Image forming apparatus

Abstract

To suppress the accuracy of detecting a toner concentration in a developing agent from decreasing.SOLUTION: An image forming apparatus comprises: an image carrier; a developing device having a developing container that accommodates a developer containing a toner and a carrier, a developer carrier that carries and supplies the developer to the image carrier, and a transport member that is rotatably located to the developing container and transports the developer; an inductance sensor that is located facing the transport member, and that detects the magnetic permeability of the developer and outputs a signal corresponding to the detected magnetic permeability; a magnet part that is provided on the transport member and located at a position facing the inductance sensor, and that carries the developer by a magnetic force; and control means that detects a toner concentration in the developer from the output value of the inductance sensor. The control means performs corrective operation to correct, from the output value of the inductance sensor in the state of a developer of known toner concentration being accommodated in the developing container, a change value per unit toner concentration of the output value to a change value corresponding to a difference in the magnetic permeability of the magnet part.SELECTED DRAWING: Figure 15

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus provided with a developing device that develops an electrostatic latent image formed on an image carrier into a toner image. [Background Art]

[0002] An image forming apparatus includes a developing device provided with a developing sleeve serving as a rotatable developer carrier that carries a two-component developer containing non-magnetic toner and a magnetic carrier. In a developing method using a two-component developer, 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 obtain reproducibility of the image density of an output image. In order to maintain the toner concentration of the two-component developer circulating in the developing vessel within a predetermined range, a technology is used in which a sensor for detecting the toner concentration is provided on the wall surface of the developing vessel, and the replenishment amount of replenishment toner is adjusted according to the detection result.

[0003] As a sensor for detecting the toner concentration of a developer in a developing vessel, an inductance sensor whose inductance changes according to the proportion of magnetic material in the developer is known. Some inductance sensors have a configuration in which a detection portion protrudes from a substrate, and the detection portion is formed by winding a coil 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).

[0004] An inductance sensor in which a coil is pattern-printed on a substrate does not have an iron core, so it can be manufactured at a relatively low cost compared to an inductance sensor having an iron core.

[0005] Furthermore, inductance sensors with patterned coils do not have an iron core, making them less prone to magnetic field concentration. Compared to inductance sensors with an iron core, they have a wider detection range. 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]

[0006] [Patent Document 1] Japanese Patent Publication No. 2016-012078 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, in configurations using inductance sensors with patterned coils, the detection range is wide, and it may not be possible 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 density of developer present in the sensor's detection range may fluctuate, potentially changing the sensor's output. In other words, if the amount of developer in the developing container decreases, the density of developer in the inductance sensor's detection range will fluctuate accordingly, which may reduce the accuracy of detecting the toner concentration in the developer.

[0008] 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]

[0009] A typical configuration of the present invention for achieving the above objective is a developing apparatus comprising: an image carrier; a developing container containing a developer including toner and a carrier; a developer carrier that carries the developer and supplies it to the image carrier; a transport member rotatably arranged in the developing container and transporting the developer; an inductance sensor positioned opposite the transport member, which detects the permeability of the developer and outputs a signal corresponding to the detected permeability; a magnet unit provided on the transport member and positioned opposite the inductance sensor, which carries the developer by magnetic force; and a control means for detecting the concentration of toner in the developer from the output value of the inductance sensor, wherein the control means performs a correction operation to correct the fluctuation value per unit toner concentration of the output value from the output value of the inductance sensor when the developing container contains a developer of a known toner concentration to a fluctuation value corresponding to the difference in permeability of the magnet unit, and uses the corrected fluctuation value to detect the toner concentration in the developer. [Effects of the Invention]

[0010] According to the present invention, it is possible to suppress the decrease in the detection accuracy of toner concentration in the developer. [Brief explanation of the drawing]

[0011] [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] Diagram showing the distance sensitivity of an inductance sensor. [Figure 6] Control block diagram of an image forming apparatus [Figure 7] Flowchart showing the toner concentration control process [Figure 8] (a)(b)(c) Diagram showing the configuration of the second transport screw around the inductance sensor. [Figure 9]Figure showing the configuration of a second conveying screw around an inductance sensor in a comparative example [Figure 10] Figure showing a change in an output result of the inductance sensor when an amount of developer changes [Figure 11] Figure showing a result obtained by converting, into toner density, a change in an output result of the inductance sensor when an amount of developer changes [Figure 12] Figure showing signal values output from the inductance sensor while the screw makes approximately one rotation in (a) and (b) of the comparative example [Figure 13] Figure showing signal values output from the inductance sensor while the screw makes approximately one rotation in (a) and (b) of Example 1 [Figure 14] Figure showing a correspondence relationship between a toner density of developer and a fluctuation value of a signal value output from the inductance sensor [Figure 15] Flowchart showing correction control for suppressing the influence of magnetic permeability of a magnet sheet in Example 1 [Figure 16] Flowchart showing correction control for suppressing the influence of magnetic permeability of a magnet sheet in Example 2 [Figure 17] Figure showing a result obtained by converting, into toner density, a change in an output result of the inductance sensor when an amount of developer changes in Example 3 [Figure 18] Flowchart for correcting the correspondence relationship between an output pulse count and toner density in Example 4 DETAILED DESCRIPTION OF EMBODIMENTS

[0012] 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, and the like of components described in the following embodiments should be appropriately changed depending on the configuration of an 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.

[0013] Example 1 The image forming apparatus according to Example 1 will be described below with reference to Figures 1 to 15.

[0014] (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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] (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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] The image forming apparatus is equipped with a developer replenishment device (not shown) that contains either toner only or a replenishment developer consisting of toner and a magnetic carrier. The developer replenishment device is fitted with a supply screw, which allows the amount of replenishment developer used for image formation to be supplied from the developer replenishment device to the stirring chamber 44b 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 replenishment motor 54 shown in Figure 6) that drives the supply screw.

[0029] 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 4). 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, and the toner concentration can be detected by detecting this change in magnetic permeability with the inductance sensor 47.

[0030] (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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] (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.

[0035] 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 a pulse signal as a detection signal corresponding to the permeability of the developer.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] In this way, the inductance sensor 47 makes it possible to detect the toner concentration in the developer as the count (count value) of the output pulse signal.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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 47f compared to the detection sensitivity at a position on the surface of the sensor surface 47f. 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 47f.

[0050] 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.

[0051] (Inductor sensor toner concentration control operation) 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.

[0052] In this embodiment, the CPU 51, which acts as a control means for controlling the image formation 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 signal 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 4 and is a drive motor that drives the supply screw located in the developer supply device (not shown) described above.

[0053] 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).

[0054] (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.

[0055] 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.

[0056] 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)).

[0057] 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.

[0058] 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.

[0059] The developer t contained in the developing container 44 is a two-component developer in which a non-magnetic toner and a magnetic carrier are mixed. As a result, the magnetic carrier is constrained by the magnetic force of the magnet sheet 32, 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.

[0060] The magnet sheet 32 ​​is magnetized by mixing ferrite, a magnetic material, into chlorinated polyethylene, which is used as a binder (resin). The magnetic force of the magnet sheet 32 ​​is preferably in the range of 20 [mT] to 60 [mT]. By setting the magnetic force of the magnet sheet 32 ​​within this range, the developer can be densely supported on the surface of the magnet sheet 32. Furthermore, the conveying force of the second conveying screw 45b allows the developer on the surface of the magnet sheet 32 ​​to be replaced, and even when the toner concentration in the developer in the developing container fluctuates, the toner concentration fluctuation can be detected well. In this embodiment, the magnetic force of the magnet sheet 32 ​​is 40 [mT].

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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).

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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, changes in the density of the developer in the detection area of ​​the inductance sensor 47 can be suppressed. In other words, 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.

[0070] (Correction control according to the difference in magnetic permeability of the magnetic sheet 32) Next, using Figures 14 and 15, we will explain the correction operation that adjusts the fluctuation value per unit toner concentration of the output value (count value) of the inductance sensor 47 to a fluctuation value corresponding to the difference in magnetic permeability of the magnet sheet 32.

[0071] Figure 14 shows the relationship between the toner concentration of the developer and the fluctuation value (signal fluctuation value) of the signal value (output value, count value) output from the inductance sensor 47. Figure 15 is a flowchart showing the correction control to suppress the influence of the magnetic permeability of the magnet sheet 32 ​​in Example 1.

[0072] As mentioned above, by placing the magnetic sheet 32 ​​on the second transport screw 45b facing the inductance sensor 47, it becomes possible to stably detect the toner concentration in the developer. However, the following problems arise.

[0073] Since the inductance sensor 47 in this embodiment does not have an iron core, magnetic field concentration is less likely to occur, and the detection range of the sensor is wider compared to a sensor with an iron core. However, since magnetic material is also contained inside the magnet sheet 32 ​​placed on the second transport screw 45b, the inductance sensor 47 also detects the amount of magnetic material inside the magnet sheet 32. The amount of magnetic material contained in the magnet sheet 32 ​​may vary depending on manufacturing variations (individual differences) of the magnet sheet 32. Also, the amount of magnetic material inside the magnet sheet 32 ​​detected by the inductance sensor 47 may differ depending on the mounting position of the magnet sheet 32. For this reason, the inductance sensor 47 may misdetect the toner concentration even if the developer can be carried on the transport screw at a constant density.

[0074] Therefore, in this embodiment, even when the magnetic sheet 32 ​​is placed near the inductance sensor 47, which has a wide detection range, the detection accuracy of the toner concentration in the developer is improved by compensating for the influence of the magnetic sheet.

[0075] Since the magnet sheet 32 ​​is a magnetic material, it has magnetic permeability. Therefore, the signal value output from the inductance sensor 47 is also affected by the magnetic permeability of the magnet sheet 32. In particular, in the case of the inductance sensor 47 in which the coil 47a is pattern-printed on the substrate 47e as shown in Figure 4 of this embodiment, as mentioned above, since there is no iron core, magnetic field concentration is less likely to occur, and the detection range of the sensor is wider than that of a sensor with an iron core. Therefore, the signal value output from the inductance sensor 47 is easily affected by the magnetic permeability of the magnet sheet 32. The magnetic permeability of the magnet sheet 32 ​​varies slightly from magnet sheet to magnet sheet due to the effects of manufacturing inconsistencies and other factors.

[0076] Figure 14 illustrates the relationship between the toner concentration of the developer and the variation in the output value (signal value) of the inductance sensor 47 from a toner concentration of 9%, using the cases where the permeability of the magnet sheet 32 ​​is at the center value and the upper limit value of the manufacturing variation as examples. In Figure 14, the solid line shows the relationship when the permeability of the magnet sheet is at the center value of the manufacturing variation, and the dashed line shows the relationship when the permeability of the magnet sheet is at the upper limit value of the manufacturing variation. The horizontal axis of Figure 14 represents the toner concentration [%] of the developer, and the vertical axis represents the variation [cnt] of the signal value (output value, count value) output from the inductance sensor 47.

[0077] When the permeability of the magnetic sheet 32 ​​is the center value of the manufacturing variation, compared to when it is the upper limit of the manufacturing variation, the output value of the inductance sensor 47 becomes larger. Therefore, if the relationship between the signal fluctuation value [cnt] created with the permeability as the center value of the manufacturing variation and the toner concentration [%] is used, for example, a developer that is actually a toner concentration of 6 [%] will be incorrectly detected as a toner concentration of 5.2 [%] if the permeability is the upper limit of the manufacturing variation.

[0078] Therefore, in this embodiment, after installing the developing device 4 in the image forming apparatus 10, a correction is performed to suppress the influence of the magnetic permeability of the magnetic sheet 32. This correction to suppress the influence of the magnetic sheet 32 ​​will be explained with reference to Figure 15.

[0079] For example, an IC tag placed in the developing device is detected by a detection unit (not shown) located in the image forming apparatus, thereby detecting when a new developing device has been installed in the image forming apparatus, such as during the initial startup of the image forming apparatus and when a developing device is replaced. Then, the CPU 51 (see Figure 6), which is the control means of the image forming apparatus 10, starts a correction operation to suppress the influence of the magnetic permeability of the magnet sheet 32 ​​of the newly installed developing device (S201). First, the CPU 51 drives the transport screw to start stirring the developer in the developing device 4 (S202). Then, the CPU 51 counts the pulse signals output from the inductance sensor 47 per predetermined time and detects the counted value (count number) as the output value of the inductance sensor 47 (S203). The CPU 51 stores the average value of the output value for one cycle of the transport screw in storage (RAM 53) (S204). Simultaneously, the CPU 51 reads from the ROM 52 the correspondence between the output pulse count of the inductance sensor 47 and the toner density, which corresponds to the output value of the inductance sensor 47 (S205). After that, the CPU 51 terminates the correction operation (S206).

[0080] In other words, during the correction operation, the CPU 51 corrects the output value of the inductance sensor 47 to a variation value corresponding to the difference in magnetic permeability of the magnet sheet 32 ​​(T / D ratio sensitivity in Table 1). The CPU 51 then uses this corrected variation value to detect the toner concentration in the developer.

[0081] The correspondence between the output pulse count of the inductance sensor 47, which the CPU 51 reads from the ROM 52 during the aforementioned correction operation, and the toner density will now be explained. The ROM 52, which is the memory unit, stores (stores) a table showing the correspondence between the output value during the correction operation and the T / D ratio sensitivity, as shown in Table 1. In Table 1, the output during the correction operation [cnt] is the output value (count value, output pulse count) of the signal output from the inductance sensor 47 per predetermined time during the correction operation shown in Figure 14. In Table 2, each output value is shown as a range, such as 117500 to 122500. In Table 2, the T / D ratio sensitivity [cnt / 1%] is the fluctuation value (signal fluctuation value) per unit toner density (1% toner density) according to the difference in magnetic permeability of the magnet sheet 32, and corresponds to the slope of the solid or dashed line shown in Figure 14. Note that the values ​​shown in Table 1 are examples and are not limiting, and should be set as appropriate.

[0082] (Table 1) TIFF0007919978000001.tif57130

[0083] In this embodiment, 120g of developer with a toner concentration of 9% is stored in the new developing device. That is, during the correction operation described above, the developing container of the new developing device contains developer with a known toner concentration. In this state, when the CPU 51 detects the output value from the inductance sensor 47, since the toner concentration and amount of developer in the developing device are known, the difference in the output value of the inductance sensor 47 is due to the difference in the permeability of the magnet sheet 32. Therefore, it is possible to predict the difference in the permeability of the magnet sheet 32 ​​from the output value of the inductance sensor 47 during the correction operation described above. If the permeability of the magnet sheet 32 ​​is different, the relationship between the output value (signal fluctuation value) of the inductance sensor 47 and the toner concentration of the developer will be different, as shown in Figure 14. In other words, the slopes of the solid line relationship and the dashed line relationship shown in Figure 14 are different. Therefore, by correcting the fluctuation value per unit toner concentration of the output value from the output value of the inductance sensor 47 during the correction operation to a fluctuation value corresponding to the difference in the permeability of the magnet sheet 32, it is possible to improve the prediction accuracy of the toner concentration of the developer.

[0084] Table 2 shows the difference in toner concentration prediction results for the developer with and without correction in this embodiment, when a developer of a known toner concentration is placed in a developing container. In Table 2, the known toner concentration of the developer is 9%. In Table 2, "with correction" is the toner concentration prediction result when the correction operation shown in Figure 14 is performed, and "without correction" is the toner concentration prediction result when the correction operation is not performed.

[0085] (Table 2) TIFF0007919978000002.tif57157

[0086] For example, if the permeability of the magnet sheet 32 ​​is at the center value, the output value (output pulse count) of the inductance sensor 47 during the correction operation will be 120,000 [cnt]. Then, from Table 1, the relationship between the output pulse count and toner density is 1050 [cnt] = 1 [%]. That is, when the output value is 120,000 [cnt], the T / D ratio sensitivity corresponding to the first range including that output value is 1050 [cnt / %].

[0087] In other words, during a correction operation, if the output value of the inductance sensor 47 is the first output value, the CPU 51 reads the first fluctuation value corresponding to the first output value from the correspondence relationship (Table 1) stored in the ROM 52. That is, if the output value of the inductance sensor 47 is 120000 [cnt] during a correction operation, the CPU 51 reads 1050 [cnt / %] from the ROM 52, which is the first fluctuation value corresponding to the first range that includes 120000 [cnt].

[0088] Suppose that an image is formed using a developing device equipped with this magnetic sheet 32, toner is consumed, the toner concentration in the developing container changes from 9% to 5%, and the output pulse count changes to 124300 cnt. Then, the changed toner concentration is (124300 - 120000) ÷ 1050 = 4.1%, so the toner concentration in the developing container is predicted to be 4.9%.

[0089] Next, the same prediction is performed when the permeability of the magnet sheet 32 ​​is lower than the aforementioned center value. In this case, assume that the output pulse count of the inductance sensor 47 during the correction operation was 116500 [cnt]. Then, from Table 1, the value corresponding to 116500 [cnt] is 1125 [cnt] = 1 [%]. That is, when the output value is 116500 [cnt], the T / D ratio sensitivity corresponding to the second range including that output value is 1125 [cnt / %].

[0090] In other words, during a correction operation, if the output value of the inductance sensor 47 is a second output value that is lower than the first output value, the CPU 51 reads a second fluctuation value that is greater than the first fluctuation value corresponding to the second range including the second output value from the correspondence relationship (Table 1) stored in the ROM 52. That is, during a correction operation, if the output value of the inductance sensor 47 is 116500 [cnt], the CPU 51 reads 1125 [cnt / %] from the ROM 52, which is the second fluctuation value corresponding to the second range including 116500 [cnt].

[0091] When a developer with a toner concentration of 5% is measured under the condition that the permeability of the magnet sheet 32 ​​is lower than the aforementioned center value, the output value of the inductance sensor 47 becomes 121100 [cnt]. Assuming that this output value is the same as when the permeability of the magnet sheet 32 ​​is the center value, the toner concentration is predicted using the first fluctuation value of 1050 [cnt / %]. That is, the toner concentration is predicted without correction. Then, the fluctuating toner concentration is (121110 - 116500) ÷ 1050 = 4.4 [%], so the toner concentration in the developing container becomes 4.6 [%], resulting in an error of 0.4 [%] from the actual toner concentration of 5 [%].

[0092] On the other hand, we use a second fluctuation value of 1125 [cnt / %], which corresponds to the magnetic permeability of the magnet sheet 32 ​​read from Table 1. That is, we predict the toner concentration with correction applied. Then, the fluctuating toner concentration is (121100 - 116500) ÷ 1125 = 4.1 [%], so the toner concentration in the developing container becomes 4.9 [%], and the error with the actual toner concentration of 5 [%] can be suppressed to 0.1 [%].

[0093] Next, the same prediction is performed when the permeability of the magnet sheet 32 ​​is higher than the aforementioned center value. In this case, assume that the output pulse count of the inductance sensor 47 during the correction operation was 126600 [cnt]. Then, from Table 1, the value corresponding to 126600 [cnt] is 975 [cnt] = 1 [%]. That is, when the output value is 126600 [cnt], the T / D ratio sensitivity corresponding to the third range including that output value is 975 [cnt / %].

[0094] In other words, during the correction operation, if the output value of the inductance sensor 47 is a third output value that is higher than the first output value, the CPU 51 reads a third fluctuation value that is smaller than the first fluctuation value that corresponds to the third range including the third output value from the correspondence relationship (Table 1) stored in the ROM 52. That is, during the correction operation, if the output value of the inductance sensor 47 is 126600 [cnt], the CPU 51 reads 975 [cnt / %] from the ROM 52, which is the third fluctuation value that corresponds to the third range including 126600 [cnt].

[0095] When a developer with a toner concentration of 5% is measured under the condition that the permeability of the magnet sheet 32 ​​is higher than the aforementioned center value, the output value of the inductance sensor 47 becomes 130400 [cnt]. Assuming that this output value is the same as when the permeability of the magnet sheet 32 ​​is the center value, the toner concentration is predicted using the first fluctuation value of 1050 [cnt / %]. That is, the toner concentration is predicted without correction. Then, the fluctuating toner concentration is (130400 - 126600) ÷ 1050 = 3.6 [%], so the toner concentration in the developing container becomes 5.4 [%], resulting in an error of 0.4 [%] from the actual toner concentration of 5 [%].

[0096] On the other hand, a third fluctuation value of 975 [cnt / %], corresponding to the magnetic permeability of the magnet sheet 32 ​​read from Table 1, is used. That is, the toner concentration is predicted with correction applied. Then, the fluctuating toner concentration is (130400 - 126600) ÷ 975 = 3.9 [%], so the toner concentration in the developing container becomes 5.1 [%], and the error with the actual toner concentration of 5 [%] can be suppressed to 0.1 [%].

[0097] It can be seen that the accuracy of detecting the toner concentration of the developer is improved by implementing the correction control in this embodiment.

[0098] Subsequently, the correspondence between the output pulse count of the inductance sensor 47 and the toner concentration is determined using the relationship read in S205 as shown in Figure 14, to detect the toner concentration in the developer. Furthermore, even if the power to the image forming apparatus is turned off, upon restart, the output value during the correction operation is read from the storage (RAM 53), and the corresponding fluctuation value is read from the ROM 52 and used, thereby correcting the effect of the magnetic permeability of the magnet sheet.

[0099] As described above, according to this embodiment, during the correction operation, the CPU 51 reads out the fluctuation value corresponding to the difference in magnetic permeability of the magnet sheet 32, which corresponds to the output value of the inductance sensor 47, from the correspondence relationship (Table 1) stored in the ROM 52. The CPU 51 then uses the read-out fluctuation value to detect the toner concentration in the developer. This makes it possible to suppress a decrease in the detection accuracy of the toner concentration in the developer. In particular, even when the magnet sheet 32 ​​is used near the inductance sensor 47, the detection accuracy of the toner concentration in the developer can be improved by correcting for the influence of the magnet sheet 32.

[0100] [Example 2] The image forming apparatus according to Example 2 will be described.

[0101] The image forming apparatus according to Embodiment 2 is characterized in that a data storage unit (not shown), such as an IC tag located in the developing apparatus 4, stores in advance a corresponding value corresponding to the magnetic permeability of the magnet sheet, which was measured in advance at the time of manufacture or factory shipment. The features of this embodiment will be explained below with reference to Figure 16. Note that, apart from the configuration described below, it is the same as the embodiment described above, and therefore the explanation will be omitted.

[0102] For example, an IC tag placed in the developing unit is detected by a detection unit (not shown) located in the image forming apparatus, thereby detecting when the image forming apparatus is powered on or when the developing unit is replaced, etc., that a new developing unit has been installed in the image forming apparatus. Then, the CPU 51 (see Figure 6), which is the control means of the image forming apparatus 10, starts a correction operation to suppress the influence of the magnetic permeability of the magnet sheet 32 ​​of the newly installed developing unit (S301). First, the CPU 51 reads a corresponding value corresponding to the magnetic permeability of the magnet sheet, which was measured in advance at the time of manufacture or factory shipment and stored in the data storage unit of the developing unit 4 (S302). This corresponding value is obtained, for example, by driving the developing container before pouring the developer into the developing container and recording the value output from the inductance sensor 47. Next, the CPU 51 reads the correspondence between the output pulse count of the inductance sensor 47 and the toner density, corresponding to the read corresponding value, from the ROM 52 (S303).

[0103] Table 3 shows the correspondence between the permeability of the magnet sheet measured during manufacturing (IC tag storage value) and the variation value per unit toner concentration (1% toner concentration) (T / D ratio sensitivity) according to the difference in permeability of the magnet sheet 32.

[0104] (Table 3) TIFF0007919978000003.tif57130

[0105] From this point onward, the correspondence between the output pulse count of the inductance sensor 47 and the toner density is calculated using the relationship read from the ROM 52. After that, the transport screw is driven and stirring of the developer in the developing device 4 begins (S304). The CPU 51 then counts the pulse signals output from the inductance sensor 47 per predetermined time and detects the counted value (count number) as the output value of the inductance sensor 47 (S305). The CPU 51 stores the average value of that output value over one cycle of the transport screw in storage (RAM 53) (S306). After that, the CPU 51 finishes the correction operation (S307).

[0106] Table 4 shows the difference in toner concentration prediction results for the developer with and without correction in this embodiment, when a developer of a known toner concentration is placed in a developing container. In Table 4, the known toner concentration of the developer is 9%. In Table 4, "with correction" is the toner concentration prediction result when the correction operation shown in Figure 16 is performed, and "without correction" is the toner concentration prediction result when the correction operation is not performed.

[0107] (Table 4) TIFF0007919978000004.tif56156

[0108] For example, if the permeability of the magnet sheet 32 ​​is the central value, then suppose the corresponding value read from the data storage unit of the developing device 4, which corresponds to the permeability of the magnet sheet 32 ​​measured during manufacturing, is 75000. Then, from Table 3, the relationship between the output pulse count and toner density becomes 1050 [cnt] = 1 [%]. That is, if the corresponding value is 75000, the T / D ratio sensitivity corresponding to the first range including that corresponding value is 1050 [cnt / %].

[0109] In other words, during a correction operation, if the corresponding value read from the data storage unit for the permeability of the magnet sheet 32 ​​is the first corresponding value, the CPU 51 reads the first fluctuation value corresponding to the first corresponding value from the correspondence relationship (Table 4) stored in the ROM 52. That is, if the corresponding value read from the data storage unit for a correction operation is 75000, the CPU 51 reads 1050 [cnt / %] from the ROM 52, which is the first fluctuation value corresponding to the first range including 75000.

[0110] Suppose that an image is formed using a developing device equipped with this magnetic sheet 32, and toner is consumed, causing the toner concentration of the developer in the developing container to change from 9% to 5%. At this time, assume that the output pulse count changed by 4300 cnt from the output value of the inductance sensor 47 stored in the storage (RAM 53) during the correction operation (S306 in Figure 16). Then, the changed toner concentration is 4300 ÷ 1050 = 4.1%, so the toner concentration in the developing container is predicted to be 4.9%.

[0111] Next, a similar prediction is performed when the permeability of the magnet sheet 32 ​​is lower than the aforementioned center value. Suppose the corresponding value read from the data storage unit of the developing device 4, which corresponds to the permeability of the magnet sheet 32 ​​measured during manufacturing, is 74200. Then, from Table 3, the value corresponding to 74200 is 1125 [cnt] = 1 [%]. That is, when the corresponding value is 74200, the T / D ratio sensitivity corresponding to the second range including that corresponding value is 1125 [cnt / %].

[0112] When measuring a developer with a toner concentration of 5% under the condition that the magnetic permeability of the magnet sheet 32 ​​is lower than the aforementioned center value, the output value of the inductance sensor 47 stored in the storage (RAM 53) during the correction operation (S306 in Figure 16) changed by 4610 [cnt]. Assuming that this output value is the same as when the magnetic permeability of the magnet sheet 32 ​​is the center value, the toner concentration is predicted using the first fluctuation value of 1050 [cnt / %]. That is, the toner concentration is predicted without correction. Then, the fluctuating toner concentration is 4610 ÷ 1050 = 4.4 [%], so the toner concentration in the developing container becomes 4.6 [%], resulting in an error of 0.4 [%] from the actual toner concentration of 5 [%].

[0113] On the other hand, we use a second fluctuation value of 1125 [cnt / %], which corresponds to the magnetic permeability of the magnet sheet 32 ​​read from Table 3. That is, we predict the toner concentration with correction applied. Then, the fluctuating toner concentration becomes 4610 ÷ 1125 = 4.1 [%], so the toner concentration in the developing container becomes 4.9 [%], and the error with the actual toner concentration of 5 [%] can be suppressed to 0.1 [%].

[0114] Next, a similar prediction is performed when the permeability of the magnet sheet 32 ​​is higher than the aforementioned center value. Suppose the corresponding value read from the data storage unit of the developing device 4, which corresponds to the permeability of the magnet sheet 32 ​​measured during manufacturing, is 76200. Then, from Table 3, the value corresponding to 76200 is 975[cnt]=1[%]. That is, when the corresponding value is 76200, the T / D ratio sensitivity corresponding to the third range including that corresponding value is 975[cnt / %].

[0115] When a developer with a toner concentration of 5% was measured under the condition that the magnetic permeability of the magnet sheet 32 ​​was higher than the aforementioned center value, the output value of the inductance sensor 47 stored in the storage (RAM 53) during the correction operation (S306 in Figure 16) changed by 3800 [cnt]. Assuming that the magnetic permeability of the magnet sheet 32 ​​is the same as the center value, the toner concentration is predicted using the first fluctuation value of 1050 [cnt / %]. That is, the toner concentration is predicted without correction. Then, the fluctuating toner concentration is 3800 ÷ 1050 = 3.6 [%], so the toner concentration in the developing container becomes 5.4 [%], resulting in an error of 0.4 [%] from the actual toner concentration of 5 [%].

[0116] On the other hand, a third fluctuation value of 975 [cnt / %], corresponding to the magnetic permeability of the magnet sheet 32 ​​read from Table 3, is used. That is, the toner concentration is predicted with correction applied. Then, the fluctuating toner concentration becomes 3800 ÷ 975 = 3.9 [%], so the toner concentration in the developing container becomes 5.1 [%], and the error with the actual toner concentration of 5 [%] can be suppressed to 0.1 [%].

[0117] It can be seen that the accuracy of predicting the developer toner concentration is improved by implementing the correction control in this embodiment.

[0118] As described above, according to this embodiment, during the correction operation, the CPU 51 reads a fluctuation value corresponding to the difference in magnetic permeability of the magnet sheet 32, which corresponds to the corresponding value read from the data storage unit, from the correspondence relationship (Table 3) stored in the ROM 52. The CPU 51 then uses the read fluctuation value to detect the toner concentration in the developer. This makes it possible to suppress a decrease in the detection accuracy of the toner concentration in the developer. In particular, even when the magnet sheet 32 ​​is used near the inductance sensor 47, the detection accuracy of the toner concentration in the developer can be improved by correcting for the influence of the magnet sheet 32.

[0119] Furthermore, when using the configuration of this embodiment, the corresponding value for the magnetic permeability of the magnet sheet is stored in the data storage unit of the developing device 4 in advance during manufacturing or factory shipment. Therefore, there is no need to store the initial value for correction in the storage of the image forming device, making it possible to correct the effect of the magnetic permeability of the magnet sheet with a simpler configuration.

[0120] [Example 3] The image forming apparatus according to Example 3 will now be described. Note that, apart from the configuration described below, it is the same as in the previously described example, and therefore the explanation will be omitted.

[0121] In the image forming apparatus according to Example 1, the output value of the inductance sensor 47 used to calculate the toner density was the average value of the output values ​​over one cycle of the transport screw. In contrast, in the image forming apparatus according to Example 3, the output value of the inductance sensor 47 used to calculate the toner density was the maximum output value over one cycle of the transport screw.

[0122] Specifically, using the characteristics described in the aforementioned Embodiment 1 with reference to Figures 13(a) and 13(b), 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 maximum value of the signal output from the inductance sensor during one rotation of the second transport screw 45b is used as the data. This makes it possible to further reduce toner density misdetection.

[0123] As mentioned above, when the magnet sheet 32 ​​attached to the rib 31 passes near the inductance sensor 47, the signal value exhibits small fluctuations in the amount of developer because the developer is densely supported on the surface of the magnet sheet 32 ​​by magnetic force. Therefore, it is possible to suppress fluctuations in the output of the inductance sensor 47 due to fluctuations in the amount of developer more effectively than using the average value over one cycle of the transport screw.

[0124] Figure 17 shows the amount of developer in the developing container 44 and the toner concentration prediction results by the inductance sensor 47 for the configuration of Example 1 and the configuration of this embodiment. From Figure 17, it can be seen that the dependency of the toner concentration of the developer on the amount of developer is suppressed in the configuration of this embodiment compared to the configuration of Example 1.

[0125] [Example 4] The image forming apparatus according to Example 4 will now be described.

[0126] In the image forming apparatus according to Embodiment 4, the inductance sensor 47 is located in the image forming apparatus 10. The image forming apparatus 10 also includes a pressing mechanism (not shown), such as a spring, which positions the inductance sensor 47 at a predetermined location in the developing apparatus 4 after the developing apparatus 4 is installed in the image forming apparatus 10.

[0127] In this case, the positional relationship between the inductance sensor 47 and the developing device 4 may vary slightly due to shifts in installation position, and this variation may cause errors in the correspondence between the output pulse count of the inductance sensor 47 and the toner density.

[0128] Therefore, in this embodiment, similar to Embodiment 2 described above, a value corresponding to the magnetic permeability of the magnet sheet, measured in advance at the time of manufacture or factory shipment, is stored in a data storage unit (not shown), such as an IC tag, located in the developing device 4. Furthermore, in this embodiment, the value corresponding to the magnetic permeability of the magnet sheet, the output value of the inductance sensor 47 during the initial correction operation, and the correspondence between the output pulse count and the toner density are stored in advance in the storage unit (ROM 52) of the image forming apparatus 10. The CPU 51 then corrects the correspondence between the output pulse count and the toner density based on the value corresponding to the magnetic permeability of the magnet sheet and the output value of the inductance sensor 47 during the initial correction operation. In other words, the CPU 51 corrects the fluctuation value corresponding to the difference in magnetic permeability of the magnet sheet 32 ​​based on the value corresponding to the magnetic permeability of the magnet sheet and the output value of the inductance sensor 47 during the initial correction operation. The features of this embodiment will be explained below with reference to Figure 18. Note that, apart from the configuration described below, this embodiment is the same as the embodiment described above, and therefore the explanation will be omitted.

[0129] For example, an IC tag placed in the developing unit is detected by a detection unit (not shown) located in the image forming apparatus, thereby detecting when a new developing unit has been installed in the image forming apparatus, such as during the initial startup of the image forming apparatus or when a developing unit is replaced. Then, the CPU 51 (see Figure 6), which is the control means of the image forming apparatus 10, starts a correction operation to suppress the influence of the magnetic permeability of the magnet sheet 32 ​​of the newly installed developing unit (S401). First, the CPU 51 reads a corresponding value corresponding to the magnetic permeability of the magnet sheet, which was measured in advance at the time of manufacture or factory shipment and stored in the data storage unit of the developing unit 4 (S402). Next, the CPU 51 drives the transport screw to start stirring the developer inside the developing unit 4 (S403).

[0130] The CPU 51 then counts the pulse signals output from the inductance sensor 47 per predetermined time interval and detects the counted value (counts) as the output value of the inductance sensor 47 (S404). The CPU 51 stores the average value of this output value over one cycle of the transport screw in storage (RAM 53) (S405). At the same time, the CPU 51 reads from ROM 52 the correspondence between the output pulse count of the inductance sensor 47 and the toner density, which corresponds to the value corresponding to the permeability of the magnet sheet 32 ​​and the output value of the inductance sensor 47 during the initial correction operation (S406). After that, the CPU 51 terminates the correction operation (S407).

[0131] Table 5 shows an example of the correspondence between the output pulse count of the inductance sensor 47 and the toner density, corresponding to the values ​​for the magnetic permeability of the magnet sheet and the output values ​​of the inductance sensor 47 during the initial correction operation.

[0132] (Table 5) TIFF0007919978000005.tif75154

[0133] From this point forward, the correspondence between the output pulse count of the inductance sensor 47 and the toner concentration is calculated using the correspondence read from the ROM 52. That is, the CPU 51 detects the toner concentration of the developer in the developing container using the fluctuating value read from the ROM 52. Here, the fluctuating value read from the ROM 52 is the T / D ratio sensitivity shown in Table 5, which corresponds to the permeability of the magnetic sheet (IC tag stored value) and the output value of the inductance sensor 47 during the initial correction operation.

[0134] According to this embodiment, even when the inductance sensor 47 is located in the image forming apparatus 10, it becomes possible to calculate the toner density with higher accuracy.

[0135] Table 6 shows the difference in predicted toner concentration of the developer with and without the correction described in this embodiment, when a developer of a known toner concentration is placed in a developing container. In Table 6, the known toner concentration of the developer is 9%. In Table 6, "with correction" is the toner concentration prediction result when the correction operation shown in Figure 18 is performed, and "without correction" is the toner concentration prediction result when the correction operation is not performed.

[0136] (Table 6) TIFF0007919978000006.tif42150

[0137] It can be seen that the accuracy of predicting the developer toner concentration is improved by performing the correction operation in this embodiment.

[0138] As described above, according to this embodiment, the CPU 51 reads out the variation values ​​corresponding to the difference in the permeability of the magnet sheet 32, which correspond to the value corresponding to the permeability of the magnet sheet 32 ​​and the output value of the inductance sensor 47 during the initial correction operation, from the correspondence relationship (Table 5) stored in the ROM 52. The CPU 51 then uses these read-out variation values ​​to detect the toner concentration in the developer. This makes it possible to suppress a decrease in the detection accuracy of the toner concentration in the developer. In particular, even when the inductance sensor 47 is located in the image forming apparatus 10, the detection accuracy of the toner concentration in the developer can be improved.

[0139] In the above-described 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. [Explanation of symbols]

[0140] t...developer t1…High density part 1Y, 1M, 1C, 1K... Photosensitive drum (image carrier) 4Y, 4M, 4C, 4Y… Developing equipment 31... Ribs 32…Magnetic sheet (magnetic part) 41…Developing sleeve (developer carrier) 42…Magnetic Roll 43…Developing blade 44 ... developing container 44a...Developing chamber (1st chamber) 44b…Stirring chamber (2nd chamber) 44c…bulkhead 45a ... First conveying screw (first conveying member) 45b ... Second conveying screw (second conveying member) 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... feathers 49 ... Rotation axis 51 ...CPU 52...ROM (memory section) 53...RAM 54... Toner supply motor

Claims

1. Image carrier and, A developing apparatus comprising: a developing container for containing a developer containing toner and a carrier; a developer carrier for carrying the developer and supplying it to an image carrier; and a transport member rotatably disposed in the developing container for transporting the developer. An inductance sensor is positioned opposite the transport member, detects the magnetic permeability of the developer, and outputs a signal corresponding to the detected magnetic permeability. A magnet portion is provided on the transport member and positioned opposite the inductor sensor, which carries the developer by magnetic force, A control means for detecting the concentration of toner in the developer from the output value of the inductance sensor, Equipped with, The control means performs a correction operation to correct the fluctuation value per unit toner concentration of the output value of the inductance sensor, when the developing container is filled with developer of a known toner concentration, to a fluctuation value corresponding to the difference in magnetic permeability of the magnet part, and uses the corrected fluctuation value to detect the toner concentration in the developer.

2. The system includes a storage unit that pre-stores the correspondence between the output value of the inductance sensor when the developing container is filled with developer of a known toner concentration and the fluctuation value per unit toner concentration corresponding to the difference in magnetic permeability of the magnet section. The image forming apparatus according to claim 1, characterized in that, during the correction operation, the control means reads out a fluctuation value corresponding to the difference in magnetic permeability of the magnet portion that corresponds to the output value of the inductance sensor from the correspondence relationship stored in the storage unit, and uses the read fluctuation value to detect the toner concentration in the developer.

3. The control means, during the correction operation, determines that the output value of the inductance sensor is If it is the first output value, the first fluctuation value corresponding to the first output value is read from the correspondence stored in the storage unit. If the second output value is lower than the first output value, a second fluctuation value that is greater than the first fluctuation value corresponding to the second output value is read from the correspondence stored in the storage unit. The image forming apparatus according to claim 2, characterized in that, if the third output value is higher than the first output value, a third fluctuation value smaller than the first fluctuation value corresponding to the third output value is read from the correspondence stored in the storage unit.

4. The developing apparatus includes a data storage unit that pre-stores corresponding values ​​corresponding to the magnetic permeability of the magnet section, A storage unit that pre-stores the correspondence between the aforementioned corresponding value and the fluctuation value per unit toner concentration corresponding to the difference in magnetic permeability of the magnet part, Equipped with, The image forming apparatus according to claim 1, characterized in that, during the correction operation, the control means reads a fluctuation value corresponding to the difference in magnetic permeability of the magnet part, which corresponds to the corresponding value read from the data storage unit, from the correspondence relationship stored in the storage unit, and uses the read fluctuation value to detect the toner concentration in the developer.

5. The control means, during the correction operation, reads a corresponding value from the data storage unit that corresponds to the magnetic permeability of the magnet unit. If it is the first corresponding value, the first fluctuation value corresponding to the first corresponding value is read from the correspondence relationship stored in the storage unit. If the second corresponding value is lower than the first corresponding value, a second variation value that is larger than the first variation value corresponding to the second corresponding value is read from the correspondence relationship stored in the storage unit. The image forming apparatus according to claim 4, characterized in that, if the third corresponding value is higher than the first corresponding value, a third fluctuation value smaller than the first fluctuation value corresponding to the third corresponding value is read from the correspondence relationship stored in the storage unit.

6. The image forming apparatus according to claim 1, characterized in that when the magnet portion rotates in synchronization with the rotation of the transport member, the maximum value of the signal output during one rotation of the transport member is used as the signal output from the inductance sensor.

7. The inductance sensor is located in the image forming apparatus. The image forming apparatus according to claim 5, further comprising a pressing mechanism for positioning the inductance sensor at a predetermined location in the developing apparatus after the developing apparatus has been installed in the image forming apparatus.

8. The inductor sensor is, The system 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 transport member is 10% or more of the detection sensitivity at a position in contact with the detection unit. The aforementioned transport member is The axis of rotation and The rotating shaft has blades formed spirally on its outer circumference, A rib is provided at a position opposite the detection portion of the inductance sensor, protruding from the outer circumference of the rotating shaft separately from the vanes, and rotating in synchronization with the rotation of the conveying member, It has, The magnet portion is provided on the rib, The image forming apparatus according to claim 1, characterized in that the region in which the magnet portion carries the developer overlaps with the region in which the inductance sensor has the detection sensitivity when the rib rotates in synchronization with the rotation of the transport member.

9. The inductor sensor is, This is an area on a substrate in which a coil pattern is printed, and it has a detection unit for detecting the magnetic permeability of the developer. The aforementioned transport member is The axis of rotation and The rotating shaft has blades formed spirally on its outer circumference, A rib is provided at a position opposite the detection portion of the inductance sensor, protruding from the outer circumference of the rotating shaft separately from the vanes, and rotating in synchronization with the rotation of the conveying member, It has, The magnet portion is provided on the rib, The image forming apparatus according to claim 1, characterized in that the region on which the magnet portion carries the developer overlaps with the detection region of the inductance sensor when the rib rotates in synchronization with the rotation of the transport member.

10. The image forming apparatus according to claim 9, characterized in that the coil is a wiring pattern formed on the substrate so as not to overlap in the direction from the substrate toward the transport member.

Images