JPS6262351B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a toner concentration detection device for a two-component developer in a copying machine such as an electrophotographic copying machine or an electrostatic recording device.

Conventionally, various types of methods for detecting the toner concentration of a developer are known. Among these, when using a magnetic carrier for the developer,
Since the amount of carrier in a constant volume changes in response to changes in toner concentration, devices have been used that utilize this to detect changes in the amount of carrier as changes in inductance to control toner concentration. There are also known devices in which the developer flow path is configured as part of a magnetic detection circuit, and the change in the amount of carrier in the developer is detected as a change in inductance to control the toner concentration. .

Incidentally, the permissible control range for the toner concentration of the developer is determined in accordance with the image density of the copying machine, and the toner amount is usually 2±0.2wt% by weight.
controlled to a certain degree. Therefore, factors that change the inductance other than changes in toner concentration must also be held within ±0.2%, and in particular, changes in the flow of developer at the toner concentration detection area may cause a large control error.

Therefore, in order to always flow a constant amount of developer into the toner concentration detection area, we devised the shape and surface condition of the developer passage, but if we continuously flow developer into the detection area, the initial A phenomenon occurred in which the control system was well controlled, but after a certain period of time, it suddenly became unstable. The experimental results of the present inventors are shown in FIG. In the figure, the horizontal axis indicates the operating time of the copying machine or the number of copies, and the vertical axis indicates the inductance of the detection unit. As can be seen from the graph, after a period of time corresponding to the number of copies from 50 to 100 has passed, the inductance rapidly decreases as shown by the solid line. The inventors investigated the cause of this problem and found that the wall of the developer passage near the detection section was charged to a high potential, and the carrier was attached thereto. That is, polyacetal resin was used as the material for forming the developer passage, but since this came into contact with the iron powder carrier and the two were separated in their triboelectrification order, the resin had a tendency to become negatively charged. Ta. The frictional charging relationship between the toner and the carrier is such that the toner is negatively charged and the carrier is positively charged.
It is believed that the carrier adhered to the wall of the developer flow path, which was charged with opposite polarity. In Figure 1,
The charged potential of the resin by the carrier is shown by a broken line. That is, the wall of the developer flow path is triboelectrically charged by the carrier, and the carrier adheres thereto.If the wall becomes charged to a certain extent, the flow of the developer will be disturbed due to the adhered carrier. This is thought to have caused an error in concentration detection. The same thing can be said about toner, but since toner is about 1/100 the size of the carrier, it was found that it has almost no effect on the flow of developer.

Furthermore, if the carrier adheres to the wall of the developer passage in the detection section, the carrier will always be detected, making it impossible to accurately detect toner concentration.

The present invention has been made in view of the above points, and an object of the present invention is to provide a toner concentration detection device that can always perform stable and accurate toner concentration detection.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a cross-sectional view of a developing device equipped with the toner concentration detection device of the present invention. Reference numeral 1 denotes a photosensitive drum rotating in the direction indicated by the arrow. As the photoreceptor, selenium, zinc oxide, cadmium sulfide, organic photoconductor, etc. are used, and a three-layer photoreceptor having a transparent insulating layer on the surface may also be used. The developing device 2 includes a developing roller 4 that magnetically attracts and draws up a two-component developer D consisting of toner and a magnetic carrier contained in a developer container 3, and a toner replenishing device 5. The developing roller 4 includes a sleeve 6 made of a non-magnetic material that rotates counterclockwise, and a plurality of permanent magnets 7 ₁ , 7 ₂ , 7 fixedly installed inside the sleeve 6 .
It consists of ₃ . Permanent magnets are arranged so that different poles are adjacent to each other. A scraper 8 is disposed diagonally around or in contact with the sleeve 6 . This scraper 8 extends over the entire length of the sleeve 6, has an opening near its center, and has a toner concentration detection device 9 attached below the opening. The toner concentration detection device 9 is composed of a funnel-shaped container 10, a cylinder 11 integrally formed at the bottom thereof, and a coil 12 wound around the cylinder.The cylinder 11 and the coil 12 form a detection section. It consists of The inner diameter of the cylinder 11 is formed to be slightly larger than the lower opening of the funnel-shaped container 10,
Both the container 10 and the cylinder 11 are made of non-magnetic material. A stirring member 13 for stirring the developer D is rotatably attached in the developer container 3. A toner replenishing device 5 detachably attached to the left side of the developer container 3 includes a cylindrical toner container 14 and a replenishing member 15 that rotates intermittently within the toner container 14. Next, the operation of the developing device 2 will be explained. sleeve 6
When the developer rotates, the developer is magnetically attracted to the sleeve 6 by the magnets 7 ₁ to 7 ₃ to form a magnetic brush, drawn up in the direction of rotation, and brought into contact with the photoreceptor drum 1 . The electrostatic latent image formed on the photosensitive drum 1 is rubbed by a magnetic brush and made into a visible image by toner. During development, it is effective to apply a developing bias voltage of the same polarity as the background portion to the sleeve 6 in order to prevent background staining. The developer that has contributed to the development is removed from the sleeve 6 by the scraper 8, slides down on the scraper 8, and is returned to the developer container 3 again. A portion of the developer flows into the container 10 and falls through the cylinder 11 into the developer container 3 as well. The toner concentration detection device 9 uses a toner concentration detection method that utilizes the fact that the fluidity of the developer changes in response to changes in toner concentration. That is,
The fluidity of the developer is defined as the amount of developer flowing per unit time, and if the toner concentration is low, the developer will flow more easily and the amount of magnetic carrier per unit time will increase. Since the flow of the developer is very closely related to the toner concentration, this toner concentration detection device 9 uses a conductive coating 1 on the inner surface of the funnel-shaped container 10 and the cylinder 11, as shown in FIG.
6 and ground it.
This conductive film 16 is, for example, Cu-Ni-Cr or Cu-
It is metal plating such as Cr. As a result, even if the developer comes into contact with the container 10 and the cylinder 11, it will not be charged by frictional charging, and the flow of the developer will not be obstructed. A coil 12 is wound around the cylinder 11 and detects changes in the inductance of the developer passing through the cylinder 11. This control circuit is shown in a block diagram in Fig. 4. Normally, the detection section has a capacitor installed in parallel with the detection inductance to create a resonant frequency r, and a separate reference inductance section has a capacitor installed in parallel with the detection inductance. A reference frequency o is created, the two are compared by a comparison circuit, and a toner replenishment command is generated by frequency-voltage conversion and sent to the toner replenishment section. Such a toner concentration detection circuit is disclosed in U.S. Patent No. 3970036.
The one listed in the number is used. Returning to FIG. 2 again, when the toner concentration falls below the reference value, a toner replenishment command is issued as described above, and a drive device (not shown) is controlled to rotate the toner replenishing member 15 of the toner replenishing device 5 clockwise. . When the toner replenishing member 15 rotates, it draws up a predetermined amount of toner T from the toner container 14 and releases the toner T into the developer container 3. The supplied toner T, the developer that has fallen from the rear end of the scraper 8, and the developer that has fallen through the toner concentration detection device 9 are uniformly stirred in the axial direction of the developing roller 4 by the stirring member 13, and the toner is Make the concentration distribution uniform.

FIG. 5 shows another embodiment of the present invention, in which the container 10' and the cylinder 11' are made of a resin that is non-magnetic and has a low volume resistivity. In the triboelectrification hierarchy, the resin needs to be higher than the carrier. As such a resin, an olefin-based GL resin or a resin mixed with carbon is suitable. That is, since this resin has a tendency to be triboelectrically charged with the positively charged carrier and also to be positively charged, the carrier will not electrostatically adhere thereto.

FIG. 6 shows yet another embodiment of the present invention, in which an antistatic layer 17 is formed on the inner surfaces of the container 10'' and the cylinder 11''. This antistatic layer 17
is a coating with a surfactant, an antistatic agent, etc. As an antistatic agent, a colloidal dispersion of partially hydrolyzed glass-like silica is produced by reacting tetrafunctional silicon tetrachloride with water in a predetermined amount of monohydric alcohols and esters.The product name is Colcoat. What is called can be used. The surface leakage resistance value of this material is
It is about 10 ⁹ Ω. In addition, guanidine derivatives, phosphate-containing anionic activators, quaternary ammonium salts, polyethylene glycol-based nonionic activators, cationic quaternary-ammonium salt type polymer conductive agents, etc. can be used. With such an antistatic layer 17,
It was possible to almost eliminate triboelectric charging on the parts that come into contact with the developer.

In the above-mentioned embodiment, a case was described in which an antistatic material due to frictional charging was applied to both the container 10 and the cylinder 11. If the value is large, that processing is unnecessary. In addition, in the embodiment shown in FIG.
0' is charged to the opposite polarity to the toner, and toner may adhere to it, but since its diameter is about 1/100 of the carrier, it has almost no effect on the flow of developer, and the toner served as a lubricant for the developer, and the flow of the developer hardly changed.

FIG. 7 shows a modified embodiment of the invention. The developer D is caused to flow down between two non-magnetic guide plates 18 and 19 that form a flow path for the developer D. The upper surface of the lower guide plate 18 is coated with a tribostatic material 20 by means of a carrier. As the material, those mentioned above are used. On the back side of this lower guide plate 18 is a toner concentration detection device 23 consisting of a magnetic core 22 around which a coil 21 is partially wound.
is arranged to detect the toner concentration using the developer flowing down on the guide plate 18 as part of a magnetic circuit. In this case, it is necessary to prevent the carrier from adhering to the guide plate 18 both in the toner concentration detection area A and in the areas before and after it. If necessary, the upper guide plate 19 may also be subjected to similar treatment. FIG. 8 shows another type of toner concentration detection device, in which the outlet of a non-magnetic bobbin 24 attached to a scraper 8 is squeezed and a certain amount of developer is always stored therein. The toner concentration is detected by magnetically detecting the amount of carrier in the developer. In this case, the flow of the developer is not affected as much as in the first embodiment described above, but the bobbin 2
4. If the inner surface of bobbin 24 is frictionally charged and the carrier adheres thereto, and the amount thereof gradually increases, it will be detected that the amount of carrier in the bobbin 24 is large even if the concentration is normal, making accurate detection impossible. Accurate detection could therefore be carried out by forming the inner surface 25 of the bobbin 24 or the entire surface of the bobbin 24 with a material that is not triboelectrically charged or does not accumulate electric charge even if triboelectrically charged.

As described above, according to the present invention, the portion of the toner concentration detection section that comes into contact with the moving developer due to the carrier in the developer is made of a material that prevents the carrier from electrostatically adhering. Stable and accurate toner concentration detection can be performed at all times. Moreover, since it is an extremely simple device, it is inexpensive.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the inductance of the detection section and the amount of charge on the wall of the developer flow path that change depending on the operating time of the copying machine in a conventional toner concentration detection device, and FIG. 2 is a diagram showing an example of the present invention. 3 is an enlarged sectional view of the toner concentration detection device shown in FIG. 2, FIG. 4 is a block diagram of a toner concentration control circuit, and FIGS. 5 and 6. 7 is a cross-sectional view of a toner concentration detecting device showing another embodiment of the present invention, FIG. 7 is a cross-sectional view of a toner concentration detecting device showing a modified embodiment of the present invention, and FIG. 8 is a still another modified embodiment of the present invention. FIG. 2 is a cross-sectional view of an exemplary toner concentration detection device. 1...Photosensitive drum, 2...Developing device, 5...
Toner supply device, 9, 23... Toner concentration detection device, 10, 10', 10''... Funnel-shaped container, 11,
11', 11''...Cylinder, 12...Coil, 16...
...Conductive coating, 17,20,25...Antistatic layer, 24...Bobbin.

Claims (1)

[Claims] 1. A flow path forming member that forms a flow path for a two-component developer consisting of toner and carrier, and a toner mixing ratio in the developer flowing on the flow path forming member by changing inductance. In a toner concentration detection device having a toner concentration detection means for detecting a toner concentration, at least a surface of the flow path forming member that comes into contact with the developer;
A toner concentration detection device characterized in that the carrier is made of a substance that does not electrostatically adhere. 2. The toner concentration detection device according to claim 1, wherein the substance is a conductive film. 3. The toner concentration detection device according to claim 1, wherein the substance is a resin having a low volume resistivity and a triboelectrification ranking higher than that of the carrier. 4. The toner concentration detection device according to claim 1, wherein the substance is an antistatic coating.