JPH06222691A - Image forming device - Google Patents

Abstract

PURPOSE:To eliminate defective transfer in terms of void at the rear end of the second face copy in both-side copying. CONSTITUTION:The image forming device transfers a toner image on an image carrier to the surface of paper by moving the paper between the image carrier and the transfer electrifier, that is actuated by the application of a voltage in which an AC voltage and a DC voltage are superimposed to a transfer corotron, in synchronization with the movement of the image carrier, and by emitting a transfer beam from the transfer corotron of the transfer electrifier. In this image forming device, a transfer auxiliary roller 13 made of metal is disposed a fixed distance away from the image carrier, on the side of the entrance of the transfer electrifier 6 into which the paper advances and within the range of the emission of the transfer beam from the transfer corotron 6b. This transfer auxiliary roller 13 is grounded via a circuit in which a voltage with reverse polarity to a transfer polarity can be induced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for transferring a toner image formed on an image carrier to a transfer paper and fixing it to form an image.

[0002]

2. Description of the Related Art An image forming apparatus for an electrophotographic copying machine, a laser printer, a facsimile, etc., for example, an image forming apparatus for an electrophotographic copying machine using a laser beam is as shown in FIG. Is provided with an image carrier (photoreceptor) 2, and a primary charger 3, a developing device 4, a pre-transfer charger 5, a transfer charger 6 having a halo baffle 6a, and a peeler around the image carrier 2. A charging charger 7, a cleaner 8 and the like are sequentially arranged, the surface of the image carrier 2 is uniformly charged by the primary charger 3, and then an image exposure mechanism 9 performs image exposure to form an electrostatic latent image. The electrostatic latent image is developed into a visible image by the developing device 4, and the paper in the paper tray 10 is fed by the paper feeding mechanism 11
Then, the visible image is conveyed toward the image carrier 2 and transferred to a sheet by the transfer charger 6, and the sheet is sent to the fixing device 12 to be fixed to form a copy. The image exposure mechanism 9 is a laser system including a laser oscillator, a rotating mirror, and a plurality of mirrors, and is configured to receive image information from an office automation device such as an external computer or a word processor and perform image exposure on an image carrier. There is. In this copying process, both single-sided copying and double-sided copying are performed.

[0003]

In the past, it was usual that no particular difference was made between single-sided copying and double-sided copying. In recent years, most of the products have been commercialized that try to obtain the optimum transfer image quality by switching the output level of the transfer current applied to the transfer charger. But,
Even with the method of switching the transfer current of the transfer charger, it has not been possible to satisfy all of the copy image qualities for double-sided copying. In particular, due to the curl of the transfer paper after single-sided copying that occurs during double-sided copying, there is no definitive effective means for defective transfer at the leading and trailing edges (white spots, image blurring, double-colored images, image defects), so there is no choice. In general, the above-mentioned transfer failure occurs on the second surface, especially on the rear end, up to about 7 to 8 mm. In addition, high-end machines and some low-end machines that do not have automatic both sides have commercialized products using a bias transfer roll, but 10-40 sheets /
The high class machines are too expensive for minute class machines, and the low class machines have problems with reliability / life, and those suitable for general purpose machine classes have not been put to practical use.

The present invention has been conceived in view of the above, and it is possible to perform double-sided copying when the conventional double-sided copying is performed up to about 7 to 8 mm.
An object of the present invention is to provide an image forming apparatus capable of improving a transfer failure due to blanking or the like of the trailing end portion of the first copy.

[0005]

In order to achieve the above object, an image forming apparatus according to the present invention runs a sheet between an image carrier and a transfer charger in synchronization with the movement of the image carrier. In the image forming apparatus in which the toner image on the image carrier is transferred onto the paper by the transfer beam of the transfer corotron of the transfer charger, the transfer charger 6 is provided at the entrance side of the paper 18 in the entrance direction. In addition, at a position within the irradiation range of the transfer beam of the transfer corotron 6b, the metal transfer auxiliary roller 13
Is installed with a certain distance from the image carrier, and the transfer assisting roller 13 is grounded via a circuit capable of inducing a voltage of reverse polarity to the transfer polarity. The grounding circuit of the transfer assisting roller 13 is composed of a diode or a Zener diode having a constant voltage function.

[0006]

[Working] Paper 1 guided by hello baffle 6a
8 is guided to the gap between the image carrier 2 and the transfer assist roller 13, and the paper 18 at this time is held by the transfer assist roller 13 toward the image carrier 2. At this time, the transfer assist roller 13
Is located within the irradiation range of the transfer beam of the transfer corotron 6b of the transfer charger 6 and is made of metal, so that when the leading edge and the trailing edge of the paper 18 pass through the area where the transfer electric field is applied. However, the leading end and the trailing end of the sheet 18 are held in contact with the image carrier 2 side. At this time, since the transfer auxiliary roller 13 is installed via a circuit capable of inducing a voltage having a polarity opposite to the transfer polarity, the transfer auxiliary roller 13 is discharged by superimposing an AC voltage and a DC voltage from the transfer beam. The average (effective) potential of the voltage induced in the toner becomes a potential having a polarity opposite to the transfer polarity, electrically repels the toner, and is not attached thereto. As shown in FIG. 6, the transfer corotron 6b of the transfer charger 6 is applied with a corotron voltage a in which an AC voltage and a DC voltage are superposed.

[0007]

EXAMPLE An example of the present invention will be described with reference to FIG. The same components as those of the conventional example shown in FIG. The image carrier 2 is located at the entrance side of the transfer charger 6 in the sheet entry direction and at a position within the transfer beam irradiation range of the transfer corotron 6b of the transfer charger 6.
A metal transfer auxiliary roller 13 is rotatably provided so as to face each other with a slight distance of 0.1 to 1.0 mm. A corotron voltage obtained by superimposing an AC voltage and a DC voltage is applied to the transfer corotron 6b of the transfer charger 6 as indicated by a in FIG.

As shown in FIGS. 3 and 4, the transfer assisting roller 13 includes a pair of brackets 15, both ends of which are vertically rotatably supported by the shield case 14 of the transfer charger 6. It is rotatably supported at the tip.
And this bracket 15 is a torsion spring 16
At, the roller support side is spring-biased in a direction toward the image carrier 2 side. The transfer assist roller 13 is, as shown in FIG.
The torsion springs 1 of the bracket 15 are provided with rolling contact portions (tracking portions) 17, 17 having both ends thereof having a diameter corresponding to a gap corresponding to the image carrier 2.
The rolling contact portions 17, 17 are adapted to follow the rolling contact with both ends of the image carrier 2 in accordance with the biasing rotation by 6.

The outer diameter of the transfer assisting roller 13 is appropriately 10 mm or less, preferably 4 to 7 mm so as not to interrupt the transfer beam from the transfer corotron 6b, and is electrically grounded. . A circuit capable of inducing a voltage having a polarity opposite to the transfer polarity with respect to the image carrier 2 such as a Zener diode 19 is interposed in the ground path. Note that this may simply be a diode.

Rolling portions 17, 1 of the transfer assist roller 13
7 is composed of a semiconductive member having elasticity such as synthetic resin. The gaps are positioned on the extension of the guide surface of the hello baffle 6a by the contact portions 17 and 17 abutting on the image carrier 2. The transfer assist roller 13
Since the halo baffle 6a is supported on the shield case 14 side of the transfer charger 6, the positional relationship between the halo baffle 6a and the transfer corotron 6b of the transfer charger 6 can be made constant. Further, these can be attached and detached integrally with the transfer charger 6. The halo baffle 6a is grounded via a constant voltage element, and a shoot bias is applied to the guide plates 20 and 21.
Hello baffle 6a is shield case 1 through insulator
It is fixed to 4.

In the above structure, the paper 18 fed from the paper feeding mechanism 11 is guided by the transfer charging device 6 by the hello baffle 6a, and the image carrier 2 and the transfer auxiliary roller 1 are guided.
It is guided to a gap between the transfer roller 3 and 3, and moves into the gap and moves above the transfer corotron 6b. At this time, since the transfer auxiliary roller 13 is arranged at a position approximately at the end of the transfer electric field (electric force line) exerted by the transfer corotron 6b on the transfer, the leading end and the rear end of the paper 18 act on the transfer electric field. Even when passing through the receiving area, the leading end and the trailing end of the paper 18 are suppressed so as to be forcibly brought into contact with the image carrier 2.

At this time, the transfer auxiliary roller 13 receives the transfer beam (corona discharge) in which the AC voltage and the DC voltage are superposed from the transfer corotron 6b, and the Zener diode 19 is interposed in the ground circuit thereof. Therefore, when the transfer beam has the same polarity as the transfer polarity, the Zener diode 19 does not act, and only when the transfer beam has the reverse polarity, a constant reverse polarity self-bias is generated, and the roller voltage b as shown in FIG. 6 is generated. The effective voltage of the transfer assist row 13 at this time is as shown by c in FIG. When a diode is provided in the ground circuit, substantially the same operation is performed.

FIG. 7 shows the polarity of the effective voltage of the transfer assisting roller 13 and the dirt grade of the surface of the transfer assisting roller 13 with respect to the voltage, as shown in FIG. 7. Contamination does not occur on the reverse polarity side of this effective voltage. On the other hand, it was found that the transfer polarity side caused a quadratic curve.

FIGS. 8A, 8B and 8C show the trailing edge transfer defect (white spots) on the second surface during double-sided copying in the prior art.
Data is shown, and 6 mm of 50 copies in each of the lab shown in (a), the 28 ° C. and 85% environment shown in (b), and the 10 ° C. and 30% environment shown in (c).
Many white spots occurred over the entire range.

On the other hand, in the above-described embodiment of the present invention, the trailing edge transfer defect (white spot) on the second side during duplex copying is shown in FIG.
As shown in (a), (b), and (c), any of the laboratory shown in (a), 28 ° C. and 85% environment shown in (b), and 10 ° C. and 30% environment shown in (c). Also in the case of 50 copies, the white spot width was significantly narrowed and the number of copies was also reduced.

10 (a) and 10 (b) show the effect of the transfer assisting roller 13 at the time of high-moisture paper, single-sided copying. In the conventional case, as shown in FIG. 10 (a), 50 sheets are copied. Among them, white spots of 6 mm or less and 12 mm or more occurred on all the papers, whereas in the embodiment of the present invention, FIG.
As shown in, the amount of white spots on all the sheets was 3 mm or less.

[0017]

According to the present invention, the transfer electric field can be surely applied to the image carrier even in the case of corrugated paper containing moisture and corrugated paper or curled downward paper after passing through the fixing device during automatic double-sided stacking. Even if the paper has such a curl, it is possible to suppress the white spot transfer failure at the end portion in the traveling direction of the paper within a maximum of 5 mm. Further, the transfer assist roller 13 for pressing the above-mentioned sheet against the image carrier is grounded through a circuit capable of inducing a voltage having a polarity opposite to the transfer polarity, so that the transfer charger 6 is attached to the transfer assist roller 13.
When a transfer beam in which the AC voltage and the DC voltage are superposed from the transfer corotron 6a is received, a self-bias of reverse polarity is generated, whereby the toner is electrically repelled and the surface of the transfer auxiliary roller 13 is soiled by the toner. Therefore, the transfer auxiliary roller 13 prevents the paper 18 from being soiled.

[Brief description of drawings]

FIG. 1 is a schematic configuration explanatory view showing a conventional example of an electrophotographic copying machine to which the present invention is applied.

FIG. 2 is a schematic configuration explanatory view showing an electrophotographic copying machine to which the present invention is applied.

FIG. 3 is a sectional view showing a main part of the present invention.

FIG. 4 is a perspective view showing a main part of the present invention.

FIG. 5 is a plan view showing an embodiment of a transfer auxiliary roller.

FIG. 6 is a diagram showing a voltage of a transfer corotron of a transfer charger and a voltage of a transfer auxiliary roller.

FIG. 7 is a diagram showing a dirt grade on the roller surface depending on the charging polarity of the transfer auxiliary roller.

FIGS. 8A, 8B, and 8C are diagrams showing the trailing edge whiteout amount on the second side in double-sided copying according to the related art.

9A, 9B, and 9C are diagrams showing the trailing edge whiteout amount of the second surface in double-sided copying in the apparatus of the present invention.

10 (a) and 10 (b) are diagrams showing a defect amount due to white spots on the trailing end of the leading end in the prior art and the device of the present invention when performing one-sided copying with high water content paper.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Device body, 2 ... Image carrier, 6 ... Transfer charger, 6a
... Hello baffle, 6b ... Transfer corotron, 13 ... Transfer assist roller, 14 ... Shield case, 15 ... Bracket, 16 ... Torsion spring, 17 ... Rolling contact part, 18
… Paper, 19… Zener diode.

Front page continued (72) Inventor Masahiko Kitamura 2274 Hongo, Ebina, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor Akio Arai 2274, Hongo, Ebina, Kanagawa Prefecture, Fuji Xerox Co., Ltd.

Claims (3)

[Claims] 1. A transfer charging is performed by moving a sheet between an image carrier and a transfer charger that operates by superimposing an AC voltage and a DC voltage on a transfer corotron in synchronization with the movement of the image carrier. In the image forming apparatus in which the toner image on the image carrier is transferred onto the paper by the transfer beam from the transfer corotron of the container, at the entrance side of the transfer charger 6 in the direction of entry of the paper 18,
In addition, a metal transfer assist roller 13 is installed at a position within the transfer beam irradiation range of the transfer corotron 6b with a constant space from the image carrier.
Is grounded via a circuit capable of inducing a voltage of reverse polarity to the transfer polarity. 2. The image forming apparatus according to claim 1, wherein the grounding circuit of the transfer auxiliary roller 13 is a diode. 3. The image forming apparatus according to claim 1, wherein the grounding circuit of the transfer auxiliary roller 13 is a constant voltage element such as a Zener diode having a rectifying function.