Image forming apparatus

Abstract

To provide an image forming apparatus that prevents a reduction in the accuracy of correcting geometrical characteristics of images on the front and back surfaces during double-sided printing.SOLUTION: An image forming apparatus comprises: image forming units 304-307 that form images; an intermediate transfer belt 308; and primary transfer units 341Y, 341M, 341C, 341K that transfer the images from the image forming units 304-307 to the intermediate transfer belt 308. The image forming apparatus forms images on a sheet in one of a YMCK fixing and printing mode where it forms color images and a K fixing and printing mode where it forms monochrome images. The image forming apparatus, in performing double-sided printing of monochrome images, selects the YMCK fixing and printing mode when performing correction of an image forming condition and selects the K fixing and printing mode when not performing correction of the image forming condition, before forming images on the sheet.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus such as a printer, a copier, a facsimile, or a multifunction peripheral. [Background technology]

[0002] Printed materials produced by commercial printing machines require stable print position accuracy on the front and back sides of paper during double-sided printing. Patent Document 1 discloses an image forming device that aims to stabilize print position accuracy. In order to stabilize the print position accuracy, this image forming device creates an adjustment chart by printing an adjustment image that serves as a print position marker on paper. The adjustment chart is read by an image reading sensor provided on the paper transport path. The image forming device feeds back the reading result of the adjustment image to the image formation conditions to adjust the print position, image geometric characteristics such as the image inclination, etc.

[0003] There is a tandem type of image forming apparatus that prints full-color images. In a tandem type image forming apparatus, multiple photoconductors are arranged in relation to a transfer body, and toner images are transferred from each photoconductor in sequence to the transfer body in multiple layers. For example, four photoconductors are provided corresponding to the four colors of yellow, magenta, cyan, and black. A full-color toner image is formed on the transfer body by multiplexing the toner images of yellow, magenta, cyan, and black in sequence from the four photoconductors. The toner images of each color are transferred from the transfer body to the paper at once. The toner images are fixed by a fixing device, and the full-color image is printed on the paper. Yellow, magenta, cyan, and black may be referred to as Y, M, C, and K below.

[0004] In a tandem type image forming apparatus, a separation mechanism is provided for separating / contacting the Y, M, and C photoconductors and the transfer body. When printing a monochrome image, the Y, M, and C photoconductors and the transfer body that are not required for printing a monochrome image are separated, and the driving of the Y, M, and C photoconductors is stopped. The print mode for printing a monochrome image is called the "K-print mode". When printing a color image, all of the Y, M, C, and K photoconductors and the transfer body are in contact. The print mode for printing a color image is called the "YMCK-print mode". The image forming apparatus disclosed in Patent Document 2 is provided with such a separation mechanism, and by printing in the K-print mode as necessary when printing a monochrome image, the progress of deterioration over time of the Y, M, and C photoconductors is suppressed, and running costs are reduced. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2006-11285 A [Patent Document 2] Japanese Patent Application Publication No. 11-167238 Summary of the Invention [Problem to be solved by the invention]

[0006] Specifically, the separation mechanism described in Patent Document 2 controls the separation between the photoconductor and the intermediate transfer body by moving a transfer unit that transfers a toner image from the photoconductor to the intermediate transfer body. The transfer units are disposed opposite the photoconductor with the intermediate transfer body sandwiched between them, and are provided corresponding to a plurality of photoconductors. The K photoconductor and the intermediate transfer body are always in contact with each other regardless of the color being printed. Therefore, the separation mechanism does not control the K transfer unit corresponding to the K photoconductor.

[0007] Each of the Y, M, and C transfer units, except for the K transfer unit, moves toward the photoconductor when the photoconductor and intermediate transfer unit are brought into contact with each other, and moves in a direction away from the photoconductor when the photoconductor and intermediate transfer unit are separated from each other. When printing a color image, the Y, M, and C transfer units corresponding to the Y, M, and C photoconductors move toward the photoconductor to bring the intermediate transfer unit into contact with the Y, M, and C photoconductors. This state is called the "YMCK contact state." When printing a monochrome image, the Y, M, and C transfer units corresponding to the Y, M, and C photoconductors do not move toward the photoconductor, and the intermediate transfer unit is separated from the Y, M, and C photoconductors. As a result, only the K photoconductor is brought into contact with the intermediate transfer unit. This state is called the "K contact state."

[0008] A case will be described in which an image forming apparatus includes a drum-shaped photosensitive drum as a photosensitive body, an endless belt-like intermediate transfer belt as a transfer body, and transfer rollers as a transfer unit. The number of transfer rollers that contact the intermediate transfer belt is different between the YMCK and K transfer states. Therefore, the tension acting on the intermediate transfer belt by the transfer rollers is different between the YMCK and K transfer states. Such a change in tension causes the time it takes for the toner image formed on each photosensitive drum to reach the transfer position onto the paper to differ between the YMSK and K transfer states. Specifically, the time is slower in the K transfer state than in the YMCK transfer state. Therefore, when the same image is printed, the distance from the leading edge of the paper in the paper transport direction to the image is longer when printed in the K transfer state than when printed in the YMCK transfer state.

[0009] For this reason, the positions of the adjustment images when correcting the image formation conditions are not the same between the YMCK and K printing states, and the correction values ​​are different. For example, the correction values ​​when correcting geometric characteristics such as the image print position as an image formation condition are different between the YMCK and K printing states. In this case, when a monochrome image is printed on both sides using the correction values ​​of the geometric characteristics generated in the YMCK printing state, the correction accuracy of the geometric characteristics of each image on the front and back sides is lower than when a color image is printed on both sides.

[0010] The present invention has been made in consideration of the above problems, and has an object to provide an image forming apparatus that suppresses a decrease in the accuracy of correction of the geometric characteristics of images on the front and back sides during double-sided printing. [Means for solving the problem]

[0011] The image forming apparatus of the present invention includes a first image forming means for forming a first chromatic image based on image forming conditions, a second image forming means for forming a second achromatic image based on the image forming conditions, an intermediate transfer body, a first transfer means for transferring the first image from the first image forming means to the intermediate transfer body, a second transfer means for transferring the second image from the second image forming means to the intermediate transfer body, a secondary transfer means for transferring an image from the intermediate transfer body to a sheet of paper, a fixing means for fixing the image transferred to the sheet of paper to the sheet of paper, and a fixing means for fixing the first image transferred to the intermediate transfer body by the first transfer means. and a control means for forming an image on the paper in either a first print mode in which the first transfer means transfers the first image to the intermediate transfer body and the second transfer means transfers the second image to the intermediate transfer body, or a second print mode in which the first transfer means does not transfer the first image to the intermediate transfer body and the second transfer means transfers the second image to the intermediate transfer body, wherein the control means, when performing double-sided printing of a monochrome image, forms an image on the paper by selecting the first print mode if the image formation conditions are to be corrected, and by selecting the second print mode if the image formation conditions are not to be corrected. Effect of the Invention

[0012] According to the present invention, it is possible to suppress a decrease in the accuracy of correction of the geometric characteristics of images on the front and back sides during double-sided printing. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing the configuration of an image processing system. [Diagram 2] system configuration diagram. [Diagram 3] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Figure 4] 4A and 4B are explanatory diagrams showing a contact state between an image forming unit and an intermediate transfer belt. [Diagram 5] Diagram of CIS. [Figure 6] 4A to 4D are explanatory diagrams of setting screens for registering paper. [Figure 7] 11 is a flowchart showing a process for acquiring a front and back position correction value. [Figure 8] FIG. 13 is a diagram showing an example of an adjustment image. [Figure 9] 5A and 5B are diagrams illustrating a method for calculating a front / back position correction value. [Figure 10] FIG. 11 is a diagram illustrating registration information of a paper. [Figure 11] 4 is a flowchart showing a printing process including a print mode selection process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0015] (Image Processing System) 1 is a configuration diagram of an image processing system including an image forming apparatus according to this embodiment. The image processing system includes an image forming apparatus 101 and an external controller 102. The image forming apparatus 101 is, for example, a multifunction peripheral (MFP), etc. The external controller 102 is, for example, an image processing controller, a digital front end (DFE), a print server, etc.

[0016] The image forming apparatus 101 and the external controller 102 are communicatively connected via an internal LAN (Local Area Network) 105 and a video cable 106. The external controller 102 is connected to a client PC (Personal Computer) 103 via an external LAN 104. The external controller 102 obtains a print instruction (print job) from the client PC 103.

[0017] A printer driver having a function of converting image data into a print description language that can be processed by the external controller 102 is installed in the client PC 103. A user can instruct printing via the printer driver using various applications. The printer driver transmits a print job including image data to the external controller 102 based on an instruction from the user. The external controller 102 accepts a print job including image data from the client PC 103, performs data analysis and rasterization processing, and instructs the image forming apparatus 101 to print (form an image) based on the image data.

[0018] The image forming apparatus 101 is configured by connecting a plurality of devices having different functions including a printing device 107, and is capable of complex printing processes such as bookbinding. The image forming apparatus 101 of this embodiment includes a printing device 107 and a finisher 109. The printing device 107 forms an image on paper fed from a paper feed unit provided at the bottom of the main body by using a developer (e.g., toner). The printing device 107 forms images in yellow (Y), magenta (M), cyan (C), and black (K). On the paper, a full-color image in which images of each color are superimposed, or a monochrome image using black (K) can be formed. The paper on which the image has been formed is transported from the printing device 107 to the finisher 109. The finisher 109 stacks the paper on which the image has been formed.

[0019] In this image processing system, an external controller 102 is connected to an image forming apparatus 101, but the external controller 102 is not necessarily required. For example, the image forming apparatus 101 may be configured to directly obtain a print job including image data from a client PC 103 via an external LAN 104. In this case, the image forming apparatus 101 performs the data analysis and rasterization processing performed by the external controller 102. In other words, the image forming apparatus 101 and the external controller 102 are configured as an integrated unit.

[0020] (System Configuration) 2 is a system configuration diagram for controlling the operation of the image processing system. Here, controllers for controlling the operation of the image forming apparatus 101, the external controller 102, and the client PC 103 will be described.

[0021] ·Printing device The printing device 107 includes a communication interface (I / F) 217, a LAN I / F 218, and a video I / F 220 for communicating with other devices. The printing device 107 includes a CPU (Central Processing Unit) 222, a memory 223, a storage 221, an image reading unit 231, and an image processing unit 232 for controlling the operation of the printing device 107. The printing device 107 includes an exposure unit 227, an image creating unit 228, a fixing unit 229, and a paper feeding unit 230 for forming an image. The printing device 107 includes an operation unit 224 and a display 225 as user interfaces. These components are connected to each other via a system bus 233 so as to be able to communicate with each other.

[0022] The communication I / F 217 is connected to the finisher 109 via a communication cable 249 and controls communication with the finisher 109. When the printing device 107 and the finisher 109 work together, information and data are sent and received via the communication I / F 217. The LAN I / F 218 is connected to the external controller 102 via the internal LAN 105 and controls communication with the external controller 102. The printing device 107 receives print settings from the external controller 102 via the LAN I / F 218. The video I / F 220 is connected to the external controller 102 via a video cable 106 and controls communication with the external controller 102. The printing device 107 receives image data representing an image to be formed from the external controller 102 via the video I / F 220.

[0023] The CPU 222 comprehensively controls image processing and printing by executing computer programs stored in the storage 221. The memory 223 provides a work area for the CPU 222 to execute various processes. When performing image formation processing, the CPU 222 controls an exposure unit 227, an image forming unit 228, a fixing unit 229, and a paper feed unit 230.

[0024] The exposure unit 227 includes a photoconductor, a charging wire for charging the photoconductor, and a light source for exposing the photoconductor charged by the charging wire to light in order to form an electrostatic latent image on the photoconductor. The photoconductor is, for example, a photosensitive belt having a photosensitive layer formed on the surface of a belt-shaped elastic member, or a photosensitive drum having a photosensitive layer formed on the surface of a cylinder. A charging roller may be used instead of the charging wire. The exposure unit 227 charges the surface of the photoconductor to a uniform negative potential by the charging wire. The exposure unit 227 outputs a laser beam based on image data from a light source. The laser beam scans the surface of the photoconductor that is uniformly charged. As a result, the potential of the photoconductor at the position where the laser beam is irradiated fluctuates, and an electrostatic latent image is formed on the surface. Four photoconductors are provided corresponding to four colors, namely, yellow (Y), magenta (M), cyan (C), and black (K). Electrostatic latent images corresponding to images of different colors are formed on the four photoconductors.

[0025] The image creating unit 228 transfers the toner image formed on the photoconductor onto paper. The image creating unit 228 includes a developing unit, a transfer unit, a toner supply unit, and the like. The developing unit forms a toner image by attaching negatively charged toner from a developing cylinder to an electrostatic latent image formed on the surface of the photoconductor. Four developing units are provided corresponding to the four colors of yellow (Y), magenta (M), cyan (C), and black (K). The developing units make the electrostatic latent image on the photoconductor visible using toner of the corresponding color.

[0026] The transfer unit has an intermediate transfer belt, which is an intermediate transfer body, and transfers a toner image from the photoconductor to the intermediate transfer belt. A primary transfer roller is provided at a position facing the photoconductor across the intermediate transfer belt. A positive potential is applied to the primary transfer roller, so that the toner images are transferred from each of the four photoconductors in sequence, superimposed on the intermediate transfer belt. As a result, a full-color toner image is formed on the intermediate transfer belt. The toner image formed on the intermediate transfer belt is transferred to paper by a secondary transfer roller, which will be described later. A positive potential is applied to the secondary transfer roller, so that the full-color toner image is transferred from the intermediate transfer belt to paper.

[0027] The fixing unit 229 fixes the transferred toner image onto the paper. The fixing unit 229 has a heater and a pair of rollers. The fixing unit 229 melts and fixes the toner image onto the paper by heating and pressurizing the toner image on the paper using the heater and the pair of rollers. This produces a printed matter with an image formed on the paper. The paper feed unit 230 has a transport roller and various sensors on the transport path, and controls the paper feed operation.

[0028] The image reading unit 231 reads an image printed on the transported paper based on an instruction from the CPU 222. For example, when adjusting image formation conditions, the CPU 222 uses the image reading unit 231 to read an adjustment image for correcting the image formation conditions formed on the paper. The operation unit 224 is an input device that accepts input of various settings and operation instructions from a user. The operation unit 224 is, for example, various input keys or a touch panel. The display 225 is an output device that displays setting information of the image forming apparatus 101 and the processing status (status information) of a print job.

[0029] Finisher The finisher 109 performs post-processing on a printed matter output from the printing device 107, for example. The finisher 109 includes a communication I / F 241, a CPU 242, a memory 243, and a paper discharge control unit 244. These components are connected to be able to communicate with each other via a system bus 245. The communication I / F 241 is connected to the printing device 107 via a communication cable 249, and controls communication with the printing device 107. When the finisher 109 and the printing device 107 operate in cooperation with each other, information and data are transmitted and received via the communication I / F 241. The CPU 242 executes a control program stored in the memory 243, and performs various controls required for post-processing. The memory 243 stores the control program. The memory 243 also provides a work area when the CPU 242 executes various processes. The paper discharge control unit 244 performs post-processing on the transported paper and discharges it based on an instruction from the CPU 242.

[0030] External Controller The external controller 102 includes a LAN I / F 213, a LAN I / F 214, and a video I / F 215 for communicating with other devices. The external controller 102 includes a CPU 208, a memory 209, and a storage 210 for controlling the operation of the external controller 102. The external controller 102 includes a keyboard 211 and a display 212 as user interfaces. These components are connected to each other via a system bus 216 so as to be able to communicate with each other.

[0031] The LAN I / F 213 is connected to the client PC 103 via the external LAN 104, and controls communication with the client PC 103. The external controller 102 obtains a print job from the client PC 103 via the LAN I / F 213. The LAN I / F 214 is connected to the printing device 107 via the internal LAN 105, and controls communication with the printing device 107. The external controller 102 transmits print settings to the printing device 107 via the LAN I / F 214. The video I / F 215 is connected to the printing device 107 via the video cable 106, and controls communication with the printing device 107. The external controller 102 transmits image data to the printing device 107 via the video I / F 215.

[0032] The CPU 208 executes computer programs stored in the storage 210 to comprehensively perform processes such as receiving image data transmitted from the client PC 103, RIP processing, and transmitting image data to the image forming apparatus 101. The memory 209 provides a work area for the CPU 208 to execute various processes. The keyboard 211 is an input device that accepts input of various settings and operation instructions from the user. The display 212 is an output device that displays information about applications executed by the external controller 102 as still images or moving images.

[0033] Client PC The client PC 103 includes a CPU 201, a memory 202, a storage 203, a keyboard 204, a display 205, and a LAN I / F 206. These components are connected via a system bus 207 so as to be able to communicate with each other.

[0034] The CPU 201 controls the operation of the client PC 103 by executing a computer program stored in the storage 203. In this embodiment, the CPU 201 creates image data and transmits a print job. The memory 202 provides a work area for the CPU 201 to execute various processes. The keyboard 204 and the display 205 are user interfaces. The keyboard 204 is an input device that accepts instructions from a user. The display 205 is an output device that displays information about an application executed by the client PC 103 as a still image or a moving image. The LAN I / F 206 is connected to the external controller 102 via the external LAN 104 and controls communication with the external controller 102. The client PC 103 transmits a print job including image data to the external controller 102 via the LAN I / F 206.

[0035] The external controller 102 and the image forming apparatus 101 are connected via the internal LAN 105 and the video cable 106, but any configuration is acceptable as long as data necessary for printing can be transmitted and received, and for example, the connection may be made only by the video cable 106. The memory 202, the memory 209, the memory 223, and the memory 243 may each be a storage device for holding data and programs. For example, these memories may be volatile random access memory (RAM), non-volatile read only memory (ROM), storage, universal serial bus (USB) memory, etc.

[0036] (Configuration of Image Forming Apparatus) 3 is a configuration diagram of the image forming apparatus 101. A display 225 is provided on the top of the printing device 107. The display 225 displays information on the printing status and settings of the image forming apparatus 101. Paper (printed material) on which an image has been formed by the printing device 107 is transported to a finisher 109 provided at a subsequent stage.

[0037] The printing device 107 includes a plurality of paper feed decks 301, 302 and a transport path 303 as the paper feed section 230. Each of the paper feed decks 301, 302 can store different types of paper. The top sheet of paper stored in each of the paper feed decks 301, 302 is separated and fed to the transport path 303. The printing device 107 includes image forming sections 304, 305, 306, and 307 for forming images as the exposure section 227. The printing device 107 can form color images. To this end, the image forming section 304 forms an image (toner image) of black (K), which is an achromatic color. The image forming section 305 forms an image (toner image) of cyan (C), which is a chromatic color. The image forming section 306 forms an image (toner image) of magenta (M), which is a chromatic color. The image forming section 307 forms an image (toner image) of yellow (Y), which is a chromatic color.

[0038] The printing device 107 includes, as the image creating unit 228, an intermediate transfer belt 308 and a secondary transfer roller 309 onto which toner images are transferred from the image forming units 304, 305, 306, and 307. The intermediate transfer belt 308 rotates clockwise in the figure, and the toner images are transferred and superimposed on each other in the order of the image forming units 307, 306, 305, and 304. As a result, a full-color toner image is formed on the intermediate transfer belt 308. The intermediate transfer belt 308 conveys the toner image to the secondary transfer roller 309 by rotating. A sheet is conveyed to the secondary transfer roller 309 in accordance with the timing at which the toner image is conveyed to the secondary transfer roller 309. The secondary transfer roller 309 transfers the toner image on the intermediate transfer belt 308 to the conveyed sheet.

[0039] FIG. 4 is an explanatory diagram of the contact state between the image forming units 304, 305, 306, and 307 and the intermediate transfer belt 308. The printing device 107 of this embodiment includes a separation mechanism 345 that controls the contact state between the image forming units 304, 305, 306, and 307 and the intermediate transfer belt 308. The image forming units 304, 305, 306, and 307 include drum-shaped photosensitive drums 340Y, 340M, 340C, and 340K as photosensitive bodies. As described above, the photosensitive drums 340Y, 340M, 340C, and 340K form electrostatic latent images by scanning with laser light. The main scanning direction by the laser light is the drum axial direction of the photosensitive drums 340Y, 340M, 340C, and 340K, and is perpendicular to the conveying direction of the paper. The intermediate transfer belt 308 is an endless belt-shaped transfer body. Primary transfer rollers 341Y, 341M, 341C, and 341K, which are transfer units, are disposed at positions facing the photosensitive drums 340Y, 340M, 340C, and 340K with the intermediate transfer belt 308 interposed therebetween.

[0040] The separation mechanism 345 includes a separation motor 342 serving as a drive source, a separation sensor flag 343 rotated by the drive of the separation motor 342, and a separation home position sensor 344. The driving force output from the separation motor 342 is transmitted to the primary transfer rollers 341Y, 341M, and 341C via a predetermined transmission mechanism. The primary transfer rollers 341Y, 341M, and 341C move toward the photosensitive drums 340Y, 340M, and 340C or are separated from the photosensitive drums 340Y, 340M, and 340C by the transmitted driving force. When the primary transfer rollers 341Y, 341M, and 341C move toward the photosensitive drums 340Y, 340M, and 340C, the photosensitive drums 340Y, 340M, and 340C come into contact with the intermediate transfer belt 308. When the primary transfer rollers 341Y, 341M, and 341C are separated from the photosensitive drums 340Y, 340M, and 340C, the photosensitive drums 340Y, 340M, and 340C are separated from the intermediate transfer belt 308. When the primary transfer rollers 341Y, 341M, and 341C move, the movement amounts of the primary transfer rollers 341Y, 341M, and 341C are measured by a separation sensor flag 343 and a separation home position sensor 344. In this configuration, the primary transfer rollers 341Y, 341M, and 341C are prevented from moving beyond an allowable range.

[0041] FIG. 4(a) shows a state in which all the photosensitive drums 340Y, 340M, 340C, and 340K are in contact with the intermediate transfer belt 308 (YMCK state). In the YMCK state, full-color images can be printed. In the YMCK state, monochrome images can be printed by stopping the operations of the image forming units 305, 306, and 307. FIG. 4(b) shows a state in which only the photosensitive drum 340K is in contact with the intermediate transfer belt 308, and the photosensitive drums 340Y, 340M, and 340C are separated from the intermediate transfer belt 308 (K state). In the K state, monochrome images can be printed. A separation mechanism 345 switches between the YMCK state and the K state.

[0042] The printing device 107 includes a first fixing device 311 and a second fixing device 313 as the fixing unit 229. The first fixing device 311 and the second fixing device 313 have the same configuration and fix the toner image to the paper. To this end, the first fixing device 311 and the second fixing device 313 each include a pressure roller and a heating roller. The paper is heated and pressurized by passing between the pressure roller and the heating roller, and the toner image is melted and pressed. The paper that has passed the second fixing device 313 is transported to a transport path 314. The second fixing device 313 is disposed downstream of the first fixing device 311 in the paper transport direction, and is used to add gloss to the image on the paper that has been fixed by the first fixing device 311 and to ensure fixability. For this reason, the second fixing device 313 may not be used depending on the type of paper and the content of the image forming process. In order to transport the paper that has been subjected to the fixing process by the first fixing device 311 to a transport path 314 without passing through the second fixing device 313, a transport path 312 is provided.

[0043] After the conveying path 314 and the conveying path 312 join, a conveying path 315 and a reversing path 316 are provided. When double-sided printing is instructed, the paper is conveyed to the reversing path 316. The conveying direction of the paper conveyed to the reversing path 316 is reversed by the reversing path 316, and the paper is conveyed to a double-sided conveying path 317. The reversing path 316 and the double-sided conveying path 317 reverse the side on which the image is to be formed (first side). The paper is conveyed to the conveying path 303 by the double-sided conveying path 317, and passes through a secondary transfer roller 309 and a fixing unit 229, whereby an image is formed on a second side different from the first side on which the image was formed.

[0044] In the case of single-sided printing, or in the case of double-sided printing in which images are formed on both sides, the paper is transported to a transport path 315. A transport path 323 is arranged downstream of the transport path 315 in the transport direction of the paper. On the transport path 323, CISs (Contact Image Sensors) 321 and 322 are arranged facing each other across the transport path 323 as the image reading unit 231. FIG. 5 is an explanatory diagram of the CISs 321 and 322. The CIS 321 is an optical sensor that reads an image on the upper surface of the paper transported on the transport path 323. The CIS 322 is an optical sensor that reads an image on the lower surface of the paper transported on the transport path 323.

[0045] The CIS 321 includes an LED (Light Emitting Diode) 350 as a light source, a reading sensor 351 as a light receiving unit, and a white reference plate 352. The LED 350 irradiates light onto the upper surface of the paper when the paper conveyed along the conveying path 323 reaches the reading position. The reading sensor 351 includes a plurality of light receiving elements (photoelectric conversion elements) in a direction perpendicular to the conveying direction of the paper. Therefore, the direction perpendicular to the conveying direction of the paper is the main scanning direction of the CIS 321. The reading sensor 351 receives light reflected by the paper. The plurality of light receiving elements of the reading sensor 351 output an output value (electrical signal) based on the intensity of the reflected light received. The output value (electrical signal) output from the plurality of light receiving elements is transmitted to the CPU 222. In this manner, the image formed on the paper is read.

[0046] The white reference plate 352 is a calibration member (reference member) used during shading correction of the CIS 321. During shading correction, the LED 350 and the reading sensor 351 move to a position where the white reference plate 352 can be read. Alternatively, during shading correction, the white reference plate 352 moves to the reading position of the LED 350 and the reading sensor 351. Shading correction of the CIS 321 is performed based on the reading result of the white reference plate 352. Therefore, the CIS 321 cannot read an image formed on a paper sheet during shading correction.

[0047] Similar to CIS 321, CIS 322 includes an LED 353, a reading sensor 354, and a white reference plate 355. CIS 322 operates similarly to CIS 321, and reads an image formed on the lower surface of a sheet of paper when the sheet of paper transported along transport path 323 reaches the reading position. Note that, in addition to CIS 321 and 322, image reading unit 231 can also be realized by a CCD or CMOS sensor.

[0048] The printing device 107 of this embodiment is capable of forming an adjustment image for adjusting image formation conditions on both sides of a sheet of paper. The sheet of paper on which the adjustment image is formed is called an adjustment chart. The printing device 107 prints the adjustment image on a sheet of paper to create an adjustment chart, and reads the adjustment image using CIS321 and CIS322. The results of reading the adjustment chart (read data) by CIS321 and CIS322 are stored in memory 223. The CPU 222 refers to memory 223, analyzes the read data by CIS321 and CIS322, and feeds it back to the image formation conditions to adjust the image formation conditions.

[0049] For example, the printing device 107 changes the geometric characteristics of an image formed on paper between a YMCK printing state and a K printing state. The printing device 107 creates a chart for adjusting the geometric characteristics and detects the geometric characteristics based on the reading results (read data) of the CISs 321 and 322. The CPU 222 performs affine transformation on the image data so that the detected geometric characteristics become ideal geometric characteristics. The printing device 107 forms an image on paper based on the image data converted by the CPU 222, thereby controlling the geometric characteristics of the image formed on the paper. This allows the printing device 107 to suppress the variation in the geometric characteristics of the image.

[0050] The adjustment image formed on the adjustment chart may be an image for detecting image density or an image for detecting color shift, in addition to an image for detecting geometric characteristics. When the adjustment image for detecting image density is formed, the CPU 222 generates image forming conditions for suppressing fluctuations in image density based on the reading result (read data) of the CIS 321 (or CIS 322). The CPU 222 controls the intensity of the light source of the exposure unit 227 based on the image forming conditions, thereby adjusting the image density of the printing device 107 to an ideal image density. Alternatively, the CPU 222 generates a one-dimensional gradation correction table for suppressing fluctuations in image density based on the reading result (read data) of the CIS 321 (or CIS 322). The CPU 222 converts image data based on the gradation correction table. The printing device 107 forms an image on paper based on the image data converted by the CPU 222, thereby adjusting the image density of the printing device 107 to an ideal image density.

[0051] Furthermore, when an adjustment image for detecting color misregistration is formed, the CPU 222 detects the color misregistration based on the reading result (read data) of the CIS 321 (or CIS 322). The CPU 222 corrects the color misregistration by controlling the position of the image formed on the photoconductor by the exposure unit 227 based on the detected color misregistration.

[0052] The adjustment image may be printed as an adjustment chart on a paper sheet different from the user image, or may be printed on the same paper sheet as the user image. When the adjustment image is printed as an adjustment chart, the CPU 222 creates image data in which the adjustment chart is inserted between the user image on the Nth page and the user image on the N+1th page from the image data acquired from the client PC 103 each time the number of printed sheets reaches a predetermined number N. When the adjustment image is formed on the same paper sheet as the user image, it is preferable that the adjustment image is formed in the cutting area of ​​the paper sheet. This is because the adjustment image is removed from the printed matter by performing a cutting process. Here, the user image is an image included in the image data transferred from the client PC 103.

[0053] The adjustment chart is removed so as not to be mixed in with the printed matter corresponding to the print job. For this purpose, the printing apparatus 107 is provided with a flapper 324, a discharge path 326, a transport sensor 327, and a discharge tray 328. The adjustment chart, whose image (adjustment image) has been read by the CIS 321, 322, is transported to the discharge path 326 by the flapper 324. The paper transported to the discharge path 326 is discharged to the discharge tray 328.

[0054] If the paper is not an adjustment chart, the paper is transported from the transport path 323 to the downstream transport path 325 by the flapper 324. The paper transported to the downstream transport path 325 is delivered to the finisher 109. When the printing device 107 receives a notification of the occurrence of a transport jam from the finisher 109, the printing device 107 switches the flapper 324 to the discharge path 326 side, regardless of whether the paper is an adjustment chart or not, and discharges all the paper (residual paper) in the machine to the discharge tray 328. Discharging the residual paper to the discharge tray 328 reduces the burden on the user of clearing the jam.

[0055] The finisher 109 can stack paper sheets delivered from the printing device 107. The finisher 109 includes a transport path 331 and a stack tray 332 for stacking paper sheets. The transport path 331 is provided with transport sensors 333, 334, 335, and 336. Paper sheets transported from the printing device 107 are stacked on the stack tray 332 via the transport path 331. The transport sensors 333, 334, 335, and 336 detect the passage of paper sheets transported along the transport path 331. If the transport sensors 333, 334, 335, and 336 do not detect the leading or trailing edge of the paper sheets in the transport direction even after a predetermined time has elapsed since the start of transport of the paper sheets, the CPU 242 determines that a transport jam (transport abnormality) has occurred in the finisher 109. In this case, the CPU 242 notifies the printing device 107 that a transport jam has occurred.

[0056] (How to generate correction values ​​for front and back print positions) Even if the basis weight is the same, the moisture absorption state and physical properties of each type of paper are different, and therefore each type of paper has different shrinkage characteristics after passing through the fixing unit 229. In order to improve the correction accuracy of the image formation conditions (geometric characteristics), the image forming apparatus 101 needs to generate correction values ​​for the image formation conditions (geometric characteristics) for each type of paper used. In this embodiment, the image forming apparatus 101 generates a correction value for the print position for each type of paper used in order to improve the print position accuracy on the front and back sides.

[0057] 6 is an explanatory diagram of a setting screen for registering paper that can be used for printing. When a user registers paper that can be used for printing, the image forming apparatus 101 can set image formation conditions suitable for the paper. The setting screen is displayed on the display 225 by the CPU 222. The user can register paper from the setting screen using the operation unit 224.

[0058] FIG. 6(a) shows an initial screen. When the user selects a softkey "Application Mode" button 501 from the initial screen, the CPU 222 displays an application mode selection screen shown in FIG. 6(b) on the display 225. When the user selects a softkey "Paper Registration" button 502 from the application mode selection screen, the CPU 222 displays a paper registration screen shown in FIG. 6(c) on the display 225. On the paper registration screen, the name, size, basis weight, and paper type such as plain paper or coated paper of the paper to be registered can be set. When printing with improved accuracy of the print position on the front and back sides is performed, a softkey "Front and Back Position Correction" button 503 is selected from the paper registration screen. By selecting the "Front and Back Position Correction" button 503, automatic adjustment of the print position on the front and back sides is enabled. When the "Front and Back Position Correction" button 503 is selected, the CPU 222 displays a front and back position correction screen shown in FIG. 6(d) on the display 225.

[0059] The user can select the paper feed tray for registering paper by selecting the "paper feed tray" soft key button from the front / back position correction screen. When the "start" button 504 is selected, front / back position correction is started. Note that if there is no need to improve the print position accuracy of the front and back sides, there is no need to perform front / back position correction.

[0060] 7 is a flowchart showing a process for acquiring the correction values ​​for the front and back positions of the paper to be registered (front and back position correction values). This process is started by selecting the "Start" button 504 on the front and back position correction screen in FIG. 6(d).

[0061] The CPU 222 starts a printing operation for a predetermined number of sheets of paper in a YMCK-onset print mode, which is a print mode in a YMCK-onset state (S601). In this embodiment, double-sided printing of an adjustment image for image formation conditions (here, print positions on the front and back sides) is started for five sheets of paper. FIG. 8 is an example of an adjustment image. The adjustment image is the same image on both the front and back sides, and is a V-shaped image placed at the four corners of the paper.

[0062] First, the CPU 222 performs a printing operation of an adjustment image on the front side of the paper (S602: N). When printing of the adjustment image on the front side is completed (S602: Y), the CPU 222 performs a printing operation of an adjustment image on the back side of the paper (S603: N). When printing of the adjustment image on the back side is completed (S603: Y), double-sided printing of the adjustment image is completed.

[0063] Next, the CPU 222 reads the adjustment image printed on the front side of the paper by the CIS 321 (S604: N). When the reading of the adjustment image on the front side is completed (S604: Y), the CPU 222 reads the adjustment image printed on the back side of the paper by the CIS 322 (S605: N). When the reading of the adjustment image on the back side is completed (S605: Y), the CPU 222 judges whether or not the adjustment images have been read from both sides of a predetermined number of sheets of paper (S606). Here, it is judged whether or not the adjustment images have been read from both sides of five sheets of paper. When the reading of the adjustment images on both sides of five sheets of paper has not been completed (S606: N), the CPU 222 performs the processes from S602 onward in order to print and read the adjustment images on both sides of the next sheet of paper.

[0064] When reading of the adjustment images from both sides of a predetermined number of sheets (five sheets) is completed (S606: Y), the CPU 222 calculates front and back position correction values ​​in the YMCK print mode based on the reading results of the adjustment images from both sides of the predetermined number of sheets (five sheets) that have been read (S607). The CPU 222 associates the calculated front and back position correction values ​​with the type of paper and stores them in the memory 223. This ends the process of acquiring front and back position correction values. During double-sided printing, the CPU 222 corrects the image formation conditions using the front and back position correction values ​​associated with the paper to be printed, and performs double-sided printing of the image under the corrected image formation conditions. This allows the positions of the images printed on the front and back sides to be optimally corrected.

[0065] FIG. 9 is an explanatory diagram of a method for calculating the front-back position correction value. FIG. 9 shows the measurement positions of the paper by the CIS 321 and 322. In the following description, the main scanning direction is the direction in which the photosensitive drums 340Y, 340M, 340C, and 340K are scanned with laser light by the exposure unit 227 during image formation. The sub-scanning direction is the direction perpendicular to the main scanning direction and is the paper transport direction. The front-back position correction value in this embodiment is the main scanning magnification correction value, the sub-scanning magnification correction value, the main scanning image writing position correction value, and the sub-scanning direction writing position correction value of the front and back surfaces of the paper. The main scanning magnification correction value is the image magnification correction value in the main scanning direction. The sub-scanning magnification correction value is the image magnification correction value in the sub-scanning direction. The main scanning image writing position correction value is the image writing position correction value in the main scanning direction. The sub-scanning direction writing position correction value is the image writing position correction value in the sub-scanning direction.

[0066] The image magnification correction value will now be described. When printing on the front side, the size of the paper is reduced by being heated as it passes through fixing unit 229 in the image fixing process. As a result, the image printed on the front side is also reduced in size by the same ratio. When printing on the back side, the size of the paper has already been reduced by the fixing process when printing on the front side. As a result, the image printed on the back side does not become smaller. As a result, the image printed on the back side is larger than the image printed on the front side.

[0067] In order to accurately correct the print position of the image on the front side and the back side, it is necessary to correct the magnification of the image size on the front side and the back side to make the image size on the front side the same as that on the back side. The correction value of the image size magnification (magnification correction value) is derived from the distance Len(ab) between vertices a and b of the V-shape shown in Fig. 9(a) and the distance Len(bc) between vertices b and c. The distances Len(ab) and Len(bc) on the front side are calculated from the results of reading the adjustment image on the front side by CIS321. The distances Len(ab) and Len(bb) on the back side are calculated from the results of reading the adjustment image on the back side by CIS322.

[0068] The CPU 222 calculates the magnification correction value in the main scanning direction by the following formula so that the distance Len(ab) becomes the length Len_main (not shown) of the paper in the main scanning direction that serves as a reference. Main scanning magnification correction value = Len_main / Len(ab)

[0069] The CPU 222 calculates the magnification correction value in the sub-scanning direction by the following formula so that the distance Len(bc) becomes the length Len_sub (not shown) of the reference paper in the sub-scanning direction. Sub-scanning magnification correction value = Len_sub / Len(bc)

[0070] The main scanning image writing position correction value, which corrects the image writing position in the main scanning direction, will be described. The main scanning image writing position correction value is a value for correcting the image writing position in the main scanning direction so that the distance Len (side-a) from the edge of the paper to vertex a shown in Figure 9(b) is the same as the distance Len (side-b) from the edge of the paper to vertex d. The main scanning image writing position correction value corrects the position of the image in the main scanning direction so that it is placed at the center of the paper in the main scanning direction. The CPU 222 calculates the main scanning direction writing position correction value using the following formula. Correction value for writing position in the main scanning direction = (-1 x (Len(side-a) - Len(side-b)) / 2) + (-1 x ((Len_main - Len(ab)) / 2))

[0071] A negative correction value for the main scanning direction writing position indicates that the writing start position in the main scanning direction is to be corrected to be earlier, and a positive value indicates that the writing start position in the main scanning direction is to be corrected to be later.

[0072] The correction value of the sub-scanning image writing position that corrects the image writing position in the sub-scanning direction will be explained. The correction value of the sub-scanning image writing position is a value for correcting the image writing position in the sub-scanning direction so that the distance Len (top-a) from the edge of the paper to the vertex a and the distance Len (tail-d) from the edge of the paper to the vertex d shown in Figure 9(b) are the same. The correction value of the sub-scanning image writing position corrects the image position in the sub-scanning direction so that it is placed at the center of the paper in the sub-scanning direction. The CPU 222 calculates the correction value of the sub-scanning direction writing position using the following formula. Sub-scanning direction writing position correction value = (-1 x (Len(top-a) - Len(tail-b)) / 2) + (-1 x (Len_sub-Len(bc)) / 2)

[0073] The correction value for the sub-inspection output position indicates that a negative value will cause the position where writing starts in the sub-scanning direction to be advanced, and a positive value will cause the position where writing starts in the sub-scanning direction to be delayed.

[0074] In the process of S607, the CPU 222 generates a main scanning magnification correction value, a sub-scanning magnification correction value, a main scanning image writing position correction value, and a sub-scanning direction writing position correction value for the front and back sides of the paper as front and back position correction values. The CPU 222 corrects the image formation conditions for the front and back sides using the main scanning magnification correction value, the sub-scanning magnification correction value, the main scanning image writing position correction value, and the sub-scanning direction writing position correction value. By printing an image on the paper under the corrected image formation conditions, the print position accuracy for the front and back sides is improved.

[0075] (Paper registration information) 10 is a diagram illustrating an example of registration information of a paper. The registration information of a paper is registered by a user from the setting screen of FIG. 6 and stored in the memory 223. The registration information of a paper includes a media ID 901 for identifying the registered paper, a paper name 902, a length 903 of the paper in the main scanning direction, a length 904 of the paper in the sub-scanning direction, a paper type 905, and a paper basis weight 906. The registration information of a paper also includes the front and back position correction values ​​calculated in the process of FIG. 7. The front and back position correction values ​​include a main scanning image writing position correction value 907, a sub-scanning direction writing position correction value 908, a main scanning magnification correction value 911, and a sub-scanning magnification correction value 912 for the front side. Furthermore, the front and back position correction values ​​include a main scanning image writing position correction value 909, a sub-scanning direction writing position correction value 910, a main scanning magnification correction value 913, and a sub-scanning magnification correction value 914 for the back side.

[0076] (Print mode selection) 11 is a flowchart showing a print process including a print mode selection process. The print mode can be automatically selected by the image forming apparatus 101.

[0077] The CPU 222 starts a printing operation in response to the print job (S1101: Y). Here, the print job includes print mode information indicating whether a monochrome image or a color image is to be printed. The CPU 222 determines whether front and back position correction is enabled (S1102). In this embodiment, the determination as to whether front and back position correction is enabled is made based on whether a front and back position correction value is set (registered) in the registration information of the paper used for printing. Note that the determination as to whether front and back position correction is enabled may also be made by a dedicated setting switch that sets whether front and back position correction is enabled / disabled.

[0078] If the front and back position correction is enabled (S1102: Y), the CPU 222 applies image processing based on the front and back position correction value to the image data so as to correct the geometric characteristics of the image formed on the paper using the front and back position correction value (S1103). If the front and back position correction is disabled (S1102: N), or after the image processing based on the front and back position correction value is executed, the CPU 222 determines whether or not to perform color printing according to the print mode information of the print job (S1104). If the print mode information instructs printing of a monochrome image (color printing is not performed) (S1104: N), the CPU 222 determines whether or not the front and back position correction is enabled (S1105).

[0079] If the front / back position correction is enabled (S1105: Y), the CPU 222 selects the YMCK print mode as the print mode even if the print mode information indicates printing of a monochrome image (S1106). In other words, if the front / back position correction is enabled when printing a monochrome image, the CPU 222 sets the print mode to the YMCK print mode in which all the photosensitive drums 340Y, 340M, 340C, and 340K come into contact with the intermediate transfer belt 308.

[0080] If the front and back position correction is disabled (S1105: N), the CPU 222 selects the K-printing mode as the printing mode (S1107). In other words, if the front and back position correction is disabled when printing a monochrome image, the CPU 222 separates the photosensitive drums 340Y, 340M, and 340C from the intermediate transfer belt 308, and sets the printing mode to the K-printing mode in which only the photosensitive drum 340K abuts against the intermediate transfer belt 308.

[0081] If the print mode information indicates printing of a color image (color printing is performed) (S1104: Y), the CPU 222 selects the YMCK print mode as the print mode (S1106). In other words, if the front / back position correction is valid for the printed characters of a color image, the CPU 222 sets the print mode to the YMCK print mode in which all the photosensitive drums 340Y, 340M, 340C, and 340K come into contact with the intermediate transfer belt 308.

[0082] The CPU 222 determines whether printing is complete according to the print mode (S1108). Depending on the print mode, the toner image is transferred to the intermediate transfer belt 308 as follows. When the front / back position correction is enabled for a monochrome image, the intermediate transfer belt 308 contacts the photosensitive drums 340Y, 340M, 340C, and 340K, but the toner image is formed only on the photosensitive drum 340K and transferred to the intermediate transfer belt 308. When the front / back position correction is disabled for a monochrome image, the intermediate transfer belt 308 contacts only the photosensitive drum 340K, and the toner image is formed only on the photosensitive drum 340K and transferred to the intermediate transfer belt 308. When a color image is printed, the intermediate transfer belt 308 comes into contact with the photosensitive drums 340Y, 340M, 340C, and 340K, and the toner images are formed on the photosensitive drums 340Y, 340M, 340C, and 340K and transferred to the intermediate transfer belt 308.

[0083] If printing is not complete (S1108: N), the CPU 222 returns to the process of S1120 and performs printing processing for the image of the next page. If printing is complete (S1108: Y), the CPU 222 ends the process.

[0084] The image forming apparatus 101 of this embodiment as described above automatically selects the print mode with YMCK delivery when print position accuracy of the images on the front and back sides is required when printing double-sided monochrome images. The image forming apparatus 101 automatically selects the print mode with K delivery when print position accuracy is not required when printing monochrome images. Since the print mode can be selected automatically, when printing a monochrome image on both sides with a setting that requires high print position accuracy for the front and back images, the correction accuracy for the front and back print positions can be improved even if the front and back position correction value obtained from the adjustment image printed in the YMCK state is used. When printing a monochrome image with a setting that does not require high print position accuracy for the front and back images, the Y, M, and C photosensitive drums 340Y, 340M, and 340C are separated from the intermediate transfer belt 308. This makes it possible to prevent the photosensitive drums 340Y, 340M, and 340C from deteriorating over time.

Claims

1. An image forming apparatus for forming an image on a sheet, comprising: first image forming means for forming a first colored image on a first image carrier; second image forming means for forming a second black image on a second image carrier; an intermediate transfer member onto which the first image formed on the first image carrier and the second image formed on the second image carrier are transferred; transfer means for transferring an image from the intermediate transfer member to the sheet; reading means for reading an adjustment image on the sheet; switching means for switching between a first mode in which the first image carrier and the second image carrier contact the intermediate transfer member and a second mode in which the first image carrier is separated from the intermediate transfer member and the second image carrier contacts the intermediate transfer member; control means; wherein the control means: controls the image forming apparatus to form the adjustment image in the first mode; generates an adjustment value for adjusting the position of an image to be formed on the sheet by the image forming apparatus based on a reading result of the adjustment image by the reading means; in a job in which the second image is formed on the sheet without forming the first image, when adjusting the position where the second image is to be formed on the sheet based on the adjustment value, controls the switching means to form the second image in the first mode. An image forming apparatus.

2. The control means controls the switching means to form the second image in the second mode when not adjusting the position where the second image is to be formed on the sheet based on the adjustment value in the job in which the second image is formed on the sheet without forming the first image. The image forming apparatus according to claim 1.

3. The control means determines whether to adjust the position where the second image is to be formed on the sheet based on the adjustment value in the job based on registration information related to the sheet used in the job, wherein the registration information includes information indicating whether to adjust the position of the image to be formed based on the adjustment value. The image forming apparatus according to claim 1.

4. The image forming apparatus according to claim 1, further comprising a switch used for inputting user instruction information indicating that the position of the image to be formed is to be adjusted based on the adjustment value. The image forming apparatus according to claim 1.

5. The control means generates the adjustment value based on a reading result of the adjustment image formed on a plurality of the sheets. The image forming apparatus according to claim 1.

6. The apparatus further includes a tray on which the sheet on which the image is formed is stacked, and a conveyance path for conveying the sheet from a transfer position where the transfer means transfers the image onto the sheet to the tray. The reading means reads the adjustment image from the sheet conveyed through the conveyance path. The image forming apparatus according to claim 1.

7. The adjustment value is generated in relation to the type of the sheet. The image forming apparatus according to claim 1.

Images