JP2008309974A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing the occurrence of leakage on an amorphous silicon photoreceptor drum. <P>SOLUTION: The image forming apparatus is provided with: an electrifying roller 14 which electrifies the surface of the amorphous silicon photoreceptor drum 13; a determination circuit 23 which determines that the environment has high humidity, when the standard deviation of a current value when the photoreceptor drum 13 is electrified is a previously set threshold or more; and a control circuit 22 which carries out the aging operation of the photoreceptor drum 13, when it is determined that as the determination result of the determination circuit 23, the environment has high humidity. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  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, and more particularly to charging a charging device for power failure of an amorphous silicon photosensitive drum. The present invention relates to an image forming apparatus using a roller.

  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).

  In an image forming apparatus using such a charging roller, as the image forming process is repeated, a toner external additive such as silica or a discharge product at the time of charging is likely to adhere to the surface of the charging roller. Resistance unevenness occurs on the surface.

  In addition, since the discharge product is water-soluble, the resistance value is significantly lowered particularly in a high humidity environment.

  For this reason, not only an excessive current flows from the portion where the surface resistance value of the charging roller is reduced due to the adhesion of the discharge product, but also a local portion on the surface portion of the photoreceptor facing the portion where the surface resistance value is reduced. Current flows.

Further, the current that flows locally to the photoconductor causes a white spot-like abnormal image due to overcharging if the photoconductor has a withstand voltage, and if the photoconductor has insufficient withstand voltage, the photoconductor Destruction causes black spot-like abnormal images.
JP-A-2005-352162

  When an amorphous silicon photosensitive drum is used as the photosensitive member of the above-described charging roller type image forming apparatus, the surface resistance of the charging roller varies depending on the charging roller surface because amorphous silicon has low surface resistance. In particular, resistance unevenness is likely to occur remarkably in a high-humidity environment, and the photosensitive drum may be destroyed due to leakage from a portion with low resistance.

  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 leakage in an amorphous silicon photosensitive drum.

  The image forming apparatus of the present invention has a charging roller for charging the surface of an amorphous silicon photosensitive drum, and a high value when a standard deviation of a current value when charging the photosensitive drum is equal to or larger than a preset threshold value. And a control circuit that performs an aging operation of the photosensitive drum when a determination result of the determination circuit is determined to be a high-humidity environment. .

  At this time, the determination circuit measures the standard deviation of the current value at the time of charging the photosensitive drum after rotating the photosensitive drum for one turn or more, and the control circuit has the standard deviation equal to or less than the threshold value. It is preferable to continue the aging operation until the value decreases.

  Further, it is preferable that the voltage applied to the charging roller is lower in the measurement by the determination circuit than in the normal printing operation.

  The image forming apparatus of the present invention can suppress the occurrence of leakage in the amorphous silicon photosensitive drum.

  Next, an image forming apparatus according to an embodiment of the present invention will be 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. is there.

(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 are provided. 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. used. Further, the surface potential is set to be about 250 V, and the application of the charging roller 14 is performed under normal settings as shown in FIG. 3, DC (Vdc) = 400 V, AC (Vpp) = 1.4 KV, frequency 1 .5 kHz. Further, the peripheral speed of the photosensitive drum 13 is 150 mm / s.

  In the present embodiment, the standard deviation is calculated from the measurement data of the current flowing into the charging roller 14 for one or more revolutions of the photosensitive drum 13, and when the standard deviation is equal to or greater than a preset threshold value, the printing operation is performed. First, the idling (aging) operation of the photosensitive drum 13 is performed until the standard deviation falls below the threshold value.

  Here, when the standard deviation is large, that is, when the variation in the measurement current is large, the surface resistance unevenness of the charging roller 14 is large, and unevenness due to water absorption of the deposit on the surface of the charging roller 14 occurs.

  If printing is performed under the charging bias conditions for normal printing in this state, the photosensitive drum 13 may be destroyed due to leakage from a portion of the charging roller 14 having a low surface resistance. For example, it is desirable to apply Vdc = 200 V, Vpp = 1.4 KV, frequency 1.5 kHz) to the charging roller 14.

  If the standard deviation is less than or equal to the threshold value, it can be determined that the moisture on the surface of the charging roller 14 has been removed and the unevenness of resistance has been reduced, and the normal printing operation can be started. Further, since it is possible to determine from the current measurement value that the inside of the printer main body 2 is in a high humidity environment, it also serves as a trigger when performing an aging operation for preventing image flow of the photosensitive drum 13.

  FIG. 4 is a graph showing the relationship between charging time and charging current in a high humidity environment. The peaks P1 and P2 shown in FIG. 4 indicate an overcurrent state and indicate that the image forming processing operation is not executed until the waveform is settled.

  FIG. 5 is a graph showing the relationship between charging time and charging current. As shown in FIG. 5, the standard deviation δ = 22.9 is 10 seconds from the start of application to the charging roller 14, but the standard deviation δ is 0.9 after 30 seconds from the start of application. Here, assuming that the current leakage resistance is 20%, if the limit is 60 μA, which is 20% up from 50 μA, it is necessary that 20 seconds or more and σ = 3.6 or less.

  Therefore, the above-described threshold is set to 60 μA and σ = 3.6 or less, and this threshold is monitored by the determination circuit 23. If the threshold is greater than or equal to the threshold, an aging start signal is output to the control circuit 22.

  Based on the determination result, the control circuit 22 controls a 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.

  The determination circuit 23 outputs an aging stop signal to the control circuit 22 when it is determined that the standard deviation has fallen below the threshold due to the aging of the photosensitive drum 13.

  Based on the determination result, the control circuit 22 controls the drive source of the photosensitive drum 13 (not shown), stops the aging (idle rotation) of the photosensitive drum 13, and then starts image forming processing (normal printing operation). To do.

  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. Application to the charging roller is a graph of voltage. It is a graph which shows the relationship between the charging time and charging current in a high-humidity environment. It is a graph which shows the relationship between charging time and charging current.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Printer 13 ... Photoconductor drum 14 ... Charging roller 22 ... Control circuit 23 ... Determination circuit

Claims (3)

  A determination to determine that the environment is a high humidity environment when a charging roller for charging the surface of an amorphous silicon photosensitive drum and a standard deviation of a current value when charging the photosensitive drum is equal to or greater than a preset threshold value An image forming apparatus comprising: a circuit; and a control circuit that performs an aging operation of the photosensitive drum when the determination result of the determination circuit is a high humidity environment.   The determination circuit measures the standard deviation of the current value when charging the photosensitive drum after rotating the photosensitive drum for one or more revolutions, and the control circuit reduces the standard deviation below the threshold value. The image forming apparatus according to claim 1, wherein the aging operation is continued until the image forming apparatus continues.   3. The image forming apparatus according to claim 1, wherein the voltage applied to the charging roller is lower in the measurement by the determination circuit than in the normal printing operation.

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