JPH05333687A - Image carrying member of image forming device and surface potential destaticizing method - Google Patents

Abstract

PURPOSE:To lessen the run-out of carriers and the adhesion of toners by stepwise lowering the surface potential of an image carrying member to be subjected to photoirradiation down to the developing bias value by a developing means at the time of forming an image by reversal development. CONSTITUTION:The surface potential is lowered to the surface potential VA by the light obtd. by controlling the intensity of the light beam from a first LED optical head, which is thus at the surface potential VH in a time T verses electrostatic charge potential V characteristic diagram, so as to attain the same voltage value as the voltage value applied on a developing tank or slightly higher than the value. The surface of a photosensitive drum 1 is then projected with the light beam at the intensity of the light at which the surface potential drops down to nearly zero V by turning on the bias voltage applied on a developing device 4. Since the developing device 4 is provided downstream of the point to be cast with the light beam, the light intensity is increased slightly earlier by as much as the time required for the photosensitive drum 1 to rotate. The destaticizing stage is ended by irradiating the drum for the time for one turn of the drum after the control to drop the surface potential down to near zero V is started.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of removing the surface potential of an image carrier of an image forming apparatus by electrophotography, and more specifically, the surface potential of the image carrier at the time of image formation of the image forming apparatus by electrophotography. Regarding static elimination method.

[0002]

2. Description of the Related Art An image forming apparatus using an electrophotographic system is described in, for example, P. 1 of the book "Basics and Applications of Electrophotographic Technology" edited by the Institute of Electrophotography. 46-line 11 to p. 47-as described in line 7, a photoconductor drum 1 (see FIG. 4) having a photoconductive film formed on a conductive support, and a photoconductor drum 1 around the photoconductor drum 1. 1 is arranged in the downstream direction of rotation of the photosensitive drum 1 in order, and the photosensitive drum 1 to which a charging voltage is applied by the charger 2 is irradiated with light to discharge the charge on the exposed surface of the photosensitive drum 1. An exposure device 3 which is an exposure writing means for forming an electrostatic latent image,

Further, a developing device 4 which is a developing means for adhering toner to the photosensitive drum 1 on which the electrostatic latent image is formed to visualize the electrostatic latent image, and the toner image on the photosensitive drum 1 is recorded on a recording paper. 5
On the photoconductor drum 1, and a fixing device 7 for heating (pressurizing) the toner image transferred on the recording paper 5 to fuse it to the recording paper 5, and irradiating the photoconductor drum 1 with light. It is composed of a static eliminator 8 for eliminating the electrostatic charge remaining on the photosensitive drum 1, and a cleaner 9 for removing the residual toner on the photosensitive drum 1.

In such an image forming apparatus, a toner having the same sign as the polarity of the charging surface is attached to the surface of the photosensitive drum 1 on which the electrostatic latent image is formed to form a negative-positive type image.
In so-called reversal development, OPC (organic photoreceptor: Or
ganic photoconductor) does not have photosensitivity to the transfer potential, and a method of removing charge after negatively charging has been adopted. In some cases, a static eliminator by light irradiation is not provided before the charging step of the photosensitive drum 1. In this case, even if the applied voltage of the developing device is turned “OFF” with the completion of the image forming process, the surface potential remains on the photosensitive drum 1, so that the two-component developer (for example, , A mixed developer using iron powder as the carrier component and colored particles as the toner component), the carrier is developed, that is, so-called carrier rising occurs. Further, even in the case of a one-component developer, there is an undesirable phenomenon that the toner is developed because the toner contains a slight amount of the opposite polarity component. Therefore, in the conventional reversal development method, a method of irradiating the photoconductor drum 1 with light from the exposure device 3 to eliminate the charge before the charging process of the photoconductor drum 1 is completed.

Now, when the charging voltage of the photosensitive drum 1 is lowered by the light irradiation from the exposure device 3, the timing of turning off the developing bias voltage from the position of the developing device 4 and the rotation speed of the photosensitive drum 1. Then, the timing is 2πγ · α / 360 · 1 / x (sec). However, here, γ is the radius of the photosensitive drum,
α is the angle between the light irradiation point on the photoconductor drum by the exposure unit 3 and the installation point of the developing unit with respect to the rotation center of the photoconductor drum, and x is the rotation speed of the photoconductor drum, that is, the exposure unit 3 The developing bias voltage may be turned off after 2πγ · d / 360 · x (sec) from the irradiation with light. When the light irradiation on the photosensitive drum 1 described above and the developing bias voltage off operation are ideally performed, the relationship between the time T and the applied voltage V is as shown in FIG. 5 (however, the surface potential of FIG. Is a value at the magnet roller position of the developing device 4 which will be described later).

[0006]

However, since the timing is deviated due to uneven rotation of the photosensitive drum and the like, if the developing bias voltage is turned off before the exposure charge elimination as shown in FIG. 6, it takes a short time (to). However, there was a problem that career advancement occurred. Therefore, the present invention provides a method of removing the surface potential of an image carrier of an image forming apparatus that eliminates such a bad point in the image forming process by the conventional reversal development method and does not cause problems such as rising of the carrier. It is the one we are trying to provide.

[0007]

In order to solve the above-mentioned problems, a method of removing the surface potential of an image carrier of an image forming apparatus according to the present invention includes an image carrier and a charging for uniformly charging the image carrier. Device, exposing and writing means for forming an electrostatic latent image on the charged image carrier, developing means for visualizing the electrostatic latent image formed on the image carrier, and visualizing on the image carrier In an image forming apparatus comprising a transfer means for transferring the formed image to a transfer material, during the image formation of the reversal development, the exposure writing means irradiates the image carrier with light, and the surface potential of the image carrier during the image formation is It is characterized in that the developing bias voltage applied by the developing means is gradually lowered.

[0008]

As described above, according to the method of removing the surface potential of the image carrier of the image forming apparatus of the present invention, the surface potential of the image carrier is adjusted by adjusting the light intensity of the light irradiated from the exposure writing means. Since the surface potential at that time is gradually decreased to the development bias voltage value, the exposure start portion due to the edge effect is not developed unlike the image formation by the conventional reversal development method.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a printer 35 used in the method of removing the surface potential of an image carrier of the image forming apparatus of this embodiment. This printer 35
A photosensitive drum 1, a charging roller 21, an LED head 22 as an exposure writing unit, a developing unit 4 as a developing unit, and a recording paper conveyance path around the photosensitive drum 1 toward the downstream in the rotation direction thereof. 24, a transfer roller 26, and a cleaner 9. The charging roller 21 is in contact with the photosensitive drum 1 and is driven to rotate as the photosensitive drum 1 rotates (direction A). Further, the LED head 22 is configured to irradiate the charged photosensitive drum 1 with light R corresponding to an image to be written onto the exposure point B of the photosensitive drum 1 to expose the photosensitive drum 1. ..

The developing device 4 sends the toner tank 4a, an agitator roller 4b, a supply roller 4c, a mixer roller 4d, and a developing roller 4f equipped with a magnet roller 4e to a developing tank 4f. The roller 4d mixes and stirs with a carrier (not shown), and then the magnet roller 4e attaches the electrostatic latent image on the photosensitive drum 1 to visualize the electrostatic latent image. One end of the recording paper transport path 24 is arranged near the contact portion between the photosensitive drum 1 and the transfer roller 26 (described later), and the other end is arranged near the lower end portion of the paper feed cassette 10. The transfer roller 26 is in pressure contact with the photosensitive drum 1, and the cleaner 9
Is a cleaning blade 9 that contacts the surface of the photosensitive drum 1.
a.

The recording paper on which the toner image on the photosensitive drum 1 has been transferred passes through the discharge / conveyance path 27, the heat roller 28 and the pressure roller 29, which are arranged in pressure contact with each other, and through the discharge roller to the discharge tray. It is discharged to 33. The recording paper is pressed between the heat roller 28 and the pressure roller 29 to fix the transferred toner image. Further, below the printer 35, a controller 31 and an engine controller 32 are arranged. The controller 31 receives a signal from a host computer (not shown), receives an image signal and a printer engine control signal, and controls the engine. The operation of each member is controlled.

Next, an embodiment of a method for removing the charge potential of the photosensitive drum in the image forming process by the reversal development method using the printer 35 of this embodiment will be described. The time T vs. voltage V characteristic diagram of FIG. 2 can be shown by showing the falling state of the charge potential elimination of the photosensitive drum 1 according to the present embodiment.
Curves a, b, c, d and e in the T vs. V characteristic diagram of FIG. 2 respectively represent a drive voltage signal for rotationally driving the photosensitive drum 1, a bias applied voltage curve supplied to the charging roller 21,
The bias applied voltage curve supplied to the developing device, the light intensity curve of the light beam projected from the LED optical head 22 onto the photosensitive drum 1, and the light beam emission control signal curve supplied to the LED optical head 22 are shown. As is clear from FIG.
The projection point B of the light beam projected from the LED optical head 22 onto the photosensitive drum 1 is located downstream of the charging roller 21 when viewed from the rotation direction of the charging roller 21, so that the photosensitive drum 1
The light beam projected from the LED optical head 22 onto the charging surface is irradiated to time earlier than when the bias charging voltage applied to the charging roller 21 is off. As for the intensity of the light beam from the first LED optical head, as shown in the characteristic diagram of time T vs. charging potential V in FIG. 3, what was at the surface potential V _H was changed to the voltage value V _D applied to the developing tank 4f. The surface potential is lowered to V _A by the light d whose light intensity is controlled to be the same voltage value or slightly higher.

Next, the bias voltage applied to the developing device 4 is turned off. Then, a light beam is projected onto the surface of the photosensitive drum 1 with a light intensity such that the surface potential is reduced to near zero V. The timing is shown at t ₁ in FIG. Developing device 4
Is provided downstream from the point R where the light beam hits,
The light intensity is increased earlier by the time required for the photosensitive drum 1 to rotate. After the surface potential is started to drop to near zero V, the photosensitive drum is irradiated for one rotation and the static elimination step is completed. The sequence process described above is as shown in FIGS. 2 and 3. By doing so, it is possible to suppress the consumption of the carrier when the charging potential of the photosensitive drum is lowered. Further, in the process using the transfer roller, it is possible to prevent stains caused by their adhering to the transfer roller 26 or stains on the back side of the print caused by the stains. Further, it is possible to prevent the carrier from adhering to the transfer roller and damaging the surface of the photosensitive drum.

[0014]

As is apparent from the above description, according to the method of removing the surface potential of the image carrier of the image forming apparatus of the present invention, the image writing member is irradiated with light from the exposure writing means during the image formation of the reversal development. However, the phenomenon of carrier rising or toner adhesion can be greatly reduced by a simple operation of gradually lowering the surface potential level of the image bearing member to the developing bias value by the developing means.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a printer of an embodiment used in a method of removing surface potential of an image carrier of an image forming apparatus of the present invention.

FIG. 2 is a diagram illustrating a photosensitive drum, a charging roller, and an LE according to an embodiment of a method of removing the surface potential of the image carrier of the image forming apparatus according to the present invention.
6 is a time chart showing a state of applied voltage versus time of a D optical head and a developing device.

FIG. 3 is a characteristic diagram showing the relationship between the time (T) and the charging potential (V) of the sequence for lowering the charging potential in the method of removing the surface potential of the image carrier of the image forming apparatus of the embodiment shown in FIG. ..

FIG. 4 is a longitudinal sectional view of an essential part showing the basic configuration of an electrophotographic image forming apparatus.

FIG. 5 is a characteristic diagram showing a relationship between time (T) and applied voltage (V) in the surface potential lowering method of the image carrier of the image forming apparatus in the conventional reversal development method.

FIG. 6 is a characteristic diagram showing the relationship between time (T) and applied voltage (V) in the surface potential lowering method of the image carrier of the image forming apparatus in the conventional reversal development method.

[Explanation of symbols]

 1 Photosensitive Drum 2 Charging Roller 3 Exposure Device 4 Developing Device 5 Recording Paper 21 Charging Roller 22 LED Optical Head 26 Transfer Roller

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shiro Wakahara 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (1)

[Claims] 1. An image carrier, a charging device for uniformly charging the image carrier, an exposure writing unit for forming an electrostatic latent image on the charged image carrier, and an image forming unit formed on the image carrier. An image forming apparatus comprising: a developing unit that visualizes an electrostatic latent image; and a transfer unit that transfers an image visualized on an image carrier to a transfer material. The surface potential of the image carrier of the image forming apparatus is gradually reduced to the applied value of the developing bias voltage by the developing device by irradiating the image carrier with light from the surface of the image carrier. Static elimination method.