JPH0371068B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to the presence, amount,
The present invention relates to a magnetic detection device that magnetically detects density, distance, etc., and particularly to a magnetic detection device suitable as a toner concentration detection device for electrophotographic developing materials containing a magnetic carrier and an insulating toner.

BACKGROUND ART Electrophotographic developing materials are used for developing electrophotography or electrostatic recording, but when the mixing ratio of toner to magnetic carrier decreases, the density of the developed image becomes thinner, and conversely, the mixing ratio decreases. If it becomes too high, the density of the image becomes too high and fogging increases. Therefore, in order to continuously obtain images of appropriate color tone, it is necessary to detect the toner concentration in the developing material and maintain the concentration at an appropriate constant level. As a means of achieving this, various detection devices have been proposed in the past. One of them uses a differential transformer, the drive coil of which is driven by an AC drive source, and a detection device coupled to the drive coil. A differential transformer type magnetic detection device is known that detects concentration from differential outputs of a coil and a reference coil (for example, Japanese Patent Laid-Open No. 10814/1983).

FIG. 6 is an electrical circuit diagram of a conventional magnetic detection device used as a toner concentration detection device.
In the figure, 1 is an AC drive source constituted by an oscillation circuit, etc., and 2 is a differential transformer. The differential transformer 2 includes a drive coil N ₁ driven by an AC drive source 1 and a detection coil coupled to the drive coil N ₁ whose output voltage E ₁ changes depending on the toner concentration.
N ₂₁ and a reference coil N ₂₂ coupled to the drive coil N ₁ but whose output voltage E ₂ is independent of toner concentration.

Then, the differential output E ₀ (=E ₁ - E ₂ ) of the output voltage E ₁ of the detection coil N ₂₁ and the output voltage E ₂ of the reference coil N ₂₂ is input to the signal processing circuit 3, and the phase of the differential output E ₀ is input to the signal processing circuit 3. The toner concentration is detected by means such as discrimination or voltage discrimination.

Next, the operation when the signal processing circuit 3 is a phase discrimination circuit will be explained with reference to the waveform diagram of FIG. 7. Drive coil given from AC drive source 1
If the voltage Vin between the terminals of N ₁ has a waveform as shown in FIG. 7a, the reference coil N ₂₂ has a drive coil N ₁
A constant voltage E ₂ is generated, as shown in FIG. 7b, depending on the turns ratio between . The voltage E ₂ is approximately in phase with the drive voltage Vin applied to the drive coil N ₁ . On the other hand, as shown in FIG. 7c, a voltage _E1 is generated in the detection coil _N21 , which depends on the turns ratio with respect to the drive coil _N1 and the toner concentration. this voltage
Since E ₁ is differentially connected to the reference coil N ₂₂ , it has a phase difference of 180° (electrical angle) with respect to the terminal voltage Vin of the drive coil N ₁ and the voltage E ₁ of the reference coil N ₂₁ . have

Here, if the output voltage 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 E ₀ is E ₀ =E ₂ −E ₁ >0, and as shown in FIG. 7d, a differential output E ₀₁ that is in phase with the drive voltage Vin of the AC drive source 1 is generated.

Next, when toner becomes insufficient, the magnetic carrier concentration becomes relatively high, so the output voltage _E1 generated in the detection coil _N21 increases, and when the toner concentration exceeds the predetermined toner concentration, the output voltage E1 generated in the detection coil _N21 increases. _The output voltage E ₁ generated in _{the detection coil N 21 becomes} higher than the output voltage _{E 2 of} is reversed. Therefore, the sensing coil N ₂₁ is arranged such that a phase reversal occurs after a certain defined toner concentration
By designing a reference coil _N22 and phase discrimination in the signal processing circuit 3, the output voltage Vout from the signal processing circuit 3 as shown in FIG. 7e is obtained.
can be output and the toner density can be detected.

Problems to be Solved by the Invention By the way, important characteristics of this type of differential transformer type magnetic sensing device include the operating concentration and differential sensitivity. Figure 8 is a diagram explaining the working density and differential sensitivity, where the working density is the toner concentration TC ₁ (%) when the output voltage Vout becomes the set value Vd, and the differential sensitivity is the output voltage Vout with respect to the change in the working density. This is a characteristic that represents the degree of change (ΔVout/ΔTC).

Of these, the working concentration is, in principle, the difference between the voltage E ₁ of the detection coil N ₂₁ and the voltage E ₂ of the reference coil N ₂₂ when no toner is present, that is, the turns ratio of the detection coil N ₂₁ and the reference coil N ₂₂ . Determined by but,
Depending on the winding method of these coils N ₂₁ and N ₂₂ and the position of the center core, variations will occur in the differential output and operating concentration even if the turns ratio is the same. In particular, since the operating transformer is highly sensitive, large variations in the characteristics occur during mass production, which is a factor that lowers the yield of the product.

As a means for adjusting the working concentration and differential sensitivity, the ninth
As shown in the figure, two sets of differential transformers 21 and 22
A core 23 is prepared for the main differential transformer 21.
A coarse adjustment adjustment mechanism is provided to coarsely move the core 24 in the direction of the arrow a, and the other differential transformers 22 have the core 24 moved in the direction of the arrow b.
A device equipped with an adjustment mechanism for fine adjustment in the direction is known, but two sets of differential transformers 21, 2
2 is required, which has the disadvantage of increasing the overall size and cost at the same time.

As another adjustment means, as shown in FIG.
A voltage variable circuit VR ₁ is connected between the terminals of the reference coil N ₂₂ or the detection coil N ₂₁ or both.
It is possible to provide VR ₂ , but a voltage variable circuit
When the phase of the differential output E ₀ changes due to the addition of VR ₁ and VR ₂ and the processing circuit 3 adopts the phase discrimination method,
Differential sensitivity will drop significantly.

As a means to suppress the phase change caused by the voltage variable circuit, as shown in FIG. 11, buffer circuits B ₁ and B ₂ are connected to _the coil output.
A circuit configuration in which the voltage variable circuit VR ₃ is connected after B ₂ is conceivable, but this would require buffer circuits B ₁ and B ₂ , resulting in a significant increase in cost.

Means for Solving the Problems In order to solve the above problems, the present invention includes a drive coil excited with alternating current, a detection coil and a reference coil coupled to the drive coil, and a detection coil and a reference coil coupled to the drive coil. The magnetic detection device uses a differential output between an output and the output of the reference coil as a detection signal, and is characterized by having a circuit that adds a part of the drive coil drive voltage to the differential output.

Embodiment FIG. 1 is an electrical circuit connection diagram of a magnetic sensing device according to the present invention. In the figure, the same reference numerals as in FIG. 6 indicate the same components. 4 is a voltage adding circuit that adds a part of the drive voltage Vin applied from the AC drive source 1 to the drive coil N ₁ to the differential output E ₀ of the detection coil N ₂₁ and the reference coil N ₂₂ . In this embodiment, a resistive voltage divider circuit VR consisting of a variable resistor is connected between the terminals of the drive coil _N1 , and the variable terminal of the variable resistor constituting the resistive voltage divider circuit VR and the reference coil _N22 are connected. The circuit configuration is such that a capacitor _C1 is connected between one end and the other end. The voltage addition circuit 4 may be connected to the detection coil _N21 side.

In the above circuit configuration, the drive voltage Vin is divided according to the resistance division ratio of the resistor voltage divider circuit VR, and the divided voltage Vin is passed through the capacitor C ₁ to the differential output E ₀ at one end of the reference coil N ₂₂ . The differential output E ₀ is E ₀ =E ₂ −E ₁ +Vin ₁ . Therefore, since the output voltage E ₁ of the detection coil N ₂₁ required to cause phase reversal changes corresponding to the additional voltage Vin ₁ , the working concentration also changes depending on the additional voltage.
It will change corresponding to Vin ₁ .

Moreover, this embodiment adopts a configuration in which the drive voltage Vin is divided by a resistive voltage divider circuit VR consisting of a variable resistor, so that the additional voltage Vin ₁ can be freely adjusted, and the operating concentration can be freely adjusted. It is possible to adjust. Also, the phase of the added voltage Vin ₁ is
Depending on the position of the variable terminal of the variable resistance circuit VR, it is possible to have it in phase with the drive voltage Vin or to have a phase difference of 180°, so the drive voltage
No matter which side the phase of the differential output E ₀ deviates from Vin, it can be easily variably adjusted.

Furthermore, in this embodiment, since the circuit configuration is such that addition is performed through the capacitor C ₁ , the DC bias circuits on the drive coil N ₁ side, the detection coil N ₂₁ , and the reference coil N ₂₁ side can be separated from each other. In addition, the capacitor
C ₁ is selected to a value that does not make the coupling between the drive coil N ₁ side and the detection coil N ₂₁ and reference coil N ₂₂ sides too tight, for example, a value of about 1 to 50 PF.

FIG. 2 is an electrical circuit connection diagram in another embodiment of the magnetic sensing device according to the present invention. In the figure, the same reference numerals as in FIG. 1 indicate the same components. The feature of this embodiment is that, in addition to the voltage adding circuit 4, a capacitor is provided on the detection coil N ₂₁ and reference coil N ₂₂ side, which together with the inductance L of these coils N ₂₁ and N ₂₂ constitutes a resonant circuit.
This is because C ₂ was connected. As is well known, the resonant frequency f ₀ of the resonant circuit in this case is f ₀ =1/ _2π√.2 . Further, a resonant circuit generally has resonance characteristics as shown in FIG. 3 and phase characteristics as shown in FIG. 4. Therefore, in this embodiment, the resonance characteristics shown in FIG _. 3 and FIG. Temperature compensation is performed by changing the phase characteristics shown to absorb phase changes and voltage value changes in the differential output E ₀ due to temperature fluctuations in the entire system.

When equipped with a resonant circuit as described above, the value of capacitor _C2 is relatively large, so the drive coil
There is concern that the time constant of the circuit from the _N1 side to the capacitor _C2 through the voltage addition circuit 4 described above becomes large, causing a phase shift in the differential output _E0 , and problems such as a decrease in differential sensitivity. However, in the present invention, the capacitor constituting the voltage adding circuit 4
Since C ₁ is selected to have a small capacitance value of, for example, 1 to 50 PF, the time constant of the circuit from the drive coil N ₁ side to the capacitor C ₂ through the voltage addition circuit 4 is determined by the capacitor C ₁ . is controlled, and the phase shift is hardly a problem. Therefore, according to the present invention, even when a resonant circuit is added to improve the temperature characteristics, it is possible to variably adjust the working concentration without reducing the differential sensitivity.

FIG. 5 is a sectional view showing a specific example of a differential transformer constituting the magnetic sensing device according to the present invention. In this embodiment, a pair of cores 5 and 6 with one side of the magnetic path open, such as a pot-shaped core, are combined back to back, and a drive coil N ₁ is connected to the middle legs 51 and 61 of the cores 5 and 6. While continuously winding, the middle leg portion 5
1 is wound with a detection coil N ₂₁ , and the middle leg 61 is wound with a reference coil N ₂₂ . The surface side of the face plate 71 of the non-magnetic case 7 located on the front surface of the core 5 on the open magnetic path side is used as a toner detection surface that the toner 8 comes into contact with.

Reference numeral 9 denotes a conductor that is movably provided in a part of the open magnetic path of the reference coil _N22 . In this embodiment, a screw-shaped conductor 9 made of a conductive material such as brass or aluminum is screwed to the side plate 72 of the non-magnetic case 7, and this conductor 9 is connected to the core constituting the reference coil _N22 . On the open magnetic path side formed in front of a single surface of the core 5, it is attached so that it can be adjusted to advance and retreat parallel to the end surface of the core 5, as shown by arrow A.

When the conductor 9 as described above is provided, the drive coil
When N ₁ is driven, an eddy current is generated in the conductor 9 due to the magnetic flux generated in the reference coil N ₂₂ , and an output voltage E ₂ is generated in the reference coil N ₂₂ due to this eddy current effect.
changes. Therefore, by adjusting the movement of the conductor 9, the output voltage E ₂ generated at the reference coil N ₂₂ is variably adjusted, and thereby this output voltage E ₂ and the detection coil
By adjusting the differential output E ₀ with the output voltage E ₁ generated at N ₂₁ , it is possible to adjust the working concentration. Therefore, this embodiment has two types of working concentration adjustment functions: the working concentration adjustment by the conductor 9 and the working concentration adjustment by the voltage adding circuit 4 described above. With such two types of working concentration adjustment mechanisms, the working concentration adjustment by the voltage adding circuit 4 is as follows:
This is used exclusively as a means for absorbing manufacturing variations in the operating transformer, and the adjustment of the operating concentration using the conductor 9 is a means for the user to adjust the operating concentration according to the characteristics required by the device in which the magnetic sensing device is installed. This allows for great flexibility in adjusting the working concentration.

Moreover, as shown in the embodiment, the configuration is simple, simply moving the conductor 9 forward and backward on the open magnetic path side of the reference coil _N22 , so the user can easily and reliably adjust the operating concentration, reducing costs. A magnetic detection device that is inexpensive and operates stably can be provided.

It should be noted that the conductor 9 only needs to be able to variably adjust the output voltage E ₂ of the reference coil N ₂₂ by adjusting its movement, and it is not limited to the screw connection as shown in the drawings, but can have various structures.

Further, the conductor 9 can also be replaced with a magnetic material such as ferrite. When a magnetic body is used instead of the conductor 9, the magnetic efficiency of the magnetic path of the reference coil _N22 and its output voltage _E2 are adjusted by adjusting the advance and retreat of this magnetic body. The detection level can be adjusted in the same way as when using .

Further, in order to make the explanation more concrete, the above embodiments have been explained using a magnetic detection device that detects toner concentration as an example, but the present invention is not limited to this, and the presence, amount, concentration, distance, etc. of a magnetic material, etc. It can be widely used for detection in general, and can also be used for detecting not only magnetic materials but also conductive materials. In the case of conductor detection, the output voltage of the detection coil decreases with the eddy current loss of the conductor, and the differential output changes, so this is utilized.

Effects of the Present Invention As described above, the present invention includes a drive coil excited with alternating current, a detection coil and a reference coil coupled to the drive coil, and the output of the detection coil and the reference coil are connected to each other. A magnetic detection device that uses a differential output with an output as a detection signal is characterized by having a circuit that adds a part of the drive coil drive voltage to the differential output. With a simple configuration that requires only a voltage adding circuit such as a variable resistor or a capacitor with a small capacitance on the detection coil side, variations in differential concentration due to manufacturing variations in differential transformers can be easily and reliably adjusted. Therefore, it is possible to provide a compact and inexpensive magnetic sensing device that can be used.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram of a magnetic sensing device according to the present invention, FIG. 2 is an electric circuit diagram of another embodiment of the magnetic sensing device according to the present invention, and FIG. 3 is a resonance characteristic diagram thereof. Figure 4 is also a phase characteristic diagram, and Figure 5
The figure is a sectional view of a differential transformer constituting the magnetic sensing device according to the present invention, FIG. 6 is an electric circuit diagram of a conventional magnetic sensing device, and FIG. 7 explains the circuit operation of the conventional magnetic sensing device. Figure 8 is a diagram showing the relationship between toner concentration and output voltage, Figures 9~
FIG. 11 is a wiring diagram of a differential transformer in a conventional magnetic sensing device. 1...AC drive source, 2...Differential transformer, 3...
...Signal processing circuit, 4...Voltage addition circuit, N ₁ ...
Drive coil, _N21 ...detection coil, _N22 ...reference coil, VR...resistance voltage divider circuit, _C1 ...capacitor.

Claims (1)

[Claims] 1. A drive coil excited by alternating current, a detection coil and a reference coil coupled to the drive coil, and a differential output between the output of the detection coil and the output of the reference coil. What is claimed is: 1. A magnetic detection device that uses a detection signal as a detection signal, comprising a circuit that adds a part of the drive coil drive voltage to the differential output. 2. The circuit is characterized by comprising a resistive voltage divider circuit connected between both ends of the drive coil, and a capacitor circuit connected from the resistive voltage divider circuit to either the reference coil or the detection coil. A magnetic sensing device according to claim 1. 3. The magnetic sensing device according to claim 2, wherein the resistance voltage divider circuit is a variable resistance circuit. 4. The magnetic sensing device according to claim 1, 2, or 3, characterized in that it has a resonant circuit on the side of the detection coil and the reference coil.