JPH10161399A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device which detects a decrease in the resistance value of an insulation block and prevents beforehand damage to the insulation block from occurring. SOLUTION: The device has a corona electrifier 20, a high-voltage generation circuit (voltage generation circuit) 30 for applying a voltage to the corona electrifier 20, a current detection means for detecting a current flowing in the corona electrifier 20 from the high-voltage generation circuit 30, and a CPU (control means) 34 for controlling the high-voltage generation circuit 30. In the case, after a voltage which is lower than a voltage applied at the start of corona discharge is applied to the corona electrifier 20 for a fixed length of time or longer before the start of the corona discharge in an image formation preparation period, a voltage which is equal to or higher than the voltage applied at the start of the corona discharge is applied to the corona electrifier 20.

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 an electrostatic process, such as an electrophotographic copying machine or an electrostatic printer.

[0002]

2. Description of the Related Art An image forming apparatus utilizing an electrostatic process forms an electrostatic latent image on the surface of a photosensitive drum as an image carrier, and develops the electrostatic latent image with a developing device to form a toner image. The transfer material, which runs synchronously with the photosensitive drum, is brought into close contact with the photosensitive drum, and the reverse side of the transfer material is charged with a polarity opposite to that of the toner. Is formed.

In this type of image forming apparatus, various types of corona discharge devices such as a primary charger, a pre-transfer charger (post-charger), a transfer charger, a separation charger, and a pre-cleaning charger are commonly used. Have been.

FIG. 9 shows a conventional corona discharger. This corona discharger has a corona wire 194 made of tungsten or the like having a wire diameter of 30 to 100 μm and a conductive wire approximately 1 cm away from the corona wire 194. It is configured such that a voltage of about 5 to 10 kV can be applied between the shield plate 195 and the transparent shield plate 195.

The distance between the corona wire 194 and the shield plate 195 is kept constant by insulating blocks 196 and 197, one end of which is connected to the electrode 198, and the other end of which is pulled by a spring 199.
Here, the insulating blocks 196 and 197 are not only high in volume resistivity but also high in withstand voltage, arc resistance, tracking resistance and flame-retardant, and harmless. , And as the material, polybutylene terephthalate, liquid crystal polymer, polyphenylene sulfide, and the like are generally used.

[0006]

However, when the corona discharge is repeated in the corona discharger, the corona discharge product generates an electrolytic substance together with the moisture in the air, and this electrolytic substance adheres to the insulating block. Has a problem that the resistance value of the insulating block decreases, which causes the deterioration of the insulating block to be accelerated and causes dielectric breakdown.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to detect a decrease in the resistance value of an insulating block and take measures to prevent the insulation block from breaking before it occurs. An object of the present invention is to provide an image forming apparatus.

[0008]

According to one aspect of the present invention, there is provided a corona discharger, a voltage generation circuit for applying a voltage to the corona discharger, and the corona discharger. In an image forming apparatus having current detection means for detecting a current flowing through a discharger and control means for controlling a voltage generation circuit, a voltage lower than a corona discharge start voltage is applied to the corona discharger before the start of corona discharge in an image formation preparation period. After applying for a certain time or more, a voltage higher than a corona discharge starting voltage is applied to the corona discharger.

According to a second aspect of the present invention, there is provided a corona discharger,
An image forming apparatus comprising: a voltage generation circuit for applying a voltage to the corona discharger; current detection means for detecting a current flowing from the voltage generation circuit to the corona discharger; and control means for controlling the voltage generation circuit. A resistance detecting means for detecting the resistance value of the corona discharger at a voltage lower than the corona discharge start voltage before the start of discharge is provided, and the corona discharger is controlled based on the resistance value of the corona discharger detected by the resistance detection means. It is characterized by doing.

According to a third aspect of the present invention, in the second aspect of the present invention, a heating device is provided near the insulating block of the corona discharger, and the resistance value of the corona discharger detected by the resistance detecting means. The heating device is controlled on the basis of the resistance value of the corona discharger detected based on the above.

According to a fourth aspect of the present invention, in the second aspect of the invention, heat of another unit in the apparatus main body is led to the insulating block of the corona discharger.

According to the first aspect of the present invention, the voltage is gradually applied to the corona discharger, and a voltage lower than the corona discharge starting voltage is preliminarily applied before the voltage is applied. The resistance value can be increased, and damage to the corona discharger due to leakage or the like can be prevented. Further, since the resistance value of the corona discharger is detected by the pre-applied voltage, the application of high voltage to the corona discharger can be controlled, and damage to the corona discharger can be prevented.

According to the second aspect of the present invention, it is possible to control the heating of the charger based on the resistance value detection signal of the corona discharger, and it is possible to more reliably prevent damage to the corona discharger.

Further, according to the third or fourth aspect of the present invention, the heat of the heating device such as the fixing unit in the apparatus main body is led to the insulating block of the corona discharger, so that the corona discharger can be effectively manufactured at low cost. Can be prevented from lowering.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 1 is a schematic sectional view of an image forming apparatus according to the present invention. In FIG. 1, reference numeral 101 denotes a platen glass on which a document is placed, and 103 denotes an illumination lamp for illuminating the document. (Exposure lamps), 105, 107 and 109 are scanning reflection mirrors (scanning mirrors) for changing the optical path of the reflected light of the original, 111 is a lens having focusing and zooming functions, and 113 is an optical path. A fourth reflection mirror (scanning mirror) 115 is an optical system motor for driving the optical system, and 117, 119 and 121 are sensors.

Reference numeral 131 denotes a photosensitive drum; 133, a main motor for driving the photosensitive drum 131; 135, a primary charger; 137, a blank exposure unit; 139, a developing device; 140, a pre-transfer charger; Charger, 1
43 is a separation charger, 144 is a pre-cleaning charger, 1
45 is a cleaning device.

Reference numeral 151 denotes an upper cassette, 153 denotes a lower cassette, 171 denotes a manual feed port, 155 and 157 feed rollers, 159 denotes a registration roller, and 161 denotes a conveyance for conveying recording paper on which an image is recorded to a fixing side. Belt, 163
Is a fixing unit for fixing the conveyed recording paper by heat, and 165 is a paper discharge roller for discharging the recording paper on which the toner image has been fixed to the outside of the apparatus main body. The transport belt 161 is arbitrarily stopped.

The surface of the photosensitive drum 131 is composed of a photoconductor and a seamless photosensitive member using a conductor, and the photosensitive drum 131 is rotatably supported by a shaft.

The photosensitive drum 131 starts rotating in the direction of the arrow (clockwise) in FIG. 1 by the main motor 133 which operates in response to the pressing of a copy start key (not shown).

Next, when the predetermined rotation control and potential control processing (pre-processing) of the photosensitive drum 131 is completed, the original placed on the original table glass 101 is moved to the first scanning mirror 105.
Illuminated by an illumination lamp 103 integrally formed with
The reflected light of the original forms an image on the photosensitive drum 131 via the first scanning mirror 105, the second scanning mirror 107, the third scanning mirror 109, the lens 111 and the fourth scanning mirror 113.

The photosensitive drum 131 is corona-charged by the primary charger 135, and thereafter, the image (original image) irradiated by the illumination lamp 103 is slit-exposed, and is placed on the photosensitive drum 131 by a known Carlson process. An electrostatic latent image is formed.

Next, the electrostatic latent image on the photosensitive drum 131 is developed by the developing device 139 and visualized as a toner image, and the toner image is transferred onto recording paper by the transfer charger 141 as described later. .

That is, the recording paper in the upper cassette 151 or the lower cassette 153 or the recording paper set in the manual paper feed port 171 is fed into the apparatus main body by the paper feed roller 155 or 157, and is transferred to the transfer charger 141 by the photosensitive drum 141. By passing through the space between the transfer charger 141 and the drum 131,
Receives the transfer of the toner image on the photosensitive drum 131. Then, the recording paper to which the toner image has been transferred is sent to the fixing device 163 by the conveyance belt 161, and after the toner image is fixed by heat, the recording paper is discharged out of the apparatus main body by the discharge roller 165.

The photosensitive drum 131 after the transfer of the toner image
Continues its rotation, and its surface is cleaned by the cleaning device 145 including the cleaning roller and the elastic blade.

FIG. 2 is a block diagram showing a configuration of a control system of the corona charger.

The corona charger 20 shown in FIG. 2 includes a primary charger 135 and a pre-transfer charger 14 of the image forming apparatus shown in FIG.
0, can be used for the transfer charger 141, the separation charger 143, and the pre-cleaning charger 144.

First, a case where the corona charger 20 is used as a transfer charger will be described.

The transfer charger is a corona charger that transfers the toner to the transfer material by exposing the transfer material to ions of the opposite polarity to the toner. For this reason, a voltage of 5 to 10 kV is usually applied to the transfer charger from a DC high-voltage power supply.

In the transfer charger 20 shown in FIG. 2, reference numeral 21 denotes a corona wire having a wire diameter of 30 to 100 μm.
It is made of a tungsten wire of about 30 μm and its outer surface may be plated with gold to take measures to prevent corrosion. Reference numeral 22 denotes a conductive shield plate spaced from the corona wire 21 by about 5 to 15 mm, and is often made of stainless steel, Al, or the like. Reference numerals 23 and 24 denote insulating blocks which insulate the shield plate 22 and the corona wire 21 while keeping them at a fixed interval. 28,
Reference numeral 29 denotes a height adjusting piece for keeping the height of the corona wire 21 from the shield plate 22 constant. The height of the corona wire 21 is determined by the size of these pieces 28 and 29. Reference numeral 25 denotes a metal fitting for hooking one end of the corona wire 21, which is connected to the high voltage electrode terminal 27.

The other end of the corona wire 21 is connected to a spring 26.
It is connected to and pulled so as not to loosen. The high-voltage electrode terminal 27 is connected to the output of the high-voltage generation circuit 30, and a voltage of 5 to 10 kV is normally applied from the high-voltage electrode terminal 27. Reference numeral 31 denotes a current value monitoring resistor of the high voltage generation circuit 30, and 32 denotes an I / O for converting and transmitting a control signal from the CPU 34 to the high voltage generation circuit 30.

Next, a case where a voltage is applied to the high voltage generating circuit 30 will be described.

Normally, the corona discharge starting voltage is about 3 to 4 kV. Therefore, for example, when 1 kV is applied, the corona discharge does not occur and the current value is almost 0. Then, the resistance when 1 kV is applied is measured. Shield plate 2 using high-voltage resistance meter
Even when the resistance between the high voltage electrode terminal 27 and the high voltage electrode terminal 27 is measured, the resistance is too high and out of the measurement range.

However, usually, a copying machine, a printer, or the like,
When the resistance value of a charger of 100,000 to 500,000 sheets is measured under high temperature and high humidity (for example, at a temperature of 32.5 ° C. and a humidity of 85%) using a high-voltage resistance meter, the resistance is reduced to 100 MΩ or less. Often do. This is because the corona discharge products generated during corona discharge form various electrolytes together with the moisture in the air and adhere to the insulating block surface, or the insulating block surface is partially modified by the influence of the corona discharge. It is considered that the resistance value of the surface is reduced due to the above factors.

FIG. 3 is a diagram showing how the resistance value of the charger used in the copying machine changes with the number of endurance sheets. As shown in FIG.
The sudden increase in the resistance value near 50,000 sheets is a result of cleaning and removing the electrolyte substance attached to the inner wall of the insulating block. However, although the resistance value is recovered by cleaning, it is difficult to return the resistance value to the initial state.

Further, when the durability is advanced in a state where the resistance value is reduced, a current may suddenly start to flow toward the shield plate through the inner wall, and the current may burn the inner wall of the insulating block. The resistance value shown in FIG. 3 is a value measured 30 seconds after the application of the voltage, and this resistance value shows a sudden change immediately after the application of the voltage. This situation is shown in FIG.

As shown in FIG. 4, the resistance shows a considerably low resistance for about two seconds after the application of the voltage, but thereafter the resistance rapidly increases and then gradually increases. This is considered to be due to a decrease due to the movement of the electrolyte to the electrode caused by the energization, and a divergence of water due to heat generation due to the energization. It is important to note that since the resistance value is low at the beginning of energization, leakage is likely to occur due to dielectric breakdown when a high voltage is initially applied, and once leakage occurs, the inner wall of the insulating block starts to carbonize, and furthermore, the resistance value Is going into a bad cycle that causes a decrease in

FIG. 5 is a diagram showing how the resistance value of the charger in the copying machine changes during one day. FIG.
As shown in (1), immediately after the main power of the copying machine is turned on in the morning, the resistance value of the charger is the lowest. Since the temperature inside the copying machine gradually rises due to the temperature rise of the fixing device and the like, the temperature of the charging device also rises, the humidity decreases, and the resistance value of the charging device rises.

The resistance value also rises due to self-heating or the like caused by the electrification itself. And the main power supply O
After the FF, the temperature inside the device decreases, and accordingly, the resistance value decreases. Such a cycle is repeated, and the leak burnout of the charger easily occurs when the resistance value is low before the inside of the apparatus is warmed after the main power supply is turned on.

In the present embodiment, the following control is performed based on the above observation results.

The voltage is applied so as to gradually increase the voltage. Immediately after the main power supply is turned on, corona discharge is performed after sufficient power supply (10 seconds or more) so as to particularly increase the resistance value. Also, the resistance value is below a certain value (for example, below 15 MΩ)
In this case, the corona discharge was not started.

FIGS. 6 (a) to 6 (c) show the temporal transition of the applied voltage depending on the method of applying the voltage to the charger.

FIG. 6A shows a conventional case. After the main power supply is turned on and the fixing device is warmed, a voltage is first applied to the charging device to control the potential of the photosensitive member. After that, every time copying is performed, a voltage is applied to the charger.
This is a sudden voltage application by only the ON-OFF signal.

FIG. 6B shows the case of the present embodiment. First, immediately after the main power is turned on, a voltage is applied to the charger. This is a voltage of about 1 kV that does not start corona discharge, and is an energization for checking the resistance value of the charger and increasing the resistance of the charger. If the value of the resistance check is equal to or more than a fixed value (for example, 15 MΩ), a high voltage is applied for potential control while gradually increasing the voltage. After that, a voltage is applied for a certain period of time. The pre-rotational voltage is also gradually increased during copying. Further, after a certain period of time, the voltage is not applied because the temperature inside the device rises.

FIG. 6C shows an example in which the resistance value is low in the resistance check. First, the potential control after warm-up is not performed. Then, after it is confirmed that the resistance value is equal to or higher than a predetermined value by a resistance value check performed at regular time intervals, potential control is performed, and thereafter, copying is enabled. The resistance value check is performed by applying a voltage to the charger 20 by a voltage application signal from the CPU 34 shown in FIG. 2 and sending a signal from the current detection resistor 31 to the CPU 34 via the I / O 33. . The high voltage is gradually applied by the high voltage generation circuit 30 based on a signal from the CPU 34.

Although the above description has been made on the transfer charger which discharges with a direct current, the charger 31 which discharges with an alternating current, such as a separate charger or a post-charger, also has a current detecting resistor 31 shown in FIG. Rectified and smoothed to detect the magnitude of the voltage. Alternatively, the high voltage generating circuit 30 may be separately provided for switching.

In the resistance value check, if the resistance value does not increase while falling below a certain resistance value, the CP shown in FIG.
A signal can be sent from the U34 to the main body display unit 35 to display a warning that the resistance value of the charger 20 has decreased.

Second Embodiment Next, a second embodiment of the present invention will be described.

In the first embodiment, since the resistance value of the charger was caused by a rise in the temperature inside the apparatus or self-heating of the charger, the resistance value could not be rapidly increased or recovered.

Therefore, the present embodiment shows a case where the charger is rapidly heated by the external heating means. It should be noted that this rapid heating needs to be performed immediately after the main power is turned on until warm-up, as is evident from the change in the resistance value shown in FIG. 5, and must be controlled using a large heat source. . Hereinafter, an example of the control method will be described.

FIG. 7 shows an insulating block 73 of the charger 70,
An example is shown in which heaters 71 and 72 are attached to the lower part of 74.
The heaters 71 and 72 are heaters of about 100 W, and the power from the AC power supply 75 is turned on and off by the SSR 76.
It is configured to control. The ON-OFF control is performed based on a signal from the CPU 34.

The control is performed by applying a voltage to the charger 70 and checking the resistance value of the charger 70. The resistance value check is performed every 20 seconds after the main power is turned on. When the resistance value becomes equal to or more than a fixed value (1000 MΩ), a heater OFF signal is output from the CPU 34 and the heaters 71 and 72 are turned off. Thereafter, the temperature of the charger 70 does not suddenly decrease. After that, the interval between the resistance value checks may be set to be long in order to warm the apparatus by elevating the temperature inside the apparatus.

If the resistance does not increase for a certain period of time after the heaters 71 and 72 are turned on, the heaters 71 and 72, the SSR 76, the resistance check circuit, and the like may fail. A failure signal is output as an occurrence. A safety measure may be taken by attaching a thermal fuse or a thermoswitch or the like in the heaters 71 and 72 to prevent excessive temperature rise.

Further, the heaters 71 and 72 are connected to the shield plate 77.
However, it is of course possible to mount the heater on the heater or in the vicinity of the insulating blocks 73 and 74, although the heating rate is slightly reduced.

As described above, by using the heaters 71 and 72, the resistance value of the charger 70 can be rapidly increased, and the insulating blocks 73 and 74 can be prevented from being damaged by leakage under high humidity. . Further, by using the resistance value detection signal, the high power heaters 71 and 7 can be used.
2 can be controlled to quickly increase the resistance value of the charger 70.

<Third Embodiment> Next, a third embodiment of the present invention will be described.

In the second embodiment, the heaters 71 and 72
8 is attached near the charger 70. In the present embodiment, an example in which warm air is blown to the charger block is shown in FIG.
Shown in

In FIG. 8, reference numeral 80 denotes a fixing unit which is a heating source. A fixing roller 81 and a pressure roller 82 are accommodated in the fixing unit 80. A fixing roller 81 is maintained at a constant temperature by incorporating a heater. The fixing unit 80 is connected to a transfer / separation charger unit 90 by a pipe 94, and the transfer / separation charger unit 90 includes a charger 91 and a lower duct 92. The lower duct 92 is a lower duct 1 of the pre-transfer charger unit 1000.
020.

By the way, a suction fan unit 110 is provided in the middle of the pipe 94, and a fan (not shown) incorporated therein can rotate in both directions and generate airflow in both directions.

When the power supply of the fan is turned on in the morning (when the temperature of the fixing unit is a constant value (for example, 50 ° C. or less)), first, in order to warm the chargers 91 and 1010, arrows A shown in FIG. Create airflow in the direction. Then, it rotates so as to generate an airflow in the A direction until it warms up or the resistance value of the chargers 91 and 1010 becomes a certain value or more. After the resistance value reaches a certain value or more or after warm-up, the rotation is controlled so as to generate an airflow in the direction of arrow B in the figure.

As described above, by generating an air current in the reverse direction, when the resistance value is low in the morning, the charger 9
1 and 1010, and when the temperature rises, the charger 9
1, 1010 can be configured to discharge discharge products such as O ₃ generated therein and prevent the fixing unit 80 from rising in temperature.

As described above, in this embodiment, since the heat of the fixing unit 80 is used, the chargers 91 and 1010 can be rapidly heated without providing a separate heater. In addition, the surfaces of the chargers 91 and 1010 can be quickly dried by blowing the air current.

In addition, heat of a drum heater, which is a heating source used in a copying machine, may be blown to a charger by a fan, heat of a power supply unit may be blown, or a radiator plate of the power supply unit may be arranged near the charger unit. Is also effective.

[0064]

As is apparent from the above description, claim 1
According to the described invention, the voltage is gradually applied to the corona discharger, and a voltage lower than the corona discharge start voltage is preliminarily applied before the voltage is applied, so that the resistance value of the corona discharger can be increased. Thus, damage to the corona discharger due to leakage, etc. can be prevented. In addition, since the resistance value of the corona discharger is detected based on the pre-applied voltage, it is possible to control the application of high voltage to the corona discharger, which has the effect of preventing damage to the corona discharger. can get.

According to the second aspect of the present invention, it is possible to control the heating of the charger based on the resistance value detection signal of the corona discharger, and to more reliably prevent the damage of the corona discharger. The effect is obtained.

Further, according to the third or fourth aspect of the present invention, the heat of the heating device such as the fixing unit in the apparatus main body is led to the insulating block of the corona discharger, so that the corona discharger can be effectively manufactured at low cost. The effect that the reduction of the resistance value can be prevented is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an image forming apparatus according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of a control system of the corona charger.

FIG. 3 is a diagram illustrating a relationship between a resistance value of a charger and a number of durable sheets.

FIG. 4 is a diagram illustrating a relationship between a resistance value of a charger and an elapsed time after voltage application.

FIG. 5 is a diagram showing a change in resistance value of a charger over one day.

FIG. 6 is a diagram showing a temporal transition of an applied voltage due to a difference in a method of applying a voltage to a charger.

FIG. 7 is a block diagram illustrating a configuration of a control system of the corona charger.

FIG. 8 is a perspective view showing a configuration for guiding heat of a fixing device to an insulating block of a charger.

FIG. 9 is a perspective view of a corona charger.

[Explanation of symbols]

 Reference Signs List 20 corona charger (corona discharger) 23, 24 insulating block 30 high-voltage generation circuit (voltage generation circuit) 31 resistor 34 CPU (control means) 80 fixing unit (heating device) 90 transfer separation unit 1000 pre-transfer charger unit

Claims (4)

[Claims] 1. A corona discharger, a voltage generation circuit for applying a voltage to the corona discharger, current detection means for detecting a current flowing from the voltage generation circuit to the corona discharger, and controlling the voltage generation circuit. In the image forming apparatus having the control unit, after applying a voltage lower than the corona discharge start voltage to the corona discharge device for a predetermined time or more before the start of the corona discharge in the image formation preparation period, the corona discharge device has a voltage higher than the corona discharge start voltage. An image forming apparatus, wherein a voltage is applied. 2. A corona discharger, a voltage generation circuit for applying a voltage to the corona discharger, current detection means for detecting a current flowing from the voltage generation circuit to the corona discharger, and controlling the voltage generation circuit. In an image forming apparatus having a control unit, a resistance detection unit that detects a resistance value of the corona discharger at a voltage lower than a corona discharge start voltage before the start of the corona discharge is provided, and a corona discharger detected by the resistance detection unit is provided. An image forming apparatus wherein a corona discharger is controlled based on a resistance value. 3. A heating device is provided in the vicinity of the insulating block of the corona discharger, and based on the resistance value of the corona discharger detected based on the resistance value of the corona discharger detected by the resistance detecting means. The image forming apparatus according to claim 2, wherein the heating device is controlled by controlling the heating device. 4. The image forming apparatus according to claim 2, wherein heat of another unit in the apparatus main body is led to an insulating block of the corona discharger.