JP4533544B2 - Ultrasonic vehicle detector and its ultrasonic frequency control method - Google Patents

Ultrasonic vehicle detector and its ultrasonic frequency control method Download PDF

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JP4533544B2
JP4533544B2 JP2001045462A JP2001045462A JP4533544B2 JP 4533544 B2 JP4533544 B2 JP 4533544B2 JP 2001045462 A JP2001045462 A JP 2001045462A JP 2001045462 A JP2001045462 A JP 2001045462A JP 4533544 B2 JP4533544 B2 JP 4533544B2
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frequency
transmission
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ultrasonic
frequencies
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JP2002251694A (en
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実 鈴木
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Panasonic Corp
Panasonic Holdings Corp
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Panasonic Corp
Matsushita Electric Industrial Co Ltd
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【０００１】
【発明の属する技術分野】
本発明は、道路上の走行車両を検知する超音波式車両感知器と、その送信する超音波周波数を制御する方法に関し、特に、車両感知精度の向上を図るものである。
【０００２】
【従来の技術】
超音波式車両感知器は、道路上に設置した超音波ヘッドから道路面に向けて一定周期で超音波を送信し、その反射波を受信するまでの時間を計って、道路上の車両の有無を判定する。
【０００３】
この超音波式車両感知器では、送信波の最適周波数が、車両感知器の温度変化や経年変化等によって変動する。そのため、従来の超音波式車両感知器では、超音波の送信時期に最適周波数ｆの超音波を送信し、次の送信時期に周波数（ｆ＋Δ）の超音波を送信し、その次の送信時期に周波数（ｆ−Δ）の超音波を送信し、それぞれの信号が道路面で反射して戻って来たときの受信信号レベルを比較して、周波数ｆが最適周波数を維持しているかどうかを確認しており、この確認結果に基づいて、次に送る送信信号の周波数を制御している。
【０００４】
図６は、従来の超音波式車両感知器を示している。この装置は、道路脇のポール31から走行路上に延びるアーム30に取り付けられた超音波ヘッド20と、その制御器110とから成り、超音波ヘッド20は、超音波を路面に向けて送信する送信器22と、超音波の反射波を受信して電気信号に変換する受信器21とを具備し、この送信器22及び受信器21は、同一の超音波素子を用いて構成されている。
【０００５】
また、制御器110は、指定された周波数の信号を生成する発振部111と、送信信号を一定周期で出力する送信信号出力部112と、受信信号を増幅する受信信号増幅部113と、受信信号をデジタル信号に変換するＡ／Ｄ変換部114と、受信信号の周波数を計測する周波数計測部115と、時間を計時するタイマ116と、超音波の直接反射による受信信号を識別するために設定された閾値118と、送信信号の周波数を制御するＣＰＵから成る制御部117とを備えている。
【０００６】
超音波ヘッド20は、標準的には、路面から５．５ｍの高さに設置されている。超音波ヘッド20には、制御器110の送信信号出力部112から、２５ｋＨｚ近傍の周波数を有し、送信時間が２ｍｓの送信信号が１００ｍｓの周期で繰り返し送られてくる。超音波ヘッド20の送信器22は、内蔵する圧電素子を送信信号で励起し、送信信号に応じた周波数の超音波を真下に送信する。図８（ａ）は、送信波形を示している。
【０００７】
道路上に車両が存在していない状態では、図８（ｂ）に示すように、路面で反射した超音波が受信器21に達する。受信器21は、これを電気信号に変換し、制御器110の受信信号増幅部113は、これを増幅する。周波数計測部115は、受信信号の周波数を計測して制御部117に伝え、また、Ａ／Ｄ変換部114は、受信信号レベルをデジタル値（ＡＤ値と云う）に変換して制御部117に出力する。
【０００８】
制御部117は、ＡＤ値が閾値118より高い場合に、送信信号の直接反射波による受信信号と判断し、送信時点からの時間を調べ、その時間により車両の有無を識別する。また、制御部117は、ＡＤ値から次に送信する送信信号の周波数を決定し、発振部111の発振周波数を制御する。
【０００９】
図７は、この送信信号周波数の制御手順を示している。
ステップ１：送信信号の周波数を最適周波数ｆ（例えば、ｆ＝２５ｋＨｚ）に設定して送信し、
ステップ２：反射波を受信し、ＡＤ値（路面波ａ）を取り込む。
【００１０】
ステップ３：次の送信タイミングまで待ち、
ステップ４：送信タイミングに、送信信号の周波数を（ｆ＋Δ）（Δは、例えば２５Ｈｚ）に設定して送信し、
ステップ５：反射波を受信し、ＡＤ値（路面波ｂ）を取り込む。
【００１１】
ステップ６：次の送信タイミングまで待ち、
ステップ７：送信タイミングに、送信信号の周波数を（ｆ−Δ）に設定して送信し、
ステップ８：反射波を受信し、ＡＤ値（路面波ｃ）を取り込む。
【００１２】
図８（ａ）は、ステップ１、ステップ４、ステップ７で送信される送信信号を表し、図８（ｂ）は、ステップ２、ステップ５、ステップ８で受信された路面波形を表している。
【００１３】
ステップ９：路面波ａ、ｂ、ｃを比較する。
ステップ９において、路面波ａが一番大きい場合は、
ステップ11：最適周波数ｆの値は変更せず、
ステップ13：次の送信タイミングまで待って、ステップ１からの手順を繰り返す。
【００１４】
ステップ９において、路面波ｂが一番大きい場合は、
ステップ12：周波数（ｆ＋Δ）を最適周波数ｆに変更し、
ステップ13：次の送信タイミングまで待って、ステップ１からの手順を繰り返す。
【００１５】
ステップ９において、路面波ｃが一番大きい場合は、
ステップ10：周波数（ｆ−Δ）を最適周波数ｆに変更し、
ステップ13：次の送信タイミングまで待って、ステップ１からの手順を繰り返す。
【００１６】
図９は、超音波感度の周波数特性の推移と、周波数ｆ、（ｆ＋Δ）及び（ｆ−Δ）との関係を模式的に示している。周波数特性がＡの状態では、ｆが最適周波数であり、送信周波数ｆに対応する受信感度が、送信周波数（ｆ＋Δ）及び（ｆ−Δ）に対応する受信感度に比べて一段と高い。この状態では、ｆが最適周波数として維持される。周波数特性がＢの状態に推移すると、送信周波数ｆに対応する受信感度より、送信周波数（ｆ＋Δ）に対応する受信感度の方が高くなる。この場合には、送信周波数（ｆ＋Δ）が最適周波数とされる。また、周波数特性がＡの状態からＣの状態に推移すると、送信周波数ｆに対応する受信感度より、送信周波数（ｆ−Δ）に対応する受信感度の方が高くなる。この場合には、送信周波数（ｆ−Δ）が最適周波数とされる。
【００１７】
このように、超音波式車両感知器が、最適周波数をｆとするとき、周波数ｆ、ｆ＋Δ、及び、ｆ−Δの３種類の送信信号を送信し、その中で受信信号レベルが最も高い周波数を次の最適周波数として、その前後の周波数とともに３種類の送信信号を送信する送信周波数制御を続けることにより、温度変化等により特性が推移した場合でも、最適周波数を検出して、特性推移に追従することが可能になる。
【００１８】
【発明が解決しようとする課題】
しかし、従来の超音波式車両感知器では、最適周波数が変移しない場合でも、それを確認するために常に３種類の信号を送信しているため、次のような問題が生じる。
【００１９】
超音波式車両感知器が車両を感知できるエリアは、受信感度が最も高い最適周波数ｆの信号を送信した場合に最も広くなり、周波数ｆ＋Δ及びｆ−Δの信号を送信した場合には、これに比べて狭くなる。このエリアの差分は、受信感度の周波数特性等に依存するが、例えば、最適周波数ｆにおいて、道路の長さ方向の１．２ｍの距離の間に位置する車両が感知できる場合に、周波数ｆ＋Δ及びｆ−Δでは、この距離が１．１ｍに減少する。
【００２０】
そのため、渋滞等により車両が感知エリアぎりぎりに停車すると、感知エリアの広い周波数ｆの信号を送信した場合には、その車両が感知され、感知エリアの狭い周波数ｆ＋Δ及びｆ−Δの信号を送信した場合には、その車両が感知されないと云う状態が発生する。このように感知エリアのばらつきは、車両感知精度の低下を招来する。
【００２１】
本発明は、こうした従来の問題点を解決するものであり、車両感知精度を高めることができる超音波式車両感知器を提供し、また、その超音波周波数制御方法を提供することを目的としている。
【００２２】
【課題を解決するための手段】
そこで、本発明では、超音波の送信信号を周期的に送信して車両を感知する超音波式車両感知器において、送信信号の周波数として２種類の周波数を設定し、各々の周波数を持つ送信信号が交互に送信されるように制御する送信周波数設定手段と、各々の周波数を持つ送信信号が路面で反射されたときの受信レベルを比較し、受信レベルが高い送信信号の周波数を前記送信周波数設定手段に伝える比較手段とを設け、送信周波数設定手段は、２種類の周波数のいずれか一方の周波数の信号の受信レベルが高いことを比較手段から伝えられたときに、当該周波数を新しい最適周波数ｆと見做し、新しい最適周波数ｆからプラス側に変移した周波数（ｆ＋α）を２種類の周波数の一方として設定する手段と、最適周波数ｆからマイナス側に変移した周波数（ｆ−α）の付近で送信周波数を徐々に変えて送信し、周波数（ｆ＋α）の信号の受信レベルと同じ受信レベルになる周波数（ｆ−β）を探して、周波数（ｆ−β）を２種類の周波数の他方として設定する手段とを有するように構成している。
【００２３】
また、超音波の送信信号を周期的に送信して車両を感知する超音波式車両感知器の超音波周波数制御方法において、最適周波数ｆからプラス側に変移した周波数（ｆ＋α）を送信信号の一方の周波数として設定し、最適周波数ｆからマイナス側に変移した周波数（ｆ−α）の付近で送信周波数を徐々に変えて送信し、周波数（ｆ＋α）の信号の受信レベルと同じ受信レベルになる周波数（ｆ−β）を探して、周波数（ｆ−β）を送信信号の他方の周波数として設定し、この２種類の周波数を持つ送信信号を交互に送信し、各々の周波数を持つ送信信号が路面で反射されたときの受信レベルを比較して、一方の周波数を持つ送信信号の受信レベルが他方の周波数を持つ送信信号の受信レベルより高くなったときは、高い方の周波数を新しい最適周波数と見做して２種類の周波数を同様に求めて送信信号の周波数として設定するようにしている。
【００２４】
そのため、２種類の周波数の送信信号による感知エリアは同じになる。従って、送信信号の周波数を最適周波数に追随させながら、送信信号の感知エリアを一定に保つことができる。
【００２５】
【発明の実施の形態】
実施形態の超音波式車両感知器は、図１に示すように、送信器22及び受信器21を有する超音波ヘッド20と、制御器10とから成り、制御器10は、図６と同様、発振部11、送信信号出力部12、受信信号増幅部13、Ａ／Ｄ変換部14、周波数計測部15、タイマ16、閾値18及び制御部17を備えている。
【００２６】
図２は、ＣＰＵから成る制御部17をプログラムで複数の手段として機能させるときの各手段の構成を機能ブロックで示している。この制御部17は、Ａ／Ｄ変換部14から入力するＡＤ値を閾値18と比較して、送信信号の直接反射波による受信信号を識別する反射信号識別部41と、反射信号識別部41により識別された受信信号が車両から反射した受信信号か路面から反射した受信信号かを識別する車／路面反射信号識別部42と、路面から反射した受信信号のＡＤ値を、前回受信した路面から反射した受信信号のＡＤ値と比較する路面反射信号比較部43と、路面反射信号比較部43の比較結果に基づいて発振部11の発振周波数を制御する送信周波数設定部44とを備えている。
【００２７】
この装置の制御部17を除く各部の動作は、図６の場合と同じである。
制御部17は、図５に示すように、周波数特性がＡの状態であり、最適周波数がｆであるとき、最適周波数ｆより僅かにプラス側に変移した周波数（ｆ＋α）の送信信号を送信し、次に、この送信信号による受信レベルと同じ受信レベルを持つ、最適周波数ｆよりマイナス側に変移した周波数（ｆ−β）の送信信号を送信する。この周波数（ｆ−β）は、周波数（ｆ−α）の近辺に存在するので、当初、送信周波数を周波数（ｆ−α）の付近で徐々に変えて送信し、送信周波数（ｆ＋α）の受信レベルと同じ受信レベルになる周波数位置を探して決定する。
【００２８】
周波数（ｆ−β）が求まると、図４（ａ）に示すように、送信周波数（ｆ＋α）の信号と、送信周波数（ｆ−β）の信号とを交互に送信する。図４（ｂ）は、このとき路面から反射された路面波形を示している。
【００２９】
温度変化等により周波数特性が変化し、送信周波数（ｆ＋α）に対応する受信信号レベルの方が送信周波数（ｆ−β）に対応する受信信号レベルより高くなると、送信周波数（ｆ＋α）を最適周波数と見做し、この最適周波数のプラス側にαだけ変移した周波数の送信信号と、この送信信号の受信レベルと同じ受信レベルを持つ、最適周波数よりマイナス側に位置する周波数の送信信号とを交互に送信する。
【００３０】
また、送信周波数（ｆ＋α）の信号と、送信周波数（ｆ−β）の信号とを交互に送信している過程で、送信周波数（ｆ−β）に対応する受信信号レベルの方が送信周波数（ｆ＋α）に対応する受信信号レベルより高くなると、送信周波数（ｆ−β）を最適周波数と見做し、この最適周波数のプラス側にαだけ変移した周波数の送信信号と、この送信信号の受信レベルと同じ受信レベルを持つ、最適周波数よりマイナス側に位置する周波数の送信信号とを交互に送信する。
【００３１】
このとき、制御部17の反射信号識別部41は、Ａ／Ｄ変換部14から入力するＡＤ値を閾値18と比較し、ＡＤ値が閾値18より大きい場合に、受信信号が直接反射波による受信信号である旨を車／路面反射信号識別部42に伝える。車／路面反射信号識別部42は、その受信信号の周波数を周波数計測部15から取得し、同一周波数の送信信号が送信信号出力部12から送出されてからの経過時間をタイマ16より取得して、受信信号が車両から反射したものか、路面から反射したものかを識別する。受信信号が車両からの反射信号である場合、車／路面反射信号識別部42は、車両感知出力を送出する。また、受信信号が路面からの反射信号である場合、その受信信号のＡＤ値を路面反射信号比較部43に渡す。
【００３２】
路面反射信号比較部43は、前回、車／路面反射信号識別部42から渡された受信信号のＡＤ値と、周波数計測部15から取得したその受信信号の周波数とを保持し、車／路面反射信号識別部42から新たな受信信号のＡＤ値が渡されると、その受信信号の周波数を周波数計測部15から取得して、新たな受信信号のＡＤ値と、保持している受信信号のＡＤ値とを比較する。そして、一方の受信信号のＡＤ値が大きければ、その受信信号の周波数を送信周波数設定部44に伝える。
【００３３】
送信周波数設定部44は、路面反射信号比較部43から、受信信号の周波数の情報が与えられない限り、図４（ａ）の周波数（ｆ＋α）及び周波数（ｆ−β）の２種類の信号を交互に発振するように発振部11を制御する。また、路面反射信号比較部43から、受信信号の周波数ｆ’の情報が与えられると、周波数（ｆ'＋α）の信号を発振するように発振部11を制御し、その送信信号に対応する受信信号のＡＤ値と同じＡＤ値を持つ周波数（ｆ'−β）を求め（この周波数（ｆ'−β）は、前述するように、送信周波数を徐々に変えて送信し、送信周波数（ｆ'＋α）の受信レベルと同じ受信レベルになる周波数位置を探して決定する）、周波数（ｆ'＋α）及び周波数（ｆ'−β）の２種類の送信信号を交互に発振するように発振部11を制御する。
【００３４】
図３は、制御部17による送信信号周波数の制御手順を示している。
ステップ21：送信信号の周波数をｆ＋α（ｆは最適周波数、αは、例えば２５Ｈｚ）に設定して送信し、
ステップ22：反射波を受信し、ＡＤ値（路面波α）を取り込む。
【００３５】
ステップ23：次の送信タイミングまで待ち、
ステップ24：送信タイミングに、送信信号の周波数をｆ−βに設定して送信し、
ステップ25：反射波を受信し、ＡＤ値（路面波β）を取り込む。
【００３６】
ステップ26：路面波α、βを比較する。
ステップ26において、路面波α、βが同じであれば、
ステップ28：最適周波数ｆの値は変更せず、
ステップ30：次の送信タイミングまで待って、ステップ21からの手順を繰り返す。
【００３７】
ステップ26において、路面波αが大きい場合は、
ステップ29：周波数ｆ＋αを最適周波数ｆに変更し、
ステップ30：次の送信タイミングまで待って、ステップ１からの手順を繰り返す。
【００３８】
ステップ26において、路面波βが大きい場合は、
ステップ27：周波数ｆ−βを最適周波数ｆに変更し、
ステップ30：次の送信タイミングまで待って、ステップ１からの手順を繰り返す。
【００３９】
この制御部17が制御する２種類の周波数の送信信号に対応する受信信号レベルは同一である。そのため、２種類の周波数の送信信号での感知エリアは同じになり、車両の感知性能が安定化する。
【００４０】
【発明の効果】
以上の説明から明らかなように、本発明の超音波式車両感知器及び超音波周波数制御方法では、送信信号の周波数を最適周波数に追随させながら、送信信号の感知エリアを一定に保つことができ、車両感知精度を高めることができる。
【図面の簡単な説明】
【図１】本発明の実施形態における超音波式車両感知器の構成を示すブロック図、
【図２】実施形態の超音波式車両感知器における制御部の構成を示すブロック図、
【図３】実施形態の超音波式車両感知器における動作手順を示すフロー図、
【図４】（ａ）実施形態の超音波式車両感知器での送信波形を示す図、
（ｂ）実施形態の超音波式車両感知器での路面波の受信波形を示す図、
【図５】実施形態の超音波周波数制御方法において、受信感度の周波数特性と、設定される周波数との関係を示す図、
【図６】従来の超音波式車両感知器の構成を示すブロック図、
【図７】従来の超音波式車両感知器における動作手順を示すフロー図、
【図８】（ａ）従来の超音波式車両感知器での送信波形を示す図、
（ｂ）従来の超音波式車両感知器での路面波の受信波形を示す図、
【図９】従来の超音波周波数制御方法において、受信感度の周波数特性と、設定される周波数との関係を示す図である。
【符号の説明】
10、110 制御器
11、111 発振部
12、112 送信信号出力部
13、113 受信信号増幅部
14、114 Ａ／Ｄ変換部
15、115 周波数計測部
16、116 タイマ
17、117 制御部
18、118 閾値
20 超音波ヘッド
21 受信器
22 送信器
31 ポール
30 アーム
41 反射信号識別部
42 車／路面反射信号識別部
43 路面反射信号比較部
44 送信周波数設定部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic vehicle detector for detecting a traveling vehicle on a road and a method for controlling an ultrasonic frequency transmitted from the ultrasonic vehicle detector, and particularly to improving vehicle detection accuracy.
[0002]
[Prior art]
The ultrasonic vehicle detector transmits ultrasonic waves from the ultrasonic head installed on the road toward the road surface at regular intervals and measures the time until the reflected wave is received. Determine.
[0003]
In this ultrasonic vehicle sensor, the optimum frequency of the transmission wave varies depending on the temperature change or aging of the vehicle sensor. For this reason, in the conventional ultrasonic vehicle sensor, an ultrasonic wave having the optimum frequency f is transmitted at an ultrasonic transmission timing, an ultrasonic wave having a frequency (f + Δ) is transmitted at the next transmission timing, and the next transmission timing is transmitted. Send ultrasonic waves of frequency (f-Δ) and compare the received signal level when each signal is reflected back on the road surface to check whether the frequency f maintains the optimum frequency Based on the confirmation result, the frequency of the transmission signal to be sent next is controlled.
[0004]
FIG. 6 shows a conventional ultrasonic vehicle sensor. This device is composed of an ultrasonic head 20 attached to an arm 30 extending on a traveling road from a pole 31 on the roadside, and a controller 110 for the ultrasonic head 20. The ultrasonic head 20 transmits ultrasonic waves toward a road surface. And a receiver 21 that receives an ultrasonic reflected wave and converts it into an electrical signal. The transmitter 22 and the receiver 21 are configured using the same ultrasonic element.
[0005]
Further, the controller 110 includes an oscillation unit 111 that generates a signal having a specified frequency, a transmission signal output unit 112 that outputs a transmission signal at a constant period, a reception signal amplification unit 113 that amplifies the reception signal, and a reception signal Is set to identify the A / D converter 114 that converts the signal into a digital signal, the frequency measuring unit 115 that measures the frequency of the received signal, the timer 116 that measures the time, and the received signal due to the direct reflection of ultrasonic waves And a control unit 117 composed of a CPU for controlling the frequency of the transmission signal.
[0006]
The ultrasonic head 20 is typically installed at a height of 5.5 m from the road surface. A transmission signal having a frequency near 25 kHz and a transmission time of 2 ms is repeatedly sent from the transmission signal output unit 112 of the controller 110 to the ultrasonic head 20 at a cycle of 100 ms. The transmitter 22 of the ultrasonic head 20 excites a built-in piezoelectric element with a transmission signal, and transmits an ultrasonic wave having a frequency corresponding to the transmission signal directly below. FIG. 8A shows a transmission waveform.
[0007]
In a state where no vehicle is present on the road, the ultrasonic waves reflected on the road surface reach the receiver 21 as shown in FIG. The receiver 21 converts this into an electrical signal, and the received signal amplification unit 113 of the controller 110 amplifies it. The frequency measurement unit 115 measures the frequency of the received signal and transmits it to the control unit 117, and the A / D conversion unit 114 converts the received signal level into a digital value (referred to as AD value) and sends it to the control unit 117. Output.
[0008]
When the AD value is higher than the threshold value 118, the control unit 117 determines that the received signal is a direct reflected wave of the transmission signal, checks the time from the transmission time, and identifies the presence or absence of the vehicle based on the time. Further, the control unit 117 determines the frequency of the transmission signal to be transmitted next from the AD value, and controls the oscillation frequency of the oscillation unit 111.
[0009]
FIG. 7 shows a control procedure of the transmission signal frequency.
Step 1: The transmission signal frequency is set to an optimum frequency f (for example, f = 25 kHz) and transmitted.
Step 2: A reflected wave is received and an AD value (road surface wave a) is captured.
[0010]
Step 3: Wait until the next transmission timing,
Step 4: At the transmission timing, the frequency of the transmission signal is set to (f + Δ) (Δ is, for example, 25 Hz) and transmitted,
Step 5: Receive the reflected wave and capture the AD value (road wave b).
[0011]
Step 6: Wait until the next transmission timing,
Step 7: At the transmission timing, set the frequency of the transmission signal to (f−Δ) and transmit,
Step 8: Receive the reflected wave and take in the AD value (road surface wave c).
[0012]
FIG. 8A shows the transmission signal transmitted in Step 1, Step 4 and Step 7, and FIG. 8B shows the road surface waveform received in Step 2, Step 5 and Step 8. FIG.
[0013]
Step 9: Compare road surface waves a, b, and c.
In step 9, when the road surface wave a is the largest,
Step 11: Do not change the value of the optimal frequency f
Step 13: Wait until the next transmission timing and repeat the procedure from Step 1.
[0014]
In step 9, when the road wave b is the largest,
Step 12: Change the frequency (f + Δ) to the optimum frequency f,
Step 13: Wait until the next transmission timing and repeat the procedure from Step 1.
[0015]
In step 9, when the road surface wave c is the largest,
Step 10: Change the frequency (f−Δ) to the optimum frequency f,
Step 13: Wait until the next transmission timing and repeat the procedure from Step 1.
[0016]
FIG. 9 schematically shows the relationship between the transition of the frequency characteristics of the ultrasonic sensitivity and the frequencies f, (f + Δ), and (f−Δ). In the state where the frequency characteristic is A, f is the optimum frequency, and the reception sensitivity corresponding to the transmission frequency f is much higher than the reception sensitivity corresponding to the transmission frequencies (f + Δ) and (f−Δ). In this state, f is maintained as the optimum frequency. When the frequency characteristic shifts to the state B, the reception sensitivity corresponding to the transmission frequency (f + Δ) becomes higher than the reception sensitivity corresponding to the transmission frequency f. In this case, the transmission frequency (f + Δ) is the optimum frequency. Further, when the frequency characteristic transitions from the A state to the C state, the reception sensitivity corresponding to the transmission frequency (f−Δ) becomes higher than the reception sensitivity corresponding to the transmission frequency f. In this case, the transmission frequency (f−Δ) is the optimum frequency.
[0017]
In this way, when the ultrasonic vehicle sensor has an optimum frequency f, three types of transmission signals of frequencies f, f + Δ, and f−Δ are transmitted, and the frequency with the highest received signal level is among them. Is the next optimal frequency, and by continuing transmission frequency control that transmits three types of transmission signals along with the frequencies before and after that, even if the characteristics change due to temperature changes, etc., the optimum frequency is detected and the characteristics change is followed. It becomes possible to do.
[0018]
[Problems to be solved by the invention]
However, in the conventional ultrasonic vehicle detector, even when the optimum frequency does not change, three types of signals are always transmitted in order to confirm that, so the following problem occurs.
[0019]
The area where the ultrasonic vehicle detector can sense the vehicle is the widest when the signal of the optimum frequency f with the highest reception sensitivity is transmitted, and when the signal of the frequencies f + Δ and f−Δ is transmitted, Compared to narrower. The difference between the areas depends on the frequency characteristics of the reception sensitivity. For example, when a vehicle located within a distance of 1.2 m in the length direction of the road can be detected at the optimum frequency f, the frequency f + Δ and At f−Δ, this distance decreases to 1.1 m.
[0020]
Therefore, when the vehicle stops at the limit of the sensing area due to traffic jam or the like, when a signal with a wide frequency f in the sensing area is transmitted, the vehicle is sensed and signals with frequencies f + Δ and f−Δ having a narrow sensing area are transmitted. In some cases, a situation occurs where the vehicle is not sensed. As described above, the variation in the sensing area causes a decrease in vehicle sensing accuracy.
[0021]
SUMMARY OF THE INVENTION The present invention solves such conventional problems, and an object thereof is to provide an ultrasonic vehicle detector capable of increasing vehicle detection accuracy and to provide an ultrasonic frequency control method thereof. .
[0022]
[Means for Solving the Problems]
Therefore, in the present invention, in an ultrasonic vehicle detector that senses a vehicle by periodically transmitting ultrasonic transmission signals, two types of frequencies are set as the frequencies of the transmission signals, and the transmission signals having the respective frequencies. The transmission frequency setting means for controlling the transmission signal to be transmitted alternately and the reception level when the transmission signal having each frequency is reflected on the road surface, the frequency of the transmission signal having a high reception level is set to the transmission frequency. A comparison means for transmitting to the means, and the transmission frequency setting means transmits the frequency to a new optimum frequency f when the comparison means informs that the reception level of the signal of one of the two frequencies is high. And a means for setting the frequency (f + α) shifted from the new optimum frequency f to the plus side as one of the two types of frequencies, and a shift from the optimum frequency f to the minus side. The transmission frequency is gradually changed in the vicinity of the frequency (f-α), and the frequency (f-β) is searched for a frequency (f-β) that has the same reception level as the reception level of the signal of the frequency (f + α). It is configured to have a means for setting as the other two types of frequency.
[0023]
Further, in the ultrasonic frequency control method of an ultrasonic vehicle detector that periodically transmits an ultrasonic transmission signal to sense a vehicle, the frequency (f + α) shifted from the optimum frequency f to the plus side is set to one of the transmission signals. The frequency is set as the frequency of the transmission frequency, and the transmission frequency is gradually changed in the vicinity of the frequency (f−α) shifted from the optimum frequency f to the minus side, so that the reception level is the same as the reception level of the signal of the frequency (f + α). Searching for (f-β), setting the frequency (f-β) as the other frequency of the transmission signal, transmitting the transmission signals having these two types of frequencies alternately, and transmitting the signals having the respective frequencies to the road surface When the reception level of the transmission signal with one frequency is higher than the reception level of the transmission signal with the other frequency, the higher frequency is replaced with the new optimum frequency. In consideration of the number, two types of frequencies are similarly obtained and set as the frequency of the transmission signal .
[0024]
Therefore, the sensing area by the transmission signal of two types of frequencies becomes the same. Therefore, the sensing area of the transmission signal can be kept constant while the frequency of the transmission signal is made to follow the optimum frequency.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1, the ultrasonic vehicle sensor according to the embodiment includes an ultrasonic head 20 having a transmitter 22 and a receiver 21, and a controller 10. The controller 10 is similar to FIG. An oscillation unit 11, a transmission signal output unit 12, a reception signal amplification unit 13, an A / D conversion unit 14, a frequency measurement unit 15, a timer 16, a threshold 18 and a control unit 17 are provided.
[0026]
FIG. 2 is a functional block diagram showing the configuration of each means when the control unit 17 composed of a CPU functions as a plurality of means in a program. The control unit 17 compares the AD value input from the A / D conversion unit 14 with a threshold value 18, and uses a reflected signal identifying unit 41 that identifies a received signal based on a direct reflected wave of a transmission signal, and a reflected signal identifying unit 41. The vehicle / road surface reflection signal identification unit 42 for identifying whether the identified reception signal is a reception signal reflected from the vehicle or the road surface, and the AD value of the reception signal reflected from the road surface is reflected from the previously received road surface. A road surface reflection signal comparison unit 43 that compares the AD value of the received signal, and a transmission frequency setting unit 44 that controls the oscillation frequency of the oscillation unit 11 based on the comparison result of the road surface reflection signal comparison unit 43.
[0027]
The operation of each part except for the control part 17 of this apparatus is the same as in the case of FIG.
As shown in FIG. 5, when the frequency characteristic is A and the optimum frequency is f, the control unit 17 transmits a transmission signal having a frequency (f + α) slightly shifted to the plus side from the optimum frequency f. Next, a transmission signal having the same reception level as that of the transmission signal and having a frequency (f−β) shifted to the minus side from the optimum frequency f is transmitted. Since this frequency (f-β) exists in the vicinity of the frequency (f-α), the transmission frequency is initially changed gradually in the vicinity of the frequency (f-α), and the transmission frequency (f + α) is received. The frequency position where the reception level is the same as the level is searched and determined.
[0028]
When the frequency (f−β) is obtained, as shown in FIG. 4A, the signal of the transmission frequency (f + α) and the signal of the transmission frequency (f−β) are alternately transmitted. FIG. 4B shows the road surface waveform reflected from the road surface at this time.
[0029]
When the frequency characteristics change due to a temperature change or the like, and the reception signal level corresponding to the transmission frequency (f + α) becomes higher than the reception signal level corresponding to the transmission frequency (f−β), the transmission frequency (f + α) is set as the optimum frequency. Assuming that the transmission signal of the frequency shifted by α to the plus side of the optimum frequency and the transmission signal of the frequency located on the minus side of the optimum frequency having the same reception level as the reception level of the transmission signal are alternately Send.
[0030]
Further, in the process of alternately transmitting the signal of the transmission frequency (f + α) and the signal of the transmission frequency (f−β), the reception signal level corresponding to the transmission frequency (f−β) is higher than the transmission frequency (f−β). When it becomes higher than the received signal level corresponding to f + α), the transmission frequency (f−β) is regarded as the optimum frequency, the transmission signal having a frequency shifted by α to the plus side of the optimum frequency, and the reception level of this transmission signal And the transmission signal having the same reception level and the frequency located on the minus side of the optimum frequency are alternately transmitted.
[0031]
At this time, the reflected signal identification unit 41 of the control unit 17 compares the AD value input from the A / D conversion unit 14 with the threshold value 18, and when the AD value is larger than the threshold value 18, the received signal is received directly by the reflected wave. The vehicle / road surface reflection signal identification unit 42 is informed that the signal is a signal. The vehicle / road surface reflection signal identifying unit 42 obtains the frequency of the received signal from the frequency measuring unit 15 and obtains the elapsed time from when the transmission signal of the same frequency is transmitted from the transmission signal output unit 12 from the timer 16. Identifies whether the received signal is reflected from the vehicle or the road surface. When the received signal is a reflected signal from the vehicle, the vehicle / road surface reflected signal identifying unit 42 sends a vehicle sensing output. When the received signal is a reflected signal from the road surface, the AD value of the received signal is passed to the road surface reflected signal comparing unit 43.
[0032]
The road surface reflection signal comparison unit 43 holds the AD value of the reception signal passed from the vehicle / road surface reflection signal identification unit 42 last time and the frequency of the reception signal acquired from the frequency measurement unit 15, and the vehicle / road surface reflection When the AD value of the new received signal is passed from the signal identifying unit 42, the frequency of the received signal is obtained from the frequency measuring unit 15, and the AD value of the new received signal and the AD value of the received received signal are held. And compare. If the AD value of one of the received signals is large, the frequency of the received signal is transmitted to the transmission frequency setting unit 44.
[0033]
The transmission frequency setting unit 44 outputs two types of signals, frequency (f + α) and frequency (f−β) in FIG. 4A, unless the information on the frequency of the reception signal is given from the road surface reflection signal comparison unit 43. The oscillator 11 is controlled so as to oscillate alternately. Further, when information on the frequency f ′ of the reception signal is given from the road surface reflection signal comparison unit 43, the oscillation unit 11 is controlled to oscillate the signal of frequency (f ′ + α), and the reception corresponding to the transmission signal is performed. A frequency (f′−β) having the same AD value as the AD value of the signal is obtained (this frequency (f′−β) is transmitted by gradually changing the transmission frequency as described above, and the transmission frequency (f′−β) is transmitted). The oscillation unit 11 so as to alternately oscillate two types of transmission signals of frequency (f ′ + α) and frequency (f′−β). To control.
[0034]
FIG. 3 shows a control procedure of the transmission signal frequency by the control unit 17.
Step 21: Set the frequency of the transmission signal to f + α (f is the optimum frequency, α is, for example, 25 Hz) and transmit,
Step 22: The reflected wave is received and the AD value (road surface wave α) is captured.
[0035]
Step 23: Wait until the next transmission timing,
Step 24: At the transmission timing, set the frequency of the transmission signal to f-β and transmit,
Step 25: The reflected wave is received and the AD value (road surface wave β) is captured.
[0036]
Step 26: Compare road surface waves α and β.
In step 26, if the road surface waves α and β are the same,
Step 28: The value of the optimum frequency f is not changed,
Step 30: Wait until the next transmission timing and repeat the procedure from Step 21.
[0037]
In step 26, if the road surface wave α is large,
Step 29: Change the frequency f + α to the optimum frequency f,
Step 30: Wait until the next transmission timing and repeat the procedure from Step 1.
[0038]
In step 26, when the road surface wave β is large,
Step 27: Change the frequency f-β to the optimum frequency f,
Step 30: Wait until the next transmission timing and repeat the procedure from Step 1.
[0039]
The reception signal levels corresponding to the transmission signals of the two types of frequencies controlled by the control unit 17 are the same. Therefore, the sensing areas for the transmission signals of two types of frequencies are the same, and the sensing performance of the vehicle is stabilized.
[0040]
【The invention's effect】
As is clear from the above description, the ultrasonic vehicle detector and the ultrasonic frequency control method of the present invention can keep the transmission signal sensing area constant while keeping the frequency of the transmission signal following the optimum frequency. The vehicle detection accuracy can be increased.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an ultrasonic vehicle sensor according to an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of a control unit in the ultrasonic vehicle sensor according to the embodiment;
FIG. 3 is a flowchart showing an operation procedure in the ultrasonic vehicle sensor according to the embodiment;
FIG. 4A is a diagram showing a transmission waveform in the ultrasonic vehicle sensor according to the embodiment;
(B) The figure which shows the received waveform of the road surface wave in the ultrasonic vehicle sensor of embodiment,
FIG. 5 is a diagram showing a relationship between a frequency characteristic of reception sensitivity and a set frequency in the ultrasonic frequency control method of the embodiment;
FIG. 6 is a block diagram showing a configuration of a conventional ultrasonic vehicle sensor;
FIG. 7 is a flowchart showing an operation procedure in a conventional ultrasonic vehicle detector;
FIG. 8A is a diagram showing a transmission waveform in a conventional ultrasonic vehicle sensor;
(B) The figure which shows the received waveform of the road surface wave in the conventional ultrasonic vehicle detector,
FIG. 9 is a diagram showing a relationship between frequency characteristics of reception sensitivity and set frequencies in a conventional ultrasonic frequency control method.
[Explanation of symbols]
10, 110 controller
11, 111 Oscillator
12, 112 Transmission signal output section
13, 113 Received signal amplifier
14, 114 A / D converter
15, 115 Frequency measurement unit
16, 116 timer
17, 117 Control unit
18, 118 threshold
20 Ultrasonic head
21 Receiver
22 Transmitter
31 Paul
30 arms
41 Reflected signal identification section
42 Car / Road Reflection Signal Identification Unit
43 Road reflection signal comparator
44 Transmission frequency setting section

Claims (3)

超音波の送信信号を周期的に送信して車両を感知する超音波式車両感知器において、送信信号の周波数として２種類の周波数を設定し、各々の周波数を持つ送信信号が交互に送信されるように制御する送信周波数設定手段と、各々の周波数を持つ送信信号が路面で反射されたときの受信レベルを比較し、受信レベルが高い送信信号の周波数を前記送信周波数設定手段に伝える比較手段とを備え、前記送信周波数設定手段は、前記２種類の周波数のいずれか一方の周波数の信号の受信レベルが高いことを前記比較手段から伝えられたときに、当該周波数を新しい最適周波数ｆと見做し、前記新しい最適周波数ｆからプラス側に変移した周波数（ｆ＋α）を前記２種類の周波数の一方として設定する手段と、前記最適周波数ｆからマイナス側に変移した周波数（ｆ−α）の付近で送信周波数を徐々に変えて送信し、前記周波数（ｆ＋α）の信号の受信レベルと同じ受信レベルになる周波数（ｆ−β）を探して、前記周波数（ｆ−β）を前記２種類の周波数の他方として設定する手段とを有することを特徴とする超音波式車両感知器。In an ultrasonic vehicle sensor that periodically transmits ultrasonic transmission signals to sense a vehicle, two types of frequencies are set as transmission signal frequencies, and transmission signals having the respective frequencies are alternately transmitted. A transmission frequency setting means for controlling the transmission frequency, and a comparison means for comparing the reception level when a transmission signal having each frequency is reflected on the road surface, and transmitting the frequency of the transmission signal having a high reception level to the transmission frequency setting means, The transmission frequency setting means considers the frequency as the new optimum frequency f when the comparison means informs that the reception level of the signal of one of the two types of frequencies is high. And means for setting the frequency (f + α) shifted from the new optimum frequency f to the plus side as one of the two types of frequencies, and changing the optimum frequency f from the minus side to the minus side. The transmission frequency is gradually changed in the vicinity of the frequency (f−α), and a frequency (f−β) having the same reception level as the reception level of the signal of the frequency (f + α) is searched for. ultrasonic vehicle sensor, characterized by chromatic and means for setting-beta) as the other of the two kinds of frequencies. 超音波の送信信号を周期的に送信して車両を感知する超音波式車両感知器の超音波周波数制御方法において、最適周波数ｆからプラス側に変移した周波数（ｆ＋α）を前記送信信号の一方の周波数として設定し、前記最適周波数ｆからマイナス側に変移した周波数（ｆ−α）の付近で送信周波数を徐々に変えて送信し、周波数（ｆ＋α）の信号の受信レベルと同じ受信レベルになる周波数（ｆ−β）を探して、前記周波数（ｆ−β）を前記送信信号の他方の周波数として設定し、この２種類の周波数を持つ送信信号を交互に送信し、各々の周波数を持つ送信信号が路面で反射されたときの受信レベルを比較して、一方の周波数を持つ送信信号の受信レベルが他方の周波数を持つ送信信号の受信レベルより高くなったときは、高い方の周波数を新しい最適周波数と見做して前記２種類の周波数を同様に求めて前記送信信号の周波数として設定することを特徴とする超音波周波数制御方法。In an ultrasonic frequency control method for an ultrasonic vehicle detector that senses a vehicle by periodically transmitting an ultrasonic transmission signal, a frequency (f + α) shifted from the optimum frequency f to the plus side is set to one of the transmission signals. A frequency that is set as a frequency and is transmitted by gradually changing the transmission frequency in the vicinity of the frequency (f−α) shifted from the optimum frequency f to the minus side, and becomes the same reception level as the reception level of the signal of the frequency (f + α). Searching for (f-β), setting the frequency (f-β) as the other frequency of the transmission signal, transmitting transmission signals having these two types of frequencies alternately, and transmitting signals having the respective frequencies When the reception level of a transmission signal having one frequency is higher than the reception level of a transmission signal having the other frequency, the higher frequency is renewed. The ultrasonic frequency control method characterized in that the two types of frequencies are obtained in the same manner as the optimum frequency and set as the frequency of the transmission signal . 超音波の送信信号を周期的に送信して車両を感知する超音波式車両感知器の制御プログラムにおいて、最適周波数ｆからプラス側に変移した周波数（ｆ＋α）を前記送信信号の一方の周波数として設定する手順と、前記最適周波数ｆからマイナス側に変移した周波数（ｆ−α）の付近で送信周波数を徐々に変えて送信し、周波数（ｆ＋α）の信号の受信レベルと同じ受信レベルになる周波数（ｆ−β）を探して、前記周波数（ｆ−β）を前記送信信号の他方の周波数として設定する手順と、この２種類の周波数を持つ送信信号を交互に送信するように制御する手順と、各々の周波数を持つ送信信号が路面で反射されたときの受信レベルを比較する手順と、前記比較において、一方の周波数を持つ送信信号の受信レベルが他方の周波数を持つ送信信号の受信レベルより高いとき、高い方の周波数を新しい最適周波数と見做して前記２種類の周波数を同様に求めて前記送信信号の周波数として設定する手順とをコンピュータに実行させるためのプログラム。In a control program for an ultrasonic vehicle detector that senses a vehicle by periodically transmitting an ultrasonic transmission signal, a frequency (f + α) shifted from the optimum frequency f to the plus side is set as one frequency of the transmission signal. The transmission frequency is gradually changed near the frequency (f−α) shifted from the optimum frequency f to the minus side, and the frequency (f + α) becomes the same reception level as the reception level of the signal of the frequency (f + α) ( searching for f-β), setting the frequency (f-β) as the other frequency of the transmission signal, and controlling the transmission signal to transmit the two types of frequencies alternately; The procedure for comparing the reception level when the transmission signal having each frequency is reflected on the road surface, and in the comparison, the transmission signal having the other frequency is the transmission level of the transmission signal having one frequency. A program for causing a computer to execute a procedure for obtaining the two types of frequencies in the same manner and setting them as the frequencies of the transmission signals, assuming that the higher frequency is a new optimum frequency when the signal is higher than the reception level of the signal .
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