Image forming apparatus

Abstract

To provide a configuration capable of appropriately discharging a developer regardless of the fluidity of the developer.SOLUTION: The developing container accommodates a developer. The developer discharge portion discharges the developer to the outside of the developer container. The developer surface detection sensor detects a developer surface in the developer container. The control part executes a developer discharge mode for forcibly discharging the developer from the developer discharge part based on Vpp which is a difference between a maximum output value Vmax and a minimum output value Vmin of the developer surface detection sensor in a predetermined time.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as a copier, printer, facsimile, or a multifunction machine having multiple functions of these. [Background technology]

[0002] In an electrophotographic image forming apparatus, an electrostatic latent image formed on an image carrier is developed into a toner image by a developing device. Conventionally, such developing devices use a two-component developer containing toner and magnetic carrier. To prevent deterioration of the carrier, developing devices using two-component developers widely use the so-called ACR (Auto Carrier Refresh) method, in which toner containing a small amount of carrier is replenished to the developing device while the resulting excess developer is discharged from the developing device.

[0003] In an ACR-type developing device, it is necessary to maintain a constant amount of developer in the developing device to maintain consistent quality of developed images. Patent Document 1 proposes a configuration including a developer level detection sensor that detects the developer level in the developing device, a transport screw that transports the developer, and an outlet that discharges the developer, with excess developer overflowing from the outlet when transported by the transport screw. Patent Document 1 adjusts the amount of developer discharged from the outlet by controlling the rotation speed of the transport screw based on the developer level detected by the developer level detection sensor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-191485 Summary of the Invention [Problem to be solved by the invention]

[0005] In a developing device, the developer discharge speed from the discharge port (hereinafter referred to as the developer discharge speed) changes depending on the fluidity of the developer inside the developing device. In particular, if the fluidity of the developer decreases, the developer will not be discharged from the discharge port and the amount of developer inside the developing device will increase, which may cause the developer to overflow from the developing device or screw lock due to an increase in the rotational torque of the transport screw.

[0006] In the developing device described in Patent Document 1, the developer discharge speed from the discharge port is adjusted by controlling the rotation speed of the conveying screw based on the developer surface height. However, because the developer discharge speed varies depending on the fluidity of the developer, even if the developer discharge speed is adjusted according to the developer surface, the developer may not be discharged properly depending on the fluidity of the developer. For example, if the developer surface detection sensor detects a developer level above a threshold and the rotation speed of the conveying screw is increased to increase the developer discharge speed, a sufficient developer discharge speed can be maintained if the developer has high fluidity. On the other hand, if the developer has low fluidity, the developer may not be discharged sufficiently, or it may take a long time for the developer surface to reach the appropriate position due to the slow developer discharge speed.

[0007] An object of the present invention is to provide a configuration that can appropriately discharge developer regardless of the fluidity of the developer. [Means for solving the problem]

[0008] One aspect of the present invention is an image forming apparatus comprising: an image carrier; a developer carrier that carries a developer containing toner and carrier to develop an electrostatic latent image formed on the image carrier; a developing container having a first chamber that contains the developer and supplies the developer to the developer carrier; and a second chamber that forms a circulation path for the developer between the first chamber and the second chamber; a developing device having a first transport screw that is disposed in the first chamber and transports the developer in a first direction; a second transport screw that is disposed in the second chamber and transports the developer in a second direction opposite to the first direction; an agent level detection sensor that detects the agent level of the developer contained in the developing container; and a developer discharge section that discharges the developer outside the developing container; and a control section, wherein the control section performs a developer discharge operation to forcibly discharge the developer from the developer discharge section based on Vpp, which is the difference between the maximum output value Vmax and the minimum output value Vmin of the agent level detection sensor at a predetermined time. [Effects of the Invention]

[0009] According to the present invention, the developer can be appropriately discharged regardless of the fluidity of the developer. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a control block diagram of the image forming apparatus according to the first embodiment. [Figure 3] FIG. 2 is a cross-sectional view showing the schematic configuration of the developing device according to the first embodiment. [Figure 4] 2 is a schematic diagram showing the developing device according to the first embodiment, cut in a direction parallel to the rotation axis of the first developing roller; FIG. [Figure 5] 3 is a schematic cross-sectional view showing the developer surface when the developer has high fluidity in the developing device according to the first embodiment; FIG. [Figure 6] 6 is a graph showing the output result of the developer level detection sensor when the developer has high fluidity in the developing device according to the first embodiment. [Figure 7]3 is a schematic cross-sectional view showing the developer surface when the developer has low fluidity in the developing device according to the first embodiment; FIG. [Figure 8] 6 is a graph showing the output result of the developer level detection sensor when the fluidity of the developer is low in the developing device according to the first embodiment. [Figure 9] 6 is a graph showing the relationship between the fluidity index of the developer and the fluctuation in the output value of the developer level detection sensor in the developing device according to the first embodiment. [Figure 10] 6 is a flowchart of control relating to execution of a developer discharging mode according to the first embodiment. [Figure 11] 10 is a graph showing the relationship between the rotation speed of the developer supply screw and the developer discharging speed in a developing device according to a second embodiment. [Figure 12] 10 is a flowchart of control relating to execution of a developer discharging mode according to a second embodiment. [Figure 13] 11 is a graph showing the relationship between the fluidity index of the developer and the developer discharging speed in a developing device according to a third embodiment. [Figure 14] 11 is a graph showing the relationship between the rotation speed of the developer supply screw and the developer discharging speed when the fluidity of the developer is different in a developing device according to a third embodiment. [Figure 15] 11 is a flowchart of control relating to execution of a developer discharging mode according to the third embodiment. [Figure 16] 11 is a graph showing the relationship between the fluctuation of the output value of the developer level detection sensor and the rotational speed correction coefficient of the developer supply screw in a developing device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] First Embodiment The first embodiment will be described with reference to Figures 1 to 10. First, the schematic configuration of an image forming apparatus according to this embodiment will be described with reference to Figure 1.

[0012] [Image forming equipment] The image forming apparatus 100 is a full-color image forming apparatus, and in this embodiment, is, for example, 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 has image forming units PY, PM, PC, and PK arranged in parallel, which respectively perform the image forming process of four toner images of yellow, magenta, cyan, and black.

[0013] The image forming units PY, PM, PC, and PK for each color include primary chargers 21Y, 21M, 21C, and 21K, developing units 1Y, 1M, 1C, and 1K, optical writing units (exposure units) 22Y, 22M, 22C, and 22K, photosensitive drums 28Y, 28M, 28C, and 28K, and cleaning units 26Y, 26M, 26C, and 26K. The image forming apparatus 100 also includes a transfer unit 2 and a fixing unit 3. Since the image forming units PY, PM, PC, and PK for each color have the same configuration, the following description will be given using the image forming unit PY as a representative.

[0014] The photosensitive drum 28Y, which serves as a rotatable image carrier, is a photosensitive member having a photosensitive layer made of a resin such as polycarbonate containing an organic photoconductor (OPC), and is configured to rotate at a predetermined speed. The primary charger 21Y is made of a corona discharge electrode disposed around the photosensitive drum 28Y, and charges the surface of the photosensitive drum 28Y with generated ions.

[0015] 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 area and forming a charge pattern (electrostatic latent image) corresponding to the image data. The developing device 1Y transfers the contained developer to the photosensitive drum 28Y to develop the electrostatic latent image formed on the photosensitive drum 28Y. The developer is a mixture of carrier and toner corresponding to each color, and the electrostatic latent image is visualized by the toner.

[0016] The transfer device 2 has primary transfer rollers 23Y, 23M, 23C, and 23K, an intermediate transfer belt 24, and a secondary transfer roller 25. The intermediate transfer belt 24 is wound around the primary transfer rollers 23Y, 23M, 23C, and 23K and multiple rollers and is supported so that it can run. From the top in FIG. 1, the primary transfer rollers 23Y, 23M, 23C, and 23K correspond to the colors Y (yellow), M (magenta), C (cyan), and K (black), respectively. The secondary transfer roller 25 is disposed outside the intermediate transfer belt 24 and is configured so that a recording material can pass between it and the intermediate transfer belt 24. The recording material is, for example, a sheet such as paper or a plastic sheet.

[0017] The toner images of each color formed on the photosensitive drums 28Y, 28M, 28C, and 28K are transferred successively onto the intermediate transfer belt 24 by the primary transfer rollers 23Y, 23M, 23C, and 23K, forming a color toner image in which yellow, magenta, cyan, and black layers are superimposed. The formed toner image is transferred by the secondary transfer roller 25 onto a recording material conveyed from a cassette or the like containing the recording material. The recording material onto which the toner image has been transferred is subjected to pressure and heat in the fixing device 3. This melts the toner on the recording material, and the color image is fixed to the recording material.

[0018] Developer storage units 27Y, 27M, 27C, and 27K are provided corresponding to developing devices 1Y, 1M, 1C, and 1K, respectively, and are filled with replaceable bottles containing developers corresponding to the respective colors of yellow, magenta, cyan, and black, from top to bottom. Developer storage units 27Y, 27M, 27C, and 27K are configured to be able to transport (supply) developers to developing devices 1Y, 1M, 1C, and 1K corresponding to the colors of the developers stored therein.

[0019] For example, the toner weight ratio of the developer stored in the bottle (i.e., toner concentration: the ratio of toner weight to the total weight of 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, developer containing toner corresponding to the consumed amount is replenished, and the toner weight ratio of the developer in the developing devices 1Y, 1M, 1C, and 1K is maintained constant.

[0020] [Control configuration] FIG. 2 is a control block diagram showing the main components 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 conveying unit 98, a fixing unit 99, and a control unit 80. The operation unit 96 includes a display unit and operation buttons capable of displaying various information. The display unit may be a touch panel that allows touch operation. The image forming unit 97 includes various motors that drive components such as the photosensitive drums 28Y, 28M, 28C, and 28K of the image forming units PY, PM, PC, and PK, which form images on the recording material, and the developing devices 1Y, 1M, 1C, and 1K, as well as power supplies that apply voltages to these components. The recording material conveying unit 98 includes various motors that drive conveying rollers that convey the recording material. The fixing unit 99 includes a heater for the fixing device 3 and a motor that drives the fixing device. The operation unit 96 , the image forming unit 97 , the recording material conveying unit 98 , and the fixing unit 99 are connected to the control unit 80 and controlled by the control unit 80 .

[0021] The control unit 80 includes a CPU (Central Processing Unit) 81, a ROM (Read Only Memory) 82, a RAM (Random Access Memory) 83, etc. The CPU 81 reads a program corresponding to the processing content from the ROM 82, loads it into the RAM 83, and controls the operation of each component of the image forming apparatus 100 in cooperation with the loaded program. At this time, various data stored in the storage unit 91 is referenced.

[0022] The storage unit 91 is configured, for example, by a non-volatile semiconductor memory (so-called flash memory) or a hard disk drive. The control unit 80 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or 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 configured, for example, by a communication control card such as a LAN card.

[0023] The control unit 80 is also connected to a toner concentration sensor 49, a developer level detection sensor 50, and a supply unit 93. The toner concentration sensor 49 is provided in each of the developing devices 1Y, 1M, 1C, and 1K, and detects the toner concentration of the developer in each of the developing devices 1Y, 1M, 1C, and 1K, as described below. The developer level detection sensor 50 is also provided in each of the developing devices 1Y, 1M, 1C, and 1K, and detects the developer level in each of the developing devices 1Y, 1M, 1C, and 1K, as described below. The supply unit 93, which serves as a developer supply unit, includes a motor that drives a supply mechanism that supplies developer from 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 other components based on the detection results of the toner concentration sensor 49 and the developer level detection sensor 50.

[0024] [Developing device] Next, developing devices 1Y, 1M, 1C, and 1K will be described in detail using Figures 3 and 4. Since developing devices 1Y, 1M, 1C, and 1K have the same configuration, the following description will focus on developing device 1Y as a representative. Figure 3 is a conceptual diagram illustrating developing device 1Y shown in Figure 1, and Figure 4 is a schematic diagram of developing device 1Y cut in a direction parallel to the rotational axis direction of first developing roller 30 and viewed from above.

[0025] As shown in FIG. 3, the developing device 1Y has 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 components are housed in a developing container 60.

[0026] The first developing roller 30 is a developer carrier that is driven to rotate, and is disposed adjacent to the photosensitive drum 28Y so that its rotation axis is substantially parallel to the rotation axis of the photosensitive drum 28Y. The first developing roller 30 has a rotating first sleeve 33 and a first magnet (fixed magnet) 36 that is disposed non-rotatingly inside the first sleeve 33 and that magnetically attracts the developer to the surface of the first sleeve 33. The first developing roller 30 magnetically attracts (carries) the developer pumped up by a developer supply screw 42, and uses the developer to develop an electrostatic latent image formed on the rotating photosensitive drum 28Y (image carrier).

[0027] The first sleeve 33 is a non-magnetic cylindrical member that is driven to rotate around a rotation shaft 39. The rotation direction of the first sleeve 33 is clockwise as indicated by the arrow in FIG. 3, which is opposite to the rotation direction of the photosensitive drum 28Y in this embodiment. Therefore, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction while facing each other. That is, forward development is achieved in which the photosensitive drum 28 rotates from a vertically downward direction to a vertically upward direction while facing the first sleeve 33. A space that allows the first sleeve 33 to rotate is provided between the inner periphery of the first sleeve 33 and the outer periphery of the first magnet 36.

[0028] The developer attracted to the first sleeve 33 is transported toward the photosensitive drum 28Y by the rotation of the first sleeve 33, and develops 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 transported to the vicinity of the second developing roller 31 by the rotation of the first sleeve 33. Then, near the closest position between the first developing roller 30 and the second developing roller 31, the developer is peeled off from the first sleeve 33 and transferred onto the second sleeve 34 by the magnetic fields generated by the first magnet 36 contained in the first developing roller 30 and the second magnet 37 contained in the second developing roller 31.

[0029] As will be described below, the second developing roller 31 of the developing device 1Y of this embodiment is disposed vertically above the first developing roller 30. Therefore, the transfer of developer from the first sleeve 33 to the second sleeve 34 must also be performed vertically from below to above against gravity. The first sleeve 33 and the second sleeve 34 are disposed with a predetermined gap between them at their closest portions.

[0030] The second developing roller 31 is a developer carrier that is driven to rotate, and is disposed downstream of the first developing roller 30 in the rotation direction of the photosensitive drum 28Y and such that the rotation center O2 of the second developing roller 31 is positioned above the rotation center O1 of the first developing roller 30 in the vertical direction, and developer is transferred from the first developing roller 30 by magnetic force. In this embodiment, the entire second developing roller 31 is positioned above the rotation center O1 of the first developing roller 30. Like the first developing roller 30, the second developing roller 31 is disposed 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.

[0031] The second developing roller 31 has a rotating second sleeve 34 and a second magnet (fixed magnet) 37 that is non-rotatingly disposed inside the second sleeve 34 and that magnetically attracts the developer to the surface of the second sleeve 34. The second developing roller 31 receives the developer from the first developing roller 30 (first sleeve 33) and attracts (carries) the developer using the magnetic force, and develops the electrostatic latent image formed on the rotating photosensitive drum 28Y with the developer. A peeling roller 32, which will be described later, is located on the side of the second developing roller 31.

[0032] The second sleeve 34 is a non-magnetic cylindrical member and is driven to rotate around a rotation shaft 40. The rotation direction of the second sleeve 34 is the same clockwise direction as the first sleeve 33, as shown by the arrow in FIG. 3, and in this embodiment, it is the opposite direction to the rotation direction of the photosensitive drum 28Y. Therefore, the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction when facing each other. That is, when the photosensitive drum 28 faces the second sleeve 34, the photosensitive drum 28 rotates from a lower vertical position to an upper vertical position, which is a forward development. Furthermore, the second sleeve 34 and the first sleeve 33 rotate in opposite directions when facing each other. A space that allows the second sleeve 34 to rotate is provided between the inner periphery of the second sleeve 34 and the outer periphery of the second magnet 37.

[0033] The developer attracted to the second sleeve 34 is transported 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 the latent image formed on the photosensitive drum 28Y is developed, the developer remaining on the second sleeve 34 is transported to the vicinity of the peeling roller 32 by the rotation of the second sleeve 34. Then, near 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 fields generated by the second magnet 37 contained in the second developing roller 31 and the third magnet 38 contained in the peeling roller 32.

[0034] The peeling roller 32 as a peeling unit is disposed on the opposite side of the photosensitive drum 28Y with respect to the rotation center of the second sleeve 34, and peels off the developer from the second developing roller 31 after the electrostatic latent image on the photosensitive drum 28Y is developed by the second developing roller 31. Specifically, the peeling roller 32 is a developer carrier that is driven to rotate, and is disposed between the second developing roller 31 and the developer recovery screw 44 so that its rotation center is above the rotation center R of the second developing roller 31.

[0035] The peeling roller 32 is disposed so that its rotation axis is substantially parallel to the rotation axis of the second developing roller 31. The peeling roller 32 has a rotating third sleeve 35 and a third magnet (fixed magnet) 38 that is disposed non-rotatingly inside the third sleeve 35 and that attracts the developer to the surface of the third sleeve 35 by magnetic force, and is configured to transfer the developer from the second developing roller 31 to the peeling roller 32 by magnetic force.

[0036] The third sleeve 35 is a non-magnetic cylindrical member that is driven to rotate around the rotation axis 41. The rotation direction of the third sleeve 35 is counterclockwise as indicated by the arrow in FIG. 2, which is opposite to the rotation direction of the second sleeve 34 in this embodiment. Therefore, the third sleeve 35 and the second sleeve 34 rotate in the same direction while facing each other. A space that allows the third sleeve 35 to rotate is provided between the inner periphery of the third sleeve 35 and the outer periphery of the third magnet 38.

[0037] The developer attracted onto the third sleeve 35 is transported downstream in the rotation direction by the rotation of the third sleeve 35, and is peeled off from the third sleeve 35 by the third magnet 38 contained in the peeling roller 32 at a position close to the developer recovery screw 44, and falls by its own weight toward the guide member 45 located vertically below. The developer that has fallen onto the guide member 45 is then guided by its own weight toward the developer recovery screw 44.

[0038] The guide member 45 and the developer recovery screw 44 constitute a developer recovery section 47 as a recovery section that recovers the developer peeled off from the third sleeve 35 on the peeling roller 32. In the developer recovery section 47, the developer recovery screw 44 is disposed so that its center of rotation is positioned lower than the center of rotation of the peeling roller 32 in the vertical direction, and conveys the developer handed over (recovered) from the peeling roller 32 while stirring it.

[0039] The guide member 45 serving as a guide section is disposed vertically below the peeling roller 32 and guides the developer peeled off by the peeling roller 32 toward the developer recovery screw 44. Such a guide member 45 has an inclined surface 45a along which the developer slides down under its own weight, in order to more reliably guide the peeled off developer toward the developer recovery screw 44. The inclined surface 45a is inclined relative to the horizontal direction so that the developer recovery screw 44 side is lower than the position below the peeling roller 32.

[0040] The developer recovery screw 44, which serves as a recovery member and a transport section, transports the recovered developer to a developer circulation section 46, which will be described next. That is, the developer recovery screw 44 is a screw transport member used to transport the recovered developer in one direction while stirring it as it slides down the inclined surface of the guide member 45.

[0041] The developer circulation unit 46 is a supply unit for supplying the developer to the first developing roller 30, and includes a regulating member 52, a developer supply screw 42 as a first transport screw, and a developer stirring screw 43 as a second transport screw. In the developer circulation unit 46, the developer is stirred in the developer supply screw 42 and the developer stirring screw 43 while being transported in a substantially horizontal direction and supplied to the first developing roller 30. As described above, the developer collected by the developer collection unit 47 falls by its own weight and is introduced into the developer circulation unit 46.

[0042] The developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are screw conveying members that convey the developer in one direction while stirring it, and the developer supply screw 42 and developer stirring screw 43 are located vertically below the developer recovery screw 44. The developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are also arranged so that their rotation axes are approximately parallel to each other. The rotation axis of each screw is also approximately parallel to the rotation axis of the first developing roller 30.

[0043] The developer supply screw 42 is located between the first developing roller 30 and the developer agitating screw 43, and a partition wall 48 of the developer container 60 is disposed between the developer supply screw 42 and the developer agitating screw 43. The partition wall 48 of the developer container 60 extends along the rotational axis direction of the developer supply screw 42 and the developer agitating screw 43. The partition wall 48 is provided with communication openings 48a and 48b (FIG. 4) that communicate a first transport path 61 serving as a first chamber through which the developer is transported by the developer supply screw 42 with a second transport path 62 serving as a second chamber through which the developer is transported by the developer agitating screw 43. A developer circulation path is formed between the first transport path 61 and the second transport path 62.

[0044] The developer stirred by the developer recovery screw 44 passes through a communication port (not shown) formed in a partition wall 63 of the developing container 60 located between the developer recovery screw 44 and the developer supply screw 42, and falls by its own weight toward the developer supply screw 42. That is, the developer stirred by the developer recovery screw 44 is introduced into the developer supply screw 42. The above-mentioned guide member 45 is formed integrally with the partition wall 63, and the developer recovery screw 44 is disposed above the partition wall 63.

[0045] The position of the communication port through which the developer stirred by the developer recovery screw 44 falls under its own weight and is introduced into the developer circulation section 46 is preferably arranged to avoid the area where the developer is supplied toward the first developing roller 30 (the middle part with respect to the rotational axis direction of the developer supply screw 42). In this embodiment, the communication port is positioned at a position included in the range of the downstream end (terminal end) in the developer transport direction of the first transport path 61 in which the developer supply screw 42 is arranged.

[0046] The developer transport 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 . That is, the developer supply screw 42 is disposed in the first transport path 61 and transports the developer in a first direction. The developer agitation screw 43 is disposed in the second transport path 62 and transports the developer in a second direction opposite to the first direction. The start side (upstream end in the developer transport direction) and end side (downstream end in the developer transport direction) of the first transport path 61 in which the developer supply screw 42 is disposed communicate with the end side and start side of the second transport path 62 in which the developer agitation screw 43 is disposed via communication openings 48a and 48b provided in the partition wall 48. Therefore, the developer circulates in the rotational direction of the developer supply screw 42 and the developer agitation screw 43, indicated by the arrows in FIG. 3 , and in a substantially horizontal direction within the developing container 60, and a portion of the developer is supplied toward the first developing roller 30.

[0047] The developer supply port 51 is disposed above the developer stirring screw 43 in the developing container 60, and is connected to the developer storage unit 27Y (see FIG. 1). The developer supply port 51 is configured so that the developer stored in a bottle loaded in the developer storage unit 27Y can be supplied to the second conveying path 62 in which the developer stirring screw 43 is disposed.

[0048] As described above, the toner concentration (toner weight ratio) of the developer stored in the bottle of developer storage section 27Y is greater than the toner concentration of the developer in developing device 1Y, so by adjusting the developer supplied to developer stirring screw 43, it is possible to maintain a constant toner weight ratio of the developer in developing device 1Y.

[0049] 4, developer discharge portion 53 is disposed at the most downstream position in the developer transport direction of developer supply screw 42, and discharges excess developer in developing device 1Y to the outside of developing device 1Y from developer discharge port 54. Developer discharge portion 53 is formed with screw 55, the developer transport direction of which is opposite to the developer transport direction of developer supply screw 42. Screw 55 is disposed coaxially with developer supply screw 42, rotates together with developer supply screw 42, and generates a flow that pushes developer back from developer discharge portion 53 toward developer circulation portion 46.

[0050] Further, downstream of the screw 55 with respect to the developer transport direction of the developer supply screw 42, a screw 56 that transports the developer in the same direction as the developer transport direction of the developer supply screw 42 is provided coaxially with the developer supply screw 42 and the screw 55. The screw 56 rotates together with the developer supply screw 42 and the screw 55, and transports the developer that has been transported over the screw 55 to the developer discharge port 54 and is discharged from the developer discharge port 54.

[0051] As a result, when the amount of developer in the developing device 1Y is maintained at an appropriate level, the developer is pushed back by the screw 55, thereby reducing the amount of developer discharged from the developer discharge port 54. On the other hand, when toner is supplied to the developing device 1Y from the developer resupply port 51 and the amount of developer attempting to move from the developer supply screw 42 to the developer discharge portion 53 increases, the developer moves over the screw 55 to the screw 56, and the excess developer is discharged from the developing device 1Y through the developer discharge port 54. In this case, if the rotation speeds of the developer supply screw 42 and the developer agitation screw 43 are increased, the developer is more likely to move to the developer discharge portion 53, and 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 reduced, the movement of developer to the developer discharge portion 53 is reduced, and the amount of developer discharged from the developer discharge port 54 can be reduced.

[0052] The toner concentration sensor 49, which serves as a toner concentration detection sensor, is disposed to detect the toner concentration in the developer contained in the developer circulating unit 46. The toner concentration sensor 49 is an inductance sensor that detects the magnetic permeability of the developer. The toner concentration corresponds to the amount of toner consumed in the developing device 1Y, and is therefore used to control the supply of developer from the developer storage unit 27Y. For example, when the control unit 80 (FIG. 2) detects that the toner concentration has dropped below a predetermined toner concentration, the control unit 80 supplies developer from the developer storage unit 27Y (executes a supply operation). Note that the magnetic permeability of the developer varies depending on the toner concentration, so the toner concentration can be detected using the magnetic permeability. The toner concentration sensor 49 is disposed in the second conveying path 62. Specifically, as shown in FIG. 3, the toner concentration sensor 49 is disposed vertically below the rotation axis of the developer stirring screw 43, and as shown in FIG. 4, at the downstream end of the second conveying path 62 with respect to the developer conveying direction of the developer stirring screw 43.

[0053] The developer level detection sensor 50 is disposed to detect the developer level of the developer contained in the developer circulation unit 46. The developer level detected by the developer level detection sensor 50 corresponds to the amount of developer contained in the developing device 1Y and is therefore used for developer discharge control. For example, if it is detected that the developer level is higher than a predetermined value, the rotation speed of the developer supply screw 42 and the developer stirring screw 43 is increased, thereby discharging the developer from the developer discharge port 54. The developer level detection sensor 50 is an inductance sensor that detects the magnetic permeability of the developer. The developer level detection sensor 50 is disposed in the second conveying path 62. Specifically, as shown in FIG. 3, the developer level detection sensor 50 is disposed vertically above the rotation axis of the developer stirring screw 43. It is desirable that the detection surface of the developer level detection sensor 50 be positioned vertically above the detection surface of the toner concentration sensor 49.

[0054] The regulating member 52 is disposed adjacent to the first developing roller 30 and is used to regulate the amount of developer supplied from the developer circulating unit 46 to the first developing roller 30. The regulating member 52 can be configured to regulate the amount of developer attracted to 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 regulating member 52.

[0055] The developer circulation path in the developing container 60 is such that the developer is transported in a substantially horizontal direction while being stirred in the developer circulation section 46, and then supplied to the first developing roller 30, and is transferred from the first developing roller 30 to the second developing roller 31 above by magnetic force. Next, the developer is transferred from the second developing roller 31 to the peeling roller 32 on the side of the second developing roller 31 by magnetic force again, and then peeled off from the peeling roller 32 by a third magnet 38 contained in the peeling roller 32, and further collected in the developer collection section 47, and introduced again into the developer circulation section 46.

[0056] [Developer] As described above, this embodiment uses a two-component development system, and the developer is a mixture of negatively charged non-magnetic toner and magnetic carrier. The non-magnetic toner is a resin such as polyester or styrene acrylic, which contains colorants, wax components, etc. and is then pulverized or polymerized to form a powder, to which fine powders such as titanium oxide and silica are added on the surface. The magnetic carrier is a core made of resin particles kneaded with ferrite particles or magnetic powder, with a resin coating on the surface. In this embodiment, the toner concentration in the initial developer (the weight ratio of toner contained in the developer) is 8%.

[0057] Generally, two-component development systems using toner and carrier charge both to a predetermined polarity through frictional contact between the toner and carrier, which means that the toner is subjected to less stress than single-component development systems using single-component developers. However, over long periods of use, the amount of dirt (spent) adhering to the carrier surface increases, gradually reducing the toner's ability to charge. This results in problems such as fogging and toner scattering. While increasing the amount of carrier contained in the development device is one way to extend the life of a two-component development device, this is undesirable because it increases the size of the development device.

[0058] To solve the above problems associated with two-component developers, this embodiment employs an ACR (Auto Carrier Refresh) method. The ACR method is a method for suppressing an increase in degraded carrier by gradually replenishing new developer from the developer storage unit 27Y into the developing device 1Y and gradually discharging developer with degraded charging performance from the developer discharge port 54 of the developing device 1Y. This allows the degraded carrier in the developing device 1Y to be gradually replaced with new carrier, making it possible to maintain the charging performance of the carrier in the developing device 1Y at a substantially constant level.

[0059] [Relationship between developer fluidity and developer level sensor output value] Incidentally, in a developing device 1Y equipped with an ACR system such as that of this embodiment, for example, a change in fluidity due to deterioration of the developer may inhibit the discharge of the developer, and the amount of developer inside the developing device 1Y may increase, leading to overflow of the developer near the first developing roller 30 and the second developing roller 31 and locking of various screws inside the developing device 1Y. Fig. 5 is a schematic diagram of the developer surface T when the developer fluidity is high, and Fig. 6 shows the output result of the developer surface detection sensor 50 in the state shown in Fig. 5.

[0060] When the developer moves in the transport direction due to the rotation of the developer supply screw 42 and the developer stirring screw 43, the developer level T fluctuates according to the pitch of the blades of the developer supply screw 42 and the developer stirring screw 43. For this reason, as shown in FIG. 6, the output value of the developer level detection sensor 50 fluctuates periodically. The period of the output value of the developer level detection sensor 50 depends on the rotation speed of the developer stirring screw 43 and the number of threads of the blades. Therefore, when the rotation speed of the developer stirring screw 43 is constant, the output value of the developer level detection sensor 50 has a specific periodicity. In this case, the developer level height is taken as the average value of the output values ​​of the developer level detection sensor 50 within a specified time period.

[0061] Next, FIG. 7 is a schematic diagram of the developer surface T when the developer fluidity is low, and FIG. 8 shows the output result of the developer surface detection sensor 50 in the state shown in FIG. 7. When the developer fluidity is low, the developer tends to accumulate in the gap between the developer stirring screw 43 and the inner wall of the developer container 60. As shown in FIG. 4 in particular, the installation position of the developer surface detection sensor 50 is the most downstream position in the developer transport direction of the developer stirring screw 43, near the communication port 48b, which is the portion where the developer is transferred from the second transport path (stirring chamber) 62 to the first transport path (supply chamber) 61. Therefore, since the developer does not move in one direction at the installation position of the developer surface detection sensor 50, the developer tends to accumulate near the installation position of the developer surface detection sensor 50.

[0062] As the developer stirring screw 43 transports the developer, the accumulated developer continues to pile up in the vertical direction. After accumulating to a predetermined height, it collapses, and the collapsed developer is transported by the rotation of the developer stirring screw 43. The developer then repeats accumulation and collapse. FIG. 8 shows the output result of the developer level detection sensor 50 at this time. The developer level detection sensor 50 detects the amount of developer near the detection surface, so it is affected not only by the movement of developer by the developer stirring screw 43 but also by the developer accumulated near the detection surface. For this reason, as shown in FIG. 8, the accumulation and collapse of developer, accompanied by a period due to the rotation of the developer stirring screw 43, causes the output value of the developer level detection sensor 50 to fluctuate more greatly than when the developer has high fluidity (FIG. 6).

[0063] Here, if the maximum output value of the developer level detection sensor 50 in a predetermined time is Vmax and the minimum output value is Vmin, the fluctuation Vpp of the output value of the developer level detection sensor 50 is the difference between Vmax and Vmin. The predetermined time is preferably an integer multiple of the rotation pitch of the developer stirring screw 43. For example, the predetermined time is set to the rotation time of one pitch of the developer stirring screw 43. Specifically, if the pitch of the developer stirring screw 43 is 30 mm and the rotation speed is 600 rpm, the time required for one pitch is 100 msec, and this is set as the predetermined time.

[0064] In consideration of variations in Vpp, the predetermined time may be the time it takes for the developer to make one circuit through the developer circulation section 46. Specifically, if the circulation path length within the developer circulation section 46 is 660 mm, the pitch of the developer supply screw 42 and the developer stirring screw 43 is 30 mm, and the rotation speed is 600 rpm, the time it takes for the developer to make one circuit through the developer circulation section 46 is approximately 2.2 seconds, and this is set as the predetermined time.

[0065] The results of an investigation into the fluctuation Vpp of the output value of the developer level detection sensor 50 relative to the fluidity of the developer are shown in Figure 9. When the fluidity of the developer is high, the developer does not accumulate, and the fluctuation Vpp of the output value of the developer level detection sensor 50 is small. On the other hand, when the fluidity of the developer is low, the developer is likely to accumulate, and the fluctuation Vpp of the output value of the developer level detection sensor is large.

[0066] Therefore, in this embodiment, the control unit 80 executes a developer discharge mode as a developer discharge operation in which the developer is forcibly discharged from the developer discharge unit 53 based on Vpp, which is the difference between the maximum output value Vmax and the minimum output value Vmin of the developer level detection sensor 50 over a predetermined time. That is, when Vpp is equal to or greater than a predetermined value, the developer discharge mode is executed, and when Vpp is less than the predetermined value, the developer discharge mode is not executed. In the developer discharge mode, the developer supply screw 42 and the developer stirring screw 43 are rotated forward and backward repeatedly for a predetermined time, thereby discharging excess developer out of the developing device 1Y.

[0067] Furthermore, the developer discharge mode is preferably performed during non-image formation periods. Examples of non-image formation periods include before the start of an image formation job, between one image formation job and the next, during image stabilization operations, and during various operational corrections. However, even during continuous image formation, the image formation operation may be stopped midway and operational control executed to execute the developer discharge mode may be inserted. Note that an image formation job is the period from the start of image formation based on a print signal (image formation signal) for forming an image on a recording material to the completion of image formation. In other words, an image formation job is a period during which a series of operations are performed, based on the input of an image formation signal, including pre-operations (pre-rotation) performed before the image formation operation, image formation operation, and post-operations (post-rotation) performed after the image formation operation.

[0068] The procedure for executing the developer discharge mode of this embodiment will be described with reference to the flowchart shown in FIG. 10. First, the control unit 80 starts an image formation operation using the image forming unit 97 and the like (S101). Next, the control unit 80 calculates the fluctuation Vpp of the output value of the developer level detection sensor 50 after the start of driving of the developing device 1Y (S102). Then, the control unit 80 determines whether the fluctuation Vpp of the developer level detection sensor 50 calculated in S102 is less than a preset threshold value (predetermined value) (S103). The threshold value (predetermined value) is set appropriately depending on the device, but in this embodiment, it is set to 2V.

[0069] In S103, if Vpp is less than the threshold value (S103YeS), the control unit 80 does not execute the developer discharge mode, but executes the normal image formation mode (image forming operation) using the image forming unit 97, the recording material conveying unit 98, and the fixing unit 99 (S104). On the other hand, if the deflection Vpp of the developer level detection sensor 50 calculated in S102 is equal to or greater than the threshold value (above a predetermined value) (No in S103), the control unit 80 executes the developer discharge mode using the image forming unit 97 (S105). After executing the developer discharge mode, the normal image formation mode is executed (S104). After the image formation mode ends, this control ends (S106).

[0070] By executing this control flow, the amount of developer in the developing device 1Y can be maintained at an appropriate level both when the deflection Vpp of the developer level detection sensor 50 is below the threshold, i.e., when the developer fluidity is high, and when the deflection Vpp of the developer level detection sensor 50 is equal to or greater than the threshold, i.e., when the developer fluidity is low. In this manner, in this embodiment, the developer can be appropriately discharged regardless of the developer fluidity. As a result, overflow of the developer from the developing device 1Y and screw lock caused by an increase in the rotational torque of the developer supply screw 42 or the developer agitation screw 43 can be suppressed.

[0071] <Second embodiment> The second embodiment will be described with reference to Figures 11 and 12. In this embodiment, in the developer discharge mode, the rotation speeds of the developer supply screw 42 and the developer stirring screw 43 are increased compared to those during normal image formation. Since the other configurations and functions are the same as those of the first embodiment described above, the same reference numerals are used for the same configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the points that are different from the first embodiment.

[0072] In this embodiment, the control unit 80 sets the rotation speeds of the developer supply screw 42 and the developer stirring screw 43 to a first rotation speed when an image forming operation is being performed, and sets the rotation speeds of the developer supply screw 42 and the developer stirring screw 43 to a second rotation speed that is faster than the first rotation speed when the developer discharging mode is being performed. The developer discharging mode is performed for a preset time. In this embodiment, the developer supply screw 42 and the developer stirring screw 43 are driven by the same drive source, and therefore the developer supply screw 42 and the developer stirring screw 43 are driven at the same rotation speed.

[0073] The developer supply screw 42 and the developer agitating screw 43 may be driven by separate drive sources and may be driven at different rotational speeds. In this case, since the developer discharge unit 53 is located downstream of the developer supply screw 42 in the developer transport direction of the developer supply screw 42, the rotational speed of the developer supply screw 42 is increased in the developer discharge mode. That is, the control unit 80 sets the rotational speed of the developer supply screw 42 to a first rotational speed during image formation, and sets the rotational speed of the developer supply screw 42 to a second rotational speed, which is faster than the first rotational speed, during the developer discharge mode. The rotational speed of the developer agitating screw 43 is set to the first rotational speed, for example, both during image formation and the developer discharge mode.

[0074] 11 shows the relationship between the rotation speed of the developer supply screw 42 and the developer discharge speed from the developer discharge port 54. As shown in Fig. 11, as the rotation speed of the developer supply screw 42 increases, the developer discharge speed from the developer discharge port 54 increases. This is because the force of transporting the developer in the transport direction due to the increase in the rotation speed of the developer supply screw 42 becomes greater than the force of transporting the developer in the opposite direction to the transport direction by the screw 55 located upstream of the developer discharge port 54 in the transport direction, and therefore the amount of developer that overcomes the screw 55 increases.

[0075] Therefore, when the developer discharge mode is executed, the rotation speed of the developer supply screw 42 and the developer stirring screw 43 can be temporarily increased relative to the rotation speed during image formation, thereby increasing the amount of developer discharged from the developer discharge port 54.

[0076] The procedure for executing the developer discharge mode of this embodiment will be described using the flowchart shown in FIG. 12. Steps S201, S202, S203, S204, and S206 in FIG. 12 are the same as steps S101, S102, S103, S104, and S106 in FIG. 10 of the first embodiment. If the deflection Vpp of the developer level detection sensor 50 calculated in S202 is equal to or greater than the threshold value (predetermined value) (No in S203), the control unit 80 executes the developer discharge mode using the image forming unit 97 (S205). In the developer discharge mode of this embodiment, the rotational speeds of the developer supply screw 42 and the developer stirring screw 43 are temporarily increased relative to the rotational speeds during image formation. In the developer discharge mode, the developer supply screw 42 and the developer stirring screw 43 operate at preset rotational speeds and for preset periods of time.

[0077] By executing this control flow, when the deflection Vpp of the developer level detection sensor 50 is equal to or greater than the threshold, i.e., when the developer fluidity is low, the amount of developer discharged from the developer discharge port 54 is increased, thereby preventing an excessive amount of developer in the developing device 1Y. Therefore, in this embodiment, developer can be appropriately discharged regardless of the developer fluidity. As a result, it is possible to prevent developer overflow from the developing device 1Y and screw lock due to an increase in the rotational torque of the developer supply screw 42 or the developer stirring screw 43. In this embodiment, when the developer discharge mode is executed, the first developing roller 30 and the second developing roller 31 are rotated at the same speed as during image formation. However, the rotation of the first developing roller 30 and the second developing roller 31 may be stopped.

[0078] <Third embodiment> The third embodiment will be described with reference to Figures 13 to 16. In this embodiment, in the developer discharge mode, the rotation speeds of the developer supply screw 42 and the developer stirring screw 43 are changed according to the fluidity of the developer. Since the other configurations and functions are the same as those of the second embodiment described above, the same reference numerals are used for the same configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the points that are different from the second embodiment.

[0079] In this embodiment, when the developer discharge mode is executed, the control unit 80 sets the rotation speed of the developer supply screw 42 and the developer stirring screw 43 to a first speed when the fluctuation Vpp of the detection value of the developer level detection sensor 50 is a first value, and sets the rotation speed of the developer supply screw 42 and the developer stirring screw 43 to a second speed faster than the first speed when Vpp is a second value greater than the first value. In other words, the lower the fluidity of the developer, the faster the rotation speed of the developer supply screw 42 and the developer stirring screw 43 is made.

[0080] In this embodiment, the developer supply screw 42 and the developer agitating screw 43 may also be driven by separate drive sources and may be driven at different rotational speeds. In this case, when the fluctuation Vpp of the detection value of the developer level detection sensor 50 is a first value, the rotational speed of the developer supply screw 42 is set to a first speed, and when Vpp is a second value greater than the first value, the rotational speed of the developer supply screw 42 is set to a second speed greater than the first speed. The rotational speed of the developer agitating screw 43 may be the same as that during image formation whether Vpp is the first value or the second value, or may be set to the first speed whether Vpp is the first value or the second value.

[0081] 13 shows the developer discharge speed from the developer discharge port 54 versus the fluidity index of the developer. When the rotation speed of the developer supply screw 42 is constant, the higher the fluidity, the faster the developer discharge speed from the developer discharge port 54. This is because, as the fluidity of the developer increases, the conveying force in the opposite direction to the conveying direction by the screw 55 located upstream of the developer discharge port 54 in the conveying direction decreases, making it easier for the developer to overcome the screw 55.

[0082] For this reason, in the second embodiment described above, when the fluidity of the developer decreases, the rotation speed of the developer supply screw 42 is increased to temporarily increase the developer discharge speed. However, depending on the fluidity of the developer, there is a risk that the discharge amount may not be adjusted to an appropriate amount of developer in the developing device 1Y. Specifically, when the fluctuation Vpp of the output value of the developer level detection sensor 50 deviates significantly from the threshold value, i.e., when the fluidity has decreased significantly, the developer discharge speed is slow, so that the developer is not sufficiently discharged, and there is a possibility that the amount of developer in the developing device 1Y may remain excessive. For this reason, in the Japanese embodiment, the developer discharge speed is adjusted according to the fluidity of the developer.

[0083] Figure 14 shows the developer discharge speed versus the rotation speed of the developer supply screw 42 when the fluidity of the developer is different. As shown in Figure 14, when the rotation speed of the developer supply screw 42 is the same, the developer discharge speed decreases when the fluidity of the developer is low. Therefore, when the fluidity of the developer is low, it is possible to achieve the same developer discharge speed as when the fluidity is high by increasing the rotation speed of the developer supply screw 42.

[0084] The procedure for executing the developer discharging mode of this embodiment will be described with reference to the flowchart shown in Fig. 15. S301, S302, S303, S304, and S307 in Fig. 15 are the same as S101, S102, S103, S104, and S106 in Fig. 10 of the first embodiment. If the deflection Vpp of the developer level detection sensor 50 calculated in S302 is equal to or greater than the threshold value (above a predetermined value) (No in S303), the control unit 80 calculates rotational speed correction coefficients for the developer supply screw 42 and the developer stirring screw 43 in the developer discharging mode from Vpp and the image formation speed (S305).

[0085] Next, the control unit 80 drives the developer supply screw 42 and the developer stirring screw 43 at rotational speeds obtained by multiplying the central setting value in the developer discharge mode by the rotational speed correction coefficient calculated in S305 (S306). In this embodiment, the rotational speed correction coefficient is set in advance based on experimental results and corresponds to the deflection Vpp of the developer level detection sensor 50, as shown in FIG. 16. As is clear from FIG. 16, the larger Vpp is, i.e., the lower the fluidity of the developer, the higher the rotational speed correction coefficient becomes. Therefore, the lower the fluidity of the developer is, the faster the rotational speeds of the developer supply screw 42 and the developer stirring screw 43 become in the developer discharge mode.

[0086] By executing this control flow, even when the fluidity of the developer is significantly reduced, the rotation speed in the developer discharge mode is increased compared to the second embodiment, thereby increasing the amount of developer discharged from the developer discharge port 54 and preventing the amount of developer in the developing device 1Y from becoming excessive. Therefore, in the present embodiment as well, the developer can be appropriately discharged regardless of the fluidity of the developer. As a result, it is possible to prevent the developer from overflowing from the developing device 1Y and screw lock caused by an increase in the rotational torque of the developer supply screw 42 or the developer stirring screw 43.

[0087] <Other embodiments> In each of the above-described embodiments, the developer level detection sensor 50 detects the developer level in the developer storage unit by measuring the magnetic permeability of the developer in the developer storage unit. Other examples of the developer level detection sensor 50 include a sensor that measures the developer level using an optical method such as an optical sensor, or a sensor that measures the developer level by physical contact. Generally, the developer level detection sensor 50 may be any sensor that can measure the developer level in the developer container 60.

[0088] In the above-described embodiments, the developing device has been described as having two developing rollers, but the present invention can also be applied to a configuration with one developing roller. That is, the present invention can also be applied to a configuration with one developing roller for developing an electrostatic latent image on an image carrier such as a photosensitive drum, and a developer level detection sensor for detecting the developer level in a developer container.

[0089] 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, but may be a copier, printer, or facsimile machine. Furthermore, the configurations of the developer supply screw 42, developer stirring screw 43, and developer recovery screw 44 are not particularly limited as long as they can transport the developer. For example, spiral blades or paddle-shaped blades can be applied.

[0090] In the above-described embodiment, the first sleeve 33 and the photosensitive drum 28Y rotate in the same direction while facing each other, and the second sleeve 34 and the photosensitive drum 28Y rotate in the same direction while facing each other. However, this is not limited to this. Alternatively, the rotation center O2 of the second developing roller 31 may be positioned vertically higher than the rotation center O1 of the first developing roller 30, and the first sleeve 33 and the photosensitive drum 28Y may rotate in opposite directions while facing each other, and the second sleeve 34 and the photosensitive drum 28Y may rotate in opposite directions while facing each other. That is, the photosensitive drum 28 may rotate from an upper position to a lower position in the vertical direction when facing the first developing roller 30, and the photosensitive drum 28 may rotate from an upper position to a lower position in the vertical direction when facing the second developing roller 31. The present invention can also be applied to such a configuration. Furthermore, when three or more developing rollers are provided, the present invention can be applied to any two of the developing rollers. [Explanation of symbols]

[0091] 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 (first conveying screw) 43 Developer stirring screw (second conveying screw) 49 Toner concentration sensor (toner concentration detection sensor) 50···Adhesive level detection sensor 53 Developer discharge section 60....Developing container 61 First conveying path (first chamber) 62 Second transport path (second chamber) 80 Control unit 100 Image forming device

Claims

1. an image carrier; a developing device including: 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 having a first chamber that contains the developer and supplies the developer to the developer carrier; and a second chamber that forms a circulation path for the developer between the first chamber and the second chamber; a first transport screw that is disposed in the first chamber and transports the developer in a first direction; a second transport screw that is disposed in the second chamber and transports the developer in a second direction opposite to the first direction; a developer level detection sensor that detects the developer level of the developer contained in the developing container; and a developer discharge section that discharges the developer out of the developing container; A control unit; Equipped with The control unit executes a developer discharging operation for forcibly discharging the developer from the developer discharging unit based on Vpp, which is a difference between a maximum output value Vmax and a minimum output value Vmin of the developer level detection sensor in a predetermined time. An image forming apparatus characterized by:

2. The control unit executes the developer discharging operation when the Vpp is equal to or greater than a predetermined value, and does not execute the developer discharging operation when the Vpp is less than the predetermined value.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. The control unit sets the rotation speeds of the first conveying screw and the second conveying screw to a first rotation speed when an image forming operation is performed, and sets the rotation speeds of the first conveying screw and the second conveying screw to a second rotation speed that is faster than the first rotation speed when the developer discharging operation is performed.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. The control unit, during the execution of the developer discharging operation, sets the rotation speeds of the first conveying screw and the second conveying screw to a first speed when the Vpp is a first value, and sets the rotation speeds of the first conveying screw and the second conveying screw to a second speed faster than the first speed when the Vpp is a second value greater than the first value.

4. The image forming apparatus according to claim 3, wherein the image forming apparatus is a recording medium.

5. the developer discharge portion is disposed downstream of the first conveying screw in a developer conveying direction of the first conveying screw, the first conveying screw and the second conveying screw can be driven at different rotational speeds, The control unit sets the rotation speed of the first conveying screw to a first rotation speed during an image forming operation, and sets the rotation speed of the first conveying screw to a second rotation speed higher than the first rotation speed during a developer discharging operation.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. The control unit, during the execution of the developer discharging operation, sets the rotation speed of the first conveying screw to a first speed when the Vpp is a first value, and sets the rotation speed of the first conveying screw to a second speed faster than the first speed when the Vpp is a second value greater than the first value.

6. The image forming apparatus according to claim 5,

7. The agent level detection sensor is an inductance sensor.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

8. a toner concentration detection sensor for detecting the toner concentration of the developer contained in the developer container; a developer supply unit that supplies developer to the developing container, The control unit executes a supply operation of supplying the developer to the developing container by the developer supply unit when the toner concentration detected by the toner concentration detection sensor is lower than a predetermined toner concentration.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

9. The detection surface of the toner level detection sensor is located vertically above the detection surface of the toner concentration detection sensor.

9. The image forming apparatus according to claim 8,

Images