Soundness inspection device of bolt and nut

Abstract

To inspect the soundness correctly even for a bolt and a nut provided at a position that cannot be directly hit by a hammer.SOLUTION: A soundness inspection device 1 is constituted by: a wave guide rod 3 whose tip comes into contact with a nut 2 serving as an inspection object, and the wave guide rod 3 being composed of an elastic rod material having a constant cross-sectional area; a distortion gauge 4 for force measurement provided at a tip of the wave guide rod 3; and a calculation device 5 which acquires a time waveform of a striking force from the data measured by the distortion gauge 4 when a striking force is applied to the wave guide rod 3, and which inspects the soundness of the nut 2 from the time waveform of the striking force. As the wave guide rod 3 is provided, a striking force can be applied even to the nut 2 provided at the position that cannot be directly hit by a hammer. From the time waveform of the striking force, the soundness of the bolt and nut can be accurately inspected.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an apparatus for inspecting the soundness of fastenings such as wheel bolts and nuts of an automobile. [Background technology]

[0002] Traditionally, hammering tests have been widely used to test the soundness of bolts and nuts, such as wheel bolts and nuts for trucks and other automobiles, and anchor bolts and nuts for civil engineering and construction. In this hammering test, a nut or bolt is lightly hit with a small hand hammer called an inspection hammer, and an inspector listens to the sound that is produced and judges the soundness. However, the inspector's judgment is based on the inspector's subjective judgment, and no objective criteria are prepared for the judgment. For this reason, problems have been pointed out with hammering tests, such as no records being kept and the fact that it is a human judgment and lacks objectivity.

[0003] In order to solve these problems, the applicant has proposed in Patent Document 1 listed below a method of directly striking a bolt with an impact hammer equipped with an accelerometer to measure the impact force waveform, calculating the degree of repulsion, which is the ratio between the maximum impact force and the maximum reaction force against the impact force, and calculating the delay time, which is the difference between the time when the maximum impact force occurs and the time when the maximum reaction force occurs, and diagnosing the soundness of the bolt based on the maximum impact force, the degree of repulsion and the delay time. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-81767 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technology described in Patent Document 1 above is only applied to bolts and nuts that have a relatively large space above the head of the bolt or nut, such as anchor bolts and nuts for civil engineering and construction, into which a striking hammer can be swung down, and has the disadvantage that it cannot be applied to soundness inspection of bolts and nuts that are located in locations where it is difficult to directly strike with a striking hammer.

[0006] In addition, in the above-mentioned Patent Document 1, soundness diagnosis is performed by directly striking the bolt with an impact hammer equipped with an accelerometer and measuring the impact force waveform which is the superposition of the impact force and the reaction force to this impact force. However, there is a drawback in that if the bolt / nut cannot be directly struck with an impact hammer equipped with an accelerometer, the evaluation items for soundness diagnosis cannot be calculated.

[0007] Therefore, the main object of the present invention is to provide a bolt / nut soundness inspection device that can accurately inspect the soundness of bolts and nuts that are located in a position where they cannot be directly struck with a hammer. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention according to claim 1 comprises a waveguide rod having a tip that contacts the bolt or nut to be inspected and is made of an elastic rod material with a constant cross-sectional area; a strain gauge for measuring force provided at the tip of the waveguide rod; A bolt / nut soundness inspection device is provided, comprising: a calculation device which, when an impact force is applied to the waveguide rod, obtains a time waveform of the impact force from data measured by the strain gauge, and inspects the soundness of the bolt / nut from this time waveform of the impact force.

[0009] In the invention described in claim 1 above, the tip of a waveguide rod made of an elastic rod with a constant cross-sectional area is brought into contact with a bolt or nut, and a striking force is applied to this waveguide rod to inspect the soundness of the bolt or nut. This makes it possible to apply a striking force to bolts and nuts that are located in positions where they cannot be directly struck with a hammer, thereby making it possible to inspect their soundness.

[0010] In addition, in the soundness inspection device of the present invention, a force measuring strain gauge is provided at the tip of the waveguide rod where it comes into contact with the bolt or nut, and a calculation device is provided which obtains a time waveform of the impact force from the data measured by this strain gauge and inspects the soundness of the bolt or nut based on the time waveform of the impact force generated by the balance of forces at the tip of the waveguide rod, thereby making it possible to accurately inspect the soundness of the bolt or nut from the time waveform of the impact force.

[0011] The present invention according to claim 2 provides a bolt / nut soundness inspection device as described in claim 1, in which an attachment adapted to the size and shape of the bolt / nut is attached to the tip of the waveguide rod.

[0012] In the invention described in claim 2 above, an attachment is attached to the tip of the waveguide rod to allow the tip of the waveguide rod to be adapted to various bolt and nut sizes and shapes.

[0013] According to a third aspect of the present invention, there is provided a bolt / nut soundness inspection device as set forth in the first aspect, wherein the waveguide rod is formed in a straight line or in a shape that is bent partway along the line.

[0014] In the invention described in claim 3 above, as long as waves can be transmitted through the waveguide rod, the waveguide rod is not limited to being straight, and depending on the position of the bolt or nut to be inspected, one that is bent along the way can be used.

[0015] The present invention as claimed in claim 4 provides a bolt and nut soundness inspection device as claimed in claim 1, in which the calculation device calculates, from the time waveform of the impact force, a decay time, which is the time it takes for the impact force to be reduced to half from its maximum value, and a theoretical duration time T1 of the impact force defined by the following equation (5), and estimates the spring constant at the contact point between the tip of the waveguide rod and the inspection object from the decay time ratio defined by the following equation (12), thereby inspecting the soundness of the bolt and nut.

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[0016] The invention described in claim 4 above is a first method for inspecting the soundness of bolts and nuts from the time waveform of the impact force, and utilizing the fact that the decay time of the impact force (the time it takes for the impact force to be halved from its maximum value) normalized by the theoretical duration of the impact force is a constant value relative to the spring constant, the time it takes for the impact force to be halved from its maximum value and the theoretical duration time T1 of the impact force defined by the above equation (5) are calculated from the time waveform of the impact force, and the spring constant at the contact point between the tip of the waveguide rod and the inspection object is estimated from the decay time ratio defined by the above equation (12).

[0017] According to the present invention as claimed in claim 5, in the calculation device, a rising gradient S at a time in the front half of the maximum value of the impact force and a maximum impact force F are calculated from the time waveform of the impact force. max and estimating the spring constant at the contact portion between the tip of the waveguide rod and the object to be inspected from the gradient ratio defined by the following equation (13), thereby inspecting the soundness of the bolts and nuts.

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[0018] The invention described in claim 5 is a second method for inspecting the soundness of bolts and nuts from the time waveform of the impact force. If the spring constant of the test object is the same, the gradient S on the rising side of the impact force waveform measured at the tip of the waveguide rod is affected only by the strength of the impact force. In other words, the gradient S is calculated by multiplying the maximum impact force F by the time waveform. max When normalized by , this value becomes an index value of the spring constant, and this is used to estimate the spring constant at the contact point between the tip of the waveguide and the test object.

[0019] The present invention as claimed in claim 6 provides a bolt / nut soundness inspection device as defined in claim 1, in which the computing device measures the duration and maximum value of the impact force from the time waveform of the impact force, and inspects the bolts and nuts for looseness based on these.

[0020] The invention described in claim 6 above is a third method for inspecting the soundness of bolts and nuts from the time waveform of the impact force, and utilizes the fact that when the fastening part of a bolt or nut is loose, the spring resistance is not fully exerted, and the duration and maximum value of the time waveform of the measured impact force are reduced compared to a sound fastening part, thereby inspecting for looseness of the bolt or nut.

[0021] The present invention according to claim 7 provides a bolt / nut soundness inspection device as described in claim 1, in which an impact force is applied to the waveguide rod by striking the head of the waveguide rod with a hammer.

[0022] In the invention described in claim 7, one of the means for applying a striking force to the waveguide rod is striking the head of the waveguide rod with a hammer.

[0023] The present invention relates to claim 8, and there is provided a bolt and nut soundness inspection device as described in claim 7, wherein the hammer is formed in a cylindrical shape with a cross-sectional area of ​​the head portion equal to or larger than the cross-sectional area of ​​the waveguide rod, and the head portion is made of the same material as the waveguide rod.

[0024] In the invention described in claim 8 above, since the time waveform of the impact force generated when the head of the waveguide rod is struck with a hammer differs depending on the shape of the hammer, the hammer has a striking portion that is cylindrical with a cross-sectional area equal to or larger than that of the waveguide rod and is made of the same material as the waveguide rod so that an impact force consisting of a rectangular wave of a predetermined duration acts.

[0025] The present invention as claimed in claim 9 provides a bolt / nut soundness inspection device as claimed in claim 7, wherein the striking surface of the hammer is formed flat, and the head end surface of the waveguide rod is formed in a spherical crown shape.

[0026] In the invention described in claim 9 above, the striking surface of the hammer is formed flat and the head end surface of the waveguide rod is formed into a spherical crown shape so that a constant striking force can be obtained when the head of the waveguide rod is struck with a hammer.

[0027] The present invention according to claim 10 provides a bolt / nut soundness inspection device as described in claim 1, in which an impact force is applied to the waveguide rod by directly striking the bolt / nut with the waveguide rod.

[0028] In the invention described in claim 10 above, one of the means for applying a striking force to the waveguide rod is to directly strike the bolts and nuts with the waveguide rod. Effect of the Invention

[0029] As explained above in detail, according to the present invention, it is possible to accurately inspect the soundness of bolts and nuts that are located in positions where they cannot be directly struck with a hammer. [Brief description of the drawings]

[0030] [Figure 1] 1 is a system configuration diagram of a soundness inspection device 1 according to the present invention. [Diagram 2] FIG. 11 is a system configuration diagram of a soundness inspection device 1 according to a modified example. [Diagram 3] 1 is an enlarged view of the head of the waveguide rod 3 and the hammer 6. FIG. [Figure 4] This is the time waveform of the impact force generated at the head of the three waveguide rods. [Diagram 5] This is a time waveform of the impact force at the tip of the waveguide rod 3. [Figure 6] 13 is a graph showing the relationship between striking speed and maximum striking force. [Figure 7] 1 is a graph showing maximum values ​​of striking force normalized by striking speed. [Figure 8] 13 is a graph showing a difference in time waveform of impact force due to differences in spring constant. [Figure 9] 13 is a graph showing the relationship between the spring constant and the damping time ratio. [Figure 10] 1 is a graph showing the relationship between the spring constant and the amount of displacement according to contact theory. [Figure 11] 1 is a graph showing the relationship between the spring constant and the rising gradient. [Figure 12]11 is a graph showing similarity of time waveforms due to differences in impact speed. [Figure 13] 4 shows the time waveforms of the impact force when the nut 2 is loose and when it is not. [Figure 14] This is a time waveform of the impact force when the nut 2 is loose. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The soundness inspection device according to the present invention inspects the fastening state of a bolt or nut. The following mainly describes the inspection of the soundness of nuts, but the same can be applied to bolts.

[0032] (Configuration of soundness inspection device 1) As shown in FIG. 1, the soundness inspection device 1 of the present invention is composed of a waveguide rod 3 made of an elastic rod with a constant cross-sectional area and whose tip is in contact with the nut 2 to be inspected, a strain gauge 4 for measuring force provided at the tip of the waveguide rod 3, and a calculation device 5 that obtains a time waveform of the impact force from data measured by the strain gauge 4 when an impact force is applied to the waveguide rod 3, and inspects the soundness of the nut 2 from this time waveform of the impact force.

[0033] The waveguide rod 3 is made of an elastic rod such as a metal with a constant cross-sectional area over its entire length, and one end (tip) is held in intimate contact with the nut 2, while the other end (head) is struck with a hammer 6 to input an impact force. If the cross-sectional area at each position of the waveguide rod 3 is equal, the impact force input to the head by the hammer 6 propagates through the waveguide rod 3 as a one-dimensional elastic wave and reaches the tip of the waveguide rod 3 in contact with the nut 2. At this time, the time history data of the impact force generated by the balance of forces at the tip of the waveguide rod 3 is measured by the strain gauge 4.

[0034] Since the head of the waveguide rod 3 protrudes from the nut 2, it is possible to inspect the soundness of nuts that are located in positions where they cannot be directly struck with a hammer.

[0035] In order to make the tip of the waveguide rod 3 compatible with the size and shape of the nut 2, an attachment 7 that matches the size and shape of the nut 2 is attached to the tip of the waveguide rod 3. The attachment 7 has an opening in the center along the axial direction of the waveguide rod 3 that can accommodate the head of the bolt protruding from the nut 2, and a number of different opening sizes are provided according to the size of the nut 2 (bolt).

[0036] As long as the cross-sectional area is constant, the waveguide rod 3 may be formed straight as shown in Fig. 1, or may be bent halfway as shown in Fig. 2. The bent shape may be a roughly dogleg shape with a gentle curved bend at both ends as shown in Fig. 2, a curved shape that curves over the entire length, or a zigzag shape with two or more bends along the way. Even if the shape is bent halfway, as long as the cross-sectional area at each position along the axial direction is constant, there is no effect on the propagation of one-dimensional waves, and the impact force applied to the head by the hammer 6 propagates to the tip with the same waveform.

[0037] Any known strain gauge can be used without any restrictions as the strain gauge 4. Data measured by the strain gauge 4 is transmitted to the computing device 5 wirelessly or via wire.

[0038] The calculation device 5 is a calculation device such as a personal computer or a portable tablet capable of storing and calculating data, and obtains a time waveform of the impact force from the data measured by the strain gauge 4, and evaluates the soundness of the nut 2 from the time waveform of this impact force.

[0039] As shown in Fig. 1, the hammer 6 used is a normal hand hammer with a head 6a provided at the tip of a handle 6b. The handle 6b is held and the head 6a is struck against the part to be struck, thereby inputting an impact force. The time waveform of the impact force generated when the head 6a of the hammer 6 strikes the head of the waveguide rod 3 depends on the shape of the head 6a. Any shape of the head 6a can be used as long as the time waveform of the obtained impact force can be controlled, but it is preferable that the head 6a be formed in a cylindrical shape with a cross-sectional area larger than that of the waveguide rod 3 and that the head 6a be made of the same material as the waveguide rod 3.

[0040] Here, the cross-sectional area of ​​the head portion 6a of the hammer 6 is A H , the cross-sectional area of ​​the waveguide rod 3 is A P , the longitudinal elastic modulus of the head portion 6a is E H , the longitudinal elastic modulus of the waveguide rod 3 is E P , the longitudinal acoustic wave velocity of the head portion 6a is c H , the longitudinal acoustic wave velocity of the waveguide rod 3 is c P Then, the mechanical impedance Z of the head 6a of the hammer 6 is H and the mechanical impedance Z of the waveguide rod 3 P are expressed as the following equations (1) and (2), respectively.

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[0041]

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[0042] If the ratio between these (mechanical impedance ratio) is η, then the following equation (3) is obtained.

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[0043] The initial impact force F1 generated at the head of the waveguide rod 3 is expressed by the following equation (4), where the initial velocity of the head portion 6a of the hammer 6 is V0.

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[0044] The duration (theoretical duration of the impact force) T1 at this time is equal to the time it takes for the elastic wave to make one round trip inside the head portion 6a, and the length of the head portion 6a is L H This gives the following equation (5).

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[0045] In other words, when the head portion 6a of the hammer 6 strikes the head of the waveguide rod 3, the striking force F1 expressed by the formula (4) becomes a square wave that continues for the time T1 expressed by the formula (5).

[0046] When the cross-sectional area of ​​the head portion 6a of the hammer 6 and the cross-sectional area of ​​the waveguide rod 3 are equal or larger, the impact force ends with only the initial rectangular wave (equations (4) and (5)).

[0047] On the other hand, when the cross-sectional area of ​​the head portion 6a of the hammer 6 is larger than the cross-sectional area of ​​the waveguide rod 3, the impact force F expressed by the following formula (6) is generated after the theoretical duration T1 of the impact force expressed by the formula (5). N continues for the time given by equation (5) above.

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[0048] Here, if the cross-sectional area of ​​the head portion 6a: the cross-sectional area of ​​the waveguide rod 3 is 3:1, the impact force F N is expressed as the following equation (7).

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[0049] That is, when this relationship is represented in a graph, as shown in Fig. 4, the wave applied to the waveguide rod 3 is attenuated stepwise by half, which well represents the attenuation state of the waveform actually observed. Therefore, it is desirable that the cross-sectional area of ​​the head portion 6a is three times that of the waveguide rod 3.

[0050] In this way, the cross-sectional area ratio, which is the ratio of the cross-sectional area of ​​the head part 6a of the hammer 6 to the cross-sectional area of ​​the waveguide rod 3, affects the time waveform of the impact force to be measured. If the cross-sectional area of ​​the head part 6a is smaller than that of the waveguide rod 3, the head part 6a bounces off the head of the waveguide rod 3, and the impact force theoretically becomes a square wave of one wave, but in reality, it takes time for the impact force to become a plane wave inside the waveguide rod 3, and it does not become a square wave. Even if the cross-sectional areas are equal (cross-sectional area ratio is 1), the impact force theoretically becomes a square wave of one wave, but the waveform differs depending on the way the head part 6a and the waveguide rod 3 contact each other, and does not become as theoretically expected. In order to reduce such practical problems, it is desirable to make the cross-sectional area of ​​the head part 6a larger than that of the waveguide rod 3 (preferably three times larger) so that stable impact can be obtained.

[0051] The sampling time for measuring the wave motion can be determined from the theoretical duration T1 of the impact force shown in the above formula (5). H When the impact force is 100 mm, the theoretical duration T1 of the impact force is about 40 μs, so that it is preferable to set the sampling time to about 2 μs so that about 20 or more samples can be taken during this duration.

[0052] (Effect of impact speed of hammer 6 on time waveform of impact force) When striking the head of the waveguide rod 3 with a hand hammer, the striking speed of the hammer 6 cannot be kept constant, so it is important to consider how a change in the striking speed of the hammer 6 affects the time waveform of the striking force.

[0053] FIG. 5 shows the results of measuring the time waveform of the impact force by the strain gauge 4 when the impact speed of the hammer 6 was changed to 0.2 m / s, 1.2 m / s, and 2.5 m / s. As a result, when the impact speed was changed, the magnitude of the measured force changed, but the shape of the waveform was basically the same. The relationship between the impact speed of the hammer 6 and the maximum impact force (the maximum value of the impact force measured in FIG. 5) at this time is directly proportional, as shown in FIG. 6. This means that the apparent spring constant of the structure to be measured cannot be measured at the maximum value of the impact force. Note that FIG. 6 shows the measured value when the spring constant at the contact part between the tip of the waveguide rod 3 and the nut 2 was set to 980 MN / m.

[0054] Next, when considering whether the impact speed of the hammer 6 affects the spring constant index value of the tip of the waveguide rod 3, the spring constant index value (mechanical impedance) is determined by the maximum impact force F max is obtained by dividing the deformation velocity of the tip of the waveguide rod 3. However, when only the time waveform of the impact force is measured, the deformation velocity of the tip of the waveguide rod 3 is unknown, so the estimated value of the deformation velocity v ind Request.

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[0055] The above formula (8) utilizes the fact that the product of mass and acceleration corresponds to force, and estimates acceleration by dividing the impact force by the hammer mass, and then estimates velocity by integrating this. The estimated value of this deformation velocity, ν ind Using the spring constant index value Z I This can be expressed as the following equation (9).

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[0056] The spring constant index value Z obtained in this way I The relationship between the impact speed of the hammer 6 and the spring constant index value Z Iis not affected by the impact speed of the hammer 6. Therefore, when measuring the spring constant of the tip of the waveguide rod 3, it is not necessary to take the impact speed of the hammer 6 into consideration.

[0057] (Method of inspecting the soundness of bolts and nuts from the time waveform of impact force) When the tip of the waveguide rod 3 is pressed against the nut 2 and the head of the waveguide rod 3 is struck with a hammer 6, the wave motion at the tip of the waveguide rod 3 is expressed by the following equation (10) due to the balance of forces.

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[0058] If the sum of the forward wave and backward wave on the left side of the above equation (10) is denoted as F, then the following equation (11) can be expressed from the strain ε measured by the strain gauge 4 provided at the tip of the waveguide rod 3.

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[0059] Of the right-hand side of the above equation (10), the apparent spring constant K at the contact point between the tip of the waveguide rod 3 and the nut 2 is an important index value that is the measurement target in inspecting the soundness of the nut. However, even if the strain ε at the tip of the waveguide rod 3 is measured, the spring constant K cannot be determined because the displacement x at the tip of the waveguide rod 3 is not measured. Therefore, in the present invention, the soundness of the nut is inspected by estimating the spring constant K from the time waveform of the impact force, as described below.

[0060] (Method to estimate spring constant K from damping time) When the spring constant K at the contact part between the tip of the waveguide rod 3 and the nut 2 is small, it takes time for the force to decay due to the action of the impact force. On the other hand, when the spring constant K is large, the force decays quickly. Figure 8 compares the time waveforms of the impact force due to different spring constants at the contact part between the tip of the waveguide rod 3 and the nut 2. It is clear from this figure that the time until the impact force reaches its maximum value (rise time) and the time until the impact force decays from its maximum value (fall time) are steeper when the spring constant at the contact part between the tip of the waveguide rod 3 and the nut 2 is large (490MN / m) and are gentler when the spring constant is small (294MN / m). Therefore, the spring constant K at the contact part between the tip of the waveguide rod 3 and the nut 2 can be estimated by calculating the decay time of the impact force from the time waveform of the impact force.

[0061] However, when calculating the fall time, the time when the impact force becomes 0 cannot be determined strictly, so in this invention, the time when the impact force is reduced to half (1 / 2) from the maximum value is defined as the "decay time". In addition, this decay time (the time when the impact force is reduced to half from the maximum value) is divided by the theoretical duration time T1 of the impact force shown in the above formula (5) and normalized, and is defined as the "decay time ratio" shown in the following formula (12).

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[0062] This damping time ratio is an inherent value between the waveguide rod 3 and the hammer 6, regardless of the impact force (the impact speed of the hammer 6), and for example, as shown in Fig. 9, a relationship curve is obtained between the damping time ratio and the spring constant K at the contact portion between the tip of the waveguide rod 3 and the nut. Therefore, the damping time, which is the time it takes for the damping force to be reduced to half from the maximum value, is measured from the time waveform of the impact force, and the damping time ratio is calculated from the above formula (12). From the relationship between the damping time ratio shown in Fig. 9 and the spring constant K at the contact portion between the tip of the waveguide rod 3 and the nut 2, the spring constant K can be estimated. If this spring constant K is equal to or greater than a predetermined value, the connection between the nut 2 and the fixing member is ensured, and it can be determined that the nut 2 is sound.

[0063] As mentioned above, Fig. 9 shows the relationship between the spring constant and the damping time ratio. As is clear from this, as the spring constant increases, the damping time ratio tends to converge to 1. When the damping time ratio is 1, the time it takes for the impact force to be halved from its maximum value (damping time) is equal to the theoretical duration T1 of the impact force. From Fig. 9, it can be seen that in the range of spring constants of about 1000 MN / m or less, the spring constant and damping time ratio tend to increase monotonically, and this is considered to be the range in which the spring constant can be accurately estimated from the damping time ratio.

[0064] To examine the degree of elasticity of a spring constant of 1000MN / m, Hertz's contact theory is used to determine the spring constant when the spherical cap contacts semi-infinite steel. In contact theory, the tip penetration amount and reaction force are not directly proportional, so the ball constant value is obtained from the penetration amount and reaction force value. From Figure 10, it can be seen that to obtain a spring constant of 1000MN / m, a spherical cap with a radius of 25mm needs to be displaced by 50μm (0.05mm). If the radius of the spherical cap is 100mm, the spring constant of 1000MN / m is reached with a displacement of 0.01mm, and the reaction force exceeds 800kgf, so for the waveguide tip shape (radius 100mm or more) used for inspecting the soundness of nuts, an index value of the spring constant can be obtained within the range where the graph slope in Figure 9 does not saturate.

[0065] (Method of estimating spring constant K from rising slope) Next, a method for estimating the spring constant K from the rising gradient in the time waveform of the impact force will be described.

[0066] As mentioned above, the larger the spring constant K at the contact portion of the tip of the waveguide rod 3 with the nut 2, the larger the rising gradient of the impact force. Here, if the spring constant at the contact portion of the tip of the waveguide rod 3 with the test object is small, the impact force may not reach its maximum value within the theoretical duration T1 of the impact force, and this may not be appropriate as an index value for the spring constant. For this reason, the index value is determined based on the rising gradient S of the waveform at the time when the impact force is 1 / 2 of the maximum value in the time waveform of the impact force.

[0067] Specifically, from the time waveform of the impact force, the rising slope S at the time of the front half of the maximum impact force is calculated as the maximum impact force F max The value obtained by dividing this by the maximum impact force is defined as the gradient ratio (the following equation (13)), and the spring constant K at the contact point between the tip of the waveguide rod 3 and the test object is estimated based on this gradient ratio, and the soundness of the nut 2 is inspected.

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[0068] The relationship between the spring constant K and the gradient ratio can be graphed as shown in Figure 11. As shown in Figure 11, the gradient ratio generally tends to increase monotonically with respect to the spring constant K, and it can be seen that it can be used as an index value for the spring constant in evaluation. In the present invention, evaluation using this gradient ratio is used as an index value for inspecting the soundness of bolts and nuts, either alone or in combination with the evaluation using the damping time ratio described above.

[0069] In the above formula (13), the reason for normalizing with the maximum impact force when calculating the gradient ratio is that, as shown in FIG. 12, when the impact speed of the hammer 6 was changed (1 m / s, 2 m / s) and the time waveform of the impact force was measured, it was found that while the amplitude was proportional to the impact speed of the hammer 6, the waveform was relatively similar in shape depending on the impact speed of the hammer 6. Therefore, by normalizing with the maximum impact force, the effect of the impact speed of the hammer 6 can be nullified.

[0070] (Method of inspecting bolts and nuts for looseness from the time waveform of impact force) If the nut 2 is loose, the spring constant at the contact point between the tip of the waveguide rod 3 and the test object will decrease, and the reaction force may fluctuate irregularly. This causes minute wavy fluctuations in the initial waveform of the time waveform of the impact force measured at the tip of the waveguide rod 3, and a delay in the rise time. As a result, the duration of the impact force will be shortened, and the maximum value of the impact force will also be smaller. By observing the initial waveform of the time waveform of the impact force, and detecting abnormalities such as minute fluctuations, a delay in the rise time, a shortened duration, or a decrease in the maximum value, the nut 2 can be inspected for looseness.

[0071] If the loosening of the nut 2 is considered as a gap formed between the nut 2 and the fixed member, the microscopic measurement situation when a striking force is applied to the waveguide rod 3 including this gap portion is that the spring resistance at the tip of the waveguide rod 3 is measured as being minute until the displacement of the tip of the waveguide rod 3 eliminates the gap, and then the spring resistance is measured when the gap is eliminated and the nut 2 is in close contact with the fixed member and integrated. In other words, it takes time to measure the spring resistance when the nut 2 and the fixed member are integrated.

[0072] If the gap size is g, the time required for this gap g to disappear is T in is expressed as the following equation (14).

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[0073] By transforming the above equation (15) based on the sampling time Δt in the actual measurement, the discretized delay time N is obtained as shown in the following equation (15). in is obtained.

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[0074] Figure 13 shows the time waveforms of the impact force when the gap g is 0.002 mm due to improper fastening of the nut 2 (looseness present) and when there is no gap (no looseness). The impact speed by the hammer 6 is 1 m / s. As shown in the figure, when there is looseness, there is a delay in the start time of the waveform rise and a decrease in the maximum value compared to when there is no looseness. This is because the velocity component of the impact wave generated by the impact is consumed in the movement to close the gap (displacement at the tip of the waveguide rod 3), and the impulse that deforms the spring resistance at the tip of the waveguide rod 3 is reduced.

[0075] The delay in the start of the rise of the waveform can be calculated by the ratio of the actually observed rise time to the standard time of the impact force. However, since it is difficult to precisely determine the rise position of the waveform in an actual measured waveform, another method is to calculate the time from the time when the impact force reaches a certain ratio (for example, 5%) of the maximum value to the time when the impact force reaches the maximum value.

[0076] Figure 14 shows a model of the time waveform of the impact force when the nut 2 is loose. If the nut 2 is loose, the waveform does not rise all at once at the beginning, and in some cases this part may become a random waveform. After that, the force acting on the nut 2 causes it to adhere to the fixing member, and a reaction force (spring resistance) from the fixing member via the nut 2 comes into play. The presence or absence of this initial waveform is an indicator of the degree of looseness of the nut 2. [Explanation of symbols]

[0077] 1... soundness inspection device, 2... nut, 3... waveguide rod, 4... strain gauge, 5... computing device, 6... hammer, 7... attachment

Claims

1. A waveguide rod made of an elastic rod material with a constant cross-sectional area, the tip of which contacts the bolt / nut to be inspected; a strain gauge for measuring force provided at the tip of the waveguide rod; a calculation device which, when an impact force is applied to the waveguide rod, obtains a time waveform of the impact force from data measured by the strain gauge, and inspects the soundness of the bolt / nut from this time waveform of the impact force.

2. 2. The bolt / nut soundness inspection device according to claim 1, wherein an attachment adapted to the size and shape of the bolt / nut is attached to the tip of the waveguide rod.

3. 2. The bolt / nut soundness inspection device according to claim 1, wherein the waveguide rod is formed in a straight line or in a shape that is bent partway.

4. In the calculation device, from the time waveform of the impact force, a damping time, which is the time it takes for the impact force to be reduced to half from the maximum value, and a theoretical duration T of the impact force defined by the following formula (5) are calculated. １ 2. The bolt and nut soundness inspection device according to claim 1, which estimates the spring constant at the contact portion between the tip of the waveguide rod and the inspection target from the damping time ratio defined by the following equation (12) to inspect the soundness of the bolt and nut. [0050] ##EQU00012##

5. 2. A bolt and nut soundness inspection device as claimed in claim 1, wherein the calculation device determines the maximum impact force and the rising gradient at the time 1 / 2 of the time forward of the maximum impact force from the time waveform of the impact force, and estimates the spring constant at the contact portion between the tip of the waveguide rod and the inspection object from the gradient ratio defined by the following equation (13), thereby inspecting the soundness of the bolt and nut. ##EQU00013##

6. 2. An apparatus for inspecting the soundness of bolts and nuts as claimed in claim 1, wherein said calculation device measures the duration and maximum value of the impact force from the time waveform of the impact force and inspects the bolts and nuts for looseness based on these.

7. 2. An apparatus for inspecting the soundness of bolts and nuts according to claim 1, wherein a striking force is applied to said waveguide rod by striking the head of said waveguide rod with a hammer.

8. 8. A bolt and nut integrity inspection device as described in claim 7, wherein the hammer is formed in a cylindrical shape with a cross-sectional area of ​​a head portion equal to or larger than the cross-sectional area of ​​the waveguide rod, and the head portion is made of the same material as the waveguide rod.

9. 8. An apparatus for inspecting the soundness of bolts and nuts according to claim 7, wherein the striking surface of said hammer is formed flat, and the head end surface of said waveguide rod is formed in a spherical crown shape.

10. 2. The bolt / nut soundness inspection device according to claim 1, wherein the impact force is applied to the waveguide rod by directly striking the bolt / nut with the waveguide rod.

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