JPH0672826B2 - Bolt / nut looseness detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention uses a striking force of a striking hammer or an acceleration pulse to strike a bolt / nut fastened to a structure in a non-destructive manner. -It relates to a method for detecting looseness of nuts.

[Prior art]

Generally, when detecting an abnormality in the degree of adherence of a structure, such as loose bolts or peeling of a honeycomb structure, the structure is lightly hit with a hammer, and a person makes a judgment based on the impact sound and repulsive force at this time. Method is used. However, this method largely depends on the "feeling" of the person, and as a result, there is a large difference between individuals, and not only can it be judged that the user is not a skilled person, but there is a problem that if it is loosened only a highly skilled person can make a distinction. It was

For this reason, there has been proposed a method of hitting a structure, particularly a rotating electric machine, and detecting a loosening in the rotating electric machine by detecting a pulse waveform generated in the rotating electric machine (for example, JP-A-60-29660, 60-260582). ) That is, this looseness detecting method quantitatively measures the looseness by obtaining the ratio of the time (width) before and after the maximum value of the pulse waveform.

[Problems to be Solved by the Invention]

However, according to the knowledge of the present inventors, when the structure is assembled using bolts and nuts, the pulse as described above is generated even if the bolts and nuts are loosened. There is a problem that the time before and after the waveform does not change, and as a result, the looseness cannot be detected.

[Means for Solving the Invention]

The present invention has been made to solve the above-mentioned conventional problems, and detects a striking force of a hexagonal portion of a bolt / nut in a shearing direction and a striking force of an impact hammer or an acceleration pulse waveform. It is characterized by comprising means and means for detecting the ratio of the slope (or angle) of the rising and falling edges of the pulse waveform.

[Object of the Invention]

According to the present invention, when loosening occurs in the tightened state of the bolts and nuts, the pulse waveform generated by striking the fastening portion, that is, the bolts and nuts, has an upward slope α (or angle) and a downward slope β ( Or, the phenomenon that the ratio α / β of the angle becomes large) (the ratio β / α becomes small) is found, and the change of the pulse waveform is used to detect the looseness of the bolt / nut.

Then, specifically, the pulse waveform generated by hitting the hexagonal part of the bolt / nut is generated by A / D conversion of the signal from the force or acceleration sensor, and this is printed by the printer. (Or slope) and the method of calculating the ratio of the falling angle (or slope),
There is a method in which the converted signal is supplied to an arithmetic unit, the ratio between the rising and falling angles (or the slope) of the pulse waveform is calculated in this arithmetic unit, and this value is displayed.

〔Example〕

An embodiment of the bolt / nut looseness detecting method according to the present invention will be described below.

As shown in Fig. 1, bolts are inserted into the holes 11 provided in the steel structure 10.
A case will be described in which 12 is inserted and the tightened state of the portion tightened with the nut 14 via the washer 13 is measured.

In the present invention, for example, a nut 16 or a head 12a of a bolt 12 with a hammer 16 to which a sensor 15 such as a load detector or an acceleration detector using a piezoelectric element or a strain gauge is attached.
(Hexagonal part) is hit in the shearing direction (direction orthogonal to the axis of the bolt 12), the signal obtained by the sensor 15 is electrically processed to obtain a waveform, and the waveform is further processed to obtain the bolt. The tightening state between the nut 12 and the nut 14 is determined.

2 is a diagram showing an example of a hammer, a sensor 15 is provided at the striking portion of the hammer 16, and a pulse signal detected by the sensor 15 is connected via a lead wire 17 to an A / D converter 18 including an amplification section. The display portion 19 is led.

Specifically, as shown in FIG. 3, the sensor 15 detects a pulse generation time point and a pulse end time point, and a time change of “force or acceleration” between the generation time point and the end time point as a striking pulse signal 25. This striking pulse signal 25 is supplied to the amplification unit 26,
The amplified pulse signal S is A / D converted by an A / D converter 18, and this is printed as a waveform by an XY blotter or printer 19.

Then, using the printed waveform, a person measures the rising and slope (or angle) and the descending or slope (or angle) using a ruler or a protractor, and discriminates the ratio from looseness to looseness.

Further, if necessary, it is possible to discriminate this by comparing it with a manual obtained by processing a large number of experimental data. When the analog recorder is used in the apparatus shown in FIG. 3, the A / D converter 18 is unnecessary.

Further, as shown in FIG. 4, the striking pulse 25 from the sensor 15 is supplied to the amplification unit 26, the amplified pulse signal S is A / D converted in the A / D converter 18, and this is converted into a microcomputer. It is possible to calculate the characteristic value of the rising angle or the gradient, the downward angle or the gradient, which is used by the calculating unit 27, and display it on the display unit 19 similar to the above, or display it as a numerical value by the LED 30.

Then, the looseness can be easily determined by visually observing the characteristic value displayed on the display unit 19 or the LED 30 as a figure, a color or a numerical value by using the characteristic value thus calculated.

FIG. 5 shows another method for detecting looseness, in which a reference value, for example, the ratio of the rising angle α of the pulse waveform to the falling angle β at the end, α / β, is compared with a reference value L. When α / β> L, the comparator 28 determines that there is slackness, and the sound generator 31 issues an alarm to determine the slackness.

Next, an experimental example is shown.

The bolts 12 and nuts 14 actually used were M22, and the weights shown in Table 1 were used.

In this case, the hammer 16 weighs 0.25 kg, and when the hammer 16 strikes the hexagonal parts of the bolt / nut in the shearing direction, the pulse waveform of the striking force of the striking hammer is examined. Representative examples of the waveforms are shown in FIGS. 6 (a) to 9 (b).

That is, the axial force of the bolt 12 is 3 tons, 5 tons, 10 tons and 22.5 tons.
The pulse waveform A obtained when changing to tons is 2
It is illustrated.

Then, for this pulse waveform A, the ratio lb / la of the width la from the rising to the peak value and the width lb from the peak value to the falling and the ratio α / β of the rising slope α and the falling slope β were measured. The results are shown in Table 2.

Then, in order to clarify the deformation state of the pulse waveform A due to the change of the bolt axial force, as shown in FIG.
It is as shown in Figure 11.

Fig. 10 shows the bolt axial force on the horizontal axis and lb / la on the vertical axis. As is clear from this figure, the width la and the peak value of the pulse waveform A from the rise to the peak value are shown. It can be seen that the ratio of the width lb from the to the fall does not change in response to the change in the bolt axial force.

Therefore, the ratio of the width before and after the center of the pulse waveform is lb / l
It can be seen that a cannot detect looseness of the bolt.

On the other hand, in FIG. 11, as in FIG. 10, the horizontal axis represents the bolt axial force, and the vertical axis represents the rising slope α and the falling slope β of the pulse waveform A.
It is shown by taking the ratio α / β from the above. As is clear from this figure, α / β corresponds to the change in the bolt axial force.
You can see how is changing.

Therefore, the looseness of the bolt can be clearly detected by using the change in α / β, which is the ratio of the rising angle or gradient α obtained from the pulse waveform A and the falling angle or gradient β, as a reference.

〔The invention's effect〕

As is clear from the above description, the bolt according to the present invention
According to the looseness detecting method of the nut, means for detecting a pulse waveform of a striking force or acceleration generated when the hexagonal portion of the bolt / nut is striking in the shearing direction by a hammer,
A means for calculating the ratio of the rising angle or gradient of the pulse waveform to the falling angle or gradient is employed to determine the looseness of the bolt and nut.

Therefore, according to the present invention, the looseness of the bolts and nuts is detected without being affected by various conditions such as the size of the bolts and nuts, the rigidity of the bolts and nuts, or the size of the plate thickness, and individual differences at the time of determination, The quality can be determined.

The present invention has great versatility by eliminating the individual differences as described above and by eliminating the data generated due to the bolts and nuts and the plate thickness, and the bolt and nut loosening detection work can be performed quickly and easily. It can be carried out and is extremely beneficial in the industry.

[Brief description of drawings]

FIGS. 1 and 2 explain an embodiment of a bolt / nut looseness detecting method according to the present invention. FIG. 1 is an explanation of inspection of looseness when a plurality of plate materials are fastened with bolts / nuts. FIG. 2 and FIG. 2 are explanatory views showing examples of a hammer and a display device. 3 to 5 are block diagrams showing examples of the signal processing device. 6 (a) to 9 (b) are explanatory views of changes in the pulse waveform when the experiment is performed by changing the bolt axial force. FIG. 10 is an explanatory diagram of changes in the width of the pulse waveform, and FIG. 11 is an explanatory diagram of changes in the rising slope and the falling slope of the pulse waveform. 10 …… Steel structure, 11 …… Hole, 12 …… Bolt, 12a ……
Head of bolt, 13 …… washer, 14 …… nut, 15 ……
Sensor, 16 ... hammer.

Claims (1)

[Claims] 1. A means for striking a hexagonal portion of a bolt / nut in a shearing direction, a means for detecting a striking force of an impact hammer or an acceleration pulse waveform, and a ratio of a rising angle or gradient to a descending angle or gradient of the pulse waveform. A method for detecting looseness of bolts and nuts, which comprises a means for calculating