JP7284475B1 - Axial tightening force detection method and axial tightening force detection device - Google Patents

Abstract

A stable tightening axial force detection method is provided. A tightening axial force detection method for detecting the tightening axial force of a bolt in a bolted body, wherein the bolt is directly or indirectly pulled while holding down a predetermined portion of the bolted body to displace the point of force application and an information acquisition step of acquiring information about a change in the tensile force; a compliance calculation step of obtaining the compliance of the bolt based on the information acquired in the information acquisition step; A compliance correction step that corrects the compliance in the spring constant indefinite portion of the bolt whose spring constant is indefinite before reaching , and a correction that is the displacement of the spring constant indefinite portion based on the corrected compliance and tensile force corrected in the compliance correction step Based on a corrected displacement calculating step of calculating a displacement, the maximum value of the corrected compliance and the value of the corrected displacement corresponding to the maximum value of the corrected compliance, the axial force increase amount is obtained, and the obtained axial force increase amount is used as the corrected compliance value. and a tightening axial force calculation step of calculating the tightening axial force of the bolt by subtracting from the tensile force corresponding to the maximum value. [Selection drawing] Fig. 6

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection method for detecting a tightening axial force of a bolt in a bolted body.

Fastening by a bolt fastening body is indispensable for the assembly of machines such as automobiles and structures such as bridges. The strength of a bolted body is greatly affected by the axial tightening force. The method for detecting the tightening axial force disclosed in Non-Patent Document 1 will be described in detail below.

FIG. 14 is a citation of Non-Patent Document 1. FIG. FIG. 14(a) is a schematic diagram of a bolted assembly. FIG. 14(b) is a graph showing the relationship between the three parameters of force application point displacement δ, tensile force P, and axial force F. The horizontal axis is force application point displacement δ, and the vertical axis is tensile force P (bolt axis force F). The tensile force P is indicated by a solid line, and the axial force F is indicated by a wavy line. FIG. 14(c) is an enlarged view of a part of FIG. 14(a), the left side of which shows the state before the thread surfaces of the bolt and nut are separated, and the right side of the drawing shows the state of the bolt and nut. It shows the state after the threaded surfaces are separated.

A bolted body includes at least a bolt and a body to which the bolt is fastened. In addition to these, other members related to fastening such as nuts and washers may be included. In the illustrated example, the bolted body consists of a bolt 10, a nut 11, and an object H to be fastened, and the bolt 10 and the nut 11 are fastened to the object H to be fastened.
The object to be fastened H is a stack of two objects to be fastened. A through hole through which the bolt shaft portion 10b of the bolt 10 passes is formed in the object H to be fastened. The through hole is not threaded. Therefore, the bolt 10 is screwed only into the nut 11 and is not screwed into the through hole of the body H to be fastened.

Referring to FIG. 14(a), when a tensile force is applied to the tip of the bolt shaft portion 10b while pressing the nut upper surface 11b so that the nut 11 does not move upward, as shown in FIG. 14(b), The tensile force P and the tightening axial force F increase non-linearly with respect to the force application point displacement δ. Furthermore, when the tensile force P is increased, the bolt threaded surface 10b1 is completely separated from the nut threaded surface 11a (see FIG. 14(c)), and when the tensile force P reaches Pc, the tensile force P and the tightening axial force F be equivalent. When the tensile force P and the axial tightening force F become equal (that is, when the bolt threaded surface 10b1 is completely separated from the nut threaded surface 11a), the tensile force P and the axial tightening force F are linear with respect to the force application point displacement δ. increase exponentially.

Before the nut threaded surface 11a and the bolt threaded surface 10b1 are separated from each other, the bolt 10 is elongated within the range of the grip length lg in FIG. 14(a). The grip length lg is the distance from the upper surface to the lower surface of the object H to be fastened. On the other hand, in the state after the nut threaded surface 11a and the bolt threaded surface 10b1 are separated from each other, the bolt 10 extends within the range of the length _l0 . The length _l0 is a value obtained by adding the engagement length of the bolt 10 and the nut 11 to the aforementioned grip length lg.

Thus, the length of extension of the bolt 10 differs before and after the nut threaded surface 11a and the bolt threaded surface 10b1 are separated from each other. Therefore, the apparent spring constant (hereinafter referred to as spring constant), which is the relationship between the tensile force P and the force application point displacement δ, also differs before and after the nut threaded surface 11a and the bolt threaded surface 10b1 are separated from each other. In Non-Patent Document 1, focusing on the change in this spring constant, the tensile force P when the nut threaded surface 11a and the bolt threaded surface 10b1 are separated from each other is measured.

Specifically, process 1 is the state before the bolt threaded surface 10b1 separates from the nut threaded surface 11a, process 2 is the state after the bolt threaded surface 10b1 separates from the nut threaded surface 11a, and gradient C is the gradient of the tensile force P in process 1. _A , the gradient of tensile force P in process 2 is defined as gradient _CB . Then, the intersection point I of the straight lines of the gradients _CA and _CB is obtained, and the tensile force P corresponding to this intersection point I is calculated as the tightening axial force _F0 .

Transactions of the Japan Society of Mechanical Engineers (C edition) Vol.68 No.671 (2002-7) Method for detecting tightening force in bolt-nut joints Shinji Uemura Takanori Murakami

However, since the method of Non-Patent Document 1 is unstable in determining the gradient _CA , a detection method different from the detection method of Non-Patent Document 1 has been desired. That is, before the tensile force P is applied, substantially the entire nut threaded surface 11a is in contact with the bolt threaded surface 10b1. When a tensile force P is applied, the bolt threaded surface 10b1 is continuously separated from the nut threaded surface 11a, and the spring constant of the portion of the bolt 10 below the nut upper surface changes. Since it is not clear from where to draw the straight line that determines the slope _CA , the determination of the slope _CA becomes unstable.

In order to solve the above problems, the tightening axial force detection method according to the present invention provides (1) a tightening axial force detection method for detecting the tightening axial force of a bolt in a bolted body, An information acquisition step of directly or indirectly pulling the bolt while holding down a predetermined portion to acquire information on the displacement of the point of application of force and the change in the tensile force; a calculating step, a compliance correcting step of correcting the compliance calculated in the compliance calculating step to compliance in a spring constant indefinite portion of the bolt where the spring constant is inconstant before the tensile force reaches a predetermined value, and the compliance correcting step. Based on the corrected compliance and the tensile force, a corrected displacement calculation step of calculating a corrected displacement, which is the displacement of the part with an indefinite spring constant, and based on the maximum value of the corrected compliance and the value of the corrected displacement corresponding to the maximum value, and a tightening axial force calculation step of calculating the tightening axial force of the bolt by obtaining an axial force increase amount and subtracting the obtained axial force increase amount from the tensile force corresponding to the maximum value of the corrected compliance. It is characterized by

(2) The tightening axial force detection method according to (1) above, wherein the tensile force at which the change of the tensile force with respect to the displacement of the force application point changes from non-linear to linear is set as the predetermined value.

(3) The compliance correction step is a step of obtaining the minimum value of the compliance calculated in the compliance calculation step and subtracting this minimum value from the compliance calculated in the compliance calculation step to obtain the corrected compliance. The tightening axial force detection method according to the above (1) or (2).

(4) The tightening axial force detecting method according to (1) or (2) above, wherein in the corrected displacement calculating step, the corrected displacement is calculated by integrating the corrected compliance with the tensile force.

(5) The tightening axial force detecting method according to (3) above, wherein in the corrected displacement calculating step, the corrected displacement is calculated by integrating the corrected compliance with the tensile force.

(6) The tightening axial force detection method according to (1) or (2) above, wherein the portion of the bolt below the predetermined portion is an indeterminate spring constant portion.

(7) The tightening axial force detection method according to (3) above, wherein the portion of the bolt below the predetermined portion is a spring constant variable portion.

(8) The tightening axial force detection method according to (4) above, wherein the portion of the bolt below the predetermined portion is a spring constant variable portion.

(9) The tightening axial force detection method according to (5) above, wherein the portion of the bolt below the predetermined portion is an indeterminate spring constant portion.

(10) The tightening axial force detection method according to (1) or (2) above, wherein the predetermined portion is the upper surface of the nut included in the bolt fastening body.

(11) The axial tightening force detection method according to (3) above, wherein the predetermined portion is an upper surface of a nut included in the bolt fastening body.

(12) The axial tightening force detecting method according to (4) above, wherein the predetermined portion is an upper surface of a nut included in the bolt fastening body.

(13) The axial tightening force detection method according to (5) above, wherein the predetermined portion is an upper surface of a nut included in the bolt fastening body.

(14) The axial tightening force detection method according to (1) or (2) above, wherein the predetermined portion is an upper surface of a body to be fastened in the bolt fastening body.

(15) The axial tightening force detection method according to (3) above, wherein the predetermined portion is an upper surface of an object to be fastened in the bolt fastening object.

(16) The axial tightening force detection method according to (4) above, wherein the predetermined portion is an upper surface of a body to be fastened in the bolt fastening body.

(17) The axial tightening force detection method according to (5) above, wherein the predetermined portion is an upper surface of a body to be fastened in the bolt fastening body.

The tightening axial force detection device according to the present invention is (18) a tightening axial force detection device for detecting the tightening axial force of a bolt in a bolted body, wherein the bolt is pressed while holding a predetermined portion of the bolted body. an information acquisition unit that acquires information on changes in force application point displacement and tensile force when the bolt is pulled directly or indirectly; and a compliance calculation unit that calculates the compliance of the bolt based on the information acquired by the information acquisition unit; a compliance correction unit that corrects the compliance calculated by the compliance calculation unit to the compliance in the spring constant indefinite portion of the bolt where the spring constant is indefinite before the tensile force reaches a predetermined value; and the corrected compliance corrected by the compliance correction unit. and a corrected displacement calculation unit that calculates a corrected displacement, which is the displacement of the indeterminate spring constant portion, based on the tensile force, and an axial force increase amount based on the maximum value of the corrected compliance and the corrected displacement value corresponding to the maximum value. and a tightening axial force calculation unit that calculates the tightening axial force of the bolt by subtracting the obtained axial force increase amount from the tensile force corresponding to the maximum value of the corrected compliance. do.

(19) The axial tightening force detecting device according to (18), wherein the predetermined value is the tensile force when the change of the tensile force with respect to the force applied point displacement changes from non-linear to linear.

(20) The compliance correction unit obtains the minimum value of the compliance calculated by the compliance calculation unit, and subtracts this minimum value from the compliance calculated by the compliance calculation unit to obtain the corrected compliance. The tightening axial force detection device according to (18) or (19) above.

(21) The axial tightening force detecting device according to (18) or (19), wherein the corrected displacement calculation unit performs a process of calculating the corrected displacement by integrating the corrected compliance with the tensile force.

(22) The axial tightening force detecting device according to (20), wherein the corrected displacement calculation unit performs a process of calculating the corrected displacement by integrating the corrected compliance with the tensile force.

According to the present invention, it is possible to stably detect the tightening axial force.

Fig. 2 is a schematic diagram of a bolted connection and a tensioning device; 5 is a graph showing the relationship among force application point displacement δ, tensile force P and axial force F; 5 is a graph showing the relationship between acquired force application point displacement δ and tensile force P. FIG. 4 is a graph of calculated compliance C; FIG. 4 is a transition diagram showing behavior when a bolt thread surface separates from a nut thread surface. 4 is a graph of modified compliance C', etc.; 7 is a graph of correction displacement δ' and the like; 1 is an embodiment of an axial tightening force detection device; FIG. 11 is a first modification of the tightening axial force detection device; FIG. Fig. 2 is a second modified example of the tightening axial force detection device; Fig. 3 is a modification 3 of the tightening axial force detection device; Fig. 4 is a fourth modified example (pulling washer) of the tightening axial force detection device; Fig. 4 is a modification 4 (nut tensioning) of the tightening axial force detection device; FIG. 5 is an explanatory diagram of a conventional tightening axial force detection method;

A method for detecting axial tightening force, which is an embodiment of the present invention, will be described. FIG. 1 illustrates a state in which an axial tightening force detector is attached to the bolted body of FIG. 14(a). However, for convenience of explanation, the length of the bolt shaft portion is shown to be slightly longer than that in FIG. 14(a). Since the bolt fastening body has been described in Background Art, detailed description thereof will be omitted.

A recess 1a is formed at the lower end of the tightening axial force detection device 1, and a thread groove is cut on the inner peripheral surface of this recess 1a. The upper end of the bolt shaft portion 10b protrudes from the nut upper surface 11b and is screwed into the recess 1a. The tightening axial force detection device 1 is provided with a pressing mechanism (not shown) that presses the nut upper surface 11b. Therefore, in a state where the upper end of the bolt shaft portion 10b is screwed into the concave portion 1a of the tightening axial force detecting device 1, the holding mechanism holds the nut upper surface 11b so that the nut 11 does not move upward, and the bolt 10 is pulled. Tests can be conducted.

FIG. 2 is a graph showing the relationship between the force application point displacement δ, the tensile force P, and the axial force F detected in the tensile test, and corresponds to FIG. 14(b). As shown in FIG. 14(a), when the bolt 10 fastened with the tightening axial force _F0 is pulled while pressing the nut upper surface 11b, as described above, the axial force F and the tensile force P correspond to the wavy line and the solid line, respectively. increases along The wavy line is the axial force F, and the solid line is the tensile force P. Here, the tensile force P immediately after the bolt threaded surface 10b1 is completely separated from the nut threaded surface 11a (corresponding to the “predetermined value” in the claims, hereinafter also referred to as “predetermined value”) or the tensile force exceeding this P is P _Max (corresponding to the "tensile force corresponding to the maximum value of the corrected compliance" described in the claims), and the increase amount of the axial force F with respect to the tightening axial force F ₀ (described in the claims is defined as ΔF, the tightening axial force _F0 is defined by the following equation (1). In FIG. 2, the tensile force P immediately after the bolt threaded surface 10b1 is completely separated from the nut threaded surface 11a is defined as P _Max , but as will be described later, a higher tensile force than the tensile force P may be defined as P _Max .

Here, P _Max can be obtained by sequentially detecting the tensile force P during the tensile test. Specifically, as described above, when the tensile force P increases and the bolt threaded surface 10b1 is completely separated from the nut threaded surface 11a, the change of the tensile force P with respect to the force application point displacement δ changes from nonlinear to linear. The tensile force P at or above which it occurs can be defined as P _Max (corresponding to "the tensile force corresponding to the maximum value of the modified compliance" in the claims). That is, the tensile force P is differentiated by the force application point displacement δ, and the tensile force P when the differentiated value stops changing or the tensile force P exceeding it can be defined as P _Max .

Here, when a tensile force P is applied, the bolt threaded surface 10b1 is continuously separated from the nut threaded surface 11a, and the spring constant of the portion of the bolt 10 below the nut upper surface 11b changes moment by moment. When the bolt threaded surface 10b1 is completely separated from the nut threaded surface 11a, the spring constant becomes constant. That is, the spring constant of the portion of the bolt 10 below the nut upper surface 11b changes from indefinite to constant when the tensile force P reaches the above-described predetermined value. In this specification, the portion of the bolt 10 where such behavior occurs (in this embodiment, the portion below the nut upper surface 11b) is defined as the variable spring constant portion. As the state of engagement between the bolt 10 and the nut 11 changes, the force acting on the portion of the bolt 10 below the lower surface of the nut also changes. Therefore, the spring constant indefinite portion includes the portion of the bolt 10 below the lower surface of the nut. The boundary between the variable spring constant portion and the constant spring constant portion corresponds to the position where the reaction force is applied.
On the other hand, the portion of the bolt 10 above the nut upper surface 11b, which does not mesh with the nut 11, has a constant spring constant without changing, and is defined as a constant spring constant portion.

Here, in the tensile test, if the displacement of the part with an indefinite spring constant (corresponding to the "correction displacement δ' _Max " described later) can be obtained, the axial force increase amount ΔF can be calculated according to Hooke's law. can.
The inventors of the present invention have studied a method of using the amount of change in the spring constant when calculating the displacement of the portion with the indefinite spring constant, but it was technically difficult as described below.

To simplify the explanation, the difficulty of using the spring constant is explained using a composite equation for springs connected in series.
When the spring constant of one spring 1 connected in series is k1 and the spring constant of the other spring 2 is k2, the combined spring constant k is defined by the following equation (2).

Here, when the spring constant k2 of the spring 2 changes to k2' and the composite spring constant K changes to K', the amount of change in the composite spring constant is defined by the following equation (3).

In equation (3), one of spring constant k1 and spring constant k2 must be known in order to obtain the amount of change from spring constant k2 to k2' based on the amount of change in spring constant k. That is, when the spring constant k1 and the spring constant k2 are unknown, the amount of change from the spring constant k2 to k2' cannot be obtained based on the amount of change in the spring constant k. Therefore, it is mathematically difficult to obtain the axial force increase amount ΔF based on the amount of change in the spring constant.

Therefore, the inventors of the present invention have studied a method of obtaining the axial force increase amount ΔF using the amount of change in apparent compliance (hereinafter referred to as compliance), which is the reciprocal of the spring constant.
Now consider the combined compliance of the springs connected in series as well as the spring constant. When the compliance of one spring 1 connected in series is c1 and the compliance of the other spring 2 is c2, the combined compliance c is defined by the following equation (4).

Here, when the composite compliance c changes to c' due to the change of the compliance c2 of the spring 2 to c2', the amount of change in the composite compliance is defined by the following equation (5).

Thus, when the spring elements are connected in series, the change in compliance can be used to remove the effect of the constant term in series springs, including springs with unknown compliance. The constant term is the term in which the compliance does not change, that is, the compliance c1 in the formula (5). In FIG. It's about.

式（６）は、以下の算出ステップに基づき、導出される。
情報取得ステップ：ナット上面１１ｂ（請求項１に記載の「所定の部位」に相当する）を押さえながら、ボルト軸部１０ｂを引っ張ることにより、着力点変位δ及び引張力Ｐの変化に関する情報を取得する。
コンプライアンス算出ステップ：情報取得ステップで取得した情報に基づき、ボルト１０のコンプライアンスを求める。
コンプライアンス修正ステップ：コンプライアンス算出ステップで取得したコンプライアンスを、バネ定数不定部におけるコンプライアンスに修正して、修正コンプライアンスを算出する。
修正変位算出ステップ：コンプライアンス修正ステップで算出した修正コンプライアンス及び引張力に基づき、バネ定数不定部の変位である修正変位を算出する。
以下、各ステップに項分けして詳細に説明する。 Based on the above considerations, the present inventors arrived at a method of estimating the axial force increase amount ΔF based on the change in compliance in the spring constant indefinite portion and the displacement of the spring constant indefinite portion. The axial force increase amount ΔF is defined by a formula as follows.

Equation (6) is derived based on the following calculation steps.
Information Acquisition Step: Acquiring information on changes in force application point displacement δ and tensile force P by pulling the bolt shaft portion 10b while pressing the nut upper surface 11b (corresponding to the “predetermined portion” in claim 1). do.
Compliance calculation step: Find the compliance of the bolt 10 based on the information acquired in the information acquisition step.
Compliance correction step: correcting the compliance obtained in the compliance calculation step to the compliance in the spring constant indeterminate portion to calculate the corrected compliance.
Corrected displacement calculation step: Based on the corrected compliance and tensile force calculated in the compliance correction step, a corrected displacement, which is the displacement of the spring constant indefinite portion, is calculated.
Each step will be described in detail below.

(About the information acquisition step)
Information on changes in the force application point displacement δ and the tensile force P of the bolt 10 is obtained by performing the above-described tensile test. The details of how to acquire the tensile force P and the force application point displacement δ will be described later.
FIG. 3 is a graph showing the relationship between the acquired force application point displacement δ and the tensile force P, in which the vertical axis and the horizontal axis of FIG. 2 are interchanged. Before the tensile force reaches the above-described predetermined value, the force application point displacement δ increases nonlinearly with respect to the tensile force P, and when the tensile force reaches the above-described predetermined value, the force application point displacement δ becomes increases linearly with The reason for this has been described above and will not be repeated.

図４は、式（７）に基づき算出したコンプライアンスＣのグラフであり、右側の縦軸がコンプライアンスＣ[ｍｍ／ｋＮ]であり、左側の縦軸が引張力Ｐ又は軸力Ｆ[ｋＮ]であり、横軸が着力点変位δ[ｍｍ]である。コンプライアンスＣの変化の挙動を把握するため、コンプライアンスＣとともに、引張力Ｐ及び軸力Ｆのグラフも示している。なお、引張力Ｐ及び軸力Ｆのグラフは、図２の引用である。 (Compliance calculation step)
The compliance C of the bolt 10 is calculated based on the information (information in FIG. 3) acquired in the information acquisition step.
Here, since the compliance C is the reciprocal of the spring constant, it is defined by the following equation (7) based on Hooke's law.

FIG. 4 is a graph of the compliance C calculated based on the formula (7), the vertical axis on the right side is the compliance C [mm/kN], and the vertical axis on the left side is the tensile force P or the axial force F [kN]. , and the horizontal axis is the force application point displacement δ [mm]. In order to grasp the behavior of changes in the compliance C, graphs of the tensile force P and the axial force F are also shown together with the compliance C. FIG. Graphs of the tensile force P and the axial force F are quoted from FIG.

この式では、バネ定数一定部のコンプライアンスをｃ_１と定義している。また、バネ定数不定部をボルト１０の軸方向に沿ってｎ-１個の要素に分割しており、それぞれの要素のコンプライアンスをｃ_２～ｃ_ｎと定義している。なお、ｃ_２がバネ定数不定部の上端に位置する要素のコンプライアンスであり、ｃ_ｎがバネ定数不定部の下端に位置する要素のコンプライアンスである。
引張試験を実施すると、バネ定数不定部における上端の要素から順にコンプライアンスが変化する。一方、コンプライアンスｃ_１は、ナット上面１１ｂよりも上側のコンプライアンスであるから、引張試験中に変動しない。
つまり、コンプライアンスＣ_（１）は、引張を開始する前のコンプライアンスであり、引張力Ｐを高めることにより、Ｃ_（２）→Ｃ_（３）→・・・・・→Ｃ_（ｎ）の順に、コンプライアンスが変化する。なお、ナットネジ面１１a及びボルトネジ面１０ｂ１が完全に離間したときのコンプライアンスがＣ_（ｎ）であり、この状態から引張力を更に高めても、ボルトネジ面１０ｂ１及びナットネジ面１１aは互いに離間したままであるから、コンプライアンスはＣ_（ｎ）のままである。 Here, as described above, the spring constant of the spring-constant variable portion changes moment by moment in the process of separating the bolt screw surface 10b1 from the nut screw surface 11a, so the compliance C, which is the reciprocal of the spring constant, also changes. FIG. 5 is a transition diagram when the bolt threaded surface 10b1 is separated from the nut threaded surface 11a. As shown in the figure, when the tensile force P is applied, the nut threaded surface 11a and the bolt threaded surface 10b1 are separated continuously in this order from the upper side to the lower side. The dotted line shown in the figure is the boundary line between the engagement area and the separation area of the bolt 10 and the nut 11. The area below the boundary line is the engagement area, and the area above the boundary line is the separation area. This boundary line gradually decreases as the tensile force P increases, and along with this, the compliance C of the bolt 10 changes from moment to moment. The following formula expresses the behavior in which the compliance C changes.

In this equation, the compliance of the constant spring constant portion is defined as _c1 . Also, the spring constant indefinite portion is divided into n−1 elements along the axial direction of the bolt 10, and the compliance of each element is defined as c ₂ to c _n . Note that _c2 is the compliance of the element positioned at the upper end of the spring constant variable portion, and _cn is the compliance of the element positioned at the lower end of the spring constant variable portion.
When a tensile test is performed, the compliance changes in order from the upper end element in the spring constant indefinite portion. On the other hand, since the compliance _c1 is the compliance above the nut upper surface 11b, it does not fluctuate during the tensile test.
That is, the compliance C ₍₁₎ is the compliance before starting the tension, and by increasing the tensile force P, in the order of C ₍₂₎ → C ₍₃₎ → ... → C _(n) , Compliance changes. The compliance when the nut threaded surface 11a and the bolt threaded surface 10b1 are completely separated is C _(n) , and even if the tensile force is further increased from this state, the bolt threaded surface 10b1 and the nut threaded surface 11a remain separated from each other. , the compliance remains C _(n) .

修正コンプライアンスＣ´のグラフを図４に描き、これを図６に示す。 (compliance fix step)
As described above, the portion of the bolt 10 above the top surface of the nut (constant spring constant portion) has a constant spring constant during the tensile test, so it need not be taken into account when calculating ΔF. In other words, when calculating ΔF, attention should be paid only to the spring constant indeterminate portion where the spring constant changes. On the other hand, since the compliance C calculated based on the formula (7) is the compliance of the entire bolt 10, the compliance of the constant spring constant portion is subtracted from the compliance C to obtain the corrected compliance C', which is the compliance of the indeterminate spring constant portion. There is a need.
Here, as shown in FIG. 4, as the displacement δ of the point of application of force increases, the compliance C decreases once and then gradually increases. C)) can be obtained. Since the compliance is the reciprocal of the spring constant, the spring constant is maximized at the position where the compliance C is minimized. By subtracting the minimum value minimum(C) from the compliance C, the corrected compliance C' can be calculated. When this is expressed by a formula, it is as follows.

A graph of modified compliance C' is plotted in FIG. 4 and is shown in FIG.

In FIG. 6, _C'Max, which is the maximum value of C', is specified. In the figure, since the maximum value _C'Max is substantially the same in the range indicated by the double arrow, the maximum value _C'Max should be selected within this range. The tensile force P corresponding to the selected maximum value _C'Max corresponds to _PMax in equation (1). The maximum value _C'Max may be considered to be equivalent to the compliance of the spring-constant variable portion when the nut threaded surface 11a and the bolt threaded surface 10b1 are completely separated from each other.

なお、修正コンプライアンスＣ´はボルト１０のバネ定数不定部におけるコンプライアンスであるから、修正変位δ´は、バネ定数不定部の引張力Ｐによる変位と見做すことができる。
積分区間を「引張力Ｐの負荷の開始から、修正コンプライアンスＣ´が最大値Ｃ´_Ｍａｘになるまで」に設定して、式（１０）を計算することにより、式（６）の修正変位の値であるδ´_Ｍａｘ（特許請求の範囲に記載の「最大値に対応する修正変位の値」に相当する）を求めることができる。 (Correction displacement calculation step)
By integrating the corrected compliance C' with the tensile force P, the corrected displacement ?' can be calculated. When this is defined by the formula, it is as follows.

In addition, since the corrected compliance C' is the compliance in the spring constant indefinite portion of the bolt 10, the corrected displacement .delta.' can be regarded as the displacement due to the tensile force P in the spring constant indefinite portion.
By setting the integration interval to "from the start of the load of the tensile force P until the corrected compliance C' reaches the maximum value _C'Max " and calculating the formula (10), the corrected displacement of the formula (6) A value δ′ _Max (corresponding to the “correction displacement value corresponding to the maximum value” described in the claims) can be obtained.

FIG. 7 shows a graph of the corrected displacement δ' calculated by Equation (10). FIG. 7 is a graph corresponding to FIG. However, the vertical axis on the right side is the axial force increase amount ΔF of the tightening axial force, and a graph of the amount of change in the axial force is also shown. The “selection range of δ′ _Max ” indicated by a double arrow corresponds to the “selection range of C′ _Max ” in FIG. 6, and “C′ _Max ” in FIG. 6 corresponds to “δ′ _Max ” in FIG. do. Therefore, the value on the right vertical axis corresponding to _δ'Max in FIG. 7 is the _amount of increase in axial force ΔF _. Calculated by multiplying. Note that when another "_{C'Max "} is selected in the "C'Max selection range", the values of " _PMax " and "_δ'Max" also change, but these correspond to each other. Therefore, the calculated values of the tightening axial force _F0 are substantially the same.

Therefore, by dividing the corrected displacement value _δ'Max by _C'Max , which is the maximum value of the corrected compliance C', the axial force increase amount ΔF can be obtained. That is, by multiplying the reciprocal of _C'Max by the correction displacement value _.delta.'Max , the axial force increase amount .DELTA.F can be obtained based on Hooke's law.
Then, the tightening axial force _F0 can be obtained by subtracting the axial force increase amount ΔF from P _Max corresponding to the selected maximum value C′ _Max (see formula (1)).

A more detailed embodiment of the axial tightening force detection device will be described. FIG. 8 is a schematic diagram of a tightening axial force detection device. The tightening axial force detection device of this embodiment has a function of tightening a bolted body and a function of pulling the tightened bolt and detecting the tightening axial force _F0 . Since the description of the bolt fastening body is redundant, it will be omitted.

The tightening axial force detection device 1 includes a tension rod 5, a holder 6, a load cell 7 (corresponding to an information acquisition section), a drive socket 8, a motor M1, a motor M2, a controller C, a displacement sensor DS (corresponding to an information acquisition section). )including.
A recessed portion 5a is formed in the lower end portion of the tension rod 5, and a threaded portion that meshes with the threaded portion of the bolt shaft portion 10b is formed in the inner peripheral surface of the recessed portion 5a. By rotating the tension rod 5 in one direction, the bolt 10 can be pulled upward by the meshing of the bolt shaft portion 10b and the screw portion of the recess 5a.

A motor M1 is used as a power source for rotating the tension rod 5 . For example, the power of the motor M1 can be transmitted to the tension rod 5 by connecting the tension rod 5 and the motor M1 via a reduction mechanism. The controller C controls driving of the motor M1. Note that the tension rod 5 can also be rotated manually by the operator instead of the motor M1.

The holder 6 is arranged outside the outer peripheral surface of the tension rod 5, and the lower end surface 6a of the holder 6 contacts the nut upper surface 11b. The holder 6 holds the nut 11 when the tension rod 5 pulls the bolt 10 upward.

The load cell 7 is arranged between the tension rod 5 and the holder 6 in the axial direction of the bolt 10, and detects the force (pulling force) P [kN] when pulling the bolt 10 upward while holding down the nut 11. . That is, the tensile force P necessary for estimating the tightening axial force _F0 is acquired by the load cell 7. FIG. Information on the tensile force P detected by the load cell 7 is transmitted to the controller C.
The displacement sensor DS detects the displacement (force application point displacement δ) at the force application point of the tension rod when a tensile force P is applied. That is, the force application point displacement δ required for estimating the tightening axial force _F0 is obtained by the displacement sensor DS. Information on the force application point displacement δ detected by the displacement sensor DS is transmitted to the controller C. As shown in FIG.

The drive socket 8 is arranged outside the outer peripheral surface of the holder 6 , and the lower end of the drive socket 8 engages the outer surface of the nut 11 . By rotating the drive socket 8 in one direction, the nut 11 can be screwed in the direction of tightening the body H to be fastened (downward). Further, by rotating the drive socket 8 in the other direction, the nut 11 can be screwed in the direction of releasing the fastening (upward).

A motor M2 is used as a power source for rotating the drive socket 8 . For example, the drive socket 8 and the motor M2 can be connected via a reduction mechanism, and the power of the motor M2 can be transmitted to the drive socket 8. The controller C controls driving of the motor M2.
However, since the drive socket 8 and the motor M2 are not used when calculating the tightening axial force _F0 , they may be omitted.

The controller C executes the compliance calculation step, the compliance correction step, the correction displacement calculation step, and the tightening axial force calculation step based on the tensile force P and the force application point displacement δ acquired from the load cell 7 and the displacement sensor DS. In other words, the controller corresponds to the “compliance calculator, compliance corrector, corrected displacement calculator, and axial tightening force calculator” recited in the claims.
These steps may be performed programmatically. That is, the controller C reads a program from a storage unit (not shown) and executes it to calculate the tightening axial force _F0 .

In this embodiment, the controller C installed in the axial tightening force detection device 1 calculates the axial tightening force _F0 , but the present invention is not limited to this. For example, the tensile force P and the force application point displacement δ acquired by the load cell 7 and the displacement sensor DS are temporarily stored in a hard disk or the like, and the above-mentioned compliance calculation step, compliance correction step, corrected displacement calculation step, tightening The tightening axial force _F0 may be calculated by executing the axial force calculating step. In this case, the load cell 7, the displacement sensor DS, the personal computer, etc. cooperate to realize the axial tightening force detection device 1. FIG.

(Modification 1)
FIG. 9 is a schematic diagram of a tension device of Modification 1, and elements having functions common to those of the axial tightening force detection device of the above embodiment are denoted by the same reference numerals. The tightening axial force detection device of this modification applies the tensile force P to the bolt 10 while pressing the upper surface of the object to be fastened H (object to be fastened H1). Differs from equipment. That is, by applying a tensile force to the bolt 10 while pressing the object H to be fastened with the lower surface of the holder 6, the tensile force P and the force application point displacement δ can be detected via the load cell 7 and the displacement sensor DS. . In addition, the upper surface of the object to be fastened H (the object to be fastened H1) corresponds to the "predetermined part" described in claim 1.
In the illustrated example, the bolt shaft portion 10b is screwed into the nut 11 and the recessed portion 5a, and is not screwed into the body H to be fastened.

In the configuration of this modification, since the position where the reaction force is applied is the upper surface of the object H1 to be fastened, the portion of the bolt 10 above the upper surface of the object H1 (the lower surface of the nut) has a constant spring constant. The portion below the upper surface of the body H1 (the lower surface of the nut) is the spring constant variable portion.

The tensioning device of this modified example also differs from the tightening axial force detecting device of the embodiment in that it does not have the drive socket 8 and the motor M2.

Since the method of calculating the tightening axial force _F0 is the same as in the embodiment, description thereof is omitted.

(Modification 2)
FIG. 10 is a schematic diagram of a tension device of Modification 2, and elements having functions common to those of the axial tightening force detection device of the above embodiment are denoted by the same reference numerals.
This modification differs from the embodiment in the structure of the bolt fastening body. The differences are as follows.
(1) A stat bolt having no bolt head (hereinafter also referred to as a stat bolt 10) is fastened to the fastened body H.
(2) The fastened body H2 of the embodiment in which the threaded portion H21 with which the stat bolt 10 is screwed is formed in the fastened body H2, and the threaded portion is not formed in the hole of the fastened body H2. differ.

Also in the configuration of this modification, with reference to the position where the reaction force is applied, the portion of the bolt 10 above the nut upper surface 11a has a constant spring constant, and the portion of the bolt 10 below the nut upper surface 11a has an indefinite spring constant. Department.

Since the method of calculating the tightening axial force _F0 is the same as in the embodiment, description thereof is omitted.

(Modification 3)
FIG. 11 is a schematic diagram of a tension device of Modification 3, and elements having functions common to those of the axial tightening force detection device of the above-described embodiment are denoted by the same reference numerals.
The tightening axial force detection device of this modified example is configured to pull the bolt 10 via the connecting member 9 connected to the tension rod 5 .
A projection 9a is formed on the upper end of the connecting member 9, and a thread groove is formed on the outer surface of the projection 9a. The concave portion 5a of the tension rod 5 and the convex portion 9a of the connecting member 9 are screwed together. A recess 9b is formed at the lower end of the connecting member 9, and a thread groove is formed on the inner surface of the recess 9b.

The bolt shaft portion 10b is screwed into a threaded portion formed in a through hole of the body H to be fastened. A thread groove is formed on the outer surface of the bolt head 10a, and the bolt head 10a and the recess 9b of the connecting member 9 are screwed together.

FIG. 11 shows a state immediately before tensile force is applied to the bolt 10, the holder 6 is in contact with the upper surface of the object to be fastened H1, and the lower end of the connection member 9 and the object to be fastened H1 are in contact with each other. A clearance is formed therebetween, and a clearance is also formed between the convex portion 9a of the connecting member 9 and the top surface of the concave portion 5a of the tension rod 5. As shown in FIG.

By operating the motor M<b>1 to rotate the tension rod 5 , the connection member 9 moves upward, and a tensile force can be applied to the bolt 10 . Note that the connection member 9 does not rotate when it moves upward.

In the configuration of this modified example, since the reaction force is taken by the upper surface of the object H1 to be fastened, the portion of the bolt 10 above the upper surface of the object H1 to be fastened has a constant spring constant, and The portion of the bolt 10 on the lower side is the spring constant variable portion. Since the method of calculating the tightening axial force _F0 is the same as in the embodiment, description thereof is omitted.

(Modification 4)
In the above-described embodiment and modified examples 1 to 3, the configuration for directly pulling the bolt 10 has been described, but the present invention can also be applied to a tightening axial force detection device for indirectly pulling the bolt 10.
For example, as shown in FIG. 12, a washer 21 is interposed between the bolt head 10a and the body H to be fastened, and a thread groove formed on the outer peripheral surface of the washer 21 and a recess 9b of the connection member 9 are formed. The bolt 10 may be pulled indirectly through the washer 21 by threading the threads together.
Further, as shown in FIG. 13, by screwing together the thread groove formed on the outer peripheral surface of the nut 11 and the thread groove formed on the recess 9b of the connecting member 9, the bolt can be indirectly connected through the nut 11. You can pull 10.
In the configuration of this modified example, since the reaction force is taken by the upper surface of the object H1 to be fastened, the portion of the bolt 10 above the upper surface of the object H1 to be fastened has a constant spring constant, and The portion of the bolt 10 on the lower side is the spring constant variable portion. Since the method of calculating the tightening axial force _F0 is the same as in the embodiment, description thereof is omitted.

1 Tightening Axial Force Detector 5 Tension Rod 6 Holder 7 Load Cell 8 Drive Socket 9 Connection Member 10 Bolt 10a Bolt Head 10b Bolt Shaft 11 Nut 11b Nut Upper Surface M1, M2 Motor C Controller DS Displacement Sensor

Claims (22)

A tightening axial force detection method for detecting the tightening axial force of a bolt in a bolted joint,
an information acquisition step of directly or indirectly pulling the bolt while pressing a predetermined portion of the bolted assembly to acquire information on the displacement of the point of force application and the change in the tensile force;
a compliance calculation step for obtaining the compliance of the bolt based on the information obtained in the information obtaining step;
a compliance correction step of correcting the compliance calculated in the compliance calculation step to the compliance in the spring constant indefinite portion of the bolt where the spring constant is indefinite before the tensile force reaches a predetermined value;
a corrected displacement calculation step of calculating a corrected displacement, which is the displacement of the indeterminate spring constant portion, based on the corrected compliance and the tensile force corrected in the compliance correction step;
Obtaining an axial force increase amount based on the maximum value of the corrected compliance and the corrected displacement value corresponding to the maximum value, and subtracting the obtained axial force increase amount from the tensile force corresponding to the maximum value of the corrected compliance. a tightening axial force calculation step for calculating the tightening axial force of the bolt;
A tightening axial force detection method characterized by comprising: 2. The tightening axial force detection method according to claim 1, wherein the predetermined value is the tensile force when the change of the tensile force with respect to the force application point displacement changes from non-linear to linear. The compliance correction step is a step of obtaining the minimum value of the compliance calculated in the compliance calculation step, and subtracting this minimum value from the compliance calculated in the compliance calculation step to obtain corrected compliance.
3. The tightening axial force detection method according to claim 1 or 2, characterized in that: 3. The tightening axial force detection method according to claim 1, wherein the corrected displacement is calculated by integrating the corrected compliance with the tensile force in the corrected displacement calculating step. 4. The tightening axial force detection method according to claim 3, wherein the corrected displacement is calculated by integrating the corrected compliance with the tensile force in the corrected displacement calculating step. 3. The tightening axial force detection method according to claim 1, wherein the portion of the bolt below the predetermined portion is a spring constant variable portion. 4. The tightening axial force detection method according to claim 3, wherein the portion of the bolt below the predetermined portion is a spring constant variable portion. 5. The tightening axial force detection method according to claim 4, wherein the portion of the bolt below the predetermined portion is a spring constant variable portion. 6. The tightening axial force detection method according to claim 5, wherein the portion of the bolt below the predetermined portion is a spring constant variable portion. 3. The tightening axial force detection method according to claim 1, wherein the predetermined portion is an upper surface of a nut included in the bolt fastening body. 4. The tightening axial force detection method according to claim 3, wherein the predetermined portion is an upper surface of a nut included in the bolt fastening body. 5. The axial tightening force detection method according to claim 4, wherein the predetermined portion is an upper surface of a nut included in the bolt fastening body. 6. The tightening axial force detection method according to claim 5, wherein the predetermined portion is an upper surface of a nut included in the bolt fastening body. 3. The axial tightening force detection method according to claim 1, wherein the predetermined portion is an upper surface of an object to be fastened in the bolt fastening object. 4. The tightening axial force detection method according to claim 3, wherein the predetermined portion is an upper surface of a body to be fastened in the bolt fastening body. 5. The tightening axial force detection method according to claim 4, wherein the predetermined portion is an upper surface of a body to be fastened in the bolt fastening body. 6. The tightening axial force detection method according to claim 5, wherein the predetermined portion is an upper surface of a body to be fastened in the bolt fastening body. A tightening axial force detection device for detecting the tightening axial force of a bolt in a bolted body,
an information acquisition unit that acquires information about the displacement of the point of application of force and the change in tensile force when the bolt is directly or indirectly pulled while pressing a predetermined portion of the bolted assembly;
a compliance calculation unit that obtains the compliance of the bolt based on the information acquired by the information acquisition unit;
a compliance correction unit that corrects the compliance calculated by the compliance calculation unit to the compliance in the spring constant indefinite portion of the bolt where the spring constant is indefinite before the tensile force reaches a predetermined value;
a corrected displacement calculator that calculates a corrected displacement, which is the displacement of the indeterminate spring constant portion, based on the corrected compliance and the tensile force corrected by the compliance corrector;
Obtaining an axial force increase amount based on the maximum value of the corrected compliance and the corrected displacement value corresponding to the maximum value, and subtracting the obtained axial force increase amount from the tensile force corresponding to the maximum value of the corrected compliance. a tightening axial force calculation unit that calculates the tightening axial force of the bolt by
A tightening axial force detection device characterized by comprising: 19. The axial tightening force detecting device according to claim 18, wherein the predetermined value is the tensile force when the change of the tensile force with respect to the force application point displacement changes from non-linear to linear. 18. The compliance correction unit obtains the minimum value of the compliance calculated by the compliance calculation unit, and subtracts this minimum value from the compliance calculated by the compliance calculation unit to calculate the corrected compliance. Or the tightening axial force detection device according to 19. 20. The tightening axial force detection device according to claim 18, wherein the corrected displacement calculation unit performs a process of calculating the corrected displacement by integrating the corrected compliance with the tensile force. 21. The tightening axial force detection device according to claim 20, wherein the corrected displacement calculation unit performs a process of calculating the corrected displacement by integrating the corrected compliance with the tensile force.

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