JPH05232247A - Metal detector - Google Patents
Metal detectorInfo
- Publication number
- JPH05232247A JPH05232247A JP7292892A JP7292892A JPH05232247A JP H05232247 A JPH05232247 A JP H05232247A JP 7292892 A JP7292892 A JP 7292892A JP 7292892 A JP7292892 A JP 7292892A JP H05232247 A JPH05232247 A JP H05232247A
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- Prior art keywords
- magnetic field
- inspected
- metal
- balance
- coil
- Prior art date
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- Geophysics And Detection Of Objects (AREA)
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、磁界中を被検査体が通
過したときの磁界変化によって、被検査体に金属が混入
しているか否かを判定する金属検出装置に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal detecting device for determining whether or not a metal is mixed in an object to be inspected by a magnetic field change when the object to be inspected passes through a magnetic field.
【０００２】[0002]
【従来の技術】食品等の生産ラインでは、製品に金属が
混入しているか否かを、ライン上で検査するために、図
６に示す金属検出装置１が用いられている。2. Description of the Related Art In a production line for food or the like, a metal detector 1 shown in FIG. 6 is used to inspect whether or not a product contains metal.
【０００３】この種の金属検出装置１は、信号発生器２
からの正弦波信号で送信コイル３を励磁して、被検査体
の搬送路Ｃへ交番磁界を発生させる。This type of metal detection device 1 includes a signal generator 2
The transmission coil 3 is excited by the sine wave signal from to generate an alternating magnetic field in the transport path C of the device under test.
【０００４】そして、搬送路Ｃに沿って並んだ２つの受
信コイル４、５で磁界をほぼ等量ずつ受ける。２つの受
信コイル４、５は、抵抗Ｒを介して差動接続され、それ
ぞれのコイルに誘起された信号の不平衡成分が増幅器６
で増幅され、検波回路７で検波される。Then, the magnetic fields are received by the two receiving coils 4 and 5 arranged along the transport path C in substantially equal amounts. The two receiving coils 4 and 5 are differentially connected via a resistor R, and the unbalanced component of the signal induced in each coil is amplified by the amplifier 6.
Is amplified by and detected by the detection circuit 7.
【０００５】したがって、被検査体が磁界中にないとき
には、差動出力（不平衡）出力は小さく、検波出力も小
さい。Therefore, when the object to be inspected is not in the magnetic field, the differential output (unbalanced) output is small and the detection output is also small.
【０００６】ところが、例えば鉄金属が混入された被検
査体Ｗが一方の受信コイル４に近づくと、この受信コイ
ル４側の磁束密度が増加し、他方側の受信コイル５の磁
束密度が減少して、受信コイル４の電圧が受信コイル５
の電圧より大となる。また、さらに被検査体Ｗが進んで
受信コイル５側に近づくと、受信コイル４側の磁束密度
が減少し、受信コイル５側の磁束密度が増加して受信コ
イル５の電圧が受信コイル４の電圧より大となる。However, when the object W to be inspected containing, for example, iron metal approaches the receiving coil 4 on one side, the magnetic flux density on the receiving coil 4 side increases and the magnetic flux density on the receiving coil 5 on the other side decreases. The voltage of the receiving coil 4 is
Will be greater than the voltage. Further, when the object W to be inspected further approaches the receiving coil 5 side, the magnetic flux density on the receiving coil 4 side decreases, the magnetic flux density on the receiving coil 5 side increases, and the voltage of the receiving coil 5 becomes equal to that of the receiving coil 4. Greater than voltage.
【０００７】このため、検波出力は、図７の（ａ）に示
すように被検査体の通過にともなって、ほぼ正弦状に変
化する。この変化の大きさは、金属の磁界に与える影
響、即ち、混入金属の大きさに依存している。Therefore, the detection output changes in a substantially sinusoidal shape as the object to be inspected passes, as shown in FIG. The magnitude of this change depends on the effect of the metal on the magnetic field, that is, the size of the mixed metal.
【０００８】従って、検波出力を、コンパレータ８によ
って所定の基準値Ｖｒと比較すれば、同図の（ｂ）に示
すように、金属有りを示す判定信号を出力することがで
きる。Therefore, if the detected output is compared with a predetermined reference value Vr by the comparator 8, it is possible to output a determination signal indicating the presence of metal, as shown in FIG.
【０００９】しかして、このような構成の金属検出装置
では、磁界に対する２つの受信コイル４、５の平衡度が
高い程、基準値Ｖｒを小さくすることができ、混入金属
に対する感度を高くすることができる。However, in the metal detecting device having such a structure, the higher the balance between the two receiving coils 4 and 5 with respect to the magnetic field, the smaller the reference value Vr can be made, and the higher the sensitivity to the mixed metal is. You can
【００１０】このため、従来の金属検出装置では、送信
コイル３に対する受信コイル４、５の相対位置を、両受
信コイル４、５の誘起電圧が等しくなるように調整した
後に、各コイル間の位置が変わらないように、コイル枠
（図示せず）等を含めて接着固定するようにしている。Therefore, in the conventional metal detector, the relative positions of the receiving coils 4 and 5 with respect to the transmitting coil 3 are adjusted so that the induced voltages of the receiving coils 4 and 5 are equalized, and then the positions between the coils are adjusted. The coil frame (not shown) and the like are bonded and fixed so that the above does not change.
【００１１】[0011]
【発明が解決しようとする課題】しかしながら、前記の
ように、磁界に対して受信コイルを予め平衡した状態に
位置決め固定しても、温度の変化や外部からの衝撃によ
るコイル間の僅かな位置ずれを防ぐことはできない。However, as described above, even if the receiving coil is positioned and fixed in a state in which the receiving coil is preliminarily balanced with respect to the magnetic field, a slight positional deviation between the coils due to a change in temperature or an external shock is generated. Can't be prevented.
【００１２】したがって、高い検出感度を長期間維持す
るためには、定期的に各コイルの位置調整を行なうか、
あるいは、適当な大きさの金属片を、両受信コイルが平
衡状態となる位置に取付ける等の極めて煩雑な作業が必
要であった。Therefore, in order to maintain high detection sensitivity for a long period of time, the position of each coil should be adjusted periodically, or
Alternatively, an extremely complicated work such as attaching a metal piece of an appropriate size to a position where both receiving coils are in a balanced state has been required.
【００１３】本発明は、この課題を解決した金属検出装
置を提供することを目的としている。It is an object of the present invention to provide a metal detecting device that solves this problem.
【００１４】[0014]
【課題を解決するための手段】前記課題を解決するため
に、本発明の金属検出装置は、被検査体の通過経路に磁
界を発生する磁界発生手段と、前記被検査体の通過経路
に沿って並んで配置され、前記磁界発生手段によって発
生する磁界をほぼ等量ずつ受け、該磁界の変化をそれぞ
れ検出する１対の磁界センサとを有し、前記磁界中を被
検査体が通過したときの前記１対の磁界センサの不平衡
出力の大きさに基づいて、通過した被検査体に金属が含
まれているか否かを判定する金属検出装置において、前
記磁界中に被検査体が無いときの前記１対の磁界センサ
の不平衡出力の大きさを検出するバランスずれ検出手段
と、前記磁界発生手段が発生する磁界中にさらに磁界を
発生させて、前記バランスずれ検出手段によって検出さ
れた不平衡出力をゼロに近づけるバランス用磁界発生手
段とを設けている。In order to solve the above-mentioned problems, a metal detecting apparatus according to the present invention comprises a magnetic field generating means for generating a magnetic field in a passage of an object to be inspected and a passage path of the object to be inspected. A pair of magnetic field sensors that are arranged side by side and receive substantially equal amounts of magnetic fields generated by the magnetic field generating means and detect changes in the magnetic fields, respectively, and when the inspection object passes through the magnetic fields. In the metal detection device for determining whether or not the inspected object that has passed through contains metal, based on the magnitudes of the unbalanced outputs of the pair of magnetic field sensors, when there is no inspected object in the magnetic field. Balance deviation detecting means for detecting the magnitude of the unbalanced outputs of the pair of magnetic field sensors, and the balance deviation detecting means for further generating a magnetic field in the magnetic field generated by the magnetic field generating means. Balanced output It is provided with a magnetic field generation means for the balance closer to Russia.
【００１５】[0015]
【作用】このように構成したため、本発明の金属検出装
置では、磁界発生手段が発生する磁界に対して、１対の
磁界センサが不平衡な状態であっても、その不平衡出力
がバランスずれ検出手段によって検出され、バランス用
磁界発生手段が発生する磁界によって、その不平衡出力
をゼロに近づけることができる。With this configuration, in the metal detecting device of the present invention, even if the pair of magnetic field sensors are in an unbalanced state with respect to the magnetic field generated by the magnetic field generating means, the unbalanced outputs are out of balance. The unbalanced output can be brought close to zero by the magnetic field detected by the detecting means and generated by the balancing magnetic field generating means.
【００１６】[0016]
【実施例】以下、図面に基づいて本発明の一実施例を説
明する。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.
【００１７】図１は、一実施例の金属検出装置２０の構
成を示す図である。FIG. 1 is a diagram showing the structure of a metal detection device 20 of one embodiment.
【００１８】この金属検出装置２０の磁界発生手段は、
基準信号発生器２１から出力される所定周波数の矩形波
信号をフィルタ２２によって正弦波に変換し、この正弦
波を電力増幅器２３で増幅して送信コイル２４を励磁
し、被検査体Ｗの搬送路Ｃへ交番磁界を発生している。The magnetic field generating means of the metal detecting device 20 is
The rectangular wave signal of a predetermined frequency output from the reference signal generator 21 is converted into a sine wave by the filter 22, the sine wave is amplified by the power amplifier 23 to excite the transmission coil 24, and the transport path of the object W to be inspected. An alternating magnetic field is generated in C.
【００１９】搬送路Ｃに沿って並んだ２つの受信コイル
２５、２６は、交番磁界の変化を検出するための１対の
磁界センサとして、交番磁界をほぼ等しく受ける。The two receiving coils 25, 26 arranged along the transport path C receive the alternating magnetic field substantially equally as a pair of magnetic field sensors for detecting changes in the alternating magnetic field.
【００２０】受信コイル２５、２６は抵抗Ｒを介して差
動接続され、両コイルの誘起信号の不平衡出力は、増幅
器２７で増幅され、第１の検波回路２８および後述する
バランスずれ検出部３４へ出力されている。The receiving coils 25 and 26 are differentially connected via a resistor R, and the unbalanced outputs of the induced signals of both coils are amplified by an amplifier 27, and a first detection circuit 28 and a balance deviation detecting section 34 described later are provided. Is output to.
【００２１】一方、基準信号発生器２１からの矩形波信
号は、第１の移相器２９で所定位相遅延され、第１の検
波回路２８へ入力されている。第１の検波回路２８は、
移相器２９からの矩形波信号によって増幅器２７の出力
を同期検波する。On the other hand, the rectangular wave signal from the reference signal generator 21 is delayed by a predetermined phase in the first phase shifter 29, and is input to the first detection circuit 28. The first detection circuit 28 is
The output of the amplifier 27 is synchronously detected by the rectangular wave signal from the phase shifter 29.
【００２２】なお、移相器２９による位相遅延量は、金
属の混入していない被検査体（以下、良品と記す）が磁
界中を通過する際の誘起信号の位相ずれによる検波出力
が小さく、しかも混入金属による位相ずれによる検波出
力が大きくなる最適値に予め決められている。The phase delay amount by the phase shifter 29 is such that the detection output due to the phase shift of the induced signal when an object to be inspected (hereinafter referred to as non-defective product) in which no metal is mixed passes through the magnetic field is small, Moreover, the optimum value is set in advance so that the detection output becomes large due to the phase shift due to the mixed metal.
【００２３】第１の検波回路２８の出力信号は、ＬＰＦ
（低域通過フィルタ）３０によって、搬送波成分（基準
信号発生器２１の出力周波数成分）が除去され、Ａ／Ｄ
変換器３１に入力される。The output signal of the first detection circuit 28 is the LPF.
A carrier component (output frequency component of the reference signal generator 21) is removed by the (low-pass filter) 30, and the A / D
It is input to the converter 31.
【００２４】Ａ／Ｄ変換器３１は、検波出力を高速にサ
ンプリングして、各サンブリング値に対応したディジタ
ル信号を、レベル判定手段３２へ出力する。The A / D converter 31 samples the detected output at high speed and outputs a digital signal corresponding to each sambling value to the level determining means 32.
【００２５】レベル判定手段３２は、検波出力と基準値
Ｖｒとを比較して、被検査体に金属が混入しているか否
かを判定する。The level determining means 32 compares the detection output with the reference value Vr and determines whether or not metal is mixed in the inspected body.
【００２６】一方、バランスずれ検出部３４は、磁界中
に被検査体がないときの増幅器２７の出力を検出するた
めに、第２の検波回路３５、ＬＰＦ３６およびＡ／Ｄ変
換器３７で構成されている。第２の検波回路３５は、第
１の検波回路２８と同様に、基準信号発生器２１の矩形
波信号を第２の移相器３３で所定位相遅延させた信号に
よって増幅器２７の出力を同期検波する。なお、第２の
移相器３３の移相量は、第２の検波回路３５への矩形波
信号の位相と、被検査体が磁界中にないときの一方の受
信コイルに誘起される信号の位相とが一致するように予
め設定されている。On the other hand, the balance deviation detecting section 34 is composed of a second detection circuit 35, an LPF 36 and an A / D converter 37 in order to detect the output of the amplifier 27 when there is no object to be inspected in the magnetic field. ing. Similarly to the first detection circuit 28, the second detection circuit 35 synchronously detects the output of the amplifier 27 by a signal obtained by delaying the rectangular wave signal of the reference signal generator 21 by a predetermined phase by the second phase shifter 33. To do. The amount of phase shift of the second phase shifter 33 depends on the phase of the rectangular wave signal to the second detection circuit 35 and the signal induced in one of the receiving coils when the device under test is not in the magnetic field. It is set in advance so that the phase matches.
【００２７】第２の検波回路３５の検波出力は、ＬＰＦ
３６によって搬送波成分が除去され、Ａ／Ｄ変換器３７
でディジタル信号に変換される。The detection output of the second detection circuit 35 is the LPF.
The carrier component is removed by 36, and the A / D converter 37
Is converted into a digital signal by.
【００２８】このディジタル化された検波出力は、通過
変動検出手段３８およびスイッチ３９へ出力される。The digitized detection output is output to the passage variation detecting means 38 and the switch 39.
【００２９】通過変動検出手段３８は、この検波出力が
被検査体の通過によって変動している間、スイッチ３９
を開成させ、それ以外の期間中はスイッチ３９を閉成さ
せて、検波出力をバランス用磁界発生部４０の補正制御
手段４１へ入力させる。The passage variation detecting means 38 is provided with a switch 39 while the detection output is varying due to passage of the object to be inspected.
Is opened, and the switch 39 is closed during the other period to input the detection output to the correction control means 41 of the balancing magnetic field generation unit 40.
【００３０】この通過変動検出手段３８による通過変動
の検出は、図２に示すように、被検査体の通過によっ
て、検波出力が所定範囲±Ｖｓを越えたことを検出して
スイッチ３９を開らき、この検出時から、被検査体が完
全に磁界中を通過するのに必要な時間Ｔａが経過した後
に再び検波出力の大きさを調べ、その値が所定範囲±Ｖ
ｓに戻っているときにはスイッチ３９を閉じ、所定範囲
に戻っていないときには、次の被検査体の通過中である
と判定して、さらにＴａ時間スイッチ３９を開成させ
る。The passage variation detecting means 38 detects the passage variation, as shown in FIG. 2, by detecting that the detection output exceeds a predetermined range ± Vs due to passage of the object to be inspected, and opens the switch 39. After this detection, the magnitude of the detection output is checked again after the time Ta required for the inspection object to completely pass through the magnetic field has passed, and the value is within a predetermined range ± V.
When it has returned to s, the switch 39 is closed, and when it has not returned to the predetermined range, it is determined that the next inspection object is passing, and the Ta time switch 39 is further opened.
【００３１】バランス用磁界発生部４０の補正制御手段
４１は、スイッチ３９から受けた検波出力をゼロに近づ
けるように、後述する第３の移相器４２と可変減衰器
（あるいは利得可変増幅器）４３の移相量と減衰量を制
御する。The correction control means 41 of the balance magnetic field generating section 40 makes a third phase shifter 42 and a variable attenuator (or variable gain amplifier) 43 described later so that the detection output received from the switch 39 approaches zero. Control the amount of phase shift and the amount of attenuation.
【００３２】第３の移相器４２には、送信コイル２４を
励磁している信号と等しい周波数の正弦波信号がフィル
タ２２から入力されており、この信号が移相され、可変
減衰器４３でその振幅が調整されて電力増幅器４４へ送
られ、その出力によってバランス磁界発生コイル４５が
励磁されている。To the third phase shifter 42, a sine wave signal having the same frequency as the signal exciting the transmission coil 24 is input from the filter 22, the signal is phase-shifted, and the variable attenuator 43 is used. The amplitude is adjusted and sent to the power amplifier 44, and the output thereof excites the balance magnetic field generating coil 45.
【００３３】このバランス磁界発生コイル４５は、一方
の受信コイル２６に近接して配置されており、前記補正
制御手段４１の制御によって、両受信コイル２５、２６
の誘起信号を、互いに逆相で、振幅が完全に等しくなる
ためのバランス磁界を発生する。The balance magnetic field generating coil 45 is arranged close to one of the receiving coils 26, and under the control of the correction control means 41, both receiving coils 25, 26 are provided.
A balanced magnetic field is generated so that the induced signals of (1) and (2) are in opposite phases and the amplitudes are completely equal.
【００３４】図３は、補正制御手段４１の処理手順を示
すフローチャートであり、以下、このフローチャートに
従って金属検出装置の動作を説明する。FIG. 3 is a flow chart showing the processing procedure of the correction control means 41. The operation of the metal detecting apparatus will be described below with reference to this flow chart.
【００３５】予め、２つの受信コイル２５、２６は、送
信コイル２４が発生する磁界に対して、一方の受信コイ
ル２５の方が僅かに磁束密度が高い状態で運転が開始さ
れると、補正制御手段４１は、可変減衰器４３の減衰量
を最大にして、バランス磁界発生コイル４５から磁界が
発生しない状態にする（ステップ１）。In advance, the two receiving coils 25 and 26 are subjected to correction control when the operation is started in a state where the magnetic flux density of the one receiving coil 25 is slightly higher than the magnetic field generated by the transmitting coil 24. The means 41 maximizes the amount of attenuation of the variable attenuator 43 so that the balance magnetic field generating coil 45 does not generate a magnetic field (step 1).
【００３６】このとき、２つの受信コイル２５、２６に
は、図４の（ａ）に示すように、互いに逆相で振幅が僅
かに異なる誘起信号Ｖ1 、Ｖ2 が発生する。At this time, induced signals V 1 and V 2 having opposite phases and slightly different amplitudes are generated in the two receiving coils 25 and 26, as shown in FIG. 4A.
【００３７】このため、増幅器２７からは、同図の
（ｂ）に示すように、Ｖ1 と同相の不平衡信号が出力さ
れ、この信号が同期検波されて、同図の（ｃ）に示すよ
うに、誘起信号Ｖ1 、Ｖ2 の振幅差に対応した直流の検
波出力がＡ／Ｄ変換器３７によってディジタル信号に変
換される。Therefore, the amplifier 27 outputs an unbalanced signal having the same phase as V 1 as shown in (b) of the figure. This signal is synchronously detected and shown in (c) of the figure. As described above, the DC detection output corresponding to the amplitude difference between the induced signals V 1 and V 2 is converted into a digital signal by the A / D converter 37.
【００３８】この検波出力は、所定値Ｖｓより低いた
め、スイッチ３９が閉成され、補正制御手段４１へ入力
される。Since this detection output is lower than the predetermined value Vs, the switch 39 is closed and input to the correction control means 41.
【００３９】補正制御手段４１は、この検波出力の値Ｖ
ｕを受け、この値に対応した振幅の交流信号が電流増幅
器４４に出力されるように、可変減衰器４３の減衰量を
設定する（ステップ２）。なお、この減衰量は、例え
ば、送信コイル２４を励磁しない状態で、バランス磁界
発生コイル４５から磁界を発生させて受信コイル２６に
誘起信号を発生させ、その検波出力と減衰量との関係を
予め求めておき、Ｖｕに近い検波出力に対応した値にす
ればよい。The correction control means 41 determines the value V of this detection output.
Upon receiving u, the attenuation amount of the variable attenuator 43 is set so that an AC signal having an amplitude corresponding to this value is output to the current amplifier 44 (step 2). Note that, for this attenuation amount, for example, in a state where the transmission coil 24 is not excited, a magnetic field is generated from the balance magnetic field generation coil 45 to generate an induced signal in the reception coil 26, and the relationship between the detection output and the attenuation amount is preset. It may be obtained in advance and set to a value corresponding to the detection output close to Vu.
【００４０】次に、検波出力Ｖｕの値を監視しながら、
第３の移相器４２の移相量を可変し、その値Ｖｕが最小
となる移相量に設定する（ステップ３）。Next, while monitoring the value of the detection output Vu,
The phase shift amount of the third phase shifter 42 is varied, and the value Vu is set to the minimum phase shift amount (step 3).
【００４１】そして、この最小値がゼロでない場合に
は、検波出力を監視しながら、可変減衰器４３の減衰量
を微調整して、Ｖｕがゼロとなる減衰量に設定する（ス
テップ４、５）。When this minimum value is not zero, the attenuation amount of the variable attenuator 43 is finely adjusted while monitoring the detection output to set the attenuation amount at which Vu becomes zero (steps 4, 5). ).
【００４２】この初期設定動作によって、受信コイル２
６には、同図の（ｄ）に示すように、送信コイル２４が
発生する磁界による誘起信号Ｖ2 と同相で、受信コイル
２５側の誘起信号Ｖ1 との振幅差に等しい振幅の誘起信
号Ｖ3 がバランス磁界によって加わったことになり、２
つの受信コイル２５、２６は、磁界に対して完全に平衡
な状態となる。By this initial setting operation, the receiving coil 2
As shown in (d) of FIG. 6, an induced signal 6 has the same phase as the induced signal V 2 due to the magnetic field generated by the transmitting coil 24 and an amplitude equal to the amplitude difference from the induced signal V 1 on the receiving coil 25 side. V 3 is added by the balance magnetic field, and 2
The two receiving coils 25, 26 are in perfect equilibrium with the magnetic field.
【００４３】そして、温度や衝撃等の影響によって不平
衡信号が現れると、ステップ５の処理を行なってその不
平衡出力をゼロにする（ステップ６）。When an unbalanced signal appears due to the influence of temperature, shock, etc., the process of step 5 is performed to zero the unbalanced output (step 6).
【００４４】このようにして、増幅器２７からの不平衡
出力は、常にゼロに近づくように補正制御されているた
め、第１の検波回路２８の検波出力は、被検査体が磁界
を通過するまで現れない。In this way, the unbalanced output from the amplifier 27 is corrected and controlled so as to always approach zero, so that the detection output of the first detection circuit 28 remains unchanged until the object under test passes through the magnetic field. It does not appear.
【００４５】したがって、レベル判定手段３２の判定基
準となる基準値Ｖｒも検波出力の雑音レベルに極めて近
い値に設定することができる。Therefore, the reference value Vr serving as the determination reference of the level determination means 32 can be set to a value very close to the noise level of the detection output.
【００４６】ここで、例えば、鉄金属の混入している被
検査体Ｗが磁界中に進入して、受信コイル２５上に達す
ると、受信コイル２５側の誘起信号Ｖ1 が受信コイル２
６側の誘起信号Ｖ2 ′より大となり、被検査体が受信コ
イル２６上に達すると、受信コイル２５側の誘起信号Ｖ
1 より受信コイル２６側の誘起信号Ｖ2 ′の方が大とな
る。Here, for example, when the object W to be inspected containing the ferrous metal enters the magnetic field and reaches the receiving coil 25, the induced signal V 1 on the receiving coil 25 side causes the receiving coil 2 to receive the induced signal V 1.
When the object to be inspected reaches the receiving coil 26, the induced signal V 2 ′ on the receiving coil 25 side becomes larger than the induced signal V 2 ′ on the 6 side.
The induced signal V 2 ′ on the side of the receiving coil 26 is larger than that of 1 .
【００４７】このため、増幅器２７からは、例えば、図
５の（ａ）に示すような不平衡信号（Ｖ1 −Ｖ2 ′）が
出力され、第１の検波回路２８からは、同図の（ｂ）の
ように不平衡信号から被検査体自身の影響（波形の前後
部分）が抑圧された検波信号が出力される。また、第２
の検波回路３５は、その検波位相が第１の検波位相と異
なるため、同図の（ｃ）に示すような検波信号が出力さ
れる。Therefore, the amplifier 27 outputs, for example, an unbalanced signal (V 1 -V 2 ′) shown in FIG. 5A, and the first detection circuit 28 outputs the unbalanced signal shown in FIG. As shown in (b), the unbalanced signal outputs a detection signal in which the influence of the inspected object itself (the front and rear portions of the waveform) is suppressed. Also, the second
Since the detection phase of the detection circuit 35 is different from the first detection phase, the detection signal as shown in (c) of FIG.
【００４８】第１の検波回路の検波出力は、基準値Ｖｒ
を越えるため、レベル判定手段３２から金属混入を示す
判定信号が出力される。The detection output of the first detection circuit is the reference value Vr.
Therefore, the level determining means 32 outputs a determination signal indicating that metal is mixed.
【００４９】また、第２の検波回路３５の検波出力も、
直ちに所定範囲±Ｖｓを越えるため、通過変動検出手段
３８によって、Ｔａ時間スイッチ３９が開成される。The detection output of the second detection circuit 35 is also
Immediately beyond the predetermined range ± Vs, the passage variation detecting means 38 opens the Ta time switch 39.
【００５０】したがって、この被検査体通過による磁界
の変動期間中には、補正制御手段４１によるバランス磁
界の可変はなされず、バランス磁界は、変動検出の直前
の強さに保持される。Therefore, during the fluctuation period of the magnetic field due to the passage of the object to be inspected, the balance magnetic field is not changed by the correction control means 41, and the balance magnetic field is held at the strength immediately before the fluctuation detection.
【００５１】そして、Ｔａ時間経過した後に、検波出力
の大きさが±Ｖｓの範囲内にあれば、スイッチ３９が閉
じて、再び磁界の補正制御がなされる。After the Ta time has elapsed, if the magnitude of the detected output is within the range of ± Vs, the switch 39 is closed and the magnetic field correction control is performed again.
【００５２】このように、この金属検出装置２０では、
被検査体が通過する期間を除いて、２つの受信コイル２
５、２６の平衡状態が常に保たれているため、常に高感
度に金属混入を検出できる。As described above, in the metal detecting device 20,
The two receiving coils 2 are excluded except for the period in which the inspection object passes.
Since the equilibrium state of 5 and 26 is always maintained, metal contamination can be detected with high sensitivity at all times.
【００５３】なお、この実施例では、被検査体通過によ
る検波出力の変動を、通過変動検出手段３８によって検
出し、この変動期間中にバランス磁界を変化させないよ
うにしていたが、温度等による各コイルの相対的な位置
ずれは、被検査体の通過による変動期間に比べて十分長
いため、この通過変動の周波数に対して、十分低い周波
数成分のみを通過させるＬＰＦを、通過変動検出手段３
８とスイッチ３９の代わりに用いてもよい。この場合の
ＬＰＦは、ＬＰＦ３６を兼用してもよいし、補正制御手
段４１と可変減衰器４３との間に挿入してもよい。In this embodiment, the fluctuation of the detection output due to the passage of the object to be inspected is detected by the passage fluctuation detecting means 38, and the balance magnetic field is not changed during this fluctuation period. Since the relative positional deviation of the coils is sufficiently longer than the fluctuation period due to the passage of the object to be inspected, the LPF that passes only a sufficiently low frequency component with respect to the frequency of this passage fluctuation is detected as the passage fluctuation detecting means 3
8 and the switch 39 may be used instead. The LPF in this case may also serve as the LPF 36, or may be inserted between the correction control means 41 and the variable attenuator 43.
【００５４】また、前記実施例では、被検査体が磁界中
にないときの不平衡信号の大きさを検出するために、同
期検波型の検波回路を用いていたが、これは本発明を限
定するものでなく、例えばダイオード等によるピーク検
波器を用いてもよいし、検波せずに、直接ディジタル信
号に変換してから、そのピーク値を検出するようにして
もよい。Further, in the above embodiment, the synchronous detection type detection circuit is used to detect the magnitude of the unbalanced signal when the object to be inspected is not in the magnetic field, but this limits the present invention. However, a peak detector such as a diode may be used, or the peak value may be detected after direct conversion into a digital signal without detection.
【００５５】また、前記実施例では、被検査体が通過し
ている期間を除いて常時磁界の補正制御を行なっていた
が、タイマ回路を用いて一定時間毎に、あるいは温度セ
ンサを用いて一定温度変化毎に磁界のバランス補正を行
なうようにしてもよい。また、スイッチの操作によっ
て、随時バランス補正ができるようにしてもよい。Further, in the above-mentioned embodiment, the magnetic field correction control is always carried out except for the period during which the object to be inspected is passed. However, the timer circuit is used for constant time intervals, or the temperature sensor is used for constant time intervals. The magnetic field balance may be corrected for each temperature change. The balance may be corrected at any time by operating the switch.
【００５６】また、前記実施例では、バランス磁界を発
生するバランス磁界発生コイル４５を、一方の受信コイ
ル２６側に近接させていたが、他方の受信コイル２５側
に設けてもよいし、送信コイル２４側に設けてもよい。Further, in the above-mentioned embodiment, the balance magnetic field generating coil 45 for generating the balance magnetic field is arranged close to one receiving coil 26 side, but it may be provided on the other receiving coil 25 side or the transmitting coil side. It may be provided on the 24 side.
【００５７】なお、前記実施例では、被検査体を交番磁
界中に通過させていたが、永久磁石等による静磁界や脈
流磁界を用いた金属検出装置にも本発明を同様に適用で
きる（静磁界の場合には、補正制御手段４１による移相
可変制御が不要となる）。Although the object to be inspected is passed through the alternating magnetic field in the above-described embodiment, the present invention can be similarly applied to a metal detecting device using a static magnetic field or a pulsating magnetic field by a permanent magnet or the like ( In the case of a static magnetic field, the phase shift variable control by the correction control means 41 becomes unnecessary).
【００５８】また、前記実施例のように、２つの受信コ
イル２５、２６を搬送路に沿って同一面に並べて送信コ
イル２４に対向させた対向形式の金属検出装置だけでな
く、２つの受信コイルを送信コイルの両側に同軸状に配
置し、各コイルの中に被検査体を通過させる同軸形式の
金属検出装置についても本発明を適用できる。Further, as in the above-described embodiment, the two receiving coils 25 and 26 are arranged on the same plane along the conveying path so as to face the transmitting coil 24. The present invention can also be applied to a coaxial type metal detection device in which the antennas are coaxially arranged on both sides of the transmission coil and the object to be inspected is passed through each coil.
【００５９】この場合には、送信コイルと一方の受信コ
イルとの間にバランス磁界発生用のコイルを同軸状に配
置すればよい。また、磁界センサとしてコイル形式のも
のだけでなく、ホール素子等の磁気センサを用いてもよ
い。In this case, a balance magnetic field generating coil may be coaxially arranged between the transmitting coil and one of the receiving coils. Further, the magnetic field sensor is not limited to the coil type, but a magnetic sensor such as a Hall element may be used.
【００６０】また、前記実施例のレベル判定手段３２
は、検波出力の＋側が基準値Ｖｒを越えるか否かを判定
していたが、混入金属が鉄金属あるいは非鉄金属のいず
れにも対応できるように、検波出力の＋側と−側とを区
別なく判定するようにしてもよい。Further, the level judging means 32 of the above embodiment.
Determines whether or not the + side of the detection output exceeds the reference value Vr, but distinguishes the + side and-side of the detection output so that the mixed metal can correspond to either ferrous metal or non-ferrous metal. The determination may be made instead.
【００６１】[0061]
【発明の効果】以上説明したように、本発明の金属検出
装置は、磁界発生手段によって発生された磁界中に被検
査体がないときの一対の磁界センサの不平衡出力を検出
して、この不平衡出力をバランス磁界発生手段から発生
する磁界によってゼロに近づけることができる。このた
め、温度変化や衝撃等によって、磁界に対する磁界セン
サの位置ずれがあっても、磁界センサの位置調整等の煩
雑な作業をすることなく、その平衡状態を維持すること
ができ、混入金属を極めて高感度に検出することができ
る。As described above, the metal detecting device of the present invention detects the unbalanced outputs of the pair of magnetic field sensors when there is no object to be inspected in the magnetic field generated by the magnetic field generating means, and The unbalanced output can be brought close to zero by the magnetic field generated by the balance magnetic field generating means. Therefore, even if the magnetic field sensor is misaligned with respect to the magnetic field due to a change in temperature or impact, the equilibrium state can be maintained without complicated work such as position adjustment of the magnetic field sensor. It can be detected with extremely high sensitivity.
【図面の簡単な説明】[Brief description of drawings]
【図１】本発明の一実施例の構成を示すブロック図であ
る。FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.
【図２】一実施例の要部の動作を説明するためのタイミ
ング図である。FIG. 2 is a timing chart for explaining an operation of a main part of one embodiment.
【図３】一実施例の要部の処理手順を示すフローチャー
トである。FIG. 3 is a flowchart showing a processing procedure of a main part of one embodiment.
【図４】一実施例の動作を説明するための信号図であ
る。FIG. 4 is a signal diagram for explaining the operation of the embodiment.
【図５】一実施例の動作を説明するための信号図であ
る。FIG. 5 is a signal diagram for explaining the operation of the embodiment.
【図６】従来装置の構成を示すブロック図である。FIG. 6 is a block diagram showing a configuration of a conventional device.
【図７】従来装置の動作を示すタイミング図である。FIG. 7 is a timing chart showing the operation of the conventional device.
２０ 金属検出装置 ２１ 基準信号発生器 ２４ 送信コイル ２５、２６ 受信コイル ２８ 第１の検波回路 ３２ レベル判定手段 ３４ バランスずれ検出部 ３５ 第２の検波回路 ３８ 通過変動検出手段 ４０ バランス用磁界発生部 ４１ 補正制御手段 ４２ 第３の移相器 ４３ 可変減衰器 ４５ バランス磁界発生コイル 20 metal detection device 21 reference signal generator 24 transmission coil 25, 26 reception coil 28 first detection circuit 32 level determination means 34 balance deviation detection section 35 second detection circuit 38 passage variation detection means 40 balance magnetic field generation section 41 Correction control means 42 Third phase shifter 43 Variable attenuator 45 Balanced magnetic field generating coil
Claims (1)
発生手段と、 前記被検査体の通過経路に沿って並んで配置され、前記
磁界発生手段によって発生する磁界をほぼ等量ずつ受
け、該磁界の変化をそれぞれ検出する１対の磁界センサ
とを有し、 前記磁界中を被検査体が通過したときの前記１対の磁界
センサの不平衡出力の大きさに基づいて、通過した被検
査体に金属が含まれているか否かを判定する金属検出装
置において、 前記磁界中に被検査体が無いときの前記１対の磁界セン
サの不平衡出力の大きさを検出するバランスずれ検出手
段と、 前記磁界発生手段が発生する磁界中にさらに磁界を発生
させて、前記バランスずれ検出手段によって検出された
不平衡出力をゼロに近づけるバランス用磁界発生手段と
を設けたことを特徴とする金属検出装置。1. A magnetic field generating means for generating a magnetic field in a passage of an object to be inspected, and a magnetic field generating means which are arranged side by side along the passage of the object to be inspected and which receive magnetic fields generated by the magnetic field generating means in substantially equal amounts. , A pair of magnetic field sensors that detect changes in the magnetic field, respectively, and passes the magnetic field based on an unbalanced output of the pair of magnetic field sensors when the object passes through the magnetic field. In a metal detection device for determining whether or not a metal is contained in an inspection object, a balance deviation detection for detecting the magnitude of an unbalanced output of the pair of magnetic field sensors when the inspection object is not present in the magnetic field And a balance magnetic field generating means for further generating a magnetic field in the magnetic field generated by the magnetic field generating means to bring the unbalanced output detected by the balance deviation detecting means close to zero. Money Genus detection device.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7292892A JP3096788B2 (en) | 1992-02-24 | 1992-02-24 | Metal detector |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7292892A JP3096788B2 (en) | 1992-02-24 | 1992-02-24 | Metal detector |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH05232247A true JPH05232247A (en) | 1993-09-07 |
| JP3096788B2 JP3096788B2 (en) | 2000-10-10 |
Family
ID=13503514
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP7292892A Expired - Lifetime JP3096788B2 (en) | 1992-02-24 | 1992-02-24 | Metal detector |
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| Country | Link |
|---|---|
| JP (1) | JP3096788B2 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2021169980A (en) * | 2020-04-16 | 2021-10-28 | 株式会社 システムスクエア | Metal detector |
| JP2021185363A (en) * | 2015-12-23 | 2021-12-09 | ストライカー・コーポレイション | Metal detection system for use with medical waste container |
-
1992
- 1992-02-24 JP JP7292892A patent/JP3096788B2/en not_active Expired - Lifetime
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2021185363A (en) * | 2015-12-23 | 2021-12-09 | ストライカー・コーポレイション | Metal detection system for use with medical waste container |
| US11446109B2 (en) | 2015-12-23 | 2022-09-20 | Stryker Corporation | Metal detection system for use with medical waste container |
| JP2021169980A (en) * | 2020-04-16 | 2021-10-28 | 株式会社 システムスクエア | Metal detector |
Also Published As
| Publication number | Publication date |
|---|---|
| JP3096788B2 (en) | 2000-10-10 |
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