JP2001083777A - Electrophotographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stable image with high quality by setting the frequencies of the respective AC components of electrifying bias and developing bias so that a beat frequency generated by interference between the AC component of the electrifying bias and that of the developing bias becomes sufficiently small or sufficiently large. SOLUTION: The beat spatial frequency of a photoreceptor 3 is defined as (fd-n×fc)/ v. Provided that (v) is the carrying speed of a transfer material, (fc) is the frequency of the electrifying bias, (fd) is the frequency of the developing bias and (n) is an integer. Then, the originating frequency generated by an AC power source for electrifying E4a and the frequency generated by an AC power source for developing E5a are set so that the beat frequency becomes sufficiently small or sufficiently large. When they are set to be fd-fc=560Hz and the carrying seed is set to be v=50mm, the spatial frequency by which an image variabledensity stripe appears is (fd-fc)/v=25.6 pieces/mm and (fd-2fc)/v=11.2 pieces/mm and it does not become under 10 pieces/mm. Thus, since the frequency of the image variable-density stripe is sufficiently large, the deterioration of the image quality is not felt by the eye of a person. Besides, even when the frequency of the image variable-density stripe is set to be sufficiently small, the image variable-density stripe is not viewed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus. More specifically, the present invention relates to an improvement in a method of performing charging by applying a voltage having an AC component.

[0002]

2. Description of the Related Art Conventionally, an electrophotographic apparatus includes a process of uniformly charging a surface of a photosensitive member to a predetermined potential, as is well known. As the charging means, a corona discharger having a wire electrode and a shield electrode as main components is mainly used. However, the charging system using the corona discharger has the following problems. 1) High voltage application To obtain a surface potential of 700 to 800 V on the photoreceptor,
A high voltage such as ８8 kV must be applied. 2) Low charging efficiency Most of the discharge from the wire flows to the shield electrode, and the current flowing to the photoreceptor is only a few% of the total discharge current. 3) Generation of corona discharge products Ozone and the like are generated by the corona discharge, and it is necessary to consider deterioration of an image and influence on a human body. 4) Contamination of the Wire The high electric field formed on the surface of the wire collects minute dust in the device, and contaminates the surface of the wire. The wire contamination tends to cause uneven discharge, which causes image unevenness.

Therefore, recently, it has been studied to use a contact charging means without using a corona discharger having many problems as described above.

Specifically, a charge is directly injected into the surface of the photoreceptor by bringing a conductive member such as a conductive elastic roller to which a DC voltage of about 1 kV is applied from the outside into contact with the surface of the photoreceptor to be charged. To charge the surface of the photosensitive member to a predetermined potential. However, actually, since the surface of the conductive member to which the voltage is applied and the surface of the photoreceptor in contact therewith have microscopic unevenness, spot-like unevenness occurs on the photoreceptor surface.

As a means for solving this problem, Japanese Patent Laid-Open No.
As disclosed in Japanese Patent Application Laid-Open No. 3-149669, an oscillating electric field obtained by superimposing an alternating current having a peak voltage twice or more of a charging start voltage when a DC voltage is applied to the charging member on the DC voltage is applied to the charging member and the member to be charged. And a method of performing charging by forming between them has been proposed and put to practical use.

In the case of an electrophotographic apparatus using roller charging, as an example, as shown in FIG. 1, the charging member 4 and the charged body 3 are cylindrical rollers, respectively. Is charged in the vicinity of the contact of Since charging is performed by applying to the charging member 4 a voltage in which an AC component is superimposed on a DC component, the surface potential of the member to be charged fluctuates in the same cycle as the cycle of the AC component.

At this time, since the charged body 3 is charged while rotating, a charged surface of the charged body 3 has a stripe-shaped surface potential distribution which fluctuates periodically in the circumferential direction of the drum. Is done. Assuming that the frequency of the AC component to be applied is f and the speed of the surface of the member to be charged is v, the spatial frequency of the surface potential fluctuation generated on the surface of the member to be charged is (f / v).

When such a surface potential that fluctuates in the circumferential direction of the photoconductor is formed, the periodic fluctuation is reflected in an output image after the subsequent image forming process. For example, when an image is formed such that the entire surface becomes black, the output image has light and dark stripes corresponding to the periodic fluctuation of the surface potential of the photoconductor.

However, such a light and shade stripe cannot be recognized by human eyes if the spatial frequency is sufficiently high, so that the output does not become a factor of deteriorating the image quality. For example, fc =
At 900 Hz and v = 50 mm / s, the spatial frequency is 18 lines / mm, and the density of the image is not seen.

In the electrophotographic process, after the above-described charging process, an exposure process for exposing the charged object to form an electrostatic latent image is performed. The image is visualized by performing a developing step of attaching the toner to the image.

As a developing method, means such as a magnetic brush method, a cascade method or a jumping developing method is used.

Among them, the jumping development method has the following effects: 1) The dependence on the process speed of electrophotography is small. 2) Less scattering of toner. 3) Simple structure. 4) It can be made compact. Because of these advantages, they are widely used from low-speed machines to high-speed machines.

The jumping development will be briefly described with reference to FIG. In the jumping development, the insulating magnetic toner t having no electric field dependence is charged by frictional charging, a thin layer of the charged toner t is formed on the surface of the sleeve 5a, and charged and exposed as described above. This is a method in which an AC bias is applied between the charged body 3 on which the electrostatic latent image is formed and the sleeve 5a to perform development while causing the toner to reciprocate between the sleeve 5a and the charged body 3.

[0014]

However, the conventional method has the following problems.

Since the potential of the member to be charged after the charging step decreases with time due to dark current, generally, in electrophotography, the exposure and development steps are started immediately after the charging step is performed. When a bias having two AC components, such as charging and developing, is applied simultaneously in a short distance region, the charging bias is applied to the charging bias by wiring on the high voltage power supply substrate, electromagnetic induction of the charging device and the developing device itself, and the like. The AC component induces the AC component of the charging bias in the developing bias.

When such induction occurs, particularly when an AC component of a developing bias is induced in the charging bias,
In the AC component of the charging bias, a growling occurs between the induced frequency and the original frequency of the charging bias. Such a humming of the charging bias potential is reflected in the formation of the electrostatic latent image as described above, and as a result, appears as light and dark stripes of the image formed on the transfer material. The spatial frequency of the image formed on the transfer material is determined by the beat frequency determined by the difference between the two frequencies (or the difference between the respective harmonic frequencies) and the transfer speed of the transfer material.

For example, charging bias frequency fc = 900
Hz, the developing bias frequency fd = 2000 Hz, and the transfer speed of the transfer material v = 50 mm / s, the spatial frequency of the light and dark stripes generated on the transfer material is (fd-fc) / v = 22.
Lines / mm, (fd-2fc) / v = 4 lines / mm, ...
・ ・Such spatial frequency fringes of several lines / mm or less can be clearly confirmed on the image (particularly, the second-order fd-
2fc), which degrades the quality of the image.

Further, there has been proposed a configuration in which the charging bias and the developing bias are supplied from a single power supply so that no growl is generated. However, the frequency of the charging bias AC component and the developing bias AC component is as follows. Since the value is determined by various factors, it may not be possible to divide from a single power supply, which limits the design and requires a divider circuit.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the image density stripes generated by the induction of the AC component of the developing bias by the charging bias cause image quality deterioration to the human eye. It is intended to prevent the user from feeling it and to increase the degree of freedom in design.

[0020]

In order to achieve this object, an electrophotographic apparatus according to a first aspect of the present invention comprises: a charging device for charging by applying a voltage having an AC component as a charging bias; An electrophotographic apparatus comprising: a developing device that performs development by applying a voltage having a voltage as a developing bias; and a transfer device that transfers an image visualized by the developing device to a transfer material. And a developing power supply for supplying the developing bias to the developing device, wherein the charging bias AC component from the charging power supply and the developing from the developing power supply are provided. The charging bias AC from the charging power source is set so that the frequency of the growl generated by the interference with the bias AC component becomes sufficiently small or sufficiently large. It has set minute frequency and the frequency of the developing bias AC component from the developing power source.

In the electrophotographic apparatus according to the first aspect of the present invention, a charging bias having an AC component supplied from a charging power source is applied to the charging device, and the charging bias is also supplied to the developing device from the developing power source. A developing bias having an applied AC component is applied, and the frequency of the growl reflected on the transfer material by the growl of the two AC components is set to be sufficiently small or sufficiently large from the charging power supply. By setting the frequency of the charging bias AC component and the frequency of the developing bias AC component from the developing power source, the deterioration of the image due to the fluctuation of the charging potential caused by the groan is not perceived by human eyes.

According to a second aspect of the present invention, there is provided the electrophotographic apparatus according to the first aspect, wherein a period of a growl generated by interference between the charging bias AC component and the developing bias AC component is changed in a transport direction. The frequency of the AC component of the charging bias and the frequency of the AC component of the developing bias are set so as to be four times or more the length of the transfer material in FIG.

In the electrophotographic apparatus according to the second aspect of the present invention, the charging and developing frequencies are set so that the period of the beat is at least four times the length of the transfer material in the transport direction. In one transfer material, 1/4 or less of the humming cycle appears, that is, a density difference of １ ／ or less of the maximum density difference (difference between the maximum density and the minimum density) in the humming cycle appears on the transfer material. As a result, the deterioration of the image due to the fluctuation of the charged potential caused by the groan becomes invisible to human eyes.

According to a third aspect of the present invention, there is provided the electrophotographic apparatus according to the first aspect, wherein a frequency fc of an AC component of a charging bias, a frequency fd of an AC component of a developing bias, and transfer of a transfer material. The frequency fc of the AC component of the charging bias and the frequency fc of the AC component of the developing bias are controlled so that the frequency of the growling (fd−n × fc) / v defined by the speed v does not become less than 10 lines / mm (n is a positive number). The frequency fd and the transfer speed v of the transfer material are set.

Further, in the electrophotographic apparatus according to the third aspect,
The frequency of the growl (fd−n × fc) / v is 10 on the transfer material.
The frequency fc of the AC component of the charging bias, the frequency fd of the AC component of the developing bias, and the transfer speed v of the transfer material are set so as not to be less than the number of lines / mm. Image degradation will not be noticeable to the human eye.

[0026]

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

FIG. 1 shows an example of an electrophotographic apparatus to which the charging device of the present invention can be applied. In this embodiment, an electrophotographic apparatus in which a sheet material feeding section A and a laser beam printer section B are combined. 4 shows a photographic device.

The configuration and the image forming operation of the printer B of this embodiment will be described. It should be noted that the printer in the present embodiment has the right end face in the drawing as the front face.

The printer front panel 1A is a
As shown by the two-dot chain line with the hinge axis 1B on the lower side as the center, the flip-up operation and the raising and closing operation as shown by the solid line can be freely performed. The operation of attaching and detaching the process cartridge 2 to and from the inside of the printer, and checking and maintaining the inside of the printer are performed by opening the front plate 1A to open the inside of the printer.

The process cartridge 2 of this embodiment is a cartridge housing 2a in which four image forming process devices including a photosensitive drum 3, a charging roller 4, a developing unit 5, and a cleaner 6 are included. Is folded down as shown by a two-dot chain line and can be freely attached to and detached from a predetermined storage portion in the printer exterior housing 1. Process cartridge 2
The mechanical drive system of both the process cartridge 2 side and the printer side by being properly mounted in the printer
An electric circuit system is coupled via a mutual coupling member (not shown) so as to be mechanically and electrically integrated.

In the present embodiment, the photosensitive drum 3, the charging roller 4, the developing device 5, and the cleaner 6 are integrally provided in the process cartridge 2. However, the present invention is not limited to this. It is only necessary that the drum 3 and the charging roller 4 be integrally supported and be detachable from the main unit.

The laser beam scanner unit 7 is disposed on the back side inside the outer casing 1 of the printer, and includes a semiconductor laser (not shown), a scanner motor 7a, a polygon mirror 7b, a lens system 7c, and the like. The laser beam L from the scanner unit 7 enters the cartridge housing 2a substantially horizontally from the exposure window 2b of the cartridge housing 2a mounted in the printer, and the cleaner 6 disposed vertically in the cartridge housing 2a. The light enters the exposure unit 3a on the left side of the photosensitive drum 3 through the passage between the developing unit 5 and the photosensitive drum 3 is scanned and exposed in the generatrix direction.

When an image formation start signal is input to the printer control system, the photosensitive drum 3 is driven to rotate at a predetermined peripheral speed in a counterclockwise direction indicated by an arrow, and the peripheral surface thereof is positively or negatively charged by the charging roller 4. It is uniformly charged to a predetermined polarity. The charging roller 4 converts the DC voltage of -650 V to a frequency fc of 720H.
a conductive member to which a bias in which a sine wave AC voltage controlled by a constant current of z (800 μA rms) is controlled is applied,
The photosensitive drum 3 is charged by a charging roller 4 by a contact (or direct) charging method. The charging roller 4 may be driven to rotate by the photosensitive drum 3, may be rotated in the opposite direction, or may not rotate.

Next, pixel laser light L corresponding to a time-series electrical image signal of image information output from the laser beam scanner 7 is incident on the uniformly charged surface of the photosensitive drum 3 at the exposure unit 3a. Then, the surface of the photosensitive drum 3 is sequentially subjected to the main scanning by the laser beam L in the drum generatrix direction, whereby an electrostatic latent image of image information is formed on the surface of the photosensitive drum 3.

A DC voltage of -500 V and a peak-to-peak voltage of 16
The electrostatic latent image formed on the photosensitive drum 3 is applied between the sleeve 5 a and the photosensitive drum 3 by applying a bias in which a rectangular wave alternating current of 00 V and a frequency fd = 2 kHz is applied between the sleeve 5 a and the sleeve 5 a of the developing device 5. (Or a roller) are sequentially developed with toner carried on the roller and are visualized.

On the other hand, the uppermost sheet material among the sheet materials (transfer sheets) S set on the multi-feed tray 8 is drawn into the printer from the feed roller 10 rotated and driven in the direction of the arrow, and subsequently fed. The photosensitive drum 3 is fed between the roller 10 and the transport roller 12 toward a contact portion (transfer portion) between the photosensitive drum 3 and the transfer roller 13 at a constant speed equal to the rotational peripheral speed of the photosensitive drum 3.

The sheet material S fed to the transfer section is applied to the transfer roller 13 in the process of sequentially passing between the photosensitive drum 3 and the transfer roller 13 (a voltage having a polarity opposite to that of the toner). Then, the transfer of the toner image on the surface of the photosensitive drum 3 is sequentially performed by the pressing force of the transfer roller against the photosensitive drum 3. The voltage applied to the transfer roller 13 is such that the leading edge of the fed sheet material S contacts the photosensitive drum 3 and the transfer roller 13.
This is performed when it reaches the contact portion (transfer portion).

The sheet material S having passed through the transfer section is separated from the surface of the photosensitive drum 3, guided by the guide plate 14, and introduced into the pair of fixing rollers 15a and 15b. The roller 15a of the fixing roller pair 15a, 15b that contacts the image transfer surface of the sheet material S is a heating roller having a built-in halogen heater, and the roller 15b that contacts the back surface of the sheet material S is an elastic material. The sheet material S to which the image has been transferred is fixed on the surface of the sheet material S by heat and pressure in the course of passing through the fixing roller pair 15a, 15b. The sheet is discharged as an image formed product (print) onto the tray 17 by the roller 16.

After the transfer of the toner image, the surface of the photosensitive drum 3 is cleaned and cleaned by the cleaning blade 6a of the cleaner 6 to remove residual toner and other contaminants, and is repeatedly used for image formation.

When the sheet is fed from the cassette 40 of the sheet feeding device A instead of using the multi-feed tray 8, the uppermost sheet among the sheets S stacked in the cassette 40 is picked up by the pickup roller 26. The sheet material S is sent to the registration rollers 28 and 55 and proceeds in the direction of the arrow, and the sheet material S is fed between the feed roller 10 and the transport roller 12 as described above.

Next, a charging method according to the present embodiment will be described with reference to FIG. FIG. 2 is a simplified view of the configuration of the main part of the present invention in FIG.

The charging power source E4 is composed of a DC power source E4a and an AC power source E4b. The charging power source E4 supplies the charging roller 4 with a bias in which an AC component is superimposed on DC. Similarly, a developing power supply E5 for supplying a developing bias includes a DC power supply E5a and an AC power supply E5b, and a bias in which an AC component is superimposed on DC is supplied from the developing power supply E5 to the sleeve 5a.

At this time, the transmission frequency of the charging AC power supply E4a and the developing AC power supply E5a is fd-2fc = 56.
It is set to be 0 Hz. When the two biases have a frequency relationship in this manner, the charged photoconductor 3
As described above, the spatial frequency of the growl generated by the transfer speed v, the charging bias frequency fc, and the developing bias frequency fd is (fd−fc) / v, (fd−2f).
c) / v,... That is, the spatial frequency of the growl is defined by (fd−n × fc) / v, n is a positive number, and n = 1, 2,.

In the present embodiment, the transfer material transport speed v = 5
Assuming 0 mm / s, the spatial frequency at which the image light and dark stripes appear is (fd−fc) /v=25.6 lines / mm and (fd−fc).
2fc) /v=11.2 lines / mm, that is, since the spatial frequency does not become less than 10 lines / mm (that is, since the frequency of the image density stripe is sufficiently large), the image density stripe generated on the transfer material Is a high frequency that human eyes cannot perceive as a deterioration in image quality.

Conversely, even if the frequency difference (fd−2fc) is made sufficiently small to make the frequency of the image light and dark stripes formed on the transfer material sufficiently small, the light and dark stripes will not be visible. For example, the frequency of the AC component of the charging bias and the frequency of the AC component of the developing bias may be adjusted so that the period of the image light and dark stripes is about four times or more the length of the transfer material in the transport direction. As described above, when the period of the image light and dark stripes (the period of the growl) is set to about four times or more the length of the transfer material in the transport direction, the transfer of the image light and dark stripes (the period of the growl) in one transfer material 1/4 or less, that is, a density difference of 1/2 or less of the maximum density difference (difference between the maximum density and the minimum density) in the period of the image dark and light stripes (the period of the beat) appears on the transfer material. Becomes invisible to human eyes.

Next, this principle will be described with reference to FIG. 3 showing one period of a growling.

As is apparent from FIG. 3, one cycle has a maximum density h1 and a minimum density h2, and the maximum density difference H is h
1-h2.

Therefore, for example, if the groaning cycle is the same as the length of the transfer material in the transport direction (ie, 1 time), then 1
Since one cycle of growl appears on one transfer material, the maximum density difference H always appears. Further, if the period of the growl is set to 1/2 of the length of the transfer material in the transport direction, since the period of the growl appears twice in one transfer material, the maximum density difference H always appears. Further, if the period of the growl is set to 1/3, 1/4... Times the length of the transfer material in the transport direction, the growl period appears twice, three times,. The difference H appears. Then, assuming that the period of the growl is twice the length of the transfer material in the transport direction, one transfer material has a half of the growl.
Since the cycle appears, the maximum density difference H may appear.

If the period of the growl is four times the length of the transfer material in the transport direction, one-fourth of the period of the growl appears in one transfer material. Is ＨH at the maximum (H is the maximum density difference). Further, the period of the growl is set to 5, which is the length of the transfer material in the transport direction.
6 ... times, one transfer material has 1 /
, 1/6... Appear, the density difference appearing on one transfer material is smaller than 1 / 2H (H is the maximum density difference).

As described above, since the frequency of the image light and dark stripes formed on the transfer material is sufficiently small, a part of the period of the growl appears on one transfer material, and the density appearing on one transfer material is obtained. The difference is smaller than the maximum density difference H. Therefore, the deterioration of the image due to the fluctuation of the charging potential on one transfer material is not perceived by human eyes, and a stable high quality image can be obtained.

Further, in this embodiment, instead of supplying a charging bias and a developing bias from a single power supply,
Since a charging bias having an AC component is supplied to the charging roller 4 from a charging power source E4, and a developing bias having an AC component is supplied to the sleeve 5a from the developing power source E5.
The charging bias and the developing bias determined by each factor can be supplied, the degree of freedom in design is improved, and a frequency dividing circuit is not required.

The present invention is not limited to the embodiment described in detail above, and various changes can be made without departing from the gist of the present invention.

The charging member described above is not limited to the charging roller, but may be a blade, a brush, or a belt. Further, the waveform of the AC power supply used for the charging bias and the developing bias is not limited to a sine wave and a rectangular wave, and any other waveform such as a triangular wave and a sawtooth wave may be used.

[0054]

As is apparent from the above description, in the electrophotographic apparatus of the present invention, the charging and developing frequencies are adjusted so that the spatial frequency of the stripes generated during charging is inconspicuous. Since the deterioration of the image due to the fluctuation of the potential is not perceived by human eyes, a stable high-quality image can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an electrophotographic apparatus embodying the present invention.

FIG. 2 is a block diagram illustrating a main configuration of the electrophotographic apparatus.

FIG. 3 is an explanatory view showing one cycle of a growl.

[Explanation of symbols]

 Reference Signs List 3 charged body (photosensitive drum) 4 charging member (charging roller) 5 developing unit 5a sleeve E4 charging power supply E5 developing power supply

Claims (3)

[Claims] A charging device that performs charging by applying a voltage having an AC component as a charging bias; a developing device that performs development by applying a voltage having an AC component as a developing bias; An electrophotographic apparatus including: a transfer device that transfers an image visualized by a developing device onto a transfer material; a charging power supply that supplies the charging bias to the charging device; and a supply of the developing bias to the developing device. A power supply for development, the frequency of a growl generated by interference between the charging bias AC component from the charging power supply and the developing bias AC component from the developing power supply is set to be sufficiently small or Set the frequency of the charging bias AC component from the charging power source and the frequency of the developing bias AC component from the developing power source so that they are sufficiently large. The electrophotographic apparatus is characterized in that the deterioration of the image due to the fluctuation of the charging potential caused by the growling is not perceived by human eyes. 2. The developing method according to claim 1, wherein the frequency of the AC component of the charging bias and the frequency of the developing process are set so that the period of the beat generated by the interference between the charging bias AC component and the developing bias AC component is at least four times the length of the transfer material in the transport direction. 2. The electrophotographic apparatus according to claim 1, wherein a frequency of a bias AC component is set. 3. A growling frequency (fd−n × f) defined by a frequency fc of an AC component of a charging bias, a frequency fd of an AC component of a developing bias, and a transfer speed v of a transfer material.
c) The frequency fc of the AC component of the charging bias, the frequency fd of the AC component of the developing bias, and the transfer speed v of the transfer material are set so that / v does not become less than 10 lines / mm (n is a positive number). The electrophotographic apparatus according to claim 1, wherein: