JPS6183560A - Electrophotographic copying device - Google Patents

Abstract

PURPOSE:To prevent deterioration of quality by warning of the lowering of discharge efficiency than a set value, if it occurs, and inhibiting successive copying over the predetermined quantity of copies. CONSTITUTION:The surface potential of a photosensitive body 1 electrostatically charged with a corona charger 3 is detected with a potential sensor 15 to estimate the discharge efficiency of the corona discharge wire 31. When the efficiency drops below a set value, a signal is sent to a display circuit 16 from a control circuit 14 to display warning to an operator, and a successive copying quantity regulating circuit 18 is actuated to inhibit successive copying over the predetermined quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an electrophotographic copying apparatus, and more particularly to an electrophotographic copying apparatus that uses a corona discharge device to remove static electricity from a photoreceptor band 1u.

(Background Art) Generally, in an electrophotographic copying apparatus, a photoreceptor is charged and neutralized to a predetermined level using a corona discharge device that uses a discharge wire as a corona discharge electrode. Since the corona discharge device uses corona discharge by applying a high voltage, its dust collection effect is unavoidable, and the discharge wire may be contaminated with developer, oxides, chlorides, nitrogen compounds, or dust in the air due to the discharge. It is easy to adhere, and this adhesion causes a decrease in discharge efficiency and uneven discharge. This eventually causes a decline in the quality of the copied image, and the adhesion of the foreign matter to the discharge line causes electric field concentration in a part or several places of the discharge line, causing an abnormality of more than twice the normal discharge current in that part. High-density corona currents tend to occur. This abnormal discharge often damages the photoreceptor, which is the object to be charged, and its service life is often shortened.

In order to solve these defects, conventionally, copying machine users or service personnel have to periodically remove the corona discharge device from inside the machine and clean it, or use a cleaning tool provided for the corona discharge device inside the machine. Measures are being taken, such as turning on the discharge wires to clean them or replacing the discharge wires.

However, conventional devices cannot automatically detect contamination of the corona discharge device, or even if it is detected, there is no means to restrict copying operations, and during this time, abnormal discharge occurs, causing damage to the photoreceptor or This has the disadvantage that electrical components may be damaged or malfunction, causing the system to become unbalanced. For example, Japanese Patent Application Laid-Open No. 54-28655 discloses a device that automatically performs cleaning using a cleaning means and a cleaning signal generating means, and Japanese Patent Application Laid-Open No. 54-97027 discloses a device for automatically cleaning dirt. The means have been disclosed. However, if the dirt cannot be removed by simple cleaning and the desired discharge characteristics cannot be obtained, the user must voluntarily suspend the copying operation until the discharge wire is replaced by a specialist. , or Hou1! Until the characteristics are recovered, two or more copying operations are performed, resulting in inconveniences such as a serious deterioration in the quality of the electrophotographic copying apparatus as described above.

In elucidating the mechanism of the above-mentioned abnormal discharge, the inventor found that there is a close relationship between the occurrence of abnormal discharge and the contamination of the discharge wire, and that the occurrence of abnormal discharge is determined by the degree of contamination of the discharge wire. It was discovered that, depending on the applied voltage and the diameter of the discharge wire, this phenomenon suddenly occurs several tens of seconds to several minutes or more after the start of discharge. In other words, even if the discharge wire becomes dirty and abnormal discharge is likely to occur, the possibility of abnormal discharge occurring within several tens of seconds to several minutes after the start of discharge is small, and even if abnormal discharge occurs, it will occur within several seconds. It has been found that if the discharge body is allowed to stop for several tens of seconds, it will take several tens of seconds to several minutes for the next discharge to occur.

(Object of the Invention) The present invention has been made in view of the above points, and detects the discharge efficiency of corona discharge to estimate the degree of contamination of the corona discharge electrode and to reduce the possibility of abnormal discharge occurring. To provide an electrophotographic copying device which warns and urges measures to restore discharge efficiency, such as cleaning or replacing a discharge electrode, and prohibits speed-reading copying of more than a predetermined number of sheets. The purpose is to

(Summary of the Invention) The present invention provides an electrophotographic copying apparatus having a corona discharge device that applies a voltage to a corona discharge electrode to generate a corona discharge. It has a warning means that warns of a decrease, and a regulating means that regulates the number of copies to be made, and when the discharge efficiency becomes lower than the set value, the above-mentioned warning means is activated and the number of copies is set in advance. This is to prohibit speed-reading copies of more than the number of sheets.

(Example) FIG. 3 is an electronic copy of Xe'0. Tokuko Sho 4 as an example of photographic lending.
2-23910 and Japanese Patent Publication No. 43-24748; FIG. Reference numeral 1 denotes a photoconductor drum as a charged body that rotates at a constant speed in the direction of the arrow. At the same time as it receives υ pre-exposure from a light source 21, pre-static discharge is performed by a charger 6, so that the surface of the photoconductor drum is uniform. The potential level is maintained at a certain level. After that, the charger 4 receives a primary charge with a polarity different from that of the pre-static charge removal, and then the charger 5 performs a secondary charge with a polarity different from the primary charge, or performs charge removal using alternating current or corona, and at the same time or Immediately thereafter, a light pattern is irradiated through the lens 6 of the optical system to form a latent image corresponding to the original on the photoreceptor drum, and after the electrostatic latent image is exposed on the entire surface by the light source 22, the developing unit 7 The image is developed with colored powder (hereinafter referred to as toner) to make it visible. This visible image is transferred to the transfer material 9 by the charging action of the transfer charger 8. After transcription,
The toner remaining on the photosensitive drum 1 is cleaned by the cleaning device 10, and the same process as described above is repeated thereafter. The copying process is not limited to the one described above, but the present invention can also be applied to a so-called Carlson process. In this case, ¥4 electric appliances 3゜5 and light source 2□
is not necessary.

Conventionally, the corona discharge device used as a charger in the above-mentioned electrophotographic copying device has a tendency for toner, other dust, foreign matter, etc. to adhere to the corona discharge KiE electrode (hereinafter referred to as the discharge wire) in the device. Adhesion causes a decrease in the amount of discharge or a stoppage of discharge. Furthermore, non-uniformity of corona discharge current density occurs, which adversely affects the quality of the final image.

Figures 2A-2D show family 1! The distribution of the corona discharge current knee p in the longitudinal direction of the discharge wire according to the dirt on the heel was measured. As shown in FIG. 4, a corona discharge wire 31 is connected to a high voltage power source (not shown) above the center of the discharge opening 34.
is arranged, surrounded by a grounded shield plate 3□ and an insulating plate 33 on both sides, and a conductive plate 11 for current measurement is provided opposite the discharge opening 34, and the current flowing through the conductive plate 11 is connected to the resistor 13. The voltage drop across the resistor 13 is measured as a discharge current and recorded on the recorder 12.

The current measuring conductive plate 11 is movable in the longitudinal direction of the charger 6, and a grounded guard electrode (not shown) is arranged around it.

Figure 2A shows an unused clean gold-plated tungsten wire with a diameter of 60 μm stretched over the charger 3,
This is the discharge current in the discharge opening 34 when the current flowing in the line opposite to the gate is +350μ. The applied voltage is 6.4 Y.

In this case, since there is no dirt on the discharge wire, an even discharge current distribution is shown as shown in FIG. 2A.

FIG. 2B shows the discharge current distribution after copying 10,000 sheets of A4 size paper in an actual electrophotographic copying apparatus. At the end of the discharge wire in FIG. 2B, toner etc.
1, the discharge current is uneven, but it can be almost recovered by simple cleaning means, and it is possible to return to the uneven state as shown in FIG. 2A. However, the applied voltage required to obtain a predetermined discharge current is υ higher than initially. Furthermore, if simple cleaning and continuous copying are repeated, the large discharge unevenness shown in Figure 2B can be removed by cleaning, but the applied voltage will increase and some discharge unevenness will remain. . (Figure 2C).

When observing a discharge wire in such a state, even after simple cleaning, the gold-plated tungsten wire is almost uniformly covered with black deposits. This deposit is an oxide produced by corona discharge.

It consists of chlorides, nitrogen compounds, etc., but the details are not clear.

In this way, discharge wire 3. If the discharge wire is almost uniformly covered with deposits, the image actually obtained by the electrophotographic copying device will be a good quality image with small unevenness, so copying may continue without noticing the dirt on the discharge wire. many. However, since the high voltage applied to obtain a predetermined discharge current is higher than usual, an abnormal discharge phenomenon may occur in which the discharge current partially increases, as shown in FIG. 2D. This phenomenon occurs suddenly after a certain period of time has passed after the start of discharge, and even if an abnormal discharge occurs once, if the discharge starts again after the discharge body has stopped, it will occur only after a certain period of time has elapsed. It turned out that there is a characteristic that it does not.

When such an abnormal discharge occurs, a high-density discharge current that is several times higher than the normal discharge current is generated in some parts, and the photoreceptor in that part may be damaged. In addition, this phenomenon may cause malfunctions of other electrical components, which may cause the entire system of the electrophotographic copying apparatus to become unbalanced and cause a malfunction.

It is difficult to completely remove the deposits that coat the discharge wire and restore the discharge wire to its initial state.In order to avoid the above-mentioned abnormal discharge phenomenon, the discharge wire 3. However, replacing the discharge wire usually has to be done by a professional service person, and careless copying must be interrupted during this time, which is a real inconvenience for the user. . In addition, if the main unit is driven in a state where abnormal discharge is likely to occur, the copy interruption time (which may cause a failure as explained above) will further increase, and repair and recovery will become difficult. It was convenient.

FIG. 1 is a schematic diagram of main parts showing one embodiment of the present invention, and 3
1 is a charger, 12 is a high-voltage power supply, 14 is a control circuit, 15 is a potential sensor, 16 is a display circuit, 17 is a display device, and 1 is a speed reading copy number regulating circuit.

In this embodiment, the potential sensor 15 detects the surface potential of the photoreceptor 1 charged by the corona charger 3, so that the discharge efficiency of the corona discharge line 31 can be estimated. When the discharge efficiency, that is, the surface potential of the photoreceptor becomes smaller than a certain set value, a signal is sent from the control circuit 14 to the display circuit 16 to display a warning to the user, thereby cleaning the discharge wire. Alternatively, it urges replacement and activates the speed-reading copy number regulation circuit 18 to prohibit speed-reading copies beyond a predetermined number of copies (for example, set to 0 to 10). t, b. If the discharge efficiency decreases and the abnormal discharge becomes more likely to occur, whether the number of copies can be reduced to the predetermined number even if the user sets the speed reading copy to be more than the predetermined number of copies. Alternatively, it is also possible to intermittently complete copying of the number of sheets set by the user while copying is interrupted and paused.

As described above, in this embodiment, changes in discharge efficiency are detected by measuring the surface potential of the photoreceptor, which is the charged object, and if the discharge efficiency has significantly decreased, the speed of copying is increased beyond the predetermined number of copies. By prohibiting reading and copying, the occurrence of abnormal discharge can be suppressed as much as possible. Furthermore, when measuring the surface potential, it is also possible to measure the voltage input to the high-voltage power supply with a predetermined reference value.

In this embodiment, the decrease in discharge efficiency may be detected by a change in the input voltage of the high-voltage power supply or the total current value.

(Effects of the Invention) As described above, according to the present invention, even if the discharge efficiency decreases due to dirt on the discharge wire, the condition can be displayed to the user on the nozzle stand, thereby making it possible to prevent the discharge wire from becoming dirty. In addition to prompting cleaning or replacement, speed copying of more than a predetermined number of copies is prohibited, making it possible to prevent the entire system of the electrophotographic copying apparatus from becoming unbalanced due to abnormal discharge. Long-term stability of the system can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of main parts showing an embodiment of the present invention, Fig. 2A-2
Figure D is a graph showing the discharge current distribution, Figure 6 is a schematic diagram of an electrophotographic copying apparatus to which the present invention is applicable, and Figure 4 is an explanatory diagram illustrating a method of measuring discharge current. 1... Photoreceptor 3.4.5... Corona discharge device 51... Corona discharge wire 3... Salary shield plate 12... High voltage power supply 14... Control circuit 15... Potential sensor 16 ...Display circuit 17...Display device 18...Regulation circuit No. 2C Kasumi perforation number Electrical equipment direction towards a certain electrical equipment manager

Claims (1)

[Claims] In an electrophotographic copying apparatus having a corona discharge device that applies a voltage to a corona discharge electrode to generate corona discharge,
It has a detection means for detecting the discharge efficiency of the corona discharge electrode, a warning means for warning of a decrease in discharge efficiency, and a regulation means for regulating the number of continuous copies, and when the discharge efficiency becomes lower than a set value, An electrophotographic copying apparatus characterized in that the above-mentioned warning means is activated and speed-read copying beyond a preset number of copies is prohibited.