JP2006293132A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of handling a thick transfer paper with a simple configuration.
SOLUTION: Photosensitive drums 1a to 4a, an optical scanning device that exposes the photosensitive drums 1a to 4a to form an electrostatic latent image on the photosensitive drums 1a to 4a, and toner adheres to the electrostatic latent image. Developing devices 1b to 4b for forming toner images on the image carrier, an intermediate transfer belt 5 to which the toner images on the photosensitive drums 1a to 4a are primarily transferred, and a pressure contact with the intermediate transfer belt 5, An image forming apparatus including a secondary transfer roller 9 that secondarily transfers a toner image on the intermediate transfer belt 5 onto a transfer sheet S that passes through a nip portion between the intermediate transfer belt 5 and a paper feed tray 20. Are provided with a plurality of ribs 24 </ b> A to 24 </ b> D having different protrusion amounts from the back surface of the side wall 21 of the paper feed tray body 22 so that the transfer paper S is skewed in advance. Then, the transfer sheet S is made to enter the nip portion in a skewed state.
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus such as a copying machine.

  Conventionally, as an electrophotographic image forming apparatus, a plurality of image forming units are arranged along an intermediate transfer member such as a belt, and images of different colors are sequentially transferred onto the intermediate transfer member using each image forming unit. Various types of color image forming apparatuses have been proposed.

  FIG. 6 shows a schematic configuration of a general color image forming apparatus, in which image forming units 1, 2, 3, 4 are arranged along the intermediate transfer belt 5. The image forming units 1, 2, 3, and 4 have photosensitive drums 1a, 2a, 3a, and 4a, respectively. The photosensitive drums 1a, 2a, 3a, and 4a are exposed by an optical scanning device (not shown). An electrostatic latent image is formed. The image forming units 1, 2, 3, and 4 have developing units 1b, 2b, 3b, and 4b, respectively. The developing units 1b, 2b, 3b, and 4b are on the photosensitive drums 1a, 2a, 3a, and 4a. A toner image is formed by adhering the toner. Further, the image forming units 1, 2, 3 and 4 are provided with cleaning devices 1c, 2c, 3c and 4c for cleaning the photosensitive drums 1a, 2a, 3a and 4a, respectively.

  The intermediate transfer belt 5 is wound around a driving roller 6, a driven roller 7 and a transfer counter roller 8. The toner on the photosensitive drums 1a, 2a, 3a, and 4a is held on the intermediate transfer belt 5 by the photosensitive drums 1a, 2a, 3a, and 4a and the primary transfer rollers 1d, 2d, 3d, and 4d, respectively. The image is sequentially transferred first.

  Further, a secondary transfer roller 9 is disposed opposite to the transfer counter roller 8, and the intermediate transfer belt 5 is sandwiched between the transfer counter roller 8 and the secondary transfer roller 9. A nip portion is formed in the sandwiched portion, and the toner image on the intermediate transfer belt 5 is secondarily transferred onto the transfer paper S passing through the nip portion.

  The transfer paper S is accommodated in the paper feed tray 10. At the time of transfer, the transfer paper S is pulled out from the paper feed tray 10 one by one by the paper feed roller 11, passes through the transport roller pair 12 and the registration roller pair 13, and then the transfer counter roller 8. And the secondary transfer roller 9 are supplied to the nip portion.

  In the nip portion, the transfer sheet S on which the toner image on the intermediate transfer belt 5 is secondarily transferred is sent to the fixing device 15 via the transport unit 14 and is fixed by the fixing device 15.

  By the way, in the image forming apparatus, the conveyance speed of the intermediate transfer belt 5 is required to be constant. When the transfer speed of the intermediate transfer belt 5 fluctuates, a shift between colors occurs when a toner image is transferred from the photosensitive drums 1a, 2a, 3a, 4a to the intermediate transfer belt 5, and so-called "color shift". An image defect called “occurs” occurs. Even in the case of using a single color, if an instantaneous speed difference occurs between the photosensitive drums 1a, 2a, 3a, 4a and the intermediate transfer belt 5, a lateral band-like abnormal image is generated.

  In recent years, with the widespread use of color image forming apparatuses, the number of users who create posters and the like using the color image forming apparatus is increasing. In this case, cardboard is often used as the transfer sheet S. When the thick paper drawn from the paper feed tray 10 reaches the nip portion between the transfer facing roller 8 and the secondary transfer roller 9, the paper thickness particularly when the leading edge of the paper enters the nip portion, and the trailing edge of the paper When the toner passes through the nip portion, a large load fluctuation occurs instantaneously, and the conveyance speed of the intermediate transfer belt 5 changes momentarily. As a result, as shown in FIG. 7, the transfer sheet S generates a lateral band-like abnormal image, so-called “thick paper shock jitter”, in a direction perpendicular to the transfer direction of the transfer sheet S.

  FIG. 8 shows the belt speed fluctuation of the intermediate transfer belt 5 when the transfer sheets having various thicknesses are continuously passed. Here, it can be seen that the paper thickness increases from the thick paper 1 to the thick paper 3, and the fluctuation of the belt speed increases accordingly.

  Further, FIG. 9 shows the amount of color misregistration when plain paper / thick paper 1 / thick paper 2 / thick paper 3 is passed. Similar to FIG. 8, the amount of color misregistration increases as the paper thickness increases.

  As a method of solving such a problem when passing the thick transfer sheet S, the transfer member (that is, the secondary transfer roller) is swung while being regulated in a direction in which the image carrier or the intermediate transfer belt is pressed and separated. There has been proposed an image forming apparatus configured so as to be supported (see, for example, Patent Document 1).

In this image forming apparatus, when a cardboard or the like enters the nip portion, the transfer member swings according to the generated external force, so that it is possible to absorb the impact of entering the nip portion and the impact of separating from the nip portion, A good image can be obtained.
JP 2001-265127 A

  However, the technique disclosed in Patent Document 1 is configured to support the transfer member so as to be able to swing while restricting the transfer member in the press-contacting / separating direction. . Further, it is difficult to keep the nip width with the image carrier or the intermediate transfer belt constant because the transfer member swings.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that can handle a thick transfer sheet with a simple configuration.

  In order to solve the above-described problems, the invention described in claim 1 includes an image carrier, an optical scanning device that exposes the image carrier to form an electrostatic latent image on the image carrier, and the static A developer for attaching toner to the electrostatic latent image to form a toner image on the image carrier, an intermediate transfer member on which the toner image on the image carrier is primarily transferred, and a pressure contact with the intermediate transfer member An image forming apparatus comprising: a transfer member that secondarily transfers a toner image on the intermediate transfer body to a transfer paper that passes through a nip portion between the intermediate transfer body and both ends of the front end of the transfer paper And a control mechanism for allowing the transfer paper to enter the nip portion with a time difference.

  According to the above configuration, when the transfer sheet is a thick sheet, both ends of the transfer sheet can be plunged with a time difference, so that the load variation due to the rush of the transfer sheet can be minimized, and the speed variation of the intermediate transfer belt due to the load variation. Can be reduced. As a result, it is possible to obtain a good image with few image defects such as jitter and color misregistration due to the speed fluctuation of the intermediate transfer belt with an inexpensive configuration with a small number of parts.

  According to a second aspect of the present invention, in the first aspect, the control mechanism forcibly skews the transfer paper to enter the nip portion.

  According to a third aspect of the present invention, in the second aspect, a paper thickness sensor for detecting a paper thickness of the transfer paper is provided, and the control mechanism is configured to detect the transfer paper based on a detection result from the paper thickness sensor. It is characterized by controlling the amount of skew.

  According to a fourth aspect of the present invention, in the second or third aspect, when the control mechanism skews the transfer paper, the optical scanning device adjusts an exposure position according to the skew amount of the transfer paper. It is a feature. In this way, since the position of the laser beam scanning line from the optical scanning device can be corrected according to the skew amount of the transfer paper, a good image that does not become oblique can be obtained.

  According to the present invention, it is possible to realize an image forming apparatus that can handle a thick transfer sheet with a simple configuration.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol shall be described in the part same as the prior art.

  FIG. 1 shows a schematic configuration of an image forming apparatus according to the present invention. In FIG. 1, reference numerals 1, 2, 3, and 4 denote image forming units arranged along an intermediate transfer belt (intermediate transfer member) 5. Each of the image forming units 1, 2, 3 and 4 has photosensitive drums 1a, 2a, 3a and 4a as image carriers, and an optical scanning device (illustrated) is provided on each of the photosensitive drums 1a, 2a, 3a and 4a. (Omitted), exposure is performed according to the image signal to form an electrostatic latent image. The image forming units 1, 2, 3 and 4 have developing units 1b, 2b, 3b and 4b, respectively. The developing units 1b, 2b, 3b and 4b are connected to the photosensitive drums 1a, 2a, 3a and 4a. Toner is attached to form toner images on the photosensitive drums 1a, 2a, 3a, 4a. Further, the image forming units 1, 2, 3 and 4 are provided with cleaning devices 1c, 2c, 3c and 4c for cleaning the photosensitive drums 1a, 2a, 3a and 4a, respectively.

  The intermediate transfer belt 5 is an endless belt and is wound around a driving roller 6, a driven roller 7 and a transfer counter roller 8. The drive roller 6 is rotationally driven by a motor (not shown), whereby the intermediate transfer belt 5 moves around the drive roller 6, the driven roller 7 and the transfer counter roller 8. Each of the photosensitive drums 1a, 2a, 3a, 4a is provided with primary transfer rollers 1d, 2d, 3d, 4d so as to sandwich the intermediate transfer belt 5. The toner images on the photosensitive drums 1a, 2a, 3a, and 4a are sequentially primary-transferred onto the intermediate transfer belt 5.

  Further, a secondary transfer roller (transfer member) 9 that sandwiches the intermediate transfer belt 5 between the transfer facing roller 8 is provided, and the transfer sheet S that passes through the nip portion with the transfer facing roller 8 has an intermediate position. The toner image on the transfer belt 5 is secondarily transferred.

  The transfer paper S is accommodated in the paper feed tray 20. At the time of transfer, the transfer paper S is pulled out from the paper feed tray 20 one by one by the paper feed roller 11, passes through the transport roller pair 12 and the registration roller pair 13, and then the transfer counter roller 8. And the secondary transfer roller 9 are supplied to the nip portion.

  The transfer sheet S on which the toner image on the intermediate transfer belt 5 is secondarily transferred is sent to the fixing device 15 via the transport unit 14. Here, the transport unit 14 includes a drive roller 14A that is rotationally driven by a motor (not shown), a driven roller 14B, and an endless transport belt 14C that is wound around the drive roller 14A and the driven roller 14B. Yes. The fixing device 15 includes a fixing roller 15A having a heater (not shown) therein, and a pressure roller 15B that presses the fixing roller 15A.

  In this embodiment, of the side walls of the paper feed tray 20, the side wall 21 near the paper feed roller 11 is detachable. That is, as shown in FIG. 2, the side wall 21 is formed as a separate member from the paper feed tray main body 22, and can be separated from the paper feed tray main body 22. 22 can also be attached. When the side wall 21 is separated from the paper feed tray main body 22, a concave opening 22 </ b> A is formed in the paper feed tray main body 22 where the side wall 21 was present.

  On the side wall 21, protrusions 21 </ b> A are formed on the left and right sides, respectively, and on the other hand, the concave opening 22 </ b> A of the paper feed tray body 22 is formed with vertical grooves 22 </ b> B on both sides. When the side wall 21 is attached to the paper feed tray main body 22, the protrusion 21A is fitted into the vertical groove 22B (see FIG. 3).

  The paper feed tray main body 22 has an end fence 22C at a position opposite to the side wall 21 across the transfer paper S (see FIG. 1), and side fences 22D, 22D at positions where the upper and lower sides of the transfer paper S are locked. 22E is provided.

  In this embodiment, two types of side walls 21 are prepared as shown in FIG. The first side wall 21 is provided with four identically-shaped ribs 23A, 23B, 23C, and 23D on the back surface side as shown in FIG. The protruding amounts of the ribs 23A, 23B, 23C, and 23D from the back surface of the side wall 21 are all the same. The second side wall 21 is provided with four ribs 24A, 24B, 24C, and 24D on the back surface side as shown in FIG. The protruding amounts of the ribs 24A, 24B, 24C, and 24D from the rear surface of the side wall 21 are all different, and the protruding amounts decrease in the order of rib 24A> rib 24B> rib 24C> rib 24D. Here, the ribs 24A, 24B, 24C, and 24D constitute a part of the control mechanism.

  The side fences 22D and 22E can be moved in the direction of arrow A, respectively. In the case of FIG. 3B, the distance between the side fences 22D and 22E is slightly larger than that in the case of FIG. It has become.

  Next, the operation of this embodiment will be described.

  When using plain paper with a small paper thickness, the side wall 21 shown in FIG. Since the ribs 23 </ b> A, 23 </ b> B, 23 </ b> C, and 23 </ b> D all have the same amount of protrusion from the back surface of the side wall 21, the transfer paper S is set parallel to the side wall 21 when the transfer paper S is accommodated in the paper feed tray 20. . In this case, as in the conventional case, the transfer sheet S is in a normal posture at the nip portion between the transfer facing roller 8 and the secondary transfer roller 9, that is, the leading edge S3 (see FIG. 4) of the transfer sheet S is nipped. It will rush straight in parallel with the part.

  On the other hand, when using thick paper, the side wall 21 shown in FIG. Since the ribs 24A, 24B, 24C, and 24D protrude from the rear surface of the side wall 21 in the order of rib 24A> rib 24B> rib 24C> rib 24D, transfer paper S is accommodated in the paper feed tray 20 when the transfer paper S is accommodated. The paper S is set obliquely with respect to the side wall 21. In this case, as shown in FIG. 4, the transfer sheet S is inclined at the nip portion 25 between the transfer facing roller 8 and the secondary transfer roller 9, that is, the leading edge S1 and the leading edge S2 of the transfer sheet S. Enter with a time difference.

  Normally, when the leading edge of the transfer paper S reaches the registration roller pair 13 and stops, the conveyance roller pair 12 is slightly rotated to abut the leading edge of the transfer paper S against the nip portion of the registration roller pair 13 and transfer paper. Although the parallelism of S is corrected, this operation is not performed when the transfer paper S is thick paper. In this way, the transfer sheet S that has been output from the registration roller pair 13 while being inclined at a predetermined angle has a time difference between the left and right ends S1 and S2 (that is, the transfer sheet S is skewed), and the secondary transfer roller 9 And a nip portion 25 formed between the transfer opposing roller 8.

  As shown in FIG. 4, since the transfer sheet S is skewed and enters the nip portion 25, the leading edge S3 of the transfer sheet S and the edge of the nip portion 25 are in point contact, and the leading edge of the transfer sheet S as in the prior art. Compared with the case where S3 enters the nip portion 25 in a straight line, a large load fluctuation does not occur. Therefore, a good image can be obtained without causing so-called “thick paper shock jitter” and “color shift” even when the thick paper is passed.

  If secondary transfer is performed while the transfer sheet S is skewed, the image becomes slanted. Therefore, a preset skew amount (difference in protrusion amount between the ribs 24A and 24D) is set to an image control board (illustrated). The correction signal from (omitted) can be corrected by changing the angle of the folding mirror of the optical scanning device (not shown).

  FIG. 5 shows a schematic configuration of an image forming apparatus according to another example. In this example, a pair of skew detection sensors 30 is provided in the middle of the transfer path of the transfer sheet S (between the conveyance roller pair 12 and the registration roller pair 13), and the above-described signal is output according to an output signal from the skew detection sensor 30. The angle of the folded mirror or the like is changed.

  Moreover, although the said Example was an example which prepared two types of side walls 21, the side wall 21 can also prepare three or more types according to the kind of cardboard.

  Further, the control mechanism for tilting the transfer sheet S is not limited to the ribs 24A, 24B, 24C, and 24D. For example, a deviation is given to the conveying force of the registration roller pair 13 so But you can. That is, it is important to reduce the load fluctuation at the time of entering the thick paper by entering the nip portion formed between the transfer facing roller 8 and the secondary transfer roller 9 with a time difference at both ends of the transfer paper S. is there. Therefore, any method may be used for conveying the transfer paper S with a predetermined angle.

1 is a schematic configuration diagram of an image forming apparatus according to the present invention. It is a perspective view of a paper feed tray when a side wall is removed. 4A and 4B are top views of the paper feed tray, in which FIG. 4A is a view when the transfer paper is set parallel to the side wall, and FIG. 4B is a view when the transfer paper is set inclined with respect to the side wall. It is a figure which shows a mode that a transfer paper skews and plunges into a nip part. It is a schematic block diagram of the image forming apparatus by the other example of this invention. It is a schematic block diagram of the image forming apparatus by a prior art. It is a figure which shows a mode that the cardboard shock jitter generate | occur | produced on the transfer paper. It shows the belt speed fluctuation of the intermediate transfer belt when transfer paper of various thicknesses is continuously passed. (A) shows the case of plain paper, (b) shows the case of thick paper 1 thicker than plain paper. (C) is a diagram showing the case of a thick paper 2 thicker than the thick paper 1, and (d) is a diagram showing the case of a thick paper 3 thicker than the thick paper 2. FIG. 6 is a diagram illustrating color misregistration amounts when plain paper, thick paper 1, thick paper 2, and thick paper 3 are passed.

Explanation of symbols

1, 2, 3, 4 Image forming unit 5 Intermediate transfer belt (intermediate transfer member)
8 Transfer counter roller 9 Secondary transfer roller (transfer member)
DESCRIPTION OF SYMBOLS 15 Fixing device 20 Paper feed tray 21 Side wall 22 Paper feed tray main body 22C End fence 22D, 22E Side fence 23A-23D Rib 24A-24D Rib (a part of control mechanism)
30 Skew detection sensor S Transfer paper

Claims (4)

An image carrier, an optical scanning device that exposes the image carrier to form an electrostatic latent image on the image carrier, and attaches toner to the electrostatic latent image to form a toner image on the image carrier. A developing device to be formed; an intermediate transfer member to which a toner image on the image carrier is primarily transferred; and a transfer sheet provided in pressure contact with the intermediate transfer member and passing through a nip portion between the intermediate transfer member A transfer member for secondary transfer of the toner image on the intermediate transfer member,
An image forming apparatus comprising a control mechanism for causing the transfer paper to enter the nip portion with a time difference between both ends of the transfer paper.   The image forming apparatus according to claim 1, wherein the control mechanism forcibly skews the transfer paper to enter the nip portion.   The paper thickness sensor which detects the paper thickness of the said transfer paper is provided, and the said control mechanism controls the skew amount of the said transfer paper based on the detection result from the said paper thickness sensor. The image forming apparatus described.   The image forming apparatus according to claim 2, wherein when the control mechanism skews the transfer paper, the optical scanning device adjusts an exposure position according to a skew amount of the transfer paper.

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