JP2013156418A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a reduction in productivity of printing by reducing a time required for cleaning a contact charging member.SOLUTION: An image forming apparatus includes an image carrier 2, a contact charging member 3 that charges the surface of the image carrier by being applied with bias at least during image formation, and a cleaning member 5 that cleans the surface of the image carrier. The image forming apparatus stops application of bias to the contact charging member after completion of an imaging process and before attenuation of the bias applied to charge the surface of the image carrier during image formation (charging member cleaning sequence), and applies bias having the same polarity as the bias applied to the contact charging member during the imaging process to an element tube 2B of the image carrier included in the image carrier simultaneously with the charging member cleaning sequence.

Description

  The present invention relates to an image forming apparatus provided with a contact-type charging member used for image formation, such as a copying machine, a printer, and a FAX.

In an electrophotographic image forming apparatus, there are a charging method using a non-contact charger and a contact charging method for charging an organic photoreceptor (hereinafter referred to as “photoreceptor”) as an image carrier. In the case of the contact charging method, a charging roller is generally used as a charging member, and the generation of corona and ozone is small. However, since it is in direct contact with the surface of the photoreceptor (photosensitive layer), residual toner and scattering during the image forming process As a result, the charging roller is soiled by toner or the like, resulting in non-uniform charging, and image quality is impaired due to uneven charging.
Therefore, there are a method for preventing charging unevenness due to contamination of the charging roller, a method of bringing a cleaning member into contact with the charging roller, and a method of electrical cleaning. As cleaning members, those that contact plate members or roller members such as velvet, sponge or melamine are already on the market, but the materials used are limited due to the durability and cost of process cartridges with charging rollers. End up.
As a method for electrical cleaning, there is a method for storing developer attached to the charging roller by using a bias to fly to the photosensitive member side.
For example, in Patent Document 1, a bias is applied to the writing electrode to rotate the photoconductor one time, the bias is turned off, a bias of the same polarity is applied, and the developer adsorbed on the writing electrode is released to the photoconductor. Technology is disclosed.
Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for applying positive -100V to the charging roller at the time of non-transferring and returning positive adhesion to the photosensitive member.

In Patent Document 1, writing is performed on the photosensitive member by bias control and the developer attached to the electrode is released. However, since the bias is turned off by rotating the photosensitive member by applying a bias, the time for executing the control is long. As a result, the number of printable sheets per minute decreases, leading to a decrease in productivity.
In Patent Document 2, positive polarity deposits are transferred to the photoconductor by charging bias control. However, after applying the application bias for image formation at the time of non-image formation before the first sequence for at least one rotation of the photoconductor, Since switching to the 1st or 2nd level, the time required for image formation becomes longer, leading to a decrease in productivity.
SUMMARY OF THE INVENTION An object of the present invention is to shorten the time required for cleaning a contact charging member so as not to reduce print productivity.

  In an image forming apparatus comprising an image carrier, a contact charging member that charges the surface of the image carrier by applying a bias at least during image formation, and a cleaning member that cleans the surface of the image carrier. After the completion of the process, before the bias that charged the surface of the image carrier at the time of image formation attenuates, the charging member cleaning sequence for stopping the bias application to the contact charging member, and simultaneously with this charging member cleaning sequence, the image carrier It is characterized by having control means for performing a sequence of applying a bias having the same polarity as the bias applied to the contact charging member during the image forming process to the elementary tube of the image carrier.

  According to the present invention, the bias applied to the contact charging member in contact with the image carrier is contacted after the image forming process is finished, before the bias that has charged the surface of the image carrier during image formation attenuates. Since the bias application to the charging member is stopped, before the bias application is stopped, the adherent having the same polarity as the bias attached to the contact charging member is transferred to the image carrier and cleaned by the cleaning member, and the bias is stopped. Later, the deposit having the opposite polarity to the bias attached to the contact charging member is sucked and transferred to the image carrier and cleaned by the cleaning member. In addition, since a bias having the same polarity as the bias applied to the contact charging member during the image forming process is applied to the elementary tube of the image carrier, it is not necessary to apply a bias more than one rotation as in the prior art. The time required for cleaning the contact charging member can be shortened, and the print productivity does not decrease.

1 is a diagram showing a schematic configuration of an embodiment of an image forming apparatus according to the present invention. FIG. 3 is an enlarged view for explaining an outline of a process cartridge included in the image forming apparatus. The block diagram which shows the relationship between the control system of a process cartridge, and a power supply. The timing chart of the control with respect to a general contact charging member. FIG. 6 is a diagram illustrating a relationship between an applied bias and a charged state of the image carrier surface during a start sequence. FIG. 4 is a diagram showing a relationship between an applied bias and a charged state of an image carrier surface during an image forming sequence. The figure which shows the relationship between the applied bias at the time of an end sequence, and the charging state of the image carrier surface. The timing chart of the applied bias at the time of a printing sequence when not performing the control content which concerns on this invention. The timing chart of the applied bias at the time of a printing sequence at the time of performing the contents of control concerning the present invention. 6 is a timing chart of an applied bias during an initialization sequence for a process cartridge. The timing chart of the applied bias at the time of another initialization sequence for the process cartridge. The figure explaining the subject at the time of reverse rotation of an image carrier. Schematic which shows the structure of the image forming part provided with the some contact charging member. 6 is a timing chart showing an embodiment of an applied bias during a printing sequence for a process cartridge including a plurality of contact charging units. The block diagram which shows the relationship between the control system of a process cartridge provided with the some contact charging member, and a power supply. The block diagram which shows the relationship between the control system of a process cartridge provided with the some contact charging member, and a power supply.

  Embodiments of the present invention will be described below with reference to the drawings. First, the overall configuration and operation of the image forming apparatus will be described, and then the characteristic portions will be described. In the embodiment, constituent elements such as members and components having the same function or shape are given the same reference numerals as much as possible, and overlapping description with the previous description is omitted as much as possible.

  FIG. 1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. The image forming apparatus includes a transfer belt 10 serving as a transfer body (intermediate transfer body) conveyed by a driving roller 8 rotating in the direction of arrow A in the image forming apparatus main body 100, and a drum-shaped photoconductor serving as an image carrier. 2Y, 2M, 2C, and 2K, the charging rollers 3Y, 3M, 3C, and 3K that are contact charging members for charging the photosensitive members, and the surfaces of the photosensitive members 2Y, 2M, 2C, and 2K charged by the charging rollers. Development devices 4Y, 4M, 4C, and 4K that develop the electrostatic latent image formed on each photosensitive member by exposure L modulated by image information with toner T as a developer, and a primary as a transfer member An intermediate transfer type color image forming printer that includes transfer rollers 11Y, 11M, 11C, and 11K and forms a toner image on each photoconductor on a transfer belt 10 by a bias current applied to each primary transfer roller. A. The image forming apparatus includes a secondary transfer roller 12 as a secondary transfer member that transfers a toner image on the transfer belt 10 onto a sheet S as a recording medium, and a fixing device 16 that fixes the toner image transferred onto the sheet S. And a paper tray 13 serving as a paper feed unit for storing the paper S, and a belt cleaning device 21 for cleaning the surface of the transfer belt 10. The image forming apparatus main body 100 is provided with a cover member 101 for opening and closing an opening accessible to the inside. Since the image forming apparatus is a printer, it is connected to an external output device such as a personal computer (not shown) via a printer cable or a network.

  An image forming operation (image forming process) in the image forming apparatus will be described. When an original image signal created by an external output device (not shown) is input to an image processing unit (not shown), appropriate image processing is performed, and the input image signal modulates the exposure L (laser beam) to generate light. The surface of the photoreceptors 2Y, 2M, 2C, and 2K, which are uniformly charged by the charging rollers 3Y, 3M, 3C, and 3K, is irradiated with the raster from the irradiation device 7. When exposure L is irradiated onto the surface of each photoconductor, the potential of the exposed portion decreases, and an electrostatic latent image corresponding to the input image signal is formed on each photoconductor.

  The electrostatic latent images formed on the photoreceptors 2Y, 2M, 2C, and 2K are developed with the toners T of the respective colors included in the developing devices 4Y, 4M, 4C, and 4K, and are visible on the photoreceptors. A toner image to be an image is formed. The toner images formed on the photoconductors 2Y, 2M, 2C, and 2K are arranged to face the photoconductors, and are driven roller by the action of the primary transfer rollers 11Y, 11M, 11C, and 11K to which a transfer bias is applied. 8 is transferred onto the transfer belt 10 conveyed along with the rotation in the arrow A direction, and is conveyed toward the secondary transfer roller 12.

  On the other hand, the paper S stored in the paper tray 13 is supplied by a paper feed roller 14 and a registration roller 15 toward a secondary transfer nip portion formed between the transfer belt 10 and the secondary transfer roller 12. The toner image on the transfer belt 10 is transferred onto the paper S by the secondary transfer roller 12 on which the secondary transfer bias is acting. The toner image transferred onto the sheet S is conveyed to a fixing nip portion formed between a fixing roller 17 and a pressure roller 18 included in the fixing device 16 so that unfixed toner is fixed on the sheet S, and a desired image is obtained. (Printed material) is obtained. The fixed paper S is stacked on a paper discharge tray 20 formed on the upper part of the image forming apparatus main body 100 by a pair of paper discharge rollers 19. Deposits such as residual toner adhering to the surface of the transfer belt 10 after the transfer of the toner image onto the paper S are cleaned by the belt cleaning device 21 and an image forming operation (image forming process) on one paper P Ends. Then, the image forming operation is executed for the preset number of printed sheets from the first image forming operation, thereby completing one job.

  Next, the configuration of an AIO cartridge serving as a detachable product that is replaceably attached to the image forming apparatus main body 100 will be described with reference to FIG. Since the configuration of the photoconductor, developing device, charging roller, primary transfer roller, and the like corresponding to each color is substantially the same except that the color of the toner is different, only one of them will be described here. In the following description, the alphabet symbols (Y, M, C, K) for identifying the toner color are omitted.

  An AIO cartridge 300 shown in FIG. 2 includes a photoreceptor 2, a process cartridge unit (hereinafter referred to as “PCU”) 200 including a charging roller 3 and a cleaning blade 5 that are in contact with the surface of the photoreceptor 2, and a developing roller 40. The PCU 200 and the developing device 4 are integrated with each other in a state where the developing roller 4 is pressed against the surface of the photosensitive member 2. The AIO cartridge 300 is configured to be detachable from the image forming apparatus main body 100 shown in FIG. Here, the PCU 200 and the developing device 4 are integrally attached to and detached from the image forming apparatus main body 100 as an AIO cartridge 300. However, the developing device 4 alone or the AIO cartridge 300 that can be attached to and detached from the PCU 200 alone may be used.

  The photoreceptor 2 is configured to be rotationally driven in a clockwise direction indicated by an arrow R in the drawing by a drive motor M1 serving as a drive source shown in FIG. The photoreceptor 2 has a photoreceptor tube 2B disposed below the surface 2A. In FIG. 2, the symbol TM indicates unfixed toner scraped from the photoreceptor 2 by the cleaning blade 5.

  Next, the configuration of the power supply unit and control means for the AIO cartridge 300 will be described with reference to FIG. In the image forming apparatus main body 100, a low voltage power source 400, a high voltage power source 500, and a control means 50 are provided. Here, the low voltage power source 400 supplies driving power to a driving motor M1 that rotationally drives the photosensitive member 2. The high voltage power source 500 includes a photoconductor power source 501, a developing power source 502, a charging power source 503, and a transfer power source 504. The photoreceptor power source 501 is connected to the photoreceptor element tube 2B so that a bias can be applied. The developing power source 502 is connected to the developing roller 40 so that a developing bias can be applied. The charging power source 503 is connected to the charging roller 3 so that a charging bias and a bias other than the charging bias can be applied. The transfer power source 504 is connected to the primary transfer roller 11 so that a transfer bias and other biases can be applied. Here, the bias other than the charging bias, the transfer bias and the other bias are cleaning biases for cleaning the toner by fouling the adhering matter to the photosensitive member 2 side mainly due to dirt such as toner adhering to the charging roller 3. is there.

  The low voltage power supply 400 and the high voltage power supply 500 are connected to the control means 50 via a signal line. The control unit 500 includes a known computer having a processing unit and a storage unit, and controls the low voltage power supply 400, the high voltage power supply 500, and the drive motor M1 by various sequence controls stored in advance in the storage unit. Thus, it has a function of controlling the operation of each part.

  Various sequence controls include start sequence control that is performed when the image forming apparatus is turned on (started up), image formation sequence control that is performed at the time of image formation, end sequence control that is performed after the end of image formation, and initialization sequence control. A sequence for executing the sequence control is referred to as a print sequence.

  4 to 6 show the relationship between the photosensitive member 2 and various biases supplied to each part during the printing sequence.

  When a print signal is input, the control unit 50 executes start sequence control. In the start sequence control, as shown in FIG. 4, the charging power source 503 is controlled to apply a negative polarity bias to the charging roller 3, and the developing power source 502 is controlled to apply a negative polarity bias to the developing roller 40. To do. In addition, the transfer power source 504 and the photoreceptor power source 501 are controlled to apply a negative polarity bias to the primary transfer roller 11 and the photoreceptor element tube 2B, respectively. That is, in the start sequence control, a negative polarity bias is applied to the charging roller 3, so that the photosensitive member surface 2A is negatively charged. For this reason, the adhering material such as the positive polarity toner adhering to the charging roller 3 is not attracted and transferred to the surface 2A of the photoconductor, and the adhering material having the same polarity as the applied bias is here. Is electrostatically attracted and transferred to the surface 2A of the photoreceptor. Also, a negative polarity bias is applied to the charging roller 3 and the first transfer roller 11 and the photosensitive element tube 2B which are arranged to be shifted in the circumferential direction (moving direction) of the photosensitive element 2. For this reason, since the surface 2A of the photosensitive member 2 is applied with a negative polarity bias from the portion other than the contact portion with the charging roller 3 as in the prior art, that is, from the contact portion with the first transfer roller 11, the photosensitive member 2 is exposed. Can be charged with a minus polarity sufficiently even if it does not rotate once. Therefore, the negative polarity adhering matter adhering to the charging roller 3 can be removed in a shorter cleaning time than in the prior art. Can be transferred to the side. Further, the deposit transferred to the photosensitive member surface 2A side is scraped off from the photosensitive member surface 2A by the cleaning member 5 and cleaned.

  In the image forming sequence control shown in FIG. 5, the control unit 50 controls the charging power source 503 to apply a negative polarity bias to the charging roller 3 to charge the photosensitive member surface 2A negatively, By controlling 502, a developing bias having a negative polarity is applied to the developing roller 40. Then, the negative polarity deposit having the same polarity as the applied bias attached to the charging roller 3 is transferred to the photoreceptor surface 2 </ b> A by the exclusion force from the charging roller 3.

  In the image forming sequence control, the exposure surface L of the photosensitive member surface 2A is exposed and the potential of the exposed photosensitive member surface 2A is lowered, so that the toner T is transferred from the developing roller 40 to the exposed portion where the potential is lowered. Develop the part. Therefore, the control unit 50 controls the transfer power source 504 to apply a positive primary transfer bias to the primary transfer roller 11 to transfer the toner T adhering to the surface 2A of the photoreceptor to the intermediate transfer belt 10 side. To do. Also in this control, the control means 50 controls the photoreceptor power source 501 to apply a negative polarity bias to the photoreceptor base tube 2B. For this reason, in this image forming sequence control, the positive polarity adhering matter adhering to the charging roller 3 is electrostatically attracted to the photosensitive member surface 2A and is not transferred.

  In the end sequence control shown in FIG. 6, the control unit 50 controls the charging power source 503 to stop the bias application to the charging roller 3, and controls the developing power source 502 to apply the developing bias to the developing roller 40. Also stop. The control unit 50 controls the transfer power source 504 to apply a negative polarity bias to the primary transfer roller 11, and controls the photoconductor power source 501 to apply a negative polarity bias to the photosensitive element tube 2B. For this reason, the positive polarity adhering matter adhering to the developing roller 3 is electrostatically attracted and transferred to the photosensitive member surface 2A.

  Here, a printing sequence when the charging roller cleaning sequence of the present invention is not executed will be described with reference to FIG. FIG. 7 is a timing chart showing the control sequence and the operation of each part in the printing sequence. As a start sequence, the control unit 50 applies a negative polarity bias to the charging roller 3, the developing roller 40, and the photosensitive element tube 2B as soon as the drive motor M1 is turned on. A negative polarity bias is also applied to the primary transfer roller 11.

  In the image forming sequence, after switching from the cleaning bias to the primary transfer roller 11 to the transfer current (transfer bias), an electrostatic latent image is formed (development → transfer to paper S → untransferred). The process proceeds with cleaning of the toner image by the cleaning blade 5. When the sheet S passes through the transfer nip formed between the primary transfer roller 11 and the photosensitive member 2, a cleaning bias is applied to the primary transfer roller 11 as an end sequence, and the developing roller 40, the charging roller 3, and the photosensitive roller are exposed. Each bias to the body tube 2B is also turned off, and the drive motor M1 is stopped.

  A printing sequence when the charging roller cleaning sequence according to the present invention is executed will be described with reference to FIG.

  The start sequence and the image forming sequence in the print sequence are the same as those in FIG. 7, but in the end sequence, the charging bias and the developing bias are turned off (the bias potential is lowered) before the drive motor M1 is stopped. Here, the photoconductor bias is continuously applied even after the charging bias is turned off. For example, the photosensitive member bias is turned off after being delayed by one rotation of the charging roller 3. That is, the charging roller cleaning sequence (hereinafter referred to as “charging cleaning”) is performed before the driving motor M1 is stopped, that is, while the photosensitive member 2 is rotating.

  When such charge cleaning is executed, a positive polarity toner or paper powder adhering to the charging roller 3 or an adhering substance such as a negative polarity toner or paper powder can be transferred to the photoreceptor 2. By performing cleaning on the charging roller 3 at a time when the number of prints is not affected without adding new parts, good image quality without charging unevenness is maintained and the influence on the image forming time is minimized. The decrease in productivity can be suppressed to the limit.

  The bias for transfer cleaning may be controlled so as to continue to be applied even when the charging bias is off.

  In FIG. 8, charging cleaning is performed during the end sequence, but good image quality without charging unevenness can also be obtained, for example, by executing it between the first and second sheets in the image forming sequence. However, if electrification cleaning is performed every other sheet, there is a concern that the paper interval will be longer and the productivity will be reduced. Therefore, electrification cleaning is performed only at the end sequence after the end of the job when the image forming sequence for the preset number of prints has been completed. Is preferably carried out.

  In addition, when charging cleaning is performed, the charging bias is turned off before the drive motor M1 is stopped. Therefore, the photosensitive member surface 2A rotating in the charging bias off state is not charged, and the developing roller 40 is excessively soiled. Become. This is because background staining occurs because analog development is performed even when the development bias is turned off. Due to this background stain, the primary transfer roller 11 becomes dirty, and the background stain on the back surface of the paper S becomes worse. As a measure against this background stain, the toner or the like adhering to the surface 2A of the photosensitive member is attracted to the primary transfer roller 11 by applying a transfer cleaning bias with the charging bias applied in the start sequence shown in FIG. Photoconductor cleaning is performed.

  The start sequence shown in FIG. 8 is preferably executed within the image processing + feeding time, and the end sequence is preferably executed within the time during which the paper S passes between the fixing transfer and the paper discharge after passing through the secondary transfer nip. .

  In this embodiment, the start sequence is a preparatory step for cleaning the surface of the photoreceptor 2 and making the surface potential constant in order to perform the image forming sequence. In the image forming sequence, an electrostatic latent image is formed on the photosensitive member 2, a toner layer is formed, and the actual printing process for transferring to the paper S, the end sequence is the cleaning and surface potential on the photosensitive member 2 after the image forming. It is fixed so that it can go to the start sequence as soon as the next print command comes.

  In this embodiment, it can be said that the state in which the applied bias at the time of image formation is applied also during the charging member cleaning sequence is not applied to the gap 2B of the photosensitive member 2 during the charging member cleaning sequence.

  Incidentally, the AIO cartridge 300 shown in FIG. 2 is used after being shipped in various forms after being shipped from the factory. For example, it is conceivable that the charging roller 3 becomes dirty due to toner scattering or jetting during transportation. Furthermore, there is a possibility that the charging roller 3 is contaminated by toner scattering or jetting due to movement when the image forming apparatus main body 100 is bundled or vibration during opening / closing operation of the cover member 101 shown in FIG.

  Therefore, as a countermeasure for these, immediately after the image forming apparatus is turned on, when a new AIO cartridge 300 is mounted, or when an opening / closing operation of the cover member 101 is detected by a detecting means such as a sensor (not shown), the control means 50 performs an initialization sequence. Bias control as shown in FIG. 9 may be performed, and charging cleaning similar to the end sequence of FIG. 8 may be performed.

  This can be implemented by previously setting the initialization sequence shown in FIG. In the initialization sequence, the charging bias and the developing bias are applied to the charging roller 3 and the developing roller 40 simultaneously with the driving motor M1 being turned on, and the transfer current (bias) is applied to the primary transfer roller 11 to perform the transfer cleaning. A bias is applied to the photosensitive element tube 2B. In this case, the bias applied to each member is stopped before the drive motor M1 is stopped. Among them, the charging cleaning is achieved by stopping the application of the charging bias earlier than the developing bias, the transfer current, and the photosensitive member bias. can do.

  Since the initialization sequence shown in FIG. 9 also occurs when the photosensitive member surface 2A is not charged, the background is excessively soiled. Therefore, it is possible to eliminate the influence on the image by performing the start sequence of FIG. 8 in the job after the initialization sequence.

  If the start sequence of FIG. 8 cannot be performed, the photosensitive member cleaning may be forcibly performed after the charge cleaning as shown in FIG. Similarly, in the case of the end sequence of FIG. 8, when this end sequence cannot be performed, the photosensitive member cleaning may be performed immediately after the charge cleaning. However, in this case, the sequence time becomes long, which is disadvantageous in terms of productivity. Here, the photoconductor cleaning means that the bias potential applied to the charging roller 3 is once set to 0 V, and then a negative polarity bias is applied to the charging roller 3 again.

  Next, as disclosed in Japanese Patent Application Laid-Open No. 2010-26380, in this embodiment, when the life end of the photoconductor 2 or the like is detected by a sensor or the number of printed sheets, the intermediate transfer belt 10 is reversed at regular intervals. Assume a photoreceptor reverse sequence in which the photoconductor 2 is rotated in the reverse direction.

  In this case, as shown in FIG. 11, it exceeds the maximum reversible amount (maximum reversible angle) α of the photoreceptor 2 obtained from the relationship between the arrangement of the charging roller 3 and the developing roller 40, and in FIG. When the photosensitive member 2 is reversed by the drive motor M1 in the direction of the direction R1, the charging roller 3 runs on the photosensitive member 2 soiled by the reverse rotation, and the charging roller 3 becomes dirty. Even when such a photosensitive member reverse rotation sequence is executed, the control unit 50 executes the initialization sequence shown in FIGS. 9 and 10 or the charge cleaning + photosensitive member cleaning sequence control described above, whereby charging is performed. The roller 3 can be cleaned and uneven charging can be prevented.

  In the AIO cartridge 300, if the photosensitive member 2 and the developing device 4 are connected by a gear serving as a drive transmission means, the developing roller 40 may reverse during reverse rotation, and toner T may be ejected from the developing device 4. . Also at this time, by performing the above-described sequence control of charging cleaning + photoconductor cleaning, charging unevenness can be prevented. However, the driving of the PCU 200 and the developing device 4 is separated, or the driving gear of the developing roller 40 is coupled. It is only necessary to perform control so that only the photosensitive member 2 is rotated and the developing roller 40 is not rotated during the reverse rotation sequence, for example, by performing reverse rotation prevention. That is, it is possible to perform the reverse rotation sequence only on the PCU 200 side and not to reverse the developing device 4 side.

  Even in this case, if the developing roller 40 of the developing device 4 does not reverse and there is no scattering or ejection of toner, the risk of the charging roller 3 becoming dirty is reduced, and the rate of occurrence of charging unevenness is further reduced.

  FIG. 12 includes a first charging roller 3A and a second charging roller 3B as a plurality of contact charging members, and charging unevenness occurs by charging the photoreceptor 2 with the first charging roller 3A and the second charging roller 3B. The form which suppresses is shown.

  In FIG. 12, dirt is attached to the first charging roller 3A. If a charging bias is applied to the photoreceptor 2 only with the first charging roller 3A in this state, charging unevenness occurs in the part where the dirt is attached. . However, by applying a charging bias also to the second charging roller 3B, the charging unevenness generated by the first charging roller 3A can be repaired by the second charging roller 3B.

  In this embodiment, as shown in FIGS. 14 and 15, the first charging roller 3 </ b> A and the second charging roller 3 </ b> B are connected to the charging power source 502 of the high voltage power source 500. As a connection form, as shown in FIG. 14, the first charging roller 3A and the second charging roller 3B may be connected in parallel to the charging power source 502. As shown in FIG. 14, when the first charging roller 3A and the second charging roller 3B are connected in parallel, as shown in FIG. 13, the first charging roller 3A and the second charging roller 3B are connected as shown in FIG. The charging cleaning may be performed by controlling the charging power source 503 by the control means 50 so that the total amount of bias applied to the two charging rollers 3B is the same.

  In this case, the first charging roller 3A and the second charging roller 3B are connected in parallel, the first charging roller 3A and the second charging roller 3B become GND (zero) at the same time, and the photosensitive member 2 becomes negative. Dirt is electrically attracted to the photoreceptor 2 side. For this reason, it is possible to prevent the negative dirt moved on the photosensitive member 2 from being electrically transferred again to the second charging roller 3B.

  In the case of the configuration shown in FIG. 14, the first charging roller 3A and the second charging roller 3B are supported by an integral conductive bearing, and a bias is applied to the bearing. The bias application timing to the roller 3A and the second charging roller 3B is the same.

  As another connection formation, there is a case where individual connections are made as shown in FIG. As shown in FIG. 15, when the first charging roller 3A and the second charging roller 3B are individually connected to the charging power source 503, the bias applied to the first charging roller 3A is applied to the second charging roller 3B. The controller 50 controls the charging power source 502 so as to increase the bias application amount.

  In the case of the form shown in FIG. 15, the first charging roller 3A and the second charging roller 3B are supported by independent bearings, and the pressing to the photosensitive member 2 and the applied bias are controlled independently, so that the cleaning sequence is different. An effect can be obtained.

  As shown in FIG. 14, when the first charging roller 3 </ b> A and the second charging roller 3 </ b> B are connected to the charging power source 503 in parallel, when each roller volume resistance value / surface resistance value is the same, an applied bias (voltage) To be the same. However, when changing the resistance value of each roller, a different bias may be intentionally applied. Of course, as shown in FIG. 15, even when the first charging roller 3A and the second charging roller 3B are individually connected to the charging power source 503 and controlled independently, the volume resistance value / surface resistance value of each roller is the same. In this case, the applied bias (voltage) may be the same, or when the resistance value of each roller is changed, an independent bias may be applied even with the same resistance value.

  In the embodiment described above, the example in which the charge cleaning is performed by the intermediate transfer type image forming apparatus has been described. However, the image forming apparatus is not limited to such an example, and has the secondary transfer roller 12. Alternatively, the transfer belt 10 may be applied to an image forming apparatus of a type that conveys the sheet S to a portion facing each photoconductor. In this case, the transfer body is not the transfer belt 10 but the sheet S.

  7, 8, and 13 show one form of bias setting values of the charging bias, the developing bias, the transfer current, and the photosensitive member bias in the start sequence, the image forming sequence, and the end sequence. The actual bias is changed in stages (not at -500V at a stretch, but at -250V and set for several milliseconds for -500V). This controls the bias in the same manner as the so-called slow-up / slow-down control for the stepping motor.

  Also, the bias value is often varied depending on environmental conditions, driving time, and the like. In FIGS. 7, 8, and 13, values at initial and normal temperatures are assumed, and these bias values are the bias values of the present invention. It is not limited as a value.

  7, 8, and 13, when the photosensitive member bias is −250 V, the charging bias is set to 0 V all at once, so that the positive deposit on the charging roller is transferred from the charging roller to the photosensitive member side. .

  In the specification, the image forming process indicates the meaning of an image forming sequence. “At the time of image formation” means a meaning at the time of operation of the image forming apparatus. When an image is formed, a wide range from a print command is received to a start / image formation / end sequence, paper conveyance, paper discharge, and machine stop (sleep transition / power off) is shown.

2 (Y, M, C, K) Image carrier 2A Surface of image carrier 2B Element tube of image carrier 3 (Y, M, C, K) Contact charging member 3A, 3B Multiple charging members 5 (Y, M, C, K) Cleaning member 10 Transfer body 11 (Y, M, C, K) Transfer member 40 (Y, M, C, K) Developing member 50 Control means 100 Image forming apparatus main body 101 Cover member 300 Removable product T Developer

JP 2002-103694 A JP 2003-302816 A

Claims (9)

In an image forming apparatus comprising: an image carrier; a contact charging member that charges the surface of the image carrier by applying a bias at least during image formation; and a cleaning member that cleans the surface of the image carrier.
A charging member cleaning sequence for stopping bias application to the contact charging member before the bias for charging the surface of the image carrier at the time of image formation is attenuated after completion of the image forming process; and At the same time, it has a control means for performing a sequence for applying a bias having the same polarity as the bias applied to the contact charging member during the image forming process to the tube of the image carrier provided in the image carrier. apparatus. A transfer member disposed opposite to the image carrier and applied with a bias for transferring a toner image formed on the surface of the image carrier to a transfer member;
The image forming apparatus according to claim 1, wherein the control unit performs a transfer cleaning sequence in which a bias having a polarity opposite to that at the time of image formation is applied to the transfer member before execution of the charging member cleaning sequence. .   The control means does not execute the charging member cleaning sequence between sheets at the time of continuous image formation, but only at the end sequence performed after the set number of prints is completed, and starts before the next new image formation. 3. The image forming apparatus according to claim 1, wherein an image carrier cleaning sequence for cleaning dirt transferred to the image carrier by the charging member cleaning sequence is executed during the sequence.   The control means includes the charging member when the power is turned on or when an opening / closing operation of a cover member that is detachably attached to the image forming apparatus main body or when an initialization operation is performed when a detachable part that is replaceably provided in the image forming apparatus is replaced. 3. The image forming apparatus according to claim 1, wherein a cleaning sequence is executed.   When the initialization sequence is executed, the control means does not execute an image carrier cleaning sequence for cleaning dirt transferred to the image carrier after the charging member cleaning sequence, but starts a next new image forming operation start sequence. 5. The image forming apparatus according to claim 4, wherein the image carrier cleaning sequence is sometimes executed.   6. The control unit according to claim 1, wherein the control unit executes an image carrier cleaning sequence for cleaning dirt transferred to the image carrier immediately after the charging member cleaning sequence. The image forming apparatus described.   3. The image forming apparatus according to claim 1, wherein the control unit executes the charging member cleaning sequence in a start sequence immediately after a reverse rotation sequence to the image carrier is executed. A developing member that is disposed opposite the image carrier and is rotatable, and that supplies a developer to the surface of the image carrier;
The image forming apparatus according to claim 7, wherein the control unit performs control so that only the image carrier is rotated and the developing member is not rotated during the reverse rotation sequence.   The image forming apparatus according to claim 1, wherein the image carrier is charged by a plurality of charging members.

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