Image forming apparatus

Abstract

To accurately acquire a correction value of an image formation position in an image forming apparatus that can switch a contact state between image forming means and an intermediate transfer body.SOLUTION: An image forming apparatus has first image forming means, second image forming means, and an intermediate transfer body. The image forming apparatus can switch a contact state between the second image forming means and the intermediate transfer body to a touched state or a separation state. The image forming apparatus can form an image in both the touched state and the separation state. The image forming apparatus forms a test image in both the touched state and the separation state to acquire a correction value of an image formation position for the touched state and a correction value of an image formation position for the separation state. The correction value is acquired for both a front face and a rear face of a sheet. The image forming apparatus corrects the image formation position by using the correction value according to the contact state.SELECTED DRAWING: Figure 10

Description

Technical Field

[0005] , , , ,

[0001] The present invention relates to an image forming apparatus.

Background Art

[0002] For printed materials generated by image forming apparatuses such as commercial printing machines, high precision is required for the image forming positions on the front and back surfaces. According to Patent Document 1, it has been proposed to print a reference chart and determine correction values for the front and back image forming positions according to the reading results of the reference chart.

[0003] By the way, in a tandem type image forming apparatus that forms a full-color image, four photosensitive drums are worn by contacting a transfer belt. According to Patent Document 2, in monochrome mode, it has been proposed to separate three photosensitive drums except for the photosensitive drum for black from the transfer belt.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In an image forming apparatus where the contact state between the four photosensitive drums and the transfer belt changes between color mode and monochrome mode, the image formation position on the front and back surfaces differ during double-sided printing. When the three photosensitive drums, excluding the black photosensitive drum, move away from the transfer belt, the tension of the transfer belt decreases, causing the toner image to arrive at the transfer roller more slowly. On the other hand, when all four photosensitive drums are in contact with the transfer belt, the tension of the transfer belt increases, causing the toner image to arrive at the transfer roller more quickly. Therefore, if a correction value for the image formation position for color mode is created using a chart printed in monochrome mode, an error will occur. Similarly, if a correction value for the image formation position for monochrome mode is created using a chart printed in color mode, an error will occur. Thus, the present invention aims to accurately obtain a correction value for the image formation position in an image forming apparatus that can switch the contact state between the image forming means and the intermediate transfer body. [Means for solving the problem]

[0006] The present invention, for example, An image forming means comprising a first image carrier on which a black image is formed, and a second image carrier on which a color image of a different color from the black image is formed, An intermediate transfer body onto which the black image and the color image are transferred, A transfer means for transferring the black image and the color image from the intermediate transfer body to a sheet, A switching means for switching the contact state between the intermediate transfer body, the first image transfer body, and the second image transfer body, including a first contact state in which the first image transfer body and the intermediate transfer body are in contact and the second image transfer body and the intermediate transfer body are separated, and a second contact state in which the first image transfer body and the intermediate transfer body are in contact and the second image transfer body and the intermediate transfer body are in contact, A receiving means for receiving instructions to perform correction control of the image formation position, When the aforementioned instruction is received by the aforementioned receiving means,Control means to control the image forming means and the switching means so as to form a first test image in the first contact state, which is used to adjust the image forming position on the sheet of the image to be formed in the first contact state, and control means to control the image forming means and the switching means so as to form a second test image in the second contact state, which is used to adjust the image forming position on the sheet of the image to be formed in the second contact state, The present invention provides an image forming apparatus equipped with the following features. [Effects of the Invention]

[0007] According to the present invention, in an image forming apparatus capable of switching the contact state between the image forming means and the intermediate transfer body, it becomes possible to accurately acquire a correction value for the image forming position. [Brief explanation of the drawing]

[0008] [Figure 1] Diagram illustrating the image formation system. [Figure 2] Diagram illustrating an image forming apparatus. [Figure 3] Diagram illustrating the contact and separation states of the transfer belt. [Figure 4] Diagram explaining the CIS unit [Figure 5] Diagram explaining test patterns [Figure 6] Diagram explaining the measurement method [Figure 7] Block diagram showing the internal controller of the printing device. [Figure 8] Block diagram showing the internal controller of the finisher. [Figure 9] Diagram explaining the settings screen. [Figure 10] A flowchart showing how to create correction values. [Figure 11] Diagram explaining the database [Figure 12] A flowchart illustrating an image formation method that includes the process of selecting correction values. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential for the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0010] (Image forming system) FIG. 1 shows an image forming system 100. The image forming system 100 includes an image forming apparatus 101 and an external controller 102. The image forming apparatus 101 and the external controller 102 are communicably connected via an internal LAN 105 and a video cable 106. LAN is an abbreviation for Local Area Network. The external controller 102 is communicably connected to a client PC 103 via an external LAN 104 and receives a print instruction from the client PC 103. PC is an abbreviation for Personal Computer.

[0011] The client PC 103 has a printer driver. The printer driver converts print data into a print description language that can be processed by the external controller 102. The user creates print data in various applications and gives a print instruction via the printer driver. The printer driver transmits the print data to the external controller 102 based on the print instruction from the user.

[0012] When the external controller 102 receives a print instruction from the client PC 103, it performs data analysis and rasterization processing. The external controller 102 inputs the print data to the image forming apparatus 101 and gives a print instruction.

[0013] The image forming apparatus 101 is configured such that devices having a plurality of different functions are connected thereto and complex printing processes such as binding are possible. In this example, the image forming apparatus 101 has a printing apparatus 107 and a finisher 109.

[0014] The printing device 107 forms an image on the sheets transported from the feeding unit located at the bottom of the printing device 107 and outputs the sheets to the finisher. The finisher 109 is a post-processing device capable of loading sheets. The finisher 109 may have a post-processing unit that performs post-processing such as sheet stack alignment, punching, and stapling.

[0015] In Figure 1, an external controller 102 is connected to the image forming apparatus 101, but this is just one example. That is, the image forming apparatus 101 may be connected to an external LAN 104 and receive print data that it can process from a client PC 103. In this case, the image forming apparatus 101 performs data analysis and rasterization. In other words, the image forming apparatus 101 may also have the functions of the external controller 102.

[0016] (Image forming apparatus) Figure 2 shows the main parts of the image forming apparatus 101. The printing apparatus 107 has feed decks 201a and 201b. In the following, lowercase letters appended to the end of reference numerals are used to distinguish identical or similar components. When describing matters common to multiple components, the lowercase letters may be omitted from the reference numerals.

[0017] Each of the feeding decks 201a and 201b can accommodate a large number of sheets. Each feeding deck 201a and 201b feeds the topmost sheet from among the multiple sheets to the transport path R1. The transport path R1 has multiple transport roller pairs 202 for transporting the sheets. As shown in Figure 2, the two connected circles represent transport roller pairs 202.

[0018] Developing stations 203a to 203d each form a toner image using colored toners Y (yellow), M (magenta), C (cyan), and K (black), respectively, and transfer it to the transfer belt 204. The transfer belt 204 rotates to transport the toner image to the secondary transfer unit 205. The secondary transfer unit 205 transfers the toner image to a sheet. The secondary transfer unit 205 is configured to transport the sheet while gripping the transfer belt 204 and the sheet with two rollers.

[0019] The operation unit 225 has a display device (e.g., a liquid crystal panel) that displays information for the printing status and settings of the image forming apparatus 101. Furthermore, the operation unit 225 has an input device (e.g., a touch sensor, keys) that receives user instructions.

[0020] Fuser units 206a and 206b fix the toner image to the sheet. Fuser units 206a and 206b are equipped with a pressure roller 217 and a heating roller 218. As the sheet passes between the pressure roller 217 and the heating roller 218, the toner melts and is pressed onto the sheet. The sheet that has passed through fuser unit 206a is transported through transport path R2 to transport path R4. Depending on the type of sheet, further melting and pressing may be required for fixing. In this case, the sheet that has passed through fuser unit 206a is transported through transport path R3 to fuser unit 206b, where additional melting and pressing are performed, and then it is transported to transport path R4.

[0021] When the printing mode is double-sided printing, the sheet with the image formed on the first side is transported to transport path R5, after which the direction of travel of the sheet is reversed. The sheet is fed from transport path R5 to transport path R6, and then transported again from transport path R6 to transport path R1. The secondary transfer unit 205 transfers the toner image to the second side of the sheet.

[0022] The transport path R4 has CIS units 207a and 207b. CIS unit 207a reads the image of the first side of the sheet. CIS unit 207b reads the image of the second side of the sheet. CIS is an abbreviation for contact image sensor.

[0023] The flapper 208 guides the sheet to either the transport path R7 or the transport path R8. Transport path R7 transports the sheet to the finisher 109. Transport path R8 transports the sheet to the discharge tray 210. Sheets discharged to the discharge tray 210 include sheets on which test images have been formed, and sheets that remained inside the printing device 107 when a jam occurred. Discharging the remaining sheets to the discharge tray 210 reduces the burden of jam handling on the user.

[0024] In this example, the finisher 109 has a stack tray 211 capable of loading a large number of sheets. Sheets transported from the printing device 107 are loaded onto the stack tray 211 via the transport path R9. The finisher 109 uses sheet sensors 212a to 212d to detect the normal passage of the sheets. If normal passage of the sheets is not detected, the finisher 109 determines that a transport jam has occurred and notifies the printing device 107 of the transport jam. As a result, any remaining sheets that were being transported inside the printing device 107 are discharged to the discharge tray 210.

[0025] (Contact / separation mechanism) The developing station 203 includes a charger for charging the photosensitive drum 301, an exposure unit for exposing the photosensitive drum 301 to create an electrostatic latent image, a developing unit for developing the electrostatic latent image with toner to form a toner image, and a transfer roller 302 for transferring the toner image to a transfer belt. The exposure unit may be located outside the developing station 203.

[0026] The printing device 107 has a monochrome mode and a full-color mode. The monochrome mode is a mode in which a toner image is formed using only black toner. The full-color mode is a mode in which a toner image is formed using each of the YMCK toners. In monochrome mode, the developing stations 203d, 203c, and 203b corresponding to YMC are not used. Therefore, in monochrome mode, the developing stations 203d, 203c, and 203b are separated from the transfer belt 204. This reduces wear on the photosensitive drums corresponding to YMC. Note that even if the developing stations 203d, 203c, and 203b are in contact with the transfer belt 204, a monochrome image can be formed using only black toner.

[0027] figure 3 (A) shows the full contact state (total contact state), as shown in the figure. 3 (B) shows the single contact state (single contact condition). 3 In (A), the transfer rollers 302a to 302d are in contact with the inner circumferential surface of the transfer belt 204, and together with the photosensitive drums 301a to 301d, they clamp the transfer belt 204. This is referred to as the full contact state. 3 In (B), the transfer rollers 302b to 302d are separated from the inner surface of the transfer belt 204. As a result, the transfer belt 204 is separated from the photosensitive drums 301b to 301d. In other words, only the photosensitive drum 301a is in contact with the transfer belt 204. This is called the single-contact state.

[0028] Motor 311 is a drive source that switches the contact state between the transfer belt 204 and the photosensitive drums 301b~301d between a contact state and a separated state. The light-shielding plate 313 is directly or indirectly connected to the rotation axis of motor 311 and is located in different places depending on whether it is in the contact state or the separated state. The light-shielding plate 313 works in cooperation with an optical HP sensor 312 to detect the contact state or the separated state. HP is an abbreviation for home position. The HP sensor 312 has a light-emitting element and a light-receiving element. In the contact state, the light output from the light-emitting element is blocked by the light-shielding plate 313 and cannot enter the light-receiving element. On the other hand, in the separated state, the light output from the light-emitting element is not blocked by the light-shielding plate 313 and can enter the light-receiving element. Therefore, the output signal of the light-emitting element in the contact state and the output signal of the light-emitting element in the separated state are clearly distinguishable signals. Therefore, the printing device 107 can distinguish between a contact state (full contact state) and a separated state (single contact state) based on the output signal (detection signal) of the HP sensor 312.

[0029] (Image reading device) As shown in Figure 4, CIS unit 207a is positioned to read the top surface of sheet P, and CIS unit 207b is positioned to read the bottom surface of sheet P. The top surface may also be called the front surface or first surface. The bottom surface may also be called the back surface or second surface. CIS unit 207 includes a light source 401 for illuminating sheet P, an image sensor 402 for reading sheet P, and a white reference plate 403. The light source 401 is a light-emitting element such as a white LED (light-emitting diode). The image sensor 402 is a CCD image sensor or a CMOS image sensor. CCD is an abbreviation for charge-coupled device. CMOS is an abbreviation for complementary metal-oxide-semiconductor. The white reference plate 403 serves as the white reference for the image read by the image sensor 402.

[0030] In this embodiment, CIS units 207a and 207b read test images formed on both sides of sheet P, respectively. When the internal temperature of the printing device 107 rises, the position of the image formed on sheet P changes compared to when the internal temperature of the printing device 107 is low. Therefore, the printing device 107 acquires the amount of change in the image formation position based on the test image reading results and adjusts the image formation position based on the acquired amount of change. This improves the accuracy of the image formation position. In particular, in this embodiment, the image formation position on the front surface of sheet P and the image formation position on the back surface of sheet P become aligned.

[0031] (Method for generating correction values ​​for image formation position) Figure 5 shows the test patterns 501a to 501d formed at the four corners of the surface 500a of sheet P, and the test patterns 502a to 502d formed at the four corners of the back surface 500b. In this example, the test patterns 501a to 501d and 502a to 502d are V-shaped patterns consisting of two line segments. The junctions (vertices) of the two line segments serve as measurement targets for the image formation position.

[0032] Figure 6(A) illustrates how to determine the image magnification correction value. The toner image transferred to sheet P is fixed to sheet P by passing through fusers 206a and 206b. During this process, sheet P is heated by fusers 206a and 206b, causing the moisture contained in sheet P to evaporate and sheet P to shrink. An image is formed on the back surface of this shrunk sheet P. After that, sheet P absorbs moisture and returns to its original size. As a result, the image on the back surface of sheet P becomes larger than the image on the front surface. Therefore, image magnification correction is necessary to match the size of the image on the front surface of sheet P with the size of the image on the back surface. Image magnification correction is achieved by reducing the size of the toner image on the back surface in advance. The degree to which it should be reduced depends on the measurement results of test patterns 501a~501d and 502a~502d.

[0033] Figure 6(A) shows, as an example, the measurement method for test patterns 501a to 501d formed on the surface 500a. The measurement method for test patterns 502a to 502d formed on the back surface 500b is the same. Therefore, in the following, test patterns 501a to 501d can be read as test patterns 502a to 502d. Arrow 600 indicates the transport direction. Here, it is assumed that the transport direction (sub-scanning direction) and the short side of sheet P are parallel. The main scanning direction is perpendicular to arrow 600, and in this example, it is parallel to the long side of sheet P.

[0034] Len(ab) is the distance between the intersection of two line segments in test pattern 501a and the intersection of two line segments in test pattern 501b. Len(bc) is the distance between the intersection of two line segments in test pattern 501b and the intersection of two line segments in test pattern 501c. In this case, the correction value CMma for the main scan magnification of surface 500a is obtained from the following formula.

[0035] CMma=Len_main / Len(ab) ···(1) Here, Len_main is the length that serves as the basis for the magnification in the main scanning direction. The correction value CMmb for the main scanning magnification of the back side 500b is also obtained by applying equation (1) to the reading result of the back side 500b. The notation method for the correction value is as follows. 1 The first letter C indicates a correction value, the second letter M indicates magnification correction, the third letter m indicates the main scanning direction, and the fourth letter a indicates the front side. Additionally, the second letter S indicates writing position correction, the third letter s indicates the sub-scanning direction, and the fourth letter b indicates the back side.

[0036] The correction value CMsa for the magnification in the sub-scanning direction of surface 500a is obtained from the following formula.

[0037] CMsa=Len_sub / Len(bc) ···(2) Here, Len_sub is the reference length for the magnification in the sub-scanning direction. The correction value CMsb for the sub-scanning magnification of the back surface 500b is also obtained by applying equation (2) to the reading result of the back surface 500b.

[0038] Figure 6(B) illustrates the method for correcting the image output position in the main scanning direction. Arrow 601 indicates the main scanning direction. Len(side-a) is the distance from the edge of sheet P in the main scanning direction to the intersection of two line segments in test pattern 501a. Len(side-b) is the distance from the edge of sheet P in the main scanning direction to the intersection of two line segments in test pattern 501b. Here, the image output position in the main scanning direction is corrected so that Len(side-a) and Len(side-b) are equal. This causes the image to be centered on sheet P in the main scanning direction. The correction value CSma for the image output position in the main scanning direction is calculated from the following formula.

[0039] CSma=(-1×(Len(side-a)-Len(side-b)) / 2)+(-1×((Len_main-Len(ab)) / 2)) ···(3) If the correction value CSma is negative, the image export position is corrected so that the export timing in the main scan direction is advanced. If the correction value CSma is positive, the image export position is corrected so that the export timing in the main scan direction is delayed. The correction value CSmb for the back side is also obtained by applying equation (3) to the reading result of the back side 500b.

[0040] figure 6(B) also shows how to determine the correction value for the image output position in the sub-scanning direction. Len(top-a) is the distance from the end (front) of sheet P in the sub-scanning direction to the intersection of two line segments in test pattern 501a. Len(tail-d) is the distance from the end (rear) of sheet P in the sub-scanning direction to the intersection of two line segments in test pattern 501d. The image output position in the sub-scanning direction is corrected so that Len(top-a) and Len(tail-d) are equal. This causes the image to be centered on sheet P in the sub-scanning direction. The correction value CSsa for the image output position of surface 500a in the sub-scanning direction can be obtained from the following formula.

[0041] CSsa=(-1×(Len(top-a)-Len(tail-b)) / 2)+(-1×(Len_sub-Len(bc)) / 2) ···(4) If the correction value CSsa is negative, the image write position is corrected so that the image write timing in the sub-scan direction becomes earlier. If the correction value CSsa is positive, the image write position is corrected so that the image write timing in the sub-scan direction becomes later. The correction value CSsb for the image write position in the sub-scan direction of the back surface 500b is also obtained by applying equation (4) to the reading result of the back surface 500b.

[0042] According to this embodiment, it is possible to align the image formation position on the surface of sheet P with the image formation position on the back surface. For example, the main scanning magnification of the surface and the main scanning magnification of the back surface will match. Also, the sub-scanning magnification of the surface and the sub-scanning magnification of the back surface will match. Furthermore, the image writing position in the main scanning direction of the surface and the image writing position in the main scanning direction of the back surface will match. Furthermore, the image writing position in the sub-scanning direction of the surface and the image writing position in the sub-scanning direction of the back surface will match. As a result, the accuracy of the image formation position is improved.

[0043] (CPU function) Figure 7 shows the internal controller of the printing device 107. The CPU 701 implements various functions according to the control program stored in the ROM (read-only memory) area of ​​the memory 702. Some or all of these functions may be implemented in hardware circuits such as ASICs or FPGAs located outside the CPU 701. This is because the program modules that constitute the control program can be implemented by logic circuits, and logic circuits can be implemented by program modules. ASIC is an abbreviation for Application Integrated Circuit. FPGA is an abbreviation for Field Programmable Gate Array. CPUs, ASICs, FPGAs, etc., may also be called processors or processing circuits.

[0044] Memory 702 has a RAM (Random Access Memory) area and temporarily stores data in the RAM area. Memory 702 may also have a high-speed image memory for processing image data. Memory 702 is an SSD (Solid State Drive) or is H It may have a DD (hard disk drive). The CPU 701 communicates with the external controller 102 or client PC 103, or with the finisher 109, via the communication circuit 703. The CPU 701 displays information on the display device of the operation unit 225 and receives instructions input from the input device of the operation unit 225.

[0045] The CPU 701 outputs image signals to the exposure unit 730 and acquires readings from the CIS units 207a and 207b. The CPU 701 also controls the developing stations 203a to 203d and the fusers 206a and 206b.

[0046] The CPU 701 controls the motor 704 to drive multiple transport roller pairs 202, or to drive the feed decks 201a and 201b. Although only one motor 704 is shown here, multiple motors may actually be used.

[0047] The test unit 710 performs various processes to determine the correction values ​​CMma, CMmb, CMsa, CMsb, CSma, CSmb, CSsa, and CSsb for the image formation position. For example, the pattern generation unit 711 generates image data for forming test patterns 501a to 501d on the surface 500a of sheet P. The pattern generation unit 711 also generates image data for forming test patterns 502a to 502d on the back surface 500b of sheet P. This image data may be data supplied to the exposure unit 730, or it may be data supplied to the exposure unit 730 via the image processing unit 722.

[0048] The measurement unit 712 acquires the reading result of the surface 500a from the CIS unit 207a and measures the position of each intersection of test patterns 501a to 501d. The measurement unit 712 acquires the reading result of the back surface 500b from the CIS unit 207b and measures the position of each intersection of test patterns 502a to 502d.

[0049] The correction value determination unit 713 determines various correction values ​​based on the measurement results output from the measurement unit 712. For example, the correction value determination unit 713 applies equations (1) to (4) to the measurement results output from the measurement unit 712 to determine various correction values. Len(ab), Len(bc), Len(side-a), Len(side-b), Len(top-a), and Len(tail-d) may be calculated in the measurement unit 712 or in the correction value determination unit 713. Fixed values ​​such as Len_main and Len_sub are stored in the ROM area of ​​the memory 702.

[0050] The correction unit 721 corrects the image formation position based on the correction value determined by the correction value determination unit 713. For example, the correction unit 721 corrects the main scan magnification and sub scan magnification by slightly scaling the image based on the correction value. The correction unit 721 corrects the image write position by adjusting the timing of supplying the image signal to the exposure unit 730 based on the correction value.

[0051] The image processing unit 722 generates an image signal by converting the color space of the image data and performing gradation correction, and supplies it to the exposure unit 730. The transport control unit 723 controls the motor 704. When the transport control unit 723 receives a jam notification from the finisher 109, it switches the flapper 208 to transport the sheet P to the discharge tray 210. The transport control unit 723 also controls the flapper 208 to transport the sheet P (test chart) with the test patterns 501 and 502 formed on it to the discharge tray 210.

[0052] The contact control unit 724 controls the motor 311 in full-color mode to achieve a full-contact state. The contact control unit 724 controls the motor 311 in monochrome mode to achieve a single-contact state. The contact control unit 724 may also confirm the completion of the transition from the full-contact state to the single-contact state and the completion of the transition from the single-contact state to the full-contact state based on the detection signal from the HP sensor 312.

[0053] The environmental sensor 760 is optional and measures the environmental conditions (e.g., temperature, humidity) inside the printing apparatus 107. The CPU 701 periodically acquires the environmental conditions and may update the correction values ​​when the amount of variation in the environmental conditions exceeds a threshold. The counter 725 counts the number of images formed. The CPU 701 may create or update correction values ​​when the count value of the counter 725 reaches a threshold.

[0054] Figure 8 shows the internal controller of the finisher 109. The CPU 801 controls the finisher 109 according to the control program stored in the memory 802. The CPU 801 communicates with the CPU 701 via the communication circuit 803. The transport control unit 811 controls the motor 805 to drive the transport roller pair provided inside the finisher 109. The jam detection unit 812 detects the occurrence of a jam inside the finisher 109 based on the detection results of the sheet sensors 212a to 212d. When the jam detection unit 812 detects the occurrence of a jam, the jam notification unit 813 issues a jam notification and transmits the jam notification to the CPU 701 via the communication circuit 803.

[0055] (User Interface) Figure 9 shows an example of the setting screens 900a to 900d displayed on the display device of the operation unit 225. As mentioned above, there are various types of sheets P. For example, even with the same basis weight, there are multiple types of sheets P with different moisture absorption states or physical properties. Such multiple types of sheets P may have different shrinkage characteristics after passing through the fusers 206a and 206b. In order to correct the image formation position on the front and back with greater accuracy, it is necessary to generate the above-mentioned correction values ​​for each type of sheet P.

[0056] The settings screen 900a has a button 901a for selecting an application mode. When the CPU 701 detects that the user has pressed button 901a, it displays the settings screen 900b on the control unit 225.

[0057] The settings screen 900b has a button 901b for registering a sheet. When the CPU 701 detects that the user has pressed button 901b, it displays the settings screen 900c on the operation unit 225.

[0058] The settings screen 900c accepts registration of sheet name, sheet size, basis weight, and sheet type (e.g., plain paper, coated paper, embossed paper). The sheet name may be a product name or a name arbitrarily chosen by the user. Furthermore, the settings screen 900c has buttons 901c to support printing test patterns 501 and 502 and creating correction values. When the CPU 701 detects that the user has operated button 901c, it displays the settings screen 900d on the operation unit 225. When button 901c is pressed, correction of the image formation position using the correction values ​​stored in memory 702 is activated.

[0059] The setting screen 900d accepts the specification of the feed deck 201 containing the sheets P on which the test patterns 501 and 502 are formed, and an instruction to start the correction. When the CPU 701 detects that the user has operated button 901d, it instructs the test unit 710 to start generating the test patterns 501 and 502 and creating the correction values.

[0060] (flowchart) Figure 10 is a flowchart showing how to create correction values ​​for each type of sheet P. Here, test images (test patterns 501, 502) are formed on N sheets P in order to improve the accuracy of determining the correction values. It is also specified via the setting screen 900d that the sheets P are fed from the feed deck 201a. When button 901d is pressed on the setting screen 900d, the CPU 701 executes the following process.

[0061] In S1001, the CPU 701 switches the print mode from monochrome mode (single contact state) to full color mode (full contact state). The CPU 701 (contact control unit 724) controls the motor 311 to switch the developing stations 203b to 203d from a separated state to a contact state.

[0062] In step S1002, the CPU 701 forms a test image on the surface 500a of sheet P. The transport control unit 723 feeds sheet P from the feed deck 201a specified by the user. The pattern generation unit 711 supplies a test image signal for surface 500a to the exposure unit 730. The exposure unit 730 exposes the photosensitive drum 301, forming an electrostatic latent image. The developing station 203 develops the electrostatic latent image with toner to form a toner image. The transfer roller 302 transfers the toner image from the photosensitive drum 301 to the transfer belt 204. The secondary transfer unit 205 transfers the toner image from the transfer belt 204 to the surface 500a of sheet P. The fuser unit 206 fixes the toner image to the surface 500a of sheet P.

[0063] In step S1003, the CPU 701 forms a test image on the back surface 500b of sheet P. The transport control unit 723 feeds sheet P back from transport path R6 to transport path R1. The pattern generation unit 711 supplies a test image signal for the back surface 500b to the exposure unit 730. The exposure unit 730 exposes the photosensitive drum 301, forming an electrostatic latent image. The developing station 203 develops the electrostatic latent image with toner to form a toner image. The transfer roller 302 transfers the toner image from the photosensitive drum 301 to the transfer belt 204. The secondary transfer unit 205 transfers the toner image from the transfer belt 204 to the back surface 500b of sheet P. The fuser unit 206 fixes the toner image to the back surface 500b of sheet P.

[0064] In S1004, the CPU 701 reads surface 500a of sheet P. For example, the CPU 701 controls the CIS unit 207a to read surface 500a of sheet P, obtains the reading result, and saves the reading result to memory 702.

[0065] In step S1005, the CPU 701 reads the back side 500b of sheet P. For example, the CPU 701 controls the CIS unit 207b to read the back side 500b of sheet P, obtains the reading result, and saves the reading result to memory 702.

[0066] In S1006, CPU 701 determines whether the reading of N sheets P is complete. If the reading of N sheets P is complete, CPU 701 proceeds to S1007. If the reading of N sheets P is not complete, CPU 701 proceeds to S1002.

[0067] In S1007, the CPU 701 determines correction values ​​for full-color mode (full-contact state). The CPU 701 (correction value determination unit 713) statistically processes (e.g., averages) the reading results obtained from N sheets P to reduce the impact of reading errors. Furthermore, the CPU 701 (correction value determination unit 713) applies equations (1) to (7) to the statistically processed reading results to determine various correction values.

[0068] In S1008, CPU701 switches the print mode from full-color mode (full contact state) to monochrome mode (single contact state). CPU701 (contact control unit 724) controls motor 311 to switch developing stations 203b~203d from contact state to separated state.

[0069] In step S1009, the CPU 701 forms a test image on the surface 500a of sheet P. The transport control unit 723 feeds sheet P from the feed deck 201a specified by the user. The pattern generation unit 711 supplies a test image signal for surface 500a to the exposure unit 730. The exposure unit 730 exposes the photosensitive drum 301, forming an electrostatic latent image. The developing station 203 develops the electrostatic latent image with toner to form a toner image. The transfer roller 302 transfers the toner image from the photosensitive drum 301 to the transfer belt 204. The secondary transfer unit 205 transfers the toner image from the transfer belt 204 to the surface 500a of sheet P. The fuser unit 206 fixes the toner image to the surface 500a of sheet P.

[0070] In step S1010, the CPU 701 forms a test image on the back surface 500b of sheet P. The transport control unit 723 feeds sheet P back from transport path R6 to transport path R1. The pattern generation unit 711 supplies a test image signal for the back surface 500b to the exposure unit 730. The exposure unit 730 exposes the photosensitive drum 301, forming an electrostatic latent image. The developing station 203 develops the electrostatic latent image with toner to form a toner image. The transfer roller 302 transfers the toner image from the photosensitive drum 301 to the transfer belt 204. The secondary transfer unit 205 transfers the toner image from the transfer belt 204 to the back surface 500b of sheet P. The fuser unit 206 fixes the toner image to the back surface 500b of sheet P.

[0071] In step S1011, the CPU 701 reads surface 500a of sheet P. For example, the CPU 701 controls the CIS unit 207a to read surface 500a of sheet P, obtains the reading result, and saves the reading result to memory 702.

[0072] In S1012, the CPU 701 reads the back side 500b of sheet P. For example, the CPU 701 controls the CIS unit 207b to read the back side 500b of sheet P, obtains the reading result, and saves the reading result to memory 702.

[0073] In S1013, the CPU 701 determines whether the reading of M sheets P is complete. If the reading of M sheets P is complete, the CPU 701 proceeds to S1014. If the reading of M sheets P is not complete, the CPU 701 proceeds to S1009. Note that N and M may be the same or different. N and M may be specified or selected by the user through the operation unit 225.

[0074] In S1014, the CPU 701 determines correction values ​​for monochrome mode (single contact state). The CPU 701 (correction value determination unit 713) statistically processes (e.g., averages) the reading results obtained from M sheets P to reduce the influence of reading errors. Furthermore, the CPU 701 (correction value determination unit 713) applies equations (1) to (7) to the statistically processed reading results to determine various correction values.

[0075] In S1015, CPU701 registers the correction value in association with the identification information of sheet P. In other words, the correction value is written to the ROM area of ​​memory 702.

[0076] (Database) Figure 11 shows an example of record 1100 in a database that manages correction values. This database is stored in memory 702, and records 1100 are added or updated in S1015. The database may also be stored in a storage server located outside the image forming apparatus 101, such as an external controller 102.

[0077] Field 1101 stores the media ID. This is a type of identification information used to identify sheet P. Field 1101 also functions as an ID to identify record 1100.

[0078] Field 1102 stores the name of sheet P registered by the user through the settings screen 900c. Field 1103 stores the main scanning direction length of sheet P registered by the user through the settings screen 900c. Field 1104 stores the sub-scanning direction length of sheet P registered by the user through the settings screen 900c. Field 1105 stores the type of sheet P registered by the user through the settings screen 900c (e.g., plain paper, coated paper, embossed paper, etc.). Field 1106 stores the basis weight of sheet P registered by the user through the settings screen 900c.

[0079] Fields 1107 to 1114 store the correction values ​​for the full-contact state (full-color mode). In particular, fields 1107 to 1110 store the correction value CS for the write position. Fields 1111 to 1114 store the correction value CM for the magnification. Field 1107 stores the correction value CSma for the front surface in the main scanning direction. Field 1108 stores the correction value CSsa for the front surface in the sub-scanning direction. Field 1109 stores the correction value CSmb for the back surface in the main scanning direction. Field 1110 stores the correction value CSsb for the back surface in the sub-scanning direction. Field 1111 stores the correction value CMma for the front surface in the main scanning direction. Field 1112 stores the correction value CMsa for the front surface in the sub-scanning direction. Field 1113 stores the correction value CMmb for the back surface in the main scanning direction. Field 1114 stores the correction value CMsb for the back surface in the sub-scanning direction.

[0080] Fields 1115 to 1122 store the correction values ​​for the single-contact state (monochrome mode). In particular, fields 1115 to 1118 store the correction value CS for the write position. Fields 1119 to 1122 store the correction value CM for the magnification. Field 1115 stores the correction value CSma for the front surface in the main scanning direction. Field 1116 stores the correction value CSsa for the front surface in the sub-scanning direction. Field 1117 stores the correction value CSmb for the back surface in the main scanning direction. Field 1118 stores the correction value CSsb for the back surface in the sub-scanning direction. Field 1119 stores the correction value CMma for the front surface in the main scanning direction. Field 1120 stores the correction value CMsa for the front surface in the sub-scanning direction. Field 1121 stores the correction value CMmb for the back surface in the main scanning direction. Field 1122 stores the correction value CMsb for the back surface in the sub-scanning direction.

[0081] (Correction method) Figure 12 is a flowchart showing how to select correction values ​​according to the print mode. When the user instructs image formation from the client PC 103 or the operation unit 225, the CPU 701 executes the following processes.

[0082] In S1201, CPU 701 determines whether the print target is a color image. CPU 701 determines this by analyzing the image data or the contents of the printing press. If the print target is a color image, CPU 701 proceeds to S1202. S120 2The CPU 701 then sets the developing stations 203b to 203d to a full-contact state. For example, the CPU 701 (contact control unit 724) controls the motor 311 to switch the developing stations 203b to 203d from a separated state to a contact state. After that, the CPU 701 proceeds to process S1203. If the print target is a monochrome image, the CPU 701 proceeds to process S1211. In S1211, the CPU 701 sets the developing stations 203b to 203d to a single-contact state. For example, the CPU 701 (contact control unit 724) controls the motor 311 to switch the developing stations 203b to 203d from a contact state to a separated state. After that, the CPU 701 proceeds to process S1203.

[0083] In S1203, the CPU 701 determines whether correction of the front and back image formation positions is effective. For example, if button 901c has been pressed down beforehand, the CPU 701 determines that correction of the front and back image formation positions is effective and proceeds to S1204. If button 901c has not been pressed down beforehand, the CPU 701 determines that correction of the front and back image formation positions is not effective and proceeds to S1207. Button 901c is a type of toggle switch. Alternatively, whether correction is effective or ineffective may be determined based on whether correction values ​​are stored in fields 1107 to 1122 of the database held in memory 702.

[0084] In S1204, the CPU 701 determines whether the developing stations 203b to 203d are in a full-contact state. For example, the CPU 701 may perform the same determination as in S1201. Alternatively, the CPU 701 may determine whether the developing stations 203b to 203d are in a full-contact state based on the detection result of the HP sensor 312. If the developing stations 203b to 203d are in a full-contact state, the CPU 701 proceeds to S1205. In S1205, the CPU 701 reads the correction values ​​for the full-contact state from the memory 702. That is, the correction values ​​are read from the fields 1107 to 1114 corresponding to the type of sheet P, identification information, and record specified by the user, and set in the correction unit 721.

[0085] If developing stations 203b to 203d are in a single-contact state, the CPU 701 proceeds to S1221. In S1221, the CPU 701 reads correction values ​​for the single-contact state from memory 702. Specifically, correction values ​​are read from fields 1115 to 1122 corresponding to the type of sheet P, identification information, and record specified by the user, and set in the correction unit 721.

[0086] In S1206, CPU 701 corrects the image formation position according to the read correction value. This appropriately corrects the image output position and magnification. In S1207, CPU 701 performs image formation.

[0087] In S1208, CPU701 determines whether all printing is complete based on the print job. If not all printing is complete, CPU701 proceeds to S1201. If all printing is complete, CPU701 terminates the series of processes.

[0088] In single-contact mode, black test patterns 501 and 502 can be formed, but in full-contact mode, any of the YMCK test patterns 501 and 502 can be formed. Therefore, in full-contact mode, the four YMCK test patterns 501 and 502 may be formed on a single sheet P without overlapping. Alternatively, the four YMCK test patterns 501 and 502 may be formed on different sheets P. Alternatively, the measurement values ​​obtained using one of the test patterns 501 or 502 may be used as the measurement values ​​for the remaining three colors.

[0089] <Technical concepts derived from examples> [Perspective 1] A first image forming means that forms a toner image using a first color toner, A second image forming means for forming a toner image using a toner of a different color from the first color, An intermediate transfer body is arranged facing the first image forming means and the second image forming means, A switching means for switching the second image forming means and the intermediate transfer body between a contact state and a separated state, A transfer means for transferring a toner image from the intermediate transfer body to a sheet, Fixing means for fixing the toner image onto the sheet, A reading means for reading the first and second sides of the aforementioned sheet, An acquisition means for acquiring a correction value for the image formation position on the sheet based on the reading result of the sheet by the reading means, The system includes a correction means for correcting the image formation position on the sheet based on the correction value obtained by the acquisition means, In the first mode, in which the first image forming means and the intermediate transfer body are brought into contact, and the second image forming means and the intermediate transfer body are brought into contact, to form a toner image on the sheet, test images are formed on the first and second surfaces of the sheet, respectively, the reading means generates the reading result of the test image on the first surface and the reading result of the second surface, and the acquisition means acquires a correction value for the image forming position on the first surface for the first mode based on the reading result of the test image on the first surface, and a correction value for the image forming position on the second surface for the first mode based on the reading result of the test image on the second surface. In the second mode, in which the first image forming means and the intermediate transfer body are brought into contact and the second image forming means and the intermediate transfer body are separated to form a toner image on the sheet, the test image is formed on the first surface and the second surface of the sheet, respectively, the reading means generates the reading result of the test image on the first surface and the reading result of the second surface, and the acquisition means acquires a correction value for the image forming position on the first surface for the second mode based on the reading result of the test image on the first surface, and a correction value for the image forming position on the second surface for the second mode based on the reading result of the test image on the second surface. In the first mode, the correction means corrects the image formation position on the first surface based on the correction value for the image formation position on the first surface for the first mode, and corrects the image formation position on the second surface based on the correction value for the image formation position on the second surface for the first mode. An image forming apparatus characterized in that, in the second mode, the correction means corrects the image forming position on the first surface based on the correction value of the image forming position on the first surface for the second mode, and corrects the image forming position on the second surface based on the correction value of the image forming position on the second surface for the second mode.

[0090] The developing station 203a is an example of the first image forming means. The developing stations 203b to 203d are examples of the second image forming means. The transfer belt 204 is an example of an intermediate transfer body. The motor 311 is an example of a switching means. The secondary transfer unit 205 is an example of a transfer means. The fuser 206 is an example of a fixing means. The CIS unit 207 is an example of a reading means for reading the first and second surfaces of the sheet P. The CPU 701 and test unit 710 are examples of acquisition means. The CPU 701 and correction unit 721 are examples of correction means. The full-color mode (full contact state) is an example of the first mode. The monochrome mode (single contact state) is an example of the second mode.

[0091] According to perspective 1, a correction value is acquired for each operating mode, and the correction value corresponding to the operating mode actually used is read out to correct the image formation position. Therefore, in an image forming apparatus that can switch the contact state between the image forming means and the intermediate transfer body, it becomes possible to acquire the correction value of the image formation position with high accuracy.

[0092] [Perspective 2] The image forming apparatus according to viewpoint 1, characterized in that the acquisition means acquires the correction value so that the image forming position on the first surface and the image forming position on the second surface are aligned.

[0093] This will make it easier to align the image formation positions on the surface with those on the back surface.

[0094] [Perspective 3] In the first mode, the reading means obtains the reading result of the test image on the first side and the reading result of the test image on the second side from N sheets. The image forming apparatus according to viewpoint 1 or 2, characterized in that the acquisition means acquires, in the first mode, the correction value for the image forming position on the first surface for the first mode and the correction value for the image forming position on the second surface for the first mode, based on the reading result of the test image on the first surface and the reading result of the test image on the second surface acquired from the N sheets.

[0095] This should improve the accuracy of the correction values ​​for the first mode.

[0096] [Perspective 4] In the second mode, the reading means obtains the reading result of the test image on the first side and the reading result of the test image on the second side from M sheets. The image forming apparatus according to viewpoint 3, characterized in that the acquisition means acquires, in the second mode, the correction value for the image forming position on the first surface for the second mode and the correction value for the image forming position on the second surface for the second mode, based on the reading result of the test image on the first surface and the reading result of the test image on the second surface acquired from the M sheets.

[0097] This should improve the accuracy of the correction values ​​for the second mode.

[0098] [Perspective 5] The image forming apparatus according to viewpoint 4, characterized in that the N sheets and the M sheets are the same value.

[0099] This would make it possible to unify the calculation process for the correction values ​​for the first mode and the second mode.

[0100] [Perspective 6] The image forming apparatus according to viewpoint 4, characterized in that the N sheets and the M sheets are different values.

[0101] There may be modes that require more samples than the first mode. In this case, it would be possible to change the number of samples for each mode.

[0102] [perspective 7] The correction value for the image formation position is The correction value for the image output position in a first direction parallel to the conveying direction of the sheet, The correction value for the image output position in a second direction perpendicular to the conveying direction of the sheet, The correction value for the image magnification in the first direction, The correction value for the image magnification in the second direction, An image forming apparatus according to any one of views 1 to 6, characterized by including at least one of the following.

[0103] Here, the sub-scanning direction is an example of the first direction. The main scanning direction is an example of the second direction. Furthermore, the correction value may include a correction value for the write position or a correction value for the magnification. This will allow the write position or magnification to be corrected accurately for each contact state.

[0104] [Perspective 8] The system further includes a storage means for storing the correction value for the first mode and the correction value for the second mode in association with the identification information of the sheet. The image forming apparatus according to any one of views 1 to 7, characterized in that the correction means reads a correction value corresponding to the identification information specified by the user from the storage means, which is a correction value for the mode specified by the user among the first mode and the second mode, and corrects the image forming position based on the read correction value.

[0105] As explained in relation to Figure 11, the appropriate correction value may differ depending on the type of sheet P. Therefore, by managing the correction value in association with the identification information of sheet P, it will be possible to correct the image formation position more appropriately.

[0106] [Perspective 9] The aforementioned identification information is The identification number (e.g., ID) assigned to the aforementioned sheet, The name assigned to the aforementioned sheet, Size information indicating the size of the sheet (e.g., length in the main scanning direction, length in the sub-scanning direction), Information indicating the surface treatment applied to the aforementioned sheet (e.g., presence or absence of coating, presence or absence of embossing), and Basis weight of the aforementioned sheet The image forming apparatus according to viewpoint 8, characterized in that it includes at least one of the following.

[0107] This makes it possible to manage various pieces of information that characterize Sheet P in association with correction values. In other words, it will be possible to obtain and use appropriate correction values ​​according to a more detailed classification of Sheet P.

[0108] [Perspective 10] The system further includes a receiving means (e.g., an operation unit 225) for receiving an input of an instruction indicating whether or not to perform the correction of the image formation position, The image forming apparatus according to any one of views 1 to 9, characterized in that the correction means performs correction of the image forming position based on the correction value when an instruction to perform correction of the image forming position is input, and does not perform correction of the image forming position using the correction value when an instruction to not perform correction of the image forming position is input.

[0109] As illustrated with Figure 9, the user may be instructed whether or not to perform the correction via the settings screen 900c. This will allow the correction to be performed or skipped according to the user's preference. For example, for users who are not concerned with the misalignment of the image formation positions on the front and back sides, this will offer the advantage of reduced consumption of test image sheets P and toner. In addition, the period during which the image forming apparatus 101 is temporarily unavailable for creating correction values ​​will be reduced.

[0110] [Perspective 11] The image forming apparatus according to viewpoint 10, characterized in that the correction means determines that an instruction has been received to perform correction of the image forming position when double-sided printing is instructed, and determines that an instruction has been received to not perform correction of the image forming position when single-sided printing is instructed.

[0111] Thus, double-sided / single-sided printing may be associated with whether or not correction is performed, because single-sided printing is independent of the misalignment of the image formation positions on the front and back sides.

[0112] [Perspective 12] The first image forming means has a first image carrier that carries the toner image of the first color, The second image forming means includes a second image carrier that carries a second-color toner image, a third image carrier that carries a third-color toner image, and a fourth image carrier that carries a fourth-color toner image. In the first mode, the first image carrier, the second image carrier, the third image carrier, and the fourth image carrier all come into contact with the intermediate transfer body. The image forming apparatus according to any one of views 1 to 11, characterized in that, in the second mode, the first image carrier is in contact with the intermediate transfer body, and the second image carrier, the third image carrier, and the fourth image carrier are all separated from the intermediate transfer body.

[0113] As shown in Figure 2, viewpoints 1 to 11 may be applied to an image forming apparatus 101 that forms an image on a sheet P using YMCK toner. However, the above-described embodiment is applicable to any image forming apparatus that uses two or more toners and has multiple different contact states.

[0114] [Perspective 13] The image forming apparatus according to any one of views 1 to 12, characterized in that the test image includes at least four reference images (e.g., test patterns 501, 502) indicating a reference position relative to the sheet.

[0115] As illustrated in Figure 5, at least four reference images may be formed on sheet P, and their positions may be measured.

[0116] [Perspective 14] The image forming apparatus according to viewpoint 13, characterized in that the at least four reference images are formed at the four corners of the sheet.

[0117] As illustrated in Figure 5, reference images may be formed at the four corners of sheet P. This will allow for accurate acquisition of measured values ​​of the image formation positions.

[0118] [Perspective 15] It further includes measuring means for measuring environmental conditions (e.g., environmental sensor 760), The image forming apparatus according to any one of views 1 to 14, characterized in that when the environmental conditions measured by the measuring means satisfy the conditions for acquiring the correction value, the process for acquiring the correction value is executed.

[0119] When the environmental conditions of the image forming apparatus 101 change significantly, the image formation position is likely to shift. Therefore, when the environmental conditions change, the correction value may be reacquired and updated.

[0120] [Perspective 16] The image forming apparatus according to viewpoint 15, characterized in that the environmental conditions include the internal temperature of the image forming apparatus.

[0121] The internal temperature of the image forming apparatus 101 affects the expansion and contraction state of the transfer belt 204. Therefore, if the internal temperature changes significantly, the correction value may be updated.

[0122] [Perspective 17] The system further includes a counting means (e.g., CPU 701) for counting the number of images formed, The image forming apparatus according to any one of views 1 to 14, characterized in that when the number of images formed by the counting means satisfies the conditions for acquiring the correction value, the process for acquiring the correction value is executed.

[0123] Here, the number of images formed may be a long-term cumulative value or a short-term cumulative value. A long-term cumulative value may be the number of images formed that correlates with the lifespan of the transfer belt 204. A short-term cumulative value may be the number of sheets P on which images are continuously formed. Both of these affect the image formation position. The CPU 701 may count the number of images formed, and when the count value reaches a threshold, it may acquire a correction value. This will make it possible to maintain the accuracy of the correction value.

[0124] [Perspective 18] The system further includes, together with the second image forming means, a transfer roller arranged to hold the intermediate transfer belt, which is the intermediate transfer body, The aforementioned switching means is By moving the transfer roller away from the second image forming means, the second image forming means and the intermediate transfer body are transitioned from the contact state to the separated state. The image forming apparatus according to any one of views 1 to 17, characterized in that the transfer roller is brought closer to the second image forming means to transition the second image forming means and the intermediate transfer body from the separated state to the contact state.

[0125] As explained in relation to Figure 3, the change in contact state may be achieved by the movement of the transfer rollers 302b to 302d. This would simplify the required mechanism. Note that the movement of the transfer rollers 302b to 302d is relative. Therefore, the second image forming means may also move.

[0126] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention. [Explanation of Symbols]

[0127] 203: Developing station, 204: Transfer belt, 311: Motor, 205: Secondary transfer unit, 206: Fuser, 207: CIS unit, 701: CPU

Claims

1. An image forming means comprising a first image carrier on which a black image is formed, and a second image carrier on which a color image of a different color from the black image is formed, An intermediate transfer body onto which the black image and the color image are transferred, A transfer means for transferring the black image and the color image from the intermediate transfer body to a sheet, A switching means for switching the contact state between the intermediate transfer body, the first image transfer body, and the second image transfer body, including a first contact state in which the first image transfer body and the intermediate transfer body are in contact and the second image transfer body is separated, and a second contact state in which the first image transfer body and the intermediate transfer body are in contact and the second image transfer body is in contact. A receiving means for receiving instructions to perform correction control of the image formation position, When the receiving means receives the instruction, the control means controls the image forming means and the switching means to form a first test image in the first contact state, which is used to adjust the image forming position on the sheet of the image to be formed in the first contact state, and controls the image forming means and the switching means to form a second test image in the second contact state, which is used to adjust the image forming position on the sheet of the image to be formed in the second contact state. An image forming apparatus equipped with the following features.

2. A reading means for reading the test image on the sheet, The system further comprises an adjustment means for adjusting the image formation position on a sheet of the image to be formed by the image forming means, The adjustment means adjusts the image formation position on the sheet of the image to be formed in the first contact state based on the reading result of the first test image read by the reading means. The adjustment means adjusts the image formation position on the sheet of the image to be formed in the second contact state, based on the reading result of the second test image read by the reading means. The image forming apparatus according to claim 1.

3. It also includes a tray from which the sheets are ejected. The image forming apparatus according to claim 2, wherein the reading means reads the test image on the sheet while transporting the sheet from the image forming means toward the tray.

4. The system further comprises fixing means for fixing the test image transferred by the transfer means onto the sheet, The image forming apparatus according to claim 2, wherein the reading means reads the test image on the sheet downstream of the fixing means in the direction in which the sheet is transported.

5. The image forming apparatus according to claim 1, wherein the image forming position includes a position where writing of the image to be formed begins.

6. The image forming apparatus according to claim 1, wherein the image forming position includes the magnification of the image to be formed.

7. The image forming means forms the image based on the image data. The image forming apparatus according to claim 1, wherein the switching means switches the contact state based on the image data.

8. The first test image above shows marks formed on both sides of the sheet. The image forming apparatus according to claim 1, wherein the second test image is a mark formed on both sides of a sheet.

9. The image forming apparatus according to claim 1, wherein both the first test image and the second test image are black marks.

10. The image forming apparatus according to claim 1, wherein the first test image has a V-shaped mark.

Images