JPH02214907A - Magnetic sensor - Google Patents

Abstract

PURPOSE:To facilitate the position control of a sensor coil by forming a sensor coil with using at least two coils by adding together the conductive voltage signals of both coils after amplifying them with each prescribed amplification factor. CONSTITUTION:The sensor coils 4 and 4a containing two coils 41/42 and 43/44 respectively are set against an exciting coil 2. The signals of coils 41 and 42 are amplified and added together via an addition circuit 5. In this case, the amplification factors are varied by the variable resistors 51 and 52. Both coils 41 and 42 are set opposite to each other centering on the balanced point of a magnetic field and therefore their inductive voltage phases are set adverse to each other. The coil 4a also has the same structure as the coil 4. Thus the positions of the sensor coils can be controlled via the control of the variable resistors. Then the position control is facilitated for the sensor coils.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic detector for detecting a magnetic material or a conductive material, and in particular, it is used for an automatic guided vehicle that travels using a magnetic material or a conductive material as a guide lane. This invention relates to a magnetic detector for guide lanes.

[Conventional technology]

One type of magnetic detector that detects the presence of a magnetic substance is a self-excitation type that includes an excitation coil that generates an alternating magnetic field and a detection coil that generates an induced voltage by the generated magnetic field. This has been widely used and has been effective because it has a simple structure and a high degree of freedom in design.

As one field of application, this technology is used and useful in various vehicle guidance systems. In these guidance systems, a conductive material such as a magnetic or metal strip is installed as a guide lane on the road to be guided, and the direction of the guided lane is determined from the signal of a detector attached to the object to be guided (vehicle, etc.). This information is used to guide the vehicle to the desired location by steering the vehicle accordingly.

As a conventional magnetic detector, the coil arrangement shown in Fig. 4 is
The circuit configuration shown in the figure is known.

The operation of this magnetic detector will be explained. First, connect the oscillator 1 to the excitation coil 2 and apply an alternating current to the excitation coil 2.
flow to. Then, an excitation magnetic field 9 is generated from the excitation coil 2. A part of this excitation magnetic field 9 penetrates the sensing coils 3, 3a, so that an induced voltage is generated in the sensing coils 3, 33.

This dielectric voltage is input to the signal processing circuit shown in FIG. The induced voltages of the detection coils 3 and 3a are respectively amplified by an amplifier circuit 8.
．． After passing through 8a and being rectified by a rectifier circuit Fl@6.6a, it is input to a differential circuit 7, and the difference between the two signals by the detection coil 3.3fi is output.

In a magnetic detector having such a structure and function, when a magnetic body having a relative magnetic permeability larger than air approaches the detection coil 3.31, the magnetic field distribution changes and the magnetic flux passing through the detection coil 3.3a also changes. Furthermore, when a conductor approaches, the magnetic field changes due to eddy currents generated in the dielectric. This 1. Result,
The voltage induced in sensing coil 338 will also change. If the magnetic material or dielectric material is located at a symmetrical position with respect to the two detection coils 3, 3a (on the center axis in Fig. 4), the magnetic field distribution will be symmetrical, and the induced voltages of the two detection coils 336 will be equal, so that detection will not be possible. The device output also becomes zero. However, when the guide lane made of magnetic or dielectric material approaches one side of the sensing coil, the voltages of the left and right sensing coils become unbalanced, and the output voltage of the differential circuit 7 becomes positive or negative depending on the degree of unbalance. becomes. Therefore, by using this voltage as a control signal, an object to be guided (such as a vehicle) can be caused to travel along the guided lane.

Next, changes in the magnetic field when a magnetic body approaches will be explained in more detail.

FIG. 5(a) shows the detection coil 3. It shows the magnetic body 11 and lines of magnetic force around it.

The solid line is the magnetic force line 101 when the magnetic body 11 is not present, and the broken line is the magnetic force line 10b when the magnetic body 11 approaches the detection coil 3. As shown in FIG. 5(a), the magnetic body 11
When approaches, the lines of magnetic force change from a solid line to a broken line as if being sucked into the magnetic body 11. At this time,
The total sum of magnetic flux that perpendicularly penetrates the detection coil 3 is also shown in Fig. 5(b).
decreases from the size of the solid arrow to the size of the dashed arrow,
The induced voltage becomes smaller. Therefore, in FIG. 3, the output of the rectifying circuit on the side closer to the magnetic body 11 is smaller than the output of the other rectifying circuit, and the output of the differential circuit 7 becomes positive or negative accordingly.

[Problem to be solved by the invention]

In the conventional magnetic detector described above, in order to increase the difference in output voltage value when an object to be detected (magnetic material or conductive material) is close to the detection coil and when there is no object to be detected in the surrounding area, It is necessary to reduce the voltage applied to the detection circuit when there is no object to be detected. That is, it is necessary to fix the sensing coil near a point where the horizontal magnetic fields are balanced on the left and right sides, such as point A on straight line C of balanced straight lines B and C shown by broken lines in FIG. However, since the rate of change in the magnetic field strength near the equilibrium point is large, it has the disadvantage that position setting is difficult.

[Means to solve the problem]

The magnetic detector of the present invention includes an oscillation circuit, an excitation coil that generates a DC magnetic field with the output signal of the oscillation circuit, and at least two that generate an induced voltage signal by the AC magnetic field generated by the excitation coil. It is configured to include two detection coils each consisting of a coil, and two adder circuits that amplify and add induced voltage signals from the respective coils at a predetermined ratio.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

As shown in FIG. 1, this embodiment includes an oscillation circuit 1, an excitation coil 2 that generates an alternating current magnetic field with the output signal of the oscillation circuit 1,
Two coils 41.42 and 43.4 each generate an induced voltage signal by the alternating magnetic field created by the excitation coil 2.
Detection coils 4, 4a formed from coils 41.4 and 41.4a;
42 and coils 43 and 44 at a predetermined ratio for each of the detection coils 4 and 46, and an addition circuit 5.51, and an addition circuit 5.
, 58, and a differential circuit 7 that outputs the difference value between the outputs of the rectifier circuits 6, 68.

FIG. 2 is a plan view of the coil arrangement of the embodiment of FIG. 1.

As shown in FIG.
Detection coils 4, 4a having coils 41, 42 and 43, 44 are arranged.

The signals from the coils 41 and 42 of the detection coil 4 are each amplified and added by the adder circuit 5, and the degree of amplification is made variable by variable resistors 51 and 52. Since the two coils 41 and 42 are placed on the left and right with the magnetic field equilibrium point in between, the induced voltage phases are opposite to each other. Also, the detection coil 4. The side is also the same as above.

Therefore, by calculating the sum of these values, it is possible to reduce the voltage when the object to be detected is not around. Also,
When trying to set this voltage value to an arbitrary value,
Instead of adjusting the position of the detection coil, only the variable resistor can be adjusted, making the adjustment easier.

〔Effect of the invention〕

As explained above, the present invention provides at least two detection coils.
By amplifying the induced voltage signals of each coil at a predetermined amplification factor and adding them together, the position of the detection coil can be adjusted electrically instead of mechanically. This has the effect of making adjustment extremely easy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, and FIG. 2 is a block diagram of an embodiment of the present invention.
FIG. 3 is a block diagram of an example of a conventional magnetic detector; FIG. 4 is a plan view showing the coil arrangement of the magnetic detector of FIG. 3; FIG. a) and (
b) is an explanatory diagram showing changes in magnetic lines of force passing through the detection coil and changes in magnetic flux perpendicularly penetrating the detection coil due to an object to be detected, respectively, to explain the operation of the magnetic detector shown in Fig. 3;
This figure is an explanatory diagram showing an excitation magnetic field of an excitation coil for explaining the operation of the magnetic detector of FIG. 3. 1... Oscillation circuit, 2... Excitation coil, 3, 3. . 4.4a...detection coil, 5,5a...addition circuit,
6.68... Rectifier circuit, 7... Differential circuit, 8, 8a
...Amplification circuit, 9...Excitation magnetic field, 10. ．． 10.・
... Lines of magnetic force, 11... Magnetic material, 41, 42, 43.4
4... Coil, 51.52... Variable resistor.

Claims (1)

[Claims] an oscillator circuit, an excitation coil that generates a DC magnetic field with an output signal of the oscillation circuit, and two sensing coils each consisting of at least two coils that generate an induced voltage signal by the AC magnetic field generated by the excitation coil. and two adder circuits that amplify and add induced voltage signals from each of the coils at a predetermined ratio.