JPH04369661A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an excellent image including a color image whose color is well-balanced without receiving the effect of deterioration caused by long-term use or ambient environment by measuring the sensitivity of an image carrier by a simple method without requiring a complicated and expensive measurement device such as a potential measurement device. CONSTITUTION:An electrostatic charge roller 2 which electrostatically charges a photosensitive drum 1 is used as an electrical conductive contact member. Then, the contact part of the drum 1 and a roller 2 is irradiated with light from a light source 19 while a current is made to flow to the roller 2 and the current value flowing to the roller 2 at this time is detected. Since the detected current value corresponds to the sensitivity of the drum 1, the sensitivity of the drum 1 can be easily measured by it. Thus, the color image whose color is well-balanced is obtained without receiving the effect of the deterioration of the drum 1 caused by the long-term use thereof or the ambient environment by controlling the emitted light quantity of an LD 5 which exposes the image.

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 using electrophotography, and more particularly to an image forming apparatus suitable for color copying machines, color printers, and the like.

0002

[Prior Art] Color image forming apparatuses such as color copying machines and color printers using electrophotography etc. charge, expose and develop to form a toner image on an image carrier. By repeating the process of transferring each color onto the intermediate transfer body, a multicolor image is formed by superimposing toner images of each color on the intermediate transfer body, and this multicolor image is transferred all at once onto recording paper. This is a so-called intermediate transfer image. Toners of each color are formed on the recording paper by repeating the process of forming a toner image by charging, exposing, and developing the image carrier and transferring the toner image onto the recording paper for each color. A method employing a method of forming a multicolor image by superimposing images has been proposed and has already been put into practical use.

[0003] In these color image forming apparatuses, the sensitivity of the image carrier fluctuates due to long-term use, and the characteristics of the image carrier fluctuate due to changes in the surrounding environment. Depending on the environment and usage of the device, images with poor color balance may occur, which is not desirable.

[0004] In order to eliminate this drawback, a method is proposed in which the surface potential of the image carrier is measured after being charged or exposed, and the charging, exposure, and developing bias voltages of the developing device are controlled using the measured output signal, or these methods are proposed. A method in which the density of the toner image on the image carrier or intermediate transfer member is measured, and a method in which charging, exposure, or developing bias voltage is controlled in the same way as above based on the toner image density has been put into practical use. has been proposed.

[0005]

However, the conventional method described above requires a device for measuring the surface potential on the image carrier, an optical reflection density measuring device for measuring the toner image density, or a device for measuring the dielectric constant. is necessary. Incorporating such a complicated measuring device increases the size of the main body of the image forming apparatus, and since the measuring device is expensive, the cost of the image forming apparatus increases significantly.

An object of the present invention is to measure the sensitivity of an image bearing member in a simple manner without requiring a complicated and expensive measuring device, and to improve the color balance without deterioration due to long-term use or dependence on the surrounding environment. An object of the present invention is to provide an image forming apparatus capable of obtaining good images including clear color images.

[0007]

Means for Solving the Problems The above object is achieved by an image forming apparatus according to the present invention. To summarize, the present invention performs image exposure on an image carrier to form a latent image, develops the latent image to form a toner image, and transfers the toner image onto a recording material to obtain an image. In the image forming apparatus, while disposing a conductive contact member on the image carrier and applying a current,
The image carrier is irradiated with light and the current value flowing through the conductive contact member at that time is detected, and the light amount for the image exposure or the development bias for the development is determined according to the detection level of the obtained current value. The image forming apparatus is characterized in that at least one of voltages is controlled.

According to one aspect of the present invention, the charging roller that charges the image bearing member before image exposure or the cleaning blade that cleans the image bearing member after the toner image transfer is provided with the electrically conductive material. It also serves as a contact member.

[0009]

Embodiment FIG. 1 is a longitudinal sectional view showing an embodiment of an image forming apparatus according to the present invention. As shown in the figure, a photosensitive drum 1 is installed as an image carrier in a main body 30 of the image forming apparatus. , a charging roller 2, four developing devices 3, namely a yellow developing device 3Y, a magenta developing device 3M, a cyan developing device 3C, a black developing device 3B, and a cleaning device 4 are arranged around the charging roller 2, and inside the device main body 30. Above the photosensitive drum 1, a laser diode (LD) 5 and a high-speed motor 6 are installed.
An exposure device consisting of a polygon mirror 7 rotated by a lens, a lens 8 for correcting image formation and fθ characteristics, and a folding mirror 9 is arranged, and an optical image is formed on the photosensitive drum 1 by the exposure device. Ru.

A transfer roller 10 is disposed below the photosensitive drum 1, and this transfer roller 10 is made of a metal ring 10a with a diameter of 116 mm and a conductive sheet 10b with a thickness of 2 mm wrapped around it, and is driven by a driving means (not shown). It is designed to be rotated in the direction of the arrow. Conductive sheet 10b
Carbon, zinc oxide, etc. are dispersed in the resin, and its specific resistance is set to 107 to 1013 Ωcm. A transfer voltage is applied to the transfer roller 10 by a power source 11 in order to apply a transfer electric field for transferring the toner image on the photosensitive drum 1 onto the transfer paper P.

A transfer paper cassette 12, a paper feed roller 13, and a fixing device 14 are located on the left and right sides of the transfer roller 10 in the apparatus main body 30.
is provided, and a paper discharge tray 15 is attached to the outside of the apparatus main body 30.

The operation of the present color image forming apparatus will be explained. The photosensitive layer 1b of the photosensitive drum 1 includes an organic semiconductor (OP
C), photoconductive materials such as amorphous silicon, selenium, and zinc oxide can be used, but in this device, an azo pigment is coated as a CGL (carrier generation layer) as the photosensitive layer 1b, and hydrazine and resin are coated on top of it. The mixture is CTL (
Negative polarity OPC stacked to a thickness of 19 μm was formed as a carrier transport layer. Photosensitive drum 1 moves at 4 per second in the direction of the arrow.
It was rotated at a circumferential speed of 4 mm and charged by bringing the charging roller 2 into contact with it. The high-voltage power supply 16 supplies the charging roller 2 with a DC voltage of -600V and an AC voltage of 1300V peak-to-voltage.
When a superimposed peak (pp) is applied, a surface potential of -580V is obtained on the photosensitive drum 1 due to charging.

Next, an electrical signal of a yellow image is applied from the signal source 22 of the exposure device to the LD driver circuit 21, and the output signal is applied to the LD 5. An optical image of the yellow image is irradiated from the LD 5 and is focused on the photosensitive drum 1. An electrical latent image is formed. The light irradiation energy at this time is 2.4μJ
/cm2, and the surface potential of the photosensitive drum 1 is -80V.
Became.

The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 3Y and visualized as a yellow toner image. For this purpose, the photosensitive drum 1 is
So-called reversal development is performed in which a voltage of -500 V, which is approximately the same potential as the above charging polarity, is applied to the developing roller 3Ya for development. If necessary, add several hundred volts to the above -500V DC voltage.
An alternating voltage of up to several thousand Vp-p may be superimposed.

[0015] In the above development, a one-component development method was used in which toner is attached to the developing roller 3Ya, but known development means such as a two-component development method, a cascade development method, a jumping development method, a cloud development method, etc. Of course, it may be used. Furthermore, when the developing device 3Y is performing development, it is necessary to stop the developing operations of the other developing devices 3M, 3C, and 3B. Developing device 3M, 3C in order to stop toner supply.
, 3B may be applied to prevent the toner from flying to the photosensitive drum 1, or the rotation of each developing roller 3Ma, 3Ca, and 3Ba may be stopped, or a combination thereof may be adopted.

On the other hand, the recording paper P in the recording paper cassette 12 is fed to the transfer roller 10 by the paper feed roller 13.
It is wound around the transfer roller 10. In order to hold the leading edge of the recording paper P, the transfer roller 10 may be provided with a gripper or air suction means as necessary, or an insulating material such as a Mylar sheet may be provided on the surface of the transfer roller 10 in order to electrostatically attract the sheet. may be placed.

A DC voltage of +1 to +5 kV with a polarity opposite to that of the toner is applied to the transfer roller 10 from an external power source 11, and when the width of the recording paper P is 210 mm and the basis weight is 80 g/m2, the transfer current is set to 1 to +5 kV. By selecting 1.5 μA, the yellow toner image on the photosensitive drum 1 is transferred onto the recording paper P wound around the transfer roller 10.

The toner remaining on the photosensitive drum 1 after transfer is removed by a cleaning device 4 having cleaning means such as a blade, a fur brush, a magnetic brush, or the like. Next, the photosensitive drum 1 is uniformly charged again by the charging roller 2, and then exposed to a magenta color image to form an electrostatic latent image on its surface, and this electrostatic latent image is transferred to the developing device 3M containing magenta toner. It is developed and visualized as a magenta toner image. And the magenta toner image is
The yellow toner image is transferred onto the recording paper P wound around the transfer roller 10, overlapping with the yellow toner image.

In the same manner as described above, a cyan toner image,
A black toner image is sequentially formed, and the cyan toner image and the black toner image are further transferred onto the recording paper P in a superimposed manner. Thereafter, the recording paper P is peeled off from the transfer roller 10 by a separation static eliminator 17 and a separation claw 18 and sent to a fixing device 14. In the fixing device 14, the yellow toner image, magenta toner image, cyan toner image, and black toner image transferred onto the recording paper P are fixed by heating and pressure, and the recording paper P on which the toner images have been fixed is ejected. The paper is discharged onto the paper tray 15.

Although the change in the characteristics of the photosensitive drum 1 has not been described above, this will be explained below. According to what the inventor has discovered, when the light source 19 irradiates the contact portion of the photosensitive drum 1 with the charging roller 2,
It was found that the amount of current flowing to the charging roller 2 changes, and this change in the amount of current correlates with the change in sensitivity of the photosensitive drum 1.

FIG. 2 shows changes in the surface potential of the photosensitive drum 1 when the amount of light irradiated by the LD 5 of the image forming apparatus shown in FIG. 1 is changed, and the horizontal axis represents the light irradiation energy (μJ/cm
2), the vertical axis indicates the surface charge (V) of the photosensitive drum 1. In the figure, A to C represent the sensitivity characteristics of the photosensitive drum 1,
A is a fast response, B is a standard response, and C is a slow response.

As the photosensitive drum 1, these sensitivity characteristics A,
When three types B and C are used and light is irradiated from the light source 19 using the image forming apparatus shown in FIG. It was 24 μA for the photosensitive drum B, and 19 μA for the photosensitive drum with characteristic C, which has a slow response. At this time, light source 1
It was found that even if the light irradiation from 9 was stopped, the DC component of the current flowing from the charging roller 2 to the photosensitive drum 1 remained unchanged at 12 μA for each of the photosensitive drums having characteristics A, B, and C.

From the above, it can be seen that the amount of current flowing to the charging roller 2 when the light source 19 irradiates the contact portion of the photosensitive drum 1 with the charging roller 2 changes depending on the sensitivity characteristics of the photosensitive drum 1. Therefore, the current flowing to the charging roller 2 is detected by the current detector 20, and the detected signal level is applied to the LD driver 21, which is an LD control circuit, to control the amount of light emitted from the LD 5, which is an electrostatic latent image forming section. It has become possible to always keep the surface potential (VL) of the light irradiated part constant.

FIG. 3 shows the DC component of the current flowing to the charging roller 2 and the amount of light emitted from the LD 5 (irradiation energy) when the surface potential (VL) becomes -80V for the photosensitive drum 1 with sensitivity characteristics A, B, and C. ), and it can be seen that there is a correlation between them.

From this, from the detection signal level of the current flowing into the charging roller 2 detected by the above-mentioned current detector 20, it is found that the voltage required to maintain the surface potential of the photosensitive drum 1 at -80V (generally a desired constant value) is The amount of light emitted by the LD is determined, and as a result, the LD driver 21
By controlling the current value of the LD 5 and correcting the light amount, it is possible to always obtain a constant density in the image, and the photosensitive drum 1 is not deteriorated due to long-term use and is not dependent on the surrounding environment. A good image with good color balance can be obtained.

Although the present invention has been described above using a color image forming apparatus as an example, the present invention can also be applied to a monochrome image forming apparatus having a developing device for only one color, and similar effects can be obtained. In addition, although the case where the LD5 is used as the light source for image exposure of the photosensitive drum 1 has been described, an LED solid-state scanner, an LCD light source, etc. may also be used, and the same effect can be obtained by feeding back the detection signal from the current detector 20 to this. is obtained. In addition, although the charging roller 2 was used to detect the value of the current flowing through it, a conductive contact member that comes into contact with the photosensitive drum 1 was newly provided, and while the current was flowing through the contact member, the contact portion of the photosensitive drum 1 with the contact member was measured. It is also possible to perform the same procedure as above by irradiating the contact member with light and detecting the current flowing through the contact member at that time.

FIG. 4 is an explanatory diagram showing the main parts of another embodiment of the present image forming apparatus. In this embodiment, as shown in FIG. 4, the cleaning blade 4a of the cleaning device 4 is made conductive, and a light source 19 irradiates the contact portion of the photosensitive drum 1 with the cleaning blade 4a. At that time, the current flowing from the DC power supply 23 to the cleaning blade 4a is detected, the sensitivity characteristics of the photosensitive drum 1 are read out, and the amount of light emitted from the LD 5 of the image forming apparatus shown in FIG. 1 is controlled based on the detected current value. It is characterized by the fact that it is made as follows. The rest of the configuration of this embodiment is the same as that of the embodiment shown in FIG.

There is no problem even if the amount of light emitted from the LD 5 is controlled by the value of the current flowing through the cleaning blade 4a, and in this embodiment, it is also possible to always obtain a constant density of the image, and the photosensitive It is possible to obtain a good color-balanced image that is not affected by deterioration due to long-term use of the drum 1 or dependence on the surrounding environment.

In the above, the cleaning blade 4a of the cleaning device 4 is used, but when other blade blocks that contact the photosensitive drum 1 are used and light is irradiated to the contact portions of the photosensitive drum 1, the blade block It goes without saying that the same thing as above may be done by detecting the current flowing through the circuit.

FIG. 5 is an explanatory diagram showing the main parts of still another embodiment of the image forming apparatus of the present invention. In this embodiment, a light source 19 is arranged between the charging roller 2 and the cleaning device 4 on the downstream side in the traveling direction of the photosensitive drum, and the residual potential on the surface of the photosensitive drum 1 after cleaning by the cleaning device 4 is set to about 0V. After that, the cleaning device 4
The feature is that the photosensitive drum 1 is irradiated with light between the charging roller 2 and the charging roller 2. Other configurations of this embodiment are as follows:
This is the same as in the embodiment shown in FIG.

Also in this embodiment, when the photosensitive drum 1 is irradiated with light from the light source 19, the current flowing through the charging roller 2 is detected and the sensitivity characteristics of the photosensitive drum 1 are read out, and the LD5 is determined based on the detected current value. Similarly, by controlling the amount of light emitted by the photosensitive drum 1, it is possible to always obtain a constant density of the image, and to obtain a good image with good color balance that is not affected by deterioration due to long-term use of the photosensitive drum 1 or dependence on the surrounding environment. be able to.

FIG. 6 is an explanatory diagram showing the main parts of still another embodiment of the image forming apparatus of the present invention. In this embodiment, a mirror 24 is arranged in the optical path of the LD 5 of the image forming apparatus shown in FIG. 1 as shown in FIG. In addition, when detecting the value of the current flowing to the charging roller 2 while the photosensitive drum 1 is being irradiated with light, the mirror 24 can be moved as shown by the solid line to make it possible to irradiate the photosensitive drum 1 with light. .

According to this, the wavelength when detecting the current under light irradiation can be made the same as when forming the latent image, so the value of the current flowing to the charging roller 2 can be detected more accurately, and the light emission amount of the LD 5 can be controlled. There is an advantage that it can be done. In this regard, the same effect can be obtained in the image forming apparatus shown in FIG. 1 by making the wavelength of the LD 5 and the wavelength of the light source 19 substantially the same.

In all of the above embodiments, the sensitivity of the photosensitive drum 1 is measured by detecting the value of the current flowing to the charging roller 2 etc. while the photosensitive drum 1 is irradiated with light, and the LD5 is determined based on the detected current value. has been described, the present invention is not limited to this, and the developing bias voltages to the developing rollers 3Ya, 3Ca, 3Ma, and 3Ba may be controlled based on the detected current values, or This and LD
5 may be combined. A similar effect can be obtained.

[0035]

As explained above, in the image forming apparatus of the present invention, a conductive contact member is arranged to be in contact with an image carrier, and the image carrier is brought into contact with the contact member while passing a current through the contact member. The sensitivity of the image carrier is measured by irradiating the area with light and detecting the value of the current flowing through the contact member at that time, so it is easy to carry the image without the need for complex and expensive measuring devices such as potential measuring devices. By measuring the sensitivity of the body and controlling either or both of the amount of light for image exposure or the developing bias voltage applied to the developing roller of the developing device using the current value flowing through the contact member, image bearing can be maintained over a long period of time. It is possible to easily obtain good images including well-balanced color images without depending on the deterioration of the body or the surrounding environment.

[Brief explanation of drawings]

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

FIG. 2 is a graph of sensitivity characteristics showing changes in the surface potential of the photosensitive drum 1 when the amount of light irradiated by the LD of the image forming apparatus of FIG. 1 is changed.

3 is a graph showing the relationship between the LD irradiation energy and the DC component of the current flowing to the charging roller for obtaining a constant value of the surface potential of the photosensitive drum having the sensitivity characteristics shown in FIG. 2. FIG.

FIG. 4 is an explanatory diagram showing main parts in another embodiment of the image forming apparatus of the present invention.

FIG. 5 is an explanatory diagram showing essential parts in still another embodiment of the image forming apparatus of the present invention.

FIG. 6 is an explanatory diagram showing main parts in still another embodiment of the image forming apparatus of the present invention.

[Explanation of symbols]

1 Photosensitive drum 2
Charging roller 3Y~3B
Developing devices 3Ya to 3Ba Developing roller 5 Laser diode (L
D) 19 Light source

Claims (3)

[Claims] 1. Image formation in which an image bearing member is exposed to light to form a latent image, the latent image is developed to form a toner image, and the toner image is transferred onto a recording material to obtain an image. In the apparatus, a conductive contact member is disposed on the image carrier, and while a current is flowing, light is irradiated onto the image carrier, and a value of the current flowing through the conductive contact member at that time is detected. An image forming apparatus characterized in that at least one of a light amount for image exposure or a development bias voltage for development is controlled according to a detection level of a current value. 2. The image forming apparatus according to claim 1, wherein a charging roller that charges the image carrier before image exposure also serves as the conductive contact member. 3. The image forming apparatus according to claim 1, wherein a cleaning blade for cleaning the image carrier after the toner image is transferred also serves as the conductive contact member.