JPH05241406A - Image forming device - Google Patents

Abstract

PURPOSE:To always stably obtain an excellent image corresponding to environmental change by detecting a current which flows when, a charge applying means directly comes into contact with a transfer belt and controlling the image forming condition of an image forming means based on the detected current value. CONSTITUTION:The current value flowing when the charge applying means such as a brush 34 which applies charge to a recording paper p so as to attract the recording paper P to the transfer belt 31 abuts on the transfer belt 31 not through the recording paper P is detected, and the image forming condition of the image forming means is controlled based on the detected current value. Namely, a considerable difference exists in the value of the current (brush current) flowing in a state where the charge applying means such as the brush 34 slides on the transfer belt 31 between the state of low temperature and low humidity and of high temperature and high humidity. Therefore, a condition how the image forming means is controlled in a state of standard temperature and standard humidity are attained is set as reference, so as to always obtain the image at the same level regardless of the temperature and humidity is experimentally obtained, and the specified image forming means is controlled based on the current value detected by referring to the obtained condition.

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]

BACKGROUND OF THE INVENTION In an image forming apparatus such as an electrophotographic copying machine, a charging device uniformly charges a peripheral surface of an image carrier, for example, a photosensitive drum, and then an image exposure is performed 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 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 photosensitive drum onto the recording paper, the toner image is charged by a transfer device which discharges from the back of the recording paper and which has a polarity opposite to that of the toner. Is transferred onto the recording paper, and after the transfer, a high AC voltage is applied by the separator to remove the electric charge, and the recording paper is 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 imparting means for applying an electric charge to the recording paper and attracting the recording paper to the transfer belt by an electrostatic force. In contact with the drum, 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 image forming apparatus, the surface of the photosensitive drum is electrostatically charged by a charging means such as a scorotron, and after image exposure is performed, the developing means to which a developing bias is applied is electrostatically charged. Although the toner is attached to the latent image portion by using the attractive force to perform the development, the image obtained by the relationship of forming the image by using the electrostatic force is affected by the environment such as temperature and humidity. ..

Conventionally, a heater is provided in the image forming apparatus, and this influence is removed by heating by the heater in the high humidity season. However, it was impossible to make fine adjustments by such means. There is also a proposal that a temperature / humidity meter is built in the image forming apparatus to detect environmental changes and change the image forming conditions, but providing a new temperature / humidity detecting means complicates the apparatus. It was

An object of the present invention is to provide an image forming apparatus which can always obtain a stable and good image in response to a change in environment without newly providing a temperature and humidity detecting means in the image forming apparatus. To do.

[0009]

SUMMARY OF THE INVENTION The present invention achieves the above object. The present invention is provided with an image forming means such as a charging means, an image exposing means, a developing means or the like at the peripheral portion of a rotating image carrier, and the charging, image exposing and developing are performed. In the image forming apparatus that transfers the toner image formed on the image carrier via the transfer belt device having a rotating transfer belt, and conveys the recording paper, an electric charge is applied to the recording paper. The transfer belt is provided with an electric charge applying means for adsorbing a recording sheet, the electric current applied when the electric charge applying means directly contacts the transfer belt is detected, and the image forming condition of the image forming means is controlled by the detected electric current value. The present invention provides an image forming apparatus characterized by the following.

[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,
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 having a ferrite core as a core and coated with an insulating resin around the core, and a toner containing a polyester as a main material, a pigment corresponding to a color, a charge control agent, silica, titanium oxide, etc.,
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, D of the AC bias 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. In the portion to be performed, the latent image of V _M ′ is formed by the light shielding by the toner attached to 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 ′. 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. The photosensitive drum 10 holding the visible image in this way further rotates, and if necessary, the image exposure means 13
Re-exposure is performed on the image portion by the laser scanning. 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 by the paper feed mechanism 22 by the paper feed cassette 21 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 ⁸ 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 Nos. 2 and 33, and at a position in contact with the shaft 32a via the transfer belt 31, the recording paper P is electrically charged as a means for giving a charge. The sex brush 34 is installed in a 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, which holds 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 at a close position inside or outside one roller. The applied toner is melted by applying heat and pressure between the pressure bonding rollers, and the recording paper P
After being fixed on the top, it is discharged to the outside of the device.

After the transfer, the residual toner remaining on the peripheral surface of the photoreceptor belt 10 is subjected to static elimination by the static eliminator 15 using an AC corona discharger, and then the cleaning device 16 or the rubber material contacting the photoreceptor is removed. 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 uniformly charged by the scorotron charger 12 exposed by the PCL 11 and enters the next image forming cycle. During the formation of the multicolor image, the cleaning blade 16a is separated from the surface of the photosensitive member, and the static eliminator 15
AC neutralization by is kept in the OFF state.

In the above-mentioned image forming apparatus shown as an embodiment of the present invention, charge imparting means such as a brush 34 for applying an electric charge to the recording paper P and adsorbing the recording paper P to the transfer belt 31 does not have to interpose the recording paper P. The current value flowing when the transfer belt 31 is contacted is detected, and the image forming condition of the image forming unit is controlled by the detected current value.

That is, according to the present invention, the present inventors have found that the current value (brush current) flowing in the state where the charge applying means such as the brush 34 is in sliding contact with the transfer belt 31 is low temperature low humidity (LL) and high temperature high humidity (LL). Noting that there is a considerable difference in HH) time, how to control the image forming means with reference to standard temperature and standard humidity (NN) time can always obtain an image of the same level regardless of temperature and humidity. The following table shows these conditions experimentally obtained.

[0029]

[Table 1]

The above table shows the control conditions when negatively charged OPC is used as the image carrier and the process speed is 74 mm / sec. In the table, a difference of 8 μA or more in brush current value between low temperature and low humidity (LL) and high temperature and high humidity was recognized. In the table, the photoconductor charging is the scorotron charger.
It is shown that the grid voltage V _G applied to the 12 grids is controlled according to the environment so that V _H does not change depending on the environment. Developing bias is controlled in accordance with the environment developing bias to be applied by superimposing the DC component of V _AC of the AC component and V _DC applied to the developing sleeve 141 of the developing device 14, compensates for the change of the charge amount of the developer by the environment Indicates that you should do so. The image exposure amount indicates that the laser exposure amount by the image exposure means 13 is controlled according to the environment to compensate the sensitivity change due to the environment of the photoconductor. The L detection frequency is provided in the developing device 14 and consists of toner and carrier.
To control the frequency of the L detection means for measuring the toner concentration of the component developer according to the environment, and to change the toner replenishment amount to change the toner concentration according to the environment, and to keep the charge amount of the developer constant. Is shown. The image area re-exposure amount indicates that the re-exposure amount on the toner image by the image exposing means 13 is controlled according to the environment, and the proper charge elimination for preventing transfer repelling is performed.

Controls (1) to (4) in the table indicate control conditions for independent control in order to eliminate the influence of the environment. Therefore, for example, if the developing bias is controlled to correct the change in developing property, it is not necessary to control the L detection frequency.

Further, for example, in order to compensate for the change in developability,
In some cases, it is possible to reduce the load on each unit by controlling and little by little rather than controlling them individually, and it may be better to perform multiple controls depending on the item to be controlled.

In FIG. 2, a transfer belt 31 is provided by applying an electric charge to the recording paper P.
The electric current value flowing when the charge applying means such as the brush 34 for adsorbing the recording paper P to the transfer belt 31 contacts the transfer belt 31 without passing through the recording paper P, and depending on the detected electric current value, any one of image formation It shows a circuit configuration for controlling the means.

[0034] 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, electric charges are injected into the recording paper P and uniformly charged, and then the recording paper P is adsorbed by the transfer belt 31 and sent to the transfer area. However, in the present invention, the recording paper P does not pass, that is, the brush 34. The current detecting circuit 41 detects the current flowing through the charge applying means while the sheet is in contact with the transfer belt 31. FIG. 3 shows a specific circuit configuration of the current detection circuit 41, which is 0.18 V / μA with respect to the input interface 45.
The current value is output in the form of voltage conversion.

The relationship between the voltage-converted brush current value of the charge applying means and the control value of any one of the image forming means is stored in the ROM 43 as a program necessary for the arithmetic processing of the input signal. In the table, the environmental condition is L
Although only three points of L, NN, and HH are taken up, it is desirable that each process condition value be controlled in multiple stages as long as the current detection resolution and the output control resolution permit, in response to changes in the environment. This relationship is stored in the ROM 43.

In the above table, the process speed is 74 mm / sec.
In the case of the image forming apparatus in which the process speed is changed depending on the operation mode, another correspondence table corresponding to the process speed is used.
This relationship is stored in the ROM 43. FIG. 4 shows an example of this correspondence table. The image area re-exposure amount (PWM value)
Process speed (G: 12 mm / sec, E: 37 mm / sec, N: 74
mm / sec) is a corresponding table.

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 to control any one of the image forming means of, and the intended purpose can be achieved by such a configuration.

In this embodiment, the brush is used as the charge applying means, but the present invention is also applied to the case where a conductive roller rotating on the transfer belt is used instead of the brush. Since the brush current value varies depending on the brush material, the belt material, and the design conditions even in the same environment, it is necessary to use the correspondence table according to the material and the design.

[0039]

The present invention relates to environmental temperature and humidity by using a charge applying means for recording paper provided in an image forming apparatus without providing a heater and a hygrometer conventionally used in the apparatus. Therefore, an image forming apparatus that can always obtain a good and stable image is provided.

[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 is a graph showing the relationship between the brush current and the image area re-exposure amount.

[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) Application means) 35 Nip part (transfer area) 36 Corona discharger (for transfer) 37 Cleaning blade (transfer belt) 38 Power supply 41 Current detection circuit 42 Control part 43 ROM 44 RAM 45 Input interface 46 Output interface

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[Procedure amendment]

[Submission date] March 23, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

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

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Fig. 4

[Correction method] Added

[Correction content]

FIG. 4 is a graph showing the relationship between the brush current and the image area re-exposure amount.

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

[Procedure amendment 4]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

[Fig. 2]

Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location G03G 15/16

Claims (6)

[Claims] 1. A toner image formed on an image carrier through the steps 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 recording paper onto the recording paper by a transfer belt device having a rotating transfer belt and conveying the recording paper, a charge applying means for applying an electric charge to the recording paper and adsorbing the recording paper to the transfer belt is provided. An image forming apparatus, wherein the electric charge applying unit detects a current flowing when the electric charge applying unit directly contacts the transfer belt, and controls an image forming condition of the image forming unit according to the detected electric current value. 2. The image forming apparatus according to claim 1, wherein the image forming unit to be controlled is a charging unit, and controls the grid voltage of the charging unit. 3. The image forming apparatus according to claim 1, wherein the image forming means to be controlled is a developing means, and the developing bias applied to the developing means is controlled. 4. The image forming apparatus according to claim 1, wherein the image forming means to be controlled is an image exposing means, and the image exposing amount of the image exposing means is controlled. 5. The image forming apparatus according to claim 1, wherein the image forming unit to be controlled is a developing unit, and controls the frequency of the L detecting unit to control the toner density. 6. The image forming apparatus according to claim 1, wherein the image forming unit to be controlled is an image exposing unit and controls a re-exposure amount for re-exposing the toner image.