JP2006329798A

JP2006329798A - Method and circuit for correcting offset of vehicle detection device by magnetic sensor

Info

Publication number: JP2006329798A
Application number: JP2005153321A
Authority: JP
Inventors: Tamotsu Inagaki; 保稲垣; Noriyasu Shida; 哲康志田; Yoshihisa Adachi; 義久足立
Original assignee: Systec KK
Current assignee: Systec KK
Priority date: 2005-05-26
Filing date: 2005-05-26
Publication date: 2006-12-07

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for correcting offset errors of a magnetic sensor circuit and an amplifier without having to use a temperature measurement element and acquiring output values (reference values) of the once determined amplifier with an object to be magnetically detected such as a vehicle absent above the magnetic sensor circuit. <P>SOLUTION: On the basis of comparison results of two inputs of a reference value set at a reference voltage value setting part for setting a reference value for comparing output of the amplifier when a vehicle to be detected is absent above the magnetic sensor and output of the amplifier at any time, it is determined whether the output of the amplifier at any time is due to the presence of a vehicle above the magnetic sensor or due to changes in offset. An offset correction value stored in an offset correction memory or the reference value set at the reference voltage value setting part is held or altered to perform offset correction without having to measure temperature. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、磁気センサを用いて車両を検出する装置において、磁気センサばらつき、温度ドリフト等による出力オフセットを補正する方法とその回路に関するものである。 The present invention relates to a method and a circuit for correcting an output offset due to magnetic sensor variation, temperature drift, etc. in an apparatus for detecting a vehicle using a magnetic sensor.

従来、車両の存在を検知するセンサとして、赤外線、超音波を検出媒体とするもの、画像をカメラで取得するものなどがあったが、設備費が比較的少ない理由で、コイルにより磁気を検出するものが多く利用されてきた。これはループコイルと呼ばれているが、車両の存在による磁気の変化をコイルの自己誘導係数の変化として捉えるものであった。しかるに、ループコイルは、検知の感度を確保するためには、適当な大きなコイル面積が必要であり、更に地下埋設をして使用する必要があり、更に低コストで簡便に利用できるものが必要となっていた。このような背景にあって、いくつかの案が提案されてきた。特許文献１では、二個の電磁コイルを互いに直交するように配置して、１個のコイルに数ｋＨｚの交流を流して、磁場を発生させ、車両が存在する場合に車両が磁気回路を形成して、他方のコイルに磁束を伝達させることを利用して車両検知するものである。この特徴は、磁界を交流を流して発生させるので、強い磁界を得ることができ、コイルの面積がループコイルより小さくてよいことである。然しながら、コイルを小さくするには、大きい電流の交流を流す装置が必要となって、低消費電力に実現できない欠点があった。コイルを使わないものでは、特許文献２では、高感度地磁気センサにより構成した車両検知器が提案されているが、この文献では具体的構成は述べられていない。更に、特許文献３、及び特許文献４では、磁気センサを用いて車両の存在を検知する方法について提案されている。ここでは、地磁気を検出するのではなく、個々の車両が有している磁場を検出している。方法としては、複数の磁気センサを用い、センサ出力の絶対値を取り、その和が所定の値より小さい場合には車両無しと判定するものである。センサ出力で車両が棒磁石のように磁化されていることを解説し、車両が存在する場合には、複数センサのどちらかが零にならないことを利用して、出力の絶対値を取り、和を見れば、車両がある場合は所定値以上の値になるが、車両が無い場合は、複数のセンサ出力は全部零になるため、検出が確定するというものであった。これは、センサの上を車両を通過させた場合のセンサ出力波形を考慮した卓見した提案であったが、ここでもかなりものが単純な棒磁石のような磁気特性ではなく、車両の個々により複雑なセンス波形を呈するために、この方法では、車両が存在するのに、存在しないと誤判定する不都合があった。即ち、当出願人が先に提案した特願２００４−２９８４３４の実験結果で示したように車両によっては、複数のセンサが同時に零出力になる例が多く見出された。以上の車両検出装置において、本願が提出する課題は、車両が無いという判定において、複数のセンサ出力は全部零になるということに基づいているが、この点に関して以下のようなオフセット誤差の問題があった。図３は従来の温度測定素子を有するオフセット補正の回路ブロック図である。以下、図３を用いて、オフセット誤差とその通常の対処法を述べる。4個の磁気抵抗素子のブリッジ構成で磁気センサ回路３０１は出来ていて、電源端子３０２、グランド３０３に接続されている。磁気センサ回路３０１のブリッジの中間端子は、増幅器３０４の入力に接続されている。車両等の磁気検出物体が、磁気センサ回路３０１の上に無い場合は、磁気センサ回路３０１のブリッジの各磁気抵抗素子の抵抗値が揃っていて、増幅器３０４の出力電圧は、基準電圧と呼ぶ値（通常、電源端子電圧の2分の１）になっていて、所謂、無信号電圧となっている。車両等の磁気検出物体が磁気センサ回路３０１の上に存在すると、その磁界により、磁気センサ回路３０１のブリッジの各磁気抵抗素子の抵抗値が変化して、バランスがくずれ、増幅器３０４の出力電圧は、基準電圧からずれた値となる。ところが、車両等の磁気検出物体が、磁気センサ回路３０１の上に無い場合でも、増幅器３０４の出力電圧が基準電圧からずれた値となることがあり、これをオフセットと呼んでいる。増幅器３０４の出力電圧の基準電圧からの差を車両等の磁気検出物体検出の判断に用いるので、オフセットの存在は極めて好ましくない。オフセットの原因は、主に3つあり、１つ目は、磁気センサ回路３０１のブリッジの４つの磁気抵抗素子が初めから有している抵抗値ばらつきである。２つ目は、増幅器３０４が初めから有している入力オフセット電圧であり、3つ目は、磁気センサ回路３０１のブリッジの４つの磁気抵抗素子と増幅器３０４が温度の変化により発生するオフセットであり、主に４つの磁気抵抗素子の温度変化による影響が大きい。１つ目と２つ目のオフセットは、図３で示す回路の全体の製造段階で調整により補正してしまうので問題は回避される。このような対処の例としては、特許文献３に見ることが出来る。３つ目は、使用環境の温度変化により毎度変わるので、各時点の温度に対応して補正する必要があり、一般には、図３のような方法で行われている。即ち、増幅器３０４の出力は、ＡＤ変換器３０５に入力され、アナログ量がデジタル値に変換される。この回路には、磁気センサ回路３０１に間近に設置された温度測定素子３０６が付設され、その出力は、ＡＤ変換器３０７に接続されていて、測定された温度のデジタル値が得られるようになっている。車両等の磁気検出物体が、磁気センサ回路３０１の上に無い場合において、ＡＤ変換器３０５及びＡＤ変換器３０７の各出力の値は、温度／オフセットテーブル３０８に、コンピュータの制御の元に格納される。従って、温度／オフセットテーブル３０８には、各温度におけるオフセット電圧が記憶されているので、車両等の磁気検出物体を検出する時点において、温度測定素子３０６で温度を測定すれば、その温度でのオフセットの数値が温度／オフセットテーブル３０８から読み取ることができ、この値を増幅器３０４のオフセット補正端子に戻すことで、オフセットを補正した出力が得られる。このような補正を利用した従来例は、特許文献４及び特許文献５に見ることが出来る。然しながら、この様な補正には、温度測定素子３０６、ＡＤ変換器３０７が余分に必要であり、本願の使用用途には余分なことになる。即ち、本願の使用用途では、車両等の磁気検出物体が磁気センサ回路３０１の上に存在しない状態で、一度決めた増幅器３０４の出力の値（基準値）が温度の変化によっても変わらないようにする手段があればよいので、温度が何度であるかどうかを知ることは必要ではない。従って、車両等の磁気検出物体が磁気センサ回路３０１の上に存在しない状態で、増幅器３０４の出力を強制的に初期に決めた基準値に戻してやる手段があればよいことになる。そのことによって、温度測定素子３０６、ＡＤ変換器３０７を余分に設置する無駄が回避できることになる。
特開平１０−２８８６７３特開平１１−１４４１８７特開２００３−５０２７０特開２００２−１０７２５６特開２００４−１０９０９３ Conventionally, there are sensors that detect the presence of a vehicle, such as those using infrared and ultrasonic waves as detection media, and those that acquire images with a camera. Many things have been used. Although this is called a loop coil, the change in magnetism due to the presence of a vehicle is regarded as a change in the self-induction coefficient of the coil. However, in order to ensure the sensitivity of detection, the loop coil needs an appropriate large coil area, and further needs to be buried underground, and must be able to be used easily at low cost. It was. Against this background, several proposals have been proposed. In Patent Document 1, two electromagnetic coils are arranged so as to be orthogonal to each other, an alternating current of several kHz is applied to one coil to generate a magnetic field, and the vehicle forms a magnetic circuit when the vehicle exists. Then, the vehicle is detected by utilizing transmission of magnetic flux to the other coil. This feature is that a magnetic field is generated by flowing an alternating current, so that a strong magnetic field can be obtained and the area of the coil may be smaller than that of the loop coil. However, in order to reduce the size of the coil, a device for passing an alternating current with a large current is required, and there is a disadvantage that low power consumption cannot be realized. In the case where no coil is used, Patent Document 2 proposes a vehicle detector configured by a highly sensitive geomagnetic sensor, but this document does not describe a specific configuration. Furthermore, Patent Literature 3 and Patent Literature 4 propose a method for detecting the presence of a vehicle using a magnetic sensor. Here, instead of detecting geomagnetism, the magnetic field of each vehicle is detected. As a method, a plurality of magnetic sensors are used, the absolute value of the sensor output is taken, and when the sum is smaller than a predetermined value, it is determined that there is no vehicle. Explaining that the vehicle is magnetized like a bar magnet with sensor output, and if there is a vehicle, take the absolute value of the output using the fact that one of multiple sensors does not become zero. When the vehicle is present, the value becomes a predetermined value or more when there is a vehicle, but when there is no vehicle, a plurality of sensor outputs are all zero, so that the detection is confirmed. This was a proposal that considered the sensor output waveform when the vehicle was passed over the sensor, but here too, it is not a magnetic characteristic like a simple bar magnet but rather more complicated for each individual vehicle. In order to present a simple sense waveform, this method has the disadvantage of misjudging that a vehicle is present but not present. That is, as shown in the experimental results of Japanese Patent Application No. 2004-298434 previously proposed by the applicant, there have been found many examples in which a plurality of sensors have zero output at the same time. In the above vehicle detection device, the problem to be submitted by the present application is based on the fact that the plurality of sensor outputs are all zero in the determination that there is no vehicle. there were. FIG. 3 is a circuit block diagram of offset correction having a conventional temperature measuring element. Hereinafter, the offset error and its normal countermeasure will be described with reference to FIG. The magnetic sensor circuit 301 is formed by a bridge configuration of four magnetoresistive elements, and is connected to a power supply terminal 302 and a ground 303. The intermediate terminal of the bridge of the magnetic sensor circuit 301 is connected to the input of the amplifier 304. When a magnetic detection object such as a vehicle is not on the magnetic sensor circuit 301, the resistance values of the magnetoresistive elements of the bridge of the magnetic sensor circuit 301 are uniform, and the output voltage of the amplifier 304 is a value called a reference voltage. (Usually half the power supply terminal voltage), which is a so-called no-signal voltage. When a magnetic sensing object such as a vehicle is present on the magnetic sensor circuit 301, the resistance value of each magnetoresistive element of the bridge of the magnetic sensor circuit 301 changes due to the magnetic field, and the balance is lost, and the output voltage of the amplifier 304 is The value deviates from the reference voltage. However, even when a magnetic detection object such as a vehicle is not on the magnetic sensor circuit 301, the output voltage of the amplifier 304 may become a value deviated from the reference voltage, which is called an offset. Since the difference from the reference voltage of the output voltage of the amplifier 304 is used for determination of detection of a magnetic detection object such as a vehicle, the presence of an offset is extremely undesirable. There are mainly three causes of the offset, and the first is a variation in resistance value that the four magnetoresistive elements of the bridge of the magnetic sensor circuit 301 have from the beginning. The second is the input offset voltage that the amplifier 304 has from the beginning, and the third is the offset generated by the four magnetoresistive elements of the bridge of the magnetic sensor circuit 301 and the amplifier 304 due to temperature changes. The influence of temperature change of the four magnetoresistive elements is large. Since the first and second offsets are corrected by adjustment in the entire manufacturing stage of the circuit shown in FIG. 3, the problem is avoided. An example of such a countermeasure can be found in Patent Document 3. The third one changes every time depending on the temperature change of the use environment, so it is necessary to correct it according to the temperature at each time point. Generally, the method shown in FIG. 3 is used. That is, the output of the amplifier 304 is input to the AD converter 305, and the analog quantity is converted into a digital value. This circuit is provided with a temperature measuring element 306 installed close to the magnetic sensor circuit 301, and its output is connected to the AD converter 307 so that a digital value of the measured temperature can be obtained. ing. When there is no magnetic detection object such as a vehicle on the magnetic sensor circuit 301, the output values of the AD converter 305 and AD converter 307 are stored in the temperature / offset table 308 under the control of the computer. The Therefore, since the offset voltage at each temperature is stored in the temperature / offset table 308, if the temperature is measured by the temperature measuring element 306 at the time of detecting a magnetic detection object such as a vehicle, the offset at that temperature is detected. Can be read from the temperature / offset table 308, and by returning this value to the offset correction terminal of the amplifier 304, an output in which the offset is corrected can be obtained. Conventional examples using such correction can be found in Patent Documents 4 and 5. However, such a correction requires an extra temperature measuring element 306 and an AD converter 307, which are extra for the intended use of the present application. In other words, in the usage application of the present application, the output value (reference value) of the amplifier 304 once determined is not changed by a change in temperature in a state where no magnetic detection object such as a vehicle exists on the magnetic sensor circuit 301. It is not necessary to know how many times the temperature is, as long as there is a means to do so. Therefore, it is only necessary to have a means for forcibly returning the output of the amplifier 304 to the initially determined reference value in a state where no magnetic detection object such as a vehicle exists on the magnetic sensor circuit 301. As a result, unnecessary installation of the temperature measuring element 306 and the AD converter 307 can be avoided.
JP-A-10-288673 JP-A-11-144187 JP2003-50270 JP 2002-107256 JP 2004-109093 A

本発明の課題は、温度測定素子を用いないで、磁気センサ回路と増幅器のオフセット誤差を補正し、車両等の磁気検出物体が磁気センサ回路３０１の上に存在しない状態で、一度決めた増幅器３０４の出力の値（基準値）を得る手段を提供することにある。 An object of the present invention is to correct an offset error between a magnetic sensor circuit and an amplifier without using a temperature measuring element, and to determine an amplifier 304 once determined in a state where a magnetic detection object such as a vehicle does not exist on the magnetic sensor circuit 301. It is to provide a means for obtaining the output value (reference value).

本発明は、以上のような背景であって従来の問題点を解決するために提案されたものであり、検出されるべき車両が磁気センサ上に無い場合の増幅器の出力の比較のための基準値を設定する基準電圧値設定部に設定した基準値と、前記増幅器の随時の出力との二つの入力の比較結果に基づいて、前記増幅器の随時の出力が前記磁気センサ上での車両の存在によるものか、又はオフセットの変化によるものかを判定して、オフセット補正メモリに格納したオフセット補正値を保持又は変更するようにして、温度測定を行うことなくオフセット補正を行うことを特徴としている。以下説明する。 The present invention has been proposed to solve the conventional problems in the background as described above, and is a reference for comparing the output of the amplifier when the vehicle to be detected is not on the magnetic sensor. Based on the comparison result of two inputs, the reference value set in the reference voltage value setting unit for setting the value and the output at any time of the amplifier, the output at any time of the amplifier is the presence of the vehicle on the magnetic sensor. The offset correction is performed without measuring the temperature by determining whether the offset is due to the offset or the change in the offset and holding or changing the offset correction value stored in the offset correction memory. This will be described below.

請求項１記載の発明は、磁気センサによる車両検出装置のオフセット補正方法であって、磁気センサと、前記磁気センサの検出出力を増幅する増幅器と、検出されるべき車両が前記磁気センサ上に無い場合の前記増幅器の出力の比較のための基準値を設定する基準電圧値設定部と、前記増幅器の随時の出力と前記基準値の二つの入力を比較する比較器と、前記比較器の出力の値が前記車両の前記磁気センサ上での存在によるものか、又はオフセットの変化によるものかを判定するための磁気検出物／オフセット判別器と、前記判定の比較の基準となる閾値を設定する所定閾値設定部と、前記磁気検出物／オフセット判別器の出力であって、前記オフセット補正を行うためのオフセット補正値を格納するためのオフセット補正メモリとを少なくとも有し、前記磁気検出物／オフセット判別器において、前記比較器の前記二つの入力の差による出力の絶対値が前記所定閾値設定部の前記閾値より小さいか、又は、前記比較器の前記二つの入力の比による出力が、１に近い値である場合には、前記増幅器の前記随時の出力は、オフセットの変化によるものと判定し、前記オフセット補正メモリに格納した前記オフセット補正値を前記増幅器の前記随時の出力に対応して変更し、前記比較器の前記二つの入力の差による出力の絶対値が前記所定閾値設定部の前記閾値より大きいか、又は、前記比較器の前記二つの入力の比による出力が、１から離れた値である場合には、前記増幅器の前記随時の出力は、前記磁気センサ上に前記車両が存在することによるものと判定し、前記オフセット補正メモリに格納した前記オフセット補正値を変更せず保持するようにしたことを特徴とする。 The invention according to claim 1 is an offset correction method for a vehicle detection device using a magnetic sensor, wherein there is no magnetic sensor, an amplifier for amplifying the detection output of the magnetic sensor, and a vehicle to be detected on the magnetic sensor. A reference voltage value setting unit for setting a reference value for comparison of the output of the amplifier in a case, a comparator for comparing two inputs of the amplifier at any time and the reference value, and an output of the comparator A magnetic detection object / offset discriminator for determining whether the value is due to the presence of the vehicle on the magnetic sensor or due to a change in offset, and a predetermined threshold value for comparison of the determination Less threshold setting unit and offset correction memory for storing an offset correction value for performing the offset correction, which is an output of the magnetic detection object / offset discriminator In the magnetic detection object / offset discriminator, an absolute value of an output due to a difference between the two inputs of the comparator is smaller than the threshold value of the predetermined threshold setting unit, or the two values of the comparator When the output by the ratio of two inputs is a value close to 1, it is determined that the occasional output of the amplifier is due to a change in offset, and the offset correction value stored in the offset correction memory is used as the amplifier. The absolute value of the output due to the difference between the two inputs of the comparator is greater than the threshold of the predetermined threshold setting unit, or the two inputs of the comparator When the output by the ratio is a value away from 1, the output from the amplifier is determined to be due to the presence of the vehicle on the magnetic sensor, and the offset correction is performed. Characterized by being adapted to hold unchanged the offset correction value stored in the memory.

請求項２記載の発明は、磁気センサによる車両検出装置のオフセット補正回路であって、磁気センサと、前記磁気センサの検出出力を増幅する増幅器と、検出されるべき車両が前記磁気センサ上に無い場合の前記増幅器の出力の比較のための基準値を設定する基準電圧値設定部と、前記増幅器の随時の出力と前記基準値の二つの入力を比較する比較器と、前記比較器の出力の値が前記車両の前記磁気センサ上での存在によるものか、又はオフセットの変化によるものかを判定するための磁気検出物／オフセット判別器と、前記判定の比較の基準となる閾値を設定する所定閾値設定部と、前記磁気検出物／オフセット判別器の出力であって、前記オフセット補正を行うためのオフセット補正値を格納するためのオフセット補正メモリとを少なくとも有し、前記磁気検出物／オフセット判別器において、前記比較器の前記二つの入力の差による出力の絶対値が前記所定閾値設定部の前記閾値より小さいか、又は、前記比較器の前記二つの入力の比による出力が、１に近い値である場合には、前記増幅器の前記随時の出力は、オフセットの変化によるものと判定し、前記オフセット補正メモリに格納した前記オフセット補正値を前記増幅器の前記随時の出力に対応して変更し、前記比較器の前記二つの入力の差による出力の絶対値が前記所定閾値設定部の前記閾値より大きいか、又は、前記比較器の前記二つの入力の比による出力が、１から離れた値である場合には、前記増幅器の前記随時の出力は、前記磁気センサ上に前記車両が存在することによるものと判定し、前記オフセット補正メモリに格納した前記オフセット補正値を変更せず保持するようにしたことを特徴とする磁気センサによる車両検出装置のオフセット補正回路。 The invention according to claim 2 is an offset correction circuit for a vehicle detection device using a magnetic sensor, and there is no magnetic sensor, an amplifier for amplifying the detection output of the magnetic sensor, and a vehicle to be detected on the magnetic sensor. A reference voltage value setting unit for setting a reference value for comparison of the output of the amplifier in a case, a comparator for comparing two inputs of the amplifier at any time and the reference value, and an output of the comparator A magnetic detection object / offset discriminator for determining whether the value is due to the presence of the vehicle on the magnetic sensor or due to a change in offset, and a predetermined threshold value for comparison of the determination Less threshold setting unit and offset correction memory for storing an offset correction value for performing the offset correction, which is an output of the magnetic detection object / offset discriminator In the magnetic detection object / offset discriminator, an absolute value of an output due to a difference between the two inputs of the comparator is smaller than the threshold value of the predetermined threshold setting unit, or the two values of the comparator When the output by the ratio of two inputs is a value close to 1, it is determined that the occasional output of the amplifier is due to a change in offset, and the offset correction value stored in the offset correction memory is used as the amplifier. The absolute value of the output due to the difference between the two inputs of the comparator is greater than the threshold of the predetermined threshold setting unit, or the two inputs of the comparator When the output by the ratio is a value away from 1, the output from the amplifier is determined to be due to the presence of the vehicle on the magnetic sensor, and the offset correction is performed. Offset correction circuit of the vehicle detection device according to the magnetic sensor, characterized in that it has to hold unchanged the offset correction value stored in the memory.

請求項３記載の発明は、磁気センサによる車両検出装置のオフセット補正方法であって、磁気センサと、前記磁気センサの検出出力を増幅する増幅器と、検出されるべき車両が前記磁気センサ上に無い場合の前記増幅器の出力の比較のための基準値を設定する基準電圧値設定部と、前記増幅器の随時の出力と前記基準値の二つの入力を比較する比較器と、前記比較器の出力の値が前記車両の前記磁気センサ上での存在によるものか、又はオフセットの変化によるものかを判定するための磁気検出物／オフセット判別器と、前記判定の比較の基準となる閾値を設定する所定閾値設定部とを少なくとも有し、前記磁気検出物／オフセット判別器において、前記比較器の前記二つの入力の差による出力の絶対値が前記所定閾値設定部の前記閾値より小さいか、又は、前記比較器の前記二つの入力の比による出力が、１に近い値である場合には、前記増幅器の前記随時の出力は、オフセットの変化によるものと判定し、前記基準電圧値設定部の前記基準値を、前記増幅器からの出力値に更新し、前記比較器の前記二つの入力の差による出力の絶対値が前記所定閾値設定部の前記閾値より大きいか、又は、前記比較器の前記二つの入力の比による出力が、１から離れた値である場合には、前記増幅器の前記随時の出力は、前記磁気センサ上に前記車両が存在することによるものと判定し、前記基準電圧値設定部の前記基準値を変更せず保持するようにしたことを特徴とする。 The invention according to claim 3 is an offset correction method for a vehicle detection device using a magnetic sensor, wherein the magnetic sensor, an amplifier for amplifying the detection output of the magnetic sensor, and a vehicle to be detected are not on the magnetic sensor. A reference voltage value setting unit for setting a reference value for comparison of the output of the amplifier in a case, a comparator for comparing two inputs of the amplifier at any time and the reference value, and an output of the comparator A magnetic detection object / offset discriminator for determining whether the value is due to the presence of the vehicle on the magnetic sensor or due to a change in offset, and a predetermined threshold value for comparison of the determination A threshold value setting unit, and in the magnetic detection object / offset discriminator, an absolute value of an output due to a difference between the two inputs of the comparator is greater than the threshold value of the predetermined threshold value setting unit. Or, if the output by the ratio of the two inputs of the comparator is a value close to 1, it is determined that the occasional output of the amplifier is due to a change in offset, and the reference voltage value The reference value of the setting unit is updated to an output value from the amplifier, and an absolute value of an output due to a difference between the two inputs of the comparator is greater than the threshold value of the predetermined threshold setting unit, or the comparison If the output by the ratio of the two inputs of the device is a value away from 1, the occasional output of the amplifier is determined to be due to the presence of the vehicle on the magnetic sensor, and The reference value of the reference voltage value setting unit is held without being changed.

請求項４記載の発明は、磁気センサによる車両検出装置のオフセット補正回路であって、磁気センサと、前記磁気センサの検出出力を増幅する増幅器と、検出されるべき車両が前記磁気センサ上に無い場合の前記増幅器の出力の比較のための基準値を設定する基準電圧値設定部と、前記増幅器の随時の出力と前記基準値の二つの入力を比較する比較器と、前記比較器の出力の値が前記車両の前記磁気センサ上での存在によるものか、又はオフセットの変化によるものかを判定するための磁気検出物／オフセット判別器と、前記判定の比較の基準となる閾値を設定する所定閾値設定部とを少なくとも有し、前記磁気検出物／オフセット判別器において、前記比較器の前記二つの入力の差による出力の絶対値が前記所定閾値設定部の前記閾値より小さいか、又は、前記比較器の前記二つの入力の比による出力が、１に近い値である場合には、前記増幅器の前記随時の出力は、オフセットの変化によるものと判定し、前記基準電圧値設定部の前記基準値を、前記増幅器からの出力値に更新し、前記比較器の前記二つの入力の差による出力の絶対値が前記所定閾値設定部の前記閾値より大きいか、又は、前記比較器の前記二つの入力の比による出力が、１から離れた値である場合には、前記増幅器の前記随時の出力は、前記磁気センサ上に前記車両が存在することによるものと判定し、前記基準電圧値設定部の前記基準値を変更せず保持するようにしたことを特徴とする。 According to a fourth aspect of the present invention, there is provided an offset correction circuit for a vehicle detection device using a magnetic sensor, the magnetic sensor, an amplifier for amplifying the detection output of the magnetic sensor, and a vehicle to be detected not on the magnetic sensor. A reference voltage value setting unit for setting a reference value for comparison of the output of the amplifier in a case, a comparator for comparing two inputs of the amplifier at any time and the reference value, and an output of the comparator A magnetic detection object / offset discriminator for determining whether the value is due to the presence of the vehicle on the magnetic sensor or due to a change in offset, and a predetermined threshold value for comparison of the determination A threshold value setting unit, and in the magnetic detection object / offset discriminator, an absolute value of an output due to a difference between the two inputs of the comparator is greater than the threshold value of the predetermined threshold value setting unit. Or, if the output by the ratio of the two inputs of the comparator is a value close to 1, it is determined that the occasional output of the amplifier is due to a change in offset, and the reference voltage value The reference value of the setting unit is updated to an output value from the amplifier, and an absolute value of an output due to a difference between the two inputs of the comparator is greater than the threshold value of the predetermined threshold setting unit, or the comparison If the output by the ratio of the two inputs of the device is a value away from 1, the occasional output of the amplifier is determined to be due to the presence of the vehicle on the magnetic sensor, and The reference value of the reference voltage value setting unit is held without being changed.

以上の様に構成されているので、本発明の磁気センサによる車両検出装置のオフセット補正方法及びその回路では、温度測定素子３０６、ＡＤ変換器３０７を余分に設置する無駄を回避して、温度測定を行うことなくオフセットが補正できる。 Since it is configured as described above, according to the offset correction method and circuit of the vehicle detection device using the magnetic sensor of the present invention, the temperature measurement element 306 and the AD converter 307 are avoided from being redundantly installed, and the temperature measurement is performed. The offset can be corrected without performing.

発明を実施するための最良の形態として提案するものであって、温度が何度に変わっても、温度測定をすることなく、車両等の磁気検出物体が磁気センサ回路の上に存在しない状態で増幅器の出力を一度決めた増幅器の出力の値（基準値）又はその近傍の所定値に補正するものであって、その手段として、基準電圧値設定部を付設し、車両等の磁気検出物体が磁気センサ回路の上に存在しない状態で増幅器の出力の値（基準値）を一旦設定し、これを基準電圧値設定部に格納する。各時点においては、車両等の磁気検出物体が磁気センサ回路の上に存在しない状態で増幅器の出力を求め、この時点の出力値と基準電圧値設定部内の基準値との差分を取り、これをＤＡ変換した値を増幅器のオフセット補正端子に戻すことで、強制的にオフセットを補正することに特徴があるものであり、以下、実施態様を用いて説明する。 It is proposed as the best mode for carrying out the invention, and no matter how many times the temperature changes, the temperature is not measured and a magnetic sensing object such as a vehicle is not present on the magnetic sensor circuit. The output of the amplifier is corrected to the value (reference value) of the amplifier once determined or a predetermined value in the vicinity thereof. As a means for this, a reference voltage value setting unit is attached, and a magnetic detection object such as a vehicle is used. The amplifier output value (reference value) is temporarily set in a state where it does not exist on the magnetic sensor circuit, and is stored in the reference voltage value setting unit. At each time point, the output of the amplifier is obtained in a state where there is no magnetic detection object such as a vehicle on the magnetic sensor circuit, and the difference between the output value at this time point and the reference value in the reference voltage value setting unit is taken, and this is calculated. This is characterized in that the offset is forcibly corrected by returning the DA-converted value to the offset correction terminal of the amplifier, which will be described below using an embodiment.

図１は、本発明に係る磁気センサによる車両検出装置のオフセット補正回路の１実施態様を説明するブロック図である。図１において、4個の磁気抵抗素子のブリッジ構成で磁気センサ回路１０１は出来ていて、電源端子１０２、グランド１０３に接続されている。磁気センサ回路１０１のブリッジの中間端子は、増幅器１０４の入力に接続されている。増幅器１０４の出力は、ＡＤ変換器１０５に入力され、アナログ量がデジタル値に変換される。基準電圧値設定部１０６には、車両等の磁気検出物体が磁気センサ１０１の上に存在しない状態で増幅器１０４の出力をAD変換器１０５で処理された値（基準電圧値と呼ぶことにする）が設定されていて、この値を比較の基準に、ＡＤ変換器１０５の随時の出力が判定され、車両等の磁気検出物体が存在するか、存在しないかを判定する。従って、基準電圧値設定部１０６に設定される基準電圧値の値は、車両等の磁気検出物体が磁気センサ１０１の上に存在しない状態で増幅器１０４の出力をAD変換器１０５で処理された実際の計測値であるか、或る設定値（例えば、処理の中心値である電源端子電圧の１／２の値）でもよい。比較器１０７は、ＡＤ変換器１０５の随時の出力と基準電圧値設定部１０６に設定された基準値との差分又は、比を取るものであり、引き算器又は、割り算器となっている。比較器１０７の出力は、磁気検出物／オフセット判別器１０８において、所定閾値設定部１０９に設定された所定閾値と比較され、比較器１０７の変化が、磁気検出物の存在によるものか、又は、オフセット変化によるものかを判定される。即ち、オフセット変化の場合は、変化が緩慢なので差分が小さいか、比が１に近いが、磁気検出物の存在の場合は、変化が急峻なので、差分が比較的大きいか、比が１から離れた値になるために、所定閾値設定部１０９の所定の閾値を判定基準に判断することが出来て、所定の閾値（例えば、０．５ｖ）より差分が小さいか又は比が１に近い場合は、オフセット変化であり、差分が大きいか又は比が１から離れている場合は、磁気検出物存在による変化に起因していると見ることが出来る。差分が、オフセット変化によるとの判定では、差分はオフセット補正値メモリ１１０に格納され、その値は、ＤＡ変換器１１１を通じてアナログ量に変換されて、増幅器１０４のオフセット補正端子１１２に入力して、ＡＤ変換器１０５の出力が基準電圧値設定部１０６の基準値と一致するように補正を行う。オフセット補正値メモリ１１０に格納される値は、その値を増幅器１０４のオフセット補正端子１１２に入力すれば、比較器１０７の出力が零、即ち、ＡＤ変換器１０５の出力が基準電圧値設定部１０６の基準値に一致する値となっている。差分が、磁気検出物の存在によるものと判断された場合は、オフセット変化はないものと見なして、オフセット補正値メモリ１１０に格納される値は、以前の値が保持される。以上のようにして、磁気検出物が、磁気センサ１０１の上に存在しない場合は、増幅器１０４のオフセットは、強制的に補正されることになる。尚、基準電圧値設定部１０６は、以上の説明では、デジタル値を設定しているが、アナログ値を設定するようにして、ＡＤ変換器１０５を除去して、増幅器１０４の出力と直接にアナログ値として差分を取ることも出来る。比較器１０７、更には磁気検出物／オフセット判別器１０８、所定閾値設定部さえもアナログ値で扱うことも可能なことは勿論である。更に、この図の例では、オフセット補正値メモリ１１０の値をＤＡ変換器１１１でＤＡ変換した値で増幅器１０４のオフセットを制御しているが、増幅器１０４のオフセットを制御しないで、基準電圧値設定部１０６の設定値に増幅器１０４の出力値を与えるかどうかを制御することもできる。そして、この場合には、更にオフセット補正値メモリ１１０とＤＡ変換器１１１を除いて、磁気検出物／オフセット判別器１０８の出力により、この制御を行うこともできる。このような例では、増幅器１０４のオフセットを補正せずに、等価的に基準電圧値設定部１０６の設定値を補正するものであり、本発明の主旨の範囲であり、図1の点線矢印がその制御信号を表している。 FIG. 1 is a block diagram for explaining one embodiment of an offset correction circuit of a vehicle detection apparatus using a magnetic sensor according to the present invention. In FIG. 1, a magnetic sensor circuit 101 is formed by a bridge configuration of four magnetoresistive elements, and is connected to a power supply terminal 102 and a ground 103. The intermediate terminal of the bridge of the magnetic sensor circuit 101 is connected to the input of the amplifier 104. The output of the amplifier 104 is input to the AD converter 105, and the analog quantity is converted into a digital value. The reference voltage value setting unit 106 is a value obtained by processing the output of the amplifier 104 by the AD converter 105 in a state where no magnetic detection object such as a vehicle exists on the magnetic sensor 101 (referred to as a reference voltage value). Is set, and the output at any time of the AD converter 105 is determined using this value as a reference for comparison, and it is determined whether or not a magnetic detection object such as a vehicle is present. Therefore, the value of the reference voltage value set in the reference voltage value setting unit 106 is the actual value obtained by processing the output of the amplifier 104 by the AD converter 105 in a state where no magnetic detection object such as a vehicle exists on the magnetic sensor 101. Or a certain set value (for example, a value of ½ of the power supply terminal voltage, which is the central value of the processing). The comparator 107 takes a difference or ratio between the output of the AD converter 105 at any time and the reference value set in the reference voltage value setting unit 106, and is a subtractor or a divider. The output of the comparator 107 is compared with a predetermined threshold set in the predetermined threshold setting unit 109 in the magnetic detection object / offset discriminator 108, and the change of the comparator 107 is due to the presence of the magnetic detection object, or It is determined whether it is due to an offset change. That is, in the case of offset change, the change is slow and the difference is small or the ratio is close to 1. However, in the presence of a magnetic detection object, the change is steep and the difference is relatively large or the ratio is far from 1. When the predetermined threshold of the predetermined threshold setting unit 109 can be determined based on the determination criterion and the difference is smaller than the predetermined threshold (for example, 0.5 v) or the ratio is close to 1, If the difference is offset and the difference is large or the ratio is far from 1, it can be considered that the change is due to the presence of the magnetic detection object. In the determination that the difference is due to an offset change, the difference is stored in the offset correction value memory 110, and the value is converted into an analog quantity through the DA converter 111 and input to the offset correction terminal 112 of the amplifier 104. Correction is performed so that the output of the AD converter 105 matches the reference value of the reference voltage value setting unit 106. If the value stored in the offset correction value memory 110 is input to the offset correction terminal 112 of the amplifier 104, the output of the comparator 107 is zero, that is, the output of the AD converter 105 is the reference voltage value setting unit 106. The value matches the reference value. When it is determined that the difference is due to the presence of the magnetic detection object, it is assumed that there is no offset change, and the previous value is stored as the value stored in the offset correction value memory 110. As described above, when the magnetic detection object does not exist on the magnetic sensor 101, the offset of the amplifier 104 is forcibly corrected. In the above description, the reference voltage value setting unit 106 sets a digital value. However, the analog voltage is set, the AD converter 105 is removed, and the output of the amplifier 104 is directly analog. Differences can be taken as values. Of course, the comparator 107, the magnetic detection object / offset discriminator 108, and even the predetermined threshold value setting unit can be handled as analog values. Furthermore, in the example of this figure, the offset of the amplifier 104 is controlled by the value obtained by DA conversion of the value of the offset correction value memory 110 by the DA converter 111, but the reference voltage value setting is performed without controlling the offset of the amplifier 104. It is also possible to control whether or not to give the output value of the amplifier 104 to the set value of the unit 106. In this case, this control can also be performed by the output of the magnetic detection object / offset discriminator 108 except for the offset correction value memory 110 and the DA converter 111. In such an example, the set value of the reference voltage value setting unit 106 is equivalently corrected without correcting the offset of the amplifier 104, which is within the scope of the present invention, and the dotted line arrow in FIG. The control signal is shown.

又、図２は、増幅器の補正回路の１例を示す図である。全体が増幅器１０４を示している。磁気センサ１０１のブリッジの２つの中間出力は、増幅器１０４の入力（図２では、増幅器入力２０１、２０２）に入力されていて、その差が増幅して増幅器出力２０３に現れる。Ｖoff端子２０４がオフセットの補正端子であり、ここに与える電圧により、オフセット値を変化させて補正することが出来る。尚、Ｒ１、Ｒ２、Ｒ３、Ｒｆは差動増幅器を構成する抵抗２０５、２０６、２０７、２０８であり、Ｒｃはオフセット補正用の抵抗２０９である。 FIG. 2 is a diagram showing an example of an amplifier correction circuit. The whole shows the amplifier 104. The two intermediate outputs of the bridge of the magnetic sensor 101 are input to the input of the amplifier 104 (the amplifier inputs 201 and 202 in FIG. 2), and the difference is amplified and appears at the amplifier output 203. The Voff terminal 204 is an offset correction terminal, and can be corrected by changing the offset value according to the voltage applied thereto. R1, R2, R3 and Rf are resistors 205, 206, 207 and 208 constituting a differential amplifier, and Rc is a resistor 209 for offset correction.

以上のような、本発明の磁気センサによる車両検出装置のオフセット補正方法及びその回路では、温度測定素子３０６、ＡＤ変換器３０７を余分に設置する無駄を回避してオフセットが補正でき、特に駐車場等に使用して、車両等の存在を検知する応用において産業上利用性が極めて大きい。 In the offset correction method and circuit of the vehicle detection device using the magnetic sensor according to the present invention as described above, the offset can be corrected by avoiding unnecessary installation of the temperature measuring element 306 and the AD converter 307, particularly in a parking lot. Industrial applicability is extremely high in applications that detect the presence of vehicles and the like.

本発明の磁気センサによる車両検出装置のオフセット補正回路の１実施態様を説明するブロック図である。It is a block diagram explaining 1 embodiment of the offset correction circuit of the vehicle detection apparatus by the magnetic sensor of this invention. 本発明の磁気センサによる車両検出装置のオフセット補正回路に使用できる増幅器の補正回路の１例を示す図である。It is a figure which shows an example of the correction circuit of the amplifier which can be used for the offset correction circuit of the vehicle detection apparatus by the magnetic sensor of this invention. 温度測定素子を有する従来のオフセット補正の回路ブロック図である。It is a circuit block diagram of the conventional offset correction which has a temperature measurement element.

Explanation of symbols

１０１、３０１磁気センサ
１０２、３０２電源端子
１０３、３０３グランド
１０４、３０４増幅器
１０５、３０５、３０７ＡＤ変換器
１０６基準電圧値設定部
１０７比較器
１０８磁気検出物／オフセット判別器
１０９所定閾値設定部
１１０オフセット補正値メモリ
１１１ＤＡ変換器
１１２オフセット補正端子
２０１、２０２増幅器入力
２０３増幅器出力
２０４Ｖoff端子
２０５、２０６、２０７、２０８抵抗
２０９オフセット補正用の抵抗
３０６温度測定素子
３０８温度／オフセットテーブル
３０９ＤＡ変換器 101, 301 Magnetic sensor 102, 302 Power supply terminal 103, 303 Ground 104, 304 Amplifier 105, 305, 307 AD converter 106 Reference voltage value setting unit 107 Comparator 108 Magnetic detection object / offset discriminator 109 Predetermined threshold setting unit 110 Offset Correction value memory 111 DA converter 112 Offset correction terminal 201, 202 Amplifier input 203 Amplifier output 204 Voff terminals 205, 206, 207, 208 Resistor 209 Offset correction resistor 306 Temperature measuring element 308 Temperature / offset table 309 DA converter

Claims

A method for correcting an offset of a vehicle detection apparatus using a magnetic sensor, comprising: comparing a magnetic sensor, an amplifier for amplifying a detection output of the magnetic sensor, and an output of the amplifier when a vehicle to be detected is not on the magnetic sensor A reference voltage value setting unit for setting a reference value for the vehicle, a comparator for comparing the input of the amplifier at any time with two inputs of the reference value, and an output value of the comparator for the magnetic sensor of the vehicle Magnetic detection object / offset discriminator for determining whether it is due to the presence in the above or a change in offset, a predetermined threshold setting unit for setting a threshold value as a reference for comparison of the determination, and the magnetic detection An output of the object / offset discriminator, and at least an offset correction memory for storing an offset correction value for performing the offset correction, the magnetic detection In the offset discriminator, the absolute value of the output due to the difference between the two inputs of the comparator is smaller than the threshold of the predetermined threshold setting unit, or the output due to the ratio of the two inputs of the comparator is If the value is close to 1, it is determined that the occasional output of the amplifier is due to a change in offset, and the offset correction value stored in the offset correction memory corresponds to the occasional output of the amplifier. The absolute value of the output due to the difference between the two inputs of the comparator is greater than the threshold of the predetermined threshold setting unit, or the output according to the ratio of the two inputs of the comparator is from 1 If it is a remote value, it is determined that the occasional output of the amplifier is due to the presence of the vehicle on the magnetic sensor, and the offset stored in the offset correction memory is determined. Offset correction method for a vehicle detection device according to the magnetic sensor, characterized in that it has to hold unchanged set correction value.

An offset correction circuit for a vehicle detection device using a magnetic sensor, which compares a magnetic sensor, an amplifier that amplifies the detection output of the magnetic sensor, and an output of the amplifier when the vehicle to be detected is not on the magnetic sensor A reference voltage value setting unit for setting a reference value for the vehicle, a comparator for comparing the input of the amplifier at any time with two inputs of the reference value, and an output value of the comparator for the magnetic sensor of the vehicle Magnetic detection object / offset discriminator for determining whether it is due to the presence in the above or a change in offset, a predetermined threshold setting unit for setting a threshold value as a reference for comparison of the determination, and the magnetic detection An output of the object / offset discriminator, and at least an offset correction memory for storing an offset correction value for performing the offset correction, the magnetic detection In the offset discriminator, the absolute value of the output due to the difference between the two inputs of the comparator is smaller than the threshold of the predetermined threshold setting unit, or the output due to the ratio of the two inputs of the comparator is If the value is close to 1, it is determined that the occasional output of the amplifier is due to a change in offset, and the offset correction value stored in the offset correction memory corresponds to the occasional output of the amplifier. The absolute value of the output due to the difference between the two inputs of the comparator is greater than the threshold of the predetermined threshold setting unit, or the output according to the ratio of the two inputs of the comparator is from 1 If it is a remote value, it is determined that the occasional output of the amplifier is due to the presence of the vehicle on the magnetic sensor, and the offset stored in the offset correction memory is determined. Offset correction circuit of the vehicle detection device according to the magnetic sensor, characterized in that it has to hold unchanged set correction value.

A method for correcting an offset of a vehicle detection apparatus using a magnetic sensor, comprising: comparing a magnetic sensor, an amplifier for amplifying a detection output of the magnetic sensor, and an output of the amplifier when a vehicle to be detected is not on the magnetic sensor A reference voltage value setting unit for setting a reference value for the vehicle, a comparator for comparing the input of the amplifier at any time with two inputs of the reference value, and an output value of the comparator for the magnetic sensor of the vehicle At least a magnetic detection object / offset discriminator for determining whether it is due to presence in the above or a change in offset, and a predetermined threshold value setting unit for setting a threshold value as a reference for comparison of the determination In the magnetic detection object / offset discriminator, an absolute value of an output due to a difference between the two inputs of the comparator is smaller than the threshold of the predetermined threshold setting unit, or the ratio When the output by the ratio of the two inputs of the amplifier is a value close to 1, it is determined that the occasional output of the amplifier is due to a change in offset, and the reference value of the reference voltage value setting unit Is updated to an output value from the amplifier, and an absolute value of an output due to a difference between the two inputs of the comparator is greater than the threshold value of the predetermined threshold setting unit, or the two inputs of the comparator When the output by the ratio is a value away from 1, the occasional output of the amplifier is determined to be due to the presence of the vehicle on the magnetic sensor, and the reference voltage value setting unit An offset correction method for a vehicle detection apparatus using a magnetic sensor, wherein the reference value is maintained without being changed.

An offset correction circuit for a vehicle detection device using a magnetic sensor, which compares a magnetic sensor, an amplifier that amplifies the detection output of the magnetic sensor, and an output of the amplifier when the vehicle to be detected is not on the magnetic sensor A reference voltage value setting unit for setting a reference value for the vehicle, a comparator for comparing the input of the amplifier at any time with two inputs of the reference value, and an output value of the comparator for the magnetic sensor of the vehicle At least a magnetic detection object / offset discriminator for determining whether it is due to the presence in the above or a change in offset, and a predetermined threshold value setting unit for setting a threshold value as a reference for comparison of the determination In the magnetic detection object / offset discriminator, an absolute value of an output due to a difference between the two inputs of the comparator is smaller than the threshold of the predetermined threshold setting unit, or the ratio When the output by the ratio of the two inputs of the amplifier is a value close to 1, it is determined that the occasional output of the amplifier is due to a change in offset, and the reference value of the reference voltage value setting unit Is updated to the output value from the amplifier, and the absolute value of the output due to the difference between the two inputs of the comparator is greater than the threshold value of the predetermined threshold setting unit, or the two inputs of the comparator When the output by the ratio is a value away from 1, the occasional output of the amplifier is determined to be due to the presence of the vehicle on the magnetic sensor, and the reference voltage value setting unit An offset correction circuit for a vehicle detection apparatus using a magnetic sensor, wherein the reference value is maintained without being changed.