JP2010008986A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent reduction in throughput while preventing the deterioration of positional accuracy of image by solving the problem in which occurrence of skew during carrying of a sheet having image formed thereon deteriorates the positional accuracy when forming image on the sheet again. <P>SOLUTION: A double-faced carrying roller 50 capable of performing skew correction is provided in a double-faced carrying path for carrying the sheet having image formed thereon to an image forming part again. Operation of skew correction by the double-faced carrying roller 50 is selectively executed based on a printing ratio or a difference between right and left printing ratios. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus capable of forming an image on a sheet.

  In recent years, color printers are commonly used by being connected to a plurality of host computers via a network and used for POD (Print On Demand).

  In order to use for POD, it is important that the accuracy of the image position is good and the productivity is high.

When an image is formed on a skewed sheet, the image position is shifted and the position accuracy of the image is deteriorated. As a technique for correcting the skew of the sheet, a technique for correcting the skew by locking the leading end of the sheet at the nip of a pair of rollers is known (for example, see Patent Document 1).
JP 2000-351488 A

  As a usage form in POD, a color image is often formed on a sheet. When transporting a sheet on which a color image is formed at a high printing rate, the sheet and the transport roller easily slip. Thus, for example, when an image is formed on the first surface of the sheet at a high printing rate and then the sheet is conveyed to form an image on the second surface, the sheet and the conveyance roller slip so that the sheet is skewed. There is a fear. If an image is formed on the second surface of the skewed sheet, the position of the image formed on the second surface is shifted.

  Therefore, for example, after image formation on the first surface and before image formation on the second surface, the skew correction is performed by locking the leading edge of the sheet with the nip of a roller pair as described in Patent Document 1. It is conceivable to apply the technology to do this. However, in such a technique, the rotation of the roller pair is stopped until a sufficient loop is formed on the leading edge side of the sheet so that the skew is corrected by locking the leading edge of the sheet at the nip of the roller pair. Become. Accordingly, the productivity of sheet conveyance is lowered, and the throughput of the image forming apparatus is lowered.

  The present invention is intended to meet the demands for high throughput and high positional accuracy of an image. In the case where an image is formed again on a sheet on which an image has already been formed, the throughput is improved while improving the positional accuracy of the image. It aims at improving.

  The present invention is provided in an image forming unit that forms an image on a sheet, a resupply path for supplying the sheet on which an image is formed by the image forming unit to the image forming unit, and the resupply path. The skew correction unit capable of performing a correction operation for correcting the skew of the sheet and the correction operation selectively according to the printing rate of the image formed on the sheet conveyed through the refeed path. And a control unit to be executed by the line correction unit.

  The present invention also provides an image forming unit that forms an image on a sheet, a resupply path for supplying again the sheet on which an image has been formed by the image forming unit to the image forming unit, and the resupply path. And a skew correction unit capable of executing a correction operation for correcting the skew of the sheet, and printing of an image formed on the sheet conveyed through the refeed path in a direction crossing the sheet conveyance direction. And a control unit that selectively causes the skew correction unit to execute a correction operation according to a difference in rate.

  According to the present invention, the skew correction operation is selectively executed according to the difference in the printing rate of the image formed on the sheet and the printing rate in the sheet width direction. Throughput is improved while improving the positional accuracy of the image when the image is formed again.

(First embodiment)
First, the entire image forming apparatus will be described with reference to FIG.

  FIG. 3 is a cross-sectional view showing an outline when the present invention is implemented in a full-color image forming apparatus having four image carriers.

  In the printer main body (image forming apparatus main body), the laser scanner 25 constituting the image forming unit, the photosensitive drums 1, 2, 3, and 4, the developing rollers 5, 6, 7, and 8, the intermediate transfer belt 18, and the fixing A film 20 and a pressure roller 21 are disposed. In the printer main body, a paper feed tray 13, a paper feed roller 15, and the like are installed.

  The sheets M stacked and stored in the sheet feed tray 13 are separated and fed by a sheet feed roller 15 and a separation roller 30 that rotate counterclockwise in the drawing, and are driven by a belt via a registration roller 31 and a registration roller 32. It is sent to the nip portion between the roller 16 and the transfer roller 17.

  The photosensitive drums 1, 2, 3, and 4 are rotated counterclockwise in the figure, and electrostatic latent images are sequentially formed on the outer peripheral surface by the laser light from the laser scanner 25, and then the electrostatic latent images are formed. The image is developed by the developing rollers 5, 6, 7, and 8 to form a toner image.

  The toner images formed on the photosensitive drums 1, 2, 3, and 4 are transferred to the intermediate transfer belt 18. When forming a color image, yellow, magenta, cyan, and black colors are developed on the photosensitive drums 1, 2, 3, and 4, and the toner images formed on the respective colors are transferred to the intermediate transfer belt 18.

  Next, the toner image formed on the intermediate transfer belt 18 is transferred to the sheet M sent to the nip portion between the belt driving roller 16 and the transfer roller 17.

  Further, the sheet M on which the toner image has been transferred is sent to the nip portion between the fixing film 20 and the pressure roller 21, where it is heated and pressed to fix the toner image on the sheet M.

  The sheet M on which the toner image is fixed is reversed by a double-side reversing roller 22 that also serves as a paper discharge roller and a double-side reversing roller 23. That is, the double-side reversing roller 22 can be rotated forward and backward. The double-side reversing roller 22 rotates in the forward direction in which the sheet is conveyed to the sheet discharge tray 24 and then reversely rotates to feed the sheet into the refeed path 49. A double-sided conveyance roller 50 is provided in the resupply path 49. The sheet fed into the resupply path 49 is conveyed to the registration roller 31 by the double-sided conveyance roller 50 and the downstream-side double-sided conveyance roller 52, and the toner image is transferred to the second side as with the first side.

  A double-sided conveyance roller 51 that rotates following the double-sided conveyance roller 50 is pressed against the double-sided conveyance roller 50. The double-sided conveyance roller 50 and the double-sided conveyance roller 51 nipping and conveying the sheet. The double-sided conveyance roller 50 and the double-sided conveyance roller 51 can execute an operation of correcting the skew of the sheet that is received so as to engage the leading edge of the sheet conveyed from the double-side reversing roller 22 in a state where the rotation is stopped. The skew correction roller pair of the present invention is configured. The sheet M on which the toner image is fixed on the second surface is discharged to the paper discharge tray 24 by the double-side reversing roller 22 and the double-side reversing roller 23.

  FIG. 4 is a control block diagram of the image forming apparatus. The control unit 110 that controls the operation of the image forming apparatus includes a CPU 111, a memory (RAM) 112, and a ROM 113 that stores programs and data for controlling the operation of the image forming apparatus. The control unit 110 causes the image forming apparatus 100 to perform a sequence operation according to data, programs, and the like stored in the ROM 113. An image processing unit 120 is connected to the control unit 110, and the image processing unit 120 receives an image signal from an external device such as a personal computer or a document reading device connected to the apparatus main body so as to be communicable. At the same time, a signal related to image formation is transmitted to the control unit 110. For example, an image signal is transmitted from the personal computer to the image processing unit 120 as a print job.

  The CPU 111 functions as a determination unit for obtaining the image printing rate for one page. In other words, the CPU 111 obtains the printing rate on the sheet based on the image formation signal transmitted from the image processing unit. Here, the image printing rate is a ratio of printing pixels (pixels on which toner dots are to be formed) to all pixels of the image per page. Alternatively, the printing rate is a value based on an integrated value of video count for one page, that is, a value based on an integrated value of density data for each pixel for one page.

  The control unit 110 controls the operation of each part of the image forming unit via the image forming control unit 121 in accordance with a signal related to image formation sent from the image processing unit 120.

  An output from the sheet detection sensor is input to the control unit 110. In this embodiment, the first sheet detection sensor S1 (see FIG. 2) provided between the nip portion of the fixing film 20 and the pressure roller 21 constituting the fixing device and the double-side reversing roller 22 is the sheet detection sensor. It corresponds to. The operation of the clutch 122 for driving and stopping the duplex conveying roller 50 is also performed by the control unit 110.

  Next, the skew correction operation by the duplex conveying roller 50 will be described in detail with reference to FIGS.

  FIG. 1 is a partial cross-section including a double-sided conveyance unit for reversing and conveying the sheet to supply the sheet to the image forming unit again in FIG.

  When a print job is input to the image forming apparatus, the CPU 111 of the control unit 110 obtains a printing rate of an image formed on the first surface of the sheet. The CPU 111 determines whether the print rate of the first side of the print job, that is, the print rate of the image formed on the first side is equal to or higher than a predetermined value.

  First, an operation in the case where the printing rate on the first surface of the print job is equal to or greater than a predetermined value will be described.

  A predetermined time after the toner image on the first surface is transferred to the sheet M and the rear end of the sheet M passes through the first sheet detection sensor S1 installed on the downstream side of the fixing film 20, a drive switching unit (not shown) is used. Then, the double-side reversing roller 22 is reversed.

  After the duplex reversing roller 22 is reversed, the duplex conveying roller 50 is stopped for a predetermined time T1, and then rotated by a driving unit (not shown).

  The predetermined time T1 is set so that the leading edge of the sheet M reaches the nip of the double-sided conveyance roller 50 while the double-sided conveyance roller 50 is stopped. Therefore, the leading edge of the sheet conveyed from the duplex reversing roller 22 is received by the duplex conveying roller 50 in a stopped state, a loop is formed on the leading edge side of the sheet M, and the skew of the sheet is corrected.

  When the printing rate of the image formed on the first surface is high, the sheet and the roller slip when the sheet on which the image with the high printing rate is formed is likely to be skewed. In the present embodiment, since the double-sided conveyance roller 50 performs an operation of correcting the skew, the skew that has occurred even if the sheet is skewed is corrected by forming an image with a high printing rate.

  Next, an operation when the printing rate on the first surface of the print job is less than a predetermined value will be described.

  The toner image on the first surface is transferred to the sheet M, and a predetermined time after the trailing edge of the sheet M passes the first sheet detection sensor S1, the double-side reversing roller 22 is reversed by a drive switching unit (not shown). Here, when the printing rate of the first surface of the print job is less than a predetermined value, the sheet M is conveyed without stopping the double-sided conveyance roller 50.

  When the printing rate is low, it is difficult for skew to occur, so the skew correction operation is not performed by the double-sided conveyance roller 50, so the time for skew correction is shortened and throughput is improved.

  Note that the value of the printing rate as a threshold value for determining whether or not to perform skew correction is obtained in advance by experiments or the like.

  Next, the skew feeding correction control operation of the double-sided conveyance roller 50 by the CPU 111 will be described with reference to the flowchart of FIG.

  The CPU 111 obtains the printing rate of the sheet formed on the first surface based on the image signal transmitted to the image processing unit 120, and determines whether or not the printing rate is equal to or higher than the predetermined printing rate (S10).

  If the printing rate is equal to or higher than the predetermined printing rate, the CPU 111 causes the duplex conveying roller 50 to execute the skew feeding correction operation. That is, the CPU 111 operates the clutch 122 that stops the rotation of the double-sided conveyance roller 50, and stops the rotation of the double-sided conveyance roller 50 (S11). Then, the CPU 111 determines whether or not the first sheet detection sensor S1 detects the sheet (S12). When the first sheet detection sensor S1 detects a sheet, the CPU 111 determines whether or not a predetermined time has passed (S13). When a predetermined time elapses after the first sheet detection sensor S1 detects the sheet, the CPU 111 stops the operation of the clutch (S14), and starts the rotation of the duplex conveying roller 50 (S14).

  As described above, the time from when the first sheet detection sensor S1 detects a sheet until the double-sided conveyance roller 50 starts rotating is set as follows. That is, the time is set such that a sufficient loop is formed on the front side of the sheet for receiving the front end of the sheet sent from the double-side reversing roller 22 in a stopped state and correcting the skew of the front end.

  On the other hand, if the printing rate is less than the predetermined printing rate in S11, the CPU 111 does not stop the rotation of the duplex conveying roller 50. Therefore, the CPU 111 accepts the sheet conveyed by the double-side reversing roller 22 without conveying the rotation of the double-sided conveyance roller 50 and conveys the sheet, so that time for skew correction is eliminated. Increases throughput.

  In this way, the CPU 111 controls to selectively execute the skew feeding correction operation of the duplex conveying roller 50 in accordance with the printing rate of the sheet formed on the first surface. That is, in the case of a high printing rate, the sheet on which an image is formed and the double-side reversing roller 22 slip and the sheet is likely to be skewed. Even if skew occurs due to this slip, skew correction is performed by the double-sided conveyance roller 50, so that the positional deviation of the image forming the image on the second surface is reduced. On the other hand, when the first surface of the print job has a low printing rate, the double-sided conveyance roller 50 does not perform the skew feeding correction operation, thereby preventing a decrease in throughput.

  The image forming apparatus of this embodiment has the following effects.

  By correcting the skew with the double-sided conveyance roller 50 in the vicinity of the downstream side of the double-side reversing roller 22 that is likely to be skewed, the deviation amount of the left end margin when the skew is corrected can be reduced. Therefore, the printing accuracy on the sheet is good.

  Further, only when the first side of a print job that is likely to be skewed has a high printing rate, the duplex conveying roller 50 is stopped and skew correction is performed. That is, when the first surface of the print job that is difficult to skew is low in printing rate, the sheet is conveyed without stopping the duplex conveying roller 50, so that the sheet can be conveyed at a high speed and the throughput is not reduced. In this way, the presence or absence of skew of the sheet is estimated according to the printing rate of the image formed on the first surface of the sheet, and execution or non-execution of the skew operation is selected accordingly. Therefore, it is possible to provide double-sided conveyance of a color image forming apparatus suitable for POD requiring high throughput and high image positional accuracy.

(Second Embodiment)
In the first embodiment, the double-sided conveyance roller 50 is based on the output from the first sheet detection sensor S1 disposed between the double-side reversing roller 22, the fixing film 20, and the pressure roller 21 and the nip portion. The CPU 111 determines the timing for starting the rotation. In the second embodiment, a second sheet detection sensor S <b> 2 that detects the arrival of the leading edge of the sheet M is installed on the downstream side of the duplex reversing roller 22 and the upstream side of the duplex conveyance roller 50. And the point from which CPU111 determines the timing which the double-sided conveyance roller 50 starts rotation based on the output from this 2nd sheet | seat detection sensor S2 differs from 1st Embodiment. Since other points are the same as those of the first embodiment, detailed description thereof is omitted.

  In the present embodiment, the second sheet detection sensor S2 is provided. The second sheet detection sensor S2 detects the arrival of the leading edge of the sheet M, and stops the double-sided conveyance roller 50 for a certain period of time, thereby more accurately controlling the loop amount formed on the sheet M and skew correction capability. Can be made more stable and improved.

(Third embodiment)
In the first or second embodiment, whether to perform skew feeding correction is selected based on the printing rate. In the present embodiment, the CPU 111 determines whether or not to perform the skew feeding correction operation based on the difference in the printing rate in the width direction intersecting the sheet conveyance direction of the image on the sheet M. Here, the difference in the printing ratio in the width direction intersecting with the image conveyance direction is the difference between the portion on one side (left side) and the other side (right side) in the width direction of the image formed on the sheet. This is a difference in printing rate, and is hereinafter referred to as a difference between left and right printing rates. Since the skew correction operation is the same as in the first or second embodiment except that the CPU 111 controls the skew feeding correction operation based on the difference between the left and right printing ratios, a detailed description is omitted.

  When the roller positions of the double-side reversing roller 22 and the double-sided conveyance roller 50 are symmetrical in the width direction, even if the printing rate is high, skewing is unlikely to occur if the difference between the printing rates on the left and right is small.

  Therefore, when the difference between the left and right printing rates is equal to or greater than a predetermined value, the double-sided conveyance roller 50 is stopped and skew correction is performed. On the other hand, when the difference between the left and right printing ratios is less than a predetermined value, skew is unlikely to occur, and therefore, skew correction for stopping the double-sided conveyance roller 50 is not performed and throughput is not reduced.

  Here, the difference between the left and right printing ratios is the difference between the printing ratios in the left side area and the right side area in the width direction of the sheet. That is, the difference between the left and right print ratios is the difference between the ratio of print pixels to all pixels of the image in the left region and the ratio of print pixels to all pixels of the image in the left region. Alternatively, the difference between the left and right printing ratios is a value based on the difference in the integrated value of the video count between the left area and the right area.

  In the image forming apparatus described in the third embodiment, the throughput can be improved without sacrificing the skew correction capability.

  The double-sided conveyance roller 50 and the double-sided conveyance roller according to the image formed on the first surface of the sheet as exemplified by the difference in the printing rate and the left and right printing rates shown in the first and third embodiments. The CPU 111 selectively executes the skew correction operation by 51. That is, according to the image formed on the sheet, the correction operation of the double-sided conveyance roller 50 and the double-sided conveyance roller 51 as a skew feeding correction unit that performs the skew feeding correction of the sheet carrying the image is selectively executed. . Therefore, both throughput and image position accuracy can be achieved at a high level.

(Fourth embodiment)
In the fourth embodiment, the CPU 111 can determine the difference between the left and right printing rates. The CPU 111 can also determine the printing rate of the image on the sheet M. If the difference between the left and right printing rates is low, skew correction is not performed even if the printing rate is high.

  That is, the CPU 111 causes the double-sided conveyance roller 50 to execute skew correction if the difference between the left and right printing rates is equal to or greater than a predetermined value and the print rate is equal to or greater than a predetermined value. When the difference between the left and right printing rates is less than a predetermined value and the printing rate is greater than or equal to the predetermined value, the CPU 111 does not execute the skew correction on the duplex conveying roller 50. When the difference between the left and right printing rates is equal to or greater than a predetermined value and the printing rate is less than the predetermined value, the CPU 111 does not cause the double-sided conveyance roller 50 to execute skew correction. When the difference between the left and right printing ratios is less than a predetermined value and the printing ratio is less than the predetermined value, the CPU 111 does not cause the double-sided conveyance roller 50 to execute skew correction.

  If the difference between the left and right printing rates is greater than or equal to a predetermined value and the printing rate is greater than or equal to a predetermined value, the double-sided conveyance roller 50 is stopped and skew feeding correction is performed to increase the printing rate and Even if skew occurs due to the high difference, it is corrected. If the difference between the left and right printing ratios is less than a predetermined value or the printing ratio is less than a predetermined value, skewing is unlikely to occur. Will improve.

  Therefore, the image forming apparatus described in the fourth embodiment can improve the throughput without sacrificing the skew correction capability.

  In this case as well, as described in the second embodiment, the second sheet detection sensor S2 that detects the arrival of the leading edge of the sheet M is provided downstream of the duplex reversing roller 22 and upstream of the duplex conveying roller 50. You may have. Then, the second sheet detection sensor S2 detects the arrival of the leading edge of the sheet M, and stops the double-sided conveyance roller 50 for a certain period of time, thereby controlling the loop amount formed on the sheet M more accurately and correcting skew feeding. Capabilities can be more stable and improved.

1 is a partial cross-sectional view illustrating a configuration of an image forming apparatus according to a first embodiment. FIG. 6 is a partial cross-sectional view illustrating a configuration of an image forming apparatus according to a second embodiment. 1 is a side sectional view showing an entire image forming apparatus according to a first embodiment. 1 is a control block diagram of an image forming apparatus according to an embodiment of the present invention. The flowchart which concerns on the operation | movement of skew feeding correction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 15 Paper feed roller 16 Belt drive roller 17 Transfer roller 18 Intermediate transfer belt 20 Fixing film 21 Pressure roller 22 Double-side reversing roller 23 Double-side reversing roller 50 Double-sided conveyance roller 51 Double-sided conveyance roller S1 1st sheet detection sensor S2 2nd sheet detection sensor

Claims (8)

An image forming unit for forming an image on a sheet;
A resupply path for supplying again the sheet on which the image is formed by the image forming unit to the image forming unit;
A skew correction unit that is provided in the refeed path and capable of performing a correction operation for correcting the skew of the sheet;
A control unit that selectively causes the skew feeding correction unit to perform a correction operation according to a printing rate of an image formed on a sheet conveyed through the resupply path;
An image forming apparatus comprising: The skew correction unit is a pair of skew correction rollers capable of performing a correction operation for receiving the leading edge of the conveyed sheet in a stopped state and correcting the skew of the sheet,
When the printing rate of the image is equal to or higher than a predetermined printing rate, the skew feeding correction roller pair stops rotating to perform the correction operation, and when the printing rate is less than the predetermined printing rate, The image forming apparatus according to claim 1, wherein the control unit controls the pair of skew correction rollers not to stop rotation for the correction operation.   The sheet forming apparatus includes a forward / reverse roller for rotating the sheet on which an image is formed by the image forming unit in the forward direction and then rotating the sheet in the reverse direction to convey the sheet, and with respect to the sheet conveyed by the reverse rotation of the forward / reverse roller. The image forming apparatus according to claim 2, wherein the row correction roller pair corrects skew. The control unit obtains a difference in printing rate in a direction intersecting a sheet conveyance direction of an image formed on a sheet conveyed through the refeed path,
If the difference between the printing rates is less than a predetermined value, the control unit causes the skew feeding correction unit to stop rotation for the correction operation even if the printing rate is equal to or higher than the predetermined printing rate. The image forming apparatus according to claim 2, wherein the image forming apparatus is controlled so as not to exist. An image forming unit for forming an image on a sheet;
A resupply path for supplying again the sheet on which the image is formed by the image forming unit to the image forming unit;
A skew correction unit that is provided in the refeed path and capable of performing a correction operation for correcting the skew of the sheet;
A control unit that selectively causes the skew feeding correction unit to perform a correction operation in accordance with a difference in a printing rate in a direction intersecting a sheet conveyance direction of an image formed on the sheet conveyed through the refeed path. When,
An image forming apparatus comprising: The skew feeding correction unit is a pair of skew feeding correction rollers capable of performing a correction operation for correcting the skew feeding of the sheet in a state in which the leading edge of the conveyed sheet is received and the rotation is stopped.
When the printing rate difference is equal to or greater than a predetermined value, the skew feeding correction roller pair stops for the correction operation, and when the printing rate difference is less than the predetermined value, the correction operation is performed. The image forming apparatus according to claim 5, wherein the control unit controls so that the rotation of the skew correction roller pair is not stopped for rotation. A forward / reverse roller for rotating the sheet on which an image has been formed by the image forming unit in the forward direction and then rotating the sheet in reverse to convey the sheet,
The image forming apparatus according to claim 5, wherein the skew feeding correction unit corrects the skew feeding of the sheet conveyed by the reverse rotation of the forward / reverse roller.   An image forming unit that forms an image on the sheet; a refeed path for supplying the sheet on which the image has been formed by the image forming unit to the image forming unit; and a skew feeding of the sheet provided in the refeed path. A skew correction unit capable of performing an operation for correcting the image, and a control unit that selectively operates the skew correction unit according to an image formed on a sheet conveyed through the refeed path. An image forming apparatus.

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