JPH055784A - Metal detector - Google Patents

Abstract

PURPOSE:To stably and finely adjust the phase of a metal detector. CONSTITUTION:The reference pulse signal of frequency 2f from a reference signal generator 21 is divided to 1/2 in frequency by a first frequency divider 50 and a transmission coil 24 generates an alternating magnetic field of frequency (f). The differential output of the voltages induced in receiving coils 26, 27 rosonated to the frequency (f) is inputted to a detection circuit 40. A triangle wave generating circuit 34 receiving a reference pulse signal outputs a thriangle wave signal with frequency 2f to a comparator 33 which in turn outputs the comparison output of the voltage Vp corresponding to phase data Dp with a triangle wave to a second frequency divider 51. The second frequency divider 51 divides the comparison output with frequency 2f outputted from the comparator 33 to 1/2 in frequency to output a pulse signal with frequency (f) having the phase corresponding to phase data to the detection circuit 40 in a duty ratio of 1:1. The detection circuit 40 synchronously detects a differential output signal on the basis of said pulse signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal detector for detecting the presence or absence of metal contained in an article by detecting a change in magnetic flux due to the article passing through an alternating magnetic field.

[0002]

2. Description of the Related Art In order to detect a metal mixed in an article in a non-contact manner, there has been a metal detecting apparatus which passes an article through an alternating magnetic field and discriminates the presence or absence of the metal by the change of the magnetic field.

FIG. 9 is a block diagram showing the structure of a conventional metal detecting device.

This metal detecting device has a transmitting coil 2 for generating an alternating magnetic field in response to an AC signal from an exciting circuit 1, and two receiving coils 3, 4 arranged at positions for receiving magnetic flux from the transmitting coil 2 in equal amounts. And have.

The receiving coils 3 and 4 are differentially connected via a balance resistor VR, and the differential output signal of the signal induced in the receiving coils 3 and 4 is synchronously detected by the detection circuit 5.

The output of the detection circuit 5 is subjected to removal of high frequency components including the excitation frequency by an LPF (low pass filter) 6 and is input to a determination circuit 7.

The determination circuit 7 compares the output of the LPF 6 between the transmitting coil 2 and the receiving coils 3 and 4 and when the article W passes through with an output of a predetermined reference voltage to determine the presence or absence of metal in the article W. judge.

The phase varying circuit 8 is a circuit for varying the phase of the differential output signal so that the influence of the product itself (including the packaging material) on the magnetic field is minimized. The fixed capacitor C ₀ has a resonance characteristic close to the excitation frequency of the excitation circuit 1, and the capacitors C _{1 to} C _n are connected by the switches S _{1 to} S _{n which} are turned on / off according to the phase data signal, thereby providing a differential output signal. Change the phase of.

The phase variable circuit 8 is adjusted in advance according to the type of article to be inspected, and by this adjustment, the presence or absence of metal contained in the article can be determined in a state in which the influence of the article confidence is the least. ..

[0010]

However, as described above, in the conventional service detecting device for varying the phase of the differential output signal, the phase adjustment is performed by changing the reception tuning frequency. There is a problem that the receiving sensitivity changes accordingly.

Further, as described above, the switching adjustment using the capacitor has a problem that the minimum variable capacitance is limited and cannot be adjusted to the optimum value.

For this reason, the output signal of the excitation circuit is converted into a sine wave and passed through an integrating circuit by a variable resistor and a variable capacitor so that its phase can be changed, and this signal is further converted into a rectangular wave to detect the wave. Although there was an analog type phase variable circuit for outputting to, there was a problem that switching control of resistors and capacitors was complicated and was greatly affected by temperature changes and variations of these analog elements.

It is an object of the present invention to provide a metal detecting device which solves these problems.

[0014]

In order to solve the above-mentioned problems, the metal detecting device of the first invention is a magnetic field generating means for generating an alternating magnetic field by an AC signal of a predetermined frequency, and an article passing through the alternating magnetic field. A magnetic flux change detecting means for outputting a detection signal corresponding to a magnetic flux change due to the magnetic field, a signal generating circuit for outputting a signal whose amplitude periodically changes at the same repetition frequency as the AC signal of the magnetic field generating means, and the signal generating circuit A comparator for comparing the output signal with a predetermined DC voltage, a voltage varying means for varying the predetermined DC voltage or the bias voltage of the output signal from the signal generating circuit according to the phase data, and the output pulse of the comparator. Synchronized and having a duty ratio of 1: 1 with the same frequency as the output pulse
A timer circuit that outputs a rectangular wave signal, a detection circuit that synchronously detects the detection signal from the magnetic flux change detection means by the rectangular wave signal from the timer circuit, and based on the detection output from the detection circuit, And a determination unit that determines the presence or absence of metal contained in the article.

Further, the metal detecting apparatus of the second invention comprises magnetic field generating means for generating an alternating magnetic field by an AC signal having a frequency obtained by dividing a reference signal having a predetermined frequency by 2N (N is an integer),
A magnetic flux change detecting means for outputting a detection signal corresponding to a magnetic flux change due to an article passing through the alternating magnetic field; a signal generating circuit for outputting a signal whose amplitude periodically changes at the same repetition frequency as the reference signal; A comparator for comparing the output signal from the generating circuit with a predetermined DC voltage; a voltage varying means for varying the predetermined DC voltage or the bias voltage of the output signal from the signal generating circuit according to the phase data; Divide the output pulse by 2N,
A frequency divider that outputs a rectangular wave signal with a duty ratio of 1: 1;
The detection signal from the magnetic flux change detection means is synchronously detected by a rectangular wave signal from the frequency divider, and the presence or absence of metal contained in the article is determined based on the detection output from the detection circuit. And a determining means.

The metal detecting device of the third invention outputs a magnetic field generating means for generating an alternating magnetic field by an alternating current signal having a predetermined frequency and a detection signal corresponding to a magnetic flux change due to an article passing through the alternating magnetic field. Magnetic flux change detection means, time data setting means for setting time data corresponding to arbitrary phase data, pulse signal of the same frequency as the AC signal of the magnetic field generation means, and a state of the pulse signal to one level Setting means for setting the level of the output pulse to one level at the first timing delayed from the transition time by the time data of the time data setting means, and the time corresponding to the half period of the pulse signal from the first timing. Reset means for resetting the level of the set output pulse to the other level at the second timing delayed by
Included in the article based on a detection circuit that synchronously detects the detection signal from the magnetic flux change detection means by the output pulse set and reset by the setting means and the reset means, and a detection output from the detection circuit. And a determination means for determining the presence or absence of metal.

[0017]

In the metal detector of the first aspect of the present invention, when the phase data is changed, the DC voltage to the comparator or the bias voltage of the signal generating circuit changes accordingly, and the phase of the comparison output of the comparator changes. Therefore, the rectangular wave signal having the phase corresponding to the phase data is output from the timer circuit to the detection circuit, and the detection signal from the magnetic flux change detection means is synchronously detected.

In the metal detecting apparatus of the second invention, an alternating magnetic field is generated by an AC signal having a frequency obtained by dividing the reference signal by 2N, and a signal whose amplitude periodically changes at the same repetition frequency as the reference signal is a signal. Output from the generation circuit to the comparator.

When the phase data changes, the DC voltage to the comparator or the bias voltage of the output signal of the signal generating circuit changes, and the phase of the comparison output of the comparator changes.
Therefore, a rectangular wave signal having a phase corresponding to the phase data and having a duty ratio of 1: 1 divided by 2N is output from the frequency divider to the detection circuit, and the detection signal from the magnetic flux change detection means is synchronously detected. It

Further, in the metal detector of the third invention, one level is set at the first timing delayed by the time data after receiving the pulse signal of the same frequency as the AC signal of the magnetic field generating means, An output pulse reset at the second timing delayed by a half cycle of the pulse signal is output to the detection circuit, and the detection signal from the magnetic flux change detection means is synchronously detected.

[0021]

First Embodiment A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the structure of the metal detecting apparatus of the first embodiment.

In FIG. 1, the magnetic field generator 20 passes the reference pulse signal of the predetermined frequency f output from the reference signal generator 21 through the filter circuit 22 into a sine wave signal and inputs it to the excitation circuit 23. The excitation coil 23 excites the transmission coil 24.

The magnetic flux change detecting section 25 differentiates the receiving coils 26 and 27 arranged side by side at positions where the magnetic flux generated from the transmitting coil 24 is received in equal amounts and the signals induced in the receiving coils 26 and 27. The two receiving coils 26 and 27 are tuned to the frequency f of the reference pulse signal by the capacitor C ₀ .

On the other hand, the reference pulse signal is input to a phase variable circuit 30 for outputting a rectangular wave signal having the same frequency as the reference pulse signal in an arbitrary phase.

The phase variable circuit 30 includes a phase data setting means 31, a D / A converter 32 for outputting a DC voltage Vp corresponding to the phase data Dp set in the phase data setting means 31, and a D / A converter. The output of 32 is input to one input terminal of the comparator 33, the triangular wave signal generation circuit 34 for outputting the triangular wave signal of the frequency f synchronized with the reference pulse signal to the other input terminal of the comparator 33, and the output of the comparator 33. The timer circuit 38 is activated.

The triangular wave generating circuit 34 forming the signal generating circuit of this embodiment has a first constant current source 35 and a second constant current source 36, respectively, as shown in FIG. By alternately connecting to the capacitor C via a switch 37 that switches in synchronization with the level inversion, charging and discharging of the capacitor C are repeated, and the terminal voltage of the capacitor C is changed in a symmetrical triangular waveform.

Further, the timer circuit 38 includes a comparator 3
It is preset so as to output a rectangular wave signal having a pulse width (duty ratio 1: 1) equal to the half cycle of the reference pulse signal from the rising edge of the output of 3, for example, in a mono-multi circuit or a preset type counter. It is configured.

The rectangular wave signal from the timer circuit 38 is input to the detection circuit 40. The detection circuit 40 synchronously detects the differential output signal from the magnetic flux change detection unit 25 with the rectangular wave signal from the timer circuit 38, and the detected output is LPF 41.
Output to.

The LPF 41 passes only the low frequency component contained in the detection output and outputs it to the determination circuit 42.

The determination circuit 42 compares the output signal from the LPF 41 with a preset level to determine whether or not metal is mixed in the article passing between the transmitting coil 24 and the receiving coils 26 and 27. To judge.

The determination result of the determination circuit 42 is sent to a sorting device (not shown) or the like, and is used for sorting defective products containing metal and non-defective products.

Next, the operation of this metal detector will be described.

For example, as shown in FIG. 3, when the article W containing the ferrous metal F enters the alternating magnetic field, the magnetic flux concentrates on one of the receiving coils 26, so that a differential output is produced.

On the other hand, with respect to the reference pulse signal shown in FIG. 4A, the triangular wave generation circuit 34 of the phase variable circuit 30 outputs the triangular wave signal shown in FIG. The output of 33 is high (H) level for a period in which this triangular wave signal is higher than the DC voltage Vp corresponding to the phase data Dp, as shown in FIG.

Therefore, from the timer circuit 38, as shown in (d) of the figure, the duty which rises in synchronization with the rise of the comparator output and becomes the high (H) level for a half cycle of the reference pulse signal. A rectangular wave signal having a ratio of 1: 1 is output.

Therefore, the phase of the rectangular wave signal from the timer circuit 38 is always delayed by T from the reference pulse signal, and if the DC voltage Vp is changed (the phase data Dp is changed), the phase delay is also proportional. And change.

On the other hand, since the phase of the differential output signal is constant with respect to the reference pulse, if the phase data Dp is varied, the phase of the rectangular wave signal relative to the differential output signal is relatively varied. Become.

Therefore, if the phase data Dp which minimizes the influence of the product W on the magnetic flux is set in advance, the detection sensitivity of the detection circuit 40 to the mixed metal becomes high.

The output synchronously detected with the optimum phase in this manner is sent to the determination circuit 42 via the LPF 41.

In the judgment circuit 42, as shown in FIG. 5, the detection signal which changes with the movement of the mixed ferrous metal F and the predetermined judgment standard value H are compared to detect the mixing of the metal. It

[0042]

Second Embodiment In the above embodiment, the timer circuit 38 is preset by adjustment or the like so as to output a rectangular wave with a duty ratio of 1: 1 at the same frequency f as the reference pulse signal. An example in which the above is unnecessary will be described below as a second embodiment.

FIG. 6 shows the structure of the metal detector of the second embodiment. The same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In this metal detecting device, the reference signal generator 2 is used.
The reference pulse signal of frequency 2f is output from 1, and the reference pulse signal is divided into ½ by the first frequency divider 50 and output to the filter circuit 22.

The reference signal of the frequency 2f is input to the triangular wave generation circuit 34 of the phase variable circuit 30, and the output of the comparator 33 is divided by the second frequency divider 51 into 1/2, It is supplied to the detection circuit 40.

In the metal detecting device constructed as described above,
Similar to the first embodiment, the transmission coil 24 has a frequency f
The differential outputs of the receiving coils 26 and 27 are input to the detection circuit 40.

On the other hand, the triangular wave generating circuit 34 receives the reference pulse signal of the frequency 2f shown in FIG. 7A, and the triangular wave signal of the frequency f synchronized with this signal is generated as shown in FIG. 7B.
Output as shown in.

This triangular wave signal is compared with the DC voltage Vp from the D / A converter 32 in the comparator 33,
The comparator 33 outputs the pulse signal shown in FIG.

The second frequency divider 51 divides a rectangular wave signal having a frequency f whose level is inverted at each rising edge of the output pulse of the comparator 33 at a duty ratio of 1: 1 as shown in FIG. It outputs a cycle.

The phase of this rectangular wave signal is the phase data Dp.
Is changed in accordance with the change in the DC voltage Vp.

On the other hand, since the phase of the frequency-divided signal of the first frequency divider 50 is constant, the phase of the rectangular wave signal from the second frequency divider 51 is relative to the phase of the differential output signal. Will be variable.

Therefore, as in the first embodiment,
If the phase data Dp is set so that the influence of the article on the magnetic field is minimized, the mixed metal can be detected with high detection sensitivity.

Further, in the second embodiment, even when the frequency of the reference pulse signal is arbitrarily changed, the frequency of the AC signal excited by the transmission coil 24 is always kept from the second frequency divider 51. A rectangular wave signal with a duty ratio of 1: 1 can be obtained at the same frequency.

Therefore, unlike the timer circuit 38 of the first embodiment, it is not necessary to adjust the time constant or set the preset value, and a more stable metal detecting device with fewer adjustment points can be realized.

In this embodiment, the case where the frequency division ratio of the first and second frequency dividers 50 and 51 is 2 has been described.
Considering the general circuit configuration of the frequency divider, if the frequency division ratio is an even number, that is, 2N (N is an integer), the duty ratio of 1 A rectangular wave of 1 can be output.

In the first and second embodiments, the comparison output of the DC voltage corresponding to the phase data and the triangular wave signal is input to the timer circuit or the frequency divider, but as shown in FIG. By the CPU that repeatedly executes various processing procedures,
You may make it comprise a phase variable circuit.

That is, when the timing of the rise of the reference pulse is detected, the timer is started, and the output pulse is set high (first timing) when the preset time data Dt corresponding to the phase data has passed (first timing). H) Set to level and start timer.

Then, the output pulse is reset at the timing (second timing) when the timer time reaches T ₀ for the half cycle of the reference pulse.

By performing this processing, a rectangular wave signal having a duty ratio of 1: 1 can be output to the detection circuit 40, and if the time data Dt is varied, a rectangular wave signal (output pulse) for the differential output signal can be obtained. The phase of can be finely changed.

If the timer time T ₀ can be variably set in accordance with the frequency of the reference pulse signal, no adjustment can be performed as in the second embodiment.

Further, in the first and second embodiments, the phase of the rectangular wave is changed by changing the DC voltage with respect to the triangular wave signal, but this does not limit the present invention, and the input is not limited. A signal whose amplitude periodically changes in synchronization with a pulse signal to be generated, and may be an asymmetrical triangular wave (sawtooth wave) or a sine wave. Alternatively, the DC voltage for the comparator may be fixed and the bias voltage of the triangular wave signal may be varied according to the phase data.

In each of the above-described embodiments, the two receiving coils 26 and 27 are arranged at positions facing the transmitting coil 24 which generates the alternating magnetic field, and the article is passed between them. The present invention is not limited to this. For example, two receiving coils may be coaxially arranged at a position sandwiching the transmitting coil so that an article can pass through each coil. You may arrange | position so that the receiving coil of a small diameter may be put in order inside.

Further, as a sensor for detecting a change in magnetic flux, a magnetic sensor (Hall element or the like) may be used instead of the receiving coil.

Further, in the above embodiment, the triangular wave signal is generated by charging / discharging by the constant current source, but charging / discharging may be directly performed by the reference pulse to the integrating circuit by the resistor and the capacitor.

[0065]

As described above, the metal detecting apparatus according to the first aspect of the present invention includes a signal whose amplitude periodically changes at the same repetition frequency as the AC signal for generating the alternating magnetic field and a DC voltage corresponding to the phase data. Are compared by a comparator, a rectangular wave signal having a duty ratio of 1: 1 synchronized with the comparison output is output from the timer circuit to the detection circuit, and the detection signal from the magnetic flux change detection means is synchronously detected. ..

In the metal detector of the third invention, the first timing is delayed by the time data corresponding to the phase data from the rise (fall) of the pulse signal having the same frequency as the AC signal for generating the alternating magnetic field. , The output pulse is set to one level, and at a second timing delayed by a half cycle of the pulse signal, the output pulse is reset to the other level by a rectangular wave signal with a duty ratio of 1: 1, The detection signal is synchronously detected.

Therefore, by changing the phase data,
The relative phase of the rectangular wave signal with respect to the detection signal can be arbitrarily and variably set with extremely fine accuracy, and stable metal detection with high sensitivity can be performed.

Further, the metal detecting apparatus of the second invention generates an alternating magnetic field by an AC signal having a frequency obtained by dividing the reference signal by 2N, and a signal and phase data whose amplitude periodically changes at the same repetition frequency as the reference signal. Is compared with a DC voltage according to the above, and the comparison output is divided into 2N by a frequency divider and output to the detection circuit.

Therefore, in addition to the above effect, there is a special effect that a stable rectangular wave signal that follows the change in the frequency of the reference signal without adjustment can always be output to the detection circuit.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a circuit example of a main part of the first embodiment.

FIG. 3 is a schematic diagram for explaining the operation of the first embodiment.

FIG. 4 is a timing chart for explaining an operation of a main part of the first embodiment.

FIG. 5 is a timing chart for explaining an operation of a main part of the first embodiment.

FIG. 6 is a block diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 7 is a timing chart for explaining an operation of a main part of the second embodiment.

FIG. 8 is a flowchart showing a processing procedure of another embodiment of the present invention.

FIG. 9 is a block diagram showing a configuration of a conventional device.

[Explanation of symbols]

 20 magnetic field generation section 25 magnetic flux change detection section 30 phase variable circuit 31 phase data setting means 32 D / A converter 33 comparator 34 triangular wave generation circuit 38 timer circuit 40 detection circuit 42 determination circuit 50 first divider 51 second Divider

Claims (1)

Claim: What is claimed is: 1. A magnetic field generating means for generating an alternating magnetic field by an alternating current signal having a predetermined frequency, and a magnetic flux change detecting means for outputting a detection signal corresponding to a magnetic flux change due to an article passing through the alternating magnetic field. A signal generating circuit that outputs a signal whose amplitude changes periodically at the same repetition frequency as the AC signal of the magnetic field generating means; a comparator that compares the output signal from the signal generating circuit with a predetermined DC voltage; Of the DC voltage or the bias voltage of the output signal from the signal generating circuit, which is synchronized with the output pulse of the voltage varying means for varying according to the phase data and the output pulse of the comparator, and the duty ratio of the output pulse is 1: 1. Of the rectangular wave signal output from the timer circuit and the detection signal from the magnetic flux change detecting means are synchronously detected by the rectangular wave signal from the timer circuit. A metal detection device comprising: a wave detection circuit; and a determination unit that determines the presence or absence of metal contained in the article based on a detection output from the detection circuit. 2. A reference signal of a predetermined frequency of 2N (N is an integer)
Magnetic field generating means for generating an alternating magnetic field by an alternating signal of a divided frequency, magnetic flux change detecting means for outputting a detection signal corresponding to a magnetic flux change due to an article passing through the alternating magnetic field, and the same repetition as the reference signal A signal generating circuit that outputs a signal whose amplitude periodically changes at a frequency, a comparator that compares the output signal from the signal generating circuit with a predetermined DC voltage, and a bias of the predetermined DC voltage or the output signal from the signal generating circuit. The voltage varying means for varying the voltage according to the phase data, the frequency divider for dividing the output pulse of the comparator by 2N and outputting a rectangular wave signal with a duty ratio of 1: 1, and the magnetic flux change detecting means. The detection signal of, based on the detection output from the detection circuit and the detection circuit for synchronous detection by the rectangular wave signal from the frequency divider,
A metal detection device comprising: a determination unit that determines the presence or absence of a metal contained in the article. 3. Magnetic field generating means for generating an alternating magnetic field by an alternating current signal having a predetermined frequency, magnetic flux change detecting means for outputting a detection signal corresponding to a magnetic flux change due to an article passing through the alternating magnetic field, and arbitrary phase data. And a pulse signal having the same frequency as the AC signal of the magnetic field generating means and receiving the pulse signal of the same frequency as the AC signal of the magnetic field generating means from the state transition time point to one level of the pulse signal. The setting means sets the level of the output pulse to one level at the first timing delayed by the time data, and the second timing delayed by the pulse signal half cycle time from the first timing. Resetting means for resetting the level of the set output pulse to the other level, and setting and resetting by the setting means and the resetting means. A detection circuit that synchronously detects the detection signal from the magnetic flux change detection means by the output pulse that is set, and a determination means that determines the presence or absence of metal contained in the article based on the detection output from the detection circuit. And a metal detection device.