JPH02205736A - Method for detecting looseness of bolt and nut - Google Patents

Abstract

PURPOSE:To make it possible to detects looseness without being effected by the size and rigidity of a bolt and a nut or by personal differences by detecting the pulse waveform of the striking force of a striking hammer or acceleration and the ratio between the rising gradient and the falling gradient of the pulse waveform. CONSTITUTION:A sensor 15 using a piezoelectric element, a strain gage and the like is attached to a hammer 16. A nut 14 of a head part 12a of a bolt 12 is hit with the hammer 16 in the shearing direction. The obtained symbol is electrically processed, and a waveform is obtained. The waveform is further processed, and the tightening state between the bolt 12 and the nut 14 is judged. Namely, the generated time and the terminating time of the pulse and the force or acceleration between the generated time and the terminating time are detected as a strike pulse signal 25. The signal 25 is amplified in an amplifier 26 and undergoes A/D conversion in an A/D converter 18. Thereafter, the characteristic values of the rising angle or gradient and the falling angle or gradient are computed in an operating part 27. The results are displayed on a display part 19 or displayed as numerical values with an LED 30.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention non-destructively removes bolts and nuts by striking bolts and nuts fastened to a structure using the striking force or acceleration pulse of a striking hammer. -Relates to a method for detecting loosening of nuts.

[Prior art]

Generally, when detecting an abnormality in the adhesion of a structure, such as loosening of bolts or peeling of a honeycomb structure, the structure is lightly struck with a hammer, and a human being makes a judgment based on the sound of the strike and the repulsive force. A method is used. However, this method is highly dependent on human ``misconceptions'', and as a result there are large individual differences, and there is a problem that not only can only an expert make a judgment, but when the degree of loosening is small, only a highly skilled person can make a determination. Ta.

For this reason, a method has been proposed in which a structure, particularly a rotating electrical machine, is struck and the pulse waveform generated in the rotating electrical machine is detected to detect loosening in the rotating electrical machine (for example, Japanese Patent Application Laid-open No. 60-29660.60260582). In other words, this looseness detection method calculates the time before and after the maximum value of the pulse waveform (
Looseness is quantitatively measured by determining the ratio of width).

[Problem to be solved by the invention]

However, according to the findings of the present inventors, if a structure is assembled using bolts and nuts, the above-mentioned pulse may occur even though the bolts and nuts are loosened. There is a problem in that there is no change in the time before and after the waveform, and as a result, loosening cannot be detected.

[Means for solving the invention]

The present invention has been made in order to solve the conventional problems as described above, and includes a means for striking the hexagonal part of a bolt/nut in a shearing direction, and a means for detecting the striking force or acceleration pulse waveform of a striking hammer. and means for detecting the ratio of the slope (or angle) of the rise and fall of the pulse waveform.

[Purpose of the invention]

The present invention provides that when the bolt/nut is loosened in the tightened state, the pulse waveform generated by striking the fastened portion, that is, the bolt/nut, has an upward slope α (or angle) and a downward slope β ( The inventors discovered the phenomenon that the ratio α/β (or angle) increases (β/α decreases), and attempts to detect the loosening of bolts and nuts by utilizing this change in pulse waveform.

Specifically, the pulse waveform generated in the hexagonal part of the bolt or nut by hitting the hexagonal part of the bolt or nut is generated by A/D conversion processing of the signal from the force or acceleration sensor, and then printed by a printer. (or slope) and the falling angle (or slope), and how to calculate the ratio of the falling angle (or slope),
The /D-converted signal is supplied to a calculation unit, which calculates the ratio of the rising and falling angles (or slopes) of the pulse waveform.
There are several ways to display this value.

〔Example〕

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

As shown in FIG. 1, a case will be described in which a bolt 12 is inserted into a hole 11 provided in a steel structure 10, and the tightening state of a portion is measured by inserting a bolt 12 into a hole 14 through a washer 13.

In the present invention, a sensor 15 such as a load detector or an acceleration detector using a piezoelectric element, a strain gauge, etc.
Use the hammer 16 with the nut 14 or pole 1-12
head 12a (hexagonal part) in its shear direction (bolt 1
The signal obtained by the sensor 15 hit in the direction perpendicular to the axis of the nut 12) is electrically processed to obtain a waveform, and by further processing this waveform, the tightening state between the bolt 12 and the nut 14 is determined. It is something to do.

FIG. 2 is a diagram showing an example of a hammer, and the hammer 1
A sensor 15 is provided at the striking portion of the drum 6, and a pulse signal detected by the sensor 15 is led to an A/D converter 18 including an amplification section and a display section 19 via a lead wire 17.

Specifically, as shown in FIG. 3, the sensor 15 detects the occurrence and termination points of repa and rus, and the temporal changes in "force or acceleration" between the generation and termination times as the impact pulse signal 25. This striking pulse signal 25 is supplied to an amplifying section 26, the amplified pulse signal S is A/D converted by an A/D converter 18, and is printed as a waveform by an XY plotter or printer 19.

Then, using the printed waveform, a person uses a ruler or a protractor to measure the rise, slope (or angle), and fall or slope (or angle), and determines looseness from the degree of the ratio.

Further, if necessary, this can be determined by comparing it with a manual obtained by processing a large number of experimental data. Note that when an analog recorder is used in the apparatus shown in FIG. 3, the A/D converter 18 is not necessary.

In addition, as shown in FIG. 4, the impact pulse 2 from the sensor 15
5 is supplied to the amplifying section 26, and the amplified pulse signal S is
A/D converter 18 performs A/D conversion, and a calculation unit 27 using a microcomputer calculates the characteristic values of the rising angle or slope, and the falling angle or slope, and displays them on the display unit 19 similar to the above. Or,
It can be displayed as a numerical value by the LED 30.

Looseness can be easily determined by visually observing the characteristic values displayed graphically, in color, or numerically on the display unit 19 or the LED 30 using the characteristic values calculated in this way.

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 the reference value. Looseness can be determined by using the comparator 28 to determine that there is looseness when α/β>L, and by emitting an alarm using the sound generator 31, etc.

Next, an experimental example will be shown.

The bolt 12 and the cross-section 4 actually used were M22, and the first
I used the weights shown in the table.

The pulse waveform of the striking force shown in Table 1 was examined. Representative examples of the waveforms are shown in FIGS. 6(a) to 9(b).

That is, two examples of pulse waveforms A obtained when the axial force of the bolt 12 is changed to 3 tons, 5 tons, 10 tons, and 22.5 tons are shown.

And for this pulse waveform A, the width 1a from the rising edge to the peak value and the width from the peak value to the falling edge! ! , the ratio 1b/Qa of b and the ratio α/ of the rising slope α and the falling slope β
β was measured. The results are shown in Table 2.

Table 2 The weight of the hammer 16 in this case is 0.25 kg, and when the hexagonal part of the bolt/nut is struck in the shearing direction by the hammer 16, the pulse waveform due to the change in the bolt axial force is In order to make the deformed state clearer, it is shown in figures as shown in FIGS. 10 and 11.

Figure 10 shows bolt axial force on the horizontal axis and lb/la on the vertical axis.
As is clear from this figure, the width 2a from the rise to the peak value of the pulse waveform and the width from the peak value to the fall! It can be seen that the ratio b does not change in response to changes in the bolt axial force.

Therefore, the ratio of the widths before and after the center of the pulse waveform is 1b
/1. It can be seen that the loosening of the bolt cannot be detected in case a.

On the other hand, in Fig. 11, the horizontal axis shows the bolt axial force and the vertical axis shows the ratio α/β of the rising slope α and the falling slope β of the pulse waveform A, as in Fig. 10. However, as is clear from this figure, α/
It can be seen that β is changing.

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

〔Effect of the invention〕

As is clear from the above explanation, the bolt according to the present invention
According to the nut loosening detection method, a means for detecting a pulse waveform of impact force or acceleration generated when a hexagonal part of a bolt/nut is hit in a shearing direction with a hammer;
Looseness of bolts and nuts is determined by employing means for calculating the ratio of the rising angle or slope and the falling angle or slope of the pulse waveform.

Therefore, according to the present invention, the looseness of bolts and nuts can be detected without being influenced 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 in judgment, It is possible to judge whether it is good or bad.

As mentioned above, the present invention completely eliminates individual differences, and also eliminates data generated due to bolts, nuts, and plate thickness, making it highly versatile, and the work of detecting loosening of bolts and nuts is quick and easy. It is extremely useful industrially.

[Brief explanation of the drawing]

Figures 1 and 2 explain an embodiment of the method for detecting looseness of bolts and nuts according to the present invention, and Figure 1 explains how to inspect the looseness when a plurality of plates are fastened with bolts and nuts. FIG. 2 is an explanatory diagram showing an example of a hammer and a display device. 3 to 5 are block diagrams showing examples of signal processing devices. FIGS. 6(a) to 9(b) are explanatory diagrams of changes in pulse waveforms when experiments were conducted 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 and falling slopes of the pulse waveform. lO... Steel structure, 11... Hole, 12... Bolt, 12a... Bolt head, 13... Washer,
14...Nut, 15...Sensor, 16...Hammer 10th axial force on 11th axial force on

Claims (1)

[Claims] means for striking the hexagonal part of the bolt/nut in the shearing direction; means for detecting the striking force or acceleration pulse waveform of the striking hammer; and means for calculating the ratio of the rising angle or slope to the falling angle or slope of the pulse waveform. A method for detecting looseness of bolts and nuts, characterized by the following.