Image forming apparatus

Abstract

To provide an image forming apparatus that can prevent an image defect caused by an electrifying roller.SOLUTION: In a non-image forming operation of applying an electrification voltage to an electrifying member while rotating an image carrier, an image forming apparatus executes: i) a first step of applying a first electrification voltage not discharging between the electrifying member and the image carrier and having a first polarity to a surface potential; ii) a second step of, after the first step, applying a second electrification voltage not discharging between the electrifying member and the image carrier and having a polarity opposite to the first polarity to the surface potential; and iii) a third step of, after the second step, controlling to apply a third electrification voltage having a second polarity to the surface potential and apply a fourth electrification voltage having a polarity opposite to the second polarity to the surface potential, and controlling to discharge between the electrifying member and the image carrier when at least one electrification voltage of the third electrification voltage and the fourth electrification voltage is applied.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a laser printer, a copier, a facsimile machine, etc., which obtains a recorded image by transferring a toner image formed on an image carrier using an electrophotographic method or the like onto a recording material.

Background Art

[0002] As an image recording method used in an image forming apparatus such as a printer or a copier, an electrophotographic method is known. The electrophotographic method is the method described below using an electrophotographic process. An electrostatic latent image is formed by a laser beam on a photosensitive drum (hereinafter referred to as a drum) whose surface is charged by a charging member, and a developer image is formed by developing a charged coloring material (hereinafter referred to as toner) with the electrostatic latent image. Then, image formation is performed by transferring and fixing the developer image onto a recording material. In recent years, for the purpose of miniaturizing an image forming apparatus, a cleanerless method has been proposed. The cleanerless method is a method in which toner, which is a developer remaining on the surface of the drum after the transfer process, is removed, recovered, and reused by performing simultaneous development cleaning in the developing means. In the cleanerless method, since there is no cleaner for cleaning the surface of the drum, in particular, it is a configuration in which member contamination due to toner remaining on the drum surface after the transfer process is likely to occur. When the surface of the charging member is contaminated with toner, the discharge amount between the charging member and the drum changes, so the potential formed on the drum surface also changes. The amount of toner stain on the surface of the charging member varies depending on the shape, contact pressure, surface layer roughness, etc. of the charging member, and in many cases, the degree of stain varies depending on the position on the surface of the charging member, so an image with density unevenness occurs in the charging member cycle. As a countermeasure, a configuration has been proposed in Patent Document 1 in which the voltage applied to the charging member is changed to change the potential difference from the drum, thereby transferring the toner attached to the charging roller to the surface of the drum and performing a cleaning operation for cleaning the charging member.

Prior Art Documents

Patent Documents

[0003] [Patent Document 1] Japanese Patent Publication No. 2010-26198 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, the configuration of Patent Document 1 had the following problems. During a cleaning operation to clean a charged member as described in Patent Document 1, if the charging voltage applied to the charged member is set to be higher than the discharge threshold with respect to the drum, the toner adhering to the charging roller may become charged with the opposite polarity to the charging voltage. This increases the adhesion force between the charging roller and the toner, making it difficult to transfer the toner from the charging roller to the drum.

[0005] The object of the present invention is to provide an image forming apparatus that can suppress image defects caused by electrostatic rollers. [Means for solving the problem]

[0006] From the above, the above objective is achieved by the image forming apparatus according to the present invention. In summary, a typical configuration of the present invention is an image forming apparatus capable of performing an image forming operation to form an image on a recording material, comprising: an image carrier; a drive unit for rotating the image carrier; a charging member that contacts the surface of the image carrier to form a charged portion and charges the surface of the image carrier with the charged portion; a developing member for supplying a developer to the surface of the image carrier; a charging voltage application unit for applying a charging voltage to the charging member; and a control unit for controlling the drive unit and the charging voltage application unit, wherein the control unit controls the image forming operation and a non-image forming operation different from the image forming operation, which is a non-image forming operation in which the charging voltage is applied to the charging member while the image carrier is rotating, and in the non-image forming operation, the control unit performs the following control. i) A first step of applying a first charging voltage to the charging member, which does not discharge between the charging member and the image carrier and has a first polarity with respect to the surface potential formed on the surface of the image carrier. ii) A second step, after the first step, of applying a second charging voltage to the charging member, which does not discharge between the charging member and the image carrier and has a polarity opposite to the first polarity with respect to the surface potential, iii) A third step, after the second step, of applying a third charging voltage having a second polarity with respect to the surface potential to the charging member, and controlling the application of a fourth charging voltage having the opposite polarity to the second polarity with respect to the surface potential to the charging member, wherein when at least one of the third charging voltage or the fourth charging voltage is applied, a discharge occurs between the charging member and the image carrier. [Effects of the Invention]

[0007] As described above, the present invention can suppress image defects caused by the electrostatic roller. [Brief explanation of the drawing]

[0008] [Figure 1] This is an explanatory diagram of the image forming apparatus in Example 1. [Figure 2] This is a control block diagram for Example 1. [Figure 3] This is an explanatory diagram of the operation of an image forming apparatus in conventional form 1. [Figure 4] This is an explanatory diagram of the mechanism by which toner on the charging roller is transferred to the surface of the photosensitive drum in Example 1. [Figure 5] This is an explanatory diagram of the operation of the image forming apparatus in conventional form 2. [Figure 6] This is an explanatory diagram of the operation of the image forming apparatus in Example 1. [Figure 7] This is an explanatory diagram of the operation of the image forming apparatus in Example 2. [Figure 8] This is an explanatory diagram of the operation of the image forming apparatus in Example 3. [Figure 9] This is an explanatory diagram of another form of image forming apparatus in Example 1. [Modes for carrying out the invention]

[0009] The embodiments for carrying out this invention will be described in detail below with reference to the drawings, based on examples. However, the dimensions, materials, shapes, and relative arrangements of the components described in these embodiments should be appropriately modified depending on the configuration of the device to which the invention is applied and various conditions. In other words, the scope of this invention is not intended to be limited to the following embodiments. [Examples]

[0010] 1. Image forming apparatus Figure 1 shows a schematic configuration of one embodiment of the image forming apparatus 100 according to the present invention. The image forming apparatus 100 in this embodiment is a monochrome laser beam printer employing a cleanerless system and a contact charging system.

[0011] In this embodiment, the image forming apparatus 100 is provided with a cylindrical photosensitive drum 1 as an image carrier. Around the photosensitive drum 1 are a charging roller 2 as a charging means and a developing device 3 as a developing means. In Figure 1, an exposure device 4 is provided between the charging roller 2 and the developing device 3 in the rotational direction of the photosensitive drum 1. A transfer roller 5 is pressed against the photosensitive drum 1 as a transfer means.

[0012] In this embodiment, the photosensitive drum 1 is a negatively charged organic photoreceptor. This photosensitive drum 1 has a photosensitive layer on an aluminum drum-shaped substrate and is rotated at a predetermined process speed in the direction of the arrow in the figure (clockwise direction) by a drive motor (drive unit) 110 (Figure 2) as a driving means. In this embodiment, the process speed corresponds to the peripheral speed (surface moving speed) of the photosensitive drum 1, which is 140 mm / sec, and the outer diameter of the photosensitive drum 1 is 24 mm.

[0013] The charging roller 2, which is a charged member, contacts the photosensitive drum 1 with a predetermined pressure contact force and is rotationally driven with respect to the photosensitive drum 1 while forming a charging portion. The charging roller 2 may be abutted against the photosensitive drum 1 and be driven to rotate passively. Further, a desired charging voltage is applied by a charging voltage power supply 120 (FIG. 2) as charging voltage applying means, and the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential. In the present embodiment, the surface of the photosensitive drum 1 is charged to a negative polarity by the charging roller 2. At the time of the charging process, a predetermined charging voltage is applied to the charging roller 2 by the charging voltage power supply 120 as a charging voltage applying portion. In the present embodiment, at the time of the charging process, a DC voltage of a negative polarity is applied to the charging roller 2 as the charging voltage. Thereby, the surface of the photosensitive drum 1 is uniformly charged to the dark portion potential Vd. Incidentally, the charging roller 2, more specifically, charges the surface of the photosensitive drum 1 by discharge occurring in at least one of minute gaps between the photosensitive drum 1 formed on the upstream side and the downstream side of the contact portion with the photosensitive drum 1 with respect to the rotation direction of the photosensitive drum 1. However, here, the contact portion between the charging roller 2 and the photosensitive drum 1 with respect to the rotation direction of the photosensitive drum 1 is assumed to be a charging portion for explanation.

[0014] The exposure device 4, which is an exposure unit, is a laser scanner device in the present embodiment, outputs laser light 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 this exposure, an electrostatic latent image (electrostatic image) corresponding to the image information is formed on the surface of the photosensitive drum 1. In the present embodiment, the absolute value of the dark portion potential Vd of the surface of the photosensitive drum 1 formed by being uniformly charged is reduced by being exposed by the exposure device 4 and becomes the bright portion potential Vl. Here, the position on the photosensitive drum 1 exposed by the exposure device 4 with respect to the rotation direction of the photosensitive drum 1 is assumed to be an exposure portion (exposure position). Note that the exposure device 4 is not limited to a laser scanner device, and for example, an LED array in which a plurality of LEDs are arranged along the longitudinal direction of the photosensitive drum 1 may be adopted.

[0015] In this embodiment, a contact development method is used as the development method. The development apparatus 3 includes a developing member, a developing roller 31 as a developer carrier, a toner supply roller 32 as a developer supply means, a developer storage chamber (developing container) 33 for storing toner, and a developing blade 34. The toner supplied from the developer storage chamber 33 to the developing roller 31 by the toner supply roller 32 is charged to a predetermined polarity by passing through the blade nip, which is the contact point between the developing roller 31 and the developing blade 34. The toner carried on the developing roller 31 moves from the developing roller 31 to the photosensitive drum 1 in the developing section according to the electrostatic image. Here, the contact point between the developing roller 31 and the photosensitive drum 1 with respect to the rotation direction of the photosensitive drum 1 is considered to be the developing section. In this embodiment, the developing roller 31 and the photosensitive drum 1 are in constant contact. In this embodiment, the developing roller 31 is driven to rotate counterclockwise in the developing section so that the photosensitive drum 1 and the developing roller 31 move in the forward direction. The drive motor 110, which is the driving means for driving the developing roller 31, may be the same main motor 110 as the driving means for the photosensitive drum 1, as in this embodiment. Alternatively, separate drive motors, such as a photosensitive drum drive unit and a developing roller drive unit, may rotate the photosensitive drum 1 and the developing roller 31, respectively. During development, a predetermined developing voltage is applied to the developing roller 31 by a developing voltage power supply 140 (Figure 2), which is the developing voltage application means. The control unit 200 controls the developing roller 31 to apply a DC voltage of -350V as the developing voltage Vdc to the core metal of the developing roller 31 from the developing voltage power supply 140 when the developing roller 31 and the photosensitive drum 1 are in contact and rotating during the image formation operation. During image formation, the electrostatic force generated by the potential difference between the developing voltage Vdc = -350V and the image formation potential Vl = -100V of the photosensitive drum 1 causes the toner carried on the developing roller 31 to be developed at the image formation potential Vl of the photosensitive drum 1.

[0016] In the following explanation, with respect to potential and applied voltage, a large absolute value on the negative side (for example, -1200V compared to -600V) will be referred to as a high potential, and a small absolute value on the negative side (for example, -350V compared to -600V) will be referred to as a low potential. This is because we are considering the negatively charged toner in this embodiment as the reference.

[0017] Also, the voltage in this embodiment is expressed as the potential difference from the ground potential (0 V). Therefore, the development voltage Vdc = -350 V is interpreted as having a potential difference of -350 V with respect to the ground potential due to the development voltage applied to the core metal of the development roller 31. This is the same for the charging voltage, transfer voltage, and the like.

[0018] In this embodiment, a negative-polarity DC voltage is applied as the development voltage, and after being uniformly charged, it is exposed. As a result, toner charged with the same polarity (negative polarity in this embodiment) as the charging polarity of the photosensitive drum 1 adheres to the exposure surface (image portion), which is the image forming portion on the photosensitive drum 1 where the absolute value of the surface potential has decreased. This developing method is called the reversal developing method. In this embodiment, the normal polarity, which is the charging polarity of the toner during development, is negative. In this embodiment, a one-component non-magnetic contact developing method is adopted, but the present invention is not limited to such an aspect, and a two-component non-magnetic contact developing method, a non-contact developing method, a magnetic developing method, or the like may be adopted. The two-component non-magnetic contact developing method is a method in which a two-component developer including a non-magnetic toner and a magnetic carrier is used as the developer, and the developer (magnetic brush) carried on the developer carrier is brought into contact with the photosensitive drum 1 for development. The non-contact developing method is a method in which toner is caused to fly from a developer carrier disposed opposite to the photosensitive member in a non-contact manner onto the photosensitive member for development. The magnetic developing method is a method in which magnetic toner is carried by magnetic force on a developer carrier having a built-in magnet as a magnetic field generating means, which is disposed opposite to the photosensitive member in a contact or non-contact manner, for development. In this embodiment, toner having a central average particle diameter of 6 μm and a normal charging polarity of negative polarity is used.

[0019] As the transfer member, the transfer roller 5 can preferably be made of an elastic material such as polyurethane rubber, EPDM (ethylene propylene diene rubber), or NBR (nitrile butadiene rubber) sponge rubber. The transfer roller 5 is pressed toward the photosensitive drum 1, forming a transfer area where the photosensitive drum 1 and the transfer roller 5 are in contact. During transfer, a predetermined transfer voltage is applied to the transfer roller 5 by a transfer voltage power supply 160 (Figure 2), which serves as a transfer voltage application means. In this embodiment, during transfer, a DC voltage with the opposite polarity to the normal polarity of the toner (positive polarity in this embodiment) is applied to the transfer roller 5 as the transfer voltage. Then, due to the action of the electric field formed between the transfer roller 5 and the photosensitive drum 1, the toner image is electrostatically transferred from the photosensitive drum 1 to the recording material S.

[0020] The recording material S stored in the cassette 6 is fed by the paper feeding unit 7 at the same time that the toner image formed on the photosensitive drum 1 reaches the transfer section, and is transported to the transfer section via the registration roller pair 8. The toner image formed on the photosensitive drum 1 is transferred onto the recording material S by the transfer roller 5, to which a predetermined transfer voltage is applied by the transfer voltage power supply 160, which acts as the transfer voltage application section.

[0021] After the toner image has been transferred, the recording material S is transported to the fuser unit 9. The fuser unit 9 is a film heating type fuser equipped with a fuser heater (not shown), a fuser film 91 containing a thermistor (not shown) for measuring the temperature of the fuser heater, and a pressure roller 92 for pressing the fuser film 91 against the film. The recording material S is then heated and pressurized, fixing the toner image, and is discharged outside the machine by passing through the paper discharge roller pair 12.

[0022] In this embodiment, the brush 10, which serves as a paper dust removal member, is positioned in contact with the downstream of the transfer section on the photosensitive drum 1, and removes paper dust that has been transferred to the photosensitive drum 1 as the recording material S passes through the transfer section.

[0023] Furthermore, in this embodiment, a pre-exposure device 13 is arranged as a pre-charging exposure means to equalize the potential on the photosensitive drum 1 after transfer downstream of the contact area between the photosensitive drum 1 and the brush 10 and upstream of the charging area in the rotational direction of the photosensitive drum 1. In this embodiment, the pre-exposure device 13 operates an LED attached to the side of a main body (not shown) and irradiates the photosensitive drum 1 parallel to the main scanning direction. A light guide or the like can also be used as a light guide member to suppress uneven irradiation in the main scanning direction.

[0024] The transfer residue toner that remains on the photosensitive drum 1 without being transferred to the recording material S passes through the contact area of ​​the brush 10, and after the potential on the photosensitive drum 1 is leveled in the pre-exposure device 13, it is recharged to a negative polarity by discharge at the charging part of the charging roller 2. The transfer residue toner, which has been recharged to a negative polarity at the charging roller 2, reaches the developing section as the photosensitive drum 1 rotates. Upon reaching the developing section, the transfer residue toner moves to the surface of the developing roller 31 and is collected inside the developing container 33.

[0025] In this embodiment, the brush 10 and pre-exposure device 13 are arranged, but the configuration can also be applied without them.

[0026] 2. Control Unit Next, the control unit 200 will be described. Figure 2 is a control block diagram showing the schematic control configuration of the main parts of the image forming apparatus 100 in this embodiment. The controller 202 exchanges various electrical information with the host device and comprehensively controls the image forming operation of the image forming apparatus 100 via the control unit 200 through the interface 201 according to a predetermined control program and reference table. The control unit 200 is composed of a CPU 155, which is a central element that performs various calculations, and memory 154 such as ROM and RAM, which are memory elements. The RAM stores sensor detection results, counter count results, calculation results, etc., and the ROM stores the control program, data tables obtained in advance through experiments, etc. Each control target, sensor, counter, etc. in the image forming apparatus 100 is connected to the control unit 200. The control unit 200 controls the exchange of various electrical information signals and the timing of the driving of each part, etc., and controls a predetermined image forming sequence. For example, the control unit 200 controls the voltages and exposure amounts applied by the charging voltage power supply 120, the developing voltage power supply 140, the exposure unit 4, the transfer voltage power supply 160, and the pre-exposure device 13. It also controls the main motor (drive unit) 110. The image forming apparatus 100 then forms an image on the recording material P based on the electrical image signal input to the controller 202 from the host device. Examples of host devices include image readers, personal computers, facsimile machines, and smartphones.

[0027] 3. Toner stains on the electrostatic roller Here, the surface of the photosensitive drum 1 has a region where an electrostatic latent image is formed and an image-forming area is created, and a region where an electrostatic latent image is not formed and a non-image-forming area is created. The behavior of the residual toner generated during the image-forming operation will be explained separately for the image-forming area and the non-image-forming area of ​​the photosensitive drum 1.

[0028] 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 in the developing section. Instead, it moves from the developing roller 31 to the transfer section along with the developed toner, and is transferred to the recording material S for image formation.

[0029] Meanwhile, the residual toner adhering to the non-image-forming area of ​​the photosensitive drum 1 is recharged to its normal polarity, negative, by the charging unit. In the developing unit, the potential difference between the potential of the non-image-forming area of ​​the photosensitive drum 1 and the developing voltage causes the toner to be transferred to the developing roller 31 and recovered in the developer storage chamber 33. The toner recovered in the developer storage chamber 33 is then used again for image formation.

[0030] Toner remaining on the surface of the photosensitive drum 1 after transfer, such as transfer residue toner, passes through the charged area, which is the contact point between the photosensitive drum 1 and the charging roller 2, before the developing area. Therefore, the toner comes into contact with the charging roller 2, which is in physical contact with the surface of the photosensitive drum 1. Furthermore, in a configuration where the developing roller 31 and the photosensitive drum 1 are in constant contact, as in this embodiment, the following phenomena occur when the developing container 33 is new or when a long time has passed since the last printing. In the above case, if the chargeability of the toner in the developing container 33 is low, the potential difference formed between the photosensitive drum 1 and the developing roller 31 alone is not enough to retain the toner on the surface of the developing roller 31. Therefore, a large amount of toner is transferred to the surface of the photosensitive drum 1. The phenomenon in which toner is transferred to the surface of the photosensitive drum 1 in response to the potential difference (called back contrast) formed between the non-image forming area of ​​the photosensitive drum 1 and the developing roller 31 is called fogging, and the toner transferred to the surface of the photosensitive drum 1 during fogging is called fogging toner. In this embodiment, the toner's chargeability is low and the amount of condensate is high from the time the developing container 33 is new until approximately 100 sheets have been fed through. In this way, the toner that has been transferred to the photosensitive drum 1 has low chargeability, so even if the potential difference formed between the charging roller 2 and the photosensitive drum 1 is set to a potential difference that makes it difficult for negatively charged toner to move to the charging roller 2, the toner that has been transferred to the photosensitive drum 1 will contaminate the charging roller 2. When the toner adhering to the charging roller 2 receives a discharge that occurs when a charging voltage above the discharge threshold is applied to the charging part, it becomes positively charged. Positively charged toner adheres firmly to the surface of the charging roller 2 to which a negatively charged voltage is applied. In particular, toner with relatively small particle sizes is easily charged, so under conditions where the proportion of small-particle-sized toner in the condensate is high, the charging roller 2 is heavily contaminated with toner, and it becomes difficult to move the toner from the charging roller 2 to the surface of the photosensitive drum 1. Small-particle-sized toner, which is easily charged and has low mass, moves easily in the electric field and is preferentially consumed as a developer. Therefore, the proportion of small particle sizes is higher in the toner in the developing container 33 filled with new toner than in the toner in the developing container 33 filled with durable toner. Furthermore, in the case of an image forming apparatus 300 (Figure 9) in which the developing device 3, the developing container 33, or the toner container 21 connected to the developing container 33 (described later) are replaced together, the following phenomena occur.After replacing the developing unit 3 and developing container 33, or after replenishing toner in the developing container 33, the proportion of small particle size increases. Therefore, when the developing container 33 or toner container is new, or after toner replenishment, there is a large amount of coated toner. Furthermore, even within the coated toner, the proportion of small particle size is high, and in a cleanerless configuration like this embodiment, much of this coated toner reaches the charged area, which is the contact point of the charging roller 2. As a result, the amount of toner contamination on the charging roller 2 is large. If a charging voltage above the discharge threshold is applied in this state, the small particle size toner, which is more easily charged, becomes charged in the opposite polarity to the charging voltage and adheres firmly to the charging roller 2. The configuration of toner replenishment will be explained using Figure 9 in the modified example described later.

[0031] On the other hand, when performing a cleaning operation, which involves transferring toner adhering to the surface of the charging roller 2 to the surface of the photosensitive drum 1, the force that transfers the toner from the charging roller 2 to the photosensitive drum 1 is proportional to the potential difference formed between the charging roller 2 and the photosensitive drum 1. Therefore, the larger the potential difference, the greater the cleaning force on the surface of the charging roller 2. Thus, within a charging voltage below the discharge threshold, applying a larger potential difference allows for cleaning the surface of the charging roller 2 while suppressing strong charging of small-particle toner. However, toner with relatively large particle sizes has low chargeability and high mass, making it less responsive to electric fields, and the cleaning force may be insufficient at potential differences below the discharge threshold.

[0032] Furthermore, an effective method for cleaning the charging roller 2 is to apply charging voltages higher and lower than the surface potential of the photosensitive drum 1. For example, if the surface potential formed on the surface of the photosensitive drum 1 is charged to -600V, and then the charging voltage is alternately switched between -1200V and 0V, a potential difference of 600V is created for both the negative and positive polarity toner on the charging roller 2. Therefore, it becomes possible to efficiently move (discharge) both positive and negative polarity toner on the charging roller 2 to the surface of the photosensitive drum 1. As a control of the cleaning operation of the surface of the charging roller 2, control is performed by alternately applying two certain voltages. One effect of alternately applying two certain charging voltages is that the potential gradient generated when switching the charging voltages becomes larger, which strengthens the force that moves the toner from the charging roller 2 to the surface of the photosensitive drum 1.

[0033] 4. Control of the cleaning operation of the charged roller surface (Control of Conventional Form 1) Next, in order to facilitate understanding of the various potential controls in this embodiment, the control of Conventional Embodiment 1 will be explained using Figure 3. Figure 3 shows the cleaning operation of the charging roller 2 performed when the developing container 33 is new in the conventional image forming apparatus of Conventional Embodiment 1. From top to bottom, it shows the drive signal of the motor 110, which is the drive unit that drives the photosensitive drum 1, the charging voltage control applied to the charging roller 2, the surface potential of the photosensitive drum 1, and the time progression of the difference between the surface potential of the photosensitive drum 1 and the charging voltage applied to the charging roller 2. The charging roller 2 is subjected to an operation in which -1200V is applied for one rotation of the photosensitive drum 1 to charge the surface of the photosensitive drum 1 to -600V, and then two voltages, -1200V and 0V (OFF), are applied alternately 10 times each. Thereafter, the cleaning operation control of the charging roller surface is performed by alternately applying two voltages.

[0034] (Operation of Conventional Form 1) As in Conventional Configuration 1, a potential difference of 600V is applied to both positive and negative polarity toners relative to the surface potential of the photosensitive drum 1 (-600V), thereby transferring toner from the charging roller 2 to the surface of the photosensitive drum 1. As shown in Figure 4, both positive and negative polarity toners on the surface of the charging roller 2 are moved towards the photosensitive drum 1 by the potential difference formed between the surface of the photosensitive drum 1 and the charging roller 2. Meanwhile, after the operation of Conventional Configuration 1, the charge distribution on the charging roller 2 was measured using an E-spart analyzer (manufactured by Hosokawa Micron Corporation), and the ratio of positively charged toner was calculated, as shown in Table 1. Here, "no charging voltage applied" in Table 1 refers to the measurement of toner adhering to the charging roller after being ejected from the developer when the system was driven without applying a charging voltage. From Table 1, it can be seen that more positively polarity toner remains on the charging roller 2 in Conventional Configuration 1 than when no charging voltage is applied. In this embodiment, the discharge threshold is approximately 600V. If the charging roller 2 is cleaned with a charging voltage exceeding the discharge threshold, the toner on the charging roller 2 becomes positively charged due to the discharge, increasing the adhesion between the charging roller 2 and the toner. Therefore, even if the surface of the charging roller 2 is subsequently cleaned, it is difficult to remove the toner from the charging roller 2 due to its high adhesion. After operation in the conventional embodiment 1, when a halftone image was printed, a density unevenness image occurred in the period of the charging roller 2. This is thought to be due to the positively charged toner remaining on the charging roller 2, resulting in density unevenness.

[0035] [Table 1]

[0036] (Control of Conventional Form 2) Next, in order to facilitate understanding of the various potential controls in this embodiment, the control of the conventional embodiment 2 will be explained using Figure 5. Figure 5 is a diagram showing the cleaning operation of the charging roller 2 performed when the developing container 33 is new in the conventional embodiment 2 image forming apparatus 100. From top to bottom, it shows the drive signal of the main motor 110 that drives the photosensitive drum 1, the charging roller 2, and the developing roller 31, the control of the charging voltage applied to the charging roller 2, the surface potential of the photosensitive drum 1, and the time progression of the difference between the surface potential of the photosensitive drum 1 and the charging voltage. First, -1000V is applied to the charging roller 2 for one rotation of the photosensitive drum 1, and after the surface of the photosensitive drum 1 is charged to -400V, the operation is performed to alternately apply two levels of charging voltage, -700V and -100V, 10 times each.

[0037] (Effect of Conventional Form 2) In Conventional Configuration 2, unlike Conventional Configuration 1, the potential difference formed between the charging roller 2 and the surface of the photosensitive drum 1 is set to a potential difference below the discharge threshold. By setting such a potential difference, as in Figure 4, the relatively high charge of toner with both positive and negative polarity on the charging roller 2 is discharged to the photosensitive drum 1 side by the potential difference, even though the potential difference is small. Here, after the operation of Conventional Configuration 2, the charge distribution of the toner attached to the charging roller 2 was measured, as described in the operation of Conventional Configuration 1, and the results are shown in Table 1. In order to clean the toner with both positive and negative polarity, it is necessary to charge the surface of the photosensitive drum 1. Therefore, although there is a tendency for the proportion of positive polarity to increase because a charging voltage above the discharge threshold is applied for a short time at the beginning, it can be seen that the proportion of positive polarity toner only increases by about 4% compared to when no charging voltage is applied.

[0038] In the conventional configuration 2, the discharge threshold is approximately 600V, and the charging roller 2 is cleaned with the surface potential of the photosensitive drum 1 and a non-discharging charging voltage. As a result, the amount of toner that becomes positively charged by discharge is small, and the adhesion force with the charging roller 2 does not increase. However, on the other hand, when a halftone image was printed after operation of the conventional configuration 2, a density uneven image occurred in the period of the charging roller 2. This is thought to be because the cleaning performance of the charging roller 2 weakened, causing toner to remain on the charging roller 2 and resulting in density unevenness.

[0039] In other words, by lowering the charging voltage below the discharge threshold and suppressing the amount of discharge between the charging roller 2 and the photosensitive drum 1, the amount of toner that becomes positively polarized decreased. However, because the potential difference between the charging roller 2 and the photosensitive drum 1 was small, the cleaning performance of the charging roller 2 was weakened.

[0040] (Control of this embodiment) Therefore, in this embodiment, as shown in Figure 6, the charging voltage is switched so that the potential difference with the surface of the photosensitive drum 1 is below the discharge threshold to clean the surface of the charging roller 2, and then the charging voltage is switched to a potential difference above the discharge threshold to clean the charging roller 2. First, -1000V is applied to the charging roller 2 for one full rotation of the photosensitive drum 1 to charge the surface of the photosensitive drum 1 to -400V, and then two voltages, -700V and -100V, are applied alternately five times each. After that, two voltages, -1200V and 0V (OFF), are applied alternately five times each.

[0041] (Operation of this embodiment) Next, we will describe the operation when the charged roller 2 is cleaned using the control of this embodiment.

[0042] First, the discharge threshold in this embodiment is approximately 600V, and by performing a cleaning operation with a potential difference below the discharge threshold (300V in this embodiment), the toner adhering to the charging roller 2, particularly the toner with relatively high charge, is selectively transferred to the photosensitive drum 1. Subsequently, the toner remaining on the charging roller 2, which has relatively low charge and is unlikely to become highly charged even if discharge occurs between the charging roller 2 and the photosensitive drum 1, is transferred to the photosensitive drum 1 by increasing the potential difference.

[0043] (Explanation of effects) Two test methods and their results, a tape test and a paper-feeding experiment, conducted to confirm the effectiveness of this embodiment, will be described.

[0044] The tape test was conducted under the following conditions: A new developing container 33 was set in the image forming apparatus 100 under conditions of 25°C and 50% relative humidity (normal temperature and humidity environment), and the photosensitive drum 1, charging roller 2, and developing roller 31 were rotated for 5 seconds. This transferred the capritner from the developing roller 31 to the photosensitive drum 1 and then to the charging roller 2. Subsequently, various control methods for cleaning the charging roller 2 were implemented, and after attaching tape (polyester tape No. 5511 manufactured by Nichiban Co., Ltd.) to the surface of the charging roller 2, it was peeled off and attached to a white piece of paper. Through the above process, the amount of toner remaining on the surface of the charging roller 2 could be quantified and compared as a density. The densitometer used was an X-Rite spectrophotometer (eXact Basic). A lower value indicates a lower density and a smaller amount of toner remaining on the charging roller 2, indicating that the cleaning of the charging roller 2 was more effective.

[0045] Furthermore, the paper feeding experiment was conducted under the following conditions: After conducting the tape test, one 25% density halftone image was printed using Xerox Vitality Multipurpose Printer Paper (product name, basis weight 75g) manufactured by Xerox Corporation as the recording material P. If, at that time, an image with uneven density due to toner contamination of the charging roller 2 occurred, it was determined that the charging roller was contaminated (NG).

[0046] Table 2 shows the results of evaluating tape density by the tape test and image quality by paper feeding experiment under the control of Conventional Embodiment 1, Conventional Embodiment 2, and this embodiment, compared to the case where electrostatic roller cleaning is not performed. When the tape density falls below 0.5, there is almost no effect on the image actually output.

[0047] [Table 2]

[0048] In the conventional configuration 1, where charging roller cleaning is performed with a charging voltage above the discharge threshold, the toner on the charging roller 2 becomes highly positively charged, as described above, resulting in increased adhesion to the charging roller 2. Therefore, as can be seen from the tape test results in Table 2, the difference in tape density compared to the case without charging roller cleaning is small at 0.2, indicating that the cleaning effect is small because positively polarized toner remains on the charging roller 2. Furthermore, the paper feed test results also showed that density unevenness occurred in the periodicity of the charging roller 2, which was unacceptable.

[0049] Furthermore, in the conventional configuration 2, where charging roller cleaning is performed with a charging voltage below the discharge threshold, as mentioned above, there is a cleaning effect on highly charged toners. However, for less charged toners, the potential difference is small, resulting in insufficient force to transfer them from the charging roller 2 to the photosensitive drum 1. As a result, the difference in tape density compared to when the charging roller cleaning operation is not performed is small at 0.6, and the paper feed test results were also unsatisfactory.

[0050] In contrast, in this embodiment, where charging roller cleaning is performed with a charging voltage below the discharge threshold, and then with a charging voltage above the discharge threshold, the difference in tape density is a large 1.1 compared to the case where no charging roller cleaning is performed. The tape density itself was 0.2, a value that is almost unaffected by toner. Furthermore, the paper feed test results were OK, with no density unevenness in the image.

[0051] The configuration of Example 1 has the following characteristics. The image forming apparatus 100, which is capable of performing an image forming operation to form an image on a recording material S, has the following configuration: a photosensitive drum 1, a main motor 110 that rotates the photosensitive drum 1, and a charging roller 2 that contacts the surface of the photosensitive drum 1 to form a charged portion and charges the surface of the photosensitive drum 1 with the charged portion. In addition, it has a developing roller 31 that supplies a developer charged with the normal polarity to the surface of the photosensitive drum 1, a charging voltage application unit 120 that applies a charging voltage to the charging roller 2, and a control unit 220 that controls the main motor 110 and the charging voltage application unit 120.

[0052] The control unit 220 controls the image forming operation and the non-image forming operation, which involves applying a charging voltage to the charging roller 2 while the photosensitive drum 1 is rotating. In the non-image forming operation, it performs the following control.

[0053] i) A first step of applying a first charging voltage to the charging roller 2 that does not discharge between the charging roller 2 and the photosensitive drum 1 and has a first polarity with respect to the surface potential formed on the surface of the photosensitive drum 1.

[0054] ii) A second step, after the first step, in which a second charging voltage is applied to the charging roller 2, which does not discharge between the charging roller 2 and the photosensitive drum 1 and has a polarity opposite to the first polarity with respect to the surface potential.

[0055] iii) After the second step, a third charging voltage having a second polarity with respect to the surface potential is applied to the charging roller 2, and a fourth charging voltage having the opposite polarity to the second polarity with respect to the surface potential is applied to the charging roller 2. The third step is to control the process so that a discharge occurs between the charging roller 2 and the photosensitive drum 1 when at least one of the third or fourth charging voltages is applied.

[0056] As described above, the control of this embodiment first performs charging roller cleaning with a charging voltage below the discharge threshold, thereby selectively transferring relatively highly charged toner to the photosensitive drum 1. Subsequently, by increasing the potential difference, relatively less charged toner can be transferred to the photosensitive drum 1, thereby suppressing the occurrence of density unevenness images on the charging roller 2 that occur when a large amount of toner adheres to the charging roller 2.

[0057] Here, the first polarity and the second polarity may be the same polarity, or they may be opposite polarities. That is, in the first and third steps, the charging voltage may be applied from the normal polarity side to the surface potential of the photosensitive drum 1, or it may be applied from the reverse polarity side. The first repeating operation, in which the first and second steps are repeatedly performed, is controlled to be executable. The second repeating operation, in which the third step is repeatedly performed, is also controlled to be executable.

[0058] The system includes a developing container 33 for containing the developer, and the developing container 33 may be configured to allow the attachment and detachment of a developer supply container 21. In such a configuration, the system may be controlled to perform non-image forming operations after the developer supply container 21 is attached to the developing container 33 and the developer is supplied into the developing container 33. Alternatively, the developing container 33 may be detachable from the image forming apparatus, and the system may be controlled to perform non-image forming operations after the developing container 33 has been replaced.

[0059] For example, as a variation of this embodiment, a toner supply configuration using a direct supply method will be described. As shown in Figure 9(a), the image forming apparatus 300 in this embodiment is provided with an opening 35 which is the mounting port for the toner bottle, and toner can be supplied from here. As shown in Figure 9(b), the toner bottle 41 is attached to the opening 35, and the toner moves from the toner bottle 41 to the developing container 33 by gravity, so that toner can be supplied without requiring any special equipment such as a toner supply path.

[0060] When the toner 21 sealed in the toner bottle 41 shown in Figure 9(a) is supplied to the developing container 33 shown in Figure 9(a), almost all of the toner 21 in the toner bottle 41 is stored in the developing container 33, as shown in Figure 9(b). The developing container 33 extends in the longitudinal direction and has a volume sufficient to accommodate all of the toner 21 sealed in the toner bottle 41.

[0061] Furthermore, in this embodiment, in the section where a charging voltage above the discharge threshold is applied, a charging voltage above the discharge threshold was applied to both positive and negative polarities. However, depending on the ease with which the toner being handled charges, its tendency to reverse to positive polarity, etc., a voltage above the discharge threshold may be applied to only one of the polarities. Also, when the developing container is new or after replenishing the developer, there are many small-particle toners that tend to reverse to positive polarity, which is the opposite polarity of the normal polarity. Due to this phenomenon, depending on the progress of durability (number of printed pages, toner consumption, rotation speed of the photosensitive drum 1, rotation speed of the developing roller 31, etc.), it may be possible to switch between applying a charging voltage above the discharge threshold to both polarities or only one of the polarities in the section where a voltage above the discharge threshold is applied. In this embodiment, the amount of toner filled in a new developing container is 120g. In that case, for example, when printing at a print coverage rate of 5% (print area rate when a completely black image is 100% and a completely white image is 0%), it has been found that the proportion of small-particle toners is suppressed after approximately 100 sheets have been fed through. Therefore, the same operation as in this embodiment, which is performed during the post-rotation operation after image printing, is performed until 100 sheets have been fed through. After that, the proportion of small particle sizes that are easily positively charged becomes sufficiently low. Therefore, an operation similar to that of the conventional form 1, where the potential difference with the surface of the photosensitive drum 1 is larger, may be performed to improve the cleaning performance of the charging roller. In this way, the post-rotation operation may be switched depending on the amount of toner replenished, the printing rate, the amount of toner consumed, etc.

[0062] Furthermore, although this embodiment describes the effect of cleaning the charging roller 2, similar effects can be obtained by performing the cleaning operation of other components that come into contact with the surface of the photosensitive drum 1, which is the image carrier, such as the transfer roller 5 and the brush 10, as in this embodiment.

[0063] Furthermore, the value of the charging voltage, the number of charging voltage switching cycles, the charging voltage application time, etc., may be adjusted depending on the change in capacitance due to wear of the surface of the photosensitive drum 1 over time, the degree of deterioration in cleaning performance due to toner degradation, and the ambient temperature and humidity. [Examples]

[0064] Next, other embodiments 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 denoted by the same reference numerals as those of the image forming apparatus of Embodiment 1, and detailed descriptions are omitted.

[0065] 1. Control of the cleaning operation of the electrostatic roller surface (Control of this embodiment) Next, the control of the charging voltage in this embodiment will be explained using Figure 7. Figure 7 shows the charging roller cleaning operation performed when the developing container 33 is new in the image forming apparatus 100 of this embodiment, and the other operations are the same as in Embodiment 1. In this embodiment, the charging voltage is controlled to change in steps. In Embodiment 1, there were two levels of charging voltage below the discharge threshold, but in this embodiment, two or more levels of charging voltage are applied in a direction that gradually increases the potential difference. More specifically, the charging voltage is applied in a direction that increases the absolute value of the potential difference between the surface potential of the photosensitive drum 1 and the charging voltage by 100V from 100V in increments of 100V.

[0066] (Explanation of effects) Table 3 shows the results of a test conducted using the control of this embodiment described above, similar to that of Example 1, and a comparison with Example 1.

[0067] [Table 3]

[0068] These results show that the image and positively charged toner ratio are equivalent to those of Example 1. However, the tape density was higher than in Example 1. Since the force applied to the toner on the surface of the charging roller 2 is proportional to the potential difference, it is thought that the number of times a relatively large potential difference is applied within the discharge threshold was reduced compared to Example 1, assuming the total time for charging roller cleaning was the same. However, in the case of Embodiment 2, since the tape density is below 0.5, there is almost no impact on the image that is actually output.

[0069] On the other hand, in this embodiment, the amount of toner transferred from the charging roller 2 to the photosensitive drum 1 at one time can be reduced. Table 4 shows the results of the tape test performed in Example 1 on the photosensitive drum 1 immediately after the start of charging roller cleaning. Specifically, the image forming operation was forcibly stopped at the stop timing shown in Figure 6 for Example 1 and in Figure 7 for this embodiment, and the test was performed on the photosensitive drum 1 immediately after passing the charged portion, which is the contact point between the charging roller 2 and the photosensitive drum 1, at that timing.

[0070] [Table 4]

[0071] From these results, it can be seen that the amount of toner transferred to the photosensitive drum 1 at one time is less in this embodiment compared to the configuration of Embodiment 1. This is because the potential difference between the charging roller 2 and the photosensitive drum 1 is gradually increased. The toner discharged from the charging roller 2 is collected in the developing container 33, but even if a large amount of toner reaches the developing section, which is the contact point between the photosensitive drum 1 and the developing roller 31, it may not be collected all at once. If it is not collected all at once, components such as the transfer roller 5 located downstream of the developing container 33 in the rotational direction of the photosensitive drum 1 will be contaminated with toner.

[0072] The configuration of Embodiment 2 is characterized by performing the following control: In the first iterative operation, the first potential difference formed between the surface potential of the photosensitive drum 1 and the first charging voltage is controlled to increase in steps. In the first iterative operation, the second potential difference formed between the surface potential of the photosensitive drum 1 and the second charging voltage may also be controlled to increase in steps. Furthermore, in the second iterative operation, the third potential difference formed between the surface potential of the photosensitive drum 1 and the third charging voltage is controlled to increase in steps. In the second iterative operation, the fourth potential difference formed between the surface potential of the photosensitive drum 1 and the fourth charging voltage may also be controlled to increase in steps.

[0073] Based on the above, by using the control of this embodiment, it is possible to improve the development and recovery performance compared to Example 1 and suppress toner contamination not only of the charging roller 2 but also of other components in contact with the photosensitive drum 1. [Examples]

[0074] Next, other embodiments 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 apparatuses of Embodiments 1 and 2. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatuses of Embodiments 1 and 2 are denoted by the same reference numerals as those of the image forming apparatuses of Embodiments 1 and 2, and detailed descriptions are omitted.

[0075] 1. Control of the cleaning operation of the electrostatic roller surface (Control of this embodiment) Next, the control of the charging voltage in this embodiment will be explained using Figure 8. Figure 8 shows the charging roller cleaning operation performed when the developing container 33 is new in the image forming apparatus 100 of this embodiment, and the other operations are the same as in Examples 1 and 2. In this embodiment, after charging the surface of the photosensitive drum 1 to -400V, first, charging voltages of 0V and -300V are applied alternately three times each to eject positive polarity toner. After that, similar to Example 2, the charging voltage is controlled to change in steps with respect to the surface potential of the photosensitive drum 1, and charging voltages of two or more levels are applied in a direction in which the potential difference gradually increases. The charging voltage is applied in a direction in which the absolute value of the potential difference between the surface potential of the photosensitive drum 1 and the charging voltage increases from 100V in increments of 100V.

[0076] (Explanation of effects) Table 5 shows the results of measuring the charge distribution on the surface of the charging roller 2 and calculating the ratio of positively charged toner using the control method of this embodiment described above, similar to Examples 1 and 2.

[0077] [Table 5]

[0078] These results indicate that the image performance is equivalent to that of Examples 1 and 2. Furthermore, the positively charged toner ratio was better than that of Examples 1 and 2. Tape density showed a worsening trend compared to Example 1, but an improvement compared to Example 2.

[0079] As mentioned in the explanation of Conventional Embodiment 2 using Table 1, the increase in the positively charged toner ratio after implementing the control of Conventional Embodiment 2 compared to when no charging voltage is applied is thought to be because the positively charged toner ratio increases when the surface of the photosensitive drum 1 is initially charged. The toner on the surface of the charging roller 2, which has been positively charged by the discharge that occurs between the charging roller 2 and the surface of the photosensitive drum 1, is located on the relatively outermost layer of the charging roller 2. Therefore, it is effective for charging roller cleaning to discharge the toner from the charging roller 2 to the photosensitive drum 1 side as early as possible. Thus, as in this embodiment, by dischargeing the positively polarized toner, which increases after the surface of the photosensitive drum 1 is charged, early in the charging roller cleaning operation, it is thought that the positively charged toner ratio decreased compared to Examples 1 and 2. Furthermore, by switching and applying the charging voltage between 0V and -300V, the toner can be effectively transferred from the charging roller 2 to the surface of the photosensitive drum 1. On the other hand, tape density shows an improvement compared to Example 2 due to increased ejection of positive polarity toner. Compared to Example 1, the potential difference between the surface potential of the photosensitive drum 1 and the charging roller 2 decreases, similar to Example 2. Therefore, tape density is considered to be slightly deteriorating. However, in the case of Embodiment 3, since the tape density is below 0.5, there is virtually no impact on the image actually output.

[0080] The configuration of Embodiment 3 is characterized by performing the following control. First, a first charging voltage is applied to the charging roller 2, which does not discharge between the charging roller 2 and the photosensitive drum 1 and has a polarity opposite to the normal polarity with respect to the surface potential formed on the surface of the photosensitive drum 1, and a second charging voltage has the opposite polarity and a magnitude different from the first charging voltage. Next, after the above process, a third charging voltage having the first polarity with respect to the surface potential is applied to the charging roller 2, and then the system is controlled to apply a fourth charging voltage having the opposite polarity to the first polarity with respect to the surface potential. At that time, the system is controlled to discharge between the charging roller 2 and the photosensitive drum 1 when at least one of the third or fourth charging voltages is applied.

[0081] As described above, by using the control of this embodiment, the ratio of positively charged toner adhering to the charging roller 2 can be reduced compared to Example 2. Therefore, by more effectively cleaning the charging roller 2, toner contamination can be suppressed not only on the charging roller 2 but also on other components in contact with the photosensitive drum 1.

[0082] In this embodiment, as shown in Figure 8, the surface of the photosensitive drum 1 is charged to -400V, and then, after that, charging voltages of 0V and -300V are applied alternately three times each to eject positive polarity toner. However, the charging voltage is not limited to 0V and -300V as long as it is a voltage that moves the positive polarity toner towards the photosensitive drum 1 relative to the surface potential of the photosensitive drum 1. Furthermore, although only two levels, 0V and -300V, are used, the voltage can be varied to more than two levels. In addition, although the effect of the configuration in Embodiment 3 was explained using control in combination with the configuration in Embodiment 2, it goes without saying that the same effect can be obtained with Embodiment 3 alone or in combination with the configuration in Embodiment 1.

[0083] In the configurations of Examples 1 to 3, a cleanerless configuration was adopted in which no cleaning member is provided to actively clean the surface of the photosensitive drum 1. However, a cleaning member may be provided between the transfer section and the charging section in the rotational direction of the photosensitive drum 1. Alternatively, the brush member 10 may be provided with a function similar to that of a cleaning member. [Explanation of symbols]

[0084] 1 Photosensitive drum 2 Charging rollers 3. Developing device 31 Developing roller 33 Developer Storage Room 100 Image forming apparatus 110 Main motor 120V electrostatic voltage power supply 200 Control Unit

Claims

1. In an image forming apparatus capable of performing an image forming operation to form an image on a recording material, Image carrier and, A drive unit that rotates the image carrier, A charging member that contacts the surface of the image carrier to form a charged portion, and charges the surface of the image carrier at the charged portion, A developing member that supplies a developer to the surface of the image carrier, A charging voltage application unit that applies a charging voltage to the charging member, The system comprises the drive unit and the charging voltage application unit, and a control unit that controls the drive unit and the charging voltage application unit. The control unit controls the image forming operation and a non-image forming operation different from the image forming operation, which involves applying the charging voltage to the charging member while the image carrier is rotated, and the control unit performs the following control during the non-image forming operation, characterized in that the image forming apparatus i) A first step of applying a first charging voltage to the charging member, which does not discharge between the charging member and the image carrier and has a first polarity with respect to the surface potential formed on the surface of the image carrier. ii) A second step, after the first step, in which a second charging voltage is applied to the charging member, which does not discharge between the charging member and the image carrier and has a polarity opposite to the first polarity with respect to the surface potential, iii) A third step, after the second step, of applying a third charging voltage having a second polarity with respect to the surface potential to the charging member, and controlling the application of a fourth charging voltage having the opposite polarity to the second polarity with respect to the surface potential to the charging member, wherein when at least one of the third charging voltage or the fourth charging voltage is applied, a discharge occurs between the charging member and the image carrier.

2. The image forming apparatus according to claim 1, characterized in that the developing member is configured to come into contact with the image carrier during the non-image forming operation.

3. The developing container comprises a developing container for holding the developer, The developing container is configured to be able to accommodate a developer supply container. The image forming apparatus according to claim 1 or 2, characterized in that the control unit controls the non-image forming operation after attaching the developer supply container to the developing container and supplying developer into the developing container.

4. The developing container comprises a developing container for holding the developer, The developing container is detachable from the image forming apparatus, The image forming apparatus according to any one of claims 1 to 3, characterized in that the control unit controls the non-image forming operation to be performed after the developing container has been replaced.

5. The image forming apparatus according to any one of claims 1 to 4, characterized in that the control unit makes the first polarity and the second polarity the same polarity.

6. The image forming apparatus according to any one of claims 1 to 4, characterized in that the control unit sets the first polarity and the second polarity to opposite polarities.

7. The image forming apparatus according to any one of claims 1 to 6, characterized in that the control unit controls the first repeat operation to enable the execution of the first step and the second step repeatedly, and controls the first potential difference formed between the surface potential and the first charging voltage to increase in steps during the first repeat operation.

8. The image forming apparatus according to claim 7, characterized in that the control unit controls the second potential difference formed between the surface potential and the second charging voltage to increase in steps during the first repetitive operation.

9. The image forming apparatus according to any one of claims 1 to 8, characterized in that the control unit controls a second repetitive operation to enable the repeated execution of the third step, and controls the third potential difference formed between the surface potential and the third charging voltage to increase in steps during the second repetitive operation.

10. The image forming apparatus according to claim 9, characterized in that the control unit controls the fourth potential difference formed between the surface potential and the fourth charging voltage to increase in steps during the second repetitive operation.

11. In an image forming apparatus capable of performing an image forming operation to form an image on a recording material, Image carrier and, A drive unit that rotates the image carrier, A charging member that contacts the surface of the image carrier to form a charged portion, and charges the surface of the image carrier at the charged portion, A developing member that supplies a developer charged with normal polarity to the surface of the image carrier, A charging voltage application unit that applies a charging voltage to the charging member, The system comprises the drive unit and the charging voltage application unit, and a control unit that controls the drive unit and the charging voltage application unit. The control unit controls the image forming operation and a non-image forming operation different from the image forming operation, which involves applying the charging voltage to the charging member while the image carrier is rotated, and the control unit performs the following control during the non-image forming operation, characterized in that the image forming apparatus i) A first step of applying to the charging member a first charging voltage that does not discharge between the charging member and the image carrier and has a polarity opposite to the normal polarity with respect to the surface potential formed on the surface of the image carrier, and a second charging voltage that has the opposite polarity and a magnitude different from the first charging voltage, ii) A second step, after the first step, in which a third charging voltage having a first polarity with respect to the surface potential is applied to the charging member, and a fourth charging voltage having the opposite polarity to the first polarity with respect to the surface potential is applied to the charging member, wherein when at least one of the third charging voltage or the fourth charging voltage is applied, a discharge occurs between the charging member and the image carrier.

Images