JP2007131385A - Image forming device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of securely preventing inside of the device (transfer part) from becoming dirty even when paper size set by a user by mistake is different from actual paper size. <P>SOLUTION: By using a line sensor 257, the length in the main scanning direction of paper to be carried is detected at predetermined timing. Based on this detection result of the length in the main scanning direction, an image frame is narrowed, and image data to be transferred positioned outside the image frame are deleted. Thus, even when the size set by a user does not correspond to the actual size of the paper placed on a multi manual paper feed tray 254, transfer of toner to a transfer belt 234 is prevented. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and method for forming an image on a fed sheet.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copiers, printers, and facsimile machines are provided with a manual feed tray as well as a paper feed stage for storing standard size paper. The length in the main scanning direction is determined by using the value of the volume attached to the movable guide on the manual feed tray as the size of the paper loaded on the manual feed tray.

  When the control unit of the image forming apparatus detects that the paper is stacked on the manual feed tray, the control unit displays a preset paper size on the operation unit by using the length in the main scanning direction obtained from the volume value. . The user sets the size of the paper actually set on the manual feed tray from the plurality of paper sizes displayed on the operation unit.

  However, in the following cases, the control unit erroneously recognizes the paper size. That is, the A3 size paper is set first so as to be long in the transport direction of the paper transport path, and image formation is performed. Thereafter, A4 size paper is set to form an image so as to be shorter in the transport direction. At this time, since the length in the main scanning direction is the same, it is not necessary to move the position of the guide on the manual feed tray. In such a case, if the user forgets to change the paper size, the control unit of the image forming apparatus erroneously recognizes that the paper set on the manual feed tray is A3 size paper. Become.

  As a result, an image corresponding to A3 size paper is formed, and when this image is transferred to A4 size paper, the toner image of the portion that protrudes from the A4 size stains the transfer portion. Since the transfer portion is dirty, the back side of the paper passing through the transfer portion is subsequently dirty. Alternatively, by executing a special sequence for cleaning the dirt, the image forming apparatus is temporarily brought down.

In order to solve such a problem, there has been proposed an image forming apparatus in which a sensor for detecting a sheet is provided on a sheet conveyance path, and the generation of a toner image is stopped by detecting the trailing edge of the sheet with this sensor ( (See Patent Documents 1, 2, and 3).
JP 2001-117431 A JP 2003-058015 A Japanese Patent No. 2769349

  However, the conventional image forming apparatus has the following problems. The pattern in which the user's operation is incorrect is not limited to the pattern in which the set value of the length in the paper transport direction does not match the actual length of the paper. That is, the case where the length in the main scanning direction (direction perpendicular to the sheet conveyance direction) does not coincide with the actual sheet length has been sufficiently considered.

  For example, this is the case as shown below. After loading A3 size paper on the manual feed tray so that its longitudinal direction matches the paper transport direction, the manual feed tray also keeps the longitudinal direction of A4 size paper so that its longitudinal direction matches the paper transport direction. To load. In this case, if the guide on the manual feed tray is not moved, the length of the sheet in the conveyance direction of the image formed by the image forming apparatus becomes the length in the longitudinal direction of A4 size. However, the length in the main scanning direction is the length in the short direction of A3 size.

  In addition, when the guide on the manual feed tray is not sufficiently brought into close contact with both ends of the sheet, the size recognized by the control unit of the image forming apparatus is different. For example, the length of the LTR size (= 216 mm) may be slightly larger than the length of the A4 size (= 210 mm).

  As described above, when an error occurs in the recognition of the sheet size in the image forming apparatus, a portion of the transfer belt outside the sheet is contaminated with toner. Then, the back side of the sheet passing thereafter is stained, or the image forming apparatus is temporarily brought down by a cleaning sequence.

  Therefore, the present invention provides an image forming apparatus and method that can reliably prevent the inside of the apparatus (transfer unit) from becoming dirty even when the paper size set by the user is different from the actual paper size. Objective.

  In order to achieve the above object, an image forming apparatus according to the present invention is an image forming apparatus that forms an image on a fed sheet based on image data, and is arranged in the sheet conveyance path and fed. Main scanning length detection means for detecting the length of the sheet in the main scanning direction, sheet storage means for storing the actual sheet size obtained from the detected length in the main scanning direction, and the fed sheet And comparing means for comparing with a preset sheet size, and as a result of the comparison, a difference between the actual sheet size and the preset sheet size is determined.

  The image forming method of the present invention is an image forming method for forming an image on a fed sheet based on image data, and the sheet is fed by a main scanning length detection unit arranged in the sheet conveyance path. A step of detecting the length of the sheet in the main scanning direction, an actual sheet size obtained from the detected length in the main scanning direction, and a sheet storage means for storing the fed sheet are preset. A step of comparing the sheet size of the sheet, and a difference between the actual sheet size and the preset sheet size is determined as a result of the comparison.

  The image forming apparatus of the present invention is an image forming apparatus that forms an image on a fed sheet based on image data, and is disposed in the sheet conveyance path, and the length of the fed sheet in the main scanning direction. A main scanning length detecting means for detecting the image, and an image area setting means for setting the area of the image to be formed so that the image fits on the sheet based on the detected length in the main scanning direction. It is provided with.

  The image forming method of the present invention is an image forming method for forming an image on a fed sheet based on image data, and the sheet is fed by a main scanning length detection unit arranged in the sheet conveyance path. Detecting a length of the sheet in the main scanning direction, and setting a region of the image to be formed so that the image fits on the sheet based on the detected length in the main scanning direction. It is characterized by having.

  According to the image forming apparatus according to the first and second aspects of the present invention, the actual sheet size obtained in advance from the length in the main scanning direction detected by the main scanning length detection unit arranged in the sheet conveyance path is stored in advance. Since the difference from the set sheet size is determined, even if the paper size set by the user is different from the actual paper size, the inside of the apparatus (transfer unit) can be reliably prevented from being stained.

  The image forming apparatus according to claims 3, 4 and 5 can be applied to an electrophotographic image forming apparatus. According to the image forming apparatus of the sixth aspect, it is possible to eliminate the influence of sheet cutting and expansion and contraction due to the surrounding environment. According to the image forming apparatus of the twelfth aspect, an image can be reliably formed only on the sheet by repeatedly detecting the length in the main scanning direction even if the sheet has an irregular size. According to the image forming apparatus of the fourteenth aspect, it is possible to easily detect the length of the sheet in the main scanning direction. According to the image forming apparatus of the fifteenth aspect, it is possible to accurately detect the length in the main scanning direction even for tab paper or perforated paper. According to the image forming apparatus of the sixteenth aspect, the length in the main scanning direction can be detected even if the size is irregular. According to the image forming apparatus of the nineteenth aspect, when the actual sheet size and the preset size are greatly deviated, the conveyance of the paper is interrupted before the image formation is performed, and the setting of the paper size is changed. can do. According to the image forming apparatus of the twentieth aspect, the inside of the apparatus (transfer section) can be prevented from being soiled.

  Embodiments of an image forming apparatus and method according to the present invention will be described with reference to the drawings. The image forming apparatus of this embodiment is applied to a digital copying machine.

[First Embodiment]
FIG. 1 is a longitudinal sectional view showing the internal configuration of the digital copying machine. The digital copying machine 1 has a digital copying machine main body including a printer unit 100 and a reader unit 200. The digital copying machine main body is provided with a paper feed deck 250 and a paper discharge processing device 290. The reader unit 200 is equipped with an automatic document feeder (DF) 280.

  The reader unit 200 mainly includes a platen glass 201 as a document placement table, a scanner unit 202, mirrors 205 and 206, a lens 207, and an image sensor unit 208. The scanner unit 202 is provided with a document illumination lamp 203 and a scanning mirror 204. The scanner unit 202 is driven by a motor (not shown) and scans in the left-right direction (sub-scanning direction) in the drawing while irradiating a document. At this time, the reflected light from the original is reflected by the mirrors 204, 205 and 206, passes through the lens 207, and forms an image on the CCD sensor in the image sensor unit 208. Here, as a scanning direction of the CCD sensor and the exposure control unit 210, a direction perpendicular to the recording paper conveyance direction is a main scanning direction, and a recording paper conveyance direction is a sub-scanning direction.

  On the other hand, the exposure control unit 210 in the printer unit 100 includes a laser, a polygon scanner, and the like. The exposure control unit 210 irradiates the photosensitive drum 211 with a laser beam 219 converted into an electrical signal by the image sensor unit 208 and modulated in accordance with an image signal subjected to predetermined image processing.

  Around the photosensitive drum 211, a primary charger 212, a developing device 213, a transfer roller 216, a pre-exposure lamp 214, and a cleaning device 215 are provided. In the image forming unit 209, the photosensitive drum 211 is rotationally driven in the direction of arrow n in the drawing by a motor (not shown). The surface of the photosensitive drum 211 is charged to a desired potential by the primary charger 212. Thereafter, when the surface of the photosensitive drum 211 is irradiated with the laser beam 219 from the exposure control unit 210, an electrostatic latent image is formed. The electrostatic latent image formed on the surface of the photosensitive drum 211 is developed by the developing unit 213 and visualized as a toner image.

  On the other hand, recording paper is fed from right cassette deck 221, left cassette deck 222, upper cassette 223 or lower cassette 224 by pickup rollers 225, 226, 227 or 228, respectively. This recording paper is fed to the transport path by paper feed rollers 229, 230, 231 or 232, and is fed to the transfer belt 234 by registration rollers 233.

  Then, the toner image visualized on the photosensitive drum 211 is transferred onto the recording paper by the transfer roller 216. In the photosensitive drum 211 after the transfer, the residual toner is cleaned by the cleaner device 215, and the residual charge is erased by the pre-exposure lamp 214.

  The recording sheet after transfer moves along with the transfer belt 234, is separated from the transfer belt 234 by the separation charger 217, and is sent to the fixing device 235 as it is. The toner transferred from the photosensitive drum 211 to the area outside the recording paper adheres to the transfer belt 234. The adhered toner is cleaned by the transfer belt cleaner 218. On the other hand, the recording paper sent to the fixing device 217 and fixed with toner by pressure and heating is discharged out of the copying machine main body by the inner discharge roller 236 and the discharge roller 244.

  On the other hand, the multi-manual feed tray 254 provided in the copying machine main body can accommodate 100 recording sheets. A volume is attached to the movable guide on the multi-manual feed tray 254. The value of this volume represents the paper width and is notified to the copying machine main body. The recording paper is conveyed to the registration roller 233 by the paper supply roller 255 and the conveyance roller 256. A line sensor 257 is provided between the paper feed roller 255 and the transport roller 256, and detects the length in a direction perpendicular to the transport direction of the paper fed from the multi manual feed tray 254.

  Further, as described above, the paper feed deck 250 is connected to the copying machine main body, and this paper feed deck 250 can store 4000 sheets of recording paper. The lifter 251 in the paper feed deck 250 rises according to the amount of recording paper so that the recording paper always abuts against the pickup roller 252. Then, the recording paper is sent to a conveyance path in the copying machine main body by a paper feed roller 253.

  In addition, a discharge flapper 237 that switches the conveyance path to the conveyance path 238 side or the discharge path 243 side is provided in the copying machine main body. By switching the paper discharge flapper 237, the recording paper sent out from the internal paper discharge roller 236 is turned over by the reverse path 239 and guided to the refeed path 241 via the lower transport path 240. Further, the recording paper fed from the left cassette deck 222 by the paper feed roller 230 is also guided to the refeed path 241. The refeed roller 242 refeeds the recording sheet guided to the refeed path 241 to the image forming unit 209.

  On the other hand, the discharge roller 244 is disposed in the vicinity of the paper discharge flapper 237 and discharges the recording paper to the outside through the discharge path 243 switched by the paper discharge flapper 237.

  Further, during double-sided recording (double-sided copying), the paper discharge flapper 237 is switched upward, and the copied recording paper is guided to the refeeding path 241 via the reverse path 239 and the lower transport path 240. At this time, the reverse roller 245 pulls the reverse end of the recording paper to the reverse path 239 and reverses the reverse roller 245 to send it to the lower conveyance path 240. When the recording paper is reversed and discharged from the copying machine main body, the paper discharge flapper 237 is switched upward, and the reverse roller 245 leaves a part of the trailing edge of the recording paper and draws it into the reverse path 239. Thereafter, the reversing roller 245 is reversed to turn the recording paper upside down and send it to the discharge roller 244 side.

  The paper discharge processing device 290 includes a stapler 299, an inserter 298, a Z folding machine 295, a bookbinding machine 296, and the like. The stapler 299 aligns and binds recording sheets discharged from the copying machine main body. When aligning the recording paper, the recording paper discharged one by one is stacked on the processing tray 294. When a part of the recording sheets is stacked, the bundle of recording sheets is bound and discharged onto the discharge tray 292 or 293. The paper discharge tray 293 is driven by a motor (not shown) to move up and down, and moves so as to be positioned on the processing tray 294 before the image forming operation is started. As the discharged recording paper is stacked, the recording paper moves so that the height of the paper surface becomes the position of the processing tray 294.

  The inserter 298 inserts a separator between the discharged recording sheets, and the separator to be inserted is stacked on the paper tray 291. The Z folding machine 295 Z-folds the discharged recording paper. The bookbinding machine 296 collectively folds a part of the discharged recording paper and performs bookbinding by stapling. The bundle of bound recording sheets is discharged to a discharge tray 297.

  FIG. 2 is a diagram showing a schematic configuration of a control unit of the digital copying machine. The control unit 150 mainly includes a CPU 101, ROM 102, RAM 103, external interface (I / F) 111, and image processing unit 107. The CPU 101 controls the entire digital copying machine. The ROM 102 stores a control program executed by the CPU 101.

  The RAM 103 is used as a work area necessary when the CPU 101 executes a control program. In addition to being used as a work area for the CPU 101, the RAM 103 is a digital image obtained by reading a document by a reader unit (document reading unit) 200, or an external of a digital copying machine via an external I / F 111. The digital image etc. which are sent from are stored. The image processing unit 107 has a work area where image processing is performed on a digital image obtained from the reader unit (document reading unit) 200 or the external I / F 111.

  In addition to the reader unit (document reading unit) 200, an operation unit 104, a paper size detection unit 105, a paper feeding unit 108, a conveyance unit 109, and an image forming unit 209 are connected to the control unit 150.

  The operation unit 104 is for setting a print job that the user wants to execute for the digital copying machine 1. In addition to the operation unit 104, a print job can be executed via the external I / F 111. The paper size detection unit 105 is installed on the transport path, and can detect the paper size by reading the edge of the paper being transported. In the present embodiment, a line sensor described later is used as the paper size detection unit.

  A reader unit (document reading unit) 200 reads an image of a document placed on the document table of the digital copying machine according to the setting of the operation unit 104, digitizes it, and stores it in the RAM 103. The image processing unit 107 performs necessary image processing on the digital image according to the setting by the operation unit 104, the detection result by the paper size detection unit 105, and the content of the read image from the reader unit (original reading unit) 200.

  The paper feeding unit 108 feeds a sheet stored in the digital copying machine 1. The sheet fed by the paper feeding unit 108 is conveyed to the image forming unit 209 by the conveying unit 109. Specifically, the paper feed unit 108 includes paper feed rollers 229, 230, 231, 232, 253, a re-feed roller 242 and the like.

  The image forming unit 209 forms a toner image from the digital image stored in the RAM 103, and transfers and fixes the toner image onto the sheet conveyed by the conveyance unit 109. Thereafter, the sheet is discharged from the digital copying machine by the conveyance unit 109. Specifically, the transport unit 109 includes an inner discharge roller 236, a discharge roller 244, and the like.

  The external I / F 111 is connected to a network such as TCP / IP. Then, it receives a print job execution instruction from a computer connected to the network, and conversely notifies the computer of information in the digital copying machine.

  FIG. 3 is a diagram showing an external configuration of the operation unit 104. The operation unit 104 includes various keys and a display panel 508. The numeric keypad 502 is used for inputting various numerical values when setting the number of image forming (copying) copies or setting the operation mode. By pressing the start key 505, the copy operation can be started. A stop key 506 is used to stop the image forming operation. A copy function key 520 and a printer function key 529 are function keys used for setting the functions of the copying operation and the printer operation, respectively.

  The display panel 508 is composed of a liquid crystal touch panel, and the display content is switched according to the mode. Here, a copy operation mode setting screen is displayed on the display panel 508. A plurality of touch keys are displayed on the setting screen, and a paper selection key 511 among them is a touch key for selecting a recording paper having a desired size.

  By using the paper selection key 511, it is possible to select not only the sheets of the paper feed cassettes 221 to 224 in the image forming apparatus 101 but also the sheets of the paper feed deck 250 and the manual multi-tray 254.

  Above the display panel 508, the contents of the set copying operation and the current operation state are displayed. A setting screen at the center of the display panel 508 is a setting screen related to copying.

  FIG. 4 is a block diagram illustrating a configuration of the image processing unit 107. The image processing unit 107 includes an analog signal processing unit 301, an A / D conversion unit 302, a LOG conversion unit 303, an image conversion unit 304, a γ correction unit 305, a binarization processing unit 306, a smoothing processing unit 307, and an image frame forming unit. 308.

  The analog signal processing unit 301, the A / D conversion unit 302, and the LOG conversion unit 303 perform processing until the image data from the reader unit (document reading unit) 200 is stored in the RAM 103. As described above, the reflected light from the document forms an image on the CCD sensor in the image sensor 208 through the mirrors 202, 205, 206 and the lens 207. When an image of reflected light from the imaged original is input to the CCD sensor as black luminance data, it is converted into an analog electrical signal by the CCD sensor.

  When an image signal as an analog electric signal is input to the analog signal processing unit 301, the analog signal processing unit 301 performs signal processing such as sample & hold and black level correction. Thereafter, the A / D converter 302 performs analog / digital conversion (A / D conversion), and shading correction is performed on the digitized signal. In this shading correction, the variation in sensitivity of the CCD sensor that reads the document and the light distribution characteristic of the document illumination lamp are corrected.

  The digital signal after the shading correction is sent to the LOG conversion unit 303. The LOG converter 302 stores a look-up-table (LUT) that converts input luminance data into density data. Using this LUT, the table value of the LUT corresponding to the input data is output. Thereby, the luminance data obtained by reading the document is converted into density data of the document image. This density data is stored in the RAM 103.

  On the other hand, the image conversion unit 304, the γ correction unit 305, the binarization processing unit 306, the smoothing processing unit 307, and the image frame forming unit 308 process image data (density data) stored in the RAM 103. In this process, a part of the process until the image forming unit 110 forms an image on the recording paper is performed.

  The image data stored in the RAM 103 is scaled to image data of a desired size by the image scaling unit 304 according to the size of the recording paper set by the operation unit 104. Then, it is sent to the γ correction unit 305. The γ correction unit 305 does not output the density information in the image data as it is, but performs LUT conversion in consideration of the input / output characteristics of the image forming unit, and adjusts the output in accordance with the density value instructed from the operation unit 104. I do. Thereafter, the multi-value density data as 8-bit information is binarized by the binarization processing unit 306 and converted to “0” or “1”.

  Image data composed of binarized density data is sent to the smoothing processing unit 307. The smoothing processing unit 307 performs data interpolation so as to smooth the edge of the binarized image, and sends the data to the image frame forming unit 308.

  The image frame forming unit 308 forms an image frame corresponding to the paper size and margin width of the recording paper on which an image is to be formed. When forming the image frame, the image frame is applied to the output image data from the smoothing processing unit 404, and the portion of the image data that protrudes from the frame, that is, the portion larger than the area where the image can be formed on the paper is deleted. This deletion of image data is performed by changing to white data. As described above, after the image frame forming unit 308 generates image data corresponding to the paper size, the image data is output to the image forming unit 209. As described above, the image forming unit 209 controls the laser irradiation from the exposure control unit 210 according to the image data.

  An image forming operation of the image forming apparatus having the above configuration will be described. In particular, a case where a document placed on the platen glass 201 is copied to a sheet placed on the multi manual feed tray 254 according to the setting of the operation unit 104 is shown. In this embodiment, an A3 size document is placed so that its longitudinal direction matches the conveyance direction of the recording paper, and A3 size paper is placed on the multi-bypass tray, and its longitudinal direction matches the conveyance direction of the recording paper. To be placed. Further, since the A3 size original is copied onto the A3 size paper, the magnification of the image is equal (= 100%). As the current state of the image forming apparatus, the guide is positioned on the multi-manual feed tray 254 so as to set the A3 size paper used in the previous copy job.

  FIG. 5 is a flowchart showing the document reading processing procedure. FIG. 6 is a flowchart showing a procedure for detecting the length of the paper in the main scanning direction. FIG. 7 is a flowchart showing an image forming process procedure. These processing programs are stored in the ROM 102 and executed by the CPU 101. If YES is determined in step S5 in FIG. 5, the step processing in FIGS. 6 and 7 is started, and parallel processing is performed together with the step processing in FIG. In this case, the CPU 101 performs parallel processing in a time-sharing manner as shown in FIG. 5, FIG. 6 and FIG. Alternatively, the CPU 101 may be configured by a plurality of microprocessors, and each processor may execute the step processes of FIGS. 5, 6, and 7.

  First, the user determines whether or not there is an A3 size document placed on the platen glass 201 (step S1). Step S1 is repeated until the document is placed. On the other hand, when the document is placed, when the automatic document feeder (ADF) 280 is closed, the document size is detected by a document size detection sensor (not shown) (step S2).

  Thereafter, it is determined whether or not a sheet is placed on the multi manual feed tray 254 (step S3). If the paper is not placed, the process of step S3 is repeated until the paper is placed. Here, a case is shown in which the A4 paper is not set on the multi-manual feed tray 254 by mistake so that the longitudinal direction of the A4 paper coincides with the conveyance direction of the recording paper.

  When a sheet on the multi manual feed tray 254 is detected by a paper detection sensor (not shown), the width of the guide of the multi manual feed tray 254 is detected, and the paper size is obtained from the value (step S4).

  Here, when a sheet is placed on the multi-manual feed tray, the digital copying machine 1 recognizes that the width of the guide is the width of the sheet in the main scanning direction when the user abuts the guide against both ends of the sheet. However, setting the paper size each time paper is placed on the multi-manual feed tray is a troublesome operation for a specific user. Therefore, the digital copying machine 1 has a mode in which the paper size of the multi manual feed tray is set in advance and the paper size is automatically set only by the user placing the paper on the multi manual feed tray.

  For this reason, when the user sets the longitudinal direction of the A4 size paper in the sub-scanning direction (in this case, the length in the main scanning direction is 210 mm) and places it on the multi-manual tray, the following situation occurs. Arise. Since the paper size is set to A3 size in advance, if the guide is not moved from the position of A3 size, the length of the paper in the main scanning direction is recognized as the length in the short side direction of A3 (297 mm). Is done. As a result, the digital copying machine 1 determines that the size of the paper placed on the multi-manual feed tray is A3 size.

  On the other hand, when the guide is moved and the detection result of the guide width in step S4 is smaller than the A3 size, the user is warned that the paper set in the multi-manual tray is different from the preset paper size. Displayed on the unit 104.

  Note that either the document placing process in steps S1 and S2 or the sheet placing process on the multi-manual tray in steps S3 and S4 may be performed first.

  After these settings are completed, it is determined whether or not the user has pressed the copy start key 505 to start copying (step S5). If the copy start key 505 has not been pressed, step S5 is repeated. On the other hand, when the copy start key 505 is pressed, copying is started and reading of a document is started in order to shorten the copy output time (step S6). As described above, in parallel with this process, the paper feeding process from the multi-manual tray shown in FIG. 6 and the image forming process shown in FIG. 7 are started.

  In reading a document, reflected light from the document is received by the CCD sensor while moving the scanner unit 202 in the sub-scanning direction. The received signal is converted into image data, and the obtained image data is sequentially transferred to the RAM 103 (step S7). The scanner unit 202 is moved by a distance corresponding to the document size, and it is determined whether or not all reading of the document is completed (step S8). If the reading of all the originals is not completed, the process of step S8 is repeated, and when the reading of all the originals is completed, this process is terminated.

  On the other hand, when the copy start key 505 is pressed in step S5, as shown in FIG. 6, the paper feeding process from the multi-manual feed tray 254 is started as the above-described parallel processing (step S11). In this paper feed process, the paper on the multi-manual feed tray 254 is fed by rotating the paper feed roller 255. At the timing when the leading edge of the fed paper reaches the line sensor 257, the line sensor 257 detects the length of the paper in the main scanning direction (step S12).

  FIG. 8 is a diagram showing the line sensor 257 and its peripheral portion seen through from the lower side of the digital copying machine 1. The sheet is conveyed in the direction of arrow a in the figure, and is sandwiched between both the pair of paper feed rollers 255 and the pair of conveyance rollers 256. A line sensor 257 is provided between the paper feed roller 255 and the transport roller 256, and detects the length of the transported paper in the main scanning direction.

  FIG. 9 is a diagram illustrating the configuration of the line sensor 257. The line sensor 257 includes a CCD sensor 257a and a pair of lamps 257b arranged on both sides thereof. The light from the lamp 257b irradiates the paper, and the reflected light is incident on the CCD sensor 257a, whereby the presence or absence of the paper located directly above is determined. Then, by using this CCD sensor 257a to determine the presence or absence of a sheet for each cell, the edge of the sheet can be detected.

  Here, as a control method for detecting the edge of the paper, the following four methods (A) to (D) are studied.

  A. Detection is performed only once when the leading edge of the paper reaches the detection area of the line sensor 257.

  B. Detection is performed only once at the timing when the leading edge of the sheet has moved a predetermined distance after reaching the detection area of the line sensor 257.

  C. The detection operation is repeated after the leading edge of the sheet reaches the detection area of the line sensor 257 until the trailing edge of the sheet comes out of the detection area of the line sensor 257.

  D. The detection operation is repeated after the leading edge of the paper reaches the detection area of the line sensor 257 until the detection result of the line sensor 257 detects the absence of paper in all cells.

  In the control method (A), the length of the sheet in the main scanning direction is determined only by the leading end portion. When a standard size sheet is conveyed in parallel with the sub-scanning direction, the length of the entire sheet in the main scanning direction can be sufficiently determined by this method.

  In the control method (B), the length of the paper in the main scanning direction is determined not at the front end but at a position behind the front end by a predetermined distance. This is to shift the detection timing in order to prevent the hole portion from being erroneously detected as the edge of the paper even if it is a standard size paper in the case of tab paper or perforated paper. This method can also sufficiently determine the length of the entire sheet in the main scanning direction when the sheet is conveyed in parallel in the sub-scanning direction.

  In the control method (C), the length of the paper in the main scanning direction is determined not only at the leading edge but at all positions from the leading edge to the trailing edge. When a non-standard size paper is conveyed, the shape of the paper can be read accurately. However, since the detection operation is repeatedly performed in a short cycle, the load on this control process becomes heavy. For this reason, it is necessary to reduce the load within the limit of the processing capability by reducing the detection accuracy or reducing the paper conveyance speed.

  In the control method (D), the trailing edge of the paper is detected. Conventionally, it is possible to accurately determine the trailing edge detection that has been performed by the flag sensor for paper conveyance by the line sensor.

  Further, the line sensor 257 is arranged only at both end portions, not the central portion of the sheet. This is because, from the type of paper width that can be passed by the digital copying machine, there is usually an area where the end of the paper does not come.

  Specifically, in the digital copying machine 1, among the papers that can be passed, the longest paper size in the main scanning direction is A3 size or A4 size when the longitudinal direction of the paper is set in the main scanning direction. . At this time, the length in the main scanning direction is 297 mm. On the contrary, the shortest paper is STMT size, and its length in the main scanning direction is 140 mm.

  FIG. 10 is a diagram showing a detectable region. Since the transport path is based on the center, if the transport accuracy in the main scanning direction of the transport path is 10 mm in front, the detectable area of the line sensor is expressed by Equation (1).

(297-140) ÷ 2 + 10 × 2 = 98.5 mm (1)
Therefore, by using two devices having a detectable area of the line sensor of 98.5 mm or more, it is possible to sufficiently detect paper that can be passed by a digital copying machine. On the other hand, if the end of the paper cannot be detected by one line sensor, the paper is misaligned in the main scanning direction beyond the assumed range. In this case, it can be handled as a conveyance jam, assuming that the accuracy of the subsequent sheet conveyance cannot be maintained.

  As a result of the detection in step S12, it is determined whether or not the length of the sheet in the main scanning direction can be detected by the line sensor 257 (step S13). If the length in the main scanning direction can be detected, the detected length in the main scanning direction is stored in the RAM 103 (step S14). Thereafter, the process returns to step S12. In step S12, the length in the main scanning direction is detected again. That is, by using the combination of the control methods (C) and (D) described above, the length of the sheet in the main scanning direction is repeatedly detected until the sheet cannot be detected.

  Specifically, the length of the paper in the main scanning direction is repeatedly detected at a cycle of 2 msec from the timing when the leading edge of the paper reaches the detection area of the line sensor 257. The process is performed until the trailing edge of the sheet passes through the detection area of the line sensor 257. At this time, the conveyance speed of the digital copying machine 1 is 500 mm / sec, and the length of the paper in the sub-scanning direction is 297 mm. Accordingly, the length in the main scanning direction is detected in increments of 1 mm, and the detection is repeated 297 times until the sheet is removed.

  If the sheet cannot be detected in step S13 due to the trailing edge of the sheet passing through the detection area of the line sensor 257, the sheet length is set to 0 (step S15), and the process is terminated.

  In the present embodiment, the combination of the control methods (C) and (D) is used for detection control of the length in the main scanning direction, but other methods may be used. For example, when plain paper is fed from the right cassette deck 221, there is almost no skew of the paper and no shift in the main scanning direction of the placement position. In this case, it is assumed that there is no problem even if the control method (A) is used. In addition, for a paper having a special tip shape such as perforated paper or tab paper, the possibility of erroneous detection can be eliminated by using the control method (B).

  On the other hand, when the copy start key 505 is pressed in step S5, as described above, the image forming process shown in FIG. 7 is started as the parallel process.

  A plurality of paper presence / absence detection sensors (not shown) are arranged in the paper transport path, and the position of the paper transported in the digital copying machine can be estimated from the detection timing of these sensors. Then, the time from the estimated position until the paper reaches the transfer roller 216 which is the transfer position of the toner image onto the paper is obtained. This time and the time it takes for the laser light 219 emitted from the exposure control unit 210 to move from the position where the latent image is formed on the photosensitive drum 211 to the location of the transfer roller 216 as the photosensitive drum 211 rotates. And compare.

  As a result of this comparison, when the time until the sheet reaches the transfer roller 216 from the current position becomes shorter than the time required for the latent image on the photosensitive drum 211 to move to the position of the transfer roller 216. Thus, the exposure control unit 210 starts the exposure. That is, exposure starts after the paper passes a predetermined position on the transport path. Conversely, by the time this point is reached, it is necessary to detect the length in the main scanning direction in step S12 for the paper fed from the multi manual feed tray. That is, the line sensor 257 is provided at a position where the distance from the transfer position is longer than the distance from the exposure position of the photosensitive drum 211 to the transfer position. In other words, the line sensor 257 is provided at a position where the time taken for the sheet to be conveyed to the transfer position is longer than the time taken for the photosensitive drum 211 to rotate from the exposure position to the transfer position. As a method of accurately aligning the toner image and the paper position after the exposure is started, it is possible to turn off the registration roller 233 and wait for a necessary time before turning it on.

  First, it is determined whether or not the timing for starting exposure has been reached (step S21). If the timing has not been reached, step S21 is repeated. On the other hand, when it is time to start exposure, the length of the paper stored in the RAM 103 in the main scanning direction is read (step S22). It is determined whether or not the length in the main scanning direction is 0 (step S23). If the length is not 0, the length in the main scanning direction of the set paper size is compared with the detected length in the main scanning direction (step S23). Step S24).

  As a result of this comparison, when the detected length is within the predetermined range (1 to 2 mm) compared to the set paper size, this dimensional deviation is caused by the paper cutting or the expansion / contraction of the paper due to the surrounding environment. Treat as an impact. Then, it is determined whether or not image data remains in the RAM 103 (step S26). If the image data remains, the image data obtained by reading the document need only correspond to the margin width of the paper in the image frame forming unit 308, and is transferred to the image forming unit 209 as it is (step S27).

  However, in the present embodiment, since the paper placed on the multi-manual feed tray 254 is A4 size, the length read in step S22 is about 210 mm. Thus, since it is significantly different from the preset 297 mm, “NO” is determined in the process of step S24. When the image data is transferred to the image forming unit 110 as it is, a toner image including an area that cannot be transferred onto the sheet is formed on the photosensitive drum 211.

  FIG. 11 is a diagram illustrating a state in which the image frame is narrowed so as not to generate a toner image that cannot be transferred to a sheet. FIG. 2A shows an image of a document. The toner image is A4 size, but the output paper setting is A3 size, so the upper left position of the A3 paper is output as the reference position. On the other hand, since the sheet is conveyed so as to pass through the central portion of the conveyance path, it reaches the inside of the dotted line portion m shown in FIG. If the transfer onto the paper is performed as it is, a toner image that cannot be transferred onto the paper is transferred onto the transfer belt 234 located outside the area of the dotted line portion m. As a result, the transfer belt 234 is significantly soiled.

  However, in the present embodiment, the length of the paper in the main scanning direction and the position in the main scanning direction are known in advance by the processing in step S22. Therefore, if it is determined in step S24 that the preset paper size (297 mm) is significantly different from the detected paper size (210 mm), the image frame is narrowed (step S25). That is, the image frame forming unit 308 sets the image frame to a value determined from the size, position, and margin size of the paper.

  In accordance with the setting of the image frame, the data corresponding to the upper left position of the document is moved as it is to the upper left position in the image frame with respect to the image data stored in the RAM 103. The exposure position is a position where the image data is shifted by 43.5 mm (= (297-210) / 2) in the main scanning direction because the sheet is located at the center of the transport path. FIG. 4C shows an output image after the image frame is narrowed.

  Further, since the image data of the portion corresponding to the outside of the image frame is deleted, the exposure control unit 210 does not perform the laser exposure for the portion where the image data does not exist.

  Thus, after setting the image frame in step S25, the image data remaining in the RAM 103, that is, the image data in the image frame is transferred to the image forming unit 110 in step S26 (step S27). Then, based on the transferred image data, an image forming operation on a sheet is executed (step S28). Then, it returns to step S22 and repeats the same process. That is, the reading of the length of the paper stored in the RAM 103 in the main scanning direction, the image frame forming process on the image data, and the image forming operation are repeated.

  On the other hand, if the detected length becomes 0 in step S23, it is determined that the trailing edge of the sheet has been reached, and the subsequent image forming operation is terminated (step S29). Then, this process is complete | finished.

  In the present embodiment, the image position is shifted in the main scanning direction in accordance with the setting of the image frame in step S25. That is, the image data is moved so that one end of the image data corresponds to one end of the area of the paper, and the exposure target area of the photoconductor is changed. However, it is also possible to select not to move the position of the image by switching the reading order of the image data stored in the RAM 103. In this case, as shown in FIG. 4D, the central portion of the original image is left. The selection of how to leave an image when deleting an image can be made by the user switching the setting contents in the digital copying machine.

  As described above, according to the digital copying machine of the first embodiment, the length of the sheet in the main scanning direction is detected, and the exposure target area on the photoconductor is changed according to the detection result. Therefore, even if the user mistakenly sets a paper size different from the actual paper size in the digital copying machine, it is possible to reliably prevent the inside of the machine including the transfer unit from being soiled.

  In other words, the length of the paper in the main scanning direction is set at a timing when the time from the current position of the paper to the transfer position is longer than the time from the exposure start position to the transfer position to the paper. Detect. Then, the image data to be transferred is deleted according to the detection result of the length in the main scanning direction. Thereby, even when the size set by the user and the actual size of the paper placed on the multi manual feed tray do not match, the transfer of toner to the transfer belt can be surely prevented.

[Second Embodiment]
Since the internal configuration of the digital copying machine and the configuration of the control unit in the second embodiment are substantially the same as those in the first embodiment, description thereof will be omitted. However, in the digital copying machine 1 of the second embodiment, no volume is provided in the guide portion of the multi-manual tray 254, and the user sets the paper size from the operation unit 104 as necessary. The right cassette deck 221, the left cassette deck 222, the upper cassette 223, and the lower cassette 224 also have no paper size detection function. For this reason, the user sets the paper size from the operation unit 104 according to the size of the paper set by the user.

  FIG. 12 is a diagram showing a configuration in the vicinity of the registration roller 233 in the digital copying machine according to the second embodiment. In the second embodiment, the second line sensor 261 is arranged at the junction of the conveyance path from the refeed roller 242 to the registration roller 233 and the conveyance path from the paper supply roller 229 to the registration roller 233. Yes. The second line sensor 261 and the above-described line sensor 257 can detect the paper size for all paper feed stages other than the paper feed deck 250. That is, it is possible to compare the paper size set by the user from the operation unit 104 with the actual paper size detection result.

  Conventionally, for example, an LTR size paper (length in the main scanning direction: 279 mm) that the user accidentally had beside is mistakenly considered as an A4 size paper, and the longitudinal direction of the paper is the main scanning direction. It is conceivable to store in the right cassette deck 221. In such a case, the A4 size (length in the main scanning direction: 297 mm) is set from the operation unit 104, but the difference in the paper size is small, so that it is buried in the conveyance jam margin. As a result, the digital copying machine cannot be determined to be abnormal and may output normally. Then, when a copy job is performed from the right cassette deck 221 and an image formed on the sheet is viewed, the user notices that the sheet size is strange.

  In such a case, the digital copying machine 1 of the present embodiment detects the length of the sheet in the main scanning direction by the line sensor (in this case, the second line sensor 261) on the conveyance path. Accordingly, it can be recognized that the paper size set by the operation unit 104 is different from the actual paper size before the image is formed.

  FIG. 13 is a flowchart showing an image forming process procedure when the copy start key 505 is pressed in step S5. This processing program is stored in the ROM 102 and executed by the CPU 101. The same step number is assigned to the same step process as in the first embodiment.

  That is, the detected size of the paper read in step S22 is compared with a preset paper size, and it is determined whether or not there is a large deviation (different from a predetermined value) (step S22A). If the detected size and the set size are compared, as a result of a large deviation, the paper conveyance is interrupted at that time (step S22B). Further, a paper size setting error is displayed on the operation unit 104 (step S22C), and the user is prompted to reset the paper size. Then, this process is complete | finished. On the other hand, if the result of comparison between the detected size and the set size in step S22A shows that there is no significant shift, the processing from step S23 is performed as in the first embodiment.

  As described above, according to the digital copying machine of the second embodiment, the length in the main scanning direction of the paper fed from the paper feed stage other than the manual multi-tray is set on the paper transport path. 2 line sensors 261 can detect. Accordingly, the difference between the paper size set by the user from the operation unit 104 and the actual paper size detected by the second line sensor 261 can be determined. In addition, when the detected size and the set size are significantly different from each other, the conveyance of the sheet can be interrupted before the image formation is performed, and the setting of the sheet size can be changed.

[Third Embodiment]
Since the internal configuration of the digital copying machine and the configuration of the control unit in the third embodiment are the same as those in the first embodiment, description thereof will be omitted. However, in the third embodiment, as a line sensor, two short devices are not used, but one long device that can detect all the lengths in the main scanning direction is used. In the multi-manual tray, a free size can be set as the paper size.

  The free size is set when using paper of a size other than the standard size (non-standard size). In the standard size, the size of the paper is uniquely determined based on the size code used in the apparatus. On the other hand, in the free size, it is necessary for the apparatus itself to measure the paper size and form an image accordingly.

  Further, in the conventional method, that is, the method of measuring the length in the main scanning direction with the guide on the multi-manual tray and detecting the trailing edge of the paper with the paper detection sensor arranged on the conveyance path, There were limitations. That is, it is necessary that the paper has a rectangular shape and is parallel to the transport direction.

  In the digital copying machine of the third embodiment, all the lengths in the main scanning direction can be detected by one line sensor. In addition, when the paper is skewed, when the paper is a triangle, it is possible to accurately detect the shape of the paper by repeatedly detecting the length in the main scanning direction in a short cycle. FIG. 14 is a diagram showing how the length in the main scanning direction is detected when the paper is skewed or triangular in the third embodiment. FIG. 4A shows a case where the paper is skewed, and FIG. 4B shows a case where the paper is a triangle.

  Detection and storage of the length of the paper in the main scanning direction are performed in the process from step S12 to step S14 in the flowchart of FIG. At this time, as the control for detecting the length in the main scanning direction, the above-described control method (A) (detected once at the front end of the paper) and control method (B) (detected once at a predetermined distance at the rear). Cannot be used. That is, it is necessary to repeat the detection operation with a short cycle using the control method (C).

  FIG. 15 is a flowchart showing an image forming process procedure. These processing programs are stored in the ROM 102 and executed by the CPU 101. The same step number as that of the first step process is denoted by the same step number, and the description thereof is omitted.

  If the length in the main scanning direction detected in step S23 is not 0, it is determined whether or not the paper size set by the user on the operation unit 104 is a free size (step S23A). If it is not a free size, the process proceeds to step S24, and the same process as in the first embodiment is performed. On the other hand, in the case of the free size, an image frame determined from the length in the main scanning direction read in step S22 is set in the main scanning direction (step S23B). At this time, the position of the image data stored in the RAM 103 is shifted in the main scanning direction in accordance with the setting of the image frame. That is, the image data is moved so that one end of the image data corresponds to one end of the area of the paper, and the exposure target area of the photoconductor is determined. Thereafter, the process proceeds to step S26, and the same process as in the first embodiment is performed.

  As described above, according to the digital copying machine of the third embodiment, the detection of the length in the main scanning direction is repeated in a short cycle with respect to a sheet fed from a sheet feeding stage whose sheet size is set to a free size. . As a result, an image can be reliably formed only on the sheet regardless of the skew or shape of the sheet.

  The present invention is not limited to the configuration of the above-described embodiment, and any configuration can be used as long as the functions shown in the claims or the functions of the configuration of the present embodiment can be achieved. Is also applicable.

  For example, in the above embodiment, when the paper sizes are different, the image formation is performed using only the image data of a part of the area so as to be applied to the image frame. However, the image data is compressed and stored in the image frame. It may be.

  In the above embodiment, when the paper sizes are different, the image frame is narrowed. Instead of this processing, the image forming operation (including the paper transport operation) is interrupted to indicate that the paper sizes are different. May be displayed. Thus, the operator can cancel the image forming job before the image is formed on the sheet.

  Further, the present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device. In addition to the original printing device, the printing device may be a facsimile device having a printing function, a multifunction device (MFP) having a printing function, a copy function, a scanner function, or the like.

  In the above embodiment, the case where the printing method of the composite apparatus is an electrophotographic method has been described as an example. However, the present invention is not limited to the electrophotographic method, and an inkjet method, a thermal transfer method, a thermal method, a static method, and the like. It can be applied to various printing methods such as an electric method and a discharge destruction method.

  Further, the type of sheet is not limited to plain paper, and various types such as thick paper, tab paper, and porous paper can be used.

  Another object of the present invention is to supply a storage medium storing software program codes for realizing the functions of the above-described embodiments to a system or apparatus, and the computer of the system or apparatus (or CPU, MPU, or the like). Is also achieved by reading and executing the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code and the storage medium storing the program code constitute the present invention. .

  Examples of the storage medium for supplying the program code include a floppy (registered trademark) disk, a hard disk, a magneto-optical disk, a CD-ROM, a CD-R, a CD-RW, a DVD-ROM, a DVD-RAM, and a DVD. An optical disc such as RW or DVD + RW, a magnetic tape, a nonvolatile memory card, a ROM, or the like can be used. Alternatively, the program code may be downloaded via a network.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (Operating System) running on the computer based on the instruction of the program code Includes a case where the functions of the above-described embodiments are realized by performing part or all of the actual processing.

  Furthermore, after the program code read from the storage medium is written to a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the expanded function is based on the instruction of the program code. This includes a case where a CPU or the like provided on the expansion board or the expansion unit performs part or all of the actual processing and the functions of the above-described embodiments are realized by the processing.

1 is a longitudinal sectional view showing an internal configuration of a digital copying machine. It is a figure which shows schematic structure of the control part of a digital copying machine. 3 is a diagram showing an external configuration of an operation unit 104. FIG. 2 is a block diagram illustrating a configuration of an image processing unit 107. FIG. 6 is a flowchart illustrating a document reading processing procedure. 6 is a flowchart illustrating a length detection processing procedure in the main scanning direction of a sheet. It is a flowchart which shows an image formation process procedure. FIG. 2 is a diagram illustrating a line sensor 257 and its peripheral portion seen through from the lower side of the digital copying machine 1. 3 is a diagram illustrating a configuration of a line sensor 257. It is a figure which shows a detectable region. FIG. 6 is a diagram illustrating a state in which an image frame is narrowed so as not to generate a toner image that cannot be transferred to a sheet. FIG. 6 is a diagram illustrating a configuration in the vicinity of a registration roller 233 in a digital copying machine according to a second embodiment. 10 is a flowchart illustrating an image forming process procedure when a copy start key 505 is pressed in step S5. FIG. 10 is a diagram illustrating a state in which a length in a main scanning direction is detected when a sheet in the third embodiment is skewed or a triangle. It is a flowchart which shows an image formation process procedure.

Explanation of symbols

1 Digital MFP 100 Printer Unit 101 CPU
102 RAM
DESCRIPTION OF SYMBOLS 104 Operation part 200 Reader part 211 Photosensitive drum 216 Transfer roller 234 Transfer belt 254 Manual multi-tray 257 Line sensor 308 Image frame formation part

Claims (23)

An image forming apparatus that forms an image on a fed sheet based on image data,
A main scanning length detection unit that is disposed in the sheet conveyance path and detects the length of the fed sheet in the main scanning direction;
Comparing means for comparing an actual sheet size obtained from the detected length in the main scanning direction and a sheet size preset in a sheet storing means for storing the fed sheet,
As a result of the comparison, a difference between the actual sheet size and the preset sheet size is determined.   When the actual sheet size is different from the preset sheet size, the region of the image to be formed is set so that the image fits on the sheet based on the detected length in the main scanning direction. The image forming apparatus according to claim 1, further comprising an image area changing unit that changes   The electrophotographic image forming apparatus that forms an image by exposing a photoconductor based on image data, wherein the image area changing unit changes an exposure target area of the photoconductor. 2. The image forming apparatus according to 2.   The main scanning length detection means is provided at a position where the distance from the transfer position to the main scanning length detection means is longer than the distance from the exposure position of the photoconductor to the transfer position. The image forming apparatus according to claim 3.   The main scanning length detection unit conveys the sheet from the position detected by the main scanning length detection unit to the transfer position based on the time required for the photosensitive member to move from the exposure position to the transfer position. The image forming apparatus according to claim 3, wherein the image forming apparatus is provided at a position where a longer time is required.   The image area changing unit is configured to expose the photoconductor when a length of the fed sheet in the main scanning direction is shorter than a predetermined length by a predetermined value compared to a length of the preset sheet size in the main scanning direction. 4. The image forming apparatus according to claim 3, wherein the target area is changed.   7. The image according to claim 6, wherein when the exposure target area of the photoconductor is changed, the photoconductor is not exposed to a portion where the exposure target area in the main scanning direction is larger than the sheet. Forming equipment.   7. The image formation according to claim 6, wherein when changing the exposure target area of the photoconductor, the image data corresponding to a portion where the exposure target area in the main scanning direction is larger than the sheet is changed to white data. apparatus.   The image data is moved so that one end of the image data corresponds to one end of the area on the sheet on which the image is formed when changing the exposure target area of the photoconductor. The image forming apparatus according to any one of 6 to 8.   The sheet storage means is a tray on which manually fed sheets are placed, and the sheet size is set in advance by moving a guide provided in the tray and movable in a main scanning direction. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, further comprising a selection unit that is provided in an operation unit operable by a user and that selects an arbitrary sheet storage unit from among the plurality of sheet storage units.   The image area changing unit determines an exposure target area of the photoconductor based on the detected length in the main scanning direction when the preset sheet size is an irregular size. The image forming apparatus according to claim 3.   The image data is arranged so that one end of the image data corresponds to one end of an area on a sheet on which the image is formed when determining an exposure target area of the photoconductor. 12. The image forming apparatus according to 12.   The image forming apparatus according to claim 1, wherein the main scanning length detection unit detects a length of the sheet in the main scanning direction based on a detection result performed on a leading end portion of the sheet.   2. The main scanning length detection unit detects a length of the sheet in the main scanning direction based on a detection result performed on a portion rearward by a predetermined distance from the leading edge of the sheet. The image forming apparatus described.   3. The image forming apparatus according to claim 1, wherein the main scanning length detection unit detects the length of the sheet in the main scanning direction based on a result of repeated detection from the leading edge to the trailing edge of the sheet. apparatus.   The image forming apparatus according to claim 1, wherein the main scanning length detection unit includes a line sensor. The line sensor has a detectable area longer than a predetermined length by a half of a difference between a maximum value and a minimum value in a main scanning direction of a sheet that can be fed.
18. The image forming apparatus according to claim 17, wherein the main scanning length detection unit includes two line sensors arranged in the main scanning direction.   2. The conveyance of the fed sheet is interrupted before the image is formed when the actual sheet size and the preset sheet size are different from each other by a predetermined value or more. The image forming apparatus described. An image forming apparatus that forms an image on a fed sheet based on image data,
A main scanning length detection unit that is disposed in the sheet conveyance path and detects the length of the fed sheet in the main scanning direction;
An image forming apparatus comprising: an image region setting unit configured to set a region of the image to be formed so that the image fits on the sheet based on the detected length in the main scanning direction. . An image forming method for forming an image on a fed sheet based on image data,
Detecting a length of a fed sheet in a main scanning direction by a main scanning length detection unit arranged in the sheet conveyance path;
Comparing the actual sheet size obtained from the detected length in the main scanning direction with a sheet size preset in a sheet storage means for storing the sheet to be fed;
As a result of the comparison, a difference between the actual sheet size and the preset sheet size is determined. An image forming method for forming an image on a fed sheet based on image data,
Detecting a length of a fed sheet in a main scanning direction by a main scanning length detection unit arranged in the sheet conveyance path;
An image forming method comprising: setting a region of the image to be formed so that the image fits on the sheet based on the detected length in the main scanning direction.   21. A program having computer-readable program code for realizing the image forming apparatus according to claim 1.

Images