JPH0618372Y2 - Development device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is applied to, for example, an electrostatic transfer copying machine or a laser printer, and is used for developing an electrostatic latent image or the like formed on a recording medium. The present invention relates to a developing device.

[Conventional technology]

In a copying machine or the like, toner made of a color pigment is attached to the electrostatic latent image for the purpose of visualizing the electrostatic latent image formed on the recording medium. In this case, in order to not only visualize the electrostatic latent image in black but also colorize it into each color, a plurality of developing devices containing toners of various colors are provided inside the copying machine. The developing device can be selected and used.

For example, in the case of forming a full-color image, a developing device containing cyan, magenta, yellow, and, if necessary, black toner is separately provided, and an electrostatic latent image on a recording medium that is color-separated through filters of each color is formed. Each color toner is developed, and each color toner is overlaid on the recording medium to obtain a full-color copy image.

Therefore, the developing device needs to be configured so that toner does not adhere to the electrostatic latent image when it is not used for development.

To prevent the toner of the developing device not used for development from adhering to the electrostatic latent image on the recording medium, conventionally, for example, switching is performed by changing the developing gap, that is, the gap between the recording medium and the developing unit of the developing device. In general, the developing area toner facing the recording medium is not fed.

[Problems to be solved by the invention]

However, in the configuration in which the development gaps are switched as described above, unless the development gaps are accurately positioned, the development conditions tend to vary and the image density tends to change, so that a normal image is formed. There was a problem that I could not do it.

Further, in the developing device adopting the magnetic brush developing method, the position of the magnet forming the developing unit is shifted so that the magnetic brush does not come into contact with the recording medium. When the position of the magnet shifts inside, not only the image density is changed, but when a two-component developer is used, the carrier adheres to the recording medium, resulting in a marked deterioration in image quality.

Therefore, a stirring roller is arranged in the developer supply passage for supplying the developer to the developing magnet roller which is disposed facing the recording medium and performs the development, and a slit is formed concentrically with the stirring roller on the outer periphery of the stirring roller. A cylindrical shutter is fitted, and the developer supply passage is closed or opened by a shutter mechanism whose rotation is controllable, while the developer sent through the developer supply device is transferred onto a recording medium by a developing magnet roller. It is conceivable that the electrostatic latent image is developed, and the developer after development is drawn up by the developing magnet roller and conveyed to a portion where the developer is stirred by the conveying magnet roller. This makes it possible to prevent the toner of the developing device, which is not used for development, from adhering to the electrostatic latent image on the recording medium without switching the developing gap.

Further, a toner concentration detecting sensor is provided in the developer supply passage between the shutter and the developing magnet roller, and the toner concentration detecting sensor detects a decrease in toner concentration in the developer sent to the developing magnet roller. By supplying the toner to the developer supply passage while the toner is being supplied, the image density can be kept constant.

However, the toner concentration detection sensor having the above configuration is capable of detecting the toner concentration when the developer is sent to the developing magnet roller and the magnetic brush is formed on the outer periphery of the developing magnet roller. After the development is completed, the shutter is closed to block the developer supply passage, and the developer existing in the developer supply passage between the shutter and the developing magnet roller is developed by the developing magnet roller and the conveying magnet roller. When the developer is no longer present due to being returned to the agent stirring section, the toner concentration detection sensor cannot detect the toner concentration. Therefore, when the magnetic brush is formed, that is, when the developing time for one time is short, a decrease in toner concentration is detected by the toner concentration detecting sensor during the development, and the toner concentration is detected by the toner concentration detecting sensor. Even if the replenishment is started, if the developing time is short, the toner concentration detection sensor immediately becomes unable to detect the toner concentration, so that the replenishment is interrupted in a short time, and the toner is sufficiently replenished. You will not have the time to do it.

In particular, in a full-color developing device, the developing time for one type of color, that is, the time during which the magnetic brush is formed is as short as about 2 seconds, so at this time, the toner density detecting sensor detects the toner density. Even if a drop in
It becomes very difficult to replenish the consumed toner amount in a short time.

As described above, when the toner replenishment amount is insufficient, not only the image density is lowered due to the toner concentration lowering, but also the carrier adheres to the recording medium, which causes the image quality lowering. It will be.

[Means for solving problems]

In order to solve the above-mentioned problems, the developing device according to the present invention includes a shutter that can open and close a developer supply passage to a developing unit that develops a recording medium, and a shutter that closes when the development is completed. A developing device comprising a developer returning means for returning the developer existing in a developer supply passage between the shutter and the developing portion to the developer supply passage upstream of the shutter, the shutter and the developing portion. Between the toner concentration detecting sensor for detecting the toner concentration in the developer supplied to the developing unit and the toner concentration detecting sensor for detecting a level corresponding to a predetermined toner concentration lowering state at the end of development, And a timer circuit that controls the time so that a certain amount of toner is replenished to the developer supply passage on the upstream side of the shutter after the shutter is closed.

[Action]

With the above configuration, when the toner concentration detection sensor detects a predetermined toner concentration decrease state at the end of development, even if the magnetic brush is not formed in the developing unit even if the shutter is closed and the magnetic brush is not formed in the developing unit, a certain amount of toner is discharged. Is replenished. As a result, even when the developing time is short, it is possible to reinforce a certain amount of toner regardless of the developing time. Therefore, as a result of keeping the toner density substantially constant, the image density can be kept good, and the adhesion of the carrier to the recording medium can be prevented to maintain high image quality.

Also, by providing the above timer circuit,
The sampling of the toner concentration detection sensor can be set to a very short time interval at the end of development.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

As shown in FIG. 1, inside the developing tank 1 in which the developer is stored, the developing tank 1 is disposed so as to face the photoconductor 3 as a recording medium,
A developing magnet roller 2 for developing a developer by forming a magnetic brush with a magnetic force to bring the developer into contact with an electrostatic latent image on the photoconductor 3 is rotatably attached. The developing magnet roller 2 constitutes a developing portion of the developing device, and has a rotatable cylindrical non-magnetic sleeve having an outer peripheral portion made of A or the like and is rotatable with respect to the developing tank 1. Being directed. Inside the non-magnetic sleeve, a magnet magnetized around each pole is fitted, and the S pole of this magnet forms a main pole and is fixed to the developing tank 1 so as to face the photoconductor 3. Has been done. With this configuration, when the non-magnetic sleeve rotates, the developer is magnetically attracted to the surface of the non-magnetic sleeve, and the developer moves along the magnetic force of the main pole of the magnet facing the photoconductor 3. Are formed in a brush shape, and the magnetic brush slides on the electrostatic latent image formed on the photoconductor 3 to transfer it to the photoconductor 3, whereby the photoconductor 3 is developed.

Above the developing magnet roller 2, a carrying magnet roller (developer returning means) 4 for pumping up the developed developer and carrying the developer to a portion where the developer is stirred is attached. This transport magnet roller 4 is
It has the same structure as the above-mentioned developing magnet roller 2, and rotates the non-magnetic sleeve, and the magnetic action of the magnet in a fixed state with respect to the developing tank 1 causes the developer on the surface of the non-magnetic sleeve. Are transported in a state of being magnetically attracted.

The scraper 5 for scraping off the developer on the surface of the non-magnetic sleeve is provided in contact with almost the top of the transport magnet roller 4. The scraper 5 is arranged in a downwardly inclined state from one end to the other end, and the other end of the scraper 5 is extended to a stirring section for stirring the developer.

Further, toner is supplied from a toner hopper (not shown) to a developer supply passage inside the developing tank 1, and the toner is supplied into the developing tank 1 based on a command from the toner concentration control means. The developer is agitated and mixed with the developer, and is fed to the agitator.

The agitating section described above is provided with a rotatably provided agitating roller 6 and a cylindrical shutter fitted concentrically with the outer circumference of the agitating roller 6 and having slits 7a, 7a on opposing walls on the circumference. 7 and 7. The agitating roller 6 is arranged in the middle of a developer supply passage for supplying the developer sent by the carrying magnet roller 4 to the developing magnet roller 2. The shutter 7 and the agitating roller 6 are independently controlled in rotation, and when the slits 7a, 7a of the shutter 7 are set to open the developer supply passage as shown in FIG. While the supply of the developer to the developer is controlled, the shutter 7 is rotated by an angle of about 90 ° from the state shown in FIG. When set in the closed state, the developer supply passage is blocked, and the supply of the developer is stopped.

Then, while the electrostatic latent image formed on the photoconductor 3 is being developed, only the necessary developing device sets the shutter 7 to the open state to prevent the developer from being applied to the developing magnet roller 2. When the supply of the toner is continued and the development of the electrostatic latent image on the photoconductor 3 is completed and the shutter 7 is still open, the toner concentration detection sensor 9 described later detects the toner concentration, and then the shutter 7 is released. Rotate 90 degrees to release the shutter 7
The slits 7a, 7a of the developing tank 1 are closed by the curved portion 1a of the developing tank 1 and the partition member 11, while the developer supply passage is shut off by the wall portion of the shutter 7, and the shutter 7 is closed to the developing magnet roller 2. Is configured to stop the supply of the developer.

Further, in the developer supply passage between the shutter 7 and the developing magnet roller 2 serving as the developing section during the supply of the developing agent to the developing magnet roller 2, the developing agent attracted to the developing magnet roller 2 is developed. A regulating doctor grade 8 for regulating the amount of the developer is provided, and the regulating doctor grade 8 is a toner for detecting the toner concentration of the developer supplied to the developing magnet roller 2 which is the developing section. A density detection sensor 9 is attached.

The toner concentration detection sensor 9 is connected to a timer circuit 10 for time-controlling a toner concentration control means for replenishing toner, and the concentration of toner supplied to the developing magnet roller 2 is, for example, a fixed value or less. If so, the toner concentration detection sensor 9 is at a constant level (for example, High
h) is detected, the timer circuit 10 is turned on, the toner concentration control means is operated for a preset time by the timer circuit 10, and a certain amount of toner is replenished to the developer supply passage after the shutter 7 is closed. Is configured to.

In the above configuration, when the non-magnetic sleeve of the developing magnet roller 2 is rotated in the arrow direction of FIG. 1 during development, the developer formed by being magnetically attracted to the surface of the non-magnetic sleeve. Magnetic brush rubs the electrostatic latent image formed on the photoconductor 3 to develop it.

The developed developer is drawn up by the developing magnet roller 2 and transferred to the carrying magnet roller 4. In the carrying magnet roller 4, the non-magnetic sleeve rotates in the direction of the arrow in FIG. 1, so the developer is carried while being magnetically attracted to the surface of the non-magnetic sleeve,
After that, the developer is scraped off from the surface of the non-magnetic sleeve by the scraper 5.

The developer scraped off by the scraper 5 is stirred and mixed with the toner, and then transferred to the stirring unit along the scraper 5.

In the stirring unit, when the shutter 7 is rotated and set to the open state as shown in FIG. 1, the developer flows into the stirring roller 6 from the slit 7a on the entrance side of the shutter 7, and the developer is here. Is stirred. Then, the stirring roller 6
Is sent out from the slit 7a on the exit side of the shutter 7, and the developer is sent to the developing magnet roller 2 through the developer supply passage, and is again provided for development by the developing magnet roller 2 forming the developing section. Become.

Next, when the development is to be ended, the shutter 7 is rotated about 90 to shut off the developer supply passage. As a result, the developer is not sent to the developing magnet roller 2, so that the magnetic brush is not formed on the non-magnetic sleeve of the developing magnet roller 2, and therefore the photoreceptor 3 is not developed.

After the magnetic development is completed, as shown in FIG. 2, the toner concentration detection sensor 9 is provided after the development is completed (S1) and before the shutter 7 blocks the developer supply passage.
Detects the toner concentration (S2), and if the sensor level of the toner concentration detection sensor 9 is, for example, High, after closing the shutter 7 (S3), the drive system of each roller 2, 4, 6 is stopped. From (S4), the timer of the timer circuit 10 is turned on (S5). When the timer circuit 10 is turned on, the toner concentration control means is started to start toner replenishment (S6), and the toner concentration control means is operated for a preset time (S7), and a predetermined amount of toner is supplied. Are replenished (S8).

If the toner concentration detection sensor 9 does not reach a certain sensor level when the toner concentration is detected, the toner concentration is within the allowable range and toner replenishment is not yet required. After closing (S
9) Stop the drive system of each roller 2, 4 and 6 (S1
0), toner is not replenished.

[Effect of device]

As described above, the developing device according to the present invention includes the shutter that can open and close the developer supply passage to the developing unit that develops the recording medium, and the shutter and the developing unit when the shutter is closed after the development is completed. And a developer returning means for returning the developer existing in the developer supply passage between the shutter and the developing unit to the developer supply passage on the upstream side of the shutter. Toner concentration detecting sensor for detecting the toner concentration in the developer supplied to the developing unit and when the toner concentration detecting sensor detects a level corresponding to a predetermined toner concentration lowering state at the end of development, the toner concentration is fixed after the shutter is closed. And a timer circuit for controlling the time so as to replenish a certain amount of toner to the developer supply passage on the upstream side of the shutter.

As a result, at the end of development, when the shutter is still open and the magnetic brush is being formed by the developing unit, and the toner concentration detection sensor detects a predetermined toner concentration low state, the shutter closes. Even after the magnetic brush is no longer formed in the developing portion, the timer circuit replenishes a certain amount of toner, so that a certain amount of toner can be reinforced regardless of the developing time in which the magnetic brush is formed. Therefore, as a result of keeping the toner density substantially constant, it is possible to keep the image density good, and it is possible to prevent the carrier from adhering to the recording medium and maintain high image quality. In addition, by providing the timer circuit as described above, the effect that the sampling of the toner concentration detection sensor can be set at an extremely short time interval at the end of development is also achieved.

[Brief description of drawings]

1 and 2 show an embodiment of the present invention. FIG. 1 is a vertical sectional view showing the entire structure of a developing device, and FIG. 2 is a flow chart showing a toner replenishing process. 1 is a developing tank, 2 is a developing magnet roller (developing section),
Reference numeral 3 is a photoconductor (recording medium), 4 is a conveying magnet roller (developer returning means), 6 is a stirring roller, 7 is a shutter, 7a is a slit, 9 is a toner density detection sensor, 10
Is a timer circuit.

Claims (1)

[Scope of utility model registration request] 1. A shutter that can open and close a developer supply passage to a developing unit for developing a recording medium, and a developer supply passage between the shutter and the developing unit when the shutter is closed after development is completed. A developing device comprising a developer returning means for returning the existing developer to a developer supply passage on the upstream side of the shutter, the developer being supplied to the developing section between the shutter and the developing section. Of the toner density detecting sensor for detecting the toner density of the
A developing device, comprising: a timer circuit for controlling time so that a certain amount of toner is replenished to a developer supply passage upstream of the shutter after the shutter is closed.