JP3602511B2 - Image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for preventing a decrease in image quality in an image forming apparatus such as a copying machine, a printer, and other electrophotographic output machines.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in a developing unit of an image forming apparatus, toner is adhered to an electrostatic latent image on a photosensitive drum and developed. Inside the developing section, the developing roller rotates to stir the toner and carrier inside. A part of the developing unit is opened, and toner is adhered to an external photosensitive drum at this opening. Further, a seal member is provided in contact with the photosensitive drum at the opening so that toner does not scatter from the opening. The seal member is attached to a metal support member to prevent deformation due to bending or the like.
[0003]
Since the seal member is an insulator, it does not normally have an adverse effect even when it is in contact with the photosensitive drum. However, in a high-temperature, high-humidity environment, a phenomenon may occur in which charge on the photosensitive drum leaks from a part of the seal member. When this phenomenon occurs, a linear toner image called a black streak is generated on the image formed on the recording paper, which causes a deterioration in image quality. Conventionally, in order to prevent the occurrence of the black streaks, a bias voltage applied to the developing unit is also applied to the supporting member to prevent the leakage of electric charges from the seal. The voltage applied to the developing unit includes a method of applying a DC (DC) bias and a method of applying an AC (AC) bias.
[0004]
[Problems to be solved by the invention]
However, the conventional image forming apparatus as described above has the following problems. That is, since a grounded metal such as an LED print head unit (hereinafter referred to as an LPH unit) is located near the developing unit, in a developing system model to which an AC bias is applied, a writing optical system is generated due to generation of noise or the like due to an AC voltage. May cause runaway, resulting in poor printing.
[0005]
The present invention has been made in view of the above circumstances, and provides an image forming apparatus that can stably prevent the occurrence of black streaks without being affected by the type of voltage applied to a developing unit.
[0006]
[Means for Solving the Problems]
The present invention according to claim 1 is an image forming apparatus that forms an image by developing an electrostatic latent image on a photosensitive drum with toner, and transferring and fixing the electrostatic latent image on paper, wherein a DC grid voltage is applied. A charging unit including a grid, a developing unit that attaches toner to the photoconductor drum, and a blocking member formed of an insulator that is provided in pressure contact with the photoconductor drum and blocks scattering of the toner from the developing unit. And a metal support member for supporting the blocking member, wherein the grid voltage is applied to the support member.
[0007]
According to the present invention, since the DC grid voltage is applied to the support member, the charge of the photosensitive drum is prevented from leaking to the support member via the seal member. For this reason, the generation of black streaks can be prevented even in a high-temperature and high-humidity environment. In particular, in a development type model to which an AC bias is applied, even if a grounded metal such as an LPH unit is in the vicinity of the development section, the applied voltage is DC and no noise or the like is generated. Runaway of the printing does not occur, and the occurrence of printing failure can be prevented.
[0008]
Therefore, regardless of whether the developing bias is the AC bias or the DC bias, black streaks can be stably prevented in both types of models.
[0009]
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, a resistor is provided in a circuit for guiding the grid voltage to the support member.
[0010]
According to the present invention, when the grid voltage is higher than the charged voltage of the photoconductor drum, the voltage applied to the support member is reduced, and the voltage close to the charged voltage of the photoconductor drum can be obtained. Can be prevented.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing a schematic configuration of, for example, a tandem type full-color image forming apparatus as one embodiment of the present invention. As shown in FIG. 1, in a printer 1 (an example of an image forming apparatus), a developing device 3 is provided in a printer main body 2 for each of cyan, magenta, yellow, and black. Each developing device 3 is provided with a photosensitive drum 4 made of a-Si (amorphous silicon) or the like, and is configured to rotate in a direction indicated by an arrow in FIG. The photosensitive drum 4 is uniformly charged by a scorotron-type charging unit 5, and an LED light based on document image data input from an external PC or the like is radiated from the LPH unit 6 onto the drum surface to form an electrostatic latent image. It is formed. The toner is attached to the electrostatic latent image formed on the photosensitive drum 4 by the developing roller 31, and a toner image is formed. The toner is supplied from toner supply containers 7C, 7M, 7Y, and 7B, respectively. Below the four photosensitive drums 4 arranged in parallel for each color, a paper transport belt 8 is provided. The paper transport belt 8 is rotated by rollers 10 and 11 in the forward direction of the rotation direction of the photosensitive drum 4. A voltage having a polarity opposite to that of the toner is applied to the transfer roller 9 in a state where the paper transport belt 8 is pressed, and the toner is transferred to the transported paper by electrostatic force.
[0012]
When the paper is conveyed from the paper feed mechanism 12 via the paper conveyance path 13 between the photoconductor drum 4 and the paper conveyance belt 8, the paper is transferred between each photoconductor drum 4 and the paper conveyance belt 8. While being conveyed, the toner images of each color on the surface of each photoconductor drum 4 are sequentially transferred to the paper. After the transfer, the photosensitive drum 4 is cleaned of residual toner and the like by the cleaning device 20, and is ready for the next transfer. The sheet on which the toner image has been transferred by all the photosensitive drums 4 is conveyed to the fixing roller pair 14, where the toner image is fixed on the sheet to form a color image. The sheet that has passed the fixing roller pair 14 is sent to a sheet transport path 15 and discharged from a discharge unit 16.
[0013]
FIG. 2 is a cross-sectional view showing the developing device 3 of each color in detail. The mechanism shown in FIG. 2 is provided for each color. The scorotron-type charging unit 5 provided on the upper portion of the photosensitive drum 4 applies a high voltage to the charging wire 51 to generate corona discharge, and charges the surface of the photosensitive drum 4 to a predetermined potential via the grid 52. . A bias voltage is applied to the grid 52. A developing unit 35 is disposed on the right side of the photosensitive drum 4, and a developing roller 31 and a toner 39 (including a carrier) are provided therein. With the rotation of the developing roller 31, the toner 39 adheres to the electrostatic latent image formed on the photosensitive drum 4. An upper developing seal 33 is provided in an upper opening of the developing unit 35 as a blocking member for blocking scattering of the toner 39. The upper developing seal 33 is an insulator and is in pressure contact with the photosensitive drum 4. The upper developing seal 33 is attached to the support member 32 which is a metal plate in order to prevent deformation due to bending or the like and maintain the pressure contact accuracy with the drum. A bias voltage applied to the grid 52 is applied to the support member 32 in parallel. Therefore, even under a high-temperature and high-humidity environment, electric charges do not leak from the photosensitive drum 4 to the support member 32 via the upper developing seal 33. Therefore, it is possible to prevent the occurrence of black streaks in the image on the recording paper.
[0014]
FIG. 3 is a main circuit diagram around the charging unit 5. A wire voltage Vc for generating a corona is applied to the charging wire 51, and a grid voltage Vg is applied to the grid 52. Further, the circuit to the grid branches at a branch S on the way and is electrically connected to the support member 32. A resistor 37 is provided in the middle of the path. Therefore, a voltage that is slightly reduced by the resistor 37 from the grid voltage Vg applied to the grid 52 is applied to the support member 32.
[0015]
The voltage applied to the support member 32 is desirably close to the charged voltage of the photosensitive drum 4, but does not necessarily have to match. Therefore, the resistor 37 is not always necessary. For example, it has been confirmed that under the condition that the charged voltage of the photosensitive drum 4 is about 450 V and the grid voltage Vg is about 600 V, there is no electric charge leakage or backflow even without the resistor 37, and the predetermined function is satisfied.
[0016]
The timing of applying a voltage to the support member 32 may be the same as the timing of applying a voltage to the grid 52, but the environment in which the voltage is applied, such as temperature and humidity, may be limited as necessary.
[0017]
【The invention's effect】
As is apparent from the above description, the image forming apparatus of the present invention is an image forming apparatus that forms an image by developing an electrostatic latent image on a photosensitive drum with toner, transferring the image onto paper, and fixing the image. A charging unit having a grid to which a DC grid voltage is applied, a developing unit for attaching toner to the photosensitive drum, and a pressing unit provided to be in pressure contact with the photosensitive drum. A shielding member made of an insulator; and a metal supporting member for supporting the shielding member, wherein the grid voltage is applied to the supporting member. Irrespective of DC or DC, it is possible to stably prevent the occurrence of black streaks even in a high temperature and high humidity environment.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a schematic configuration of a tandem-type full-color image forming apparatus according to an embodiment of the invention.
FIG. 2 is a cross-sectional view illustrating a developing device of the exemplary embodiment in detail.
FIG. 3 is a main circuit diagram around a charging unit of the embodiment.
[Explanation of symbols]
1 Printer (image forming device)
2 Printer body 3 Developing device 4 Photoreceptor drum 5 Charging unit 6 LPH (LED print head) unit 31 Developing roller 32 Support member 33 Developing upper seal (blocking member )
35 developing unit 37 resistor 39 toner 51 charging wire 52 grid Vc wire voltage Vg grid voltage

Claims (2)

An image forming apparatus that forms an image by developing an electrostatic latent image on a photosensitive drum with toner, transferring the image to paper, and fixing the image, wherein a charging unit including a grid to which a DC grid voltage is applied; A developing unit for adhering toner to the photosensitive drum, a blocking member made of an insulator , provided to be in pressure contact with the photosensitive drum, and blocking scattering of the toner from the developing unit ; and a metal supporting the blocking member. An image forming apparatus comprising: a support member made of a material; and the grid voltage is applied to the support member. 2. The image forming apparatus according to claim 1, wherein a resistor is provided in a circuit for guiding the grid voltage to the support member.

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