JPH0218583A - Developing device - Google Patents

Abstract

PURPOSE:To agitate a developer and to prevent irregular toner density and a deficiency in electrostatic charging by carrying on driving operation for a prescribed time at a lower speed at the end of development than in developing operation. CONSTITUTION:A control means operates at the end of the developing operation and conveyance parts 61 and 62 of a developing unit are drive continuously for the constant time at the lower speed than in the developing operation. A developer is therefore agitated even not in the development time to compensate an irregularity in toner density and a deficiency in electrostatic charging, thereby improving picture quality. Further, the agitation is carried out at the low speed only for the prescribed time, so the deterioration of the developer due to overagitation is not caused. The agitation is carried out even no in the development to supply toner during the low-speed driving according to the toner density detection of the developer, so that an image of high quality with constant density is secured.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a developing device used in an electrophotographic image forming apparatus such as a copying machine or a laser beam printer, and particularly relates to a developing device using a two-component developer. It is.

(Prior Art) This type of developing device stirs the developer in a circulation path so that the toner concentration of the developer, that is, the amount of toner relative to the carrier, is uniform, and the toner is appropriately charged by friction. During the general transport, a part of the film is subjected to development.

On the other hand, it is desirable that the developed image density after development be constant with respect to a specific set density. However, each time the developer is used for development, toner is consumed and the toner density decreases, causing a decrease in image density. To solve this problem, a density detection means detects the toner density or the developed image density after development.
Conventionally, when the detected density is below a predetermined value, toner is replenished to the developer being circulated (Japanese Patent Laid-Open No. 62-28780).

(Problems to be Solved by the Invention) However, even if toner is replenished in response to a shortage of toner concentration, if the toner is not sufficiently stirred, the toner concentration may become non-uniform or the toner may be insufficiently charged. This causes image unevenness and insufficient density.

Therefore, it is conceivable to continue transporting the developer even after the development is completed. However, simply continuing to drive the developing device may cause the developer to be excessively agitated and deteriorated. In addition, even during non-development, power consumption is significant and noise is high.

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device that can sufficiently agitate the developer and eliminate uneven toner concentration and insufficient charging without such problems.

(Means for Solving the Problems) In order to achieve the above-mentioned objects, the present invention provides a developing device that agitates and conveys a two-component developer in a circulation path and performs development on the way. The present invention is characterized in that it includes a control means for continuing to drive the conveying section at a lower speed than during the time-developing operation.

It is preferable to drive the conveyance unit at low speed even during non-development periods during continuous image forming operations, and toner replenishment may be performed based on the detection of the toner concentration of the developer while the conveyance unit is driven at low speed. .

(Function) By driving the developing device at a predetermined speed during development,
The developer can be stirred and transported at a predetermined speed and subjected to development at a predetermined speed midway through, thereby achieving a predetermined development function. When the development is completed, the control means causes the conveying section to continue driving at a lower speed than during the development operation for a predetermined period of time, so that the developer is stirred even when not during development to compensate for uneven toner concentration or insufficient charging. You can leave it there. In addition, stirring at times other than during development is performed at a low speed and only for a predetermined period of time, so that it is possible to prevent excessive stirring and deterioration of the developer. Furthermore, since it is driven at low speed, power consumption is low and noise is low.

1. If the general feed section is driven at low speed not only at the end of the image forming operation, but also during non-developing periods during continuous image forming operations, the number of machines used to stir the developer increases accordingly. In response to the fact that toner is replenished every time a shortage of toner concentration is detected, it is possible to quickly eliminate temporary uneven toner concentration or insufficient charging of replenished toner due to toner replenishment. can.

If you replenish toner based on the detection of the toner concentration of the developer while the transport section is running at low speed, it is necessary to replenish the toner during non-development and thoroughly stir it to eliminate uneven toner concentration and insufficient charging. This can reduce the need for toner replenishment during development, which greatly limits the amount of toner replenishment at one time due to temporary uneven density or insufficient charging, and reduces the need for toner replenishment during development. The influence of toner replenishment can be prevented.

(Embodiment) FIG. 1 shows a simplified internal structure of a full-color copying machine 1 showing an embodiment of the present invention, and is equipped with four types of developing devices. The original placed on the original glass 2 is exposed to the CCD line sensor 5 by an exposure lamp 3 and lens array 4, and is read as color signals of three primary colors: R (red), G (green), and B (blue). . This RGBO
The color signals are converted into Y (yellow) and M by the image processing circuit.
(magenta), C (cyan), or a three-value or four-value signal including Bk (black), and is transmitted to the laser optical system 6 as an output signal. The copying machine of this embodiment does not have an image memory for three colors, and the image league unit 7 scans each time when forming an image for each color, and based on this, Y, MSC or Y, MSC1Bk signals are sequentially transmitted to the laser optical system 6. can be conveyed to.

The laser optical system 6 includes a scanning polygon mirror 8, an fθ lens 9, a reflection mirror 10, etc., and emits image forming laser light for each color based on the Y, M, C or Y, M, C, Bk signals. Exposure is performed by irradiating the light onto the photosensitive drum 11. The photosensitive drum 11 is rotationally driven in the direction of the arrow. The surface of the photosensitive drum 11 is provided with an organic photoreceptor formed into a laminated unit on a conductive substrate, and in particular, the photosensitive drum 11 has a laser emission wavelength of 780 nm.
Those showing high sensitivity around nm i4 are used.

Further, in this embodiment, the photosensitive tram 11 is negatively charged by a charger 12. A drum cleaner 13, a toner collection roll 14, an eraser lamp 15, and the charger 12 are arranged around the photosensitive tram 11, as well as the four types of developing devices. The first developer 16 uses yellow toner, the second developer 7 uses magenta 1-toner, the third developer 16 uses cyan 1-toner, and the fourth developer 16 uses cyan 1-toner. Reference numerals 19 supply toners of blank color, and toners 1 to 19 are negatively charged. In addition, the 1~ner replenishment is performed by the 1~ner supply of each color that is checked on the I~nerbo sopar 20a~20d.
Based on the toner replenishment signal, each developing device 16.17.1
8.19 via pipe 8 (not shown).

Recording materials 56 such as plain paper and 0IIP film are stored in stacks in paper feed cassettes yl-21a and 2Fh, and are bent and fed into the apparatus one by one by paper feed rollers 22a and 22b. Then, when the leading edge contacts the register roller 23, the recording material 56 is temporarily stopped to determine the subsequent timing and perform skew correction at the same time.

24 is a paper sensor used for this purpose.

A transfer drum 25 is provided at the transfer portion of the photosensitive drum 11 and is driven to rotate in the direction of the arrow. Inside this transfer drum 25, a suction charger 26 and a transfer charger 2 are arranged along the circumferential direction.
7. A separate charger 28 is provided. Further, a transfer charger 29 is provided inside the photosensitive drum 11 facing the transfer charger 27, and a separation charger 30 is provided on the outer side of the transfer drum 25 facing the separation charger 28.
is installed.

The electrostatic latent image formed on the photosensitive drum 11 by exposure by the laser optical system 6 is visualized as a toner image by any one of the developing devices 16 to 19.

On the other hand, the recording material 56 fed from the sister roller 23 is gripped by the gripper 31, and as the transfer drum 25 rotates, the suction charger 26 moves the recording material 56 to the transfer drum 25.
It is attracted to the top and is wound onto the transfer tram 25 as the transfer drum 25 rotates. Then, while the recording material 56 passes between the transfer chargers 27 and 29, the toner image on the photosensitive drum 11 is transferred to the recording material 56. It should be noted that in full color mode, the recording material 56 is transferred by the transfer drum 25 into four
Rotate times.

The recording material 56 after the transfer process is transferred to the separation charger 28
．． 30, the toner is separated from the transfer tram 25 by a sorting claw 32, and fed to a heat fixing device 40 by a transport heald 33. The transferred recording material 56 is heated and pressurized by passing through the heat fixing device 40, and the recording material 56 is
The image is fixed on the sheet 6 and discharged onto the paper discharge tray 35.

Each developing device 16 to 19 is located in the second area (as shown in FIG. 3).
- A developer transport section that repeatedly transports a two-component developer consisting of a mixture of toner and carrier between the forward transport section 61 and the reverse transport section 62 in the direction of the arrow in FIG. 2 while mixing and agitating it. 63, a developing section 65 that transfers the developer from the reverse direction conveyance section 62 of the developer conveyance section 63 to the photosensitive drum 11, and a toner storage section 66 that replenishes toner to the forward direction conveyance section 61 of the developer conveyance section 63. It is equipped with

Each of the conveyance sections 61 and 62 has a gutter-like conveyance path formed adjacently by the bottom of the casing 67, and has a partition wall 70 between them.
partitioned by. However, there are communicating portions 70a and 70 at two locations on the left and right sides of this partition wall 70 in FIG.
b, and communicates with the conveying sections 61 and 62.

The forward conveyance section 61 is provided with a forward agitation general feed roller 71 that conveys the developer while stirring it from the left side to the right side in FIG. A reverse stirring and conveying roller 72 is provided that conveys while stirring from the right side to the left side. Gorera stirring conveyance roller 71.7
2, the developer passes through the conveyance sections 61 and 62 to the communication section 70.
a and 70b while being circulated and stirred.

The reverse agitation transport roller 72 has a bucket 73 that transports the developer transported through the reverse transport section 62 to the developing section 65 .

The developing section 65 includes a developing roller 76 which is made of a non-magnetic conductive material (for example, aluminum) and has a magnetic member 75 built in a developing sleeve 74 that receives a bias voltage, and is held by suction on the surface of the developing roller 76. A brush height regulating member 77 is provided to regulate the spike height of the developer in a magnetic brush state.

Here, the developing sleeve 74 is supplied with the developer conveyed by the reverse agitation conveyance roller 72 through the reverse conveyance path 62 by scooping up the developer from the bucket 73, sucks it onto its surface, and conveys it to the photosensitive drum 11 side. The transported developer forms a magnetic brush along the lines of magnetic force formed by the different poles of the magnetic member 75 being arranged alternately, passes through the portion facing the photosensitive drum 4, and is applied to the surface of the drum. When the electrostatic latent image that has been formed is rubbed, toner is attracted and transferred by a potential stronger than the developing sleeve 74 of the electrostatic latent image, and the electrostatic latent image is visualized.

The developer on the developing sleeve 74 after the above-mentioned development is
After that, when the bucket 73 is conveyed and faces the rotating part, the magnetic poles (S) of the same polarity of the magnet member 75 are lined up next to each other and form a repulsive magnetic field, so that the developing sleeve 74 is separated from the developing sleeve 74. The developer is taken into the developer conveyed through the reverse direction conveyance section 62 and circulated again.

On the other hand, a toner storage section 66 for replenishing toner is partitioned from the forward transport section 61 by a partition wall 80, and a toner hopper 2
Toner is replenished from 0a to 20d.

A toner replenishment port 81 is formed in a portion of the partition wall 80 on the downstream side of the forward conveyance section 61, and toner concentration detection sensors 82a to 82 are provided at appropriate positions upstream of the replenishment port 81.
d faces the conveyance section 61 from the toner storage section 66 side of each of the developing devices 16 to 19. Sensors 82a-B2
The sensor surface d is smooth and substantially flush with the inner surface of the conveyance section 61.

The sensors 82a to 82d detect changes in the toner concentration contained in the developer as changes in magnetic permeability, and output the detected values to the CPU 201 shown in FIG. 5 as a control section. This CPU 201 is for controlling the operation of the copying machine.

By the way, as a carrier material for the developer, an appropriate material such as magnetic iron powder, ferrite, a resin-based coating of these materials, or a material in which magnetic powder is dispersed in a resin material is selected and used. In this example, magnetic ferrite (
A carrier coated with an acrylic resin and having an average particle diameter of φ-30 μm to 40 μm is used. On the other hand, the toner used is one based on polyester resin and has an average particle diameter of about φ-10 μm to 15 μm. The optimum mixing ratio of these carrier materials with toner is 7ωt%~
It is 10ωt%.

Inside the toner storage portion 66, there is a toner receiving port 66a above the toner storage portion 66.
A replenishment roller 83 is provided that brings the toner introduced through the replenishment port 81 toward the replenishment port 81 and sends it out from the replenishment port 81.

As shown in FIG. 4, in each of the developing devices 16 to 19, the rotation of a dedicated developing motor 84a to 84d is transmitted to the rotating shaft 72a of the reverse stirring and conveying roller 72 via gears 85 and 86. Axis of rotation? 2a is rotated by gear 87, B8.
89 to the rotating shaft 71a of the forward stirring conveyance roller 71. Further, the gear 86 is connected to the rotating shaft 83a of the supply roller 83 via gears 90 and 93. As a result, when the motors 84a to 84d are driven, the stirring conveyance rollers 71, 72 and the replenishment roller 83 are simultaneously driven.

Further, a gear 87 is connected to the rotating shaft 74a of the developing sleeve 74, and one of the sleeve clutches 94a to 94d is connected to the rotating shaft 74a of the developing sleeve 74.
．． They are connected via 97. Therefore, motor 84a
Even if ~84d is driven, its rotation is caused by clutches 94a~94.
Whether or not the developing sleeve 74 is driven is determined depending on whether or not 4d is on.

When the developing devices 16 to 19 are not in use, they are driven to replenish toner, but the developing sleeve 74 is stopped so that toner is not supplied to the photosensitive drum 11, that is, development is not performed. This is to do so.

Each of the toner hoppers 20a to 20d is provided with a replenishment motor 98a to 98d. Supply motor 98'a
indicates the toner concentration detection sensor 82a in the corresponding developing device 16.
is activated when the toner concentration detection output by
The toner is supplied to the toner storage section 66 of No. 6. At this time, in the toner storage section 66, the replenishment roller 83 is rotated, so that the supplied toner is sent to the forward direction conveying section 71 through the toner replenishment port 81 to be replenished. Other supply motor 98b
Similarly, hoppers 20b to 98d are activated in response to toner concentration detection in the corresponding developing units 17 to 19, and hoppers 20b to 98d
2 Od of toner is sent out in a timely manner and supplied to the toner storage portions 6G of the developing devices 17 to 19, so that the toner is replenished.

Here, the toner replenishment port 81 is provided at a distance downstream from the toner concentration detection sensor 82, as shown in FIG. Therefore, Δ1 in FIG. 7 when the toner concentration detection sensor 82 detects that the toner concentration is below a predetermined value. To replenish toner to the developer in the area, when the developer in the area ΔL reaches the position of the toner replenishment port 81 indicated by ΔL′ in FIG. The toner must be delivered within 71.

This timing adjustment is performed by adjusting the operation timing of the replenishment motors 98a to 98d, that is, the toner replenishment start timing under operation control by the CPII 201. For this purpose, toner concentration detection sensors 82a to 82d are connected to the CPU 201 via comparison circuits 202a to 202d, and driver circuits 203a to 203d for developing motors 84a to 84d and replenishment motors 98a to 98 are connected to the CPU 201.
8d driver circuits 204a to 204d are connected. Further, the CPU 201 is connected to the ROM 205 as well as other inputs and outputs for controlling the operation of the copying machine 1.

Furthermore, in this embodiment, each of the developing units 16 to 19 is selected and used in sequence to develop a full-color image, but even when not in use, they continue to be driven to agitate and transport toner, and can replenish toner. That's what I do. This makes it possible to eliminate the effects on image quality caused by a delay in the rise of toner concentration due to toner replenishment or insufficient stirring.

However, excessive agitation causes the toner to fuse to the surface of the carrier, resulting in poor charging and other deterioration of the developer. To prevent this, a DC speed control motor is used for the developing motors 84a to 84d.
When the developing units 16 to 19 are not in use, they are controlled to be driven at a lower speed than when in use.

As shown in FIG. 10, this control outputs a speed reduction signal when the developing sleeve tarunches 94a to 94d are turned off at the end of development, and the speed is reduced for a certain period of time t+St! Do this as follows. Time 1. Of course, is determined regardless of the auto-shut of the copying machine main body.

The conveyance speed of the developer in the image forming devices 16 to 19 differs between when they are in use and when they are not in use. This also changes the timing at which the developer whose concentration is detected by the toner concentration detection sensors 82a to 82d reaches the toner replenishment port 81. For this reason, the toner replenishment start timing is also changed at the same time as the conveyance speed is changed.

Also, when the conveyance speed changes, the sensor 82 for toner concentration changes.
The output level of a to 82d changes. For example, the relationship between the rotation speed of the forward stirring conveyance roller 71 and the sensor output is as shown in FIG.
00r, p, m, and the rotation speed when not in use is 10Or, p
, m, the relationship between toner concentration and sensor output is the 9th
As shown in the figure. In order to cope with this, the comparison circuit 20
As shown in FIG. 6, reference voltages 2a to 202d are connected to a reference voltage (11) for the sensor output at high speed and a reference voltage (1) for the sensor output at low speed. This switching is performed automatically by relay contact 206.

Toner replenishment is performed even while developing units 16 to 19 are in use.
This is done every time it is detected that the toner density is below a predetermined value, but when multi-copying is performed, a slowdown signal is issued even when the developer is not in use between each copy, as shown in Figure 11, to prevent excessive copying. It is also possible to enable toner replenishment while preventing stirring. However, in order to prevent this low-speed conveyance from impairing the stability of the high-speed conveyance necessary for copying, it is carried out with a margin of time t2 and t3 before and after the time shown in the figure.

Note that even when toner replenishment is performed based on the detection of the density of the developed image formed on the photosensitive drum, the developed area where the density is detected is the developing area of the specific area in the reverse direction conveyance unit that supplied the toner to that area. Since it represents the toner concentration of the developer, if the developed density is below a predetermined value, toner must be replenished to the developer that was in the specific area at the time it is detected. Therefore, in this case as well, the toner replenishment start timing may be adjusted so that the toner is replenished at the time when the developer present in the specific portion passes through the toner replenishment port, as described above.

Further, the toner replenishment method is suitable not only for full-color copying machines but also for any machine that has two or more developing units and is selectively used.

Further, the developing device can easily adjust the developed density by changing the developing speed. In this case, since the conveyance speed of the developer changes, the start timing of toner replenishment may be changed in accordance with the conveyance speed, as in the case described above.

Although it is preferable to stop the rotation of the developing sleeve during low-speed driving when the developing device is not in use in order to prevent wasteful consumption and spillage of toner, it is not necessary to stop the rotation.

(Effects of the Invention) According to the present invention, at the end of the development operation, the conveying section of the developer continues to be driven at a lower speed than during the development operation for a predetermined period of time due to the action of the control means, so that the developer can be stirred even when not during development. It is possible to compensate for non-uniformity of toner concentration and insufficient charging, and the quality of the fractionation can be improved. In addition, since stirring is performed at low speed and only for a predetermined period of time other than during development, it is possible to prevent excessive stirring from degrading the developer and affecting image quality.

If the conveyance unit is driven at low speed not only at the end of the image forming operation but also during non-developing periods during continuous image forming operations, the number of machines used to agitate the developer will increase accordingly. By replenishing toner each time a lack of density is detected, it is possible to quickly eliminate temporary uneven toner density or insufficient charging of replenishing toner due to toner replenishment. Image quality can be further improved.

If you replenish toner based on the detection of the toner concentration of the developer while the transport section is running at low speed, it is necessary to replenish the toner during non-development and thoroughly stir it to eliminate uneven toner concentration and insufficient charging. Therefore, it is possible to reduce the need for toner replenishment during development, prevent the influence of toner replenishment during development, and ensure high quality with constant density.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the internal structure of a full-color copying machine showing an embodiment of the present invention, FIG. 2 is a cross-sectional view of a developing device taken along a horizontal plane, and FIG. 3 is a cross-sectional view taken along a vertical plane of the developing device. Figure 4 is a perspective view showing the drive mechanism of the developer, Figure 5 is a block wiring diagram of the control circuit, Figure 6 is a detailed diagram of the comparison circuit, and Figure 7 is from the developer toner concentration detection position to the toner replenishment position. Fig. 8 is a graph of the relationship between the rotation speed of the sensor agitation conveyance roller and the sensor output, Fig. 9 is a graph of the relationship between the toner concentration and the sensor output, and Fig. 10 is the drive of the developing device. FIG. 11 is a time chart showing a modification of the drive control state of the developing unit. 16-19-1---------Developer 61.62
−・−−−−−−−−−・Forward and reverse direction conveyance section 71.7
2---------Forward and reverse stirring conveyance rollers 81
----) Toner supply ports 82a to 82d ---- Toner concentration detection sensor 83
--- --- Replenishment rollers 98a to 98d ---- One replenishment motor 201
-・-cpu

Claims (3)

[Claims] (1) A developing device that agitates and conveys a two-component developer in a circulation path while subjecting it to development during the process, is equipped with a control means that continues to drive the conveying section at a lower speed than during the developing operation for a predetermined period of time at the end of the developing operation. A developing device characterized by: (2) The developing device according to claim 1, wherein the low-speed drive of the conveying section is performed even during non-developing times during continuous image forming operations. (3) The developing device according to (1) or (2), wherein toner replenishment is performed based on detection of toner concentration of the developer while the conveying section is driven at low speed.