Developing device

Abstract

To prevent a reduction in the accuracy of detecting the concentration of toner in developer caused by a variation in the density of the developer at a detection unit of an inductance sensor.SOLUTION: A developing device comprises: a developer carrier that carries developer including toner and carrier; a first conveying screw that is arranged in a first chamber for supplying the developer to the developer carrier, and conveys the developer in a first direction; a second conveying screw that is arranged in a second chamber partitioned from the first chamber by a partition wall, and conveys the developer in a second direction; and an inductance sensor that is arranged opposite to the second conveying screw, and detects the magnetic permeability of the developer in the second chamber. The second conveying screw has a first conveying unit, and a second conveying unit that is provided on the downstream side of the first conveying unit in the second direction, wherein the flow rate of the developer is smaller than that of the first conveying unit. The inductance sensor has a detection unit that detects the magnetic permeability of the developer, and the detection unit is arranged at a position immediately before the second conveying unit in the second direction and opposite to the first conveying unit.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a developing device and an image forming apparatus including a conveying screw for conveying a developer.

Background Art

[0002] In an image forming apparatus using an electrophotographic method or the like, an electrostatic latent image formed on a photosensitive drum is developed into a toner image by a developing device. As such a developing device, a device using a two-component developer containing non-magnetic toner and magnetic carrier has been conventionally used. In the case of a developing device using a two-component developer, the developer accommodated in a developing container is conveyed while being stirred by a screw.

[0003] In such a developing method using a two-component developer, in order to obtain reproducibility of the image density of an output image, it is necessary to stably maintain the weight ratio of toner in the developer (hereinafter referred to as toner concentration) within a narrow range. In order to maintain the toner concentration of the two-component developer circulating in the developing container within a predetermined range, a technique is used in which a sensor for detecting the toner concentration is provided on the wall surface of the developing container, and the supply amount of the replenishing toner is adjusted according to the detection result.

[0004] As a sensor for detecting the toner concentration of the developer in the developing container, an inductance sensor whose inductance changes according to the ratio of the magnetic material in the developer is known. The inductance sensor detects the toner concentration in the developer by changing its output according to the amount of the magnetic material present in the detection range.

[0005] Some inductance sensors have a configuration in which a detection portion protrudes with respect to a substrate, and a coil is wound around an iron core. In addition, some inductance sensors have a configuration in which a coil is directly pattern-printed on a substrate (Patent Document 1).

[0006] An inductance sensor with a coil pattern-printed on a substrate can be manufactured at a relatively low cost because it does not have an iron core compared to an inductance sensor having an iron core.

[0007] Furthermore, inductance sensors with coils pattern-printed do not have an iron core, which makes them less prone to magnetic field concentration and gives them a wider detection range compared to inductance sensors with an iron core. These inductance sensors detect the toner concentration in the developer by changing their output according to the amount of magnetic material present in the detection range. Therefore, the density of the developer present in the detection range of the inductance sensor must be constant. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2016-012078 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, the density of the developer within the detection range of an inductance sensor with a coil pattern printed on it may fluctuate, making it impossible to completely fill the detection range with developer. In this case, even if the toner concentration in the developer in the developing container remains constant, the sensor output changes due to fluctuations in the developer density within the sensor's detection range, resulting in a change in the toner concentration detection result. Therefore, proper toner replenishment cannot be performed.

[0010] Factors that cause fluctuations in developer density include changes in the amount of developer in the developing container and changes in the image forming speed of the image forming apparatus. As an example, Figure 15 shows the result of converting the output of an inductance sensor in response to changes in the amount of developer to toner concentration. In Figure 15, the relationship between the amount of developer and the toner concentration is compared using an inductance sensor with an iron core and an inductance sensor with a coil pattern printed on it. From Figure 15, it can be seen that the detection result of the toner concentration in response to changes in the amount of developer changes more significantly with the inductance sensor with a coil pattern printed on it compared with the inductance sensor with an iron core. In other words, when the amount of developer in the developing container decreases, the density of the developer in the detection range of the inductance sensor changes accordingly, and this reduces the accuracy of detecting the toner concentration in the developer.

[0011] Therefore, the objective of the present invention is to suppress the decrease in the detection accuracy of toner concentration in the developer. [Means for solving the problem]

[0012] A typical configuration of the present invention to achieve the above objective is a rotatable developer carrier that carries a developer including toner and a carrier; a first chamber for supplying the developer to the developer carrier; a second chamber separated from the first chamber by a partition wall; a first connecting section that allows the developer to move from the first chamber to the second chamber; a second connecting section that allows the developer to move from the second chamber to the first chamber; a first transport screw located in the first chamber that transports the developer in a first direction from the second connecting section toward the first connecting section; a second transport screw located in the second chamber that transports the developer in a second direction from the first connecting section toward the second connecting section; and a third section located opposite the second transport screw, A developing apparatus comprising two inductance sensors for detecting the magnetic permeability of the developer in two chambers, wherein the second transport screw has a first transport section and a second transport section provided downstream of the first transport section in the second direction, and transporting less developer per unit time than the first transport section, the inductance sensor has a detection section for detecting the magnetic permeability of the developer, the detection sensitivity at a position 1 mm away from the detection section in the direction toward the second transport screw is 10% or more of the detection sensitivity at a position in contact with the detection section, and the detection section is positioned directly in front of the second transport section in the second direction and opposite to the first transport section. [Effects of the Invention]

[0013] According to the present invention, the density of the developer in the detection section of the inductance sensor can be stabilized, and a decrease in the detection accuracy of the toner concentration in the developer caused by fluctuations in the developer density can be suppressed. [Brief explanation of the drawing]

[0014] [Figure 1] Schematic diagram of an image forming apparatus [Figure 2] Cross-sectional view of a developing apparatus [Figure 3] Diagram showing the circulation pathway of the developer. [Figure 4] Inductance sensor configuration diagram [Figure 5] Figure showing the distance sensitivity of the inductance sensor [Figure 6] Control block diagram of the image forming apparatus [Figure 7] Flowchart showing the toner density control process [Figure 8] (a)(b) Figure showing the configuration of the second conveyance screw around the inductance sensor [Figure 9] Figure showing the change in the output result of the inductance sensor when the developer amount changes [Figure 10] Figure showing the developer amount density distribution in the agitation chamber in the configurations of the example and the comparative example [Figure 11] Figure showing the change in the flow rate of the developer [Figure 12] Figure showing the change in the flow rate when the shaft diameter of a part of the second conveyance screw is changed [Figure 13] (a)(b) Figures showing other embodiments of the second conveyance screw [Figure 14] (a)(b)(c) Figures showing the configuration of the second conveyance screw around the inductance sensor according to other embodiments [Figure 15] Figure showing the result of converting the change in the output result of the inductance sensor when the developer amount changes into the toner density

Best Mode for Carrying Out the Invention

[0015] Hereinafter, preferred embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions, and are not intended to limit the scope of the present invention only thereto.

[0016] 〔Example 1〕 Hereinafter, an image forming apparatus including a developing device according to Example 1 will be described using FIGS. 1 to 12.

[0017] (Image forming apparatus) First, the general configuration of the image forming apparatus will be explained using Figure 1. The image forming apparatus 10 is an electrophotographic image forming apparatus having four image forming units PY, PM, PC, and PK, corresponding to four colors: yellow Y, magenta M, cyan C, and black K. In this embodiment, a so-called tandem system is adopted in which the image forming units PY, PM, PC, and PK are arranged along the rotation direction of the intermediate transfer belt 62, which will be described later. The image forming apparatus 10 forms a toner image (image) on a recording medium such as recording paper in response to an image reading device (not shown) connected to the image forming apparatus body or an image signal from a host device such as a personal computer that is communicatively connected to the image forming apparatus body. Examples of recording media include paper, plastic film, and sheet materials such as cloth.

[0018] To briefly explain this image formation process, first, in each image formation unit PY, PM, PC, and PK, toner images of each color are formed on the photosensitive drums 1Y, 1M, 1C, and 1K, respectively. These toner images are then transferred to the intermediate transfer belt 62, and subsequently transferred from the intermediate transfer belt 62 to the recording medium. The recording medium on which the toner images have been transferred is then transported to the fuser unit 7, where the toner images are fixed to the recording medium. A more detailed explanation follows.

[0019] The four image forming units PY, PM, PC, and PK of the image forming apparatus 10 have substantially the same configuration except for the difference in development color. Therefore, the image forming unit PY will be described as a representative unit below, and the configurations of the other image forming units will be shown by replacing the subscript "Y" attached to the configuration of the image forming unit PY with M, C, and K respectively, and their descriptions will be omitted.

[0020] The image forming unit PY is equipped with a cylindrical photosensitive drum, i.e., a photosensitive drum 1Y, as the image carrier. Around the photosensitive drum 1Y are a charging roller 2Y (charging device), a developing device 4Y, a primary transfer roller 61Y, and a cleaning device 8Y. An exposure device (laser scanner) 3Y is positioned above the photosensitive drum 1Y in the diagram.

[0021] Furthermore, an intermediate transfer belt 62 is positioned opposite the photosensitive drums 1Y, 1M, 1C, and 1K. The intermediate transfer belt 62 is stretched by multiple rollers and moves in a circular motion by the drive of one of the drive rollers. A secondary transfer outer roller 64, which acts as a secondary transfer member, is positioned opposite the secondary transfer inner roller 63 and the intermediate transfer belt 62, and constitutes a secondary transfer section T2 that transfers the toner image on the intermediate transfer belt 62 to the recording medium. A fixing device 7 is positioned downstream of the secondary transfer section T2 in the recording medium transport direction.

[0022] The process of forming an image using the image forming apparatus 10 configured as described above will now be explained. First, when the image forming operation starts, the surface of the rotating photosensitive drum 1Y is uniformly charged by the charging roller 2Y. Next, the photosensitive drum 1Y is exposed to laser light corresponding to the image signal emitted from the exposure device 3Y. As a result, an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 1Y. The electrostatic latent image on the photosensitive drum 1Y is revealed by toner contained in the developing device 4Y, becoming a visible image.

[0023] The toner image formed on the photosensitive drum 1Y is transferred to the intermediate transfer belt 62 in the primary transfer section T1Y, which consists of the drum and the primary transfer roller 61Y positioned on either side of the intermediate transfer belt 62. After the primary transfer, the toner remaining on the surface of the photosensitive drum 1Y (transfer residue toner) is removed by the cleaning device 8Y.

[0024] This process is sequentially performed in the magenta, cyan, and black image forming units, superimposing the four toner images on the intermediate transfer belt 62. Subsequently, in accordance with the toner image formation timing, the recording medium housed in the recording medium storage cassette (not shown) is transported to the secondary transfer unit T2, and the four toner images on the intermediate transfer belt 62 are transferred to the recording medium all at once. Toner remaining on the intermediate transfer belt 62 after secondary transfer is removed by an intermediate transfer belt cleaner (not shown).

[0025] Next, the recording medium is transported to the fuser unit 7. The fuser unit 7 then heats and pressurizes the recording medium, melting and mixing the toner, and fixing it to the recording medium as a full-color image. Afterward, the recording medium is discharged from the machine. This completes the image formation process. It is also possible to form a single-color or multi-color image of a desired color using only the desired image forming unit.

[0026] (Developing equipment) Next, the developing device 4Y will be described using Figures 2 and 3. Figure 2 is a cross-sectional view of the developing device 4Y. Figure 3 is a diagram showing the circulation path of the developer. The same applies to the developing devices 4M, 4C, and 4K. The developing device 4Y has a developing container 44 that contains a two-component developer including a non-magnetic toner and a magnetic carrier. The developing container 44 has an opening in the developing area facing the photosensitive drum 1Y, and a developing sleeve 41, which serves as a developer carrier with a magnetic roll 42 arranged inside in a non-rotating manner, is rotatably installed so as to be partially exposed to this opening.

[0027] In this embodiment, the developing sleeve 41 is made of a non-magnetic material and rotates at a predetermined process speed (circumferential speed) during the developing operation. The magnetic roll 42, which serves as a magnetic field generating means, has multiple magnetic poles along the circumferential direction, and the generated magnetic field causes the developer to be carried on the surface of the developing sleeve 41.

[0028] The developer supported on the surface of the developing sleeve 41 has its layer thickness restricted by the developing blade 43, which acts as a regulating member, and a thin layer of developer is formed on the surface of the developing sleeve 41. The developing sleeve 41 is transported to the developing area while supporting the thin layer of developer formed thereon. In the developing area, the developer on the developing sleeve 41 rises up to form a magnetic pile. In this embodiment, the magnetic pile is brought into contact with the photosensitive drum 1Y, and the toner of the developer is supplied to the photosensitive drum 1Y, thereby developing the electrostatic latent image on the photosensitive drum 1Y as a toner image. After developing the latent image, the developer is collected in the developing chamber 44a in the developing container 44 as the developing sleeve 41 rotates.

[0029] The interior of the developing container 44 is divided into a developing chamber 44a, which is the first chamber, and a stirring chamber 44b, which is the second chamber, by a partition wall 44c that extends vertically. At both ends of the partition wall 44c in the longitudinal direction (direction of the rotation axis of the developing sleeve 41), there are connecting ports 46a and 46b, which connect the developing chamber 44a and the stirring chamber 44b, respectively. The connecting port 46a is the first connecting port that allows the developer to move from the developing chamber 44a to the stirring chamber 44b. The connecting port 46b is the second connecting port that allows the developer to move from the stirring chamber 44b to the developing chamber 44a. This forms a developer circulation path between the developing chamber 44a and the stirring chamber 44b. The arrows shown in Figure 3 indicate the direction of developer circulation.

[0030] Furthermore, the developing container 44 is equipped with a first conveying screw 45a as a first conveying member and a second conveying screw 45b as a second conveying member, respectively, which agitate and convey the developer. The first conveying screw 45a is located in the developing chamber 44a and agitates and conveys the developer in the developing chamber 44a in a first direction from the communication port 46b toward the communication port 46a, and also supplies the developer to the developing sleeve 41. The second conveying screw 45b is located in the agitation chamber 44b and agitates and conveys the developer in the agitation chamber 44b in a second direction from the communication port 46a toward the communication port 46b.

[0031] The image forming apparatus is equipped with a developer supply device (not shown) that contains either toner only or a replenishment developer consisting of toner and a magnetic carrier. The developer supply device is fitted with a supply screw, which allows the amount of replenishment developer used for image formation to be supplied from the developer supply device to the stirring chamber in the developing container 44. The amount of replenishment developer supplied is adjusted by a control means (CPU 51 shown in Figure 6) controlling the number of rotations of the supply screw through a drive motor (toner supply motor 54 shown in Figure 6) that drives the supply screw.

[0032] The developing apparatus 4Y has a concentration detection means (toner concentration detection unit) capable of detecting the toner concentration in the developing container 44 (the ratio of the weight of toner particles to the total weight of carrier particles and toner particles, T / D ratio). In this embodiment, an inductance sensor 47 is used as the toner concentration detection unit. The inductance sensor 47 is installed in the stirring chamber 44b and detects the magnetic permeability within a predetermined detection range from the sensor surface 47f (see Figure 8(a)). When the toner concentration of the developer changes, the magnetic permeability due to the mixing ratio of magnetic carriers and non-magnetic toner also changes, so the toner concentration can be detected by detecting this change in magnetic permeability with the inductance sensor 47.

[0033] (Recirculation of developer) Next, the circulation of the developer within the developing container 44 will be described. The first transport screw 45a and the second transport screw 45b are arranged substantially parallel to each other along the rotation axis direction of the developing sleeve 41. The first transport screw 45a and the second transport screw 45b transport the developer in opposite directions along the rotation axis direction of the developing sleeve 41. In this way, the developer is circulated within the developing container 44 through the communication ports 46a and 46b by the first transport screw 45a and the second transport screw 45b.

[0034] In other words, the transport force of the first transport screw 45a and the second transport screw 45b causes the developer in the developing chamber 44a, whose toner concentration has decreased due to toner consumption in the developing process, to be transported to the stirring chamber 44b via the communication port 46a and move within the stirring chamber 44b.

[0035] Here, upstream of the communication port 46a of the agitation chamber 44b in the developer transport direction of the second transport screw 45b, there is a supply port (not shown) through which developer is supplied from a developer supply device. Therefore, in the agitation chamber 44b, the developer transported from the developing chamber 44a via the communication port 46a and the replenished developer supplied from the developer supply device via the supply port are transported while being agitated by the second transport screw 45b. Then, the developer transported by the second transport screw 45b moves to the developing chamber 44a via the communication port 46b.

[0036] In this embodiment, the developer contained in the developing container 44 is a two-component developer in which a negatively charged non-magnetic toner and a magnetic carrier are mixed. The non-magnetic toner is made by pulverizing or polymerizing a resin such as polyester or styrene, which contains colorants, wax components, etc. The magnetic carrier is made by coating the surface of a core consisting of resin particles mixed with ferrite particles or magnetic powder with resin.

[0037] (Inductance sensor) Next, the inductance sensor 47 used in this embodiment will be described with reference to Figures 4 and 5. Figure 4 is a diagram showing the configuration of the inductance sensor. Figure 5 is a diagram showing the distance sensitivity of the inductance sensor.

[0038] In this embodiment, an inductance sensor 47 is positioned on the bottom surface of the stirring chamber 44b, opposite the second transport screw 45b, in order to detect the toner concentration of the developer contained in the developing container 44 (see Figure 2). The inductance sensor 47 is a permeability sensor that utilizes the inductance of a coil to output an output pulse as a detection signal corresponding to the permeability of the developer.

[0039] As shown in Figure 4, the inductance sensor 47 has a coil 47a pattern printed on a substrate. Furthermore, the inductance sensor 47 includes a coil drive unit 47b that electrically drives the coil 47a, an output unit 47c that generates an output pulse signal, and a connector 47d.

[0040] The inductance sensor 47 has a sensor surface 47f as a detection unit for detecting the magnetic permeability of the developer. The sensor surface 47f of the inductance sensor 47 is the area on the substrate 47e where the coil 47a is pattern printed (the dashed area shown in Figure 4). The inductance sensor 47 does not have an iron core in the center of the coil 47a.

[0041] Coil 47a is a wiring pattern formed on the substrate so as not to overlap in the direction from the substrate 47e toward the second transport screw 45b, and generates an inductance component. The coil drive unit 47b is composed of a circuit having a capacitor, and is an LC resonant circuit that resonates due to the inductance of the capacitor and the coil 47a. The output unit 47c is a pulse generation circuit having a comparator that converts the analog signal oscillated by the coil drive unit 47b into a digital signal. The output unit 47c outputs a binarized pulse signal.

[0042] Although the coil 47a is shown as having a pattern printed on a substrate as an example, it is not limited to this configuration. The coil 47a may also be configured by winding wiring vertically on a substrate, as long as it does not have an iron core.

[0043] The resonant period of the resonant circuit, which consists of coil 47a and coil drive unit 47b, varies depending on the density of magnetic material present in the detection range of the sensor surface 47f. Specifically, when the toner concentration of the developer in the detection range of coil 47a is low, the proportion of magnetic carriers contained in the developer per unit volume increases, the apparent permeability of the developer increases, and the resonant period lengthens. Conversely, when the toner concentration of the developer is high, the proportion of magnetic carriers contained in the developer per unit volume decreases, the apparent permeability of the developer decreases, and the resonant period shortens.

[0044] By utilizing this property, the toner concentration of the developer within the detection range of the coil 47a is detected by measuring the time required to count a predetermined number of pulses from the pulse signal output from the output unit 47c.

[0045] As a specific example, if the resonant frequency of a developer with a toner concentration of 10% within the detection range of coil 47a is 1000 kHz, and the number of pulses to be counted is 5000, and the clock used to measure the time required for counting is 200 MHz, then the time required to count 5000 pulses is 5000 μsec, and when measured with a 20 MHz clock, this is measured as 100000 cnt.

[0046] On the other hand, when the toner density is 8%, the resonant period of the resonant circuit composed of coil 47a and coil drive unit 47b becomes longer than when the toner density is 10%, and the resonant frequency becomes 990 kHz. In this case, the time required to count 5000 pulses is approximately 5050 μsec, and when measured with a 20 MHz clock, this is measured as 101000 cnt.

[0047] In this way, the inductance sensor 47 can be used to detect the toner concentration in the developer as the number of pulses.

[0048] Here, the detection range of the sensor surface 47f of the inductance sensor 47 is the area on the substrate 47e where the coil 47a is pattern-printed, as shown in Figure 4, and also the area of ​​output sensitivity shown in Figure 5 in the vertical direction from the sensor surface 47f. In other words, the sensor surface 47f of the inductance sensor 47 has a detection sensitivity at a position 1 mm away from the sensor surface 47f in the direction toward the second transport screw 45b that is 10% or more higher than the detection sensitivity at the position in contact with the sensor surface 47f.

[0049] Figure 5 shows the static distance characteristics of the inductance sensor. This measures the detection sensitivity of the inductance sensor when the distance of a magnetic plate (not shown) from the sensor surface of the inductance sensor is changed vertically. A ferrite magnetic plate with a diameter of 13 mm and a thickness of 1.5 mm (relative permeability of approximately 200) was used. In addition to the inductance sensor 47 according to this embodiment, Figure 5 also shows measurements of an inductance sensor with an iron core at the center of the coil as a comparative example.

[0050] Figure 5 shows the distance [mm] from the sensor surface of the inductance sensor on the horizontal axis and the output sensitivity (detection sensitivity) of the inductance sensor on the vertical axis. The sensitivity shown on the vertical axis of Figure 5 represents the ratio of the output at each position when the magnetic plate is moved away from the sensor surface, with the output at the position where the magnetic plate is in contact with the sensor surface of the inductance sensor being set to 1 (change in detection sensitivity). Furthermore, the above measurements were taken using a magnetic plate with the inductance sensor removed from the developing container and with no developer on the sensor surface of the inductance sensor.

[0051] As can be seen from the measurement results in Figure 5, the detection sensitivity of the inductance sensor 47 in this embodiment decreases as the magnetic plate moves vertically away from the sensor surface 47f, but it retains sensitivity up to a distance of about 4-5 mm from the sensor surface 47f. On the other hand, the detection sensitivity of the inductance sensor in the comparative example is such that, because an iron core is provided in the center of the coil, the magnetic field used to detect the magnetic plate is concentrated around the sensor surface compared to this embodiment. Therefore, the detection sensitivity of the inductance sensor in the comparative example is almost zero at a distance of 1 mm from the sensor surface.

[0052] In other words, the inductance sensor of this embodiment has a wider detection range in the vertical direction from the sensor surface compared to the inductance sensor of the comparative example. To put it another way, the inductance sensor 47 of this embodiment has a detection sensitivity of 10% or more at a position 1 mm vertically away from the surface of the sensor surface compared to the detection sensitivity at the surface of the sensor surface. Here, the statement that the inductance sensor 47 has the above-mentioned detection sensitivity is intended to exclude the inductance sensor of the comparative example, which has a detection sensitivity of almost 0 at a distance of less than 1 mm from the sensor surface.

[0053] In the comparative example, the inductance sensor has a coil and iron core that protrudes vertically from the surface of the substrate. Therefore, the sensor surface of the comparative example's inductance sensor is the end face of the tip of the protruding portion.

[0054] Next, the toner concentration control operation using the inductance sensor 47 will be explained with reference to Figures 6 and 7. Figure 6 is a control block diagram of the image forming apparatus in this embodiment.

[0055] In this embodiment, the CPU 51, which acts as a control means for controlling the image forming operation, detects the toner density based on the output pulse of an inductance sensor 47 provided in the developing device 4. Here, the correspondence between the output pulse count of the inductance sensor 47 and the toner density is recorded in the ROM 52. Therefore, the CPU 51 detects the toner density based on the output pulse of the inductance sensor 47 and the aforementioned correspondence recorded in the ROM 52. The RAM 53 is the system work memory for the operation of the CPU 51. The toner supply motor 54 is a motor driven to supply toner to the developing device and is a drive motor that drives the supply screw located in the developer supply device (not shown) described above.

[0056] Figure 7 is a flowchart showing the toner concentration control process, which is executed by the CPU 51 reading a program recorded in ROM 52. When the developing operation starts (S101) and the developer is stirred (S102), the CPU 51 reads the output value of the inductance sensor 47 and calculates the average value of that output value over one cycle of the transport screw (one rotation of the transport screw). Using the calculated output value (average value), the CPU 51 detects the toner concentration from the correspondence between the output pulse count of the inductance sensor 47 recorded in ROM 52 and the toner concentration (S103), and determines the amount of toner to be supplied (S104). When the CPU 51 outputs a signal instructing toner to be supplied, the toner supply motor 54 is driven, and a predetermined amount of toner is supplied to the developing device 4 from a developer supply device (not shown) (S105). The CPU 51 performs image formation (S106), determines whether or not continuous paper is being fed (S107), and if YES, follows the control process in S101, and if NO, terminates control (S108).

[0057] (Configuration of the transport screw around the inductor sensor) Next, the configuration of the transport screw around the inductance sensor will be explained using Figure 8. Figures 8(a) and 8(b) show the configuration of the transport screw around the inductance sensor.

[0058] The first conveying screw 45a and the second conveying screw 45b each have a rotating shaft 49 and blades 48 formed spirally on the outer circumference of the rotating shaft 49. Both the first conveying screw 45a and the second conveying screw 45b have an outer diameter R3 of 16 [mm] and a blade pitch P1 of 20 [mm]. The second conveying screw 45b has a rotating shaft diameter R2 of 6 [mm], except for the rotating shaft 49b of the second conveying section 45b2 which will be described later (see Figure 8(a)).

[0059] As shown in Figure 8(a), the second transport screw 45b has a first transport section 45b1 and a second transport section 45b2. The second transport section 45b2 is located downstream of the first transport section 45b1 in the second direction (the direction of the arrow shown in Figure 8(a)). The second transport section 45b2 is configured to transport a smaller amount of developer per unit time (hereinafter referred to as the developer flow rate) than the first transport section 45b1.

[0060] In this embodiment, the second conveying screw 45b has a configuration in which the shaft diameter R1 of the rotating shaft 49b in the second conveying section 45b2 is larger than the shaft diameter R2 of the rotating shaft 49a in the first conveying section 45b1.

[0061] Furthermore, the inductance sensor 47 is positioned such that its sensor surface 47f is directly in front of the second transport unit 45b2 in the second direction and facing the first transport unit 45b1. In addition, the inductance sensor 47 has a detection sensitivity at a position 1 mm away from the sensor surface 47f in the direction toward the second transport unit 45b2 that is 10% or more higher than the detection sensitivity at the position in contact with the sensor surface 47f. This detection sensitivity will be described later.

[0062] Figure 8(a) shows an enlarged, horizontal view of the configuration of the second transport screw 45b around the inductance sensor 47 in this embodiment. The second transport screw 45b basically has a rotating shaft 49a with a shaft diameter R2 of 6 mm. Downstream from the sensor surface 47f of the inductance sensor 47 in the transport direction, there is a 20 mm long region where the rotating shaft 49b has a shaft diameter R2 of 11 mm. In the region with a shaft diameter of R2, the developer flow rate (developer transport force) decreases compared to other regions. Therefore, just upstream of the point where the shaft diameter of the rotating shaft 49 changes, that is, on the sensor surface 47f of the inductance sensor 47, developer stagnation occurs.

[0063] Figure 8(b) shows an enlarged, horizontal view of the configuration of the second transport screw 45b around the inductance sensor 47 of the comparative example. The second transport screw 45b has a rotational shaft diameter of 6 mm along its entire length.

[0064] Here, the detection sensitivity of the inductance sensor 47 will be explained using Figure 9. Figure 9 shows the results of measuring the output of the inductance sensor 47 while changing the amount of developer in the developing container 44 for both the configuration of this embodiment and the configuration of the comparative example. At this time, the toner concentration in the developer was 8% and the rotation speed of the second transport screw 45b was 300 rpm.

[0065] Figure 9 shows the relationship between the amount of developer [g] in the developing container, the output of the inductance sensor [cnt], and the converted value of toner concentration [%] corresponding to the output of the inductance sensor. The output of the inductance sensor corresponds to the detection sensitivity of the inductance sensor.

[0066] As can be seen from the results shown in Figure 9, in both this embodiment and the comparative example, even though the same toner concentration of developer was measured, the output result of the inductance sensor changed depending on the amount of developer in the developer container 44. This is due to a change in the density of the developer present in the detection range of the inductance sensor 47. When the density of the developer present in the detection range of the inductance sensor 47 decreases, the apparent permeability decreases, so the resonance period shortens and the output pulse of the inductance sensor decreases. Conversely, when the density of the developer present in the detection range of the inductance sensor 47 increases, the apparent permeability increases, so the resonance period lengthens and the output pulse of the inductance sensor increases.

[0067] Due to this property, even if the toner concentration does not change, fluctuations in the amount of developer in the developing container 44 cause a change in the density of the developer within the detection range of the inductance sensor 47, resulting in fluctuations in the output pulse of the inductance sensor 47. This phenomenon causes a deviation from the toner concentration that should be detected.

[0068] In Figure 9, the first vertical axis shows the output value of the inductance sensor, and the second vertical axis shows the output pulse converted to toner concentration when the amount of developer in the developing container changes. At this time, the toner concentration of the developer in the developing container 44, which is the target of detection, is 8%. Therefore, the deviation from the 8% toner concentration represents the detection error due to the change in the amount of developer (developer density in the detection range).

[0069] The amount of developer contained in the developing container 44 varies depending on the driving speed of the developing device during image formation, the temperature and humidity environment, and the output image density. The developing device 4 used in this embodiment and comparative example assumes a developer amount variation range of 120 g to 200 g. In the configuration of the comparative example, a maximum detection error of 2% in toner density occurs due to variations in the developer amount within the assumed usage range. On the other hand, in the configuration of this embodiment, the detection error range is suppressed to about 0.5%. The difference in output is particularly noticeable when the amount of developer in the developing container is small.

[0070] This indicates that when the amount of developer in the developing container 44 is small, the density of the developer within the detection range of the inductance sensor 47 changes significantly. In other words, in the comparative example, when the amount of developer in the developing container 44 is small, the density of the developer within the detection range of the inductance sensor 47 changes significantly, and the output pulse of the inductance sensor 47 decreases accordingly. In contrast, in this embodiment, even when the amount of developer in the developing container 44 is small, the change in the density of the developer within the detection range of the inductance sensor 47 is kept small, and the change in the output pulse of the inductance sensor 47 is suppressed accordingly. In other words, according to this embodiment, even when the amount of developer in the developing container 44 is small, the density of the developer within the detection range of the inductance sensor 47 remains stable, thereby suppressing a decrease in the toner concentration detection accuracy of the inductance sensor 47.

[0071] The reason for this effect will be explained using Figure 10. Figure 10 shows the distribution of developer density in the stationary state of the stirring chamber 44b after adding 120 g of developer and stirring for a sufficient amount of time in the configurations of this embodiment and the comparative example. The developer density was calculated by dividing the developer in the stirring chamber 44b into 10 mm intervals along its length, removing the weights of the removed portions, and measuring the developer density [g / mm] in each region.

[0072] As can be seen from the results shown in Figure 10, in the comparative example configuration, the developer density distribution in the longitudinal direction of the stirring chamber 44b is almost uniform, as shown by the dashed line in Figure 10. In contrast, in the configuration of this embodiment, as shown by the solid line in Figure 10, the developer density increases around the point where the shaft diameter of the second transport screw 45b switches from R2 (6 [mm]) to R1 (11 [mm]). This is because the developer flow rate (developer transport force) is lower in the region where the shaft diameter of the second transport screw 45b is larger (second transport section 45b2) compared to other regions (first transport section 45b1), causing developer stagnation just upstream of the point where the shaft diameter switches. In other words, developer stagnation occurs at the position of the sensor surface 47f of the inductance sensor 47. This allows the detection range of the inductance sensor 47 to be filled with developer even when the amount of developer in the developing container 44 is small, thereby suppressing a decrease in the accuracy of toner density detection. In other words, even when the amount of developer in the developing container is small, the density of the developer at the position of the sensor surface 47f of the inductance sensor 47 can be stabilized.

[0073] On the other hand, in the comparative example configuration, when the amount of developer in the developing container 44 is small, the developer density in the detection range of the inductance sensor 47 decreases. As a result, the detection range of the inductance sensor 47 cannot be filled with developer, and the apparent magnetic permeability decreases. Consequently, in the comparative example configuration, the output pulse of the inductance sensor 47 decreases, resulting in toner density detection errors and a decrease in toner density detection accuracy.

[0074] Therefore, in this embodiment, as described above, the second transport screw 45b, which is located downstream of the first transport section 45b1 in the second direction (the direction of the arrow shown in Figure 8(a)), has a configuration in which the developer flow rate is less than that of the first transport section 45b1. In other words, the second transport screw 45b, which is located downstream of the first transport section 45b1 in the second direction, has a configuration in which the developer transport force is weaker than that of the first transport section 45b1.

[0075] Furthermore, the inductance sensor 47 is positioned such that its sensor surface 47f is directly in front of the second transport unit 45b2 in the second direction and facing the first transport unit 45b1.

[0076] As a result, according to this embodiment, the developer is allowed to remain within the detection range of the inductance sensor 47, thereby stabilizing the toner concentration detection result even when the amount of developer is small.

[0077] (Developer flow rate) Here, we will explain the degree to which the developer transport force of the second transport screw 45b should be reduced, using a physical quantity called the developer flow rate. Here, the developer flow rate indicates the amount of developer transported per unit time and is expressed by the following relationship (Equation 1).

[0078] Developer flow rate [g / sec] = Developer transport speed [mm / sec] × Developer density [g / mm] (Equation 1)

[0079] The developer is circulated in a circulation path formed between the developing chamber 44a and the stirring chamber 44b in such a way that the flow rate is preserved. Therefore, the flow rate of the developer is constant regardless of which region is measured in, divided into predetermined distances along the longitudinal direction.

[0080] The developer transport speed can be measured by removing the lid from the top of the developing device 4, capturing images from vertically above the developer surface using a high-speed video camera, and measuring the particle image flow velocity. For example, a FASTCAM-SA-5.0 (manufactured by Photoron) can be used as the high-speed video camera. Furthermore, by measuring the developer density in each region, the developer flow rate can be calculated using Equation 1.

[0081] Figure 11 shows the change in developer flow rate when the amount of developer in the developing container 44 is 120 [g], 160 [g], and 200 [g] using the developing apparatus 4 of this embodiment. The vertical axis of Figure 11 represents the developer flow rate [g / sec]. The horizontal axis of Figure 11 represents the developer density [g / mm] in the downstream region of the inductance sensor 47 (the region where the shaft diameter of the second transport screw 45b is R1). From this, it can be seen that the developer flow rate changes linearly with respect to the developer density in the downstream region of the inductance sensor 47.

[0082] Figure 12 shows the flow rate ratio of the developer when developer is added to the developing container so that the developer density in the downstream region of the inductance sensor 47 is equal, after performing such measurements while varying the shaft diameter R1 of the second transport screw 45b in the region downstream of the inductance sensor 47. In Figure 12, measurements were taken with the shaft diameter R1 of the second transport screw 45b varied to 6 [mm], 8 [mm], 11 [mm], and 13 [mm]. The flow rate ratio of the developer when developer is added to the developing container so that the developer density in the downstream region of the inductance sensor 47 is 0.4 [g / mm] is shown for each shaft diameter R1. Here, the developer density of 0.4 [g / mm] is an example and is not limited to this.

[0083] Figure 12 shows that the horizontal axis represents the axial diameter R1 of the second transport screw 45b in the region downstream of the sensor surface 47f of the inductance sensor 47. The vertical axis represents the flow rate ratio when the developer flow rate is set to 1 when the axial diameter of the second transport screw 45b is uniform (6 mm) throughout the entire longitudinal direction.

[0084] This shows that in order to keep the range of false detection due to developer amount fluctuations to 0.5%, it is necessary to use a screw configuration in which the conveying force is reduced to about 0.8 times the flow rate downstream of the sensor surface 47f of the inductance sensor 47 for the region upstream of the inductance sensor 47. When attempting to achieve this by switching the shaft diameter of the second conveying screw 45b, the shaft diameter R1 in the downstream region of the inductance sensor 47 should be set to satisfy the following relationship (Equation 2), where R2 is the shaft diameter at the upstream position of the inductance sensor 47 and R3 is the outer diameter of the second conveying screw 45b.

[0085] R1>(R2+R3) / 2 (Formula 2)

[0086] In other words, the second conveying screw 45b is configured to satisfy the above relational equation (Equation 2) when the shaft diameter of the rotating shaft 49b of the second conveying section 45b2 is R1, the shaft diameter of the rotating shaft 49a of the first conveying section 45b1 is R2, and the outer diameter of the second conveying screw is R3.

[0087] Furthermore, the starting point for the configuration that weakens the transport force of the developer is more effective the closer it is to the downstream end in the transport direction of the coil 47a that forms the sensor surface 47f of the inductance sensor 47. For this reason, it is desirable to set it within a length of one pitch of the second transport screw 45b located upstream of the inductance sensor 47 from the downstream end of the coil 47a in the transport direction (the downstream end in the direction of the arrow shown in Figure 8(a)). In this embodiment, for example, the length of one pitch of the second transport screw 45b is 20 [mm] downstream in the transport direction from the downstream end of the coil 47a.

[0088] Furthermore, while a certain length is necessary for the configuration to weaken the transport force of the developer, making it longer than necessary will hinder the overall circulation, raising concerns that, for example, the time it takes for replenishment toner to reach the position of the developer sleeve 41 will be longer in relation to the toner consumed by the image. Therefore, it is desirable to set the range in which the configuration to weaken the transport force of the developer to be about 0.5 to 2 times the length of one pitch of the second transport screw 45b upstream of the inductance sensor 47.

[0089] As described above, in this embodiment, the second transport screw 45b, which is located downstream of the first transport section 45b1 in the second direction (the direction of the arrow shown in Figure 8(a)), has a configuration in which the developer flow rate is less than that of the first transport section 45b1. The inductance sensor 47 is positioned such that its sensor surface 47f is directly in front of the second transport section 45b2 in the second direction and facing the first transport section 45b1.

[0090] As a result, according to this embodiment, the developer can be retained within the detection range of the inductance sensor 47, stabilizing the density of the developer within the detection range of the inductance sensor 47, and suppressing a decrease in the accuracy of toner concentration detection even when the amount of developer is small.

[0091] In this embodiment, the suppression of erroneous detection of toner concentration by the inductance sensor 47 was explained by illustrating the case in which the developer density in the detection area of ​​the inductance sensor 47 fluctuates due to fluctuations in the amount of developer in the developing container. However, the developer density in the detection area of ​​the inductance sensor 47 may also fluctuate due to fluctuations in the driving speed of the developing device 4, that is, fluctuations in the driving speed of the first transport screw 45a and the second transport screw 45b. Therefore, according to this embodiment, the developer density in the detection area of ​​the inductance sensor 47 can be stabilized, and thus it is effective even in image forming apparatuses that have multiple driving speeds for the developing device 4 during image formation.

[0092] [Other examples] In the above-described embodiment, the second transport screw 45b was exemplified in which the shaft diameter R1 of the rotating shaft 49b in the second transport section 45b2 is larger than the shaft diameter R2 of the rotating shaft 49a in the first transport section 45b1. However, the present invention is not limited thereto. In the second transport screw 45b, the second transport section 45b2, which is provided downstream of the first transport section 45b1 in the second direction, only needs to be configured such that the developer flow rate is less than that of the first transport section 45b1.

[0093] In other words, in order to obtain the effect of stabilizing the developer density within the detection range of the inductance sensor 47, the second transport screw 45b should be configured to reduce the developer flow rate in the region downstream of the inductance sensor 47 compared to the region facing the inductance sensor 47.

[0094] For example, as shown in Figure 13(a), the pitch of the blades of the second transport screw 45b may be made smaller in the region downstream of the sensor surface 47f of the inductance sensor 47 compared to the region facing the sensor surface 47f of the inductance sensor 47.

[0095] The second conveying screw 45b has a configuration in which the pitch P2 of the blades 48b in the second conveying section 45b2 is smaller than the pitch P1 of the blades 48a in the first conveying section 45b1.

[0096] In this case, in order to obtain the same effect as the configuration of the embodiment described above, the developer flow rate in the region downstream of the second transport screw 45b should be 80% or less compared to the region facing the inductance sensor 47. To achieve this, the pitch P2 of the blades 48b of the second transport screw 45b in the region downstream of the inductance sensor 47 should be 1 / 2 or less compared to the pitch P1 of the blades 48a upstream of it. For example, if the pitch P1 of the blades 48a in the region where the second transport screw 45b faces the inductance sensor 47 is 20 [mm], then the pitch P2 of the blades 48b in the region downstream of this pitch P1 should be 10 [mm] or less.

[0097] Even with this configuration, the same effects as in the previously described embodiment can be obtained.

[0098] Furthermore, as shown in Figure 13(b), the second transport screw 45b may be configured to have reverse-wound blades in the region downstream from the region facing the sensor surface 47f of the inductance sensor 47.

[0099] The second transport section 45b2 of the second transport screw 45b has, as blades 48 formed on the outer circumference of the rotating shaft 49, a first blade 48a that transports the developer in a second direction, and a second blade 48b that transports the developer in a first direction which is opposite to the second direction.

[0100] In this case, in order to make the developer flow rate in the second transport section 45b2 80% or less compared to the developer flow rate in the first transport section 45b1 of the second transport screw 45b, the following configuration is used.

[0101] In other words, the second conveying section 45b2 should have an outer diameter R4 of the second blade 48b that is smaller than the outer diameter R3 of the first blade 48a, and at least half the size. Furthermore, the second blade 48b of the second conveying section 45b2 should be provided with reverse-wound blades with a 20 mm pitch. For example, the second conveying section 45b2 can be configured by adding a second reverse-wound blade 48b with an outer diameter R4 of 8 mm or more and a 20 mm pitch to the first blade 48a in the region downstream from the region facing the sensor surface 47f of the inductance sensor 47.

[0102] Even with this configuration, the same effects as in the previously described embodiment can be obtained.

[0103] In addition to the embodiments described above, the second transport screw 45b facing the inductance sensor 47 may also be configured as follows. This will be explained using Figure 14. Figure 14(a) shows an enlarged view from the horizontal of the configuration of the second transport screw 45b around the inductance sensor 47 in another embodiment. Figures 14(b) and 14(c) show enlarged views from the cross-sectional direction of the developing container 44 of the configuration of the second transport screw 45b around the inductance sensor 47 in this embodiment.

[0104] The second conveying screw 45b, in addition to the configuration described above, further has a rib 31 that rotates in synchronization with the rotation of the second conveying screw 45b. The rib 31 is positioned opposite the sensor surface 47f of the inductance sensor 47. The rib 31 is provided on the outer circumference of the rotation axis 49 of the second conveying screw 45b, separately from the blades 48 described above. The rib 31 is formed to protrude outward from the outer circumference of the rotation axis 49 and is formed in a straight line along the axial direction of the rotation axis 49.

[0105] The rib 31 is provided with a magnetic sheet 32, which serves as a magnet for holding the developer by magnetic force. The magnetic sheet 32 ​​is attached to one side of the rib 31. Here, the side of the rib 31 to which the magnetic sheet 32 ​​is attached is the surface that pushes the developer in the developing container in the rotational direction when the second transport screw 45b rotates. Therefore, the magnetic sheet 32 ​​is provided together with the rib 31 in a straight line along the axial direction of the rotation axis 49.

[0106] The magnet sheet 32 ​​is magnetized by mixing ferrite, a magnetic material, into chlorinated polyethylene, which is used as a binder (resin). The developer T contained in the developing container 44 is a two-component developer in which non-magnetic toner and magnetic carriers are mixed. As a result, the magnetic carriers are constrained by the magnet sheet 32 ​​by magnetic force, and a high-density portion T1 of the developer T is formed, as shown in Figure 14(c). The magnet sheet 32 ​​is magnetized perpendicular to the surface to which it is attached to the rib 31.

[0107] The magnetic sheet 32 ​​provided on the rib 31 can densely support developer on its surface due to its magnetic force, and the developer supported on the surface of the magnetic sheet 32 ​​is replaced by the transport force of the second transport screw 45b. As a result, even if the toner concentration in the developer in the developing container changes, the developer supported on the magnetic sheet 32 ​​can be replaced accordingly.

[0108] In this embodiment, the dimensions of the magnet sheet 32 ​​are as follows: the length s1 in the axial direction (longitudinal direction) of the second transport screw 45b is 8 [mm], the length s2 in the perpendicular direction (vertical direction) perpendicular to the axial direction is 3 [mm], and the thickness s3 is 1 [mm]. The magnetic material (ferrite) used for the magnet sheet 32 ​​has a relative permeability of approximately 200, and the magnetic force is 40 [mT]. The magnet sheet 32 ​​is positioned 2.5 [mm] away from the sensor surface 47f of the inductance sensor 47. Note that the dimensions of the magnet sheet 32 ​​and the distance from the sensor surface 47f of the inductance sensor 47 to the magnet sheet 32 ​​are illustrative and not limited to these.

[0109] The high-density area T1 formed by the developer T supported by the magnetic sheet 32 ​​is maintained at a constant developer density by the magnetic force of the magnetic sheet 32, regardless of changes in the amount of developer in the developing container 44. The area of ​​developer T supported on the magnetic sheet 32 ​​(high-density area T1) overlaps with the area where the inductance sensor 47 has a detection sensitivity of 10% or more when the rib 31 rotates in synchronization with the rotation of the second transport screw 45b. In other words, the high-density area T1 formed by the developer T supported by the magnetic sheet 32 ​​occupies the area where the inductance sensor 47 can detect toner density (detection range of the sensor surface 47f).

[0110] This configuration further stabilizes the developer density within the detection range of the inductance sensor 47, suppressing a decrease in toner concentration detection accuracy even when the amount of developer is small. [Explanation of Symbols]

[0111] 1Y, 1M, 1C, 1K... Photosensitive drum 4Y, 4M, 4C, 4Y… Developing equipment 31... Ribs 32…Magnetic sheet 41…Developing sleeve 42…Magnetic Roll 43…Developing blade 44 ... developing container 44a ... Developing room 44b…Stirring chamber 44c…bulkhead 45a ... First conveying screw 45b ... Second conveyor screw 45b1 ...First transport section 45b2 ... Second transport section 46a, 46b...Communication port 47 ... Inductance sensor 47a ... coil 47b ... Coil drive unit 47d ... connector 47e ... circuit board 47f ... Recovery surface 48, 48a, 48b... feathers 49, 49a, 49b... axis of rotation 51 ...CPU 52 …ROM 53...RAM 54... Toner supply motor

Claims

1. a developer carrier that carries a developer containing toner and a carrier for developing an electrostatic latent image formed on the image carrier; a developer container for accommodating the developer; a conveying screw that conveys the developer contained in the developing container; an inductance sensor having a detection portion that detects the magnetic permeability of the developer contained in the developing container; an output value when the detection unit detects the magnetic permeability of a predetermined magnetic body in a state in which the inductance sensor is not attached to the developing container and a predetermined magnetic body is disposed at a position in contact with the detection unit is defined as A; in a state where the inductance sensor is not attached to the developing container and the predetermined magnetic body is disposed at a position 1 mm away from the detection unit in a vertical direction passing through the detection unit, when an output value when the detection unit detects the magnetic permeability of the predetermined magnetic body is defined as B, B / A≧0.1 is satisfied, The conveying screw is a first conveying section including a first rotating shaft section and a first blade section formed in a spiral shape on an outer circumferential surface of the first rotating shaft section and conveying the developer in a conveying direction of the conveying screw; a second conveying portion including a second rotating shaft portion and a second blade portion formed in a spiral shape on an outer circumferential surface of the second rotating shaft portion and conveying the developer in a conveying direction of the conveying screw, the first conveying unit is disposed on an opposite side of the detection unit with respect to a conveying direction of the conveying screw, the second conveying portion is disposed downstream of the downstream end of the detection portion by one pitch or less of the first blade portion in a conveying direction of the conveying screw, The shaft diameter of the second rotating shaft portion is larger than the shaft diameter of the first rotating shaft portion. A developing device characterized by the above.

2. When a shaft diameter of the second rotating shaft portion is R1, a shaft diameter of the first rotating shaft portion is R2, and an outer diameter of the first blade portion is R3, R1>(R2+R3) / 2 is satisfied.

2. The developing device according to claim 1,

3. The length of the second conveying portion in the conveying direction of the conveying screw is 0.5 to 2 times the length of one pitch of the first blade portion.

2. The developing device according to claim 1,

4. The conveying screw further includes a rib formed so as to protrude outward from an outer periphery of the first rotating shaft portion, The rib is disposed in a conveying direction of the conveying screw and faces the detection unit.

2. The developing device according to claim 1,

5. The rib is provided with a magnet.

5. The developing device according to claim 4.

6. The inductance sensor further includes an output unit that outputs a pulse signal according to the magnetic permeability detected by the detection unit.

2. The developing device according to claim 1,

7. The inductance sensor further comprises a substrate; The detection unit is an area in which a coil is formed by a pattern on the substrate.

2. The developing device according to claim 1,

8. a developer carrier that carries a developer containing toner and a carrier for developing an electrostatic latent image formed on the image carrier; a developer container for accommodating the developer; a conveying screw that conveys the developer contained in the developing container; an inductance sensor having a detection portion that detects the magnetic permeability of the developer contained in the developing container; an output value when the detection unit detects the magnetic permeability of a predetermined magnetic body in a state in which the inductance sensor is not attached to the developing container and a predetermined magnetic body is disposed at a position in contact with the detection unit is defined as A; in a state where the inductance sensor is not attached to the developing container and the predetermined magnetic body is disposed at a position 1 mm away from the detection unit in a vertical direction passing through the detection unit, when an output value when the detection unit detects the magnetic permeability of the predetermined magnetic body is defined as B, B / A≧0.1 is satisfied, The conveying screw is A rotating shaft portion, a first blade portion for conveying the developer contained in the developing container in a conveying direction, the first blade portion being formed in a spiral shape on an outer circumferential surface of the rotating shaft portion; a second blade portion that is disposed downstream of the first blade portion with respect to the transport direction and transports the developer contained in the developing container in the transport direction, the second blade portion being formed in a spiral shape on an outer circumferential surface of the rotating shaft portion, At least a portion of the first blade portion is disposed opposite the detection portion, At least a portion of the second blade portion is disposed downstream of the downstream end of the detection portion by one pitch or less from the first blade portion in the conveying direction, The pitch of the second blade portion is smaller than the pitch of the first blade portion. A developing device characterized by the above.

9. The pitch of the second blade portion is 1 / 2 or less of the pitch of the first blade portion.

9. The developing device according to claim 8.

10. The length of the second blade portion in the conveying direction is 0.5 to 2 times the length of one pitch of the first blade portion.

9. The developing device according to claim 8.

11. the conveying screw has a third blade portion disposed downstream of the second blade portion in the conveying direction and configured to convey the developer contained in the developing container in the conveying direction, the third blade portion being formed in a spiral shape on an outer circumferential surface of the rotating shaft portion; The pitch of the second blade portion is smaller than the pitch of the third blade portion.

9. The developing device according to claim 8.

12. The conveying screw further includes a rib formed so as to protrude outward from an outer periphery of the rotating shaft portion, The rib is disposed in a conveying direction of the conveying screw and faces the detection unit.

9. The developing device according to claim 8.

13. The rib is provided with a magnet. The developing device according to claim 12 .

14. The inductance sensor further includes an output unit that outputs a pulse signal according to the magnetic permeability detected by the detection unit.

9. The developing device according to claim 8.

15. The inductance sensor further comprises a substrate; The detection unit is an area in which a coil is formed by a pattern on the substrate.

9. The developing device according to claim 8.

Images