JPS61149859A - Magnetic detecting device - Google Patents

Abstract

PURPOSE:To adjust variance in operation density due to variance of the manufacture of a differential transformer easily and securely by adding part of the driving voltage of a driving coil to a differential output. CONSTITUTION:The differential transformer 2 is equipped with the driving coil N1 which is driven by an AC driving source 1, a detection coil N21 whose output voltage E1 varies with toner density, and a reference coil N22 which is not influenced by the toner density. The driving voltage Vin is divided by a resistance voltage dividing circuit VR and added to the differential output E0 between the output voltage E1 of the detection coil N21 and the output voltage E2 of the refernce coil N22 at one terminal side of the reference coil N22, so that E0=E2-E1+Vin1. This output is inputted to a signal processing circuit 3 and a phase or voltage discriminating means detects the toner density.

Description

[Detailed description of the invention] Industrial applications The present invention relates to the presence and amount of a magnetic material or a conductive material.

A magnetic detection device that magnetically detects concentration or distance, etc.
In particular, the present invention relates to a magnetic detection device suitable as a toner concentration detection device for electrophotographic developing materials containing magnetic carriers and insulating toner.

Conventional 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 capri 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. 59-10
No. 814).

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 Nl driven by the AC drive source 1, a detection coil N21 coupled to the drive coil N and whose output voltage E1 changes depending on the toner concentration, and a drive coil N1.
a reference coil N22 coupled to the reference coil N22, but whose output voltage E2 is not affected by toner concentration.

And a differential output E between the output voltage E1 of the detection coil N21 and the output voltage E2 of the reference coil N27.

(-E+ -E2) is input to the signal processing circuit 3, and the toner concentration is detected by means such as phase discrimination or voltage discrimination of the differential output Eo.

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. The voltage Vi between the terminals of the drive coil N1 which is also supplied with the AC drive source 1
If n has a waveform as shown in FIG. 7(a), a constant voltage E2 as shown in FIG. 7(b) will be applied to the reference coil N22 depending on the turns ratio between it and the drive coil N1. It has occurred. The voltage E2 is approximately in phase with the drive voltage Vin applied to the drive coil N1. On the other hand, as shown in FIG. 7(C), 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. Since this voltage E+ is differentially connected to the reference coil N22, the voltage Vin between the terminals of the drive coil N1
and has a phase difference of 180° (electrical angle) with respect to the voltage E1 of the reference coil N21.

Here, when the toner concentration shows a normal value, the detection coil N
21 is the output voltage E1 of the reference coil N22?
Assuming that the differential output Eo is set to be smaller, the differential output Eo becomes Eo = E2 - E1 > 0, and as shown in FIG. 7(d), the difference in phase with the drive voltage Vin of the AC drive source 1 Generates dynamic output EOI.

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 of the reference coil N27 increases. Detection coil N from E2
The output voltage E1 generated at 21 becomes higher, and the differential output Eo
Eo =E2-E+ <0, and the phase of the AC drive source l with respect to the drive voltage Vin is reversed. Therefore, the detection coil N21 and the reference coil N22 are designed so that a phase reversal occurs at a certain determined toner concentration, and by performing phase discrimination in the signal processing circuit 3, the signal processing circuit 3 as shown in FIG. The toner concentration can be detected by outputting an output voltage V out as shown in (e).

Problems to be Solved by the Invention By the way, important characteristics of this type of differential transformer type magnetic sensing device include the 1 working concentration and the differential sensitivity. Figure 88 is a diagram explaining the working density and differential sensitivity, where the working density is the toner density T when the output voltage V out becomes the set value Vd.
C+ ($), and the differential sensitivity is the degree of change in output voltage V out with respect to change in working concentration (ΔVout/ΔT
G).

Of these, the operating concentration is, in principle, the voltage E1 of the detection coil N21 when no toner is present and the voltage E1 of the reference coil N22.
The difference in voltage E2 between the detection coil N21 and the reference coil N
It is determined by a turns ratio of 22. However, depending on the winding method of these coils N21 and N22 and the position of the center core, there will be variations in the differential output and operating concentration even if the turns ratio is the same.In particular, since the operating transformer is highly sensitive, it will be difficult during mass production. Significant variations in the properties have occurred, which has been a factor in lowering the yield of products.

As a means for adjusting the working concentration and differential sensitivity, two sets of differential transformers 21 and 22 are prepared as shown in FIG. It is known that the other differential transformer 22 is provided with an adjustment mechanism for fine adjustment to slightly move the core 24 in the direction indicated by the arrow.
1.22 is required, which has the disadvantage of increasing the overall size and cost.

Another adjustment means is as shown in FIG. 1O.

It is also possible to provide a voltage variable circuit VR, , VR2 between the terminals of the reference coil N22 or the detection coil N21 or both, but the voltage variable circuits VR, , VR
2 changes the phase of the differential output EO, and if the processing circuit 3 adopts a phase discrimination method, the differential sensitivity will drop significantly.

As a means of suppressing the phase change caused by the voltage variable circuit, the first
As shown in Figure 1, a buffer circuit Bl is connected to the coil output.
B2 is connected, and after this buffer circuit B+, B: (
Fi Niden 11: +i (A circuit configuration in which the transformer circuit VR3 is connected is conceivable, but buffer circuits B1 and B2 are required, 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 FIG. 0, 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 Win applied from the AC drive source 1 to the drive coil N1 to the differential output EO of the detection coil N21 and the reference coil N22. In this embodiment, a resistive voltage divider circuit V consisting of a variable resistor is connected between the terminals of the drive coil N1.
The circuit configuration is such that a capacitor CI is connected between the variable terminal of the variable resistor constituting the resistance voltage divider circuit VR and one end of the reference coil N22. 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 resistance voltage divider circuit VR, and the divided voltage V
inl is connected to the reference coil N22 through the capacitor CI.
is added to the differential output EO at one end of the differential output ED.

Eo=E2-E1+Vin+. Therefore, since the output voltage El of the detection coil N21 required to cause one phase reversal changes in accordance with the added voltage Vin+, the 1 actuation source also changes in accordance with the added voltage Vin1.

Furthermore, this embodiment adopts a configuration in which the driving voltage Vin is divided by a resistive voltage dividing circuit VR made up of a variable resistor, so that the additional voltage Vinl can be freely adjusted, and the operating concentration can be freely adjusted. is possible. Furthermore, depending on the position of the variable terminal of the variable resistance circuit VR, the phase of the added voltage V irH can be in phase with the drive voltage Vin or have a phase difference of 180°, so the drive voltage No matter which side the phase of the differential output Eo shifts with respect to Vin, variable adjustment can be easily performed.

Furthermore, in this embodiment, since the circuit configuration is such that addition is performed through the capacitor C1, the drive coil N1 side and the detection coil N1 side are connected to each other.
21. The DC bias circuits on the reference coil N22 side can be separated from each other. Note that the capacitor CI is selected to a value that does not make the coupling between the drive coil N1 side and the detection coil N21 and reference coil N22 sides too tight, for example, a value of about 1 to 50 PF.

FIG. 2 is an electrical circuit connection diagram of another embodiment of the magnetic sensing device according to the present invention. In FIG. 0, 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, these coils N2 are provided on the detection coil N21 and reference coil N22 sides.
This is because the capacitor C2, which forms a resonant circuit, is connected together with the interface L of + and N27. As is well known, the resonant frequency fO of the resonant circuit in this case is f
o = 1/2gr and Td, and a resonant circuit generally has resonance characteristics as shown in Fig. 3 and phase characteristics as shown in Fig. 4. Therefore, in this embodiment, Capacitor C forming the resonant circuit
2. Selection of temperature characteristics or capacitance value or AC drive source l
By adjusting the frequency, etc., the resonance characteristics shown in Fig. 3 and the phase characteristics shown in Fig. 4 are changed, and the phase change and voltage value change of the differential output EO due to temperature fluctuation of the entire system are absorbed.
Perform temperature compensation.

When a resonant circuit as described above is provided, the value of the capacitor C2 becomes relatively large, so the time constant of the circuit from the drive coil Nl side to the capacitor C2 via the voltage addition circuit 4 described above becomes large, and the differential output Eo becomes There are concerns that this may cause a phase shift and a decrease in differential sensitivity. However, in the present invention, since the capacitor C1 constituting the voltage adding circuit 4 is selected to have a small capacitance value of, for example, about 1 to 50 PF, the voltage adding circuit 4 is connected to the capacitor C2 from the drive coil N side. The time constant of the circuit leading to
It is dominated by the capacitor CI, and phase shift poses almost no 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 example,
For example, 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 N1 is continuously wound around the middle leg portion 51.61 of the core 5.6. At the same time, a detection coil N21 is attached to the middle leg portion 51, and a detection coil N21 is attached to the middle leg portion 6.
1 is wound with a reference coil N22, respectively. Face plate 7 of non-magnetic case 7 located at the front of core 5 on the open magnetic path side
The surface side of the toner 1 is used as a toner detection surface that the toner 8 comes into contact with.

Reference numeral 9 denotes a conductor movably provided in a part of the open magnetic path of the reference coil N72. In this embodiment, the non-magnetic case 7
A screw-shaped conductor 9 made of a conductive material such as brass or aluminum is screwed to the side plate 72 of the
On the open magnetic path side formed in front of the end face of the core 5 constituting the reference coil N22, as shown by the arrow (A), the core 5
It is installed so that it can be adjusted forward and backward parallel to the end face of the

When the conductor 9 as described above is provided, when the drive coil N1 is driven, an eddy current is generated in the conductor 9 due to the magnetic flux generated in the reference coil N22, and the output voltage E2 generated in the reference coil N22 is increased due to this eddy current effect. Change. Therefore, the output voltage E? produced in the reference coil N22 by adjusting the movement of the conductor 9? It becomes possible to variably adjust the differential output EO between this output voltage E2 and the output voltage E1 generated at the detection coil N21, thereby adjusting the operating concentration. Therefore, this embodiment has two types of working concentration adjustment functions: one using the conductor 9 and the other using the voltage application circuit 4 described above. With such two types of working concentration adjustment mechanisms, the working concentration adjustment by the voltage adding circuit 4 is exclusively used as a means for absorbing manufacturing variations in the differential transformer, and the working concentration adjustment by the conductor 9 is performed by the magnetic detection. It can be used as a means for the user to adjust the working concentration according to the characteristics required by the equipment in which the device is installed, and the flexibility in adjusting the working concentration is extremely high.

Moreover, as shown in the embodiment, since the configuration is simple, simply moving the conductor 9 forward and backward on the open magnetic path side of the reference coil N22, the user can easily and reliably adjust the operating concentration.
A magnetic detection device that is inexpensive and operates stably can be provided.

The conductor 9 adjusts its movement to adjust the output voltage E? of the reference coil N22. It is only necessary to be able to adjust fff, and it is not limited to a screw connection as shown in the figure, but various structures can be used.

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. Similarly, the detection level can be adjusted.

Furthermore, 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 substance, etc.
Can be widely used for detecting magnetic substances in general, and is not limited to magnetic substances.
It can also be used to detect conductors. In the case of conductor detection, the output voltage of the detection coil decreases due to 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. A magnetic detection device that uses a differential output as a detection signal is characterized by having a circuit that adds a part of the driving coil drive pressure to the differential output,
From the drive coil side to the base coil or detection coil side,
For example, with a simple configuration that includes a voltage addition circuit using a variable resistor, a small capacitance Ida 1 capacitor, etc., it is possible to eliminate /< irregularities in the operating concentration due to manufacturing variations in differential transformers.
A compact and inexpensive magnetic sensing device that can be easily and reliably adjusted can be provided.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram of a magnetic sensing device according to the present invention, f
Figure s2 is an electric circuit diagram of another embodiment of the magnetic sensing device according to the present invention, Figure 3 is a resonance characteristic diagram thereof, and Figure 4 is a diagram of its resonance characteristics.
5 is a cross-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 is a diagram of a conventional magnetic sensing device. FIG. 8 is a waveform diagram for explaining the circuit action of the magnetic detection device, and FIG. 8 is a diagram showing the relationship between toner concentration and output voltage. 9 to 11 are wiring diagrams of a differential transformer in a conventional magnetic sensing device. 1-・-AC drive M 2・Fist・Differential transformer 3...
Signal processing circuit 4・φ・Voltage addition circuit N, ... Drive coil N21 ''-φ detection coil N72・Reference coil VR...Resistor voltage divider circuit C1...Capacitor Fig. 1 R Fig. 2 3 Figure 1 Shipi Liaowen □ Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 B+

Claims (4)

[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 is used as a detection signal. What is claimed is: 1. A magnetic sensing device comprising: a circuit for adding a part of the drive coil drive voltage to the differential output. (2) The circuit includes 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, characterized in that: (3) The magnetic sensing device according to claim 2, wherein the resistance voltage divider circuit is a variable resistance circuit. (4) Claims 1 and 2 include a resonant circuit on the detection coil and reference coil sides.
The magnetic sensing device according to item 1 or 3.