JPH0643767A - Image forming device - Google Patents

Abstract

PURPOSE:To keep the electrostatic charge and the printing density of a form constant and to improve printing quality by providing a switching means for switching transfer potential, and switching the transfer potential in accordance with humidity and the thickness of the form. CONSTITUTION:A ROM 24 storing a program for controlling the operation of an entire device and a RAM 25 storing data in course of calculation are connected to a CPU 23 being the switching means. Then, signals from a form thickness chageover switch 22 and a humidity sensor are inputted in the CPU 23. Meanwhile, a transfer device 15 is connected to the CPU 23 through a driver 26 for the output of the CPU 23, so that the transfer potential is given to the back surface of the form. The transfer potential can be switched to three steps, and the optimum transfer potential is selected in accordance with the humidity and the thickness of the form.

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 in which an image is formed on a sheet using a photosensitive drum, and in particular, it is of high quality regardless of the humidity inside the apparatus and the thickness of the sheet. The present invention relates to a configuration for obtaining the image of.

[0002]

2. Description of the Related Art In this type of image forming apparatus, an exposing device forms an electrostatic latent image on a photosensitive drum, and a toner is attached to the electrostatic latent image by a developing device, and the toner is transferred. It is designed to be transferred onto paper by a container. The toner transfer by the transfer device is performed by applying a predetermined potential by corona discharge to the contact portion of the sheet in a state where the sheet is in close contact with the photosensitive drum, and the toner moves to the sheet side due to the potential difference between the sheet and the toner. .

[0003]

In the above prior art, the predetermined potential for toner transfer, that is, the transfer potential, is always set to be constant. However, when the humidity inside the apparatus changes, the amount of water contained in the sheet changes, and the charge on the sheet changes even if the transfer potential is constant. For this reason, the print density varies due to changes in the humidity inside the apparatus. Further, corona discharge is applied from the back side of the paper, but when the thickness of the paper changes, the charging charge changes. Therefore, there is a problem that the print density varies even if the thickness of the paper changes.

The present invention has been made by paying attention to the problems existing in such a conventional technique, and the purpose thereof is to always be irrespective of changes in humidity or changes in the thickness of paper. An object of the present invention is to provide an image forming apparatus capable of ensuring a constant print density and having high print quality.

[0005]

In order to achieve the above object, in the present invention, a sheet is brought into close contact with a photosensitive drum, and a transfer potential is applied to the close contact portion to transfer the toner on the photosensitive drum onto the sheet. The gist of the image forming apparatus is a provision of switching means for switching the transfer potential.

[0006]

With the above structure, the transfer potential can be switched according to the humidity and the thickness of the paper. Therefore, the charge of the paper can be kept substantially constant, and the print density can be made constant.

[0007]

An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the photosensitive drum 2 is rotatably supported in the substantial center of the apparatus case 1, and a photoconductive film 3 is formed on the outer peripheral surface thereof. A charger 4 for uniformly charging the outer periphery of the photosensitive drum 2 and an exposing device 5 for forming an electrostatic latent image on the outer periphery of the photosensitive drum 2 face the photosensitive drum 2. The developing device 6 uses the toner T
And a developing roller 8.

The paper feed cassette 9 is detachably attached to the lower part of the apparatus case 1, and a large number of papers Y are accommodated in the paper feed cassette 9 in a stacked state. Paper feed roller 1
0 is arranged in the apparatus frame 1 so as to be positively rotatable, and the paper Y in the paper feed cassette 9 is fed by the paper feed roller 10 one by one. Then, the paper Y is sent to the lower part of the photosensitive drum 2 via the paper guide 11 and the feed roller 12. Further, in the paper guide 11, the paper feed cassette 9
A humidity sensor 13 for detecting humidity is provided at a position close to, and at which it does not interfere with the sheet feeding. The humidity sensor 13 contains a porous ceramic electrolyte, the electrolyte ionizes due to moisture in the air, and a current flows, and the humidity is measured by measuring the resistance value of the ceramic. You can

The transfer roller 14 is arranged so that the sheet Y from the feed roller 12 is brought into close contact with the photosensitive drum 2, and the transfer unit 15 sandwiches the sheet Y so as to face the photosensitive drum 2. It is fixed. The transfer device 15 applies a predetermined potential to the contact portion between the paper Y and the photosensitive drum 2,
The toner image is transferred onto the paper Y based on the difference between the potential and the potential of the toner image.

The static elimination lamp 16 irradiates the outer peripheral surface of the photosensitive drum 2 after transfer with light to eliminate static electricity. Further, the brush 17 and the memory removing brush 18 made of a conductive brush cleans the outer peripheral surface of the photosensitive drum 2.

The heat fixing device 19 is arranged on the downstream side of the photosensitive drum 2 and heat-fixes the image on the paper Y. The stacker 20 holds the sheet Y after the image is fixed. Device case 1
A switch panel 21 on which various switches and numeric keys are arranged is provided on the upper surface, and a switch 22 for inputting the thickness of the paper Y is provided therein.

Next, the circuit configuration of the portion related to the transfer potential control of this image forming apparatus will be described. As shown in FIG. 2, a CPU (central processing unit) 23, which is a switching means,
A ROM (Read Only Memory) 24 storing a program for controlling the operation of the entire apparatus and a RAM (Random Access Memory) temporarily storing data during calculation.
25 are connected. Further, signals from the paper thickness changeover switch 22 and the humidity sensor 13 are input to the CPU 23.
On the other hand, as an output, the transfer device 15 is connected via a driver 26, and a transfer potential is applied to the back surface of the paper Y. This transfer potential can be switched in three steps, and the optimum transfer potential is selected according to the humidity and the thickness of the paper.

Next, the operation of the image forming apparatus configured as described above will be described based on the flowchart shown in FIG. This flowchart proceeds under the control of the CPU 23 by the program in the ROM 24.

When the image forming operation is started by the start switch (not shown) (step 1), CP
U23 detects the signal from the paper thickness changeover switch 22, and subsequently detects the signal from the humidity sensor 13 to set the transfer potential (steps S2 to S8). That is, as described above, when the humidity inside the apparatus changes, the amount of water contained in the paper Y changes, and even if the transfer potential is constant, the charge on the paper Y changes and the print density varies. Become.
Further, the corona discharge is applied from the back side of the paper Y, but when the thickness of the paper Y changes, the charge charge changes and the print density varies. Therefore, when the humidity is high, the transfer potential is set high, and when the humidity is low, the transfer potential is set low. Also, paper Y
When T is thick, the transfer potential is set high, and when Y is thin, the transfer potential is set low. That is, as shown in FIG. 4, when the humidity is low and the sheet Y is thin, the low level is obtained. When the humidity is high and the sheet Y is thin, the medium level is low and the sheet Y is low.
Is set to a middle level when the sheet thickness is thick, and a high level is set when the humidity is high and the sheet Y is thick.

As described above, in the image forming apparatus of this embodiment, the transfer potential is adjusted according to the humidity and the thickness of the paper Y, so that an appropriate print density can be obtained and the print quality is improved. can do.

The present invention is not limited to the configuration of the above embodiment, and for example, the paper thickness setting switch 22 is used.
Instead of, the photo interrupter may be used to automatically detect the paper thickness based on the degree of light transmission. Further, it is possible to embody it by arbitrarily changing it within a range not departing from the gist of the present invention, such as calculating the optimum transfer potential from the paper thickness and humidity and adjusting it steplessly.

[0017]

According to the present invention, it is possible to always obtain a uniform print density regardless of changes in humidity and paper thickness.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a circuit configuration of a portion related to transfer potential control of the image forming apparatus.

FIG. 3 is a flowchart showing an operation in transfer potential control of the image forming apparatus.

FIG. 4 is a table showing settings of transfer potentials.

[Explanation of symbols]

2 Photosensitive drum, 23 CPU, T toner, Y paper.

Claims (1)

[Claims] 1. An image forming apparatus in which a sheet is brought into close contact with a photosensitive drum and a transfer potential is applied to the closely contacted portion to transfer toner on the photosensitive drum onto the sheet, a switching means for switching the transfer potential. An image forming apparatus characterized by being provided.