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 copying machine, a facsimile machine, and a multifunction peripheral.

Background Art

[0002] For printed matter produced by commercial printing presses, stabilization of printing position accuracy on the front and back sides of paper is required during double-sided printing. Patent Document 1 discloses an image forming apparatus that achieves stabilization of printing position accuracy. In order to stabilize printing position accuracy, this image forming apparatus prints an adjustment image serving as a printing position mark on a sheet of paper to create an adjustment chart. The adjustment image on the adjustment chart is read by an image reading sensor provided in a paper conveyance path. The image forming apparatus feeds back the read result of the adjustment image to image forming conditions to adjust geometric characteristics of an image such as a printing position and an inclination of the image.

[0003] Some image forming apparatuses that print full-color images are of a tandem type. In a tandem-type image forming apparatus, a plurality of photoconductors are arranged opposite a transfer body, and toner images from each photoconductor are sequentially multiple-transferred onto the transfer body. 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 sequentially multiple-transferring yellow, magenta, cyan, and black toner images from the four photoconductors. The toner images of respective colors are collectively transferred from the transfer body to a sheet of paper. A full-color image is printed on the paper after the toner image is subjected to fixing processing by a fixing device. Hereinafter, yellow, magenta, cyan, and black may also be referred to as Y, M, C, and K.

[0004] In a tandem-type image forming apparatus, a separation mechanism is provided to separate / bring together the Y, M, and C photoreceptors and the transfer medium. When printing a monochrome image, the Y, M, and C photoreceptors and the transfer medium that are not needed for printing the monochrome image are separated, and the driving of the Y, M, and C photoreceptors is stopped. The printing mode for printing monochrome images is called the "K-contact printing mode". When printing a color image, all of the Y, M, C, and K photoreceptors and the transfer medium are in contact. The printing mode for printing color images is called the "YMCK-contact printing mode". The image forming apparatus disclosed in Patent Document 2 is equipped with such a separation mechanism and, when printing a monochrome image, prints in the K-contact printing mode as needed, thereby suppressing the progression of changes in the Y, M, and C photoreceptors over time and reducing running costs. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2006-11285 [Patent Document 2] Japanese Patent Application Publication No. 11-167238 [Overview of the project] [Problems that the invention aims to solve]

[0006] The separation mechanism described in Patent Document 2 specifically controls the separation between the photoreceptor and the intermediate transfer medium by moving a transfer unit that transfers the toner image from the photoreceptor to the intermediate transfer medium. The transfer unit is positioned opposite the photoreceptor with the intermediate transfer medium in between, and is provided to correspond to multiple photoreceptors. The K photoreceptor and the intermediate transfer medium are always in contact regardless of the color being printed. For this reason, the separation mechanism does not control the K transfer unit corresponding to the K photoreceptor.

[0007] The Y, M, and C transfer areas, excluding the K transfer area, move towards the photoreceptor when bringing the photoreceptor and the intermediate transfer area into contact, and move away from the photoreceptor when separating the photoreceptor and the intermediate transfer area. When printing a color image, the Y, M, and C transfer areas corresponding to the Y, M, and C photoreceptors move towards the photoreceptor, bringing the intermediate transfer area into contact with the Y, M, and C photoreceptors. This state is called the "YMCK contact state". When printing a monochrome image, the Y, M, and C transfer areas corresponding to the Y, M, and C photoreceptors do not move towards the photoreceptor, and the intermediate transfer area moves away from the Y, M, and C photoreceptors. As a result, only the K photoreceptor is in contact with the intermediate transfer area. This state is called the "K contact state".

[0008] This explanation describes a case where an image forming apparatus is equipped with a drum-shaped photosensitive drum as the photosensitive element, an endless belt-shaped intermediate transfer belt as the transfer element, and transfer rollers as the transfer section. The number of transfer rollers in contact with the intermediate transfer belt differs between the YMCK and K toner transfer states. As a result, the tension acting on the intermediate transfer belt by the transfer rollers changes between the YMCK and K toner transfer states. This change in tension causes the time it takes for the toner image formed on each photosensitive drum to reach the transfer position on the paper to change between the YMCK and K toner transfer states. Specifically, the time is slower in the K toner transfer state than in the YMCK transfer state. Therefore, when printing the same image, the distance from the leading edge of the paper in the paper transport direction to the image is longer when printing in the K toner transfer state than in the YMCK transfer state.

[0009] Therefore, the correction values ​​differ between the YMCK and K states because the position of the adjustment image used to correct image formation conditions is not the same. For example, the correction values ​​when correcting geometric characteristics such as the image printing position as an image formation condition differ between the YMCK and K states. In this case, if double-sided printing of a monochrome image is performed using the geometric characteristic correction values ​​generated in the YMCK state, the accuracy of the geometric characteristic correction of each image on the front and back sides will be lower than when double-sided printing of a color image.

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

[0011] The present invention relates to an image forming apparatus for forming an image on paper, comprising: a first image forming means for forming a chromatic first image on a first image carrier; a second image forming means for forming a black second image on a second image carrier; an intermediate transfer body onto which the first image formed on the first image carrier and the second image formed on the second image carrier are transferred; a transfer means for transferring the image from the intermediate transfer body to paper; a reading means for reading an adjustment image on the paper; a first mode in which the first image carrier and the second image carrier are in contact with the intermediate transfer body; and a mode in which the first image carrier is separated from the intermediate transfer body and the second image carrier The device comprises a switching means for switching between a second mode in which a user makes contact and a 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 the image to be formed on the paper by the image forming apparatus based on the reading result of the adjustment image by the reading means, and in a job in which the second image is formed on the paper without forming the first image, when adjusting the position in which the second image should be formed on the paper based on the adjustment value, the switching means controls the device to form the second image in the first mode. The system determines, based on registration information related to the paper used in the job, whether to adjust the position where the second image should be formed on the paper in the job based on the adjustment value, and the registration information includes information indicating whether to adjust the position of the image to be formed based on the adjustment value. It is characterized by the following: Another image forming apparatus of the present invention is an image forming apparatus for forming an image on paper, comprising: a first image forming means for forming a chromatic first image on a first image carrier; a second image forming means for forming a black second image on a second image carrier; an intermediate transfer body onto which the first image formed on the first image carrier and the second image formed on the second image carrier are transferred; a transfer means for transferring the image from the intermediate transfer body to paper; a reading means for reading an adjustment image on the paper; and a switching means for switching between a first mode in which the first image carrier and the second image carrier are in contact with the intermediate transfer body, and a second mode in which the first image carrier is separated from the intermediate transfer body and the second image carrier is in contact with it. The device comprises a 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 the image to be formed on the paper by the image forming apparatus based on the reading result of the adjustment image by the reading means, and in a job in which the second image is formed on the paper without forming the first image, if the position in which the second image is to be formed on the paper is adjusted based on the adjustment value, the switching means controls the device to form the second image in the first mode, and generates the adjustment value based on the reading results of the adjustment images formed on a plurality of sheets of paper. [Effects of the Invention]

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

[0013] [Figure 1] A diagram illustrating the configuration of an image processing system. [Figure 2] system configuration diagram. [Figure 3]Configuration diagram of an image forming apparatus. [Figure 4] (a) and (b) are explanatory diagrams of the contact state between an image forming unit and an intermediate transfer belt. [Figure 5] Explanatory diagram of CIS. [Figure 6] (a) to (d) are explanatory diagrams of a setting screen for registering paper. [Figure 7] Flowchart illustrating processing for acquiring front-back position correction values. [Figure 8] Exemplary diagram of an adjustment image. [Figure 9] (a) and (b) are explanatory diagrams of the calculation method for front-back position correction values. [Figure 10] Exemplary diagram of paper registration information. [Figure 11] Flowchart illustrating print processing including print mode selection processing. DESCRIPTION OF EMBODIMENTS

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

[0015] (Image Processing System) FIG. 1 is a configuration diagram of an image processing system including the image forming apparatus according to the present 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, a multifunction peripheral (MFP), or the like. The external controller 102 is, for example, an image processing controller, a digital front end (DFE), a print server, or the like.

[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 acquires a print instruction (print job) from the client PC 103.

[0017] The client PC 103 has a printer driver installed that has the function of converting image data into a print description language that can be processed by the external controller 102. Users can instruct printing via the printer driver using various applications. Based on the user's instructions, the printer driver sends a print job containing image data to the external controller 102. The external controller 102 receives the print job containing 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 multiple 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 section located at the bottom of the main body using a developer (e.g., toner). The printing device 107 forms images of yellow (Y), magenta (M), cyan (C), and black (K). Full-color images with images of each color superimposed, or monochrome images using black (K), can be formed on the paper. The paper with the image formed on it is transported from the printing device 107 to the finisher 109. The finisher 109 loads the paper with the image formed on it.

[0019] This image processing system is configured with an external controller 102 connected to the 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 acquire print jobs containing image data from a client PC 103 via an external LAN 104. In this case, the image forming apparatus 101 would perform the data analysis and rasterization processing that is done by the external controller 102. In other words, the image forming apparatus 101 and the external controller 102 would be configured as a single unit.

[0020] (System Configuration) Figure 2 is a system configuration diagram showing the control of the image processing system. Here, the controllers that control the operation of the image forming apparatus 101, the external controller 102, and the client PC 103 are 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 communication with other devices. The printing device 107 includes a CPU (Central Processing Unit) 222, memory 223, 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 making unit 228, a fixing unit 229, and a paper feeding unit 230 for forming images. The printing device 107 includes an operation unit 224 and a display 225 as a user interface. These components are connected to each other so as to be able to communicate with each other via a system bus 233.

[0022] The communication interface 217 is connected to the finisher 109 via the communication cable 249 and controls communication with the finisher 109. When the printer 107 and the finisher 109 operate in cooperation, information and data are sent and received via the communication interface 217. The LAN interface 218 is connected to the external controller 102 via the internal LAN 105 and controls communication with the external controller 102. The printer 107 receives print settings from the external controller 102 via the LAN interface 218. The video interface 220 is connected to the external controller 102 via the video cable 106 and controls communication with the external controller 102. The printer 107 receives image data representing the image to be formed from the external controller 102 via the video interface 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 perform various processes. When performing image forming processing, the CPU 222 controls the exposure unit 227, the image formation unit 228, the fixing unit 229, and the paper feeding unit 230.

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

[0025] The image-forming unit 228 transfers the toner image formed on the photoreceptor to the paper. The image-forming unit 228 includes a developer, a transfer unit, a toner supply unit, etc. The developer forms a toner image by attaching negatively charged toner from a developing cylinder to the electrostatic latent image formed on the surface of the photoreceptor. There are four developers, one for each of the four colors: yellow (Y), magenta (M), cyan (C), and black (K). The developer makes the electrostatic latent image on the photoreceptor visible using the corresponding color toner.

[0026] The transfer unit has an intermediate transfer belt, which is an intermediate transfer body, and transfers the toner image from the photoreceptor to the intermediate transfer belt. A primary transfer roller is provided at a position opposite the photoreceptor, with the intermediate transfer belt in between. When a positive potential is applied to the primary transfer roller, toner images are sequentially transferred from each of the four photoreceptors onto the intermediate transfer belt. This forms a full-color toner image on the intermediate transfer belt. The toner image formed on the intermediate transfer belt is then transferred to the paper by a secondary transfer roller, which will be described later. When a positive potential is applied to the secondary transfer roller, it transfers the full-color toner image from the intermediate transfer belt to the paper.

[0027] The fuser unit 229 fixes the transferred toner image onto the paper. The fuser unit 229 has a heater and a pair of rollers. The fuser unit 229 heats and pressurizes the toner image on the paper using the heater and the pair of rollers, melting and fixing the toner image to the paper. This produces a printed document with an image formed on the paper. The paper feed unit 230 is equipped with transport rollers and various sensors in the transport path and controls the paper feeding operation.

[0028] The image reading unit 231 reads the image printed on the transported paper based on instructions from the CPU 222. When the CPU 222 adjusts the image formation conditions, for example, it reads an adjustment image for correcting the image formation conditions formed on the paper from the image reading unit 231. The operation unit 224 is an input device that receives various settings inputs and operation instructions from the user. The operation unit 224 consists of various input keys and 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 print jobs.

[0029] · Finisher The finisher 109 performs post-processing on printed materials output from, for example, the printing device 107. The finisher 109 includes a communication interface 241, a CPU 242, a memory 243, and a paper discharge control unit 244. These components are connected to each other via a system bus 245 so that they can communicate with one another. The communication interface 241 is connected to the printing device 107 via a communication cable 249 and controls communication between the finisher 109 and the printing device 107. When the finisher 109 and the printing device 107 operate in cooperation, information and data are sent and received via the communication interface 241. The CPU 242 executes a control program stored in the memory 243 and performs various controls necessary for post-processing. The memory 243 stores the control program. The memory 243 also provides a work area for the CPU 242 when it performs various processes. The paper discharge control unit 244 performs post-processing on the transported paper and discharges it based on instructions 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 communication with other devices. The external controller 102 includes a CPU 208, memory 209, and storage 210 to control the operation of the external controller 102. The external controller 102 includes a keyboard 211 and a display 212 as a user interface. These components are connected to each other so as to be able to communicate with each other via a system bus 216.

[0031] 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 print jobs from the client PC 103 via LAN I / F 213. LAN I / F 214 is connected to the printer 107 via the internal LAN 105 and controls communication with the printer 107. The external controller 102 sends print settings to the printer 107 via LAN I / F 214. Video I / F 215 is connected to the printer 107 via video cable 106 and controls communication with the printer 107. The external controller 102 sends image data to the printer 107 via video I / F 215.

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

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

[0034] The CPU 201 controls the operation of the client PC 103 by executing computer programs stored in the storage 203. In this embodiment, the CPU 201 performs image data creation and print job transmission processing. The memory 202 provides a work area for the CPU 201 to perform various processes. The keyboard 204 and display 205 are the user interface. The keyboard 204 is an input device that receives instructions from the user. The display 205 is an output device that displays information about the application being executed on the client PC 103 as still images or videos. 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 sends 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 by an internal LAN 105 and a video cable 106, but any configuration that allows for the transmission and reception of data necessary for printing is acceptable, and for example, they may be connected by only the video cable 106. Memories 202, 209, 223, and 243 can each be storage devices for holding data and programs. These memories can be, for example, volatile RAM (Random Access Memory), non-volatile ROM (Read Only Memory), storage, USB (Universal Serial Bus) memory, etc.

[0036] (Configuration of an image forming apparatus) Figure 3 is a diagram showing the configuration of the image forming apparatus 101. A display 225 is provided above the printing device 107. The display 225 displays information for the printing status and settings of the image forming apparatus 101. The paper (printed material) on which the image has been formed in the printing device 107 is transported to the finisher 109 located downstream.

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

[0038] The printing apparatus 107 includes an image-forming unit 228, an intermediate transfer belt 308 and a secondary transfer roller 309, to which toner images are transferred from each of the image-forming units 304, 305, 306, and 307. The intermediate transfer belt 308 rotates clockwise in the figure, and toner images are superimposed and transferred in the order of image-forming unit 307, image-forming unit 306, image-forming unit 305, and image-forming unit 304. As a result, a full-color toner image is formed on the intermediate transfer belt 308. The intermediate transfer belt 308 transports the toner image to the secondary transfer roller 309 by rotating. Paper is transported to the secondary transfer roller 309 at the same time that the toner image is transported to the secondary transfer roller 309. The secondary transfer roller 309 transfers the toner image on the intermediate transfer belt 308 to the transported paper.

[0039] Figure 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 apparatus 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 are equipped with drum-shaped photosensitive drums 340Y, 340M, 340C, and 340K as photosensitive elements. As described above, an electrostatic latent image is formed on the photosensitive drums 340Y, 340M, 340C, and 340K by scanning with laser light. The main scanning direction by laser light is in the drum axis direction of the photosensitive drums 340Y, 340M, 340C, and 340K, and is perpendicular to the paper transport direction. The intermediate transfer belt 308 is an endless belt-shaped transfer body. The primary transfer rollers 341Y, 341M, 341C, and 341K, which are the transfer sections, are positioned opposite the photosensitive drums 340Y, 340M, 340C, and 340K, with the intermediate transfer belt 308 in between.

[0040] The separation mechanism 345 includes a separation motor 342 that serves as a drive source, a separation sensor flag 343 that rotates when driven by 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 separate from the photosensitive drums 340Y, 340M, and 340C, due to the transmitted driving force. As 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. As the primary transfer rollers 341Y, 341M, and 341C move away from the photosensitive drums 340Y, 340M, and 340C, the photosensitive drums 340Y, 340M, and 340C move away from the intermediate transfer belt 308. When the primary transfer rollers 341Y, 341M, and 341C move, the amount of movement of the primary transfer rollers 341Y, 341M, and 341C is measured by the separation sensor flag 343 and the separation home position sensor 344. In this configuration, it is prevented that the primary transfer rollers 341Y, 341M, and 341C move beyond the allowable range.

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

[0042] The printing apparatus 107 includes a first fuser 311 and a second fuser 313 as a fixing unit 229. The first fuser 311 and the second fuser 313 have the same configuration and fix the toner image to the paper. For this purpose, the first fuser 311 and the second fuser 313 are each equipped with a pressure roller and a heating roller. The paper is heated and pressurized as it passes between the pressure roller and the heating roller, and the toner image is melted and pressed onto it. The paper that has passed through the second fuser 313 is transported to the transport path 314. The second fuser 313 is located downstream of the first fuser 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 fuser 311 and to ensure fixation. For this reason, the second fuser 313 may not be used depending on the type of paper and the content of the image forming process. A transport path 312 is provided to transport the paper that has been fixed in the first fuser 311 to the transport path 314 without passing through the second fuser 313.

[0043] After the transport paths 314 and 312 merge, a transport path 315 and a reversal path 316 are provided. When double-sided printing is instructed, the paper is transported to the reversal path 316. The paper transported to the reversal path 316 has its transport direction reversed and is transported to the double-sided transport path 317. The reversal path 316 and the double-sided transport path 317 reverse the side of the paper on which the image is formed (the first side). The paper is transported to the transport path 303 via the double-sided transport path 317, and as it passes through the secondary transfer roller 309 and the fixing unit 229, an image is formed on a second side that is different from the first side on which the image was formed.

[0044] In the case of single-sided printing, or when an image is formed on both sides in double-sided printing, the paper is transported to the transport path 315. A transport path 323 is located downstream of the transport path 315 in the direction of paper transport. In the transport path 323, two Contact Image Sensors (CIS) 321 and 322 are arranged opposite each other on either side of the transport path 323 as image reading units 231. Figure 5 is an explanatory diagram of the CIS 321 and 322. CIS 321 is an optical sensor that reads the image on the top surface of the paper being transported along the transport path 323. CIS 322 is an optical sensor that reads the image on the bottom surface of the paper being transported along the transport path 323.

[0045] The CIS321 comprises 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 illuminates the top surface of the paper when the paper being transported along the transport path 323 reaches the reading position. The reading sensor 351 has multiple light receiving elements (photoelectric conversion elements) oriented perpendicular to the paper transport direction. Therefore, the direction perpendicular to the paper transport direction becomes the main scanning direction of the CIS321. The reading sensor 351 receives reflected light from the paper. The multiple light receiving elements of the reading sensor 351 output an output value (electrical signal) based on the intensity of the received reflected light. The output values ​​(electrical signals) output from the multiple light receiving elements are transmitted to the CPU 222. In this way, the image formed on the paper is read.

[0046] The white reference plate 352 is a calibration member (reference member) used when correcting the shading of the CIS321. During shading correction, the LED 350 and the reading sensor 351 move to a position where they can read the white reference plate 352. 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 CIS321 is performed based on the reading result of the white reference plate 352. For this reason, the CIS321 cannot read the image formed on the paper during shading correction.

[0047] Like the CIS321, the CIS322 includes an LED 353, a reading sensor 354, and a white reference plate 355. The CIS322 operates similarly to the CIS321, reading the image formed on the underside of the paper when the paper being transported along the transport path 323 reaches the reading position. In addition to the CIS321 and 322, the image reading unit 231 can also be implemented using a CCD or CMOS sensor.

[0048] The printing apparatus 107 of this embodiment is capable of forming adjustment images on both sides of a sheet of paper to adjust image formation conditions. The sheet of paper on which the adjustment images have been formed is called an adjustment chart. The printing apparatus 107 prints the adjustment images onto the paper to create an adjustment chart, and reads the adjustment images using CIS321 and CIS322. The reading results (read data) of the adjustment chart 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 into the image formation conditions to adjust the image formation conditions.

[0049] For example, the geometric properties of the image formed on the paper by the printing device 107 vary depending on whether the paper is in a YMCK state or a K state. The printing device 107 creates a geometric properties adjustment chart and detects the geometric properties based on the reading results (read data) from CIS 321 and 322. The CPU 222 performs an affine transformation on the image data so that the detected geometric properties become ideal geometric properties. The printing device 107 can control the geometric properties of the image formed on the paper by forming the image on the paper based on the image data transformed by the CPU 222. In this way, the printing device 107 can suppress variations in the geometric properties of the image.

[0050] The adjustment image formed on the adjustment chart may be an image for detecting geometric characteristics, an image for detecting image density, or an image for detecting color shift. If an adjustment image for detecting image density is formed, the CPU 222 generates image formation conditions to suppress fluctuations in image density based on the reading results (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 formation 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 to suppress fluctuations in image density based on the reading results (read data) of the CIS 321 (or CIS 322). The CPU 222 converts the image data based on the gradation correction table. The printing device 107 forms an image on the 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, if an adjustment image for detecting color misalignment is formed, the CPU 222 detects the color misalignment based on the reading result (read data) of the CIS 321 (or CIS 322). Based on the detected color misalignment, the CPU 222 corrects the color misalignment by controlling the position of the image formed on the photoreceptor by the exposure unit 227.

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

[0053] The adjustment chart is excluded so as not to be mixed with the printed materials corresponding to the print job. For this purpose, the printing device 107 is equipped with a flapper 324, an output path 326, a transport sensor 327, and an output tray 328. The adjustment chart, whose image (adjustment image) has been read by CIS 321 and 322, is transported to the output path 326 by the flapper 324. The paper transported to the output path 326 is discharged into the output tray 328.

[0054] If the paper is not an adjustment chart, it is transported by the flapper 324 from the transport path 323 to the downstream transport path 325. The paper transported to the downstream transport path 325 is handed over to the finisher 109. When the printing device 107 receives notification of a transport jam from the finisher 109, it switches the flapper 324 to the discharge path 326, regardless of whether it 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 in handling jams.

[0055] The finisher 109 can load paper received from the printing device 107. The finisher 109 includes a transport path 331 and a stack tray 332 for loading paper. Transport sensors 333, 334, 335, and 336 are provided in the transport path 331. Paper transported from the printing device 107 is loaded onto the stack tray 332 via the transport path 331. Transport sensors 333, 334, 335, and 336 detect the passage of paper being transported along the transport path 331. If the CPU 242 determines that a transport jam (transport abnormality) has occurred in the finisher 109 if the leading or trailing end of the paper in the transport direction is not detected by the transport sensors 333, 334, 335, or 336 even after a predetermined time has elapsed since the start of paper transport. In this case, the CPU 242 notifies the printing device 107 that a transport jam has occurred.

[0056] (Method for generating correction values ​​for front and back printing positions) Even if the basis weight is the same, the paper has different moisture absorption states and physical properties, resulting in different shrinkage characteristics after passing through the fixing unit 229 for each type of paper. To improve the accuracy of correcting the image forming conditions (geometric properties), the image forming apparatus 101 needs to generate correction values ​​for the image forming conditions (geometric properties) for each type of paper used. In this embodiment, the image forming apparatus 101 generates correction values ​​for the print position for each type of paper used to improve the print position accuracy on the front and back surfaces.

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

[0058] Figure 6(a) shows the initial screen. When the user selects the "Advanced Mode" button 501, a soft key, from the initial screen, the CPU 222 displays the Advanced Mode selection screen shown in Figure 6(b) on the display 225. When the user selects the "Paper Registration" button 502, a soft key, from the Advanced Mode selection screen, the CPU 222 displays the Paper Registration screen shown in Figure 6(c) on the display 225. On the Paper Registration screen, it is possible to set the name, size, basis weight, and paper type (such as plain paper or coated paper) of the paper to be registered. To perform printing with improved accuracy of the print position on both sides, the "Front / Back Position Correction" button 503, a soft key, is selected from the Paper Registration screen. Selecting the "Front / Back Position Correction" button 503 enables automatic adjustment of the print position on both sides. When the "Front / Back Position Correction" button 503 is selected, the CPU 222 displays the Front / Back Position Correction screen shown in Figure 6(d) on the display 225.

[0059] The user can select the paper feed tray for paper registration by selecting the "Paper Feed Tray" soft key from the front / back position correction screen. Selecting the "Start" button 504 initiates the front / back position correction. Note that if there is no need to improve the print position accuracy on the front and back sides, front / back position correction is not required.

[0060] Figure 7 is a flowchart illustrating the process of obtaining the front / back position correction value (front / back position correction value) for the paper to be registered. This process is started when the "Start" button 504 is selected from the front / back position correction screen in Figure 6(d).

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

[0062] CPU222 first prints the adjustment image on the front side of the paper (S602:N). Once printing of the adjustment image on the front side is complete (S602:Y), CPU222 prints the adjustment image on the back side of the paper (S603:N). Once printing of the adjustment image on the back side is complete (S603:Y), the double-sided printing of the adjustment image is finished.

[0063] Next, the CPU 222 uses the CIS 321 to read the adjustment image printed on the front side of the paper (S604:N). Once the reading of the adjustment image on the front side is complete (S604:Y), the CPU 222 uses the CIS 322 to read the adjustment image printed on the back side of the paper (S605:N). Once the reading of the adjustment image on the back side is complete (S605:Y), the CPU 222 determines whether or not adjustment images have been read from both sides of a predetermined number of sheets of paper (S606). Here, it is determined whether adjustment images have been read from both sides of five sheets of paper. If the reading of adjustment images from both sides of five sheets of paper is not complete (S606:N), the CPU 222 performs the processing from S602 onwards to print and read adjustment images on both sides of the next sheet of paper.

[0064] When the reading of adjustment images from both sides of a predetermined number (5 sheets) of paper is complete (S606:Y), the CPU 222 calculates a front-to-back position correction value in YMCK printing mode based on the reading results of the adjustment images from both sides of the predetermined number (5 sheets) (S607). The CPU 222 stores the calculated front-to-back position correction value in memory 223, linked to the type of paper. This completes the process of obtaining the front-to-back position correction value. When printing on both sides, the CPU 222 corrects the image formation conditions using the front-to-back position correction value linked to the paper to be printed, and performs double-sided printing of the image under the corrected image formation conditions. This ensures that the position of the image printed on the front and back sides is optimally corrected.

[0065] Figure 9 is an explanatory diagram of the calculation method for front / back position correction values. Figure 9 shows the paper measurement positions by CIS321 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 by the laser light of 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 values ​​in this embodiment are the main scanning magnification correction value, sub-scanning magnification correction value, main scanning image output position correction value, and sub-scanning direction output position correction value for the front and back sides 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 output position correction value is the image output position correction value in the main scanning direction. The sub-scanning direction output position correction value is the image output position correction value in the sub-scanning direction.

[0066] Let's explain the image magnification correction value. When printing on the front side of the paper, the paper is heated as it passes through the fixing unit 229 during the image fixing process, causing its size to decrease. As a result, the image printed on the front side also decreases proportionally. When printing on the back side, the paper has already decreased in size due to the fixing process on the front side. Therefore, the image printed on the back side does not decrease in size. As a result, the image printed on the back side becomes larger than the image printed on the front side.

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

[0068] The CPU222 calculates the magnification correction value for the main scanning direction using the following formula, such that the distance Len(ab) is equal to the length Len_main (not shown) of the paper in the main scanning direction, which is the reference paper. Main scan magnification correction value = Len_main / Len(ab)

[0069] The CPU222 calculates the magnification correction value for the sub-scanning direction using the following formula, such that the distance Len(bc) is equal to the length Len_sub (not shown) of the reference paper in the sub-scanning direction. Sub-scan magnification correction value = Len_sub / Len(bc)

[0070] This section explains the correction value for the main scan image output position, which corrects the image output position in the main scan direction. The correction value for the main scan image output position is a value used to correct the image output position in the main scan direction so that the distance Len(side-a) from the edge of the paper to vertex a and the distance Len(side-b) from the edge of the paper to vertex d, as shown in Figure 9(b), are the same. The correction value for the main scan image output position corrects the position of the image in the main scan direction so that it is centered on the paper in the main scan direction. The CPU 222 calculates the correction value for the main scan direction output position using the following formula. Correction value for main scan direction write position = (-1 × (Len(side-a) - Len(side-b)) / 2) + (-1 × ((Len_main - Len(ab)) / 2))

[0071] The correction value for the main scan direction write position indicates that a negative value corrects the start position of the main scan direction write to be earlier, while a positive value corrects the start position of the main scan direction write to be later.

[0072] This section describes the correction value for the sub-scan image output position, which corrects the image output position in the sub-scan direction. The correction value for the sub-scan image output position is a value used to correct the image output position in the sub-scan direction so that the distance Len(top-a) from the edge of the paper to vertex a and the distance Len(tail-d) from the edge of the paper to vertex d, as shown in Figure 9(b), are the same. The correction value for the sub-scan image output position corrects the image position in the sub-scan direction so that it is centered on the paper in the sub-scan direction. The CPU 222 calculates the correction value for the sub-scan direction output position using the following formula. Correction value for sub-scan direction write position = (-1 × (Len(top-a) - Len(tail-b)) / 2) + (-1 × (Len_sub - Len(bc)) / 2)

[0073] The correction value for the secondary document output position indicates that a negative value corrects the start position of writing in the secondary scanning direction to be earlier, while a positive value corrects the start position of writing in the secondary scanning direction to be later.

[0074] CPU222, through processing in S607, generates front-to-back position correction values ​​for the front and back sides of the paper, including a main scan magnification correction value, a sub-scan magnification correction value, a main scan image output position correction value, and a sub-scan direction output position correction value. CPU222 corrects the image formation conditions of the front and back sides using the main scan magnification correction value, sub-scan magnification correction value, main scan image output position correction value, and sub-scan direction output position correction value. By printing the image on the paper according to the corrected image formation conditions, the print position accuracy on the front and back sides is improved.

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

[0076] (Select printing mode) Figure 11 is a flowchart representing the printing process, including the selection of the printing mode. The printing mode can be automatically selected by the image forming apparatus 101.

[0077] The CPU 222 starts printing according to the print job (S1101:Y). Here, the print job includes print mode information indicating whether it is printing a monochrome image or a color image. The CPU 222 determines whether front-to-back position correction is enabled or not (S1102). In this embodiment, the determination of whether front-to-back position correction is enabled or not is made by whether a front-to-back position correction value is set (registered) in the registration information of the paper used for printing. Alternatively, the determination of whether front-to-back position correction is enabled or not may also be made by a dedicated setting switch that sets whether front-to-back position correction is enabled or disabled.

[0078] If front-to-back position correction is enabled (S1102:Y), the CPU 222 applies image processing based on the front-to-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-to-back position correction value (S1103). If front-to-back position correction is disabled (S1102:N), or after image processing based on the front-to-back position correction value has been performed, 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 (no color printing) (S1104:N), the CPU 222 determines whether or not front-to-back position correction is enabled (S1105).

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

[0080] If front-to-back position correction is disabled (S1105:N), the CPU 222 selects the K-print mode as the printing mode (S1107). In other words, when printing a monochrome image and front-to-back position correction is disabled, 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-print mode, in which only the photosensitive drum 340K is in contact with the intermediate transfer belt 308.

[0081] When the print mode information instructs the printing of a color image (to perform color printing) (S1104:Y), the CPU 222 selects the YMCK print mode as the print mode (S1106). In other words, if front-to-back position correction is effective for printing color images, the CPU 222 sets the print mode to the YMCK print mode, in which all photosensitive drums 340Y, 340M, 340C, and 340K are in contact with the intermediate transfer belt 308.

[0082] The CPU 222 determines the completion of printing according to the printing mode (S1108). Depending on the printing mode, the toner image is transferred to the intermediate transfer belt 308 as follows: When front-to-back position correction is enabled for a monochrome image, the intermediate transfer belt 308 comes into contact with 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 front-to-back position correction is disabled for a monochrome image, the intermediate transfer belt 308 comes into contact only with 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 printing a color image, the intermediate transfer belt 308 comes into contact with the photosensitive drums 340Y, 340M, 340C, and 340K, and the toner image is 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), CPU222 returns to process S1120 and prints the image for the next page. If printing is complete (S1108:Y), CPU222 terminates processing.

[0084] In this embodiment, the image forming apparatus 101 automatically selects a YMCK printing mode when precise print position accuracy is required for both the front and back images during double-sided printing of monochrome images. When precise print position accuracy is not required during monochrome image printing, the image forming apparatus 101 automatically selects a K printing mode. Because the printing mode can be automatically selected, when printing monochrome images on both sides with settings that require precise print position accuracy for the front and back images, the accuracy of the correction of the print position on the front and back sides can be increased even when using front-to-back position correction values ​​obtained from adjustment images printed in the YMCK state. When printing monochrome images with settings that do not require precise 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. Therefore, it is possible to prevent the progression of changes in the photosensitive drums 340Y, 340M, and 340C over time.

Claims

1. An image forming apparatus for forming an image on paper, A first image forming means for forming a chromatic first image on a first image carrier, A second image forming means for forming a black second image on a second image carrier, An intermediate transfer body onto which the first image formed on the first image carrier and the second image formed on the second image carrier are transferred, A transfer means for transferring an image from the intermediate transfer body to paper, A reading means for reading adjustment images on paper, A switching means for switching between a first mode in which the first image carrier and the second image carrier are in contact with the intermediate transfer body, and a second mode in which the first image carrier is separated from the intermediate transfer body and the second image carrier is in contact with it. Equipped with control means, The control means is In the first mode, the image forming apparatus is controlled to form the adjustment image, Based on the reading result of the adjustment image by the reading means, adjustment values ​​are generated to adjust the position of the image to be formed on the paper by the image forming apparatus. In a job in which the second image is formed on paper without forming the first image, if the position where the second image should be formed on the paper is adjusted based on the adjustment value, the switching means is controlled to form the second image in the first mode. Based on the registration information related to the paper used in the job, it is determined whether or not to adjust the position in which the second image should be formed on the paper in the job based on the adjustment value. The registration information is characterized by including information indicating whether or not to adjust the position of the image to be formed based on the adjustment value. Image forming apparatus.

2. An image forming apparatus for forming an image on paper, A first image forming means for forming a chromatic first image on a first image carrier, A second image forming means for forming a black second image on a second image carrier, An intermediate transfer body onto which the first image formed on the first image carrier and the second image formed on the second image carrier are transferred, A transfer means for transferring an image from the intermediate transfer body to paper, A reading means for reading adjustment images on paper, A switching means for switching between a first mode in which the first image carrier and the second image carrier are in contact with the intermediate transfer body, and a second mode in which the first image carrier is separated from the intermediate transfer body and the second image carrier is in contact with it. Equipped with control means, The control means is In the first mode, the image forming apparatus is controlled to form the adjustment image, Based on the reading result of the adjustment image by the reading means, adjustment values ​​are generated to adjust the position of the image to be formed on the paper by the image forming apparatus. In a job in which the second image is formed on paper without forming the first image, if the position where the second image should be formed on the paper is adjusted based on the adjustment value, the switching means is controlled to form the second image in the first mode. The adjustment value is generated based on the reading results of the adjustment images formed on multiple sheets of paper, Image forming apparatus.

3. The control means is characterized in that, in the job in which the second image is formed on the paper without forming the first image, if the position in which the second image should be formed on the paper is not adjusted based on the adjustment value, the switching means controls the switching means to form the second image in the second mode. The image forming apparatus according to claim 1 or 2.

4. The control means determines, based on registration information related to the paper used in the job, whether or not to adjust the position where the second image should be formed on the paper in the job based on the adjustment value. The registration information is characterized by including information indicating whether or not to adjust the position of the image to be formed based on the adjustment value. The image forming apparatus according to claim 2.

5. The device further comprises a switch used to input user instruction information indicating that the position of the image to be formed should be adjusted based on the adjustment value, The image forming apparatus according to claim 1 or 2.

6. The control means is characterized by generating the adjustment value based on the reading results of the adjustment images formed on a plurality of sheets of paper. The image forming apparatus according to claim 1.

7. The system further includes a tray on which the paper on which the image is formed is stacked, and a transport path for transporting the paper from a transfer position where the transfer means transfers the image onto the paper to the tray, The reading means is characterized by reading the adjustment image from the paper being transported along the transport path. The image forming apparatus according to claim 1 or 2.

8. The adjustment value is characterized by being generated in relation to the type of paper. The image forming apparatus according to claim 1 or 2.

Images