JPH0345833B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developer concentration detection device for detecting the concentration of a developer, which is a mixed powder of a magnetic carrier and toner, used in an image forming apparatus such as an electronic copying machine.

Generally, in electronic copying machines that use this type of developer, most of the developer is used at a concentration such that the amount of toner is about 3 to 5% of chiralia in terms of weight ratio. The amount used as a toner image during this process is automatically replenished by detecting the developer concentration.

This type of concentration detection device is designed to detect changes in the magnetic resistance of the developer when detecting changes in developer concentration (weight ratio), and can easily be detected at concentrations below 5%. It is possible to replenish toner with high precision. However, when the density of the developer is increased to about 10%, for example, it is difficult to detect density changes in the vicinity because the ratio of magnetic resistance to the ratio of density changes is almost negligible. was extremely difficult.

By the way, when using a ferrite carrier with particularly high electrical resistance as a developer, the amount of charge on the toner is high and it is therefore difficult to separate it from the chiral carrier. By making it easier to separate the carrier from the electrostatic latent image on the photosensitive layer and make it easier to adsorb it to the electrostatic latent image on the photosensitive layer, it is possible to obtain a high-quality image, and furthermore, it is possible to prevent the carrier from adhering to the electrostatic latent image that occurs at low density. There are advantages such as being able to prevent Therefore, there is a need for a concentration detection device that can detect developer concentration at high concentrations.

This invention was made in view of the above-mentioned circumstances, and its purpose is to have a simple configuration,
It is an object of the present invention to provide a developer concentration detection device that is capable of detecting density changes even around 10%, which is a particularly high concentration.

Hereinafter, this invention will be specifically described based on embodiments shown in the drawings. First, a developing device of a dry type electronic copying machine will be schematically explained with reference to FIG. A magnet roller 2 that rotates clockwise is arranged inside a case 1 of this developing device.
The developer 4 is adsorbed onto the non-magnetic sleeve 3 formed on the outer periphery of the case 1.
Then, the hair is styled and the magnetic brush part 6 is formed. Development is carried out by bringing the surface of the magnetic brush portion 6 into contact with the surface of the photosensitive layer of the photosensitive drum 7, which rotates clockwise. The developer 4 used for development is scraped off by a scraping plate 8 whose tip is close to the sleeve 3, and the developer 4 is scraped off by the clockwise rotation of the stirring roller 10 having blades 9. By stirring, a new magnetic brush portion 6 is formed on the sleeve 3.

In addition, the case 1 is formed with a delivery port 12 for replenishing the developer to the reactor 11 that detects the concentration of the developer.
An introduction port 13 is formed for returning the detected developer discharged from the case 2, and a toner replenishment port 14 is further formed for replenishing the toner inside the case 2.

Next, the configuration of the reactor 11 will be explained with reference to FIGS. 2 and 3. The reactor 11 of this embodiment includes a pair of coils 23 on the outer periphery of the cylindrical body 22,
24 are respectively wound, and a magnetic path 25 is attached to the cylindrical body 22 so as to straddle the coil 23, and a magnetic path 26 is attached to the cylindrical body 22 so as to straddle the coil 24. That is, a pair of coils 2
3 and 24 and magnetic paths 25 and 26. The magnetic paths 25 and 26 are formed by laminating a plurality of thin U-shaped iron plates, and each of the magnetic paths 25 and 26 has an insertion opening the same size as the outer diameter of the cylinder 22 on the upper and lower sides of the U-shape. It is attached to the cylinder body 22 by inserting the cylinder body 22 through the holes 25a, 25b, 26a, and 26b. Note that a predetermined AC voltage is applied to lead wires 27a, 27b, 28a, and 28b drawn out from the coils 23 and 24.

FIG. 3 shows a cross-sectional view of the reactor 11, in which a cylinder 22 is filled with developer 29, and coils 25, 26 are contained in the cylinder 22.
The magnetic powder of the developer 29 creates a magnetic path 3 corresponding to the
0,31 are formed.

FIG. 8 shows a circuit for detecting the concentration of developer 29, and an alternating current voltage V ₁ is applied between input terminals 32 and 33. FIG. Further, one end of the coil 23 and the negative electrode side of a diode 34 are connected to the input terminal 32, and one end of the coil 24 and the negative electrode side of the diode 35 are connected to the input terminal 33. And, at the other end of the coil 23,
A capacitor 36 is connected in series. Also,
A capacitor 37 is connected between the other end of the capacitor 36 and the positive electrode side of the diode 34, and a resistor 38 is connected in parallel to the capacitor 37. Further, a capacitor 39 is connected between the other end of the coil 24 and the positive electrode side of the diode 35.
is connected to the capacitor 39, and a resistor 40 is connected in parallel to the capacitor 39. Furthermore, the positive electrode side of the diode 34 is connected to the output terminal 41, and the positive electrode side of the diode 35 is connected to the output terminal 42.

Next, the operation of the above embodiment will be explained using FIGS. 4 and 5. Coil 23 at predetermined concentration
When the inductance of is _L1 , the capacitance of the capacitor 36 is C, the inductance of the coil 24 at a given concentration is _L2 , and the frequency of the AC voltage _V1 is f, the current I flowing through the coil 23, capacitor 36, and coil 24 is I=V ₁ /j (ωL ₂ +ωL ₁ −1/ωC) (however, ω=2πf
) becomes.

Therefore, the voltage V ₂ generated across the coil 23 and the capacitor 36 is V ₂ =j(ωL ₁ −1/ωC)・I=ωL ₁ −1/ωC/ωL ₂ +ωL ₁ −1/ωC・V ₁ , the DC voltage, that is, the voltage at the output terminal 41 |V ₂ | is |V ₂ |=|ωL ₁ −1/ωC/ωL ₂ +ωL ₁ −1/ωC・V ₁
｜……(1) becomes.

Further, the voltage V ₃ generated across the coil 24 is V ₃ =j ωL ₂ · I = ωL ₂ /ωL ₂ +ωL ₁ −1/ωC · V ₁ , and the DC voltage, that is, the voltage at the output terminal 42 |V ₃ | is |V ₃ |=|ωL ₂ /ωL ₂ +ωL ₁ −1/ωC・V ₁ |……(2).

Here, the series circuit of the coil 23 and the capacitor 36 is set to be capacitive, that is, ωL ₁ <1/ωC, and the coil 23 and the capacitor 3
The series circuit of 6 and the coil 24 is set to be inductive, that is, ωL ₂ >ωL ₁ −1/ωC. When the toner concentration of the developer decreases, in other words, when the carrier concentration increases, the coils 23 and 24
The inductances L ₁ and L ₂ increase to become L ₁ ′ and L ₂ ′.

Therefore, the voltage |V ₂ ′|, which is the DC voltage of the voltage V ₂ ′ generated across the coil 23 and capacitor 36 when the toner concentration decreases, is |V ₂ ′|= |ωL ₁ ′−1/ωC/ωL ₂ ′ +ωL ₁ ′−1/ωC・V ₁ |
…(3) becomes.

Comparing equations (1) and (3) here, since the series circuit of the coil 23 and capacitor 36 is capacitive, when the inductance L ₁ increases to L ₁ ', it approaches the resonance point,
Since the impedance decreases, the relationship is |ωL ₁ ′−1/ωC| <|ωL ₁ −1/ωC|. Also, since the series circuit of the coil 2 3, capacitor 36, and coil 24 is inductive, the inductances L ₁ and L ₂ are L ₁ ',
When added to L ₂ ′, the impedance also increases |
ωL ₂ ′+ωL ₁ ′−1/ωC｜＞｜ωL ₂ +ωL ₁ −1/ωC｜
It becomes a relationship.

Therefore, when looking at equations (1) to (3), the numerator becomes smaller and the denominator becomes larger, so the relationship is |V ₂ '|< |V ₂ |, and the voltage generated at the output terminal 41 has a lower toner concentration. This means that it will be considerably lower.

Next, the voltage |V ₃ ′|, which is a direct current reduction of the voltage V ₃ ′ generated across the coil 24 when the toner concentration decreases, is |V ₃ ′|= |ωL ₂ ′/ωL ₂ ′+ωL ₁ ′−1/ωC・V ₁
｜……(4) becomes. Here, ωL ₁ '-1/ωC is negative because it is capacitive, and as L ₁ increases to L ₁ ', it approaches the resonance point and approaches zero. Therefore |V ₃ ′|>|
V ₃ |, and the voltage generated at the output terminal 42 increases as the toner concentration decreases.

Therefore, as shown in FIG. 5, if the concentration decreases with respect to the set concentration position A, the voltage V ₂ of the series circuit of the coil 23 and the capacitor 36 decreases, and furthermore, the voltage V ₃ of the coil 24 decreases. will rise, so
The two changes have opposite characteristics and appear as a large difference, making it possible to detect even minute changes in density in the high-density developer 29. The voltage |V ₂ | of the output terminal 41 and the voltage |V ₃ | of the output terminal 42 are compared by a comparator, and when |V ₃ |>|V ₂ |, the toner concentration is kept constant by replenishing toner by an appropriate means. can be maintained. In this way, a pair of coils 23 and 24 are wound around the cylindrical body 22, and each coil 23,
The detection ability can be improved by forming 24 dedicated magnetic paths and making the change in reactance have an inverse characteristic.

As explained in detail above, according to the present invention, the capacitive load and the inductive load are reduced by connecting the capacitive load in series to only one of the pair of coils wound around the container containing the developer. Since the voltage change of both loads can be extracted with inverse characteristics, it is possible to detect even a slight change in inductance, especially in the case of a highly concentrated developer.

[Brief explanation of drawings]

1 to 3 show an embodiment of the present invention, in which FIG. 1 is a schematic configuration diagram of a developing device, FIG. 2 is a perspective view of a reactor for detecting the concentration of developer, and FIG.
The figure is a vertical sectional view of the reactor, FIG. 4 is a configuration diagram of a concentration detection circuit, and FIG. 5 is a characteristic diagram showing the ability to detect the concentration of developer. 21...Reactor, 22...Cylinder, 23,2
4... Coil, 25, 26... Magnetic path, 25a, 2
5b, 26a, 26b...insertion port.

Claims (1)

[Scope of Claims] 1. A container containing a developer made of toner and carrier; a first coil wound around the container; a detection circuit including a capacitive load connected in series; a second coil connected in series to the detection circuit and wound around the container so as to make the combined impedance of the detection circuit inductive; and the detection circuit. an AC power source that applies an AC voltage to a series circuit of the second coil; a first rectifier that rectifies the AC voltage generated in the detection circuit; and a first capacitor that smoothes the output of the first rectifier. a second rectifier that rectifies the alternating current voltage generated in the second coil; a second capacitor that smoothes the output of the second rectifier; and potentials of the first capacitor and the second capacitor. A developer concentration detection device characterized by comprising a voltage comparator for comparing the voltage and the voltage.