JP2547218B2 - Reverse image forming device - Google Patents

Description

The present invention relates to a reversal image forming apparatus equipped with a scorotron charger, and is used, for example, in an electrostatic transfer copying machine, a laser printer, or the like.

(B) Conventional Technology Generally, in image forming apparatuses such as an electrostatic transfer copying machine, a reverse image forming method for obtaining an image obtained by reversing an original image has come to be implemented with the diversification of image formation. ing. In the reversal image forming method, for example, when the polarity of the main charging device is negative, the polarity of the toner is also set to be negative, and a negative developing bias is applied to the developing device, so that the charge is canceled by the exposure. The negative polarity toner is made to adhere to the area, that is, the area corresponding to the white background of the document. Therefore, when the non-charged region of the photoconductor is opposed to the developing operation region of the biased developing device, the toner adheres to the entire non-charged region. When the charged area of the photoconductor is opposed to the developing operation area of the developing device which is not biased, carriers are attached to the entire charged area.

Therefore, conventionally, in order to prevent the toner and the carrier from being wasted due to such a phenomenon, the main charging device, the photoconductor driving motor, and the developing bias power source are set at a preset order and timing at the start and end of image formation. It is driven and stopped by.

(C) Problems to be Solved by the Invention By the way, for example, at the start of the image forming operation,
It is theoretically possible to apply a developing bias when the tip of the main charging area charged by the main charging device has just reached the developing operation area of the developing device. It is arranged apart from the developing device, and due to backlash of the drive system of the photoconductor or transient phenomenon of the electric system, as shown in FIG. 3 or FIG. There is a difference between the timing t11 in FIG. 11B and the operation timing t12 in the developing bias (FIG. 11B). That is, in the case of FIG. 3, the uncharged region in the period from t11 to t12 is
In order to pass through the developing operation area of the developing device biased to −400V, the toner adheres to the entire surface, and in FIG. 4, the main charging area of the photoconductor having a potential of −600V in the period from t11 to t12. Reaches the developing operation area of the developing device which is not biased, so that the carrier adheres to the photoreceptor.

The present invention has been made in consideration of such circumstances, and uses a scorotron charging device as a main charging device to control the grid voltage thereof, thereby forming an auxiliary charging region having a lower potential than the main charging region. However, by turning on and off the bias of the developing device while the auxiliary charging area passes through the operating area of the developing device, it is possible to prevent unnecessary toner and carrier from adhering to the photoconductor. A forming apparatus is provided.

(D) Means for Solving the Problems The present invention provides a main charging device, a developing device, and
A transfer device, a cleaning device, and a static eliminator are provided, and the photosensitive member is moved so as to face each of these devices in order, and a developer is attached to the exposed portion of the photosensitive member so that the formed image is transferred to a sheet. In the configured reversal image forming apparatus, the corona discharger installed in the main charging device so as to face the photoconductor, the grid electrode interposed between the corona discharger and the photoconductor, and the voltage applied to the corona discharger Discharge power supply, a main power supply that applies a voltage to the grid electrode during discharge of the corona discharger to form a main charging area on the photoconductor, and a voltage lower than the output of the main power supply on the grid electrode during discharge of the corona discharger. An auxiliary power source for applying an electric charge to form an auxiliary charging area on the photoconductor, a bias power source for applying a bias voltage to the developing device, and a control means for controlling the output application timing of each of the power sources. At the start and end of formation, a voltage is applied to the grid electrode from the auxiliary power source for a predetermined time to form an auxiliary charging area on the photosensitive member, and the bias charging area is applied while the auxiliary charging area passes through the developing operation area of the developing device. It is an inversion image forming apparatus characterized by outputting and stopping a power supply.

(E) Operation If the potential of the auxiliary charging area is set to a predetermined value that is lower than the potential of the main charging area, when the auxiliary charging area reaches the operating area of the developing device, the presence or absence of bias of the developing device Nevertheless, since the potential difference between the photoconductor and the toner or carrier becomes small, the toner or carrier does not adhere to the photoconductor. Therefore, if the bias of the developing device is turned on or off while the auxiliary charging region passes through the operating region of the developing device, unnecessary toner and carrier are prevented from adhering to the photoconductor at the start and end of image formation. It That is, even if there is a mismatch between the timings t11 and t12 shown in FIG. 3 and FIG. 4, it is within the passage period of the auxiliary charging area.

(F) Embodiments The present invention will be described in detail below based on embodiments shown in the drawings. This does not limit the invention.

FIG. 1 is a constitutional explanatory view showing the constitution of one embodiment of the present invention, in which 1 is a photosensitive drum rotating in the direction of arrow A, 2 is a scorotron charging device composed of a shield electrode 2a, a wire electrode 2b and a grid electrode 3. Numeral 4 is image light for forming an electrostatic latent image on the photoconductor drum, 5 is a developing device which incorporates the developing drum 5a and develops the electrostatic latent image on the photoconductor drum 1 into a toner image, and 6 is a paper feed roller 10. A transfer charger that transfers the toner image on the photoconductor drum 1 to the fed paper 9, a cleaning device 7 that cleans the surface of the photoconductor drum 1 that has finished the transfer, and 8 a unnecessary residual charge on the photoconductor drum 1. A static elimination lamp to be removed, E1 is a power source applied to the electrode wire 2b via the switch S1, E2 and E3 are main power sources and auxiliary power sources applied to the grid 3 via the switches S2 and S3 (output voltage of the main power source> Output voltage of auxiliary power supply), E4 is Baiyasu power applied to the sleeve of the developing roller 5a via the switch S4, M is a motor for rotating the photosensitive drum 1, E5 is the drive power source for driving the motor M via a switch S5, 11 is the switch S1
~ It is a control circuit for operating S5.

FIG. 2 is a time chart showing a temporal change of the potential of the photosensitive drum 1 in the developing operation area P of the developing device 5 of FIG. 1, and the operation of this embodiment will be described with reference to FIGS. 1 and 2. It will be described next.

First, the switch S5 is turned on, the motor M is driven, and the rotary drum 1 starts rotating in the direction of arrow A, and at the same time,
The switches S1 and S3 are turned on, and the output of the power source E1 is applied to the wire electrode 2b and the output of the power source E3 is applied to the grid 3. Then, when the scorotron discharge device 2 starts discharging, the auxiliary charging region starts to be formed at the point Q on the photoconductor 1. After that, when the switch S2 is turned on after the time T1 and the output of the power source E2 is applied to the grid electrode 3, the photosensitive member 1 starts to form the main charging region at the point Q from that point.

In this embodiment, the developing device 5 has a bias potential of −300 V or less and the photosensitive drum 1 has a main charging potential of −50.
The main charging potential is set to -600V and the developing bias potential is set to -350V because an inverted image with good contrast can be obtained at 0V or less. Further, when the potential of the auxiliary charging area is set to -500V or less, the carrier of the developing device adheres to the auxiliary charging area when the bias is not applied, so the potential of the auxiliary charging area is a value between -500V and the bias potential of -350V, that is, -350V. 40
It is set to 0V. Therefore, the output voltage of each power source E1, E2, E3, E4 was set to -6.0kV, -650V, -450V, -350V, respectively.
Therefore, when the auxiliary charging area reaches the point P of the photosensitive drum 1 at the time t1, the potential of the photosensitive drum 1 at the point P becomes −40 at the time t1 as shown by the curve (a) in FIG.
It becomes 0V, and after that, it will be switched to -600V after time T1, that is, at time t3. Therefore, if the switch S4 is turned on and the bias voltage of -350V is applied from the power source E4 to the developing roller 5a during the time from t1 to t3 in FIG. 2, the photosensitive drum 1 at the point P on the photosensitive drum 1 before the time t1. Is 0 and the bias potential of the developing device 5 is 0, the bias potential is 0 in the period of t1 to t2, the surface potential of the photoconductor drum is −400V, and the bias potential is −400V in the period of t2 to t3. Since the photoreceptor surface potential is −400 V at 350 V, unnecessary toner and carrier do not adhere to the photoreceptor drum 1 in any period.
Further, the irradiation of the image light 4 is started from the time when the main charging area formed by the scorotron charging device 2 reaches the point R of the photoconductor 1, and the main charging area has several latent images corresponding to the image light 4. Is formed. Further, when the image forming operation is stopped, first, the switch S2 is turned off to turn on the point Q of the photosensitive drum 1.
, The main charging area is switched to the auxiliary charging area, and after the period T1, the switches S1 and S3 are turned off to turn on the scorotron charging device 2.
Stop the charging operation. Thereby, the point P on the photoconductor 1
In FIG. 2, the surface of the photosensitive drum 1 is switched from the main charging area to the auxiliary charging area at time t4 as shown in FIG. 2, and the charging potential becomes 0 at time t1 after time T1. Therefore, at time t5 between t4 and t6, if the switch S4 is turned off and the bias potential of the developing device 5 is set to 0, the image is generated even during the period from t4 to t5, the period from t5 to t6, or the period after t6. As at the start of the forming operation,
Unwanted toner and carrier do not adhere to the surface of the photoconductor 1.

(G) Effect of the Invention According to the present invention, at the start and end of the image forming operation, the auxiliary charging area having a lower potential than the main charging area is formed on the surface of the photoconductor, and the auxiliary charging area serves as the developing operation area of the developing device. Since the bias voltage of the developing device is turned on and off during the passage, the potential difference between the surface of the photosensitive drum and the developer on the developing device is reduced, and unnecessary developer is prevented from adhering to the photosensitive drum.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of the present invention, and FIG. 2 is a time chart showing a temporal change between the potential of the surface of the photosensitive member and the bias potential of the developing device of FIG. 1, FIG. 3 and FIG. FIG. 4 is a time chart showing temporal changes in the potential on the surface of the photoconductor and the bias potential of the developing device in the conventional example. 1 ... Photosensitive drum, 2 ... Scorotron charging device, 3 ... Grid electrode, 4 ... Image light, 5 ... Developing device, 6 ... Transfer charger, 7 ... Cleaning device, 8 ... Static elimination lamp, 9 ... Paper, 10 ... Feed roller, 11 ... Control device, E1, E2, E3, E4, E5 ... Power supply, S1, S2, S3, S4, S5 ... Switch.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP 54-115233 (JP, A) JP 55-40458 (JP, A) JP 60-249171 (JP, A) JP 61- 18980 (JP, A) JP 61-290455 (JP, A) JP 60-78461 (JP, A) JP 59-218469 (JP, A) JP 60-154261 (JP, A) JP 61-240263 (JP, A) Actually opened 63-74654 (JP, U)

Claims (1)

(57) [Claims] 1. A main charging device, a developing device, a transfer device, a cleaning device, and a charge eliminating device are arranged around a photoconductor, and the photoconductor is moved so as to sequentially face each of these devices, and an exposure unit of the photoconductor is provided. In a reversal image forming apparatus configured to transfer an image formed by adhering a developer to a sheet, a corona discharger provided in a main charging device so as to face a photoconductor, and the corona discharger and the photoconductor. A grid electrode interposed between the body and a discharge power supply for applying a voltage to the corona discharger, and a main power supply for applying a voltage to the grid electrode during discharge of the corona discharger to form a main charging area on the photoreceptor. , An auxiliary power supply that applies a voltage lower than the output of the main power supply to the grid electrode during discharge of the corona discharger to form an auxiliary charging region on the photoconductor, a bias power supply that applies a bias voltage to the developing device, and each of the power supplies. Out of Control means for controlling the force application timing, and at the start and end of image formation, a voltage is applied from the auxiliary power source to the grid electrode for a predetermined time to form an auxiliary charging area on the photoconductor, and the auxiliary charging area is formed. An inversion image forming apparatus, wherein the bias power source is output and stopped while the toner passes through the developing operation area of the developing device.