JP2005250381A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably perform electrifying processing without causing defective electrification over a long period of time while securing electrifying performance required for an electrifier in a cleaner-less system image forming apparatus in which discharge product is not positively removed. <P>SOLUTION: In the case of an image in a black-and-white mode or in the case of only a text image when one job for forming an image is equivalent to run length 1, a control means 54 performs switching control so that the electrifier 52 may perform electrifying processing by applying only DC voltage to an image carrier used in an electrophotographic image forming process, whereby a situation that the electrifier 52 performs electrifying processing by superposing AC voltage on the DC voltage is restrained to the minimum to delay the accumulation of the discharge product on the surface of the image carrier. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  This invention is equipped with a charging system having a function of superimposing and applying an AC voltage to a DC voltage in order to charge an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric during the image forming process. The present invention relates to an image forming apparatus of a cleanerless system such as a laser printer, a copying machine, a facsimile machine or the like.

  In general, in an image forming apparatus employing an electrophotographic system, the entire apparatus is reduced in size, copes with ecology by eliminating the generation of waste toner, and extends the life of an electrophotographic photosensitive member (photosensitive drum) as an image carrier. To reduce the consumption of toner as a developer per page, the toner remaining on the surface of the photosensitive member (the surface of the photosensitive drum, which is the surface of the image carrier) after the toner image is transferred to the transfer material on the developing unit. The image bearing member (photoreceptor) is cleaned by a so-called simultaneous development cleaning or development / cleaning type image processing apparatus, or a cleaning blade, in which the cleaning means as a dedicated device is eliminated by using the cleaning means for (transfer residual toner). A cleanerless image forming apparatus called a cleanerless system has been proposed.

  Such an image processing apparatus of the simultaneous development cleaning or development / cleaning system, or an image forming apparatus of a cleanerless system that does not actively scrape discharge products without using a cleaning blade, is detachable from the main body of the image forming apparatus. Some of the process cartridges mounted on the printer use a direct charging type charging processing means.

  For example, only a DC voltage is applied to a roll-type charger that is a contact charging means (contact charging member) that contacts the photosensitive drum, and the voltage value of the photosensitive drum is approximately equal to the voltage value obtained by subtracting the discharge start voltage from the applied DC voltage. Means for obtaining the surface potential are used. This method generates less ozone because it does not actively use discharge. In this method, it is possible to suppress discharge products such as nitrogen oxides from adhering to the photosensitive drum, and impairing the photosensitive drum from impairing the charge retention, resulting in white-out image defects (so-called white spots or image flow). Can be prevented.

  However, in the image processing apparatus of the simultaneous development cleaning or development and cleaning system equipped with the charging processing means of the direct charging system, or the image forming apparatus of the cleanerless system that does not actively scrape the discharge product without using the cleaning blade. As the number of sheets passing increases, the photosensitive drum and the roll-type charger may be contaminated due to accumulation of transfer residual toner adhering to the photosensitive drum, resulting in poor charging and image defects. In particular, in images with high image density such as maps, graphs, and photographs, the amount of residual toner that adheres to the roll-type charger increases, so the contamination of the roll-type charger advances quickly, and the charging uniformity of the photosensitive drum decreases rapidly. End up.

  Therefore, a roll type charger that is more resistant to contamination of a charging roll in an image processing apparatus of a simultaneous development cleaning or a development and cleaning system, or an image forming apparatus of a cleanerless system that does not actively scrape discharge products without using a cleaning blade. By applying a DC voltage superimposed on the DC voltage with an amplitude about twice the discharge start voltage, the surface of the photosensitive drum is uniformly charged to a predetermined potential without any unevenness. A method for obtaining a high-quality output image has been proposed (see, for example, Patent Document 1).

However, when the roll type charger uses charging processing means for applying an AC voltage superimposed on a DC voltage, toner adhesion to the roll type charger is suppressed by positive and negative discharges. However, white spots are more likely to occur due to the accumulation of a large amount of discharge products on the surface of the photosensitive drum, which is the surface of the photosensitive member, and the charge retention is impaired. When a large amount of discharge product deposits occur on the roll-type charger in this way, in a cleanerless system that does not use a cleaning blade and actively scrapes off the discharge product, white image defects will occur after the image forming apparatus is stopped. A secondary failure defect such as a so-called morning depletion may occur, which causes a problem that the life of the image forming apparatus and the process cartridge cannot exceed a certain number.
JP 2002-229308 A

  In view of the above problems, the present invention can obtain a good image by stably performing a charging process without causing a charging failure over a long period of time while ensuring the charging performance required for the charger. An object of the present invention is to newly provide an image forming apparatus of a cleanerless system.

  The image forming apparatus according to claim 1 is an electrophotographic image forming apparatus configured as a cleaner-less system, an image carrier used in an electrophotographic image forming process, and only a DC voltage is applied to the image carrier. A charger that can be selected and executed between a process for charging by applying an AC voltage and a process for charging by applying an AC voltage superimposed on a DC voltage, and printing as a single print job that forms an image by electrophotography It is detected whether or not the amount is equivalent to run length 1 that can be processed within the maximum size capable of image formation. If the amount is not equivalent to run length 1, charging is performed by applying an AC voltage superimposed on a DC voltage by a charger. Switch to perform processing, and in the case of run length 1, it is switched to perform processing for charging by applying only DC voltage with a charger. After running the blanking and a control means for performing a removal cycle for removing the applied toner stain a reverse bias to the charger, to have a said.

  By configuring as described above, after executing a print job corresponding to run length 1, a reverse cycle is applied to the charger to execute a removal cycle for removing toner stains, thereby cleaning the charger and causing poor charging. Therefore, when charging the surface of the image carrier with a charger, only the DC voltage is applied while maintaining the charging uniformity that meets the requirements of the image to be formed. Image formation of a cleanerless system that does not use a cleaning blade by delaying the accumulation of discharge products on the surface of the image carrier by minimizing the operation of the charging process in which an alternating voltage is applied on the surface of the image carrier. The apparatus can also achieve both high image quality satisfaction and long-term image quality maintenance.

  The image forming apparatus according to claim 2 is an electrophotographic image forming apparatus configured as a cleaner-less system, an image carrier used in an electrophotographic image forming process, and only a DC voltage is applied to the image carrier. A black and white mode image that can be executed by electrifying and electrifying a process in which an AC voltage is superimposed on a DC voltage and a process in which an AC voltage is superimposed and applied. If the image is in black and white mode, it is switched so that only the DC voltage is applied for charging by the charger, and if the image is not in black and white mode, it is switched to DC voltage by the charger. And control means for switching to perform a process of charging by applying a voltage in a superimposed manner.

  With the configuration described above, when forming an image in black and white mode, the required level of charge uniformity tends to be low, so it should be formed when charging the image carrier surface with a charger. Minimize the operation of charging by applying only a DC voltage while maintaining charging uniformity that meets the requirements of black and white mode images, and applying an AC voltage superimposed on the DC voltage. By delaying the accumulation of discharge products on the surface of the image carrier to the minimum, it is possible to achieve both high image quality satisfaction and long-term image quality maintenance even in cleanerless system image forming devices that do not use a cleaning blade. Can do.

  The image forming apparatus according to claim 3 is an electrophotographic image forming apparatus configured as a cleaner-less system, an image carrier used in an electrophotographic image forming process, and only a DC voltage is applied to the image carrier. A charger that can be executed by electrifying and charging a DC voltage by superimposing an AC voltage on the DC voltage, and an image formed by electrophotography is a text image only. When it is only a text image, it is switched so that only the DC voltage is applied by the charger and charged. When it is not only the text image, the AC voltage is changed to the DC voltage by the charger. And a control means for switching so as to perform a process of charging by applying the charge in a superimposed manner.

  By configuring as described above, when only a character image that is a text image is formed, when a character image is formed by applying a direct current voltage to the image carrier and charging it with a charger, Since the amount of toner adhering to the charger falls below the value of the amount of toner adhering to the charger that causes charging failure and falls within the allowable range, when charging the image carrier surface with the charger, an image of only the character image to be formed The process of charging by applying only the DC voltage while maintaining the uniformity of charging that meets the requirements of the charging is performed, and the operation of the charging process of applying the AC voltage superimposed on the DC voltage is minimized. By delaying the accumulation of discharge products on the surface of the image carrier, high image quality satisfaction and long-term image quality can be achieved even in cleaner-less system image forming devices that do not use a cleaning blade. It is possible to achieve both the maintenance.

  The image forming apparatus according to claim 4 is an electrophotographic image forming apparatus configured as a cleaner-less system, an image carrier used in an electrophotographic image forming process, and only a DC voltage is applied to the image carrier. A charger that can be selected and executed between a process for charging by applying an AC voltage and a process for charging by applying an AC voltage superimposed on a DC voltage, and printing as a single print job that forms an image by electrophotography It is detected whether or not the amount is equivalent to run length 1 that can be processed within the maximum size capable of image formation, and whether or not the image formed by the electrophotographic method is a monochrome mode image, It is detected whether the image created by the photographic method is only a text image. If the image created by the electrophotographic method is equivalent to run length 1 or is an image in the monochrome mode. Alternatively, when the image is only a text image, the charging device is switched so as to perform a charging process by applying only a DC voltage, and when the image is not equivalent to run length 1, or when the image is not a monochrome image or not only a text image, And control means for switching to perform a process of charging by applying an AC voltage superimposed on a DC voltage.

  With the configuration described above, when a print job corresponding to run length 1 is executed, toner contamination of the charger does not proceed greatly, and when the image to be formed is a monochrome mode image or only a text image. Since the charging uniformity required in this case is moderate, when it is detected that these images are to be formed, there is a request for an image to be formed when the image carrier surface is charged by the charger. The image is carried by minimizing the operation of the charging process in which only the DC voltage is applied while maintaining the charging uniformity conforming to By delaying the accumulation of discharge products on the surface of the body, high image quality satisfaction and high image quality over a long period of time can be achieved even in an image forming apparatus with a cleanerless system that does not use a cleaning blade. It is possible to achieve both the maintenance of.

  The image forming apparatus according to claim 5 is an electrophotographic image forming apparatus configured as a cleaner-less system, an image carrier used in an electrophotographic image forming process, and only a DC voltage is applied to the image carrier. A charger capable of selecting and executing a process of charging by applying an AC voltage to a DC voltage and a process of charging by applying an AC voltage superimposed on a DC voltage, and one of one print job for forming an image by electrophotography. Detects whether the image is a monochrome mode image by acquiring two images, and further detects whether it is only a text image, and if the acquired single image is a monochrome mode image or only a text image If the image is not a black-and-white image or only a text image, it is switched directly by the charger. And having a control means for switching so as to perform the process of charging is applied by superimposing an AC voltage on a voltage.

  By configuring as described above, each time a process of creating one image from one print job, it is detected whether the image to be created is only a monochrome mode image or a text image. When performing charging, the charging uniformity required when charging the surface of the image carrier with a charger is moderate, so only DC voltage is maintained while maintaining charging uniformity that meets the medium requirements. Is applied to charge, and the accumulation of discharge products on the surface of the image carrier is delayed by minimizing the operation of the charging process in which an AC voltage is superimposed on the DC voltage. In a cleanerless system image forming apparatus that does not use a cleaning blade, both high image quality satisfaction and long-term image quality maintenance can be achieved.

  According to the image forming apparatus of the present invention, when charging is performed on the surface of the image carrier by the charger, the AC voltage is superimposed on the DC voltage while maintaining charging uniformity that meets the requirements of the image to be formed. High image quality satisfaction even in an image forming apparatus of a cleanerless system that does not use a cleaning blade by delaying the accumulation of discharge products on the surface of the image carrier by minimizing the operation of the charging process applied There is an effect that it is possible to maintain both high quality and high image quality over a long period of time.

  Embodiments of the image forming apparatus according to the present invention will be described with reference to FIGS.

  An image forming apparatus 10 that employs a cleanerless system that does not use a cleaning blade in the electrophotographic method according to the present embodiment is configured as a printer, a multifunction peripheral, or the like as shown in the overall block diagram of FIG. An image capturing device (IIT) 12, an image processing device (IPS) 14, and an image output device (IOT) 16 are provided inside the main body of the image forming apparatus 10. Further, the image forming apparatus 10 can be connected to an image input means such as a personal computer 18 via an interface 72 (shown in FIG. 4).

  In the image forming apparatus 10, RGB image data captured from the image capturing device 12, the personal computer 18, or an input device (not shown) and a signal of print information (image mode information, etc.) are transmitted to the image processing device 14. That is, the personal computer 18 allows a user to select a color mode, a black and white mode, or an automatic selection of a color mode and input a command as the selected print information. By selecting a character, a graph, a photograph, or the like, which is a selection, a command as the selected print information can be input. Further, the personal computer 18 is configured to transmit a command information signal including print information input by the user and RGB image data to the image processing apparatus 14.

  The image forming apparatus 10 transmits the RGB image data and the image forming condition signal generated by the image processing apparatus 14 to the image output apparatus 16 including the process cartridge, and outputs the sheet on which the image is formed. It has a configuration.

  The developing device 34 in the image forming apparatus 10 is configured as a cleanerless system using a roll-type charging device (BCR which is a charging means) and using a toner recovery brush and a toner polarity ordering brush.

  In the lower part of the process cartridge in the image output device 16 of the image forming apparatus 10, as schematically shown in FIG. 2, a sheet supply unit 20 for supplying a sheet to be an image forming object and an upper part thereof are arranged. Between the sheet discharge unit 22 for discharging the sheet on which the formed image is formed, a sheet conveyance path 24 is arranged to convey the sheet while being sandwiched between a pair of conveyance rollers.

  On the sheet conveyance path 24, a full-color print image transfer unit 26 and a fixing unit 28 are arranged in this order from the upstream side in the conveyance direction.

  An endless track-shaped intermediate transfer belt 32 wound around a plurality of pulleys 30 is disposed in the image transfer unit 26. These pulleys 30 include a pulley connected to a drive source (not shown) and functioning as a driving pulley for driving the intermediate transfer belt 32 and a pulley functioning as a tension pulley for adjusting the tension of the intermediate transfer belt 32. The pulley 30 </ b> A is a backup roll disposed at a position facing the secondary transfer device (secondary BTR) 31 for transferring the image on the intermediate transfer belt 32 onto the sheet with the image forming sheet interposed therebetween. Configure as.

  Four developing devices containing a developer containing yellow (Y), magenta (M), cyan (C) or black (K) toner for full color development on the running path of the intermediate transfer belt 32 The (developing means) 34 is disposed at each predetermined position at equal intervals. Further, a sensor 36 for detecting the toner density and a belt cleaner 38 for scraping off residual toner on the intermediate transfer belt 32 with a cleaner blade are disposed on the traveling path of the intermediate transfer belt 32.

  Each of these four developing devices (developing means) 34 is configured as shown in FIG. The developing device 34 is provided with a photosensitive drum 40 that is a photosensitive member (image carrier) that is in rolling contact with the intermediate transfer belt 32. Further, a primary transfer device (primary BTR) 42 for charging the intermediate transfer belt 32 is disposed at a position facing the photosensitive drum 40 with the intermediate transfer belt 32 interposed therebetween.

  Further, around the photosensitive drum 40, a brush unit 44, a roll charger 46, an exposure device (imager) 48, and a developing device 50 are disposed.

  The brush portion 44 is configured as a rotating brush.

  The roll type charger 46 is a charging device (BCR which is a charging means) for uniformly negatively charging the surface of the photosensitive drum 40 with a predetermined charging portion potential. The photosensitive drum 40 is configured to be capable of performing control by selecting and executing either a charging process in which only a DC voltage is applied or a charging process in which an AC voltage is superimposed on the DC voltage. A power supply 52 is connected.

  The exposure device 48 (exposure means) turns on the exposure device 48 based on an image signal supplied from a control device of an exposure device (not shown) so that the charged image portion on the photosensitive drum 40 becomes a predetermined exposure portion potential. -It is configured to be able to form a latent image corresponding to an image by performing exposure by turning off.

  The developing device 50 supplies toner by applying a developing bias to develop the latent image on the photosensitive drum 40 with yellow (Y), magenta (M), cyan (C), or black (K) toner. The image is developed with an agent and visualized as a toner image. Each color toner image developed on the photosensitive drum 40 by each developing device 50 is sequentially transferred to the intermediate transfer belt 32 by each primary transfer device 42, and finally the four color toner images are superimposed. It becomes a state.

  In the image forming apparatus 10 configured as described above, an image is formed as follows. First, in each developing device 34, a predetermined voltage is applied to the roll charger 46 to uniformly charge the surface of the photosensitive drum 40 at a predetermined charging portion potential. Subsequently, exposure processing is performed by the exposure device 48 so that each image portion of the charged photosensitive drum 40 has a predetermined exposure portion potential, thereby forming a latent image.

  The photosensitive drums 40 on which the respective latent images are formed are developed by the respective developing units 50 to form toner images of the respective colors, and the toner images of the respective colors are sequentially transferred to the intermediate transfer belt 32 by the respective primary transfer units 42. As a result, a toner image for transfer in which toner images of four colors are superimposed is formed.

  Further, the sheet pulled out from the recording paper cassette (not shown) in the sheet supply unit 20 onto the sheet conveyance path 24 is conveyed on the sheet conveyance path 24 and fed to the secondary transfer unit 31. Then, after the transfer toner image formed on the intermediate transfer belt 32 of the image transfer unit 26 is transferred to the sheet by the secondary transfer unit 31, the sheet is further conveyed on the sheet conveyance path 24. It is carried into the fixing unit 28 and thermally fixed. The sheet on which the image is formed in this manner is conveyed on the sheet conveying path 24 and discharged onto a tray (not shown) of the sheet discharging unit 22.

  The toner remaining on the intermediate transfer belt 32 is removed by the belt cleaner 38 and collected.

  Next, in the image forming apparatus 10 configured as described above, roll-type charging is performed so as to delay the accumulation of discharge products on the surface of the photosensitive drum 40 when the photosensitive drum 40 is charged in the course of the image forming process. For the configuration of the control means for controlling the charging bias application power source 52 in order to select and execute either the charging process for applying only the DC voltage to the battery 46 or the charging process for applying the AC voltage superimposed on the DC voltage, This will be described with reference to the block diagram shown in FIG.

  The control means for controlling the charging bias application power source 52 provided in the image forming apparatus 10 includes a RAM (Random Access Memory) 58 via a bus 56 and a CPU (Central Processing Unit) 54 that is a control unit of the image processing apparatus 14. An image processing unit 66 having a text classification circuit 64 is connected.

  The image processing unit 66 detects when the RGB image signals received by the image processing device 14 all match (R = G = B) (when the self-black image becomes the main image), and receives the received RGB image signals. The image signal is configured to be able to determine whether the self-black image is a main image or a color image.

  Further, the text classification circuit 64 of the image processing device 14 is configured to detect whether the image signal is a text file and to determine whether the image signal is a character image or a photographic image other than that. Note that the image processing device 14 may be configured to perform character separation processing to determine whether the image is a character image.

  A BCR DC driver 60 and a BCR AC driver 62 of the image output device 16 are connected to the CPU 54 via a bus 56. The BCR DC driver 60 is configured to drive a DC bias application power supply unit 52A in the charging bias application power supply 52. The BCR AC driver 62 is configured to drive the AC bias application power supply unit 52B in the charging bias application power supply 52.

  An image capturing unit 68 of the image capturing device 12 and a control panel 70 are connected to the CPU 54 via a bus 56. The control panel 70 allows a user to select a color mode, a black and white mode, or an automatic selection of a color mode and input the selected command. Furthermore, the user can select characters, A graph or a photograph is selected, and the selected command can be input. Further, the control panel 70 is configured so that the user can input a command for specifying the print amount as one print job.

  The personal computer 18 is connected to the CPU 54 via an interface 72 connected to the bus 56 so that image data can be input.

  In the control means for controlling the charging bias application power source 52 of the image forming apparatus 10 configured as described above, when the CPU 54 performs the charging process on the photosensitive drum 40 during the image forming process, the discharge product on the surface of the photosensitive drum 40. The operation is controlled so as to satisfy the condition for delaying the accumulation.

  In this control means, the following conditions are considered in order to control to delay the accumulation of discharge products on the surface of the photosensitive drum 40.

  First, in an image forming apparatus configured as a cleaner-less system using a BCR as a charging device and using a toner recovery brush or a toner polarity ordering brush, the toner remains on the photoreceptor (image carrier) after transfer. Since the toner is leveled to some extent when passing through the brush, the amount of residual toner that enters the BCR is substantially proportional to the density of the developed image.

  Second, when a charging method that applies an AC bias to the BCR is used, toner adhesion to the BCR is suppressed by positive and negative discharges that are alternately performed, and even if the residual toner amount increases, the BCR contamination is almost deteriorated. do not do.

  The charging method for applying an AC bias to the BCR is, as illustrated in FIG. 10, DC having a voltage corresponding to a desired charging potential (−500 V in the present embodiment) by a DC bias applying power supply unit to the charger. In addition to applying a bias voltage, an AC bias voltage having an amplitude about twice that of the discharge start voltage (500 V in the present embodiment) is applied in a superimposed manner so that the photoreceptor surface potential is converged to -500 V. .

  As shown in FIG. 6, the relationship between the image density and the amount of BCR adhering toner shows that the BCR adhering toner amount is substantially constant even when the image density increases when the charging method of applying an AC bias is used for BCR. It becomes.

  However, when a charging method in which an AC bias is applied to the BCR is used, a large amount of discharge products accumulate and so-called white spots are likely to occur. This is a major problem in cleanerless systems that do not use a cleaning blade and do not aggressively scrape off the discharge products.

  Third, when a charging method in which a DC bias is applied is used for the BCR, there is an advantage that white spots due to deposition of discharge products hardly occur.

  In the charging method of applying a DC bias, as illustrated in FIG. 9, by applying a DC bias voltage equal to or higher than a discharge start voltage (500 V in the present embodiment) to a charger by a DC bias application power supply unit, The photosensitive member surface potential is charged to a desired potential (-500 V in this embodiment).

  However, when a charging method in which a DC bias is applied to the BCR is used, when the image density is high, the amount of residual toner adhering to the BCR increases, so that the BCR stains rapidly. For example, in the case of an image such as a map, a graph, or a photograph having a high image density, the charging uniformity of the BCR is reduced to the extent that two A3 images are created.

  That is, as shown in FIG. 6, the relationship between the image density and the amount of BCR attached toner is that when the charging method for applying a DC bias is used for the BCR, the amount of BCR attached toner is increased as the image density increases. It tends to increase. Further, when a charging method in which a DC bias is applied to the BCR is used, the amount of BCR adhering toner when an image such as a map, graph, or photograph having a high image density is formed is as shown in the graph photograph shown in FIG. The value is in the image area A. Therefore, when the charging method for applying a DC bias is used, the value in the image area A such as a graph photograph is mostly the value of the BCR adhering toner amount causing the charging failure indicated by the alternate long and short dash line B in FIG. It will exceed the allowable range.

  Further, even when a charging method in which a DC bias is applied to the BCR is used, in the case of forming a character image, the BCR dirt is almost always within an allowable range. Since the required level of charge uniformity for the BCR is slightly lower than that of the above-described image, even when a charging method in which only a DC bias is applied is selected, a practical use can be sufficiently achieved.

  That is, as shown in FIG. 6, when the charging method of applying a DC bias is used for the BCR, the amount of BCR adhering toner when the character image is formed is a value in the character image region C shown in FIG. It becomes. Therefore, when the charging method for applying a DC bias is used, the value in the character image region C is entirely lower than the value of the BCR adhering toner amount causing the charging failure shown by the one-dot chain line B in FIG. And within the allowable range.

  Further, when a monochrome mode image is formed, the required level of charge uniformity is often low. Therefore, when forming a monochrome mode image, the DC charging method can be selected.

  When one print job is within A3 size, the DC charging method can be used if the BCR is cleaned by performing a toner discharge cycle at the image forming job end.

  In consideration of the above conditions, in this control means, the CPU 54 drives only the DC bias application power supply unit 52 </ b> A to the roll charger 46 in the control for delaying the accumulation of discharge products on the surface of the photosensitive drum 40. Thus, a condition for switching between a process for charging by applying a DC bias and a process for applying and charging the AC bias by driving the DC bias applying power supply unit 52A and the AC bias applying power supply unit 52B simultaneously, Set as follows.

  As a first condition, when the color mode is selected in the image processing apparatus 14 (for example, a user instruction input from the control panel of the multifunction peripheral or a user included in print information transmitted from the personal computer 18) When the command is “color mode”), an AC bias is applied by weight and charged.

  Further, in the image processing apparatus 14, when the monochrome mode is selected, a charging process is performed by applying only a DC bias.

  As a second condition, when the color mode selection is “automatic selection” in the image processing apparatus 14, the AC bias is weighted and applied and charged.

  However, if all the RGB image signals received by the image processing device 14 match (R = G = B), it is determined that the self-black image is the main image, and only the DC bias is applied for charging. Perform the process.

  As a third condition, in the image processing apparatus 14, when the image mode selection is other than “character” (graph / photograph, etc.), an AC bias is applied by weight and charged.

  Further, in the image processing device 14, when the image mode selection is “character”, charging processing is performed by applying only the DC bias.

  If the result of “character separation” performed by the image processing apparatus 14 as the fourth condition is “character image”, the charging process is performed by applying only the DC bias.

  As the fifth condition, when the print amount of one job input to the image processing apparatus 14 is run length 1 (however, when the length is two, it is run length 2. Normally, the print amount of one job is the maximum size. When it is within one sheet of A3 size paper, it is two sheets for B5 size paper).

  Next, in the image forming apparatus 10 that employs a cleanerless system that does not scrape off the discharge products without using a cleaning blade in an electrophotographic method, when the CPU 54 performs image forming processing, the first condition to the first condition described above are used. An example of specific control contents for switching between the charging process by the DC bias and the charging process by the weight of the AC bias according to the fifth condition will be described with reference to the flowchart of FIG.

  The charging process switching control shown in FIG. 5 is started when an instruction to start the image forming process is input, and the process proceeds to step 80. In step 80, when the print information and the RGB image data are transmitted to the image processing apparatus 14 from the control panel 70, the image capturing section 68, or the personal computer 18 of the image capturing apparatus 12, the text classification circuit 64 or the image processing section 66 is received. When the print amount as one print job is equivalent to run length 1 that can be processed within the maximum size capable of forming an image (R / L = 1, which is run length 1; When the run length is equivalent to the run length 1, the process proceeds to step 86, where the CPU 54 drives only the BCR DC driver 60 and the DC bias application power supply unit 52A controls the roll charger 46. Switch to charge processing. If it is determined in step 80 that the run length is not 1, the process proceeds to step 82.

  In this step 82, if it is determined from the analysis of the RGB image data or the command information that the image to be formed is a self-black image as the main image, the process proceeds to step 86 where only the DC bias is applied for charging. Switch to process. If it is determined in step 82 that the image to be formed is not a self-black image as a main image (color image), the process proceeds to the next step 84.

  In step 84, when the image to be formed is analyzed by the text classification circuit 64, if it is determined that the image is only a text image, the process proceeds to step 86 where only the DC bias is applied and the charging process is performed. In step 84, if it is determined that the image is not only a text image (such as a photographic image), the process proceeds to the next step 88.

  In step 88, the CPU 54 drives the BCR DC driver 60 and the BCR AC driver 62 to switch the DC bias application power source 52A and the AC bias application power source 52B so as to perform the charging process on the roll charger 46. Proceed to step 90.

  In step 90, one print job is executed under the setting for performing the charging process by the DC bias or the charging process by the weight of the AC bias set in step 86 or 88 described above. When a job end of one print job is completed, a removal cycle (toner discharge cycle) is performed in which a reverse bias is applied to a member that contacts the photosensitive drum 40 such as the roll charger 46 to remove toner contamination. Then, the roll charger 46 and the like are cleaned to end the charging process switching control, and the machine is stopped.

  Next, verification of the effect in the case of performing control for switching between the charging process using the DC bias and the charging process using the weight of the AC bias will be described with reference to FIGS. 7, 8 </ b> A, and 8 </ b> B.

  In the verification of the effect when switching control of the charging process is performed, three types of long-term running tests are performed, and the effect is confirmed by examining the change in the water contact angle of the surface of the photoconductor (image carrier surface) and the occurrence of white spots. did.

In the first long-term running test, all of them were charged with a DC bias, and the same running pattern (color mode, image type, R / L, repetition and No. different PV as shown in FIG.
)

  In the second long-term running test, 60% of the total number of running sheets was charged with AC bias, and 40% was charged with DC bias, and the running pattern shown in FIG.

In the third long-term running test, 25% of the total number of running sheets was charged with an AC bias and 75% was charged with a DC bias, and the running pattern shown in FIG. 8B was performed.
Three long-term driving test conditions 28 ° C, 85% RH
Potential conditions V _H = _−500V , V _L = _−100V , V _DEVE = −400V
AC bias condition V _DC = -500V
AC Vpp = 1.4kV (fine adjustment while watching VH), f = 600Hz
DC bias condition V _DC = -1000V (fine adjustment while watching VH)
The results of the three types of long-term running tests are as shown in FIG.
From this result, in the first long-term running test, white spots started to appear around 20 kpv, the potential could not be stabilized, and the experiment was canceled at 30 kpv.
In both the second long-term running test and the third long-term running test, white spots were not generated up to 50 kpv. In particular, in the third long-term running test, the contact angle hardly decreases, and the possibility of maintaining good image quality over a long period of time is shown. It has been proved that the effect is great.

  Next, in the image forming apparatus 10 that employs a cleanerless system that does not scrape off the discharge products without using a cleaning blade in an electrophotographic method, when the CPU 54 performs image forming processing, the first condition to the first condition described above are used. Another example of the specific control contents for switching between the charging process by the DC bias and the charging process by the weight of the AC bias according to the fifth condition will be described with reference to the flowchart of FIG.

  In the charging process switching control shown in the flowchart of FIG. 11, the control process is executed in units of run length 1 that can be processed within the maximum image formable size in one print job.

  The charging process switching control shown in FIG. 11 is started when an instruction to start the image forming process is input, and the process proceeds to step 100. In this step 100, when the print information and the RGB image data are transmitted to the image processing apparatus 14, one RGB image data to be subjected to image formation processing first in one print job is acquired, and the next step 102 is performed. move on.

  In step 102, it is determined whether or not the image to be formed is the main image of the self-black image based on the analysis or command information of one piece of RGB image data acquired by the text classification circuit 64 or the image processing unit 66. If it is determined that it is determined that the self-black image is the main image, the process proceeds to the next step 106, where only the DC bias is applied and the charging process is performed. If it is determined in step 102 that the acquired one RGB image data does not have a self-black image as a main image (color image), the process proceeds to the next step 104.

  In step 104, when the acquired one RGB image data is analyzed by the text classification circuit 64, and it is determined that only the text image is obtained, the process proceeds to step 106 and only the DC bias is applied to perform the charging process. Switch to. If it is determined in step 104 that the image is not only a text image (such as a photographic image), the process proceeds to the next step 108.

  In step 108, the CPU 54 drives the BCR DC driver 60 and the BCR AC driver 62 to switch the DC bias application power supply unit 52 </ b> A and the AC bias application power supply unit 52 </ b> B to perform the charging process on the roll charger 46. Proceed to step 110.

  In step 110, one print job is executed under the setting for performing the charging process by the DC bias or the charging process by the weight of the AC bias set in the above-described step 106 or step 108, and the process proceeds to the next step 112. .

  In step 112, it is determined whether there is an unprocessed image in which no image is formed in one print job. If it is determined that there is an unprocessed image, the process returns to step 100, and there is an unprocessed image. If it is determined, the process proceeds to the next step 114.

  In step 114, a removal cycle (toner discharge cycle) in which a reverse bias is applied to a member that contacts the photosensitive drum 40, such as the roll charger 46, to remove toner stains is performed, and the roll charger 46 and the like are cleaned. Then, the charging process switching control is finished and the machine is stopped.

  The present invention is not limited to the above-described embodiment, and is a means for charging an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric used in the image forming process. Of course, it can be used.

1 is a block diagram illustrating a schematic configuration of an image forming apparatus configured as a printer or a multifunction peripheral according to an embodiment of the present invention. 1 is a schematic configuration diagram illustrating a main part of an image output apparatus in an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing a main part of a developing device in an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram illustrating a schematic configuration of a portion that performs charging process switching control in the image forming apparatus according to the embodiment of the present invention. 6 is a flowchart for explaining an example of a charging control switching control procedure in the image forming apparatus according to the embodiment of the present invention. 6 is a graph for explaining a relationship between an image density and a BCR adhering toner amount which is a problem in an image forming process performed by the image forming apparatus according to the embodiment of the present invention. 6 is a graph showing the results of three types of long-term running tests for demonstrating the effect of performing image forming processing by performing charging control switching control in the image forming apparatus according to the embodiment of the present invention. (A) (B) is a table | surface which shows the specific conditions of the running pattern in a long-term running test, respectively. 6 is a graph for explaining a charging method for applying a DC bias performed in the image forming apparatus according to the embodiment of the present invention. 6 is a graph for explaining a charging method in which a DC bias voltage is applied and an AC bias voltage is superimposed and applied in the image forming apparatus according to the embodiment of the present invention. 10 is a flowchart for explaining another example in the procedure of the charging process switching control in the image forming apparatus according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Image capture apparatus 14 Image processing apparatus 16 Image output apparatus 18 Personal computer 26 Image transfer part 28 for full color printing Fixing part 32 Intermediate transfer belt 34 Developing apparatus 40 Photosensitive drum 44 Brush part 46 Roll type charger 50 Developer 52 Charging Bias Application Power Supply 52A Bias Application Power Supply Unit 52B Bias Application Power Supply Unit 60 BCR DC Driver 60
62 BCR AC driver 64 Text classification circuit 66 Image processing unit 68 Image capturing unit 70 Control panel

Claims (5)

In an electrophotographic image forming apparatus configured as a cleanerless system,
An image carrier used in the electrophotographic image forming process;
A charger capable of selecting and executing a process of charging the image carrier by applying only a DC voltage and a process of applying an AC voltage superimposed on the DC voltage and charging;
It is detected whether or not the print amount as one print job to be imaged by the electrophotographic method is equivalent to run length 1 that can be processed within the maximum size capable of forming an image. The charging device is switched so as to perform the charging process by superimposing the DC voltage on the DC voltage, and when the run length is 1, the charging unit is switched to perform the charging process by applying only the DC voltage. Control means for executing a removal cycle for applying a reverse bias to the charger and removing toner stains after executing one print job;
An image forming apparatus comprising: In an electrophotographic image forming apparatus configured as a cleanerless system,
An image carrier used in the electrophotographic image forming process;
A charger capable of selecting and executing a process of charging the image carrier by applying only a DC voltage and a process of applying an AC voltage superimposed on the DC voltage and charging;
Whether or not an image formed by the electrophotographic method is a monochrome mode image is detected, and when the image is a monochrome mode image, a process of applying only a DC voltage by the charger to perform charging is performed. Switching means for switching to perform charging processing by applying an AC voltage superimposed on a DC voltage by the charger when the image is not in monochrome mode; and
An image forming apparatus comprising: In an electrophotographic image forming apparatus configured as a cleanerless system,
An image carrier used in the electrophotographic image forming process;
A charger capable of selecting and executing a process of charging the image carrier by applying only a DC voltage and a process of applying an AC voltage superimposed on the DC voltage and charging;
Detect whether or not the image formed by the electrophotographic method is only a text image, and when it is only a text image, switch to perform a process of charging by applying only a DC voltage by the charger, Control means for switching to perform charging by applying an AC voltage superimposed on a DC voltage by the charger when not only a text image; and
An image forming apparatus comprising: In an electrophotographic image forming apparatus configured as a cleanerless system,
An image carrier used in the electrophotographic image forming process;
A charger capable of selecting and executing a process of charging the image carrier by applying only a DC voltage and a process of applying an AC voltage superimposed on the DC voltage and charging;
An image formed by the electrophotographic method is detected by detecting whether or not the print amount as one print job formed by the electrophotographic method is equivalent to run length 1 that can be processed within the maximum size capable of image formation. Detects whether the image is a monochrome mode image, detects whether the image formed by the electrophotographic method is only a text image, and the image formed by the electrophotographic method is a run image. In the case of the length 1 equivalent or in the monochrome mode image or in the case of only the text image, the charger is switched so as to perform the charging process by applying only the DC voltage. When the image is not an image or only a text image, the charger performs charging by applying an AC voltage superimposed on a DC voltage. And control means for switching manner,
An image forming apparatus comprising: In an electrophotographic image forming apparatus configured as a cleanerless system,
An image carrier used in the electrophotographic image forming process;
A charger capable of selecting and executing a process of charging the image carrier by applying only a DC voltage and a process of applying an AC voltage superimposed on the DC voltage and charging;
One image is acquired from one print job to be imaged by the electrophotographic method to detect whether the image is a monochrome mode image, and further, whether it is only a text image, and is acquired. When the single image is a monochrome mode image or only a text image, the charging unit is switched to perform a charging process by applying only a DC voltage. When the image is not a monochrome mode image or only a text image If not, control means for switching to perform the process of charging by applying the AC voltage superimposed on the DC voltage by the charger,
An image forming apparatus comprising:

Images