JPS5843710B2 - Kinzokubutsutaino Kenchihouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting a metal object using phase changes caused by eddy currents of alternating magnetic flux.

Conventionally, to detect the edge of a steel plate, etc., an optical means has been adopted in which a projector and a light receiver are appropriately arranged and the light is blocked or reflected.

However, in this case, the optical device may malfunction due to dust, dirt, oil, water, etc., and may also malfunction due to surface conditions such as unevenness of the metal object to be detected, resulting in poor reliability. Become.

In addition, a non-contact sensor using inductance is used to detect the approach and passage of a metal object to be detected, but in this case, such a non-contact sensor has low resolution and cannot detect with high precision. It is unsuitable for detecting parts of the body.

Therefore, at present, microsinches are still used to detect the approach, passage, and edge of metal objects.

Since such a micro-sinch uses contacts, its lifespan is limited and the micro-sinch must be replaced frequently, which is uneconomical.

U.S. Pat. No. 3,872,380 describes a metal detector, commonly known as a mine detector, which detects metal objects on the ground or underground by analyzing changes in the magnetic field generated by a large transmitter coil and a receiver coil. To detect.

Although this detector has the ability to distinguish between currency on the ground or underground, it is not a device that detects the relative position of an object with respect to the coil.

SUMMARY OF THE INVENTION The object of the present invention is to eliminate the above-mentioned drawbacks and to provide an economical detection method that allows semi-permanently detecting the approach, passage and edge of a metal object using one type of device.

The present invention will be explained with reference to the drawings.

First, the basic principle of the present invention will be explained.

When an alternating current is passed through a coil with an air core or an iron core, an alternating magnetic flux (primary magnetic flux) is generated, and this magnetic flux forms a closed magnetic path that exits from one end of the coil and returns to the other end.

When a metal conductor enters the magnetic flux of this closed magnetic path, an eddy current is induced in this metal conductor, and this eddy current causes the magnetic flux (
secondary magnetic flux) is generated.

The present invention focuses on the primary magnetic flux generated by this magnetic flux generating coil and the
The purpose is to utilize the composite magnetic flux of the secondary magnetic flux and the secondary magnetic flux caused by the eddy current.

FIG. 1 shows a basic configuration for explaining the detection method of the present invention.

In the figure, 1 indicates a steel plate being transferred on rollers 2.

As shown in FIG. 2, a coil 3 for generating an alternating magnetic field is disposed below the steel plate 1, and a search coil 4 for detecting an alternating magnetic field is disposed on the side of the steel plate 1.

Now, if we assume that the minute component of the magnetic flux that comes out of the alternating magnetic field generating coil 3 and interlinks with the search coil 4 is a composite vector, if the inclination direction of the composite vector is positive, the X-direction component of this vector will also be positive. Therefore, the phase of the signal induced in the search coil 4 varies between 0 and 90' with respect to the phase of the reference signal supplied to the alternating magnetic field generating coil 3, depending on the inclination angle of the composite vector.

When the direction of the resultant vector becomes perpendicular to the search coil 4, the X-direction component of the vector becomes zero, but in reality, there is a spatial spread of the search coil and the asymmetry of the magnetic flux, so there is a slight signal in the search coil. induced.

The phase of that signal is therefore shifted by 90' with respect to the phase of the reference signal.

Furthermore, when the inclination direction of the composite vector is negative, the X-direction component of this vector is negative, and therefore the phase of the signal induced in the search coil 4 is 90 to 90% relative to the phase of the reference signal depending on the inclination angle of the composite vector. Shifts between 180°.

Therefore, the phase change of the signal induced in the search coil 4, that is, the change of 0 to 180°, is due to the slight movement of the metal object to be detected (
2 to 3 M), and as will be described later, it is an extremely effective method particularly for detecting the edge of a metal object to be detected.

Therefore, in combination with the magnetic flux generated by the eddy current when the search coil 4 passes through the steel plate 1, the phase of the induced signal is reliably 18.
Position it in advance at a point where it changes by 0°.

Therefore, when the steel plate 1 approaches, the amplitude of the induced voltage of the search coil 4 changes to decrease, so the external device is started to operate by the voltage signal when this amplitude reaches a certain value.

When the steel plate 1 begins to pass, the phase of the signal induced in the search coil 4 shifts by 180° as described above.

When the steel plate 1 finishes passing, the phase of the signal induced in the search coil 4 returns to its original phase.

In this way, the approach and passage of the steel plate 1 can be detected.

In addition, when detecting the edge, the search coil 4 is moved parallel to the width direction of the steel plate 1 as shown in FIG. so that it can be set to

Furthermore, even if the width of the steel plate 1 changes, if feedback is applied so that the phase of the induced signal can always shift by 90' with respect to the phase of the reference signal, the edges can be traced.

Next, an apparatus for carrying out the detection method of the present invention will be explained.

As shown in FIG. 3, a reference signal is supplied from a reference alternating signal generator 5 to an alternating magnetic field generating coil 3 provided below the steel plate 1, so that the coil 3 generates an alternating magnetic flux.

The output signal of this reference signal generator 5 is also supplied to a phase comparator 6.

The output signal of the search coil 4 provided on the side of the steel plate 1 is supplied to a waveform shaper 8 for extracting a signal with the same amplitude as the reference signal via an amplifier T, and the output signal of the waveform shaper 8 is phase-compared. to the other input side of the device 6.

Therefore, when the steel plate 1 approaches the search coil 4, the amplitude of the output voltage induced in the coil 4 begins to decrease, and when this amplitude reaches a predetermined value, this voltage signal activates the required external device. Make it.

This external device activation signal is taken out from the output side of amplifier γ.

When the steel plate 1 begins to pass, the phase 5 of the signal induced in the search coil 4 (shifted by 180 degrees with respect to the phase of the reference signal) is detected by the phase comparator 6 and displayed on the display device 9. .

The phase shift state of 90' in the case of detecting the end of the steel plate 1 can also be displayed in the same manner as described above.

As is clear from the above, according to the present invention, there is no adverse effect from dust, dirt, oil, or water, or from the surface condition of the metal object to be detected.

In addition, high-precision resolution can be obtained by detecting phase changes in the signal, and therefore detection of approach (voltage amplitude), passage (180° phase shift), and edge (90° phase shift) of the metal object to be detected can be achieved. can be performed at the same time, and since it is non-contact detection, it is extremely economical.

Further, in order to utilize the phenomenon of eddy current, not only a steel plate but also a voltage-sensitive non-magnetic metal such as a red-hot steel plate, copper, aluminum, etc. can be used as the metal object to be detected.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the basic configuration of the detection method of the present invention;
The figure is also a sectional view taken along line n-I, and FIG. 3 is a block diagram showing an apparatus for carrying out the detection method of the present invention. 1...Metal object to be detected (steel plate), 2...
・Roller, 3... Coil for generating alternating magnetic field, 4.
... Search coil, 5 ... Reference signal generator, 6 ... Phase comparator, γ ... Amplifier, 8 ... Waveform shaper , 9...display device.

Claims (1)

[Claims] 1. In a method for detecting the proximate end, passage, and away end of a moving metal object in metal object manufacturing/processing equipment, an air space fixed above or below in a direction perpendicular to the metal object passage path is used. An alternating magnetic flux is generated by an alternating magnetic flux generating device consisting of a core or a coil containing an iron core, and the alternating magnetic flux is detected by a magnetic flux detection search coil fixed laterally in a direction perpendicular to the path through which the metal object passes. The approach of the object to be detected is detected by decreasing the voltage amplitude value of the induced voltage of the search coil, and the passage of the object to be detected and the phase shift of 90 degrees are caused by a 180° phase shift of the phase change of the detected induced voltage of the search coil. A method for detecting a metal object, comprising detecting an end of the object to be detected.