JPH08160718A - Image forming device - Google Patents

Abstract

PURPOSE: To provide an image forming device capable of stably outputting a high-quality image by preventing the occurrence of moire and the melt-sticking of toner even in the case the device is stopped for a fixed time. CONSTITUTION: In this image forming device equipped with a contact electrifying device which electrifies a photoreceptor drum (body to be electrified) 1 by impressing voltage obtained by superposing an AC component and a DC component on an electrifying roller (electrifying member) 2, and allowing the roller 2 to abut on the drum 1 while rotating it; the frequency of the AC component of the voltage impressed on the roller 2 or interpeak voltage is temporarily changed in the case of outputting the image after the device is continuously stopped for the fixed time. Or, in the device provided with the contact electrifying device which electrifies the drum 1 by impressing a current obtained by superposing the AC component and the DC component on the roller 2, and allowing the roller 2 to abut on the drum 1 while rotating it and where the AC component of the current impressed on the roller 2 is constant-current controlled to a specified value, the current impressed on the roller 2 is temporarily changed in the case of outputting the image after the device is continuously stopped for the fixed time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a contact charging device.

[0002]

2. Description of the Related Art A conventional image forming apparatus is constructed, for example, as shown in FIG. That is, FIG. 5 is a cross-sectional view of a main part of a conventional image forming apparatus. This image forming apparatus includes a photosensitive drum 1, which is an image carrier, which is rotationally driven in a direction indicated by an arrow by a driving unit (not shown), and the photosensitive drum 1. A charging roller 2 that is a contact charging member that uniformly charges the surface of the drum 1 to a predetermined potential, a developing device 3 that visualizes the latent image formed on the photosensitive drum 1 as a toner image with a developer, and A transfer charger 5 that transfers the toner image developed by the developing device 3 onto the transfer material 7, and a fixing device 6 that melts and fixes the toner image transferred onto the transfer material 7 by heating and pressing to obtain a desired image. It has and.

By the way, the above-mentioned photosensitive drum 1 has an organic semiconductor (OPC), A-S on the outer peripheral surface of an aluminum cylinder.
A latent image is formed on the photosensitive drum 1 by applying a photoconductor made of i, CdS, Se or the like and irradiating the surface of the photoconductor with laser exposure 8 along an image pattern. The transfer residual toner remaining on the photosensitive drum 1 is cleaned by a cleaning device 4 having a known blade means.

Further, the contact charging roller 2 shown in FIG. 6 has been practically used in recent years because it has an advantage that ozone, which is harmful to a human body, is extremely small as compared with the conventional corona charger. The charging roller 2 is configured by providing a conductive rubber 2b and a high resistance surface layer 2c on a core metal 2a,
In order to uniformly charge the photosensitive drum 1 to about -700V, a voltage in which a DC voltage of -700V and an AC voltage are superimposed is applied to the core metal 2a. Then, in the vicinity of the nip portion between the charging roller 2 and the photosensitive drum 1, discharge occurs in a region of a distance satisfying Paschen's law, and the discharge charges the photosensitive drum 1 to a predetermined potential.

By the way, when an AC voltage is applied to the charging roller 2 as described above, a moiré may occur due to the interference between the cycle mark on the electrostatic latent image and the image pattern due to the ripple of the AC voltage. This occurs when the repeating period of the image pattern is almost equal to the period of the cycle mark or is almost twice as long.

In order to prevent the moire from occurring, the frequency of the AC voltage may be set while avoiding the cycle of the image pattern. Here, the process speed is V (mm /
sec), the resolution is s (dpi), and the basic unit of the image pattern is n (dots), the period of the image pattern is (25.4 × n) / s (mm), and the spatial frequency of the image is (s ×). V) / (25.4 × n) (Hz). Therefore, as the frequency of the AC voltage, it suffices to avoid the above-mentioned spatial frequency and a frequency that is twice as high as the above-mentioned frequency, and it is sufficient to set the frequency as high as possible in order to reliably avoid moire.

However, when the frequency is high, the toner is likely to be fused to the surface of the photosensitive drum 1. Therefore, from the viewpoint of toner fusion, it is necessary to keep the frequency as low as possible.

Therefore, conventionally, the fusion of the moire and the toner is prevented by setting an intermediate frequency between the spatial frequency when n = 2 and the spatial frequency when n = 3 as the frequency of the AC voltage. It is preventing.

[0009]

However, if the machine remains stopped for a long time, only a part of the charging roller 2 contacts the photosensitive drum 1 and the charging roller 2 continues to press the photosensitive drum 1. The charging roller 2
The rubber 2b may be permanently deformed. The state of charging of the charging roller 2 at this time will be considered.

It is assumed that the photosensitive drum 1 rotates clockwise and the charging roller 2 rotates counterclockwise. As shown in FIG. 2, in the undeformed portion of the charging roller 2, the portion having the maximum discharge distance d determined by Paschen's law is the portion p1 on the photosensitive drum.

However, as shown in FIG. 3, when the deformed portion of the charging roller 2 just approaches the vicinity of the nip portion, the portion of the maximum discharge distance d shifts to p2 on the left side of p1 shown in FIG. I will end up. That is, each time the deformed portion of the charging roller 2 approaches the nip portion, the interval between the cycle marks formed on the electrostatic latent image becomes wider. For this reason, for example, the spatial frequency when n = 2 and n =
Even though the frequency intermediate the spatial frequency in the case of 3 was set as the frequency of the AC voltage, the deformed portion of the charging roller 2 was as if the frequency had become lower, and the deformation of the charging roller 2 was the basis. Until returning, a moire band was output at the rotation cycle of the charging roller 2 as shown in FIG.

The present invention has been made in view of the above problems, and an object thereof is to prevent generation of moire and toner fusion even when the image forming apparatus is stopped for a certain time. An object of the present invention is to provide an image forming apparatus capable of stably outputting a high quality image.

[0013]

In order to achieve the above object, the invention according to claim 1 applies a voltage in which an alternating current component and a direct current component are superposed to a charging member and is charged while rotating the charging member. In an image forming apparatus equipped with a contact charging device that contacts a body to charge a body to be charged, when an image is output after a state of being stopped for a certain period of time, an AC component of a voltage applied to the charging member. It is characterized in that the frequency of is temporarily changed.

According to the second aspect of the present invention, a voltage in which an alternating current component and a direct current component are superposed is applied to the charging member, and the charging member is rotated and brought into contact with the charged member to charge the charged member. An image forming apparatus having a contact charging device is characterized in that the peak-to-peak voltage of the voltage applied to the charging member is temporarily changed when an image is output after being stopped for a certain period of time. .

Further, according to the third aspect of the present invention, an electric current in which an alternating current component and a direct current component are superposed is applied to the charging member, and the charging member is rotated and brought into contact with the charged member to charge the charged member. In an image forming apparatus having a contact charging device for controlling the AC component of the current applied to the charging member to a predetermined value with a constant current, in the case of outputting an image after being stopped for a certain period of time, It is characterized in that the current applied to the charging member is temporarily changed.

[0016]

Even if the charging member is deformed because the image forming apparatus is stopped for a certain period of time, the frequency of the AC component of the voltage applied to the charging member when the image is output thereafter is temporarily increased. Alternatively, by temporarily increasing the peak-to-peak voltage or temporarily changing the current applied to the charging member, it is possible to prevent the occurrence of moire and toner fusion and to stably output a high-quality image. It was experimentally confirmed that

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings. [Embodiment 1] FIG. 1 is a longitudinal sectional view of an image forming apparatus according to the present invention. In this figure, the same elements as those of the conventional image forming apparatus shown in FIG. The description thereof is omitted as appropriate.

The feature of this embodiment is that the charging roller 2 is used when an image is output after the machine has been stopped for a certain period of time.
This is to temporarily increase the peak-to-peak voltage of the AC voltage applied to the charging roller 2 to prevent the occurrence of moire between the charging rollers 2 and the fusion of the toner.

The effects of this embodiment will be described below by comparing this embodiment with a comparative example.

(Common conditions) -Process speed: 103.26 mm / sec-Resolution: 600 dpi-Charging frequency: 1008 Hz-Charging DC voltage: -700 V <Example 1> (1) Normal output condition-Charging AC voltage: 1500 Vpp (2) Output condition after the machine is stopped for a certain period of time: Charging AC voltage: 2000 Vpp <Comparative example 1> • Charging AC voltage: 1500 Vpp <Comparative example 2> • Charging AC voltage: 2000 Vpp Occurrence of moire fringes,
Table 1 shows the results of evaluation of the fusion of the toner onto the photosensitive drum 1.

[0021]

[Table 1] In Table 1, ◯ indicates no occurrence (good), Δ indicates some occurrence (acceptable), and x indicates occurrence (impossible) (see Table 2 below).
The same applies to Table 3).

As is clear from the results in Table 1, when an image is output after the machine has been stopped for a certain period of time, the peak-to-peak voltage of the AC voltage applied to the charging roller 2 as in this embodiment. The charging roller 2
It is possible to suppress the generation of moire fringes at intervals and to prevent the toner from being fused to the photosensitive drum 1. [Embodiment 2] This embodiment is characterized in that the charging roller 2 is used when an image is output after the machine has been stopped for a certain period of time.
This is to temporarily increase the frequency of the AC voltage applied to the charging roller 2 to prevent the occurrence of moire between the charging rollers 2 and the fusion of the toner.

The effects of this embodiment will be described below by comparing this embodiment with a comparative example.

(Common conditions) -Process speed: 103.26 mm / sec-Resolution: 600 dpi-Charging AC voltage: 1500 Vpp-Charging DC voltage: -700 V <Example 2> (1) Normal output condition-Charging frequency: 1008 Hz (2) Output conditions after the machine is stopped for a certain period of time-Charging frequency: 2016 Hz <Comparative example 1> -Charging frequency: 1008 Hz <Comparative example 2> -Charging frequency: 2016 Hz Occurrence,
Table 2 shows the results of evaluation of the fusion of the toner onto the photosensitive drum 1.

[0025]

[Table 2] As is clear from the results in Table 2, when an image is output after the machine has been stopped for a certain period of time, the frequency of the AC voltage applied to the charging roller 2 is temporarily increased as in this embodiment. By doing so, it is possible to suppress the generation of moire fringes in the interval between the charging rollers 2 and to prevent the toner from being fused to the photosensitive drum 1. [Embodiment 3] The high resistance surface layer 2c of the charging roller 2 is an environment,
In particular, due to the influence of humidity, the impedance of the charging part may increase in a low humidity environment due to an increase in resistance and a decrease in dielectric constant, and conversely, the impedance may decrease in a high humidity environment due to a decrease in resistance and an increase in dielectric constant. . In such a case, if the AC voltage is controlled to a constant voltage, the high resistance surface layer 2
Since the voltage in the charging unit cannot be made constant due to the impedance variation of c, it is preferable to control the AC voltage with a constant current. For this control, see Japanese Patent Laid-Open No. 1-2676.
No. 67 publication.

Thus, in this embodiment, even when constant current control is performed, when the image is output after the machine has stopped for a certain period of time, the constant current value is temporarily changed to change the environment. Even if occurs, the generation of moire fringes at the interval between the charging rollers 2 is suppressed, and the fusion of the toner to the photosensitive drum 1 is suppressed.

(Common conditions) -Process speed: 103.26 mm / sec-Resolution: 600 dpi-Charging DC voltage: -700 V-Charging frequency: 1008 Hz <Example 3> (1) Normal output condition-Charging AC current: 840 μA (2) Output conditions after the machine has stopped for a certain period of time: Charging AC current: 1500 μA <Comparative example 1> * Charging AC current: 840 μmA <Comparative example 2> * Charging AC current: 1500 μmA Charging roller 2 for each of the above examples Occurrence of moire fringes at intervals,
Table 3 shows the results of the evaluation of the fusion of the toner onto the photosensitive drum 1.

[0028]

[Table 3] As is clear from the results of Table 3, when an image is output after the machine has been stopped for a certain period of time, if the constant current value is temporarily changed as in the present embodiment, environmental changes will occur. Even if it occurs, it is possible to suppress the generation of moire fringes in the interval between the charging rollers 2 and suppress the fusion of the toner to the photosensitive drum 1.

[0029]

As is apparent from the above description, according to the present invention, even if the charging member is deformed due to the image forming apparatus being stopped for a certain period of time, charging is performed when an image is output thereafter. Since the frequency of the AC component of the voltage applied to the member or the peak-to-peak voltage is temporarily changed, or the current applied to the charging member is temporarily changed, moire and toner fusion are prevented. The effect that a high-quality image can be stably output is obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a main part of an image forming apparatus according to the present invention.

FIG. 2 is a sectional view showing an undeformed charging roller.

FIG. 3 is a cross-sectional view showing a deformed charging roller.

FIG. 4 is a diagram showing a moiré sample.

FIG. 5 is a sectional view of a main part of a conventional image forming apparatus.

FIG. 6 is a sectional view of a charging roller used in a conventional image forming apparatus.

[Explanation of symbols]

 1 Photosensitive Drum (Charge Object) 2 Charging Roller (Charging Member) 3 Developing Device 4 Cleaning Device 5 Transfer Charging Device 6 Fixing Device

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yoichiro Maebashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (3)

[Claims] 1. An image provided with a contact charging device for applying a voltage in which an alternating current component and a direct current component are superposed to a charging member and contacting the charged member while rotating the charging member to charge the charged member. In the image forming apparatus, when an image is output after the image forming apparatus is stopped for a certain period of time, the frequency of the AC component of the voltage applied to the charging member is temporarily changed. 2. An image provided with a contact charging device for applying a voltage in which an alternating current component and a direct current component are superposed to a charging member, and contacting the charged member while rotating the charging member to charge the charged member. In the image forming apparatus, when the image is output after being stopped for a certain period of time, the peak-to-peak voltage of the voltage applied to the charging member is temporarily changed. 3. A contact charging device for applying a current in which an alternating current component and a direct current component are superimposed to a charging member, and contacting the charged member while rotating the charging member to charge the charged member, In an image forming apparatus that controls the AC component of the current applied to the charging member to a predetermined value with a constant current, when outputting an image after a state in which the AC component is stopped for a certain period of time, the current applied to the charging member is temporarily changed. An image forming apparatus characterized in that the image forming apparatus is changed.