JPH01164980A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain stable transfer and separation performance by controlling a power source to be supplied to a separation means by output detecting the difference of current values between the current supplied to a transfer means and the current that flows in a shielding member. CONSTITUTION:A high voltage power source 6 for transfer is connected to a corona transfer device 3, and a transfer current It is detected by a transfer current detection circuit 8 as a detecting voltage et. Also, a conductive shield 4 is grounded via a shield current detection circuit 9, and a shield current Is is detected as a detecting voltage es. The voltages et and es are inputted to a subtractor 10, and a result (et-es) is outputted, and the output of a high voltage power source 7 for separation is controlled so that an optimum separation current IB corresponding to the above result can be supplied to a corona separator 5. In such a way, it is possible to always keep a supplied current value IB within an appropriate range even when the currents It and Is change, and to obtain the stable transfer and separation performance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming apparatus that uses an electrophotographic method, and includes a transfer device and a separation device that neutralizes the electric charge charged on the transfer material during transfer and separates the transfer material. Regarding those that have equipment,
In particular, it relates to a technique for always obtaining stable transfer performance and separation conveyance performance regardless of changes in the type, thickness, peripheral environment, etc. of the transfer material.

In an image forming apparatus that uses an electrophotographic method, a sheet-like transfer material is brought close to an image bearing member on which a toner image has been formed, and an electric charge of the opposite polarity to that of the toner is applied from the back side of the transfer material. 2. Description of the Related Art Image forming apparatuses are conventionally known that are configured to transfer a toner image onto a transfer material, then separate the transfer material carrying the toner image from an image carrier and convey it to the next process.

In this type of image forming apparatus, the transfer material after transfer is
In order to obtain a high-quality image, it is important to electrostatically separate the toner image carried by the transfer material from the image carrier so as not to disturb the toner image carried on the transfer material by a relatively weak adhesion force.

In order to separate the transfer material, there is a method of forcibly separating the transfer material from the image carrier at the post-transfer area using a separation claw, a separation belt, a separation roller, etc. Since tangential charging is carried out on the back side of the transfer material, the charge on the transfer material is further dissipated by applying a charge with the opposite polarity to that during transfer at the position after transfer.
Many methods have already been proposed, including electrostatic separation means that utilizes the elasticity and weight of the transfer material itself to separate it from the image carrier.

However, mechanical separation means, such as using separation claws, are inherently capable of forming images! Because members such as the image carrier, toner, and transfer material are appropriately charged during the holding and transfer process, the transfer material tends to be electrostatically attracted to the image carrier even at the separation site, and the transfer material Depending on the presence or absence of toner at the tip, the transfer material may tend to adhere strongly to the image carrier, and depending on the configuration of the separating claw and the speed of the image carrier, the claw may impact the transfer material with an impact. There was a risk that the leading edge of the transfer material would be damaged by coming into contact with it, and that the toner image would be disturbed.

Furthermore, electrostatic separation means is superior in that no mechanical force is locally applied to the transfer material as described above, but transfer materials, which are primarily paper, become charged due to changes in the environment. Changes occur in the characteristics, and furthermore, due to fluctuations in the discharge characteristics of the transfer charger and the separation charger, static removal after transfer becomes insufficient and there is a risk of poor separation.

After the toner image is transferred to the transfer material by an electrostatic transfer means, such as a corona transfer device, the transfer material is given an electric charge of the opposite polarity to that of the transfer, neutralizing the excess charge on the transfer material, and transferring the toner image to the transfer material. In an image forming apparatus having a separation means for separating the image carrier from the image carrier, for example, a corona separation device, in order to obtain good transfer performance and separation performance, it is necessary to reduce the amount of charge remaining on the transfer material when the transfer material is separated. It is important that it be approximately constant.

However, corona chargers ionize the surrounding air by applying a high voltage to a metal wire surrounded by a conductive shield. Since discharge is accompanied by ionization, the discharge current easily fluctuates depending on the surrounding environment, such as temperature and humidity, atmospheric pressure, or ion density. Furthermore, since the voltage around the wire is high, dirt and toner are strongly attracted to it, and the wire itself may be oxidized and worn out due to discharge, and the discharge current fluctuates depending on these factors.

Conventional electrostatic separation means supply a constant current to the corona separation device regardless of such environmental fluctuations, deterioration of the corona wire, etc. For this reason, it is not possible to adequately respond to variations in various conditions, resulting in problems such as poor separation or retransfer. For example, the value (It-1,
) and the current value (assumed to be In) supplied to the corona separation device to examine the transfer performance and separation performance, as shown in Figure 2, it is found that (It-1-) The appropriate range differs depending on the value, that is, the value of the amount of charge X that is substantially applied to the transfer material. Good transfer/separation is possible within this range, but in area A beyond this upper limit,
Compared to the amount of charge applied to the transfer material, the proportion of charge that is neutralized during separation is excessive, so good separation performance can be obtained, but due to the excess charge, the toner image on the transfer material may be distorted. , problems such as retransfer to the image carrier occur. In addition, in region B, which exceeds the lower limit, the adhesion between the transfer material and the image carrier decreases because the ratio of the amount of charge neutralized during separation is insufficient compared to the amount of charge applied to the transfer material. Large, resulting in poor separation.

As is clear from Fig. 2 above, the appropriate value of Is differs depending on the value of <1+-T-, and even if a is set to a certain appropriate value, due to the fluctuation of (rt-r,), the appropriate value of Is will vary. It may come off.

As a means to eliminate these defects,
There is a method disclosed in Japanese Patent No. 7335, which detects fluctuations in the discharge current of the transfer charger and optimally controls the voltage applied to the static elimination separation charger. However, although this method can cope with fluctuations in the discharge current caused by environmental changes and deterioration of the corona wire, it cannot cope with fluctuations in the discharge current caused by the type and thickness of the transfer material. Depending on the type of transfer material, each type has a volume resistivity,
Electrical characteristics such as inductivity are different, and characteristics also vary depending on the environment, and as a result, fluctuations in discharge current are inevitable. According to Japanese Unexamined Patent Publication No. 54-7335, since a detection electrode is provided in the transfer charger or at the end of the photosensitive drum as a means for detecting the transfer current, it is possible to detect the transfer current. , it is not possible to detect variations in the transfer current due to the type and thickness of the transfer material. This is because in the method of detecting the transfer current by providing a detection means at one end of the transfer charger, the detected value is affected by changes in load such as the thickness of the transfer paper.

1-” An object of the present invention is to eliminate the drawbacks of the above-mentioned conventional techniques and provide an image forming apparatus that has stable transfer and separation performance regardless of environmental changes, deterioration of the corona wire, type of transfer material, etc. That's true.

"-" In order to achieve the above object, the present invention includes a toner image carrier that carries an electrostatically formed toner image, and a conductive shield member that is installed in the vicinity of the toner image carrier. a transfer means for applying a charge having a polarity opposite to that of the toner image to a sheet-like transfer material and transferring the toner image to the transfer material; In an image forming apparatus, the image forming apparatus includes a separation means for applying electric charge to a material to neutralize the electric charge on the transfer material and separating the transfer material from the toner image bearing member, the current being supplied to the transfer means; The present invention is characterized in that a difference in current value from the current flowing into the shield member is detected, and the power supply to be supplied to the separation means is controlled based on the difference in current value.

Embodiments of the present invention will be described in detail below based on the drawings. In the drawings, the discharge polarities of the corona transfer device and the corona separation device are different from each other, and the current values are expressed in absolute values.

FIG. 1 is a control block diagram showing an embodiment of the present invention.

A transfer high-voltage power source 6 is connected to the corona transfer device 3, and a transfer current detection circuit 8 interposed therebetween detects a transfer current (2) as a detection voltage et. In addition, conductive shield 4
is grounded via the shield current detection circuit 9, and the shield current I3 is detected as the detection voltage es. These detected It,1. et, e, corresponding to is input to the subtracter 10, and the result (ei-es) is output. The output of the separation high-voltage power supply 7 is controlled so that an appropriate separation current IB corresponding to this (et-es) is supplied to the corona separation device 5. By such control, even if It and I- change, In can always be kept within the appropriate range shown in FIG. 2.

Note that by using a constant current output type high voltage power source for the transfer high voltage power source 6, the transfer current detection circuit 8 can be omitted, and the circuit can be simplified by inputting the reference voltage et corresponding to (2) to the subtracter 10. It is possible.

In addition, problems caused by timing shifts due to placement can be solved by, for example, providing a trigger gate in each current detection circuit.
This problem can be solved by appropriately designing the subtracter by adjusting the detection timing or the like.

Although the combination of the corona transfer device and the corona separation device has been described above, the present invention is not limited to the embodiments, and the present invention can be applied to electrostatic transfer and separation means. Further, the same applies when a separating means such as a separating claw or the like is used in combination as the separating means.

Circle-1 As described above, according to the present invention, it is possible to obtain stable transfer and separation performance regardless of environmental changes, deterioration of the corona wire, type and thickness of the transfer material, etc.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a control program diagram, and FIG. 2 is a curve diagram showing the appropriate range of separation current due to the difference between transfer current and shield current. ■... Toner image carrier, 2... Transfer material, 3... Corona transfer bag W (transfer means), 4... Conductive shield member, 5... Corona separation bag W (separation means) , 6... High voltage power supply for transfer, 7... High voltage power supply for separation, 8... Current detection circuit for transfer, 9... Shield current detection circuit, 1o... Subtractor 1st
Figure 2 H-Is (PA)

Claims (2)

[Claims] (1) A toner image carrier that carries an electrostatically formed toner image, and a conductive shield member that is installed close to the toner image carrier, and a sheet-like transfer material that carries the toner image. a transfer means for applying an electric charge with a polarity opposite to that of the electric charge and transferring the toner image to the transfer material; In an image forming apparatus having a separating means for separating the transfer material from the toner image carrier, the difference in current value between the current supplied to the transfer means and the current flowing into the shield member. Detects,
An image forming apparatus characterized in that the power supply to the separation means is controlled based on the difference in current value. (2) Claim 1, wherein the separation means is a corona separation device having a conductive fibrous electrode.
The image forming apparatus described in .