JP3835023B2 - Screw tightening axial force measuring method, screw tightening method using the measuring method, and apparatus thereof - Google Patents

Description

【００１０】
本発明は、このような事情に鑑み、塑性域までねじを締め付けた場合においても、ねじの締付軸力に対応した値を正確に測定することができるとともに、この測定値に基づいてねじの締付力を適正に制御することができるねじの締付軸力測定方法及び該測定方法を用いたねじ締付方法並びにこれらの装置を提供するものである。
【００１１】
【課題を解決するための手段】
請求項１に係る発明は、ねじ締付手段を使用したねじの締付過程で、このねじの弾性域における締付トルクの変化量と締付角度の変化量との比からなるトルクレートを求めた後、このトルクレートに基づいてねじの塑性変形量を除いた締付軸力の測定基準角度を求めるとともに、この測定基準角度に基点として締付軸力の測定時点におけるねじの締付角度を測定し、この締付角度の測定値に対応したねじの締付軸力を、予め求めた締付角度と締付軸力との関係から測定するものである。
【００１２】
この構成によれば、上記トルクレートに応じて求められたねじの塑性変形量を除いた締付軸力の測定基準角度を基点として、締付軸力の測定時点におけるねじの弾性変形量に対応した締付角度が求められるとともに、この締付角度に対応した締付軸力が測定されることにより、塑性域までねじを締め付けた場合においても、ねじの締付軸力が正確に求められることになる。
【００１３】
請求項２に係る発明は、上記請求項１記載のねじの締付軸力測定方法において、締め付けられるねじの弾性域内における少なくとも二点の締付角度に対応した締付トルクからトルクレートを求めるように構成したものである。
【００１４】
この構成によれば、ねじの締付角度と、締付トルクとが比例関係にあるねじの弾性域内において、締付トルクの変化量と締付角度の変化量との比からなるトルクレートが容易かつ適正に求められるため、このトルクレートに基づいてねじの弾性変形量に対応したねじの塑性変形量を除いた締付軸力の測定基準角度が正確に求められることになる。
【００１５】
請求項３に係る発明は、上記請求項１または請求項２記載の締付軸力測定方法において、ねじの締付角度及び締付トルクを座標軸とする座標系の測定点を通ってねじの弾性域におけるトルク勾配と平行に伸びるラインと、上記座標系の締付トルクが０となるラインとの交点を求め、この交点の締付角度を締付軸力の測定基準角度として設定するように構成したものである。
【００１６】
この構成によれば、ねじの締付角度と締付トルクを座標軸とする座標系から、上記ねじの塑性変形量を除いた測定基準角度が容易かつ適正に求められ、この測定基準角度を基点として締付軸力の測定時点におけるねじの弾性変形量に対応した締付角度が正確に求められることになる。
【００１７】
請求項４に係る発明は、上記請求項１〜請求項３のいずれかに記載の締付軸力測定方法において、ねじの締付角度及び締付トルクを座標軸とする座標系に表示されるねじの弾性域におけるトルク勾配の延長ラインと、上記座標系の締付トルクが０となるラインとの交点を求め、この交点の座標を理論着座点として設定した後、この理論着座点を基点にして締付軸力の測定時点における締付角度を測定するとともに、上記測定基準角度を求め、上記締付角度の測定値から測定基準角度を減算することにより、この測定基準角度を基点とした締付軸力の測定時点におけるねじの締付角度を求めるように構成したものである。
【００１８】
この構成によれば、ねじの締付角度及び締付トルクを座標軸とする座標系から、上記理論着座点を基点にして、締付軸力の測定時点におけるねじの塑性変形量を除いた締付角度が容易かつ適正に求められ、この締付角度に基づいてねじの弾性変形量に対応した締付軸力が正確に求められることになる。
【００１９】
請求項５に係る発明は、ねじ締付手段を使用したねじの締付過程で、このねじの弾性域における締付トルクの変化量と締付角度の変化量との比からなるトルクレートを求めた後、このトルクレートに基づいてねじの塑性変形量を除いた締付軸力の測定基準角度を求めるとともに、この測定基準角度を基点として締付軸力の測定時点におけるねじの締付角度を測定し、この締付角度の測定値に基づいて、予め設定された締付軸力が得られるようにねじの締付状態を制御するものである。
【００２０】
この構成によれば、上記トルクレートに基づいて、ねじの塑性変形量を除いたを除いた締付軸力の測定基準角度が求められるとともに、この測定基準角度を基点として締付軸力の測定時点におけるねじの弾性変形量に対応した締付角度が容易かつ適正に求められるとともに、この締付角度の測定値に基づいてねじの締付状態が制御されることにより、塑性域までねじを締め付けた場合においても、ねじの締付軸力が予め設定された適正値になるように調節されることになる。
【００２１】
請求項６に係る発明は、ねじ締付手段を使用したねじの締付過程で、このねじの弾性域における締付トルクの変化量と締付角度の変化量との比からなるトルクレートを求め、このトルクレートに基づいてねじの塑性変形量を除いた締付軸力の測定基準角度を求めるとともに、この測定基準角度を基点として締付軸力の測定時点におけるねじの締付角度を測定し、この締付角度の測定値に対応したねじの締付軸力を、予め求めた締付角度と締付軸力との関係から測定した後、この締付軸力の測定値に基づいてねじの締付状態が適正であるか否かを判別するものである。
【００２２】
この構成によれば、ねじの締付の締付過程で上記トルクレートに応じて求められた測定基準角度を基点としてねじの塑性変形量を除いた締付軸力の測定基準角度が求められるとともに、この測定基準角度を基点として締付軸力の測定時点におけるねじの弾性変形量に対応した締付角度が容易かつ適正に求められ、この締付角度の測定値に対応した締付軸力が求められることにより、塑性域までねじを締め付けた場合においても、ねじの締付軸力が正確に求められるとともに、この締付軸力の測定値に基づき、ねじの締付状態が適正であるか否か正確に判別されることになる。
【００２３】
請求項７に係る発明は、ねじ締付手段を使用したねじの締付過程で、このねじの弾性域における締付トルクの変化量と締付角度の変化量との比からなるトルクレートを求めるトルクレート演算部と、このトルクレートの演算値に基づいてねじの塑性変形量を除いた締付軸力の測定基準角度を求める基準角度演算部と、この基準角度演算部によって求められた測定基準角度を基点として締付軸力の測定時におけるねじの締付角度を測定する締付角度測定部と、この締付角度の測定値に対応した締付軸力を、予め求めた締付角度と締付軸力との関係から求める締付軸力測定部とを備えたものである。
【００２４】
この構成によれば、上記トルクレート演算部により求められたトルクレートに基づいてねじの塑性変形量を除いた締付軸力の測定基準角度が上記基準角度演算部により求められるとともに、この測定基準角度を基点として締付軸力の測定時におけるねじの弾性変形量に対応した締付角度が上記締付角度測定部により正確かつ容易に求められることにより、塑性域までねじが締め付けられた場合であっても、上記締付角度測定部によって求められた締付角度に対応した締付軸力が上記締付軸力測定部により正確に求められることになる。
【００２５】
請求項８に係る発明は、上記請求項７記載のねじの締付軸力測定装置において、締め付けられるねじの弾性域内における少なくとも二点の締付角度に対応した締付トルクから上記トルクレート演算部によりトルクレートを求めるように構成したものである。
【００２６】
この構成によれば、ねじの締付角度と、締付トルクとが比例関係にあるねじの弾性域内で、締付トルクの変化量と締付角度の変化量との比からなるトルクレートがトルクレート演算部において適正に求められることになる。
【００２７】
請求項９に係る発明は、上記請求項７または請求項８記載のねじの締付軸力測定装置において、ねじの締付角度及び締付トルクを座標軸とする座標系の測定点を通ってねじの弾性域におけるトルク勾配と平行に伸びるラインと、上記座標系の締付トルクが０となるラインとの交点の締付角度を基準角度演算部により求め、この交点の締付角度を締付軸力の測定基準角度として設定するように構成したものである。
【００２８】
この構成によれば、ねじの締付角度及び締付トルクを座標軸とする座標系から、上記ねじの塑性変形量を除いた締付軸力の測定基準角度が容易かつ適正に求められ、この測定基準角度を基点として締付角度の測定時点におけるねじの弾性変形量に対応した締付角度が正確に求められることになる。
【００２９】
請求項１０に係る発明は、上記請求項７〜請求項９のいずれかに記載のねじの締付軸力測定装置において、ねじの締付角度及び締付トルクを座標軸とする座標系に表示されるねじの弾性域におけるトルク勾配の延長ラインと、上記座標系の締付トルクが０となるラインとの交点を求め、この交点の座標を理論着座点として設定し、この理論着座点を基点として締付軸力の測定時点における締付角度を締付角度測定部により測定するとともに、上記測定基準角度を基準角度演算部により求め、上記締付角度の測定値から締付軸力の測定基準角度を減算することにより、この測定基準角度を基点とした締付軸力の測定時点における締付角度を求めるように構成したものである。
【００３０】
この構成によれば、上記理論着座点を基点にして、ねじの締付角度及び締付トルクを座標軸とする座標系から、上記ねじの塑性変形量を除いた締付軸力の測定時点における締付角度が上記締付角度測定部により容易かつ適正に測定され、この締付角度の測定値に基づいてねじの弾性変形量に対応した締付軸力が上記締付軸力測定部により正確に測定されることにより、塑性域までねじを締め付けた場合においても、ねじの締付軸力が正確に求められることになる。
【００３１】
請求項１１に係る発明は、ねじ締付手段を使用したねじの締付過程で、このねじの弾性域における締付トルクの変化量と締付角度の変化量との比からなるトルクレートを求めるトルクレート演算部と、このトルクレートの演算値に基づいてねじの塑性変形量を除いた締付軸力の測定基準角度を求める基準角度演算部と、この基準角度演算部により求められた測定順角度を基点として締付軸力の測定時点におけるねじの締付角度を測定する締付角度測定部と、この締付角度の測定値に基づき、予め設定された締付軸力が得られるようにねじの締付状態を制御する締付状態制御部とを備えたものである。
【００３２】
この構成によれば、上記トルクレート演算部により求められたトルクレートに基づいて、ねじの塑性変形量を除いた締付軸力の測定基準角度が上記基準角度演算部により求められるとともに、この基準角度演算部により求められた測定基準角度を基点として締付軸力の測定時点におけるねじの弾性変形量に対応した締付角度が容易かつ適正に上記締付角度測定部により測定され、この締付角度の測定値に基づいてねじの締付状態が上記締付状態制御部により制御されることにより、塑性域までねじを締め付けた場合においても、ねじの締付軸力が予め設定された適正値となるように調節されることになる。
【００３３】
請求項１２に係る発明は、ねじ締付手段を使用したねじの締付過程で、このねじの弾性域における締付トルクの変化量と締付角度の変化量との比からなるトルクレートを求めるトルクレート演算部と、このトルクレートの演算値に基づいてねじの塑性変形量を除いた締付軸力の測定基準角度を求める基準角度演算部と、この基準角度演算部によって演算された測定基準角度を基点として締付軸力の測定時におけるねじの締付角度を測定する締付角度測定部と、この締付角度の測定値に対応したねじの締付軸力を、予め求めた締付角度と締付軸力との関係から測定する締付軸力測定部と、この締付軸力測定部により測定されたねじの締付軸力に基づいてねじの締付状態が適正であるか否かを判別する締付状態判別部とを備えたものである。
【００３４】
この構成によれば、上記トルクレート演算部により求められたトルクレートに基づいて、ねじの塑性変形量を除いた締付軸力の測定基準角度が上記基準角度演算部により求められるとともに、この測定基準角度の演算値に基づいて締付軸力の測定時点におけるねじの弾性変形量に対応したねじの締付角度が上記締付角度測定手段により測定された後、この締付軸力の測定値と、予め設定された締付軸力の目標値とが上記締付状態判別部において比較される等により、塑性域までねじを締め付けた場合においても、ねじの締付状態が適正であるか否かが正確に判別されることになる。
【００３５】
請求項１３に係る発明は、上記請求項１２記載のねじの締付装置において、上記締付状態判別部によるねじの締付状態の判別結果を表示する表示手段を備えたものである。
【００３６】
上記構成によれば、表示手段において表示されるねじの締付状態の判別結果に応じ、ねじの締付状態が適正であるか否かが容易かつ適正に判別されることになる。
【００３７】
【発明の実施の形態】
図１は本発明に係るねじの締付装置の実施形態を示している。このねじの締付装置には、ねじの頭部に係合されるソケット１と、このソケット１によってねじに付与されるトルクを調節するトルクトランスデューサ２と、上記ソケット１によって締め付けられるねじの締付トルクを検出する締付トルク検出器３と、上記ソケット１を回転駆動する駆動モータ４と、この駆動モータ４の回転角度を検出することによりねじの締付角度を測定する角度エンコーダ５とを備えたナットランナ６からなるねじ締付手段が設けられている。
【００３８】
また、上記ねじの締付装置は、ねじの弾性域内において第１締付トルクを設定する第１締付トルク設定器７と、ねじの弾性域内において上記第１締付トルクよりも大きな値の第２締付トルクを設定する第２締付トルク設定器８と、上記締付トルク検出器３によって検出されたねじの締付トルクと上記第１締付トルク設定器７によって設定された第１締付トルクとを比較して両トルクの一致信号を出力する第１コンパレータ９と、上記締付トルク検出器３によって検出されたねじの締付トルクと上記第２締付トルク設定器８によって設定された第２締付トルクとを比較して両トルクの一致信号を出力する第２コンパレータ１０と、第１，第２コンパレータ９，１０から出力される一致信号に対応した制御信号をＣＰＵ１１に出力する第１，第２アナログスイッチ１２，１３とを備えている。
【００３９】
さらに、上記ねじの締付装置には、ねじを締め付けることにより生じる締付軸力の目標値に対応した目標締付角度を設定する目標締付角度設定部１４と、上記第１，第２アナログスイッチ１２，１３から制御信号が出力された時点における上記角度エンコーダ５の検出角度を測定するための制御信号をＣＰＵ１１に入力する角度ゲート１５と、ＣＰＵ１１から出力される制御信号に応じて上記駆動モータ４を制御するサーボアンプ１６と、ＣＰＵ１１から出力される制御信号に応じてねじの締付軸力を表示する表示手段１７とが設けられている。
【００４０】
また、上記ＣＰＵ１１には、ナットランナ６によるねじの締付過程で、このねじの弾性域における締付トルクの変化量と締付角度の変化量との比からなるトルクレートを求めるトルクレート演算部１８と、このトルクレート演算部１８により求められたトルクレートに基づいてねじの塑性変形量を除いた締付軸力の測定基準角度を求める基準角度演算部１９と、この基準角度演算部１９により求められた測定基準角度を基点として締付軸力の測定時におけるねじの締付角度を測定する締付角度測定部２０と、この締付角度測定部２０により測定された締付角度に対応した締付軸力を、予め求めた締付角度と締付軸力との関係から測定する締付軸力測定部２１と、上記締付角度測定部２０により測定された締付角度に基づいてねじの締付状態を制御する締付状態制御部２２とが設けられている。
【００４１】
次に、上記ねじの締付装置によってねじを締め付ける際に実行されるねじの締付軸力測定方法及びこの測定方法を用いたねじの締付方法を、図２及び図３に示すフローチャートに説明する。まずステップＳ１において、図外の入力スイッチの操作に応じ、ナットランナ６の駆動モータ４を回転させてねじの締付を開始した後、ステップＳ２において、図外のキーボード等からなる入力手段により入力されたねじのサイズ等に対応した第１締付トルクＴ１を上記第１設定器７により設定する。次いで、ステップＳ３において、上記締付トルク検出器３によって検出されたねじの締付トルクＴと、上記第１締付トルクＴ１とを第１コンパレータ９で比較して両トルクＴ，Ｔ１が等しいか否かを判定する。
【００４２】
上記ステップＳ３でＹＥＳと判定されると、ステップＳ４において上記角度ゲート１５をＯＮ状態とし、この時点における上記ねじの締付角度θ１の測定値を入力するとともに、ステップＳ５において上記ねじのサイズ等に対応した第２締付トルクＴ２を上記第２設定器８により設定する。次いで、ステップＳ６において、上記締付トルク検出器３により検出されたねじの締め付けトルクＴと、上記第２締付トルクＴ２とを第２コンパレータ１０で比較して両トルクＴ，Ｔ２が等しいか否かを判定する。
【００４３】
上記ステップＳ６でＹＥＳと判定されると、ステップＳ７において上記角度ゲート１５をＯＦＦ状態とし、この時点における上記ねじの締付角度θ２の測定値を入力するとともに、ステップＳ８において、上記第１，第２締付トルクＴ１，Ｔ２と、上記ねじの締付角度θ１，θ２の検出値とに基づき、ねじの弾性域における締付トルクＴの変化量ΔＴ（＝Ｔ２−Ｔ１）と、締付角度θの変化量Δθ（＝θ２−θ１）との比からなるトルクレートＣを上記トルクレート演算部１８により演算して求める。その後、ステップＳ９において、上記トルクレートＣに基づいてねじの理論着座点θＯを上記基準角度演算部１９により演算して求める。
【００４４】
すなわち、ねじの締付開始当初は、ねじの座面と被締付面との間の摩擦係数に対応した一定の滑りが生じた後、弾性域内では、図４に示すように、ねじの締付角度θに比例して締付トルクＴが増大するため、上記締付トルクＴの変化量ΔＴ（＝Ｔ２−Ｔ１）と、締付角度θの変化量Δθ（＝θ２−θ１）とに基づいてトルクレートＣ（＝ΔＴ／Δθ）を算出する。そして、ねじの締付角度θ及び締付トルクＴを座標軸とした図４に示す座標系に表示されるねじの弾性域におけるトルク勾配α、つまり上記弾性域内においてトルクレートＣを演算する際に測定した締付トルクＴの変化状態を示す直線αの延長ラインと、上記座標系の締付トルクＴが０となるライン、つまり上記座標系の横軸との交点を求め、この交点の座標を理論着座点θＯとして設定することにより、ねじの座面と被締付面との間に上記滑りがないと仮定した理論着座点を求める。
【００４５】
次いで、ステップＳ１０において、締付軸力の測定時点である現時点の締付トルクＴの検出値ＴＢと、締付角度θの検出値θＢとを入力した後、ステップＳ１１において、ねじの締付角度θ及び締付トルクＴを座標軸とする図４に示す座標系の測定点Ｂを通って上記ねじの弾性域におけるトルク勾配αと平行に伸びるラインβと、上記座標系の締付トルクＴが０となるライン（横軸）との交点を上記基準角度演算部１９により演算して求め、この交点の締付角度θを締付軸力の測定基準角度θＡとして設定する。
【００４６】
そして、ステップＳ１２において、上記測定基準角度θＡから現時点の締付角度θＢまでの締付角度θの変化量ΔθＡ（＝θＢ−θＡ）を上記締付角度測定部２０により演算して求め、上記変化量ΔθＡを締付軸力測定時点における締付角度ΔθＡとして設定した後、ステップＳ１３において、上記締付角度ΔθＡに対応したねじの締付軸力ＦＡを、予め設定された締付角度θと締付軸力Ｆと関係から上記締付軸力測定部２１により測定し、この締付軸力ＦＡを上記表示手段１７において表示させる。
【００４７】
すなわち、ねじの理論着座点θＯからねじの締付が開始されると仮定した場合、ねじの弾性域内においては、図５に示すように、ねじの締付角度θに比例して締付軸力Ｆが変化するとともに、ねじの締付軸力Ｆが弾性域ＦＣを越えると、ねじに塑性変形が生じるため、ねじの締付角度θと締付軸力Ｆとの比例関係が崩れ、締付角度θの増大量に対する締付軸力Ｆの増大量が次第に低下する傾向が生じる。そして、上記弾性域ＦＣをわずかに越えた締付軸力ＦＡとなるまでねじを締め付けた後、このねじの塑性域から引張り荷重を除去すると、上記弾性域内におけるねじの変位ラインα１と平行なラインβ１に沿って締付軸力Ｆが減少し、ねじには、上記理論着座点θＯから、上記ラインβ１と、図５に示す座標系の横軸との交点における締付角度θＡまでの締付角度θの変化量ΔθＯに相当する塑性変形が生じることになる。
【００４８】
また、上記のように弾性域ＦＣをわずかに越えた締付軸力ＦＡとなるまでねじを締め付けた場合には、上記ねじの塑性変形量ΔθＯを除いた締付軸力Ｆの測定基準角度θＡを基点としたねじの締付角度に比例して、締付軸力Ｆが変化することになる。そして、ねじの弾性域内においては、下記式（数２）に示す関係があるため、この式（数２）からねじに締付角度θに対応した締付軸力Ｆを求め、あるいは予め求めた実験データから上記締付軸力Ｆを推定することができる。なお、下記式（数２）において、ｐはねじのピッチ、Ｋｂはねじの引張りばね定数、Ｋｃは被締付体の圧縮ばね定数である。
【００４９】
【数２】

【００５０】
したがって、図４に示す座標系において、測定点Ｂを通ってねじの弾性域におけるトルク勾配αと平行に伸びるラインβと、上記座標系の締付トルクＴが０となるラインとの交点を求め、この交点の締付角度θを締付軸力Ｆの測定基準角度θＡとして設定し、この測定基準角度θＡから現時点の締付角度θＢまでの締付角度θの変化量ΔθＡを求め、この変化量ΔθＡを、上記測定基準角度θＡを基点とした測定時点における締付角度ΔθＡとして設定することにより、この締付角度ΔθＡと、上記式（数２）とに基づいて、現時点の締付軸力Ｆを求めることができる。つまり、上記理論着座点θＯを基点として測定した現時点における締付角度θの変化量ΔθＢから、上記理論着座点θＯを基点として求めた締付角度θの塑性変形量ΔθＯを減算することにより、上記軸力基準角度θＡから現時点の締付角度θＢまでの締付角度θの変化量ΔθＡを求め、この変化量ΔθＡに基づいて上記締付軸力ＦＡを間接的に測定することができる。
【００５１】
次いで、ステップＳ１４において、入力手段により入力されたねじのサイズ等に基づき、初期に締付部品に必要とする目標締付角度θａを上記目標締付角度設定部１４により設定した後、ステップＳ１５において、上記目標締付角度θａと、ステップＳ１２で求めた上記測定基準角度θＡを基点とする締付角度ΔθＡとを比較することにより、ねじの締付軸力Ｆが、目標値となったか否かを上記締付状態制御部２２により判定する。このステップＳ１５でＮＯと判定された場合には、上記ステップＳ１０にリターンしてねじの締付動作を継続する。
【００５２】
そして、上記ステップＳ１５でＹＥＳと判定されて、現時点における締付軸力Ｆに対応した上記測定基準角度θＡを基点とする締付角度ΔθＡが、上記目標締付角度θａと等しくなり、ねじの締付軸力Ｆが、目標値となったことが確認された時点で、ステップＳ１６において、ねじ締付手段を構成するナットランナ６の駆動モータ４を停止させる制御信号を上記締付状態制御部２２からサーボアンプ１６に出力してねじの締付動作を終了する。
【００５３】
このようにナットランナ６からなるねじ締付手段を使用したねじの締付過程で、このねじの弾性域における締付トルクＴの変化量ΔＴと締付角度θの変化量Δθとの比からなるトルクレートＣを求めた後、このトルクレートＣからねじの塑性変形量ΔθＯを除いた締付軸力Ｆの測定基準角度θＡを求めるとともに、この測定基準角度θＡを基点にして締付軸力Ｆの測定時点におけるねじの締付角度ΔθＡを測定し、この締付角度ΔθＡに対応したねじの締付軸力Ｆを、予め求めた締付角度θと締付軸力Ｆとの関係から上記締付軸力測定部２１において測定するようにしたため、ねじの弾性限度を越えて塑性域までねじを締め付けた場合においても、ねじの締付軸力Ｆを正確に測定することができるとともに、この締付軸力Ｆの測定値に基づいてねじの締付状態を適正に制御することができる。
【００５４】
すなわち、同一サイズのねじにおいて、図６に示すように、ねじの座面と被締付面との間の摩擦係数が高いねじＨと、同摩擦係数が低いねじＬとを、弾性限度を越えて塑性域まで締め付けた場合、摩擦係数の高いねじＨは、摩擦係数の低いねじＬに比べてねじを締め付けるのに大きな締付トルクＴが必要であるとともに、早期に弾性限度を越える傾向があるため、θＯからの角度制御よる締付では、締付後に生じる塑性変形量ΔθＯも大きくなる傾向がある。また、上記のように弾性域をわずかに越えた締付軸力Ｆとなるまでねじを締め付けた場合には、上記ねじの塑性変形量ΔθＯを除いた締付軸力Ｆの測定基準角度θＡを基点としたねじの締付角度θに比例して、締付軸力Ｆが変化することが分かっているため、上記塑性変形量ΔθＯを除いた締付軸力Ｆの測定基準角度θＡを求め、この測定基準角度θＡを基点にして締付軸力Ｆの測定時点におけるねじの締付角度ΔθＡを測定することにより、このねじの締付角度ΔθＡと、予め求めた締付角度θと締付軸力Ｆとの関係から、ねじの締付過程でその締付軸力Ｆを適正に求めることができる。
【００５５】
したがって、上記理論着座点θＯから締付軸力Ｆの測定時点までの締付角度の変化量ΔθＢから上記塑性変形量ΔθＯを減算した値からなる締付角度θの変化量ΔθＡに基づいて上記締付軸力測定部２１により測定された締付軸力Ｆを、上記表示手段１７において表示し、この表示を見ながらねじの締付状態を制御することにより、上記摩擦係数の高いねじＨにおいてねじの能力が最大限に発揮されるようにねじの締付量を調節することができる。また、摩擦係数の小さいねじＬにおいても、上記摩擦係数の高いねじＨと同一の値に設定された目標締付軸力となるようにねじの締付状態を制御することにより、上記ねじＨと同一の締付軸力に設定してねじの能力を充分に発揮させることができる。
【００５６】
そして、ねじの締付作業の終了後に、上記表示手段１７に表示された締付軸力Ｆに応じてねじの締付状態が適正であるか否かを判別し、上記締付軸力Ｆが目標値よりも小さい場合には、ねじをさらに締め付けて増締を行い、逆に上記締付軸力Ｆが目標値よりも大きい場合には、ねじの締付量が過多であると判断して新たなねじと交換するなど、ねじの締付不良が発生するのを確実に防止することができる。
【００５７】
また、上記実施形態では、締め付けられるねじの弾性域内における少なくとも二点の締付角度θ１，θ２に対応した締付トルクＴ１，Ｔ２からトルクレートＣを求めるように構成したため、ねじの締付角度θと、締付トルクＴとが比例関係にあるねじの弾性域内において、締付トルクの変化量ΔＴと締付角度の変化量Δθとの比からなるトルクレートＣを容易かつ適正に求めることができ、このトルクレートＣに基づいて上記ねじの塑性変形量ΔθＯを除いた締付軸力Ｆの測定基準角度θＢを正確に求めることができる。
【００５８】
さらに、上記実施形態では、ねじの締付角度θ及び締付トルクＴを座標軸とする座標系の測定点Ｂを通ってねじの弾性域におけるトルク勾配αと平行に伸びるラインβと、上記座標系の締付トルクが０となるラインとの交点を求め、この交点の締付角度θを締付軸力Ｆの測定基準角度θＡとして設定するように構成したため、上記座標系から、ねじの塑性変形量ΔθＯを除いた測定基準角度θＡを容易かつ適正に求めることができ、この測定基準角度θＢを基点として締付軸力Ｆの測定時点における上記ねじの締付角度ΔθＡを正確に求めることができる。
【００５９】
また、上記実施形態に示すように、ねじの締付角度θ及び締付トルクＴを座標軸とする座標系に表示されるねじの弾性域におけるトルク勾配αの延長ラインと、上記座標系の締付トルクが０となるラインとの交点を求め、この交点の座標を理論着座点θＯとして設定した後、この理論着座点θＯを基点として締付軸力Ｆの測定時点における締付角度θＢを測定するとともに、上記理論着座点θＯを基点として測定基準角度θＡを求め、上記締付角度θＢの測定値から測定基準角度θＡを減算することにより、ねじの塑性変形量ΔθＯを除いたねじの締付角度ΔθＡを求めるように構成した場合には、同じ着座点θＯを基点として測定された締付角度θに基づき、上記ねじの塑性変形量ΔθＯを除いたねじの締付角度ΔθＡを容易かつ適正に測定することができる。
【００６０】
また、上記実施形態では、トルクレートＣの演算値に基づいてねじの塑性変形量ΔθＯを除いた締付軸力Ｆの測定基準角度θＡを基準角度演算部１９により求めるとともに、この基準角度演算部１９により求められた測定基準角度θＡを基点として締付軸力Ｆの測定時点におけるねじの締付角度ΔθＡを締付角度測定部２０により測定し、この締付角度ΔθＡの測定値に基づき、予め設定された締付軸力Ｆが得られるようにねじの締付状態を締付状態制御部２２により制御し、この締付状態制御部２２において、上記締付角度ΔθＡの測定値と、予め設定された目標締付角度θａとを比較して両者が一致した時点でねじの締付作業を終了させるように構成したため、ねじの締付作業を自動化してねじの締付量を適正に制御することができる。
【００６１】
なお、上記実施形態に代え、締付軸力測定部２１により測定されたねじの締付軸力Ｆに基づいてねじの締付状態が適正であるか否かを判別する締付状態判別部とを設け、この締付状態判別部において、上記締付軸力Ｆの測定値と、予め設定された締付軸力Ｆの目標値とを比較して両者が一致した時点でねじの締付作業を終了させる締付状態制御部を設けた構造としてもよい。このように構成した場合には、上記ねじの締付軸力Ｆに基づいてねじの締付状態を、より正確に制御することができる。
【００６２】
また、上記締付状態判別部によるねじの締付状態の判別結果を表示する表示手段を設け、この表示手段において表示された締付状態の判別結果に応じ、ねじの締付状態が適正であるか否かを作業者が判別するように構成してもよい。
【００６３】
さらに、上記のように測定基準角度θＡを基点とした締付角度ΔθＡの測定値に基づき、予め設定された締付軸力Ｆが得られるようにねじの締付状態を制御する締付状態制御部２２を備えたねじの締付装置において、ねじの締付時における摩擦係数を測定する摩擦係数測定部を設け、この摩擦係数の測定値に基づいてねじの降伏軸力に対応したねじの目標締付角度を上記目標締付角度設定部１４により設定するように構成してもよい。
【００６４】
すなわち、図６に示すように上記摩擦係数に応じて、ねじの締付角度θと締付トルクＴとの関係が変化するため、この関係に基づいて上記ねじの締付時における摩擦係数を摩擦係数測定部により測定するようにしてもよい。そして、上記式（数１）に示すように、上記摩擦係数μに基づいてねじの降伏軸力Ｆｙが変化するため、このねじの降伏軸力Ｆｙに応じて、ねじの能力が最大限に発揮されるように上記目標締付角度を設定することにより、上記摩擦係数μに対応したねじの締付制御を適正に実行することができる。
【００６５】
また、上記のように締付軸力測定部２１により測定されたねじの締付軸力Ｆに基づいてねじの締付状態が適正であるか否かを判別する締付状態判別部を備えたねじの締付装置において、ねじの締付時における摩擦係数を測定する摩擦係数測定部と、この摩擦係数の測定値に基づいてねじの降伏軸力に対応したねじの目標締付軸力を設定する目標締付軸力設定部を設けた構造としてもよい。この場合においても、上記摩擦係数μに応じて変化するねじの降伏軸力Ｆｙに基づき、上記ねじの締付状態が適正であるか否かの判別基準となる締付軸力Ｆの目標値を適正に設定することにより、上記摩擦係数μに対応したねじの締付制御を適正に実行することができる。
【００６６】
【発明の効果】
以上説明したように、本発明に係るねじの締付軸力測定方法及び同装置は、ねじ締付手段を使用したねじの締付過程で、このねじの弾性域における締付トルクの変化量と締付角度の変化量との比からなるトルクレートを求めた後、このトルクレートに基づいてねじの塑性変形量を除いた締付軸力の測定基準角度を求めるとともに、この測定基準角度を基点として締付軸力の測定時点におけるねじの締付角度を測定し、この締付角度の測定値に対応したねじの締付軸力を、予め求めた締付角度と締付軸力との関係から測定するように構成したため、ねじの弾性限度を越えて塑性域までねじを締め付けた場合においても、ねじの締付軸力を正確に測定することができる。
【００６７】
また、本発明に係るねじの締付方法及び同装置は、ねじ締付手段を使用したねじの締付過程で、このねじの弾性域における締付トルクの変化量と締付角度の変化量との比からなるトルクレートを求めた後、このトルクレートに基づいてねじの塑性変形量を除いた締付軸力の測定基準角度を求めるとともに、この測定基準角度を基点として締付軸力の測定時点におけるねじの締付角度を測定し、この締付角度の測定値に基づいて、予め設定された締付軸力が得られるようにねじの締付状態を制御するように構成したため、ねじの弾性限度を越えて塑性域までねじを締め付けた場合においても、上記ねじの締付軸力が適正値となるように、ねじの締付状態を容易かつ正確に制御することができる。
【００６８】
さらに、本発明に係るねじの締付方法及び同装置は、ねじ締付手段を使用したねじの締付過程で、このねじの弾性域における締付トルクの変化量と締付角度の変化量との比からなるトルクレートを求めた後、このトルクレートに基づいてねじの塑性変形量を除いた締付軸力の測定基準角度を求めるとともに、この測定基準角度を基点として締付軸力の測定時点におけるねじの締付角度を測定し、この締付角度の測定値に対応したねじの締付軸力を、予め求めた締付角度と締付軸力との関係から求め、この締付軸力に基づいてねじの締付状態が適正であるか否かを判別するように構成したため、ねじの弾性限度を越えて塑性域までねじを締め付けた場合においても、上記ねじの締付軸力が適正であるか否かを容易かつ正確に判別できるという利点がある。
【図面の簡単な説明】
【図１】本発明に係るねじの締付装置の実施形態を示す説明図である。
【図２】ねじの締付制御動作の前半部を示すフローチャートである。
【図３】ねじの締付制御動作の後半部を示すフローチャートである。
【図４】ねじの締付角度と締付トルクとの対応関係を示すグラフである。
【図５】ねじの締付角度と締付軸力との対応関係を示すグラフである。
【図６】摩擦係数の異なるねじを締め付けた場合におけるねじの締付角度と締付トルクとの対応関係を示すグラフである。
【図７】摩擦係数の異なるねじを締め付けた場合におけるねじの締付角度と締付軸力との対応関係を示すグラフである。
【符号の説明】
６ ナットランナ（ねじ締付手段）
１４ 目標締付角度設定部
１８ トルクレート演算部
１９ 基準角度演算部
２０ 締付角度測定部
２１ 締付軸力測定部
２２ 締付状態制御部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a screw tightening axial force measuring method, a screw tightening method using the measuring method, and an apparatus thereof.
[0002]
[Prior art]
The most important factor for determining whether or not a screw is properly tightened is the tightening axial force acting by tightening the screw, but it is difficult to directly measure this tightening axial force. is there. For this reason, conventionally, a torque control method for controlling the tightening state of the screw while monitoring the torque of the drive motor acting at the time of tightening the screw with a torque transducer or the like, or an encoder detection signal for detecting the tightening angle. Using a constant torque / rotation angle control system that terminates screw tightening when it is confirmed that the screw has further rotated from a constant torque to a preset angle, tightening is performed by controlling the tightening state of the screw. Axial force is set within the elastic range.
[0003]
The torque control method is configured to control the tightening state of the screw regardless of the friction coefficient between the seat surface of the screw and the tightened surface. Axial force control cannot be executed. The constant torque / rotation angle control method is also affected by the coefficient of friction between the screw seating surface and the surface to be tightened until constant torque is reached. The axial force of fluctuates.
[0004]
Further, in tightening a screw, torsional stress acts on the screw due to friction between the seating surface of the screw and the surface to be tightened together with the tightening stress. For this reason, when the torsional stress is high, that is, when the friction coefficient is high, the screw yields with a low tightening axial force. In order to control the torque so that the yield of the screw does not occur, the torque is controlled in consideration of the case where the friction coefficient is low. Therefore, in the case of a high friction coefficient, the tightening shaft can reach the limit of the capability of the screw. There is a problem that power cannot be applied. On the other hand, in the constant torque / angle control method, the tightening axial force after tightening greatly varies depending on the set value of the constant torque, and there is a problem that it is difficult to tighten to the limit of the capability of the screw.
[0005]
For this reason, for example, as shown in Japanese Patent No. 2619628, in the first stroke, a torque rate corresponding to the friction coefficient between the screw seating surface and the tightened surface is obtained in the middle of the screw tightening, In the second stroke, the theoretical seating point is calculated from the torque rate. In the third stroke, the theoretical seating point is calculated based on the tightening coefficient determined by the screw size and the spring constant of the tightened body. Theory to elastic limit Tightening Calculate the angle, and in the fourth step, the above theory Tightening It is known that a high tightening axial force can be obtained by fully utilizing the capability of a screw by controlling the tightening angle of the screw based on the angle.
[0006]
[Problems to be solved by the invention]
As shown in the above publication, after obtaining the torque rate corresponding to the friction coefficient during screw tightening, the theoretical seating point is calculated from this torque rate and from the theoretical seating point to the elastic limit point. The theory of Tightening When the angle is set, the tightening axial force can be set within the elastic range of the screw without being affected by the friction coefficient between the seat surface of the screw and the tightened surface. The tightening axial force acting on the screw can be appropriately controlled.
[0007]
However, in order to make full use of the screw capacity to obtain a high tightening axial force, if this tightening axial force is set to a plastic range exceeding the elastic limit of the screw, this plasticity In the region, it is known that the relationship between the screw tightening angle and the tightening axial force changes greatly according to the friction coefficient, and control is performed so that a preset tightening axial force is obtained thereby. There was a problem that I could not.
[0008]
That is, the yield axial force Fy of the screw is expressed by the following equation (Equation 1) defined in JISB 1083, and from this equation (Equation 1), as shown in FIG. When tightened, it can be seen that the tightening axial force F acting on the screw increases as the friction coefficient μ decreases even when the screw tightening angles are equal. In the following equation (Equation 1), σy is the yield axial force of the screw, As is the effective sectional area of the screw, p is the pitch of the screw, ds is the effective diameter of the screw, and U is the full angle of the thread.
[0009]
[Expression 1]

[0010]
In view of such circumstances, the present invention can accurately measure the value corresponding to the tightening axial force of the screw even when the screw is tightened to the plastic region. The present invention provides a screw tightening axial force measuring method capable of appropriately controlling a tightening force, a screw tightening method using the measuring method, and these devices.
[0011]
[Means for Solving the Problems]
According to the first aspect of the present invention, in the process of tightening the screw using the screw tightening means, a torque rate comprising a ratio of a change amount of the tightening torque and a change amount of the tightening angle in the elastic region of the screw is obtained. After that, based on this torque rate, the measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw is obtained, and the screw tightening angle at the time of measurement of the tightening axial force is determined based on this measurement reference angle. The screw tightening axial force corresponding to the measured value of the tightening angle is measured from the relationship between the previously determined tightening angle and the tightening axial force.
[0012]
According to this configuration, it corresponds to the elastic deformation amount of the screw at the time of measuring the tightening axial force, with the measurement reference angle of the tightening axial force excluding the plastic deformation amount of the screw determined according to the torque rate as a base point. The tightening angle of the screw is determined and the tightening axial force corresponding to the tightening angle is measured, so that the screw tightening axial force can be accurately determined even when the screw is tightened to the plastic range. become.
[0013]
According to a second aspect of the present invention, in the screw tightening axial force measuring method according to the first aspect, the torque rate is obtained from the tightening torque corresponding to at least two tightening angles in the elastic region of the screw to be tightened. It is configured.
[0014]
According to this configuration, a torque rate composed of a ratio of a change amount of the tightening torque and a change amount of the tightening angle is easy in the elastic range of the screw in which the screw tightening angle and the tightening torque are in a proportional relationship. And since it is calculated | required appropriately, based on this torque rate, the measurement reference | standard angle of the fastening axial force except the amount of plastic deformation of the screw corresponding to the amount of elastic deformation of a screw will be calculated | required correctly.
[0015]
According to a third aspect of the present invention, in the tightening axial force measuring method according to the first or second aspect, the elasticity of the screw passes through a measurement point of a coordinate system having the screw tightening angle and the tightening torque as coordinate axes. The intersection of the line extending in parallel with the torque gradient in the region and the line where the tightening torque of the coordinate system is 0 is obtained, and the tightening angle of this intersection is set as the measurement reference angle of the tightening axial force It is a thing.
[0016]
According to this configuration, the measurement reference angle excluding the amount of plastic deformation of the screw can be easily and appropriately obtained from the coordinate system having the screw tightening angle and the tightening torque as coordinate axes, and the measurement reference angle is used as a base point. A tightening angle corresponding to the amount of elastic deformation of the screw at the time of measuring the tightening axial force is accurately obtained.
[0017]
According to a fourth aspect of the present invention, there is provided the tightening axial force measuring method according to any one of the first to third aspects, wherein the screw is displayed in a coordinate system having the screw tightening angle and the tightening torque as coordinate axes. After obtaining the intersection of the torque gradient extension line in the elastic region and the line where the tightening torque of the above coordinate system is 0, and setting the coordinates of this intersection as the theoretical seating point, the theoretical seating point is used as the base point. While measuring the tightening angle at the time of measuring the tightening axial force, obtaining the measurement reference angle, and subtracting the measurement reference angle from the measured value of the tightening angle, tightening with this measurement reference angle as the base point The screw tightening angle at the time of measuring the axial force is obtained.
[0018]
According to this configuration, from the coordinate system having the screw tightening angle and tightening torque as the coordinate axes, the tightening is performed by removing the plastic deformation amount of the screw at the time of measuring the tightening axial force from the theoretical seating point. The angle is obtained easily and appropriately, and the tightening axial force corresponding to the elastic deformation amount of the screw is accurately obtained based on the tightening angle.
[0019]
In the invention according to claim 5, in the process of tightening the screw using the screw tightening means, a torque rate comprising a ratio of a change amount of the tightening torque and a change amount of the tightening angle in the elastic region of the screw is obtained. After that, based on this torque rate, the measurement reference angle of the tightening axial force excluding the plastic deformation amount of the screw is obtained, and the tightening angle of the screw at the time of measurement of the tightening axial force is determined based on this measurement reference angle. Based on the measured value of this tightening angle, the tightening state of the screw is controlled so as to obtain a preset tightening axial force.
[0020]
According to this configuration, the measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw is obtained based on the torque rate, and the tightening axial force is measured using the measurement reference angle as a base point. The tightening angle corresponding to the amount of elastic deformation of the screw at the time is determined easily and appropriately, and the tightening state of the screw is controlled based on the measured value of the tightening angle, so that the screw is tightened to the plastic range. Even in this case, the screw tightening axial force is adjusted so as to have a preset appropriate value.
[0021]
The invention according to claim 6 is the screw tightening using the screw tightening means. In the process Then, a torque rate comprising the ratio of the change amount of the tightening torque and the change amount of the tightening angle in the elastic region of the screw is obtained, and the tightening axial force is measured by excluding the plastic deformation amount of the screw based on the torque rate. Determine the reference angle, measure the tightening angle of the screw at the time of measuring the tightening axial force with this measurement reference angle as the base point, and obtain the tightening axial force of the screw corresponding to the measured value of the tightening angle in advance. After measuring from the relationship between the tightening angle and the tightening axial force, it is determined whether or not the tightening state of the screw is appropriate based on the measured value of the tightening axial force.
[0022]
According to this configuration, screw tightening Tightening process The measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw is obtained from the measurement reference angle obtained according to the torque rate as described above, and the tightening axial force is measured using the measurement reference angle as the reference point. When the tightening angle corresponding to the amount of elastic deformation of the screw at the time is determined easily and appropriately, and the tightening axial force corresponding to the measured value of the tightening angle is determined, the screw is tightened to the plastic range. In addition, the tightening axial force of the screw is accurately obtained, and whether or not the tightening state of the screw is proper is accurately determined based on the measured value of the tightening axial force.
[0023]
In the invention according to claim 7, in the process of tightening the screw using the screw tightening means, a torque rate comprising a ratio of a change amount of the tightening torque and a change amount of the tightening angle in the elastic region of the screw is obtained. A torque rate calculation unit, a reference angle calculation unit for determining a measurement reference angle of the tightening axial force excluding the plastic deformation amount of the screw based on the calculated value of the torque rate, and a measurement reference obtained by the reference angle calculation unit A tightening angle measuring unit that measures the tightening angle of the screw at the time of measuring the tightening axial force with the angle as a base point, and the tightening axial force corresponding to the measured value of the tightening angle is determined as A tightening axial force measurement unit obtained from the relationship with the tightening axial force is provided.
[0024]
According to this configuration, the measurement reference angle of the tightening axial force excluding the plastic deformation amount of the screw based on the torque rate obtained by the torque rate calculation unit is obtained by the reference angle calculation unit, and the measurement reference When the tightening angle corresponding to the amount of elastic deformation of the screw when measuring the tightening axial force with the angle as the base point is obtained accurately and easily by the tightening angle measuring section, the screw is tightened to the plastic range. Even in this case, the tightening axial force corresponding to the tightening angle obtained by the tightening angle measuring unit can be accurately obtained by the tightening axial force measuring unit.
[0025]
According to an eighth aspect of the present invention, there is provided the screw tightening axial force measuring device according to the seventh aspect, wherein the torque rate calculation unit is based on a tightening torque corresponding to at least two tightening angles within an elastic region of the screw to be tightened. Thus, the torque rate is obtained.
[0026]
According to this configuration, the torque rate, which is the ratio between the change amount of the tightening torque and the change amount of the tightening angle, is within the elastic range of the screw in which the screw tightening angle and the tightening torque are in a proportional relationship. It will be calculated | required appropriately in a rate calculating part.
[0027]
According to a ninth aspect of the present invention, in the screw tightening axial force measuring device according to the seventh or eighth aspect, the screw passes through a measurement point of a coordinate system having the screw tightening angle and the tightening torque as coordinate axes. The reference angle calculator determines the tightening angle at the intersection of the line extending in parallel with the torque gradient in the elastic region and the line where the tightening torque in the coordinate system is 0, and the tightening angle at this intersection is determined by the tightening axis. It is configured to be set as a force measurement reference angle.
[0028]
According to this configuration, the measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw is easily and appropriately obtained from the coordinate system having the screw tightening angle and the tightening torque as the coordinate axes. A tightening angle corresponding to the amount of elastic deformation of the screw at the time of measuring the tightening angle with the reference angle as a base point is accurately obtained.
[0029]
The invention according to claim 10 is the screw tightening axial force measuring device according to any of claims 7 to 9, wherein the screw tightening axial force measuring device is displayed in a coordinate system having the screw tightening angle and the tightening torque as coordinate axes. Find the intersection of the extension line of the torque gradient in the elastic region of the screw and the line where the tightening torque in the above coordinate system is 0, set the coordinate of this intersection as the theoretical seating point, and use this theoretical seating point as the base point The tightening angle at the time of measurement of the tightening axial force is measured by the tightening angle measuring unit, the measurement reference angle is obtained by the reference angle calculating unit, and the measurement reference angle of the tightening axial force is determined from the measured value of the tightening angle. By subtracting, the tightening angle at the time of measurement of the tightening axial force with the measurement reference angle as a base point is obtained.
[0030]
According to this configuration, the tightening force at the time of measurement of the tightening axial force excluding the amount of plastic deformation of the screw from the coordinate system with the screw tightening angle and the tightening torque as the coordinate axes from the theoretical seating point as a base point. The tightening angle is measured easily and appropriately by the tightening angle measuring unit, and the tightening axial force corresponding to the elastic deformation amount of the screw is accurately measured by the tightening axial force measuring unit based on the measured value of the tightening angle. By measuring, even when the screw is tightened to the plastic region, the tightening axial force of the screw can be accurately obtained.
[0031]
According to an eleventh aspect of the present invention, in the process of tightening the screw using the screw tightening means, a torque rate comprising a ratio of a change amount of the tightening torque and a change amount of the tightening angle in the elastic region of the screw is obtained. A torque rate calculation unit, a reference angle calculation unit for determining a measurement reference angle of the tightening axial force excluding the plastic deformation amount of the screw based on the calculated value of the torque rate, and a measurement order obtained by the reference angle calculation unit A tightening angle measuring unit that measures the tightening angle of the screw at the time of measuring the tightening axial force with the angle as a base point, and a preset tightening axial force based on the measured value of the tightening angle. And a tightening state control unit for controlling the tightening state of the screw.
[0032]
According to this configuration, the measurement reference angle of the tightening axial force excluding the plastic deformation amount of the screw is determined by the reference angle calculation unit based on the torque rate determined by the torque rate calculation unit, and the reference The tightening angle corresponding to the amount of elastic deformation of the screw at the time of measurement of the tightening axial force is measured easily and appropriately by the tightening angle measuring section with the measurement reference angle obtained by the angle calculation section as the base point. The tightening state of the screw is controlled by the tightening state control unit based on the measured value of the angle, so that even when the screw is tightened to the plastic range, the screw tightening axial force is set to an appropriate value. Will be adjusted.
[0033]
According to a twelfth aspect of the present invention, in the process of tightening the screw using the screw tightening means, a torque rate comprising a ratio of a change amount of the tightening torque and a change amount of the tightening angle in the elastic region of the screw is obtained. A torque rate calculation unit, a reference angle calculation unit for obtaining a measurement reference angle of the tightening axial force excluding the plastic deformation amount of the screw based on the calculated value of the torque rate, and a measurement reference calculated by the reference angle calculation unit The tightening angle measuring unit that measures the tightening angle of the screw when measuring the tightening axial force from the angle as the base point, and the tightening axial force of the screw corresponding to the measured value of the tightening angle The tightening axial force measurement unit measured from the relationship between the angle and the tightening axial force, and whether the screw is tightened properly based on the screw tightening axial force measured by the tightening axial force measurement unit A tightening state determining unit for determining whether or not.
[0034]
According to this configuration, the measurement reference angle of the tightening axial force excluding the plastic deformation amount of the screw is obtained by the reference angle calculation unit based on the torque rate obtained by the torque rate calculation unit, and the measurement After the tightening angle of the screw corresponding to the amount of elastic deformation of the screw at the time of measuring the tightening axial force is measured by the tightening angle measuring means based on the calculated value of the reference angle, the measured value of the tightening axial force is measured. And whether or not the tightening state of the screw is appropriate even when the screw is tightened to the plastic range by comparing the preset target value of the tightening axial force in the tightening state determination unit, etc. Is accurately determined.
[0035]
According to a thirteenth aspect of the present invention, in the screw tightening apparatus according to the twelfth aspect of the present invention, the screw tightening apparatus includes a display unit that displays a result of determining the tightening state of the screw by the tightening state determining unit.
[0036]
According to the above configuration, whether or not the screw tightening state is appropriate is easily and appropriately determined according to the determination result of the screw tightening state displayed on the display means.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of a screw tightening device according to the present invention. The screw tightening device includes a socket 1 engaged with a screw head, a torque transducer 2 for adjusting a torque applied to the screw by the socket 1, and a screw tightened by the socket 1. A tightening torque detector 3 that detects torque, a drive motor 4 that rotationally drives the socket 1, and an angle encoder 5 that measures the tightening angle of the screw by detecting the rotation angle of the drive motor 4 are provided. Screw tightening means comprising a nut runner 6 is provided.
[0038]
The screw tightening device includes a first tightening torque setting unit 7 for setting a first tightening torque within the elastic range of the screw, and a first value larger than the first tightening torque within the elastic range of the screw. A second tightening torque setter 8 for setting two tightening torques, a screw tightening torque detected by the tightening torque detector 3 and a first tightening torque set by the first tightening torque setter 7. A first comparator 9 that compares the torque and outputs a coincidence signal of both torques, and the screw tightening torque detected by the tightening torque detector 3 and the second tightening torque setter 8. The second comparator 10 that compares the second tightening torque and outputs a coincidence signal of both torques, and outputs a control signal corresponding to the coincidence signal output from the first and second comparators 9 and 10 to the CPU 11. 1st and 2nd And a Na log switches 12 and 13.
[0039]
The screw tightening device further includes a target tightening angle setting unit 14 for setting a target tightening angle corresponding to a target value of the tightening axial force generated by tightening the screw, and the first and second analogs. An angle gate 15 for inputting a control signal for measuring the detection angle of the angle encoder 5 at the time when the control signal is output from the switches 12 and 13 to the CPU 11, and the drive motor according to the control signal output from the CPU 11 4 and a display means 17 for displaying the screw tightening axial force in accordance with a control signal output from the CPU 11.
[0040]
Further, the CPU 11 obtains a torque rate calculation unit 18 for obtaining a torque rate which is a ratio of a change amount of the tightening torque and a change amount of the tightening angle in the elastic region of the screw in the process of tightening the screw by the nut runner 6. A reference angle calculation unit 19 for obtaining a measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw based on the torque rate obtained by the torque rate calculation unit 18; The tightening angle measuring unit 20 that measures the tightening angle of the screw at the time of measuring the tightening axial force with the measured reference angle as a base point, and the tightening angle corresponding to the tightening angle measured by the tightening angle measuring unit 20 The tightening axial force measuring unit 21 that measures the axial force from the relationship between the previously determined tightening angle and the tightening axial force, and the screw angle based on the tightening angle measured by the tightening angle measuring unit 20. Tightening state And tightening state control unit 22 Gosuru is provided.
[0041]
Next, the screw tightening axial force measuring method executed when the screw is tightened by the screw tightening device and the screw tightening method using this measuring method will be described with reference to the flowcharts shown in FIGS. To do. First, in step S1, according to the operation of an input switch (not shown), the drive motor 4 of the nut runner 6 is rotated to start screw tightening, and then in step S2, an input means such as a keyboard (not shown) is used. A first tightening torque T1 corresponding to the size of the screw is set by the first setting device 7. Next, in step S3, the tightening torque is detected. vessel The screw tightening torque T detected by 3 and the first tightening torque T1 are compared by the first comparator 9 to determine whether the torques T and T1 are equal.
[0042]
If YES is determined in step S3, the angle gate 15 is turned on in step S4, and the measured value of the screw tightening angle θ1 at this time is input. In step S5, the screw size is set. The corresponding second tightening torque T2 is set by the second setting device 8. Next, in step S6, the tightening torque is detected. vessel The screw tightening torque T detected in step 3 and the second tightening torque T2 are compared by the second comparator 10 to determine whether or not both torques T and T2 are equal.
[0043]
If YES is determined in step S6, the angle gate 15 is turned off in step S7, and the measured value of the screw tightening angle θ2 at this time is input. In step S8, the first and first 2 Based on the detected values of the tightening torques T1 and T2 and the tightening angles θ1 and θ2 of the screw, the amount of change ΔT (= T2−T1) of the tightening torque T in the elastic region of the screw and the tightening angle θ A torque rate C comprising a ratio to the change amount Δθ (= θ2−θ1) is calculated by the torque rate calculation unit 18. Thereafter, in step S9, the theoretical seating point θO of the screw is calculated by the reference angle calculation unit 19 based on the torque rate C.
[0044]
That is, at the beginning of screw tightening, after a certain slip corresponding to the coefficient of friction between the screw seating surface and the surface to be tightened occurs, within the elastic region, as shown in FIG. Since the tightening torque T increases in proportion to the tightening angle θ, the tightening torque T change amount ΔT (= T2−T1) and the tightening angle θ change amount Δθ (= θ2−θ1) are used. Torque rate C (= ΔT / Δθ) is calculated. Then, the torque gradient α in the elastic region of the screw displayed in the coordinate system shown in FIG. 4 with the screw tightening angle θ and the tightening torque T as coordinate axes, that is, measured when calculating the torque rate C within the elastic region. The intersection of the extension line of the straight line α indicating the change state of the tightening torque T and the line where the tightening torque T of the coordinate system is 0, that is, the horizontal axis of the coordinate system is obtained, and the coordinates of this intersection are calculated theoretically. By setting as the seating point θO, a theoretical seating point assuming that there is no slippage between the seating surface of the screw and the tightening surface is obtained.
[0045]
Next, in step S10, after inputting the detected value TB of the current tightening torque T, which is the time of measurement of the tightening axial force, and the detected value θB of the tightening angle θ, in step S11, the screw tightening angle. A line β extending parallel to the torque gradient α in the elastic region of the screw through the measurement point B in the coordinate system shown in FIG. 4 with θ and the tightening torque T as coordinate axes, and the tightening torque T in the coordinate system is 0. The intersection with the line (horizontal axis) is calculated by the reference angle calculation unit 19 and the tightening angle θ of this intersection is set as the measurement reference angle θA of the tightening axial force.
[0046]
In step S12, a change amount ΔθA (= θB−θA) of the tightening angle θ from the measurement reference angle θA to the current tightening angle θB is calculated by the tightening angle measuring unit 20 to obtain the change. After setting the amount ΔθA as the tightening angle ΔθA at the time of measuring the tightening axial force, in step S13, the screw tightening axial force FA corresponding to the tightening angle ΔθA is set to the tightening angle θ set in advance. The tightening axial force measurement unit 21 measures the axial force F in relation to the axial force F and displays the tightening axial force FA on the display means 17.
[0047]
That is, assuming that the screw tightening starts from the theoretical seating point θO of the screw, the tightening axial force is proportional to the screw tightening angle θ within the elastic range of the screw as shown in FIG. When F is changed and the screw tightening axial force F exceeds the elastic range FC, the screw is plastically deformed. Therefore, the proportional relationship between the screw tightening angle θ and the tightening axial force F is lost, and tightening is performed. There is a tendency that the increase amount of the tightening axial force F with respect to the increase amount of the angle θ gradually decreases. Then, after tightening the screw until the tightening axial force FA slightly exceeding the elastic region FC is reached, when the tensile load is removed from the plastic region of the screw, a line parallel to the screw displacement line α1 in the elastic region The tightening axial force F decreases along β1, and the screw is tightened from the theoretical seating point θO to the tightening angle θA at the intersection of the line β1 and the horizontal axis of the coordinate system shown in FIG. Plastic deformation corresponding to the change amount ΔθO of the angle θ occurs.
[0048]
When the screw is tightened until the tightening axial force FA slightly exceeds the elastic range FC as described above, the measurement reference angle θA of the tightening axial force F excluding the plastic deformation amount ΔθO of the screw. The tightening axial force F changes in proportion to the tightening angle of the screw with reference to. In the elastic range of the screw, since there is a relationship expressed by the following equation (Equation 2), the tightening axial force F corresponding to the tightening angle θ of the screw is obtained from this equation (Equation 2), or obtained in advance. The tightening axial force F can be estimated from the experimental data. In the following formula (Equation 2), p is the pitch of the screw, Kb is the tension spring constant of the screw, and Kc is the compression spring constant of the tightened body.
[0049]
[Expression 2]

[0050]
Therefore, in the coordinate system shown in FIG. 4, the intersection of a line β extending parallel to the torque gradient α in the elastic region of the screw through the measurement point B and a line where the tightening torque T of the coordinate system is 0 is obtained. Then, the tightening angle θ of this intersection is set as the measurement reference angle θA of the tightening axial force F, and the change amount ΔθA of the tightening angle θ from the measurement reference angle θA to the current tightening angle θB is obtained, and this change By setting the amount ΔθA as the tightening angle ΔθA at the time of measurement with the measurement reference angle θA as a base point, the current tightening axial force is based on the tightening angle ΔθA and the above equation (Equation 2). F can be obtained. That is, by subtracting the amount of plastic deformation ΔθO of the tightening angle θ obtained from the theoretical seating point θO as the base point from the change amount ΔθB of the tightening angle θ measured at the present time using the theoretical seating point θO as the base point, A change amount ΔθA of the tightening angle θ from the axial force reference angle θA to the current tightening angle θB can be obtained, and the tightening axial force FA can be indirectly measured based on the change amount ΔθA.
[0051]
Next, in step S14, the target tightening angle θa initially required for the tightening part is set by the target tightening angle setting unit 14 based on the screw size or the like input by the input means, and then in step S15. Whether the screw tightening axial force F has reached the target value by comparing the target tightening angle θa with the tightening angle ΔθA based on the measurement reference angle θA obtained in step S12. Is determined by the tightening state control unit 22. If it is determined NO in step S15, the process returns to step S10 and the screw tightening operation is continued.
[0052]
Then, when the determination in step S15 is YES, the tightening angle ΔθA based on the measurement reference angle θA corresponding to the current tightening axial force F is equal to the target tightening angle θa, and the screw tightening is performed. When it is confirmed that the axial force F has reached the target value, a control signal for stopping the drive motor 4 of the nut runner 6 constituting the screw tightening means is sent from the tightening state control unit 22 in step S16. Output to the servo amplifier 16 to finish the screw tightening operation.
[0053]
Thus, in the process of tightening the screw using the screw tightening means comprising the nut runner 6, the torque comprising the ratio of the change amount ΔT of the tightening torque T and the change amount Δθ of the tightening angle θ in the elastic region of the screw. After obtaining the rate C, the measurement reference angle θA of the tightening axial force F obtained by removing the plastic deformation amount ΔθO of the screw from the torque rate C is obtained, and the tightening axial force F is determined based on the measurement reference angle θA. The screw tightening angle ΔθA at the time of measurement is measured, and the screw tightening axial force F corresponding to the tightening angle ΔθA is determined from the relationship between the previously determined tightening angle θ and the tightening axial force F. Since the axial force measurement unit 21 measures the screw, the screw tightening axial force F can be accurately measured even when the screw is tightened to the plastic range beyond the elastic limit of the screw. Based on the measured value of axial force F, It is possible to properly control the urging state.
[0054]
That is, in the screw of the same size, as shown in FIG. 6, the screw H having a high friction coefficient between the screw seating surface and the tightened surface and the screw L having a low friction coefficient exceed the elastic limit. When tightened to the plastic range, the screw H having a high friction coefficient requires a larger tightening torque T to tighten the screw than the screw L having a low friction coefficient, and tends to exceed the elastic limit at an early stage. Therefore, in tightening by angle control from θO, the amount of plastic deformation ΔθO generated after tightening tends to increase. When the screw is tightened until the tightening axial force F slightly exceeds the elastic range as described above, the measurement reference angle θA of the tightening axial force F excluding the plastic deformation amount ΔθO of the screw is set. Since it is known that the fastening axial force F changes in proportion to the fastening angle θ of the screw as the base point, the measurement reference angle θA of the fastening axial force F excluding the plastic deformation amount ΔθO is obtained, By measuring the tightening angle ΔθA of the screw at the time of measuring the tightening axial force F using the measurement reference angle θA as a base point, the tightening angle ΔθA of the screw, the previously determined tightening angle θ and the tightening shaft are measured. From the relationship with the force F, the tightening axial force F can be appropriately obtained in the screw tightening process.
[0055]
Therefore, the tightening angle θ changes from the theoretical seating point θO to the tightening axial force F measurement time ΔθB, and the tightening angle θ change ΔθA is obtained by subtracting the plastic deformation amount ΔθO from the tightening angle change ΔθB. The tightening axial force F measured by the attached axial force measuring unit 21 is displayed on the display means 17, and the screw tightening state is controlled while observing this display, so that the screw H in the screw H having a high friction coefficient is screwed. The tightening amount of the screw can be adjusted so that the ability of the screw can be maximized. Further, even in the screw L having a small friction coefficient, the screw H and the screw H are controlled by controlling the tightening state of the screw so that the target tightening axial force is set to the same value as that of the screw H having the high friction coefficient. By setting the same tightening axial force, the screw capability can be fully exerted.
[0056]
Then, after completion of the screw tightening operation, it is determined whether or not the screw tightening state is appropriate according to the tightening axial force F displayed on the display means 17, and the tightening axial force F is If it is smaller than the target value, the screw is further tightened and tightened. Conversely, if the tightening axial force F is larger than the target value, it is judged that the screw tightening amount is excessive. It is possible to surely prevent the occurrence of screw tightening failure such as replacement with a new screw.
[0057]
In the above embodiment, since the torque rate C is obtained from the tightening torques T1 and T2 corresponding to at least two tightening angles θ1 and θ2 in the elastic range of the screw to be tightened, the screw tightening angle θ And the torque rate C, which is the ratio of the change amount ΔT of the tightening torque and the change amount Δθ of the tightening angle, within the elastic range of the screw in which the tightening torque T is in a proportional relationship. Based on the torque rate C, the measurement reference angle θB of the tightening axial force F excluding the plastic deformation amount ΔθO of the screw can be accurately obtained.
[0058]
Furthermore, in the above embodiment, the line β extending in parallel with the torque gradient α in the elastic region of the screw through the measurement point B of the coordinate system having the screw tightening angle θ and the tightening torque T as coordinate axes, and the coordinate system Since the intersecting point with the line where the tightening torque is zero is determined, and the tightening angle θ of the intersecting point is set as the measurement reference angle θA of the tightening axial force F, the plastic deformation of the screw is determined from the above coordinate system. amount ΔθO The measurement reference angle θA excluding the above can be obtained easily and properly, and the tightening angle ΔθA of the screw at the time of measurement of the tightening axial force F can be accurately obtained using the measurement reference angle θB as a base point.
[0059]
In addition, as shown in the above embodiment, the extension line of the torque gradient α in the elastic region of the screw displayed in the coordinate system with the screw tightening angle θ and the tightening torque T as the coordinate axes, and the tightening of the coordinate system The intersection point with the line where the torque becomes 0 is obtained, the coordinates of this intersection point are set as the theoretical seating point θO, and then the tightening angle θB at the time of measuring the tightening axial force F is measured using the theoretical seating point θO as a base point. The screw tightening angle excluding the screw plastic deformation amount ΔθO by obtaining the measurement reference angle θA from the theoretical seating point θO as a base point and subtracting the measurement reference angle θA from the measured value of the tightening angle θB. When configured to obtain ΔθA, the screw tightening angle ΔθA excluding the plastic deformation amount ΔθO of the screw is easily and appropriately measured based on the tightening angle θ measured using the same seating point θO as a base point. To do Kill.
[0060]
In the above embodiment, the reference angle calculation unit 19 obtains the measurement reference angle θA of the tightening axial force F excluding the plastic deformation amount ΔθO of the screw based on the calculated value of the torque rate C, and the reference angle calculation unit 19, the screw tightening angle ΔθA at the time of measurement of the tightening axial force F is measured by the tightening angle measuring unit 20 with the measurement reference angle θA obtained in 19 as a base point. Based on the measured value of the tightening angle ΔθA, The tightening state control unit 22 controls the tightening state of the screw so that the set tightening axial force F is obtained. In the tightening state control unit 22, the measured value of the tightening angle ΔθA is set in advance. The screw tightening operation is completed by comparing the target tightening angle θa and the screw tightening operation is finished when the two coincide with each other. Therefore, the screw tightening operation is automated to appropriately control the screw tightening amount. be able to.
[0061]
In place of the above-described embodiment, a tightening state determination unit that determines whether the screw tightening state is appropriate based on the screw tightening axial force F measured by the tightening axial force measurement unit 21. In this tightening state discriminating section, the measured value of the tightening axial force F is compared with a preset target value of the tightening axial force F, and when the two values coincide with each other, the screw tightening operation is performed. It is good also as a structure which provided the tightening state control part which complete | finishes. When configured in this manner, the tightening state of the screw can be more accurately controlled based on the tightening axial force F of the screw.
[0062]
Also, the above tightening state determination Part Display means for displaying the result of determining the tightening state of the screw is provided, and the operator determines whether the tightening state of the screw is appropriate according to the result of determining the tightening state displayed on the display means. You may comprise.
[0063]
Further, a tightening state control for controlling the tightening state of the screw so as to obtain a preset tightening axial force F based on the measured value of the tightening angle ΔθA with the measurement reference angle θA as a base point as described above. In the screw tightening device provided with the portion 22, a friction coefficient measuring unit for measuring a friction coefficient at the time of screw tightening is provided, and the screw target corresponding to the yield axial force of the screw based on the measured value of the friction coefficient The tightening angle may be set by the target tightening angle setting unit 14.
[0064]
That is, as shown in FIG. 6, the relationship between the screw tightening angle θ and the tightening torque T changes according to the friction coefficient, and the friction coefficient at the time of tightening the screw is determined based on this relationship. You may make it measure by a coefficient measurement part. Then, as shown in the above formula (Equation 1), since the yield axial force Fy of the screw changes based on the friction coefficient μ, the capability of the screw is exhibited to the maximum according to the yield axial force Fy of the screw. Thus, by setting the target tightening angle, the screw tightening control corresponding to the friction coefficient μ can be properly executed.
[0065]
In addition, a tightening state discriminating unit for discriminating whether or not the screw tightening state is appropriate based on the screw tightening axial force F measured by the tightening axial force measuring unit 21 as described above is provided. In the screw tightening device, the friction coefficient measurement unit that measures the friction coefficient when tightening the screw, and the target tightening axial force of the screw corresponding to the yield axial force of the screw is set based on the measured value of the friction coefficient The target tightening axial force setting unit may be provided. Even in this case, the target value of the tightening axial force F, which is a criterion for determining whether or not the tightening state of the screw is appropriate, is determined based on the yield axial force Fy of the screw that changes according to the friction coefficient μ. By appropriately setting, the screw tightening control corresponding to the friction coefficient μ can be properly executed.
[0066]
【The invention's effect】
As described above, the screw tightening axial force measuring method and apparatus according to the present invention are the amount of change in tightening torque in the elastic region of the screw during the screw tightening process using the screw tightening means. After obtaining the torque rate that is the ratio to the change amount of the tightening angle, obtain the measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw based on this torque rate. Measure the tightening angle of the screw at the time of measuring the tightening axial force, and determine the tightening axial force of the screw corresponding to the measured value of the tightening angle as Therefore, even when the screw is tightened to the plastic region beyond the elastic limit of the screw, the screw tightening axial force can be accurately measured.
[0067]
Further, the screw tightening method and device according to the present invention include the amount of change in the tightening torque and the amount of change in the tightening angle in the elastic region of the screw in the screw tightening process using the screw tightening means. After obtaining the torque rate consisting of the ratio of the torque, based on this torque rate, determine the measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw, and measure the tightening axial force using this measurement reference angle as a base point. Since the screw tightening angle at the time is measured, and the tightening state of the screw is controlled based on the measured value of the tightening angle so as to obtain a preset tightening axial force. Even when the screw is tightened to the plastic range beyond the elastic limit, the tightening state of the screw can be easily and accurately controlled so that the tightening axial force of the screw becomes an appropriate value.
[0068]
Furthermore, the screw tightening method and apparatus according to the present invention include a screw tightening means using a screw tightening means. In the tightening process After obtaining a torque rate comprising the ratio of the amount of change in tightening torque and the amount of change in tightening angle in the elastic region of the screw, the tightening axial force excluding the amount of plastic deformation of the screw based on this torque rate Measure the screw tightening angle at the time of measuring the tightening axial force with this measurement reference angle as the base point, and determine the screw tightening axial force corresponding to the measured value of the tightening angle. Since it is determined from the relationship between the previously determined tightening angle and the tightening axial force, and based on this tightening axial force, it is configured to determine whether the tightening state of the screw is appropriate. Even when the screw is tightened to the plastic range, there is an advantage that it can be easily and accurately determined whether or not the tightening axial force of the screw is appropriate.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an embodiment of a screw tightening device according to the present invention.
FIG. 2 is a flowchart showing a first half of a screw tightening control operation;
FIG. 3 is a flowchart showing the latter half of the screw tightening control operation;
FIG. 4 is a graph showing a correspondence relationship between a screw tightening angle and a tightening torque.
FIG. 5 is a graph showing a correspondence relationship between a screw tightening angle and a tightening axial force.
FIG. 6 is a graph showing a correspondence relationship between screw tightening angles and tightening torques when screws having different friction coefficients are tightened.
FIG. 7 is a graph showing a correspondence relationship between a screw tightening angle and a tightening axial force when screws having different friction coefficients are tightened.
[Explanation of symbols]
6 Nutrunner (screw tightening means)
14 Target tightening angle setting section
18 Torque rate calculator
19 Reference angle calculator
20 Tightening angle measurement unit
21 Tightening axial force measurement unit
22 Tightening state controller

Claims (13)

In the tightening process of the screw using the screw tightening means, after obtaining a torque rate that is the ratio of the change amount of the tightening torque and the change amount of the tightening angle in the elastic region of the screw, the torque rate is calculated based on the torque rate. The measurement reference angle of the tightening axial force excluding the plastic deformation amount of the screw is obtained, and the screw tightening angle at the time of measurement of the tightening axial force is measured using this measurement reference angle as a base point. A screw tightening axial force measuring method characterized in that a screw tightening axial force corresponding to a measured value is measured from a relationship between a predetermined tightening angle and a tightening axial force. 2. The screw tightening axial force measuring method according to claim 1, wherein the torque rate is calculated from a tightening torque corresponding to at least two tightening angles in an elastic region of the screw to be tightened. Screw tightening axial force measurement method. 3. The tightening axial force measuring method according to claim 1, wherein the line extends in parallel with the torque gradient in the elastic region of the screw through a measurement point of a coordinate system having the screw tightening angle and the tightening torque as coordinate axes. And a line at which the tightening torque of the coordinate system is zero, and a tightening angle of the intersection is set as a measurement reference angle of the tightening axial force. Axial force measurement method. The tightening axial force measuring method according to any one of claims 1 to 3, wherein the torque gradient extension line in the elastic region of the screw is displayed in a coordinate system having the screw tightening angle and the tightening torque as coordinate axes. And an intersection with the line where the tightening torque in the coordinate system is zero, and the coordinates of the intersection are set as the theoretical seating point, and then the tightening force at the time of measurement of the tightening axial force with the theoretical seating point as the base point. In addition to measuring the attachment angle, obtaining the measurement reference angle, and subtracting the measurement reference angle from the measurement value of the tightening angle, the screw tightening at the time of measurement of the tightening axial force based on the measurement reference angle is performed. A method for measuring a tightening axial force of a screw, characterized in that the angle is determined. In the tightening process of the screw using the screw tightening means, after obtaining a torque rate that is the ratio of the change amount of the tightening torque and the change amount of the tightening angle in the elastic region of the screw, the torque rate is calculated based on the torque rate. The measurement reference angle of the tightening axial force excluding the plastic deformation amount of the screw is obtained, and the screw tightening angle at the time of measurement of the tightening axial force is measured using this measurement reference angle as a base point. A screw tightening method using a screw tightening axial force measuring method, wherein the tightening state of a screw is controlled so as to obtain a preset tightening axial force based on a measured value. In the process of tightening the screw using the screw tightening means, a torque rate that is the ratio of the change amount of the tightening torque and the change amount of the tightening angle in the elastic region of the screw is obtained, and the screw rate is determined based on the torque rate. The measurement angle of the tightening axial force, excluding the amount of plastic deformation, is measured, and the tightening angle of the screw at the time of measuring the tightening axial force is measured using this measurement reference angle as a base point. After measuring the tightening axial force of the screw corresponding to the above-mentioned relationship between the tightening angle and the tightening axial force, the screw tightening state is appropriate based on the measured value of the tightening axial force. Or a screw tightening method using a screw tightening axial force measuring method. A torque rate calculation unit for obtaining a torque rate comprising a ratio of a change amount of the tightening torque and a change amount of the tightening angle in the elastic region of the screw in the screw tightening process using the screw tightening means; A reference angle calculation unit that calculates the measurement reference angle of the tightening axial force excluding the amount of plastic deformation of the screw based on the calculated value of the rate, and the tightening axial force based on the measurement reference angle obtained by this reference angle calculation unit From the relationship between the tightening angle and the tightening axial force obtained in advance, the tightening angle measuring section that measures the tightening angle of the screw at the time of measurement and the tightening axial force corresponding to the measured value of the tightening angle A screw tightening axial force measuring device comprising: a tightening axial force measuring unit to be obtained. 8. The screw tightening axial force measuring device according to claim 7, wherein the torque rate calculating unit obtains a torque rate from a tightening torque corresponding to at least two tightening angles within an elastic region of the screw to be tightened. A screw tightening axial force measuring device characterized by that. 9. The screw tightening axial force measuring device according to claim 7, wherein the screw tightening axial force measuring device is parallel to the torque gradient in the elastic region of the screw through a measurement point of a coordinate system having the screw tightening angle and the tightening torque as coordinate axes. The reference angle calculation unit obtains the tightening angle at the intersection of the extending line and the line where the tightening torque in the coordinate system is 0, and sets the tightening angle at the intersection as the measurement reference angle of the tightening axial force. A screw tightening axial force measuring device characterized by comprising: The screw tightening axial force measuring device according to any one of claims 7 to 9, wherein the torque gradient in the elastic region of the screw is displayed in a coordinate system having the screw tightening angle and the tightening torque as coordinate axes. Find the intersection of the extension line and the line where the tightening torque in the above coordinate system is 0, set the coordinate of this intersection as the theoretical seating point, and tighten the tightening axial force at the time of measurement of the tightening axial force with this theoretical seating point as the base point. The measurement angle is measured by the tightening angle measurement unit, the measurement reference angle is obtained by the reference angle calculation unit, and the measurement reference angle of the tightening axial force is subtracted from the measurement value of the tightening angle. An apparatus for measuring a tightening axial force of a screw, characterized in that a tightening angle at the time of measuring the tightening axial force with respect to the angle is obtained. A torque rate calculation unit for obtaining a torque rate comprising a ratio of a change amount of the tightening torque and a change amount of the tightening angle in the elastic region of the screw in the screw tightening process using the screw tightening means; A reference angle calculation unit for obtaining a measurement reference angle of the tightening axial force excluding the plastic deformation amount of the screw based on the calculated value of the rate, and a tightening axial force based on the measurement reference angle calculated by the reference angle calculation unit The tightening angle measuring unit that measures the tightening angle of the screw at the time of the measurement and the tightening state of the screw are controlled based on the measured value of the tightening angle so that a preset tightening axial force can be obtained. A screw tightening device comprising: a tightening state control unit. A torque rate calculation unit for obtaining a torque rate comprising a ratio of a change amount of the tightening torque and a change amount of the tightening angle in the elastic region of the screw in the screw tightening process using the screw tightening means; A reference angle calculation unit for obtaining a measurement reference angle of the tightening axial force excluding the plastic deformation amount of the screw based on the calculated value of the rate, and a tightening axial force based on the measurement reference angle calculated by the reference angle calculation unit The tightening angle measuring section that measures the tightening angle of the screw at the time of measuring the tightening angle and the tightening axial force of the screw corresponding to the measured value of the tightening angle Tightening axial force measurement unit measured from the relationship and a tightening state for determining whether the screw tightening state is appropriate based on the screw tightening axial force measured by the tightening axial force measurement unit A screw tightening device comprising a determination unit. 13. The screw tightening apparatus according to claim 12, further comprising display means for displaying a determination result of a screw tightening state by the tightening state determining unit.

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