JPS6367653B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a toner concentration detection circuit, in particular, a method for detecting a change in reactance corresponding to a mixture ratio of toner and carrier. A toner concentration detection circuit that detects a phase difference between a base voltage and a power supply voltage, supplies toner to reduce the phase difference to within a predetermined phase difference, and maintains the toner concentration at a predetermined concentration. It is.

Conventionally known circuits for detecting and processing changes in impedance, especially reactance, include a method using an AC bridge,
The second method is to configure a series/parallel resonant circuit and extract it as a change in the magnitude of voltage or current.The second method is to use the change in reactance described above as a change in reactance when configured as part of an oscillation element in an oscillation circuit. There are known methods for extracting the signal as a change in the oscillation frequency or a change in the level of the oscillation output.

When detecting changes in inductance in the first AC bridge method, for example, even when using a Maxwell bridge circuit that is relatively suitable for detecting changes in inductance,
As long as the Maxwell bridge circuit is an AC bridge, the deviation output (deviation voltage) of the Maxwell bridge circuit will not become zero unless the magnitude and phase of the voltage on the opposite side completely match each other. In the AC bridge circuit normally used as a detection circuit, the deviation output is detected only by the magnitude of the voltage of the deviation output, so even if the Q of the detection coil is increased, the deviation output does not become completely zero. Even if we try to increase the detection sensitivity by amplifying it, there are limits. Furthermore, as a method of configuring the first resonant circuit, for example, when considering a series resonant circuit, the current flowing due to the resonance between the inductance and capacitance changes greatly.
If a large variation area near the resonance point is used, the single-peak characteristic causes the direction of current flow to reverse around the resonance point as a boundary, making it difficult to utilize. Since the first method has the above-mentioned problems, a second method, that is, a method of detecting a change in the oscillation frequency or a change in the level of the oscillation output may be considered.
However, since this second method also configures an oscillation circuit and functions as an active circuit, the temperature
It has the disadvantage of instability in that the oscillation frequency and the level of the oscillation output change depending on the environment such as humidity.

The present invention aims to solve the above-mentioned drawbacks, and provides a toner concentration detection circuit that detects changes in the phase of impedance that change according to changes in inductance and capacitance, and has good detection sensitivity and accuracy. is intended to provide. Therefore, the toner concentration detection circuit of the present invention detects changes in the toner concentration of a two-component developer used in a printing device, consisting of toner and a carrier that carries the toner, by detecting changes in the impedance of an electrical means. In the toner concentration detection circuit for detection, a reactance varying means is provided which varies as a reactance change in the impedance in accordance with the mixture ratio of the toner and carrier mixture, and the phase is adjusted based on the reactance change. It is equipped with a phase difference detection means that extracts the fluctuated voltage and detects the phase difference between the voltage and the power supply voltage, and the phase difference monitored by the phase difference detection means is changed by the amount of change with respect to the preset phase difference. The present invention is characterized in that it includes a control voltage generating means for supplying the toner in accordance with the amount of change in the phase difference when this occurs, so that the toner concentration is maintained at a predetermined concentration. This will be explained below with reference to the drawings. FIG. 1 shows the configuration of an embodiment of the toner concentration detection circuit of the present invention, and FIG.
3 is an operation explanatory diagram for explaining the processing operation of two signals having a phase difference, FIG. 4 is a vector diagram for the case of the configuration shown in the figure, FIG. The figure is a phase characteristic curve diagram, Figure 6 is an example configuration of a phase difference voltage generation circuit, and Figure 7 is a phase characteristic curve diagram.
The figures show the output characteristic diagrams of FIG. 6, respectively.

In FIG. 1, reference numeral 1 denotes an alternating current power source, in which a power source having a sine wave is generally used, and 2 denotes a detection coil, into which a mixture of toner and carrier is passed. 3, 4, whose inductance L changes depending on the mixing ratio of the mixture of toner and carrier;
5 represents resistance.

The voltage of AC power supply 1 is V ₀ , the voltage of detection coil 2 is V _L , the voltage of resistors 3, 4, and 5 is V ₃ , respectively.
When V ₄ and V ₅ are expressed, and the deviation voltage at midpoints P and Q between the detection coil 2 and the resistor 3, and between the resistors 4 and 5, which constitute the AC bridge, is expressed as V _D , the following equation holds true.

V〓 ₀ =V〓 ₄ +V〓 ₅ =V〓 _L +V〓 ₃ ………(1) V〓 _D =V〓 ₃ −V〓 ₅ ………(2) Here, the resistor 4 that constitutes the AC bridge, Regarding 5, if R ₄ = R ₅ is selected, equations (1) and (2) are V〓 ₀ = 2V〓 ₄ = 2V〓 ₅ = V〓 _L + V〓 ₃ ………(3) ∴V〓 _D = V 〓 ₃ −1/2V〓 ₀ (4) Also, as is well known, the phase difference between the voltage V _L of the detection coil 2 and the voltage V ₃ of the resistor 3 is 90°. Then, the voltage V ₀ of the AC power supply 1 is constant, and as the inductance L of the detection coil 2 changes, the voltage V _L
When V 3 changes, the voltage V ₃ across the resistor 3 changes while maintaining the relationship of equation (3). This change is the second
Illustrated in the vector diagram of fig. In the figure, the symbols V ₀ , V _L , V ₃ , V _D , P, and Q correspond to those in FIG. 1.

As is clear from the vector diagram in Figure 2, resistance 3
The vector of the voltage V ₃ is a vector that moves at a point Q on the circumference whose diameter is the voltage V ₀ of the AC power supply 1. On the other hand, the deviation voltage V _D at the intermediate points P and Q expressed by equation (4)
The vector of is represented by PQ→ in FIG.

When the inductance L of the detection coil 2 changes, the voltage V ₃ of the resistor 3 also changes at the point Q on the circumference, so the magnitude of the deviation voltage V _D between the intermediate points P and Q remains unchanged, but its phase changes. I understand that. That is, as the inductance L of the detection coil 2 changes, the phase of the deviation voltage V _D at the intermediate points P and Q also changes. Therefore, the reference value of the intance L of the detection coil 2 is determined so that the deviation voltage V _D at the intermediate points P and Q has a phase delayed by α from the phase of the voltage V ₀ of the AC power source 1. Then, using the phase difference α at this time as a reference, a change in the phase difference with respect to the reference phase difference α is detected. If the inductance L of the _detection coil 2 changes away from the above reference value, the _change in phase difference ±θ will be appear. Therefore, for example, if the inductance L of the detection coil 2 becomes smaller than the above reference value, the voltage V _L also becomes smaller, so the vector of the deviation voltage V _D between the midpoints P and Q changes from PQ→ to PQ→′. As a result, a change θ in the phase difference with respect to the reference phase difference α appears as shown in FIG. Moreover, if the inductance L of the detection coil 2 becomes larger than the above reference value, the change in the phase difference -θ with respect to the reference phase difference α (if the displacement in the clockwise direction with respect to the reference phase difference α is negative, the change in the counterclockwise direction If it is displaced, it will be positive) will appear.

This method of detecting the change ±θ of the phase difference with respect to the change in the inductance L of the sensing coil 2 can _be used to Since the phase difference α between the intermediate points P and Q and the deviation voltage V _D can be set arbitrarily, taking into account the loss resistance mentioned above,
There exists an inductance L of the detection coil 2 such that the change in phase difference ±θ is completely zero with respect to the reference phase difference α, and even if the magnitude of the voltage V ₀ of the AC power supply 1 fluctuates, the second Since the vector diagram shown in the figure only changes due to the similarity relationship, it is not affected at all by the magnitude of the deviation output corresponding to the phase difference, and is suitable as a detection circuit for obtaining control signals.

A mixture of carbon, which is the main component of the toner, and iron powder, which is the main component of the carrier, is used in the detection coil 2.
, the inductance L of the detection coil 2 changes depending on the mixture ratio of toner and carrier in the mixture.
changes. Detection coil 2 detects toner density when printed matter is printed with normal density
When the inductance of is L ₀ , AC power supply 1
The reference phase difference is set so that the phase difference between the voltage V ₀ at the point P and the deviation voltage V _D at the intermediate points P and Q becomes α. When the toner concentration decreases, that is, the toner mixing ratio decreases, the print density of the printed matter decreases. Then, the inductance of the detection coil 2 is L ₁ (L ₁ >
L ₀ ), a change in phase difference -θ appears between the voltage V ₀ of the AC power supply 1 and the deviation voltage V _D at the midpoints P and Q, as described above.

FIG. 3 is an operation explanatory diagram illustrating the processing operation of two signals having a phase difference, and FIG. 3A shows a case where the phase difference is relatively small, and FIG. 3B shows a case where the phase difference is relatively large. .

The phase difference between waveform V _D and waveform V ₀ is θ _A in FIG. 3A and θ _B in FIG. 3B. υ _D is V ₀ and
It is obtained by each rising edge of V _D. That is,
It represents an output having a width proportional to the phase difference θ _A and θ _B between V ₀ and V _D. To obtain this υ _D signal, for example, a circuit configuration is used in which a comparator having 0 volts as a comparison reference value and an RS type flip-flop are connected. υ _S is a signal with a width that is, for example, 1/4 of the period of V ₀ , and a one-shot signal occurs at the rise of υ _D.
Obtained by operating a multi-vibrator circuit. υ _S - υ _D is the signal obtained by subtracting the above υ _S , as shown in Figure 3A.
3B, a positive signal is output, whereas in FIG. 3B, a negative signal is output. If we take the average of the above υ _S - υ _D , we will get a positive DC voltage in Figure 3A and a negative DC voltage in Figure 3B. This can be obtained by passing the signal υ _S - υ _D through a low pass filter, for example. Since this DC voltage is proportional to the phase difference between the two signals having the phase difference, it can be used as a control voltage.

From this, the detection coil 2 shown in FIG.
When a change in phase difference θ appears between V ₀ and the deviation voltage V _D at intermediate points P and Q, the change in phase difference θ
Since a control voltage proportional to is generated, if toner is supplied using this control voltage, an appropriate print density is always guaranteed.

In the above description, a change in the inductance of the detection coil 2 is detected, but it is also possible to detect a change in capacitance using the dielectric constant of the toner.

FIG. 4 shows another embodiment of the toner concentration detection circuit of the present invention, in which reference numeral 6 is an AC power supply;
represents a resistor, 8 represents an inductance, and 9 represents a capacitor. The circuit configuration shown in FIG. 4 is a series resonant circuit, and a change in inductance of an inductor 8 or a change in capacitance of a capacitor 9 is used as a detector. The resistor 7 is inserted to adjust the sensitivity of the series resonant circuit, and changes in current are detected from the resistor 7.

As is well known, the series resonant circuit shown in FIG. 4 exhibits a single peak characteristic, and FIG. 5 shows the change in phase thereof.

In FIGS. 4 and 5, when the resistor 7 is changed, the phase change curve of the current flowing through the series resonant circuit changes, and as the resistor 7 becomes smaller, the phase change becomes steeper with the resonant frequency f ₀ as the boundary. That is, it changes from the one-dot chain line to the solid line in FIG. 5, and the detection sensitivity increases accordingly. In the series resonant circuit, if the control point is adjusted to the resonance point f ₀ at a certain set value, for example, if inductance 8 is used as a detector, a slight change in inductance 8 will cause As a result, the phase changes greatly, and the changed output can be obtained accurately. As explained in Figure 1,
By replacing changes in toner concentration with changes in inductance 8, the voltage of AC power source 6 and resistance 7 can be changed.
The change in toner concentration can be extracted as the change in phase difference with respect to the voltage.

FIG. 6 shows the configuration of an embodiment of the phase difference voltage generation circuit, and in the figure, reference numerals 10 and 11 are signal converters, and 12 is a phase detection circuit, which is used for the PLL circuit. 13 is an operational amplifier; 14 to 17;
represents a resistor, and 18 represents a capacitor.

The voltage of AC power supply 6 and the voltage of resistor 7 corresponding to the phase of the current are input to signal converters 10 and 11, respectively. The pulse signal processed into a phase change by the signal converters 10 and 11 is input to the phase detection circuit 12. The output of the phase detection circuit 12 is input to the operational amplifier 13, which is used as a low pass filter, and
High frequency components are attenuated, and the output voltage changes to low or low depending on the phase change between the voltage of the AC power supply 6 and the voltage of the resistor 7.
It is output from the operational amplifier 13 that constitutes a pass filter. If the above-mentioned toner supply is controlled by this output, it is always controlled to be constant with respect to a preset printing density, that is, a preset phase difference between the voltage of the AC power source 6 and the voltage of the resistor 7. Therefore, if the density of the print becomes lighter, toner is supplied until the density of the print becomes appropriate.

FIG. 7 shows the output characteristic diagram of FIG. 6, and shows that the phase change θ is proportional to the output.

Note that the low pass filter in FIG. 6, that is,
By changing the voltage V _S applied to the non-inverting input terminal of the operational amplifier 13, the set value of the control output is changed.

As explained above, according to the present invention, the toner concentration is detected by a change in reactance, the detected toner concentration is converted into a change in phase difference, and compared with a preset phase difference, and the toner concentration is detected according to the change in phase difference. Since a control voltage is generated, it is possible to supply toner that always guarantees a constant print density, and also ensures reliable print density based on the stability of the detection circuit.

[Brief explanation of drawings]

FIG. 1 shows the configuration of an embodiment of the toner concentration detection circuit of the present invention, FIG. 2 is a vector diagram for the configuration shown in FIG. 1, and FIG. 3 explains the processing operation of two signals having a phase difference. An operation explanatory diagram, FIG. 4 shows another embodiment of the toner concentration detection circuit according to the present invention, and FIG.
6 shows a phase characteristic curve diagram, FIG. 6 shows an embodiment of a phase difference voltage generating circuit, and FIG. 7 shows an output characteristic diagram of FIG. 6. In the figure, 1 is an AC power supply, 2 is a detection coil, 3 to 5 are resistors, 6 is an AC power supply, 7 is a resistor, 8 is an inductance, 9 is a capacitor, 10 and 11 are signal converters, 12 is a phase detection circuit, 13 represents an operational amplifier, 14 to 17 resistors, and 18 a capacitor.

Claims (1)

[Claims] 1. In a toner concentration detection circuit that detects a change in toner concentration of a two-component developer, which is a developer used in a printing device and is a two-component developer consisting of toner and a carrier that carries the toner, by a change in impedance of an electric means, the above-mentioned A reactance varying means is provided which varies as a reactance change in the impedance in accordance with the mixture ratio of the mixture of toner and carrier, and a voltage whose phase is varied based on the reactance change is extracted and the voltage is A phase difference detection means for detecting a phase difference with the power supply voltage is provided, and when the phase difference monitored by the phase difference detection means changes with respect to a preset phase difference, the phase difference is detected. 1. A toner concentration detection circuit comprising a control voltage generating means for supplying the toner in accordance with the amount of change, so that the toner concentration is maintained at a predetermined concentration.