JPH0452767Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to image forming apparatuses such as copying machines, liquid crystal printers, and laser beam printers that apply electrophotographic technology. The present invention relates to an image forming apparatus using a photographic process.

[Prior art]

In image forming devices such as copying machines, liquid crystal printers, and laser beam printers that apply electrophotographic technology, in order to prevent the so-called thinning of characters and lines, the area where characters, lines, etc. are to be printed is placed on a charged photoreceptor. A reversal development method is usually used in which negative exposure is performed by irradiating light to form a low potential area, and toner is attached to the low potential area to form a positive image.

For example, an image forming apparatus using the above-mentioned reversal development method includes a photoreceptor, a charger, a light irradiation head, a developer, a transfer device, a static eliminator, etc. An electrostatic latent image is formed on the charged photoreceptor by the light irradiation head so that the light irradiation portion has a low potential, and the formed electrostatic latent image is developed with toner in a developing device. FIG. 4 shows the potential levels corresponding to the image area and non-image area on the photoreceptor at this time, and the electrostatic latent image described above is formed in the image area. Then, a bias potential at a level shown by the dotted line in the figure is applied to the developing device, and the toner adheres to the low potential portion of the electrostatic latent image to form a toner image on the photoreceptor. Thereafter, after the toner image is transferred onto the paper by a transfer device, static electricity is removed by a static eliminator to remove the surface potential of the photoreceptor. This charge removal is a process for making it possible to charge the surface of the photoreceptor to a uniform potential again. That is, if static elimination is not performed, the photoreceptor at the potential level shown in FIG. 5a will be charged by the charger, but as shown in FIG. Therefore, the surface potential of the photoreceptor after charging becomes a non-uniform potential level as shown in FIG. Therefore, it is necessary to remove the charge remaining on the photoreceptor with a static eliminator before the charging process.

On the other hand, in recent years, there has been a demand for downsizing of image forming apparatuses, and accordingly, internal parts of image forming apparatuses are also being downsized, used for multiple purposes, or eliminated. Conventionally, static eliminators differ from other image forming process members such as photoreceptors, chargers, developers, transfer devices, etc.
This is an auxiliary member, and an image forming apparatus has been proposed in which this is omitted. FIG. 6 is a diagram illustrating a charger used in such an image forming apparatus. This charger is a scorotron charger,
This is to compensate for the removal of the static eliminator as described above.

The scorotron charger 1 is disposed near the circumferential surface of the photoreceptor 2 and includes a charging wire 3, a shield case 4, and a grid 5 provided between the photoreceptor 2 and the charging wire 3. A voltage is applied to the charging wire 3 from a high voltage source 6, and the shield case 4
And the grid 5 is grounded via a varistor 7. Such a scorotron charger 1 attempts to charge the grid 5 to a uniform potential level by keeping the grid 5 at a predetermined potential using a varistor 7, regardless of dirt on the charging wire or residual charge on the photoreceptor before charging. .

[Problems with conventional technology]

By using such a scorotron charger, it is possible to achieve a certain degree of uniformity. However, when the reversal development method is applied as described above, non-uniformity in the charging potential directly appears as stains on the white background, so even when a Scorotron charger is used, satisfactory uniformity cannot be obtained.

[Purpose of invention]

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the conventional technology, an object of the present invention is to provide an image forming apparatus that can uniformly charge a photoreceptor and downsize the apparatus without using a special static eliminator. .

[Key points of the idea]

In order to achieve the above object, the present invention charges a photoreceptor to a predetermined potential of a predetermined polarity, irradiates it with a light image corresponding to the image to be formed, forms an electrostatic latent image, and forms an electrostatic latent image. A toner image is created by attaching toner to a low potential area, a transfer material is superimposed on the toner image, and the toner image is transferred to the transfer material by the action of an electric field having a polarity opposite to the predetermined polarity. In an image forming apparatus that separates a transfer material from the photoreceptor by a separation means and forms an image on the transfer material, the separation means includes a static eliminating member disposed at a predetermined distance from the photoreceptor; Voltage supply means for selectively supplying positive and negative voltages lower than the voltage at which the static elimination member starts self-discharging to the static elimination member; and switching means for switching the polarity of the voltage output from the voltage supply means to positive or negative. The voltage supply means supplies the voltage having the same polarity as the predetermined polarity when the transfer material faces the static elimination member by the switching action of the switching means, and the non-exposed area of the photoconductor supplies the voltage of the same polarity as the predetermined polarity. It is characterized in that the voltage having a polarity opposite to the predetermined polarity is supplied when facing the static eliminating member.

[Example of idea]

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

FIG. 1 is a block diagram showing an example of a liquid crystal printer as an example of an image forming apparatus according to the present invention.

In the figure, a photosensitive drum 8 as an image carrier is made of a conductive metal tube made of aluminum or the like, and has its outer peripheral surface coated with, for example, an organic semiconductor (OPC) to form a photosensitive surface 8a, and is directed in the direction of arrow a. Rotate to. Near the circumferential surface of the photoreceptor drum 8, there is a charger 9 that uniformly charges the photoreceptor drum 8, and a liquid crystal display that irradiates the photoreceptor surface 8a with a light image corresponding to a recording signal to form an electrostatic latent image. Head 10 and photosensitive surface 8a
A developing device 1 that develops the electrostatic latent image formed on the toner with toner.
1, a transfer device 12 for transferring the developed toner image onto the paper P, and separating the paper P from the photosensitive surface 8a,
and a separation static eliminator 16 for eliminating static from the photosensitive surface 8a.
and the photosensitive surface 8a that was not transferred by the transfer device 12.
A cleaner 13 is provided to remove residual toner thereon.

In the charger 9, a discharge wire 9b is stretched in a shield case 9a which is open on the side facing the photosensitive surface 8a. The discharge line 9b is connected to a negative high voltage power source 9d, and the negative high voltage of the high voltage power source 9d applied to the discharge line 9b causes corona discharge and negatively charges the photosensitive surface 8a.

The liquid crystal head 10 is composed of a light source 10a, a liquid crystal light shutter 10b, an imaging lens array 10c, a shutter drive circuit (not shown), etc., and the light emitted by the light source 10a is transmitted through a line-shaped shutter (not shown) arranged in the liquid crystal light shutter 10b. The light is transmitted or blocked by a microshutter, and the light that has passed through the microshutter is exposed onto the photosensitive surface 8a by an imaging lens array 10c having an imaging function.

The developer 11 stores toner 11 in the developer container 11a.
A developing roll 11c is disposed in the lower part of the developing container 11a and close to the photosensitive surface 8a. The toner 11b is a magnetic toner containing magnetite as a magnetic substance, and has negative charge polarity. The developing roll 11c is a developing sleeve 11d.
A magnet roll 11e is disposed inside the developing sleeve 11d, and a voltage slightly lower than that of the negative high potential portion (portion not irradiated with light) of the electrostatic latent image is applied to the developing sleeve 11d. The bias voltage source 11f is connected to the bias voltage source 11f. The developing device 11 is
Low potential part (light irradiated part) of the electrostatic latent image formed on the photosensitive surface 8a by the developing roll 11c
The toner 11b is attached to form a toner image.

Furthermore, an upper guide plate 14a and a lower guide plate 14b are disposed near the surface of the photoreceptor drum 8 on the downstream side of the developing device 11, for conveying the paper P carried out from the paper feed section (not shown) to the transfer section. Forms a paper transport route.

The transfer device 12 includes a discharge wire 12 in a shield case 12a that is open on the side facing the photoreceptor drum 8.
b is stretched, the discharge wire 12b is connected to the positive high voltage power supply 12c, and the shield case 12a
is grounded. Further, on the downstream side of the transfer section, a guide plate 15 is installed to guide the paper P separated from the drum of the photoreceptor 8 to the left in the drawing.

A static eliminating separator 16 is disposed between the transfer device 12 and the guide plate 15 described above. This static eliminator separator 1
6 is a static elimination brush 16a, a separation guide 16b,
It is composed of a power supply circuit 16c. Static elimination brush 1
6a is a brush-shaped conductive fiber such as carbon fiber or stainless steel metal fiber, and the distance between the tip of the brush and the photoreceptor drum 8 is
It is 4.5mm. Further, the static eliminating brush 16a is electrically connected to a power supply circuit 16c. The power supply circuit 16c includes a switch 17, a positive power supply 18 that outputs a predetermined voltage, and a negative power supply 19. The predetermined voltage values of the positive power supply 18 and the negative power supply 19 are determined by the static elimination brush 16.
a is set to a voltage lower than the voltage value at which self-discharge starts. For example, when the distance between the static elimination brush 16a and the photosensitive drum 8 is 4.5 mm as described above, the voltage is set to 2 KV. Further, switching control of the switch 17 is performed by remote signals a and b from a control circuit (not shown).

For example, both remote signals a and b are H (high)
If input as a signal, the switch 17 will be connected to the negative power supply 1.
9 side, and outputs a negative predetermined voltage to the static elimination brush 16a. Further, when the remote signal a is an H signal and the remote signal b is an L (low) signal, the switch 17 is switched to the positive power supply 18 side, and the static elimination brush 16
A predetermined positive voltage is output to a. Furthermore, if the remote signals a and b are both L signals, the switch 17 outputs a ground potential (0V), not shown, to the static elimination brush 16a.

On the other hand, on the downstream side of the guide plate 15, a fixing device 20 for thermally fixing the transferred toner image onto the paper P;
A discharge roll (not shown) for discharging the paper P on which the toner image has been fixed is disposed outside the machine. The fixing device 20 includes a heating roll 20 having a built-in heater 20a.
b, and a pressure roll 20c that is pressed against the surface of the heating roll 20b. Further, the cleaner 13 includes a blade 13a that scrapes off residual toner on the circumferential surface of the photosensitive drum 8, and a collection roller 13b that collects the scraped off toner.

The operation of the liquid crystal printer configured as above will be explained below.

First, the photosensitive surface 8a of the photosensitive drum 8 is charged substantially uniformly by the initial corona discharge of the charger 9. In the liquid crystal head 10, a microshutter in a liquid crystal optical shutter 10b is driven to open and close based on a recording signal from a shutter drive circuit (not shown), thereby exposing the photosensitive surface 8a. Through this exposure, an electrostatic latent image is formed on the photosensitive surface 8a in accordance with the image data to be printed.
Thereafter, as the photosensitive drum 8 rotates in the direction of the arrow, the electrostatic latent image on the photosensitive drum 8 is developed into a toner image by the developing device 11, and the toner image is transferred onto the paper P by the transfer device 12. The paper P onto which the toner has been transferred is separated from the photoreceptor drum 8 by self-discharge from the static elimination brush 16a of the static elimination separator 16, which will be described in detail later. Thereafter, the thermally fixed paper P is discharged outside the machine, and image printing on the paper P is completed.

On the other hand, the toner on the photosensitive drum 8 that has not been completely transferred to the paper P by the transfer device 12 is removed by the cleaner 13.
removed by

FIGS. 2a to 2g are time charts showing various signals and operation timings of each member in the above-described printing process. As shown in figures a to e,
When a print switch (not shown) is pressed, the light source 10a is turned on and irradiates the liquid crystal optical shutter 10b with light, and at the same time, the motor (not shown) is started to rotate the photosensitive drum 8 in the direction of the arrow. Thereafter, the high-voltage power supply 9d is turned on, and the charger 9 causes corona discharge to the photosensitive surface 8a of the photosensitive drum 8, thereby forming a uniform charge on the photosensitive surface 8a. Thereafter, an opening/closing signal based on the image signal is output to the liquid crystal optical shutter 10b, and the liquid crystal head 10 exposes the photosensitive surface 8a to form an electrostatic latent image. The electrostatic latent image thus formed is converted into a toner image by the developing device 11 as described above. Thereafter, the toner image is transferred onto the paper P by turning on the transfer device 12.

In response to such timings of each member, remote signals a and b are outputted to the switch 17 in the power supply circuit 16c at the timings shown in f and g in the figure. When the remote signals a and b are both at H (high) level, a voltage of, for example, -2 KV from the negative power supply 19 is applied to the static eliminating brush 16a as described above.
At this time, the toner image is transferred to the paper P by the transfer device 12, and the paper P passes between the static elimination brush 16a and the photosensitive drum 8. At this time, the paper P is positively charged by the corona discharge of the transfer device 12. Therefore, a non-uniform electric field is formed between the paper P and the static elimination brush 16a, and the air in between is ionized, causing corona discharge. As a result, the paper P is neutralized, the electrostatic attraction force between the paper P and the photoreceptor drum 8 is weakened, and the paper P
is separated from the photosensitive drum 8 by its own strength and gravity. Further, the separated paper P is conveyed to the guide plate 15 side by the separation guide 16b without coming into contact with the static elimination brush 16a.

On the other hand, a negative high potential is formed on the photosensitive surface 8a corresponding to the non-image areas before and after the image area. That is, although a charging voltage is applied due to charging, this is a region that is at a high potential because it is not exposed to light. For this region, the remote signal a is controlled to be at H level and the remote signal b is controlled to be at L level, so that a potential of, for example, +2 KV is applied to the static eliminating brush 16a as described above. As a result, a non-uniform electric field is formed between the high potential portion of the photosensitive surface 8a and the static elimination brush 16, and the air in between is ionized to generate corona discharge. As a result, the high potential portion on the photoreceptor drum 8 is neutralized and becomes approximately 0V.

Further, for the photosensitive surface 8a which is not charged, a voltage of 0V is applied to the static eliminating brush 16a by controlling the remote signals a and b to the L level, and no discharge occurs. In this way, the potential of the photosensitive surface 8a after passing above the static eliminating separator 16 becomes a relatively uniform potential, although there are some differences. Therefore, when charging is performed again by the charger 9, the charging potential becomes uniform.

FIG. 3 is a characteristic diagram showing the relationship between the voltage applied to the static elimination brush 16a and the potential of the photosensitive surface 8a after static elimination.

Photosensitive surface 8a charged to -620V (curve A), -420V (curve B), and -260V (curve C) when the distance between static elimination brush 16 and photosensitive drum 8 is set to 4.5 mm as described above. shows the potential after passing through the opposing portion of the static elimination brush 16a.

As is clear from the figure, the applied voltage is +2KV
If so, the static electricity can be removed to approximately 0V regardless of the potential of the photosensitive surface 8a. Here, the image area shown in FIG. 4 is approximately transferred by the transfer device 12 as shown in FIG. 5a.
Since the charge is attenuated to 0V, by eliminating the charge in the non-exposed area as described above, almost the entire area of the photoreceptor is removed.
Can be equalized to 0V.

Note that the static elimination brush 16a is not limited to a conductive brush, and may be a number of needle-shaped members disposed with the tips facing the photoreceptor drum 16, or may be a member made of a saw-shaped metal plate. good. Furthermore, although this embodiment has been described with respect to a liquid crystal printer, it goes without saying that the present invention can also be applied to other image forming apparatuses.

[Effect of idea]

As explained in detail above, according to the present invention, a static eliminating member to which a voltage lower than the self-discharge starting voltage is supplied is used as a static eliminating means, and positive and negative voltages are supplied to this static eliminating member at a predetermined timing. Since the high potential portion on the photoreceptor is eliminated, it becomes possible to obtain a uniform charging potential without providing a dedicated charge eliminating means, and it becomes possible to form a good image at low cost.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the image forming apparatus of this embodiment, FIGS. 2 a to 2 g are time charts showing the operation of the image forming apparatus of this embodiment, and FIG. 3 is a characteristic diagram of the potential of the photosensitive surface after static elimination. 4 and 5 a and b are time charts explaining problems in conventional image forming apparatuses,
FIG. 6 is a block diagram of a scorotron charger used in a conventional image forming apparatus. 8... Photosensitive drum, 9... Charger, 10...
Liquid crystal head, 11...developing device, 12...transfer device,
13... Cleaner, 16... Static eliminator separator, 16a
... Static elimination brush, 16b... Guide, 16c...
Power supply circuit, 17... switch, 18... positive power supply,
19... Negative power supply.

Claims (1)

[Claims for Utility Model Registration] A photoreceptor is charged to a predetermined potential with a predetermined polarity, and a light image corresponding to the image to be formed is irradiated to form an electrostatic latent image, and a low potential portion of the electrostatic latent image is charged. A toner image is created by attaching toner to the toner, a transfer material is superimposed on the toner image, and the toner image is transferred to the transfer material by the action of an electric field having a polarity opposite to the predetermined polarity. In an image forming apparatus in which an image is separated from the photoreceptor by a separation means and formed on the transfer material, the separation means includes a static eliminator disposed at a predetermined distance from the photoreceptor; comprising a voltage supply means for selectively supplying a positive or negative voltage lower than a voltage at which self-discharge starts to the static eliminator, and a switching means for switching the polarity of the voltage output from the voltage supply means to positive or negative, The voltage supply means supplies the voltage having the same polarity as the predetermined polarity when the transfer material faces the static elimination member by the switching action of the switching means, and the non-exposed area of the photoreceptor faces the static elimination member. An image forming apparatus characterized in that the voltage having a polarity opposite to the predetermined polarity is supplied when the image forming apparatus is used.