JP2011220713A - Bolt tightening force test equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bolt tightening force test equipment capable of accurately and easily measuring a tightening force by electromagnetically measuring a change of permeability caused by a change of a compression stress acting on a bolt head or a nut, thereby eliminating a measurement error due to individual circumstantial differences such as contact condition between a bolt shaft portion and an object to be tightened and the influences of external vibration noise.SOLUTION: On the head of a bolt 2 or the peripheral portion of a nut 3 that transmit a tightening force to an object to be tightened 4 are concentrically disposed an excitation coil 8 and detection coils 6,7 wound so as to be almost orthogonal to the axial direction. An annular yoke 5 is disposed to surround the both coils so as to form a magnetic circuit in a poloidal direction with the head of the bolt or the nut. An AC current or a pulse current supplied to the excitation coil magnetizes the head of the bolt or the side face portion of the nut in the substantially axis direction, and the tightening force of the bolt shaft portion is determined by measuring an induction current induced to the detection coils in accordance with the degree of the permeability of the side face portion.

Description

本発明は、ボルト締付力検査装置に係わり、更に詳しくはボルトの頭部又はナットに装着するだけでボルトの締付力を検査することが可能なボルト締付力検査装置に関するものである。   The present invention relates to a bolt tightening force inspection device, and more particularly to a bolt tightening force inspection device capable of inspecting a bolt tightening force only by being attached to a bolt head or a nut.

従来のハンマー打撃法に代わり、ボルト頭部に超音波発生器から振動を与え、超音波がボルト軸端で反射する時間から締付力を計測する手法や電磁的にボルト頭部に超音波振動を与え、振動数の変化から締付力を測定する手法等、いくつかの試みはある。   Instead of the conventional hammering method, vibration is applied to the bolt head from an ultrasonic generator, and the tightening force is measured from the time when the ultrasonic wave is reflected at the bolt shaft end, or the ultrasonic vibration is applied to the bolt head electromagnetically. There are several attempts, such as a method of measuring the tightening force from the change in frequency.

ボルト頭部に一定方向の外部磁界を作用させながら交流励振用コイルにより渦電流を発生させることにより、外部磁界と渦電流との相互作用によりボルト内部に交流励振用コイルの周波数に応じた振動が発生すること、そしてボルトの締付力に応じて振動数が変化することが知られている。そこで、交流励振用コイルの周波数を変化させ、ボルトに発生した振動数を測定し、その共振周波数を測定することで、ボルトの締付力を非破壊的に検査するボルト締付力検査装置が開発されてきた。例えば特許文献１に開示された検査装置がある。この公報記載のボルト締付力検査装置は、ボルト頭部や他端部を納める空間部を備え、この空間部の半径方向外周に励振コイルを配設するとともに、前記励振コイルの外周に、複数の永久磁石を環状配列した環状永久磁石を配設して構成される振動生成体と、この振動生成体に振動緩和材を介して連結し且つ前記空間部に突出する振動伝達棒と接続した振動検出器を中心軸に配設して構成される検出体とを備えたものである。更に、このボルト締付力検査装置は、前記励振コイルに周波数が連続的に繰り返し変わる励振電流を供給する励振回路と、前記振動伝達棒からの縦振動を検出する振動検出回路と、この振動検出回路の出力信号に基づきボルトの固有振動数即ち共振周波数を検出する共振検出回路とを備えた制御装置とを備えている。   By generating an eddy current with an AC excitation coil while applying an external magnetic field in a certain direction to the bolt head, vibration corresponding to the frequency of the AC excitation coil is generated inside the bolt due to the interaction between the external magnetic field and the eddy current. It is known that the vibration frequency changes depending on the occurrence and the tightening force of the bolt. Therefore, a bolt tightening force inspection device that non-destructively inspects the bolt tightening force by changing the frequency of the AC excitation coil, measuring the frequency generated in the bolt, and measuring its resonance frequency. Has been developed. For example, there is an inspection apparatus disclosed in Patent Document 1. The bolt tightening force inspection device described in this publication includes a space for accommodating a bolt head and the other end, and an excitation coil is disposed on the outer periphery in the radial direction of the space, and a plurality of outer periphery of the excitation coil is provided on the outer periphery of the excitation coil. A vibration generator configured by arranging an annular permanent magnet in which the permanent magnets are annularly arranged, and a vibration connected to the vibration generator via a vibration reducing material and connected to a vibration transmission rod protruding into the space portion And a detector configured by arranging a detector on the central axis. Furthermore, the bolt tightening force inspection device includes an excitation circuit that supplies an excitation current whose frequency continuously and repeatedly changes to the excitation coil, a vibration detection circuit that detects longitudinal vibration from the vibration transmission rod, and the vibration detection And a control device including a resonance detection circuit that detects a natural frequency of the bolt, that is, a resonance frequency, based on an output signal of the circuit.

また、特許文献２には、軸心に貫通孔を有し、該貫通孔の半径方向外周において、軸方向に互いに相反する磁極を有する環状磁石と励振コイルとを同軸状に配設して構成される振動生成体と、前記振動生成体にボルト頭部が当接したとき前記貫通孔を通して突出してボルト頭部に一端を当接する振動伝達棒と、該振動伝達棒の他端に接続した振動検出器とを有する振動検出体と、を備えるとともに、前記励振コイルに段階的に周波数の変動するパルス電流を供給する励振回路と、前記振動検出器において前記振動伝達棒の縦振動を検出して出力される発振信号をデジタル信号に変換するＡ−Ｄ変換器と、該Ａ−Ｄ変換器の出力信号に基づき共振周波数を算出する演算部とからなる制御装置を備えたボルト締付力検査装置を提供している。   In Patent Document 2, a through-hole is formed in the shaft center, and an annular magnet having excitation poles opposite to each other in the axial direction and an excitation coil are coaxially arranged on the outer periphery in the radial direction of the through-hole. A vibration generating body, a vibration transmission rod that protrudes through the through-hole and abuts one end of the bolt head when the bolt head contacts the vibration generation body, and a vibration connected to the other end of the vibration transmission rod A vibration detector having a detector, an excitation circuit for supplying a pulse current whose frequency varies stepwise to the excitation coil, and detecting a vertical vibration of the vibration transmitting rod in the vibration detector. Bolt tightening force inspection device provided with a control device comprising an AD converter that converts an output oscillation signal into a digital signal, and an arithmetic unit that calculates a resonance frequency based on the output signal of the AD converter Is provided.

このようなボルト締付力検査装置により、以下のようにボルトの締付力が測定される。先ず、ボルトの頭部に振動伝達棒の先端が当接した状態で、励振コイルに所定の周波数を有する励振電流を供給すると、ボルト頭部に電磁誘導起電力による渦電流が流れ、この渦電流とボルト頭部に形成された環状永久磁石がつくる外部磁界との相互作用により、ボルトが励振電流の周波数に対応して縦振動する。この縦振動の周波数が、ボルトの軸部の張力に対応した固有振動数と一致するときボルトは固有振動数で振動し、その共振周波数が制御装置において検出され、検出された共振周波数に相当するボルト締付力（ボルト軸力）が算出される。このボルト締付力検査装置は、電磁的にボルトに直接振動を発生させるので、従来の超音波を外部から導入する方式のものに比べて、前処理が不要、取扱いが簡単といった利点がある。また、振動生成体と振動検出体が分離しているので、振動ノイズに対しても強いといった特長がある。   With such a bolt tightening force inspection device, the bolt tightening force is measured as follows. First, when an excitation current having a predetermined frequency is supplied to the excitation coil while the tip of the vibration transmission rod is in contact with the bolt head, an eddy current due to electromagnetic induction electromotive force flows to the bolt head, and this eddy current And the external magnetic field produced by the annular permanent magnet formed on the head of the bolt causes the bolt to vibrate longitudinally corresponding to the frequency of the excitation current. When the frequency of the longitudinal vibration coincides with the natural frequency corresponding to the tension of the shaft portion of the bolt, the bolt vibrates at the natural frequency, the resonance frequency is detected by the control device, and corresponds to the detected resonance frequency. Bolt tightening force (bolt axial force) is calculated. Since this bolt tightening force inspection device generates vibration directly on the bolt electromagnetically, it has the advantages that no pre-treatment is required and handling is simple compared with the conventional method of introducing ultrasonic waves from the outside. In addition, since the vibration generating body and the vibration detecting body are separated, there is a feature that they are resistant to vibration noise.

特許第２９９８７２５号公報Japanese Patent No. 2998725 特許第３１７２７２２号公報Japanese Patent No. 3172722

しかしながら、前述のボルト締付力検査装置は、ボルトの頭部に電磁的手段で振動を与え、ボルトの軸部の固有振動を、振動伝達棒を介して機械的に拾うものであるので、ボルトの軸部が被締結体に接触していると、正確な固有振動数を検出することができず、またボルトで締め付けられる被締付体に機械的な振動ノイズが伝達されていると、その振動ノイズがボルトの頭部に伝達されるので、弱い検出信号が不可避の振動ノイズに埋もれて検出できないという課題がある。   However, the above-described bolt tightening force inspection device applies vibration to the bolt head by electromagnetic means, and mechanically picks up the natural vibration of the shaft portion of the bolt via the vibration transmission rod. If the shaft part is in contact with the body to be fastened, an accurate natural frequency cannot be detected, and if mechanical vibration noise is transmitted to the body to be fastened with bolts, Since vibration noise is transmitted to the head of the bolt, there is a problem that a weak detection signal is buried in inevitable vibration noise and cannot be detected.

ところで、鉄鋼、ニッケルなどの強磁性体を磁化したとき、その寸法が変化する現象が磁気ひずみ効果として知られている。この材料に応力を加えると、逆効果によって透磁率が変化する。この透磁率の変化から応力を測定する方法が、磁気ひずみ応力測定法として良く知られており、主応力差が測定されるのである。しかし、この磁気ひずみ応力測定法が、ボルト締付力の測定に用いられたことはなかった。   By the way, a phenomenon in which the size of a ferromagnetic material such as steel or nickel is changed is known as a magnetostrictive effect. When stress is applied to this material, the permeability changes due to the adverse effect. This method of measuring stress from the change in magnetic permeability is well known as a magnetostrictive stress measurement method, and the principal stress difference is measured. However, this magnetostrictive stress measurement method has never been used for measuring bolt tightening force.

そこで、本発明が前述の状況に鑑み、解決しようとするところは、ボルト軸部に締付力が作用すると、ボルトの頭部若しくはナットに部分的に圧縮応力が作用する現象を利用し、この圧縮応力の変化による透磁率の変化を電磁的に計測することで、ボルト軸部と被締結体との接触状態等の個別環境の違いによる測定誤差や外部からの振動ノイズの影響を排除し、ボルト締付力を正確且つ簡単に測定することが可能なボルト締付力検査装置を提供する点にある。   Therefore, in view of the above-mentioned situation, the present invention intends to solve the problem by utilizing a phenomenon in which a compressive stress is partially applied to a bolt head or a nut when a tightening force is applied to the bolt shaft. By electromagnetically measuring changes in permeability due to changes in compressive stress, it eliminates the effects of measurement errors and external vibration noise due to differences in individual environments such as the contact state between the bolt shaft and the body to be fastened, It is in providing a bolt tightening force inspection device capable of accurately and easily measuring the bolt tightening force.

本発明は、前述の課題解決のために、被締結体に締付力を伝達するボルト頭部若しくはナットの外周部に、ボルト軸部の軸方向と直交するように巻回した励磁コイルと検出コイルとを同芯状に配置するとともに、該励磁コイルと検出コイルとを取り囲み前記ボルト頭部若しくはナットとでポロイダル方向の磁気回路を形成するように環状ヨークを配置し、前記検出コイルは独立した第１検出コイルと第２検出コイルとからなり、前記ボルト頭部若しくはナットの外周部で、被締結体とは反対側の先端部に第１検出コイルを配置するとともに、被締結体側の基端部に第２検出コイルを配置し、前記励磁コイルに供給した交流電流又はパルス電流によって前記ボルト頭部若しくはナットの側面部を略軸方向に磁化し、該側面部の透磁率の大きさに応じて前記第１検出コイルと第２検出コイルに誘起する誘導電流の差動出力を計測し、ボルト軸部の締付力を測定することを特徴とするボルト締付力検査装置を構成した（請求項１）。 In order to solve the above-described problems, the present invention detects an excitation coil and a coil wound around a bolt head or an outer periphery of a nut that transmits a tightening force to a fastened body so as to be orthogonal to the axial direction of the bolt shaft. The coil is arranged concentrically, and an annular yoke is arranged so as to surround the exciting coil and the detection coil so as to form a magnetic circuit in the poloidal direction with the bolt head or nut, and the detection coil is independent. The first detection coil is composed of a first detection coil and a second detection coil, and the first detection coil is disposed at the distal end of the bolt head or the nut on the side opposite to the body to be fastened, and the base end on the body to be fastened the second detection coil arranged parts, a side surface portion of the bolt head or nut by an alternating current or pulsed current supplied to the exciting coil is magnetized substantially in the axial direction, the magnitude of the magnetic permeability of the side surface portion Flip the differential output of the induction current induced in the first detection coil and the second detection coil and measured, it was constituted the bolt clamping force testing device according to claim to measure the clamping force of the bolt shank ( Claim 1).

更に、前記ボルト頭部若しくはナットの外周部に装着するプローブに前記環状ヨークを備え、前記励磁コイル及び第１検出コイルと第２検出コイルとを、該第１検出コイルと第２検出コイルとの間に空間を設けて前記環状ヨークの断面略コ字形のコイル収容溝内に収容してなることがより好ましい（請求項２）。 Further, the probe attached to the bolt head or the outer periphery of the nut includes the annular yoke, and the excitation coil, the first detection coil, and the second detection coil are connected to the first detection coil and the second detection coil. and more preferably provided with a space formed by housing the coil accommodating groove of approximately C-shaped cross section of the annular yoke between (claim 2).

そして、前記第１検出コイルと第２検出コイルの出力を差動増幅器又は減算器からなる検出回路に入力し、その差動出力を増幅回路で増幅した後、ＤＣ変換回路で整流して直流電圧に変換して出力信号とするのである（請求項３）。 Then, the outputs of the first detection coil and the second detection coil are input to a detection circuit comprising a differential amplifier or a subtractor, the differential output is amplified by an amplification circuit, and then rectified by a DC conversion circuit to be a DC voltage. Is converted into an output signal (claim 3 ).

あるいは、前記第１検出コイルと第２検出コイルのそれぞれの出力をＤＣ変換回路で整流して直流電圧に変換し、両出力電圧を差動増幅器又は減算器からなる検出回路に入力し、その差動出力を出力信号とするのである（請求項４）。 Alternatively, the respective outputs of the first detection coil and the second detection coil are rectified by a DC conversion circuit and converted into a DC voltage, and both output voltages are input to a detection circuit comprising a differential amplifier or a subtractor, and the difference it is taken as the output signal dynamic output (claim 4).

そして、被締結体とボルト頭部若しくはナットとの間にワッシャを備える締結構造において、前記環状ヨークの軸方向一端部を前記ワッシャに当接するとともに、軸方向他端部をボルト頭部若しくはナットの先端部に当接し、前記環状ヨーク、前記ボルト頭部若しくはナット及び前記ワッシャとでポロイダル方向の磁気回路を形成してなることも可能である（請求項５）。 In the fastening structure including a washer between the fastened body and the bolt head or nut, the axial end of the annular yoke is brought into contact with the washer and the other end in the axial direction of the bolt head or nut. in contact with the distal end portion, the annular yoke, it is also possible by forming a magnetic circuit of poloidal direction between the bolt head or nut and the washer (claim 5).

また、前記環状ヨークの一部が、前記ボルト頭部若しくはナットに係合し、回転締付可能なレンチを構成していることも好ましい（請求項６）。 Further, it is also preferable that a part of the annular yoke constitutes a wrench capable of being engaged with the bolt head or nut and capable of being rotationally tightened (Claim 6 ).

以上にしてなる請求項１に係る発明のボルト締付力検査装置は、被締結体に締付力を伝達するボルト頭部若しくはナットの外周部に、ボルト軸部の軸方向と直交するように巻回した励磁コイルと検出コイルとを同芯状に配置するとともに、該励磁コイルと検出コイルとを取り囲み前記ボルト頭部若しくはナットとでポロイダル方向の磁気回路を形成するように環状ヨークを配置し、前記検出コイルは独立した第１検出コイルと第２検出コイルとからなり、前記ボルト頭部若しくはナットの外周部で、被締結体とは反対側の先端部に第１検出コイルを配置するとともに、被締結体側の基端部に第２検出コイルを配置し、前記励磁コイルに供給した交流電流又はパルス電流によって前記ボルト頭部若しくはナットの側面部を略軸方向に磁化し、該側面部の透磁率の大きさに応じて前記第１検出コイルと第２検出コイルに誘起する誘導電流の差動出力を計測し、ボルト軸部の締付力を測定するので、ボルト軸部と被締結体との接触状態等の個別環境の違いによる測定誤差や外部からの振動ノイズの影響を排除し、ボルト締付力を正確且つ簡単に測定することができる。そして、第１検出コイルは圧縮応力が殆ど作用していないボルト頭部若しくはナットの先端部を検出し、第２検出コイルは圧縮応力が最も作用している基端部を検出し、それらの差動出力を得るので、ノイズやその他の不具合を相殺し、真に圧縮応力による透磁率の変化のみが反映された出力信号となり、正確なボルト締付力を測定できるのである。尚、ボルト軸部に装着したひずみゲージ等によって実測したボルト締付力と、本発明のボルト締付力検査装置の出力信号とをデータテーブルとして取得しておけば、出力信号からボルト締付力を絶対値として数値的に算出することは簡単である。また、正常に締め付けられたボルトを基準として、他のボルトの締付具合を相対的に診断することも可能である。本発明はボルト締付力の検査以外にも、ボルトに生じたクラックの有無を検査することも可能である。また、励磁コイルと検出コイルは、環状ヨークとボルト頭部若しくはナットの外周部とで囲まれているので、磁気シールド効果があり、外部の電磁ノイズにも影響されないのである。 In the bolt tightening force inspection device according to the first aspect of the present invention as described above, the outer periphery of the bolt head or nut that transmits the tightening force to the body to be fastened is orthogonal to the axial direction of the bolt shaft portion. The wound excitation coil and the detection coil are arranged concentrically, and an annular yoke is arranged so as to surround the excitation coil and the detection coil and form a magnetic circuit in the poloidal direction with the bolt head or nut. The detection coil includes an independent first detection coil and a second detection coil, and the first detection coil is disposed on the outer periphery of the bolt head or the nut at the tip opposite to the body to be fastened. , the second detection coil disposed on the base end portion of the fastening side, by an alternating current or pulsed current supplied to the exciting coil to magnetize the side surface portion of the bolt head or nut in a substantially axial direction, the The differential output of the induction current induced in the first detection coil and the second detection coil measured in accordance with the magnitude of the magnetic permeability of the surface portion, so measuring the clamping force of the bolt shank, the bolt shank It is possible to accurately and easily measure the bolt tightening force by eliminating the influence of measurement errors due to differences in individual environments such as the contact state with the fastening body and vibration noise from the outside. The first detection coil detects the bolt head or the tip of the nut to which almost no compressive stress is applied, and the second detection coil detects the base end to which the compressive stress is most applied. Since dynamic output is obtained, noise and other problems are offset, and an output signal that reflects only the change in magnetic permeability due to the compressive stress is reflected, and an accurate bolt tightening force can be measured. If the bolt tightening force measured with a strain gauge or the like attached to the bolt shaft and the output signal of the bolt tightening force inspection device of the present invention are acquired as a data table, the bolt tightening force can be obtained from the output signal. It is easy to calculate numerically as an absolute value. It is also possible to relatively diagnose the tightening condition of other bolts based on the bolts that have been tightened normally. The present invention can inspect for the presence or absence of cracks in the bolt in addition to the inspection of the bolt tightening force. Further, since the excitation coil and the detection coil are surrounded by the annular yoke and the bolt head or the outer periphery of the nut, there is a magnetic shielding effect and it is not affected by external electromagnetic noise.

請求項２によれば、プローブをボルト頭部若しくはナットの外周部に装着だけで、励磁コイル及び第１検出コイルと第２検出コイルを所定位置にセットすることができ、また第１検出コイルと第２検出コイルとの間に空間を設けて前記環状ヨークの断面略コ字形のコイル収容溝内に収容しているので、第１検出コイルと第２検出コイルとの干渉を少なくすることができ、正確且つ簡単なボルト締付力の測定に寄与するのである。 According to claim 2 , the excitation coil, the first detection coil, and the second detection coil can be set at predetermined positions only by attaching the probe to the bolt head or the outer periphery of the nut. Since a space is provided between the second detection coil and the coil is accommodated in a coil housing groove having a substantially U-shaped cross section of the annular yoke, interference between the first detection coil and the second detection coil can be reduced. It contributes to the accurate and simple measurement of the bolt tightening force.

請求項３又は４によれば、第１検出コイルと第２検出コイルで拾った出力を処理し、ボルト締付力に対応した出力信号を取得するための回路構成が簡単であり、また励磁コイルに交流電流又はパルス電流を供給する発振回路も簡単であるので、携帯可能なコンパクトな制御装置とすることができる。 According to claim 3 or 4 , the circuit configuration for processing the output picked up by the first detection coil and the second detection coil and acquiring the output signal corresponding to the bolt tightening force is simple, and the excitation coil Since an oscillation circuit for supplying an alternating current or a pulse current to the circuit is also simple, a portable and compact control device can be obtained.

請求項５によれば、被締結体とボルト頭部若しくはナットとの間にワッシャを備える締結構造において、前記環状ヨークの軸方向一端部を前記ワッシャに当接するとともに、軸方向他端部をボルト頭部若しくはナットの先端部に当接し、前記環状ヨーク、前記ボルト頭部若しくはナット及び前記ワッシャとでポロイダル方向の磁気回路を形成してなるので、ワッシャが存在しても同様にボルト締付力を正確且つ簡単に測定することができる。 According to the fifth aspect of the present invention, in the fastening structure including a washer between the body to be fastened and the bolt head or nut, the axial one end of the annular yoke is brought into contact with the washer and the other axial end is bolted. A magnetic circuit in the poloidal direction is formed by the annular yoke, the bolt head or nut and the washer in contact with the head or the tip of the nut, so that the bolt tightening force is the same even if a washer is present. Can be measured accurately and easily.

請求項６によれば、環状ヨークの一部に設けたレンチを、ボルト頭部若しくはナットに係合して回転させ、締め付けながらボルト軸部の締付力を確認することができ、トルクレンチに代わる正確な締め付けが可能である。 According to the sixth aspect , the wrench provided in a part of the annular yoke can be engaged with the bolt head or the nut and rotated to check the tightening force of the bolt shaft portion while tightening. Alternative precise tightening is possible.

本発明に係るボルト締付力検査装置のプローブの斜視図である。It is a perspective view of the probe of the bolt clamping force inspection device according to the present invention. 同じくプローブの縦断面図である。It is the longitudinal cross-sectional view of a probe similarly. ボルト・ナットによる被締結体の締結状態においてナットにプローブを装着して締結力を計測する状態を示す部分断面図である。It is a fragmentary sectional view which shows the state which mounts a probe to a nut and measures fastening force in the fastening state of the to-be-fastened body by a volt | bolt nut. 本発明のボルト締付力検査装置を構成する制御回路の第１例を示すブロック図である。It is a block diagram which shows the 1st example of the control circuit which comprises the bolt clamping force test | inspection apparatus of this invention. 本発明のボルト締付力検査装置を構成する制御回路の第２例を示すブロック図である。It is a block diagram which shows the 2nd example of the control circuit which comprises the bolt clamping force test | inspection apparatus of this invention. ＳＣＭ４００の磁気特性を示し、（ａ）は各圧縮応力に応じた初期磁化曲線（Ｂ−Ｈ曲線）、（ｂ）は各圧縮応力に応じた透磁率（μ_r−Ｈ曲線）を示すグラフである。The magnetic characteristic of SCM400 is shown, (a) is an initial magnetization curve (BH curve) according to each compressive stress, (b) is a graph which shows the magnetic permeability ((micro | micron | mu) _r- H curve) according to each compressive stress. is there. ＳＳ４００の磁気特性を示し、（ａ）は各圧縮応力に応じた初期磁化曲線（Ｂ−Ｈ曲線）、（ｂ）は各圧縮応力に応じた透磁率（μ_r−Ｈ曲線）を示すグラフである。Shows the magnetic properties of SS400, (a) the initial magnetization curve corresponding to each compression stress (B-H curve), a graph showing the (b) permeability (mu _r -H curve) corresponding to each compressive stress is there. ＳＣＭ４００とＳＳ４００の圧縮応力に対する導電率を示すグラフである。It is a graph which shows the electrical conductivity with respect to the compressive stress of SCM400 and SS400. 励磁電流が０．５Ａ、１ｋＨｚの場合にボルト締付力を変化させたときの磁束密度の減衰率の計算値と実測値を示すグラフである。It is a graph which shows the calculated value and measured value of the attenuation factor of magnetic flux density when changing the bolt fastening force when the excitation current is 0.5 A and 1 kHz. 励磁電流が０．５Ａ、各周波数におけるボルト締付力を変化させたときの磁束密度の減衰率の計算値を示すグラフである。It is a graph which shows the calculated value of the attenuation factor of magnetic flux density when exciting current is 0.5A and the bolt fastening force at each frequency is changed. トルクレンチで締め付けたＭ３０のボルトの頭部に本発明のプローブを装着して測定した場合のトクルレンチの読みと出力との関係を示すグラフである。It is a graph which shows the relationship between the reading and output of a tow wrench at the time of measuring by attaching the probe of this invention to the head of the bolt of M30 fastened with the torque wrench.

次に、添付図面に示した実施形態に基づき、本発明を更に詳細に説明する。図１及び図２は本発明に係るボルト締付力検査装置のプローブを示し、図３はプローブを実際に装着してボルトの締付力を測定する状態を示し、図中符号１はプローブ、２はボルト、３はナット、４は被締結体、５は環状ヨーク、６は第１検出コイル、７は第２検出コイル、８は励磁コイルをそれぞれ示している。   Next, the present invention will be described in more detail based on the embodiments shown in the accompanying drawings. 1 and 2 show a probe of the bolt tightening force inspection apparatus according to the present invention, FIG. 3 shows a state in which the probe is actually mounted and the bolt tightening force is measured, and reference numeral 1 in the figure denotes a probe, 2 is a bolt, 3 is a nut, 4 is a body to be fastened, 5 is an annular yoke, 6 is a first detection coil, 7 is a second detection coil, and 8 is an excitation coil.

本発明のボルト締付力検査装置は、ボルト２による締付力によってボルトの頭部若しくはボルト２に螺合したナット３に生じる圧縮応力による透磁率の変化を電磁的に測定し、ボルトの軸部に作用する締付力を測定するものである。本発明の測定原理は、磁気ひずみ応力測定法である。ここで、ボルト２による締付力、即ち軸部９に作用する引張応力と、ボルトの頭部若しくはナット３に生じる圧縮応力に関する相関データを、ボルト・ナットの種類毎に取得しておく必要がある。   The bolt tightening force inspection apparatus of the present invention electromagnetically measures a change in magnetic permeability due to compressive stress generated in a bolt head or a nut 3 screwed into the bolt 2 by a tightening force of the bolt 2, and the shaft of the bolt The clamping force acting on the part is measured. The measurement principle of the present invention is a magnetostrictive stress measurement method. Here, it is necessary to acquire the correlation data regarding the tightening force by the bolt 2, that is, the tensile stress acting on the shaft portion 9 and the compressive stress generated in the bolt head or the nut 3 for each bolt and nut type. is there.

ボルト２を被締結体４の貫通孔１０に挿通し、本体部の螺孔に螺合して本体部に被締結体４を締め付ける場合、あるいは複数の被締結体４の貫通孔１０にボルト２の軸部９を挿通し、該軸部９の先端部にナット３を螺合して、ボルト頭部とナット３とで被締結体４，４同士を締め付ける場合、ボルト２の軸部９には引張応力が作用し、ボルト頭部若しくはナット３の側面部であって、被締結体４側の基端部に圧縮応力が作用し、被締結体４とは反対側の先端部には殆ど応力が生じない。   When the bolt 2 is inserted into the through hole 10 of the body to be fastened 4 and screwed into the screw hole of the main body to fasten the fastened body 4 to the main body, or the bolt 2 is inserted into the through hole 10 of the plurality of fastened bodies 4. When the nut 3 is screwed into the tip of the shaft 9 and the bolt head 4 and the nut 3 are tightened to each other with the bolts 4 and 4, Is applied to the bolt head or the side surface of the nut 3, compressive stress is applied to the base end of the body to be fastened 4, and almost no tip is located on the side opposite to the body to be fastened 4. No stress is generated.

一般的に、鋼材に圧縮応力が作用すると、磁気ひずみ効果のため圧縮応力の方向には磁化し難く、つまり透磁率は小さくなり、圧縮応力に直交する方向では磁化し易くなることは良く知られている。引張応力の場合にはこの関係は逆になる。本発明の場合には、ボルト２の軸部に引張応力が作用すると、ボルト頭部若しくはナット３で被締結体４に直接又はワッシャを介して接触している部位を最大として、その近傍に圧縮応力が作用する。ボルト締結時にボルト頭部若しくはナット３の外周部に作用する圧縮応力の方向は、軸部９の軸方向と略平行であり、また被締結体４と反対側の先端部には殆ど応力が作用しないことがシミュレーション結果により確認されている。また、鋼材の微視組織によっても透磁率は変化し、これを分離して測定することは困難をともなう場合が多いので、実際にはひずみゼロの同一材料との差から応力測定精度の向上を図るのである。   In general, it is well known that when compressive stress acts on steel materials, it is difficult to magnetize in the direction of compressive stress due to the magnetostrictive effect, that is, the permeability is small and it is easy to magnetize in the direction perpendicular to the compressive stress. ing. In the case of tensile stress, this relationship is reversed. In the case of the present invention, when tensile stress acts on the shaft portion of the bolt 2, the portion that is in direct contact with the fastened body 4 with the bolt head or nut 3 or via a washer is maximized and compressed in the vicinity thereof. Stress acts. The direction of the compressive stress acting on the bolt head or the outer peripheral portion of the nut 3 at the time of bolt fastening is substantially parallel to the axial direction of the shaft portion 9, and almost no stress acts on the tip portion on the opposite side to the fastened body 4. It has been confirmed by simulation results that this is not done. In addition, the permeability changes depending on the microstructure of the steel material, and it is often difficult to measure this separately.Therefore, the accuracy of stress measurement is actually improved due to the difference from the same material with zero strain. It is for illustration.

そこで、本発明のボルト締付力検査装置は、被締結体４に締付力を伝達するボルト頭部若しくはナット３の外周部に、ボルト軸部９の軸方向と直交するように巻回した励磁コイル８と検出コイル６，７とを同芯状に配置するとともに、該励磁コイル８と検出コイル６，７とを取り囲み前記ボルト頭部若しくはナット３とでポロイダル方向の磁気回路を形成するように断面略コ字形のコイル収容溝１１を設けた環状ヨーク５を配置し、前記励磁コイル８に供給した交流電流又はパルス電流によって前記ボルト頭部若しくはナット３の側面部を略軸方向に磁化し、該側面部の透磁率の大きさに応じて前記検出コイル６，７に誘起する誘導電流を計測し、ボルト軸部の締付力を測定するのである。ここで、前記励磁コイル８と検出コイル６，７は、環状ヨーク５とボルト頭部若しくはナット３の外周部とで囲まれているので、磁気シールド効果もあり、電磁ノイズを遮蔽することができる。   Therefore, the bolt tightening force inspection device of the present invention is wound around the outer periphery of the bolt head or nut 3 that transmits the tightening force to the fastened body 4 so as to be orthogonal to the axial direction of the bolt shaft portion 9. The excitation coil 8 and the detection coils 6 and 7 are arranged concentrically and surround the excitation coil 8 and the detection coils 6 and 7 so as to form a magnetic circuit in the poloidal direction with the bolt head or the nut 3. An annular yoke 5 provided with a coil receiving groove 11 having a substantially U-shaped cross section is arranged on the side, and the bolt head or the side surface of the nut 3 is magnetized in a substantially axial direction by an alternating current or pulse current supplied to the exciting coil 8. The induced current induced in the detection coils 6 and 7 is measured according to the magnetic permeability of the side surface portion, and the tightening force of the bolt shaft portion is measured. Here, since the exciting coil 8 and the detection coils 6 and 7 are surrounded by the annular yoke 5 and the outer periphery of the bolt head or the nut 3, there is also a magnetic shielding effect, and electromagnetic noise can be shielded. .

具体的には、前記検出コイルは独立した第１検出コイル６と第２検出コイル７とからなり、前記ボルト頭部若しくはナット３の外周部で、被締結体４とは反対側の先端部に第１検出コイル６を配置するとともに、被締結体４側の基端部に第２検出コイル７を配置し、前記第１検出コイル６と第２検出コイル７の差動出力を計測してボルト軸部の締付力を測定するのである。原理的には、前記検出コイルは一つあれば検出可能であるが、前述のように、応力が殆ど作用しない、つまりひずみがゼロのボルト頭部若しくはナット３の先端部を第１検出コイル６で計測し、圧縮応力が作用するボルト頭部若しくはナット３の基端部を第２検出コイル７で計測し、両検出コイルの出力の差分を取ることにより、応力測定精度を高めるのである。勿論、測定対象が小型のボルト等では、コイル巻回スペースが大きく取れないので、一つの検出コイルを用いて励磁コイル８と内外に同心状に巻回することも可能である。   Specifically, the detection coil includes a first detection coil 6 and a second detection coil 7 that are independent from each other, and the outer periphery of the bolt head or nut 3 at the tip end opposite to the fastened body 4. While arrange | positioning the 1st detection coil 6, the 2nd detection coil 7 is arrange | positioned in the base end part by the side of the to-be-fastened body 4, and the differential output of the said 1st detection coil 6 and the 2nd detection coil 7 is measured, and a volt | bolt The tightening force of the shaft is measured. In principle, detection is possible if there is only one detection coil. However, as described above, the bolt head or the tip of the nut 3 with almost no stress, that is, zero strain, is attached to the first detection coil 6. Thus, the accuracy of the stress measurement is improved by measuring the bolt head or the base end of the nut 3 on which the compressive stress acts with the second detection coil 7 and taking the difference between the outputs of the two detection coils. Of course, if the measuring object is a small bolt or the like, the coil winding space cannot be made large, so that it can be wound concentrically on the inside and outside of the exciting coil 8 using one detection coil.

ここで、前記ボルト頭部若しくはナット３に作用する応力は、外周部と深部では異なるので、ボルト締付力によって圧縮応力が現れる外周部のみを計測範囲とする。そのため、前記励磁コイル８に供給する交流電流の周波数は適度に高い方が好ましい。前記励磁コイル８に供給する交流電流の周波数が高くなると、前記ボルト頭部若しくはナット３に浸透する磁場の深さは浅くなるからである。また、前記励磁コイル８にパルス電流を供給する場合も、パスルの立上り部、立下り部は周波数が非常に高い交流電流と同様の作用をするので、前記ボルト頭部若しくはナット３に浸透する磁場の深さを浅くすることができる。 Here, since the stress acting on the bolt head or the nut 3 is different between the outer peripheral portion and the deep portion, only the outer peripheral portion where the compressive stress appears due to the bolt tightening force is set as the measurement range. Therefore, it is preferable that the frequency of the alternating current supplied to the exciting coil 8 is appropriately high. This is because when the frequency of the alternating current supplied to the exciting coil 8 is increased, the depth of the magnetic field penetrating the bolt head or the nut 3 is decreased. Also, when a pulse current is supplied to the exciting coil 8, the rising and falling parts of the pulse operate in the same manner as an alternating current having a very high frequency, so that the magnetic field penetrating into the bolt head or nut 3 can be obtained. The depth of can be reduced.

更に詳しく、前記プローブ１の構造を図１及び図２に基づいて説明する。前記プローブ１は、少なくとも環状ヨーク５の部分が透磁率の高い材料で作製し、該環状ヨーク５の断面略コ字形のコイル収容溝１１には、前記第１検出コイル６と第２検出コイル７及び励磁コイル８を収容するとともに、環状ヨーク５の一側に各コイルに接続する配線のコネクター１２を設けている。前記第１検出コイル６と第２検出コイル７及び励磁コイル８は、空芯となっており、前記ボルトの頭部若しくはナット３にプローブ１を装着した際に、該ボルトの頭部若しくはナット３がヨーク芯となり、環状ヨーク５とでコイルの周囲を取り囲み、磁力線が外部に逃げないようにしている。   More specifically, the structure of the probe 1 will be described with reference to FIGS. The probe 1 is made of a material having a high magnetic permeability at least in the annular yoke 5, and the first detection coil 6 and the second detection coil 7 are provided in the coil receiving groove 11 having a substantially U-shaped cross section of the annular yoke 5. The exciting coil 8 is accommodated, and a wiring connector 12 connected to each coil is provided on one side of the annular yoke 5. The first detection coil 6, the second detection coil 7, and the excitation coil 8 are air-core, and when the probe 1 is mounted on the bolt head or nut 3, the bolt head or nut 3. Serves as a yoke core and surrounds the periphery of the coil with the annular yoke 5 so that the magnetic lines of force do not escape to the outside.

前記プローブ１は、軸方向一側面に開放した箱型の本体部１３と、該本体部１３の開放面側を閉じるカバー体１４とから構成されている。前記本体部１３は、底面部に前記ボルトの頭部若しくはナット３に係合する六角孔１５を形成するとともに、該六角孔１５の最大径よりも内径が大きな円筒状立壁１６を形成し、更に該円筒状立壁１６に連続して全周に側面部１７を形成している。前記カバー体１４は、前記本体部１３の平面視形状と同じ外形を有し、前記円筒状立壁１６及び側面部１７の端面に当接してネジ止め固定される。また、前記カバー体１４には、前記六角孔１５と対面した位置に同軸状に円孔１８を形成し、前記プローブ１を前記ボルトの頭部若しくはナット３に装着した際に、該円孔１８の口縁がボルトの頭部若しくはナット３の上端周囲に当接するようになっている。そして、前記本体部１３の六角孔１５の周囲の底面部と円筒状立壁１６及び前記カバー体１４の円孔１８の周囲部分とで、内方へ開放した環状ヨーク５を形成している。更に、前記円筒状立壁１６より外側へ連続した部分の前記カバー体１４には前記コネクター１２を取付けている。尚、ワッシャを介して締め付ける場合には、前記プローブ１の六角孔１５の周辺部を該ワッシャの上面に当接するようにする。   The probe 1 includes a box-shaped main body portion 13 opened on one side surface in the axial direction, and a cover body 14 that closes the open surface side of the main body portion 13. The main body 13 has a hexagonal hole 15 that engages with the bolt head or the nut 3 on the bottom surface, and a cylindrical standing wall 16 having an inner diameter larger than the maximum diameter of the hexagonal hole 15. A side surface portion 17 is formed around the entire circumference of the cylindrical standing wall 16. The cover body 14 has the same outer shape as the planar view of the main body portion 13, and is fixed to the end surfaces of the cylindrical standing wall 16 and the side surface portion 17 by screws. The cover body 14 is formed with a circular hole 18 coaxially at a position facing the hexagonal hole 15, and when the probe 1 is mounted on the head of the bolt or the nut 3, the circular hole 18 is formed. The lip of this is in contact with the head of the bolt or the periphery of the upper end of the nut 3. An annular yoke 5 opened inward is formed by the bottom surface portion around the hexagonal hole 15 of the main body portion 13 and the peripheral portion of the cylindrical standing wall 16 and the circular hole 18 of the cover body 14. Further, the connector 12 is attached to the cover body 14 at a portion continuous to the outside from the cylindrical standing wall 16. When tightening via a washer, the peripheral portion of the hexagonal hole 15 of the probe 1 is brought into contact with the upper surface of the washer.

本実施形態では、前記第１検出コイル６と第２検出コイル７及び励磁コイル８の内周面の形状を、前記ボルトの頭部若しくはナット３に密着して効率良く磁化できるように六角形の筒状としているが、円筒形としても良い。また、前記第１検出コイル６と第２検出コイル７及び励磁コイル８の内周面に、薄い非磁性体の保護層１９を設けても良い。しかし、前記プローブ１の構造は、前記環状ヨーク５以外の構成は任意であり、各種の構造を採用し得る。本実施形態では、前記環状ヨーク５の一部に六角孔１５を設けてレンチを構成しているので、前記コネクター１２を設けた部分を延長してハンドルとすれば、前記ボルトの頭部若しくはナット３に係合し、回転締め付けと同時に、締付力を測定できるのである。 In the present embodiment, the shapes of the inner peripheral surfaces of the first detection coil 6, the second detection coil 7, and the excitation coil 8 are hexagonal so as to be in close contact with the bolt head or the nut 3 and efficiently magnetized. Although it is cylindrical, it may be cylindrical. Further, the inner peripheral surface of the first detection coil 6 and the second detection coil 7 and the excitation coil 8, may be provided a protective layer 19 of a thin non-magnetic material. However, the structure of the probe 1 is arbitrary except for the annular yoke 5, and various structures can be adopted. In this embodiment, since the hexagonal hole 15 is provided in a part of the annular yoke 5 to constitute a wrench, if the portion provided with the connector 12 is extended to serve as a handle, the bolt head or nut 3 can be engaged, and the tightening force can be measured simultaneously with the rotational tightening.

次に、本発明のボルト締付力検査装置における制御回路を簡単に説明する。図４は制御回路の第１例である。第１例の制御回路は、先ず発振回路２０で所定周波数の発振信号を作り、それを励磁電流供給回路２１で所定の電流値まで増幅して前記プローブ１の励磁コイル８に供給する。励磁コイル８で発生させた交番磁場により、前記ボルトの頭部若しくはナット３の側面部の内部に誘起された磁束が、断面略コ字形の前記環状ヨーク５内を通ってボルトの頭部若しくはナット３の側面部に戻る、閉じた磁気回路が形成される。つまり、前記励磁コイル８を中心部に有するトーラスにおいて、磁力線はポロイダル方向に向いている。このとき、前記第１検出コイル６と第２検出コイル７には、それぞれボルトの頭部若しくはナット３の側面部であって先端部と基端部の透磁率を反映した磁束の変化によって誘導電流が流れる。ここで、前記ボルト２を締め付けると、ボルトの頭部若しくはナット３の側面部の基端部に、軸部９の軸方向と略平行な方向に圧縮応力が作用し、軸方向に対する透磁率が低下するので、前記第１検出コイル６の誘導電流より第２検出コイル７の誘導電流が小さくなる。この場合、第１検出コイル６と第２検出コイル７との間に空間を設けて前記環状ヨーク５のコイル収容溝１１内に収容することにより、両コイル６，７の干渉を極力抑制し、それぞれ独立した誘導電流を得るのである。そして、前記第１検出コイル６と第２検出コイル７の出力を差動増幅器又は減算器からなる検出回路２２に入力し、その差動出力を増幅回路２３で増幅した後、ＤＣ変換回路２４で整流して直流電圧に変換して出力信号とし、表示器２５に表示するのである。前記表示器２５での表示は、アナログ表示でもデジタル表示でも良く、更に締付力が基準値以上か以下か、良否の場合には音声等で検査結果を表しても良い。   Next, a control circuit in the bolt tightening force inspection apparatus of the present invention will be briefly described. FIG. 4 shows a first example of the control circuit. The control circuit of the first example first generates an oscillation signal having a predetermined frequency by the oscillation circuit 20, amplifies it to a predetermined current value by the excitation current supply circuit 21, and supplies it to the excitation coil 8 of the probe 1. The magnetic flux induced in the bolt head or the inside of the side surface of the nut 3 by the alternating magnetic field generated by the exciting coil 8 passes through the annular yoke 5 having a substantially U-shaped cross section, and the bolt head or nut. A closed magnetic circuit is formed which returns to the side surface 3. That is, in the torus having the exciting coil 8 at the center, the magnetic lines of force are directed in the poloidal direction. At this time, the first detection coil 6 and the second detection coil 7 have induced currents due to changes in magnetic flux reflecting the permeability of the distal end portion and the proximal end portion of the bolt head or the side surface of the nut 3, respectively. Flows. Here, when the bolt 2 is tightened, a compressive stress acts in a direction substantially parallel to the axial direction of the shaft portion 9 on the head portion of the bolt or the base end portion of the side surface portion of the nut 3, and the magnetic permeability in the axial direction is increased. Therefore, the induced current in the second detection coil 7 becomes smaller than the induced current in the first detection coil 6. In this case, by providing a space between the first detection coil 6 and the second detection coil 7 and accommodating it in the coil accommodation groove 11 of the annular yoke 5, interference between the coils 6 and 7 is suppressed as much as possible. Independent currents are obtained. Then, the outputs of the first detection coil 6 and the second detection coil 7 are input to a detection circuit 22 comprising a differential amplifier or a subtracter, and the differential output is amplified by an amplification circuit 23, and then a DC conversion circuit 24. It is rectified and converted into a DC voltage to be an output signal and displayed on the display 25. The display on the display unit 25 may be an analog display or a digital display, and the inspection result may be expressed by voice or the like when the tightening force is greater than or equal to a reference value or acceptable.

また、図５は制御回路の第２例である。第２例の制御回路は、前記同様に発振回路２０で所定周波数の発振信号を作り、それを励磁電流供給回路２１で所定の電流値まで増幅して前記プローブ１の励磁コイル８に供給する。前記第１検出コイル６と第２検出コイル７の出力をそれぞれ増幅回路２６，２７で増幅した後、それぞれの出力をＤＣ変換回路２８，２９で整流して直流電圧に変換し、両出力電圧を差動増幅器又は減算器からなる検出回路３０に入力し、その差動出力を出力信号とし、表示器３１で表示するのである。   FIG. 5 shows a second example of the control circuit. The control circuit of the second example generates an oscillation signal of a predetermined frequency by the oscillation circuit 20 as described above, amplifies it to a predetermined current value by the excitation current supply circuit 21, and supplies it to the excitation coil 8 of the probe 1. After the outputs of the first detection coil 6 and the second detection coil 7 are amplified by the amplifier circuits 26 and 27, respectively, the respective outputs are rectified by the DC conversion circuits 28 and 29 and converted into DC voltages, and both output voltages are converted. The signal is input to a detection circuit 30 composed of a differential amplifier or a subtracter, and the differential output is used as an output signal and displayed on the display 31.

次に、鋼材に圧縮応力が作用すると、その応力の方向に対して初期磁化曲線と透磁率及び導電率がどのように変化するかを測定した結果を図６〜図８に示す。試験した鋼材は高張力ボルト（ＳＣＭ４００）とワッシャ用鋼板（ＳＳ４００）である。図６（ａ）はＳＣＭ４００の各圧縮応力に応じた初期磁化曲線（Ｂ−Ｈ曲線）、図６（ｂ）はＳＣＭ４００の各圧縮応力に応じた透磁率（μ_r−Ｈ曲線）を示すグラフである。また、図７（ａ）はＳＳ４００の各圧縮応力に応じた初期磁化曲線（Ｂ−Ｈ曲線）、図６（ｂ）はＳＳ４００の各圧縮応力に応じた透磁率（μ_r−Ｈ曲線）を示すグラフである。そして、図８は、ＳＣＭ４００とＳＳ４００の圧縮応力に対する導電率を示すグラフである。導電率は、ケルビンダブルブリッジ回路の４端子法を用いて各圧縮応力における導電率を測定した。 Next, when compressive stress is applied to the steel material, results of measuring how the initial magnetization curve, the magnetic permeability, and the conductivity change with respect to the direction of the stress are shown in FIGS. The steel materials tested were high tension bolts (SCM400) and washer steel plates (SS400). 6A is an initial magnetization curve (BH curve) corresponding to each compressive stress of the SCM 400, and FIG. 6B is a graph showing magnetic permeability (μ _r -H curve) corresponding to each compressive stress of the SCM 400. It is. Further, FIG. 7 (a) initial magnetization curve corresponding to each compression stress of SS400 is (B-H curve), permeability (mu _r -H curve) corresponding to each compression stress in FIG. 6 (b) SS400 It is a graph to show. And FIG. 8 is a graph which shows the electrical conductivity with respect to the compressive stress of SCM400 and SS400. For the conductivity, the conductivity at each compressive stress was measured using a four-terminal method of a Kelvin double bridge circuit.

これらの結果から、ＳＣＭ４３５とＳＳ４００は圧縮応力に比例して磁気特性が低下することがわかった。更に、圧縮応力の変化によって透磁率が大きく変化する外部磁場（Ｈ）の大きさは比較的小さい範囲にあることもわかる。従って、前記励磁コイル８によって発生する磁場の大きさをこの範囲に設定すると、検出コイル７で検出する信号の変化が大きくなる。ＳＣＭ４００とＳＳ４００とでは、透磁率が大きく変化する外部磁場（Ｈ）の範囲は異なり、ＳＣＭ４００の方がやや大きい方にシフトしている。実際には、前記励磁コイル８で発生する磁場の強さは、測定対象の鋼種に応じて決定すべきであるが、本実施形態では１０００〜２０００Ａ／ｍ程度になるように巻数と励磁電流量を決定した。尚、導電率は、圧縮応力によって殆ど変化しないことがわかったので、以後導電率は一定として扱うことにした。   From these results, it was found that the magnetic properties of SCM435 and SS400 deteriorated in proportion to the compressive stress. It can also be seen that the magnitude of the external magnetic field (H), whose permeability changes greatly with changes in compressive stress, is in a relatively small range. Therefore, when the magnitude of the magnetic field generated by the excitation coil 8 is set within this range, the change in the signal detected by the detection coil 7 increases. The SCM 400 and SS 400 have different external magnetic field (H) ranges in which the magnetic permeability changes greatly, and the SCM 400 is shifted to a slightly larger one. Actually, the strength of the magnetic field generated by the exciting coil 8 should be determined according to the steel type to be measured, but in this embodiment, the number of turns and the amount of exciting current are about 1000 to 2000 A / m. It was determined. In addition, since it has been found that the electrical conductivity hardly changes due to the compressive stress, the electrical conductivity is assumed to be constant thereafter.

次に、ボルト頭部の各圧縮応力を有限要素法の３次元応力解析で求め、各応力に見合った磁化曲線を使用した非線形電磁界解析を行い、ボルトの締め付けによって変化する電磁気特性差を検出することで、ボルトの締付力と対応させる検討を検証実験も含めて行った。解析にはＭ１０のボルトの諸元を用いた。図９に、励磁コイル８に供給する励磁電流が０．５Ａ、１ｋＨｚの場合に、ボルト締付力を変化させたときの検出コイル内の磁束密度の減衰率の変化を解析した結果を示す。この結果、ボルトの締付力が１〜３０ｋＮで変化させたとき、磁束密度は約１％低下することがわかる。   Next, each compressive stress of the bolt head is obtained by a three-dimensional stress analysis of the finite element method, a nonlinear electromagnetic field analysis using a magnetization curve corresponding to each stress is performed, and an electromagnetic characteristic difference that changes due to bolt tightening is detected. As a result, a study to make it correspond to the bolt tightening force was conducted, including verification experiments. The specifications of M10 bolts were used for the analysis. FIG. 9 shows the result of analyzing the change in the attenuation rate of the magnetic flux density in the detection coil when the bolt fastening force is changed when the exciting current supplied to the exciting coil 8 is 0.5 A and 1 kHz. As a result, it can be seen that when the bolt tightening force is varied from 1 to 30 kN, the magnetic flux density decreases by about 1%.

また、本発明の測定原理の整合性を検証するため検証実験を行った。実験では長さ７５ｍｍのＭ１０半ねじ六角ボルトを用い、軸部の中心部にひずみゲージを埋め込み、基準となるボルトの締付力を測定した。実験結果を併せて図９に示す。磁束密度の減衰率において、前述の解析の計算結果と実験による測定結果では同じ傾向が見られた。   In addition, a verification experiment was performed to verify the consistency of the measurement principle of the present invention. In the experiment, a 75 mm long M10 half screw hex bolt was used, a strain gauge was embedded in the central portion of the shaft portion, and the tightening force of the reference bolt was measured. The experimental results are also shown in FIG. The same tendency was observed in the calculation results of the above-mentioned analysis and the experimental measurement results in the decay rate of the magnetic flux density.

次に、本発明のボルト締付力検査装置を用いて、ボルトの締付力の検査を行う場合の最適な励磁周波数を実験によって検討した。ボルトに与える締付力は、１〜３０ｋＮとし、励磁電流は０．５Ａで固定し、励磁周波数は５０Ｈｚ〜２０ｋＨｚで評価を行った。検出コイルに得られる磁束密度の減衰率の実験結果を図１０に示す。図１０より、磁束密度の減衰率が一番大きくなる周波数は２０ｋＨｚであることがわかった。しかし、励磁電流の周波数が高くなり過ぎると、表皮効果によって磁場の浸透深さが浅くなり、圧縮応力が作用している領域を十分にカバーできなくなるため、適度な周波数に設定する必要がある。   Next, by using the bolt tightening force inspection device of the present invention, the optimum excitation frequency when examining the bolt tightening force was examined by experiments. The tightening force applied to the bolt was 1 to 30 kN, the excitation current was fixed at 0.5 A, and the excitation frequency was evaluated at 50 Hz to 20 kHz. FIG. 10 shows the experimental results of the magnetic flux density attenuation rate obtained in the detection coil. From FIG. 10, it was found that the frequency at which the attenuation rate of the magnetic flux density is the largest is 20 kHz. However, if the frequency of the excitation current becomes too high, the penetration depth of the magnetic field becomes shallow due to the skin effect, and it becomes impossible to sufficiently cover the region where the compressive stress is acting, so it is necessary to set an appropriate frequency.

図１１は、Ｍ３０のボルトを手動トルクレンチで締め付けたときのトルクレンチの読み（締付トルク）と第１検出コイルと第２検出コイルの差動出力の関係を示したグラフである。ここで、励磁コイルに供給する励磁電流は０．５Ａ、周波数２．５ｋＨｚである。視覚的に理解し易いように、締付トルクの増加につれて差動出力が増加するように極性を表示した。締付トルクは、ボルト頭部と被締結体との間の摩擦力、あるいはワッシャを介在させる場合には、ボルト頭部、ワッシャ、被締結体の各間の摩擦力が反映されるので、ボルトの締付力に正確に対応しないが、締付トルクと検出コイルの差動出力は略比例する関係が得られた。本発明によりボルト締付力が比較的正確に測定できることが実証された。   FIG. 11 is a graph showing the relationship between the torque wrench reading (tightening torque) and the differential output of the first detection coil and the second detection coil when the M30 bolt is tightened with a manual torque wrench. Here, the excitation current supplied to the excitation coil is 0.5 A and the frequency is 2.5 kHz. For ease of visual understanding, the polarity was displayed so that the differential output increased as the tightening torque increased. The tightening torque reflects the frictional force between the bolt head and the body to be fastened, or the frictional force between the bolt head, washer, and the body to be fastened. The tightening torque and the differential output of the detection coil are approximately proportional to each other. It has been demonstrated by the present invention that the bolt clamping force can be measured relatively accurately.

また、前述のプローブ１をナットランナーのソケット体に内蔵させることも可能である。つまり、ナットランナーのソケット体は、円筒状の端部に六角孔が形成された円板が交換可能に取付けられており、その円板の内方に断面略コ字形の環状ヨークを形成するとともに、環状ヨークの断面略コ字形のコイル収容溝に励磁コイルと検出コイルを収容した構造となる。このナットランナーは、例えばエンジンのシリンダヘッドの取付ボルトを締め付けると同時に、その締付力を測定することが可能となる。   It is also possible to incorporate the probe 1 in the socket body of the nut runner. That is, the socket body of the nut runner is attached so that a disk having a hexagonal hole formed at a cylindrical end portion is replaceable, and an annular yoke having a substantially U-shaped cross section is formed inside the disk. In this structure, the exciting coil and the detecting coil are accommodated in the coil accommodating groove having a substantially U-shaped cross section of the annular yoke. This nut runner can measure the tightening force at the same time as tightening a mounting bolt of a cylinder head of an engine, for example.

本発明のボルト締付力検査装置は、各種産業機器や構造物のボルトの締付具合を検査するために使用することができる。例えば、車両のタイヤの取付ボルトや橋梁等の鋼材の締結ボルト等の締付力の測定あるいは締付状態の良否を検査することができる。   The bolt tightening force inspection device of the present invention can be used for inspecting the tightening condition of various industrial equipment and structures. For example, it is possible to measure the tightening force of a vehicle tire mounting bolt or a fastening bolt of a steel material such as a bridge, or to check the quality of the tightening state.

１ プローブ
２ ボルト
３ ナット
４ 被締結体
５ 環状ヨーク
６ 第１検出コイル
７ 第２検出コイル
８ 励磁コイル
９ 軸部
１０ 貫通孔
１１ コイル収容溝
１２ コネクター
１３ 本体部
１４ カバー体
１５ 六角孔
１６ 円筒状立壁
１７ 側面部
１８ 円孔
１９ 保護層
２０ 発振回路
２１ 励磁電流供給回路
２２ 検出回路
２３ 増幅回路
２４ ＤＣ変換回路
２５ 表示器
２６，２７ 増幅回路
２８，２９ 変換回路
３０ 検出回路
３１ 表示器。
DESCRIPTION OF SYMBOLS 1 Probe 2 Bolt 3 Nut 4 Fastened body 5 Annular yoke 6 1st detection coil 7 2nd detection coil 8 Excitation coil 9 Shaft part 10 Through-hole 11 Coil accommodating groove 12 Connector 13 Main-body part 14 Cover body 15 Hexagonal hole 16 Cylindrical shape Standing wall 17 Side surface portion 18 Hole 19 Protective layer 20 Oscillation circuit 21 Excitation current supply circuit 22 Detection circuit 23 Amplification circuit 24 DC conversion circuit 25 Display 26, 27 Amplification circuit 28, 29 Conversion circuit 30 Detection circuit 31 Display.

Claims (7)

被締結体に締付力を伝達するボルト頭部若しくはナットの外周部に、ボルト軸部の軸方向と直交するように巻回した励磁コイルと検出コイルとを同芯状に配置するとともに、該励磁コイルと検出コイルとを取り囲み前記ボルト頭部若しくはナットとでポロイダル方向の磁気回路を形成するように環状ヨークを配置し、前記励磁コイルに供給した交流電流又はパルス電流によって前記ボルト頭部若しくはナットの側面部を略軸方向に磁化し、該側面部の透磁率の大きさに応じて前記検出コイルに誘起する誘導電流を計測し、ボルト軸部の締付力を測定することを特徴とするボルト締付力検査装置。   An excitation coil and a detection coil wound so as to be orthogonal to the axial direction of the bolt shaft portion are arranged concentrically around the outer periphery of the bolt head or nut that transmits the tightening force to the fastened body, An annular yoke is disposed so as to surround the excitation coil and the detection coil to form a magnetic circuit in the poloidal direction with the bolt head or nut, and the bolt head or nut is supplied by the alternating current or pulse current supplied to the excitation coil. Is magnetized in a substantially axial direction, the induced current induced in the detection coil is measured according to the magnetic permeability of the side surface, and the tightening force of the bolt shaft is measured. Bolt tightening force inspection device. 前記検出コイルは独立した第１検出コイルと第２検出コイルとからなり、前記ボルト頭部若しくはナットの外周部で、被締結体とは反対側の先端部に第１検出コイルを配置するとともに、被締結体側の基端部に第２検出コイルを配置し、前記第１検出コイルと第２検出コイルの差動出力を計測してボルト軸部の締付力を測定する請求項１記載のボルト締付力検査装置。   The detection coil is composed of an independent first detection coil and a second detection coil, and the first detection coil is arranged at the tip of the bolt head or the nut on the opposite side of the body to be fastened, The bolt according to claim 1, wherein a second detection coil is arranged at a base end portion on the fastened body side, and a differential output between the first detection coil and the second detection coil is measured to measure a tightening force of the bolt shaft portion. Tightening force inspection device. 前記ボルト頭部若しくはナットの外周部に装着するプローブに前記環状ヨークを備え、前記励磁コイル及び第１検出コイルと第２検出コイルとを、該第１検出コイルと第２検出コイルとの間に空間を設けて前記環状ヨークの断面略コ字形のコイル収容溝内に収容してなる請求項２記載のボルト締付力検査装置。   The probe attached to the bolt head or the outer periphery of the nut includes the annular yoke, and the excitation coil, the first detection coil, and the second detection coil are disposed between the first detection coil and the second detection coil. The bolt tightening force inspection device according to claim 2, wherein a space is provided and received in a coil receiving groove having a substantially U-shaped cross section of the annular yoke. 前記第１検出コイルと第２検出コイルの出力を差動増幅器又は減算器からなる検出回路に入力し、その差動出力を増幅回路で増幅した後、ＤＣ変換回路で整流して直流電圧に変換して出力信号とする請求項２又は３記載のボルト締付力検査装置。   The outputs of the first detection coil and the second detection coil are input to a detection circuit comprising a differential amplifier or a subtractor, the differential output is amplified by an amplification circuit, and then rectified by a DC conversion circuit to be converted into a DC voltage. The bolt tightening force inspection device according to claim 2 or 3, wherein the output signal is an output signal. 前記第１検出コイルと第２検出コイルのそれぞれの出力をＤＣ変換回路で整流して直流電圧に変換し、両出力電圧を差動増幅器又は減算器からなる検出回路に入力し、その差動出力を出力信号とする請求項２又は３記載のボルト締付力検査装置。   The respective outputs of the first detection coil and the second detection coil are rectified by a DC conversion circuit and converted into a DC voltage, and both output voltages are input to a detection circuit comprising a differential amplifier or a subtractor, and the differential output thereof. The bolt tightening force inspection device according to claim 2 or 3, wherein is an output signal. 被締結体とボルト頭部若しくはナットとの間にワッシャを備える締結構造において、前記環状ヨークの軸方向一端部を前記ワッシャに当接するとともに、軸方向他端部をボルト頭部若しくはナットの先端部に当接し、前記環状ヨーク、前記ボルト頭部若しくはナット及び前記ワッシャとでポロイダル方向の磁気回路を形成してなる請求項１〜５何れか1項に記載のボルト締付力検査装置。   In the fastening structure having a washer between the body to be fastened and the bolt head or nut, the axial end of the annular yoke abuts on the washer and the other end in the axial direction is the tip of the bolt head or nut. 6. The bolt tightening force inspection device according to claim 1, wherein a magnetic circuit in a poloidal direction is formed by the annular yoke, the bolt head or nut, and the washer. 前記環状ヨークの一部が、前記ボルト頭部若しくはナットに係合し、回転締付可能なレンチを構成している請求項１〜６何れか1項に記載のボルト締付力検査装置。
The bolt tightening force inspection device according to any one of claims 1 to 6, wherein a part of the annular yoke is engaged with the bolt head or the nut to constitute a wrench that can be rotationally tightened.

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