JP2688445B2 - Ultrasonic bolt axial force measuring device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an axial force measuring device for measuring the axial force of a bolt after fastening or during fastening using ultrasonic waves, and in particular, At the same time, it is suitable for measuring the bending of the bolt.

[Conventional technology]

Measuring the axial force of the bolt after or during fastening is an effective means for knowing the bolt fastening state such as whether the bolt is loose and whether the axial force is too large or too small. 2. Description of the Related Art Conventionally, an axial force measuring device that can easily measure using ultrasonic waves has been put into practical use. FIG. 5 is a block diagram showing one example thereof. First, with respect to the probe 2 that is in contact with one end surface (the top surface of the head of the bolt 1 in the figure) 1a of the bolt 1 before the bolt is fastened. A pulse is applied by the pulsar 3 and an ultrasonic pulse is incident toward the other end surface 1b of the bolt 1 (the end surface on the screw side of the bolt 1 in the figure) 1b. The incident pulse is reflected by the other end surface 1b and propagates back and forth in the bolt 1,
The reflected wave signal propagating back and forth propagates through the probe 2 to the receiver 4
Sent to The reflected wave signal received by the receiver 4 is amplified to a desired amplitude by the amplifier 5 and sent to the A / D converter 7 through the gate circuit 6 to quantify the propagation time of the reflected wave signal. The digitized propagation time is calculated by the arithmetic processing unit 8
Is input to the storage unit 10 via. Reference numeral 9 denotes an input section, in which dimensions such as the total length, effective length, diameter, and screw pitch of the bolt 1, material constants, and initial setting values such as sonic velocity are input, and work such as fastening work and measuring work of the bolt 1 is performed. Output a command signal. Next, after the bolt 1 is fastened, the propagation time after fastening is input to the arithmetic processing unit 8 in the same procedure as before the fastening, and the arithmetic processing unit 8 inputs the propagation time before fastening the bolt 1 previously input to the storage unit 10. A comparison operation is performed using the value of the propagation time and the input value of the input unit 9. The comparison calculation is performed by the following equation (1).

Where F… Bolt axial force (ton) t ₁ … Echo propagation time before bolt fastening (se
c) t ₂ … Echo propagation time after bolt fastening (se
c) δ… Bolt compliance (mm / Kgf) K… Bolt material constant during measurement V ₀ … Bolt sound velocity (m / sec) The bolt compliance δ is the unit axial force (kgf) applied to the bolt 1. It represents the elastic elongation (mm) of the bolt 1 when it is loaded, and is calculated from the initial setting value input in advance in the input unit 9.

The value calculated by the comparison is displayed on the display unit 11 to check whether it is a predetermined value or not. If the value is too large or too small, re-fastening is performed to obtain a predetermined bolt axial force.

On the other hand, when the surface of the member to be fastened is not parallel, the seat surface of the bolt is tilted, or when a bending load is applied to the bolt, bending stress is generated in addition to the axial force of the bolt. . In such a case, if the bolt is damaged due to bending stress even if it is intended to be fastened with a predetermined axial force, or if there is severe vibration during operation even when fastened with a predetermined axial force, the bending stress causes the bolt to break. An unfavorable state that causes an accident or the like will occur.

In order to avoid such an unfavorable state, the bending stress or bending angle generated in the bolt is measured. The conventional measurement method is to attach strain gauges to multiple points on the shaft of the bolt in advance, measure the amount of strain that occurs in each strain gauge during or after fastening the bolt with a strain gauge, and change the measured strain amount. Bending stress or bending angle is measured from the quantity.

[Problems to be solved by the invention]

As mentioned above, the axial force measuring device that can easily measure the axial force of the bolt using ultrasonic waves is provided, but the bending stress or bending angle generated in the bolt is the amount of strain from the strain gauge. Therefore, the following problems were encountered.

(A) In order to accurately measure the bending stress or bending angle of a bolt, it is necessary to attach as many strain gauges to each part of the bolt as possible, but it takes time and effort to attach the strain gauges. It takes time to measure many strain gauges.

(B) The number of bolts used in important parts of the structure is not usually singular, but many, so it is difficult to measure the strain on all of the bolts, and it is necessary to perform random sampling inspection. Inevitably, it will be an unsatisfactory inspection that remains uneasy for bolts that are not inspected.

(C) In addition, there is usually no place to attach the strain gauge to the bolt actually used in the structure. In such a case, the strain gauge is attached to the bolt or the member to be fastened. There is no choice but to use a model experiment that has been subjected to the processing described above, and an error with the actual product occurs accordingly, and the measurement result needs to be corrected.

In view of the problems of the above-mentioned conventional techniques, the present invention simultaneously measures the axial force and bending of the bolt after or during fastening,
Moreover, it is an object of the present invention to provide a device for measuring the axial force of a bolt by ultrasonic waves that can be easily measured.

[Means for solving the problem]

In order to achieve the above object, the ultrasonic axial force measuring device for a bolt according to the present invention is such that an ultrasonic beam incident from a probe abutting on one end face of the bolt toward the other end face of the bolt is the bolt. Input the propagation time before and after bolt fastening of the reflected wave signal reflected on the other end surface of the bolt and propagating back and forth in the bolt, compare and compute both, and output the computed value to the display unit. In a bolt axial force measuring device provided, in parallel with the input of the propagation time, the echo height before bolt fastening and the echo height after bolt fastening of the reflected wave signal are input, and both echo heights are compared and calculated. The calculation value is output to the display unit to measure the axial force and bending of the bolt at the same time.

Further, an ultrasonic beam incident from the probe abutting on one end face of the bolt toward the other end face of the bolt is reflected on the other end face of the bolt, and the bolt of the reflected wave signal propagated back and forth in the bolt. In a bolt axial force measuring device having an arithmetic processing unit for inputting the propagation time before and during fastening and comparing and calculating the both, and outputting the calculated value to the display unit, in parallel with the input of the propagation time. Input the echo height before bolt fastening of the reflected wave signal and the echo height during bolt fastening,
The two echo heights are compared and calculated, the calculated value is output to the display unit, and the arithmetic processing unit that enables simultaneous measurement of the axial force and bending of the bolt during fastening is provided.

[Action]

With the above configuration, the propagation time before the bolt fastening and the propagation time after the fastening of the reflected wave signal propagating back and forth in the bolt are compared in the arithmetic processing unit and output to the display unit. In parallel, the echo height before bolting and the echo height after bolting of the reflected wave signal are input to the arithmetic processing unit or an arithmetic processing unit provided separately, and the arithmetic processing unit compares and calculates the result. The calculated value is output to the display unit. Then, the axial force of the bolt after fastening the bolt is measured from the calculated value of the propagation time, and the bending angle of the bolt is measured from the calculated value of the echo height at the same time.

Here, in the case of a bolt that is fastened without bending, even if the axial force of the bolt increases, the echo height values before and after fastening the bolt may be almost constant with almost no change. Since it is confirmed by the experimental data, it is easy to detect that the bolt is bent by detecting that the echo height is lower after bolt fastening than before bolt fastening, in the display section. The bending angle can be easily calculated by a formula. And
The decrease in echo height due to the bending of the bolt is caused by a change in parallelism between the contact surface of the probe which is the ultrasonic beam incident surface of the bolt and the other end surface of the bolt which is the reflective surface of the ultrasonic beam. Therefore, the echo height decreases corresponding to the bending angle of the bolt.

In addition, the measurement and calculation of the propagation time and the echo height before and after bolt fastening can be performed by the same procedure before and during bolt fastening, and any measurement during bolt fastening can be performed. It is possible to measure and calculate at any time in stages. Then, the cause and the situation of the echo height reduction when the bolt is bent is the same as the above description, and the axial force and the bending angle of the bolt at the desired stage during fastening are simultaneously and easily measured. It becomes possible to do.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. FIG. 1 is a flowchart for simultaneously measuring the bolt axial force and the bending of the bolt according to the present invention. In this case, the bolt axial force measuring device has a propagation time and an echo height of a reflected wave signal propagating back and forth in the bolt. Is provided with an arithmetic processing unit capable of performing comparative arithmetic before and after bolt fastening, and other configurations may be the same as those of the conventional device.

At the start of the measurement, the echo height of the reflected wave signal before bolt fastening is measured in parallel with the measurement of the propagation time described in the above-mentioned prior art, and the measured value is sent to the storage unit via the arithmetic processing unit. To be Then, after the bolt is fastened, the propagation time after fastening and the echo height are measured in the same procedure as before fastening and are input to the arithmetic processing unit, and in the arithmetic processing unit, the propagation time before bolt fastening stored in the previous section. And the echo height are read from the storage unit and are compared and calculated. The comparison calculation of the echo height in this case is performed by the following equation (2).

h _θ / h ₀ = D ² (θ) × cos θ × H (2θ) (2) Here, h _θ ... Echo height when the bolt bending angle θ = ψ _b (echo height after bolt fastening and H ₀ … Echo height when the bending angle of the bolt is θ = 0 (Echo height before bolting is taken) D… Transducer diameter of the probe (mm) D (θ)… of the probe Sound field characteristics H… Reflectivity of reflection surface H (θ)… Sound field characteristics of reflection surface The value calculated by the above formula is displayed on the display, and it is easy to check whether the bolt is bent and its angle after fastening. Can be measured.

On the other hand, the axial force of the bolt is obtained at the same time as the bending of the bolt by calculating the propagation time, as described in the above-mentioned prior art. However, when the bending of the bolt occurs, the axial force of the bolt is calculated as follows. If the axial force is set to the same value as that in the state where no bending occurs, the axial force may become excessive by the amount corresponding to the bending stress. This excessive axial force is expressed by the following relational expression (3) between the bending angle θ of the bolt and the bolt axial force.
A, it can be calculated the degree by substituting the skew angle theta = _b of the bolt obtained by equation (2).

Here, _b … Bolt bending angle θ (degree) d… Bolt head radius (mm) (In the case of hexagon bolts, the distance across the head /
2) F… Bolt axial force (Kgf) l _f … Length from the end surface of the bolt head to the other end surface (total length of the bolt) (mm) Ε _b Ι _b … The average value of the bending rigidity of the bolt FIG. 6 is a diagram showing a case where the bending angle θ = _b , and shows a state in which an ultrasonic beam incident from the contact surface of the probe 2 propagates back and forth inside the bolt at an incident angle _b . Also,
FIG. 3 is a diagram showing an example of an experiment of the relationship between the axial force of the bolt and the echo height when the bending angle θ of the bolt changes, where the symbol ○ indicates θ = 0 degrees, the * symbol indicates θ = 0.47 degrees, + Means θ = 0.82
Degree, ● indicates θ = 1.64 degrees, ◎ indicates θ = 1.8 degrees, the horizontal axis is the axial force of the bolt (ton), and the vertical axis is the echo height (d
B). As can be seen from the figure, when θ is small from 0 to 0.82 degrees, the echo height remains almost constant even if the bolt axial force increases, but when θ exceeds 1.64 degrees, the echo height decreases. However, it decreases rapidly as the axial force increases. However, the damping also stops when the axial force reaches a certain value.

FIG. 4 is a graph showing the result of theoretical calculation by the formula (2), which shows the incident angle (degree) of the beam and the echo height (dB) for three types of circular reflecting surfaces with diameters d ₀ = 5 mm, 10 mm, and 20 mm. It shows the relationship. As you can see from the figure, this figure and the third
It is in good agreement with the experimental results in the figure.

On the display, when the bending angle θ of the bolt increases, the decrease in echo height becomes remarkable, so that the decrease can be easily detected, and at the same time as the detection, the bending angle θ and the axial force at that time are calculated. Since it is displayed, it is possible to immediately detect whether or not the displayed value is a desired value, and it is possible to measure even a large number of bolts in a short time. If the bending angle θ and the axial force of the bolt are not desired values, it is possible to quickly re-fasten them to the optimum values according to the displayed values.

Although the description of the above embodiment is to measure the axial force and the bending angle of the bolt after fastening the bolt, the measurement can be performed at any time during fastening of the bolt,
It can be measured at any stage during the fastening. Therefore, particularly for bolts and the like used in important parts of the structure, the propagation time and the echo height at a desired stage during fastening are measured by the same procedure as in the above-mentioned embodiment, and the arithmetic processing unit The propagation time before the bolt is fastened and the echo height, which have been input and stored in the arithmetic processing unit, are read out from the storage unit and are compared and calculated. By this comparison calculation, the axial force and the bending of the bolt in the middle of the fastening can be inspected as necessary, the fastening can be completed, and the fastening work with high reliability can be performed.

By measuring the axial force and bending of the bolt after tightening and during tightening, individually or in combination, depending on the importance of the bolt and the type of bolt, ensure the desired correct tightening work. It has become possible to prevent accidents of various bolts that have been conventionally caused by bending. Since the above-mentioned measurement can be performed easily and immediately, it becomes possible to inspect a large number of bolts in a short time, and periodical maintenance inspection management can be efficiently performed.

〔The invention's effect〕

Since the present invention is configured as described above,
It is possible to simultaneously and easily measure the axial force and the bending of the bolt after or during the fastening.

[Brief description of the drawings]

FIG. 1 is a flowchart 1 in the case where bolt axial force and bending are simultaneously measured by the bolt axial force measuring device of the present invention.
The figure which shows an example, FIG. 2 is a figure which shows the propagation state of the ultrasonic beam injected into the bolt which has a curve, FIG. 3 shows the axial force and echo height of a bolt which change according to the bending angle of a bolt. FIG. 4 is a diagram showing the relationship, and FIG. 4 is a diagram showing the relationship between the incident angle of the ultrasonic beam and the echo height. FIG. 5 shows a conventional ultrasonic axial force measuring device for bolts.
It is a block diagram showing an example. 1 ... Bolt, 1a ... 1 end surface, 1b ... other end surface, 2 ... probe, 8 ... arithmetic processing section, 11 ... display section.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiaki Suzuki 650 Jinrachi-cho, Tsuchiura-shi, Ibaraki Hitachi Construction Machinery Co., Ltd. Tsuchiura factory (72) Inventor Yoshikazu Hamasaki 1952, Shingu-cho, Kasuya-gun, Fukuoka Prefecture Hitachi Construction Machinery Kyushu Branch (56) Reference JP-A-55-82935 (JP, A) JP-A-60-216235 (JP, A) JP-A-58-19525 (JP, A) JP-A-58-122438 ( JP, A)

Claims (2)

(57) [Claims] 1. A reflected wave in which an ultrasonic beam incident from a probe contacting one end face of a bolt toward the other end face of the bolt is reflected at the other end face of the bolt and reciprocally propagates in the bolt. In a bolt axial force measuring device having an arithmetic processing unit for inputting the propagation time of a signal before and after fastening the bolt and comparing and calculating both, and inputting the propagation time, In parallel, the echo height before bolt fastening of the reflected wave signal and the echo height after bolt fastening are input, both echo heights are compared and output, and the calculated value is output to the display unit, and the axial force of the bolt and A bolt axial force measuring device using ultrasonic waves, comprising an arithmetic processing unit capable of simultaneously measuring bending and bending. 2. A reflected wave in which an ultrasonic beam incident from a probe contacting one end face of a bolt toward the other end face of the bolt is reflected at the other end face of the bolt and reciprocally propagates in the bolt. In the axial force measuring device of the bolt having an arithmetic processing unit for inputting the propagation time of the signal before and after fastening the bolt and comparing and computing the both, and inputting the propagation time, In parallel, the echo height before bolt fastening of the reflected wave signal and the echo height during bolt fastening are input, both echo heights are compared and output, and the calculated value is output to the display unit. An ultrasonic bolt axial force measuring device comprising an arithmetic processing unit capable of simultaneously measuring axial force and bending.