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.SOLUTION: An inductance sensor arranged opposite to a second conveying screw for detecting the magnetic permeability of developer has a detection unit that detects the magnetic permeability of developer, and has a detection sensitivity at a position separate 1 mm from the detection unit in a direction toward the second conveying screw which is one-tenth or more of a detection sensitivity at a position in contact with the detection unit. The second conveying screw has a rotation shaft, a blade spirally formed on an outer periphery of the rotation shaft, a rib provided at a position opposite to the detection unit of the inductance sensor, provided projecting from the outer periphery of the rotation shaft separately from the blade, and rotating in synchronization with the rotation of the second conveying screw, and a magnet part provided on the rib and carrying developer by a magnetic force. When the rib rotates in synchronization with the rotation of the second conveying screw, an area of the developer carried by the magnet part overlaps an area where the inductance sensor has the detection sensitivity.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 agitated by a screw.

[0003] In such a developing method using a two-component developer, in order to obtain reproducibility of the image density of the 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 the 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 from a substrate and a coil is wound around an iron core. In addition, some inductance sensors have a form in which a coil is directly pattern-printed on a substrate (Patent Document 1).

[0006] Since the inductance sensor with a coil pattern-printed on the substrate does not have an iron core, it can be manufactured at a relatively low cost compared to the 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 16 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 16, 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 16, 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 for achieving the above objective is a developing apparatus comprising: a rotatable developer carrier carrying 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 communication section allowing the developer to move from the first chamber to the second chamber; a second communication section allowing the developer to move from the second chamber to the first chamber; a first transport screw disposed in the first chamber for transporting the developer in a first direction from the second communication section toward the first communication section; a second transport screw disposed in the second chamber for transporting the developer in a second direction from the first communication section toward the second communication section; and an inductance sensor disposed opposite the second transport screw for detecting the magnetic permeability of the developer in the second chamber, wherein the inductance sensor is located in the first chamber. The ductance sensor has a detection unit for detecting the magnetic permeability of the developer, and the detection sensitivity at a position 1 mm away from the detection unit in the direction toward the second transport screw is 10% or more of the detection sensitivity at a position in contact with the detection unit. The second transport screw has a rotating shaft, blades formed spirally on the outer circumference of the rotating shaft, a rib provided at a position opposite the detection unit of the inductance sensor and protruding from the outer circumference of the rotating shaft separately from the blades, and rotating in synchronization with the rotation of the second transport screw, and a magnet part provided on the rib that carries the developer by magnetic force, and the region of the developer carried on the magnet part overlaps with the region in which the inductance sensor has the detection sensitivity when the rib rotates in synchronization with the rotation of the second transport screw. [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 the developing device [Figure 3] Diagram showing the circulation path of the developer [Figure 4] Configuration diagram of the inductance sensor [Figure 5] Diagram 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)(c) Diagram showing the configuration of the second conveyance screw around the inductance sensor [Figure 9] Diagram showing the configuration of the second conveyance screw around the inductance sensor in the comparative example [Figure 10] Diagram showing the change in the output result of the inductance sensor when the developer amount changes [Figure 11] Diagram showing the result of converting the change in the output result of the inductance sensor when the developer amount changes into toner density [Figure 12] (a)(b) Diagram showing the signal values output from the inductance sensor while the screw rotates approximately once in the comparative example [Figure 13] (a)(b) Diagram showing the signal values output from the inductance sensor while the screw rotates approximately once in the example [Figure 14] Diagram showing the relationship between the detection area of the inductance sensor and the magnetic spikes of the magnetic sheet [Figure 15] Diagram showing the magnetic spike occupancy rate and the toner density misdetection amount [Figure 16] Diagram showing the result of converting the change in the output result of the inductance sensor when the developer amount changes into toner density

Mode for Carrying Out the Invention

[0015] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately modified depending on the configuration and various conditions of the apparatus to which the present invention is applied, and the scope of the present invention is not intended to be limited to those.

[0016] [Example 1] The image forming apparatus equipped with the developing device according to Example 1 will be described below with reference to Figures 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 is composed 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 pulses 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 pulses 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), 8(b), and 8(c) show the configuration of the transport screw around the inductance sensor.

[0058] 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. Figures 8(b) and 8(c) also show enlarged views of the configuration of the second transport screw 45b around the inductance sensor 47 in this embodiment, viewed from the cross-sectional direction of the developing container 44.

[0059] 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 P of 20 mm. The second conveying screw 45b has a shaft diameter R2 of the rotating shaft 49 of 6 mm (see Figure 8(a)).

[0060] The second conveying screw 45b 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 aforementioned blades 48. 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.

[0061] 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.

[0062] 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 8(c). The magnet sheet 32 ​​is magnetized perpendicular to the surface to which it is attached to the rib 31.

[0063] 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.

[0064] 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.

[0065] As a comparative example, a configuration in which the magnet sheet 32 ​​is not attached to the rib 31 of the second transport screw 45b is shown. Figure 9 is an enlarged view of the configuration of the second transport screw 45b around the inductance sensor 47 in the comparative example, as seen from the cross-sectional direction of the developing container 44.

[0066] Here, the detection sensitivity of the inductance sensor 47 will be explained using Figure 10. Figure 10 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. In Figure 10, the amount of developer in the developing container 44 [g] is shown on the horizontal axis, and the output of the inductance sensor 47 [cnt] is shown on the vertical axis. The toner concentration in the developer at this time was 7 [%], and the rotation speed of the second transport screw 45b was 300 [rpm]. The output of the inductance sensor corresponds to the detection sensitivity of the inductance sensor.

[0067] As can be seen from the results shown in Figure 10, in both this embodiment and the comparative example, even though the same toner concentration of developer is being measured, the output result of the inductance sensor 47 changes 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 increases, the apparent permeability increases, so the resonance period lengthens and the output pulse of the inductance sensor increases.

[0068] 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.

[0069] Figure 11 shows the results of converting the change in the output of the inductance sensor 47 to toner concentration when the amount of developer in the developing container 44 is changed in two configurations: this embodiment and the comparative example. In Figure 11, the horizontal axis shows the amount of developer in the developing container [g], and the vertical axis shows the value [%] obtained by converting the output pulse of the inductance sensor 47 to toner concentration. At this time, the toner concentration of the developer in the developing container 44, which is the target of detection, is 7[%]. Therefore, the deviation from the toner concentration of 7[%] represents the detection error due to fluctuations in the amount of developer (developer density in the detection range).

[0070] 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 0.7%. The difference in output is particularly noticeable when the amount of developer in the developing container is small.

[0071] 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.

[0072] The reason for this effect will be explained using Figures 12 and 13. Figures 12(a) and 12(b) show the signal values ​​output from the inductance sensor 47 during approximately one rotation of the second transport screw 45b in the configuration of Comparative Example 1. Figure 12(a) shows the case where the amount of developer in the developing container is 120 [g], and Figure 12(b) shows the case where the amount of developer in the developing container is 160 [g]. When the amount of developer in the developing container 44 increases, the developer is compressed by its own weight, increasing the density of the developer near the inductance sensor 47, and the apparent permeability increases, so the resonance period becomes longer and the output pulse of the inductance sensor increases. Therefore, compared to Figure 12(a), in Figure 12(b) the signal value output from the inductance sensor 47 during approximately one rotation of the second transport screw 45b is larger regardless of the rotation phase of the second transport screw 45b.

[0073] On the other hand, Figures 13(a) and 13(b) show the signal values ​​output from the inductance sensor 47 during approximately one rotation of the second transport screw 45b in the configuration of this embodiment. Figure 13(a) shows the case when the amount of developer in the developing container is 120 [g], and Figure 13(b) shows the case when the amount of developer in the developing container is 160 [g]. Looking at Figures 13(a) and 13(b), the signal values ​​when the magnet sheet 32 ​​attached to the rib 31 passes near the inductance sensor 47 are almost the same in Figures 13(a) and 13(b). This is because, regardless of the amount of developer in the developing container, the developer is densely supported on the surface of the magnet sheet 32 ​​by the magnetic force of the magnet sheet 32 ​​attached to the rib 31. Therefore, compared to the configuration of the comparative example, the output fluctuation of the inductance sensor 47 due to fluctuations in the amount of developer is suppressed in the configuration of this embodiment.

[0074] Utilizing this characteristic, the data is obtained by extracting only the output value at which the output of the inductance sensor 47 is highest, based on the rotation period of the second transport screw 45b. In other words, in this embodiment, when the rib 31 on which the magnet sheet 32 ​​is provided rotates in synchronization with the rotation of the second transport screw 45b, the data used as the signal output from the inductance sensor 47 is the maximum value of the signal output from the inductance sensor during one rotation of the second transport screw 45b. This makes it possible to further reduce toner density misdetection.

[0075] As in this embodiment, by forming a high-density area T1 of developer T on the opposite side of the sensor surface 47f of the inductance sensor 47 due to the magnetic force of the magnet sheet 32, even when the amount of developer in the developing container is small, changes in the density of the developer in the detection area of ​​the inductance sensor 47 can be suppressed, and the toner concentration detection result can be stabilized. In other words, even when the amount of developer in the developing container is small, the density of the developer in the detection area of ​​the inductance sensor 47 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.

[0076] (Relationship between the detection range of the inductance sensor and the developer density) This embodiment is an example of how to accurately detect toner concentration. Here, we will further explain a configuration that reduces erroneous detection of toner concentration by the inductance sensor 47 even when there are fluctuations in the amount of developer, based on the relationship between the region in which the inductance sensor 47 can detect toner concentration and the region of the high-density area T1 formed by the developer T supported by the magnet sheet 32.

[0077] In this embodiment, the high-density area T1 formed by the developer T supported by the magnet sheet 32 ​​is maintained at a constant developer density by the magnetic force of the magnet sheet 32, regardless of changes in the amount of developer in the developing container 44. The area of ​​developer T supported on the magnet 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 magnet sheet 32 ​​occupies the area (detection range of the sensor surface 47f) in which the inductance sensor 47 can detect toner density. By having the inductance sensor 47 detect the toner density only in the high-density area T1 formed by the developer T, false detections can be reduced regardless of changes in the amount of developer in the developing container 44.

[0078] Let me explain in detail. First, as shown in Figure 5, when the distance from the sensor surface 47f of the inductance sensor 47 is 2.5 [mm] or more, the output sensitivity becomes 0.1 or less, and the influence on the detection of toner density becomes small. For this reason, it is necessary to stabilize the developer density in the region within 2.5 [mm] of the sensor surface 47f of the inductance sensor 47. In practice, the detection area (detection range) of the inductance sensor 47 can be represented by the longitudinal length, which is the axial length of the second transport screw 45b, and the sensor detection height, which is the height in the direction (vertical direction) from the sensor surface 47f toward the second transport screw 45b. Therefore, when the region in which the detection sensitivity (output sensitivity) of the inductance sensor 47 becomes 0.1 is shown as the detection area (detection range of the sensor surface 47f) of the inductance sensor 47, the distribution is as shown in Figure 14. In Figure 14, the longitudinal length [mm] of the detection area of ​​the inductance sensor 47 is shown on the horizontal axis, and the sensor detection height [mm] is shown on the vertical axis. For example, the longitudinal length of the detection area of ​​the inductance sensor 47 is set to a region of 20 mm, centered at a distance of 2.5 mm from the sensor surface 47f where the output sensitivity is 0.1 or less, with a range of ±10 mm in the longitudinal direction.

[0079] The magnetic tuft occupancy rate in the detection area of ​​the inductance sensor 47 is used as an indicator to show how much of the detection area of ​​the inductance sensor 47 is occupied by the high-density portion T1 of the developer T supported by the magnet sheet 32. The magnet sheet 32 ​​forms magnetic tufts with the developer T it supports. These magnetic tufts formed by the developer T supported by the magnet sheet 32 ​​correspond to the high-density portion T1 formed by the developer T supported by the magnet sheet 32. The magnetic tuft occupancy rate is the proportion of the detection area of ​​the inductance sensor 47 that the shape of the magnetic tufts occupies when the magnetic tufts of the developer T supported by the magnet sheet 32 ​​are placed opposite the inductance sensor 47. The shape of the magnetic tufts of the high-density portion T1 of the developer T supported by the magnet sheet 32 ​​can be measured using a non-contact 3D measuring instrument, such as the VR-3000 (manufactured by KEYENCE).

[0080] Furthermore, Figure 14 shows the magnetic spike shape of the high-density portion T1 of the magnet sheet 32 ​​relative to the detection area of ​​the inductance sensor 47. Figure 14 shows the detection area of ​​the inductance sensor 47 and the magnetic spike shape of the high-density portion T1 of each magnet sheet 32 ​​with magnetic flux densities of 30 [mT], 40 [mT], and 50 [mT]. It can be seen that the shape of the magnetic spikes of the magnet sheet 32 ​​changes depending on the magnetic flux density (magnetic force) when the magnetic flux density is changed to 30 [mT], 40 [mT], and 50 [mT], respectively. Note that Figure 14 illustrates the case where the longitudinal length of the detection area of ​​the inductance sensor 47 is approximately 20 [mm] and a magnet sheet 32 ​​with a longitudinal length s1 of 8 [mm] is used.

[0081] Here, the shape of the magnetic spikes of the developer T supported on the magnet sheet 32 ​​was compared with the detection area of ​​the inductance sensor 47, and the ratio of the magnetic spike shape of the magnet sheet 32 ​​to the detection area of ​​the inductance sensor 47 was quantified as the magnetic spike occupancy rate.

[0082] Table 1 shows the relationship between the length [mm] in the screw axis direction of the magnet sheet 32 ​​and the magnetic flux density [mT], and the magnetic occupancy rate, which is the percentage of the detection area of ​​the inductance sensor 47 occupied by the magnetic occupants of the high-density portion T1 of the magnet sheet 32.

[0083] [Table 1]

[0084] A high magnetic occupancy rate suppresses changes in developer density within the detection area of ​​the inductance sensor 47 in response to fluctuations in the amount of developer in the developing container 44, thereby reducing false detections of toner concentration. Figure 15 shows the relationship between the magnetic occupancy rate [%] and the amount of false toner concentration [%] when the amount of developer in the developing container 44 fluctuates from 120 [g] to 200 [g]. Here, the amount of false toner concentration refers to the detection error [%] of the toner concentration calculated from the detection result by the inductance sensor relative to the toner concentration [%] in the developer in the developing container.

[0085] Table 2 shows the relationship between the amount of toner concentration misdetection [%] when the amount of developer in the developing container 44 varies from 120 [g] to 200 [g], given the conditions of the screw axial length [mm] of the magnet sheet 32 ​​and the magnetic flux density [mT].

[0086] [Table 2]

[0087] When the target amount of toner density misdetection to reduce image defects caused by misdetection of toner density is set to 1.0% or less, the target magnetic particle occupancy rate is 70% or more. In other words, when the magnetic particle occupancy rate is defined as the proportion of the detection area of ​​the inductance sensor 47 (the detection range of the sensor surface 47f) that the magnetic particle occupancy rate of the magnetic particle T supported on the magnetic sheet 32 ​​covers, the magnetic sheet 32 ​​is configured such that the magnetic particle occupancy rate is 70% or more.

[0088] From the data in Tables 1 and 2 above, the configuration of the axial length and magnetic flux density of the magnet sheet 32 ​​that achieves this can be determined. Increasing the axial length and magnetic flux density of the magnet sheet 32 ​​can reduce false detection of toner concentration. However, if the axial length and magnetic flux density of the magnet sheet 32 ​​are made too large, it will create resistance to the transport of the developer in the screw axis direction by the second transport screw 45b, which may cause the developer to accumulate. Therefore, the length s1 of the magnet sheet 32 ​​in the screw axis direction that can reduce false detection of toner concentration while preventing the accumulation of the developer is preferably 8 to 12 [mm] (a length of approximately 40 to 60 [%] of the detection width of the inductance sensor 47). In other words, it is preferable that the length s1 of the magnet sheet 32 ​​provided on the rib 31 in the axial direction of the second transport screw 45b is 40% or more of the detection width in the axial direction of the detection area of ​​the inductance sensor 47. Furthermore, it is preferable that the magnetic flux density of the magnet sheet 32 ​​be in the range of 20 [mT] to 60 [mT].

[0089] 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.

[0090] As described above, when the rib 31 is rotated in synchronization with the rotation of the second transport screw 45b, the high-density section T1 made of the magnet sheet 32 ​​is superimposed on the detection area of ​​the inductance sensor 47, thereby increasing the magnetic fiber occupancy rate of the detection area. More specifically, by configuring the magnet sheet 32 ​​so that the magnetic fiber occupancy rate is 70% or more of the detection area of ​​the inductance sensor 47, the density of the developer in the detection range of the inductance sensor 47 can be stabilized, and a decrease in the detection accuracy of toner concentration can be suppressed even when the amount of developer is small. [Explanation of Symbols]

[0091] T... Developer T1…high density area 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 ... Darkroom 44b…Stirring chamber 44c…bulkhead 45a ... First conveying screw 45b ... Second transport screw 45b1 ...First conveying 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... feathers 49 ... Rotation axis 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 rotation axis; a blade formed in a spiral shape on an outer periphery of the rotating shaft; a rib formed so as to protrude outward from the outer periphery of the rotating shaft, The rib is disposed in a conveying direction of the conveying screw and faces the detection unit, A magnet is attached to the rib, and the magnetic flux density of the magnet is in the range of 20 mT to 60 mT. A developing device characterized by the above.

2. when the rib rotates in synchronization with the rotation of the conveying screw, a ratio of a magnetic brush of the developer carried by the magnet to a region where the detection sensitivity of the inductance sensor is 10% or more is 70% or more; The detection sensitivity of the inductance sensor is the ratio of an output value when the detection unit detects the magnetic permeability of the specified magnetic material in a state where the specified magnetic material is placed at a position X mm away from the detection unit (X>0) in the vertical direction passing through the detection unit, to an output value when the detection unit detects the magnetic permeability of the specified magnetic material in a state where the specified magnetic material is placed at a position where it contacts the detection unit.

2. The developing device according to claim 1,

3. a length of the magnet in the rotation axis direction of the conveying screw is 40% or more of a length of a region in the rotation axis direction of the conveying screw where the detection sensitivity of the inductance sensor is 10% or more, The detection sensitivity of the inductance sensor is a ratio between an output value when the detection unit detects the magnetic permeability of the specified magnetic body in a state where the specified magnetic body is placed at a position X mm away from the detection unit (X>0) in the vertical direction passing through the detection unit, and an output value when the detection unit detects the magnetic permeability of the specified magnetic body in a state where the specified magnetic body is placed at a position in contact with the detection unit.

2. The developing device according to claim 1,

4. 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,

5. 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,

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