JP2021196406A - Image forming apparatus, control program, and control method - Google Patents

Abstract

To supply an appropriate amount of developer to an electrostatic latent image carrier to prevent a reduction in toner concentration and overflow of developer.SOLUTION: An image forming apparatus (10) comprises: a process unit including a photoreceptor drum (36) on a surface of which an electrostatic latent image is formed, a developing roller (76) that supplies developer to the photoreceptor drum (36), and an electrification unit 40 that electrifies the surface of the photoreceptor drum (36); a developing voltage control section (88b) that applies a developing voltage to the developing roller (76); and a conveyance amount detection section (66) that acquires the amount of developer conveyed on the developing roller (76). In the image forming apparatus (10), in accordance with the distance between the photoreceptor drum (36) and the developing roller (76) and the amount of conveyed developer, an inhibition range for the potential difference between carriers is set between the developing roller (76) and a portion of the photoreceptor drum (36) where the electrostatic latent image is not formed, and the potential difference between carriers is inhibited from falling into the inhibition range.SELECTED DRAWING: Figure 6

Description

The present invention relates to an image forming apparatus, a control program and a control method, and particularly develops, for example, an electrostatic latent image carrier on which an electrostatic latent image is formed on the surface and an electrostatic latent image formed on the electrostatic latent image carrier. The present invention relates to an image forming apparatus, a control program, and a control method, which comprises a developer carrier for carrying a developer.

Patent Document 1 discloses an example of an image forming apparatus as a background technique. The image forming apparatus of the background technique includes a photoconductor as an electrostatic latent image carrier on which an electrostatic latent image is formed, and a developing roller as a developer carrier.

In recent years, there has been a tendency for the distance (DSD: Drum Sleeve Distance) between the photoconductor and the developing roller to be set small due to a demand for improved image quality. However, if the amount of the developer supplied to the developing roller or the photoconductor is too large when the DSD is set small, density unevenness may occur due to runout of the developing roller or toner may adhere to the developing roller. Problems may occur.

In order to solve such a problem, in the image forming apparatus of the background technology, the upper limit of the amount of the developer supplied between the photoconductor and the developing roller is set according to the DSD, and the photoconductor and the developing roller are used. The amount of developer supplied during this period does not exceed the upper limit.

Japanese Unexamined Patent Publication No. 2005-02476

However, since the image forming apparatus of the background technology does not set the lower limit of the amount of the developer, if the amount of the developer supplied to the developing roller or the photoconductor is too small, the density of the toner image transferred to the paper is high. There is a problem that the density is reduced and uneven density appears remarkably.

Further, in the image forming apparatus of the background technology, the upper limit of the amount of the developer supplied between the photoconductor and the developing roller is set only by the DSD, that is, only by the mechanical factor. The amount of developer that can pass between is not determined solely by mechanical factors. Therefore, if the upper limit of the amount of the developer is set only according to mechanical factors, the amount of the developer passing between the photoconductor and the developing roller may exceed the upper limit, which may lead to overflow of the developer. be.

Therefore, a main object of the present invention is to provide a novel image forming apparatus, control program and control method.

Another object of the present invention is an image forming apparatus, a control program and a control method capable of supplying an appropriate amount of a developer to an electrostatic latent image carrier and suppressing a decrease in toner concentration and an overflow of the developer. Is to provide.

According to the first invention, an electrostatic latent image carrier on which an electrostatic latent image is formed, a developing tank containing a developer, and a developing agent contained in the developing tank are carried on the electrostatic latent image carrier. The amount of the developing roller to be supplied, the charging means for charging the surface of the electrostatic latent image carrier to a predetermined potential, the developing voltage applying means for applying a predetermined developing voltage to the developing roller, and the amount of the developing agent present on the developing roller. An electrostatic latent image of the electrostatic latent image carrier is not formed depending on the acquisition means for acquiring the carrier amount, the distance between the carriers, which is the distance between the electrostatic latent image carrier and the developing roller, and the carrier amount. Image formation comprising a prohibition range setting means for setting a prohibition range of a potential difference between carriers, which is a potential difference between a portion and a developing roller, and a prohibition means for prohibiting the potential difference between carriers from being within the prohibition range. It is a device.

The second invention is dependent on the first invention, further comprising a determination means for determining whether or not the potential difference between the carriers is within the prohibited range, and the prohibited means is such that the potential difference between the carriers is determined by the determination means. It includes a correction means for controlling at least one of the charging means and the developing voltage applying means to correct the potential difference between the carriers out of the prohibited range when it is determined to be within the prohibited range.

The third invention is subordinate to the second invention, and the acquisition means includes a toner concentration sensor for detecting the toner concentration of the developer contained in the developing tank, and an estimated transfer amount according to the toner concentration is obtained. get.

In the fourth invention, an electrostatic latent image carrier on which an electrostatic latent image is formed, a developing tank containing a developing agent, and a developing agent contained in the developing tank are carried on the electrostatic latent image carrier. It is a control program of an image forming apparatus provided with a charging means for charging the surface of a developing roller and an electrostatic latent image carrier to be supplied to a predetermined potential, and a predetermined developing voltage is applied to the developing roller to the processor of the image forming apparatus. Processing, processing to acquire the transport amount, which is the amount of the developer existing on the developing roller, the distance between the electrostatic latent image carrier and the developing roller, the distance between the carriers, and the transport amount. The process of setting the prohibited range of the potential difference between the carriers, which is the potential difference between the portion of the electrostatic latent image carrier where the electrostatic latent image is not formed and the developing roller, and the potential difference between the carriers are within the prohibited range. Execute the process that prohibits this.

In the fifth invention, an electrostatic latent image carrier on which an electrostatic latent image is formed, a developing tank containing a developing agent, and a developing agent contained in the developing tank are carried on the electrostatic latent image carrier. A control method for an image forming apparatus including a charging means for charging the surface of a developing roller and an electrostatic latent image carrier to be supplied to a predetermined potential, wherein (a) a predetermined developing voltage is applied to the developing roller. b) Steps to obtain the amount of carrier, which is the amount of developer present on the developing roller, (c) Depending on the distance between the carriers and the amount of carrier, which is the distance between the electrostatic latent image carrier and the developing roller. The step of setting the prohibited range of the potential difference between the carriers, which is the potential difference between the portion of the electrostatic latent image carrier where the electrostatic latent image is not formed and the developing roller, and (d) the potential difference between the carriers Includes a step that prohibits you from being within the prohibited range.

According to the present invention, an appropriate amount of a developer can be supplied to the electrostatic latent image carrier, and a decrease in toner concentration and an overflow of the developer can be suppressed.

The above-mentioned object, other object, feature and advantage of the present invention will be further clarified from the detailed description of the following examples made with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing the internal structure of the image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing the structures of the developing unit and the photoconductor unit. FIG. 3 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. FIG. 4 is a schematic view showing the distance between the developing roller and the photoconductor drum. FIG. 5 is an illustrated diagram showing an example of the memory map of the RAM shown in FIG. FIG. 6 is a flow chart showing an example of the potential difference adjusting process of the image forming apparatus.

FIG. 1 is a schematic diagram showing an internal structure of an image forming apparatus 10 according to an embodiment of the present invention. The image forming apparatus 10 shown in FIG. 1 is a multifunction device having a copying function, a printing function (printing function), a scanner function, a facsimile function, and the like, and is a monochromatic image (monochrome image) with respect to a recording medium by an electrophotographic method. To form. However, the image forming apparatus 10 may have at least a printing function, and may be, for example, a printing apparatus (printer). As the recording medium, paper, a sheet for an overhead projector, or the like can be used, but the case where paper is used will be described below.

First, the configuration of the image forming apparatus 10 will be schematically described. As shown in FIG. 1, the image forming apparatus 10 includes an apparatus main body 12 including an image forming unit 30 and an image reading apparatus 14 arranged above the apparatus main body 12.

The image reading device 14 includes a document mounting table 16 formed of a transparent material. A document holding cover 18 can be opened and closed above the document mounting table 16 via a hinge or the like. A document supply tray 20 is provided on the upper surface of the document holding cover 18, and an automatic document feeder (ADF: Auto Document Feeder) is provided inside the document supply tray 20. The ADF automatically supplies the documents placed on the document supply tray 20 one by one to the image reading position 22, and ejects the documents to the document ejection tray 24.

Further, the image reading unit 26 built in the image reading device 14 includes a light source, a plurality of mirrors, an imaging lens, a line sensor, and the like. The image reading unit 26 exposes the surface of the document with a light source, and guides the reflected light reflected from the surface of the document to the imaging lens by a plurality of mirrors. Then, the reflected light is imaged on the light receiving element of the line sensor by the imaging lens. The line sensor detects the luminance and chromaticity of the reflected light imaged on the light receiving element, and generates image data based on the image on the surface of the document. As the line sensor, a CCD (Charge Coupled Device), a CIS (Contact Image Sensor) or the like is used.

An operation panel (not shown) that accepts input operations such as printing instructions by the user is provided on the front side of the image reading device 14. The operation panel has a display with a touch panel, a plurality of operation buttons, and the like.

As shown in FIGS. 1 and 2, the image forming unit 30 includes an exposure unit (optical scanning unit) 32, a developing unit 34, a photoconductor drum 36, a cleaner unit (cleaning unit) 38, a charging unit 40, and a transfer unit 42. A fixing unit 44, a toner replenishing device 46, and the like are provided, an image is formed on the paper conveyed from the paper feed tray 48 and the like, and the image-formed paper is discharged to the paper ejection tray 50. As the image data for forming an image on the paper, the image data read by the image reading unit 26, the image data transmitted from an external computer, or the like is used.

The photoconductor drum 36 is an electrostatic latent image carrier in which a photosensitive layer is formed on the surface of a conductive cylindrical substrate, and is around its axis (not shown in FIG. 1) by a rotational drive source (not shown) such as a motor. It is rotated counterclockwise). The photosensitive layer is formed of a material that exhibits conductivity when irradiated with light (for example, amorphous silicon (a-Si), selenium (Se), organic optical semiconductor (OPC), or the like). However, as the electrostatic latent image carrier, a photoconductor belt may be used instead of the photoconductor drum 36.

The charging unit 40 charges the surface of the photoconductor drum 36 to a predetermined potential. As the charging unit 40, a corona discharge device, a brush type charging device, a roller type charging device, an ion generator, or the like can be used.

The exposure unit 32 is configured as a laser scanning unit (LSU) provided with a laser emitting unit, a reflection mirror, and the like, and by exposing the surface of the charged photoconductor drum 36, an electrostatic latent image corresponding to image data can be obtained. It is formed on the surface of the photoconductor drum 36.

However, in the region where the electrostatic latent image is formed on the outer peripheral surface of the photoconductor drum 36, there is an image region to which the laser beam is irradiated by the exposure unit 32 and a non-image region to which the laser beam is not irradiated. The electrostatic latent image formed in the image region irradiated with the laser beam is called a "bright latent image", and the surface potential thereof is called a "bright potential". On the other hand, a latent image formed in a non-image region by not irradiating a laser beam is called a "dark latent image". The surface potential of the dark latent image, that is, the surface potential of the non-image region is called "dark potential".

The developing unit 34 supplies a developer containing toner to the surface of the photoconductor drum 36, and the electrostatic latent image formed on the surface of the photoconductor drum 36 is visualized by the toner. That is, the developing unit 34 forms a toner image on the surface of the photoconductor drum 36. As shown in FIG. 2, the developing unit 34 includes a first transport member 72, a second transport member 74, a developing roller 76, a doctor blade 78, and the like, which are integrally held by the developing housing 62 in a predetermined arrangement mode. Will be done.

Inside the developing housing 62, a developing tank 64 in which the developing agent is stored (accommodated) is formed. Each of the first transport member 72 and the second transport member 74 is arranged inside the developing tank 64 so that the respective rotation axes are parallel to each other. The first transport member 72 and the second transport member 74 are auger screws having spiral blades formed on the outer peripheral surface of a columnar rotating shaft (screw shaft). The first transport member 72 and the second transport member 74 transport the developer while stirring to circulate the developer in a predetermined direction inside the developing tank 64.

Further, the developing roller 76 is a magnet roller that functions as a developing agent carrier, and is arranged above the second conveying member 74. The developing rollers 76 are arranged so that their rotation axes are parallel to each other with respect to the photoconductor drum 36, and are rotated around the axis (counterclockwise in FIGS. 1 and 2) by a rotation drive source (not shown) such as a motor. ) Is rotated. That is, the rotation direction of the photoconductor drum 36 and the rotation direction of the developing roller 76 are opposite to each other, and the development method of the process unit of this embodiment is so-called reverse development (counter development). Further, the developing roller 76 and the photoconductor drum 36 are arranged so that the distance between the outer peripheral surfaces of each other (distance between carriers: DSD) is a predetermined distance. The DSD is predetermined for each device according to the specifications of the image forming device 10.

Further, the developing roller 76 supports the developer housed in the developing housing 62 (development tank 64) on the surface, and supplies the supported developer to the surface of the photoconductor drum 36. As a result, the electrostatic latent image formed on the surface of the photoconductor drum 36 is visualized by the toner contained in the developer (the toner image is formed on the surface of the photoconductor drum 36). However, when the developer is supplied from the developing roller 76 to the photoconductor drum 36, a predetermined voltage (development voltage) is applied to the developing roller 76 so that the surface of the developing roller 76 has a predetermined potential. .. The developing voltage is applied so that the developer carried on the developing roller 76 moves smoothly toward the electrostatic latent image. However, the developing voltage not only affects the movement of the developer, but also affects the image density of the image region on the outer peripheral surface of the photoconductor drum 36 to which the toner adheres, and also affects the image density on the outer peripheral surface of the photoconductor drum 36. It also affects the toner density (fog density) of the fog phenomenon in which toner adheres to the non-image area.

Further, the doctor blade 78 is arranged inside the developing tank 64 so as to have a predetermined gap with respect to the surface of the developing roller 76. The doctor blade 78 is a plate-shaped member extending in the axial direction of the developing roller 76. The doctor blade 78 regulates the amount of the developer supported on the developing roller 76 (the thickness of the developer supported on the developing roller 76) to a predetermined amount.

In this embodiment, a developer (two-component developer) in which toner and a carrier are mixed is used. However, the carrier is a magnetic material such as iron powder or ferrite. Therefore, a two-component developer composed of a toner and a carrier is housed inside the developing tank 64 of the developing unit 34, and the toner contained in the developing agent is supplied from the developing roller 76 to the photoconductor drum 36.

Returning to FIG. 1, the toner replenishing device 46 is connected to the developing unit 34. The toner replenishment device 46 is a container for storing unused toner, and supplies (replenishes) toner to the developing unit 34 (development tank 64).

The developing unit 34 may be a trickle developing type developing unit. To briefly explain the trickle development method, a new carrier is mixed with the toner in the toner replenishing device 46 at a constant ratio, and the new carrier is supplied (replenished) into the developing tank 64 at the same time as the toner is supplied (replenished). ), And by discharging the excess developer from the developing tank 64, the deteriorated carriers in the developing tank 64 are sequentially replaced with new carriers.

The cleaner unit 38 includes a cleaning blade that comes into contact with the surface of the photoconductor drum 36, and removes toner (developer) remaining on the surface of the photoconductor drum 36 after development and image transfer.

However, in the image forming apparatus 10 of the present embodiment, the developing unit 34, the photoconductor drum 36, the charging unit 40, and the cleaner unit 38 are further unitized, and are provided detachably on the apparatus main body 12 as a process unit including these. Be done.

The transfer unit 42 is arranged on the right side of the developing unit 34 and is a unit for transferring the toner image formed on the surface of the photoconductor drum 36 to paper. The transfer unit 42 includes a transfer roller 422. As shown in FIGS. 1 and 2, the transfer roller 422 is arranged to face the photoconductor drum 36 and is provided so as to press the photoconductor drum 36. At the time of image formation, a predetermined voltage is applied to the transfer roller 422 to form a transfer electric field between the photoconductor drum 36 and the transfer roller 422. Then, due to the action of this transfer electric field, the toner image formed on the outer peripheral surface of the photoconductor drum 36 is formed while the paper passes through the nip area (transfer nip portion) between the photoconductor drum 36 and the transfer roller 422. Transferred to paper.

Returning to FIG. 1, the fixing unit 44 includes a heat roller and a pressure roller, and is arranged above the transfer unit 42. The heat roller is set to have a predetermined fixing temperature, and the toner image transferred to the paper is transferred to the paper by passing the paper through the nip area (fixing nip portion) between the heat roller and the pressure roller. The toner image is heat-fixed to the paper by melting, mixing and pressure welding.

Further, in such a device main body 12, a first paper transport path L1 for sending the paper placed on the paper feed tray 48 to the paper discharge tray 50 via the transfer nip portion and the fixing nip portion is formed. Will be done. Further, in the apparatus main body 12, when double-sided printing is performed on paper, the paper after single-sided printing is completed and has passed through the fixing nip portion is first placed on the upstream side of the transfer nip portion in the paper transport direction. A second paper transport path L2 for returning to the paper transport path L1 is formed. A resist roller 56 is provided in the first paper transport path L1, and a plurality of transport rollers 58 for giving propulsive force to the paper are appropriately provided in the first paper transport path L1 and the second paper transport path L2. Be done.

When single-sided printing is performed on the apparatus main body 12, the paper placed on the paper feed tray 48 is guided one by one to the first paper transport path L1 by the pickup roller 52 and the separation roller 54, and is conveyed to the resist roller 56. To. Then, the resist roller 56 conveys the paper to the transfer nip portion at the timing when the tip of the paper and the tip of the image information (toner image) on the photoconductor drum 36 match, and the toner image is transferred onto the paper. After that, the unfixed toner on the paper is heat-fixed by passing the paper through the fixing nip portion. The heat-fixed paper is conveyed through the first paper transport path L1 by the transport roller 58, and is discharged to the paper discharge tray 50 by the discharge roller 60 provided at the downstream end of the first paper transport path L1.

On the other hand, when double-sided printing is performed, when the rear end of the paper that has passed through the fixing nip portion reaches the discharge roller 60 after single-sided printing is completed, the paper is reversed by rotating the discharge roller 60 in the reverse direction. It runs and is guided to the second paper transport path L2. The paper guided to the second paper transport path L2 is conveyed by the transport roller 58 through the second paper transport path L2, and is guided to the first paper transport path L1 on the upstream side of the resist roller 56 in the paper transport direction. At this point, the front and back sides of the paper are reversed, and then the paper passes through the transfer nip portion and the fixing nip portion, so that printing is performed on the back surface of the paper.

The image forming apparatus 10 may be provided with a manual paper feed tray or may be equipped with an external paper feed unit. In such a case, instead of the paper feed tray 48, paper may be fed from the manual paper feed tray or the external paper feed unit to the first paper transport path L1.

FIG. 3 is a block diagram showing an example of the electrical configuration of the image forming apparatus 10 shown in FIG. As shown in FIG. 3, the image forming apparatus 10 includes a CPU 80, and the CPU 80 includes a RAM 84, an auxiliary storage unit 86, an image reading unit 26, an image forming unit 30, a transport amount detecting unit 66, and a power supply via a bus 82. A control unit 88 or the like is connected. Although not shown, each component such as an operation panel is also connected to the CPU 80 via the bus 82.

The CPU 80 controls the overall control of the image forming apparatus 10, and comprehensively controls the operation of each component of the image forming apparatus 10 described above. Since the image forming apparatus 10 includes the process unit, it can be said that the process unit and each component included in the process unit are controlled.

The RAM 84 is the main storage device of the image forming apparatus 10, and is used as a work area and a buffer area of the CPU 80. The auxiliary storage unit 86 is, for example, an HDD, and is an auxiliary storage device of the image forming apparatus 10 that stores a control program for controlling the operation of each component of the image forming apparatus 10 and various data. However, other non-volatile memory such as SSD, flash memory, EEPROM may be used instead of the HDD or together with the HDD.

The transport amount detection unit 66 is provided to detect the amount of the developer supplied (conveyed) from the developing roller 76 to the photoconductor drum 36 (hereinafter, referred to as “developer transport amount”). The method for detecting the amount of the developer conveyed is not particularly limited, but for example, the developer is conveyed from the toner concentration of the developer contained in the developing tank 64 (T / D: T is the toner and D is the developer). There is a method of estimating (indirectly detecting) the amount. In this case, the transport amount detection unit 66 includes a toner concentration detection sensor (toner concentration sensor) for detecting the toner concentration of the developer contained in the developing tank 64. For example, the toner concentration sensor is attached to the bottom wall of the developing tank 64 or the like. As the toner concentration sensor, a transmission type optical sensor, a reflection type optical sensor, a magnetic permeability sensor, or the like can be used. Among these, it is preferable to use a magnetic permeability sensor. Permeability varies with the proportion of magnetic material in the developer. That is, when the mixing ratio of the magnetic material (carrier) and the non-magnetic material (toner) in the developer, that is, the relative concentration of the magnetic material changes, the output of the magnetic permeability sensor changes. Then, the magnetic permeability of the developer is detected according to the output of the magnetic permeability sensor, and the toner concentration is calculated (detected) from the magnetic permeability of the developer. The toner concentration sensor has been conventionally provided for detecting the toner concentration of the developer or the amount of the developer contained in the developing tank 64. By analyzing the output of this toner concentration sensor (amplitude of frequency components, etc.), the amount of the developer contained in the developing tank 64 is estimated, and the amount of the developing agent contained in the developing tank 64 varies according to the fluctuation. , The developer transport amount can be estimated. Specifically, it is estimated that when the amount of the developer contained in the developing tank 64 increases, the amount of the developing agent conveyed increases, and when the amount of the developing agent contained in the developing tank 64 decreases, the amount of the developing agent conveyed decreases. Presumed.

As a method for detecting the amount of the developing agent conveyed, instead of the above method, a method of measuring the surface of the developing roller 76 or the surface of the photoconductor drum 36 with an optical sensor and directly detecting the amount of the developing agent conveyed is used. It can also be used.

The power supply control unit 88 stops and supplies power (voltage) to each component under the instruction of the CPU 80. Although not shown, a DC voltage (DC power supply) obtained by appropriately stepping down and rectifying (noise removal) the AC voltage from the commercial power supply is applied to the power supply control unit 88. Further, the power supply control unit 88 includes a charge voltage control unit 88a and a development voltage control unit 88b.

The charging voltage control unit 88a applies a charging voltage to the charging unit 40 under the instruction of the CPU 80. The charging voltage means a voltage applied to the charging unit 40 in order to control the surface potential of the photoconductor drum 36 by the charging unit 40. The developing voltage control unit 88b applies a developing voltage to the developing roller 76 under the instruction of the CPU 80.

Here, the potential difference between the dark potential, which is the surface potential of the non-image region of the photoconductor drum 36, and the developing roller 76 is referred to as “potential difference between carriers”. The potential difference between the carriers may be referred to as a cleaning field (CLF). The potential difference between the carriers is set so as to exclude the developer from the photoconductor drum 36 so that the toner does not adhere to the non-image region of the photoconductor drum 36. Further, the potential difference between the carriers is adjusted by changing at least one of the charging voltage and the developing voltage. In this embodiment, the potential difference between the carriers is controlled by changing the charging voltage. This is because keeping the development voltage constant has less effect on developability and, in turn, less adverse effect on print quality.

The electrical configuration of the image forming apparatus 10 shown in FIG. 3 is merely an example, and is not limited to this.

With respect to the image forming apparatus configured as described above, conventionally, the upper limit of the developer transfer amount transferred from the developing roller 76 to the photoconductor drum 36 is set according to the DSD, and the developer transfer amount does not exceed the upper limit. There is a technology to adjust so.

However, in the prior art, since the lower limit of the developer transfer amount is not set, if the developer transfer amount is too small, the density of the toner image transferred to the paper may decrease and the density unevenness may appear remarkably. There is.

Further, in the prior art, the upper limit of the developer transport amount is set only by the DSD, that is, only by the mechanical factor, but the developer transport amount that can pass between the photoconductor drum and the developing roller is a mechanical factor. It is not determined solely by, but also by electrical factors between the photoconductor drum and the developing roller, such as the potential difference between the carriers between the photoconductor drum and the developing roller.

Therefore, if the upper limit of the developer transport amount is set only according to mechanical factors, the developer may be supplied in excess of the upper limit, which may lead to overflow of the developer. The overflow of the developer means that the developer cannot pass between the photoconductor drum and the developing roller, and the developer overflows to the outside of the developing tank.

The inventor conducted an experiment to clarify the relationship between the mechanical and electrical factors between the photoconductor drum and the developing roller, and the image density and the overflow of the current agent. Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to the following description.
1. 1. Manufacture of Image Forming Unit First, for use in each of the following examples, the process units of Examples 1 to 24 or an image forming apparatus provided with the process units were prepared. However, the process unit used in each of the following examples includes a photoconductor drum and a developing roller, and has the same configuration as the process unit shown in FIGS. 1 and 2.

Common conditions are described below for the configuration of the process unit of each embodiment.
-Toner particle size: 5-10 μm
-Carrier particle size: 35-40 μm
-Developer bulk density: 1.5 to 1.7 g / cc
-Toner concentration: 7-8%
-Toner charge amount: 25 to 30 μC / g
・ Process speed: 175 mm / s
・ Peripheral speed ratio of developing roller to photoconductor drum: 2.00
Then, in each example, the image density (ID) and the presence or absence of overflow of the developer were evaluated while changing the distance between the carriers (DSD) and the developer transport amount ρ. The DSD and the developer transfer amount ρ in each of the process units used in Examples 1 to 24 are shown in Table 1. As the developer transport amount ρ in Table 1, the entire amount of the developer in the range of 10 mm in width in the circumferential direction of the developing roller around the main electrode and 40 to 50 mm in width in the center in the longitudinal direction of the developing roller was collected. The weight per unit area when the weight is measured is used.

First, the evaluation of the image density will be described with reference to Table 1. The image density is measured using a color difference meter (manufactured by X-Rite, model: X-Rite938), the reference density (reference ID) is set to 1.35, and the reference density (1.35) or higher is set to "○". "(" OK "), and" x "(" Impossible ") below the standard concentration. That is, when the image density is lower than the reference density, it is evaluated as impossible. The reference density is a density that can ensure the quality of the image transferred to the paper. Since the image density is proportional to the developer transport amount ρ, it is considered that the image density is evaluated as impossible from the viewpoint of the image density when the developer transport amount ρ is too small.

Looking at Examples 1 to 8 in which the DSD is 0.4 mm, in Example 1 in which the developer transport amount ρ is 15 mg / cm ² , the image density is lower than the reference density, and it is evaluated as impossible from the viewpoint of the image density. rice field. On the other hand, in ^{Examples 2 to 8 in which the developer transport amount ρ exceeds 20 mg / cm 2} , the image density exceeds the reference density, and it was evaluated as acceptable from the viewpoint of the image density.

Looking at Examples 9 to 16 in which the DSD is 0.5 mm, in Example 9 in which the developer transport amount ρ is 35 mg / cm ² , the image density is lower than the reference density, and it is evaluated as impossible from the viewpoint of the image density. rice field. On the other hand, in ^{Examples 10 to 16 in which the developer transport amount ρ exceeds 40 mg / cm 2} , the image density exceeds the reference density, and it was evaluated as acceptable from the viewpoint of the image density.

Looking at Examples 17 to 24 in which the DSD is 0.6 mm, in Example 17 in which the developer transport amount ρ is 55 mg / cm ² , the image density is lower than the reference density, and it is evaluated as impossible from the viewpoint of the image density. rice field. On the other hand, in ^{Examples 18 to 24 in which the developer transport amount ρ exceeds 60 mg / cm 2} , the image density exceeds the reference density, and it was evaluated as acceptable from the viewpoint of the image density.

From the above results, it is considered that the lower limit of the developer transport amount ρ in which the decrease in image density is a problem is defined according to the DSD (mechanical factor).

Next, the evaluation of the presence or absence of overflow of the developer will be described with reference to Table 1.

Looking at Examples 1 to 8 in which the DSD is 0.4 mm, in Examples 1 to 3 in which the developer transport amount ρ is ^{less than 40 mg / cm 2} , the developer is used at all the potential differences (100 V to 350 V) tested. It didn't overflow. On the other hand, in Example 4 where the developer transport amount ρ is 40 mg / cm ² , the developer overflows when the potential difference between the carriers is 350 V, and in ^{Example 5 where the developer transport amount ρ is 45 mg / cm 2} , the carrier When the inter-potential difference exceeds 300 V, the developer overflows, and in ^{Example 6 where the developer transport amount ρ is 50 mg / cm 2} , the developer overflows when the potential difference between the supports exceeds 250 V, and the developer transport amount ρ is 55 mg / cm /. In ^{Example 7 which is cm 2} , the developer overflows when the potential difference between the carriers exceeds 175 V, and in Example 8 ^{where the developer transport amount ρ is 60 mg / cm 2, the developer is charged when the potential difference between the carriers exceeds 100 V.} It overflowed.

Looking at Examples 9 to 16 having a DSD of 0.5 mm, in ^{Examples 9 to 11 in which the developer transport amount ρ was less than 60 mg / cm 2} , the developer did not overflow at all the potential differences tested. On the other hand, in Example 12 where the developer transport amount ρ is 60 mg / cm ² , the developer overflows when the potential difference between the carriers is 350 V, and in ^{Example 13 where the developer transport amount ρ is 65 mg / cm 2} , the carrier When the inter-potential difference exceeds 300 V, the developer overflows, and in ^{Example 14 where the developer transport amount ρ is 70 mg / cm 2} , the developer overflows when the potential difference between the supports exceeds 250 V, and the developer transport amount ρ is 75 mg / cm /. cm ² in an exemplary 15 carrier potential difference in exceeds 175V and the developer overflows, the potential difference between the developer conveying quantity ρ is supported in example 16 is 80 mg / cm ² body is the developer exceeds 100V It overflowed.

Looking at Examples 17 to 24 having a DSD of 0.6 mm, the developer did not overflow in Examples 17 to 19 in which the developer ^{transport amount ρ was less than 80 mg / cm 2.} On the other hand, in Example 20 where the developer transport amount ρ is 80 g / cm ² , the developer overflows when the potential difference between the carriers is 350 V, and in ^{Example 21 where the developer transport amount ρ is 85 mg / cm 2} , the carrier When the inter-potential difference exceeds 300 V, the developer overflows, and in ^{Example 22 where the developer transport amount ρ is 90 mg / cm 2} , the developer overflows when the potential difference between the supports exceeds 250 V, and the developer transport amount ρ is 95 mg / cm /. In ^{Example 23, which is cm 2} , the developer overflows when the potential difference between the carriers exceeds 175 V, and in Example 24, ^{where the developer transport amount ρ is 100 mg / cm 2, the developer is charged when the potential difference between the carriers exceeds 100 V.} It overflowed.

As described above, it was found that when the amount of the developer conveyed ρ is larger than a certain amount and the potential difference between the carriers exceeds a predetermined potential difference, the developer overflows. Further, the larger the developer transport amount ρ, the easier it is for the developer to overflow, and the upper limit of the potential difference between the carriers where the developer does not overflow (the lower limit of the potential difference between the carriers where the developer overflows) becomes lower. I understood. Furthermore, it was also found that the relationship between the developer transport amount ρ and the potential difference between the carriers differs depending on the DSD. Therefore, it is considered that the upper limit of the developer transport amount ρ in which the overflow of the developer becomes a problem is defined according to the DSD, the actual developer transport amount ρ, and the potential difference between the carriers.

Through these experiments, the inventor may define the lower limit of the developer transport amount ρ according to the DSD (mechanical factor), and the upper limit of the developer transport amount ρ is the actual developer transport amount ρ and the carrier. I came to be convinced that it should be specified according to the potential difference.

Based on the results of the above experiment, in this embodiment, the upper limit and the lower limit of the developer transport amount are appropriately defined according to the mechanical and electrical factors between the developing roller 76 and the photoconductor drum 36. did. Briefly, the lower limit of the developer transport amount is defined according to the mechanical factor, and the upper limit of the developer transport amount is defined according to the mechanical factor and the electrical factor. Then, the potential difference between the carriers is controlled so that the amount of the developer conveyed does not exceed the upper limit.

Hereinafter, an operation example of the image forming apparatus 10 of this embodiment will be described. First, a method of setting the lower limit of the developer transport amount will be described with reference to FIG.

The lower limit of the developer transport amount should be set so that the image density does not decrease too much. Specifically, the distance from the surface of the developer supported on the developing roller 76 to the surface of the photoconductor drum 36 needs to be the minimum distance d or less. The minimum distance d is the distance at which the minimum amount of the developer that can ensure the quality of the image transferred to the paper can move from the developing roller 76 to the photoconductor drum 36.

As shown in FIG. 4, the distance from the surface of the developer supported on the developing roller 76 to the surface of the photoconductor drum 36 varies depending on the thickness of the developer supported on the developing roller 76. From this, the relationship between the thickness of the developer supported on the developing roller 76 and the minimum distance d can be expressed as the following equation 1.

[Number 1]
DSD-a × ρ ≦ d
In the number 1, "DSD" is the distance (mm) between the carrier of the photoconductor drum 36 and the developing roller 76, and "a" is the reciprocal of the density of the developing agent carried on the developing roller 76 (100 × mm). ³ / mg), where "ρ" is the amount of developer transported (mg / cm ² ). The thickness of the developer supported on the developing roller 76 is represented by a × ρ.

From this number 1, the lower limit ρmin of the developer transport amount can be expressed as the following number 2.

[Number 2]
ρmin = A × DSD + B
In Equation 2, "A" is 1 / a (mg / 100 × mm ³ ) and “B” is −d / a (mg / cm ² ). As described above, the lower limit ρmin of the developer transport amount is defined according to the DSD which is the distance between the carriers. That is, the lower limit ρmin of the developer transport amount is defined according to the mechanical factor. As described above, the DSD is predetermined for each device according to the specifications of the image forming device 10. That is, the DSD is determined at the time of manufacturing the image forming apparatus 10, and the lower limit ρmin of the developer transport amount related to the DSD is also determined at the time of manufacturing the image forming apparatus 10. Then, the amount of the developer pumped onto the surface of the developing roller 76 is set so that the amount of the developer conveyed does not fall below the lower limit ρmin.

Next, a method of setting the upper limit ρmax of the developer transport amount will be described. Regarding the upper limit ρmax of the developer transport amount, the developer transport amount is the maximum amount (passable amount) of the developer that can pass between the photoconductor drum 36 and the developing roller 76 so that the developer does not overflow. It must be less than a large amount (maximum passable amount).

Here, regarding the upper limit ρmax of the developer transport amount, the matters related to DSD (mechanical factor) can be expressed as the following equation 3.

[Number 3]
C × DSD + b
In the number 3, "C" is the passable amount (mg / 100 × mm ³ ) per unit distance between the photoconductor drum 36 and the developing roller 76, and “b” secures the minimum required DSD. The amount of developer (mg / cm ² ) that would otherwise not pass. Here, when the DSD is extremely small, the developer may not be able to pass between the photoconductor drum 36 and the developing roller 76 even if there is a gap between the photoconductor drum 36 and the developing roller 76. Therefore, if the DSD exceeds the minimum required DSD, the developer can pass between the photoconductor drum 36 and the developing roller 76, and if the DSD does not exceed the minimum required DSD, the photosensitivity is exposed. The developer cannot pass between the body drum 36 and the developing roller 76. From this, the amount of the developer that does not pass unless the minimum required DSD is secured can pass between the photoconductor drum 36 and the developing roller 76 when the minimum required DSD is secured. It is the amount of developer that can be produced.

From the above number 3, the upper limit ρmax of the developer transport amount, that is, whether or not the developer overflows, is proportional to the DSD (opening area between the photoconductor drum 36 and the developing roller 76) with respect to mechanical factors. Recognize.

Further, regarding the upper limit ρmax of the developer transport amount, the matters concerning the potential difference (electrical factor) between the carriers can be expressed as the following equation 4.

[Number 4]
D × E + c
^{In the number 4, "D" is the amount (mg / cm 2} V) per 1 V in which the developer carried on the developing roller 76 is pulled by the photoconductor drum 36, and "E" is the photoconductor drum 36 and the developing roller. It is the potential difference (V) between the carriers with the 76, and “c” indicates that the developer carried on the developing roller 76 pulls the photoconductor drum 36 on the photoconductor drum 36 when the photoconductor drum 36 and the developing roller 76 have the same potential. The amount to be processed (mg / cm ² ). In addition, "c" is basically "0". From Equation 4, it can be seen that the upper limit ρmax of the developer transport amount is proportional to the potential difference between the carriers with respect to the electrical factor.

However, the "b" of the equation 3 changes depending on the potential difference between the carriers, and the "c" of the equation 4 changes according to the DSD. Therefore, the equation 3 holds when the potential difference between the carriers is fixed to a certain value, and the equation 4 holds when the DSD is fixed to a certain value.

From the above equations 3 and 4, the upper limit ρmax of the developer transport amount can be expressed as the following equation 5.

[Number 5]
ρmax = C × DSD + D × E + F
In equation 5, "F" is b + c. As shown in the number 5, the upper limit ρmax of the developer transport amount is defined according to the DSD (mechanical factor) and the potential difference between the carriers (electrical factor). However, as described above, the DSD is determined at the time of manufacturing the image forming apparatus 10 and is a fixed value. On the other hand, the potential difference between the carriers can be adjusted by changing at least one of the charging voltage and the developing voltage. Therefore, it is necessary to adjust the potential difference between the carriers so that the amount of the developer conveyed is not more than the upper limit ρmax.

From the equation 5, the potential difference “E” between the carriers for reducing the amount of the developer conveyed to the upper limit ρmax or less can be expressed as the following equation 6.

[Number 6]
E <(1 / D) x (ρr- (C x DSD) -F)
By adjusting the potential difference "E" between the carriers according to the number 6, the developer transport amount ρ does not exceed the upper limit ρmax, and the overflow of the developer can be prevented. However, the upper limit of the potential difference between the carriers varies depending on the current developer transport amount (actual developer transport amount) ρr detected by the transport amount detection unit 66. Therefore, in this embodiment, the upper limit Emax of the potential difference between the carriers is calculated according to the actual amount of the developer conveyed ρr, and the potential difference between the carriers is adjusted so as not to exceed the upper limit Emax of the potential difference between the carriers. .. That is, the prohibited range (range exceeding Emax) of the potential difference between the carriers is set according to the known DSD of the own device and the actual developer transport amount ρr, and the potential difference between the carriers is within the prohibited range. Is prohibited. In other words, the permitted range of the potential difference between the carriers (range below Emax) is set according to the DSD of the own device and the actual amount of the developer conveyed ρr, and the potential difference between the carriers is controlled to be within the permitted range. To. When it is determined that the potential difference between the carriers is within the prohibited range, the potential difference between the carriers is corrected so that the potential difference between the carriers is outside the prohibited range (within the permitted range).

For example, when the DSD is 0.4 mm and the actual developer transport amount ρ is 50 mg / cm ² , the range exceeding 175 V is set as the prohibited range of the potential difference between the carriers, and the potential difference between the carriers is set. It is prohibited to exceed 175V.

However, the process of adjusting the potential difference between the carriers (potential difference adjusting process) is periodically executed at a predetermined timing. The potential difference adjustment process may be performed, for example, when printing a predetermined number of sheets (for example, 200 sheets), when a predetermined time (when a predetermined cumulative time is reached) has elapsed, or when environmental fluctuations (temperature fluctuates by 5 ° C or more, humidity fluctuates by 10% or more, etc.). ), The potential difference adjustment process is performed. Further, the potential difference adjusting process may be executed in accordance with the conventional toner concentration adjusting process. This is because in the toner concentration adjusting process, the charging voltage is changed in order to make the toner concentration an appropriate concentration, and the potential difference between the carriers may fluctuate. If the potential difference between the carriers is within the prohibited range due to the toner concentration adjustment process, the potential difference between the carriers is corrected so as to be outside the prohibited range (for example, the upper limit Emax of the potential difference between the carriers) by the potential difference adjustment process. Will be done.

The above-mentioned operation of the image forming apparatus 10 is realized by the CPU 80 executing a control program stored in the RAM 84. The specific processing will be described later using a flow chart.

FIG. 5 is an illustrated diagram showing an example of the memory map 300 of the RAM 84 shown in FIG. As shown in FIG. 5, the RAM 84 includes a program storage area 302 and a data storage area 304. As described above, the control program of the image forming apparatus 10 is stored in the program storage area 302 of the RAM 84. The control program includes a charging voltage control program 302a, a developing voltage control program 302b, a transport amount detection program 302c, a prohibition range setting program 302d, a determination program 302e, a prohibition program 302f, and an image forming program 302g. However, since the image forming apparatus 10 includes the process unit, this control program is also a control program for the process unit.

The charging voltage control program 302a is a program for controlling the charging voltage control unit 88a to supply and stop power to the charging unit 40 and to control the charging voltage applied to the charging unit 40.

The development voltage control program 302b is a program for controlling the development voltage control unit 88b to supply and stop power to the development roller 76 and to control the development voltage applied to the development roller 76.

The transport amount detection program 302c is a program for detecting the actual developer transport amount ρr transported from the developing roller 76 to the photoconductor drum 36 according to the output of the transport amount detection unit 66.

The prohibition range setting program 302d sets the upper limit Emax of the potential difference between the carriers according to the DSD of the own device and the actual developer transport amount ρr detected according to the carrier amount detection program 302c, and sets the upper limit Emax of the potential difference between the carriers. This is a program for setting a range exceeding the upper limit Emax as a prohibited range.

The determination program 302e is a program for determining whether or not the potential difference between the carriers is within the prohibited range (exceeds the upper limit Emax).

The prohibition program 302f is a program for prohibiting the potential difference between the carriers from being within the prohibited range when it is determined that the potential difference between the carriers is within the prohibited range. The prohibition program 302f is also a program for correcting the potential difference between carriers so that the potential difference between carriers is out of the prohibited range when it is determined that the potential difference between carriers is within the prohibited range.

The image forming program 302g is a program for controlling an image forming unit 30 including a process unit to print a multicolored or single color printed image on paper according to a printed image when a print job is executed. ..

Although not shown, the program storage area 302 also stores programs for selecting and executing various functions of the image forming apparatus 10.

The data storage area 304 of the RAM 84 stores distance data 304a between carriers, transport amount data 304b, prohibited range data 304c, charging voltage data 304d, development voltage data 304e, potential difference data 304f between carriers, correction value data 304g, and the like. Will be done.

The distance data 304a between the carriers is the data of the DSD of the own device. The transport amount data 304b is data of the actual developer transport amount ρr detected according to the transport amount detection program 302c. The prohibited range data 304c is data that defines the prohibited range set according to the prohibited range setting program 302d. The charging voltage data 304d is data of the charging voltage applied to the charging unit 40. The development voltage data 304e is data of the development voltage applied to the developing roller 76. The potential difference data 304f between the carriers is data of the potential difference between the carriers, which is the potential difference between the dark potential, which is the surface potential of the non-image region of the photoconductor drum 36, and the developing roller 76. The correction value data 304g is data of the value of the potential difference for correcting the potential difference between the carriers. The potential difference data 304f between the carriers is data corresponding to the potential difference between the carriers determined by the charging voltage indicated by the charging voltage data 304d and the developing voltage indicated by the developing voltage data 304e.

Although not shown, the data storage area 304 is provided with a register necessary for executing the control program, or stores other data necessary for executing the control program.

FIG. 6 is a flow chart showing an example of the potential difference adjusting process of the CPU 80 of the image forming apparatus 10. This potential difference adjusting process is periodically executed at a predetermined timing. As shown in FIG. 6, when the CPU 80 starts the potential difference adjustment process, the CPU 80 acquires the DSD of its own device in step S1, and in step S3, the actual (current) developer transport amount ρr according to the transport amount detection program 302c. (Read), and in step S5, the prohibited range of the potential difference between the carriers according to the upper limit Emax of the potential difference between the carriers is set according to the DSD of the own device and the actual developer transport amount ρr, and the prohibited range is set in step S7. Then, the current potential difference between the carriers is obtained. When the toner concentration adjusting process is executed in parallel with the potential difference adjusting process, the potential difference between the carriers determined by the toner concentration adjusting process is acquired as the current potential difference between the carriers.

Subsequently, in step S9, it is determined whether or not the current potential difference between the carriers is within the prohibited range. If it is "NO" in step S9, that is, if it is determined that the current potential difference between the carriers is not within the prohibited range, the potential difference adjustment process is terminated. On the other hand, if "YES" in step S9, that is, when it is determined that the current potential difference between the carriers is within the prohibited range, the potential difference between the carriers is set to be outside the prohibited range in step S11 (. The voltage difference adjustment process is completed after making corrections (so that the potential difference between the carriers is equal to or less than the upper limit Emax).

According to the present embodiment, the prohibited range of the potential difference between the carriers is set according to the mechanical and electrical factors of the process unit including the photoconductor drum 36 and the developing roller 76, and the potential difference between the carriers is within the prohibited range. Therefore, an appropriate amount of the developing agent can be supplied to the developing roller 76 or the photoconductor drum 36, and the decrease in the toner concentration and the overflow of the developing agent can be suppressed.

Further, according to the present embodiment, when it is determined that the potential difference between the carriers is within the prohibited range, the potential difference between the carriers is corrected so as to be outside the prohibited range, so that the developing roller 76 or the photoconductor drum is used. An appropriate amount of developer can be supplied to 36.

Further, according to the present embodiment, the transport amount detecting unit 66 is housed in the developing tank 64 by analyzing the output of the toner concentration detecting sensor for detecting the toner concentration of the developing agent contained in the developing tank 64. Since the amount of the developing agent to be processed is estimated and the amount of the developing agent conveyed is estimated according to the fluctuation of the amount of the developing agent contained in the developing tank 64, it is not necessary to provide a dedicated sensor, and it is usually used in an image forming apparatus. The amount of developer transported can be estimated using the existing configuration mounted.

In the above embodiment, the image forming apparatus 10 is configured as a monochrome multifunction device, but the image forming apparatus of the present invention may be configured as a color printing machine or a color multifunction device. In this case, for example, for each color of Y (yellow), M (magenta), C (cyan), K (black), an image forming station including a photoconductor drum 36, a charging unit 40, a developing unit 34, and the like is configured. An intermediate transfer belt and a transfer roller (secondary transfer roller) are provided. The intermediate transfer belt is provided so as to be in contact with the photoconductor drum 36 of each image forming station, and the toner images of each color formed on each photoconductor drum 36 are sequentially superposed on the intermediate transfer belt and transferred to the intermediate. A multicolored toner image is formed on the transfer belt. Further, when the paper passes through the nip area (transfer nip portion) between the intermediate transfer belt and the transfer roller, the toner image formed on the intermediate transfer belt is transferred to the paper. In the case of a color printing machine or a color multifunction device, the potential difference adjustment process is executed for each image station (for each color).

Further, the specific configuration and the like given in the above-described embodiment are examples, and can be appropriately changed according to the actual product. Further, the order in which each step of the flow chart shown in the above-described embodiment is processed can be appropriately changed as long as the same result can be obtained.

10 ... Image forming device 36 ... Photoreceptor drum 76 ... Developing roller 88 ... Power supply control unit

Claims (5)

An electrostatic latent image carrier on which an electrostatic latent image is formed,
A developing tank that houses the developing agent,
A developing roller that carries a developer housed in the developing tank and supplies it to the electrostatic latent image carrier.
A charging means for charging the surface of the electrostatic latent image carrier to a predetermined potential,
A developing voltage applying means for applying a predetermined developing voltage to the developing roller,
An acquisition means for acquiring a transport amount, which is the amount of a developer existing on the developing roller.
The portion of the electrostatic latent image carrier where the electrostatic latent image is not formed and the portion according to the distance between the carriers, which is the distance between the electrostatic latent image carrier and the developing roller, and the amount of transport. Image formation comprising a prohibition range setting means for setting a prohibition range of a potential difference between carriers, which is a potential difference between a developing roller, and a prohibition means for prohibiting the potential difference between the carriers from being within the prohibition range. Device. Further, a determination means for determining whether or not the potential difference between the carriers is within the prohibited range is provided.
When the determination means determines that the potential difference between the carriers is within the prohibited range, the prohibiting means controls at least one of the charging means or the developing voltage applying means between the carriers. The image forming apparatus according to claim 1, further comprising a correction means for correcting the potential difference of the above to the outside of the prohibited range. The image according to claim 2, wherein the acquisition means includes a toner concentration sensor for detecting the toner concentration of the developer contained in the developing tank, and acquires the conveyed amount estimated according to the toner concentration. Forming device. An electrostatic latent image carrier on which an electrostatic latent image is formed, a developing tank that houses a developer, and a developing roller that carries the developer contained in the developing tank and supplies it to the electrostatic latent image carrier. And a control program of an image forming apparatus including a charging means for charging the surface of the electrostatic latent image carrier to a predetermined potential.
To the processor of the image forming apparatus
A process of applying a predetermined development voltage to the developing roller,
A process for acquiring a transport amount, which is the amount of a developer existing on the developing roller.
The portion of the electrostatic latent image carrier on which the electrostatic latent image is not formed and the portion according to the distance between the carriers, which is the distance between the electrostatic latent image carrier and the developing roller, and the amount of transport. A control program for executing a process of setting a prohibited range of a potential difference between carriers, which is a potential difference between a developing roller, and a process of prohibiting the potential difference between the carriers from being within the prohibited range. An electrostatic latent image carrier on which an electrostatic latent image is formed, a developing tank that houses a developer, and a developing roller that carries the developer contained in the developing tank and supplies it to the electrostatic latent image carrier. And a control method of an image forming apparatus including a charging means for charging the surface of the electrostatic latent image carrier to a predetermined potential.
(A) A step of applying a predetermined development voltage to the developing roller.
(B) A step of acquiring a conveyed amount, which is the amount of the developer existing on the developing roller.
(C) The electrostatic latent image of the electrostatic latent image carrier is not formed depending on the distance between the carriers, which is the distance between the electrostatic latent image carrier and the developing roller, and the amount of transportation. The step includes setting a prohibited range of the potential difference between the carriers, which is the potential difference between the portion and the developing roller, and (d) prohibiting the potential difference between the carriers from being within the prohibited range. Control method.

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