JPH04338774A - Color developing device - Google Patents

Abstract

PURPOSE:To provide the color developing device which is so constituted as not to generate a bristle cutting defect when developers are subjected to bristle cutting by rotating a developing sleeve backward while respective developing devices are not used. CONSTITUTION:The rotating speed of the developing sleeve 11 at the time of the bristle cutting operation is set higher than the rotating speed of the developing sleeve 11 at the time of the development operation to surely remove the developer D from the developing sleeve 11 and to dispose the part of the developing sleeve 11 subjected to the bristle cutting so as to face a photosensitive body 2.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention has a plurality of developing devices which are placed opposite to a latent image carrier and each contains a developer of a different color, and each developing device is selectively operated to perform a developing operation. The present invention relates to a color developing device that sequentially visualizes an electrostatic latent image formed on a latent image carrier with toner of each color.

0002

2. Description of the Related Art Color developing devices of the above type employed in color image forming apparatuses such as color copying machines, color facsimiles, and color printers are well known.

Each of the above-mentioned developing devices has a developing sleeve that is rotationally driven and a magnet that is fixedly arranged inside the developing sleeve.
During the developing operation of the developing device, the developing sleeve is driven to rotate, and the magnetic force of the magnet inside the developing device carries the developer while carrying it on the sleeve, and transfers the developer to the developing area between the developing sleeve and the latent image carrier. The electrostatic latent image is visualized.

Each developing device selectively performs the above-described developing operation, and when one developing device is performing the developing operation, the other developing devices stand by without performing any developing operation. When the developing device is not in use, if the developer in the developing device comes into contact with the latent image carrier, unnecessary toner will adhere to the visible image formed by the developing device during the developing operation, causing visible damage. Color mixing occurs in the image.

[0005] Therefore, various configurations have been proposed to prevent the above-mentioned color mixture. For example, JP-A-49-51
953, JP 50-93438, JP 52-188332, JP 51-11456, JP 50-151532, JP 50-
No. 151530, Japanese Patent Application Laid-open No. 50-93438,
JP-A No. 52-105832, Utility Model Application No. 52-152
The specific structure is explained in detail in Publication No. 742 and the like.

Among these, the one disclosed in Japanese Patent Application Laid-Open No. 50-93438 rotates the developing sleeve in the opposite direction to the direction of rotation during the developing operation when the developing device is not in use, thereby carrying the developer. This configuration performs a cutting operation to position the unused spiked developing sleeve portion in the developing area to prevent the developer of the unused developing device from coming into contact with the latent image carrier. According to the above, it is possible to save space and simplify the structure of the developing device.

However, in the conventional color developing device of this type, there is a risk that defective cutting of the developer may occur if only the developing sleeve is reversed. In many cases, a complicated configuration as shown in FIG.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a color developing device in which the above-mentioned conventional drawbacks are improved or eliminated by a simple construction.

[0009]

[Means for Solving the Problems] In order to achieve the above object, the present invention has a plurality of developing devices which are placed opposite to a latent image carrier and each contain a developer of a different color. A color developing device that sequentially visualizes an electrostatic latent image formed on a latent image carrier with toner of each color by selectively performing a developing operation, and each developing device includes a developing sleeve that is rotationally driven. and a magnet fixedly arranged inside the developing device. During the developing operation of the developing device, the developing sleeve is driven to rotate, and the developer is conveyed while being supported on the sleeve by the magnetic force of the internal magnet. , the electrostatic latent image is visualized in the developing area between the developing sleeve and the latent image carrier, and when the developing device is not in use, the developing sleeve is rotated in the opposite direction to the rotating direction during the developing operation. The developing sleeve is rotated to perform a cutting operation in which the cut developing sleeve portion that does not carry developer is positioned in the development area, thereby preventing the developer of the unused developing device from coming into contact with the latent image carrier. In the color developing device, the rotational speed of the developing sleeve in at least one developing unit is set such that the rotational speed of the developing sleeve during the cutting operation is lower than the rotational speed during the developing operation. We propose a color developing device with special features.

[0010] At this time, when each developing device has a developer scooping rotary body that supplies developer to its developing sleeve, the rotation of the developer scooping rotary body in at least one developing device during the ear cutting operation. It is desirable to set the rotational speed of the pumping rotor so that the rotational speed is lower than the rotational speed during the developing operation.

[0011] Furthermore, it is desirable to control the rotation of the developing sleeve so that the rotation of the developing sleeve during the ear cutting operation is within one rotation.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be explained in detail with reference to the drawings, and the above-mentioned problems of the conventional art will be explained more specifically with reference to the drawings.

FIG. 1 is a schematic diagram of a color copying machine equipped with a color developing device 1 according to the present invention. It is rotated clockwise by. At this time, the surface of the photoreceptor is uniformly charged by the charger 3,
Next, the surface of the photoreceptor is imagewise exposed as shown by arrow P, and an electrostatic latent image for a first image is formed on the surface of the photoreceptor.

The latent image is visualized as a toner image by the color developing device 1, which includes a plurality of developing devices, in this example, four developing devices 4Y, 4M, 4C, and 4B.
It has L. Each of the developing units 4Y, 4M, 4C, and 4BL disposed opposite to the photoreceptor 2 contains developers of different colors, and in this example, each developer includes toner and carrier. A two-component developer is used. That is, the first developing device 4Y along the rotational direction of the photoreceptor 2 contains a developer containing yellow toner and a magnetic carrier, and the second developing device 4M contains a developer containing magenta toner and a magnetic carrier. The third developer 4C contains a developer containing cyan toner and a magnetic carrier, and the fourth and final developer 4BL contains a developer containing a black toner and a magnetic carrier.

[0015] As described above, the first
The electrostatic latent image of is made visible with yellow toner by one of the four developers, in this example the first developer 4Y, and such visible image is rotated counterclockwise. The image is transferred onto a transfer paper 6 wrapped around a driven transfer drum 5 by the action of a transfer charger 7. The toner remaining on the photoreceptor 2 after the transfer is cleaned by a cleaning device 8, and the surface of the photoreceptor is subjected to a static eliminating action by a static eliminator 9.

Next, the photoreceptor 2 is again charged to the charger 3.
, and then an electrostatic latent image for a second image is formed by image exposure, and this latent image is visualized with magenta toner by the second developing device 4M, and this visible image is also transferred by the above-mentioned transfer. The yellow image is transferred onto the paper 6 in an overlapping manner. The residual toner on the photoreceptor 2 is removed by a cleaning device 8.
The surface of the photoreceptor is then cleaned to eliminate static electricity.

In exactly the same manner, 3
and a fourth electrostatic latent image are formed, which form the third and fourth electrostatic latent images.
The toner image is visualized by cyan toner and black toner by the developing devices 4C and 4BL, respectively, and these images are sequentially transferred onto the same transfer paper 6.

After being separated from the transfer drum 5, the transfer paper 6 on which the visible images of four colors of toner have been superimposed and transferred passes through a fixing device (not shown), at which time the visible images are fixed, and the transfer paper is It is ejected outside the machine as full-color copy paper.

When the copying operation is performed as described above, each of the developing units 4Y, 4M, 4C, and 4BL of the developing device 1 selectively performs a developing operation, and each electrostatic latent image formed on the photoreceptor 2 is visualized using toner of each color sequentially.

FIG. 2 shows a typical example of four developing units.
The developing device 4Y is shown. The basic configuration of the other developing devices is the same as that of the developing device 4Y shown in FIG. 2, so detailed illustrations of the other three developing devices 4M, 4C, and 4BL will be omitted.

The developer casing 10 of the developer device 4Y shown in FIG. A developing sleeve 11 is rotatably supported. Further, an immovably fixed roller-shaped magnet 12 is disposed inside the developing sleeve 11, and the magnet 12 has first to sixth magnetic poles labeled P1 to P6. S is set as illustrated in FIG.

A paddle wheel 13, which is an example of a developer pumping rotating body, is disposed inside the developer casing 10, and the wheel 13 stirs the developer D while rotating counterclockwise. While pumping up the developing sleeve 11
It serves the purpose of supplying

When the first developing device 4Y performs the developing operation as described above, the developing sleeve 11 is rotationally driven in the counterclockwise direction (arrow X direction) in FIG. 2, and the paddle wheel 13 also rotates in the counterclockwise direction. By developer sleeve 11
The developer pumped up and supplied adheres to the developing sleeve 11 due to the magnetic force of the fourth magnetic pole P4 of the magnet 12 disposed inside the sleeve 11.
The rotation of the sleeve 12 causes the material to be conveyed counterclockwise. This developer continues to be applied to the fifth and sixth magnetic poles P5 and P5.
6 is supported on the developing sleeve 11 and conveyed while forming ears.

Excess developer among the developer transported as described above is scraped off by the doctor blade 14, and a predetermined amount of developer is deposited in the development area 15 between the development sleeve 11 and the photoreceptor 2. Here, the first magnetic pole P1
The toner in the developer is electrostatically transferred to the electrostatic latent image on the photoreceptor 2 while standing up due to the magnetic force of the toner, and the latent image is visualized.

The developer that has passed through the developing area 15 is taken into the developing casing 10 by the magnetic force of the second magnetic pole P2.

[0026] The third magnetic pole P3 has magnetic poles P2 on both sides thereof,
This magnetic pole P3 is not actively magnetized during the manufacture of the magnet 12, and its magnetic force is almost non-existent or extremely weak. Magnet 1 so that the magnetic force of the third magnetic pole P3 becomes zero.
2 is most preferred. With this configuration, the developer taken into the developing casing 10 by the second magnetic pole P2 falls from the developing sleeve 11 at the third magnetic pole P3, which has almost no magnetic force, and is returned to the paddle wheel 13. Further, the developer scraped off by the doctor blade 14 is also guided to the lower paddle wheel 13 through the separator 16, where it is subjected to a stirring action.

[0027] The third magnetic pole P has almost no magnetic force on the magnet 12.
3, that is, a portion with substantially no magnetic force exists between the second magnetic pole P2 and the fourth magnetic pole P4, and the developing area 15
The reason why the developer that has passed through the development area 15 is once separated from the development sleeve 11 and circulated while being stirred by the paddle wheel 13 is that the developer that has passed through the development area 15 has consumed toner, so it is removed from the development casing 10. This is because it is necessary to sufficiently stir and mix it with the other developer D. In this way, since no developer is present in the portion of the developing sleeve 11 facing the third magnetic pole, the distribution of the developer D on the sleeve 11 is as shown in FIG. 3.

Note that when the toner concentration of the developer D contained in the developer casing 10 falls below a predetermined value, the toner replenishing roller 17 is driven to rotate, and the toner in the toner replenishing section 18 is replenished into the developer D. be done.

In the other developing units 4M, 4C, and 4BL, operations generally similar to those described above are performed during their developing operations, and visible images of toner of each color are formed on the photoreceptor 2.

By the way, when one of the four developing devices is performing a developing operation, the other developing devices do not perform a developing operation. At this time, if the developer in the unused developing device, which is not performing the developing operation, comes into contact with the photoreceptor 2 and the toner adheres to the photoreceptor 2, as explained earlier, the developing operation will be stopped. Color mixture occurs in the visible image formed by the developing device, and the image quality deteriorates.

Therefore, after each developing device finishes its developing operation,
Next, a cutting operation to be described is performed to remove the developer from the surface of the developing sleeve in the developing area 15.

Here again, the panicle cutting operation will be explained with reference to FIG.
It is rotationally driven in the direction opposite to the direction of rotation during the developing operation (direction of arrow Y). That is, the developing sleeve 11 rotates clockwise in FIG. 2. Hereinafter, the rotation of the developing sleeve 11 in the opposite direction will be referred to as reverse rotation, and the rotation during the developing operation will be referred to as normal rotation.

When the developing sleeve 11 is reversed as described above, at the end of the developing operation, the portion of the developing sleeve that had been facing the fourth magnetic pole P4 now faces the third magnetic pole P3; Since there is almost no magnetic force, the developer that had been supported on the developing sleeve 11 by the magnetic force of the fourth magnetic pole P4 falls downward. Such operations are sequentially performed by reversing the developing sleeve 11, and the portion of the developing sleeve where no developer is present is sequentially enlarged. Eventually, this portion of the developing sleeve where no developer is present will face the photoreceptor 2. That is, the torn developing sleeve portion that does not carry developer is located in the developing area 15.
In this state, the reverse rotation of the developing sleeve 11 is stopped.

Such a cutting operation prevents the developer in the developing device from coming into contact with the photoreceptor 2 when the developing device is not in use, thereby preventing the above-mentioned color mixture from occurring. A similar operation is performed in other developing devices, and the problem of the developer coming into contact with the photoreceptor 2 when the developing device is not in use is prevented.

The developing operation and the ear-cutting operation described above are similar to those in conventionally proposed color developing apparatuses, and a developing apparatus that performs such ear-cutting operations can simplify its configuration and reduce costs. Cost and space savings can be achieved.

However, in the conventional color developing device of this type, the developer does not reliably leave the developing sleeve 11 during the above-mentioned panicle cutting operation, and some developer remains in the developing area 15 when the panicle cutting operation is completed. However, there was a risk that this would come into contact with the photoreceptor 2 and cause color mixing. In particular, photoreceptor 2
A developing device other than the developing device located directly below the photoreceptor 2, for example, a developing device located laterally of the photoreceptor 2 as shown in FIG.
Although not shown in the figure, in a developing device disposed above the photoreceptor 2, the cutting of the ears is insufficient. For this reason, no structure has been put into practical use that performs the ear cutting operation as described above for a developing device disposed at such a position.

Conventionally, the developing device 4Y is arranged as shown in FIG.
The reason why the ear cutting was particularly insufficient is as follows.

When the developing device is arranged as shown in FIG. 2, the region from which the developer is removed from the developing sleeve 11 during the ear cutting operation is the lower region of the developing sleeve 11 facing the third magnetic pole P3. becomes. Here, the average height level of the developer D in the developer casing 10 needs to be set below the developer sleeve 11, as shown by the dashed line with the symbol L in FIG. When this level L becomes higher than the state shown in FIG. 2, the level L approaches the second magnetic pole P2, so when the developing sleeve 11 is reversed during the ear cutting operation, the developer D stored in the developing casing 10 is Second
This is because they are attracted to the magnetic pole P2 by their magnetic force and are carried to the development area 15, making it impossible to cut the ears. Therefore, it is necessary to lower the developer level L as low as possible.

However, when the level L is lowered, the developer D is applied from below to the developing sleeve 11 during the developing operation.
must be supplied by the paddle wheel 13. As a result, from the developer supply point to the developing sleeve 11,
The distance to the development area 15 increases. Therefore, in order to reliably transport the developer to the development area 15 during the development operation, it is necessary to provide a large number of magnetic poles between these areas, and in the example of FIG.
A magnetic pole P4, a fifth magnetic pole P5, and a sixth magnetic pole P6 are provided so that the developer can be reliably conveyed to the development area 15. The first magnetic pole P1 is also called a main pole, and is absolutely necessary for the developing operation. Furthermore, when the developing device 4Y is arranged as shown in FIG. 2, the second magnetic pole P2 is always required because the developer that has passed through the developing area during the developing operation must be returned to the developing casing 10. Without the second magnetic pole P2, the developer that has passed through the development area 15 would not be taken into the development casing 10 and would be scattered outside the casing.

For the above-mentioned reasons, in the developing device 4Y arranged as shown in FIG. 2, the number of magnetic poles of the magnet must be very large. At times, it is not possible to increase the width of the area between the fourth magnetic pole P4 and the second magnetic pole P2, that is, the third magnetic pole P3 in the circumferential direction of the developing sleeve for separating the developer from the developing sleeve 11. In particular, when the diameter of the developing sleeve 11 is reduced in order to downsize the developing device, the diameter of the magnet 12 is also reduced, and the width of the third magnetic pole P3 is further narrowed. If the width of the third magnetic pole P3 is small in this way, the width of the fourth magnetic pole P3 is small during the ear cutting operation.
The developer that had been attached to the developing sleeve 11 due to the magnetic force of the magnetic pole P4 is moved to the third
When it reaches the area of magnetic pole P3, this is the developing sleeve 1.
There is a possibility that the developing sleeve 11 is not separated from the developing sleeve 11 and is carried to the developing area 15 before it completely falls from the developing sleeve 11 due to the magnetic force of the second magnetic pole P2.

In the case of a developing device placed below the photoreceptor 2, such as the third developing device 4C shown in FIG. It is possible to shorten the developer conveyance distance in the development area, and it is also possible to return the developer that has passed through the development area into the development casing by its own weight, so the number of magnetic poles of the magnet located in the development sleeve can be reduced, and therefore Since the length in the circumferential direction of the developing sleeve from which the developer is separated from the developing sleeve during the panicle cutting operation can be made relatively large, it is unlikely that the panicle cutting will be insufficient. In this case, there is a particular risk that the ear cutting will be insufficient.

Since the color developing device 1 has a plurality of developing devices, in order to make the photosensitive member 2 smaller, the developing devices must be arranged laterally of the photosensitive member 2 as shown in FIG. In such cases, the above-mentioned problems are particularly likely to occur.

Furthermore, the surface of the developing sleeve provided in the developing device is roughened by sandblasting or the like, or has a large number of Vs extending in the axial direction of the sleeve, in order to increase the developer conveying force during the developing operation. Although grooves are formed, if the developing sleeve is formed in this way, the developer will be easily carried to the development area during the ear cutting operation, which may cause defective ear cutting. This is true for all the developing devices shown in FIG.

As mentioned above, in the conventional developing device,
During the cutting operation, there was a risk that the developer would be defective in cutting, but in the color developing device 1 according to the present invention,
The above conventional drawbacks can be easily eliminated as follows.

That is, in the developing device 4Y, the rotational speed (reverse rotation) of the developing sleeve 11 during the ear cutting operation is set to be lower than the rotational speed (normal rotation) of the developing sleeve 11 when the developing operation is performed. The rotation speed of the developing sleeve 11 is set accordingly.

With this configuration, the developing sleeve 11
When the is reversed, the developer that had been attached to the developing sleeve 11 due to the magnetic force of the fourth magnetic pole P4 slowly moves to the third magnetic pole P4.
Therefore, even if the width of the magnetic pole P3 in the circumferential direction of the developing sleeve is narrow, or even if the circumferential surface of the developing sleeve 11 is roughened or V-grooves are formed, the developer will surely flow downward. Fall. In the example shown in FIG. 2, the angle formed by the third magnetic pole P3 and the developing area 15 is small, approximately 90 degrees, so that as soon as the developing sleeve 11 is reversed, the amount of rotation of the sleeve changes. Within one rotation, the portion of the developing sleeve where no developer is present is located in the developing area 15 and faces the photoreceptor 2, so even if the rotation of the developing sleeve 11 in reverse is slow, the ear cutting operation can be completed quickly. can.

[0047] Also, during the ear cutting operation, the developing sleeve 11
When the developer is reversed one or more rotations, a large amount of developer falls downward from the sleeve 11, so the developer accumulates in the lower area of the developing sleeve, its height rises, and the level reaches the second magnetic pole P2. Since the magnetic pole P2 approaches the magnetic pole P2, the developer D is attracted to the magnetic pole P2 and transported to the development area 15, which may result in incomplete ear cutting.

For the above-mentioned reasons, in this example, the rotation of the developing sleeve 11 during the ear cutting operation is limited to one revolution or less, so that the ears are completely cut.

Furthermore, during the developing operation, the developing sleeve 11 can be rotated at high speed, so that a sufficient amount of developer can be conveyed to the developing area 15, making it possible to cope with high-speed copying operations.

Note that if the speed at which the developing sleeve 11 reverses during the ear cutting operation is made too slow, a large amount of developer is present in the portion of the developing sleeve 11 facing the photoreceptor 2, and other developing The electrostatic latent image visualized by the device is
Since the developer passes through the developing sleeve 11 and causes color mixing, it is natural that the speed at which the developing sleeve 11 is reversed should be set to such an extent that such a problem does not occur.

By the way, since the paddle wheel 13 supplies developer to the developing sleeve 11 during the developing operation, the paddle wheel 13 is rotated at high speed so that a sufficient amount of developer can be supplied to the developing sleeve 11. There is a need. However, if the paddle wheel 13 rotates at high speed during the ear cutting operation, the developer may be supplied by the paddle wheel 13 to the portion of the developing sleeve to be cut, resulting in incomplete ear cutting.

Therefore, it is conceivable to stop the paddle wheel 13 during the ear cutting operation. If this is done, the supply of developer to the developing sleeve 11 will be completely eliminated, and the above-mentioned problem will not occur. However, when the paddle wheel 13 is stopped, the developer that has fallen from the developing sleeve 11 during the ear-cutting operation accumulates below the sleeve 11, and its height increases, which causes the ear-cutting process to be interrupted as described above. may become incomplete.

Therefore, in this example, the rotational speed of the paddle wheel 13 during the panicle cutting operation is the same as that of the paddle wheel 13 during the developing operation.
paddle wheel 1 so that the rotation speed is lower than the rotation speed of
A rotation speed of 3 was set. According to this configuration, since the paddle wheel 13 rotates at a low speed during the ear cutting operation, the amount of developer supplied to the developing sleeve 11 by the wheel 13 becomes extremely small or is not substantially supplied.
It is possible to prevent the developer from being supplied to the portion of the developing sleeve 11 to be cut into ears, and it is possible to completely cut the ears.

On the other hand, since the paddle wheel 13 rotates at a low speed during the ear cutting operation, the developing sleeve 11
The developer dropped from the developer sleeve 10 can be stirred with other developer in the developer casing 10 to even out the entire developer, and the developer accumulates below the developer sleeve 11 and its height level increases. can be prevented.

The configuration regarding the rotational speed of the developing sleeve 11 and the paddle wheel and the configuration regarding the amount of rotation of the developing sleeve 11 during the ear cutting operation described above are similar to the configuration regarding the rotation speed of the developing sleeve 11 and the paddle wheel, and the configuration regarding the rotation amount of the developing sleeve 11 during the ear cutting operation. In the example, the present invention can be particularly advantageously applied to the developing devices other than the third developing device 4C), but it goes without saying that it can also be applied to the third developing device 4C. Further, it is particularly preferable to apply these configurations to all the developing devices in the developing device, but the intended purpose of the present invention can be achieved even if the configuration is applied to at least one of the plurality of developing devices.

By the way, the simplest control mode when facing the photoreceptor 2 to the part of the developing sleeve where no developer is present during the cutting operation is to start counting after the developing sleeve 11 is reversed, and after a predetermined time, the developing sleeve is stopped. sleeve 1
1 is to be stopped. However, developing sleeve 11
The extent and width of the area where no developer is present on the developing sleeve, that is, the area where there is no developer, is formed in the circumferential direction of the developing sleeve varies depending on each developer, and even in the same developer depending on the situation at the time. fluctuate. Therefore, the time until the agent-absent portion faces the photoreceptor 2 varies, and with the above-described control mode, it is possible that the agent-absent portion of the developing sleeve 11 does not reliably oppose the photoreceptor 2. That is, due to variations in the magnetic force distribution of the magnet 12 itself and variations when the magnet 12 is assembled into a developing device, the range of the agent-absent portion in each developing device varies. Furthermore, even in the same developing device, the range of the developer-absent area may vary depending on the toner concentration and humidity of the developer. When the toner concentration increases, the height level L of the developer D increases, causing defective ear trimming. This is more likely to occur, and as the toner concentration decreases, the magnetic permeability of the developer increases, making it easier for the developer to be attracted to the developing sleeve 11.

Therefore, in the illustrated embodiment, as shown in FIG. 2, a conductor 20 in an electrically floating state is provided in the developing casing portion in the region between the first magnetic pole P1 and the third magnetic pole P3. It is fixedly arranged with respect to the sleeve 11 with a predetermined gap. On the other hand, a predetermined developing bias voltage is applied to the developing sleeve 11 by a power source 21. Here, when there is no developer between the conductor 20 and the developing sleeve 11, no voltage is applied to the conductor 20 even if a bias voltage is applied to the developing sleeve 11. However, when a developer exists between the conductor 20 and the developing sleeve 11, the conductor 20 that comes into contact with the developer has
A reduced developing bias voltage is applied due to the resistance of the developer, and this can be detected by the detection section 22. Using this principle, the developing sleeve 1 during the ear cutting operation is
The reversal of 1 is controlled as follows.

During the developing operation and at the end of the developing operation, since developer exists between the developing sleeve 11 and the conductor 20, the voltage is detected by the detecting section 22. Next, when the developing sleeve 11 begins to be reversed in order to perform the ear cutting operation, the agent-absent portion gradually approaches the conductor 20 and finally reaches the conductor 20. At that moment, the voltage is no longer detected by the detection unit 22. This point is the standard. Then, the developing sleeve 11 is stopped after a predetermined period of time has elapsed from this reference point, that is, after a predetermined period of time has elapsed until the agent-absent portion faces the photoreceptor 2.

According to the above configuration, even if the range of the agent-absent portion varies to some extent, the range can be accurately detected and the developing sleeve 11 can be stopped correctly. The timing at which the developing sleeve 11 is stopped is uniquely determined by the distance from the conductor 20 to the developing area 15 and the surface linear velocity of the developing sleeve 11. At this time, the shorter the distance from the conductor 20 to the developing area 15, the shorter the developing sleeve 11 needs to be stopped after a short period of time after the conductive part 20 detects the absence of the agent. This makes it less susceptible to factors such as speed fluctuations, making it possible to stop the developing sleeve at a more correct position.

By the way, with the configuration according to the present invention described above, it is possible to reliably cut the ears, but if there are variations in the magnetic force distribution of the magnet 12 or various other factors overlap, When the developer is being dropped from the developing sleeve 11 while reversing the developing sleeve 11,
It cannot be said that there is no possibility that the developer will start to adhere to the upstream portion in the rotational direction. In the case of such a developing device, it is also possible to control the reversal of the developing sleeve 11 by using the above-mentioned conductor 20, as described below for reference. Note that this control mode can be particularly advantageously applied when the above-described configuration according to the present invention is not adopted.

First, the time from when the conductor 20 detects the absence of the developer until the presence of the developer is detected again is detected, thereby detecting the actual range of the absence of the developer. Then, when the center of this agent-absent range reaches the developing area facing the photoreceptor 2, the reverse rotation of the developing sleeve 11 is stopped. In this way, when the developer adheres to the upstream side of the area where no agent is present during the ear cutting operation, the correct stop timing of the developing sleeve can be automatically set.

In reality, after the copying machine is completed, a developing operation is performed, and then a cutting operation is performed. At this time, the range (time) in which no developer is present on the developing sleeve 11 is measured. Let this be t1. Also, the center of the area where the agent is absent is the conductor 20.
Assuming that the time from t2 to reaching the development area 15 is (t1/2) +
The control device of the developing device is set so that the developing sleeve stops rotating in reverse after t2.

In addition, the agent-absent range changes due to changes over time such as changes in toner concentration, and as a result, (t1/2)+
Since t2 also changes, t is periodically changed (for example, when the power is turned on).
If 1 is measured and corrected, the optimum stopping position of the developing sleeve can be obtained even if there is a change over time.

Furthermore, by periodically checking the agent-absent range as described above, it is also possible to check whether the developing device is operating normally. For example, even if the toner concentration of developer D goes out of control and it becomes impossible to cut the ears, you can detect the abnormality before making a copy and discovering an abnormality such as color mixture on the image, and you can prevent copy mistakes. It can be prevented. Conversely, even if the developer is not pumped up, it is possible to detect this as an abnormality before copying.

It goes without saying that the configuration related to the conductor 20 described above can also be applied to the other developing units 4M, 4C, and 4BL.

The present invention can also be applied to a color developing device using a one-component developer of magnetic toner, and can also be applied to a developing device having a number of developing devices other than four.

[0067]

According to the structure set forth in claim 1, it is possible to perform ear cutting more reliably than before and to effectively prevent color mixture from occurring.

According to the configuration set forth in claim 2, the above-mentioned effects can be made more reliable.

According to the configuration set forth in claim 3, the above-mentioned effects can be further ensured.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing an outline of a color copying machine.

FIG. 2 is an enlarged sectional view of a first developing device.

FIG. 3 is an explanatory diagram showing the developing sleeve shown in FIG. 2 and a magnet taken out.

[Explanation of symbols]

1 Color developing device 4Y developer 4M developer 4C developer 4BL developer 11 Developing sleeve 12 Magnet 15 Development area D Developer

Claims (3)

[Claims] Claim 1: A plurality of developing devices are arranged opposite to the latent image carrier and each contains a developer of a different color, and by selectively operating each developing device, the latent image carrier is developed. A color developing device that sequentially visualizes a formed electrostatic latent image with toner of each color, and each developing device has a developing sleeve that is rotationally driven and a magnet that is fixedly arranged inside the developing sleeve. During the developing operation of the developing device, the developing sleeve is driven to rotate, and the magnetic force of the magnet inside the developing device carries the developer while carrying it on the sleeve, and the developing device moves between the developing sleeve and the latent image carrier. The electrostatic latent image is visualized in the region, and when the developing device is not in use, the developing sleeve is rotated in the opposite direction to the direction of rotation during the developing operation, and the cut ears that do not carry developer are In a color developing device that performs a cutting operation to position the developing sleeve portion in the developing area and prevents the developer of the unused developing device from coming into contact with the latent image carrier, the developing sleeve of at least one developing device is A color developing device characterized in that the rotational speed of the developing sleeve is set so that the rotational speed during the ear cutting operation is lower than the rotational speed during the developing operation. 2. Each developing device has a developer pumping rotating body that supplies developer to its developing sleeve, and the rotational speed of the developer pumping rotating body in at least one developing device during the ear cutting operation is such that 2. The color developing device according to claim 1, wherein the rotational speed of the pumping rotor is set to be lower than the rotational speed during the developing operation. 3. The color developing device according to claim 1, wherein the developing sleeve rotates within one rotation during the ear cutting operation.