JP2018097111A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which a print position adjustment cannot executed at a proper timing.SOLUTION: An image formation device includes: a sheet feeding part 140 that accommodates sheets; an image formation unit 151 that forms images on the sheet; a conveyance roller 314 that conveys a test sheet; a reading unit 160 that reads test images on the test sheet; and a controller 110 that prepares the test sheet, using a sheet of attention, makes the reading unit 160 read a test image on the sheet of attention, executes acquisition processing for acquiring an amount of deviation of an image formation position of the test image with respect to the sheet of attention, and adjusts an image formation position of an output image with respect to the sheet of attention on the basis of the amount of deviation. The controller 110 is configured to, for the purpose of updating the amount of deviation, execute the acquisition processing on the basis of a time in which the sheet of attention is accommodated in the sheet feeding part 140, and make a time interval in which the acquisition processing is executed longer as the time in which the sheet of attention is accommodated in the sheet feeding part 140 gets longer.SELECTED DRAWING: Figure 9

Description

  The present invention relates to printing position adjustment control for adjusting an image forming position on a sheet.

  A general image forming apparatus has a printing position adjustment function for adjusting an image printing position (also referred to as an image forming position) with respect to a sheet so that the image is printed at an intended position of the sheet. By adjusting the printing position, for example, in double-sided printing, it is possible to provide a high-quality printed material by aligning the printing positions of the front side image and the back side image with high accuracy. In addition, for example, when an image is printed on a preprint sheet on which ruled lines or the like are printed in advance, it is possible to provide a high-quality printed matter that is printed so that the ruled lines do not overlap with the image.

  The print position adjustment needs to be executed for each type of sheet on which an image is printed. This is because the amount of expansion and contraction of the sheet differs due to the size, basis weight, material, etc. of the sheet.

  The print position adjustment uses a test sheet created by printing a test image on a target sheet in order to detect a shift in the print position. For example, the image forming apparatus detects a shift in the print position based on information on the length from the reference position of the test sheet to the test image, and determines a correction condition for correcting the print position based on the detection result. The image forming apparatus corrects the printing position based on the correction condition when performing the printing process using the same type of sheet as the target sheet.

  By the way, it was found by experiments that the sheet fluctuates depending on the moisture content of the sheet. As a result of printing an image using the same type of sheet left in an environment with different humidity, the printing position on the sheet was different. Generally, a sheet used for printing is sold in a state of being wrapped in a wrapping paper in order to maintain the quality of the sheet. For example, the wrapping paper is specially processed so that the sheet does not absorb moisture. When the sheet is stored in the storage unit of the image forming apparatus, the operator opens the wrapping paper and stores the sheet in the storage unit. Therefore, the moisture content of the sheet may start to change after the wrapping paper is opened.

  Here, when the sheet taken out from the wrapping paper is accommodated in the accommodating portion of the image forming apparatus installed in the low-humidity room, the moisture content of the sheet decreases with time. Therefore, the dimension of the sheet accommodated in the accommodating part for a long time is reduced compared with the dimension of the sheet immediately after opening the wrapping paper. Or depending on the kind of sheet | seat, the dimension of the sheet | seat accommodated in the accommodating part over a long time may extend compared with the dimension of the sheet | seat immediately after opening a wrapping paper.

  In view of this, an image forming apparatus that automatically executes print position adjustment every time a predetermined time has elapsed for the operation of the image forming apparatus is known (Patent Document 1). The image forming apparatus of Patent Document 1 includes a timer, and automatically prints a test sheet every time the operation time of the image forming apparatus reaches a predetermined time, conveys the test sheet to a reading sensor, and performs a test on the test sheet. The print position is adjusted based on the result of reading the image.

JP 2005-221582 A

  However, the image forming apparatus described in the cited document 1 cannot execute the printing position adjustment according to the change in the moisture content of the sheet.

  The moisture content of the sheet immediately after the wrapping paper is opened changes immediately, but the moisture content of the sheet becomes stable as time passes after the wrapping paper is opened. Then, the moisture content of the sheet converges to the moisture content that is balanced with the environment in which the image forming apparatus is installed, specifically, the humidity in the housing portion of the image forming apparatus. Furthermore, it has been experimentally found that the amount of deviation of the printing position over time does not change much when the moisture content of the sheet is balanced with the environmental humidity. A state where the moisture content of the sheet is balanced with the environmental humidity is called an equilibrium state.

  For this reason, the image forming apparatus described in Patent Document 1 that performs print position adjustment at predetermined time intervals may cause the print position shift amount with respect to the sheet immediately after being opened from the wrapping paper to exceed an allowable range, or print position adjustment. May be executed excessively. Further, since the image forming apparatus has a downtime for executing the printing position adjustment, the productivity decreases when the printing position adjustment is performed excessively. That is, the image forming apparatus described in Patent Document 1 does not print the test sheet for adjusting the printing position at an appropriate timing in consideration of the change in the moisture content of the sheet.

  Accordingly, an object of the present invention is to execute printing position adjustment at an appropriate timing.

  In order to solve the above-described problems, an image forming apparatus according to the present invention includes a storage unit that stores a sheet, an image forming unit that forms an image on the sheet, and a transport unit that transports the sheet on which a test image is formed. Reading means for reading the test image formed on the sheet; controlling the image forming means to form the test image on the attention sheet; and conveying the attention sheet on which the test image is formed on the conveying means. Control means for controlling the reading means to read the test image and executing acquisition processing for obtaining information relating to an image forming position of the test image with respect to the target sheet; and image formation of an output image with respect to the target sheet. Adjusting means for adjusting the position based on the information, and the control means is configured to adjust the attention to the accommodating portion in order to update the information. The acquisition unit executes the acquisition process based on a time during which the sheet is stored, and the control unit sets a time interval at which the acquisition process is performed as the time during which the attention sheet is stored in the storage unit becomes longer. Characterized by lengthening.

  According to the present invention, the print position adjustment can be executed at an appropriate timing.

Overall configuration diagram of the printing system Cross section of the main part of the image forming unit Configuration of reading unit Schematic diagram of the interface screen for operating the paper library Schematic diagram of the interface screen for entering sheet attributes Illustration of the paper library Illustration of test sheet Schematic for explaining the derivation process of the printing position deviation amount Flowchart diagram showing printing position adjustment operation The flowchart figure which shows the acquisition sequence which acquires printing position deviation | shift amount The flowchart figure which shows the operation | movement of the modification of printing position adjustment. Flowchart diagram showing the adjustment interval initialization sequence Flowchart diagram showing adjustment interval editing processing

(Configuration of printing system)
FIG. 1 is an overall configuration diagram of a printing system having an image forming apparatus according to the present embodiment. The printing system 1 includes an image forming apparatus 100 and a host computer 101. The image forming apparatus 100 and the host computer 101 are communicably connected via a network 105. The network 105 is a communication line such as a LAN (Local Area Network) and a WAN (Wide Area Network). Note that a plurality of image forming apparatuses 100 and host computers 101 may be connected to the network 105.

  The host computer 101 is, for example, a server, creates a print job in response to an input operation by an operator, and transmits the created print job to the image forming apparatus 100 via the network 105. The print job includes various types of information necessary for printing, such as image data, the type of sheet used for printing, the number of sheets to be printed, and instructions for double-sided or single-sided printing.

  The image forming apparatus 100 includes a controller 110, an operation panel 120, a scanner 130, a paper feed unit 140, a printer engine 150, and a reading unit 160. The reading unit 160 may be connected to the image forming apparatus 100 as an accessory device different from the image forming apparatus 100. The image forming apparatus 100 forms a printed material by forming an image on a sheet based on a print job acquired from the host computer 101. The controller 110, the operation panel 120, the scanner 130, the paper feed unit 140, the printer engine 150, and the reading unit 160 are connected to each other via a system bus 117 so that they can communicate with each other.

  The controller 110 controls each unit of the image forming apparatus 100. The operation panel 120 is a user interface and includes an operation button, a numeric keypad, a display device such as an LCD (Liquid Crystal Display), a touch panel, and the like. An operator can input print jobs, commands, print settings, and the like to the image forming apparatus 100 through the operation panel 120. The operation panel 120 displays a setting screen and a state by a display device. The scanner 130 scans an image of a document and generates image data. The controller 110 causes the image forming apparatus 100 to print an image based on the image data generated by the scanner 130.

  The paper feed unit 140 includes a plurality of storage units that store sheets. The sheets stored in the storage unit are fed to the printer engine 150 one by one from the uppermost sheet of the sheet bundle stacked in the storage unit. The paper feeding unit 140 includes an environmental sensor 141 that detects environmental conditions such as temperature and humidity around each housing unit.

  The printer engine 150 prints an image corresponding to the image data on a sheet fed from the sheet feeding unit 140 under the control of the controller 110. The printer engine 150 includes an image forming unit 151 including a developing device 152, a photosensitive drum 153, and a transfer belt 154, and a fixing device 155. The printer engine 150 forms an image according to the image data on a sheet, generates a printed matter, and outputs it. A specific configuration of the image forming unit 151 will be described later. The reading unit 160 reads the printed matter generated by the printer engine 150 and transfers the reading result to the controller 110. A specific configuration of the reading unit 160 will be described later.

  The configuration of the controller 110 will be described. The controller 110 is a computer that includes a ROM (Read Only Memory) 112, a RAM (Random Access Memory) 113, and a CPU (Central Processing Unit) 114. The controller 110 includes an I / O control unit 111, a storage 115, and a network control unit 116.

  The I / O control unit 111 is an interface that controls communication with the operation panel 120, the scanner 130, the paper feeding unit 140, the printer engine 150, the reading unit 160, and the like. The controller 110 communicates with each unit constituting the image forming apparatus 100 through the I / O control unit 111. The storage 115 is a mass storage device such as a hard disk drive (HDD) or a solid state drive (SSD). The storage 115 stores various data such as control data and image data used for image forming processing (printing processing). The network control unit 116 is an interface that performs communication control with another device (host computer 101) via the network 105. The image forming apparatus 100 communicates with other apparatuses via the network by the network control unit 116.

  The CPU 114 reads the activation program from the ROM 112 and executes it using the RAM 113 as a work area, thereby performing activation processing of the image forming apparatus 100. In addition, the CPU 114 controls the image forming process (printing process) by the image forming apparatus 100 by reading the control program from the storage 115 after the activation and executing it using the RAM 113 as a work area. The CPU 114 stores operation mode setting information of the image forming apparatus 100 input from the operation panel 120 in the RAM 113 or the storage 115. The controller 110 may be configured to include a non-volatile and rewritable memory and store operation mode setting information input from the operation panel 120 in the memory.

  FIG. 2 is a cross-sectional view of the main part of the image forming unit 151. The image forming unit 151 forms a toner image on the photosensitive drum 153 using the toner in the developing device 152. A sheet fed from the sheet feeding unit 140 is conveyed to the photosensitive drum 153 by the transfer belt 154. The toner image on the photosensitive drum 153 is transferred to the sheet conveyed to the transfer belt 154. The sheet on which the toner image is transferred is conveyed to a fixing device 155 (FIG. 1). The fixing device 155 (FIG. 1) fixes the toner image on the sheet by, for example, heating and pressing the sheet on which the toner image is transferred. Thereby, the printing of the image on the sheet is completed.

  The photosensitive drum 153 is a drum-shaped image carrier, and rotates in the direction of the arrow about the drum axis. Around the photosensitive drum 153, a primary charger 220 that uniformly charges the surface of the photosensitive drum 153, a developing unit 152, a transfer charger 221 that transfers a toner image to a sheet, a transfer belt 154, and a drum cleaner 222 are disposed. Is done. In addition, the image forming unit 151 includes an exposure unit 223 that irradiates the surface of the photosensitive drum 153 between the primary charger 220 and the developing unit 152 with a laser beam.

  The exposure unit 223 includes a semiconductor laser, a rotating polygon mirror, a reflecting mirror, and the like. The semiconductor laser emits laser light according to the image data. Laser light emitted from the semiconductor laser scans the photosensitive drum 153 in the drum axis direction by a reflecting mirror, a rotary polygon mirror, or the like. The exposure device 223 exposes the photosensitive drum 153 whose surface is uniformly charged by the primary charger 220 based on the image data transferred from the controller 110. As a result, an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum 153.

  The developing device 152 develops the electrostatic latent image formed on the photosensitive drum 153 to form a toner image. The inside of the developing device 152 is divided into a developing chamber 202 and a stirring chamber 203 by a partition wall 201. The developing chamber 202 contains a two-component developer containing toner and a magnetic carrier. Further, the developing device 152 includes a developing sleeve 204 and a blade 206 on which a magnet 205 is fixedly arranged. The developing sleeve 204 carries the developer in the developing chamber 202 by the magnetic force of the magnet 205. The blade 206 regulates the layer thickness of the developer carried on the developing sleeve 204 to a predetermined thickness. The developing sleeve 204 conveys the developer carried on the developing sleeve 204 to a developing position for developing the electrostatic latent image as the developing sleeve 204 rotates. As a result, the electrostatic latent image formed on the photosensitive drum 153 is developed. A developing voltage is applied to the developing sleeve 204 from a power supply unit (not shown). As a result, a potential difference is generated between the developing sleeve 204 and the photosensitive drum 153. The toner in the developer carried on the developing sleeve 204 adheres to the electrostatic latent image on the photosensitive drum 153, and the electrostatic latent image is visualized.

  In the developing chamber 202 and the stirring chamber 203, stirring screws 207 and 208 are provided, respectively. The stirring screws 207 and 208 agitate the developer in the developing chamber 202 to frictionally charge the developer in the developing chamber 202. The stirring screw 207 also has a function of supplying the developer in the developing chamber 202 to the developing sleeve 204. A toner supply tank 210 is connected to the stirring chamber 203, and the toner 213 is supplied from the toner supply tank 210 via the toner discharge port 211. The agitating screw 208 agitates the toner 213 supplied to the agitating chamber 203 and the developer already in the developing device 152. As a result, the toner concentration of the developer (ratio of the toner weight to the total developer weight) is made uniform.

  In the partition wall 201, a passage for communicating the developing chamber 202 and the stirring chamber 203 is formed at the front and back end portions in FIG. 2. The two-component developer whose toner concentration is reduced by the consumption of toner by development is conveyed from the developing chamber 202 to the agitating chamber 203 via the one passage by the conveying screw 207. The two-component developer whose toner concentration has been recovered in the stirring chamber 203 is transported from the stirring chamber 203 to the developing chamber 202 through the other passage by the transport screw 208.

  The transfer belt 154 is provided between the developing device 152 and the drum cleaner 222 so as to be close to the photosensitive drum 153. The transfer belt 154 is an endless belt that rotates counterclockwise in FIG. 2, and is stretched between the rollers. A transfer charger 221 is provided at a position facing the photosensitive drum 153 with the transfer belt 154 interposed therebetween. At the upstream side of the transfer charging device 221 with respect to the rotation direction of the transfer belt 154, an adsorption charging device 230 is disposed opposite to the transfer belt 154. A neutralizing charger 231 is provided downstream of the transfer charger 221 in the rotation direction of the transfer belt 154.

  The sheet fed from the sheet feeding unit 140 is conveyed to the transfer belt 154 and is sucked to the transfer belt 154 by the suction charger 230. The sheet is conveyed by the rotation of the transfer belt 154. When the sheet passes between the photosensitive drum 153 and the transfer charger 221, the toner image formed on the photosensitive drum 153 is transferred by the action of the transfer charger 221. The sheet onto which the toner image has been transferred is conveyed to the transfer belt 154 and separated from the transfer belt 154 by the charge eliminating charger 231. The sheet is conveyed to the fixing device 155 after separation, and the toner image is fixed. Note that the toner remaining on the photosensitive drum 153 after the transfer of the toner image to the sheet is removed by the drum cleaner 222.

  FIG. 3 is a configuration diagram of the reading unit 160. The reading unit 160 includes a reading controller 310, a sheet detection sensor 311, and a line sensor 312. The reading unit 160 reads a sheet on which a test image (hereinafter referred to as “adjustment chart”) is printed by the printer engine 150 while being conveyed along the conveyance path 313. The conveyance rollers 314 and 315 function as a conveyance unit that conveys the sheet on which the adjustment chart is printed along the conveyance path 313. Details of the adjustment chart will be described later. In the following description, the sheet on which the adjustment chart is printed is referred to as a test sheet.

  The sheet detection sensor 311 is an optical sensor having a light emitting unit and a light receiving unit, for example. The sheet detection sensor 311 detects the leading edge in the transport direction of the test sheet transported along the transport path 313. A plurality of sheet detection sensors 311 are provided in a direction orthogonal to the sheet conveyance direction. Each sheet detection sensor 311 detects the leading edge of the sheet and notifies the reading controller 310 of the detection timing of the leading edge. The reading controller 310 derives the skew amount of the sheet based on the timing at which each sheet detection sensor 311 detects the leading edge of the sheet and the sheet conveyance speed.

  The reading controller 310 controls the line sensor 312 and reads the adjustment chart printed on the sheet. For example, the adjustment chart is printed on both the front side and the back side of the sheet. Two line sensors 312 are provided across the conveyance path 313 in order to read both sides of the sheet at once. The reading controller 310 transfers the sheet skew angle and the reading data of the line sensor 312 to the controller 110. The controller 110 detects the print position (image forming position) of the adjustment chart for the sheet based on the skew angle of the sheet and the read data.

(Paper Library)
FIG. 4 is a view showing an example of an interface screen for performing operations such as editing a paper library in the image forming apparatus 100 of the present embodiment. The paper library is a database for managing sheets that can be used for printing in the image forming apparatus 100. The paper library is stored in, for example, a host computer 101 (server) connected to the image forming apparatus 100 via a network. Details of the paper library will be described later.

  An interface screen for operating the paper library is displayed on the operation panel 120 of the image forming apparatus 100. The interface screen 400 includes a paper list 410, a “new addition” button 420, an “edit” button 421, a “delete” button 422, and a “register” button 423.

  The sheet list 410 displays a list of sheets managed by the sheet library. In columns 411 to 417, sheet attribute information is displayed. A column 411 displays sheet names. The name of the sheet is information that allows the types of the sheets to be distinguished from each other. In columns 412, 413, sheet sizes are displayed. A column 412 represents a sheet length in a direction in which the sheet is conveyed (sub-scanning direction), and a column 413 represents a sheet length in a direction (main scanning direction) orthogonal to the direction in which the sheet is conveyed. Column 414 displays the basis weight of the sheet.

  In a column 415, information for the user to identify the surface property of the sheet is displayed. Note that the information for the user to identify the surface property of the sheet is information relating to physical characteristics of the sheet surface. For example, when a sheet that has been surface-treated to increase glossiness is registered in the paper list 410, “Coat” is displayed in the column 415. In addition, when a sheet that has been subjected to uneven processing is registered in the paper list 410, “Emboss” is displayed in the column 415. When a sheet that has not been subjected to special processing is registered in the paper list 410, “plain paper” is displayed in the column 415.

  A column 416 displays the color of the sheet. A column 417 displays information for instructing automatic execution of print position adjustment. “Yes” is displayed in the column 417 corresponding to the sheet on which the user has performed the print position adjustment. In response to registration of a sheet with “OK” displayed in column 417 in the paper library, the image forming apparatus 100 performs print position adjustment from the paper supply unit 140 using the target sheet.

  In the sheet list 410, a sheet to be displayed can be selected by a touch operation on the operation panel 120 or the like. The sheet attribute of the selected sheet is highlighted so that it can be seen that it has been selected. Here, the case where “XYZ paper color 81” is selected is exemplified. If the number of sheets managed by the paper library is larger than the number that can be displayed at one time in the paper list 410, the display and selection of sheet attributes can be performed by operating the scroll bar 418.

  An “add new” button 420 is a button for adding a new sheet to the paper library. The “edit” button 421 is a button for editing the sheet attribute of the sheet selected in the paper list 410. The “delete” button 422 is a button for deleting the sheet selected in the paper list 410 from the paper library. The “Register” button 423 is a button for registering the type of sheet stored in the storage unit.

  When an “add new” button 420 or an “edit” button 421 is pressed, an interface screen for inputting sheet attributes is displayed on the operation panel 120 of the image forming apparatus 100. An interface screen for inputting sheet attributes will be described with reference to FIG. The interface screen 500 includes text boxes 501 to 504, combo boxes 505 and 506, check boxes 507 and 508, a display area 509, an “edit end” button 520, and a “cancel” button 521.

  A text box 501 is an input area for a sheet name (paper name). A text box 502 is an input area for the sheet length in the sub-scanning direction of the sheet (paper length in the sub-scanning direction). A text box 503 is an input area for the sheet length in the main scanning direction of the sheet (sheet length in the main scanning direction). A text box 504 is an input area for the basis weight of the sheet. Input to each of the text boxes 501 to 504 is performed by an input key or the like provided on the software keyboard or the operation panel 120.

  A combo box 505 is an input area for inputting the surface property of the sheet. In the combo box 505, one is designated from a pull-down list of surface properties of sheets that can be used in the image forming apparatus 100 registered in advance. A combo box 506 is an input area for inputting a sheet color. In the combo box 506, one is specified from a pull-down list of colors registered in advance.

  A check box 507 is an input area for designating whether the sheet is preprinted paper. The operator checks the check box 507 when the sheet is preprinted paper. A check box 508 is an input area for designating whether or not to issue a warning for print position adjustment. When the check box 508 is checked, the column 417 of the interface screen 400 in FIG. When the column 417 is “permitted”, a warning for print position adjustment described later is performed after the sheet is stored in the sheet feeding unit 140. In a display area 509, an initial value of a time interval at which a print position adjustment warning is given is displayed. The time interval at which the print position adjustment warning is issued is not allowed to be changed by the operator. The print position adjustment warning is given at time intervals according to the initial value.

  By pressing the “end editing” button 520, the sheet attribute input at that time is determined and stored in the paper library. After saving the sheet attributes in the paper library, the interface screen 500 is switched to the interface screen 400 of FIG. When the “Cancel” button 521 is pressed, the editing of the sheet attribute is stopped. When the “Cancel” button 521 is pressed, the interface screen 500 is switched to the interface screen 400 of FIG. 4 without saving the sheet attributes in the paper library.

  FIG. 6 is an explanatory diagram of the paper library. The paper library is stored in the storage 115 of the image forming apparatus 100 in a file format such as XML (Extensible Markup Language) or CSV (Comma-Separated Values). The paper library is read, written, and updated as appropriate.

  Rows 601 to 605 represent sheet attributes for each sheet registered in the paper library. Columns 611 to 622 represent items of sheet attributes. Each item is input from the interface screens 400 and 500 through the operation panel 120. Column 611 represents the name of the sheet. Columns 612-615 represent the physical properties of the sheet. A column 612 represents the sheet length in the sub-scanning direction of the sheet, a column 613 represents the sheet length in the main scanning direction of the sheet, a column 614 represents the basis weight of the sheet, and a column 615 represents the surface property of the sheet. Column 616 represents the color of the sheet. Column 617 indicates whether the sheet is preprinted paper.

  Columns 618 and 619 represent printing position deviation amounts on the front and back surfaces of the sheet, respectively. The print position deviation amount is a value that quantitatively represents a deviation between an ideal print area and a predicted print area predicted from a test image reading result. Note that the ideal print area is a rectangle having four predetermined lengths, one side of the print area is parallel to the predetermined side of the sheet, and the predetermined side of the sheet and the predetermined side are The distance from one side of the parallel print area is a predetermined distance.

  The printing position deviation amount is represented by parameters such as right angle correction amount, trapezoidal correction amount, lead position, side position, main scanning magnification, and sub scanning magnification, for example. The right angle correction amount represents a deviation amount of the perpendicularity between the printing direction in the sub-scanning direction and the main scanning direction with respect to the sheet. For example, the right angle correction amount is a deviation amount between an ideal perpendicular line calculated with respect to a straight line printed in the sub-scanning direction and the straight line printed in the main scanning direction. The trapezoidal correction amount represents the amount of sheet expansion / contraction deviation. For example, the trapezoidal correction amount is a straight line printed from the printing start position to the sub scanning rear end in the sub scanning direction with respect to the sheet, and a straight line printed from the main scanning rear end position of the sheet to the sub scanning rear end in the sub scanning direction. The amount of deviation. The lead position and the side position represent the printing position deviation amount in the sub-scanning direction and main scanning direction with respect to the sheet, respectively.

  The lead position is adjusted by changing the print start position of the image starting from the leading edge of the sheet conveyance direction. The side position is adjusted by changing the print start position of the image starting from the left end in the sheet conveyance direction. Specifically, the lead position and the side position are adjusted by adjusting the irradiation start timing of the laser light that the exposure device 223 irradiates the photosensitive drum 153. For example, the CPU 114 controls the exposure unit 223 to adjust the laser beam irradiation start timing.

  The sub-scanning direction magnification represents an image length shift in the sub-scanning direction (a magnification with respect to an ideal length). Specifically, the sub-scanning direction magnification is adjusted by controlling the rotation speed of the transfer belt 154. For example, the CPU 114 adjusts the rotation speed of a motor (not shown) that rotates the transfer belt 154. The magnification in the main scanning direction represents a shift in image length in the main scanning direction (a magnification with respect to an ideal length). Specifically, the magnification in the main scanning direction is adjusted by controlling the clock frequency of the laser beam when the exposure unit 223 modulates the laser beam based on the image data. For example, the CPU 114 controls the exposure unit 223 to control the clock frequency. Alternatively, the CPU 114 may perform image processing on the image data so that the print position of the output image becomes an ideal print position. Image processing for making the print position of the output image an ideal print position is, for example, image processing such as affee conversion.

  The controller 110 adjusts the print position so that an image is formed at an ideal print position based on the print position deviation amount during actual printing. The controller 110 refers to the printing position shift amount of the paper library and performs image processing on the image data so that the printing position becomes an ideal printing position. Then, the controller 110 transfers the image processed image data to the printer engine 150, and controls the image forming unit 151 to print an image on a target sheet based on the image data.

  The initial value of each item of the printing position deviation amount is “0”. When a new sheet is registered in the paper library, or when the print position is not adjusted even though the sheet is registered, the initial value is used as the print position deviation amount.

  Here, the time until the displacement amount of the printing position exceeds the allowable amount varies depending on the type, size, basis weight, and surface property of the sheet. For example, the time until the displacement amount of the printing position regarding the target sheet (target sheet) exceeds the allowable amount is obtained from the test result in the high temperature and high humidity environment and the experimental result in the low temperature and low humidity environment, and is previously stored in the host computer 101 (server). Stored. The experimental result represents a change with time in the length of the sheet due to a change in humidity. Among the times exceeding the allowable amount obtained from the experimental results, the shortest time during which the deviation amount exceeds the allowable value ΔTH is the adjustment interval (column 620) for the printing position adjustment of the sheet. The unit of the adjustment interval registered in the column 620 is minutes.

  From the above experimental results, it was found that the amount of change in the sheet length decreases as the moisture content of the sheet approaches the equilibrium state. The expansion / contraction amount of the sheet size converges to a saturation value depending on the sheet type. That is, the relationship between the elapsed time and the amount of expansion / contraction of the sheet can be approximated by a logarithmic function. Therefore, the image forming apparatus 100 executes the print position adjustment so that the longer the time from when the sheet is stored in the storage unit, the longer the time from when the print position adjustment is performed the previous time to when it is performed again. .

  Specifically, after the operator stores the sheet in the storage unit of the image forming apparatus 100, the image forming apparatus 100 performs print position adjustment. This corresponds to the first print position adjustment. Thereafter, the image forming apparatus 100 performs the second print position adjustment after the adjustment interval (column 620) has elapsed. In the third and subsequent print position adjustments, the adjustment interval (column 620) is updated based on the value obtained by multiplying the adjustment interval (column 620) by the increase rate (column 621). It is executed after elapse. For example, if the value of the adjustment interval (column 620) is 10 and the value of the increase rate (column 621) is 1.5, the third time after 15 minutes have passed since the second print position adjustment was performed. Printing position adjustment is executed. At this time, the value of the adjustment interval (column 620) is updated from 10 to 15. The increase rate displayed in the column 621 is a value (ratio) obtained for each sheet from the experimental result.

  Accordingly, the image forming apparatus 100 can execute the print position adjustment again before the deviation amount of the print position of the sheet on which the print position adjustment has been performed again exceeds the allowable amount. Furthermore, since the image forming apparatus 100 does not perform excessive printing position adjustment, it is possible to suppress the consumption of sheets, and it is possible to suppress a decrease in productivity due to frequent execution of the printing position adjustment by the image forming apparatus 100.

  Further, the amount of expansion and contraction of the sheet due to sheet moisture absorption varies depending on the environmental humidity. In the above description, it has been proposed to set the shortest time of the experimental result as the initial adjustment interval (column 620) of the print position, but the adjustment interval may be determined by other methods. For example, the environment sensor 141 of the paper feed unit 140 may acquire the temperature and humidity of the surrounding environment of the paper feed unit 140, and the optimum print position adjustment interval may be obtained from the temperature and humidity of the ambient environment.

(Print position adjustment)
FIG. 7 is a schematic diagram of a test sheet. The adjustment chart on the test sheet is printed on the sheet by the printer engine 150. The same adjustment chart is printed on the front surface 700 and the back surface 701 of the sheet.

  An image 710 is an arrow and a character printed on the front surface 700, and is used for identifying the test sheet conveyance direction and the front and back sides. The image 711 is an arrow and a character printed on the back surface 701, and is used for identifying the test sheet conveyance direction and the front and back sides. The images 710 and 711 are printed so that the operator does not mistake the direction when the reading unit 160 reads the test sheet. Note that the images 710 and 711 do not have to be printed because they are not directly related to the derivation of the print position deviation amount.

  The mark 720 is an image printed at a specific position on the adjustment chart. The mark 720 is formed in a color having a large difference in reflectance with respect to the sheet. In the present embodiment, the mark 720 is formed in black. In the present embodiment, the marks 720 are formed at a total of eight positions at the four corners of the front surface 700 and the back surface 701 of the sheet. The mark 720 is formed at a position away from the edge of the sheet by a predetermined distance if the printing position is ideal. By obtaining the distance from the edge of the test chart to the edge of the mark 720, the printing position deviation amount is derived. In the present embodiment, distances A to V in FIG. 7 are measured. The distance A is the length of the test sheet in the sub-scanning direction. The distance B is the length of the test sheet in the main scanning direction. The ideal length of the distances A and B is the paper length set in the paper library. Each of the distances C to V is a length from the mark 720 to the end of the nearest sheet.

  A process for deriving the print position deviation amount based on the measured distances A to V will be described. FIG. 8 is an explanatory diagram of the derivation process of the printing position deviation amount.

  The print position deviation amount is represented by an item for the front surface and an item for the back surface. The surface items include a lead position 801, a side position 802, a main scanning magnification 803, a sub scanning magnification 804, a right angle correction amount 805, and a trapezoid correction amount 806. Items on the back surface include a lead position 807, a side position 808, a main scanning magnification 809, a sub-scanning magnification 810, a right angle correction amount 811, and a trapezoid correction amount 812. For the same item on the front and back surfaces, the measured value 820 and the print position deviation amount 822 are calculated by the same calculation formula, and the same ideal value is set.

  The measured value 820 of each item is calculated from the measured values of the distances A to V described with reference to FIG. 7 using a calculation formula set for each item. The measured value 820 of the lead position 801 (807) is an average value of the distances C and E (K, M) from the leading end portion in the sheet conveyance direction to the corresponding mark 720. The measured value 820 of the side position 802 (808) is an average value of distances F and J (N, R) from the left end to the corresponding mark 720 in the sheet conveyance direction. The measured value 820 of the main scanning magnification 803 (809) is an average value of the distance between the marks 720 arranged on the same line in the main scanning direction. The measured value 820 of the sub-scanning magnification 804 (810) is an average value of the distance between the marks 720 arranged on the same line in the sub-scanning direction. The measured value 820 of the right angle correction amount 805 (811) is the amount of deviation in the sub-scanning direction of the mark 720 on the reading rear end side with respect to the straight vertical line connecting the marks 720 arranged on the same scanning line in the main scanning direction on the reading leading end side. The average value of S and T (U, V). The measured value 820 of the trapezoidal correction amount 806 (812) is a difference in distance between the marks 720 arranged on the same scanning line in the sub scanning direction.

  The ideal value 821 of each item is a value obtained based on the mark 720 formed at a position 1 [cm] away from the edge of the sheet. The ideal value 821 of the lead position 801 (807) and the side position 802 (808) is 1 [cm]. The ideal value 821 of the main scanning magnification 803 (809) is a value obtained by subtracting 2 [cm] from the sheet length in the main scanning direction of the sheet registered in the sheet library. The ideal value 821 of the sub-scanning magnification 804 (810) is a value obtained by subtracting 2 [cm] from the sheet length in the sub-scanning direction of the sheet registered in the sheet library. The ideal value 821 of the right angle correction amount 805 (811) and the trapezoid correction amount 806 (812) is 0 [cm].

  The print position deviation amount 822 of each item is calculated from the corresponding measured value 820 and ideal value 821 using a calculation formula set for each item. The print position deviation amount 822 at the lead position 801 (807) and the side position 802 (808) is calculated by subtracting the ideal value 821 from the measured value 820 (unit: mm). The print position deviation amount 822 of the main scanning magnification 803 (809) and the sub scanning magnification 804 (810) is calculated by dividing the value obtained by subtracting the ideal value 821 from the measured value 820 by the ideal value (unit:%). . The measured value 820 is used as it is for the print position deviation amount 822 of the right angle correction amount 805 (811) and the trapezoid correction amount 806 (812). The calculated print position deviation amount 822 of each item is managed by the columns 1218 and 1219 of the paper library.

  The distances A to V can be calculated by measurement using a ruler or the like by an operator, or by reading a test sheet with the scanner 130. In the present embodiment, a method for measuring the distances A to V using the reading unit 160 provided in the image forming apparatus 100 will be described.

  The reading unit 160 reads the adjustment chart on the test sheet. The reading unit 160 scans the test sheet conveyed along the conveyance path 313 with the line sensor 312. The reading unit 160 detects the edge of the mark 720 (the boundary between the sheet base and the mark 720) based on the density difference between the images acquired by scanning. The distances A to V are calculated from the detected edge of the mark 720 and the end of the sheet.

  Next, the print position adjustment executed by the controller 110 will be described. The operator performs a registration operation for the sheets stored in the storage units of the paper feeding unit 140 in order to cause the image forming apparatus 100 to perform the printing position adjustment. The operator uses the operation panel 120 to select a storage unit that stores sheets, and selects a sheet stored in the storage unit selected from the paper library. Alternatively, the operator selects a sheet to be stored in the storage unit selected from the paper library. The paper library has a check box that allows execution of print position adjustment. The operator checks a check box corresponding to the sheet whose print position is to be adjusted.

  Hereinafter, the print position adjustment will be described with reference to the flowchart of FIG. The CPU 114 reads and executes the program stored in the ROM 112 while the main power supply of the image forming apparatus 100 is turned on.

  In step S1001, the CPU 114 acquires an adjustment interval 620 for automatic print position adjustment included in the database of FIG. In step S <b> 1002, the CPU 114 determines whether a sheet exists in the storage unit of the paper feeding unit 140 by using a sheet sensor (not shown) provided in the paper feeding unit 140. If there is a sheet in the paper supply unit 140 (S1002: Yes), in S1003, the CPU 114 confirms the time (elapsed time) that the paper is stored in the storage unit. The CPU 114 uses a counter (not shown) to count the time elapsed since the previous printing position adjustment was executed, and the CPU 114 acquires the counter value as the elapsed time. Note that the CPU 114 sets the count value of the counter to 0 in response to executing the print position adjustment.

  On the other hand, if there is no sheet in the paper feeding unit 140 (S1002: No), the automatic execution sequence is terminated without executing the automatic print position adjustment. In step S <b> 1004, the CPU 114 compares the print position adjustment interval 620 with the time (elapsed time) that the sheet is stored in the storage unit.

  If the elapsed time exceeds the adjustment interval 620 (S1004: Yes), the CPU 114 performs print position adjustment. Then, the CPU 114 stores the printing position deviation amount 619 in the database of FIG. The adjustment of the print position will be described with reference to FIG. If the elapsed time does not exceed the print position adjustment interval 620 (S1004: No), the CPU 114 proceeds to step S1001. The CPU 114 repeats the processing from step S1001 to step S1004 until the elapsed time exceeds the adjustment interval 620 or the sheet of the storage portion is exhausted.

  In step S1006, the CPU 114 acquires the print position adjustment interval 620 and the increase rate 621 on the database, and updates the next print position adjustment interval in step S1006. At this time, in order to save the initial value of the print position adjustment interval, the CPU 114 stores the initial value in an area (not shown) prepared in the database. In step S <b> 1006, the CPU 114 obtains the next print position adjustment interval by multiplying the print position adjustment interval 620 by the increase rate 621. The print position adjustment interval and the increase rate are determined based on the test results, but may be configured to be input by the user.

  Next, a method of determining the printing position correction condition from the result of the image forming apparatus 100 printing a test sheet and the reading unit 160 reading the test sheet will be described with reference to the flowchart of FIG.

  When the timing for executing the print position adjustment comes while the image based on the print job is being formed, the CPU 114 stops the image forming process and executes the print position adjustment. In step S <b> 1101, the CPU 114 controls the image forming apparatus 100 to feed the target sheet (target sheet) from the storage unit, and causes the printer engine 150 to print the adjustment chart on the target sheet. As a result, a test sheet printed with markers as shown in FIG. 7 is created. The CPU 114 controls the conveyance rollers 314 and 315 to convey the test sheet to the reading unit 160. The reading controller 310 reads both sides of the test sheet conveyed by the conveying rollers 314 and 315 and transfers the read data to the controller 110. Step S1101 corresponds to an acquisition process for acquiring information related to the image forming position of the mark with respect to the target sheet.

  In S1102, the CPU 114 analyzes the read data and extracts the distance from the end of the test sheet to the test image. When the detection of the paper edge is successful (S1102: Yes), the length of the portion indicated by (A) to (V) in FIG. 7 is obtained in S1103. In S1104, each correction amount is calculated based on the calculation formula of FIG. In step S1105, the correction amount for the selected sheet is stored in the paper library (FIG. 6) as the correction amount for adjusting the print position of the paper selected in FIG. The CPU 114 ends the print position adjustment after updating the print position deviation amount 619 of the paper library. Note that when the print position adjustment is performed in the middle of the print job, the CPU 114 restarts the image formation based on the print job after the print position adjustment is completed.

  On the other hand, if the reading unit 160 fails to detect the edge of the test sheet (S1102: No), the CPU 114 displays a dialog notifying that the printing position adjustment has failed on the touch panel. In consideration of the convenience of the user, this dialog may not record and display only the failure depending on the setting. Then, the CPU 114 ends the print position adjustment without updating the print position deviation amount 619. When the print position adjustment is executed in the middle of the print job, the CPU 114 restarts image formation based on the print job after finishing the print position adjustment.

  Next, a modified example of the print position adjustment will be described based on the flowchart of FIG. Note that the processing from step S1201 to step S1205 in FIG. 11 is the same as the processing from step S1001 to step S1105 described above, and a description thereof will be omitted.

  In S1206, the CPU 114 calculates the difference between the previous positional deviation amount and the current positional deviation amount. In step S <b> 1207, the CPU 114 determines whether the difference in print position deviation amount is smaller than the predetermined value D <b> 1. As the difference between the moisture content of the sheet and the moisture content in the air decreases, the amount of change in the amount of expansion and contraction of the sheet also decreases. For this reason, if the difference between the moisture content of the sheet and the moisture content in the air is reduced, the difference between the previous printing position deviation amount and the current printing position deviation amount is also reduced. Therefore, if the difference between the previous printing position deviation amount and the current printing position deviation amount is smaller than the predetermined value D1 (S1207: Yes), the CPU 114 further increases the adjustment interval of the next printing position adjustment in S1208. Thus, the image forming apparatus 100 can further suppress the amount of sheet consumption and further suppress the occurrence of downtime.

  On the other hand, if the difference in the printing position deviation amount is larger than the predetermined value D1 (S1207: No), the CPU 114 determines whether or not the printing position deviation amount difference is larger than the predetermined value D2 in S1209. When the difference between the moisture content of the sheet and the moisture content in the air increases, the change in the amount of expansion / contraction of the sheet may increase. For this reason, if the difference between the moisture content of the sheet and the moisture content in the air increases, the difference between the previous printing position deviation amount and the current printing position deviation amount also increases. Therefore, if the difference between the previous printing position deviation amount and the current printing position deviation amount is larger than the predetermined value D2 (S1209: Yes), the CPU 114 shortens the adjustment interval in S1210. As a result, even if a sudden change in the surrounding environment occurs, the adjustment interval can be changed to an appropriate adjustment interval, and the printing position can be adjusted with high accuracy.

The predetermined values D1 and D2 are determined from the results of experiments for each sheet in a high temperature and high humidity environment and a low temperature and low humidity environment. Further, the predetermined values D1 and D2 may be set by an operator using the operation panel, for example. FIG. 12 shows the operation of the printing apparatus that checks the change of the sheet of the paper feeding unit 140 and changes the adjustment interval of the print position. The flow is shown. This flow is processed in parallel with the execution determination of the printing position adjustment described so far. This flow is repeatedly executed after the main power supply of the image forming apparatus 100 is turned on until the main power supply is turned off. The sheet feeding unit 140 includes an open / close detection sensor for detecting opening / closing of the storage unit and a sheet number sensor for detecting the number of sheets stored in the storage unit. The CPU 114 determines whether or not the storage unit of the paper feeding unit 140 is opened in S1301 based on the detection result of the open / close detection sensor.

  If the storage unit has changed from a closed state to an open state (S1301: Yes), in S1302, the CPU 114 determines whether the amount of sheets stored in the storage unit has changed after the storage unit is closed. The determination is made based on the detection result of the sensor. When the operator adds sheets to the storage unit and the number of sheets increases (S1302: Yes), the adjustment interval is changed to an initial value. When the number of sheets in the storage unit is changed, there is a possibility that sheets having different moisture amounts are stacked on the sheets stored in the storage unit. Therefore, the CPU 114 changes the adjustment interval to the initial value. Accordingly, even if the operator adds a new sheet to the storage unit, the print position can be adjusted at an appropriate adjustment interval. The initial value of the adjustment interval for print position adjustment is a value stored in an area (not shown) prepared in the database.

  In the above description, in order to change the adjustment interval, the adjustment interval has to be edited in advance before the sheet is registered in the paper library. In the following description, an editing process for changing the initial value of the adjustment interval after the sheet attribute information is registered in the paper library will be described with reference to FIG.

  The CPU 114 automatically executes the print position adjustment when a check is entered in the check box for the print position adjustment on the interface screen of FIG. When the sheet accommodated in the accommodating portion is a sheet targeted for print position adjustment, the CPU 114 displays a print position adjustment customization dialog and allows the operator to set an adjustment interval and the like.

  In step S <b> 1401, the CPU 114 acquires information on the storage unit of the sheet feeding unit 140 selected by the operator at the time of sheet registration. In step S <b> 1402, the CPU 114 displays a paper library interface screen (FIG. 4) on the operation panel, and assigns the sheet (the attention sheet) selected by the operator to the storage unit of the paper feeding unit 140. In step S1403, the CPU 114 determines whether a check box corresponding to the sheet selected by the operator has been input. If no check is input in the check box (S1403: No), the CPU 114 ends the flow.

  On the other hand, if a check is entered in the check box (S1403: Yes), the CPU 114 displays a screen for editing sheet attribute information on the operation panel so that the operator can set the adjustment interval in S1404. Let As a result, the operator can confirm the adjustment interval of the printing position, and can customize the adjustment interval according to the climate, printing environment, and printing state at the time of printing. The CPU 114 stores the adjustment interval set on the editing screen in the paper library. Subsequent operations are the same as the operations of the image forming apparatus 100 described above, and a description thereof will be omitted.

110 Controller 140 Paper Feed Unit 151 Image Forming Unit 160 Reading Unit 314 Conveying Roller

Claims (7)

An accommodating portion for accommodating the sheet;
Image forming means for forming an image on the sheet;
Conveying means for conveying the sheet on which the test image is formed;
Reading means for reading the test image formed on the sheet;
Controlling the image forming means to form the test image on the attention sheet, causing the conveying means to convey the attention sheet on which the test image is formed, and controlling the reading means to read the test image; Control means for executing acquisition processing for acquiring information related to the image forming position of the test image with respect to the target sheet;
Adjusting means for adjusting the image forming position of the output image with respect to the target sheet based on the information;
The control means executes the acquisition process based on a time during which the attention sheet is stored in the storage unit in order to update the information.
The image forming apparatus according to claim 1, wherein the control unit increases a time interval at which the acquisition process is performed as the time during which the attention sheet is stored in the storage unit becomes longer. The image forming means forms the output image based on image data;
The image forming apparatus according to claim 1, wherein the adjusting unit adjusts an image forming position of the output image with respect to the target sheet by performing image processing on the image data based on the information.   The image forming apparatus according to claim 1, wherein the control unit lengthens the time interval based on a predetermined ratio.   The control unit determines a deviation amount of the image forming position based on the information acquired in the previous acquisition process and the information acquired in the current acquisition process, and the deviation amount is greater than a first predetermined value. 4. The image forming apparatus according to claim 1, wherein the time interval is extended if the time is smaller. 5.   The control unit determines a deviation amount of the image forming position based on the information acquired in the previous acquisition process and the information acquired in the current acquisition process, and the deviation amount is the first predetermined value. The image forming apparatus according to claim 4, wherein the time interval is shortened if it is larger than a second predetermined value that is larger.   The image forming apparatus according to claim 1, wherein the control unit sets the time interval according to a type of the sheet.   The image forming apparatus according to claim 1, wherein the control unit changes the time interval based on humidity information of the housing unit.

Images