JPS6150313B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the discharge of a corona discharger commonly used for latent image formation, transfer, separation, etc. in an electrophotographic apparatus.

In an electrophotographic device such as an electrostatic copying machine, corona discharge of both polarities (+) and (-) is normally generated, as shown in the example below, and corona discharge of one polarity (for example, +) is generated at a certain timing and only for a certain period of time. There may be cases where it is necessary to stop the corona discharge and allow only the other (-) polarity corona discharge to occur. Conventionally, when such a need arose, voltage was applied to each corona discharger with different on-off timing by a separate high-voltage generator, or a high-voltage switch was installed at the output of the high-voltage generator, and this switch was used. The above operation was achieved by switching.

However, in the former case, each corona discharger must be equipped with its own high-voltage generating device, which increases costs, and in the latter case, the high-voltage circuit is disconnected, which is dangerous and requires high voltage resistance. This has the disadvantage that an expensive switch is required and the cost is high.

SUMMARY OF THE INVENTION In view of the above-mentioned conventional drawbacks, it is an object of the present invention to provide a method for controlling corona discharge with an inexpensive and simple configuration.

The present invention that achieves this object is a method for controlling the discharge of a corona discharger using a high-voltage generator, in which the high-voltage generator that applies voltage to the corona discharger is connected to a primary winding to which an alternating current voltage is applied. , a secondary winding for applying a voltage of a specific polarity to the corona discharger via a rectifying element, and a tertiary winding connected to a load circuit including a rectifying element that forms a voltage of the same polarity as the specific polarity. By activating a load circuit connected to the tertiary winding, a voltage of a specific polarity applied to the corona discharger can be set to a corona discharge limit to generate a corona discharge. This is a corona discharge control method characterized by reducing the corona discharge below the voltage and stopping the corona discharge.

Therefore, according to the present invention, it is possible to selectively control on/off of the corona discharger with a simple configuration.

Hereinafter, one embodiment of the present invention will be described in detail while comparing it with a conventional example.

FIG. 1 shows a conventionally known electrophotographic apparatus using a three-layered photoreceptor having an insulating layer on its surface. In Fig. 1, numeral 1 is a photosensitive layer provided on a metal drum, which consists of a three-layer structure of a conductive support, a photoconductive layer, and an insulating layer as disclosed in Japanese Patent Publication No. 42-23910. It is something.

The photosensitive layer 1 is uniformly charged to about 1400V by a primary corona discharger 2 to which a voltage of about +6.3KV is applied, and then the static electricity is removed by a secondary corona discharger 3 to which a pressure of -6.5KV is applied. At the same time, the original image is irradiated 3a. As a result, an electrostatic latent image is formed on the surface insulating layer of the photosensitive layer 1 due to the difference in surface charge density. Next, the entire surface of the photosensitive layer 1 is uniformly exposed using the full-surface exposure lamp 4 to create a difference in surface potential depending on the brightness of the original image, thereby forming a high-contrast electrostatic latent image on the insulating layer. At this time, the surface potential of the photosensitive layer is +500V in the dark areas of the original image, and 0V in the bright areas. Next, toner was deposited on the latent image by the developer 5 to form a visible image on the photosensitive layer 1, and a corona discharger applied a voltage of approximately +6.3 KV to the transfer paper 7 fed from the paper feed guide. 8, this visible image is corona-transferred. After the transfer, the paper is separated and sent to a fixing device (not shown) via a conveyance roller 9. On the other hand, the photosensitive layer 1 has been transferred
Then, the residual toner on the photosensitive layer 1 is removed and collected by the cleaner 10, and the above-described copying process is repeated again.

In the above-mentioned electrophotographic apparatus, the surface of the photosensitive layer 1 is generally in a very non-uniformly charged state as schematically shown in FIG. Leaving it as it is will have a negative effect on the next image formation. For this reason, conventionally, after the transfer of the toner image to the transfer paper is completed, the corona discharge of the primary corona discharger 2 and the transfer discharger 8 is stopped, and the shutter 11 shown in FIG.
While opening the lamp 4 and applying light to the photosensitive layer 1,
By eliminating static electricity using only the secondary discharger for an appropriate period of time (for example, during one rotation of the drum), the entire surface of the photosensitive layer 1 is maintained at a uniform potential of about -200 V, thereby eliminating the above-mentioned disadvantages.

In order to perform this kind of operation, conventionally, as shown in Figure 3, high voltage transformers are used for the primary and transfer dischargers, which have different on-off timings, and a high voltage transformer that applies voltage to the secondary discharger. A total of two transformers are provided, as shown in Figure 3 A and B, transformers T ₁ and T ₂ .
The operation of the corona discharger was controlled by controlling the input voltage of each transformer to turn on and off. However, this method requires two transformers, resulting in high costs and a large size, making it unsuitable for modern electrophotographic devices that tend to be more compact.

FIG. 4 is a circuit diagram showing an embodiment of the high pressure generator according to the present invention, which improves the above-mentioned drawbacks. Fourth
The high-voltage transformer T shown in the figure has a tertiary winding _N3 , and a load circuit L consisting of a diode D, a resistor R, a capacitor C, and a switch S is connected to this tertiary winding. During normal operation, S is open, and the output of the secondary winding _N2 generates the above (+) or (-) output, respectively, and is transmitted to each charger through conductors a, b, and c. Then, latent image formation, transfer, etc. are performed. At this time, the output voltage of the tertiary winding under load is approximately 50V. When the transfer of the last transfer paper is completed, the switch S is turned on at that timing, and a (+) polarity load is applied to the tertiary winding as well as the output of the secondary winding. The transformer used here has a primary winding
Since the secondary winding N ₁ , the secondary winding N ₂ and the tertiary winding N ₃ are coupled by leakage magnetic flux, the (+) high voltage output on the secondary side is relatively reduced. The output on the (-) side also decreases slightly, but remains almost constant.

In the figure, D ₁ and D ₂ are diodes for half-wave rectification, C ₁ and C ₂ are capacitors that reduce ripple, R ₁ and R ₂ are resistors for obtaining output, and C ₃
is a resonant capacitor, which is inserted so that the output fluctuations are minimal with respect to input fluctuations.

The (+) output and (-) output in the above case depend on the magnitude of the load resistance R. FIG. 5 shows the schematic characteristics when the secondary side output is measured while changing this R.
The vertical axis in the figure represents the output voltage (KV) as an absolute value, and the (-) output curves A and B are due to the difference in the structure of the transformer, and the curve A shows the case of an almost ideal transformer. There is. _R1 is the value of the load resistance R when the (+) output falls below the discharge limit voltage,
This value is determined by the performance of the transformer and other conditions. That is, in order to stop the corona discharge of the primary corona discharger and the transfer discharger, it is not necessary to set the applied voltage to each of them to 0V.

FIG. 6A shows the voltage-current characteristics of each corona discharger. Figures 6B and 6C also show the cross-sectional shapes of the primary and transfer electric devices used in the experiment. Figure 6B shows the shape of the primary discharger, and C shows the shape of the transfer discharger, and their dimensions are l ₁ =
Measurements were made with l ₂ = l ₃ = l ₄ = 20 mm, and the distance l between the discharge line and the photosensitive layer was l = 9.5 mm.

As is clear from Figure 6A, both are about 3.5~
3.7KV is the discharge limit, so corona discharge can be stopped if the voltage falls below 3.5KV. Therefore, the value of R ₁ in Fig. 5 is equal to the load resistance R
If , the primary and transfer dischargers will not generate corona. On the other hand, the voltage applied to the secondary discharger (-) is
If it looks like curve A in Figure 5, the same level of output as normal (approximately -6.5KV) can be obtained, which is ideal.
Even if the output is slightly reduced (approximately -5.5 KV) when the load resistance is _R1 as shown in curve B, the static elimination ability can be maintained sufficiently and the above objective can be achieved. As described above, according to the present invention, only one transformer is required, and ON/OFF control of only the (+) side corona discharge can be performed using a simple tertiary winding load circuit. , it becomes possible to achieve corona discharge control using an inexpensive and compact high-pressure generator.

In the graph of FIG. 6, the horizontal axis shows the applied voltage (KV), and the vertical axis shows the discharge voltage (μA) in absolute value.

Next, another embodiment of the present invention will be described below. FIG. 7 shows a part of an electrophotographic apparatus to which the present invention is applied. In FIG. 7, reference numeral 12 denotes a photosensitive drum, which is a metal cylinder coated with a photoconductive material, which is uniformly charged by a corona discharger 13, and then electrostatically charged by irradiating the original image (as shown by arrow 14). A latent image is formed. Furthermore, toner is adhered onto the latent image by the developing device 14, and a corona discharge having a polarity opposite to that of the toner is applied to the transfer paper 16 fed by the transfer guide 15 by the transfer discharger 17, thereby performing corona transfer. Reference numeral 18 is a separation charger for separating the transfer paper from the photosensitive drum, and by acting on the corona-charged transfer paper, which has a polarity opposite to that of the transfer charge, electrostatic adsorption between the photosensitive drum and the transfer paper is caused by the transfer charge. The force is reduced to smoothly separate the transfer paper 16 from the photosensitive drum 12.

However, if separation charging is continued and strongly performed at this time, reverse transfer of the toner image on the photosensitive drum may occur, resulting in a reduction in copy quality. Therefore, as disclosed in Japanese Patent Publication No. 53-17495, it is known that if only the leading edge of the transfer paper is charged with a polarity opposite to that of the transfer charge, separation can be carried out smoothly.

In this case, each charger must operate at the timing shown in FIG. 8, and normally two transformers are required as shown in FIG. 3. However, according to the present invention, the desired operation can be achieved with one transformer even in this case. That is, a transformer having a tertiary winding and a load circuit as shown in Fig. 4 is used, and in this case, the diode D of the tertiary winding load circuit is
Reverse the direction. Then, the characteristics of the transformer are obtained by reversing the (+) and (-) in Fig. 5.
8), the switch S is turned on, the voltage applied to the separation charger becomes below the corona discharge limit voltage, and no corona discharge occurs. When switch S is opened when the leading edge of the transfer paper 16 reaches the position of the separation charger 18, the (-) applied voltage is applied to the separation charger 18.
In addition to this, the charge on the transfer paper is removed, and the leading edge is separated. By turning on the switch S again after a certain period of time, the applied voltage (-) is changed to the separation charger 1.
The voltage becomes below the discharge limit of 8, and the corona discharge stops again.

In FIG. 8, reference numeral 19 is a transfer paper conveying device, 20 is a lamp for static elimination and fatigue recovery, and 21 is a web-like cleaning member.

In the embodiments of the present invention, the load circuit of the tertiary winding is not limited to the one having the diode shown in FIG. Applicable.

Furthermore, in explaining the embodiments of the present invention, an example was shown in which a (+) voltage was applied to the primary corona discharger and a (-) voltage was applied to the secondary corona discharger. The polarity of the voltage may be opposite to the above,
Further, even when AC is applied to the secondary corona discharger, it is possible to similarly turn off the primary and transfer corona dischargers to perform operations such as removing static electricity from the photoreceptor.
In this case, the above AC is the bias voltage applied.
AC may also be used. In addition to the ones shown in the embodiments, it is also possible to combine other corona dischargers, such as a corona discharger for removing static from a photoreceptor.

As described above, according to the present invention, even when corona discharge is stopped, a predetermined voltage is applied to the corona discharger, so the rise time of the next discharge is short, and a stable discharge state can be quickly achieved. It will be done. Preferably, a corona discharger to which a positive voltage is applied;
Especially when it is desired to stop only one polarity of corona discharge for a certain period of time in an apparatus having a corona discharger to which a negative voltage is applied or a discharger to which AC is applied, the present invention can reduce costs. It is possible to provide an electrophotographic apparatus having a high-pressure generating device that is inexpensive and compact, and thereby enables effective control of corona discharge.

[Brief explanation of the drawing]

1 to 3 are explanatory diagrams showing the outline of a conventional electrophotographic device, FIG. 4 is a circuit diagram of a high-pressure generator showing an embodiment of the present invention, and FIG. 5 is a diagram showing corona discharge characteristics according to the present invention. Graph, Figure 6A is Figure 6B,C
7 is an explanatory diagram showing another embodiment of the present invention, and FIG. 8 is a timing chart showing the timing of applying voltage to each discharger. represents. In the figure, 2... primary corona discharger, 3...
Secondary corona discharger, 8...Transfer charger, T...High voltage transformer, _N1 ...Primary winding, _N2 ...Secondary winding, _N3 ...Tertiary winding, L...Load Circuit, R...
Load resistance, S...represents a switch.

Claims (1)

[Claims] 1. In a method of controlling the discharge of a corona discharger using a high-voltage generator, the high-voltage generator that applies voltage to the corona discharger has a primary winding to which an alternating current voltage is applied, and a rectifying element in the corona discharger. A high-voltage transformer having a secondary winding for applying a voltage of a specific polarity through the transformer, and a tertiary winding connected to a load circuit including a rectifying element that forms a voltage of the same polarity as the specific polarity. , by activating the load circuit connected to the tertiary winding, the voltage of a specific polarity applied to the corona discharger is reduced to a level below the corona discharge limit voltage that generates corona discharge, and the corona discharge is stopped. A corona discharge control method characterized by: