This application claims the benefit of priority under 35 USC 119 of Japanese patent application no. 2008-009205, filed on Jan. 18, 2008, and Japanese patent application no. 2008-321936, filed on December 18, 2008, which are incorporated herein by reference.
1. Technical Field
The present invention relates to a lens array in which a plurality of lenses are arranged, an exposure head using the lens array, and an image forming apparatus.
2. Related Art
A lens array, for example, described in JP-A-6-278314 (
In order to cope with exposure with higher resolution, a lens array may be formed by arranging a plurality of lenses in a two-dimensional manner. That is, in this lens array, a plurality of lenses are arranged at different positions in a lateral direction (second direction) perpendicular or substantially perpendicular to a longitudinal direction to form a lens column, and a plurality of lens columns are arranged in the longitudinal direction.
In terms of preferable exposure, it is preferable to increase the amount of light incident on the lens. To this end, for example, it is considered to increase the diameter of the lens. However, in a lens array in which a plurality of lenses are arranged in a two-dimensional manner, in order to increase the diameter of the lens, it is necessary to increase a lens pitch in the lateral direction in the lens column. As a result, the width of the lens array (that is, the length in the lateral direction) increases, and the lens array increases in size.
An advantage of some aspects of the invention is that it provides a lens array that can cope with exposure with high resolution and can be reduced in size, an exposure head using the lens array, and an image forming apparatus.
According to a first aspect of the invention, a lens array includes a light-transmissive substrate that satisfies the condition W1>W2, where W1 is the length of the light-transmissive substrate in a first direction and W2 is the length of the light-transmissive substrate in a second direction perpendicular to the first direction, a first lens that is provided on the light-transmissive substrate, and a second lens that is provided on the light-transmissive substrate on the second direction side of the first lens. The first lens and the second lens are connected to each other.
In this aspect (the lens array) of the invention having the above-described configuration, the first lens and the second lens are provided on the light-transmissive substrate. The light-transmissive substrate satisfies the condition W1>W2, where W1 is the length of the light-transmissive substrate in the first direction and W2 is the length of the light-transmissive substrate in the second direction perpendicular or substantially perpendicular to the first direction. That is, the light-transmissive substrate is long in the first direction. The second lens is provided on the second direction side of the first lens. In other words, the first lens and the second lens are provided at different positions in the second direction. In this aspect of the invention, the first lens and the second lens are connected to each other. Therefore, the first lens and the second lens can be adapted to receive a larger amount of light without increasing a clearance between the first lens and the second lens. As a result, the lens array of this aspect can perform an exposure operation by a large light amount without increasing the width of the lens array in the second direction, can cope with exposure with high resolution, and can be reduced in size.
The light-transmissive substrate may be provided with a third lens in the first direction of the first lens, and a clearance may be provided between the first lens and the third lens. As described below, this configuration can prevent the lens array from being deformed due to a change in temperature, and thus ensures a more preferable exposure operation.
The light-transmissive substrate may be a glass member. That is, glass has a comparatively small linear expansion coefficient. Therefore, the configuration in which the light-transmissive substrate is a glass member can prevent the lens array from being deformed due to a change in temperature, and thus ensures a more preferable exposure operation.
The first lens, the second lens, and the third lens may be formed of a resin material. The resin material has a comparatively larger linear expansion coefficient than glass. For this reason, if the temperature changes, the lens array may be deformed due to a difference in linear expansion coefficient between the resin material and glass. Therefore, in the configuration in which the first lens, the second lens, and the third lens are formed of a resin material, a clearance is preferably provided between the first lens and the third lens in order to suppress deformation of the lens array due to a change in temperature.
The resin material may be photocurable resin. The photocurable resin is cured by light irradiation. Therefore, if the lens is formed of photocurable resin, the lens array can be simply manufactured.
According to a second aspect of the invention, an exposure head includes a lens array that has a light-transmissive substrate satisfying the condition W1>W2, where W1 is the length of the light-transmissive substrate in a first direction and W2 is the length of the light-transmissive substrate in a second direction perpendicular to the first direction, a first lens provided on the light-transmissive substrate, and a second lens provided on the light-transmissive substrate on the second direction side of the first lens, and a light emitting element substrate that has a first light emitting element emitting light toward the first lens and a second light emitting element emitting light toward the second lens. The first lens and the second lens are connected to each other.
In this aspect (the exposure head) of the invention having the above-described configuration, the lens array has the first lens and the second lens provided on the light-transmissive substrate. The light-transmissive substrate satisfies the condition W1>W2, where W1 is the length of the light-transmissive substrate in the first direction and W2 is the length of the light-transmissive substrate in the second direction perpendicular to the first direction. That is, the light-transmissive substrate is long in the first direction. The second lens is provided on the second direction side of the first lens In other words, the first lens and the second lens are provided at different positions in the second direction. In this aspect of the invention, the first lens and the second lens are connected to each other. Therefore, the first lens and the second lens can be adapted to receive a larger amount of light without increasing a clearance between the first lens and the second lens. As a result, the lens array of this aspect can perform an exposure operation by a large light amount without increasing the width of the lens array in the second direction, can cope with exposure with high resolution, and can be reduced in size.
In the configuration in which the first lens is connected to the second lens provided on the second direction side of the first lens, the lens can be adapted to receive a large light amount without increasing the clearance between the first lens and the second lens. In other words, the width of the lens array in the second direction can be suppressed. As a result, a region where a light emitting element is disposed to correspond to each lens can also be comparatively reduced in the second direction. For this reason, in the light emitting element substrate on which the light emitting elements are disposed, a space can be allowed on both sides in the second direction. A driving circuit for driving the light emitting element may be provided in the empty space. That is, the light emitting element substrate may be configured such that driving circuits for driving the first light emitting element and the second light emitting element are provided on the second direction sides of the first light emitting element and the second light emitting element.
In this case, the light emitting element substrate may be configured such that a first wiring connecting the first light emitting element and the driving circuit, and a second wiring connecting the second light emitting element and the driving circuit are provided. In this configuration, it is preferable that the driving circuits are provided on the second direction sides of the first light emitting element and the second light emitting element This is because the driving circuits can be disposed so as to be comparatively close to the light emitting elements, and thus the wirings can be reduced in length and driving signals having a small depression due to stray capacitance of the wirings can be supplied to the light emitting elements, thereby performing a preferable exposure operation. The driving circuit may include a TFT.
In the configuration in which an organic EL element is used as the light emitting element, the invention is preferably applied. That, is, when an organic EL element is used as the light emitting element, the light amount of the light emitting element is small, as compared with a case in which an LED or the like is used. In particular, when a bottom emission type organic EL element is used as the light emitting element, the light amount of the light emitting element becomes smaller. Therefore, the invention is preferably applied to such a configuration such that the lens receives a large light amount.
According to a third aspect of the invention, an image forming apparatus includes an exposure head that has a lens array having a light-transmissive substrate satisfying the condition W1>W2, where W1 is the length of the light-transmissive substrate in a first direction and W2 is the length of the light-transmissive substrate in a second direction perpendicular or substantially perpendicular to the first direction, a first lens provided on the light-transmissive substrate, and a second lens provided on the light-transmissive substrate on the second direction side of the first lens, and a light emitting element substrate having a first light emitting element emitting light toward the first lens and a second light emitting element emitting light toward the second lens, and a latent image carrier that images light incident on the first lens from the first light emitting element and images light incident on the second lens from the second light emitting element. The first lens and the second lens are connected to each other.
In this aspect (the image forming apparatus) of the invention having the above-described configuration, the lens array has the first lens and the second lens provided on the light-transmissive substrate. The light-transmissive substrate satisfies the condition W1>W2, where W1 is the length of the light-transmissive substrate in the first direction and W2 is the length of the light-transmissive substrate in the second direction perpendicular or substantially perpendicular to the first direction. That is, the light-transmissive substrate is long in the first direction. The second lens is provided on the second direction side of the first lens. In other words, the first lens and the second lens are provided at different positions in the second direction. In this aspect of the invention, the first lens and the second lens are connected to each other. Therefore, the first lens and the second lens can be adapted to receive a larger amount of light without increasing a clearance between the first lens and the second lens. As a result, the lens array of this aspect can perform an exposure operation by a large light amount without increasing the width of the lens array in the second direction, can cope with exposure with high resolution, and can be reduced in size.
A photoconductor drum may be used as a latent image carrier. In this case, if the imaging position of light having entered and been imaged on the first lens and the imaging position of light having entered and been imaged on the second lens are adjusted in accordance with the shape of the photoconductor drum, as described below, the photoconductor drum 21 can be reduced in diameter, and as a result the image forming apparatus can be reduced in size and preferable exposure can be achieved.
A clearance between the first lens and the second lens in the second direction may be set so as to be smaller than 1/20 of the diameter of the photoconductor drum. With this configuration, lens design can be simplified without considerably changing the shapes of the first lens and the second lens.
The first lens and the second lens may be free-form surface lenses. This is because the free-form surface lens ensures improvement of imaging characteristics of the lenses, thereby achieving more preferable exposure.
According to a fourth aspect of the invention, a lens array includes a light-transmissive lens array substrate, on which a plurality of lens columns each having a plurality of lenses arranged at different positions in a second direction perpendicular or substantially perpendicular to a first direction are arranged in the first direction. In each of the lens columns, adjacent lenses are connected to each other.
According to a fifth aspect of the invention, a line head includes a head substrate on which a plurality of light emitting element groups each having a plurality of light emitting elements are arranged, and a lens array in which a lens is provided on a light-transmissive lens array substrate for each light emitting element group. On the lens array substrate, a plurality of lens columns each having a plurality of lenses arranged at different positions in a second direction perpendicular or substantially perpendicular to a first direction are arranged in the first direction. In each of the lens columns, adjacent lenses are connected to each other.
According to a sixth aspect of the invention, an image forming apparatus includes a line head that has a head substrate, on which a plurality of light emitting element groups each having a plurality of light emitting elements are arranged, and a lens array, in which a lens is provided on a light-transmissive lens array substrate for each light emitting element group, and a latent image carrier that is exposed by the line head and has formed thereon a latent image. On the lens array substrate, a plurality of lens columns each having a plurality of lenses arranged at different positions in a second direction perpendicular or substantially perpendicular to a first direction are arranged in the first direction. In each of the lens columns, adjacent lenses are connected to each other.
In these aspects (the lens array, the line head, and the image forming apparatus) of the invention having the above-described configuration, a plurality of lenses are provided on the light-transmissive lens array substrate, and on the lens array substrate, a plurality of lens columns each having a plurality of lenses arranged at different positions in the second direction perpendicular or substantially perpendicular to the first direction are arranged in the first direction. In each of the lens columns, adjacent lenses are connected to each other. Therefore, the lenses can be adapted to receive a large amount of light without increasing the lens pitch in the lateral direction in each lens column. That is, the lens array of this aspect can cope with exposure with high resolution, is reduced in size, and is preferable.
In the lens array substrate, a clearance may be provided between adjacent lens columns in the first direction. With this configuration, it is possible to suppress occurrence of a trouble due to connection of a plurality of lenses arranged in the first direction, as described below.
The lens array substrate may be formed of glass. Glass has a comparatively small linear expansion coefficient. Therefore, if the lens array substrate is formed of glass, the lens array can be prevented from being deformed due to a change in temperature, and as a result, preferable exposure can be achieved without depending on the temperature.
The lenses may be formed of photocurable resin. The photocurable resin is cured by light irradiation. Therefore, if the lenses are formed of photocurable resin, the lens array can be simply manufactured. As a result, costs for the lens array can be suppressed.
The lenses may be free-form surface lenses. This is because the free-form surface lens ensures improvement of imaging characteristics of the lenses, thereby achieving more preferable exposure.
The invention will now be described with reference to the accompanying drawings, wherein like numbers reference like elements.
Hereinafter, the terms initially used herein will be described (see “A. Description of Terms”). Next to the description of terms, embodiments of the invention will be described (see “B. Embodiments”).
A collection of a plurality (in
As shown in the “ON IMAGE PLANE” column of
As shown in the “LENS ARRAY” column of
As shown in the “HEAD SUBSTRATE” column of
As shown in the “LIGHT EMITTING ELEMENT GROUP” column of
As shown in the “SPOT GROUP” column of
Provided inside a main housing 3 of the image forming apparatus is an electric component box 5 housing a power supply circuit board, the main controller MC, the engine controller EC, and the head controller HC. An image forming unit 7, a transfer belt unit 8, and a sheet feed unit 11 are also provided inside the main housing 3. In
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 images in different colors. Each of the image forming stations Y, M, C, and K is provided with a cylindrical photoconductor drum 21 having a surface with a predetermined length in the main scanning direction MD. Each of the image forming stations Y, M, C, and K forms a toner image of the corresponding color on the surface of the photoconductor drum 21. The photoconductor drum is disposed such that the axial direction thereof is substantially parallel to the main scanning direction MD. Each of the photoconductor drums 21 is connected to a dedicated driving motor and is driven to rotate at a predetermined speed in a direction of an arrow D21 in
The charging section 23 includes a charging roller having a surface made of elastic rubber. The charging roller is configured so as to be rotated by contact with the photoconductor drum 21 at a charging position, and is rotated in accordance with the rotational operation of the photoconductor drum 21 in a driven direction with respect to the photoconductor drum 21 at a circumferential speed. The charging roller is connected to a charging bias generating section (not shown), is supplied with power for a charging bias from the charging bias generating section, and charges the surface of the photoconductor drum 21 at the charging position where the charging section 23 and the photoconductor drum 21 come into contact with each other.
The line head 29 is disposed with respect to the photoconductor drum 21 such that the longitudinal direction thereof corresponds to the main scanning direction MD, and the lateral direction thereof corresponds to the sub scanning direction SD. The longitudinal direction of the line head 29 is substantially parallel to the main scanning direction MD. The line head 29 has a plurality of light emitting elements arranged in the longitudinal direction, and is separated from the photoconductor drum 21. Light emitted from the light emitting elements is irradiated onto the surface of the photoconductor drum 21 charged by the charging section 23, and therefore an electrostatic latent image is formed on the surface of the photoconductor drum 21.
The developing section 25 has a developing roller 251 having toner born on the surface thereof. A developing bias is applied to the developing roller 251 from a developing bias generating section (not shown) electrically connected to the developing roller 251. Thus, toner is moved from the developing roller 251 to the photoconductor drum 21 at a developing position where the developing roller 251 and the photoconductor drum 21 come into contact with each other, and the electrostatic latent image formed by the line head 29 is visualized.
The toner image visualized at the developing position is moved in the rotational direction D21 of the photoconductor drum 21, and then primary transferred to the transfer belt 81 described below in detail at a primary transfer position TR1 where the transfer belt 81 and each of the photoconductor drums 21 come into contact with each other.
In this embodiment, the photoconductor cleaner 27 is provided on a downstream side of the primary transfer position TR1 and on an upstream side of the charging section 23 in the rotational direction D21 of the photoconductor drum 21 so as to come into contact with the surface of the photoconductor drum 21. The photoconductor cleaner 27 removes residual toner on the surface of the photoconductor drum 21 after the primary transfer to clean the surface of the photoconductor drum by contact with the surface of the photoconductor drum.
The transfer belt unit 8 includes a driving roller 82, a driven roller 83 (blade-opposed roller) provided on a left side of the driving roller 82 in
When the monochrome mode is executed, the color primary transfer rollers 85Y, 85M, and 85C from among the four primary transfer rollers 85 are separated from the image forming stations Y, M, and C correspondingly opposite to the color primary transfer rollers 85Y, 85M, and 85C, and only the monochrome primary transfer roller 85K comes into contact with the image forming station K. That is, only the monochrome image forming station K comes 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, the primary transfer bias is applied from the primary transfer bias generating section to the monochrome primary transfer roller 85K with appropriate timing. Thus, the toner image formed on the surface of the photoconductor drum 21 is transferred to the surface of the transfer belt 81 at the primary transfer position TR1 to form a monochrome image.
The transfer belt unit 8 includes a downstream guide roller 86 that is provided on a downstream side of the monochrome primary transfer roller 85K and an upstream side of the driving roller 82. The downstream guide roller 86 is configured to come into contact with the transfer belt 81 on a common internal tangent of the primary transfer roller 85K and the photoconductor drum 21 at the primary transfer position TR1 formed by contact of the monochrome primary transfer roller 85K with the photoconductor drum 21 of the image forming station K.
The driving roller 82 is circularly driven in the direction of the arrow D81 in
The sheet feed unit 11 includes a sheet feed portion that has a sheet feed cassette 77 that can hold a stack of sheets, and a pickup roller 79 that feeds the sheet one by one from the sheet feed cassette 77. The sheet fed by the pickup roller 79 from the sheet feed section is fed to the secondary transfer position TR2 along the sheet guide member 15 after the feed timing thereof is adjusted by a pair of register rollers 80.
The secondary transfer roller 121 is provided so as to be freely separated from or come into contact with the transfer belt 81, and is driven to be separated from or come into contact with the transfer belt 81 by a secondary transfer roller driving mechanism (not shown). The fixing unit 13 has a rotatable heating roller 131 that has an internal heater, such as a halogen heater, and a pressing section 132 that presses and urges a heating roller 131. The sheet with the image secondary transferred to the surface thereof is guided by the sheet guide member 15 to a nip portion, which is formed between the heating roller 131 and a pressing belt 1323 of the pressing section 132, and the image is thermally fixed in the nip portion at a predetermined temperature. The pressing section 132 has two rollers 1321 and 1322, and the pressing belt 1323 stretched between the rollers 1321 and 1322. If a tensioned part of the surface of the pressing belt 1323 stretched by the two rollers 1321 and 1322 is pressed against the peripheral surface of the heating roller 131, the nip portion formed between the heating roller 131 and the pressing belt 1323 increases. The sheet subjected to the fixing process is fed to a sheet discharge tray 4 provided in an upper surface of the main housing 3.
In this apparatus, a cleaner section 71 is provided so as to be opposite to the blade-opposed roller 83. The cleaner section 71 has a cleaner blade 711 and a waste toner box 713. The cleaner blade 711 removes foreign substances, such as residual toner on the transfer belt after the secondary transfer or paper dust, by bringing a tip portion thereof into contact with the blade-opposed roller 83 through the transfer belt 81. The thus-removed foreign substances are collected into the waste toner box 713. The cleaner blade 711 and the waster toner box 713 are formed integrally with the blade-opposed roller 83. Therefore, as described below, when the blade-opposed roller 83 moves, the cleaner blade 711 and the waste toner box 713 also move together with the blade-opposed roller 83.
The line head 29 includes a case 291, and positioning pins 2911 and screw insertion holes 2912 are provided at both ends of the case 291 in the longitudinal direction LGD. The positioning pins 2911 are fitted into positioning holes (not shown) provided in a photoconductor cover (not shown) covering the photoconductor drum 21 and being positioned with respect to the photoconductor drum 21, thereby positioning the line head 29 with respect to the photoconductor drum 21. In addition, set screws are screwed into and fixed to screw holes (not shown) of the photoconductor cover through the screw insertion holes 2912, thereby positioning and fixing the line head 29 with respect to the photoconductor drum 21.
Inside the case 291, the head substrate 293, a light shielding member 297, and two lens arrays 299 (299A and 299B) are disposed. The inside of the case 291 comes into contact with a surface 293-h of the head substrate 293, and a back lid 2913 comes into contact with a reverse side surface 293-t of the head substrate 293. The back lid 2913 is pressed into contact with the inside of the case 291 through the head substrate 293 by a retainer 2914. That is, the retainer 2914 has an elastic force for pressing the back lid 2913 against the inside of the case 291 (an upper side in
On the reverse side surface 293-t of the head substrate 293, a light emitting element group 295 having a plurality of light emitting elements is provided. The head substrate 293 is formed of a light-transmissive member, such as glass, and the light beam emitted from each of the light emitting elements in the light emitting element group 295 can transmit from the reverse side surface 293-t of the head substrate 293 to the surface 293-h. The light emitting element is a bottom emission type organic EL (Electro-Luminescence) element, and is covered with a seal member 294. The details of the arrangement of the light emitting elements on the reverse side surface 293-t of the head substrate 293 are as follows.
On the reverse side surface 293-t of the head substrate 293, a plurality of light emitting element groups 295 configured as described above are arranged. That is, three light emitting element groups 295 are arranged at different positions in the lateral direction LTD to form the light emitting element group column 295C, and a plurality of light emitting element group columns 295C are arranged along the longitudinal direction LGD. In each of the light emitting element group columns 295C, three light emitting element groups 295 are out of alignment in the longitudinal direction LGD by the light emitting element group pitch Peg. As a result, the positions PTE of the light emitting element groups 295 in the longitudinal direction LGD are different from each other. In other words, on the reverse side surface 293-t of the head substrate 293, a plurality of light emitting element groups 295 are arranged in the longitudinal direction LGD to form the light emitting element group row 295R, and three light emitting element group rows 295R are provided in the lateral direction LTD. The light emitting element group rows 295R are out of alignment in the longitudinal direction LGD by the light emitting element group pitch Peg. As a result, the positions PTE of the light emitting element groups 295 in the longitudinal direction LGD are different from each other. As described above, in this embodiment, a plurality of light emitting element groups 295 are arranged on the head substrate 293 in a two-dimensional manner. In
The light emitting elements 2951 formed on the head substrate 293 in the above-described manner are driven by, for example, a TFT (Thin Film Transistor) circuit or the like, and emit light beams having the same wavelength. A light emitting surface of each of the light emitting elements 2951 is a so-called perfect diffuse surface light source, and a light beam emitted from the light emitting surface follows the Lamberts' cosine law.
The description will be continued with reference to
As described above, the light shielding member 297 that is provided with the light guide hole 2971 for each light emitting element group 295 is arranged between the light emitting element group 295 and the lens array 299 in the beam travel direction Doa. Therefore, the light beams emitted from the light emitting element group 295 pass through the light guide hole 2971 corresponding to the light emitting element group 295 and go toward the lens array 299. To put it the other way around, from among the light beams emitted from the light emitting element group 295, a light beam toward the light guide holes 2971 other than the light guide hole 2971 corresponding to the light emitting element group 295 is shielded by the light shielding member 297. In this way, the light beams emitted from one light emitting element group 295 all go toward the lens array 299 through the same light guide hole 2971, and inference between light beams emitted from different light emitting element group 295 is prevented by the light shielding member 297.
In other words, in the lens array 299, a plurality of lenses LS are arranged in the longitudinal direction LGD to form the lens row LSR, and three lens rows LSR are provided in the lateral direction LTD. The lens rows LSR are arranged so as to be out of alignment in the longitudinal direction LGD by the lens pitch Pls, and the positions PTL of the lenses LS in the longitudinal direction LGD are different from each other. As described above, in the lens array 299, a plurality of lenses LS are arranged in a two-dimensional manner. In
As shown in
In the line head 29, two lens arrays 299 (299A and 299B) having the above-described configuration are arranged in the beam travel direction Doa, and two lenses LS1 and LS2 arranged in the beam travel direction Doa are disposed for each light emitting element group 295 (
As described above, the line head 29 includes an optical system having the first and second lenses LS1 and LS2. Therefore, the light beams emitted from the light emitting element group 295 are imaged by the first lens LS1 and the second lens LS2, and the spots SP are formed on the surface (image plane) of the photoconductor drum. Meanwhile, as described above, the surface of the photoconductor drum is charged by the charging section 23 before the spots are formed. Therefore, regions where the spots SP are formed are neutralized, and spot latent images Lsp are formed. The thus-formed spot latent images Lsp are born on the surface of the photoconductor drum and sent toward the downstream side in the sub scanning direction SD. Then, as described below, the spots SP are formed with timing according to the movement of the surface of the photoconductor drum, and thus a plurality of spot latent images Lsp are formed so as to be arranged in the main scanning direction MD.
Specifically, in the line head 29, a plurality of light emitting element groups 295 (for example, light emitting element groups 295_1, 295_2, and 295_3) are disposed at different positions in the lateral direction LTD. The light emitting element groups 295 disposed at different positions in the lateral direction LTD form spot groups SG (for example, spot groups SG_1, SG_2, and SG_3) in the sub scanning direction SD.
In other words, in the line head 29, a plurality of light emitting element 2951 are disposed at difference positions in the lateral direction LTD (for example, the light emitting element 2951 belonging to the light emitting element group 295_1 and the light emitting element 2951 belonging to the light emitting element group 295_2 are disposed at different positions in the lateral direction LTD). The light emitting elements 2951 disposed at different positions in the lateral direction LTD form the spots SP at different positions in the sub scanning direction SD (for example, the spot SP belonging to the spot group SG_1 and the spot SP belonging to the spot group SG_2 are formed at different positions in the sub scanning direction SD).
As described above, the forming positions of the spots SP in the sub scanning direction SD by the light emitting elements 2951 are different from each other. Therefore, in order to form a plurality of spot latent images Lsp arranged in the main scanning direction MD (that is, in order to form a plurality of spot latent images Lsp at the same positions in the sub scanning direction SD), a difference between the spot forming positions should be taken into consideration. Therefore, in the line head 29, the light emitting elements 2951 emit light with timing according to the movement of the surface of the photoconductor drum.
First, from among the light emitting element rows 2951R belonging to the light emitting element groups 295_1, 295_4 on the uppermost stream side in the lateral direction LTD (
Next, from among the light emitting element rows 2951R belonging to the light emitting element groups 295_1, 295_4, the light emitting element rows 2951R on the upstream side in the lateral direction LTD perform the light emission operation. Then, a plurality of light beams emitted by this light emission operation are imaged by the lenses LS, and the spots SP are formed on the surface of the photoconductor drum. Therefore, the spot latent images Lsp are formed at the positions corresponding to the hatched patterns in the “SECOND” line of
Next, from among the light emitting element rows 2951R belonging to the light emitting element group 295_2 and the like on the second uppermost stream side in the lateral direction, the light emitting element rows 2951R on the downstream side in the lateral direction LTD perform the light emission operation. Then, a plurality of light beams emitted by this light emission operation are imaged by the lenses LS, and the spots SP are formed on the surface of the photoconductor drum. Therefore, the spot latent images Lsp are formed at the positions corresponding to the hatched patterns in the “THIRD” line of
Next, from among the light emitting element rows 2951R belonging to the light emitting element group 295_2 and the like on the second uppermost stream side in the lateral direction, the light emitting element rows 2951R on the upstream side in the lateral direction LTD perform the light emission operation. Then, a plurality of light beams emitted by this light emission operation are imaged by the lenses LS, and the spots SP are formed on the surface of the photoconductor drum. Therefore, the spot latent images Lsp are formed at the positions corresponding to the hatched patterns in the “FOURTH” line of
Next, from among the light emitting element rows 2951R belonging to the light emitting element group 295_3 and the like on the third uppermost stream side in the lateral direction, the light emitting element rows 2951R on the downstream side in the lateral direction LTD perform the light emission operation. Then, a plurality of light beams emitted by this light emission operation are imaged by the lenses LS, and the spots SP are formed on the surface of the photoconductor drum. Therefore, the spot latent images Lsp are formed at the positions corresponding to the hatched patterns in the “FIFTH” line of
Finally, from among the light emitting element rows 2951R belonging to the light emitting element group 295_3 and the like on the third uppermost stream side in the lateral direction, the light emitting element rows 2951R on the upstream side in the lateral direction LTD perform the light emission operation. Then, a plurality of light beams emitted by this light emission operation are imaged by the lenses LS, and the spots SP are formed on the surface of the photoconductor drum. Therefore, the spot latent images Lsp are formed at the positions corresponding to the hatched patterns in the “SIXTH” line of
As described above, in this embodiment, a plurality of lenses LS are provided on the light-transmissive lens array substrate 2991. On the lens array substrate 2991, a plurality of lens columns LSC each having a plurality of lenses LS arranged at different positions in the lateral direction LTD (second direction) are arranged in the longitudinal direction LGD (second direction). Adjacent lenses LS in each of the lens columns LSC are connected to each other. That is, in each of the lens columns LSC, no clearance is provided between adjacent lenses LS, and adjacent lenses LS are connected to each other. Therefore, the lenses LS can be adapted to receive a large amount of light, without increasing the lens pitch (Corresponding to the lens row pitch Plsr) in the lateral direction LTD in each of the lens columns LSC. The lens array 299 of this embodiment can cope with exposure with high resolution, is reduced in size, and is preferable. With this lens array 299, the line head 29 or the image forming apparatus 1 can be reduced in size.
In this embodiment, the clearance CL is provided between adjacent the lens columns LSC in the longitudinal direction LGD on the lens array substrate 2991. Therefore, the lens array 299 can be prevented from being flexed due to a change in temperature, and thus this embodiment is preferable. When no clearance CL is provided between adjacent lens columns LSC in the longitudinal direction LGD, and the lenses LS are connected to each other between adjacent lens columns LSC, a plurality of lenses LS arranged in the longitudinal direction LGD are connected to each other. In this case, since the lenses LS are formed of photocurable resin, resin is stretched in the longitudinal direction LGD on the lens array substrate 2991. In other words, a long agglomerate of resin in the longitudinal direction LGD is formed on the lens array substrate 2991. The resin has a comparatively larger linear expansion coefficient than glass as a base material of the lens array substrate 2991. For this reason, while the agglomerate of resin significantly expands and contracts in the longitudinal direction LGD due to the change in temperature, the amount of expansion and contraction of the lens array substrate 2991 in the longitudinal direction LGD is comparatively small. As a result, if the temperature changes, the lens array 299 may be flexed. In contrast, in this embodiment, the clearance CL is provided between adjacent lens columns LSC in the longitudinal direction LGD, and thus occurrence of flex is suppressed
In this embodiment, an organic EL element is used as the light emitting element 2951, and since the organic EL element has a light amount smaller than an LED (Light Emitting Diode) or the like, the amount of light received by the lens LS tends to become small. In particular, when a bottom emission type organic EL element is used, some of light beams emitted from the organic EL element are absorbed by the head substrate 293, and accordingly the amount of light received by the lens LS becomes smaller. In contrast, in this embodiment, adjacent lenses LS in each of the lens columns LSC are connected to each other, and thus the lenses LS can receive a large amount of light. Therefore, even in the configuration in which a bottom emission type organic EL element is used as the light emitting element 2951, preferable exposure can be performed.
In
The symbol h in the “SECTIONAL VIEW” column of FIG. 14 denotes a height from the flat region Ap at a position (vertex Lt) on the lens surface of each lens LS where the height from the flat region Ap has a maximum value. That is, the symbol h denotes the height of the vertex Lt of each lens LS from the flat region Ap, and each lens LS has the same height h. The function f(x,y) denotes a height from the lens surface at the position (x,y) to the vertex Lt (first position) of the lens LS. In addition, in
f(p1/2,p2/2)<h
That is, the first lens LS11 and the second lens LS21 are connected to each other in the lens row arrangement direction Dlsc, and the boundary ED of the first lens LS11 and the second lens LS21 has a height Δ(=h−f(p1/2,p2/2)>0) from the flat region Ap.
As described above, since adjacent lenses LS in the lens row arrangement direction Dlsc are connected to each other, the lenses LS can receive a larger amount of light without increasing the interval p3 between the lenses LS. The details are as follows.
With the configuration of
In the second embodiment, the clearance CL is provided between adjacent lenses LS (for example, the lens LS11 and the lens LS12) in the longitudinal direction LGD, thereby preventing the lens array 299 from being deformed due to a change in temperature. As described above, while the lens array substrate 2991 is formed of glass, the lenses LS are formed of resin. That is, the lens array substrate 2991 and the lenses LS are formed of different materials. For this reason, when no clearance CL is provided between adjacent lenses LS in the longitudinal direction LGD, a long agglomerate in the longitudinal direction LGD is formed on the lens array substrate 299. Accordingly, if the temperature changes, the lens array 299 may be deformed due to a difference in linear expansion coefficient between the agglomerate and the lens array substrate 299. In particular, when the lenses LS are formed of resin, since the resin has a comparatively large linear expansion coefficient, this deformation may be noticeable. If the lens array 299 is deformed, the imaging position of light maybe changed, and thus a preferable exposure operation may not be performed. In contrast, in the second embodiment, since the clearance CL is provided between adjacent lenses LS (for example, the lens LS11 and the lens LS12) in the longitudinal direction LGD, the lens array 299 can be prevented from being deformed, and thus a preferable exposure operation can be performed.
In the second embodiment, the lenses LS are formed of photocurable resin. The photocurable resin is cured by light irradiation. Therefore, if the lenses LS are formed of photocurable resin, the lens array 299 can be simply manufactured.
In the foregoing embodiments, the longitudinal direction LGD and the main scanning direction MD correspond to the “first direction” of the invention, the lateral direction LTD and the sub scanning direction SD correspond to the “second direction” of the invention, and the photoconductor drum 21 corresponds to the “latent image carrier” of the invention. In the second embodiment, the lens LS11 and the lens LS21 provided on the lateral direction LTD side of the lens LS11 are connected to each other. The lens LS11 corresponds to the “first lens” of the invention, and the lens LS21 corresponds to the “second lens” of the invention. In addition, the clearance CL is provided between the lens LS11 and the lens LS12 provided on the longitudinal direction LGD side of the lens LS11. The lens LS12 corresponds to the “third lens” of the invention. The head substrate 293 corresponds to the “light emitting element substrate” of the invention.
The invention is not limited to the foregoing embodiments, and various modifications may be made without departing from the scope of the invention. In the foregoing embodiments, each of the light emitting element groups 295 has two light emitting element rows 2951R. However, the number of light emitting element rows 2951R constituting each of the light emitting element groups 295 is not limited to two. For example, the number of light emitting element rows 2951R may be one. In addition, in the foregoing embodiments, each of the light emitting element rows 2951R has four light emitting elements 2951. However, the number of light emitting elements 2951 constituting each of the light emitting element rows 2951R is not limited to four. Therefore, each of the light emitting element groups 295 can be constituted as follows.
In
In the example of
In the foregoing embodiments, the lens array 299 is formed by forming the lenses LS on the reverse side surface 2991-t of the lens array substrate. However, the configuration of the lens array is not limited thereto. For example, the lens array 299 may be formed by forming the lenses LS on the surface 2991-h of the lens array substrate, or the lens array 299 may be formed by forming the lenses LS on both surfaces 2991-t and 2991-h of the lens array substrate.
In the foregoing embodiment, the three lens rows LSR are arranged in the lateral direction LTD. However, the number of lens rows LSR is not limited to three. For example, the number of lens rows LSR may be one.
In the foregoing embodiments, the two lens arrays 299 are used, but the number of lens arrays 299 is not limited thereto.
In the foregoing embodiment, an organic EL element is used as the light emitting element 2951. However, an element other than the organic EL element may be used as the light emitting element 2951, or an LED (Light Emitting Diode) may be used as the light emitting element 2951.
Next, an example of the invention will be described. It should be noted that the invention is not limited to the example, and various modifications, which also fall within the technical scope of the invention, may be made without departing from the scope of the invention.
The following example refers to the configuration capable of reducing the size of the image forming apparatus and achieving preferable exposure. Specifically, the diameter of the photoconductor drum 21 becomes a factor in determining the size of the image forming apparatus. For this reason, in terms of reduction of the size of the image forming apparatus, it is demanded to reduce the diameter of the photoconductor drum 21. Meanwhile, around the photoconductor drum 21, the functional sections, such as the charging section 23, the developing section 25, and the like, need to be disposed in the sub scanning direction SD, in addition to the line head 29. Therefore, if the photoconductor drum 21 is simply reduced in diameter, these functional sections may not be disposed. In contrast, as described in the foregoing embodiments, the line head 29 of the invention becomes small in size in the lateral direction LTD (sub scanning direction SD). Therefore, a space for the functional sections can be ensured, and the photoconductor drum 21 can be reduced in diameter.
When the photoconductor drum 21 is reduced in diameter, the following problems may occur. That is, when the photoconductor drum 21 is reduced in diameter, the curvature of the surface shape of the photoconductor drum 21 increases. For this reason, like the above-described line head 29, when a plurality of lenses LS are provided in the lateral direction LTD, if the imaging position of each lens LS in the beam travel direction Doa is set so as to be identical, there may be a lens LS in which the imaging position is out of alignment with the surface of the photoconductor drum 21. As a result, preferable exposure may not be performed. In the following example, a technology capable of reducing the diameter of the photoconductor drum 21 and achieving preferable exposure will be described.
In this example, the optical systems are arranged in the left-right direction of
In this way, the imaging position of each of the lenses LS is adjusted in accordance with the surface shape of the photoconductor drum 21. Therefore, the photoconductor drum 21 is reduced in diameter, thereby reducing the size of the image forming apparatus, and thus preferable exposure can be achieved.
In the foregoing example, the lenses LS of the lens array 299 are free-form surface lenses. The free-form surface lens is a lens whose lens surface is a free-form surface. Therefore, the imaging characteristics of the lenses can be improved, and thus preferable exposure can be achieved.
The diameter of the photoconductor drum 21 is not limited to the above-described value, but it may be changed. For example, as shown in
In addition, in order to adjust the imaging position FP for each lens LS in accordance with the shape of the photoconductor drum 21 having a diameter of 36 [mm], the imaging position varies between the optical system including the upstream lens LS-u (or the downstream lens LS-d) and the optical system including the middle lens LS-m. Specifically, the distance ΔFP is set to 0.078 [mm]. In another example of the numerical values, the distance ΔFP is obtained on the basis of data of the optical systems shown in
As described above, in yet another example of the numerical values, the distance ΔFP is suppressed small, as compared with another example of the numerical values described above. As a result, lens design can be simplified without significantly changing the lens characteristic of each lens LS so much. This is because the lens row pitch Plsr (=1.5 [mm]) is set so as to be smaller than the diameter (=45 [mm]) of the photoconductor drum 21. What is necessary to simplify lens design is that the lens row pitch Plsr is equal to or less than ½ of the diameter (=45 [mm]) of the photoconductor drum 21. In this example, the lens row pitch Plsr corresponds to the “clearance between the first lens and the second lens in the second direction” of the invention.
Number | Date | Country | Kind |
---|---|---|---|
2008-009205 | Jan 2008 | JP | national |
2008-321936 | Dec 2008 | JP | national |