JPS6054673B2 - electrophotographic equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an electrophotographic apparatus using a three-layered photoreceptor having an insulating layer on the surface that is used repeatedly. This article relates to an effective method for preventing the effects of

In conventional electrophotographic devices of this type, a plurality of corona discharger chargers are installed around a cylindrical or belt-shaped photoreceptor (hereinafter also referred to as a photosensitive layer) and are linked to the operation of the device. It is common practice to switch between two states, a charged state and a stopped state, to perform latent image formation, transfer, etc.

In such devices, the surface potential of the photosensitive layer is often uneven immediately after the charger has finished operating, and as is well known, if the photosensitive layer is left in that state for a long time, the next When used, it causes negative effects such as uneven images. In order to avoid such adverse effects, as is well known, in the xerographic method using a photosensitive layer provided with a photoconductive insulating material on the surface of a conductor, as described in US Pat. No. 2,297,691, the photosensitive layer is All you have to do is irradiate the entire surface with light and leave the charge alone. However, in an electrophotographic method using a three-layered photosensitive layer having a conductive support, a photoconductive layer, and an insulating layer, as disclosed in Japanese Patent Publication No. 42-239W, light is applied to the photosensitive layer. Irradiation alone does not cause the charge to be lost, but corona discharge with a polarity opposite to that of the primary charge or by AC is applied at the same time or in sequence to uniformly level the potential on the surface of the photoreceptor. An object of the present invention is to provide an electrophotographic apparatus that achieves the above-mentioned reverse polarity or discharge control of an AC corona discharger with an inexpensive and simple configuration.

The present invention that achieves this object includes a three-layer structure basically consisting of an insulating layer, a photoconductive layer, and a conductive support, a means for applying primary charging almost uniformly to the photoreceptor, and irradiation with original image light. In an electrophotographic apparatus in which a latent image is formed using a secondary corona discharge means for applying a corona discharge or an alternating current corona discharge with a polarity opposite to that of the primary charging, and then a means for applying irradiation light almost uniformly to the surface of the photoreceptor. , a high voltage generator that generates a voltage to be applied to a corona discharger, a primary winding to which an input power supply voltage is applied, a secondary winding to output a voltage to be applied to the corona discharger, and a load circuit. A high-voltage transformer is provided with a tertiary winding, and the voltage is applied to the corona discharger by controlling the tertiary winding load circuit during relative movement of the photoreceptor other than the normal latent image forming process. The electrophotographic apparatus is characterized in that only one polarity of the voltage is lowered to a voltage lower than the corona discharge limit voltage of the corona discharger, and only the corona discharge of that polarity is stopped to eliminate static electricity from the photoreceptor. .
Therefore, according to the present invention, the potential distribution on the surface of the photoreceptor can be made uniform by a simple control method using a small and inexpensive high-voltage generator, and it is possible to prevent an adverse effect on the next image formation. becomes.

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 two-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 consisting of a conductive support, a photoconductive layer, and an insulating layer, as disclosed in Japanese Patent Publication No. 42-23910. be. The photosensitive layer 1 is electrically charged to about 1400 cm by a primary corona discharger 2 to which a voltage of about +6.3 KV is applied, and then charged to a secondary corona discharger 3 to which a voltage of about -6.5 KV 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 +5 in the part corresponding to the dark part of the original image.
00V1 bright part becomes O■. Next, toner is applied onto the latent image by the developing device 5 to form a visible image on the photosensitive layer 1, and the transfer paper 7 fed from the paper feed guide 6 is coated with about +
This visible image is corona-transferred by a corona charger 8 to which a voltage of 6.3K is applied. After the transfer, the paper is separated,
The image is sent to a fixing device (not shown) via a conveyance roller 9.
On the other hand, after the photosensitive layer 1 has been transferred, residual toner on the photosensitive layer 1 is removed and collected by a 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 immediately after a series of image forming steps are completed, and leaving it in this state is not recommended for the next image formation. have a negative impact on

FIG. 2 shows the potential distribution of the transfer paper of the electrophotographic apparatus shown in FIG. 1 immediately after the transfer is completed.

The surface of the photosensitive layer d between the secondary corona discharger 3 and the transfer charger 8 is covered with the shutter 1 shown in FIG.
While being irradiated with light from lamp 4 by 1 (blank exposure)
Because static electricity is removed by the secondary corona discharger 3, approximately -150
■It is.

Further, the surface potential e between the transfer charger 8 and the primary corona discharger 2 is approximately +700V, and the surface potential f between the primary corona discharger 2 and the secondary corona discharger is approximately +1400V as described above.
In order to make such an uneven potential distribution uniform, corona discharge of the primary corona discharger 2 and the transfer discharger 8 is conventionally stopped after the transfer of the toner image to the transfer paper is completed, as shown in FIG. By opening the shutter 11 and applying light from the lamp 4 to the photosensitive layer 1, the entire surface of the photosensitive layer 1 is heated to about -200 V by removing static electricity using only the secondary discharger for an appropriate period of time (for example, during one rotation of the drum). This eliminates the above-mentioned disadvantages by maintaining a uniform potential. In order to perform such an operation, conventionally, as shown in FIG. 3, high-voltage transformers for the primary and transfer dischargers with different on-off timings,
The high-voltage transformer that applies voltage to the secondary discharger is shown in Figure 3A.
A total of two transformers T, T2 of B were provided, and the operation of the corona discharger was controlled by controlling the on/off of the input voltage of each transformer.

However, this method ultimately requires two transformers, resulting in high cost and a large size, making it unsuitable for recent electrophotographic apparatuses 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.

The high voltage transformer T shown in FIG. 4 has a tertiary winding N3.
A load circuit L consisting of a diode D1, a resistor R1, a capacitor C1, and a switch S is connected to the next winding. During normal operation, S is open and the output of the secondary winding N2 produces the above (+) or (-) output, respectively, and the conductors A, b, c
The latent image is transmitted to each charger through the charger, and latent image formation, transfer, etc. are performed. At this time, the output voltage of the tertiary winding in the no-load state is approximately 5
It is 0■. When the final transfer paper has been transferred, the switch S is turned on at that timing, and the tertiary winding is also transferred.
Similar to the next winding output, a (+) polarity load is applied. In the transformer used here, the primary winding N1, secondary winding N2, and tertiary winding N3 are coupled by leakage magnetic flux, so the (+) voltage on the secondary side is relatively low due to the drooping characteristics of the transformer. High pressure output decreases. The output on the (-) side also decreases slightly, but remains almost constant. In the figure, Dl and D2 are diodes for half-wave rectification, Cl and C2 are capacitors that reduce ripple, Rl and R2 are resistors for obtaining output, and C is a resonant capacitor that changes the output in response to input fluctuations. are inserted in such a way that the fluctuations in the values are minimal.

FIG. 5 is an example of a timing chart showing the sequence of an electrophotographic apparatus using the high voltage generator shown in FIG.

In the figure, the switch S is turned on after the last transfer is completed, and as a result, a current of (+) polarity is consumed in the load circuit L of FIG. 4, and the (+) output voltage of the secondary winding N2 of the transformer T is The voltage drops below the discharge limit voltage, and the discharge of the primary and transfer corona dischargers stops. The (+) output and (-) output in the above case depend on the magnitude of the load resistance R.

FIG. 6 shows 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 curve A is 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, and is a value 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 O■. Figure 7 A1
Figure 2 shows the voltage and current characteristics of each corona discharger.

FIGS. 7B and 7C also show the cross-sectional shapes of the primary and transfer dischargers used in the experiment. FIG. 7B shows the shape of the primary discharger, and C shows the shape of the transfer discharger, and their dimensions are 11=1. =13=14=2
The distance 1 between the discharge line and the photosensitive layer was measured at 9.571 rm. As is clear from Figure 7A, both are about 3.5
~3.7KV is the discharge limit, and therefore, corona discharge can be stopped if the voltage falls below 3.5KV.

Therefore, if the load resistance R is selected as the value of R1 in Fig. 6,
The primary and transfer dischargers no longer generate corona. on the other hand,
If the voltage applied to the secondary discharger (-) is like curve A in Figure 6, it is ideal because the same output as normal (approximately -6.5 KV) can be obtained, but if it is like curve A in Figure 6, it is ideal. The load resistance is R1
Even if the output is slightly reduced (approximately -5.5 K) at this time, the static elimination ability can be maintained sufficiently and the above objective can be achieved. Thus, according to the present invention, the transformer is essentially 1.
By using a tertiary winding load circuit with a simple structure,
) side, corona discharge can be controlled by an inexpensive and compact high-pressure generator. In addition, in the graph of Figure 7,
The horizontal axis shows the applied voltage (K), and the vertical axis shows the discharge current (μA) in absolute value. FIGS. 8 and 9 show the state of the surface potential of the photoreceptor when the high voltage generator shown in FIG. 4 is used to eliminate the charges on the photoreceptor in the sequence shown in FIG. 5.

FIG. 18 shows a photosensitive layer exhibiting a potential distribution as shown in FIG. 2, immediately after the transfer is completed, by closing the switch S of the load circuit L shown in FIG. This shows the potential distribution after Figure 9 shows the potential distribution after the photosensitive drum is rotated one more time.
As a result, it was possible to maintain a substantially uniform potential, and even after being left for a long time, there was hardly any significant non-uniformity in the image the next time it was used. In Figure 9, there is also some unevenness in the potential, and by making one more rotation, the potential distribution becomes even more uniform, but in this case, the surface potential drops to nearly -300■, and when the photosensitive layer is placed at such a low level, In this case, the potential of the electrostatic latent image becomes too low the next time it is used, and a good image with large contrast cannot be obtained in many cases. Therefore, the 8th
After creating the potential distribution as shown in the figure, further install the secondary corona discharger 3.
When the applied voltage is lowered and the static elimination ability is lowered, a nearly uniform potential distribution of around -200V can be obtained by rotating once or twice. FIG. 10 is a circuit diagram showing one series of such applied voltage switching, in which a load Ra is connected in parallel to the load resistor R of the load circuit L in FIG. 4, and a switch Sa is connected in series with Ra.
, reduce the value of the composite load resistance, and reduce the load circuit L''
The voltage applied to the secondary corona discharger is lowered by reducing the current flowing through the secondary corona discharger.

FIG. 11 shows a timing chart of an electrophotographic apparatus having a high voltage generator using the circuit shown in FIG. Close transformer T (-)
The output, ie, the voltage applied to the secondary corona discharger, is further lowered to converge the potential on the surface of the photoreceptor to a substantially uniform value of around -200V.

At this time, both (+) outputs of the transformer T are below the corona limit voltage, and no corona discharge occurs. In the embodiment of the present invention, the load circuit of the tertiary winding is shown in FIG.
In addition to the diode shown in FIG. 0, various other circuits such as those using other rectifying elements and load circuits using transistors can be applied.

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, and even when AC is applied to the secondary corona discharge voltage, it is possible to similarly turn off the primary and transfer corona dischargers to perform operations such as removing static from the photoreceptor. It is.

In this case, the AC may be a biased AC to which a bias voltage is applied. 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, in the present invention, in an electrophotographic apparatus that forms an electrostatic latent image on a three-layer photoreceptor, a load circuit is connected to the tertiary winding of a high voltage generator and this is adjusted to the operating timing of the apparatus. The voltage applied to only the corona discharger with a specific polarity is reduced to below the corona limit voltage, and the static electricity on the surface of the photoreceptor is removed by the other corona dischargers, making it possible to use a small and inexpensive high-voltage generator. By using a simple control method, it is possible to make the potential distribution of the photosensitive drum uniform after copying is completed, so as not to adversely affect the next copying.

[Brief explanation of the drawing]

1 to 3 are explanatory diagrams showing the outline of a conventional electrophotographic apparatus, FIG. 4 is a circuit diagram of a high-pressure generator showing an embodiment of the present invention, and FIG. 5 is a circuit diagram of a high-pressure generator shown in FIG. A timing chart showing the sequence of the electrophotographic apparatus used, FIG. 6 is a graph showing the corona discharge characteristics according to the present invention, and FIG. 7A shows the voltage/current characteristics of the corona discharger having the shape shown in FIGS. 7B and C. FIG. 8 and FIG. 9 are explanatory diagrams showing the state of the surface potential of the photoreceptor after applying the present invention, FIG. 10 is a circuit diagram showing another embodiment of the present invention, and FIG. 11 is the 10th
3 shows a timing chart of an electrophotographic apparatus to which the circuit shown in the figure is applied. 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, Ra... Load resistance, S, Sa... ...Represents a switch.

Claims (1)

[Scope of Claims] 1. A three-layer structure basically consisting of an insulating layer, a photoconductive layer, and a conductive support, means for applying a primary charge to the photoreceptor substantially uniformly, and substantially simultaneously with the irradiation of the original image light. In an electrophotographic apparatus that forms a latent image using a secondary corona discharge means that performs corona discharge or alternating current corona discharge with a polarity opposite to that of the primary charging, and then means that applies irradiation light almost uniformly to the surface of the photoreceptor, corona discharge is used. A high voltage generator that generates voltage to be applied to electrical appliances has a primary winding to which an input power supply voltage is applied, a secondary winding to output voltage to be applied to the corona discharger, and a tertiary winding to which a load circuit is connected. of the voltage applied to the corona discharger by controlling the tertiary winding load circuit during relative movement of the photoreceptor other than the normal latent image forming process. An electrophotographic apparatus characterized in that only one polarity is reduced to a voltage lower than the corona discharge limit voltage of a corona discharger, and only the corona discharge of that polarity is stopped to eliminate static from a photoreceptor. 2 The load circuit has at least one rectifying element,
2. The electrophotographic apparatus according to claim 1, wherein only the voltage applied to a corona discharger of a specific polarity is lowered below a corona discharge limit voltage. 3. Claim 1, wherein the load circuit has means for switching the voltage applied to other corona dischargers while keeping the voltage applied to the corona discharger of a specific polarity below the discharge limit voltage. The electrophotographic device described in .