JP2021056287A - Image forming system and image reading device - Google Patents

Abstract

To take measures against turning of a sheet during a reading operation.SOLUTION: After image forming means (150) forms a test image on a sheet, adjustment means (213) adjusts an image position when the image forming means forms an image based on image data for printing, based on image data read by reading means from the sheet on which the test image is formed. The adjustment means corrects the image data so as to reduce distortion of the sheet occurring due to turing of the sheet while the sheet passes through a reading position of the reading means, and adjusts the image position based on the position of the test image with respect to the sheet in the image data after the correction.SELECTED DRAWING: Figure 2

Description

The present invention relates to an image forming system that forms an image on a sheet and an image reading device that reads an image from the sheet.

Image forming devices such as printers, copiers, and multifunction devices are equipped with a function that automatically adjusts (registers) the image position when an image is formed on a sheet, which is a recording material, to obtain a product. is there. In Patent Document 1, as a method of adjusting the image magnification at the time of double-sided printing based on the sheet width measured by using a line sensor, the sheet width is measured before and after image formation on one side to perform heat fixing processing. It is stated that the image magnification is obtained in consideration of the expansion and contraction of the sheet that accompanies it.

Japanese Unexamined Patent Publication No. 2014-092554

However, when an image is read from a sheet being conveyed by a line sensor as in the above document, the sheet may rotate due to wear of the transfer roller or the like. In this case, in the read image data, the sheet is apparently distorted. When such apparent distortion of the sheet occurs, the desired accuracy cannot be obtained when the print position is automatically adjusted based on the read image data, or the quality of the image read by the scanner deteriorates. There was such an inconvenience.

Therefore, an object of the present invention is to provide an image forming system and an image reading device in which measures are taken against the turning of the sheet during the reading operation.

One aspect of the present invention is an image forming means for forming an image on a sheet, a conveying means for conveying an image formed by the image forming means, and a reading means for reading image data from the sheet conveyed by the conveying means. After forming a test image on the sheet by the image forming means, the image forming means is based on the image data for printing based on the image data read by the reading means from the sheet on which the test image is formed. The adjusting means includes an adjusting means for adjusting the image position when forming an image, and the adjusting means reduces the distortion of the sheet caused by the rotation of the sheet while the sheet passes through the reading position of the reading means. The image forming system is characterized in that the image data is corrected and the position of the image is adjusted based on the position of the test image with respect to the sheet in the corrected image data.

Another aspect of the present invention is to read a line image in the main scanning direction perpendicular to the sub-scanning direction from the conveying means for conveying the sheet in the sub-scanning direction and the sheet conveyed by the conveying means line by line. The reading means for acquiring the image data of the sheet and the image correction means for correcting the image data acquired by the reading means are provided, and the image correction means includes a set value of the sheet length in the main scanning direction and the said. Based on the distance between both ends of the sheet detected from the line image read by the reading means, the rotation of the sheet while the sheet is passing through the reading position of the reading means is detected, and the distortion of the sheet caused by the rotation of the sheet is detected. It is an image reading device characterized in that image data is corrected so as to reduce the amount.

According to the present invention, it is possible to provide an image forming system and an image reading device in which measures are taken against the turning of a sheet during a reading operation.

The schematic diagram of the image formation system which concerns on 1st Embodiment. The control block diagram of the image formation system which concerns on 1st Embodiment. The figure (a, b) which shows the example of the adjustment pattern. The figures (a-c) for explaining the distortion of the scanned image caused by the rotation of a sheet. The figure (a, b) for demonstrating the correction method of the scanned image which concerns on Example 1. FIG. The figures (a to c) for demonstrating the correction method of the scanned image which concerns on Example 2. FIG. The figures (a to c) for demonstrating the correction method of the scanned image which concerns on Example 2. FIG. The figure (a, b) for demonstrating the correction method of the scanned image which concerns on Example 2. FIG. The figure (a, b) for demonstrating the correction method of the scanned image which concerns on Example 2. FIG. The flowchart of the print position adjustment process which concerns on Example 2. FIG. The figure which shows the example of the sheet management table which concerns on 1st Embodiment. The schematic diagram of the image forming apparatus which concerns on 2nd Embodiment.

Hereinafter, exemplary embodiments for carrying out the present invention will be described with reference to the drawings.

<First Embodiment>
FIG. 1 is a schematic view of an image forming system 10 according to the first embodiment of the present disclosure. The image forming system 10 forms an image including a printer main body 100 which is an image forming apparatus main body, a scanner 200 installed on the upper part of the printer main body 100, and an automatic adjustment unit 600 connected to the side of the printer main body 100. It is a system.

The printer engine 150 mounted on the printer main body 100 is a tandem type intermediate transfer type electrophotographic mechanism including a plurality of image forming stations 101y, 101m, 101c, 101k, an exposure device 103, and an intermediate transfer belt 109. The image forming stations 101y-101k produce yellow, magenta, cyan, or black toner images by an electrophotographic process, respectively. That is, the photosensitive drum 102 as an image carrier provided in each station is rotationally driven at a target speed, and the surface of the photosensitive drum 102 is uniformly charged by the charger. The exposure apparatus 103 as an exposure means exposes the photosensitive drum 102 based on the image data of the image to be printed, and forms an electrostatic latent image on the drum surface. This electrostatic latent image is visualized (that is, developed) as a toner image by using a developer supplied from the developer 104 as a developing means.

The toner image carried on the photosensitive drum 102 of each station is primarily transferred by the primary transfer roller 105 to the intermediate transfer belt 109 as the intermediate transfer body. At this time, the four-color toner images are multiple-transferred so as to overlap each other, so that a full-color toner image is formed on the intermediate transfer belt 109. This toner image is conveyed to the secondary transfer portion, which is the nip portion between the intermediate transfer belt 109 and the secondary transfer roller 106, by the rotation of the intermediate transfer belt 109. The intermediate transfer unit including the intermediate transfer belt 109, the primary transfer roller 105, and the secondary transfer roller 106 constitutes the transfer means of the present embodiment for transferring the toner image carried on the image carrier to the sheet.

In parallel with such an image forming process, a transport process of feeding and transporting a sheet as a recording material is executed. Sheets are stored in the accommodating portions 110a and 110b assembled to the printer main body 100. In the present embodiment, the recording material includes paper such as plain paper and cardboard, sheet material with surface treatment such as plastic film, cloth, and coated paper, and sheet material having a special shape such as envelope and index paper. A variety of sheets of different sizes and materials can be used. The sheets in the accommodating portions 110a and 110b are fed one by one by the feeding rollers, and are conveyed to the registration rollers 111 along the conveying path. The registration roller 111 adjusts the sheet transfer timing and transfer speed so that the timing at which the image on the intermediate transfer belt 109 reaches the secondary transfer section and the timing at which the sheet reaches the secondary transfer section are synchronized. ..

A bias voltage is applied from the power supply unit to the secondary transfer roller 106 while the image and sheet on the intermediate transfer belt 109 pass through the secondary transfer section, so that the toner image is secondarily transferred from the intermediate transfer belt 109 to the sheet. Will be done. Adhesions such as transfer residual toner that remain on the intermediate transfer belt 109 without being transferred to the sheet are cleaned by the belt cleaner 108.

The sheet on which the toner image is transferred is conveyed to the fixing device 107. The fuser 107 has a roller pair that rotates while sandwiching the sheet and a heat source such as a halogen lamp, and applies heat and pressure to the toner image on the sheet while conveying the sheet. As a result, the toner melts and then sticks, so that the image is fixed on the sheet. The sheet that has passed through the fuser 107 is discharged from the printer main body 100 by the discharge roller 112.

On the other hand, when performing double-sided printing in which an image is formed on both sides of the sheet, the sheet in which the image is formed on the first surface that has passed through the fuser 107 is switched back and conveyed by the discharge roller 112 to both sides. It is transported to the path 114. The sheet transported along the double-sided path 114 is again controlled by the registration roller 111 at the sheet transfer speed and the sheet transfer timing, and is transferred to the secondary transfer unit. Then, after the image is formed on the second surface in the same process as the first surface, the sheet is discharged from the printer main body 100 by the discharge roller 112.

The printer engine 150 described above is an example of an image forming means, and may be a direct transfer type electrophotographic mechanism that directly transfers a toner image formed on an image carrier to a recording material, or an offset printing type printing mechanism. ..

(About the scanner)
The configuration of the scanner 200, which is an example of the image reading device, will be described. As shown in FIG.
The scanner 200 includes a scanner main body 400 fixed to the upper part of the printer main body 100, and an automatic document feeder (ADF) 280 that can be opened and closed with respect to the scanner main body 400.

A CCD-type reading mechanism is arranged in the scanner main body 400. Specifically, an optical system including a movable scanning unit 404 having a lamp 402 and the like, mirrors 405 and 406, and a lens 407, and an image sensor 408 using a CCD (charge coupling element) as an image pickup element are arranged. .. When the sheet S as a document is irradiated with light from the lamp 402, the reflected scattered light of the sheet S is imaged on the light receiving surface of the image sensor 408 via the optical system. Then, the photoelectric conversion of the image sensor 408 reads a line image in the main scanning direction, which is the arrangement direction of the image sensor.

Further, the scanner main body 400 is provided with a scanning glass 230 for a scanning operation and a platen glass for a fixed reading operation. The scanning operation is an operation of reading an image from the sheet S conveyed by the ADF 280 while the scanning unit 404 is stationary below the scanning glass 230. The fixed reading operation is an operation of reading an image by moving the scanning unit 404 in the sub-scanning direction (left-right direction in the drawing) with respect to the still document placed on the platen glass.

A white plate 223 for stabilizing the behavior of the sheet at the scanning position (reading position) by the scanning unit 404 is provided above the scanning glass 230. The white plate 223 is arranged with a predetermined gap with respect to the scanning glass 230. Further, the original placed on the platen glass with the ADF280 opened upward is pressed against the platen glass by the pressure plate provided on the lower surface of the ADF280 by closing the ADF280 downward.

The ADF280 has a document tray 211 on which the sheet S, which is a document, is loaded. When the scanning operation is started, the sheet S loaded on the document tray 211 is fed out from the uppermost sheet by the feeding roller 201 and conveyed by the separating roller 203. At this time, the separation pad 204 facing the separation roller 203 uses frictional force to prevent the transfer of sheets other than the uppermost sheet, so that the sheets S are separated one by one. The separated sheet S is conveyed toward the scanning glass 230 by the transfer roller pair 224 downstream of the separation roller 203.

When scanning only one side of the sheet, the sheet S is optically scanned by the scanning unit 404 as it passes through the scanning glass 230, and the image sensor 408 reads the image line by line. The read line image is temporarily stored in the image memory of the scanner main body 400 and then transferred to the image memory of the printer main body 100. The sheet S from which the image is read is discharged to the discharge tray 219 by the discharge roller 216.

When scanning both sides of the sheet, the following operations are performed. The sheets S separated one by one by the separation roller 203 can read the image of the first surface when passing through the scanning glass 230 in the same manner as in the case of single-sided scanning. The sheet S from which the image has been read is conveyed by the discharge roller 216, but when the rear end of the sheet (upstream end in the transport direction) passes through the flap 215 in the transport path, the discharge roller 216 temporarily stops, and then reverses. Driven. The sheet S switched back by the reversal of the discharge roller 216 is transported again to the transfer roller pair 224 via the reversal transfer path 217.

The transport roller pair 224 is configured to always rotate in the forward feed direction regardless of the rotation direction of the discharge roller 216. Downstream of the transport roller pair 224, there is a sensor flag 225 and a sensor that detects the position of this flag, and by discriminating the sensor signal, it is determined that the sheet tip (downstream end in the transport direction) has reached the transport roller pair 224. It is configured to be detectable. After the inverted sheet tip is sandwiched between the transport rollers 224, the discharge rollers 216 are separated by the separating means. Then, in a state where the discharge roller 216 is rotated in the progressive direction, the sheet S is passed through the scanning glass 230, and the image is read from the second surface of the sheet S.

The repressurization of the discharge roller 216 is performed when the rear end of the sheet transported through the reversing transport path 217 has passed through the discharge roller 216. As a result, even when handling a sheet that is long in the transport direction, it is possible to prevent the transport rollers 216 and the transport roller pair 224 from having different transport directions. The sheet S whose images have been read from both sides passes through the reverse transfer path 217 again in order to align the page order, and is discharged from the discharge roller 216 via the transfer roller pair 224 and the scanning glass 230.

(Automatic adjustment unit)
Next, the automatic adjustment unit 600 will be described. In the image forming system 10 of FIG. 1, the automatic adjustment unit 600 is installed on the side of the printer main body 100 in the horizontal direction (left-right direction in the drawing). That is, the upstream device of the automatic adjustment unit 600 in this embodiment is the printer main body 100.

As shown in FIG. 1, the automatic adjustment unit 600 includes an image reading unit 700, and a through path 630 and a measurement path 631 that form a sheet transport path in the unit. The through pass 630 communicates a receiving port for receiving the sheet ejected from the printer main body 100 and an discharging port for ejecting the sheet from the automatic adjustment unit 600. Further, the transport rollers 601, 602, 603, 604 arranged along the through pass 630 transport the sheet from the receiving port to the discharging port.

The measurement path 631 is a path in which the image reading unit 700 is arranged, and is formed so as to bypass the lower part of the through path 630. That is, the measurement path 631 communicates with the through path 630 at two points, a branch portion that branches from the through path 630 and a merging portion that joins the through path 630 downstream from the branch portion. At the branch portion of the measurement path 631 from the through path 630, a first flap 621, which is a guide member capable of switching the sheet transport path between the through path 630 and the measurement path 631, is arranged. Further, in the measurement path 631, transfer rollers for conveying the sheet are arranged at a plurality of positions along the sheet transfer direction in the measurement path 631.

The image reading unit 700 includes at least one reading means. In this embodiment, a contact image sensor (CIS) is used as the reading means, and the front surface CIS 701 that reads an image from the first surface of the sheet and the back surface CIS 702 that reads an image from the second surface of the sheet are used together. As described above, the configuration in which the image is read simultaneously from both sides of the sheet to which the image reading unit 700 is conveyed by the two CIS has an advantage that the reading operation can be completed quickly. A CCD-type reading mechanism such as the scanner 200 may be used as the reading means, or an inversion transport mechanism may be provided instead of arranging the two CIS to read the image from both sides of the sheet.

The configuration of the front surface CIS701 and the back surface CIS702 is common. That is, it includes an LED array as a light source, a sensor array composed of an image pickup element such as CMOS, and a plurality of lenses (lens arrays) that image the reflected light from the sheet S on the sensor array. These LED arrays, sensor arrays, and lens arrays are arranged along the main scanning direction (the width direction of the sheet perpendicular to the sheet transport direction in the image reading unit 700). It is preferable that the reading range of the CIS 701 and 702 in the main scanning direction is wider than the maximum size of the sheet on which the printer body 100 can form an image (for example, 320 mm of SRA3 size) in order to perform the rotation correction described later.

The sheet that has reached the image reading unit 700 passes through the reading positions of the back surface CIS 702 and the front surface CIS 701 in order while being conveyed in the sub-scanning direction by the transfer roller pair 611, 612, 613 as the transfer means. The reading positions of the back surface CIS 702 and the front surface CIS 701 refer to the optical axis positions of the lens arrays provided by each. At the reading position, the back surface CIS 702 faces the black guide 706 with the transparent guide 704 sandwiched between them, and the front surface CIS 701 faces the black guide 705 with the transparent guide 703 sandwiched between them. The sheet is conveyed through the space formed between the transparent guides 703 and 704 and the black guides 705 and 706 facing the transparent guides 703 and 704. The black guides 705 and 706 are transport guides that guide the sheet, and are members that serve as a background when the CIS 701 and 702 scan the sheet, and the contrast with the sheet is clearly black. The transparent guides 703 and 704 face the opposite black guides 705 and 706 with a predetermined gap, and stabilize the position of the sheet in the reading region in the depth of focus direction.

Further, the image reading unit 700 is provided with speed sensors 801, 802 for measuring the sheet conveying speed. In this embodiment, speed sensors 801 and 802 are arranged at the reading positions of the back surface CIS 702 and the front surface CIS 701, respectively. Further, one speed sensor 801, 802 is arranged at the center position of the reading range of each CIS 701 and 702 in the main scanning direction. As the speed sensors 801, 802, for example, a laser Doppler speedometer can be used.

In the image forming system 10, a downstream device such as a finisher may be connected downstream of the automatic adjustment unit 600. The finisher refers to a device that has a processing unit that performs processing such as binding processing and saddle processing on a sheet, and discharges the processed sheet bundle as a final product.

Further, the devices connected to the upstream and downstream of the automatic adjustment unit 600 change depending on the configuration of the image forming system 10. For example, the automatic adjustment unit 600 is not always directly connected to the printer main body 100, an intermediate unit is arranged between the printer main body 100 and the automatic adjustment unit 600, and the automatic adjustment unit 600 takes a sheet from the intermediate unit. It may be configured to receive. An example of the intermediate unit is an apparatus that performs a coating process of adhering transparent toner to the image surface of an image-formed sheet to impart gloss. Further, a sheet processing device other than the finisher may be connected to the downstream side of the automatic adjustment unit 600. Examples of such a sheet processing device include an inserter for inserting a cover sheet into a sheet bundle, a trimmer for cutting and aligning the ends of the bound sheet bundle, and a trolley containing a large amount of deliverables. Examples include movable stackers.

(Control circuit of image formation system)
Next, a control block diagram of the image forming system 10 will be described with reference to FIG. The CPU 241 is an arithmetic unit that controls each unit of the image forming system 10 by executing a control program. The ROM 242 stores a control program executed by the CPU 241 to execute various processes of the flowchart described later. That is, the ROM 242 is an example of a non-transient storage medium that stores a control program for controlling an image forming system by a specific control method. The RAM 243 is a system work memory for operating the CPU 241. The HDD 244 stores image data received from the scanner 200 or the PC, setting information input from the operation unit 20, and the like. The printer engine 150 corresponds to the electrophotographic mechanism including the image forming station 101y-101k and the fuser 107 described above.

The operation unit 20 is an example of a user interface unit. The operation unit 20 includes a display unit including an output device such as a liquid crystal display and an LED lamp, and an input unit including a touch panel function unit of the display and an input device such as a physical key such as a numeric keypad. The operation unit 20 has a function of displaying a setting screen on the display unit and receiving setting information and the like input by the user via an operation on the input unit. Further, the operation unit 20 has a function of providing information to the user via the display unit. The input unit includes, for example, a start key for instructing the start of execution such as scanning and copying, a stop key for instructing the stop of operation such as scanning and copying, and a numeric keypad.

The image processing unit 210 performs various image processing on the image data to correct the image data. The image data corrected by the image processing unit 210 is transferred to the exposure apparatus 103. The exposure apparatus 103 exposes the photosensitive drum 102 under control based on the image data corrected by the image processing unit 210 to form an electrostatic latent image based on the image data on the photosensitive drum 102 as described above.

The print position correction unit 212 corrects the image data so that the position of the image with respect to the sheet becomes the target position. The position (printing position) of the image formed on the sheet by the printer body 100 may deviate from the ideal position for various reasons. For example, when the sheet conveyed by the registration roller 111 is tilted, the slanted sheet passes through the secondary transfer portion, so that the image on the sheet is formed tilted with respect to the sheet. Further, for example, when the pressure distribution of the rollers of the fixing device 107 is not uniform, the sheet after passing through the fixing device 107 may be deformed and the image on the sheet may be tilted. Further, for example, in double-sided printing, when an image is formed on the first surface of the sheet, the sheet expands and contracts due to the heat and pressure of the fixing device 107, so that the size of the image formed on the first surface of the sheet is increased. The size of the image formed on the second surface of the sheet may be different. In this case, the print position of the image formed on the first surface of the sheet and the print position of the image formed on the second surface of the sheet are different.

Such deviation of the printing position caused by the inclination of the sheet passing through the secondary transfer portion and the deformation of the sheet in the fixing device 107 is highly reproducible if the size, basis weight, material and the like of the sheet are the same. Therefore, the image forming system 10 deforms the position and shape of the image formed by the printer engine 150 according to the attributes of the sheet so that the printing position of the image with respect to the sheet becomes an ideal position.

Specifically, the print position correction unit 212 converts the image data based on the conversion formula for correcting the deviation of the print position of the image with respect to the sheet stored in the sheet management table 214. Each image forming station forms an image based on the image data converted by the print position correction unit 212. For example, by converting the image data, the position and shape of the electrostatic latent image written on the photosensitive drum by the exposure apparatus 103 are corrected. As a result, an image that cancels out the deviation of the printing position that occurs in the secondary transfer unit and the fixing device 107 is formed on the intermediate transfer belt 109. In the sheet management table 214, the amount of deviation of the print position generated by the print position calculation unit 213, which will be described later, and the conversion formula for correcting the amount of deviation are stored for each attribute of the sheet. Further, the sheet management table 214 is stored in a non-volatile storage medium such as HDD 244.

When the print position adjustment process (adjustment process of the present embodiment), which is a process for measuring the amount of deviation of the print position, is executed, the image data of the adjustment pattern is transmitted from the pattern generator 70 to the printer engine 150. The adjustment pattern is a pattern image predetermined as a test image (reference image) for adjusting the print position, and is stored in ROM 242 or the like. The printer engine 150 that has received the image data of the adjustment pattern forms the adjustment pattern on the sheet to be measured. After that, the image reading unit 700 of the automatic adjustment unit 600 reads the image of the sheet on which the adjustment pattern is formed. The image data acquired as the reading result of the image reading unit 700 is transmitted to the print position calculation unit 213.

The print position calculation unit 213 calculates the value of the adjustment parameter for adjusting the print position from the coordinate data of the feature points of the adjustment pattern in the image data received from the automatic adjustment unit 600, and calculates the calculation result in the sheet management table 214. To memorize. As a result, the print position for the sheet type is determined.

The print position calculation unit 213 has an image correction unit 213a for correcting distortion of the read image due to skewing or turning of the sheet when reading the adjustment pattern, as described later, and the corrected image. Determine the value of the adjustment parameter based on the data. The print position calculation unit 213 is the adjustment means of the present embodiment, and the image correction unit is the image correction means of the present embodiment. Further, in the present disclosure, "adjustment of the image position with respect to the sheet" is a concept including not only translation of the printing position in the vertical and horizontal directions of the sheet but also change of vertical and horizontal magnification, change of rotation angle, and change of squareness. is there.

The control circuit including the CPU 241, the pattern generator 70, the image processing unit 210, and the print position calculation unit 213 functions as a control means for controlling the image forming system 10 of the present embodiment. The control elements that perform specific functions such as the image processing unit 210 and the print position calculation unit 213 may be realized by an integrated circuit such as an ASIC, or may be realized by the CPU 241 executing a control program. Good.

(Front and back registration)
Next, a print position adjustment process for adjusting the print position of the printer main body using the automatic adjustment unit 600, which is an in-line measuring device, will be described. The image forming system 10 starts the process when, for example, the user explicitly requests the execution of the print position adjustment process via the operation unit 20. When the print position adjustment process is started, the image data of the adjustment pattern generated by the pattern generator 70 described above is transmitted to the printer engine 150, and the printer engine 150 forms the adjustment pattern on the sheet. The sheet on which the adjustment pattern is formed is delivered from the printer main body 100 to the automatic adjustment unit 600, and reaches the image reading unit 700 via the measurement path 631.

3 (a) and 3 (b) show the adjustment pattern in this embodiment. (A) is a front surface pattern 810 formed on the front surface 1a of the sheet, and (b) is a back surface pattern 820 formed on the back surface 1b of the sheet. The adjustment pattern of the present embodiment is composed of four rectangular patch images arranged at the corners of the sheet, but other pattern images may be used.

In the image reading unit 700, the front surface CIS701 reads the image of the entire front surface of the sheet including the front surface pattern 810, and the back surface CIS702 reads the image of the entire back surface of the sheet including the back surface pattern 820. That is, while the sheet conveyed by the transfer roller pair 611, 612, 613 passes through the reading positions of the front surface CIS 701 and the back surface CIS 702, each CIS reads a line image in the main scanning direction one line at a time at a predetermined sampling frequency of the sheet. .. The read line image is transferred to an image memory for temporarily storing the image data. Further, in parallel with reading the line image, the speed sensors 801 and 802 measure the sheet transport speed at the center position in the main scanning direction.

When all the line images from when the front end of the sheet reaches the reading position to when the rear end exits the reading position are arranged in the sub-scanning direction, the scanned image is displayed as image data representing a two-dimensional image of the entire sheet including the adjustment pattern. Is obtained. At this time, by adjusting the scale in the sub-scanning direction using the sampling frequency of CIS701,702 and the transport speed measured by the speed sensors 801 and 802, a read image having a correct aspect ratio can be obtained. However, as will be described later, if the sheet is swiveled while the sheet is passing through the reading position, there is a difference in the transport speed between both side ends of the sheet, so that the image data needs to be corrected.

Here, it is assumed that the sheet does not rotate, and a method of adjusting the print position based on the scanned image of the sheet will be described. First, the print position calculation unit 213 first specifies the corner coordinates of the sheet and the coordinates of the feature points of the front surface pattern 810 and the back surface pattern 820 in the scanned images of the front surface and the back surface. The corner coordinates of the sheet are the positions of the four corners of the contour of the sheet (X01, Y01) to (X31, Y31), (X01, Y31), when the main scanning direction is the X-axis and the sub-scanning direction is the Y-axis. Represents X02, Y02) to (X32, Y32). The corner coordinates of the sheet include information on the sheet shape such as the long side length (A) and the short side length (B) of the sheet and the squareness of the corner. Further, the coordinates of the feature points of the adjustment pattern are the positions (X41, Y41) to (X71, Y71), (X42, Y42) to the points representing the adjustment pattern in the same coordinate system as the coordinates of the corners. Represents (X72, Y72). In the illustrated example, the corners on the center side of the sheet in the main scanning direction and the sub-scanning direction of each patch are defined as the feature points of the adjustment pattern.

The print position calculation unit 213 measures the amount of distortion of the adjustment pattern and the positional deviation with respect to the sheet for each of the front surface pattern and the back surface pattern from the corner coordinates of the sheet and the coordinates of the feature points of the adjustment pattern. Then, the values of the adjustment parameters for correcting such distortion and misalignment are calculated for each of the front surface and the back surface, and stored in the sheet management table 214. FIG. 11 shows an example of the sheet management table 214, and the values of the adjustment parameters for adjusting the print position are specified in addition to the information such as the size and the basis weight for each brand of the sheet.

In the present embodiment, the adjustment parameters calculated by the print position calculation unit 213 can include the lead position, the side position, the main scanning magnification, the sub-scanning magnification, the rotation angle, and the right angle. The lead position is a parameter that defines the image position in the sub-scanning direction with respect to the sheet, and changes the distance from the tip of the sheet to the image. The side position is a parameter that defines the image position in the main scanning direction with respect to the sheet, and changes the distance from one side edge of the sheet to the image. The main scanning magnification is a parameter that defines the size of the image in the main scanning direction. The sub-scanning magnification is a parameter that defines the size of the image in the sub-scanning direction. The rotation angle is a parameter that defines the angle at which the image is rotated. Right angle is a parameter that defines the degree of deformation of an image from a rectangle (for example, the degree of keystone correction). However, the print position calculation unit 213 may calculate only a part of the above adjustment parameters, or may calculate other parameters.

As described above, when the image forming system 10 performs the image forming process in order to obtain the deliverable, the print position correction unit 212 (FIG. 2) of the image processing unit 210 sets the adjustment parameters stored in the sheet management table 214. Use to correct the image data to be printed. The printer engine 150 forms an image on the sheet based on the corrected image data. Therefore, the value of the adjustment parameter calculated by the print position calculation unit 213 is the desired adjustment pattern on the front and back surfaces when the adjustment pattern is output again based on the image data corrected using the parameter. It is a value that is formed at the position. The desired position means that, for example, in FIGS. 3A and 3B, all the errors from the set values are within the permissible range for the gaps (C) to (J) from the adjustment pattern to the edge of the sheet. .. Further, in the present embodiment, since the front and back sides are registered even in the printing position adjustment process, it is required that the amount of deviation between the front surface image and the back surface image is within the permissible range.

(Effect of turning the sheet during reading)
By the way, in the print position adjusting process, it is conceivable that the sheet is swirled while the sheet on which the adjustment pattern is formed passes through the image reading unit 700. This is because the transfer speed equivalent to that of the transfer roller varies depending on the surface properties of the sheet, the aged deterioration of the transfer roller, and the environmental conditions such as temperature and humidity.

With reference to FIG. 4, the distortion of the read image when the sheet is swirled during the reading operation by the back surface CIS702 will be described. Here, regarding the transport roller pair 611 on the upstream side, it is assumed that there is no difference in the magnitude of the transport force applied to the seat by the left and right transport rollers 611a and 611b, and the seat does not rotate. On the other hand, regarding the transport roller pair 612 on the downstream side, the transport force of the transport roller 612a on the left side is smaller than that of the transport roller 612b on the right side, indicating that there is a difference in transport speed (VL2 <VR2). .. Therefore, the seat travels straight until the tip of the seat reaches the transport roller pair 612 on the downstream side (FIG. 4A), and after the tip of the seat reaches the transport roller pair 612 on the downstream side, it gradually turns to the left. (Fig. 4 (b)).

As shown in FIG. 4C, the reading result of the back surface CIS702 in this case is distorted due to the rotation of the sheet from the middle of the read image. That is, while the region of "A" read before the tip of the sheet reaches the transport roller pair 612 on the downstream side is not distorted, the region of "B" read after reaching is distorted. appear. Here, since the sheet conveying speed at the right side end 1R in the drawing becomes faster than the left side end 1L due to the rotation of the sheet, the right side end 1R'in the scanned image is compressed in the sub-scanning direction. Then, the left side end portion 1L'extends in the sub-scanning direction.

When the print position adjustment process is performed based on the scanned image in which the distortion caused by the rotation of the sheet is generated, the print position may not be adjusted appropriately. For example, even though the adjustment pattern is formed in the ideal position on the actual sheet, the misalignment or distortion of the adjustment pattern is detected due to the distortion of the scanned image, and the adjustment parameters are inappropriate. May be set to a value.

Further, even when the sheet is obliquely running, the printing position may not be adjusted appropriately because the entire sheet is tilted in the scanned image. In particular, when the seat is swiveled and slanted at the same time, it is not possible to distinguish between the seat swiveled and the slanted from the individual line images, which may hinder the removal of the effect of the seat swiveled. Be done.

Therefore, in the present embodiment, the image correction unit 213a (FIG. 2) is provided as an image correction means for correcting the scanned image read by the image reading unit 700, and the print position calculation unit 213 adjusts based on the corrected image data. It was configured to calculate the parameters. This makes it possible to more appropriately adjust the print position even if the sheet is swirled while passing through the reading position.

Hereinafter, Examples 1 and 2 in which the correction method by the image correction unit 213a is different will be described in order. In the following Examples 1 and 2, the correction method of the reading result will be described by taking the scanned image of the back surface read by the back surface CIS702 as an example, but the same method is applied to the scanned image of the front surface.

(Example 1)
In the first embodiment, the influence of the rotation of the sheet is reduced by applying the keystone correction to the scanned image distorted by the rotation of the sheet. FIG. 5A shows a scanned image before correction, and similarly to the example described with reference to FIG. 4, the section “A” is the reading result of the period during which the sheet was not swiveled, and “B”. The section of is the reading result of the period during which the seat was swiveled. As described above, the read image before correction acquired by the image reading unit 700 is in a state where the scale in the sub-scanning direction is deviated between the right side end portion and the left side side end portion in the drawing of the sheet.

Therefore, in this embodiment, trapezoidal correction is performed on the scanned image so as to correct the contour of the sheet to be rectangular. Specifically, the image correction unit 213a acquires the corner coordinates (X02, Y02) to (X32, Y32) of the sheet in the scanned image before correction from the sheet management table, and the sheet in the main scanning direction and the sub-scanning direction. Coordinates are transformed to match the rectangle defined by the length setting. Further, the image correction unit 213a converts the coordinates (X42, Y42) to (X72, Y72) of the feature points of the adjustment pattern by linear conversion along with the conversion of the corner coordinates of the sheet.

Here, due to the rotation of the sheet, only the Y coordinate of the lower right corner of the sheet in the read image before correction in FIG. 5A is the original Y coordinate corresponding to the set value of the sheet length in the sub-scanning direction. It illustrates a simple case that deviates from. In this case, the trapezoidal correction converts the lower right corner coordinates from (X32, Y32) to (X32, Y32'), so that the outline of the sheet becomes rectangular. Further, according to the coordinates (X42, Y42) to (X72, Y72) with respect to the contour of the sheet before the keystone correction, the coordinates (X42, Y42') to (X72, Y72') of the feature points of the adjustment pattern after the keystone correction. ) Is calculated.

In this embodiment, the corner coordinates (X02, Y02) to (X22, Y22) and (X32, Y32') of the sheet after the keystone correction in this way and the coordinates of the feature points of the adjustment pattern (X42, Y42) The adjustment parameters are calculated based on') to (X72, Y72'). Since the influence of the sheet turning is partially reduced in these coordinate data as compared with the coordinate data before correction, the printing position should be adjusted appropriately even if the sheet turns while passing through the reading position. Is possible.

The correction method of this embodiment is relatively effective when the turning direction of the sheet and the turning amount per unit time while passing through the reading position are substantially constant.

(Example 2)
In the second embodiment, a method of correcting the distortion of the scanned image due to the rotation of the sheet is used with higher accuracy than the keystone correction used in the first embodiment.

First, the distortion in the scanned image after the keystone correction will be described with reference to FIG. FIG. 6A shows a scanned image before correction, and similarly to the example described with reference to FIG. 4, the region “A” is the reading result in the section where the sheet does not rotate, and “B The area of "" is the reading result of the section where the seat was swiveled. Further, in order to express the distortion of the scanned image, the scanned image is shown when a sheet in which dot-shaped grid patterns are physically formed at equal intervals in the main scanning direction and the sub scanning direction is scanned.

FIG. 6B shows a read image after correction when the keystone correction used in Example 1 is performed. In this method, the keystone correction is performed without distinguishing between the sections "A" and "B", so that the correction is also applied to the section "A" in which the seat is not actually turned. Therefore, it can be seen that even if the keystone correction is performed, distortion remains in the adjustment pattern, which may reduce the adjustment accuracy of the print position.

Therefore, in this embodiment, the amount of rotation of the sheet per unit time is calculated based on the reading width H of the sheet in the line image and the sheet width W of the sheet used for the print position adjustment process. Then, by performing correction according to the amount of rotation for each region where the sheet is swirled in the scanned image, it is possible to correct the scanned image with higher accuracy. However, the reading width H of the sheet is the distance between both ends of the sheet in the line image read by CIS, and is a function (H (t)) of time (t). The sheet width W is a set value of the length of the sheet used in the print position adjustment process in the main scanning direction, and is a value that can be obtained by referring to the sheet management table 214.

A method of calculating the amount of rotation of the seat per unit time will be specifically described with reference to FIGS. 7 to 9. FIG. 7A shows how the CIS 702 reads an image of the sheet S that is conveyed while being delivered from the upstream transfer roller pair 611 to the downstream transfer roller pair 612. The reading range of CIS702 in the main scanning direction is wider than the sheet width W. Here, it is assumed that the seat width W is 320 mm. Further, the speed sensor 802 is provided at a position facing the CIS702 and at the center position of the reading range of the CIS702 with respect to the main scanning direction.

In the print position adjustment process, the image correction unit 213a detects both ends of the sheet S in the line image read by CIS702, and acquires the distances HL and HR in the main scanning direction from the speed sensor 802 to both ends, respectively. The reading width H (t) of the sheet at time t is the sum of HL and HR (H (t) = HL + HR).

Similar to the case described with reference to FIG. 4, there is a difference in the transport forces of the left and right transport rollers 612a and 612b between the transport roller pairs 612 on the downstream side, and after the sheet tip reaches the transport roller pair 612, the sheet The turn shall begin. At this time, the reading width H (t) of the sheet is a value larger than the sheet width W in the section of "B" after the tip of the sheet reaches the transport roller pair 612, and the inclination angle (turning amount of the sheet). ) Gradually increases with time.

Here, there is the following relationship between the reading width H (t) and the sheet width W.
θ = arccos (W / H)

FIG. 7C shows the relationship between the reading width H (t) and the inclination angle θ of the sheet when the sheet width W is 320 mm. From this relationship, the amount of turning of the sheet Δθ per unit time can be obtained by using the reading width H (t) at a certain point in time and the amount of change ΔH of the reading width H per unit time Δt.

A method of calculating the moving distances YR and YL at both ends of the sheet will be described with reference to FIG. 8 using the amount of rotation Δθ of the sheet per unit time. FIG. 8A shows a state in which the sheet is swiveled by Δθ while the unit time Δt has elapsed from the time t. During this period, the transfer speed of the right end of the sheet is defined as VR, the transfer speed of the left end of the sheet is VL, and the transfer speed of the sheet measured by the speed sensor 802 is VS.

First, the moving distance YR and the transport speed VR at the right end of the sheet will be described. FIG. 8B schematically shows the changes in YR and VR due to the turning of the seat. Focusing on the central part of the sheet, the transfer speed measured by the speed sensor 802 is VS, but considering that the sheet is actually fed diagonally at an angle of Δθ, the transfer speed at the central part of the sheet is VScosΔθ. Can be represented.

If the seat is not swiveled, the transport speed VR at the right end of the seat will be the same VScosΔθ as at the center, but as the seat swivels counterclockwise in the figure, the transport speed VR will increase during Δt. It will be. The increase in the transport speed VR at this time is defined as ΔVR, and the increase in the travel distance YR due to the increase in the transport speed by ΔVR is defined as ΔYR. At this time, using the distance HR from the center of the seat (detection position of the speed sensor 802) to the right end and the amount of rotation Δθ of the seat per unit time, the increase in the movement distance ΔYR (the length of the arrow indicated by ΔVR). ) Can be expressed by the following equation (Equation 1).

By definition, there is the following relationship between ΔYR and ΔVR.

From the equations (Equation 1 and Equation 2), ΔVR is expressed as follows.

Further, the relationship between the above-mentioned ΔVR and VS is expressed by the following equation (Equation 4).

Rewrite this as follows.

From the equations (Equation 3 and 5), the transport speed VR at the right end of the seat in consideration of the turning of the seat is as follows.

Here, there is the following relationship between the moving distance YR and the transport speed VR.

From the equations (Equation 6 and 7), the moving distance YR at the right end of the seat in consideration of the turning of the seat is as follows. However, sgn is a sign function, and when Δθ is positive (the turning direction is the counterclockwise direction in the figure), sgn (Δθ) = +1 and Δθ is negative (the turning direction is the clockwise direction in the figure). In this case, sgn (Δθ) = -1.

According to the same argument, the moving distance YL at the left end of the seat in consideration of the turning of the seat is as follows. Compared with the equation (Equation 8), the sign of the first term on the right side corresponding to the amount of change (ΔYL) in the moving distance caused by the turning of the seat is reversed.

When the moving distances YR and RL per unit time at the left and right sheet edges are obtained and plotted by the equations (Equation 8 and Eq. 9), the result is as shown in FIG. 9A. Here, it is assumed that the sheet is conveyed by 1 mm per unit time when the sheet is conveyed without turning. However, in the illustrated example, the feeding of the right end portion (R end portion) of the seat is delayed due to the turning of the seat, and the displacement amount 901 of the right end portion of the seat gradually increases in the section “B”.

Therefore, in the scanned image read by CIS702 from this sheet, the image may be corrected so as to cancel the deviation amount 901 as shown in FIG. 9B for the portion corresponding to the section “B”. In this case, in the range corresponding to the section of "B", which is 300 mm from the front end of the sheet to the rear end side, the right end portion (R end portion) of the sheet in the scanned image is in the sub-scanning direction as compared with the left end portion (L end portion) of the sheet. Image correction is performed so that the image is stretched to. On the other hand, in the range from the tip of the sheet corresponding to the section "A" to 300 mm, the image is not particularly expanded or contracted.

As a result, as shown in FIG. 6C, image correction is performed to reduce image distortion due to sheet rotation only in the image region corresponding to the section “B” where the sheet rotation has occurred. It is said. Then, by calculating the adjustment parameter from the coordinate data of the feature points of the adjustment pattern in the corrected image data, it is possible to adjust the print position with higher accuracy than in the first embodiment.

FIG. 10 shows a flowchart of the print position adjustment process. This flowchart proceeds by reading and executing the control program by the CPU 241 shown in FIG. 2 and appropriately instructing control elements such as the print position calculation unit 213. When the user selects the print position adjustment mode by the operation unit 20 (S00), this flow is started. In this embodiment, when the print position adjustment mode is selected, the user selects whether or not to perform the rotation correction of the sheet (S01).

When performing the turning correction, the user subsequently inputs the information of the sheet to be printed position adjusted via the operation unit 20 (S02). Based on the information input at this time, the sheet width W, which is the set value of the sheet length in the main scanning direction, is determined (S03). After that, the printer engine 150 forms the adjustment pattern on the designated sheet based on the image data of the adjustment pattern generated by the pattern generator 70 (S04). The sheet on which the adjustment pattern is formed is conveyed to the image reading unit 700 of the automatic adjustment unit 600, and the images are read from both sides of the sheet by the front surface CIS701 and the back surface CIS702. At this time, in parallel with the acquisition of the scanned image, the sheet conveying speed is measured by the speed sensors 801, 802, and the scanning width H (t), which is the distance between both ends of the sheet in the line image, is measured (S05). ).

The image correction unit 213a calculates the amount of rotation of the sheet per unit time at the reading positions of the front surface CIS701 and the back surface CIS702 by the above-mentioned method using the sheet width W, the reading width H (t), and the sheet conveying speed. (S06). Then, the read image before correction acquired by CIS701 and 702 is image-corrected so as to cancel the distortion of the image due to the rotation of the sheet. The print position calculation unit 213 compares the position of the adjustment pattern in the image data generated by the pattern generator 70 with the position of the adjustment pattern in the read image corrected by the image correction unit 213a, and compares the position of the adjustment pattern in the image data corrected by the image correction unit 213a with the print position adjustment parameter. The value of is calculated (S07). If it is selected not to perform swivel correction in the print position adjustment process (S01: NO), the print position is adjusted by the same procedure except that the steps S03, S05, and S06 related to swivel correction are omitted. The value of the parameter is calculated (S12, S13).

Then, the value calculated by the print position calculation unit 213 is stored in the storage area of the adjustment parameter in the sheet management table 214 (S08). As a result, the print position correction unit 212 can use new adjustment parameters when adjusting the position of the image data for printing in the next and subsequent image formation processes, and the print position adjustment process ends (S09).

Although the case where the print position adjustment process is executed based on an explicit instruction from the user has been described here, the print position adjustment process may be started by another trigger. For example, when an image formation job is submitted, as a preparatory operation before executing the job, an adjustment pattern may be formed on the same sheet as the one specified in the job and the adjustment parameters may be updated. .. Further, during the execution of the image forming job that requires a large number of deliverables, the print position adjustment process may be executed every time a fixed number of deliverables are output.

Further, the print position adjustment process is not limited to the process of aligning the images on both sides in double-sided printing, and may be aimed at adjusting the position of the image printed on one side.

Further, as a method of acquiring the sheet width W, the user explicitly selects the sheet size. Not limited to this, for example, the seat width W may be automatically detected from the signal of the sensor that detects the position of the seat position regulating member provided in the accommodating portions 110a and 110b (FIG. 1).

Further, in the present embodiment, the configuration in which the automatic adjustment unit 600 having the image reading unit 700 is detachable from the printer main body 100 having the printer engine 150 is illustrated. However, this technique can also be applied to an image forming system (image forming apparatus) in which the image reading unit 700 is incorporated inside the printer main body 100.

<Second Embodiment>
In the first embodiment, in a configuration in which an automatic adjustment unit receives a sheet on which an adjustment pattern is formed from a printer body and reads an image to adjust the print position, a technique for correcting distortion of the read image due to rotation of the sheet. Was applied to the example. This technique is not limited to this, and can be applied to an image reading device that reads an image from a sheet as a document.

FIG. 12 shows an image forming system 10 including a scanner 200. The image forming system 10 has the same configuration as that of the first embodiment except that the automatic adjustment unit 600 is not connected to the printer main body 100. That is, the scanner 200 executes a scanning operation of reading the image of the sheet S by the scanning mechanism of the scanner main body 400 while feeding and transporting the sheets S loaded on the document tray 211 one by one. In other words, the scanner 200 is an image reading device that reads an image by acquiring a line image line by line from a sheet conveyed by a transfer roller pair 224 as a transfer means by an image sensor 408 as a reading means. The acquired scanned image is stored in an image memory provided in the scanner main body 400 or the printer main body 100, and then used as image data for printing in a copy job or transferred as a scanned image to an external device via a network. Will be done.

Here, while the sheet S conveyed by the transfer roller pair 224 passes through the reading position of the scanning unit 404, the sheet S may rotate due to reasons such as deterioration of the rollers. In that case, the printed image output by the copy job and the scanned image transferred to the outside are distorted due to the rotation of the sheet S.

Therefore, in the present embodiment, distortion of the scanned image due to the rotation of the sheet is reduced by performing image correction on the scanned image read by the scanner 200 by the correction method described in the first embodiment. In this case, the scanned image corrected by the image correction unit 213a (FIG. 2), which is an image correction means, is stored in the image memory provided in the scanner main body 400 or the printer main body 100. As a specific correction method, any of the methods described in the first and second embodiments may be applied, but the second embodiment can obtain a more accurate scanned image.

Further, after the printer body 100 ejects the sheet on which the adjustment pattern is formed, the user manually sets the sheet in the document tray 211 of the scanner 200 and executes the scanning operation to perform the print position adjustment process. You may do it. In this case, the print position can be adjusted by the same configuration as that of the first embodiment except that the procedure for the user to move the sheet is inserted between S04 and S05 in the flow of FIG.

(Other embodiments)
The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

10 ... Image forming system / 20 ... Input unit (operation unit) / 100 ... Image forming device main body (printer main body) / 150 ... Image forming means (printer engine) / 200 ... Image reading device (scanner) / 213 ... Adjustment means ( Printing position calculation unit) / 213a ... Image correction means (image correction unit) / 408, 701, 702 ... Reading means (image sensor, front surface CIS, back surface CIS) / 600 ... Unit (automatic adjustment unit) / 611,612,613 , 224 ... Conveying means (conveying roller pair)

Claims (13)

An image forming means for forming an image on a sheet and
A transport means for transporting a sheet image-formed by the image-forming means, and a transport means.
A reading means for reading image data from a sheet conveyed by the conveying means, and
After forming a test image on a sheet by the image forming means, the image forming means obtains an image based on the image data for printing based on the image data read by the reading means from the sheet on which the test image is formed. It is provided with an adjusting means for adjusting the image position at the time of forming.
The adjusting means corrects the image data so as to reduce the distortion of the sheet caused by the rotation of the sheet while the sheet passes through the reading position of the reading means, and the corrected image data of the test image with respect to the sheet. Adjusting the image position based on the position,
An image forming system characterized by this. The reading means is configured to read line images in the main scanning direction perpendicular to the sub-scanning direction line by line from a sheet conveyed in the sub-scanning direction by the conveying means.
The adjusting means detects the rotation of the sheet based on the set value of the sheet length in the main scanning direction and the distance between both ends of the sheet detected from the line image read by the reading means.
The image forming system according to claim 1. The adjusting means calculates the amount of turning of the sheet per unit time based on the set value of the sheet length in the main scanning direction and the distance between both ends of the sheet detected from the line image read by the reading means. In the image data acquired by the reading means, the amount of rotation of the sheet per unit time is different. For each region in the sub-scanning direction, correction is performed according to the amount of rotation of the sheet.
The image forming system according to claim 2. A speed sensor for measuring the transport speed of the sheet passing through the reading position is provided.
The adjusting means has a unit time based on the set value of the sheet length in the main scanning direction, the distance between both ends of the sheet detected from the line image read by the reading means, and the transport speed measured by the speed sensor. Calculate the amount of turning of the winning seat,
The image forming system according to claim 2 or 3. Includes an input section that accepts input of information to the image formation system
The adjusting means acquires a set value of the sheet length in the main scanning direction based on the information input via the input unit.
The image forming system according to any one of claims 2 to 4, wherein the image forming system is characterized. The adjusting means trapezoidally corrects the image data so that the outline of the sheet in the image data read by the reading means is rectangular.
The image forming system according to claim 1. The adjusting means adjusts the image position with respect to the sheet when the image forming means forms an image based on the image data for printing.
The image forming system according to any one of claims 1 to 6, wherein the image forming system is characterized. The adjusting means adjusts the magnification of the image when the image forming means forms an image based on the image data for printing.
The image forming system according to any one of claims 1 to 7, wherein the image forming system is characterized. The adjusting means adjusts the rotation angle of the image when the image forming means forms an image based on the image data for printing.
The image forming system according to any one of claims 1 to 8, wherein the image forming system is characterized. The adjusting means adjusts the squareness of an image when the image forming means forms an image based on image data for printing.
The image forming system according to any one of claims 1 to 9, wherein the image forming system is characterized. The image forming means is arranged in the image forming apparatus main body, and is arranged in the image forming apparatus main body.
The reading means and the transporting means are arranged in a unit connected to the image forming apparatus main body and receiving a sheet discharged from the image forming apparatus main body.
The image forming system according to any one of claims 1 to 10. The image forming means develops a rotating image carrier, an exposure means for exposing the image carrier to form an electrostatic latent image, and an electrostatic latent image formed on the image carrier into a toner image. Includes a developing means and a transfer means for transferring a toner image developed by the developing means and carried on the image carrier onto a sheet.
The adjusting means adjusts the position where the exposure means forms an electrostatic latent image on the image carrier based on the position of the test image with respect to the sheet in the corrected image data.
The image forming system according to any one of claims 1 to 11. A transport means for transporting the sheet in the sub-scanning direction, and
A reading means for acquiring image data of a sheet by reading line images in the main scanning direction perpendicular to the sub-scanning direction line by line from the sheet conveyed by the conveying means.
An image correction means for correcting the image data acquired by the reading means is provided.
The image correction means allows the sheet to pass through the reading position of the reading means based on the set value of the sheet length in the main scanning direction and the distance between both ends of the sheet detected from the line image read by the reading means. Detects the rotation of the sheet during the operation and corrects the image data to reduce the distortion of the sheet caused by the rotation of the sheet.
An image reader characterized by this.

Images