Patent Application
20110123210
1. Technical Field
The present invention relates to an image forming device and an image forming method using an exposure head adapted to image a light beam emitted from a light emitting element with an imaging optical system.
2. Related Art
As the exposure head of this kind, there is known a line head adapted to image light beams emitted from a plurality of light emitting elements as a plurality of spots. In the line head (the exposure head in the document) described in JP-A-2004-66758, for example, there are arranged a corresponding number of light emitting elements to one line in a direction corresponding to the main scanning direction, and the light beams emitted from the respective light emitting elements are imaged as spots by a gradient index lens. Then, by sequentially forming a latent image of every line on a surface of a latent image carrier moving in a sub-scanning direction, a two-dimensional latent image corresponding to a desired image can be formed.
Incidentally, in order for achieving latent image formation with higher resolution, it is possible to use a line head having light emitting element groups obtained by grouping a plurality of light emitting elements. Specifically, in this line head, there is formed a plurality of light emitting element group columns, each of which has a plurality of light emitting element groups disposed at positions different from each other in a direction (a width direction) corresponding to a sub-scanning direction, disposed in a direction (a longitudinal direction) corresponding to a main-scanning direction. However, in the line head having a plurality of light emitting element groups disposed at positions different from each other in the width direction as described above, if a moving velocity of the surface of the latent image carrier varies, the position at which the latent image is formed is shifted in the sub-scanning direction, and in some cases, preferable latent image formation is not achievable.
In view of the problem described above, the invention has an advantage of providing a technology capable of preventing the misalignment of the position at which the latent image is formed caused by the variation in the moving velocity of the surface of the latent image carrier from occurring, thereby achieving preferable latent image formation.
An image forming device according to an aspect of the invention includes an exposure head having a plurality of light emitting elements arranged in a first direction, a first imaging optical system adapted to image light emitted from the light emitting elements, and a second imaging optical system disposed in a second direction with respect to the first imaging optical system, a latent image carrier movable in the second direction, a detection section adapted to detect a moving time the latent image carrier takes to move from a first position to a second position in the second direction, and a control section adapted to control the time from emission of a first part of the light emitting elements adapted to emit light to be imaged by the first imaging optical system to emission of a second part of the light emitting elements adapted to emit light to be imaged by the second imaging optical system based on the detection result of the detection section, thereby aligning a latent image formed on the latent image carrier by the first imaging optical system and a latent image formed on the latent image carrier by the second imaging optical system in the first direction.
Further, an image forming method according to another aspect of the invention includes (a) detecting time a latent image carrier takes to move from a first position to a second position, (b) controlling time from emission of a first light emitting element adapted to emit light to be image by a first imaging optical system to emission of a second light emitting element adapted to emit light to be image by a second imaging optical system based on the detection result in step (a).
These aspects of the invention (the image forming device, the image forming method) configured as described above, detects the time the latent image carrier takes to move from the first position to the second position. Further, the time from emission of a first light emitting element adapted to emit light to be image by a first imaging optical system to emission of a second light emitting element adapted to emit light to be image by a second imaging optical system is controlled based on the detection result described above. Therefore, even in the case in which the variation is caused in the velocity of the latent image carrier in the period from emission of the light emitting elements adapted to emit light to be imaged by the first imaging optical system to emission of the light emitting elements adapted to emit light to be imaged by the second imaging optical system disposed in the second direction from the first imaging optical system, a favorable latent image can be formed.
Further, the control section controls the time from the emission of the first part of the light emitting elements adapted to emit light to be imaged by the first imaging optical system to emission of a third part of the light emitting elements adapted to emit light to be imaged by the first imaging optical system and disposed on the second direction side of the first part of the light emitting elements based on the detection result of the detection section, thereby aligning the latent image formed on the latent image carrier by the first part of the light emitting elements and a latent image formed on the latent image carrier by the third part of the light emitting elements in the first direction. In such a configuration, even in the case in which the variation is caused in the velocity of the latent image carrier in the period from emission of the first light emitting elements adapted to emit light to be imaged by the first imaging optical system to emission of the third light emitting elements adapted to emit light to be imaged by the first imaging optical system and disposed in the second direction side from the first light emitting elements, a favorable latent image can be formed.
Further, the invention is preferably adapted to the image forming device using the photoconductor drum rotating in the second direction as the latent image carrier. In particular, the invention is preferably applied to the image forming device having a drive source and a gear adapted to transmit the driving power from the drive source to the photoconductor drum. In other words, in such a configuration, there are some cases in which the rotational velocity is varied. Therefore, by applying the present invention to the device, a favorable latent image can be formed regardless of the rotational velocity variation.
On this occasion, it is preferable that a distance between the first imaging optical system and the second imaging optical system in the second direction is longer than a distance of the photoconductor drum obtained by multiplying a velocity variation period of the photoconductor drum by an average velocity of the photoconductor drum.
It should be noted that the velocity variation period can easily be obtained from an inverse of a value obtained by multiplying the number of rotations per unit time of the photoconductor drum by the number of teeth of the gear.
It is possible to apply the invention to the image forming device in which the gear is connected to the photoconductor drum via the coupling, or the image forming device in which the gear and the photoconductor drum are connected integrally. In either of the configurations, since there are some cases in which the rotational velocity of the photoconductor drum is varied, it is preferable to realize the preferable latent image formation independently of the rotational velocity variation of the photoconductor drum by applying the invention.
Further, it is also possible that the detection section has an encoder disc with a plurality of slits arranged radially from a rotational axis of the photoconductor drum, and an optical sensor adapted to detect the at least one slit. According to the detection section, the position of the photoconductor drum can be obtained with high accuracy, and it is advantageous to realize the preferable latent image formation.
Further, the detection section can be configured to have two optical sensors disposed on both sides of the rotational center of the photoconductor drum in the radial direction of the photoconductor drum. By disposing the two optical sensors in the radial direction of the photoconductor drum on both sides of the rotational center of the photoconductor drum, it becomes possible to suppress the influence of the eccentricity of the two optical sensors with respect to the rotational center of the photoconductor drum, thus the position of the photoconductor drum can be obtained with good accuracy.
Further, it is also possible to configure that a distance between light beam imaged by the first imaging optical system and light beam imaged by the second imaging optical system in the second direction of the latent image carrier is a value obtained by multiplying a pixel-to-pixel distance in the pixels in the second direction by an integral number. By configuring as described above, the emission timing control of the light emitting elements can be simplified.
It is also possible to configure that the pixel-to-pixel distance in the second direction is shorter than the pixel-to-pixel distance in the first direction in the pixel. By configuring as described above, the latent image formation in the second direction can be executed with high resolution. On this occasion, when the control section controls the emission of the light emitting elements with the PMW control, such latent image formation with high resolution can be achieved with relative ease.
Further, it is possible to configure the image forming device so as to include a latent image carrier, an exposure head a light emitting element, and an imaging optical system adapted to image the light from the light emitting element on the latent image carrier, a detection section adapted to detect a position of the latent image carrier, and a control section controls the emission of the light emitting element based on the detection result of the detection section, thus forming the latent image on the latent image carrier. The image forming device thus configured detects the position of the latent image carrier. Further, the control section controls the emission of the light emitting elements based on the detection result to form the latent image on the latent image carrier. Therefore, even in the case in which the variation is caused in the velocity of the latent image carrier, the latent image can preferably be formed.
An image forming device according to still another aspect of the invention includes a latent image carrier having a surface moving in a second direction one of perpendicular and substantially perpendicular to a first direction, a line head having a head substrate having a plurality of light emitting element groups each including a plurality of light emitting elements as a group disposed on the head substrate, and a lens array having a plurality of imaging optical systems provided respectively to the light emitting element groups and adapted to image the light beams emitted by the light emitting elements of the light emitting element group to form spots on a surface of the latent image carrier, a control section adapted to light the light emitting elements at a timing corresponding to the movement of the surface of the latent image carrier, and a detection section adapted to detect moving velocity of the surface of the latent image carrier, and in the head substrate of the line head, a plurality of light emitting element group columns, each of which has a plurality of light emitting element groups arranged at different positions from each other in the second direction, arranged in the first direction, assuming that the plurality of spots formed when each of the light emitting elements of the light emitting element group emit light beams simultaneously is defined as a spot group, the light emitting element groups of the light emitting element group column forms the spot groups at positions different from each other in the second direction, the control section adjusts the emission timing of the light emitting elements in accordance with the moving velocity of the surface of the latent image carrier detected by the detection section.
Further, a control method of a line head according to still another aspect of the invention includes exposing a latent image carrier surface moving in a second direction perpendicular to or substantially perpendicular to a first direction by making each of light emitting elements of a line head at a predetermined timing, the line head having a head substrate having a plurality of light emitting element groups each having a plurality of light emitting elements as a group arranged thereon, and a lens array having a plurality of imaging optical systems adapted to image light beams emitted by the light emitting elements of the light emitting element group to form spots on a surface of latent image carrier disposed corresponding respectively to the light emitting element groups, and in the head substrate of the line head, a plurality of light emitting element group columns, each of which has a plurality of light emitting element groups arranged at different positions from each other in the second direction, arranged in the first direction, assuming that the plurality of spots formed when each of the light emitting elements of the light emitting element group emit light beams simultaneously is defined as a spot group, the light emitting element groups of the light emitting element group column forms the spot groups at positions different from each other in the second direction, and in the exposing step, the moving velocity of the latent image carrier surface is detected, and the emission timing of the light emitting elements is adjusted based on the detection result.
In these aspects of the invention (the image forming device, the control method of a line head) configured as described above, the moving velocity of the latent image carrier surface is detected, and at the same time, the emission timing is adjusted based on the detection result. Therefore, it becomes possible to prevent the shift of the latent image formation position caused by the variation in the moving velocity of the surface of the latent image carrier from occurring, thus the preferable latent image formation becomes possible.
Further, the control section can be configured to adjust the emission timing of the light emitting elements in accordance with the difference between the moving velocity of the latent image carrier surface and the reference velocity. In such a configuration, since the emission timing of the light emitting elements is adjusted based on the shift of the moving velocity of the surface of the latent image carrier from the reference velocity, it becomes possible to efficiently prevent the shift of the latent image formation position, thus the preferable latent image formation becomes possible.
Further, the reference velocity can be an average value of the moving velocity of the surface of the latent image carrier. In such a configuration, since the emission timing of the light emitting elements is adjusted based on the shift of the moving velocity of the surface of the latent image carrier from the average value, it becomes possible to efficiently prevent the shift of the latent image formation position, thus the preferable latent image formation becomes possible.
Further, it is particularly preferable to apply the invention to the image forming device using the photoconductor drum rotating around the rotating shaft perpendicular to or substantially perpendicular to the second direction as the latent image carrier, and the circumferential surface of the photoconductor drum moves in the second direction as the latent image carrier surface. The reason therefor is that there are some cases in which the variation in the rotational velocity occurs in the photoconductor drum, and the variation in the rotational velocity causes the variation of the moving velocity of the circumferential surface of the photoconductor drum as the latent image carrier surface. Therefore, it is preferable to apply the invention to such an image forming device to prevent the shift of the latent image formation position caused by the variation in the moving velocity of the surface of the latent image carrier from occurring.
Further, it is possible that the detection section has a encoder disc having a plurality of slits disposed radially from the rotating shaft of the photoconductor drum, and an optical sensor adapted to detect the slit, and is configured to detect the moving velocity of the circumferential surface of the photoconductor drum based on the detection result of the optical sensor. According to such a configuration, the detection of the moving velocity of the circumferential surface of the photoconductor drum is executed based on the plurality of slits disposed radially from the rotating shaft of the photoconductor drum. Therefore, it becomes possible to detect the moving velocity of the circumferential surface of the photoconductor drum with high accuracy.
Further, the detection section can be configured to have two optical sensors disposed on both sides of the rotating shaft of the photoconductor drum. In such a configuration, the two optical sensors are provided. Further, the two optical sensors are disposed on both sides of the rotating shaft of the photoconductor drum. Therefore, as described later, even in the case in which the two optical sensors are disposed eccentrically with respect to the rotating shaft, it is possible to prevent the influence of the eccentricity, and to preferably detect the moving velocity.
Further, the control section makes the light emitting elements emit light at the timing corresponding to the movement of the latent image carrier surface to form the spots to the pixels of the latent image carrier surface, and further, it is possible to configure that the pitch of a plurality of spot groups formed by the light emitting element group columns in the second direction is a value obtained by multiplying the pixel pitch in the second direction by an integral number. The reason therefor is that as described later, by adopting such a configuration, it becomes possible to simplify the emission timing control of the light emitting elements.
The invention will now be described with reference to the accompanying drawings, wherein like numbers reference like elements.
Before explaining embodiments of the invention, the terms used in the present specification will be explained.
An aggregate of a plurality (eight in
Further, spot group row SGR and spot group column SGC are defined as shown in the “SURFACE OF IMAGE PLANE” section in
Lens row LSR and lens column LSC are defined as shown in the “LENS ARRAY” section in the drawing. Specifically, a plurality of lenses LS arranged in the longitudinal direction LGD is defined as the lens row LSR. Further, a plurality of lens rows LSR is arranged side by side in the width direction LTD at a predetermined lens row pitch Plsr. Further, a plurality (three in the drawing) of lenses LS arranged consecutively at a pitch having a component of the width direction LTD equal to the lens row pitch Plsr and a component of the longitudinal direction LGD equal to a lens pitch Pls is defined as a lens column LSC. It should be noted that the lens row pitch Plsr is a distance in the width direction LTD between the geometric centroids of the respective two lens rows LSR adjacent to each other in the width direction LTD. Further, the lens pitch Pls is a distance in the longitudinal direction LGD between the geometric centroids of the respective two lens LS adjacent to each other in the longitudinal direction LGD.
Light emitting element group row 295R and light emitting element group column 295C are defined as shown in the “HEAD SUBSTRATE” section in the drawing. Specifically, a plurality of light emitting element groups 295 arranged in the longitudinal direction LGD is defined as the light emitting element group row 295R. Further, a plurality of light emitting group rows 295R is arranged side by side in the width direction LTD at a predetermined light emitting element group row pitch Pegr. Further, a plurality (three in the drawing) of light emitting element groups arranged consecutively at a pitch having a component of the width direction LTD equal to the light emitting element group row pitch Pegr and a component of the longitudinal direction LGD equal to a light emitting element group pitch Peg is defined as a light emitting element group column 295C. It should be noted that the light emitting element group row pitch Pegr is a distance in the width direction LTD between the geometric centroids of the respective two light emitting element group rows 295R adjacent to each other in the width direction LTD. Further, the light emitting element group pitch Peg is a distance in the longitudinal direction LCD between the geometric centroids of the respective two light emitting element groups 295 adjacent to each other in the longitudinal direction LCD.
Light emitting element row 2951R and light emitting element column 2951C are defined as shown in the “LIGHT EMITTING ELEMENT GROUP” section in the drawing. Specifically, in each of the light emitting element groups 295, a plurality of light emitting elements 2951 arranged in the longitudinal direction LGD is defined as the light emitting element group row 2951R. Further, a plurality of light emitting element rows 2951R is arranged side by side in the width direction LTD at a predetermined light emitting element row pitch Pelr. Further, a plurality (two in the drawing) of light emitting elements 2951 arranged consecutively at a pitch having a component of the width direction LTD equal to the light emitting element row pitch Pelr and a component of the longitudinal direction LCD equal to a light emitting element pitch Pel is defined as a light emitting element column 2951C. It should be noted that the light emitting element row pitch Pelr is a distance in the width direction LTD between the geometric centroids of the respective two light emitting element rows 2951R adjacent to each other in the width direction LTD. Further, the light emitting element pitch Pel is a distance in the longitudinal direction LGD between the geometric centroids of the respective two light emitting elements 2951 adjacent to each other in the longitudinal direction LGD.
Spot row SPR and spot column SPC are defined as shown in the “SPOT GROUP” section in the drawing. Specifically, in each of the spot groups SG, a plurality of spots SP arranged in the longitudinal direction LGD is defined as the spot row SPR. Further, a plurality of spot rows SPR is arranged side by side in the width direction LTD at a predetermined spot row pitch Pspr. Further, a plurality (two in the drawing) of spots SP arranged consecutively at a pitch having a component of the width direction LTD equal to the spot row pitch Pspr and a component of the longitudinal direction LGD equal to a spot pitch Psp is defined as a spot column SPC. It should be noted that the spot row pitch Pspr is a distance in the sub-scanning direction SD between the geometric centroids of the respective two spot rows SPR adjacent to each other in the sub-scanning direction SD. Further, the spot pitch Psp is a distance in the longitudinal direction LGD between the geometric centroids of the respective two spots SP adjacent to each other in the main-scanning direction MD.
Inside a main housing 3 provided to the image forming device, there is disposed an electric component box 5 housing a power supply circuit board, the main controller MC, the engine controller EC, and the head controller HC. Further, an image forming unit 7, a transfer belt unit 8, and a paper feed unit 11 are also disposed inside the main housing 3. Further, inside the main housing 3 and on the right side thereof in
The image forming unit 7 is provided with four image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) for forming images with plural colors different from each other. Further, each of the image forming stations Y, M, C, and K is provided with a cylindrical photoconductor drum 21 having a surface (a circumferential surface) with a predetermined length in the main-scanning direction MD. Further, 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 so as to have the axial direction thereof substantially parallel to the main-scanning direction MD. Further, each of the photoconductor drums 21 is connected to a dedicated drive motor, and is driven to rotate at a predetermined velocity in a direction of the arrow D21 in the drawing. Thus, the surface, of the photoconductor drum 21 is moved in the sub-scanning direction SD perpendicular to or substantially perpendicular to the main-scanning direction MD. Further, around the photoconductor drum 21, there are disposed along the rotational direction, a charging section 23, the line head 29, a developing section 25, and a photoconductor cleaner 27. Further, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional sections. Therefore, when executing the color mode, the toner images respectively formed by all of the image forming stations Y, M, C, and K are overlapped on a transfer belt 81 provided to a transfer belt unit 8 to form a color image, and when executing the monochrome mode, a monochrome image is formed using only the toner image formed by the image forming station K. It should be noted that in
The charging section 23 is provided with a charging roller having a surface made of elastic rubber. The charging roller is configured so as to be rotated by the contact with the surface of the photoconductor drum 21 at a charging position, and is rotated in association with the rotational operation of the photoconductor drum 21 in a driven direction with respect to the photoconductor drum 21 at a circumferential velocity. Further, the charging roller is connected to a charging bias generating section (not shown), accepts the power supply for the 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 have contact with each other.
The line head 29 is disposed corresponding to the photoconductor drum 21 so that the longitudinal direction thereof corresponds to the main-scanning direction MD and the width direction thereof corresponds to the sub-scanning direction SD, and the longitudinal direction of the line head 29 is arranged to be substantially parallel to the main-scanning direction MD. The line head 29 is provided with a plurality of light emitting elements arranged in the longitudinal direction, and is disposed separately from the photoconductor drum 21. Further, these light emitting elements emit light onto the surface of the photoconductor drum 21 charged by the charging section 23, thereby forming an electrostatic latent image on the surface thereof (an exposure process).
The developing section 25 has a developing roller 251 with a surface holding the toner. Further, the charged toner is moved to the photoconductor drum 21 from the developing roller 251 by a developing bias applied to the developing roller 251 from a developing bias generating section (not shown) electrically connected to the developing roller 251 at the developing position where the developing roller 251 and the photoconductor drum 21 have contact with each other, thereby making the electrostatic latent image formed by the line head 29 visible.
The toner image thus made visible at the developing position is fed in the rotational direction D21 of the photoconductor drum 21, and then primary-transferred to the transfer belt 81 described in detail later at a primary transfer position TR1 at which the transfer belt 81 and each of the photoconductor drums 21 have contact with each other.
Further, in the present embodiment, the photoconductor cleaner 27 is disposed downstream of the primary transfer position TR1 and upstream of the charging section 23 in the rotational direction D21 of the photoconductor drum 21 so as to have contact with the surface of the photoconductor drum 21. The photoconductor cleaner 27 remove the residual toner on the surface of the photoconductor drum 21 after the primary transfer to clean the surface thereof by having contact with the surface of the photoconductor drum 21.
The transfer belt unit 8 is provided with a drive roller 82, a driven roller 83 (hereinafter also referred to as a blade-opposed roller 83) disposed on the left of the drive roller 82 in
On the other hand, when executing the monochrome mode, the primary transfer rollers 85Y, 85M, and 85C for color printing out of the four primary transfer rollers 85 are separated from the image forming stations Y, M, and C respectively opposed thereto, while only the primary transfer roller 85K mainly for monochrome printing is pressed against the image forming station K, thus making only the image forming station K mainly for monochrome printing have contact with the transfer belt 81. As a result, the primary transfer position TR1 is formed only between the primary transfer roller 85K mainly for monochrome printing and the corresponding image forming station K. Then, by applying the primary transfer bias to the primary transfer roller 85K mainly for monochrome printing from the primary transfer bias generating section with appropriate timing, 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.
Further, the transfer belt unit 8 is provided with a downstream guide roller 86 disposed on the downstream side of the primary transfer roller 85K mainly for monochrome printing and on the upstream side of the drive roller 82. Further, the downstream guide roller 86 is arranged to have 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 the primary transfer roller 85K mainly for monochrome printing having contact with the photoconductor drum 21 of the image forming station K.
The drive roller 82 circularly drives the transfer belt 81 in the direction of the arrow D81 shown in the drawing, and at the same time functions as a backup roller of a secondary transfer roller 121. On the peripheral surface of the drive roller 82, there is formed a rubber layer with a thickness of about 3 mm and a volume resistivity of no greater than 1000 kΩ·cm, which, when grounded via a metal shaft, serves as a conducting path for a secondary transfer bias supplied from a secondary transfer bias generating section not shown via the secondary transfer roller 121. By thus providing the rubber layer having an abrasion resistance and a shock absorbing property to the drive roller 82, the impact caused by a sheet entering the contact section (a secondary transfer position TR2) between the drive roller 82 and the secondary transfer roller 121 is hardly transmitted to the transfer belt 81, thus the degradation of the image quality can be prevented.
The paper feed unit 11 is provided with a paper feed section including a paper feed cassette 77 capable of holding a stack of sheets and a pickup roller 79 for feeding the sheet one-by-one from the paper feed cassette 77. The sheet fed by the pickup roller 79 from the paper 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 resist rollers 80.
The secondary transfer roller 121 is provided so as to be able to be selectively contacted with and separated from the transfer belt 81, and is driven to be selectively contacted with and separated from the transfer belt 81 by a secondary transfer roller drive mechanism (not shown). The fixing unit 13 has a rotatable heating roller 131 having a heater such as a halogen heater built-in and a pressing section 132 for biasing the heating roller 131 to be pressed against an object. Then, the sheet with the image, which is secondary-transferred on the surface thereof, is guided by the sheet guide member 15 to a nipping section formed of the heating roller 131 and a pressing belt 1323 of the pressing section 132, and the image is thermally fixed in the nipping section at predetermined temperature. The pressing section 132 is composed of two rollers 1321, 1322 and the pressing belt 1323 stretched across the two rollers. Further, it is arranged that by pressing a tensioned part of the surface of the pressing belt 1323, which is stretched by the two rollers 1321 and 1322, against the peripheral surface of the heating roller 131, a large nipping section can be formed between the heating roller 131 and the pressing belt 1323. Further, the sheet on which the fixing process is thus executed is fed to a paper catch tray 4 disposed on an upper surface of the main housing 3.
Further, in the present device, a cleaner section 71 is disposed facing 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 matters such as the toner remaining on the transfer belt 81 after the secondary transfer process or paper dust by pressing a tip section thereof against the blade-opposed roller 83 via the transfer belt 81. Then the foreign matters thus removed are collected into the waste toner box 713. Further, the cleaner blade 711 and the waste toner box 713 are configured 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 should also move together with the blade-opposed roller 83.
The case 291 holds a lens array 299 at a position opposed to the surface of the photoconductor drum 21, and is provided with a light shielding member 297 and a head substrate 293 disposed inside thereof in this order from the lens array 299. The head substrate 293 is made of a material (e.g., glass) capable of transmitting a light beam. Further, on the reverse surface (the opposite surface to the surface with the lens array 299 out of the two surfaces provided to the head substrate 293) of the head substrate 293, there is disposed a plurality of bottom emission type, organic Electro-Luminescence (EL) elements as the light emitting elements 2951. As described later, the plurality of light emitting elements 2951 is divided into light emitting element groups 295 and separately disposed as groups. Further, the light beams emitted from each of the light emitting element groups 295 penetrate the head substrate 293 from the reverse side to the obverse side thereof and proceed towards the light shielding member 297.
The light shielding member 297 is provided with a plurality of light guide holes 2971 penetrating the light shielding member corresponding one-on-one to the plurality of light emitting element groups 295. Further, such a light guide hole 2971 is provided as a substantially cylindrical hole penetrating the light shielding member 297 along a line parallel to the normal line of the head substrate 293 as the center axis thereof. Therefore, the light beams proceeding towards other areas than the light guide holes 2971 corresponding to the light emitting element group 295 out of the light beams emitted from the light emitting element group 295 are shielded by the light shielding member 297. Thus, all of the light beams emitted from the same light emitting element group 295 proceed towards the lens array 299 via the same light guide hole 2971, and the interference between the light beams emitted from different light emitting element groups 295 can be prevented by the light shielding member 297. Further, the light beams passing through the light guide hole 2971 provided to the light shielding member 297 are each imaged by the lens array 299 on the surface of the photoconductor drum 21 as a spot.
As shown in
The lens array 299 has a plurality of lenses LS arranged so as to have the respective optical axes OA substantially parallel to each other. Further, the lens array 299 is disposed so that the optical axes OA of the respective lenses LS are substantially perpendicular to the reverse surface (the surface on which the light emitting elements 2951 are disposed) of the head substrate 293. The lenses LS are disposed corresponding one-on-one to the light emitting element groups 295, and arranged two-dimensionally corresponding to the arrangement of the light emitting groups 295 described later. Specifically, a plurality of lens columns LSC composed of three lenses LS disposed at different positions from each other in the width direction LTD is arranged in the longitudinal direction LGD.
In each of the light emitting element groups 295, two light emitting element rows 2951R each having four light emitting elements 2951 arranged along the longitudinal direction LGD are arranged in parallel in the width direction LTD (
In correspondence with the light emitting element group rows 295R_A, 295R_B, and 295R_C, there are provided drive circuits DC_A (for the light emitting element group row 295_A), DC_B (for the light emitting element group row 295_B), and DC_C (for the light emitting element group row 295_C), respectively, and the drive circuits DC_A, DC_B, and DC_C are composed of thin film transistors (TFTs) (
The drive operation of the drive circuit DC is controlled based on the video data VD. Specifically, when receiving a vertical request signal VREQ from the head controller HC, the main controller MC generates the video data VD corresponding to one page (
It should be noted that in the first embodiment, corresponding respectively to the colors of YMCK, there are four sets of the signals described above, namely the request signals VREQ, HREQ transmitted from the head controller HC to the main controller MC, and the video data VD transmitted from the main controller MC to the head controller HC. The colors are hereinafter discriminated by adding a hyphen and a symbol representing one of the colors to signal names, if necessary. For example, the vertical request signal, the horizontal request signal, and video data for yellow are denoted as VREQ-Y, HREQ-Y, and VD-Y, respectively.
The main-side communication module 52 time-division multiplexes the four colors of video data VD-Y, VD-M, VD-C, and VD-K output from the image processing section 51, and transmits the video data VD thus multiplexed to the head controller HC serially via differential output terminals TX+, TX−. On the other hand, the vertical request signals VREQ_Y, VREQ_M, VREQ_C, and VREQ_K, and the horizontal request signals HREQ_Y, HREQ_M, HREQ_C, and HREQ_K are time-division multiplexed and input from the head controller HC via differential input terminals RX+, RX−. These request signals VREQ, HREQ are developed into parallel signals, and the vertical request signals VREQ (e.g., VREQ-Y) are input to the image processing blocks 512 (e.g., 512Y) for the respective colors.
The head control module 54 is provided with four head control blocks 541Y (for yellow), 541M (for magenta), 541C (for cyan), and 541K (for black) corresponding to the respective colors. The head control blocks 541Y, 541M, 541C, and 541K output the request signals VREQ_Y, VREQ_M, VREQ_C, VREQ_K, HREQ_Y, HREQ_M, HREQ_C, and HREQ_K for requesting the video data VD-Y, VD-M, VD-C, and VD-K, respectively, and meanwhile, control the exposure operations of the line heads 29 of the respective colors based on the video data VD-Y, VD-M, VD-C, and VD-K, thus received.
The horizontal request signal HREQ-Y is also input to a divisional HREQ signal generation section 543, and the divisional HREQ signal generation section 543 multiplies the request signal HREQ-Y by, for example, 16 to generate the divisional HREQ signal. The divisional HREQ signal is input to an emission order control section 544, and the emission order control section 544 reorders the video data VD-Y based on the divisional HREQ signal. Specifically, as described later, each of the light emitting element group rows 295R forms the spot groups SG at the positions a sub-scanning spot group pitch Psgs shifted from each other in the sub-scanning direction SD (e.g.,
An output buffer 545 supplies the drive circuits DC_A, DC_B, and DC_C with the video data VD-Y_A, VD-Y_B, and VD-Y_C, respectively, via the data transfer lines. The output buffer 545 is composed of, for example, shift registers. Further, the drive circuits DC_A, DC_B, and DC_C drive the light emitting elements 2951 to emit light based on the video data VD-Y_A, VD-Y_B, and VD-Y_C supplied from the output buffer 545, respectively. On this occasion, the driving of emission by the drive circuits DC_A, DC_B, and DC_C is performed in sync with emission timing Tu supplied from an emission timing signal generation section 546 explained as follows.
The divisional HRFQ signal is also input to the emission timing signal generation section 546, and the emission timing signal generation section 546 generates the emission timing Tu based on the divisional HREQ signal. The emission timing signal generation section 546 is connected to each of the drive circuits DC_A, DC_B, and DC_C via emission timing control lines LTu, and each of the emission timing control lines LTu is used commonly by the drive circuits. The emission timing signal generation section 546 supplies each of the drive circuits DC_A, DC_B, and DC_C with the emission timing Tu via the emission timing control lines LTu. Further, the drive circuits DC_A, DC_B, and DC_C drive the corresponding light emitting elements 2951 of the light emitting element group rows 295R_A, 295R_B, and 295R_C to emit light at the emission timing Tu based on the video data VD-Y_A, VD-Y_B, and VD-Y_C supplied previously, respectively. By thus controlling the driving of emission of the light emitting elements 2951 at every emission timing Tu, it becomes possible to form the spots SP respectively to the pixels PX on the surface of the photoconductor drum. Therefore, the spot forming operation will hereinafter be explained.
As shown in
As illustrated with the broken lines shown in
Incidentally, the pixel pitch on the surface of the photoconductor drum can be obtained from, for example, the pixel pitch of an image formed on a paper sheet. It should be noted that there are some cases in which the moving velocity of the surface of the photoconductor drum and the conveying velocity of the paper sheet are slightly different from each other in the sub-scanning direction. SD, and in such cases, the sub-scanning pixel pitch is different between the surface of the photoconductor drum and the paper sheet. Therefore, in the case in which the sub-scanning pixel pitch on the surface of the photoconductor drum is obtained from the image formed on the paper sheet, it is possible to multiply the sub-scanning image pitch obtained from the image on the paper sheet by the velocity ratio of the moving velocity of the surface of the photoconductor drum to the conveying velocity of the paper sheet. It should be noted that as the velocity ratio, a value described in the specification of the image forming device such as a printer can be used.
As shown in
As described above, in the line head of the first embodiment, since the sub-scanning spot group pitch Psgs is set to a value obtained by multiplying the sub-scanning pixel pitch Rsd by an integral number, it is possible to form all of the spots SP to the pixels PX simultaneously at the emission timing Tu. Therefore, in the first embodiment, the emission timing Tu is common to all of the light emitting element groups 295. Therefore, the emission of the light emitting elements 2951 forming the respective spots SP is switched at the timing Tu at which the respective spots SP reach the positions corresponding to the pixels PX (
Incidentally, as described above, in the image forming device of the present embodiment, the surface of the photoconductor drum 21 moves in the sub-scanning direction SD. Further, each of the light emitting element group rows 295R_A, 295R_B, and 295R_C expose the points different from each other in the sub-scanning direction SD at a timing according to the movement of the surface of the photoconductor drum, thereby forming the latent image. However, there are some cases in which the velocity of the surface of the photoconductor drum varies for the reason of, for example, a variation in the internal environment of the device, and as a result, there are some in which the latent image is not formed preferably.
The encoder ECD has an encoder disc ED having a disc like shape and a transmissive photo sensor SC. The center portion of the encoder disc ED is attached to the rotating shaft AR21 of the photoconductor drum 21, and the encoder disc is also rotated in conjunction with rotation of the photoconductor drum 21. Further, the encoder disc ED is provided with a plurality of slits SL disposed radially from a rotational axis AX. Further, the slits SL are detected by the photo sensor SC. Specifically, the photo sensor SC has a light emitting section SCe and a light receiving section SCr, and the light emitting section SCe emits light towards the light receiving section SCr. The photo sensor SC is disposed so as to accommodate the encoder disc ED between the light emitting section SCe and the light receiving section SCr. Therefore, the light passing through the slits SL out of the light emitted from the light emitting section SCe enters the light receiving section SCr. Meanwhile, the light receiving section SCr, which has detected the incident light, outputs an encoder signal Senc. Therefore, by measuring the interval of the encoder signal Senc, the moving velocity of the surface SF21 of the photoconductor drum can be detected. The encoder signal Senc output by the light receiving section SCr is supplied to the head controller HC via the engine controller EC (
Tt(2)=(Ts(2)/Ts(ref))×Tt(ref)
In other words, in a generalized manner, the emission interval Tt(n+1) is set based on the following formula with respect to the interval Ts(n) between the nth encoder signal Senc(n) and the n+1th encoder signal Senc(n+1).
Tt(n+1)=(Ts(n)/Ts(ref)×Tt(ref)
Further, the emission timing Tu is adjusted so that the interval of the emission timing Tu becomes the emission interval Tt(n+1).
As described above, in the first embodiment, the moving velocity of the surface SF21 (the circumferential surface) of the photoconductor drum 21 is detected by the encoder ECD, and the emission timing Tu of the light emitting elements 2951 is adjusted based on the result of the detection. Therefore, the shift of the latent image formation position based on the variation in the moving velocity of the surface SF21 of the photoconductor drum can be prevented from occurring, thus the preferable latent image formation becomes possible.
Further, in the first embodiment, the head controller HC (a control section) adjusts the emission timing Tu of the light emitting elements 2951 based on the difference between the moving velocity of the surface SF21 of the photoconductor drum and the ideal velocity (the reference velocity). Therefore, since the emission timing Tu of the light emitting elements 2951 is adjusted based on the shift of the moving velocity of the surface SF21 of the photoconductor drum from the ideal velocity, it becomes possible to efficiently prevent the shift of the latent image formation position, thus the preferable latent image formation becomes possible.
Further, in the image forming device 1 according to the first embodiment, the photoconductor drum 21 rotating around the rotating shaft AR21 is used as the latent image carrier, and it is particularly preferable to apply the invention to such an image forming device 1. The reason therefor is that there are some cases in which a variation is caused in the rotational velocity of the rotation of such a photoconductor drum 21 around the rotating shaft AR21, and the variation in the rotational velocity causes the variation in the moving velocity of the surface SF21 (the circumferential surface) of the photoconductor drum. Therefore, it is preferable to apply the invention to such an image forming device 1 to prevent the shift of the latent image formation position caused by the variation in the moving velocity of the surface SF21 of the photoconductor drum from occurring.
Further, in the first embodiment, the moving velocity of the surface SF21 of the photoconductor drum is detected by the encoder ECD having the encoder disc ED provided with a plurality of slits SL disposed radially from the rotating shaft AR21 of the photoconductor drum 21 and the photo sensor SC for detecting the slits SL. In other words, the detection of the moving velocity of the surface SF21 of the photoconductor drum is executed based on the plurality of slits SL disposed radially from the rotating shaft AR21 of the photoconductor drum 21. Therefore, it becomes possible to perform the detection of the moving velocity of the surface SF21 of the photoconductor drum with high accuracy.
Further in the first embodiment, since the sub-scanning spot group pitch Pegs is set to be a value obtained by multiplying the sub-scanning pixel pitch Rsd by an integral number, it becomes possible to control the light emission of each of the light emitting elements 2951 of each of the light emitting element groups 295 with the common emission timing Tu. Therefore, the simplification of the control of the emission timing for the light emitting elements 2951 is achieved, and the image forming device 1 of the first embodiment is preferable.
In the first embodiment described above, the sub-scanning spot group pitch Psgs is set to be a value obtained by multiplying the sub-scanning pixel pitch Rsd by an integral number, and each of the light emitting element group rows 295R emits light at the same emission timing Tu. However, it is also possible to set the sub-scanning spot group pitch Psgs to be a value obtained by multiplying the sub-scanning pixel pitch Rsd by a non-integral number. On this occasion, the light emitting element group rows 295R_A, 295R_B, and 295R_C are provided with emission timings Tu_A, Tu_B, and Tu_C, respectively. Such a case will hereinafter be explained.
As shown in the drawing, the emission timing Tu_A is adjusted based on the difference between a reference signal interval Ts(ref) as the interval of the encoder signal Senc in the case in which the surface SF21 of the photoconductor drum is moving at the ideal velocity, and a signal interval Ts(n) of the encoder signal Senc measured actually. In the drawing, the signal interval Ts(1) between the first encoder signal Senc(1) and the second encoder signal Senc(2) is equal to the reference signal interval Ts(ref). Therefore, in the period between the first encoder signal Senc(1) and the second encoder signal Senc(2), the interval (the emission interval Tt_A(1)) of the emission timing Tu_A is set to the reference emission interval Tt_A(ref). Then, in the case in which the signal interval Ts(2) between the second encoder signal Senc(2) and the third encoder signal Senc(3) is shorter, it is determined that the velocity of the surface of the photoconductor drum is shifted to be higher, and the emission interval Tt_A(2) is set to be shorter. Specifically, the emission interval Tt_A(2) is set based on the following formula.
Tt
—
A(2)=(Ts(2)/Ts(ref))×Tt—A(ref)
In other words, in a generalized manner, the emission interval Tt_A(n+1) is set based on the following formula with respect to the interval Ts(n) between the nth encoder signal Senc(n) and the n+1th encoder signal Senc(n+1).
Tt
—
A(n+1)=(Ts(n)/Ts(ref))×Tt—A(ref)
Further, the emission timing Tu_A is adjusted so that the interval of the emission timing Tu_A becomes the emission interval Tt_A(n+1).
Further, the emission intervals Tt_B(n+1), Tt_C(n+1) of the other emission timings Tu_B, Tu_C are also set based on substantially the same formulas.
Tt
—
B(n+1)=(Ts(n)/Ts(ref))×Tt—B(ref)
Tt
—
C(n+1)=(Ts(n)/Ts(ref))×Tt—C(ref)
As described above, in the second embodiment, the moving velocity of the surface SF21 (the circumferential surface) of the photoconductor drum 21 is detected by the encoder ECD, and the emission timings Tu_A, Tu_B, and Tu_C of the light emitting elements 2951 are adjusted based on the result of the detection. Therefore, the shift of the latent image formation position based on the variation in the moving velocity of the surface SF21 of the photoconductor drum can be prevented from occurring, thus the preferable latent image formation becomes possible.
Incidentally, in the first and second embodiments described above, the communication of the video data VD between the main controller MC and the head controller HC is executed with asynchronous serial communication. However, the communication method of the video data VD is not limited thereto.
On the reverse surface of the head substrate 293 of the line head 29, there are formed three light emitting element group rows 295R (295R_A, 295R_B, and 295R_C), each of which has a plurality of light emitting element groups 295 arranged in the longitudinal direction LGD, arranged side-by-side in the width direction. Further, on the reverse surface of the head substrate 293, there are disposed three drive circuits DC_A (for the light emitting element group row 295R_A), DC_B (for the light emitting element group row 295R_B), DC_C (for the light emitting element group row 295R_C) corresponding respectively to the light emitting element group rows 295R_A, 295R_B, and 295R_C.
In each of the light emitting element groups 295, two light emitting element rows 2951R each having eight light emitting elements 2951 aligned in the longitudinal direction LGD are arranged side by side in the width direction LTD. Further, the light emitting elements 2951 in each of the light emitting element group rows 295R_A, 295R_B, and 295R_C are connected to the drive circuits DC_A, DC_B, and DC_C, respectively, via the wires WL. Therefore, each of the drive circuits DC_A, DC_B, and DC_C is capable of driving the corresponding light emitting element group rows 295R_A, 295R_B, and 295R_C via the wires WL. In a manner as described above, the light emitting element groups 295 driven by the drive circuits DC_A, DC_B, and DC_C emit light, thus forming the spot groups SG on the surface SF21 of the photoconductor drum 21.
The emission operation of such light emitting element groups 295 is controlled as follows. Firstly, each of the video data VD_A, VD_B, and VD_C transmitted from the head controller HC is temporarily stored in an interface circuit I/F. When receiving the horizontal sync signal Hsync from the head controller HC, the interface circuit I/F outputs each of the video data VD_A, VD_B, and VD_C to the drive circuits DC_A, DC_B, and DC_C (
Further, in the third embodiment, similarly to the first embodiment, the sub-scanning spot group pitch Psgs is set to be a value obtained by multiplying the sub-scanning pixel pitch Rsd by an integral number, and when each of the light emitting element group rows 295R emit light at the same timing, the spot latent image can be formed at each of the pixels PX. Therefore, it is possible to make the light emitting element group rows 295R_A, 295R_B, and 295R_C emit light in sync with the common horizontal sync signal Hsync, thus the simplification of the control is achieved.
Incidentally, also in the third embodiment, each of the light emitting element group rows 295R_A, 295R_B, and 295R_C expose the points at the positions different from each other in the sub-scanning direction SD at a timing according to the movement of the surface SF21 of the photoconductor drum, thereby forming the latent image. Therefore, there are some cases in which the latent image is not preferably formed due to the velocity variation of the surface SF21 of the photoconductor drum. Therefore, in the third embodiment, the encoder ECD detects the velocity of the surface SF21 of the photoconductor drum, and the horizontal sync signal Hsync is adjusted based on the result of the detection.
Th(2)=(Ts(2)/Ts(ref))×Th(ref)
In other words, in a generalized manner, the synchronization interval Th(n+1) is set based on the following formula with respect to the interval Ts(n) between the nth encoder signal Senc(n) and the n+1th encoder signal Senc(n+1).
Th(n+1)=(Ts(n)/Ts(ref))×Th(ref)
Then, the horizontal sync signal Hsync is adjusted so that the interval of the horizontal sync signal Hsync becomes the synchronization interval Th(n+1). In a manner as described above, in the third embodiment, the horizontal sync signal Hsync is adjusted, thereby the emission timing of the light emitting elements 2951 is adjusted.
As described above, in the third embodiment, the encoder ECD detects the moving velocity of the surface SF21 (the circumferential surface) of the photoconductor drum 21, and the emission timing of the light emitting elements 2951 is adjusted based on the result of the detection. Therefore, the shift of the latent image formation position based on the variation in the moving velocity of the surface SF21 of the photoconductor drum can be prevented from occurring, thus the preferable latent image formation becomes possible.
Incidentally, in the third embodiment described above, the sub-scanning spot group pitch Pegs is set to be a value obtained by multiplying the sub-scanning pixel pitch Red by an integral number, and each of the light emitting element group rows 295R emits light at the same emission timing. However, it is also possible to set the sub-scanning spot group pitch Pegs to be a value obtained by multiplying the sub-scanning pixel pitch Rsd by a non-integral number. On this occasion, the light emitting element group rows 295R_A, 295R_B, and 295R_C are provided with horizontal sync signals Hsync_A, Hsync_B, and Hsync_C, respectively. Such a case will hereinafter be explained.
In the line head 29, each of the video data VD_A, VD_B, and VD_C transmitted from the head controller HC is temporarily stored in the interface circuit I/F. The interface circuit I/F is provided with the three types of horizontal sync signals Hrync_A, Hrync_B, and Hrync_C described above input thereto. Further, when receiving the horizontal sync signal Hrync_A, the interface circuit I/F outputs the video data VD_A to the drive circuit DC_A, when receiving the horizontal sync signal Hsync_B, the interface circuit I/F outputs the video data VD_B to the drive circuit DC_B, and when receiving the horizontal sync signal Hrync_C, the interface circuit I/F outputs the video data VD_C to the drive circuit DC_C (
Incidentally, also in the fourth embodiment, each of the light emitting element group rows 295R_A, 295R_B, and 295R_C expose the points at the positions different from each other in the sub-scanning direction SD at a timing according to the movement of the surface SF21 of the photoconductor drum, thereby forming the latent image. Therefore, there are some cases in which the latent image is not preferably formed due to the velocity variation of the surface SF21 of the photoconductor drum. Therefore, also in the fourth embodiment, the encoder ECD detects the velocity of the surface SF21 of the photoconductor drum, and the horizontal sync signals Hsync are adjusted based on the result of the detection.
As shown in the drawing, the horizontal sync signal Hsync_A is adjusted based on the difference between a reference signal interval Ts(ref) as the interval of the encoder signal Senc in the case in which the surface SF21 of the photoconductor drum is moving at the ideal velocity, and a signal interval Ts(n) of the encoder signal Senc measured actually. In the drawing, the signal interval Ts(1) between the first encoder signal Senc(1) and the second encoder signal Senc(2) is equal to the reference signal interval Ts(ref). Therefore, in the period between the first encoder signal Senc(1) and the second encoder signal Senc(2), the interval (the synchronization interval Th_A(1)) of the horizontal sync signal Hsync_A is set to a reference synchronization interval Th_A(ref). Then, in the case in which the signal interval Ts(2) between the second encoder signal Senc(2) and the third encoder signal Senc(3) is shorter, it is determined that the velocity of the surface SF21 of the photoconductor drum is shifted to be higher, and the synchronization interval Th_A(2) is set to be shorter. Specifically, the synchronization interval Th_A(2) is set based on the following formula.
Th
—
A(2)=(Ts(2)/Ts(ref))×Th—A(ref)
In other words, in a generalized manner, the synchronization interval Th_A(n+1) is set based on the following formula with respect to the interval Ts(n) between the nth encoder signal Senc(n) and the n+1th encoder signal Senc(n+1).
Th
—
A(n+1)=(Ts(n)/Ts(ref))×Th—A(ref)
Then, the horizontal sync signal Hsync_A is adjusted so that the interval of the horizontal sync signal Hsync_A becomes the synchronization interval Th_A(n+1).
Further, the horizontal sync signals Th_B(n+1), Th_C(n+1) of the other horizontal sync signals Hsync_B, Hsync_C are also set based on substantially the same formulas.
Th
—
B(n+1)=(Ts(n)/Ts(ref))×Th—B(ref)
Th
—
C(n+1)=(Ts(n)/Ts(ref))×Th—C(ref)
In a manner as described above, in the fourth embodiment, the horizontal sync signals Hrync_A, Hrync_B, and Hrync_C are adjusted, thereby the emission timing of the light emitting elements 2951 is adjusted.
As described above, in the fourth embodiment, the encoder ECD detects the moving velocity of the surface SF21 (the circumferential surface) of the photoconductor drum 21, and the emission timing of the light emitting elements 2951 is adjusted based on the result of the detection. Therefore, the shift of the latent image formation position based on the variation in the moving velocity of the surface SF21 of the photoconductor drum can be prevented from occurring, thus the preferable latent image formation becomes possible.
Incidentally, the image forming device is capable of sequentially forming a plurality of linear latent images, each of which has a length corresponding to one page in the main-scanning direction MD, in the sub-scanning direction SD, thereby forming a two-dimensional latent image corresponding to one page. Therefore, in the fifth embodiment, this latent image formation operation will be explained. It should be noted that in order for making it easy to understand the latent image formation operation, the explanation will be presented focusing attention to one linear latent image to be formed at a predetermined position (the position indicated by the arrow FL in
In the present embodiment, it is assumed that the light emitting element row pitch (the distance between the light emitting element rows) Pelr=0.1 mm, the lens row pitch (the distance between the lens rows) Plsr=1 mm, and the circumferential velocity of the photoconductor is equal to 100 mm/s. Further, the spot group pitch (the distance between the spot groups) Psgs is a value obtained by multiplying the sub-scanning pixel pitch (the distance between the sub-scanning pixels) Rsd by an integral number, while the spot row pitch (the distance between the spot rows) Pspr is a value obtained by multiplying the sub-scanning pixel pitch (the distance between the sub-scanning pixels) Rsd by a non-integral number (not shown). Further, for the sake of easier understanding of the emission timing control, in the present embodiment, it is assumed that the lens LS1 is an electing lens with equal magnification.
As the circumferential surface (the surface of the latent image carrier) of the photoconductor drum 21 moves, the predetermined position FL on which the linear latent image is formed moves in the sub-scanning direction SD. As is explained below, each of the light emitting elements 2951 emits light at the timing at which the predetermined position FL reaches the position where each of the light emitting elements 2951 can form the spot SP. Thus, the linear latent image can be formed at the predetermined position. A specific operation is as follows.
As shown in
Then, as shown in
Further, as shown in
It should be noted that as shown in
Incidentally, there are some cases in which the variation in the circumferential velocity of the photoconductor drum 21 causes unevenness in the one page length linear latent image. For example, as a result of the variation in the velocity of the photoconductor drum 21 in the period from the time point of 0 ms to the time point of 10 ms, there are some cases in which the predetermined position FL goes beyond the spot formation position of the lenses LS2 or the predetermined position do not reach the spot formation position at the time point of 10 ms (
Therefore, in the present embodiment, the encoder ECD as shown in
It should be noted that in the fifth embodiment, since the time difference ΔT between the emission of the light emitting element row 2951Ra and the emission of the light emitting element row 2951Rb belonging to the same light emitting element group 295 is sufficiently short, the adjustment based on the position of the photoconductor drum 21 is not executed on the time difference ΔT assuming that there is no substantial influence of the variation in the velocity of the photoconductor drum 21 during the time difference ΔT on the latent image formation position. However, in the case in which the variation in the velocity of the photoconductor drum 21 during the time difference ΔT exerts a considerable influence on the latent image formation position, it is also possible to adjust the time difference ΔT based on the position of the photoconductor drum 21. In other words, the time from the emission of the light emitting elements 2951 (the first light emitting element) in the light emitting element row 2951Ra to the emission of the light emitting elements 2951 (the third light emitting element) in the light emitting element row 2951Rb can be adjusted. Thus, the latent image by the light emitting element row 2951Ra and the latent image by the light emitting element row 2951Rb are aligned straight in the main-scanning direction MD at the predetermined position FL.
In such a configuration of driving the photoconductor drum 21 by the gear GR, there are some cases in which a variation in the circumferential velocity of the photoconductor drum 21 is caused by, for example, the variation in the pitch of the gear teeth GRt. Therefore, with respect to such a configuration, it is preferable to adjust the time difference (e.g., the time difference (T2−T1)) between the emission of the light emitting elements 2951 for emitting light to be imaged by the first lenses LS (e.g., LS1) to the emission of the light emitting elements 2951 for emitting light to be imaged by the second lenses LS (e.g., LS2) in accordance with the position of the circumferential surface of the photoconductor drum 21 based on the result of the detection of the position of the photoconductor drum 21.
Incidentally, the velocity variation of the circumferential surface of the photoconductor drum 21 caused in the configuration using the gear GR described above includes periodicity. The velocity variation period can easily be obtained from the inverse of a value obtained by multiplying the number of rotations of the photoconductor drum 21 per unit time by the number (number of teeth) of the teeth GRt of the gear GR, and can specifically be obtained by the following formula.
(velocity variation period [s])=60/(CT21×NT)
Here, the value CT21 is the number of rotations per unit time [rpm] of the photoconductor drum 21, and the NT is the number of teeth of the gear GR. Further, it is preferable that the lens row pitch Plsr, namely the distance (lens-to-lens distance) Plsr between the lens LS1 and the lens LS2 in the width direction LTD, or the distance Plsr between the lens LS2 and the lens LS3 in the width direction LTD is longer than the value (the distance of the photoconductor drum 21) obtained by multiplying the velocity variation period by the average value of the circumferential velocity of the photoconductor drum. For example, assuming CT21=60[rpm] and (the number of teeth)=40, (velocity variation period)=0.025 [s] is obtained. Therefore, assuming that the average value of the circumferential velocity of the photoconductor drum is 94.2 [mm/s], the value obtained by multiplying the velocity variation period by the average value of the circumferential velocity of the photoconductor drum becomes 2.355 [mm]. Therefore, it is preferable that the lens-to-lens distance Plsr is equal to or longer than 2.36 [mm]. In particular, it is preferable that the lens-to-lens distance Plsr is set to be 25 through 100 times as large as the value obtained by multiplying the velocity variation period by the average value of the circumferential velocity of the photoconductor drum.
As described above, in the embodiments described above, the main-scanning direction MD and the longitudinal direction LGD correspond to “a first direction” of the invention, the sub-scanning direction SD and the width direction LTD correspond to “a second direction” of the invention, the lenses LS correspond to “an imaging optical system” of the invention, the photoconductor drum 21 corresponds to “a latent image carrier” of the invention, and the surface SF21 (circumferential surface) of the photoconductor drum 21 corresponds to “a surface of the latent image carrier” of the invention. Further, the head controller HC corresponds to “a control section” of the invention, the encoder ECD corresponds to “a detection section” of the invention, and the photo sensor SC corresponds to “an optical sensor” of the invention. Further, the relationship between the lens LS1 and the lens LS2 (or the lens LS2 and the lens LS3) corresponds to the relationship between “a first imaging optical system” and “a second imaging optical system” of the invention. Further, the line head 29 corresponds to “an exposure head” of the invention.
It should be noted that the invention is not limited to the embodiment described above, but can variously be modified besides the embodiment described above within the scope of the invention. For example, in the encoder ECD in the above embodiments, one photo sensor SC is provided (
As described above, in the encoder ECD shown in
Further, in the embodiments described above, the emission timing of the light emitting elements is adjusted based on the difference between the moving velocity of the surface of the photoconductor drum and the ideal velocity. However, it is also possible to configure that the emission timing of the light emitting element is adjusted based on the difference between the moving velocity of the surface of the photoconductor drum and the average value of the moving velocity. Specifically, it is possible to perform the adjustment operation as shown in
Further, although in the embodiment described above, both of the main-scanning resolution and the sub-scanning resolution are 600 dpi, the resolutions are not limited to 600 dpi. In particular, regarding the sub-scanning resolution, the resolution higher than 600 dpi can be realized with relative ease by breaking the emission time of the light emitting elements 2951 into small parts using pulse width modulation control called PWM control. Therefore, it is possible to increase the sub-scanning resolution to be 2400 dpi while setting the main-scanning resolution to 600 dpi. On this occasion, since the sub-scanning resolution is four times as high as the main-scanning resolution, the sub-scanning pixel pitch Rsd becomes one fourth of the main-scanning pixel pitch Rmd.
Further, although the light emitting element group column 295C is formed of the three light emitting element groups 295 in the first through the fourth embodiments, the number of the light emitting element groups 295 composing the light emitting element group column 295C is not limited thereto, but can be two or more.
Further, although the spot group SG is composed of the two spot rows SPR in the first through the fourth embodiments, the number of spot rows SPR composing the spot group SG is not limited thereto, but can be one, or three or more.
Further, although the spot row SPR is composed of four spots SP in the first and the second embodiments, the number of spots SP forming the spot row SPR is not limited thereto.
Further, although the light emitting element group 295 is composed of two light emitting element rows 2951R in the first through the fourth embodiments, the number of light emitting element rows 2951R forming the light emitting element group 295 is not limited thereto.
Further, in the sixth embodiment, the gear GR is integrally connected to the photoconductor drum 21. However, it is possible to configure the embodiment as shown in
Although a specific example of the invention will hereinafter be described, it is obvious that the invention is not limited by the specific example described below, and can be put into practice with appropriate modification within the scope of the invention described in the anteroposterior descriptions, either of which is included in the scope and sprit of the present invention.
Then, the “LATENT IMAGE FORMATION POSITION (BEFORE CORRECTION CONTROL)” section on the middle of
Then, the “LATENT IMAGE FORMATION POSITION (AFTER CORRECTION CONTROL)” section on the bottom of
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-323665 | Dec 2007 | JP | national |
| 2008-265034 | Oct 2008 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12332204 | Dec 2008 | US |
| Child | 13014618 | US |
