JP2010191064A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus capable of performing image adjustment, without wasting user's own paper, in a belt-less direct transfer system. <P>SOLUTION: In the image forming apparatus, paper is conveyed, without being carried on the belt in a plurality of image transfer parts, including a photoreceptor drum 11 and a transfer roller 13, and an image is transferred onto the paper. The image forming apparatus includes a double-sided printing conveyance path B for printing on a second side of the paper on whose first side printing has been performed. An image-adjusting sheet S for transferring a toner pattern image for image adjustment is accommodated in the conveyance path B. The image-adjusting sheet S is fed to a conveyance path A from the conveyance path B, and the toner pattern image for image adjustment is transferred to the sheet S. The toner pattern image is detected by an optical sensor 61. Thereafter, the image adjusting sheet S is branched from the conveyance path A by rollers 51 and 52 and is returned to the conveyance path B, after the toner is removed therefrom. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that transfers an image onto a sheet while transporting the sheet without carrying a plurality of image transfer units composed of a photoreceptor and a transfer member with a belt.

  In general, an intermediate transfer method and a direct transfer method are known for electrophotographic tandem color image forming apparatuses such as copying machines and printers. In the intermediate transfer method, images of four colors (Y: yellow, M: magenta, C: cyan, Bk: black) are overlaid on a transfer belt that rotates endlessly, and then primary transfer is performed, followed by secondary transfer onto paper. To do. In the direct transfer method, a sheet is carried on a belt that rotates in an endless manner, and images of four colors are superimposed and transferred on the sheet. In these image forming apparatuses, an endless belt is used, so the conveyance speed is stable. Adjustment of the superimposed image is performed by optically reading the toner pattern image formed on the belt and feeding it back to the image forming operation. It is addressed.

  On the other hand, a beltless transfer system has been developed for the purpose of reducing the cost and reducing the size of the conventional transfer system. In the beltless transfer system, an image is transferred onto a sheet while the sheet is conveyed without being carried by a belt. However, this beltless transfer system has a problem that paper transportability is unstable and color misregistration is likely to occur. However, since there is no belt, image adjustment using the belt cannot be performed.

  Therefore, Japanese Patent Laid-Open No. 2004-228561 describes that image misregistration correction control is performed by forming a toner pattern image for image adjustment on a sheet and reading it. Here, in order to suppress wasteful consumption of paper, toner pattern images are formed on both sides of the paper, but the paper held by the user is eventually consumed only for image adjustment.

  Patent Document 2 describes going back to the cause of color misregistration, for example, measuring the distance between photoconductors, converting it to an image misalignment amount, and performing feedback control. Although this measure has an advantage that paper can be constantly monitored without wasting paper, a large number of detection sensors are required, resulting in an increase in cost. Also, it is impossible to detect even the quality of the paper passing state.

JP 2003-156906 A JP 2006-276394 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of performing image adjustment without wasting user-owned paper in a beltless direct transfer system.

In order to achieve the above object, an image forming apparatus according to an aspect of the present invention includes:
A plurality of image transfer units each including a photoconductor and a transfer member disposed so as to face the photoconductor are juxtaposed, and an image is transferred onto the paper while the plurality of image transfer units are transported without being supported by a belt. In an image forming apparatus for transferring
An image adjustment sheet for transferring a toner pattern image for image adjustment;
Detecting means for detecting the toner pattern image;
Control means for performing image adjustment based on a detection result by the detection means;
A duplex printing transport path for printing on the second side of the paper printed on the first side;
With
The image adjustment sheet is stored in the duplex printing conveyance path;
It is characterized by.

  In the image forming apparatus, a toner pattern image is transferred from the double-sided printing conveyance path in which the image adjustment sheet is stored to the image transfer unit, and the toner pattern image is detected and fed back to the image adjustment control. Therefore, it is not necessary to use user-owned paper for image adjustment. The image adjustment sheet is preferably of the same quality as the paper used for normal printing. By cleaning the toner pattern image transferred to the image adjustment sheet and returning it to the double-sided printing conveyance path, the image adjustment sheet can be reused many times, which is economical.

  In the image forming apparatus, a pattern for detecting the conveyance state may be printed in advance on the image adjustment sheet, and by detecting the conveyance state such as a sheet passing time and feeding back to the image adjustment control, Image adjustment with high accuracy is possible.

  According to the present invention, it is possible to perform image adjustment without wasting user-owned paper, and it is possible to perform high-precision image adjustment because a pattern is detected in an actual paper passing state.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus to which the present invention is applied. FIG. 2 is an elevation view illustrating a main part of the image forming apparatus. FIG. 6 is an explanatory diagram illustrating a sheet passing state of a sheet and an image adjustment sheet during printing. FIG. 4 is an explanatory diagram illustrating a sheet passing state of a sheet and an image adjustment sheet during printing (continuation of FIG. 3). FIG. 5 is an explanatory diagram illustrating a sheet passing state of paper and an image adjustment sheet during printing (continuation of FIG. 4). FIG. 6 is an explanatory diagram illustrating a sheet passing state of paper and an image adjustment sheet during printing (continuation of FIG. 5). FIG. 6 is a plan view illustrating an example of a toner pattern image. FIG. 3 is a plan view illustrating an example of a toner pattern image and a preprinted pattern.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings. Note that, in each embodiment, the same members and parts are denoted by the same reference numerals, and redundant descriptions are omitted. The letters Y, M, C, and Bk attached to the reference numerals indicate that the members are for forming yellow, magenta, cyan, and black images.

(Schematic configuration of image forming apparatus, see FIG. 1)
As shown in FIG. 1, an image forming apparatus to which the present invention is applied includes an image forming unit 10 (10Y) for forming images of Y (yellow), M (magenta), C (cyan), and Bk (black). , 10M, 10C, 10Bk) are sequentially arranged from the lower stage to the upper stage. Each image forming unit 10 includes a photosensitive drum 11 (11Y, 11M, 11C, 11Bk), a developing device 12 (12Y, 12M, 12C, 12Bk), a charging charger (not shown), and the like. A transfer roller 13 (13Y, 13M, 13C, 13Bk) that is paired with each of the photosensitive drums 11 is disposed.

  In each image forming unit 10, the sheet is conveyed upward through a nip portion (image transfer portion) formed by the photosensitive drum 11 and the transfer roller 13. Here, the sheet conveyance path A is slightly curved as shown by a dotted line in FIG.

  Further, the laser scanning optical unit 15 emits a modulated laser beam based on the image data from the gaps between the image forming units 10 toward the photosensitive drums 11 and electrostatically strikes the surface of the photosensitive drums 11. A latent image is formed. The image data is transmitted to the control unit 5 of the image forming apparatus directly from a computer (not shown) or via a network. The control unit 5 performs sheet conveyance control, control of other devices, and image adjustment control including image data processing.

  In the image adjustment control, an image adjustment sheet S (see FIG. 2) to be described below is passed through the image transfer unit, and a toner pattern image for image adjustment (see FIG. 7) at the Y, M, C, Bk image transfer unit. Control), the toner pattern image is detected by the optical sensor 61, and the shift of the transfer position of each color is measured and fed back to the formation of the image on the photosensitive drum 11. This image adjustment control is well-known control in this type of image forming apparatus except that the image adjustment sheet S is used. The image adjustment control is executed when the power is turned on, when the photosensitive drum 11 or the like is replaced, or when a predetermined number of printing operations are performed.

  A plurality of sheets of paper used for printing are accommodated in a stacked state in the automatic paper feed tray 20, and are fed upward one by one by a paper feed roller 21, and a predetermined timing is taken by a timing roller pair 22. In addition, the paper skew is corrected and sent to the conveyance path A. During the color image formation, yellow, magenta, cyan, and black images are transferred from the photosensitive drums 11Y, 11M, 11C, and 11Bk during the conveyance. When a monochrome image is formed, a black image is transferred from the photosensitive drum 11Bk. After the image has been transferred, the paper is fixed with toner by a fixing unit 30 including a heating roller 31 and a pressure roller 32, and is discharged from a discharge roller pair 35 onto a tray 36. Note that this type of image forming process is well known, and a detailed description thereof will be omitted.

  At the time of image formation, each transfer roller 13 comes into contact with each photoconductor drum 11 with a predetermined pressure, and a sheet is a nip formed by each photoconductor drum 11 and each transfer roller 13 that are rotationally driven at a predetermined speed. It is conveyed by the part. The transfer roller 13 is rotated by the rotation driving force transmitted or following the rotation of the photosensitive drum 11.

  Further, this image forming apparatus is provided with a double-sided printing conveyance path B including conveyance roller pairs 41, 42, 43, and 44 for printing on the second surface of the paper printed on the first surface. . The paper printed on the first surface is switched back by the discharge roller pair 35 and conveyed on the conveyance path B, conveyed again on the conveyance path A from the timing roller pair 22, and printed on the second surface.

  In this image forming apparatus, the image adjustment sheet S for transferring the toner pattern image for image adjustment is stored in the duplex printing conveyance path B as shown in FIG. Further, an optical sensor 61 for image detection and rollers 51 and 52 are arranged between the photosensitive drum 11Bk and the fixing unit 30 in the conveyance path A.

  The roller 52 can be brought into contact with and separated from the roller 51, and the separated state is indicated by a dotted line in FIG. The roller 52 is usually separated from the roller 51 and opens the conveyance path A. In this state, the print sheet is conveyed to the fixing unit 30. During image adjustment, the roller 52 enters the conveyance path A and contacts the roller 51. As a result, the image adjustment sheet S conveyed on the conveyance path A enters the nip portion of the rollers 51 and 52, is guided by the guide plate 53, and is conveyed to the conveyance path B for double-sided printing, as shown in FIG. Returned to

  The roller 52 also functions as a cleaning member that removes the toner transferred to the surface of the image adjustment sheet S. The toner is removed by making the rotational peripheral speed of the roller 52 different from the conveying speed of the sheet S to scrape the toner by a frictional force, or by charging the roller 52 to a polarity different from that of the toner. It can be performed by electrically adsorbing the roller 52. Although not shown, a blade for scraping off the toner may be disposed. Thus, by arranging the toner cleaning means, the image adjustment sheet S can be used repeatedly.

  The image adjustment sheet S is preferably the same quality as the paper used for normal printing, for example, a material having the same waist strength and thickness. However, a dedicated sheet may be used.

  When printing on the first side of the paper, the image adjustment sheet S remains stored in the double-sided printing conveyance path B. On the other hand, when the paper is introduced into the duplex printing conveyance path B for printing on the second side, the image adjustment sheet S is conveyed from the duplex printing conveyance path B to the image transfer unit so as not to interfere with the printing paper. And returned to the conveyance path B for double-sided printing. In this case, the sheet S is merely conveyed and image adjustment control is not performed.

  Hereinafter, the state of paper passing in such double-sided printing will be described with reference to FIGS. When printing on the first surface is started, the print paper S1 is conveyed from the paper feed roller 21 through the timing roller pair 22 through the image transfer portion (conveyance path A) (FIGS. 3A, 3B, 3). (See (C)), an image is formed on the first surface, and the fixing unit 30 and the discharge roller pair 35 are conveyed (see FIGS. 3D, 4A, and 4B). At this time, the image adjustment sheet S stands by on the duplex printing conveyance path B in a state where the lower end thereof is in contact with the nip portion of the conveyance roller pair 44.

  The print sheet S1 is switched back by the discharge roller pair 35 and sent to the duplex printing conveyance path B for printing on the second side (see FIGS. 4C and 4D). Here, the conveyance roller pairs 43 and 44 are driven, and the image adjustment sheet S is sent out from the lower part of the duplex printing conveyance path B, and conveyed through the timing roller pair 22 through the image transfer unit (conveyance path A). (See FIGS. 5A, 5B, and 5C).

  The roller 52 moves and contacts the roller 51 at the timing before and after the image adjustment sheet S passes through the most downstream image transfer portion (photosensitive drum 11Bk). The image adjustment sheet S branches from the conveyance path A and is conveyed to the conveyance path B for double-sided printing (see FIGS. 5D, 6A, and 6B), and the leading end is in the nip portion of the conveyance roller pair 44. It stops in the contacted state (see FIG. 6C). The roller 52 is separated from the roller 51 after the rear end of the image adjustment sheet S passes (see FIG. 6A).

  On the other hand, the printing paper S1 is conveyed from the lower part of the duplex printing conveyance path B through the timing roller pair 22 to the image transfer portion (conveyance path A) (FIGS. 5C, 5D, 6A). , (B)), an image is formed on the second surface, and is discharged from the discharge roller pair 35 via the fixing unit 30 (see FIGS. 6C and 6D).

  FIG. 7 shows a toner pattern image transferred onto the image adjustment sheet S. The pattern image 71 is for adjusting the color shift in the sub-scanning direction, and the pattern image 72 is for adjusting the color shift in the main scanning direction. These pattern images 71 and 72 have been conventionally used, and the alternate long and short dash line is a reading locus by the optical sensor 61.

  As shown in FIG. 8, separately from the pattern images 71 and 72 to be transferred, patterns 73a and 73b for detecting the conveyance state may be printed in advance. In the beltless transfer system, the paper is not held by the belt, and therefore the transportability is unstable. Therefore, the patterns 73a and 73b are fixedly printed in advance on the image adjustment sheet S at predetermined positions. By detecting the patterns 73a and 73b with the optical sensor 61, it is possible to detect the conveyance performance (conveyance time) in the image transfer unit. By feeding back the detection result to image writing control by the control unit 5 or paper conveyance control, the image transfer position on the paper by each image transfer unit can be corrected with high accuracy.

  In addition to using the image adjustment sheet S, the sheet conveyance time can be detected by the time from the drive start timing of the timing roller pair 22 until the leading edge of the sheet is detected by the optical sensor 61. Alternatively, it can be detected based on the timing at which the other optical sensor provided on the upstream side of the photosensitive drum 11Y and the optical sensor 61 detect the leading edge of the sheet.

(Other examples)
Note that the image forming apparatus according to the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the gist thereof.

  In particular, the basic configuration of the image forming apparatus is arbitrary, and may be a copying machine or a facsimile multifunction peripheral in addition to a single printer.

  As described above, the present invention is useful for an image forming apparatus of a beltless direct transfer system, and is particularly excellent in that the image quality is improved without wasting paper possessed by a user.

DESCRIPTION OF SYMBOLS 5 ... Control part 10 ... Image forming unit 11 ... Photosensitive drum 13 ... Transfer roller 52 ... Switching guide and cleaning roller 61 ... Optical sensor 71, 72 ... Toner pattern image 73a, 73b ... Print pattern image A ... Conveyance path B ... Both sides Print transport path S ... Image adjustment sheet

Claims (6)

A plurality of image transfer units each including a photoconductor and a transfer member disposed so as to face the photoconductor are juxtaposed, and an image is transferred onto the paper while the plurality of image transfer units are transported without being supported by a belt. In an image forming apparatus for transferring
An image adjustment sheet for transferring a toner pattern image for image adjustment;
Detecting means for detecting the toner pattern image;
Control means for performing image adjustment based on a detection result by the detection means;
A duplex printing transport path for printing on the second side of the paper printed on the first side;
With
The image adjustment sheet is stored in the duplex printing conveyance path;
An image forming apparatus. A transport path switching unit installed between the image transfer unit and the image fixing unit disposed on the most downstream side in the paper transport direction;
A cleaning unit for removing toner from the image adjustment sheet;
With
After the transfer of the toner pattern image and the detection of the toner pattern image, the image adjustment sheet passes through the transport path switching section and the cleaning section without passing through the image fixing section, and is returned to the transport path for duplex printing. ,
The image forming apparatus according to claim 1.   The image forming apparatus according to claim 2, wherein the conveyance path switching unit and the cleaning unit are shared by the same member.   4. The image forming apparatus according to claim 1, wherein when the image is printed on the first side of the sheet, the image adjustment sheet is stored in the double-sided printing conveyance path. 5. .   When a sheet is introduced into the duplex printing conveyance path for printing on the second side, the image adjustment sheet is conveyed from the duplex printing conveyance path to the image transfer unit so as not to interfere with the sheet, and The image forming apparatus according to claim 1, wherein the image forming apparatus is returned to the conveyance path for double-sided printing.   6. The image forming apparatus according to claim 1, wherein a pattern for detecting a conveyance state is printed in advance on the image adjustment sheet.

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