Image formation device

Abstract

To properly implement control in response to a level of a developer.SOLUTION: An image formation device comprises: a developing device; a developer replenishment unit; a drive unit that rotates to drive a conveyance screw in a first rotation condition at a time of a developing action; and a control unit. A second detection unit of a second magnetic permeability sensor exists upward in a vertical direction with respect to a first detection unit of a first magnetic permeability sensor. The control unit is configured to: implement first control of controlling the developer replenishment unit to replenish the developer to a developer container on the basis of an output value of the first magnetic permeability sensor during a period of the drive unit rotating for driving the conveyance screw; and implement second control of controlling the drive unit to rotate for driving the conveyance screw in a second rotation condition different from the first rotation condition at a time of a non-developing action when the developing action is not implemented, on the basis of an output value of the first permeability sensor during a period of the drive unit rotating for driving the conveyance screw, and an output value of the second permeability sensor during a period of the drive unit rotating for driving the conveyance screw.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine having a plurality of these functions.

Background Art

[0002] In an image forming apparatus using an electrophotographic method, an electrostatic latent image formed on an image carrier is developed into a toner image by a developing device. As such a developing device, one using a two-component developer having toner and a magnetic carrier has been conventionally used. In a developing device using a two-component developer, for the purpose of suppressing deterioration of the carrier, while supplying toner containing a small amount of carrier to the developing device, the surplus developer is discharged outside the developing device, and the so-called ACR (Auto Carrier Refresh) method is widely adopted.

[0003] In an ACR method developing device, in order to keep the quality of the developed image constant, it is required to maintain a constant amount of developer in the developing device. In Patent Document 1, a sensor for detecting the surface height (bulk height) of the developer in the developing device is used to indirectly predict the amount of developer in the developing device, and the amount of developer in the developing device is adjusted according to the result, for example, by controlling the rotation speed of a conveying screw. A developing device has been proposed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the developing device of Patent Document 1, the surface height of the developer is detected by measuring the magnetic permeability of the developer in the developing device. In the inductance sensor that measures the magnetic permeability of the developer, a change in the abundance of the magnetic carrier contained in the developer is detected as a change in the apparent magnetic permeability. As a result, when the surface of the developer rises, the magnetic carrier near the sensor increases, so the magnetic permeability increases and the output value of the sensor rises. Conversely, when the surface level drops and the magnetic carrier near the sensor decreases, the output value of the sensor drops.

[0006] However, it is known that the magnetic permeability of the developer changes depending on the weight ratio of the toner contained in the developer (hereinafter referred to as the toner concentration) in addition to the abundance of the carrier. For example, if the toner concentration is low, the apparent magnetic permeability increases, and conversely, if the toner concentration is high, the magnetic permeability decreases. As a result, the output value of the sensor that detects the developer surface fluctuates under the influence of the toner concentration of the developer in addition to the height of the developer surface. This may result in misdetection of the developer surface.

[0007] An object of the present invention is to provide an image forming apparatus capable of appropriately executing control according to the surface level of the developer.

Means for Solving the Problems

[0008] One aspect of the present invention is an image forming apparatus including: an image carrier; a developer carrier that carries a developer including toner and a carrier for developing an electrostatic latent image formed on the image carrier; a developer container that stores the developer supplied to the developer carrier; a transport screw that transports the developer stored in the developer container; a developer discharge portion for discharging a part of the developer stored in the developer container; a first magnetic permeability sensor having a first detection portion for detecting the magnetic permeability of the developer stored in the developer container; a second magnetic permeability sensor having a second detection portion for detecting the magnetic permeability of the developer stored in the developer container; a developer supply portion for supplying the developer to the developer container; a drive portion that rotationally drives the transport screw under a first rotation condition during a developing operation in which the image forming apparatus develops an electrostatic latent image formed on the image carrier; and a control portion. The second detection portion is located vertically above the first detection portion. The control portion executes first control for controlling the developer supply portion to supply the developer to the developer container based on an output value of the first magnetic permeability sensor while the drive portion is rotationally driving the transport screw. The control portion executes second control for controlling the drive portion to rotationally drive the transport screw under a second rotation condition different from the first rotation condition during a non-developing operation in which the developing operation is not performed, based on the output value of the first magnetic permeability sensor while the drive portion is rotationally driving the transport screw and the output value of the second magnetic permeability sensor while the drive portion is rotationally driving the transport screw.

[0009] One aspect of the present invention includes an image carrier, a developer carrier that carries a developer containing toner and a carrier for developing an electrostatic latent image formed on the image carrier, a developer container that stores the developer supplied to the developer carrier, a transport screw that transports the developer stored in the developer container, a developer discharge unit for discharging a part of the developer stored in the developer container, a first magnetic permeability sensor having a first detection unit that detects the magnetic permeability of the developer stored in the developer container, a second magnetic permeability sensor having a second detection unit that detects the magnetic permeability of the developer stored in the developer container, a developing device having the above, a developer supply unit that supplies the developer to the developer container, a drive unit that rotationally drives the transport screw under a first rotation condition during a developing operation in which the developing device develops an electrostatic latent image formed on the image carrier, and a control unit. The second detection unit is located vertically above the first detection unit. The control unit executes a first control for controlling the developer supply unit to supply the developer to the developer container based on an output value of the first magnetic permeability sensor while the drive unit is rotationally driving the transport screw. When the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the transport screw is a first value, and the output value of the second magnetic permeability sensor while the drive unit is rotationally driving the transport screw is equal to or greater than a first threshold value, the control unit executes a second control for controlling the drive unit to rotationally drive the transport screw under a second rotation condition different from the first rotation condition during a non-developing operation in which the developing operation is not performed. When the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the transport screw is the first value, and the output value of the second magnetic permeability sensor while the drive unit is rotationally driving the transport screw is less than the first threshold value, the second control is not executed. When the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the transport screw is a second value greater than the first value, and the output value of the second magnetic permeability sensor while the drive unit is rotationally driving the transport screw is equal to or greater than a second threshold value greater than the first threshold value, the second control is executed.When the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is the second value, and the output value of the second magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is less than the second threshold value, the second control is not executed. The image forming apparatus is characterized by this.

[0010] One aspect of the present invention is an image forming apparatus including: an image carrier; a developer carrier that holds a developer including toner and carrier for developing an electrostatic latent image formed on the image carrier; a developer container that stores the developer supplied to the developer carrier; a conveyance screw that conveys the developer stored in the developer container; a developer discharge unit for discharging a part of the developer stored in the developer container; a first magnetic permeability sensor having a first detection unit that detects the magnetic permeability of the developer stored in the developer container; a second magnetic permeability sensor having a second detection unit that detects the magnetic permeability of the developer stored in the developer container; a developer supply unit that supplies the developer to the developer container; a drive unit that rotationally drives the conveyance screw; and a control unit. The second detection unit is located vertically above the first detection unit. The control unit controls the developer supply unit to supply the developer to the developer container based on an output value of the first magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw. When the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is a first value and the output value of the second magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is equal to or less than a first threshold value, the control unit controls the drive unit to rotationally drive the conveyance screw at a second rotation speed slower than a first rotation speed during a developing operation in which the image forming apparatus develops the electrostatic latent image formed on the image carrier. When the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is the first value and the output value of the second magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is greater than the first threshold value, the control unit controls the drive unit to rotationally drive the conveyance screw at the first rotation speed during the developing operation. When the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is a second value greater than the first value and the output value of the second magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is equal to or less than a second threshold value greater than the first threshold value,During the development operation, the drive unit is controlled to rotationally drive the conveyance screw at the second rotational speed, and when the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is the second value and the output value of the second magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is greater than the second threshold value, the drive unit is controlled to rotationally drive the conveyance screw at the first rotational speed. An image forming apparatus characterized by this.

Advantages of the Invention

[0011] According to the present invention, control according to the agent surface of the developer can be appropriately executed.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

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Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Embodiments for Carrying Out the Invention

[0013] <First Embodiment> The first embodiment will be described with reference to FIGS. 1 to 11(b). First, the schematic configuration of the image forming apparatus of this embodiment will be described with reference to FIG. 1.

[0014] [Image Forming Apparatus] The image forming apparatus 100 is a full-color image forming apparatus, and in this embodiment, for example, it is an MFP (Multi-Function Peripheral) having a copy function, a printer function, and a scan function. As shown in FIG. 1, the image forming apparatus 100 is provided with image forming units PY, PM, PC, and PK that perform image forming processes of four-color toner images of yellow, magenta, cyan, and black in parallel.

[0015] The color image forming units PY, PM, PC, and PK each include a primary charger 21Y, 21M, 21C, 21K, a developing device 1Y, 1M, 1C, 1K, an optical writing unit (exposure device) 22Y, 22M, 22C, 22K, a photosensitive drum 28Y, 28M, 28C, 28K, and a cleaning device 26Y, 26M, 26C, 26K. The image forming apparatus 100 also includes a transfer device 2 and a fixing device 3. Since the configurations of the color image forming units PY, PM, PC, and PK are the same, hereinafter, the image forming unit PY will be described as a representative.

[0016] The photosensitive drum 28Y, which is a rotatable image carrier, is a photoreceptor having a photosensitive layer made of a resin such as polycarbonate containing an organic photo conductor (OPC), and is configured to rotate at a predetermined speed. The primary charger 21Y is composed of a corona discharge electrode disposed around the photosensitive drum 28Y, and charges the surface of the photosensitive drum 28Y with the generated ions.

[0017] The optical writing unit 22Y incorporates a scanning optical device, and exposes the charged photosensitive drum 28Y based on image data, thereby reducing the potential of the exposed portions and forming a charge pattern (electrostatic latent image) corresponding to the image data. The developing device 1Y transfers the contained developer onto the photosensitive drum 28Y to develop the electrostatic latent image formed on the photosensitive drum 28Y. The developer is a mixture of a carrier and toner corresponding to each color, and the electrostatic latent image is visualized by the toner.

[0018] The transfer device 2 includes primary transfer rollers 23Y, 23M, 23C, 23K, an intermediate transfer belt 24, and a secondary transfer roller 25. The intermediate transfer belt 24 is wound by the primary transfer rollers 23Y, 23M, 23C, 23K and a plurality of rollers and is supported so as to be capable of running. The primary transfer rollers 23Y, 23M, 23C, 23K correspond to the respective colors of Y (yellow), M (magenta), C (cyan), and K (black) in order from the top in FIG. 1. The secondary transfer roller 25 is disposed outside the intermediate transfer belt 24 and is configured such that a recording material can pass between the secondary transfer roller 25 and the intermediate transfer belt 24. The recording material is, for example, a sheet such as paper or a plastic sheet.

[0019] The toner images of respective colors formed on the photosensitive drums 28Y, 28M, 28C, 28K are sequentially transferred onto the intermediate transfer belt 24 by the primary transfer rollers 23Y, 23M, 23C, 23K, and a color toner image in which layers of yellow, magenta, cyan, and black are superimposed is formed. The formed toner image is transferred by the secondary transfer roller 25 onto a recording material conveyed from a cassette or the like in which the recording material is accommodated. The recording material onto which the toner image is transferred is subjected to pressure and heat in the fixing device 3. Thereby, the toner on the recording material is melted and the color image is fixed to the recording material.

[0020] The developer storage units 27Y, 27M, 27C, 27K are respectively provided corresponding to the developing devices 1Y, 1M, 1C, 1K, and bottles filled with developers corresponding to the respective colors of yellow, magenta, cyan, and black are loaded therein so as to be replaceable in order from the top. The developer storage units 27Y, 27M, 27C, 27K are configured to be capable of conveying (supplying) the developer to the developing devices 1Y, 1M, 1C, 1K corresponding to the colors of the stored developers.

[0021] For example, the toner weight ratio of the developer stored in the bottle (i.e., toner concentration: the ratio of the toner weight to the total weight of the carrier and toner) is 80 to 95%, and the toner weight ratio of the developer in the developing devices 1Y, 1M, 1C, and 1K is 5 to 10%. Therefore, when toner is consumed by development in the developing devices 1Y, 1M, 1C, and 1K, a developer containing toner corresponding to the consumption amount is replenished, and the toner weight ratio of the developer in the developing devices 1Y, 1M, 1C, and 1K is maintained constant.

[0022] [Control Configuration] FIG. 2 is a control block diagram showing the main part of the control system of the image forming apparatus 100. The image forming apparatus 100 includes an operation unit 96, an image forming unit 97, a recording material conveyance unit 98, a fixing unit 99, and a control unit 80. The operation unit 96 has a display unit capable of displaying various information, operation buttons, and the like. The display unit may be a touch panel capable of touch operation. The image forming unit 97 includes various motors for driving the configurations such as the photosensitive drums 28Y, 28M, 28C, and 28K of the image forming units PY, PM, PC, and PK for forming an image on the recording material as described above, and the developing devices 1Y, 1M, 1C, and 1K, and a power source for applying a voltage to these configurations. The image forming unit 97 has a driving unit 94 such as a motor for rotationally driving the developer supply screw 42 and the developer agitation screw 43 described later. The recording material conveyance unit 98 includes various motors for driving the conveyance rollers for conveying the recording material. The fixing unit 99 includes a heater of the fixing device 3 and a motor for driving the fixing device. These operation unit 96, image forming unit 97, recording material conveyance unit 98, and fixing unit 99 are connected to the control unit 80 and controlled by the control unit 80.

[0023] The control unit 80 includes a CPU (Central Processing Unit) 81, a ROM (Read Only Memory) 82, a RAM (Random Access Memory) 83, and the like. The CPU 81 reads out a program corresponding to the processing content from the ROM 82 and expands it in the RAM 83, and controls the operations of the respective configurations of the image forming apparatus 100 in cooperation with the expanded program. At this time, various data stored in the storage unit 91 are referred to.

[0024] The storage unit 91 is composed of, for example, a non-volatile semiconductor memory (so-called flash memory) or a hard disk drive. The control unit 80 performs transmission and reception of various data with an external device (e.g., a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 92. The control unit 80 receives, for example, image data (input image data) transmitted from an external device, and forms an image on a recording material based on this image data. The communication unit 92 is composed of, for example, a communication control card such as a LAN card.

[0025] Also, the control unit 80 is connected to a toner density sensor 49, a developer surface detection sensor 50, and a supply unit 93. The toner density sensors 49 are respectively provided in the developing devices 1Y, 1M, 1C, and 1K, and detect the toner density of the developer in the developing devices 1Y, 1M, 1C, and 1K as will be described later. The developer surface detection sensors 50 are also respectively provided in the developing devices 1Y, 1M, 1C, and 1K, and detect the surface of the developer in the developing devices 1Y, 1M, 1C, and 1K as will be described later. The supply unit 93 as a developer supply unit includes a motor that drives a supply mechanism for supplying developer from the developer storage units 27Y, 27M, 27C, and 27K to the developing devices 1Y, 1M, 1C, and 1K. The control unit 80 controls the supply unit 93 and the like based on the detection results of the toner density sensor 49 and the developer surface detection sensor 50.

[0026] [Developing Device] Next, the developing devices 1Y, 1M, 1C, and 1K will be described in detail with reference to FIGS. 3 and 4. Since the configurations of the developing devices 1Y, 1M, 1C, and 1K are the same, hereinafter, the developing device 1Y will be described as a representative. FIG. 3 is a conceptual diagram for explaining the developing device 1Y shown in FIG. 1, and FIG. 4 is a schematic view of the developing device 1Y seen from above after being cut in a direction parallel to the rotation axis direction of the first developing roller 30.

[0027] As shown in FIG. 3, the developing device 1Y includes a first developing roller 30, a second developing roller 31, a peeling roller 32, a developer supply screw 42, a developer stirring screw 43, and a developer recovery screw 44, and these members are accommodated in a developing container 60.

[0028] The first developing roller 30 is a developer carrier that is rotationally driven, and is arranged at a position adjacent to the photosensitive drum 28Y such that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. The first developing roller 30 includes a rotating first sleeve 33 and a first magnet (fixed magnet) 36 that is non-rotationally arranged inside the first sleeve 33 and adsorbs the developer to the surface of the first sleeve 33 by magnetic force. Then, the first developing roller 30 sucks up the developer pumped from the developer supply screw 42, adsorbs (carries) it based on magnetic force, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y (on the image carrier) with the developer.

[0029] The first sleeve 33 is a non-magnetic cylindrical member and is rotationally driven about the rotation axis 39. The rotation direction of the first sleeve 33 is clockwise as shown by the arrow in FIG. 3, and in this embodiment, it is in the opposite direction to the rotation direction of the photosensitive drum 28Y. Therefore, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction at positions facing each other. That is, it is forward development in which the photosensitive drum 28 rotates from vertically downward to vertically upward at the position where the photosensitive drum 28 faces the first sleeve 33. A space that allows the rotation of the first sleeve 33 is arranged between the inner circumference of the first sleeve 33 and the outer circumference of the first magnet 36.

[0030] The developer adsorbed on the first sleeve 33 is conveyed toward the photosensitive drum 28Y by the rotational movement of the first sleeve 33 to develop the latent image formed on the photosensitive drum 28Y. After developing the latent image formed on the photosensitive drum 28Y, the developer on the first sleeve 33 is conveyed by the rotational movement of the first sleeve 33 to the vicinity of the second developing roller 31. Then, in the vicinity of the closest position between the first developing roller 30 and the second developing roller 31, due to the magnetic field generated by the first magnet 36 enclosed in the first developing roller 30 and the second magnet 37 enclosed in the second developing roller 31, the developer is peeled off from the first sleeve 33 and transferred onto the second sleeve 34.

[0031] As described below, the second developing roller 31 of the developing device 1Y of the present embodiment is disposed vertically above the first developing roller 30. Therefore, it is also necessary to transfer the developer from the first sleeve 33 to the second sleeve 34 against gravity from the vertical downward direction to the upward direction. Note that the first sleeve 33 and the second sleeve 34 are disposed with a predetermined gap at the closest part.

[0032] The second developing roller 31 is a developer carrier that is rotationally driven, and is disposed downstream of the first developing roller 30 with respect to the rotation direction of the photosensitive drum 28Y, and the rotation center O2 of the second developing roller 31 is located above the rotation center O1 of the first developing roller 30 in the vertical direction, and the developer is transferred from the first developing roller 30 by magnetic force. In the present embodiment, the entire second developing roller 31 is located above the rotation center O1 of the first developing roller 30. Similar to the first developing roller 30, the second developing roller 31 is disposed at a position adjacent to the photosensitive drum 28Y such that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. Therefore, the rotation axes of the second developing roller 31 and the first developing roller 30 are substantially parallel to each other.

[0033] Such a second developing roller 31 includes a rotating second sleeve 34 and a second magnet (fixed magnet) 37 that is non-rotatably disposed inside the second sleeve 34 and adsorbs a developer to the surface of the second sleeve 34 by magnetic force. Then, based on magnetic force, the second developing roller 31 receives the developer from the first developing roller 30 (first sleeve 33), adsorbs (carries) it, and develops an electrostatic latent image formed on the rotating photosensitive drum 28Y with the developer. Note that a peeling roller 32, which will be described later, is positioned on the side of the second developing roller 31.

[0034] The second sleeve 34 is a non-magnetic cylindrical member and is rotationally driven about a rotation axis 40. The rotation direction of the second sleeve 34 is the same as that of the first sleeve 33, i.e., clockwise as indicated by the arrow in FIG. 3. In the present embodiment, it is in the direction opposite to the rotation direction of the photosensitive drum 28Y. For this reason, the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction at positions facing each other. That is, it is forward development in which the photosensitive drum 28 rotates from vertically downward to vertically upward at the position where the photosensitive drum 28 faces the second sleeve 34. Also, the second sleeve 34 and the first sleeve 33 rotate in opposite directions at positions facing each other. A space that allows the rotation of the second sleeve 34 is disposed between the inner circumference of the second sleeve 34 and the outer circumference of the second magnet 37.

[0035] The developer adsorbed on the second sleeve 34 is conveyed toward the photosensitive drum 28Y by the rotation of the second sleeve 34 and develops the latent image formed on the photosensitive drum 28Y. After developing the latent image formed on the photosensitive drum 28Y, the developer remaining on the second sleeve 34 is conveyed to the vicinity of the peeling roller 32 by the rotation of the second sleeve 34. Then, in the vicinity of the closest position between the second developing roller 31 and the peeling roller 32, the developer is transferred from the second sleeve 34 to the third sleeve 35 of the peeling roller 32 by the magnetic field generated by the second magnet 37 included in the second developing roller 31 and the third magnet 38 included in the peeling roller 32.

[0036] The peeling roller 32 as the peeling part is disposed on the side opposite to the photosensitive drum 28Y with respect to the rotation center of the second sleeve 34, and peels the developer after developing the electrostatic latent image on the photosensitive drum 28Y from the second developing roller 31. Specifically, the peeling roller 32 is a developer carrier that is rotationally driven, and is disposed between the second developing roller 31 and the developer recovery screw 44 such that its rotation center is above the rotation center R of the second developing roller 31.

[0037] Further, the peeling roller 32 is disposed such that its rotation axis is substantially parallel to the rotation axis of the second developing roller 31. Such a peeling roller 32 has a rotating third sleeve 35 and a third magnet (fixed magnet) 38 that is non-rotationally disposed inside the third sleeve 35 and adsorbs the developer to the surface of the third sleeve 35 by magnetic force, and is configured to receive the developer from the second developing roller 31 based on magnetic force.

[0038] The third sleeve 35 is a non-magnetic cylindrical member and is rotationally driven about the rotation axis 41. The rotation direction of the third sleeve 35 is counterclockwise as shown by the arrow in FIG. 3, and in this embodiment, it is the opposite direction to the rotation direction of the second sleeve 34. For this reason, the third sleeve 35 and the second sleeve 34 rotate in the same direction at positions facing each other. A space that allows the rotation of the third sleeve 35 is disposed between the inner circumference of the third sleeve 35 and the outer circumference of the third magnet 38.

[0039] The developer adsorbed on the third sleeve 35 is conveyed to the downstream side in the rotation direction by the rotation operation of the third sleeve 35, and at a position close to the developer recovery screw 44, is peeled from the third sleeve 35 by the third magnet 38 included in the peeling roller 32, and falls toward the guide member 45 located vertically downward by its own weight. Then, the developer that has fallen onto the guide member 45 is guided by its own weight toward the developer recovery screw 44.

[0040] The guide member 45 and the developer recovery screw 44 constitute a developer recovery unit 47 as a recovery unit that recovers the developer peeled from the third sleeve 35 on the peeling roller 32. In the developer recovery unit 47, the developer recovery screw 44 is arranged such that the rotation center is located below the rotation center of the peeling roller 32 with respect to the vertical direction, and conveys (recovers) the developer delivered from the peeling roller 32 while stirring it.

[0041] The guide member 45 as a guide portion is arranged below the peeling roller 32 in the vertical direction, and guides the developer peeled by the peeling roller 32 toward the developer recovery screw 44. Such a guide member 45 has an inclined surface 45a on which the peeled developer slides down due to its own weight in order to more surely guide the peeled developer toward the developer recovery screw 44. The inclined surface 45a is inclined with respect to the horizontal direction such that the side closer to the developer recovery screw 44 is lower than the position below the peeling roller 32.

[0042] The developer recovery screw 44 as a recovery member and a conveyance unit conveys the recovered developer to a developer circulation unit 46 described below. That is, the developer recovery screw 44 is a screw conveyance member used to convey the developer recovered by sliding down the inclined surface of the guide member 45 in one direction while stirring it.

[0043] The developer circulation unit 46 is a supply unit for supplying the developer to the first developing roller 30. The developer circulation unit 46 includes a regulating member 52, a developer supply screw 42 as a first conveyance screw, and a developer agitation screw 43 as a second conveyance screw. The developer supply screw 42 and the developer agitation screw 43 are rotationally driven by a drive unit 94. In the developer circulation unit 46, the developer is conveyed substantially horizontally while being stirred in the developer supply screw 42 and the developer agitation screw 43, and is supplied to the first developing roller 30. Also, as described above, the developer recovered by the developer recovery unit 47 falls due to its own weight and is introduced into the developer circulation unit 46.

[0044] The developer supply screw 42, the developer agitation screw 43, and the developer recovery screw 44 are screw conveyance members that convey the developer in one direction while agitating the developer. The developer supply screw 42 and the developer agitation screw 43 are located vertically below the developer recovery screw 44. Further, these developer supply screw 42, developer agitation screw 43, and developer recovery screw 44 are arranged such that their rotation axes are substantially parallel to each other. The rotation axes of these respective screws are also substantially parallel to the rotation axis of the first developing roller 30.

[0045] The developer supply screw 42 is located between the first developing roller 30 and the developer agitation screw 43, and a partition wall 48 of the developing container 60 is arranged between the developer supply screw 42 and the developer agitation screw 43. The partition wall 48 of the developing container 60 extends along the rotation axis direction of the developer supply screw 42 and the developer agitation screw 43. The partition wall 48 is provided with communication ports 48a, 48b (FIG. 4) that communicate a first conveyance path 61 as a first chamber in which the developer is conveyed by the developer supply screw 42 and a second conveyance path 62 as a second chamber in which the developer is conveyed by the developer agitation screw 43. And a circulation path of the developer is formed between the first conveyance path 61 and the second conveyance path 62.

[0046] The developer agitated by the developer recovery screw 44 falls by its own weight toward the developer supply screw 42 via a communication port (not shown) formed in a partition wall 63 of the developing container 60 that is between the developer recovery screw 44 and the developer supply screw 42. That is, the developer agitated by the developer recovery screw 44 is introduced into the developer supply screw 42. Incidentally, the above-described guide member 45 is formed integrally with the partition wall 63, and the developer recovery screw 44 is arranged above the partition wall 63.

[0047] The position of the communication port where the developer stirred by the developer recovery screw 44 falls due to its own weight and is introduced into the developer circulation unit 46 is preferably arranged to avoid the area where the developer is supplied toward the first developing roller 30 (the intermediate part in the axial direction of the developer supply screw 42). In the present embodiment, the position of the communication port is set to a position included in the range of the downstream end (terminal end) in the developer conveyance direction of the first conveyance path 61 where the developer supply screw 42 is arranged.

[0048] The developer conveyance directions of the developer supply screw 42 and the developer agitation screw 43 are opposite to each other as indicated by the arrows in FIG. 4. And the start end side (the upstream end side in the developer conveyance direction) and the end side (the downstream end side in the developer conveyance direction) of the first conveyance path 61 where the developer supply screw 42 is arranged communicate with the end side and the start end side of the second conveyance path 62 where the developer agitation screw 43 is arranged via the communication ports 48a and 48b provided in the partition wall 48. Therefore, the developer circulates in the developing container 60 in the substantially horizontal direction in the rotation directions of the developer supply screw 42 and the developer agitation screw 43 indicated by the arrows in FIG. 3, and a part of it is supplied toward the first developing roller 30.

[0049] The developer supply port 51 is arranged above the developer agitation screw 43 in the developing container 60 and is connected to the developer storage unit 27Y (see FIG. 1). And the developer supply port 51 is configured to be able to supply the developer stored in the bottle loaded in the developer storage unit 27Y to the second conveyance path 62 where the developer agitation screw 43 is arranged.

[0050] As described above, since the toner concentration (toner weight ratio) of the developer stored in the bottle of the developer storage unit 27Y is higher than the toner concentration of the developer in the developing device 1Y, it is possible to maintain the toner weight ratio of the developer in the developing device 1 constant by adjusting the developer supplied to the developer agitation screw 43.

[0051] As shown in FIG. 4, the developer discharge unit 53 is disposed at the most downstream position in the developer conveyance direction of the developer supply screw 42, and discharges the surplus developer in the developing device 1Y from the developer discharge port 54 to the outside of the developing device 1Y. A screw 55 is formed in the developer discharge unit 53, the conveyance direction of the developer of which is opposite to the developer conveyance direction of the developer supply screw 42. The screw 55 is provided coaxially with the developer supply screw 42, rotates together with the developer supply screw 42, and generates a flow that pushes the developer back from the developer discharge unit 53 toward the developer circulation unit 46.

[0052] Also, with respect to the developer conveyance direction of the developer supply screw 42, a screw 56 that conveys the developer in the same direction as the developer conveyance direction of the developer supply screw 42 is provided coaxially with the developer supply screw 42 and the screw 55 on the downstream side of the screw 55. The screw 56 rotates together with the developer supply screw 42 and the screw 55, conveys the developer that has been conveyed over the screw 55 to the developer discharge port 54, and discharges it from the developer discharge port 54.

[0053] Thereby, when the amount of developer in the developing device 1Y is appropriately maintained, the developer is pushed back by the screw 55, thereby suppressing the amount of developer discharged from the developer discharge port 54. On the other hand, when toner is replenished from the developer replenishment port 51 into the developing device 1Y and the amount of developer that tries to move from the developer supply screw 42 to the developer discharge unit 53 increases, the developer moves over the screw 55 to the screw 56, and the surplus developer is discharged from the developer discharge port 54 to the outside of the developing device 1Y. At this time, if the rotation speeds of the developer supply screw 42 and the developer agitation screw 43 are increased, the developer easily moves to the developer discharge unit 53, so that the amount of developer discharged from the developer discharge port 54 can be increased. Conversely, if the rotation speeds of the developer supply screw 42 and the developer agitation screw 43 are decreased, the movement of the developer to the developer discharge unit 53 is suppressed, so that the amount of developer discharged from the developer discharge port 54 can be decreased.

[0054] The toner concentration sensor 49 as the first inductance sensor (first magnetic permeability sensor) is arranged to detect the toner concentration in the developer contained in the developer circulation unit 46. The toner concentration sensor 49 is an inductance sensor that detects the magnetic permeability of the developer. Since the toner concentration corresponds to the consumption amount of toner in the developing device 1Y, it is used for controlling the replenishment of the developer from the developer storage unit 27Y. When it is detected that the toner concentration has dropped below a predetermined toner concentration, for example, the control unit 80 (Fig. 2) replenishes the developer from the developer storage unit 27Y (executes a replenishment operation). That is, the control unit 80 executes a replenishment operation as the first control for controlling the replenishment unit 93 to replenish the developer to the developing container 60 based on the output value of the toner concentration sensor 49 while the drive unit 94 is rotationally driving the developer supply screw 42 and the developer stirring screw 43.

[0055] Note that since the magnetic permeability of the developer changes more than the toner concentration, it is possible to detect the toner concentration using the magnetic permeability, which is the output value of the toner concentration sensor 49. To detect the magnetic permeability of the developer, the toner concentration sensor 49 has an output value that increases as the toner concentration decreases. That is, the toner concentration sensor 49 has a lower toner concentration when the output value is a second value greater than the first value than when the output value is the toner concentration of the first value. The toner concentration sensor 49 is arranged in the second conveyance path 62. Specifically, as shown in Fig. 3, the toner concentration sensor 49 is vertically below the rotation axis of the developer stirring screw 43, and as shown in Fig. 4, it is provided at the downstream end of the second conveyance path 62 with respect to the developer conveyance direction of the developer stirring screw 43.

[0056] The developer surface detection sensor 50 as the second inductance sensor (second magnetic permeability sensor) is arranged to detect the surface of the developer contained in the developer circulation unit 46. The developer surface detection sensor 50 is an inductance sensor that detects the magnetic permeability of the developer. The control unit 80 executes developer discharge control to keep the amount of developer in the developing device 1Y constant based on the developer surface detected by the developer surface detection sensor 50 and the toner concentration detected by the toner concentration sensor 49. The developer surface detection sensor 50 is arranged in the second conveyance path 62. Specifically, as shown in FIG. 3, the developer surface detection sensor 50 is provided above the rotation axis of the developer agitation screw 43 in the vertical direction and upstream of the toner concentration sensor 49 in the developer conveyance direction of the developer agitation screw 43 as shown in FIG. 4.

[0057] The detection surface (second detection unit) of the developer surface detection sensor 50 is located above the detection surface (first detection unit) of the toner concentration sensor 49 in the vertical direction and is preferably arranged within a range corresponding to 4 pitches of the blades of the developer agitation screw 43 in the rotation axis direction of the developer agitation screw 43. Thereby, the detection range of the toner concentration of the developer and the detection range of the surface of the developer can be regarded as substantially the same. In this embodiment, one pitch of the blades of the developer agitation screw 43 is 30 mm, and the detection surface of the developer surface detection sensor 50 is located 20 mm above the detection surface of the toner concentration sensor 49 in the vertical direction. Also, in the rotation axis direction of the developer agitation screw 43, the detection surface of the developer surface detection sensor 50 is arranged at a position 50 mm upstream in the developer conveyance direction of the developer agitation screw 43 from the detection surface of the toner concentration sensor 49.

[0058] The restricting member 52 is arranged adjacent to the first developing roller 30 and is used to restrict the amount of developer supplied from the developer circulation unit 46 to the first developing roller 30. The restricting member 52 can be configured to restrict the amount of developer adsorbed on the first developing roller 30 based on, for example, the gap between the surface of the first sleeve 33 of the first developing roller 30 and the end of the restricting member 52.

[0059] The circulation path of the developer in the developing container 60 is conveyed in a substantially horizontal direction while being agitated in the developer circulation unit 46, then supplied to the first developing roller 30, and transferred from the first developing roller 30 to the upper second developing roller 31 based on magnetic force. Next, it is transferred again from the second developing roller 31 to the peeling roller 32 on the side surface of the second developing roller based on magnetic force, and then peeled off from the peeling roller 32 by the third magnet 38 enclosed in the peeling roller 32, and further recovered by the developer recovery unit 47 and introduced again into the developer circulation unit 46.

[0060] [Developer] As described above, in this embodiment, a two-component development method is used as the development method, and the developer is a mixture of a negatively charged non-magnetic toner and a magnetic carrier. The non-magnetic toner contains a coloring agent, a wax component, etc. in a resin such as polyester or styrene acrylic, and fine powders such as titanium oxide and silica are added to the surface of the powder obtained by pulverization or polymerization. The magnetic carrier is obtained by applying a resin coat to the surface layer of a core made of resin particles kneaded with ferrite particles or magnetic powder. The toner concentration (weight ratio of toner contained in the developer) in the developer in the initial state is 9% in this embodiment.

[0061] Generally, the two-component development method using toner and carrier charges both of them to a predetermined polarity by frictionally contacting the toner and the carrier. Therefore, it has the characteristic that the stress received by the toner is less than that of the one-component development method using a one-component developer. On the other hand, due to long-term use, the dirt (spent) adhering to the surface of the carrier increases, and therefore the ability to charge the toner gradually decreases. As a result, problems such as fogging and toner scattering occur. In order to extend the life of the two-component developing device, it is conceivable to increase the amount of carrier accommodated in the developing device, but this is not desirable because it leads to an increase in the size of the developing device.

[0062] In order to solve the above problems related to the two-component developer, in this embodiment, the ACR (Auto Carrier Refresh) method is adopted. The ACR method replenishes a small amount of new developer from the developer storage unit 27Y into the developing device 1Y little by little, and discharges the developer with deteriorated charging performance little by little from the developer discharge port 54 of the developing device 1Y, thereby suppressing the increase of deteriorated carriers. As a result, the deteriorated carriers in the developing device 1Y are gradually replaced by new carriers, and it becomes possible to keep the charging performance of the carriers in the developing device 1Y substantially constant.

[0063] By the way, in the developing device 1Y equipped with the ACR method as in this embodiment, for example, due to the change in fluidity accompanying the deterioration of the developer, the discharge of the developer is suppressed, and the developer inside the developing device 1Y increases, which leads to the overflow of the developer from the vicinity of the first developing roller 30 and the second developing roller 31, and the occurrence of locking of various screws in the developing device 1Y. FIG. 5(a) shows the developer surface T in a state where the developer inside the developing device 1Y is properly maintained. On the other hand, FIG. 5(b) shows the developer surface T in a state where the discharge of the developer is suppressed.

[0064] In preparation for such a situation, in this embodiment, a developer surface detection sensor 50 for detecting the height of the developer surface in the developing device 1Y is provided. When the developer surface in the developing device 1Y deviates from a predetermined range, developer discharge control is performed to change the rotation speed (rotation rate) of the developer supply screw 42 and the developer agitation screw 43 so that the developer surface enters the predetermined range. For example, when the developer surface in the developing device 1Y falls below a predetermined position, a developer discharge suppression mode is executed in which the rotation speeds of the developer supply screw 42 and the developer agitation screw 43 are slowed down to suppress the discharge of the developer. Also, when the developer surface in the developing device 1Y exceeds a predetermined position, the image forming operation is stopped, and the forward and reverse rotation operations of the developer supply screw 42 and the developer agitation screw 43 are repeated for a predetermined time to execute a developer discharge mode for discharging the excess developer outside the developing device 1Y.

[0065] That is, the rotation conditions of the developer supply screw 42 and the developer agitation screw 43 in the developer discharge mode are different from those in the operation of developing the electrostatic latent image formed on the photosensitive drum 28Y with the developer (hereinafter referred to as the developing operation). Specifically, when the developing device 1Y develops the electrostatic latent image formed on the photosensitive drum 28Y, the drive unit 94 rotationally drives the developer supply screw 42 and the developer agitation screw 43 under the first rotation conditions. On the other hand, as will be described later, when the drive unit 94 executes the developer discharge mode during a non-developing operation in which the developing operation is not performed, the drive unit 94 rotationally drives the developer supply screw 42 and the developer agitation screw 43 under second rotation conditions different from the first rotation conditions. The first rotation conditions are, for example, rotating the developer supply screw 42 and the developer agitation screw 43 in a first rotation direction (forward rotation). The second rotation conditions are repeating rotating the developer supply screw 42 and the developer agitation screw 43 in the first rotation direction and rotating the developer supply screw 42 and the developer agitation screw 43 in a second rotation direction (reverse rotation) opposite to the first rotation direction. Such a developer discharge suppression mode and a developer discharge mode are referred to as developer discharge control.

[0066] [False detection of the agent surface due to toner concentration] However, when performing such control, based on the output value of the developer surface detection sensor 50, it is determined whether the developer surface inside the developing device 1Y is within a predetermined range. In this case, there is a possibility that the output value of the developer surface detection sensor 50 may fluctuate due to the influence of the toner concentration inside the developing device 1Y. In the present embodiment, the developer surface detection sensor 50 uses a permeability-type sensor. FIG. 6 shows the relationship between the output value of the developer surface detection sensor 50 and the developer surface inside the developing device 1Y. The developer surface detection sensor 50 detects a change in the abundance of the magnetic carrier contained in the developer as a change in permeability. As a result, when the developer surface rises, the magnetic carrier in the vicinity of the sensor increases, increasing the permeability and causing the output value of the sensor to rise. Conversely, when the developer surface drops and the magnetic carrier in the vicinity of the sensor decreases, the output value of the sensor drops. Thus, the developer surface and the output of the developer surface detection sensor 50 can be related to a primary straight line as shown in FIG. 6.

[0067] On the other hand, it is known that the permeability of the developer changes not only with the abundance of the carrier but also with the toner concentration of the developer. For example, if the toner concentration of the developer is low, the apparent permeability increases, and conversely, if the toner concentration is high, the permeability decreases. As a result, the output value of the developer surface detection sensor 50 detects an influence affected by the toner concentration of the developer in addition to the height of the developer surface. FIG. 7 shows the relationship between the output value of the developer surface detection sensor 50 and the toner concentration. FIG. 7 shows the influence of the toner concentration on the output value of the developer surface detection sensor 50 when the developer surface is the same. From this, it can be seen that as the toner concentration increases, the output value of the developer surface detection sensor 50 decreases.

[0068] In this way, since the surface detection sensor 50 is affected by the toner concentration, as shown in FIG. 8, the output value of the surface detection sensor 50 with respect to the developer surface will have different output characteristics depending on the toner concentration. FIG. 8 shows the threshold value of the developer surface inside the developing device 1Y and the corresponding output value of the surface detection sensor 50. The threshold value of the developer surface is the upper limit value within the range where the amount of developer inside the developing device 1Y is appropriate, and the corresponding output value of the surface detection sensor 50 is the execution threshold value (predetermined value) of the developer discharge mode. When an output value equal to or greater than this is detected, the developer discharge mode is executed. That is, when the output value of the surface detection sensor 50 becomes equal to or greater than the predetermined value, the control unit 80 can execute the developer discharge mode as a developer forced discharge operation for forcibly discharging the developer from the developer discharge unit 53.

[0069] In this embodiment, the reference toner concentration inside the developing device 1Y is 9%, but in this case, the execution threshold value of the developer discharge mode is 4V. However, for example, when the toner concentration has increased to 10%, if the execution threshold value of the developer discharge mode remains at 4V, it means that the threshold value of the developer surface has already been exceeded. Thus, depending on the toner concentration inside the developing device 1Y, the surface detection sensor 50 may erroneously detect the developer surface. Therefore, depending on the toner concentration, there is a possibility that the developer discharge mode for maintaining the developer surface within an appropriate range may not be properly executed.

[0070] [Control according to toner concentration] Therefore, in the present embodiment, an execution threshold for determining whether to execute a developer discharge mode (second control) based on the output value of the developer surface detection sensor 50 is changed according to the toner concentration detected by the toner concentration sensor 49 of the developing device 1Y. That is, when the toner concentration detected by the toner concentration sensor 49 is the first toner concentration (the output value of the toner concentration sensor 49 is the first value), the control unit 80 sets a predetermined value (execution threshold) to the first predetermined value (first threshold), and when the toner concentration detected by the toner concentration sensor 49 is a second toner concentration lower than the first toner concentration (the output value of the toner concentration sensor 49 is a second value larger than the first value), the control unit 80 sets the predetermined value to a second predetermined value larger than the first predetermined value (a second threshold larger than the first threshold). Thereby, even when there is a variation in the toner concentration inside the developing device 1Y, it becomes possible to execute an appropriate developer discharge mode.

[0071] Also, the developer discharge mode is performed during non-image formation (that is, during a non-developing operation in which the developing operation is not executed). Examples of non-image formation include before the start of an image formation job, between an image formation job and the next image formation job, during an image stabilization operation, and during various operation corrections. However, even during continuous image formation, an operation control for interrupting the image formation operation and executing the developer discharge mode may be inserted. Note that an image formation job is a period from the start of image formation to the completion of image formation based on a print signal (image formation signal) for forming an image on a recording material. That is, an image formation job is a period in which a series of operations including a pre-operation (pre-rotation) performed before the image formation operation, the image formation operation, and a post-operation (post-rotation) performed after the image formation operation are performed in response to the input of the image formation signal.

[0072] The execution procedure of the developer discharge mode will be described using the flowchart shown in FIG. 9. In S101, during the image formation operation or during the previous rotation of the image formation, a determination process is started to determine whether or not to execute the developer discharge mode. In S102, the toner concentration of the developer inside the developing device 1Y is detected by the toner concentration sensor 49. For the detection of the toner concentration, for example, the output value can be stabilized by taking the average value of the toner concentration with respect to the rotation cycle of the developer stirring screw 43 during a sampling time longer than the time for one rotation of the developer stirring screw 43. That is, the output value of the toner concentration sensor 49 is, for example, the average value of the output values at times that are integer multiples of the rotation pitch of the developer stirring screw 43.

[0073] In S103, according to the toner concentration inside the developing device 1Y detected in S102, the execution threshold of the developer discharge mode based on the output value of the developer surface detection sensor 50 is changed. The change of the execution threshold of the developer discharge mode is executed by referring to the threshold change coefficient for the toner concentration classification shown in FIG. 10.

[0074] This will be described. As shown in FIG. 7, the output value of the developer surface detection sensor 50 shows fluctuations related to a primary straight line under the influence of the toner concentration even when the developer surface is the same. Also, from FIG. 8, it can be seen that when the toner concentration inside the developing device 1Y changes by ±1%, it is necessary to change the execution threshold of the developer discharge mode by about ±9% accordingly. Based on these relationships, it is possible to calculate how much the execution threshold of the developer discharge mode should be changed according to the toner concentration inside the developing device 1Y. As an example, in the present embodiment, the table of the threshold change coefficient for the toner concentration classification in FIG. 10 is used.

[0075] The threshold change coefficient in this table represents the coefficient indicating how much the execution threshold of the developer discharge mode is changed according to the toner concentration inside the developing device 1Y. Accordingly, for example, when the toner concentration is 8%, the execution threshold change coefficient becomes 1.09. In this embodiment, since the reference value of the toner concentration is 9% and the execution threshold of the developer discharge mode at that time is 4V (see FIG. 8), when the toner concentration is 8%, the execution threshold is changed to 4.4V which is obtained by multiplying the execution threshold of 4V at a toner concentration of 9% by 1.09 (see FIG. 11(a)). Further, when the toner concentration is 10%, the execution threshold change coefficient becomes 0.91 and the changed execution threshold becomes 3.6V (see FIG. 11(b)). That is, as shown in FIGS. 11(a) and (b), when the toner concentration is 10% (for example, corresponding to the first toner concentration), the execution threshold is set to 3.6V (for example, corresponding to the first predetermined value), and when the toner concentration is 8% (for example, corresponding to the second toner concentration), the execution threshold is set to 4.4V (for example, corresponding to the second predetermined value).

[0076] In S104, the developer surface inside the developing device 1Y is detected by the developer surface detection sensor 50. For the detection of the developer surface, for example, the output value can be stabilized by taking the average value with respect to the rotation cycle of the developer stirring screw 43 during a sampling time that is longer than the time for one rotation of the developer stirring screw 43. That is, the output value of the developer surface detection sensor 50 is, for example, the average value of the output values at times that are integer multiples of the rotation pitch of the developer stirring screw 43. In S105, it is determined whether or not the output value of the developer surface detection sensor 50 detected in S104 is equal to or greater than the execution threshold of the developer discharge mode. At this time, as the execution threshold of the developer discharge mode, the execution threshold changed according to the toner concentration by S103 is used. For example, when the toner concentration is 8%, the execution threshold of the developer discharge mode is 4.4V. However, if the output value of the developer surface detection sensor 50 detected in S104 is 4.4V or more (Yes in S105), S106 is executed, and if the output value of the developer surface detection sensor 50 is less than 4.4V (No in S105), the control is terminated by S107.

[0077] In S106, a developer discharge mode is executed. In this case, since the developer level inside the developing device 1Y exceeds a predetermined range, if it is during the image forming operation, the image forming operation is interrupted, and the forward and reverse rotation operations of the developer supply screw 42 and the developer agitation screw 43 are repeated for a predetermined time (second rotation condition) to execute an operation to promote the discharge of the developer. Then, the process proceeds to S107.

[0078] Note that when the environmental humidity is low, the fluidity of the developer is lower than when the environmental humidity is high, and the developer is less likely to be discharged. Therefore, in the developer discharge mode of S106, the rotation speeds (rotation rates) of the developer supply screw 42 and the developer agitation screw 43 when repeating the forward and reverse rotation operations for a predetermined time may be made variable according to the environmental humidity. That is, the second rotation condition may be set according to the environmental humidity.

[0079] Specifically, when the environmental humidity is the first humidity, the developer supply screw 42 and the developer agitation screw 43 are rotated forward and backward at the first rotation speed. On the other hand, when the environmental humidity is the second humidity lower than the first humidity, by setting the rotation speeds of the developer supply screw 42 and the developer agitation screw 43 to a second rotation speed higher than the first rotation speed when repeating the forward and reverse rotation operations for a predetermined time, the discharge of the developer may be promoted. At this time, the rotation speed of the developer recovery screw 44 may also be increased in the same manner.

[0080] Also, in S106, as the rotation condition of the developer supply screw 42 and the developer agitation screw 43 when executing the developer discharge mode, instead of repeating the forward and reverse rotation operations of the developer supply screw 42 and the developer agitation screw 43 for a predetermined time, the following modification may be used.

[0081] For example, in S106, when executing the developer discharge mode, the rotation speeds of the developer supply screw 42 and the developer agitation screw 43 may be made faster than the rotation speeds of the developer supply screw 42 and the developer agitation screw 43 during the developing operation, thereby promoting the discharge of the developer. That is, under the first rotation condition, the developer supply screw 42 and the developer agitation screw 43 rotate at the first rotation speed, and under the second rotation condition, the developer supply screw 42 and the developer agitation screw 43 may rotate at a second rotation speed faster than the first rotation speed. At this time, the rotation speed of the developer recovery screw 44 may also be increased similarly.

[0082] Also, in this modification example, in S106, the rotation speed (rotation number) of the developer supply screw 42 and the developer agitation screw 43 when executing the developer discharge mode may be made variable according to the environmental humidity. This is because, as described above, when the environmental humidity is low, the fluidity of the developer is lower than when the environmental humidity is high, and the discharge of the developer tends to be difficult. Therefore, specifically, when the environmental humidity is low, the rotation speeds of the developer supply screw 42 and the developer agitation screw 43 when executing the developer discharge mode may be made faster than when the environmental humidity is high, thereby promoting the discharge of the developer. That is, when the environmental humidity is the first humidity, the developer supply screw 42 and the developer agitation screw 43 rotate at a second rotation speed faster than the first rotation speed, and when the environmental humidity is a second humidity lower than the first humidity, the developer supply screw 42 and the developer agitation screw 43 may rotate at a third rotation speed faster than the second rotation speed. At this time, the rotation speed of the developer recovery screw 44 may also be increased similarly.

[0083] As described above, in the present embodiment, the execution threshold based on the detection result of the developer surface detection sensor 50 for executing the developer discharge mode is changed according to the toner concentration detected by the toner concentration sensor 49 inside the developing device 1Y. Thereby, regardless of the toner concentration of the developer, false detection of the developer surface detection sensor 50 for detecting the developer surface can be suppressed, and appropriate discharge of the developer and maintenance of the developer surface can be achieved. And, it is possible to suppress the occurrence of developer overflow and screw lock caused by an excessive amount of developer inside the developing device 1Y.

[0084] <Second Embodiment> The second embodiment will be described with reference to FIGS. 12 to 14(b). In the present embodiment, when executing the developer discharge suppression mode for suppressing developer discharge based on the detection result of the developer surface detection sensor 50, the execution threshold of the developer discharge suppression mode is changed according to the toner concentration detected by the toner concentration sensor 49. Since the other configurations and operations are the same as those of the first embodiment described above, the same reference numerals are given to the same configurations, and the description and illustration are omitted or simplified. Hereinafter, the differences from the first embodiment will be mainly described.

[0085] In the developing device 1Y using the ACR method as described in the first embodiment, when the amount of developer in the developing device decreases, there is a risk that a sufficient amount of developer cannot be supplied to the first developing roller 30 or the second developing roller 31, resulting in the occurrence of screw mura. Screw mura means that when the amount of developer in the developing device is small, a coat mura corresponding to the screw shape of the developer supply screw 42 occurs on the first developing roller 30 or the second developing roller 31, and image defects due to the coat mura occur in the formed image.

[0086] Therefore, in this embodiment, the developer surface detection sensor 50 detects the developer surface inside the developing device 1Y, and when the detected developer surface falls below a predetermined range, a developer discharge mode is performed such as varying the rotation speeds (rotation rates) of the developer supply screw 42 and the developer agitation screw 43. That is, when the output value of the developer surface detection sensor 50 becomes equal to or less than a predetermined value for discharge suppression, the control unit 80 can execute a developer discharge suppression mode as a developer discharge suppression operation for suppressing the discharge amount of the developer from the developer discharge unit 53.

[0087] For example, in the developer discharge suppression mode, by reducing the rotation speeds of the developer supply screw 42 and the developer agitation screw 43 during image formation, the amount of developer that the developer supply screw 42 conveys to the developer discharge unit 53 is reduced to suppress the discharge of the developer. That is, the developer supply screw 42 and the developer agitation screw 43 can be changed between a first speed (first rotation speed) and a second speed (second rotation speed) that is slower than the first speed, and the control unit 80 sets the rotation speeds of the developer supply screw 42 and the developer agitation screw 43 to the second speed (second rotation condition) in the developer discharge suppression mode. Then, until the output value of the developer surface detection sensor 50 exceeds a predetermined value for discharge suppression (execution threshold of the developer discharge suppression mode), the developer supply screw 42 and the developer agitation screw 43 are driven at the second speed. At this time, the rotation speed of the developer recovery screw 44 may also be reduced similarly. Further, the developer discharge suppression mode can be executed during the image formation operation. In this case, the first developing roller 30, the second developing roller 31, and the separation roller 32 are driven at the same speed as during a normal image formation operation without reducing the speed. Note that in the developer discharge suppression mode, regardless of the output value of the developer surface detection sensor 50, the developer supply screw 42 and the developer agitation screw 43 may be driven at the second speed for a preset time.

[0088] However, as described above, the output value of the developer surface detection sensor 50 fluctuates under the influence of the toner concentration inside the developing device 1Y. Therefore, depending on the toner concentration, there is a possibility that the developer discharge suppression mode for maintaining the developer surface within an appropriate range may not be properly executed.

[0089] Therefore, in the present embodiment, according to the toner concentration detected by the toner concentration sensor 49 inside the developing device 1Y, the execution threshold of the developer discharge suppression mode (second control) based on the output value of the developer surface detection sensor 50 is changed. That is, when the toner concentration detected by the toner concentration sensor 49 is the third toner concentration (or the first toner concentration, and the output value of the toner concentration sensor 49 is the first value), a predetermined value (execution threshold) for discharge suppression is set to the first predetermined value for discharge suppression (or the first predetermined value, the first threshold), and when the toner concentration detected by the toner concentration sensor 49 is the fourth toner concentration lower than the third toner concentration (or the second toner concentration, and the output value of the toner concentration sensor 49 is the second value larger than the first value), the predetermined value for discharge suppression is set to the second predetermined value for discharge suppression larger than the first predetermined value for discharge suppression (or the second predetermined value, the second threshold larger than the first threshold). Thereby, it becomes possible to execute an appropriate developer discharge suppression mode without being affected by the toner concentration.

[0090] The execution procedure of the developer discharge suppression mode will be described using the flowchart shown in FIG. 12. Since S201 and S202 are the same as S101 and S102 in the control content described in FIG. 9, the details will be omitted.

[0091] In S203, the execution thresholds for the developer discharge mode and the developer discharge suppression mode are changed according to the toner concentration inside the developing device 1Y detected in S202. In the first embodiment, only the execution threshold for the developer discharge mode (hereinafter also referred to as the upper limit threshold) was changed, but in this embodiment, a change in the execution threshold for the developer discharge suppression mode (hereinafter also referred to as the lower limit threshold), which is executed when the developer surface falls below a predetermined range, is added. The change in the execution threshold for the developer discharge suppression mode is executed by referring to the lower limit threshold change coefficient for the toner concentration classification shown in FIG. 13. Although FIG. 13 also shows the upper limit threshold change coefficient, the upper limit threshold change coefficient is the same as the threshold change coefficient shown in FIG. 10. That is, the method for changing the execution threshold (upper limit threshold) of the developer discharge mode is the same as that in the first embodiment.

[0092] Also, the method for changing the lower limit threshold is the same as the method for changing the execution threshold of the developer discharge mode described in the first embodiment. FIG. 14(a) shows the execution threshold (lower limit threshold) of the developer discharge suppression mode when the toner concentration is 8%, and FIG. 14(b) shows the execution threshold (lower limit threshold) of the developer discharge suppression mode when the toner concentration is 10%. From FIGS. 14(a) and (b), it can be seen that when the toner concentration changes by ±1%, it is necessary to change the execution threshold of the developer discharge suppression mode by about ±14% accordingly. In this embodiment, as an example, the table of the lower limit threshold change coefficient for the toner concentration classification in FIG. 13 is used.

[0093] The lower limit threshold change coefficient in this table represents the coefficient for how much the lower limit threshold is changed according to the toner concentration inside the developing device 1Y. For example, when the toner concentration is 8%, the lower limit threshold change coefficient is 1.14, and when the toner concentration is 10%, it is 0.86. Assuming that the execution threshold of the developer discharge suppression mode when the reference toner concentration is 9% in this embodiment is 2.6V, then when the toner concentration is 8%, the lower limit threshold is changed to 3.0V, which is obtained by multiplying the lower limit threshold of 2.6V at 9% toner concentration by 1.14. When the toner concentration is 10%, the lower limit threshold is changed to 2.2V. That is, as shown in FIGS. 14(a) and (b), when the toner concentration is 10% (for example, corresponding to the third toner concentration), the execution threshold is set to 2.2V (for example, corresponding to the first predetermined value for discharge suppression), and when the toner concentration is 8% (for example, corresponding to the fourth toner concentration), the execution threshold is set to 3.0V (for example, corresponding to the second predetermined value for discharge suppression).

[0094] In S204 to S206, since it is the same as S104 to 106 whose control content is described in FIG. 9, the details are omitted. However, in S205, if the output value of the agent surface detection sensor 50 is less than the upper limit threshold (No in S205), the process proceeds to S207.

[0095] In S207, it is determined whether or not the output value of the agent surface detection sensor 50 detected in S204 is less than or equal to the lower limit threshold. At this time, the lower limit threshold of the developer discharge suppression mode uses the lower limit threshold changed by S203. For example, when the toner concentration inside the developing device 1Y is 8%, the lower limit threshold of the developer discharge suppression mode is 3.0V. However, if the output value of the agent surface detection sensor 50 detected in S204 is 3.0V or less (Yes in S207), S208 is executed, and if the output value of the agent surface detection sensor 50 is greater than 3.0V, the control is terminated by S209.

[0096] In S208, a developer discharge suppression mode is executed. In this case, since the developer level inside the developing device 1Y is below a predetermined range, by reducing the rotation speeds of the developer supply screw 42 and the developer agitation screw 43 during image formation (by setting them to the second speed), the amount of developer that the developer supply screw 42 conveys to the developer discharge section 53 is reduced, and an operation to suppress the discharge of the developer is executed. Then, the process proceeds to S209.

[0097] Note that when the environmental humidity is high, the fluidity of the developer is higher than when the environmental humidity is low, and the developer is more likely to be discharged. Therefore, in S208, the rotation speeds (rotation rates) of the developer supply screw 42 and the developer agitation screw 43 when executing the developer discharge suppression mode may be made variable according to the environmental humidity. Specifically, when the environmental humidity is high, the rotation speeds of the developer supply screw 42 and the developer agitation screw 43 when executing the developer discharge suppression mode may be reduced compared to when the environmental humidity is low, thereby suppressing the discharge of the developer. At this time, the rotation speed of the developer recovery screw 44 may also be reduced in the same manner.

[0098] Note that in the developer discharge suppression mode executed when the developer level inside the developing device 1Y is below a predetermined range, an example of reducing the rotation speeds of the developer supply screw 42 and the developer agitation screw 43 during image formation (during the developing operation) has been described, but it is not limited to this. A modification may be made in which, when the developer level inside the developing device 1Y is below a predetermined range, the developer discharge suppression mode is performed during non-image formation (during non-developing operation) instead of during image formation (during the developing operation). In this modification, the rotation conditions of the developer supply screw 42 and the developer agitation screw 43 in the developer discharge suppression mode are different from the rotation conditions of the developer supply screw 42 and the developer agitation screw 43 during the developing operation.

[0099] Specifically, during the development operation in which the developing device 1Y develops the electrostatic latent image formed on the photosensitive drum 28Y, the driving unit 94 rotationally drives the developer supply screw 42 and the developer agitation screw 43 under the first rotation condition. On the other hand, when the driving unit 94 executes the developer discharge suppression mode during the non-development operation in which the development operation is not performed, the driving unit 94 rotationally drives the developer supply screw 42 and the developer agitation screw 43 under a second rotation condition different from the first rotation condition. In the developer discharge suppression mode, the first rotation condition is to rotate the developer supply screw 42 and the developer agitation screw 43 at a first rotation speed, and the second rotation condition is to rotate the developer supply screw 42 and the developer agitation screw 43 at a second rotation speed slower than the first rotation speed. Further, even in a modified example in which the developer discharge suppression mode is performed not only during image formation (during the development operation) but also during non-image formation (during the non-development operation) when the developer surface inside the developing device 1Y falls below a predetermined range.

[0100] As described above, in the present embodiment, the lower limit threshold based on the detection result of the agent surface detection sensor 50 for executing the developer discharge suppression mode is changed according to the toner concentration detected by the toner concentration sensor 49 inside the developing device 1Y. Thereby, regardless of the toner concentration of the developer, false detection of the agent surface detection sensor 50 for detecting the agent surface of the developer can be suppressed, and appropriate discharge of the developer and maintenance of the developer surface can be achieved. And it is possible to suppress the occurrence of image defects such as screw marks due to a decrease in the amount of developer inside the developing device 1Y.

[0101] <Other Embodiments> In each of the above-described embodiments, the developing device having two developing rollers has been described, but the present invention is applicable even to a configuration having one developing roller. That is, the present invention is applicable even to a configuration having one developing roller for developing an electrostatic latent image on an image carrier such as a photosensitive drum and including an inductance sensor for detecting the developer surface in the developing container and an inductance sensor for detecting the toner concentration.

[0102] The present invention is not limited to the configurations of the above-described embodiments. For example, the image forming apparatus 100 is not limited to an MFP, and may be a copying machine, a printer, or a facsimile apparatus. Further, the configurations of the developer supply screw 42, the developer agitation screw 43, and the developer recovery screw 44 are not particularly limited as long as they can convey the developer. For example, spiral blades or paddle-shaped blades can be applied.

[0103] Also, in the above-described embodiment, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction at positions facing each other, and the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction at positions facing each other. However, the present invention is not limited to this. The rotation center O2 of the second developing roller 31 may be disposed vertically above the rotation center O1 of the first developing roller 30. The first sleeve 33 and the photosensitive drum 28Y may rotate in opposite directions at positions facing each other, and the second sleeve 34 and the photosensitive drum 28Y may rotate in opposite directions at positions facing each other. That is, it is a counter-development in which the photosensitive drum 28 rotates from vertically above to vertically below at the position where the photosensitive drum 28 faces the first developing roller 30, and it is a counter-development in which the photosensitive drum 28 rotates from vertically above to vertically below at the position where the photosensitive drum 28 faces the second developing roller 31. The present invention can also be applied to such a configuration. Further, when three or more developing rollers are provided, the present invention can be applied to any two developing rollers.

Explanation of Reference Numerals

[0104] 1Y, 1M, 1C, 1K ··· Developing device 28Y, 28M, 28C, 28K ··· Photosensitive drum (image carrier) 30 ··· First developing roller (developer carrier) 31 ··· Second developing roller (developer carrier) 42 ··· Developer supply screw (conveying screw) 43 ··· Developer agitation screw (conveying screw) 49 ··· Toner density sensor (first magnetic permeability sensor) 50 ··· Agent surface detection sensor (second magnetic permeability sensor) 53 ··· Developer discharge section 60 ··· Developer container 80 ··· Control unit 93 ··· Supply section (developer supply section) 94 ··· Driving unit 100 ··· Image forming apparatus

Claims

1. an image carrier; a developer carrier that carries a developer containing toner and a carrier for developing an electrostatic latent image formed on the image carrier; a developing container that houses the developer supplied to the developer carrier; a conveying screw that conveys the developer housed in the developing container; a developer discharge portion for discharging a part of the developer housed in the developing container; a first magnetic permeability sensor having a first detection portion for detecting the magnetic permeability of the developer housed in the developing container; a second magnetic permeability sensor having a second detection portion for detecting the magnetic permeability of the developer housed in the developing container; a developing device having the same; a developer supply portion for supplying the developer to the developing container; a driving portion that rotationally drives the conveying screw under a first rotation condition during a developing operation in which the developing device develops an electrostatic latent image formed on the image carrier; a control portion; comprising; the second detection portion is located vertically above the first detection portion; the control portion executes first control for controlling the developer supply portion to supply the developer to the developing container based on an output value of the first magnetic permeability sensor while the driving portion is rotationally driving the conveying screw; the control portion executes second control for controlling the driving portion to rotationally drive the conveying screw under a second rotation condition different from the first rotation condition during a non-developing operation in which the developing operation is not executed, based on the output value of the first magnetic permeability sensor while the driving portion is rotationally driving the conveying screw and the output value of the second magnetic permeability sensor while the driving portion is rotationally driving the conveying screw; An image forming apparatus characterized by the above.

2. the first rotation condition is to rotate the conveying screw in a first rotation direction; the second rotation condition is to repeat rotating the conveying screw in the first rotation direction and rotating the conveying screw in a second rotation direction opposite to the first rotation direction; The image forming apparatus according to claim 1, characterized by the above.

3. the first rotation condition is to rotate the conveying screw in a first rotation direction; The second rotation condition is, when the environmental humidity is the first humidity, rotating the conveying screw in the first rotation direction at the first rotation speed, and rotating the conveying screw in a second rotation direction opposite to the first rotation direction at the first rotation speed, and repeating these operations; when the environmental humidity is a second humidity lower than the first humidity, rotating the conveying screw in the first rotation direction at a second rotation speed higher than the first rotation speed, and rotating the conveying screw in the second rotation direction at the second rotation speed, and repeating these operations. The image forming apparatus according to claim 1, characterized in that.

4. The first rotation condition is rotating the conveying screw at the first rotation speed. The second rotation condition is rotating the conveying screw at a second rotation speed higher than the first rotation speed. The image forming apparatus according to claim 1, characterized in that.

5. The first rotation condition is rotating the conveying screw at the first rotation speed. The second rotation condition is, when the environmental humidity is the first humidity, rotating the conveying screw at a second rotation speed higher than the first rotation speed; when the environmental humidity is a second humidity lower than the first humidity, rotating the conveying screw at a third rotation speed higher than the second rotation speed. The image forming apparatus according to claim 1, characterized in that.

6. The first rotation condition is rotating the conveying screw at the first rotation speed. The second rotation condition is rotating the conveying screw at a second rotation speed lower than the first rotation speed. The image forming apparatus according to claim 1, characterized in that.

7. The first detection unit and the second detection unit are arranged within a range of a distance corresponding to four pitches of the blades of the conveying screw with respect to the developer conveying direction of the conveying screw. The image forming apparatus according to claim 1, characterized in that.

8. An image carrier, A developing device having a developer carrier that carries a developer containing toner and a carrier for developing an electrostatic latent image formed on the image carrier, a developing container that houses the developer supplied to the developer carrier, a conveying screw that conveys the developer housed in the developing container, a developer discharge unit for discharging a part of the developer housed in the developing container, a first magnetic permeability sensor having a first detection unit that detects the magnetic permeability of the developer housed in the developing container, and a second magnetic permeability sensor having a second detection unit that detects the magnetic permeability of the developer housed in the developing container, a developer supply unit that supplies the developer to the developing container, a driving unit that rotationally drives the conveying screw under a first rotation condition during a developing operation in which the developing device develops an electrostatic latent image formed on the image carrier, a control unit, and comprising, wherein the second detection unit is vertically above the first detection unit, the control unit executes first control to control the developer supply unit to supply the developer to the developing container based on an output value of the first magnetic permeability sensor while the driving unit is rotationally driving the conveying screw, the control unit, when the output value of the first magnetic permeability sensor while the driving unit is rotationally driving the conveying screw is a first value and the output value of the second magnetic permeability sensor while the driving unit is rotationally driving the conveying screw is equal to or greater than a first threshold value, executes second control to control the driving unit to rotationally drive the conveying screw under a second rotation condition different from the first rotation condition during a non-developing operation in which the developing operation is not executed, when the output value of the first magnetic permeability sensor while the driving unit is rotationally driving the conveying screw is the first value and the output value of the second magnetic permeability sensor while the driving unit is rotationally driving the conveying screw is less than the first threshold value, does not execute the second control, when the output value of the first magnetic permeability sensor while the driving unit is rotationally driving the conveying screw is a second value greater than the first value and the output value of the second magnetic permeability sensor while the driving unit is rotationally driving the conveying screw is equal to or greater than a second threshold value greater than the first threshold value, executes the second control, When the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is the second value, and the output value of the second magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is less than the second threshold value, the second control is not executed. An image forming apparatus characterized by the above.

9. The first rotation condition is to rotate the conveyance screw in a first rotation direction. The second rotation condition is to repeat rotating the conveyance screw in the first rotation direction and rotating the conveyance screw in a second rotation direction opposite to the first rotation direction. The image forming apparatus according to claim 8, characterized by the above.

10. The first rotation condition is to rotate the conveyance screw in a first rotation direction. The second rotation condition is, when the environmental humidity is a first humidity, to repeat rotating the conveyance screw in the first rotation direction at a first rotation speed and rotating the conveyance screw in a second rotation direction opposite to the first rotation direction at the first rotation speed; and when the environmental humidity is a second humidity lower than the first humidity, to repeat rotating the conveyance screw in the first rotation direction at a second rotation speed higher than the first rotation speed and rotating the conveyance screw in the second rotation direction at the second rotation speed. The image forming apparatus according to claim 8, characterized by the above.

11. The first rotation condition is to rotate the conveyance screw at a first rotation speed. The second rotation condition is to rotate the conveyance screw at a second rotation speed higher than the first rotation speed. The image forming apparatus according to claim 8, characterized by the above.

12. The first rotation condition is to rotate the conveyance screw at a first rotation speed. The second rotation condition is, when the environmental humidity is a first humidity, to rotate the conveyance screw at a second rotation speed higher than the first rotation speed; and when the environmental humidity is a second humidity lower than the first humidity, to rotate the conveyance screw at a third rotation speed higher than the second rotation speed. The image forming apparatus according to claim 8, characterized by the above.

13. The first detection unit and the second detection unit are arranged within a range of a distance corresponding to four pitches of the blades of the conveyance screw with respect to the developer conveyance direction of the conveyance screw. The image forming apparatus according to claim 8, characterized in that.

14. An image carrier, A developer carrier that carries a developer containing toner and a carrier for developing an electrostatic latent image formed on the image carrier, a developing container that houses the developer supplied to the developer carrier, a conveyance screw that conveys the developer housed in the developing container, a developer discharge unit for discharging a part of the developer housed in the developing container, a first magnetic permeability sensor having a first detection unit for detecting the magnetic permeability of the developer housed in the developing container, and a second magnetic permeability sensor having a second detection unit for detecting the magnetic permeability of the developer housed in the developing container. A developer supply unit that supplies the developer to the developing container, A drive unit that rotationally drives the conveyance screw, A control unit, Comprising, The second detection unit is vertically above the first detection unit. The control unit controls the developer supply unit to supply the developer to the developing container based on the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw. The control unit, When the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is a first value, and the output value of the second magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is equal to or less than a first threshold value, the control unit controls the drive unit to rotationally drive the conveyance screw at a second rotational speed slower than the first rotational speed during the developing operation in which the developing device develops the electrostatic latent image formed on the image carrier. When the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is the first value, and the output value of the second magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is greater than the first threshold value, the control unit controls the drive unit to rotationally drive the conveyance screw at the first rotational speed during the developing operation. When the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is a second value greater than the first value, and the output value of the second magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is equal to or less than a second threshold value greater than the first threshold value, the drive unit is controlled to rotationally drive the conveyance screw at the second rotational speed during the development operation. When the output value of the first magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is the second value, and the output value of the second magnetic permeability sensor while the drive unit is rotationally driving the conveyance screw is greater than the second threshold value, the drive unit is controlled to rotationally drive the conveyance screw at the first rotational speed. An image forming apparatus characterized by the above.

15. The first detection unit and the second detection unit are arranged within a range of a distance corresponding to four pitches of the blades of the conveyance screw with respect to the developer conveyance direction of the conveyance screw. The image forming apparatus according to claim 14, characterized by the above.

Images