Image forming apparatus

Abstract

To provide a configuration capable of suppressing erroneous detection of a toner concentration detection sensor even when there is a variation in a developer amount.SOLUTION: The developer supply portion supplies the developer to the developer container. The toner density sensor outputs magnetic permeability to detect the toner density of the developer in the developing container. The developer surface detection sensor has a detection surface located above the detection surface of the toner concentration sensor in the vertical direction, and outputs magnetic permeability to detect the developer surface of the developer in the developer container. In a case where the toner concentration in the developing container is constant, when the developer surface height detected by the developer surface detection sensor is the first height, the control portion executes a replenishment operation of replenishing the developer to the developing container by the developer replenishment portion in a case where the output value of the toner concentration sensor is the first output value. Further, when the developer surface height detected by the developer surface detection sensor is a second height higher than the first height, the replenishment operation is executed in a case where the output value of the toner concentration detection sensor is a second output value larger than the first output value.SELECTED DRAWING: Figure 9

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] Furthermore, the accuracy of detecting the toner concentration in the developing device is important for maintaining a constant image density of the output. This is because low accuracy in detecting the toner concentration can lead to image defects such as fogging and carrier adhesion. For example, Patent Document 1 discloses a method for controlling the toner concentration by calculating the change in toner charge amount from the output value of a temperature sensor and adding the change in charge amount to the output value of a toner concentration sensor. Furthermore, Patent Document 2 discloses a method for correcting the output value of a toner concentration sensor when forming images by driving a developer stirring member at different linear velocities. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-30877 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-206288 Summary of the Invention [Problem to be solved by the invention]

[0005] In a developing device employing the ACR method, image formation is performed while the amount of developer in the developing device repeatedly increases and decreases. While a method for detecting toner concentration is widely used based on magnetic permeability, there is a risk of erroneous detection of toner concentration if the bulk density of the developer fluctuates due to an increase or decrease in the amount of developer during image formation. The aforementioned Patent Documents 1 and 2 do not describe control that takes into account the increase or decrease in the amount of developer.

[0006] SUMMARY OF THE INVENTION An object of the present invention is to provide a configuration that can prevent erroneous detection by a toner concentration detection sensor even when there is a fluctuation in the amount of developer. [Means for solving the problem]

[0007] One aspect of the present invention is a developing container including: 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 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 toner concentration detection sensor that outputs magnetic permeability to detect the toner concentration of the developer contained in the developing container; and a toner concentration detection sensor whose detection surface is located vertically above the detection surface of the toner concentration detection sensor and that outputs magnetic permeability to detect the developer surface of the developer contained in the developing container. The image forming apparatus comprises a developing device having a surface detection sensor, a developer supply unit that supplies developer to the developing container, and a control unit, wherein the control unit is capable of executing a supply operation to supply 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, and when the toner concentration in the developing container is constant, the control unit executes the supply operation when the agent surface height detected by the agent surface detection sensor is a first height and the output value of the toner concentration detection sensor is a first output value, and when the agent surface height detected by the agent surface detection sensor is a second height higher than the first height and the output value of the toner concentration detection sensor is a second output value higher than the first output value.

[0008] One aspect of the present invention is a developing container including: 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 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 toner concentration detection sensor that outputs magnetic permeability to detect the toner concentration of the developer contained in the developing container; and a toner concentration detection sensor whose detection surface is located vertically above the detection surface of the toner concentration detection sensor and that outputs magnetic permeability to detect the developer surface of the developer contained in the developing container. The image forming apparatus comprises a developing device having a surface detection sensor, a developer supply unit that supplies developer to the developing container, and a control unit, wherein the control unit is capable of executing a supply operation to supply 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, and when the toner concentration in the developing container is constant, the control unit executes the supply operation when the agent surface height detected by the agent surface detection sensor is a first height and the output value of the toner concentration detection sensor is a first output value, and when the agent surface height detected by the agent surface detection sensor is a third height lower than the first height and the output value of the toner concentration detection sensor is a third output value smaller than the first output value.

[0009] One aspect of the present invention is a developing container including 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 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, and a magnetic permeability sensor that outputs a magnetic permeability signal to detect the toner concentration of the developer contained in the developing container. An image forming apparatus comprising: a developing device having a toner concentration detection sensor; a developer surface detection sensor whose detection surface is located vertically above the detection surface of the toner concentration detection sensor and which outputs magnetic permeability to detect the developer surface of the developer contained in the developing container; a developer supply unit that supplies developer to the developing container; and a control unit, wherein the control unit is capable of performing a supply operation to supply developer to the developing container using the developer supply unit when the output value of the toner concentration detection sensor is higher than a predetermined value, and corrects the output value of the toner concentration detection sensor based on the output value of the developer surface detection sensor. [Effects of the Invention]

[0010] According to the present invention, even when there is a fluctuation in the amount of developer, erroneous detection by the toner concentration detection sensor can be suppressed. [Brief explanation of the drawings]

[0011] [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] (a) A schematic diagram of the developing device according to the first embodiment, cut in a direction parallel to the rotation axis of the first developing roller, viewed from above; (b) A schematic diagram of the second conveying path, cut in a direction parallel to the rotation axis of the first developing roller, viewed from the side. [Figure 5] 5 is a graph showing the relationship between the toner concentration of the developer and the output value of the toner concentration sensor in the developing device according to the first embodiment. [Figure 6] 6 is a graph showing an example of an output result of a developer level detection sensor in the developing device according to the first embodiment. [Figure 7] 6 is a graph showing the relationship between the amount of developer and the output value of the developer surface detection sensor in the developing device according to the first embodiment. [Figure 8] 6 is a graph showing the relationship between the output value of the developer level detection sensor and the toner concentration detected by the toner concentration sensor in the developing device according to the first embodiment. [Figure 9] 6 is a flowchart of control relating to the execution of a replenishment operation according to the first embodiment. [Figure 10] (a) A schematic diagram of a developing device according to a second embodiment, cut in a direction parallel to the rotation axis of the first developing roller, viewed from above; (b) A schematic diagram of a second conveying path, cut in a direction parallel to the rotation axis of the first developing roller, viewed from the side. [Figure 11] 10 is a graph showing the relationship between the amount of developer and the output value of the developer surface detection sensor in a developing device according to a second embodiment. [Figure 12] 10 is a graph showing the relationship between the output value of the developer level detection sensor and the toner concentration detected by the toner concentration sensor in the developing device according to the second embodiment. [Figure 13] FIG. 10 is a cross-sectional view showing the schematic configuration of a developing device according to a comparative example. [Figure 14] (a) A schematic diagram of a developing device according to a comparative example, cut in a direction parallel to the rotation axis of the first developing roller and viewed from above; (b) A schematic diagram of a second conveying path, cut in a direction parallel to the rotation axis of the first developing roller and viewed from the side. [Figure 15] 10 is a graph showing the relationship between the amount of developer and the output value of the developer surface detection sensor in a developing device according to a comparative example. [Figure 16] 10 is a graph showing the relationship between the output value of the developer level detection sensor and the toner concentration detected by the toner concentration sensor in a developing device according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0012] First Embodiment The first embodiment will be described with reference to Figures 1 to 9. First, the schematic configuration of an image forming apparatus according to this embodiment will be described with reference to Figure 1.

[0013] [Image forming device] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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, also known as the TD ratio) 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.

[0021] [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 .

[0022] 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.

[0023] 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.

[0024] 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.

[0025] [Developing device] Next, developing devices 1Y, 1M, 1C, and 1K will be described in detail using FIG. 3 and FIGS. 4(a) and (b). Since developing devices 1Y, 1M, 1C, and 1K have the same configuration, the following description will focus on developing device 1Y as a representative. FIG. 3 is a conceptual diagram illustrating developing device 1Y shown in FIG. 1, and FIG. 4(a) is a schematic diagram of developing device 1Y cut in a direction parallel to the rotational axis of first developing roller 30 and viewed from above. FIG. 4(b) is a schematic diagram of second conveying path 62 of developing device 1Y cut in a direction parallel to the rotational axis of first developing roller 30 and viewed from the left side of FIG. 3.

[0026] 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.

[0027] 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).

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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, 48b (FIG. 4(a)) 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.

[0045] 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.

[0046] 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.

[0047] The developer transport directions of the developer supply screw 42 and the developer agitating screw 43 are opposite to each other, as shown by the arrows in Figures 4(a) and 4(b). 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 agitating 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 the 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 the start side of the second transport path 62 in which the developer agitating screw 43 is disposed via communication openings 48a and 48b provided in the partition wall 48. Therefore, the developer circulates in the rotation direction of the developer supply screw 42 and the developer stirring screw 43 indicated by the arrows in FIG. 3 and in the approximately horizontal direction within the developing container 60, and a portion of the developer is supplied toward the first developing roller 30.

[0048] 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.

[0049] 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.

[0050] As shown in FIG. 4(a), 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 from developer discharge port 54 to the outside of developing device 1Y. Developer discharge portion 53 is formed with a screw 55 whose developer transport direction 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.

[0051] 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.

[0052] 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.

[0053] 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 circulation unit 46. The toner concentration sensor 49 is an inductance sensor that detects the magnetic permeability of the developer and outputs the magnetic permeability to detect the toner concentration. 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). That is, when the output value of the toner concentration sensor 49 is higher than a predetermined value, the control unit 80 can execute a supply operation in which the supply unit 93, which serves as a developer supply unit, supplies developer to the developing container 60. The predetermined toner concentration is the toner concentration when the output value of the toner concentration sensor 49 is a predetermined value. Note that the magnetic permeability of the developer changes depending on the toner concentration, so the toner concentration can be detected using the magnetic permeability. Figure 5 shows the output value Vtd of toner concentration sensor 49 when the toner concentration is varied with a constant amount of developer. As is clear from Figure 5, the output value Vtd of toner concentration sensor 49 decreases as the toner concentration increases. Therefore, if the output value Vtd of toner concentration sensor 49 is higher than a predetermined value, it can be determined that the toner concentration has decreased below the predetermined value.

[0054] 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 provided vertically below the rotation axis of the developer stirring screw 43, and as shown in Figs. 4(a) and 4(b), the toner concentration sensor 49 is provided at the downstream end of the second conveying path 62 with respect to the developer conveying direction of the developer stirring screw 43.

[0055] The developer level detection sensor 50 is disposed to detect the developer level of the developer contained in the developer circulation section 46. The developer level height 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, when 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 to discharge 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 and outputs the magnetic permeability to detect the developer level.

[0056] FIG. 6 shows an example of the output result of the developer level detection sensor 50. 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 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 blade threads. The developer level height corresponds to the average value of the output value of the developer level detection sensor 50 within a specified time period, and hereinafter, the output value Vo of the developer level detection sensor 50 is referred to as the average value within a specified time period.

[0057] The control unit 80 performs developer discharge control to maintain a constant amount of developer in the developing device 1Y based on the developer level detected by the developer level detection sensor 50 and the toner concentration detected by the toner concentration sensor 49. 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, and as shown in FIGS. 4(a) and 4(b), the sensor 50 is disposed at approximately the same position as the toner concentration sensor 49 in the developer conveying direction of the developer stirring screw 43. The detection surface of the developer level detection sensor 50 is positioned vertically above the detection surface of the toner concentration sensor 49. As shown in FIG. 4(b), the sensor 50 is preferably disposed at a position where fluctuations in the developer level can be easily detected.

[0058] 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.

[0059] 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.

[0060] [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%.

[0061] 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.

[0062] 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.

[0063] [Relationship between developer amount and toner concentration sensor output value] When the ACR method described above is adopted, image formation is performed while the amount of developer in the developing device 1Y repeatedly increases and decreases. Meanwhile, the toner concentration is detected by the toner concentration sensor 49 using magnetic permeability, as described above. Therefore, if the bulk density of the developer fluctuates due to an increase or decrease in the amount of developer during image formation, there is a risk that the toner concentration will be detected erroneously. If the accuracy of toner concentration detection is low, there is a risk that image defects such as fogging and carrier adhesion will occur. This will be explained in detail using Figures 7 and 8.

[0064] FIG. 7 shows the output value Vo of the developer level detection sensor 50 when the developer amount is changed at a toner concentration of 8%. It can be seen from FIG. 7 that the greater the amount of developer in the developer container 60, the higher the output value Vo of the developer level detection sensor 50. Next, FIG. 8 shows the toner concentration (TD ratio) detected by the toner concentration sensor 49 relative to the output value Vo of the developer level detection sensor 50. Since the actual toner concentration is 8%, the smaller the output value Vo of the developer level detection sensor 50 (the smaller the amount of developer), the higher the toner concentration will be erroneously detected. Conversely, the larger the output value Vo of the developer level detection sensor 50 (the greater the amount of developer), the lower the toner concentration will be erroneously detected. If a discrepancy occurs between the actual toner concentration and the toner concentration detected by the toner concentration sensor 49 (i.e., the toner concentration based on the output value Vtd of the toner concentration sensor 49), image defects such as fogging and carrier adhesion may occur.

[0065] [Toner density correction based on the output value of the toner level detection sensor] Therefore, in this embodiment, the control unit 80 corrects the output value (magnetic permeability) of the toner concentration sensor 49 based on the output value (magnetic permeability) of the developer level detection sensor 50. In this embodiment, the output value of the toner concentration sensor 49 is corrected based on the output value of the developer level detection sensor 50 as follows: The output value Vtd (magnetic permeability) of the toner concentration sensor 49 is multiplied by a toner concentration correction coefficient α corresponding to the output value (magnetic permeability) of the developer level detection sensor 50 shown in Table 1, and the multiplied value (Vtd × α) is used as the corrected output value (magnetic permeability) of the toner concentration sensor 49. Then, if the toner concentration corresponding to this corrected output value (magnetic permeability) is lower than a predetermined toner concentration, in other words, if the corrected output value (magnetic permeability) is higher than a predetermined value, a replenishment operation is performed in which the replenishing unit 93 replenishes the developer to the developer container 60. [Table 1]

[0066] Table 1 shows the toner concentration correction coefficient α corresponding to the output value of the developer level detection sensor 50 when the toner concentration in the developer container is constant. As explained above in FIG. 8, the smaller the output value Vo of the developer level detection sensor 50 (the smaller the amount of developer), the higher the toner concentration detected by the toner concentration sensor 49 becomes compared to the actual toner concentration. Also, the larger the output value Vo of the developer level detection sensor 50 (the larger the amount of developer), the lower the toner concentration detected by the toner concentration sensor 49 becomes compared to the actual toner concentration.

[0067] Here, when the output value Vo of the developer level detection sensor 50 is equal to or greater than 2.5V and less than 3.0V (2.5V to 3.0V), the amount of developer in the developing container is appropriate, and so the toner concentration correction coefficient α is set to 1. When the output value Vo of the developer level detection sensor 50 is less than this value (2.5V to 3.0V), i.e., when the amount of developer is small, the toner concentration correction coefficient α is set to greater than 1, and the toner concentration used in the replenishment operation is corrected to be lower than the toner concentration detected by the toner concentration sensor 49. When the output value Vo of the developer level detection sensor 50 is greater than this value (2.5V to 3.0V), i.e., when the amount of developer is large, the toner concentration correction coefficient α is set to less than 1, and the toner concentration used in the replenishment operation is corrected to be higher than the toner concentration detected by the toner concentration sensor 49.

[0068] Therefore, in this embodiment, when the developer level height detected by the developer level detection sensor 50 is a first height and the output value Vtd of the toner concentration sensor 49 is a first output value, the control unit 80 executes a replenishment operation to replenish the developer to the developing container 60 using the replenishment unit 93. For example, when the output value Vo of the developer level detection sensor 50 is 2.5 V to 3.0 V, the toner concentration correction coefficient α is 1, so the control unit 80 controls the replenishment operation according to the uncorrected value (1.00 × Vtd) of the actual output value Vtd of the toner concentration sensor 49. Therefore, when the output value Vo is 2.5 V to 3.0 V, the replenishment operation is executed if the first output value is higher than a predetermined value.

[0069] Furthermore, when the developer level detected by the developer level detection sensor 50 is at a second height higher than the first height, and the output value of the toner concentration sensor 49 is a second output value higher than the first output value, the control unit 80 executes a replenishment operation to replenish the developer to the developer container 60 using the replenishment unit 93. For example, when the output value Vo of the developer level detection sensor 50 is between 3.0 V and 3.5 V, the toner concentration correction coefficient α is 0.95, and the control unit 80 controls the replenishment operation according to the value obtained by multiplying the actual output value Vtd of the toner concentration sensor 49 by 0.95 (0.95 × Vtd). Therefore, when the output value Vo is between 3.0 V and 3.5 V, the replenishment operation is not executed simply because the second output value is higher than a predetermined value. Instead, the replenishment operation is executed only when the value obtained by multiplying the second output value by 0.95 is higher than the predetermined value. Note that instead of multiplying the actual output value Vtd of the toner concentration sensor 49 by the toner concentration correction coefficient α, the predetermined value serving as the execution threshold for the replenishment operation may be changed. In this case, the predetermined value is set higher than the predetermined value when the amount of developer in the developing container is the appropriate amount.

[0070] Furthermore, when the developer level detected by the developer level detection sensor 50 is at a third height lower than the first height, and the output value of the toner concentration sensor 49 is a third output value lower than the first output value, the control unit 80 executes a replenishment operation to replenish the developer to the developer container 60 using the replenishment unit 93. For example, when the output value Vo of the developer level detection sensor 50 is between 1.5 V and 2.0 V, the toner concentration correction coefficient α is 1.15, and the control unit 80 controls the replenishment operation according to the value obtained by multiplying the actual output value Vtd of the toner concentration sensor 49 by 1.15 (1.15 × Vtd). Therefore, when the output value Vo is between 1.5 V and 2.0 V, even if the third output value is lower than the predetermined value, the replenishment operation is executed if the value obtained by multiplying the third output value by 1.15 is higher than the predetermined value. Note that instead of multiplying the actual output value Vtd of the toner concentration sensor 49 by the toner concentration correction coefficient α, the predetermined value serving as the execution threshold for the replenishment operation may be changed. In this case, the predetermined value is set lower than the predetermined value when the amount of developer in the developing container is the appropriate amount.

[0071] The control relating to the execution of the replenishment operation in this embodiment will be described with reference to the flowchart in Fig. 9. First, the control unit 80 starts the image formation operation using the image forming unit 97 and the like (S101). Next, the control unit 80 measures the output value Vo of the developer level detection sensor 50 after the start of driving of the developing device 1Y (S102). Then, the control unit 80 determines the toner concentration correction coefficient α from the obtained output value Vo based on the table shown in Table 1 (S103). The control unit 80 measures the output value Vtd of the toner concentration sensor 49 (S104) and obtains the corrected toner concentration by multiplying Vtd by α (S105).

[0072] If the toner concentration after correction is insufficient compared to the predetermined toner concentration (No in S106), toner is replenished from the developer storage unit 27 (S107). That is, if the toner concentration after correction is lower than the predetermined toner concentration, a replenishment operation is performed to replenish developer to the developing container 60 by the replenishment unit 93, and this control ends. On the other hand, if the toner concentration after correction is equal to or higher than the predetermined toner concentration (Yes in S106), this control ends without performing a replenishment operation.

[0073] As described above, according to this embodiment, erroneous detection by toner concentration sensor 49 can be suppressed even when the amount of developer fluctuates. That is, in a configuration using toner concentration sensor 49 that detects the toner concentration of the developer in the developing device based on magnetic permeability, the relationship between the output value of toner concentration sensor 49 and the toner concentration can be corrected even when the amount of developer in the developing device changes. This prevents the correspondence between the toner concentration of the developer in the developing device and the output value of toner concentration sensor 49 from deviating, making it possible to provide an image forming apparatus that does not produce image defects such as fogging or carrier adhesion. Note that there is no problem with adding a method of correcting the toner concentration sensor based on information about the charge amount of the developer, as in Patent Document 1, to the configuration of this embodiment.

[0074] <Second embodiment> The second embodiment will be described with reference to Figures 10(a) to 12. In this embodiment, the developer level detection sensor 50 is disposed at a position offset from the toner concentration sensor 49 in the direction (second direction) in which the developer is transported by the developer stirring screw 43. 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.

[0075] 10(a) and 10(b), the detection surface of the developer level detection sensor 50 is located vertically above the detection surface of the toner concentration sensor 49, and is disposed within a distance corresponding to four pitches of the blades of the developer agitating screw 43 in the direction of the rotation axis of the developer agitating screw 43 (second direction). In this embodiment, the developer level detection sensor 50 is located 3.5 pitches upstream of the toner concentration sensor 49 in the direction of developer transport by the developer agitating screw 43 (second direction). FIG. 11 shows the output value Vo of the developer level detection sensor 50 when the developer amount is changed at a toner concentration of 8% in the configuration of this embodiment. As with FIG. 7 for the first embodiment, the output value Vo of the developer level detection sensor 50 changes sensitively depending on the developer amount. This is because the installation position of the developer level detection sensor 50 is appropriate. If the installation position of the developer level detection sensor 50 is too high, the sensor output value Vo will be biased toward small values, reducing the resolution for the developer amount. Conversely, if the installation position is too low, the sensor output value Vo will be biased toward large values, which is also undesirable.

[0076] Therefore, it is preferable that the installation position of the agent level detection sensor 50 is such that the detection surface is at least vertically above the detection surface of the toner concentration sensor 49. Furthermore, it is undesirable that the agent level detection sensor 50 is too far away from the toner concentration sensor 49 in the direction of the rotation axis of the developer agitating screw 43. Therefore, in order to properly reflect the output value Vo of the agent level detection sensor 50 in the toner concentration correction, it is preferable that the agent level detection sensor 50 is located at a distance equivalent to within four pitches of the blades of the developer agitating screw 43 in the direction of the rotation axis of the developer agitating screw 43.

[0077] 12 shows the toner concentration (TD ratio) detected by the toner concentration sensor 49 relative to the output value Vo of the developer level detection sensor 50 in this embodiment. In this embodiment, the relationship between the output value Vo of the developer level detection sensor 50 and the toner concentration is the same as that in FIG. 8 of the first embodiment. Table 2 shows the toner concentration correction coefficient α corresponding to the output value of the developer level detection sensor 50 when the toner concentration in the developing container is constant in the configuration of this embodiment. [Table 2]

[0078] In this embodiment, as in the first embodiment, the execution of the replenishment operation is controlled using Table 2 in accordance with the flowchart shown in FIG. 9. In this embodiment, as in the first embodiment, erroneous detection by toner concentration sensor 49 can be suppressed even when the amount of developer fluctuates. That is, in a configuration using toner concentration sensor 49 that detects the toner concentration of the developer in the developing device based on magnetic permeability, the relationship between the toner concentration sensor 49 and the toner concentration can be corrected even when the amount of developer in the developing device changes. This prevents a deviation between the toner concentration of the developer in the developing device and the output value of toner concentration sensor 49, making it possible to provide an image forming apparatus that does not produce image defects such as fogging or carrier adhesion.

[0079] <Comparative Example> A comparative example will be described with reference to Figures 13 to 16. In the comparative example, as shown in Figures 13, 14(a) and 14(b), the developer level detection sensor 50 is positioned 3.5 pitches upstream of the toner concentration sensor 49 in the direction of developer transport by the developer stirring screw 43 (second direction). However, the heights (vertical positions) of the detection surfaces of the developer level detection sensor 50 and the toner concentration sensor 49 are the same. The other configurations and operations are the same as those of the first embodiment described above.

[0080] 15 shows the output value Vo of the developer level detection sensor 50 when the developer amount is changed at a toner concentration of 8% in the configuration of the comparative example. Unlike FIG. 7 of the first embodiment and FIG. 11 of the second embodiment, it can be seen that the sensitivity of the output value Vo of the developer level detection sensor 50 in response to the developer amount is reduced in the comparative example.

[0081] 16 shows the toner concentration (TD ratio) detected by the toner concentration sensor 49 relative to the output value Vo of the developer level detection sensor 50 in the comparative example. Table 3 also shows the toner concentration correction coefficient α corresponding to the output value of the developer level detection sensor 50 when the toner concentration in the developing container is constant in the configuration of the comparative example. [Table 3]

[0082] In the comparative example, as in the first embodiment, the execution of the replenishment operation was controlled using Table 3 in accordance with the flowchart shown in FIG. 9. As a result, in the comparative example, image defects such as fogging and carrier adhesion sometimes occurred. This was because the relationship between the toner concentration and the toner concentration measured by the toner concentration sensor 49 when the amount of developer changed was not properly corrected. In other words, the toner concentration of the developer in the developing device was deviated from the output value of the toner concentration sensor 49. This was because the position of the developer level detection sensor 50 was inappropriate, and as shown in FIG. 15, the output value Vo of the developer level detection sensor 50 relative to the amount of developer was biased toward a high value, resulting in low resolution.

[0083] <Other embodiments> 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 with a developer level detection sensor for detecting the developer level in a developer container and a toner concentration detection sensor for detecting the toner concentration.

[0084] 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.

[0085] 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]

[0086] 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 toner concentration detection sensor that outputs magnetic permeability to detect the toner concentration of the developer contained in the developing container; and a developer level detection sensor whose detection surface is located vertically above the detection surface of the toner concentration detection sensor and outputs magnetic permeability to detect the developer level of the developer contained in the developing container; a developer supply unit that supplies developer to the developing container; A control unit; Equipped with the control unit is capable of executing a supply operation of supplying 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, When the toner concentration in the developing container is constant, When the developer level detected by the developer level detection sensor is at a first level, the supply operation is performed if the output value of the toner concentration detection sensor is at a first output value; When the developer level detected by the developer level detection sensor is at a second level higher than the first level, the supply operation is executed if the output value of the toner concentration detection sensor is a second output value higher than the first output value. An image forming apparatus characterized by:

2. The control unit When the toner concentration in the developing container is constant, When the developer level detected by the developer level detection sensor is at a first level, the supply operation is performed if the output value of the toner concentration detection sensor is at a first output value; When the developer level detected by the developer level detection sensor is at a third level lower than the first level, the supply operation is executed if the output value of the toner concentration detection sensor is a third output value lower than the first output value.

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

3. The toner concentration detection sensor and the toner surface detection sensor are disposed in the second chamber.

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

4. The toner concentration detection sensor and the toner surface detection sensor are disposed within a distance range corresponding to four pitches of the blades of the second conveying screw in the second direction.

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

5. 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 toner concentration detection sensor that outputs magnetic permeability to detect the toner concentration of the developer contained in the developing container; and a developer level detection sensor whose detection surface is located vertically above the detection surface of the toner concentration detection sensor and outputs magnetic permeability to detect the developer level of the developer contained in the developing container; a developer supply unit that supplies developer to the developing container; A control unit; Equipped with the control unit is capable of executing a supply operation of supplying 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, When the toner concentration in the developing container is constant, When the developer level detected by the developer level detection sensor is at a first level, the supply operation is performed if the output value of the toner concentration detection sensor is at a first output value; When the developer level detected by the developer level detection sensor is at a third level lower than the first level, the supply operation is executed if the output value of the toner concentration detection sensor is a third output value lower than the first output value. An image forming apparatus characterized by:

6. The toner concentration detection sensor and the toner surface detection sensor are disposed in the second chamber.

6. The image forming apparatus according to claim 5,

7. The toner concentration detection sensor and the toner surface detection sensor are disposed within a distance range corresponding to four pitches of the blades of the second conveying screw in the second direction.

7. The image forming apparatus according to claim 6, wherein the image forming apparatus is a recording medium.

8. 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 toner concentration detection sensor that outputs magnetic permeability to detect the toner concentration of the developer contained in the developing container; and a developer level detection sensor whose detection surface is located vertically above the detection surface of the toner concentration detection sensor and outputs magnetic permeability to detect the developer level of the developer contained in the developing container; a developer supply unit that supplies developer to the developing container; A control unit; Equipped with The control unit is capable of executing a supply operation of supplying developer to the developing container by the developer supply unit when the output value of the toner concentration detection sensor is higher than a predetermined value, and corrects the output value of the toner concentration detection sensor based on the output value of the developer level detection sensor. An image forming apparatus characterized by:

9. The toner concentration detection sensor and the toner surface detection sensor are disposed in the second chamber.

9. The image forming apparatus according to claim 8,

10. The toner concentration detection sensor and the toner surface detection sensor are disposed within a distance range corresponding to four pitches of the blades of the second conveying screw in the second direction.

10. The image forming apparatus according to claim 9,

Images