JP2004093362A

JP2004093362A - Axial force measuring instrument, axial force measuring method and tightening device for bolt

Info

Publication number: JP2004093362A
Application number: JP2002255130A
Authority: JP
Inventors: Itaru Matsuno; 松野　到
Original assignee: Isuzu Motors Ltd
Current assignee: Isuzu Motors Ltd
Priority date: 2002-08-30
Filing date: 2002-08-30
Publication date: 2004-03-25

Abstract

<P>PROBLEM TO BE SOLVED: To provide an axial force measuring instrument, an axial force measuring method and a tightening device for a bolt for estimating the axial force of the bolt with high accuracy in a continuous region from an elastic region to a plastic region and screwing to the target axial force with high accuracy. <P>SOLUTION: The axial force measuring instrument for the bolt is provided with an ultrasonic sensor 4 contacting the head end face 3 of the bolt 2 to oscillate ultrasonic wave and measuring time until receiving reflected wave reflected by a shank end face 5; a storage means (a memory) 8 storing a relational expression of a delay time X obtained by subtracting the time measured before tightening the bolt, from the time measured after tightening the bolt, and bolt axial force Y as two expressions (1), (2) divided into the elastic region and the plastic region and storing a boundary delay time B at a yield point Y which divides the elastic region and plastic region; and an arithmetic means 21 for computing the axial force of the bolt 2 using the relational expression (1) of the elastic region if the delay time X measured by the ultrasonic sensor 4 when tightening the bolt 2 into a work 18 is shorter than the boundary delay time B, and using the relational expression (2) of the plastic region if the delay time X is longer than the boundary delay time B. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、ボルトの軸力測定装置及び軸力測定方法並びに締付装置に関する。
【０００２】
【従来の技術】
本発明者は、図９及び図１０に示すように、ボルトａの軸力を測定する装置として、ボルトａをワークにネジ込んだときのボルトａの伸びを超音波センサｂ（図９参照）によって測定し、測定された伸びを予め作成しておいたボルト伸びとボルト軸力との関係式ｃ（図１０の校正線参照）に代入することで、ボルトａの軸力を算出するものを研究している。
【０００３】
上記超音波センサｂは、ボルトａの頭部端面に接触された状態で超音波を発振すると共に軸部端面で反射した反射波を受信し、発振から受信までの時間（ボルトの長さ）を測定するものである。この超音波センサｂによれば、ネジ込み前の測定時間とネジ込み後の測定時間との差（超音波遅延時間）を求めることで、ボルトの伸びを算出できる。
【０００４】
他方、上記関係式ｃは、予め、同種のサンプルボルトを公知の軸力試験器にネジ込んで、ボルト軸力を複数点検出すると共に、ボルト頭部に上記超音波センサｂを接触させて各検出点における超音波遅延時間を測定することで、ボルトの伸びによる超音波遅延時間とボルト軸力との関係データを求め、そのデータから最小二乗法などの計算手法によって決定される。
【０００５】
【発明が解決しようとする課題】
ところで、図１１に示すように、ボルトａが弾性域で軸力によって伸ばされる領域では、超音波遅延時間とボルト軸力との関係は略直線関係（線形）となるが（但し、僅かに２次要素が加わることもある）、軸力が塑性域に入ると、超音波遅延時間とボルト軸力との関係は、明らかな曲線となる。
【０００６】
しかし、これまでの超音波式ボルト軸力測定装置においては、軸力の全ての領域（弾性域＋塑性域）において１つの関係式ｃ（近似式）を用いて超音波遅延時間からボルト軸力を推定していたため、誤差が大きくなっていた。たとえば、図１１に示すように、全ての軸力の領域をカバーするように無理に１次近似式を設定すると、弾性域でも塑性域でも大きな誤差が生じる。よって、ボルトａの弾性域から塑性域に至る連続領域の軸力推定は、実際上不可能であった。このため、連続領域にてボルトａを目標軸力まで精度良く締め付けることが困難であった。
【０００７】
以上の事情を考慮して創案された本発明の目的は、弾性域から塑性域に至る連続領域において、高精度でボルトの軸力推定が可能となり、高精度で目標軸力までネジ込むことができるボルトの軸力測定装置及び軸力測定方法並びに締付装置を提供することにある。
【０００８】
【課題を解決するための手段】
上記目的を達成するために第１の発明に係るボルトの軸力測定装置は、ボルトの頭部端面に接触して超音波を発振し軸部端面で反射した反射波を受信するまでの時間を測定する超音波センサと、ボルト締付後に測定した上記時間からボルト締付前に測定した時間を引いた遅延時間とボルト軸力との関係式が弾性域と塑性域とに分けて２式記憶されていると共に弾性域と塑性域とを分ける降伏点における境界遅延時間が記憶された記憶手段と、ワークにボルトを締め付けた際に超音波センサによって測定された遅延時間が上記境界遅延時間よりも短ければ弾性域の関係式を用い長ければ塑性域の関係式を用いてボルトの軸力を算出する演算手段とを備えたものである。
【０００９】
また、第２の発明に係るボルトの軸力測定方法は、サンプルボルトを締め付けてボルト軸力を検出しつつ、サンプルボルトの頭部端面にて超音波を発振して軸部端面で反射した反射波を受信するまでの時間を測定し、ボルト締付後に測定した上記時間からボルト締付前に測定した時間を引いた遅延時間とボルト軸力との関係データを求め、上記データからサンプルボルトの伸びが弾性域から塑性域に移行する降伏点を決定してその降伏点における境界遅延時間を求め、降伏点以下のデータから遅延時間とボルト軸力との弾性域関係式を求めると共に降伏点以上のデータから塑性域関係式を求め、実際にワークにボルトを締め付けた際に超音波センサで測定された遅延時間が上記境界遅延時間よりも短ければ弾性域関係式を用い長ければ塑性域関係式を用いてボルトの軸力を算出するようにしたものである。
【００１０】
また、第３の発明は、ボルトを所定の目標軸力で締め付けるためのボルトの締付装置であって、ボルトの頭部端面に接触して超音波を発振し軸部端面で反射した反射波を受信するまでの時間を測定する超音波センサと、ボルト締付後に測定した上記時間からボルト締付前に測定した時間を引いた遅延時間とボルト軸力との関係式が弾性域と塑性域とに分けて２式記憶されていると共に弾性域と塑性域とを分ける降伏点における境界遅延時間が記憶された遅延時間・軸力記憶手段と、ボルトの締付角度とボルト軸力との関係式が弾性域と塑性域とに分けて２式記憶された軸力・締付角度記憶手段と、ボルトを所定角度締め付けた後に超音波センサによって遅延時間を求めこれが上記境界遅延時間より短いか長いかに応じて上記遅延時間・軸力記憶手段の弾性域関係式又は塑性域関係式に代入しそのときの前段ボルト軸力を算出する前段軸力演算手段と、その前段ボルト軸力を上記軸力・締付角度記憶手段の弾性域関係式又は塑性域関係式に代入すると共に予め設定された目標軸力を上記軸力・締付角度記憶手段の塑性域関係式に代入してそれらの差すなわち目標軸力までの相対締付角度を算出する増締角度演算手段とを備えたものである。
【００１１】
【発明の実施の形態】
本発明の一実施形態を添付図面に基いて説明する。
【００１２】
先ず、請求項１のボルトの軸力測定装置及び請求項２の軸力測定方法についての一実施形態を図１乃至図３を用いて説明する。
【００１３】
図１に示すように、本実施形態に係るボルトの軸力測定装置１は、ボルト２の頭部端面３に接触される超音波センサ４を有する。超音波センサ４は、ボルト２の頭部端面３に接触された状態で超音波を発振すると共に軸部端面５で反射した反射波を受信し、発振から受信までの時間Ｔ（ボルト２の長さ）を測定する。超音波センサ４は、ボルト２の頭部６に被せられるソケット７の内部に、ソケット７の回転とは切り離されて上下方向に移動自在に収容されている。ソケット７は、図示しない回転駆動装置（ナットランナー等）によって回転駆動される。
【００１４】
また、図１に示す軸力測定装置１は、超音波センサ４に接続された記憶手段８（以下メモリ８という）を有する。メモリ８には、図２に示すように、ボルト締付後に測定した上記時間Ｔ２からボルト締付前に測定した時間Ｔ１を引いた遅延時間（ボルト締付に伴う伸びによって増大した時間）ΔＴとボルト軸力Ｆｂとの関係式が弾性域と塑性域とに分けて２式記憶されていると共に、弾性域と塑性域とを分ける降伏点Ｙにおける境界遅延時間Ｔｙが記憶されている。これらの式や時間は、図３に示す試験器９によって、以下のようにして求められる。
【００１５】
試験器９は、所定間隔を隔てて配置された一対の挟持部材１０、１１と、これら挟持部材１０、１１の間に介在された圧縮型ロードセル１２と、上側挟持部材１０の挿通穴に挿通されて下側挟持部材１１のネジ穴にネジ込まれるサンプルボルト１３と、サンプルボルト１３の頭部１４に被せられて回転駆動されるソケット１５と、ソケット１５内に設けられサンプルボルト１３の頭部端面１６に接触される超音波センサ１７と、ソケット１５に連結された公知のナットランナー（図示せず）とを備えている。
【００１６】
ナットランナーは、ソケット１５をその回転トルクや回転角度を検出しながら回転駆動するものである。なお、図３において試験器９にネジ込まれるサンプルボルト１３と、図１においてワーク１８にネジ込まれるボルト２とは、同型のボルトが用いられる。また、図３に示す超音波センサ１７は、図１に示す超音波センサ４と共用してもよく、図３に示すソケット１５のナットランナーは、図１に示すソケット７の回転駆動装置と共用してもよい。
【００１７】
この試験器９は、ナットランナーによってソケット１５を回転させてサンプルボルト１３を締め付け、ロードセル１２によってボルト軸力Ｆｂを検出しつつ、超音波センサ１７によってサンプルボルト１３の頭部端面１６にて超音波を発振し軸部端面１９で反射した反射波を受信するまでの時間Ｔを測定する。そして、ボルト締付後に測定した上記時間Ｔ２からボルト締付前に測定した時間Ｔ１を引いた遅延時間（ボルト締付に伴う伸びによって増大した時間）ΔＴを求める。そして、遅延時間ΔＴとボルト軸力Ｆｂとの関係を、超音波センサ１７とロードセル１２とに接続されたレコーダ２０に、プロットデータとして記録する（図２のグラフの各プロット点参照）。
【００１８】
このプロットデータの各点を繋いだグラフから、サンプルボルト１３の伸びが略直線から明確に曲線に移行する境界点、すなわちサンプルボルト１３の伸びが弾性域から塑性域に移行する降伏点Ｙを求める。そして、その降伏点Ｙにおける境界遅延時間Ｔｙを図１に示すメモリ８に記憶する。また、降伏点Ｙ以下のΔＴ−Ｆｂデータから遅延時間ΔＴとボルト軸力Ｆｂとの弾性域関係式▲１▼を求め、降伏点以上のΔＴ−Ｆｂデータから塑性域関係式▲２▼を求め、それらをメモリ８に記憶する。
【００１９】
図２のプロットデータから弾性域関係式▲１▼および塑性域関係式▲２▼を求める近似手法には、公知の最小二乗法等が用いられる。図例では、弾性域関係式▲１▼はＦｂ＝Ａ_１ΔＴ２＋Ｂ_１ΔＴ＋Ｃ_１となり（Ａ_１＜＜１）、塑性域関係式▲２▼はＦｂ＝Ａ_２ΔＴ２＋Ｂ_２ΔＴ＋Ｃ_２となった。
【００２０】
但し、弾性域関係式▲１▼は１次式であってもよく、塑性域関係式▲２▼は３次以上の高次式であってもよい。また、降伏点Ｙの決定は、それほど厳密でなくてもよい。降伏点の近傍では、２つの関係式（弾性域関係式▲１▼、塑性域関係式▲２▼）は略同じ値を出すからである。
【００２１】
また、図１に示す軸力測定装置１は、超音波センサ４及びメモリ８に接続された演算手段２１（コンピュータ）を有する。演算手段２１は、ワーク１８にボルト２を締め付けた際に上記超音波センサ４によって得られた遅延時間ΔＴが、上記境界遅延時間Ｔｙよりも短ければ弾性域の関係式▲１▼：Ｆｂ＝Ａ_１ΔＴ２＋Ｂ_１ΔＴ＋Ｃ_１を用い、長ければ塑性域の関係式▲２▼：Ｆｂ＝Ａ_２ΔＴ２＋Ｂ_２ΔＴ＋Ｃ_２を用いて、ボルト２の軸力を算出する。
【００２２】
上記超音波センサ４とメモリ８と演算手段２１とは、図１に示すように接続されており、超音波センサ４で測定された超音波遅延時間ΔＴの信号が、自動的に演算手段２１に入力されるようになっている。そして、演算手段２１において、測定された超音波遅延時間ΔＴについて自動的に境界超音波遅延時間Ｔｙとの大小判定がなされ、その結果に応じて自動的にメモリ８の２つの関係式▲１▼、▲２▼のうちのいずれかが選択され、その関係式に測定された超音波遅延時間ΔＴが自動的に代入され、ボルト軸力が算出されるようになっている。
【００２３】
本実施形態の作用を述べる。
【００２４】
図１に示すように、ボルト２をワーク１８に所定量（所定角度）ネジ込んだときのボルト軸力は、次のようにして測定（算出）される。
【００２５】
先ず、ボルト２をネジ込む前にボルト頭部端面３に超音波センサ４を接触させ、超音波を発振すると共に軸部端面５で反射した反射波を受信し、発振から受信までの時間Ｔ１を測定する。そして、ボルト２を所定量ネジ込んだ後にボルト頭部端面３に超音波センサ４を接触させ、同様に超音波を発振すると共に軸部端面５で反射した反射波を受信し、発振から受信までの時間Ｔ２を測定する。そして、ボルト締付に伴う伸びによって増大した時間、すなわちＴ２−Ｔ１を計算し、これを遅延時間ΔＴとする。
【００２６】
そして、遅延時間ΔＴが境界遅延時間Ｔｙよりも短ければ弾性域の関係式▲１▼：Ｆｂ＝Ａ_１ΔＴ２＋Ｂ_１ΔＴ＋Ｃ_１を用い、長ければ塑性域の関係式▲２▼：Ｆｂ＝Ａ_２ΔＴ２＋Ｂ_２ΔＴ＋Ｃ_２を用いて、ボルト２の軸力が算出される。このように、ボルト２が弾性域か塑性域かによって２つの関係式（近似式）を使い分けているので、各域（弾性域、塑性域）ごとに信頼性の高い近似式▲１▼、▲２▼を得ることができ、高精度の軸力推定が可能となる。
【００２７】
また、このように精度の高い近似式▲１▼、▲２▼を切り替えて使用しているので、従来不可能と言われていた弾性域から塑性域に至る連続領域における高精度の軸力算出が可能となる。よって、例えば、公知のナットランナーのソケット７内に上記超音波センサ４を内蔵したものを使用すれば、その超音波センサ４により得られる遅延時間ΔＴが境界遅延時間Ｔｙより長いか短いかに応じて２つの近似式▲１▼、▲２▼を選択して用いることで、ボルトの締付を弾性域から塑性域まで高い信頼性で実施できる。
【００２８】
次に、請求項３のボルトの締付装置についての一実施形態を図４乃至図８を用いて説明する。
【００２９】
図４に示すように、本実施形態に係るボルトの締付装置３０は、ボルト３１を所定の目標軸力で締め付けるための装置である。
【００３０】
この締付装置３０は、ボルト３１の頭部端面３２に接触された状態で超音波を発振すると共に軸部端面３３で反射した反射波を受信し、発振から受信までの時間Ｔを測定する超音波センサ３４を有する。超音波センサ３４は、ボルト３１の頭部３５に被せられるソケット３６の内部に、ソケット３６の回転とは切り離されて上下方向に移動自在に収容されており、図１又は図３の超音波センサ４、１７と同様のものが用いられる。ソケット３６は、図示しない駆動装置（ナットランナー等）によって回転駆動される。
【００３１】
また、図４に示す締付装置３０は、ボルト締付後に測定した上記時間Ｔ２からボルト締付前に測定した時間Ｔ１を引いた遅延時間（ボルト締付に伴う伸びによって増大した時間）ΔＴとボルト軸力Ｆｂとの関係式が、弾性域と塑性域とに分けて２式記憶された遅延時間・軸力記憶手段３７（以下第１メモリ３７という）を有する。第１メモリ３７には、図５に示すように、弾性域関係式▲１▼ａ：Ｆｂ＝Ｂ_３ΔＴと、塑性域関係式▲２▼ａ：Ｆｂ＝Ａ_４ΔＴ^２＋Ｂ_４ΔＴ＋Ｃ_４と、境界超音波遅延時間Ｔｙとが、記憶されている。これらの式や時間は、前実施形態と同様に図３に示す試験器９によって求められる。
【００３２】
また、図４に示す締付装置３０は、ボルト３１の締付角度θとボルト軸力Ｆｂとの関係式が、弾性域と塑性域とに分けて２式記憶された軸力・締付角度記憶手段３８（以下第２メモリ３８という）を有する。第２メモリ３８には、図６に示すように、弾性域関係式▲１▼ｂ：θ＝Ｃ_５Ｆｂ＋Ｄ_５と、塑性域関係式▲２▼ｂ：θ＝Ａ_６Ｆｂ^３＋Ｂ_６Ｆｂ^２＋Ｃ_６Ｆｂ＋Ｄ_６とが、記憶されている。これらの式は、図３に示す試験器９によって求められる。
【００３３】
また、図４に示す締付装置３０は、ボルト３１を所定角度締め付けた後の伸びによる遅延時間ΔＴを超音波センサ３４によって求め、この遅延時間ΔＴが上記境界遅延時間Ｔｙよりも短ければ弾性域の関係式▲１▼ａ：Ｆｂ＝Ｂ_３ΔＴを用い、長ければ塑性域の関係式▲２▼ａ：Ｆｂ＝Ａ_４ΔＴ^２＋Ｂ_４ΔＴ＋Ｃ_４を用いて、そのときの前段ボルト軸力Ｆ１を算出する前段軸力演算手段３９（以下第１演算手段３９という）を有する。
【００３４】
また、図４に示す締付装置３０は、算出された前段ボルト軸力Ｆ１を上記第２メモリ３８の図６に示す弾性域関係式▲１▼ｂ：θ＝Ｃ_５Ｆｂ＋Ｄ_５、又は塑性域関係式▲２▼ｂ：θ＝Ａ_６Ｆｂ^３＋Ｂ_６Ｆｂ^２＋Ｃ_６Ｆｂ＋Ｄ_６に代入すると共に、予め設定された目標軸力Ｆｔを上記第２メモリ３８の塑性域関係式▲２▼ｂ：θ＝Ａ_６Ｆｂ^３＋Ｂ_６Ｆｂ^２＋Ｃ_６Ｆｂ＋Ｄ_６　に代入し、それらの差すなわち前段ボルト軸力Ｆ１から目標軸力Ｆｔまでの相対締付角度θを算出する増締角度演算手段４０（以下第２演算手段４０という）を有する。
【００３５】
上記超音波センサ３４と第１メモリ３７と第２メモリ３８と第１演算手段３９と第２演算手段４０とは、図４に示すように接続されており、超音波センサ３４で測定された遅延時間ΔＴの信号が、自動的に第１演算手段３９及び第２演算手段４０に入力されるようになっている。そして、第１演算手段３９において、自動的に第１メモリ３７のデータを用いて前段ボルト軸力Ｆ１が算出され、第２演算手段４０において、自動的に第２メモリ３８のデータを用いて相対締付角度θが算出されるようになっている。
【００３６】
本実施形態の作用を図７及び図８を用いて説明する。
【００３７】
先ず、装置３０のコンピュータ（図示せず）に目標軸力Ｆｔと軸力ばらつき許容範囲とを入力する。そして、図４に示すように、ボルト３１をワーク４１にセットし、ナットランナーのソケット３６を下降させてボルト頭部３５に係合させ、ソケット３６を回転させてボルト３１をねじ込み、ボルト頭部３５をワーク４１の上面に無負荷で着座させる。そして、超音波センサ３４で発振から受信までの時間：無負荷超音波時間Ｔ０を測定する。測定後、超音波センサ３４を上方へ退避させる（以下退避に関しては記述しない）。
【００３８】
そして、ソケット３６をナットランナーで、目標軸力Ｆｔの５０％程度の締付を行う。この軸力は、最終締付角度θをある程度確保するため、図５にてボルト軸力Ｆｂの弾性域の領域（弾性域関係式▲１▼ａ：Ｆｂ＝Ｂ_３ΔＴが用いられる領域）にとることが好ましい。但し、高い軸力として塑性域にとることも可能である。そして、超音波センサ３４を下降させてボルト頭部３５に着座させ、当該超音波センサ３４で発振から受信までの時間：前段超音波時間Ｔ１を測定する。
【００３９】
そして、前段超音波時間Ｔ１と無負荷超音波時間Ｔ０との差、すなわちボルト３１の伸びによる遅延時間ΔＴ１を算出する。そして、この遅延時間ΔＴ１が、境界遅延時間Ｔｙよりも短ければΔＴ１−Ｆ１換算式すなわち図５に示す弾性域関係式▲１▼ａ：Ｆｂ＝Ｂ_３ΔＴに代入し、境界遅延時間Ｔｙよりも長ければΔＴ１−Ｆ１換算式すなわち図５に示す塑性域関係式▲２▼ａ：Ｆｂ＝Ａ_４ΔＴ^２＋Ｂ_４ΔＴ＋Ｃ_４に代入し、前段ボルト軸力Ｆ１を算出する。
【００４０】
そして、前段ボルト軸力Ｆ１を、Ｆ１−θ１換算式すなわち図６に示す弾性域関係式▲１▼ｂ：θ＝Ｃ_５Ｆｂ＋Ｄ_５又は塑性域関係式▲２▼ｂ：θ＝Ａ_６Ｆｂ^３＋Ｂ_６Ｆｂ^２＋Ｃ_６Ｆｂ＋Ｄ_６に代入し、前段締付角度θ１を算出する。そして、予め設定された目標軸力Ｆｔを、Ｆｔ−θｔ換算式すなわち図６に示す塑性域関係式▲２▼ｂ：θ＝Ａ_６Ｆｂ^３＋Ｂ_６Ｆｂ^２＋Ｃ_６Ｆｂ＋Ｄ_６に代入し、目標締付角度θｔを算出する。
【００４１】
そして、前段締付角度θ１と目標締付角度θｔとの差、すなわち増締角度Δθを算出する。そして、ソケット３６をナットランナーにより増締角度Δθ回転させる。そして、超音波センサ３４を下降させてボルト頭部３５に着座させ、当該超音波センサ３４で発振から受信までの時間：最終超音波時間Ｔ２を測定する。
【００４２】
そして、最終超音波時間Ｔ２と無負荷超音波時間Ｔ０との差、すなわち最終締付時の遅延時間ΔＴ２を算出する。この遅延時間ΔＴ２が、図５に示す境界遅延時間Ｔｙよりも短ければΔＴ２−Ｆ２換算式すなわち図５に示す弾性域関係式▲１▼ａ：Ｆｂ＝Ｂ_３ΔＴに代入し、境界遅延時間Ｔｙよりも長ければΔＴ２−Ｆ２換算式すなわち図５に示す塑性域関係式▲２▼ａ：Ｆｂ＝Ａ_４ΔＴ^２＋Ｂ_４ΔＴ＋Ｃ_４に代入し、最終軸力Ｆ２を算出する。
【００４３】
そして、この最終軸力Ｆ２と目標軸力Ｆｔとの差、すなわち軸力誤差ΔＦを算出する。そして、この軸力誤差ΔＦと予め設定した許容範囲とを比較し、誤差ΔＦが許容範囲内ならＯＫの判定となり、誤差が許容範囲外ならＮＧの判定となる。
【００４４】
本実施形態によれば、遅延時間ΔＴに基づく軸力Ｆｂの算出、軸力Ｆｂに基づく締付角度θの算出を、それぞれ弾性域関係式（近似式）▲１▼ａ、▲１▼ｂと塑性域関係式（近似式）▲２▼ａ、▲２▼ｂとに分けて算出しているので、各関係式（近似式）の信頼性を高めることができ、高精度の増締が可能となる。また、前段締付角度において軸力Ｆ１を測定して増締角度θを算出しているので、座面摩擦ばらつき等による軸力ばらつきの影響を受けない。
【００４５】
【発明の効果】
以上説明したように本発明に係るボルトの軸力測定装置及び軸力測定方法並びに締付装置によれば、弾性域から塑性域に至る連続領域において、高精度でボルトの軸力推定が可能となり、高精度で目標軸力までネジ込むことができる。
【図面の簡単な説明】
【図１】第１の発明に係るボルトの軸力測定装置の一実施形態を示す側断面図である。
【図２】上記装置の記憶手段に記憶されているデータを示す説明図である。
【図３】上記データを獲得するための試験器を示す側断面図である。
【図４】第３の発明に係るボルトの締付装置の一実施形態を示す側断面図である。
【図５】上記装置の遅延時間・軸力記憶手段に記憶されているデータを示す説明図である。
【図６】上記装置の軸力・締付角度記憶手段に記憶されているデータを示す説明図である。
【図７】上記装置の増締角度演算手段に記憶されているデータを示す説明図である。
【図８】上記装置のブロック図である。
【図９】超音波センサの説明図である。
【図１０】従来例を示す説明図である。
【図１１】従来例を示す説明図である。
【符号の説明】
１　ボルトの軸力測定装置
２　ボルト
３　頭部端面
４　超音波センサ
５　軸部端面
８　記憶手段
１８　ワーク
２１　演算手段
Ｆｂ　ボルト軸力
ΔＴ　遅延時間
Ｔｙ　境界遅延時間
Ａ　降伏点
▲１▼　弾性域関係式
▲２▼　塑性域関係式
３０　ボルトの締付装置
３１　ボルト
３２　頭部端面
３３　軸部端面
３４　超音波センサ
Ｆｔ　目標軸力
Ｆｂ　ボルト軸力
ΔＴ　遅延時間
３７　遅延時間・軸力記憶手段
▲１▼ａ　弾性域関係式
▲２▼ａ　塑性域関係式
３８　軸力・締付角度記憶手段
▲１▼ｂ　弾性域関係式
▲２▼ｂ　塑性域関係式
３９　前段軸力演算手段
４０　増締角度演算手段[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an axial force measuring device, an axial force measuring method, and a tightening device for a bolt.
[0002]
[Prior art]
As shown in FIGS. 9 and 10, the present inventor uses an ultrasonic sensor b (see FIG. 9) to measure the elongation of the bolt a when the bolt a is screwed into the work as an apparatus for measuring the axial force of the bolt a. By calculating the axial force of the bolt a by substituting the measured elongation into a previously prepared relational expression c between the bolt elongation and the bolt axial force (see the calibration line in FIG. 10). Studying.
[0003]
The ultrasonic sensor b oscillates ultrasonic waves while being in contact with the head end face of the bolt a and receives the reflected wave reflected at the shaft end face, and determines the time from oscillation to reception (the length of the bolt). It is to be measured. According to the ultrasonic sensor b, the elongation of the bolt can be calculated by determining the difference (ultrasonic delay time) between the measurement time before screwing and the measurement time after screwing.
[0004]
On the other hand, the above-mentioned relational expression c is obtained by previously screwing a sample bolt of the same type into a known axial force tester, detecting a plurality of points of the axial force of the bolt, and bringing the ultrasonic sensor b into contact with the head of the bolt. By measuring the ultrasonic delay time at the detection point, relation data between the ultrasonic delay time due to the elongation of the bolt and the axial force of the bolt is obtained, and the data is determined by a calculation method such as the least square method.
[0005]
[Problems to be solved by the invention]
By the way, as shown in FIG. 11, in a region where the bolt a is stretched by the axial force in the elastic region, the relationship between the ultrasonic delay time and the bolt axial force has a substantially linear relationship (linear). When the axial force enters the plastic region, the relationship between the ultrasonic delay time and the bolt axial force becomes a clear curve.
[0006]
However, in the conventional ultrasonic bolt axial force measuring device, the bolt axial force is calculated from the ultrasonic delay time using one relational expression c (approximate expression) in all the axial force regions (elastic region + plastic region). , The error was large. For example, as shown in FIG. 11, if a first-order approximation formula is forcibly set so as to cover all axial force regions, a large error occurs in both the elastic region and the plastic region. Therefore, it is practically impossible to estimate the axial force in a continuous region from the elastic region of the bolt a to the plastic region. For this reason, it has been difficult to accurately tighten the bolt a to the target axial force in the continuous region.
[0007]
An object of the present invention created in consideration of the above circumstances is that, in a continuous region from an elastic region to a plastic region, the axial force of a bolt can be estimated with high accuracy, and the screw can be screwed up to a target axial force with high accuracy. It is an object of the present invention to provide an axial force measuring device, an axial force measuring method and a tightening device for a bolt.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the bolt axial force measuring device according to the first aspect of the present invention measures the time from contact with the head end face of the bolt to oscillation of ultrasonic waves and reception of the reflected wave reflected at the shaft end face. The ultrasonic sensor to be measured and the relational expression between the delay time obtained by subtracting the time measured before tightening the bolt from the above time measured after tightening the bolt and the axial force of the bolt are divided into an elastic region and a plastic region, and two types are stored. The storage means in which the boundary delay time at the yield point separating the elastic region and the plastic region is stored, and the delay time measured by the ultrasonic sensor when the bolt is tightened to the work is longer than the boundary delay time. It is provided with arithmetic means for calculating the axial force of the bolt using the relational expression of the elastic range if it is shorter and using the relational expression of the plastic range if it is longer.
[0009]
Further, the method for measuring the axial force of a bolt according to the second invention is that, while detecting the bolt axial force by tightening the sample bolt, an ultrasonic wave is oscillated at the head end face of the sample bolt and reflected at the shaft end face. Measure the time until the wave is received, obtain the delay time obtained by subtracting the time measured before tightening the bolt from the time measured after tightening the bolt, and obtain the relationship data between the bolt axial force and the sample bolt from the above data. Determine the yield point at which elongation shifts from the elastic range to the plastic range, find the boundary delay time at that yield point, find the elastic range relational expression between the delay time and the bolt axial force from the data below the yield point, and calculate the yield range above the yield point. The plastic region relation formula is obtained from the data of the above, and when the delay time measured by the ultrasonic sensor when the bolt is actually tightened to the work is shorter than the above boundary delay time, the elastic region relation formula is used. It is obtained to calculate the axial force of the bolt with the engaging type.
[0010]
Further, a third invention is a bolt tightening device for tightening a bolt with a predetermined target axial force, the ultrasonic wave being oscillated by coming into contact with a head end face of the bolt, and a reflected wave reflected by a shaft end face. The ultrasonic sensor that measures the time until receiving the bolt and the relational expression between the delay time obtained by subtracting the time measured before tightening the bolt from the time measured after tightening the bolt and the axial force of the bolt are the elastic range and the plastic range. A delay time / axial force storage means in which a boundary delay time at a yield point which separates an elastic region and a plastic region is stored, and a relationship between a bolt tightening angle and a bolt axial force. Axial force / tightening angle storage means in which two equations are stored separately in an elastic area and a plastic area, and a delay time is obtained by an ultrasonic sensor after tightening a bolt at a predetermined angle, and the delay time is shorter or longer than the boundary delay time. How to write the above delay time and axial force Means for calculating the pre-stage bolt axial force by substituting into the elastic range relational expression or the plastic range relational expression of the means, and the elastic range relation between the pre-stage bolt axial force and the axial force / tightening angle storage means. Substituting into the equation or the plastic zone relational equation and substituting the preset target axial force into the plastic zone relational equation of the above-mentioned axial force / tightening angle storage means to calculate the difference between them, that is, the relative tightening angle up to the target axial force. And a tightening angle calculating means for calculating.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to the accompanying drawings.
[0012]
First, an embodiment of a bolt axial force measuring device of claim 1 and an axial force measuring method of claim 2 will be described with reference to FIGS. 1 to 3.
[0013]
As shown in FIG. 1, a bolt axial force measuring device 1 according to the present embodiment has an ultrasonic sensor 4 that is in contact with a head end surface 3 of a bolt 2. The ultrasonic sensor 4 oscillates ultrasonic waves while being in contact with the head end face 3 of the bolt 2 and receives a reflected wave reflected by the shaft end face 5, and a time T from oscillation to reception (the length of the bolt 2). Measure). The ultrasonic sensor 4 is housed in a socket 7 that is placed on the head 6 of the bolt 2 so as to be vertically movable while being separated from the rotation of the socket 7. The socket 7 is rotationally driven by a rotation driving device (not shown) such as a nut runner.
[0014]
The axial force measuring device 1 shown in FIG. 1 has a storage unit 8 (hereinafter, referred to as a memory 8) connected to the ultrasonic sensor 4. As shown in FIG. 2, the memory 8 has a delay time (time increased by elongation due to bolt tightening) ΔT obtained by subtracting the time T1 measured before bolt tightening from the time T2 measured after bolt tightening, as shown in FIG. Two relational expressions for the bolt axial force Fb are stored separately for an elastic region and a plastic region, and a boundary delay time Ty at a yield point Y separating the elastic region and the plastic region is stored. These equations and time are obtained by the tester 9 shown in FIG. 3 as follows.
[0015]
The tester 9 is inserted through a pair of holding members 10, 11 arranged at a predetermined interval, a compression type load cell 12 interposed between the holding members 10, 11, and an insertion hole of the upper holding member 10. Bolt 13 that is screwed into the screw hole of the lower holding member 11, a socket 15 that is put on the head 14 of the sample bolt 13 and is driven to rotate, and a head end face of the sample bolt 13 that is provided in the socket 15. The ultrasonic sensor 17 includes an ultrasonic sensor 17 that is in contact with the socket 16 and a known nut runner (not shown) connected to the socket 15.
[0016]
The nut runner drives the socket 15 to rotate while detecting its rotation torque and rotation angle. The sample bolt 13 screwed into the tester 9 in FIG. 3 and the bolt 2 screwed into the work 18 in FIG. 1 use the same type of bolt. The ultrasonic sensor 17 shown in FIG. 3 may be shared with the ultrasonic sensor 4 shown in FIG. 1, and the nut runner of the socket 15 shown in FIG. 3 is shared with the rotary drive of the socket 7 shown in FIG. May be.
[0017]
In the tester 9, the socket 15 is rotated by a nut runner to tighten the sample bolt 13, and the ultrasonic sensor 17 detects the bolt axial force Fb by the load cell 12, while the ultrasonic sensor 17 detects the ultrasonic wave at the head end face 16 of the sample bolt 13. Is measured until the reflected wave reflected by the shaft end face 19 is received. Then, a delay time (time increased by elongation due to bolt tightening) ΔT is obtained by subtracting the time T1 measured before bolt tightening from the time T2 measured after bolt tightening. Then, the relationship between the delay time ΔT and the bolt axial force Fb is recorded as plot data in the recorder 20 connected to the ultrasonic sensor 17 and the load cell 12 (see each plot point in the graph of FIG. 2).
[0018]
From a graph connecting the points of the plot data, a boundary point where the elongation of the sample bolt 13 shifts from a substantially straight line to a clear curve, that is, a yield point Y at which the elongation of the sample bolt 13 shifts from an elastic region to a plastic region is determined. . Then, the boundary delay time Ty at the breakdown point Y is stored in the memory 8 shown in FIG. Further, an elastic region relational expression (1) between the delay time ΔT and the bolt axial force Fb is obtained from the ΔT-Fb data below the yield point Y, and a plastic region relational expression (2) is obtained from the ΔT-Fb data above the yield point. Are stored in the memory 8.
[0019]
A known least squares method or the like is used as an approximation method for obtaining the elastic range relational expression (1) and the plastic range relational expression (2) from the plot data of FIG. In the illustrated example, the elastic region relation ▲ 1 ▼ is _{_{Fb = A 1 ΔT2 + B 1}} ΔT + C 1 becomes _(A 1 << 1), plastic zone relationship ▲ 2 ▼ became _{_{Fb = A 2 ΔT2 + B 2}} ΔT + C 2.
[0020]
However, the elastic region relational expression (1) may be a linear expression, and the plastic region relational expression (2) may be a tertiary or higher order expression. Further, the determination of the yield point Y may not be so strict. This is because the two relational expressions (elastic region relational expression (1) and plastic region relational expression (2)) give substantially the same value near the yield point.
[0021]
Further, the axial force measuring device 1 shown in FIG. 1 has an arithmetic unit 21 (computer) connected to the ultrasonic sensor 4 and the memory 8. If the delay time ΔT obtained by the ultrasonic sensor 4 when the bolt 2 is tightened to the work 18 is shorter than the boundary delay time Ty, the calculating means 21 relates to the elastic region: (1): Fb = A The axial force of the bolt 2 is calculated using ₁ ΔT2 + B ₁ ΔT + C ₁ and, if it is long, the relational expression (2) of the plastic region: Fb = A ₂ ΔT ₂ + B ₂ ΔT + C ₂ .
[0022]
The ultrasonic sensor 4, the memory 8, and the calculating means 21 are connected as shown in FIG. 1, and the signal of the ultrasonic delay time ΔT measured by the ultrasonic sensor 4 is automatically sent to the calculating means 21. Is to be entered. Then, the arithmetic means 21 automatically determines the magnitude of the measured ultrasonic delay time ΔT with respect to the boundary ultrasonic delay time Ty, and automatically determines two relational expressions {1} of the memory 8 according to the result. , {Circle around (2)} is selected, and the measured ultrasonic delay time ΔT is automatically substituted into the relational expression to calculate the bolt axial force.
[0023]
The operation of the present embodiment will be described.
[0024]
As shown in FIG. 1, the bolt axial force when the bolt 2 is screwed into the work 18 by a predetermined amount (predetermined angle) is measured (calculated) as follows.
[0025]
First, before screwing the bolt 2, the ultrasonic sensor 4 is brought into contact with the bolt head end face 3 to oscillate ultrasonic waves and receive the reflected wave reflected by the shaft end face 5, and determine the time T 1 from oscillation to reception. Measure. Then, after the bolt 2 is screwed in a predetermined amount, the ultrasonic sensor 4 is brought into contact with the bolt head end surface 3, similarly oscillating the ultrasonic wave and receiving the reflected wave reflected by the shaft end surface 5, from oscillation to reception. Is measured at time T2. Then, the time increased by the elongation due to the bolt tightening, that is, T2-T1, is calculated, and this is set as the delay time ΔT.
[0026]
If the delay time ΔT is shorter than the boundary delay time Ty, the elastic region relational expression (1): Fb = A ₁ ΔT2 + B ₁ ΔT + C ₁ is used, and if longer, the plastic region relational expression (2): Fb = A ₂ ΔT2 + B with ₂ [Delta] T + _{C 2,} the axial force of the bolt 2 is calculated. As described above, since the two relational expressions (approximate expressions) are properly used depending on whether the bolt 2 is in the elastic region or the plastic region, highly reliable approximate expressions {1} and ▲ are used for each region (elastic region and plastic region). 2) can be obtained, and highly accurate axial force estimation can be performed.
[0027]
In addition, since the highly accurate approximation formulas (1) and (2) are switched and used in this manner, highly accurate axial force calculation in a continuous region from an elastic region to a plastic region, which was conventionally considered impossible, is performed. Becomes possible. Therefore, for example, if a known nut runner having the above-described ultrasonic sensor 4 incorporated in the socket 7 is used, the delay time ΔT obtained by the ultrasonic sensor 4 depends on whether the delay time ΔT is longer or shorter than the boundary delay time Ty. By selecting and using the two approximate expressions (1) and (2), the bolt can be tightened with high reliability from the elastic range to the plastic range.
[0028]
Next, one embodiment of the bolt tightening device of claim 3 will be described with reference to FIGS.
[0029]
As shown in FIG. 4, the bolt tightening device 30 according to the present embodiment is a device for tightening the bolt 31 with a predetermined target axial force.
[0030]
The tightening device 30 oscillates ultrasonic waves while being in contact with the head end surface 32 of the bolt 31 and receives the reflected wave reflected by the shaft end surface 33 and measures the time T from oscillation to reception. It has a sound wave sensor 34. The ultrasonic sensor 34 is housed in a socket 36 which is put on the head 35 of the bolt 31 so as to be vertically movable while being separated from the rotation of the socket 36. The ultrasonic sensor shown in FIG. 1 or FIG. The same ones as 4 and 17 are used. The socket 36 is rotationally driven by a drive device (not shown) such as a nut runner.
[0031]
Further, the fastening device 30 shown in FIG. 4 has a delay time (time increased by elongation due to bolt tightening) ΔT obtained by subtracting the time T1 measured before bolt tightening from the time T2 measured after bolt tightening. There is a delay time / axial force storage means 37 (hereinafter referred to as a first memory 37) in which two relational expressions with respect to the bolt axial force Fb are stored separately for an elastic region and a plastic region. As shown in FIG. 5, the first memory 37 stores the elastic region relational expression (1) a: Fb = B ₃ ΔT and the plastic region relational expression (2) a: Fb = A ₄ ΔT ² + B ₄ ΔT + C ₄ . , And the boundary ultrasonic delay time Ty are stored. These equations and times are obtained by the tester 9 shown in FIG. 3 as in the previous embodiment.
[0032]
Further, in the tightening device 30 shown in FIG. 4, the relational expression between the tightening angle θ of the bolt 31 and the bolt axial force Fb is divided into an elastic region and a plastic region, and two types are stored. It has a storage means 38 (hereinafter referred to as a second memory 38). As shown in FIG. 6, the second memory 38 stores the elastic region relational expression (1) b: θ = C ₅ Fb + D ₅ and the plastic region relational expression (2) b: θ = A ₆ Fb ³ + B ₆ Fb ^2. + C ₆ Fb + D ₆ is stored. These equations are obtained by the tester 9 shown in FIG.
[0033]
In addition, the tightening device 30 shown in FIG. 4 obtains a delay time ΔT due to elongation after the bolt 31 is tightened at a predetermined angle by the ultrasonic sensor 34, and if the delay time ΔT is shorter than the boundary delay time Ty, the elastic range is reduced. relation _{▲ 1 ▼ a: Fb = B} 3 with [Delta] T, equation of plastic zone longer ▲ 2 ▼ a: Fb = with _{^{_{a 4 ΔT 2 + B 4 ΔT}}} + C 4, front bolt axial force F1 at this time Is calculated. (Hereinafter referred to as first calculating means 39).
[0034]
Further, the tightening device 30 shown in FIG. 4 converts the calculated front-stage bolt axial force F1 into the elastic range relational expression (1) b: θ = C ₅ Fb + D ₅ shown in FIG. Relational expression {circle around (2)} b: θ = A ₆ Fb ³ + B ₆ Fb ² + C ₆ Fb + D ₆ and a preset target axial force Ft in the plastic region relational expression of the second memory 38. θ = A ₆ Fb ³ + B ₆ Fb ² + C ₆ Fb + D ₆ , and a tightening angle calculating means 40 (hereinafter referred to as a tightening angle calculating means 40 (hereinafter, referred to as a tightening angle calculating means 40) for calculating a difference between them, that is, a relative tightening angle θ from the pre-stage bolt axial force F 1 to the target axial force Ft Second operating means 40).
[0035]
The ultrasonic sensor 34, the first memory 37, the second memory 38, the first calculating means 39, and the second calculating means 40 are connected as shown in FIG. The signal of the time ΔT is automatically inputted to the first calculating means 39 and the second calculating means 40. The first calculating means 39 automatically calculates the pre-stage bolt axial force F1 using the data in the first memory 37, and the second calculating means 40 automatically calculates the relative bolt force using the data in the second memory 38. The tightening angle θ is calculated.
[0036]
The operation of the present embodiment will be described with reference to FIGS.
[0037]
First, the target axial force Ft and the allowable axial force variation range are input to a computer (not shown) of the device 30. Then, as shown in FIG. 4, the bolt 31 is set on the work 41, the socket 36 of the nut runner is lowered to engage with the bolt head 35, and the socket 36 is rotated to screw the bolt 31 into the bolt head. 35 is seated on the upper surface of the work 41 without load. Then, the ultrasonic sensor 34 measures the time from oscillation to reception: the no-load ultrasonic time T0. After the measurement, the ultrasonic sensor 34 is retracted upward (hereinafter, the retract is not described).
[0038]
Then, the socket 36 is tightened with a nut runner to about 50% of the target axial force Ft. In order to secure the final tightening angle θ to some extent, this axial force is applied to the region of the elastic region of the bolt axial force Fb (the region where the elastic region relational expression (1) a: Fb = B ₃ ΔT is used) in FIG. It is preferred to take. However, it is also possible to take a high axial force in a plastic region. Then, the ultrasonic sensor 34 is lowered and seated on the bolt head 35, and the ultrasonic sensor 34 measures the time from oscillation to reception: the former ultrasonic time T1.
[0039]
Then, a difference between the preceding ultrasonic time T1 and the no-load ultrasonic time T0, that is, a delay time ΔT1 due to the extension of the bolt 31 is calculated. Then, the delay time Delta] T1 is elastic range equation shown in Delta] T1-F1 conversion formula i.e. 5 is shorter than the boundary the delay time Ty ▲ 1 ▼ a: Fb = substituted into _{B 3} [Delta] T, the boundary delay time Ty If it is longer, ΔT1−F1 conversion formula, that is, the plastic region relational formula (2) shown in FIG. 5A: Fb = A ₄ ΔT ² + B ₄ ΔT + C ₄ is substituted to calculate the pre-stage bolt axial force F1.
[0040]
Then, the front bolt axial force F1, the elastic band relationship shown in F1-.theta.1 conversion formula i.e. FIG _{6 ▲ 1 ▼ b: θ =} C 5 Fb + D 5 or plastic zone relationship _{▲ 2 ▼ b: θ = A} 6 Fb 3 + B ₆ Fb ² + C ₆ Fb + D ₆ to calculate the preceding stage tightening angle θ1. Then, the preset target axial force Ft is substituted into an Ft-θt conversion equation, that is, a plastic zone relational equation (2) b: θ = A ₆ Fb ³ + B ₆ Fb ² + C ₆ Fb + D ₆ shown in FIG. The fastening angle θt is calculated.
[0041]
Then, the difference between the first-stage tightening angle θ1 and the target tightening angle θt, that is, the additional tightening angle Δθ is calculated. Then, the socket 36 is rotated by the nut runner by the tightening angle Δθ. Then, the ultrasonic sensor 34 is lowered to be seated on the bolt head 35, and the ultrasonic sensor 34 measures a time from oscillation to reception: a final ultrasonic time T2.
[0042]
Then, a difference between the final ultrasonic time T2 and the no-load ultrasonic time T0, that is, a delay time ΔT2 at the time of final fastening is calculated. If this delay time ΔT2 is shorter than the boundary delay time Ty shown in FIG. 5, it is substituted into the ΔT2-F2 conversion equation, that is, the elastic range relational equation (1) a: Fb = B ₃ ΔT shown in FIG. longer than Delta] T2-F2 conversion formula i.e. plastic zone relational expression shown in FIG. 5 ▲ 2 ▼ a: Fb = substituted in _{^{_{a 4 ΔT 2 + B 4 ΔT}}} + C 4, and calculates the final axial force F2.
[0043]
Then, a difference between the final axial force F2 and the target axial force Ft, that is, an axial force error ΔF is calculated. The axial force error ΔF is compared with a preset allowable range. If the error ΔF is within the allowable range, the determination is OK, and if the error is outside the allowable range, the determination is NG.
[0044]
According to the present embodiment, the calculation of the axial force Fb based on the delay time ΔT and the calculation of the tightening angle θ based on the axial force Fb are performed according to elastic region relational expressions (approximate expressions) (1) a and (1) b, respectively. Plastic area relational formulas (approximate formulas) Calculated separately for (2) a and (2) b, so the reliability of each relational formula (approximate formula) can be increased, and high-precision tightening is possible It becomes. In addition, since the axial tightening angle θ is calculated by measuring the axial force F1 at the preceding stage tightening angle, there is no influence from the axial force variation due to the bearing surface friction variation and the like.
[0045]
【The invention's effect】
As described above, according to the axial force measuring device, the axial force measuring method, and the tightening device of the bolt according to the present invention, it is possible to estimate the axial force of the bolt with high accuracy in a continuous region from an elastic region to a plastic region. It can be screwed up to the target axial force with high accuracy.
[Brief description of the drawings]
FIG. 1 is a side sectional view showing an embodiment of a bolt axial force measuring device according to a first invention.
FIG. 2 is an explanatory diagram showing data stored in a storage unit of the device.
FIG. 3 is a side sectional view showing a tester for acquiring the data.
FIG. 4 is a side sectional view showing an embodiment of a bolt tightening device according to the third invention.
FIG. 5 is an explanatory diagram showing data stored in a delay time / axial force storage means of the device.
FIG. 6 is an explanatory diagram showing data stored in an axial force / tightening angle storage means of the device.
FIG. 7 is an explanatory diagram showing data stored in a tightening angle calculating means of the above device.
FIG. 8 is a block diagram of the device.
FIG. 9 is an explanatory diagram of an ultrasonic sensor.
FIG. 10 is an explanatory diagram showing a conventional example.
FIG. 11 is an explanatory diagram showing a conventional example.
[Explanation of symbols]
1 Bolt axial force measuring device 2 Bolt 3 Head end face 4 Ultrasonic sensor 5 Shaft end face 8 Storage means 18 Work 21 Calculation means Fb Bolt axial force ΔT Delay time Ty Boundary delay time A Yield point (1) Elastic area relational expression {Circle around (2)} Plastic region relation formula 30 Bolt tightening device 31 Bolt 32 Head end surface 33 Shaft end surface 34 Ultrasonic sensor Ft Target axial force Fb Bolt axial force ΔT Delay time 37 Delay time / axial force storage means <1> a Elastic range relational expression (2) a Plastic range relational expression 38 Axial force / tightening angle storage means (1) b Elastic range relational expression (2) b Plastic range relational expression 39 Pre-stage axial force calculating means 40 Additional tightening angle calculating means

Claims

An ultrasonic sensor that oscillates ultrasonic waves in contact with the head end face of the bolt and measures the time until the reflected wave reflected at the shaft end face is received, and from the above time measured after bolt tightening before bolt tightening The relational expression between the delay time obtained by subtracting the measured time and the axial force of the bolt is stored separately for the elastic region and the plastic region, and the boundary delay time at the yield point separating the elastic region and the plastic region is stored. Memory means, and when the delay time measured by the ultrasonic sensor when the bolt is tightened to the workpiece is shorter than the boundary delay time, the relational expression of the elastic region is used. An axial force measuring device for a bolt, comprising: an arithmetic unit for calculating an axial force.

While detecting the bolt's axial force by tightening the sample bolt, measure the time from receiving ultrasonic waves oscillating at the head end face of the sample bolt and receiving the reflected wave reflected at the shaft end face, and measuring after bolt tightening Obtain the delay time obtained by subtracting the time measured before bolt tightening from the above time and the relation data between the bolt axial force and determine the yield point at which the elongation of the sample bolt shifts from the elastic range to the plastic range from the above data. Obtain the boundary delay time at the yield point, obtain the elastic area relational expression between the delay time and the bolt axial force from the data below the yield point, and obtain the plastic area relational expression from the data above the yield point, and actually attach the bolt If the delay time measured by the ultrasonic sensor when tightening is shorter than the above boundary delay time, use the elastic region relational expression if it is longer, use the plastic region relational expression to calculate the axial force of the bolt Axial force measuring method of a bolt according to claim and.

A bolt tightening device for tightening a bolt with a predetermined target axial force. It measures the time from contacting the head end face of the bolt, oscillating ultrasonic waves and receiving the reflected wave reflected at the shaft end face. An ultrasonic sensor to be stored, and two relational expressions of a delay time obtained by subtracting a time measured before bolt tightening from the above time measured after bolt tightening and a bolt axial force are stored separately in an elastic region and a plastic region. And the delay time / axial force storage means in which the boundary delay time at the yield point separating the elastic region and the plastic region is stored, and the relational expression between the bolt tightening angle and the bolt axial force is defined as the elastic region and the plastic region. An axial force / tightening angle storage means stored in two sets, and a delay time is determined by an ultrasonic sensor after the bolt is tightened at a predetermined angle, and the delay time / axis is determined depending on whether this is shorter or longer than the boundary delay time. Elastic range relational expression of force storage means Is the pre-stage axial force calculating means for substituting into the plastic range relational expression and calculating the pre-stage bolt axial force at that time, and the pre-stage bolt axial force is used as the elastic range relation expression or the plastic range relation expression of the axial force / tightening angle storage means. And a preset target axial force is substituted for the plastic range relational expression of the axial force / tightening angle storage means to calculate a difference between them, that is, a relative tightening angle up to the target axial force. Means for tightening bolts.