JPH0345832B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a toner concentration detection device for a two-component developer in an image forming apparatus such as an electronic copying machine.

The two-component developer used in image forming devices consists of a magnetic carrier such as iron powder or ferrite and toner whose main component is resin. Only the toner is consumed during development and the toner density decreases, but in order to obtain the optimal image. It is necessary to replenish the consumed amount of toner and keep the toner concentration constant.

As a conventional method for detecting this toner concentration, a method is known in which a coil is provided in the developer and the inductance of the coil is detected to detect the toner concentration. For example, Japanese Patent Laid-Open No. 55369/1983 discloses a device in which the toner concentration is detected by an inductance and the voltage generated by an LC series resonance circuit is compared with a reference voltage by a comparator. Further, Japanese Patent Application Laid-open No. 7352/1983 discloses a method of detecting toner concentration using two coils. This method uses two coils, one coil detects the concentration of the standard developer, the other coil detects the concentration of the developer in the developing device, and the two are compared.

The toner concentration of the two-component developer is 5 in terms of weight ratio.
%, and it is necessary to detect changes of about 0.2%. In other words, the carrier amount is 95% to 95.2
%, and this 0.2% change is extremely small even when converted to a change in output voltage, and the difference from the reference voltage, which is always constant in response to concentration changes, is also small. It's just a voltage. Also, the input offset voltage of the comparator is 2
About 5 mV is required, so a noise voltage of 2 to 5 mV or more is not allowed at the input terminal of the comparator. Therefore, in the case of a detection device with a constant reference voltage as described above, it is difficult to detect a density drop of about 0.2%, and as a result, the overshoot and undershoot of toner density become large and the image density becomes uniform. The change becomes immeasurable.
Further, it has the disadvantage that a special noise killer is required to keep the noise voltage low, making the device large and expensive.

The present invention was made in view of the above-mentioned drawbacks, and it generates two types of voltages in response to changes in toner concentration, makes these voltages have opposite characteristics, and compares the two to detect even subtle changes in toner concentration. It is an object of the present invention to provide a toner concentration detection device for a developer that can be easily detected.

According to the present invention, the above object is achieved by a container containing a developer made of toner and carrier, a pair of coils wound around the container, and a capacitance of a composite impedance at a predetermined concentration in one coil of the pair of coils. a first sensing circuit consisting of a capacitive load connected in parallel to achieve the same effect, and a first full-wave rectifier connected in series to the parallel connected circuit; a second detection circuit including a second full-wave rectifier connected in series to the other coil; an AC power source that applies an AC voltage to the first detection circuit and the second detection circuit; a first resistor connected between the DC outputs of the full-wave rectifier; a second resistor connected between the DC outputs of the second full-wave rectifier; This is achieved by providing a developer concentration detection device characterized by comprising a voltage comparator that compares a first voltage and a second voltage generated in the second resistor.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. In FIG. 1, 1 is a reactor for detecting the concentration of developer, and this reactor 1 includes a rectangular tube 2 formed of an insulator such as a resin material, and a rectangular tube 2 wrapped around the rectangular tube 2. It consists of coils 3 and 4, and an iron core 5 which serves as a magnetic path and a shield and is fixed to the side surface of the rectangular tube 2 so as to straddle the coils 3 and 4. Also square tube 2
A bottom cover 6 that rotates around a shaft 7 is provided on the bottom side. When measuring the concentration of the developer, the bottom cover 6 is closed and the rectangular tube 2 is sufficiently filled with the developer 8, and changes in the current flowing through the coils 3 and 4 are detected by the circuit shown in FIG. 3, which will be described later. be done. After the density measurement, the bottom cover 6 is opened and closed every time the photosensitive drum is transferred, the developer 8 is discharged, and a new developer is replenished.

The mechanism of the reactor 1 described above is implemented using the principle described below. That is, when the amount of toner in the rectangular tube 2 decreases, the amount of carrier, for example, the amount of iron powder, increases relatively, so that the magnetic field generated by the current flowing through the coils 3 and 4 is affected by the magnetic path caused by the iron powder. The resistance decreases and the number of magnetic field lines increases, thus increasing the reactance of the coils 3, 4 and reducing the inflow current. Conversely, as the amount of toner increases, the amount of iron powder decreases relatively, so the magnetic resistance increases, the lines of magnetic force also decrease, the reactance of the coils 3 and 4 decreases, and the inflow current increases.

The characteristic curve diagram in FIG. 2 shows the above-mentioned principle, and shows the reactance X (Ω) and current i of the coils 3 and 4 with respect to changes in toner concentration (%).
(mA) for each change in curve 9 or curve 10, respectively.
It is shown by Note that the applied voltage is constant.

Next, with reference to FIG. 3, a circuit for detecting the concentration of developer by capturing the above-mentioned current change will be explained. An alternating current voltage is supplied between input terminals 23 and 24. In addition, the input terminal 23 has a capacitor 11, a coil 3,
4, and the other ends of the capacitor 11 and coil 3 are connected to one AC terminal of the rectifier 12.
The other end of the coil 4 is connected to one AC terminal of a rectifier 15. The other AC terminals of the rectifiers 12 and 15 are both connected to the input terminal 24.

A capacitor 13 is connected between the DC terminals of the rectifier 12.
Volume 14 is connected in parallel, and rectifier 15
A capacitor 16 and a volume 1 are connected between the DC terminals of the
Connect 7 in parallel. Both negative electrode sides are grounded.

Each sliding terminal 14A, 1 of volume 14, 17
7A are connected to the input terminal and input terminal of the comparator 18, respectively. A DC voltage is supplied to the comparator 18 and other illustrated circuits through a terminal 25 (positive electrode) and a terminal 26 (negative electrode). A resistor 19 is connected between the output terminal of the comparator 18 and the input terminal 25, and the output terminal of the comparator 18 and the base terminal of the transistor 20 are connected. The emitter terminal of the transistor 20 is grounded,
Further, a solenoid 21 and a diode 22 are connected in parallel between the collector terminal and the input terminal 25.

Next, the operation will be explained with reference to FIGS. 4 to 6. Note that in the following explanation of the operation, the internal resistance and mutual inductance of the coils 3 and 4 will be ignored. Now, if the inductance of the coil 4 at a predetermined concentration is L ₄ and the resistance of the volume 17 is R ₁₇ , the inductance Z ₁ of both becomes Z ₁ =R ₁₇ +jwL ₄ . Therefore, the absolute value of impedance Z ₁ |Z ₁ |
becomes ｜Z ₁ ｜√ ₁₇ ² + ( ₄ ) ² . The inflow current when the developer has a specified concentration |
If i ₁ |, then |i ₁ |=|V|/|Z ₁ |. Further, when the concentration of the developer decreases, the inductance L ₄ increases as described above, and the inflow current |i ₁ | decreases. The inductance at this time is
When L ₄ ′, impedance is |Z ₁ ′|, and current is |i ₁ ′|, |Z ₁ |=√ ₁₇ ² + ( ₄ ′) ² > |Z ₁ |. Therefore, |i ₁ ′| < |i ₁ |, and the voltage across the volume 17 when the current |i ₁ | is V _R17 , and when |i ₁ ′|
If V _R17 ′, then V _R17 = R ₁₇ |i ₁ |, V _R17 ′=R ₁₇ |
i ₁ ′|, and the relationship between the two is V _R17 ′<V _R17 . The voltage across the volume 17 when the developer concentration decreases in this way becomes lower than the voltage across the volume 17 when the developer has a predetermined concentration. Curve 27 in FIG. 6 shows such a change.

The above operation will be explained using the vector diagram shown in FIG. This figure is a vector diagram showing the relationship among the voltage V applied between the input terminals 23 and 24, the voltage V _L4 across the coil 4, and the voltage V _R17 across the volume 17.

Since the inflow current i ₁ when the developer has a predetermined concentration is an inductive load, its phase lags behind the applied voltage V, and the current
The voltage across the volume 17 that is in phase with i ₁ is V _R17 , and the voltage across the coil 4 is the above voltage V _R17.
The phase advances by 90 degrees and becomes V _L4 .

Further, when the concentration of the developer decreases, the current decreases to i ₁ ' for the reason mentioned above. Therefore, the voltage across volume 17 also decreases to V _R17 ',
Further, the voltage across the coil 4 becomes V _L4 ', which increases more than V _L4 .

Next, a circuit in which the volume 14 is connected in series to the parallel circuit of the capacitor 11 and the coil 3 will be explained. Now, assuming that the capacitance of the capacitor 11 is C, the inductance of the coil 3 at a predetermined concentration is _L3 , and the resistance of the volume 14 is _R14 , the impedance _Z2 becomes _Z2 = _R14 +1/jwc+1/ _jWL3 . Therefore, the absolute value of impedance Z ₂ |Z ₂ |
teeth becomes. When the developer has a predetermined concentration, the capacitor 11
If the current flowing through the coil 3 is i _c and the current flowing through the coil 3 is i _L , the current i ₂ flowing through the volume 14 is i ₂ = i _C + i _L. At this time, the capacitance C of the capacitor 11
The relationship between and the inductance L ₃ of the coil 3 at a predetermined concentration is determined to be capacitive in a parallel circuit, that is, |i _C |>|i _L |.
Since i _C and i _L have a 180° phase difference, the absolute value current |i ₂ | flowing through the volume 14 is |i ₂ |=|i _C |−|i _L |.

As can be seen from equation (1), in the LC parallel circuit, at the resonance point, that is, when 1-W ² L ₃ =0, the impedance |Z ₂ | becomes infinite and the current |i ₂ | becomes zero.

Under the above conditions, when the concentration of the developer decreases, the inductance of the coil 3 increases (L ₃ ') and the current flowing through the coil 3 decreases (i _L ').
Therefore, the current i ₂ ′ flowing through the volume 14 is i ₂ ′=i _C ′+i _L ′, and its absolute value current |i ₂ ′| is |i ₂ ′|=|i _C ′|−|i _L ′| , ｜i _L ′｜＜｜i _L ｜, so ｜i ₂ ′｜＞｜i ₂
becomes ｜. (However, the current i _C ′ flowing through the capacitor 11 at this time has a different phase from i _C and is equal in absolute value, that is, |i _C |= |i _C ′|.) When the current |i ₂ | The voltage across the volume 14 when the concentration is high is V _R14 , and the voltage across the volume 14 when the current is |i ₂ ′|, that is, when the concentration is decreasing, is V _R14 ′
Then, V _R14 = R ₁₄ |i ₂ |, V _R14 ′=R ₁₄ |i ₂ ′|
Then, the relationship between the two is |i ₂ ′|＞|i ₂ |
V _R14 ′＞V _R14 . The voltage across the volume 14 when the developer concentration decreases as described above becomes higher than the voltage across the volume 14 when the developer concentration is a predetermined concentration. Curve 28 in FIG. 6 shows such a change.

The above operation will be explained using the vector diagram shown in FIG. The figure shows the voltage V applied between input terminals 23 and 24, and the voltage across coil 3 and capacitor 11.
5 is a vector diagram showing the relationship between V _CL and the voltage V _R14 across the volume 14. FIG. The current i ₂ flowing through the volume 14 when the developer has a predetermined concentration is the vector sum of i _C and i _L , and is set so that |i _C | > | i _L |, so i ₂ is in phase with i _C become. V _R14 is in phase with i ₂ , and V _CL is a leading voltage of 90° with respect to V _R14 . When the concentration of the developer decreases, the inductance increases, and the current flowing through the coil 3 becomes i _L ', which is smaller than i _L. As the current flowing through the coil 3 decreases, the current flowing through the volume 14
i ₂ ′ becomes i ₂ ′=i _C ′−i _L ′ and increases more than i ₂ . Therefore, the voltage across the volume 14 is also V _R14 ', and V _R14
This will increase further.

FIG. 6 shows changes in the voltages across the volumes 17 and 14 described above, where a curve 27 is a change curve for V _R17 and a curve 28 is a change curve for V _R14 . Now, the density setting value is set at density position 2 where curves 27 and 28 intersect.
9 and the concentration has decreased to position 30, the potential of the terminal is higher than the terminal of comparator 18 in FIG.
The output of 8 is in a high state, and the base current of the transistor 20 flows through the resistor 19.
turns on. Therefore, the solenoid 21 is energized to drive a toner supply device (not shown), replenishes toner into the developing device, and after stirring it with the already existing developer,
The square cylinder 2 is replenished with developer. This operation continues until the concentration returns to position 29 again.

That is, the unbalanced voltage generated between the terminals of the comparator 18 is an extraction signal based on the change in developer concentration. In this way, in the developer concentration detection device of the present invention, the change characteristics of the terminal of the comparator 18 and the change characteristics of the terminal are opposite characteristics, so that the offset voltage of the comparator is different from that of the conventional comparator whose reference voltage is fixed. This is equivalent to 1/2, and it is possible to detect even subtle changes in concentration.

The above explanation of the operation was about the process of generating a change signal when the concentration decreases from the set concentration.
If you want to change the density setting, use Volume 14.
Alternatively, by adjusting 17 and moving the intersection position 29 of the curves 27 and 28, the desired density can be obtained. Further, when the frequency of the voltage applied to the terminals 23 and 24 is increased, the capacitance of the reactor 1 and the capacitor 11 can be reduced in size, and even in this case, a sufficient extraction signal can be obtained.

As described in detail above, according to the present invention, by connecting a capacitive load to only one of a pair of coils wound around a container containing developer, inductive load and inductance are not included. Since a capacitive load can be constructed, the accuracy of developer concentration detection is extremely high, and noise resistance can also be improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the configuration of a reactor 1 according to an embodiment of the present invention, and FIG. 2 is a curve 9 of changes in reactance X (Ω) of coils 3 and 4 and electrode i (mA) with respect to developer concentration. A diagram showing a change curve 10,
Figure 3 is a circuit configuration diagram, Figures 4 and 5 are vector diagrams, and Figure 6 is a shared voltage with respect to developer concentration.
FIG. 3 is a diagram showing a change curve 27 of V _R17 and a change curve 28 of shared voltage V _R14 , respectively. 1... Reactor, 2... Square tube, 3, 4... Coil, 5... Iron core, 6... Bottom cover, 11... Capacitor, 12, 15... Rectifier, 14, 17... Volume, 18... ...Comparator, 20...Transistor, 21...Relay.

Claims (1)

[Scope of Claims] 1. A container containing a developer consisting of toner and carrier, a pair of coils wound around the container, and one coil of the pair of coils having a composite impedance capacitively set at a predetermined concentration. a first sensing circuit consisting of a capacitive load connected in parallel, and a first full-wave rectifier connected in series to the parallel connected circuit; a second detection circuit including a second full-wave rectifier connected in series to a coil; an AC power source that applies an AC voltage to the first detection circuit and the second detection circuit; a first resistor connected between the DC outputs of the full-wave rectifier; a second resistor connected between the DC outputs of the second full-wave rectifier; and a first resistor connected between the DC outputs of the second full-wave rectifier; 1. A developer concentration detecting device comprising: a voltage comparator for comparing a voltage generated in the second resistor with a second voltage generated in the second resistor.