JP2001249545A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate trouble that the toner concentration of developer gets uneven and the density of an image formed on a sheet gets unstable when the developer whose toner concentration is lowered is reused or development. SOLUTION: The developer stirred and carried by a 2nd lower screw auger is moved to a 3rd screw auger through an aperture part provided on the outside from the width of an image area where a latent image is formed by an image carrier, shut off by a partition by which the developer stirred and carried by other screw augers is not mixed, stirred and carried by the 3rd screw auger, and moved to a 1st upper screw auger communicating with the 3rd screw auger.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a printer, and more particularly to an image forming apparatus provided with a developing device for making a toner concentration of a developer uniform.

[0002]

2. Description of the Related Art In a known image forming apparatus such as a copying machine, an electrostatic latent image is formed by irradiating an image carrier with laser light to form an electrostatic latent image based on image data to be formed. The developed latent image is developed with toner, transferred to a sheet, and thermally fixed to form an image.
In the development of the image forming apparatus, an electrostatic latent image formed on an image carrier is visualized using a one-component developer or a two-component developer including a toner and a carrier.

In the case of using a two-component developer, the developer is magnetically attracted by a developing magnet roller having a rotatable sleeve disposed on the outer circumference of a plurality of magnetic poles provided at fixed positions around the image carrier. A magnetic brush is formed, and the rotation of the sleeve conveys the magnetic brush to the image carrier. The magnetic brush conveyed to the image carrier adheres toner according to the potential of the latent image formed on the image carrier to visualize the image. After the completion of the development, the developer is collected and reused together with the toner appropriately replenished from the outside. The developer used in such a configuration needs to maintain a constant amount of toner (toner density) and a charge amount to be applied according to the potential of the latent image in order to form a stable toner image. The toner concentration is determined by the distribution of the toner consumed in the development and the replenishment toner, and the charge amount of the toner is determined by the friction at the time of mixing the carrier and the toner. Therefore, the developing device sufficiently stirs the developer composed of the toner and the carrier to make the toner concentration distribution uniform, and saturates the charge amount applied to the toner to stabilize the toner image.

FIG. 1 is a schematic view of a developing device of a conventional image forming apparatus. In the figure, a developing device 20 is provided with an image carrier 10.
A first screw auger 7, a second screw auger 8, an auxiliary screw auger 8A, which is installed substantially parallel to the two-component developer and transports the two-component developer, and a magnetic roller including a plurality of magnetic poles whose positions are fixed. A developing magnet roller 3 having a rotatable sleeve disposed on the outer periphery is provided.
The first screw auger 7 includes the developing magnet roller 3
Is supplied to the developer. The supplied developer is held by the magnetic force of the developing magnet roller 3 and develops the latent image on the image carrier 10. The developer after the development is collected in a stirring tank in which the auxiliary screw auger 8A and the second screw auger 8 are arranged. The collected developer is agitated and conveyed by the auxiliary screw auger 8A, and toner is externally supplied at a downstream position in the conveying direction. Second screw auger 8
Transports the developer in the stirring tank in a direction opposite to the auxiliary screw auger 8A, and transfers the developer to the upstream of the first screw auger 7 due to the stagnation of the developer at a downstream position in the transport direction. We are using. That is, the auxiliary screw auger 8 </ b> A conveys the developer in the opposite direction to the second screw auger 8 to prevent the developer from excessively staying downstream of the second screw auger 8.

[0005]

However, in the conventional structure as described above, the auxiliary screw auger 8A
Before the part of the developer having the reduced toner concentration collected near the upstream position of the second screw auger 8 receives the toner replenishment, it is received by the first screw auger together with the developer remaining at the downstream position of the second screw auger 8. May be passed. When the developer having the reduced toner density is delivered to the first screw auger 7 and reused for development, the toner density of the developer becomes non-uniform, and the density of the image formed on the sheet becomes uneven. Become stable.

An object of the present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus for forming a stable image.

[0007]

The above object is achieved by the following means.

(1) In an image forming apparatus having a developing device for developing a latent image formed on an image carrier with a developer having a toner, the developing device includes at least three developing devices that stir and transport the developer by rotation. Having the above screw auger, the rotation axis of the screw auger is parallel to the image carrier, and, of the upper first screw auger and the lower second screw auger arranged in a vertical relationship A third screw auger is provided at an intermediate height, and the developer agitated and conveyed by the second screw auger is provided outside the width of an image area where the image carrier forms a latent image. The third screw auger moves to the third screw auger through the opening, and is shielded by a partition wall of the other screw auger that is not mixed with the developer being stirred and transported, and the third screw auger is stirred and transported. Was carried out, the image forming apparatus characterized by being configured to move to the first screw auger communicating.

(2) In an image forming apparatus having a developing device for developing a latent image formed on an image carrier with a developer including toner, the developing device includes a plurality of screws for stirring and transporting the developer by rotation. An auger, at least one screw auger of the plurality of screw augers is provided at a position where a downstream rotating shaft end is higher than an upstream rotating shaft end with respect to a developer conveying direction. An image forming apparatus wherein the developer is stirred and conveyed by another screw auger while being shielded by a partition wall in which the developer conveyed is not mixed.

(3) In an image forming apparatus having a developing device for developing a latent image formed on an image carrier with a developer containing toner, the developing device rotates the developer and transports the developer by stirring. Has a screw auger, the first screw auger, agitating and transporting the developer to supply the image carrier,
The second screw auger agitates and conveys and collects the developer after developing the image carrier, and the third screw auger collects the developer collected by the second screw auger.
The developer being stirred and conveyed by another screw auger is shielded and conveyed by a partition wall in which the developer is not mixed. An image forming apparatus, wherein the screw auger is stirred and conveyed while being shielded by a partition wall in which the developer conveyed by stirring is not mixed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic diagram showing the configuration of the image forming apparatus 1. 1, an image forming apparatus 1 includes an automatic document feeder (ADF) A and a document image reading unit B for reading an image of a document fed by the automatic document feeder.
Image processing means C for encoding and reading the image of the read original and performing data processing; a writing unit D; an image carrier 10 formed of a photosensitive drum;
An image forming unit E including a charger 17, a developing device 20, and a cleaning member 21 for forming a toner image on the image carrier 10, and an image forming sheet (hereinafter, referred to as a sheet)
It has paper feed units 22 and 24 for storing P, and a reversing path 25 for reversing the front and back of the sheet.

The automatic document feeder A includes a document table 37
And a document transport processing unit 36 including a roller group including the roller R1 and a switching unit (without reference symbols) for appropriately switching a document moving path. The original image reading unit B is located under the top glass G, and includes two mirror units 30 and 31 that can reciprocate while maintaining the optical path length, a fixed imaging lens 33, an image sensor 35, and the like. The writing unit D includes a laser light source 38, a polygon mirror 39, and the like. Note that, when viewed from the transport direction of the sheet P, a pair of rollers shown on the front side of the transfer device 18 is a registration roller R10, and a pair of rollers shown on the downstream side of the separation electrode 19 is a fixing roller R15 having a heat source.

First, a process for forming an image on a sheet will be described below. One of the originals (not shown) placed on the original placing table 37 is transported in the original transport processing unit 36, passes under the roller R1, and moves to the mirror units 30, 31 and An image is formed on the image sensor 35 via the lens 33 and read. The read image information of the document is processed by the image processing means C, and the encoded image information data is stored in the image memory. The writing unit D drives the laser light source 38 to irradiate the rotating image carrier 10 with the laser light according to the image information data stored in the image memory on the image carrier 10 which is rotated by a driving source (not shown). I do. Prior to the exposure, the image carrier 10 rotating in the direction of the arrow (counterclockwise) is given a predetermined surface potential by the corona discharge action of the charger 17. As a result, the electrostatic latent image corresponding to the data of the image information is formed on the image carrier 10. The electrostatic latent image is visualized by the toner of the developer supplied from the developing device 20, and becomes a toner image.

On the other hand, the symbol S in the paper feed unit 22
Is always urged by a biasing means such as a coil spring (not shown).
The free end is a movable plate which is urged upward, and the uppermost sheet P comes into contact with the feed roller 50. The sheet P that has come into contact with the feed roller 50 is sent out from the paper feed unit 22 and sent out to a pair of rotatable rollers, a drive roller 51 and a driven roller 52.
The driving roller 51 rotates to separate the sheets P one by one and conveys the sheets P toward the loop forming roller 57. The loop creation roller 57 is provided on the upstream side of the registration roller R10 when viewed from the sheet conveyance direction, and rotates to convey the sheet P and start the registration roller R1 before rotation.
The loop of the sheet P is formed by applying the leading end of the sheet to 0. By forming the loop, the skew of the sheet P due to the conveyance is corrected. After that, the registration roller R10 contacts the image carrier 1
The rotation of the sheet P is started in synchronization with the toner image formed at 0, and the sheet P is conveyed. The toner image of the image carrier 10 overlaps the sheet P conveyed in synchronization with the image carrier 10, and the toner image is transferred to the sheet P by the urging of the transfer device 18.
After the sheet P is separated from the image carrier 10 by the urging of the separation electrode 19, the toner powder for forming a toner image is melted and fixed on the sheet P by pressing and heating of the fixing roller R15. The sheet P on which the toner has been fixed is discharged onto a discharge tray T via a discharge roller 79.

Next, the developing device according to the present invention will be described. FIG. 3 is a schematic view of a screw auger that stirs and transports the developer in the developing device. In the figure, the screw auger has a rotating shaft 11 and a screw blade 12, and when a rotational driving force is transmitted to the rotating shaft 11, the rotating shaft 11 is rotated. The screw blade 12 installed on the rotary shaft 11 rotates, and transports the developer in the axial direction of the rotating shaft 11 while stirring the developer.

First, a first embodiment of the present invention will be described with reference to FIG. FIG. 4 is a schematic diagram of a developing device having a plurality of screw augers, (A) is a cross-sectional view of the developing device 20,
FIG. 3B is a side view of the inside of the developing device 20 seen from the Y direction of FIG. 3A, and FIG. 3C is an explanatory diagram showing a direction of transport of the developer in the developing device 20. In (C), the arrow indicates the direction of transport of the developer.

The developing device 20 has a developing magnet roller 3, at least three screw augers 7, 8, 9 and a blade 4. The rotation shafts 11 of the screw augers 7, 8, 9 are parallel to the image carrier 10 and of the upper first screw auger 7 and the lower second screw auger 8 arranged in a vertical relationship. A third screw auger 9 is provided at a height between them.
The screw augers 7, 8, and 9 are rotated by the driving force of a driving source (not shown) to stir and transport the developer in the developing device 20.

The first screw auger 7 supplies the developer to the developing magnet roller 3 while stirring and transporting the developer. The sleeve of the developing magnet roller 3, which rotates counterclockwise, holds the supplied developer by magnetic force to form a magnetic brush. The blade 4 regulates the height of the formed magnetic brush and returns the regulated developer to the first screw auger 7. The developing magnet roller 3 conveys the magnetic brush regulated to a certain height to the image carrier 10 and attaches the toner of the developer to the latent image on the image carrier 10 to perform development to form a toner image. . The developer that is not supplied to the developing magnet roller 3 and is agitated and conveyed to the downstream position (right side in the figure) of the first screw auger 7 moves due to stagnation and moves from the opening N3 to the downstream position of the second screw auger 8. (Right side in the figure). Further, the developer whose toner concentration has decreased due to the development falls from the developing magnet roller 3 to the periphery of the screw auger 8. The dropped developer is recovered by stirring and transporting the screw auger 8 and transported to a downstream position (right side in the drawing) of the screw auger 8. Each developer conveyed to the downstream position of the screw auger 8 moves to the third screw auger 9 obliquely upward through the opening N1 due to a fixed amount of stagnation. The moved developer is conveyed to a downstream position (left side in the figure) by stirring and conveying the screw auger 9 together with the toner supplied from the supply port N4. The developer is stirred and transported by the third screw auger 9 in the width of the image area where the image carrier forms a latent image, and the partition 5 is provided so as not to be mixed with the developer being stirred and transported by another screw auger. It is going to be shielded by. The developer conveyed to the downstream position of the screw auger 9 moves to the first screw auger 7 obliquely upward through the opening N2 due to stagnation. The developer that has moved to the screw auger 7 is again supplied to the developing magnet roller 3 by stirring and transporting, and develops the image carrier 10.
The openings N1, N2, and N3 through which the developer that moves due to stagnation at the downstream position of the screw auger are provided outside the width of the image area where the image carrier 10 forms a latent image. The developer is reliably collected and supplied, and excessive retention of the developer generated near the opening is reduced.

That is, the second screw auger 8 is used for circulating and transporting the developer by supplying toner from the outside.
The developer which has been stirred and conveyed moves to the third screw auger 9 through the opening N1 provided outside the width of the image area where the image carrier 10 forms a latent image, and is stirred and conveyed by another screw auger. The third screw auger 9 is agitated and conveyed by being shielded by the partition wall 5 where the developer does not mix, and moves to the first screw auger 7 through the communicating opening N1.

The provision of the third screw auger 9 has two effects. First, since the movement of the developer due to stagnation is performed in two stages, the developer can be moved with a smaller stagnation amount than when the developer is moved directly upward. Therefore, the temperature of the developer itself and the stress applied to the rotation shaft of the screw auger due to the excessive stagnation of the developer are reduced, so that the developer can be stably transported. The second is that the developer collected near the downstream position of the second screw auger 8 is separated from the developer supplied from the outside together with the developer agitated and conveyed by another screw auger with a predetermined conveying length so that the developer is not mixed. 5, the third screw auger 9 surely carries out the stirring and conveying, so that the predetermined stirring of the developer is secured and the toner concentration can be stabilized.

In the first embodiment, the movement of the developer due to stagnation is divided into two due to the configuration of the three screw augers. However, in order to reduce the amount of stagnation, two or more movements are required. A configuration in which the developer is moved in a plurality of times, that is, a configuration of at least three screw augers may be used.

Next, a second embodiment of the present invention will be described with reference to FIG. FIGS. 5A and 5B are schematic views of a developing device having a plurality of screw augers. FIG. 5A is a cross-sectional view of the center of the developing device 20, FIG. 5B is one end of the developing device 20, and FIG.
0 is the other end, and (D) is a developing device 2 viewed from the Y direction of (A).
It is the side view which saw through the inside of No. 0.

FIG. 4 of the first embodiment shows a configuration in which the rotation shaft 11 of the third screw auger 9 is parallel to the rotation shafts of the other screw augers, but the developing device 20 of FIG. , At least one of the plurality of screw augers
The screw auger 9A has a rotary shaft end 1A downstream of the upstream rotary shaft end 11A in the developer transport direction.
1B is installed at a high position, and is stirred and conveyed by the other screw auger while being blocked by the partition wall 5 where the developer being conveyed is not mixed. here,
The same members as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted.

The developer which has been developed and whose toner concentration has decreased is recovered by stirring and transporting the second screw auger 8 and transported downstream of the screw auger 8. The developer conveyed downstream has the opening N
1 and moves to the rotation shaft end 11A (right side in the figure) upstream of the third screw auger 9A on the side. The moved developer is together with the toner supplied from the supply port N4,
The screw auger 9A is stirred and conveyed and is conveyed to the downstream rotating shaft end 11B (left side in the figure) by being shielded by the partition wall 5 which is not mixed with the developer being conveyed and stirred by another screw auger. The developer conveyed to the periphery of the downstream rotating end 11B moves to the first screw auger 7 on the side through the opening N2 due to stagnation. The developer that has moved to the screw auger 7 is supplied to the developing magnet roller 3.

In the screw auger 9 of the first embodiment or the screw auger 9A of the second embodiment, the shielding by the partition wall 5 is performed in the width of the image area where the image carrier 10 forms a latent image. The developer is agitated as much as possible in the developing device 20, but a shorter transport length may be used as long as the agitation of the developer is ensured. Furthermore, the partition 5
Not only is the shield from the developer being stirred and conveyed by another screw auger, but also the toner supplied from the supply port N4, the developer dropped from the developing magnet roller 3, and the like.

A third embodiment of the present invention will be described with reference to FIG. 4 and FIG. 5
Is provided by a second screw auger 8 provided below.
The developer whose toner concentration has decreased during development is collected. The collected developer is replenished with the toner of the developer consumed in the development according to the formed image and used again for the development. However, the developer collected near the downstream of the screw auger 8 in the transport direction of the developer may be insufficiently agitated because the transport path through which the developer is agitated and transported is short. Therefore, if the toner concentration of the developer with insufficient stirring is detected based on the detection of the concentration sensor provided near the downstream of the screw auger 8, the toner concentration of the developer may become unstable. Was. Therefore, it is necessary to stir only the collected developer with a screw auger.

FIGS. 6A and 6B are schematic views of a developing device having a plurality of screw augers. FIG. 6A is a sectional view of the center of the developing device 20, FIG. 6B is one end of the developing device 20, and FIG. 20
(D) is an explanatory view showing the flow of the developer transport in the developing device 20. In the figure, the arrow indicates the direction of transport of the developer stirred and transported by the screw auger. The developing device 20 includes a developing magnet roller 3, screw augers 6, 7, 8, and 9, and a blade 4. The rotation shafts 11 of the screw augers 6, 7, 8, and 9 are installed in parallel with the image carrier 10, and rotate and transport the developer while stirring.

The first screw auger 7 stirs and transports the developer and supplies it to the image carrier 10 via the developing magnet roller 3 as described above.

The third screw auger 9 transports the developer recovered by the second screw auger 8 while being shielded by a partition wall of the other screw auger which is not mixed with the developer being agitated and transported. Screw auger 6
The developer agitated and transported by the third screw auger 9 and the toner supplied from the outside are agitated and transported by being shielded by a partition wall of another screw auger where the agitated and transported developer is not mixed.

The developer which has not contributed to the development is conveyed to the downstream position by the first screw auger 7 and stays there, so that the opening N3 communicating with the second screw auger 8 is formed.
From the second screw auger 8. The second screw auger 8 stirs and collects the developer dropped from the developing magnet roller 3 after developing the image carrier and the developer dropped from the opening N3, and conveys the developer to a downstream position. . The developer conveyed to the downstream position moves to the third screw auger 9 through the opening N1 by staying. The third screw auger 9 transports the developer collected by the second screw auger 8 to the downstream position by being shielded by the partition wall 5B where the developer being agitated and transported by the other screw auger is not mixed and stirred and transported. I do. The developer conveyed to the downstream position moves to the fourth screw auger 6 through the opening N5 due to stagnation. The fourth screw auger 6 shields the developer agitated and conveyed by the third screw auger 9 and the toner supplied from the supply port N4 by the partition wall 5A in which the developer agitated and conveyed by another screw auger is not mixed. And agitate and transport to the downstream position. The developer transported to the downstream position moves to the first screw auger 7 again through the opening N2 due to stagnation.

That is, in the circulating transport of the developer in the developing device 20, the developer is supplied to the image carrier, the developer is collected,
The four steps of stirring the collected developer and stirring the collected developer and the replenished toner are agitated and conveyed by dedicated screw augers to secure the stirring of the developer. Furthermore, the stirring and conveying performed while being shielded by the partition walls of the third screw auger 9 and the fourth screw auger 6,
When the width is set to the width W of the image carrier 10, the longest stirring of the developer in the developing device 20 can be ensured, and the stirring can stabilize the toner concentration.

A density sensor 15 for detecting the toner density of the developer is provided near the downstream of the third screw auger 9 with respect to the direction of transport of the developer. For this reason, since the toner concentration can be detected after the collected developer is agitated, the developer can be accurately replenished from the supply port N4 based on the detected toner concentration. Density sensor 15
May be provided upstream of the replenishing port N4 of the fourth screw auger 6 with respect to the transport direction of the developer.

FIG. 7 is an explanatory view of a developing device according to a fourth embodiment in which the opening N3 in FIG. 6 is provided so that the downstream of the first screw auger 7 and the upstream of the fourth screw auger 6 communicate with each other. It is.

In the third embodiment, the opening N3 is connected to the downstream of the first screw auger 7 and the second screw auger 8
Are connected to each other upstream. However, if an opening N3 communicating the downstream of the first screw auger 7 and the upstream of the fourth screw auger 6 is provided, the sheet is not supplied to the image carrier 10 and is transported downstream of the first screw auger 7. The accumulated developer moves upstream of the fourth screw auger 6 due to stagnation.

For this reason, the developer which does not contribute to the development and does not lower the toner concentration has a shorter transport length due to the circulating transport, so that a decrease in the developing ability due to stress such as transport pressure can be prevented.

[0037]

According to the present invention, there is provided an image forming apparatus in which the toner concentration of the developer in the developing device is stable.

[Brief description of the drawings]

FIG. 1 is a schematic view of a developing device of a conventional image forming apparatus.

FIG. 2 is a schematic diagram illustrating a configuration of an image forming apparatus.

FIG. 3 is a schematic diagram of a screw auger that stirs and transports a developer in a developing device.

FIG. 4 is a schematic view of a developing device having a plurality of screw augers.

FIG. 5 is a schematic view of a developing device having a plurality of screw augers.

FIG. 6 is a schematic diagram of a developing device having a plurality of screw augers.

FIG. 7 is an explanatory diagram of a developing device having a plurality of screw augers.

[Explanation of symbols]

 Reference Signs List 3 developing magnet roller 4 blade 5 partition wall 7 first screw auger 8 second screw auger 9 third screw auger 10 image carrier 11 rotation shaft 20 developing device

Claims (6)

[Claims] 1. An image forming apparatus having a developing device for developing a latent image formed on an image carrier with a developer including a toner, wherein the developing device rotates at least three or more stirring and transporting the developer. The rotation axis of the screw auger is parallel to the image carrier, and between the upper first screw auger and the lower second screw auger arranged in a vertical relationship. A third screw auger is provided at a height of, the developer stirred and transported by the second screw auger,
The image carrier moves to the third screw auger through an opening provided outside the width of an image area where a latent image is formed, and is blocked by a partition in which the developer being stirred and conveyed by another screw auger is not mixed. Wherein the third screw auger is configured to perform agitation and conveyance and move to the first screw auger communicating therewith. 2. An image forming apparatus having a developing device for developing a latent image formed on an image carrier with a developer including toner, wherein the developing device includes a plurality of screw augers for stirring and transporting the developer by rotation. At least one screw auger of the plurality of screw augers is provided at a position where a downstream shaft end is higher than a upstream shaft end with respect to a developer conveying direction. In addition, the image forming apparatus is characterized in that another screw auger agitates and transports the developer while being shielded by a partition wall in which the developer being agitated and transported is not mixed. 3. An image forming apparatus having a developing device for developing a latent image formed on an image carrier with a developer including a toner, wherein the developing device rotates the developer and stirs and transports the developer. A first screw auger, wherein the first screw auger agitates and conveys the developer and supplies the developer to the image carrier; and a second screw auger agitates the developer after developing the image carrier. The third screw auger agitates and transports the developer collected by the second screw auger while being shielded by the partition wall of the other screw auger that is not mixed with the developer being agitated and transported. In the screw auger, the developer agitated and transported by the third screw auger and the toner supplied from the outside are agitated and transported by being shielded by a partition wall of the other screw auger where the agitated and transported developer is not mixed. Image forming apparatus characterized by. 4. A density sensor for detecting a toner density of the developer, wherein the density sensor is located downstream of the third screw auger or upstream of the fourth screw auger with respect to a developer conveying direction. The image forming apparatus according to claim 3, wherein the image forming apparatus is installed. 5. The developer that has been agitated and transported downstream of the first screw auger without being supplied to the image carrier is moved to a position upstream of the fourth screw auger and agitated and transported to the fourth screw auger. The image forming apparatus according to claim 3, wherein the image forming apparatus is configured to: 6. The image forming apparatus according to claim 1, wherein the shielding by the partition is performed by a width of an image area where a latent image is formed on the image carrier.