JP2008110596A - Line head and image formation device using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology which can suppress the generation of ghost and form an excellent spot even when the thermal expansion of a shading part and lens array, or of a substrate and the shading part become different with a temperature change. <P>SOLUTION: When defining the internal diameter of a light guide hole in the longitudinal direction as a longitudinal light guide hole diameter Ds, the aperture of an imaging lens in the longitudinal direction as a longitudinal lens diameter Dl and the internal diameter of a diaphragm in the longitudinal direction as a longitudinal diaphragm diameter Dd, the longitudinal diaphragm diameter Dd is smaller than the longitudinal light guide hole diameter Ds, and the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a line head that scans a surface to be scanned with a light beam and an image forming apparatus using the line head.

  As a line head that scans a scanned surface with a light beam, a light emitting diode element (LED (Light Emitting Diode)) that is a light emitting element is provided on a base plate that is a substrate, for example, as in the image device described in Patent Document 1. A device using a plurality of light emitting element groups ("light emitting diode element array" in the same patent document) arranged in a plurality has been proposed.

In the image device described in Patent Document 1, a resin lens plate having a plurality of imaging lenses each corresponding to one imaging lens for each of a plurality of light emitting element groups is disposed to face each other with a spacer interposed therebetween. Yes. Here, the linear expansion coefficients of the base plate, the lens plate, and the spacer are set in the range of −2 to 3 × 10 ⁻⁶ / ° C. in the temperature range of −30 to 100 ° C., and the relative position due to the temperature change among the base plate, the lens plate, and the spacer. The deviation is suppressed.

  In addition, the space between the LED array chip and the imaging lens is enclosed in a box shape by a light shielding plate or the like that is a light shielding member, and light from the LED array chip leaks into the adjacent space or outside to deteriorate print quality. The structure which suppresses generation | occurrence | production phenomenon, what is called a crosstalk, is known (refer patent document 2).

  That is, the light shielding portion is provided with a plurality of light guide holes so that one light guide hole corresponds to each of the plurality of light emitting element groups. The light guide hole is provided from the corresponding light emitting element group toward the imaging lens corresponding to the light emitting element group. Then, the light beam emitted from the light emitting element group passes through the light guide hole corresponding to the light emitting element group and enters the imaging lens corresponding to the light emitting element group. In other words, only the light beam that has passed through the light guide hole among the light beams emitted from the light emitting element group enters the imaging lens corresponding to the light emitting element group. Then, the light beam incident on the imaging lens is imaged on the surface to be scanned, and a spot is formed on the surface to be scanned.

JP-A-6-297767 Japanese Patent No. 2510423

  In the line head, in order to suppress the occurrence of crosstalk, when a light shielding plate or the like as a light shielding member is provided, if the lens plate and the light shielding plate are bonded together, the difference in thermal expansion and contraction between the light shielding plate and the lens plate, If the temperature changes, warping will occur. This warpage causes a deviation from the original spot formation position.

  That is, when the above-described line head is configured, if the light shielding portion and the lens plate as the lens array are bonded together, there is a possibility that the line head may be deflected due to a temperature change. That is, a difference in thermal expansion / contraction between the light-shielding part and the lens array due to a temperature change may occur due to a difference in coefficient of linear expansion between the light-shielding part and the lens array. Becomes prominent. As a result, the line head may be warped. Such warpage becomes a cause of deviation of the spot forming position.

  On the other hand, when the light shielding plate and the lens plate are not adhered to the entire surface, the relative position between the imaging lens and the corresponding light shielding plate is shifted due to a difference in thermal expansion and contraction between the light shielding plate and the lens plate. Therefore, there is a problem that the light beam emitted from the light emitting element is incident on a position other than the corresponding imaging lens, so that a so-called ghost is generated, and a good spot cannot be obtained. In particular, this problem is remarkable when glass is used for the substrate of the lens plate and metal, resin, or the like is used for the light shielding member. Further, in an image forming apparatus using such a line head, the image deteriorates.

  In other words, even when the light shielding portion and the lens array are not adhered to the entire surface, if the temperature change occurs due to the difference in thermal expansion and contraction between the light shielding portion and the lens array due to the temperature change, the imaging lens and the imaging lens The relative position with the corresponding light guide hole may shift. In some cases, the light beam emitted from the light emitting element group is incident on a position deviated from the imaging lens corresponding to the light emitting element group due to the shift of the relative position. As a result, there is a possibility that a so-called ghost is generated and a good spot cannot be obtained. Particularly, when the material of the substrate of the lens array is glass and the material of the light shielding part is metal or carbon steel, such spot formation failure is likely to occur. This is because the linear expansion coefficient of glass is smaller than the linear expansion coefficient of metal or carbon steel, and as a result, the difference in the linear expansion coefficient between the lens array and the light shielding portion increases.

  Further, in the line head as described above, there is a case where a diaphragm portion is provided for the purpose of adjusting the light quantity of a light beam related to spot formation, for example. In other words, the diaphragm unit is disposed between the light emitting element group and the imaging lens, and can adjust the amount of light beam incident on the imaging lens. Specifically, the aperture section has an aperture opening provided in the aperture section. Of the light beams emitted from the light emitting element group, the light beam that has passed through the aperture opening can enter the imaging lens. And in a line head provided with a light-shielding part as described above, the aperture part can be arranged inside the light guide hole provided in the light-shielding part.

  However, a difference in the thermal expansion and contraction between the substrate and the light-shielding part due to a temperature change may occur due to the difference in linear expansion coefficient between the substrate on which the light emitting element group is provided and the light-shielding part. Tends to be prominent in the longitudinal direction of the line head. Then, due to the difference in thermal expansion and contraction, the relative position between the light emitting element group and the aperture opening of the light shielding portion may be shifted. As a result, there is a possibility that a light beam that should not pass through the aperture opening passes through the aperture opening and becomes stray light. When such stray light is incident on the imaging lens, a so-called ghost is caused and a spot formation defect that a good spot cannot be obtained may occur. In the present specification, a light beam that does not originally pass through the aperture opening and that passes through the aperture opening is referred to as “stray light”.

  The present invention has been made in view of the above problems, and even if a difference occurs in thermal expansion and contraction between the light-shielding portion and the lens array due to a temperature change, it is possible to suppress the occurrence of ghosts and form a favorable spot. The first object is to provide the technology.

  Further, the present invention provides a second technique for suppressing the generation of ghosts and enabling good spot formation even when there is a difference in thermal expansion and contraction between the substrate and the light shielding portion due to temperature changes. Objective.

  In order to achieve the above object, a line head according to the present invention includes a plurality of light emitting element groups arranged in a longitudinal direction, each of the plurality of light emitting element groups having a plurality of light emitting elements that emit light beams, and a plurality of light emitting element groups. A lens array having a plurality of imaging lenses provided so that one imaging lens corresponds to each of the light emitting element groups, and disposed between the substrate and the lens array. A light-shielding portion having a plurality of light guide holes provided so that one light guide hole corresponds to each, and each of the plurality of light guide holes is a light emitting element group corresponding to the light guide hole. The light emitting element group is provided toward the corresponding imaging lens to guide the light beam from the light emitting element group to the imaging lens, and the lens array and the light shielding portion are separated from each other. The light-shielding portion is disposed for each of the plurality of light guide holes, and a diaphragm aperture that allows a part of the light beams incident on the light guide holes to pass through the imaging lens corresponding to the light guide holes. The aperture in the longitudinal direction of the light guide hole is the longitudinal light guide hole diameter Ds, the aperture in the longitudinal direction of the imaging lens is the longitudinal lens diameter Dl, and the aperture aperture is elongated in the longitudinal direction. When defined as the aperture diameter Dd, the longitudinal aperture diameter Dd is smaller than the longitudinal light guide hole diameter Ds, and the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl.

  In order to achieve the above object, an image forming apparatus according to the present invention has a latent image carrier whose surface is conveyed in the sub-scanning direction, and a plurality of light emitting elements in the longitudinal direction corresponding to the main scanning direction orthogonal to the sub-scanning direction. A plurality of light emitting element groups are arranged, and each of the plurality of light emitting element groups is provided with a substrate having a plurality of light emitting elements that emit light beams, and an imaging lens corresponding to each of the plurality of light emitting element groups. A plurality of imaging lenses, each of which is disposed between a lens array that forms a spot on the surface of the latent image carrier by imaging a light beam by each of the plurality of imaging lenses; A light shielding portion having a plurality of light guide holes provided so that one light guide hole corresponds to each of the light emitting element groups, and each of the plurality of light guide holes is provided in the light guide hole. Corresponding departure The light emitting element group is provided from the element group toward the corresponding imaging lens, guides the light beam from the light emitting element group to the imaging lens, and the lens array and the light shielding portion are arranged apart from each other. The light-shielding portion has, for each of the plurality of light guide holes, a stop aperture that allows a part of the light beam incident on the light guide hole to pass through the imaging lens corresponding to the light guide hole. The aperture portion is provided, the inner diameter in the longitudinal direction of the light guide hole is the longitudinal light guide hole diameter Ds, the aperture in the longitudinal direction of the imaging lens is the longitudinal lens diameter Dl, and the inner diameter in the longitudinal direction of the aperture opening is the longitudinal aperture. When defined as the aperture diameter Dd, the longitudinal aperture diameter Dd is smaller than the longitudinal light guide hole diameter Ds, and the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl.

  The invention thus configured (line head, image forming apparatus) includes a lens array having a plurality of imaging lenses provided so that one imaging lens corresponds to each of the plurality of light emitting element groups. And a light shielding portion having a plurality of light guide holes provided so that one light guide hole corresponds to each of the plurality of light emitting element groups. Each of the plurality of light guide holes is provided from the light emitting element group corresponding to the light guide hole toward the imaging lens corresponding to the light emitting element group. Accordingly, the light beam emitted from the light emitting element included in the light emitting element group enters the imaging lens corresponding to the light emitting element group through the light guide hole corresponding to the light emitting element group.

  In the above invention, the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl. Here, the longitudinal light guide hole diameter Ds is the inner diameter in the longitudinal direction of the light guide hole, and the longitudinal lens diameter Dl is the aperture in the longitudinal direction of the imaging lens. Therefore, even if the relative position between the light shielding portion and the imaging lens is shifted due to a temperature change, the occurrence of a situation where the light guide hole is out of the aperture range of the imaging lens is suppressed. Therefore, the light beam passing through the light guide hole is guided to the imaging lens corresponding to the light guide hole. That is, the problem that the light beam emitted from the light emitting element group is incident on the position deviated from the imaging lens corresponding to the light emitting element group and a ghost is generated is suppressed. Therefore, in the above invention, even if the relative position between the light shielding portion and the imaging lens is shifted due to a temperature change, it is possible to form a favorable spot, and the first object is achieved.

  Furthermore, in the above-described invention, the light-shielding portion passes, for each of the plurality of light guide holes, a part of the light beam incident on the light guide hole to the imaging lens corresponding to the light guide hole. And a diaphragm portion provided with a diaphragm aperture. Therefore, the light beam incident on the imaging lens among the light beams emitted from the light emitting element group is a light beam that passes through the aperture opening provided in the aperture section. In other words, the above-described invention suppresses an unnecessary light beam from entering the imaging lens by having the stop portion.

  In the above invention, the longitudinal aperture diameter Dd is smaller than the longitudinal light guide hole diameter Ds, and the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl. Here, the longitudinal aperture diameter Dd is an internal diameter in the longitudinal direction of the aperture. Therefore, stray light is generated due to the relative position between the light emitting element group and the aperture opening corresponding to the light emitting element group being shifted in the longitudinal direction due to the difference in thermal expansion and contraction between the substrate and the light shielding portion due to temperature change. However, the incidence of stray light on the imaging lens is suppressed.

  That is, in the above invention, the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl. Therefore, even if the relative position between the light shielding portion and the imaging lens is shifted due to a temperature change, the occurrence of a situation where the light guide hole is out of the aperture range of the imaging lens is suppressed. Therefore, even when stray light is generated, the stray light is blocked by the light guide hole within the range of the lens diameter of the imaging lens before reaching the imaging lens. As a result, in the above invention, the occurrence of ghost due to the incidence of stray light on the imaging lens is suppressed, and the second object is achieved.

Further, the light shielding portion is composed of one or a plurality of light shielding members, and the plurality of light guide holes are provided for the light shielding member, and one of the plurality of light guide holes provided in the light shielding member in the longitudinal direction is provided. When the light guide hole located at the end is defined as one end light guide hole and the light guide hole located at the other end in the longitudinal direction is defined as the other end light guide hole, it corresponds to the one end light guide hole. A distance L in the longitudinal direction between the optical axis of the imaging lens and the optical axis of the imaging lens corresponding to the other end light guide hole, a linear expansion coefficient αm in the longitudinal direction of the lens array, and a line in the longitudinal direction of the light shielding member The expansion coefficient αs, the operating temperature fluctuation range T, the longitudinal light guide hole diameter Ds, and the longitudinal lens diameter Dl are expressed by the following formula: Dl− (αs−αm) · L · T ≧ Ds
The line head may be configured to satisfy the above.

  When the line head is configured so as to satisfy the above formula, the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl in the operating temperature fluctuation range. In addition, even if the temperature change occurs in the operating temperature fluctuation range and the relative position between the light shielding part and the imaging lens shifts, the occurrence of the situation where the light guide hole is out of the aperture range of the imaging lens is suppressed. Is done. Therefore, the problem that the light beam emitted from the light emitting element group is incident on the position deviated from the imaging lens corresponding to the light emitting element group to generate a ghost is suppressed, and the stray light is incident on the imaging lens. Occurrence of ghosts due to the occurrence is suppressed.

  Further, a portion of the light shielding member located in the middle in the longitudinal direction between the optical axis of the imaging lens corresponding to the one end light guide hole and the optical axis of the imaging lens corresponding to the other end light guide hole is shielded. When defined as the central part of the member, the light shielding member may constitute the line head so as to be fixed to the lens array at the central part.

  That is, when the light shielding member is fixed to the lens array at a predetermined fixing position, the relative position shift between the light shielding member and the lens array can be kept small in the vicinity of the light shielding member fixing position regardless of the temperature change. On the other hand, as the distance from the fixed position increases in the longitudinal direction, the relative position shift between the light shielding member and the lens array tends to increase. Therefore, it is preferable that the fixed position is set so that the distance (maximum distance) between the position farthest from the fixed position among the positions on the light shielding member and the fixed position can be kept small.

  Therefore, as described above, it is preferable that the light shielding member is fixed to the lens array at the central portion, that is, the central portion is set to a fixed position. In such a configuration, the fixing position is substantially the center in the longitudinal direction of the light shielding member, and the maximum distance is approximately half the longitudinal length of the light shielding member. That is, for example, the maximum distance when the fixed position is the longitudinal end of the line head is substantially the same as the length of the light shielding member in the longitudinal direction. Is preferred. In addition, in the above configuration, since the light shielding member is fixed at the central portion, the displacement of the relative position between the light shielding member and the lens array is substantially symmetrical in the longitudinal direction with respect to the central portion. Therefore, the relative positional deviation is made uniform and suppressed in the entire light-shielding member, so that generation of ghosts is suppressed and favorable spot formation is possible.

First Embodiment FIG. 1 is a diagram showing an image forming apparatus 1 according to the present embodiment and a line head 29 as an exposure unit. FIG. 2 is a diagram showing an electrical configuration of the image forming apparatus 1 and the line head 29 of FIG.

  The image forming apparatus 1 includes a color mode in which four color toners of black (K), cyan (C), magenta (M), and yellow (Y) are superimposed to form a color image, and only black (K) toner. It is possible to selectively execute a monochrome mode for forming a monochrome image using. In FIG. 1, the image forming apparatus 1 includes a line head 29 for forming an image corresponding to each color. FIG. 1 is a diagram corresponding to the execution of the color mode.

  In FIG. 2, in the image forming apparatus 1, when an image forming command is given from an external device such as a host computer to a main controller MC having a CPU, a memory, etc., the main controller MC gives a control signal to the engine controller EC. At the same time, the video data VD corresponding to the image formation command is given to the head controller HC. The head controller HC controls the line head 29 for each color based on the video data VD from the main controller MC, the vertical synchronization signal Vsync from the engine controller EC, and parameter values. As a result, the engine unit EG executes a predetermined image forming operation, and forms an image corresponding to the image forming command on a sheet such as a copy sheet, a transfer sheet, a sheet, and an OHP transparent sheet.

  In FIG. 1, the image forming apparatus 1 includes a housing body 3. In the housing main body 3, an electrical component box 5 is provided that contains a power circuit board, a main controller MC, an engine controller EC, and a head controller HC. An image forming unit 7, a transfer belt unit 8, and a paper feeding unit 11 are also disposed in the housing body 3. Further, a secondary transfer unit 12, a fixing unit 13, and a sheet guide member 15 are disposed in the housing body 3. Note that the paper feed unit 11 and the transfer belt unit 8 can be removed and repaired or exchanged.

  The image forming unit 7 includes four image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) for forming a plurality of different color images. Each of the image forming stations Y, M, C, and K is provided with a photosensitive drum 21 as a latent image carrier on which the respective color toner images are formed. Each photosensitive drum 21 is connected to a dedicated drive motor, and is driven to rotate at a predetermined speed in the direction of arrow D21 in the figure. As a result, the surface 211 of the photosensitive drum 21 as the surface to be scanned is conveyed in the sub-scanning direction.

  A charging unit 23, a line head 29, a developing unit 25, and a photoconductor cleaner 27 are disposed around the photoconductive drum 21 along the rotation direction. Thus, a charging operation, an electrostatic latent image forming operation, a toner developing operation, and a cleaning operation are executed, respectively. When the color mode is executed, the toner images formed by all the image forming stations Y, M, C, and K are superimposed on the transfer belt 81 of the transfer belt unit 8 to form a color image, and when the monochrome mode is executed. A monochrome image is formed using only the toner image formed at the image forming station K. In FIG. 1, the image forming stations of the image forming unit 7 have the same configuration, and therefore, for convenience of illustration, only some image forming stations are denoted by reference numerals, and the other image forming stations are omitted. .

  The charging unit 23 includes a charging roller whose surface is made of elastic rubber. The charging roller is configured to rotate in contact with the surface 211 of the photosensitive drum 21 at the charging position, and the peripheral speed in the driven direction with respect to the photosensitive drum 21 as the photosensitive drum 21 rotates. Rotate following. The charging roller is connected to a charging bias generating unit (not shown), and receives the charging bias from the charging bias generating unit, and the photosensitive drum 21 is in a charging position where the charging unit 23 and the photosensitive drum 21 come into contact with each other. The surface 211 is charged.

  The line head 29 irradiates light onto the surface 211 of the photosensitive drum 21 charged by the charging unit 23 to form an electrostatic latent image on the surface 211. Hereinafter, the control of the line head 29 will be described in detail with reference to FIG. Image data included in the image formation command is input to the image processing unit 51 of the main controller MC. Various image processing is performed on the image data to create video data VD for each color, and the video data VD is given to the head controller HC via the main-side communication module 52. In the head controller HC, the video data VD is given to the head control module 54 via the head side communication module 53. As described above, the head controller module 54 is supplied with the signal indicating the parameter value related to the electrostatic latent image formation and the vertical synchronization signal Vsync from the engine controller EC. Based on these signals, video data VD, and the like, the head controller HC creates a signal for controlling element driving for the line head 29 of each color, and outputs the signal to each line head 29. Thus, the operation of the light emitting element 2951 (see FIG. 3) (not shown) is appropriately controlled in each line head 29, and an electrostatic latent image corresponding to the image formation command is formed. The configuration of the line head 29 including the light emitting element 2951 will be described in detail later.

  In FIG. 1, the developing unit 25 has a developing roller 251 that carries toner on its surface. The charged toner is developed at a developing position where the developing roller 251 and the photosensitive drum 21 come into contact with each other by a developing bias applied to the developing roller 251 from a developing bias generating unit (not shown) electrically connected to the developing roller 251. The electrostatic latent image formed by the line head 29 by moving from the roller 251 to the photosensitive drum 21 is manifested to become a toner image.

  The toner image that has been made visible at the development position in this way is conveyed in the rotational direction D21 of the photosensitive drum 21, and then the primary transfer position TR1 where the transfer belt 81, which will be described in detail later, and each photosensitive drum 21 come into contact with each other. 1 is primarily transferred to the transfer belt 81.

  A photoreceptor cleaner 27 is provided in contact with the surface 211 of the photoreceptor drum 21 on the downstream side of the primary transfer position TR1 in the rotation direction D21 of the photoreceptor drum 21 and on the upstream side of the charging unit 23. The photoconductor cleaner 27 is in contact with the surface 211 of the photoconductor drum 21 to remove the toner remaining on the surface 211 of the photoconductor drum 21 after the primary transfer.

  The photosensitive drum 21, the charging unit 23, the developing unit 25, and the photosensitive cleaner 27 of each image forming station Y, M, C, and K are unitized as a photosensitive cartridge. Each photoconductor cartridge is provided with a nonvolatile memory for storing information related to the photoconductor cartridge. Then, wireless communication is performed between the engine controller EC and each photoconductor cartridge. In this way, information on each photoconductor cartridge is transmitted to the engine controller EC, and information in each memory is updated and stored.

  The transfer belt unit 8 includes a driving roller 82, a driven roller 83 (blade facing roller) disposed on the left side of the driving roller 82 in FIG. 1, and stretched around these rollers in a direction indicated by an arrow D81 (conveying direction). And a transfer belt 81 that is driven to circulate. Further, the transfer belt unit 8 is disposed on the inner side of the transfer belt 81 so as to be opposed to each of the photosensitive drums 21 included in the image forming stations Y, M, C, and K when the photosensitive cartridge is mounted. Four primary transfer rollers 85Y, 85M, 85C, and 85K are provided. These primary transfer rollers 85 are electrically connected to a primary transfer bias generator (not shown). As will be described in detail later, when the color mode is executed, as shown in FIG. 1, all the primary transfer rollers 85Y, 85M, 85C, and 85K are positioned on the image forming stations Y, M, C, and K side. Then, the transfer belt 81 is pushed and brought into contact with the photosensitive drums 21 included in the image forming stations Y, M, C, and K, so that the primary transfer position TR1 is set between each photosensitive drum 21 and the transfer belt 81. Form. Then, by applying a primary transfer bias from the primary transfer bias generating unit to the primary transfer roller 85 at an appropriate timing, the toner images formed on the surface 211 of each photosensitive drum 21 are respectively corresponding. A color image is formed by transferring to the surface of the transfer belt 81 at the primary transfer position TR1.

  On the other hand, when the monochrome mode is executed, among the four primary transfer rollers 85, the color primary transfer rollers 85Y, 85M, and 85C are separated from the image forming stations Y, M, and C facing each other, and the monochrome primary transfer is performed. By bringing only the roller 85K into contact with the image forming station K, only the monochrome image forming station K is brought into contact with the transfer belt 81. As a result, the primary transfer position TR1 is formed only between the monochrome primary transfer roller 85K and the image forming station K. Then, by applying a primary transfer bias from the primary transfer bias generator to the monochrome primary transfer roller 85K at an appropriate timing, the toner image formed on the surface 211 of each photosensitive drum 21 is converted into a primary image. The image is transferred onto the surface of the transfer belt 81 at the transfer position TR1 to form a monochrome image.

  Further, the transfer belt unit 8 includes a downstream guide roller 86 disposed downstream of the monochrome primary transfer roller 85K and upstream of the driving roller 82. Further, the downstream guide roller 86 is formed between the primary transfer roller 85K and the photosensitive drum 21 at the primary transfer position TR1 formed by the monochrome primary transfer roller 85K contacting the photosensitive drum 21 of the image forming station K. It is configured to contact the transfer belt 81 on a common inscribed line.

  The paper feed unit 11 includes a paper feed unit having a paper feed cassette 77 capable of stacking and holding sheets and a pickup roller 79 for feeding sheets one by one from the paper feed cassette 77. The sheet fed from the sheet feeding unit by the pickup roller 79 is fed to the secondary transfer position TR2 along the sheet guide member 15 after the sheet feeding timing is adjusted by the registration roller pair 80.

  The secondary transfer unit 12 includes a secondary transfer roller 121 and a driving roller 82. The drive roller 82 circulates and drives the transfer belt 81 in the direction of the arrow D81 in the figure, and also serves as a backup roller for the secondary transfer roller 121. A rubber layer having a thickness of about 3 mm and a volume resistivity of 1000 kΩ · cm or less is formed on the peripheral surface of the drive roller 82, and a secondary transfer bias (not shown) is generated by grounding through a metal shaft. This is a conductive path of a secondary transfer bias supplied from the part via the secondary transfer roller 121. As described above, by providing the driving roller 82 with a rubber layer having high friction and shock absorption, the sheet enters the secondary transfer position TR2 where the driving roller 82 and the secondary transfer roller 121 are in contact with each other. It is difficult to transmit the impact at the time of the transfer to the transfer belt 81, and deterioration of image quality can be prevented. The secondary transfer roller 121 is provided so as to be able to come into contact with and separate from the transfer belt 81, and is driven to come into contact with a secondary transfer roller drive mechanism (not shown). The image transferred to the transfer belt 81 is secondarily transferred to the sheet fed to the secondary transfer position TR2.

  The fixing unit 13 includes a heating roller 131 that includes a heating element such as a halogen heater and is rotatable, and a pressure unit 132 that presses and biases the heating roller 131. The pressure unit 132 includes two rollers 1321 and 1322 and a pressure belt 1323 stretched between them. The sheet on which the image has been secondarily transferred is guided by the sheet guide member 15 to a nip portion formed by the heating roller 131 and the pressure belt 1323 of the pressure portion 132, and the image is heated at a predetermined temperature in the nip portion. It is fixed. By pressing the belt tension surface stretched by the two rollers 1321 and 1322 on the surface of the pressure belt 1323 against the peripheral surface of the heating roller 131, the nip portion formed by the heating roller 131 and the pressure belt 1323 is wide. It is configured to be taken. The sheet subjected to the fixing process is conveyed to a paper discharge tray 4 provided on the upper surface of the housing body 3.

  In the image forming apparatus 1, a cleaner unit 71 is disposed to face the blade facing roller 83. The cleaner unit 71 includes a cleaner blade 711 and a waste toner box 713. The cleaner blade 711 removes foreign matters such as toner and paper dust remaining on the transfer belt 81 after the secondary transfer by bringing the tip of the cleaner blade 711 into contact with the blade facing roller 83 via the transfer belt 81. The foreign matter removed in this way is collected in a waste toner box 713. Further, the cleaner blade 711 and the waste toner box 713 are integrally formed with the blade facing roller 83.

  Below, the line head 29 is demonstrated in detail based on figures. FIG. 3 is a perspective view showing an outline of the line head 29. FIG. 4 is a cross-sectional view of the line head 29 in the width direction LTD corresponding to the sub-scanning direction YY. 1 and 3, the line head 29 includes a light emitting element group 295 including a plurality of light emitting elements 2951 arranged in the axial direction of the photosensitive drum 21 (direction perpendicular to the paper surface of FIG. 1). It is spaced from the photosensitive drum 21. Then, light is emitted from the light emitting elements 2951 to the surface 211 that is the surface to be scanned of the photosensitive drum 21 charged by the charging unit 23 to form an electrostatic latent image on the surface 211.

  In FIG. 3, the line head 29 includes a case 291 whose main scanning direction XX is the longitudinal direction LGD, and positioning pins 2911 and screw insertion holes 2912 are provided at both ends of the case 291. The positioning head 2911 is fitted into a positioning hole that covers the photosensitive drum 21 and is formed in a photosensitive cover (not shown) that is positioned with respect to the photosensitive drum 21, so that the line head 29 is inserted into the photosensitive drum. 21 is positioned. Further, the line head 29 is positioned and fixed with respect to the photosensitive drum 21 by screwing and fixing a fixing screw into a screw hole (not shown) of the photosensitive member cover via the screw insertion hole 2912. In other words, the line head 29 is arranged so that the longitudinal direction LGD of the line head 29 corresponds to the main scanning direction XX, and the width direction LTD of the line head 29 corresponds to the sub-scanning direction YY.

  3 and 4, the case 291 holds a microlens array 299 in which microlenses ML as imaging lenses are arranged at a position facing the surface 211 of the photosensitive drum 21, and a microlens is disposed therein. A light shielding portion 297 and a glass substrate 293 as a substrate are provided in the order close to the array 299. The glass substrate 293 is a transparent substrate. The microlens array 299, the light shielding unit 297, and the glass substrate 293 have a substantially rectangular parallelepiped outer shape with the main scanning direction XX being the longitudinal direction LGD. The light shielding portion 297 is provided with a step portion 298 on a surface facing the region where the microlenses ML are arranged. The stepped portion 298 is separated from the region of the light shielding portion 297 in which the light guide hole 2971 facing the microlens ML is formed. A plurality of light emitting element groups 295 are provided on the back surface 2932 of the glass substrate 293 (the surface opposite to the front surface 2931 facing the light shielding portion 297 among the two surfaces of the glass substrate 293). As shown in FIG. 3, the plurality of light emitting element groups 295 are arranged on the back surface 2932 of the glass substrate 293 by a predetermined distance from each other in the longitudinal direction LGD corresponding to the main scanning direction XX and in the width direction LTD corresponding to the sub scanning direction YY. They are arranged two-dimensionally and discretely side by side. Here, each of the plurality of light emitting element groups 295 is configured by two-dimensionally arranging a plurality of light emitting elements 2951 as shown by the circled portion in FIG. An organic EL element is used as the light emitting element. That is, the organic EL element is disposed as the light emitting element 2951 on the back surface 2932 of the glass substrate 293. A light beam emitted from each of the plurality of light emitting elements 2951 toward the photosensitive drum 21 is directed to the light shielding unit 297 via the glass substrate 293. An LED element can also be used as the light emitting element.

  In FIG. 3 and FIG. 4, a plurality of light guide holes 2971 are formed in the light shielding portion 297 on a one-to-one basis with respect to the plurality of light emitting element groups 295. That is, the plurality of light guide holes 2971 are provided to the light shielding portion 297 so that one light guide hole 2971 corresponds to each of the plurality of light emitting element groups 295. The light guide hole 2971 is formed as a substantially cylindrical hole that penetrates the light shielding portion 297 with a line parallel to a perpendicular to the glass substrate 293 (indicated by a one-point difference line in FIG. 4) as a central axis. That is, the light emitted from the light emitting elements 2951 belonging to the light emitting element group 295 is guided to the microlens ML through the light guide hole 2971 corresponding to the light emitting element group 295. Then, the light beam that has passed through the light guide hole 2971 formed in the light shielding portion 297 is imaged as a spot on the surface 211 of the photosensitive drum 21 by the microlens ML as indicated by a two-dot chain line. Become.

  As shown in FIG. 4, the back cover 2913 is pressed against the case 291 through the glass substrate 293 by the fixing device 2914. That is, the fixing device 2914 has an elastic force that presses the back cover 2913 toward the case 291, and presses the back cover 2913 with the elastic force, so that the inside of the case 291 is light-tight (that is, inside the case 291). From the outside of the case 291 so that no light leaks from the case 291). Note that a plurality of fixing devices 2914 are provided in the longitudinal direction LGD of the case 291. The light emitting element group 295 is covered with a sealing member 294.

  FIG. 5 is a perspective view showing an outline of the microlens array 299. FIG. 6 is a cross-sectional view of the microlens array 299 in the longitudinal direction LGD corresponding to the main scanning direction XX. The microlens array 299 includes a glass substrate 2991 and a plurality of lens pairs configured by two lenses 2993A and 2993B arranged one-on-one so as to sandwich the glass substrate 2991. These lenses 2993A and 2993B can be formed of resin.

  Hereinafter, the microlens ML will be described in detail. In FIG. 6, a plurality of lenses 2993A are arranged on the front surface 2991A of the glass substrate 2991, and a plurality of lenses 2993B are arranged on the back surface 2991B of the glass substrate 2991 so as to correspond to the plurality of lenses 2993A on a one-to-one basis. Yes. Further, the two lenses 2993A and 2993B constituting the lens pair share a common optical axis OA indicated by a one-dot chain line in the drawing. The plurality of lens pairs are arranged one-on-one in the plurality of light emitting element groups 295. In this specification, an optical system including lenses 2993A and 2993B forming a one-to-one pair and a glass substrate 2991 sandwiched between the lens pairs is referred to as a “microlens ML”. The microlens ML as an imaging lens corresponds to the arrangement of the light emitting element groups 295 and is separated by a predetermined distance in the longitudinal direction LGD corresponding to the main scanning direction XX and the width direction LTD corresponding to the sub-scanning direction YY. Dimensionally arranged.

  FIG. 7 is a diagram showing an arrangement of a plurality of light emitting element groups 295. In the present embodiment, two light emitting element rows L2951 configured by arranging four light emitting elements 2951 in the longitudinal direction LGD corresponding to the main scanning direction XX at predetermined intervals, and two rows in the width direction LTD corresponding to the sub scanning direction YY. One light emitting element group 295 is formed side by side. That is, eight light emitting elements 2951 corresponding to the position of one circular microlens ML indicated by a two-dot chain line in FIG. The plurality of light emitting element groups 295 are arranged as follows.

  A light emitting element group row L295 (group row) configured by arranging a predetermined number (two or more) of light emitting element groups 295 in the longitudinal direction LGD corresponding to the main scanning direction XX includes three rows in the width direction LTD corresponding to the sub scanning direction YY. The light emitting element groups 295 are two-dimensionally arranged so that they are arranged. Further, all the light emitting element groups 295 are arranged at different main scanning direction positions. Further, the plurality of light emitting element groups 295 are arranged so that the sub scanning direction positions of the light emitting element groups (for example, the light emitting element group 295C1 and the light emitting element group 295B1) whose main scanning direction positions are adjacent to each other are different. The main scanning direction position and the sub scanning direction position mean the main scanning direction component and the sub scanning direction component at the position of interest, respectively. Further, in this specification, “geometric centroid of light emitting element group” means the geometric centroid of the positions of all the light emitting elements 2951 belonging to the same light emitting element group 295.

  Then, as shown in FIG. 4, corresponding to the arrangement of the light emitting element groups 295, the light guide hole 2971 is formed in the light shielding portion 297 and the microlens ML is arranged. That is, in the present embodiment, the center of gravity of the light emitting element group 295, the central axis of the light guide hole 2971, and the optical axis OA of the microlens ML are configured to substantially coincide. As shown in FIG. 4, the light beam emitted from the light emitting element 2951 of the light emitting element group 295 enters the microlens array 299 through the corresponding light guide hole 2971, and is also photosensitive by the microlens array 299. An image is formed as a spot on the surface 211 of the drum 21.

FIG. 8 is a plan view of the line head 29 in a state of being housed in the case 291. The light shielding part 297 is composed of one light shielding member. FIG. 9 is a diagram showing an image formation state by the microlens array 299. In FIG. 8, the center portion of the light shielding portion 297 (not shown) located below the microlens array 299 is fixed to the microlens array 299 with a fixing adhesive 2977. The length between the optical axes OA of the microlenses ML at both ends in the longitudinal direction LGD (main scanning direction XX) of the microlens array 299 is L (that is, the distance between the optical axis OA1 and the optical axis OA2 in the longitudinal direction LGD). Is L). In FIG. 9, the inner diameter of the light guide hole 2971 in the longitudinal direction is Ds, and the diameter of the microlens in the longitudinal direction is Dl. If L is determined, the relationship between Ds and Dl is that the linear expansion coefficient in the longitudinal direction of the microlens array 299 is αm, the linear expansion coefficient in the longitudinal direction of the light shielding portion 297 is αs, and the operating temperature fluctuation range of the line head 29 is Assuming that T, the relationship of Equation 1 is satisfied.
Dl− (αs−αm) · L · T ≧ Ds Equation 1
For example, when L is 320 mm, the operating temperature variation range T is 30 ° C., the light shielding part 297 is made of iron, titanium, stainless steel, and the glass substrate 2991 of the microlens array 299 is made of glass or heat-resistant glass, Ds and Dl Values are shown in the table below.

  Hereinafter, the state of image formation of spots on the surface 211 of the photosensitive drum 21 by the microlens array 299 will be described. In FIG. 9, the light emitting element group 295 is provided on the back surface 2932 of the glass substrate 293. A micro lens ML is arranged for the light emitting element group 295. Further, the light shielding portion 297 is disposed so that one surface thereof faces the front surface 2931 of the glass substrate 293 and the other surface thereof faces the plurality of microlenses ML. A light guide hole 2971 is formed in the light shielding portion 297 so as to penetrate the light emitting element group 295 from one surface of the light shielding portion 297 to the other surface. In addition, the light guide hole 2971 is formed so as to be symmetrical with respect to the optical axis OA of the corresponding microlens ML. Further, since the stepped portion 298 is provided and spaced apart on the surface of the light shielding portion 297 facing the microlens ML, as shown in FIGS. 3 and 4, the microlens array 299 and the light shielding portion 297 are disposed. However, even if these relative positions shift, they are prevented from contacting each other. For example, when the diameter of the microlens ML is 900 μm and the length in the longitudinal direction is 300 mm, a deviation of 20 to 30 μm occurs. The displacement of the relative position due to the temperature change is larger as the lengths of the microlens array 299, the light shielding unit 297, and the glass substrate 293 in the main scanning direction XX which is the longitudinal direction LGD are longer.

  In these figures, in order to show the imaging characteristics of the microlens array 299, the light is emitted from the geometric gravity center position E0 of the light emitting element group 295 and the positions E1 and E2 that are separated from the geometric gravity center position E0 by a predetermined interval. The locus of the principal ray of the light beam is represented by a one-dot chain line. As indicated by the locus, the light beam emitted from each position enters the back surface 2932 of the glass substrate 293 and then exits from the front surface 2931 of the glass substrate 293. Then, the light beam emitted from the front surface 2931 of the glass substrate 293 reaches the surface 211 of the photosensitive drum 21 that is the surface to be scanned via the microlens array 299.

  The light beam emitted from the geometric gravity center position E0 of the light emitting element group 295 forms an image at the intersection point I0 between the surface 211 of the photosensitive drum 21 and the optical axis OA of the microlens ML shown in FIG. As described above, this is because, in the present embodiment, the geometric gravity center position E0 of the light emitting element group 295 is on the optical axis OA of the microlens ML. The light beams emitted from the positions E1 and E2 are imaged at positions I1 and I2 on the surface 211 of the photosensitive drum 21, respectively. That is, the light beam emitted from the position E1 is imaged at the position I1 on the opposite side across the optical axis OA of the microlens ML in the main scanning direction XX, and the light beam emitted from the position E2 is the main beam. In the scanning direction XX, an image is formed at a position I2 on the opposite side across the optical axis OA of the microlens ML. That is, the microlens ML is a so-called inverted optical system having reversal characteristics.

  Further, the distance between the positions I1 and I0 where the light beam is imaged is longer than the distance between the positions E1 and E0. That is, the absolute value of the magnification (optical magnification) of the optical system in the present embodiment is greater than 1. That is, the optical system in the present embodiment is a so-called magnifying optical system having magnifying characteristics. Thus, in this embodiment, the microlens ML functions as the “imaging lens” in the present invention.

  FIG. 10 is a diagram showing a spot forming operation by the line head 29. Hereinafter, the spot forming operation by the line head in this embodiment will be described with reference to FIGS. 2, 7, and 10. In order to facilitate understanding of the invention, here, a case where a plurality of spots are formed side by side on a straight line extending in the main scanning direction XX will be described. In the present embodiment, while the surface 211 of the photosensitive drum 21 is transported in the sub-scanning direction YY, the head control module 54 causes the light-emitting elements to emit light at a predetermined timing, thereby forming a straight line extending in the main scanning direction XX. A plurality of spots are formed side by side.

  In FIG. 7, in the line head 29 of this embodiment, six sets of light emitting element rows L2951 are arranged side by side in the sub-scanning direction YY (width direction LTD) corresponding to each position of the sub-scanning direction positions Y1 to Y6. Yes. In the present embodiment, the light emitting element rows L2951 at the same sub scanning direction position emit light at substantially the same timing, and the light emitting element rows L2951 at different sub scanning direction positions emit light at different timings. More specifically, the light emitting element array L2951 is caused to emit light in the order of the sub-scanning direction positions Y1 to Y6. A plurality of spots are arranged on a straight line extending in the main scanning direction XX of the surface 211 by causing the light emitting element array L2951 to emit light in the order described above while transporting the surface 211 of the photosensitive drum 21 in the sub scanning direction YY. Form.

  Such an operation will be described with reference to FIGS. First, the light emitting elements 2951 of the light emitting element row L2951 in the sub scanning direction position Y1 belonging to the most upstream light emitting element groups 295A1, 295A2, 295A3,. The plurality of light beams emitted by the light emission operation are enlarged while being inverted by the “imaging lens” having the above-described inversion enlarging characteristic, and are imaged on the surface 211 of the photosensitive drum 21. That is, a spot is formed at the position of the “first” hatching pattern in FIG. In the figure, white circles represent spots that have not yet been formed and are to be formed in the future. In the same figure, the spots labeled with reference numerals 295C1, 295B1, 295A1, and 295C2 indicate spots formed by the light emitting element groups 295 corresponding to the reference numerals assigned thereto.

  Next, the light emitting elements 2951 of the light emitting element row L2951 in the sub-scanning direction position Y2 belonging to the same light emitting element group 295A1, 295A2, 295A3,. The plurality of light beams emitted by the light emission operation are enlarged while being inverted by the microlens ML and imaged on the surface 211 of the photosensitive drum 21. That is, in FIG. 10, a spot is formed at the position of the “second” hatching pattern. Here, while the conveyance direction of the surface 211 of the photosensitive drum 21 is the sub-scanning direction YY, the light emitting element rows L2951 on the downstream side in the sub-scanning direction YY are sequentially arranged (that is, the sub-scanning direction positions Y1, Y2). The reason for emitting light is that the microlens ML has a reversal characteristic.

  Next, the light emitting elements 2951 of the light emitting element array L2951 in the sub scanning direction position Y3 belonging to the second light emitting element groups 295B1, 295B2, 295B3,... From the upstream side in the sub scanning direction YY are caused to emit light. Then, the plurality of light beams emitted by the light emission operation are inverted and magnified by the microlens ML and imaged on the surface 211 of the photosensitive drum 21. That is, a spot is formed at the position of the “third” hatching pattern in FIG.

  Next, the light emitting elements 2951 of the light emitting element row L2951 in the sub-scanning direction position Y4 belonging to the light emitting element groups 295B1, 295B2, 295B3,. The plurality of light beams emitted by the light emission operation are enlarged while being inverted by the microlens ML and imaged on the surface 211 of the photosensitive drum 21. That is, a spot is formed at the position of the “fourth” hatching pattern in FIG.

  Next, the light emitting elements 2951 of the light emitting element row L2951 in the sub scanning direction position Y5 belonging to the light emitting element groups 295C1, 295C2, 295C3,. The plurality of light beams emitted by the light emission operation are enlarged while being inverted by the microlens ML and imaged on the surface 211 of the photosensitive drum 21. That is, a spot is formed at the position of the “fifth” hatching pattern in FIG.

  Finally, the light emitting elements 2951 of the light emitting element row L2951 in the sub-scanning direction position Y6 belonging to the light emitting element groups 295C1, 295C2, 295C3,. The plurality of light beams emitted by the light emission operation are enlarged while being inverted by the microlens ML and imaged on the surface 211 of the photosensitive drum 21. That is, a spot is formed at the position of the “sixth” hatching pattern in FIG. In this way, by performing the first to sixth light emitting operations, a plurality of spots are formed side by side on a straight line extending in the main scanning direction XX.

  According to this embodiment, there are the following effects. That is, the inner diameter Ds of the light guide hole 2971 in the longitudinal direction is the microlens ML in the longitudinal direction in which the relative position shift is large due to the difference between the thermal expansion coefficient of the material of the microlens array 299 and the thermal expansion coefficient of the material of the light shielding portion 297. Is smaller than the diameter Dl in the longitudinal direction. Here, even if the light shielding portion 297 expands and contracts due to a temperature change and the relative position of the microlens ML facing the light guide hole 2971 shifts, there is a possibility that the light guide hole 2971 may be out of the range of the diameter of the microlens ML. Less. Therefore, the light beam passing through the light guide hole 2971 is guided to the opposing microlens ML, and is less likely to enter the position other than the opposing microlens ML, so that the occurrence of ghost can be suppressed and a good spot can be obtained. A line head 29 to be formed can be obtained.

In addition, the inner diameter Ds of the light guide hole 2971 of the light shielding portion 297 and the aperture Dl of the microlens ML are formed with values determined by Equation 1. According to Equation 1, even if a temperature change occurs in the operating temperature fluctuation range of the line head 29, the inner diameter Ds of the light guide hole 2971 is smaller than the aperture Dl of the imaging lens. The possibility that the relative position of the light hole 2971 with respect to the opposing microlens ML is shifted and the light guide hole 2971 is out of the range of the diameter of the microlens ML can be reduced.
Dl− (αs−αm) · L · T ≧ Ds Equation 1

  In addition, the relative position of the light shielding part 297 with respect to the microlens array 299 can be determined more accurately by fixing the relative position of the light shielding part 297 in the vicinity of the central part, which is a position that is substantially the same distance from both longitudinal ends of the light shielding part 297. In addition, since it is fixed in the vicinity of the central portion as compared with the case where it is fixed in the vicinity of the end portion of the light shielding portion 297, the distance to both end portions 2980 can be made substantially the same, and the expansion and contraction due to the temperature change from the fixing portion can be reduced. It can be made small with approximately the same size. Therefore, the displacement due to expansion and contraction is substantially uniform and small, and the occurrence of ghost can be suppressed, and the line head 29 in which a good spot is formed can be obtained.

  In addition, since the exposure unit having the same configuration as the line head 29 having the above-described effect is provided, the occurrence of crosstalk and ghost can be suppressed. Therefore, an image can be formed from the spot imaged at the original position, and the image forming apparatus 1 with little deterioration in image quality can be obtained.

Second Embodiment FIG. 11 is a plan view showing another configuration of the line head 29 in a state of being housed in a case 291. The microlens array 299 is omitted. The light shielding unit 297 includes a light shielding member 297A and a light shielding member 297B. The light shielding members 297A and 297B are arranged in the longitudinal direction LGD corresponding to the main scanning direction XX through the gap 2975. The gap 2975 is provided so as to skew the three light guide holes 2971 that are arranged with their positions shifted in the width direction LTD corresponding to the sub-scanning direction YY. The central part of each light shielding member 297A, 297B, which is substantially the same distance from both longitudinal ends 2980 of each light shielding member 297A, 297B, is fixed to a microlens array 299 (not shown) with a fixing adhesive 2977.

The length between the optical axes OA of the microlenses ML facing the light guide holes 2971 at both ends in the longitudinal direction of the light shielding member 297A is L1 (that is, the distance between the optical axis OAa1 and the optical axis OAa2 in the longitudinal direction LGD). L1). The length between the optical axes OA of the microlenses ML facing the light guide holes 2971 at both ends in the longitudinal direction of the light shielding member 297B is defined as L2 (that is, the distance between the optical axis OAb1 and the optical axis OAb2 in the longitudinal direction LGD). L2). Here, the light guide hole 2971 is drilled symmetrically with respect to the optical axis OA of the corresponding microlens ML. For each of the light shielding members 297A and 297B, the inner diameter Ds of the light guide hole 2971 and the aperture Dl of the microlens ML are formed so as to satisfy Expressions 2 and 3, respectively, corresponding to L1 and L2.
Dl− (αs−αm) · L1 · T ≧ Ds Equation 2
Dl− (αs−αm) · L2 · T ≧ Ds Equation 3

  According to this embodiment, there are the following effects. That is, compared to the relative position shift in the case of a single long light blocking member, the relative position shift per one of the divided light blocking members 297A and 297B can be reduced because the length is short. Therefore, the light beam emitted from the light emitting element 2951 is less likely to be incident on a position other than the opposing microlens ML, and the generation of ghost can be suppressed and a line head 29 in which a good spot is formed is obtained. be able to. In particular, the difference between the thermal expansion coefficient of the material of the microlens array 299 and the thermal expansion coefficient of the material of the light-shielding part 297 is large, and the difference in size between the inner diameter Ds and the aperture Dl increases due to temperature change, and the inner diameter Ds is extremely reduced. This is effective when the diameter is small or the diameter Dl must be extremely large.

Third Embodiment FIGS. 12 and 13 are cross-sectional views showing a line head 29 in the longitudinal direction LGD corresponding to the main scanning direction XX in the third embodiment. The line head 29 shown in FIGS. 12 and 13 includes a glass substrate 293, a light shielding part 297, and a microlens array 299, similarly to the line head 29 described above. A plurality of light emitting element groups 295 are arranged on the back surface 2932 of the glass substrate 293. Then, the light beam emitted from each light emitting element group 295 travels from the back surface 2932 to the front surface 2931 of the glass substrate 293.

  The microlens array 299 is disposed to face the glass substrate 293 in the traveling direction of light from the light emitting element group 295. The microlens array 299 has a plurality of microlenses ML. The plurality of microlenses ML are provided so that one microlens ML corresponds to each of the plurality of light emitting element groups 295.

  The light shielding portion 297 is disposed so that one surface thereof faces the head substrate 293 and the other surface faces the microlens array 299. At this time, the light shielding portion 297 is in contact with the head substrate 293, but is separated from the microlens array 299. That is, the light shielding portion 297 is provided with a step portion 298 on a surface facing the region where the microlenses ML are arranged. The stepped portion 298 is separated from the region of the light shielding portion 297 in which the light guide hole 2971 facing the microlens ML is formed. The light shielding portion 297 is provided with a plurality of light guide holes 2971. The plurality of light guide holes 2971 are provided so that one light guide hole 2971 corresponds to each of the plurality of light emitting element groups 295. That is, each of the plurality of light guide holes 2971 is provided by being drilled from the light emitting element group 295 corresponding to the light guide hole 2971 toward the microlens ML corresponding to the light emitting element group 295. Therefore, the light beam emitted from the light emitting element group 295 is guided to the microlens ML corresponding to the light emitting element group 295 through the light guide hole 297 corresponding to the light emitting element group 295.

  The line head 29 shown in FIGS. 12 and 13 is different from the line head 29 described above in the following points. That is, the line head shown in FIGS. 12 and 13 includes the aperture portion Dp inside the light guide hole 2971. The diaphragm portion Dp is provided with a diaphragm opening Dpa. As shown in FIGS. 12 and 13, the aperture opening Dpa is open to the microlens ML and to the light emitting element group 295. Accordingly, a part of the light beam emitted from the light emitting element group 295 passes through the aperture opening Dpa and enters the microlens ML, while the other part of the light beam is blocked by the aperture portion Dp and enters the microlens ML. Not incident.

  In FIG. 12, in order to show the imaging characteristics of the microlens array 299, the light beams emitted from the geometric gravity center position E0 of the light emitting element group 295 and the positions E1 and E2 that are separated from the geometric gravity center position E0 by a predetermined interval. The locus of the chief ray is represented by a one-dot chain line. As indicated by the locus, the light beam emitted from each position enters the back surface 2932 of the glass substrate 293 and then exits from the front surface 2931 of the glass substrate 293. All the light beams emitted from the positions E0 to E2 pass through the center of the aperture opening Dpa. Then, the light beam emitted from the front surface 2931 of the glass substrate 293 reaches the surface 211 of the photosensitive drum 21 that is the surface to be scanned via the microlens array 299.

  The light beam emitted from the geometric gravity center position E0 of the light emitting element group 295 is imaged at the intersection point I0 between the surface 211 of the photosensitive drum 21 and the optical axis OA of the microlens ML. This is because the geometric gravity center position E0 of the light emitting element group 295 is on the optical axis OA of the microlens ML. The light beams emitted from the positions E1 and E2 are imaged at positions I1 and I2 on the surface 211 of the photosensitive drum 21, respectively. That is, the light beam emitted from the position E1 is imaged at the position I1 on the opposite side across the optical axis OA of the microlens ML in the main scanning direction XX, and the light beam emitted from the position E2 is the main beam. In the scanning direction XX, an image is formed at a position I2 on the opposite side across the optical axis OA of the microlens ML. That is, the microlens ML is a so-called inverted optical system having reversal characteristics.

  Further, the distance between the positions I1 and I0 where the light beam is imaged is longer than the distance between the positions E1 and E0. That is, the absolute value of the magnification (optical magnification) of the optical system in the present embodiment is greater than 1. That is, the optical system in the present embodiment is a so-called magnifying optical system having magnifying characteristics.

  As shown in FIGS. 12 and 13, the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl. Here, the longitudinal light guide hole diameter Ds is an inner diameter in the longitudinal direction LGD of the light guide hole 2951. Further, the longitudinal lens diameter Dl is a diameter of the microlens ML in the longitudinal direction LGD. Therefore, even if the relative position between the light shielding unit 297 and the microlens ML is shifted due to the temperature change, the situation that the light guide hole 2971 is out of the range of the diameter of the microlens ML is generated as shown in FIG. Is suppressed.

  FIG. 14 is a diagram showing a positional relationship between the light guide hole 2971 and the microlens ML. FIG. 14 shows a case where the microlens ML and the light guide hole 2971 are viewed from the direction of the optical axis OA of the microlens ML. As shown in the figure, since the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl, the light guide hole 2971 is in the range of the aperture of the microlens ML. Here, the situation where the light guide hole 2971 is in the range of the aperture of the microlens ML is, as shown in the figure, the lens side opening of the light guide hole 2971 when viewed from the optical axis direction of the microlens ML. In this situation, 2971a is entirely inside the microlens ML.

  Therefore, the light beam passing through the light guide hole 2971 is guided to the microlens ML corresponding to the light guide hole 2971. That is, the problem that a ghost is generated when a light beam emitted from the light emitting element group 295 enters a position off the microlens ML corresponding to the light emitting element group 295 is suppressed. Therefore, in the embodiment shown in FIG. 12 and FIG. 13, even if the relative position between the light shielding part 297 and the microlens ML is shifted due to a temperature change, it is possible to form a favorable spot. Further, as can be understood from the description of the effect of the present embodiment using FIG. 14, the longitudinal light guide hole diameter Ds is the inner diameter in the longitudinal direction LGD of the lens side opening 2971a of the light guide hole 2971.

  Further, in the embodiment shown in FIG. 12 and FIG. 13, the light shielding portion 297 is arranged inside the light guide hole 2971 from the light emitting element group 295 corresponding to the light guide hole 2971 to the microlens corresponding to the light guide hole 2971. It has a diaphragm portion Dp in which a diaphragm aperture Dpa through which a part of the light beam toward the ML passes is formed. Therefore, the light beam incident on the microlens ML among the light beams emitted from the light emitting element group 295 is a light beam that passes through the aperture opening Dpa formed in the aperture portion Dp. That is, the embodiment shown in FIG. 12 and FIG. 13 has the diaphragm portion Dp to suppress the unnecessary light beam from entering the microlens ML.

  The longitudinal aperture diameter Dd is smaller than the longitudinal light guide hole diameter Ds, and the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl. Here, the longitudinal aperture diameter Dd is the inner diameter in the longitudinal direction LGD of the aperture opening Dpa. Accordingly, the relative position between the light emitting element group 295 and the aperture opening Dp corresponding to the light emitting element group 295 is shifted in the longitudinal direction LGD due to the difference in thermal expansion and contraction between the glass substrate 293 and the light shielding portion 297 due to temperature change. Even when stray light is generated, the stray light is prevented from entering the microlens ML.

  As described above, the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl. Therefore, even if the relative position between the light shielding unit 297 and the microlens ML is shifted due to the temperature change, the occurrence of the situation that the light guide hole 2971 is out of the range of the diameter of the microlens ML is suppressed. Therefore, even when stray light is generated, the stray light is blocked by the light guide hole 2971 within the range of the lens diameter of the microlens ML before reaching the microlens ML.

  FIG. 15 is a diagram illustrating how stray light is prevented from entering the microlens ML. That is, FIG. 15 shows a case where a difference in thermal expansion / contraction occurs between the glass substrate 293 and the light shielding portion 297 due to a temperature change. Further, in FIG. 15, the light emitting element group 295 is shifted in the left direction in FIG. 15 (the direction opposite to the arrow direction of the longitudinal direction LGD) in FIG. As a result, in FIG. 15, a part of the light beam emitted from the light emitting element 2951 at the position E2 becomes stray light SL and passes through the aperture opening Dpa. However, since the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl, the progress of the stray light SL is blocked by the light guide hole 2971 before reaching the microlens ML. Specifically, as shown in FIG. 15, the stray light SL is incident on a position BLP on the inner wall surface of the light guide hole 2971, and further progress is prevented. In this way, the generation of ghosts due to the incidence of stray light SL on the microlens ML is suppressed. Here, the stray light SL refers to the light emitting element group 295 among the light beams that do not originally pass through the aperture opening Dpa if there is no deviation between the light emitting element group 295 and the light guide hole 2971 corresponding to the light emitting element group 295. This is a light beam that has passed through the aperture opening Dpa due to a deviation between the light guide hole 2971 and the light guide hole 2971.

  In the embodiment shown in FIGS. 12 and 13, as shown in FIG. 8 or FIG. 11, the light shielding portion 297 or the light shielding members 297A and 297B (light shielding portion 297 and the like) is arranged on the lens array 299 at the central portion. It is preferable to be fixed. That is, when the light shielding unit 297 or the like is fixed to the lens array 299 at a predetermined fixed position, the relative position shift between the light shielding unit 297 and the lens array 299 depends on a temperature change in the vicinity of the fixed position of the light shielding unit 297 or the like. Can be kept small. On the other hand, as the distance from the fixed position in the longitudinal direction LGD increases, the relative position shift between the light shielding portion 297 and the lens array 299 tends to increase. Therefore, it is preferable to set the fixed position so that the distance (maximum distance) between the position farthest from the fixed position and the fixed position among the positions in the light shielding portion 297 and the like can be suppressed small.

  Here, the central part of the light shielding part 297 is as follows. First, among the plurality of light guide holes 2971 formed in the light shielding portion 297, the light guide hole 2971 positioned at one end in the longitudinal direction LGD corresponding to the main scanning direction XX is defined as one end light guide hole, The light guide hole 2971 located at the other end in the longitudinal direction LGD is referred to as the other end light guide hole. The central portion is located in the middle in the longitudinal direction LGD between the optical axis OA1 of the microlens 1 corresponding to the one end light guide hole and the optical axis OA2 of the microlens 2 corresponding to the other end light guide hole. , Part of the light shielding member.

  The central part of the light shielding member 297A is as follows. First, among the plurality of light guide holes 2971 formed in the light shielding member 297A, the light guide hole 2971 positioned at one end in the longitudinal direction LGD corresponding to the main scanning direction XX is defined as one end light guide hole, The light guide hole 2971 located at the other end in the longitudinal direction LGD is referred to as the other end light guide hole. The “central portion of the light shielding member 297A” is the longitudinal direction of the optical axis OAa1 of the microlens a1 corresponding to the one end light guide hole and the optical axis OAa2 of the microlens a2 corresponding to the other end light guide hole. This is a portion of the light shielding member 297A located in the middle of the LGD. The same applies to the central portion of the light shielding member 297B.

  Therefore, as shown in FIG. 8 or FIG. 11, it is preferable to fix the light shielding portion 297 and the like to the lens array 299 at the center portion or the like, that is, to set the center portion as a fixed position. When configured in this manner, the fixed position is substantially the center in the longitudinal direction LGD of the light shielding portion 299 and the like, and the maximum distance is about half of the longitudinal length of the light shielding portion 297 and the like. That is, for example, the maximum distance when the fixed position is set to the longitudinal end portion of the line head 29 is substantially the same as the longitudinal length of the light shielding portion 297 and the like. The above configuration is preferable. In addition, in the above configuration, since the light shielding portion 297 and the like are fixed at the center portion and the like, the displacement of the relative position between the light shielding portion 297 and the lens array 299 is substantially symmetrical in the longitudinal direction LGD with respect to the center portion and the like. . Therefore, the relative positional deviation is uniformized and suppressed to be small in the entire light shielding portion 297 and the like, so that the occurrence of ghost is suppressed and favorable spot formation is possible.

  Also in the embodiment shown in FIGS. 12 and 13, it is preferable that the line head is configured so as to satisfy the above-described expression 1, or to satisfy the expressions 2 and 3. The reason for this will be described next.

  FIG. 16 and FIG. 17 are explanatory diagrams of the effects achieved by satisfying the expression 1. FIG. In FIG. 16, in order to show the correspondence between the lens array 299 and the light shielding part 297, the lens array 299 and the light shielding part 297 are shown side by side. That is, in FIG. 16, the lens array 299 and the light shielding unit 297 are shown side by side for convenience of explanation, and actually the lens array 299 and the light shielding unit 297 overlap each other as described above. Has been fixed. Specifically, FIGS. 16 and 17 assume a case where the lens array 299 and the light shielding portion 297 are fixed at one end EP1 in the longitudinal direction LGD. That is, FIG. 16 and FIG. 17 assume a case where the lens array 299 and the light shielding portion 297 are fixed at the most disadvantageous position with respect to the relative position shift between the microlens ML and the light guide hole 2971. In FIG. 16, among the plurality of light guide holes 2971 formed in the light shielding portion 297, one end light guide hole located at one end in the longitudinal direction LGD is denoted by reference numeral 2971 _ 1, Reference numeral 2971_2 is attached to the other end light guide hole located at the other end. FIG. 16 shows the distance L in the longitudinal direction LGD between the optical axis OA1 of the microlens ML1 corresponding to the one end light guide hole 2971_1 and the optical axis OA2 of the microlens ML2 corresponding to the other end light guide hole 2971_2. It is said.

  In this way, when the light shielding portion 297 is fixed to the lens array 299 at the one end portion EP1, the movement amount in the longitudinal direction LGD accompanying the thermal expansion and contraction is the maximum at the other end portion EP2. Accordingly, a condition is considered in which the light guide hole 2971_2 closest to the other end EP2 in the operating temperature fluctuation range T is within the range of the microlens ML corresponding to the light guide hole 2971_2. That is, a condition is considered in which the lens side opening 2971a of the light guide hole 2971_2 is within the range of the microlens ML2 in both cases of the lowest temperature and the highest temperature in the operating temperature fluctuation range T.

The column “microlens” in FIG. 17 indicates the microlens ML2 corresponding to the light guide hole 2971_2, and the column “at the lowest temperature” indicates the relative position of the light guide hole 2971_2 to the microlens ML at the lowest temperature. The column “at the highest temperature” indicates the relative position of the light guide hole 2971_2 to the microlens ML at the highest temperature. That is, the light guide hole 2971_2 moves in the arrow direction of the longitudinal direction LGD in FIG. When the temperature fluctuates from the lowest temperature to the highest temperature, the movement amount of the microlens ML2 in the longitudinal direction LGD is αm · L · T, and the movement amount of the light guide hole 2971_2 is αs · L · T. Here, the linear expansion coefficient αm is a linear expansion coefficient in the longitudinal direction LGD of the lens array 299, and the linear expansion coefficient αs is a linear expansion coefficient in the longitudinal direction LGD of the light shielding portion 297. Therefore, the movement amount ΔL of the light guide hole 2971_2 relative to the microlens ML2 is expressed by the following equation: ΔL = (αs−αm) · L · T
Given in. As shown in FIG. 17, even if the light shielding portion 297 moves with respect to the lens array 299, the inner diameter of the light guide hole 2971_2 (that is, the inner diameter of the lens side opening 2971_a of the light guide hole 2971_2) is reduced. In order not to deviate from the range of the aperture, the inner diameter Ds of the light guide hole 2971_2 should be smaller than the value obtained by subtracting the movement amount ΔL from the aperture Dl of the microlens ML2. Therefore, Formula 1, that is, the following formula D1- (αs-αm) · L · T ≧ Ds
By configuring the line head 29 to satisfy the above condition, the occurrence of a situation where the light guide hole 2971 is out of the range of the diameter of the microlens ML in the operating temperature fluctuation range T is suppressed. Therefore, the problem that the light beam emitted from the light emitting element group 295 is incident on the position outside the microlens ML corresponding to the light emitting element group 295 to generate a ghost is suppressed, and the microlens ML of the stray light SL is suppressed. Generation of ghosts due to incidence on the light is suppressed.

  The present invention is not limited to the above-described embodiments, and various modifications other than those described above can be made without departing from the spirit of the present invention. In other words, in the embodiment shown in FIG. 11, the light shielding portion 297 is composed of two members, the light shielding member 297A and the light shielding member 297B, but may be composed of three or more members. If a larger number of members are used, the relative position shift can be further reduced. Further, the shape of the gap 2975 may be any shape.

  Moreover, in each said embodiment, although the transparent substrate is comprised with glass, it cannot be overemphasized that the material of a transparent substrate is not restricted to glass. That is, the transparent substrate can be made of a material that can transmit a light beam.

  In each of the above embodiments, a plurality of light emitting element groups 295 are arranged as shown in FIG. That is, one light emitting element group 295 is configured by arranging two light emitting element rows L2951 arranged in the main scanning direction XX at predetermined intervals and arranged in two rows in the sub scanning direction YY. However, the number of the light emitting elements 2951 constituting the light emitting element group 295 and the arrangement method of the plurality of light emitting elements 2951 are not limited thereto, and can be changed as appropriate. However, as described above, the arrangement of the plurality of light emitting elements 2951 is preferable in that a favorable spot formation can be easily realized by adopting the above-described symmetrical arrangement.

  Further, in each of the above embodiments, the light emitting element group row L295 (group row) configured by arranging a predetermined number (two or more) of the light emitting element groups 295 in the main scanning direction XX is arranged in three rows in the sub scanning direction YY. The light emitting element groups 295 are two-dimensionally arranged. However, the arrangement of the plurality of light emitting element groups 295 is not limited to this, and can be changed as appropriate.

  In each of the above embodiments, the magnifying optical system is used as the imaging lens, but this is not an essential requirement for the present invention. That is, a reduction optical system having a magnification (optical magnification) of less than 1 or a 1 × optical system having a magnification of approximately 1 may be used as the imaging lens.

  In each of the above embodiments, a plurality of spots are arranged in a straight line in the main scanning direction XX as shown in FIG. 10 using the line head according to the present invention. However, the spot forming operation is an example of the operation of the line head according to the present invention, and the operation that can be executed by the line head is not limited thereto. That is, the formed spots do not need to be formed in a straight line along the main scanning direction XX. For example, the spots may be formed side by side with a predetermined angle in the main scanning direction XX, You may form in a waveform.

  In each of the above embodiments, the present invention is applied to a color image forming apparatus. However, the application target of the present invention is not limited to this, and a monochrome image forming apparatus that forms a so-called monochromatic image. The present invention can also be applied.

1 is a diagram illustrating an image forming apparatus and a line head according to a first embodiment of the present invention. 1 is a diagram illustrating an electrical configuration of an image forming apparatus and a line head. The perspective view which shows the outline of a line head. Sectional drawing of the subscanning direction of a line head. The perspective view which shows the outline of a microlens array. Sectional drawing of the main scanning direction of a micro lens array. The figure which shows arrangement | positioning of a several light emitting element group. The top view of the line head in the state accommodated in the case. The figure which shows the image formation state by the micro lens array in 1st Embodiment. The figure which shows the spot formation operation | movement by a line head. The top view of the line head in the state accommodated in the case in 2nd Embodiment of this invention. Sectional drawing which shows the line head in 3rd Embodiment. Sectional drawing which shows the line head in 3rd Embodiment. The figure which shows the positional relationship of a light guide hole and micro lens ML. The figure which shows a mode that incidence | injection of the micro lens ML of a stray light is suppressed. Explanatory drawing of the effect show | played by satisfy | filling Formula 1. FIG. Explanatory drawing of the effect show | played by satisfy | filling Formula 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 21 ... Photosensitive drum as latent image carrier, 211 ... Surface of photosensitive drum as scanning surface, 29 ... Line head as exposure means, 293 ... Glass substrate as substrate and transparent substrate , 2931 ... front surface, 2932 ... back surface, 295 ... light emitting element group, 2951 ... organic EL element as light emitting element, 297 ... light shielding part, 297A, 297
B ... light shielding member, 2971 ... light guide hole, 299 ... microlens array that is a collection of imaging lenses, 295C1, 295B1, 295A1, 295C2 ... spot collection, Dp ... diaphragm, Dpa ... diaphragm aperture

Claims (4)

A plurality of light emitting element groups are arranged in a longitudinal direction, and each of the plurality of light emitting element groups has a substrate having a plurality of light emitting elements that emit light beams;
A lens array having a plurality of imaging lenses provided so that one imaging lens corresponds to each of the plurality of light emitting element groups;
A light-shielding portion that is disposed between the substrate and the lens array and has a plurality of light guide holes provided so that one light guide hole corresponds to each of the plurality of light emitting element groups. ,
Each of the plurality of light guide holes is provided from a light emitting element group corresponding to the light guide hole toward an imaging lens corresponding to the light emitting element group, and transmits a light beam from the light emitting element group to the imaging lens. Guided to
The lens array and the light-shielding part are arranged apart from each other,
The light-shielding portion has, for each of the plurality of light guide holes, a stop aperture that allows a part of the light beam incident on the light guide hole to pass through an imaging lens corresponding to the light guide hole. Having a throttle part provided,
The inner diameter of the light guide hole in the longitudinal direction is the longitudinal light guide hole diameter Ds, the aperture diameter of the imaging lens in the longitudinal direction is the longitudinal lens diameter Dl, and the inner diameter of the diaphragm aperture in the longitudinal direction is the longitudinal aperture diameter Dd. When defined as
The line head characterized in that the longitudinal aperture diameter Dd is smaller than the longitudinal light guide hole diameter Ds, and the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl. The light shielding portion is composed of one or a plurality of light shielding members, and the plurality of light guide holes are provided for the light shielding members,
Of the plurality of light guide holes provided in the light shielding member, the light guide hole located at one end in the longitudinal direction is arranged at one end light guide hole and the other end in the longitudinal direction. When the light guide hole is defined as the other end light guide hole,
A distance L in the longitudinal direction between the optical axis of the imaging lens corresponding to the one end light guide hole and the optical axis of the imaging lens corresponding to the other end light guide hole; The linear expansion coefficient αm in the longitudinal direction, the linear expansion coefficient αs in the longitudinal direction of the light-shielding member, the operating temperature variation range T, the longitudinal light guide hole diameter Ds, and the longitudinal lens diameter Dl are expressed by the following formula: (Αs−αm) · L · T ≧ Ds
The line head according to claim 1, wherein: The light shielding member positioned in the middle in the longitudinal direction between the optical axis of the imaging lens corresponding to the one end light guide hole and the optical axis of the imaging lens corresponding to the other end light guide hole; When the part is defined as the central part of the light shielding member,
The line head according to claim 2, wherein the light shielding member is fixed to the lens array at the central portion. A latent image carrier whose surface is conveyed in the sub-scanning direction;
A plurality of light emitting element groups arranged in a longitudinal direction corresponding to a main scanning direction orthogonal to the sub-scanning direction, each of the plurality of light emitting element groups each having a plurality of light emitting elements that emit light beams;
A plurality of imaging lenses provided so that one imaging lens corresponds to each of the plurality of light emitting element groups; A lens array that forms spots on the surface of the latent image carrier;
A light-shielding portion that is disposed between the substrate and the lens array and has a plurality of light guide holes provided so that one light guide hole corresponds to each of the plurality of light emitting element groups. ,
Each of the plurality of light guide holes is provided from a light emitting element group corresponding to the light guide hole toward an imaging lens corresponding to the light emitting element group, and transmits a light beam from the light emitting element group to the imaging lens. Guided to
The lens array and the light-shielding part are arranged apart from each other,
The light-shielding portion has, for each of the plurality of light guide holes, a stop aperture that allows a part of the light beam incident on the light guide hole to pass through an imaging lens corresponding to the light guide hole. Having a throttle part provided,
The inner diameter of the light guide hole in the longitudinal direction is the longitudinal light guide hole diameter Ds, the aperture diameter of the imaging lens in the longitudinal direction is the longitudinal lens diameter Dl, and the inner diameter of the diaphragm aperture in the longitudinal direction is the longitudinal aperture diameter Dd. When defined as
The image forming apparatus, wherein the longitudinal aperture diameter Dd is smaller than the longitudinal light guide hole diameter Ds, and the longitudinal light guide hole diameter Ds is smaller than the longitudinal lens diameter Dl.

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