JPH05181371A - Image forming device - Google Patents

Abstract

PURPOSE:To provide a device having a transfer belt device capable of satisfactory transfer regardless of temperature and humidity and kind of paper by detecting a current carried to a charge imparting means through a recording paper and controlling transfer condition according to the detected current value. CONSTITUTION:A charge is given to a recording paper P, the current carried to a charge imparting means such as a brush 34 for attracting the recording paper P to a transfer belt through the recording paper P is detected, and the current control of a transfer corona discharger 36 is conducted according to the detected current value. A control circuit has a control part 42 for conducting a determined operation on the current signal inputted to an input interface 45 on the basis of a program stored in a ROM 43, and a RAM 44 for temporarily storing the operation result and data. The signal based on the operation result is outputted through an output interface 46, and the corona discharge voltage is fluctuated to control the current value of the rated current control circuit 39 of the transfer corona discharger 36.

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 conveys the recording sheet to a fixing means for fixing.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine, after the peripheral surface of a photosensitive drum, which is an image carrier, is uniformly charged by a charger, the peripheral surface of the photosensitive drum is exposed to an image. To form an electrostatic latent image. This latent image is developed and visualized by developing means to become a toner image. The toner image formed on the peripheral surface of the photoconductor drum is transferred by a physical means onto the recording paper fed at a timing,
The recording paper on which the toner image has been transferred is separated from the photoconductor drum and conveyed to the fixing means. The toner image is fixed on the recording paper and then discharged to the outside of the apparatus.

As a transfer means for transferring the toner image adhering to the peripheral surface of the photoconductor drum onto the recording paper, a transfer device for discharging from the back of the recording paper applies a charge having a polarity opposite to that of the toner to a toner image. Is transferred to the recording paper, and after transfer, a high AC voltage is applied by the separator to remove the charge,
The recording paper is designed to be separated from the photosensitive drum. However, it is difficult to reliably maintain transferability and separability, and it is difficult to separate, especially when the drum diameter of the photoconductor drum is large, and the recording paper on which the toner image has been transferred adheres to the photoconductor drum without being separated. It has the drawback that it tends to cause paper jams. A transfer belt device is used as a technique for improving this drawback.

The transfer belt device rotates a transfer belt 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 the recording paper and attracts the recording paper to the transfer belt by an electrostatic force. Then, a high voltage having a polarity opposite to that of the toner charge is applied under constant current control at the transfer portion to transfer the toner image.
In such a transfer belt device, excellent transfer efficiency and separation effect can be obtained in the transfer section.

Such a transfer belt device is used as a particularly preferable device in a color image forming device in which toner images are superposed on a photosensitive drum and transferred onto a recording sheet at a time. In such a color image forming apparatus, since a plurality of developing devices are provided on the peripheral portion of the photosensitive drum in order to superimpose toner images on the photosensitive member, the drum diameter becomes large, and sufficient separation performance cannot be obtained by the conventional electrostatic transfer separation method. Therefore, more reliable separation performance is required, and in the method of superposing toner images, a large amount of transfer charge is required because the toner adhesion amount is large, and thus it is necessary to have a large transfer charge holding ability. This is because the transfer belt device is excellent in two respects.

[0006]

SUMMARY OF THE INVENTION In the above-mentioned image forming apparatus, when the installation place is a humid place or when it is used in a humid season, the recording paper absorbs moisture to increase the water content, and the resistance value of the recording paper fluctuates, In the transfer of the toner image adhering to the photosensitive drum, the transfer is incomplete and the transferred image quality deteriorates.
There was a problem that the transfer current was insufficient under low humidity and the toner transfer was insufficient.

In order to solve such a problem, heating is performed by a heater. However, it was impossible to finely adjust the heating humidity according to the water content of the recording paper. Further, a thermo-hygrometer is built in the image forming apparatus to detect the environmental change and set the transfer condition, or a measuring means for measuring the resistance value of the recording paper is provided to set the transfer condition from the measured resistance value. Things have been done. However, the new installation of such means causes a complicated configuration and an increase in cost.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus having a transfer belt device capable of performing good transfer regardless of temperature and humidity and the type of paper without relying on such complicated means.

[0009]

SUMMARY OF THE INVENTION The present invention achieves the above object. The present invention is to transfer a toner image obtained by developing a latent image on an image bearing member onto recording paper by a transfer belt device having a rotating transfer belt. In an image forming apparatus that transfers and conveys the recording paper, a charge applying unit that applies an electric charge to the recording paper and attracts the recording paper to the transfer belt is provided, and the electric current flowing through the recording paper is detected by the charge applying unit. Then, the image forming apparatus is characterized in that the transfer condition is controlled according to the detected current value.

[0010]

FIG. 1 is a sectional view showing the construction of a color image forming apparatus as an embodiment of the image forming apparatus of the present invention.

First, the structure and operation will be described.

In the figure, reference numeral 10 denotes a photosensitive drum which is an image bearing member, which is formed by coating an OPC photosensitive member on the drum and is grounded and driven and rotated clockwise. Reference numeral 12 denotes a scorotron charger, which uniformly charges V _{H on} the peripheral surface of the photosensitive drum 10 to V _G.
It is provided by a corona discharge with a grid and a corona discharge wire held at a potential. This scorotron charger
Prior to the charging by 12, the PCL 11 using a light emitting diode or the like is used to expose the peripheral surface of the photoconductor in order to eliminate the history of the photoconductor until the previous printing.

After uniformly charging the photoconductor, the image exposing means 13 performs image exposure based on the image signal. Image exposure means
Reference numeral 13 is a reflection mirror 1 via a polygon mirror 131 that rotates using a laser diode (not shown) as a light emitting source, an fθ lens, and the like.
The optical path is bent by 32 and scanning is performed, and a latent image is formed by the rotation (sub-scanning) of the photosensitive drum 10.
In this embodiment, the character portion is exposed to form an inverted latent image in which the character portion has a lower potential V _L.

Yellow (Y) on the periphery of the photosensitive drum 10,
Developers each containing a developer composed of toner such as magenta (M), cyan (C), black (K), and a carrier.
14 is provided, and first, the development of the first color is performed by the developing sleeve 141 which contains a magnet and holds the developer and rotates. The developer is a carrier in which ferrite is used as a core and an insulating resin is coated around the core, polyester is used as a main material, and a pigment and a charge control agent are used according to the color.
It consists of toner to which silica, titanium oxide, etc. have been added.
The layer is regulated to a layer thickness (developer) of up to 600 μm and conveyed to the developing area.

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).
As 0.7mm, D of AC Baaisu and V _DC of V _AC during this time
The C bias is superimposed and applied. Since V _DC and V _H and the toner are charged with the same polarity, the toner given the opportunity to be separated from the carrier by V _AC does not adhere to the V _H portion, which has a higher potential than V _{DC, and} has a potential higher than V _DC. attached to a lower V _L portion of visualized (reversal development) is carried out.

After the visualization of the first color is completed, the process proceeds to the image forming process of the second color, the uniform charging is performed again by the scorotron charger 12, and a latent image based on 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 process of the first color is not performed because the toner attached to the image portion of the first color scatters due to the sudden decrease in the potential around the image.

Again, V is applied over the entire surface of the photosensitive drum 10.
A latent image similar to that of the first color is formed on the portion of the photoconductor having the _H potential and no image of the first color is developed, but the portion of the photoreceptor having the first color image is developed again. At the portion to be performed, the latent image of V _M ′ is formed by the toner attached to the first color to shield the light and the electric charge of the toner itself, and V _DC
And development is performed according to the potential difference between V _M ′ and V _M ′. At the overlapping portion of the images of the first color and the second color, the development of the first color is V _L
When the latent image of is formed, the balance between the first color and the second color is lost, so the exposure amount of the first color is reduced and V _H > V _M > V
_It may be an intermediate potential that becomes _L.

An image forming process similar to that for the second color is performed for the third and fourth colors, and a visible image of four colors is 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 is fed to the transfer area by the transfer belt device 30 in which the transfer belt 31 is stretched, and the peripheral surface of the photosensitive drum 10 is fed. The above multicolored images are collectively transferred onto the recording paper P.

The transfer belt 31 has a thickness of 0.4 having a resistance of 10 ⁶ to 10 ¹⁴ Ω · cm formed by forming an outer FLC layer of a urethane rubber base.
An endless rubber belt of ~ 1.0mm, ribs may be provided at the ends to prevent deviation during rotation.

It should be noted that a film such as PET or a high resistance belt such as a film coated with these may be provided by providing a charge removing mechanism or the like.

A holding roller 3 for stretching the transfer belt 31.
A voltage of V _PC is applied to the shaft 32a of the upstream side holding rollers 32 of the second and the third rollers 33, and at the position where the shaft 32a is installed via the transfer belt 31, as a means for imparting charge to the recording paper P. The conductive brush 34 is grounded in the grounded state. The fed recording paper P enters between the brush 34 and the transfer belt 31, and the brush 34 injects an electric charge into the recording paper P, so that an attraction force is exerted between the recording paper P and the transfer belt 31. Occurs. After that, the recording paper P enters a nip portion (transfer area) 35 formed by the photosensitive drum 10 and the transfer belt 31, and a transfer electric field is generated from the back surface of the transfer belt 31 by a corona discharger 36 or a bias roller instead. The multicolor image is transferred onto the recording paper P.

The recording paper P separated from the photosensitive drum 10 is
Shaft 33a of the holding roller 33 on the downstream side that stretches the transfer belt 31
Transfer belt 31 after receiving static electricity by AC corona discharge with the counter electrode as the counter electrode or while receiving AC corona discharge.
Separate from. A cleaning blade 37 removes the toner attached to the rotating transfer belt 31. The transfer belt 31 of the transfer belt device 30 is separated from the photoconductor drum 10 about the shaft 33a of the holding roller 33 on the downstream side as a rotation center during the formation of the multicolor image.

The recording paper P holding the multicolor image separated from the transfer belt device 30 is conveyed to a fixing device 23 composed of two pressure bonding rollers having a heater inside at least one of the rollers, and is transferred between the pressure bonding rollers. The applied toner is melted by applying heat and pressure, 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 photoconductor drum 10 is subjected to static elimination by a static eliminator 15 using an AC corona discharger, and then the rubber material contacted with the photoconductor is moved to the cleaning device 16. It is scraped off into the cleaning device 16 by the cleaning blade 16a and is discharged or stored by a screw or the like. The above static eliminator 15
Depending on the arrangement of the recording sheets, it is possible to also serve as static elimination of the recording paper as shown in FIG.

The photosensitive 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.
Enter the next image forming cycle. The cleaning blade 16a is separated from the surface of the photoconductor during the formation of the multicolor image,
AC neutralization by 15 is kept in OFF state.

In the image forming apparatus described above as an embodiment of the present invention, the recording paper P is supplied to the charge applying means such as a brush 34 for applying an electric charge to the recording paper P to attract the recording paper P to the transfer belt 31. The flowing current is detected, and the current of the transfer corona discharger 36 is controlled according to the detected current value. FIG. 2 shows this circuit configuration.

[0028] 38 V _PC to the axis 32a of the upstream-side holding roller 32
Power supply for applying the bias voltage of the holding roller 32
Is a roller made of a conductive metal material. The brush 34 made of a conductive fiber material is always in a grounded state, and the bristle tips of the brush 34 come into contact with the transfer belt 31 at the time of transfer, and the recording paper P fed is transferred between the brush 34 and the transfer belt 31. Sent in between. Here, the electric charge is injected into the recording paper P to be uniformly charged, and is adsorbed by the transfer belt 31 and sent to the transfer area. However, in the present invention, the electric current is applied while the recording paper P is passing. The detection circuit 41 detects the current flowing through the charge applying means. FIG. 3 shows a specific circuit configuration of the current detection circuit 41, which is 0.18 V with respect to the input interface 45.
The current value is output to / μA in the form of voltage conversion.

The present inventors have made various recording papers of different thicknesses and types, such as postcards, and transparency for OHP, the current value of the paper charging brush of the charging means of the recording paper and an appropriate corona discharger 36. The relationship with the current value of the transfer power source applied to the was calculated. FIG. 4 shows this relationship 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 has 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, and the corona discharge voltage is changed so as to control the current value of the constant current control circuit 39 of the corona discharger 36 for transfer. Could be achieved.

In this embodiment, a brush is used as the charge applying means for the recording paper, but the same applies to the case where a conductive roller rotating on the transfer belt is used instead of the brush. Although the corona discharger provided on the back surface of the transfer belt has been described as the transfer means for the recording paper, the bias roller which is in contact with and rotates behind the transfer belt can also be applied.

[0032]

According to the present invention, recording is performed by using a charge imparting means for a recording sheet provided in an image forming apparatus without providing a heater, a hygrometer, a resistance measuring apparatus, etc. which have been conventionally provided in the apparatus. An image forming apparatus has been provided which can always obtain a good transferred image regardless of the thickness of paper and humidity.

[Brief description of drawings]

FIG. 1 is a configuration sectional view 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 present invention.

FIG. 3 shows an example of a current detection circuit diagram.

FIG. 4 is a graph showing a relationship between a paper charging brush current and an appropriate transfer power supply current.

[Explanation of symbols]

 10 Photoconductor drum 11 PCL 12 Scorotron charger 13 Image exposure unit 14 Developer 15 Static eliminator 16 Cleaning device 21 Paper cassette 22 Paper feeding mechanism 23 Fixing device 30 Transfer belt device 31 Transfer belt 32, 33 Holding roller 34 Brush (charge) Applying means) 35 Nip part (transfer area) 36 Corona discharger (for transfer) 37 Cleaning blade (transfer belt) 38 Power supply 39 Constant current control circuit 41 Current detection circuit 42 Control part 43 ROM 44 RAM 45 Input interface 46 Output interface face

Claims (1)

[Claims] 1. An image forming apparatus for transferring a toner image obtained by developing a latent image on an image bearing member onto a recording paper by a transfer belt device having a rotating transfer belt, and carrying the recording paper. Providing a charge giving means for giving a charge to the recording paper to attract the recording paper to the transfer belt, detecting a current flowing through the recording paper in the charge giving means, and controlling the transfer condition according to the detected current value. An image forming apparatus characterized by.