JP2024035999A - Image forming device - Google Patents

Abstract

An object of the present invention is to suppress a decrease in detection accuracy of toner concentration in a developer. [Solution] An image carrier, a developer container containing a developer including toner and a carrier, a developer carrier supporting the developer and supplying the developer to the image carrier, and a developer container rotatably disposed in the developer container. , a developing device having a conveying member that conveys the developer, and an inductance sensor that is arranged opposite to the conveying member and detects the magnetic permeability of the developer and outputs a signal according to the detected magnetic permeability. A magnet section provided on the conveyance member at a position facing the inductance sensor and supporting 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. , the control means calculates a variation value per unit toner concentration of the output value from the output value of the inductance sensor in a state in which a developer with a known toner concentration is contained in the developer container, according to a difference in magnetic permeability of the magnet portion. Performs a correction operation to correct the fluctuating value. [Selection diagram] Figure 15

Description

The present invention relates to an image forming apparatus equipped with a developing device that develops an electrostatic latent image formed on an image carrier into a toner image.

The image forming apparatus includes a developing device including a developing sleeve as a rotatable developer carrier that supports a two-component developer containing non-magnetic toner and a magnetic carrier. In a development method using a two-component developer, it is necessary to keep the weight ratio of toner in the developer (hereinafter referred to as toner concentration) stable within a narrow range in order to obtain reproducibility of the image density of the output image. be. In order to maintain the toner concentration of the two-component developer circulating in the developer container within a predetermined range, a sensor is installed on the wall of the developer container to detect the toner concentration, and the amount of replenishment toner is adjusted according to the detection result. techniques are used.

As a sensor for detecting the toner concentration of a developer in a developer container, an inductance sensor whose inductance changes depending on the proportion of magnetic material in the developer is known. In some inductance sensors, a detection part protrudes from a substrate, and the detection part has a configuration in which a coil is wound around an iron core. In addition, there is also a type of inductance sensor in which a coil pattern is printed directly on a substrate (Patent Document 1).

An inductance sensor in which a pattern of coils is 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 that has an iron core.

Furthermore, since an inductance sensor in which a pattern of coils is printed does not have an iron core, magnetic field concentration is less likely to occur, and the detection range of the sensor is wider than that of an inductance sensor having an iron core. The inductance sensor detects the toner concentration in the developer by changing its output depending on 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 needs to be constant.

Japanese Patent Application Publication No. 2016-012078

However, in a configuration using an inductance sensor in which a pattern of coils is printed, the detection range is wide, so it may not be possible to fill the entire detection range with developer. In this case, even if the toner concentration in the developer in the developer container is constant, the output of the sensor may change due to variations in the density of the developer present in the detection range of the sensor. That is, when the amount of developer in the developer container decreases, the density of the developer in the detection range of the inductance sensor changes accordingly, which may reduce the accuracy of detecting the toner concentration in the developer.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to suppress a decrease in the accuracy of detecting the toner concentration in a developer.

A typical configuration of the present invention for achieving the above object includes an image carrier, a developer container containing a developer containing toner and a carrier, and a developer container that supports the developer and supplies it to the image carrier. a developing device including a developer carrier, a conveying member rotatably disposed in the developer container and conveying the developer; and a developing device disposed opposite to the conveying member to detect magnetic permeability of the developer. an inductance sensor that outputs a signal according to the detected magnetic permeability; a magnet section that is provided on the conveying member and is located opposite to the inductance sensor and that supports the developer by magnetic force; control means for detecting the concentration of toner in the developer from the output value of the sensor, the control means detecting the output value of the inductance sensor when the developer container contains the developer with a known toner concentration Then, a correction operation is performed to correct the fluctuation value per unit toner concentration of the output value to a fluctuation value corresponding to the difference in magnetic permeability of the magnet portion, and the corrected fluctuation value is used to adjust the toner concentration in the developer. It is characterized by detecting concentration.

According to the present invention, it is possible to suppress a decrease in the detection accuracy of the toner concentration in the developer.

Schematic diagram of image forming device Cross-sectional view of developing device Diagram showing the developer circulation path Configuration diagram of inductance sensor Diagram showing distance sensitivity of inductance sensor Control block diagram of image forming apparatus Flowchart showing the toner density control process (a) (b) (c) Diagrams showing the configuration of the second conveyance screw around the inductance sensor A diagram showing the configuration of the second conveyance screw around the inductance sensor in a comparative example. Diagram showing changes in the output results of the inductance sensor when the amount of developer changes A diagram showing the results of converting changes in the output results of the inductance sensor into toner concentration when the amount of developer changes. (a) (b) Diagrams showing signal values output from the inductance sensor during approximately one rotation of the screw in a comparative example (a) (b) Diagrams showing signal values output from the inductance sensor during approximately one rotation of the screw in Example 1 Diagram showing the correspondence between the toner concentration of the developer and the fluctuation value of the signal value output from the inductance sensor Flowchart showing correction control for suppressing the influence of magnetic permeability of the magnet sheet in Example 1 Flowchart showing correction control for suppressing the influence of magnetic permeability of the magnet sheet in Example 2 A diagram showing the results of converting the change in the output result of the inductance sensor into toner concentration when the amount of developer changes in Example 3. Flowchart for correcting the correspondence between output pulse count and toner density in Embodiment 4

Hereinafter, preferred embodiments of the present invention will be described in detail by way of example with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be changed as appropriate depending on the configuration of the device to which the present invention is applied and various conditions, and the It is not intended to limit the scope of the invention only to these.

[Example 1]
An image forming apparatus according to a first embodiment will be described below with reference to FIGS. 1 to 15.

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

To outline such an image forming process, first, each image forming unit PY, PM, PC, and PK forms a toner image of each color on the photosensitive drums 1Y, 1M, 1C, and 1K, respectively. The toner images of each color thus formed are transferred onto the intermediate transfer belt 62, and then transferred from the intermediate transfer belt 62 to a recording medium. The recording medium onto which the toner image has been transferred is conveyed to a fixing device 7, and the toner image is fixed onto the recording medium. This will be explained in detail below.

Note that the four image forming units PY, PM, PC, and PK included in the image forming apparatus 10 have substantially the same configuration except that the developing colors are different. Therefore, the image forming unit PY will be described as a representative, and the configurations of the other image forming units will be described by replacing the suffix “Y” of the reference numerals attached to the configurations of the image forming unit PY with M, C, and K, respectively. The description will be omitted.

The image forming portion PY is provided with a cylindrical photoreceptor, ie, a photosensitive drum 1Y, as an image carrier. A charging roller 2Y (charging device), a developing device 4Y, a primary transfer roller 61Y, and a cleaning device 8Y are arranged around the photosensitive drum 1Y. An exposure device (laser scanner) 3Y is arranged above the photosensitive drum 1Y in the figure.

Further, an intermediate transfer belt 62 is arranged facing the photosensitive drums 1Y, 1M, 1C, and 1K. The intermediate transfer belt 62 is stretched around a plurality of rollers, and rotates by being driven by a drive roller. A secondary transfer outer roller 64 as a secondary transfer member is disposed at a position facing the secondary transfer inner roller 63 and the intermediate transfer belt 62, and transfers the toner image on the intermediate transfer belt 62 to a recording medium. It constitutes a secondary transfer section T2. A fixing device 7 is arranged downstream of the secondary transfer section T2 in the recording medium conveyance direction.

A process of forming an image using the image forming apparatus 10 configured as described above will be described. 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 is formed on the photosensitive drum 1Y according to the image signal. The electrostatic latent image on the photosensitive drum 1Y is visualized by toner contained in the developing device 4Y, and becomes a visible image.

The toner image formed on the photosensitive drum 1Y is primarily transferred onto the intermediate transfer belt 62 at a primary transfer portion T1Y configured between the primary transfer roller 61Y and the primary transfer roller 61Y disposed with the intermediate transfer belt 62 in between. The toner remaining on the surface of the photosensitive drum 1Y after the primary transfer (transfer residual toner) is removed by the cleaning device 8Y.

Such an operation is also performed sequentially at each of the magenta, cyan, and black image forming sections, and the four color toner images are superimposed on the intermediate transfer belt 62. Thereafter, the recording medium accommodated in the recording medium storage cassette (not shown) is conveyed to the secondary transfer section T2 in accordance with the toner image formation timing, and the four-color toner images on the intermediate transfer belt 62 are transferred to the recording medium. Secondary transfer is performed all at once. Toner remaining on the intermediate transfer belt 62 after the secondary transfer is removed by an intermediate transfer belt cleaner.

Next, the recording medium is conveyed to the fixing device 7. The fixing device 7 heats and pressurizes the toner on the recording medium, melts and mixes the toner, and fixes the toner on the recording medium as a full-color image. After that, the recording medium is ejected out of the machine. This completes a series of image forming processes. Note that it is also possible to form a single-color or multi-color image of a desired color using only a desired image forming section.

(Developing device)
Next, the developing device 4Y will be explained using FIGS. 2 and 3. FIG. 2 is a sectional view of the developing device 4Y. FIG. 3 is a diagram showing a developer circulation path. Note that the same applies to the developing devices 4M, 4C, and 4K. The developing device 4Y includes a developing container 44 containing a two-component developer containing non-magnetic toner and magnetic carrier. The developing container 44 has an opening in the developing area facing the photosensitive drum 1Y, and serves as a developer carrier in which a magnet roll 42 is non-rotatingly disposed so as to be partially exposed through this opening. A developing sleeve 41 is rotatably installed.

In this embodiment, the developing sleeve 41 is made of a non-magnetic material and rotates at a predetermined process speed (peripheral speed) during the developing operation. The magnet roll 42 as a magnetic field generating means has a plurality of magnetic poles along the circumferential direction, and causes the developer to be supported on the surface of the developing sleeve 41 by the generated magnetic field.

The layer thickness of the developer supported on the surface of the developing sleeve 41 is regulated by the developing blade 43 as a regulating member, and a thin layer of the developer is formed on the surface of the developing sleeve 41 . The developing sleeve 41 carries the developer formed in a thin layer and conveys it to the developing area. In the developing area, the developer on the developing sleeve 41 stands up to form magnetic spikes. In this embodiment, the electrostatic latent image on the photosensitive drum 1Y is developed as a toner image by bringing the magnetic tip into contact with the photosensitive drum 1Y and supplying toner as a developer to the photosensitive drum 1Y. The developer after developing the latent image is collected into the developing chamber 44a in the developing container 44 as the developing sleeve 41 rotates.

The inside of the developer container 44 is divided into a developer chamber 44a as a first chamber and a stirring chamber 44b as a second chamber by a partition wall 44c extending in the vertical direction. Communication ports 46a and 46b are formed at both ends of the partition wall 44c in the longitudinal direction (rotation axis direction of the developing sleeve 41), respectively, to communicate the developing chamber 44a and the stirring chamber 44b. The communication port 46a is a first communication portion that allows the developer to move from the development chamber 44a to the stirring chamber 44b. The communication port 46b is a second communication portion that allows the developer to move from the stirring chamber 44b to the developing chamber 44a. Thereby, the developing chamber 44a and the stirring chamber 44b form a developer circulation path. The arrows shown in FIG. 3 indicate the direction of developer circulation.

Further, inside the developer container 44, a first conveyance screw 45a as a first conveyance member and a second conveyance screw 45b as a second conveyance member are arranged, respectively, for stirring and conveying the developer. The first conveying screw 45a is disposed in the developing chamber 44a, and conveys the developer in the developing chamber 44a while stirring it in a first direction from the communication port 46b toward the communication port 46a, and also transfers the developer to the developing sleeve 41. supply the agent. The second transport screw 45b is disposed in the stirring chamber 44b, and transports the developer in the stirring chamber 44b while stirring it in a second direction from the communication port 46a toward the communication port 46b.

Note that the image forming apparatus is provided with a developer replenishing device (not shown) that accommodates replenishment developer consisting of only toner or toner and magnetic carrier. A supply screw is installed in the developer replenishment device, so that the amount of replenishment developer used for image formation can be supplied from the developer replenishment device to the stirring chamber 44b in the developer container 44. The replenishment amount of developer is adjusted by the control means (CPU 51 shown in FIG. 6) controlling the number of rotations of the supply screw through a drive motor (toner replenishment motor 54 shown in FIG. 6) that drives the supply screw. .

The developing device 4Y has a concentration detecting means (toner concentration detecting section) capable of detecting the toner concentration in the developing container 44 (ratio of toner particle weight 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 section. The inductance sensor 47 is provided in the stirring chamber 44b and detects magnetic permeability in a predetermined detection range from the sensor surface 47f (see FIG. 4). When the toner concentration of the developer changes, the magnetic permeability due to the mixing ratio of magnetic carrier and non-magnetic toner also changes, so by detecting the change in magnetic permeability with the inductance sensor 47, the toner concentration can be detected.

(Developer circulation)
Next, the circulation of the developer within the developer container 44 will be explained. The first conveyance screw 45a and the second conveyance screw 45b are arranged substantially parallel to each other along the direction of the rotational axis of the developing sleeve 41. The first conveyance screw 45a and the second conveyance screw 45b convey the developer in mutually opposite directions along the rotational axis direction of the developing sleeve 41. In this way, the developer is circulated within the developer container 44 via the communication ports 46a and 46b by the first conveyance screw 45a and the second conveyance screw 45b.

In other words, due to the conveying force of the first conveying screw 45a and the second conveying screw 45b, the developer in the developing chamber 44a whose toner concentration has decreased due to the toner consumed in the developing process is transferred to the stirring chamber through the communication port 46a. 44b and moves within the stirring chamber 44b.

Here, a replenishment port (not shown) through which developer is supplied from a developer replenishment device is provided upstream of the communication port 46a of the stirring chamber 44b in the developer transport direction of the second transport screw 45b. There is. Therefore, in the stirring chamber 44b, the developer transported from the developing chamber 44a through the communication port 46a and the replenishment developer supplied from the developer replenishing device through the replenishment port are transferred to the second transport screw 45b. The material is transported while being agitated. Then, the developer transported by the second transport screw 45b moves to the developing chamber 44a via the communication port 46b.

In this embodiment, the developer contained in the developer container 44 is a two-component developer in which a negatively charged non-magnetic toner and a magnetic carrier are mixed. Non-magnetic toner is made by encapsulating a coloring agent, a wax component, etc. in a resin such as polyester or styrene, and turning it into powder by pulverization or polymerization. A magnetic carrier is a core made of resin particles kneaded with ferrite particles or magnetic powder, and the surface layer of the core is coated with a resin.

(Inductance sensor)
Next, the inductance sensor 47 used in this embodiment will be explained using FIGS. 4 and 5. FIG. 4 is a configuration diagram of an inductance sensor. FIG. 5 is a diagram showing the distance sensitivity of the inductance sensor.

In this embodiment, in order to detect the toner concentration of the developer contained in the developer container 44, an inductance sensor 47 is arranged on the bottom surface of the stirring chamber 44b, facing the second conveying screw 45b. (See Figure 2). The inductance sensor 47 is a magnetic permeability sensor that can output a pulse signal corresponding to the magnetic permeability of the developer as a detection signal by using the inductance of a coil.

As shown in FIG. 4, the inductance sensor 47 has a coil 47a with a pattern printed on a substrate. Further, the inductance sensor 47 includes a coil drive section 47b that electrically drives the coil 47a, an output section 47c that generates an output pulse signal, and a connector 47d.

The inductance sensor 47 has a sensor surface 47f as a detection section that detects the magnetic permeability of the developer. A sensor surface 47f of the inductance sensor 47 is an area (area indicated by a broken line in FIG. 4) in which a pattern of a coil 47a is printed on a substrate 47e. The inductance sensor 47 has a structure that does not include an iron core at the center of the coil 47a.

The 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 conveying screw 45b, and generates an inductance component. The coil drive unit 47b is an LC resonant circuit that is configured of a circuit having a capacitor and resonates due to the inductance of the capacitor and the coil 47a. The output section 47c is a pulse generation circuit having a comparator that converts the analog signal oscillated by the coil drive section 47b into a digital signal. The output unit 47c outputs a binary pulse signal.

Although the coil 47a is illustrated as having a pattern printed on the substrate, the present invention is not limited to this. The coil 47a may have a structure in which wiring is wound vertically on a substrate as long as it does not have an iron core.

The resonance period of the resonance circuit constituted by the coil 47a and the coil drive section 47b varies depending on the density of the magnetic material present in the detection range of the sensor surface 47f. That is, when the toner concentration of the developer in the detection range of the coil 47a is small, the proportion of magnetic carrier contained in the developer per unit volume increases, the apparent magnetic permeability of the developer increases, and the resonance period becomes longer. . Conversely, when the toner concentration of the developer is high, the proportion of magnetic carrier contained in the developer per unit volume is small, the apparent magnetic permeability of the developer is low, and the resonance period is shortened.

Utilizing this property, the toner concentration of the developer in the detection range of the coil 47a is detected by measuring the time required to count a predetermined number of pulses of the pulse signal output from the output section 47c. .

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

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

In this way, the toner concentration in the developer can be detected as the count number (count value) of the output pulse signal using the inductance sensor 47.

Here, the detection range of the sensor surface 47f of the inductance sensor 47 is the area where the coil 47a is pattern-printed on the substrate 47e as shown in FIG. 4, and in the vertical direction from the sensor surface 47f as shown in FIG. This is the area of output sensitivity. In other words, the detection sensitivity of the sensor surface 47f of the inductance sensor 47 at a position 1 [mm] away from the sensor surface 47f in the direction toward the second conveying screw 45b is 10% of that at a position in contact with the sensor surface 47f. The detection sensitivity is as follows.

FIG. 5 shows the static distance characteristics of the inductance sensor. This uses a magnetic plate (not shown) to measure the detection sensitivity of the inductance sensor when the distance of the magnetic plate is changed in the vertical direction from the sensor surface of the inductance sensor. As the magnetic plate, one made of ferrite (relative magnetic permeability of about 200) and having a diameter of 13 [mm] and a thickness of 1.5 [mm] was used. In FIG. 5, static characteristics of the inductance sensor are measured using an inductance sensor 47 according to the present example as well as an inductance sensor having an iron core provided at the center of the coil as a comparative example.

Further, in FIG. 5, the horizontal axis shows the distance [mm] from the sensor surface of the inductance sensor, and the vertical axis shows the output sensitivity (detection sensitivity) of the inductance sensor. The sensitivity shown on the vertical axis in Figure 5 is the ratio of the output at each position where the magnetic plate is separated from the sensor surface (detection (change in sensitivity). Further, the above-mentioned measurement is performed using a magnetic plate with the inductance sensor removed from the developer container and with no developer on the sensor surface of the inductance sensor.

Looking at the measurement results in FIG. 5, the detection sensitivity of the inductance sensor 47 of this example attenuates as the magnetic plate moves away from the sensor surface 47f in the vertical direction; It can be seen that the sensor has sensitivity up to a position (distance) approximately 1 mm] away. On the other hand, regarding the detection sensitivity of the inductance sensor of the comparative example, since the iron core is provided at the center of the coil, the magnetic field used for detecting the magnetic plate is concentrated around the sensor surface compared to the present example. Therefore, the detection sensitivity of the inductance sensor of the comparative example is approximately 0 at a distance of 1 [mm] from the sensor surface.

That is, the inductance sensor of this example has a wider detection range in the vertical direction from the sensor surface than the inductance sensor of the comparative example. In other words, the inductance sensor 47 of this embodiment has a detection sensitivity of 10% or more at a position 1 [mm] away from the surface of the sensor surface 47f in the vertical direction compared to the detection sensitivity at the position of the surface of the sensor surface 47f. have. Here, the reason why the inductance sensor 47 is said to have the above-mentioned detection sensitivity is to exclude the inductance sensor of the comparative example whose detection sensitivity is almost 0 at a position where the distance from the sensor surface 47f is less than 1 [mm]. are doing.

Note that in the inductance sensor of the comparative example, the coil and the iron core protrude from the surface of the substrate in the vertical direction. Therefore, the sensor surface of the inductance sensor of the comparative example is the end surface of the tip of the protrusion.

(Toner concentration control operation of inductance sensor)
Next, toner concentration control operation using the inductance sensor 47 will be explained using FIGS. 6 and 7. FIG. 6 is a control block diagram of the image forming apparatus in this embodiment.

In this embodiment, the CPU 51, which serves as a control means for controlling the image forming operation, detects the toner density based on the output pulse of the 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 concentration is recorded in the ROM 52. Therefore, the CPU 51 detects the toner concentration based on the output pulse signal of the inductance sensor 47 from the above-mentioned correspondence relationship recorded in the ROM 52. The RAM 53 is a system work memory for the CPU 51 to operate. The toner replenishment motor 54 is a motor driven to replenish toner to the developing device 4, and is a drive motor that drives a supply screw disposed in the aforementioned developer replenishment device (not shown).

FIG. 7 is a flowchart showing a toner density control process, and this process is executed by the CPU 51 reading a program recorded in the ROM 52. When the developing operation is started (S101) and stirring of the developer is started (S102), the CPU 51 reads the output value of the inductance sensor 47, and calculates the output value for one cycle of the conveyance screw (one rotation of the conveyance screw). Calculate the average value. 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 and the toner concentration recorded in the ROM 52 (S103), and determines the amount of toner to be replenished. (S104). When the CPU 51 outputs a signal instructing toner replenishment, the toner replenishment motor 54 is driven, and a predetermined amount of toner is replenished from the developer replenishment device (not shown) to the developing device 4 (S105). The CPU 51 performs image formation (S106), and determines whether or not continuous sheet feeding is performed (S107). If YES, the control process of S101 is followed, and if NO, the control ends (S108).

(Configuration of the conveyance screw around the inductance sensor)
Next, the configuration of the conveying screw around the inductance sensor will be explained using FIG. 8. 8(a), FIG. 8(b), and FIG. 8(c) are diagrams showing the configuration of the conveyance screw around the inductance sensor.

FIG. 8(a) shows an enlarged view of the configuration of the second conveying screw 45b around the inductance sensor 47 of this embodiment, viewed from the horizontal direction. Further, FIGS. 8(b) and 8(c) are enlarged views of the configuration of the second conveyance screw 45b around the inductance sensor 47 of this embodiment, as seen from the cross-sectional direction of the developer container 44. .

The first conveyance screw 45a and the second conveyance screw 45b each have a rotating shaft 49 and a blade 48 spirally formed around the outer circumference of the rotating shaft 49. The first conveyance screw 45a and the second conveyance screw 45b both have an outer diameter R3 of 16 [mm] and a pitch P of the blades 48 of 20 [mm]. The shaft diameter R2 of the rotating shaft 49 of the second conveying screw 45b is 6 [mm] (see FIG. 8(a)).

The second conveyance screw 45b has a rib 31 that rotates in synchronization with the rotation of the second conveyance screw 45b. The rib 31 is provided at a position facing the sensor surface 47f of the inductance sensor 47. The rib 31 is provided on the outer periphery of the rotating shaft 49 of the second conveyance screw 45b, in addition to the aforementioned blades 48. The rib 31 is formed to protrude outward from the outer periphery of the rotating shaft 49, and is formed linearly along the axial direction of the rotating shaft 49.

The rib 31 is provided with a magnet sheet 32 serving as a magnet portion that supports developer by magnetic force. The magnet sheet 32 is attached to one side of the rib 31. Here, one surface of the rib 31 to which the magnetic sheet 32 is attached is a surface that pushes the developer in the developer container in the rotational direction when the second conveyance screw 45b rotates. Therefore, the magnet sheet 32 is provided linearly along the axial direction of the rotating shaft 49 together with the rib 31 .

Since the developer t stored in the developer container 44 is a two-component developer in which non-magnetic toner and magnetic carrier are mixed, the magnetic carrier is magnetically restrained by the magnet sheet 32, and as shown in FIG. 8(c). As shown, a high density portion t1 of developer t is formed. The magnet sheet 32 is magnetized in a direction perpendicular to the surface attached to the rib 31.

The magnet sheet 32 is magnetized by mixing ferrite as a magnetic material into chlorinated polyethylene as a binder (resin) and magnetizing the mixture. 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 the above range, the developer can be carried on the surface of the magnet sheet 32 at a high density. Furthermore, the developer on the surface of the magnet sheet 32 can be replaced by the conveyance force of the second conveyance screw 45b, and even when the toner concentration in the developer in the developer container fluctuates, toner concentration fluctuations can be suppressed. becomes detectable. In this embodiment, the magnetic force of the magnet sheet 32 is 40 [mT].

As a comparative example, a configuration in which the magnetic sheet 32 is not attached to the rib 31 of the second conveyance screw 45b is shown. FIG. 9 shows an enlarged view of the configuration of the second conveyance screw 45b around the inductance sensor 47 in a comparative example, as seen from the cross-sectional direction of the developer container 44.

Here, the detection sensitivity of the inductance sensor 47 will be explained using FIG. 10. FIG. 10 shows the results of measuring the output of the inductance sensor 47 while changing the amount of developer in the developer container 44 in each of the configuration of the present example and the configuration of the comparative example. In FIG. 10, the horizontal axis shows the amount of developer [g] in the developer container 44, and the vertical axis shows the output [cnt] of the inductance sensor 47. Note that the toner concentration in the developer at this time is 7%, and the rotation speed of the second conveying screw 45b is 300 rpm. Further, the output of the inductance sensor corresponds to the detection sensitivity of the inductance sensor.

Looking at the results shown in FIG. 10, in both the present example and the comparative example, even though the developer with the same toner concentration was measured, due to the change in the amount of developer in the developer container 44, It can be seen that the output result of the inductance sensor 47 is changing. 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 magnetic permeability decreases, so the resonance period becomes shorter 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 magnetic permeability increases, so the resonance period becomes longer and the output pulse of the inductance sensor increases.

Because of this property, even if the toner concentration does not change, the amount of developer in the developer container 44 changes, and as a result, the density of the developer in the detection range of the inductance sensor 47 changes, and the output pulse of the inductance sensor 47 also changes. It will fluctuate. This phenomenon causes a deviation from the toner density that should originally be detected.

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

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, the density of the output image, and the like. The developing device 4 used in the present example and the comparative example is assumed to have a variation range of developer amount of 120 [g] to 200 [g]. In the configuration of the comparative example, a variation in the amount of developer within the expected usage range causes a detection error of up to 2% in toner concentration. On the other hand, in the configuration of this embodiment, the range of detection error is suppressed to about 0.7%. The difference in output is particularly noticeable when the amount of developer in the developer container is small.

The reason why this effect was obtained will be explained using FIGS. 12 and 13. 12(a) and 12(b) are diagrams showing signal values output from the inductance sensor 47 while the second conveying screw 45b makes about one rotation in the configuration of Comparative Example 1. FIG. 12A shows a case where the amount of developer in the developer container is 120 [g], and FIG. 12B shows a case where the amount of developer in the developer container is 160 [g]. When the amount of developer in the developer container 44 increases, the developer is compressed by its own weight, the density of the developer near the inductance sensor 47 increases, the apparent magnetic permeability increases, and the resonance period becomes longer. The output pulse of the inductance sensor increases. Therefore, compared to FIG. 12(a), in FIG. 12(b), the signal value output from the inductance sensor 47 during approximately one rotation of the second conveying screw 45b is in the rotational phase of the second conveying screw 45b. It's getting bigger regardless.

On the other hand, FIGS. 13(a) and 13(b) are diagrams showing signal values output from the inductance sensor 47 while the second conveyance screw 45b rotates about one rotation in the configuration of this embodiment. FIG. 13A shows a case where the amount of developer in the developer container is 120 [g], and FIG. 13B shows a case where the amount of developer in the developer container is 160 [g]. Looking at FIGS. 13(a) and 13(b), the signal values when the magnetic sheet 32 attached to the rib 31 passes near the inductance sensor 47 are shown in FIGS. 13(a) and 13(b). ) are almost equivalent. This is because the magnetic force of the magnetic sheet 32 attached to the ribs 31 causes the developer to be supported at high density on the surface of the magnetic sheet 32 regardless of the amount of developer in the developer container. Therefore, compared to the configuration of the comparative example, in the configuration of the present example, fluctuations in the output of the inductance sensor 47 due to fluctuations in the amount of developer are suppressed.

As in the present embodiment, by forming a high-density part t1 of the developer t by the magnetic force of the magnet sheet 32 on the opposite part of the sensor surface 47f of the inductance sensor 47, the density of the developer in the detection area of the inductance sensor 47 can be reduced. change 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 due to fluctuations in developer density can be suppressed.

(Correction control according to the difference in magnetic permeability of the magnet sheet 32)
Next, referring to FIGS. 14 and 15, a correction operation will be described in which the fluctuation value per unit toner concentration of the output value (count value) of the inductance sensor 47 is corrected to a fluctuation value corresponding to the difference in magnetic permeability of the magnet sheet 32. explain.

FIG. 14 is a diagram showing the correspondence 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. FIG. 15 is a flowchart showing correction control for suppressing the influence of the magnetic permeability of the magnet sheet 32 in the first embodiment.

As described above, by arranging the magnet sheet 32 on the second conveyance screw 45b facing the inductance sensor 47, it becomes possible to stably detect the toner concentration in the developer. However, on the other hand, the following problems arise.

Since the inductance sensor 47 of 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 than that of a sensor having an iron core. However, since magnetic material is also contained inside the magnet sheet 32 disposed on the second conveyance 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. Furthermore, the amount of magnetic material inside the magnet sheet 32 detected by the inductance sensor 47 may vary due to a misalignment of the attachment position of the magnet sheet 32 or the like. Therefore, the inductance sensor 47 may incorrectly detect the toner concentration even if the developer can be carried on the conveying screw at a constant density.

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 correcting the influence of the magnetic sheet.

Since the magnet sheet 32 is a magnetic material, it has magnetic permeability. Therefore, the signal value output from the inductance sensor 47 also includes the influence of 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 FIG. It is wider than a sensor with an iron core. Therefore, the signal value output from the inductance sensor 47 is easily influenced 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 mixed unevenness during manufacturing.

FIG. 14 illustrates a case where the magnetic permeability of the magnetic sheet 32 is the center value of manufacturing unevenness and a case where the upper limit value is the toner concentration of the developer and the output value (signal value) of the inductance sensor 47. %]. In FIG. 14, the solid line shows the above relationship when the magnetic permeability of the magnet sheet is the center value of the manufacturing unevenness, and the broken line shows the above relationship when the magnetic permeability of the magnet sheet is the upper limit value of the manufacturing unevenness. In FIG. 14, the horizontal axis shows the toner concentration [%] of the developer, and the vertical axis shows the fluctuation value [cnt] of the signal value (output value, count value) output from the inductance sensor 47.

In contrast to the case where the magnetic permeability of the magnet sheet 32 is the center value of the manufacturing unevenness, when the magnetic permeability is the upper limit value of the manufacturing unevenness, the output value of the inductance sensor 47 becomes larger. Therefore, if we use the relationship between the signal variation value [cnt] created with the magnetic permeability as the center value of the manufacturing unevenness and the toner concentration [%], for example, we can use the relationship between the magnetic permeability and the toner concentration [%] to If it is the upper limit of , the toner concentration will be falsely detected as 5.2%.

Therefore, in this embodiment, after the developing device 4 is installed in the image forming apparatus 10, correction is performed to suppress the influence of the magnetic permeability of the magnetic sheet 32. Correction for suppressing the influence of the magnetic permeability of the magnet sheet 32 will be explained using FIG. 15.

For example, by detecting an IC tag or the like placed on the developing device by a detection unit (not shown) placed in the image forming device, a new developing device can be detected when starting up the image forming device for the first time or when replacing the developing device. is installed in the image forming apparatus. Then, the CPU 51 (see FIG. 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 conveying 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 values for one cycle of the conveying screw in the storage (RAM 53) (S204). At the same time, the CPU 51 reads from the ROM 52 the correspondence between the output pulse count of the inductance sensor 47 and the toner concentration, which corresponds to the output value of the inductance sensor 47 (S205). After that, the CPU 51 ends the correction operation (S206).

In other words, during the correction operation, the CPU 51 converts the output value of the inductance sensor 47 into a fluctuation value per unit toner concentration according to the difference in magnetic permeability of the magnet sheet 32 (T/ in Table 1). A correction operation is performed to correct for D ratio sensitivity). Then, the CPU 51 detects the toner concentration in the developer using the corrected fluctuation value.

The correspondence between the output pulse count of the inductance sensor 47 and the toner concentration, which the CPU 51 reads from the ROM 52 during the above-mentioned correction operation, will be explained. The ROM 52, which is a storage unit, stores (memorizes) 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 correction operation output [cnt] is the output value (count value, output pulse count) of the signal output from the inductance sensor 47 during the correction operation shown in FIG. 14 per predetermined time. Further, in Table 2, each output value is shown in a range such as 117,500 to 122,500. In Table 2, the T/D specific sensitivity [cnt/1%] is the fluctuation value (signal fluctuation value) per unit toner concentration (toner concentration 1%) according to the difference in magnetic permeability of the magnet sheet 32, and is shown in FIG. This corresponds to the slope of the solid line or broken line shown in . In addition, each numerical value shown in Table 1 is an illustration, Comprising: It is not limited to this, Comprising: It should be set suitably.

(Table 1)

In the case of this embodiment, 120 g of developer with a toner concentration of 9% is stored in the new developing device. That is, at the time of the above-mentioned correction operation, a developer having a known toner concentration is contained in the developing container of the new developing device. When the CPU 51 detects the output value from the inductance sensor 47 in this state, the difference in the output value of the inductance sensor 47 is due to the difference in magnetic permeability of the magnet sheet 32, since the toner concentration and developer amount in the developing device are known. It becomes an influence. Therefore, it is possible to predict the difference in magnetic permeability of the magnet sheet 32 from the output value of the inductance sensor 47 during the above-described correction operation. When the magnetic permeability of the magnet sheet 32 differs, the relationship between the output value (signal fluctuation value) of the inductance sensor 47 and the toner concentration of the developer differs as shown in FIG. In other words, the relationship indicated by the solid line and the relationship indicated by the broken line shown in FIG. 14 have different slopes. Therefore, by correcting the variation value per unit toner concentration of the output value from the output value of the inductance sensor 47 during the correction operation to a variation value corresponding to the difference in magnetic permeability of the magnet sheet 32, the developer It becomes possible to improve the prediction accuracy of toner concentration.

Table 2 shows the difference in the toner concentration prediction results of the developer depending on whether or not the correction is performed in this embodiment when a developer with a known toner concentration is stored in the developer container. In Table 2, the known toner concentration of the developer is 9%. In Table 2, with correction is the toner density prediction result when the correction operation shown in FIG. 14 is performed, and without correction is the toner density prediction result when the correction operation is not performed.

(Table 2)

For example, when the magnetic permeability of the magnet sheet 32 is a central value, the output value (output pulse count) of the inductance sensor 47 during the correction operation is 120,000 [cnt]. Then, from Table 1, the relationship between the output pulse count and the toner concentration is 1050 [cnt] = 1 [%]. That is, when the output value is 120000 [cnt], the T/D ratio sensitivity corresponding to the first range including the output value is 1050 [cnt/%].

In other words, when the output value of the inductance sensor 47 is the first output value during the correction operation, the CPU 51 selects the first fluctuation value corresponding to the first output value from the correspondence relationship (table 1) stored in the ROM 52. Read from 1). That is, when the output value of the inductance sensor 47 is 120,000 [cnt] during the correction operation, the CPU 51 calculates the first fluctuation value of 1,050 [cnt/%] corresponding to the first range including 120,000 [cnt]. ] is read from the ROM 52.

Image formation is performed using the developing device in which this magnetic sheet 32 is installed, toner is consumed, the toner concentration of the developer in the developer container changes from 9 [%] to 5 [%], and the output pulse count decreases. Suppose that it changes to 124,300 [cnt]. Then, the changed toner concentration is (124300-120000)÷1050=4.1 [%], so the toner concentration in the developer container is predicted to be 4.9 [%].

Next, when the magnetic permeability of the magnet sheet 32 is lower than the center value, a similar prediction is performed. At this time, it is assumed that the output pulse count of the inductance sensor 47 during the correction operation is 116,500 [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 the output value is 1125 [cnt/%].

In other words, when the output value of the inductance sensor 47 is a second output value lower than the first output value during the correction operation, the CPU 51 corresponds to a second range including the second output value. A second variation value larger than the first variation value is read from the correspondence relationship (Table 1) stored in the ROM 52. That is, during the correction operation, when the output value of the inductance sensor 47 is 116,500 [cnt], the CPU 51 calculates a second fluctuation value of 1125 [cnt/ %] is read from the ROM 52.

When a developer with a toner concentration of 5% is measured under the condition that the magnetic permeability of the magnetic sheet 32 is lower than the above-mentioned center value, the output value of the inductance sensor 47 is 121100 [cnt]. Assuming that this output value is the same as when the magnetic permeability of the magnetic sheet 32 is the center value, the toner concentration is predicted using the first fluctuation value of 1050 [cnt/%]. That is, the toner density is predicted without correction. Then, the changed toner concentration is (121110-116500) ÷ 1050 = 4.4 [%], so the toner concentration in the developer container is 4.6 [%], which is equal to the actual toner concentration 5 [%]. This results in an error of 0.4%.

On the other hand, a second variation value of 1125 [cnt/%] corresponding to the magnetic permeability of the magnet sheet 32 read from Table 1 is used. That is, the toner density is predicted with correction. Then, the changed toner concentration is (121100-116500) ÷ 1125 = 4.1 [%], so the toner concentration in the developer container is 4.9 [%], which is equal to the actual toner concentration 5 [%]. The error can be suppressed to 0.1%.

Next, when the magnetic permeability of the magnet sheet 32 is higher than the center value, similar prediction is performed. At this time, it is assumed that the output pulse count of the inductance sensor 47 during the correction operation is 126,600 [cnt]. Then, from Table 1, the value corresponding to 126600 [cnt] is 975 [cnt]=1 [%]. That is, when the output value is 126,600 [cnt], the T/D ratio sensitivity corresponding to the third range including the output value is 975 [cnt/%].

In other words, when the output value of the inductance sensor 47 is a third output value higher than the first output value during the correction operation, the CPU 51 corresponds to the third range including the third output value. A third variation value smaller than the first variation value is read out from the correspondence relationship (Table 1) stored in the ROM 52. That is, during the correction operation, when the output value of the inductance sensor 47 is 126,600 [cnt], the CPU 51 calculates a third fluctuation value of 975 [cnt/ %] is read from the ROM 52.

When a developer with a toner concentration of 5% is measured under the condition that the magnetic permeability of the magnetic sheet 32 is higher than the above-mentioned center value, the output value of the inductance sensor 47 is 130400 [cnt]. Assuming that this output value is the same as when the magnetic permeability of the magnetic sheet 32 is the center value, the toner concentration is predicted using the first fluctuation value of 1050 [cnt/%]. That is, the toner density is predicted without correction. Then, the changed toner concentration is (130400-126600) ÷ 1050 = 3.6 [%], so the toner concentration in the developer container is 5.4 [%], which is equal to the actual toner concentration 5 [%]. This results in an error of 0.4%.

On the other hand, a third variation value of 975 [cnt/%] corresponding to the magnetic permeability of the magnet sheet 32 read from Table 1 is used. That is, the toner density is predicted with correction. Then, the changed toner concentration is (130400-126600) ÷ 975 = 3.9 [%], so the toner concentration in the developer container is 5.1 [%], which is equal to the actual toner concentration 5 [%]. The error can be suppressed to 0.1%.

It can be seen that by implementing the correction control of this embodiment, the detection accuracy of the toner concentration of the developer is improved.

Thereafter, the correspondence between the output pulse count of the inductance sensor 47 and the toner concentration is determined by using the relationship read in S205 shown in FIG. 14 to detect the toner concentration in the developer. Furthermore, even if the power of the image forming apparatus is once turned off, the output value during the correction operation is read from the storage (RAM 53) when the image forming apparatus is restarted, and the fluctuation value corresponding to the output value is read from the ROM 52 and used. It becomes possible to correct the influence of magnetic permeability.

As described above, according to this embodiment, during the correction operation, the CPU 51 stores in the ROM 52 a variation value corresponding to the difference in magnetic permeability of the magnet sheet 32, which corresponds to the output value of the inductance sensor 47. Read from the correspondence (Table 1). Then, the CPU 51 detects the toner concentration in the developer using the read fluctuation value. Thereby, it is possible to suppress a decrease in the detection accuracy of the toner concentration in the developer. In particular, even when the magnetic sheet 32 is used near the inductance sensor 47, the accuracy of detecting the toner concentration in the developer can be improved by correcting the influence of the magnetic sheet 32.

[Example 2]
An image forming apparatus according to a second embodiment will be described.

The image forming apparatus according to the second embodiment stores a corresponding value corresponding to the magnetic permeability of the magnetic sheet measured in advance at the time of manufacturing or factory shipment in a data storage unit (not shown) such as an IC tag placed in the developing device 4. is characterized in that it is stored in advance. Hereinafter, the features of this embodiment will be explained using FIG. 16. Note that the configurations other than those described below are the same as those of the above-described embodiments, and therefore descriptions thereof will be omitted.

For example, by detecting an IC tag or the like placed on the developing device by a detection unit (not shown) placed in the image forming device, a new developing device is activated when the image forming device is powered on or when the developing device is replaced. Detects that it is installed in the image forming apparatus. Then, the CPU 51 (see FIG. 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 (S301). First, the CPU 51 reads a corresponding value corresponding to the magnetic permeability of the magnetic sheet, which is stored in the data storage section of the developing device 4 and is measured in advance at the time of manufacturing or factory shipment (S302). This corresponding value is obtained, for example, by driving the developer container and recording the value output from the inductance sensor 47 before charging the developer into the developer container. Next, the CPU 51 reads from the ROM 52 the correspondence between the output pulse count of the inductance sensor 47 and the toner concentration, which corresponds to the read corresponding value (S303).

Table 3 shows the corresponding values (values stored in IC tags) corresponding to the magnetic permeability of the magnetic sheet measured at the time of manufacturing, and the fluctuation values per unit toner concentration (toner concentration 1%) according to the difference in magnetic permeability of the magnetic sheet 32. (T/D specific sensitivity).

(Table 3)

Thereafter, the correspondence between the output pulse count of the inductance sensor 47 and the toner concentration is calculated using the relationship read from the ROM 52. Thereafter, the conveying screw is driven to start stirring the developer in the developing device 4 (S304). 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 (S305). The CPU 51 stores the average value of the output values for one cycle of the conveying screw in the storage (RAM 53) (S306). After that, the CPU 51 ends the correction operation (S307).

Table 4 shows the difference in the toner concentration prediction results of the developer depending on whether or not the correction is performed in this embodiment when a developer with a known toner concentration is stored in the developer container. In Table 4, the known toner concentration of the developer is 9%. In Table 4, with correction is the toner density prediction result when the correction operation shown in FIG. 16 is performed, and without correction is the toner density prediction result when the correction operation is not performed.

(Table 4)

For example, when the magnetic permeability of the magnetic sheet 32 is a central value, it is assumed that the corresponding value corresponding to the magnetic permeability of the magnetic sheet 32 read from the data storage section of the developing device 4 and measured at the time of manufacture is 75,000. Then, from Table 3, the relationship between the output pulse count and the toner density is 1050 [cnt] = 1 [%]. That is, when the corresponding value is 75000, the T/D ratio sensitivity corresponding to the first range including the corresponding value is 1050 [cnt/%].

In other words, when the corresponding value corresponding to the magnetic permeability of the magnet sheet 32 read from the data storage section during the correction operation is the first corresponding value, the CPU 51 selects the first corresponding value corresponding to the first corresponding value. The fluctuation value is read from the correspondence relationship (Table 4) stored in the ROM 52. That is, when the corresponding value read from the data storage unit is 75,000 during the correction operation, the CPU 51 reads from the ROM 52 a first fluctuation value of 1,050 [cnt/%] corresponding to a first range including 75,000. read out.

Assume that image formation is performed using a developing device in which this magnetic sheet 32 is installed, toner is consumed, and the toner concentration of the developer in the developer container changes from 9 [%] to 5 [%]. At this time, it is assumed that the output pulse count changes by 4300 [cnt] from the output value of the inductance sensor 47 stored in the storage (RAM 53) during the correction operation (S306 in FIG. 16). Then, the changed toner concentration is 4300÷1050=4.1%, so the toner concentration in the developer container is predicted to be 4.9%.

Next, when the magnetic permeability of the magnet sheet 32 is lower than the center value, a similar prediction is performed. Assume that the corresponding value corresponding to the magnetic permeability of the magnetic sheet 32 measured at the time of manufacture and read from the data storage section of the developing device 4 is 74,200. 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 the corresponding value is 1125 [cnt/%].

When a developer with a toner concentration of 5% is measured under the condition that the magnetic permeability of the magnetic sheet 32 is lower than the above-mentioned center value, the inductance sensor stored in the storage (RAM 53) during the correction operation (S306 in FIG. 16) The output value changed by 4610 [cnt] from the output value of 47. Assuming that this output value is the same as when the magnetic permeability of the magnetic sheet 32 is the center value, the toner concentration is predicted using the first fluctuation value of 1050 [cnt/%]. That is, the toner density is predicted without correction. Then, the changed toner concentration is 4610÷1050=4.4 [%], so the toner concentration in the developer container is 4.6 [%], and the actual toner concentration 5 [%] is 0.4 An error of [%] will occur.

On the other hand, a second variation value of 1125 [cnt/%] corresponding to the magnetic permeability of the magnet sheet 32 read from Table 3 is used. That is, the toner density is predicted with correction. Then, the changed toner concentration is 4610÷1125=4.1 [%], so the toner concentration in the developer container is 4.9 [%], and the error from the actual toner concentration of 5 [%] is reduced to 0. It can be suppressed to .1%.

Next, when the magnetic permeability of the magnet sheet 32 is higher than the center value, similar prediction is performed. Assume that the corresponding value corresponding to the magnetic permeability of the magnetic sheet 32 measured at the time of manufacture and read from the data storage section of the developing device 4 is 76,200. 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 the corresponding value is 975 [cnt/%].

When a developer with a toner concentration of 5% is measured under the condition that the magnetic permeability of the magnetic sheet 32 is higher than the above-mentioned center value, the inductance sensor stored in the storage (RAM 53) during the correction operation (S306 in FIG. 16) The output value changed by 3800 [cnt] from the output value of 47. Assuming that this output value is the same as the center value of the magnetic permeability of the magnetic sheet 32, the toner concentration is predicted using the first fluctuation value of 1050 [cnt/%]. That is, the toner density is predicted without correction. Then, the changed toner concentration is 3800÷1050=3.6%, so the toner concentration in the developer container is 5.4%, and the actual toner concentration of 5% is 0.4%. An error of [%] will occur.

On the other hand, a third variation value of 975 [cnt/%] corresponding to the magnetic permeability of the magnet sheet 32 read from Table 3 is used. That is, the toner density is predicted with correction. Then, the changed toner concentration is 3800÷975=3.9 [%], so the toner concentration in the developer container is 5.1 [%], and the error from the actual toner concentration of 5 [%] is reduced to 0. It can be suppressed to .1%.

It can be seen that by implementing the correction control of this example, the prediction accuracy of the developer toner concentration is improved.

As described above, according to the present embodiment, during the correction operation, the CPU 51 stores in the ROM 52 a variation value according to the difference in magnetic permeability of the magnet sheet 32, which corresponds to the corresponding value read from the data storage section. Read from the stored correspondence (Table 3). Then, the CPU 51 detects the toner concentration in the developer using the read fluctuation value. Thereby, it is possible to suppress a decrease in the detection accuracy of the toner concentration in the developer. In particular, even when the magnetic sheet 32 is used near the inductance sensor 47, the accuracy of detecting the toner concentration in the developer can be improved by correcting the influence of the magnetic sheet 32.

Further, when the configuration of this embodiment is used, the corresponding value corresponding to the magnetic permeability of the magnetic sheet is stored in advance in the data storage section of the developing device 4 at the time of manufacturing or factory shipment. Therefore, there is no need to store the initial value at the time of correction in the storage of the image forming apparatus, and it becomes possible to correct the influence of the magnetic permeability of the magnetic sheet with a simpler configuration.

[Example 3]
An image forming apparatus according to a third embodiment will be described. Note that the configurations other than those described below are the same as those of the above-described embodiments, and therefore descriptions thereof will be omitted.

In the image forming apparatus according to the first embodiment, for the output value of the inductance sensor 47 used to calculate the toner density, a value obtained by averaging the output values for one cycle of the conveyance screw was used. On the other hand, the image forming apparatus according to the third embodiment uses the maximum output value for one period of the conveyance screw as the output value of the inductance sensor 47 used to calculate the toner density.

Specifically, by using the characteristics explained using FIGS. 13(a) and 13(b) in the first embodiment described above, the inductance sensor 47 is Only the output value that gives the highest output is extracted and used as data. In other words, in this embodiment, when the rib 31 provided with the magnet sheet 32 rotates in synchronization with the rotation of the second conveyance screw 45b, the second conveyance screw 45b is output as a signal output from the inductance sensor 47. The maximum value of the signal output from the inductance sensor during one rotation is used as the data. This makes it possible to further reduce false detection of toner concentration.

As mentioned above, when the magnetic sheet 32 attached to the rib 31 passes near the inductance sensor 47, the signal value varies due to the amount of developer being carried at high density on the surface of the magnetic sheet 32 due to the magnetic force. is small. Therefore, fluctuations in the output of the inductance sensor 47 due to fluctuations in the amount of developer can be suppressed more than using a value obtained by averaging the output value over one cycle of the conveying screw.

FIG. 17 shows the amount of developer in the developer container 44 and the toner concentration prediction result by the inductance sensor 47 in the configuration of Example 1 and the configuration of this example. It can be seen from FIG. 17 that, compared to the configuration of Example 1, the dependence of the toner concentration of the developer on the amount of developer is suppressed by the configuration of this example.

[Example 4]
An image forming apparatus according to a fourth embodiment will be described.

In the image forming apparatus according to the fourth embodiment, the inductance sensor 47 is arranged in the image forming apparatus 10. The image forming apparatus 10 also includes a pressing mechanism (not shown) such as a spring that arranges the inductance sensor 47 at a predetermined position of the developing apparatus 4 after the developing apparatus 4 is installed in the image forming apparatus 10.

In this case, the positional relationship between the inductance sensor 47 and the developing device 4 may vary slightly due to misalignment of the installation position, and this variation may cause an error in the correspondence between the output pulse count of the inductance sensor 47 and the toner concentration. There is a possibility of having it.

Therefore, in this embodiment, similarly to the above-mentioned embodiment 2, a data storage unit (not shown) such as an IC tag disposed in the developing device 4 is provided with the magnetic permeability of the magnetic sheet measured in advance at the time of manufacture or factory shipment. Save the corresponding value in advance. Furthermore, in this embodiment, the storage unit of the image forming apparatus 10 stores the value corresponding to the magnetic permeability of the magnetic sheet, the output value of the inductance sensor 47 during the initial correction operation, and the correspondence relationship between the output pulse count and the toner density. It is stored in advance in the ROM 52). The CPU 51 is characterized in that it corrects the correspondence between the output pulse count and the toner concentration from 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. That is, the CPU 51 corrects the variation value corresponding to the difference in the magnetic permeability of the magnet sheet 32 from 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. Hereinafter, the features of this embodiment will be explained using FIG. 18. Note that the configurations other than those described below are the same as those of the above-described embodiments, and therefore descriptions thereof will be omitted.

For example, by detecting an IC tag or the like placed on the developing device by a detection unit (not shown) placed in the image forming device, a new developing device can be detected when starting up the image forming device for the first time or when replacing the developing device. is installed in the image forming apparatus. Then, the CPU 51 (see FIG. 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 magnetic sheet 32 of the newly installed developing device (S401). First, the CPU 51 reads a corresponding value corresponding to the magnetic permeability of the magnetic sheet, which is stored in the data storage section of the developing device 4 and is measured in advance at the time of manufacturing or factory shipment (S402). Next, the CPU 51 drives the conveying screw to start stirring the developer in the developing device 4 (S403).

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 (S404). The CPU 51 stores the average value of the output values for one cycle of the conveying screw in the storage (RAM 53) (S405). At the same time, the CPU 51 reads from the ROM 52 the correspondence between the output pulse count of the inductance sensor 47 and the toner concentration, which corresponds to the value corresponding to the magnetic 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 ends the correction operation (S407).

Table 5 shows an example of the correspondence between the output pulse count of the inductance sensor 47 and the toner concentration, which corresponds to 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.

(Table 5)

Thereafter, 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 uses the fluctuation value read from the ROM 52 to detect the toner concentration of the developer in the developer container. Here, the fluctuation values read from the ROM 52 are the T/D ratio sensitivity shown in Table 5, a value corresponding to the magnetic permeability of the magnet sheet (value stored in the IC tag), and an output value of the inductance sensor 47 during the initial correction operation. The value corresponds to

According to this embodiment, even if the inductance sensor 47 is disposed in the image forming apparatus 10, it is possible to calculate the toner concentration with higher accuracy.

Table 6 shows the difference in the prediction results of the toner concentration of the developer depending on the presence or absence of correction in this embodiment when the developer with a known toner concentration is stored in the developer container. In Table 6, the known toner concentration of the developer is 9%. In Table 6, with correction is the toner density prediction result when the correction operation shown in FIG. 18 is performed, and without correction is the toner density prediction result when the correction operation is not performed.

(Table 6)

It can be seen that by implementing the correction operation of this example, the prediction accuracy of the developer toner concentration is improved.

As described above, according to this embodiment, the CPU 51 determines the difference in the magnetic permeability of the magnetic sheet 32, which corresponds to the value corresponding to the magnetic permeability of the magnetic sheet 32 and the output value of the inductance sensor 47 during the initial correction operation. The corresponding fluctuation value is read out from the correspondence relationship (Table 5) stored in the ROM 52. Then, the CPU 51 detects the toner concentration in the developer using the read fluctuation value. Thereby, it is 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 disposed in the image forming apparatus 10, the accuracy of detecting the toner concentration in the developer can be improved.

In the above-described embodiment, the case where the developer amount density in the detection area of the inductance sensor 47 fluctuates due to fluctuations in the developer amount in the developer container is exemplified. Explained suppression. However, the developer amount density in the detection area of the inductance sensor 47 may vary due to fluctuations in the driving speed of the developing device 4, that is, the driving speed of the first conveyance screw 45a and the second conveyance screw 45b. be. Therefore, according to this embodiment, since the developer amount density in the detection area of the inductance sensor 47 can be stabilized, the effect is exhibited even in an image forming apparatus in which the developing device 4 has a plurality of drive speeds during image formation. do.

t...Developer t1...High density portion 1Y, 1M, 1C, 1K...Photosensitive drum (image carrier)
4Y, 4M, 4C, 4Y...Developing device 31...Rib 32...Magnet sheet (magnet part)
41...Developing sleeve (developer carrier)
42...Magnet roll 43...Developing blade 44...Developing container 44a...Developing chamber (first chamber)
44b... Stirring chamber (second chamber)
44c...Partition wall 45a...First conveyance screw (first conveyance member)
45b...Second conveyance screw (second conveyance member)
45b1...First conveyance part 45b2...Second conveyance part 46a, 46b...Communication port 47...Inductance sensor 47a...Coil 47b...Coil drive part 47d...Connector 47e...Substrate 47f...Sensor surface 48...Blade 49...Rotary shaft 51 ...CPU
52...ROM (storage unit)
53...RAM
54...Toner replenishment motor

Claims (10)

an image carrier;
a developer container that stores a developer including toner and a carrier; a developer carrier that supports the developer and supplies it to the image carrier; and a developer carrier that is rotatably disposed in the developer container and transports the developer. a developing device having a conveyance member that
an inductance sensor that is disposed opposite to the conveyance member, detects magnetic permeability of the developer, and outputs a signal according to the detected magnetic permeability;
a magnet portion that is provided on the conveyance member and is provided at a position facing the inductance sensor, and that supports the developer using 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 calculates a fluctuation value per unit toner concentration of the output value from the output value of the inductance sensor in a state in which a developer with a known toner concentration is stored in the developer container. An image forming apparatus characterized in that a correction operation is performed to correct a variation value according to the difference, and a toner concentration in a developer is detected using the corrected variation value. Preliminarily storing a correspondence relationship between an output value of the inductance sensor in a state where a developer with a known toner concentration is stored in the developer container and a variation value per unit toner concentration depending on a difference in magnetic permeability of the magnet portion. Equipped with a memory section that
The control means reads, during the correction operation, a variation value corresponding to the output value of the inductance sensor according to the difference in magnetic permeability of the magnet part from the correspondence relationship stored in the storage part, and reads the variation value corresponding to the output value of the inductance sensor. 2. The image forming apparatus according to claim 1, wherein the toner concentration in the developer is detected using the variation value. The control means is configured such that during the correction operation, the output value of the inductance sensor is
If it is a first output value, read a first fluctuation value corresponding to the first output value from the correspondence stored in the storage unit,
If the second output value is lower than the first output value, a second fluctuation value larger than the first fluctuation value corresponding to the second output value is stored in the storage unit. Read from the correspondence,
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 stored in the storage unit. The image forming apparatus according to claim 2, wherein the image forming apparatus is read based on a correspondence relationship. a data storage unit provided in the developing device and storing in advance a corresponding value corresponding to the magnetic permeability of the magnet portion;
a storage section that stores in advance a correspondence relationship between the corresponding value and a variation value per unit toner concentration according to a difference in magnetic permeability of the magnet section;
Equipped with
The control means reads, from the correspondence relationship stored in the storage unit, a variation value according to a difference in magnetic permeability of the magnet unit, which corresponds to the corresponding value read out from the data storage unit during the correction operation. 2. The image forming apparatus according to claim 1, wherein the read fluctuation value is used to detect the toner concentration in the developer. The control means is configured such that during the correction operation, a corresponding value corresponding to the magnetic permeability of the magnet section read from the data storage section is
If it is a first corresponding value, read a first variation value corresponding to the first corresponding value from the correspondence stored in the storage unit,
If the second corresponding value is lower than the first corresponding value, a second variation value larger than the first variation value corresponding to the second corresponding value is stored in the storage unit. Read from the correspondence,
If the third corresponding value is higher than the first corresponding value, a third variation value smaller than the first variation value corresponding to the third corresponding value is stored in the storage unit. The image forming apparatus according to claim 4, wherein the image forming apparatus is read based on a correspondence relationship. When the magnet section rotates in synchronization with the rotation of the conveying member, the maximum value of the signal output during one rotation of the conveying member is used as the signal output from the inductance sensor. The image forming apparatus according to claim 1. The inductance sensor is arranged in the image forming apparatus,
The image forming apparatus according to claim 5, further comprising a pressing mechanism that arranges the inductance sensor at a predetermined position of the developing device after the developing device is installed in the image forming device. The inductance sensor is
It has a detection part that detects the magnetic permeability of the developer, and the detection sensitivity at a position 1 [mm] away from the detection part in the direction toward the conveyance member is 10% of that at a position in contact with the detection part. It has a detection sensitivity of
The conveying member is
a rotating shaft;
a spiral blade formed on the outer periphery of the rotating shaft;
a rib provided at a position facing the detection portion of the inductance sensor, protruding from the outer periphery of the rotating shaft separately from the blade, and rotating in synchronization with the rotation of the conveying member;
has
The magnet portion is provided on the rib,
1 . The region in which the magnet portion carries the developer overlaps the region in which the inductance sensor has the detection sensitivity when the rib rotates in synchronization with the rotation of the conveyance member. The image forming apparatus described in . The inductance sensor is
A region where a coil pattern is printed on the substrate, and has a detection section that detects the magnetic permeability of the developer,
The conveying member is
a rotating shaft;
a spiral blade formed on the outer periphery of the rotating shaft;
a rib provided at a position facing the detection portion of the inductance sensor, protruding from the outer periphery of the rotating shaft separately from the blade, and rotating in synchronization with the rotation of the conveying member;
has
The magnet portion is provided on the rib,
1 . The area in which the magnet part carries the developer overlaps the detection area by the detection part of the inductance sensor when the rib rotates in synchronization with the rotation of the conveying member. The image forming apparatus described in . The image forming apparatus according to claim 9, wherein the coil is a wiring pattern formed on the substrate so as not to overlap in a direction from the substrate to the conveying member.

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