JPS6367583A - Magnetism detector - Google Patents

Abstract

PURPOSE:To clearly discriminate whether or not there is a magnetic body by detecting synchronously the detected value signal of a detection coil by a phase detection coil as a phase reference. CONSTITUTION:An exciting coil 2 produces a magnetic field with an alternating current from an oscillator 1. Part of this magnetic field penetrates detection coils 3 and 3a, which induce voltages. Further, the phase detection coil 8 is arranged so as to penetrate the magnetic field produced by the coil 2 the same phase at all times. Then the voltage induced cross the coils 3 and 3a are amplified to become detection signals a1 and a2, which are detected synchronously by synchronous detecting circuits 13 and 13a with a synchronizing signal (b) generated by the coil 8.

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 is particularly applicable to an automatic guided vehicle that runs using a magnetic material or a conductive material as a guide lane. The present invention relates to a magnetic detector used for KaiDrain.

[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,
Objects to be guided (vehicles, etc.) by installing a conductive material such as a magnetic material or metal in the form of a strip on the road to be guided as a guide lane.
The system learns the direction of the guide lane from the signal from a detector attached to the vehicle, and steers accordingly to guide the vehicle to its destination.

As a conventional magnetic detector, the coil arrangement shown in Figure 9 is the first one.
The circuit configuration shown in Fig. 0 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 4 is generated from the excitation coil 2. When a portion of this excitation magnetic field 4 penetrates the sensing coils 3, 3a, an induced voltage is generated in the sensing coil 3.3a.

This induced voltage is input to the signal processing circuit shown in FIG. The induced voltages of the detection coils 3 and 3a are respectively rectified by rectifier circuits 6 and 6a through amplifier circuits 5.5a and then input to a differential circuit 7, where the difference between the two signals from the detection coils 3 and 3a is output. Ru.

In a magnetic detector having such a configuration and function, when a magnetic body having a relative magnetic permeability larger than air approaches the detection coil 3, the magnetic field distribution changes and the magnetic flux passing through the detection coil also changes. Furthermore, when a conductor approaches, the magnetic field changes due to eddy currents generated in the conductor. As a result, the voltage induced in the sensing coil will also change. Magnetic material or conductive material is 2
Symmetrical position from the two detection coils (on the center axis in Figure 9)
, the magnetic field distribution becomes symmetrical and the induced voltages of the two detection coils are also equal, so the detector output is also zero. However, when a guide lane made of a magnetic or conductive material approaches one of the sensing coils, 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 guide lane.

Next, changes in the magnetic field when a magnetic body approaches will be explained in more detail. FIG. 3(a) shows the detection coil 3, the Tli material 11, and the lines of magnetic force around them. A solid line 9 is a line of magnetic force when the magnetic body 11 is not present, and a broken line 10 is a line of magnetic force when the magnetic body 11 approaches the detection coil 3. As shown in FIG. 3(a), when the magnetic body 11 approaches, the lines of magnetic force change from a solid line 9 to a broken line 9 as if being sucked into the magnetic body 11. At this time, the total sum of magnetic flux that perpendicularly passes through the detection coil 3 is also calculated as shown in Figure 3 (
'b) decreases from the size of the solid line arrow to the size of the broken line arrow, and the induced voltage becomes smaller. Therefore, in FIG. 10, the output of the rectifier circuit 6 on the side closer to the magnetic body 11 is smaller than the output of the other rectifier circuit 6a, and the output of the differential circuit 7 becomes positive or negative accordingly.

[Problem that the invention seeks to solve]

When the guide lane is very close to the conventional detector described above, the magnetic field line distribution changes greatly from the solid line 9 in FIG. , the same figure (the direction shown by the solid line arrow in BL is reversed from the direction shown by the broken line arrow).The induced voltage in the detection coil 3 is passed through the rectifier circuit 6 as described above, so it decreases as the distance from the magnetic body becomes smaller. When the magnetic body 11 approaches further and the direction of the lines of magnetic force becomes reversed, the output voltage of the rectifier circuit 6 increases as the distance from the magnetic body 11 decreases.

That is, when the magnetic body 11 approaches a certain distance or more,
The disadvantage was that it could not be distinguished from the case without magnetic material.

[Means for solving problems]

In order to eliminate such drawbacks, the present invention provides an excitation coil that generates an alternating magnetic field, a detection coil that generates an induced voltage by the magnetic field generated by the excitation coil, and a detection coil that generates an induced voltage by the magnetic field and detects the phase of the generated magnetic field. The detector is provided with a phase detection coil and a synchronous detection circuit that synchronously detects a detection signal caused by the voltage induced in the detection coil using a synchronous signal caused by the voltage induced in the phase detection coil.

[Effect]

In the present invention, a negative voltage is output when the direction of the magnetic flux passing through the sensing coil is reversed.

〔Example〕

An embodiment of the magnetic detector according to the present invention is shown in FIGS. 1 and 2. FIG. 1 is a layout diagram showing the arrangement of each component of the present detector, and FIG. 2 is a circuit diagram showing the circuit of the present detector. In FIGS. 1 and 2, the same or equivalent parts as in FIGS. 9 and 10 are given the same reference numerals.

In FIG. 1, an excitation coil 2 generates a magnetic field using an alternating current from an oscillator 1. A part of this magnetic field penetrates the sensing coil 3.3a, so that an induced voltage is generated in the sensing coils 3, 3a. The phase detection coil 8 is installed at a position where the magnetic field generated from the excitation coil 2 always penetrates with the same phase.

In FIG. 2, the induced voltage of the detection coil 3.3a is amplified by the amplifier circuit 12.12a to become detection signals al and a2. These detection signals al and a2 are transmitted to the synchronous detection circuit 13.
13a, synchronous detection is performed using a synchronous signal S which is a signal obtained by amplifying the induced voltage generated in the phase detection coil 8.

Figure 5 shows the waveforms of various parts of the circuit in Figure 2 when a magnetic body approaches this detector with such a configuration and function and the magnetic field line distribution changes as shown in Figure 3+8). FIG. 6 shows waveforms of various parts when changing as shown in (a). Figure 5 (a
) and FIG. 6(a) show detection signals al (broken line) and a2 (solid line), which are signals obtained by amplifying the induced voltage of the detection coil 3.3a by the amplifier circuit 12.12a, and FIG. 5(b)
) and FIG. 6(b) show the synchronous signal S which is a signal obtained by amplifying the induced voltage of the phase detection coil 8 by the amplifier circuit 12b, and FIG.
．． Detection signals cl (broken line) and c2 (solid line), which are the outputs of 13a, are shown.

Detection signal al shown in broken line shown in Fig. 5 (a) + Fig. 5 TC)
The detected signal C1 indicated by the broken line is generated by the magnetic body 1 in FIG. 3(a).
This is a signal based on 1. The detection signal C2 is due to the induced voltage of the detection coil 3a, which is not affected by the magnetic body 11. The level of the detection signal CI becomes ■1 due to the decrease in the amount of magnetic flux penetrating the detection coil 3 as shown in FIG. ing.

Furthermore, the detection signal al shown in the broken line shown in FIG. 6(a) and the detection signal c1 shown in the broken line shown in FIG.
This is a signal based on 1. As in the case of FIG. 5, the detection signal C2 is due to the induced voltage of the detection coil 3a, which is not affected by the magnetic body 11. As shown in FIG. 6 [al], the level of the detection signal c1 is inverted in polarity from positive to negative because the phase of the detection signal a1 is inverted.

Since the phase detection coil 8 is installed at a position where the lines of magnetic force penetrate in a constant phase (direction) even when the magnetic field is disturbed by the magnetic body 11, it can serve as a reference for the phase (direction) of the lines of magnetic force passing through the detection coils 3 and 3a. .

Therefore, the detection signal that is synchronously detected using the synchronous signal generated by the voltage induced in the phase detection coil 8 changes from positive to negative as the distance to the magnetic body 11 becomes smaller.

In this embodiment, it is sufficient that the phase detection coil 8 is located at a position where the phase will not be reversed due to the disturbance of the magnetic field even when a magnetic body or a conductive body approaches, and the phase detection coil 8 is wound around the excitation coil 2 as shown in FIG. It may be something that you do. Furthermore, the same effect can be obtained even if the detection coils 3 and 3a are installed with the axes of the coils perpendicular to the plane of the paper, as shown in FIG.

[Effects of the Invention] As explained above, the present invention provides a phase detection coil serving as a phase reference, and uses a synchronization signal caused by the induced voltage of the phase detection coil to synchronously detect a detection signal caused by the induced voltage of the detection coil. By doing this, it is possible to output a negative voltage when the direction of the magnetic flux passing through the detection coil is reversed, and the detection signal can be monotonically decreased as the magnetic object approaches, making it possible to clearly distinguish whether there is a magnetic object or not. effective.

[Brief explanation of the drawing]

Fig. 1 is a layout diagram showing an embodiment of a magnetic detector according to the present invention, Fig. 2 is a circuit diagram showing its circuit, and Figs. 3 and 4 show changes in magnetic flux distribution due to the approach of a magnetic body. Explanatory drawings, FIGS. 5 and 6 are waveform diagrams corresponding to FIGS. 3 and 4, showing waveforms of various parts of the circuit in FIG. 2, and FIG. 7 is a layout showing a second embodiment of the present invention. 8 is a layout diagram showing a third embodiment of the present invention, FIG. 9 is a layout diagram showing the configuration of a conventional magnetic detector, and FIG. 10 is a circuit diagram showing the circuit. 1... Oscillator, 2... Excitation coil, 3.3a...
Detection coil, 4... Line of magnetic force, 7... Differential circuit, 8...
・・Phase detection coil, 12.12a, 12b=-・
Amplifier circuit, 13.13a... synchronous detection circuit.

Claims (1)

[Claims] an excitation coil that generates an alternating magnetic field; a detection coil that generates an induced voltage by the magnetic field created by the excitation coil; a phase detection coil that generates an induced voltage by the magnetic field and detects the phase of the generated magnetic field; A magnetic detector comprising: a synchronous detection circuit that synchronously detects a detection signal using a synchronous signal generated by an induced voltage of the phase detection coil.