JP2012040749A - Condensing element, condensing element array, exposure device, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a condensing element capable of improving the light utilization efficiency by forming a large hologram element irrespective of a spreading angle of reference light, when condensing light on the surface to be exposed by diffracting the read-out light emitted from a light-emitting element, and also capable of extending an operating distance; to provide a condensing element array; and to provide an exposure device and image forming apparatus.SOLUTION: The exposure device includes: the light-emitting element array arranged so that a plurality of light-emitting elements are arranged in a predetermined direction; an optical path changing unit for changing the optical path of each light emitted respectively from the plurality of light-emitting elements; and a hologram recording layer, which is arranged on the optical path changed, records the plurality of hologram elements for diffracting each light emitted correspondingly to the plurality of light-emitting elements and for condensing the light on the surface to be exposed that is separated by the predetermined operation distance, and has multiple records of the plurality of hologram elements configured such that a plurality of condensing points formed on the surface to be exposed may be arranged in the predetermined direction.

Description

  The present invention relates to a condensing element, a condensing element array, an exposure apparatus, and an image forming apparatus.

  In Patent Document 1, an image is divided into a large number of minute pixels, a light beam having an intensity corresponding to the density of each pixel is emitted from one or a plurality of light sources, and a bright spot by the light beam is set to a light intensity density equal to or higher than a threshold value. Is exposed to light to form a latent image such as a surface potential change or chemical change, or the image is scanned onto an image recording medium on which an image having a density change is formed by exposure. In the optical writing device for writing an image by sequentially exposing each pixel area, a light focusing element unit for focusing the light beam in order from the light source side between the light source and the image recording medium, and the light beam is focused. A small optical opening provided at a position where the light beam exits, a collimator that converts the light beam emitted from the optical opening portion into a substantially parallel light beam, and radiates the light beam by decomposing it in a plurality of directions and emits a plurality of light beams. Mostly on the same plane A hologram element for the one unit that is arranged, an optical writing device, characterized in that arranged in the pixel as many array in the main scanning direction is described.

  Patent Document 2 discloses a first lens array having a plurality of light-emitting elements arranged on a light source substrate and a plurality of diffractive positive lenses that diffract the transmitted light to converge the light bundle of the light to form an image. And a second lens array having a plurality of lenses and sandwiching the first lens array between each of the plurality of light emitting elements, wherein each of the plurality of diffractive positive lenses is perpendicular to the light source substrate. An exposure apparatus characterized in that it overlaps each of the plurality of light emitting elements in a specific direction is described.

JP 2000-330058 A JP 2007-237576 A

  The object of the present invention is to enable the formation of a large hologram element regardless of the divergence angle of the reference light when the readout light emitted from the light emitting element is diffracted by the hologram element and condensed on the exposed surface. An object of the present invention is to provide a condensing element, a condensing element array, an exposure apparatus, and an image forming apparatus that can improve the efficiency and increase the working distance.

  According to the first aspect of the present invention, a light emitting element that emits light, an optical path changing unit that changes an optical path of light emitted from the light emitting element, an optical path that is arranged on the optical path changed by the optical path changing unit, and irradiation And a hologram recording layer on which a hologram element for diffracting the emitted light and condensing the light onto a surface to be exposed separated by a predetermined working distance is provided.

  A second aspect of the present invention is a condensing element array in which a plurality of the condensing elements according to the first aspect are arranged in a one-dimensional or two-dimensional manner.

  The invention according to claim 3 is a light emitting element array in which a plurality of light emitting elements are arranged in a predetermined direction, and an optical path changing means for changing the optical path of each light emitted from each of the plurality of light emitting elements. And a hologram recording layer disposed on the optical path changed by the optical path changing means, wherein the irradiated light is diffracted corresponding to the plurality of light emitting elements and separated by a predetermined working distance. A hologram recording layer in which a plurality of hologram elements focused on an exposure surface are recorded, and the plurality of hologram elements are multiplexed and recorded such that a plurality of focusing points formed on the exposed surface are aligned in the predetermined direction And an exposure apparatus.

According to a fourth aspect of the present invention, each of the plurality of hologram elements is recorded by interference between signal light reproduced as diffracted light and reference light intersecting with the signal light, and the signal light for the hologram recording layer is recorded. The exposure apparatus according to claim 3, wherein an incident angle θs of the reference light and an incident angle θr of the reference light with respect to the hologram recording layer satisfy the following expression (1).
0 ° <θr + θs ≦ 90 ° (1)

  The invention according to claim 5 is the exposure apparatus according to claim 4, wherein an optical axis of the signal light and an optical axis of the reference light are orthogonal to each other.

  According to a sixth aspect of the present invention, in any one of the third to fifth aspects, the optical path changing means is a reflecting mirror having a flat or curved reflecting surface that reflects the light emitted from the light emitting element. 2. An exposure apparatus according to item 1.

  The invention according to claim 7 is the exposure apparatus according to any one of claims 3 to 6, wherein the optical path changing means and the hologram recording layer are integrally formed.

  According to an eighth aspect of the present invention, there is provided the exposure apparatus according to any one of the third to seventh aspects of the present invention, an exposed surface that is separated from the exposure apparatus by a predetermined working distance, and image data. And a photosensitive image recording medium on which an image is recorded by main scanning in the predetermined direction by the exposure apparatus.

  According to the first aspect of the present invention, when the readout light emitted from the light emitting element is diffracted by the hologram element and condensed on the exposed surface, a large hologram element can be formed regardless of the spread angle of the reference light. As a result, the light utilization efficiency can be improved and the working distance can be increased.

  According to the second aspect of the present invention, even when an array is formed, when the readout light emitted from the light emitting element is diffracted by the hologram element and condensed on the exposed surface, the reference light is large regardless of the spread angle of the reference light. The hologram element can be formed, the light use efficiency can be improved, and the working distance can be increased.

  According to the third aspect of the present invention, when reading light emitted from a plurality of light emitting elements is diffracted by the corresponding hologram element and condensed on the exposed surface, a large hologram is obtained regardless of the spread angle of the reference light. The element can be formed, the light utilization efficiency can be improved, and the working distance can be increased.

  According to the fourth aspect of the invention, the crossing angle between the signal light and the reference light can be increased, and crosstalk can be suppressed by improving the shift selectivity. In addition, the crossing angle between the diffracted light and the transmitted reference light can be increased, and the transmitted reference light that becomes background noise can be easily blocked.

  According to the fifth aspect of the present invention, the crossing angle between the signal light and the reference light can be maximized, the crosstalk can be further suppressed, and the transmitted reference light serving as background noise can be further easily blocked. .

  According to the sixth aspect of the present invention, the optical path can be freely changed with a simple configuration, and the apparatus can be downsized.

  According to the seventh aspect of the present invention, the position of the optical path changing means is fixed, and no subsequent alignment is required.

  According to the eighth aspect of the present invention, when the readout light emitted from the plurality of light emitting elements of the exposure apparatus is diffracted by the corresponding hologram element and condensed on the exposed surface, the reference light is related to the spread angle. Therefore, it is possible to form a large hologram element, improve the light utilization efficiency, increase the working distance, and reduce the size of the image forming apparatus.

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 which concerns on embodiment of this invention. (A) is a perspective view which shows the schematic shape of a hologram element. FIG. 4B is a cross-sectional view of the LED print head in the sub-scanning direction. (C) is a sectional view of the LED print head taken along line AA in the main scanning direction, and (D) is a sectional view of the LED print head taken along line BB in the main scanning direction. (A) And (B) is a figure which shows a mode that a hologram is recorded on a hologram recording layer. It is a figure which shows a mode that a hologram is reproduced | regenerated and a diffracted light is produced | generated. It is a figure which shows a mode that a hologram is recorded on a hologram recording layer in the structure which irradiates the light-emission light of LED directly to a hologram. (A) is a figure which shows a mode that a hologram is recorded when the optical axis of signal light and the optical axis of reference light are not orthogonally crossed. (B) is a diagram showing how the hologram is reproduced and diffracted light is generated when the optical axis of the signal light and the optical axis of the reference light are not orthogonal. It is a figure which shows an example of a structure of LPH in which the optical path change means and the hologram recording layer were integrally formed. (A) is sectional drawing of the subscanning direction which shows an example of a structure of the LED print head which concerns on a modification. (B) is a figure which shows a mode that a hologram is recorded on the hologram recording layer of the LED print head of (A).

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

<Image forming apparatus equipped with LED print head>
First, an image forming apparatus equipped with an LED print head according to an embodiment of the present invention will be described. In copiers, printers, and the like that form images by electrophotography, light-emitting diodes (instead of conventional optical scanning exposure devices (that is, optical scanning writing devices)) are used as exposure devices that write latent images on photosensitive drums. LED type exposure apparatuses using LEDs as light sources are becoming mainstream. The LED type exposure apparatus does not require a scanning optical system, and can be significantly reduced in size as compared with the optical scanning method. In addition, a driving motor for driving the polygon mirror is unnecessary, and there is an advantage that no mechanical noise is generated.

  The LED type exposure apparatus is called an LED print head and is abbreviated as LPH. A conventional 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. In the LED array, for example, 1200 pixels per inch (that is, 1200 dpi (dot per inch)) and a large number of LEDs corresponding to the number of pixels in the main scanning direction are arranged, where “dpi” is 1 inch. Conventionally, a rod lens such as SELFOC (registered trademark) is used for a lens array, and light emitted from each LED is condensed by the rod lens to be a photosensitive drum. An erecting equal-magnification image is formed on the top.

  An LED print head using a “hologram element” instead of a rod lens has been studied. The image forming apparatus according to the present embodiment includes an LED print head including a “hologram element array” described below. In LPH using a rod lens, the optical path length (working distance) from the lens array end face to the image formation point is as short as several millimeters, and the occupation ratio of the exposure device around the photosensitive drum is increased. On the other hand, the LPH 14 provided with the hologram element array has a long working distance of about several centimeters, and the periphery of the photosensitive drum is not crowded, and the image forming apparatus is downsized as a whole.

  In general, in LPH using an LED that emits incoherent light (incoherent light), coherence decreases and spot blurring (so-called chromatic aberration) occurs, and it is not easy to form a minute spot. On the other hand, the LPH 14 provided with the hologram element array has high incident angle selectivity and wavelength selectivity of the hologram element, and a fine spot with a clear outline is formed on the photosensitive drum 12.

  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 of the image forming units 11 includes a photosensitive drum 12 as an image holding body that forms an electrostatic latent image and holds a toner image, and a charger 13 that uniformly charges the surface of the photosensitive drum 12 with a predetermined potential. , An LED print head (LPH) 14 as an exposure device for exposing the photosensitive drum 12 charged by the charger 13, a developing unit 15 for developing the electrostatic latent image obtained by the LPH 14, and the photosensitive drum 12 after transfer. A cleaner 16 for cleaning the surface 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. 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. In the present embodiment, in the LPH 14, a plurality of LEDs are arranged in an array (row shape) along the length direction. A plurality of hologram elements corresponding to the plurality of LEDs are arranged in an array on the LED array.

  As will be described later, the working distance of the LPH 14 provided with the hologram element array is long, and is arranged 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 emitted by the LPH 14 that emits light based on the image data obtained from the image processing unit 40. As a result of exposure, 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.

<LED print head (LPH)>
FIG. 2 is a schematic perspective view showing an example of the configuration of the LED print head according to the embodiment of the present invention. As shown in FIG. 2, the LED print head (LPH 14) includes an LED array 52 having a plurality of LEDs 50 and a hologram element array 56 having a plurality of hologram elements 54 provided corresponding to each of the plurality of LEDs 50. And. 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 arranged on the LED chip 53. The LED chip 53 is mounted on a long LED substrate 58 together with a drive circuit (not shown) that drives each of the LEDs 50. The LED chip 53 is positioned on the LED substrate 58 so that the plurality of LEDs 50 are aligned in the main scanning direction. Accordingly, the LEDs 50 are 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”. In addition, each of the LEDs 50 is arranged so that the interval (LED pitch) in the main scanning direction between two adjacent LEDs 50 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”.

  As the LED array 52, various types of LED arrays such as an LED array in which a plurality of LEDs are mounted on a substrate in units of chips may be used. When arranging a plurality of LED chips 53 in which a plurality of LEDs are arranged, the plurality of LED chips 53 may be arranged in series or in a staggered manner. Two or more may be arranged in the sub-scanning direction. In FIG. 2, the LED array 52 in which a plurality of LEDs 50 are arranged in a one-dimensional manner on one LED chip 53 is only schematically shown.

  The LED array 52 may have a plurality of LED chips 53 arranged in a staggered manner. That is, the plurality of LED chips 53 may be arranged in a line so as to be arranged in the main scanning direction, and may be arranged in two lines with a certain interval shifted in the sub-scanning direction. Even if the LEDs 50 are divided into the plurality of LED chips 53, each of the plurality of LEDs 50 is arranged such that the interval between the two adjacent LEDs 50 in the main scanning direction is a constant interval.

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

  On the LED substrate 58 on which the LED chip 53 is arranged, the optical path changing means 32 and the hologram recording layer 60 are arranged. The optical path changing means 32 is disposed above the LED chip 53. The hologram recording layer 60 is disposed on the light exit side of the optical path changing unit 32. The optical path changing unit 32 bends the optical path of the light emitted from each LED 50 of the LED chip 53 and irradiates the hologram recording layer 60. In FIG. 2, the hologram recording layer 60 is formed so as to be in contact with the LED substrate 58, but the hologram recording layer 60 may be formed away from the LED substrate 58 by a predetermined distance.

  In the present embodiment, the optical path changing means 32 is composed of a long plane mirror whose longitudinal direction is the main scanning direction. The plane mirror which is the optical path changing means 32 is arranged so as to form about 45 ° with the normal direction of the LED substrate 58. As a result, each light emitted from each LED 50 of the LED chip 53 in the normal direction is bent by about 90 ° by the optical path changing means 32 and irradiated onto the hologram recording layer 60 from the side. That is, each light emitted from the plurality of LEDs 50 is reflected by the plane mirror, and each reflected light is applied to the hologram element 54 corresponding to the LED 50.

The hologram element array 56 is formed in a hologram recording layer 60 formed on the LED substrate 58. In the hologram recording layer 60, a plurality of hologram elements LEDs 54 _{1 to} 54 ₆ are formed along the main scanning direction corresponding to the plurality of LEDs 50 ₁ to 50 ₆ . Each of the hologram elements 54 is arranged so that the interval in the main scanning direction between the two hologram elements 54 adjacent to each other is substantially the same as the interval in the main scanning direction of the LED 50 described above. That is, the hologram element 54 having a large diameter is formed so that the two hologram elements 54 adjacent to each other overlap each other. Moreover, the two hologram elements 54 adjacent to each other may have different shapes.

  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 may be used. The photopolymer records a hologram by utilizing a refractive index change caused by polymerization of a photopolymerizable monomer.

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 is bent by the optical path changing means 32. The hologram recording layer 60 is irradiated from the side and enters _{one of the} corresponding hologram elements 54 _{1 to} 54 ₆ . That is, the light emitted from the LED 50 is not directly incident on the hologram element 54 but is incident via the optical path changing means 32. The hologram elements 54 _{1 to} 54 ₆ diffract the incident light to generate diffracted light. In the present embodiment, each diffracted light generated by each of the hologram elements 54 _{1 to} 54 ₆ is emitted so that its optical axis coincides with the normal direction of the LED substrate 58, 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 diffracts and collects the corresponding light emitted from the corresponding LED 50 and whose optical path is bent by the optical path changing means 32, and forms an image on the surface of the photosensitive drum 12. Function as. 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”.

<Shape and arrangement of hologram element>
3A is a perspective view showing a schematic shape of the hologram element, and FIG. 3B is a cross-sectional view of the LED print head in the sub-scanning direction. 3C is a cross-sectional view of the LED print head taken along line AA in the main scanning direction, and FIG. 3D is a cross-sectional view of the LED print head taken along line BB in the main scanning direction.

  As shown in FIG. 3A, each of the hologram elements 54 is a volume hologram generally called a thick hologram. As described above, the hologram element has high incident angle selectivity and wavelength selectivity, and controls the exit angle (diffraction angle) of the diffracted light with high accuracy to form a fine spot with a clear outline. The accuracy of the diffraction angle increases as the thickness of the hologram increases.

As shown in FIGS. 3A to 3C, each of the hologram elements 54 has a cone that converges toward the surface side from which the diffracted light is emitted, with the surface on the LED 50 side of the hologram recording layer 60 as one bottom surface. It is formed in a trapezoid shape. 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 is good also as shapes, such as a cone, an elliptical cone, and an elliptical truncated cone. The diameter of the truncated cone-shaped hologram element 54 is the largest on one bottom surface. The diameter of this circular bottom is defined as “hologram diameter r _H ”.

Each of the hologram elements 54 has a “hologram diameter r _H ” that is larger than the interval of the LEDs 50 in the main scanning direction. For example, the interval in the main scanning direction of the LED 50 is 30 μm, the hologram diameter r _H is 2 mm, and the hologram thickness h _H is 250 μm. By using such a large hologram element 54, a spot size φ of about 40 μm (about 30 μm at half width) is realized at a working distance of about 4 cm. Therefore, the two hologram elements 54 adjacent to each other are formed so as to greatly overlap each other as compared to the illustrated example. The plurality of hologram elements 54 are multiplexed and recorded by, for example, spherical wave shift multiplexing.

  Each of the plurality of LEDs 50 is arranged on the LED substrate 58 with its light emitting surface directed toward the optical path changing means 32 so as to emit light toward the optical path changing means 32 arranged above. The “light emitting optical axis” of the LED 50 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. That is, here, the “light emitting optical axis” is the center line of diffused light emitted from the light emitting region of the LED 50, and coincides with the normal direction of the LED substrate 58 when the LED 50 is regarded as a light emitting point (point light source). To do.

  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 is shown in FIG. It is attached at a predetermined position in the image forming unit 11. The LPH 14 may be configured to move in the optical axis direction of the diffracted light by an adjusting means such as an adjusting screw (not shown). The adjustment means adjusts the image formation position (focal plane) by the hologram element 54 so as to be positioned on the surface of the photosensitive drum 12. Further, a protective layer may be formed on the hologram recording layer 60 with a cover glass or a transparent resin. The protective layer prevents dust from adhering.

<Recording method of hologram>
Next, a hologram recording method will be described. 4A and 4B are views showing a state where the hologram element 54 is formed on the hologram recording layer 60, that is, a state where a hologram is recorded 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. Signal light is a light that passes through the optical path of the diffused light that spreads toward the surface 12A Ueno condensing point on the LED substrate 58, extends to the desired hologram diameter r _H when passing through the holographic recording layer 60A. At the same time, coherent light passing through the optical path of convergent light that converges toward the light emission point that is virtually set 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 reference light is irradiated at an angle at which the overlap with the signal light in the hologram recording layer 60A is the largest. In this example, the optical axis of the signal light coincides with the normal direction of the LED substrate 58, and the optical axis of the reference light is orthogonal to the optical axis of the signal light. Here, the “virtually set light emission point” that is the convergence point of the reference light is a case where it is assumed that the hologram element 54 is directly irradiated with the light emitted from the LED 50 without the optical path changing means 32 at the time of reproducing the hologram. In addition, the LED 50 regarded as a point light source is a position to be disposed.

  The signal light and the reference light are applied to the hologram recording layer 60A from the same side (the side opposite to the side on which the LED substrate 58 is disposed). Thereby, the hologram recording layer 60 in which the transmission type hologram element 54 is formed in the hatched portion is obtained. Here, the “same side” is a reference based on the positional relationship between the hologram recording layer 60 </ b> A and the LED substrate 58. Actually, as shown in FIG. 4A, the signal light is irradiated from above the hologram recording layer 60A, and the reference light is irradiated from the side (left side in the figure) of the hologram recording layer 60A.

  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. 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. The LPH 14 is manufactured by attaching the hologram recording layer 60 and the optical path changing means 32 on the LED substrate 58 on which the LED array 52 is mounted.

  As shown in FIG. 4B, the hologram may be recorded by irradiating the hologram recording layer 60A with the signal light and the reference light from the same side (the side on which the LED substrate 58 is disposed). Actually, the signal light is irradiated from below the hologram recording layer 60A, and the reference light is irradiated from the side (right side in the drawing) of the hologram recording layer 60A. In this case as well, the hologram recording layer 60 in which the transmissive hologram element 54 is formed in the hatched portion is obtained.

<Reproduction method of hologram>
Next, a method for reproducing a hologram will be described. FIG. 5 is a diagram illustrating a state in which diffracted light is generated from the hologram element, that is, a state in which the hologram recorded in the hologram recording layer is reproduced and diffracted light is generated. In the present embodiment, as illustrated by the dotted line, the diffused light emitted from the LED 50 as the readout light is irradiated to the hologram recording layer 60 from the side with the optical path bent by the optical path changing means 32. The light whose optical path is bent passes through the optical path of the reference light that converges toward the virtually set light emitting point. Accordingly, the LED 50 emits light in substantially the same situation as the reference light is applied to the hologram element 54.

As shown in FIG. 5, the same light as the signal light is reproduced from the hologram element 54 and emitted as diffracted light by irradiation with diffused light (that is, reproduction reference light) shown by a dotted line, as shown by a solid 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 FIG. 5, 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.

As shown in FIG. 2, six spots 62 _{1 to} 62 ₆ are formed on the photosensitive drum 12 so as to correspond to the LEDs 50 ₁ to 50 ₆ of the LED array 52 in a line in the main scanning direction. The The six spots 62 _{1 to} 62 ₆ are imaging spots on which the diffracted lights of the hologram elements 54 _{1 to} 54 ₆ are imaged. Volume holograms have high incident angle selectivity and wavelength selectivity, and generally have high diffraction efficiency. For this reason, the signal light is reproduced with higher accuracy, and a fine spot (condensing point) with a sharp outline is formed on the surface 12A.

<Comparison with direct irradiation of reading light to hologram element>
Next, the advantage when the hologram element is irradiated with the readout light via the optical path changing means will be described in comparison with the case where the readout light is directly applied to the hologram element. FIG. 6 is a diagram illustrating a state in which a hologram is recorded on a hologram recording layer in a configuration in which light emitted from an LED is directly irradiated onto the hologram.

As shown in FIG. 6, coherent light passing through the optical path of diffracted light that is imaged on the surface 12A (converged to a condensing point 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. In this example, the optical axis of the reference light coincides with the normal direction of the LED substrate 58, and the optical axis of the signal light intersects with the optical axis of the reference light.

  As described above, when the large hologram element 54 is used, the working distance becomes long. In order to record a large hologram element 54 with the configuration shown in FIG. 5, the divergence angle (numerical aperture: NA) of the reference light may be increased. Further, when the divergence angle of the reference light is increased, the intensity of diffracted light is increased, and the light use efficiency is improved by increasing the light amount. However, when the divergence angle of the reference light is increased, the hologram diameter in the sub-scanning direction is increased, and the width of the LPH in the sub-scanning direction is increased. Further, it becomes difficult to separate the readout light (the light emitted from the LED 50) and the diffracted light during reproduction.

  On the other hand, as shown in FIGS. 4A and 4B, in the LPH 14 of the present embodiment, each light emitted from each of the LEDs 50 is converted into a corresponding hologram element 54 via the optical path changing means 32. It is set as the structure which injects into. In accordance with this configuration, coherent light (signal light) that passes through the optical path of diffracted light imaged on the surface 12A and coherent light that passes through the optical path of convergent light that converges toward the light emission point that is virtually set (see Light) is applied to the hologram recording layer 60A, and the transmissive hologram element 54 is recorded.

  With the above configuration, the LPH 14 of the present embodiment does not necessarily determine the hologram diameter depending on the divergence angle of the reference light, and the degree of freedom in designing the working distance is improved. Further, by increasing the divergence angle of the reference light, the light use efficiency is improved as described above. Further, by increasing the intersection angle between the optical axis of the signal light and the optical axis of the reference light, it becomes easier to separate the readout light and the diffracted light during reproduction.

<Intersection of signal light and reference light>
Next, an aspect of intersection between the signal light and the reference light will be described. In the above description, the optical axis of the signal light coincides with the normal direction of the LED substrate 58, and the optical axis of the reference light is orthogonal to the optical axis of the signal light. However, the intersection of the signal light and the reference light has been described. However, the embodiment is not limited to this. FIG. 7A is a diagram illustrating a state where a hologram is recorded when the optical axis of the signal light and the optical axis of the reference light are not orthogonal to each other. FIG. 7B is a diagram illustrating a state in which the hologram is reproduced and diffracted light is generated when the optical axis of the signal light and the optical axis of the reference light are not orthogonal to each other.

  As shown in FIG. 7A, coherent light passing through the optical path of the diffracted light imaged on the surface 12A is applied to the hologram recording layer 60A as signal light. At the same time, coherent light passing through the optical path of convergent light that converges toward the light emission point that is virtually set is applied to the hologram recording layer 60A as reference light. The signal light and the reference light are irradiated from the same side to the hologram recording layer 60A, and the hologram recording layer 60 in which the transmission type hologram element 54 is formed in the hatched portion is obtained. Note that the hologram element 54 may be formed by phase conjugate recording.

  In the present embodiment, the optical axis of the signal light intersects with the optical axis of the reference light at an angle other than 90 °. Since the transmission hologram is used here, a condition of 0 ° <θr + θs ≦ 90 ° is set between the incident angle θs of the signal light with respect to the hologram recording layer 60A and the incident angle θr of the reference light with respect to the hologram recording layer 60A. It is necessary to satisfy. The crossing angle between the signal light and the reference light may be changed within a range that satisfies this condition. As the crossing angle between the signal light and the reference light increases, the interference fringes between the signal light and the reference light are formed at a shorter pitch, so that the shift selectivity is improved, and as a result, a reduction in crosstalk is achieved.

  As shown in FIG. 7B, the diffused light emitted from the LED 50 as readout light is bent by the optical path changing means 32 and irradiated to the hologram recording layer 60 from an oblique side to be reproduced on the hologram element 54. The situation is almost the same as when the reference light is irradiated. By irradiation with diffused light (reproduction reference light) illustrated by a dotted line, the same light as the signal light is reproduced from the hologram element 54 and emitted as diffracted light, as illustrated by a solid 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 the present embodiment, the interference fringes between the signal light and the reference light are formed at a short pitch, crosstalk is suppressed by improving the shift selectivity, and the transmitted reference light serving as background noise can be easily blocked. When the optical axis of the signal light and the optical axis of the reference light are orthogonal, that is, when the crossing angle between the signal light and the reference light is maximized, the interference fringes between the signal light and the reference light have the shortest pitch. The shift selectivity is maximized and crosstalk is further suppressed (see FIG. 4).

<Modification of LPH (1)>
As described with reference to FIGS. 2 and 3, in the above embodiment, the optical path changing means 32 and the hologram recording layer 60 are configured as LPHs 14 formed of different members, but the configuration of the LPH is limited to this. It doesn't mean. FIG. 8 is a diagram illustrating an example of a configuration of an LPH in which an optical path changing unit and a hologram recording layer are integrally formed. Except for the fact that the optical path changing means and the hologram recording layer are integrally formed and the number of parts is reduced, the configuration is the same as in the above embodiment. Omitted.

  In the LPH 14 </ b> A according to the modification (1), the hologram recording layer 60 </ b> B is disposed on the LED substrate 58. The hologram recording layer 60B is also disposed above the LED chip 53. In the hologram recording layer 60B, the arrangement side of the LED chip 53 is a light incident side (for reading light), and the opposite side is a light emitting side (for diffracted light). The hologram recording layer 60 </ b> B has an inclined surface 60 </ b> C in which one side surface located above the LED chip 53 intersects the normal direction of the LED substrate 58. The inclined surface 60C is a long inclined surface with the main scanning direction as the longitudinal direction, and is formed such that the width of the hologram recording layer 60B in the sub-scanning direction becomes narrower from the light incident side toward the light emitting side.

  A reflective film 32A is formed on the inclined surface 60C of the hologram recording layer 60B. The reflective film 32A is formed, for example, by a method such as vapor deposition of a metal having a high reflectance with respect to the light emitted from the LED 50 on the inclined surface 60C. By integrating the reflective film 32 with the hologram recording layer 60B, compared with the case where the optical path changing means and the hologram recording layer are formed of separate members (see FIGS. 2 and 3), a means for preventing interface reflection is provided. No need to take. In addition, the reflective film 32A formed in advance does not require post hoc alignment.

  The light emitted from each LED 50 of the LED chip 53 is incident from the light incident side surface of the hologram recording layer 60B. The reflective film 32A formed on the inclined surface 60C bends the optical path of each incident light. That is, the reflective film 32 </ b> A functions as an “optical path changing unit” that changes the optical path of each light emitted from each LED 50. Note that when the interface reflection on the inclined surface 60C is used, the formation of the reflective film 32A may be omitted.

  Each light whose optical path is bent is guided through the hologram recording layer 60 </ b> B and irradiated to the hologram element 54 corresponding to each LED 50. Each of the plurality of hologram elements 54 diffracts each light incident from the corresponding LED to generate diffracted light, and emits each diffracted light toward the photosensitive drum 12. On the surface 12A of the photosensitive drum 12, a minute spot 62 is formed by each diffracted light.

  In the present embodiment, the reflective film 32 is formed on an inclined surface 60 </ b> C that forms about 45 ° with the normal direction of the LED substrate 58. Thereby, each light emitted from the plurality of LEDs 50 in the normal direction is propagated from the right side to the left side in the hologram recording layer 60B with the optical path bent by about 90 ° by the reflective film 32A, and the corresponding hologram element 54 is irradiated.

<Modification of LPH (2)>
As described with reference to FIGS. 2 and 3, in the above embodiment, the example in which the optical path changing unit 32 is configured by a plane mirror has been described. However, the optical path changing unit is not limited to the plane mirror. FIG. 9A is a cross-sectional view in the sub-scanning direction showing an example of the configuration of the LPH according to the modification (2). FIG. 9B is a diagram illustrating a state in which a hologram is recorded on the LPH hologram recording layer of FIG. 9A. Since the configuration is substantially the same as that of the above-described embodiment except that a reflecting mirror having a curved reflecting surface is provided as the optical path changing means, the same components are denoted by the same reference numerals and description thereof is omitted.

  In the LPH 14 </ b> B according to the modification (2), the optical path changing unit 32 </ b> B and the hologram recording layer 60 are disposed on the LED substrate 58. The optical path changing means 32B is arranged above the LED chip 53. The hologram recording layer 60 is disposed on the light exit side (that is, the light condensing side) of the optical path changing unit 32B. The light emitted from the optical path changing unit 32B enters from one side surface of the hologram recording layer 60. On the other side surface opposite to one side surface of the hologram recording layer 60, a light absorber 34 that absorbs transmitted reference light is disposed. Note that, similarly to the LPH according to the modification (1), the optical path changing means and the hologram recording layer may be integrally formed.

  In the present embodiment, the optical path changing unit 32B is a long reflecting mirror (for example, an elliptical mirror or a parabolic mirror) whose longitudinal direction is the main scanning direction, and the cross section in the sub-scanning direction is an arc shape. The inside of the curved surface is the reflecting surface. The optical path changing means 32B bends the optical path of the light emitted from each LED 50 and condenses the light in the direction of the changed optical path. The light emitted from each LED 50 is diffused light, and the light utilization efficiency is improved by condensing and irradiating.

  The hologram recording layer 60 is irradiated with the light whose optical path is bent and condensed. That is, the light reflected and condensed by the optical path changing unit 32B is irradiated to the hologram element 54 corresponding to each LED 50. Each of the plurality of hologram elements 54 diffracts each light incident from the corresponding LED to generate diffracted light, and emits each diffracted light toward the photosensitive drum 12. On the surface 12A of the photosensitive drum 12, a minute spot 62 is formed by each diffracted light.

  In the present embodiment, the optical path changing means 32B is a reflecting mirror having a curved reflecting surface. By changing the reflecting mirror in this way, each light emitted from the plurality of LEDs 50 in the normal direction is bent by about 90 ° by the optical path changing means 32B and condensed in the direction of the changed optical path. Then, it propagates in the hologram recording layer 60B from the right side to the left side and is irradiated to the corresponding hologram element 54. The light transmitted without being diffracted by the hologram element 54 is absorbed by the light absorber 34.

Next, a hologram recording method in the LPH 14B according to the modification (2) will be described. As shown in FIG. 9B, the 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. Signal light is a light that passes through the optical path of the diffused light that spreads toward the surface 12A Ueno condensing point on the LED substrate 58, extends to the desired hologram diameter r _H when passing through the holographic recording layer 60A. At the same time, the diffused light is reflected and condensed by the optical path changing means 32B, and the coherent light passing through the optical path of the convergent light that converges toward the light emitting point where the LED 50 is to be disposed is applied to the hologram recording layer 60A as reference light. The For the irradiation of coherent light, a laser light source such as a semiconductor laser is used.

  In this example, the diffused light emitted from the coherent light source 36 is relayed by a lens 38 such as a cylindrical lens and irradiated to the hologram recording layer 60A from the side (from the left side in the figure). The diffused light to be irradiated is designed so that the light transmitted through the hologram recording layer 60A is reflected and collected by the optical path changing means 32B and converges toward the light emitting point where the LED 50 is to be disposed. The signal light and the reference light are applied to the hologram recording layer 60A from the same side, whereby the hologram recording layer 60 in which the transmission type hologram element 54 is formed in the hatched portion is obtained.

<Other variations>
In addition, although the example provided with the LED print head provided with several LED was demonstrated above, it replaced with LED and you may use other light emitting elements, such as an electroluminescent element (EL) and a laser diode (LD). 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 description, an example in which a plurality of hologram elements are multiplexed and recorded by spherical wave shift multiplexing has been described. However, if a multiplexing method that can obtain a desired diffracted light is used, a plurality of hologram elements can be multiplexed and recorded by another multiplexing method. May be. 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. . Separately diffracted light is reproduced without crosstalk from the multiple recorded holograms.

  In the above description, 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 in which an image is formed by imagewise exposing a medium may be used, and the present invention is not limited to the above application examples. 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 according to the above application example may also be applied to exposure of a sheet-shaped photoreceptor, a photographic material, a photoresist, a photopolymer, and the like.

  In the above description, an example in which an LED print head including a plurality of LEDs (LED array) and a plurality of hologram elements (hologram element array) is provided as an exposure apparatus has been described. A similar LED print head may be configured by a light condensing element array in which a plurality of “light condensing elements” including one set of LEDs, an optical path changing unit, and a hologram element are arranged one-dimensionally or two-dimensionally.

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)
14A LPH
14B LPH
DESCRIPTION OF SYMBOLS 15 Developing device 16 Cleaner 21 Intermediate transfer belt 22 Primary transfer roll 23 Secondary transfer roll 24 Conveyor belt 25 Fixing device 30 Controller 32 Optical path changing means 32A Reflecting film 32B Optical path changing means 34 Light absorber 36 Light source 38 Lens 40 Image processing section 50 LED
52 LED array 53 LED chip 54 Hologram element 56 Hologram element array 58 LED substrate 60 Hologram recording layer 60A Hologram recording layer 60B Hologram recording layer 60C Slope 62 Spot

Claims (8)

A light emitting element that emits light;
An optical path changing means for changing an optical path of light emitted from the light emitting element;
A hologram recording layer on which a hologram element is arranged which is arranged on the optical path changed by the optical path changing means and diffracts the irradiated light and is condensed on an exposed surface separated by a predetermined working distance; and
Condensing element equipped with.   A condensing element array in which a plurality of the condensing elements according to claim 1 are arranged one-dimensionally or two-dimensionally. A light emitting element array in which a plurality of light emitting elements are arranged in a predetermined direction;
An optical path changing means for changing an optical path of each light emitted from each of the plurality of light emitting elements;
A hologram recording layer disposed on the optical path changed by the optical path changing means, wherein the exposed surface is diffracted by a plurality of light emitting elements and separated by a predetermined working distance. A hologram recording layer in which a plurality of hologram elements are recorded, and the plurality of hologram elements are multiplexed and recorded such that a plurality of focusing points formed on the exposed surface are aligned in the predetermined direction;
An exposure apparatus comprising: Each of the plurality of hologram elements is recorded by interference between signal light reproduced as diffracted light and reference light intersecting with the signal light, and the incident angle θs of the signal light with respect to the hologram recording layer and the hologram recording layer The exposure apparatus according to claim 3, wherein an incident angle θr of the reference light with respect to satisfies the following expression (1).
0 ° <θr + θs ≦ 90 ° (1)   The exposure apparatus according to claim 4, wherein an optical axis of the signal light and an optical axis of the reference light are orthogonal to each other.   The exposure apparatus according to any one of claims 3 to 5, wherein the optical path changing unit is a reflecting mirror having a flat or curved reflecting surface that reflects light emitted from the light emitting element.   The exposure apparatus according to any one of claims 3 to 6, wherein the optical path changing unit and the hologram recording layer are integrally formed. An exposure apparatus according to any one of claims 3 to 7,
A photosensitive image recording medium having a surface to be exposed that is separated from the exposure apparatus by a predetermined working distance, and on which main scanning is performed in the predetermined direction by the exposure apparatus in accordance with image data to record an image; ,
An image forming apparatus including: