JP2008309973A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the occurrence of image flowing on a photoreceptor drum. <P>SOLUTION: The image forming apparatus is provided with: an electrifying roller 14 which electrifies the surface of an amorphous silicon photoreceptor drum 13; a determination circuit 23 which determines whether the image flowing occurs or not on the photoreceptor drum 13 due to a current flowing into the photoreceptor drum 13; an exposure device which forms an electrostatic latent image on the surface of the photoreceptor drum 13; and a static eliminating device 19 which eliminates the potential by electrification of the photoreceptor drum 13 after image formation processing. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a printer, a copier, a facsimile machine, or a multifunction machine equipped with these functions. The present invention relates to an image forming apparatus.

In recent years, a scorotron charging method with a large amount of ozone generation has been installed as a method to place electric charge on the surface of the photosensitive drum of image forming apparatuses such as printers, copiers, facsimiles, or multifunction devices equipped with these functions using electrophotographic technology. This is an environmental problem, and a charging roller system that generates very little ozone is becoming mainstream (see, for example, Patent Document 1).
JP 2004-126295 A

  Incidentally, the charging current of the photosensitive drum and the charging potential have a positive correlation, and charging, exposure, development, transfer, and charge removal processes are repeated in this order during a general image forming process.

  At this time, when the current required to obtain the desired charging potential Vo is Idc-0, charging from the charging potential of 0 V is always required through the static elimination step, so that the current flowing into the photosensitive drum (charging current) ) Becomes Idc-0.

  On the other hand, in the case where the static elimination process is not performed, during the period from charging to returning to the original charging potential again, due to the dark decay characteristics as shown in FIG. Return and recharge.

  Therefore, the current required at this time can obtain a desired charging potential Vo with a current supplemented by the dark decay.

  Furthermore, by creating an electrostatic latent image on the surface of the photosensitive drum during the exposure process, the charged potential of the photosensitive drum is reduced. However, when a latent image of fine dots is formed, the photosensitive drum is in a high humidity environment. In the state where the surface resistance of the photosensitive drum is low, a latent image flow (image flow) occurs.

  This means that the latent image flows toward the surface of the photosensitive drum and the latent image becomes shallow. FIG. 8 shows the state of such a latent image change. Therefore, the state where the image flow is occurring and the state where the image flow is not occurring are different in the latent image state, and as a result, the charging potential is also different, resulting in a difference in the current value necessary for recharging. As shown in FIG. 9, there is a problem that the recharging current is smaller when no image flow occurs.

  In addition, when amorphous silicon is used for the photosensitive drum, the surface resistance of the photosensitive drum is low, and the latent image formed by the optical means flows in the direction of the photosensitive member surface due to adhesion of ozone products. There has been a problem that defects are likely to occur in a high humidity environment.

  For this reason, it is conceivable to provide a heater inside the photosensitive drum, or to determine the image flow using a potential sensor or the like, but either method requires an expensive member.

  In view of the above circumstances, an object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of image flow on a photosensitive drum.

  The image forming apparatus of the present invention determines whether or not an image flow is generated on the photosensitive drum by a charging roller for charging the surface of the amorphous silicon photosensitive drum and an inflow current to the photosensitive drum. It comprises a detection circuit, an exposure device that forms an electrostatic latent image on the surface of the photosensitive drum, and a static elimination device that neutralizes the charged potential of the photosensitive drum after image formation processing. .

  At this time, the detection circuit detects that the current required for obtaining the charging potential Vo when the photosensitive drum is charged by the charging roller is Idc-0, and the charging roller when the discharging device does not perform discharging. After forming the electrostatic latent image on the surface of the photosensitive drum by the exposure device, Idc-1 is a current that flows when the photosensitive drum is recharged by Vo, and the charging potential immediately below the charging roller is Vo-1. The difference α between Idc-0 and Idc-1 and the difference between Idc-0 and Idc-2 when the current that flows when the photosensitive drum rotates once is Idc-2 and the charging potential at that time is Vo-2. It is preferable to determine the image flow based on β.

  Further, when the detection circuit determines that an image flow is generated from β-α, the photoconductor drum is aged until it is determined that no image flow is generated by constantly monitoring β-α. It is preferable to perform the operation.

  The image forming apparatus of the present invention can suppress the occurrence of image flow on the photosensitive drum.

  Next, an image forming apparatus according to an embodiment of the present invention is applied to a printer and described with reference to the drawings.

  FIG. 1 is an explanatory diagram of a printer as an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of a main part (image forming unit) of the printer as an image forming apparatus according to an embodiment of the present invention. FIG. 3 is an explanatory diagram of a print pattern (25%) when confirming the occurrence of image flow using a printer as an image forming apparatus according to an embodiment of the present invention, and FIG. 4 is according to an embodiment of the present invention. FIG. 5 is a comparative graph showing the relationship between the surface potential and the printing rate when the image flow is generated and when no image flow is detected, using a printer as an image forming apparatus. FIG. 6 is a graph showing the relationship between the surface potential of the photosensitive drum and the charging current of the charging roller when the occurrence of image flow is confirmed using the printer as the image forming apparatus according to the embodiment. In a printer as an image forming apparatus It is a graph showing a criterion of the determination circuit.

(Overall configuration of printer 1)
As shown in FIG. 1, a printer 1 as an image forming apparatus according to an embodiment of the present invention includes a paper feed cassette 3 that is slidably stored in a printer main body 2 as an image forming apparatus main body, and a paper supply cassette 3. A paper feed unit 4 for taking out transfer paper (not shown) stored in the paper cassette 3, a manual feed tray 5 installed in front of the printer main body 2, and transfer paper (not shown) set on the manual feed tray 5. ), A conveyance path 7 on which transfer paper supplied from each of the sheet feeding sections 4 and 6 is conveyed, and each sheet feeding section 4 and 6 on the upstream side of the conveyance path 7 in the sheet conveyance direction. The registration roller pair 8 disposed downstream of the part where the toner flows and the registration roller pair 8 and the registration roller pair 8 disposed downstream of the registration roller pair 8 in the sheet conveyance direction and forming an image on one surface of the transfer paper More than the forming unit 9 and the image forming unit 9 A fixing device 10 for fixing an image (unfixed toner image) formed on one surface of the transfer paper that is disposed on the downstream side in the sheet conveying direction of the feeding path 7 and an image on the other surface of the transfer paper that has passed through the fixing device 10. When forming, a reversing path 11 that pulls back from the conveyance path downstream side of the conveyance path 7 from the conveyance path 7 to the upstream side of the conveyance path 7 in the sheet conveyance direction from the registration roller pair 8, and a terminal portion of the conveyance path 7. A paper discharge unit 12.

(Configuration of the image forming unit 9)
The image forming unit 9 includes a photoconductive drum 13, a charging roller 14 disposed around the photoconductive drum 13, an exposure device 15, a developing device 16, a transfer device 17, a cleaning device 18, and a static elimination device 19. .

  As the photosensitive drum 13, an amorphous silicon type photosensitive drum is used, and the structure thereof is a carrier injection blocking layer made of Si: H: B: O or the like on a conductive substrate, and carrier excitation made of Si: H or the like. A transport layer (photoconductive layer) and a surface protective layer made of SiC: H or the like are sequentially laminated.

  The charging roller 14 is installed above the photosensitive drum 13 and is a device for uniformly charging the photosensitive drum 13.

  The exposure device 15 forms an electrostatic latent image on the photosensitive drum 13 based on, for example, image data for a document image read by an image data input unit (not shown) or image data output from a personal computer or the like. It is a device for.

  The developing device 16 is an apparatus that forms a toner image by supplying toner to the surface of the photosensitive drum 13 on which the electrostatic latent image is formed via a developing roller 20. The toner used in this embodiment contains magnetic powder, and abrasive particles are fixed on the surface of the toner particles. As the abrasive fine particles, fine particles having high hardness, for example, metal oxides such as alumina, zirconia, and titania are suitable. In addition to the abrasive fine particles, a tracer such as silica may be added to the toner particles for the purpose of adjusting fluidity and chargeability.

  As a result, in the image forming unit 9, the photosensitive drum 13 is rotationally driven at a predetermined process speed (circumferential speed) by a driving unit (not shown), and the surface thereof is uniformly charged to a predetermined polarity and potential by the charging roller 14. .

  An electrostatic latent image is formed on the surface of the charged photosensitive drum 13 by the exposure device 15. Here, the exposure device 15 irradiates the surface of the photosensitive drum 13 with laser light (see the chain line) based on image data output from a personal computer or the like, and the laser light irradiation portion of the surface of the photosensitive drum 13 is irradiated. The electrostatic latent image corresponding to the image information is formed by removing the charge.

  The electrostatic latent image formed on the surface of the photosensitive drum 13 is an unfixed toner image formed by electrostatically attaching toner having a charge supplied from the toner container 21 by the developing roller 20 of the developing device 16. Developed. Further, the unfixed toner image is transferred onto the transfer paper as a transfer image by the transfer device 17.

  Further, the photosensitive drum 13 on which the unfixed toner image is transferred onto the transfer paper is subjected to a charge removal process by a charge removal device 19 for charging at the next image formation after the residual toner is removed by the cleaning device 18. The

  Incidentally, the charging potential of the charging roller 14 in the image forming apparatus of the present invention is controlled by a determination circuit 23 via a control circuit 22 that controls the entire printer 1 as shown in FIG.

  A control circuit (CPU) 22 performs control related to the entire image forming process based on various control programs stored in a memory 24 such as a ROM. The memory 24 also stores a control program related to charging control according to the present invention, and a microcomputer is configured with the control circuit 22 that executes the control program. Note that image data or the like when executing the image forming process is temporarily stored in a storage medium (not shown) such as a RAM or HDD different from the memory 24.

  Next, a control example of charging control using the determination circuit 23 will be described with reference to experimental examples.

  The amorphous silicon photosensitive drum 13 used in this experiment has an outer diameter of 30 mm, a film thickness of 20 μm, and a length of 254 mm. The charging roller 14 has an outer diameter of 12 mm, a length of 220 mm, and an outer diameter of the core metal of 6 mm. did. Further, the surface potential was set to about 250 V, and the application of the charging roller 14 was set to DC = 400 V, AC = 1.4 KV, and frequency 1.5 kHz. Further, the peripheral speed of the photosensitive drum 13 is 150 mm / s.

  An example of the 25% pattern used in this experiment is shown in FIG. At this time, when the printing performance (resolution) is 600 dpi, since 1 inch = 25.4 mm, 25.4 mm / 600 dpi = 0.42 mm, and one dot is 0.042 mm (42.2 μm).

  As shown in FIG. 4, when the charging potential Vo is set to 250 V and a pattern with a printing rate of 25% is used, the surface potential in the state where the image flow is generated on the photosensitive drum 13 is 160 V, and the image flow is generated. The surface potential in the state of not being turned into 45V. In addition, when the surface potential was actually 75 V or more in a 25% pattern, the flow could be detected on the image.

  Here, if the charging current when the charging potential Vo = 160V is Idc-2 and the charging current when Vo = 45V is Idc = 1, the current values are about 59 μA and 110 μA, respectively, as shown in FIG. It can be seen that the difference between the latent images causes a difference in the recharging current. If Vo = 75V is the limit line, it can be seen that the current Idc needs to be 85 μA or more.

  Accordingly, the determination circuit 23 sets the current required for obtaining the charging potential Vo when the photosensitive drum 13 is charged by the charging roller 14 to Idc-0, and the charge roller 14 when the charge removal device 19 does not perform charge removal. An electrostatic latent image was formed on the surface of the photosensitive drum 13 by the exposure device 15 with Idc-1 being the current that flows when the photosensitive drum 13 was recharged by Vd, the charging potential immediately below the charging roller 14 being Vo-1. When the current that flows when the photosensitive drum 13 makes one rotation later is Idc-2 and the charging potential at that time is Vo-2, as shown in FIG. 6, the difference α between Idc-0 and Idc-1, and Idc The occurrence of image flow is determined based on the difference β between −0 and Idc−2.

  Further, when the determination circuit 23 determines that the image flow is generated from β-α, the determination circuit 23 constantly monitors β-α and controls the image flow generation signal until it is determined that the image flow is not generated. Output to the circuit 22.

  Based on the determination result, the control circuit 22 controls the driving source of the photosensitive drum 13 (not shown), and agees the photosensitive drum 13 (idle rotation) to remove moisture from the photosensitive drum 13, thereby Eliminate the flow.

  As described above, according to the image forming apparatus of the present invention, the determination circuit 23 detects the disturbance of the latent image due to the image flow from the charging flow current value of the amorphous silicon photosensitive drum 13, thereby suppressing the image flow. be able to.

  In the above embodiment, the image forming apparatus of the present invention is applied to the printer 1. However, it is needless to say that the image forming apparatus can be applied to all image forming apparatuses such as multifunction peripherals.

1 is an explanatory diagram of a printer as an image forming apparatus according to an embodiment of the present invention. FIG. FIG. 3 is an explanatory diagram of a main part (image forming unit) of a printer as an image forming apparatus according to an embodiment of the present invention. FIG. 10 is an explanatory diagram of a print pattern (25%) when confirming the occurrence of image flow using a printer as an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a comparative graph showing a relationship between a surface potential and a printing rate when an image flow is generated and when no image flow is confirmed using a printer as an image forming apparatus according to an embodiment of the present invention. is there. FIG. 6 is a graph showing the relationship between the surface potential of the photosensitive drum and the charging current of the charging roller when the occurrence of image flow is confirmed using a printer as an image forming apparatus according to an embodiment of the present invention. FIG. 4 is a graph showing determination criteria of a determination circuit in a printer as an image forming apparatus according to an embodiment of the present invention. It is a graph of dark attenuation characteristics in the photosensitive drum. FIG. 6 is a comparative graph showing a difference in potential between normal and high humidity in the surface potential of the photosensitive drum and the post-exposure potential. FIG. 6 is a graph showing a relationship between a surface potential and a current detection pattern in a state where an image flow occurs on a photosensitive drum and a state where no image flow occurs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Printer 13 ... Photosensitive drum 14 ... Charging roller 15 ... Exposure device 19 ... Static elimination device 22 ... Control circuit (detection circuit)
23: Determination circuit (detection circuit)

Claims (3)

  A charging roller for charging the surface of the amorphous silicon photosensitive drum; a detection circuit for determining whether or not an image flow is generated on the photosensitive drum due to a current flowing into the photosensitive drum; and the photosensitive drum An image forming apparatus comprising: an exposure device that forms an electrostatic latent image on the surface of the photosensitive drum; and a static elimination device that neutralizes the charged potential of the photosensitive drum after the image formation processing.   The detection circuit uses Idc-0 as a current necessary for obtaining a charging potential Vo when the photosensitive drum is charged by the charging roller, and the charging roller causes the charging roller to perform the neutralization by the charging roller. The current flowing when the photosensitive drum is recharged is Idc-1, the charging potential immediately below the charging roller is Vo-1, and an electrostatic latent image is formed on the surface of the photosensitive drum by the exposure device. When the current flowing when the body drum makes one rotation is Idc-2, and the charging potential at that time is Vo-2, the difference α between Idc-0 and Idc-1, and the difference β between Idc-0 and Idc-2, The image forming apparatus according to claim 1, wherein the image flow is determined by:   When the detection circuit determines that the image flow is generated from β-α, the detection circuit performs the aging operation of the photosensitive drum until it is determined that the image flow is not generated by constantly monitoring β-α. The image forming apparatus according to claim 1, wherein the image forming apparatus is implemented.

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