Image forming apparatus

Abstract

An image forming apparatus is disclosed. The image forming apparatus includes an image bearing member, a charging member, a developing member, a transfer member, a charging voltage application unit, a developing voltage application unit, and a control unit. The developing member collects toner remaining on a surface of the image bearing member after a toner image is transferred from the surface of the image bearing member to a transfer material. The control unit controls application of the developing voltage to apply, to the developing member in a cleaning operation, a developing voltage having a polarity opposite to a normal polarity, and controls application of the charging voltage to apply, to the charging member, a charging voltage having the normal polarity, so that a potential difference formed at a charging portion between the applied charging voltage and a surface potential formed at the surface of the image bearing member is lower than or equal to a discharge start voltage.

Description

Technical Field

[0001] This disclosure relates to an image forming apparatus using, for example, electrophotographic processing. Background Technology

[0002] Japanese Patent Application Publication No. 2-272589 discusses an image forming apparatus using a drumless cleaner method as a method for use in electrophotographic image forming apparatuses such as copiers or laser printers. In the drumless cleaner method, the photosensitive drum is not provided with a dedicated toner cleaning device.

[0003] In image forming apparatuses using a drumless cleaner method, the developing unit also functions as a collection unit for residual toner remaining on the photosensitive drum after transfer. The residual toner collected by the developing unit is reused in toner image development. Therefore, a dedicated toner cleaning unit and a container for storing the collected residual toner are unnecessary. This allows for a reduction in the size and cost of the image forming apparatus.

[0004] However, the disclosure of Japanese Patent Application Publication No. 2-272589 has the following problems. In the drumless cleaner method, when a large amount of residual toner remains on the photosensitive drum, the toner may adhere to the charging member that charges the photosensitive drum. This causes charging failure from the charging member to the photosensitive drum, and it becomes difficult to control the potential difference between the surface potential formed on the surface of the photosensitive drum and the developing member to a desired value. This sometimes leads to residual toner collection failure in the developing unit or unexpected image defects caused by toner development in the developing unit. Summary of the Invention

[0005] This disclosure addresses preventing charging failures on the surface of the photosensitive drum caused by toner adhering to the charging components and properly collecting residual toner through the developing unit.

[0006] According to one aspect of the present invention, an image forming apparatus includes: an image carrier member configured to be rotatable; a charging member configured to contact the image carrier member to form a charging portion and to charge a surface of the image carrier member at the charging portion; a developing member configured to be rotatable and to contact the image carrier member to form a developing portion, and to develop a toner image at the developing portion by supplying a toner charged to a normal polarity to the surface of the image carrier member; a transfer member configured to form a transfer portion opposite to the image carrier member and to transfer a toner image from the image carrier member to a transfer material at the transfer portion; a charging voltage applying unit configured to apply a charging voltage to the charging member; a developing voltage applying unit configured to apply a developing voltage to the developing member; and a control unit. The control unit is configured to control the charging voltage application unit and the developing voltage application unit, wherein the developing member collects toner images formed on the surface of the image carrier member at the transfer portion, and the toners remaining on the surface of the image carrier member after the toner image is transferred from the transfer portion to the transfer material, wherein the control unit controls the image forming operation of forming a toner image on the transfer material and the cleaning operation of cleaning the surface of the charging member while the image carrier member, the charging member, and the developing member are rotating, and wherein the control unit controls the application of the developing voltage to apply a developing voltage with a polarity opposite to the normal polarity to the developing member during the cleaning operation, and controls the application of the charging voltage to apply a charging voltage with the normal polarity to the charging member, such that the potential difference formed at the charging portion between the applied charging voltage and the surface potential formed at the surface of the image carrier member is less than or equal to the discharge start voltage.

[0007] Further features of this disclosure will become clear from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0008] Figure 1 An image forming apparatus according to a first exemplary embodiment is illustrated.

[0009] Figure 2A and 2B The illustration shows a schematic diagram of a brush component according to a first exemplary embodiment.

[0010] Figure 3 A control block diagram according to a first exemplary embodiment is illustrated.

[0011] Figure 4The illustration shows the potential relationship at the developing portion according to a first exemplary embodiment.

[0012] Figure 5 The illustration depicts a charging failure caused by toner stains on the charging roller according to a first exemplary embodiment.

[0013] Figure 6 The illustration depicts a charging failure caused by toner stains on the charging roller according to a first exemplary embodiment.

[0014] Figure 7 The illustration depicts the operation of cleaning toner stains on a charging roller according to a first exemplary embodiment.

[0015] Figure 8 The illustration shows an image forming apparatus according to a third exemplary embodiment. Detailed Implementation

[0016] Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. It should be noted that the dimensions, materials, shapes, and relative positions of the components described below may vary depending on the structure of the apparatus to which the present disclosure is applied or various conditions. In other words, the exemplary embodiments described below are not intended to limit the scope of the present disclosure.

[0017] 1. Image forming apparatus

[0018] Figure 1 The illustration shows a schematic structure of an image forming apparatus 100 according to an exemplary embodiment of the present disclosure.

[0019] The image forming apparatus 100 according to the first exemplary embodiment is a monochrome laser beam printer employing a cleaner-free method and a contact charging method.

[0020] The image forming apparatus 100 according to the first exemplary embodiment includes a photosensitive drum 1, which is a cylindrical photosensitive member serving as an image carrier. A charging roller 2, serving as a charging unit, and a developing device 3, serving as a developing unit, are arranged around the photosensitive drum 1. An exposure device 4, serving as an exposure unit, is arranged in the... Figure 1 The photosensitive drum 1 shown is positioned between the charging roller 2 and the developing device 3 in the direction of rotation. The transfer roller 5, which serves as a transfer unit, is in pressure contact with the photosensitive drum 1.

[0021] According to the first exemplary embodiment, the photosensitive drum 1 is an organic photosensitive component with negative charge. The photosensitive drum 1 includes a photosensitive layer on a drum-shaped aluminum substrate and is driven by a drive motor serving as a drive unit. Figure 1The image shows the image being driven and rotated at a predetermined processing speed in the direction indicated by the arrow (clockwise). According to the first exemplary embodiment, the processing speed corresponds to the circumferential speed (surface movement speed) of the photosensitive drum 1 and is 140 mm / sec, and the outer diameter of the photosensitive drum 1 is 24 mm.

[0022] The charging roller 2, serving as a charging component, contacts the photosensitive drum 1 with a predetermined pressure contact force to form a charging unit. Additionally, a high-voltage charging power supply E1, serving as a charging voltage application unit, ( Figure 3 A predetermined charging voltage is applied to the charging roller 2, and the charging roller 2 uniformly charges the surface of the photosensitive drum 1 to a predetermined potential. According to the first exemplary embodiment, the surface of the photosensitive drum 1 is charged by the charging roller 2 to have a negative polarity. During the charging process, the charging power supply E1 applies a predetermined charging voltage (charging bias) to the charging roller 2. According to the first exemplary embodiment, a negative polarity DC voltage as the charging voltage is applied to the charging roller 2 during the charging process. According to the first exemplary embodiment, the charging voltage is, for example, -1300V (volts). Therefore, according to the first exemplary embodiment, the surface of the photosensitive drum 1 is uniformly charged to a dark region potential Vd of -700V. More specifically, the charging roller 2 charges the surface of the photosensitive drum 1 by discharging in at least one of the small spaces between the charging roller 2 and the photosensitive drum 1, these small spaces being formed upstream and downstream of the contact portion between the charging roller 2 and the photosensitive drum 1 in the rotational direction of the photosensitive drum 1, respectively. However, in this embodiment, the contact portion between the charging roller 2 and the photosensitive drum 1 in the rotational direction of the photosensitive drum 1 will be described as a charging portion.

[0023] According to the first exemplary embodiment, the exposure device 4, which serves as an exposure unit, is a laser scanner that outputs a laser corresponding to image information input from an external device such as a host computer, and scans and exposes the surface of the photosensitive drum 1. By performing exposure, an electrostatic latent image (electrostatic image) based on the image information is formed on the surface of the photosensitive drum 1. According to the first exemplary embodiment, the exposure performed by the exposure device 4 reduces the absolute value of the dark area potential Vd of the surface of the photosensitive drum 1 formed by the uniform charging process, and the dark area potential Vd becomes a bright area potential Vl of -100V. In this embodiment, the position on the photosensitive drum 1 exposed by the exposure device 4 in the rotation direction of the photosensitive drum 1 is referred to as the exposure portion (exposure position). The exposure device 4 is not limited to a laser scanning device and can be, for example, an array of light-emitting diodes (LEDs) including a plurality of LEDs arranged along the length direction of the photosensitive drum 1.

[0024] According to a first exemplary embodiment, a contact developing method is used as a developing method. The developing apparatus 3 includes a developing roller 31 serving as a developing member and a developing agent carrying member, a toner supply roller 32 serving as a developing agent supply member, a toner storage chamber 33 storing toner, and a developing blade 34. Toner supplied from the toner storage chamber 33 to the developing roller 31 via the toner supply roller 32 passes through a blade clamping portion, whereby the toner is charged to a predetermined polarity. The blade clamping portion is the contact portion between the developing roller 31 and the developing blade 34. Toner carried on the developing roller 31 moves from the developing roller 31 to the photosensitive drum 1 at the developing portion based on an electrostatic image. In this specification, the contact portion between the developing roller 31 and the photosensitive drum 1 in the rotational direction of the photosensitive drum 1 is the developing portion. According to the first exemplary embodiment, the developing roller 31 is driven counterclockwise and rotated to move the photosensitive drum 1 and the developing roller 31 in the forward direction at the contact portion between the photosensitive drum 1 and the developing roller 31. The drive motor, which serves as the drive unit for the developing roller 31, can be the main motor, which also serves as the drive unit for the photosensitive drum 1, or a separate drive motor that can rotate the photosensitive drum 1 and the developing roller 31 respectively. During development, the developing power supply E2, which serves as the developing voltage application unit, ( Figure 3A predetermined developing voltage (developing bias) is applied to the developing roller 31. According to the first exemplary embodiment, a negative DC voltage, which is the developing voltage, is applied to the developing roller 31 during development, and the developing voltage is -380V. According to the first exemplary embodiment, toner charged to have the same polarity as the charging polarity of the photosensitive drum 1 (negative polarity according to the first exemplary embodiment) is attached to the exposure surface (image portion), which is the image forming portion on the photosensitive drum 1 that has a reduced absolute value of potential as a result of exposure after uniform charging treatment. This developing method is called a reverse developing method. According to the first exemplary embodiment, the normal polarity of the charging polarity of the toner during development is negative. Although a single-component nonmagnetic contact developing method is employed according to the first exemplary embodiment, this disclosure is not limited to this form. A two-component nonmagnetic contact developing method, a non-contact developing method, or a magnetic developing method may be employed. A two-component nonmagnetic contact developing method is a method in which a two-component developer comprising a nonmagnetic toner and a magnetic carrier is used as the developing agent, and the developing agent carried on a developing agent carrier member is brought into contact with the photosensitive drum 1 to perform developing. Non-contact development is a method in which toner is moved non-contactly from a developer carrier member arranged to face the photosensitive member via air to perform development. Magnetic development is another method in which magnetic toner is carried on a developer carrier member by magnetic force to perform development. The developer carrier member is arranged to face the photosensitive member, or in contact with the photosensitive member, or not in contact with the photosensitive member, and a magnet, as a magnetic field generating unit, is included in the developer carrier member. According to a first exemplary embodiment, a toner having an average particle size of 6 μm (micrometers) and having a negative polarity as the normal charging polarity is used.

[0025] The transfer roller 5 is suitable as a transfer component made of an elastic member, such as a sponge rubber made of polyurethane rubber, ethylene propylene diene monomer (EPDM) rubber, or nitrile butadiene rubber (NBR). The transfer roller 5 presses against the photosensitive drum 1 to form a transfer portion in which the photosensitive drum 1 and the transfer roller 5 are in pressure contact with each other. During transfer, the transfer power supply E3 (which serves as the transfer voltage application unit)... Figure 3 A predetermined transfer voltage (transfer bias) is applied to the transfer roller 5. According to the first exemplary embodiment, a DC voltage having a polarity opposite to the normal polarity of the toner (positive polarity according to the first exemplary embodiment) is applied to the transfer roller 5 as the transfer voltage during transfer. According to the first exemplary embodiment, the transfer voltage during transfer is, for example, +1000V.

[0026] The toner image is then electrostatically transferred from the photosensitive drum 1 to the recording material S by the action of the electric field formed between the transfer roller 5 and the photosensitive drum 1.

[0027] Synchronously with the arrival of the toner image formed on the photosensitive drum 1 at the transfer section, the transfer material S, which serves as the recording material, stored in the cartridge 6, is fed by the sheet feeding unit 7 and transferred to the transfer section via the alignment roller pair 8. The toner image formed on the photosensitive drum 1 is transferred onto the transfer material S by the transfer roller 5, to which a predetermined transfer voltage is applied by the high-voltage transfer power supply E3.

[0028] The transfer material S, onto which a toner image is transferred, is conveyed to the fixing device 9. The fixing device 9 is a fixing device using a film heating method and includes a fixing film 91 and a pressure roller 92. The fixing film 91 includes a fixing heater (not shown) and a thermistor (not shown) for measuring the temperature of the fixing heater. The pressure roller 92 is in pressure contact with the fixing film 91. The transfer material S is then heated and pressurized to fix the toner image onto the transfer material S, and the resulting transfer material S is conveyed to the outside of the image forming apparatus 100 via a sheet discharge roller pair 12.

[0029] In addition, the toner that was not transferred to the transfer material S and remained on the photosensitive drum 1 as residual toner was removed by the process described below.

[0030] The residual toner comprises a mixture of toner charged to the positive polarity and toner charged to the negative polarity but lacking sufficient charge. The residual toner is recharged to the negative polarity by the charging roller 2 through discharge at the charging section. The residual toner, recharged to the negative polarity by the charging roller 2, is conveyed to the developing section by the rotation of the photosensitive drum 1. There are cases where an electrostatic latent image forms on the surface of the photosensitive drum 1 that has reached the developing section to form an image forming section, and there are cases where a non-image forming section is formed without an electrostatic latent image. The behavior of the residual toner reaching the developing section will now be described. The residual toner on the image forming section of the photosensitive drum 1 and the residual toner on the non-image forming section of the photosensitive drum 1 will be described separately.

[0031] The residual toner adhering to the image forming section of the photosensitive drum 1 is not transferred from the photosensitive drum 1 to the developing roller 31 at the developing section. Instead, it moves to the transfer section together with the developing toner from the developing roller 31 and is transferred to the transfer material S to be used in image forming.

[0032] In contrast, the residual toner adhering to the non-image forming portion of the photosensitive drum 1 is recharged to the negative polarity (normal polarity) at the charging portion. The potential difference between the potential of the non-image forming portion of the photosensitive drum 1 and the developing voltage is transferred to the developing roller 31 at the developing portion and collected in the toner storage chamber 33. The toner collected in the toner storage chamber 33 is then reused in image forming.

[0033] The pre-exposure device 13 is provided as a device for removing the charging potential of the photosensitive drum 1 between the transfer portion and the charging portion in the rotational direction of the photosensitive drum 1. This is to reduce the non-uniformity of the surface potential of the photosensitive drum 1 caused by the transfer, so as to stabilize the discharge at the charging portion and obtain a uniform charging potential.

[0034] 2. Structure of brushed components

[0035] Next, a paper dust removal mechanism according to a first exemplary embodiment will now be described. Figure 1 As shown, the image forming apparatus 100 according to the first exemplary embodiment includes a brush member 10 (collecting member). The brush member 10 is a contact member serving as a paper dust removal mechanism. According to the first exemplary embodiment, the image forming apparatus 100 includes a brush member 10. The brush member 10 contacts the surface of the photosensitive drum 1 downstream of the transfer portion and upstream of the charging portion in the rotational direction of the photosensitive drum 1, and forms a brush contact portion (brush contact position). In this embodiment, the contact portion between the brush member 10 and the photosensitive drum 1 in the rotational direction of the photosensitive drum 1 is referred to as the brush contact portion.

[0036] Figure 2A The illustration shows the individual brush member 10 as viewed along its length. This length direction is substantially parallel to the rotation axis of the photosensitive drum 1. Figure 2B The illustration shows the brush member 10 in contact with the photosensitive drum 1 when viewed along the length of the brush member 10.

[0037] The brush portion of the brush component 10 is composed of a fixed brush 11 that is fixed in a specific position and has electrical conductivity. For example... Figure 2A and 2B As shown, the brush member 10 includes a pile yarn (conductive yarn) 11a and a base fabric 11b supporting the pile yarn 11a. The pile yarn 11a is a plurality of strands of material used for rubbing the surface of the photosensitive drum 1 and is made of conductive nylon 6. As described above, the brush member 10 is arranged downstream of the transfer portion and upstream of the charging portion of the photosensitive drum 1 in the moving direction (rotation direction) of the photosensitive drum 1, and is in contact with the photosensitive drum 1.

[0038] The brush member 10 is arranged such that its longitudinal direction is substantially parallel to the rotation axis of the photosensitive drum 1. According to a first exemplary embodiment, the fixed brush 11 is composed of a conductive yarn 11a made of nylon fibers containing a conductive material and a base fabric 11b made of synthetic fibers containing carbon as a conductive agent, with the conductive yarn 11a woven into the base fabric 11b. The conductive yarn 11a may be made of materials other than nylon (such as rayon, acrylic, or polyester).

[0039] like Figure 2AAs shown, distance L1 is the distance from the base fabric 11b to the distal end of the exposed conductive yarn 11a when the brush member 10 is in a standby state (i.e., without any external force applied to bend the conductive yarn 11a). According to the first exemplary embodiment, distance L1 is 6.5 mm. The base fabric 11b of the brush member 10 is fixed to a support member (not shown) arranged at a predetermined position in the image forming apparatus 100 using a fixing device such as double-sided tape, and the distal end of the conductive yarn 11a is arranged to penetrate the photosensitive drum 1. According to the first exemplary embodiment, the gap between the support member and the photosensitive drum 1 is fixed. The shortest distance from the base fabric 11b of the brush member 10 fixed to the support member to the photosensitive drum 1 is distance L2. According to the first exemplary embodiment, the difference between distance L2 and distance L1 is defined as the amount of penetration of the brush member 10 into the photosensitive drum 1. According to the first exemplary embodiment, the amount of penetration of the brush member 10 into the photosensitive drum 1 is 1 mm. According to the first exemplary embodiment, as Figure 2A As shown, when the brush member 10 is in a standalone state, the length L3 of the brush member 10 in the circumferential direction (hereinafter referred to as the "width direction") of the photosensitive drum 1 is 5 mm. Additionally, according to the first exemplary embodiment, the length of the brush member 10 in the longitudinal direction is 216 mm. The brush member 10 can thus contact the entire image forming area (the area where the toner image can be formed) on the photosensitive drum 1 in the direction of its rotation axis. According to the first exemplary embodiment, the conductive yarn 11a has a thickness of two deniers and a density of 240 kF / inch. 2 The density. Here, "kF / inch" 2 " is a unit of brush density and specifies the number of filaments per square inch. As described above, the brush member 10 is supported by a support member (not shown) and arranged in a fixed position relative to the photosensitive drum 1, and as the photosensitive drum 1 moves, the brush member 10 rubs against the surface of the photosensitive drum 1.

[0040] The brush member 10 captures (collects) deposits (such as paper dust) that have transferred from the recording material S to the photosensitive drum 1 at the transfer section. The brush member 10 reduces the amount of paper dust that moves downstream of the brush member 10 to the charging and developing sections in the direction of movement of the photosensitive drum 1.

[0041] According to the first exemplary embodiment, the length L3 of the brush member 10 in the width direction of the photosensitive drum 1 is set to 5 mm. However, the length L3 is not limited to this. For example, the length L3 can be changed as needed based on the lifespan of the image forming apparatus 100 or the processing cartridge. The longer the brush member 10 is in the width direction, the longer the brush member 10 can capture paper dust.

[0042] According to the first exemplary embodiment, the length of the brush member 10 in the longitudinal direction is set to 216 mm. However, the length is not limited to the length specified above, and the length can be changed as needed based on, for example, the maximum sheet size of the image forming apparatus 100 by means of the width.

[0043] Although the fineness of the brush member 10 according to the first exemplary embodiment is 220T / 96F (indicating 96 bundles of thread, each bundle having a thickness of 220 grams per 10,000 meters), and the fineness is preferably determined taking into account the slippage characteristics of paper dust, a brush member 10 with low fineness does not have sufficient ability to block paper dust, and paper dust easily slips past the brush member 10. This may prevent the charging of the photosensitive drum 1 caused by the charging roller 2 and lead to image defects. In contrast, a brush member 10 with high fineness cannot collect toner and fine paper dust. Therefore, image defects may occur due to uneven concentration caused by non-uniform transfer of toner along the longer side of the charging roller 2 or charging failures at the location of paper dust adhesion.

[0044] The density of the brush component 10 according to the first exemplary embodiment is 240 kF / inch. 2 (kF / inch 2 The density is a unit of brush density, specifying the number of filaments per square inch, and is preferably determined taking into account the toner's passing characteristics and paper dust collection characteristics. Specifically, when the density of the brush member 10 is high, the toner's passing characteristics decrease, which can lead to defects. Specifically, the toner may adhere, and the adhered toner may splatter, making a mess in the image forming apparatus 100. Additionally, when the density of the brush member 10 is low, the ability to collect paper dust decreases. Therefore, from the viewpoint of paper dust collection characteristics, the thickness of the conductive yarn 11a is preferably one to six deniers and 150 to 350 kF / inch. 2 Furthermore, the density of the conductive yarn 11a is preferably 150 to 350 kF / inch. 2 From the viewpoint of long lifespan, the length of the brush component 10 in the width direction is preferably three mm or longer.

[0045] The brush power supply E4 serves as the brush voltage application unit. Figure 3 The brush power supply E4 is connected to the brush member 10. During image formation, the brush power supply E4 applies a predetermined brush voltage (brush bias) to the brush member 10. According to the first exemplary embodiment, a negative DC voltage as the brush voltage is applied to the brush member 10 during image formation. According to the first exemplary embodiment, the brush voltage during image formation is, for example, -350V.

[0046] 3. Image output operation

[0047] According to a first exemplary embodiment, the image forming apparatus 100 performs an image output operation (job). The image output operation is a series of operations that form an image on one or more recording materials S based on a single start command from an external device (not shown), such as a personal computer. The job generally includes image forming processing (printing processing), pre-rotation processing, sheet separation processing in the case of forming images on multiple recording materials S, and post-rotation processing. Image forming processing is, for example, the process of forming an electrostatic image on a photosensitive drum 1, developing an electrostatic image (forming a toner image), transferring a toner image, and fixing a toner image. The term "timing for image forming" refers to the time period used to perform the image forming processing. More specifically, the timing for image forming varies depending on the location where electrostatic image forming, toner image forming, toner image transfer, or toner image fixing is performed. Pre-rotation processing is the time period used for preparatory operations before performing the image forming processing. Sheet separation processing is a process performed during the time period corresponding to the interval between the recording materials S when the image forming apparatus 100 continuously performs image forming processing on multiple recording materials S (timing for continuous image forming). Post-rotation processing is a preparation operation performed after image forming processing. The term "timing for non-image forming" refers to a time period other than the timing for image forming. Examples of timing for non-image forming include, for example, pre-rotation processing, sheet separation processing, post-rotation processing, and multi-rotation pre-processing periods. Multi-rotation pre-processing is a preparation operation performed when the image forming apparatus 100 is turned on or when the image forming apparatus 100 returns from a sleep state.

[0048] 4. Forms of control

[0049] Figure 3 This is a schematic block diagram illustrating the control configuration of the main components of an image forming apparatus 100 according to a first exemplary embodiment. The image forming apparatus 100 includes a control unit 150. The control unit 150 includes a central processing unit (CPU) 151, a memory (storage element) 152, and an input / output unit (not shown). The CPU 151 is the central element of the computational control unit that performs computational processing. The memory 152 is a storage unit such as a read-only memory (ROM) and a random access memory (RAM). The input / output unit controls the transmission and reception of signals to and from various elements connected to the control unit 150. The RAM stores sensor detection results and calculation results. The ROM stores, for example, control programs and pre-required data tables.

[0050] Control unit 150 is a control unit that comprehensively controls the operation of image forming apparatus 100. Control unit 150 controls the transmission and reception of various electrical information signals and drive timing, and executes a predetermined image forming sequence. Components of image forming apparatus 100 are connected to control unit 150. For example, in relation to the first exemplary embodiment, charging power supply E1, developing power supply E2, transfer power supply E3, brush power supply E4, drive motor 110, and pre-exposure device 13 are connected to control unit 150.

[0051] 5. Residual toner treatment process

[0052] Next, the steps for processing toners that were not used in image formation (such as residual toners remaining on the photosensitive drum 1 after transfer) will now be described.

[0053] The residual toner remaining on the photosensitive drum 1 comprises a mixture of toner charged to a positive polarity opposite to the normal polarity of the toner and toner charged to a negative polarity but without sufficient charge. These toners are fully charged to a negative polarity by discharge caused by the potential difference formed between the charging roller 2 and the photosensitive drum 1, immediately before reaching the charging section, which is the contact point between the charging roller 2 and the photosensitive drum 1. As a result, an electrostatic repulsion force is obtained against the charging roller 2 to which a negative polarity charging voltage is applied, so that the toner passes through the charging section without adhering to the charging roller 2. Additionally, a portion of the toner that was not fully charged to a negative polarity by the discharge at the charging section adheres to the charging roller 2 at one point. However, through friction between the charging roller 2 and the photosensitive drum 1 and the application of the charging voltage, the toner is recharged to a negative polarity at the charging section, and the charged toner is moved from the charging roller 2 to the photosensitive drum 1 by the electrostatic repulsion force against the charging roller 2 to which a negative polarity charging voltage is applied.

[0054] After being charged to negative polarity at the charging section, the residual toner on the photosensitive drum 1 is moved to the developing section by the rotation of the photosensitive drum 1 and is then processed as follows.

[0055] Figure 4 The illustration shows the relationship between the surface potential formed on the photosensitive drum 1 at the developing portion according to a first exemplary embodiment and the developing voltage. For example... Figure 4 As shown, in the non-image forming portion where no electrostatic latent image is formed at the developing portion, the developing voltage is relatively closer to the positive polarity value than the surface potential of the photosensitive drum 1 charged by the charging roller 2. Therefore, the residual toner on the photosensitive drum 1, which is charged to the negative polarity, is moved from the photosensitive drum 1 to the developing roller 31 due to the aforementioned potential relationship and is then collected in the toner storage chamber 33.

[0056] Figure 4The potential difference between the surface potential of the photosensitive drum 1 in the non-image forming section shown (which is the back contrast (Vback)) is preferably set as described below. To collect the toner charged to the negative polarity on the photosensitive drum 1 onto the developing roller 31, the back contrast (Vback) at the developing section is set to a sufficient value. Furthermore, the back contrast (Vback) is preferably set to prevent unintended development (i.e., atomized toner described below) of the toner carried on the developing roller 31 onto the surface of the photosensitive drum 1. Specifically, the back contrast (Vback) is preferably set to approximately 100V to approximately 500V. When the back contrast (Vback) is less than or equal to 100V, it is difficult to ensure that the toner charged to the negative polarity and attached to the surface of the photosensitive drum 1 is collected. Furthermore, unintended development (i.e., atomized toner) of the toner charged to the negative polarity on the developing roller 31 onto the photosensitive drum 1 may occur. In contrast, when the back contrast Vback is higher than 500V, the toner on the developing roller 31 is charged towards the positive polarity due to the excessively high back contrast Vback, caused by the discharge generated between the developing roller 31 and the photosensitive drum 1. Therefore, it is possible for the toner to atomize from the developing roller 31 to the photosensitive drum 1. According to the first exemplary embodiment, the surface potential Vd of the photosensitive drum 1 is set to -600V, the developing voltage is set to -300V, and the back contrast Vback is set to 300V.

[0057] In addition, such as Figure 4 As shown, a development contrast (Vcont) is formed at the image forming section where an electrostatic latent image is formed at the developing section. The development contrast (Vcont) is the potential relationship between the toner charged to the negative polarity and the photosensitive drum 1. Therefore, the toner charged to the negative polarity on the photosensitive drum 1 is directly used as the toner image, and furthermore, the development of the toner from the developing roller 31 forms the toner image, which is then moved to the transfer section and transferred to the transfer material S.

[0058] However, with a large amount of residual toner remaining on the photosensitive drum 1 after transfer, it is difficult to fully charge the residual toner on the photosensitive drum 1 to the negative polarity at the charging section. Therefore, toner charged to the positive polarity may adhere to the charging roller 2, causing toner stains to accumulate on the charging roller 2.

[0059] Examples of situations where a large amount of residual toner remains on the photosensitive drum 1 after transfer include cases where printing is performed in a humid or hot environment, when printing is performed after new toner has been supplied to the toner storage chamber 33 as in the third exemplary embodiment, when printing is performed on a sheet containing a large amount of talc as filler (talc sheet), when printing is performed using the image forming apparatus 100 nearing the end of its lifespan, or when clogging occurs. In these cases, a large amount of toner stains can be generated due to the reduced rechargeability of the toner. This can cause toner stains to accumulate on the charging roller 2.

[0060] like Figure 5 As shown, when a large amount of toner accumulates on the charging roller 2, the charging roller 2 cannot charge the photosensitive drum 1 at the toner-stained portion of the charging roller 2, and the back contrast Vback decreases. Because the toner on the surface of the charging roller 2 increases resistance, it becomes difficult to perform the expected discharge, resulting in a charging failure. Especially when the back contrast Vback becomes below 100V, as described above, residual toner charged to the negative polarity on the photosensitive drum 1 cannot be successfully collected by the developing roller 31 at the non-image-forming portion of the developing section. Furthermore, fogged toner may appear on the photosensitive drum 1. Residual toner or fogged toner on the photosensitive drum 1 that has not yet been developed or collected adheres to the charging roller 2 as toner stains, which contributes to the charging failure. Then, the discharge amount at the charging section decreases due to the toner stains on the charging roller 2, which reduces the absolute value of the surface potential of the photosensitive drum 1. As the discharge amount decreases, the back contrast Vback decreases, causing the amount of fogged toner to increase. As a result, charging the photosensitive drum 1 eventually becomes virtually impossible at the toner-stained areas of the charging roller 2, such as Figure 6 As shown in the figure. Furthermore, a portion of the toner that was not successfully charged in the portion developed onto the photosensitive drum 1 due to toner stains on the charging roller 2 is transferred to the recording material S, thereby causing image defects due to toner stains.

[0061] The image forming apparatus 100 according to the first exemplary embodiment therefore includes a cleaning operation for the charging roller 2 as described below. Figure 7 The illustration shows a timing diagram of a cleaning operation according to a first exemplary embodiment. The cleaning operation can be triggered by user selection of a mode or by detecting a anticipated large amount of residual toner on the photosensitive drum 1 after transfer.

[0062] At time T1, a charging voltage and a developing voltage are applied, and the pre-exposure device 13 is turned on. According to the first exemplary embodiment, various voltages are applied before driving the photosensitive drum 1. According to the first exemplary embodiment, the charging voltage is set to -500V, and the developing voltage is set to +200V. The charging voltage is a voltage lower than or equal to the discharge start voltage. According to the first exemplary embodiment, the discharge start voltage is set to -550V. The charging voltage and developing voltage are applied such that a potential difference for cleaning operation is formed at the contact portion and the developing portion between the photosensitive drum 1 and the brush member 10, and between the photosensitive drum 1 and the developing roller 31. After the charging voltage and developing voltage have sufficiently increased, driving of the photosensitive drum 1 begins at time T2. The charging voltage is thus applied, and the toner discharged to the surface of the photosensitive drum 1 having the potential difference formed at the charging portion is appropriately collected at the developing portion. At time T3, after a desired period of time following the cleaning operation, driving of the photosensitive drum 1 is first turned off. Subsequently, at time T4, the charging voltage, developing voltage, and exposure of the pre-exposure device 13 are essentially turned off simultaneously. From time T2 to time T3, a cleaning operation is performed on the charging roller 2, and according to the first exemplary embodiment, the time period from time T2 (when the drive motor 110 is turned on) to time T3 (when the drive motor 110 is turned off) is set to correspond to one rotation of the photosensitive drum 1. During the cleaning operation, the developing roller 31 and the charging roller 2 are in contact with the photosensitive drum 1. Furthermore, time T3 and T4 can be the same.

[0063] According to the first exemplary embodiment, the charging voltage, the developing voltage, and the pre-exposure device 13 are switched on simultaneously at the same timing. Although the charging voltage and the developing voltage are applied before the drive motor 110 is driven, the exposure timing of the pre-exposure device 13 can be controlled. Specifically, exposure can begin at the timing when the surface of the photosensitive drum 1, where the developing portion is formed, reaches the opposite surface of the pre-exposure device 13 (i.e., the pre-exposure portion where the surface of the photosensitive drum 1 is exposed) while the drive of the photosensitive drum 1 is stopped. Alternatively, exposure can begin at the timing when the surface of the photosensitive drum 1, where the charging portion is formed, reaches the pre-exposure portion where the surface of the photosensitive drum 1 is exposed.

[0064] The cleaning operation is preferably performed for at least the time corresponding to one rotation of the charging roller 2 and the time during which the surface of the photosensitive drum 1, forming the charging portion, moves to the developing portion. This is because the rotation needs to be performed long enough to clean the entire circumference of the charging roller 2 and collect the toner discharged from the charging roller 2 onto the surface of the photosensitive drum 1 at the developing portion. The length of the cleaning operation can obviously be set longer than the length specified above. According to the first exemplary embodiment, the length of the cleaning operation is set to correspond to one rotation of the photosensitive drum 1.

[0065] The function of cleaning the charging roller 2 according to the first exemplary embodiment will now be described.

[0066] Because the developing voltage is positive, the back contrast Vback is properly formed even if the charging of the photosensitive drum 1 fails due to toner contamination on the charging roller 2. Therefore, it is possible to prevent the inability to collect residual toner on the photosensitive drum 1 and the generation of fogged toner due to charging failure.

[0067] If the charging roller 2 and the photosensitive drum 1 are driven and rotated under the condition of applying a negative polarity charging voltage, the toner attached to the charging roller 2 is thereby charged to the negative polarity, and the electrostatic repulsion force on the charging roller 2 causes the charged toner to move from the charging roller 2 to the photosensitive drum 1.

[0068] In order to obtain electrostatic repulsion between the charging roller 2 and the toner charged to the negative polarity, the charging voltage should be directed towards the surface potential of the photosensitive drum 1 where the negative polarity is greater than that of the charging portion.

[0069] However, when the charging voltage is excessively greater than the surface potential of the photosensitive drum 1 towards the negative polarity, the amount of discharge between the charging roller 2 and the photosensitive drum 1 increases immediately before the charging portion of the charging roller 2 and the photosensitive drum 1. This can promote the charging of the toner attached to the charging roller 2 towards the positive polarity and make it difficult to charge the toner attached to the charging roller 2 towards the negative polarity.

[0070] Specifically, the charging voltage during the cleaning operation is set towards the surface potential of the photosensitive drum 1 where the negative polarity is greater than that of the charging section. Furthermore, the potential difference between the charging voltage during the cleaning operation and the surface potential of the photosensitive drum 1 at the charging section is set to be greater than or equal to the development contrast Vcont during the image forming operation.

[0071] Furthermore, a charging voltage lower than or equal to the discharge initiation voltage is set to be applied as a discharge threshold lower than or equal to the discharge between the charging roller 2 and the photosensitive drum 1. This produces the effect of moving the toner charged to the negative polarity on the charging roller 2 to the photosensitive drum 1 and charging the toner on the charging roller 2 to the negative polarity. By controlling the potential difference at the charging section to be greater than the development contrast Vcont set to enable development, the performance of toner discharge from the charging roller 2 is improved. In other words, forming a potential difference greater than or equal to the development contrast Vcont at the charging section moves the fully charged toner to the surface of the photosensitive drum 1.

[0072] According to a first exemplary embodiment, the pre-exposure apparatus 13 removes static electricity from the photosensitive drum 1 during the cleaning operation of the charging roller 2, such that the history of the surface potential of the photosensitive drum 1 before the cleaning operation is performed is eliminated and the charging potential of the photosensitive drum 1 is set to substantially zero V. This facilitates control of the potential difference between the charging voltage and the surface potential of the photosensitive drum 1.

[0073] The toner, which has been charged to the negative polarity and moved from the charging roller 2 to the photosensitive drum 1, is then moved to the developing roller 31 and collected in the toner storage chamber 33 at the developing section where the back contrast Vback is properly formed, thereby removing the toner adhering to the charging roller 2.

[0074] 6. Effects of the first exemplary embodiment

[0075] Next, a method for checking the effectiveness of a cleaning operation on toner stains on the charging roller 2 according to the first exemplary embodiment will now be described.

[0076] Double-page printing is repeatedly performed using the image forming apparatus 100 according to the first exemplary embodiment in a humid and hot environment with a temperature of 32.5 degrees Celsius and a humidity of 90%. The image forming apparatus 100 is in a new state, the toner storage chamber 33 stores 50 grams of toner, and the image has a text image style with a printing rate of 5%.

[0077] Talc sheets were used as the recording material S, and Century Star sheets (product name, manufactured by CenturyPulp And Paper) were used. In the first comparative example and the first example, the presence / absence of image defects on the printed recording material S and the state of toner stains on the charging roller 2 were checked every predetermined number of sheets. In the first comparative example, no cleaning operation was performed on the toner stains on the charging roller 2. In the first example, a cleaning operation on the toner stains on the charging roller 2 was performed every 250 sheets.

[0078] [Table 1]

[0079]

[0080]

[0081] In the first comparative example specified in Table 1, when the cumulative number of printed sheets reached 500, toner stains began to appear at both edges of the charging roller 2. When the cumulative number of printed sheets reached 750, image defects caused by toner stains appeared on the sheet at positions corresponding to the toner stain locations at the edges of the charging roller 2. Printing continued thereafter, and when the cumulative number of printed sheets reached 1200, image defects appeared across the entire sheet due to toner stains on the sheet resulting from the toner stains on the charging roller 2.

[0082] Conversely, using the structure according to the first example, the stains on the charging roller 2 worsened slightly, but no image defects appeared during the printing of 1200 sheets. This indicates that periodically performing a cleaning operation on the charging roller 2 successfully moved the toner on the charging roller 2 to the photosensitive drum 1. Despite the periodic cleaning operation, there is a situation where toner stains on the charging roller 2 gradually appear, making it possible to increase the number of sequential executions or the length of the time as the cumulative number of printed sheets increases, as described in the second exemplary embodiment.

[0083] Furthermore, the change in the state of toner stains on the charging roller 2 was examined when a cleaning operation according to the first exemplary embodiment was performed on the charging roller 2 at the point when the cumulative number of printed pages reached 1200 from the state of the first comparative example. Each time a cleaning operation was performed, the toner stains on the charging roller 2 became less severe, and after five cleaning operations, the toner stains on the charging roller 2 were essentially completely removed. Based on the foregoing results, it can be said that even when the charging roller 2 was in a state causing image defects, performing a cleaning operation corresponding to five rotations of the photosensitive drum 1 successfully removed the toner from the charging roller 2.

[0084] Based on the above results, the structure of the first example is described as follows.

[0085] The system includes a rotatable photosensitive drum 1 and a charging roller 2. The charging roller 2 is brought into contact with the photosensitive drum 1 to form a charging portion, and the surface of the photosensitive drum 1 is charged at the charging portion. Additionally, a rotatable developing roller 31 is included. The rotatable developing roller 31 is brought into contact with the photosensitive drum 1 to form a developing portion, and the toner image is developed at the developing portion by supplying toner charged to the normal polarity to the surface of the photosensitive drum 1. Furthermore, a transfer roller 5 is included. The transfer roller 5 forms a transfer portion opposite to the photosensitive drum 1, and at the transfer portion, the toner image is transferred from the photosensitive drum 1 to the recording material S, which is the transfer material. Additionally, a charging voltage application unit E1, a developing voltage application unit E2, and a control unit 150 are included. The charging voltage application unit E1 applies a charging voltage to the charging roller 2, and the developing voltage application unit E2 applies a developing voltage to the developing roller 31. The control unit 150 controls the charging voltage application unit E1 and the developing voltage application unit E2.

[0086] According to this structure, the toner image formed on the surface of the photosensitive drum 1 is transferred to the recording material S at the transfer section, and the residual toner remaining on the surface of the photosensitive drum 1 is then collected by the developing roller 31. The image forming operation of forming the toner image on the recording material S and the cleaning operation of cleaning the surface of the charging roller 2 are performed while the photosensitive drum 1, the charging roller 2, and the developing roller 31 are rotating.

[0087] The control unit 150 controls the application of the developing voltage to apply a developing voltage with a polarity opposite to the normal polarity to the developing roller 31 at the developing section during the cleaning operation. Additionally, the control unit 150 controls the application of a charging voltage with the normal polarity such that the potential difference between the charging voltage at the charging section and the surface potential formed at the photosensitive drum 1 is lower than or equal to the discharge initiation voltage. Furthermore, the control unit 150 performs control such that the potential difference between the charging voltage formed at the charging section and the surface potential formed at the photosensitive drum 1 during the cleaning operation is greater than the potential difference between the developing voltage formed at the developing section and the surface potential formed at the photosensitive drum 1 during the image forming operation. Furthermore, during the cleaning operation, static electricity is removed from the surface of the photosensitive drum 1, downstream of the transfer section and upstream of the charging section in the rotational direction of the photosensitive drum 1. A pre-exposure device 13, as a static electricity removal component, is used to remove static electricity from the surface of the photosensitive drum 1.

[0088] The photosensitive drum 1 is preferably driven and rotated such that the length of movement of the surface of the photosensitive drum 1 during the cleaning operation is longer than the total length corresponding to one rotation of the charging roller 2 and the length from the charging section to the developing section in the rotation direction of the photosensitive drum 1.

[0089] As described above, performing a cleaning operation on the charging roller 2 according to the first exemplary embodiment has the following advantages: It prevents charging malfunctions of the charging roller 2 to the photosensitive drum 1 caused by a large amount of toner adhering to the charging roller 2. Furthermore, it prevents the collection of residual toner on the photosensitive drum 1 at the developing section and the generation of fogged toner due to charging malfunctions.

[0090] Although the structure described above according to the first exemplary embodiment includes a pre-exposure device 13, it may not be necessary to include the pre-exposure device 13. During the cleaning operation of toner stains on the charging roller 2, static electricity can be removed from the surface potential of the photosensitive drum 1 by exposure of the exposure device 4 or by applying a positive voltage to the transfer roller 5, without using the pre-exposure device 13.

[0091] Furthermore, according to the first exemplary embodiment, the charging roller 2 can be driven and rotated. The charging roller 2 is driven and rotated to have a different circumferential speed from the photosensitive drum 1, so that the toner on the surface of the charging roller 2 is easily charged to the normal polarity. When the moving speed of the surface of the photosensitive drum 1 is 100%, the moving speed of the surface of the charging roller 2 is preferably 95% to 105%.

[0092] According to a first exemplary embodiment, a sheet member can be provided as a friction member that contacts the surface of the charging roller 2. The toner on the surface of the sheet member and the charging roller 2 rubs against each other, making it easy for the toner to be charged to its normal polarity.

[0093] Next, a second exemplary embodiment, which is another exemplary embodiment of this disclosure, will be described. The configuration and operation of the image forming apparatus according to this exemplary embodiment are substantially the same as those of the image forming apparatus 100 according to the first exemplary embodiment. Therefore, each component of the image forming apparatus according to this exemplary embodiment that has the same or corresponding function or configuration as the components of the image forming apparatus 100 according to the first exemplary embodiment is given the same reference numerals as those of the image forming apparatus 100 according to the first exemplary embodiment, and thus their repeated description is omitted.

[0094] 1. Cleaning operation according to the second exemplary embodiment

[0095] In the second example, as specified in Table 2, the cleaning operation is configured to be performed more frequently as the cumulative number of printed sheets by the image forming apparatus 100 increases. The cleaning operation is controlled to be performed during a post-rotation operation performed after the image forming operation is completed, and the frequency of the cleaning operation varies for each cumulative number of printed sheets. The remainder of the configuration is similar to that of the first example, and therefore its repeated description is omitted.

[0096] [Table 2]

[0097]

[0098]

[0099] As the cumulative number of prints by the image forming apparatus 100 increases, cleaning operations are performed more frequently to prevent an increase in toner stains caused by talc accumulation in the toner storage chamber 33, which is a result of the increased cumulative number of prints using talc sheets. Furthermore, the frequency of cleaning operations is optimized based on the increase in toner stains caused by toner deterioration in the developing container, which is a result of the increased cumulative number of prints.

[0100] 2. Effects of the second exemplary embodiment

[0101] A method for checking the effectiveness of a cleaning operation on toner stains on the charging roller 2 according to a second exemplary embodiment will now be described.

[0102] In a humid and hot environment with a temperature of 32.5 degrees Celsius and a humidity of 90%, double-page printing is repeatedly performed using the image forming apparatus 100 according to the second exemplary embodiment to obtain a total of 2,500 printed sheets. The image forming apparatus 100 is in a new state, the developing container stores 50 grams of toner, and the image uses a text-image style with a print rate of 5%. Talc sheets are used as the recording material S, and Century Star sheets are used. Every predetermined number of sheets, the presence of image defects on the printed recording material S and the state of toner stains on the charging roller 2 are checked.

[0103] As a result of the inspection, in the image forming apparatus 100 according to the second exemplary embodiment, when the cumulative number of printed sheets is 2500, no toner stains on the charging roller 2 or image defects on the printed sheet were detected.

[0104] As described above, the cleaning operation on the charging roller 2 is performed based on the state of stains caused by the reverse toner, which is the opposite polarity of the positive polarity, so that the toner stains on the charging roller 2 are reduced without over-performing the cleaning operation.

[0105] Furthermore, although, according to the second exemplary embodiment, the cleaning operation is performed more frequently as the cumulative number of printed sheets by the image forming apparatus 100 increases, the duration of the cleaning operation can be increased while maintaining the same frequency. Additionally, a suitable combination of frequency and time can be used when performing the cleaning operation.

[0106] Next, a third exemplary embodiment, which is another exemplary embodiment according to this disclosure, will now be described. The configuration and operation of the image forming apparatus according to this exemplary embodiment are substantially the same as those of the image forming apparatus 100 according to the first exemplary embodiment. Therefore, each component of the image forming apparatus according to this exemplary embodiment that has the same or corresponding function or configuration as the components of the image forming apparatus 100 according to the first exemplary embodiment is given the same reference numerals as those of the image forming apparatus 100 according to the first exemplary embodiment, and repeated descriptions thereof are omitted.

[0107] 1. Image forming apparatus

[0108] According to the third exemplary embodiment, such as Figure 8As shown, the image forming apparatus 200 includes a toner supply mechanism 40 for a toner storage chamber 33. Using the toner supply mechanism 40, new toner is supplied to the toner storage chamber 33 at a desired timing. A toner package 41 is mounted on the toner supply mechanism 40. The toner package 41 is a toner supply container that can be attached to or detached from the image forming apparatus 200. Although the toner package 41 is mounted on the image forming apparatus 200 according to the third exemplary embodiment, the toner package 41 can be directly mounted on the toner storage chamber 33, which serves as a developing container. Furthermore, the toner supply container is not limited to the toner package 41. The toner supply container can have a toner bottle shape and can adopt any shape or structure, as long as toner can be directly supplied to the toner supply container.

[0109] According to this exemplary embodiment, a method (direct supply method) is employed in which a user supplies toner from a toner pack 41 storing toner for supply. Therefore, when the toner level in the toner storage chamber 33 is low, replacing the toner storage chamber 33, which serves as a developing container, is unnecessary, thus improving usability. The image forming apparatus 200 and the toner pack 41 form an image forming system.

[0110] However, when printing operations using the image forming apparatus 200 are performed a certain number of times and new toner is supplied, the following problem arises. When new toner is supplied to the toner storage chamber 33 while the toner in the chamber is deteriorating, the deteriorated toner and the new toner rub against each other in the toner storage chamber 33, and the new toner, which has a higher charging capacity, is often charged toward the normal polarity of the toner. Specifically, deteriorated toner with a low charging capacity that is pre-stored in the toner storage chamber 33 may be charged toward the polarity opposite to that of the toner. Therefore, when new toner is supplied to the toner storage chamber 33, a large amount of reverse toner stains caused by deteriorated toner charged to the opposite polarity may occur. This often occurs, especially when a large amount of new toner is supplied at once when the toner level in the toner storage chamber 33 is low, as described in the third exemplary embodiment. In other words, this is not a major problem for the configuration in which stored toner is consumed and new toner is continuously supplied to the toner storage chamber 33 to maintain a predetermined toner level.

[0111] When the image forming apparatus 200 performs printing after new toner has been supplied to the toner storage chamber 33, the toner reversal stains caused by the deterioration of the toner as a result of the toner supply tend to gradually decrease as the newly supplied toner deteriorates. Therefore, it can be said that toner reversal stains are most likely to occur immediately after the toner supply, and toner reversal stains caused by the toner supply may appear for a certain period of time thereafter.

[0112] 2. Cleaning operation according to the third exemplary embodiment

[0113] The details of the cleaning operation in the image forming apparatus 200 according to the third exemplary embodiment are similar to those in the first exemplary embodiment. The cleaning operation is controlled to be performed during a post-rotation operation following the completion of the image forming operation, and, as in the second exemplary embodiment, the frequency of execution is varied for each cumulative number of printed sheets. As indicated in Table 3, the cleaning operation is performed frequently during a predetermined time period after the toner is supplied to the toner storage chamber 33. After the predetermined time period, the cumulative number of printed sheets of the image forming apparatus 200 is set to increase and the frequency of the cleaning operation is set to decrease.

[0114] Subsequently, if the cumulative number of printed sheets in the image forming apparatus 200 further decreases, control as in the second exemplary embodiment is performed. Specifically, the frequency of performing the cleaning operation is set to increase as the cumulative number of printed sheets increases, to accommodate the increase in toner stains caused by talc accumulation in the toner storage chamber 33 or the increase in toner stains caused by deteriorated toner in the toner storage chamber 33.

[0115] Similar to the second exemplary embodiment, the cleaning operation of toner stains on the charging roller 2 from the time the image forming apparatus 200 is in a new state until the toner is supplied is set to be performed at the frequency specified in Table 2.

[0116] [Table 3]

[0117]

[0118] As specified in Table 3, according to the third exemplary embodiment, cleaning operations are performed frequently when the toner deteriorates immediately after toner supply, causing a large amount of toner reversal stains. The frequency of cleaning operations decreases as multiple prints are performed after toner supply and as the toner reversal stains caused by toner supply decrease. This allows for minimizing the frequency of cleaning operations to accommodate the change in toner reversal stains caused by toner supply, while preventing toner stains on the charging roller 2. According to the third exemplary embodiment, the cleaning operation is also controlled to be performed immediately after toner supply, because toner reversal stains are most likely to occur immediately after toner supply.

[0119] 3. Effects of the third exemplary embodiment

[0120] In a humid environment with a temperature of 32.5 degrees Celsius and a humidity of 90%, double-page printing is repeatedly performed using the image forming apparatus 200 according to the third exemplary embodiment to obtain a total of 2,500 printed sheets. Thereafter, the toner supply mechanism 40 supplies 35 grams of new toner to the developing container, and double-page printing is repeated again after the toner supply to obtain a total of 2,500 printed sheets. The image forming apparatus 200 is in a new state, the toner storage chamber 33 stores 50 grams of toner, and the image uses a text-image style with a print rate of 5%. Talc sheet is used as the recording material S, and Century Star sheet is used.

[0121] Every predetermined number of sheets, check the presence / absence of image defects on the printed recording material S and the condition of toner stains on the charging roller 2.

[0122] As a result of the inspection, no toner stains or image defects on the printed sheets caused by toner stains were detected in 2,500 prints after the toner was supplied to the image forming apparatus 200.

[0123] As described above, the cleaning operation on the charging roller 2 is performed based on the state of reverse toner stains caused by toner supply, thereby reducing toner stains on the charging roller 2 and image defects caused by toner stains.

[0124] As described above, according to this disclosure, charging failures on the surface of the photosensitive drum caused by toner on the charging component are prevented, and the developing unit properly collects residual toner.

[0125] While this disclosure has been described with reference to exemplary embodiments, it is to be understood that this disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be given the broadest interpretation in order to cover all such modifications and equivalent structures and functions.

Claims

1. An image forming apparatus, comprising: An image carrier member configured to be rotatable; A charging member configured to contact the image carrier member to form a charging portion, and to charge the surface of the image carrier member at the charging portion; A developing member configured to rotate and contact the image carrier member to form a developing portion, and to develop a toner image at the developing portion by supplying a toner charged to normal polarity to the surface of the image carrier member; A transfer member configured to form a transfer portion opposite to the image carrier member, and to transfer a toner image from the image carrier member to a transfer material at the transfer portion; A charging voltage application unit, the charging voltage application unit being configured to apply a charging voltage to the charging member; A developing voltage applying unit, the developing voltage applying unit being configured to apply a developing voltage to the developing member; as well as The control unit is configured to control the charging voltage application unit and the developing voltage application unit. The developing component collects the toner image formed on the surface of the image carrier at the transfer portion, which remains on the surface of the image carrier after the image is transferred from the transfer portion to the transfer material. The control unit controls the image forming operation of forming a toner image on the transfer material and the cleaning operation of cleaning the surface of the charging component while the image carrier, charging component, and developing component are rotating. In the cleaning operation, before the image carrier member, the charging member, and the developing member rotate, the control unit controls the application of the developing voltage to apply a developing voltage with a polarity opposite to the normal polarity to the developing member, and controls the application of the charging voltage to apply a charging voltage with the normal polarity to the charging member, such that the potential difference formed at the charging portion between the applied charging voltage and the surface potential formed at the surface of the image carrier member is lower than or equal to the discharge start voltage. The control unit then controls the rotation of the image carrier member, the charging member, and the developing member while the developing voltage with the opposite polarity is applied to the developing member and the charging voltage with the normal polarity is applied to the charging member, such that the potential difference formed at the charging portion is lower than or equal to the discharge start voltage.

2. The image forming apparatus according to claim 1, wherein the control unit performs control such that the potential difference formed at the charging portion during the cleaning operation is greater than the potential difference between the developing voltage formed at the developing portion and the surface potential formed at the surface of the image carrier member during the image forming operation.

3. The image forming apparatus of claim 1, further comprising an electrostatic removal member configured to remove static electricity from the surface of the image carrier member downstream of the transfer portion and upstream of the charging portion in the rotational direction of the image carrier member. The control unit controls the removal of static electricity from the surface of the image-bearing member during the cleaning operation.

4. The image forming apparatus according to claim 1, wherein the control unit controls the driving and rotation of the charging member such that the surface movement speed of the image carrying member and the surface movement speed of the charging member are different from each other during the cleaning operation.

5. The image forming apparatus of claim 1, further comprising an exposure unit configured to expose the surface of the image carrier member charged by the charging member to form an electrostatic latent image on the surface of the image carrier member. The control unit controls the exposure unit to expose the surface of the image carrier member during the cleaning operation.

6. The image forming apparatus according to claim 1, further comprising a transfer voltage applying unit configured to apply a transfer voltage to the transfer member. in, During the cleaning operation, the control unit controls the application of a transfer voltage with a polarity opposite to the normal polarity to the transfer member.

7. The image forming apparatus according to claim 1, wherein the control unit controls the cleaning operation to perform the cleaning operation during a post-rotation operation performed after the image forming operation is completed.

8. The image forming apparatus according to claim 1, wherein the control unit controls the frequency of the cleaning operation to increase the frequency as the cumulative number of prints by the image forming apparatus increases.

9. The image forming apparatus according to claim 1, further comprising a toner storage unit, the toner storage unit being configured to store toner in the storage unit. in, When supplying toner, the toner is supplied from a toner supply container, in which the toner is stored in the toner storage unit.

10. The image forming apparatus of claim 9, wherein the toner supply container is attachable to and detachable from the toner storage unit.

11. The image forming apparatus of claim 9, wherein the toner supply container is attachable to and detachable from the image forming apparatus.

12. The image forming apparatus according to any one of claims 9 to 11, wherein the control unit controls the toner storage unit to perform the cleaning operation when toner is supplied to the toner storage unit.

13. The image forming apparatus of claim 9, wherein the control unit increases the frequency of the cleaning operation during a predetermined period immediately following the supply of toner to the toner storage unit.

14. The image forming apparatus according to claim 1, wherein the control unit controls the driving and rotation of the image carrier member such that, during the cleaning operation, the length by which the surface of the image carrier member moves is greater than the sum of the length corresponding to one rotation of the charging member and the length from the charging portion to the developing portion in the rotation direction of the image carrier member.

15. The image forming apparatus according to claim 1, wherein the toner supplied to the surface of the image carrier member is a single-component developer.

Images