Image forming apparatus

Abstract

To prevent the occurrence of an adverse effect on an image even if toner adheres onto an electrifying member before a stop operation of an image forming apparatus.SOLUTION: In transition from a first state where an image carrier rotates to a second state where the image carrier stops, when a surface potential of the image carrier formed in a developing unit is defined as V1, a development voltage applied to a developing member as V2, an electrification voltage applied to an electrifying member as V3, and a surface potential of the image carrier formed in an electrifying unit as V4, a control unit controls a first potential difference that is the potential difference between V2 and V1 and a second potential difference that is the potential difference between V3 and V4 based on information on the number of times of execution of an image forming operation.SELECTED DRAWING: Figure 7

Description

Technical Field

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

Background Art

[0002] As an image recording method used in an image forming apparatus such as a printer or a copying machine, an electrophotographic method is known. The electrophotographic method forms an electrostatic latent image on a photosensitive drum (hereinafter referred to as a drum) by a laser beam by using an electrophotographic process, and develops a charged coloring material (hereinafter referred to as toner) into the electrostatic latent image to form a developer image. Then, the developer image is transferred to a recording material and fixed to form an image. In recent years, a cleanerless method has been proposed for the purpose of miniaturizing the image forming apparatus. 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.

[0003] In cleanerless systems, there is no cleaner on the drum. Therefore, material contamination by toner remaining on the drum surface after the transfer process is likely to occur. In particular, in configurations where the drum is charged by a charging component that comes into contact with the drum, such as a charging roller, toner charged with normal polarity and toner charged with reverse polarity (hereinafter referred to as reverse toner) tends to adhere electrostatically to the charging component when the drum is charged. Reverse toner adhering to the charging component can hinder the charging of the drum by the charging component, which can cause image defects. Furthermore, when the drum drive is stopped after turning off the voltage applied to the charging component as part of the stopping operation of the image forming apparatus, the reverse toner adhering to the charging component may cause the following phenomenon: By turning off the voltage applied to the charging component, the electrostatic adhesion force to the charging component is released and it is discharged onto the drum, which can cause image defects during the next image formation. Therefore, Patent Document 1 proposes a configuration in which the voltage applied to the charging component is changed, thereby changing the potential difference with the drum, to transfer the toner adhering to the charging roller to the surface of the drum and clean the charging component. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2010-26198 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, Patent Document 1 had the following problems: Depending on the state of the image forming apparatus, so-called fogging occurs on the non-image drum, where the developing material is developed from the developing material, resulting in increased fogging of inverted toner. Also, since the amount of residual toner is affected by the state of the image forming apparatus, it is necessary to perform a cleaning operation of the charged material periodically. However, even if the cleaning operation is performed periodically, inverted toner may adhere to the charged material before the image forming apparatus is shut down.

[0006] Therefore, the present invention aims to provide an image forming apparatus that suppresses the occurrence of image defects even when toner is adhering to a charged member before the stopping operation of the image forming apparatus. [Means for solving the problem]

[0007] Therefore, 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: a rotatable image carrier; a charging member that contacts the image carrier to form a charged portion and charges the surface of the image carrier with the charged portion; a developing member that supplies toner to the image carrier in a developing portion facing the image carrier; a drive unit that rotates the image carrier; a storage unit that stores information regarding the number of times the image forming operation is performed; a charging voltage application unit that applies a charging voltage to the charging member; a developing voltage application unit that applies a developing voltage to the developing member; and the drive unit and the charging In an image forming apparatus having a voltage application unit and a control unit that controls the development voltage application unit, when transitioning from a first state in which the image carrier is rotating to a second state in which the image carrier is stopped, if V1 is the surface potential of the image carrier formed in the development unit, V2 is the development voltage applied to the development member, V3 is the charging voltage applied to the charging member, and V4 is the surface potential of the image carrier formed in the charging unit, then the control unit controls, based on the information, a first potential difference which is the potential difference between V2 and V1, and a second potential difference which is the potential difference between V3 and V4. Furthermore, when forming the second potential difference, the second potential difference is controlled to be below the discharge threshold. It is characterized by the following: [Effects of the Invention]

[0008] As described above, according to the present invention, even if toner is attached to the charged member before the image forming apparatus stops, the occurrence of image defects can be suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] This is an explanatory diagram of the image forming apparatus in Example 1. [Figure 2]This is a schematic block diagram showing the control configuration of the main parts of the image forming apparatus in Example 1. [Figure 3] This figure shows the results of measuring the fouling toner concentration of the image forming apparatus in Example 1. [Figure 4] This is an explanatory diagram of the stopping operation of an image forming apparatus in a conventional configuration. [Figure 5] This is the first explanatory diagram of the potential relationship between the charging unit and the developing unit when the image forming apparatus is stopped in a conventional configuration. [Figure 6] This is a second explanatory diagram of the potential relationship between the charging unit and the developing unit when the image forming apparatus is stopped in a conventional configuration. [Figure 7] This is an explanatory diagram of the stopping operation of the image forming apparatus in Example 1. [Figure 8] This is an explanatory diagram illustrating the potential relationship between the charging unit and the developing unit when the image forming apparatus is stopped in Example 1. [Figure 9] This is an explanatory diagram of the stopping operation of the image forming apparatus in Example 2. [Figure 10] This is an explanatory diagram of the stopping operation of the image forming apparatus in Example 3. [Figure 11] This is an explanatory diagram of the stopping operation of the image forming apparatus in Example 4. [Figure 12] This is an explanatory diagram of an image forming apparatus in another embodiment. [Modes for carrying out the invention]

[0010] 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]

[0011] 1. Image forming apparatus FIG. 1 shows a schematic configuration of an embodiment of an image forming apparatus 100 according to the present invention. The image forming apparatus 100 of this embodiment is a monochrome laser beam printer adopting a cleanerless system and a contact charging system.

[0012] In the image forming apparatus 100 of this embodiment, a cylindrical photoreceptor, that is, a photosensitive drum 1 is provided as an image carrier. Around the photosensitive drum 1, a charging roller 2 as charging means and a developing device 3 as developing means are provided. Further, an exposure device 4 as exposure means is provided between the charging roller 2 and the developing device 3 in the rotational direction of the photosensitive drum 1 in FIG. 1. Further, a transfer roller 5 as transfer means is pressed against the photosensitive drum 1.

[0013] The photosensitive drum 1 in this embodiment is a negatively charged organic photoreceptor. This photosensitive drum 1 has a photosensitive layer on an aluminum drum-shaped substrate and is rotationally driven at a predetermined process speed in the direction of the arrow in the figure (clockwise direction) by a drive motor (drive unit) 110 (FIG. 2) as drive means. In this embodiment, the process speed corresponds to the peripheral 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.

[0014] The charging roller 2, which is a charged member, contacts the photosensitive drum 1 with a predetermined pressure contact force to form a charging portion. Also, a desired charging voltage is applied by a charging voltage power supply 120 (Fig. 2) as a charging voltage applying means to uniformly charge the surface of the photosensitive drum 1 to a predetermined potential. In this embodiment, the surface of the photosensitive drum 1 is charged negatively by the charging roller 2. During the charging process, a predetermined charging voltage is applied to the charging roller 2 by the charging voltage power supply 120. In this embodiment, during the charging process, a negative DC voltage 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. The charging voltage during the image forming operation is -1400V and the dark portion potential Vd is -800V. Note that the charging roller 2 more specifically charges the surface of the photosensitive drum 1 by discharge occurring in at least one of the 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, for the sake of explanation, it is assumed that 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 the charging portion.

[0015] The exposure device 4, which is an exposure unit, is a laser scanner device in this 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 this embodiment, the absolute value of the dark portion potential Vd on the surface of the photosensitive drum 1 formed by being uniformly charged decreases by being exposed by the exposure device 4 and becomes the bright portion potential Vl. The exposure intensity of the exposure device 4 is set so that the bright portion potential Vl becomes -150V. Here, it is assumed that 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 the 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 employed.

[0016] 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 always in contact and do not have a mechanism for separating them. 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 drives the developing roller 31, may be the same main motor 110 as the drive 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 serves as a developing voltage application means. The control unit 200 controls the developing roller 31 to apply a DC voltage of -400V 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 = -400V and the image formation potential Vl = -150V 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.

[0017] In the following explanation, with respect to potential and applied voltage, a large absolute value on the negative side (for example, -1400V compared to -800V) will be referred to as a high potential, and a small absolute value on the negative side (for example, -400V compared to -800V) will be referred to as a low potential. This is because we are considering the negatively charged toner in this embodiment as the reference.

[0018] Furthermore, the voltage in this embodiment is expressed as a potential difference from the ground potential (0V). Therefore, the developing voltage Vdc = -400V is interpreted as having a potential difference of -400V with respect to the ground potential due to the developing voltage applied to the core metal of the developing roller 31. The same applies to the charging voltage, transfer voltage, etc.

[0019] In this embodiment, a negative polarity DC voltage is applied as the development voltage, and the drum is uniformly charged before exposure. 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 area), which is the image forming area on the photosensitive drum 1, where the absolute value of the surface potential of the photosensitive drum 1 has decreased. This development method is called the inverse development method. In this embodiment, the normal polarity, which is the charging polarity of the toner during development, is set to negative polarity. During the image forming operation, a development voltage of -400V is applied, and the toner is developed from the developing roller 31 onto the photosensitive drum 1 by electrostatic force due to the potential difference between the development voltage of -400V and the bright area potential Vl = -150V of the photosensitive drum 1. In this embodiment, a one-component non-magnetic contact development method is employed, but the present invention is not limited to this embodiment, and a two-component non-magnetic contact development method, a non-contact development method, a magnetic development method, etc., may also be employed. The two-component non-magnetic contact development method uses a two-component developer comprising a non-magnetic toner and a magnetic carrier as the developer, and develops by bringing the developer (magnetic brush) supported on the developer carrier into contact with the photosensitive drum 1. The non-contact development method develops by flying toner from a developer carrier positioned opposite the photosensitive surface in a non-contact manner onto the photosensitive surface. The magnetic development method develops by supporting magnetic toner on a developer carrier containing a magnet as a means of generating a magnetic field, which is positioned opposite the photosensitive surface in contact or non-contact manner, and developing by using magnetic force. In this embodiment, a toner with a central average particle size of 6 μm and a normal charge polarity of negative polarity is used.

[0020] 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 (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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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 in the direction of rotation of the photosensitive drum 1, downstream of the brush 10 and upstream of the charging roller 2. 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 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.

[0025] 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.

[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 a memory 154, which is a memory unit such as a ROM and RAM. The memory 154 stores information regarding the number of times the image forming operation has been performed, which is a feature of this embodiment. Specifically, this includes information on the number of prints, the rotation speed of the photosensitive drum 1, and the rotation speed of the developing roller 31. The number of prints is the number of prints since the image forming apparatus 100 was new. 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. The control unit 200 is connected to various control targets, sensors, counters, etc., in the image forming apparatus 100. The control unit 200 controls the transmission and reception of various electrical information signals and the timing of the drive of each part, thereby controlling a predetermined image forming sequence. For example, the control unit 200 controls the voltage and exposure amount 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 from the host device to the controller 202. Examples of host devices include image readers, personal computers, facsimile machines, and smartphones.

[0027] 3. Image output operation The image forming apparatus 100 executes a series of operations to form an image on one or more recording materials S in response to a start instruction for one image output operation (job) from an external device (not shown), such as a personal computer. A job generally includes a pre-rotation process, an image forming process (printing process), a paper-intermediate process when forming an image on multiple recording materials S, and a post-rotation process. The image forming process is a process that performs the formation of an electrostatic image on the photosensitive drum 1, development of the electrostatic image (formation of a toner image), transfer of the toner image, fixing of the toner image, etc., and the image forming time refers to the period during which this image forming process is performed. During the image forming time, that is, the period during which the image forming process is performed, the timing of each operation such as the formation of the electrostatic image, the formation of the toner image, the transfer of the toner image, and the fixing of the toner image is different. The pre-rotation process is a process that performs preparatory operations before the image forming process. The inter-paper process is a process performed between the image forming process for the first recording material S and the image forming process for the second recording material S that follows the first recording material S when the image forming process is performed consecutively on multiple recording materials S (continuous image forming). The post-rotation process is a process that performs the sorting operation (preparation operation) after the image forming process. Non-image forming time refers to the period other than the image forming time, and includes the pre-rotation process, the inter-paper process, and the post-rotation process. The pre-multi-rotation process, which is a preparation operation when the image forming apparatus 100 is powered on or when it returns from sleep mode, is also included in non-image forming time.

[0028] 4. 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.

[0029] 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.

[0030] 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.

[0031] In this embodiment, Vback, which is the potential difference (back contrast) in the developing section calculated from "developing voltage - dark area potential Vd of the photosensitive drum 1", is set to 400V in order to sufficiently transfer the negatively charged toner from the photosensitive drum 1 to the developing roller 31. The larger Vback, the easier it is for the negatively charged toner to transfer from the photosensitive drum 1 to the developing roller 31, improving the development and recovery efficiency.

[0032] The image forming apparatus 100 in this embodiment does not have a toner cleaning means on the photosensitive drum 1. Therefore, compared to a configuration in which a toner cleaning means is provided on the photosensitive drum 1, image defects are more likely to occur due to residual toner that was not transferred from the photosensitive drum 1 to the recording material S in the transfer section, or toner fouling onto the photosensitive drum 1 from the developing section.

[0033] Figure 3 shows the results of measuring the toner fouling density (%) on the photosensitive drum 1 generated in the developing section of the image forming apparatus 100 in this embodiment. The measurement was performed using the following method.

[0034] First, the image forming apparatus 100 of this embodiment is started in the same way as during printing, and the latent image setting is brought to the desired state by setting the charging voltage, developing voltage, etc., to the above conditions. After that, the rotation drive of the photosensitive drum 1 is stopped, and after the rotation drive of the photosensitive drum 1 is stopped, polyester tape (manufactured by Nichiban, No. 5511) is attached to the surface of the photosensitive drum 1 that is located between the developing unit and the transfer unit in the rotation direction of the photosensitive drum 1. The toner overlay on the surface of the photosensitive drum 1 is collected by peeling off the attached tape.

[0035] Toner fouling on the surface of the photosensitive drum 1 was collected multiple times with varying latent image settings, and the Vback (back contrast), which is the difference between the surface potential and development voltage of the photosensitive drum 1 in the development unit, was set appropriately in 50V increments from 50V to 500V.

[0036] Tapes containing toner fouling from the surface of photosensitive drum 1 were attached to Xerox Vitality Multipurpose Paper (Letter size, 20 lb). Then, the whiteness D1 (%) of the area where the tape was attached and the whiteness D2 (%) of the area where the tape was not attached were measured using a fouling meter (product name: REFLECTMETER MODEL TC-6DS, manufactured by Tokyo Denshoku Co., Ltd.). From these results, the toner fouling density (%) was calculated as "D2 (%) - D1 (%)".

[0037] The toner density (%) on the photosensitive drum 1 was measured in the image forming apparatus 100 of this embodiment when it was new, i.e., when the toner was new, after a cumulative total of 100 prints, and after a cumulative total of 1000 prints.

[0038] As shown in Figure 3, in the new state of the image forming apparatus 100 of this embodiment, as the Vback increases, the amount of toner fouling on the photosensitive drum 1 tends to increase, and it can be confirmed that fouling due to inverted toner (hereinafter referred to as inverted fouling) is likely to occur on the photosensitive drum 1. Since the Vback of the image forming apparatus 100 of this embodiment during image forming operation is 400V, it can be seen that in the initial state of the image forming apparatus 100 of this embodiment, a large amount of inverted toner is likely to adhere to the charging roller 2 after image forming operation. Furthermore, as shown in Figure 3, even when the Vback is small in the new state of the image forming apparatus 100, fouling due to development of toner charged to the normal polarity on the developing roller 31 onto the photosensitive drum 1 (hereinafter referred to as normal fouling) tends to be less likely to occur. This is because the closer the image forming apparatus 100, i.e., the toner, is to a new state, the higher the proportion of toner that is not sufficiently charged to the normal polarity, and these toners are more likely to become inverted toner due to the potential difference in the developing section.

[0039] As shown in Figure 3, when the image forming apparatus 100 has produced 100 cumulative prints, inversion toner is less likely to occur, and it can be seen that even after the image forming operation, inversion toner is less likely to adhere to the charging roller 2. Also, as shown in Figure 3, when the image forming apparatus 100 has produced 100 cumulative prints, it can be seen that when the Vback is small, inversion toner is more likely to occur on the photosensitive drum 1. This is because, as the image forming apparatus 100, i.e., as toner is used, the toner is sufficiently charged to the normal polarity, and inversion toner is less likely to occur due to the potential difference in the developing unit.

[0040] Furthermore, as shown in Figure 3, the tendency of toner fouling on the photosensitive drum 1 is almost the same when the image forming apparatus 100 has accumulated 1000 prints as when it has accumulated 100 prints. This is because, as the image forming apparatus 100 is used, once the toner in the developing unit becomes sufficiently charged with the correct polarity, that state is maintained for a long period of time.

[0041] Figure 4 shows an example of the stopping operation of a conventional image forming apparatus 100. The timing at which the motor 110 that drives the photosensitive drum 1 shown in Figure 4 is turned OFF (step 5) is defined as the stopping of the image forming apparatus 100. The surface potential (before charging) of the photosensitive drum 1 shown in Figure 4 is the potential of the surface of the photosensitive drum 1 just before it enters the charged area, and the drum potential (before development) is the potential of the surface of the photosensitive drum 1 just before it enters the developing area.

[0042] As shown in Figure 4, in step 1, the photosensitive drum 1 is exposed using the exposure device 4, and the surface potential of the photosensitive drum 1 is set to V1, which is the set potential when the image forming apparatus 100 is stopped. By performing the exposure in the exposure device 4 with the same exposure intensity as during the image forming operation, V1 becomes -150V, which is the same as the bright area potential Vl.

[0043] Next, in step 2, the development voltage is changed to V2, which is the set voltage when the image forming apparatus 100 is stopped. The change to the development voltage of V2 is performed 80 msec after exposure of the exposure apparatus 4 has started in step 1. This ensures that the development voltage is set to V2 at the exact moment when the surface of the photosensitive drum 1, which was at V1 in step 1, reaches the development section. In this embodiment, since the development voltage is turned OFF in step 2, V2 is 0V. Here, the development voltage is turned OFF, but it does not have to be OFF as long as Vback is properly formed. It is sufficient if it has the same polarity as the normal polarity and its absolute value is smaller than that of the image forming operation. In the subsequent step 5, the development voltage can be turned OFF.

[0044] Next, in step 3, 500 msec after exposure by exposure means 4 is started in step 1, the charging voltage is changed to V3, which is the set voltage when the image forming apparatus 100 is stopped. By changing the charging voltage to V3 500 msec after exposure by exposure means 4 is started in step 1, the charging voltage is changed at the timing when the surface of the photosensitive drum 1, whose surface potential became V1 in step 1, reaches the charged area. In this embodiment, V3 is 0V because the charging voltage is turned OFF in step 3. Here, the charging voltage is turned OFF, but it does not have to be OFF as long as Vback is properly formed. It is sufficient if it is the same polarity as the normal polarity and has an absolute value smaller than the image forming operation voltage. Furthermore, it is preferable that the voltage is smaller than the discharge start voltage. In the subsequent step 5, the charging voltage can be turned OFF.

[0045] Next, in step 4, the exposure of the exposure device 4 is turned OFF 600 msec after exposure was started in step 1. Here, the exposure of the exposure device 4 is turned OFF, but it does not have to be turned OFF if V1 is properly formed. It is sufficient that the exposure amount is less than that of the image forming operation. In the subsequent step 5, the exposure can be turned OFF. By turning OFF the exposure of the exposure device 4 600 msec after exposure was started in step 1, the surface potential formed around the entire circumference of the photosensitive drum 1 is set to V1, which is the set potential at the time of stopping the image forming apparatus 100. By stopping the image forming apparatus 100 with the same surface potential around the entire circumference of the photosensitive drum 1, it is possible to suppress the occurrence of image defects caused by uneven surface potential of the photosensitive drum 1 during the next image forming operation. For this reason, it is preferable to stop the image forming apparatus 100 with the same surface potential around the entire circumference of the photosensitive drum 1.

[0046] Finally, as step 5, 100 msec after turning off the exposure of the exposure apparatus 4, the motor 100 that drives the photosensitive drum 1 is turned off, ending the shutdown operation of the image forming apparatus 100. In order to suppress the occurrence of potential memory and leakage on the surface of the photosensitive drum 1, it is common practice to turn off the voltage applied to the components in contact with the photosensitive drum 1 before stopping the drive motor of the photosensitive drum 1 when the image forming apparatus 100 is stopped.

[0047] Figures 5 and 6 are schematic diagrams showing the potential relationship between the charging section and the developing section during the stopping operation of the conventional image forming apparatus shown in Figure 4, as well as the amount and polarity of toner adhering to the charging roller 2 and developing roller 31, respectively, when the image forming apparatus is stopped.

[0048] First, Figure 5 shows the case when Vback is fixed at 400V and the stopping operation is performed. As shown in Figure 5, in the initial state of the image forming apparatus 100, which is close to new, there is a lot of inverted toner on the photosensitive drum 1, so a large amount of positively charged inverted toner adheres to the charging roller 2. Since the surface of the photosensitive drum 1 is negatively charged, V1 is located on the negative side than V3, and if "V3-V1" is large, the inverted toner on the charging roller 2 is easily transferred from the charging roller 2 to the photosensitive drum 1 due to electrostatic force.

[0049] Furthermore, in the initial state of the image forming apparatus 100, the toner in the developing section is not sufficiently charged to the normal negative polarity. As a result, some reversed toner adheres to the developing roller 31. As explained in Figure 3, if the Vback "V2-V1" is large, reversed fogging from the developing roller 31 to the photosensitive drum 1 is likely to occur, but even if "V2-V1" is small, normal fogging from the developing roller 31 to the photosensitive drum 1 is unlikely to occur.

[0050] Conversely, as shown in Figure 5, when the image forming apparatus 100 prints 100 times, there is little inversion overlay on the photosensitive drum 1. Therefore, the amount of inversion toner adhering to the charging roller 2 is small, and regardless of the size of "V3-V1", the amount of inversion toner on the charging roller 2 that is transferred from the charging roller 2 to the photosensitive drum 1 due to electrostatic force is small.

[0051] Furthermore, when the image forming apparatus 100 produces 100 cumulative prints, the toner is sufficiently charged to the normal negative polarity in the developing section. Therefore, the developing roller 31 is almost entirely composed of toner charged to the normal polarity. Thus, as explained in Figure 3, even if the Vback "V2-V1" is large, inverted fouling from the developing roller 31 to the photosensitive drum 1 is unlikely to occur, but if "V2-V1" is small, normal fouling from the developing roller 31 to the photosensitive drum 1 is likely to occur.

[0052] Next, Figure 6 shows the case when the Vback is fixed at 150V and the stopping operation is performed. As shown in Figure 6, in the stopping operation of a conventional image forming apparatus, "V3-V1" and "V2-V1" are both small at 150V. Therefore, in the initial state of the image forming apparatus 100, the transfer of inverted toner from the charging roller 2 to the photosensitive drum 1 during stopping, and both inverted fogging and normal fogging from the developing roller 31 to the photosensitive drum 1 are unlikely to occur.

[0053] However, when the image forming apparatus 100 is producing 100 cumulative prints, the "V2-V1" value is small at 150V, which, as shown in Figure 3, results in a large amount of normal fogging from the developing roller 31 to the photosensitive drum 1 when the image forming apparatus 100 is stopped.

[0054] 5. Features of this embodiment Therefore, in this embodiment, taking into consideration the changes in the tendency of toner fouling on the photosensitive drum 1 in accordance with the usage state of the image forming apparatus 100 described above, and the problems that arise when the image forming apparatus 100 is stopped as a result, the stopping operation of the image forming apparatus shown in Figure 7 is performed.

[0055] The stopping operation of the image forming apparatus 100 in this embodiment, as shown in Figure 7, involves changing "V2-V1" and "V3-V1" respectively from the initial operation of the image forming apparatus 100 up to the 99th cumulative print, and from the 100th cumulative print onwards. This is characterized by simultaneously suppressing the transfer of inverted toner from the charging roller 2 to the photosensitive drum 1 when the image forming apparatus 100 is stopped, and the occurrence of fogging on the photosensitive drum 1 in the developing section.

[0056] Specifically, the exposure intensity of the exposure device 4 in step 1 is changed from the initial stage of the image forming apparatus 100 to the 99th cumulative print and from the 100th cumulative print onwards. As a result, V1 is set to -150V from the initial stage to the 99th cumulative print, and to -400V from the 100th cumulative print onwards.

[0057] Other operations are the same as the stopping operation of the image forming apparatus 100 in Figure 4, so their explanation will be omitted.

[0058] The effect of control during the stopping operation of the image forming apparatus 100 in this embodiment will be explained. Figure 8 shows the potential relationship between the charging section and the developing section when the image forming apparatus 100 is stopped due to the stopping operation of the image forming apparatus 100 in this embodiment. As shown in Figure 8, for the period from the initial number of accumulated prints until 99 prints, V1 was set to -150V and V3 to 0V. As a result, "V3-V1" = 150V, and from the 100th accumulated print onwards, V1 was set to -400V and V3 to 0V, so "V3-V1" = 400V.

[0059] As explained in Figure 3, in this embodiment, in the initial stages of the image forming apparatus 100, there is a large amount of inversion toner from the developing unit. Therefore, a large amount of inversion toner adheres to the charging roller 2. After the 100th cumulative print of the image forming apparatus 100, the amount of inversion toner from the developing unit decreases, and the amount of inversion toner adhering to the charging roller decreases. Therefore, in the initial stages of the image forming apparatus 100, when the transfer of inversion toner from the charging roller 2 to the photosensitive drum 1 is likely to occur, the "V3-V1" value is controlled to be small. By implementing such control, the transfer of inversion toner from the charging roller 2 to the photosensitive drum 1 can be suppressed. In addition, after the 100th cumulative print of the image forming apparatus 100, when the "V3-V1" value is controlled to be larger than in the initial stages, the amount of inversion toner adhering to the charging roller 2 is small to begin with, making the transfer of inversion toner from the charging roller 2 to the photosensitive drum 1 less likely to occur.

[0060] In summary, in this embodiment, "V3-V1" is changed according to the amount of inverted toner adhering to the charging roller 2 from the initial stage of the image forming apparatus 100 up to the 99th cumulative print and from the 100th cumulative print onwards. This makes it possible to suppress the transfer of inverted toner from the charging roller 2 to the photosensitive drum 1 regardless of the usage conditions of the image forming apparatus 100.

[0061] Furthermore, as explained in Figure 3, in this embodiment, even if the Vback is small in the initial stages of the image forming apparatus 100, normal flicker from the developing unit is less likely to occur. However, after the 100th cumulative print, if the Vback is small, normal flicker from the developing unit is more likely to occur. The Vback when the image forming apparatus 100 is stopped can be calculated as "V2-V1". In this embodiment, from the initial stages of the image forming apparatus 100 until the 99th cumulative print, V1 is set to -150V and V2 to 0V, resulting in a Vback of 150V. Then, after the 100th cumulative print, V1 is set to -400V and V3 to 0V, resulting in a Vback of 400V. Therefore, in the initial stages of the image forming apparatus 100, the Vback is small when the image forming apparatus 100 is stopped. However, even if the Vback is small in the initial stages of the image forming apparatus 100, normal flicker from the developing unit is less likely to occur. Therefore, even when the image forming apparatus 100 is stopped, no normal fogging occurs in the developing section, and from the 100th cumulative print onwards, increasing the Vback when the image forming apparatus 100 is stopped further suppresses the occurrence of normal fogging in the developing section.

[0062] Based on the above, by changing "V3-V1" in accordance with the tendency of normal flicker to occur from the developing unit at the beginning and from the 100th image onwards, the occurrence of normal flicker from the developing unit when the image forming apparatus 100 is stopped can be suppressed regardless of the usage status of the image forming apparatus 100.

[0063] The configuration of Example 1 has the following characteristics.

[0064] An image forming apparatus 100 capable of performing an image forming operation to form an image on a recording material S, comprising a rotatable photosensitive drum 1 and a charging roller 2 that contacts 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 comprises a developing roller 31 in a developing section facing the photosensitive drum 1 that supplies toner to the photosensitive drum 1, a drive unit 110 that rotates the photosensitive drum 1, and a storage unit 154 that stores information regarding the number of times the image forming operation has been performed.

[0065] The system includes a charging voltage application unit 120 that applies a charging voltage to the charging roller 2, a developing voltage application unit 140 that applies a developing voltage to the developing roller 31, and a control unit 200 that controls the drive unit 110, the charging voltage application unit 120, and the developing voltage application unit 140. When transitioning from a first state in which the photosensitive drum 1 is rotating to a second state in which the photosensitive drum 1 is stopped, the surface potential formed on the surface of the photosensitive drum 1, the developing voltage, and the charging voltage are defined as follows: V1 is the surface potential of the photosensitive drum 1 formed in the developing unit, V2 is the developing voltage applied to the developing roller 31, V3 is the charging voltage applied to the charging roller 2, and V4 is the surface potential of the photosensitive drum 1 formed in the charging unit. The control unit 200 controls a first potential difference, which is the potential difference between V2 and V1, and a second potential difference, which is the potential difference between V3 and V4, based on information regarding the number of times the image forming operation has been performed.

[0066] In this embodiment, it is explained that the surface potential V1 formed in the developing section and the surface potential V4 formed in the charging section of the photosensitive drum 1 are the same. The surface potentials formed on the surface of one circumference of the photosensitive drum 1 can be considered to be almost the same unless there is an influence from the material. Therefore, since V4 = V1, the controlled values ​​are "V2 - V1" and "V3 - V1". Thus, the second difference value is "V3 - V4", but it can also be considered as "V3 - V1".

[0067] Furthermore, the control unit 200 controls the first potential difference when the number of prints is less than the first number, such as when the number of prints is a second number. And it controls the second potential difference when the number of prints is less than the third number, such as when the number of prints is a fourth number. In other words, the control unit 200 controls the first potential difference when the number of prints is a second number, such as when the number of prints is a third number, such as when the number of prints is a fourth number. Furthermore, the control unit 200 controls the first potential difference to be below the discharge threshold when forming the first potential difference, and the second potential difference to be below the discharge threshold when forming the second potential difference. It controls V2 to be the opposite polarity to the normal polarity which is the charging polarity of the toner, and V3 to be the normal polarity which is the charging polarity of the toner. In addition, when the rotation drive of the photosensitive drum 1 is stopped, the charging roller 2 and the developing roller 3 are in contact with the photosensitive drum 1. This significantly reduces the adverse effects that occur in the charging and developing sections when the photosensitive drum 1 is stopped.

[0068] As explained above, the "V2-V1" and "V3-V1" settings are changed in accordance with the tendency for inverted toner and normal toner to occur in the developing unit from the initial stage of the image forming apparatus 100 up to the 99th cumulative print and from the 100th cumulative print onwards. This makes it possible to simultaneously suppress the transfer of inverted toner attached to the charging roller 1 to the photosensitive drum 1 when the image forming apparatus 100 stops, and the occurrence of normal toner to behaved in the developing unit.

[0069] In this embodiment, the values ​​of "V2-V1" and "V3-V1" were changed according to the cumulative number of prints made by the image forming apparatus 100. However, the degree of toner charge in the developing unit and the resulting tendency of toner fouling on the photosensitive drum 1 can also be determined by the cumulative rotation speed of the developing roller 31. Therefore, the values ​​of "V2-V1" and "V3-V1" may be changed according to the cumulative rotation speed of the developing roller 31 or similar factors. Examples include the rotation speed of the photosensitive drum 1, the remaining amount of toner in the developing container 33, and the toner consumption calculated from the print density.

[0070] In this embodiment, the values ​​of "V2-V1" and "V3-V1" were changed when the cumulative number of prints in the image forming apparatus 100 reached 100. However, the amount of printing required from the start for the toner used in the image forming apparatus 100 and the developing roller 31 to sufficiently charge the toner in the developing section and change the tendency of the toner fouling on the photosensitive drum 1 varies. Therefore, the threshold for the cumulative number of prints at which the values ​​of "V2-V1" and "V3-V1" are changed should be set according to the configuration of the image forming apparatus 100. For example, it may be changed according to differences in print density as described above, or according to environmental factors such as temperature and humidity. 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 density of 5% (print area ratio when a completely black image is 100% and a completely white image is 0%), it has been found that the proportion of small particle size is suppressed after approximately 100 sheets have been fed through. Therefore, the control is switched at 100 sheets. In this way, the control can be switched based on factors such as the amount of toner replenished, the print density, and the amount of toner consumed.

[0071] Furthermore, in this embodiment, the values ​​of "V2-V1" and "V3-V1" were changed only when the cumulative number of prints of the image forming apparatus 100 reached 100. However, the threshold for the cumulative number of prints at which the values ​​of "V2-V1" and "V3-V1" are changed may be increased. Such control can more accurately suppress both the transfer of inverted toner attached to the charging roller 1 to the photosensitive drum 1 that occurs when the image forming apparatus 100 stops, and the occurrence of normal fogging in the developing section.

[0072] Furthermore, in this embodiment, as the cumulative number of prints of the image forming apparatus 100 increased, "V3-V1" and "V2-V1" were changed to be larger in accordance with the fact that the toner in the developing unit was sufficiently charged to the correct polarity. However, as the cumulative number of prints of the image forming apparatus 100 increases further, the deterioration of the toner in the developing unit may become significant. In such cases, when the chargeability of the toner in the developing unit decreases, the image forming apparatus 100 may return to a state similar to its initial state, where a large amount of inversion fogging occurs when Vback is large. In such cases, it is sufficient to control "V3-V1" and "V2-V1" to be smaller again. As explained above, "V3-V1" and "V2-V1" should be changed according to the tendency of fogging to occur on the photosensitive drum 1 in the developing unit as the cumulative number of prints of the image forming apparatus 100 increases. [Examples]

[0073] Next, Embodiment 2 of the present invention will be described. The basic configuration and operation of the image forming apparatus in Embodiment 2 are the same as those of the image forming apparatus in Embodiment 1. Therefore, in the image forming apparatus in Embodiment 2, elements having the same or corresponding functions or configurations as those of the image forming apparatus in Embodiment 1 are denoted by the same reference numerals as those in the image forming apparatus in Embodiment 1, and detailed descriptions are omitted.

[0074] In this embodiment, the stopping operation of the image forming apparatus 100 shown in Figure 9 is performed. Other aspects are the same as in Embodiment 1, so their explanation is omitted.

[0075] First, as shown in Figure 9, step 1 involves removing static electricity from the photosensitive drum 1 by exposure using the pre-exposure device 13.

[0076] Next, in step 2, the charging voltage is changed to charge the surface of the photosensitive drum 1, which has been de-charged by the pre-exposure device 13, to V1, which is the set potential when the image forming apparatus 100 is stopped. By changing the charging voltage 80 msec after the pre-exposure device 13 starts de-charged the photosensitive drum 1, the charging voltage is changed to coincide with the timing when the surface of the photosensitive drum 1, which has been de-charged by the pre-exposure device 13, reaches the charged area. Initially, in step 2, the charging voltage of the image forming apparatus 100 is changed to -750V. The surface potential V1 of the photosensitive drum 1 to which a charging voltage of -750V is applied is -150V, and from the 100th sheet onward, the charging voltage is changed to -1000V in step 2, so that V1 is -400V.

[0077] Next, in step 3, 160 msec after changing the charging voltage in step 2, the development voltage is changed to V2, which is the set voltage for the stopping operation of the image forming apparatus 100. By changing the development voltage to V2 160 msec after changing the charging voltage in step 2, the development voltage changes at the exact moment when the surface of the photosensitive drum 1, whose surface potential became V1 in step 2, reaches the development section. In this embodiment, V2 is set to 0V by turning off the development voltage in step 2. Here, the development voltage is turned off, but it does not have to be turned off if Vback is properly formed. It is sufficient if it is the same polarity as the normal polarity and has an absolute value smaller than that of the image forming operation. In the subsequent step 6, the development voltage can be turned off. Alternatively, a control such as that in Embodiment 3 described later may be adopted.

[0078] Next, in step 4, the exposure of the pre-exposure device 13 is turned OFF 600 msec after the exposure of the pre-exposure device 13 was started in step 1. Here, the exposure of the pre-exposure device 13 is turned OFF, but it may be ON instead of OFF if V1 is formed properly. For example, if exposure is performed by the pre-exposure device 13 during the image formation operation, the exposure amount should be less than the exposure amount during the image formation operation. By turning OFF the exposure of the pre-exposure device 13 600 msec after the exposure of the pre-exposure device 13 was started in step 1, the photosensitive drum 1 is discharged for exactly one rotation, and the discharge of the photosensitive drum 1 by the pre-exposure device 13 is completed.

[0079] Next, in step 5, 600 msec after changing the charging voltage in step 2, the charging voltage is changed to V3, which is the charging voltage at the time of stopping the image forming apparatus 100. This makes it possible to set the surface potential of the entire circumference of the photosensitive drum 1 to V1. In this embodiment, V3 is set to 0V by turning off the charging voltage in step 5. Here, the charging voltage is turned off, but it does not have to be turned off if Vback is properly formed. It is sufficient if it is the same polarity as the normal polarity and has an absolute value smaller than that of the image forming operation. Furthermore, it is preferable that the voltage is smaller than the discharge start voltage. In the subsequent step 6, the charging voltage can be turned off. Alternatively, a control such as that in Embodiment 4 described later may be adopted.

[0080] Finally, as step 6, 100 msec after the charging voltage change in step 5, the motor 110 that drives the photosensitive drum 1 is turned OFF, ending the shutdown operation of the image forming apparatus 100.

[0081] In this embodiment, similar to Embodiment 1, "V2-V1" is set to -150V from the start of the image forming apparatus 100 until the 99th cumulative print, and to -400V from the 100th cumulative print onwards. Furthermore, "V3-V1" is set to 150V from the start of the image forming apparatus 100 until the 99th cumulative print, and to 400V from the 100th cumulative print onwards. This allows for the same effect as in Embodiment 1 to be obtained. [Examples]

[0082] In this embodiment, a voltage power supply capable of applying a positive polarity DC voltage to the developing power supply was added to the image forming apparatus 100 of Example 2. Furthermore, the following modifications were made to the stopping operation of the image forming apparatus 100 of Example 2.

[0083] Figure 10 shows the stopping operation of the image forming apparatus 100 in this embodiment. As shown in Figure 10, in this embodiment, the setting value of the charging voltage after changing the charging voltage in step 2 was set to -500V from the start of the image forming apparatus 100 until the 99th cumulative image, and to -850V from the 100th cumulative image onwards. As a result, V1 was set to 0V initially, and to -250V from the 100th image onwards.

[0084] Furthermore, the development voltage setting after changing the development voltage in step 3 was set to 150V.

[0085] Furthermore, step 7 is added, in which, after turning off the motor that drives the photosensitive drum 1 in step 6, the developing voltage is turned off to end the stopping operation of the image forming apparatus 100.

[0086] Between step 6 and step 7, a developing voltage is applied to the stopped photosensitive drum 1. Therefore, to prevent memory or leakage of the photosensitive drum 1, it is preferable to keep the potential difference between the surface potential of the photosensitive drum 1 and the charging voltage in the charging section between step 6 and step 7 below the discharge threshold.

[0087] In this embodiment, "V3-V1" was set to 0V from the start of the image forming apparatus 100 until the 99th cumulative print, and "V3-V1" was set to -250V from the 100th cumulative print onwards. Furthermore, "V2-V1" was set to 150V from the start of the image forming apparatus 100 until the 99th cumulative print, and "V2-V1" was set to 400V from the 100th cumulative print onwards. Therefore, compared to Embodiment 2, the transfer of inverted toner from the charging roller 2 to the photosensitive drum 1 can be suppressed more effectively.

[0088] As described above, in this embodiment, when the image forming apparatus 100 stops, a voltage with the opposite polarity to the normal polarity of the toner is applied to the developing roller 31 so that the potential difference between the photosensitive drum 1 and the developing roller 31 in the developing unit is below the discharge threshold. This more effectively suppresses the transfer of reversed toner from the charging roller 2 to the photosensitive drum 1, while also suppressing normal fogging in the developing unit and the occurrence of memory and leakage on the photosensitive drum 1 in the developing unit. [Examples]

[0089] In this embodiment, the following modifications were made to the stopping operation of the image forming apparatus 100 in Example 3.

[0090] Figure 11 shows the stopping operation of the image forming apparatus 100 in this embodiment.

[0091] As shown in Figure 11, in Example 3, the charging voltage was turned OFF in step 5, whereas in this embodiment, the charging voltage is not turned OFF in step 5, and the motor 110 that drives the photosensitive drum 1 is turned OFF in step 6, and then the charging voltage is turned OFF in step 7. Between step 6 and step 7, the charging voltage is applied to the stationary photosensitive drum 1. Therefore, in order to prevent memory or leakage of the photosensitive drum 1 in the charged area, it is preferable to keep the potential difference between the surface potential of the photosensitive drum 1 and the charging voltage in the charged area between step 6 and step 7 below the discharge threshold.

[0092] In this embodiment, the "V3-V1" voltage from the initial stage of the image forming apparatus 100 up to the 99th cumulative print is 500V, and the "V3-V1" voltage from the 100th cumulative print onwards is 250V. The "V2-V1" voltage from the initial stage of the image forming apparatus 100 up to the 99th cumulative print is 150V, and the "V2-V1" voltage from the 100th cumulative print onwards is 400V. Therefore, compared to Embodiment 3, the transfer of inverted toner from the charging roller 2 to the photosensitive drum 1 can be suppressed more effectively.

[0093] As described above, in this embodiment, when the image forming apparatus 100 stops, a voltage is applied to the charging roller 2 so that the potential difference between the photosensitive drum 1 and the charging roller 2 in the charging section is below the discharge threshold. This more effectively suppresses the transfer of reversed toner from the charging roller 2 to the photosensitive drum 1, while also suppressing the occurrence of normal fogging in the developing section and memory and leakage of the photosensitive drum 1 in the charging section.

[0094] [Other examples] In addition to the configurations of Examples 1 to 4, the system may also include a developing container 33 for containing developer, and the developing container 33 may be configured to allow the developer supply container 21 to be attached to it. In such a configuration, the system may be controlled to perform non-image forming operations after the developer supply container 21 has been attached to the developing container 33 and the developer has been supplied to the developing container 33. Furthermore, the developing container 33 may be detachable from the image forming apparatus, and the system may be configured to count the number of prints after the developing container 33 has been replaced and then execute the control of this embodiment.

[0095] For example, as a variation of this embodiment, a toner supply configuration using a direct supply method will be described. As shown in Figure 12(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 12(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.

[0096] When the toner 21 sealed in the toner bottle 41 shown in Figure 12(a) is supplied to the developing container 33 shown in Figure 12(a), almost all of the toner 21 in the toner bottle 41 is stored in the developing container 33, as shown in Figure 12(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.

[0097] Furthermore, the values ​​of the charging voltage and developing voltage, the number of switching cycles, the application time, etc., may be adjusted according to the change in capacitance due to wear of the surface of the photosensitive drum 1 over time, the degree of toner degradation, and the temperature and humidity of the environment. [Explanation of Symbols]

[0098] 1 Photosensitive drum 2 Charging rollers 31 Developing roller 100 Image forming apparatus 110 Main motor 120V electrostatic voltage power supply 140 Developing voltage power supply 200 Control Unit

Claims

1. An image forming apparatus capable of performing an image forming operation to form an image on a recording material, A rotatable image carrier, A charging member that contacts the image carrier to form a charged portion and charges the surface of the image carrier with the charged portion, A developing member that supplies toner to the image carrier in a developing unit facing the image carrier, A drive unit for rotating the image carrier, A storage unit that stores information regarding the number of times the image forming operation has been performed, A charging voltage application unit that applies a charging voltage to the charging member, A developing voltage application unit that applies a developing voltage to the developing member, In an image forming apparatus having a drive unit, a charging voltage application unit, and a control unit for controlling the developing voltage application unit, When transitioning from a first state in which the image carrier is rotating to a second state in which the image carrier is stopped, If V1 is the surface potential of the image carrier formed in the developing section, V2 is the developing voltage applied to the developing member, V3 is the charging voltage applied to the charging member, and V4 is the surface potential of the image carrier formed in the charging section, then The control unit controls a first potential difference, which is the potential difference between V2 and V1, and a second potential difference, which is the potential difference between V3 and V4, based on the information, and when forming the second potential difference, controls the second potential difference so that it is below a discharge threshold.

2. The image forming apparatus according to claim 1, characterized in that V1 and V4 are substantially the same.

3. The image forming apparatus according to claim 1 or 2, characterized in that the aforementioned information is the number of prints printed since the initial installation of the image forming apparatus.

4. The image forming apparatus according to claim 1 or 2, characterized in that the information is the number of rotations of the image carrier since the initial installation of the image forming apparatus.

5. The image forming apparatus according to claim 1 or 2, characterized in that the information is the rotation speed of the developing member from the time of initial installation of the image forming apparatus.

6. The image forming apparatus according to claim 3, characterized in that the control unit controls the first potential difference formed when the number of prints is a second number less than the first number, so that the magnitude of the electrostatic force acting between the image carrier and the developing member for toner charged with normal polarity to move from the developing member to the image carrier is smaller than the first potential difference formed when the number of prints is a first number.

7. The image forming apparatus according to claim 3 or 6, characterized in that the control unit controls the second potential difference formed when the number of prints is a fourth number, which is less than the third number, to be smaller than the second potential difference formed when the number of prints is a third number, so that the magnitude of the electrostatic force acting between the image carrier and the developing member for toner charged with a polarity opposite to the normal polarity to move from the charging member to the image carrier is smaller.

8. The image forming apparatus according to any one of claims 1 to 7, characterized in that the control unit controls the first potential difference to be less than or equal to a discharge threshold when forming the first potential difference.

9. The image forming apparatus according to any one of claims 1 to 8, characterized in that the control unit controls V2 to have a polarity opposite to the normal polarity which is the charging polarity of the toner.

10. The image forming apparatus according to any one of claims 1 to 9, characterized in that the control unit controls V3 to have a normal polarity which is the charging polarity of the toner.

11. The image forming apparatus according to any one of claims 1 to 10, characterized in that, when the rotational drive of the image carrier is stopped, the charging member and the developing member are each in contact with the image carrier.

Images