JPH02156150A - Toner concentration sensor - Google Patents

Abstract

PURPOSE:To facilitate the adjustment of an output voltage and to make it possible to set stabilized, highly reliable density by connecting a driving coil which is connected to an oscillation source and a differential output terminal with a variable capacitance element. CONSTITUTION:The oscillated output from an oscillator 1 is applied to a driving coil 2. A reference coil 3 and a detecting coil 4 of a differential transformer are selected so that the output of the driving coil 2 becomes the differential value. The output from a differential output terminal 15 is inputted into a signal processing circuit 8. The applied voltage on the coil 2 is inputted into the other terminal of the circuit 8. The coil 2 is connected to the output terminal 15 through a capacitor 5 and a variable capacitance element 10. The oscillated output from the oscillator 1 is outputted to the coils 3 and 4 which are coupled with the coil 2. The differential output between the coils 3 and 4 is detected, and the concn. of toner is detected. The change in concn. causes the change in output of the coil 4. The differential output depending on the difference in outputs is generated between the coils 4 and 3. The phases of the output is controlled with the element 10.

Description

DETAILED DESCRIPTION OF THE INVENTION A.8 Object of the Invention (Field of Industrial Application) The present invention relates to a toner concentration sensor, particularly a differential amplification type toner concentration sensor intended for electrophotographic developers.

(Prior Art) Conventionally, there has been known a device that detects and controls toner concentration from differential output using a drive coil, a detection coil, and a reference coil.

This device, whose outline is shown in FIG. 5, utilizes a differential transformer consisting of a detection coil 22 and a reference coil 23 coupled to an i generator 20 and a drive coil 21. Further, there is a voltage adding circuit consisting of a variable resistor 23 that divides the voltage applied to the drive coil 21, a variable resistor 24 connected in series with the variable resistor 23, and a capacitor parallel circuit. This and a differential output made up of the detection coil 22 and the reference coil 23 are input to the signal processing circuit 25.

The operation of this device is to detect the toner concentration from the differential output, divide the voltage applied to the drive coil 21 with the first variable resistor 23, and then divide the voltage applied to the drive coil 21 through the parallel circuit of the second variable resistor 24 and the capacitor. The configuration was such that the divided voltage was added to the differential output. Then, by changing these variable resistors, you can create a differential output! II! ! ! ! There was something to do.

FIG. 6 shows the relationship between the output voltage of the sensor and the toner concentration when the first variable resistance is changed.

Here, the X-axis is the toner concentration, and the Y-axis is the output voltage of the sensor corresponding to the toner concentration. Now, when the first variable resistor is changed, its characteristic curve changes from a to b or C in Fig. 6. For example, when the toner concentration is A, the output voltage of the sensor changes from ■1 to ■2 or ■3. Changes to.

However, in this method, the slope of the characteristic curve (sensitivity slope) changes as shown in FIG. 6, so it is difficult to adjust Im as it is.

For this reason, a method has been adopted in which a second variable resistor is added and adjusted in conjunction with the first variable resistor to change the output voltage of the sensor without changing the sensitivity gradient as shown in FIG.

As described above, in the conventional technology, in order to maintain a constant sensitivity gradient between the toner concentration and the output voltage of the sensor and change the output voltage, it is necessary to set two variable resistors to 1iia at the same time, and the adjustment is extremely difficult. It was difficult and impractical. In addition, increasing the number of variable resistors has the disadvantage that stability and reliability are difficult to guarantee.

(Problems to be Solved by the Invention) Therefore, the toner concentration sensor of the present invention changes the sensitivity gradient of the output voltage of the sensor with respect to the toner concentration by connecting a capacitive element between the drive coil and the differential output terminal. The purpose of the present invention is to easily adjust the output voltage tIl without any trouble, and also to be able to set the concentration stably and with high reliability. Furthermore, it is an object of the present invention to provide a highly reliable sensor in which the toner concentration in the differential transformer can be easily adjusted by adjusting both the screw core and the capacitive element.

9. Configuration of the Invention (Means for Solving the Problems) In order to achieve the above object, the present invention provides a drive coil connected to an oscillation source, a reference coil and a detection coil coupled to the drive coil, and the reference coil. A toner concentration sensor that detects a differential output between a coil and a detection coil is provided, characterized in that the drive coil and the differential output end are connected through a variable capacitance element.

Further, in order to effectively achieve the purpose of the toner concentration sensor, it is preferable that the toner concentration sensor has the following characteristics.

This is the case when the variable capacitance element includes a variable capacitor or a variable capacitance diode.

Furthermore, it is effective to include a circuit that divides the voltage applied to the drive coil and directly adds it to the differential output terminal.

(Operation) The operation of the toner concentration sensor configured as described above is as follows.

First, oscillation output from an oscillation source applied to the drive coil of the differential transformer is output to a reference coil and a detection coil coupled to the drive coil, respectively. Further, a differential output between the reference coil and the detection coil is detected to detect the toner concentration.

A change in toner concentration causes a change in the output of the detection coil, and a differential output depending on the toner concentration is generated between the detection coil and the reference coil. Further, a variable capacitance element provided to facilitate fine adjustment is connected between the drive coil and the differential output terminal, and changes this junction capacitance to control the phase of the differential output.

(Example) To explain an example, the basic configuration of the toner concentration sensor of the present invention is shown in FIG.

Oscillation output from the oscillator 1 is applied to the drive coil 2.

Further, the reference coil 3 and the detection coil 4 of the differential transformer carry the polarity of the coil windings so that the output of the drive coil 1 is differential. The output from the differential output terminal 15 is input to the signal processing circuit 8.

Furthermore, the voltage applied to the drive coil 2 is input to the other input terminal of the signal processing circuit 8 . Drive coil 2 to capacitor 5
It is connected to the differential output terminal 15 via.

In this embodiment, a fixed capacitor is shown as the capacitor 5 to illustrate the principle, but a variable capacitor is suitable for the present invention.The oscillator 1 has a frequency of about 400 kHz, the coils have a frequency of about 100 μH, the coupling coefficient is about 0.6, Capacitor 5 is 0
．． 01 μF, but it goes without saying that it should be changed as appropriate depending on the characteristics of the coil, etc.

FIG. 2 shows an example in which a variable capacitor 10 is added to the fixed capacitor 5. For fine adjustment of the differential output, a capacitance smaller than that of the fixed capacitor 5 is selected.

FIG. 3 shows another embodiment. A variable capacitance diode 12 was connected in series with the capacitor 5 to the differential output terminal 15.

The capacitance of variable capacitance diode 12 is changed to resistor 1 using another control power supply.
1. Thereby, the junction capacitance (inter-terminal capacitance) of the capacitor 5 can be controlled, and the phase of the differential output can be controlled.

Note that in the present invention, the reliability of the differential output can be improved by performing temperature compensation on the variable capacitance diode 12 as well.

Further, with only the above configuration, the phase change in the capacitance of the differential output when changing the capacitance of the variable capacitance element may be too large. This case can be solved by another embodiment shown in FIG. The voltage applied to the drive coil 2 is connected to the resistor 6.7.
By dividing the voltage and adding it directly to the differential output, the amount of change in phase can be controlled.

C1 Effects of the Invention Since the present invention is configured as described above, it produces the following effects.

The drive coil provided to easily perform the fine Y4 adjustment required when detecting toner concentration and the differential output terminal are connected by a variable capacitance element, and the phase of the differential output can be controlled by changing this capacitance. We were able to realize this easily and without changing the sensitivity gradient.

Also, when using a variable capacitance diode.

It can be controlled via the resistor 11 by a separate control power supply, so that
Although the junction capacitance of the capacitor 5 can be controlled and the phase of the differential output can be controlled, adjustment can be made independently of the adjustment of the differential transformer.

Furthermore, the amount of phase change can be controlled by dividing the voltage applied to the drive coil and directly adding it to the differential output.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of a toner concentration sensor of the present invention, and FIGS. 2 to 4 are basic configuration diagrams of other embodiments of the present invention.
Figure 5 is a basic configuration diagram of a conventional toner concentration sensor;
The figure shows a characteristic curve showing the relationship between the output voltage of the sensor and the toner concentration, and FIG. 7 shows another characteristic curve showing the relationship between the output voltage of the sensor and the toner concentration. Here, the X-axis is the toner concentration, and the Y-axis is the output voltage of the sensor corresponding to the toner concentration. 1.20: Oscillator 2.21: Drive coil 3.2
2: Reference coil 4.23: Detection coil 5: Capacitor 6, 7.11: Resistor 8.25: Signal processing circuit 10: Variable capacitor 12: Variable capacitance diode 23.24: Variable resistor Fig. 1

Claims (1)

[Claims] 1. A drive coil connected to an oscillation source, a reference coil and a detection coil coupled to the drive coil, and a toner concentration sensor that detects a differential output between the reference coil and the detection coil. 2. The toner concentration sensor according to claim 1, wherein the drive coil and the differential output terminal are connected by a variable capacitance element. 2. The toner concentration sensor according to claim 1, wherein the variable capacitance element includes a variable capacitor or a variable capacitance diode. 3. The toner concentration sensor according to claim 1, further comprising a circuit that divides the voltage applied to the drive coil and directly adds the divided voltage to the differential output terminal.