JP2000056032A - Metal detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal detecting device capable of detecting a ferrous metal and a nonferrous metal respectively by itself with high sensitivity. SOLUTION: A transmitting coil 5 is driven to generate alternating magnetic field, two receiving coils 6A, 6B are arranged to receive the alternating magnetic field, signals induced in the receiving coils 6A, 6B are changed by the effect of a metal mixed in an inspected object 7 passing through the magnetic field, and the metal is detected by this metal detecting device. The transmitting coil 5 is driven by a circuit system driving the transmitting coil 5 at two frequencies 1A, 1B in turn in time division, the unbalanced output signal of the difference between voltages V1 and V2 induced in the receiving coils 6A, 6B is extracted in time division to separate two frequency components, and a ferrous metal and a nonferrous metal are detected with high sensitivity by the metal detecting device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal detecting device for detecting ferrous and non-ferrous metals mixed in a test object.

[0002]

2. Description of the Related Art Many prior arts are based on the principle of FIG.

A signal from a transmitter is sent to a transmission coil via a drive circuit to generate an alternating magnetic field. Receiving coil R1, R
2 is a voltage V that generates an induced voltage by receiving magnetic field lines of an alternating magnetic field.
If they are arranged so that 1, V2 are equal, the voltage difference V1-V2 becomes zero. When the inspection object W is conveyed from one receiving coil R1 direction to the other receiving coil R2 direction (FIG. 2) so as to be affected by the magnetic field lines, the magnetic field lines change, resulting in V
1. A voltage difference of V2 occurs. This voltage difference is output as an unbalanced signal to detect metal. When ferrous metal is mixed in the inspection object W, as shown in FIG. 2, the magnetic field lines where the magnetic field crosses the receiving coil R1 increase, and the induced voltage V1 becomes larger than V2. When a non-ferrous metal is mixed in the inspection object W, the magnetic field consumes magnetic flux energy as an eddy current in the non-ferrous metal as shown in FIG.
And the induced voltage V1 becomes smaller than V2. As a detection method, a metal signal is extracted by detecting and extracting an unbalanced signal with a time-shifted phase signal using a signal given to a transmission coil as a reference time.

[0004] The phase position is proportional to the magnitude of the magnetic field energy driven by the transmitting coil, but the steeper the magnetic field change, the higher the non-iron is extracted, that is, the higher the frequency, the more advantageous.

[0005] Iron is less affected by frequency and is extracted higher as the magnetic field energy generated by driving the transmission coil is larger. It is known that the phase at which the extraction sensitivity of the detection metal becomes the highest is shifted by 90 degrees between iron and non-iron.

Further, the inspection object itself affects the magnetic field.
This effect strongly affects the vicinity of the phase detected by iron, but the lower the frequency, the lower the effect of the inspection object itself.

Therefore, in the prior art, in order to detect both ferrous and non-ferrous metals, one frequency is selected and the transmitting coil is driven to detect metal. However, since the optimum frequency of detection differs between iron and non-ferrous, increasing the extraction sensitivity of one decreases the extraction sensitivity of the other. For this reason, it is difficult to detect both ferrous and non-ferrous metals with the highest sensitivity using a single metal detector or device.Therefore, two metal detectors or devices are prepared independently, and they are separately set by setting the frequency exclusively for iron and non-ferrous. Detected.

The present invention has found such a problem,
An object of the present invention is to provide an epoch-making metal detection device which can detect ferrous or non-ferrous metals with high sensitivity with one device.

[0009]

The gist of the present invention will be described with reference to the accompanying drawings.

The transmitting coil 5 is driven to generate an alternating magnetic field, and the receiving coils 6A, 6B
In a metal detection device that detects metal by changing signals induced in the receiving coils 6A and 6B due to the effect of metal mixed into the inspection object 7 that passes through the magnetic field, A circuit system for driving the coil 5 drives the transmitting coil 5 alternately in a time-division manner at two frequencies 1A and 1B, and a voltage difference V1 induced in the receiving coils 6A and 6B.
The present invention relates to a metal detection apparatus characterized in that an unbalanced output signal of −V2 is separated into two frequency components by time division extraction to detect both ferrous and non-ferrous metals with high sensitivity. is there.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention (how to implement the invention) will be briefly described with reference to the drawings, showing the operational effects thereof.

For non-ferrous metals, the extraction sensitivity increases as the frequency increases, and for iron, the extraction sensitivity increases as the frequency decreases. Therefore, in order to detect iron and non-ferrous at the highest sensitivity, low frequency 1A and high frequency 1B, which are optimal for iron and non-ferrous, respectively, are prepared separately, and two different frequencies 1A and 1B are alternately switched by the switching signal from timing generation 3. The transmission coil 5 is driven by division.
Since the transmitting coil 5 is driven alternately at the frequencies 1A and 1B, alternating magnetic fields at two frequencies are generated alternately.

The receiving coils 6A and 6B are arranged so that the voltages V1 and V2 induced by receiving the magnetic field lines of the alternating magnetic field become equal. The test object 7 is moved in the magnetic field by the transport device, and the receiving coils 6A, 6
A voltage difference between the voltages V1 and V2 induced in B is output. Since this unbalanced output contains two frequency components, the two frequency components are alternately time-division-separated, and the phase at which the extraction sensitivity of the detected metal is the highest is 90 degrees different between ferrous and non-ferrous. In this case, phase detection is performed with a shift of 90 degrees.

Therefore, it is possible to detect both ferrous and non-ferrous metals with high sensitivity using this apparatus.

[0015]

Embodiment A specific embodiment of the present invention will be described with reference to FIG.

The frequency used for iron detection is 1 KHz to 40
One of the optimal frequencies is selected within the range of 0 kHz, and the frequency used for non-ferrous detection is 400 kHz to 1.5 MHz.
Select one optimal frequency in the range. The wide frequency range of both ferrous and non-ferrous metals is due to the nature of the test object.

The two selected frequencies 1A and 1B are output from the transmitter. The two frequency signals are alternately switched by the switch 2 in a time-sharing manner with the switching signal from the timing generator 3. This switching signal is particularly important and plays a central role in the present invention, and includes an element that determines the sensitivity of metal detection. For this reason, it is necessary to further confirm the ratio and time of the signal to be switched by time division in the future.

The signal switched by the switch 2 is amplified by the drive 4 in voltage and current to drive the transmission coil 5. Since the transmitting coil 5 is driven alternately at the frequencies 1A and 1B, alternating magnetic fields at two frequencies are generated alternately. The lines of magnetic force due to this alternating magnetic field are equally received by the two receiving coils 6A and 6B, and the induced voltages V1 and V2 are equal. Receiving coil 6
A case in which no metal is mixed in the inspection object 7 by moving the inspection object 7 in a magnetic field that outputs the voltage difference between the voltages V1 and V2 induced in A and 6B as an unbalanced signal of 8 No unbalanced output signal is output because no voltage difference V1-V2 occurs. When the metal is mixed, the lines of magnetic force change and a voltage difference of V1-V2 induced in the receiving coils 6A and 6B occurs. Since this unbalanced output signal contains two frequency components, the two frequency components are alternately time-division-separated by the separator 9 by the switching signal from the timing generator 3 and enter the phase detectors 10A and 10B, respectively. Since the phase at which the detection metal has the highest extraction sensitivity is shifted by 90 degrees, phase detection is performed by shifting 90 degrees when detecting iron and non-ferrous metals.

The filters 11A and 11B are provided with vibration noises from the transfer device for moving the inspection object 7 and the receiving coils 6A and 6B.
The noise due to metal other than the metal included in the test object 7 near B is removed, the metal signal is amplified by the 12A and 12B amplifiers, and the detection reference level and the metal signal level are compared by the 13A and 13B comparators. And output when the metal signal level is high. The output of ferrous and non-ferrous is synthesized by the synthesizer 14 and the metal contained in the test object 7 is detected with the highest sensitivity.

[0020]

Since the present invention is configured as described above, the transmission frequency is driven by alternately time-divisionally driving the two frequencies using the optimum frequency for iron detection and the optimum frequency for non-ferrous detection. In order to separate and detect two frequency components by time-division extraction of the unbalanced output signal of the voltage difference induced in the receiving coil by the metal contained in the object, Since this metal is detected with the highest sensitivity whether it is ferrous or non-ferrous, extremely small metals can be detected, so the safety and reliability of the test object can be further improved, and two metal detectors or devices are used. In the case where detection is performed independently at frequencies dedicated to iron and non-ferrous, the detection can be performed by one device, so that a metal detection device that can reduce costs can be realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a general principle of metal detection.

FIG. 2 is an explanatory diagram showing a principle of detecting a ferrous metal.

FIG. 3 is an explanatory diagram showing a principle of detecting a non-ferrous metal.

FIG. 4 is a block diagram illustrating a schematic configuration of the embodiment.

[Explanation of symbols]

 1A, 1B Frequency 5 Transmission coil 6A, 6B Receiving coil 7 Inspection object

Claims (1)

[Claims] An alternating magnetic field is generated by driving a transmitting coil, two receiving coils are arranged so as to receive the alternating magnetic field, and the receiving coil is affected by metal mixed into an object to be inspected passing through the magnetic field. In the metal detection device that detects metal by the signal induced to change, the circuit system that drives the transmission coil alternately drives the transmission coil in a time-division manner at two frequencies, and is induced in the reception coil. A metal detection device characterized by being configured to separate an unbalanced output signal of a voltage difference into two frequency components by time-division extraction to detect both ferrous and non-ferrous metals with high sensitivity.