JPS6140989B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates generally to an electrophotographic developing apparatus, and more particularly to an electrophotographic developing apparatus equipped with means for detecting the concentration of a developer composed of a mixture of carrier and toner. Generally, electrophotographic or electrostatic development methods use a developer consisting of a mixture of carrier and toner. For this reason, when applying a magnetic development method, for example, the mixing ratio of the magnetic carrier of the developer and the toner (eg, colored resin fine powder) is an extremely important factor in terms of the development effect. That is, the developer attached to the magnet rubs against the electrostatic latent image, and the latent image is developed with toner. As a result, toner is gradually consumed from the developer and the ratio of toner to carrier is reduced, that is, the density of the developer is reduced and the density of the developed image is gradually reduced. Therefore, toner is appropriately replenished, but in this case, if more toner is replenished than appropriate, the image density becomes too high and fogging increases. Therefore, in order to continuously obtain images with desirable color tones, it is necessary to maintain the concentration of the developer at an appropriate level and at all times. Conventionally, several methods are known for automatically controlling the concentration of developer. It uses different colors of carrier and toner, and uses the fact that the mixed color density of developer, which is a mixture of carrier and toner, changes as the toner is consumed, and optically detects the change. The mechanism for replenishing toner to the developer is controlled accordingly to keep the developer concentration constant. However, this method cannot be used if the color tones of the carrier and toner are similar, and it is not practical because it has drawbacks such as the color detection optical system becoming dirty due to toner scattering and not being able to detect an appropriate density. Nakatsuta. SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic developing apparatus to which a density detection means having a completely different principle from the optical detection method described above is applied. The principle of concentration detection in the present invention will be described below. The specific gravity of the developer carrier is significantly greater than that of the toner. For example, in the magnetic development method, metal powder such as iron, iron oxide, or nickel is generally used as the carrier, and colored resin powder is used as the toner. In other words, the toner being developed occupies a sufficient volume to be detectable. The volume of the developer composed of the carrier and toner decreases as the toner content ratio in the developer decreases toward the volume of the carrier alone. Therefore, the developer concentration can be determined by the decrease in the volume value of the developer. FIG. 1 shows the relationship between the volume of a developer made of a mixture of iron powder and styrene resin and the toner content ratio. As described above, since the present invention utilizes changes in the volume of the developer determined by the total volume of the carrier and toner to determine the toner concentration in the developer, all physical quantities of the carrier and toner, such as (specific gravity)・It has the advantage of being able to accurately detect objects with the same hue, electrical permeability, conductivity, magnetic permeability, etc.). The present invention utilizes the above-mentioned physical phenomena to detect and adjust the developer concentration, thereby making it possible to always obtain stable images. A detailed explanation will be given below based on the drawings. In Fig. 2 and Fig. 3, reference numeral 1 denotes a fixed magnet installed in a rotating sleeve 2 (preferably non-magnetic or semi-magnetic) with arbitrary polarity. The magnets within the sleeve are arranged with suitable magnetic poles so that the magnetic field on the surface of the sleeve substantially opposite to the development position is so weak that it cannot attract developer, or becomes zero. Then, a developer D having a magnetic carrier and colored charged particles is sucked and pumped up from inside the developer container 3 to form a magnetic brush. The pumped-up magnetic brush is then formed into a fixed amount by the regulating plate 4. The magnetic brush rubs the surface of the photosensitive drum 5 rotating in the direction of the arrow to develop the image. The rotation of the sleeve weakens the magnetic attraction of the magnetic brush from the fixed magnet in the sleeve after the development has been completed, and the magnetic brush is scraped off by the scraper 6 provided on the sleeve as the magnetic attraction weakens. An inclined partition plate 7 is provided at the position where the developer falls, and a conveyor blade 8 inclined in the axial direction of the sleeve is provided on the inclined partition plate. The developer moves on the inclined support plate 7 according to the conveyor blades 8, and is displaced in the axial direction of the sleeve by the falling force due to the developer's own gravity and the momentum of the centrifugal force due to the rotation of the sleeve, while developing a certain amount. The agent is stirred and moved. The developer sent in the axial direction of the sleeve finally falls from the first hole 11 onto the conveyance screw roller 10 in the developer passage 9 provided separately from the developer container at the rear end of the sleeve in the axial direction, and is tilted. Split plate 7
It is conveyed in the opposite direction to the conveyance direction by the upper conveyor blade 8. Finally, it is sent back into the developing container through the second hole 12 by the conveying force of the conveying screw roller 10 and the magnetic attraction of the magnet in the sleeve, and is attracted by the sleeve-type magnetic roller to be used for development. By the way, the conveying screw 10 is constructed to have a developer conveying capacity 20 to 40% greater than that of the conveying blade 8. With this configuration, all the developer returned to the front position by the transport blade is sent to the back position by the transport screw, and is swelled upward by the transport force of the screw. The level of the developer at the rear position changes as shown in FIG. 4, depending on the amount of developer in the developer container. A broken line 13 indicates a small amount of developer, and a solid line 14 indicates a large amount of developer. As a result of the experiment, the upper and lower positions of the level changed by about 1 cm due to a change in the amount of developer of 30 c.c. This corresponded to a 1% change in toner density when only toner was consumed by development. The level position change becomes maximum by setting the diameter of the developer transfer hole 11 of the dividing plate 7 so that the developer sent by the conveyor blade 8 just passes through, and the level position detection becomes extremely difficult. This makes it easier. In the embodiment shown in FIG. 4, a method using an electric, magnetic, extra-light, ultrasonic, or other detection element as the detection means 15 can be applied. When the developing position level is detected by the detection means 15, it is then judged by the discrimination circuit 18, and the solenoid 20 is operated according to the output signal from the discrimination circuit 18, and the toner replenishing device 19
Toner is replenished from In FIG. 5, a case will be explained in which a micro-operation microswitch, which is the simplest method, is used as the detection means. Numeral 16 is a float that comes into contact with the developer and moves up and down as the level changes. This float is micro switch 1
7 is connected to the switch according to the vertical movement.
Turn ON and OFF. The electric signal from the microswitch is discriminated by a discrimination circuit 18. Reference numeral 19 denotes a device that replenishes toner into the developing device according to the output signal from the discrimination circuit 18, and uses the suction force of the solenoid 20 to control the drop hole of the toner falling from the hopper to the developing device, thereby improving the image quality. This control means is designed to promptly replenish toner consumed due to printing. The amount of toner replenishment can also be controlled by using a timer circuit to control the operating time of the hopper. As another embodiment, shown in FIG. 6, changes in magnetic permeability due to the level of magnetic developer are detected as changes in coil inductance. A coil L is used as the detection element 21, and is coupled with a capacitor C to form a resonant circuit. Developer level is curve 14
, that is, when the detection coil is close to or immersed in the developer, the magnetic permeability increases, the inductance of the coil increases, and the resonant circuit reaches a resonance point. Also, when the developer level is on curve 13, that is, when the developer moves away from the coil, the magnetic resistance of the coil increases, the inductance value decreases, and the coil deviates from the resonance point. 2
2 is the resonant frequency

It is an oscillation circuit that emits the expression [Formula], and 23 is an amplifier circuit that amplifies the output from the resonant circuit. The output from the amplifier circuit is discriminator circuit 1
8, and the toner replenishing devices 19 and 20 are activated. FIG. 7 shows a different embodiment from FIG. 2, in which the developing device of the present invention is implemented using two screws. The same symbols as in FIG. 2 indicate the same things. The screw 24 is set so as to be buried in the developer, and exhibits constant developer transport. The screw 25 is configured to have a greater conveying capacity than the screw 24. Reference numeral 7 denotes a dividing plate for the screw, which is set so that the developer is moved and accumulated in the back side appropriately, and a means for detecting the developer level is provided at this position. It is. Although various other developing means are known, the developer concentration detecting means described above is applicable to any of them and is included in the present invention. According to the present invention, since it is possible to amplify at a local position the volume change accompanying the toner consumption of the developer flowing and circulating in the developing device, even an extremely small volume change can be easily and accurately detected. I can do it. Further, even when replenishing the amount of developer in accordance with the detection, the replenishment result can be accurately detected, so that highly accurate density control can be performed.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between developer volume and toner content ratio, FIG. 2 is an embodiment of the developing device of the present invention, FIG. 3 is a partial perspective view of FIG. 2, and FIG.
5 and 6 are views showing respective embodiments of the toner concentration detection means, and FIG. 7 is a view showing another embodiment of the developing device of the present invention. In the figure, 1 is a magnet, 2 is a non-magnetic sleeve, and 4 is a magnet.
is a regulation plate, 5 is a photosensitive drum, 7 is a tilted dividing plate, 8
1 is a conveyor blade, and 15 is a detection means.

Claims (1)

[Scope of Claims] 1. A first conveyance means for conveying the developer in the developer container in the longitudinal direction of the developer container; A second conveyance means that conveys the developer in a direction opposite to the conveyance direction, and is arranged between the first and second conveyance means, and supports movement of the developer in the developer conveyance direction with respect to the longitudinal direction of the developer container. a dividing plate to be cut; developer transfer holes provided at both ends of the dividing plate in the longitudinal direction of the developing container to allow the developer to be transferred between the first and second conveying means; In the vicinity of the hole for moving the developer from the conveyance means to the first conveyance means and on the side of the second conveyance means, according to the developer position level of the developer conveyed by the large conveyance force of the second conveyance means. An electrophotographic developing device comprising: a detection means for detecting developer concentration; and a means for controlling replenishment of developer according to a signal from the detection means.