Image formation apparatus

Abstract

To correct magnification deviation of a toner image.SOLUTION: An image formation apparatus 100 comprises: an image forming unit 105 that forms a toner image on an intermediate transfer belt 113; a secondary transfer unit 117 that transfers the toner image formed on the intermediate transfer belt 113 onto a sheet; a current detection unit 127 that detects a transfer current value when the toner image is transferred by the secondary transfer unit 117; an image reader 102 that reads an image fixed on the sheet; and a CPU 128 that measures the size of the image on the basis of a reading result of the image reader 102. The CPU 128 obtains a relationship between the transfer current value detected by the current detection unit 127 and the magnification of the image derived from the size of the image fixed on the sheet, and adjusts the size of an image to be formed on the basis of the relationship when forming the image based on a print job.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Image forming devices have an image position adjustment function to correct the image size (magnification of the toner image). By adjusting the image position, it is possible to align the magnification of the toner image between multiple sheets of paper and between both sides of a single sheet of paper. Patent Document 1 discloses an image forming device that measures the current value of the transfer current flowing through the paper during transfer and calculates the magnification of the toner image based on the measured current value so that the magnification of the toner image on both sides of the paper is consistent. Paper absorbs moisture when the ambient humidity is high and releases moisture when the humidity is low. Paper expands and contracts with changes in the amount of moisture it contains, and its electrical resistance also changes. Therefore, Patent Document 1 discloses that the amount of expansion and contraction of the paper can be estimated from the current value of the transfer current to determine the magnification of the toner image. This image forming device can print an image with its magnification corrected on both sides of the paper based on the magnification of the toner image. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-139428 Summary of the Invention [Problem to be solved by the invention]

[0004] When an image forming device prints the same image on multiple sheets of paper, the paper may expand or contract due to changes in the amount of moisture contained in the paper caused by changes in environmental humidity. By placing multiple sheets of paper in the same environment after printing, the amount of expansion or contraction becomes approximately the same. If the amount of expansion or contraction differs during printing and becomes approximately the same after printing, the same image printed on multiple sheets of paper will end up being different sizes on each sheet.

[0005] Furthermore, in image forming devices that heat paper when fixing an image, such as electrophotographic devices, the moisture contained in the paper evaporates when heated during fixing, causing the paper to shrink. Therefore, when performing double-sided printing, the paper shrinks when heated when an image is printed on the first side. The image printed on the paper also shrinks. When an image is printed on the second side, which is different from the first side, the image is printed on the shrunk paper. As a result, even when images of the same size are printed, the image on the second side is formed relatively larger than the image on the first side, and the magnification of the toner image changes between the first and second sides.

[0006] Since the amount of moisture contained in paper changes due to changes in environmental humidity, etc., it is preferable to adjust the image position for each print job. However, adjusting the image position for each print job is a cumbersome task for the user. The image forming apparatus of Cited Document 1 automatically adjusts the image position, improving user convenience. The image forming apparatus of Cited Document 1 aims to make the magnifications of the toner images on the first and second sides the same as those that occur during double-sided printing, and is capable of correcting the relative magnification discrepancy between the front and back sides. However, the image forming apparatus of Cited Document 1 has difficulty correcting the magnification discrepancy that occurs when the environmental humidity changes between jobs.

[0007] In view of the above-mentioned problems, an object of the present invention is to correct deviations in the magnification of a toner image even when the environmental humidity changes between jobs. [Means for solving the problem]

[0008] The image forming apparatus of the present invention is characterized by comprising an image forming means for forming an image on an image carrier, a transfer means for transferring the image formed on the image carrier to paper, a fixing means for fixing the image to the paper, a current detection means for detecting the transfer current value when the image is transferred by the transfer means, a reading means for reading the image fixed to the paper, a measuring means for measuring the size of the image fixed to the paper based on the reading result by the reading means, and a control means for obtaining the relationship between the transfer current value detected by the current detection means and the magnification of the image obtained from the size of the image fixed to the paper, and adjusting the size of the image to be formed based on the relationship when forming an image based on a print job. [Effects of the Invention]

[0009] According to the present invention, it is possible to correct the deviation in magnification of a toner image. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. [Figure 2] A simplified diagram of the controller. [Figure 3] 10 is a flowchart showing an image position adjustment process. [Figure 4] FIG. 10 is a diagram illustrating an example of an adjustment image. [Figure 5] 10 is a flowchart showing an image position adjustment process. [Figure 6] 10A and 10B are diagrams illustrating the relationship between the amount of expansion and contraction of paper relative to the amount of moisture and the transfer current value. [Figure 7] FIG. 4 is a diagram illustrating the relationship between the transfer current value and the magnification of a toner image. [Figure 8] 10 is a flowchart showing a single-sided printing process. [Figure 9] 10 is a flowchart showing a double-sided printing process. [Figure 10] 10 is a flowchart showing a double-sided printing process. [Figure 11] 10 is a flowchart showing an image position adjustment process. [Figure 12]10 is a flowchart showing an image position adjustment process. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following detailed description of preferred embodiments of the present invention will be given with reference to the accompanying drawings. The technical scope of the present invention is defined by the claims and is not limited to the following individual embodiments.

[0012] (First embodiment) FIG. 1 is a diagram showing the configuration of an image forming apparatus according to this embodiment. The image forming apparatus 100 according to this embodiment includes a printing device 101 and an automatic document image reading device 106. In this embodiment, the printing device 101 is described as being capable of printing full-color images, but it may also be configured to print monochrome images. In addition, in this embodiment, the printing device 101 is described as being of an intermediate transfer type, but other types that do not use an intermediate transfer body may also be used. The automatic document image reading device 106 includes an image reading device 102 that reads an image (document image) formed on a document, and an automatic document feeder (ADF) 103 that automatically feeds the document.

[0013] The image reading device 102 is provided above the printing device 101, and the ADF 103 is provided above the image reading device 102. A platen glass 108 on which an original can be placed is provided between the image reading device 102 and the ADF 103 above the image reading device 102. The image reading device 102 is equipped with a sensor unit 107 that reads the original image. The ADF 103 automatically transports the original to a reading position by the sensor unit 107. The sensor unit 107 irradiates light onto the original placed on the platen glass 108 or the original transported by the ADF 103, and reads the original image by receiving the reflected light. The image reading device 102 generates image data representing the read original image.

[0014] The printing device 101 is equipped with multiple image forming units, each used to form a different color image, in order to form a full-color image. In this embodiment, four image forming units 105Y, 105M, 105C, and 105K are provided to form images of four colors (black (K), cyan (C), magenta (M), and yellow (Y)). The image forming units 105Y, 105M, 105C, and 105K have the same configuration and form images by the same operation, but differ only in the color of the images they form. The suffixes Y, M, C, and K at the end of the reference numbers indicate the corresponding colors. When it is not necessary to distinguish between colors, the suffixes Y, M, C, and K at the end of the reference numbers are omitted. The same applies to other components.

[0015] The image forming unit 105 includes a photoconductor 110, a charging unit 111, and a developing unit 112. A laser scanner 109 is disposed above the image forming unit 105. The photoconductor 110 is a drum-shaped image carrier having a photosensitive layer on its surface. The photoconductor 110 rotates around the drum axis. The charging unit 111 uniformly charges the surface of the rotating photoconductor 110.

[0016] The laser scanner 109 irradiates the charged surface of the photoconductor 110 with laser light modulated based on image data acquired from an external device or the image reading device 102. The laser scanner 109 scans the surface of the rotating photoconductor 110 with the laser light, with the drum axis direction being the main scanning direction. As a result, an electrostatic latent image corresponding to the image data is formed on the surface of the photoconductor 110.

[0017] The developing unit 112 develops the electrostatic latent image with a developer (toner in this case) of the corresponding color to form an image (toner image in this case) on the surface of the photoconductor 110. A yellow toner image is formed on the photoconductor 110Y of the image forming unit 105Y. A magenta toner image is formed on the photoconductor 110M of the image forming unit 105M. A cyan toner image is formed on the photoconductor 110C of the image forming unit 105C. A black toner image is formed on the photoconductor 110K of the image forming unit 105K.

[0018] The toner images of each color formed on each photoconductor 110 of each image forming unit 105 are transferred to an intermediate transfer belt 113. The intermediate transfer belt 113 is an image carrier made up of an endless belt member. The intermediate transfer belt 113 is stretched over multiple rollers including a secondary transfer opposing roller 115, and rotates in the direction from image forming unit 105Y to image forming unit 105K. A primary transfer roller 114 is disposed opposite each photoconductor 110, with the intermediate transfer belt 113 sandwiched between them.

[0019] Each primary transfer roller 114 transfers a toner image from the corresponding photoconductor 110 to the intermediate transfer belt 113 at a timing that corresponds to the interval between the photoconductors 110 in each image forming unit 105 and the rotation speed of the intermediate transfer belt 113. The primary transfer roller 114 transfers the toner image by applying a primary transfer bias (primary transfer voltage), which is a DC voltage of opposite polarity to the charge polarity of the toner. As a result, the toner images of each color are transferred onto the intermediate transfer belt 113 in a superimposed manner. Note that any toner remaining on the photoconductor 110 after transfer is removed by a cleaner (not shown).

[0020] A secondary transfer roller 116 is disposed at a position opposite to the secondary transfer opposing roller 115 across the intermediate transfer belt 113. The secondary transfer opposing roller 115 and the secondary transfer roller 116 constitute a secondary transfer unit 117. The intermediate transfer belt 113 carries the transferred toner images of each color and conveys the toner images of each color to the secondary transfer unit 117 by rotating.

[0021] The secondary transfer unit 117 transfers the toner images of each color carried by the intermediate transfer belt 113 onto the paper all at once. At this time, a secondary transfer bias (secondary transfer voltage), which is a DC voltage of opposite polarity to the charge polarity of the toner, is applied to the secondary transfer roller 116. As a result, the toner image on the intermediate transfer belt 113 is attracted to the secondary transfer roller 116 and transferred onto the paper that has been transported to the secondary transfer unit 117.

[0022] Paper is fed from paper feed units 104a to 104c. Paper feed units 104a and 104b are provided at the bottom of printing device 101. Paper feed unit 104c is provided on the side of printing device 101. Paper is stored in the bottom paper feed units 104a and 104b. Paper is manually loaded into side paper feed unit 104c. Paper from bottom paper feed units 104a and 104b is fed by paper feed rollers 118a and 118b and transported along the transport path. Paper from side paper feed unit 104c is fed by paper feed roller 118c and transported along the transport path. Registration rollers 119 are provided on the transport path. Registration rollers 119 correct the skew of the paper and transport the paper to secondary transfer unit 117 in accordance with the timing at which the toner image carried on intermediate transfer belt 113 is transported to secondary transfer unit 117. By adjusting the timing, the toner image is transferred to a predetermined position on the paper.

[0023] The paper onto which the toner image has been transferred by secondary transfer unit 117 is transported by conveyor belt 120 to fixing unit 121. Fixing unit 121 includes fixing roller 121a, which contains heater 121c, which serves as a heat source, and pressure roller 121b. The paper is nipped and transported between fixing roller 121a and pressure roller 121b. At this time, fixing roller 121a heats the paper with heat from heater 121c. Pressure roller 121b is urged toward fixing roller 121a and applies pressure to the paper. The toner image melts when heated, and the melted toner image is fixed when pressure is applied. In this way, the toner image is fixed to the paper.

[0024] A discharge conveying path 131 and a reversing path 132 are provided downstream of the fixing unit 121 in the paper conveying direction. The discharge conveying path 131 is a conveying path that conveys the paper to discharge rollers 122 for discharging the paper from the printing device 101. The reversing path 132 is a conveying path that has reversing rollers 123 for reversing the paper conveying direction when printing on both sides. A reversing flapper 124 is provided at the branch point between the discharge conveying path 131 and the reversing path 132. The reversing flapper 124 guides the paper to either the discharge conveying path 131 or the reversing path 132.

[0025] After printing on the first side during double-sided printing, the paper is guided to a reversing path 132 for image formation on the second side, which is the opposite side to the first side. The paper guided to the reversing path 132 has its conveying direction reversed by a reversing roller 123, and is conveyed to a double-sided conveying path 133 for returning to the secondary transfer unit 117. By being conveyed through the reversing path 132 and the double-sided conveying path 133, the side on which the image is printed (printing side) of the paper is reversed from the first side to the second side. After printing on one side during single-sided printing or after printing on both sides during double-sided printing, the paper is guided to an ejection conveying path 131 and is ejected outside the machine by an ejection roller 122. The ejected paper is stacked on an ejection tray 125.

[0026] 2 is a simplified diagram of a controller 1000 that controls the operation of the image forming apparatus 100 configured as described above. Here, a configuration for controlling the operation of the image reading device 102, the secondary transfer unit 117, and the fixing unit 121 will be described, but the controller 1000 is also used to control the operation of other components within the image forming apparatus 100.

[0027] The controller 1000 is an information processing device that includes a CPU (Central Processing Unit) 128, a ROM (Read Only Memory) 129, and a RAM (Random Access Memory) 130. The CPU 128 controls the operation of the image forming apparatus 100 by executing a control program stored in the ROM 129. The ROM 129 stores in advance computer programs such as the control program as well as data tables such as setting values ​​required for various controls. The RAM 130 provides a working area for the CPU 128 when it executes processing. The RAM 130 provides a temporary storage area for input information (various data such as the number of prints that changes for each job), detected information, calculation results, etc.

[0028] The CPU 128 is electrically connected to the image reading device 102, the secondary transfer unit 117, and the fixing unit 121. The secondary transfer unit 117 has a secondary transfer power supply 126 for applying a secondary transfer bias to the secondary transfer roller 116, and a current detection unit 127 for detecting the value of the current (transfer current value) flowing through the secondary transfer roller 116.

[0029] Such an image forming apparatus 100 has an image position adjustment function that corrects the size of an image (magnification of a toner image). Image position adjustment will now be described. FIG. 3 is a flowchart showing the image position adjustment process. This process is started when a double-sided print job for a test chart is instructed from an external device or a user interface (not shown). The test chart is a sheet of paper on which an image for adjusting image position (adjustment image) is printed.

[0030] CPU 128 controls image forming unit 105 to form a toner image of the adjustment image to be printed on the first side of the paper on photoconductor 110 (S101). CPU 128 controls secondary transfer unit 117 to transfer the toner image of the adjustment image formed on photoconductor 110 to the first side of the paper via intermediate transfer belt 113 (S102). CPU 128 controls fixing unit 121 to fix the transferred toner image of the adjustment image on the first side of the paper (S103).

[0031] Next, CPU 128 controls image forming unit 105 to form a toner image of the adjustment image to be printed on the second side of the paper on photoconductor 110 (S104). CPU 128 controls secondary transfer unit 117 to transfer the toner image of the adjustment image formed on photoconductor 110 to the second side of the paper via intermediate transfer belt 113 (S105). CPU 128 controls fixing unit 121 to fix the transferred toner image of the adjustment image on the second side of the paper (S106).

[0032] As a result of the above, a test chart is generated in which adjustment images are printed on both sides (first and second sides) of the paper. The test chart is placed on the platen glass 108 of the image reading device 102 or on the tray of the ADF 103. The CPU 128 controls the image reading device 102 to read the adjustment images from both sides of the test chart and measures the position of the adjustment images based on the reading results (S107). The position of the image can be measured in both the main scanning direction and the sub-scanning direction that intersects with the main scanning direction. Here, the sub-scanning direction can also be said to be the paper transport direction.

[0033] 4 is an example diagram of an adjustment image. The adjustment image includes four patch images 400a to 400d formed near the four vertices of the paper, and the same image is used on the first and second sides. Patch images 400a and 400c, and patch images 400b and 400d, are formed at the same positions in the sub-scanning direction. Patch images 400a and 400b, and patch images 400c and 400d, are formed at the same positions in the main scanning direction.

[0034] Based on the measurement results of the position of the adjustment image, CPU 128 calculates the size of the image in the main scanning direction and sub-scanning direction on both sides (magnification of the toner image) (S108). CPU 128 stores the toner image magnification obtained as a result of the calculation in RAM 130 (S109). In image position adjustment, magnification correction is performed for the paper after the test chart by expanding or contracting the image according to the magnification of the toner image stored in RAM 130. Magnification correction is performed, for example, by CPU 128 performing image processing (affine transformation) on the image data. In other words, CPU 128 adjusts the size of the image.

[0035] The magnification of the toner image in the main scanning direction is calculated, for example, based on the distance between patch image 400a and patch image 400c. For example, the magnification of the toner image in the main scanning direction is calculated based on the difference between the ideal distance between patch image 400a and patch image 400c and the distance between patch image 400a and patch image 400c obtained from the results of reading the test chart. The magnification of the toner image in the sub-scanning direction is calculated, for example, based on the distance between patch image 400a and patch image 400b. For example, the magnification of the toner image in the sub-scanning direction is calculated based on the difference between the ideal distance between patch image 400a and patch image 400b and the distance between patch image 400a and patch image 400b obtained from the results of reading the test chart.

[0036] In this embodiment, when performing image position adjustment, in addition to the process of FIG. 3, the secondary transfer unit 117 detects the transfer current value. The current detection unit 127 detects the value of the transfer current that flows from the secondary transfer power supply 126 through the secondary transfer roller 116, the paper, the intermediate transfer belt 113, and the secondary transfer opposing roller 115. FIG. 5 is a flowchart showing the image position adjustment process that acquires the relationship between the transfer current value and the magnification of the toner image. As with the process of FIG. 3, this process begins when an external device or a user interface (not shown) issues an instruction to execute a double-sided print job for a test chart on which an image for image position adjustment (adjustment image) is printed.

[0037] CPU 128 controls image forming unit 105 to form a toner image of the adjustment image to be printed on the first side of the paper on photoconductor 110 (S201). CPU 128 controls secondary transfer unit 117 to transfer the toner image of the adjustment image formed on photoconductor 110 to the first side of the paper via intermediate transfer belt 113, and detects transfer current value IS_1 during transfer to the first side with current detection unit 127 (S202). CPU 128 controls fixing unit 121 to fix the transferred toner image of the adjustment image on the first side of the paper (S203).

[0038] Next, CPU 128 controls image forming unit 105 to form a toner image of the adjustment image to be printed on the second side of the paper on photoconductor 110 (S204). CPU 128 controls secondary transfer unit 117 to transfer the toner image of the adjustment image formed on photoconductor 110 to the second side of the paper via intermediate transfer belt 113, and detects transfer current value IS_2 during transfer to the second side with current detection unit 127 (S205). CPU 128 controls fixing unit 121 to fix the transferred toner image of the adjustment image on the second side of the paper (S206).

[0039] The test chart is placed on the platen glass 108 of the image reading device 102 or on the tray of the ADF 103. The CPU 128 controls the image reading device 102 to read adjustment images from both sides of the test chart and measure the positions of the adjustment images based on the reading results (S207). The CPU 128 calculates magnifications XS_1 and XS_2 of the toner images in the main scanning direction and sub-scanning direction on both sides based on the measurement results of the positions of the adjustment images (S208). The CPU 128 stores the toner image magnifications XS_1 and XS_2 and transfer current values ​​IS_1 and IS_2 obtained as a result of the calculation in the RAM 130 (S209).

[0040] The relationship between the magnifications XS_1 and XS_2 of the toner images obtained by the process in Fig. 5, the transfer current values ​​IS_1 and IS_2, and the amount of moisture contained in the paper measured in advance by a separate means is explained below. Fig. 6 is an explanatory diagram of the relationship between the amount of expansion and contraction of the paper relative to the amount of moisture and the transfer current value.

[0041] Figure 6(a) shows the change in the amount of expansion and contraction of paper depending on its moisture content. Paper expands as the moisture content increases, and shrinks as the moisture content decreases. There is a roughly proportional relationship between the moisture content and the amount of expansion and contraction. Paper also tends to expand and contract in the direction perpendicular to the gaps.

[0042] Figure 6(b) shows the change in transfer current value depending on the moisture content of the paper. As the moisture content of the paper increases, the resistance value decreases, so the transfer current value increases. However, if the moisture content decreases, the resistance value of the paper increases, so the transfer current value decreases. There is also an approximately proportional relationship between the moisture content and the transfer current value.

[0043] In this way, the amount of expansion and contraction of the paper (magnification of the toner image) and the transfer current value are correlated with the moisture content. Therefore, it can be said that there is also a correlation between the amount of expansion and contraction of the paper (magnification of the toner image) and the transfer current value.

[0044] In image forming apparatus 100, the heat generated by the fixing process evaporates the moisture contained in the paper, causing the paper and the toner image carried by the paper to shrink. Furthermore, as the moisture evaporates, the resistance value of the paper increases and the transfer current value decreases. Therefore, when performing double-sided printing with image position adjustment, the paper is heated by fixing unit 121 when printing the adjustment image on the first side, causing the amount of moisture in the paper to change between when the adjustment image is printed on the first side and when the adjustment image is printed on the second side. For this reason, in this embodiment, when performing double-sided printing with image position adjustment, the transfer current value and the magnification of the toner image are acquired when printing the adjustment image on the first side and when printing the adjustment image on the second side.

[0045] 7 is a diagram illustrating the relationship between the transfer current values ​​IS_1 and IS_2 and the magnifications XS_1 and XS_2 of the toner images. The transfer current values ​​and the magnifications of the toner images are proportional to each other and are expressed by equation (1). X = aI + b …(1) X: Magnification of toner image I: Transfer current value a, b: Parameter values ​​obtained from the transfer current value and the magnification of the toner image

[0046] As described above, since there is a correlation between the transfer current value and the magnification of the toner image, the magnification of the toner image formed on the paper can be calculated (estimated) by substituting the transfer current value detected by secondary transfer unit 117 into equation (1). As a result, by expanding or contracting the toner image by the amount of the deviation in the magnification of the toner image obtained from the transfer current value so that it matches the magnification of the toner image obtained by image position adjustment, it is possible to form an image while eliminating the effects of environmental changes since the image position adjustment.

[0047] In image position adjustment, multiple test charts can be printed to improve adjustment accuracy. In this embodiment, multiple print processes can be performed to obtain multiple transfer current values ​​and toner image magnifications, making it possible to obtain equation (1) of the transfer current value and toner image magnification more accurately. For example, by averaging the transfer current values ​​and toner image magnifications obtained from multiple test charts, it is possible to obtain equation (1) of the transfer current value and toner image magnification more accurately.

[0048] The single-sided printing process after the image position adjustment process is described below. In magnification correction using the transfer current value, the transfer current value of the paper to be corrected is detected after the toner image has been created, so magnification correction cannot be performed on the toner image to be transferred to that paper. Therefore, in this embodiment, the moisture content of the paper to be corrected and the immediately preceding paper is assumed to be similar, and the transfer current value of the immediately preceding paper is used to calculate the magnification of the toner image on the paper to be corrected. In single-sided printing, an image is printed only on the first side of the paper, so the magnification of the toner image on the paper to be corrected is calculated based on the transfer current value of the first side of the final paper of the previous job.

[0049] 8 is a flowchart showing the single-sided printing process, which starts when a single-sided printing job is instructed from an external device or a user interface (not shown).

[0050] CPU 128 determines whether the printing process is for the first sheet (S301). If it is for the first sheet (S301: Y), CPU 128 saves the magnification of the toner image on the first side of the first sheet in RAM 130 (S302). The magnification of the toner image on the first side of the first sheet is the magnification X1_1 obtained by substituting the transfer current value I0_1 detected on the first side of the final sheet of paper in the previous print job into equation (1) based on the transfer current value and toner image magnification saved in RAM 130 during image position adjustment. Equation (1) is correlation data showing the correspondence between the transfer current value and the magnification. Note that in the first print job after the image position adjustment process is executed, the printing process for the first sheet is executed using the magnification determined in the image position adjustment process.

[0051] CPU 128 controls image forming unit 105 to form on photoconductor 110 a toner image that has been scaled by the amount of magnification deviation of magnification XN_1 (N=1) of the toner image stored in RAM 130 in the processing of S302 (S303). CPU 128 controls secondary transfer unit 117 to transfer the toner image formed on photoconductor 110 to the first side of the paper via intermediate transfer belt 113, and detects the transfer current value IN_1)N=1 during transfer to the first side with current detection unit 127 (S304). CPU 128 controls fixing unit 121 to fix the transferred toner image on the first side of the paper (S305).

[0052] The CPU 128 determines whether printing of all images specified in the job has been completed (S306). If not completed (S306: N), the CPU 128 repeats the processing from S301 onwards. If completed (S306: Y), the CPU 128 ends the single-sided printing process.

[0053] If the printing process is not for the first sheet (S301: N), CPU 128 stores the magnification of the toner image for the second and subsequent sheets (here, Nth sheet: N is an integer equal to or greater than 2) in RAM 130 (S307). The magnification of the toner image for the Nth sheet is the magnification XN_1 obtained by substituting the transfer current value IN-1_1 detected for the immediately preceding sheet (N-1th sheet) into equation (1), which is determined by the transfer current value and toner image magnification stored in RAM 130 during image position adjustment. In other words, the magnification of the toner image for the Nth sheet can be obtained by substituting the transfer current value detected in the process of S304 during printing on the immediately preceding sheet into equation (1). CPU 128 then performs the processes of S303 to S306, and ends the single-sided printing process (S303 to S306).

[0054] As described above, by using the relational expression (1) between the transfer current value and the toner image magnification obtained from the paper for double-sided printing during single-sided printing and the transfer current value of the immediately preceding paper, it is possible to form an image with the same toner image magnification as immediately after image position adjustment. Therefore, even in a print job in which a long time has passed since the previous image position adjustment and the environmental humidity has fluctuated, it is possible to reduce the magnification deviation caused by the moisture content of the paper without the user having to adjust the image position each time.

[0055] In this embodiment, the paper for which the transfer current value is detected to calculate the magnification of the first toner image needs to be at least the paper that was passed through the printer immediately before, and does not necessarily have to be the final paper of the previous print job. Also, if there is no previous print job, the transfer current value obtained during image position adjustment may be used.

[0056] (Second embodiment) The configuration of the image forming apparatus 100 and the configuration of the controller 1000 in the second embodiment are the same as those in the first embodiment. Therefore, a description of the configuration of the image forming apparatus 100 and the configuration of the controller 1000 will be omitted. In this embodiment, a double-sided printing process after image position adjustment is performed will be described. In this embodiment, when forming an image on the second side of a sheet of paper to be corrected, the magnification of the toner image is calculated based on the transfer current value of the second side of the immediately preceding sheet of paper. This makes it possible to correct the magnification of the toner image on the second side as well as the first side.

[0057] 9 is a flowchart showing the double-sided printing process, which starts when a double-sided printing job is instructed from an external device or a user interface (not shown).

[0058] CPU 128 determines whether or not to print on the first side (S401). If printing on the first side is to be performed (S401: Y), CPU 128 performs printing on the first side through the same processes as S301 to S305 and S307 in FIG. 8 (S402 to S406, S408). CPU 128 determines whether or not printing of all images specified in the job has been completed (S407). Because double-sided printing has only completed printing on the first side, CPU 128 determines that printing has not been completed (S407: N) and returns to the process of S401.

[0059] If printing on the second side is to be performed (S401: N), CPU 128 determines whether or not this is the first sheet of printing processing (S409). If it is the first sheet of printing processing (S409: Y), CPU 128 saves the magnification of the toner image on the second side of the first sheet of printing processing in RAM 130 (S410). The magnification of the toner image on the second side of the first sheet of printing processing is the magnification X1_2 obtained by substituting the transfer current value I0_2 detected on the second side of the final sheet of printing processing in the previous print job into formula (1) based on the transfer current value and toner image magnification saved in RAM 130 during image position adjustment.

[0060] CPU 128 controls image forming unit 105 to form on photoconductor 110 a toner image that has been expanded or contracted by the amount of the magnification deviation of magnification XN_2 (N=1) of the toner image stored in RAM 130 in the processing of S410 (S411). CPU 128 controls secondary transfer unit 117 to transfer the toner image formed on photoconductor 110 to the second side of the paper via intermediate transfer belt 113, and detects transfer current value IN_2 (N=1) during transfer to the second side with current detection unit 127 (S412). CPU 128 controls fixing unit 121 to fix the transferred toner image on the second side of the paper (S413).

[0061] If the printing process is not for the first sheet (S409: N), CPU 128 stores the magnification of the toner image for the second and subsequent sheets (here, N-th sheet: N is an integer equal to or greater than 2) in RAM 130 (S414). The magnification of the toner image for the Nth sheet is the magnification XN_2 obtained by substituting the transfer current value IN-1_2 detected on the second side of the immediately preceding sheet (N-1th sheet) into equation (1) based on the transfer current value and toner image magnification stored in RAM 130 during image position adjustment. In other words, the magnification of the toner image for the Nth sheet can be obtained by substituting the transfer current value detected in the process of S412 when printing on the immediately preceding sheet into equation (1). CPU 128 then performs the processes of S411 to S413.

[0062] Thereafter, CPU 128 determines whether printing of all images specified in the job has been completed (S407). If printing has not been completed (S407: N), CPU 128 repeats the processing from S401 onwards. If printing has been completed (S407: Y), CPU 128 ends the double-sided printing processing.

[0063] Through the above process, by using the transfer current value of the immediately preceding sheet (the N-1th sheet), it is possible to appropriately correct the magnification of the toner image on both the first and second sides during double-sided printing. Therefore, even in a print job in which a long time has passed since the previous image position adjustment and the environmental humidity has fluctuated, it is possible to reduce the magnification deviation caused by the moisture content of the paper, without the user having to adjust the image position each time.

[0064] (Third embodiment) The configuration of the image forming apparatus 100 and the configuration of the controller 1000 in the third embodiment are the same as those in the first embodiment. Therefore, a description of the configuration of the image forming apparatus 100 and the configuration of the controller 1000 will be omitted. In this embodiment, a description will be given of the double-sided printing process after image position adjustment is performed. In the double-sided printing process of the second embodiment, the moisture content of the Nth sheet and the (N-1)th sheet is set to be the same. In the third embodiment, magnification correction is performed for each sheet when the moisture content continuously changes for each sheet.

[0065] In the second embodiment, in the processing from S409 onward in FIG. 9, the transfer current value for the second side of the immediately preceding sheet (the N-1th sheet) is regarded as the transfer current value for the Nth sheet, and the magnification of the toner image for the Nth sheet is calculated. In the third embodiment, it is assumed that the change in moisture content between sheets due to environmental humidity occurs by the same amount on the first and second sides, and the difference in the transfer current values ​​for the Nth and N-1th sheets on the first and second sides is regarded as equal, as shown in the following equation (2). Therefore, the transfer current value ISEQ_N_2 predicted to flow on the second side of the Nth sheet can be calculated from the transfer current value detected by secondary transfer unit 117 before image formation on the second side of the Nth sheet, as shown in equation (3). IN_1-IN-1_1=IN_2-IN-1_2 …(2) IN_1: Transfer current value for the first side of the Nth sheet IN-1_1: Transfer current value for the first side of the N-1th sheet IN_2: Transfer current value for the second side of the Nth sheet IN-1_2: Transfer current value for the second side of the N-1th sheet ISEQ_N_2=IN_1-IN-1_1+IN-1_2 …(3) ISEQ_N_2: Transfer current value predicted to flow on the second side of the Nth sheet

[0066] 10 is a flowchart showing the double-sided printing process, which is started when a double-sided printing job is instructed from an external device or a user interface (not shown).

[0067] 9, CPU 128 determines whether or not to print on the first side (S501). If printing on the first side is to be performed (S501: Y), CPU 128 performs printing on the first side through the same processes as S301 to S305 and S307 in FIG. 8 (S502 to S506, S508). CPU 128 determines whether or not printing of all images specified in the job has been completed (S507). Because double-sided printing has only completed printing on the first side, CPU 128 determines that printing has not been completed (S507: N) and returns to the process of S501.

[0068] If printing on the second side is to be performed (S501: N), CPU 128 determines whether or not the first sheet is being printed (S509). If the first sheet is being printed (S509: Y), CPU 128 calculates the transfer current value ISEQ_1_2 expected for the second side of the first sheet (S510). Transfer current value ISEQ_1_2 is calculated using equation (3) from transfer current values ​​I0_1 and I0_2 for both sides of the final sheet of paper in the previous print job and transfer current value I1_1 for the first side of the first sheet of paper.

[0069] The CPU 128 stores the magnification of the toner image on the second side of the first sheet in the RAM 130 (S511). The magnification of the toner image on the second side of the first sheet is the magnification X1_2 obtained by substituting the calculated transfer current value ISEQ_1_2 for the second side of the first sheet into equation (1) based on the transfer current value and toner image magnification stored in the RAM 130 during image position adjustment.

[0070] CPU 128 controls image forming unit 105 to form on photoconductor 110 a toner image that has been scaled by the amount of magnification deviation of magnification XN_2 (N=1) of the toner image stored in RAM 130 in the processing of S511 (S512). CPU 128 controls secondary transfer unit 117 to transfer the toner image formed on photoconductor 110 to the second side of the paper via intermediate transfer belt 113, and detects transfer current value IN_2 (N=1) during transfer to the second side with current detection unit 127 (S513). CPU 128 controls fixing unit 121 to fix the transferred toner image on the second side of the paper (S514).

[0071] If the printing process is not for the first sheet (S509: N), the CPU 128 calculates the expected transfer current value ISEQ_N_2 for the second side of the second or subsequent sheet (here, the Nth sheet: N is an integer equal to or greater than 2) (S515). The transfer current value ISEQ_N_2 is calculated using equation (3) from the transfer current values ​​IN-1_1 and IN-1_2 for both sides of the immediately preceding sheet (N-1) and the transfer current value IN_1 for the first side of the Nth sheet. The CPU 128 saves the magnification of the toner image for the Nth sheet in RAM 130 (S516). The magnification of the toner image for the Nth sheet is the magnification XN_2 obtained by substituting the calculated transfer current value ISEQ_N_2 detected for the second side of the Nth sheet into equation (1) based on the transfer current value and toner image magnification saved in RAM 130 during image position adjustment. The CPU 128 then performs the processes of S512 to S514.

[0072] Thereafter, CPU 128 determines whether printing of all images specified in the job has been completed (S507). If printing has not been completed (S507: N), CPU 128 repeats the processing from S501 onwards. If printing has been completed (S507: Y), CPU 128 ends the double-sided printing processing.

[0073] When multiple sheets of paper (a stack of paper) stored in paper feeders 104a and 104b are left unattended, the moisture content of the paper stack varies continuously from the outside to the inside due to differences in the amount of moisture absorbed from the environment between the outside of the stack, which has a larger surface area in contact with the air, and the inside of the stack, which has a smaller surface area in contact with the air. The method of the third embodiment, which uses the difference in transfer current values ​​on both sides of the Nth and N-1th sheets of paper, takes into account the fluctuations in moisture content between consecutive sheets of paper, thereby improving the accuracy of predicting the magnification of the toner image. Therefore, even in a print job in which a long time has passed since the previous image position adjustment and the environmental humidity has fluctuated, it is possible to reduce magnification deviations caused by the moisture content of the paper, without the user having to adjust the image position each time.

[0074] (Fourth embodiment) The configuration of the image forming apparatus 100 and the configuration of the controller 1000 in the fourth embodiment are the same as those in the first embodiment, so a description of the configuration of the image forming apparatus 100 and the configuration of the controller 1000 will be omitted.

[0075] In the fourth embodiment, in order to obtain the relationship between the transfer current value and the magnification of the toner image, the position of the adjustment image is not measured after printing the adjustment image on both sides of the paper, but is measured each time an adjustment image is printed on one side. In other words, in the fourth embodiment, automatic double-sided printing is not used, and the adjustment image on the second side is formed by manually feeding the paper discharged onto the paper discharge tray 125 after forming the adjustment image on the first side, and the position of the adjustment image is measured.

[0076] 11 is a flowchart showing the image position adjustment process for acquiring the relationship between the transfer current value and the magnification of the toner image for each side. As with the process in FIG. 3, this process starts when an external device or a user interface (not shown) issues an instruction to print two sides of a test chart on which images for adjusting image position (adjustment images) are printed.

[0077] CPU 128 controls image forming unit 105 to form a toner image of the adjustment image to be printed on the first side of the paper on photoconductor 110 (S601). CPU 128 controls secondary transfer unit 117 to transfer the toner image of the adjustment image formed on photoconductor 110 to the first side of the paper via intermediate transfer belt 113, and detects transfer current value IS_1 during transfer to the first side of the paper with current detection unit 127 (S602). CPU 128 controls fixing unit 121 to fix the transferred toner image of the adjustment image on the first side of the paper (S603).

[0078] As a result of the above, a test chart is generated in which an adjustment image is printed on the first side of a sheet of paper. The test chart is placed on the platen glass 108 of the image reading device 102 or on the tray of the ADF 103. The CPU 128 controls the image reading device 102 to read the adjustment image from the first side of the test chart and measures the position of the adjustment image based on the reading result (S604). The CPU 128 calculates the size of the image in the main scanning direction and sub-scanning direction on the first side (magnification XS_1 of the toner image) based on the measurement result of the position of the adjustment image (S605).

[0079] Next, the CPU 128 prints an adjustment image on the second side of the test chart on which the adjustment image has been printed on the first side. The user places the test chart on which the adjustment image has been printed on the first side in the paper feed unit 104c on the side.

[0080] CPU 128 controls image forming unit 105 to form a toner image of the adjustment image to be printed on the second side of the test chart (paper) on photoconductor 110 (S606). CPU 128 controls secondary transfer unit 117 to transfer the toner image of the adjustment image formed on photoconductor 110 to the second side of the paper via intermediate transfer belt 113, and detects transfer current value IS_2 during transfer to the second side of the paper using current detection unit 127 (S607). CPU 128 controls fixing unit 121 to fix the transferred toner image of the adjustment image on the second side of the test chart (paper) (S608).

[0081] As a result of the above, a test chart is generated with an adjustment image printed on its second side. The test chart is placed on the platen glass 108 of the image reading device 102 or on the tray of the ADF 103. The CPU 128 controls the image reading device 102 to read the adjustment image from the second side of the test chart and measures the position of the adjustment image based on the reading result (S609). The position of the image can be measured in both the main scanning direction and the sub-scanning direction that intersects the main scanning direction. The CPU 128 calculates the size of the image in the main scanning direction and the sub-scanning direction on the second side (magnification XS_2 of the toner image) based on the measurement result of the position of the adjustment image (S610).

[0082] The CPU 128 stores the transfer current values ​​IS_1 and IS_2 and the toner image magnifications XS_1 and XS_2 for the first and second surfaces obtained by the above processing in the RAM 130 (S611). This completes the image position adjustment processing for each surface.

[0083] In the process of Fig. 11, the position of the image is measured after the toner image is fixed by the fixing unit 121, but the paper size of the test chart may also be measured. When measuring the paper size, there is no need to form an adjustment image on paper, and therefore there is no need to cut the adjustment image formed on the paper after image formation. Also, there is no need to perform printing processing on paper that is unnecessary for the user, as with a test chart for image position adjustment.

[0084] In the above process, the position of the adjustment image or the paper size is measured by the image reading device 102, but these measurements may also be performed using a sensor provided on the transport path within the image forming device 100. Also, the position of the adjustment image or the paper size may be measured using an external measuring device instead of the image forming device 100. When printing an adjustment image on the second side of a test chart with an adjustment image printed on the first side, paper may be fed from paper feed units 104a and 104b at the bottom of the printing device 101.

[0085] 12 is a flowchart showing the image position adjustment process for acquiring the relationship between the transfer current value and the paper size for each side when measuring the paper size before feeding. In the process of FIG. 12, the paper size is measured after passing through the fixing unit 121, but by measuring before feeding, it is possible to measure the paper size before shrinkage on both sides. As with the process of FIG. 3, this process is started when an external device or a user interface (not shown) issues an instruction to execute a single-sided print job for two sides of a test chart on which an image for adjusting the image position (adjustment image) is printed.

[0086] The CPU 128 measures the paper size XS_1 of the first side of the paper using the image reading device 102 (S701). In this case, the user places the paper on the platen glass 108 of the image reading device 102 or on the ADF 103, and reads the paper. The CPU 128 measures the paper size XS_1 by, for example, detecting the edges of the paper from the paper reading results obtained from the image reading device 102. The paper size XS_1 is the length of the paper in the main scanning direction and the sub-scanning direction of the first side. After measuring the paper size XS_1 of the first side, the CPU 128 causes the paper feeding unit 104 to feed the paper.

[0087] The CPU 128 fixes the toner image of the adjustment image on the first side of the paper by processing similar to S601 to S603 of FIG. 10 (S702 to S704). The CPU 128 measures the paper size XS_2 of the second side of the paper, on whose first side the adjustment image has been printed, using the image reading device 102 (S705). The measurement of the paper size XS_2 of the second side is performed in the same manner as the measurement of the paper size XS_1 of the first side. The paper size XS_2 is the length of the paper in the main scanning direction and the sub-scanning direction on the second side. After measuring the size of the second side, the CPU 128 causes the paper feed unit 104c to feed the paper. The CPU 128 fixes the toner image of the adjustment image on the second side of the paper by processing similar to S606 to S608 of FIG. 10 (S706 to S708).

[0088] The CPU 128 stores the transfer current values ​​IS_1, IS_2 and paper sizes XS_1, XS_2 for the first and second sides obtained through the above process in the RAM 130 (S709). This completes the image position adjustment process for each side.

[0089] In the above process, the paper size is measured by the image reading device 102, but these measurements may also be performed using a sensor provided on the transport path within the image forming device 100. Also, the position of the adjustment image or the paper size may be measured using an external measuring device instead of the image forming device 100. When printing an adjustment image on the second side of a test chart with an adjustment image printed on the first side, the paper may be fed from paper feed units 104a and 104b at the bottom of the printing device 101.

Claims

1. an image forming means for forming an image on an image carrier; a transfer means for transferring the image formed on the image carrier onto a sheet of paper; a fixing means for fixing the image onto the paper; a current detection means for detecting a transfer current value when the image is transferred by the transfer means; a reading means for reading the image fixed on the paper; a measuring means for measuring the size of the image fixed on the paper based on the reading result by the reading means; and a control means for acquiring a relationship between the transfer current value detected by the current detection means and the magnification of the image obtained from the size of the image fixed on the paper, and adjusting the size of the image to be formed based on the relationship when forming the image based on a print job. Image forming device.

2. the control means, when forming an image on a first sheet of paper in accordance with the print job, adjusts the size of the image to be formed from the transfer current value at the time of transferring the image onto at least the sheet of paper that has been passed immediately before, based on the relationship.

2. The image forming apparatus according to claim 1.

3. the control means, when forming an image on the first side of the first sheet of paper in accordance with the print job, adjusts the size of the image formed by the image forming means from the transfer current value at the time of transferring the image onto the first side of at least the sheet of paper that has been passed immediately before, based on the relationship.

3. The image forming apparatus according to claim 2.

4. the control means, when forming an image on the first side of the second or subsequent sheets of paper in accordance with the print job, adjusts the size of the image formed by the image forming means from the transfer current value at the time of transferring the image onto the first side of at least the most recently passed sheet of paper, based on the relationship.

4. The image forming apparatus according to claim 3.

5. the control means, when forming an image on a second side different from the first side of the first sheet of paper in accordance with the print job, adjusts the size of the image formed by the image forming means from the transfer current value at the time of transferring the image to the second side of at least the sheet of paper that has been passed through immediately before, based on the relationship.

4. The image forming apparatus according to claim 3.

6. the control means, when forming an image on the second side of the second or subsequent sheets of paper in accordance with the print job, adjusts the size of the image formed by the image forming means from the transfer current value at the time of transferring the image onto the second side of at least the most recently passed sheet of paper, based on the relationship.

6. The image forming apparatus according to claim 5.

7. When forming an image on a second side different from the first side of the first sheet of paper in accordance with the print job, the control means predicts a transfer current value when transferring an image to the second side of the first sheet of paper based on transfer current values ​​when transferring images to both sides of at least the most recently passed sheets of paper and transfer current values ​​when transferring an image to the first side of the first sheet of paper, and adjusts the size of the image to be formed based on the saved transfer current value, the magnification of the image, and the predicted transfer current value.

4. The image forming apparatus according to claim 3.

8. When forming an image on the second side of the second or subsequent sheets of paper in accordance with the print job, the control means predicts the transfer current value when transferring the image to the second side of the paper based on at least the transfer current value when transferring the image to both sides of the paper that has been passed up until now and the transfer current value when transferring the image to the first side of the paper, and adjusts the size of the image to be formed based on the saved transfer current value, the magnification of the image, and the predicted transfer current value.

8. The image forming apparatus according to claim 7.

9. The measuring means measures the size of the paper, The control means acquires and stores the magnification of the image based on the size of the paper.

2. The image forming apparatus according to claim 1.

Images