predetermined potential, An LED print head (LPH) 14 as an exposure device for exposing the photosensitive drum 12 charged by the developing device 13, a developing device 15 for developing the electrostatic latent image obtained by the LPH 14, and the surface of the photosensitive drum 12 after transfer. A cleaner 16 for cleaning is provided.

  The LPH 14 is a long print head having substantially the same length as the length of the photosensitive drum 12 in the axial direction. In the LPH 14, a plurality of LEDs are arranged in an array along the length direction. The LPH 14 is disposed around the photosensitive drum 12 so that the length direction thereof faces the axial direction of the photosensitive drum 12. Further, in the present embodiment, the working distance of the LPH 14 is long, and is disposed several cm away from the surface of the photosensitive drum 12. For this reason, the occupation width in the circumferential direction of the photosensitive drum 12 is small, and congestion around the photosensitive drum 12 is reduced.

  The image forming process unit 10 also intermediate-transfers each color toner image of each image forming unit 11 and the intermediate transfer belt 21 onto which the toner images of each color formed on the photosensitive drum 12 of each image forming unit 11 are transferred in a multiple manner. A primary transfer roll 22 that sequentially transfers (primary transfer) to the belt 21; a secondary transfer roll 23 that collectively transfers (secondary transfer) the superimposed toner image transferred onto the intermediate transfer belt 21 to a sheet P that is a recording medium; and A fixing device 25 for fixing the secondary transferred image on the paper P is provided.

Next, the operation of the image forming apparatus will be described.
First, the image forming process unit 10 performs an image forming operation based on a control signal such as a synchronization signal supplied from the control unit 30. At that time, the image data input from the image reading device 3 or the PC 2 is subjected to image processing by the image processing unit 40 and supplied to each image forming unit 11 via the interface.

  For example, in the yellow image forming unit 11Y, the surface of the photosensitive drum 12 uniformly charged at a predetermined potential by the charger 13 is exposed by the LPH 14 that emits light based on the image data obtained from the image processing unit 40. Thus, an electrostatic latent image is formed on the photosensitive drum 12. That is, each LED of the LPH 14 emits light based on the image data, so that the surface of the photoconductive drum 12 is main-scanned, and the photoconductive drum 12 is rotated and sub-scanned, and the photoconductive drum 12 is scanned on the photoconductive drum 12. An electrostatic latent image is formed. The formed electrostatic latent image is developed by the developing device 15, and a yellow toner image is formed on the photosensitive drum 12. Similarly, magenta, cyan, and black toner images are formed in the image forming units 11M, 11C, and 11K.

  Each color toner image formed by each image forming unit 11 is sequentially electrostatically attracted and transferred by the primary transfer roll 22 onto the intermediate transfer belt 21 rotating in the direction of arrow A in FIG. 1 (primary transfer). A superimposed toner image is formed on the intermediate transfer belt 21. The superimposed toner image is conveyed to a region (secondary transfer portion) where the secondary transfer roll 23 is disposed as the intermediate transfer belt 21 moves. When the superimposed toner image is conveyed to the secondary transfer unit, the paper P is supplied to the secondary transfer unit in accordance with the timing at which the toner image is conveyed to the secondary transfer unit.

  The superimposed toner images are collectively electrostatically transferred onto the conveyed paper P (secondary transfer) by the transfer electric field formed by the secondary transfer roll 23 in the secondary transfer portion. The sheet P on which the superimposed toner image has been electrostatically transferred is peeled off from the intermediate transfer belt 21 and conveyed to the fixing device 25 by the conveyance belt 24. The unfixed toner image on the paper P conveyed to the fixing device 25 is fixed on the paper P by being subjected to a fixing process by heat and pressure by the fixing device 25. The paper P on which the fixed image is formed is discharged to a paper discharge tray (not shown) provided in the discharge unit of the image forming apparatus.

  Note that when the LPH working distance is longer, the periphery of the photosensitive drum is not crowded, and the image forming apparatus can be downsized as a whole. In the conventional LPH, the optical path length (working distance) from the lens array end face of the rod lens to the imaging point is as short as several millimeters, and the occupation ratio of the exposure device around the photosensitive drum is increased. In general, in LPH using an LED that emits incoherent light, coherence decreases and spot blurring (so-called chromatic aberration) occurs, and it is not easy to form a minute spot.

<LED Print Head (LPH)-First Reference Example->
(Configuration of LPH)
FIG. 2 is a schematic perspective view showing an example of the configuration of an LED print head as an exposure apparatus according to the first reference example. 3A is a perspective view showing a schematic shape of the hologram element, FIG. 3B is a sectional view of the LED print head in the sub-scanning direction, and FIG. 3C is a main scanning direction of the LED print head. FIG.

As shown in FIG. 2, the LED print head (LPH 14) according to the first reference example includes an LED array 52 including a plurality of LEDs 50 and a plurality of hologram elements 54 provided corresponding to each of the plurality of LEDs 50. And a hologram element array 56 provided. In the example illustrated in FIG. 2, the LED array 52 includes six LEDs 50 ₁ to 50 ₆ , and the hologram element array 56 includes six hologram elements 54 _{1 to} 54 ₆ . In addition, when it is not necessary to distinguish each from each other, the LEDs 50 ₁ to 50 ₆ are collectively referred to as “LED 50”, and the hologram elements 54 _{1 to} 54 ₆ are collectively referred to as “hologram element 54”.

  Each of the plurality of LEDs 50 is mounted on a long LED substrate 58 together with a drive circuit (not shown) that drives each of the LEDs 50. As described above, each of the LEDs 50 is arranged along a direction parallel to the axial direction of the photosensitive drum 12. The arrangement direction of the LEDs 50 is the “main scanning direction”. Further, each of the LEDs 50 is arranged so that the interval (light emission point pitch) in the main scanning direction between two adjacent LEDs 50 (light emission points) is a constant interval. Although the sub-scan is performed by the rotation of the photosensitive drum 12, the direction orthogonal to the “main scanning direction” is illustrated as the “sub-scanning direction”.

  The hologram element array 56 is formed in a hologram recording layer 60 formed on the LED substrate 58. As will be described later, the LED substrate 58 and the hologram recording layer 60 do not need to be in close contact with each other. In the example of FIGS. 3B and 3C, the hologram recording layer 60 is separated from the LED substrate 58 by a predetermined height. The holding position is held by a holding member (not shown).

  The hologram recording layer 60 is made of a polymer material capable of permanently recording and holding a hologram. As such a polymer material, a so-called photopolymer can be used. The photopolymer records a hologram by utilizing a refractive index change caused by polymerization of a photopolymerizable monomer. Each of the hologram elements 54 is arranged along the main scanning direction corresponding to each of the LEDs 50 similarly to the LEDs 50. Further, each of the hologram elements 54 is arranged such that the interval between the two hologram elements 54 adjacent to each other in the main scanning direction is the same as the above-described light emitting point pitch.

As shown in FIGS. 3A and 3B, each of the hologram elements 54 is formed in a truncated cone shape that has the surface side of the hologram recording layer 60 as a bottom surface and converges toward the LED 50 side. In this example, a truncated cone-shaped hologram element will be described, but the shape of the hologram element is not limited to this. For example, it may be a shape such as a cone, an elliptical cone, an elliptical truncated cone. The diameter of the truncated cone-shaped hologram element 54 is largest at the bottom surface. The diameter of this circular bottom is defined as “hologram diameter r _H ”. Each of the hologram element 54 has a larger hologram size r _H than the light emitting point pitch. For example, the light emitting point pitch is 30 μm, the hologram diameter r _H is 2 mm, and the hologram thickness h _H is 250 μm. Therefore, as shown in FIGS. 2 and 3C, the two hologram elements 54 adjacent to each other are formed so as to greatly overlap each other.

  Each of the plurality of LEDs 50 is arranged on the LED substrate 58 with the light emitting surface facing the surface side of the hologram recording layer 60 so as to emit light toward the corresponding hologram element 54 side. The “light emission optical axis” of the LED 50 passes through the vicinity of the center (symmetric axis of the truncated cone) of the corresponding hologram element 54 and faces the direction orthogonal to the LED substrate 58. As shown in the figure, the light emission optical axis is orthogonal to each of the main scanning direction and the sub-scanning direction.

  The LED array 52 is preferably an SLED array in which a plurality of SLED chips (not shown) in which a plurality of self-scanning LEDs (SLEDs) are arranged are arranged in series. . In the SLED array, the switch is turned on / off by two signal lines, and each SLED can be made to emit light selectively, so that the data line can be shared. By using this SLED array, the number of wires on the LED substrate 58 can be reduced.

  Although not shown, the LPH 14 is held by a holding member such as a housing or a holder so that the diffracted light generated by the hologram element 54 is emitted in the direction of the photosensitive drum 12, and the image forming unit 11. It is attached at a predetermined position. The LPH 14 is preferably configured to be movable in the optical axis direction of the diffracted light by an adjusting means such as an adjusting screw (not shown). The image forming position (focal plane) by the hologram element 54 is adjusted by the adjusting means so as to be positioned on the surface of the photosensitive drum 12. In addition, a protective layer is preferably formed on the hologram recording layer 60 with a cover glass, a transparent resin, or the like. The protective layer prevents dust from adhering.

(Operation of LPH)
Next, the operation of the LPH 14 will be briefly described.
First, the principle of recording / reproducing of the hologram element 54 will be briefly described. FIG. 4A is a diagram illustrating a state in which a hologram element is formed on the hologram recording layer. The illustration of the photosensitive drum 12 is omitted, and only the surface 12A, which is an imaging surface, is illustrated. The hologram recording layer 60A is a recording layer before the hologram element 54 is formed. The hologram recording layer 60A is given a reference symbol A to distinguish it from the hologram recording layer 60 on which the hologram element 54 is formed.

As shown in FIG. 4A, coherent light passing through the optical path of the diffracted light imaged on the surface 12A is irradiated to the hologram recording layer 60A as signal light. At the same time, when passing through the holographic recording layer 60A, coherent light through the optical path of the diffused light that spreads from the light emitting point to the desired hologram diameter r _H is applied to the hologram recording layer 60A as reference light. For the irradiation of coherent light, a laser light source such as a semiconductor laser is used.

  The signal light and the reference light are applied to the hologram recording layer 60A from the same side (the side on which the LED substrate 58 is disposed). Interference fringes (intensity distribution) obtained by interference between the signal light and the reference light are recorded over the thickness direction of the hologram recording layer 60A. Thereby, the hologram recording layer 60 in which the transmission type hologram element 54 is formed is obtained. The hologram element 54 is a volume hologram in which the interference fringe intensity distribution is recorded in the surface direction and the thickness direction. By attaching this hologram recording layer 60 onto the LED substrate 58 on which the LED array 52 is mounted, the LPH 14 is produced.

  The hologram recording layer 60A may be formed in contact with the LED 50, or may be separated via an air layer, a transparent resin layer, or the like. When in contact with the LED 50, the hologram element 54 is formed in a conical shape or an elliptical cone shape, and when separated from the LED 50, it is formed in a truncated cone shape (or an elliptical truncated cone shape) as shown in FIG. Is done.

Further, in FIG. 4 (A), the The surface 12A is depicted schematically, the hologram diameter r _H number mm, the working distance L is from a few cm, the surface 12A is in quite distant. For this reason, the hologram element 54 is not formed in a conical shape as illustrated, but is formed in a truncated cone shape as shown in FIG. FIG. 4B is a diagram showing a state where a hologram element is formed as in FIG. Unlike the forming method of FIG. 4A, signal light and reference light are irradiated from the surface side of the hologram recording layer 60A. That is, the hologram is recorded by the phase conjugate wave. This forming method will be described later in detail as a method for manufacturing the LPH 14.

5A and 5B are diagrams showing how diffracted light is generated from the hologram element. As shown in FIG. 5 (A), when emit LED 50, the light emitted from the LED 50, passes through the optical path of the diffused light that spreads from the light emitting point to the hologram diameter _{r H.} Due to the light emission of the LED 50, the situation is almost the same as when the hologram element 54 is irradiated with the reference light.

  As shown in FIG. 5 (B), the same light as the signal light is reproduced from the hologram element 54 and emitted as diffracted light as shown by the solid line by irradiation of the reference light shown by the dotted line. The emitted diffracted light converges and forms an image on the surface 12A of the photosensitive drum 12 with a working distance of several centimeters. A spot 62 is formed on the surface 12A. In particular, the volume hologram has high incident angle selectivity and wavelength selectivity, and the signal light is reproduced with high accuracy, and a fine spot with a clear outline is formed on the surface 12A.

  A phase-type zone plate called volume hologram or kinoform can theoretically obtain 100% diffraction efficiency by design with respect to coherent light of a specific wavelength and a specific incident direction. However, even if such a hologram element is used, especially for an incoherent light source, there is an unavoidable decrease in diffraction efficiency due to the spread of the wavelength distribution and the spread of the emission angle. In addition, it is difficult to achieve 100% diffraction efficiency even for a coherent light source due to variations and fluctuations in the wavelength of the light source and manufacturing variations during the production of the hologram element.

  The 0th-order light component that is not diffracted becomes background noise of the focused spot, and hinders achieving high-contrast imaging performance. In the present embodiment, as shown in FIG. 5B, the light emitted from the LED 50 is irradiated as reference light to the hologram element 54 formed in the hologram recording layer 60. However, a part of the light emitted from the LED 50 is transmitted through the hologram recording layer 60 and diffused without being diffracted by the hologram element 54 (that is, as zero-order light). This zero-order light component is referred to as “transmitted reference light”.

  FIG. 7 is a cross-sectional view showing an example of the positional relationship between the LED print head and the photosensitive drum. The optical axis of the diffracted light imaged on the surface 12A of the photosensitive drum 12 is made to coincide with the optical axis of the signal light so that the optical axis of the signal light and the optical axis of the reference light intersect at a predetermined angle θ. When the hologram element 54 is recorded by causing the signal light and the reference light to interfere with each other, diffracted light is emitted in a direction that forms an angle θ with the light emitting optical axis.

As described above, the light emitted from the LED 50, passes through the optical path of the diffused light that spreads from the light emitting point to the hologram diameter r _H. In the present embodiment, the angle θ formed by the light emitting optical axis and the diffracted light optical axis is set so that the photosensitive drum 12 is positioned outside the optical path of the diffused light. Therefore, the transmitted reference light is not irradiated as background light to the photosensitive drum 12 positioned outside the optical path of the diffused light.

  In other words, the hologram element 54 emits diffracted light to the outside of the transmission region of the transmitted reference light, so that the 0th-order light component (transmitted reference light) is not included in the diffracted light. As a result, the background noise due to the 0th-order light is reduced, and a high-contrast spot is formed. Further, a light shielding film 68 such as a light absorbing film is preferably disposed on the diffused light transmitting side of the hologram recording layer 60 in order to prevent the generation of stray light. The light shielding film 68 is disposed on the optical path of the diffused light that has been transmitted.

Similarly, as shown in FIG. 2, in the LPH 14 including the LED array 52 and the hologram element array 56, each light emitted from each of the _six LEDs 50 ₁ to 50 ₆ corresponds to the corresponding hologram elements 54 ₁ to 54. 54 ₆ incident on either. The hologram elements 54 _{1 to} 54 ₆ diffract the incident light to generate diffracted light. Each diffracted light generated by each of the hologram elements 54 _{1 to} 54 ₆ is emitted in a direction in which the optical axis forms an angle θ with the emission optical axis, avoiding the optical path of the diffused light, and in the direction of the photosensitive drum 12. Focused.

Each of the emitted diffracted lights converges in the direction of the photosensitive drum 12 and forms an image on the surface of the photosensitive drum 12 disposed on the focal plane several cm ahead. That is, each of the plurality of hologram elements 54 functions as an optical member that diffracts and collects light emitted from the corresponding LED 50 and forms an image on the surface of the photosensitive drum 12. On the surface of the photosensitive drum 12, minute spots 62 _{1 to} 62 ₆ due to the diffracted lights are formed so as to be arranged in a line in the main scanning direction. In other words, the photosensitive drum 12 is main-scanned by the LPH 14. In addition, when it is not necessary to distinguish each, the spots 62 _{1 to} 62 ₆ are collectively referred to as “spots 62”.

(Size of each element of LPH)
In FIG. 2, an example in which six LEDs 50 ₁ to 50 ₆ are roughly arranged in one row is illustrated. However, several thousand LEDs 50 are arranged in accordance with the resolution in the main scanning direction of the image forming apparatus. ing. For example, taking an SLED array as an example, 58 SLED chips in which 128 LEDs are arranged at an interval of 1200 spi (spots per inch) are arranged in series to constitute an SLED array. In terms of conversion, in an image forming apparatus having a resolution of 1200 dpi, 7424 SLEDs are arranged at an interval of 21 μm.

When a spot is formed by condensing light from a condenser lens, the limit of spot miniaturization is determined based on the light diffraction phenomenon. The spot formed by the condenser lens is called an Airy disk from the following relational expression. The diameter (spot size) φ of the Airy disk is expressed as φ = 1.22λ / NA (= 2.44λF) using the wavelength λ and the numerical aperture NA of the condenser lens. Accordingly, when the working distance (≈focal length) is f, f = r _H φ / 2.44λ.

NA = sin θ = r _H / 2f
F (F number) = f / r _H
f: Focal length f = r _H φ / 2.44λ

  In LPH using a conventional hologram element array, each of the plurality of hologram elements is arranged so that the pitch interval of the LEDs (light emitting point) does not overlap each other as in the case where a plurality of lenses are arranged corresponding to each LED. (Pitch) It is made with the following diameter. The light emitting point pitch is approximately the same length as the interval (pixel pitch) of the minute spots formed on the photosensitive drum, and is several tens of μm. With a hologram element having a diameter of several tens of μm, a working distance of the order of several mm can be obtained due to the spread of the beam by diffraction (diffraction limit), similar to a rod lens. On the other hand, in the present embodiment, the working distance of the order of cm is realized by making the diameter of the hologram element larger than the light emitting point pitch.

For example, conventionally, when the diameter of the hologram element and less emission point pitch, the 1200dpi resolution must be less than about 20μm hologram size r _H. At this time, assuming that the wavelength is 780 nm, the working distance is limited to 420 μm at most even if the spot size φ is allowed to about 40 μm. Thus, in the prior art, the working distance cannot be increased to the cm order.

On the other hand, when the diameter of the hologram element is made larger than the light emitting point pitch as in the present embodiment, the working distance becomes longer to the order of cm. For example, when the diameter of the hologram element 54 functioning as a condensing lens (hologram diameter r _H ) is 1 mm or more, the working distance is 1 cm or more. For example, as will be described later, a spot size φ of about 40 μm (half-value width of about 30 μm) is realized at a working distance of 4 cm at a hologram diameter r _H = 2 mm and hologram thickness h _H = 250 μm.

  As described above, the diameter of the hologram element may be 1 mm or more. Further, when the diameter of the hologram element exceeds 10 mm, the multiplicity of the hologram element becomes extremely high, which causes a problem that the diffraction efficiency limited by the dynamic range of the material is lowered. Therefore, the diameter of the hologram element may be 10 mm or less.

(LPH production method)
Next, the manufacturing method of LPH14 is demonstrated. 6A to 6E are process diagrams showing the manufacturing process of the LED print head. The outline is as described as the principle of recording / reproducing of the hologram element 54. Here, since the sectional view in the sub-scanning direction is illustrated, only one LED 50 and one hologram element 54 are illustrated, but the manufacturing process of the LPH 14 including the LED array 52 and the hologram element array 56 will be described.

  First, as shown in FIG. 6A, an LED array 52 in which a plurality of LEDs 50 are mounted on an LED substrate 58 is prepared. A bank portion 64 for damming the photopolymer is formed in a frame shape around the surface of the LED substrate 58. The bank portion 64 is formed, for example, by applying a curable polymer with substantially the same thickness as the hologram recording layer 60 and then curing it by heating or light irradiation. For example, when recording a thin volume hologram, the hologram recording layer 60 has a thickness of about several hundred μm, and similarly, a bank portion 64 having a thickness of several hundred μm is formed. In the case of recording a thick volume hologram, the hologram recording layer 60 has a thickness in the range of 1 mm to 10 mm, and similarly, a bank portion 64 having a thickness of 1 mm to 10 mm is formed.

  Next, as shown in FIG. 6 (B), a photopolymer is poured from a dispenser onto the LED substrate 58 having a frame-shaped bank portion 64 formed on the peripheral portion so as not to overflow from the bank portion 64, and hologram recording is performed. Layer 60A is formed. Next, a protective layer 66 is formed on the hologram recording layer 60A by attaching a thin plate-like cover glass transparent to the recording light and reproducing light on the surface of the hologram recording layer 60A. Thereafter, a chip alignment inspection is performed, and the positions of the plurality of LEDs 50 that are light emitting points are measured.

Next, as shown in FIG. 6C, the hologram recording layer 60A made of a photopolymer is simultaneously irradiated with signal light and reference light from the protective layer 66 side, so that the hologram recording layer 60A has a plurality of hologram elements 54. Form. Laser light that passes through the optical path of desired diffracted light in the opposite direction is irradiated as signal light. Further, when passing through the holographic recording layer 60A, the laser light passing through the optical path of the convergent light converging to the light emitting point from the desired hologram diameter r _H, irradiated as the reference light. That is, as shown in FIG. 4B, a hologram is recorded with a phase conjugate wave. As the laser light for signal light and reference light, for example, laser light having a wavelength of 780 nm oscillated from a semiconductor laser is used.

First, from the measurement data obtained by the above chip alignment inspection and the design values of the hologram element 54 (hologram diameter r _H , hologram thickness h _H ), the laser beam irradiation position, irradiation angle, spread angle, and convergence angle Etc., signal light and reference light are designed. Here, the optical axis of the diffracted light (reproduced signal light) generated by the hologram element 54 is emitted in a direction that forms an angle θ with the emission optical axis, and is condensed in the direction of the photosensitive drum 12. Signal light is designed. Then, a writing optical system for irradiating the designed signal light and reference light is arranged.

  While the writing optical system is fixedly arranged, the LED substrate 58 on which the hologram recording layer 60A is formed is moved with respect to the signal light and the reference light using a spherical wave that converges as the reference light. The LED substrate 58 is moved at a light emitting point pitch so that the reference light converges sequentially on each of the plurality of LEDs 50. A plurality of hologram elements 54 are multiplexed and recorded on the hologram recording layer 60A by spherical wave shift multiplexing.

  Next, as shown in FIG. 6D, the entire surface of the hologram recording layer 60A is exposed by ultraviolet irradiation to polymerize all of the photopolymerizable monomer. By this fixing process, the refractive index distribution is fixed to the hologram recording layer 60A. For example, the photopolymer is provided as a mixture of a photopolymerizable monomer and another non-polymerizable compound. In this case, when the photopolymer is irradiated with interference fringes, the photopolymerizable monomer is polymerized in the bright portion, and a concentration gradient is generated in the photopolymerizable monomer. As a result, the photopolymerizable monomer diffuses into the bright part, and a refractive index distribution is generated between the bright part and the dark part.

  Next, the entire surface is exposed to polymerize the photopolymerizable monomer remaining in the dark part to complete the polymerization reaction, so that additional writing or erasing cannot be performed. As hologram recording materials, methods based on various recording mechanisms have been proposed. Any material that can record refractive index modulation according to the light intensity distribution may be used in the present invention.

  Finally, as shown in FIG. 6 (E), the plurality of LEDs 50 are caused to emit light sequentially, and it is inspected whether or not desired diffracted light can be obtained by the hologram element 54 formed corresponding to each LED 50. The entire manufacturing process is completed by this inspection process.

  In the above embodiment, the example in which the LED 50 and the hologram recording layer 60A are in contact with each other has been described. However, the hologram recording layer 60A may be formed separately from the LED 50 through an air layer, a transparent resin layer, or the like. At this time, a sheet made of a hologram recording layer sandwiched between protective layers may be separately prepared and placed on the light emitting element array.

(First embodiment)
FIG. 8 is a schematic perspective view showing an example of the configuration of the LED print head according to the first embodiment. The arrangement of the plurality of LEDs 50 in the LED array 52 and the arrangement of the plurality of hologram elements 54 in the hologram element array 56 are the same as those of the image forming apparatus and the LED print head according to the first reference example, except that the arrangement is changed. Since it is a structure, the same code | symbol is attached | subjected to the same component and description is abbreviate | omitted. Further, the LED substrate 58 and the hologram recording layer 60 are displayed with virtual lines.

As shown in FIG. 8, the LPH 14 </ b> A according to the first embodiment is similar to the LPH according to the first reference example, and includes an LED array 52 including a plurality of LEDs 50 and a plurality of LEDs 50 corresponding to each of the plurality of LEDs 50. And a hologram element array 56 including a hologram element 54. In this example, the LED array 52 includes six LEDs 50 ₁ to 50 ₆ , and the hologram element array 56 includes six hologram elements 54 _{1 to} 54 ₆ .

Each of the plurality of LEDs 50 is arranged in a staggered pattern along the main scanning direction. In this example, three LEDs 50 ₁ , LED 50 ₃ and LED 50 ₅ are arranged on a first straight line parallel to the main scanning direction, and three LEDs 50 ₂ , LED 50 ₄ and LED 50 ₆ are parallel to the main scanning direction. Are arranged on a second straight line. The first straight line and the second straight line are spaced apart at a constant interval in the sub-scanning direction. The interval between the first straight line and the second straight line is substantially the same as the light emitting point pitch. In other words, all the LEDs 50 (six LEDs 50 ₁ to 50 ₆ ) constituting the LED array 52 are arranged so as to be shifted in the sub-scanning direction so as not to be positioned on a straight line.

Further, each of the LEDs 50 is arranged so that the interval (light emission point pitch) in the main scanning direction between two adjacent LEDs 50 (light emission points) is a constant interval. For example, the distance between the LED 50 ₁ and the LED 50 _{2 in} the main scanning direction is equal to the distance between the LED 50 ₂ and the LED 50 _{3 in} the main scanning direction. By arranging the plurality of LEDs 50 in a staggered manner, the light emitting point pitch is narrowed.

  Each of the hologram elements 54 is arranged in a staggered manner along the main scanning direction like the LED 50 corresponding to each of the LEDs 50. Further, each of the hologram elements 54 is arranged such that the interval between the two hologram elements 54 adjacent to each other in the main scanning direction is the same as the above-described light emitting point pitch.

In the example shown in FIG. 8, the plurality of hologram elements 54 are illustrated so as not to overlap. However, as described above, in order to obtain a working distance on the order of several centimeters, the hologram diameter r _H is set on the order of several millimeters. And shall be. Therefore, when the plurality of LEDs 50 are arranged close to each other, the plurality of hologram elements 54 are formed so that the two hologram elements 54 adjacent to each other overlap each other.

FIGS. 9A and 9B are diagrams showing how diffracted light is generated from the hologram element. When emit LED 50, the light emitted from the LED 50, passes through the optical path of the diffused light that spreads from the light emitting point to the hologram diameter _{r H.} Due to the light emission of the LED 50, the situation is almost the same as when the hologram element 54 is irradiated with the reference light. By irradiation with the reference light, the same light as the signal light is reproduced from the hologram element 54 and emitted as diffracted light. The emitted diffracted light converges and forms an image on the surface 12A of the photosensitive drum 12 with a working distance of several centimeters. A spot 62 is formed on the surface 12A.

The second straight line is spaced from the first straight line at a constant interval in the sub-scanning direction. As shown in FIG. 9A, each of the light emitted from the _three LEDs 50 ₁ , LED 50 ₃ , and LED 50 ₅ arranged on the first straight line corresponds to the corresponding hologram element 54 ₁ , hologram element 54 ₃ , by the hologram element 54 ₅ is diffracted in the direction forming an emitting optical axis angle theta _1. Further, as shown in FIG. 9B, each light emitted from the three LEDs 50 ₂ , LED 50 ₄ , and LED 50 ₆ arranged on the second straight line corresponds to the corresponding hologram element 54 ₂ and hologram element 54. _4, the hologram element 54 _6, is diffracted in the direction forming an emitting optical axis angle theta _2.

In FIGS. 9A and 9B, “LED50 ₁ ” is illustrated as an LED arranged on the first straight line, and “LED50 ₂ ” is illustrated as an LED arranged on the second straight line. . As in the first reference example, the photosensitive drum 12 is, LED 50 to be positioned outside of the optical path from the (light emission point) diffuse light spreads to the hologram diameter r _H, emitting optical axis and the diffracted light optical axis The formed angle θ ₁ and angle θ ₂ are set. The diffused light is not irradiated on the photosensitive drum 12 as background light.

Each of the emitted diffracted lights converges in the direction of the photosensitive drum 12 and forms an image on the surface of the photosensitive drum 12 disposed on the focal plane several cm ahead. On the surface 12A of the photosensitive drum 12, the hologram element 54 _1, the hologram element 54 _3, by the hologram element 54 ₅ spot 62 _1, spot 62 _3, spots 62 ₅ is formed. Further, a spot 62 ₂ , a spot 62 ₄ , and a spot 62 ₆ are formed by the hologram element 54 ₂ , the hologram element 54 ₄ , and the hologram element 54 ₆ .

As shown in FIG. 8, the spots 62 _{1 to} 62 _{6 formed} by the diffracted lights are formed so as to be arranged in a line in the main scanning direction. As shown in FIGS. 9A and 9B, the plurality of LEDs 50 are arranged in a staggered manner and distributed in the sub-scanning direction. Depending on the position in the sub-scanning direction (that is, depending on whether it is on the first straight line or the second straight line), the angle θ ₁ that determines the diffraction direction so as to be arranged in a line in the main scanning direction , The angle θ ₂ is set. Angle theta _1, the angle theta ₂ are appropriately set, without each of the plurality of LED arranged in a zigzag shape to emit light at different timings, formed in a line spot 62 _{1-62 6} in the main scanning direction Is done.

In other words, all the LEDs 50 ₁ to 50 ₆ constituting the LED array 52 are shifted in the sub-scanning direction so as not to be positioned on a straight line. For example, the three LEDs 50 ₁ , LED 50 _2, and LED 50 ₃ are not positioned on a straight line. If the LED array 52 includes only two LEDs 50 in total, the two LEDs 50 are positioned on a straight line, so the LED array 52 of the present embodiment includes three or more LEDs 50. Shall be included.

On the other hand, six hologram elements 54 _{1 to} 54 ₆ are provided corresponding to each of the LEDs 50 ₁ to 50 ₆ . Spots 62 _{1 to} 62 ₆ diffracted and condensed by the _six hologram elements 54 _{1 to} 54 ₆ and formed on the surface 12 A of the photosensitive drum 12 are positioned on a substantially straight line.

  Here, “located on substantially a straight line” means including the case of being positioned on a straight line within a range of design errors. In the above description, the example in which the plurality of LEDs 50 are arranged in a staggered manner has been described. However, even if the plurality of LEDs 50 are arranged at random, the spot 62 is arranged so as to be positioned on a substantially straight line. The hologram element 54 may be designed as appropriate.

(Second Embodiment)
FIG. 10 is a schematic perspective view showing an example of the configuration of the LED print head according to the second embodiment. Except that the plurality of LEDs 50 in the LED array 52 are arranged in a zigzag pattern on a chip basis, the configuration is the same as the configuration of the above-described image forming apparatus and the LED print head according to the first reference example. The description is omitted. Further, the LED substrate 58 (LED chip 58 ₁ and LED chip 58 ₂ described later) and the hologram recording layer 60 are displayed by virtual lines.

  As described above, as the LED array 52, an SLED array configured by arranging a plurality of SLED chips in which a plurality of SLEDs are arranged in series can be used. Thus, when arranging a plurality of chips on which a plurality of LEDs are arranged, the plurality of LEDs may be arranged in a zigzag pattern on a chip basis.

As shown in FIG. 10, the LPH 14B according to the second embodiment includes three LED 50 ₁ , LED 50 ₂ and LED 50 ₃ mounted on a long LED substrate, and three LED chips 58 _1. LED 50 _4, the LED 50 ₅ and LED 50 ₆ LED chip 58 ₂ mounted on the elongated LED substrate, and a. The LED chip 58 ₁ and the LED chip 58 _2, while being positioned so as to align in the main scanning direction, are arranged offset regular intervals in the sub-scanning direction.

Also it is divided into a LED chip 58 ₁ and the LED chip 58 _2, each of the plurality of LED 50, the main scanning direction between two adjacent LED 50 (light emitting point) (light emission point pitch) with each other, and a predetermined distance It is arranged to be. For example, the distance between the LED 50 ₂ and LED 50 ₃ in the main scanning direction is equal to the LED 50 ₃ and LED 50 main scanning direction of the spacing of _4.

Three LEDs 50 ₁ , LED 50 _2, and LED 50 ₃ are arranged on a first straight line along the main scanning direction to constitute an LED array 52 ₁ . Further, three LED 50 _4, LED 50 ₅ and LED 50 ₆ are arranged in a second straight line along the main scanning direction, LED array 52 ₂ is formed. The first straight line and the second straight line are spaced apart at a constant interval in the sub-scanning direction. The interval between the first straight line and the second straight line is substantially the same as the light emitting point pitch.

So as to cover the LED chip 58 ₁ and the LED chip 58 ₂ above, on the LED chip 58 ₁ and the LED chip 58 _2, the hologram recording layer 60 is formed. In the hologram recording layer 60, a plurality of hologram elements 54 are formed along the main scanning direction corresponding to each of the plurality of LEDs 50. Each of the hologram elements 54 is arranged such that an interval in the main scanning direction between two hologram elements 54 adjacent to each other is the same as the above-described light emitting point pitch.

Specifically, in response to each of the three LED50 LED chips 58 _1, three hologram elements 54 _1, the hologram element 54 ₂ and the hologram element 54 ₃ is formed. Further, in correspondence to each of the three LED50 LED chips 58 _2, three hologram elements 54 _1, the hologram element 54 ₂ and the hologram element 54 ₃ is formed. In the example shown in FIG. 10, the hologram elements 54 are illustrated so as not to overlap. However, as described above, the plurality of hologram elements 54 are formed so that the two hologram elements 54 adjacent to each other overlap each other.

Similarly to the example shown in FIGS. 9A and 9B, the light emitted from the LED 50 on the first straight line is diffracted in a direction that forms an angle θ ₁ with the light emission optical axis, and the second straight line is obtained. The light emitted from the LED 50 located above is diffracted in a direction that forms an angle θ ₂ with the light emitting optical axis. As in the first reference example, the photosensitive drum 12 is, LED 50 to be positioned outside of the optical path from the (light emission point) diffuse light spreads to the hologram diameter r _H, emitting optical axis and the diffracted light optical axis An angle θ ₁ and an angle θ _{2 formed} are set. For this reason, the diffused light (0th-order light) is not irradiated on the photosensitive drum 12 as background light.

In the present embodiment, each of the light emitted from the _three LEDs 50 ₁ , LED 50 ₂ , and LED 50 ₃ arranged on the first straight line corresponds to the corresponding hologram element 54 ₁ , hologram element 54 ₂ , hologram element 54 _3. Thus, the light is diffracted in a direction that forms an angle θ ₁ with the emission optical axis. Each light emitted from the three LEDs 50 ₄ , LED 50 ₅ , and LED 50 ₆ arranged on the second straight line is emitted by the corresponding hologram element 54 ₄ , hologram element 54 ₅ , and hologram element 54 _6. Diffracted in a direction that forms an angle θ ₂ with the axis.

As shown in FIG. 10, each of the emitted diffracted lights converges in the direction of the photosensitive drum 12 and forms an image on the surface of the photosensitive drum 12 disposed on the focal plane several cm ahead. On the surface 12 </ b> A of the photosensitive drum 12, spots 62 _{1 to} 62 ₆ are formed so as to be arranged in a line in the main scanning direction corresponding to the hologram elements 54 _{1 to} 54 ₆ . The plurality of LED chips 58 ₁ and 58 ₂ are arranged in a staggered manner, and the plurality of LEDs 50 are distributed in the sub-scanning direction. By appropriately setting the angles θ ₁ and θ ₂ according to the position of the LED 50 in the sub-scanning direction, it is not necessary to cause each of the plurality of LEDs to emit light at different timings for each of the LED chips arranged in a staggered pattern. spot ₆₂ 1-62 ₆ is formed in a line in the main scanning direction.

In the example shown in FIG. 10, an example is shown in which two LED chips 58 ₁ and 58 ₂ each mounting three LEDs 50 are arranged in a staggered manner, but LED chips 58 mounting more LEDs 50 are illustrated. More LED chips 58 may be arranged in a staggered manner.

FIG. 11 is a schematic perspective view showing an example of the configuration of an LED print head according to a modification of the second embodiment. For example, as shown in FIG. 11, the LPH 14 </ b> C according to the modification includes four LED chips 58 ₁ , 58 ₂ , 58 ₃ , and 58 ₄ each having three LEDs 50 mounted thereon. Even if four LED chips are arranged in a staggered manner so that the LED chips 58 ₁ and 58 ₃ are arranged on the first straight line and the LED chips 58 ₃ and 58 ₄ are arranged on the second straight line, Good.

<LPH-Second Reference Example->
FIG. 12 is a schematic perspective view showing an example of the configuration of the LED print head according to the second reference example. FIG. 13 is a cross-sectional view of the LED print head in the sub-scanning direction. Since the LED print head has the same configuration as that of the above-described image forming apparatus and the LED print head according to the first reference example except that a light-blocking body that blocks 0th-order light due to Lambertian orientation is provided on the LED print head, Are denoted by the same reference numerals and description thereof is omitted. In FIG. 12, the illustration of the surface 12A of the photosensitive drum 12 is omitted, and the LED substrate 58 and the hologram recording layer 60 are indicated by virtual lines.

  As shown in FIG. 12, the LPH 14D according to the second reference example includes an LED array 52 including a plurality of LEDs 50 and a plurality of hologram elements 54 corresponding to each of the plurality of LEDs 50, as in the first reference example. And a hologram element array 56. The LED array 52 is mounted on the LED substrate 58, and the hologram element array 56 is formed on the hologram recording layer 60.

On the surface of the hologram recording layer 60, a long light shielding body 70 extending in the main scanning direction is provided. The long light-shielding body 70 is disposed adjacent to the photosensitive drum 12 side with respect to the surface where the optical path of the diffracted light (reproduced signal light) by the hologram element 54 intersects the surface of the hologram recording layer 60. ing. That is, the light shield 70 is disposed avoiding the optical path of diffused light (reference light) extending from the light emitting point to the hologram diameter r _H and the optical path of diffracted light (signal light) by the hologram element 54.

As in the first reference example, the LED array 52 includes six LEDs 50 ₁ to 50 ₆ . The six LEDs 50 ₁ to 50 ₆ are arranged in a line at regular intervals (light emitting point pitch) along the main scanning direction. Similarly to the first embodiment, the hologram element array 56 includes six hologram elements 54 _{1 to} 54 ₆ . The six hologram elements 54 _{1 to} 54 ₆ are arranged in a line at regular intervals (the same pitch as the light emitting point pitch) along the main scanning direction.

As shown in FIG. 14, it is known that the emitted light 72 emitted from the LED 50 that is an incoherent light source diverges and spreads. This phenomenon is called “Lambertian light distribution”. The same phenomenon is observed in the electroluminescent element (EL) which is also an incoherent light source. Among the emitted light 72, only light passing through the optical path of the diffused light that spreads from the light emitting point to the hologram diameter r _H (indicated by solid line) is irradiated as the reference light to the hologram element 54, diffracted light is reproduced. The other emitted light 72 diffuses as “stray light”. Note that the zero-order light (transmission reference light) that has passed through the hologram recording layer 60 is not irradiated onto the photosensitive drum 12 in the same manner as in the first embodiment.

  As shown in FIG. 13, when the LED 50 is caused to emit light, the situation becomes almost the same as that when the hologram element 54 is irradiated with the reference light, and the same light as the signal light is reproduced from the hologram element 54 and emitted as diffracted light. The emitted diffracted light converges and forms an image on the surface 12A of the photosensitive drum 12 with a working distance of several centimeters. A spot 62 is formed on the surface 12A. The light shielding body 70 blocks light other than the diffracted light by the hologram element array 56 and prevents stray light from being applied to the photosensitive drum 12.

(Third embodiment)
FIG. 15 is a schematic perspective view showing an example of the configuration of the LED print head according to the third embodiment. The configuration is the same as the configuration of the image forming apparatus and the LED print head according to the second embodiment except that the LED print head is provided with a light blocking body that blocks light other than the diffracted light by the hologram element 54. Parts are denoted by the same reference numerals and description thereof is omitted. In FIG. 15, the illustration of the surface 12A of the photosensitive drum 12 is omitted, and the LED substrate 58 and the hologram recording layer 60 are indicated by virtual lines.

As shown in FIG. 15, LPH14E according to the third embodiment, as in the second embodiment, the LED chip 58 ₁ in which a plurality of LED50 is mounted on an elongated LED substrate, a plurality LED50 is provided with a LED chip 58 ₂ mounted on elongated LED substrate of. On the LED chip 58 ₁ and the LED chip 58 _2, the hologram recording layer 60 is formed. A hologram element array 56 including a plurality of hologram elements 54 corresponding to the plurality of LEDs 50 is formed on the hologram recording layer 60.

On the surface of the hologram recording layer 60, a long light shielding body 70 extending in the main scanning direction is provided. The LED chip 58 ₁ and the LED chip 58 ₂ are staggered a predetermined interval in the sub-scanning direction, the diffraction light corresponding to the LED chips 58 _1, and the diffracted light corresponding to the LED chip 58 _2, different positions From different angles. Thus, the elongated light shield 70, a narrow width at a portion corresponding to the LED chips 58 _1, and is formed with a wide width at the portion corresponding to the LED chip 58 _2. The light blocking body 70 blocks light other than the diffracted light by the hologram element array 56 and prevents the photosensitive drum 12 from being irradiated with stray light.

  In the third embodiment, the example in which the light shielding body 70 is provided on the surface of the hologram recording layer 60 has been described. However, the shape and arrangement of the light shielding body 70 are not limited to this. The light shielding body 70 only needs to play a role of blocking light other than the diffracted light by the hologram element array 56 and preventing the other emitted light 72 diffused as stray light from being irradiated to the photosensitive drum 12. The modified example is assumed.

  As shown in FIG. 16, the light shield 70 may be disposed above the hologram recording layer 60 so as to be separated from the surface of the hologram recording layer 60. For example, the long light shielding body 70 is held at a predetermined position above the hologram recording layer 60 by a holding member (not shown).

  As shown in FIG. 17, the light shielding body 70 may be embedded in the hologram recording layer 60 and disposed inside the hologram recording layer 60. For example, when the hologram recording layer 60A is formed (see FIG. 6B), the light shield 70 is embedded in advance so as to avoid the optical paths of the signal light and the reference light. Alternatively, as shown in FIG. 18, the light shield 70 may be disposed on the surface of the LED substrate 58 (that is, between the LED substrate 58 and the hologram recording layer 60). For example, the long light-shielding body 70 is previously formed on the surface of the LED substrate 58 while avoiding the optical paths of the signal light and the reference light before forming the hologram recording layer 60A.

  As shown in FIGS. 19 and 20, the light shielding body 70 may be formed as a light shielding layer continuous from the front surface to the back surface of the hologram recording layer 60. That is, a part of the hologram recording layer 60 is replaced with a light shield. In the example shown in FIG. 19, the inclined surface 70 </ b> A on the sub-scanning direction side of the light shield 70 is in contact with the optical path of the reference light on the front surface and the back surface of the hologram recording layer 60. In the example shown in FIG. 20, the side surface 70 </ b> B on the sub-scanning direction side of the light shield 70 is perpendicular to the surface of the LED substrate 58 and is in contact with the optical path of the reference light on the surface of the hologram recording layer 60. For example, these light shields 70 are formed in advance on the LED substrate 58 before the hologram recording layer 60A is formed. Alternatively, after the hologram recording layer 60A or the hologram recording layer 60 is formed, it is formed by coloring with a black pigment.

  Further, as shown in FIG. 21, a support 72 is inserted between the LED substrate 58 and the hologram recording layer 60, the LED substrate 58 and the hologram recording layer 60 are separated from each other, and the light shielding body 70 is connected to the hologram recording layer. You may arrange | position on the back surface of 60. As shown in FIG. 22, the light shielding body 70 may be disposed on the surface of the hologram recording layer 60 after the LED substrate 58 and the hologram recording layer 60 are separated from each other. For example, the long light shielding body 70 is formed on the front surface or the back surface of the hologram recording layer 60 after forming the hologram recording layer 60 separately from the LED substrate 58.

  Further, as shown in FIG. 23, a light shielding body 70 may be inserted between the LED substrate 58 and the hologram recording layer 60 to separate the LED substrate 58 and the hologram recording layer 60 from each other.

  In addition, in said embodiment, although the LED print head provided with several LED was demonstrated, it replaced with LED and other light emitting elements, such as EL, may be used. LD that emits coherent light even when an LED or EL that emits incoherent light is used as a light emitting element by designing a hologram element according to the characteristics of the light emitting element and preventing unnecessary exposure by incoherent light. As in the case of using as a light emitting element, a fine spot with a clear outline is formed.

  In the above-described embodiment, an example in which a plurality of hologram elements are multiplexed and recorded by spherical wave shift multiplexing has been described. However, as long as a multiplexing system capable of obtaining desired diffracted light is used, a plurality of hologram elements can be obtained by other multiplexing systems. May be recorded multiple times. A plurality of types of multiplexing methods may be used in combination. Other multiplexing methods include angle multiplex recording for recording while changing the incident angle of the reference light, wavelength multiplex recording for recording while changing the wavelength of the reference light, and phase multiplex recording for recording while changing the phase of the reference light. . If multiple recording is possible, separate diffracted light is reproduced without crosstalk from a plurality of holograms recorded in multiple recording.

  In the above embodiment, the image forming apparatus is a tandem type digital color printer, and the LED print head as an exposure apparatus that exposes the photosensitive drum of each image forming unit has been described. Any image forming apparatus capable of forming an image by performing imagewise exposure on a photographic image recording medium is not limited to the above embodiment. For example, the image forming apparatus is not limited to an electrophotographic digital color printer. The exposure apparatus of the present invention may be mounted on a writing apparatus such as a silver salt type image forming apparatus or optical writing type electronic paper. The photosensitive image recording medium is not limited to the photosensitive drum. The exposure apparatus of the present invention may also be applied to exposure of sheet-like photoreceptors, photographic photosensitive materials, photoresists, photopolymers, and the like.

2 PC
3 Image Reading Device 10 Image Forming Process Unit 11 Image Forming Unit 12 Photosensitive Drum 12A Surface 13 Charger 14 LED Print Head (LPH)
15 Developing Device 16 Cleaner 21 Intermediate Transfer Belt 22 Primary Transfer Roll 23 Secondary Transfer Roll 24 Conveying Belt 25 Fixing Device 30 Control Unit 40 Image Processing Unit 50 LED
52 LED array 54 Hologram element 56 Hologram element array 58 LED substrate 60 Hologram recording layer 62 Spot 64 Bank 66 Protective layer 70 Light shield 72 Support

Claims (7)

Three or more light emitting elements are arranged on the same substrate, and the light emitting element array is arranged so that all of the three or more light emitting elements are not positioned on a straight line.
Each light emitted from each of the three or more light emitting elements corresponds to a position corresponding to each of the three or more light emitting elements in a single hologram recording layer laminated adjacently on the substrate. A hologram element array in which a plurality of hologram elements are formed so that the hologram elements are irradiated and condensed on a substantially straight line;
An exposure apparatus comprising: The three or more light emitting elements are arranged at predetermined intervals in the length direction of the substrate,
The plurality of hologram elements are formed such that a diameter in a length direction of the substrate is larger than the predetermined interval and overlaps each other.
The exposure apparatus according to claim 1. The plurality of hologram elements are formed in such a manner that a plurality of condensing points formed on the imaging surface by collecting each light are arranged in a predetermined direction.
The exposure apparatus according to claim 1 or 2.   4. The exposure apparatus according to claim 1, wherein each of the plurality of condensing points is located outside an irradiation region of each light emitted from each of the corresponding light emitting elements. 5.   The exposure apparatus according to claim 1, wherein each of the three or more light emitting elements is a non-coherent light source.   6. The light-blocking body according to claim 1, further comprising: a light-blocking body that blocks light that passes through the outside of the plurality of hologram elements among the light emitted from each of the three or more light-emitting elements. The exposure apparatus described in 1. An exposure apparatus according to any one of claims 1 to 5,
A photosensitive image recording medium on which an image is recorded by imagewise exposure by the exposure apparatus;
Moving means for moving the image recording medium relative to the exposure apparatus;
Based on the image data, the moving means is controlled so that the image recording medium is sub-scanned in a direction intersecting the length direction of the substrate, and lighting control of each of the three or more light emitting elements is performed. Means,
An image forming apparatus.