Image forming apparatus

Abstract

The goal is to achieve both improved accuracy in image alignment on the sheet and reduced sheet waste. [Solution] The image forming apparatus includes an image forming means for forming an image on a sheet, a reading means for reading a test chart formed on the sheet by the image forming means, a determination means for determining an adjustment amount for adjusting the magnification of the image forming range in which the image should be formed by the image forming means, based on the result of reading the test chart, for each toner amount category, and a control means for controlling the formation of an image by the image forming means according to the determined adjustment amount. The determination means determines the adjustment amount for a first toner amount category based on a first reading result for the corresponding test chart, and determines the adjustment amount for a second toner amount category based on the first reading result and an adjustment coefficient between the first toner amount category and the second toner amount category.

Description

[Technical Field]

[0001] This disclosure relates to an image forming apparatus. [Background technology]

[0002] Conventionally, there are image forming machines that have a function (hereinafter referred to as the alignment function) to align the image formation positions on the front and back surfaces of a sheet when performing double-sided printing. For example, when forming an image on preprinted paper with ruled lines, the alignment function can be used to maintain the correct positional relationship between the printed image and the ruled lines. In a typical alignment function, a test chart containing known marks is formed on the front and back surfaces of an adjustment sheet, and the amount of adjustment for the image formation position is calculated from the misalignment of the marks in the read images obtained by reading the front and back surfaces of the adjustment sheet. The calculated adjustment amount is used to adjust the image formation positions on the front and back surfaces of the sheet in the subsequent image forming operation.

[0003] The accuracy of the alignment is affected by the type of sheet used for printing. This is because the amount of expansion and contraction of the sheet before and after printing differs depending on the sheet's characteristics such as size, basis weight, and material. In order to capture these differences in expansion and contraction and reflect them in the alignment, it is necessary to create a test chart on an adjustment sheet, read the adjustment sheet, calculate the adjustment amount, and store the adjustment amount for each type of sheet.

[0004] Patent Document 1 focuses on the fact that differences in the amount of toner adhering to a sheet (hereinafter referred to as toner amount) cause a shift in the image formation position, and discloses a technique for using two test charts with different toner amounts to calculate the adjustment amount in the alignment function. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-135466 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, during the execution of a job spanning multiple sheets, changes in environmental conditions or sheet characteristics may occur that cause misalignment of the image formation position. For example, an increase in the temperature inside the device, moisture absorption by the sheet, changes in surface smoothness due to differences in the manufacturing lot of the sheet, and errors in the size of the cut sheet are examples of causes of misalignment during job execution. If adjustment amounts are calculated using multiple test charts, as in the technology described in Patent Document 1, during job execution to capture such misalignment, it becomes necessary to create test charts on a large number of adjustment sheets, increasing sheet waste and reducing the productivity of job execution.

[0007] In light of the circumstances described above, this disclosure aims to provide a mechanism that can achieve both improved accuracy in image alignment on a sheet and reduced sheet waste. [Means for solving the problem]

[0008] From one perspective, an image forming apparatus is provided, comprising: an image forming means for forming an image on a sheet using toner; a reading means for reading a test chart formed on the sheet by the image forming means; a determination means for determining an adjustment amount for adjusting the magnification of the image forming range in which the image should be formed by the image forming means, based on the result of reading the test chart by the reading means, for each toner amount category; and a control means for controlling the formation of an image by the image forming means according to the adjustment amount determined by the determination means. The determination means determines the adjustment amount for a first toner amount category based on a first reading result for the test chart corresponding to the first toner amount category, and determines the adjustment amount for a second toner amount category based on the first reading result and an adjustment coefficient between the first toner amount category and the second toner amount category. [Effects of the Invention]

[0009] According to this disclosure, it is possible to achieve both improved accuracy in image alignment on the sheet and reduced waste of the sheet. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic diagram showing an example of the configuration of an image forming apparatus according to one embodiment. [Figure 2] A block diagram showing an example of the configuration of a controller according to one embodiment. [Figure 3] An explanatory diagram showing an example of the configuration of a sheet management screen according to one embodiment. [Figure 4] An explanatory diagram showing an example of the configuration of an attribute editing screen according to one embodiment. [Figure 5] An explanatory diagram showing an example of the data structure for adjustment parameters other than the sub-scan magnification. [Figure 6] An explanatory diagram showing an example of the data structure for the sub-scanning magnification. [Figure 7A] An explanatory diagram showing how the surface test chart is formed on the adjustment sheet. [Figure 7B] An explanatory diagram showing how the test chart on the reverse side is formed on the adjustment sheet. [Figure 8] An explanatory diagram showing examples of test charts corresponding to the five categories of toner application amount. [Figure 9] An explanatory diagram illustrating the omission of creating test charts during the mid-term adjustment process. [Figure 10] An explanatory diagram showing an example of the configuration of the cassette allocation status screen according to one embodiment. [Figure 11A] An explanatory diagram showing an example of the configuration of a position adjustment menu screen according to one embodiment. [Figure 11B] An explanatory diagram showing an example of the configuration of the initial adjustment screen according to one embodiment. [Figure 11C] An explanatory diagram showing an example of the configuration of the intermediate adjustment settings screen according to one embodiment. [Figure 12]A flowchart showing an example of the flow of the initial adjustment process according to one embodiment. [Figure 13] A flowchart showing an example of the job control process flow according to one embodiment. [Figure 14] A flowchart showing a more detailed example of the execution flow of a print job in Figure 13. [Figure 15] A flowchart showing an example of the flow of the intermediate adjustment process according to one embodiment. [Figure 16] A flowchart showing an example of the flow of the intermediate adjustment process related to one modified example. [Modes for carrying out the invention]

[0011] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims. While the embodiments describe multiple features, not all of these features are essential to the invention, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0012] <1. System Overview> Figure 1 is a schematic diagram showing an example of the configuration of an image forming apparatus 100 according to one embodiment. Referring to Figure 1, the image forming apparatus 100 includes a controller 110, an operating unit 130, a paper feeding unit 140, a printer unit 150, a reader unit 170, and a finisher 190.

[0013] (1) Controller The controller 110 is a control means that controls the overall operation of the image forming apparatus 100. The controller 110 sets up print jobs and causes the image forming apparatus 100 to execute the set print jobs in response to instructions received via the operation unit 130 (or received from an external device). The settings for a print job may include, for example, the number of copies to print, single-sided / double-sided printing, sheet type (or paper source cassette), and the type of post-processing to be applied.

[0014] In this embodiment, the controller 110 provides an alignment function for adjusting the image formation range on one or both of the front and back surfaces of the sheet. The following description mainly describes an example of performing alignment on both sides by adjusting the image formation range on the front and back surfaces, but the technology of this disclosure is also applicable to adjusting the image formation range on only one side. The controller 110 causes the printer unit 150 to form test charts on the front and back surfaces of the adjustment sheet, and then causes the reader unit 170 to read the front and back surfaces of the adjustment sheet on which the test charts have been formed. Based on the read images generated by the reader unit 170, the amount of adjustment for the image formation range on the front and back surfaces is determined. The amount of adjustment thus determined is then used to adjust the image formation range on each surface when the printer unit 150 subsequently forms images on the front and back surfaces of the sheet. The adjustment of the image formation range using test charts will be described in detail later.

[0015] (1) Operating unit The operation unit 130 is an operating means that provides a user interface to the user (also called the operator) of the image forming apparatus 100. The operation unit 130 may be a combination of input devices such as touch sensors, buttons, numeric keypads and switches, and output devices such as liquid crystal displays (LCDs) and speakers. For example, the execution of a job or the execution of alignment may be instructed by the user on a screen displayed on the operation unit 130's display. The controller 110 may display various statuses of the image forming apparatus 100 on its screen.

[0016] (2) Paper feed unit The paper feed unit 140 is a paper feeding means that supplies sheets to the printer unit 150. The paper feed unit 140 includes a plurality of cassettes 141a to 141c, each capable of holding different types of sheets. Each cassette 141a to 141c contains a stack of sheets, and the corresponding paper feed roller picks up the top sheet of the stack one by one and feeds it to the transport path 142. The sheets are supplied to the printer unit 150 via the transport path 142.

[0017] (3) Printer unit The printer unit 150 is an image forming means capable of forming an image on a sheet. In this embodiment, the printer unit 150 is a color printer capable of forming a color image. In other embodiments, the printer unit 150 may be a monochrome printer. The printer unit 150 is capable of double-sided printing, that is, it can form an image on both the front and back surfaces of a sheet. In the example shown in Figure 1, the printer unit 150 includes image forming sections 151Y, 150M, 150C, 150K, an intermediate transfer belt 156, a transfer unit 157, a cleaner 158, cassettes 160a, 160b, a first fuser 162, a second fuser 163, and a flapper 166.

[0018] Image forming unit 151Y forms a yellow (Y) toner image on the intermediate transfer belt 156. Image forming unit 151M forms a magenta (M) toner image on the intermediate transfer belt 156. Image forming unit 151C forms a cyan (C) toner image on the intermediate transfer belt 156. Image forming unit 151K forms a black (K) toner image on the intermediate transfer belt 156. Since image forming units 151Y, 150M, 150C, and 150K have the same configuration as each other, the configuration of image forming unit 151Y will be used as an example for this explanation. Image forming unit 151Y includes a photosensitive drum 152, a charger 153, an exposure unit 154, and a developer unit 155. The photosensitive drum 152 is a drum-shaped photoreceptor having a photosensitive layer on its surface. The photosensitive drum 152 is driven by a motor (not shown) and rotates around the drum axis in the direction of arrow R in the figure. The charger 153 uniformly charges the surface of the rotating photosensitive drum 152. The exposure unit 154 irradiates the photosensitive drum 152 with laser light according to the image data (representing a yellow image in this case) input from the controller 110. The laser light output from the exposure unit 154 scans the surface of the charged photosensitive drum 152 in the direction of the drum axis, thereby forming an electrostatic latent image on the surface of the photosensitive drum 152. In the following description, the direction parallel to the drum axis is called the main scanning direction, and the direction perpendicular to the drum axis and parallel to the sheet transport direction in the printer unit 150 is called the sub-scanning direction. Alternatively, the sub-scanning direction is also called the first direction, and the main scanning direction perpendicular to the sub-scanning direction is also called the second direction. The developer unit 155 develops the electrostatic latent image on the photosensitive drum 152 by supplying toner (in this case, yellow) toner to the surface of the photosensitive drum 152. As a result, a toner image is formed on the surface of the photosensitive drum 152. In the image forming unit 151Y, the yellow toner image formed on the surface of the photosensitive drum 152 is transferred to the intermediate transfer belt 156. Furthermore, in the image forming units 151M, 150C, and 150K, the magenta, cyan, and black toner images formed on the surface of the respective photosensitive drums 152 are sequentially transferred to the intermediate transfer belt 156, superimposed on the yellow toner image. As a result, a full-color toner image is formed on the intermediate transfer belt 156. The intermediate transfer belt 156 is an endless belt member that rotates clockwise in the figure.The intermediate transfer belt 156 transports the full-color toner image to the position of the transfer unit 157 (transfer position).

[0019] Cassettes 160a and 160b house bundles of sheets, similar to cassettes 141a to 141c of the paper feed unit 140. The transport path 161 receives sheets supplied from the paper feed unit 140 or sheets fed from cassettes 160a or 160b. Sheets transported along the transport path 161 by multiple transport rollers are fed to the transfer position under the control of the controller 110, in accordance with the timing when the toner image on the intermediate transfer belt 156 reaches the transfer position.

[0020] The transfer unit 157 transfers the toner image supported on the intermediate transfer belt 156 to the sheet at the transfer position. The first fuser 162 includes a heater, a fuser roller, and a pressure belt. The heater of the first fuser 162 heats the fuser roller, and the heated fuser roller melts the toner in the toner image on the sheet. The melted toner is fixed to the sheet by being pressurized by the pressure belt. The cleaner 158 is positioned downstream of the transfer position on the trajectory of the intermediate transfer belt 156 and removes any toner remaining on the intermediate transfer belt 156 after the transfer of the toner image. The second fuser 163 also includes a heater, a fuser roller, and a pressure belt. The second fuser 163 further heats and pressurizes the toner image on the sheet to increase gloss or improve fixability when an image is formed on a specific type of sheet.

[0021] The transport path 161 branches into transport paths 164 and 165 downstream of the second fuser 163. The flapper 166 switches the sheet transport path between transport paths 164 and 165. When single-sided printing is performed, the sheet after the fixing process enters transport path 165 from transport path 161, then switches back and is discharged to the reader unit 170 in a so-called face-down state with the surface on which the image has been formed facing downwards.

[0022] When double-sided printing is performed, the sheet after fixing enters transport path 165 from transport path 161, switches back to reverse direction of travel, passes through transport path 167, returns to transport path 161 with the front and back sides reversed, and passes through the transfer position again. At the transfer position, the transfer unit 157 transfers the toner image to the back side of the sheet, and the first fuser unit 162 further fixes the toner image to the back side of the sheet. The sheet, with images formed on both sides in this way, is discharged to the reader unit 170 via transport path 164.

[0023] (4) Leader Unit The reader unit 170 is a reading means that optically reads a sheet and generates a read image. In the example in Figure 1, the reader unit 170 includes a sheet sensor 172, a first line sensor 173, and a second line sensor 174. The sheet output from the printer unit 150 to the reader unit 170 is transported along a transport path 171 by a plurality of transport rollers. The sheet sensor 172 detects the leading edge of the sheet being transported along the transport path 171. The sheet sensor 172 may be, for example, an optical sensor having a light-emitting element and a light-receiving element. The first line sensor 173 optically reads the first surface (front) of the sheet and generates a read image, and outputs the read image data to the controller 110. The second line sensor 174 optically reads the second surface (back) of the sheet and generates a read image, and outputs the read image data to the controller 110. The first line sensor 173 and the second line sensor 174 may be, for example, an array of CMOS (Complementary Metal Oxide Semiconductor) sensors. The timing at which the first line sensor 173 and the second line sensor 174 read the sheet is controlled by the controller 110 based on the timing at which the sheet sensor 172 detects the leading edge of the sheet. The sheet that has passed the reading position of the reader unit 170 is discharged to the finisher 190.

[0024] (5) Finisher The finisher 190 is a post-processing means that performs post-processing on the sheets output from the reader unit 170. The finisher 190 may perform various post-processing on multiple sheets, such as stapling, sorting, or cutting. The finisher 190 discharges the processed sheets to the discharge tray 191 or 192.

[0025] <2. Example of Controller Configuration> Figure 2 is a block diagram showing an example configuration of the controller 110. Referring to Figure 2, the controller 110 includes a system bus 111, ROM 112, RAM 13, HDD 114, communication interface (I / F) 115, and CPU 116. The controller 110 is connected to the aforementioned operating unit 130, paper feed unit 140, printer unit 150, reader unit 170, and finisher 190 via the system bus 111. The system bus 111 further interconnects the ROM 112, RAM 13, HDD 114, communication I / F 115, and CPU 116.

[0026] ROM (Read Only Memory) 112 is a non-volatile memory that stores one or more computer programs executed by the CPU 116. RAM (Random Access Memory) 113 is a volatile memory that provides the CPU 116 with temporary storage space for calculations. HDD (Hard Disk Drive) 114 is a large-capacity storage that stores various data, including image data processed by the image forming apparatus 100. In this embodiment, HDD 114 stores a sheet database (DB) 121. The sheet DB 121 is a database (also called a library) that holds attribute information for each sheet type for various sheets used in the image forming apparatus 100. In other embodiments, the sheet DB 121 may be implemented by having the host computer 20, described later, function as a database server. The data of the sheet DB 121 may be written in a data file in XML (Extensible Markup Language) format or CSV (Comma-Separated Values) format. An example of the configuration of the sheet DB 121 will be described further later.

[0027] The communication interface 115 is an interface for the image forming apparatus 100 to communicate with external devices. The communication interface 115 may be a wired communication interface or a wireless communication interface. In the example in Figure 2, the communication interface 115 is connected to the network 10 and can communicate with the host computer 20. The network 10 may be, for example, a local area network (LAN), a wide area network (WAN), or a combination thereof. The host computer 20 may be, for example, a server device or terminal device that issues print jobs to the image forming apparatus 100.

[0028] The CPU (Central Processing Unit) 116 is a processing circuit that controls the operation of each unit of the image forming apparatus 100 by executing a computer program stored in the ROM 112. In this embodiment, the CPU 116 functions as a print control unit 122 and an adjustment unit 123.

[0029] The print control unit 122 controls the execution of jobs by the printer unit 150. When the print control unit 122 is instructed to execute a print job, it controls the printer unit 150 to supply a sheet from the cassette corresponding to the sheet type specified in the print job to the transport path 161 of the printer unit 150, and to form an image on the sheet based on the input image data. The print control unit 122 may also read attribute information corresponding to the sheet type specified in the print job from the sheet DB 121 and control the operating conditions of the printer unit 150 based on the read attribute information. The print control unit 122 causes the printer unit 150 to adjust the image formation range of each surface according to the adjustment amount values ​​determined by the adjustment unit 123 for the front and back surfaces. This can eliminate discrepancies in the image formation range of each surface.

[0030] The adjustment unit 123 provides a positioning function for adjusting the image formation area. For positioning, the adjustment unit 123 determines the adjustment amount for the first image formation area where an image is formed on the surface of the sheet by the printer unit 150, and the second image formation area where an image is formed on the back of the sheet. The determination of the adjustment amount by the adjustment unit 123 will be explained in detail in the next section.

[0031] <3. Alignment function> <3-1. Sheet DB> (1) Basic attribute information The sheet DB121 holds attribute information of sheets that may be used in the image forming apparatus 100. For example, the sheet DB121 may hold one or more of the following information items for each sheet type: "ID" "name" "Main scan size" "Subscan size" "Basic weight" "Superficiality" "color" "Preprint" "ID" is an identifier used to uniquely identify each sheet type. "Name" represents the name set by the user to distinguish each sheet type. "Main scan size" represents the size of the sheet in the main scan direction. "Sub scan size" represents the size of the sheet in the sub scan direction. "Basis weight" represents the weight per unit area of ​​the sheet. "Surface properties" is information related to the physical properties of the sheet surface (e.g., smoothness). "Color" represents the color of the sheet. "Preprint" is a flag indicating whether the sheet is preprinted paper or not.

[0032] The print control unit 122 may provide the user with a management screen for registering, editing, and deleting the attribute information described above in the sheet DB 121. Figure 3 is an explanatory diagram showing an example of the configuration of such a sheet management screen 30. The sheet management screen 30 can be displayed, for example, on the display of the operation unit 130 or the host computer 20.

[0033] The sheet management screen 30 includes a list display area 31, a new registration button 32, an edit button 33, a delete button 34, and an assignment button 35. The list display area 31 displays attribute information for one or more sheet types registered in the sheet DB 121 in list format. In the example in Figure 3, the six columns represent the "name," "main scan size," "sub scan size," "basis weight," "surface finish," and "color" for each sheet type. Regarding "surface finish," "plain paper" indicates that the sheet surface has no special processing, "embossed" indicates that the sheet surface has a textured finish, and "coated" indicates that the sheet surface has a finish to improve gloss. If the list display area 31 does not have enough width to display all information items of the attribute information at once, a horizontal scroll bar may be provided for horizontal scrolling of the display. Also, if the list display area 31 does not have enough height to display all sheet types at once, a vertical scroll bar may be provided for vertical scrolling of the display.

[0034] When a user operates the new registration button 32, a record of a new sheet type is added to sheet DB121, and attribute information for the new sheet type can be entered on the attribute editing screen 40, which will be described next. When a user selects (for example, touches) any sheet type in the list display area 31 and then operates the edit button 33, the attribute information of the selected sheet type can be edited. In the example in Figure 3, the user has selected a sheet type named "XY COLOR B1," and the selection state is distinguished by the display method of the record (for example, shading or display color). When a user selects any sheet type in the list display area 31 and then operates the delete button 34, the record of the selected sheet type is deleted from sheet DB121. When a user selects any sheet type in the list display area 31 and then operates the assign button 35, the selected sheet type can be assigned to one of the cassettes of the image forming apparatus 100 on a further screen.

[0035] Figure 4 is an explanatory diagram showing an example of the configuration of the attribute editing screen 40 that may be displayed when the new registration button 32 or the edit button 33 is operated on the sheet management screen 30. The attribute editing screen 40 includes a name field 41, a main scan size field 42, a sub scan size field 43, a basis weight field 44, a surface quality selection field 45, a color selection field 46, a checkbox 47, a cancel button 48, and an OK button 49.

[0036] The Name field 41 is a field that accepts input for the name of the sheet type. The Main Scan Size field 42 is a field that accepts input for the Main Scan Size. The Sub Scan Size field 43 is a field that accepts input for the Sub Scan Size. The Basis Weight field 44 is a field that accepts input for the Basis Weight. The Surface Texture Selection field 45 is a field that accepts selection of one of several candidate values ​​for surface texture that have been registered in advance. The Color Selection field 46 is a field that accepts selection of one of several candidate values ​​for color that have been registered in advance. The Checkbox 47 is an object that accepts selection for whether or not it is pre-printed paper. If Checkbox 47 is checked, it means that the target sheet type is pre-printed paper. The Cancel button 48 is a button that cancels the editing of attribute information on the attribute editing screen 40 and returns to the sheet management screen 30. The OK button 49 is a button that reflects the editing of attribute information on the attribute editing screen 40 to the database and returns to the sheet management screen 30.

[0037] (2) Parameters for alignment In addition to the basic attribute information described above, sheet DB121 holds one or more parameters for the alignment of the front and back surfaces of the sheet. For example, sheet DB121 may hold one or more of the following adjustment parameters related to the first image-forming area on the front surface of the sheet and the second image-forming area on the back surface of the sheet: • Regarding the surface (first surface) "Angle correction" "Trapezoidal correction" "Main scan start offset" "Sub-scanning start offset" "Main scan magnification" "Sub-scan magnification" Regarding the reverse side (page 2): "Angle correction" "Trapezoidal correction" "Main scan start offset" "Sub-scanning start offset" "Main scan magnification" "Sub-scan magnification"

[0038] "Angle Correction" represents the amount of adjustment (angle correction amount) to correct the overall tilt of the image. "Keystone Correction" represents the amount of adjustment (keystone correction amount) to correct distortion in the image forming area (for example, the difference in the lengths of two opposing sides). "Main Scan Start Offset" represents the amount of adjustment (main scan start offset amount) to align the starting position of the image forming area in the main scan direction to the ideal position. "Sub Scan Start Offset" represents the amount of adjustment (sub scan start offset amount) to align the starting position of the image forming area in the sub scan direction to the ideal position. "Main Scan Magnification" represents the amount of adjustment (magnification) to align the size of the image forming area in the main scan direction to the ideal size. "Sub Scan Magnification" represents the amount of adjustment (magnification) to align the size of the image forming area in the sub scan direction to the ideal size.

[0039] Of the adjustment parameters mentioned above, the sub-scanning magnification is particularly susceptible to errors due to the influence of the amount of toner applied to the printed image. That is, when comparing two sheets in which images with different amounts of toner are formed, the sheet in which an image with a larger amount of toner is formed experiences a greater degree of reduction in transport force due to slippage during sheet transport, and the image formation area tends to shrink in the sub-scanning direction. Therefore, in this embodiment, the sheet DB121 maintains a sub-scanning magnification value for each of the multiple categories of toner application to suppress variations in the size of the image formation area in the sub-scanning direction caused by differences in toner application. Other adjustment parameters may be common across multiple categories of toner application.

[0040] Figure 5 shows an example of the data structure for adjustment parameters other than the sub-scan multiplier in sheet DB121. Figure 6 also shows an example of the data structure for the sub-scan multiplier in sheet DB121.

[0041] Referring to Figure 5, the first parameter table 50 contains the values ​​for the front and back surfaces of five adjustment parameters for each sheet type: "Angle Correction: W", "Trapezoidal Correction: Z", "Main Scan Start: ML", "Sub Scan Start: SL", and "Main Scan Magnification: MS". The subscript for each parameter in the figure consists of a single letter, "T" or "B", and a number, where "T" and "B" represent the front and back surfaces, respectively, and the number corresponds to the sheet type ID. These adjustment values ​​can be determined by forming a predetermined test chart on the front and back surfaces of the adjustment sheet and analyzing the read images of the front and back surfaces of the adjustment sheet, as will be explained later.

[0042] Referring to Figure 6, the second parameter table 60 includes the values ​​for the adjustment amount on the front and back sides of the "sub-scanning magnification (SS)" for each sheet type and each toner load category. In the illustrated example, the toner load is classified into one of N categories. For example, N may be 5, in which case the range of toner load from 0 to 100% is divided into 5 categories.

[0043] <3-2. Determining the adjustment amount using a test chart> In this embodiment, to calculate the values ​​of each of the adjustment parameters described above, the adjustment unit 123 controls the printer unit 150 to form test charts on the front and back surfaces of the adjustment sheet. The reader unit 170 reads the front and back surfaces of the adjustment sheet on which the test charts are formed and generates read images of the front and back surfaces. Based on the read images of the front and back surfaces generated by the reader unit 170, the adjustment unit 123 functions as a determination means for determining the adjustment amounts of the first and second image formation ranges. The adjustment sheet is discharged from the finisher 190 in the same way as a normal sheet. A normal sheet may be discharged to one of the discharge trays 191 and 192, and the adjustment sheet may be discharged to the other of the discharge trays 191 and 192.

[0044] Figure 7A is an explanatory diagram showing how the surface test chart 71 is formed on the adjustment sheet. The test chart 71 includes four marks M1 to M4, each located near one of the four corners. The color of marks M1 to M4 may be black, for example, to ensure sufficient contrast (e.g., difference in reflected light intensity) against a white background to accurately detect contours. The positions of marks M1 to M4 on the sheet are such that, when the test chart 71 is formed within the ideal image formation range, they are located at a predetermined distance from the edge of the sheet.

[0045] Figure 7B is an explanatory diagram showing how the test chart 72 on the reverse side is formed on the adjustment sheet. The test chart 72 includes four marks M5 to M8, each located near one of the four corners. The color of marks M5 to M8 may be black, similar to marks M1 to M4. The positions of marks M5 to M8 on the sheet are such that, when the test chart 72 is formed within the ideal image formation range, they are located at a predetermined distance from the edge of the sheet.

[0046] The adjustment unit 123 measures 12 variables A to J, S, and T, which are enclosed in parentheses in Figure 7A, by analyzing the surface reading image (i.e., based on the surface reading results). The analysis of the reading image may include, for example, detecting the edges of the adjustment sheet in the reading image, measuring the length of the edges, detecting the contours of the marks within the area of ​​the adjustment sheet, and measuring the distance from the edges to the contours of each mark. The measurement of length and distance may be performed, for example, by counting the number of pixels. Variable A represents the length of the side of the adjustment sheet parallel to the sub-scanning direction. Variable B represents the length of the side of the adjustment sheet parallel to the main scanning direction. Variable C represents the distance between the left side of the adjustment sheet and mark M1. Variable D represents the distance between the top side of the adjustment sheet and mark M1. Variable E represents the distance between the left side of the adjustment sheet and mark M3. Variable F represents the distance between the bottom side of the adjustment sheet and mark M3. Variable G represents the distance between the right side of the adjustment sheet and mark M2. Variable H represents the distance between the top edge of the adjustment sheet and mark M2. Variable I represents the distance between the right edge of the adjustment sheet and mark M4. Variable J represents the distance between the bottom edge of the adjustment sheet and mark M4. Variable S represents the offset of mark M2 with respect to the perpendicular line drawn from mark M1 to the right of the line connecting mark M1 and mark M3. Variable T represents the offset of mark M4 with respect to the perpendicular line drawn from mark M3 to the right of the line connecting mark M1 and mark M3. For the sake of explanation, the leading edge and trailing edge of the two sides of the adjustment sheet parallel to the main scanning direction are referred to as the left edge and right edge, respectively. Also, the leading edge and trailing edge of the two sides of the adjustment sheet parallel to the sub-scanning direction are referred to as the bottom edge and top edge, respectively.

[0047] Furthermore, the adjustment unit 123 measures 10 variables K~R, U, and V, enclosed in parentheses in Figure 7B, by analyzing the image read from the back side (i.e., based on the reading results from the back side). Variable K represents the distance between the left side of the adjustment sheet and mark M5. Variable L represents the distance between the top side of the adjustment sheet and mark M5. Variable M represents the distance between the left side of the adjustment sheet and mark M7. Variable N represents the distance between the bottom side of the adjustment sheet and mark M7. Variable O represents the distance between the right side of the adjustment sheet and mark M6. Variable P represents the distance between the top side of the adjustment sheet and mark M6. Variable Q represents the distance between the right side of the adjustment sheet and mark M8. Variable R represents the distance between the bottom side of the adjustment sheet and mark M8. Variable U represents the offset of mark M6 with respect to a perpendicular line when the perpendicular line connecting mark M5 and mark M7 is extended to the right from mark M5. The variable V represents the offset of mark M8 relative to the perpendicular line drawn from mark M7 to the right of the line connecting mark M5 and mark M7.

[0048] The adjustment unit 123 adjusts the angle correction amount W of the surface. T and angle correction amount W on the back surface B These are calculated as follows. Note that the following calculation formulas are independent of the sheet type, so the sheet type ID is omitted in each parameter:

number

[0049] Furthermore, the adjustment unit 123 adjusts the trapezoidal correction amount Z of the surface. T and the trapezoidal correction amount Z on the reverse side B These are calculated as follows:

number

[0050] Also, the adjustment unit 123 calculates the main scanning start offset amount ML on the front surface T and the main scanning start offset amount ML on the back surface B as follows:

Equation

[0051] Also, the adjustment unit 123 calculates the sub-scanning start offset amount SL on the front surface T and the sub-scanning start offset amount SL on the back surface B as follows:

Equation

[0052] Also, the adjustment unit 123 calculates the main scanning magnification MS on the front surface T and the main scanning magnification MS on the back surface B as follows:

Equation

[0053] Furthermore, the adjustment unit 123 controls the sub-scanning magnification SS of the surface. T and the sub-scanning magnification SS on the back side B These are calculated as follows:

number

[0054] <3-3. Test charts for each toner load category> The values ​​of the adjustment parameters mentioned above are determined for each sheet type, as described above. In addition, the sub-scan magnification SS T and SS B The value is determined for each toner load category. Sub-scan magnification SS for each toner load category T and SS B In this embodiment, multiple test charts with different toner amounts are used to determine the value of . Figure 8 shows an example of five test charts when the number of toner amount categories N is equal to 5.

[0055] Referring to Figure 8, five test charts 71a to 71e are shown. Test chart 71a is the test chart corresponding to the 0% toner load category. Test chart 71a is the same as test chart 71 explained using Figure 7A. Test chart 71b is the test chart corresponding to the 25% toner load category. In addition to the four marks similar to test chart 71, test chart 71b includes the toner load area 75b. The signal value of the image signal in the toner load area 75b is uniform throughout the entire toner load area 75b and corresponds to 25% of the signal value range. Test chart 71c is the test chart corresponding to the 50% toner load category. In addition to the four marks similar to test chart 71, test chart 71c includes the toner load area 75c. The signal value of the image signal in the toner load area 75c is uniform throughout the entire toner load area 75c and corresponds to 50% of the signal value range. Test chart 71d is the test chart corresponding to the 75% toner load category. Test chart 71d includes the same four marks as test chart 71, plus the toner application area 75d. The signal value of the image signal in the toner application area 75d is uniform throughout the entire toner application area 75d and corresponds to 75% of the signal value range. Test chart 71e is a test chart corresponding to the 100% toner application area. Test chart 71e includes the same four marks as test chart 71, plus the toner application area 75e. The signal value of the image signal in the toner application area 75e is uniform throughout the entire toner application area 75e and corresponds to 100% of the signal value range. The areas of toner application areas 75b to 75e are the same. Therefore, comparing the five test charts 71a to 71e, test chart 71a has the smallest toner application amount, and test chart 71e has the largest toner application amount.

[0056] The adjustment unit 123, for example, reads the surface image of the adjustment sheet on which the test chart 71a is formed, and determines the sub-scan magnification SS of the first division of the toner amount for sheet type i. Ti_1The adjustment unit 123 determines the second to fifth divisions of the toner amount for sheet type i from the reading images of the surfaces of the four adjustment sheets on which test charts 71b to 71e are formed, using the sub-scan magnification SS. Ti_2 SS Ti_3 SS Ti_4 and SS Ti_5 To decide.

[0057] On the reverse side, similar to test charts 71a to 71e, test charts corresponding to five different toner load amounts are provided (four of which include toner load areas with different signal values). The adjustment unit 123 then reads the image from the reverse side of the adjustment sheet on which these test charts are formed and scans the sub-scan magnification SS for the 1st to 5th divisions of the toner load amount for sheet type i. Bi_1 ~SS Bi_5 To decide.

[0058] <3-4. Adjustment of the image formation area> As described above, the adjustment unit 123 determines the values ​​of the adjustment parameters for the first and second image formation ranges and stores the determined values ​​in the sheet DB 121. In subsequent print jobs, the print control unit 122 adjusts the positions where images are formed on the front and back surfaces of the sheet according to the values ​​of the adjustment parameters stored in the sheet DB 121.

[0059] For example, sheet DB121 stores the values ​​of adjustment parameters for the first and second image forming ranges for each sheet type. The print control unit 122 selectively reads the corresponding adjustment parameter values ​​from sheet DB121 according to the sheet type selected for the job to be executed, and adjusts the first and second image forming ranges for that job according to the read values.

[0060] The adjustment of the first and second image forming ranges may be performed by controlling the operation of the components involved in the image forming operation of the printer unit 150. Additionally or alternatively, the adjustment of the first and second image forming ranges may be performed through a geometric transformation (typically an affine transformation) of the input image data of the print job.

[0061] Specifically, the print control unit 122 can correct the tilt and distortion of the image formation area by applying an affine transformation to the input image data according to the angle correction amount and the trapezoidal correction amount.

[0062] Furthermore, the print control unit 122 can adjust the starting position of the image formation range in the main scanning direction to an ideal position by displacing the scanning start position of the photosensitive drum 152 by the exposure unit 154 according to the main scanning start offset amount. In addition, the print control unit 122 can adjust the starting position of the image formation range in the sub-scanning direction to an ideal position by adjusting the timing of the scanning start of the photosensitive drum 152 by the exposure unit 154 according to the sub-scanning start offset amount.

[0063] Furthermore, the print control unit 122 can adjust the size of the image formation area in the main scanning direction to an ideal size by adjusting the clock frequency for modulating the laser light irradiated onto the photosensitive drum 152 by the exposure unit 154 according to the main scanning magnification. In addition, the print control unit 122 can adjust the size of the image formation area in the sub-scanning direction to an ideal size by adjusting the rotation speed of the photosensitive drum 152 and the intermediate transfer belt 156 according to the sub-scanning magnification. The rotation speed of the photosensitive drum 152 and the intermediate transfer belt 156 can be adjusted by changing the rotation speed of the corresponding motor (not shown).

[0064] The print control unit 122 calculates the amount of toner to be applied to the front and back surfaces of each sheet based on the input image data. The print control unit 122 then reads the sub-scanning magnification corresponding to the calculated toner amount from the second parameter table 60 and uses the read sub-scanning magnification to adjust the size of the image formation area on the front and back surfaces of each sheet.

[0065] Multiple categories of toner load typically include a category corresponding to 0% toner load, a category corresponding to 100% toner load, and one or more categories corresponding to intermediate toner loads. For example, in an example where the number of toner load categories N=5, each category shall correspond to the following range of toner loads: ·Category 1 0~12.5% ·Category 2 12.5~37.5% ·Category 3 37.5~62.5% ·Category 4 62.5~87.5% ·Category 5 87.5~100% Then, when an image with a toner content of 10% is formed on the surface of a sheet of the sheet type identified by ID "1", the sub-scan magnification SS is used to adjust the size of the image formation area on the surface of the sheet. T1_1 The following may be used. Also, if an image with a toner coverage of 90% is formed on the back of the same sheet, the sub-scan magnification SS may be used to adjust the size of the image formation area on the back of the sheet. B1_5 It can be used.

[0066] As a result of this image processing and control of the printer unit 150's operation, the misalignment between the first image formation area on the front surface of the sheet and the second image formation area on the back surface is reduced, and alignment of the front and back surfaces can be achieved. For example, it is known that the amount of toner applied differs greatly between document images and photographic images (usually the latter has significantly more toner), but by selecting the sub-scanning magnification according to the amount of toner applied as described above, positional misalignment caused by such differences can be suppressed.

[0067] Before the values ​​of the adjustment parameters are determined using the test chart, the values ​​of the adjustment parameters in sheet DB121 may be zero, or they may represent values ​​determined through pre-shipment testing of the product.

[0068] <3-5. Initial and Intermediate Adjustments> In this embodiment, the image forming apparatus 100 provides an intermediate adjustment function that allows for the re-determination of the adjustment amount during job execution in order to reduce adjustment errors in the image forming range caused by changes in environmental conditions or sheet characteristics during the execution of a job spanning multiple sheets. Specifically, the print control unit 122 causes the printer unit 150 to form at least one test chart on the front and back surfaces of the adjustment sheet each time a predetermined number of sheets are output during the execution of a job spanning multiple sheets. The adjustment unit 123 updates the values ​​of the adjustment amounts for the first and second image forming ranges based on the front and back surface reading images generated by the reader unit 170 for this adjustment sheet.

[0069] If, each time an intermediate adjustment is performed, all N test charts, as explained using Figure 8, were to be formed on the corresponding adjustment sheet, a large number of adjustment sheets would be consumed, increasing the waste of sheets and prolonging the time required to complete the job. Therefore, in this embodiment, during intermediate adjustment, the formation of some of the test charts corresponding to multiple categories of toner application amount is omitted.

[0070] Figure 9 is an explanatory diagram illustrating the omission of test chart formation during intermediate adjustments. Figure 9 shows a series of normal and adjustment sheets that may be output in a single print job, arranged chronologically from left to right and top to bottom. Here, the number of toner load categories N=5, and intermediate adjustments are performed at intervals equivalent to M sheets.

[0071] First, when the print job starts, sheets P1-P are created with images based on the input image data. M These are output sequentially from the printer unit 150. Next, if a test chart corresponding to all five categories of toner load is formed on the adjustment sheet, adjustment sheet P a1 ~P a5 This will be output. However, in this embodiment, for example, the adjustment sheet P on which the test chart 71a is formed is used. a1Only the following is output. Next, sheet P is created with an image based on the input image data. M+1 ~P 2M These are output in order. Next, if a test chart corresponding to all five categories of toner amount is formed on the adjustment sheet, adjustment sheet P b1 ~P b5 This will be output. However, in this embodiment, for example, the adjustment sheet P on which the test chart 71a is formed is used. b1 Only the following is output. Next, sheet P is created with an image based on the input image data. 2M+1 ~P 3M These are output in order. This omission reduces the waste of 8 sheets during the normal image formation process for up to 300 sheets, for example, when M=100.

[0072] To control the intermediate adjustments described above, at least one of the multiple toner load categories is pre-set as a category in which the formation of a test chart is not omitted. In this specification, the category in which the formation of a test chart is not omitted is referred to as a "specific category," and the other categories are referred to as "non-specific categories." In the example in Figure 9, category 1 of the five categories is a specific category, and categories 2 to 5 are non-specific categories.

[0073] Typically, the calculation of the sub-scan magnification using test charts for all toner load categories (hereinafter referred to as initial adjustment) is performed prior to the execution of the print job. In the following description, we will assume that the number of toner load categories N=5. In initial adjustment, the printer unit 150 forms five test charts with different toner loads on the front and back surfaces of five adjustment sheets. The adjustment unit 123 determines the initial values ​​of the sub-scan magnification for the front and back surfaces of the five toner load categories based on the front and back surface reading images generated by the reader unit 170 for the five adjustment sheets.

[0074] Subsequently, during intermediate adjustments while a job spanning multiple sheets is running, the printer unit 150 forms test charts on the front and back surfaces of the corresponding adjustment sheets, corresponding to specific sections. The adjustment unit 123 updates the front and back surface values ​​of the sub-scan magnification for the specific section based on the front and back surface reading images generated by the reader unit 170 for the adjustment sheet. Furthermore, the adjustment unit 123 updates the front and back surface values ​​of the sub-scan magnification for non-specific sections based on the updated sub-scan magnification values ​​for the specific section.

[0075] The adjustment unit 123 determines the sub-scan magnification value for each non-specific category using an adjustment coefficient for the sub-scan magnification between the specific category and each non-specific category. In this embodiment, the adjustment coefficient is based on the ratio of the initial values ​​of the sub-scan magnification. Therefore, in the following description, the adjustment coefficient will also be called the magnification ratio. For example, category 1 is the specific category, categories 2 to 5 are non-specific categories, and the initial values ​​of the sub-scan magnification for categories 1 to 5 are SS Ti_1 SS Ti_2 SS Ti_3 SS Ti_4 and SS Ti_5 Assume the following: The magnification ratios SR2 to SR5 of the sub-scan magnification of non-specific categories 2 to 5 relative to the sub-scan magnification of specific category 1 can be derived as follows: SR2 = SS Ti_2 / SS Ti_1 SR3 = SS Ti_3 / SS Ti_1 SR4 = SS Ti_4 / SS Ti_1 SR5 = SS Ti_5 / SS Ti_1 The updated sub-scan magnification value for specific category 1 is SS Ti_1 If it is ', the updated sub-scan magnification value SS for non-specific categories 2-5 is obtained using the above magnification ratio. Ti_2 '~SS Ti_5 The values ​​of ' can be calculated as follows: SS Ti_2 ' = SS Ti_1 '×SR2 SS Ti_3 ' = SS Ti_1 '×SR3 SS Ti_4 ' = SS Ti_1 '×SR4 SS Ti_5 ' = SS Ti_1 '×SR5

[0076] Here, we have explained an example where the category with the smallest toner load (Category 1) is selected as the specific category, but a category with a larger toner load (Category 5) may also be selected as the specific category. Furthermore, the magnification ratio of the front surface and the magnification ratio of the back surface may be determined separately for each category. For example, the updated sub-scanning magnification value of the front surfaces of non-specific categories 2 to 5 can be calculated by multiplying the updated sub-scanning magnification value of the front surface of specific category 1 by the magnification ratio of the front surfaces of non-specific categories 2 to 5. Similarly, the updated sub-scanning magnification value of the back surfaces of non-specific categories 2 to 5 can be calculated by multiplying the updated sub-scanning magnification value of the back surface of specific category 1 by the magnification ratio of the back surfaces of non-specific categories 2 to 5.

[0077] When intermediate adjustments are performed, the print control unit 122 uses a value selected from the updated sub-scan magnification values ​​during the intermediate adjustments, according to the amount of toner applied to each image, to adjust the size of the image formation range in the sub-scan direction when forming images on subsequent sheets of the same job. As a result, even though the formation of some test charts is omitted during the intermediate adjustments, the first and second image formation ranges can be appropriately adjusted across multiple toner application ranges in response to changes in environmental conditions or sheet characteristics.

[0078] For adjustment parameters other than the sub-scan magnification, the adjustment unit 123 may determine or update the values ​​of the adjustment parameters based on the read image of the adjustment sheet on which a test chart corresponding to a specific category is formed, both during initial and intermediate adjustments. As described above, the values ​​of these adjustment parameters may be common across multiple categories of toner load.

[0079] <3-6. UI for initial and intermediate adjustments> In this specification, the term "initial adjustment" simply means that the determination of adjustment amounts using test charts for all toner load categories is performed before "intermediate adjustment." In other words, initial adjustment is not necessarily performed only once. As described below, initial adjustment may be performed any number of times in response to function calls from the user via the user interface (UI).

[0080] Figures 10–11C show some examples of UIs that may be provided to the user in relation to adjusting the image formation range.

[0081] The cassette assignment status screen 80 shown in Figure 10 is a screen for managing the assignment status of sheet types to the five cassettes of the image forming apparatus 100. The cassette assignment status screen 80 includes five sheet type fields 81 to 81e, a sheet assignment button 82, and a position adjustment button 83. The five sheet type fields 81a to 81e are fields that display the sheet types currently assigned to each of the five cassettes. Sheet type field 81a indicates that the sheet type "BC RECYCLE 1" is assigned to cassette 1 (for example, cassette 141a) (meaning that a sheet of that type is contained in it). Sheet type field 81b indicates that the sheet type "BC RECYCLE 2" is assigned to cassette 2 (for example, cassette 141b). Sheet type field 81c indicates that the sheet type "DE EMBOSS A1" is assigned to cassette 3 (for example, cassette 141c). The sheet type field 81d indicates that the sheet type "XY COLOR B1" is assigned to cassette 4 (for example, cassette 160a). The sheet type field 81e indicates that no sheet type is assigned to cassette 5 (for example, cassette 160b). When the user selects (for example, touches) any of the sheet type fields and then operates the sheet assignment button 82, it becomes possible to assign any of the registered sheet types to the cassette corresponding to the selected field on a subsequent screen. When the user operates the position adjustment button 83, the cassette assignment status screen 80 transitions to the position adjustment menu screen 85, which will be described next.

[0082] The position adjustment menu screen 85 shown in Figure 11A is a screen for calling up functions provided by the image forming apparatus 100 in relation to the adjustment of the image forming range. The position adjustment menu screen 85 includes an initial adjustment execution button 86, an intermediate adjustment setting button 87, and a back button 88. When the user operates the initial adjustment execution button 86, the position adjustment menu screen 85 transitions to the initial adjustment screen 90, which will be described next. When the user operates the intermediate adjustment setting button 87, the position adjustment menu screen 85 transitions to the intermediate adjustment setting screen 95, which will be described next. When the user operates the back button 88, the display of the position adjustment menu screen 85 ends, and the cassette allocation status screen 80 shown in Figure 10 is displayed again.

[0083] The initial adjustment screen 90 shown in Figure 11B is a screen for triggering the execution of the initial adjustment. The initial adjustment screen 90 includes a cassette selection field 91, an execute button 92, and a cancel button 93. The cassette selection field 91 is a field for selecting the cassette (or corresponding sheet type) to be used for the initial adjustment. The cassette selection field 91 allows selection of one cassette from among the five cassettes of the image forming apparatus 100 that have already been assigned a sheet type. The execute button 92 is a button for triggering the execution of the initial adjustment for the sheet type corresponding to the cassette selected in the cassette selection field 91. The cancel button 93 is a button for canceling the execution of the initial adjustment and returning to the position adjustment menu screen 85.

[0084] The Intermediate Adjustment Settings screen 95 shown in Figure 11C is a screen for changing settings regarding intermediate adjustments. The Intermediate Adjustment Settings screen 95 includes a checkbox 96, an execution interval setting field 97, an OK button 98, and a Cancel button 99. The checkbox 96 is an object for setting whether or not to enable intermediate adjustments. If the checkbox 96 is checked, intermediate adjustments are enabled, and intermediate adjustments may be performed at intervals set in the execution interval setting field 97 during the execution of a job spanning multiple sheets. If the checkbox 96 is not checked, intermediate adjustments are disabled, and intermediate adjustments will not be performed during the execution of a job spanning multiple sheets. The execution interval setting field 97 is a field for setting the interval at which intermediate adjustments are performed, in terms of the number of sheets. The OK button 98 is a button for saving the changed settings on the Intermediate Adjustment Settings screen 95 to memory. The Cancel button 99 is a button for canceling the setting changes on the Intermediate Adjustment Settings screen 95 and returning to the Position Adjustment Menu screen 85.

[0085] <4. Processing Flow> In this section, several examples of processing flows that can be performed by the image forming apparatus 100 in this embodiment will be described using flowcharts. In each flowchart, 'S' represents a processing step.

[0086] (1) Initial adjustment process Figure 12 is a flowchart showing an example of the flow of the initial adjustment process according to one embodiment. The initial adjustment process in Figure 12 is started when the user operates the execute button 92 on the initial adjustment screen 90 in Figure 11B, for example.

[0087] First, in S11, the print control unit 122 selects one of several categories of toner load and retrieves test chart data from memory that represents the test charts for the front and back sides corresponding to the selected category. Next, in S12, the print control unit 122 causes the printer unit 150 to form a test chart on both sides of a single adjustment sheet based on the retrieved test chart data. The adjustment sheet here may be a sheet fed from the cassette selected in the cassette selection field 91 of the initial adjustment screen 90 (a sheet of the selected sheet type).

[0088] Next, in S13, the reader unit 170 reads the front and back surfaces of the adjustment sheet on which the test chart is formed, and generates reading images of the front and back surfaces. The adjustment unit 123 acquires the reading images of the front and back surfaces. Next, in S14, the adjustment unit 123 analyzes the reading images of the front and back surfaces generated in S13 and measures the aforementioned variables related to the positional relationship between the adjustment sheet and each test chart.

[0089] Next, in S15, the adjustment unit 123 calculates the sub-scan magnification for the front and back surfaces for the selected section using the variable values ​​measured in S14. Then, in S16, the initial adjustment process branches depending on whether the selected section is the first section (or a specific section). If the section selected in S16 is the first section, in S17, the adjustment unit 123 calculates one or more adjustment amounts other than the sub-scan magnification for the front and back surfaces for that section using the variable values ​​measured in S14. If the section selected in S16 is not the first section, the adjustment unit 123 skips S17, and the initial adjustment process proceeds to S18.

[0090] In S18, the adjustment unit 123 updates the sheet DB 121 with the values ​​of the adjustment amounts calculated for the selected category. For example, the values ​​of the sub-scan magnification for the front and back surfaces are stored in the second parameter table 60 in association with the selected sheet type and category combination. In addition, the values ​​of one or more adjustment amounts other than the sub-scan magnification for the front and back surfaces are stored in the first parameter table 50 in association with the selected sheet type.

[0091] Next, the adjustment unit 123 determines whether the adjustment amount (sub-scanning magnification) has been calculated for all of the multiple categories of toner load. If there are still categories for which the adjustment amount (sub-scanning magnification) has not been calculated, the initial adjustment process returns to S11, and the adjustment unit 123 repeats steps S11 to S19 until the adjustment amount (sub-scanning magnification) has been calculated for all categories. If the adjustment amount (sub-scanning magnification) has been calculated for all categories, the initial adjustment process shown in Figure 12 is completed.

[0092] The adjustment values ​​calculated during this initial adjustment process are used as initial values ​​to adjust the first and second image formation ranges when forming images on sheets in the print job that is started later.

[0093] (2) Job control processing Figure 13 is a flowchart showing an example of the job control process flow according to this embodiment. The job control process in Figure 13 is started when the print control unit 122 receives a print job from an external device or via the operation unit 130.

[0094] First, in S21, the print control unit 122 obtains the settings for the print job. The print job settings may include, for example, the number of copies to print, single-sided / double-sided, sheet type, and the type of post-processing to be applied. Next, in S22, the print control unit 122 determines whether initial adjustments have been performed for the sheet type specified in the print job. If initial adjustments have been performed for the sheet type specified in the print job, in S23, the print control unit 122 obtains initial values ​​for the adjustment amounts for adjusting the first image forming area on the front side and the second image forming area on the back side from the sheet DB 121. If initial adjustments have not been performed for the sheet type specified in the print job in S22, the print control unit 122 skips S23, and the job control process proceeds to S24.

[0095] Next, in S24, the print control unit 122 executes the print job according to the settings acquired in S21. During the execution of the print job, the sheets are fed from the cassette (or designated cassette) to which the sheet type specified in the print job is assigned. The print control unit 122 converts the input image data so that the tilt and distortion of the image forming area are corrected, for example, according to the angle correction amount and the trapezoidal correction amount. The print control unit 122 also adjusts the position of the image forming area in the main scanning direction and the sub-scanning direction according to the main scanning start offset amount and the sub-scanning start offset amount (i.e., aligns the start position with the reference position). The print control unit 122 also adjusts the size of the image forming area in the main scanning direction and the sub-scanning direction according to the main scanning magnification and the sub-scanning magnification. For each of the front and back sides, the adjustment of the size of the image forming area in the sub-scanning direction is performed using the sub-scanning magnification associated with the division corresponding to the amount of toner in the printed image. If double-sided printing is specified, these adjustments are performed for both the front and back sides, thereby aligning the first image forming area on the front side and the second image forming area on the back side. If initial adjustments have not been performed for the sheet type specified in the print job, the image will be formed on the sheet without such adjustments.

[0096] (3) Executing a print job If duplex printing is specified in a print job and mid-job adjustments are enabled, the mid-job adjustment process is executed during the execution of the print job in S24. Figure 14 is a flowchart showing a more detailed example of the execution flow of such a print job.

[0097] First, in S31, the print control unit 122 sets the execution interval M as the setting value for intermediate adjustment. INT The value is obtained from memory. Next, in S32, the print control unit 122 uses counter C to count the number of normal sheets output from the printer unit 150. SHEET Reset to zero. Then, in S33, the print control unit 122 controls counter C SHEET The execution interval is M INT Determine whether or not it has reached the target. In S33, counter C SHEET The execution interval is M INT If it has not reached (C SHEET <M INT ), the process then proceeds to S34.

[0098] In S34, the print control unit 122 controls the printer unit 150 to form images on the front and back surfaces of a normal sheet based on the input image data. At this time, the first image formation area on the front surface and the second image formation area on the back surface may be adjusted according to the adjustment amount values ​​stored in the sheet DB 121, as described above. When the sheet with the image formed on it is output from the printer unit 150, in S35, the print control unit 122 controls the counter C SHEET The value is incremented (1 is added). Next, in S36, the print control unit 122 determines whether the execution of the print job is complete or not. For example, if there are still parts or pages that have not been printed in S36, the execution of the print job is not complete, and the process returns to S33.

[0099] Counter C in S33 SHEET The execution interval is M INTIf it is determined that the value has been reached, the process proceeds to S37. In S37, the adjustment unit 123 performs an intermediate adjustment process and updates the values ​​of the adjustment amounts for adjusting the first and second image forming ranges. A more detailed example of the flow of the intermediate adjustment process performed here will be explained later. When the intermediate adjustment process is completed, the print control unit 122 performs a counter C in S32. SHEET The value is reset to zero, and the printer unit 150 is controlled in S34 to form an image on the subsequent sheet.

[0100] When image formation is completed for all pages of all sections in S36, the print control unit 122 determines that the print job has been completed, and the process in Figure 14 ends.

[0101] (4) Intermediate adjustment process Figure 15 is a flowchart showing an example of the flow of the intermediate adjustment process that may be performed in S37 of Figure 14.

[0102] First, in S41, the print control unit 122 retrieves test chart data from memory, which represents test charts for the front and back sides corresponding to a pre-set specific category among several categories of toner load. Next, in S42, the print control unit 122 causes the printer unit 150 to form test charts on both sides of a single adjustment sheet based on the retrieved test chart data. The adjustment sheet is fed from the cassette selected for the currently running print job.

[0103] Next, in S43, the reader unit 170 reads the front and back surfaces of the adjustment sheet on which the test chart is formed, and generates reading images of the front and back surfaces. The adjustment unit 123 acquires the reading images of the front and back surfaces. Next, in S44, the adjustment unit 123 analyzes the reading images of the front and back surfaces generated in S43 and measures the aforementioned variables related to the positional relationship between the adjustment sheet and each test chart.

[0104] Next, in S45, the adjustment unit 123 uses the variable values ​​measured in S44 to calculate the sub-scanning magnification for the front and back surfaces, as well as one or more adjustment amounts other than the sub-scanning magnification for the specified section. Next, in S46, the adjustment unit 123 calculates the ratio of the initial value of the sub-scanning magnification to that of the specified section, i.e., the magnification ratio, for one or more non-specified sections. Note that in subsequent intermediate adjustment processes for the same print job, the magnification ratio calculated once may be reused. Next, in S47, the adjustment unit 123 calculates the sub-scanning magnification for the non-specified sections based on the updated value of the sub-scanning magnification for the specified section and the magnification ratio of one or more non-specified sections.

[0105] The values ​​of the adjustment amounts calculated during this intermediate adjustment process are stored in memory and used to adjust the first and second image formation ranges when forming images on subsequent sheets during the execution of the same job. For example, the calculated values ​​of the sub-scan magnification for multiple sections are stored in the second parameter table 60. The adjustment of the image formation range for each subsequent sheet is performed using the calculated value of the sub-scan magnification corresponding to the amount of toner on that sheet. On the other hand, the calculated values ​​of adjustment amounts other than the sub-scan magnification are stored in the first parameter table 50. The adjustment of the image formation range other than the sub-scan magnification for each subsequent sheet is performed using the calculated values ​​stored in the first parameter table 50, regardless of the amount of toner on that sheet.

[0106] <5. Variation> If a long time has passed since the initial adjustment was performed, or if there are significant changes in environmental conditions or sheet characteristics during job execution, the estimation of the sub-scanning magnification of non-specific sections based on the sub-scanning magnification of specific sections may not be able to sufficiently reduce the adjustment error of the image formation range. Therefore, in the modified embodiment described above, if it is determined that the adjustment amount of the image formation range calculated for a specific section fluctuates beyond a predetermined upper limit during intermediate adjustment, the adjustment amount for non-specific sections is also calculated using the corresponding test chart.

[0107] Specifically, during the execution of a job across multiple sheets, the adjustment unit 123 updates the sub-scanning magnification of the front and back surfaces based on the read image of the adjustment sheet on which a test chart of a specific section is formed by the above-described mid-course adjustment process. For example, assuming that section 1 is the specific section, the sub-scanning magnification of the front surface changes from SS T_1 to SS T_1 ´, and the sub-scanning magnification of the back surface changes from SS B_1 to SS B_1 ´. The difference between the value after the change and the initial value of the sub-scanning magnification of the front surface, that is, the change amount ΔSS T T_1 to SS T_1 ´, and the sub-scanning magnification of the back surface changes from SS B_1 to SS B_1 ´. The difference between the value after the change and the initial value of the sub-scanning magnification of the front surface, that is, the change amount ΔSS T is calculated as ΔSS T =|SS<000009...is calculated as ΔSS T =|SS T_1 -SS T_1 ´|. Similarly, the difference between the value after the change and the initial value of the sub-scanning magnification of the back surface, that is, the change amount ΔSS B is calculated as ΔSS B =|SS B_1 -SS B_1 ´|. The adjustment unit 123 determines whether the adjustment amount of the image formation range fluctuates beyond a predetermined upper limit by comparing these change amounts ΔSS T and ΔSS B with a threshold value. For example, the adjustment unit 123 may determine that the adjustment amount of the image formation range fluctuates beyond a predetermined upper limit when either ΔSS T [[ID=3... ´|. The adjustment unit 123 determines whether the adjustment amount of the image formation range fluctuates beyond a predetermined upper limit by comparing these change amounts ΔSS T [[ID=... with a threshold value. For example, the adjustment unit 123 may determine that the adjustment amount of the image formation range fluctuates beyond a predetermined upper limit when either ΔSS T and ΔSS B exceeds the threshold value. Note that the change amount of the sub-scanning magnification may be determined based on the ratio of the value after the change to the initial value instead of the difference between the value after the change and the initial value of the sub-scanning magnification.

[0108] If it is determined that the adjustment amount fluctuates beyond a predetermined upper limit, the print control unit 122 controls the printer unit 150 to form all of a plurality of test charts with different toner loading amounts on the corresponding adjustment sheets. Then, the adjustment unit 123 updates the values of the sub-scanning magnification of the front and back surfaces for all corresponding non-specific sections based on the read images of the front and back surfaces generated by the reader unit 170 for those adjustment sheets.

[0109] ΔSS T and ΔSS BThe threshold values ​​used for comparison can be determined, for example, by measuring the adjustment error of the sub-scan magnification while varying test conditions such as ambient temperature, internal temperature of the device, or moisture absorption state of the sheet during pre-shipment testing of the product, and can be written to memory. Multiple candidate values ​​for the threshold values ​​may be provided, and one of these candidate values ​​may be selectable by the user via a UI such as the intermediate adjustment setting screen 95 described above. This allows the user to flexibly change the number of adjustment sheets used for intermediate adjustment according to their needs, such as selecting a relatively large threshold value when cost reduction is a priority, or a relatively small threshold value when alignment accuracy is a priority.

[0110] Figure 16 is a flowchart showing an example of the flow of an intermediate adjustment process that can be performed in this modified example. The intermediate adjustment process in Figure 16 can be performed during the execution of a job spanning multiple sheets, whenever the number of output sheets reaches a predetermined execution interval.

[0111] Since steps S51 to S55 in Figure 16 are the same processing steps as S41 to S45 in Figure 15 described above, we will omit repeating their explanations here.

[0112] In S56, the adjustment unit 123 adjusts the change in surface sub-scanning magnification ΔSS. T and the change in the sub-scanning magnification of the back side ΔSS B Calculate ΔSS. For example, ΔSS T This may be the difference between the initial value of the surface sub-scan magnification and the value calculated in S55, ΔSS B This may be the difference between the initial value of the sub-scan magnification on the back side and the value calculated in S55. Next, in S57, the adjustment unit 123 adjusts ΔSS T and ΔSS B This is compared to a pre-set threshold. For example, ΔSS T and ΔSS B If neither of these exceeds the threshold, the process proceeds to S58. ΔSS T and ΔSS B If any of these conditions exceed the threshold, the process proceeds to S61.

[0113] In S58, the adjustment unit 123 calculates the sub-scanning magnification of one or more non-specific categories based on the sub-scanning magnification of a specific category. For example, the adjustment unit 123 can calculate the sub-scanning magnification of each non-specific category by calculating the magnification ratio for each non-specific category relative to the specific category, and multiplying the calculated magnification ratio by the sub-scanning magnification of the specific category.

[0114] In S61, the print control unit 122 selects one of the non-specific categories and retrieves test chart data from memory representing the front and back test charts corresponding to the selected non-specific category. Then, in S62, the print control unit 122 causes the printer unit 150 to form a test chart on both sides of a single adjustment sheet based on the retrieved test chart data.

[0115] Next, in S63, the reader unit 170 reads the front and back surfaces of the adjustment sheet on which the test chart is formed, and generates reading images of the front and back surfaces. Then, in S64, the adjustment unit 123 analyzes the reading images of the front and back surfaces generated in S63 and measures the aforementioned variables related to the positional relationship between the adjustment sheet and each test chart.

[0116] Next, in S65, the adjustment unit 123 calculates the sub-scan magnification for the front and back surfaces of the selected non-specific section using the variable values ​​measured in S64. The subsequent processing branches in S66 depending on whether or not the sub-scan magnification has been calculated for all non-specific sections. If there are still non-specific sections for which the sub-scan magnification has not been calculated, the process returns to S61, and steps S61 to S66 are repeated for the new non-specific sections. If the sub-scan magnification has been calculated for all non-specific sections, the intermediate adjustment process shown in Figure 16 is terminated.

[0117] As shown in this modified example, when the amount of adjustment of the image formation range fluctuates beyond a predetermined upper limit, the formation of test charts corresponding to multiple categories of toner application can be kept from being omitted, thereby preventing the expansion of adjustment errors caused by the passage of time or significant changes in characteristics.

[0118] Furthermore, whether or not the adjustment amount of the image forming range fluctuates beyond a predetermined upper limit may be determined by measuring changes in environmental conditions or sheet characteristics using sensors installed in the image forming apparatus 100, instead of comparing the change in sub-scanning magnification with a threshold.

[0119] <6. Summary> Up to this point, various embodiments and modifications of the technology relating to this disclosure have been described using Figures 1 to 16. In the embodiments described above, an image forming apparatus capable of forming an image on a sheet forms a plurality of test charts corresponding to different toner load categories on a plurality of adjustment sheets prior to the execution of a job, and reads these adjustment sheets to generate front and back surface reading images. The image forming apparatus then determines initial values ​​for the adjustment amounts of the image forming range on the front and back surfaces for a plurality of toner load categories based on the front and back surface reading images. Furthermore, the image forming apparatus forms at least one test chart on an adjustment sheet during the execution of a job spanning multiple sheets, and reads the adjustment sheet to generate front and back surface reading images. The image forming apparatus then updates the value of the adjustment amount of the image forming range for at least one corresponding toner load category (first toner load category) based on the read image (first reading result). Furthermore, the image forming apparatus updates the adjustment value of the image forming range for other toner load categories (second toner load categories) based on the updated adjustment value. With this configuration, by forming test charts corresponding to only some, rather than all, toner load categories on the adjustment sheet, the adjustment amount suitable for alignment when forming images with various toner loads on the sheet can be appropriately updated during job execution. Therefore, it is possible to achieve both improved alignment accuracy for each surface and reduced sheet waste.

[0120] Furthermore, in the embodiments described above, the adjustment amount for the image forming range includes the magnification of the image forming range. Therefore, even if the degree of slippage of the transported sheet changes during job execution due to differences in the amount of toner applied to the printed image, the effects of this change can be absorbed by adjusting the magnification of the image forming range, and an image of uniform size can continue to be formed on the sheet. The above magnification may be the magnification in a first direction parallel to the sheet transport direction (for example, the sub-scanning direction).

[0121] Furthermore, in the embodiments described above, the magnification for a specific category may be updated based on the magnification updated for that category based on the reading of the test chart, and an adjustment coefficient for the magnification between the specific category and the non-specific category. The adjustment coefficient here may be, for example, a coefficient based on the ratio of the initial values ​​of the magnification between the specific category and the non-specific category. In this case, for the non-specific category, the magnification of the image formation range can be estimated or calculated with good accuracy without forming a corresponding test chart on the adjustment sheet. For example, the initial value of the magnification of the image formation range for the second toner amount category is determined based on the second reading result for the test chart corresponding to the second toner amount category. The initial value of the magnification of the image formation range for the first toner amount category is determined based on the third reading result for the test chart corresponding to the first toner amount category. If the adjustment coefficient is equal to the ratio of the former initial value to the latter initial value, the updated magnification for the second toner amount category can be easily calculated by multiplying the updated magnification for the first toner amount category by the adjustment coefficient. The configuration of the test chart used to determine the initial value of the magnification may be the same as or different from the configuration of the test chart used to update the magnification.

[0122] Furthermore, in the embodiments described above, one or more adjustment amounts other than the magnification of the image forming range can be determined as common parameters across multiple toner amount divisions. Therefore, since the values ​​of the adjustment amounts corresponding to multiple toner amount divisions are stored only for the magnification, which is susceptible to the toner amount of the printed image, memory resources for storing the set of adjustment amount values ​​can be used efficiently.

[0123] Furthermore, in the embodiment described above, the value of the adjustment amount for the image forming range is stored in a database in association with the sheet type. The image forming apparatus then adjusts the image forming range for a job according to the value of the adjustment amount stored in the database in association with the sheet type selected for that job. Therefore, even if differences in the characteristics of each sheet type and differences in the amount of toner applied have a combined effect on the misalignment of the image forming range, such misalignment of the image forming range can be sufficiently reduced, and the accuracy of image alignment on the sheet can be effectively improved.

[0124] In this specification, we have mainly described an example in which one of the multiple categories of toner application amount is a specific category and the other categories are non-specific categories, but the number of specific categories may be two or more. Also, in this specification, we have mainly described an example in which only the sub-scan magnification among the adjustment parameters of the image forming range has different values ​​for each category of toner application amount, but other adjustment parameters may also have different values ​​for each category of toner application amount. For example, for the main scan magnification, the value for the specific category may be updated based on the reading of the test chart, and the value for the non-specific category may be updated based on the updated value and the magnification ratio between the specific category and the non-specific category.

[0125] To reiterate, while this specification primarily describes examples of aligning both sides by adjusting the image-forming areas on the front and back surfaces, the technology described herein is also applicable to adjusting the image-forming area on only one side.

[0126] <7. Other Embodiments> The above embodiment can also be implemented in the form of a process in which a program that implements one or more functions is supplied to a system or device via a network or storage medium, and one or more processors in the computer of that system or device read and execute the program. It can also be implemented by a circuit (e.g., AS.IC) that implements one or more functions.

[0127] 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]

[0128] 10: Network, 20: Host computer, 71, 71a~71e, 72: Test chart, 75b~75e: Toner application area, 100: Image forming apparatus, 110: Controller, 121: Sheet DB (database), 122: Print control unit (control means), 123: Adjustment unit (determination means), 130: Operation unit, 140: Paper feeding unit, 150: Printer unit (image forming means), 170: Reader unit (reading means), 190: Finisher, P1~P M : Regular seat, P a1 ~P a5 ,P b1 ~P b5 : Adjustment sheet

Claims

1. Image forming means for forming an image on a sheet using toner, A reading means for reading the test chart formed on the sheet by the image forming means, Based on the results of reading the test chart by the reading means, a determination means determines an adjustment amount for adjusting the magnification of the image formation area in which an image should be formed by the image forming means, for each toner amount category. A control means for controlling the formation of an image by the image forming means according to the adjustment amount determined by the determination means, It has, The aforementioned determination means is The adjustment amount for the first toner load category is determined based on the first reading result for the test chart corresponding to the first toner load category. The adjustment amount for the second toner load category is determined based on the first reading result and the adjustment coefficient between the first toner load category and the second toner load category. Image forming apparatus.

2. The image forming apparatus according to claim 1, wherein the determination means determines the adjustment coefficient based on a second reading result for a test chart corresponding to the second toner amount category and a third reading result for a test chart corresponding to the first toner amount category.

3. The determination means determines the initial value of the adjustment amount for the second toner amount category based on the second reading result, and determines the initial value of the adjustment amount for the first toner amount category based on the third reading result. The adjustment coefficient is based on the ratio between the initial value of the adjustment amount for the second toner load category and the initial value of the adjustment amount for the first toner load category. The image forming apparatus according to claim 2.

4. The aforementioned determination means is Based on the change in the adjustment amount for the first toner amount category determined based on the first reading result, relative to the initial value, it is determined whether or not to have the image forming means form a test chart corresponding to the second toner amount category. If it is decided not to have the image forming means form a test chart corresponding to the second toner amount category, the adjustment amount for the second toner amount category is determined based on the first reading result and the adjustment coefficient. The image forming apparatus according to claim 3.

5. The determination means, when the amount of change of the adjustment amount for the first toner amount category relative to the initial value exceeds a threshold, It was decided to have the image forming means form a test chart corresponding to the second toner load category. The adjustment amount for the second toner load category is determined based on the fourth reading result for the test chart corresponding to the second toner load category. The image forming apparatus according to claim 4.

6. The image forming apparatus according to claim 4, wherein the amount of change of the adjustment amount with respect to the initial value is based on the difference between the value of the adjustment amount after the change and the initial value, or the ratio of the value of the adjustment amount after the change to the initial value.

7. The image forming apparatus according to claim 5, wherein the threshold is selectable by the user.

8. The image forming apparatus according to claim 1, wherein the magnification is the magnification in a first direction parallel to the conveying direction of the sheet.

9. The image forming apparatus according to claim 1, wherein the control means causes the image forming means to form the test chart on the adjustment sheet each time a predetermined number of sheets are output by the image forming means during the execution of a job spanning multiple sheets.

10. The determination means determines one or more other adjustment amounts related to the image forming range during the execution of the job across multiple sheets, The aforementioned one or more adjustment amounts are common to the first toner load category and the second toner load category. The image forming apparatus according to claim 9.

11. The magnification is the magnification in a first direction parallel to the conveying direction of the sheet. The other one or more adjustment amounts are: The magnification of the image forming range in the second direction perpendicular to the first direction, The start offset of the image forming range in the second direction, The start offset of the image forming range in the first direction, The angle correction amount of the image forming range, and The amount of trapezoidal correction in the aforementioned image formation range, The image forming apparatus according to claim 10, comprising at least one of the following.

12. The aforementioned first toner load category corresponds to a toner load of 0%, The second toner load category mentioned above corresponds to a larger toner load. The image forming apparatus according to claim 1.

13. The image forming apparatus further includes a database for storing the value of the adjustment amount determined by the determination means, The image forming means forms an image on the sheet while adjusting the image forming range according to the value of the adjustment amount stored in the database. The image forming apparatus according to claim 1.

14. The database stores the values ​​of the adjustment amounts in association with the sheet type. The image forming means adjusts the image forming range in the job according to the value of the adjustment amount stored in the database in association with the sheet type selected for the job to be executed. The image forming apparatus according to claim 13.

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