JPH0627831A - Image forming device - Google Patents

Abstract

PURPOSE:To provide a highly reliable image-forming device capable of preventing partial image-omission, such as transfer repulsion and image development of low transfer rate being an imperfect transfer, even in such environmental conditions as high temperature/high humidity or low temperature/low humidity, and always forming images of high image quality. CONSTITUTION:A charge application means, such as a brush 34, which applies charges to recording paper P and attracts the recording paper P to a transfer belt 31 detects the value of a flowing current via the recording paper P, and detects the environmental conditions of the image forming device by using the detected current value. The information of the detecting means is inputted to a circuit which controls the rotation of a stepping motor driving a cam 38a for pressing the transfer belt 31 to a photosensitive drum 10. Thereby the transfer belt 31 is pressed to the photosensitive drum 10 at a prescribed pressure.

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, in which a toner image obtained by developing a latent image on an image carrier is transferred by a transfer belt device which is a transfer material conveying means. The present invention relates to an image forming apparatus that transfers a recording sheet on which a toner image is attached to a fixing unit after transferring the recording sheet onto a recording sheet, which is a transfer material, by a physical unit for fixing.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine, after uniformly charging a peripheral surface of a photosensitive drum, which is an image carrier, by a charger, an image is exposed on the peripheral surface of the photosensitive drum. 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 a 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 toner having a polarity opposite to that of the toner is charged by a transfer device which discharges from the back of the recording paper. 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 particularly when the drum diameter of the photoconductor drum is large, it is difficult to separate, and the recording paper after the transfer of the toner image adheres to the photoconductor drum without being separated. It has the drawback that it tends to cause paper jams. As a technique for improving this drawback, a transfer belt device, which is a transfer material conveying unit, is used.

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 causes the recording paper to be attracted to the transfer belt by an electrostatic force. And 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.
With such a transfer belt device, excellent transfer efficiency and separation effect can be obtained at the transfer portion.

Such a transfer belt device is used as a particularly preferable device in a color image forming device in which a toner image is 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 at the peripheral portion of the photoconductor drum in order to superimpose toner images on the photoconductor, the drum diameter becomes large, and sufficient separation performance cannot be obtained by the conventional electrostatic transfer separation system. Therefore, more reliable separation performance is required, and in the method of superposing toner images, the toner adhesion amount is large, so that a large transfer charge amount is required, and thus it is necessary to have a large transfer charge holding ability. The transfer belt device is excellent in two respects.

[0006]

As described above, the image forming apparatus which uses the transfer belt device as a means for transferring to the recording paper enables the image forming apparatus to be an excellent device. However, the dependence on the environment remains less than usual, but still remains.

That is, in the above-mentioned image forming apparatus, the surface of the photosensitive drum is electrostatically charged by a charging means such as a scorotron, image exposure is performed, and then the developing means to which a developing bias is applied is electrostatically charged. The toner is attached to the latent image part by using the attractive force to develop the image, and then the image is transferred to the recording paper.The image obtained by the image forming and the transfer using the electrostatic force is obtained. It will be affected by the environment such as temperature and humidity.

[0008] When the temperature is high and the humidity is high, partial image omission occurs. Further, this phenomenon is more likely to occur as the pressing force of the transfer belt on the photosensitive drum is increased. This is a phenomenon that occurs because the electric field in the transfer area is too strong.

Further, when the temperature is low and the humidity is low, an image having a low transfer rate is produced as a whole. Further, this phenomenon is more likely to occur as the pressing force of the transfer belt on the photosensitive drum is smaller. This is a phenomenon that occurs because the electric field in the transfer area is too weak.

The present invention has been made to solve the above problems. In other words, even under environmental conditions such as high temperature and high humidity, or low temperature and low humidity, partial image omissions and images with a low transfer rate do not occur, and reliable high-quality image formation is possible. The purpose is to provide a high image forming apparatus.

[0011]

The above object is to provide an image forming means such as a charging means, an image exposing means and a developing means on the peripheral portion of a rotating image bearing member, and to carry out the image bearing through the steps of charging, image exposing and developing. In an image forming apparatus for transferring a toner image formed on a body onto a transfer material conveyed by a transfer material conveying member and fixing the transferred toner image, a detection unit for detecting an environmental condition of the image forming apparatus. And the pressing force of the transfer material conveying member to the image carrier is changed based on the detected environmental condition.

The above object is also achieved by an image forming apparatus characterized in that the detecting means for detecting the environmental condition is a detecting means for detecting a current flowing through the transfer material and / or the transfer material conveying member. It is a thing.

[0013]

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 FIG. 1, 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 applies a uniform charge of V _{H to} the peripheral surface of the photosensitive drum 10 by corona discharge by a grid and a corona discharge wire whose potential is held at V _G. Prior to the charging by the scorotron charger 12, a PCL using a light emitting diode or the like to eliminate the history of the photoconductor until the previous printing.
The surface of the photoconductor is neutralized by exposure using 11.

After uniformly charging the photosensitive member, the image exposing means 13 performs image exposure based on the image signal. Image exposure means
Reference numeral 13 is a reflection mirror 1 through 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,
Developing device 14 in which a developer including toner such as magenta (M), cyan (C), black (K), and a carrier is incorporated.
First, the development of the first color is carried out by the developing sleeve 141 which contains a magnet and holds the developer and rotates. 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 containing a pigment as a main material and a charge control agent, silica, titanium oxide, etc., according to the color,
The developer is 300 to 60 on the developing sleeve 141 by the layer forming rod.
The layer is regulated to a layer thickness of 0 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 1.0mm, V _AC AC ice and V _DC D
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 the 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 process of the first color is not performed because the toner attached to the image portion of the first color scatters due to the rapid 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 the image of the first color is not developed, but development is performed again on the portion having the image of the first color. In the portion to be performed, the latent image of V _M ′ is formed due to the light shielding by the toner of the first color 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 '. In 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 of 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. The photoconductor drum 10 holding the visible image in this way may further rotate, and the image portion may be re-exposed by the laser scanning of the image exposing means 13. The re-exposure on the toner image with the laser is performed so that good transfer is performed in the next transfer step.

On the other hand, the recording paper P fed from the paper feeding cassette 21 by the paper feeding 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 multicolor image is collectively transferred onto the recording paper P.

The transfer belt 31 has a thickness of 0.4 with a resistance of 10 ⁸ to 10 ¹⁴ Ω · cm formed by forming an outer FLC layer of a urethane rubber base.
Endless rubber belt of ~ 1.0mm, ribs may be provided at the end 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 that stretches the transfer belt 31.
A voltage of V _PC is applied to the shaft 32a of the upstream side holding rollers 32 of the reference numerals 2, 33, and as a means for applying a charge to the recording paper P at a position where the shaft 32a is installed via the transfer belt 31. 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 the corona discharger 36 or a bias roller instead. A multicolor image is transferred onto the recording paper P.

The recording paper P separated from the photosensitive drum 10 is
The shaft 33a of the holding roller 33 on the downstream side which 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 photosensitive drum 10 about a shaft 33a of a holding roller 33 on the downstream side as a rotation center during the formation of a multicolor image.

That is, the shaft 32a of the holding roller 32 on the upstream side of the transfer belt device 30 is attached to the tip of the slide plate 32b as shown in the figure, and by two pins for guiding the groove provided in the slide plate 32b. The slide plate 32b can be guided vertically. And the slide plate 32b is a cam
By the rotation of 38a, it is moved in the vertical direction via a pressing spring 32c sandwiched therebetween. In addition, holding roller
The shafts 32a and 33a of 32 and 33 and the shafts of the auxiliary rollers 39a and 39b are attached to the transfer belt device plate 30a, and the transfer belt 31 is stretched to form a unit as the transfer belt device 30.
The transfer belt device plate 30a is rotatable about the shaft 33a of the holding roller 33. And this slide plate 32
By moving b in the vertical direction, the transfer belt device 30 rotates about the shaft 33a of the holding roller 33 as described above, so that the transfer belt 31 contacts the photosensitive drum 10 or separates from it. become.

The illustrated state shows that the slide plate 32b is moved by the counterclockwise rotation of the cam 38a so that the transfer belt 31 presses the photosensitive drum 10 via the pressing spring 32c. During the above-described multicolor image formation, the cam 38a rotates clockwise and the slide plate 32b moves downward, so that the transfer belt 31 is separated from the photosensitive drum 10 as described above. The rotation of the cam 38a is controlled by the rotation power of a stepping motor or the like controlled by a microcomputer (not shown). Then, the slide plate 32b, the pressing spring 32c, the cam 38a, and, for example, a stepping motor or the like that serves as the rotational power of the cam 38a constitute the pressing force converting means 38 described later.

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 or in the immediate vicinity thereof, and pressure bonded. The applied toner is melted by applying heat and pressure between the rollers, is fixed on the recording paper P, and is 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 is removed from a rubber material which is in a cleaning device 16 and abuts on the photoconductor. 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 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.

The inventor of the present invention lowers the pressing force of the transfer belt 31 for pressing the photoconductor drum 10 when the temperature and humidity are high, and increases the pressing force when the temperature and humidity are low, whereby partial image omission and It has been found that it is possible to compensate for both problems of low overall transfer rate.

That is, according to the present invention, in the above-mentioned image forming apparatus shown as the embodiment, the information of the environment detecting means in the apparatus is used as the cam 38a constituting the pressing force converting means 38.
Is input to a microcomputer that controls the rotation of, for example, a stepping motor that drives the transfer belt 31
Is pressed against the photosensitive drum 10 with a predetermined pressing force. Of course, other structures may be used as long as the pressing force is variable.

In FIG. 2, a transfer belt 31 is provided by applying an electric charge to the recording paper P.
A detection unit that detects a current value that flows when a charge applying unit such as a brush 34 that attracts the recording paper P contacts the transfer belt 31 with or without the recording paper P is provided. This shows a configuration in which the environmental condition of the image forming apparatus is detected and the transfer belt 31 of the transfer belt device 30 is pressed against the photosensitive drum 10 with a predetermined pressing force as described above.

In FIG. 2, the pressing force converting means 38, which is microcomputer-controlled by the environmental state detection information as described above, is used.
When the slide plate 32b is moved upward via the pressing spring 32c by the cam 38a which is rotationally driven by the stepping motor 38b, which is a series of members, the transfer belt 31 of the transfer belt device 30 moves the transfer belt 31. The auxiliary roller 39
The area where the transfer belt 31 on the left side of FIG. Then, the transfer area 35 is pressed by a predetermined pressing force.

In the present embodiment, the auxiliary roller 39
By providing a, the transfer area can be widened, and the transfer can be performed better.

Reference numeral 32d denotes V on the shaft 32a of the holding roller 32 on the upstream side.
Power supply for applying _PC bias voltage, holding roller
32 is a roller made of a conductive metal material. The brush 34 made of a conductive fiber material is always kept in a grounded state or at a predetermined potential, and at the time of transfer, the bristle tips of the brush 34 come into contact with the transfer belt 31, and the recording paper P that has been fed is transferred to the brush 34. It is fed between the transfer belt 31 and the transfer belt 31. Here, an electric charge is injected into the recording paper P to be uniformly charged, and the recording paper P is adsorbed by the transfer belt 31 and sent to the transfer area. However, as a detecting means, the recording paper P is passing, that is, the brush 34. Is in contact with the transfer belt 31 via the recording paper P, or in a state in which the recording paper P is not passing, that is, in the state where the brush 34 is in contact with the transfer belt 31, the current detection circuit 41 causes the charge applying means to contact the transfer belt 31. Detect the flowing current. FIG. 3 shows a specific circuit configuration of the current detection circuit 41. The input interface 45
In contrast, the current value of 0.18 V / μA is output in the form of voltage conversion.

FIG. 4 is a graph showing the relationship between the output voltage of the current detection circuit and the pressing force of the transfer belt 31 for pressing the photosensitive drum 10.

That is, FIG. 4 shows the relationship between the output voltage obtained by converting the current into the input interface 45 from the current detection circuit 41 at a rate of 0.18 V / μA and the pressing force. And the pressing force is 200gr, 150gr, 10 depending on the output voltage.
The transfer belt 31 is applied to the photosensitive drum 10 with three types of pressing force of 0 gr.
Will be pressed. Of course, it is more preferable to perform more multi-step control or continuously control the pressing force.

The pressing force is defined as follows.

That is, the pressing force is the value of the static frictional force when a paper having a width of 25 mm is sandwiched across the entire transfer area and pulled from the downstream side.

The control circuit subsequent to the detecting means shown in FIG. 2 stores the voltage signal input to the input interface 45 in the ROM.
A control unit 42 that performs a predetermined calculation based on a program that satisfies the graph of FIG. 4 stored in 43 and a RAM 44 that temporarily stores the calculation result, data, etc., and a signal based on the calculation result. Is output via the output interface 46 and is the rotational power of the cam 38 described above.
38b is rotationally controlled so that the pressing force shown in FIG. 4 is obtained.

Further, in the above-mentioned image forming apparatus shown as the embodiment, the case where the pressing force is controlled by the information of the temperature and humidity detecting sensor as the environment detecting means installed in the apparatus will be described.

In FIG. 5, the image forming apparatus is controlled by controlling the pressing force so that the pressing force is 100 gr in the area A, 150 gr in the area B, and 200 gr in the area C depending on the combination of temperature and humidity. 4 is a graph showing that the image of FIG.

Then, the signals from the temperature and humidity detecting sensors are input to the input interface 45 as in the case of FIG.
A control unit 42 that performs a predetermined calculation based on a program that stores the signal in the ROM 43 and that satisfies the graph of FIG.
The stepping motor 38b, which is the rotational power of the cam 38 described above, is processed by a control circuit having a RAM 44 for temporarily storing the calculation result, data, etc. and outputs a signal based on the calculation result via an output interface 46. The rotation is controlled to control the pressing force shown in FIG.

[0046]

EFFECTS OF THE INVENTION According to the present invention, an image of high quality is always obtained, which does not cause partial image loss even under environmental conditions such as high temperature and high humidity, or low temperature and low humidity, and which does not cause an image with a low transfer rate. Thus, a highly reliable image forming apparatus that can be formed is provided.

[Brief description of drawings]

FIG. 1 is a configuration cross-sectional view showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a diagram showing a main part configuration and a circuit configuration of the present invention.

FIG. 3 is a diagram showing an example of a current detection circuit diagram.

FIG. 4 is a graph showing the relationship between the output voltage of the current detection circuit and the pressing force of the transfer belt.

FIG. 5 is a graph showing transfer belt pressing force that guarantees an image depending on temperature and humidity.

[Explanation of symbols]

 10 photoconductor drum 30 transfer belt device 30a transfer belt device plate 31 transfer belts 32, 33 holding rollers 32a, 33a shaft 32b slide plate 32c pressing spring 34 brush 35 transfer area 38 pressing force converting means 38a cam 38b stepping motors 39a, 39b auxiliary Roller 41 Current detection circuit 42 Controller 43 ROM 44 RAM 45 Input interface 46 Output interface P Recording paper

Claims (2)

[Claims] 1. A toner image formed on an image carrier through a process of charging, image exposure and development by providing an image forming unit such as a charging unit, an image exposing unit and a developing unit on a peripheral portion of a rotating image carrier. In the image forming apparatus for transferring the toner image on the transfer material conveyed by the transfer material conveying member and fixing the transferred toner image, the image forming apparatus having a detecting means for detecting the environmental condition placed in the image forming apparatus. An image forming apparatus, wherein the pressing force of the transfer material conveying member to the image carrier is changed based on the environmental condition. 2. The image forming apparatus according to claim 1, wherein the detecting unit that detects the environmental condition is a detecting unit that detects a current flowing through the transfer material and / or the transfer material conveying member.