JP2010060707A - Developing device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device capable of precisely measuring a toner concentration and replenishing a suitable amount of toner even when the fluidity of a two-component developer is drastically deteriorated, and to provide an image forming apparatus with the developing device. <P>SOLUTION: In order to eliminate a void generated in the two-component developer and block the degradation of the fluidity of the two-component developer, a supersonic vibration element 39 applies supersonic vibrations to the two-component developer when measuring the toner concentration with a magnetic permeability sensor 38. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image using a two-component developer containing toner and a magnetic carrier, and more particularly to an image forming apparatus that can accurately measure toner density.

2. Description of the Related Art Conventionally, electrophotographic image forming apparatuses are often used as image forming apparatuses such as copying machines and printers.
An electrophotographic image forming apparatus forms an electrostatic latent image on the surface of a photoreceptor (toner image carrier). Then, the electrostatic latent image is developed with toner supplied from a developing device, and the developed toner image is transferred and fixed on a sheet such as paper.

  In recent years, a two-component developer having excellent toner charging stability has been used as a developer for the purpose of achieving color and high image quality. The two-component developer is composed of toner and a carrier, and the toner and the carrier are rubbed by stirring them in the developing device, and a properly charged toner is obtained by the friction.

In such a two-component developer, when the toner is consumed, the toner concentration in the two-component developer is reduced and the image density is lowered. Therefore, the toner concentration is kept constant by replenishing the consumed toner. Control to keep on.
As a toner density control method, for example, there is a method in which the permeability of a two-component developer that changes in accordance with the toner density is measured by a permeability sensor (toner density sensor) and toner is supplied so that the value becomes constant. .

  However, when the fluidity of the two-component developer changes, the measured value of the magnetic permeability sensor fluctuates, so that there is a problem that the toner density cannot be accurately controlled.

  Accordingly, a method for solving the above-mentioned problem by obtaining the sharpness of resonance vibration in the piezoelectric vibrator as a measure of the fluidity of the two-component developer and correcting the measured value of the magnetic permeability sensor based on the sharpness. Has been proposed (see Patent Document 1).

In recent years, there has been a demand for speeding up and downsizing of an image forming apparatus, and it is necessary to quickly and sufficiently charge the two-component developer and to carry the two-component developer quickly.
Therefore, two two-component developer transport paths that form a path through which the two-component developer is circulated and two two-component developer transports that transport the two-component developer while stirring in the two-component developer transport path. A circulation type developing device including a member is mounted on the image forming apparatus (see Patent Document 2).
JP 2006-220909 A JP-A-10-63081

  The circulation type developing device has an advantage that the developing device can be downsized, but there is a limit to a space for measuring the toner concentration with a magnetic permeability sensor, and the fluidity of the two-component developer is kept constant while keeping the fluidity constant. It is difficult to measure magnetic susceptibility.

  In particular, when using a two-component developer composed of a toner having a small particle size and a carrier having a small particle size and printing a large number of images with a small printing rate, the fluidity improver added to the toner surface is a toner resin. The fluidity of the two-component developer is extremely lowered (debemoco phenomenon).

  However, in the method disclosed in Patent Document 1, when the fluidity of the two-component developer is extremely lowered as described above, the two-component developer flowing on the surface of the magnetic permeability sensor, that is, the two-component development to be measured. The agent flow becomes irregular.

As a result, a cavity is generated inside the two-component developer, and the permeability of the two-component developer is measured low.
Therefore, there is a problem that the toner concentration of the two-component developer is measured lower than the actual value, and toner that greatly exceeds the appropriate value of the toner concentration is supplied.

  The present invention has been made in view of such a situation, and even when the fluidity of a two-component developer becomes extremely low, development capable of accurately measuring the toner concentration and supplying an appropriate amount of toner. It is an object of the present invention to provide an apparatus and an image forming apparatus including the developing device.

  A first technical means is a developing device that stores a two-component developer containing toner and a magnetic carrier in a developing tank and supplies the two-component developer to a photoreceptor on which an electrostatic latent image is formed. A magnetic permeability sensor that measures the toner concentration of the two-component developer in the developing tank, and an ultrasonic vibration element that vibrates the two-component developer when the toner concentration is measured by the magnetic permeability sensor. Is a developing device.

  According to a second technical means, in the first technical means, the inside of the developing tank is partitioned by a partition wall, and first and second transport paths communicating at both ends of the partition wall are formed. First and second transport members whose transport directions are opposite to each other are provided inside the second transport path, and the first and second transport members include toner supplied from the upstream side of the first transport path, and The two-component developer in the first and second conveyance paths is circulated and conveyed while stirring, and the two-component developer is supplied to the photoconductor from the second conveyance path, and the magnetic permeability sensor and the ultrasonic vibration element Is arranged in the second transport path.

  According to a third technical means, in the first or second technical means, the magnetic permeability sensor is disposed on a bottom surface of the developing tank vertically below the second conveying member, and the ultrasonic vibration element is the first vibration means. It is arranged on the partition wall on the horizontal side of the two conveying members.

  According to a fourth technical means, in any one of the first to third technical means, the width of the vibration surface in contact with the two-component developer in the ultrasonic vibration element is equal to the two-component developer in the magnetic permeability sensor. It is characterized by being 3 times or less the width of the sensor surface in contact.

  According to a fifth technical means, in any one of the first to fourth technical means, an output of the ultrasonic vibration element is 5 W or more and 30 W or less.

  According to a sixth technical means, in any one of the first to fifth technical means, a vibration frequency by the ultrasonic vibration element is 20 KHz or more and 500 KHz or less.

  A seventh technical means is any one of the first to sixth technical means, wherein the ultrasonic vibration element is disposed upstream of the magnetic permeability sensor in the direction in which the two-component developer is conveyed. It is characterized by being.

  An eighth technical means is any one of the first to seventh technical means, wherein the magnetic permeability sensor is disposed on the most downstream side in the direction in which the two-component developer is conveyed. And

  A ninth technical means is an image forming apparatus comprising the developing device of any one of the first to eighth technical means.

According to the present invention, even when the fluidity of the two-component developer becomes extremely low, the fluidity is increased by causing the micro-vibration of the two-component developer by the ultrasonic vibration generated from the ultrasonic vibration element. Cavity of the component developer is suppressed.
As a result, the bulk density of the two-component developer on the surface of the magnetic permeability sensor is stabilized and the toner density can be measured with high accuracy, so that the toner density control is stable and a print image free from fogging can be obtained.

First, an image forming apparatus provided with a developing device according to the present invention will be described.
FIG. 1 is a schematic diagram showing an internal configuration of the image forming apparatus 100. The image forming apparatus 100 is a predetermined sheet (printing paper) according to a print job (image data) output from an information processing apparatus (not shown). A multi-color or single-color image is formed.

  Reference numeral 1 denotes an exposure unit provided in the lower part of the image forming apparatus 100, which scans the charged photosensitive drum 2 with laser light emitted from the LD, thereby electrostatic latent images corresponding to input image data. An image is formed on the photosensitive drum 2.

  A developing device 3 is provided in the vicinity of the photosensitive drum 2 and visualizes the electrostatic latent image formed on the photosensitive drum 2 with K, C, M, and Y toners.

A cleaner unit 4 is provided in the vicinity of the photosensitive drum 2 and removes and collects toner remaining on the surface of the photosensitive drum 2 after development and image transfer.
Reference numeral 5 denotes a charger provided in the vicinity of the photosensitive drum 2, which uniformly charges the surface of the photosensitive drum 2 to a predetermined potential.
Reference numeral 6 denotes a toner container (toner hopper) for storing toner to be supplied to the developing device 3.

  Note that image data handled in the image forming apparatus 100 corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Accordingly, the photosensitive drum 2 (2a, 2b, 2c, 2d), the developing device 3 (3a, 3b, 3c, 3d), the cleaner unit 4 (4a, 4b, 4c, 4d), the charger 5 (5a, 5b, 5c, 5d) and four toner hoppers 6 (6a, 6b, 6c, 6d) are provided to form four types of latent images corresponding to the respective colors. Then, a corresponds to black, b corresponds to cyan, c corresponds to magenta, d corresponds to yellow, and four image stations are configured.

  Reference numeral 7 denotes an intermediate transfer belt unit disposed above the photosensitive drum 2, and an intermediate transfer belt 70, an intermediate transfer belt driving roller 71, an intermediate transfer belt driven roller 72, an intermediate transfer belt tension mechanism 73, and an intermediate transfer belt, which will be described later. It includes a transfer roller 74 (74a, 74b, 74c, 74d) and an intermediate transfer belt cleaning unit 75. The intermediate transfer belt drive roller 71, the intermediate transfer belt driven roller 72, the intermediate transfer belt tension mechanism 73, and the intermediate transfer roller 74 stretch the intermediate transfer belt 70 and rotate it in the direction of arrow B.

  The intermediate transfer belt 70 is provided so as to be in contact with the photosensitive drum 2, and the toner images of the respective colors formed on the photosensitive drum 2 are sequentially superimposed and transferred onto the intermediate transfer belt 70 to thereby transfer the intermediate transfer belt 70. It has a function of forming a color toner image (multicolor toner image) thereon.

  The transfer of the toner image from the photosensitive drum 2 to the intermediate transfer belt 70 is performed by an intermediate transfer roller 74 that is in contact with the back side of the intermediate transfer belt 70. The intermediate transfer roller 74 is rotatably supported by the intermediate transfer roller mounting portion of the intermediate transfer belt tension mechanism 73 of the intermediate transfer belt unit 7, and transfers the toner image on the photosensitive drum 2 onto the intermediate transfer belt 70. A transfer bias for the transfer.

  The toner image thus formed is transferred onto the sheet by the transfer roller 9 disposed at the contact position between the sheet and the intermediate transfer belt 70.

  Further, the toner adhering to the intermediate transfer belt 70 due to contact with the photosensitive drum 2 or the toner remaining on the intermediate transfer belt 70 which is not transferred onto the sheet by the transfer roller 9 is mixed in the next step. As a result, the intermediate transfer belt cleaning unit 75 removes and collects them. The intermediate transfer belt cleaning unit 75 is provided with a cleaning blade as a cleaning member that comes into contact with the intermediate transfer belt 70, for example. The intermediate transfer belt 70 at the portion in contact with the cleaning blade is driven by an intermediate transfer belt driven roller 72 from the back side. It is supported.

  Reference numeral 8 denotes a registration roller that temporarily holds the sheet conveyed by the sheet conveyance path, and has a function of conveying the sheet to the transfer roller 9 at a timing when the leading edge of the toner image on the photosensitive drum 2 and the leading edge of the sheet are aligned. Yes.

  A fixing unit 10 is a heat roller 10b having a function of heat-pressing the sheet together with the pressure roller 10a so that the multicolor toner image transferred to the sheet is melted, mixed, and pressed and thermally fixed to the sheet. The pressure roller 10a and the heat roller 10b rotate with the sheet interposed therebetween.

Reference numeral 11 denotes a paper feed tray that is provided below the exposure unit 1 and stores sheets used for image formation.
S is a substantially vertical sheet conveyance path, and in the vicinity of the sheet conveyance path S, a registration roller 8, a transfer roller 9, a pressure roller 10a, a heat roller 10b, a pickup roller (12-1, 12-2), Conveyance rollers (13-1 to 13-8) and the like are provided. Reference numeral 14 denotes a paper discharge tray that is provided on the upper part of the image forming apparatus 100 and places printed sheets face down.

The pickup roller 12-1 is a pull-in roller that is provided at the end of the paper feed tray 11 and supplies sheets from the paper feed tray 11 to the paper transport path S one by one. The pickup roller 12-2 is a drawing roller that supplies sheets from the manual feed tray 15 to the sheet conveyance path S one by one.
The conveyance rollers 13 are small rollers for promoting and assisting conveyance of the sheet, and a plurality of conveyance rollers 13 are provided along the sheet conveyance path S.

  The sheet on which the multicolor toner image has been fixed is conveyed to the reverse paper discharge path of the paper conveyance path S by the conveyance rollers 13-2 and 13-3, and in a reversed state (the multicolor toner image is placed on the lower side). Toward the paper discharge tray 13.

(Configuration of developing device)
Next, details of the developing device 3 provided in the image forming apparatus 100 will be described.
FIG. 2 is a cross-sectional view of the developing device 3 according to the present embodiment.
The developing device 3 is formed on the surface of the photosensitive drum 2 by supplying a two-component developer (toner) to the surface of the photosensitive drum 2 by a developing roller 31 disposed so as to face the photosensitive drum 2. This is a device for developing (developing) an electrostatic latent image.

The developing roller 31 is a rotating magnet roller that draws and carries the two-component developer in the developing tank 32 on the surface, and supplies the toner contained in the two-component developer carried on the surface to the photosensitive drum 2. Is.
The developing tank 32 contains a two-component developer containing toner and a carrier. The carrier is a magnetic carrier having magnetism.

  A doctor blade 33 is disposed at a position close to the surface of the developing roller 31 and regulates the thickness of the toner layer carried on the developing roller 31.

  Reference numeral 34 denotes a developing tank cover which is attached to the upper side of the developing tank 32 and covers the developing tank 32 and is removable. The developer tank cover 34 is provided with a toner supply port (described later) for supplying unused toner stored in the toner hopper 6 shown in FIG.

  Reference numeral 35 denotes a first conveying member, and 36 denotes a second conveying member, which is a screw auger made of helical conveying blades for stirring and conveying the two-component developer in the developing tank 32. Each conveying member (35, 36) agitates and conveys the two-component developer by rotating the shaft by driving means (not shown) such as a motor.

  The first and second transport members (35, 36) are arranged in parallel so that their peripheral surfaces face each other via a partition wall (partition plate) 37 and their axes are parallel to each other, and are opposite to each other. It is set to rotate in the direction.

  A magnetic permeability sensor 38 measures (detects) the toner concentration of the two-component developer. For example, the magnetic permeability sensor 38 is disposed on the bottom surface of the developing tank 32 below the second conveying member 36 in the vertical (vertical) direction. 32 so as to be exposed inside.

Reference numeral 39 denotes an ultrasonic vibration element that applies ultrasonic vibration to the two-component developer when the toner density is measured by the magnetic permeability sensor 38. For example, the ultrasonic vibration element 39 is disposed on the partition wall 37 on the horizontal side of the second conveying member 36. It is provided so that the vibration surface is exposed inside the developing tank 32.
The ultrasonic vibration is applied to the two-component developer by the operation of the ultrasonic vibration element 39. As a result, it is possible to eliminate voids generated in the two-component developer and prevent the fluidity of the two-component developer from being lowered.

3 is a cross-sectional view taken along the line AA ′ of the developing device 3 shown in FIG. 2, and FIG. 4 is a cross-sectional view taken along the line B-B ′.
The first conveying member 35 conveys the two-component developer in the X direction shown in FIG. 3, and the second conveying member 36 conveys the two-component developer in the Y direction opposite to the X direction.

A partition wall 37 is disposed in the developing tank 32 between the first and second transport members (35, 36).
The partition wall 37 is extended in parallel with each axial direction (each rotational axis direction) of the first and second transport members (35, 36).
The inside of the developing tank 32 is partitioned by a partition wall 37, and first and second transport paths (P, Q) communicating with both ends of the partition wall 37 are formed, and the first and second transport paths (P, Q) are formed. Are provided with a first transport member 35 and a second transport member 36 whose transport directions are opposite to each other.

The partition wall 37 is disposed away from the inner wall surface of the developing tank 32 at both axial ends of the first and second transport members (35, 36). As a result, the developing tank 32 is formed with a communication path that connects the first transport path P and the second transport path Q in the vicinity of both axial ends of the first and second transport members (35, 36). Has been.
In the following description, as shown in FIG. 3, the communication path formed on the X direction side is referred to as a first communication path a, and the communication path formed on the Y direction side is referred to as a second communication path b.

The first and second transport members (35, 36) are rotationally driven by driving means (not shown) such as a motor, and the toner supplied from the upstream side of the first transport path P and the first and second transport paths. The two-component developer in (P, Q) is circulated and conveyed while stirring.
Specifically, the two-component developer is transported in the X direction while being stirred by the first transport member 35 in the first transport path P, and reaches the first communication path a. The two-component developer that has reached the first communication path a passes through the first communication path a and is conveyed to the second conveyance path Q.

  The two-component developer transported to the second transport path Q is transported in the Y direction while being stirred by the second transport member 36 and reaches the second communication path b. The two-component developer that has reached the second communication path b passes through the second communication path b and is conveyed to the first conveyance path P.

That is, the first transport member 35 and the second transport member 36 transport the two-component developer in the opposite directions while stirring.
In this manner, the two-component developer circulates in the developing tank 32 through the first transport path P, the first communication path a, the second transport path Q, and the second communication path b in this order.

  The two-component developer is carried on the surface of the developing roller 31 by the rotation of the developing roller 31 while being transported in the second transport path Q, and the toner in the pumped two-component developer is pumped up. Are supplied to the photosensitive drum 2 and are consumed sequentially.

  In addition, in order to supplement the consumed toner, replenishment toner is replenished from the toner hopper 6 to the first transport path P through the toner replenishment port 34a (see the dotted line). The toner supply port 34a is a region in the first transport path P and is formed at a position closer to the X direction than the second communication path b. Therefore, in the first transport path P, the second communication path b. The toner is replenished downstream of the toner.

  5 and 6 are conceptual diagrams showing a state in which the two-component developer whose fluidity is extremely lowered due to the debemoco phenomenon in the developing device 3 in FIG. 4 is transported by the second transport member 36. Indicates a state in which the ultrasonic vibration element 39 is not in operation, and FIG. 6 shows a state in which the ultrasonic vibration element 39 is in operation.

As shown in FIG. 5, in the state where the ultrasonic vibration element 39 is not in operation, a void is formed inside the two-component developer having lowered fluidity (the bulk density is reduced). Get higher.
However, as shown in FIG. 6, in the state where the ultrasonic vibration element 39 is operating, the fluidity of the peripheral two-component developer is improved by the ultrasonic vibration generated from the ultrasonic vibration element 39. The agent surface D becomes low. As a result, the magnetic permeability sensor 38 can measure a stable toner concentration without being affected by the bulk density of the two-component developer.

FIG. 7 is a functional block diagram of the image forming apparatus 100 according to the present invention.
Reference numeral 101 denotes a network I / F that provides an interface function with respect to the network N and performs data transmission / reception with a PC (not shown) connected to the network N.
An operation panel 102 for operating the image forming apparatus 100 includes a touch panel, a numeric keypad, and the like.

  An image forming unit 103 having an image forming function includes the photosensitive drum 2, the developing device 3 (the magnetic permeability sensor 38, the ultrasonic vibration element 39, and the like), the intermediate transfer belt unit 7, the fixing unit 10, and the like. .

  The magnetic permeability sensor 38 is a type of sensor that receives a control voltage and outputs a measurement result of toner density as an output voltage value. Since the sensitivity in the vicinity of the median value of the output voltage is basically good, a control voltage that can obtain an output voltage in the vicinity is applied. Such a type of magnetic permeability sensor is commercially available, for example, TS-L, TS-A, TS-K (all are trade names, manufactured by TDK Corporation) and the like.

  The ultrasonic vibration element 39 is formed by, for example, sandwiching ceramics (PZT) that is a piezoelectric element between two annular electrodes and bonding them. Such a vibrator is commercially available.

  When an alternating voltage is applied to the ultrasonic vibration element 39, the stretching vibration of the ceramics is excited. The resulting ultrasonic vibration is propagated to the two-component developer. The vibration frequency can be changed by changing the thickness and shape of the ultrasonic vibration element.

  The ultrasonic vibration element 39 is applied with an alternating voltage sufficient to generate ultrasonic vibration that eliminates a cavity in the two-component developer.

At this time, the output of the ultrasonic vibration element 39 is preferably 5 W or more and 30 W or less. If it is less than 5 W, it is difficult to give sufficient vibration, and if it exceeds 30 W, aggregation and deterioration of the developer are easily promoted by heat generation and friction.
The frequency of ultrasonic vibration generated by the ultrasonic vibration element 39 is preferably 20 KHz or more and 500 KHz or less. If it is less than 20 KHz, unpleasant sound is likely to be generated, and if it exceeds 500 KHz, aggregation and deterioration of the developer are easily promoted by heat generated by friction.

Reference numeral 104 denotes a memory for storing various control information, and reference numeral 105 denotes an HDD for recording electronic data transmitted by a PC or the like.
A control unit 106 controls each functional block, and is a control circuit configured by a microcomputer, a microprocessor, or the like that includes a central processing unit (CPU).

Reference numeral 107 denotes a vibration element control unit that controls the voltage value applied to the ultrasonic vibration element 39 and the application timing.
For example, when the printing process starts, the control unit 106 starts driving a motor (not shown) connected to the first and second transport members (35, 36).

At the same time, the magnetic permeability sensor 38 starts measuring the magnetic permeability of the two-component developer. Accordingly, the vibration element control unit 107 starts processing for applying a predetermined AC voltage to the ultrasonic vibration element 39.
When the printing process ends, the control unit 106 ends the printing end process, for example, the motor driving process. At the same time, the vibration element control unit 107 ends the process of applying an AC voltage to the ultrasonic vibration element 39.

(Other)
The width of the vibration surface in contact with the two-component developer in the ultrasonic vibration element 39 is preferably not more than three times the width of the sensor surface in contact with the two-component developer in the magnetic permeability sensor 38.
In this way, since ultrasonic vibration can be exerted only on the two-component developer near the magnetic permeability sensor 38, heat generation and wear due to friction can be minimized, and the toner external additive It is possible to suppress burying and deterioration of the two-component developer.

The magnetic permeability sensor 38 and the ultrasonic vibration element 39 may be disposed in the second conveyance path Q, but the ultrasonic vibration element 39 is in the direction in which the two-component developer is conveyed with respect to the magnetic permeability sensor 38. It is preferable that it is arrange | positioned upstream.
In this way, the two-component developer whose fluidity has been increased by the ultrasonic vibration element 39 moves to the sensor surface of the magnetic permeability sensor 38 as the second conveying member 36 rotates, so that it is super Even if the sonic vibration element 39 is operated, the bulk density of the sensor surface of the magnetic permeability sensor 38 can be stabilized.

Similarly, the magnetic permeability sensor 38 is preferably disposed on the most downstream side in the transport direction of the two-component developer.
By doing so, the toner concentration of the two-component developer immediately after the toner is consumed can be measured, and the toner replenishment amount can be accurately calculated.

1 is a schematic diagram illustrating an internal configuration of an image forming apparatus according to the present invention. It is sectional drawing of a developing device. It is (A-A ') arrow finger sectional drawing of a developing device. It is (BB ') arrow sectional drawing of a developing device. FIG. 9 is a conceptual diagram showing a state in which a two-component developer whose fluidity is extremely lowered is conveyed by a second conveying member in a state where an ultrasonic vibration element is not operated. FIG. 6 is a conceptual diagram illustrating a state in which a two-component developer whose fluidity is extremely lowered is transported by a second transport member in a state where an ultrasonic vibration element is operating. 1 is a functional block diagram of an image forming apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus, 1 ... Exposure unit, 2 ... Photosensitive drum, 3 ... Developing device, 31 ... Developing roller, 32 ... Developing tank, 33 ... Doctor blade, 34 ... Developing tank cover, 34a ... Toner supply port, 35 ... 1st conveyance member, 36 ... 2nd conveyance member, 37 ... Partition wall, 38 ... Magnetic permeability sensor, 39 ... Ultrasonic vibration element, P ... 1st conveyance path, Q ... 2nd conveyance path, a ... 1st series Path: b ... second communication path, 4 ... cleaner unit, 5 ... charger, 6 ... toner hopper, 7 ... intermediate transfer belt unit, 70 ... intermediate transfer belt, 71 ... intermediate transfer belt drive roller, 72 ... intermediate transfer belt Follower roller 73 ... Intermediate transfer belt tension mechanism 74 ... Intermediate transfer roller 75 ... Intermediate transfer belt cleaning unit 8 ... Registration roller 9 ... Transfer roller 10 ... Fixing unit 10a ... Addition Roller, 10b ... Heat roller, 11 ... Paper feed tray, 12 ... Pickup roller, 13 ... Conveyance roller, 14 ... Paper discharge tray, 15 ... Manual feed tray, 101 ... Network I / F, 102 ... Operation panel, 103 ... Image formation 104, memory, 105, HDD, 106, control unit, 107, vibration element control unit.

Claims (9)

In a developing device that stores a two-component developer containing toner and a magnetic carrier in a developing tank and supplies the two-component developer to a photoreceptor on which an electrostatic latent image is formed.
A magnetic permeability sensor for measuring the toner concentration of the two-component developer in the developing tank;
A developing device, comprising: an ultrasonic vibration element that vibrates the two-component developer when the toner concentration is measured by the magnetic permeability sensor. The developing tank is partitioned by a partition wall to form first and second transport paths that communicate with each other at both ends of the partition wall, and the transport directions are opposite to each other inside the first and second transport paths. First and second transport members are provided,
The first and second transport members circulate and transport the toner supplied from the upstream side of the first transport path and the two-component developer in the first and second transport paths while stirring, and the second transport A two-component developer is supplied to the photoconductor from the path,
The developing device according to claim 1, wherein the magnetic permeability sensor and the ultrasonic vibration element are disposed in the second conveyance path.   The magnetic permeability sensor is disposed on the bottom surface of the developing tank vertically below the second conveying member, and the ultrasonic vibration element is disposed on a partition wall on the horizontal side of the second conveying member. The developing device according to claim 1, wherein   The width of the vibration surface in contact with the two-component developer in the ultrasonic vibration element is not more than three times the width of the sensor surface in contact with the two-component developer in the magnetic permeability sensor. The developing device according to claim 3.   The developing device according to claim 1, wherein an output of the ultrasonic vibration element is 5 W or more and 30 W or less.   The developing device according to claim 1, wherein a vibration frequency by the ultrasonic vibration element is 20 KHz or more and 500 KHz or less.   The development according to claim 1, wherein the ultrasonic vibration element is disposed upstream of the magnetic permeability sensor in a direction in which the two-component developer is conveyed. apparatus.   The developing device according to claim 1, wherein the magnetic permeability sensor is disposed on a most downstream side in a direction in which the two-component developer is conveyed.   An image forming apparatus comprising the developing device according to claim 1.

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