Developing device

Abstract

To increase the accuracy of detecting the concentration of toner in developer by preventing a variation in the amount of developer within a detection range of a sensor that detects the concentration of toner in the developer.SOLUTION: A developing device 4 has: an inductance sensor 47 that, when detection sensitivity in a state where a detection surface S is in contact with a magnetic substance is assumed to be 100%, has a detection sensitivity of 10% or more at a position where the detection surface S is separated by 1 mm from the magnetic substance, and has an area with a detection sensitivity of 0.02% or more as a detection area; and a second screw 45b that includes a rotatable shank 45b1, a blade part 45b4 provided spirally around the shank 45b1, and an intrusion part 45b2 provided on the shank 45b1 and intruding into the detection area.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a developing device used in a copying machine or a laser beam printer that utilizes a dry electrophotographic system, and to an image forming apparatus equipped with this developing device. [Background technology]

[0002] Conventionally, a developing device includes a developing sleeve as a rotatable developer carrier that carries a two-component developer containing a non-magnetic toner and a magnetic carrier. In a developing method using a two-component developer, in order to obtain reproducibility of the image density of an output image, it is necessary to stably maintain the weight ratio of the non-magnetic toner in the two-component developer (hereinafter, referred to as "toner concentration") within a narrow range. Conventionally, in such a developing method, in order to maintain the toner concentration of the two-component developer circulating in the developing container within a predetermined range, a sensor for detecting the toner concentration is provided on the wall surface of the developing container, and the amount of developer replenished is adjusted according to the detection result by the sensor.

[0003] 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 magnetic material in the developer is known. Such an inductance sensor detects the toner concentration in the developer based on an output value that changes according to the amount of magnetic material present in the detection range. Therefore, in a developing device using an inductance sensor, the amount of developer present in the detection range needs to be constant, and it is common to adopt a configuration in which the detection range is filled with developer.

[0004] Furthermore, conventional inductance sensors have a configuration in which a coil is wound around an iron core and has a detection part that protrudes from a board, or a configuration in which a coil is pattern-printed directly on a board (for example, Patent Document 1). An inductance sensor in which a coil is pattern-printed directly on a board (hereinafter, referred to as a "pattern coil sensor") does not have an iron core in the detection part, and can be produced relatively inexpensively. Since such a pattern coil sensor does not have an iron core, magnetic field concentration is less likely to occur, and the sensor has a wider detection range than a sensor with an iron core. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-012078 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in a developing device using a conventional pattern coil sensor, the detection range is so wide that it may not be possible to completely cover the entire detection range with developer. In this case, even if the toner concentration in the developer is constant, the amount of developer present in the detection range fluctuates, causing the output of the pattern coil sensor to change, and the detection result of the toner concentration changes, resulting in a problem of reduced detection accuracy of the toner concentration.

[0007] An object of the present invention is to provide a developing device and an image forming apparatus that can improve the detection accuracy of the toner concentration of a developer by suppressing fluctuations in the amount of developer within the detection range of a sensor that detects the toner concentration of the developer. [Means for solving the problem]

[0008] The developing device according to the present invention includes a developer carrier that supplies a developer containing a non-magnetic toner and a magnetic carrier to a development area of ​​an image carrier, a first transport chamber that supplies the developer to the developer carrier, a second transport chamber that forms a circulation path for the developer together with the first transport chamber, a first screw that transports the developer in the first transport chamber, a second screw that transports the developer in the second transport chamber, and a detection surface that faces the second transport chamber, and detects the toner of the developer based on the magnetic permeability of the developer measured via the detection surface. and a toner concentration sensor that detects a toner concentration, wherein the toner concentration sensor has a detection sensitivity of 10% or more at a position 1 mm away from the magnetic body when the detection sensitivity is 100% when the detection surface is in contact with the magnetic body, and the detection area is an area where the detection sensitivity is 0.02% or more, and the second screw has a rotatable shaft portion, a blade portion spirally arranged around the shaft portion, and an intrusion portion that is provided on the shaft portion and intrudes into the detection area. Effect of the Invention

[0009] According to the present invention, the detection accuracy of the toner concentration of the developer can be improved by suppressing the fluctuation of the developer amount within the detection range of the sensor that detects the toner concentration of the developer. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to a first embodiment of the present invention. [Diagram 2] 1 is a schematic side sectional view of a developing device according to a first embodiment of the present invention. [Diagram 3] 1 is a schematic cross-sectional plan view of a developing device according to a first embodiment of the present invention. [Figure 4] 3 is a schematic diagram of an inductance sensor of the developing device according to the first embodiment of the present invention. [Diagram 5] 5 is a diagram showing the relationship between the output sensitivity of the developing device according to the first embodiment of the present invention and the distance from the sensor surface. [Figure 6]1 is a block diagram showing a configuration of a developing device according to a first embodiment of the present invention. [Figure 7] 4 is a flowchart showing the operation of the image forming apparatus according to the first embodiment of the present invention. [Figure 8] 1 is a diagram showing a part of the configuration of a developing device according to a first embodiment of the present invention and a comparative example; [Figure 9] 5 is a diagram showing the relationship between the amount of developer and a toner concentration conversion value in the developing device according to the first embodiment of the present invention. FIG. [Figure 10] 2 is a cross-sectional view of a portion of the configuration of a developing device according to the first embodiment of the present invention and a comparative example. [Figure 11] 5 is a diagram showing the relationship between shaft diameter and toner concentration fluctuation amount in the developing device according to the first embodiment of the present invention. FIG. [Figure 12] 5 is a diagram showing the relationship between intrusion detection sensitivity and toner concentration fluctuation in the developing device according to the first embodiment of the present invention. FIG. [Figure 13] 11 is a diagram showing a part of a configuration of a developing device according to a second embodiment of the present invention. FIG. [Figure 14] 6 is a time chart showing the operation of a developing device according to the second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0012] (Embodiment 1) <Configuration of Image Forming Apparatus> The configuration of an image forming apparatus 100 according to the first embodiment of the present invention will be described in detail with reference to FIG.

[0013] The image forming apparatus 100 employs a so-called tandem system and is provided with drum cartridges (not shown) for forming toner images of four colors, yellow, magenta, cyan, and black.

[0014] Specifically, the image forming apparatus 100 includes photosensitive drums 1A, 1B, 1C, and 1D, chargers 2A, 2B, 2C, and 2D, exposure devices 3A, 3B, 3C, and 3D, and developing devices 4A, 4B, 4C, and 4D. The image forming apparatus 100 also includes a fixing device 7, cleaners 8A, 8B, 8C, and 8D, primary transfer rollers 61A, 61B, 61C, and 61D, an intermediate belt 62, a secondary transfer roller 63, and a secondary outer transfer roller 64.

[0015] A toner image is formed on each of the photosensitive drums 1A, 1B, 1C, and 1D serving as image carriers by rotating them at a predetermined speed.

[0016] The chargers 2A, 2B, 2C, and 2D uniformly charge the photosensitive drums 1A, 1B, 1C, and 1D.

[0017] The exposure devices 3A, 3B, 3C, and 3D expose the surfaces of the charged photosensitive drums 1A, 1B, 1C, and 1D with a laser, thereby forming electrostatic latent images on the photosensitive drums 1A, 1B, 1C, and 1D.

[0018] The developing devices 4A, 4B, 4C, and 4D form toner images on the photosensitive drums 1A, 1B, 1C, and 1D by applying a developer to the electrostatic latent images formed on the photosensitive drums 1A, 1B, 1C, and 1D and developing them. The configurations of the developing devices 4A, 4B, 4C, and 4D will be described in detail later.

[0019] Here, a two-component developer, which is a mixture of a magnetic carrier and a non-magnetic toner, is used as the developer. The developing devices 4A, 4B, 4C, and 4D are supplied with non-magnetic toner. The developing devices 4A, 4B, 4C, and 4D may be configured to supply magnetic carriers together with the non-magnetic toner.

[0020] The fixing device 7 heats and pressurizes the recording medium conveyed from the secondary transfer unit 65 described below, thereby fixing the toner image transferred to the recording medium in the secondary transfer unit 65 to the recording medium. The fixing device 7 conveys the recording medium with the fixed toner image toward a discharge roller (not shown).

[0021] The cleaners 8A, 8B, 8C, and 8D remove residual toner remaining on the photosensitive drums 1A, 1B, 1C, and 1D after transfer onto the intermediate belt 62 by the primary transfer rollers 61A, 61B, 61C, and 61D.

[0022] The primary transfer rollers 61A, 61B, 61C, and 61D transfer the toner images formed on the photosensitive drums 1A, 1B, 1C, and 1D onto the intermediate belt 62.

[0023] A plurality of color toner images are transferred onto the intermediate belt 62 in a superimposed manner by primary transfer rollers 61A, 61B, 61C, and 61D.

[0024] The secondary transfer roller 63 and the outer secondary transfer roller 64 come into contact with each other to form a secondary transfer section 65. The secondary transfer section 65 transfers a four-color toner image onto a recording medium conveyed from a paper feed cassette (not shown), and conveys the recording medium onto which the four-color toner image has been transferred to the fixing device 7.

[0025] <Configuration of the developing device> The configurations of developing devices 4A, 4B, 4C, and 4D according to the first embodiment of the present invention will be described in detail with reference to Figures 2, 3, 6, and 8(a). In Figure 3, the arrows indicate the direction in which the developer is transported. Since the developing devices 4A, 4B, 4C, and 4D each have the same configuration, the developing devices 4A, 4B, 4C, and 4D will be collectively described as the developing device 4.

[0026] The developing device 4 includes a developing sleeve 41, a magnetic field generating section 42, a restricting member 43, a developing container 44, a first screw 45a, a second screw 45b, a first connecting section 46a, and a second connecting section 46b. The developing device 4 also includes an inductance sensor 47, a CPU 51, a ROM 52, a RAM 53, and a toner supply motor 54.

[0027] The developing sleeve 41 as a developer carrier is non-magnetic, contains a magnetic field generating unit 42, and rotates around the outer periphery of the magnetic field generating unit 42. The developing sleeve 41 supplies the developer contained in a developing container 44 to the developing areas of the photosensitive drums 1A, 1B, 1C, and 1D.

[0028] The magnetic field generating section 42 generates a magnetic field to cause the surface of the developing sleeve 41 to carry the developer.

[0029] The regulating member 43 regulates the height of the magnetic brush formed on the developing sleeve 41 .

[0030] The developing container 44 contains a developer, and includes a developing chamber 44a, an agitating chamber 44b, and a partition wall 44c.

[0031] The developing chamber 44a, which serves as a first transport chamber, is provided with a first screw 45a that is rotatable. The developing chamber 44a supplies the developer to the developing sleeve 41.

[0032] A second screw 45b is rotatably provided in the mixing chamber 44b as a second transport chamber. The mixing chamber 44b and the developing chamber 44a form a circulation path for the developer.

[0033] The partition wall 44c extends vertically from the bottom wall of the developing container 44, and divides the developing container 44 into a developing chamber 44a and an agitating chamber 44b.

[0034] The developer contained in the developing container 44 is a two-component developer made of a mixture of negatively charged non-magnetic toner and magnetic carrier. The non-magnetic toner is made of a resin such as polyester or styrene that contains coloring agents and wax components, and is powdered by pulverization or polymerization. The magnetic carrier is made of a core made of resin particles kneaded with ferrite particles and magnetic powder, and has a resin coating on the surface.

[0035] The first screw 45a conveys the developer in the developing chamber 44a while stirring it. The first screw 45a has an outer diameter D1 of 16 mm, for example. The first screw 45a includes a shaft portion 45a1 and a blade portion 45a2.

[0036] The shaft portion 45a1 is rotatably supported by the developing container 44. The shaft portion 45a1 has a shaft diameter d1 of, for example, 6 mm.

[0037] The blade portion 45a2 is provided spirally around the shaft portion 45a1 along the axial direction of the shaft portion 45a1 (the direction perpendicular to the paper surface in FIG. 2 and the left-right direction in FIG. 3) (hereinafter simply referred to as the "axial direction"). The pitch of the blade portion 45a2 is, for example, 20 mm.

[0038] The second screw 45b conveys the developer supplied to the mixing chamber 44b from a toner bottle (not shown) and the developer in the mixing chamber 44b while stirring them, thereby making the toner concentration uniform. The second screw 45b has an outer diameter D2 of 16 mm, for example. The second screw 45b includes a shaft portion 45b1, a blade portion 45b4, and an intrusion portion 45b2.

[0039] The shaft portion 45b1 is rotatably supported by the developing container 44. The shaft portion 45b1 has a shaft diameter d2 of, for example, 6 mm.

[0040] The blade portion 45b4 is provided in a spiral shape along the axial direction around the shaft portion 45b1. The pitch P1 of the blade portion 45b4 is, for example, 20 mm.

[0041] The intrusion portion 45b2 is provided on the shaft portion 45b1 and intrudes into a detection area X (described later) of the inductance sensor 47. The intrusion portion 45b2 has a larger diameter than the shaft portion 45b1, and the volume of the intrusion portion 45b2 in the mixing chamber 44b is larger than that of the shaft portion 45b1. The intrusion portion 45b2 is provided in a range including the detection area X of the inductance sensor 47 along the axial direction, which is the developer transport direction.

[0042] Considering the developer transport force, it is preferable that the axial length L of the intrusion portion 45b2 is about 0.5 to 2.0 times (0.5×P1 to 2×P1) the pitch P1 of the second screw 45b. The axial length L of the intrusion portion 45b2 includes the position of a coil 47a (described later) of the inductance sensor 47 in the axial direction, and is preferably centered on the position of the coil 47a in the axial direction as shown in FIG. 8(a). For example, the intrusion portion 45b2 has an axial diameter d3 of 12 mm and an axial length L of 20 mm.

[0043] The first screw 45a and the second screw 45b transport the developer in opposite directions along the axial direction of the developing sleeve 41. The first screw 45a and the second screw 45b circulate the developer in the developing container 44 via the first connecting portion 46a and the second connecting portion 46b.

[0044] The first communication portion 46a is formed at the left end of the partition wall 44c between the developing chamber 44a and the stirring chamber 44b in FIG. 3, and communicates the developing chamber 44a with the stirring chamber 44b. The first communication portion 46a is an area through which the developer is transferred from the developing chamber 44a to the stirring chamber 44b.

[0045] The second communication portion 46b is formed at the right end of the partition wall 44c between the developing chamber 44a and the stirring chamber 44b in FIG. 3, and communicates the developing chamber 44a with the stirring chamber 44b. The second communication portion 46b is an area that transfers the developer from the stirring chamber 44b to the developing chamber 44a.

[0046] The inductance sensor 47, which serves as a toner concentration sensor, is provided on the bottom surface of the stirring chamber 44b. The inductance sensor 47 has a detection surface S that faces and abuts against the stirring chamber 44b. The inductance sensor 47 is a magnetic permeability sensor that detects the toner concentration of the developer based on the magnetic permeability of the developer measured via the detection surface S. Specifically, the inductance sensor 47 utilizes the inductance of a coil to output a pulse signal corresponding to the magnetic permeability of the developer in the stirring chamber 44b as a detection signal to the CPU 51.

[0047] The contact position of the inductance sensor 47 with respect to the stirring chamber 44b is not limited to the bottom surface of the stirring chamber 44b, but may be slightly above the bottom surface. The configuration of the inductance sensor 47 will be described in detail later.

[0048] The CPU 51 reads out and executes a control program stored in the ROM 52 to control the image forming operation while using the RAM 53. The CPU 51 controls the driving of the toner supply motor 54 based on a detection signal input from the inductance sensor 47 and a table stored in the ROM 52.

[0049] The ROM 52 stores a control program and a table in which the output pulse count value corresponds to the toner concentration.

[0050] The RAM 53 is a system work memory for the CPU 51 to operate.

[0051] The toner supply motor 54 operates under the control of the CPU 51 to supply developer from a toner bottle (not shown) to the mixing chamber 44b. The mixing chamber 44b may be supplied with only non-magnetic toner of the developer, not limited to the case where developer is supplied.

[0052] In the developing device 4 having the above-described configuration, the developer in the developing chamber 44a, in which the non-magnetic toner has been consumed by the developing process and the toner concentration has decreased, moves into the mixing chamber 44b through the first connecting portion 46a by the conveying forces of the first screw 45a and the second screw 45b.

[0053] <Inductance sensor configuration> The configuration of the inductance sensor 47 of the developing device 4 according to the first embodiment of the present invention will be described in detail with reference to FIG.

[0054] The inductance sensor 47 includes a coil 47a, a coil driving section 47b, an output section 47c, a connector 47d, and a substrate 47e.

[0055] The coil 47a is a wiring pattern formed on a substrate 47e.

[0056] The coil driving unit 47b electrically drives the coil 47a based on a control signal input from the connector 47d. The coil driving unit 47b is configured with a circuit having a capacitor, and configures an LC resonant circuit with the coil 47a that resonates due to the inductance of the coil 47a. The LC resonant circuit configured by the coil 47a and the coil driving unit 47b oscillates with a resonance period corresponding to the magnetic permeability of the developer.

[0057] The output unit 47c is a pulse generating circuit having a comparator that converts an analog signal waveform generated when an LC resonant circuit formed by the coil 47a and the coil driving unit 47b oscillates into a digital signal, and outputs a binarized pulse signal, which is a digital signal, to the connector 47d.

[0058] The connector 47d is connected to the CPU 51. The connector 47d outputs a control signal input from the CPU 51 to the coil driving unit 47b, and outputs to the CPU 51 a pulse signal input from the output unit 47c.

[0059] The substrate 47e has the coil 47a, the coil driving section 47b, and the output section 47c formed thereon, and also has a connector 47d mounted thereon.

[0060] The resonance period of the resonance circuit formed by the coil 47a and the coil driving unit 47b varies depending on the density of the magnetic material present in the vicinity of the coil 47a. Specifically, when the toner concentration of the developer in the vicinity of the coil 47a is low, the ratio of magnetic carriers contained in the developer per unit volume becomes large, the apparent magnetic permeability of the developer becomes high, and the resonance period becomes long. On the other hand, when the toner concentration of the developer is high, the ratio of magnetic carriers contained in the developer per unit volume becomes small, the apparent magnetic permeability of the developer becomes low, and the resonance period becomes short.

[0061] Using the above-mentioned characteristics, the CPU 51 measures the time required to count a predetermined number of pulses of the pulse signal output from the output portion 47c, thereby detecting the toner concentration of the developer in the vicinity of the coil 47a.

[0062] For example, when the toner concentration near the coil 47a is 10[%], the resonance period of the resonance circuit formed by the coil 47a and the coil driving unit 47b is 1000[kHz]. In this case, when the number of pulses to be counted is set to 5000 pulses, the time required to count 5000 pulses is 5000[μsec]. In addition, when the clock used to measure the time required for counting is set to 20[MHz], 5000[μsec] measured with the 20[MHz] clock is measured as 100000[cnt]. In this case, the output pulse count value is 100000[cnt].

[0063] Furthermore, when the toner concentration near the coil 47a is 8[%], the resonance period of the resonance circuit formed by the coil 47a and the coil driving unit 47b becomes longer than that when the toner concentration is 10[%], and becomes 990[kHz]. In this case, when the number of pulses to be counted is set to 5000 pulses, the time required to count 5000 pulses is about 5050[μsec]. Furthermore, when the clock used to measure the time required for counting is set to 20[MHz], 5050[μsec] measured with the 20[MHz] clock is measured as 101000[cnt]. In this case, the output pulse count value becomes 101000[cnt].

[0064] <Distance characteristics of inductance sensors> The distance characteristic of the inductance sensor 47 of the developing device 4 according to the first embodiment of the present invention will be described in detail with reference to FIG.

[0065] 5 shows the output sensitivity as a ratio of the output at each position when the distance between the magnetic plate and the detection surface S is changed to the output of the inductance sensor 47 at the position where the detection surface S of the inductance sensor 47 contacts the magnetic plate, which is a magnetic body. The magnetic plate used was made of ferrite (relative magnetic permeability is about 200) with a diameter of 13 [mm] and a thickness of 1.5 [mm]. In addition, FIG. 5 also shows the output sensitivity of an inductance sensor configured with an iron core provided at the center of the detection coil, as a comparison with the inductance sensor 47 of this embodiment, which is a pattern coil sensor.

[0066] 5, the inductance sensor 47 has a certain degree of output sensitivity up to a distance of about 4 to 5 mm, although the output sensitivity attenuates as the distance from the magnetic plate increases. On the other hand, an inductance sensor using an iron core has an iron core at the center of the coil, so the magnetic field used to detect the magnetic plate is concentrated around the coil. For this reason, the output sensitivity of an inductance sensor using an iron core is approximately 0 at a distance of 1 mm from the sensor surface.

[0067] When the detection sensitivity of the inductance sensor 47 is 100% in a state where the sensor is in contact with the magnetic plate (a state where the output sensitivity is 1), it is preferable that the sensor has a detection sensitivity of 10% or more (output sensitivity of 0.1 or more) at a position where the detection surface S is 1 mm away from the magnetic plate. As shown in FIG. 5, the output sensitivity of the inductance sensor 47 is 0.3 at a position where the detection surface S is 1 mm away from the magnetic plate, and the detection sensitivity at this time is 30%. Therefore, the detection sensitivity of the inductance sensor 47 at this time is 10% or more.

[0068] On the other hand, an inductance sensor with an iron core provided at the center of a detector coil has an output sensitivity of approximately 0 at a position 1 mm away from the magnetic plate. Therefore, the detection sensitivity of the inductance sensor with an iron core provided at the center of a detector coil in this case is 0%.

[0069] The inductance sensor 47 has a detection region X where the detection sensitivity is 0.02% (output sensitivity 0.002) or more, and the detection region X is the region where the detection surface S is 6 mm away from the magnetic plate according to FIG.

[0070] <Operation of the image forming device> The operation of image forming apparatus 100 according to the first embodiment of the present invention will be described in detail with reference to FIG.

[0071] The operation shown in FIG. 7 is started by the CPU 51 reading out and executing a control program stored in the ROM 52.

[0072] First, the CPU 51 starts the developing operation, and starts stirring the developer in the developing device 4 by driving the first screw 45a and the second screw 45b of the developing device 4 (S1).

[0073] Next, the CPU 51 reads the output value of the detection signal input from the inductance sensor 47, and calculates an average value of the read output value for one screw cycle as an output pulse count value. Then, the CPU 51 detects the toner concentration associated with the calculated output pulse count value in a table stored in the ROM 52 (S2).

[0074] Next, the CPU 51 determines the amount of toner to be replenished based on the determined toner concentration (S3).

[0075] Next, the CPU 51 outputs a signal to the toner supply motor 54 to instruct the toner supply motor 54 to supply developer, thereby driving the toner supply motor 54 to supply the determined amount of developer from a toner bottle (not shown) to the mixing chamber 44b (S4).

[0076] Next, the CPU 51 performs image formation (S5).

[0077] Next, the CPU 51 determines whether or not the paper is being passed continuously (S6).

[0078] If continuous paper passing is determined (S6: Yes), the CPU 51 returns to the operation of step S1.

[0079] On the other hand, if continuous paper passing is not being performed (S6: No), the CPU 51 stops the operation of the image forming apparatus 100.

[0080] <Operation of the developing device> The operation of the developing device 4 according to the first embodiment of the present invention will be described in detail with reference to FIGS.

[0081] In Figure 8, Figure 8(a) shows a portion of the second screw 45b of the developing device 4 of this embodiment, and Figure 8(b) shows a portion of the screw 145b having a shaft diameter of 6 mm over the entire axial direction, as a comparison with this embodiment.

[0082] In Fig. 10, Fig. 10(a) shows the second screw 45b of the developing device 4 according to this embodiment, and Fig. 10(b) shows the comparative example shown in Fig. 8(b) (hereinafter simply referred to as "comparative example"). In Fig. 10, D represents the developer in the developing container 44, and X represents the detection region of the inductance sensor 47 with a detection sensitivity of 0.02[%] (output sensitivity 0.002) or more.

[0083] 9 shows the results of measuring the output of inductance sensor 47 while changing the amount of developer in developer container 44 in this embodiment and a comparative example. In FIG. 9, the toner concentration in the developer is 8[%], and the rotation speed of second screw 45b is 300[rpm]. In addition, in FIG. 9, the toner concentration conversion value on the vertical axis is a value obtained by converting the output pulse count value into a toner concentration. In FIG. 9, the toner concentration of the developer to be detected is 8[%], so the deviation of the toner concentration conversion value from 8[%] is a detection error caused by a change in the amount of developer (developer density in the detection range).

[0084] 9, it can be seen that, in both the present embodiment and the comparative example, even though the toner concentration does not change, the output result of the inductance sensor 47 changes depending on the amount of developer in the developing container 44. This is because the amount of developer present within the detection range of the inductance sensor 47 fluctuates.

[0085] Specifically, as the amount of developer present within the detection range of inductance sensor 47 decreases, the apparent magnetic permeability decreases, so the resonance period becomes shorter and the output pulse count value decreases. Also, as the amount of developer present within the detection range of inductance sensor 47 increases, the apparent magnetic permeability increases, so the resonance period becomes longer and the output pulse count value increases. Therefore, even if the toner concentration does not change, the amount of developer in the detection range of inductance sensor 47 changes as the amount of developer in developer container 44 changes, and as a result, the output pulse count value also changes. In this case, a deviation from the toner concentration that should be detected occurs.

[0086] The amount of developer contained in the developing container 44 varies depending on the temperature and humidity environment, the density of the image to be output, and the like. In this embodiment and the comparative example, the developer amount is assumed to vary within a range of 120 [g] to 200 [g]. In this case, the toner concentration in the comparative example has a detection error of up to 2 [%] due to the assumed fluctuation in the developer amount. On the other hand, the toner concentration in the embodiment has a detection error of up to 0.5 [%] due to the assumed fluctuation in the developer amount. Such a difference between the detection error in this embodiment and the detection error in the comparative example is particularly noticeable when the developer capacity is small.

[0087] <Detection error of inductance sensor> The detection error of the inductance sensor 47 in the developing device according to the first embodiment of the present invention will be described in detail with reference to FIGS.

[0088] As shown in Fig. 10(a), the second screw 45b of the developing device 4 of this embodiment has an intrusion portion 45b2 intruding into the detection area X of the inductance sensor 47. On the other hand, as shown in Fig. 10(b), the screw 145b of the comparative example has only the shaft portion 145b1 and the blade portion 145b4 and does not have the intrusion portion 45b2, and therefore does not intrude into the detection area X of the inductance sensor 47. As a result, the amount of developer D in the detection area X in the developing device 4 of this embodiment shown in Fig. 10(a) is less than the amount of developer D in the detection area X in the developing device of the comparative example shown in Fig. 10(b).

[0089] Therefore, in the comparative example shown in FIG. 10(b), the screw 145b rotates in the direction of the arrow to scatter the developer D, causing the amount of developer D in the detection area X to fluctuate significantly. On the other hand, in the present embodiment shown in FIG. 10(a), the provision of the intrusion portion 45b2 causes less scatter of developer D by the second screw 45b, and the change in the amount of developer D in the detection area X is small, compared to the comparative example shown in FIG. 10(b). Therefore, the detection accuracy of the inductance sensor 47 in the present embodiment is improved compared to the comparative example shown in FIG. 10(b), because the variation in the output value of the detection signal in the detection area X during the rotation of the second screw 45b is suppressed, and the detection error is reduced.

[0090] Fig. 11 shows the effect on the detection result of the inductance sensor 47 due to differences in the shaft diameter of the shaft portion 45b1 of the second screw 45b in the detection region X. The toner concentration fluctuation amount on the vertical axis of Fig. 11 is the difference between the maximum and minimum values ​​of the toner concentration detected by the inductance sensor 47. Fig. 11 also shows the case where the second screw 45b is rotated at 300 rpm for one minute in the developing container 44 containing 160 g of developer with a toner concentration of 10%.

[0091] As shown in FIG. 11, it can be seen that the larger the shaft diameter, the smaller the toner concentration fluctuation amount and the smaller the detection error.

[0092] <Intrusion detection sensitivity of intrusion part> The intrusion detection sensitivity of the intrusion portion 45b2 of the developing device 4 according to the first embodiment of the present invention will be described in detail with reference to FIG.

[0093] The toner concentration fluctuation amount on the vertical axis of Fig. 12 is the difference between the maximum and minimum values ​​of the toner concentration detected by inductance sensor 47, similar to the toner concentration fluctuation amount on the vertical axis of Fig. 11. The intrusion detection sensitivity on the horizontal axis of Fig. 12 is the sensitivity at which intrusion part 45b2 intrudes in the output sensitivity shown in Fig. 5. Fig. 12 also shows the case where second screw 45b is rotated at 300 rpm for one minute in developing container 44 containing 160 g of developer with a toner concentration of 10%.

[0094] As shown in FIG. 12, if the toner concentration fluctuation amount is 1.00 [% / min] when the intrusion detection sensitivity of the comparative example is 0.000, when the intrusion detection sensitivity of the intrusion section 45b2 is 0.090, the toner concentration fluctuation amount decreases to 0.34 [% / min].

[0095] However, the intrusion detection sensitivity varies depending on the required detection accuracy of the toner concentration. In the developing device 4, the required toner concentration fluctuation amount is within 0.80 [% / min], so it is necessary to intrude the intrusion part 45b2 until the intrusion detection sensitivity is at least 0.030. In other words, the intrusion part 45b2 intrudes into the area where the detection sensitivity is 0.3%.

[0096] In this embodiment, the inductance sensor 47 has a detection sensitivity of 10% or more when the detection surface is 1 mm away from the magnetic body, assuming that the detection sensitivity is 100% when the detection surface is in contact with the magnetic body. The inductance sensor 47 has a detection area where the detection sensitivity is 0.02% or more. The second screw 45b further includes a rotatable shaft portion 45b1, a blade portion spirally provided around the shaft portion 45b1, and an intrusion portion 45b2 that is provided on the shaft portion 45b1 and intrudes into the detection area. This suppresses the fluctuation of the developer amount within the detection range of the inductance sensor 47 that detects the toner concentration of the developer, thereby improving the detection accuracy of the toner concentration of the developer.

[0097] In the present embodiment, the intrusion portion 45b2 is integral with the shaft portion 45b1, but the present invention is not limited to this, and the intrusion portion may be separate from the shaft portion 45b1.

[0098] (Embodiment 2) The configuration of the image forming apparatus according to the second embodiment of the present invention is the same as that of the image forming apparatus 100, and therefore a description thereof will be omitted.

[0099] <Configuration of the developing device> The configuration of developing device 40 according to the second embodiment of the present invention will be described in detail with reference to Fig. 13. In Fig. 13, the same components as those in Fig. 8 and Fig. 10(a) are designated by the same reference numerals, and the description thereof will be omitted. In addition, the configuration of developing device 40 other than the second screw 245b is the same as that of developing device 4, and therefore the description thereof will be omitted.

[0100] 13, FIG. 13(a) shows an enlarged cross section of a portion near the inductance sensor 47 of the developing device 40, and FIG. 13(b) shows an enlarged cross section of the portion near the inductance sensor 47 of the developing device 40.

[0101] The developing device 40 includes a developing sleeve 41, a magnetic field generating section 42, a restricting member 43, a developing container 44, a first screw 45a, a first connecting section 46a, a second connecting section 46b, and an inductance sensor 47. The developing device 40 includes a CPU 51, a ROM 52, a RAM 53, a toner supply motor 54, and a second screw 245b.

[0102] The second screw 245b includes a rotatably supported shaft portion 45b1, a blade portion 45b4 spirally provided around the shaft portion 45b1, and an intrusion portion 45b3 provided on the shaft portion 45b1 and intruding into the detection area of ​​the inductance sensor 47. The second screw 245b conveys the developer supplied to the stirring chamber 44b from a toner bottle (not shown) and the developer in the stirring chamber 44b while stirring them, thereby making the toner concentration uniform. For example, the second screw 245b has an outer diameter D2 of 16 mm and a pitch P1 of the blade portion 45b4 of 20 mm.

[0103] The penetration portion 45b3 occupies a larger volume in the mixing chamber 44b than the shaft portion 45b1 by making a part of the shaft portion 45b1 larger in diameter than the shaft portion 45b1 in the circumferential direction. In consideration of the developer conveying force, it is preferable that the axial length L of the penetration portion 45b3 is about 0.5 to 2.0 times the length P1 of one pitch of the second screw 245b centered on the coil 47a of the inductance sensor 47. The axial length L of the penetration portion 45b3 includes the position of the coil 47a of the inductance sensor 47 in the axial direction, and is preferably centered on the position of the coil 47a in the axial direction as shown in FIG. 13(b). The axial length L of the penetration portion 45b3 is, for example, 20 mm.

[0104] The first screw 45a and the second screw 245b transport the developer in the opposite directions along the axial direction. The first screw 45a and the second screw 245b circulate the developer in the developing container 44 via the first connecting portion 46a and the second connecting portion 46b.

[0105] In the developing device 40 having the above-described configuration, the developer in the developing chamber 44a, whose toner concentration has decreased due to the development process, moves into the mixing chamber 44b through the first connecting portion 46a by the conveying forces of the first screw 45a and the second screw 245b.

[0106] <Operation of the developing device> The operation of the developing device 40 according to the second embodiment of the present invention will be described in detail with reference to FIG.

[0107] At time t1, the developing device 40 is driven. At time t2, the power supply (not shown) of the inductance sensor 47 is turned ON. At time t3, the inductance sensor 47 starts reading the toner concentration. At time t4, the intrusion portion 45b3 moves to the side facing the inductance sensor 47 across the developing container 44 (the lower side in FIG. 13(b)). At time t5, the inductance sensor 47 finishes reading the toner concentration. At time t6, the intrusion portion 45b3 moves to the side not facing the inductance sensor 47 across the developing container 44 (the upper side in FIG. 13(b)). Thereafter, the operation from time t3 to time t6 is repeated for a predetermined time.

[0108] At time t7, the power supply to the inductance sensor 47 is turned off. At time t8, the driving of the developing device 40 is stopped.

[0109] In this way, the inductance sensor 47 detects the toner concentration at the timing when the intrusion portion 45b3 moves to the side opposite the inductance sensor 47 via the developing container 44. This suppresses fluctuations in the amount of developer within the detection range of the inductance sensor 47 at the timing when the toner concentration is detected, thereby improving the detection accuracy of the toner concentration of the developer.

[0110] Furthermore, by providing the intrusion portion 45b3 at a portion of the circumferential direction of the shaft portion 45b1, it is possible to suppress a decrease in the developer transport force.

[0111] In the present embodiment, the intrusion portion 45b3 is integral with the shaft portion 45b1, but the present invention is not limited to this, and the intrusion portion may be separate from the shaft portion 45b1.

[0112] The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0113] 1A Photosensitive drum 1B Photosensitive drum 1C Photosensitive drum 1D photosensitive drum 4. Developing device 40 Developing device 41 Developing sleeve 44 Developer container 44a Developing Room 44b Mixing chamber 44c Bulkhead 45a First screw 45b Second screw 45b1 Shaft 45b2 Intrusion 45b3 Intrusion part 45b4 Wing 47 Inductance Sensor 47a Coil 47b Coil driver 47c Output section 47d Connector 47e Board 51 CPU 54 Toner supply motor 100 Image forming device 245b Second screw

Claims

1. A developer carrier that carries a developer containing toner and carrier for developing an electrostatic latent image formed on an image carrier; a developer container that contains 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; and When the inductance sensor is not attached to the developer container and the predetermined magnetic body is placed at a position where the inductance sensor contacts the detection unit, and the output value when the detection unit detects the magnetic permeability of the predetermined magnetic body is defined as A, and when the inductance sensor is not attached to the developer container and the predetermined magnetic body is placed at a position 1 mm away from the detection unit in a vertical direction passing through the detection unit, and the output value when the detection unit detects the magnetic permeability of the predetermined magnetic body is defined as B, the detection unit has an output sensitivity that satisfies B / A≧0.1, the conveying screw has a first conveying section including a first rotating shaft section and a first blade section that is spirally formed on an outer circumferential surface of the first rotating shaft section and that conveys the developer in a conveying direction of the conveying screw, and a second conveying section that is second rotating shaft section and a second blade section that is spirally formed on an outer circumferential surface of the second rotating shaft section and that conveys the developer in a conveying direction of the conveying screw, the first conveying unit is disposed upstream of a detection region of the detecting unit having the output sensitivity of 0.02 or more in a conveying direction of the conveying screw, the second conveying unit is disposed in a conveying direction of the conveying screw and is disposed opposite the detection area, The shaft diameter of the second rotating shaft portion is larger than the shaft diameter of the first rotating shaft portion. A developing device characterized by:

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

2. The developing device according to claim 1.

3. The inductance sensor further has an output unit that outputs a pulse signal corresponding to the magnetic permeability detected by the detection unit.

2. The developing device according to claim 1.

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

2. The developing device according to claim 1.

Images