JPH0611932A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device which does not give rise to defects in an image formed or a failuce to clean an image holder even if potential disturbance occurs at the image holder after transfer because of memory effects. CONSTITUTION:A static elimination/electrification means 6 for eliminating potential disturbance due to memory effects which is caused by transfer at an image holder 1 is provided between a transfer means 10 and a cleaning means 7 and the conditions required to the static elimination/electrification means 6 in eliminating static electricity from or electrifying the image holder 1 are controlled by a control means 19 in accordance with the potential of an electrostatic latent image on the image holder 1. Since the extent of the potential disturbance caused by the memory effects varies with the potential of the electrostatic latent image on the image holder 1, the conditions required to the static elimination/electrification means 6 in eliminating static electricity from or electrifying the image holder are controlled according to the potential of the electrostatic latent image, whereby the potential disturbance caused by the memory effects on the image holder 1 can readily be eliminated by the static elimination/electrification means 6.

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 such as an electrophotographic system or an electrostatic photography system, and more particularly to an image forming apparatus suitably embodied in a color copying machine or a color printer.

[0002]

2. Description of the Related Art In a color copying machine or the like capable of forming a multicolor image, a toner image which is a developed image is transferred from a photosensitive drum which is an image carrier onto a transfer material which is held on a transfer drum. Then, due to the peeling discharge of the transfer material after the transfer from the photosensitive drum, a potential disturbance called a memory effect occurs on the photosensitive drum. This will be described below with reference to FIGS. 31 and 32.
Will be described.

FIG. 31 shows a state around a photosensitive drum and a transfer drum of an image forming apparatus having a plurality of developing devices and capable of forming a multicolor image. In the figure, 1 is a primary charger (not shown)
Is charged to a negative potential (e.g., -500V), and a predetermined image light is exposed to a negative potential (e.g., -100V) by an exposure unit (not shown) to form an electrostatic latent image on its outer surface. It's a drum. To the photosensitive drum 1, the electrostatic latent image is supplied with negatively charged toner via a developing device (not shown), and a toner image T is formed by reversal development.

Further, reference numeral 5 in the drawing is arranged so as to face the photosensitive drum 1, and a transfer paper P which is a transfer material is held on a transfer material carrying sheet 5a (made of, for example, polyvinylidene fluoride resin film) on the outer peripheral surface thereof. And a rotating transfer drum. A transfer charger 10 is provided inside the transfer drum 5 at a position facing the photosensitive drum 1. The transfer charger 10 has a polarity opposite to that of the toner (in this case, positive polarity).
Is applied to the transfer paper P side to attract the toner image T on the photosensitive drum 1 onto the transfer paper P, and the toner image T is transferred from the photosensitive drum 1 to the transfer paper P side.

When the toner image T on the photosensitive drum 1 is transferred onto the transfer paper P via the transfer charger 10, the volume resistivity of the polyvinylidene fluoride resin film is, for example, 10 ¹³ Ω.
.Cm, and the low volume efficiency of the transfer paper P is, for example, 10 ⁹
(At high temperature) to 10 ¹² (at high temperature) Ω · cm, a positive charge is injected from the transfer charger 10 into the transfer paper P through the transfer material carrying sheet 5a of the transfer drum 5,
This charge is accumulated in the surface area of the transfer paper P. And
This electric charge on the surface of the transfer paper P forms a high electric field with the surface of the photosensitive drum 1, and as shown in FIG. 32, peeling discharge occurs when the transfer paper P separates from the photosensitive drum 1.

In this case, the negative charges in the air are attracted by the positive charges and move onto the transfer sheet P, but the positive charges in the air are negatively charged.
Moving upward, a potential disturbance called a memory effect occurs on the photosensitive drum 1 after transfer. The transfer paper P
At the end portion PO, the positive charge due to transfer is likely to be accumulated on the transfer paper P, resulting in a strong memory effect.

FIG. 33 shows the surface potential of the photosensitive drum 1 when the memory effect occurs, and shows the portion of the portion where the memory effect does not occur (the portion where transfer is not performed in the gap between the transfer paper P and the transfer paper P). The electric potential after the transfer is slightly negative, whereas the electric potential after the transfer in the portion where the memory effect occurs (memory effect area) reaches + 100V to + 700V. There is no change when the charge-removing exposure is performed (not shown). After that, even if the photosensitive drum 1 is primarily charged to -500V, the potential of the memory effect region remains as -100 to -450V. For example, if the developing bias voltage by the developing device is -350V, this A toner image T is formed in the memory effect region having a potential higher than −350 V, and the toner image T is transferred onto the transfer paper P, causing strong streak-like image unevenness along the axial direction of the photosensitive drum 1. Further, when the image light is exposed in the memory effect area of the photosensitive drum 1, for example, when the potential becomes −100 V, a part of this portion has a potential close to 0 V, so that the formed toner image T has a density. It causes unevenness.

In FIG. 34, the photosensitive drum 1 is set to -700V.
In this case, the potential of the memory effect area is −300V to −650V, and if the developing bias voltage is −550V, image unevenness is generated in the memory effect area portion having a potential higher than −550V. (Toner image) is formed.

That is, the memory effect is that the photosensitive drum 1 is charged to a potential (positive polarity in this case) opposite to the potential of the electrostatic latent image on the photosensitive drum 1 (negative polarity in this case) during transfer or the like. This is the disturbance of the potential generated on the photosensitive drum 1, and the charge cannot be removed by the discharge exposure by the discharge lamp. When the photosensitive drum having the memory effect is primarily charged, the portion of the memory effect area is charged to a potential on the 0V side as compared with the normally primary-charged portion, so the memory effect area portion is excluded. In order to do so, it is necessary to carry out more charging only in this portion.

Therefore, for the purpose of reducing the memory effect, means are taken such as destaticizing the photosensitive drum 1 after transfer by a constant charging device or precharging the photosensitive drum 1 to the same polarity as the primary charging. ing.

[0011]

However, the potential disturbance caused by the memory effect on the photosensitive drum 1 after the transfer is caused by the potential of the electrostatic latent image formed on the photosensitive drum, the transfer condition by the transfer charger 10, and a plurality of conditions. It has been clarified by the applicant's research and experiment that the number of times of transfer when the toner images T are superposed on each other and the value of the potential contrast of the electrostatic latent image formed on the photosensitive drum 1 are variously changed.

Therefore, it is difficult to sufficiently reduce the memory effect even if the photosensitive drum 1 after transfer is discharged by a constant charging device. Further, if the photosensitive drum 1 is charged to the same polarity as the primary charging potential, the memory effect is considerably reduced, but at the same time, the residual toner on the photosensitive drum 1 is also charged,
There is a problem that the toner is strongly attracted to the photosensitive drum 1 and the residual toner is not sufficiently cleaned thereafter, resulting in cleaning failure.

The present invention has been made in view of the above problems, and an object of the present invention is to form an image defect in a formed image even if a potential disturbance due to a memory effect occurs in an image carrier after transfer. An object of the present invention is to provide an image forming apparatus that does not cause cleaning failure on the image carrier.

[0014]

In order to achieve the above object, the first invention of the present invention is to provide a developed image formed by developing an electrostatic latent image on an image bearing member, after the developed image is transferred by a transfer means. In the image forming apparatus, the residual developer on the image carrier is cleaned by a cleaning unit, and the potential disturbance generated on the image carrier by the transfer is removed by the decharging unit before the cleaning after the transfer. It is characterized in that a control means is provided for controlling the decharge condition of the decharge means based on the potential of the electrostatic latent image on the image carrier.

In order to achieve the above object, the second aspect of the present invention
According to the invention, after the developed image formed on the image carrier is transferred by the transfer means, the residual developer on the image carrier is cleaned, and after the transfer and before the cleaning, the image carrier is transferred by the transfer. In the image forming apparatus in which the disturbance of the electric potential that occurs in the image forming apparatus is removed by the decharging unit, a control unit that controls the decharging condition of the decharging unit based on the transfer charging condition of the transfer unit is provided. To do.

The third aspect of the present invention is to achieve the above object.
According to the invention, after the developed image formed on the image carrier is transferred by the transfer means, the residual developer on the image carrier is cleaned, and after the transfer and before the cleaning, the image carrier is transferred by the transfer. In the image forming apparatus in which the disturbance of the electric potential generated in the image forming apparatus is removed by the decharging unit, and the images are formed by multiple-transferring the developed images on the same transfer material a plurality of times in multiple transfer, It is characterized in that a control means for controlling the decharging condition on the basis of the transfer charging condition of the transfer means and the number of times of multiple transfer is provided.

Further, in order to achieve the above object, the fourth aspect of the present invention
In the invention, after the developed image formed by developing the electrostatic latent image on the image carrier is transferred by the transfer means, the residual developer on the image carrier is cleaned by the cleaning means, and the transferred image is transferred. In the image forming apparatus in which the disturbance of the electric potential generated on the image carrier by the transfer is removed by the decharging unit before the post-cleaning, the destaticizing condition of the decharging unit is set to the electrostatic latent image on the image carrier. It is characterized in that a control means for controlling on the basis of the value of the potential contrast is provided.

[0018]

First, the operation of the first invention will be described. When a developed image formed by developing an electrostatic latent image on an image carrier is transferred to a transfer material or the like by a transfer means, it is called a memory effect on the image carrier due to peeling discharge of the transfer material or the like. Disturbance of electric potential occurs. If the potential of the image carrier is disturbed, the electrostatic latent image formed on the image carrier is disturbed thereafter, which causes an image defect. By being decharged by the decharging means, the disturbance of the potential due to the transfer is removed.

However, the disturbance of the electric potential is not constant, and its size changes according to the electric potential of the electrostatic latent image on the image carrier. Therefore, even if a constant voltage is applied to the image carrier by the decharging means, the disturbance of the electric potential cannot always be removed. That is, even if the disturbance of the potential can be made into an averaged value with little change to some extent by the decharging means, the averaged value as a whole has a constant potential, so that it remains on the image carrier. The developer is also charged by this decharging means, resulting in defective cleaning.

Therefore, in the first aspect of the invention, a control means for controlling the decharging voltage of the decharging means is provided, and the decharging voltage of the decharging means is controlled by the control means. By controlling based on the potential of the image, the potential of the image carrier of the decharging means in the memory effect region is made to converge to around 0V, for example. Therefore, due to the disturbance of the potential due to the memory effect, neither the cleaning failure of the image carrier will occur nor the image failure of the image carrier will occur.

Next, the operation of the second invention will be described. Second
The invention is made in view of the fact that the disturbance of the surface potential of the image carrier due to the memory effect changes depending on the transfer charging condition of the transfer unit. That is, the decharging voltage of the decharging unit is controlled by the control unit controlling the decharging voltage of the decharging unit based on the transfer current value of the transfer unit. The potential of the subsequent image carrier is made to converge, for example, near 0V.

Next, the operation of the third invention will be described. Third
The invention is made in view of the fact that the disturbance of the surface potential of the image carrier due to the memory effect changes depending on the condition of transfer charging by the transfer means and the number of times of multiple transfer. That is, the control unit that controls the decharging voltage of the decharging unit controls the decharging voltage of the decharging unit based on the transfer current value of the transfer unit and the number of times of multiple transfer. The electric potential of the image carrier after decharging the effective area is made to converge to, for example, about 0V.

Next, the operation of the fourth invention will be described. Fourth
The invention is made in view of the fact that the disturbance of the surface potential of the image carrier due to the memory effect changes depending on the value of the potential contrast of the electrostatic latent image of the image carrier. That is, the control unit for controlling the decharging voltage of the decharging unit controls the decharging voltage of the decharging unit based on the value of the potential contrast of the electrostatic latent image on the image carrier, The electric potential of the image carrier after decharging the memory effect area is made to converge to, for example, about 0V.

[0024]

【Example】

[First Invention] Next, an embodiment of the first invention will be described with reference to the accompanying drawings. First, a first embodiment of the present invention will be described with reference to FIGS.

FIG. 2 shows a main part of an image forming apparatus capable of forming a full-color image having a rotary developing device.
In the figure, reference numeral 1 denotes a photosensitive drum (a drum having an electrophotographic photosensitive member) which is an image bearing member. The photosensitive drum 1 has an outer diameter of 80 mm and is rotationally driven in the arrow direction at a peripheral speed of 160 mm / s. Around the photosensitive drum 1, a primary charger 2, an exposure unit 3, a rotary developing device 4 as a developing unit,
A transfer drum 5, an auxiliary charging device 6, a cleaning device 7, a charge eliminating lamp 8, and a drum surface potential sensor 9 are provided.
A transfer charger 10, which is a corona charger, is provided as a transfer unit at a position facing the photosensitive drum 1 in the transfer drum 5, and a pair of static eliminator chargers 11 and 11 are provided inside and outside the discharge side of the transfer drum 5. Is provided. A paper feed guide 12 is provided on the paper feed side of the transfer drum 5, and a transport device 13 and a fixing device 14 are provided on the paper ejection side. Incidentally, reference numeral 20 in FIG. 2 denotes a DC power source for the transfer charger 10.

The primary charger 2 is, for example, a scorotron type charger, and as shown in FIG. 3, the charging wire 2a is discharged by a high voltage applied from a high voltage power source 15.
The amount of discharge is controlled by applying a predetermined control voltage from the grid bias power source 16 to the grid line 2b to charge the surface of the photosensitive drum 1 to a desired negative potential, for example. The exposing means 3 is composed of, for example, a laser beam scanner, and irradiates the photosensitive drum 1 with color-separated image light to form an electrostatic latent image on the photosensitive drum 1.

The rotary developing device 4 includes a yellow developing device 400Y having yellow toner, a magenta developing device 400M having magenta toner, a cyan developing device 400C having cyan toner, and a black developing device 400B having black toner. The electrostatic latent image formed on the photosensitive drum 1 is positioned inside the body 401 by rotating in the direction of the arrow in the figure to position the desired developing device 400 at a position facing the outer peripheral surface of the photosensitive drum 1. Is to be developed. In this case, the toner in each developing device 400 is charged to, for example, a negative polarity, and this toner is used in each developing device 4
00 is carried to the photosensitive drum 1 side while being carried by the developing sleeve 400a, and is moved to the photosensitive drum 1 side by the developing bias voltage applied to the developing sleeve 400a.
The electrostatic latent image on the photosensitive drum 1 is developed by reversal development.

As shown in FIG. 4, the transfer drum 5 has a transfer material holding sheet 5b and a transfer material grip 5c around a cylindrical frame 5a, for example, a rotary transfer material holder having a diameter of 160 mm. And is driven to rotate in the direction of the arrow in the figure. The transfer material carrying sheet 5b has a thickness of 10
It is composed of a polyvinylidene fluoride resin film having a volume reduction efficiency of 0 ^{13 to} 175 μm and a volume efficiency of 10 ¹³ Ω · cm.

Next, a full-color image forming process by the image forming apparatus will be described. By the primary charger 2, for example-
When the photosensitive drum 1 uniformly charged to 500V is exposed to image light of, for example, yellow image information through the exposure means 3, an electrostatic latent image having an image contrast value of 400V is formed on the photosensitive drum 1. It is formed. This electrostatic latent image is moved to the rotary developing device 4 in which the yellow developing device 400Y is positioned as the photosensitive drum 1 rotates, toner is supplied by the yellow developing device 400Y, and a toner image (development image is developed by reversal development). Image) is visualized.
Then, this toner image is transferred onto the transfer material P held on the transfer material carrying sheet 5b of the transfer drum 5 via the transfer charger 10. In this case, the transfer charger 10 is + 6K
A voltage of V to +9 KV can be applied to the transfer material P side, and the transfer current value at this time is set to +100 μA to +500 μA.

After the transfer of the photosensitive drum 1 is completed, after the disturbance of the potential is removed by the auxiliary charger 6 which will be described later in detail, the residual toner is cleaned by the cleaning device 7 and the charge is removed by the discharge lamp 8. Next, in the same procedure, toner images of respective colors of magenta, cyan, and black toner are transferred onto the transfer material P of the transfer drum 5 in an overlapping manner (multiple transfer) on the photosensitive drum 1.

On the other hand, the transfer material P supplied to the transfer drum 5 through the paper feed guide 12 is wound around the transfer material carrying sheet 5b while being held by the transfer material grip 5c, and is exposed as the transfer drum 5 rotates. The drum 1 is rotated toward the drum 1, and first, the toner image of the yellow toner on the photosensitive drum 1 is transferred via the transfer charger 10. As a result, the transfer material P is transferred to the transfer material carrying sheet 5 of the transfer drum 5.
It is electrically adsorbed on b. Then, as the transfer drum 5 rotates, multiple toner images of magenta, cyan, and black toners are transferred onto the transfer material P one after another. Then, the transfer material P which has been transferred is discharged by the pair of discharging chargers 11 and 11 to be separated from the transfer drum 5, and is conveyed to the fixing device 14. Then, the four color toner images on the transfer material P are heated and pressed by the fixing device 14 to be melt-mixed, and fixed as a full color image.

Next, the memory effect that occurs on the photosensitive drum 1 after transfer and the means for removing this memory effect will be described.
The memory effect is as described in detail in the section of the prior art,
The potential disturbance generated on the photosensitive drum 1 after transfer, which has the opposite polarity to the potential of the electrostatic latent image on the photosensitive drum 1, is referred to. It was found that the potential changes significantly depending on the magnitude of the potential of the latent image. In this case, the potential of the electrostatic latent image means, for example, in the case of reversal development, the dark portion potential (primary charging potential) of the image and the light portion potential (exposed portion potential) of the image. For example, in FIG. 5, the primary charging potential (dark portion potential Vd) of the photosensitive drum 1 is -50.
The surface potential of the memory effect area of the photosensitive drum 1 after transfer is shown for 0V, -600V, -700V, and -800V. It is understood that the magnitude of the potential disturbance caused by the memory effect varies depending on the primary charging potential (dark portion potential Vd). On the other hand, when the photosensitive drum 1 is primarily charged, the photosensitive drum 1 is, for example, -300 V while the potential is monitored by the drum surface potential sensor 9 in accordance with the surrounding environmental conditions and the sensitivity state of the photosensitive member.
It is primarily charged to an optimum potential in the range of -900V. Therefore, if the potential of the primary charging of the photosensitive drum 1 is different, the magnitude of the surface potential of the memory effect area generated on the photosensitive drum 1 changes.

Therefore, in order to remove the potential disturbance caused by the memory effect on the photosensitive drum 1, a predetermined voltage is applied to the photosensitive drum 1 according to the potential of the electrostatic latent image formed on the photosensitive drum 1. It becomes necessary to apply. That is,
As shown in FIG. 1, between the cleaning device 7 and the transfer charging device 10 in the transfer drum 5, an auxiliary charging device 6 is provided as a decharging device for destaticizing the photosensitive drum 1 after transfer. A bias voltage in which a DC voltage and an AC voltage are superposed is applied from the DC power supply 17 and the AC power supply 18 to the container 6, and the potential of the electrostatic latent image on the photosensitive drum 1, in this case, the magnitude of the dark portion potential Vd. DC power supply 17
A control unit 19 for controlling the above is provided, and the DC bias voltage of the auxiliary charger 6 is changed by this control unit 19 so as to remove the potential disturbance caused by the memory effect on the photosensitive drum 1.

For example, the DC bias voltage Vdc from the DC power supply 17 is a variable voltage from -1 KV to +2 KV, and the AC bias voltage Vac from the AC power supply 18 has a frequency Vf =
It is set to 500 Hz and peak-to-peak voltage Vpp = 10 kV.

Next, the operation of the auxiliary charger 6 will be described with reference to FIGS. FIG. 6 shows the dark potential V of the photosensitive drum 1.
The transition of the surface potential of the photosensitive drum 1 when d is set to -500V is shown. In this case, the DC bias voltage Vdc of the auxiliary charger 6 is controlled to -300V. Under the above conditions, the photosensitive drum 1 receives a charging memory (potential disturbance) of about +100 V to +700 V due to the action of the transfer charger 10 during transfer, but after the auxiliary charging by the auxiliary charger 6, the surface of this memory effect area is affected. Potential is OV
It converges to the neighborhood.

Therefore, the residual toner on the photosensitive drum 1 is not strongly charged by the auxiliary charging device 6 and is sufficiently cleaned by the cleaning device 7. Also,
After that, since the photosensitive drum 1 is neutralized to approximately 0V after the static elimination exposure by the static elimination lamp 8, the memory effect does not appear on the photosensitive drum 1 even if the photosensitive drum 1 is primarily charged to -500V. Therefore, the photosensitive drum 1 can be uniformly primary-charged.

In FIG. 7, the dark potential Vd of the photosensitive drum 1 is -8.
Transition of the surface potential of the photosensitive drum 1 when the value of the DC bias voltage Vdc of the auxiliary charger 6 is set to -300V as in the above example and when it is set to + 200V when set to 00V. Are shown in comparison. When the DC bias voltage Vdc is -300V, the surface potential of the memory effect region after the auxiliary charging by the auxiliary charger 6 is -300.
Since it is converged to a value near V, it is neutralized to approximately 0 V by the static elimination exposure by the static elimination lamp 8, and this memory effect area is uniformly primary-charged, but the residual toner on the photosensitive drum 1 is strongly charged by the auxiliary charger 6. Therefore, the adhesive force of the residual toner to the photosensitive drum 1 increases, and the cleaning device 7 cannot sufficiently clean the residual toner, resulting in defective cleaning.

On the other hand, according to the dark part potential Vd, the auxiliary charger 6
When the DC bias voltage Vdc of is set to +200 V, the surface potential of the memory effect area after auxiliary charging is converged to a value near OV, so that the residual toner on the photosensitive drum 1 is sufficiently cleaned, and further, this memory The effect area is also uniformly primary-charged.

FIG. 8 shows one of the photosensitive drums 1 in this embodiment.
The control value of the DC bias voltage Vdc of the auxiliary charger 6 with respect to the next charging potential (dark portion potential Vd) by the control unit 19 is shown. From the figure, when the negative value of the primary charging potential becomes large, the DC bias voltage Vdc shifts from 0 to the positive side,
It can be seen that the DC bias voltage Vdc shifts to the negative side when the negative value of the primary charging potential becomes small. If a superposed voltage having a DC bias voltage value Vdc on this graph is applied to the photosensitive drum 1 via the auxiliary charging device 6 in accordance with the primary charging potential, the surface potential of the photosensitive drum 1 after transfer is a memory effect. Both the area and the normal area are always controlled to be near 0V.

FIG. 9 shows that the dark portion potential Vd of the photosensitive drum 1 in this embodiment is -500V, -600V, -700V,-.
The surface potential of the memory effect area of the photosensitive drum 1 in the case of 800V is shown. In this figure, the value of the DC bias voltage Vdc of the auxiliary charger 6 is shown as the dark portion potential Vd shown in FIG.
And the case where the value of the DC bias voltage Vdc when the dark portion potential Vd is −500 V is used for all (dashed line). From the figure, in the case of the solid line in which the value of the DC bias voltage Vdc of the auxiliary charger 6 is changed according to the dark part potential Vd shown in the figure, the surface potential of the photosensitive drum 1 in the memory effect area after the auxiliary charging is near 0V. Although it can be seen that they converge, the dark potential Vd is -5.
In the case of the broken line using only the value of the DC bias voltage Vdc in the case of 00V, the surface potential of the photosensitive drum 1 in the memory effect area after the auxiliary charging is increased as the negative value of the dark portion potential Vd of the photosensitive drum 1 is increased. You can see that it is getting bigger on the minus side.

As described above, the toner image on the photosensitive drum 1 is transferred onto the transfer material P via the transfer material carrying sheet 5b of the transfer drum 5.
When transfer is performed by the transfer charger 10, the potential disturbance called the memory effect occurs on the photosensitive drum 1 after the transfer. Even in such a case, the auxiliary charger is provided between the transfer charger 10 and the cleaning device 7. 6 is provided and the value of the DC bias voltage Vdc applied to the photosensitive drum 1 is controlled by the potential of the electrostatic latent image on the photosensitive drum 1, the surface potential of the photosensitive drum 1 in the memory effect area after transfer is It can be converged to near 0V. Therefore, in the next primary charging, the photosensitive drum 1 can be uniformly charged without leaving the influence of the memory effect on the photosensitive drum 1 at all, and at the time of cleaning the residual toner, the residual toner is removed by the auxiliary charger 6. Therefore, the photosensitive drum 1 can be sufficiently cleaned without causing a cleaning failure.

Next, a second embodiment of the present invention will be described with reference to FIG. It should be noted that components having the same functions as those of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

The figure shows a cross section of an electrophotographic copying machine (image forming apparatus) having four image units and capable of forming a full-color image. In the main body 29 of the copying machine,
Photosensitive drum 1, primary charging device 2, exposing device 3, developing device 2
Four image units 22 each including a transfer charger 10, an auxiliary charger 6, a cleaning device 7, a cleaning device 7, a charge eliminating lamp 8 and a drum surface potential sensor 9 are provided. 22A, a yellow image is formed by the yellow toner, a second image unit 22B indicated by the subscript B forms a magenta image by the magenta toner, and a third image unit 22 indicated by the subscript C is formed.
In C, a cyan image is formed by cyan toner, and in the fourth image unit 22D indicated by the suffix D, a black image is formed by black toner.

The four image units 22A, 22B,
A transfer material conveying device 23 including a transfer belt 23a, a driving roller 23b, and the like is arranged below the 22C and 22D. A sheet feeding cassette 24, a sheet feeding roller 25, and a registration roller 26 are provided on the sheet feeding side of the transfer material conveying device 23, and a discharging charger 27, a fixing device 14, and a sheet discharging tray 28 are provided on the sheet discharging side. Is provided.

Here, the developing device 21 is the same as the developing device 400 in the rotary developing device 4 of the first embodiment in terms of its basic structure, used toner and developing method. In addition, the transfer material transport device 23
Is an endless transfer belt 23a in which the transfer material P is positioned and fixed at a predetermined position is rotated by a driving roller 23b or the like to convey the transfer material P to each image unit 22, but the transfer belt 23a is the first embodiment. The transfer material carrying sheet 5b of the transfer drum 5 of the example has substantially the same configuration and function.

Next, a full color image forming process by the image forming apparatus will be described. In the first image unit 22A, the photosensitive drum 11A uniformly charged by the primary charger 2A is exposed with image light based on yellow image information via the exposing means 3A, and an electrostatic latent image is formed on the photosensitive drum 1A. Then, the electrostatic latent image is directed toward the developing device 21 as the photosensitive drum 1A rotates, and yellow toner is supplied by the developing device 21A to be visualized as a toner image (developed image). Then, this toner image is transferred to the transfer charger 1.
The transfer charger 10A is directed toward 0A and is transferred onto the transfer material P on the transfer belt 23a of the transfer material conveying device 23. Further, the residual toner is cleaned by the cleaning device 7A, and the photosensitive drum 1A after the transfer is prepared for the next image formation. Similarly, in the second, third, and fourth image units 22B, 22C, and 22D, the toner images of magenta, cyan, and black are transferred and superposed on the transfer material P.

On the other hand, the transfer materials P picked up one by one from the paper feed cassette 24 via the paper feed roller 25 are supplied to the transfer material conveying device 23 with timing by the registration rollers 26, and the transfer material P is transferred. It is electrically adsorbed on the transfer belt 23a of the transport device 23 and positioned and fixed.
The transfer material P is moved by the rotational movement of the transfer belt 23a by the drive roller 23b, and the photosensitive drums 1A, 1B, 1C, and 1D of the first, second, third, and fourth image units 22A, 22B, 22C, and 22D. 1D and transfer charger 10A, 1
The toner images of four colors are transferred while passing between 0B, 10C, and 10D. Then, the transfer material P, which has been transferred, is discharged by the discharging charger 27, separated from the transfer belt 23a of the transfer material conveying device 23 and sent to the fixing device 14, and the fixing device 14 forms the toner images of the four colors. After the colors are dissolved and mixed to be fixed as a full-color image, they are stacked on the paper discharge tray 28.

In each image unit 22, the photosensitive drum 1 is primarily charged to the optimum potential while the potential of the photosensitive drum 1 is monitored by the drum surface potential sensor 9 according to the surrounding environmental conditions and the sensitivity state of the photosensitive member. .

In the above-mentioned image forming apparatus, when the toner image on the photosensitive drum 1 is transferred onto the transfer material P by the transfer charger 10 via the transfer belt 23a of the transfer material conveying device 23, after the transfer. Distortion of potential called a memory effect occurs on the photosensitive drum 1. Further, since the disturbance of the electric potential changes significantly depending on the size of the electric potential of the electrostatic latent image on the photosensitive drum 1, also in this embodiment, the auxiliary charging is performed between the transfer charger 10 and the cleaning device 7 for each image unit 22. The auxiliary charging device 6 is provided with a bias voltage in which a DC voltage and an AC voltage are superimposed from the AC power supply 18 and the DC power supply 17, and an electrostatic latent image formed on the photosensitive drum 1 is formed. The controller 19 controls the DC power supply 17 according to the magnitude of the dark portion potential Vd to apply the DC bias voltage Vdc corresponding to the dark portion potential Vd to the photosensitive drum 1.

Therefore, also in this embodiment, in each image unit 22, the surface potential of the photosensitive drum 1 in the memory effect area after transfer can be converged to near 0V,
In the next primary charging, the photosensitive drum 1 can be uniformly charged without leaving the influence of the memory effect on the photosensitive drum 1 at all, and the residual toner is strongly charged by the auxiliary charger 6 even when cleaning the residual toner. Therefore, cleaning failure does not occur in the photosensitive drum 1.

Next, a third embodiment of the present invention will be described with reference to FIG. In addition, the same reference numerals are given to those having the same functions as those according to the first and second embodiments, and the description thereof will be omitted.

The figure shows a cross section of an electrophotographic laser beam printer (image forming apparatus) for forming a monochrome monochromatic image. The photosensitive drum 1 is surrounded by a primary charger 2 and a laser beam device as an exposing means. 30, a developing device 21, a transfer charging device 10, an auxiliary charging device 6, a cleaning device 7, a discharging lamp 8 and a drum surface potential sensor 9 are provided. In addition,
Although the description of the image forming process by this image forming apparatus is omitted, the potential of the photosensitive drum 1 is also monitored by the drum surface potential sensor 9 according to the surrounding environmental conditions and the sensitivity state of the photoconductor in this image forming apparatus. Meanwhile, it is primarily charged to the optimum potential.

In the above-mentioned image forming apparatus, when the toner image is transferred onto the transfer material P, a transfer drum, a transfer belt or the like is not used, so that the potential disturbance called the memory effect hardly occurs on the photosensitive drum 1 after the transfer. However, even in such an image forming apparatus, a certain memory effect occurs on the photosensitive drum 1 after transfer. Therefore, also in this embodiment, the auxiliary charging device 6 is provided between the transfer charging device 10 and the cleaning device 7, and the bias in which the DC voltage and the AC voltage are superposed on the auxiliary charging device 6 from the AC power supply 18 and the DC power supply 17. A voltage is applied and the control unit 19 is controlled depending on the magnitude of the dark potential Vd of the electrostatic latent image formed on the photosensitive drum 1.
Thus, the DC power supply 17 is controlled to apply the DC bias voltage Vdc corresponding to the dark potential Vd to the photosensitive drum 1. Therefore, also in this embodiment, the surface potential of the photosensitive drum 1 in the memory effect area after transfer can be converged to near 0 V, and the same effect as in the first and second embodiments can be obtained.

Next, a fourth embodiment of the present invention will be described. The present embodiment relates to the case where the individual devices of the image forming apparatus according to the first to third embodiments are replaced with other devices, and the operation method and control method of the auxiliary charger 6 are changed.

First, in the first to third embodiments, the case where the corona charger is used as the transfer means has been described, but the present invention is not limited to this, and for example, the brush type transfer means 30 as shown in FIG. Alternatively, even if a contact type transfer unit such as the roller type transfer unit 31 shown in FIG. 13 is used, the same effect as in the case of the corona charger can be obtained.

In the first to third embodiments, the auxiliary charger 6 is controlled so that the surface potential of the photosensitive drum 1 after transfer converges to around 0 V. However, the memory effect produced on the photosensitive drum 1 is more effective. In order to remove it, the surface potential of the photosensitive drum 1 is set to, for example, -50V or -100V by the auxiliary charging device 6 within a range in which the photosensitive drum 1 does not cause cleaning failure.
As described above, it may be converged so as to be slightly offset to the same polarity side as the primary charging potential. Further, in order to further sufficiently clean the photosensitive drum 1, the surface potential of the photosensitive drum 1 is set to, for example, +2 by the auxiliary charger 6 within a range in which the memory effect generated on the photosensitive drum 1 can be reduced to a practical range.
It may be converged so as to be slightly offset to the opposite polarity side to the primary charging potential, such as 0 V or +50 V.

Further, although the DC bias voltage Vdc of the auxiliary charger 6 is controlled in the first to third embodiments, instead of this, the amplitude of the AC bias voltage Vac of the auxiliary charger 6 and the duty of the AC bias voltage Vac are controlled. The same effect can be obtained by controlling any one of the ratio, the charging current value, or the combination of two or more of them including the DC bias voltage Vdc. The auxiliary charger 6 has a DC bias Vdc or an AC bias voltage Vac in addition to the superimposed voltage of the DC bias voltage Vdc and the AC bias voltage Vac.
Only one of the above may be applied.

In the first to third embodiments, the auxiliary charger 6 is controlled according to the dark portion potential Vd (primary charging potential) of the photosensitive drum 1, but the bright portion when the photosensitive drum 1 is exposed to the maximum, for example. The same effect can be obtained by controlling the auxiliary charger 6 according to the potential.

In addition to the copying machines and laser beam printers described in the first to third embodiments, various image forming apparatuses such as electrophotographic type and electrostatic recording type copying machines and printers can be used. Of course, the invention can be applied. In addition,
It is needless to say that the numerical values used in each example are mere examples and are not limited to these. [Second Invention] Next, an embodiment of the second invention will be described with reference to FIGS. The present invention is intended to eliminate potential disturbance caused by a memory effect on a photosensitive drum after transfer by an auxiliary charger whose direct current bias voltage and the like are controlled by transfer charging conditions. First, an explanation will be given by taking as an example an electrophotographic copying machine capable of forming a full-color image having the rotary developing device 4 shown in FIG.

According to an experimental study by the applicant, when the toner image is transferred by the transfer charger 10, the potential disturbance caused by the memory effect on the photosensitive drum 1 after the transfer depends on the transfer charging condition, for example, the transfer current value. It was found to change significantly. For example, FIG. 15 shows the relationship between the transfer current value and the surface potential of the photosensitive drum 1 in the memory effect region. From this figure, the potential disturbance due to the memory effect on the photosensitive drum 1 is It is understood that the size varies depending on. That is, it can be seen that the surface potential of the photosensitive drum 1 in the memory effect area increases (becomes stronger) depending on the transfer current value.

On the other hand, the optimum transfer charging conditions by the transfer charging device 10 are ambient environmental conditions, the type of the transfer material P, the state of the electrostatic latent image on the photosensitive drum 1, the state of the toner in the developing device 400, or It changes depending on the state of the photosensitive member of the photosensitive drum 1. Therefore, the transfer charging condition is changed according to the image forming condition in order to obtain a high quality image. Particularly, in an image forming apparatus capable of forming a full-color image, the optimum transfer charging condition is different for each color toner. For example, when standard paper is used as the transfer material P in a normal temperature and normal humidity environment, the transfer current value is For example, + 200μA for the first color, +22 for the second color
5μA, + 250μA for 3rd color, + 300μA for 4th color
Will be changed.

Therefore, in order to remove the potential disturbance caused by the memory effect on the photosensitive drum 1, it is necessary to apply a predetermined voltage to the photosensitive drum 1 according to the transfer charging condition at the time of transfer. That is, as shown in FIG. 14, the cleaning device 7 and the transfer charger 1 in the transfer drum 5 are provided.
An auxiliary charging device 6 as a decharging means for decharging the photosensitive drum 1 after transfer is provided between 0 and a bias voltage in which a DC voltage and an AC voltage are superposed from the DC power supply 17 and the AC power supply 18 on the auxiliary charging device 6. Is applied, and a controller 40 for controlling the DC power supply 17 is provided according to the transfer charging condition of the transfer charger 10, in this case, the transfer current value, and the controller 40 controls the DC bias of the auxiliary charger 6. The voltage is changed so as to remove the potential disturbance caused by the memory effect on the photosensitive drum 1. Note that, for example, the DC bias voltage Vdc from the DC power supply 17 is -1 kV to +2 kV.
AC bias voltage Vac from the AC power source 18 has a frequency Vf = 500 Hz and a peak-to-peak voltage Vpp = 1.
It is set to 0 kV.

Next, the operation of the auxiliary charger 6 will be described with reference to FIGS. FIG. 16 shows the transition of the surface potential of the photosensitive drum 1 when the transfer current value of the transfer charger 10 is set to +450 μA. In this case, the DC bias voltage Vdc of the auxiliary charger 6 is controlled to -300V. Under the above conditions, the photosensitive drum 1 is about +100 V to +70 V due to the action of the transfer charger 10 during transfer or the like.
Although a 0V charging memory (disturbance of potential) is received, the surface potential of this memory effect region is converged to near OV by the action of the auxiliary charger 6. Therefore, the residual toner on the photosensitive drum 1 is not strongly charged by the auxiliary charging device 6, and is sufficiently cleaned by the cleaning device 7. Even if the photosensitive drum 1 is primarily charged thereafter, the photosensitive drum 1 is not charged. The effect of the memory effect does not appear above, and the photosensitive drum 1 can be uniformly and primarily charged.

In FIG. 17, the transfer electrode value of the transfer charger 10 is +.
Transition of the surface potential of the photosensitive drum 1 when the value of the DC bias voltage Vdc of the auxiliary charger 6 is set to -300 V and when it is set to +200 V when set to 200 μA. Are shown in comparison. When the DC bias voltage Vdc is −300 V, the surface potential of the memory effect region after auxiliary charging by the auxiliary charger 6 is −3.
Since this is converged to a value near 00V, the memory effect area is uniformly primary-charged by the charge-removing exposure, but the residual toner on the photosensitive drum 1 is strongly charged by the auxiliary charger 6, and therefore remains. The adhesion of the toner to the photosensitive drum 1 increases, the residual toner cannot be sufficiently cleaned by the cleaning device 7, and defective cleaning occurs.

On the other hand, when the DC bias voltage Vdc of the auxiliary charger 6 is set to +200 V according to the transfer current value,
Since the surface potential of the memory effect area after the auxiliary charging is converged to a value near OV, the residual toner on the photosensitive drum 1 is sufficiently cleaned, and this memory effect area is also uniformly primary-charged. .

FIG. 18 shows the transfer charger 10 in this embodiment.
The control value of the DC bias voltage Vdc of the auxiliary charger 6 with respect to the transfer current value of No. From the figure, it can be seen that the DC bias voltage Vdc has a large negative value when the transfer current value becomes large, and the DC bias voltage Vdc moves from 0 to the positive side when the transfer current value becomes small. Then, according to the transfer current value, a superposed voltage having a DC bias voltage value Vdc on the graph is applied to the photosensitive drum 1 via the auxiliary charger 6, so that the surface potential of the photosensitive drum 1 after the transfer has a memory effect region and Always 0V in normal area
It will be controlled in the vicinity.

As described above, the toner image on the photosensitive drum 1 is transferred onto the transfer material P via the transfer material carrying sheet 5b of the transfer drum 5.
When transfer is performed by the transfer charger 10, the potential disturbance called the memory effect occurs on the photosensitive drum 1 after the transfer. Even in such a case, the auxiliary charger is provided between the transfer charger 10 and the cleaning device 7. 6 is provided, and the value of the DC bias voltage Vdc applied to the photosensitive drum 1 is set to the transfer charger 10.
Since it is controlled by the transfer current value, the surface potential of the photosensitive drum 1 in the memory effect area after transfer can be converged to near 0V. Therefore, in the next primary charging, the photosensitive drum 1 can be uniformly charged without leaving the influence of the memory effect on the photosensitive drum 1 at all, and at the time of cleaning the residual toner, the residual toner is removed by the auxiliary charger 6. Therefore, the photosensitive drum 1 can be sufficiently cleaned without causing cleaning failure.

Further, in the electrophotographic copying machine having the four image units shown in FIG. 10 and capable of forming a full-color image, and the electrophotographic laser beam printer shown in FIG. DC bias voltage Vdc
If the value of is controlled according to the transfer current value of the transfer charger 10, the same effects as those of the electrophotographic copying machine having the rotary developing device 4 can be obtained in these image forming apparatuses.

In the above embodiment, the case where the corona charger is used as the transfer means has been described. However, the transfer means is not limited to this, and the brush type transfer means 30 as shown in FIG. Even if a contact type transfer unit such as the roller type transfer unit 31 as shown in FIG. 3 is used, the same effect as in the case of the corona charger can be obtained. Furthermore,
Although the auxiliary charger 6 is controlled according to the transfer current value of the transfer charger 10 in the above-described embodiment, the same effect can be obtained by controlling the auxiliary charger 6 according to the voltage applied to the transfer charger 10, for example. it can. In addition, the fourth of the first invention
Matters described in the embodiments, for example, the charging method of the photosensitive drum 1 by the auxiliary charger 6 (charging to a value slightly lower or higher than 0V), the method of controlling the auxiliary charger 6 by a control function other than the DC bias voltage Vdc. The type of voltage applied to the auxiliary charger 6 and the application of the invention to other image forming apparatuses are also applicable to the invention. [Third Invention] Next, an embodiment of the third invention will be described with reference to FIGS. The present invention intends to eliminate the potential disturbance caused by the memory effect on the photosensitive drum after the transfer by the auxiliary charger whose DC bias voltage and the like are controlled by the transfer charging condition and the number of multiple transfer. Therefore, the image forming apparatus to which the present invention is applied is applied to an image forming apparatus capable of forming a multicolor image including a full color image in which a plurality of toner images are transferred to the same transfer material in an overlapping manner. . Hereinafter, description will be given by taking as an example an electrophotographic copying machine capable of forming a color image having the rotary developing device 4 shown in FIG.

In the explanation part of the second invention, it will be explained with reference to FIG. 15 and the like that the disturbance of the potential caused by the memory effect on the photosensitive drum 1 after the transfer is remarkably changed depending on the transfer charging condition by the transfer charger 10. For example, although the auxiliary charger 6 is controlled by the transfer current value to eliminate the potential disturbance caused by the memory effect on the photosensitive drum 1, an image in which a plurality of toner images are transferred in multiple transfer onto the same transfer material P is obtained. In the case of the forming apparatus, in order to remove the potential disturbance caused by the memory effect on the photosensitive drum 1, it is necessary to control the auxiliary charger 6 in consideration of the number of times of multiple transfer as well as the transfer charging condition. Crossed

For example, in FIG. 20, for the first color (toner image with yellow toner) to the fourth color (toner image with black toner), the surface potential of the photosensitive drum 1 and the transfer of the transfer charger 10 in the memory effect area for each color. The relationship with the current value is shown. From this figure, it is understood that the magnitude of the potential disturbance due to the memory effect on the photosensitive drum 1 differs not only by the transfer current value but also by the number of times of multiple transfer (for each toner image of different colors). That is, it can be seen that the surface potential of the photosensitive drum 1 in the memory effect region increases with the transfer current value, but decreases with the number of times of multiple transfer.

Therefore, in an image forming apparatus in which toner images are transferred multiple times, in order to eliminate the potential disturbance due to the memory effect generated on the photosensitive drum 1, the transfer charging condition at the time of transfer and the number of times of multiple transfer are set. Therefore, it becomes necessary to apply a predetermined voltage to the photosensitive drum 1. That is, as shown in FIG. 19, between the cleaning device 7 and the transfer charging device 10 in the transfer drum 5, the photosensitive drum 1 after the transfer is transferred.
An auxiliary charger 6 as a decharging means for decharging
A bias voltage in which a DC voltage and an AC voltage are superimposed is applied from the DC power supply 17 and the AC power supply 18 to the auxiliary charging device 6, and the transfer charging condition of the transfer charging device 10, in this case, the transfer current value, and A control unit 41 for controlling the DC power supply 17 is provided according to the number of times of multiple transfer, and the DC bias voltage of the auxiliary charger 6 is changed by this control unit 41 to eliminate the potential disturbance caused by the memory effect on the photosensitive drum 1. I did it.

For example, the DC bias voltage Vdc from the DC power supply 17 is a variable voltage of -1 kV to +2 kV,
The AC bias voltage Vac from the AC power supply 18 has a frequency Vf.
= 500 Hz, peak-to-peak voltage Vpp = 10 kV.

Next, the operation of the auxiliary charger 6 will be described with reference to FIGS. FIG. 21 shows the control values of the DC bias voltage Vdc of the auxiliary charger 6 with respect to the transfer current value of the transfer charger 10 in the present embodiment from the first color (for example, when a toner image of yellow toner is transferred) to the fourth color. 6 is a graph showing up to (for example, when a toner image is transferred with black toner) as parameters.

As shown in the figure, when the transfer current value for each color increases, the DC bias voltage Vdc increases to a negative value, and when the transfer current value decreases, the DC bias voltage Vdc decreases.
It can be seen that is shifted from 0 to the positive side, and that the above tendency is increased as the number of times of multiple transfer is increased. Then, depending on the number of times of multiple transfer, the auxiliary charger 6
If a superposed voltage having a DC bias voltage Vdc on this graph is applied to the photosensitive drum 1 via the, the surface potential of the photosensitive drum 1 after transfer is controlled to be near 0 V in both the memory effect area and the normal area. Become.

Further, FIG. 1 performed in relation to the second invention.
The description of No. 6 is also applicable to this embodiment by using the DC bias voltage Vdc shown in FIG. 20, and similarly, the description of FIG. 17 is also performed with the same number of multiple transfers. The present embodiment applies to the case where the current value is made different, or the number of times of multiple transfer is made different while keeping the same transfer current value. Therefore, also in this embodiment, the residual toner on the photosensitive drum 1 is not strongly charged by the auxiliary charger 6.
Even if the photosensitive drum 1 is fully charged by the cleaning device 7 and then the photosensitive drum 1 is primarily charged,
The effect of the memory effect does not appear above, and the photosensitive drum 1 can be uniformly charged.

Further, FIG. 22 shows the transition of the surface potential of the memory effect area of the photosensitive drum 1 after the transfer of the first, second, third and fourth colors in this embodiment.
In this figure, the value of the DC bias voltage Vdc of the auxiliary charger 6 is changed according to the transfer current value for each color shown in FIG. 20 (solid line), and the DC bias voltage for the transfer current value of the first color is applied to all of them. The case where the value of the voltage Vdc is used (broken line) is shown. From the figure, in the case of the solid line in which the value of the DC bias voltage Vdc of the auxiliary charger 6 is changed according to the transfer current value and the number of times of multiple transfer shown in FIG. 20, the photosensitive drum 1 in the memory effect area after auxiliary charging is shown. Has a surface potential of 0
It can be seen that the voltage converges near V, but in the case of the broken line using only the value of the DC bias voltage Vdc for the transfer current value of the first color, the surface potential of the photosensitive drum 1 in the memory effect area after auxiliary charging is multiple. It can be seen that as the number of times of transfer increases, it becomes larger on the minus side.

As described above, the toner image on the photosensitive drum 1 is transferred onto the transfer material P via the transfer material carrying sheet 5b of the transfer drum 5.
When transfer is performed by the transfer charger 10, the potential disturbance called the memory effect occurs on the photosensitive drum 1 after the transfer. Even in such a case, the auxiliary charger is provided between the transfer charger 10 and the cleaning device 7. 6 is provided, and the value of the DC bias voltage Vdc applied to the photosensitive drum 1 is set to the transfer charger 10.
Since it is controlled by the transfer current value and the number of times of multiple transfer, the surface potential of the photosensitive drum 1 in the memory effect area after transfer can be converged to near 0V. Therefore, in the next primary charging, the photosensitive drum 1 can be uniformly charged without leaving the influence of the memory effect on the photosensitive drum 1 at all, and at the time of cleaning the residual toner, the residual toner is removed by the auxiliary charger 6. Therefore, the photosensitive drum 1 can be sufficiently cleaned without causing cleaning failure.

Also in the electrophotographic copying machine having four image units shown in FIG. 10 and capable of forming a full-color image, each image unit 2 having a different number of multiple transfer times.
If the value of the DC bias voltage Vdc of the auxiliary charger 6 is controlled in accordance with the transfer current value of the transfer charger 10 for each two, the image forming apparatus such as this also has an electronic device including the rotary developing device 4. It is possible to obtain the same effect as the photocopier.

In the above embodiment, the case where the corona charger is used as the transfer means has been described. However, the transfer means is not limited to this. For example, the brush type transfer means 30 as shown in FIG. Even if a contact type transfer unit such as the roller type transfer unit 31 as shown in FIG. 3 is used, the same effect as in the case of the corona charger can be obtained. further,
Although the auxiliary charger 6 is controlled according to the transfer current value of the transfer charger 10 in the above-described embodiment, the same effect can be obtained by controlling the auxiliary charger 6 according to the voltage applied to the transfer charger 10, for example. it can. In addition, the fourth of the first invention
The matters described in the embodiments, for example, the charging method of the photosensitive drum 1 by the auxiliary charger 6 (charging to a value slightly lower or higher than 0V), the control method of the auxiliary charger 6 based on a control function other than the DC bias voltage Vdc. The type of voltage applied to the auxiliary charger 6 and the application of the invention to other image forming apparatuses are also applicable to this embodiment.

Further, the present invention is not limited to an image forming apparatus capable of forming a multicolor image having different colors, and a plurality of toner images (developed images) having the same color but different image forming conditions are formed on the same transfer material P. It goes without saying that the present invention is also applicable to an image forming apparatus that transfers (multi-transfers) images on top of each other. [Invention 4] Next, an embodiment of the fourth invention will be described with reference to FIGS.
The description will focus on 0. The present invention is intended to eliminate potential disturbance caused by a memory effect on a photosensitive drum after transfer by an auxiliary charger whose DC bias voltage and the like are controlled by the value of the potential contrast of the photosensitive drum. First, an explanation will be given by taking as an example an electrophotographic copying machine capable of forming a full-color image having the rotary developing device 4 shown in FIG.

FIG. 24 shows the relationship between humidity and image density, for example, and it can be seen from the figure that the image density increases as the humidity increases, and that the image density changes depending on the type of image formed. Further, FIG. 25 shows that when the humidity is constant, the image density is the value of the potential contrast, that is, the dark portion potential Vd (primary charger 2) and the light portion potential V of the photosensitive drum 1.
It can be seen that it changes depending on the difference (Vd-Ve) from e (potential of exposed portion). Therefore, in order to obtain a desired image density, it is necessary to change the value of the potential contrast according to the surrounding environmental conditions. For this reason, the image forming apparatus according to the present embodiment is provided with the environment detection sensor, the optimum value of the potential contrast is calculated according to the output value, and the electrostatic latent image is formed on the photosensitive drum 1 based on the value of the potential contrast. Are formed. On the other hand, according to the applicant's experimental research,
It was found that the potential disturbance due to the memory effect that occurs on the photosensitive drum 1 after transfer is significantly changed depending on the value of the potential contrast of the electrostatic latent image formed on the photosensitive drum 1.
For example, in FIG. 26, the potential contrast values of the electrostatic latent image on the photosensitive drum 1 are 400V, 460V, 530V, and 6V, respectively.
The surface potential of the memory effect area of the photosensitive drum 1 after transfer is shown for the case of 00 V. From this figure, the potential disturbance due to the memory effect on the photosensitive drum 1 depending on the value of the potential contrast is shown. , It is understood that their sizes are different.

Therefore, in order to eliminate the potential disturbance caused by the memory effect on the photosensitive drum 1, the photosensitive drum 1 is predetermined according to the value of the potential contrast of the electrostatic latent image formed on the photosensitive drum 1. It becomes necessary to apply the voltage of. That is, as shown in FIG. 23, between the cleaning device 7 and the transfer charging device 10 in the transfer drum 5, an auxiliary charging device 6 as a decharging means for destaticizing the photosensitive drum 1 after transfer is provided. A bias voltage in which a DC voltage and an AC voltage are superimposed is applied from the DC power supply 17 and the AC power supply 18 to the charger 6, and the DC power supply 17 is applied in accordance with the value of the potential contrast of the electrostatic latent image on the photosensitive drum 1.
The control unit 42 for controlling the
The DC bias voltage of the auxiliary charger 6 was changed to remove the potential disturbance caused by the memory effect on the photosensitive drum 1.

For example, the DC bias voltage Vdc from the DC power supply 17 is a variable voltage of -1 KV to +2 KV, and the AC bias voltage Vac from the AC power supply 18 has a frequency Vf =
It is set to 500 Hz and peak-to-peak voltage Vpp = 10 kV.

Next, the operation of the auxiliary charger 6 will be described with reference to FIGS. 27 to 30. FIG. 26 shows the transition of the surface potential of the photosensitive drum 1 when the value of the potential contrast of the electrostatic latent image on the photosensitive drum 1 is set to 400V. In this case, the DC bias voltage Vdc of the auxiliary charger 6 is -300.
It is controlled by V. Under the above conditions, the photosensitive drum 1 is about +1 by the action of the transfer charger 10 during transfer or the like.
Although it receives a charging memory (disturbance of potential) of 00V to + 700V, the surface potential of this memory effect region is converged to near OV by the action of the auxiliary charger 6. Therefore, the residual toner on the photosensitive drum 1 is not significantly charged by the auxiliary charging device 6, and is sufficiently cleaned by the cleaning device 7, and then the photosensitive drum 1 is
Even if the secondary charging is performed, the effect of the memory effect does not appear on the photosensitive drum 1, and the photosensitive drum 1 can be uniformly primary charged.

FIG. 28 shows that when the value of the potential contrast of the electrostatic latent image on the photosensitive drum 1 is set to 600 V, the value of the DC bias voltage Vdc of the auxiliary charger 6 is set to −
The transition of the surface potential of the photosensitive drum 1 when the voltage is set to 300 V and when the voltage is changed to +200 V is shown for comparison. When the DC bias voltage Vdc is −300 V, the surface potential of the memory effect area after the auxiliary charging by the auxiliary charger 6 is converged to a value near −300 V, and therefore, the memory effect area is subjected to the static elimination exposure. Is uniformly primary-charged, but since the residual toner on the photosensitive drum 1 is strongly charged by the auxiliary charging device 6, the adhesion of the residual toner to the photosensitive drum 1 is increased, and the cleaning device 7 cleans the residual toner. Cannot be sufficiently performed, resulting in poor cleaning.

On the other hand, when the DC bias voltage Vdc of the auxiliary charger 6 is set to +200 V according to the value of the potential contrast, the surface potential of the memory effect area after the auxiliary charging is O.
Since it is converged to a value near V, the residual toner on the photosensitive drum 1 is sufficiently cleaned, and this memory effect area is also uniformly primary-charged.

FIG. 29 shows the auxiliary charger 6 for the value of the potential contrast of the electrostatic latent image on the photosensitive drum 1 in this embodiment.
The control value of the DC bias voltage Vdc by the control unit 42 is shown. When the value of the potential contrast becomes larger than the figure, the DC bias voltage Vdc shifts from 0 to the positive side,
It can be seen that the DC bias voltage Vdc moves to the negative side when the value of the potential contrast decreases. And
If the DC bias voltage value Vdc on this graph is applied to the auxiliary charger 6 according to the value of the potential contrast, the surface potential of the photosensitive drum 1 after transfer is always controlled to be near 0 V in both the memory effect area and the normal area. It will be.

In FIG. 30, the value of the potential contrast of the electrostatic latent image on the photosensitive drum 1 in this embodiment is 400V, 460.
29 shows the transition of the surface potential of the memory effect area of the photosensitive drum 1 in the case of V, 530 V and 600 V. In this figure, the value of the DC bias voltage Vdc of the auxiliary charger 6 is shown in FIG.
When the value is changed according to the value of the potential contrast indicated by (solid line), the value of the potential contrast is 400 in all cases.
The case where the value of the DC bias voltage Vdc in the case of V is used (broken line) is shown. From the figure, in the case of the solid line in which the value of the DC bias voltage Vdc of the auxiliary charger 6 is changed according to the value of the potential contrast shown in FIG. 28, the surface potential of the photosensitive drum 1 in the memory effect area of the auxiliary charging is near 0V. However, in the case of the broken line using only the value of the DC bias voltage Vdc when the value of the potential contrast is 400 V, the surface potential of the photosensitive drum 1 in the memory effect area after the auxiliary charging is It can be seen that as the value of the potential contrast of the electrostatic latent image on the photosensitive drum 1 increases, it increases toward the minus side.

As described above, the toner image on the photosensitive drum 1 is transferred onto the transfer material P via the transfer material carrying sheet 5b of the transfer drum 5.
When transfer is performed by the transfer charger 10, the potential disturbance called the memory effect occurs on the photosensitive drum 1 after the transfer. Even in such a case, the auxiliary charger is provided between the transfer charger 10 and the cleaning device 7. 6 is provided and the value of the DC bias voltage Vdc applied to the photosensitive drum 1 is controlled by the value of the potential contrast of the electrostatic latent image on the photosensitive drum 1, so that the photosensitive drum 1 in the memory effect area after the transfer is transferred. The surface potential can be converged to around 0V. Therefore, in the next primary charging, the photosensitive drum 1 can be uniformly charged without leaving the influence of the memory effect on the photosensitive drum 1 at all, and at the time of cleaning the residual toner, the residual toner is removed by the auxiliary charger 6. Therefore, the photosensitive drum 1 can be sufficiently cleaned without causing cleaning failure.

Further, in the electrophotographic copying machine having the four image units shown in FIG. 10 and capable of forming a full-color image, and in the electrophotographic laser beam printer shown in FIG. 11, the auxiliary charger 6 is used. DC bias voltage Vdc
If the value of is controlled according to the value of the potential contrast of the electrostatic latent image on the photosensitive drum 1, these image forming apparatuses have the same effect as the electrophotographic copying machine having the rotary developing device 4. Obtainable.

In the above embodiment, the case where the corona charger is used as the transfer means has been described, but the transfer means is not limited to this, and for example, the brush type transfer means 30 as shown in FIG. Even if a contact type transfer unit such as the roller type transfer unit 31 as shown in FIG. 3 is used, the same effect as in the case of the corona charger can be obtained. Other,
The matters described in the fourth embodiment of the first invention, for example, the charging method of the photosensitive drum 1 by the auxiliary charger 6 (charging to a value slightly lower or higher than 0V), the DC bias voltage Vdc
The control method of the auxiliary charger 6 by the control function other than the above, the application of the invention to other image forming apparatuses, and the like are also applied to this embodiment.

In the first invention, based on the potential of the electrostatic latent image on the photosensitive drum 1, in the second invention, the transfer charger 10 is used.
The auxiliary charging device is based on the transfer charging condition of the third invention, the transfer charging condition and the number of times of multiple transfer in the third invention, and the electric potential of the electrostatic latent image of the photosensitive drum 1 in the fourth invention. Although the DC bias voltage Vdc of 6 is controlled, the DC bias voltage Vdc of the auxiliary charger 6 may be controlled based on a combination of two or more of them.

[0094]

According to the first aspect of the invention, in removing the potential disturbance (due to the memory effect) on the image carrier due to transfer by the decharging means, the decharging condition of the decharging means is set on the image carrier. Since the control is performed on the basis of the potential of the electrostatic latent image of, even if the disturbance of the potential changes according to the potential of the electrostatic latent image of the image bearing member, the potential of the potential generated on the image bearing member by the decharging means is changed. Disturbance can be removed sufficiently. Therefore, in such an image forming apparatus, even if the potential of the image carrier is disturbed due to the memory effect, the image defect does not occur in the image and the cleaning defect does not occur in the image carrier.

In the second aspect of the present invention, when the disturbance of the electric potential generated on the image carrier by the transfer is removed by the decharging means, the decharging condition of the decharging means is controlled based on the transfer charging condition of the transfer means. Therefore, even if the disturbance of the potential changes according to the transfer charging condition of the transfer unit,
By this decharging means, it is possible to sufficiently remove the disturbance of the potential generated on the image carrier. Therefore, in such an image forming apparatus, even if the potential of the image carrier is disturbed due to the memory effect, the image defect does not occur in the image and the cleaning defect does not occur in the image carrier.

In the third aspect of the present invention, when removing the disturbance of the potential generated on the image carrier by the decharging means by the decharging means, the decharging conditions of the decharging means are the transfer charging conditions of the transfer means and the number of times of multiple transfer. Therefore, even if the potential irregularity changes according to the transfer charging condition of the transfer unit and the number of times of multiple transfer, the destaticizing unit can sufficiently remove the potential irregularity generated on the image carrier. . Therefore, in such an image forming apparatus, even if the potential of the image carrier is disturbed due to the memory effect, the image defect does not occur in the image and the cleaning defect does not occur in the image carrier.

In the fourth aspect of the present invention, when removing the disturbance of the potential generated on the image carrier by transfer by the decharging means, the decharging condition of the decharging means is set to the potential contrast of the electrostatic latent image on the image carrier. Since the control is performed based on the value of, even if the potential disturbance changes according to the value of the potential contrast of the electrostatic latent image on the image carrier, the potential disturbance generated on the image carrier by the decharging means is prevented. Can be fully removed. Therefore, in such an image forming apparatus, even if the potential of the image carrier is disturbed due to the memory effect, the image defect does not occur in the image and the cleaning defect does not occur in the image carrier.

[Brief description of drawings]

FIG. 1 is an explanatory diagram around a photosensitive drum and a transfer drum of an image forming apparatus according to a first exemplary embodiment of the first invention.

FIG. 2 is a side view of a main part of the image forming apparatus.

FIG. 3 is an explanatory diagram around a primary charger of the image forming apparatus.

FIG. 4 is a perspective view of a transfer drum of the image forming apparatus.

FIG. 5 is a diagram showing a surface potential of a memory effect area or the like of a photosensitive drum according to a primary charging potential of the image forming apparatus.

FIG. 6 is a diagram showing a transition of a surface potential of a photosensitive drum 1 having a memory effect area of the image forming apparatus.

FIG. 7 is a diagram comparing and comparing changes in surface potential of a photosensitive drum having a memory effect region of the image forming apparatus.

FIG. 8 is a diagram showing a control value of a DC bias voltage of an auxiliary charger according to a primary charging potential of the image forming apparatus.

FIG. 9 is a diagram showing a comparison of surface potentials of a memory effect area and the like of a photosensitive drum according to a primary charging potential of the image forming apparatus.

FIG. 10 is a side sectional view of an image forming apparatus according to a second embodiment of the first invention.

FIG. 11 is a side sectional view of an image forming apparatus according to a third embodiment of the first invention.

FIG. 12 is an explanatory diagram around a photosensitive drum and a transfer drum of an image forming apparatus according to a fourth embodiment of the first invention.

FIG. 13 is a second explanatory diagram around the photosensitive drum and the transfer drum of the image forming apparatus.

FIG. 14 is an explanatory diagram around a photosensitive drum and a transfer drum of an image forming apparatus according to an embodiment of the second invention.

FIG. 15 is a diagram showing a relationship between a transfer current value of the image forming apparatus and a surface potential of a photosensitive drum having a memory effect area.

FIG. 16 is a diagram showing a transition of a surface potential of a photosensitive drum having a memory effect area of the image forming apparatus.

FIG. 17 is a diagram comparing and comparing changes in the surface potential of the photosensitive drum having the memory effect region of the image forming apparatus.

FIG. 18 is a diagram showing the control value of the DC bias voltage of the auxiliary charger with respect to the transfer current value of the image forming apparatus.

FIG. 19 is an explanatory diagram around a photosensitive drum and a transfer drum 5 of an image forming apparatus according to an embodiment of the third invention.

FIG. 20 is a diagram showing a relationship between a transfer current value for each color of the image forming apparatus and a surface potential of a photosensitive drum in a memory effect area.

FIG. 21 is a diagram showing, for each color, the control value of the DC bias voltage of the auxiliary charger according to the transfer current value of the image forming apparatus.

FIG. 22 is a diagram showing a comparison of surface potentials of a memory effect area and the like of the photosensitive drum for each color of the image forming apparatus.

FIG. 23 is an explanatory diagram around a photosensitive drum and a transfer drum of an image forming apparatus according to an embodiment of the fourth invention.

FIG. 24 is a diagram showing a relationship between humidity and image density of the image forming apparatus.

FIG. 25 is a diagram showing a relationship between potential contrast and image density of the image forming apparatus.

FIG. 26 is a diagram showing a surface potential of a memory effect area or the like of a photosensitive drum according to a potential contrast of the image forming apparatus.

FIG. 27 is a diagram showing a transition of the surface potential of a photosensitive drum having a memory effect area of the image forming apparatus.

FIG. 28 is a diagram showing, in comparison, changes in surface potential of a photosensitive drum having a memory effect region of the image forming apparatus.

FIG. 29 is a diagram showing a control value of the DC bias voltage of the auxiliary charger according to the potential contrast of the image forming apparatus.

FIG. 30 is a diagram showing a comparison of the surface potentials of the memory effect region of the photosensitive drum and the like according to the potential contrast of the image forming apparatus.

FIG. 31 is a diagram for explaining a memory effect of a conventional image forming apparatus.

FIG. 32 is another diagram for explaining the memory effect of the image forming apparatus.

FIG. 33 is a diagram showing a transition of the surface potential of a photosensitive drum having a memory effect area of the image forming apparatus.

FIG. 34 is another diagram showing the transition of the surface potential of the photosensitive drum having the memory effect region of the image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum (image carrier) 6 Auxiliary charger (decharging means) 7 Cleaning device (cleaning means) 10 Transfer charger (transfer means) 19 Control section (control means) 30 Brush type transfer means (transfer means) 31 Roller Type transfer means (transfer means) 40 control section (control means) 41 control section (control means) 42 control section (control means)

Claims (20)

[Claims] 1. A developing device, which is formed by developing an electrostatic latent image on an image carrier, is transferred by a transfer device, and then a residual developer on the image carrier is cleaned by a cleaning device. In the image forming apparatus in which the disturbance of the electric potential generated on the image carrier by the transfer is removed by the decharging unit before the post-transfer cleaning, the decharging condition of the decharging unit is set to the electrostatic latent image on the image carrier. An image forming apparatus comprising: a control unit that controls based on an image potential. 2. The image forming apparatus according to claim 1, wherein the potential of the electrostatic latent image on the image carrier is a light portion potential or a dark portion potential of the electrostatic latent image. 3. The decharging means is a corona charger,
3. The image forming apparatus according to claim 1, wherein the corona charger is imprinted with either a DC bias voltage or an AC bias voltage, or a superimposed voltage of both. 4. The decharging condition to be controlled by the decharging means is any one of a DC bias voltage, an AC bias voltage amplitude value, an AC bias voltage frequency, an AC bias voltage duty ratio, and a decharging current value. 4. The image forming apparatus according to claim 3, wherein the image forming apparatus comprises two or more of them. 5. The image forming apparatus according to claim 1, wherein the transfer unit is a corona charger or a contact charger. 6. The image forming apparatus according to claim 1, wherein the decharging condition of the decharging unit is also controlled based on the printing voltage or the charging current of the transfer unit. 7. The residual image developer on the image carrier is cleaned after the developed image formed on the image carrier is transferred by a transfer means, and the image carrier is transferred by the transfer before cleaning. In the image forming apparatus in which the disturbance of the electric potential generated in the body is removed by the decharging means, a control means for controlling the decharging condition of the decharging means based on the transfer charging condition of the transfer means is provided. Image forming apparatus. 8. The transfer means is a corona charger or a contact charger, and the transfer charging condition of the transfer means is a printing voltage to the transfer means or a charging current of the transfer means. The image forming apparatus according to claim 7. 9. The decharging means is a corona charger,
9. The image forming apparatus according to claim 7, wherein the corona charger is imprinted with either a DC bias voltage or an AC bias voltage, or a superimposed voltage of both. 10. A de-charging condition to be controlled by the de-charging means is a DC bias voltage, an amplitude value of an AC bias voltage,
10. The image forming apparatus according to claim 9, wherein the image forming apparatus comprises any one of the frequency of the AC bias voltage, the duty ratio of the AC bias voltage, and the current value of decharging, or a combination of two or more thereof. 11. The residual developer on the image carrier is cleaned after the developed image formed on the image carrier is transferred by a transfer unit, and after the transfer, before cleaning.
In an image forming apparatus in which the disturbance of the electric potential generated on the image carrier due to the transfer is removed by the decharging means, and the developed image is transferred multiple times over the same transfer material in multiple layers to form an image. An image forming apparatus comprising: a control unit that controls the decharging condition of the decharging unit based on the transfer charging condition of the transfer unit and the number of times of multiple transfer. 12. The image forming apparatus according to claim 11, wherein the multiple transferred transferred images are developed images having different colors. 13. The image forming apparatus according to claim 11, wherein the multiple transferred transferred images are developed images having the same color but different image forming conditions. 14. The transfer means is a corona charger or a contact charger, and the transfer condition of the transfer means is a printing voltage to the transfer means or a charging current of the transfer means. The image forming apparatus according to claim 11. 15. The decharging means is a corona charger, and the corona charger is imprinted with either a DC bias voltage or an AC bias voltage, or a superimposed voltage of both. The image forming apparatus according to claim 11 or 14. 16. A de-charging condition to be controlled by the de-charging means is a DC bias voltage, an amplitude value of an AC bias voltage,
16. The frequency of the AC bias voltage, the duty ratio of the AC bias voltage, the current value of the decharge, or a combination of two or more thereof.
The image forming apparatus described. 17. A developed image formed by developing an electrostatic latent image on an image carrier is transferred by a transfer means,
The residual developer on the image bearing member is cleaned by a cleaning unit, and after transfer and before cleaning,
In the image forming apparatus in which the disturbance of the potential generated on the image carrier by the transfer is removed by the decharging unit, the decharging condition of the decharging unit is set to the value of the potential contrast of the electrostatic latent image on the image carrier. An image forming apparatus comprising: a control unit that controls based on the above. 18. The decharging means is a corona charger, and the corona charger is imprinted with either a DC bias voltage or an AC bias voltage, or a superimposed voltage of both. The image forming apparatus according to claim 17. 19. The decharging condition to be controlled by the decharging means is a DC bias voltage, an amplitude value of an AC bias voltage,
19. The frequency of the AC bias voltage, the duty ratio of the AC bias voltage, the current value of the de-charging, or a combination of two or more thereof.
The image forming apparatus described. 20. The image forming apparatus according to claim 17, wherein the transfer unit is a corona charger or a contact charger.