JP3670701B2 - Image forming apparatus - Google Patents

Description

[0001]
[Industrial application fields]
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 facsimile machine, or a printer, a toner image formed on a photosensitive member is transferred onto a recording paper, and the recording paper is passed through a fixing device including a fixing roller and a pressure roller, and unfixed toner. What fixes an image is well known. In such an image forming apparatus, in the case of a large-sized apparatus, a conveyance means such as a conveyance belt is generally disposed between the photosensitive member and the fixing device in order to stabilize the sheet conveyance performance.
[0003]
In an apparatus provided with conveyance means such as a conveyance belt, the balance of the linear velocity among the photosensitive member, the conveyance belt, and the fixing roller is important. Here, if the linear speeds of the photosensitive member, the conveyor belt, and the fixing roller are VD, VB, and VH, respectively, when VD <VH is set, the fixing roller pair pulls the paper, and the image expands to cause a magnification error. It gets bigger. For this reason, in ordinary equipment, VD
And VH are approximately equal (VD≈VH), and VH is generally set to be slightly the same. At this time, if VB <VD is set, the sheet is loosened between the photosensitive member and the conveyor belt, and a so-called print image in which a black background portion is spotted in a black background portion such as a solid image. Cause an abnormal image. Normally, VB = VD is set. However, as shown in FIG. 6, there is a back curl (the front end of the paper curls downward) as shown in FIG. When the separation of the paper P is poor, the paper enters the belt in a state where it floats from the transport belt. When the sheet is brought into close contact with the transport belt by the action of a suction fan (not shown) disposed between the belt loops or electrostatic action, the floating part of the sheet becomes slack between the photoconductor and the transport belt. This may cause print image generation.
[0004]
Japanese Patent Application Laid-Open No. 59-77456 discloses an apparatus in which a sheet on a conveyor belt is pressed by a rotating spur to prevent sheet slack.
[0005]
[Problems to be solved by the invention]
However, the apparatus described in the above publication has a problem that the number of parts increases, the structure becomes complicated, and the cost increases. Further, since there are parts such as a spur, it is difficult to perform jam processing, and there is also a problem that a spur rotation trace remains on the image.
[0006]
Further, when VB> VD, (VD≈VH) is set in order to prevent looseness of the paper on the transport belt, the transport belt having a linear velocity higher than that of the fixing roller pair tries to push the paper into the pair of fixing rollers. There is a problem that stress is applied to the paper to cause wrinkles, or the paper is loosened between the conveying belt and the fixing roller pair, so that a print image is generated.
[0007]
It is an object of the present invention to provide an image forming apparatus that solves the above-described problems in a conventional image forming apparatus and that can prevent occurrence of abnormal images and sheet slack without requiring a complicated configuration.
[0008]
[Means for Solving the Problems]
According to the present invention, there is provided a fixing device that includes a photosensitive member, a fixing roller, and a pressure roller, and fixes the toner image formed on the photosensitive member and transferred onto the recording material to the recording material. In an image forming apparatus having a conveying belt for conveying the transferred recording material from the photosensitive member to the fixing device, when the leading end of the recording material reaches the conveying belt, the line of the conveying belt becomes faster than the linear velocity of the photosensitive member. fast increasing, the tip of the recording medium is controlled to be substantially the same and the linear speed of the conveyor belt to reach the linear speed of the photoreceptor to the fixing device, the transfer linear velocity of the fixing device This can be solved by having control means for controlling the linear velocity to substantially the same linear velocity at the same timing as the belt .
[0010]
[Action]
When the leading edge of the recording material reaches the conveying belt, the linear velocity of the conveying belt is made larger than the linear velocity of the photosensitive member, and the recording material is pulled by the conveying belt to prevent the recording material from being wrinkled or loosened. When the leading edge reaches the fixing device, the linear velocity of the conveying belt is controlled to be substantially the same as that of the photosensitive member, thereby preventing a magnification error.
[0011]
Other actions will become apparent from the description of the following examples.
[0012]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0013]
FIG. 1 is a configuration diagram showing an outline of a laser printer to which the present invention is applied. A laser printer 10 shown in FIG. 1 includes a printer main body 11 and a paper feeding unit 12 mounted below the printer main body 11.
[0014]
A photosensitive member 1 is installed at a substantially central portion of the printer main body 11. A charging charger, a developing device, a transfer charger, a cleaning device, and the like are disposed around the photosensitive member 1, and an optical writing device is disposed above the photosensitive member 1. In the figure, a fixing device 2 is disposed on the right side of the photosensitive member 1, and a sheet conveying belt (hereinafter referred to as a conveying belt) 5 is disposed between the photosensitive member 1 and the fixing device 2. The fixing device 2 includes a fixing roller 3 and a pressure roller 4. A suction fan 6 is provided in the loop of the conveyor belt 5. As shown in FIG. 2, the conveying belt 5 has a number of holes so that the sheet conveyed by the action of the suction fan 6 is in close contact with the belt. Reference numeral 7 denotes a belt driving roller. Further, a registration sensor 8 and a registration roller 9 are provided below the photoreceptor 1.
[0015]
On the other hand, three rolls of roll paper 13 are set in the paper feed unit 12 side by side. A cutter 14 for cutting the roll paper is installed between two transport roller pairs provided on the downstream side in the paper transport direction of each roll paper.
[0016]
The transfer paper sent out from the roll paper 13 is cut to a specified length by the cutter 14. The transfer paper is further fed to the registration roller 9 by a pair of downstream conveying rollers, and the front end of the transfer paper is detected by the registration sensor 8. Incidentally, a toner image is formed on the photoreceptor 1 by a known electrophotographic method. The transfer paper is conveyed by the registration roller 9 at a timing, and the toner image on the photoreceptor 1 is transferred onto the transfer paper. The transfer paper on which the toner image has been transferred is separated from the photoreceptor 1 and then conveyed by the conveyance belt 5. The unfixed toner image is fixed by the fixing device 2 and discharged onto the upper surface of the main body 11.
[0017]
Next, control of the linear velocity VB of the conveyor belt 5 in this embodiment will be described with reference to the timing chart of FIG. In FIG. 3, the linear velocity VH of the fixing device 2 is shown together with the linear velocity VB of the conveyor belt 5. First, the speed control of the conveyor belt 5 will be described.
[0018]
In this embodiment, when a predetermined time elapses after the registration sensor 8 detects the leading edge of the transfer paper by a timer (not shown) built in the apparatus (when the leading edge of the transfer paper reaches the transport belt 5), the transport belt 5 linear velocity VB of the initial _{VB 1 (VB 1 ≒ VD ≒} VH) from VB ₂ (VB _2> VD) to increase. Then, when the second predetermined time has elapsed (when the leading edge of the transfer sheet reaches the roller nip of the fixing device 2) returns the linear velocity of the conveyor belt 5 to VB _1. The same control is performed for the next sheet (second and subsequent sheets). It is assumed that the speed control of the conveying belt 5 and the speed control of the fixing device 2 described later are instructed by the control means of the main body 11. The conveyor belt 5 is assumed to change speed by speed control of a conveyor belt drive motor (not shown).
[0019]
As described above, when the leading edge of the transfer paper reaches the conveyor belt 5, the linear velocity of the conveyor belt 5 is increased, so that the conveyor belt 5 pulls the transfer sheet and removes the floating or slack of the transfer sheet from the sheet conveyor belt. be able to. For this reason, even if there is a back curl at the leading edge of the transfer paper P as shown in FIG. 4, the back curl of the paper is gradually corrected like a, b, c, and the fixing roller 3 and the pressure roller 4 The print image is effectively prevented from being generated. In addition, even when a transfer sheet with poor separation from the photoreceptor 1 as described with reference to FIG. 7 is used, the looseness of the transfer sheet is corrected, and the generation of a print image is effectively prevented. Since the leading edge of the transfer sheet is returned to the linear velocity and the initial velocity of approximately the same photoconductor linear speed of the conveyor belt 5 and reaches the fixing device, preventing the occurrence of magnification error fixing device image is stretched to pull the transfer paper be able to.
[0020]
In this embodiment, taking into account the rising and falling characteristics of the conveying belt drive motor, the timing at which the leading edge of the transfer paper reaches the conveying belt 5 and the nip between the fixing roller 3 and the pressure roller 4 are reached. A margin is given to change the speed of the belt drive motor slightly earlier than the timing (approximately 10 mm before the distance). There is no adverse effect caused by the allowance.
[0021]
Incidentally, in recent years, digitization of image forming apparatuses has progressed, and it has become possible to reduce the interval between transfer sheets and transfer sheets, that is, the interval between sheets. In such an apparatus, there is a device in which the leading edge of the succeeding transfer sheet reaches the conveying belt before the trailing edge of the preceding transfer sheet is completely removed from the conveying belt. The printer of this embodiment also are narrow interval between sheets, as shown in FIG. 5, the next transfer sheet P ₂ When the leading edge of the sheet reaches the conveying belt 5, the previous transfer paper P ₁ is still present. Is sandwiched between the fixing roller 3 and the pressure roller 4, and its rear end is on the conveying belt 5. When the linear velocity VB of the conveyor belt 5 by performing the speed control of the conveyor belt described above is increased from VB ₁ to VB ₂ at this time, the transfer is sandwiched between the fixing roller pair paper P ₁ Is pushed by the conveyor belt 5 and the preceding transfer paper P ₁ is pressed. Wrinkles and slack will occur.
[0022]
Therefore, in this embodiment, the linear speed VH of the fixing device 2 is varied at the same timing as the speed control of the conveying belt 5. That is, as shown in the timing chart of FIG. 3, when the leading edge of the transfer sheet reaches the conveyor belt 5, the initial linear velocity VH of the fixing device 2 VH ₁ To VH ₂ To rise. Next the back and the transfer sheet tip end reaches the roller nip of the fixing device 2 a linear velocity of the conveyor belt 5 to the VH _1. The same control is performed for the next sheet (second and subsequent sheets). Note that VH ₁ = VB ₁ and VH ₂ = VB ₂ are set. Thus, it is possible to prevent wrinkles and slack transfer paper P ₁ of the preceding.
[0023]
In this embodiment, the fixing roller 3 of the fixing device 2 is driven by a motor (not shown) different from the driving motor for the conveying belt 5, and the linear speed of the fixing device 2 is controlled by speed control of the fixing roller driving motor. Shall be performed. However, the fixing device 2 may be driven by the same motor as the driving motor for the conveyor belt 5. In that case, the linear speed of the fixing device 2 is automatically controlled at the same timing as the speed control of the conveying belt 5. When the linear velocity of the fixing device 2 is controlled as described above, it is more effective if the linear velocity of the conveying roller pair (see FIG. 1) on the downstream side of the fixing device 2 is controlled in the same manner. is there.
[0024]
【The invention's effect】
As described above, according to the fixing device of the present invention, the linear velocity of the conveying belt is increased when the leading edge of the transfer paper reaches the conveying belt, and the linear velocity of the conveying belt is increased when the leading edge of the transfer paper reaches the fixing device. The initial speed is almost the same as the linear speed of the paper, so that the transfer paper is not lifted or slacked from the paper transport belt, and the transfer paper is not stressed, preventing the generation of wrinkles and print images on the transfer paper. Can do.
In addition, since the speed of the fixing device is controlled to substantially the same speed at the same timing as the conveying belt, wrinkles and slacks do not occur on the preceding paper even in the case of a high-speed machine with a narrow gap between papers.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an outline of a laser printer according to an embodiment of the present invention.
FIG. 2 is a perspective view showing a paper transport belt of the printer.
FIG. 3 is a timing chart showing the speed control of the paper conveying belt in the present embodiment.
FIG. 4 is a side view illustrating a conveyance state of the back-curled transfer paper in the present embodiment.
FIG. 5 is a side view for explaining a problem in a high-speed machine with a narrower gap.
FIG. 6 is a side view for explaining a problem when a back-curled transfer sheet is passed in a conventional image forming apparatus.
FIG. 7 is a side view for explaining a problem when a transfer sheet having poor separation from a photosensitive member is passed in a conventional image forming apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Fixing device 3 Fixing roller 4 Pressure roller 5 Paper conveyance belt 6 Suction fan 8 Registration sensor 10 Laser printer 11 Printer main body 12 Paper feed part 13 Roll paper 14 Cutter P Transfer paper VB Conveyor belt linear velocity VD Photoconductor linear speed of the linear velocity VH fixing device

Claims (1)

A fixing device that includes a photoconductor, a fixing roller, and a pressure roller, and fixes the toner image formed on the photoconductor and transferred onto the recording material to the recording material; and the recording material on which the toner image is transferred to the photoconductor An image forming apparatus having a conveying belt that conveys the toner to the fixing device.
When the leading edge of the recording material reaches the conveying belt, the linear velocity of the conveying belt is made larger than the linear velocity of the photosensitive member, and when the leading edge of the recording material reaches the fixing device, the linear velocity of the photosensitive member and the conveying belt are increased. While controlling so that the linear velocity is substantially the same ,
An image forming apparatus comprising: a control unit configured to control a linear velocity of the fixing device to substantially the same linear velocity at the same timing as the conveying belt .

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