JPH04243272A - Image forming device - Google Patents

Abstract

PURPOSE:To offer an image forming device having an electrifier which can always electrify the surface of an image carrier such as a photosensitive drum to a constant potential. CONSTITUTION:The image forming device electrifying the surface of the image carrier 2 to the constant potential by the electrifier 30 using corona discharging and then, carrying out optical writing in response to an image signal, has a first high voltage power unit 40 allowing the electrifier 30 to generate the corona discharging between the electrifier 30 and the surface of the above- mentioned image carrier 2, and a second high voltage power unit 50 for regulating a discharging current generated by discharging, as a characteristic.

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 equipped with, for example, an electrophotographic printer and having a charger for charging the surface of a photoreceptor drum to a predetermined potential.

0002

2. Description of the Related Art In general, this type of printer executes the following series of image forming processes. First of all,
Uniformly charge the surface of the photoreceptor drum using a charger in a dark place. Next, L is applied to the surface of this charged photoreceptor drum.
An exposure device such as an ED array irradiates the image area with light. At this time, the charge on the image area exposed to light is removed (photoconductive phenomenon). Then, an electrostatic latent image is formed on the photoreceptor drum, with charges remaining in areas other than the image areas that are not irradiated with light. Subsequently, a developing device supplies toner (colored fine particles) charged to the same polarity as the electrostatic latent image to the latent image to obtain a toner image (visible image). Further, a recording paper is placed over this toner image, and a transfer device applies an electric charge of opposite polarity to the charged polarity of the toner to the recording paper from the back side of the recording paper, and the toner image is transferred onto the recording paper by electrostatic force. The transferred toner image is fused to the recording paper by applying heat or pressure by a fixing device to form a permanent image. On the other hand, the latent image charge on the photoreceptor drum after transfer is removed by a static eliminator (static eliminator). Further, residual toner remaining on the photosensitive drum without being transferred is removed by a cleaner.

Incidentally, in the first step of image formation, a corotron or scorotron, which is a corona charger, is often used as a charger used to uniformly charge the surface of the photoreceptor drum. Both chargers employ a non-contact charging method in which positive or negative ions generated by corona discharge in the air are applied to the surface of the photoreceptor drum, and corotron charging applies a fixed amount of charge to the surface of the photoreceptor drum. Scorotron charging has the characteristic of imparting a constant potential to the surface of the photoreceptor drum. A corotron has a structure in which a tungsten wire with a diameter of 50 to 100 μm is stretched in a shield case made of aluminum or the like, and corona ions are emitted from the opening of the shield case. Also, the high voltage applied to the wire is 5~
It is about 10kV. Since the corotron generates a fixed amount of charge as described above, it is not necessarily sufficient to charge the surface of the photoreceptor drum to a uniform constant potential.

On the other hand, a scorotron is a charger for reducing unevenness in the charging potential on the surface of a photoreceptor drum, and several wires or meshes insulated from the shield case are arranged as grid electrodes on the opening surface of the corotron. The configuration is as follows. Then, the opening surface of this scorotron is made to face the photoreceptor drum, and a bias voltage is applied to the grid electrode. A feature of the scorotron is that the charging potential on the surface of the photoreceptor drum is regulated by the grid potential, which is the potential of the grid electrode, and although it has a more complex structure and lower charging efficiency than the corotron, the uniformity of the charging potential is have the advantages that can be obtained.

FIG. 3 is a circuit diagram showing a conventional example of a scorotron. According to this circuit diagram, the high voltage power supply 60 is connected to the wire 61 of the scorotron, and the wire 61 is connected to the -
A high voltage of about 5000 V is applied, and it is connected to a grid electrode 64 through a constant voltage element 62 such as a varistor or a constant voltage diode, and a variable resistor 63 of about 1 MΩ, and a voltage of about -700 V is applied to the grid electrode 64. Apply. Here, both the constant voltage element 62 and the variable resistor 63 are for stabilizing the grid potential, which is the potential of the grid electrode 64. The variable resistor 63 is particularly useful when the constant voltage element 62 has variations in rating and a predetermined voltage cannot be obtained. On the other hand, the photosensitive drum 2 facing the planar grid electrode 64 and the high voltage supply device 60 are connected and both are grounded.

According to such a circuit configuration, the discharge current A
1 is the sum of the discharge current A2 flowing between the grid electrode 64 and the wire 61 and the discharge current A3 flowing between the photoreceptor drum 2 and the wire 61, and its value is several hundred.
It is about μA. Also, the value of the discharge current A2 is several tens of μ
It will be about A. This is a result of the electrons emitted from the wire 64 being controlled by the grid potential.

[0007]

[Problem to be Solved by the Invention] As mentioned above, the scorotron attempts to maintain the potential of the photoreceptor drum surface at a predetermined potential by keeping its grid potential constant and stabilizing the discharge current A3. . However, according to the conventional scorotron circuit configuration, it is inevitable that the resistance value of the variable resistor 63 used to stabilize the grid potential will change somewhat due to the influence of the surrounding temperature and humidity environment. Therefore, since the grid potential changes with this resistance value change, the discharge current A3
This will cause a large change in the Further, even when a fluctuation occurs in the discharge current A1 due to the high voltage supply device 60, the grid potential will fluctuate, causing a large fluctuation in the discharge current A3. In either case, if a potential fluctuation of 20 V or more occurs in the grid potential, it is no longer possible to control the discharge current A3. As a result, it becomes difficult to charge and maintain the surface of the photoreceptor drum 2 at a predetermined potential, resulting in a decrease in final image quality.

The present invention has been made in view of the current situation, and it is an object of the present invention to provide an image forming apparatus having a charger capable of always charging the surface of an image carrier such as a photosensitive drum to a constant potential. shall be.

[0009]

[Means for Solving the Problems] The present invention provides an image forming apparatus that charges the surface of an image carrier to a constant potential with a charger that utilizes corona discharge, and then performs optical writing in accordance with an image signal. a first high-voltage power supply device for generating corona discharge between the container and the surface of the image carrier;
The present invention is characterized in that it includes a second high-voltage power supply device for regulating the discharge current generated by the discharge.

0010

According to the above structure, when a high voltage is applied to the charger by the first high-voltage power supply device, a corona discharge is generated between the charger and the surface of the image carrier, and a discharge current flows. At this time, the discharge current is regulated by the second high-voltage power supply device, and the value of the current flowing between the charger and the surface of the image carrier is maintained at a constant value. As a result, the surface of the image carrier is charged to a constant potential.

[0011] After that, optical writing corresponding to the image signal will be performed on the surface of the image carrier.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a side cross-sectional view showing an example in which an image forming apparatus according to the present invention is applied to a printer. First, the schematic configuration will be explained according to the drawings. When a print switch (not shown) is turned on, the photosensitive drum 2 provided at the center of the printer 1 rotates in the direction shown by arrow B, and the charger 3 charges the surface of the photosensitive drum 2 accordingly. Note that the charger 3 will be described later. Next, the optical writing unit 4 consisting of an LED array emits light in response to an image signal given from a scanner section (not shown), and the photosensitive drum 2
expose the surface of the Thus, an electrostatic latent image is formed in the exposed area. Next, the developing device 5 installed at the upper right of the photoreceptor drum 2 in the figure supplies toner to the electrostatic latent image to form a toner image (
visible image).

Meanwhile, in synchronization with the image forming process, the paper feed roller 7 picks up the paper (not shown) stored in the paper feed cassette 8.
is fed out and supplied to the registration rollers 9. The registration rollers 9 transport the paper to the transfer device 6 in synchronization with the rotation of the photosensitive drum 2. The transfer device 6 is provided opposite to the photoreceptor drum 2, and transfers the toner image formed on the photoreceptor drum 2 onto a sheet of paper. The paper onto which the toner image has been transferred is then conveyed to the position of the fixing roller 10, where a fixing process is performed. After the fixing process, the paper is conveyed in a U-turn by a paper guide 11 for paper ejection and an ejection roller 12, and is ejected onto a paper ejection tray 13 attached to the upper part of the main body. In addition, in the figure, the pass line P of the paper is indicated by a chain line.

Next, details of the charger 3 will be explained according to FIG. 2. FIG. 2 is a circuit diagram showing the configuration of the charger 3. As shown in FIG. As is clear from the drawing, the charger 3 includes a main body 30, a high-voltage power supply 40 (encircled by a broken line in the figure), and a high-voltage power supply 50 (encircled by a chain line in the figure). The main body portion 30 corresponds to an active part of the charger 3, is provided opposite to the photoreceptor drum 2, and directly charges the surface of the photoreceptor drum 2 by corona discharge. Its structure is such that a wire 32 is stretched inside a box-shaped shield case 31 with an open surface opposite to the photoreceptor drum 2, and a grid electrode 3 is formed in a flat net shape in the opening of the shield case 31.
There are 3. The length in the longitudinal direction is the photoreceptor drum 2
The length in the longitudinal direction is approximately the same as that of .

The high-voltage power supply 40 is for supplying high voltage (for example, about -5000V) to the wire 32 in the main body 30, and includes a DC/DC converter 41 for inputting an external DC power supply, and a DC/DC converter 41 for inputting an external DC power supply. DC converter 4
1, and a rectifier 43 for rectifying the boosted DC pulse. The high DC voltage output from the rectifying section 43 is then supplied to the wire 32 in the main body section 30.

[0016] Furthermore, when the main body portion 30 operates, that is, when corona discharge occurs and a discharge current flows, the value of the discharge current is always at the level of several 100 μA.
Constant current control is performed in the high voltage power supply device 40. Regarding the control, the high DC voltage in the rectifier 43 is floated by a photocoupler 44, and the DC/DC converter 41 is controlled through a control circuit 45 so as to be able to cope with fluctuations in the entire circuit. Note that this control is variable depending on the current value to be controlled. The rectifier 43 is connected to the grid electrode 33 in order to form a circuit C1 through which a discharge current flows from the grid electrode 33 to the wire 32.

The high-voltage power supply device 50 is for supplying a high voltage (for example, about -700V) to the grid electrode 33 in the main body 30, and is also a DC/DC power supply for inputting an external DC power supply. It consists of a converter 51, a step-up transformer 52, and a rectifier 53. Then, the high DC voltage output from the rectifier 53 is applied to the grid electrode 33.
supplied to Further, in the high voltage power supply device 50, the main body 3
Constant voltage control is performed by the control circuit 54 so that a constant voltage is supplied to the grid electrode 33 at zero. The rectifier 53 is grounded together with the photoreceptor drum 2 in order to form a circuit C2 for a discharge current to flow from the surface of the photoreceptor drum 2 to the grid electrode 33.

According to the above configuration, the circuit C1 consisting of the high voltage power supply 40, the wire 32, and the grid electrode 33, and the circuit C2 consisting of the high voltage power supply 50, the grid electrode 33, and the photosensitive drum 2 are separate circuits. Therefore, even if the discharge current flowing through the circuit C1 changes, the discharge current flowing through the circuit C2 is not affected by the change. Furthermore, since a constant voltage element such as a variable resistor is not used for the grid electrode 33, and the potential thereof is kept constant by the high-voltage power supply device 50 that is controlled at a constant voltage, the grid electrode is always stable. As a result, when charging the surface of the photoreceptor drum 2, it is possible to always maintain a stable and constant charging potential.

[0019]

Effects of the Invention When using the above-described image forming apparatus according to the present invention, the first high-voltage power supply device for the charger to generate corona discharge when charging the surface of the image carrier to a predetermined potential is provided. In addition, since a second high-voltage power supply device is provided for regulating the discharge current generated by the corona discharge, the discharge current can always have a constant current value due to the second high-voltage power supply device. Therefore, it is possible to always charge the surface of the image carrier to a stable predetermined potential. As a result, it is useful to improve the image quality finally obtained and further to stabilize the image quality.

In addition to the function of charging the surface of the image carrier, the charger used in the image forming apparatus according to the present invention also functions as a transfer device for transferring the toner image formed on the image carrier to paper. is also applicable. Furthermore, it is not limited to image carriers, but can be applied to any charged object.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing an example in which an image forming apparatus according to the present invention is applied to a printer.

FIG. 2 is a circuit diagram showing the configuration of a charger used in the image forming apparatus according to the present invention.

FIG. 3 is a circuit diagram showing a conventional example of a scorotron.

[Explanation of symbols]

1 Printer 2 Photoreceptor drum 3 Charger 32 Wire 33 Grid electrode 40 High voltage power supply equipment 50 High voltage power supply equipment

Claims (1)

[Claims] 1. An image forming apparatus that charges the surface of an image carrier to a constant potential with a charger that uses corona discharge, and then performs optical writing in accordance with an image signal, wherein the charger charges the surface of the image carrier to a constant potential. An image forming apparatus comprising: a first high-voltage power supply for generating a corona discharge between the first and second high-voltage power supplies; and a second high-voltage power supply for regulating the discharge current generated by the discharge.