JPS6224790B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a toner concentration detection device used in devices such as copying machines.

Conventionally, there are various means for detecting the toner concentration of a two-component developer consisting of toner and carrier, such as optical means. A means for detecting the bulk density of the developer 2 by a change in the inductance of the coil 3 (see FIG. 1a) or a means for detecting the bulk density of the developer 2 by converting the fluidity of the developer 2 in the container 5 having the orifice portion 4 into a change in the inductance of the coil 6. There are also means to do this (see Figure 1b). However,
The two-component developer 2 is a mixture of carrier and toner at a constant ratio, and the specific gravity of the carrier containing a large amount of iron is about 7 to 8 times that of the toner.

As mentioned above, in order to measure the toner concentration of the developer 2 in the structure shown in FIGS. It is done by asking.

Further, the bulk density of the developer 2 is determined by, for example, when the developer 2 is freely dropped into the container 1 shown in FIG.
The value divided by the bulk volume of Therefore, a large bulk density means a large amount of carrier in the developer 2, and a low toner concentration. vice versa,
A low bulk density means a high toner concentration.

Furthermore, the fluidity of the developer 2 is, for example, as shown in FIG.
This refers to the amount of flow per unit time from the orifice section 4 in the container 5. This fluidity generally decreases as the toner concentration increases, and when the fluidity deteriorates, it is determined that the toner concentration has become low.

However, if the means shown in FIGS. 1a and 1b are used alone, the toner density control value will vary with respect to the initial state as the number of copies increases. In other words, even if the toner concentration is constant, if there are changes in the toner charge amount, carrier magnetic force, and carrier surface slippage in the developer, the fluidity and bulk density are shown in Figure 2 a, b, and c, respectively. It changes with such characteristics. Therefore, if the developer only fluctuates as shown in Figure 2a, it is possible to use a sensor based on flow rate as shown in Figure 1b, and if the developer only fluctuates as shown in Figure 2b, then it can be detected. First step
This is possible only with a sensor based on bulk density as shown in Figure a, but it is possible in cases where fluctuations as shown in Figure 2 a and b occur at the same time, or in the case of fluctuations as shown in Figure 2 c. is not possible with a single sensor. Therefore, if we show the variation of the control value of toner density with respect to the number of copies in such a case, the characteristics will be as shown in FIG. 3. However, the frequency of the applied voltage was kept constant. Here, the curve in the figure shows the fluctuation characteristic in the bulk density measurement shown in FIG. 1a, and the curve shows the fluctuation characteristic in the flow measurement shown in FIG. 1b. This is thought to occur mainly due to an increase in the lubricity of the surface of the carrier in the developer, and in the case of bulk density measurement alone, the increase in lubricity promotes the approach of the carriers to each other, resulting in the toner concentration. Even if there is no change in the amount of carrier, the bulk density actually increases due to the increase in the amount of carrier, so it is detected that the toner concentration is low, and the toner is oversupplied, and the toner concentration increases from the initial value. . In addition, when the carriers approach each other, the adhesion force between the carriers increases and the flow rate worsens, so even though the toner concentration has not changed, when measuring the flow rate alone, it is difficult to detect the toner. If the density is too high, the amount of toner replenishment is reduced, and the toner density becomes lower than the initial control value.

Therefore, in order to keep the control value of the toner concentration constant, a method has been proposed in which sensors as shown in Figure 1 a and b are provided separately, and the detection signals from each sensor are processed and controlled. has been done.

The present invention has been developed in view of these points, and it is possible to keep the toner density control value constant while eliminating the influence of increased slipperiness of the carrier surface that occurs as the number of copies increases. The object of this invention is to obtain a toner concentration detection device.

In the present invention, a coil A for causing a two-component developer to flow down and detecting the fluidity of the developer as a change in inductance is wound around the outer periphery of a container A for fluidity measurement, and the developer is temporarily A coil B for holding the developer and detecting the bulk density of the developer as a change in inductance is placed in a container B for bulk density measurement.
The coil A and B are connected in series to form a coil for detecting the toner concentration of the developer. Therefore, since coils A and B are connected in series, as the number of copies increases, the slipperiness of the carrier increases and the bulk density increases, and even if the flow rate deteriorates, these conditions can be offset. A constant toner concentration control value can be obtained by controlling the toner concentration, and the toner concentration can be controlled without using a special calculation circuit while eliminating the adverse effects of increased carrier slipperiness. There are things.

An embodiment of the present invention will be described based on FIG. First, a hole 9 is formed in a part of the flow plate 8 through which the developer 7 flows, and two containers A10,
B11 is provided. That is, this container B
Reference numeral 11 is for bulk density measurement and consists of a cylindrical body 13 having an orifice 12 of a predetermined diameter.
0 is a cylindrical body 14 located below the orifice 12 and having a predetermined inner diameter. Coils A15 and B16 are wound around the outer circumferences of these cylinders 14 and 13, respectively. This coil A
15 and B16 are connected in series to form a coil for detecting the toner concentration of the developer, and both ends thereof are connected to the oscillation circuit 17. An adder 19 connected to a reference oscillation circuit 18 is connected to this oscillation circuit 17, and an integral amplifier circuit 20,
Detection circuit 21, DC amplifier circuit 22, comparison circuit 2
3. Solenoids 24 for toner replenishment are sequentially connected.

In such a configuration, the bulk density of the developer 7 stored in the cylinder 13 is detected, and the orifice 1 is detected.
The fluidity of the developer 7 flowing down from the developer 7 is detected.
Each coil A15, B16 is configured as a part of an oscillation circuit 17, and each coil A1
5, the oscillation frequency changes based on the change in inductance of B16.

However, if the fluidity and bulk density are measured separately, the toner concentration control value will change from the initial state as the number of copies increases (see Figure 3), as described above, but the coil A15 and coil B
16 are directly connected, so the coil A1
On the 5 side, as the number of copies increases, the slipperiness of the carrier surface in the developer 7 increases, resulting in poor fluidity.
On the other hand, the bulk density increases on the coil B16 side, and as a result, the toner concentration control values on the coil A15 side and the coil B16 side fluctuate with opposite characteristics, and the fluctuations cancel each other out, resulting in an initial state. Therefore, the toner density control value does not change as the number of copies increases, and is maintained at the control value in the initial state.

In this way, regardless of the increase in the number of copies, it is determined whether or not toner replenishment is required based on the control value in the initial state, and when replenishment is required, the solenoid 24 is energized to perform toner replenishment.

Next, a second embodiment of the present invention will be explained based on FIGS. 5 and 6. The same parts as those shown in the previous embodiment are given the same reference numerals, and the explanation will be omitted.
In this embodiment, coils A15 and B16 are provided with a plurality of tap terminals a, b, and c so that their inductance ratios can be changed, and switches 25 and 26 are provided.
This allows the coil length to be selectively varied.

That is, depending on the developer 7 used, the relationship between the toner concentration control value and the number of copies may differ from the characteristics shown in FIG. As shown in the figure, there are cases where the variation curve ' based on bulk density measurement varies more than the curve, and in the case of the above embodiment, it is not possible to cancel out these variations, but by switching the switch 26. By making the coil length of the coil B16, whose bulk density is to be measured, shorter than that of the coil A15 and changing their inductance ratio, the curve 'can be corrected to look like the curve I'. As a result, the measurement is mainly based on the fluidity, and the bulk density works to correct the fluidity, canceling out the fluctuations and keeping the control value of the toner concentration constant.

In the present invention, as described above, a coil A for causing a two-component developer to flow down and detecting the fluidity of the developer as a change in inductance is wound around the outer circumference of a container A for fluidity measurement. A coil B for temporarily holding the developer and detecting the bulk density of the developer as a change in inductance is wound around the outer circumference of the container B for bulk density measurement, and these coils A and B are connected in series. Since the coil is connected to detect the toner concentration of the developer, the smoothness of the carrier increases as the number of copies increases, and the bulk density increases, and even if the flow rate deteriorates, these conditions can be offset and the current can be maintained at a constant level. To be able to obtain the toner concentration control value of
The toner density can be controlled without using a special arithmetic circuit while eliminating the adverse effects of increased carrier slipperiness.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one conventional example, FIGS. 2 and 3 are characteristic diagrams thereof, FIG. 4 is an explanatory diagram showing the first embodiment of the present invention, and FIG. 5 is an explanatory diagram showing the second embodiment of the present invention. FIG. 6 is a characteristic diagram. 7... Developer, 10... Container A, 11... Container B, 15... Coil A, 16... Coil B.

Claims (1)

[Scope of Claims] 1. A coil A for causing a two-component developer to flow down and detecting the fluidity of the developer as a change in inductance is wound around the outer periphery of a fluidity measuring container A. A coil B for temporarily holding the developer and detecting the bulk density of the developer as a change in inductance is wound around the outer circumference of the container B for bulk density measurement, and these coils A and B are connected in series. A toner concentration detection device characterized in that the coil is used as a coil for detecting toner concentration of a developer. 2. The toner concentration detection device according to claim 1, characterized in that coil A and coil B are used whose coil lengths can be varied separately so that inductance distribution can be changed.