JPH0419558Y2 - - Google Patents

Description

[Detailed description of the invention] <Technical field> This invention relates to a developing device that is provided opposite to a photoreceptor drum in the copying process section of an electromagnetic photocopier, and in particular detects the toner concentration of the developer stored therein. The present invention relates to a developing device equipped with a density detection sensor.

<Summary of the invention> In order to accurately detect toner concentration using a density detection sensor, the developing device according to this invention uses a conductive sheet that is charged to the opposite polarity to the toner by friction on the detection surface of the density detection sensor, and a magnet. By providing a cover that forms a recess between the magnet roller and the outer circumferential surface of the magnet roller, and providing an agitating member near the outer circumferential surface of the magnet roller, uneven distribution of toner in the developer and development in the developing device can be prevented. This is to eliminate erroneous detection by the concentration detection sensor due to coagulation of the agent, etc.

<Prior art and its drawbacks> When forming an image using a two-component developer consisting of toner and carrier in an electrophotographic copying machine, in order to obtain a good quality image, the concentration of toner in the developer must be kept at a predetermined level. must be kept above the value. For this reason, a density detection sensor that detects the toner density has conventionally been installed in the developing device, and detects the density of toner in the developer supplied to the surface of the photoreceptor by the magnetic roller. It was designed to prompt you to replenish the toner.

However, in conventional developing devices, when the toner hardens locally due to being left for a long time, the toner distribution in the developer becomes uneven, and the proportion of the carrier, which is a magnetic material, in the developer increases in some areas. The density detection sensor detects the toner density lower than the actual density.

As described above, since none of the conventional developing devices was designed to effectively prevent toner coagulation, there was a drawback that an error occurred in the detection value of the density detection sensor after being left for a long time. Further, there is a drawback that the concentration detection sensor may generate errors due to errors in the mounting angle of the magnet roller or the flow of developer within the developing device.

<Purpose of the invention> In view of the above-mentioned conventional drawbacks, the purpose of this invention is to eliminate the detection errors of the density detection sensor caused by toner solidification due to long-term storage, errors in the installation accuracy of the magnet roller, etc. An object of the present invention is to provide a developing device that can accurately adjust the toner density in the image forming apparatus.

<Structure and effects of the invention> A magnetic roller that conveys the developer, and a developer of high-density toner in a developer tank is supplied to a position where low-density toner that has been developed is sent out by this magnet roller. an agitation roller; a concentration detection sensor provided opposite to the outer circumferential surface of the magnet roller to detect the magnetic permeability of the developer as a toner concentration; The present invention is characterized by comprising: a conductive sheet that is charged to opposite polarity; and a cover that forms a recessed portion between the outer circumferential surface of the magnet roller.

With the above configuration, according to this invention, the conductive sheet, which is charged to the opposite polarity to the toner due to friction with the developer, has the effect of attracting the toner in the developer, and the toner in the developer near the concentration detection sensor is The distribution can be kept uniform.

Furthermore, a developer with a high toner concentration is supplied by an agitation roller to a position where the developer whose toner concentration has become low due to the development process is sent out. At this position, the low-density toner developer and the high-density toner developer collide and mix together.
At this time, the developer is sufficiently stirred and the toner is loosened due to the synergistic effect of the developer conveying force of the magnetic roller and the developer conveying force of the stirring roller. Furthermore, as mentioned earlier, this developer uses a conductive sheet, so the toner that tends to be attracted to the magnet roller side is attracted to the conductive sheet side, so that the toner distribution in the developer is always kept uniform. It is possible to prevent the toner from coagulating due to long-term storage.

Further, by forming a concave portion on the detection surface of the density detection sensor using the cover, it is possible to always keep the developer in an amount necessary for detecting the toner concentration on the detection surface. Therefore, it is possible to prevent density detection from becoming unstable due to installation errors of the magnet roller or developer flow.

<Example> FIG. 1 is a side sectional view showing the structure of a developing device equipped with a density detection sensor according to an example of this invention.

A developing device 1 is a photosensitive drum 2 in a copying process section.
1. The copying machine main body is provided with guides 22 and 23, and the developing device main body 11 is fixed by these guides 22 and 23. A mounting portion 11 a is formed above the developing device main body 11 . This attachment portion 11a is open to the outside. A hopper 12 is attached to the attachment portion 11a. An opening 12a is formed below the hopper 12, and the inside of the hopper 12 and the inside of the developing device 11 are connected. This hoppa 1
Reference numeral 2 supplies toner to the inside of the developing device main body 11.

Stirring rollers 8 and 9 are provided inside the developing device main body 11.
and a magnet roller 7 are rotatably attached. The magnet roller 7 is connected to the developing device main body 11
It is exposed to the outside through an opening 11b formed in a surface opposite to the surface of the photoreceptor 21. A plurality of magnetic poles are provided inside the magnet roller 7, and the developer is attracted to the outer peripheral surface. The magnet roller 7 rotates in the direction of arrow A during the copying process;
Toner is successively supplied to the surface of the photosensitive drum 21 rotating in the direction of arrow B. The stirring rollers 8 and 9 rotate in the directions of arrows C and D, respectively, and guide the developer from the hopper 12 side to the magnet roller 7 side.

A doctor 7a is attached above the magnet roller 7. This doctor 7a is for regulating the height of the spikes of developer adsorbed on the outer circumferential surface of the magnet roller 7. Magnet roller 7
A scraper shaft 6 is provided between the agitation roller 8 and the agitation roller 8 via a mounting member 6a. This scraper shaft 6 is moved by arrows A and C during the copying process.
This is for loosening the developer flowing together with the magnetic roller 7 and stirring roller 8 that rotate in the same direction.

Further, above the magnet roller 7, a density detection sensor 2 is attached with a detection surface 2a facing the outer peripheral surface of the magnet roller 7. Each density detection sensor 2 detects the magnetic flux density of the developer present between it and the magnet roller 7, and outputs this as a voltage change. The magnetic flux density of the developer is directly proportional to the proportion of the carrier, which is a magnetic substance, in the developer. Therefore, the output voltage V of the concentration detection sensor 2 and the toner concentration T/D of the developer are in an inversely proportional relationship as shown in FIG. As a result, when the output voltage V of the concentration detection sensor 2 rises above the set value, it is determined that the toner concentration T/D has fallen below the set value, and a display prompting to replenish toner is performed.
A conductive sheet 3 is attached to the detection surface 2a of the concentration detection sensor 2. The conductive sheet 3 is made of a material that is triboelectrically charged with a polarity opposite to that of the toner in the frictional order. In this example, a 0.13 mm thick polyester sheet (manufactured by Sakushin Kogyo Co., Ltd.) with added wear resistance and lubricity was used. As a result, as shown in FIG. 3, the error in the detection output after standing was significantly reduced.
Furthermore, covers 4a and 4b are attached to the outer surface of this conductive sheet 3. This cover 4
a, 4b form a recess 5 approximately at the center of the detection surface 2a.

With the above configuration, the developer stored inside the developing device main body 11 is sufficiently loosened by the scraper shaft 6 during execution of the copying process, and the toner is uniformly distributed in the developer. Furthermore, covers 4a and 4b are provided on the detection surface 2a of the concentration detection sensor 2.
Since a certain amount of developer is always present in the recess 5 formed by
The output will not become unstable. In addition, the conductive sheet 3 attached to the detection surface 2a is charged with an electric charge of a polarity opposite to that of the toner due to frictional contact with the developer, thereby attracting the toner in the developer. Due to this, the magnetic roller 7 can be
Toner, which tends to be attracted to the outer peripheral surface by the magnetic poles inside the developer, can be uniformly distributed in the developer. As described above, the scraper shaft 6 and the conductive sheet 3 enable the toner to be uniformly distributed in the developer even after being left for a long time. moreover,
By forming the recess 5, the concentration detection sensor 2
By keeping the detection conditions substantially constant, toner concentration can be detected accurately.

FIG. 2 is a diagram showing the detection results of the density detection sensor of the above-mentioned developing device and the conventional developing device. In this figure, the vertical axis represents the amount of change ΔV in the output voltage of the concentration detection sensor 2, and the horizontal axis represents time t.

As shown in FIG. 4, concentration detection is temporarily interrupted at time t1, and resumed at time t2 after a predetermined period of time has elapsed. If the value of the output voltage of the concentration detection sensor 2 at time t1 is V1, and the value of the output voltage at time t2 is V2, then the amount of change in the output voltage after a predetermined period of time ΔV
is expressed by the absolute value of the difference between V1 and V2. In Figure 2, the interval between times t1 and t2 in Figure 3 is 0.5.
This shows the results of measuring ΔV values for hours, 12 hours, and 24 hours.

In the density detection sensor of the conventional developing device, the value of ΔV increases as the interruption time increases, as indicated by the dashed line L2 in FIG. Since the copying process is not being performed during the interruption, the toner concentration in the developer does not actually change, but this is caused by the toner coagulating in the developer and causing the toner distribution to become uneven. and time t2
This shows that the value of the output voltage V2 increases at

In contrast, in the developing device of this embodiment, indicated by the solid line L1 in the figure, the amount of change ΔV in the output voltage is approximately 0 at any time. This indicates that the provision of the conductive sheet, recesses, and scraper shaft in the developing device of this example had a significant effect on uniform distribution of toner and stabilization of detection conditions.

In this example, a toner that is charged with a positive polarity due to friction with the carrier was used, but even if the developer uses a toner that is charged with a negative polarity, the conductive sheet may be charged with a negative polarity due to friction with the toner. A similar effect can be obtained by using a nylon-based material that is positively charged.

[Brief explanation of drawings]

Fig. 1 is a side sectional view showing the structure of a developing device equipped with a density detection sensor which is an embodiment of this invention, and Fig. 2 shows the amount of change in output voltage and interruption time between the developing device and a conventional developing device. 3 is a diagram showing the effect of the conductive sheet provided in the concentration detection sensor of the embodiment of the present invention compared to the conventional one, and FIG. 4 is a diagram showing the difference from the conventional one. Figure 5 shows the relationship between the output voltage of the density detection sensor and time and the experimental method conducted to obtain the relationship shown in Figure 5. Figure 5 shows the relationship between the output voltage of the density detection sensor and the toner concentration in the developer. It is a diagram. 1... Developing device, 2... Density detection sensor, 2a
...Detection surface, 3...Conductive sheet, 4a, 4b...
...Cover, 5...Recess, 6...Scraper shaft, 7
...Magnetic roller.

Claims (1)

[Scope of Claim for Utility Model Registration] A magnetic roller that conveys developer, supplies toner in a developer tank to a photoreceptor, and sends developed low-density toner developer to an agitation roller side; and the magnetic roller. an agitation roller that conveys a high-density toner developer in a developer tank in a direction opposite to the conveying direction of a low-concentration toner developer, and supplies a high-density toner developer to the low-concentration toner developer; a density detection sensor provided opposite to the outer circumferential surface of the magnet roller to detect the magnetic permeability of the developer as toner concentration; 1. A developing device equipped with a density detection sensor, comprising: a conductive sheet that is electrically charged; and a cover that forms a recessed portion between the outer peripheral surface of the magnet roller.