JP4137487B2

JP4137487B2 - Manufacturing method of spark plug

Info

Publication number: JP4137487B2
Application number: JP2002102201A
Authority: JP
Inventors: 滋久斉田
Original assignee: NGK Spark Plug Co Ltd
Current assignee: Niterra Co Ltd
Priority date: 2002-04-04
Filing date: 2002-04-04
Publication date: 2008-08-20
Anticipated expiration: 2022-04-04
Also published as: JP2003297525A

Description

【０００１】
本発明はスパークプラグの製造方法に関する。
【０００２】
【従来の技術】
近年、内燃機関の高性能化あるはリーンバーン化により、混合気への点火の確実性がますます重視されている。この場合、燃焼室内におけるスパークプラグの取付位置が点火性を左右する重要な因子となる。例えば、燃焼室内に吸入された混合気によって生じるスワールの方向に対し、火花放電ギャップが接地電極の陰になるかあるいは接地電極が火炎成長を妨げる方向に存在する場合に、スパークプラグの着火性を低下させる原因となることが指摘されている。そこで、従来まちまちだった燃焼室内の接地電極方向を、着火性を考慮した最適位置に調整することが提案されている。スパークプラグの内燃機関への取付は、主体金具に形成された取付ねじ部を内燃機関側のねじ孔に螺着することにより行なわれるが、その取付ねじ部の締め付けトルクには制限がある。従って、取付状態にて接地電極方向の向きを一定にするには、主体金具への接地電極の取付位置を、取付ねじ部のねじ山開始位置と一定の角度関係を充足するように、揃えておかなければならない。
【０００３】
スパークプラグの量産ラインでは、主体金具の取付ねじ部の形成を、加工能率の高い転造により行なっている。しかし、接地電極を取り付けた主体金具に対し、接地電極の取付位置に対しねじ山の開始位置をそろえた形で転造を行なうことは容易ではない。そこで、特開平１１−１３６１３号公報には、ねじ転造後の主体金具に対しナット状の治具を螺着し、その治具に付与された、ねじ山開始位置と一定の位置関係を満たす取付位置目印を参照して接地電極の取付を行なう方法が開示されている。
【０００４】
【発明が解決しようとする課題】
しかし、上記公報の方法は、接地電極の取付を行なう際に、その都度、主体金具へ治具を螺着しなければならず、また、接地電極の取付終了後には治具の取り外しを行なわなければならないから、工数が増加する欠点がある。また、量産をスムーズに行なうには、相当数の治具を準備しなければならないし、内燃機関の仕様により接地電極取付位置が相違する場合には、目印位置の異なる治具を用意する必要がある。いずれにしろ、治具を用意しなければならない分だけコストアップにつながる。
【０００５】
本発明の課題は、特別な治具を用いずとも、ねじ山開始位置と一定の位置関係を満たす主体金具への接地電極取付位置を容易に決定することができるスパークプラグの製造方法を提供することにある。
【０００６】
【課題を解決するための手段及び作用・効果】
本発明のスパークプラグの製造方法は、外周面の軸線方向中間位置に周方向の取付座部が突出形成され、その取付座部に続く形で取付ねじ部が形成された筒状の主体金具を有し、取付座部が規定する限界位置まで取付ねじ部を締め込んだ状態での、該取付ねじ部の周方向に定められる基準角度位置に対し、一定の角度関係を満たす接地電極取付位置にて主体金具の端面に接地電極を取り付けるスパークプラグの製造方法に係り、上記の課題を解決するために、その第一の態様は、接地電極取付前の主体金具ワークの外周面に取付ねじ部を形成する取付ねじ部形成工程と、
取付座部と取付ねじ部の少なくとも一部とが画像視野内に表れるように、カメラにより主体金具ワークの画像（以下、ワーク画像という）を撮影し、該ワーク画像に基づいて、カメラに対する取付ねじ部の角度位相を把握するねじ山位相把握工程と、
その把握結果に基づいて、主体金具ワークに接地電極を角度関係を満たすように取り付ける接地電極取付工程と、
を含むことを特徴とする。
【０００７】
上記本発明の第一の態様によると、主体金具ワークの外周面に取付ねじ部を形成した後、取付座部と取付ねじ部の少なくとも一部とが画像視野内に表れるように、カメラにより主体金具ワークの画像（ワーク画像）を撮影し、該ワーク画像に基づいて、カメラに対する取付ねじ部の角度位相を把握するねじ山位相把握する。そして、その把握結果に基づいて、主体金具ワークに接地電極を角度関係を満たすように取り付けるようにした。従って、特開平１１−１３６１３号公報に開示したような接地電極取付位置を決定するための特別な治具が不要であり、当然、治具の着脱に工数を要することもないので能率的である。
【０００８】
例えば、接地電極取付位置との位置関係が既知のカメラアングルにて、取付ねじ部が形成済みの主体金具標準品を撮影したマスター画像を用意しておき、取付位置特定工程においては、ねじ山位相把握工程において、カメラと主体金具ワークとを相対回転させながらワーク画像を撮影するとともに、マスター画像との間でパターンマッチング処理を行い、該パターンマッチング処理において画像一致するカメラと主体金具ワークとの角度位相を見出し、その角度位相に基づいて接地電極取付位置を定めることができる。カメラアングルに対して、接地電極取付位置が特定方向を向くように主体金具の画像を撮影したとき、接地電極取付位置が該特定方向から外れた画像との間には顕著な差が生ずる。そこで、主体金具ワークとカメラとを相対回転させながら、接地電極取付位置が既知のマスター画像との間でパターンマッチング処理を行なえば、主体金具ワークの現在の接地電極取付位置が、マスター画像における接地電極取付位置との間で一致しているか否かを容易に判別できる。そして、両者の画像が一致する主体金具ワークの方向を見出すことにより、接地電極取付位置を容易に決定することができる。
【０００９】
この場合、ワーク画像及びマスター画像は、主体金具ワーク又は主体金具標準品の、取付ねじ部の形成された外周面を正面方向から撮影して得られるものを使用することができる。そして、主体金具ワークの取付座部の座面上にて、該主体金具ワークの軸線から半径方向に一定長さ離間した位置に基準径位置を定め、マスター画像は、主体金具標準品を用いて、基準径位置が画像視野上の目標位置に合わせ込まれた形で撮影されたものを使用できる。そして、ワーク画像上において、主体金具ワークを画像視野上にて平行移動することにより基準径位置を目標位置に合わせこんだ後、該主体金具ワークを軸線周りに回転させつつパターンマッチング処理を行なうことにより、マスター画像とワーク画像とが一致する主体金具ワークの回転角度位相に基づいて接地電極取付位置を定めることができる。画像上に現れる基準径位置は、ワークが回転しても変化しないので、これを利用してマスター画像に対するワーク画像の軸線方向の位置合わせを行なうことができる。その後は、主体金具ワークの軸線周りの回転操作のみにより、マスター画像へのパターンマッチングを行なうことができ、そのときの主体金具ワークの回転角度位相に基づいて接地電極取付位置を簡単かつ正確に決定することができる。
【００１０】
次に、本発明のスパークプラグの製造方法の第二の態様は、外周面の軸線方向中間位置に周方向の取付座部が突出形成され、その取付座部に続く形で取付ねじ部が形成された筒状の主体金具を有し、取付座部が規定する限界位置まで取付ねじ部を締め込んだ状態での、該取付ねじ部の周方向に定められる基準角度位置に対し、一定の角度関係を満たす接地電極取付位置にて主体金具の端面に接地電極を取り付けるスパークプラグの製造方法において、上記の課題を解決するために、
接地電極取付前の主体金具ワークの外周面に取付ねじ部を形成する取付ねじ部形成工程と、
取付ねじ部を形成した主体金具ワークを、軸線と交差する向きの移動が拘束され、かつ軸線周りの回転が可能となるように保持する一方、取付座部の座面から取付ねじ部側に所定長離れた位置において、軸線周りの特定角度位置に、取付ねじ部のねじ山を検知するセンサを配置しておき、その状態で主体金具ワークを軸線周りに回転させたときの、センサの検知状態に基づいて、センサに対する取付ねじ部の角度位相を把握するねじ山位相把握工程と、
その把握結果に基づいて、主体金具ワークに接地電極を角度関係を満たすように取り付ける接地電極取付工程とを含むことを特徴とする。
【００１１】
上記本発明の第二の態様においては、取付座部の座面から取付ねじ部側に一定長さ離れた位置において、軸線周りの特定角度位置に、取付ねじ部のねじ山を検知するセンサを配置しておく。主体金具ワークの外周面に取付ねじ部を形成した後、主体金具ワークを軸線周りに回転させ、上記センサの検知状態に基づいて、センサに対する取付ねじ部の角度位相を把握する。そして、その把握結果に基づいて、主体金具ワークに接地電極を角度関係を満たすように取り付ける。その結果、特開平１１−１３６１３号公報に開示したような接地電極取付位置を決定するための特別な治具が不要であり、当然、治具の着脱に工数を要することもないので能率的である。
【００１２】
主体金具ワークを軸線周りに回転させるとともに、取付ねじ部が特定の回転角度位相に到達したとき主体金具ワークの回転を停止するとともに、その停止時の回転角度位相における主体金具ワークの、接地電極取付位置に対応する位置に接地電極の溶接装置を配置しておき、該回転停止した主体金具ワークに対し、溶接装置によりその場で接地電極の溶接を行なうことができる。このようにすれば、接地電極取付位置の決定後、接地電極の溶接を極めて迅速に行なうことができ、スパークプラグの製造能率向上に貢献する。
【００１３】
【発明の実施の形態】
以下、本発明の実施の形態を、図面を用いて説明する。
（実施の形態１）
図１は、本発明の第一の態様を実施するための、スパークプラグの製造装置の一例を示す模式的なブロック図である。製造装置１に適用する主体金具ワーク５１は筒状に構成され、一方の端部側の外周面に取付ねじ部５７が転造により形成されている。また、取付ねじ部５７に隣接してフランジ状の取付座部５２、六角部５５及び加締め予定部４９がこの順序で形成されている。そして、取付ねじ部５７が上向きとなるように、カップ状のホルダ１０に対し軸線Ｏが一致するように着脱可能に装着される。ホルダ１０は、昇降テーブル２０上において回転用モータ１８により、主体金具ワーク５１とともに軸線Ｏ周りに回転駆動される。また、昇降テーブル２０は、主体金具ワーク５１をホルダ１０とともに昇降駆動するものである。昇降機構は種々の態様のものが公知であり、そのいずれを採用してもよいが、本実施形態では以下のように構成している。すなわち、昇降テーブル２０を貫通するように設けられた複数の雌ねじ部２２に、それぞれねじ軸２１が螺合している。また、各ねじ軸２１に同心的に設けられたギア２４に、それぞれウォーム２３がかみ合っている。これらウォーム２３を、軸２５を介して昇降用モータ１７により回転駆動すると、各ねじ軸２１が同期回転して昇降テーブル２０を昇降させる。
【００１４】
また、上記の主体金具ワーク５１の取付ねじ部５７の形成された外周面を、正面方向から撮影するデジタルカメラ２７が設けられている。また、主体金具ワーク５１の取付ねじ部５７が形成された側の端面５１ａに、接地電極５４を抵抗溶接するための溶接装置２６が配置されている。
【００１５】
また、製造装置１は制御装置１０を有する。制御装置１０は、ＣＰＵ８、ＲＯＭ７、ＲＡＭ６及び入出力インターフェース９を有するコンピュータを主体とするものであり、その入出力インターフェース９に、前記したデジタルカメラ２７と溶接装置２６が接続されている。また、回転用モータ１８と昇降用モータ１７とは、それぞれサーボコントローラ１４及び１３を介して入出力インターフェース９に接続されている。各モータ１８，１７の回転角度位置はパルスジェネレータ１６，１５により検出される。サーボコントローラ１４及び１３は、その検出パルス信号により現在の角度位置を認識し、モータの位置決めや回転速度制御を自発的に行なう（その電気的構成は周知であるから詳細は省略する）。また、制御装置１０は、上記検出パルス信号を参照して、主体金具ワーク５１の軸線Ｏ周りの回転角度位相と、軸線Ｏ方向の位置を把握する。
【００１６】
なお、制御装置１０のＣＰＵ８は、ＲＯＭ７に格納された制御プログラム７ａの実行により、回転用モータ１８と昇降用モータ１７とによる主体金具ワーク５１の回転及び昇降駆動と、デジタルカメラ２７による画像撮影及びその取り込み制御、さらには、溶接装置２６の動作を司る。また、画像解析プログラム７ｂの実行により、後述するマスター画像データ７ｃと、ワーク画像との周知の手法によるパターンマッチング処理をはじめとする、接地電極取付位置を決定するために必要な画像解析処理を司る。そして、ＲＡＭ６は、該ＣＰＵ８のプログラム実行のためのワークエリアを与えるものである。
【００１７】
以下、上記製造装置１を用いたスパークプラグの製造方法の実施形態について説明する。まず、ホルダ１０に主体金具ワーク５１を装着し、図２の▲１▼に示すように、取付ねじ部５７が画像視野ＶＡ内に表れるように、デジタルカメラ２７により画像撮影する。主体金具ワーク５１の取付座部５２の座面５３上にて、該主体金具ワーク５１の軸線Ｏから半径方向に一定長さ離間した位置に基準径位置ＳＰが定められる。マスター画像は、主体金具標準品を用いて、基準径位置ＳＰが画像視野ＶＡ上の目標位置ＡＰに合わせ込まれた形で撮影されたものが、図１のＲＯＭ７に、マスター画像データ７ｃとして用意されている。
【００１８】
図１の溶接装置２６は、接地電極５４を保持しつつ抵抗溶接のための通電を行なうための溶接電極１２７を有する。該溶接電極１２７は、主体金具ワーク５１の端面５１ａに対し、軸線Ｏ周りにおいて固定的に定められた角度位置（以下、溶接実施位置という）にて接地電極５４を保持し、溶接のために待機している。この溶接電極１２７が保持する接地電極５４に対し、主体金具ワーク５１の接地電極取付位置を位置合わせして、該接地電極５４を抵抗溶接により接合する。接地電極取付位置は、取付座部５３が規定する限界位置まで取付ねじ部を締め込んだ状態において、該取付ねじ部の周方向に基準角度位置を定めたとき、その基準角度位置と一定の角度関係を満たすように定められる。基準角度位置は、同一仕様のスパークプラグであれば、スパークプラグを内燃機関のねじ孔に締め込んだ状態で、ほぼ一定角度位置として把握しうるものであれば、どのようなものを採用してもよい。例えば座面５３上の基準径位置ＳＰからの高さが特定の値Ｈとなるような、最初の完全ねじ山の角度位置を使用できる。マスター画像は、主体金具標準品をホルダ１０に装着し、その接地電極取付位置を予め定められた角度位置、すなわち、溶接装置２６による接地電極５４の溶接実施位置に合わせこんだ状態で、主体金具ワーク５１と同一の撮影条件にて撮影することにより得られるものである。
【００１９】
図２において基準径位置ＳＰは、取付座部５２の座面５３上に定められている（すなわち、座面５３が軸線上の所定位置である）。取付座部５２の外周面は主体金具の軸線を中心とする円筒面であり、図２において座面５３は平面状である。画像視野ＶＡ上には軸線は現れていないが、軸線から基準径位置ＳＰまでの半径方向距離が一定であることは、取付座部５２の外周面からの半径方向距離も一定値ΔＤとなることを意味する。従って、画像上にて取付座部５２の座面５３及び外周面を周知の画像処理法により特定し、座面５３上にて、外周面からの距離がΔＤとなる位置に、基準径位置ＳＰを決定することができる。これらの画像処理は、全て図１の画像解析プログラム７ｂが行なう。なお、図３に示すように、座面５３は、テーパ面状に形成されていてもよい。この場合も、基準径位置ＳＰを上記と同様の画像処理により決定することができる。
【００２０】
続いて、図２の▲２▼に示すように、主体金具ワーク５１を画像視野ＶＡ上にて平行移動することにより基準径位置ＳＰを目標位置ＡＰに合わせこむ。本実施形態では、主体金具５１の軸線Ｏ（つまり、図１のホルダ１０の回転軸線）と画像視野ＶＡとの位置関係が一定となるように、デジタルカメラ２７のアングルが固定的に定められている。そして、目標位置ＡＰの水平方向座標は、はじめから基準径位置ＳＰの水平方向位置と一致させてある。従って、図１の昇降用モータ１７を動作させて主体金具ワーク５１を昇降すれば、基準径位置ＳＰは画像視野ＶＡ内にて軸線Ｏ方向（上下方向）に移動する。そして、基準径位置ＳＰが目標位置ＡＰに合致したところで主体金具ワーク５１の昇降を停止し、合わせ込み処理が終了する。
【００２１】
次に、その状態で、図１の回転用モータ１８により主体金具ワーク５１を軸線Ｏ周りに回転させる。すると、図２の▲３▼に示すように、画像視野ＶＡ内にて主体金具ワーク５１の画像が回転する。この回転を微小角度ずつ進めながら、その都度取り込まれるワーク画像とマスター画像との間でパターンマッチング処理を行なう。そして、画素間の濃度の差分の合計が最小化したしたところで、両画像が一致したと判断し、主体金具ワーク５１の回転を停止する。
【００２２】
この状態において、主体金具ワーク５１の接地電極取付位置は、マスター画像を撮影した際の主体金具標準品の接地電極取付位置と同位置に合わせこまれている（つまり、ワーク画像に基づいて、カメラ２７に対する取付ねじ部５７の角度位相が把握されている）。そして、その接地電極取付位置は、前記した溶接実施位置に位置決めされることとなる。すなわち、接地電極取付位置が、主体金具ワーク５１の回転と、マスター画像とのパターンマッチング処理とを通じて決定されたわけである。
【００２３】
そして、製造装置１においては、引き続き溶接装置２６により、位置決めされた接地電極取付位置に対し、接地電極５４の溶接による取付が行なわれる。接地電極５４が取り付けられた主体金具５１ワークは、図１３に示すように、その内側に、中心電極５３を組み付けた絶縁体２が挿入され、加締め予定部４９を絶縁体２に向けて加締めることにより固定がなされる。さらに、接地電極５４を中心電極５３に向けて曲げ加工し、火花放電ギャップｇを形成すればスパークプラグ１００が完成する。
【００２４】
図２に示すように、本実施形態においてマスター画像は、取付ねじ部５７の径方向片側において、軸線方向に配列する複数の完全ねじ山（ねじ外径が一定となる区間のねじ山である）の外形線のうち、取付座部５２に最も近いもの（図２においては、最も取付座部５２に近い完全ねじ山：以下、先頭完全ねじ山という）５７ｆと、該取付座部５２とが画像視野ＶＡ内に表れるように撮影されたものが使用されている。先頭完全ねじ山５７ｆの下側には、ねじ山が現れないか、現れていても、ねじ山開始端部に形成された、ねじ山高さがこれよりも低い不完全ねじ山５７ｉが表れる形となる。主体金具５１を軸線Ｏ周りに回転させると、不完全ねじ山５７ｉの高さが変化するとともに、先頭完全ねじ山５７は、画像上にてその位置が軸線方向Ｏに沿って移動するように見える。このような先頭完全ねじ山５７を含むワーク画像を用いると、接地電極取付位置がずれているとき、マスター画像との間での画像上の差が明瞭に現れやすく、パターンマッチング処理を用いた接地電極取付位置の決定を高精度に行なうことができる利点がある。
【００２５】
他方、図４に示すように、マスター画像は、取付座部５２に近いねじ山開始位置５７ｔが画像視野ＶＡ内に表れるように撮影されたものを使用することもできる。図４では、主体金具ワーク５１の軸線Ｏが画像視野ＶＡ内の水平方向の所定位置に位置決めされ、座面５３が同じく垂直方向の指定位置に位置決めされる。画像視野ＶＡ内には、ねじ山開始位置５７ｔに続く形で、画像内には不完全ねじ山５７ｉが表れている。主体金具５１を軸線Ｏ周りに回転させると、ねじ山開始位置５７ｔは、不完全ねじ山５７ｉの画像領域ととともに、画像視野ＶＡ内を移動する。不完全ねじ山領域５７ｉの画像領域の形状は、完全ねじ山の画像領域の形状と大きく異なるため、接地電極取付位置がずれているとき、マスター画像との間での画像上の差が明瞭に現れやすい。
【００２６】
以下、本発明の第一の態様の種々の変形例について説明する。
ワーク画像として、主体金具ワークの取付ねじ部の形成された外周面を正面方向から撮影して得られるものを用いる場合、該ワーク画像上において、取付座部５２の座面５３上に基準位置を特定し、取付ねじ部の径方向片側において、軸線方向に配列する複数の完全ねじ山の外形線のうち、ねじ山開始位置からみて特定の順位に位置するものの、基準位置からの距離に基づいて取付ねじ部５７の角度位相を把握できる。この方法によれば、画像処理に時間を要するパターンマッチング処理を用いずとも、特定の完全ねじ山を画像上にて識別し、主体金具ワーク上の基準位置から該完全ねじ山までの距離によって、取付ねじ部５７の角度位相ひいては接地電極取付位置を決定できるので、画像処理の負担を軽減できる利点がある。図５にその一例を示している。基準位置は前述の基準径位置ＳＰが採用され、完全ねじ山としては、前述の先頭完全ねじ山５７ｆが採用されている。しかし、この先頭完全ねじ山５７から数えたねじ山順位が把握できるのであれば、先頭完全ねじ山５７以降の完全ねじ山のどれかを用いることも可能である。なお、この態様では、先頭完全ねじ山５７ｆの頂点ＴＰと基準径位置ＳＰとの距離（軸線方向の距離でよいが、これに限られるものではない）により、接地電極取付位置の決定を行なうようにしている。なお、主体金具ワーク上の基準位置からの、ある完全ねじ山までの距離さえ把握できればよいので、基準径位置ＳＰを、画像視野ＶＡ内の目標位置に位置合わせする処理は不要となる。
【００２７】
また、図７においては、先頭完全ねじ山５７ｆを軸線方向に横切るエッジ決定線（あるいはウィンドウ）ＥＬを設定し、そのエッジ決定線上に現れる先頭完全ねじ山５７ｆのエッジＥ１（又はＥ２）の位置を検出する例を示している。該エッジ位置の基準径位置ＳＰからの距離により接地電極取付位置の決定を行なうことができる。
【００２８】
また、ワーク画像は、該取付ねじ部のねじ山開始位置側に形成される不完全ねじ部が画像視野内に表れるように、主体金具ワークの取付ねじ部の形成された外周面を正面方向から撮影して得られるものを使用することもできる。そして。このワーク画像内に表れる不完全ねじ部の画像情報に基づいて接地電極取付位置を決定することが可能である。具体例を以下に示す。図７においては、取付ねじ部５７の径方向片側において、軸線方向に配列する複数のねじ山を撮影している。▲１▼において、先頭完全ねじ山５７ｆの下側には、ねじ山外形線は表れていない。しかし、主体金具ワーク５１を軸線Ｏ周りに回転させると、▲２▼に示すように、不完全ねじ山５７ｉの外形線が、軸線方向と直交する向きに延出してくる。そして、▲３▼に示すように、不完全ねじ山５７ｉの先端５７ｅが、例えば軸線Ｏと平行に定められた所定の基準線ＤＬ（本実施形態では、基準径位置ＳＰから一定の距離Ｌ１をなす位置に設定されている）に到達したとき、接地電極取付位置の位置合わせが完了したと判定するようにする。なお、主体金具ワーク５１を軸線Ｏ周りに回転させると、不完全ねじ山５７ｉは、軸線方向と直交する向きへの延出高さだけでなく、画像視野ＶＡ内に占有する面積も変化する。従って、その面積率により接地電極取付位置の位置合わせの完了を把握するようにしてもよい。
【００２９】
（実施の形態２）
本発明の第二の態様の実施形態について、第一の態様との相違点を中心に説明する。図８は、本発明の第二の態様を実施するための、スパークプラグの製造装置の一例を示す模式的なブロック図である。なお、図１との共通点については、同一の符号を付与して詳細な説明は省略する。該第二の態様においても、取付ねじ部５７を形成した主体金具ワーク５１をホルダ１０に装着することにより、主体金具ワーク５１を、軸線Ｏと交差する向きの移動が拘束され、かつ軸線Ｏ周りの回転が可能となるように保持する。そして、カメラによる画像撮影に代えて、取付ねじ部５７のねじ山を検知するセンサを配置しておき、その状態で主体金具ワーク５１を軸線Ｏ周りに回転させたときの、センサの検知状態が示す主体金具ワーク５１の回転角度位相に基づいて、接地電極取付位置を、該主体金具ワーク５１の軸線Ｏ周りにおいて取付ねじ部５７のねじ山開始位置と一定の角度関係を満たすように決定する。
【００３０】
図８においてセンサは、取付ねじ部５７に当接するとともに、主体金具ワーク５２の回転を許容しつつ、該主体金具ワーク５１の回転角度位相の変化に応じて特定の方向に変位を生ずる回転角度検知治具３６を含むものとされている。そして、回転角度検知治具３６を取付ねじ部５７に当接させた状態で主体金具ワーク５１を回転させたときの回転角度検知治具３６の変位を、変位検知センサ、本実施形態ではリニアエンコーダ２４により検出する。そして、その検出結果に基づいて、該主体金具ワーク５１の軸線Ｏ周りにおいて取付ねじ部５７のねじ山開始位置と一定の角度関係を満たすように接地電極取付位置を決定する。本実施形態では、回転角度検知治具３６は、取付ねじ部の互いに隣接する複数のねじ山に係合する鋸刃状の係合面３７を有している。複数のねじ山と係合する係合面３７を設けることにより、回転角度検知治具３６のがたつきが小さくなり、変位発生方向を安定化させることができる。
【００３１】
スパークプラグワーク５１は、実施の形態１と同様に、軸線Ｏ方向の位置を目標位置に合わせ込んでから、軸線Ｏ周りの回転を行って、接地電極固定位置を示す回転角度位相を見出す。図９の▲１▼に示すように、基準位置を与える基準治具３４を軸線Ｏ方向に固定配置しておき、主体金具ワーク５１を上昇させて基準治具３４に取付座部５２の座面５３を当接させることにより、基準位置への合わせ込みを行っている。なお、図１０に示すように、基準治具３４の下縁先端位置は、実施の形態１で説明した基準径位置ＳＰに位置合わせされている。テーパ状の座面５３ｔを有する主体金具ワークの場合でも、この下縁先端位置を目標位置として基準径位置ＳＰに当接させることにより、常に一定の高さにワークを位置合わせすることができる。
【００３２】
位置合わせが終了すれば、図１１の▲１▼に示すように、回転角度検知治具３６を取付ねじ部５７に対し、係合面３７により当接させる。そして、主体金具ワーク５１を軸線Ｏ周りに回転させる。すると、▲２▼に示すように、係合面３７（取付ねじ部３７との当接面）は、ねじ山面に対しスラスト方向に摺動して、軸線Ｏと直交する向き（つまり、水平方向）に変位を生ずる。図８に示すように、本実施形態では、回転角度検知治具３６は、支持体３０により下側から支持され、該支持体３０により上記水平方向の変位がガイドされるようになっている。接地電極取付位置が溶接位置に位置合わせされるときの、回転角度検知治具３６の目標変位は予め求められており、前記したリニアエンコーダ２４に検知される変位量が該目標変位に到達すれば主体金具ワーク５１の回転を停止して、以下は、実施の形態１と同様に接地電極の溶接を行なう。支持体３０は、基準治具３４との軸線Ｏ方向の位置関係が一定である。従って、回転角度検知治具３６（センサ）は、取付座部５２の座面５３（基準径位置ＳＰ）から取付ねじ部５７側に所定長離れた位置に配置されている。
【００３３】
なお、係合面３７のねじ山面に対するスラスト方向への摺動が必ずしもスムーズに進まない場合は、係合面３７とねじ山とが軸線Ｏ方向に噛み込みを起こし、回転角度検知治具３６の変位を必ずしも正確に測定できない場合がある。そこで、図１２の▲１▼に示すように、主体金具ワークを回転させることにより、回転角度検知治具３６の変位が示す主体金具ワークの回転角度位相が目標位相に到達したとき、該主体金具ワークの回転を停止し、▲２▼に示すように、その状態で、軸線と直交する向きにおいて、回転角度検知治具３６を取付ねじ部３７から一端離間させる。そして、▲３▼に示すように再度当接させたときの、回転角度検知治具３６の変位に基づいて、該停止状態における主体金具ワークの回転角度位相を特定するようにすれば、上記噛み込みの影響を軽減でき、回転角度検知治具３６の変位をより正確に測定することができる。この変位が目標変位でなかった場合は、該現在の変位と目標変位との差分から、目標変位とするのに必要な主体金具ワークの回転量を算出し、調整用の回転を追加して行なえばよい。
【００３４】
本実施形態においては、上記目的の回転角度検知治具３６の取付ねじ部３７に対する接近・離間を、エアシリンダ３１により行なうようにしている（符号３３は、制御装置１０によりエアシリンダ３１を駆動制御するためのシリンダコントローラである）。主体金具ワーク５１を回転させて回転角度検知治具３６の変位を検知する際には、バルブ３２を開いてエアシリンダ３１内を開放とし、該エアシリンダ３１による付勢力が回転角度検知治具３６に及ばないようにする。なお、回転角度検知治具は、主体金具ワークを回転させたとき、取付ねじ部の螺進作用により軸線方向の変位を生ずるものとして構成してもよい。
【００３５】
以下、本発明の第二の態様の種々の変形例について説明する。
図１４〜図１６は、ねじ山開始端部が軸線周りの特定角度位置に到来したときにこれを検知するセンサを用いる例である。図１４においては、主体金具ワーク５１の径方向の片側において、ねじ山開始端部をなす不完全ねじ山５７ｉの到来を、光学式センサ４０，４１により検知する。ここでは、投光部４０から受光部４１に向かう光を不完全ねじ山５７ｉが遮っているか否かにより検出を行なう、いわゆる透過式光センサを用いている。なお、不完全ねじ山５７ｉにより反射される投光部からの光を受光部にて検知する、反射式光センサを用いてもよい。また、図１５は、光学式センサに代えて、近接スイッチ４２により不完全ねじ山５７ｉを検知するようにした例であり、図１６は、同じくリミットスイッチ４３により不完全ねじ山５７ｉを検知するようにした例である。これらセンサは、いずれも、図２等に示す、取付座部５２の座面５３（基準径位置ＳＰ）から取付ねじ部５７側に所定長離れた位置に配置される。
【００３６】
なお、不完全ねじ山５７ｉに代えて完全ねじ山の位置をセンサにより検出してもよい。すなわち、図１７に示すように、軸線Ｏ方向におけるセンサと主体金具ワーク５１との相対位置が固定されていれば、主体金具ワーク５１を回転させたとき、見かけ上、センサ４０（４１）の位置をねじ山５７ｍとねじ谷５７ｖとが交互に通過するかのように、センサの検知状態が変わる。例えば、ねじ山５７ｍの検知状態とねじ谷５７ｖの検知状態が切り替わるときの、主体金具ワーク５７の回転角度位相は略一定であると考えられるから、この切り替わりのタイミングを基準に、回転中の主体金具ワーク５７の現在の回転角度位相を知ることができる。この実施形態では、図１４と同様の光センサ４０（４１）を用いている。
【図面の簡単な説明】
【図１】本発明の第一態様に係るスパークプラグの製造方法を実施するための装置の一例を模式的に示すブロック図。
【図２】マスター画像とのパターンマッチングを用いた第一態様に係るスパークプラグの製造方法の第一例を示す説明図。
【図３】図２の工程を、テーパ状のガスシール面を有する主体金具ワークへ適用する場合の説明図。
【図４】マスター画像とのパターンマッチングを用いた第一態様に係るスパークプラグの製造方法の第二例を示す説明図。
【図５】本発明の第一態様において、パターンマッチングを用いずに接地電極取付位置を決定する方法の第一例を示す説明図。
【図６】同じく第二例を示す説明図。
【図７】同じく第三例を示す説明図。
【図８】本発明の第二態様に係るスパークプラグの製造方法を実施するための装置の一例を模式的に示すブロック図。
【図９】第二態様に係るスパークプラグの製造方法の第一例を示す工程説明図。
【図１０】図９の工程を、テーパ状のガスシール面を有する主体金具ワークへ適用する場合の説明図。
【図１１】図９に続く工程説明図。
【図１２】図１１に続く工程説明図。
【図１３】接地電極取付後の主体金具ワークを用いたスパークプラグの組立形態を示す断面図。
【図１４】第二態様に係るスパークプラグの製造方法の第三例を示す工程説明図。
【図１５】同じく第四例を示す工程説明図。
【図１６】同じく第五例を示す工程説明図。
【図１７】同じく第六例を示す工程説明図。
【符号の説明】
２６溶接装置
３６回転角度検知治具
３７係合面
４０，４１光学式センサ
４２近接スイッチ
４３リミットスイッチ
５１主体金具ワーク
ＳＰ基準径位置
５４接地電極
５７取付ねじ部
５７ｔねじ山開始位置
５７ｆ先頭完全ねじ山
５７ｉ不完全ねじ山
ＶＡ画像視野
Ｏ軸線[0001]
The present invention relates to a method for manufacturing a spark plug.
[0002]
[Prior art]
In recent years, with the improvement in performance and lean burn of internal combustion engines, the certainty of ignition of the air-fuel mixture is increasingly emphasized. In this case, the attachment position of the spark plug in the combustion chamber is an important factor that affects the ignition performance. For example, if the spark discharge gap is behind the ground electrode or the ground electrode is in a direction that prevents flame growth relative to the direction of the swirl caused by the air-fuel mixture sucked into the combustion chamber, the spark plug can be ignited. It has been pointed out that it causes a decrease. In view of this, it has been proposed to adjust the direction of the ground electrode in the combustion chamber, which has conventionally been mixed, to an optimum position in consideration of ignitability. The spark plug is attached to the internal combustion engine by screwing an attachment screw portion formed on the metal shell into a screw hole on the internal combustion engine side, but there is a limit to the tightening torque of the attachment screw portion. Therefore, to make the direction of the ground electrode direction constant in the mounted state, align the mounting position of the ground electrode to the metal shell so as to satisfy a certain angular relationship with the screw thread start position of the mounting screw part. I have to leave.
[0003]
In the mass production line of spark plugs, the mounting screw portion of the metal shell is formed by rolling with high processing efficiency. However, it is not easy to roll the metal shell to which the ground electrode is attached in such a manner that the start position of the thread is aligned with the mounting position of the ground electrode. Japanese Patent Application Laid-Open No. 11-13613 discloses that a nut-shaped jig is screwed onto a metal shell after thread rolling, and a certain positional relationship is satisfied with a screw thread start position given to the jig. A method of attaching a ground electrode with reference to an attachment position mark is disclosed.
[0004]
[Problems to be solved by the invention]
However, according to the method of the above publication, a jig must be screwed to the metal shell each time a ground electrode is attached, and the jig must be removed after the ground electrode is attached. Therefore, there is a drawback that man-hours increase. In addition, a large number of jigs must be prepared for smooth mass production. If the ground electrode mounting position differs depending on the specifications of the internal combustion engine, it is necessary to prepare jigs with different mark positions. is there. In any case, the cost will be increased by the need to prepare a jig.
[0005]
An object of the present invention is to provide a spark plug manufacturing method capable of easily determining a ground electrode mounting position on a metal shell satisfying a certain positional relationship with a screw thread start position without using a special jig. There is.
[0006]
[Means for solving the problems and actions / effects]
In the spark plug manufacturing method of the present invention, a cylindrical metal shell having a mounting seat portion in the circumferential direction protruding and formed at an intermediate position in the axial direction of the outer peripheral surface and a mounting screw portion formed following the mounting seat portion is provided. The grounding electrode mounting position satisfying a certain angular relationship with respect to the reference angular position determined in the circumferential direction of the mounting screw part when the mounting screw part is tightened to the limit position defined by the mounting seat part. In order to solve the above-described problem, a first aspect of the present invention relates to a spark plug manufacturing method for attaching a ground electrode to an end surface of a metal shell. A mounting screw part forming step to be formed;
An image of the metal shell work (hereinafter referred to as a work image) is taken by the camera so that the mounting seat and at least a part of the mounting screw part appear in the image field of view, and the mounting screw for the camera is based on the work image. Thread phase grasping process to grasp the angle phase of the part,
Based on the grasped result, a ground electrode mounting step for mounting the ground electrode to the metal shell work so as to satisfy the angular relationship;
It is characterized by including.
[0007]
According to the first aspect of the present invention, after the mounting screw portion is formed on the outer peripheral surface of the metal shell workpiece, the camera is controlled so that the mounting seat portion and at least a part of the mounting screw portion appear in the image field of view. An image of the metal workpiece (work image) is taken, and the thread phase grasping the angle phase of the mounting screw portion with respect to the camera is grasped based on the work image. Then, based on the grasped result, the ground electrode is attached to the metal shell work so as to satisfy the angular relationship. Accordingly, there is no need for a special jig for determining the ground electrode mounting position as disclosed in Japanese Patent Application Laid-Open No. 11-13613, and it is of course efficient because no man-hour is required for attaching and detaching the jig. .
[0008]
For example, prepare a master image of a standard metal fitting with a mounting screw formed at a camera angle that has a known positional relationship with the ground electrode mounting position. In the grasping process, a work image is taken while relatively rotating the camera and the metal shell workpiece, and pattern matching processing is performed between the master image and the angle between the camera and the metal shell workpiece that match the image in the pattern matching processing. The phase can be found, and the ground electrode mounting position can be determined based on the angular phase. When an image of the metal shell is photographed so that the ground electrode mounting position is directed in a specific direction with respect to the camera angle, there is a significant difference from an image in which the ground electrode mounting position is out of the specific direction. Therefore, if the pattern matching processing is performed with the master image whose ground electrode mounting position is known while the metal shell workpiece and the camera are rotated relative to each other, the current ground electrode mounting position of the metal shell workpiece is determined as the ground image in the master image. It can be easily discriminated whether or not it matches with the electrode mounting position. And the ground electrode attachment position can be easily determined by finding the direction of the metal shell work in which both images match.
[0009]
In this case, the workpiece image and the master image can be obtained by photographing the outer peripheral surface of the metal shell workpiece or standard metal shell standard product on which the mounting screw portion is formed from the front direction. And, on the seat surface of the mounting seat part of the metal shell workpiece, a reference diameter position is defined at a position spaced apart from the axis line of the metal shell workpiece by a certain length in the radial direction. It is possible to use a photo taken in a form in which the reference diameter position is adjusted to the target position on the image field. Then, on the workpiece image, after the metal shell workpiece is translated on the image field of view, the reference diameter position is adjusted to the target position, and then the metal shell workpiece is rotated around the axis to perform pattern matching processing. Thus, the ground electrode mounting position can be determined based on the rotation angle phase of the metal shell workpiece in which the master image and the workpiece image match. Since the reference diameter position appearing on the image does not change even when the work rotates, it can be used to align the work image in the axial direction with respect to the master image. After that, pattern matching to the master image can be performed only by rotating around the axis of the metal shell workpiece, and the ground electrode mounting position can be determined easily and accurately based on the rotation angle phase of the metal shell workpiece at that time. can do.
[0010]
Next, according to a second aspect of the spark plug manufacturing method of the present invention, a circumferential mounting seat portion is formed to project at an axially intermediate position on the outer peripheral surface, and a mounting screw portion is formed following the mounting seat portion. A fixed angle with respect to a reference angular position determined in the circumferential direction of the mounting screw part when the mounting screw part is tightened to the limit position specified by the mounting seat part. In order to solve the above problem, in the spark plug manufacturing method of attaching the ground electrode to the end face of the metal shell at the ground electrode mounting position satisfying the relationship,
A mounting screw portion forming step of forming a mounting screw portion on the outer peripheral surface of the metal shell workpiece before mounting the ground electrode;
The metal shell workpiece on which the mounting screw part is formed is held so that movement in the direction crossing the axis is restricted and rotation around the axis is possible, while the seating surface of the mounting seat part is fixed to the mounting screw part side. A sensor detection state when a sensor that detects the thread of the mounting screw part is placed at a specific angular position around the axis at a long distance and the metal shell workpiece is rotated around the axis in that state. Thread phase grasping process for grasping the angle phase of the mounting screw part relative to the sensor,
And a ground electrode mounting step of mounting the ground electrode on the metal shell work so as to satisfy the angular relationship based on the grasped result.
[0011]
In the second aspect of the present invention, a sensor that detects the thread of the mounting screw portion at a specific angular position around the axis at a position that is a predetermined length away from the seating surface of the mounting seat portion toward the mounting screw portion. Arrange it. After forming the mounting screw portion on the outer peripheral surface of the metal shell workpiece, the metal shell workpiece is rotated around the axis, and the angle phase of the mounting screw portion with respect to the sensor is grasped based on the detection state of the sensor. And based on the grasping result, the ground electrode is attached to the metal shell work so as to satisfy the angular relationship. As a result, there is no need for a special jig for determining the ground electrode mounting position as disclosed in Japanese Patent Application Laid-Open No. 11-13613, and naturally no man-hour is required for attaching and detaching the jig. is there.
[0012]
Rotate the metal shell workpiece around the axis and stop the rotation of the metal shell workpiece when the mounting screw reaches a specific rotation angle phase, and attach the ground electrode to the metal shell workpiece at the rotation angle phase at the time of stoppage. A ground electrode welding device is disposed at a position corresponding to the position, and the ground electrode can be welded to the metal shell workpiece, which has stopped rotating, on the spot by the welding device. In this way, the ground electrode can be welded very quickly after the determination of the ground electrode mounting position, which contributes to an improvement in the manufacturing efficiency of the spark plug.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a schematic block diagram showing an example of a spark plug manufacturing apparatus for carrying out the first aspect of the present invention. The metal shell work 51 applied to the manufacturing apparatus 1 is formed in a cylindrical shape, and a mounting screw portion 57 is formed by rolling on the outer peripheral surface on one end side. Further, a flange-shaped mounting seat portion 52, a hexagonal portion 55 and a caulking scheduled portion 49 are formed in this order adjacent to the mounting screw portion 57. And it mounts | wears so that attachment or detachment is possible so that the axis line O may correspond with respect to the cup-shaped holder 10 so that the attachment screw part 57 may become upward. The holder 10 is rotated around the axis O together with the metal shell workpiece 51 by the rotation motor 18 on the lifting table 20. The elevating table 20 drives the metallic shell work 51 up and down together with the holder 10. Various types of lifting mechanisms are known, and any of them may be adopted. In the present embodiment, the lifting mechanism is configured as follows. That is, the screw shaft 21 is screwed into the plurality of female screw portions 22 provided so as to penetrate the lifting table 20. Further, worms 23 are engaged with gears 24 provided concentrically with the respective screw shafts 21. When these worms 23 are rotationally driven by the lifting / lowering motor 17 via the shaft 25, the screw shafts 21 are rotated synchronously to raise and lower the lifting table 20.
[0014]
Further, a digital camera 27 is provided for photographing the outer peripheral surface of the metal shell work 51 on which the mounting screw portion 57 is formed from the front direction. A welding device 26 for resistance welding the ground electrode 54 is disposed on the end surface 51a of the metal shell workpiece 51 where the mounting screw portion 57 is formed.
[0015]
Further, the manufacturing apparatus 1 has a control device 10. The control device 10 is mainly a computer having a CPU 8, a ROM 7, a RAM 6, and an input / output interface 9, and the digital camera 27 and the welding device 26 are connected to the input / output interface 9. The rotation motor 18 and the lifting motor 17 are connected to the input / output interface 9 via servo controllers 14 and 13, respectively. The rotation angle positions of the motors 18 and 17 are detected by the pulse generators 16 and 15. The servo controllers 14 and 13 recognize the current angular position based on the detected pulse signal, and spontaneously perform motor positioning and rotational speed control (the electrical configuration is well known and will not be described in detail). Further, the control device 10 refers to the detection pulse signal to grasp the rotation angle phase around the axis O of the metal shell workpiece 51 and the position in the axis O direction.
[0016]
The CPU 8 of the control device 10 executes the control program 7 a stored in the ROM 7 to rotate and drive the metal shell workpiece 51 by the rotation motor 18 and the lifting motor 17, It controls the take-in control and further the operation of the welding device 26. In addition, by executing the image analysis program 7b, it manages image analysis processing necessary for determining the ground electrode mounting position, including pattern matching processing using master image data 7c, which will be described later, and a work image by a known method. . The RAM 6 provides a work area for program execution of the CPU 8.
[0017]
Hereinafter, an embodiment of a method for manufacturing a spark plug using the manufacturing apparatus 1 will be described. First, the metal shell work 51 is mounted on the holder 10, and an image is taken by the digital camera 27 so that the mounting screw portion 57 appears in the image field of view VA as shown in (1) of FIG. On the seat surface 53 of the mounting seat portion 52 of the metal shell workpiece 51, a reference radial position SP is determined at a position spaced apart from the axis O of the metal shell workpiece 51 by a certain length in the radial direction. The master image is taken as a master image data 7c in the ROM 7 of FIG. 1, which is obtained by using a standard metal fitting and having the reference diameter position SP aligned with the target position AP on the image field VA. Has been.
[0018]
The welding apparatus 26 in FIG. 1 has a welding electrode 127 for energizing for resistance welding while holding the ground electrode 54. The welding electrode 127 holds the ground electrode 54 at an angular position fixed around the axis O (hereinafter referred to as a welding execution position) with respect to the end surface 51a of the metal shell workpiece 51, and waits for welding. is doing. The ground electrode mounting position of the metal shell workpiece 51 is aligned with the ground electrode 54 held by the welding electrode 127, and the ground electrode 54 is joined by resistance welding. When the reference angle position is determined in the circumferential direction of the mounting screw portion in a state in which the mounting screw portion is tightened to the limit position defined by the mounting seat portion 53, the ground electrode mounting position is at a fixed angle with the reference angular position. It is determined to satisfy the relationship. If the spark plug of the same specification can be grasped as a substantially constant angular position when the spark plug is tightened in the screw hole of the internal combustion engine, the reference angular position is adopted. Also good. For example, the angular position of the first complete thread can be used such that the height from the reference radial position SP on the seat surface 53 is a specific value H. In the master image, a standard metal shell is mounted on the holder 10, and the ground electrode mounting position is adjusted to a predetermined angular position, that is, a position where the ground electrode 54 is welded by the welding apparatus 26. This is obtained by shooting under the same shooting conditions as the work 51.
[0019]
In FIG. 2, the reference diameter position SP is determined on the seat surface 53 of the mounting seat portion 52 (that is, the seat surface 53 is a predetermined position on the axis). The outer peripheral surface of the mounting seat portion 52 is a cylindrical surface centering on the axis of the metallic shell, and the seat surface 53 is planar in FIG. Although the axis does not appear on the image field VA, the constant radial distance from the axial line to the reference radial position SP means that the radial distance from the outer peripheral surface of the mounting seat 52 also has a constant value ΔD. Means. Therefore, the seat surface 53 and the outer peripheral surface of the mounting seat portion 52 are specified on the image by a known image processing method, and the reference diameter position SP is located on the seat surface 53 at a position where the distance from the outer peripheral surface is ΔD. Can be determined. These image processes are all performed by the image analysis program 7b shown in FIG. In addition, as shown in FIG. 3, the seat surface 53 may be formed in the taper surface shape. Also in this case, the reference diameter position SP can be determined by the same image processing as described above.
[0020]
Subsequently, as shown in (2) of FIG. 2, the reference diameter position SP is adjusted to the target position AP by translating the metallic shell workpiece 51 on the image field of view VA. In the present embodiment, the angle of the digital camera 27 is fixedly determined so that the positional relationship between the axis O of the metal shell 51 (that is, the rotation axis of the holder 10 in FIG. 1) and the image field of view VA is constant. Yes. The horizontal coordinate of the target position AP is matched with the horizontal position of the reference diameter position SP from the beginning. Accordingly, when the lifting / lowering motor 17 in FIG. 1 is operated to raise and lower the metallic shell workpiece 51, the reference diameter position SP moves in the direction of the axis O (vertical direction) within the image field VA. Then, when the reference diameter position SP matches the target position AP, the raising / lowering of the metal shell workpiece 51 is stopped, and the fitting process is completed.
[0021]
Next, in this state, the metallic shell workpiece 51 is rotated around the axis O by the rotation motor 18 of FIG. Then, as shown in (3) in FIG. 2, the image of the metal shell workpiece 51 rotates within the image field VA. While this rotation is advanced by a minute angle, pattern matching processing is performed between the workpiece image and the master image that are captured each time. Then, when the sum of the differences in density between the pixels is minimized, it is determined that the two images match, and the rotation of the metal shell workpiece 51 is stopped.
[0022]
In this state, the ground electrode mounting position of the metal shell workpiece 51 is set to the same position as the ground electrode mounting position of the standard metal shell product when the master image is taken (that is, based on the workpiece image, The angle phase of the mounting screw part 57 with respect to 27 is grasped). And the ground electrode attachment position will be positioned in the above-mentioned welding execution position. That is, the ground electrode mounting position is determined through the rotation of the metal shell workpiece 51 and the pattern matching process with the master image.
[0023]
In the manufacturing apparatus 1, the ground electrode 54 is subsequently attached by welding to the positioned ground electrode attachment position by the welding device 26. As shown in FIG. 13, the metal shell 51 to which the ground electrode 54 is attached is inserted with the insulator 2 with the center electrode 53 assembled therein, and the caulking scheduled portion 49 is directed toward the insulator 2. It is fixed by tightening. Furthermore, if the ground electrode 54 is bent toward the center electrode 53 to form a spark discharge gap g, the spark plug 100 is completed.
[0024]
As shown in FIG. 2, in this embodiment, the master image is a plurality of complete screw threads arranged in the axial direction on one side in the radial direction of the mounting screw portion 57 (the screw threads in the section where the screw outer diameter is constant). Of the outermost line of FIG. 2 is the closest to the mounting seat portion 52 (in FIG. 2, the complete screw thread closest to the mounting seat portion 52: hereinafter referred to as the head complete screw thread) 57f and the mounting seat portion 52 are images. A photograph taken so as to appear in the field of view VA is used. Below the top full thread 57f, even if a thread does not appear or appears, an incomplete thread 57i formed at the thread start end and having a thread height lower than this appears. Become. When the metal shell 51 is rotated around the axis O, the height of the incomplete thread 57i changes and the position of the leading complete thread 57 appears to move along the axis direction O on the image. . When such a work image including the complete head thread 57 is used, when the ground electrode mounting position is shifted, a difference in the image from the master image tends to appear clearly, and the grounding using the pattern matching process is performed. There is an advantage that the electrode mounting position can be determined with high accuracy.
[0025]
On the other hand, as shown in FIG. 4, a master image that has been photographed so that the screw thread start position 57t close to the mounting seat portion 52 appears in the image field VA can be used. In FIG. 4, the axis O of the metal shell workpiece 51 is positioned at a predetermined position in the horizontal direction in the image field VA, and the seating surface 53 is also positioned at a specified position in the vertical direction. In the image field VA, an incomplete thread 57i appears in the image following the thread start position 57t. When the metal shell 51 is rotated around the axis O, the thread start position 57t moves within the image field VA together with the image area of the incomplete thread 57i. Since the shape of the image region of the incomplete thread region 57i is significantly different from the shape of the image region of the complete thread region, when the ground electrode mounting position is shifted, the difference on the image from the master image is clear. Easy to appear.
[0026]
Hereinafter, various modifications of the first aspect of the present invention will be described.
When using a workpiece image obtained by photographing the outer peripheral surface on which the mounting screw portion of the metal shell workpiece is formed from the front direction, the reference position is set on the seat surface 53 of the mounting seat portion 52 on the workpiece image. Based on the distance from the reference position, although it is located in a specific order when viewed from the screw thread start position among the plurality of complete screw thread outlines arranged in the axial direction on one side in the radial direction of the mounting screw part The angle phase of the mounting screw portion 57 can be grasped. According to this method, without using a pattern matching process that requires time for image processing, a specific complete thread is identified on the image, and depending on the distance from the reference position on the metal shell workpiece to the complete thread, Since the angle phase of the mounting screw portion 57 and thus the ground electrode mounting position can be determined, there is an advantage that the burden of image processing can be reduced. An example is shown in FIG. The aforementioned reference diameter position SP is employed as the reference position, and the aforementioned leading complete thread 57f is employed as the complete thread. However, it is possible to use any one of the complete threads after the complete head thread 57 as long as the thread rank counted from the complete head thread 57 can be grasped. In this aspect, the ground electrode mounting position is determined based on the distance between the apex TP of the leading complete thread 57f and the reference radial position SP (the distance in the axial direction is not limited to this). I have to. Note that it is only necessary to know the distance from the reference position on the metal shell workpiece to a complete screw thread, so that the process of aligning the reference diameter position SP with the target position in the image field of view VA becomes unnecessary.
[0027]
In FIG. 7, an edge determination line (or window) EL that crosses the head complete thread 57f in the axial direction is set, and the position of the edge E1 (or E2) of the head complete thread 57f that appears on the edge determination line is set. An example of detection is shown. The ground electrode mounting position can be determined by the distance of the edge position from the reference diameter position SP.
[0028]
Also, the workpiece image shows the outer peripheral surface on which the mounting screw portion of the metal shell workpiece is formed from the front side so that the incomplete screw portion formed on the screw thread starting position side of the mounting screw portion appears in the image field of view. What is obtained by photographing can also be used. And then. The ground electrode mounting position can be determined based on the image information of the incomplete screw portion appearing in the work image. Specific examples are shown below. In FIG. 7, a plurality of screw threads arranged in the axial direction are photographed on one side in the radial direction of the mounting screw portion 57. In {circle around (1)}, no thread outline appears below the full head thread 57f. However, when the metal shell workpiece 51 is rotated around the axis O, the outline of the incomplete thread 57i extends in a direction perpendicular to the axial direction as indicated by (2). Then, as shown in (3), the tip 57e of the incomplete screw thread 57i is, for example, a predetermined reference line DL defined in parallel with the axis O (in this embodiment, a fixed distance L1 from the reference radial position SP). It is determined that the positioning of the ground electrode mounting position has been completed. When the metal shell workpiece 51 is rotated around the axis O, the incomplete thread 57i changes not only the height of extension in the direction perpendicular to the axis direction but also the area occupied in the image field VA. Therefore, the completion of the alignment of the ground electrode mounting position may be grasped by the area ratio.
[0029]
(Embodiment 2)
The embodiment of the second aspect of the present invention will be described focusing on the differences from the first aspect. FIG. 8 is a schematic block diagram illustrating an example of a spark plug manufacturing apparatus for carrying out the second aspect of the present invention. In addition, about the common point with FIG. 1, the same code | symbol is provided and detailed description is abbreviate | omitted. Also in the second aspect, by attaching the metal shell workpiece 51 formed with the mounting screw portion 57 to the holder 10, the movement of the metal shell workpiece 51 in the direction intersecting the axis O is restricted, and the axis O around the axis O Is held so that it can be rotated. Then, instead of taking an image by the camera, a sensor for detecting the thread of the mounting screw portion 57 is arranged, and the detection state of the sensor when the metal shell workpiece 51 is rotated around the axis O in this state is as follows. Based on the rotation angle phase of the metal shell workpiece 51 shown, the ground electrode mounting position is determined so as to satisfy a certain angular relationship with the screw thread start position of the mounting screw portion 57 around the axis O of the metal shell workpiece 51.
[0030]
In FIG. 8, the sensor abuts against the mounting screw portion 57 and allows rotation of the metal shell workpiece 52 while detecting a rotation angle that causes displacement in a specific direction in accordance with a change in the rotation angle phase of the metal shell workpiece 51. A jig 36 is included. The displacement of the rotation angle detection jig 36 when the metal shell workpiece 51 is rotated in a state where the rotation angle detection jig 36 is in contact with the mounting screw portion 57 is expressed as a displacement detection sensor, which is a linear encoder in this embodiment. 24. Based on the detection result, the ground electrode mounting position is determined so as to satisfy a certain angular relationship with the thread start position of the mounting screw portion 57 around the axis O of the metal shell workpiece 51. In the present embodiment, the rotation angle detection jig 36 has a saw blade-like engagement surface 37 that engages with a plurality of adjacent threads of the mounting screw portion. By providing the engagement surface 37 that engages with the plurality of screw threads, the rattling of the rotation angle detection jig 36 is reduced, and the displacement generation direction can be stabilized.
[0031]
As in the first embodiment, the spark plug work 51 adjusts the position in the direction of the axis O to the target position and then rotates around the axis O to find the rotation angle phase indicating the ground electrode fixing position. As shown in (1) of FIG. 9, a reference jig 34 for giving a reference position is fixedly arranged in the direction of the axis O, and the metallic shell work 51 is raised to seat the mounting jig 52 on the reference jig 34. By bringing 53 into contact, alignment to the reference position is performed. As shown in FIG. 10, the position of the tip of the lower edge of the reference jig 34 is aligned with the reference diameter position SP described in the first embodiment. Even in the case of a metal shell workpiece having a tapered seating surface 53t, the workpiece can always be aligned at a constant height by contacting the lower edge tip position with the reference radial position SP as a target position.
[0032]
When the alignment is completed, the rotation angle detecting jig 36 is brought into contact with the mounting screw portion 57 by the engaging surface 37 as shown in (1) of FIG. Then, the metal shell workpiece 51 is rotated around the axis O. Then, as shown in (2), the engagement surface 37 (the contact surface with the mounting screw portion 37) slides in the thrust direction with respect to the thread surface, and is in a direction orthogonal to the axis O (that is, horizontal). Direction). As shown in FIG. 8, in the present embodiment, the rotation angle detection jig 36 is supported from below by the support 30, and the horizontal displacement is guided by the support 30. The target displacement of the rotation angle detection jig 36 when the ground electrode mounting position is aligned with the welding position is obtained in advance, and if the amount of displacement detected by the linear encoder 24 reaches the target displacement. After the rotation of the metal shell workpiece 51 is stopped, the ground electrode is welded in the same manner as in the first embodiment. The support 30 has a constant positional relationship with the reference jig 34 in the direction of the axis O. Accordingly, the rotation angle detection jig 36 (sensor) is disposed at a position that is a predetermined distance away from the seating surface 53 (reference diameter position SP) of the mounting seat portion 52 toward the mounting screw portion 57.
[0033]
If the sliding of the engaging surface 37 in the thrust direction with respect to the thread surface does not always proceed smoothly, the engaging surface 37 and the screw thread bite in the direction of the axis O, and the rotation angle detecting jig 36. In some cases, it is not always possible to accurately measure the displacement. Therefore, as shown in (1) of FIG. 12, when the metal shell workpiece is rotated, when the rotation angle phase of the metal shell workpiece indicated by the displacement of the rotation angle detecting jig 36 reaches the target phase, the metal shell workpiece is rotated. The rotation of the workpiece is stopped, and as shown in (2), in this state, the rotation angle detection jig 36 is separated from the mounting screw portion 37 in the direction perpendicular to the axis. Then, if the rotation angle phase of the metal shell workpiece in the stopped state is specified based on the displacement of the rotation angle detection jig 36 when it is brought into contact again as shown in (3), the above described biting And the displacement of the rotation angle detection jig 36 can be measured more accurately. If this displacement is not the target displacement, calculate the amount of rotation of the metal shell work necessary to obtain the target displacement from the difference between the current displacement and the target displacement, and add the rotation for adjustment. That's fine.
[0034]
In the present embodiment, the air cylinder 31 is used to approach and separate the target rotation angle detection jig 36 from the mounting screw portion 37 (reference numeral 33 denotes a drive control of the air cylinder 31 by the control device 10). Is a cylinder controller). When detecting the displacement of the rotation angle detection jig 36 by rotating the metal shell workpiece 51, the valve 32 is opened to open the air cylinder 31, and the urging force of the air cylinder 31 is applied to the rotation angle detection jig 36. Be less than Note that the rotation angle detection jig may be configured such that when the metal shell workpiece is rotated, displacement in the axial direction is generated by the screwing action of the mounting screw portion.
[0035]
Hereinafter, various modifications of the second aspect of the present invention will be described.
FIGS. 14-16 is an example using the sensor which detects this, when a screw thread start end part arrives at the specific angle position around an axis line. In FIG. 14, the arrival of the incomplete thread 57 i forming the thread start end is detected by the optical sensors 40 and 41 on one side in the radial direction of the metal shell work 51. Here, a so-called transmission type optical sensor that detects whether or not the light directed from the light projecting unit 40 to the light receiving unit 41 is blocked by the incomplete thread 57i is used. In addition, you may use the reflection-type optical sensor which detects the light from the light projection part reflected by the incomplete thread 57i in a light-receiving part. 15 shows an example in which the incomplete thread 57i is detected by the proximity switch 42 instead of the optical sensor, and FIG. 16 shows that the incomplete thread 57i is also detected by the limit switch 43. This is an example. Each of these sensors is disposed at a position a predetermined length away from the seating surface 53 (reference diameter position SP) of the mounting seat 52 toward the mounting screw 57 as shown in FIG.
[0036]
Note that the position of the complete thread may be detected by a sensor instead of the incomplete thread 57i. That is, as shown in FIG. 17, if the relative position between the sensor and the metal shell workpiece 51 in the direction of the axis O is fixed, the position of the sensor 40 (41) is apparent when the metal shell workpiece 51 is rotated. The detection state of the sensor changes as if the thread 57m and the thread valley 57v pass alternately. For example, since the rotation angle phase of the metal shell work 57 when the detection state of the thread 57m and the detection state of the thread valley 57v are switched is considered to be substantially constant, the rotating main body is based on the timing of this switching. The current rotation angle phase of the metal workpiece 57 can be known. In this embodiment, the same optical sensor 40 (41) as in FIG. 14 is used.
[Brief description of the drawings]
FIG. 1 is a block diagram schematically showing an example of an apparatus for carrying out a method for manufacturing a spark plug according to a first embodiment of the present invention.
FIG. 2 is an explanatory view showing a first example of a method for manufacturing a spark plug according to a first aspect using pattern matching with a master image.
FIG. 3 is an explanatory diagram when the process of FIG. 2 is applied to a metal shell workpiece having a tapered gas seal surface.
FIG. 4 is an explanatory view showing a second example of the spark plug manufacturing method according to the first aspect using pattern matching with a master image.
FIG. 5 is an explanatory diagram showing a first example of a method for determining a ground electrode mounting position without using pattern matching in the first embodiment of the present invention.
FIG. 6 is an explanatory view showing a second example.
FIG. 7 is an explanatory view showing a third example.
FIG. 8 is a block diagram schematically showing an example of an apparatus for carrying out the spark plug manufacturing method according to the second embodiment of the present invention.
FIG. 9 is a process explanatory view showing a first example of a method for manufacturing a spark plug according to a second embodiment.
FIG. 10 is an explanatory diagram when the process of FIG. 9 is applied to a metal shell workpiece having a tapered gas seal surface.
11 is a process explanatory diagram following FIG. 9;
12 is a process explanatory diagram following FIG. 11. FIG.
FIG. 13 is a cross-sectional view showing an assembly form of a spark plug using the metal shell work after the ground electrode is attached.
FIG. 14 is a process explanatory view showing a third example of the method for manufacturing a spark plug according to the second embodiment.
FIG. 15 is a process explanatory view showing a fourth example.
FIG. 16 is a process explanatory view showing a fifth example.
FIG. 17 is a process explanatory view showing a sixth example.
[Explanation of symbols]
26 Welding equipment
36 Rotation angle detection jig
37 Engagement surface
40, 41 Optical sensor
42 Proximity switch
43 Limit switch
51 Metal fitting work
SP Reference diameter position
54 Ground electrode
57 Mounting screw
57t Thread start position
57f top complete thread
57i incomplete thread
VA image field of view
O axis

Claims

A mounting bracket in the circumferential direction protrudes at an axially intermediate position on the outer peripheral surface, and has a cylindrical metal shell with a mounting screw formed in a form following the mounting seat, and the mounting seat defines Grounded to the end face of the metal shell at the ground electrode mounting position satisfying a certain angular relationship with respect to the reference angular position determined in the circumferential direction of the mounting screw part when the mounting screw part is tightened to the limit position A method of manufacturing a spark plug for attaching an electrode,
A mounting screw portion forming step of forming a mounting screw portion on the outer peripheral surface of the metal shell workpiece before mounting the ground electrode;
An image of the metal shell workpiece (hereinafter referred to as a workpiece image) is taken by a camera so that the mounting seat portion and at least a part of the mounting screw portion appear in an image field of view, and based on the workpiece image, the A thread phase grasping step for grasping an angle phase of the mounting screw portion with respect to the camera;
Based on the grasping result, a ground electrode mounting step for mounting the ground electrode to the metal shell work so as to satisfy the angular relationship;
Only including,
Prepare a master image of the standard metal fitting with the mounting screw part already formed at a camera angle with a known ground electrode mounting position.
In the thread phase grasping step, the workpiece image is photographed while the camera and the metal shell workpiece are relatively rotated, and pattern matching processing is performed between the master image and image matching is performed in the pattern matching processing. found angular phase between the camera and the metal shell work method for producing a spark plug, characterized in that defining the ground electrode mounting position on the basis of the angular phase.

The workpiece image and the master image are obtained by photographing the outer peripheral surface of the metal shell workpiece or the metal shell standard product on which the mounting screw portion is formed from the front direction,
On the seat surface of the mounting seat portion of the metal shell workpiece, a reference diameter position is defined at a position spaced apart from the axis of the metal shell workpiece by a certain length in the radial direction,
The master image is taken using the metal shell standard product, the reference diameter position being adjusted to the target position on the image field,
On the workpiece image, the pattern matching process is performed while rotating the metallic shell workpiece around the axis after the reference radial position is adjusted to the target position by translating the metallic shell workpiece on the image field of view. The method of manufacturing a spark plug according to claim 1 .

In the master image, on the one side in the radial direction of the mounting screw portion, among the plurality of complete thread outlines arranged in the axial direction, the one closest to the mounting seat portion and the mounting seat portion within the image field of view. The method of manufacturing a spark plug according to claim 2 , wherein the spark plug is photographed as shown in FIG.

The spark plug manufacturing method according to claim 2 , wherein the master image is taken so that a screw thread start position close to the mounting seat portion appears in an image field of view.

A mounting bracket in the circumferential direction protrudes at an axially intermediate position on the outer peripheral surface, and has a cylindrical metal shell with a mounting screw formed in a form following the mounting seat, and the mounting seat defines Grounded to the end face of the metal shell at the ground electrode mounting position satisfying a certain angular relationship with respect to the reference angular position determined in the circumferential direction of the mounting screw part when the mounting screw part is tightened to the limit position A method of manufacturing a spark plug for attaching an electrode,
A mounting screw portion forming step of forming a mounting screw portion on the outer peripheral surface of the metal shell workpiece before mounting the ground electrode;
While holding the metallic shell workpiece formed with the mounting screw part so that the movement in the direction intersecting the axis is restricted and allowing rotation around the axis, the mounting screw is supported from the seating surface of the mounting seat part. A sensor for detecting the thread of the mounting screw portion is arranged at a specific angular position around the axis at a position separated by a predetermined length on the part side, and the metallic shell workpiece is rotated around the axis in that state. A thread phase grasping step for grasping an angle phase of the mounting screw portion with respect to the sensor based on a detection state of the sensor at the time,
Based on the grasping result, a ground electrode mounting step for mounting the ground electrode to the metal shell work so as to satisfy the angular relationship;
Only including,
The sensor includes a rotation angle detection jig that abuts on the mounting screw part and allows a rotation of the metal shell workpiece while causing a displacement in a specific direction according to a change in a rotation angle phase of the metal shell workpiece. And detecting a displacement of the rotation angle detection jig when the metal shell work is rotated in a state where the rotation angle detection jig is in contact with the mounting screw portion, and the mounting is performed based on the detection result. method for manufacturing a spark plug, characterized in that to grasp the angular phase of the threaded portion.

The spark plug manufacturing method according to claim 5, wherein the rotation angle detection jig has a saw blade-like engagement surface that engages a plurality of adjacent threads of the mounting screw portion.

The rotation angle detection jig is oriented in a direction perpendicular to the axis line by sliding the contact surface with the mounting screw portion in the thrust direction with respect to the thread surface when the metal shell workpiece is rotated. The method for manufacturing a spark plug according to claim 5 or 6 , wherein displacement is generated.

By rotating the metal shell workpiece, when the rotation angle phase of the metal shell workpiece indicated by the displacement of the rotation angle detection jig reaches a target phase, the rotation of the metal shell workpiece is stopped, in a direction perpendicular to the axis, the rotation angle detection jig when brought into contact again once is separated from the mounting screw portion, based on the displacement of the rotational angle detecting jigs, the in the stopped state The method for manufacturing a spark plug according to claim 7 , wherein the rotational angle phase of the metal shell workpiece is specified.

The metal shell workpiece is rotated about its axis, and when the mounting screw portion reaches a specific rotation angle phase, the rotation of the metal shell workpiece is stopped, and the metal shell workpiece at the rotation angle phase at the time of stoppage is stopped. A grounding electrode welding device is disposed at a position corresponding to the grounding electrode mounting position, and the grounding electrode is welded on the spot by the welding device to the rotation-stopped metal shell workpiece. 9. The method for producing a spark plug according to any one of 8 above.