Image forming apparatus

Abstract

To prevent, with a simple configuration, an image defect caused by a change in the charging performance of toner in a developing device.SOLUTION: An image forming apparatus has: a photoreceptor; a charging member; a charge voltage application unit; an exposure device; a developing device including a developing member that forms a developing part capable of supplying developer to the photoreceptor, and a developer storage part; a developing voltage application unit that applies developing voltage to the developing member; a charge current detection unit that detects a charge current flowing in a charging unit; and a control unit. During a non-image forming operation, while a surface of the photoreceptor, which is charged by the charging member and subsequently passes through the developing unit, passes through the charging unit, the control unit can control the charge current detection unit to execute a detection operation to detect the charge current. The control unit controls at least one of the charge voltage application unit, exposure device, and developing voltage application unit, so as to change a developing contrast on the basis of a charge current value IA detected in the previous detection operation and a charge current value IB detected in the current detection operation.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, such as a copying machine, a printer, or a facsimile machine, which forms an image by an electrophotographic method or an electrostatic recording method. [Background technology]

[0002] Conventionally, in image forming apparatuses such as printers using an electrophotographic system, an electrostatic latent image is formed on a photoconductor (electrophotographic photoconductor) as an image carrier, and a developing device supplies toner to this electrostatic latent image to form a toner image on the photoconductor. The toner image formed on the photoconductor is transferred to a recording material directly or via an intermediate transfer body, and an image is formed on the recording material. The developing device may be a developing cartridge that is detachably attached to the main body of the image forming apparatus (hereinafter also simply referred to as the "main body"), or a process cartridge that is detachably attached to the main body of the apparatus together with other process means.

[0003] In such an image forming apparatus, image defects may occur due to the unknown state of the toner in the developing device. For example, it has been found that when the developing device is replenished with new toner while the developing device is outside the main body of the apparatus, image defects such as low density and step unevenness may occur due to changes in the charging performance of the toner.

[0004] For example, when the developing device is replenished with new toner and the charging performance of the toner in the developing device is improved, the amount of charge per toner particle increases, so the number of toner particles required to fill the latent image potential decreases. As a result, this may manifest as low density (a phenomenon in which image density becomes low). In addition, when the charging performance of the toner is improved, the charge on the surface of the photoconductor is more likely to be transferred to the toner due to frictional charging between the photoconductor and the toner in the developing section, and the surface potential of the photoconductor decreases. Furthermore, when the deviation (change in the amount of penetration) of the outer diameter of the developing roller as a developing member provided in the developing device is also added, it becomes more susceptible to the influence of the deviation (change in the amount of penetration) of the outer diameter of the developing roller, which is a development unevenness that occurs with the rotation period of the developing roller, and this becomes more likely to manifest as step unevenness, which is a development unevenness that occurs with the rotation period of the developing roller. This is considered to be due to the following reason. In other words, when the amount of penetration of the developing roller against the photoconductor is large, the force with which the toner is pressed against the photoconductor is larger than when it is small, and the frictional charging force between the photoconductor and the toner is larger. As a result, the charge on the photoconductor is more likely to be transferred to the toner. Therefore, there is a need for a technology that can determine the state of the toner in the developing device and change to an optimal control.

[0005] Patent Document 1 discloses a technique for detecting a toner current flowing between a developing roller and an opposing member. In the technique described in Patent Document 1, an AC voltage is applied between the developing roller and an opposing member arranged opposite the developing roller in a non-contact manner, and a toner current generated by the toner moving back and forth between the developing roller and the opposing member is detected. In this case, a capacitor is connected in parallel to the developing roller and the opposing member to cancel the charge / discharge current flowing between the developing roller and the opposing member and detect only the toner current. Then, based on the detection result of the toner current, feedback is provided to image formation conditions such as the development voltage. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2010-197464 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the technology described in Patent Document 1, for example, when the power supply of the image forming unit is configured as a DC voltage power supply, an AC voltage power supply must be newly installed. Also, in the technology described in Patent Document 1, a new circuit for measuring the toner current must be configured.

[0008] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to detect a change in the charging performance of toner in a developing device with a simple configuration and to suppress image defects caused by the change in the charging performance of toner in the developing device. [Means for solving the problem]

[0009] The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides a developing device including a rotatable photoconductor, a charging member that contacts the photoconductor to form a charging section and charges the surface of the rotating photoconductor, a charging voltage application section that applies a charging voltage to the charging member, an exposure device that exposes the surface of the photoconductor charged by the charging member to light to form an electrostatic latent image on the surface of the photoconductor, a rotatable developing member that forms a developing section capable of supplying a developer to the surface of the photoconductor, and in the developing section, supplies a developer charged to a predetermined polarity to the electrostatic latent image on the surface of the photoconductor to form a developer image on the surface of the photoconductor, and a developer storage section that stores the developer to be supplied to the developing member, and a developing voltage application section that applies a developing voltage of the predetermined polarity side with respect to the potential of the electrostatic latent image in the developing section to the developing member. In an image forming apparatus having a pressure application unit, a charging current detection unit that detects a charging current flowing through the charging unit when the surface of the photoconductor is charged by the charging member, and a control unit capable of controlling the charging voltage application unit, the exposure device, and the developing voltage application unit, the image forming apparatus performing an image forming operation for forming the developer image on the surface of the photoconductor, and a non-image forming operation in which the developer image is not formed on the surface of the photoconductor, the control unit is capable of controlling the control unit to execute a detection operation for detecting the charging current by the charging current detection unit when the surface of the photoconductor that has been charged by the charging member and then passed through the developing unit passes through the charging unit during the non-image forming operation, and the control unit is configured to detect the charging current value I detected by the detection operation prior to the current detection operation. A and the charging current value I detected by this detection operation. B and based on the above, at least one of the charging voltage application unit, the exposure device, and the developing voltage application unit can be controlled to change a development contrast, which is a potential difference between the potential of the electrostatic latent image in the developing unit and the developing voltage.

[0010] According to another aspect of the present invention, a developing device includes a rotatable photoconductor, a charging member that contacts the photoconductor to form a charging section and charges the surface of the rotating photoconductor, a charging voltage application section that applies a charging voltage to the charging member, an exposure device that exposes the surface of the photoconductor charged by the charging member to light to form an electrostatic latent image on the surface of the photoconductor, a rotatable developing member that forms a developing section capable of supplying a developer to the surface of the photoconductor, and in the developing section, supplies the developer to the electrostatic latent image on the surface of the photoconductor to form a developer image on the surface of the photoconductor, and a developer container that contains the developer to be supplied to the developing member, a speed change section that changes the rotation speed of the developing member, and a developing device that charges the surface of the photoconductor by the charging member. In an image forming apparatus having a charging current detection unit that detects a charging current that flows in the charging unit when the surface of a photoconductor is charged, and a control unit capable of controlling the charging voltage application unit and the speed change unit, the image forming apparatus performs an image forming operation in which the developer image is formed on the surface of the photoconductor, and a non-image forming operation in which the developer image is not formed on the surface of the photoconductor, the control unit is capable of controlling the control unit to execute a detection operation in which the charging current detection unit detects the charging current when the surface of the photoconductor that has been charged by the charging member and then passed through the development unit passes through the charging unit during the non-image forming operation, and the control unit is configured to detect the charging current value I detected in the detection operation prior to the current detection operation. A and the charging current value I detected by this detection operation. B and, based on the above, the speed change unit is capable of controlling a circumferential speed ratio, which is a ratio of the circumferential speed of the developing member to the circumferential speed of the photosensitive member, to change the circumferential speed ratio. Effect of the Invention

[0011] According to the present invention, it is possible to detect a change in the charging performance of the toner in the developing device with a simple configuration and to suppress image defects caused by the change in the charging performance of the toner in the developing device. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view of an image forming apparatus according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view of a process cartridge in the first embodiment. [Diagram 3] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus according to the first embodiment. [Figure 4] FIG. 11 is a graph illustrating a change in charging current value before and after toner replenishment. [Diagram 5] 5A and 5B are schematic diagrams for explaining the mechanism of change in charging current value before and after toner replenishment. [Figure 6] FIG. 4 is a flow chart of control in the first embodiment. [Figure 7] 11 is a graph showing the relationship between the intrusion amount of the developing roller and the charging current value. [Figure 8] FIG. 11 is a block diagram showing a control configuration of an image forming apparatus according to a second embodiment. [Figure 9] FIG. 11 is a flow chart of control in the second embodiment. [Figure 10] FIG. 11 is a block diagram showing a control configuration of an image forming apparatus according to a third embodiment. [Figure 11] FIG. 11 is a flow chart of control according to the third embodiment. [Figure 12] FIG. 11 is a schematic cross-sectional view of an image forming apparatus according to a fourth embodiment. [Figure 13] 13A and 13B are a front view and a schematic cross-sectional view for explaining a method of supplying toner from the toner pack to the developing device in the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings. For convenience, the magnitude (high / low) of voltage or potential refers to the magnitude (high / low) when compared in absolute value unless otherwise specified.

[0014] [Example 1] <Overall configuration of image forming apparatus> First, the overall configuration of the image forming apparatus of this embodiment will be described. FIG. 1 is a schematic cross-sectional view of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a full-color laser printer that employs an in-line system and an intermediate transfer system. The image forming apparatus 100 can form a full-color image on a sheet-shaped recording material P (e.g., recording paper, a plastic sheet, cloth, etc.) according to image information. The image information is input to the image forming apparatus 100 from an external device (not shown) such as an image reading device or a personal computer that is communicably connected to the image forming apparatus 100.

[0015] The image forming apparatus 100 has a plurality of image forming units, ie, first, second, third and fourth image forming units SY, SM, SC and SK for forming images of each color of yellow (Y), magenta (M), cyan (C) and black (K). The same or corresponding elements provided for each color may be generally described by omitting the suffixes Y, M, C and K of the reference numerals indicating that the elements are for any one of the colors. In this embodiment, the image forming unit S is configured to include a photoconductor 1, a charging roller 2, an exposure device 3, a developing device 4, a cleaning device 5 and a pre-exposure device 6, which will be described later. In this embodiment, the exposure device 3 is configured as a single unit that exposes the photoconductor 1 of each image forming unit S, but may be provided independently for each image forming unit S. In each image forming unit S, the photoconductor 1, the charging roller 2 as a process means acting on the photoconductor 1, the developing device 4 and the cleaning device 5 are integrated to form a process cartridge 7. FIG. 2 is a schematic cross-sectional view showing one representative process cartridge 7.

[0016] A rotatable drum-shaped (cylindrical) photoconductor (photoconductor drum) 1 serving as an image carrier for carrying an electrostatic latent image and a toner image is rotationally driven in the direction of arrow R1 (clockwise direction) in FIG. 2 by a driving force transmitted from a driving unit 80 (FIG. 3) serving as a driving means. In this embodiment, the four photoconductors 1 are arranged side by side in a direction intersecting the vertical direction.

[0017] The surface of the rotating photoconductor 1 is charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by the charging roller 2, which is a roller-type charging member serving as a charging means. In this embodiment, the charging roller 2 is a single-layer roller made of a conductive core metal and a conductive rubber layer (elastic layer) provided around the core metal, and has an outer diameter of 7.5 mm and a volume resistivity of 10 3 ~10 6 The surface resistance is Ω·cm. The charging roller 2 is disposed in contact with the surface of the photoconductor 1, pressed against the photoconductor 1, and rotates in accordance with the rotation of the photoconductor 1. During image formation (charging), a predetermined charging voltage (charging bias) which is a direct current (DC) voltage of a predetermined polarity (negative in this embodiment) is applied to the charging roller 2 by a charging power source (high voltage power source) 71 (FIG. 3) as a charging voltage application unit. In this embodiment, a charging voltage of −1000V is applied to the charging roller 2, and the surface of the photoconductor 1 is uniformly charged to −500V. That is, a charging voltage Vd+Vth which is a DC voltage is applied to the charging roller 2, and the surface of the photoconductor 1 is uniformly charged to Vd by discharge. Here, Vd is a dark area potential (non-image area potential), which is −500V in this embodiment. Also, Vth is a discharge start voltage, which is −500V in this embodiment. When the charging voltage applied to the charging roller 2 is small, the surface potential on the photoconductor 1 does not increase due to discharge, but when the charging voltage applied to the charging roller 2 becomes equal to or greater than the discharge start voltage Vth, the surface potential of the photoconductor 1 starts to increase due to discharge. The position in the rotation direction of the photoconductor 1 where the charging process of the surface of the photoconductor 1 is performed by the charging roller 2 is the charging portion (charging position) P1. In this embodiment, the surface of the photoconductor 1 is charged by discharge generated in minute gaps formed upstream and downstream of the contact portion between the photoconductor 1 and the charging roller 2 in the rotation direction of the photoconductor 1. However, for convenience, the contact portion between the photoconductor 1 and the charging roller 2 may be considered as the charging portion P1.

[0018] The charged surface of the photoreceptor 1 is scanned and exposed by the exposure device 3 as an exposure means, and an electrostatic latent image (electrostatic image) is formed on the photoreceptor 1. The exposure device 3 irradiates the surface of the photoreceptor 1 with laser light based on image information, forming an electrostatic latent image on the photoreceptor 1. The surface potential of the photoreceptor 1 irradiated with the laser light changes to -100 V, which is the light area potential (image area potential) Vl. The position in the rotation direction of the photoreceptor 1 where the exposure device 3 irradiates the surface of the photoreceptor 1 with light is the exposure area (exposure position) P2.

[0019] The electrostatic latent image formed on the photoconductor 1 is developed (visualized) by the developing device 4 as a developing means, which supplies toner as a developer, and a toner image (toner image, developer image) is formed on the photoconductor 1. The developing device 4 has a developing roller 41 as a developing member (developer carrier). During image formation (development), a predetermined developing voltage (developing bias), which is a DC voltage of a predetermined polarity (negative in this embodiment), is applied to the developing roller 41 by a developing power source (high voltage power source) 72 (FIG. 3) as a developing voltage application unit. In this embodiment, a developing voltage Vdc of −300V is applied to the developing roller 41, so that toner adheres to the Vl portion on the photoconductor 1. Thus, in this embodiment, toner charged to the same polarity as the charging polarity of the photoconductor 1 (negative in this embodiment) adheres to the image portion on the photoconductor 1, which has been uniformly charged and then exposed to light and has a reduced potential (reverse development method). In this embodiment, the normal charging polarity of the toner, which is the main charging polarity of the toner during development, is negative. The developing device 4 will be described in further detail later. The position in the rotation direction of the photoconductor 1 where the developing device 4 supplies toner to the surface of the photoconductor 1 (in this embodiment, the contact portion between the photoconductor 1 and the developing roller 41) is the developing portion (developing position) P3.

[0020] Opposing the four photoconductors 1, an intermediate transfer belt 31 constituted by an endless belt as an intermediate transfer body is disposed. The intermediate transfer belt 31 is stretched around a driving roller 33 and a tension roller 34 as a plurality of tension rollers and tensioned with a predetermined tension. The intermediate transfer belt 31 rotates (circulates, moves around) in the direction of arrow R2 in FIG. 1 (counterclockwise direction) as the driving roller 33 is rotated by a driving force transmitted from a driving unit 80 (FIG. 3) as a driving means. On the inner peripheral surface side of the intermediate transfer belt 31, primary transfer rollers 32, which are roller-type primary transfer members as primary transfer means, are disposed so as to face each photoconductor 1 via the intermediate transfer belt 31. The primary transfer rollers 32 are pressed toward the photoconductor 1 and come into contact with the photoconductor 1 via the intermediate transfer belt 31 to form a primary transfer portion (primary transfer nip) N1 where the photoconductor 1 and the intermediate transfer belt 31 come into contact with each other. The toner image formed on the photoconductor 1 is transferred (primary transfer) onto the rotating intermediate transfer belt 31 as a transferee by the action of the primary transfer roller 32 at the primary transfer portion N1. During image formation (primary transfer), a predetermined primary transfer voltage (primary transfer bias) which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner is applied to the primary transfer roller 32 by a primary transfer power source (high voltage power source) 73 (FIG. 3) as a primary transfer voltage application portion. For example, when a full-color image is formed, the toner images of yellow (Y), magenta (M), cyan (C), and black (K) formed on each photoconductor 1 are transferred in sequence onto the intermediate transfer belt 31 so as to be superimposed on each other. The position where the toner image is transferred from the surface of the photoconductor 1 to the intermediate transfer belt 31 in the rotation direction of the photoconductor 1 is the primary transfer position P4 (the above-mentioned primary transfer portion N1 which is the contact portion between the photoconductor 1 and the intermediate transfer belt 31 in this embodiment).

[0021] A secondary transfer roller 9, which is a roller-type secondary transfer member serving as a secondary transfer means, is disposed at a position facing the driving roller 33, which also serves as a secondary transfer opposing roller, on the outer peripheral surface side of the intermediate transfer belt 31. The secondary transfer roller 9 is pressed toward the driving roller 33 and abuts against the driving roller 33 via the intermediate transfer belt 31, forming a secondary transfer portion (secondary transfer nip) N2 where the intermediate transfer belt 31 and the secondary transfer roller 9 abut. The toner image formed on the intermediate transfer belt 31 is transferred (secondarily transferred) to a recording material P, which is a transfer target material being conveyed while being sandwiched between the intermediate transfer belt 31 and the secondary transfer roller 9, at the secondary transfer portion N2. During image formation (secondary transfer), a predetermined secondary transfer voltage (secondary transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the secondary transfer roller 33 by a secondary transfer power source (high voltage power source) 74 (FIG. 3) serving as a secondary transfer voltage application portion. A recording material (transfer material, recording medium, sheet) P is stored in a cassette 10 serving as a recording material storage section, and is sent out of the cassette 10 by a feed roller 11 serving as a feed member, and is sent to a registration roller 12 serving as a transport member. This recording material P is transported by the registration roller 12 to the secondary transfer section N2 in synchronization with the toner image on the intermediate transfer belt 31.

[0022] The recording material P onto which the toner image has been transferred is conveyed to a fixing device 13 serving as a fixing means. The fixing device 13 applies heat and pressure to the recording material P bearing the unfixed toner image, thereby fixing (melting and bonding) the toner image onto the recording material P. The recording material P onto which the toner image has been fixed is discharged (output) onto a tray 14 serving as a discharge unit provided outside the device body 110 of the image forming apparatus 100.

[0023] On the other hand, the surface potential of the photoconductor 1 after the toner image is transferred to the intermediate transfer belt 31 is non-uniform due to the primary transfer voltage. The surface of the photoconductor 1 is pre-exposed (full-surface exposure, full-surface light irradiation) by the pre-exposure device 6 as a charge removing means, and the surface potential of the photoconductor 1 that became non-uniform due to the previous image formation is uniformly leveled. In other words, the residual charge on the surface of the photoconductor 1 is removed by the pre-exposure. The pre-exposure device 6 exposes the surface of the photoconductor 1 downstream of the primary transfer section P4 and upstream of the charging section P1 in the rotation direction of the photoconductor 1. The light source of the pre-exposure device 6 can be an LED, a halogen lamp, or the like. Although the light source to be used is not particularly limited, it is preferable to use an LED from the viewpoint of low driving voltage and easy miniaturization of the device. In this embodiment, an LED is used as the light source of the pre-exposure device 6. The position where the pre-exposure device 6 irradiates light onto the surface of the photoconductor 1 in the rotation direction of the photoconductor 1 is the pre-exposure section (pre-exposure position) P5.

[0024] Furthermore, toner (primary transfer residual toner) remaining on the surface of the photoreceptor 1 without being transferred to the intermediate transfer belt 31 is removed from the surface of the photoreceptor 1 and collected by a cleaning device 5 serving as a photoreceptor cleaning means. The cleaning device 5 scrapes off the transfer residual toner from the surface of the rotating photoreceptor 1 by a cleaning blade 51 serving as a cleaning member that contacts the surface of the photoreceptor 1, and stores the transfer residual toner in a waste toner storage chamber 52 provided below the cleaning blade 51.

[0025] In addition, any adhesions such as toner (secondary transfer residual toner) remaining on the surface of the intermediate transfer belt 31 without being transferred to the recording material P are removed from the surface of the intermediate transfer belt 31 and collected by a belt cleaning device 35 serving as an intermediate transfer body cleaning means.

[0026] The intermediate transfer belt 31 can be brought into contact with and separated from each photoconductor 1 by a belt contact / separation mechanism 90 (FIG. 3). In this embodiment, the belt contact / separation mechanism 90 is configured to separate the intermediate transfer belt 31 from the photoconductor 1 by moving the primary transfer roller 32 in a direction away from the photoconductor 1, and to bring the intermediate transfer belt 31 into contact with the photoconductor 1 by moving the primary transfer roller 32 in a direction toward the photoconductor 1.

[0027] <Process cartridge configuration> Next, the process cartridge 7 to be mounted in the image forming apparatus 100 of this embodiment will be further described.

[0028] The process cartridge 7 is detachably attached to the main body 110 of the image forming apparatus 100 via attachment means (not shown) such as an attachment guide or a positioning member provided in the image forming apparatus 100. In this embodiment, the main body 110 is the portion of the image forming apparatus 100 excluding the process cartridge 7. In this embodiment, the process cartridges 7 for each color all have the same shape, and the toner t of each color, yellow (Y), magenta (M), cyan (C), and black (K), is accommodated in the process cartridge 7 for each color. In this embodiment, the configuration and operation of the process cartridges 7 for each color are substantially the same except for the type (color) of the toner t accommodated therein. The process cartridge 7 has a developing device (developing unit) 4 and a photoconductor unit 8.

[0029] The developing device (developing unit) 4 has a developing container (developing frame) 45. The developing container 45 is partitioned into a developing chamber 45a and a toner containing chamber (developer containing portion) 45b.

[0030] The toner accommodating chamber 45b accommodates toner t, which is a non-magnetic one-component developer. A toner transport member (developer transport member) 44 is provided in the toner accommodating chamber 45b. The toner transport member 44 is rotated in the direction of arrow R5 in FIG. 2 (clockwise direction) by a driving force transmitted from a driving unit 80 (FIG. 3) as a driving means, and transports the toner t to the developing chamber 45a.

[0031] In the developing chamber 45a, a developing roller 41 is disposed as a developing member (developer carrier). During image formation (development), the developing roller 41 is brought into contact with the photoconductor 1 and rotated in the direction of the arrow R3 in FIG. 2 (counterclockwise direction) by a driving force transmitted from a driving unit 80 as a driving means. In this embodiment, the developing roller 41 and the photoconductor 1 rotate so that their surfaces move in the forward direction in the developing section P3 where the developing roller 41 and the photoconductor 1 face each other (contact each other). In this embodiment, the developing roller 41 is made of a conductive core metal and a conductive rubber layer (elastic layer) provided around the core metal. The rotation direction of the developing roller 41 is not limited to the rotation direction in this embodiment, and may be a rotation direction in which the surface of the developing roller 41 and the surface of the photoconductor 1 move in opposite directions in the developing section P3.

[0032] In addition, in the developing chamber 45a, a supply roller 42 is disposed as a supply member that supplies the toner t conveyed from the toner storage chamber 45b to the developing roller 41. The supply roller 42 is disposed in contact with the developing roller 41. During image formation (development), the supply roller 42 is rotated in the direction of the arrow R4 in FIG. 2 (counterclockwise direction) by a driving force transmitted from a driving unit 80 as a driving means. In this embodiment, the supply roller 42 and the developing roller 41 rotate such that the surfaces of the supply roller 42 and the developing roller 41 move in opposite directions at the contact portion between the supply roller 42 and the developing roller 41. The rotation direction of the supply roller 42 is not limited to the rotation direction in this embodiment, and may be a rotation direction in which the surfaces of the supply roller 42 and the developing roller 41 move in the forward direction at the contact portion between the supply roller 42 and the developing roller 41.

[0033] Further, in the developing chamber 45a, there is disposed a developing blade 43 as a regulating member which regulates the coating amount of the toner t on the developing roller 41 supplied by the supply roller 42 and applies a charge to the toner t.

[0034] Independent voltages are applied from a high-voltage power supply to the developing roller 41, the supply roller 42, and the developing blade 43. The toner t supplied to the developing roller 41 by the supply roller 42 is frictionally charged by rubbing between the developing roller 41 and the developing blade 43, and is given a charge and its layer thickness is regulated. The toner t on the developing roller 41, whose layer thickness has been regulated, is transported by the rotation of the developing roller 41 to the developing section P3, which is the portion facing (contacting) the photoconductor 1, and adheres to the image portion of the electrostatic latent image on the photoconductor 1 to form a toner image on the photoconductor 1.

[0035] During image formation (development), a predetermined development voltage (development bias) Vdc, which is a DC voltage of a predetermined polarity (negative in this embodiment), is applied to the development roller 41 by a development power source (high voltage power source) 72 (FIG. 3) as a development voltage application unit. In this embodiment, the development voltage Vdc is set to -300V. As a result, in the development unit P3, the development contrast Vcont (=Vl-Vdc), which is the potential difference between the light area potential Vl on the photoconductor 1 and the development bias (potential of the development roller 41), becomes +200V. Also, during image formation (development), a predetermined supply voltage (supply bias) Vrs, which is a DC voltage of a predetermined polarity (negative in this embodiment), is applied to the supply roller 42 by a supply power source (high voltage power source) 75 (FIG. 3) as a supply voltage application unit. In this embodiment, the supply voltage Vrs is set to -350V. By adjusting the potential difference (ΔVr) between the supply roller 42 and the development roller 41, the amount of toner t supplied to the development roller 41 can be adjusted. In this embodiment, ΔVr (=Vdc-Vrs) is set to +50V. This allows the negatively charged toner t to easily move from the supply roller 42 to the development roller 41. During image formation (development), a predetermined regulated voltage (regulated bias) which is a DC voltage of a predetermined polarity (negative in this embodiment) is applied to the development blade 43 by a regulated power source (high voltage power source) 76 (FIG. 3) as a regulated voltage application unit. In this embodiment, the regulated voltage is set to -350V, similar to the supply voltage. The settings of the above-mentioned development bias Vdc and the like are default settings when the apparatus main body 110 and the process cartridge 7 are in a new state.

[0036] As mentioned above, the magnitude (high / low) of voltage or potential refers to the magnitude (high / low) when compared in absolute value, unless otherwise specified. In other words, regarding potential or applied voltage, a high potential refers to an absolute value that is large on the negative polarity side (for example, -1000V compared to -500V), and a low potential refers to an absolute value that is small on the negative polarity side (for example, -300V compared to -500V). This is because in this embodiment, the negatively charged toner t is considered as the reference. Also, the voltage is expressed as a potential difference with respect to the earth potential (0V). Therefore, a development voltage of -300V means that there is a potential difference of -300V due to the development voltage applied to the core metal of the development roller 41 with respect to the earth potential. This is also true for other voltages such as charging voltage.

[0037] The photoreceptor unit 8 has a photoreceptor unit container (photoreceptor unit frame) 53. The photoreceptor 1 is rotatably attached to the photoreceptor unit container 53 via a bearing (not shown). The photoreceptor 1 is driven to rotate in the direction of the arrow R1 in FIG. 2 (clockwise direction) by receiving a driving force transmitted from a driving unit 80 (FIG. 3) as a driving means. The photoreceptor unit 8 also has a charging roller 2 and a cleaning blade 51, which is a plate-shaped elastic body, arranged so as to contact the surface (outer circumferential surface) of the photoreceptor 1. The charging roller 2 is rotatably attached to the photoreceptor unit container 53 via a bearing (not shown). One end (fixed end) of the cleaning blade 51 is fixed to a plate-shaped metal sheet metal attached to the photoreceptor unit container 53, and the other end (free end) abuts against the photoreceptor 1 to form a cleaning nip, which is the abutment portion with the photoreceptor 1. The cleaning blade 51 rubs against the surface of the photoreceptor 1, scraping off the toner t and fine particles remaining on the photoreceptor 1 after the primary transfer process, and stores them in a waste toner storage chamber 52 formed in a photoreceptor unit container 53. This makes it possible to prevent the toner t from adhering to the charging roller 2 or the toner t from being carried around by the photoreceptor 1, which makes it impossible to form an appropriate image. The cleaning blade 51 and the waste toner storage chamber 52 (photoreceptor unit container 53) form a cleaning device 5.

[0038] The image forming apparatus 100 also has a contact / separation mechanism 60 for bringing each developing roller 41 into contact with and away from each photoconductor 1. In this embodiment, the developing container 45 is swingably coupled to the photoconductor unit container 53, and the developing container 45 is biased in a direction in which the developing roller 41 contacts the photoconductor 1 by a pressure spring, which is a biasing member serving as a biasing means. The contact / separation mechanism 60 is configured to move (rotate) the developing container 45 against the biasing force of the pressure spring, thereby separating the developing roller 41 from the photoconductor 1. The contact / separation mechanism 60 is configured to allow the developing container 45 to move (rotate) by the biasing force of the pressure spring, thereby allowing the developing roller 41 to contact the photoconductor 1. In this embodiment, when the image forming apparatus 100 is stopped, the developing roller 41 is separated from the photoconductor 1 by the contact / separation mechanism 60. During image formation (development), the developing roller 41 is brought into contact with the photoconductor 1 by the contact / separation mechanism 60. The contact / separation mechanism 60 is driven by a driving force transmitted from a driving unit 80 (FIG. 3) serving as a driving means.

[0039] <Control configuration of image forming apparatus> Next, a description will be given of the control configuration of the image forming apparatus 100 of this embodiment. Fig. 3 is a block diagram showing the control configuration of the main parts of the image forming apparatus 100 of this embodiment.

[0040] The image forming apparatus 100 is provided with a control unit 202 that controls the operation of the image forming apparatus 100. Signals indicating various information are input to and output from the control unit 202 via electrical connections. The control unit 202 processes signals input from various process devices and sensors, and processes signals output to instruct the various process devices to operate. The controller 200 provided in the image forming apparatus 100 inputs and outputs various signals to and from an external device (host device), and inputs and outputs various signals to and from the control unit 202 via an interface 201 provided in the image forming apparatus 100. The control unit 202 comprehensively controls the operation of the image forming apparatus 100 according to a predetermined control program and reference table in response to an instruction from the controller 200.

[0041] The control unit 202 has a CPU 221 as a calculation processing means which is a central element for performing various calculation processes, and a memory 222 such as a RAM, a ROM, a non-volatile memory, etc. which is a storage element for storing information. The RAM temporarily stores the detection results of the sensor, the count results of the counter, the calculation results, etc. The ROM stores a control program, a data table obtained in advance by experiments, etc. The non-volatile memory stores the count results of the counter, various setting information, the results of the sensor, etc. The control unit 202 is connected to each control target, sensor, counter, etc. in the image forming apparatus 100. The control unit 202 controls the input and output of various signals, the timing of driving each unit, etc., and controls a predetermined image formation sequence, etc.

[0042] The control unit 202 controls, for example, the charging power supply 71, the developing power supply 72, the supply power supply 75, the regulating power supply 76, the exposure device 3, the primary transfer power supply 73, the secondary transfer power supply 74, and the drive unit 80. In addition, the control unit 202 controls the contact / separation mechanism 60, the charging current detection unit (charging current detection circuit) 61 that detects the charging current flowing in the charging unit P1 (charging roller 2, charging power supply 71), and the belt contact / separation mechanism 90.

[0043] Although not shown in the figure, in this embodiment, the charging power source 71, the developing power source 72, the supply power source 75, the regulating power source 76, the primary transfer power source 73, the contact / separation mechanism 60, and the charging current detection unit 61 are provided independently for each image forming unit S. Also, the driving unit 80 is configured to have a driving motor as a driving source, a drive transmission member, and the like. The driving sources that drive the photoconductor 1, the intermediate transfer belt 31, the rotating members of the developing device 4, the contact / separation mechanism 60, and the belt contact / separation mechanism 90 may be provided independently, or at least a part of them may be shared. Also, the driving sources that drive the elements for each color may be provided independently, or at least a part of them may be shared.

[0044] Here, the image forming apparatus 100 executes an image forming operation (print job) which is a series of operations for forming and outputting an image on one or more recording materials P, which is started by one start instruction. The image forming operation generally includes an image forming process, a pre-process (pre-rotation process, pre-print operation), a paper-interval process in the case of forming images on multiple recording materials P, and a post-process (post-rotation process, post-print operation). The image forming process is a period during which an electrostatic latent image of an image to be actually formed on a recording material P and output is formed, a toner image is formed, and the toner image is primarily transferred, secondary transferred, and fixed, and the image forming time refers to this period. More specifically, the timing of the image forming time differs depending on the position where each process of charging, exposure, development, primary transfer, secondary transfer, and fixing is performed. The pre-process is a period during which a preparatory operation is performed before the image forming process from when a start instruction is input until the image actually starts to be formed. The paper-interval process is a period corresponding to the period between recording materials P when image formation is performed continuously on multiple recording materials P (continuous image formation). The post-rotation process is a period in which a tidying operation (preparatory operation) is performed after the image forming process. The non-image forming time is a period other than the image forming time, and includes the above-mentioned pre-process, inter-sheet process, post-process, and further the pre-multiple rotation process which is a preparatory operation when the image forming apparatus 100 is turned on or when the image forming apparatus 100 returns from a sleep state.

[0045] <Photoconductor Structure> Next, the photoconductor 1 in this embodiment will be further described.

[0046] The photoreceptor 1 may be a cylindrical drum base made of aluminum, nickel, or the like and a photosensitive material such as OPC (organic photoconductor), amorphous selenium, or amorphous silicon. The photoreceptor 1 may further include a wear-resistant protective layer on the outermost layer to improve wear resistance. By providing a protective layer, the durability of the photoreceptor 1 may be improved. In this embodiment, the photoreceptor 1 is an OPC photoreceptor whose photosensitive layer is made of an organic photoconductor. In this embodiment, the photoreceptor 1 is made of a cylindrical, conductive metallic support having an outer diameter of 24 mm, a conductive layer as an undercoat layer of the support, a photosensitive layer (charge generation layer, charge transport layer) formed on the undercoat layer, and a protective layer formed on the photosensitive layer.

[0047] The protective layer preferably contains conductive particles and / or a charge transport material and a resin. Examples of the conductive particles include particles of metal oxides such as titanium oxide, zinc oxide, tin oxide, and indium oxide. Examples of the charge transport material include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, benzidine compounds, triarylamine compounds, and resins having groups derived from these substances. Among these, triarylamine compounds and benzidine compounds are preferred. Examples of the resin include polyester resins, acrylic resins, phenoxy resins, polycarbonate resins, polystyrene resins, phenolic resins, melamine resins, and epoxy resins. Among these, polycarbonate resins, polyester resins, and acrylic resins are preferred.

[0048] The protective layer may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group. Examples of the reaction include thermal polymerization, photopolymerization, and radiation polymerization. Examples of the polymerizable functional group of the monomer having a polymerizable functional group include an acrylic group and a methacrylic group. A material having a charge transport function may be used as the monomer having a polymerizable functional group.

[0049] The protective layer may also contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, slipping agents, and abrasion resistance improvers. Specific examples of such additives include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, and boron nitride particles.

[0050] The average thickness of the protective layer is preferably 0.5 μm or more and 10 μm or less, and more preferably 1 μm or more and 7 μm or less In this embodiment, the average thickness of the protective layer was set to 3 μm.

[0051] The protective layer can be formed by preparing a coating solution for the protective layer containing the above-mentioned materials and solvent, forming a coating film from the coating solution, and drying and / or curing the coating film. Examples of the solvent used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, sulfoxide-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents.

[0052] <Toner composition> Next, the composition of the toner t will be further described.

[0053] In this embodiment, the toner t is an inorganic particle-added toner in which inorganic silicon is added to the base particles (toner particles) to ensure fluidity and improve charging performance. The toner t used in this embodiment is a non-magnetic one-component granular polymerized toner with a negative charging polarity and an average particle size of 7 μm.

[0054] Furthermore, in this embodiment, in order to control the fluidity and charging performance of the toner t, in addition to inorganic silicon, an external additive consisting of a fatty acid and a metal salt is added to the toner t. Specifically, metal salts of fatty acids such as stearic acid, myristic acid, lauric acid, ricinoleic acid, and octylic acid and metal species such as lithium, magnesium, calcium, barium, and zinc can be mentioned. In this embodiment, zinc stearate is added to the toner t as an external additive. The type of external additive is not limited to this, and lead stearate, cadmium stearate, barium stearate, calcium stearate, aluminum stearate, zinc stearate, magnesium stearate, zinc laurate, and zinc myristate can also be used as appropriate. At least one of the above-mentioned external additives can be selected and used. In this embodiment, zinc stearate with an average particle size of 0.60 μm was used.

[0055] Next, a method for producing the toner particles will be described.

[0056] The toner particles can be produced by a known method, such as a kneading and grinding method or a wet production method. From the viewpoint of uniform particle size and shape controllability, the wet production method is preferred. Furthermore, the wet production method can be a suspension polymerization method, a dissolution suspension method, an emulsion polymerization aggregation method, an emulsion aggregation method, or the like.

[0057] In this embodiment, the suspension polymerization method was adopted. In the suspension polymerization method, first, a polymerizable monomer for producing a binder resin and other additives such as a colorant as required are uniformly dissolved or dispersed using a dispersing machine such as a ball mill or an ultrasonic dispersing machine to prepare a polymerizable monomer composition. This process is called a preparation process of a polymerizable monomer composition. At this time, a multifunctional monomer, a chain transfer agent, a wax as a release agent, a charge control agent, a plasticizer, and the like can be appropriately added as required. As the polymerizable monomer in the suspension polymerization method, the vinyl polymerizable monomers shown below can be suitably exemplified.

[0058] Styrene; styrene derivatives such as α-methylstyrene, β-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, pn-butylstyrene, p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene, p-methoxystyrene, p-phenylstyrene; methyl acrylate, ethyl acrylate, n-propyl acrylate, iso-propyl acrylate, n-butyl acrylate, iso-butyl acrylate, tert-butyl acrylate, n-amyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, n-nonyl acrylate, cyclohexyl acrylate, benzyl acrylate, dimethyl phosphate ethyl acrylate, diethyl phosphate ethyl acrylate, dibutyl phosphate acrylic polymerizable monomers such as ethyl acrylate and 2-benzoyloxyethyl acrylate; methacrylic polymerizable monomers such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, iso-propyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, tert-butyl methacrylate, n-amyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, n-nonyl methacrylate, diethyl phosphate ethyl methacrylate, and dibutyl phosphate ethyl methacrylate; methylene aliphatic monocarboxylic acid esters; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, and vinyl formate; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, and vinyl isobutyl ether; vinyl methyl ketone, vinyl hexyl ketone, and vinyl isopropyl ketone.

[0059] Next, the polymerizable monomer composition is put into a previously prepared aqueous medium, and droplets of the polymerizable monomer composition are formed into a desired toner particle size by a stirrer or disperser having high shear force. This process is called a granulation process. It is preferable that the aqueous medium in the granulation process contains a dispersion stabilizer in order to control the particle size of the toner particles, to sharpen the particle size distribution, and to suppress the coalescence of toner particles during the manufacturing process. Dispersion stabilizers are generally broadly classified into polymers that exhibit repulsive force due to steric hindrance and poorly water-soluble inorganic compounds that stabilize dispersion by electrostatic repulsive force. Fine particles of poorly water-soluble inorganic compounds are preferably used because they dissolve in acid or alkali and can be easily removed by washing with acid or alkali after polymerization.

[0060] As the dispersion stabilizer of the poorly water-soluble inorganic compound, one containing any one of magnesium, calcium, barium, zinc, aluminum, and phosphorus is preferably used. It is more preferable that one of magnesium, calcium, aluminum, and phosphorus is contained. Specifically, the following can be mentioned.

[0061] Magnesium phosphate, tricalcium phosphate, aluminum phosphate, zinc phosphate, magnesium carbonate, calcium carbonate, magnesium hydroxide, calcium hydroxide, aluminum hydroxide, calcium metasilicate, calcium sulfate, barium sulfate, hydroxyapatide.

[0062] The above dispersion stabilizer may be used in combination with an organic compound such as polyvinyl alcohol, gelatin, methyl cellulose, methylhydroxypropyl cellulose, ethyl cellulose, sodium salt of carboxymethyl cellulose, or starch. These dispersion stabilizers are preferably used in an amount of 0.01 to 2.00 parts by mass per 100 parts by mass of the polymerizable monomer.

[0063] Furthermore, in order to make these dispersion stabilizers finer, a surfactant may be used in an amount of 0.001 to 0.1 parts by mass relative to 100 parts by mass of the polymerizable monomer. Specifically, commercially available nonionic, anionic, and cationic surfactants can be used. For example, sodium dodecyl sulfate, sodium tetradecyl sulfate, sodium pentadecyl sulfate, sodium octyl sulfate, sodium oleate, sodium laurate, potassium stearate, and calcium oleate are preferably used.

[0064] After or during the granulation step, the temperature is preferably set to 50° C. or more and 90° C. or less to polymerize the polymerizable monomer contained in the polymerizable monomer composition, thereby obtaining a toner particle dispersion. This step is called the polymerization step. In the polymerization step, it is preferable to perform a stirring operation so that the temperature distribution in the container is uniform. When a polymerization initiator is added, it can be added at any timing and for any required time. In addition, the temperature may be raised in the latter half of the polymerization reaction in order to obtain a desired molecular weight distribution, and further, in order to remove unreacted polymerizable monomers, by-products, etc. from the system, a part of the aqueous medium may be distilled off by a distillation operation in the latter half of the reaction or after the reaction is completed. The distillation operation can be performed under normal pressure or reduced pressure.

[0065] In the suspension polymerization method, an oil-soluble initiator is generally used as the polymerization initiator. Examples of the initiator include the following:

[0066] azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 1,1'-azobis(cyclohexane-1-carbonitrile), and 2,2'-azobis-4-methoxy-2,4-dimethylvaleronitrile; peroxide initiators such as acetylcyclohexylsulfonyl peroxide, diisopropyl peroxycarbonate, decanonyl peroxide, lauroyl peroxide, stearoyl peroxide, propionyl peroxide, acetyl peroxide, tert-butyl peroxy-2-ethylhexanoate, benzoyl peroxide, tert-butyl peroxyisobutyrate, cyclohexanone peroxide, methyl ethyl ketone peroxide, dicumyl peroxide, tert-butyl hydroperoxide, di-tert-butyl peroxide, tert-butyl peroxypivalate, and cumene hydroperoxide.

[0067] The polymerization initiator may be used in combination with a water-soluble initiator as necessary. Examples of the water-soluble initiator include the following.

[0068] Ammonium persulfate, potassium persulfate, 2,2'-azobis(N,N'-dimethyleneisobutyromidine) hydrochloride, 2,2'-azobis(2-aminodinopropane) hydrochloride, azobis(isobutylamidine) hydrochloride, 2,2'-azobisisobutyronitrile sodium sulfonate, ferrous sulfate, or hydrogen peroxide.

[0069] These polymerization initiators can be used alone or in combination of two or more. In order to control the degree of polymerization of the polymerizable monomer, a chain transfer agent, a polymerization inhibitor, etc. can also be further added.

[0070] The toner t may contain an organosilicon polymer, and the organosilicon polymer may have 1 to 3 carbon atoms directly bonded to the silicon atom. 3 / 2 Here, R may be a hydrocarbon group having 1 to 6 carbon atoms, or R may be a hydrocarbon group having 1 to 3 carbon atoms.

[0071] The amount of inorganic silica transferred by washing with water was controlled by changing the external addition conditions, that is, the amount of external addition, the rotation speed (circumferential speed) of the tip of the blade, and the time (hours) during which the blade rotates, using a Henschel mixer (manufactured by Nippon Coke & Engineering Co., Ltd.) as a surface modification device. The external addition conditions of toner t in this embodiment are shown in Table 1 below. Details of the surface modification device and the external addition conditions, that is, the peripheral speed and time of the surface modification device, are as described in JP 2016-38591 A. In addition, 0.20 wt % of zinc stearate was externally added to the toner t used in this embodiment.

[0072] [Table 1]

[0073] <Method of determining toner charging performance based on detection of charging current> Next, a method of determining the charging performance of the toner based on detection of the charging current in this embodiment will be described.

[0074] FIG. 4 is a graph showing an example of the measurement result of the charging current before and after refilling the developing device 4 of the process cartridge 7 with new toner outside the main body 110 of the image forming apparatus 100 having the configuration of this embodiment. The charging current was measured in a process prior to the printing operation. The charging current value I before refilling with new toner A (Dotted line) vs. charging current value I after refilling with new toner B It can be seen that is increasing.

[0075] The mechanism by which the charging current value increases as described above will be described with reference to FIG. 5. FIG. 5 is a schematic diagram of the developing section P3 where the photoconductor 1 and the developing roller 41 come into contact with each other. In the developing section P3, the photoconductor 1 and the developing roller 41 come into contact with each other via the toner t. As shown in FIG. 5, the negative charge e on the photoconductor 1 usually moves to the developing roller 41 via the toner t, but when there is an abundant amount of external additive with high charging performance on the surface, such as in the case of new toner, the amount of movement of the negative charge e also increases, and the negative charge e on the photoconductor 1 decreases. As a result, on the downstream side of the developing section P3 in the rotation direction of the photoconductor 1, the surface potential of the photoconductor 1 becomes smaller than -500V when it reaches the developing section P3. Therefore, when the surface of the photoconductor 1 next passes through the charging section P1, it becomes necessary to recharge it more, and the charging current becomes larger. By detecting the change in this charging current, it is possible to detect whether the charging performance (charge amount) of the toner has changed.

[0076] <Control procedure of image formation conditions based on detection of charging current> Next, the control of the image forming conditions based on the detection of the charging current in this embodiment will be described. Fig. 6 is a flow chart showing an outline of the procedure for controlling the image forming conditions based on the detection of the charging current in this embodiment. In this embodiment, the control of the image forming conditions based on the detection of the charging current, which will be described using Fig. 6, is executed for each image forming unit S, but here, the description will be focused on one image forming unit S.

[0077] As described above, for example, when the developing device 4 is replenished with new toner and the charging performance of the toner in the developing device 4 is improved, the charge amount per toner particle increases, so the number of toner particles required to fill the latent image potential decreases. As a result, this may become apparent as low density.

[0078] Therefore, in this embodiment, when it is determined based on the detection result of the charging current that the charging performance of the toner in the developing device 4 has improved, the control unit 202 controls to increase the development contrast. Particularly, in this embodiment, the control unit 202 controls to increase the development contrast by changing the development bias Vdc. In this embodiment, the detection operation to detect the charging current is performed in the pre-process of the printing operation. In this embodiment, the detection operation to detect the charging current is performed using the charging current detection unit 61 before the printing operation every time a printing operation is performed, and the detection result of the charging current value is stored in the storage unit (or memory 222) in the charging current detection unit 61.

[0079] First, when a print signal is input from an external device via the controller 200 and the interface 201 (S101), the control unit 202 starts the pre-process (S102). Next, the control unit 202 reads the previous charging current value I from the storage unit (or memory 222) in the charging current detection unit 61. A The control unit 202 then reads the detection result (S103). Next, the control unit 202 applies a charging voltage to the charging roller 2 by the charging power source 71 to charge the surface of the photoconductor 1 to -500 V, and applies a developing bias of -300 V to the developing roller 41 by the developing power source 75 (S104). Next, the control unit 202 starts rotating the photoconductor 1 and the developing roller 41 (S105). Next, the control unit 202 brings the developing roller 41 into contact with the photoconductor 1 (S106). Thereafter, the control unit 202 detects the charging current for a predetermined time (2 seconds in this embodiment) by the charging current detection unit 61 (S107), and determines the current charging current value I BThe control unit 202 detects the charging current by the charging current detection unit 61 for the above-mentioned predetermined time from when the surface of the photoconductor 1, which was in the development unit P3 when the development roller 41 contacted the charged surface of the photoconductor 1, first reaches the charging unit P1. Then, the control unit 202 stores the average value of the charging current detected at a predetermined sampling interval within the predetermined time in the storage unit (or memory 222) in the charging current detection unit 61 as the detection result of the current charging current value. The predetermined time for detecting the charging current can be appropriately set so that the charging current can be detected with a desired accuracy. The predetermined time for detecting the charging current is preferably, for example, 1 second or more and 5 seconds or less. Note that the photoconductor 1 and the intermediate transfer belt 31 are separated from each other while the charging current is being detected (while the surface of the photoconductor 1 passing through the charging unit P1 when detecting the charging current is passing through the primary transfer unit P4). Also, while the charging current is being detected (while the surface of the photoconductor 1 passing through the charging section P1 is passing through the pre-exposure section P5 when the charging current is being detected), pre-exposure by the pre-exposure device 6 is turned off.

[0080] Then, the control unit 202 determines the current charging current value I B Detection result and previous charging current value I A The difference between the detection result and the B -I A It is determined whether the difference between the charging current values ​​(=I B -I A ) is equal to or greater than the above-mentioned threshold (I B I A When the difference between the charging current values ​​is greater than the predetermined value by more than a predetermined value, it can be determined that the charging performance of the toner t has improved. In this embodiment, the predetermined threshold value is set to 1.0 μA. However, the threshold value of the difference between the charging current values ​​is not limited to the value in this embodiment, and can be set appropriately depending on the device configuration, the required accuracy, etc.

[0081] In step S109, the control unit 202 calculates the difference in the charging current values ​​(=I B -I AIf it is determined that the difference between the charging current values ​​(=I) in S109 is equal to or greater than the predetermined threshold, the developing bias applied to the developing roller 41 by the developing power supply 72 is changed from -300V to -350V so as to increase the developing contrast in order to suppress low density caused by new toner (S110). After that, the control unit 202 ends the pre-process (S111) and starts image formation (S112). Also, the control unit 202 determines the difference between the charging current values ​​(=I) in S109. B -I A If it is determined that the difference between the development contrast and the image forming time is not equal to or greater than the predetermined threshold (is less than the predetermined threshold), the development contrast is not changed, the previous process is ended (S111), and image formation is started (S112).

[0082] <Modification> The method of changing the development contrast to suppress low density is not limited to changing the development bias. 2 The development contrast can also be increased by increasing the charging bias and decreasing the light area potential Vl after exposure. The development contrast can also be increased by decreasing the charging bias and decreasing the light area potential Vl after exposure. Control of the development bias, the amount of laser light of the exposure device 3, and the charging bias may be arbitrarily combined.

[0083] In this embodiment, I A and I B Difference between (=I B -I A ) was used to change the image forming conditions (development contrast). A and I B Difference between (=I B -I A ) is equal to or greater than a certain threshold (I B I A It was determined that the charging performance of the toner was improved when the difference between the chargeability and the chargeability of the toner was greater than the difference between the chargeability and the chargeability of the toner. However, the present invention is not limited to this embodiment. A and I B For example, I B I A Ratio to (I B / IA It may be determined that the charging performance of the toner is improved when the chargeability of the toner is equal to or higher than a predetermined value. A and I B Compare the magnitude relationship with I B I prefer A If the difference is larger than 0.1, it may be determined that the charging performance of the toner is improved.

[0084] In addition, in this embodiment, an example has been described in which new toner is replenished to the developing device 4, but when toner is replenished to the developing device 4, regardless of whether the toner is new or not, the same control as in this embodiment can be applied to obtain the same effect as in this embodiment.

[0085] In addition, in this embodiment, as a typical example, a case where the charging performance of the toner in the developing device 4 is increased by replenishing the toner in the developing device 4 has been described, but the present invention is not limited to such an embodiment. A case where the charging performance of the toner in the developing device 4 is decreased by replenishing the toner in the developing device 4 can also be assumed. Depending on the characteristics (composition of the toner particles, formulation of external additives, etc.) and state of the toner replenishing the developing device 4, the charging performance of the toner in the developing device 4 after the toner is replenishing may be decreased. When the charging performance of the toner in the developing device 4 is decreased, for example, a phenomenon such as image density becoming too high may occur. Therefore, the control unit 202 may change the image forming conditions (development contrast) when it is determined that the charging performance of the toner in the developing device 4 is decreased based on the detection result of the charging current in addition to or instead of when it is determined that the charging performance of the toner in the developing device 4 is increased based on the detection result of the charging current. For example, when I A and I B Difference between (=I B -I A ) is below a certain negative threshold (I A I BThe development contrast can be reduced when the development contrast is greater than the predetermined value. The development contrast can be reduced by reducing the development bias, reducing the amount of laser light from the exposure device 3 to increase the light area potential Vl, or increasing the charging bias to increase the light area potential Vl after exposure. Control of the development bias, the amount of laser light from the exposure device 3, and the charging bias may be combined arbitrarily. Also, in this case, as in the above, I A and I B It is enough to compare and find the magnitude relationship between the two. A and I B The present invention is not limited to control based on the difference between the

[0086] In addition, in this embodiment, the image forming conditions (development contrast) are switched between two stages based on the detection result of the charging current, but the present invention is not limited to this embodiment. A and I B Depending on the result of the comparison, the image forming conditions (development contrast) may be changed in three or more stages. For example, A and I B Difference between (=I B -I A The larger the development contrast, the greater the contrast. In this case, for example, I A and I B Difference between (=I B -I A By previously setting information indicating the relationship between the color density (color density) and the development contrast as table data or by providing a plurality of threshold values, the development contrast can be changed in three or more stages.

[0087] Furthermore, the charging current value is not limited to being compared with the previous detection result. The current detection result of the charging current value can be compared with the previous detection result of the charging current value (detection results from a number of times before, previous detection results, an average value of previous detection results, etc.) as long as it is possible to detect that toner has been replenished with a desired degree of accuracy.

[0088] <Effects> In this embodiment, the image forming apparatus 100 includes a rotatable photoconductor 1, a charging member (charging roller) 2 that contacts the photoconductor 1 to form a charging portion P1 and charges the surface of the rotating photoconductor 1, a charging voltage application portion (charging power source) 71 that applies a charging voltage to the charging member 2, an exposure device 3 that exposes the surface of the photoconductor 1 charged by the charging member 2 to form an electrostatic latent image on the surface of the photoconductor 1, a rotatable developing member (developing roller) 41 that forms a developing portion P3 capable of supplying a developer to the surface of the photoconductor 1, and supplies a developer charged to a predetermined polarity to the electrostatic latent image on the surface of the photoconductor 1 in the developing portion P3 to form a developer image on the surface of the photoconductor 1, and The developing device 4 has a developer storage section (toner storage chamber) 45b that stores the developer to be supplied to the developing member 41, a developing voltage application section (developing power source) 72 that applies a developing voltage of the specified polarity side to the potential of the electrostatic latent image in the developing section P3 to the developing member 41, a charging current detection section 61 that detects the charging current that flows through the charging section P1 when the surface of the photoconductor 1 is charged by the charging member 2, and a control section 202 that can control the charging voltage application section 71, the exposure device 3 and the developing voltage application section 72, and performs an image forming operation that forms the developer image on the surface of the photoconductor 1, and a non-image forming operation that does not form the developer image on the surface of the photoconductor 1. In this embodiment, the control unit 202 can control the charging current detection unit 61 to execute a detection operation for detecting a charging current when the surface of the photoconductor 1, which has been charged by the charging member 2 and then passed through the development unit P3, passes through the charging unit P1 during a non-image forming operation. The control unit 202 can control the charging current detection unit 61 to execute a detection operation for detecting a charging current when the surface of the photoconductor 1, which has been charged by the charging member 2 and then passed through the development unit P3, passes through the charging unit P1. The control unit 202 can control the charging current value I A and the charging current value I detected by the above detection operation. B Based on the above, the control unit 202 controls at least one of the charging voltage application unit 71, the exposure device 3, and the development voltage application unit 72 so as to change the development contrast, which is the potential difference between the potential of the electrostatic latent image in the development unit P3 and the development voltage. A Above I B is larger, at least one of the charging voltage application unit 71, the exposure device 3, and the developing voltage application unit 72 is controlled so as to increase the absolute value of the developing contrast.B The above I A When the absolute value of the development contrast is greater than or equal to a predetermined value, the control unit 202 controls at least one of the charging voltage application unit 71, the exposure device 3, and the development voltage application unit 72 so as to increase the absolute value of the development contrast. A Above I B is smaller, at least one of the charging voltage application section 71, the exposure device 3, and the developing voltage application section 72 may be controlled so as to reduce the absolute value of the developing contrast.

[0089] In this embodiment, the control unit 202 executes the above-mentioned detection operation during a non-image forming operation prior to the first image forming operation in the print operation every time the control unit 202 executes a print operation, which is a series of operations for forming an image on one or more recording materials P. A is the charging current value detected by the previous detection operation. In this embodiment, the developing device 4 is detachable from the main body 110 of the image forming apparatus 100. Particularly in this embodiment, a unit (process cartridge) 7 having the photoconductor 1 and the developing device 4 is detachable as a whole from the main body 110 of the image forming apparatus 100. In this embodiment, the developing member 41 comes into contact with the surface of the photoconductor 1 to form the developing portion P3.

[0090] As described above, according to this embodiment, by capturing the change in the charging performance of the toner in the developing device 4, it is possible to suppress the occurrence of low density due to the change in the charging performance of the toner. As a result, even if new toner is replenished to the developing device 4 outside the device main body 110 by refilling, for example, the occurrence of low density can be suppressed by changing the image forming conditions (developing contrast) according to the charging performance of the toner in the developing device 4. In addition, a means for detecting the charging current may be provided in the image forming device in the past for the purpose of controlling the charging voltage, for example. Therefore, according to this embodiment, the need to provide a new power source or circuit in the image forming device 100 is reduced, and the above-mentioned effect can be obtained with a simple configuration.

[0091] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, the same or corresponding elements as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those of embodiment 1, and detailed explanations are omitted.

[0092] <Outline of this Example> In the first embodiment, a control for suppressing low density caused by refilling new toner into the developing device 4 is described. In the present embodiment, a control for suppressing step unevenness caused by refilling new toner into the developing device 4 is described.

[0093] 7 is a graph showing an example of the relationship between the intrusion amount of the developing roller 41 into the photoconductor 1 and the charging current value. The figure shows the above relationship when the ratio of the circumferential speed (surface movement speed) of the developing roller 41 to the circumferential speed (surface movement speed) of the photoconductor 1 (hereinafter also referred to as the "DD circumferential speed ratio") is 115% and 144%. The DD circumferential speed ratio is expressed by the following formula: (circumferential speed of the developing roller / circumferential speed of the photoconductor)×100. The intrusion amount of the developing roller 41 into the photoconductor 1 (herein also referred to simply as the "intrusion amount") can be expressed by the amount by which the elastic layer of the developing roller 41 is depressed by the photoconductor 1.

[0094] From Fig. 7, it can be seen that when the intrusion amount is large, the charging current value becomes large (the surface potential of the photoconductor 1 is likely to decrease), and when the intrusion amount is small, the charging current value becomes small (the surface potential of the photoconductor 1 is less likely to decrease). Also, from Fig. 7, it can be seen that the larger the DD peripheral speed ratio, the greater the tendency for the charging current value to become large when the intrusion amount is large, as described above.

[0095] The mechanism by which the change in the charging current value due to the intrusion amount as described above occurs will be described with reference to FIG. 5. When the intrusion amount is large, the rotational force of the toner t increases, and the frictional charging force between the toner t and the photoconductor 1 increases, so that the negative charge e on the surface of the photoconductor 1 is more likely to move to the developing roller 41. On the other hand, when the intrusion amount is small, the rotational force of the toner t decreases, and the frictional charging force between the toner t and the photoconductor 1 decreases, so that the negative charge e on the surface of the photoconductor 1 is less likely to move to the developing roller 41. As a result, when the intrusion amount is large, the degree to which the surface potential of the photoconductor 1 is reduced downstream of the developing unit P3 in the rotation direction of the photoconductor 1 increases as described in the first embodiment, and the charging current when the photoconductor 1 is next recharged increases. On the other hand, when the intrusion amount is small, the degree to which the surface potential of the photoconductor 1 is reduced downstream of the developing unit P3 in the rotation direction of the photoconductor 1 decreases as described in the first embodiment, so that the charging current when the photoconductor 1 is next recharged decreases.

[0096] From this relationship, if the intrusion amount changes due to the deviation of the outer diameter of the developing roller 41, the surface potential of the photoconductor 1 changes in the developing portion P3, and this tends to become evident as step unevenness, which is a development unevenness that occurs with the rotation period of the developing roller 41. And, the larger the DD circumferential speed ratio, the higher the rotation force of the toner and the easier it is for the negative charge e on the surface of the photoconductor 1 to move to the developing roller 41, so the step unevenness becomes more noticeable. In other words, it can be seen that reducing the DD circumferential speed ratio is effective in suppressing step unevenness. In particular, since new toner has the effect of increasing the amount of negative charge movement, it is effective to reduce the DD circumferential speed ratio when refilling with new toner.

[0097] Therefore, in this embodiment, when it is determined that the charging performance of the toner in the developing device 4 has improved based on the detection result of the charging current, the control unit 202 controls the DD peripheral speed ratio to be smaller.

[0098] <Configuration of the image forming apparatus according to this embodiment> Fig. 8 is a block diagram showing a control configuration of the main parts of the image forming apparatus 100 of this embodiment. The control configuration of the image forming apparatus 100 of this embodiment shown in Fig. 8 is generally similar to the control configuration of the image forming apparatus 100 of the first embodiment shown in Fig. 3. In this embodiment, the image forming apparatus 100 further includes a speed change unit (speed change circuit) 62 that variably controls the rotation speed of the developing roller 41. Although not shown in the figure, in this embodiment, the speed change unit 62 is provided independently for each image forming unit S.

[0099] The speed change unit 62 can variably control the rotation speed of the developing roller 41 so as to change the DD circumferential speed ratio in the range of 100% to 150%. In this embodiment, the default setting of the DD circumferential speed ratio when the apparatus main body 110 and the process cartridge 7 are in a new state is 144%. This is because the developing roller 41 is rotated faster than the photoconductor 1 so that a large amount of toner can be supplied to the photoconductor 1. In contrast, if the amount of toner placed on the developing roller 41 is increased, there is a concern that a regulation failure occurs in which the charge imparted to the toner by the developing blade 43 becomes insufficient, and fogging (a phenomenon in which toner adheres to non-image areas) occurs. Therefore, it is desirable not to increase the amount of toner placed on the developing roller 41 in order to increase the amount of toner supplied to the photoconductor 1. In this embodiment, when it is determined that new toner has been replenished based on the change in the charging performance of the toner based on the detection result of the charging current, the speed change unit 62 changes the DD circumferential speed ratio from 144% to 115%. This is because, based on the relationship between the DD circumferential speed ratio and the likelihood of occurrence of step unevenness explained using Figure 7, the DD circumferential speed ratio is reduced to suppress changes in the surface potential of the photoconductor 1, thereby suppressing step unevenness.

[0100] <Control procedure of image formation conditions based on detection of charging current> Fig. 9 is a flow chart showing an outline of the procedure for controlling the image forming conditions based on the detection of the charging current in this embodiment. In this embodiment, the control of the image forming conditions based on the detection of the charging current described with reference to Fig. 9 is executed for each image forming unit S, but here, the description focuses on one image forming unit S. In the control procedure of this embodiment shown in Fig. 9, the description of the same processes as those in the control procedure of embodiment 1 shown in Fig. 6 will be omitted as appropriate.

[0101] 9 are the same as the processes of S101 to S109 in FIG 6. In this embodiment, the control unit 202 calculates the difference in the charging current value (=I B -I A ) is equal to or greater than a certain threshold (I B I A If the difference is greater than a predetermined value, the rotation speed of the developing roller 41 is changed so that the DD peripheral speed ratio is changed from 144% to 115% in order to suppress step unevenness caused by new toner (S210). After that, the control unit 202 ends the pre-process (S211) and starts image formation (S212). Also, the control unit 202 determines the difference in charging current value (=I B -I A ) is not equal to or greater than the predetermined threshold (is less than the predetermined threshold), the rotation speed of the developing roller 41 is not changed, the previous process is ended (S211), and image formation is started (S212).

[0102] In addition, the present embodiment can also be modified in the same manner as the modified example described in the first embodiment. For example, the control unit 202 may change the image forming conditions (DD peripheral speed ratio) when it is determined that the charging performance of the toner in the developing device 4 has decreased based on the detection result of the charging current in addition to or instead of when it is determined that the charging performance of the toner in the developing device 4 has increased based on the detection result of the charging current. In this case, for example, A and I B Difference between (=I B -I A ) is below a certain negative threshold (I A I BIn addition, when I is larger than a predetermined value, the DD peripheral speed ratio can be increased. A and I B Difference between (=I B -I A The DD peripheral speed ratio may be changed in three or more stages so that the DD peripheral speed ratio decreases as the DD peripheral speed ratio increases.

[0103] In this embodiment, only the DD peripheral speed ratio is changed based on the detection of the charging current, but in addition to this, the development contrast may be changed based on the detection of the charging current as in the first embodiment. For example, A and I B Difference between (=I B -I A When I is equal to or greater than a predetermined threshold, the development contrast can be increased and the DD peripheral speed ratio can be reduced. A and I B Difference between (=I B -I A When the difference (x,y) is equal to or less than a predetermined threshold value which is a negative value, the development contrast can be reduced and the DD peripheral speed ratio can be increased.

[0104] In addition, in this embodiment, the change in the charge amount of the toner has been described with a focus on the replenishment of new toner, but the present invention is not limited to this, and control can be performed in response to changes such as replacement of the photoconductor 1. If the photoconductor 1 is replaced with a new one, a large current flows because the new photoconductor 1 has low electrical resistance, and as a result, the photoconductor 1 becomes susceptible to the influence of the runout of the outer diameter (change in the amount of penetration) of the developing roller 41. Therefore, for example, in accordance with this embodiment, when the charging current increases and it is determined that the photoconductor 1 has been replaced, the DD peripheral speed ratio can be reduced. This makes it possible to suppress step unevenness.

[0105] In addition, in this embodiment, the rotation speed of the developing roller 41 is changed to change the DD circumferential speed ratio, but the rotation speed of the photoconductor 1 may be changed to change the DD circumferential speed ratio in the same manner as in this embodiment. In this case, the speed change unit 62 is configured to variably control the rotation speed of the photoconductor 1. In addition, both the rotation speed of the developing roller 41 and the rotation speed of the photoconductor 1 may be changed to change the DD circumferential speed ratio in the same manner as in this embodiment. In this case, the speed change unit 62 is configured to variably control the rotation speed of the developing roller 41 and the rotation speed of the photoconductor 1.

[0106] Thus, in this embodiment, the image forming apparatus 100 has a speed change unit 62 that changes the rotation speed of the developing member 41, and a control unit 202 that can control the charging voltage application unit 71 and the speed change unit 62. In this embodiment, the control unit 202 can control the charging current detection unit 61 to execute a detection operation to detect the charging current when the surface of the photoconductor 1 that has been charged by the charging member 2 and then passed through the developing unit P3 passes through the charging unit P1 during a non-image forming operation, and the control unit 202 detects the charging current value I detected by the detection operation prior to the current detection operation. A and the charging current value I detected by the above detection operation. B Based on the above, the control unit 202 can control the speed changing unit 62 to change the peripheral speed ratio (DD peripheral speed ratio) which is the ratio of the peripheral speed of the developing member 41 to the peripheral speed of the photoconductor 1. A Above I B is larger, the speed change unit 62 is controlled to reduce the peripheral speed ratio. B The above I A When the peripheral speed ratio is greater than the predetermined value by more than a predetermined value, the control unit 202 controls the speed change unit 62 so as to reduce the peripheral speed ratio. A Above I B is smaller, the speed change unit 62 may be controlled to increase the peripheral speed ratio.

[0107] As described above, according to this embodiment, it is possible to suppress the occurrence of step unevenness due to the change in the charging performance of the toner by capturing the change in the charging performance of the toner in the developing device 4. As a result, even if new toner is replenished to the developing device 4 outside the apparatus main body 110 by refilling or the like, the occurrence of step unevenness can be suppressed by changing the image formation conditions (DD peripheral speed ratio) according to the charging performance of the toner in the developing device 4.

[0108] [Example 3] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, the same or corresponding elements as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those of embodiment 1, and detailed explanations are omitted.

[0109] <Outline of this Example> In the first embodiment, a description is given of the control for suppressing low density caused by refilling new toner into the developing device 4. In the present embodiment, a description is given of a configuration for detecting with higher accuracy that new toner has been refilled into the developing device 4.

[0110] <Configuration of the image forming apparatus according to this embodiment> Fig. 10 is a block diagram showing a control configuration of a main part of the image forming apparatus 100 of this embodiment. The control configuration of the image forming apparatus 100 of this embodiment shown in Fig. 10 is generally similar to the control configuration of the image forming apparatus 100 of the embodiment 1 shown in Fig. 3. Furthermore, in this embodiment, the image forming apparatus 100 has a toner remaining amount detection unit (toner remaining amount detection circuit) 63 as a developer amount detection means capable of detecting the amount of toner remaining as the developer amount in the toner storage chamber 45b of the developing device 4. Although not shown in the figure, in this embodiment, the toner remaining amount detection unit 63 is provided independently for each image forming unit S.

[0111] In addition, the toner remaining amount detection unit 63 in this embodiment can detect whether or not toner has been replenished in real time. The detection result by the toner remaining amount detection unit 63 is stored in a storage unit (or memory 222) in the toner remaining amount detection unit 63.

[0112] The developer remaining amount detection method of the toner remaining amount detection unit 63 may be, for example, a known method. The developer remaining amount detection method may be, for example, any available method such as a capacitance method or a light transmission method. The capacitance method is a method of acquiring information on the amount of developer using an electrode whose detected capacitance changes according to a change in the amount of developer inside the developing device. The light transmission method is a method of acquiring the amount of developer based on a change in the light receiving state (presence or absence of light reception, amount of light reception, time of light reception, etc.) of the light receiving unit using a light source that irradiates light into the inside of the developing device and a light receiving unit that receives the light that has passed through the inside of the developing device. In addition, a weight detection method that acquires information on the amount of developer based on a change in the weight of the developing device may also be used.

[0113] <Control procedure of image forming conditions based on detection of remaining toner amount and detection of charging current> The control of image forming conditions based on the detection of remaining toner amount and the detection of charging current in this embodiment will be described. Fig. 11 is a flow chart showing an outline of the procedure for controlling image forming conditions based on the detection of remaining toner amount and the detection of charging current in this embodiment. In this embodiment, the control described using Fig. 11 is executed for each image forming unit S, but here, the description will be focused on one image forming unit S. In the control procedure of this embodiment shown in Fig. 11, the description of the same processes as those in the control procedure of embodiment 1 shown in Fig. 6 will be omitted as appropriate.

[0114] First, when a print signal is input from an external device via the controller 200 and the interface 201 (S301), the control unit 202 starts the pre-process (S302). Next, the control unit 202 acquires the detection result of the toner remaining amount detection unit 63 (S303), and determines whether or not toner has been replenished to the developing device 4 based on the previous detection result and the current detection result (S304). Specifically, when the amount of toner remaining in the developing device 4 increases by a predetermined value or more, it can be determined that toner has been replenished to the developing device 4. Note that the toner remaining amount detection unit 63 may input a toner replenishment signal to the control unit 202 when it detects that toner has been replenished to the developing device 4.

[0115] Next, if the control unit 202 determines in S304 that toner has been replenished in the developing device 4, the process proceeds to S305. That is, the process proceeds to control the image forming conditions (developing contrast) based on detection of the charging current, similar to the first embodiment. On the other hand, if the control unit 202 determines in S304 that toner has not been replenished in the developing device 4, the process proceeds to S313. That is, detection of the charging current for controlling the image forming conditions (developing contrast) is omitted. The processes of S305 to S314 in FIG. 11 are the same as the processes of S103 to S112 in FIG. 6. However, in this embodiment, the previous charging current value I A The detection result is, for example, a detection result of a previous charging current value that is detected at a predetermined frequency and stored in a storage unit (or memory 222) in the charging current detection unit 61. Alternatively, for example, the charging current value is detected in each pre-process as in the first embodiment, and the charging current value I B I A Only when the toner remaining amount detection unit 63 detects an increase in the amount of toner, and the toner remaining amount detection unit 63 detects an increase in the amount of toner, the image forming conditions (development contrast) may be changed.

[0116] In this embodiment, as in the case of embodiment 1, an example has been described in which control is performed to suppress low density caused by replenishment of new toner. However, the present embodiment is not limited to this, and can also be applied to a case in which control is performed to suppress step unevenness caused by replenishment of new toner, as in the case of embodiment 2. Furthermore, as described in embodiment 2, this embodiment can also be applied to a case in which low density and step unevenness caused by replenishment of new toner are suppressed.

[0117] Also, for example, in a toner replenishment configuration described later, it may be possible to detect in real time that toner has been replenished to the developing device 4. Then, for example, when it is detected that toner has been replenished during continuous image formation, it may be possible to change image formation conditions (development contrast, DD peripheral speed ratio) in the inter-sheet process, etc.

[0118] In this manner, in this embodiment, a developer amount detection unit (toner remaining amount detection unit) 63 is provided for detecting the amount of toner in the developer storage unit (toner storage chamber) 45b, and when an increase in the amount of toner in the developer storage unit is detected by the developer amount detection unit 63, the control unit 202 detects the charging current value I detected by the detection operation of the charging current value before the increase in the toner amount was detected. A and the charging current value I detected by the above detection operation after the increase in the toner amount is detected. B Based on this, control is performed to change the image forming conditions (development contrast, DD peripheral speed ratio).

[0119] As described above, according to this embodiment, it is possible to more reliably detect when toner has been replenished and further capture the change in the charge amount of the toner, thereby more reliably suppressing the occurrence of low concentration, unevenness in steps, etc., caused by changes in the charging performance of the toner.

[0120] [Example 4] Next, another embodiment of the present invention will be described. In the image forming apparatus of this embodiment, the same or corresponding elements as those in the image forming apparatus of the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof will be omitted.

[0121] In the above embodiment, the case where toner is replenished to the developing device 4 outside the apparatus main body 110 has been described. However, the present invention is not limited to such an embodiment, and can also be applied to a case where toner is replenished to the developing device 4 inside the apparatus main body 110.

[0122] 12 is a schematic cross-sectional view of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a monochrome laser printer capable of forming a black monochrome image on a sheet-shaped recording material P by using an electrophotographic method.

[0123] The photoconductor (photosensitive drum) 1 is rotated in the direction of the arrow R1 in FIG. 12 (counterclockwise direction). The surface of the rotating photoconductor 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by the charging roller 2. The charged surface of the photoconductor 1 is scanned and exposed by the exposure device (scanner unit) 3, and an electrostatic latent image (electrostatic image) is formed on the photoconductor 1. The electrostatic latent image formed on the photoconductor 1 is developed (visualized) by the developing device 4 by supplying toner as a developer, and a toner image is formed on the photoconductor 1. The developing device 4 is configured to include a developing roller 41, a supply roller 42, a developing blade 43, a toner conveying member 44, a developing container 45 (developing chamber 45a, toner storage chamber 45b), and the like. The developing container 45 contains toner t, which is a non-magnetic one-component developer. In this embodiment, the normal charging polarity of the toner t, which is the main charging polarity of the toner t during development, is negative polarity.

[0124] A transfer roller 15, which is a roller-type transfer member serving as a transfer means, is disposed opposite the photoreceptor 1. The transfer roller 15 contacts the photoreceptor 1 with a predetermined contact pressure to form a transfer section N. The toner image formed on the photoreceptor 1 is transferred to a recording material P, which is sandwiched between the photoreceptor 1 and the transfer roller 15 and conveyed in the transfer section N. At the time of transfer, a predetermined transfer voltage (transfer bias), which is a DC voltage of a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment), is applied to the transfer roller 15. The recording material P is stored in a cassette 10, and is sent out of the cassette 10 by a feed roller 11 or the like and conveyed to a registration roller 12. The recording material P is conveyed to the transfer section N by the registration roller 12 in synchronization with the toner image on the photoreceptor 1. The recording material P to which the toner image has been transferred is conveyed to a fixing device 13, and after the toner image is fixed, it is discharged (output) onto a tray 14 provided outside the device main body 110.

[0125] On the other hand, the toner (transfer residual toner) remaining on the photoconductor 1 without being transferred to the recording material P during the transfer process is removed from the photoconductor 1 as follows. The surface of the photoconductor 1 after the transfer process is pre-exposed by the pre-exposure device 6 and is de-electrified. The transfer residual toner is negatively charged by discharge in the charging section. The transfer residual toner negatively charged in the charging section reaches the developing section as the photoconductor 1 rotates. Then, the transfer residual toner adhering to the non-image portion on the photoconductor 1 moves to the developing roller 41 in the developing section and is collected by the developing device 4. Also, the transfer residual toner adhering to the image portion on the photoconductor 1 forms a toner image together with the toner that has moved from the developing roller 41 to the photoconductor 1. Then, this toner is transferred onto the recording material P in the transfer section and removed from the photoconductor 1. Also, paper dust and the like generated from the recording material P that adheres to the photoconductor 1 from the recording material P during the transfer process is removed by the brush member 54.

[0126] In this embodiment, the photosensitive member 1, the charging roller 2 as a process means acting on the photosensitive member 1, the developing device 4, the pre-exposure device 6 and the brush member 54 are integrally formed into a process cartridge 7 which is detachably attached to the main body 110 of the apparatus.

[0127] Fig. 13(a) is a schematic front view of a toner pack 16 serving as a toner supply container in this embodiment, and Fig. 13(b) is a schematic cross-sectional view showing a state in which the toner pack 16 is mounted in a developing container 45 of the developing device 4.

[0128] 12, the developing container 45 is formed with a supply protrusion 45c as a connection part. The supply protrusion 45c is hollow and is formed to communicate with the toner storage chamber 45b in the developing container 45 via a supply port 45d. A top cover 17 is provided on the upper part of the apparatus main body 110 so as to be able to open and close. The upper surface of the top cover 17 constitutes the above-mentioned tray 14.

[0129] As shown in FIG. 13(a), in this embodiment, the toner pack 16 is configured to have a plastic filer 16a that is easily deformed and a connecting portion 16b provided at one end of the filer 16a. The inside of the filer 16a and the inside of the connecting portion 16b are in communication with each other. As shown in FIG. 13(b), the image forming apparatus 100 is configured so that the supply protrusion 45c is exposed to the outside by opening the top cover 17 upward. The toner pack 16 can be attached to the end of the supply protrusion 45c, and when the toner pack 16 is attached to the supply protrusion 45c, toner can be supplied from the toner pack 16 to the toner storage chamber 45b. When the top cover 17 is opened, the toner pack 16 is connected to the supply protrusion 45c by the connecting portion 16b, so that at least a part of the end side of the filer 16a opposite to the connecting portion 16b is exposed to the outside of the image forming apparatus 100.

[0130] When the toner pack 16 is attached to the supply protrusion 45c, the inside of the toner pack 16 (wrapping bag 16a, connecting portion 16b) and the inside of the supply protrusion 45c are in communication with each other. Then, the toner contained in the toner pack 16 is discharged from an opening (not shown) provided in the connecting portion 16b of the toner pack 16 into the supply protrusion 45c, and the toner is supplied from the supply protrusion 45c to the toner storage chamber 45b through the supply port 45d.

[0131] Thus, in this embodiment, the developing device 4 has a connection portion (supply protrusion portion) 45c to which a supply container (toner pack) 16 containing developer to be replenished to the developer accommodating portion (toner accommodating chamber) 45b is removably attached, and developer can be replenished from the supply container 16 to the developer accommodating portion 45c.

[0132] In this embodiment, the toner supply container is configured with a plastic wrapper that is easily deformed, but is not limited thereto. For example, the toner supply container may be configured with a bottle container having a substantially conical or cylindrical shape. For example, the toner supply container may be configured with a paper container made of paper. In addition, the method of discharging the toner from the toner supply container is preferably such that the operator squeezes the container with his / her fingers in the case of the toner pack 16 or paper container as in this embodiment, and preferably such that the operator shakes the container by tapping it in the case of a bottle container. In addition, a discharging mechanism may be provided in the bottle container to discharge the toner from the bottle container. In addition, the discharging mechanism may be configured to engage with a driving mechanism provided in the device body 110 of the image forming device 100 and to receive drive from the driving mechanism. In addition, in order to prevent the toner from leaking from the toner supply container, a rotating or sliding shutter member may be provided in the toner supply container. In addition, the shutter member may be configured to be destroyed by being attached to the supply port of the developing device 4, or may be a removable lid structure such as a seal.

[0133] The developing device 4 is also provided with a light guide member 18. The image forming apparatus 100 is also provided with a toner remaining amount detection unit 63. In this embodiment, the toner remaining amount detection unit 63 has a light emitting element, a light receiving element, and a base on which the light emitting element and the light receiving element are provided. The toner remaining amount detection unit 63 detects the amount of toner remaining based on the length of time that the light receiving element receives light from the light emitting element. When the amount of toner remaining in the toner storage chamber 45b detected by the toner remaining amount detection unit 63 falls below a predetermined value, the control unit 202 can notify the operator on an external device or a display unit (not shown) of the image forming apparatus 100 of information for urging the operator to replenish toner.

[0134] <Control of image formation conditions based on detection of charging current> Even in the image forming apparatus 100 having a toner supply configuration as in this embodiment, there is a possibility that the charging performance of the toner in the developing device 4 may change after the toner is supplied.

[0135] Therefore, even in the image forming apparatus 100 having a toner supply configuration as in this embodiment, the same effects as in Examples 1 to 3 can be obtained by controlling the image forming conditions (development contrast, DD peripheral speed ratio) based on the detection of the charging current as described in Examples 1 to 3.

[0136] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-mentioned embodiments.

[0137] In the above embodiment, the image forming apparatus is a laser printer, but the present invention is not limited to this. An image forming apparatus is an apparatus that forms an image on a recording material using an electrophotographic image forming method or the like. Examples of image forming apparatuses include copying machines, printers (laser beam printers, LED printers, etc.), facsimile machines, word processors, and combination machines (multifunction printers) of these.

[0138] In the above embodiment, the developing device (developing unit) and the photosensitive unit are integrated into a process cartridge, but the present invention is not limited to this. The developing device and the photosensitive unit may be configured to be detachable from the main body of the image forming device as a developing cartridge and a photosensitive cartridge, respectively. Also, the developing device and the photosensitive unit may be configured to be detachable from the main body of the image forming device independently. Also, in the above embodiment, the image forming device is configured to have a detachable process cartridge, but the present invention is also applicable to an image forming device in which a process unit similar to that constituting the process cartridge in the above embodiment is provided in the main body of the image forming device. In that case, only the toner supply container as described in the fourth embodiment may be detachable from the main body of the image forming device.

[0139] In the above embodiment, the developing roller rotates in contact with the surface of the photoconductor when developing the electrostatic latent image on the photoconductor into a toner image, but the present invention is not limited to this. As long as the developing roller is capable of supplying toner to the photoconductor, the present invention can be applied not only to a configuration in which the developing member and the photoconductor contact each other during development, but also to a configuration in which the developing member is separated from the photoconductor during development. In other words, the developing roller may be configured to face the photoconductor while being separated from the photoconductor, thereby forming a developing section capable of supplying toner to the photoconductor. [Explanation of symbols]

[0140] 1 photoreceptor 2. Charge roller 4. Developing device 41 Developing roller 61 Charging current detection unit 62 Speed ​​change section 63 Toner remaining amount detection unit 100 Image forming device 202 Control section t Toner P Recording material

Claims

1. A rotatable photoreceptor; a charging member that contacts the photoconductor to form a charging portion and charges the surface of the rotating photoconductor; a charging voltage application unit that applies a charging voltage to the charging member; an exposure device that exposes the surface of the photoconductor charged by the charging member to light to form an electrostatic latent image on the surface of the photoconductor; a developing device including a rotatable developing member that forms a developing section capable of supplying a developer to the surface of the photoconductor in the developing section, and that supplies a developer charged to a predetermined polarity to the electrostatic latent image on the surface of the photoconductor in the developing section to form a developer image on the surface of the photoconductor, and a developer container that contains the developer to be supplied to the developing member; a developing voltage applying section that applies a developing voltage of the predetermined polarity side with respect to the potential of the electrostatic latent image in the developing section to the developing member; a charging current detection unit that detects a charging current flowing in the charging unit when the surface of the photoconductor is charged by the charging member; a control unit capable of controlling the charging voltage application unit, the exposure device, and the developing voltage application unit; having An image forming apparatus performing an image forming operation for forming the developer image on the surface of the photoconductor and a non-image forming operation for not forming the developer image on the surface of the photoconductor, the control unit is capable of controlling, during the non-image forming operation, to execute a detection operation in which the charging current detection unit detects the charging current when a surface of the photoconductor that has been charged by the charging member and then passed through the developing unit passes through the charging unit; The control unit detects the charging current value I Ａ and the charging current value I detected by the current detection operation. Ｂ and based on the above, at least one of the charging voltage application unit, the exposure device, and the developing voltage application unit is controlled so as to change a development contrast, which is a potential difference between the potential of the electrostatic latent image in the developing unit and the developing voltage.

2. The control unit Ａ More than I Ｂ 2. The image forming apparatus according to claim 1, wherein when the absolute value of the development contrast is larger than the absolute value of the development contrast, at least one of the charging voltage application unit, the exposure device, and the development voltage application unit is controlled so as to increase the absolute value of the development contrast.

3. The control unit Ｂ The above I Ａ 3. The image forming apparatus according to claim 2, wherein when the absolute value of the development contrast is greater than or equal to a predetermined value, at least one of the charging voltage application unit, the exposure device, and the development voltage application unit is controlled so as to increase the absolute value of the development contrast.

4. The control unit Ａ More than I Ｂ 2. The image forming apparatus according to claim 1, wherein when the absolute value of the development contrast is smaller, at least one of the charging voltage application unit, the exposure device, and the development voltage application unit is controlled so as to reduce the absolute value of the development contrast.

5. a speed change unit for changing the rotation speed of the developing member; The control unit Ａ and the above I Ｂ 2. The image forming apparatus according to claim 1, further comprising: a control unit for controlling the speed changing unit so as to change a peripheral speed ratio, which is a ratio of a peripheral speed of the developing member to a peripheral speed of the photoconductor, based on the peripheral speed ratio.

6. The control unit Ａ More than I Ｂ 6. The image forming apparatus according to claim 5, wherein when the peripheral speed ratio is larger, the speed changing unit is controlled so as to reduce the peripheral speed ratio.

7. The control unit Ｂ The above I Ａ 7. The image forming apparatus according to claim 6, wherein the speed changing unit is controlled so as to reduce the peripheral speed ratio when the peripheral speed ratio is greater than the predetermined value or more.

8. The control unit Ａ More than I Ｂ 6. The image forming apparatus according to claim 5, wherein the speed changing unit is controlled so as to increase the peripheral speed ratio when the peripheral speed ratio is smaller than the peripheral speed ratio.

9. A rotatable photoreceptor; a charging member that contacts the photoconductor to form a charging portion and charges the surface of the rotating photoconductor; a charging voltage application unit that applies a charging voltage to the charging member; an exposure device that exposes the surface of the photoconductor charged by the charging member to light to form an electrostatic latent image on the surface of the photoconductor; a developing device including a rotatable developing member that forms a developing section capable of supplying a developer to the surface of the photoconductor in the developing section, and that supplies a developer to the electrostatic latent image on the surface of the photoconductor in the developing section to form a developer image on the surface of the photoconductor, and a developer container that contains the developer to be supplied to the developing member; a speed change unit for changing a rotation speed of the developing member; a charging current detection unit that detects a charging current flowing in the charging unit when the surface of the photoconductor is charged by the charging member; A control unit capable of controlling the charging voltage application unit and the speed change unit; having An image forming apparatus performing an image forming operation for forming the developer image on the surface of the photoconductor and a non-image forming operation for not forming the developer image on the surface of the photoconductor, the control unit is capable of controlling, during the non-image forming operation, to execute a detection operation in which the charging current detection unit detects the charging current when a surface of the photoconductor that has been charged by the charging member and then passed through the developing unit passes through the charging unit; The control unit detects the charging current value I Ａ and the charging current value I detected by the current detection operation. Ｂ and controlling the speed change unit to change a peripheral speed ratio, which is a ratio of the peripheral speed of the developing member to the peripheral speed of the photoconductor, based on the speed change unit.

10. The control unit Ａ More than I Ｂ 10. The image forming apparatus according to claim 9, wherein when the peripheral speed ratio is larger, the speed changing unit is controlled so as to reduce the peripheral speed ratio.

11. The control unit Ｂ The above I Ａ 11. The image forming apparatus according to claim 10, wherein the speed changing unit is controlled so as to reduce the peripheral speed ratio when the peripheral speed ratio is greater than the predetermined value or more.

12. The control unit Ａ More than I Ｂ 10. The image forming apparatus according to claim 9, wherein the speed changing unit is controlled so as to increase the peripheral speed ratio when the peripheral speed ratio is smaller than the peripheral speed ratio.

13. The image forming apparatus according to any one of claims 1 to 12, characterized in that the control unit performs the detection operation during the non-image forming operation prior to the first image forming operation in a printing operation, which is a series of operations for forming an image on a single or multiple recording materials, each time the control unit performs the printing operation, which is a series of operations for forming an image on a single or multiple recording materials.

14. I Ａ 14. The image forming apparatus according to claim 13, wherein the charging current value detected in the previous detection operation is a charging current value detected in the previous detection operation.

15. a developer amount detection means for detecting the amount of toner in the developer container, When an increase in the amount of toner in the developer accommodating unit is detected by the developer amount detecting means, the control unit detects the I detected by the detection operation before the increase in the amount of toner is detected. Ａ and the I detected by the detection operation after the increase in the toner amount is detected. Ｂ 13. The image forming apparatus according to claim 1, wherein the control is performed based on the above.

16. 13. The image forming apparatus according to claim 1, wherein the developing device is detachable from a main body of the image forming apparatus.

17. 13. The image forming apparatus according to claim 1, wherein a unit having the photoconductor and the developing device is detachably attached to a main body of the image forming apparatus as a whole.

18. The image forming apparatus according to any one of claims 1 to 12, characterized in that the developing device has a connection portion to which a supply container containing developer to be replenished to the developer accommodating portion can be removably attached, and the developer accommodating portion can be replenished with developer from the supply container.

19. 13. The image forming apparatus according to claim 1, wherein the developing member contacts a surface of the photoconductor to form the developing portion.

Images