JP2008087352A - Line head and image forming device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a line head which can form good spots and an image forming device using the same free with less quality deterioration. <P>SOLUTION: A masking section 297 is formed of a plurality of masking members 297A, 297B, 297C and 297D split in the longitudinal direction having a larger relative dislocation through clearances 2975 due to a difference in a thermal expansion coefficient between the material of a microlens array 299 and the material of the masking members 297A, 297B, 297C and 297D forming the masking section 297. Compared with relative dislocation when formed of a single long masking member, dislocation per split masking member can be made small because of short length. Consequently, incidence of light beams emitted from a luminous element 2951 in the position other than facing microlens ML can be reduced, the occurrence of a ghost can be suppressed, and a line head 29 forming good spots can be obtained. <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 surface to be scanned 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, resin lens plates including a plurality of imaging lenses corresponding to a plurality of light emitting element groups on a one-to-one basis are arranged to face each other with a spacer interposed therebetween. Here, the thermal 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. There is known a configuration that suppresses the phenomenon of occurrence, so-called crosstalk (see Patent Document 2).

JP-A-6-297767 (page 3, FIGS. 1 and 2) Japanese Patent No. 2510423 (page 4, FIGS. 1 and 2)

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.
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.
An object of the present invention is to provide a line head in which a good spot is formed and an image forming apparatus using the line head with little deterioration in image quality.

  The line head of the present invention is a line head that forms a spot by forming an image of a light beam on a surface to be scanned, and includes a substrate having a main scanning direction as a longitudinal direction and a plurality of light emitting elements. A plurality of light emitting element groups arranged in a discrete manner and a one-to-one correspondence with the light emitting element groups are arranged, and each is emitted from the plurality of light emitting elements belonging to the opposing light emitting element groups. A lens array having a plurality of imaging lenses that image a light beam on the surface to be scanned, and a part of the light beams emitted from the plurality of light emitting elements belonging to the light emitting element group, A light-shielding portion that prevents light from entering the imaging lens that is different from the imaging lens facing the image-forming lens, and the light-shielding portion includes a plurality of light-shielding devices arranged in the longitudinal direction with gaps therebetween. It characterized in that it has a member.

  According to this invention, the light shielding portion is divided through the gap 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 lens array and the thermal expansion coefficient of the material of the light shielding member constituting the light shielding portion. A plurality of light shielding members. Compared to the relative position shift in the case of a single long light blocking member, the relative position shift per divided light blocking member is small because the length is short. Therefore, the light beam emitted from the light emitting element is less likely to be incident on a position other than the opposing imaging lens, and the generation of ghost is suppressed and a line head in which a good spot is formed can be obtained.

In the present invention, the light shielding member is disposed so that one surface thereof faces the substrate and the other surface faces the plurality of imaging lenses, and further, the light shielding member has a one-to-one correspondence with the plurality of light emitting element groups. It is preferable to have a plurality of light guide holes that penetrate from the one surface to the other surface.
In the present invention, in addition to the above-described effects, the light guide holes that penetrate through the light shielding member are disposed one-to-one between the light emitting element group and the opposing imaging lens. Of the emitted light beam, the light beam directly directed to the other imaging lens is shielded to prevent crosstalk, and a line head in which a good spot is formed can be obtained.

In the present invention, the gap preferably has a bent portion.
In the present invention, since the gap has a bent portion, the light beam passing along the gap is reflected by the bent portion and hardly passes directly. Therefore, the light beam does not leak into an imaging lens different from the imaging lens facing through the gap, and a ghost and crosstalk are suppressed, and a line head in which a good spot is formed can be obtained.

In the present invention, it is preferable that the light shielding member is fixed to the lens array at substantially the same distance from both ends of the light shielding member in the longitudinal direction.
In the present invention, the relative position of each light shielding member with respect to the lens array can be determined more accurately by fixing it in the vicinity of the central portion that is substantially the same distance from both longitudinal ends of the light shielding member. In addition, compared to the case where the light shielding member is fixed near the end, the distance to the both ends is substantially the same and shorter because the light is fixed near the center, and the expansion and contraction due to temperature changes from the fixed part is substantially the same. Smaller in size. Therefore, the displacement due to expansion and contraction is substantially uniform and small, and the generation of ghost is suppressed, and a line head in which a good spot is formed can be obtained.

In the present invention, it is preferable that the light shielding members are bonded to each other with an elastic adhesive filled in the gap.
In this invention, since the positional relationship between the light shielding members can be determined by the adhesive filled in the gap, the arrangement of the light guide holes of each light shielding member corresponding to the imaging lens of the lens array becomes accurate. Furthermore, since the adhesive has elasticity, the adhesive absorbs expansion and contraction due to a temperature change of the light shielding member, and the expansion and contraction of the entire light shielding part is suppressed. Accordingly, the relative position shift between the light shielding members and between the light shielding member and the lens array is further suppressed, and a line head in which a good spot is formed can be obtained.

In the present invention, the substrate is a transparent substrate capable of transmitting the light beam disposed so that a front surface thereof faces the light shielding member, and the light emitting element is disposed on a back surface of the transparent substrate. The organic EL element provided is preferable.
In the present invention, when the organic EL element is used as the light emitting element, the above-described effects can be obtained.

  The image forming apparatus according to the present invention includes the latent image carrier whose surface is conveyed in the sub-scanning direction, and the surface of the latent image carrier as a surface to be scanned to form spots on the surface of the latent image carrier. And an exposure unit having the same configuration as the line head.

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

Embodiments of the present invention will be described below with reference to the drawings.
(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) that form a plurality of images of different colors. 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 at 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.
In the present embodiment, the 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.

  The developing unit 25 has a developing roller 251 that carries toner on the surface thereof. 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.

  In the present embodiment, the photoreceptor cleaner 27 is 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. Is provided. 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.

  In the present embodiment, the photosensitive drum 21, the charging unit 23, the developing unit 25, and the photosensitive cleaner 27 of each of the image forming stations 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, 85K are positioned on the image forming stations Y, M, C, 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, which face 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 in this embodiment is demonstrated in detail based on figures.
FIG. 3 is a perspective view showing an outline of the line head 29 according to the embodiment of the present invention. 4 is a cross-sectional view of the line head 29 in 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 in the present embodiment includes a case 291 having the main scanning direction XX as a longitudinal direction, 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.

3 and 4, the case 291 holds the microlens array 299 in which the imaging lenses are arranged at a position facing the surface 211 of the photosensitive drum 21, and in the order close to the microlens array 299. Thus, a light shielding portion 297 and a glass substrate 293 as a substrate are provided. 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 as a longitudinal direction.
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 two-dimensionally and discretely arranged on the back surface 2932 of the glass substrate 293 so as to be separated from each other by a predetermined distance in the main scanning direction XX and the sub-scanning direction YY. Has been. 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.
In the present embodiment, an organic EL element is used as the light emitting element. That is, in this embodiment, the organic EL element is arranged 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. The light guide hole 2971 is formed as a substantially cylindrical hole penetrating 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 the figure) as a central axis. That is, light emitted from the light emitting elements 2951 belonging to the light emitting element group 295 is guided to the microlens array 299 through the light guide holes 2971 corresponding to the light emitting element groups 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 array 299 as indicated by a two-dot chain line. It becomes.

  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 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 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.

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 is two-dimensionally arranged at a predetermined distance from each other in the main scanning direction XX and the sub-scanning direction YY corresponding to the arrangement of the light emitting element groups 295.
In addition, the region 2995 in which the micro lens ML is not formed on the front surface 2991A and the back surface 2991B is in contact with the light shielding portion 297 illustrated in FIGS.

FIG. 7 is a diagram showing an arrangement of a plurality of light emitting element groups 295.
In the present embodiment, 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 arranging two light emitting element rows L2951 in the sub scanning direction YY. Yes. 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.

  The light emitting element group 295 is two-dimensionally arranged such that three light emitting element group rows L295 (group row) configured by arranging a predetermined number (two or more) of light emitting element groups 295 in the main scanning direction XX are arranged in the sub scanning direction YY. Is 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.

  Corresponding to the arrangement of the light emitting element groups 295, a light guide hole 2971 is formed in the light shielding portion 297 and a micro lens 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. 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 spotted on the surface 211 of the photosensitive drum 21 by the microlens array 299. Is imaged.

FIG. 8 is a plan view of the light shielding part 297 in a state of being housed in the case 291. The microlens array 299 is omitted.
In FIG. 8, the light shielding portion 297 includes light shielding members 297A, 297B, 297C, and 297D.
The light shielding members 297A, 297B, 297C, and 297D are arranged in the longitudinal direction, which is the main scanning direction XX, via the gap 2975.
The gap 2975 is provided so as to skew the three light guide holes 2971 aligned in the sub-scanning direction YY while shifting the position in the main scanning direction XX.
The gap 2975 is filled with an elastic adhesive 2976, and the light shielding members 297A, 297B, 297C, and 297D are bonded to each other.
Further, a central portion of each light shielding member 297A, 297B, 297C, 297D that is substantially the same distance from both longitudinal ends 2980 of each light shielding member 297A, 297B, 297C, 297D is a microlens (not shown) with a fixing adhesive 2977. Fixed to the array 299.

As the material of the light shielding members 297A, 297B, 297C, and 297D, it is preferable to use high-accuracy carbon steel or inexpensive resin that allows easy processing of the light guide hole 2971.
Note that the elastic adhesive 2976 is not necessarily required as long as the light shielding members 297A, 297B, 297C, and 297D are fixed by the fixing adhesive 2977 so that the relative positions thereof are not shifted.

Hereinafter, an image formation state of spots on the surface 211 of the photosensitive drum 21 by the microlens array 299 when the temperature change occurs in the line head 29 will be described.
FIG. 9 is a diagram showing an image formation state by the microlens array 299. The position of the microlens array 299 indicated by a thin broken line indicates the original relative position where the light shielding portion 297 is in contact with the region 2995 where the microlens ML of the microlens array 299 is not formed.

Hereinafter, an imaging state in the case where the microlens array 299 and the light shielding unit 297 are at their original relative positions 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 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.

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 trajectory of the light beam is represented by a two-dot chain line.
As shown 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 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.

Next, an imaging state when a temperature change occurs in the line head 29 will be described. A position of the microlens array 299 indicated by a solid line indicates a position shifted from an original relative position with respect to the light shielding portion 297 due to a temperature change.
Here, since the light beam emitted from the light emitting element 2951 has no directivity, it travels in various directions. An example of these light beams is indicated by a thick broken line.
In FIG. 9, when the temperature change occurs, the glass substrate 293 and the glass substrate 2991 and the light shielding portion 297 made of carbon steel or resin have different coefficients of thermal expansion. Therefore, the two lenses constituting the lens pair of the microlens ML are formed. The relative positions of the lenses 2993A and 2993B and the light shielding portion 297 are shifted. The position indicated by the dotted line is the relative position between the original microlens ML and the light shielding portion 297, and the position indicated by the solid line is the relative position after the temperature change has occurred.
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 length of the main scanning direction XX, which is the longitudinal direction of the microlens array 299, the light shielding unit 297, and the glass substrate 293 is longer.

  As a result of the relative position between the light shielding portion 297 and the microlens ML being shifted, the light beam indicated by the thick broken line is incident on the region 2995 where the microlens ML is not formed or the adjacent microlens ML, and the original imaging position. It reaches the position of the IG on the surface 211 different from the above, and causes a so-called ghost.

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 corresponding to each position of the sub-scanning direction positions Y1 to Y6. 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 rows L2951 are 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.
(1) The light shielding portion 297 has a long longitudinal direction with a large relative positional shift due to the difference between the thermal expansion coefficient of the material of the microlens array 299 and the thermal expansion coefficient of the materials of the light shielding members 297A, 297B, 297C, and 297D constituting the light shielding portion 297. It is composed of a plurality of light shielding members 297A, 297B, 297C, and 297D divided in the direction through a gap 2975. Compared to the relative position shift in the case of a single long light blocking member, the relative position shift per divided light blocking member can be reduced because the length is short. Therefore, it is possible to reduce the incidence of the light beam emitted from the light emitting element 2951 to a position other than the opposing microlens ML, to suppress the generation of ghost, and to obtain the line head 29 in which a good spot is formed. be able to.

  (2) In addition to the above-described effects, the light guide holes 2971 penetrating through the light shielding members 297A, 297B, 297C, and 297D are disposed one-to-one between the light emitting element group 295 and the facing microlenses ML. Therefore, among the light beams emitted from the light emitting element group 295, the light beam directly directed to the other microlens ML can be shielded, the crosstalk can be prevented, and the line head 29 in which a good spot is formed. Obtainable.

  (3) The relative positions of the light shielding members 297A, 297B, 297C, and 297D with respect to the microlens array 299 are in the vicinity of the center that is substantially the same distance from both end portions 2980 in the longitudinal direction of the light shielding members 297A, 297B, 297C, and 297D. It can be determined more accurately by fixing with. Further, compared to the case where the light shielding members 297A, 297B, 297C, and 297D are fixed in the vicinity of the end portions, the light shielding members 297A, 297B, 297C, and 297D are fixed in the vicinity of the central portion. The expansion and contraction due to the temperature change from is reduced to approximately the same size. Accordingly, the displacement due to expansion and contraction is substantially uniform and small, and the generation of ghost is suppressed, and the line head 29 in which a good spot is formed is obtained.

  (4) Since the positional relationship between the light shielding members 297A, 297B, 297C, and 297D can be determined by the adhesive 2976 filled in the gap 2975, each light shielding member 297A, corresponding to the microlens ML of the microlens array 299 is determined. The arrangement of the light guide holes 2971 of 297B, 297C, and 297D can be accurately performed. Furthermore, since the adhesive 2976 has elasticity, the adhesive 2976 can absorb the expansion and contraction due to the temperature change of the light shielding members 297A, 297B, 297C, and 297D, and the expansion and contraction of the entire light shielding part 297 can be suppressed. Therefore, it is possible to further suppress the relative positional deviation between the light shielding members 297A, 297B, 297C, and 297D and between the light shielding members 297A, 297B, 297C, and 297D and the microlens array 299, and the line head 29 in which a good spot is formed. Can be obtained.

  (5) Since the exposure means 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.

  (6) Since the gap 2975 is provided so as to skew the three light guide holes 2971 diagonally, the interval between the light guide holes 2971 in the main scanning direction XX can be narrowed, and the resolution of the image forming apparatus 1 is increased. Can do.

(Second Embodiment)
FIG. 11 is a plan view of the light shielding portion 297 in a state of being housed in the case 291 of the present embodiment.
This embodiment differs from the first embodiment in the shape of the gap. In the present embodiment, the gap 2978 is formed in parallel to both sides in the main scanning direction XX of the light shielding portion 297 that is a substantially rectangular parallelepiped.
Also in this embodiment, the adhesive 2976 having elasticity is filled in the gap 2978. However, if the light shielding members 297A, 297B, 297C, and 297D are sufficiently fixed by the fixing adhesive 2977, the gap 2978 is filled. It does not have to be.

According to this embodiment, there are the following effects.
(7) Since the gap 2978 is linear, the gap 2978 can be easily processed.

(Third embodiment)
FIG. 12 is a plan view of the light shielding portion 297 in a state of being housed in the case 291 of the present embodiment.
In FIG. 12, the first embodiment and this embodiment differ in the shape of the gap. The gap 2979 of this embodiment has a bent portion 2981. The bent portion 2981 is bent at a right angle.
Also in this embodiment, the adhesive 2976 having elasticity is filled in the gap 2979. However, if the light shielding members 297A, 297B, 297C, and 297D are sufficiently fixed by the fixing adhesive 2977, the gap 2979 is filled. You don't have to.
In addition, as the adhesive 2976 of this embodiment, an adhesive that transmits a light beam can be used.

According to this embodiment, there are the following effects.
(8) Since the gap 2979 has the bent portion 2981, the light beam passing along the gap 2979 is reflected by the bent portion 2981 and can hardly pass. Therefore, the light beam does not leak to the microlens ML different from the microlens ML facing through the gap 2979, and ghost and crosstalk can be suppressed, and the line head 29 in which a good spot is formed is obtained. be able to.

(Modification)
FIG. 13 is a cross-sectional view of the modified line head 29 in the sub-scanning direction YY.
The relative positions of the microlens array 299 and the light shielding portion 297 can be determined without using the elastic adhesive 2976 and the fixing adhesive 2977 as in the above-described embodiments.
For example, in FIG. 13, a protrusion 2915 is provided on the photosensitive drum 21 side of the case 291 in the first embodiment to form a case 2910. Then, the micro lens array 299, the light shielding unit 297, and the glass substrate 293 are sandwiched between the projection 2915 and the back cover 2913, and pressed by the fixing device 2914, so that the micro lens array 299, the light shielding unit 297, and the glass substrate 293 are movable. It is also possible to determine the relative position while leaving room for.

  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. That is, in the third embodiment, the bent portion 2981 is bent at a right angle, but it may be bent so that the light beam does not pass directly along the gap 2979, and the gap 2979 may be curved.

  In the first to third embodiments, the transparent substrate is made of glass, but it goes without saying that the material of the transparent substrate is not limited 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 light-shielding part in the state accommodated in the case in 1st Embodiment. The figure which shows the image formation state by a micro lens array. The figure which shows the spot formation operation | movement by a line head. The top view of the light-shielding part in the state accommodated in the case in 2nd Embodiment of this invention. The top view of the light-shielding part in the state accommodated in the case in 3rd Embodiment of this invention. Sectional drawing of the subscanning direction of the line head of a modification.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 21 ... Photosensitive drum as latent image carrier, 211 ... Surface 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, 297B, 297C, 297D ... light shielding member, 2971 ... light guide hole, 299 ... connection Microlens array which is a collection of image lenses, 295C1, 295B1, 295A1, 295C2 ... Spot collection, 2975, 2978, 2979 ... Gap, 2976 ... Elastic adhesive, 2980 ... Both ends, 2981 ... Bending part.

Claims (7)

A line head that forms a spot by imaging a light beam on a surface to be scanned;
A substrate whose longitudinal direction is the main scanning direction;
A plurality of light emitting element groups, and a plurality of light emitting element groups arranged discretely on the substrate;
A plurality of light beams emitted from a plurality of the light emitting elements belonging to the light emitting element groups facing each other and arranged in a one-to-one correspondence with the light emitting element groups are formed on the surface to be scanned. A lens array with an imaging lens;
A light shielding portion for preventing a part of light beams emitted from the plurality of light emitting elements belonging to the light emitting element group from entering the imaging lens different from the imaging lens facing the light emitting element group; Prepared,
The light-shielding portion includes a plurality of light-shielding members arranged with a gap in the longitudinal direction. The line head according to claim 1, wherein
The light-shielding member is disposed so that one surface thereof faces the substrate and the other surface faces the plurality of imaging lenses, and further, one-to-one with respect to the plurality of light emitting element groups from the one surface. A line head comprising: a plurality of light guide holes that are formed through the other surface. In the line head according to claim 1 and claim 2,
The line head characterized in that the gap has a bent portion. In the line head according to any one of claims 1 to 3,
The line head, wherein the light shielding member is fixed to the lens array at a position substantially the same distance from both ends of the light shielding member in the longitudinal direction. In the line head according to any one of claims 1 to 4,
The light shielding members are bonded to each other with an adhesive having elasticity filled in the gap. In the line head according to any one of claims 1 to 5,
The substrate is a transparent substrate capable of transmitting the light beam disposed so that a front surface thereof faces the light shielding member,
The light emitting element is an organic EL element provided on the back surface of the transparent substrate. A latent image carrier whose surface is conveyed in the sub-scanning direction;
An exposure unit having the same configuration as the line head according to claim 1, wherein spots are formed on the surface of the latent image carrier using the surface of the latent image carrier as a surface to be scanned. An image forming apparatus.

Images