JPS6335946B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a self-diagnostic metal detector that allows confirmation of the operation and sensitivity of a metal detection coil without actually running a test piece through it.

Traditionally, to check whether a metal detector is working properly or whether it can detect metal pieces with the required sensitivity, a standard iron or stainless steel ball is manually run through an inspection line as a test piece. I was checking. However, with this method, the production line must be stopped each time, and confirmation cannot be made without human intervention, resulting in production stoppages and the need for human intervention. Furthermore, if the detection sensitivity is insufficient even though the purpose is to detect foreign matter contamination, defective products will be passed on as good products, and at the same time, it will be difficult to detect this fault, and operation may not always be safe. It had some flaws.

The above conventional example will be further explained with reference to the drawings.

FIG. 1 is an example of a circuit diagram of a conventional metal detector. In this figure, 1 is a high-frequency power source, 2 is a transmitting coil, and is excited by a voltage _e〓p from the high-frequency power source 1. 3
Reference numerals a and 3b are receiving coils, and the connection point between the two is grounded and electromagnetically coupled to the transmitting coil 2, and an inspection line 4 through which the inspected object M passes is formed between the transmitting coil 2 and the transmitting coil 2. ing. When the inspected object M does not pass, the receiving coils 3a, 3
Equal induced voltages e〓 ₁ and e〓 ₂ are generated at b. 5 is a phase adjuster consisting of a variable resistor, etc., and the sliding piece 5a is grounded, and when this is moved upward in FIG. 1, that is, toward the receiving coil 3a side, the parallel resistance on the receiving coil 3a side becomes smaller. , as shown in the vector diagram in Figure 2, the phase of the induced voltage e〓 ₁ advances to become e〓′ ₁ ,
The difference e〓′ ₁ −e〓 ₂ = e〓 _D from the induced voltage _e〓 2 becomes a vector e〓 _D that leads e〓 ₁ by approximately 90°.

When the sliding piece 5a of the phase adjuster 5 is moved in the opposite direction to the above, the phase of the induced voltage e〓 ₂ advances and becomes e〓' ₂ ,
The difference from the induced voltage e〓 ₁ is e〓′ ₂ −e〓 ₁ = e〓 _D , and the vector e〓 _D leads e〓 ₂ by approximately 90°. 6 is an amplitude adjuster consisting of a variable resistor, etc., and 6a is its sliding piece, and by moving this, e〓 ₁ −e〓 ₂ = e〓 _D
The ratio of extracting e〓 ₁ and e〓 ₂ changes. For example _, when _the sliding piece 6a of the amplitude adjuster 6 is moved upward in _FIG . , e〓 ₁ appears in phase with e〓 ₁ as shown in the vector diagram of Fig. 3 due to an increase in the output thereof. 7 is an amplifier, 8a and 8b are synchronous detectors, and 9 is a phase shifter.

In the conventional metal detector having such a configuration, the phase adjuster 5 and the amplitude adjuster 6 are adjusted without the object to be inspected M flowing through the inspection line 4, and the output from the synchronous detectors 8a and 8b is adjusted. Then, when the iron standard ball is passed through the inspection line 4, the induced voltage will be generated when it passes through the receiving coil 3a.
When e〓 ₁ also passes through the receiving coil 3b, the induced voltage e〓 ₂ increases, so that an output is obtained from the synchronous detector 8a. Therefore, in this case, it can be determined from the presence or absence of the output of the synchronous detector 8a whether or not the metal detector is operating normally.

Next, when a stainless steel standard ball is passed through the inspection line 4, an eddy current flows through the standard ball, causing a loss. That is, since the resistance component of the receiving coil 3a or 3b through which the standard sphere passes changes, this is equivalent to moving the phase adjuster 5, and as a result, the output _e〓D appears. This output is the induced voltage
Since it is a vector advanced by 90 degrees with respect to _e〓1 , an output is obtained from the synchronous detector 8b. Therefore, in this case, it can be determined from the presence or absence of the output of the synchronous detector 8b whether or not the metal detector is operating normally.

The above operations are summarized as shown in FIGS. 4 and 5.

_FIG . 4 shows the outputs of the synchronous detectors 8a and 8b, shown in FIG. In the case of iron, the output of the synchronous detector 8b is 0, and the output of the synchronous detector 8a has a sine waveform corresponding to the speed of the standard ball M _Fe . That is, while passing through the receiving coil 3a, e〓 ₁ > e〓 ₂ , and the receiving coil 3b
While passing through, e〓 ₁ < e〓 ₂ .

Moreover, FIG. 5 shows the outputs of the synchronous detectors 8a and 8b in (b) and (c) when a stainless steel standard ball M _SUS as shown in (a) is passed through the inspection line 4 as an object to be inspected. In the case of stainless steel, the output of the synchronous detector 8a is 0, and the output of the synchronous detector 8b has a sine waveform corresponding to the speed of the standard sphere M _SUS .
When the standard sphere M _SUS passes through the receiving coil 3a, the phase of the induced voltage e〓 ₁ advances, and when the standard sphere M _SUS passes through the receiving coil 3b, the induced voltage e〓 ₂
The phase of is advanced, and each synchronous detection signal is positive,
Output with negative polarity.

However, with the above conventional metal detector,
Iron and stainless steel standard balls as test pieces
As already mentioned, there are drawbacks such as the need to manually flow M _Fe and M _SUS into the inspection line 4.

This invention was made in order to eliminate the above-mentioned drawbacks.A circuit is provided in advance to give a phase change equivalent to that when ferrous or non-ferrous metal is detected in the receiving coil of the metal detection coil, and this is changed by a switch. By applying phase changes and amplitude changes to the receiving coil by selecting the To provide a metal detector capable of automatically diagnosing the detection of ferrous or non-ferrous metals at high speed and sensitivity without any trouble. The present invention will be explained below with reference to the drawings.

FIG. 6 is a circuit diagram showing an embodiment of the present invention. In this figure, the same reference numerals as in FIG. 1 indicate the same elements, and 10a and 10b are band pass filters provided after the synchronous detectors 8a and 8b, respectively. S ₁ and S ₂ are the contact pieces of the switch, which connect the resistor when closed.
R ₁ and R ₂ are connected in parallel to receiving coils 3a and 3b, respectively. S ₃ and S ₄ are also contact pieces of the switch, and when closed, resistors R ₃ and R ₄ are respectively connected in parallel between the sliding piece 6a of the amplitude regulator 6 and both ends thereof. In addition, 1
1 represents a phase change circuit, and 12 represents an amplitude change circuit.

Next, the operation of the embodiment shown in FIG. 6 will be explained with reference to FIGS. 7 and 8.

First, when the contact piece S ₁ provided on the phase adjuster 5 side is closed, the phase of the induced voltage e 〓 ₁ side advances by an amount corresponding to the resistance value of the resistor R ₁ in the phase change circuit 11, and
When the contact piece S ₁ opens and the contact piece S ₂ closes, the phase of the induced voltage e〓 ₂ advances by an amount corresponding to the resistance value of the resistor R ₂ , and the second
Since the output e〓 _D is obtained as shown in the vector shown in the figure, the same signal as when the stainless steel standard ball M _SUS is passed through the inspection line 4 is obtained. The waveforms of each part are as shown in A to D of FIG.

Next, when the contact piece _S3 is closed, the amplitude of the induced voltage _e〓1 increases by an amount corresponding to the resistance value of the resistor _R3 in the amplitude change circuit 12, and the output _e〓D becomes as shown in Fig. 3. The induced voltage e 〓 is the voltage in the direction of ₁ . Moreover, when the contact piece S ₃ opens and the contact piece S ₄ closes, the induced voltage e〓 ₂
The output e〓 _D in the same direction as is obtained. Therefore, the same signal as when the iron standard ball M _Fe is passed through the inspection line 4 can be obtained. The waveforms of each part in this case are shown in FIG.

FIG. 9 shows another embodiment of this invention,
Waveforms of essential parts for explaining the operation are shown in FIGS. 10 and 11.

In the embodiment of FIG. 9, the contact pieces S ₃ and S ₄ in the embodiment of FIG. 6 are combined into one contact piece S ₅ , and the contact pieces S ₃ and S ₄ are combined into one contact piece S ₆ . This is what I did. Phase change circuit 1
1, resistors R ₅ , R ₆ , R ₇ are connected in series,
Contacts a and b are provided at each connection point, and the contact piece _S5 is connected to these contacts a and b by switching. Similarly, the amplitude change circuit 12 is composed of resistors R ₈ , R ₉ , R ₁₀ and contacts a and b, to which a switch contact piece S ₆ is provided.

Next, the operation will be explained. First, when contact piece _S5 is in contact with contact point b as shown in Fig. 9,
e〓 ₁ = e〓 ₂ , that is, the induced voltage e〓 ₁ and e
〓 ₂
so that both phase and amplitude are the same,
Further, when the contact piece _S5 is switched to the contact point a, the values of the resistors _R5 to _R7 are selected so that the phase of the induced voltage _e〓1 advances. The time during which the contact piece _S5 is in contact with the contact point a is selected to be approximately equal to the time required for the standard sphere M _Fe or M _SUS to pass through one of the receiving coils 3a or 3b. The output from the synchronous detector 8b at this time becomes a square wave as shown in Fig. 10C, but the DC component is cut off by passing through the bandpass filter 10b, resulting in an AC waveform with approximately half the amplitude of the square wave. is obtained like d. Therefore, by selecting the values of the resistors R ₅ to _{R 7} so that the amplitude of the AC waveform D becomes the same value as that detected by the standard sphere M _SUS , the contact pieces S ₁ and S of the embodiment shown in FIG. ₂ can be made to have the same effect with one contact piece _S5 .

Next, FIG. 11 shows the output waveform of the main part when the contact piece _S6 is switched to the contact point a. That is, in this case, it is possible to perform a diagnosis that is exactly the same as when the iron standard ball M _Fe is passed through the inspection line 4.

Note that the phase change circuit 11 in each of the above embodiments
The adjustment means in the amplitude change circuit 12 is not limited to resistors, and other impedance elements may also be used. In addition, if the operation for self-diagnosis is performed after the inspected object M passes through the inspection line 4 and until the next inspected object M arrives, the production line can be constantly stopped for self-diagnosis. It can be done without. At this time, if the detection signal that is supposed to be generated during self-diagnosis is not detected, the inspection line 4 can be stopped or the inspected object M can be determined to be defective, which will prevent defective products from flowing due to a failure of the metal detection device. can also be prevented.

As explained in detail above, the present invention provides a conventional metal detector with a phase change circuit that changes the phase of the induced voltage in at least one of the two receiving coils, and a switch that opens and closes the circuit.
When the phase change circuit is operated, it is possible to apply a phase change to the induced voltage of the receiving coil, which is equivalent to when a non-ferrous metal standard bulb flows through the inspection line.
Further, an amplitude change circuit that similarly changes the amplitude of the induced voltage of at least one of the two receiving coils;
Since a switch is provided to open and close this, when the amplitude change circuit is operated, it is possible to give an amplitude change to the induced voltage in the receiving coil that is equivalent to when a standard iron ball flows through the inspection line. Therefore, it is not only possible to automate the operation check that was conventionally performed manually, but also to immediately detect a decrease in the sensitivity of the metal detector itself. Furthermore, since self-diagnosis can be performed automatically, there are excellent effects such as the ability to perform diagnosis at high speed by just switching by utilizing the time between the objects to be inspected.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of a conventional metal detector, Figs. 2 and 3 are vector diagrams for explaining the operation of the circuit in Fig. 1, and Figs. 6 is a circuit diagram showing an embodiment of the present invention, and FIGS. FIG. 9 is a circuit diagram showing another embodiment of the present invention, and FIGS. 10 and 11 explain the operation of the embodiment of FIG. 9. FIG. In the figure, 1 is a high frequency power supply, 2 is a transmitting coil, and 3
a, 3b are receiving coils, 4 is an inspection line, 5 is a phase adjuster, 5a is a sliding piece, 6 is an amplitude adjuster, 7 is an amplifier, 8a, 8b is a synchronous detector, 9 is a phase shifter,
10a and 10b are band pass filters, 11 is a phase change circuit, 12 is an amplitude change circuit, S ₁ to S ₆ are contact pieces, a and b are contacts, R ₁ to _{R 9} are resistors, and M _Fe is an iron standard. The ball, M _SUS , is a standard stainless steel ball.

Claims (1)

[Claims] 1 A transmitting coil driven by an AC signal, two receiving coils placed across the inspection line in which the test object flows within the electromagnetic field of this transmitting coil, and the difference between the output signals of these two receiving coils. In a metal detector comprising two synchronous detectors that synchronize the output signal of the AC signal with the AC signal and synchronously detect the output signal using two synchronous detection signals having a phase difference of approximately 90°; a phase change circuit that changes the phase of the induced voltage by an amount equivalent to the phase difference that occurs when a non-ferrous metal standard ball passes the inspection line; a first phase change circuit that opens and closes this phase change circuit;
an amplitude changing circuit that changes the amplitude of the induced voltage in at least one of the receiving coils by an amount equivalent to the amplitude difference that occurs when an iron standard ball passes the inspection line; a second amplitude changing circuit that opens and closes this amplitude changing circuit; and a switch, wherein the first and second switches are controlled to open and close after the object to be inspected has passed and before the next object to be inspected arrives. type metal detector.