JPH05265300A - Image forming device - Google Patents

Abstract

PURPOSE:To perform desirable transfer always regardless of environmental conditions so as to obtain fine transfer image stably by providing a means for changing write light quantity at the reexposure time, and forming this changing means in such a way as to change the light quantity of reexposure in correspondence with the fluctuation of the environmental conditions under which a device is placed. CONSTITUTION:An image forming device is provided with a thermo-hygrometer and other detecting means such as a detecting means 41 so as to detect the environment in which the device is placed, the thickness and moisture content of recording paper, and the like ; and a changing means 42 for changing write light quantity at the reexposure time selectively from the maximum light quantity to the no-reexposure state according to the detected conditions. The detecting means 41 detects the value of a current flowing when an electric charge providing means such as a brush 34 for providing the recording paper P with electric charge so as to get the recording paper P attracted to a transfer belt, comes in contact with the transfer belt. A control circuit has a control part 42 for performing specified operation on the basis of a current signal inputted into an input interface 45, and outputs a signal based on the computed result so as to change light quantity by the pulse width modulation of an image exposure means 13.

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 is obtained by repeating a process of forming a latent image on an image bearing member and developing the latent image into a toner image a plurality of times. The present invention relates to an image forming apparatus that transfers a multicolor toner image onto a transfer paper by a physical means and then conveys a recording paper on which a toner image is attached to a fixing means to fix the recording paper.

[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 developing means containing toners of different colors is arranged on the peripheral portion of the photoconductor drum, and the different developing means are sequentially operated to form a multicolor toner image on the peripheral surface of the photoconductor drum, and then formed. The toner image is transferred by a physical means onto the recording paper fed at a timing, the recording paper on which the toner image is transferred is separated from the photoconductor drum, and is conveyed to the fixing means, and the toner image is transferred onto the recording paper. After being fixed on, it is discharged to the outside of the device.

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. As a technique for improving this drawback, a transfer belt device, which is a transfer material conveying means, 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 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.

In the above-mentioned color image forming apparatus, the surface of the photosensitive drum is electrostatically charged by a charging means such as a scorotron, image exposure is carried out using a laser beam, and then a developing means to which a developing bias is applied. In this method, the toner is attached to the latent image portion that has been image-exposed by electrostatic attraction, and the latent image portion is developed. The reversal development is repeated a plurality of times, and then the image is transferred to the transfer material. The toner adhesion state to the surface of the photoconductor may be one layer or multi-layered, and the electrostatic toner adhesion state is not uniform but different potential state. Therefore, all the toners on the photoconductor may not be transferred in a satisfactory state upon transfer. In order to make uniform transfer under the same conditions, re-exposure with a laser beam is performed at the toner adhesion portion, which is the image portion. If only the electrostatic conditions of the adhered toner on the photoconductor are adjusted, the entire surface exposure may be performed in the state where the toner is adhered. Sharpness is damaged. From this point, re-exposure with a laser beam is performed on the adhered toner on the photoconductor prior to transfer.

[0007]

SUMMARY OF THE INVENTION However, as a result of many experiments conducted by the present inventors, the transferred image is not always the same even if re-exposure is performed under the same conditions, and it is sometimes better not to perform re-exposure. Images were sometimes obtained. It was found that the cause of such a difference is largely due to the environment in which the device is placed and the moisture content of the recording paper, etc., and it is necessary to respond in accordance with environmental conditions etc. in order to obtain a good transferred image. It was An object of the present invention is to provide an image forming apparatus that performs re-exposure so that a good transferred image can always be obtained.

[0008]

SUMMARY OF THE INVENTION The present invention achieves the above object. The present invention forms an image on an image carrier a plurality of times, and at least one formed toner image is recharged and at the same time. An image forming apparatus that performs re-exposure on one formed toner image and then transfers and fixes the toner image, the image forming apparatus including a changing unit that changes a writing light amount at the time of re-exposure. Is. Then, as an embodiment, the changing means is configured to change the light amount of the re-exposure in response to the change in the environmental condition of the apparatus.

[0009]

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 configuration 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 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 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, D of AC Baaisu and V _DC of V _AC during this time
The C bias is superimposed and applied. V _DC and V _H, for the toner charge polarity is the same polarity, the toner given the opportunity to leave from the carrier by V _AC is not adhere to a portion of the high V _H of potential than V _DC, from V _DC It adheres to the V _L portion having a low electric potential and is visualized (reverse development).

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 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 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 photosensitive drum 10 holding the visible image in this way further rotates, and the image portion is re-exposed by the laser scanning of the image exposing means 13. The re-exposure on the toner image by the laser is such that good transfer is performed in the next transfer step, and as will be described later, it has a changing means for changing the writing light amount at the time of re-exposure. It is configured to change the light amount of re-exposure in response to changes in environmental conditions.

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 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.

A film such as PET or a high resistance belt such as a film coated with these may be provided as long as a charge removing mechanism is provided.

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 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 recording paper P that has been fed enters between the brush 34 and the transfer belt 31, the recording paper P is charged by the brush 34, and the recording paper P is attracted 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 inside at least one roller or in the immediate vicinity thereof, and pressure bonding is performed. 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 photosensitive 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 has come into contact with the photosensitive member to a cleaning device 16. It is scraped off into the cleaning device 16 by the cleaning blade 16a, discharged by the screw and stored in the recovery box. Depending on the arrangement of the static eliminator 15, the static eliminator 15 can also serve as static eliminator for 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.

The color image forming apparatus of the present invention is provided with a temperature / humidity meter for detecting the environment in which the apparatus is placed, the thickness of the recording paper, the water content, etc., and other detecting means, depending on the detection conditions. Further, a changing means for changing the light quantity so as to select the writing light quantity at the time of the re-exposure from the maximum light quantity to the situation without re-exposure is provided.The detecting means described in the following embodiment is a paper charging current detecting means. The temperature and humidity, the paper thickness, and the like are detected in a composite manner, and the re-exposure light amount is controlled based on the detection result.

That is, in the above-described image forming apparatus shown as the embodiment, the charge applying means such as the brush 34 for applying the electric charge to the recording paper P and adsorbing the recording paper P to the transfer belt 31 is the recording paper P.
Transfer belt without a recording sheet P or a recording sheet P.
The value of the current flowing upon contact with 31 is detected, and the amount of writing light at the time of re-exposure is controlled by the detected current value.

In FIG. 2, a transfer belt 31 is provided by applying an electric charge to the recording paper P.
A detection means for detecting a current value flowing when a charge applying means such as a brush 34 for adsorbing the recording paper P comes into contact with the transfer belt 31 with or without the recording paper P provided is provided. 6 shows a circuit configuration for controlling the writing light amount at the time of re-exposure.

[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 in a grounded state or in an installed state via a non-linear element resistance, and the bristle tips of the brush 34 contact the transfer belt 31 during transfer, and the recording paper is fed. P is fed between the brush 34 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. As a detection means, the recording paper P is in a passing state, that is, a brush.
The charge detection means 41 is provided by the current detection circuit 41 in a state in which 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 a state in which the brush 34 is in contact with the transfer belt 31. The current I _BR flowing through is detected. FIG. 3 shows a specific circuit configuration of the current detecting circuit 41. The current value is converted into a voltage of 0.18 V / μA with respect to the input interface 45 and output as the voltage V _{BR in} a voltage converted form.

The present inventors have found that the current value I flowing in the state where the charge applying means such as the brush 34 is in direct sliding contact with the transfer belt.
_The following experimental values were obtained by experimentally determining how much _BR (or voltage-converted V _BR ) is different between low temperature and low humidity (LL) and high temperature and high humidity (HH).

Environment LL NN HH (temperature, relative humidity) 10 ° C., 20% 20 ° C., 50% 32 ° C., 80% Brush current I _BR (μA) 0-35-5-8 10- 34 is the transfer belt 31 via the recording paper P.
When detecting the current value I _BR flowing in the state of being in contact with
Since the information such as the paper thickness and the water content of the recording paper P is added to the above environmental conditions, the current value flowing when the brush 34 is in contact with the transfer belt 31 via the recording paper P. For I _BR , many experiments were performed from high temperature and high humidity (HH) to low temperature and low humidity (LL), and the optimum relation L _R (I _BR ) of the re-exposure light amount L _R by the image exposure means 13 under each condition was obtained. It was

FIG. 4 shows an example of a correspondence table between the brush current value I _BR and the optimum re-exposure light amount. In the image recording apparatus of this embodiment, the process speed is three steps (G: 12).
mm / sec, E: 37 mm / sec, N: 74 mm / sec), the correspondence table is shown for each process speed. As a changing means for changing the re-exposure light amount L _R by the image exposing means 13, a pulse width modulation (P
WM change) means for changing the light quantity, means for changing the laser power (output) to change the light quantity, means for changing the light quantity by moving the optical system slit on the optical path of the image exposing means 13, and image exposing means. A means for changing the amount of light by inserting / removing a filter on the optical path of 13 and the like can be mentioned. In the embodiment shown in FIG. 4, a changing means for changing the PWM value is provided to correspond to the brush current value I _BR. I am trying to fluctuate.

The relation L between the voltage-converted brush current value I _{BR of the} charge applying means and the control value of the re-exposure light amount L _R
R (I _BR ) is stored in the ROM 43 as a program necessary for the arithmetic processing of the input signal. The condition value L _R (I _BR )
This relationship is stored in the ROM 43 for each of the process speeds G, E, and N so that the multistage control can be performed as much as the current detection resolution and the output control resolution allow, in response to changes in the environment.

The control circuit subsequent to the detection means shown in FIG. 2 stores the current signal input to the input interface 45 in the ROM.
A control unit 42 that performs a predetermined calculation based on the program stored in 43, and an R that temporarily stores the calculation result, data, etc.
With AM44, process speed and brush current value I _BR
Output signal based on the calculation result by
To control the PWM value of the image exposure means 13.

In the embodiment described above, the detecting means for detecting the change in the environmental conditions is the detecting means by detecting the electric current in the charge applying means, but of course the invention is not limited to this. Further, in the embodiment, an example in which a brush is used as the charge applying means has been described, but the present invention is also similarly applied to the case where a conductive roller that rotates on the transfer belt is used instead of the brush, and the displayed brush current value I _Even in the same environment, _BR varies depending on the brush material, belt material, and design conditions, so it is necessary to use the correspondence table according to the material and design.

Regarding the re-exposure performed after the toner image is formed on the photosensitive drum 10, prior to the re-exposure by the image exposing means 13, the scorotron charger 12 uniformly charges the formed toner image. In a preferred embodiment, the toner image portion excluding the finally formed toner image portion is re-exposed and the writing light amount at the time of this re-exposure is changed in accordance with the change in environmental conditions. .. Of course, prior to the re-exposure by the image exposure means 13, the toner image formed by the scorotron charger 12 is uniformly charged, and the entire toner image is re-exposed. You may make it change according to a change.

[0036]

According to the image forming apparatus of the present invention, re-exposure is performed, the repelling phenomenon at high humidity is eliminated, and the transferability is not deteriorated at low humidity. An image forming apparatus has been provided which can perform stable transfer to obtain a good transferred image.

[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 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) Applying and detecting means) 35 Nip (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 section 43 ROM 44 RAM 45 Input interface 46 Output interface

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G03G 15/01 114 Z 15/04 120 9122-2H

Claims (2)

[Claims] 1. An image is formed on an image carrier a plurality of times,
In an image forming apparatus that recharges at least one formed toner image and re-exposes at least one formed toner image and then transfers and fixes the amount of writing light at the time of re-exposure. An image forming apparatus having a changing unit for changing. 2. The image forming apparatus according to claim 1, wherein the changing unit is configured to change the light amount of re-exposure in response to a change in environmental conditions.