JP2501429B2 - Magnetic detection device - Google Patents

Description

The present invention relates to a magnetic detection device for magnetically detecting the presence, quantity, concentration, distance or the like of a magnetic substance or a conductor. As this type of magnetic detection device, there is a toner concentration detection device for an electrophotographic developer containing a magnetic carrier and an insulating toner.

<Prior Art> An electrophotographic developer is used for development such as electrophotography or electrostatic recording, but when the mixing ratio of the toner to the magnetic carrier decreases, the density of the developed image decreases, and conversely the mixing ratio. If the value becomes higher, the density of the image becomes too high and the fog increases. Therefore, in order to continuously obtain an image with an appropriate color tone, it is necessary to detect the toner concentration in the developer and maintain the concentration at an appropriate constant level. Various detecting devices have been conventionally proposed as means for this, but one of them is a differential transformer that is used to drive its drive coil with an alternating current drive source and to detect it coupled to the drive coil. A differential transformer type magnetic detection device for detecting the concentration from the differential output of the coil and the reference coil is known (for example, Japanese Patent Laid-Open No. 59-10814).
issue).

FIG. 6 is an electric circuit diagram of a conventional magnetic detection device used as a toner concentration detection device. In the figure,
Reference numeral 1 is an AC drive source composed of an oscillation circuit and the like, and 2 is a differential transformer. The differential transformer 2 includes a drive coil N ₁ driven by the AC drive source 1, a detection coil N ₂₁ coupled to the drive coil N ₁ and having an output voltage E ₁ that changes according to the toner concentration, and a drive coil N ₁ . A reference coil N ₂₂ which is coupled but whose output voltage E ₂ is not influenced by toner concentration.

Then, the output E ₁ of the detection coil N ₂₁ and the differential output Eo (= E ₁ −E ₂ ) of the output voltage E ₂ of the reference coil N ₂₂ are input to the signal processing circuit 3, and the phase discrimination or voltage of the differential output Eo is input. The toner concentration is detected by means such as discrimination.

<Problems of the Prior Art> The above-mentioned differential transformer type magnetic detection device has a detection coil.
Differential output between output E _{1 of} N ₂₁ and output voltage E ₂ of reference coil N ₂₂
Both coils are used because Eo is used as a detection signal.
The temperature fluctuations of N ₂₁ and N ₂₂ are canceled by each other, and the temperature characteristics are relatively good.

However, in applications such as toner sensors that detect minute changes in density, it is necessary to design with high detection sensitivity, so not only the temperature characteristics of both coils N ₂₁ , N ₂₂ but also AC drive source 1, The influence of the temperature characteristics of the signal processing circuit 3 or the power supply thereof cannot be ignored, and the temperature compensation by the differential transformer alone cannot maintain a sufficient temperature compensation function. For example, when it is used as a toner sensor in a copying machine, it has a temperature coefficient of about 0.1 (% / ° C) in terms of toner density, which is about 2 times the ideal 0.005 (% / ° C).
Normally, the temperature coefficient is 0 times.

Although it is possible to improve the temperature characteristics by adding a temperature compensating circuit including a temperature sensor, it is unsuitable for practical use such as a toner sensor in which strong cost reduction is required, and lacks practicality.

<Object of the present invention> Therefore, the present invention solves the above-mentioned conventional problems,
It is an object of the present invention to provide a magnetic detection device that has a simple circuit configuration and an extremely excellent temperature compensation function, is low in cost, and is highly practical.

<Structure of the Present Invention> In order to achieve the above object, the first invention comprises a drive coil excited by an alternating current, and a detection coil and a reference coil coupled to the drive coil. In a magnetic detection device in which each end of a reference coil is differentially connected and a differential main force between the output of the detection coil and the output of the reference coil is used as a detection signal, the magnetic detection device includes a resonance circuit. The resonance circuit includes an inductance component of the detection coil and the reference coil, and is an LC resonance circuit configured by the inductance component and a capacitor connected between differential output terminals. It is characterized by having a resonance frequency set near the excitation frequency.

A second aspect of the present invention includes a drive coil excited by an alternating current, a detection coil and a reference coil coupled to the drive coil, and the detection coil and the reference coil are differentially connected at one end thereof to perform the detection. In a magnetic detection device that uses a differential output between an output of a coil and an output of the reference coil as a detection signal, the magnetic detection device includes a resonance circuit, and the resonance circuit includes the detection coil and the reference coil. Is an LC resonance circuit having an inductance and a capacitor different from the above, and is connected between the differential output terminals and has a resonance frequency set near the excitation frequency of the drive coil.

<Embodiment> FIG. 1 is an electric circuit connection diagram of a magnetic detection device according to the first invention. In the figure, the same reference numerals as those in FIG. 6 denote the same components. In this embodiment, a capacitor C ₁ is connected between the differential output terminals of the detection coil N ₂₁ and the reference coil N ₂₂ , and by this capacitor C ₁ and the inductance component L _{1 of the} detection coil N ₂₁ and the reference coil N ₂₂ , Second
A resonance circuit 4 as shown in the figure is constructed. As is well known, the resonance frequency fo of 4 of the resonance circuit shown in FIG. Becomes Further, the resonance circuit 4 generally has a resonance characteristic as shown in FIG. 3 and a phase characteristic as shown in FIG.

Therefore, in the present invention, the resonance characteristic shown in FIG. 3 and the resonance characteristic shown in FIG. 4 are selected by selecting the temperature characteristic or the capacitance value of the capacitor C ₁ forming the resonance circuit 4 or adjusting the frequency of the AC drive source 1. The phase characteristic is changed to absorb the phase change and the voltage value change of the differential output Eo due to the temperature change of the entire system to perform temperature compensation.

As described above, in the present invention, since the resonance circuit 4 is provided on the side of the detection coil N ₂₁ and the reference coil N ₂₂ , the temperature characteristic of the entire system can be increased by adjusting the resonance characteristic and the phase characteristic. It can be absorbed accurately and easily. For example, in a toner sensor of a copying machine, it is possible to secure the ideal temperature coefficient of 0.005 (% / ° C.) (toner density conversion value).

In addition, the capacitor C ₁
Since it is a simple circuit configuration that only needs to be added, unlike the case where a temperature compensation circuit including a temperature sensor is added, it does not cause complication of the circuit configuration, cost increase, etc. It is possible to provide a rich temperature-compensated magnetic sensing device.

Next, the temperature compensation operation will be specifically described for each processing method of the signal processing circuit 3.

A. When the signal processing circuit 3 is a phase discrimination processing circuit.

If the output E ₁ of the detection coil N ₂₁ is set to be smaller than the output voltage E ₂ of the reference coil N ₂₂ when the toner concentration shows a normal value, the differential output Eo is Eo = E ₂ -E ₁ > 0.

Next, when the toner becomes insufficient, the concentration of the magnetic carrier becomes higher by that amount, so that the voltage E ₁ induced in the detection coil N ₂₁ becomes larger than the output voltage E ₂ generated in the reference coil N ₂₂ . Therefore, the differential output Eo becomes Eo = E ₂ −E ₁ <0, and the phase with respect to the drive signal of the AC drive source 1 is reversed. In the phase discrimination method, the toner density is detected by detecting the phase inversion by the signal processing circuit 3.

In the phase discrimination method, when the phase changes due to the influence of the temperature characteristics of the entire system, the output E ₁ of the detection coil N ₂₁ that causes phase reversal changes and a detection error due to temperature occurs. In order to absorb the detection error due to this temperature, the temperature coefficient of the resonance circuit 4 may be selected so as to be opposite to the temperature coefficient of the entire system. This makes it possible to compensate for phase fluctuations due to the temperature characteristics of the entire system.

For example, the differential output is affected by the temperature characteristics of the entire system.
When the phase of Eo changes by (-φ1) from the normal temperature, the phase change due to the temperature characteristic of the entire system can be absorbed by the following means.

(A) Assuming that the excitation frequency of the AC drive source 1 has been set to the resonance frequency fo before the adjustment, the excitation frequency fo is adjusted to the frequency f ₁ having the phase (+ φ1). As a result, the phase change (−φ1) of the differential output Eo is canceled.

(B) By changing the resonance frequency fo to f ₀₁ by selecting the temperature characteristic of the capacitor C ₁ or adjusting the capacitance value, change the resonance characteristic to the characteristic Q.
Change from ₁ to characteristic Q ₂ . As a result, the phase characteristic changes from the curve A ₁ to the curve A ₂ , and the phase at the excitation frequency fo becomes (+
φ1), and the phase change (−φ1) of the differential output Eo is canceled.

B. When the signal processing circuit 3 adopts the voltage discrimination method As described above, when the toner concentration decreases, the output E ₁ of the detection coil N ₂₁ gradually increases, and the differential output Eo decreases accordingly. And finally phase inversion occurs. Therefore, the voltage value of the differential output Eo decreases in proportion to the toner concentration. The voltage discrimination method detects the toner concentration by detecting this decrease in the differential output Eo.
Eo is affected by the temperature characteristics of the entire system, and its voltage value changes for the same toner concentration. To compensate for this, the resonance characteristic of the resonance circuit 4 shown in FIG. 3 may be adjusted so as to absorb the change in the differential output Eo due to the temperature change. As the adjusting method, the resonance characteristic shown in FIG. 3 is used to adjust the excitation frequency of the AC drive source 1 to a frequency required to cancel the change in the voltage value, and the temperature characteristic of the capacitor C ₁ . Alternatively, there is a means of changing the capacitance value to change the resonance characteristic.

The resonance characteristic and the phase characteristic of the resonance circuit 4 largely change in the vicinity of the resonance frequency fo. Therefore, it is desirable that the resonance frequency fo of the resonance circuit 4 be set near the excitation frequency of the AC drive source 1, for example, about 0.6 to 1.4 times the excitation frequency.

Further, the capacitor C ₁ may be a variable capacitor. When the variable capacitor is used, the resonance frequency fo can be variably adjusted, and the advantage that the resonance characteristic of FIG. 3 and the phase characteristic of FIG. 4 can be easily variably adjusted is obtained.

FIG. 5 is a diagram showing an electric circuit diagram of the magnetic sensing device according to the second invention. In the first invention shown in FIG. ₁ , the resonance circuit 4 is configured using the inductance component L ₁ of the detection coil N ₂₁ and the reference coil N ₂₂ , but in the second invention shown in FIG. Parallel resonance circuit 4 of an inductor L ₁ and a capacitor C ₁ independent of the coil N ₂₁ and the reference coil N ₂₂
Is connected between the output terminals of the differential output Eo. In this case as well, the same operational effects as those described in the first aspect of the invention are achieved.

In the above embodiment, a magnetic detection device for detecting the toner concentration has been described as an example for the sake of concreteness of the description.
Not limited to this, the present invention can be widely used for magnetic substance detection in general, such as presence, amount, concentration or distance of a magnetic substance, and can also be used for electric conductor detection as well as magnetic substance detection. In the case of conductor detection, the detection coil N
_Since the output E _{1 of 21} decreases and the differential output Eo changes, it is used.

<Effects of the Invention> As described above, the first invention comprises a drive coil excited by an alternating current, and a detection coil and a reference coil coupled to the drive coil. In a magnetic detection device in which each end of a coil is differentially connected, and a differential output between the output of the detection coil and the output of the reference coil is a detection signal, the magnetic detection device includes a resonance circuit, The resonance circuit includes an inductance component of the detection coil and the reference coil, and is an LC resonance circuit configured by the inductance component and a capacitor connected between differential output terminals. Since it has a resonance frequency set near the frequency, it has a very excellent temperature compensation function with a simple circuit configuration, is low in cost and highly practical, and is suitable for toner concentration detection devices and the like. It is possible to provide a gas-sensing devices.

A second aspect of the present invention includes a drive coil excited by an alternating current, and a detection coil and a reference coil coupled to the drive coil, wherein the detection coil and one end of the reference coil are differentially connected, In a magnetic detection device that uses a differential output between the output of the detection coil and the output of the reference coil as a detection signal, the magnetic detection device includes a resonance circuit, and the resonance circuit includes the detection coil and the An LC resonance circuit having an inductance and a capacitor different from those of the reference coil, which is connected between the differential output terminals and has a resonance frequency set near the excitation frequency of the drive coil. It is possible to provide a magnetic detection device having a simple circuit configuration, a very excellent temperature compensation function, low cost, high practicality, and suitable for a toner concentration detection device and the like.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of a magnetic detection device according to the present invention, FIG. 2 is an electric circuit diagram of a resonance circuit constituting the magnetic detection device according to the present invention, and FIG. 3 is a resonance characteristic diagram thereof. FIG. 4 is a phase characteristic diagram, FIG. 5 is an electric circuit diagram of another embodiment of the magnetic detection device according to the present invention, and FIG. 6 is an electric circuit diagram of a conventional magnetic detection device. 1 ...... AC drive source, 2 ...... differential transformer 3 ...... signal processing circuit, 4 ...... resonant circuit C ₁ ...... capacitor N ₁ ...... driving coil, N ₂₁ ...... sensing coil N ₂₂ ...... reference coil

Claims (6)

(57) [Claims] 1. A detection coil comprising: a drive coil excited by an alternating current; and a detection coil and a reference coil coupled to the drive coil, wherein one ends of the detection coil and the reference coil are differentially connected. Of a differential output between the output of the reference coil and the output of the reference coil, the magnetic detection device includes a resonance circuit, the resonance circuit, the resonance circuit of the detection coil and the reference coil An LC resonance circuit including an inductance component and a capacitor connected between the differential output terminals, the LC resonance circuit having a resonance frequency set near an excitation frequency of the drive coil. And magnetic detection device. 2. The magnetic detection device according to claim 1, wherein the resonance frequency of the resonance circuit is 0.6 to 1.4 times the excitation frequency of the drive coil. 3. The magnetic sensing device according to claim 1, wherein the capacitor is a variable capacitor. 4. A detection coil, comprising: a drive coil excited by an alternating current; and a detection coil and a reference coil coupled to the drive coil, wherein one end of each of the detection coil and the reference coil is differentially connected. Of the output of the reference coil and the output of the reference coil as a detection signal, the magnetic detection device includes a resonance circuit, the resonance circuit, the detection coil and the reference coil and Is an LC resonant circuit with different inductances and capacitors,
A magnetic detection device, which is connected between differential output terminals and has a resonance frequency set near an excitation frequency of the drive coil. 5. The magnetic detection device according to claim 4, wherein the resonance frequency of the resonance circuit is 0.6 to 1.4 times the excitation frequency of the drive coil. 6. The magnetic sensing device according to claim 4 , wherein the capacitor is a variable capacitor.