JP2003162154A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which, when a separating voltage is applied in order to separate transfer paper from a photoreceptor drum, reduces deterioration of the photoreceptor drum, troubles in image formation, and the occurrence of discharge product. <P>SOLUTION: The image forming apparatus has a separating-voltage application part 212 by which the separating voltage that matches separating conditions for obtaining a constant current is applied to a separating unit 21 that separates the transfer paper from the photoreceptor drum 4 after a toner image is transferred to the transfer paper from the photoreceptor drum 4. The device also has a separating-voltage limiter 213 that restricts the separating voltage of the separating-voltage application part 212 to a specific voltage or below. <P>COPYRIGHT: (C)2003,JPO

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 on the surface of a photoconductor to form an image on a recording paper, and particularly to a transfer paper after the toner image is transferred from the photoconductor. It relates to the control of the separation voltage applied for separation.

[0002]

2. Description of the Related Art Generally, an electrophotographic image forming apparatus such as a copying machine or a printer that transfers a toner image on a photoconductor drum to form an image on the transfer paper has a toner image on the transfer paper from the surface of the photoconductor drum. An image is formed by transferring the transfer paper, and a separation device is provided for separating the transfer paper, which comes into close contact with the surface of the photosensitive drum after the transfer, from the photosensitive drum. As the separating device, for example, when the transfer device positively charges the transfer paper and adsorbs the negative polarity toner to the transfer paper, the transfer paper is transferred from a position facing the photoconductor drum on the transfer paper conveyance downstream side of the transfer device. There is known a DC separation structure in which a negative voltage (separation voltage) is supplied to the positive electrode to separate the positively charged transfer paper from the photosensitive drum. This separation device sets the optimum separation current value and separation voltage according to parameters such as destination, environment, process speed, and transfer paper size, and when separating the transfer paper from the photosensitive drum,
The voltage is varied so that a preset constant current can be obtained.

[0003]

In order to reliably separate the transfer paper from the photoconductor drum, the above separating device separates the transfer paper before the leading edge of the transfer paper is brought into the voltage application region between the separating device and the photoconductor drum. A voltage is applied in advance, and the separation voltage is supplied for a predetermined time even after the rear end of the transfer paper passes through the voltage application region. However, before and after carrying out the transfer paper to the voltage application area, the transfer paper does not exist in the voltage application area and the impedance increases, so when trying to obtain a constant current, the transfer paper exists in the separation area. Higher voltage than when you do. As a result, concentrated discharge from the separating device onto the surface of the photoconductor drum may occur, causing damage to the photoconductor drum and deterioration of the photoconductor drum, or deterioration of drum charging stabilization to cause a problem in image formation. Furthermore,
There is also a problem that discharge products such as ozone and NOx are generated. These problems can be solved by supplying a separation voltage at the same time when the leading edge of the transfer paper is carried into the separation area and charging the leading edge of the transfer paper so that the photoreceptor drum is not directly discharged. It is very difficult to control the voltage application timing.

The present invention has been made to solve the above-mentioned problems, and when a separation voltage is applied to separate the transfer paper from the photosensitive drum, deterioration of the photosensitive drum and a problem of image formation are caused. It is an object of the present invention to provide an image forming apparatus capable of suppressing the occurrence of electric discharge and suppressing the generation of discharge products.

[0005]

In order to achieve the above object, the invention according to claim 1 transfers a toner image on the surface of which a toner image is formed and a toner image on the surface of the photoreceptor to a transfer paper. An image forming apparatus comprising: a transfer unit; and a separation unit that separates a transfer sheet after a toner image is transferred by the transfer unit from a photoconductor, wherein the separation unit includes a separation condition for obtaining a constant current. And a voltage limiter that suppresses the separation voltage applied by the separation voltage application unit to a predetermined voltage or less.

The invention described in claim 2 is the same as claim 1
The image forming apparatus according to claim 1, wherein the predetermined voltage is lower than the voltage applied when the transfer paper is not in the voltage application region of the separation voltage application unit when the voltage control by the voltage limiter is not performed. Is.

In the above configuration, the separation voltage applied by the separation voltage application section is suppressed to a predetermined voltage or less. For example, when the voltage control by the voltage limiter does not control the separation voltage when there is no transfer paper in the voltage application region. Therefore, when the transfer paper is not present in the voltage application area by the separation voltage application section, the separation voltage at this time is also discharged when the separation means causes concentrated discharge on the surface of the photosensitive drum. It is possible to suppress the voltage to a level that does not cause the breakdown of the drum discharge or the inhibition of the stabilization of the drum charge. This makes it possible to suppress the deterioration of the photosensitive drum and the occurrence of defects in image formation when a separation voltage is applied to separate the transfer paper from the photosensitive drum, and further, to generate discharge such as ozone and NOx. It becomes possible to suppress the generation of objects.

The invention described in claim 3 is the same as that of claim 2.
In the image forming apparatus according to the item 1, the predetermined voltage is higher than a voltage applied when the transfer paper is in the voltage application region.

According to this structure, the separation voltage when the transfer paper is not in the voltage application area is made higher than the separation voltage when the transfer paper is in the area, so that the front end of the transfer paper is carried into the voltage application area. The predetermined constant current can be quickly obtained from the point of time when it comes off, and the tip of the transfer paper can be reliably separated from the photoconductor. For example, if the separation voltage when the transfer paper is not in the voltage application area is kept low by the voltage limiter to the same separation voltage as when the transfer paper is in the voltage application area, the transfer paper will be carried into the voltage application area. In this case, at the leading end portion of the transfer paper, the planned current value cannot be immediately obtained, and the leading end portion of the transfer paper cannot be reliably separated from the photoconductor. Therefore, as in the above configuration, the separation voltage when the transfer paper is not in the area is set higher than the separation voltage when the transfer paper is in the area, and a sufficient voltage is applied from the leading edge of the transfer paper. By doing so, the problem is solved.

[0010]

DETAILED DESCRIPTION OF THE INVENTION An image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a schematic configuration of an image forming apparatus according to the present invention, and FIG. 2 is a schematic diagram showing a transfer roller and a separating device portion.
As shown in FIG. 1, in a copying machine 1 which is an example of an image forming apparatus according to the present invention, in a copying machine main body 2, a charging device 3 rotates a photosensitive drum (photoreceptor or image). The carrier 4 is uniformly charged, and the photoconductor drum 4 is irradiated with a laser beam from an exposure device (laser scanning unit or the like) 6 based on a document image read by the document reading device 5.
An electrostatic latent image is formed on the electrostatic latent image, and a developer (hereinafter referred to as toner) is attached to the electrostatic latent image by the developing device 7 to form a toner image. The toner is supplied to the developing device 7 from the toner container 8.

Transfer paper is conveyed from the paper feed mechanism 9 through the paper conveyance path 10 toward the photoconductor drum 4 on which the toner image is formed as described above, and the transfer roller 11 transfers the transfer paper to the surface of the photoconductor drum 4. The toner image is transferred to the transfer paper. Then, the transfer paper on which the toner image has been transferred is separated from the photoconductor drum 4 and conveyed to the fixing device 12 having a fixing roller pair to fix the toner image. The transfer paper that has passed through the fixing device 12 is sent to a paper conveyance path 13 that is branched in a plurality of directions, and the conveyance direction is sorted by a branching member at a branch point of the paper conveyance path 13 and is as it is (or a paper conveyance path 17).
Upper sheet tray 1 after being sent to and copied on both sides)
02a, lower sheet tray 102b or sheet tray 10
3 is ejected from the transfer paper ejecting section.

In the transfer roller 11, the transfer bias section (see FIG. 3) applies a transfer bias having a polarity opposite to that of the toner to the transfer paper, so that the transfer paper is conveyed between the photosensitive drum 4 and the transfer roller 11. In addition, the toner image is transferred from the surface of the photosensitive drum 4 to the transfer paper. Further, as shown in FIG. 2, DC is provided at a position facing the photosensitive drum 4 on the downstream side of the transfer paper conveyance of the transfer roller 11.
A separation device (separation means) 21 having a separation structure is provided. The separating device 21 includes a charge eliminating needle 211, a separating voltage applying section 212, and a separating voltage limiter (voltage limiter) 213.
For example, when the transfer paper is positively charged by the transfer roller 11 and the negative polarity toner is adsorbed to the transfer paper, the separation voltage is applied from the charge removal needle 211 to the transfer paper by the separation voltage application unit 212. A voltage is supplied to separate the transfer sheet in the positively charged state from the photosensitive drum 4. The present invention relates to control of the separation voltage applied to the transfer paper by the separation device 21.

A cleaning unit 16 removes residual toner and the like on the photosensitive drum 4. The sheet feeding mechanism 9 is detachably attached to the copying machine main body 2 and includes sheet feeding cassettes 91 and 92 for storing transfer sheets, and a stack bypass (bypass tray) 93 provided above the sheet feeding cassettes 91 and 92. These are connected to an image forming unit including the photoconductor drum 4, the developing device 7, and the like by a sheet conveying path 10.

FIG. 3 is a block diagram showing a schematic structure of the copying machine 1. The copying machine 1 is provided with a control device 20 that controls the entire copying machine 1. The control device 20 includes an image forming unit including a charging device 3, an exposure device 6, and a developing device 7, a fixing device 12, a transfer device (transfer means) 15 including a transfer roller 11, a transfer bias part 151, and the like.
A separation device 21 that applies a separation voltage to separate the transfer paper after the transfer of the toner image from the photoconductor, and a drum motor 22 that drives the photoconductor drum 4 are controlled.

In the separating device 21, a separating voltage applying section 212 for applying a separating voltage to the transfer paper carried in a separating voltage applying region (hereinafter referred to as a separating region) between the photosensitive drum 4 and the separating device 21. And the separation voltage applying unit 212
Is connected to a separation voltage limiter 213 which detects the separation voltage by the above and suppresses the separation voltage below a predetermined voltage. As will be described later, the separation voltage applying section 212 is capable of applying the separation voltage varied according to the separation conditions in order to obtain a preset constant current. Further, the control unit 20 includes an operation unit 27 to which print instruction information such as a transfer paper size used for printing is input by the user,
A main switch 28 for switching ON / OFF of the power source of the copying machine 1 is connected.

Next, the control of the separation voltage by the separation device 21 will be described. FIG. 4 is a diagram showing an example of the waveform of the separation voltage when the transfer paper passes through the separation area of the separation device 21. DC to separate the transfer paper from the photosensitive drum 4.
The case where a constant current of 60 μA is required will be described as an example. Figure 4
, T1 is the time when the application of the separation voltage is started, t2 is the time when the leading edge of the transfer paper is carried into the separation area, t3 is the time when the trailing edge of the transfer paper is carried out from the separation area, and t4 is the time when the separation voltage is applied. It also shows the time when it is finished, and the separation voltage limiter 21
The voltage waveform of the separation voltage control according to the present invention using No. 3 is shown by a solid line, and the voltage waveform of the conventional voltage control without using the separation voltage limiter 213 is shown by a broken line (different from the waveform of the voltage control according to the present invention. Part only).

In order to surely separate the leading end portion of the transfer paper from the photosensitive drum 4, t1 before the transfer paper is carried into the separation area.
The application of the separation voltage is started from the time point. In this case, since there is no transfer paper in the separation area between the photosensitive drum 4 and the separation device 21 and the impedance is large, 60 μA
In order to obtain the constant current of, the separation voltage applied by the separation voltage application section 212 becomes higher than that after t2 when the transfer paper exists in the separation area. Therefore, the separation voltage limiter 21
3, the separation voltage between t1 and t2 is set to a voltage lower than a predetermined voltage (predetermined voltage) that does not damage the drum discharge or stabilize the charging of the drum even when the surface of the photosensitive drum 4 is concentratedly discharged from the separation device 21. Try to keep it down. That is, in the conventional voltage control that does not use the separation voltage limiter 213, the high voltage up to the voltage shown by the broken line in FIG. 4 is suppressed to the low voltage shown by the solid line.

In this case, the voltage limiter value of the separation voltage limiter 213 is set so that the separation voltage between t1 and t2 is higher than the separation voltage between t2 and t3 where the transfer paper exists in the separation area. . As a result, a sufficient voltage can be applied from the time when the leading edge of the transfer paper is carried into the separation area, and a scheduled constant current can be reliably obtained, and the leading edge of the transfer paper can be reliably separated from the photosensitive drum 4. can do. For example, if the separation voltage when the transfer paper is not in the separation area is kept low by the separation voltage limiter 213 to the same separation voltage as when the transfer paper is in the separation area, the transfer paper is carried into the separation area. At this time, since a sufficient voltage is not applied to the leading end portion of the transfer paper, the planned current value cannot be immediately obtained, and the leading end portion of the transfer paper cannot be reliably separated from the photosensitive drum 4. For this reason, the voltage between t1 and t2 is kept low to the extent that drum discharge breakdown and drum charging stabilization are not impaired (in this region between t1 and t2, of course, compared to the case where the voltage control by the separation voltage limiter 213 is not performed. By setting the voltage higher than the separation voltage between t2 and t3, the scheduled constant current can be obtained immediately from the leading edge of the transfer paper.

Further, the rear end of the transfer paper has come out of the separation area.
Even after time t3, the separation voltage is applied to the trailing edge of the transfer paper without fail, so that the separation voltage is applied within the predetermined time between t3 and t4 in order to properly separate the transfer paper from the photosensitive drum 4. It In this case also, since there is no transfer paper in the separation area,
Since the separation voltage becomes high as in the period between t1 and t2, the separation voltage limiter 213 suppresses the separation voltage. And t1
Similar to the suppression of the separation voltage between -t2, t2-t3 to the extent that the above-mentioned drum discharge breakdown and drum charge stabilization are not impaired.
Set higher than the isolation voltage between them. This ensures that the scheduled constant current is obtained until the trailing edge of the transfer paper completely exits the separation area.

As described above, according to the copying machine 1 of the present embodiment, the separation voltage limiter 213 causes the separation voltage applied between t1 and t2 and between t3 and t4 where the transfer paper does not exist in the separation area to be the drum discharge. Since it can be suppressed to a level that does not damage the drum and stabilizes the charging of the drum, even if a concentrated discharge is generated on the surface of the photosensitive drum 4 from the separating device 21 when the transfer paper is not present in the separating area, the photosensitive drum is discharged. It does not cause damage or impede the stabilization of charging of the photosensitive drum. As a result, it is possible to suppress the deterioration of the photosensitive drum 4 and the occurrence of defects in image formation when the separation voltage is applied. Furthermore, ozone, NO
Generation of discharge products such as x is suppressed. Moreover, since the separation voltage limiter 213 controls the separation voltage applied between t1 and t2 and between t3 and t4 to be higher than the separation voltage between t2 and t3, even at the leading edge and the trailing edge of the paper. A constant current can be reliably obtained. As a result, the leading edge and the trailing edge of the sheet can be reliably separated from the photosensitive drum 4.

The above embodiment is merely an example of the present invention, and the configuration can be appropriately changed. For example, in the above-described embodiment, the separation device 21 is applied to the transfer device 15 that transfers the toner image from the photosensitive drum 4 using the transfer roller 11, but a transfer charger or the like is used without using the transfer roller. It is also possible to apply the present invention to a transfer device configured to charge a transfer paper and transfer a toner image. Further, in the above embodiment, the separation voltage is applied to the transfer paper from the static elimination needle 211, but the present invention is not limited to this, and the separation voltage is applied to the transfer paper by another static elimination mechanism. May be.

[0022]

As described above, according to the present invention, when there is no transfer paper in the voltage application region by the separation voltage application section and the separation means causes concentrated discharge on the surface of the photosensitive drum, the separation voltage at this time is It is possible to suppress the voltage to a voltage that does not cause the breakdown of the drum discharge or the inhibition of the stabilization of the drum charge. This makes it possible to suppress the deterioration of the photosensitive drum and the occurrence of defects in image formation when a separation voltage is applied to separate the transfer paper from the photosensitive drum.
It is possible to suppress the generation of discharge products such as Ox.

If the separation voltage when the transfer paper is not in the voltage application area is set higher than the separation voltage when the transfer paper is in the area, the leading edge of the transfer paper is carried into the voltage application area. Since a sufficient separation voltage is applied, a predetermined constant current can be quickly obtained, and the leading edge of the transfer paper can be reliably separated from the photoconductor.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of a copying machine which is an example of an image forming apparatus according to the present invention.

FIG. 2 is a schematic diagram showing a transfer roller and a separating device portion of the copying machine.

FIG. 3 is a block diagram showing a schematic configuration of the copying machine.

FIG. 4 is a diagram showing a waveform of a separation voltage when a transfer sheet passes through a separation voltage application region of a separation device.

[Explanation of symbols]

1 Copier 4 Photoconductor drum (photoconductor) 11 Transfer roller (transfer means) 15 Transfer device (transfer means) 21 Separation device (separation means) 211 Static elimination needle (separation means) 212 Separation voltage application unit (separation means) 213 Separation voltage limiter (voltage limiter)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akira Matayoshi             Kyocera 1-22-28 Tamatsukuri, Chuo-ku, Osaka-shi             Within Mita Co., Ltd. (72) Inventor Takaki Kamei             Kyocera 1-22-28 Tamatsukuri, Chuo-ku, Osaka-shi             Within Mita Co., Ltd. F-term (reference) 2H200 FA06 FA07 GA23 GA44 KA02                       KA07 KA28 KA29 LA04 LA33                       NA02 PA03 PA10 PA18 PA22

Claims (3)

[Claims] 1. A photoconductor on which a toner image is formed,
An image forming apparatus comprising: a transfer unit that transfers a toner image on a surface of a photoconductor onto a transfer paper; and a separation unit that separates the transfer paper after the toner image is transferred by the transfer unit from the photoconductor. The separation means is provided with a separation voltage application unit that applies a separation voltage according to the separation condition to obtain a constant current, and a voltage limiter that suppresses the separation voltage applied by the separation voltage application unit to a predetermined voltage or less. An image forming apparatus characterized by the above. 2. The predetermined voltage is lower than the voltage applied when the transfer paper is not in the voltage application region of the separation voltage application unit and when the voltage control by the voltage limiter is not performed. The image forming apparatus according to Item 1. 3. The image forming apparatus according to claim 2, wherein the predetermined voltage is higher than a voltage applied when the transfer paper is in the voltage application region.