Patent Application
20090160926
The disclosure of Japanese Patent Applications No. 2007-332586 filed on Dec. 25, 2007 and No. 2008-273125 filed on Oct. 23, 2008 including specification, drawings and claims is incorporated herein by reference in its entirety.
1. Technical Field
This invention relates to an exposure head for forming a spot by emitting a light from a light emitting element and an image forming apparatus using this exposure head.
2. Related Art
There has been conventionally known technology for forming spots on an image plane moving in a sub scanning direction by a line head (exposure head) to expose the image plane. As such a line head, the one in which a plurality of light emitting elements are arranged in a main scanning direction orthogonal to or substantially orthogonal to the sub scanning direction like a line head, for example, disclosed in JP-A-2-4546 can be used. In other words, in an exposure operation using such a line head, a plurality of light emitting elements of the line head are driven for light emission to form a plurality of spots arranged in the main scanning direction on the image plane. The entire image plane is exposed by repeatedly performing such a spot forming operation.
In order to achieve a higher resolution, a line head can be used in which a plurality of light emitting elements are arranged at positions mutually different in a moving direction (first direction) of an image plane. However, in such a line head, the respective light emitting elements arranged at the positions mutually different in the first direction form spots at positions mutually different in the first direction. Due to such differences in spot formation positions in the first direction, various exposure failures occurred in some cases.
An advantage of some aspects of the invention is to provide technology for suppressing the occurrence of an exposure failure resulting from differences in spot formation positions in a first direction.
According to a first aspect of the invention, there is provided an image forming apparatus, comprising: a latent image carrier that moves in a first direction; an exposure head that includes a first imaging optical system, a second imaging optical system that is distanced from the first imaging optical system in the first direction, a light emitting element that emits a light to be imaged on the latent image carrier by the first imaging optical system and a light emitting element that emits a light to be imaged on the latent image carrier by the second imaging optical system; and a controller that is adapted to control a light quantity of the light emitting element that emits a light to be imaged on the latent image carrier by the first imaging optical system in accordance with an imaging characteristic of the first imaging optical system.
According to a second aspect of the invention, there is provided an image forming apparatus, comprising: a latent image carrier that moves in a first direction; an exposure head that includes an imaging optical system and a light emitting element that emits a light to be imaged on the latent image carrier by the imaging optical system; and a controller that is adapted to control a light quantity of the light emitting element in accordance with a position in the first direction of the imaging optical system which images the light emitted from the light emitting element.
According to a third aspect of the invention, there is provided an exposure head, comprising: a first imaging optical system; a second imaging optical system that is distanced from the first imaging optical system in a first direction in which a surface-to-be-exposed is moved; a light emitting element that emits a light to be imaged by the first imaging optical system; a light emitting element that emits a light to be imaged by the second imaging optical system; and a controller that is adapted to control a light quantity of the light emitting element that emits the light to be imaged by the first imaging optical system in accordance with an imaging characteristic of the first imaging optical system.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for purpose of illustration only and is not intended as a definition of the limits of the invention.
Terms used in this specification are first described below (see “A. Description of Terms”). Following this description of terms, a basic construction of an image forming apparatus including a line head as an application subject of the invention (see “B. Basic Construction”) and a basic operation of the line head (see “C. Basic Operation”) are described. Following the description of the basic construction and the basic operation, embodiments of the invention are described.
Collections of a plurality of (eight in
A spot group row SGR and a spot group column SGC are defined as shown in the column “On Image Plane” of
Lens rows LSR and lens columns LSC are defined as shown in the column of “Lens Array” of
Light emitting element group rows 295R and light emitting element group columns 295C are defined as in the column “Head Substrate” of
Light emitting element rows 2951R and light emitting element columns 2951C are defined as in the column “Light Emitting Element Group” of
Spot rows SPR and spot columns SPC are defined as shown in the column “Spot Group” of
An electrical component box 5 having a power supply circuit board, the main controller MC, the engine controller EC and the head controller HC built therein is disposed in a housing main body 3 of the image forming apparatus. An image forming unit 7, a transfer belt unit 8 and a sheet feeding unit 11 are also arranged in the housing main body 3. A secondary transfer unit 12, a fixing unit 13 and a sheet guiding member 15 are arranged at the right side in the housing main body 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) which form a plurality of images having different colors. Each of the image forming stations Y, M, C and K includes a cylindrical photosensitive drum 21 having a surface of a specified length in a 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 photosensitive drum 21. The photosensitive drum is arranged so that the axial direction thereof is substantially parallel to the main scanning direction NM. Each photosensitive drum 21 is connected to its own driving motor and is driven to rotate at a specified speed in a direction of arrow D21 in
The charger 23 includes a charging roller having the surface thereof made of an elastic rubber. This charging roller is constructed to be rotated by being held in contact with the surface of the photosensitive drum 21 at a charging position. As the photosensitive drum 21 rotates, the charging roller is rotated at the same circumferential speed in a direction driven by the photosensitive drum 21. This charging roller is connected to a charging bias generator (not shown) and charges the surface of the photosensitive drum 21 at the charging position where the charger 23 and the photosensitive drum 21 are in contact upon receiving the supply of a charging bias from the charging bias generator.
The line head 29 is arranged relative to the photosensitive 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. Hence, the longitudinal direction of the line head 29 is substantially parallel to the main scanning direction MD. The line head 29 includes a plurality of light emitting elements arrayed in the longitudinal direction and is positioned separated from the photosensitive drum 21. Light beams are emitted from these light emitting elements toward the surface of the photosensitive drum 21 charged by the charger 23, thereby forming an electrostatic latent image on this surface.
The developer 25 includes a developing roller 251 carrying toner on the surface thereof. By a development bias applied to the developing roller 251 from a development bias generator (not shown) electrically connected to the developing roller 251, charged toner is transferred from the developing roller 251 to the photosensitive drum 21 to develop the latent image formed by the line head 29 at a development position where the developing roller 251 and the photosensitive drum 21 are in contact.
The toner image developed at the development position in this way is primarily transferred to the transfer belt 81 at a primary transfer position TR1 to be described later where the transfer belt 81 and each photosensitive drum 21 are in contact after being transported in the rotating direction D21 of the photosensitive drum 21.
Further, the photosensitive drum cleaner 27 is disposed in contact with the surface of the photosensitive drum 21 downstream of the primary transfer position TR1 and upstream of the charger 23 with respect to the rotating direction D21 of the photosensitive drum 21. This photosensitive drum cleaner 27 removes the toner remaining on the surface of the photosensitive drum 21 to clean after the primary transfer by being held in contact with the surface of the photosensitive drum.
The transfer belt unit 8 includes a driving roller 82, a driven roller (blade facing roller) 83 arranged to the left of the driving roller 82 in
On the other hand, out of the four primary transfer rollers 85Y, 85M, 85C and 85K, the color primary transfer rollers 85Y, 85M, 85C are separated from the facing image forming stations Y, M and C and only the monochromatic primary transfer roller 85K is brought into contact with the image forming station K at the time of executing the monochromatic mode, whereby only the monochromatic image forming station K is brought into contact with the transfer belt 81. As a result, the primary transfer position TR1 is formed only between the monochromatic primary transfer roller 85K and the image forming station K. By applying a primary transfer bias at a suitable timing from the primary transfer bias generator to the monochromatic primary transfer roller 85K, the toner image formed on the surface of the photosensitive drum 21 is transferred to the surface of the transfer belt 81 at the primary transfer position TR1 to form a monochromatic image.
The transfer belt unit 8 further includes a downstream guide roller 86 disposed downstream of the monochromatic primary transfer roller 85K and upstream of the driving roller 82. This downstream guide roller 86 is so disposed as to come into contact with the transfer belt 81 on an internal common tangent to the primary transfer roller 85K and the photosensitive drum 21 at the primary transfer position TR1 formed by the contact of the monochromatic primary transfer roller 85K with the photosensitive drum 21 of the image forming station K.
The driving roller 82 drives to rotate the transfer belt 81 in the direction of the arrow D81 and doubles as a backup roller for a secondary transfer roller 121. A rubber layer having a thickness of about 3 mm and a volume resistivity of 1000 kΩcm or lower is formed on the circumferential surface of the driving roller 82 and is grounded via a metal shaft, thereby serving as an electrical conductive path for a secondary transfer bias to be supplied from an unillustrated secondary transfer bias generator via the secondary transfer roller 121. By providing the driving roller 82 with the rubber layer having high friction and shock absorption, an impact caused upon the entrance of a sheet into a contact part (secondary transfer position TR2) of the driving roller 82 and the secondary transfer roller 121 is unlikely to be transmitted to the transfer belt 81 and image deterioration can be prevented.
The sheet feeding unit 11 includes a sheet feeding section which has a sheet cassette 77 capable of holding a stack of sheets, and a pickup roller 79 which feeds the sheets one by one from the sheet cassette 77. The sheet fed from the sheet feeding section by the pickup roller 79 is fed to the secondary transfer position TR2 along the sheet guiding member 15 after having a sheet feed timing adjusted by a pair of registration rollers 80.
The secondary transfer roller 121 is provided freely to abut on and move away from the transfer belt 81, and is driven to abut on and move away from the transfer belt 81 by a secondary transfer roller driving mechanism (not shown). The fixing unit 13 includes a heating roller 131 which is freely rotatable and has a heating element such as a halogen heater built therein, and a pressing section 132 which presses this heating roller 131. The sheet having an image secondarily transferred to the front side thereof is guided by the sheet guiding member 15 to a nip portion formed between the heating roller 131 and a pressure belt 1323 of the pressing section 132, and the image is thermally fixed at a specified temperature in this nip portion. The pressing section 132 includes two rollers 1321 and 1322 and the pressure belt 1323 mounted on these rollers. Out of the surface of the pressure belt 1323, a part stretched by the two rollers 1321 and 1322 is pressed against the circumferential surface of the heating roller 131, thereby forming a sufficiently wide nip portion between the heating roller 131 and the pressure belt 1323. The sheet having been subjected to the image fixing operation in this way is transported to the discharge tray 4 provided on the upper surface of the housing main body 3.
Further, a cleaner 71 is disposed facing the blade facing roller 83 in this apparatus. The cleaner 71 includes a cleaner blade 711 and a waste toner box 713. The cleaner blade 711 removes foreign matters such as toner remaining on the transfer belt after the secondary transfer and paper powder by holding the leading end thereof in contact with the blade facing roller 83 via the transfer belt 81. Foreign matters thus removed are collected into the waste toner box 713. Further, the cleaner blade 711 and the waste toner box 713 are constructed integral to the blade facing roller 83. Accordingly, when the blade facing roller 83 moves, the cleaner blade 711 and the waste toner box 713 move together with the blade facing roller 83.
The case 291 carries a lens array 299 at a position facing the surface of the photosensitive drum 21, and includes a light shielding member 297 and a head substrate 293 inside, the light shielding member 297 being closer to the lens array 299 than the head substrate 293. The head substrate 293 is made of a transmissive material (glass for instance). Further, a plurality of light emitting element groups 295, each of which is a group of a plurality of light emitting elements, are provided on an under surface of the head substrate 293 (surface opposite to the lens array 299 out of two surfaces of the head substrate 293), as described later. The light emitting elements 2951 are bottom emission-type EL (electroluminescence) devices. The light beams emitted from the respective light emitting element groups 295 propagate toward the light shielding member 297 after passing through the head substrate 293 from the under surface thereof to a top surface thereof.
The light shielding member 297 is perforated with a plurality of light guide holes 2971 in a one-to-one correspondence with the plurality of light emitting element groups 295. The light guide holes 2971 are substantially cylindrical holes penetrating the light shielding member 297 and having central axes in parallel with normal to the head substrate 293. Accordingly, out of light beams emitted from the light emitting element groups 295, those propagating toward other than the light guide holes 2971 corresponding to the light emitting element groups 295 are shielded by the light shielding member 297. In this way, all the lights emitted from one light emitting element group 295 propagate toward the lens array 299 via the same light guide hole 2971 and the mutual interference of the light beams emitted from different light emitting element groups 295 can be prevented by the light shielding member 297. The light beams having passed through the light guide holes 2971 perforated in the light shielding member 297 are imaged by the lens array 299 to form spots on the surface of the photosensitive drum 21.
As shown in
The lens array 299 is arranged such that optical axes OA of a plurality of lenses LS are substantially parallel to each other. The lens array 299 is also arranged such that the optical axes OA of the lenses LS are substantially orthogonal to an under surface (surface where the light emitting elements 2951 are arranged) of the head substrate 295. The lenses LS are provided in a one-to-one correspondence with the light emitting element groups 295, and a plurality of lenses LS are two-dimensionally arranged in conformity with the arrangement of the light emitting element groups 295 to be described later. In other words, a plurality of lens columns LSC each including three lenses LS arranged at mutually different positions in the width direction LTD are arranged in the longitudinal direction LGD.
In each light emitting element group 295, two light emitting element rows 2951R each including four light emitting elements 2951 aligned in the longitudinal direction LGD are arranged at the light emitting element row pitch Pelr (=63.5 [μm]) in the width direction LTD (
Driving circuits DC_A (for the light emitting element group row 295R_A), DC_B (for the light emitting element group row 295R_B) and DC_C (for the light emitting element group row 295R_C) are provided corresponding to the respective light emitting element group rows 295R_A, 295R_B and 295R_C. These driving circuits DC_A and the like are constructed, for example, by TFTs (thin film transistors) (
Light beams emitted from the light emitting elements 2951 are imaged by the lenses LS to form spots SP on the surface (photosensitive drum surface) of the photosensitive drum 21. On the other hand, as described above, the photosensitive drum surface is charged by the charger 23 prior to spot formation. Accordingly, areas where the spots are formed are neutralized to form spot latent images Lsp. The spot latent images Lsp thus formed are conveyed to a downstream side in the sub scanning direction SD while being carried on the photosensitive drum surface. As described next in “C. Basic Operation”, the spots SP are formed at timings in conformity with the movement of the photosensitive drum surface to form a plurality of spot latent images Lsp arranged in the main scanning direction MD.
As shown in
Specifically, in this line head 29, the plurality of light emitting element groups 295 (for example, light emitting element groups 295_1, 295_2, 295_3) are arranged at positions mutually different in the width direction LTD. The respective light emitting element groups 295 arranged at the positions mutually different in the width direction LTD form spot groups SG (for example, spot groups SG_1, SG_2, SG_3) at positions mutually different in the sub scanning direction SD.
In other words, in this line head 29, the plurality of light emitting elements 2951 are arranged at positions mutually different in the width direction LTD. For example, the light emitting elements 2951 belonging to the light emitting element group 295_1 and those belonging to the light emitting element group 295_2 are arranged at positions mutually different in the width direction LTD. The respective light emitting elements 2951 arranged at the positions mutually different in the width direction LTD form spots SP at positions mutually different in the sub scanning direction SD. For example, spots SP belonging to the spot group SG_1 and those belonging to the spot group SG_2 are formed at positions mutually different in the sub scanning direction SD.
In this way, the formation positions of the spots SP in the sub scanning direction SD differ depending on the light emitting elements 2951. Accordingly, in order to form a plurality of spot latent images Lsp side by side in the main scanning direction MD (that is, in order to form a plurality of spot latent images Lsp side by side at the same position in the sub scanning direction SD), differences in such spot formation positions need to be considered. Thus, in this line head 29, the respective light emitting elements 2951 are driven at timings in conformity with the movement of the photosensitive drum surface.
First of all, out of the light emitting element rows 2951R (
Subsequently, out of the light emitting element rows 2951R belonging to the most upstream light emitting element groups 295_1, 295_4, and the like in the width direction, the light emitting element rows 2951R upstream in the width direction LTD are driven for light emission. A plurality of light beams emitted by such a light emitting operation are imaged by the lenses LS to form spots SP on the photosensitive drum surface. In this way, spot latent images Lsp are formed at hatched positions of a “Second Operation” of
Subsequently, out of the light emitting element rows 2951R belonging to the second most upstream light emitting element groups 295_2 and the like in the width direction, the light emitting element rows 2951R downstream in the width direction LTD are driven for light emission. A plurality of light beams emitted by such a light emitting operation are imaged by the lenses LS to form spots SP on the photosensitive drum surface. In this way, spot latent images Lsp are formed at hatched positions of a “Third Operation” of
Subsequently, out of the light emitting element rows 2951R belonging to the second most upstream light emitting element groups 295_2 and the like in the width direction, the light emitting element rows 2951R upstream in the width direction LTD are driven for light emission. A plurality of light beams emitted by such a light emitting operation are imaged by the lenses LS to form spots SP on the photosensitive drum surface. In this way, spot latent images Lsp are formed at hatched positions of a “Fourth Operation” of
Subsequently, out of the light emitting element rows 2951R belonging to the third most upstream light emitting element groups 295_3 and the like in the width direction, the light emitting element rows 2951R downstream in the width direction LTD are driven for light emission. A plurality of light beams emitted by such a light emitting operation are imaged by the lenses LS to form spots SP on the photosensitive drum surface. In this way, spot latent images Lsp are formed at hatched positions of a “Fifth Operation” of
Finally, out of the light emitting element rows 2951R belonging to the third most upstream light emitting element groups 295_3 and the like in the width direction, the light emitting element rows 2951R upstream in the width direction LTD are driven for light emission. A plurality of light beams emitted by such a light emitting operation are imaged by the lenses LS to form spots SP on the photosensitive drum surface. In this way, spot latent images Lsp are formed at hatched positions of a “Sixth Operation” of
In such a line head 29, the respective light emitting elements 2951 arranged at the positions mutually different in the width direction LTD form spots SP at positions mutually different in the sub scanning direction SD (
Specifically, spot latent images tend to enlarge with time, as shown in first and second embodiments for example, since the photosensitive drum surface has such a light decay characteristic as shown in
Alternatively, as shown in a third embodiment, the photosensitive drum surface has a curvature shape in a sub-scanning direction section (sub-scanning section). Accordingly, distances (element-spot distances) between the light emitting elements 2951 and the spots SP formed by the light emitting elements 2951 may differ among the respective light emitting elements 2951 arranged at the mutually different positions in the width direction LTD. However, as described later, the spot latent images formed by these spots SP tend to enlarge in some cases as the element-spot distances increase. As a result, there were cases where the size varied among the plurality of spot latent images formed by the spots SP at the positions mutually different in the sub scanning direction SD.
In contrast, in the line heads 29 shown in the following embodiments, the light quantities of the light emitting elements 2951 are adjusted according to the positions of the spots SP formed by the light emitting elements 2951 in the sub scanning direction SD. Accordingly, a good exposure can be realized by suppressing the occurrence of an exposure failure resulting from differences in the formation positions of the spots SP in the sub scanning direction SD.
On the other hand, as described with reference to
Specifically, the spot latent images Lsp formed by the upstream spots SP in the sub scanning direction SD are larger than those formed by the downstream spots SP. More specifically, the spot latent images Lsp_1 formed by the light emitting elements 2951 of the light emitting element group 295_1 are larger than the spot latent images Lsp_2, Lsp_3 formed by the light emitting elements 2951 of the light emitting element groups 295_2, 295_3. Further, the spot latent images Lsp_2 formed by the light emitting elements 2951 of the light emitting element group 295_2 are larger than the spot latent images Lsp_3 formed by the light emitting elements 2951 of the light emitting element group 295_3. Particularly, in an embodiment shown in
Dlm—1>Dlm—2>Dlm—3.
Accordingly, in order to deal with such a problem, the light quantities of the light emitting elements 2951 are adjusted as follows in the first embodiment.
As described above, in the first embodiment, the light quantities of the light emitting elements 2951 are adjusted according to the positions of the spots SP formed by the light emitting elements 2951 in the sub scanning direction SD. Accordingly, a good exposure can be realized by suppressing the occurrence of an exposure failure resulting from differences in the formation positions of the spots SP in the sub scanning direction SD.
In the first embodiment, when the light emitting element for forming a spot at an upstream side in the sub scanning direction SD is called an upstream light emitting element and the one for forming a spot at a downstream side is called a downstream light emitting element out of two light emitting elements 2951 for forming spots SP at positions different in the sub scanning direction SD, the light quantity of the upstream light emitting element is adjusted to be smaller than that of the downstream light emitting element. Specifically, the light quantity of the light emitting elements 2951 (upstream light emitting elements) of the light emitting element group 295_1 is adjusted to be smaller than that of the light emitting elements 2951 (downstream light emitting elements) of the light emitting element group 295_2. Further, the light quantity of the light emitting elements 2951 (upstream light emitting elements) of the light emitting element group 295_2 is adjusted to be smaller than that of the light emitting elements 2951 (downstream light emitting elements) of the light emitting element group 295_3. Accordingly, the variation of the plurality of spot latent images Lsp formed side by side in the main scanning direction MD can be suppressed regardless of the enlargement of the spot latent images Lsp with time, wherefore a good exposure can be realized.
On the other hand, when spot-development distances DT are distances in the sub scanning direction SD between the spots SP and the development position DP, the spot-development distances DT differ among the respective spots SP formed at positions different in the sub scanning direction SD by the above line head 29. Specifically, if a position LC_1 is the position of the spots SP formed by the light emitting elements 2951 of the light emitting element group 295_1 in the sub scanning direction SD, a position LC_2 is the position of the spots SP formed by the light emitting elements 2951 of the light emitting element group 295_2 in the sub scanning direction SD and a position LC_3 is the position of the spots SP formed by the light emitting elements 2951 of the light emitting element group 295_3 in the sub scanning direction SD, distances DT_1, DT_2 and DT_3 in the sub scanning direction SD between the positions LC_1, LC_2 and LC_3 and the development position DP differ from each other and has the following relationship (see
DT—1>DT—2>DT—3
Accordingly, the potentials of the spot latent images Lsp formed by the upstream spots SP in the sub scanning direction SD and those of the spot latent images Lsp formed by the downstream spots SP differed at the development position DP in some cases.
A more specific simulation result is described. When potentials VT_1, VT_2 and VT_3 are the potentials of the respective spot latent images Lsp_1, Lsp_2 and Lsp_3 at the development position DP, the respective potentials varied as follows in some cases.
VT
—1=−105.9 [V]
VT
—2=−102.4 [V]
VT
—3=−99.3 [V]
Such a simulation was performed on the condition that a photosensitive drum diameter=40 [mm], a photosensitive member linear speed=212 mm/sec, an exposure-development angle AG=68 degrees and the row pitch Pegr of the light emitting element group rows=1.7 [mm]. The exposure-development angle AG is an angle (
Accordingly, the spot latent images Lsp formed by the upstream spots SP in the sub scanning direction SD may differ in size at the development position DP from those formed by the downstream spots SP, that is, the sizes or the like of the spot latent images Lsp may vary at the development position DP. Thus, in order to deal with such a problem, the light quantities of the light emitting elements 2951 are adjusted as follows in the second embodiment.
As described above, in the second embodiment as well, the light quantities of the light emitting elements 2951 are adjusted according to the positions of the spots SP formed by the light emitting elements 2951 in the sub scanning direction SD. Accordingly, a good exposure can be realized by suppressing the occurrence of an exposure failure resulting from differences in the formation positions of the spots SP in the sub scanning direction SD.
Further, in the second embodiment, the light quantities of the light emitting elements 2951 are adjusted according to the distances DT in the sub scanning direction SD between the spots SP formed by the light emitting elements 2951 and the development position DP. Accordingly, good image formation can be performed by suppressing the variation of the spot latent images Lsp at the development position DP.
The surface of the photosensitive drum 21 has a curvature shape in the section (sub-scanning section) in the sub scanning direction SD (
Les—1>Les—2
As a result, the spot latent images Lsp_1 formed by the light emitting elements 2951 of the light emitting element group 295_1 are larger than the spot latent images Lsp_2 formed by the light emitting elements 2951 of the light emitting element group 295_2 (see the row “Plan View of Photosensitive Drum Surface” of
As described above, in the third embodiment, the light quantities of the light emitting elements 2951 are adjusted according to the positions of the spots SP formed by these light emitting elements 2951 in the sub scanning direction SD. Accordingly, a good exposure can be realized by suppressing the occurrence of an exposure failure resulting from differences in the spot formation positions in the sub scanning direction SD.
Particularly in the third embodiment, out of two light emitting elements 2951 adapted to form spots SP at positions mutually different in the sub scanning direction SD and having mutually different element-spot distances Les, the light quantity of the light emitting element 2951 having a longer element-spot distance Les is adjusted to be smaller than that of the light emitting element 2951 having a shorter element-spot distance Les. More specifically, the light quantity of the light emitting elements 2951 of the light emitting element group 295_1 are adjusted to be smaller than that of the light emitting elements 2951 of the light emitting element group 295_2. Accordingly, a good exposure can be realized by suppressing the size variation of the spot latent images Lsp regardless of the element-spot distances Les.
In this embodiment, after a spot variation produced due to a shift of the line head 29 relative to the photosensitive drum 21 in the width direction LTD is described, technology for suppressing the influence of this spot variation on latent image formation is described.
In
Specifically, the spots SP may enlarge depending on their formation positions (spot formation positions), with the result that good latent image formation could not be performed in some cases. Accordingly, in order to deal with such a problem, the light quantities of the light emitting elements for forming the spots at the spot formation positions LC_1, . . . may be adjusted according to the spot formation positions LC_1, . . . (from another perspective, according to the positions of the lenses in the width direction LTD). Specifically, the light quantity of the light emitting elements for forming the spots SP_2 may be set larger than that of the light emitting elements for forming the spots SP_1. In this way, any of the spots SP_1 and the spots SP_2 can form a uniform latent image.
As described above, in this embodiment, the line head 29 (exposure head) includes the lens LS_1 (first imaging optical system) and the lens LS_2 (second imaging optical system) distanced from the lens LS_1 in the width direction LTD. The light quantities of the light emitting elements are adjusted according to the lenses for imaging the lights of the light emitting elements. Accordingly, a good exposure can be realized and good image formation can be performed. The light quantity adjustment of the light emitting elements may be performed by the driving circuits DC_A, etc. (controller) provided on the head substrate 293 shown in
As described above, in the above embodiments, the line head 29 corresponds to an “exposure head” of the invention, the photosensitive drum 21 to a “latent image carrier” of the invention, the sub scanning direction SD and the width direction LTD to a “first direction” of the invention, the lens LS to an “imaging optical system” of the invention and the head substrate 293 to a “substrate” of the invention. The surface of the photosensitive drum 21 corresponds to a “surface to be exposed” of the invention. When the lens LS for imaging the lights from the light emitting element group 295_1 is a “first imaging optical system” of the invention, the lenses LS for imaging the lights from the light emitting element groups 295_2, 295_3 correspond to a “second imaging optical system” of the invention. When the lens LS for imaging the lights from the light emitting element group 295_2 is the “first imaging optical system” of the invention, the lens LS for imaging the lights from the light emitting element group 295_3 corresponds to the “second imaging optical system” of the invention. The spot SP corresponds to a “light imaged by the imaging optical system” of the invention. In the first embodiment, the light emitting element of the light emitting element group 295_1 corresponds to a “light emitting element that emits a light to be imaged at a first position of the latent image carrier by the first imaging optical system” of the invention, and the light emitting element of the light emitting element group 295_2 corresponds to a “light emitting element that emits a light to be imaged at a second position more distant from a charger than the first position by the second imaging optical system” of the invention. In the third embodiment, the diameter of the light (spot SP) imaged on the photosensitive drum 21 by the lens LS in the sub scanning direction SD corresponds to an “imaging characteristic of the imaging optical system” of the invention. In the fourth embodiment, the position of the light (spot SP) imaged on the photosensitive drum 21 by the lens LS corresponds to the “imaging characteristic of the imaging optical system” of the invention. In the second embodiment, the distances between the positions LC_1, etc. of the lights imaged on the photosensitive drum 21 by the lenses LS and the development position DP correspond to the “imaging characteristic of the imaging optical system” of the invention.
The invention is not limited to the above embodiments and various changes other than the above can be made without departing from the gist thereof. Three light emitting element group rows 295R are arranged in the width direction LTD in the above embodiments. However, the number of the light emitting element group rows 295R is not limited to three and may be two.
Further, in the above embodiments, the light emitting element group 295 is made up of two light emitting element rows 2951R. However, the number of the light emitting element row 2951R constituting the light emitting element group 295 is not limited to two and may be one.
Further, in the above embodiments, the light emitting element row 2951R is made up of four light emitting elements 2951. However, the number of the light emitting elements 2951 constituting the light emitting element row 2951R is not limited to four.
In the above embodiments, organic EL devices are used as the light emitting elements 2951. However, the devices other than the organic EL devices may be used as the light emitting elements 2951. For example, LEDs (light emitting diodes) may be used as the light emitting elements 2951.
In the above embodiments, toner development is performed by the contact developing method by which the developing roller 251 is held in contact with the photosensitive drum surface. However, the toner developing method is not limited to this and toner development may be performed by a noncontact developing method by which a developing roller is distanced from a photosensitive drum surface and toner is caused to jump from the developing roller to the photosensitive drum surface.
Although the technology for adjusting the light quantities of the imaged lights for each lens row LSR is described in the first and the second embodiments and the like, the light quantities of the imaged lights by the lenses belonging to the same lens row LSR are not particularly mentioned. However, in the case where the line head 29 is warped in the longitudinal direction LGD (main scanning direction MD), the imaged light quantities may be adjusted among the lenses belonging to the same lens row LSR as described next.
In
In the line head 29 of the above embodiments, the plurality of light emitting elements 2951 are grouped into the light emitting element groups 295 and the lenses LS are provided in a one-to-one correspondence with the light emitting element groups 295. However, the configuration of the line head 29 is not limited to this and may be configured, for example, as follows.
As shown in
In this way, the light emitting elements 2951 of the light emitting element lineup LUs_1 and those of the light emitting element lineup LUs_2 are arranged at positions mutually different in the width direction LTD. The respective light emitting element lineups LUs_1, LUs_2 form spots SP at positions LCs_1, LCs_2 mutually different in the sub scanning direction SD. Accordingly, the respective light emitting element lineups LUs_1, LUs_2 arranged at the mutually different positions in the width direction LTD are driven for light emission at timings in conformity with the movement of the photosensitive drum surface to form a plurality of spot latent images side by side in the main scanning direction MD.
As described above, also in the line head 29 shown in
As can be understood from
Accordingly, it is preferable to adjust the light quantities of the light emitting elements 2951 according to the positions of the spots SP formed by the light emitting elements 2951 in the sub scanning direction SD by applying the invention also to the line head 29 shown in
An embodiment of an image forming apparatus according to an aspect of the invention comprises: a latent image carrier that moves in a first direction; an exposure head that includes a first imaging optical system, a second imaging optical system that is distanced from the first imaging optical system in the first direction, a light emitting element that emits a light to be imaged on the latent image carrier by the first imaging optical system and a light emitting element that emits a light to be imaged on the latent image carrier by the second imaging optical system; and a controller that is adapted to control a light quantity of the light emitting element that emits a light to be imaged on the latent image carrier by the first imaging optical system in accordance with an imaging characteristic of the first imaging optical system.
An embodiment of an exposure head according to an aspect of the invention comprises: a first imaging optical system; a second imaging optical system that is distanced from the first imaging optical system in a first direction in which a surface-to-be-exposed is moved; a light emitting element that emits a light to be imaged by the first imaging optical system; a light emitting element that emits a light to be imaged by the second imaging optical system; and a controller that is adapted to control a light quantity of the light emitting element that emits the light to be imaged by the first imaging optical system in accordance with an imaging characteristic of the first imaging optical system.
In the embodiment (exposure head, image forming apparatus) thus constructed, a first imaging optical system and a second imaging optical system are provided and the respective imaging optical systems image lights on a latent image carrier moving in a first direction. Further, the second imaging optical system is distanced from the first imaging optical system in the first direction. Accordingly, the position of the imaged light by the first imaging optical system and that of the imaged light by the second imaging optical system differ in the first direction and there is a likelihood of an exposure failure since the first imaging optical system is not capable of exposure similar to the second imaging optical system due to such a difference in the positions of the imaged light. In contrast, in the invention, a controller is provided for controlling a light quantity of the light emitting element for emitting a light to be imaged by the first imaging optical system according to an imaging characteristic of the first imaging optical system. Hence, a good exposure can be realized.
At this time, the imaging characteristic may be an area of the light imaged on the latent image carrier by the first imaging optical system. Alternatively, it may be a diameter of the light imaged on the latent image carrier by the first imaging optical system in the first direction. By adjusting the light quantity of the light emitting element according to such an imaging characteristic, a good exposure can be performed.
Further, the latent image carrier may be a photosensitive drum. Such a photosensitive drum has a curvature shape. As a result, there were cases where an exposure failure occurred because the imaged positions of the lights differed depending on the imaging optical systems. Accordingly, it is preferable to apply the invention to an apparatus provided with a photosensitive drum.
The imaging characteristic may also be a position of the light imaged on the latent image carrier by the first imaging optical system. A good exposure can be made by adjusting the light quantity of the light emitting element according to such an imaging characteristic.
A charger for charging the latent image carrier may be provided and the exposure head may expose the latent image carrier charged by the charger to form a latent image. Further, the first imaging optical system may image the light from the light emitting element on the latent image carrier at a first position, and the second imaging optical system may image the light from the light emitting element on the latent image carrier at a second position which is more distant from the charger than the first position. As described above, the thus formed latent image tends to enlarge with time. Accordingly, the controller may set the light quantity of the light emitting element for emitting the light to be imaged by the first imaging optical system smaller than that of the light emitting element for emitting the light to be imaged by the second imaging optical system. This is because a good exposure can be realized regardless of the enlargement of the spot latent images with time.
A developer for developing the latent image formed on the latent image carrier by the exposure head may be provided. As described above, in such a construction, an image formation failure occurred in some cases since the distances between the imaged light and a development position differed depending on the imaging optical systems. Accordingly, the light quantity of the light emitting element may be adjusted using a distance, as the imaging characteristic, between a position of the light imaged on the latent image carrier by the first imaging optical system and a development position at which the latent image formed by the light is developed by the developer. This is because an image formation failure resulting from the difference of the distances between the imaged light and the development position depending on the imaging optical systems can be suppressed.
A substrate may be provided on which the light emitting element for emitting the light to be imaged on the latent image carrier by the first imaging optical system and that for emitting the light to be imaged on the latent image carrier by the second imaging optical system are arranged. The controller may also be provided on the substrate. At this time, the controller can be constructed by a TFT.
A light shielding member arranged between the substrate and the imaging optical systems may be provided and may be provided with a first light guide hole arranged between the light emitting element for emitting the light to be imaged by the first imaging optical system and the first imaging optical system and a second light guide hole arranged between the light emitting element for emitting the light to be imaged by the second imaging optical system and the second imaging optical system.
The light emitting element for emitting the light to be imaged on the latent image carrier by the first imaging optical system and the light emitting element for emitting the light to be imaged on the latent image carrier by the second imaging optical system may be organic EL devices. At this time, the organic EL device may be of the bottom emission-type.
Further, an embodiment of an image forming apparatus according to another aspect of the invention comprises a latent image carrier moving in a first direction, an exposure head including an imaging optical system and a light emitting element for emitting a light to be imaged on the latent image carrier by the imaging optical system, and a controller for adjusting a light quantity of the light emitting element according to a position in the first direction of the imaging optical system for imaging the light from the light emitting element.
In the image forming apparatus thus constructed, the light quantity of the light emitting element is adjusted according to the position in the first direction of the imaging optical system for imaging the light from the light emitting element. Thus, a good exposure can be realized.
An embodiment of a line head according to another aspect of the invention comprises a head substrate on which light emitting elements are arranged at positions different in a first direction which is a moving direction of an image plane. The light emitting elements emit lights to form spots on the image plane. The respective light emitting elements arranged at the positions different in the first direction form the spots at positions of the image plane mutually different in the first direction. Light quantities of the light emitting elements are adjusted according to the positions in the first direction of the spots formed by the light emitting elements.
An embodiment of an image forming apparatus according to another aspect of the invention comprises a latent image carrier whose surface moves in a first direction and a line head that includes a head substrate on which light emitting elements are arranged at positions different in the first direction. The light emitting elements emit lights to form spots on the surface of the latent image carrier. The respective light emitting elements arranged at the positions different in the first direction form the spots at positions of the latent image carrier surface mutually different in the first direction. The latent image carrier surface carries spot latent images formed by the spots. Light quantities of the light emitting elements are adjusted according to the positions in the first direction of the spots formed by the light emitting elements.
In the embodiment (line head, image forming apparatus) thus constructed, the light quantities of the light emitting elements are adjusted according to the positions in the first direction of the spots formed by the light emitting elements. Accordingly, a good exposure can be realized by suppressing the occurrence of an exposure failure resulting from differences in the spot formation positions in the first direction.
Further, the application of the invention is particularly preferable for a construction in which the image plane is a latent image carrier surface carrying the spot latent images formed by the spots and the respective light emitting elements arranged at the positions different in the first direction are driven for light emission at timings in conformity with the movement of the latent image carrier surface, thereby forming a plurality of spot latent images aligned in a second direction orthogonal to or substantially orthogonal to the first direction.
Specifically, in the above line head, the respective light emitting elements arranged at the positions different in the first direction form spots on the latent image carrier surface at the positions mutually different in the first direction, and spot latent images are formed on the latent image carrier surface by these spots. Accordingly, the respective light emitting elements are driven for light emission at timings in conformity with the movement of the latent image carrier surface to align a plurality of spot latent images in the second direction. Thus, the spots are successively formed from the upstream ones in the first direction and the plurality of spot latent images aligned in the second direction are formed. However, these spot latent images tend to become larger with time. Accordingly, out of the plurality of spot latent images formed side by side in the second direction, those formed by the upstream spots in the first direction became larger than those formed by the downstream spots in the first direction in some cases since time after formation was longer. As a result, the sizes of the plurality of spot latent images formed side by side in the second direction varied in some cases. On the other hand, when the invention is applied, such a size variation of the spot latent images can be suppressed and a good exposure can be realized since the light quantities of the light emitting elements are adjusted according to the positions in the first direction of the spots formed by the light emitting elements.
At this time, out of two light emitting elements that form spots at positions different in the first direction, when the light emitting element that forms a spot at an upstream side in the first direction is defined as an upstream light emitting element and the one that forms a spot at a downstream side is defined as a downstream light emitting element, the light quantity of the upstream light emitting element may be adjusted to be smaller than that of the downstream light emitting element. In the case of such a construction, the variation of the plurality of spot latent images formed side by side in the second direction can be suppressed regardless of the enlargement of the spot latent images with time, wherefore a good exposure can be realized.
In a construction which comprises a developer that develops the spot latent images on the latent image carrier surface at a development position downstream of the respective spots formed on the latent image carrier surface in the first direction, the following problem may occur. In other words, distances in the first direction between the spots and the development position differ among the respective spots formed at the positions different in the first direction. Accordingly, the spot latent images formed by the upstream spots in the first direction and those formed by the downstream spots may differ in the size and the like at the development position. That is, the sizes and the like of the spot latent images varied at the development position in some cases. Thus, light quantities of the light emitting elements may be adjusted according to the distances in the first direction between the spots formed by the light emitting elements and the development position. This is because, by having such a construction, the variation of the spot latent images at the development position can be suppressed and good image formation can be performed by developing such spot latent images with less variation.
The invention is particularly preferably applied to a construction in which the image plane is a latent image carrier surface that has a curvature shape in a first-direction section and carries spot latent images formed by the spots. In other words, as described above, in the line head of another aspect of the invention, the respective light emitting elements arranged at the positions different in the first direction form spots on the latent image carrier surface at positions mutually different in the first direction. Accordingly, in the case where the image plane has a curvature shape, distances between the light emitting elements and the spots formed by the light emitting elements may differ among the respective light emitting elements arranged at the positions different in the first direction. However, the spot latent images formed by these spots may tend to become larger as element-spot distances become longer. Here, the element-spot distance is a distance between the light emitting element and the spot formed by the light emitting element. As a result, size variation occurred among the respective light emitting elements arranged at the positions different in the first direction in some cases. On the other hand, in the case of applying the invention, a good exposure can be realized by suppressing the size variation of the spot latent images since the light quantities of the light emitting elements are adjusted according to the positions in the first direction of the spots formed by the light emitting elements.
At this time, out of two light emitting elements adapted to form spots at positions mutually different in the first direction and having different element-spot distances, the light quantity of the light emitting element having the longer element-spot distance may be adjusted to be smaller than that of the light emitting element having the shorter element-spot distance. In the case of such a construction, the size variation of the spots can be suppressed regardless of the element-spot distances and a good exposure can be realized.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as other embodiments of the present invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-332586 | Dec 2007 | JP | national |
| 2008-273125 | Oct 2008 | JP | national |
