JPH05297735A - Image forming device - Google Patents

Abstract

PURPOSE:To provide an image forming device in which transfer can be steadily carried out without the influence of a change in environment such as temperature and humidity. CONSTITUTION:In the image forming device which is provided with a PCL 11, a scorotron electrifier 12, a laser writing device 13, a plurality of developing units 14, a transfer belt device 30, a cleaner 16, etc., around the periphery of a photosensitive drum 10 as an image carrier and which forms a multicolor toner image by repeating an electrification/image exposure/development process to superimpose toner images on the photosensitive drum 10, the transfer belt device 30 is provided with a brush 34, as a charge application means, on the upstream holding roller 32 of the transfer belt device 30, in the position where a sheet of recording paper P is made to enter, applies a constant bias voltage to the holding roller 32 irrespective of environmental conditions during the detection of a current value, detects the current during the passing of the sheet of recording paper P with the aid of the brush 34, and controls according to the result of the output of a power source in order to supply an optimum bias voltage or current to the transfer unit 36 of the transfer belt device 30.

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 copying machine and uses a transfer belt device having a rotating transfer belt to transfer a toner image obtained by developing a latent image on an image carrier. The present invention relates to an image forming apparatus that transfers a recording sheet having a toner image attached thereto onto a recording sheet by a physical means and then fixes the recording sheet.

[0002]

2. Description of the Related Art Many methods and apparatuses have been proposed for obtaining a multicolor image using electrophotography. One of them is
Latent images are formed on the photoconductor, which is an image carrier, according to the number of separated colors of the original image, and development with color toner is repeated. Methods for obtaining color images have been proposed and implemented. The basic process of this multicolor image formation is disclosed in Japanese Patent Application Laid-Open No. 60-75850 by the present applicant.
No. 60, No. 60-76766, No. 60-95456, No. 60-95458, No. 60
-158475, etc.

In the above-mentioned image forming apparatus for obtaining a multicolor image, since a plurality of developing devices are provided at the peripheral portion of the photosensitive drum for superimposing toner images on the photosensitive member, the drum diameter becomes large and the separation performance of the transfer material deteriorates. Sufficient separation performance cannot be obtained by the conventional electrostatic transfer separation method. Therefore, a more reliable separation means is required, and a large amount of transfer charge is required because the toner adhesion amount is large in the method of superposing toner images, so that it has a large transfer charge holding ability and good separation performance. A transfer belt device is preferably used.

The transfer belt device rotates a transfer belt, which is a conveying member stretched by a plurality of holding rollers, at the same speed as the photosensitive drum. The transfer belt device is provided with a charge applying unit that applies an electric charge to a recording sheet as a transfer material and attracts the recording sheet to the transfer belt by electrostatic force. In contact with the photoconductor drum, a high voltage having a polarity opposite to that of the toner charge is applied under constant current control in the transfer area to transfer the toner image. In such a transfer belt device, excellent transfer efficiency and separation effect can be obtained in the transfer section.

[0005]

In the image forming apparatus described above, when the installation place is a humid place or when it is used in a hot and humid season, the recording paper absorbs moisture to increase the water content and the resistance of the recording paper. The value fluctuates or the resistance value of the transfer belt fluctuates, and in the transfer of the toner image adhered on the photoconductor drum, the transfer is incomplete and the transferred image quality deteriorates. Further, there is a problem that the transfer current is insufficient under low humidity and the transfer of the toner image is insufficient.

As one method for solving such a problem, a measuring means for measuring the resistance value of the transfer material or the transfer material and the conveying member of the transfer belt device is provided, and the transfer condition is set from the measured value. Is being done. And
In order to simplify the power supply, the applicant has proposed a method of dividing a power supply output for applying a transfer electric field with a resistor or the like to obtain a bias voltage for attracting recording paper. Since the output is constantly changing depending on the environmental conditions, the measured value of the resistance value of the recording paper fluctuates, and there is a problem that complete control cannot be performed.

Even when a constant voltage is applied by another power source or the like, under high humidity or the like, the transfer power source passes from the transfer portion through the transfer paper or the belt and flows into the current detecting means, so that accurate detection cannot be performed.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide an image forming apparatus having a transfer belt device capable of excellent transfer without being affected by temperature and humidity.

[0009]

The above object is to repeat the steps of charging, image exposure and development to form a multicolor toner image by superimposing toner images on an image bearing member and transferring the multicolor toner image to a transfer material. In an image forming apparatus equipped with a transfer belt device that stretches and rotates between holding rollers for transferring to a transfer roller, a power source for applying a transfer electric field to the transfer material of the transfer belt device, and the transfer material or the transfer material. A detection means for detecting a current value that fluctuates depending on the resistance value of the material and the transfer member of the transfer belt device, and the output of the power supply is fixed to a constant value when the detection means operates, This is achieved by an image forming apparatus characterized in that the current value of the power source is changed to a value selected based on the result detected by the detecting means before entering the transfer area.

[0010]

FIG. 1 is a sectional view showing the arrangement of a color image forming apparatus as an embodiment of the image forming apparatus of the present invention, and FIG. 6 shows the potential of an image carrier at the time of forming a multicolor toner image according to this embodiment. It is a flowchart which shows a change. The basic configuration and operation of this embodiment will be described with reference to FIGS.

In FIG. 1, reference numeral 10 denotes a photosensitive drum which is an image bearing member, for example, an OPC photosensitive member coated on the drum, which is grounded and driven and rotated clockwise. A scorotron charger 12 has a negative VH (-
Uniform charge of 600 to -800V is applied to a predetermined potential VG (-550 to -850).
V) provided by a corona discharge with a grid and a corona discharge wire. This scorotron charger
Prior to charging by 12, a PCL 11 using a light emitting diode or the like to remove the history of the photoconductor until the previous printing
The peripheral surface of the photoconductor is neutralized by performing exposure with.

After the photosensitive drum 10 is uniformly charged, image exposure based on an image signal is performed by a laser writing device 13 which is an image exposing means. In this image exposure, an image signal input from a computer to a laser writing device 13 or an image reading device is processed by an image signal processing unit and then input to the laser writing device 13 to form a latent image on the photosensitive drum 10. Is done.

The laser writing device 13 has a rotary polygon mirror 131 and fθ which rotate using a laser diode (not shown) as a light emitting source.
An optical path is bent by a plurality of reflecting mirrors 133 through a lens 132 and the like to perform scanning, and a latent image is formed by rotation (sub-scanning) of the photosensitive drum 10. In this embodiment, the image portion is exposed on the basis of the image signal, and as shown in FIG. 6, the image portion has a low absolute value of electric potential VL (-100 V to
A reverse latent image such as 0) is formed.

Yellow (Y) on the periphery of the photosensitive drum 10,
There are provided developing units 14 each containing a developer including a toner T and a carrier that are negatively charged such as magenta (M), cyan (C), and black (K). Built-in developing sleeve that holds developer and rotates
Performed by 141. The developer is composed of a carrier in which ferrite is used as a core and an insulating resin is coated around the core, and a toner T in which a pigment as a main material is added according to a color, a charge control agent, silica, titanium oxide, etc. The developer is applied to the developing sleeve 14 by the layer forming rod.
It is regulated to a layer thickness of 300 to 800 μm on the upper side and conveyed to the developing zone.

The gap between the developing sleeve 141 and the photosensitive drum 10 in the developing area is 0.4 to larger than the layer thickness (developer).
When the distance is 1.0 mm, AC bias voltage of VAC (1.5 to 3.0 KV _PP ) and VD are applied between the developing sleeve 141 and the photosensitive drum 10.
A DC bias voltage of C (-500 to -700V) is superimposed and applied. VDC and VH and toner T have the same polarity (negative)
Therefore, the toner T, which has been given an opportunity to be separated from the carrier by VAC, does not adhere to the portion of VH whose absolute value of the potential is higher than VDC, and it corresponds to the potential difference in the portion of VL whose absolute value of the potential is lower than VDC. A large amount of toner is attached and visualization (reverse development) is performed.

After the visualization of the first color is completed, the process for forming the second color image is started, the uniform charging is performed again by the scorotron charger 1, and a latent image by the image data of the second color is formed by the image exposing means 13. To be done. At this time, the charge elimination by the PCL 11 performed in the image forming step for the first color is not performed because the toner T attached to the image portion for the first color scatters due to the sudden decrease in the potential around the image.

Again over the entire surface of the photosensitive drum 10 V
A latent image similar to that of the first color is formed on the portion of the photoconductor having the H potential and the image of the first color is not developed, but image exposure is performed again on the portion of the image having the first color. In the developing portion, the latent image of VT is formed by the light shielding by the toner T attached to the first color and the electric charge of the toner itself, and the developing is performed according to the potential difference between VDC and VT. In the overlapping portion of the images of the first color and the second color, if the development of the first color is performed by forming a latent image of VL, the balance between the first color and the second color is lost, so the exposure amount of the first color is reduced and VH> VM
(-100 to -300V)> VL may be set as an intermediate potential.

An image forming process similar to that for the second color is performed for the third and fourth colors, and toner images of four colors are formed on the peripheral surface of the photosensitive drum 10.

On the other hand, the recording paper P fed from the paper feed cassette 21 by the paper feed mechanism 22 and the timing roller 24 in synchronism with the toner image on the photosensitive drum 10 is stretched by a transfer belt 31 which is a conveying member. The multi-color toner image on the peripheral surface of the photoconductor drum 10 is collectively transferred onto the recording paper P by being fed to the transfer area by the transfer belt device 30 mounted.

A holding roller 3 that stretches the transfer belt 31.
A bias voltage of about 2 KV is applied to the shaft 32a of the holding roller 32 on the upstream side of 2, 33 by a power supply described later immediately before the leading edge of the recording paper P arrives. Also, this shaft 32a
A conductive brush 34 is installed in a grounded state through a current detection circuit, which will be described later, as a charging unit for charging the recording paper P at a position in contact with the transfer belt 31. The recording paper P that has been fed enters between the brush 34 and the transfer belt 31, and an electric charge is injected from the brush 34 to the recording paper P to uniformly charge the recording paper P and the transfer belt 31. An attraction force is generated between them, and the recording paper P is attracted and conveyed by the transfer belt 31. As a result, the recording paper P enters the nip portion (transfer area) 35 formed by the photoconductor drum 10 and the transfer belt 31, and the transfer device 36, which is a corona discharger, or the bias roller which replaces this, from the back surface of the transfer belt 31. Since a bias voltage of about 6 KV is applied from a power source, which will be described later, through a constant current control circuit and a transfer electric field is applied, the multicolor toner images are collectively transferred onto the recording paper P and transferred.

The recording paper P, which is separated from the photoconductor drum 10 and holds the multicolor toner image, is formed by the static eliminator 15 whose position is changed by using the shaft 33a of the holding roller 33 on the downstream side around which the transfer belt 31 is stretched as a counter electrode. Transfer belt 31 after being discharged by AC corona discharge or while receiving AC corona discharge
Separate from. A cleaning blade 37 removes the toner adhering to the rotating transfer belt 31. The transfer belt 31 of the transfer belt device 30 is a holding roller with a shaft 33a of a holding roller 33 on the downstream side as a rotation center during the formation of a multicolor toner image.
32 rotates clockwise and is separated from the photosensitive drum 10.

The recording paper P, which holds the multicolor toner image separated from the transfer belt device 30, is transferred to the fixing device 23 which is composed of two pressure-bonding rollers having a heater at a close position inside or outside one of the rollers. The adhered toner is conveyed and melted by applying heat and pressure between the pressure-bonding rollers, fixed on the recording paper P, and then discharged to the outside of the apparatus.

After the transfer, the residual toner remaining on the peripheral surface of the photosensitive drum 10 is subjected to static elimination by a static eliminator 15 using an AC corona discharger, and then reaches a cleaning device 16 which is a cleaning means to contact the photoconductor. It is scraped off into the cleaning device 16 by the cleaning blade 16a made of the rubber material and discharged or stored by a screw or the like.

The photoconductor drum 10 from which the residual toner has been removed by the cleaning device 16 is exposed by the PCL 11 and then uniformly charged by the scorotron charger 12 to enter the next image forming cycle. During the formation of the multicolor toner image, the cleaning blade 16a is separated from the surface of the photoconductor, and the AC neutralization by the static eliminator 15 is deactivated.

The present invention is provided with a charge imparting means such as a brush 34 for applying an electric charge to the recording paper P and adsorbing the recording paper P on the transfer belt 31, and the recording paper flowing through a portion of the brush 34 that contacts the recording paper P. A current value that fluctuates depending on the resistance value of P and the transfer belt 31 is detected, and by the detected current value,
2 is a diagram showing a circuit configuration of a main part of the transfer belt device of FIG. 1, and FIG. 3 is a diagram showing the current value detection and transfer electric field application and power supply output current. 7 is a time chart showing the relationship of

In FIG. 2, reference numeral 38 denotes a transfer device 36, which is a corona discharger, and a switch 47 and a constant current control circuit 39 are used to provide about 6
A power source for supplying a bias voltage of KV, a power source 38 for the shaft 32a of the holding roller 32 on the upstream side, and a bias voltage of about 2 KV obtained by dividing the output from the constant current control circuit 39 by the resistors R1 and R2 is switched. Is applied via. Holding roller
Reference numeral 32 is a roller made of a conductive metal material. The brush 34 made of a conductive fiber material is always grounded or is grounded via a non-linear element or a resistor, and the brush tip of the brush 34 abuts the transfer belt 31 at the time of transfer, and the recording is sent. The paper P is sent between the brush 34 and the transfer belt 31.
Control of the control unit 42 for a period including the current value detection section t1 in FIG. 3 from immediately before the leading edge of the recording paper P enters between the transfer belt 31 and the brush 34 to just before the leading edge of the recording paper P reaches the transfer area 35. As a result, the switch 48 is turned on, and the holding roller 32 has a constant current control circuit 39 controlled by the control unit 42 as shown in FIG.
As a result, a bias voltage obtained by dividing the output of the power source 38, which is controlled to a constant current value Ia, is always applied, so that an electric charge is injected into the recording paper P and the recording paper P is uniformly charged. As a result, the recording paper P is attracted to the transfer belt 31 and conveyed to the nip portion (transfer area) 35, but the brush 34 (charge applying means) is applied by the current detection circuit 41 while the recording paper P is passing. Detects the value of the current flowing through. FIG. 4 shows a specific circuit configuration of the current detection circuit 41. The current value is converted to 0.18 V / μA and is output to the input interface 45.

In the present embodiment, with respect to various recording papers such as postcards having different thicknesses and kinds and transparent sheets for OHP, the brush current value of the charge applying means of the recording paper and the transfer applied to the proper transfer device 36. The relationship with the power supply current value was obtained. FIG. 5 shows this relation curve, and this curve is stored in the ROM 43 as a program necessary for the arithmetic processing of the input signal.

The control circuit of the present invention is an input interface.
The control unit 42 performs a predetermined calculation of the current signal input to the ROM 45 based on the program stored in the ROM 43, and the RAM 44 that temporarily stores the calculation result, data, etc., and the signal based on the calculation result. Is output via the output interface 46. As a result, the control unit 42 turns on the time switch 47 including immediately before the leading edge of the recording paper P enters the transfer area 35 and before the trailing edge of the recording paper P passes through the transfer area 35, including the transfer portion passing section t2 in FIG. And the current value to the transfer device 36 is determined by the constant current control circuit 39 based on the above calculation result I.
By controlling to b, the corona discharge voltage of the transfer device 36 is maintained at an appropriate value, and the multicolor toner images on the photoconductor drum 10 are collectively transferred onto the recording paper P. With this configuration, the current value (resistance value) is always constant bias voltage.
The detection was performed, and based on the result, the proper transfer electric field according to the environmental conditions could be applied to the transfer device 36.

In this embodiment, the brush 34 is used as the charge applying means for the recording paper P. However, when the brush 34 is replaced by a conductive roller that rotates on the transfer belt. Can also be applied.

A transfer device is used as a power source for the holding roller 32.
The case where the output of the power supply 38 for 36 is divided and used has been described, but the same applies to the case where the power supply 38 for the transfer device 36 and the power supply for the holding roller 32 are independent.

Further, in the present embodiment, the constant current is outputted at the time of detection, but the constant voltage output can be similarly applied only by changing the relation of FIG. Further, the output to be controlled can be similarly applied even if it is a voltage value instead of a current value.

[0032]

As described above, according to the present invention, the current detection using the charge applying means is performed by a constant bias voltage, and the output of the power source for transfer is controlled according to the result, so that the environmental conditions are always maintained. Therefore, it is possible to provide an image forming apparatus in which transfer is performed by an appropriate transfer electric field according to the above, and a good transferred image can always be obtained regardless of environmental conditions such as temperature and humidity.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a diagram showing a circuit configuration of a main part of the transfer belt device of FIG.

FIG. 3 is a time chart showing the relationship between current value detection and transfer electric field application and power supply output current according to the present invention.

FIG. 4 is a circuit diagram showing an example of a current detection circuit of FIG.

FIG. 5 is a graph showing the relationship between brush current and proper transfer current.

FIG. 6 is a flowchart showing changes in the potential of the image carrier when forming a multicolor toner image according to the embodiment of FIG.

[Explanation of symbols]

 10 Photosensitive drum (image bearing member) 11 PCL 12 Scorotron charger 13 Laser writing device 14 Developing device 15 Static eliminator 16 Cleaning device 16a Cleaning blade 30 Transfer belt device 31 Transfer belt 32, 33 Holding roller 34 Brush (charge imparting means) 35 Nip part (transfer area) 36 Transfer device 38 Power supply 39 Constant current control circuit 41 Current detection circuit 42 Control part 45 Input interface 46 Output interface P Recording paper

Claims (1)

[Claims] 1. A multi-color toner image is formed by superposing toner images on an image carrier by repeating the steps of charging, image exposure and development, and the multi-color toner image is transferred to a transfer material. In an image forming apparatus having a transfer belt device which is stretched and rotated in a vertical direction, a power source for applying a transfer electric field to the transfer material of the transfer belt device, and the transfer material or the transfer material and the transfer belt device being conveyed. A detection unit is provided for detecting a current value that fluctuates depending on the resistance value of the member. When the detection unit is activated, the output current or output voltage of the power supply is fixed to a constant value, and the transfer material enters the transfer area. The image forming apparatus is characterized by changing the current value or the voltage value of the power source to a value selected based on the result detected by the detecting unit before the operation.