JPH11311887A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming device equipped with a developing device being free from applying load on a developing roller, regardless of driving the developing device for the speeding up. SOLUTION: This is the color image forming device provided with developer feed preventing means 31 capable of allowing the developer to be present on the developing roller 4 only at the time under development. Meanwhile, in the case that the developer is not present on the roller surface 4A when the developer feed preventing means 31 is operated, a drive of the developing roller 4 is stopped. In addition thereto, the device is constituted so as to operate an agitating device 27, a replenishing device 29 and a developer density detecting means (a toner density sensor 28).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic color image forming apparatus such as a printer, a copying machine, and a facsimile.

[0002]

2. Description of the Related Art Various types of developing devices have been proposed for use in an electrophotographic color image forming apparatus, and they are roughly classified into a one-component developing device and a two-component developing device.
In the one-component developing device, if the toner is softened to improve the color development of the toner, the toner gradually adheres to the developing sleeve, and it is difficult to extend the life of the developing device.

On the other hand, a two-component developing device is more advantageous in extending the life than a one-component developing device, but various methods have been proposed to prevent color mixing between the developing devices. It is roughly classified into a supply blocking method. The retracting method of the developing device is characterized in that the developing device is brought close to or in contact with the photoreceptor serving as the image carrier when forming an image, and is separated when the image is not formed, but the developing device itself is moved. Therefore, it is not suitable for miniaturization because of the space required for movement, and it is necessary to adopt a developer supply blocking system for miniaturization.

Hereinafter, a developing device employing a developer supply inhibiting system will be described. FIG. 3 is a sectional view of the developing device, and FIG. 4 is a top sectional view of the developing device. The developing device has an apparatus main body composed of a case 24 having only one opened and a cover 25 also serving as a toner replenishing tank. On the open side of the apparatus main body, there is provided a developing sleeve for transporting developer in a rotational direction. A developing roller 4 having a magnet therein is rotatably supported, and a doctor blade 21 for regulating the thickness of the developer on the developing roller 4 is provided at a position separated from the developing roller 4 by a predetermined distance. The case 24 is integrally formed with the partition plate 2 having a height of about half the height of the case 24.
6, two transport rollers 27 (the developing roller side is 27A, the toner replenishing roller 29 is circulating and transporting the developer in the axial direction of the developing roller 24 across the partition plate 26).
27B), and the developer moves in the direction of the arrow.

Further, the developing roller 4 and the transport roller 27A
A rotary shaft 22 that rotates reciprocally at a certain angle is rotatably supported by a cam, and the rotary shaft 22 has a blocking plate 2 that allows and prevents the supply of the developer to the developing roller 4.
3 is fixed. A toner density sensor 28 is provided directly below the transport roller 27B at the bottom center of the case 24, and the toner supply roller 2 is provided in the case 25 in the axial direction of the developing roller 4.
9 are provided.

Next, the operation of the developing device will be described. In order to prevent color mixing, each developing device forms an electrostatic latent image corresponding to each color, and starts driving when approaching the corresponding developing device, and at the same time, the blocking plate 22 that has been in contact with the developing roller 4. Is moved to the position E by the rotation of the rotating shaft 23, the supply of the developer to the developing roller 4 is allowed, and the electrostatic latent image is converted into a toner image. When the toner image formation is completed, the blocking plate 22 is moved to the position F in contact with the developing roller 4 by the rotation of the rotating shaft 23, and the supply of the developer to the developing roller 4 is stopped. At the same time, the driving of the developing device is stopped. While the supply of the developer to the developing roller 4 is permitted, the toner concentration is controlled and the toner is supplied. In addition, the same method has been adopted when a plurality of monochrome images are continuously formed.

[0007]

As the image forming speed increases, the time required for one developing device to convert an electrostatic latent image into a toner image in a conventional developing device of the developer blocking type is also remarkably increased. Because it became shorter, replenish the developer with toner,
There was a problem that the time was too short to stir and disperse the supplied toner in the developer. For this reason, there is a method in which the developing roller 4 is continuously driven even when the electrostatic latent image is not converted to a toner image to perform toner supply control. However, since the surface of the developing roller 4 is in contact with the blocking plate, the developing roller 4 The driving torque of the developing roller increases, jitter occurs, the surface of the developing roller 4 and the blocking plate wear, and the toner in the developer sandwiched between the sleeve of the developing roller and the blocking plate melts due to frictional heat and the developer aggregates. There was a problem of doing it.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and realizes a color image forming method capable of solving the problem of the driving torque of the developing roller and realizing a good image while realizing a high printing speed. It is intended to provide a device.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a developing roller having a developing sleeve having a magnet therein and for transporting a developer in a rotational direction, and a housing for storing the developer. A stirring device for stirring and mixing the developer, a developer concentration detecting means disposed in the vicinity of the stirring device, and toner in the developing tank according to a detection signal of the developer concentration detecting device. A replenishing device for replenishing, and a developer supply inhibiting means for preventing the developer agitated by the agitating device from being supplied to the developing roller,
A developing device other than the developing device that has a plurality of developing devices arranged on the photosensitive member so as to face the developing roller, and the developing device develops developer from the developing roller to the photosensitive member, the developer supply blocking means is provided. In the color image forming apparatus configured to operate to prevent the supply of the developer to the developing roller, only the rotation of the developing roller is stopped when the developer supply preventing unit is operating. Constitute.

Thus, even if the developer blocking means is operating, since the rotation of the developing roller is stopped, an increase in torque due to the developer applied to the developing roller is prevented. Further, the agitating device, the replenishing device, and the developer concentration detecting device are configured to be operable when the developer supply inhibiting device is operating. Thus, when developing, the developer can be developed immediately with a sufficiently stirred developer, and the speed can be increased. The above-described torque problem can also be solved by configuring the developer supply blocking unit to be a magnet or a magnetic material and configured to block the supply of the developer by a magnetic force without contacting the developing roller. .

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of a color printer having a plurality of developing devices of the present invention. Hereinafter, description will be made according to the numbers in the drawings. In the case of the same as the prior art, the same numbers are used. Reference numeral 1 denotes a configuration of a color printer. The color printer 1 has a photoreceptor 2 rotatably supported. Around the photoreceptor 2, charging is performed to uniformly charge the surface of the photoreceptor 2. The roller 10, an exposure unit 11 such as a laser scanner, a black developing device 3 </ b> B having a developer containing a black toner, and a developing device containing a yellow toner are arranged in this order from the rotation direction upstream side of the photoconductor with respect to the charging roller 10. Developing device 3Y having a developer, magenta developing device 3M having a developer containing magenta toner, cyan developing device 3 having a developer containing cyan toner
C, a transfer drum 12 is provided.

In each of the developing devices, developing sleeves 4B, 4Y, 4M, and 4C are arranged with a predetermined gap from the photosensitive member 2. Inside the transfer drum 12, a first transfer roller 13 for transferring the toner image formed on the photoconductor 2 to the transfer drum is arranged. A second image transfer unit that transfers an image to a sheet S from a sheet feeding unit (not shown) in contact with the transfer drum 12.
A transfer roller 14 is provided.

Next, the operation will be described. The surface of the photoconductor 2 is uniformly charged by the charging roller 10. And
The charged photoreceptor 2 is subjected to light writing by exposure to cyan in accordance with a signal from a computer (not shown) or the like in an exposing unit 11 to form an electrostatic latent image. Then, this electrostatic latent image is developed in cyan by the developer of the developing device 3C to become a toner image. This toner image is transferred to the transfer drum 12 by the first transfer roller 13. The same operation is performed for each color, and a toner image of each color is superimposed on the transfer drum 12 to obtain a color image by subtractive color mixing. Then, the sheet is conveyed out of the apparatus through a fixing process such as heating.

Next, a developing device according to the present invention will be described with reference to FIGS. FIG. 2 is a sectional view of the developing device according to the present invention. The developing device has an apparatus main body composed of a case 24 having only one opened and a cover 25 also serving as a toner replenishing tank. On the open side of the apparatus main body, there is provided a developing sleeve for transporting developer in a rotational direction. A developing roller 4 having a magnet therein is rotatably supported.
A doctor blade 21 that regulates the thickness of the developer on the developing roller 4 and a sleeve 31 that is a developer supply inhibiting unit of the present invention are disposed at positions spaced apart from the developing roller 4 by a predetermined distance, facing the developing roller 4. I have. A magnet 32, which can rotate by a predetermined angle and can face each other, is rotatably supported inside the sleeve 31. Therefore, when the magnet 32 rotates so as to face the developing roller 4,
The magnetic shield formed here is configured to prevent the developer supplied from the transport roller from being supplied to the developing surface 4B of the developing roller 4. In this embodiment, the magnets 32 are arranged in the sleeve 31. However, the present invention is not limited to this. The magnets 32 may be used. Further, it is more preferable that the magnet body 32 has the same polarity as the carrying pole of the magnet in the developing roller (not shown) because the magnetic shielding effect is enhanced.

The case 24 is formed integrally and is partitioned by a partition plate 26 having a height of about half the height of the case 24. As shown in FIG. Two transport rollers 27A and 27B for circulating and transporting the developer in the axial direction of the roller 24 are arranged, and the developer moves in the direction of the arrow.

The transport roller 27B at the center of the bottom of the case 24
A toner concentration sensor 28 is provided directly below the developing roller 4, and a toner supply roller 29 is provided in the case 25 in the axial direction of the developing roller 4. The toner density sensor is configured to measure the magnetic permeability of the mixture of the carrier and the toner of the two-component developer, and the toner replenishment roller 29 is intermittently rotated by the toner density sensor 28 to repeat replenishment and non-replenishment.

The developing roller 4 and the conveying rollers 27A,
The drive system of 27B is separate, and the rotation drive system of the developing roller 4 is stopped during non-development, which is a feature of the present invention, so that the toner is stirred by the transport roller 27 and the toner density is detected. . Since such an operation is performed during the non-development, the speeding up of the apparatus is realized.

Next, the operation of the developing device will be described. Each developing device is driven at the same time when the printer main body starts driving each unit such as the photosensitive member 2 according to an instruction from a computer or the like (not shown). The toner replenishment control is performed except when warming up immediately after the power is turned on and before driving before forming the first electrostatic latent image after the power is turned on. When the toner is insufficient, the toner is replenished.

Next, an electrostatic latent image corresponding to each color is formed.
When the developing roller 4 approaches the developing device, the developing roller 4
Is rotated to the position H, the supply of the developer to the developing surface 4A of the developing roller 4 is allowed, and the electrostatic latent image is converted into a toner image. . While the supply of the developer to the developing roller 4 is permitted, the amount of the developer in the developing tank is temporarily changed, so that the toner density control is not performed. Since the output of the toner sensor becomes unstable because the amount of developer in the developing tank changes suddenly,
After the supply of the developer to the developing roller 4 described below is stopped, the toner replenishment control is resumed after a certain period of time determined by the capability of the developing device, and is continued until the drive system of the developing device stops.

When the toner image formation is completed, the rotation of the developing roller 4 is stopped, and the magnet 32 rotates from the position H to the position G to prevent the supply of the developer to the developing roller 4. I do. However, the transport roller 27, the toner replenishing roller 29, and the toner density sensor of the developing device continue to be driven until the printer body stops driving each unit.

Next, in the case where a plurality of monochrome images are continuously formed according to an instruction from a computer or the like (not shown), the printer detects that a continuous image is to be formed.
By this detection, when the printer main body starts driving each unit such as the photoconductor 2, the magnet 3 of the corresponding developing device
2 is rotated from the position G to the position H to allow the supply of the developer to the developing roller 4 which is being blocked. In addition, by detecting this continuous printing, the final printing time is calculated, the timing of the movement from the position H to the position G and the stop of the developing roller 4 are determined, and the electrostatic latent image is continuously converted into a toner image.

In this case, after the last toner image formation is completed, the supply of the developer to the developing roller 4 is prevented by rotating the magnet 32 from the position H to the position G rather than stopping the driving of the developing roller 4. Is performed first. This timing is determined by the value calculated by the continuous printing detection described above,
2 is moved from the position H to the position G, the developing roller 4 is rotated until at least the developer is not present on the developing surface of the developing roller, and then the rotation of the developing roller 4 is stopped. The reason for performing such control is that the driving is stopped in a state where the developer is unevenly distributed on the developing surface 4A of the developing roller 4, and the toner density control becomes inaccurate at the time of the next color image formation. Because it is.

[0023]

According to the above construction, when the developer is not supplied to the developing section on the surface of the developing roller by operating the developer supply inhibiting means during non-development, only the rotation of the developing roller is stopped. By configuring the stirrer, the replenishing device, and the developer concentration detecting means to be operable, the rotation of the developing roller is stopped even if the developer blocking means is operating. The driving torque is increased and jitter does not occur, thus making it possible to supply a good developer. In addition, when the next development is performed, a sufficiently stirred developer can be immediately supplied and developed, so that the speed can be increased without waiting for the toner concentration to be in an optimum state. Further, since the developer supply inhibiting means is constituted by a magnet or a magnetic material, and is configured to prevent the supply of the developer by a magnetic force without contacting the developing roller, the developer supply inhibiting means has a configuration similar to that of the conventional developer supply inhibiting system. It is possible to provide an apparatus which does not cause a problem that the sleeve of the developing roller and the blocking plate are worn, and that the toner in the developer sandwiched between the sleeve and the blocking plate of the developing roller is melted by frictional heat and the developer is aggregated.

[Brief description of the drawings]

FIG. 1 is a schematic view of a color printer having a developing device of the present invention.

FIG. 2 is a cross-sectional view of the developing device of the present invention.

FIG. 3 is a cross-sectional view of a conventional developing device.

FIG. 4 is a top cross-sectional view of the developing device.

[Explanation of symbols]

 1: Color printer 2: Photoreceptor 4: Developing roller 4A: Developing surface 24: Case 25: Cover 26: Partition plate 27: Conveying roller 28: Toner density sensor 29: Toner supply roller 31: Sleeve 32: Magnet

Claims (3)

[Claims] A developing roller having a developing sleeve for transporting the developer in a rotational direction, the developing roller having a magnet therein, and a stirring device for stirring and mixing the developer in a developing tank containing the developer. A developer concentration detecting means disposed in the vicinity of the stirring device; a replenishing device for replenishing the developing tank with toner in accordance with a detection signal of the developer concentration detecting device; and a developer stirred by the stirring device. And a developer supply blocking means for preventing the developer from being supplied to the developing roller, and a plurality of developing devices arranged on the photosensitive member so as to face the developing roller. In a color image forming apparatus, a developing device other than the developing device that develops on the photoreceptor is configured such that the developer supply blocking unit operates to block the supply of the developer to the developing roller. Agent when the supply blocking means is in operation, the color image forming apparatus characterized by stopping only the rotation of the developing roller 2. A collar according to claim 1, wherein said stirring device, said replenishing device and said developer concentration detecting device are operable when said developer supply inhibiting device is operating. Image forming device. 3. The developer supply blocking means is constituted by a magnet or a magnetic material, and configured to block the supply of the developer by a magnetic force without contacting the developing roller. The color image forming apparatus as described in the above.