JPH0322585B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal identification device for identifying the presence of metal and the type of metal, and in particular to a metal identification device that places a metal in an alternating magnetic field generated by an excitation coil and detects changes in the magnetic field due to the metal. The present invention relates to a metal identification device that identifies the type of metal by detecting it.

Conventionally, an excitation coil and a detection coil are provided by narrowing the metal to be identified (for example, a coin), and the alternating magnetic field generated by the excitation coil is affected by eddy current loss generated in the inserted metal, and as a result, the detection coil A method is used to identify the type of metal by utilizing the fact that the detection signal flowing through the metal changes depending on the type of metal.

For example, when a 100 yen coin, or cupronickel, is placed in an alternating magnetic field, the detection signal waveform generated in the detection coil is the first one.
The waveform will be as shown in A in Figure A, but when a different type of metal, such as lead, is placed in an alternating magnetic field, the detected signal waveform will be a signal waveform that has a smaller amplitude level and a slightly more advanced phase than the waveform in A, as shown in B. In the case of stainless steel, the signal waveform shown in C has a higher amplitude level than the waveform A and has a slightly delayed phase.

The conventional metal identification device utilizes the fact that the amplitude level of the detection signal generated in the detection coil 3 differs depending on the type of metal.As shown in FIG. A metal to be identified In place of the DC signal, the logic circuit 8 determines that this DC signal is below the upper limit signal level preset by the upper limit comparator 6 and above the lower limit signal level preset by the lower limit comparator 7. However, if this condition is met, the metal to be identified x is determined to be a predetermined metal, and if not, it is determined to be a different type of metal. That is, as shown in FIG. 1b, the judgment level of the upper limit comparator 6 is slightly lower than the amplitude level H' of the detection signal in the case of stainless steel, and the upper limit value (m1) of the variation range of the amplitude level of the detection signal in the case of cupronickel. The judgment level of the lower limit comparator 7 is slightly above the amplitude level LO' of the detection signal in the case of lead, which is the lower limit value (m2) of the variation range for cupronickel.
The amplitude level of a DC signal obtained by rectifying a detected AC signal into a DC signal corresponds to which region it corresponds to is checked and identified using two determination levels.

However, such conventional devices are susceptible to changes in temperature, power supply voltage fluctuations, level fluctuations in the oscillator output signal, fluctuations in the amplification degree of the amplifier circuit, rectification characteristics of the rectifier circuit, fluctuations in the thresholds of the upper and lower limit comparators, etc. Since it is accumulated as something involved in determining the amplitude level, as shown in Figure 1b, if the lower limit or upper limit of a different metal falls within the upper and lower limits of a given metal, this may lead to an incorrect determination. This method has disadvantages in that it tends to cause errors and the accuracy of identification is not high. This is a particular problem when identifying metals with similar characteristics and small differences in amplitude levels.In order to increase identification accuracy, each circuit must be configured as an extremely stable circuit. This has the disadvantage that the circuit becomes complicated, and the adjustment for setting the identification range is extremely troublesome because both the upper and lower limits must be determined by taking into account the range of variation. Specifically, when identifying the three types of metals mentioned above, the difference is only a few percent when considering the dispersion of each metal, so accurate identification is possible unless the variation in the judgment level of each comparator is less than a few percent. It was impossible and unsuitable for practical use.

The present invention has been made to eliminate the drawbacks of the above-mentioned conventional devices. The present invention focuses on the fact that the detection signal generated in the detection coil changes not only the amplitude level but also the phase depending on the type of metal, as shown in Fig. 1a, and synthesizes the amplitude difference and the phase difference. In addition to improving sensitivity, the output signal level is set in advance to be the lowest for a given metal, and the metal to be identified is determined by whether or not there is an output signal above a certain level. It is characterized by being able to identify whether it is a metal or not.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram showing the principle of the present invention, and FIG. 4 is a diagram showing output waveforms at each point in FIG.

The alternating current output signal (excitation signal) of the oscillator 9 is applied to the excitation coil 10, and an alternating magnetic field is generated from the excitation coil 10 and acts on the metal to be identified x. A detection signal flows through the detection coil 11 disposed opposite or in parallel to the metal to be identified by an alternating magnetic field influenced by the metal to be identified, and this detection signal is sent to the correction circuit 12 by an oscillator 9 It is input together with a branched excitation signal obtained by branching the excitation signal. Correction circuit 1
2 is for setting the amplitude level of the detection signal A flowing to the detection coil 11 and the branch excitation signal B to be the same amplitude level when a predetermined metal as the metal to be identified X is inserted between both coils. It has a level setter and a phase shifter inserted to make the detection signal A and the branch excitation signal B have the same phase or opposite phases. If the detection signal A for a given metal has a waveform as shown by the solid line in FIG. 4a, and the output signal B of the oscillator 9 has a waveform as shown by the solid line in FIG. The amplitude level of output signal B is made to match that of detection signal A by a phase shifter, and the phase of output signal B is delayed by a phase shifter so that the phase is opposite to that of detection signal A, and a signal C having a waveform as shown by the dotted line in FIG. 4b is obtained. Make it.

The correction circuit 12 inputs the output signal D, which is the detection signal A as it is, and the signal C, which is obtained by shifting the phase of the branch excitation signal B and setting the level as described above, to the operational amplifier circuit 13. This operational amplifier circuit 13 has an adder or a subtracter, and the adder has a predetermined metal that is connected to the exciting coil 10.
When inserted between the subtracter and the detection coil 11, the subtracter is used when the correction circuit 12 outputs two signals with opposite phases to each other, and the subtracter outputs two signals with the same phase from the correction circuit 12. Used in cases. Therefore, when the signals C and D have opposite phases as shown in FIG. 4a and b, an adder is used.

Therefore, in the case of a given metal, when these two signals C and D are input to the operational amplifier circuit 13 (adder), the output will be as follows, since the two signals have almost the same amplitude level and almost opposite phase. , are in a canceled form, so that a signal E of almost zero level is output at the output end, as shown in FIG. 4c.

However, when a metal other than the predetermined metal is inserted between the excitation coil 10 and the detection coil 11, as shown in FIG. 4a, the detection signal A differs in amplitude and phase from that for the predetermined metal. Become. Therefore, the output E obtained by adding the outputs C and D of the correction circuit 12 does not become zero as shown in FIG. 4c in the case of a predetermined metal. That is, if the detection signal A for a metal other than the predetermined metal has a waveform (solid line) as shown in FIG. 4d, the outputs C and D of the correction circuit 12
The signal E resulting from the addition of the two signals has a waveform as shown in FIG. 4e, in which the amplitude level difference and phase difference of both signals are combined.

The output E of this operational amplifier circuit 13 is determined by the judgment circuit 14.
sent to. The determination circuit 14 includes a rectifier circuit and a comparator, the output E is rectified by the rectifier circuit, and the rectified signal F is compared with a level L established by the comparator.

Therefore, the greater the difference between the amplitude level and phase of the detection signal A and the amplitude level and phase for a predetermined metal, the greater the amplitude of the output E of the operational amplifier circuit 13, and the greater the level of the rectified signal F. Become. That is, in the case of a certain metal, the amplitude is the smallest and almost zero, as shown in Figure 4c, so the rectified signal F
The level of will also be almost zero, but in the case of other metals, the output E will have a different amplitude level and phase, as shown in Figure 4, for example, so the rectified signal F will be as shown in Figure 4 f, and at a certain high level. The level of Therefore,
The set level L of the comparator of the determination circuit 14 is set to a predetermined value, and if the level of the rectified signal F is greater than or equal to the predetermined value, it is determined that the metal to be identified is not the predetermined metal, and if it is smaller than the predetermined value, the metal It is determined that it is metal.

Next, specific circuit examples of the correction circuit 12 and the operational amplifier circuit 13 will be explained with reference to FIGS.

In the embodiment shown in FIG. 5, the correction circuit 12a detects the detection coil 1 when a predetermined metal is present in the alternating magnetic field.
In order to match the amplitude level of the branch excitation signal B branched from the oscillator 9 to the detection signal level generated at
and a phase shifter 16 consisting of a resistor R3 and a capacitor C1 for making the phase of the output signal of the level adjuster 15 different from the phase of the detection signal of the detection coil 11 by 180 degrees. In this case, the detection signal A is outputted from the winding end side of the detection coil 11, and is set to have an opposite phase to the excitation coil 10. On the other hand, the operational amplifier circuit 13a includes capacitors C2 and C3, resistors R4 and R
5, R6, and this adder 17.
Operational amplifier Q1 and resistor R that amplify the output signal of
7, R8, and an amplifier 18 consisting of a capacitor C4.

With this configuration, in the case of a predetermined metal, the two signals C and D applied to the adder 17 have the same amplitude level and a 180° phase difference, so that the output signal E of the operational amplifier circuit 13 as the addition result becomes a signal of almost zero level, and if the metal to be identified The signal is then output from the operational amplifier circuit 13.

FIG. 6 shows another embodiment, which is suitable when the detection signal A for a predetermined metal appears in almost the same phase as the branch excitation signal, and is suitable for the operational amplifier circuit 1.
3b is operational amplifier Q2, resistor R12, R1
A subtracter consisting of 3 and R14 is used. Then, the detection signal A is directly connected to the operational amplifier Q2 via the resistor R13, and the branch excitation signal B is transmitted through a phase shifter 19 consisting of a variable resistor 9 and a capacitor C5, so that the phase shift difference between the detection signal A and the detection signal A for a predetermined metal is determined. The amplitude level of the output signal is adjusted to zero using a level adjuster 20 consisting of a resistor R10 and a variable resistor R11 to match the level of the detection signal A when a predetermined metal is present in an alternating magnetic field. The signal is inputted to the other input terminal of the operational amplifier circuit 13b so that the output of the operational amplifier circuit 13b becomes approximately zero level in the case of a predetermined metal. Therefore, if the metal is other than the predetermined metal, one input signal D of the operational amplifier circuit will have a different phase and amplitude level from the predetermined metal.
The difference between the signal C and the signal D is output from the operational amplifier circuit 13b.

In the two embodiments shown in FIGS. 5 and 6, the amplitude level and phase of the branch excitation signal B are matched to the detection signal A from a predetermined metal, but in the embodiment shown in FIG. , the phase of the detection signal is further delayed and set to the same phase as the phase of the branch excitation signal B or a phase different by 180°.

That is, the branch excitation signal B is attenuated to a predetermined level by a level adjuster 21 consisting of a resistor R15 and a variable resistor R16, and an operational amplifier Q is attenuated via a resistor R18.
At the same time, the phase of the detection signal A of the detection coil 11 in the case of a predetermined metal is input to the variable resistor R17,
The signal is input into one input terminal of the operational amplifier Q3 via a resistor R19 so as to be in the same phase as the output signal of the level adjuster 21 by a phase shifter 22 consisting of a capacitor C6. Resistor R20 serves as a feedback resistor for operational amplifier Q3.

As explained above, the metal identification device according to the present invention inputs the branch excitation signal branched from the AC signal applied to the excitation coil 10 and the detection signal generated in the detection coil 11 to the correction circuit 12, so that the excitation coil 10 If there is a certain metal to be identified in the generated alternating magnetic field, correct it in advance so that the amplitude levels of each signal or one of the signals are approximately the same and the phases are in-phase or out-of-phase. , the output signal of the operational amplifier circuit 13 is set to be substantially zero as a criterion for determination, and when an unknown metal to be identified X is present in an alternating magnetic field, a predetermined metal The difference between the characteristics of It is determined whether the metal X to be identified is a metal different from a predetermined metal. Therefore, while the conventional device determines whether the amplitude level of the metal to be identified Identification accuracy improves dramatically. Furthermore, since the criterion for determination can be set to almost zero as described above, the identification accuracy is further improved and identification becomes easier. Furthermore, while conventional devices make judgments based only on amplitude level differences, the present invention uses not only amplitude level differences as level signals, but also phase differences as level signals and synthesized level signals. Even more so, since we are making judgments based on
Identification accuracy is improved. Therefore, since conventional devices only make judgments based on amplitude level differences, if there is no large difference in amplitude even if the phase is different from that of a given metal, a different metal may be mistakenly judged as the given metal. However, since the device of the present invention converts the phase difference into a level signal and synthesizes it, even metals with small amplitude differences can be identified with high precision. Further, the output fluctuation of the oscillator 9 is canceled out by the operational amplifier circuit 13, and since the correction circuit 12, which serves as a reference for determination, is composed of passive elements, the circuit configuration is simple and is not easily affected by temperature changes. Further, since the output signal of the operational amplifier circuit 13 is outputted as an expanded deviation value based on the characteristics of the predetermined metal to be identified, the correction circuit 12 adjusts the output signal of the operational amplifier circuit 13 for the predetermined metal. Adjustment is easy because all you have to do is set the output so that it is as small as possible. Furthermore, unlike conventional devices, two comparators and a logic circuit are not required, and the operational amplifier circuit 13 and judgment circuit 14 can be simple, common circuits, resulting in high precision and high accuracy that is less susceptible to temperature fluctuations and power supply voltage fluctuations. Stable metal identification is possible.

[Brief explanation of the drawing]

Fig. 1a is a diagram showing three examples of the waveform of the detection signal A, Fig. 1b is a diagram for clarifying the principle of a conventional metal identification device, and Fig. 2 is a block diagram showing a conventional metal identification device. , FIG. 3 is a block diagram showing the principle of the device according to the invention, FIG. 4 is a diagram showing the output signal waveform of each block in FIG. 3, and FIGS. 5, 6, and 7 each show an embodiment of the invention. It is a circuit diagram. DESCRIPTION OF SYMBOLS 1... Oscillator, 2... Excitation coil, 3... Detection coil, 5... Rectifier circuit, 6... Upper limit comparator, 7... Lower limit comparator, 8... Logic circuit,
9... Oscillator, 10... Excitation coil, 11... Detection coil, 12, 12a, 12b, 12c... Correction circuit, 13, 13a, 13b, 13c... Operational amplifier circuit, 14... Judgment circuit.

Claims (1)

[Claims] 1. An oscillator that generates an excitation signal; An excitation coil that generates an excitation magnetic field in response to the excitation signal; A change in the magnetic field when a metal to be identified is present in the excitation magnetic field; a detection coil that outputs a detection signal for the purpose of the detection; and an amplitude difference between the detection signal from the detection coil when the metal to be identified is a predetermined metal, and a branch excitation signal obtained by branching the excitation signal applied to the excitation coil. a level adjuster in which an amplitude correction amount is preset to make the phase difference approximately zero; and a phase shifter in which a phase correction amount is preset to make the phase difference approximately 0° or 180°; a correction circuit that corrects one or both of the excitation signals by the amplitude correction amount and the phase correction amount; and a correction circuit that receives the branch excitation signal via the correction circuit and the detection signal from the detection coil, and subtracts both. Alternatively, a metal identification device comprising: an arithmetic circuit that performs addition; and a determination circuit that outputs a determination signal indicating that the metal to be identified is a predetermined metal when the output signal of the arithmetic circuit is below a predetermined level.