JP4438978B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.
[0002]
[Prior art]
In an image forming apparatus such as a copying machine, a printer, or a facsimile, a visible image formed on an image carrier while holding the recording material on a belt that is rotationally driven and transporting the recording material in accordance with the rotation of the image carrier Some have a transfer / conveying belt device for transferring the toner onto a recording material. In general, the recording material is sent to a transfer portion of the image carrier and the transfer / conveyance belt device with timing by a registration means such as a registration roller.
[0003]
[Problems to be solved by the invention]
However, there is a case where the conveyance of the recording material is affected in the process of transferring the recording material from the registration roller to the transfer conveyance belt device. For example, in the case of a stiff recording material, there is a problem that slight vibration or the like occurs at the moment when the trailing edge of the recording material comes off the registration roller, and as a result, the image position with respect to the recording material varies. This problem is a major problem of color misregistration in a color image forming apparatus that sequentially superimposes images of a plurality of colors on a conveyed sheet.
[0004]
An object of the present invention is to provide an image forming apparatus that solves the above-described problems in a conventional image forming apparatus and prevents adverse effects on a recording material conveyed by a transfer conveying belt apparatus.
[0005]
[Means for Solving the Problems]
According to the present invention, there is provided an image carrier, a transfer / conveying belt device disposed opposite to the image carrier, and the transfer / conveying belt device in synchronization with an image on the image carrier. An image forming apparatus including a registration unit for sending a recording material, wherein a plurality of image carriers are arranged in parallel to face the transfer conveyance belt device, and images formed on the image carriers are transferred to the transfer conveyance belt. In an image forming apparatus capable of forming a color image by being superimposed and transferred onto a recording material conveyed by the apparatus, the transfer conveying belt apparatus includes a pair of fixed frames disposed on both sides in the belt width direction, and the fixed frame. A first frame and a second frame respectively supported by the frame, wherein the first frame is located at a position corresponding to the most downstream image carrier among the plurality of image carriers arranged in parallel; is there The second frame is a frame at a position corresponding to an image carrier upstream of the one of the most downstream image carriers among the plurality of image carriers arranged in parallel. The second frame is swingably supported by the fixed frame, and an eccentric cam for swinging the second frame is pivotally supported by the fixed frame, and the endless end of the transfer / conveying belt device. An inlet roller disposed at a recording material inlet portion from the registration means and an opposing roller disposed opposite to the inlet roller are coaxial with the eccentric cam. The second frame is swung by the rotation of the eccentric cam, and the inlet roller and the front are swung through the bracket. Counter roller is swung, the recording material conveyance direction of the transfer conveyance belt device when the plurality of traveling side opposite to the image bearing member is in contact with all of the plurality of image bearing members of the endless belt resist This is solved by the fact that the recording material delivery directions by the means are substantially the same.
[0006]
In order to solve the above problems, the present invention proposes that an auxiliary roller for urging the endless belt from the inside of a belt loop is attached to the second frame .
[0007]
In order to solve the above-described problem, the present invention is configured such that a driving roller for driving the endless belt is supported by the first frame, and the driving roller is disposed on the downstream side of the plurality of image carriers. suggest.
[0008]
In order to solve the above-described problem, the present invention includes a detection unit that detects the posture of the transfer conveyance belt device, and controls the posture of the transfer conveyance belt device based on an output of the detection unit. suggest.
[0009]
In order to solve the above problems, the present invention proposes that a recording material suction bias is applied to the facing roller .
[0010]
In order to solve the above problems, the present invention proposes that the transfer / conveying belt device is disposed obliquely in the apparatus main body so that the height is different between the recording material inlet side and the outlet side.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0012]
FIG. 1 is a cross-sectional view showing a schematic configuration of a color laser printer which is an example of an image forming apparatus according to the present invention. The color laser printer 1 has a configuration in which a paper feeding unit 2 is provided at the lower part of the apparatus main body, and an image forming unit 3 is disposed above the paper feeding unit 2. A paper discharge tray 60 is formed on the upper surface of the apparatus. As shown by the broken line in the drawing, the recording paper is transported from the paper feeding unit 2, the image formed by the image forming unit 3 is transferred onto the paper, fixed by the fixing device 50, and discharged. The paper is discharged to the tray 60. Manual feed (symbol: c) is possible from the side of the apparatus, and discharge (symbol: d) to the side of the apparatus is also possible.
[0013]
The image forming unit 3 is provided with a transfer / conveying belt device 20 that is disposed so as to be inclined so that the paper feeding side is on the bottom and the paper discharge side is on the top. Four image forming units 4M, 4C, 4Y, and 4Bk for magenta (M), cyan (C), yellow (Y), and black (Bk) in order from the bottom along the upper running side of the transfer / conveying belt device 20. Are arranged side by side.
[0014]
Since the image forming units 4M, 4C, 4Y, and 4Bk have the same configuration, the cyan image forming unit 4C will be described as an example.
[0015]
As shown in FIGS. 1 and 2, each of the image forming units 4M, 4C, 4Y, and 4Bk includes a photosensitive drum 5 as an image carrier, and the photosensitive drum 5 is driven by a driving unit (not shown). It is rotated in the clockwise direction in the figure. Around the photosensitive drum 5, a charging roll 6, a developing device 10, a cleaning device 9 and the like are provided. The developing device 10 is a two-component developing device including a toner and a carrier, and applies the toner carried on the developing roll 11 to the photosensitive drum 5. Laser light from the optical writing device 8 is applied to the photosensitive drum 5 from between the charging roll 6 and the developing roll 11. In FIG. 2, alphabets (M, C, Y) indicating the respective colors are attached to the members of the respective color image forming units after the reference numerals.
[0016]
FIG. 3 is a side view showing the configuration of the transfer / conveying belt device 20.
As shown in this figure, the endless loop-shaped transfer conveyance belt 21 is wound around a driving roller 22, a driven roller 23, and two opposing rollers 24 and 24. The driven roller 23 is provided with a spring (not shown), and the transfer conveyance belt 21 is tensioned. Further, four auxiliary rollers 25 are provided along the upper running side of the transfer conveyance belt 21, and each auxiliary roller 25 is urged against the belt 21 by a coil spring 26. A transfer brush 28 is disposed slightly above each auxiliary roller 25 so as to contact the belt 21. The positions of the four transfer brushes 28 are positions facing the photosensitive drums 5 of the respective color image forming units. In this example, a transfer bias of 7 kV is applied to the transfer brush 28. A paper suction roller 27 is provided above the driven roller 23 with the belt 21 interposed therebetween. The recording paper is fed onto the belt 21 from between the driven roller 23 and the suction roller 27, and is transported while being electrostatically attracted onto the transfer transport belt 21 by the bias voltage applied to the suction roller 27.
[0017]
As shown in FIG. 4, the frame of the transfer / conveyance belt device 20 includes a fixed frame 41, a Bk frame 42, and a three-color frame 43. The fixed frame 41 is on the front side and the back side of the apparatus and supports the Bk frame 42 and the three-color frame 43, but only the back frame is shown in the figure, and the front frame is not shown. . The Bk frame 42 is an upper frame located at a position corresponding to the image forming unit 4Bk, and supports the driving roller 22, the upper opposing roller 24, and the like. The Bk frame 42 is rotatable around the axis of the drive roller 22. The three-color frame 43 is a frame at a position corresponding to the image forming units 4M, 4C, and 4Y, and the lower three transfer brushes 28 and the auxiliary roller 25 are attached thereto. The three-color frame 43 is supported by the fixed frame 41 so as to be swingable about the shaft 29. An eccentric cam 30 is pivotally supported on the fixed frame 41. Reference numeral 31 denotes a shaft of the eccentric cam 30. Further, a bracket 38 (FIG. 5) is swingably supported on the shaft 31 of the eccentric cam, and a driven roller 23 and a suction roller 27 are supported by the bracket 38. The lower facing roller 24 is attached to the fixed frame 41.
[0018]
FIG. 5 is a perspective view showing the contact / separation mechanism of the transfer / conveyance belt device 20. In FIG. 5, the upper side of the figure is the front side of the printer body, and the lower side of the figure is the back side of the printer body. Therefore, FIG. 3 is a side view of the transfer conveyance belt device 20 as viewed from the direction of the arrow S shown in FIG.
[0019]
As shown in FIG. 5, eccentric cams 30 are fixedly mounted on both sides of the shaft 31. A joint 32 is fixed to the outside of the eccentric cam 30 on the back side of the apparatus. There is a relay shaft 33 having a convex portion that fits into the joint 32, and a gear 34 is fixedly attached to the relay shaft 33. A clutch 35 is attached to the gear 34 to transmit or release the driving force from a motor (not shown) to the gear 34. The joint 32 is provided with a filler portion 36, and a photo interrupter 37 is provided so that the filler portion 36 can be detected. The relay shaft 33 is fitted with a bracket 38 for supporting the driven roller 23 and the suction roller 27.
[0020]
In FIG. 5, when the gear 34 is rotated by a motor (not shown), the shaft 31 and the eccentric cam 30 are rotated from the relay shaft 33 through the joint 32, and the three-color frame of the transfer conveyance belt device 20 is raised or lowered. Let At this time, the driven roller 23 and the suction roller 27 are also raised or lowered by swinging the bracket 38. The state of the eccentric cam 30 is detected by detecting the filler portion 36 with the photo interrupter 37, and the posture of the transfer conveyance belt device 20 is controlled.
[0021]
In the transfer / conveying belt device 20 having such a configuration, referring to FIG. 3, the three-color frame 43 is swung up and down around the shaft 29 by the rotation of the eccentric cam 30. As the three-color frame 43 moves up and down, the bracket 38 also moves up and down, and the driven roller 23 and the suction roller 27 move to a position indicated by a solid line and a position indicated by a broken line in the drawing.
[0022]
Therefore, when the eccentric cam 30 rotates and takes a position indicated by a broken line in the drawing, the eccentric cam 30 pushes up the three-color frame 43, whereby the bracket supporting the driven roller 23 and the suction roller 27 rises, and the driven roller 23 And the suction roller 27 is in a position indicated by a broken line in the figure. As a result, the upper running side of the transfer conveyance belt 21 is raised as indicated by a broken line and comes into contact with the four-color image forming units 4M, 4C, 4Y, and 4Bk (the photosensitive drum 5). At this time, the lower three auxiliary rollers 25 mounted on the three-color frame 43 are also lifted to urge the upper running side of the transfer conveyance belt 21 from the inside of the belt loop.
[0023]
Further, when the eccentric cam 30 rotates and takes the position indicated by the solid line in the figure, the three-color frame 43 descends, and the bracket 38 supported by the three-color frame 43 also descends to follow the driven roller 23 and the suction roller. 27 is a position indicated by a solid line in the figure. As a result, the transfer / conveying belt 21 is in a state indicated by a solid line in the drawing, and the upper running side of the transfer / conveying belt 21 is brought into contact with the black image forming unit 4Bk only on the upper side, thereby forming the image forming units 4M, 4C, It is separated from 4Y.
[0024]
That is, in the present embodiment, in the case of color printing, the transfer conveyance belt 21 is held in contact with the four-color image forming units 4M, 4C, 4Y, and 4Bk (photosensitive drums thereof), and in the case of black monochrome printing. The state in which the transfer conveyance belt 21 is in contact with only the image forming unit 4Bk (the photosensitive drum) is maintained.
[0025]
As described above, generally, in the case of black monochrome printing (monochrome mode) that is most frequently used, the transfer conveyance belt 21 is brought into contact with only the black image forming unit 4Bk (photosensitive drum), and image forming units of other colors are used. By separating the belt 21 from the photosensitive drums 4M, 4C, and 4Y, it is not necessary to operate the image forming units 4M, 4C, and 4Y that are not necessary for forming a monochrome image. The life of the parts related to 4C and 4Y, in particular, the photoconductor drum is not reduced.
[0026]
The Bk frame 42 of the transfer / conveyance belt device 20 is not swung by the eccentric cam 30, and in this embodiment, the Bk frame 42 and the three-color frame 43 are configured to be displaced separately. For this reason, even when the three-color frame 43 is rotated in the black-and-white mode (monochrome) and the portions facing the image forming units 4M, 4C, 4Y are lowered, the black image forming unit 4Bk of the transfer conveyance belt 21 is moved to the black image forming unit 4Bk. The corresponding portion can hold an appropriate position with respect to the photosensitive drum 5Bk of the black image forming unit 4Bk, and an appropriate image can be transferred. Of course, it goes without saying that the portion corresponding to the black image forming unit 4Bk can maintain an appropriate position even in the color mode.
[0027]
Next, the printing operation in the present embodiment will be described with reference to FIG.
In the image forming unit 4M for magenta, the surface of the photosensitive drum 5 is uniformly charged to a predetermined potential by the charging roll 6. In the exposure apparatus 8, an LD (laser diode) (not shown) is driven based on image data sent from a host machine such as a personal computer to irradiate the polygon mirror 7 with laser light, and the reflected light is transmitted through a cylinder lens or the like. An electrostatic latent image to be developed with magenta toner is formed on the photosensitive drum 5M and guided to the photosensitive drum 5M. Toner is applied to the latent image from the developing device 10 to form a visible image of magenta toner.
[0028]
On the other hand, a sheet designated as a transfer material is fed from the sheet feeding unit 2, and the fed sheet is once abutted against a registration roller pair 40 provided on the upstream side in the transport direction of the transfer transport belt device 20. At the time of color printing, in the transfer / conveyance belt device 20, as described above, the transfer / conveyance belt 21 is pushed up as indicated by a broken line in FIG. The sheet is fed onto the belt 21 in synchronism with the visible image, and reaches the transfer position facing the photosensitive drum 5M by the running of the belt. At this transfer position, a visible image of magenta toner is transferred to the paper by the action of the transfer brush 28 disposed on the back side of the transfer belt 20.
[0029]
Similarly to the case of the magenta color, in the other image forming units 4C, 4Y, and 4Bk, visible images are formed by the respective toners on the surfaces of the respective photosensitive drums 5, and these visible images are transferred by the transfer conveyance belt 21. Each time the transported sheet arrives at each transfer position, the sheet is overlaid and transferred. Therefore, in the color printer of this embodiment, a full-color image is transferred onto a sheet in a short time almost the same as that of monochrome.
[0030]
On the other hand, in the case of monochrome printing, in the transfer / conveyance belt device 20, the transfer / conveyance belt 21 is lowered as shown by the solid line in FIG. Only in the black image forming unit 4Bk, a visible image of black toner is formed on the surface of the photosensitive drum 5, and the sheet fed on the belt 21 is synchronized with the visible image of Bk. On the other hand, the Bk toner image is transferred.
[0031]
In the present embodiment, as described above, the transfer conveyance belt 21 is brought into contact with the photosensitive drums of all image forming units in the color mode, and the lower three image forming units (4M, 4M, 4C, 4Y) the belt 21 is separated from the photosensitive drum. In the color mode in which all the photosensitive drums are in contact with the conveyance belt, the sheet can be held and conveyed by each photosensitive drum and the conveyance belt (when the conveyance belt and the photosensitive member are in contact with each other) In order to prevent damage, the photosensitive member is also rotationally driven), which is advantageous for paper conveyance. However, in this embodiment, as described above, the bias voltage is applied from the paper suction roller to electrostatically attract the paper to the transfer / conveyance belt 21, so that the monochrome belt in which the belt 21 is separated from the lower three photosensitive drums. Even in the mode, stable paper conveyance is possible.
[0032]
The sheet on which the toner image has been transferred is separated from the transfer conveyance belt 21 and fixed by the fixing device 50. The fixing device of this example is a belt fixing method, and a relatively soft fixing roller 52 made of, for example, a sponge roller is pressed on a rigid pressure roller 51, and the fixing roller 52 and its upstream side in the sheet conveyance direction A belt 54 is wound around a heating roller 53 disposed on the belt. This belt fixing method has advantages such as shorter warm-up time than roller fixing.
[0033]
The sheet that has been fixed is discharged to a discharge tray 60 provided on the upper surface of the apparatus main body. At this time, the sheet is reversed and discharged from the back side. Backside paper discharge is an almost indispensable condition for a printer to align prints in page order.
[0034]
The color printer according to this embodiment includes four image forming units 4M, 4C, 4Y, and 4Bk, and sequentially transfers the toner images of the respective colors while the sheet is conveyed by the transfer belt device 20, so that one image forming unit is formed. The image forming time can be greatly reduced as compared with a system in which the toner image is transferred onto the intermediate transfer member by the image unit and then transferred onto the paper.
[0035]
In this embodiment, since the transfer / conveying belt device 20 is disposed obliquely and the color image forming units 4M, 4C, 4Y, and 4Bk are disposed along the inclination, the sheet feeding unit is disposed at the lower part of the main body, and the upper part of the main body is disposed at the upper part. Providing a paper discharge unit in the paper can shorten the paper conveyance path, which is advantageous for shortening the printing time. In the case of this layout, a triangular space is formed at the corner of the apparatus. By providing the toner storage container 70 and the waste toner tank 80 having a high degree of freedom in a shape matching the triangular space, a dead space is provided. Is prevented.
[0036]
By the way, in this embodiment, as shown in FIG. 6, the sheet feeding direction A by the registration roller pair 40 including the registration driving roller 40 a and the registration driven roller 40 b and the sheet conveyance direction B by the transfer conveyance belt device 20 are almost the same. It is comprised so that it may become the same. Therefore, in the process of transferring the paper from the pair of registration rollers 40 to the transfer / conveying belt device 20, it is possible to obtain a high-quality image without adversely affecting the conveyance of the paper and preventing variations in the image position with respect to the paper. it can. In particular, in the present embodiment, since the paper feed direction A and the paper transport direction B are substantially the same during color printing, color misregistration occurs when each color image is transferred onto the transported paper. Therefore, a high-quality color image can be obtained.
[0037]
If there is a deviation between the paper feeding direction by the registration roller pair and the paper conveyance direction by the transfer conveyance belt device, the paper is bent in the middle when the paper is held by both the transfer conveyance belt device and the registration roller. . For this reason, for example, in a stiff recording material, the rear end of the sheet tries to follow the sheet conveyance direction by the transfer conveyance belt device at the moment when the rear end of the recording material comes out of the registration roller, and thus slight vibration occurs. Sometimes. As a result, the image position with respect to the recording material may vary. In particular, color formation in color units (about 80 μm) is required in color image formation, which is a serious problem of color misregistration. However, in the present embodiment, as described above, since the paper feeding direction A and the paper transport direction B are substantially the same during color printing, a high-quality image that prevents color misregistration is obtained. be able to.
[0038]
In particular, in a color image forming apparatus in which a plurality of image forming units are arranged side by side and each color image is sequentially superimposed and transferred while transporting paper as in this embodiment, variation in image position with respect to the recording material can be prevented. Therefore, the present invention is particularly effective for the color image forming apparatus of this type.
[0039]
Further, as in the present embodiment, in a layout in which the transfer conveyance belt device 20 is disposed obliquely and each color image forming unit is disposed along the inclination, the sheet delivery direction A and the sheet conveyance direction B are substantially the same. With this configuration, the registration roller pair 40 can be disposed in the vicinity of the transfer / conveyance belt device 20, so that the space in this portion can be made compact, which contributes to downsizing of the device. be able to.
[0040]
As mentioned above, although this invention was demonstrated by embodiment of illustration, this invention is not limited to this. For example, an appropriate configuration can be adopted as a mechanism for controlling the posture of the transfer conveyance belt device. The means for detecting the posture of the transfer / conveying belt device can also employ an appropriate configuration. Further, the means for applying the recording material adsorption bias is not limited to the contact type, but may be any configuration including a non-contact type. Furthermore, the number of image forming units is not limited to four. Of course, the image forming apparatus may be a copier or a facsimile other than the printer.
[0041]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, in the color mode in which there is a large problem when color misregistration occurs, the recording material is conveyed in the process of transferring the recording material from the registration unit to the transfer conveyance belt device. It is possible to obtain a high-quality color image without influencing the image position variation with respect to the recording material. In addition, the transfer / conveying belt device and the registration unit can be arranged close to each other, and the apparatus space can be reduced.
[0042]
According to the configuration of the second aspect , the belt running side can be urged from the inside of the belt loop when the endless belt is brought into contact with the image carrier .
[0044]
According to the fourth aspect of the present invention, since there is a detecting means for detecting the posture of the transfer / conveying belt device and the posture of the transfer / conveying belt device is controlled based on the output of the detecting means, It can be controlled appropriately.
[0045]
According to the fifth aspect of the present invention, since the recording material adsorption bias is applied to the opposing roller, it is possible to always perform stable paper conveyance. In particular, it is possible to stabilize paper conveyance in the monochrome mode in which several image carriers and transfer conveyance belts are separated.
[0046]
According to the configuration of the sixth aspect, since the transfer conveyance belt device is arranged obliquely in the apparatus main body so that the height is different between the recording material inlet side and the outlet side, the paper conveyance path can be shortened and the printing time can be shortened. This is advantageous for shortening the time. Further, it is possible to appropriately transfer the recording material from the registration means to the transfer / conveyance belt device when the transfer / conveyance belt device is disposed obliquely.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a schematic configuration of a color laser printer which is an example of an image forming apparatus according to the present invention.
FIG. 2 is a partially enlarged view showing details of an image forming unit.
FIG. 3 is a side view illustrating a configuration of a transfer conveyance belt device.
FIG. 4 is a cross-sectional view illustrating a frame configuration of the transfer conveyance belt device.
FIG. 5 is a perspective view showing a contact / separation mechanism of the transfer / conveyance belt device.
FIG. 6 is a partial detail view for explaining the operation of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Color laser printer 2 Paper feed part 3 Image formation part 4 Image formation unit 5 Photosensitive drum (image carrier)
8 Optical Writing Device 20 Transfer Conveying Belt Device 21 Transfer Conveying Belt 30 Eccentric Cam 40 Registration Roller Pair

Claims (6)

An image carrier, a transfer conveyance belt device disposed opposite to the image carrier, and a registration unit that sends a recording material to the transfer conveyance belt device in synchronization with an image on the image carrier. An image forming apparatus comprising: a plurality of image carriers arranged in parallel to face the transfer conveyance belt device; and an image formed on each image carrier on a recording material conveyed by the transfer conveyance belt device In an image forming apparatus capable of forming a color image by overlapping transfer,
The transfer conveyance belt device has a pair of fixed frames disposed on both sides in the belt width direction, and a first frame and a second frame respectively supported by the fixed frame,
The first frame is a frame at a position corresponding to one of the most downstream image carriers among the plurality of image carriers arranged in parallel,
The second frame is a frame at a position corresponding to an image carrier on the upstream side of the image carrier on the most downstream side of the plurality of image carriers arranged in parallel. The frame is supported by the fixed frame in a swingable manner;
An eccentric cam for swinging the second frame is pivotally supported on the fixed frame, and is one of support rollers around which an endless belt of the transfer / conveyance belt device is stretched. An inlet roller arranged at the recording material inlet portion and a counter roller arranged opposite to the inlet roller are supported so as to be swingable via a bracket provided coaxially with the eccentric cam,
The eccentric cam pivots the second frame and the entrance roller and the opposing roller are pivoted via the bracket, and the running side of the endless belt facing the plurality of image carriers is the The image forming apparatus is configured such that the recording material conveyance direction by the transfer conveyance belt device and the recording material delivery direction by the registration means are substantially the same when contacted with all of the plurality of image carriers. apparatus. The image forming apparatus according to claim 1 , wherein an auxiliary roller that urges the endless belt from the inside of a belt loop is attached to the second frame . The driving roller for driving the endless belt is supported, characterized in that the drive roller is disposed downstream of said plurality of image bearing members, an image forming apparatus according to claim 1 to said first frame.   4. The apparatus according to claim 1, further comprising a detection unit configured to detect an attitude of the transfer / conveyance belt device, wherein the posture of the transfer / conveyance belt device is controlled based on an output of the detection unit. The image forming apparatus described in 1. The image forming apparatus according to claim 1, wherein a recording material suction bias is applied to the facing roller .   The image according to any one of claims 1 to 5, wherein the transfer / conveying belt device is disposed obliquely within the main body of the apparatus so that the height is different between the recording material inlet side and the outlet side. Forming equipment.

Images