JP2015125376A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that suppresses a reduction in the surface potential of an image carrier by using charging of a recording medium so as to constantly form stable images.SOLUTION: An image forming apparatus includes an image carrier, charging device, exposure device, developing device, transfer member, feeding unit, and resist roller pair 13. In a recording medium conveyance path between the feeding unit and resist roller pair, a conveyance guide member 30 is arranged, which is formed of a material charging a recording medium to have the same polarity as the charge polarity of the image carrier through the friction with the recording medium. The image forming apparatus can vary the conveyance speed of the recording medium in at least one of the feeding unit and resist roller pair to perform a recording medium charging mode of rubbing a contact surface of the recording medium with the image carrier on the conveyance guide member.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile using an electrophotographic system, and more particularly to charging of a photoreceptor and a recording medium.

  In an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile, etc., a powdery developer (toner) is mainly used, and a photosensitive layer on the surface of a photosensitive drum (image carrier) is predetermined by a charging device. After charging to a surface potential (same polarity as the charging polarity of the toner), an electrostatic latent image is formed on the photosensitive drum by the exposure device. Then, the formed electrostatic latent image is visualized with toner in the developing device, and the toner image is recorded on a recording medium that passes through a nip portion (transfer nip portion) between the photosensitive drum and a transfer member that contacts the photosensitive drum. Generally, a process of performing a fixing process after the image is transferred to the sheet. At this time, the transfer process of the toner image to the recording medium is performed in a state where a transfer bias having a polarity opposite to the charging polarity of the toner is applied to the transfer member.

  In the image forming apparatus as described above, the charging member such as a charging roller constituting the charging device is deteriorated with time, insufficient charging due to the use environment (temperature and humidity) of the image forming apparatus, an excessive transfer bias applied to the transfer member, and the like. As a result, the surface potential may be lower than usual over the entire region of the photosensitive drum in the rotation axis direction. As a result, there is a problem that image defects such as image fogging occur.

  On the other hand, a guide member made of synthetic resin is provided at the curved portion of the paper conveyance path in order to convey the paper smoothly. In general, since the charging sequence (charging series) of synthetic resin is lower than that of paper, it is known that when paper is rubbed strongly against a guide member made of synthetic resin, the paper is frictionally charged positively. Therefore, in Patent Document 1, for example, by providing a contact member having a charging sequence (charging series) opposite to that of the synthetic resin on the paper conveyance path, positive charging of the paper rubbed against the synthetic resin guide is performed. An image forming apparatus is disclosed which is reduced.

JP 2003-137454 A

  In the technique of Patent Document 1, when the sheet is charged to the same polarity (plus) as the charging polarity of the photosensitive drum, abnormal discharge occurs between the sheet conveyed to the transfer nip and the photosensitive drum, and the transfer is performed. This is to improve the image deterioration in which the toner image transferred at the nip portion is disturbed, and the influence on the surface potential of the photoreceptor due to the charging of the paper has not been considered. For this reason, depending on the characteristics of the photosensitive drum, paper charged to the opposite polarity (minus) to the charging polarity of the photosensitive drum may act in a direction that weakens the charging of the photosensitive drum, and image fogging and density unevenness may occur. It was.

  In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of always stably forming an image by suppressing a decrease in the surface potential of an image carrier using charging of a recording medium. To do.

  In order to achieve the above object, a first configuration of the present invention includes an image carrier, a charging device, an exposure device, a developing device, a transfer member, a feeding unit, and a registration roller pair. An image forming apparatus. A photosensitive layer is formed on the surface of the image carrier. The charging device charges the surface of the image carrier with the same polarity as the charging polarity of the toner. The exposure device exposes and scans the surface of the image carrier uniformly charged by the charging device to form an electrostatic latent image on the image carrier. The developing device is disposed on the downstream side of the charging device with respect to the rotation direction of the image carrier, and forms a toner image on the image carrier by attaching toner to the electrostatic latent image. The transfer member is disposed on the downstream side of the developing device with respect to the rotation direction of the image carrier so as to contact the image carrier to form a transfer nip portion, and transfers the toner image to a recording medium passing through the transfer nip portion. . The feeding unit separates and feeds the recording media stored in the recording medium storage unit one by one. The registration roller pair temporarily stops the recording medium fed from the feeding unit and transports it again to the transfer nip portion at a predetermined timing. A conveyance guide member made of a material that charges the recording medium to the same polarity as the charging polarity of the image carrier by friction with the recording medium is disposed in the recording medium conveyance path between the feeding unit and the registration roller pair. By changing the conveyance speed of the recording medium in at least one of the feeding unit or the registration roller pair, the recording medium charging mode can be executed in which the contact surface of the recording medium with the image carrier is rubbed against the conveyance guide member. It is.

  According to the first configuration of the present invention, when the surface potential of the image carrier is lowered due to deterioration of the charging device over time, use environment of the image forming apparatus, change of printing mode, or the like, the feeding unit or the pair of registration rollers By executing the recording medium charging mode in which the conveyance speed of the recording medium in at least one of the recording medium is varied and the contact surface of the recording medium with the image carrier is rubbed against the conveyance guide member, the conveyance speed of the recording medium is only adjusted. The reduction in the surface potential of the image carrier can be effectively eliminated by simple control.

1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention. 1 is a partially enlarged view showing a sheet conveyance path from the feeding unit 12 to the image forming unit P in the image forming apparatus 100 of FIG. A graph showing the measurement result of the potential of the paper 18 when the metal transport guide is disposed and when the transport guide member 30 made of synthetic resin whose charging series is lower than the paper 18 is disposed. The graph which shows the measurement result of the surface potential of the photosensitive drum 1 when the metal conveyance guide is arranged and when the synthetic resin conveyance guide member 30 whose charging series is lower than the paper 18 is arranged. The side view which shows the state which the conveyance guide member 30 and the paper 18 are rubbed strongly by making the linear velocity of the registration roller pair 13 faster than the paper feed roller pair 12b The side view which shows the state which the paper 18 bent between the paper feed roller pair 12b and the resist roller pair 13 by making the linear velocity of the paper feed roller pair 12b faster than the resist roller pair 13 7 is a flowchart showing the execution procedure of the sheet charging mode or the charging suppression mode in the image forming apparatus 100 of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention. FIG. 2 is a portion showing a sheet conveyance path from the feeding unit 12 to the image forming unit P in the image forming apparatus 100 of FIG. It is an enlarged view. Here, a monochrome multifunction peripheral is shown as the image forming apparatus 100. In the main body of the image forming apparatus 100, an image forming unit P, a fixing device 9, a feeding unit 12, a registration roller pair 13, and a control unit (CPU) 90 for controlling the operation of each of these devices and members are disposed. ing.

  In the image forming portion P, along the rotation direction of the photosensitive drum 1 (counterclockwise direction in FIG. 1), the charging device 2, the exposure device 3, the developing device 4, the transfer roller 7, the cleaning device 8, and the charge eliminating device. (Not shown) is provided. In the image forming unit P, an image forming process is performed in which a monochrome image is formed on the photosensitive drum 1 through the charging, exposure, development, and transfer processes while rotating the photosensitive drum 1 counterclockwise in FIG. The

  The photosensitive drum 1 is formed by, for example, a photosensitive layer laminated on the surface of an aluminum drum, and the charging device 2 charges the surface. Then, the surface is irradiated with a laser beam from an exposure apparatus 3 to be described later, thereby forming an electrostatic latent image with attenuated charging. The above-mentioned photosensitive layer is not particularly limited. For example, amorphous silicon (a-Si) having excellent durability, or an organic photosensitive layer (high-resolution image can be obtained with little generation of ozone during charging). OPC) and the like are preferable.

  The charging device 2 uniformly charges the surface of the photosensitive drum 1. For example, a contact-type charging device that applies a voltage in a state where a charging member typified by a charging roller is in contact with the surface of the photosensitive member is used as the charging device 2. Instead of the contact-type charging device, a corona discharge device that discharges by applying a high voltage using a thin wire or the like as an electrode may be used. The exposure device 3 irradiates the photosensitive drum 1 with a light beam (for example, a laser beam) based on the document image data read by the image reading unit 21 to form an electrostatic latent image on the surface of the photosensitive drum 1.

  The developing device 4 forms toner images by attaching toner to the electrostatic latent image on the photosensitive drum 1. The toner is supplied to the developing device 4 from the toner container 5 via the intermediate hopper 6. Here, a single-component developer (hereinafter also simply referred to as toner) composed only of magnetic toner components is accommodated in the developing device 4.

  The transfer roller 7 transfers the toner image formed on the surface of the photosensitive drum 1 to the paper 18 conveyed through the paper conveyance path 11 without disturbing the toner image. The cleaning device 8 includes a cleaning roller, a cleaning blade, and the like that are in linear contact with the longitudinal direction of the photosensitive drum 1, and removes residual toner remaining on the surface of the photosensitive drum 1 after the toner image is transferred to the paper 18. Remove.

  The image reading unit 21 includes a scanner lamp that illuminates the document during copying, a scanning optical system equipped with a mirror that changes the optical path of reflected light from the document, and a condensing lens that focuses the reflected light from the document to form an image. And a CCD sensor or the like (both not shown) that converts the imaged image light into an electrical signal, and reads a document image and converts it into image data.

  When performing the copy operation, the image reading unit 21 reads the image data of the document and converts it into an image signal. On the other hand, in the image forming unit P, the photosensitive drum 1 that rotates counterclockwise in FIG. 1 is uniformly charged by the charging device 2, and the exposure device is based on the original image data read by the image reading unit 21. 3 irradiates the photosensitive drum 1 with a laser beam (light beam), thereby forming an electrostatic latent image based on the image data on the surface of the photosensitive drum 1. Thereafter, the developing device 4 attaches toner to the electrostatic latent image to form a toner image.

  The paper 18 is sent from the paper feed cassette 10 by the feeding unit 12 having the pickup roller 12a and the paper feed roller pair 12b toward the image forming portion P on which the toner image is formed as described above. Then, it is conveyed to the image forming unit P via the registration roller pair 13 at a predetermined timing. A conveyance path of the sheet 18 from the feeding unit 12 to the image forming unit P is indicated by a broken line arrow A in FIG.

  Then, the toner image on the surface of the photosensitive drum 1 is transferred to the paper 18 by the transfer roller 7 in the image forming portion P. The sheet 18 on which the toner image has been transferred is separated from the photosensitive drum 1, conveyed to the fixing device 9, and heated and pressed to fix the toner image on the sheet 18. The transport direction of the paper 18 that has passed through the fixing device 9 is sorted by the branching section 16 that branches in a plurality of directions. When an image is formed on only one side of the paper 18, the image is directly discharged to the discharge tray 15 by the discharge roller pair 14.

  On the other hand, when images are formed on both sides of the paper 18, the paper 18 that has passed through the fixing device 9 is once transported in the direction of the discharge roller pair 14, and after the rear end of the paper 18 passes through the branch portion 16, the discharge roller pair 14. Is rotated in the reverse direction and the conveyance direction of the branching portion 16 is switched, so that the paper 18 is distributed from the rear end of the paper 18 to the reverse conveyance path 17 and re-conveyed to the registration roller pair 13 with the image surface reversed. Then, the next image formed on the photosensitive drum 1 is transferred to the surface of the paper 18 where the image is not formed by the transfer roller 7 and conveyed to the fixing device 9 to fix the toner image, and then the discharge tray. 15 is discharged.

  As shown in FIG. 2, a conveyance guide member 30 is disposed on the inner surface of the sheet conveyance path 11 between the feeding unit 12 and the registration roller pair 13. The conveyance guide member 30 is formed in a circular arc shape with a synthetic resin (for example, fluororesin) whose charging series is lower than the paper 18, and the inner side surface (inner corner surface) of the curved portion 11a of the paper conveyance path 11 is formed. It is composed. The dimension of the conveyance guide member 30 in the sheet width direction (perpendicular to the plane of FIG. 2) is substantially the same as that of the maximum size sheet 18 passing through the sheet conveyance path 11.

  In the charging series, when two kinds of substances are charged by friction with each other, substances that are easily charged positively (positive) are arranged on the upper side, and substances that are easily charged negatively (minus) are arranged on the lower side. The charge polarity of the substance varies depending on the frictional partner, and when the upper substance and the lower substance in the charging series are rubbed together, the upper substance is positively charged and the lower substance is negatively charged. In other words, the sheet 18 in contact with the conveyance guide member 30 is positively charged due to friction with the conveyance guide member 30 having a lower charging series.

  FIG. 3 shows the case of the paper 18 when the metal transport guide is disposed and when the transport guide member 30 made of synthetic resin whose charging series is lower than the paper 18 is attached to the surface of the metal transport guide. It is a graph which shows an electric potential measurement result. The potential measurement position of the paper 18 is immediately after the paper 18 passes through the transport guide member 30 (immediately downstream of the transport guide member 30).

  As shown in FIG. 3, when a synthetic resin conveyance guide member 30 whose charging series is lower than the sheet 18 is arranged (indicated by a line V <b> 1), a predetermined time has elapsed from the start of measurement (about 0.5 seconds). Later, the potential of the paper 18 starts to rise, and after 1.5 seconds, the potential of the paper 18 rises to about 8000 V, which is the peak potential, and then the potential of the paper 18 gradually decreases to 0 V as time passes. The potential of the paper 18 changes in this way because the rubbing with the transport guide member 30 starts after the leading edge of the paper 18 reaches the registration roller pair 13, and the rear edge of the paper 18 moves the paper feeding roller pair 12 b. This is because the sliding friction with the conveyance guide member 30 becomes weak after the passage.

  On the other hand, when the metal conveyance guide is arranged (indicated by the line V2), the potential of the paper 18 is about 2000V even at the peak potential. From this result, it is understood that the paper 18 can be positively charged by arranging the synthetic resin conveyance guide member 30 whose charging series is lower than the paper 18.

  FIG. 4 is a graph showing the measurement result of the surface potential of the photosensitive drum 1 when the paper 18 having the charging behavior as shown in FIG. 3 is passed. As shown in FIG. 4, when the synthetic resin conveyance guide member 30 whose charging series is lower than the sheet 18 (indicated by the line V3) is disposed, when the metal conveyance guide is disposed (in the line V4, the line V4). In comparison with (display), a decrease in the surface potential of the photosensitive drum 1 is suppressed. From this result, by using a resin whose charging series is lower than that of the paper 18 for the conveyance guide member 30, the positively charged electric charge of the paper 18 is supplied to the photosensitive drum 1, and the surface potential of the photosensitive drum 1 is reduced. You can see that it increases.

  Furthermore, in this embodiment, for example, when the surface potential of the photosensitive drum 1 is lowered due to deterioration of the charging device 2 with time, or the image forming apparatus 100 is in a printing mode or temperature / humidity where the surface potential of the photosensitive drum 1 is lowered. When used under conditions, a sheet charging mode in which frictional charging of the sheet 18 using the conveyance guide member 30 is positively executed is performed, so that a decrease in the surface potential of the photosensitive drum 1 is suppressed, and the photosensitive member During normal image formation in which the surface potential of the drum 1 is not lowered, the sheet 18 is not frictionally charged so that the surface potential of the photosensitive drum 1 is not changed.

  As a method of positively charging the paper 18, a method of adjusting the paper conveyance speed in the feeding unit 12 and the registration roller pair 13 can be mentioned. As shown in FIG. 5, if the linear speed (conveyance speed) of the registration roller pair 13 is faster than the linear speed of the paper feed roller pair 12 b, the paper 18 is pulled between the paper feed roller pair 12 b and the registration roller pair 13. The conveyance guide member 30 disposed on the inner corner side of the curved portion 11a and the paper 18 are rubbed strongly, and the paper 18 is strongly frictionally charged (paper charging mode).

  Conversely, as shown in FIG. 6, if the linear velocity of the paper feed roller pair 12 b is faster than the linear velocity of the registration roller pair 13, the paper 18 bends between the paper feed roller pair 12 b and the registration roller pair 13. Therefore, the sheet 18 is less likely to be frictionally charged by the conveyance guide member 30 and the sheet itself is less charged (charging suppression mode).

  That is, by adjusting the relationship (conveying speed ratio) of the conveyance speed of the paper 18 in the feeding unit 12 and the registration roller pair 13, the triboelectric charge amount of the paper 18 can be controlled, and the usage status, command, etc. As a result, the surface potential of the photosensitive drum 1 can be stabilized. As shown in Table 1 as an example, the sheet by friction between the sheet 18 and the conveyance guide member 30 can be switched to a plurality of modes in which the relationship between the conveyance speeds in the feeding unit 12 and the registration roller pair 13 is changed. 18 can be changed, and the influence on the surface potential of the photosensitive drum 1 can be varied.

  In mode 1, the conveyance speed ratio (linear speed ratio) of the feeding unit 12 to the registration roller pair 13 is 100.1%, and the conveyance speed of the feeding unit 12 is higher than the conveyance speed of the registration roller pair 13. fast. Therefore, the paper 18 is bent between the paper feed roller pair 12 b and the registration roller pair 13, and the paper 18 is not charged by the conveyance guide member 30.

  In mode 2, the conveyance speed ratio of the feeding unit 12 to the registration roller pair 13 is 100%, and the conveyance speed of the registration roller pair 13 and the conveyance speed of the feeding unit 12 are equal. For this reason, the sheet 18 is appropriately brought into contact with the conveyance guide member 30, and the sheet 18 is slightly charged positively. Note that mode 2 is set during normal image formation.

  In mode 3, the conveyance speed ratio of the feeding unit 12 to the registration roller pair 13 is 99.9%, and the conveyance speed of the feeding unit 12 is slower than the conveyance speed of the registration roller pair 13. Therefore, the paper 18 is pulled between the paper feed roller pair 12b and the registration roller pair 13, and the paper 18 is strongly rubbed against the conveyance guide member 30, and the paper 18 is strongly charged positively.

  In mode 3, the paper 18 is rubbed against the conveyance guide member 30 as shown in FIG. 3 after the leading edge of the paper 18 reaches the registration roller pair 13 and the trailing edge of the paper 18 is fed. This is until it passes through the unit 12 (feed roller pair 12b). Therefore, only a part of the transport direction of the paper 18 is positively charged. Therefore, in order to bring the charged region of the paper 18 into contact with the entire circumferential direction of the photosensitive drum 1, the length in the conveyance direction of the paper 18 rubbed by the conveyance guide member 30 is set to the length corresponding to one circumference of the photosensitive drum 1. It is preferable to set it to more than this.

  FIG. 7 is a flowchart showing a control example of the sheet charging mode in the image forming apparatus 100 of the present invention. The procedure for executing the sheet charging mode and the charging suppression mode will be described along the steps of FIG. 7 with reference to FIGS. 1 to 6 as necessary.

  A surface potential measuring device (not shown) for measuring the surface potential of the photosensitive drum 1 is disposed in the vicinity of the outer peripheral surface of the photosensitive drum 1. The measurement result of the surface potential by the surface potential measuring device is transmitted to the control unit 90 (see FIG. 1), and it is determined whether or not the measured surface potential is within a predetermined range (reference value) (step S1).

  If the surface potential is not within the predetermined range (NO in step S1), it is next determined whether or not the surface potential is lower than the predetermined range (step S2). When the surface potential is lower than the predetermined range (YES in step S2), the linear velocity of the registration roller pair 13 is increased by a control signal from the control unit 90 (step S3), and the mode is changed from mode 2 to mode 1 in Table 1. Change to 3 (paper charging mode). As a result, the contact surface of the sheet 18 with the photosensitive drum 1 is rubbed against the conveyance guide member 30 and charged positively. Then, the positively charged paper 18 is conveyed to the transfer nip portion, whereby the charge of the paper 18 moves to the photosensitive drum 1 side, and the decrease in the surface potential of the photosensitive drum 1 is suppressed.

  On the other hand, when the surface potential is higher than the predetermined range (NO in step S2), the linear velocity of the registration roller pair 13 is decreased by the control signal from the control unit 90 (step S4), and the modes shown in Table 1 are performed. 2 is changed to mode 1 (charging suppression mode). As a result, the paper 18 is bent between the paper feed roller pair 12b and the registration roller pair 13, so that the paper 18 and the conveyance guide member 30 are not rubbed, and the paper 18 is reliably prevented from being charged.

  Then, it is determined whether or not the surface potential of the photosensitive drum 1 is within a predetermined range (step S5). If the surface potential is not within the predetermined range, the process returns to step S2, and mode 1 or mode 3 is continued. If the surface potential falls within the predetermined range, the linear velocity of the registration roller pair 13 is restored (step S6), the mode 1 or mode 3 is changed to mode 2, and the process is terminated. If the surface potential of the photosensitive drum 1 is within the predetermined range in step S1 (YES in step S1), mode 2 is continued without changing to mode 1 or mode 3.

  According to the above control, when the surface potential of the photosensitive drum 1 decreases due to deterioration of the charging device 2 with time, use environment of the image forming apparatus 100, change of the printing mode, or the like, the sheet 18 is in contact with the photosensitive drum 1. By executing the sheet charging mode in which the contact surface is rubbed against the conveyance guide member 30, it is possible to effectively eliminate the lowering of the surface potential by simple control that merely adjusts the linear velocity of the registration roller pair 13.

  When the surface potential of the photosensitive drum 1 increases due to overcharging by the charging device 2 or the like, the charging is suppressed by executing a charging suppression mode in which the paper 18 is bent and the sliding with the conveyance guide member 30 is suppressed. A further increase in the surface potential of the body drum 1 can be prevented.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above embodiment, the sheet charging mode or the charging suppression mode is executed by changing the linear speed of the registration roller pair 13, but the linear speed of the paper feeding roller pair 12 b is changed instead of the registration roller pair 13. It is also possible to execute the sheet charging mode or the charging suppression mode. Furthermore, the linear speeds of both the paper feed roller pair 12b and the registration roller pair 13 may be varied.

  In the above-described embodiment, the conveyance guide member 30 having an arcuate cross section is used. However, the shape and size of the conveyance guide member 30 are appropriately determined according to the specifications of the image forming apparatus 100 or the size of the paper 18 to be used. It can be changed. In the above-described embodiment, since the charging polarity of the photosensitive drum 1 is positive (plus), the conveyance guide member 30 is formed of a synthetic resin whose charging series is lower than the paper 18, but the charging polarity of the photosensitive drum 1 is used. Is negative (minus), the conveyance guide member 30 may be formed of a synthetic resin whose charge series is higher than that of the paper 18.

  The present invention is not limited to the monochrome multifunction device shown in FIG. 1, but can be applied to other image forming apparatuses using an electrophotographic method, such as a color printer, a color multifunction device, and a monochrome printer.

  The present invention is applicable to an image forming apparatus using an electrophotographic system. By utilizing the present invention, it is possible to provide an image forming apparatus capable of always stably forming an image by suppressing the decrease in the surface potential of the image carrier using the charging of the recording medium.

1 Photosensitive drum (image carrier)
2 Charging device 3 Exposure device 4 Development device 7 Transfer roller (transfer member)
9 Fixing Device 10 Paper Feed Cassette (Recording Medium Storage Unit)
11 Paper transport path (recording medium transport path)
11a Curved portion 12 Feed unit 12a Pickup roller 12b Paper feed roller pair 13 Registration roller pair 18 Paper (recording medium)
30 Conveying guide member 90 Control unit 100 Image forming apparatus P Image forming unit

Claims (6)

An image carrier having a photosensitive layer formed on the surface;
A charging device that charges the surface of the image carrier to the same polarity as the charging polarity of the toner;
An exposure device that exposes and scans the surface of the image carrier uniformly charged by the charging device to form an electrostatic latent image on the image carrier;
A developing device that is disposed downstream of the charging device with respect to the rotation direction of the image carrier, and forms a toner image on the image carrier by attaching toner to the electrostatic latent image;
A transfer nip portion is formed on the downstream side of the developing device with respect to the rotation direction of the image carrier to form the transfer nip portion, and the toner image is transferred to a recording medium passing through the transfer nip portion. A transfer member;
A feeding unit for separating and feeding the recording media stored in the recording medium storage unit one by one;
A pair of registration rollers for temporarily stopping the recording medium fed from the feeding unit and re-transporting the recording medium to the transfer nip portion at a predetermined timing;
In an image forming apparatus comprising:
A conveyance guide member formed of a material for charging the recording medium to the same polarity as the charging polarity of the image carrier by friction with the recording medium in the recording medium conveyance path between the feeding unit and the registration roller pair Is placed,
Executes a recording medium charging mode in which a conveying surface of the recording medium is rubbed against the conveying guide member by varying a conveying speed of the recording medium in at least one of the feeding unit or the registration roller pair. An image forming apparatus characterized by being made possible. A controller that varies a recording medium conveyance speed of at least one of the registration roller pair or the feeding unit according to a change in surface potential of the image carrier;
The control unit executes the recording medium charging mode in which when the surface potential of the image carrier is lower than a predetermined value, the recording medium conveyance speed in the registration roller pair is higher than that of the feeding unit. The image forming apparatus according to claim 1, wherein: It is possible to execute a charge suppression mode in which the conveyance speed of the recording medium in the feeding unit is faster than the registration roller pair,
The image forming apparatus according to claim 2, wherein the control unit executes the recording medium charging mode when a surface potential of the image carrier rises above a predetermined value.   4. The length in the conveyance direction of the recording medium rubbed against the conveyance guide member in the recording medium charging mode is equal to or longer than the length of one circumference of the image carrier. The image forming apparatus according to any one of the above.   The recording medium conveyance path has a curved portion that curves so that the contact surface of the recording medium with the image carrier is on the inner corner side, and the conveyance guide member has an inner corner surface of the curved portion. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured.   6. The image bearing member according to claim 1, wherein a charge polarity of the image carrier is positive, and the conveyance guide member is formed of a synthetic resin having a lower charge series than the recording medium. Image forming apparatus.

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