JPH02173678A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a solid phenomenon, a large quantity of toner consumption, toner soiling inside the device, an increase in the burden imposed on a cleaning device, etc., by stopping an action when an electrification current becomes abnormal. CONSTITUTION:Owing to a constant current output from a high voltage power source 31, an electrifying electrode 13 electrifies the photoconductive layer 12a of a photosensitive drum 12. A comparator 32 detects a voltage V arising in the detected resistance R of a current generated by corona discharging in the electrode 13. When the comparator detects abnormality, a CPU 32 outputs an error signal to stop a copying process.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus that employs a reversal development method, and particularly to an image forming apparatus that can effectively deal with failures in a charging device.

[Background of the invention]

There are two types of development methods for electrostatic image forming apparatuses: regular development and reversal development. Regular development involves charging the surface of a photoconductive photoreceptor with high voltage DC, lowering that charge with image exposure light to form a latent image, and then producing a dry toner with a charge of the opposite polarity to the charged charge. This is a development method in which a toner image is formed by applying a toner to the non-exposed area (residual charge area). On the other hand, reversal development is a development method in which a dry toner having a charge of the same polarity as the above-described charge is applied and attached to an exposed area (low charge area) to form a toner image.

This reversal development method is used when reproducing a negative image as a positive image, recording character information displayed on a cathode ray tube (CRT), or using a laser beam or LED as the exposure light.
(Light-emitting diode) Used in printers etc. that use light.

[Problem to be solved by the invention]

In this way, reversal development is a method in which toner is attracted to a low potential area. Therefore, if the photoreceptor surface is not charged with a high voltage charge in advance, the photoreceptor surface will be Since the potential is uniformly low, toner adheres to the negative side, causing an accident where so-called solid development occurs.

This is often caused by an abnormality in the charging device, especially a disconnection or short circuit in the discharge wire of the charging electrode.

When such an accident occurs, not only is a large amount of toner consumed, but toner scatters inside the machine, contaminating the inside of the machine, increasing the burden on the cleaning equipment, and causing major secondary problems. Occur.

The present invention has been made in view of these points, and its purpose is to stop the image forming operation when an abnormality occurs in the charging device, thereby preventing the above-mentioned problems from occurring. That's true.

[Means to solve the problem]

To this end, the present invention provides means for detecting the value of a discharge current flowing through a charging electrode in an image forming apparatus that employs a reversal development method, and a comparison device that generates an alarm signal when the discharge current value deviates from a predetermined range. and a means for stopping the operation of the apparatus by sending out an alarm signal from the comparison means.

〔Example〕

Examples of the present invention will be described below. First, FIG. 2 is a diagram schematically showing a copying apparatus employing a reversal development method. A is an image reading device, and B is an image forming device.

In the image reading device A, an original (not shown) placed on a platen glass 1 is exposed and scanned by the movement of a rod-shaped light source 2 in the direction of arrow a, and the light image is transmitted through mirrors 3 to 5 and a lens system 6. After color separation, the signals are input to an image sensor 7 having an RGB (blue, green, red) reading section and read there. Then, the read image information is subjected to contour enhancement, partial or whole color conversion, MTF correction, trimming, masking, centering, and other image processing as necessary.

In the image forming apparatus B, a laser beam emitted from a light source (not shown) such as a laser diode is modulated by a light modulator (not shown) into light carrying the processed image information, and is scanned by a polygon mirror 10. The light then enters the photosensitive drum 12 which rotates in the direction of the arrow from the mirror 11. This photosensitive drum 12 is charged with a high voltage by a charging electrode 13, and a modulated light beam is incident on the charged portion and exposed.

Then, a selected one of the developing device 14Y having yellow toner, the developing device 14M having magenta toner, the developing device 14C having cyan toner, and the developing device 14B having black toner is applied to the portion where the electric charge has decreased due to this exposure. Toner from each developing device is attached to the developing device, and development is performed. The above-mentioned charging, image exposure, and development are performed a total of four times for yellow, magenta, cyan, and black for one image, and a full-color toner image is developed on the surface of the photoreceptor drum 12. Become. Then, when the development of this full-color toner image is completed, the paper that was previously fed from the cassette paper feed section 15A or 15B to the registration roller 16 is re-fed at a timing that coincides with the leading edge of the toner image. Transfer electrode 17
The toner image is transferred to the paper. Thereafter, the paper onto which the toner image has been transferred is separated from the photoreceptor drum 12 by the separation electrode 18, and is transported by the transport section 19 to the heat fixing section 20, where the toner image is thermally fixed, and then placed on the paper discharge tray.
The paper is ejected at 1. The toner remaining on the photosensitive drum 12 is then cleaned in the cleaning section 22 and prepared for the next charging by the charging electrode 13.

In this embodiment, in such a copying apparatus, an operation detecting section is provided at the charging electrode 13. An example is shown in FIG. Reference numeral 31 denotes a high-voltage power supply with a constant current output, and the charging electrode 13 charges the photoconductive layer 12a of the photosensitive drum 12, which is made of selenium or the like, with an electric charge of, for example, -700V.

12b is a grounded metal drum, and the photosensitive drum 1
It constitutes the second base. R is a detection resistor that indirectly detects the corona discharge current in the charged electrode 13, and the voltage (2) generated there is detected by the comparator 32. This comparator 32 consists of a window comparator, and when a voltage outside a predetermined range is input, the output terminal 32a is set to 'HJ level, and the control circuit (C
PU) Send to 33. In this control circuit 33, the input terminal 3
When the potential of 3a becomes 'HJ level, an error signal is output and the copying process is stopped. The process to be stopped here may be terminated immediately as appropriate, or may be stopped after waiting until the end of the copy cycle.

Now, in this operation detection section, the high-voltage power supply 31 functions as a constant current source, so if, for example, one or all of the discharge wires of the charging electrode 13 are disconnected, the current 1c flowing therein decreases or becomes zero. As a result, the detection resistor R
The current III flowing through the comparator 32 increases more than the normal value.
A voltage exceeding the upper limit of normal value Vll+ is applied to. Conversely, if even one of the discharge wires is short-circuited with the frame, the current Tc flowing there increases, the currents I and l flowing through the detection resistor R decrease from their normal values, and the comparator 32 A voltage below the lower limit of normal value Vat is applied.

When VIIZ≦V≦VRI, this comparator 32
The output terminal 32a is set to the 'LJ level, and when the signal goes out of this range, the 'HJ level is output. This output is then sent to the control circuit 33. This control circuit 33 outputs an error signal when the signal input to the input terminal 33a is 'HJ, and stops the copying process of the copying apparatus immediately or after a short period of time. It is also preferable to provide a display means on the operation unit or the like to display the information.

〔Effect of the invention〕

As described above, according to the present invention, since the operation is stopped when the charging current (discharge current) is abnormal, it is possible to prevent the occurrence of solid development, leading to unnecessary consumption of a large amount of toner, toner contamination inside the machine, and cleaning. It is possible to prevent an increase in the load on the device.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a portion of a charging device according to an embodiment of the present invention;
FIG. 2 is a diagram showing a schematic configuration of a color copying apparatus. A... Image reading device, B... Image forming device, 13.
... Charged electrode, 31 ... High voltage power supply, 32 ... Comparator, 33 ... Control circuit. Agent Patent Attorney Tsuneaki Nagao

Claims (1)

[Claims] (1) In an image forming apparatus employing a reversal development method, a means for detecting the value of a discharge current flowing through a charging electrode, and a comparison means for generating an alarm signal when the discharge current value deviates from a predetermined range are provided. An image forming apparatus comprising: an image forming apparatus, wherein the operation of the apparatus is stopped by sending out an alarm signal from the comparing means.