Image forming device

Abstract

To prevent the occurrence of an image defect such as toner fusion due to a reduction in polishing force of a cleaning member on a surface of a photoreceptor during the execution of continuous image formation.SOLUTION: An image forming apparatus 100 has: a detection unit 11 that detects a value correlated to drive torque of a photoreceptor 1 driven by a driving unit MTR1; and a control unit that can execute operations to suspend image formation during the execution of continuous image formation based on a result of detection performed by the detection unit 11, to apply, to an electrifying member 2, voltage generating discharge between the electrifying member 2 and the photoreceptor 1, and to rotate the photoreceptor 1 through at least one full circumference in a state in which rotation of a developing member 41 is stopped or the developing member 41 is rotated at the rotational speed lower than that during the image formation.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, a printing machine, or a multifunction machine having a plurality of functions among these. [Background technology]

[0002] In an image forming apparatus using an electrophotographic system, after a toner image is transferred from a rotatable photosensitive member such as a photosensitive drum to a transfer medium, the toner (transfer residual toner) and other deposits remaining on the surface of the photosensitive member are removed. A cleaning device that removes the transfer residual toner and other deposits on the photosensitive member is widely used, which has a configuration in which an elastic cleaning blade as a cleaning member is brought into contact with the photosensitive member.

[0003] After the residual toner on the photoreceptor is blocked by the cleaning member, a blocking layer is formed near the contact point between the cleaning member and the photoreceptor. The toner contains toner particles and external additives, and the blocking layer is mainly formed from the external additives. This blocking layer has a cleaning function and a function of supplying a lubricant between the photoreceptor and the cleaning member.

[0004] In such an image forming apparatus, in order to continuously form good images, it is important to maintain an appropriate coefficient of friction (dynamic friction coefficient, dynamic friction force) between the photosensitive member and the cleaning member.

[0005] Patent Document 1 discloses that a torque current for driving a photosensitive member is detected, and when the torque current is equal to or greater than a threshold, toner from a toner band is supplied to a cleaning member to polish the surface of the photosensitive member. The technology in Patent Document 1 aims to suppress "image deletion," a phenomenon in which the photosensitive member is subjected to discharge by a charging member, and discharge products adhere to the surface of the photosensitive member, resulting in a deterioration in charging characteristics and a disturbance in the latent image. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-234894 Summary of the Invention [Problem to be solved by the invention]

[0007] In the image forming apparatus described above, when high-area-ratio images are continuously formed, the amount of external additives supplied near the contact point between the photoreceptor and the cleaning member increases, which can reduce the coefficient of friction between the photoreceptor and the cleaning member. This can reduce the abrasive power of the cleaning member on the photoreceptor surface, resulting in image defects such as toner fusion. Specifically, toner-induced agglomerates of approximately 1 μm (length in the direction of movement of the photoreceptor surface) can form on the photoreceptor surface. Further toner can adhere to these agglomerates, growing to approximately 10 μm (length in the direction of movement of the photoreceptor surface). These agglomerates can then interfere with the exposure of the photoreceptor surface, resulting in white spots on the image (white spots where toner does not adhere). This phenomenon is called "toner fusion."

[0008] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to prevent image defects such as toner fusion caused by a decrease in the abrasive power of the cleaning member on the surface of the photosensitive member during continuous image formation. [Means for solving the problem]

[0009] The above object is achieved by the image forming apparatus according to the present invention. In summary, a typical configuration of the present invention comprises a rotatable photosensitive member, a charging member for charging the photosensitive member, a developer carrier for carrying developer, a developing device for developing a latent image formed on the photosensitive member, a blade for cleaning the photosensitive member, a detection unit for detecting information correlated with the driving torque of the photosensitive member, and a detection unit for detecting information correlated with the driving torque of the photosensitive member, and a detection unit for detecting information correlated with the driving torque of the photosensitive member, and a detection unit for detecting information correlated with the driving torque of the photosensitive member, 1stA predetermined operation is to interrupt image formation, extend the interval between successive recording materials, and rotate the photoreceptor. 1st a control unit configured to perform a predetermined operation, 1st During a predetermined operation, (i) a voltage equal to or higher than a discharge start voltage is applied to the charging member, and (ii) the operating conditions of the developing device are set to a first condition, and under the first condition, the amount of fog toner adhering to the photosensitive member from the developer carrier is less than the amount of fog toner under a second condition, which is the operating condition of the developing device during an inter-recording material step before the image formation during the continuous image formation is interrupted, and the photosensitive member is rotated over one or more revolutions. The control unit is capable of executing a second predetermined operation after the first predetermined operation and before the image formation is resumed, and during the second predetermined operation, (i) no voltage is applied to the charging member or a voltage less than a discharge start voltage is applied to the charging member, and (ii) the operating condition of the developing device is set to a third condition, and under the third condition, the amount of fog toner adhering from the developer carrier to the photosensitive member is less than the amount of fog toner under the second condition, and the photosensitive member is rotated under the condition. The image forming apparatus is characterized by the above. Another representative configuration of the present invention includes a developing device including a rotatable photosensitive member, a charging member for charging the photosensitive member, and a developer carrier for carrying a developer, the developing device developing a latent image formed on the photosensitive member, a blade for cleaning the photosensitive member, and a control unit configured to execute a predetermined operation during continuous image formation for continuously forming images on a plurality of recording materials, the predetermined operation being to interrupt image formation, extend an interval between successive recording materials, and rotate the photosensitive member, wherein the control unit executes a first predetermined operation during the predetermined operation, and then executes a second predetermined operation, and in the first predetermined operation, (i) a voltage equal to or greater than a discharge start voltage is applied to the charging member, and (ii) an operating condition of the developing device is set to a first condition, and The photosensitive member is rotated one or more times under the condition that the amount of fog toner adhering from the developer carrier to the photosensitive member is less than the amount of fog toner under the second condition, which is the operating condition of the developing device during the inter-recording material step before the image formation during the continuous image formation is interrupted, and in the second predetermined operation, (i) no voltage is applied to the charging member or a voltage less than a discharge start voltage is applied to the charging member, and (ii) the operating condition of the developing device is set to a third condition, and under the third condition, the amount of fog toner adhering from the developer carrier to the photosensitive member is less than the amount of fog toner under the second condition. Another representative configuration of the present invention includes a rotatable photosensitive member, a charging member for charging the surface of the photosensitive member, a charging power source for applying a voltage to the charging member, an exposure unit for exposing the charged surface of the photosensitive member to light to form an electrostatic image on the charged surface of the photosensitive member, a rotatable developing member for supplying toner to the electrostatic image to form a toner image on the surface of the photosensitive member, a cleaning member for contacting the surface of the photosensitive member to remove toner from the surface of the photosensitive member, a driving unit for driving the photosensitive member, and a detection unit for detecting a value correlated with a driving torque of the photosensitive member by the driving unit. a transfer device for transferring a toner image formed on the photosensitive member of each of the plurality of image forming units; and a device for transferring a toner image formed on the photosensitive member of each of the plurality of image forming units to a plurality of recording materials, wherein, during execution of continuous image formation in which image formation for forming a toner image to be transferred onto a recording material is continuously performed, image formation is interrupted in at least one of the plurality of image forming units, a voltage for causing discharge between the charging member and the photosensitive member is applied to the charging member, and rotation of the developing member is stopped or the developing member is rotated at a rotation speed lower than that during image formation. and a control unit capable of executing an operation of rotating the photosensitive member at least one revolution while the developing member is rotated, wherein the control unit determines, at a predetermined timing during the continuous image formation, whether the detection results of the detection unit obtained over time indicate that the drive torque has decreased so as to satisfy a predetermined condition, and executes the operation in at least one image forming unit when it is determined that the detection results indicate that the drive torque has decreased in at least one image forming unit among the plurality of image forming units, and the control unit, at the predetermined timing, executes image formation in an image forming unit among the plurality of image forming units where it is determined that the detection results do not indicate that the drive torque has decreased, or executes another operation of interrupting image formation, not applying a voltage to the charging member or applying a voltage to the charging member that does not cause discharge between the charging member and the photosensitive member, and stopping the rotation of the developing member or rotating the photosensitive member at least one revolution while the developing member is rotated at a rotational speed lower than that during image formation. [Effects of the Invention]

[0010] According to the present invention, it is possible to prevent image defects such as toner fusion caused by a decrease in the abrasive power of the cleaning member on the surface of the photosensitive member during continuous image formation. [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 cross-sectional view of an image forming unit. [Figure 3] FIG. 2 is a schematic block diagram showing a control mode of the image forming apparatus. [Figure 4] FIG. 10 is a graph showing the relationship between the driving torque of the photosensitive drum and the growth of deposits. [Figure 5] FIG. 4 is a flowchart of the toner melt-adhesion suppression operation in the first embodiment. [Figure 6] 4A and 4B are a sequence diagram of the toner fusion suppression operation in the first embodiment and a graph showing the transition of the driving torque of the photosensitive drum. [Figure 7] FIG. 10 is a schematic block diagram showing a control mode of an image forming apparatus according to a second embodiment. [Figure 8] FIG. 2 is a schematic block diagram showing a configuration related to image processing of a control unit. [Figure 9] FIG. 10 is a flowchart of the toner melt-adhesion suppression operation in the second embodiment. [Figure 10] FIG. 10 is a schematic block diagram illustrating a control unit of an image forming apparatus according to a third embodiment. [Figure 11] FIG. 11 is a flowchart of the toner melt-adhesion suppression operation in the third embodiment. [Figure 12] FIG. 10 is a flowchart of the toner melt-adhesion suppression operation in the fourth embodiment. [Figure 13] 10 is a sequence diagram of the toner fusion suppression operation in Example 4 and a graph showing the transition of the driving torque of the photosensitive drum. FIG. 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. Configuration and operation of image forming apparatus 1 is a schematic cross-sectional view of an image forming apparatus 100 according to this embodiment. The image forming apparatus 100 according to this embodiment is a laser beam printer employing an intermediate transfer method, capable of forming full-color images using an electrophotographic method.

[0014] Image forming apparatus 100 has four image forming units (stations) SY, SM, SC, and SK that form images of the colors yellow (Y), magenta (M), cyan (C), and black (K), respectively. Elements in each of the image forming units SY, SM, SC, and SK that have the same or corresponding functions or configurations may be generally described by omitting the Y, M, C, or K at the end of the reference numeral indicating that the element is for one of the colors.

[0015] 2 is a schematic cross-sectional view showing one representative image forming unit S. In this embodiment, the image forming unit S is configured to include a photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, a primary transfer roller 5, and a cleaning device 7, which will be described later. The four image forming units SY, SM, SC, and SK are arranged in a row along the direction of movement of the surface of an intermediate transfer belt 6, which will be described later. In this embodiment, the distance between adjacent image forming units S (the distance between the positions where the photosensitive drum 1 and the primary transfer roller 5 abut) is 100 mm.

[0016] The photosensitive drum 1, a rotatable drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) serving as an image carrier, is driven to rotate in the direction of arrow R1 (counterclockwise) in FIGS. 1 and 2 by a drum drive motor MTR1 (FIG. 3) serving as a photosensitive member drive unit (photosensitive member drive section). In this embodiment, the photosensitive drum 1 is a negatively charged organic photoconductor (OPC) drum with a circumferential length of 100 mm (outer diameter of 31.85 mm). In this embodiment, the photosensitive drum 1 is driven to rotate around a central spindle at a peripheral speed (process speed) of 200 mm / sec. In this embodiment, the photosensitive drum 1 is constructed by coating an undercoat layer, a photocharge generation layer, and a charge transport layer (approximately 20 μm thick) on the surface of an aluminum cylinder (conductive drum substrate) in this order from the bottom (the cylinder side).

[0017] The surface of the rotating photosensitive drum 1 is charged to a predetermined potential of a predetermined polarity (negative in this embodiment) by a charging roller 2, a roller-type charging member (contact charging member) serving as a charging means (charging unit). The charging roller 2 is disposed in contact with the surface of the photosensitive drum 1 and rotates in accordance with the rotation of the photosensitive drum 1. The charging roller 2 charges the surface of the photosensitive drum 1 by utilizing a discharge phenomenon that occurs 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 in the direction of rotation of the photosensitive drum 1 at the contact point between the charging roller 2 and the photosensitive drum 1 (contact charging method). In this embodiment, the charging roller 2 is a rubber roller having a length of 320 mm in the longitudinal direction (direction of rotation axis) and a diameter of 14 mm, and including a core 21 and an elastic layer 22 formed of a rubber material around the core 21. The position on the photosensitive drum 1 in the direction of rotation of the photosensitive drum 1 where charging is performed by the charging roller 2 is the charging position Pa. The charging roller 2 charges the surface of the photosensitive drum 1 by a discharge phenomenon occurring in the minute gap. The contact point between the charging roller 2 and the photosensitive drum 1 can be considered to be the charging position Pa. During the charging process, a predetermined charging voltage (charging bias) is applied to the core 21 of the charging roller 2 by a charging power supply (high-voltage power supply) PS1, which serves as a charging voltage application unit. In this embodiment, the charging power supply PS1 includes a charging DC power supply 12 that outputs a DC component (charging DC bias) and a charging AC power supply 13 that outputs an AC component (charging AC bias) (see FIG. 3). During the charging process, the charging power supply PS1 applies an oscillating voltage to the charging roller 2 as a charging bias, which is a superposition of a charging DC bias of −700 V and a charging AC bias with a peak-to-peak voltage (Vpp) sufficient to generate a sufficiently stable discharge. The peak-to-peak voltage sufficient to generate a sufficiently stable discharge is at least twice the discharge inception voltage when only a DC voltage is applied. As a result, the surface of the photosensitive drum 1 is uniformly charged to a surface potential (charging potential, dark area potential) of −700 V.

[0018] The charged surface of the photosensitive drum 1 is scanned and exposed by an exposure device 3 serving as an exposure means (exposure unit), forming an electrostatic latent image (electrostatic image) on the photosensitive drum 1. In this embodiment, the exposure device 3 is a laser beam scanner using a semiconductor laser. The exposure device 3 outputs laser light L modulated in response to an image signal sent to the image forming apparatus 100 from a host processing device, such as an image reading device (not shown) or a personal computer, connected to the image forming apparatus 100. The exposure device 3 then irradiates the laser light L onto the uniformly charged surface of the rotating photosensitive drum 1. This reduces the absolute value of the potential of the portion of the surface of the photosensitive drum 1 irradiated with the laser light L, forming an electrostatic latent image corresponding to the image information on the surface of the photosensitive drum 1. The position on the photosensitive drum 1 in the rotational direction of the photosensitive drum 1 where the laser light L is irradiated by the exposure device 3 is the exposure position Pb. In this embodiment, the distance from the charging position a to the exposure position b in the rotational direction of the photosensitive drum 1 (the distance along the surface of the photosensitive drum 1) is 20 mm.

[0019] The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by the developing device 4 serving as a developing means (developing unit), which supplies toner and forms a toner image (toner image, developer image) on the photosensitive drum 1. In this embodiment, the developing device 4 employs a two-component contact development method using a two-component developer containing toner (non-magnetic toner particles) and carrier (magnetic carrier particles). The developing device 4 includes a developing container 42 that contains the two-component developer and a developing sleeve 41 serving as a developing member (developer carrier). The developing sleeve 41 is made of a non-magnetic material and rotatably supported by the developing container 42. A magnet roller (not shown) serving as a magnetic field generating means is disposed in the hollow portion of the developing sleeve 41 and is fixed relative to the developing container 42. In this embodiment, the developing device 4 carries a magnetic brush made of the two-component developer on the surface of the developing sleeve 41, and development is performed while the magnetic brush is in contact with the photosensitive drum 1. In this embodiment, toner charged with the same polarity as the charge polarity of the photosensitive drum 1 (negative in this embodiment) adheres to the exposed area (image area) of the photosensitive drum 1, which has been uniformly charged and then exposed to light to reduce the absolute value of the potential (reverse development method). In this embodiment, the normal charge polarity of the toner during development is negative. The position on the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 where toner is supplied (developed) by the developing device 4 (developing sleeve 41) is the development position Pc. During the development process, the developing sleeve 41 is rotated in the direction of arrow R3 (counterclockwise) in FIG. 2 by a development drive motor MTR2 (FIG. 3) serving as a development drive means (developing drive unit). In other words, the developing sleeve 41 is rotated so that the photosensitive drum 1 and the developing sleeve 41 move in opposite directions at the development position Pc. During the development process, a predetermined development voltage (developing bias) is applied to the developing sleeve 41 by a development power supply (high-voltage power supply) PS2 serving as a development voltage application unit. In this embodiment, the development power supply PS2 has a development DC power supply unit 14 that outputs a DC component (development DC bias) and a development AC power supply unit 15 that outputs an AC component (development AC bias) (FIG. 3).In this embodiment, during the development process, the development power supply PS2 applies an oscillating voltage, which is a combination of a −550 V development DC bias and a development AC bias for stably adhering toner to the image area (exposed area) on the photosensitive drum 1, to the development sleeve 41 as the development bias. The development DC bias is set so that the potential difference between the DC bias and the charge potential of the photosensitive drum 1 at the development position Pc (−700 V in this embodiment) is a predetermined potential difference Vback (150 V in this embodiment). The charge potential of the photosensitive drum 1 at the development position Pc is the potential when the surface potential of the photosensitive drum 1, formed by charging by the charging roller 2, reaches the development position Pc as the photosensitive drum 1 rotates. The toner in the two-component developer transported from the developer container 42 onto the development sleeve 41 is selectively adhered to the photosensitive drum 1 at the development position Pc in accordance with the electrostatic latent image on the photosensitive drum 1 due to the electric field generated by the development bias, and the electrostatic latent image is developed into a toner image.

[0020] An intermediate transfer belt 6, which is an endless belt serving as an intermediate transfer body, is disposed facing the four photosensitive drums 1Y, 1M, 1C, and 1K. The intermediate transfer belt 6 is stretched around a plurality of support rollers, namely a drive roller 61, a tension roller 62, and a secondary transfer opposing roller 63, and is tensioned at a predetermined tension. The intermediate transfer belt 6 rotates (circulates) in the direction of arrow R2 (clockwise) in FIG. 1 when the drive roller 61 is driven and rotated by a belt drive motor MTR3 (FIG. 3) serving as an intermediate transfer body drive means (intermediate transfer body drive unit). Primary transfer rollers 5Y, 5M, 5C, and 5K, which are roller-type primary transfer members serving as primary transfer means, are disposed on the inner circumferential surface of the intermediate transfer belt 6, corresponding to the photosensitive drums 1Y, 1M, 1C, and 1K. The primary transfer roller 5 is pressed against the photosensitive drum 1 and contacts the photosensitive drum 1 via the intermediate transfer belt 6, forming a primary transfer portion (primary transfer nip) N1 where the photosensitive drum 1 and intermediate transfer belt 6 come into contact. The tension roller 62, the secondary transfer counter roller 63, and each primary transfer roller 5 are driven to rotate in accordance with the rotation of the intermediate transfer belt 6. The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the rotating intermediate transfer belt 6 at the primary transfer portion N1 by the action of the primary transfer roller 5. During the primary transfer process, a primary transfer voltage (primary transfer bias), which is a DC voltage of opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the primary transfer roller 5 by a primary transfer power supply (high-voltage power supply) PS3 serving as a primary transfer voltage application unit. In this embodiment, the primary transfer power supply PS3 includes a primary transfer DC power supply unit 16 that outputs a DC voltage (primary transfer DC bias) (FIG. 3). For example, when forming a full-color image, toner images of each color, Y, M, C, and K, formed on each photosensitive drum 1 are transferred in sequence so as to be superimposed on the intermediate transfer belt 6. Note that each image forming unit SY, SM, SC, and SK sequentially forms an image of each color, Y, M, C, and K, delayed from the previous color by an inter-color delay time calculated from the distance between each image forming unit S and the process speed, and the images of each color are superimposed on the intermediate transfer belt 6.The position on the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 where the primary transfer of the toner image onto the intermediate transfer belt 6 is performed is the primary transfer position Pd (corresponding to the above-mentioned primary transfer portion N1).

[0021] A secondary transfer roller 8, a roller-type secondary transfer member serving as a secondary transfer means, is disposed on the outer peripheral surface of the intermediate transfer belt 6, facing the secondary transfer opposing roller 63. The secondary transfer roller 8 is pressed against the secondary transfer opposing roller 63 with a predetermined pressure and contacts the secondary transfer opposing roller 63 via the intermediate transfer belt 6, forming a secondary transfer portion (secondary transfer nip portion) N2 where the intermediate transfer belt 6 and the secondary transfer roller 8 come into contact. The secondary transfer roller 8 is driven to rotate in accordance with the rotation of the intermediate transfer belt 6. At the secondary transfer portion N2, the toner image formed on the intermediate transfer belt 6 is transferred (secondarily transferred) onto the recording material P, which is sandwiched and conveyed between the intermediate transfer belt 6 and the secondary transfer roller 8. During the secondary transfer process, a secondary transfer voltage (secondary transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the secondary transfer roller 8 by a secondary transfer power supply (high-voltage power supply) PS4 ( FIG. 3 ) serving as a secondary transfer voltage application portion. In this embodiment, the secondary transfer power supply PS4 includes a secondary transfer DC power supply unit 17 that applies a DC voltage (secondary transfer DC bias) (FIG. 3). The recording material (transfer material, recording medium, sheet, paper) P is fed from the feeding unit 30 at a predetermined controlled timing. Specifically, the recording material P is stored in a cassette 31 or the like, which serves as a recording material storage unit of the feeding unit 30. The recording material P is separated and sent out one by one from the cassette 31 by a feeding roller 32 or the like, which serves as a feeding member of the feeding unit 30. The recording material P is transported to a pair of registration rollers 18, which serve as a transport member, and then transported to the secondary transfer unit N2 by the pair of registration rollers 18 in synchronization with the toner image on the intermediate transfer belt 6. The recording material P is not limited to paper and may be a plastic sheet or the like. In this embodiment, the intermediate transfer belt 6, the multiple tension rollers 61-63, the primary transfer rollers 5, the secondary transfer roller 8, and the like constitute a transfer device 19 that transfers the toner image formed on each photosensitive drum 1 to the recording material P.

[0022] The recording material P onto which the toner image has been transferred is separated from the surface of the intermediate transfer belt 6 and conveyed to a fixing device 9 serving as fixing means (fixing section). In this embodiment, the fixing device 9 is a heat roller fixing device that applies heat and pressure to the recording material P bearing the unfixed toner image, thereby fixing (melting and adhering) the toner image onto the recording material P. The recording material P onto which the toner image has been fixed is discharged (output) to the outside of the main body of the image forming apparatus 100 as an image-formed product (print, copy).

[0023] Meanwhile, after the primary transfer process, the surface of the photosensitive drum 1 is exposed to light by a static eliminator 10, which serves as a static eliminator (static eliminator), and is neutralized. In this embodiment, the static eliminator 10 is configured with an LED array. The position on the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 where the static eliminator 10 irradiates static elimination light is the static elimination position Pe. After the primary transfer process, the surface of the photosensitive drum 1 retains a history of potential formed through the processes of charging, exposure (formation of an electrostatic latent image), development, and primary transfer. By exposure by the static eliminator 10 at the static elimination position Pe, the potential remaining on the surface of the photosensitive drum 1 can be reduced to approximately 0 V.

[0024] Furthermore, toner (transfer residual toner) and other deposits remaining on the surface of the photosensitive drum 1 after the primary transfer are removed and collected from the surface of the photosensitive drum 1 by a cleaning device 7 serving as a cleaning means (cleaning unit). The cleaning device 7 includes a cleaning blade 71 serving as a cleaning member and a cleaning container 72 that accommodates the transfer residual toner and other materials removed from the surface of the photosensitive drum 1 by the cleaning blade 71. In this embodiment, the cleaning blade 71 is formed of urethane rubber as an elastic material. The cleaning blade 71 has a flat plate shape with a predetermined thickness and a predetermined length in both the longitudinal direction, which is aligned with the rotational axis of the photosensitive drum 1, and the lateral direction, which is substantially perpendicular to the longitudinal direction. One end (fixed end) of the cleaning blade 71 in the lateral direction is fixed to and supported by the cleaning container 72 (or a support member fixed thereto), and the edge of the other end (free end) facing the photosensitive drum 1 is brought into contact with the surface of the photosensitive drum 1. The position on the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 where the cleaning blade 71 removes toner (contact portion of the cleaning blade 71) is the cleaning position Pf. The free end of the cleaning blade 71 is located upstream of the fixed end in the moving direction of the surface of the photosensitive drum 1, and the free end contacts the surface of the photosensitive drum 1 with the free end facing upstream in the moving direction (counter direction to the moving direction of the surface of the photosensitive drum 1). In this embodiment, the length of the cleaning blade 71 in the longitudinal direction (axial direction) is 330 mm. In this embodiment, the cleaning blade 71 is pressed against the photosensitive drum 1 with a linear pressure of 25 to 35 gf / cm. The linear pressure is the pressure per unit length in the longitudinal direction of the cleaning blade 71, and is the value obtained by dividing the total pressure of the contact pressure of the cleaning blade 71 against the photosensitive drum 1 by the longitudinal length of the contact portion between the photosensitive drum 1 and the cleaning blade 71. This linear pressure can be determined by attaching a load converter to the photosensitive drum 1 (or a contact object for measurement that resembles the photosensitive drum 1), pressing the cleaning blade 71 against the surface of the photosensitive drum 1, and measuring the load.

[0025] In addition, the toner (residual toner) and other deposits remaining on the surface of the intermediate transfer belt 6 after the secondary transfer process are removed and collected from the surface of the intermediate transfer belt 6 by a belt cleaning device 64 serving as an intermediate transfer body cleaning means.

[0026] 2. Control mode FIG. 3 is a schematic block diagram illustrating the control mode of the main components of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 includes a control unit 50 that comprehensively controls the operation of each component of the image forming apparatus 100. The control unit 50 includes a CPU 51 as a computation control unit (computation control unit) that is a central element for performing computational processing, a memory unit 52 configured with ROM, RAM, etc. as a storage unit (storage unit), and other components. The control unit 50 also includes a timer 53 as a time measurement unit (time measurement unit), and an interface unit (input / output circuit) (not shown) that controls the input and output (communication) of signals between the control unit 50 and devices connected thereto. The RAM, which is a rewritable memory, stores information input to the control unit 50, detected information, computation results, etc., while the ROM stores control programs, pre-calculated data tables, etc. The CPU 51 comprehensively controls the operation of each component of the image forming apparatus 100 according to the programs stored in the ROM, using the RAM as a working area. In relation to this embodiment, the control unit 50 controls, for example, the driving of the drum drive motor MTR1, the development drive motor MTR2, and the belt drive motor MTR3, the application of bias from various power sources PS1, PS2, PS3, and PS4, and the processing of image information.

[0027] That is, the control unit 50 transmits control signals to the drum drive motor MTR1, the development drive motor MTR2, and the belt drive motor MTR3. In response to these signals, the drum drive motor MTR1 drives the photosensitive drum 1, the development drive motor MTR2 drives the development sleeve 41, and the belt drive motor MTR3 drives the intermediate transfer belt 6 (drive roller 61). In this embodiment, the image forming apparatus 100 includes a torque detection circuit 11 as a torque detection means (torque detection unit) that detects a value correlated with the drive torque of the photosensitive drum 1 generated by the drum drive motor MTR1. Any known torque detection means may be used. In this embodiment, a stepping motor is used as the drum drive motor MTR. The torque detection circuit 11 detects a torque current component that generates torque in the stepping motor. This allows the torque detection circuit 11 to detect the motor torque generated by the drum drive motor MTR1 as a value correlated with the drive torque of the photosensitive drum 1 generated by the drum drive motor MTR. However, the present invention does not limit the configuration or control method of the drum drive motor MTR1. For example, in the case of a stepping motor, motor torque can be detected based on the torque current component in vector control. In the case of a DC brushless motor, motor torque can be detected by detecting the current value or PWM value of the voltage. The torque detection circuit 11 inputs a signal indicating the detection result of the drive torque (motor torque) to the control unit 50. The control unit 50 stores information about the drive torque (motor torque) acquired by the torque detection circuit 11 in a memory unit 52 within the control unit 50. Note that the value (index value) correlated with the drive torque of the photosensitive drum 1 by the drum drive motor MTR1 used for processing in the control unit 50 is not limited to the torque value itself, but may be a current value, a voltage value, or the like. Here, the value correlated with the drive torque of the photosensitive drum 1 by the drum drive motor MTR1 acquired by the torque detection circuit 11 is also simply referred to as the “drive torque.”

[0028] The control unit 50 also transmits control signals to the charging power supply PS1, the developing power supply PS2, the primary transfer power supply PS3, and the secondary transfer power supply PS4. In response to these signals, the charging power supply PS1 applies a charging bias to the charging roller 2 from the charging DC power supply 12 and the charging AC power supply 13. In response to these signals, the developing power supply PS2 applies a developing bias to the developing sleeve 41 from the developing DC power supply 14 and the developing AC power supply 15. In response to these signals, the primary transfer power supply PS3 applies a primary transfer bias to the primary transfer roller 5 from the primary transfer DC power supply 16. In response to these signals, the secondary transfer power supply PS4 applies a secondary transfer bias to the secondary transfer roller 8 from the secondary transfer DC power supply 17.

[0029] Furthermore, the control unit 50 transmits a control signal corresponding to the image signal to the exposure device 3. The exposure device 3 outputs laser light L modulated in accordance with the signal. At the same time as or before the control unit 50 transmits the image signal to the exposure device 3, data of the image to be formed is written in the memory unit 52 within the control unit 50.

[0030] Although not shown in the figure, in this embodiment, the drum drive motor MTR1, development drive motor MTR2, charging power supply PS, development power supply PS2, primary transfer power supply PS3, and torque detection circuit 11 are provided independently for each of the image forming units SY, SM, SC, and SK.

[0031] Here, the image forming apparatus 100 executes a job (print job), which is a series of operations that starts with a single start command and forms and outputs an image on one or multiple recording materials P. A job generally includes an image forming process, a pre-rotation process, an inter-sheet 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 of the image to be actually formed and output on the recording material P is formed, a toner image is formed, and the toner image is primarily and secondary transferred. This period is referred to as the image formation period. More specifically, the timing of the image formation process differs depending on the position where each of the electrostatic latent image formation, toner image formation, primary transfer of the toner image, and secondary transfer is performed. The pre-rotation process is a period from when a start command is input until the actual start of image formation, during which preparatory operations are performed before the image forming process. The inter-sheet process (inter-recording material process, inter-image process) is a period corresponding to the interval between recording materials P when image formation is performed continuously on multiple recording materials P (continuous image formation). The post-rotation process is a period in which a rearrangement operation (preparatory operation) is performed after the image forming process. The non-image formation time (non-image formation period) is a period other than the image formation time, and includes the pre-rotation process, the sheet interval process, the post-rotation process, and further 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.

[0032] 3. Toner melting prevention operation Next, the toner fusion suppression operation in this embodiment will be described. Note that in this embodiment, the explanation will be focused on the control of the toner fusion suppression operation in one representative image forming unit S among the multiple image forming units S. An example of the control of the toner fusion suppression operation in the multiple image forming units S will be described in Example 4.

[0033] 3-1. Overview of toner fusion suppression operation In the image forming apparatus 100, when high-area-ratio images are continuously formed, the amount of external additive supplied to the vicinity of the cleaning position Pf increases, which can reduce the coefficient of friction (dynamic friction coefficient, dynamic friction force) between the photosensitive drum 1 and the cleaning blade 71. This reduces the abrasive force of the cleaning blade 71 on the surface of the photosensitive drum 1, potentially resulting in image defects such as toner fusion. In particular, when the photosensitive drum 1 is abraded solely by the cleaning blade 71, the abrasive force of the cleaning blade 71 on the surface of the photosensitive drum 1 is significantly affected by the coefficient of friction between the photosensitive drum 1 and the cleaning blade 71. A high-area-ratio image refers to an image with a high image area ratio. The image area ratio refers to the ratio (proportion) of the area of ​​toner adhesion to the area of ​​the image formation area (area where a toner image can be formed) on the photosensitive drum 1 or on the recording material P corresponding to one sheet of recording material P, which is preset according to the size and category of the recording material P. The image area ratio is also referred to as the print rate or image duty.

[0034] FIG. 4 is a graph showing an example of the relationship between the drive torque acquired by the torque detection circuit 11 and the growth of toner-caused deposits (aggregates) on the photosensitive drum 1. The horizontal axis of FIG. 4 represents the average drive torque measured during continuous image formation, as described below. The vertical axis of FIG. 4 represents the length of the toner-caused deposits (aggregates) on the photosensitive drum 1 measured in the direction of rotation of the photosensitive drum 1 (the direction of surface movement) after continuous image formation on 50,000 sheets of A4-sized recording material (paper) P. As can be seen from FIG. 4, the growth of toner-caused deposits (aggregates) on the photosensitive drum 1 was suppressed as the drive torque increased. Furthermore, when the drive torque was increased to a certain threshold (3.0 kgf·cm in this example), the growth of toner-caused deposits (aggregates) on the photosensitive drum 1 disappeared. This indicates that increasing the drive torque, i.e., increasing the coefficient of friction between the photosensitive drum 1 and the cleaning blade 71, enables the cleaning blade 71 to remove deposits from the photosensitive drum 1.

[0035] Therefore, in this embodiment, when the image forming apparatus 100 determines that the abrasive force of the cleaning blade 71 on the surface of the photosensitive drum 1 has decreased during continuous image formation, the image forming apparatus 100 suspends image formation and performs a toner fusion suppression operation. In this embodiment, the toner fusion suppression operation includes at least a torque increase operation (to be described later), and typically includes a torque increase operation (to be described later) and an adhering matter removal operation (to be described later).

[0036] 3-2.Operation procedure FIG. 5 is a flowchart showing an outline of the procedure of the toner fusion suppression operation (toner fusion suppression sequence) in this embodiment.

[0037] When the control unit 50 starts a job (here, a job for continuous image formation), it stores the drive torque acquired by the torque detection circuit 11 during the execution of the job (while the photosensitive drum 1 is rotating) in the memory unit 52 (S101). In addition, in S101, the control unit 50 starts measuring time using the timer 53. In this embodiment, the control unit 50 performs sampling every 50 seconds (100 ms x 10 times) and records the average value of the 10 sampling results as the drive torque at that time in the memory unit 52. In this embodiment, the control unit 50 stores a total of 10 drive torques in the memory unit 52 over a period of 500 seconds. In this embodiment, the control unit 50 then determines, after 500 seconds have elapsed, whether five or more of the 10 drive torques stored in the memory unit 52 are less than the torque increase operation start threshold (start threshold) of 3.0 kgf·cm (S102). That is, in this embodiment, the control unit 50 determines that the drive torque has become smaller than the start threshold when the average value of the drive torque acquired over time during the execution of the job operation satisfies a predetermined condition (i.e., five or more of the ten average values ​​are less than the start threshold). By making this determination based on a value obtained by performing a predetermined statistical process (averaging process) on multiple detection results from the torque detection circuit 11, it is possible to prevent the toner fusion suppression operation from being frequently performed when, for example, the drive torque drops momentarily. This makes it possible to prevent unnecessary downtime (periods during which images cannot be formed).

[0038] If the control unit 50 determines in S102 that the drive torque has fallen below 3.0 kgf·cm (start threshold) ("Yes"), it suspends image formation and performs a torque increase operation (described later) during the inter-sheet process (S103). This is because it can be determined that the cleaning blade 71 is not capable of removing toner-related deposits (aggregates) from the photosensitive drum 1 insufficiently. The control unit 50 then acquires the drive torque detection results from the torque detection circuit 11 during the torque increase operation and determines whether the drive torque has reached or exceeded the torque increase operation end threshold (end threshold) of 4.0 kgf·cm (S104). Note that the control unit 50 can also make this determination based on values ​​obtained by performing a predetermined statistical process (averaging process) on multiple detection results from the torque detection circuit 11. For example, the average value for each 100-ms sampling period can be used as the drive torque at that time. Furthermore, as in this embodiment, it is preferable to set the end threshold to a value greater than the start threshold in order to sufficiently increase the drive torque during the torque increase operation. If the control unit 50 determines in S104 that the drive torque has reached or exceeded 4.0 kgf cm (termination threshold) ("Yes"), it executes the deposit removal operation (described later) (S105). After executing the deposit removal operation for a predetermined time, the control unit 50 terminates the deposit removal operation, resets the timer 53 to its initial value (0 in this embodiment) (S106), and returns to image formation (S107).

[0039] On the other hand, if the control unit 50 determines in S102 that the driving torque is not less than 3.0 kgf cm (start threshold), i.e., that the driving torque is equal to or greater than 3.0 kgf cm (start threshold) ("No"), it proceeds as follows: it does not execute the toner fusion suppression operation (torque increase operation, deposit removal operation), resets the timer 53 to its initial value (0 in this embodiment) (S106), and continues image formation (S107). This is because it can be determined that the cleaning blade 71 has removed the deposits (aggregates) caused by the toner on the photosensitive drum 1.

[0040] 3-3. Torque increase operation The torque increase operation (torque increase sequence) in this embodiment will be further described. Fig. 6 is an explanatory diagram showing an example of the relationship between the toner fusion suppression operation in this embodiment and the transition of the driving torque of the photosensitive drum 1. The upper part of Fig. 6 is a sequence diagram of the driving of the photosensitive drum 1 and the developing sleeve 41 and the application of the charging bias and the developing bias in the toner fusion suppression operation (torque increase operation, deposit removal operation). The lower part of Fig. 6 is a graph diagram showing the transition of the driving torque of the photosensitive drum 1 during the period corresponding to the sequence diagram in the upper part.

[0041] When the torque increase operation is initiated, the developing device 4 is switched off from the bias application state during image formation to both the developing DC bias and the developing AC bias, and the driving (rotation) of the developing sleeve 41 is stopped. In other words, the supply of toner (including external additives) from the developing sleeve 41 to the photosensitive drum 1 is essentially stopped. On the other hand, in this embodiment, even when the torque increase operation is initiated, the charging roller 2 is maintained in the bias application state during image formation, and both the charging DC bias and the charging AC bias remain ON. In other words, a discharge occurs between the charging roller 2 and the photosensitive drum 1, and a state in which the surface of the photosensitive drum 1 is charged by the charging roller 2 is maintained. Then, with the charging bias ON, the developing bias OFF, and the driving (rotation) of the developing sleeve 41 stopped, the photosensitive drum 1 is driven (rotated) at least one revolution. By generating a discharge between the charging roller 2 and the photosensitive drum 1 while the supply of external additives from the developing sleeve 41 to the photosensitive drum 1 is stopped, the friction coefficient between the photosensitive drum 1 and the cleaning blade 71 can be increased. That is, by generating a discharge between the charging roller 2 and the photosensitive drum 1, discharge products are deposited on the surface of the photosensitive drum 1, thereby increasing the coefficient of friction between the photosensitive drum 1 and the cleaning blade 71. It has been found that these discharge products are sufficiently removed by the rubbing between the photosensitive drum 1 and the cleaning blade 71 during the deposit removal operation performed following the torque increase operation or during subsequent image formation, and image deletion is sufficiently suppressed.

[0042] Here, rotating the photosensitive drum 1 at least once during the torque increase operation means, more specifically, rotating the photosensitive drum 1 until the leading edge of the surface area of ​​the photosensitive drum 1 in the rotation direction of the photosensitive drum 1, which has passed the charging position Pa while a discharge is occurring between the charging roller 2 and the photosensitive drum 1 and passed the development position Pc while the supply of toner (including external additives) from the developing sleeve 41 to the photosensitive drum 1 is stopped (in this embodiment, the rotation of the developing sleeve 41 is stopped, and the developing DC bias and the developing AC bias are turned off), reaches the charging position Pa again at least once. This allows the coefficient of friction between the photosensitive drum 1 and the cleaning blade 71 to be increased at least once around the entire circumference of the photosensitive drum 1. The upper limit of the rotation time (number of rotations) of the photosensitive drum 1 during the torque increase operation can be set as appropriate from the perspective of the degree of increase in the coefficient of friction between the photosensitive drum 1 and the cleaning blade 71, minimizing downtime, and the like. For example, the upper limit of the rotation time (number of rotations) of the photosensitive drum 1 during the torque increase operation can be approximately 60 seconds in terms of time (120 rotations in terms of the number of rotations in this embodiment: peripheral length of the photosensitive drum 1 is 100 mm, peripheral speed of the photosensitive drum 1 is 200 mm / sec).

[0043] In this embodiment, the process transitions from the image forming process to the torque increasing operation in the inter-sheet process while the driving (rotation) of the photosensitive drum 1 continues, but the present invention is not limited to this. After the image forming process, the driving (rotation) of the photosensitive drum 1 may be temporarily stopped before the torque increasing operation is started.

[0044] In this embodiment, the charging bias during the torque increase operation is set to a value equivalent to that during image formation. However, the present invention is not limited to this configuration. The charging bias during the torque increase operation may be set differently from that during image formation, as long as discharge occurs between the charging roller 2 and the photosensitive drum 1. For example, the following setting may be used to reduce the possibility of carrier migration (carrier adhesion) of the two-component developer from the developing sleeve 41 to the photosensitive drum 1 at the development position Pc. That is, the absolute value of the charging DC bias can be made smaller than that during image formation so that the potential difference between the developing sleeve 41 and the developing bias (particularly the developing DC bias) when the developing bias is turned off is equivalent to the aforementioned Vback. For example, in the configuration of this embodiment, the charging DC bias during the torque increase operation can be approximately −150 V (or approximately −170 V). In this case, the charging AC bias can be maintained at a setting equivalent to that during image formation. Whether or not a voltage is sufficient to cause a discharge between the charging member and the photosensitive member (i.e., a voltage equal to or greater than the discharge initiation voltage) can be determined, for example, by measuring the current flowing through the charging member while increasing the absolute value of the voltage applied to the charging member. In other words, the slope of the change in current relative to the change in voltage differs between the non-discharged region and the discharged region, and the discharge initiation voltage can be determined by determining the voltage corresponding to the inflection point of that slope.

[0045] In this embodiment, the driving (rotation) of the developing sleeve 41 is stopped during the torque increasing operation, but the present invention is not limited to this mode. (So-called fog toner) If the supply of toner can be sufficiently reduced, the developing sleeve 41 may be driven (rotated) at a lower rotation speed during the torque increasing operation than during image formation.

[0046] Furthermore, the image forming apparatus 100 may be configured to have a moving mechanism that moves the developing member between a first position during image formation (development) and a second position that is farther from the photosensitive drum 1 than the first position. In such a configuration, the developing sleeve 41 may be positioned farther from the photosensitive drum 1 than during image formation, thereby sufficiently reducing the supply of toner (including external additives) from the developing sleeve 41 to the photosensitive drum 1. In this case, the developing sleeve 41 may also be stopped or rotated at a lower rotation speed than during image formation.

[0047] Furthermore, in this embodiment, both the developing DC bias and the developing AC bias are turned OFF during the torque increase operation, but the present invention is not limited to this embodiment. At least one of the developing DC bias and the developing AC bias may be turned ON as long as the supply of toner (including external additives) from the developing sleeve 41 to the photosensitive drum 1 can be sufficiently reduced. For example, during the torque increase operation, the developing DC bias may be turned OFF and the developing AC bias may be turned ON (for example, a setting equivalent to that during image formation).

[0048] 3-4. Deposit removal operation The deposit removal operation (deposit removal sequence) in this embodiment will be further described with reference to FIG. 6, as in the torque increase operation.

[0049] During the torque increase operation, if the drive torque acquired by the torque detection circuit 11 exceeds 4.0 kgf·cm (the termination threshold), the torque increase operation is terminated and the operation transitions to the deposit removal operation. When the deposit removal operation begins, both the charging DC bias and the charging AC bias of the charging roller 2 are switched off from the bias applied state during the torque increase operation. This means that no discharge occurs between the charging roller 2 and the photosensitive drum 1, and the surface of the photosensitive drum 1 is not charged. Meanwhile, even when the deposit removal operation begins, the bias of the developing device 4 and the drive (rotation) of the developing sleeve 14 are maintained stopped during the torque increase operation. This means that the supply of toner (including external additives) from the developing sleeve 41 to the photosensitive drum 1 is essentially stopped. Then, with the charging bias and developing bias off and the drive (rotation) of the developing sleeve 41 stopped, the photosensitive drum 1 is driven (rotated) at least one revolution. As a result, the coefficient of friction between the photosensitive drum 1 and the cleaning blade 71 is less likely to fluctuate, and the adhesion removal operation (rotation of the photosensitive drum 1) can be continued while the driving torque acquired by the torque detection circuit 11 is maintained at approximately 4.0 kgf·cm. Then, with the coefficient of friction between the photosensitive drum 1 and the cleaning blade 71 increased, adhesions (aggregates) caused by toner that may have occurred on the photosensitive drum 1 can be removed. Furthermore, because the coefficient of friction between the photosensitive drum 1 and the cleaning blade 71 can be prevented from continuing to increase, it is possible to prevent the cleaning blade 71 from turning over. In other words, if the rotation of the photosensitive drum 1 is continued with the torque increasing operation set even after the driving torque of the photosensitive drum 1 reaches the end threshold, the coefficient of friction between the photosensitive drum 1 and the cleaning blade 71 continues to increase, which may cause the cleaning blade 71 to turn over. By continuing the rotation of the photosensitive drum 1 with the adhesion removal operation set, adhesions (aggregates) caused by toner that may have occurred on the photosensitive drum 1 can be removed while preventing the cleaning blade 71 from turning over. After that, when a predetermined time has elapsed, the operation of removing the deposits is finished and image formation is resumed.

[0050] Here, rotating the photosensitive drum 1 at least once in the deposit removal operation means, more specifically, rotating the photosensitive drum 1 until the leading edge of the surface area of ​​the photosensitive drum 1 in the rotation direction of the photosensitive drum 1, which has passed the charging position Pa while the generation of discharge between the charging roller 2 and the photosensitive drum 1 is stopped and passed the development position Pc while the supply of toner (including external additives) from the developing sleeve 41 to the photosensitive drum 1 is stopped (in this embodiment, the rotation of the developing sleeve 41 is stopped, and the developing DC bias and the developing AC bias are turned off), reaches the charging position Pa again. This allows the surface of the photosensitive drum 1 to be polished by the cleaning blade 71 at least once around the entire circumference of the photosensitive drum 1. The upper limit of the rotation time (number of rotations) of the photosensitive drum 1 in the deposit removal operation can be appropriately set from the viewpoints of the degree of removal of deposits (aggregates) caused by toner from the photosensitive drum 1, minimizing downtime, etc. For example, the upper limit of the rotation time (number of rotations) of the photosensitive drum 1 during the torque increase operation can be approximately 60 seconds in terms of time (120 rotations in terms of the number of rotations in this embodiment: peripheral length of the photosensitive drum 1 is 100 mm, peripheral speed of the photosensitive drum 1 is 200 mm / sec).

[0051] In this embodiment, the torque increase operation is switched to the deposit removal operation while the driving (rotation) of the developing sleeve 41 is stopped, but the present invention is not limited to this mode. For example, when the torque increase operation is switched to the deposit removal operation, the developing sleeve 41 may be driven (rotated) for a period corresponding to less than one rotation of the photosensitive drum 1, from the viewpoint of preventing the cleaning blade 71 from turning over. At this time, at least one of the developing DC bias and the developing AC bias may be turned ON (for example, a setting corresponding to the time of image formation).

[0052] In this embodiment, the torque increase operation is switched to the deposit removal operation based on the drive torque acquired by the torque detection circuit 11. However, the present invention is not limited to this configuration. For example, the torque increase operation may be switched to the deposit removal operation based on time, from the viewpoint of minimizing downtime. In this case, the control unit 50 terminates the torque increase operation after executing the torque increase operation for a predetermined time and starts the deposit removal operation. That is, in this case, the control unit 50 controls the transition from the torque increase operation to the deposit removal operation regardless of the detection result of the torque detection circuit 11. Furthermore, in addition to performing control based on the drive torque acquired by the torque detection circuit 11 as in this embodiment, an upper limit may be set for the execution time of the torque increase operation. In this case, the torque increase operation is terminated and the deposit removal operation is started after a predetermined time has elapsed, even if the drive torque acquired by the torque detection circuit 11 does not reach the termination threshold. Furthermore, the upper limit of the execution time of the torque increase operation may be set as the upper limit for the overall execution time of the toner fusion suppression operation. In this case, the torque increase operation is terminated and image formation is resumed after a predetermined time has elapsed, even if the drive torque acquired by the torque detection circuit 11 does not reach the termination threshold. That is, in this case, the toner fusion suppression operation includes only the torque increase operation out of the torque increase operation and the deposit removal operation. This makes it possible to increase the coefficient of friction between the photosensitive drum 1 and the cleaning blade 71 as much as possible during the execution of the toner fusion suppression operation while suppressing downtime. Also in this case, the friction between the photosensitive drum 1 and the cleaning blade 71 during subsequent image formation, etc., makes it possible to remove to some extent deposits (aggregates) caused by toner that may have formed on the photosensitive drum 1.

[0053] In addition, in this embodiment, both the charging DC bias and the charging AC bias are turned OFF during the deposit removal operation, but the present invention is not limited to this. As long as the setting is such that no discharge occurs between the charging roller 2 and the photosensitive drum 1, at least one of the charging DC bias and the charging AC bias may be turned ON.

[0054] Furthermore, similarly to the torque increasing operation, the developing sleeve 41 may be driven (rotated) at a rotation speed lower during the deposit removing operation than during image formation.

[0055] As in the case of the torque increasing operation, at least one of the developing DC bias and the developing AC bias may be turned on in the deposit removing operation.

[0056] 4.Effects As described above, the image forming apparatus 100 of this embodiment includes the rotatable photoreceptor 1, the charging member 2 that charges the surface of the photoreceptor 1, the charging power source PS1 that applies a voltage to the charging member 2, the exposure unit 3 that exposes the charged surface of the photoreceptor 1 to light to form an electrostatic image on the surface of the photoreceptor 1, the rotatable developing member 41 that supplies toner to the electrostatic image to form a toner image on the surface of the photoreceptor 1, the transfer device 19 that transfers the toner image formed on the photoreceptor 1 to a recording material P, the cleaning member 71 that comes into contact with the surface of the photoreceptor 1 to remove toner from the surface of the photoreceptor 1, the drive unit MTR1 that drives the photoreceptor 1, and the drive unit The control unit 50 includes a detection unit 11 that detects a value correlated with the driving torque of the photoreceptor 1 by the MTR 1, and a control unit 50 that, based on the detection result of the detection unit 11, performs continuous image formation, which involves forming toner images to be transferred onto a recording material P and transferring the toner images to multiple recording materials P, and performs an operation (torque increase operation) to interrupt image formation, apply a voltage to the charging member 2 that causes discharge between the charging member 2 and the photoreceptor 1, and either stop the rotation of the developing member 41 or rotate the photoreceptor 1 at least one revolution while rotating the developing member 41 at a rotation speed lower than that during image formation. In this embodiment, the control unit 50 performs the operation (torque increase operation) when the detection result of the detection unit 11, acquired over time during the continuous image formation, indicates that the driving torque has decreased to satisfy a predetermined condition. In this embodiment, the control unit 50 also performs the operation (torque increase operation) when the driving torque, indicated by the average value of multiple detection results of the detection unit 11 acquired during the continuous image formation, becomes smaller than a predetermined threshold. In particular, in this embodiment, the control unit 50 performs the above operation (torque increasing operation) when the driving torque indicated by a predetermined number or more of the average values ​​obtained during the execution of the continuous image formation becomes smaller than the threshold value.

[0057] In this embodiment, the control unit 50 can perform another operation (adherent material removal operation) after the above operation (torque increase operation) and before resuming image formation, in which either no voltage is applied to the charging member 2 or a voltage that does not cause discharge between the charging member 2 and the photosensitive member 1 is applied to the charging member 2, and the rotation of the developing member 41 is stopped or the developing member 41 is rotated at a rotation speed lower than that during image formation, and the photosensitive member 1 is rotated at least one revolution at that speed. In this embodiment, the control unit 50 performs the above operation (torque increase operation) when the detection results of the detection unit 11 obtained over time during the execution of the continuous image formation indicate that the drive torque has decreased so as to satisfy a predetermined condition, and performs the other operation (adherent material removal operation) when the detection results of the detection unit 11 obtained over time during the execution of the above operation (torque increase operation) indicate that the drive torque has increased so as to satisfy a predetermined condition. In this embodiment, the control unit 50 executes the operation (torque increase operation) when the drive torque indicated by the average value of multiple detection results obtained by the detection unit 11 during the execution of the continuous image formation becomes smaller than a predetermined first threshold, and executes the other operation (adherent material removal operation) when the drive torque indicated by the average value of multiple detection results obtained by the detection unit 11 during the execution of the operation (torque increase operation) becomes equal to or greater than a predetermined second threshold. In this embodiment, the second threshold is greater than the first threshold. The control unit 50 may also execute the operation (torque increase operation) when the detection results obtained by the detection unit 11 over time during the execution of the continuous image formation indicate that the drive torque has decreased to satisfy a predetermined condition, and execute the other operation (adherent material removal operation) after a predetermined time has elapsed since the start of the operation (torque increase operation).

[0058] In this embodiment, the control unit 50 applies an oscillating voltage in which a DC component and an AC component are superimposed to the charging member 2 in the above operation (torque increasing operation). At this time, the control unit 50 can apply an oscillating voltage in which a DC component and an AC component are superimposed to the charging member 2 in the above operation (torque increasing operation). In this embodiment, the image forming apparatus 100 has a development power supply that applies a voltage to the developing member 41, and the control unit 50 does not apply a voltage to the developing member 41 in the above operation (torque increasing operation). In this embodiment, the cleaning member 71 is a cleaning blade.

[0059] In this way, in this embodiment, the photosensitive drum 1 is idly rotated in a state where the drive torque of the photosensitive drum 1 is increased by the torque increasing operation to a level that can remove deposits (aggregates) caused by toner on the photosensitive drum 1. As a result, even if the drive torque of the photosensitive drum 1 becomes low during execution of continuous image formation in which high area ratio images or the like are continuously formed, it is possible to remove deposits (aggregates) caused by toner on the photosensitive drum 1 and suppress the occurrence of image defects such as toner fusion.

[0060] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. 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 embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0061] 1. Overview of this Example It has been found that as the amount of external additives present on the photosensitive drum 1 increases, the drive torque of the photosensitive drum 1 tends to decrease. One of the reasons for the increase in the amount of external additives is the continuous formation of images with a high image area ratio (high area ratio images). This is because when high area ratio images are continuously formed, the amount of external additives supplied to the photosensitive drum 1 along with the toner increases. It has been found that as the amount of external additives on the photosensitive drum 1 increases, the probability of an increase in adhesions (aggregates) caused by the toner on the photosensitive drum 1 also increases, making toner fusion more likely to occur.

[0062] Therefore, in this embodiment, the image forming apparatus 100 controls the toner fusion suppression operation (more specifically, changes the torque increase operation start threshold) based on the image area ratio.

[0063] 2. Control mode FIG. 7 is a schematic block diagram showing the control mode of the main components of the image forming apparatus 100 of this embodiment. The control mode of this embodiment shown in FIG. 7 is similar to the control mode of the first embodiment shown in FIG. 3. However, for the purpose of explaining this embodiment, FIG. 7 shows the control unit 50 further including a video count unit 54 as an image information accumulating means. The control unit 50 transmits a control signal corresponding to an image signal to the exposure device 3. The exposure device 3 outputs a laser beam L modulated in accordance with the signal. Simultaneously with or before the control unit 50 transmits the image signal to the exposure device 3, data of the image to be formed is written to the memory unit 52 within the control unit 50. Then, for the image to be formed, the video count unit 54 counts the number of image signals for each color toner image. The video count value counted by the video count unit 54 is written and stored in the memory unit 52.

[0064] 3.Video Count Value Next, the video count value will be further explained. Fig. 8 is a block diagram showing in more detail the internal configuration of the control unit 50 in this embodiment, which is related to image processing. Here, an example will be described in which the image forming apparatus 100 forms an image based on image information read by an image reading device (not shown), but the image forming apparatus 100 can also form an image based on image information from a personal computer or the like.

[0065] An image formed on a CCD sensor 217 of the image reading device is converted into an analog electrical signal by the CCD sensor 217. The converted image information is input to an analog signal processing unit 300, where it undergoes sample-and-hold, dark level correction, and other processes. The signal then undergoes analog-to-digital (A / D) conversion in an A / D·SH processing unit 301, and shading correction is then performed on the digitized signal. The shading correction involves correction for variations in the pixel-to-pixel characteristics of the CCD sensor 217 and for variations in the amount of light due to position based on the light distribution characteristics of the document illumination lamp.

[0066] Thereafter, RGB inter-line correction is performed in an RGB inter-line correction unit 302. Since the light incident on each RGB light-receiving element of the CCD sensor 217 at a certain point in time is shifted depending on the relative positions of the RGB light-receiving elements on the document, synchronization between the RGB signals is achieved here.

[0067] Thereafter, an input masking process is performed in an input masking unit 303, and the luminance data is converted into density data. Since the RGB values ​​output directly from the CCD sensor 217 are affected by the color filters attached to the CCD sensor 217, this effect is corrected and the values ​​are converted into pure RGB values.

[0068] Thereafter, the image is subjected to a scaling process at a desired scaling factor in the scaling unit 304, and the scaled image data is sent to the memory unit 52 and stored therein.

[0069] The stored image is sent from the memory unit 52 to a gamma correction unit 306. In the gamma correction unit 306, the original density data is converted into density data corresponding to the desired output density based on a lookup table (LUT) that takes into account the printer's characteristics, so that the output corresponds to the set density value. The density data is then sent to a binarization unit 307, where the 8-bit multi-level signal is converted into a binary signal. For example, this conversion method may be a dither method, an error diffusion method, or an improved version of error diffusion. The binarized data is sent to a video count unit 54, where the binary data is counted for each color image.

[0070] 4. Toner melting prevention operation 9 is a flowchart showing an outline of the procedure for the toner fusion suppression operation in this embodiment. Note that, in this embodiment, as in the first embodiment, the explanation will be focused on the control of the toner fusion suppression operation in one representative image forming unit S among the multiple image forming units S.

[0071] When the control unit 50 starts a job (here, a job of continuous image formation), it stores the driving torque acquired by the torque detection circuit 11 in the memory unit 52 while the job operation is being executed (while the photosensitive drum 1 is rotating) (S201). The method of acquiring the driving torque in this embodiment is the same as in embodiment 1. In addition, in S201, the control unit 50 starts measuring time using the timer 53.

[0072] Furthermore, when the control unit 50 starts a job, it stores the cumulative video count value during image formation in the memory unit 52 (S202). In this embodiment, the control unit 50 calculates the image area ratio A per image from the cumulative video count value after 500 seconds have elapsed and the number of images formed. Table 1 shows a matrix showing the relationship between the image area ratio A and the torque increase operation start threshold (start threshold) B in this embodiment. Information about this matrix is ​​set in advance and stored in the memory unit 52.

[0073] [Table 1]

[0074] In this embodiment, similar to the first embodiment, the control unit 50 determines whether five or more of the ten drive torques stored in the memory unit 52 are less than the start threshold value B after 500 seconds have elapsed (S203). When making this determination, the control unit 50 references the image area ratio A at that time and determines the start threshold value B according to the matrix in Table 1. In this embodiment, similar to the first embodiment, the control unit 50 determines that the drive torque has become smaller than the start threshold value when the average value of the drive torque obtained over time during the execution of the job operations satisfies a predetermined condition (five or more of the ten average values ​​are less than the start threshold value).

[0075] If the control unit 50 determines in S203 that the driving torque has fallen below the start threshold B ("Yes"), it suspends image formation and performs a torque increase operation in the inter-sheet process (S204). This is because it can be determined that the cleaning blade 71 is not capable of removing toner-related deposits (aggregates) from the photosensitive drum 1 insufficiently. The control unit 50 then acquires the driving torque detection result from the torque detection circuit 11 while the torque increase operation is being performed, and determines whether the driving torque has reached or exceeded the torque increase operation end threshold (end threshold) of 4.0 kgf·cm (S205). If the control unit 50 determines in S205 that the driving torque has reached or exceeded 4.0 kgf·cm (end threshold) ("Yes"), it performs an deposit removal operation (S206). After performing the adhesion removal operation for a predetermined time, the control unit 50 terminates the adhesion removal operation, resets the cumulative video count value and the timer 53 to their initial values ​​(0 in this embodiment) (S207), and returns to image formation (S208).

[0076] On the other hand, if the control unit 50 determines in S203 that the driving torque is not less than the start threshold B, that is, that the driving torque is equal to or greater than the start threshold B ("No"), it proceeds as follows: It does not execute the toner fusion suppression operation (torque increase operation, deposit removal operation), resets the cumulative video count value and the timer 53 to their initial values ​​(0 in this embodiment) (S207), and continues image formation (S208). This is because it can be determined that the deposits (aggregates) caused by the toner on the photosensitive drum 1 have been removed by the cleaning blade 71 in this case.

[0077] In this embodiment, it is known that toner-induced adhesion (aggregates) do not grow if the image area ratio A is less than 10%. Therefore, in this embodiment, the start threshold B when the image area ratio A is less than 10% is set to a drive torque of 1.5 kgf cm, which is equivalent to the smallest drive torque of the photosensitive drum 1 in the configuration of this embodiment (Table 1). This effectively sets the toner fusion suppression operation (torque increase operation, adhesion removal operation) not to be performed when the image area ratio A is less than 10%.

[0078] In this embodiment, by changing the start threshold B according to the image area ratio A, whether or not to perform the toner melting prevention operation is essentially controlled according to the image area ratio A. In this embodiment, the start threshold B when the image area ratio A is a second value smaller than the first value is set to a smaller value than the start threshold B when the image area ratio A is a first value, and the toner melting prevention operation is not performed when the image area ratio A is less than the second value. However, the present invention is not limited to this embodiment, and whether or not to perform the toner melting prevention operation may be controlled more directly according to the image area ratio A. For example, the toner melting prevention operation may be performed when the image area ratio A is equal to or greater than a predetermined value, and not performed when the image area ratio A is less than the predetermined threshold.

[0079] 5.Effects As described above, this embodiment has a counting unit 54 that accumulates signal values ​​of image information that defines a toner image, and the control unit 50 controls whether or not to perform a torque increase operation based on the accumulated value of the signal values ​​accumulated by the counting unit 54 over a predetermined period of time.

[0080] According to this embodiment, the same effects as those of the first embodiment can be obtained, and downtime due to the toner fusion suppression operation can be suppressed for users who print images with a low image area ratio.

[0081] [Example 3] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. 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 embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0082] 1. Overview of this Example In this embodiment, information regarding the contact pressure (linear pressure) of the cleaning blade 71 against the photosensitive drum 1 (hereinafter simply referred to as "contact pressure information") is stored in the memory unit 52 within the control unit 50. This contact pressure information is measured when the image forming apparatus 100 and a replaceable unit including the cleaning blade 71 are manufactured (or when shipped from the factory), and is input to the control unit 50 by appropriate means, as described below, and stored in the memory unit 52. By using this contact pressure information as an auxiliary factor in determining whether or not to perform the toner fusion suppression operation, it is possible to improve the accuracy of control. As a result, even when, for example, the detection accuracy of the drive torque of the photosensitive drum 1 is low, it is possible to suppress the execution of unnecessary toner fusion suppression operation and reduce downtime.

[0083] 2. Control mode Fig. 10 is a schematic block diagram showing the control mode of the main parts of the image forming apparatus 100 of this embodiment. The control mode in this embodiment shown in Fig. 10 is the same as the control mode in the first embodiment shown in Fig. 3. However, in Fig. 10, for the purpose of explaining this embodiment, the control unit 50 is shown as being further connected to an operation unit 55 provided in the image forming apparatus 100, a storage medium 56 provided in a replacement unit including a cleaning blade 71, and an external host processing device 400.

[0084] The operation unit 55 may be configured to have a display or touch panel as a display means (display unit) that displays information under the control of the control unit 50, and keys or a touch panel as an input means (input unit) for inputting information to the control unit 50. Furthermore, an electronic memory such as a memory tag is preferably used as the storage medium 56, and may be provided in a process cartridge as a replaceable unit including a cleaning blade 71. The process cartridge is a cartridge in which the photosensitive drum 1 and at least one of the charging roller 2, developing device 4, and cleaning device 7 that act on the photosensitive drum 1 are integrated into one cartridge, and is detachably mounted on the main body of the image forming apparatus 100. The cleaning device 7 may be detachably mounted on the main body of the image forming apparatus 100 substantially independently.

[0085] In this embodiment, the contact pressure information is measured during the manufacture of the image forming apparatus 100 and the replaceable unit including the cleaning blade 71 (or at the time of shipment from the factory). The contact pressure information is input to the control unit 50 via the operation unit 55 or the host processing device 400 and stored in the memory unit 52, or stored in a storage medium 56 provided in the replaceable unit. Inputting the contact pressure information to the control unit 50 via the operation unit 55 or the host processing device 400 is not limited to inputting the information during the manufacture (or at the time of shipment from the factory). For example, an operator such as a user or a service representative may input the contact pressure information provided, for example, in a package with the product, when installing the image forming apparatus 100 or replacing the replaceable unit. Furthermore, when the contact pressure information is stored in the storage medium 56 of the replaceable unit, the control unit 50 reads the contact pressure information from the storage medium 56 via a reading unit (not shown) provided in the image forming apparatus 100 when the replaceable unit is attached to the main body of the image forming apparatus 100. The control unit 50 then stores the read contact pressure information in the memory unit 52. Note that the control unit 50 may use the contact pressure information read from the storage medium 52 for control without storing it in the memory unit 52. Also, although a plurality of means have been described here, it is sufficient for the control unit 50 to acquire the contact pressure information by at least one means including, for example, the above-mentioned operation unit 55, the storage medium 56, the host processing device 400, etc.

[0086] 3. Toner melting prevention operation 11 is a flowchart showing an outline of the procedure for the toner fusion suppression operation in this embodiment. Note that, in this embodiment, as in the first embodiment, the explanation will be focused on the control of the toner fusion suppression operation in one representative image forming unit S among the multiple image forming units S.

[0087] When the control unit 50 starts a job (here, a job of continuous image formation), it stores the driving torque acquired by the torque detection circuit 11 in the memory unit 52 while the job operation is being executed (while the photosensitive drum 1 is rotating) (S301). The method of acquiring the driving torque in this embodiment is the same as in embodiment 1. In addition, in S301, the control unit 50 starts measuring time using the timer 53.

[0088] Table 2 shows a matrix indicating the relationship between the contact pressure (linear pressure) of the cleaning blade 71 against the photosensitive drum 1 in this embodiment and the torque increase operation start threshold (start threshold) C. Information regarding this matrix is ​​set in advance and stored in the memory unit 52.

[0089] [Table 2]

[0090] In this embodiment, similar to the first embodiment, the control unit 50 determines whether five or more of the ten driving torques stored in the memory unit 52 are less than the start threshold C after 500 seconds have elapsed (S302). When making this determination, the control unit 50 references the contact pressure information (linear pressure information) stored in the memory unit 52 (or the storage medium 56) and determines the start threshold C according to the matrix in Table 2. In this embodiment, similar to the first embodiment, the control unit 50 determines that the driving torque has become smaller than the start threshold when the average value of the driving torque acquired over time during the execution of the job operations satisfies a predetermined condition (five or more of the ten average values ​​are less than the start threshold).

[0091] If the control unit 50 determines in S302 that the driving torque has fallen below the start threshold C ("Yes"), it suspends image formation and performs a torque increase operation in the inter-sheet process (S303). This is because it can be determined that the cleaning blade 71 is not capable of removing toner-related deposits (aggregates) from the photosensitive drum 1 insufficiently. The control unit 50 then acquires the driving torque detection result from the torque detection circuit 11 while the torque increase operation is being performed, and determines whether the driving torque has reached or exceeded the torque increase operation termination threshold (termination threshold) of 4.0 kgf·cm (S304). If the control unit 50 determines in S304 that the driving torque has reached or exceeded the 4.0 kgf·cm (termination threshold) ("Yes"), it performs a deposit removal operation (S305). After performing the deposit removal operation for a predetermined time, the control unit 50 terminates the deposit removal operation, resets the timer 53 to its initial value (0 in this embodiment) (S306), and returns to image formation (S307).

[0092] On the other hand, if the control unit 50 determines in S302 that the driving torque is not less than the start threshold C, that is, that the driving torque is equal to or greater than the start threshold C ("No"), it proceeds as follows: it does not execute the toner fusion suppression operation (torque increase operation, deposit removal operation), resets the timer 53 to the initial value (0 in this embodiment) (S306), and continues image formation (S307). This is because it can be determined that the deposits (aggregates) caused by the toner on the photosensitive drum 1 have been removed by the cleaning blade 71.

[0093] In this embodiment, it has been found that a linear pressure of 32.5 gf / cm or higher is sufficient to remove toner-related deposits (aggregates). Therefore, in this embodiment, the start threshold C when the linear pressure is 32.5 gf / cm or higher is set to a drive torque of 1.5 kgf cm, which is equivalent to the smallest drive torque of the photosensitive drum 1 in the configuration of this embodiment (Table 2). This effectively sets the toner fusion suppression operation (torque increase operation, deposit removal operation) to not be performed when the linear pressure is 32.5 gf / cm or higher.

[0094] In this embodiment, the start threshold C is changed depending on the contact pressure (linear pressure) of the cleaning blade 71 against the photosensitive drum 1, thereby essentially controlling whether or not to perform the toner fusion suppression operation depending on the contact pressure (linear pressure). In this embodiment, the start threshold C when the contact pressure (linear pressure) is a second value greater than the first value is set to a lower value than the start threshold C when the contact pressure (linear pressure) is a first value. Therefore, when the contact pressure (linear pressure) is equal to or greater than the second value, the toner fusion suppression operation is not performed. However, the present invention is not limited to this configuration, and the execution of the toner fusion suppression operation may be controlled more directly depending on the contact pressure (linear pressure). For example, the toner fusion suppression operation may be performed when the contact pressure (linear pressure) is less than a predetermined value, and not performed when the contact pressure (linear pressure) is equal to or greater than the predetermined threshold.

[0095] 4.Effects As described above, in this embodiment, the image forming apparatus 100 has a memory unit 52 that stores contact pressure information regarding the contact pressure of the cleaning member 71 against the photosensitive member 1, and the control unit 50 controls whether or not to perform the torque increase operation based on the contact pressure information stored in the memory unit 52.

[0096] According to this embodiment, the same effects as those of the first embodiment can be obtained, and even when the detection accuracy of the driving torque of the photosensitive drum 1 is low, the contact pressure information can be used as an auxiliary to prevent unnecessary execution of the toner fusion suppression operation, thereby making it possible to prevent downtime from occurring.

[0097] The control based on the image area ratio described in the second embodiment and the control based on the contact pressure information described in this embodiment may be combined.

[0098] [Example 4] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. 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 embodiment 1 are assigned the same reference numerals as those of embodiment 1, and detailed descriptions thereof will be omitted.

[0099] For simplicity, in Examples 1 to 3, the description has been focused on the control of the toner fusion suppression operation in one representative image forming unit S among the multiple image forming units S. In this example, an example of the control of the toner fusion suppression operation in the multiple image forming units S will be described.

[0100] When the image forming apparatus 100 has multiple image forming units S, the drive torque of the photosensitive drum 1 in each image forming unit S may differ depending on conditions such as the image formation conditions and the contact pressure of the cleaning blade 71. Therefore, when the image forming apparatus 100 has multiple image forming units S, it is preferable to individually determine whether or not to perform the toner fusion suppression operation (threshold determination) for each image forming unit S. In this embodiment, when the drive torque of the photosensitive drum 1 in at least one of the multiple image forming units S becomes less than the start threshold, the toner fusion suppression operation (torque increase operation, deposit removal operation) is performed in at least that image forming unit S.

[0101] FIG. 12 is a flow chart showing an outline of the procedure for the toner melt-adhesion suppression operation in this embodiment.

[0102] When the control unit 50 starts a job (here, a job of continuous image formation), it stores the driving torques Ty, Tm, Tc, and Tk acquired at each image forming unit S individually in the memory unit 52 while the job operation is being performed (while each photosensitive drum 1 is rotating) (S401). The method of acquiring the driving torque at each image forming unit S in this embodiment is the same as in embodiment 1. In addition, in S401, the control unit 50 starts measuring time using the timer 53.

[0103] In this embodiment, the control unit 50 compares the drive torque with the start threshold for each image forming unit S individually, as in the first embodiment, when 500 seconds have elapsed. That is, the control unit 50 determines whether or not the drive torque for five or more of the ten drive torque measurements stored in the memory unit 52 for each image forming unit S is less than 3.0 kgf / cm (torque increase operation start threshold (start threshold)) (S402). That is, in this embodiment, the control unit 50 determines that the drive torque has become smaller than the start threshold when the average value for five or more of the ten measurements is less than the start threshold, as in the first embodiment, for each image forming unit S individually.

[0104] For the image forming station S for which the control unit 50 determines in S402 that the drive torque has fallen below 3.0 kgf·cm ("Yes"), the control unit 50 suspends image formation and performs a torque increase operation in the inter-sheet process (S403). This is because the control unit 50 determines that the cleaning blade 71 is not capable of removing toner-related deposits (aggregates) from the photosensitive drum 1 for that image forming station S. The control unit 50 then acquires the drive torque detection results from the torque detection circuit 11 while the torque increase operation for that image forming station S is being performed, and determines whether the drive torque has reached or exceeded the torque increase operation termination threshold (termination threshold) of 4.0 kgf·cm (S404). The control unit 50 then performs a deposit removal operation for the image forming station S for which the control unit 50 determines in S404 that the drive torque has reached or exceeded 4.0 kgf·cm (termination threshold) ("Yes") (S405).

[0105] On the other hand, for image forming units S where the control unit 50 has determined in S402 that the drive torque is not less than 3.0 kgf cm, i.e., that the drive torque is 3.0 kgf cm or greater ("No"), in this embodiment, the control unit 50 executes the deposit removal operation (S405). In other words, for those image forming units S, the ability of the cleaning blade 71 to remove deposits (aggregates) caused by toner on the photosensitive drum 1 is sufficient, so the torque increase operation is omitted and the deposit removal operation is executed.

[0106] In this embodiment, when a predetermined time has elapsed since the start of the toner fusion suppression operation, the control unit 50 ends the toner fusion suppression operation (torque increase operation or deposit removal operation), resets the timer 53 to its initial value (0 in this embodiment) (S406), and returns to image formation in all image forming units S (S407). Note that in this embodiment, as described in the first embodiment, if the driving torque of the photosensitive drum 1 in an image forming unit S that is performing the torque increase operation does not reach the termination threshold within the predetermined time, the image forming unit S returns to image formation without proceeding to the deposit removal operation. In this embodiment, the predetermined time (the upper limit of the total execution time of the toner fusion suppression operation) is set to 60 seconds.

[0107] FIG. 13 is an explanatory diagram showing an example of the relationship between the toner fusion suppression operation and the transition of the driving torque of the photosensitive drum 1 in this embodiment. The upper part of FIG. 13 is a sequence diagram of the driving of the photosensitive drum 1 and the developing sleeve 41 and the application of the charging bias and the developing bias in the toner fusion suppression operation. The sequence diagram shows both the image forming unit S (solid line) whose driving torque is less than the start threshold at the time of the determination in S402 of FIG. 12 and the image forming unit S (dashed line) whose driving torque is equal to or greater than the start threshold at the same time. The lower part of FIG. 13 is a graph showing the transition of the driving torque of the photosensitive drum 1 during the period corresponding to the sequence diagram in the upper part. The graph diagram shows both the image forming unit S (solid line) whose driving torque is less than the start threshold at the time of the determination in S402 of FIG. 12 and the image forming unit S (dashed line) whose driving torque is equal to or greater than the start threshold at the same time.

[0108] In FIG. 13, the image forming unit S in which the driving torque of the photosensitive drum 1 during image formation is in the state indicated by the dashed line does not perform the torque increase operation because the driving torque is equal to or greater than the start threshold at the time of the determination in S402 in FIG. 12. The image forming unit S that does not perform the torque increase operation proceeds to an operation similar to the deposit removal operation. On the other hand, the image forming unit S in which the driving torque of the photosensitive drum 1 during image formation is in the state indicated by the solid line in FIG. 13 performs the torque increase operation because the driving torque is less than the start threshold at the time of the determination in S402 in FIG. 12. The image forming unit S that performs the torque increase operation proceeds to the deposit removal operation when the driving torque of the photosensitive drum 1 becomes 4.0 kgf cm or greater. Then, after the deposit removal operation is performed until the predetermined time has elapsed as described above, all image forming units S resume image formation.

[0109] In this embodiment, when a torque increase operation is performed at a certain image forming station S, an adhering matter removal operation is performed at an image forming station S that is not performing the torque increase operation, but the present invention is not limited to this embodiment. Image formation can be continued as needed at an image forming station S that is not performing the torque increase operation.

[0110] As described above, in this embodiment, the image forming apparatus 100 includes a control unit 50 that is capable of executing an operation (torque increase operation) in at least one of the image forming units S during continuous image formation, in which image formation to form toner images to be transferred onto a recording material P is continuously performed to transfer toner images onto a plurality of recording materials P, by interrupting image formation, applying a voltage to the charging member 2 that causes discharge between the charging member 2 and the photosensitive member 1, and either stopping the rotation of the developing member 41 or rotating the photosensitive member 1 at least one revolution while rotating the developing member 41 at a rotation speed lower than that during image formation. During the continuous image formation, the control unit 50 determines, at a predetermined timing during the continuous image formation, whether the detection results of the detection unit 11 acquired over time indicate that the drive torque of the photosensitive member 1 by the drive unit MTR1 has decreased so as to satisfy a predetermined condition, and if it determines that the drive torque has decreased in at least one of the image forming units S, executes the operation (torque increase operation) in the at least one image forming unit S. Furthermore, in this embodiment, at the above-mentioned predetermined timing, the control unit 50 performs image formation in an image forming unit S among the multiple image forming units S that is determined not to indicate a decrease in the driving torque, or interrupts image formation and performs another operation (adhesion removal operation) in which no voltage is applied to the charging member 2 or a voltage that does not cause discharge between the charging member 2 and the photosensitive member 1 is applied to the charging member 2, and the rotation of the developing member 41 is stopped or the developing member 41 is rotated at a rotational speed lower than that during image formation, and the photosensitive member 1 is rotated at least once.

[0111] In this way, in this embodiment, the photosensitive drum 1 can be idly rotated in a state where the driving torque is increased to a level that can remove deposits (aggregates) individually for each image forming station S based on the driving torque of the photosensitive drum 1 of each image forming station S. This makes it possible to obtain the same effect as in the first embodiment in each image forming station S.

[0112] Here, the execution or non-execution of the toner fusion suppression operation was determined individually for each image forming unit S using the same control as described in Example 1, but the determination may also be made using the control described in Examples 2 and 3.

[0113] [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.

[0114] In the above-described embodiment, the image forming apparatus is configured to apply an oscillating voltage in which a DC component and an AC component are superimposed as a charging bias, but it may also be configured to apply a charging bias consisting of only a DC component.

[0115] Furthermore, in the above-described embodiment, the image forming apparatus is configured to include only a cleaning blade as a cleaning member. However, the image forming apparatus may also include, for example, a rotatable brush (fur brush) in addition to the cleaning blade as a cleaning member. The present invention is particularly effective when the cleaning member that is disposed in contact with the surface of the photoreceptor and rubs (grinds) the surface of the photoreceptor as the photoreceptor rotates is a blade-shaped (plate-shaped) member. In this case, the torque increase operation can easily increase the drive torque, and the deposit removal operation can easily remove deposits. However, the present invention is not limited to this embodiment, and the cleaning member that rubs (grinds) the surface of the photoreceptor may be in other forms, such as a sheet-shaped member or a pad-shaped (block-shaped) member.

[0116] Furthermore, in the above-described embodiment, the photosensitive member is in the form of a drum, but the present invention is not limited to this form, and the photosensitive member may be configured as an endless belt.

[0117] Furthermore, while the image forming apparatus in the above-described embodiment employs an intermediate transfer system, the present invention is not limited to such an embodiment and may employ a direct transfer system. That is, instead of the intermediate transfer member in the above-described embodiment, a recording material carrier that supports and transports the recording material may be provided. The recording material carrier may be an endless belt similar to the intermediate transfer belt in the above-described embodiment. In this image forming apparatus, the toner image formed on the photosensitive element of each image forming unit is directly transferred onto the recording material carried and transported by the recording material carrier. Applying the present invention to an image forming apparatus with such a configuration can also achieve the same effects as those in the above-described embodiment. Furthermore, the image forming apparatus may be a monochrome image forming apparatus having only a single image forming unit, such as a black image forming unit, in which the toner image is directly transferred from the photosensitive element of the image forming unit to the recording material.

[0118] Furthermore, when determining whether to perform the toner fusion suppression operation based on the image area ratio, the toner fusion suppression operation may be performed at a predetermined timing, such as every predetermined number of images formed, regardless of the detection result of the drive torque. For example, a predetermined toner fusion suppression operation may be performed when a predetermined number of high-area-ratio images, each having an image area ratio equal to or greater than a predetermined value, are continuously formed. In other words, the image forming apparatus 100 may be capable of interrupting the image formation during continuous image formation, which is a continuous process of forming toner images to be transferred onto a recording material P, applying a voltage to the charging member 2 that generates discharge between the charging member 2 and the photosensitive member 1, and either stopping the rotation of the developing member 41 or rotating the photosensitive member 1 at least one revolution while rotating the developing member 41 at a rotational speed lower than that during image formation (torque increase operation). Furthermore, after the operation (torque increasing operation) and before resuming image formation, the image forming apparatus 100 may be capable of performing another operation in which no voltage is applied to the charging member 2 or a voltage that does not cause discharge between the charging member 2 and the photosensitive member 1 is applied to the charging member 2, and the photosensitive member 1 is rotated at least one revolution while the developing member 41 is stopped or rotated at a rotation speed lower than that during image formation. At this time, if the average value of the image area ratio of the toner images formed during the execution of the continuous image formation is smaller than a predetermined value, the image formation can be interrupted and the above operation not performed.

[0119] In the above embodiment, the case where the image formation is interrupted during the execution of continuous image formation and the toner fusion suppression operation is performed in the sheet interval process has been described, but a similar operation can also be performed during other non-image formation times. For example, based on the drive torque obtained during the execution of a job in which images are formed on one or more recording materials, the toner fusion suppression operation can be performed in the rotation process after the image formation of the job is completed, or in the pre-rotation process or pre-multiple pre-rotation process before the image formation of the next job. [Explanation of symbols]

[0120] 1 Photosensitive drum 2 Charging roller 3 Exposure equipment 4. Developing device 5 Primary transfer roller 6 Intermediate transfer belt 7 Cleaning Device 11 Torque detection circuit 41 Developing sleeve 50 control section 71 Cleaning blade MTR1 drum drive motor PS1 Charging Power Supply PS2 development power supply

Claims

1. a rotatable photoreceptor; a charging member for charging the photoreceptor; a developing device including a developer carrier that carries a developer and that develops the latent image formed on the photosensitive member; a blade for cleaning the photoreceptor; a detection unit that detects information correlated with the driving torque of the photosensitive member; a control unit configured to execute a first predetermined operation during execution of continuous image formation in which images are formed continuously on a plurality of recording materials based on a detection result of the detection unit, the first predetermined operation being to interrupt image formation, extend an interval between successive recording materials, and rotate the photosensitive member; and The control unit, during the first predetermined operation, (i) a voltage equal to or greater than a discharge start voltage is applied to the charging member, and (ii) the operating conditions of the developing device are set to first conditions, and under the first conditions, the amount of fog toner adhering from the developer carrier to the photosensitive member is less than the amount of fog toner under second conditions, which are operating conditions of the developing device during an inter-recording material step before the image formation is interrupted during the continuous image formation; The photosensitive member is rotated one or more times under the condition The control unit is capable of executing a second predetermined operation after the first predetermined operation and before the image formation is resumed, and during the second predetermined operation, (i) no voltage is applied to the charging member, or a voltage less than a discharge start voltage is applied to the charging member, and (ii) the operating condition of the developing device is set to a third condition, and under the third condition, the amount of fog toner adhering from the developer carrier to the photosensitive member is smaller than the amount of fog toner under the second condition; The image forming apparatus is characterized in that the photosensitive member is rotated under the following conditions.

2. 2. The image forming apparatus according to claim 1, wherein when the operating condition of the developing device is the first condition, rotation of the developer carrier is stopped.

3. 2. The image forming apparatus according to claim 1, wherein when the operating condition of the developing device is the first condition, no voltage is applied to the developer carrier.

4. 2. The image forming apparatus according to claim 1, wherein the control unit executes the first predetermined operation when the detection results of the detection unit acquired over time during the execution of the continuous image formation satisfy a predetermined condition.

5. The image forming apparatus according to claim 1, characterized in that the control unit executes the first predetermined operation when the driving torque indicated by the average value of multiple detection results of the detection unit obtained during the execution of the continuous image formation is smaller than a predetermined threshold value.

6. 2. The image forming apparatus according to claim 1, wherein the control unit rotates the photosensitive member at least one revolution during the second predetermined operation.

7. 2. The image forming apparatus according to claim 1, wherein the control unit switches from the first predetermined operation to the second predetermined operation based on a detection result of the detection unit detected during the first predetermined operation.

8. The image forming apparatus according to claim 1, characterized in that the control unit executes the first predetermined operation when the driving torque indicated by the average value of multiple detection results of the detection unit obtained during the execution of the continuous image formation is smaller than a predetermined first threshold, and executes the second predetermined operation when the driving torque indicated by the average value of multiple detection results of the detection unit obtained during the execution of the first predetermined operation is equal to or greater than a predetermined second threshold.

9. 9. The image forming apparatus according to claim 8, wherein the second threshold value is greater than the first threshold value.

10. 2. The image forming apparatus according to claim 1, wherein the control section applies an oscillating voltage in which a DC component and an AC component are superimposed to the charging member in the first predetermined operation.

11. 11. The image forming apparatus according to claim 10, wherein the control unit applies, in the first predetermined operation, to the charging member an oscillating voltage in which a DC component having the same polarity as that during image formation but a smaller absolute value than that during image formation and an AC component are superimposed.

12. a rotatable photoreceptor; a charging member for charging the photoreceptor; a developing device including a developer carrier that carries a developer and that develops the latent image formed on the photosensitive member; a blade for cleaning the photoreceptor; a control unit configured to execute a predetermined operation during continuous image formation in which images are formed continuously on a plurality of recording materials, the predetermined operation being to interrupt image formation, extend an interval between successive recording materials, and rotate the photosensitive member; and the control unit executes a first predetermined operation during the predetermined operation, and then executes a second predetermined operation; In the first predetermined operation, (i) a voltage equal to or greater than a discharge start voltage is applied to the charging member, and (ii) the operating conditions of the developing device are set to first conditions, and under the first conditions, the amount of fog toner adhering from the developer carrier to the photosensitive member is less than the amount of fog toner under second conditions, which are operating conditions of the developing device during an inter-recording material step before the image formation is interrupted during the continuous image formation; The photosensitive member is rotated one or more times under the condition that In the second predetermined operation, (i) no voltage is applied to the charging member, or a voltage less than a discharge start voltage is applied to the charging member, and (ii) the operating condition of the developing device is set to a third condition, and under the third condition, the amount of fog toner adhering from the developer carrier to the photosensitive member is smaller than the amount of fog toner under the second condition; The image forming apparatus is characterized in that the photosensitive member is rotated under the following condition.

13. 13. The image forming apparatus according to claim 12, wherein when the operating condition of the developing device is the first condition, rotation of the developer carrier is stopped.

14. 13. The image forming apparatus according to claim 12, wherein when the operating condition of the developing device is the first condition, no voltage is applied to the developer carrier.

15. 13. The image forming apparatus according to claim 12, wherein the control section applies an oscillating voltage in which a DC component and an AC component are superimposed to the charging member in the predetermined operation.

16. 16. The image forming apparatus according to claim 15, wherein the control unit applies, in the predetermined operation, to the charging member an oscillating voltage in which a DC component having the same polarity as that during image formation but a smaller absolute value than that during image formation and an AC component are superimposed.

17. a plurality of image forming units each including a rotatable photosensitive member, a charging member for charging the surface of the photosensitive member, a charging power source for applying a voltage to the charging member, an exposure unit for exposing the charged surface of the photosensitive member to light to form an electrostatic image on the charged surface of the photosensitive member, a rotatable developing member for supplying toner to the electrostatic image to form a toner image on the surface of the photosensitive member, a cleaning member for contacting the surface of the photosensitive member to remove toner from the surface of the photosensitive member, a driving unit for driving the photosensitive member, and a detection unit for detecting a value correlated with the driving torque of the photosensitive member by the driving unit; a transfer device that transfers the toner image formed on the photosensitive member of each of the plurality of image forming units; a control unit that is capable of executing, during execution of continuous image formation in which image formation to form toner images to be transferred onto a recording material is continuously performed in order to transfer toner images onto a plurality of recording materials, an operation of suspending image formation in at least one image forming unit among the plurality of image forming units, applying a voltage to the charging member that causes discharge between the charging member and the photosensitive member, and stopping rotation of the developing member or rotating the photosensitive member at least one revolution while rotating the developing member at a rotational speed lower than that during image formation; and the control unit determines, at a predetermined timing during the continuous image formation, whether or not the detection results of the detection unit obtained over time indicate that the drive torque has decreased so as to satisfy a predetermined condition, and when it is determined that the detection results indicate that the drive torque has decreased in at least one image forming unit among the plurality of image forming units, executes the operation in the at least one image forming unit; The control unit, at the predetermined timing, executes image formation in an image forming unit among the plurality of image forming units for which the detection result does not indicate a decrease in the drive torque, or executes another operation in which the control unit interrupts image formation, does not apply a voltage to the charging member or applies a voltage to the charging member that does not cause discharge between the charging member and the photosensitive member, and stops rotation of the developing member or rotates the photosensitive member at least one revolution while rotating the developing member at a rotational speed lower than that during image formation.

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