JPH08211725A - Developing device - Google Patents

Abstract

PURPOSE: To provide a developing device capable of accurately detecting the concentration of toner in a developer over a long period by keeping the quantity of the developer filled into the developing device to an irreducible minimum. CONSTITUTION: Screws 30 having stirring blades 35 and 37 helically formed around a shaft in its axial direction at almost the same interval are provided in a row so as to make a carrying direction different each other. One of the screws 30 is provided with the stirring blade formed to a shape that a part of the stirring blade in the axial line direction of the screw 30 is made small in a diameter with respect to the other part, to form the heaping of the developer. The sensor surface of a magnetic sensor 38 facing the heaping part, to detect the concn. of the toner in the developer is arranged. The heaping part 40 formed by the stirring of the screws 30 covers the sensor surface of the magnetic sensor 38 and the concn. of the toner in the developer carried while being stirred by the screws 30 is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device in an image forming apparatus such as a copying machine or a printer, and more particularly to a two-component developer composed of a toner and a carrier as a developer for detecting the toner density. The present invention relates to a developing device equipped with a magnetic sensor as a means.

[0002]

2. Description of the Related Art Conventionally, as a means for agitating a two-component developer composed of toner and carrier in a developing device, a substantially constant outer diameter (height) is formed around a shaft extending in one axial direction in a spiral shape along the axial direction. There is known a configuration in which two or more screws each having a stirring blade having a substantially equal interval are provided in parallel so that the conveying directions are different from each other, and the toner and the carrier are circulated uniformly by the rotation of the screws. In addition, the magnetic sensor for detecting the toner concentration is positioned so as to face a part of the screw, and the developer conveyed by the screw is brought into contact with the sensor surface to detect the toner concentration. The device is known. In this developing device, the magnetic sensor detects the amount of toner in the developer consumed as a result of image formation as the toner concentration, and when the toner concentration falls below a predetermined value based on the detection signal obtained by this, it is appropriately Replenishment toner is replenished into the developing device, for example, from a replenishing port provided on the side surface of the device main body toward one end of the above-mentioned screw in the developing device to keep the mixing ratio of the carrier and the toner constant. .

In the developing device having the above-mentioned structure, the magnetic sensor is located on the side surface of the screw, and the magnetic field of the magnetic sensor does not affect the height of the developer surface, that is, the change in the bulk due to the consumption of the developer. A relatively large amount of developer is secured so that the sensor surface is completely buried in the developer. The position where such a sensor is arranged is important. If the magnetic sensor is located below the screw, the weight of the developer (especially the carrier sinks) slows down the movement of the toner and the carrier at that position, resulting in insufficient stirring / Mixing is difficult and it becomes impossible to accurately detect the toner concentration in the developing device. Further, even in the case where the sensor is arranged on the side surface side as described above, the toner is consumed by the image formation, the volume and fluidity of the developer are reduced and the bulkiness is reduced, and the developer is entirely on the sensor surface of the magnetic sensor. If the toner is no longer covered or the amount of developer is reduced to the vicinity of the sensor surface, the magnetic sensor will detect incorrect magnetic permeability due to the change in the amount of developer surrounding the sensor surface, and accurate toner concentration will not be detected. It becomes impossible to detect. As described above, the mounting condition of the sensor surface of the magnetic sensor is restricted, and it is necessary to secure a sufficient amount of the developer to be filled in the developing device so as to always cover the sensor surface.

[Problems to be Solved by the Invention]

In particular, when forming a large size image of A2 or more, for example, at a speed of 100 mm / sec or more, the toner in the developer is quickly consumed, and the replenishment toner of the same amount as this consumption is required at any time. Is replenished in the developing device. In order to efficiently mix the replenished toner with the developer in the developing device, or to prevent the torque of the drive source such as the motor for rotating the screw from being increased more than necessary, downsizing of the device and easy mechanical design In order to improve the property, it is preferable to reduce the filling amount of the developer. Further, in an image forming apparatus that handles transfer materials of different sizes, the amount of developer consumed varies depending on the size, so it is necessary to stir the developer quickly and reliably and to accurately detect the toner concentration.

As described above, on the one hand, in order to improve the detection accuracy of the magnetic sensor as the toner concentration detection, it is necessary to store a large amount of developer in a certain amount or more in the developing device, and on the other hand, In order to achieve quick and reliable stirring and downsizing of the main body of the apparatus, it is necessary to reduce the filling amount of the developer as much as possible. For this reason, it is difficult to set the developer filling amount that satisfies any of the conditions.

On the other hand, in addition to the developing device using the above-mentioned magnetic sensor, for example, as shown in Japanese Patent Laid-Open No. 62-63969, a state where a pulsating flow is reduced by providing a conveyance interruption portion while stirring the developer with a screw. There is disclosed a developing device in which a pressure sensor detects a toner concentration in a developer by forming a swelling portion of the developer and detecting a difference in fluidity due to a change in toner concentration by a level change in the swelling portion. In this case, if the developer amount is sufficiently filled, the pulsating flow at the rising portion can be suppressed and the toner level can be detected to accurately detect the toner concentration. However, when the developer filling amount is reduced, it becomes difficult to suppress the pulsating flow at the rising portion, and it becomes impossible to accurately detect the toner concentration. That is, by reducing the amount of the developer, the pulsating flow of the developer due to the rotation of the screw is further increased, and this pulsating flow adversely affects the stable pulsating flow at the rising portion. In addition, by providing a portion for interrupting the transport of the developer, the developer transporting force is lost at that portion, unnecessary pressure is applied to the developer, the toner is melted on the carrier surface, and the phenomenon that the charging efficiency is reduced occurs. It shortens the life of the agent.

Further, in the method of measuring the change in toner concentration based on the change in the level of the developer as described above, when the main body of the apparatus is erroneously installed, the developing apparatus is also tilted, which causes swelling. The height of the part changes, and there is a deviation from the set value of the replenishment signal for the initial toner replenishment,
There is a problem that normal toner supply cannot be performed. Furthermore, the fluidity of the developer changes due to the influence of impurities such as paper powder generated from the transfer material and talc due to nitrogen oxides generated in the image forming process, and the toner is not accurately used for a long period of time. It becomes difficult to control the concentration.

The present invention has been made in view of the above-mentioned problems, and makes the filling amount of the developer into the developing device the minimum necessary amount, and accurately detects the toner concentration in the developer accurately for a long period of time. An object is to provide a developing device.

[0009]

In order to solve the above problems, the present invention provides a means for agitating a two-component developer consisting of a toner and a carrier, which is agitated around a shaft extending in a uniaxial direction in a spiral shape along the axial direction. At least two screws forming blades are arranged in parallel so as to be adjacent to the developing roller so as to have different conveying directions, and the sensor surface of the magnetic sensor is arranged so as to face a part of the screws. In a developing device configured to detect a toner concentration of a developer conveyed by a screw and replenish toner for replenishment to an end portion side of the screw based on the detection, at least one of the screws is arranged in an axial direction thereof. Part has a shape in which a part of the stirring blade is reduced in diameter with respect to the other part, and the magnetic sensor is located on the side surface side of the reduced diameter part, and the developer is placed in the part. Even for changes in the amount, characterized in that so as to cover the entire area of the sensor surface of the magnetic sensor by the raised part to form a raised part detection sensitivity does not affect the magnetic sensor.

Further, the sensor surface of the magnetic sensor and the reduced diameter portion are provided in substantially the central portion of the screw on the side away from the developing roller, and the ratio of the reduced diameter of the screw is the same as the above. It is characterized by being 0.3 to 0.7 times as large as the diameter of the screw of the part.

[0011]

In this structure, the screws having different conveying directions stir the two-component developer in the developing device so as to circulate the two-component developer. The developer agitated by the screw weakens the conveying force of the screw at a portion of which the diameter is reduced with respect to the other portion in the axial direction of the screw, so that a raised portion is formed. The sensor surface of the magnetic sensor provided on the side surface of the screw is covered by the raised portion so as to have a stable sensitivity. Toner is consumed by known image formation, the toner concentration in the developer is lowered, and the magnetic sensor detects this toner concentration. Replenishment toner is replenished based on this detection signal. The replenished toner is uniformly agitated by the time it reaches the reduced diameter screw portion.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 3 is a side sectional view showing an example of an image forming apparatus in which the developing device according to the present invention is preferably used. The image forming apparatus 1 such as a copying machine and a printer is roughly composed of an image forming section 2, a transfer material conveyance guide means 3, and a fixing device 4.

As is well known, as the image forming section 2, a corona charger 13 for uniformly charging the surface of the photosensitive drum 12 around the photosensitive drum 12 and original data read by a scanner or the like are projected by an LED or the like. The optical projection device 14 that forms a latent image on the photosensitive drum 12, the developing device 5 that develops the latent image, and the toner developed on the transfer material that is sent from the paper feed unit 15 in which roll paper (or cut paper) is loaded. A transfer corona discharger 16 for transferring an image, an AC separation corona discharger 17 for separating the transfer material from the photosensitive drum 12,
The photosensitive drum 12 has a cleaning device 6 for removing the toner remaining on the surface of the photosensitive drum 12 after transfer, and an eraser lamp 18 for uniformly removing the surface potential of the surface of the photosensitive drum 12, which are sequentially arranged. Are arranged to act on.

A toner guide cylinder 7 for guiding the waste toner collected by a cleaning blade or the like to the outside of the apparatus is provided at one end of the cleaning device 6, and the tip of the guide cylinder 7 is a discharge port provided in a waste toner container 8. 9 is connected.

Further, between the vicinity of the separation corona discharger 17 and the fixing device 4, the conveyance guide means 3 for conveying and guiding the transfer material separated from the photosensitive drum 12 by the separation corona discharger 17 to the fixing device 4. A conveyor belt 19 and a guide plate 20 are arranged. A fixing device 4 for fixing the toner image on the transfer material as a permanent image is arranged at the tip of the guide plate 20.

A toner supply port 10 is provided at one end of the developing device 5 in the longitudinal direction (on the side surface in the axial direction of the photosensitive drum), and the supply port 22 of the toner cartridge 21 scatters toner into the device during supply. Guide member 23 to prevent
, And the periphery of the mouth is pressed by the sponge 24 or the like for connection.

FIG. 1 is a side sectional view of the developing device 5 according to the present invention.
Shown in The casing 25 of the developing device 5 has an opening 60 facing a part of the surface of the photoreceptor 12 described above, and a peripheral surface is partially exposed from the opening 60 so as to be developed so as to be close to the photoreceptor 12. A roller 32 is provided. Developing roller 3
Reference numeral 2 denotes a permanent magnet 41 fixedly arranged inside, and a sleeve 42 that rotates the outer circumference of the permanent magnet 41 by an arrow C. The magnetic force of the permanent magnet 41 causes the developer to be attracted to the surface of the sleeve 42 by a magnetic brush 43. To form. The magnetic brush 43 regulates the thickness of the magnetic brush 43 to a constant thickness by the regulation plate 44, and the photosensitive drum 12 on which a latent image is formed.
Contact the surface and develop. The developer remaining on the sleeve surface after development is mixed with the agitated developer in the developing device in a place where the permanent magnet 41 is not affected, and agitated by the screws 30 and 31 described below.

Inside the casing 25 of the developing device 5,
Adjacent to the developing roller 32, at least two screws for stirring the developer, in this example, the screws 30 and 31 are provided in proximity to the inner surface of the casing 25. As shown in the figure, the bottom of the casing 25 is stepped so as to draw a double arc so as to surround a part of the screws 30 and 31.

On the screw 31 located in the vicinity of the developing roller 32, stirring blades 36 are spirally formed around the shaft 34 along the axial direction thereof at substantially equal intervals. The screw 30 on the side remote from the developing roller 32 is the screw 3
The stirring blade 35 is the same as that of No. 1 and the stirring blade 37 is formed at a substantially central portion in the shaft 33 direction so as to have a diameter reduced to form a raised portion 40 described later. A magnetic sensor 38 is provided on the side surface of the developing device 5 so as to face the stirring blade 37 in the reduced diameter portion.
Reference numerals 31 are provided in parallel so that the developer transport directions are different from each other. A partition plate 39 is provided between the screws 30 and 31, and by driving the screws 30 and 31 in the directions of arrows A and B, the developer circulates in the width direction of the screws 30 and 31, and the carrier and toner Are mixed evenly.

FIG. 2 is a front view showing a partially broken surface of the developing device 5 of FIG. The screw 30 has a stirring blade 37 having a reduced diameter in the vicinity of the central portion in the axial direction. The screws 30 and 31 are rotatably provided on the side wall of the casing 25 via bearings 50. Shaft 3
A drive source (not shown) is connected to the tips of 3, 34,
The screws 30 and 31 are rotated at a predetermined rotation speed.
The distance between the stirring blades 35 and 37 of the screw 30 is not limited, but it is preferable to form the stirring blades 37 and the stirring blades 35 of the reduced diameter portion at equal intervals in processing. Stirring blade 37 of the reduced diameter part of the screw
Magnetic sensor 3 for detecting toner concentration so as to face
The sensor surface 46 of 8 is a swelling portion 40 of the developer described later.
Provided so as to be covered by the magnetic sensor 3
The sensitivity of No. 8 is provided at a position not affected by the amount of developer.

Referring to FIG. 3, the overall operation of the image forming apparatus 1 will be described. The corona charger 13 uniformly charges the photosensitive drum 12 and the optical projection device 14 projects the image data onto the photosensitive drum 12. To form a latent image. Then, the latent image is developed by the developing device 5 to form a toner image. On the other hand, the transfer material as the roll paper loaded in the paper feeding unit 15 is conveyed to the photosensitive drum 12 in synchronization with the rotation speed of the photosensitive drum 12. On the transfer material, the toner image on the photosensitive drum 12 is transferred onto the transfer material by the transfer corona discharger 16, separated from the photosensitive drum 12 by the separation corona discharger 17, and conveyed to the fixing device 4 by the conveyor belt 19.
It is transported to the printer, fixed as a permanent image, and discharged outside the machine. The toner remaining on the photosensitive drum 12 after the development is removed from the surface of the photosensitive drum 12 by the cleaning device 6, and then the photosensitive drum 12 is gradually charged by the eraser lamp 18 and prepared for the next image formation.

The operation of the developing device 5 will be described with reference to FIGS. 1 and 2. For example, if the height of the developer is 3
Fill screw 0, 31 to the upper part and screw 3
0 and 31 are screws 30 and 3 for the developer in the developing device 5.
Stir while circulating in 1 width direction. In the stirring blade 37 in the reduced diameter portion, the developer conveying force is weakened to form a raised portion 40 having a height higher than the upper portions of the screws 30 and 31. The sensor surface 46 of the magnetic sensor 38 is completely covered by the raised portion 40, and the magnetic sensor 38 detects the toner concentration in the developer. The raised portion 40 is always raised by a certain amount, that is, the detection sensitivity of the magnetic sensor 38 is not affected by the developer amount. The magnetic sensor 38 detects the toner consumed according to the above-described image formation, and appropriately replenishes the toner in the toner cartridge 21 to the inside of the developing device 5 from the supply port 10. The toner replenished to the end portion of the screw 30 is agitated together with the developer whose toner concentration is lowered by the time it reaches the agitating blade 37 in the reduced diameter portion. The replenishment of toner is continued until the toner concentration reaches a preset toner concentration by being circulated by the screws 30 and 31, and the toner replenishment is stopped after the predetermined toner concentration is detected. The screws 30 and 31 are continuously stirred and further circulated to become a developer having a uniform toner concentration distribution. In this way, the toner density is controlled so that good image formation can be performed. Even in the portion of the stirring blade 37 whose diameter has been reduced, the stirring blade 37 exists, so that uneven density of the developer does not occur, and the rising portion 40 is formed while the developer is smoothly transported. .

In the developing device, a preferable condition is that the diameter of the stirring blade is 0.3 to 0.7 times that of the other portions, and particularly 0.3 to 0.5. A range up to double is preferable.

[0024]

According to the present invention having the above-mentioned structure, the ridge portion having a small change in toner concentration in the developer and having a smooth carrying force is formed, and the magnetic sensor provided on the side surface develops. By detecting the toner concentration of the developer, the filling amount of the developer into the developing device can be set small, the stirring efficiency of the developer is improved, the pressure applied to the developer is reduced, and long-life development is achieved. A device can be provided. Further, since the required amount of the developer can be minimized, the torque of the drive source that agitates the screw is reduced, and the screw can be driven by a small motor. Furthermore, because the sensor surface is placed at a position that is not affected by pulsating flow etc. with respect to the swelling part of the developer, the toner concentration can be detected normally even if the installation location of the main body of the device is tilted, and accurate toner concentration is obtained. Detection can be performed.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a developing device according to the present invention.

FIG. 2 is a front view showing a partially broken surface of the developing device of FIG.

FIG. 3 is a schematic side view of an image forming apparatus including a developing device according to the present invention.

[Explanation of symbols]

 1 Image Forming Apparatus 2 Image Forming Section 3 Conveying Guide Means 4 Fixing Device 5 Developing Device 6 Cleaning Device 7 Toner Guide Tube 8 Waste Toner Container 9 Ejection Port 10 Toner Supply Port 12 Photosensitive Drum 13 Corona Charger 14 Optical Projection Device 15 Paper Feed Part 16 Transfer corona discharger 17 Separation corona discharger 18 Eraser lamp 19 Conveyor belt 20 Guide plate 21 Toner cartridge 22 Supply port 23 Guide member 24 Sponge 25 Casing 30, 31 Screw 32 Developing roller 33, 34 Shafts 35, 36, 37 Stirring Blade 38 Magnetic sensor 39 Partition plate 40 Raised portion 41 Permanent magnet 42 Sleeve 43 Magnetic brush 44 Regulation plate 46 Sensor surface

Claims (3)

[Claims] 1. At least two screws formed by spirally forming stirring blades around a shaft extending in a uniaxial direction along the axial direction as means for agitating a two-component developer composed of toner and carrier, and developing the screws with each other. Adjacent to the roller and arranged in parallel so that the conveying directions are different, the sensor surface of the magnetic sensor is arranged to face a part of the screw to detect the toner concentration of the developer conveyed by the screw, In a developing device configured to replenish replenishment toner to the end side of the screw based on the detection, at least one of the screws is axially partly compressed and part of the stirring blade is compressed with respect to the other part. The magnetic sensor has a diametrical shape, and the magnetic sensor is located on the side surface side of the reduced diameter portion, and the detection sensitivity of the magnetic sensor is affected by the change in the amount of the developer. A developing device, characterized in that a raised portion which does not resonate is formed so that the raised portion covers the entire sensor surface of the magnetic sensor. 2. The developing device according to claim 1, wherein the sensor surface of the magnetic sensor and the reduced diameter portion are provided substantially in the center of the screw on the side away from the developing roller. 3. The developing device according to claim 1, wherein the ratio of the diameter reduction of the screw is 0.3 to 0.7 times the diameter of the screw of the other portion.