JP2008039990A - Color image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the life of a photoreceptor from being reduced even if a tip registration patch is formed.
A tip registration patch is formed using a photoconductor used for image formation among a plurality of photoconductors.
[Selection] Figure 1

Description

  The present invention relates to a color image forming apparatus such as a copying machine or a laser beam printer.

  In an electrophotographic image forming apparatus such as a copying machine, an electrostatic latent image is formed on a photoreceptor, and the image visualized with toner is transferred and fixed on the recording paper, thereby forming the image on the recording paper. Yes. In a color image forming apparatus that forms a color image by superposing a plurality of color toners such as yellow (Y), magenta (M), cyan (C), and black (K), each color is formed on a photoconductor. Some toner images are sequentially transferred to an intermediate transfer belt, a plurality of colors are superimposed on the intermediate transfer belt, and then transferred and fixed on a recording sheet.

  As described above, in the color image forming apparatus using the intermediate transfer belt, when the toner image on the intermediate transfer belt is transferred to the recording paper, if there is a misalignment between the toner image and the recording paper, Even if a uniform margin is provided, the image is transferred to the recording paper in a state where the image is shifted in the conveyance direction of the intermediate transfer belt, that is, in the sub-scanning direction.

Before the toner image on the intermediate transfer belt is transferred to the recording paper, a reference mark serving as a reference for the toner image is provided at a position preceding the toner image to be transferred to the recording paper in order to prevent the image from being shifted with respect to the recording paper. There is a method in which the reference mark is read and the position of the recording paper is detected, and control is performed so that the toner image is transferred onto the recording paper at a desired timing at the transfer position (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 11-194561

  In order to form a reference mark for aligning the toner image on the intermediate transfer belt with the position of the recording paper, the toner image to be the reference mark is transferred to the intermediate transfer belt using one of the photosensitive members provided for each color. There is a need to.

  For example, in a color image forming apparatus including four color toners of Y, M, C, and K, a black monochrome mode in which image formation is performed using only K as in the case of a black and white image forming apparatus, Y, M, C, and K There are image forming modes such as a full color mode using all four colors and a color single color mode using only one of Y, M, and C. Further, depending on the original image to be transferred onto the recording paper, image formation may be performed using only two or three colors of Y, M, C, and K.

  As described above, since the toner image to be transferred to the recording paper is not always formed using all colors, if the reference mark is always formed with a specific color, the color is not the toner image to be transferred to the recording paper. Not used, but only used to form fiducial marks.

  It is well known that the life of a photoconductor is shortened by charging the photoconductor to form an electrostatic latent image and applying a transfer voltage to transfer the toner image on the photoconductor to an intermediate transfer belt. An object of the present invention is to provide a color image forming apparatus that prevents the life of a photosensitive member from being shortened by forming a reference mark without applying charging or a transfer voltage to the photosensitive member only to form a reference mark. And

  The object of the present invention has been made in view of the above problems, and in order to achieve the above object, in the present invention, a plurality of image forming units having different colors and toner images of the respective image forming units are transferred after being superimposed. , An intermediate transfer belt for transferring to a recording medium, a pattern forming means for forming a registration correction mark on the intermediate transfer belt at a predetermined timing preceding an image to be transferred to the recording medium, a reading means for reading the registration correction mark, and a result of the reading means Accordingly, in a color image forming apparatus provided with a control means for aligning the image on the intermediate transfer belt and the recording medium at a predetermined position, a registration correction mark is formed by the image forming means used for the image transferred to the recording medium. To do.

  Further, charging to the image carrier and a transfer voltage for transferring the toner image to the intermediate transfer belt are not applied to the image forming means that is not used for the image transferred to the recording medium.

  In addition, one of the plurality of image forming units is a black image forming unit, and uses a black monochrome mode for generating an image to be transferred to a recording medium using only the black image forming unit, and a plurality of image forming units. A color mode for generating an image to be transferred to a recording medium, in the case of the black monochrome mode, the registration correction mark is formed by the black image forming unit, and in the case of the color mode, an image other than black among the plurality of image forming units A resist correction mark is formed by the forming means.

  Further, in the black monochrome mode, a transfer voltage for transferring the toner image to the intermediate transfer belt is not applied to the image forming unit other than black.

  As described above, in the present invention, the color of the registration correction mark is switched according to the image forming mode, so that the registration correction mark is formed by the image forming means used for the image transferred to the recording paper. Therefore, it is possible to prevent the image forming unit from being used only for the purpose of extending the life of the image forming unit.

  A color printer constructed according to the present invention will be described as an example. FIG. 1 shows a cross-sectional view of an example color printer.

  An image forming apparatus 1 is roughly divided into an image forming unit (four stations a, b, c, and d are arranged in parallel, and the configuration is the same), a paper feeding unit, an intermediate transfer unit, and a conveyance unit. Section, a fixing unit, an operation section, and a control unit (not shown).

  Next, each unit will be described in detail. The image forming unit is configured as described below. Photosensitive drums 11a, 11b, 11c, and 11d as image carriers are pivotally supported at the centers thereof and are driven to rotate by a stepping motor (not shown) in the direction of the arrow. Roller chargers 12a, 12b, 12c, 12d, scanners 13a, 13b, 13c, 13d, and developing devices 14a, 14b, 14c, 14d are arranged in the rotational direction facing the outer peripheral surfaces of the photosensitive drums 11a to 11d. . In the roller chargers 12a to 12d, charges of a uniform charge amount are given to the surfaces of the photosensitive drums 11a to 11d. Next, the photosensitive drums 11a to 11d are exposed to light beams, such as laser beams, modulated by the scanners 13a to 13d according to the recording image signal, thereby forming electrostatic latent images thereon. Further, the electrostatic latent images are visualized by developing devices 14a to 14d each containing four color developers (toners) such as black, cyan, magenta, and yellow. The visualized visible image is transferred to the intermediate transfer belt 30. By the process described above, image formation with each toner is sequentially performed.

  Next, the paper feed unit detects the passage of the recording material P, a portion for storing the recording material P, a portion for feeding the stored recording material P, a roller for conveying the recording material P, and the recording material P A sensor, a sensor for detecting the presence or absence of the recording material P, and a guide (not shown) for transporting the recording material P along the transport path. 21a, 21b, 21c, and 21d are cassettes, and 27 is a manual feed tray, in which the recording material P is stored. 22a, 22b, 22c and 22d are paper feed rollers for feeding the recording material P one by one from the cassettes 21a to 21d. The recording material P that is reliably separated by one by the paper feed rollers 22a, 22b, 22c, and 22d is further transported by the drawing rollers 24a to 24d and the pre-registration roller 26, and is transported to the registration roller 25. On the other hand, the recording material P stored in the manual feed tray 27 is separated by the BC roller 29 and conveyed to the registration roller 25 by the pre-registration roller 26.

  The intermediate transfer unit will be described in detail. 30 is an intermediate transfer belt, 32 is a drive roller for transmitting drive to the intermediate transfer belt 30, a tension roller 33 for imparting an appropriate tension to the intermediate transfer belt 30 by the biasing of a spring (not shown), and the intermediate transfer belt Is supported by a driven roller 34 that forms a secondary transfer region across the surface. The drive roller 32 is coated with rubber having a thickness of several millimeters on the surface of the metal roller to prevent slippage with the belt. The driving roller 32 is rotated by transmission of rotational force from a stepping motor that rotates the photosensitive drums 11a to 11d. Primary transfer rollers 35a to 35d to which a high voltage for transferring the toner image to the intermediate transfer belt 30 is applied to the back of the intermediate transfer belt 30 where the photosensitive drums 11a to 11d and the intermediate transfer belt 30 face each other. Is arranged. A secondary transfer roller 36 is disposed to face the driven roller 34, and a secondary transfer region is formed by a nip with the intermediate transfer belt 30. The secondary transfer roller 36 is pressed against the intermediate transfer belt 30 with an appropriate pressure. A cleaning device 50 for cleaning the image forming surface is disposed downstream of the secondary transfer region on the intermediate transfer belt 30, and the cleaning device 50 includes a cleaner blade 51 and a waste toner box for storing waste toner. Consists of 52.

  The fixing unit 40 includes a fixing roller 41a having a heat source such as a halogen heater therein, a pressure roller 41b pressed against the roller, and an inner discharge roller 44 that conveys the recording material P discharged from the roller pair.

  On the other hand, the recording material P transported to the registration rollers stops the rotation of the rollers upstream from the registration rollers, stops the recording material P, and stops the upstream rollers including the registration rollers 25 substantially in accordance with the image formation timing of the image forming unit. The rotational drive is resumed. The recording material P is fed to the secondary transfer area, and between the registration roller 25 and the secondary transfer area, the end of the recording material P described later and the end of the toner image on the intermediate transfer belt 30 are aligned. Done. The recording material P to which the image has been transferred in the secondary transfer region and the image has been fixed by the fixing unit 40 passes through the inner paper discharge roller 44, and then the transport destination is switched by the switching flapper 73. When the switching flapper 73 is on the face-up discharge side, the recording material P is discharged to the face-up discharge tray 2 by the outer discharge roller 45. On the other hand, when the switching flapper 73 is on the face-down paper discharge side, the recording material P is conveyed in the direction of the reverse rollers 72a, 72b, 72c and discharged to the face-down paper discharge tray 3. Note that a plurality of sensors are arranged in the conveyance path of the recording material P to detect the passage of the recording material P, and the paper feed retry sensors 64a, 64b, 64c, 64d, the registration sensor 67, and the inner discharge sensor 68, a face-down paper discharge sensor 69, a double-side pre-registration sensor 70, a double-side re-feed sensor 71, and the like. In addition, cassette paper presence / absence detection sensors 63a, 63b, 63c, and 63d that detect the presence or absence of the recording material P are disposed in the cassettes 21a to 21d that store the recording material P, and the manual feed tray 27 records on the manual feed tray 27. A manual tray paper presence / absence detection sensor 74 for detecting the presence / absence of the material P is disposed.

  The control unit includes a control board (not shown) for controlling the operation of the mechanism in each unit, a motor drive board (not shown), and the like.

  An operation unit (not shown) is arranged on the upper surface of the image forming apparatus 1, selects a paper feed unit (paper feed cassettes 21a to 21d, manual feed tray 27) in which the recording material P is stored, and a paper discharge tray (face). Selection of up-tray 2 and face-down tray 3) is possible.

  Next, explanation will be added in accordance with the operation of the apparatus. As an example, a case where the recording material P is transported from the cassette 21a will be described.

  After a predetermined time has elapsed since the image forming operation start signal was issued, first, the recording material P is sent out one by one from the cassette 21a by the paper feed roller 22a. Then, the recording material P is conveyed to the registration roller 25 via the drawing roller 24a and the pre-registration roller 26. At that time, the registration roller 25 is stopped, and the leading edge of the paper hits the nip portion. Thereafter, the registration roller starts rotating in accordance with the timing at which the image forming unit starts image formation. The rotation timing is set so that the recording material P and the toner image primarily transferred from the image forming unit onto the intermediate transfer belt exactly coincide with each other in the secondary transfer region.

  On the other hand, when an image forming operation start signal is generated, the image forming unit applies a high voltage to the toner image formed on the photosensitive drum 11d that is the most upstream in the rotation direction of the intermediate transfer belt 30 by the process described above. By the transferred transfer roller 35d, primary transfer is performed on the intermediate transfer belt 30 in the primary transfer region. The primarily transferred toner image is conveyed to the next primary transfer area. In this case, image formation is performed with a delay of the time during which the toner image is conveyed between the image forming units, and the next toner image is transferred with the leading edge of the image aligned on the previous image. The same process is repeated thereafter, and the four color toner images are primarily transferred onto the intermediate transfer belt 30.

  Thereafter, when the recording material P enters the secondary transfer area and contacts the intermediate transfer belt 30, a high voltage is applied to the secondary transfer roller 36 in accordance with the passing timing of the recording material P. Then, the four color toner images formed on the intermediate transfer belt by the process described above are transferred onto the surface of the recording material P. Thereafter, the recording material P is guided to the fixing roller nip portion. The toner image is fixed on the paper surface by the heat of the roller pair 41a and 41b and the pressure of the nip. Thereafter, the paper is discharged to the face-up discharge tray 2 or the face-down tray 3 according to the switching direction of the switching flapper.

  The alignment of the toner image on the intermediate transfer belt 30 and the recording paper P performed between the registration roller 25 and the secondary transfer area will be described with reference to FIGS.

  On the intermediate transfer belt 30, a leading edge registration pattern R is formed at a position preceding the toner image G on which the four colors are superimposed by a predetermined distance L. A leading edge registration pattern detection sensor 100 for detecting the leading edge registration pattern R is provided between the driving roller 32 of the intermediate transfer belt 30 and the secondary transfer region. Further, a recording paper leading edge detection sensor 101 that detects the leading edge of the recording paper P conveyed by the registration roller 25 is provided between the registration roller 25 and the secondary transfer region in the conveyance path of the recording paper P.

  The intermediate transfer belt 30 is driven at a constant speed Vp, and when the leading edge registration pattern detection sensor 100 detects the leading edge registration pattern R, the distance from the secondary transfer region to the leading edge registration pattern detection sensor 100 is L2. Then, it can be seen that the distance from the secondary transfer region to the toner image G is (L2 + L), and the time T2 until the toner image G reaches the secondary transfer region is (L2 + L) / Vp. After that, when the leading edge of the recording paper P conveyed by the registration roller 25 is detected by the recording paper leading edge detection sensor 101, the distance until the recording paper P reaches the secondary transfer area is recorded from the secondary transfer area. The distance to the paper leading edge detection sensor 101 is L1. Assuming that the delay time from the leading edge registration pattern R detection by the leading edge registration pattern detection sensor 100 to the recording paper P detection by the recording paper leading edge detection sensor 101 is T1, as shown in FIG. 4, the intermediate transfer belt 30 has a predetermined speed Vp. It is driven, and the conveyance speed of the recording paper P is controlled so as to reach the secondary transfer area in the time of (T2-T1).

  The recording paper P is transported at a speed Vs that is faster than the driving speed Vp of the intermediate transfer belt 30 when transport is started again from a state where it is temporarily stopped by the registration roller 25, and the time of (T2-T1) is determined. At that time, the timing for decelerating from Vs to Vp that is equal to the intermediate transfer belt 30 is calculated so that the distance L1 from the secondary transfer region to the recording sheet leading edge detection sensor 101 is reached at that time.

  At this time, the restart timing of the registration roller 25 is controlled so that a delay time T1 from the leading edge registration pattern R detection by the leading edge registration pattern detection sensor 100 to the recording paper P detection by the recording paper leading edge detection sensor 101 occurs. Yes.

  The toner image formation of the leading edge registration pattern R will be described with reference to FIG. FIG. 5 shows a case where the leading edge registration pattern R is formed with magenta in the full color image forming mode using all four colors of black, cyan, magenta, and yellow.

  A writing reference signal is generated for each color of black, cyan, magenta, and yellow, and after a predetermined timing from the writing reference signal, an electrostatic latent image corresponding to an image to be transferred to the recording paper P is generated by the scanners 13a to 13d as described above. A toner image is formed on the photosensitive drums 11a to 11d. In magenta that forms the leading edge registration pattern R, an electrostatic latent image of the image to be transferred to the recording paper P is similarly formed after a predetermined timing from the writing reference signal, and the electrostatic latent image of the image to be transferred to the recording paper P is also formed. An electrostatic latent image for forming the leading edge registration pattern R is formed on the photosensitive drum 11c in advance of the image by the distance L shown in FIG.

  The same applies when the tip registration pattern R is formed of other black, cyan, and yellow.

  The image forming apparatus 1 includes a black single-color image forming mode using only black, a color single-color image forming mode using only one of cyan, magenta, and yellow and a full-color image forming using all four colors of cyan, magenta, yellow, and black. Has a mode.

  In the black monochromatic image formation mode, cyan, magenta, and yellow are not used, so that the leading edge registration pattern R is formed with a black toner image transferred to the recording paper P. At this time, the unused cyan, magenta, and yellow photosensitive drums 11b to 11d are in contact with the intermediate transfer belt 30, and at the same speed as the intermediate transfer belt so as not to become a load when driving the intermediate transfer belt 30. It is rotationally driven. However, since no electrostatic latent images are formed on the photosensitive drums 11b to 11d and transfer to the intermediate transfer belt 30 is not performed, the charging and transfer voltages for the chargers 12b to 12b and the primary transfer rollers 35b to 35d are It is blocked so that it is not applied.

  Similarly, in the color single-color image forming mode, the leading edge registration pattern R forms a toner image in the used color, and the other three-color photosensitive drums 11 that are not used are driven to rotate at the same speed as the intermediate transfer belt 30. However, charging and transfer voltage to the charger 12 and the primary transfer roller 35 are not applied.

  In the full-color image forming mode, the leading edge registration pattern R is formed in any one of the colors included in the toner image transferred to the recording paper P following the leading edge registration pattern R.

  The determination of which color the leading edge registration pattern R is formed in in the single color image formation mode and the full color image formation mode will be described with reference to the flowchart of FIG.

  In step S101, it is determined whether the image forming mode is a black or color single-color image forming mode, and if it is determined that the image forming mode is a single-color image forming mode, the toner image transferred to the recording paper P as described above in step S102 The same color is selected as the color of the leading edge registration pattern R. If it is determined in step S101 that it is not a single-color image formation mode, that is, a full-color image formation mode, in step S103, it is determined which of the colors is least used, and in step S104, the color that is least frequently used is determined. Selected. The number of times of use is counted and stored for each recording sheet when the electrostatic latent images for the recording sheet are formed on the photosensitive drums 11a to 11d for each color. If it is determined in step S103 that the least frequently used color is a plurality of colors, in step S105, the most frequently used color among the plurality of colors is selected as the color of the leading edge registration pattern R. .

  In this embodiment, the color image forming apparatus using four colors of black, cyan, magenta, and yellow has been described. However, the color image forming apparatus using not only the above-described four colors but also more color types can be used. Good.

1 is an overall view of an image forming apparatus. Schematic of the tip registration pattern. The figure which shows the structure of a secondary transfer area | region upstream. FIG. 6 is a diagram illustrating control of recording paper upstream of a secondary transfer area. The figure which shows the write-in timing of an image. The flowchart which shows the discrimination | determination process of a front-end registration pattern color.

Explanation of symbols

1 Color image forming device
11 Photosensitive drum
25 Registration roller
30 Intermediate transfer belt
35 Primary transfer roller
36 Secondary transfer roller
41 Fixing roller
100 Tip registration pattern detection sensor
101 Recording paper edge detection sensor P Recording paper R Front edge registration pattern G Transferred toner image

Claims (7)

Image forming means including a plurality of image carriers each having a different color;
An intermediate transfer belt that superimposes and transfers the toner image of each image forming unit and then transfers the image to a recording medium;
Pattern forming means for forming a registration correction mark on the intermediate transfer belt at a predetermined timing preceding an image to be transferred to a recording medium;
Reading means for reading the registration correction mark,
In a color image forming apparatus including a control unit that aligns an image on an intermediate transfer belt and a recording medium at a predetermined position according to a result of a reading unit,
A color image forming apparatus, wherein a registration correction mark is formed by image forming means used for an image transferred to a recording medium. The color image forming apparatus according to claim 1.
A color characterized by not applying a charging voltage to an image carrier, a developing bias, and a transfer voltage for transferring a toner image to an intermediate transfer belt to an image forming unit that is not used for an image transferred to a recording medium. Image forming apparatus. The color image forming apparatus according to claim 1.
Among the plurality of image forming means, one is a black image forming means,
A black monochrome mode for generating an image to be transferred to a recording medium using only a black image forming unit, and a color mode for generating an image to be transferred to a recording medium using a plurality of image forming units,
In the black single color mode, a resist correction mark is formed by a black image forming unit, and in the color mode, a registration correction mark is formed by an image forming unit other than black among a plurality of image forming units. Image forming apparatus. The color image forming apparatus according to claim 3.
A color image forming apparatus characterized in that, in the black monochrome mode, charging to the image carrier, development bias, and transfer voltage for transferring the toner image to the intermediate transfer belt are not applied to image forming means other than black. . The color image forming apparatus according to claim 1.
A single color mode for generating an image to be transferred to a recording medium using only one color image forming means, and a color mode for generating an image to be transferred to a recording medium using a plurality of image forming means,
In the single color mode, the registration correction mark is formed by the image forming means having the same color as the image to be transferred to the recording medium. In the color mode, the most frequently used image forming means of the images to be transferred to the recording medium is used. A color image forming apparatus, wherein a registration correction mark is formed by an image forming means with few colors. The color image forming apparatus according to claim 5.
In the monochrome mode, the image forming means that does not transfer to a recording medium does not apply charging to the image carrier, developing bias, and transfer voltage for transferring the toner image to the intermediate transfer belt. Image forming apparatus. The color image forming apparatus according to claim 6.
In the color mode, when there are a plurality of colors of image forming means that are used the least number of times, registration correction marks are formed by the image forming means that uses the least amount of toner among the image forming means that are used the least number of times. Color image forming apparatus.

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