JPH02183154A - Toner concentration sensor - Google Patents

Abstract

PURPOSE:To facilitate an adjustment of an output voltage while enabling a stable and highly reliable setting of concn. by connecting an intermediate terminal between a reference coil and a detection coil to a differential output terminal with a capacitance element. CONSTITUTION:First, an oscillation output from an oscillation source 1 as applied to a driving coil 2 of a differential transformer is outputted to a reference coil 3 connected to the coil 2 and a detection coil 4 separately. Moreover, a differential output between the coil 3 and the coil 4 is checked to detect a toner concn. A change in the toner density cause a change in an output of the coil 4 and a differential output depending on the density of the toner is generated between the coil 4 and the coil 3. In addition, a variable capacitance element provided for fine adjustment of the differential output is connected to a midpoint of the coil 3 and the coil 4 and a differential output terminal 15 and a capacitance thereof is varied to control a phase of a differential output.

Description

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

(Prior Art) Conventionally, a device has been known that uses a drive coil, a detection coil, and a reference coil to detect and control toner 4 degrees from a differential output.

This device, whose outline is shown in FIG. 5, uses a differential transformer consisting of an oscillator 20, a detection coil 22 coupled to a drive coil 21, and a reference coil 23.

Further, there is a voltage adding circuit consisting of a variable resistor 23 that divides the voltage applied to the drive coil 21, a parallel circuit of a variable resistor 24 connected in series with the variable resistor 23, and a capacitor 25. This and the differential output made up of the detection coil 22 and the reference coil 23 are input to the signal processing circuit 26, and a DC voltage corresponding to the phase difference between the differential output and the drive voltage is output from the signal processing circuit 26. be.

The DC output voltage of this toner concentration sensor is set (roughly adjusted) by changing the position of the screw core 27 attached to the drive coil section to change the coupling coefficient between the drive coil, the detection coil, and the reference coil. . In addition, as a means for finely adjusting the output voltage after rough adjustment, the voltage applied to the drive coil 21 is divided by a first variable resistor, and further divided through a parallel circuit of a second variable resistor and a capacitor. It has a structure in which the divided voltage is added to the differential output.

The differential output was then finely adjusted by changing these variable resistors.

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 let's change the first variable resistor.

The characteristic curve changes from a to b or C in Figure 6, and 1
For example, when the toner concentration is A, the output voltage of the sensor changes from vl to v2 or v3.

(Problems to be Solved by the Present Invention) However, in the conventional method, as shown in FIG. 6, the slope of the characteristic curve (sensitivity slope) changes, so it is difficult to adjust as it is.

The reason for this is described below.

In the above circuit configuration, a drive voltage is applied to the drive coil 21, and voltages El and E2 are generated in the reference coil 23 and the detection coil 22, respectively. Further, the drive voltage applied to the drive coil is divided by a variable resistor 23,
Since the divided voltage Vin is applied to the differential output terminal through the parallel circuit of the capacitor 25 and the variable resistor 24, the differential output voltage EO becomes Eo=E1-E2+Vin. In order to change the output voltage without changing the sensitivity gradient, the phase difference between this Vin and the drive voltage is set to 0 or 180
However, in this method, V i n
is transmitted through a resistor and a capacitor, so the phase difference with the drive voltage was generally different from 0 or 180 degrees. For this reason, simply changing either the first or second variable resistor changes the slope of the characteristic curve (sensitivity slope).

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 without changing the sensitivity gradient as shown in FIG.

In this way, in the conventional technology, in order to maintain a constant sensitivity gradient between the toner concentration and the output voltage of the sensor and finely adjust the output voltage, it is necessary to adjust two variable resistors at the same time. was extremely difficult and impractical. In addition, increasing the number of variable resistors has the disadvantage that stability and reliability are difficult to guarantee.

Therefore, in the toner concentration sensor of the present invention, by connecting the intermediate terminal between the reference coil and the detection coil and the differential output terminal with a capacitive element, the output voltage can be easily adjusted and the concentration can be set stably and with high reliability. The aim is to do what is possible.

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a drive coil connected to one oscillation source, a reference coil and a detection coil coupled to the drive coil, and a reference coil and a detection coil coupled to the drive coil. A toner concentration sensor for detecting a differential output between detection coils is provided, characterized in that an intermediate terminal between the reference coil and the detection coil and a differential output terminal are connected by 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.

(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. Furthermore, the differential output between the reference coil and the detection coil is detected to detect the toner concentration.

A change in toner concentration does not cause a change in the output of the detection coil, but a differential output depending on the toner concentration is generated between the detection coil and the reference coil. Furthermore, a variable capacitance element provided for fine adjustment of the differential output is connected to the midpoint of the reference coil and the detection coil and the differential output terminal, and this capacitance is changed to control the phase of the differential output. do.

(Example) To explain an example, FIG. 1 shows the basic configuration of a concentration sensor 1 to 1 of the present invention.

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

Further, the polarity of the coil windings of the reference coil 3 and the detection coil 4 of the differential transformer are selected 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. A midpoint between the reference coil 3 and the detection coil 4 is connected to a differential output terminal 15 via a capacitor 5.

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 l has a frequency of about 400 kHz, the coils have a coupling coefficient of about 100 μH, the coupling coefficient is about 0.6, and the capacitor 5 has a coupling coefficient of about 10 pF, but it goes without saying that these should be changed as appropriate depending on the characteristics of the coils, 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 capacitor having a smaller capacitance than the fixed capacitor 5 is selected.

In the above circuit configuration, a drive voltage is applied to the drive coil 2, and a voltage E is applied to the reference coil 3 and the detection coil 4, respectively.
1 and E2 voltages are generated. Also, the voltage between the midpoint of the detection coil and the reference coil and the ground (same as E2 in this example) is transmitted to the differential output terminal by the capacitor, and the differential output voltage Eo is Eo = E2 - E1 + Vin This V in can be adjusted by changing the capacitance of the capacitor 5, and since it is transmitted only by the capacitor, its phase is either 0 or 180 degrees with respect to the drive voltage.

Therefore, in the 5-hydraulic type, the output voltage can be changed without changing the sensitivity gradient.

FIG. 3 shows another embodiment. A variable capacitance diode 2 was connected in series with a capacitor 5 to a 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 i) of the variable capacitance diode 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.

Further, even if the method of connecting the reference coil and the detection coil is reversed from the above example as shown in FIG. 4, the effects of the present invention will not be affected in any way.

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

A variable capacitance element provided to easily perform the fine adjustment required when detecting toner concentration is connected between the midpoint of the reference coil and the detection coil and the differential output terminal, and this capacitance can be changed by changing the capacitance. The phase of the differential output could be easily controlled without changing the sensitivity gradient.

Furthermore, when a variable capacitance diode is used, it can be controlled by a separate control power source via the resistor 11, thereby making it possible to control the junction capacitance of the variable capacitance diode and perform phase control of 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 sensor output voltage and toner concentration, and Figure 7 shows another characteristic curve showing the relationship between the sensor output voltage and toner concentration (here, the X axis is the toner concentration, and the Y
The 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 11: Resistor 8. 25: Signal processing circuit 10: Variable capacitor 12: Variable capacitance diode 23゜24: Variable resistor Figure Engraving of the drawing (no change in content) Figure Figure A Toner concentration Figure 6 Toner concentration Figure Procedure amendment document (method) ) 1. Indication of the case Heisei Patent Application No. 2, Name of the invention Toner concentration sensor 3, Person making the amendment Patents related to the case

Claims (1)

[Claims] 1. In a toner concentration sensor that detects a drive coil connected to an oscillation source, a reference coil and a detection coil coupled to the drive coil, and a differential output between the reference coil and the detection coil. , A toner concentration sensor characterized in that an intermediate terminal of the reference coil and the detection coil and a differential output terminal are connected by a variable capacitance element. 2. The toner concentration sensor according to claim 1, wherein the variable capacitance element is a variable capacitor or a variable capacitance diode.