Patent Application
20090060542
The disclosure of Japanese Patent Applications No. 2007-219769 filed on Aug. 27, 2007 and No. 2008-179398 filed on Jul. 9, 2008 including specification, drawings and claims is incorporated herein by reference in its entirety.
1. Technical Field
The invention relates to an image forming apparatus and an image forming in which a test image is properly detected.
2. Related Art
There has been conventionally known an image forming apparatus for forming a test image and obtaining image formation information relating to image formation by detecting this test image. For example, an image forming apparatus disclosed in Japanese Patent No. 2642351 obtains color misregistration information as image formation information to form a satisfactory color image by properly superimposing a plurality of colors. More specifically, the apparatus disclosed in this literature forms registration marks (“detection pattern” in this literature) as test images for a plurality of colors. The registration marks of the respective colors are detected by optical sensors and then the positions thereof are obtained from this detection result. The color misregistration information can be obtained from the positions of the registration marks of the respective colors thus obtained.
Further; in an image forming apparatus disclosed in JP-A-7-111591 or JP-A-2001-75325, density information is obtained as image formation information to realize a proper image density. More specifically, this apparatus forms a patch mark (“patch image” disclosed in JP-A-2001-75325) as a test image under a specified condition and detects this patch mark using an optical sensor. The density information is obtained based on the density of the patch mark obtained from the detection result of the optical sensor.
For the realization of high-resolution image formation, a surface of a latent image bearing member may be exposed by the following line head. This line head includes a plurality of light emitting elements grouped into light emitting element groups, and the respective light emitting element groups emit light beams toward the surface of the latent image bearing member moving in a sub scanning direction to expose areas mutually different in a main scanning direction orthogonal to the sub scanning direction. Further, N (N is an integer equal to or greater than 2) light emitting element groups capable of exposing areas consecutive in the main scanning direction are respectively arranged while being displaced in a direction corresponding to the sub scanning direction. In the case of forming a test image, the light emitting element groups expose the surface of the latent image bearing member to form a test latent image and this test latent image is developed to form the test image. However, there are cases where the positions of the formed latent images vary in the sub scanning direction among the N light emitting element groups displaced in the direction corresponding to the sub scanning direction due to a variation of the moving speed of the surface of the latent image bearing member. In other words, there are cases where the positions of the N latent images consecutively formed in the main scanning direction vary in the sub scanning direction. A similar variation occurs also in the test image obtained by developing the test latent image having such a variation. Accordingly, upon detecting the test image, it is preferable to properly detect the test image by reflecting such a variation on the detection result.
An advantage of some aspects of the invention is to provide technology for enabling the proper detection of a test image by reflecting a variation in a sub scanning direction of the positions of N latent images consecutively formed in a main scanning direction on the detection result on the test image.
An apparatus according to an aspect of the invention comprises: an exposure head including an imaging optical system arranged in a first direction and a light emitting element that emits light to be imaged by the imaging optical system; a latent image bearing member that moves in a second direction and carries a latent image formed by the exposure head; a developing unit that develops the latent image formed by the exposure head; a detector that detects the image developed by the developing unit; and a controller that controls image formation such that a width L1 in the first direction of a latent image formed on the latent image bearing member by one imaging optical system and a width L2 in the first direction of the image detected by the detector has a relationship of L2>L1.
A method according to an aspect of the invention comprises: forming a latent image on a latent image bearing member by an exposure head including an imaging optical system arranged in a first direction and a light emitting element for emitting light to be imaged by the imaging optical system, the latent image bearing member moving in a second direction; developing the latent image formed by the exposure head; and detecting the image formed such that a width L1 in the first direction of a latent image formed on the latent image bearing member by one imaging optical system and a width L2 in the first direction of the image detected by the detector has a relationship of L2>L1.
An apparatus according to another aspect of the invention comprises: an exposure head including an imaging optical system arranged in a first direction and a light emitting element that emits light to be imaged by the imaging optical system; a latent image bearing member that moves in a second direction and carries a latent image formed by the exposure head; a developing unit that develops the latent image formed by the exposure head; a detector that detects the image developed by the developing unit; and a controller that controls image formation such that a width L3 in the first direction of a latent image formed on the latent image bearing member by two or more imaging optical systems and a width L2 in the first direction of the image detected by the detector has a relationship of L2>L3.
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.
I. Basic Construction of an Image Forming Apparatus
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 MD. 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 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 to irradiate (in other words, expose) the surface of the photosensitive drum 21 charged by the charger 23, thereby forming a latent image on this surface. The head controller HC is provided to control the line heads 29 of the respective colors, and controls the respective line heads 29 based on the video data VD from the main controller MC and a signal from the engine controller EC. Specifically, image data included in an image formation command is inputted to an image processor 51 of the main controller MC. Then, video data VD of the respective colors are generated by applying various image processings to the image data, and the video data VD are fed to the head controller HC via a main-side communication module 52. In the head controller HC, the video data VD are fed to a head control module 54 via a head-side communication module 53. Signals representing parameter values relating to the formation of a latent image and the vertical synchronization signal Vsync are fed to this head control module 54 from the engine controller EC as described above. Based on these signals, the video data VD and the like, the head controller HC generates signals for controlling the driving of the elements of the line heads 29 of the respective colors and outputs them to the respective line heads 29. In this way, the operations of the light emitting elements in the respective line heads 29 are suitably controlled to form latent images corresponding to the image formation command.
The photosensitive drum 21, the charger 23, the developer 25 and the photosensitive drum cleaner 27 of each of the image forming stations Y, M, C and K are unitized as a photosensitive cartridge. Further, each photosensitive cartridge includes a nonvolatile memory for storing information on the photosensitive cartridge. Wireless communication is performed between the engine controller EC and the respective photosensitive cartridges. By doing so, the information on the respective photosensitive cartridges is transmitted to the engine controller EC and information in the respective memories can be updated and stored.
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 kΩ·cm 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, if the blade facing roller 83 moves as described next, the cleaner blade 711 and the waste toner box 713 move together with the blade facing roller 83.
II. Construction of Line Head
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 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). Specifically, the plurality of light emitting element groups 295 are two-dimensionally arranged on the under surface of the head substrate 293 while being spaced by specified distances in the longitudinal direction LGD and the width direction LTD. Here, each light emitting element group 295 is formed by two-dimensionally arraying a plurality of light emitting elements. This will be described in detail later. Bottom emission-type EL (electroluminescence) devices are used as the light emitting elements. In other words, the organic EL devices are arranged as light emitting elements on the under surface of the head substrate 293. Thus, all the light emitting elements 2951 are arranged on the same plane (under surface of the head substrate 293). When the respective light emitting elements are driven by a drive circuit formed on the head substrate 293, light beams are emitted from the light emitting elements in directions toward the photosensitive drum 21. These light beams 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 normals 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 as spots on the surface of the photosensitive drum 21 by the lens array 299.
As described above, in this embodiment, some lights out of lights being emitted from the light emitting elements 2951 pass through the light guide holes 2971 formed in the light shielding member 297. The some lights are incident on the lenses LS and contribute to image formation. In other words, the lights incident on the lenses LS and contributing to image formation are restricted by the light shielding member 297. Accordingly, a problem of disturbing the formed image by stray lights and the like is suppressed by the light shielding member 297, and a detection image such as a registration mark RM to be described later can be satisfactorily formed. By detecting a detection image satisfactorily formed in this way, the detection result on the detection image can be made stable.
As shown in
The lens array 299 is arranged such that optical axes OA of the 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 normal to the under surface (surface where the light emitting elements 2951 are arranged) of the head substrate 293. At this time, these plurality of lenses LS are arranged in a one-to-one correspondence with the plurality of light emitting element groups 295 to be described later. In other words, the plurality of lenses LS are two-dimensionally arranged at specified intervals in the longitudinal direction LGD and the width direction LTD in correspondence with the arrangement of the light emitting element groups 295 to be described later, and focus the lights from the corresponding light emitting element groups 295 to expose the surface of the photosensitive drum 21. These respective lenses LS are arranged as follows. Specifically, a plurality of lens rows LSR, in each of which a plurality of lenses LS are aligned in the longitudinal direction LGD, are arranged in the width direction LTD. In this embodiment, three lens rows LSR1, LSR2, LSR3 are arranged in the width direction LTD. The three lens rows LSR1 to LSR3 are arranged at specified lens pitches Pls in the longitudinal direction, so that the positions of the respective lenses LS differ in the longitudinal direction LGD. In this way, the respective lenses LS can expose regions mutually different in the main scanning direction NM.
Specifically, a plurality of light emitting element groups 295 are arranged such that a plurality of light emitting element group columns 295C, in each of which three light emitting element groups 295 are offset from each other in the width direction LTD and the longitudinal direction LGD, are arranged in the longitudinal direction LGD. Further, in conformity with such an arrangement of the light emitting element groups, a plurality of lens columns LSC, in each of which three lenses LS are offset from each other in the width direction LTD and the longitudinal direction LGD, are arranged in the longitudinal direction LGD in the lens array 299. The longitudinal-direction positions of the respective light emitting element groups 295 differ from each other, so that the respective light emitting element groups 295 can expose mutually different regions in the main scanning direction MD. A plurality of light emitting element groups 295 arranged in the longitudinal direction LGD (in other words, a plurality of light emitting element groups 295 arranged at the same width-direction position) are particularly defined as a light emitting element group row 295R. In this specification, it is defined that the position of each light emitting element is the geometric center of gravity thereof and that the position of the light emitting element group 295 is the geometric center of gravity of the positions of all the light emitting elements belonging to the same light emitting element group 295. The longitudinal-direction position and the width-direction position mean a longitudinal-direction component and a width-direction component of a particular position, respectively.
The detailed mutual relationship of the light emitting element groups 295, the light guide holes 2971 and the lenses LS is as follows. Specifically, the light guide holes 2971 are perforated in the light shielding member 297 and the lenses LS are arranged in conformity with the arrangement of the light emitting element groups 295. At this time, the center of gravity position of the light emitting element groups 295, the center axes of the light guide holes 2971 and the optical axes OA of the lenses LS substantially coincide. Accordingly, light beams emitted from the light emitting elements 2951 of the light emitting element groups 295 are incident on the lenses LS of the lens array 299 through the light guide holes 2971. Spots are formed on the surface of the photosensitive drum 21 (photosensitive member surface) by imaging these incident light beams by the lenses LS, whereby the surface of the photosensitive member is exposed. A latent image is formed in the thus exposed part.
III. Terminology in Line Head
Collections of a plurality of (eight in
Further, spot group rows SGR and spot group columns 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
IV. Exposure Operation by Line Head
In the line head 29, the light emitting element group column 295C is formed by offsetting three light emitting element groups 295 from each other in the width direction LTD and the longitudinal direction LGD. For example, as shown in
The formation positions of the spot groups SG in the sub scanning direction SD differ depending on the light emitting element groups 295. Accordingly, the respective light emitting element group rows 295R emit lights at mutually different timings to form the spot groups SG, for example, in the case of forming a latent image extending in the main scanning direction MD.
In this specification, the group latent images formed by the light emitting element group row 295R_1 (in other words, by the lens row LSR1) are called group latent image GL1 and group toner images obtained by developing the group latent images GL1 are called group toner images GM1. Further, the group latent images formed by the light emitting element group row 295R_2 (in other words, by the lens row LSR2) are called group latent image GL2 and group toner images obtained by developing the group latent images GL2 are called group toner images GM2. Furthermore, the group latent images formed by the light emitting element group row 295R_3 (in other words, by the lens row LSR3) are called group latent image GL3 and group toner images obtained by developing the group latent images GL3 are called group toner images GM3.
The respective light emitting element group rows 295R emit lights at different timings in this way, whereby the positions of the group latent images GL formed by the respective light emitting element groups 295 in the sub scanning direction SD coincide with each other. The group latent images GL whose positions in the sub scanning direction SD coincide with each other are consecutively formed in the main scanning direction MD to form a latent image LI extending in the main scanning direction MD (see
However, a moving speed of the surface of the photosensitive member may vary, for example, as shown in
If the above is summarized, the group column 295C is formed by displacing the respective N light emitting element groups 295, which can expose the areas consecutive in the main scanning direction MD, in the width direction LTD corresponding to the sub scanning direction SD in the above line head 29. Here, in this specification, N is the number of the light emitting element groups 295 constituting one light emitting element group column 295C (i.e. the number of the light emitting element group rows 295R). In the above line head 29, N=3. As described above, in the case of forming latent images by such a line head 29, the positions of the N group latent images GL consecutively formed in the main scanning direction MD may vary in the sub scanning direction SD in some cases. As a result, a similar variation occurs also in an image obtained by developing such latent images.
In order to satisfactorily perform an image forming operation, the above image forming apparatus 1 obtains image formation information relating to image formation beforehand in some cases. Although described in detail later, such image formation information includes color misregistration information, density information or information on the positional variation of the above N group latent images GL. These pieces of image formation information are obtained as follows. Specifically, a test image is formed and detected by an optical sensor and the image formation information is obtained from this detection result. In light of properly performing such a test image detection operation, it is preferable to reflect the positional variation of the N group latent images GL as described above on the detection result on the test image. Accordingly, as described in “V-1. First Example of Test Image Detection operation” to “V-3 Third Example of Test Image Detection operation”, the test image detection operation is properly performed by reflecting the positional variation of the N group latent images GL consecutive in the main scanning direction M on the detection result on the test image in the embodiment of the invention.
V-1. First Example of Test Image Detection Operation
In the test image detection operation, test images TM are formed on the outer surface of the transfer belt 81 (
The group latent images GL1 to GL3 constituting the test latent image TLI are developed to form the group toner images GM1 to GM3. In this way, the test latent image TLI is developed to form the test image TM. Such a test image TM also has the width L2 in the main scanning direction MD. This test image TM is conveyed in the conveying direction D81 to be detected at the sensor spot SS. In the first example shown in
As described above, in the first example shown in
As shown in
On the contrary, as shown in
V-2. Second Example of Test Image Detection Operation
In the second example as well, a test latent image TLI, a test image TM and a sensor spot SS have widths in the main scanning direction MD larger than the sum (=Wlm+Wlm) of the widths in the main scanning direction MD of images formed by (N-1) lenses LS adjacent in the main scanning direction MD and capable of exposure (e.g. group toner images GM1, GM2 or group toner images GM2, GM3, etc.). Particularly in the second example, the sensor spot SS has a main-scanning spot diameter Dsm larger than the N-fold of the unit width Wlm. Accordingly, the test image TM can be more properly detected by sufficiently reflecting the positional variation of N group latent images GL (GL1 to GL3) consecutive in the main scanning direction MD on the detection result on the test image TM. The reason for this will be described with reference to
In
V-3. Third Example of Test Image Detection Operation
In the third example as well, a test latent image TLI, a test image TM and a sensor spot SS have widths in the main scanning direction MD larger than the sum (=Wlm+Wlm) of the widths in the main scanning direction MD of images formed by (N-1) lenses LS adjacent in the main scanning direction MD and capable of exposure (e.g. group toner images GM1, GM2 or group toner images GM2, GM3, etc.). Particularly in the third example shown in
As described above, in the third example shown in
VI-1. Color Misregistration Correction Operation
By performing the test image detection operation as described above, the test image TM can be properly detected by reflecting the positional variation of N group latent images GL consecutive in the main scanning direction MD on the detection result. Thus, by applying the above test image detection operation to a color misregistration correction operation, such a color misregistration correction operation can be satisfactorily performed. Accordingly, a case of applying the above test image detection operation to the color misregistration correction operation is described below. Particularly, a case of applying the first example of the test image detection operation to the color misregistration correction operation is described below.
In the row “SENSING PROFILE” of
In the displacement calculator 55, the detected waveforms PR(Y), PR(M), PR(C) and PR(K) outputted from the optical sensor SC are converted into binary values using a threshold voltage Vth to obtain binary signals BS(Y), BS(M), BS(C) and BS(K) as shown in the row “AFTER BINARY CONVERSION” of
Dm=S81×(T1−T1rf)
Such a calculation is performed also for cyan (C) and black (K) to calculate displacements (color misregistration information) with respect to the respective toner colors. The color misregistration information thus calculated is outputted to the emission timing calculator 56, which then calculates optimal emission timings based on the color misregistration information. The light emission of the line head 29 is controlled based on the thus calculated emission timings to control the transfer positions of the toner images for color misregistration correction.
As described above, in this color misregistration correction operation, the registration marks RM are formed as the test images TM and the operation of detecting the registration marks RM is performed similar to the above test image detection operation. Accordingly, the registration marks RM can be properly detected by reflecting the positional variation of N group latent images GL consecutive in the main scanning direction MD on the detection result. As a result, the color misregistration information can be obtained with high accuracy. A color image forming operation is performed while the light emissions of the line heads 29 are controlled based on the color misregistration information thus obtained with high accuracy. Therefore, satisfactory color image formation can be realized.
Here, the case of applying the first example of the test image detection operation to the color misregistration correction operation was described. However, it is also possible to properly detect the registration marks RM by applying the above second or third example of the test image detection operation to the color misregistration correction operation to reflect the positional variation of N group latent images GL consecutive in the main scanning direction MD on the detection result in the color misregistration correction operation. As a result, the color misregistration information can be obtained with high accuracy, and the light emissions of the line heads 29 are controlled based on the color misregistration information thus obtained with high accuracy, wherefore satisfactory color image formation can be realized.
VI-2. Density Correction Operation
By performing the test image detection operation as described above, the test image TM can be properly detected by reflecting the positional variation of N group latent images GL consecutive in the main scanning direction MD on the detection result. Thus, by applying the above test image detection operation to a density correction operation, such a density correction operation can be satisfactorily performed. Accordingly, a case of applying the above test image detection operation to the density correction operation will be described below. Particularly, a case of applying the first example of the test image detection operation to the density correction operation will be described below
In the density correction operation, patch marks PM of the respective toner colors are formed as the test images TM. Specifically, the image forming stations Y, M, C and K form test latent images on the surfaces of the photosensitive drums 21 belonging thereto and develop these test latent images in the respective toner colors to form patch marks PM(Y), PM(M), PM(C) and PM(K) as the test images. These patch marks PM are transferred to the surface of the transfer belt 81 while being arranged in the conveying direction D81. The patch marks PM thus formed on the transfer belt 81 are conveyed in the conveying direction D81 to be detected by the optical sensor SC.
The row “SENSING PROFILE” of
In the detected voltage calculator 571, peak voltages V1 to V4 of the detected waveforms R(Y), PR(M), PR(C) and PR(K) outputted from the optical sensor SC are obtained and inputted to the voltage displacement calculator 572. The voltage displacement calculator 572 compares the respective peak voltages V1 to V4 with a reference voltage stored in the reference value storage 573 to obtain density information on the density displacement for the respective colors. If the density displacement is judged from such density information, the density correction operation is so performed that the peak voltages and the reference voltage substantially coincide. Specifically, the head controller HC corrects the exposure timings of the line heads 29 based on the density information. Further, based on the density information, the development bias controller 574 corrects a development bias value of a development bias generator 252. An image forming operation is performed based on the thus corrected image density.
As described above, in this density correction operation, the patch marks PM are formed as the test images TM and the operation of detecting the patch marks PM is performed similar to the above test image detection operation. Accordingly, the patch marks PM can be properly detected by reflecting the positional variation of N group latent images GL consecutive in the main scanning direction MD on the detection result. As a result, the density information can be obtained with high accuracy. An image forming operation is performed at an image density corrected based on the density information thus obtained with high accuracy. Therefore, satisfactory image formation can be realized.
Here, the case of applying the first example of the test image detection operation to the density correction operation was described. However, it is also possible to properly detect the patch marks PM by applying the above second or third example of the test image detection operation to the density correction operation to reflect the positional variation of N group latent images GL consecutive in the main scanning direction MD on the detection result in the density correction operation. As a result, the density information can be obtained with high accuracy, and an image forming operation is performed at an image density corrected based on the density information thus obtained with high accuracy, wherefore satisfactory image formation can be realized.
V-3. Variation Correction Operation
By performing the test image detection operation as described above, the test image TM can be properly detected by reflecting the positional variation of N group latent images GL consecutive in the main scanning direction MD on the detection result on the test image TM. In other words, the detection result on the test image TM reflects the positional variation of N group latent images GL consecutive in the main scanning direction MD. In a variation correction operation described below, the positional variation of the group latent images GL is corrected using such a detection result. Particularly, a case of applying the first example of the test image detection operation to the variation correction operation will be described below.
In the variation correction operation, variation detection marks DM are formed as the test images TM (detection mark forming process). Specifically, test latent images TLI are formed on the surfaces of the photosensitive drums 21 and developed to form variation detection marks DM. After being transferred to the surface of the transfer belt 81 and conveyed in the conveying direction D81, these variation detection marks DM are detected by the optical sensor SC (detection mark detecting process). This operation of detecting the variation detection marks DM is performed similar to the test image detection operation described in the above “V-1. First Example of Test Image Detection Operation”.
The optical sensor SC outputs the detected waveform PR(DM) of the variation detection mark DM to the engine controller EC. The engine controller EC includes a time displacement calculator 581, a reference time storage 582, a positional displacement calculator 583 and an emission timing calculator 584. This detected waveform PR(DM) is inputted to the time displacement calculator 581. The time displacement calculator 581 calculates a time interval Td which elapses until the rise of the detected waveform PR(DM) passes an upper threshold voltage Vhig after passing a lower threshold voltage Vlow. Then, the time displacement calculator 581 calculates a difference ΔT=Td−Tdr between this time interval Td and a reference time interval Tdr stored in the reference time storage 582. This reference time interval Tdr is a time interval which elapses until the rise of the reference waveform PR(DMr) passes the upper threshold voltage Vhig after passing the lower threshold voltage Vlow and is stored in the reference time storage 582.
The time displacement calculator 581 calculates a positional variation ΔDgm of the group toner image GM from this difference ΔT and a circumferential speed S21 of the photosensitive drum 21 and outputs this positional variation ΔDgm to the emission timing calculator 584. The emission timing calculator 584 calculates an emission timing of the line head 29 based on the positional variation ΔDgm (timing calculating process). Specifically, this emission timing is so calculated as to decrease the positional variation ΔDgm. The head controller HC controls the light emission of the line head 29 based on the thus calculated emission timing (emission controlling process). The detection mark forming process, the detection mark detecting process, the timing calculating process and the emission controlling process are repeatedly performed until the positional variation ΔDgm falls to or below a specified value. In this way, the positional variation ΔDgm is suppressed to correct the positional variation of the group latent images GL. An image forming operation is performed with the positional variation corrected in this way.
As described above, in this variation correction operation, the variation detection mark DM is formed as the test image TM and the operation of detecting the variation detection mark DM is performed similar to the above test image detection operation. Accordingly, it is possible to reflect the positional variation of N group latent images GL consecutive in the main scanning direction MD on the detection result of the variation detection mark DM. Using such a detection result, the positional variation of the group latent images GL is corrected and an image forming operation is performed with the positional variation corrected. Therefore, satisfactory image formation is realized.
Here, the case of applying the first example of the test image detection operation to the variation correction operation was described. However, it is also possible to properly detect the variation detection marks DM by applying the above second or third example of the test image detection operation to the variation correction operation to reflect the positional variation of N group latent images GL consecutive in the main scanning direction MD on the detection result in the variation correction operation. Using such a detection result, the positional variation of the group latent images GL is corrected and an image forming operation is performed with the positional variation corrected, wherefore satisfactory image formation is realized.
VI-4. Color Misregistration Correction Operation in the Main Scanning Direction
In the above embodiments, the invention is applied to the color misregistration correction operation for suppressing the color misregistration in the sub scanning direction SD. However, the application of the invention is not limited to this and the invention may also be applied to a color misregistration correction operation for suppressing the color misregistration in the main scanning direction MD. This will be described below.
First of all, a detection operation of the registration mark Ra, Rb free from displacement will be described. Since the transfer belt 81 moves in the moving direction D81 as described above, the registration mark Ra, Rb also moves in the moving direction D81 as this transfer belt 81 moves. Then, the registration mark Ra, Rb passes a sensor spot (not shown in
On the other hand, in an example shown in
The respective profile signals PRa(Y), PRb(Y), PRa(M) and PRb(M) thus obtained are converted into binary values to obtain binary signals BSa(Y), BSb(Y), BSa(M) and BSb(M). The edge detection times Tiv for the respective colors are calculated from rising edge intervals of the binary signals BSa(Y), BSb(Y), BSa(M) and BSb(M). Specifically, the edge detection time Tiv(Y) of yellow (Y) is calculated from the rising edges of the binary signals BSa(Y), BSb(Y), and the edge detection time Tiv(M) of magenta (M) is calculated from the rising edges of the binary signals BSa(M), BSb(M). By multiplying a difference between the edge detection times Tiv of the respective colors (=Tiv(Y)−Tiv(M)) by the moving speed S81 of the transfer belt 81, a displacement in the main scanning direction M between the registration marks RM(Y) and RM(M) can be calculated.
The above test image detection operation can be also applied to this color misregistration correction operation in the main scanning direction. Particularly, a case of applying the first example of the test image detection operation to the color misregistration correction operation will be described below.
VI-5. Operation for Correcting Color Misregistration Resulting from Sub Scanning Magnification
In the above embodiments, displacements among mutually different colors are calculated by detecting the registration marks RM. However, besides displacements among mutually different colors, there are cases where a displacement called “sub scanning magnification displacement” occurs for one color. Specifically, there are cases where the speed of the photosensitive drum 21 is faster or slower than a desired speed, for example, for a certain color to contract or extend an image transferred to the transfer belt 81, with the result that the image transferred to the transfer belt 81 looks as if the magnification thereof would have been deviated in the sub scanning direction SD (as if a sub scanning magnification displacement would have occurred). Such a sub scanning magnification displacement can also be calculated by detecting the registration mark RM as described next.
The respective profile signals PR(Y)_1, PR(Y)_2 thus obtained are converted into binary values to obtain binary signals BSa(Y), BSb(Y). An edge detection time T1 is calculated from a rising edge interval of the binary signals BSa(Y), BSb(Y), and an interval between the registration marks PR(Y)_1, PR(Y)_2 in the sub scanning direction SD is calculated by multiplying this edge detection time T1 by the conveying speed S81 of the transfer belt 81. Then, by calculating how far the thus calculated interval between the registration marks PR(Y)_1, PR(Y)_2 is deviated from a desired value, the sub scanning magnification displacement can be calculated for yellow (Y). Sub scanning magnification displacements can be similarly calculated for the colors other than yellow (Y). By controlling, for example, the emission timings of the light emitting elements 2951 based on the thus calculated sub scanning magnification displacements, the length of the image to be transferred to the transfer belt 81 in the sub scanning direction SD can be set to a suitable length.
By applying the above test image detection operation according to the invention also to the operation for correcting color misregistration resulting from a sub scanning magnification, the positional variation of the N group latent images GL consecutive in the main scanning direction MD can be reflected on the detection result on the registration mark RM. By performing the color misregistration correction operation using such a detection result, color misregistration resulting from the sub scanning magnification is properly corrected to realize satisfactory image formation.
VII. Modification of Optical Sensor
As described above, in
As described above, in the above embodiment, the main scanning direction MD corresponds to a “first direction” of the invention, and the sub scanning direction SD to a “second direction” of the invention. Further, in the above embodiment, the respective image forming stations Y, M, C and K correspond to “image forming assemblies” of the invention; the photosensitive drum 21 to a “latent image bearing member” of the invention; the light emitting element group column 295C to a “group column”; the optical sensor SC to a “detector” of the invention; and the sensor spot SS to a “detection area” of the invention. Further, the line head 29 corresponds to an “exposure head” of the invention; the lens LS corresponds to an “imaging optical system” of the invention; the light emitting element group 295 to “a plurality of light emitting elements” of the invention; the width of the test image TM in the main scanning direction MD to “a width L2 in the first direction of an image detected by the detector”; and the width which is the (N-1)-fold of the unit width Wlm in the main scanning direction MD to a “width L3 in the first direction of latent images formed on the latent image bearing member by two or more imaging optical systems”. Further, the above operation of forming the test latent images TLI is performed by the controls of the main controller MC and the head controller HC, and the main controller MC and the head controller HC function as a “controller” of the invention.
In the invention (image forming apparatus, image forming method) thus constructed, the test latent image and the detection area are wider than the (N-1)-fold of the width of the latent image formed by all the light emitting elements belonging to one light emitting element group. Accordingly, the test image can be properly detected by reflecting the variation of the above N latent images on the detection result on the test image.
In the first direction, the test latent image may be formed by latent images formed by N or more light emitting element groups and adjacent in the first direction. Each of at least N light emitting element groups capable of exposure in the first direction may form a latent image by all the light emitting elements belonging thereto. By such a construction, the test image can be more properly detected.
At this time, the test latent image may be formed by N light emitting element groups. In this case, the widths in the first direction of the N latent images constituting the test latent image may be equal to each other. As a result, the influence of the respective latent images on the detection result of the detector can be made substantially equal among the N latent images. Therefore, the test image can be more properly detected.
In the first direction, the detection area may be wider than the N-fold of the width of the latent image formed by all the light emitting elements belonging to one light emitting element group. By such a construction, the test image can be more properly detected.
Image formation information relating to image formation may be obtained based on the detection result of the detector. By such a construction, the image formation information can be obtained based on the proper detection result on the test image, with the result that the image formation information can be obtained with high accuracy.
An image forming operation may be controlled based on the image formation information. By such a construction, satisfactory image formation can be performed.
VIII. Miscellaneous
The invention is not limited to the above embodiment and various changes other than the above can be made without departing from the gist thereof. For example, in “V-1. First Example of Test Image Detection operation”, the test latent image TLI has the width in the main scanning direction MD equal to or larger than the N-fold of the unit width Wlm. However, the width of the test latent image TLI in the main scanning direction MD is not limited to this and is sufficient to be larger than the (N-1)-fold of the unit width Wlm. Accordingly, the test latent image TLI may be configured as shown in
In “V-2. Second Example of Test Image Detection operation”, the test latent image TLI is made up of the group latent images GL formed by eight light emitting element groups 295 and consecutive in the main scanning direction MD. All of these eight light emitting element groups 295 form the group latent images GL by all the light emitting elements 2951 belonging thereto. However, it is not necessary to form all the group latent images GL constituting the test latent image TLI by all the light emitting element groups 295 belonging to the light emitting element groups 295. For example, only N light emitting element groups 295 may form the group latent images GL by all the light emitting elements 2951 belonging thereto.
Although all the light emitting elements 2951 of each of the N light emitting element groups 295 emit lights to form the group latent image GL in the above embodiment, the group latent image may be formed by driving only some of the light emitting elements 2951 belonging to each light emitting element group 295 to emit lights. Further, in the above embodiment, the light emitting element group 295 includes a plurality of light emitting element rows 2951R. Accordingly, the respective group latent images GL constituting the test latent image TLI may be formed, for example, by causing only one of the plurality of light emitting element rows 295IR to emit lights. In other words, the respective group latent images GL may be formed by causing only the light emitting element column 2951R_1 of
The above embodiments correspond to the case where one light emitting element group column 295C is made up of three light emitting element groups 295, i.e. the case where “N” of the invention is 3. However, the number of the light emitting element groups 295 constituting one light emitting element group column 295C is not limited to 3 and may be any integer equal to or greater than 2 (i.e. “N” may be any integer equal to or greater than 2)
For example, as shown in
L2>L1.
By making the main-scanning spot diameter Dsm of the sensor spot SS larger than the (N-1) of the unit width Wlm, i.e. the unit width Wlm, the registration marks RM can be properly detected by reflecting the positional variation of N group latent images GL consecutive in the main scanning direction MD on the detection result.
In the above embodiments, the light emitting element group 295 includes eight light emitting elements 2951. However, the number of the light emitting elements 2951 constituting the light emitting element group 295 is not limited to this and may be 2 or greater.
In the above embodiments, organic EL devices are used as the light emitting elements 2951. However, devices usable as the light emitting elements 2951 are not limited to organic EL devices and LEDs (Light Emitting diodes) may also be used as the light emitting elements 2951.
In the case of using organic EL devices, particularly bottom-emission type EL devices as the light emitting elements 2951, emitted light quantities tend to decrease and an image to be formed is easily influenced by stray lights and the like. Accordingly, in such a case, the light shielding member 297 described with reference to
In the above embodiments, the invention is applied to the so-called tandem image forming apparatus. However, image forming apparatuses to which the invention is applicable are not limited to tandem image forming apparatuses. For example, JP-A-2002-132007 discloses a so-called rotary image forming apparatus including one photosensitive member and one exposure unit and adapted to successively form latent images corresponding to the respective colors on a photosensitive member surface using the exposure unit. The invention is also applicable to such a rotary image forming apparatus.
Although specific sizes of the sensor spot SS and the registration mark RM are not particularly described in the above embodiments, these sizes may be set as follows.
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 |
|---|---|---|---|
| 2007-219769 | Aug 2007 | JP | national |
| 2008-179398 | Jul 2008 | JP | national |
