JPH04128858A - Image forming device - Google Patents

Abstract

PURPOSE:To maintain the excellent efficiency of transfer without being affected by the environmental condition of a device and to obtain a transferred image with high image quality by controlling a bias voltage impressed on the electrode member of a toner image carrier so that a current flowing to the toner image carrier from a transfer means becomes a prescribed reference value. CONSTITUTION:A fine resistance 37 for converting a current to a voltage and a bias power source 38 whose voltage value can be changed are inserted between an electrode roller 10 and a ground so that they can be switched by a switch 36 and an amplifier circuit 35 for an output and a control part 31 are provided, besides. Then, the switch 36 is set to a terminal 36b at a preliminary rotating time and a prescribed voltage is impressed on a secondary transfer charger 25. At this time, the current I1 flowing to the roller 10 through an intermediate transfer belt 5 is measured by the resistance 37 as the voltage V1. The voltage V1 is amplified by the amplifier circuit 35 and compared with the reference voltage V0 which is previously stored in the control part 31 by the control part 31. Next, the bias voltage V' required for making the voltage V1 almost equal to the voltage V0 is calculated by the control part 31 and the voltage outputted by the bias power source 38 is changed to V'. Simultaneously, the switch 36 is switched to a terminal 36a and the power source 38 is connected to the roller 10. Besides, the charger 25 is turned off at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus using a toner image transfer type electrophotographic method.

Conventional technology Conventionally, in toner image transfer type electrophotographic copying machines,
The toner image formed on the photoreceptor is transferred from the back side of the transfer material to the transfer material by applying a charge with a polarity opposite to that of the toner using a transfer charger, or the toner image is temporarily transferred from the photoreceptor to the transfer material. After being transferred to a belt or drum, it is transferred to a transfer material (in the case of a pull color copying machine).

By the way, when transferring a toner image onto a transfer material,
It is preferable that the transfer efficiency is 100%, but in reality, the transfer efficiency decreases due to the installation environmental conditions of the copying machine (humidity, etc.), and if you try to compensate for this by adjusting the output of the transfer charger, The output of the transfer charger is large,
And it fluctuates randomly. Particularly, in a copying machine using an intermediate transfer belt, the above-mentioned problem becomes noticeable because the belt is relatively highly dependent on the environment.

Conventionally, in order to maintain good transfer efficiency, it has been proposed to control the output value of the transfer charger by detecting the humidity in the air (see Japanese Patent Publication No. 60-44662).
. However, transfer efficiency cannot always be well controlled simply by changing the output value of the transfer charger according to environmental conditions. Moreover, the output value of the transfer charger needs to be varied over a wide range at a high voltage of 2 to 3 kV, which poses a problem in control stability.

By the way, according to the experimental results of the present inventors, if the current flowing from the transfer charge to the toner image carrier is an appropriate value, good transfer characteristics can be obtained regardless of the output (applied voltage) of the transfer charge. It became clear that

OBJECTS, CONFIGURATION, AND OPERATIONS Therefore, an object of the present invention is to provide a method that has good transfer efficiency despite changes in environmental conditions, can obtain high-quality transferred images, and is capable of stable control. An object of the present invention is to provide an image forming apparatus that is capable of providing an image forming apparatus.

In order to achieve the above object, an image forming apparatus according to the present invention includes an electrode member that faces a transfer means via a toner image carrier, and a bias voltage that is applied to the electrode member so that the voltage value can be changed. tri, a means for measuring the current flowing from the transfer means to the electrode member via the toner image carrier, and a t current flowing to the electrode member based on the measured value by the measuring means to a predetermined reference value. The present invention is characterized by comprising means for controlling the bias power supply so that the bias power supply is controlled so that

The reference value of the current flowing to the electrode member is an amount of current experimentally determined in advance so as to obtain good transfer efficiency in a specific image forming apparatus.

Therefore, in an actual image forming apparatus, the current flowing from the transfer means to the electrode member via the toner image bearing member is measured.
By feeding back this measured value to the bias power source for the electrode member, an appropriate amount of current flows through the toner image carrier, and a transferred image with good transfer efficiency and high quality can be obtained. In addition, the bias voltage itself is low voltage,
The scope of change is also narrow.

Embodiments Hereinafter, embodiments of an image forming apparatus according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a full-color copying machine which is an embodiment of the present invention.A photosensitive drum 1, which can be rotated in the direction of arrow a, is surrounded by a charger 2, developing devices 4Y, 4M, and 4C.
, 4B, an intermediate transfer belt 5, a residual toner cleaning device 7, and a residual charge elimination lamp 8 are arranged.

A light image from a document placed on a document table glass (not shown) is irradiated onto the photosensitive drum 1 from the direction of the arrow by an optical system (not shown).

The developer 4Y contains yellow toner, the developer 4M contains magenta toner, the developer 4C contains cyan toner, and the developer 4B contains a black toner, each of which is selectively driven.

The intermediate transfer belt 5 includes rollers 10.11.12.13.
14 in an endless manner, and rotates in the direction of the arrow at the same speed as the photosensitive drum 1 based on the rotation of the drive roller 11. This intermediate transfer belt 5 has a volume resistance of lX1010
~1x1013Ωcm polyurethane rubber or EP
DM (ternary polymerization of ethylene, propylene, and diene components)
The terpolymer) was made into a belt shape with a thickness of about 600 μm, and a fluorine-based water-based paint with a volume resistance of about 1×109 to 1×1012 Ωcm was applied to the surface to a thickness of about 10 to 30 μm to provide smoothness and toner release properties. things are used.

The roller 10 functions as a counter electrode for secondary transfer, which will be described below. A primary transfer charger 6 is installed inside the intermediate transfer belt 5 at a position facing the photosensitive drum 1 . Further, around the intermediate transfer belt 5, a secondary transfer charger 25 and an AC separation charger 26 are provided.
is installed facing the electrode roller 10, and a residual toner cleaning device 15 is installed facing the backup roller 13.

On the other hand, 5, the transfer paper S is housed in an automatic paper feed cassette 20 that is removably attached to the copying machine, and a separating plate 22 that comes into pressure contact with the paper feed roller 21 as the paper feed roller 21 rotates in the direction of arrow d.
The sheets are separated one by one and fed to the secondary transfer section. The transfer paper conveyance path includes various guide plates and timing roller pairs 2.
3, a conveyor belt 27, and a fixing device 28.

In the above configuration, in monochrome copy mode,
A negative charge is uniformly applied to the surface of the photosensitive drum 10 by the charging charger 2, and an electrostatic latent image is formed by irradiating the original image from an optical system (not shown). This electrostatic latent image is transferred to developing devices 4Y and 4M.

The toner image is developed with toner positively charged by one of 4C and 4B selected in advance, and the toner image is transferred onto the intermediate transfer belt 5 by an electric field formed by the negative charges released from the primary transfer charger 6. The first transfer is made to Thereafter, the toner image is secondarily transferred onto the transfer paper S by an electric field formed by negative charges emitted from the second transfer charger 25.

After the secondary transfer, the transfer paper S is neutralized by the AC electric field formed by the AC separation charger 26, peeled off from the intermediate transfer belt 5, and after the toner is heat-fixed by the fixing device 28, it is discharged to a tray (not shown). be done.

On the other hand, in full-color copy mode, the original image is color-separated into yellow, magenta, cyan, and black images by the optical system, and each image is formed as an electrostatic latent image on the surface of the photoreceptor drum 1. , developing devices 4Y, 4M, 4C, having corresponding color toners,
4B, the images are sequentially primary transferred onto the intermediate transfer belt 5 and are superimposed. During this time, the transfer paper S is not fed, and the secondary transfer charger 25 and separation charger 2
6 also remains off. In addition, the cleaning device 1
5 also stops the toner scraping action. When the four types of toner images are superimposed on the intermediate transfer belt 5, the transfer paper S runs out of feeding, and the secondary transfer charger 25 and separation charger 2
6 is turned on, and the full-color toner image is secondarily transferred onto the transfer paper S.

By the way, in this embodiment, in order to maintain good transfer efficiency of the toner image, the electrode roller 1 is transferred from the secondary transfer charger 25 via the intermediate transfer belt 5 during secondary transfer.
The voltage value of the bias voltage applied to the electrode roller 10 is controlled so that the current flowing to zero always reaches a predetermined reference value regardless of changes in environmental conditions.

In other words, when we conducted a copying experiment using the above-mentioned copying machine, we found that what influences the transfer efficiency during secondary transfer is the transfer current flowing from the secondary transfer charger 25 to the intermediate transfer belt 5, and that this transfer IE flow It has been found that if the voltage is appropriately controlled, good transfer efficiency and high quality images can be obtained without the need to particularly control the voltage applied to the secondary transfer charger 25. If this transfer current is smaller than the reference value, the transfer efficiency will decrease, and if it is larger, discharge will occur and some toner will be unevenly charged, causing a decrease in the transfer efficiency and deterioration of image quality.

FIG. 2 shows the transfer current when a negative bias voltage is applied to the electrode roller 10, the horizontal axis shows the voltage [kV] applied to the secondary transfer charger 25, and the vertical axis shows the current flowing to the intermediate transfer belt 5. The transfer current [μA] is shown.

For example, the pressure applied to the secondary transfer charger 25 is 15k.
When V, the transfer current can be adjusted in the range of -30 to -7011A by changing the bias voltage in the range of θ to -600V. The transfer current, which serves as a reference value for obtaining good transfer characteristics, can be determined in advance experimentally. This value is
For example, if the voltage is -50 μA, by applying a bias voltage of -300 V to the electrode roller 10 under a charger applied voltage of -5 kV, it is possible to apply a bias voltage of -50 μA as a reference value.
A transfer current of 11 A is obtained.

However, the intermediate transfer belt 5 is relatively highly dependent on the environment, and the transfer flow changes depending on the environmental conditions during operation even if the setting conditions of the device are the same. Therefore, before the copying operation, the transfer current is measured and the measured value 1. By comparing I and a predetermined reference value of 1° and controlling the bias voltage so that the transfer current is approximately equal to the reference value I, good transfer characteristics can always be maintained.

In order to carry out such control, it is necessary to measure the transfer current and control the bias voltage.

Specifically, as shown in FIG. 1, a current is applied between the electrode roller 10 and the ground! Micro resistance 3 for converting into pressure
7 and a bias power supply 38 whose voltage value can be changed are inserted so as to be switchable by a switch 36, and an output amplification circuit 35 and a control section 31 are also provided. Measurement of the transfer current and control of the bias voltage are performed by pre-rotating the photosensitive drum 1 and the intermediate transfer belt 5 when the print switch is turned on. During this preliminary rotation, the switch 36 is set to the terminal 36b, and the secondary transfer charger 2
5, a predetermined voltage is applied. At this time, the electric current flowing to the electrode roller 10 via the intermediate transfer belt 5 is measured at the microresistance 37 as a voltage v1.

V, = LxΩ However, L:'ilE pole low crawling current Ω: resistance value of microresistance This voltage vI is amplified by the amplifier circuit 35, and is a reference voltage (2) which is stored in advance in the control section 31 here. Compare with.

Ve=IaXΩ However, engineering. 2.Reference current Next, in the control section 31, the voltage ■1 becomes the reference voltage ■. The bias voltage v' required to make the output voltage of the source 38 substantially equal to V' is calculated, and the bias is changed to V'. At the same time, the switch 36 is switched to the terminal 36a, the bias power supply 38 is connected to the electrode roller 10, and the secondary transfer charger 25
Turn off.

Through the above control, the current flowing through the intermediate transfer belt 5 can be controlled, and a transferred image with good transfer efficiency and high quality can be obtained without being influenced by the environmental conditions of the apparatus. Moreover, there is no need to control the high voltage applied to the transfer charger as in the prior art, and the bias voltage can be controlled within a low and narrow range of about 0 to 500 cm, resulting in rapid voltage control and excellent stability.

Furthermore, although the above explanation has been about adjusting the secondary transfer current, there is a correlation between the primary transfer current flowing to the transfer belt 5 due to the electric field formed by the primary transfer charger 6 and the secondary transfer current. There is a relationship. Therefore, the electric current that has been completely measured during preliminary rotation, and the secondary transfer charger 25 at that time.
By comparing the voltage applied to the current value, it is possible to estimate the optimum primary transfer current value without directly measuring it. Therefore, it is possible to also control the output of the primary transfer charger 6 based on the measurement results of the secondary transfer current during preliminary rotation.

Note that the image forming apparatus according to the present invention is not limited to the above-mentioned embodiments, and can be variously modified within the scope of the gist.

In particular, the transfer material may be not only plain paper but also special paper such as an OHP sheet.

Furthermore, the present invention is applicable not only to secondary transfer from an intermediate transfer belt, but also to transfer of a toner image from a photoreceptor to a transfer material.

Furthermore, the image exposure method may be a digital method using a laser beam instead of an analog method using visible light.

Effects of the Invention As is clear from the above explanation, according to the present invention, the bias voltage applied to the electrode member of the toner image carrier is adjusted so that the current flowing from the transfer means to the toner image carrier becomes a predetermined reference value. Since this is controlled, good transfer efficiency can be maintained at all times without being affected by the environmental conditions of the apparatus, and high-quality transferred images can be obtained.

Furthermore, the voltage to be controlled in the present invention is lower and narrower than the voltage applied to the transfer charger, allowing quick and stable control.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention, and FIG. 2 is a graph showing transfer current with respect to voltage applied to a transfer charger and bias voltage. 1... Photosensitive drum, 4Y, 4M, 4C, 4B.
...Developer, 5...Intermediate transfer belt, 6...Primary transfer charger, 10...Electrode roller, 25...Second transfer charger, 31...Control unit, 35.37...・
Transfer current measurement circuit parts, 36...switch, 38...
・Source of bias, S...transfer paper.

Claims (1)

[Claims] 1. An image forming device that transfers a toner image electrostatically supported on the surface of a toner image carrier onto a transfer material by applying an electric charge to the transfer material from the back surface of the transfer material using a transfer means. an electrode member facing the transfer means with the toner image carrier interposed therebetween; a bias power source for applying a bias voltage to the electrode member in a changeable voltage value; means for measuring the current flowing to the electrode member through the measuring means; and means for controlling the bias power supply so that the current flowing to the electrode member becomes a predetermined reference value based on the measured value by the measuring means. An image forming apparatus characterized by: