Patent Application
20090016749
This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2007-184788 filed in JAPAN on Jul. 13, 2007, the entire contents of which are hereby incorporated herein by reference.
The present invention relates to an electrophotographic image forming apparatus, for example, such as a copying machine, and more specifically relates to an image forming apparatus which performs adjustment to maintain quality of an image formed on an image carrier or a transfer sheet carrier using a patch image.
An usual electrophotographic image forming apparatuses are susceptible to an usage state of each process portion, surrounding environmental situations and the like, due to the principle of operation that image formation is performed using static electricity and therefore, they have a problem that a toner density of a formed image is also liable to change and as a result, image quality is liable to deteriorate. Against these circumstances, in Japanese Laid-Open Patent Publication No. 2003-15369, an electrophotographic image forming apparatus is developed, in which an adjustment step of adjusting control conditions (charging voltage, exposure amount, developing bias, transfer bias and the like) in each portion of an image forming portion (process control) is provided and the adjustment step is carried out in accordance with predetermined conditions, and thereby image quality is adjusted so as to be able to obtain excellent image quality at all times.
In the above-mentioned image quality adjustment, a toner patch for a test is formed on an image carrier such as a photoreceptor, an intermediate transfer body or a transfer body at a predetermined timing other than forming images, and the above control conditions are adjusted based on the value of an image (toner) density of the toner patch measured by a density sensor.
In a process control mode, a toner patch serving as a density reference is formed on an image carrier (including an intermediate transfer body such as a photoreceptor, an intermediate transfer drum or an intermediate transfer belt, or a transfer body such as a transfer drum or a transfer belt), a density of the toner patch (toner adhesion amount) is detected by an image sensor that is an optical detection means, and based on the detected density, feedback is applied to parameters (image forming conditions), such as charging voltage, exposure intensity, developing bias potential, transfer voltage and amount of toner supply (in the case of two component development) which affect the image density.
On the other hand, Japanese Laid-Open Patent Publication No. 10-272806 discloses a technology that in a color image forming apparatus, a color sensor for detecting a sheet color is provided near a sheet supply port, and at the time of performing color printing, color tones of a sheet to be printed are detected by the color sensor, so that optimization of more precise color adjustment is applied depending on the color of the sheet to be printed.
However, in a color image forming apparatus provided with a function of detecting a toner patch image by a toner density sensor to perform image quality adjustment, a color sensor for detecting the sheet color needs to be further provided on a sheet transport path in order to add a function of applying optimization of color adjustment depending on a sheet color, but this inhibits miniaturization of the apparatus.
An object of the present invention is to provide a smaller image forming apparatus with smaller number of parts which is achieved by making a common color sensor detect a sheet color and a reference toner image not to further provide a color sensor for detecting the sheet color on a sheet transport path.
Another object of the present invention is to provide an image forming apparatus including an image carrier on which a toner image depending on input image data is formed, a transfer sheet carrier for forming a transfer sheet transport path and transferring the toner image formed on the image carrier onto a sheet being transported, a color sensor disposed in a vicinity of the transfer sheet transport path, a control portion for controlling an image forming operation, and an image adjustment function which performs an image adjustment using a reference toner image prior to printing when a color print mode is selected, wherein, a separation driving mechanism for separating the transfer sheet carrier from the image carrier and then contacting them and a sheet re-feeding transport path for feeding the sheet which has passed through the transfer sheet transport path again to the transfer sheet transport path are further included, and the control portion performs a series of control at the time of the image adjustment, to form the reference toner image on a surface of the transfer sheet carrier, to detect the reference toner image by the color sensor, to adjust developing conditions based on color information of the detected reference toner image, then, to transport the sheet on the transfer sheet transport path in a state where the transfer sheet carrier is separated from the image carrier by the separation driving mechanism, to detect colors of the sheet by the color sensor, and to correct a color tone of the input image data based on the detected color of the sheet.
Another object of the present invention is to provide the image forming apparatus, wherein the sheet re-feeding transport path is the path reversing the side of the sheet.
Another object of the present invention is to provide the image forming apparatus, wherein the control portion controls to pass the sheet transported at the time of the image adjustment through the reversing transport path twice in a state where the transfer sheet transport path is separated from the image carrier, and to transfer the toner image on the same surface as that of the sheet color has been detected.
Another object of the present invention is to provide an image forming apparatus including an image carrier on which a toner image depending on input image data is formed, a transfer sheet carrier for forming a transfer sheet transport path and transferring the toner image formed on the image carrier onto a sheet being transported, a color sensor disposed in a vicinity of the transfer sheet transport path, a control portion for controlling an image forming operation, and a function which performs an image adjustment using a reference toner image prior to a start of printing when a color print mode is selected, wherein the control portion controls at the time of the image adjustment, to form the reference toner image on the sheet transported to the transfer sheet transport path, to detect a color of the sheet and the reference toner image by the color sensor, and to adjust developing conditions based on the detected color of the sheet and color information of the reference toner image.
Another object of the present invention is to provide the image forming apparatus, wherein the control portion controls to discharge the sheet on which the reference toner image has been formed at the time of the image adjustment into a sheet discharge tray different from a sheet discharge tray generally used in printing.
Another object of the present invention is to provide the image forming apparatus, wherein the image adjustment is carried out at the time of the first sheet feeding after a sheet cassette has been changed.
Another object of the present invention is to provide the image forming apparatus, wherein the image adjustment is carried out at the time of the first sheet feeding after a sheet supplying has been performed.
Another object of the present invention is to provide the image forming apparatus, wherein when a sheet is fed from a specific sheet tray, the image adjustment is carried out for each sheet feeding.
Another object of the present invention is to provide the image forming apparatus further including an operation input portion and a storage device for storing a variety of information such as color correction information based on sheet color information detected by the color sensor, wherein when sheet type information indicating a relationship between a sheet feed source of a sheet and a type of the sheet is inputted from the operation input portion, the sheet type information is stored in the storage device, and the control portion carries out the image adjustment based on the sheet type information and the color correction information which are stored in the storage portion.
The platen 111 is the glass plate on which originals for forming images are placed and is disposed on the upper side of a main body of the digital color copying machine. The reversing automatic document feeder (RADF) 112 transports documents to a predetermined position on the platen 111. The reversing automatic document feeder 112 is installed to be opened and shut like a cover for the platen 111 so as to come to the predetermined position facing the upper side of the platen 111.
The reversing automatic document feeder 112 transports a document first so that one side of the document faces the image reading portion 110 at a predetermined position of the platen 111, and after reading the image on this side is finished, the document is transported such that the other side faces the image reading portion 110 at a predetermined position of the platen 111. That is, the reversing automatic document feeder 112 transports the document so that an image or images on only one side or both sides of the document can be read, and after image reading for one document is completed, the document is discharged and the operation of reading and transporting is carried out on the following document. The transportation and the reversing operations are controlled according to an overall operation of the digital color copying machine.
The image reading portion 110 is disposed below the platen 111 to read an image in a document placed on the platen 111. The document is transported onto the platen 111 by the reversing automatic document feeder 112 or directly placed on the platen 111. The image reading portion 110 includes a document scanning body which moves to and fro in parallel along a lower side of the platen 111, an optical lens 116, and a CCD line sensor 17.
The document scanning body 115 is composed of a first scanning unit 113 and a second scanning unit 114. The first scanning unit 113 is provided with an exposure lamp for exposing the surface of an image in a document, and a first mirror M1 for changing the course of a reflection image from the document in a predetermined direction. The first scanning unit 113 moves to and fro in parallel at a predetermined scanning speed with a fixed distance maintained from the lower surface of the platen 111. The second scanning unit 114 is provided with a second mirror M2 and a third mirror M3 for further changing the course of the reflection image from the document, that has been deflected by the first mirror M1 of the first scanning unit 113, in a predetermined direction (the direction in which the optical lens 116 is disposed). The second scanning unit 114 moves to and fro in parallel with a fixed speed relative to the first scanning unit 113.
The optical lens 116 reduces the reflection image from the document, that has been deflected by the third mirror M3 of the second scanning unit 114, and causes the reduced image to be formed on a light receiving surface on the COD line sensor 117. The CCD line sensor 117, which is an optical transducer, performs optical conversion to the light image formed by the optical lens 116 one after another to output electric signals The CCD line sensor 117 is preferably a so-called three-line color CCD which can read a monochrome image or a color image and output line data decomposed into each color component of R (red), G (green) and B (blue). The original image information converted into electric signals by the CCD line sensor 117 is further transferred to an image processing portion 41 shown in
The sheet feed portion 210 is composed of a sheet tray 211, a sheet feed roller 212, a resist roller 213 and the like, and separates sheets (recording mediums) P which are stacked and stored in the sheet tray 211 one by one and supplies them to the image forming portion 220. The sheets P which have been separated and supplied one by one are transported to the image forming portion 220 with a timing being controlled by a pair of resist rollers 213 disposed between the sheet tray 211 and the image forming portion 220. In a so-called double-sided image formation mode in which images are formed on both sides of the sheet P, the sheet P is firstly transported to the image forming portion 220 and an image is formed on one side of the sheet P, subsequently the sheet P is reversed and transported again to the image forming portion 220, followed by forming an image on the other side.
In the above digital color copying machine, a cut sheet is used as the sheet P. When the sheet P is sent from the sheet tray 211 and supplied to a guide portion of a sheet feeding transport path of the sheet feed portion 210, the end of the sheet P is detected by a sensor (not shown). Then, based on a detection signal outputted from the sensor, the sheet P is temporarily stopped by the pair of resist rollers 213, and transported to the image forming portion 220 depending on a timing of the image formation. Note that, the sheet feeding can be also performed from a manual tray 214.
The image forming portion 220 forms an image on the sheet P based on the image information of the document to which the image data processing is performed by the image processing portion 41 (refer to
The transfer sheet transport belt mechanism 221 is provided with a drive roller 231, a driven roller 232, and a transfer sheet transport belt (transfer sheet carrier) 230 which is tensioned between the drive roller 231 and the driven roller 232 so as to extend almost in parallel. The transfer sheet transport belt 230 is frictionally driven in the direction indicated by an arrow Z according to the rotation of the drive roller 231. The sheet P fed through the sheet feed portion 210 is sent onto the transfer sheet transport belt 230 at the timing of forming images, and transported to the image forming station 228 in a state of being held by the transfer sheet transport belt 230 by electrostatic absorbing.
The image forming station 228 reproduces a toner image corresponding to image information of a document on the sheet P. The image forming station 228 is composed of a first image forming station 228a corresponding to a black component, a second image forming station 228b corresponding to a cyan component, a third image forming station 228c corresponding to a magenta component, and a fourth image forming station 228d corresponding to a yellow component. Each of the image forming stations 228a to 228d is disposed above the transfer sheet transport belt 230 so as to be close to the transfer sheet transport belt 230 in order from the upstream side of the sheet transport path.
The image forming stations 228a to 228 are substantially identical to one another in construction, hand respectively include photoreceptor drums 222a to 222d each of which is rotatively driven in the direction indicated by an arrow F. Around each of the photoreceptor drums 222a to 222d, charging devices 223a to 223d for electrifying each of the photoreceptor drums uniformly, developing devices 224a to 224d for developing electrostatic latent images respectively formed on the photoreceptor drums, transfer rollers 225a to 225d which function as transfer electrodes for transferring toner images, which have been developed on the photoreceptor drums, onto the sheets P, and cleaning devices 226a to 226d for removing the remaining toner on the photoreceptor drums, are disposed in this order along a rotating direction of the photoreceptor drums.
The laser writing unit 227 writes electrostatic latent images on the photoreceptor drum 222 based on image information. The laser writing unit 227 is composed of a first laser writing unit 227a corresponding to a black component, a second laser writing unit 227b corresponding to a cyan component, a third laser writing unit 227c corresponding to a magenta component, and a fourth laser writing unit 227d corresponding to a yellow component.
The laser writing units 227a to 227d are provided above each of the photoreceptor drums 222a to 222d, and are substantially identical to one another in construction. Each of the laser writing units 227a to 227d is composed of semiconductor laser elements (not shown) for emitting dot light modulated according to image data, polygon mirrors (deflecting devices) 240a to 240d for changing a direction of a laser beam from the semiconductor laser element in a main scanning direction, fθ lenses 241a to 241d, mirrors 242a to 242d, and mirrors 243a to 243d for forming an image of a laser beam, which is deflected by the polygon mirrors 240a to 240d, on the surfaces of the photoreceptor drums 222a to 222d, and the like.
A pixel signal corresponding to a black component image of a color document image is inputted to the laser writing unit 227a, a pixel signal corresponding to a cyan component image of a color document image is inputted to the laser writing unit 227b, a pixel signal corresponding to a magenta component image of a color document image is inputted to the laser writing unit 227c, and a pixel signal corresponding to a yellow component image of a color document image is inputted to the laser writing unit 227d. Each of the laser writing units 227a to 227d emits a laser beam corresponding to an inputted pixel signal, and forms an image of the laser beam on the surfaces of the photoreceptor drums 222a to 222d. Then, the laser beam is scanned and exposed so that optical writing on the photoreceptor drums 222a to 222d is performed.
Thus, electrostatic latent images corresponding to image information of a document subjected to the color conversion are formed on each of the photoreceptor drums 222a to 222d. Moreover, the developing device 224a stores black toner, the developing device 224b stores cyan toner, the developing device 224c stores magenta toner, and the developing device 224d stores yellow toner, respectively, and the electrostatic latent images on the photoreceptor drums 222a to 222d are developed by the toners of each color. Thereby, the image information of the document subjected to the color conversion in the image forming portion 220 is reproduced as toner images of each color.
The sheet P is transported to each of the image forming stations 228a to 228d in order by the transfer sheet transport belt 230, and toner images developed on the photoreceptor drums 222a to 222d are transferred to the sheet P. That is, the toner images of each color are formed in each of the image forming stations 228a to 228d, and are superimposed one after another on the sheet P which is electrostatically absorbed and transported on the transfer sheet transport belt 230. When the image transfer by all of the image forming stations 228a to 228d is completed, the sheet P is released off the transfer sheet transport belt 230 and transported to the fixing device 229.
The fixing device 229 fixes a toner image transferred and formed on the sheet P onto the sheet P. The fixing device 229 is disposed in a downstream side of the transfer sheet transport belt mechanism 221 in the sheet transport path, and is provided with a pair of fixing rollers made of a heat roller 229a and a pressure roller 229b, a release member and the like. The sheet P is transported through a nip portion between the fixing rollers so that the toner image is formed on the sheet P, and released off the fixing rollers by the release member to be transported to a sheet discharge portion 240.
The sheet discharge portion 240 discharges the sheet P on which image formation is completed to outside of the digital color copying machine. The sheet discharge portion 240 is provided with a transport direction switching gate 241, a discharge roller 242, and a sheet discharge tray 243. In a one-side image formation mode, as described above, an image is formed on one side of the sheet P, and thereafter, the sheet P transported from the fixing device 229 is transported through the transport direction switching gate 241 and ejected by the discharge roller 242 on the sheet discharge tray 243, which is mounted on an outer wall of the digital color copying machine.
The transport direction switching gate 241 switches a transport path of the sheet P on which the toner image has been fixed, and selectively switches a track for discharging the sheet P to the sheet discharge tray 243 and a sheet re-feeding transport track for feeding the sheet P again to the image forming portion 220. In a double sided image formation mode, an image is formed on one side of the sheet P as described above, and thereafter a transport direction of the sheet P is switched by the transport direction switching gate 241 so that the sheet P can be transported to the image forming portion 220 again, and the sheet P is reversed by a switchback transport path 250, to be supplied again to the image forming portion 220 through a sheet re-feeding transport path 260 which forms the sheet re-feeding transport route.
Here, in the above description, the laser writing unit 227 (227a to 227d) scans a laser beam for exposure so as to perform an optical writing on the photoreceptor drum 222 (222a to 222d). However, in the present apparatus, as a means for performing optical writing on the photoreceptor drum 222 (222a to 222d), a solid-state scanning writing optical system (LED head) which includes a light emitting diode array, an image-forming lens array and the like is also applicable, instead of the laser writing unit 227 (227a to 227d). The LED is smaller than the laser writing unit in size, and has no movable part which causes sound. Therefore, the LED head can be preferably used in an image forming apparatus such as a tandem system digital color copying machine, which requires a plurality of optical writing units.
A color sensor 15, which is a feature of the present invention, for detecting both of a reference toner image formed on the transfer transport belt 230 and a color of a sheet to be transported with one sensor is disposed above the transfer sheet transport path in front of the fixing device 229 in the present embodiment.
The image data input portion 40 includes a three-line color CCD 40a capable of reading a monochrome document or a color document image and outputting line data decomposed into RGB color components, a shading correction circuit 40b for correcting a line image level of line data which is read in the color CCD 40a, a line adjusting portion 40c such as a line buffer for correcting a shift of image line data which is read in the three-line color CCD 40a, a sensor color correction portion 40d for correcting color data of line data of each color that is outputted from the three-line color CCD 40a, an MTF correction portion 40e for making correction to emphasize a change in a signal of each pixel, a γ correction portion 40f for making visibility correction by correcting contrast of an image.
The image processing portion 41 includes a monochrome data generating portion 41a (monochrome document) for generating monochrome data from an RGB signal which is a color image signal inputted from the image data input portion 40, an input processing portion 41b for converting an RGB signal into a YMC signal corresponding to each storage portion in a storage device and performing a clock converting operation, an area segmentation portion 41c for classifying input image data into characters, a halftone picture, and a photographic-picture, a black generating portion 41d for removing a base color in response to a YMC signal outputted from the input processing portion 41b so as to generate a black color, a color correction circuit 41e for adjusting each color of a color image signal based on each color conversion table, a zoom processing circuit 41f for zooming in and out image information which is inputted based on a set magnification, a spatial filter 41g, a halftone processing portion 41h for displaying gradation such as multilevel error dispersion and multilevel dither, and the like.
Image data of each color that is subjected to halftone processing is temporarily stored in an image data storage portion 42. A hard disc device 42a in the image data storage portion 42 includes four hard disks (rotatable memory mediums), which successively receive image data of 8 bits and 4 colors (32 bits) outputted from the image processing portion 41, convert 32-bit data into 8-bit image data of four colors while temporarily storing the data in the buffer, and store and control the image data for each color. Moreover, since each of the image forming stations is disposed at different positions, an RAM 42b as a delay buffer memory is caused to temporarily store image data of each color so as to transmit the image data to each of the laser scanner units at different timings, causing no displacement of color. The image data storage portion 42 further includes an image synthesizing memory for synthesizing a plurality of images, and the like.
The image data output portion 43 includes a laser control unit 43a for carrying out pulse width modulation based on image data of each color from the halftone processing portion 41h, and laser scanner units of each color 43b, 43c, 43d, and 43e for performing laser recording based on a pulse width modulated signal corresponding to an image signal of each color that is outputted from the laser control unit 43a.
The central processing unit (CPU) 44 controls the image data input portion 40, the image processing portion 41, the image data storage portion 42, the image data output portion 43, the image editing portion 45 (described later), and the external interface portions 46 and 47, based on a predetermined sequence. The image editing portion 45 performs a predetermined image edit on image data, which has been transmitted through the image data input portion 40, the image processing portion 41, or the interfaces (described later) and has been temporarily stored in the image data storage portion 42, and the edit of the image data is carried out by using an image synthesizing memory of the image data storage portion 42.
The interface 46 is communication interface means for receiving image data from an external image input processing apparatus (a communication portable terminal, a digital camera, a digital video camera and the like) which is provided in addition to the color digital copying machine. Note that, image data, which has been inputted from the interface 46, is also temporarily inputted to the image processing portion 41 for color space correction and the like, and the data level of the image data is converted to a data level applicable to the image editing portion 45 in the color digital copying machine, and then, the image data is stored and controlled in the hard disc device 42a.
The interface 47 is a printer interface for inputting image data generated by a personal computer, or a monochrome or color FAX interface for receiving image data from a FAX machine. Image data inputted from the interface 47 which is already composed of a CMYK signal, is temporarily subjected to the halftone processing portion 41h, and stored and controlled in the four hard disks of the hard disc device 42a in the image data storage portion 42.
The control portion shown in
Operation performed by the control portion (CPU) 10 based on a control program stored in the ROM 11 in an image forming apparatus in the first embodiment of the present invention will hereinafter be described.
When a document is set on a color copying apparatus and a user executes a print job with a color print mode in the input operating portion 21, then firstly, prior to printing, a reference toner image is formed on the transfer sheet transport belt 230 through the photoreceptor drum 222 and the reference toner image is detected by the color sensor 15, so that adjustment of developing conditions is carried out based on color information of the reference toner image. The reference toner image formed on the transfer sheet transport belt 230 passes below the color sensor 15, and thereafter cleaned by cleaning means (not shown).
Now, referring to
The transfer rollers 225a to 225d are movable up and down by a contact/separation mechanism (not shown) and the transfer sheet transport belt 230 contacts with and separates from the photoreceptor drum 222 (222a to 222d) by moving the transfer rollers 225a to 225d up and down with a separation driving mechanism (not shown).
In the present embodiment, since the transfer sheet transport belt 230 separates from the photoreceptor drum 222 at the time of detecting a sheet color, the sheet P is not soiled.
When a reversing transport path is used, although an image is to be formed on the side different from the side which a sheet color has been detected, this method is applicable when both sides of a sheet have a same sheet color, and the present invention can be carried out using an existing reversing sheet transport path.
In
Next, the operation in the above-mentioned embodiment will be described using a flowchart.
In
Here, image processing of the present invention, which is carried out depending on the detected sheet color, will be described below. For example, when color component values of a sheet color, for example, a Y component value of α, an M component value of β, and a C component value of γ are detected by the color sensor, the image processing can be carried out so that the values of α, β, and γ are reduced from image data YMC values recorded in an image memory, respectively.
Specifically, for example, a following corresponding relation is satisfied between a value of yellow (X1) in print data and a value of a yellow component (X2) when the sheet color is detected by the color sensor; {X1=f(X2)}, where f denotes a function. For example, there is a following relation; X1=α·X2. In the relation of “X1=α·X2”, when a value in detecting the sheet color (yellow component) is X2, “α·X2” is subtracted from the print data (yellow) to thereby reduce the yellow component of the sheet color from the print data, so that correction can be performed.
After going back to the flowchart shown in
These are basic processing and may be carried out in the case of sheet feeding from a specific tray. For example, the processing may be carried out in the case of sheet feeding from a manual tray 214. Since various kinds of sheets are placed on the manual tray 214, the processing is always carried out at the time of sheet feeding so that color correction can be performed properly.
The present embodiment is suitable for a case where a type of sheets in the sheet tray is uniform and there is no need of detecting a sheet color for each sheet feeding.
Steps S1 to S9 are the same processing as that in the flowchart shown in
In the flowcharts, the image formation for the first sheet is performed at steps before step S9, subsequent image formation is performed at steps after step S9, and in image forming processing after step S9, the image processing is performed based on the sheet color of the first sheet.
At step S10, when it is detected that there is some sheets in the sheet tray 211 (step S10/Yes), the same processing as that of steps S2, S4, and S7 to S10 is performed (steps S11 to S16), and when it is detected that there is some sheets in the sheet tray 211 at step S16 (step S16/Yes), the processing goes back to step S11.
When there is no sheet, the processing proceeds to step S17 and waits until sheet supply is achieved. When sheet supply is achieved (step S17/Yes), the processing goes back to first step S1 and a sheet color is detected. Thus, the image processing can be performed appropriately even if the color of the supplied sheet is different from that of the previous sheet.
In the above description, although the processing is performed at the time of sheet supply, the same processing can be also performed in the case where sheet feeding is conducted from a different sheet tray by switching to the different sheet tray when there is no sheet.
Note that, when a non-reversing transport path is used, step S6 shown in
Steps S31 to S34 are the same as steps S1 to S4 shown in
Now, a fifth embodiment of the present invention will be described referring to
Next, an embodiment that a relation between a sheet feed source (sheet feed tray) and a type of a sheet is inputted from an operation panel so that image adjustment can be performed effectively, will be described.
On the input operating portion 21 (refer to
Information showing types of sheets is stored in the sheet type information, for example, a name of a sheet such as “a recycled sheet” and “a color sheet Y” is stored.
Further, color correction information related to sheet type information is stored separately in the memory 12 so that same color correction is performed when the sheet type is set. For example, as a sheet type, color correction information of “α·X2” is recorded in association with “a recycled sheet”. A value obtained by actually measuring a recycled sheet by the color sensor 15 is recorded and stored for X2.
By setting in this way, for example, when a user sets sheet type information of “a recycled sheet” for the manual tray and the manual tray is specified as a sheet feed source, an image forming apparatus reads color correction information corresponding to “a recycled sheet” and adopts it as a correction value. With such a structure, once a correction value is measured, color correction information thereof can be used thereafter, and color correction can be performed appropriately in printing from any sheet feed source.
According to the present invention, a color sensor for detecting a reference toner image on a transfer sheet carrier is also capable of detecting a sheet color and there is no need of disposing another color sensor for detecting the sheet color in a sheet transport path, and therefore, it is possible to prevent the number of components from being increased and reduce a size of an apparatus.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-184788 | Jul 2007 | JP | national |
