Image forming device

Abstract

To suppress image deletion in a configuration that has a brush member arranged so as to be in contact with a surface of a photoreceptor.SOLUTION: An image formation apparatus 100 comprises a photoreceptor 1, a charging member 2, a development device 3, a transfer member 5, a brush member 10, a drive source 110 which rotationally drives the photoreceptor 1, and a control unit 150 which controls the drive source 110 so as to be able to execute an image formation step that performs image formation on a recording material P and non-image formation steps that are steps other than the image formation step and cause the photoreceptor 1 to perform rotational driving. When the non-image formation step between a first recording material P and a second recording material P on which image formation is performed next the first recording material P is a first non-image formation step, and the non-image formation step between the second recording material P and a third recording material P on which image formation is performed next the second recording material P is a second non-image formation step, the control unit 150 is configured to determine a time of the second non-image formation step on the basis of history information correlated with a use amount of the photoreceptor 1 and a time of the first non-image formation step.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a printer, a copying machine, or a facsimile machine that uses an electrophotographic method. [Background technology]

[0002] In electrophotographic image forming apparatuses, a cleaning blade arranged in contact with the surface of a photosensitive drum is widely used as a cleaning means for removing residual toner remaining on the surface of a photosensitive member (hereinafter referred to as a "photosensitive drum") after a toner image has been transferred. A brush member arranged in contact with the surface of the photosensitive drum may also be used as this cleaning means. Patent Document 1 discloses a configuration in which a brush member for cleaning toner from the surface of the photosensitive drum is arranged downstream of a transfer unit and upstream of a charging unit in the rotational direction of the photosensitive drum.

[0003] In electrophotographic image forming apparatuses, an image defect known as "image deletion" can occur. Specifically, a discharge occurs when the surface of a photosensitive drum is charged by a charging member (hereinafter referred to as a "charging roller"), which generates ozone. Ozone generated by this discharge decomposes components in the air, generating discharge products such as NOx and SOx. These discharge products are water-soluble. Furthermore, when a recording material with a transferred toner image passes through a fixing device, the moisture contained in the recording material evaporates, generating water vapor. The discharge products adsorb this water vapor, significantly reducing the surface resistance of the photosensitive drum. This prevents the formation of an appropriate electrostatic latent image on the surface of the photosensitive drum, causing a lateral flow of potential and resulting in image deletion. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-65580 Summary of the Invention [Problem to be solved by the invention]

[0005] As a result of the inventors' investigations, it was found that in a configuration having a brush member arranged in contact with the surface of the photosensitive drum, the brush member can collect moisture adhering to the surface of the photosensitive drum, and therefore, in such a configuration, it was found that image deletion is unlikely to occur when executing a job in which only a few images are formed.

[0006] However, it has been found that when a job with a relatively large number of images is performed, the moisture capacity of the brush member may be exceeded, causing moisture to flow locally onto the photosensitive drum, resulting in image deletion in that area. This is thought to occur when moisture flowing from the brush member is adsorbed by discharge products accumulated on the surface of the photosensitive drum, significantly reducing the surface resistance of the photosensitive drum. This phenomenon is likely to occur, for example, when a job with a relatively large number of images is performed using recording materials that have been left in a humid environment and have absorbed moisture.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to suppress image deletion in a configuration having a brush member disposed in contact with the surface of a photosensitive member. [Means for solving the problem]

[0008] The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention provides a developing device comprising: a rotatable photosensitive member; a charging member that charges the surface of the photosensitive member in a charging section; a developing device that supplies toner to the surface of the photosensitive member after charging to form a toner image; a transfer member that transfers the toner image from the photosensitive member to a recording material in a transfer section; a brush member that contacts the surface of the photosensitive member downstream of the transfer section and upstream of the charging section in the rotation direction of the photosensitive member to form a contact section; a drive source that drives the photosensitive member to rotate; and a control unit that controls the drive source to enable control to execute an image forming step in which an image is formed on a recording material, and a non-image forming step that is a step other than the image forming step and is carried out so that the photosensitive member is driven to rotate, wherein the non-image forming step between a first recording material and a second recording material on which an image is formed after the first recording material is defined as a first non-image forming step, and the non-image forming step between the second recording material and a third recording material on which an image is formed after the second recording material is defined as a second non-image forming step. The number of sheets of recording material on which an image is formed in the image forming process. and the time of the first non-image forming step, The aforementioned Second non-imaging step time is controlled to be longer than the time of the first non-image forming step. The image forming apparatus is characterized by:

[0009] According to another aspect of the present invention, a developing device includes a rotatable photosensitive member, a charging member that charges the surface of the photosensitive member in a charging section, a developing device that supplies toner to the surface of the photosensitive member after charging to form a toner image, a transfer member that transfers the toner image from the photosensitive member to a recording material in a transfer section, a brush member that contacts the surface of the photosensitive member downstream of the transfer section and upstream of the charging section in the rotation direction of the photosensitive member to form a contact section, a drive source that drives the photosensitive member to rotate, and a control unit that controls the drive source to enable control to perform an image forming step in which an image is formed on a recording material, a non-image forming step that is a step other than the image forming step and is performed so that the photosensitive member is driven to rotate, and a post-rotation step in which the photosensitive member is rotated after the recording material is rotated without performing the image forming step, and when the non-image forming step between a first recording material and a second recording material on which an image is formed after the first recording material is defined as a first non-image forming step, the control unit controls the drive source to enable control to perform The number of sheets of recording material on which an image is formed in the image forming process. and a time for the post-rotation process to be executed after the second recording material based on the time for the first non-image forming process. is controlled to be longer than the time of the first non-image forming step. The image forming apparatus is characterized by: According to another aspect of the present invention, a developing device includes a rotatable photosensitive member, a charging member that charges the surface of the photosensitive member in a charging section, a developing device that supplies toner to the surface of the photosensitive member after charging to form a toner image, a transfer member that transfers the toner image from the photosensitive member to a recording material in a transfer section, a brush member that contacts the surface of the photosensitive member downstream of the transfer section and upstream of the charging section in the rotation direction of the photosensitive member to form a contact section, and a control section that controls a non-image forming time that is a time during which the photosensitive member rotates from the time when the preceding recording material passes through the transfer section until the next recording material arrives at the transfer section, and the control section controls the non-image forming time that is the time during which the photosensitive member rotates from the time when the preceding recording material passes through the transfer section until the next recording material arrives at the transfer section. The image forming apparatus is characterized in that an inter-image time, which is the non-image formation time from when a recording material to be transferred passes the transfer section until the next recording material reaches the transfer section without the rotation of the photosensitive drum being stopped, is set to a predetermined inter-image time, and the non-image formation time from when the last recording material passes the transfer section until the next recording material after the last recording material reaches the transfer section in continuous image formation in which toner images are transferred successively to a plurality of recording materials is controlled to be longer than the predetermined inter-image time based on the number of images formed, which is the number of recording materials on which images are formed during the continuous image formation when the continuous image formation is performed. [Effects of the Invention]

[0010] According to the present invention, in a configuration having a brush member disposed in contact with the surface of a photosensitive member, image deletion can be suppressed. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Figure 2] FIG. 2 is a schematic diagram of a brush member. [Figure 3] FIG. 2 is a schematic block diagram for explaining a control mode of the image forming apparatus. [Figure 4] FIG. 4 is a schematic diagram for explaining collection of water vapor by a brush member. [Figure 5] 10A and 10B are schematic diagrams for explaining the discharge of moisture from the brush member. [Figure 6] FIG. 2 is a flowchart of control in the first embodiment. [Figure 7] FIG. 10 is a flowchart of the control in the second embodiment. [Figure 8] FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to a comparative example. [Figure 9] FIG. 10 is a schematic diagram showing a method for storing usage history information. DETAILED DESCRIPTION OF THE INVENTION

[0012] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0013] [Example 1] 1. Overall configuration and operation of the image forming apparatus 1 is a schematic cross-sectional view of an image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a monochrome laser beam printer that employs a cleanerless system and a contact charging system and is capable of forming a black monochrome image.

[0014] The image forming apparatus 100 has a photosensitive drum 1, which is a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) that serves as an image carrier. When a job operation is started, the photosensitive drum 1 is driven to rotate in the direction of arrow R1 (clockwise direction) in FIG. 1 by a drive motor 110 (FIG. 3) that serves as a drive source constituting a drive means (drive unit). In this embodiment, the outer diameter of the photosensitive drum 1 is 24 mm, and the peripheral speed (surface movement speed) of the photosensitive drum 1 is 140 mm / sec.

[0015] The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative in this embodiment) by the charging roller 2, a roller-type charging member (contact charging member) serving as charging means. The position on the photosensitive drum 1 where charging is performed by the charging roller 2 in the rotational direction of the photosensitive drum 1 is the charging portion (charging position) Pa. The charging roller 2 charges the surface of the photosensitive drum 1 by discharge occurring in at least one of the minute gaps formed between the photosensitive drum 1 and the charging roller 2, which are formed upstream and downstream of the contact point between the photosensitive drum 1 and the charging roller 2 in the rotational direction of the photosensitive drum 1. In this description, it is assumed that the contact point between the photosensitive drum 1 and the charging roller 2 in the rotational direction of the photosensitive drum 1 is the charging portion (charging position) Pa. The charging roller 2 is an elastic roller configured with a conductive elastic layer provided around a core metal. The charging roller 2 is disposed in contact with the surface of the photosensitive drum 1. In this embodiment, the charging roller 2 is rotated in the direction of arrow R2 (counterclockwise) in FIG. 1 by a drive motor serving as a drive source constituting a driving means (drive unit). The drive motor that drives the charging roller 2 may be a common drive motor (main motor) with the drive motor 110 that drives the photosensitive drum 1, or it may be a separate drive motor. The charging roller 2 may also be configured to rotate in response to the rotation of the photosensitive drum 1. During the charging process, a predetermined charging voltage (charging bias), which is a negative DC voltage, is applied to the charging roller 2 by a charging power source E1 (FIG. 3) that serves as a charging voltage application means (charging voltage application unit). In this embodiment, the charging voltage is, for example, −1200 V, and the surface of the photosensitive drum 1 is uniformly charged to a dark potential Vd of −600 V.

[0016] The charged surface of the photosensitive drum 1 is scanned and exposed by an exposure device (laser scanner device) 4, which serves as an exposure means (electrostatic image forming means). The exposure device 4 repeatedly exposes the photosensitive drum 1 with the laser beam L along the main scanning direction (direction of the rotation axis) of the photosensitive drum 1 along the sub-scanning direction (direction of movement of the surface) to the laser beam L, thereby forming an electrostatic latent image (electrostatic image) on the surface of the photosensitive drum 1. In this embodiment, the dark area potential Vd of the surface of the photosensitive drum 1, which has been uniformly charged, is reduced in absolute value to a light area potential Vl of −100 V by exposure by the exposure device 4. The position on the photosensitive drum 1 exposed by the exposure device 4 in the rotation direction of the photosensitive drum 1 is the exposure area (exposure position) Pb. The exposure device 4 is not limited to a laser scanner device and may be, for example, an LED array in which multiple LEDs are arranged along the rotation axis direction of the photosensitive drum 1.

[0017] The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed (visualized) by the developing device 3 as a developing means, which supplies toner as a developer, and a toner image (toner image, developer image) is formed on the surface of the photosensitive drum 1. The developing device 3 has a developing roller 31 as a developer carrier, a toner supply roller 32 as a developer supply means, a developer storage chamber 33 that stores toner, and a developing blade 34 as a regulating member that regulates the toner on the developing roller 31. The toner stored in the developer storage chamber 33 is stirred by a stirring member 35 provided in the developer storage chamber 33 and supplied to the surface of the developing roller 31 by the toner supply roller 32. The toner supplied to the surface of the developing roller 31 is uniformly thinned as it passes through the contact area between the developing roller 31 and the developing blade 34, and is negatively charged by frictional charging. The developing roller 31 is disposed in contact with the surface of the photosensitive drum 1. In this embodiment, a one-component non-magnetic contact development method is used as the development method, but the development method is not limited to this, and a two-component non-magnetic contact development method or a non-contact development method may also be used. A magnetic development method may also be used. In this embodiment, the normal charge polarity of the toner, which is the main charge polarity of the toner during development, is negative. However, the normal charge polarity of the toner is not limited to negative, and may also be positive. If the normal charge polarity of the toner is positive, the voltage relationship described below may be appropriately set to the opposite polarity from that in this embodiment.

[0018] The developing roller 31 is driven to rotate in the direction of arrow R3 in FIG. 1 (counterclockwise) by a drive motor serving as a drive source constituting a drive means (drive unit). In this embodiment, the developing roller 31 rotates so that the surface of the photosensitive drum 1 and the surface of the developing roller 31 move in the same direction at the contact point between the photosensitive drum 1 and the developing roller 31. The drive motor that drives the developing roller 31 may be a common drive motor (main motor) with the drive motor 110 that drives the photosensitive drum 1, or may be a separate drive motor. During the development process, a predetermined developing voltage (developing bias), which is a negative DC voltage, is applied to the developing roller 31 by a development power source E2 (FIG. 3) serving as a developing voltage application means (developing voltage application unit). In this embodiment, the developing voltage is, for example, −300 V. In this embodiment, toner charged with the same polarity (negative in this embodiment) as the charge polarity of the photosensitive drum 1 adheres to the image area (exposed surface, image area) on the photosensitive drum 1, which has been uniformly charged and then exposed to light to reduce the absolute value of its potential (reverse development method). The position on the photosensitive drum 1 where development occurs relative to the rotation direction of the photosensitive drum 1 (the contact point between the developing roller 31 on the photosensitive drum 1) is the development area (development position) Pc. In this embodiment, the developing device 3 is configured so that the developing roller 31 is always in contact with the photosensitive drum 1. However, the developing device 3 is not limited to this configuration, and may be configured so that the developing roller 31 and the photosensitive drum 1 can be switched between a contact state and a separation state. For example, the image forming apparatus 100 may be provided with a development contact / separation mechanism that switches between the contact state and the separation state. Then, during the pre-rotation process described below, the photosensitive drum 1 is rotated with the developing roller 31 spaced apart from the photosensitive drum 1, and during the image formation process (development process) described below, the developing roller 31 is brought into contact with the photosensitive drum 1.

[0019] A transfer roller 5, a roller-type transfer member serving as a transfer means, is disposed opposite the photosensitive drum 1. The transfer roller 5 is disposed in contact with the surface of the photosensitive drum 1. The toner image formed on the surface of the photosensitive drum 1 is transferred to the surface of a recording material P, such as paper, being nipped between the photosensitive drum 1 and the transfer roller 5 at the transfer nip Nt, which is the contact point between the photosensitive drum 1 and the transfer roller 5, by the action of the transfer roller 5. The position where the toner image on the photosensitive drum 1 is transferred in the direction of rotation of the photosensitive drum 1 (the contact point between the photosensitive drum 1 and the transfer roller 5), i.e., the position on the photosensitive drum 1 that forms the transfer nip Nt, is the transfer portion (transfer position) Pd. In this embodiment, the transfer roller 5 is an elastic roller configured with a core metal and an elastic layer made of conductive NBR (nitrile butadiene rubber)-hydrin sponge rubber provided around it. In this embodiment, the transfer roller 5 has an outer diameter of 12 mm and a hardness of 30° (Asker-C, 500 gf load). The transfer roller 5 is pressed against the surface of the photosensitive drum 1 with a predetermined pressure. A sheet-like recording material (transfer material, recording medium, sheet) P, which is the object to be transferred, is housed in a cassette 6, which serves as a recording material housing. The recording material P housed in the cassette 6 is fed from the cassette 6 by a feed roller 7 and other rollers, and is transported to the transfer nip Nt by a transport roller 8 and other rollers in synchronization with the toner image on the photosensitive drum 1. In this embodiment, the feed roller 7, transport roller 8, and other rollers constitute a transport device 14 for the recording material P. During the transfer process, a predetermined transfer voltage (transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal polarity of the toner, is applied to the transfer roller 5 by a transfer power source E3 (FIG. 3) serving as a transfer voltage application means (transfer voltage application unit). This forms an electric field between the transfer roller 5 and the photosensitive drum 1, and the toner image is electrostatically transferred from the photosensitive drum 1 to the recording material P by the action of this electric field. In this embodiment, the transfer voltage is, for example, +1000 V.

[0020] The recording material P onto which the toner image has been transferred is conveyed to a fixing device 9 serving as a fixing means. The fixing device 9 applies heat and pressure to the recording material P bearing the unfixed toner image, thereby fixing (melting and adhering) the toner image to the surface of the recording material P. The fixing device 9 will be described in more detail later. The recording material P onto which the toner image has been fixed is discharged (output) to the outside (outside the machine) of the apparatus main body 101 of the image forming apparatus 100, and is stacked on a tray 12 provided at the top of the apparatus main body 101.

[0021] Furthermore, toner remaining on the surface of the photosensitive drum 1 without being transferred to the recording material P during the transfer process (transfer residual toner) is sent to the brush member 10, which is located downstream of the transfer roller 5 in the rotational direction of the photosensitive drum 1. For example, when high-resistivity paper, such as cardboard or paper stored in a low-humidity environment, is used as the recording material P, the amount of transfer residual toner is likely to increase and the transfer residual toner accumulates on the brush member 10. In other words, during a non-image forming process (such as an inter-sheet process), which will be described later, the surface potential of the photosensitive drum 1 may be adjusted to eject toner, etc., that has accumulated on the brush member 10 and is positively charged (i.e., the opposite polarity to the normal charging polarity), onto the photosensitive drum 1 for cleaning. The toner ejected from the brush member 10 is then discharged at the charging station Pa to be negatively charged again. As described above, the development voltage is set to a potential between the potentials of the non-image and image areas on the surface of the photosensitive drum 1. Therefore, the toner that has been negatively charged again is removed from the photosensitive drum 1, transferred to the developing roller 31, and collected in the developer storage chamber 33.

[0022] In this embodiment, the developing voltage and the surface potential of the developing roller 31 can be considered to be substantially the same, although they fluctuate somewhat depending on the charge amount of the toner coated on the developing roller 31 and the amount of toner.

[0023] The configuration and function of the brush member 10 will be described in detail later.

[0024] In addition, in this embodiment, the photosensitive drum 1, the charging roller 2 acting as a process means for acting on it, the developing device 3, and the brush member 10 described later are integrally configured as a process cartridge 13 that is detachably attached to the main body 101 of the apparatus.

[0025] 2. Fixing device In this embodiment, the fixing device 9 is a film-heating type heating device designed to shorten start-up time and reduce power consumption. The fixing device 9 has a cylindrical fixing film 24 as a rotating body. The fixing film 24 is a flexible, rotatable endless belt. The shape of the fixing film 24 is not limited to a cylindrical shape and can be designed as appropriate. The internal space (space surrounded by the inner peripheral surface) of the fixing film 24 is provided with a ceramic heater 242 as a heating member, a heater holder 241 as a holding member for holding the ceramic heater 242, an iron stay 243, and a temperature detection element 244. The heating member is not limited to the ceramic heater 242, and for example, a known heating member can be used as appropriate. Furthermore, the stay 243 is not limited to being made of iron, and for example, a known stay can be used as appropriate.

[0026] The fixing device 9 also includes a pressure roller 23 as a pressure member. The pressure roller 23, together with a ceramic heater 242 via the fixing film 24, forms a fixing nip Nf, which is a contact portion (heating portion) between the fixing film 24 and the pressure roller 23. The pressure roller 23 is driven to rotate by a drive motor serving as a drive source constituting a drive unit (drive section). The drive motor that drives the pressure roller 23 may be a common drive motor (main motor) with the drive motor 110 that drives the photosensitive drum 1, or may be a separate drive motor. The fixing film 24 is driven to rotate by receiving power from the pressure roller 23 at the fixing nip Nf. Heat from the ceramic heater 242 is transferred from the inner circumferential surface to the outer circumferential surface of the fixing film 24, and the outer circumferential surface of the pressure roller 23 is also heated at the fixing nip Nf.

[0027] In this embodiment, the pressure roller 23 has a width of 220 mm in the direction of its axis of rotation, an outer diameter of 14 mm, and is configured by forming a 2.5 mm thick elastic layer (foam rubber) made of foamed silicone rubber around an iron core having an outer diameter of 9 mm. A release surface layer made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) is formed on the elastic layer of the pressure roller 23 as a toner release layer. The surface hardness of the pressure roller 23, including the release surface layer, was 83° using an Asker-CSC2 hardness tester. However, the pressure member is not limited to this configuration and can be designed as appropriate.

[0028] Furthermore, a temperature detection element 244 is disposed on the rear surface of the ceramic heater 242 and detects the temperature of the ceramic heater 242, which rises in response to heat generated by the energized heat-generating resistance layer. A control unit 150, which will be described later, can adjust the temperature of the ceramic heater 242 by appropriately controlling the current flowing from electrode units (not shown) provided at the longitudinal ends of the ceramic heater 242 to the energized heat-generating resistance layer in response to a signal from the temperature detection element 244. The longitudinal direction of the ceramic heater is substantially parallel to the rotational axis direction of the pressure roller 23.

[0029] In this embodiment, the regulated temperature of the fixing device 9 is 180°C during the image forming process (fixing process) described below while the recording material P is passing through the fixing device 9. The regulated temperature of the fixing device 9 during non-image forming processes (such as the inter-sheet process) described below is optimized for each process with respect to the regulated temperature during the image forming process. For example, in this embodiment, the regulated temperature during the normal inter-sheet process is 180°C, the same as the regulated temperature during the image forming process. On the other hand, when the inter-sheet process is extended as described below, the regulated temperature during the inter-sheet process is lowered by approximately -100°C to -10°C compared to the regulated temperature during the image forming process. If the photosensitive drum 1 continues to rotate idly at a high regulated temperature when the inter-sheet process is extended, the toner and other components involved in image formation, such as the photosensitive drum 1 and the developing roller 31, may be damaged by heat from the fixing device 9. However, if the controlled temperature is set too low, the fixing device 9 may not be sufficiently warmed when switching from the inter-sheet process to the image forming process, which may result in poor fixing of the toner to the recording material P. Therefore, in this embodiment, when the inter-sheet process is extended as described below, the controlled temperature during the inter-sheet process is set to -60°C (i.e., 120°C) relative to the controlled temperature during the image forming process (fixing process). Also, in this embodiment, the ceramic heater 242 is turned off during the post-rotation process described below.

[0030] In such a fixing device 9, when a recording material P carrying an unfixed toner image is transported to the fixing nip portion Nf, the heat of the fixing film 24 and the pressure roller 23 is transmitted to the unfixed toner image and the recording material P, and the toner image is fixed to the recording material P.

[0031] 3. Brush component structure Next, the brush member 10 in this embodiment will be described.

[0032] 1, the image forming apparatus 100 of this embodiment has a brush member 10 arranged in contact with the surface of the photosensitive drum 1. The brush member 10 contacts the surface of the photosensitive drum 1 downstream of the transfer portion Pd and upstream of the charging portion Pa in terms of the rotation direction of the photosensitive drum 1. The contact portion of the photosensitive drum 1 with the brush member 10 in terms of the rotation direction of the photosensitive drum 1 is the brush contact portion (brush contact position) Pe.

[0033] Fig. 2(a) is a schematic diagram of the brush member 10 in a standalone state, viewed along its longitudinal direction (a direction substantially parallel to the rotational axis direction of the photosensitive drum 1). Fig. 2(b) is a schematic diagram of the brush member 10 in contact with the photosensitive drum 1, viewed along its longitudinal direction.

[0034] The brush member 10 is composed of a fixed, conductive brush. The brush member 10 includes pile yarns 11a, which are made of multiple bristles that rub against the surface of the photosensitive drum 1, and a base cloth 11b that supports the pile yarns 11a. The brush member 10 is arranged so that its longitudinal direction is substantially parallel to the rotational axis of the photosensitive drum 1. In this embodiment, the brush member 10 is configured by weaving pile yarns (conductive yarns) 11a made of nylon fibers (conductive nylon 6 fibers) blended with a conductive material into a base cloth (conductive base cloth) 11b made of synthetic fibers containing carbon as a conductive agent. Note that the pile yarns 11a may be made of rayon, acrylic, polyester, or the like, in addition to nylon.

[0035] As shown in FIG. 2(a), when the brush member 10 is in a standalone state, i.e., when no external force is being applied to bend the pile yarns 11a, the distance from the base fabric 11b to the tip of the pile yarns 11a is defined as pile length L1. In this embodiment, pile length L1 is 6.5 mm. The brush member 10 is positioned such that the base fabric 11b is fixed to a support member (not shown) installed at a predetermined position in the image forming apparatus 100 using a fixing means such as double-sided tape, and the tip of the pile yarns 11a penetrates the photosensitive drum 1. In this embodiment, the clearance between the support member and the photosensitive drum 1 is fixed. As shown in FIG. 2(b), the shortest distance from the base fabric 11b of the brush member 10 fixed to the support member to the photosensitive drum 1 is defined as L2. In this embodiment, the difference between distance L2 and pile length L1 is defined as the "intrusion amount of the brush member 10 into the photosensitive drum 1." In this embodiment, the intrusion amount of the brush member 10 into the photosensitive drum 1 is 1 mm.

[0036] In this embodiment, as shown in FIG. 2(a), when the brush member 10 is in a stand-alone state, the length L3 of the brush member 10 in the direction along the circumferential direction of the photosensitive drum 1 (hereinafter also referred to as the "short direction") is 5 mm. In this embodiment, the length of the brush member 10 in the longitudinal direction is 216 mm. This allows the brush member 10 to come into contact with the entire image forming area (area where a toner image can be formed) on the photosensitive drum 1 in the direction of the rotation axis of the photosensitive drum 1. In this embodiment, the pile yarn 11a has a thickness of 2 denier and a density of 280 kF / inch. 2 (kF / inch 2 is a unit of brush density, indicating the number of filaments per square inch), and the fineness is 220T / 96F (meaning that 96 strands of 220g thick yarn are bundled together per 10,000m).

[0037] As described above, in this embodiment, the brush member 10 is supported by a support member (not shown) and disposed so as to abut against the photosensitive drum 1 at a fixed position, and the pile yarns 11a rub against the surface of the photosensitive drum 1 as the surface of the photosensitive drum 1 moves. In this embodiment, the brush member 10 functions as a cleaning member (contact member, collection member) serving as a cleaning means (cleaning mechanism) for the photosensitive drum 1. The brush member 10 can collect transfer residual toner remaining on the surface of the photosensitive drum 1 and paper dust generated from the recording material P and adhering to the surface of the photosensitive drum 1 at the transfer portion Pd. In addition, as will be described in detail later, the brush member 10 can collect water vapor adhering to the surface of the photosensitive drum 1. The brush contact portion (brush contact position) Pe is the position on the photosensitive drum 1 relative to the rotational direction of the photosensitive drum 1 where the brush member 10 collects toner, paper dust, or water vapor.

[0038] The configuration of the brush member 10 is not limited to that of this embodiment. The configuration of the brush member 10 can be changed as appropriate depending on, for example, the lifespan of the image forming apparatus 100 or the process cartridge 13, or the maximum image forming width of the image forming apparatus 100 (the maximum width of the image forming area in the direction of the rotation axis of the photosensitive drum 1).

[0039] 4. Control mode FIG. 3 is a schematic block diagram illustrating the control mode of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 is provided with a control unit 150. The control unit 150 includes a CPU 151 as a calculation control means, which is a central element for performing calculations; a memory (storage element) 152 such as a ROM or RAM as a storage unit; and an input / output unit (not shown) for controlling the exchange of signals between various elements connected to the control unit 150. The ROM also includes a rewritable nonvolatile memory. The RAM stores sensor detection results and calculation results, while the ROM stores control programs and pre-calculated data tables. In this embodiment, the memory 152 stores, for example, information regarding the usage history of the photosensitive drum 1, such as the number of rotations and rotation distance of the photosensitive drum 1 (the surface movement distance of the photosensitive drum 1), or the number of sheets of recording material P on which images have been formed (herein also referred to as the "number of images formed"). Note that the information regarding the usage history of the photosensitive drum 1 is not limited to the above information and may be information that changes depending on the use of the photosensitive drum 1. The information relating to the usage history of the photosensitive drum 1 may be information on the film thickness of the photosensitive drum 1 (the thickness of the photosensitive layer or the surface layer), or the like.

[0040] The control unit 150 is a control unit that comprehensively controls the operation of the image forming apparatus 100. The control unit 150 controls the transmission and reception of various electrical information signals, drive timing, and the like, to execute a predetermined image formation sequence. The control unit 150 is connected to various components of the image forming apparatus 100. For example, the control unit 150 is connected to the charging power supply E1, the developing power supply E2, the transfer power supply E3, the drive motor 110, the exposure device 4, the fixing device 9, and the conveying device 14. In this embodiment, the control unit 150 controls the operation of each component of the image forming apparatus 100 (such as power ON / OFF and output value, drive / stop of the drive motor 110, and drive / stop of the conveying device 14) to control the extension operation of the sheet spacing process and post-rotation process, which will be described later. Note that FIG. 3 also illustrates the brush power supply E4, which will be described later.

[0041] In this embodiment, the normal time for the sheet interval process is 50 msec, and the normal time for the post-rotation process is 4 seconds. The times for the sheet interval process and the post-rotation process are set appropriately. The method for setting the times for the sheet interval process and the post-rotation process will be described in detail later.

[0042] The image forming apparatus 100 is capable of executing a job (image output operation), which is a series of operations for forming an image on one or more recording materials P, initiated by a single start instruction. In this embodiment, the start instruction is input to the image forming apparatus 100 from an external device (not shown), such as a personal computer. A job generally includes an image forming process (printing process) and a non-image forming process (non-printing process). The non-image forming process generally includes a pre-rotation process, an inter-sheet process (inter-image process) when forming images on multiple recording materials P, and a post-rotation process. The image forming process is a period during which an electrostatic latent image is actually formed on the photosensitive drum 1, the electrostatic latent image is developed (a toner image is formed), the toner image is transferred, the toner image is fixed, and so on. The image forming process (image formation time) refers to this period. More specifically, the timing of the image forming process differs depending on the locations where the electrostatic latent image is formed, the toner image is formed, the toner image is transferred, and the toner image is fixed. Therefore, the image forming operation may be defined as the period up to the transfer of the toner image, or the period up to the fixation of the toner image. This is because even if the image forming operation performed on the photosensitive drum 1 is completed and the operation of the photosensitive drum 1 is switched from the image forming operation to a non-image forming operation, this does not have any effect on the image that has already been transferred to the recording material P. The pre-rotation process is a period during which preparatory operations are performed before the image forming process. The inter-sheet process (inter-image process) is a period corresponding to the period between recording materials P when the image forming process is performed continuously on multiple recording materials P. The post-rotation process is a period during which an arranging operation (preparatory operation) is performed after the image forming process. The non-image forming process (non-image forming time) is a period other than the image forming process (image forming time), and includes the pre-rotation process, inter-sheet process, post-rotation process, and the pre-multiple rotation process, which is a preparatory operation when the image forming apparatus 100 is turned on or when it returns from a sleep state.

[0043] 5. Extended operation of the paper-interval process and post-rotation process <Water vapor collection by brush element> In the image forming apparatus 100, image deletion may occur when a job is executed in which images are continuously formed on multiple sheets of recording material P. This occurs when moisture that has accumulated on the brush member 10 and overflowed from the brush member 10 is adsorbed onto discharge products that have accumulated on the surface of the photosensitive drum 1 during image formation, resulting in a significant decrease in the surface resistance of the photosensitive drum 1.

[0044] FIG. 4 is a schematic diagram illustrating the action of the brush member 10 on water vapor adhering to the surface of the photosensitive drum 1. When a moist recording material P passes through the fixing device 9, water vapor is generated. This water vapor floats within the image forming apparatus 100 and adheres to the surface of the photosensitive drum 1. When the brush member 10 is dry, the water vapor adhering to the surface of the photosensitive drum 1 is captured by the brush member 10, as shown in FIG. 4(a). Then, as shown in FIG. 4(b), the brush member 10 gradually captures water vapor from the surface of the photosensitive drum 1 by sucking up the water vapor from the surface of the photosensitive drum 1 through capillary action in the narrow gaps between the individual bristles of the brush member 10 and by the bristles themselves absorbing moisture. During this process, while capturing the water vapor, the brush member 10 expels the moisture accumulated in the brush member 10 onto the surface of the photosensitive drum 1 little by little, to the extent that it does not affect image formation. The moisture that is gradually expelled onto the surface of the photosensitive drum 1 evaporates easily because its specific surface area exposed to the surrounding air increases. Therefore, if the state shown in Figure 4(b) can be maintained, the amount of moisture adsorbed to the discharge products accumulated on the surface of the photosensitive drum 1 can be reduced, thereby suppressing the decrease in surface resistance of the photosensitive drum 1 and preventing image deletion.

[0045] However, as shown in FIG. 4(c), when continuous image formation is performed on multiple sheets of recording material P, if the amount of moisture captured by the brush member 10 exceeds the brush member's moisture retention capacity, moisture may leak locally onto the surface of the photosensitive drum 1. This phenomenon is called a local breakdown of the brush member's moisture retention function. In that area, a large amount of moisture is adsorbed onto the discharge products accumulated on the surface of the photosensitive drum 1, significantly reducing the surface resistance of the photosensitive drum 1. As a result, lateral potential drift occurs at the edge of the electrostatic latent image formed on the surface of the photosensitive drum 1, resulting in image deletion. Therefore, to prevent image deletion, it is necessary to control the amount of moisture retained by the brush member 10 to maintain the state shown in FIG. 4(a) or 4(b), and prevent the amount of moisture retained by the brush member 10 from becoming excessively large, as in the state shown in FIG. 4(c).

[0046] The amount of moisture retained by the brush member 10 increases as the number of sheets of recording material P continuously transported in the normal sheet spacing time (50 msec) increases. Here, the number of sheets of recording material P continuously transported in the normal sheet spacing time (50 msec) without a post-rotation process or a sheet spacing process with a modified time is defined as the "number of continuous image formations." Furthermore, here, continuous image formation performed in the normal sheet spacing time (50 msec) without a post-rotation process or a sheet spacing process with a modified time is also simply referred to as "continuous image formation." Meanwhile, the moisture retained by the brush member 10 can be reduced by idling the photosensitive drum 1 without transporting the recording material P. This is because, as shown in FIG. 5, water vapor captured by the brush member 10 can be gradually expelled onto the surface of the photosensitive drum 1 through the brush member 10 and evaporate without new water vapor being supplied to the surface of the photosensitive drum 1. 5 is a schematic diagram similar to FIG. 4, illustrating the action of the brush member 10 on water vapor adhering to the surface of the photosensitive drum 1. In other words, the amount of moisture collected by the brush member 10 can be controlled by appropriately changing the number of consecutive image formations and the time of the subsequent non-image formation process, that is, the inter-sheet process or post-rotation process.

[0047] <Outline of how to set the time for the sheet-to-sheet process and post-rotation process> An outline of a method for setting the times of the sheet interval process and post-rotation process in this embodiment will be described.

[0048] In this embodiment, the control unit 150 determines the time of the second non-image forming process, which is the object of control, according to information on the usage history of the photosensitive drum 1 and information on the time of the first non-image forming process. In this embodiment, the information on the usage history of the photosensitive drum 1 is information on the "number of images formed on." Also, in this embodiment, the information on the time of the first non-image forming process is information on the "time of the inter-paper process between the first recording material (preceding paper) P and the subsequent second recording material (subsequent paper) P." Also, in this embodiment, the time of the second non-image forming process, which is the object of control, is "the time of the inter-paper process or post-rotation process, which is the non-image forming process immediately after the image forming process on the second recording material P."

[0049] Specifically, in this embodiment, a counter K is provided in the image forming apparatus 100. In this embodiment, as shown in FIG. 9A, a memory 152 is provided with a storage area (storage unit) for the counter K. The control unit 150 updates the value of the counter K based on information on the "number of images formed" as information on the usage history of the photosensitive drum 1 and information on the "inter-sheet step time" as information on the time of the first non-image forming step. For example, the control unit 150 increments the value of the counter K when a recording material P (first recording material P) is fed, thereby reflecting the information on the "number of images formed" as information on the usage history of the photosensitive drum 1. Next, the control unit 150 decrements the value of the counter K according to the time of the inter-sheet step immediately after the image forming step for that recording material P (first recording material P), thereby reflecting the information on the time of that inter-sheet step as the time of the first non-image forming step. Thereafter, the control unit 150 increments the value of the counter K again when the next recording material P (second recording material P) is fed. Then, the control section 150 determines the time of the sheet interval process or post-rotation process, which is the time of the second non-image forming process immediately after the image forming process on the second recording material P, according to the value of the counter K at that time.

[0050] In this embodiment, the value of counter K has the same meaning as the number of sheets of recording material P continuously transported in the normal inter-sheet process time (50 msec) without the post-rotation process or the time-changed inter-sheet process ("number of sheets of continuous image formation"). The larger the value of counter K, the more moisture has accumulated on the brush member 10, and the longer the drive (rotation) of the photosensitive drum 1 is required in the inter-sheet process or post-rotation process to evaporate the moisture accumulated on the brush member 10.

[0051] In this embodiment, the object to be controlled is the driving time of the photosensitive drum 1 in the inter-paper process or the post-rotation process, but this is not limited to this, and the object to be controlled may also be the number of rotations or rotation distance of the photosensitive drum 1 in the inter-paper process or the post-rotation process.

[0052] <Example of setting the time for the paper-to-paper process and post-rotation process> Next, a description will be given of an example of setting the times for the inter-sheet process and post-rotation process according to the value of counter K in this embodiment. Table 1 shows the relationship between the value of counter K and the times for the inter-sheet process and post-rotation process in this embodiment.

[0053] [Table 1]

[0054] First, the time required for the sheet spacing process will be described. In the configuration of this embodiment, if continuous image formation is performed on, for example, 30 sheets of recording material P that has been left in a humid environment and is in a highly moisture-absorbent state, around the 25th sheet, moisture accumulated on the brush member 10 will begin to flow locally onto the surface of the photosensitive drum 1, as shown in Figure 4(c). Then, in that area, a large amount of moisture will be adsorbed by the discharge products accumulated on the surface of the photosensitive drum 1, causing image deletion.

[0055] Therefore, in this embodiment, in order to prevent too much moisture from accumulating on the brush member 10, the following is done. The value of counter K is incremented by 1, for example, whenever a recording material P is supplied. Then, when the value of counter K reaches 5, the sheet interval process is extended and 5 is subtracted from the value of counter K. Note that in this embodiment, while image formation is being performed during the normal sheet interval process time, the value of counter K is decremented by 0 (i.e., no subtraction is made). As a result, the maximum number of sheets on which continuous image formation can be performed during the normal sheet interval process time is controlled to be 5, and a 30-second sheet interval process is performed every 5 sheets of continuous image formation.

[0056] That is, in this embodiment, for example, a job for forming images on 30 sheets is executed as follows. Note that "->" indicates the progression of operations. First, five consecutive images are formed, and the inter-sheet process time is extended to 30 seconds. Then, the following sequence is executed: five consecutive images are formed -> the inter-sheet process time is extended to 30 seconds -> five consecutive images are formed -> the inter-sheet process time is extended to 30 seconds -> five consecutive images are formed -> the inter-sheet process time is extended to 30 seconds -> five consecutive images are formed -> the inter-sheet process time is extended to 30 seconds -> five consecutive images are formed -> the inter-sheet process time is extended to 30 seconds -> five consecutive images are formed.

[0057] According to this embodiment, moisture adhering to the brush member 10 equivalent to the amount of moisture adhering to five consecutive sheets of image formation can be dried to almost zero by idling the photosensitive drum 1 for 30 seconds. Therefore, by such an operation, it is possible to maintain a state in which the brush member 10 does not have too much moisture, as shown in Figure 4(a) or 4(b), and it is possible to suppress the occurrence of image deletion.

[0058] Next, the time for the post-rotation process will be described. In this embodiment, the time for the post-rotation process is set so that the smaller the value of counter K, as shown in Table 1, the shorter the time for the post-rotation process. This is because, for example, when the post-rotation process is started when the final number of consecutive images formed is three, or when the job is originally a job with three consecutive images formed, the following can be said. In other words, in such a case, the value of counter K is 3 when the process is started. In this case, it is sufficient to perform idling of the photosensitive drum 1 only for the amount of moisture accumulated on the brush member 10 for the three consecutive images formed. In other words, in such a case, the post-rotation process can be completed in a shorter time than when the counter K value is 5 for the five consecutive images formed. In this embodiment, at the end of the job, the brush member 10 is substantially free of moisture accumulated during image formation, in preparation for the next job.

[0059] As described above, in this embodiment, the time for the next inter-sheet process or post-rotation process is determined based on the information on the "number of images formed" and the information on the "time for the inter-sheet process." According to this embodiment, it is possible to control the amount of moisture accumulated on the brush member 10 due to continuous image formation, and to prevent the moisture accumulated on the brush member 10 from overflowing. Therefore, according to this embodiment, it is possible to prevent image deletion caused by the adsorption of a large amount of moisture to the discharge products accumulated on the surface of the photosensitive drum 1.

[0060] The balance between the number of images formed on a sheet and the time for the inter-sheet step or post-rotation step varies depending on the pile length L1 of the brush member 10, the thickness of the pile yarns 11a, the density of the pile yarns 11a, etc. This is because the moisture retention capacity of the brush member 10 varies depending on the pile length L1 of the brush member 10, the thickness of the pile yarns 11a, the density of the pile yarns 11a, etc. In other words, this is because the number of consecutive images formed on a sheet before the moisture accumulated in the brush member 10 locally flows out onto the surface of the photosensitive drum 1 varies, and the speed at which the moisture retained in the brush member 10 is gradually expelled onto the photosensitive drum 1 and evaporates varies. Therefore, the relationship between the number of images formed on a sheet and the time for the inter-sheet step or post-rotation step can be changed as appropriate depending on the configuration of the brush member 10.

[0061] <Procedure for setting the time for the paper-to-paper process and post-rotation process> FIG. 6 is a flowchart showing an outline of the procedure of a job including the extension operations of the sheet interval process and post-rotation process in this embodiment.

[0062] S101: The control unit 150 acquires job information transmitted from an external device based on a user operation.

[0063] S102: The control unit 150 executes the image forming process.

[0064] S103: The control section 150 increments the value of the counter K by 1 at the timing when the recording material P is fed.

[0065] S104-S106: In S104, the control unit 150 determines whether the next image formation is the last image formation of the job, that is, whether the recording material P to be conveyed next is the last recording material P of the job (herein also referred to as "last sheet"). In S105, the control unit 150 determines whether the value of the counter K has reached 5 (matches 5). If the control unit 150 determines that it is the last sheet (Y in S104), it proceeds to a post-rotation step (S109). If the control unit 150 determines that it is not the last sheet (N in S104) and that the value of the counter K does not match 5 (is less than 5) (N in S105), it proceeds to the next image forming step (S102) via a normal sheet spacing step (S106). In this embodiment, the normal sheet spacing step takes 50 msec.

[0066] S107: If the control unit 150 determines in S105 that the value of the counter K is equal to 5 (Y in S105), it extends the inter-sheet process (S107). In this embodiment, the extended inter-sheet process time is 30 seconds (Table 1).

[0067] S108: After extending the inter-sheet step in S107, the control unit 150 resets the value of the counter K to 0, assuming that the moisture accumulated in the brush member 10 has become almost zero. This is because the moisture accumulated in the brush member 10 can be removed by being discharged little by little during the extension of the inter-sheet step in S107. After that, the control unit 150 transitions to the image forming step (S102) once the extension of the inter-sheet step is completed.

[0068] S109: If the control unit 150 determines in S104 that this is the last sheet (Y in S104), it executes the post-rotation process for a time period corresponding to the current value of the counter K according to Table 1. Furthermore, when the control unit 150 completes the post-rotation process, it resets the value of the counter K to 0, assuming that the moisture accumulated in the brush member 10 has become almost zero.

[0069] S110: When the post-rotation process is completed, the control unit 150 ends the job.

[0070] 6.Effects To confirm the effectiveness of this embodiment, an experiment was conducted to examine the occurrence of image deletion every 10 sheets when a job was executed using moisture-absorbed recording material P with 30 images formed. The experiment was conducted in an environment with a temperature of 15°C and humidity of 80% (low temperature and high humidity environment), where moisture is likely to accumulate on the brush member 10 and localized image deletion is likely to occur. The lower the temperature and the cooler the photosensitive drum 1, the more likely condensation occurs due to humidity in the environment and water vapor emitted from the recording material P after passing through the fixing device 9. As a result, more moisture adheres to the surface of the photosensitive drum 1, and moisture is also likely to accumulate on the brush member 10. Furthermore, in a humid environment, moisture absorption by the recording material P increases the amount of water vapor emitted from the recording material P after passing through the fixing device 9. The recording material P used in the experiment was Xerox Vitality Multipurpose paper, Letter size, with a basis weight of 75 g / m. 2 The paper was removed from its packaging and left in the above-mentioned environment of 15°C temperature and 80% humidity (low temperature and high humidity environment) for two days. The moisture content of this paper was measured using a Moistrex MX-8000 moisture meter manufactured by NDC Infrared Engineering and was found to be 9.2%. For comparison, the moisture content of this paper was measured immediately after opening and was found to be 5.7%.

[0071] Similar experiments were also conducted for Comparative Examples 1 to 4. Note that the evaluation was conducted with the photosensitive drum 1 in a state close to new. Comparative Example 1 is an example in which the brush member 10 is not provided and the inter-paper step is not extended. Comparative Example 2 is an example in which the brush member 10 is not provided and the inter-paper step is extended in the same manner as in this embodiment. Comparative Example 3 is an example in which the brush member 10 is not provided and the time for extending the inter-paper step ("extension time") is further increased. Comparative Example 4 is an example in which the same configuration as this embodiment (the brush member 10 is provided) is used and the inter-paper step is not extended. Note that the configuration and operation of the image forming apparatuses 100 in Comparative Examples 1 to 4 are substantially the same as those of the image forming apparatus 100 in this embodiment, except for the above points.

[0072] The results are shown in Table 2. In Table 2, "◯" indicates that no image deletion due to water vapor adhering to the surface of the photosensitive drum 1 occurred, "△" indicates that slight image deletion occurred, and "×" indicates that significant image deletion occurred.

[0073] [Table 2]

[0074] In Comparative Example 1, slight image deletion began to occur after continuous image formation of about 10 sheets. Furthermore, the level of image deletion worsened as the number of images formed increased. This is because, without the brush member 10, water vapor adhering to the surface of the photosensitive drum 1 accumulates without being removed from the surface of the photosensitive drum 1, and this moisture significantly reduces the surface resistance of the photosensitive drum 1.

[0075] In Comparative Example 2, slight image deletion occurred on the 20th image-formed sheet. This shows that in a configuration in which the brush member 10 is not installed, the time required for the inter-sheet step of 30 seconds is insufficient to dry the moisture equivalent to five consecutive image-formed sheets.

[0076] In Comparative Example 3, by setting the time for the sheet interval process to 90 seconds, image deletion was suppressed up to the 20th image formed sheet, but slight image deletion occurred on the 30th image formed sheet. This is thought to be because, in a configuration in which the brush member 10 is not installed, moisture accumulated on the surface of the photosensitive drum 1 exists in the form of a thick layer on the photosensitive drum 1, as shown in FIG. 8. In this state, the specific surface area of ​​the moisture in contact with the surrounding air is small compared to the amount of moisture present on the surface of the photosensitive drum 1, and it tends to take a long time to dry.

[0077] In Comparative Example 4, image deletion did not occur up to the 20th sheet of image formation due to the effect of the brush member 10 to collect water vapor adhering to the surface of the photosensitive drum 1. However, because continuous image formation was continued without extending the inter-sheet process, from about the 25th sheet of image formation, the amount of moisture accumulated in the brush member 10 became too large, causing localized areas where moisture began to flow out from the brush member 10, and image deletion began in those areas.

[0078] In this example, the brush member 10 was installed, and image deletion was suppressed by extending the inter-sheet interval. In contrast to Comparative Examples 2 and 3, this example was able to dry and reset the moisture captured by the brush member 10 equivalent to five consecutive image formation sheets to nearly zero within the 30-second inter-sheet interval. This is believed to be because, as shown in FIG. 5 , the moisture captured by the brush member 10 was gradually released onto the surface of the photosensitive drum 1 during the inter-sheet interval, thereby increasing the specific surface area of ​​the moisture on the surface of the photosensitive drum 1 that comes into contact with the surrounding air. This is believed to be because the moisture evaporated faster than the moisture present in a thick layer on the photosensitive drum 1 in the configurations of Comparative Examples 2 and 3, as shown in FIG. 8 . Furthermore, in this example, compared to Comparative Example 4, excessive moisture accumulation on the brush member 10 was suppressed, thereby suppressing localized image deletion due to moisture flowing locally onto the surface of the photosensitive drum 1. This was achieved by limiting the number of consecutive image formation sheets to five and extending the inter-sheet interval.

[0079] Although the effect of extending the inter-sheet process has been explained here, in this embodiment, the post-rotation process after the image forming process for the 30th sheet is also extended to 30 seconds according to Table 1. As a result, even if the next job is executed immediately after the current job, the occurrence of image deletion can be suppressed by the same effect as that described above.

[0080] As described above, in this embodiment, the image forming apparatus 100 includes a rotatable photoreceptor 1, a charging member 2 that charges the surface of the photoreceptor 1 at a charging portion Pa, a developing device 3 that supplies toner to the surface of the photoreceptor 1 after charging to form a toner image, a transfer member 5 that transfers the toner image from the photoreceptor 1 to a recording material P at a transfer portion Pd, a brush member 10 that contacts the surface of the photoreceptor 1 downstream of the transfer portion Pd and upstream of the charging portion Pa in the rotation direction of the photoreceptor 1 to form a contact portion Pe, a drive source 110 that drives the photoreceptor 1 to rotate, and an image forming device that forms an image on the recording material P by controlling the drive source 110. The control unit 150 controls the image forming process and a non-image forming process other than the image forming process, which is carried out so that the photosensitive member 1 is driven to rotate. If the non-image forming process between the first recording material P and the second recording material P on which an image is formed after the first recording material P is defined as the first non-image forming process, and the non-image forming process between the second recording material P and the third recording material P on which an image is formed after the second recording material P is defined as the second non-image forming process, the control unit 150 determines the time for the second non-image forming process based on history information correlated with the usage amount of the photosensitive member 1 and the time for the first non-image forming process. In addition, in this embodiment, the control unit 150 controls the drive source 110 to be able to execute an image formation process in which an image is formed on the recording material P, a non-image formation process which is a process other than the image formation process and in which the photosensitive member 1 is driven to rotate, and a post-rotation process in which the photosensitive member 1 is rotated after the recording material P without executing the image formation process.If the non-image formation process between the first recording material P and the second recording material P on which an image is formed after the first recording material P is defined as the first non-image formation process, the control unit 150 determines the time for the post-rotation process to be executed after the second recording material P based on historical information correlated with the usage amount of the photosensitive member 1 and the time of the first non-image formation process.

[0081] In this embodiment, the control unit 150 determines the time for the second non-image forming process according to a value that is added according to the number of sheets of recording material P on which image formation has been performed and that is controlled to be subtracted when the driving operation of the photosensitive drum 1 is performed in the non-image forming process. Here, as will be described later, when performing continuous image formation in which images are continuously formed on a plurality of first recording materials with the time for the first non-image forming process being a predetermined time, and then performing image formation on a second recording material, the control unit 150 can control the time for the second non-image forming process to be shorter when the time for the continuous image formation is a second time that is shorter than the first time than when the time for the continuous image formation is a first time. In this embodiment, the control unit 150 determines the time for the post-rotation process to be performed after the second recording material P according to a value that is added according to the number of sheets of recording material P on which image formation has been performed and that is controlled to be subtracted when the driving operation of the photosensitive drum 1 is performed in the non-image forming process. Here, when continuous image formation is performed in which images are formed continuously on a plurality of first recording materials P with the time of the first non-image forming process being a predetermined time, and a post-rotation process is performed after image formation on a second recording material P, the control unit 150 can control so that the time of the post-rotation process performed after the second recording material P is shorter when the time for which the continuous image formation is performed is a second time that is shorter than the first time than when the time for which the continuous image formation is performed is a first time. Also, in this embodiment, toner remaining on the surface of the photoreceptor 1 after the toner image is transferred from the photoreceptor 1 to the recording material P is removed and collected from the surface of the photoreceptor 1 by the developing device 3.

[0082] As described above, according to this embodiment, it is possible to control the amount of moisture accumulated on the brush member 10 due to continuous image formation, and to prevent the moisture accumulated on the brush member 10 from overflowing. Therefore, according to this embodiment, it is possible to prevent image deletion caused by adsorption of a large amount of moisture and discharge products accumulated on the surface of the photosensitive drum 1, and to form stable images.

[0083] 7. Variations In this embodiment, the image forming apparatus 100 employs a DC charging method, but the present invention can also be applied to an image forming apparatus employing an AC charging method that uses an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed as a charging voltage.

[0084] Furthermore, in this embodiment, only the DC component of the developing voltage has been described, but the developing voltage may be an oscillating voltage in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed.

[0085] In addition, in this embodiment, toner, which is a non-magnetic one-component developer, is used as the developer, but a magnetic one-component developer may also be used.

[0086] Furthermore, in this embodiment, only the brush member 10 is used as the cleaning means for the photosensitive drum 1, but the present invention is not limited to this configuration. For example, a cleaning blade may be disposed as the cleaning means downstream of the brush member 10 in the rotation direction of the photosensitive drum 1 and upstream of the charging roller 2. In this way, the present invention can also be applied to a "blade cleaning type" image forming apparatus that uses a cleaning blade in addition to the brush member 10.

[0087] The brush member 10 may be connected to a brush power supply (high-voltage power supply) E4 (FIG. 3) as a brush voltage application unit (brush voltage application section). A predetermined brush voltage (brush bias), which is a negative DC voltage, may be applied to the brush member 10 during the image formation process (during the cleaning process of the photosensitive drum 1). The brush voltage is, for example, -300 V. The brush voltage may also be applied to the brush member 10 during non-image formation processes (such as the inter-sheet process). Residual toner remaining on the surface of the photosensitive drum 1 without being transferred to the recording material P is sent to the brush member 10, which is located downstream of the transfer roller 5 in the rotation direction of the photosensitive drum 1. Setting the brush voltage as described above allows toner charged negatively, which is the normal charge polarity and is often contained in the residual toner, to pass through the brush contact area Pe without adhering to the brush member 10, relative to the potential of the image area of ​​the photosensitive drum 1. This prevents excessive toner accumulation on the brush member 10. The brush member 10 also receives paper dust that has adhered to the surface of the photosensitive drum 1 at the transfer portion Pd. By setting the brush voltage as described above, it is possible to collect paper dust that is positively charged and that has adhered to the negatively charged surface of the photosensitive drum 1 at the transfer portion Pd. Paper dust is fibrous foreign matter derived from paper, and is generally pulp fibers, primarily composed of cellulose, that have peeled off from the paper, and may also contain fillers that have peeled off from the paper.

[0088] Furthermore, in this embodiment, a pre-exposure unit may be provided that exposes the surface of the photosensitive drum 1 downstream of the transfer portion Pd and upstream of the charging portion Pa in the rotation direction of the photosensitive drum 1. The pre-exposure unit may be provided upstream or downstream of a contact portion Pe between the brush member 10 and the photosensitive drum 1. When the pre-exposure unit is provided upstream of the contact portion Pe, the surface potential of the photosensitive drum 1 may be controlled by the pre-exposure unit.

[0089] Furthermore, in this embodiment, the maximum number of sheets that can be continuously imaged and the extended time for the non-image forming process are constant, but the present invention is not limited to this configuration. For example, the maximum number of sheets that can be continuously imaged and the time for the non-image forming process may be variable so that the extended time for the non-image forming process immediately after the continuous image formation is shorter as the number of sheets that can be continuously imaged decreases. In this embodiment, the control always extends the time for the inter-sheet process after five consecutive images are formed in preparation for the case of forming images on 30 or more sheets. This may be excessive for users who often perform jobs with an image formation count of 20 or fewer sheets. However, with the configuration of this embodiment, as can be seen from the results of Comparative Example 4 in Table 2, image deletion does not occur when continuous image formation is performed on approximately 20 sheets. Therefore, for example, a job with an image formation count of 30 sheets may be performed as follows.

[0090] In the configuration of this embodiment, when continuous image formation is performed on up to 20 sheets, the rotation time of the photosensitive drum 1 required to evaporate the moisture accumulated on the brush member 10 is as shown in Table 3.

[0091] [Table 3]

[0092] Therefore, continuous image formation is performed on up to 20 sheets, and the time for the inter-sheet process immediately thereafter is extended to 60 seconds, which is required to evaporate the moisture accumulated on the brush member 10 for 20 sheets. After that, continuous image formation can be performed on the remaining 10 sheets, and the post-rotation extension can be extended by 40 seconds.

[0093] Furthermore, if a 60-second inter-sheet interval extension is deemed too long, the time for the inter-sheet interval process immediately after forming 20 consecutive images can be extended to 45 seconds. In this case, because the moisture accumulated in the brush was not completely evaporated even after the inter-sheet interval extension, slight image deletion occurred on the eighth and subsequent sheets when forming 20 consecutive images. Therefore, in this case, after the 45-second inter-sheet interval extension, seven consecutive images are formed, and the time for the inter-sheet interval process immediately after is extended to, for example, 35 seconds. Finally, the remaining three consecutive images are formed, and the time for the post-rotation process is extended to 20 seconds. In this manner, it is sufficient to balance the number of consecutive images formed and the extended inter-sheet interval and post-rotation times so that the moisture accumulation on the brush member 10 does not become too great. This control can be performed by using a counter, as in this embodiment. Alternatively, the number of consecutive images formed from the start of a job and the extended inter-sheet interval or post-rotation time at which image deletion does not occur can be determined in advance based on experimental results under strict conditions, and the operation can be controlled accordingly. This prevents moisture accumulated on the brush member 10 from flowing locally onto the surface of the photosensitive drum 1, thereby preventing image deletion. Furthermore, for example, a job with 50 images may be performed as follows: After 20 consecutive images are formed, the time for the inter-sheet step is extended to 45 seconds. After seven consecutive images are formed, the time for the inter-sheet step is extended to 35 seconds. After three consecutive images are formed, the time for the inter-sheet step is extended to 20 seconds. If the moisture accumulated on the brush member 10 is almost zero at this point, 20 consecutive images are formed again. Finally, the time for the post-rotation step is extended to 60 seconds, so that the moisture accumulated on the brush member 10 during image formation is reset to almost zero before the job is completed. This operation improves usability (improves productivity).

[0094] Furthermore, in this embodiment, the extension of the post-rotation step is configured to reduce moisture accumulated on the brush member 10 during continuous image formation to almost zero, but the present invention is not limited to this configuration. It is sufficient if moisture accumulated on the brush member 10 can be removed before the next job begins. For example, even if the number of continuous image formation sheets is large and the extension of the post-rotation step is not sufficient to remove all moisture accumulated on the brush member 10, the moisture may be removed by extending the pre-rotation step of the next job. It is also possible that moisture accumulated on the brush member 10 evaporates due to natural drying. Therefore, for example, when starting a job, the extension times of the pre-rotation step and post-rotation step may be shortened depending on the time elapsed since the previous job.

[0095] Furthermore, the parameter used to increment the value of the counter K is not limited to that used in this embodiment. This parameter may be any parameter that correlates with the phenomenon of moisture accumulation on the brush member 10. For example, this parameter may be the number of consecutive images formed during a normal sheet-to-sheet interval, or the cumulative time of the image formation process when consecutive images are formed during a normal sheet-to-sheet interval. Image deletion is a phenomenon caused by water vapor generated when the recording material P passes through the fixing device 9. Therefore, this parameter may be, for example, the cumulative time the recording material P passes through the fixing device 9 when consecutive images are formed during a normal sheet-to-sheet interval. As mentioned above, in addition to the number of sheets and time, the number of rotations, the rotation distance, etc. may also be used.

[0096] Furthermore, the parameter used to subtract the value of the counter K is not limited to that used in this embodiment. This parameter may be any parameter that correlates with the phenomenon in which moisture accumulated on the brush member 10 dries while being gradually expelled onto the surface of the photosensitive drum 1. This parameter may be, for example, the time during which the photosensitive drum 1 is driven (rotated) outside of the image forming process, i.e., the time during the non-image forming process, or the time during which the recording material P is not passing through the fixing device 9 and the photosensitive drum 1 is driven (rotated). As described above, the number of rotations or the rotation distance may be used in addition to the number of sheets or the time.

[0097] In this embodiment, the counter K value is updated at the timing shown in the flowchart of FIG. 6 , but the present invention is not limited to this configuration. For example, the counter K value may be updated every 100 msec, with an increment during the image formation process and a decrement during the non-image formation process. Furthermore, the decrement value may be changed depending on whether the non-image formation process is a sheet-interval process or a post-rotation process. Furthermore, the value added to or subtracted from the counter K value may be adjusted based on information such as the attenuation status of the surface potential of the photosensitive drum 1, temperature and humidity changes within the image forming apparatus 100, the operating environment of the image forming apparatus 100, the moisture absorption and size of the recording material P used, and temperature changes in the fixing device 9.

[0098] In this embodiment, the required extension time for the sheet interval process and the post-rotation process is set by calculating in advance the extension time that may be required depending on the number of sheets of continuous image formation, but the present invention is not limited to this. For example, the required extension time may be predicted based on information such as the attenuation state of the surface potential of the photosensitive drum 1, the temperature and humidity changes inside the image forming apparatus 100, the usage environment of the image forming apparatus 100, the moisture absorption and size of the recording material P used, and the temperature change of the fixing device 9.

[0099] Furthermore, in this embodiment, the required times for the sheet spacing process and post-rotation process are stored in memory 152 as a table as shown in Table 1, but the present invention is not limited to this configuration. For example, the values ​​stored in the table may be only the extension times ("extension times") of the normal sheet spacing process time and normal post-rotation process time. Also, for example, the values ​​stored in the table may be the ratios of the extension times of the normal sheet spacing process time and normal post-rotation process time. Also, without preparing a table, a configuration may be adopted in which coefficients according to the number of images formed and downtime are stored, and the times (or extension times) for the sheet spacing process and post-rotation process are calculated each time they are needed.

[0100] In other words, the image forming apparatus 100 of this embodiment has a control unit 150 that controls the non-image formation time, which is the time during which the photosensitive member 1 rotates between the time when the preceding recording material P passes the transfer unit Pd and the time when the next recording material P arrives at the transfer unit Pd, and the control unit 150 is capable of controlling the non-image formation time, which is the time during which the photosensitive member 1 rotates between the time when the preceding recording material P passes the transfer unit Pd and the time when the next recording material P arrives at the transfer unit Pd without the rotation of the photosensitive member 1 stopping, to be a predetermined inter-image time, so as to change the non-image formation time between the time when the last recording material P passes the transfer unit Pd and the time when the next recording material P after the last recording material P arrives at the transfer unit Pd in ​​continuous image formation in which toner images are transferred successively to multiple recording materials P, based on historical information that correlates with the usage amount of the photosensitive member 1 during the continuous image formation.

[0101] [Example 2] Next, another embodiment of the present invention will be described. This embodiment will be described with the configuration in which the maximum number of sheets for continuous image formation is 20, as described in the section "7. Modifications" of the first embodiment. The basic configuration and operation of the image forming apparatus are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of the first embodiment are assigned the same reference numerals as those of the first embodiment, and detailed description thereof will be omitted.

[0102] 1. Overview of this Example In this embodiment, as in the first embodiment, the inter-sheet step is extended to remove moisture accumulated on the brush member 10. In addition, in this embodiment, the moving speed (conveying speed) of the recording material P is made faster than the moving speed (circumferential speed) of the surface of the photosensitive drum 1, so that the recording material P rubs against the surface of the photosensitive drum 1, thereby removing discharge products from the surface of the photosensitive drum 1.

[0103] Image deletion occurs due to discharge products that accumulate on the surface of the photosensitive drum 1 due to discharges occurring between the charging roller 2 and the photosensitive drum 1, and water vapor generated when the moisture-absorbed recording material P passes through the fixing device 9. In other words, image deletion occurs because the surface resistance of the photosensitive drum 1 is significantly reduced as the discharge products adsorb the water vapor. As the total number of images formed on the photosensitive drum 1 (image forming apparatus 100) increases, more discharge products accumulate on the surface of the photosensitive drum 1, making image deletion more likely even with a small amount of moisture. For example, in the configuration of this embodiment, image deletion begins to occur with a new photosensitive drum 1 after approximately 25 consecutive images. However, in the configuration of this embodiment, image deletion begins to occur with a photosensitive drum 1 that has been used to form images on more than 10,000 sheets, even after approximately 15 consecutive images. This is thought to be due to the following reason. In other words, a photosensitive drum 1 that has been used to form images on more than 10,000 sheets has a large amount of discharge products accumulated on its surface. Therefore, in this state, even the moisture that the brush member 10 expels little by little onto the surface of the photosensitive drum 1 reduces the surface resistance of the photosensitive drum 1 as shown in FIG. 4(b).

[0104] Therefore, in this embodiment, the time of the paper interval process as the time of the second non-image forming process is extended not only to remove moisture from the brush member 10 but also to reduce the amount of discharge products accumulated on the surface of the photosensitive drum 1.

[0105] In this embodiment, the image forming apparatus 100 has a single motor configuration, and both the photosensitive drum 1 and the pressure roller 23 of the fixing device 9 are driven by a single drive motor (main motor) 110. Furthermore, in this embodiment, the drive speeds (rotational speeds of the rotation shafts) of the photosensitive drum 1 and the pressure roller 23 driven by the drive motor 110 are substantially constant during the image forming process. Therefore, in this embodiment, when the pressure roller 23 thermally expands and its outer diameter increases, increasing the circumferential speed, the conveyance speed of the recording material P by the pressure roller 23 changes, and the movement speed of the recording material P changes relative to the movement speed of the surface of the photosensitive drum 1.

[0106] In this embodiment, the thermal expansion of the pressure roller 23 is accelerated by extending the time of the sheet interval process, and the difference between the moving speed of the recording material P and the moving speed of the surface of the photosensitive drum 1 is increased, so that the surface of the photosensitive drum 1 is rubbed by the recording material P. This rubbing by the recording material P can reduce the amount of discharge products that have accumulated on the surface of the photosensitive drum 1.

[0107] In this way, in this embodiment, in addition to removing moisture from the brush member 10 as described in the first embodiment, discharge products accumulated on the surface of the photosensitive drum 1 are also removed. As a result, in this embodiment, it is possible to suppress the occurrence of image deletion throughout the life of the photosensitive drum 1. This will be explained in more detail below.

[0108] 2. Relative movement speed of the recording material with respect to the photosensitive drum In this embodiment, the conveyance speed of the recording material P by the pressure roller 23 is set to be equal to or slower than the movement speed of the surface of the photosensitive drum 1, for example, in a job in which only a few images are formed from a cold state. This is to minimize the difference between the movement speed of the surface of the photosensitive drum 1 and the movement speed of the recording material P, taking into account the life of the photosensitive drum 1, so as to prevent excessive wear of the surface of the photosensitive drum 1. Note that the cold state refers to a state in which the image forming apparatus 100 is left unattended and the atmosphere inside the apparatus main body 101 has not yet risen in temperature. However, if the conveyance speed of the recording material P by the pressure roller 23 is set too slow relative to the movement speed of the surface of the photosensitive drum 1, the loop formed between the transfer nip Nt and the fixing nip Nf may become too large, resulting in unstable conveyance of the recording material P. In view of the above, it is preferable that the conveyance speed of the recording material P by the pressure roller 23 is set to vary between −2% (the conveyance speed of the recording material P is slower) and 1.5% (the conveyance speed of the recording material P is faster) of the moving speed of the surface of the photosensitive drum 1. In this embodiment, when continuous image formation is performed from a cold state up to 20 sheets, the conveyance speed of the recording material P by the pressure roller 23 is set to vary between −0.2% and −0.1% of the moving speed of the surface of the photosensitive drum 1. Furthermore, when continuous image formation is performed, for example, when 100 sheets or more are formed, the conveyance speed of the recording material P by the pressure roller 23 becomes saturated when the conveyance speed of the recording material P is about 0.2% faster than the moving speed of the surface of the photosensitive drum 1. During continuous image formation, the recording material P continuously absorbs heat from the pressure roller 23, so the thermal expansion of the pressure roller 23 becomes saturated, and the conveyance speed of the recording material P by the pressure roller 23 does not increase any further.

[0109] After entering the transfer nip Nt, the recording material P is transported by the photosensitive drum 1 until it enters the fixing nip Nf, so the moving speed of the surface of the photosensitive drum 1 and the moving speed of the recording material P are the same. Next, when the recording material P enters the fixing nip Nf, if the conveying speed of the recording material P by the pressure roller 23 is slower than the conveying speed of the recording material P by the photosensitive drum 1, the recording material P is conveyed while forming a loop between the transfer nip Nt and the fixing nip Nf. Therefore, the moving speed of the surface of the photosensitive drum 1 and the moving speed of the recording material P are the same. On the other hand, if the conveying speed of the recording material P by the pressure roller 23 is faster than the conveying speed of the recording material P by the photosensitive drum 1, the moving speed of the recording material P follows the conveying speed of the recording material P by the pressure roller 23. In other words, the moving speed of the recording material P is faster than the moving speed of the surface of the photosensitive drum 1, and a difference occurs between the moving speed of the surface of the photosensitive drum 1 and the moving speed of the recording material P.

[0110] 3.Extending the inter-sheet process In this embodiment, when the photosensitive drum 1 and other components are idly rotated at a controlled temperature of 120°C in the fixing device 9 in the case where the sheet interval process is extended, the conveying speed of the recording material P by the pressure roller 23 increases to about 0.6% of the moving speed of the surface of the photosensitive drum 1. Due to the difference between this moving speed of the recording material P and the moving speed of the surface of the photosensitive drum 1, the recording material P rubs against the surface of the photosensitive drum 1, and discharge products accumulated on the surface of the photosensitive drum 1 can be removed.

[0111] In this way, by removing the discharge products accumulated on the surface of the photosensitive drum 1, it is possible to prevent a situation in which image deletion is likely to occur even with a small amount of moisture as the total number of images formed on the photosensitive drum 1 (image forming apparatus 100) increases. This makes it possible to prevent image deletion from occurring throughout the life of the photosensitive drum 1.

[0112] Specifically, in this embodiment, the image forming apparatus 100 is provided with a counter K that indicates the amount of moisture accumulated in the brush member 10, similar to that in the first embodiment, and a counter M that indicates the amount of discharge products accumulated on the surface of the photosensitive drum 1. In this embodiment, as shown in Fig. 9(b), the memory 152 is provided with a storage area (storage unit) for the counter K and a storage area (storage unit) for the counter M.

[0113] Table 4 shows the relationship between the value of counter K and the time for the sheet interval process in this embodiment. Table 4 also shows the relationship between the value of counter K and the time for the post-rotation process in this embodiment. The time for the post-rotation process will be described in detail later.

[0114] [Table 4]

[0115] First, the counter K will be described. As in the first embodiment, the value of the counter K indicates the amount of moisture accumulated in the brush member 10. The larger the counter K value, the greater the amount of moisture accumulated in the brush member 10. In this embodiment, to prevent excessive moisture from accumulating in the brush member 10, the larger the counter K value, the longer the time for the inter-sheet step is extended, thereby removing moisture accumulated in the brush member 10. In this embodiment, for simplicity, the value of the counter K is reset to 0 after the inter-sheet step time extension is performed under the conditions in Table 4. In the first embodiment, it was explained that the inter-sheet extension time required after forming 20 consecutive images is 60 seconds, and that 45 seconds is not enough to completely remove moisture accumulated in the brush member 10. Therefore, it can be said that the value of the counter K should not be reset to 0. However, in this embodiment, the inter-sheet step is extended more frequently by the counter M described below than in the first embodiment, so there is no problem with resetting the counter K. It should be noted that the counter K may reflect the 15 seconds that is the shortfall from the inter-sheet extension time of 60 seconds that is actually required after forming 20 consecutive images. For example, after the paper interval extending step of 45 seconds, the counter K is set to 3-4.

[0116] In the configuration of this embodiment, when continuous image formation is performed on, for example, 30 sheets of recording material P that has been left in a humid environment and is in a highly moisture-absorbent state, around the 25th sheet, the moisture accumulated on the brush member 10 begins to flow locally onto the surface of the photosensitive drum 1, as shown in Figure 4(c). Then, in that area, a large amount of moisture is adsorbed by the discharge products accumulated on the surface of the photosensitive drum 1, causing image deletion.

[0117] Therefore, in this embodiment, the following is done to prevent excessive moisture accumulation on the brush member 10. For example, the value of counter K is incremented by one each time a recording material P is supplied. When the value of counter K reaches 20, the sheet interval process is extended, and then the value of counter K is reset to 0. This controls the maximum number of consecutive images formed during the normal sheet interval process time to 20, and extends the time for the sheet interval process immediately after the image forming process for the 20th consecutive image formed sheet. As a result, excessive moisture accumulation on the brush member 10 is prevented, and the moisture accumulated on the brush member 10 is prevented from locally overflowing onto the surface of the photosensitive drum 1, thereby preventing localized image deletion. In this embodiment, the time for the sheet interval process after consecutive image formation of 20 sheets is set to 45 seconds.

[0118] Next, we will explain counter M. The value of counter M represents the amount of discharge products accumulated on the surface of the photosensitive drum 1. The larger the value of counter M, the greater the amount of discharge products accumulated on the photosensitive drum 1. The amount of discharge products accumulated on the surface of the photosensitive drum 1 gradually increases while the photosensitive drum 1 is being charged by the charging roller 2, i.e., during the image formation process. Therefore, the amount of discharge products accumulated on the surface of the photosensitive drum 1 correlates with the time of each image formation process, such as the time for applying the charging voltage to the photosensitive drum 1 and the exposure time, and the number of images formed. In this embodiment, the value of counter M is incremented, for example, when the recording material P is fed. On the other hand, the discharge products accumulated on the surface of the photosensitive drum 1 can be largely removed by image formation immediately after the inter-sheet interval is extended. This is because, as described above, when the inter-sheet interval is extended and the conveying speed of the recording material P by the pressure roller 23 becomes faster than the moving speed of the surface of the photosensitive drum 1, the recording material P rubs against the surface of the photosensitive drum 1, removing the discharge products accumulated on the surface of the photosensitive drum 1. Therefore, in this embodiment, the value of counter M is decremented when the image forming process is performed after the inter-sheet step is extended. In other words, the value of counter M can be decremented when the inter-sheet step is extended. On the other hand, as will be described later, when the post-rotation step is extended, there is no step in which the recording material P rubs against the photosensitive drum 1, and discharge products on the surface of the photosensitive drum 1 cannot be removed, so the value of counter M cannot be decremented. In this way, the conditions under which counter M can decrement its value are different from those of counter K. The post-rotation step is not a control target for counter M.

[0119] In the configuration of this embodiment, as described above, when continuous image formation is performed on, for example, 20 sheets using a recording material P that has been left in a humid environment and is in a highly moisture-absorbent state, image deletion does not occur in the case of a brand new photosensitive drum 1. However, in the case of a photosensitive drum 1 that has been used to form images on 10,000 sheets or more and has a large amount of discharge products accumulated on its surface, even a small amount of moisture that the brush member 10 gradually expels onto the surface of the photosensitive drum 1, as shown in Figure 4(b), reduces the surface resistance of the photosensitive drum 1. Then, image deletion begins to occur even in continuous image formation on about 15 sheets.

[0120] In this embodiment, to prevent too much discharge product from accumulating on the surface of the photosensitive drum 1, a sheet interval step of 20 seconds or more is periodically performed after each image is formed. The sheet interval step of 20 seconds or more allows the outer diameter of the pressure roller 23 to thermally expand, and the recording material P, which moves approximately 0.6% faster than the moving speed of the surface of the photosensitive drum 1, can rub against the surface of the photosensitive drum 1 to remove the discharge product.

[0121] In this embodiment, the process of performing the sheet interval process of 20 seconds or more every time an image is formed on one sheet is called a "discharge product removal mode," and is performed as follows.

[0122] The value of counter M is incremented by 1, for example, when a recording material P is supplied, and when the value of counter M reaches 26, the sheet interval process is extended after the image formation process for each image formed on one sheet. At this time, the value of counter M is decremented by 4 for each image formed on one sheet and each extension of the sheet interval process to 20 seconds or more. This is repeated until counter M reaches 0. When the value of counter M reaches 0, it indicates that the discharge products on the surface of the photosensitive drum 1 have been sufficiently removed.

[0123] In addition, when the sheet interval process is in the range of 20 seconds or more, the amount of thermal expansion of the pressure roller 23 is saturated, and the ability of the recording material P to remove discharge products from the surface of the photosensitive drum 1 is approximately constant. Therefore, when the sheet interval process is extended to 20 seconds or more, the value of the counter M is uniformly decremented by 4 regardless of the length of the sheet interval time.

[0124] In this embodiment, during the discharge product removal mode, the time for the inter-paper step is uniformly extended to 20 seconds. Note that this extension of the inter-paper step may also be intended to remove moisture accumulated on the brush member 10, and the value of the counter K may also be decreased.

[0125] In the discharge product removal mode, when the values ​​of counter K and counter M reach 0, it can be determined that the moisture accumulated on the brush member 10 and the discharge products on the surface of the photosensitive drum 1 have been almost completely removed, and the extension of the inter-sheet step after each image forming step is canceled, making it possible to form continuous images within the normal inter-sheet step time (50 msec). In other words, the object of control of counter M is the time of the second non-image forming step excluding the post-rotation step performed after the second recording material P, i.e., "the time of the inter-sheet step performed after the second recording material P." In addition, the "number of times the time of the second non-image forming step is extended" is also controlled by counter M.

[0126] That is, in this embodiment, a job for forming images on 50 sheets is executed as follows: Note that "->" indicates the progress of the operation. Continuous image formation of 20 sheets (counter K is 20, counter M is 20) ⇒ As counter K reaches 20, the paper gap is extended to 45 seconds (counter K is 0, counter M is 16) ⇒ Continuous image formation of 10 sheets (counter K is 10, counter M is 26) ⇒ As counter M reaches 26, the paper gap is extended to 35 seconds and the printer enters discharge product removal mode (counter K is 0, counter M is 22) ⇒ Image formation of 1 sheet (as the printer is in discharge product removal mode, the paper gap is extended for each sheet) (counter K is 1, counter M is 23) ⇒ Paper gap is extended to 20 seconds (counter K is 0, counter M is 19) ⇒ Image formation of 1 sheet (counter K is 1, counter M is 20) ⇒ Paper gap is extended to 20 seconds (counter K is 0, counter M is 16) ⇒ Image formation of 1 sheet (counter K is 1, counter M is 17) ⇒ Paper gap is extended to 20 seconds (counter K is 0, counter M is Counter K is 1, counter M is 13) ⇒ Formation of one image (counter K is 1, counter M is 14) ⇒ Inter-page interval extended to 20 seconds (counter K is 0, counter M is 10) ⇒ Formation of one image (counter K is 1, counter M is 11) ⇒ Inter-page interval extended to 20 seconds (counter K is 0, counter M is 7) ⇒ Formation of one image (counter K is 1, counter M is 8) ⇒ Inter-page interval extended to 20 seconds (counter K is 0, counter M is 4) ⇒ Formation of one image (counter K is 1, counter M is 5) ⇒ Inter-page interval extended to 20 seconds (counter K is 0, counter M is 1) ⇒ Formation of one image (counter K is 1, counter M is 2) ⇒ Inter-page interval extended to 20 seconds (counter K is 0, counter M is 0) ⇒ Counter M has reached 0, so the discharge product removal mode is canceled ⇒ Formation of 12 consecutive images (counter K is 12, counter M is 12).

[0127] In this embodiment, counter K controls the amount of moisture accumulated on the brush member 10 so that it does not become too large, and counter M controls the amount of discharge products accumulated on the surface of the photosensitive drum 1 so that it does not become too large. When the value of counter M becomes large, it is determined that the amount of discharge products has increased, and a discharge product removal mode is activated, in which the sheet interval process is frequently extended to promote thermal expansion of the pressure roller 23. This makes the moving speed of the recording material P faster than the moving speed of the surface of the photosensitive drum 1, so that the recording material P can remove the discharge products from the surface of the photosensitive drum 1. Therefore, in this embodiment, it is possible to keep the amount of discharge products on the surface of the photosensitive drum 1 from becoming too large throughout the life of the photosensitive drum 1, and it is possible to suppress image deletion throughout the life of the photosensitive drum 1.

[0128] In this embodiment, the inter-sheet step is extended for each image forming process in the discharge product removal mode, but the present invention is not limited to this configuration. In this embodiment, it is sufficient if the recording material P can remove discharge products from the surface of the photosensitive drum 1 by utilizing the thermal expansion of the pressure roller 23. For example, the inter-sheet step may be extended for every two images formed. In this case, the amount of subtraction from the value of counter M can be set as follows. That is, the amount of discharge products that can be removed during the image forming process for the second sheet after the inter-sheet step extension is considered to be smaller than the amount of discharge products that can be removed during the image forming process for the first sheet after the inter-sheet step extension, because the temperature of the pressure roller 23 drops. Therefore, the amount of subtraction from the value of counter M during the image forming process for the second sheet may be adjusted to be smaller than the amount of subtraction from the value of counter M during the image forming process for the first sheet.

[0129] In this embodiment, the time for the sheet-to-sheet step in the discharge product removal mode is limited to 20 seconds or more. This is because the image formation process is performed after the moving speed of the recording material P is approximately 0.6% faster than the moving speed of the surface of the photosensitive drum 1, and therefore the time for the sheet-to-sheet step is limited to a time that allows the thermal expansion of the pressure roller 23 to be saturated. However, the present invention is not limited to this configuration. In this embodiment, it is sufficient that the moving speed of the recording material P is faster than the moving speed of the surface of the photosensitive drum 1 due to the thermal expansion of the pressure roller 23. For example, the time for the sheet-to-sheet step in the discharge product removal mode may be 10 seconds. In this case, the subtraction amount from the value of counter M can be set as follows. That is, it is considered that the ability to remove discharge products during the image formation process for the first sheet when the sheet-to-sheet step time is 10 seconds is lower than when the sheet-to-sheet step time is 20 seconds or more. Therefore, the subtraction amount when the sheet-to-sheet step time is 10 seconds may be adjusted to be smaller than the subtraction amount when the sheet-to-sheet step time is 20 seconds or more.

[0130] 4.Extended operation of post-rotation process In this embodiment, the time for the post-rotation process is set according to the value of the counter K, which indicates the amount of moisture accumulated in the brush member 10, as in the first embodiment. Table 4 above shows the relationship between the value of the counter K and the time for the post-rotation process in this embodiment.

[0131] In this embodiment, the maximum value of counter K, which corresponds to the number of consecutive images formed during the normal sheet interval process (50 msec), is 20. Ideally, the post-rotation process should be extended until the moisture accumulated on the brush member 10 during the consecutive image formation is substantially eliminated, in preparation for the next job. Therefore, in this embodiment, the post-rotation process time is set longer as the number of consecutive images formed immediately before the job ends increases. For example, if a job ends after 20 consecutive images are formed, a 60-second post-rotation process is performed to idle the photosensitive drum 1, removing the moisture accumulated on the brush member 10 during the 20 consecutive image formations, and then the idle rotation of the photosensitive drum 1 is terminated. In the case of the sheet interval process, the value of counter K can be reset to 0 after 45 seconds of idle rotation of the photosensitive drum 1 (resetting the moisture accumulated on the brush member 10 during image formation to almost zero). However, in the case of the post-rotation process, 60 seconds of idle rotation of the photosensitive drum 1 is required to reset the value of counter K to 0 (to reset the moisture accumulated on the brush member 10 during image formation to a state of almost zero). This is thought to be due to the difference between the controlled temperature of 120°C of the fixing device 9 during the extended inter-sheet process and the controlled temperature during the post-rotation process (heater OFF). Extending the idle rotation of the photosensitive drum 1 when the controlled temperature is high increases the temperature inside the device main body 101 and decreases the relative humidity, making it easier for water vapor adhering to the surface of the photosensitive drum 1 and moisture accumulated on the brush member 10 to evaporate. Furthermore, when the value of counter K is 1 or 2, that is, after the continuous formation of one or two images, there is little moisture accumulated on the brush member 10, so there is no need to extend the post-rotation process, and the process ends with the normal post-rotation process.

[0132] On the other hand, the value of counter M is not updated even if the post-rotation process is extended. Discharge products are gradually removed by rubbing against the developing roller, charging roller, and transfer roller. However, the balance between the generation and removal of discharge products on the surface of the photosensitive drum 1, represented by the value of counter M, remains unchanged unless the recording material P is transported after the extended inter-sheet process. As described above, in this embodiment, due to thermal expansion of the pressure roller 23, the transport speed of the recording material P by the pressure roller 23 becomes faster than the moving speed of the surface of the photosensitive drum 1, so that the discharge products on the surface of the photosensitive drum 1 are removed by the recording material P. In other words, the value of counter M can be decremented when the inter-sheet process is extended. On the other hand, when the post-rotation process is extended, there is no process in which the recording material P rubs against the photosensitive drum 1, and therefore the discharge products on the surface of the photosensitive drum 1 cannot be removed. Therefore, the value of counter M cannot be decremented. The value of counter M is stored in memory 152 and is carried over when the next job starts.

[0133] In this way, by extending the post-rotation process, the moisture accumulated on the brush member 10 is removed and the brush member 10 is ready for the next job, but the discharge products accumulated on the surface of the photosensitive drum 1 are carried over to the next job as they are.

[0134] As described above, in this embodiment, the extended time for the inter-sheet step and the post-rotation step is determined according to the value of counter K, which is updated based on the information on the "number of images formed" and the "time for the inter-sheet step." This makes it possible to control the amount of moisture accumulated in the brush member 10. In addition, in this embodiment, the extended time for the inter-sheet step and the number of times the inter-sheet step time is repeatedly extended are determined according to the value of counter M, which is updated based on the information on the "number of images formed" and the "time for the inter-sheet step." This makes it possible to control the amount of discharge products accumulated on the surface of the photosensitive drum 1. Therefore, according to this embodiment, it is possible to suppress the occurrence of image deletion throughout the life of the photosensitive drum 1.

[0135] 5. Procedure for setting the time for the paper-interval process and post-rotation process FIG. 7 is a flowchart showing an outline of the procedure of a job including the extension operations of the inter-sheet step and post-rotation step in this embodiment.

[0136] S201: The control unit 150 acquires job information transmitted from an external device based on a user operation.

[0137] S202: The control unit 150 executes the image forming process.

[0138] S203: The control section 150 increments the values ​​of the counters K and M by 1 at the timing when the recording material P is fed.

[0139] S204-S207: In S204, the control unit 150 determines whether the next image formation is the last image formation of the job, that is, whether the recording material P to be conveyed next is the last sheet. In S205, the control unit 150 determines whether the value of counter M has reached 26 (matches 26). In S206, the control unit 150 determines whether the value of counter K has reached 20 (matches 20). If the control unit 150 determines that the sheet is the last sheet (Y in S204), it proceeds to a post-rotation step (S218). If the control unit 150 determines that the sheet is not the last sheet (N in S204), and that the value of counter M does not match 26 (is less than 26) (N in S205), and that the value of counter K does not match 20 (is less than 20) (N in S206), it proceeds to a normal sheet spacing step (S207) and then to the next image forming step (S202). In this embodiment, the normal time for the paper spacing step is 50 msec.

[0140] S208: If the control unit 150 determines in S206 that the value of counter K is equal to 20 (Y in S206), it extends the inter-sheet process (S208) according to the value of counter K in accordance with Table 4. In this embodiment, the time for the inter-sheet process performed in S208 is 45 seconds.

[0141] S209: After extending the inter-sheet step in S208, the control unit 150 resets the value of counter K to 0, assuming that the moisture accumulated on the brush member 10 has become almost zero. This is because the moisture accumulated on the brush member 10 can be removed by being discharged little by little during the extension of the inter-sheet step in S208. Furthermore, after extending the inter-sheet step in S208, the control unit 150 subtracts 4 from the value of counter M, assuming that the discharge products on the surface of the photosensitive drum 1 have decreased. This is because the pressure roller 23, which has expanded due to the extension of the inter-sheet step, rubs the surface of the photosensitive drum 1 with the recording material P, which is transported faster than the moving speed of the surface of the photosensitive drum 1, and the discharge products accumulated on the photosensitive drum 1 can be scraped off. Thereafter, when the extension of the inter-sheet step is completed, the control unit 150 proceeds to the image formation step (S202).

[0142] S210-S211: If the control unit 150 determines in S205 that the value of counter M is equal to 26 (Y in S205), it extends the inter-sheet process (S210) according to the value of counter K in accordance with Table 4. In this embodiment, the time for the inter-sheet process shown in Table 4 is intended to remove moisture accumulated on the brush member 10. If the time for the inter-sheet process is extended according to Table 4, the amount of moisture accumulated on the brush member 10 will be reduced to almost zero. Therefore, after extending the inter-sheet process in S210, the control unit 150 resets the value of counter K to 0 (S211). Furthermore, within the range of the inter-sheet process of 20 seconds or more, the ability of the recording material P to remove discharge products from the surface of the photosensitive drum 1 is almost constant. Therefore, after extending the inter-sheet process in S210, the control unit 150 uniformly subtracts 4 from the value of counter M (S211).

[0143] S212-S217: If the control unit 150 determines in S205 that the value of counter M is equal to 26 (Y in S205), it goes through the processes of S210 and S211 and enters the discharge product removal mode. In this embodiment, during the discharge product removal mode, the value of counter K and the value of counter M are each incremented by 1 each time the image forming process for one sheet (S212) is executed (S213). Thereafter, the control unit 150 determines in S214 whether the next image formation is the last image formation of the job, i.e., whether the recording material P to be conveyed next is the last sheet. If the control unit 150 determines that the next sheet is not the last sheet (N in S214), it executes the sheet spacing process for 20 seconds according to the value of counter K in accordance with Table 4 (S215). After extending the time for the sheet spacing process to 20 seconds, the control unit 150 resets the value of counter K to 0 and subtracts 4 from the value of counter M (S216). The control unit 150 repeats S212 to S216 until the value of the counter M reaches 0 (S217). When the value of the counter M reaches 0 (Y in S217), the control unit 150 determines that the discharge products on the surface of the photosensitive drum 1 have been almost completely removed, exits the discharge product removal mode, and transitions to the image formation process (S202) in the normal sheet interval process (S207).

[0144] S218: If the control unit 150 determines in S204 or S214 that this is the last sheet (Y in S204 or Y in S214), it executes the post-rotation process for a time period corresponding to the current value of counter K according to Table 4. Furthermore, when the control unit 150 completes the post-rotation process, it resets the value of counter K to 0, assuming that the moisture accumulated on the brush member 10 has been dried. On the other hand, the control unit 150 does not update the value of counter M because the discharge products on the surface of the photosensitive drum 1 cannot be removed unless the recording material P is conveyed, even if the control unit post-rotation process is extended. The value of counter M is stored in memory 152 and is carried over to the next job.

[0145] S219: When the post-rotation process is completed, the control unit 150 ends the job.

[0146] 6.Effects In order to confirm the effect of this embodiment, an experiment was conducted on a brand new photosensitive drum 1 and a photosensitive drum 1 that had been used to form 10,000 images, in which a job of forming 50 images on 10 sheets was executed using moisture-absorbed recording material P, and the occurrence of image smearing was examined for every 10 sheets. The experiment was conducted in an environment of 15°C temperature and 80% humidity (low temperature and high humidity environment), where moisture is likely to accumulate on the brush member 10 and localized image smearing is likely to occur. The recording material P used in the experiment was Xerox Vitality Multipurpose paper, Letter size, with a basis weight of 75 g / m 2 The paper was taken out of its wrapping and left in an environment with a temperature of 15°C and humidity of 80% (low temperature and high humidity) for two days. The moisture content of this paper was measured using a Moistrex MX-8000 moisture meter manufactured by NDC Infrared Engineering and was found to be 9.2%. For comparison, the moisture content of this paper was measured immediately after opening and was found to be 5.7%.

[0147] A similar experiment was also conducted for Comparative Example 5. Comparative Example 5 is an example in which the inter-paper step is extended in a configuration in which the brush member 10 is arranged, but the extension of the inter-paper step is carried out only from the viewpoint of preventing the amount of moisture accumulated in the brush member 10 from becoming too large. Comparative Example 5 corresponds to a modified example of the above-mentioned Example 1, and is included in the present invention.

[0148] The results are shown in Table 5. In Table 5, "◯" indicates that no image deletion occurred, "△" indicates that image deletion occurred slightly, and "×" indicates that image deletion occurred significantly.

[0149] The photosensitive drum 1 after being used for forming images on 10,000 sheets means the photosensitive drum 1 in a state where a job of forming images on 50 sheets is repeatedly executed using the image formation method in each example, and the total number of images formed on 10,000 sheets is reached. In this embodiment, the life of the device main body 101 of the image forming apparatus 100 is set to 50,000 sheets.

[0150] [Table 5]

[0151] As can be seen from the results of Comparative Example 4 (Table 2) described above, if the configuration is such that the brush member 10 is installed, image deletion does not occur even when continuous image formation is performed for up to about 20 sheets. However, if continuous image formation is continued further without extending the inter-sheet process, moisture accumulated in the brush member 10 may flow out locally, and image deletion occurs in the areas where moisture has flowed out locally from the 25th sheet onwards.

[0152] In Comparative Example 5, the inter-sheet step is extended to prevent excessive moisture accumulation on the brush member 10. In Comparative Example 5, a job with 50 images is performed as follows: After 20 consecutive images are formed, the inter-sheet step time is extended to 45 seconds. After 7 consecutive images are formed, the inter-sheet step time is extended to 35 seconds. After 3 consecutive images are formed, the inter-sheet step time is extended to 20 seconds. At this point, the moisture accumulated on the brush member 10 is almost zero, so 20 consecutive images are formed. Finally, the post-rotation step time is extended to 60 seconds, resetting the moisture accumulated on the brush member 10 during image formation to almost zero before completing the job. In Comparative Example 5, excessive moisture does not accumulate on the brush member 10 and flow locally onto the surface of the photosensitive drum 1, thereby suppressing localized image smearing. However, after repeatedly performing this 50-sheet image formation process, totaling 10,000 images, discharge products accumulate on the photosensitive drum 1. Therefore, image deletion is more likely to occur than when the photosensitive drum 1 is new, and image deletion begins to occur after continuous image formation of about 15 sheets. Therefore, slight image deletion occurred on the 20th and 50th sheets, which are the timing after continuous image formation of 20 sheets.

[0153] In this embodiment, by implementing a mode (discharge product removal mode) in which a 20-second inter-sheet step was repeated eight times for each image formation process, image deletion was suppressed even on a photosensitive drum 1 that had been used to form 10,000 images. This was due to the following advantage of this embodiment, compared to Comparative Example 5, in which continuous image formation continued and the temperature of the pressure roller 23 was likely to drop. Specifically, in this embodiment, image formation was repeated eight times for each sheet while promoting thermal expansion of the pressure roller 23 by extending the inter-sheet step. This enabled the recording material P to move faster than the surface of the photosensitive drum 1, rubbing the surface of the photosensitive drum 1 with the recording material P, thereby removing discharge products accumulated on the surface of the photosensitive drum 1. Furthermore, repeating this 20-second inter-sheet step eight times for each image formation process also gradually removed moisture accumulated on the brush member 10, thereby suppressing image deletion, which occurs when moisture locally flows from the brush member 10 onto the surface of the photosensitive drum 1.

[0154] As described above, in this embodiment, the transfer member 5 sandwiches and conveys the recording material P between itself and the photoreceptor 1 at the transfer portion Nt, and the image forming apparatus 100 further includes a pair of rotors 23 and 24 that heat the recording material P while sandwiching and conveying it at the heating portion Nf, and the control unit 150 can control the time of the second non-image forming process so that the moving speed of the third recording material P, which is simultaneously sandwiched and conveyed between the heating portion Nf and the transfer portion Nt, is faster than the moving speed of the surface of the photoreceptor 1. Furthermore, in this embodiment, when the time of the first non-image forming process is a third time and the time of the second non-image forming process is a fourth time longer than the third time, the control unit 150 can control the time so that, after the second recording material P, the non-image forming process is the fourth time, and then image formation is performed on the recording material P consecutively.

[0155] As described above, in this embodiment, the thermal expansion of the pressure roller 23 is promoted by extending the sheet interval process, and the difference between the moving speed of the recording material P and the moving speed of the surface of the photosensitive drum 1 is increased, causing the recording material P to rub against the surface of the photosensitive drum 1. As a result, in this embodiment, discharge products accumulated on the surface of the photosensitive drum 1 are reduced, and stable images can be formed throughout the life of the photosensitive drum 1 without image deletion.

[0156] 7. Variations In this embodiment, the image forming apparatus 100 is configured such that the photosensitive drum 1 and the fixing roller 23 are driven by a common motor (single motor configuration), but the present invention can also be applied to an image forming apparatus configured such that these are driven by separate motors (two motor configuration). Even with this configuration, under conditions where image deletion is likely to occur, the driving speed of the pressure roller 23 can be increased to increase the conveying speed of the recording material P by the pressure roller 23. This allows the surface of the photosensitive drum 1 to be rubbed with the recording material P, thereby removing discharge products accumulated on the surface of the photosensitive drum 1, thereby suppressing the occurrence of image deletion.

[0157] In this embodiment, the number of sheets that can be continuously formed is set to a value that takes usability (productivity) into consideration, allowing as many continuous images as possible without causing image deletion. However, the present invention is not limited to this configuration. In this embodiment, it is sufficient to control the amount of discharge products that accumulate on the surface of the photosensitive drum 1 so that they do not become too large, and to prevent excessive moisture from accumulating on the brush member 10. In this embodiment, even if the photosensitive drum 1 has accumulated enough discharge products to form 10,000 images, for example, image deletion does not occur for up to 10 consecutive images. Therefore, for example, by fixing the number of continuous image formation sheets and the extended non-image formation process time to 5 sheets and 30 seconds, respectively, image deletion can be suppressed throughout the life of the photosensitive drum 1.

[0158] Furthermore, the parameter for updating the value of counter M, which indicates the amount of discharge products accumulated on the photosensitive drum 1, is not limited to that in this embodiment. The parameter for increasing the value of counter M may be any parameter correlated with the phenomenon of discharge products accumulating on the surface of the photosensitive drum 1. Examples of such parameters include the number of consecutive images formed during a normal inter-sheet interval, the cumulative time of the image formation process when consecutive images are formed during a normal inter-sheet interval, the number of rotations or rotation distance of the photosensitive drum 1 during that interval, the charging voltage application time, and the exposure time. The parameter for decreasing the value of counter M may be any parameter correlated with the phenomenon of the decrease in the amount of discharge products accumulated on the surface of the photosensitive drum 1. Examples of such parameters include the extended inter-sheet interval time, or the number of rotations or rotation distance of the photosensitive drum 1 during that interval. As described above, the number of sheets and the time may be used as well as the number of rotations or rotation distance. In addition, coefficients corresponding to the actual moving speed of the recording material P and the amount of thermal expansion of the pressure roller 23 may be stored in memory 152, and the extent to which the recording material P rubs against the surface of the photosensitive drum 1 and the extent to which discharge products have been removed may be reflected in the parameters that decrease the value of counter M.

[0159] Furthermore, in this embodiment, a discharge product removal mode is provided in which the inter-sheet step is extended to 20 seconds for each image formed on the photosensitive drum 1, and this is repeated eight times, starting from a brand new state. However, the present invention is not limited to this embodiment. The total number of images formed on a sheet may be reflected in the counter value, and the discharge product removal mode may be executed when the total number of images formed on a sheet exceeds a predetermined value. For example, in the case of a brand new photosensitive drum 1, only the moisture accumulated on the brush member 10 may be removed as in the first embodiment. Then, when the total number of images formed on a sheet exceeds the predetermined value and the amount of discharge products accumulated on the surface of the photosensitive drum 1 becomes large, discharge products may be removed in the discharge product removal mode.

[0160] In this embodiment, the temperature during the extended inter-sheet interval process was set constant at -60°C (i.e., 120°C) relative to the temperature during the image formation process (fixing process), but the present invention is not limited to this configuration. To further promote the thermal expansion of the pressure roller 23, the temperature may be increased, for example, only in the discharge product removal mode. If the thermal expansion of the pressure roller 23 can be further promoted to increase the moving speed of the recording material P relative to the moving speed of the surface of the photosensitive drum 1, the effect of removing discharge products accumulated on the photosensitive drum 1 can be further enhanced. Therefore, the temperature during the extended inter-sheet interval process may be increased to increase the number of sheets that can be continuously formed or to reduce the number of repetitions in the discharge product removal mode. Such an operation can improve usability (improve productivity).

[0161] Furthermore, in this embodiment, the method of rubbing and scraping off the discharge products accumulated on the surface of the photosensitive drum 1 involves transporting the recording material P faster than the moving speed of the surface of the photosensitive drum 1, but the present invention is not limited to this configuration. In this embodiment, any configuration is sufficient as long as the discharge products can be removed by rubbing the surface of the photosensitive drum 1. For example, it is also effective to configure the developing roller 31 or the charging roller 2 to rotate at a different peripheral speed than the photosensitive drum 1, thereby scraping off the discharge products from the surface of the photosensitive drum 1. When using such a means, the discharge products can be removed not only by extending the paper interval process, but also by extending the post-rotation process (or the pre-rotation process).

[0162] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

[0163] The dimensions, materials, shapes and relative arrangements of the components described in the above embodiments should be modified as appropriate depending on the configuration and various conditions of the device to which the invention is applied.

[0164] In the above embodiment, a printer is used as an example of an image forming apparatus, but the present invention is not limited to this. The present invention can also be applied to other image forming apparatuses, such as a copier or facsimile machine, or a multifunction machine that combines the functions of these, and can achieve the same effects as those of the above embodiment. [Explanation of symbols]

[0165] 1 Photosensitive drum 2 Charging roller 3. Developing device 4 Exposure equipment 5 Transfer roller 6 cassettes 9 Fixing device 10 Brush member 23 Pressure roller 24 Fixing film

Claims

1. a rotatable photoreceptor; a charging member for charging the surface of the photoreceptor in a charging section; a developing device that supplies toner to the surface of the photoreceptor after charging to form a toner image; a transfer member that transfers the toner image from the photosensitive member to a recording material at a transfer section; a brush member that contacts the surface of the photosensitive member and forms a contact portion downstream of the transfer portion and upstream of the charging portion in the rotation direction of the photosensitive member; a drive source that rotates and drives the photosensitive member; a control unit that controls the drive source to execute an image forming process in which an image is formed on a recording material, and a non-image forming process that is a process other than the image forming process and is executed so that the photosensitive member is rotationally driven; If the non-image forming step between the first recording material and the second recording material on which an image is formed after the first recording material is defined as a first non-image forming step, and the non-image forming step between the second recording material and the third recording material on which an image is formed after the second recording material is defined as a second non-image forming step, The control unit controls the time of the second non-image forming process to be longer than the time of the first non-image forming process based on the number of images formed, which is the number of recording materials on which images are formed by the image forming process, and the time of the first non-image forming process.

2. a rotatable photoreceptor; a charging member for charging the surface of the photoreceptor in a charging section; a developing device that supplies toner to the surface of the photoreceptor after charging to form a toner image; a transfer member that transfers the toner image from the photosensitive member to a recording material at a transfer section; a brush member that contacts the surface of the photosensitive member and forms a contact portion downstream of the transfer portion and upstream of the charging portion in the rotation direction of the photosensitive member; a drive source that rotates and drives the photosensitive member; a control unit that controls the drive source to execute an image forming process in which an image is formed on a recording material, a non-image forming process that is a process other than the image forming process and is executed so that the photosensitive member is rotationally driven, and a post-rotation process in which the photosensitive member is rotated after the recording material without executing the image forming process, If the non-image forming step between the first recording material and the second recording material on which image formation is performed next to the first recording material is defined as a first non-image forming step, The control unit controls the time of the post-rotation process performed after the second recording material so that it is longer than the time of the first non-image forming process based on the number of image-formed sheets, which is the number of recording materials on which images have been formed by the image forming process, and the time of the first non-image forming process.

3. The image forming apparatus according to claim 1, characterized in that the control unit determines the time of the second non-image forming process according to a value that is added according to the number of sheets of recording material on which images have been formed and is controlled to be subtracted when the driving operation of the photosensitive member is performed in the non-image forming process.

4. The image forming apparatus according to claim 1 or 3, characterized in that when performing continuous image formation in which images are formed continuously on a plurality of the first recording materials with the time of the first non-image forming process being a predetermined time, and then performing image formation on the second recording material, the control unit controls the time of the second non-image forming process to be shorter when the time for which the continuous image formation is performed is a second time that is shorter than the first time than when the time for which the continuous image formation is performed is a first time.

5. the transfer member conveys the recording material while sandwiching it between itself and the photosensitive member in the transfer section; the image forming apparatus further includes a pair of rotating bodies that heat the recording material while nipping and conveying the recording material in the heating section, The image forming apparatus according to claim 1, characterized in that the control unit is capable of controlling the time of the second non-image forming process so that the movement speed of the third recording material, which is simultaneously sandwiched and transported between the heating unit and the transfer unit, is faster than the movement speed of the surface of the photosensitive member.

6. 6. An image forming apparatus according to claim 1, wherein the control unit is capable of controlling the image forming apparatus so that, when the time period for the first non-image forming process is set to a third time period and the time period for the second non-image forming process is set to a fourth time period longer than the third time period, image formation is performed continuously on a plurality of recording materials after the second recording material, with the time period for the non-image forming process set to the fourth time period, and then image formation is performed on the recording material with the time period for the non-image forming process set to the third time period.

7. The image forming apparatus according to claim 2, characterized in that the control unit determines the time of the post-rotation process to be performed after the second recording material according to a value that is added according to the number of recording materials on which image formation has been performed and is controlled to be subtracted when the driving operation of the photosensitive body is performed in the non-image forming process.

8. The image forming apparatus of claim 2 or 7, characterized in that the control unit performs continuous image formation in which images are formed continuously on multiple first recording materials, with the time of the first non-image forming process being a predetermined time, and when the post-rotation process is performed after image formation on the second recording material, controls so that the time of the post-rotation process performed after the second recording material is shorter when the time for which the continuous image formation is performed is a second time that is shorter than the first time than when the time for which the continuous image formation is performed is a first time.

9. 9. The image forming apparatus according to claim 1, wherein the toner remaining on the surface of the photosensitive member after the toner image is transferred from the photosensitive member to the recording material is removed and collected from the surface of the photosensitive member by the developing device.

10. a rotatable photoreceptor; a charging member for charging the surface of the photoreceptor in a charging section; a developing device that supplies toner to the surface of the photoreceptor after charging to form a toner image; a transfer member that transfers the toner image from the photosensitive member to a recording material at a transfer section; a brush member that contacts the surface of the photosensitive member and forms a contact portion downstream of the transfer portion and upstream of the charging portion in the rotation direction of the photosensitive member; a control unit that controls a non-image forming time, which is a time during which the photosensitive member rotates from when the preceding recording material passes through the transfer unit until when the next recording material arrives at the transfer unit; The control unit defines an inter-image time, which is the non-image formation time from when the preceding recording material passes through the transfer unit until the next recording material reaches the transfer unit without the rotation of the photosensitive drum stopping, as a predetermined inter-image time, and controls the non-image formation time from when the last recording material passes through the transfer unit until the next recording material after the last recording material reaches the transfer unit in continuous image formation in which toner images are transferred continuously to multiple recording materials, so that it is longer than the predetermined inter-image time, based on the number of images formed, which is the number of recording materials on which images are formed during the continuous image formation when the continuous image formation is performed.

Images