JPH0570003B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention provides a method for detecting bolt loosening, more specifically, a method for detecting bolt loosening by striking a bolt in a shearing direction, and non-destructively detecting the loosening of the bolt by the force and acceleration generated by this striking. The present invention relates to a bolt loosening detection method. [Prior Art] Generally, when detecting the loosening of a bolt, a method is used in which the head of the bolt is struck with a hammer in the shearing direction, and a human judge is determined based on the sound and vibration of the strike. However, this method often relies on a "feel" for the ratio, and as a result, there are large individual differences, and not only is it impossible to make an accurate judgment unless you are an expert, but even a highly skilled person can make no judgment when the amount of slack is small. The problem is that it cannot be done. For this reason, a sensor is attached to one side of the nut that is screwed into the bolt, and the opposite side of the nut is hit with a hammer.The acceleration of the bolt due to this hit is detected and sent to a signal analyzer. A method for detecting looseness has been proposed. However, this method has a problem in that when the mass of the hammer is small or the diameter of the bolt is large, a sufficient signal cannot be obtained, resulting in errors in detection. [Object of the Invention] The present invention was achieved in order to eliminate the drawbacks of the prior art described above, and it is possible to use a bolt without being affected by conditions such as the size and stiffness of the bolt or the mass of the hammer. The present invention provides a method for accurately and non-destructively detecting looseness. [Summary of the Invention] To achieve the above object, the present invention includes an acceleration sensor attached to the head of a bolt fastened to a structure or one hexagonal surface of a nut, and a force sensor attached to a hammer. striking one side of the hexagonal surface of the head of the bolt or nut that corresponds to the acceleration sensor mounting surface;
The ratio between the signal of the acceleration sensor and the signal of the force sensor obtained by this impact is compared with the ratio of the signal of the acceleration sensor and the signal of the force sensor when the bolt is in a predetermined fastened state, and the bolt is fastened. This is a bolt loosening detection method that determines the condition. In the present invention, the value of both the signal A/F of the acceleration A obtained from the acceleration sensor attached to the bolt side and the force F obtained from the force sensor attached to the hammer side when struck by the hammer, or The same is true for the opposite F/A value, and the ratio of this acceleration A to force F is compared between when the bolt is tightened with a predetermined tightening force and during inspection to determine whether the bolt's fastening condition is good or bad. It is something to do. The principle of the bolted part inspection method according to the present invention will be explained as follows. If we observe the force F that acts on the hammer when striking the hexagonal surface of a nut (or the head of a bolt), we can see that even if the hammer is struck at the same initial speed, the repulsive force will be smaller if the nut is loose. Therefore, the force F acting on the hammer becomes smaller. However, if the nut is tightly tightened against the bolt, the frictional force at the washer is not large. Therefore, a large repulsive force is generated on the hammer,
The force F obtained by the force sensor or acceleration sensor is large. As mentioned above, it is clear that the repulsive force F that acts on the hammer when hitting the nut or bolt head changes depending on whether the nut is tightly tightened against the bolt or not. be. On the other hand, the acceleration A generated when the nut is struck is large when the nut is loose, and conversely becomes small when the nut is tightened. This relationship is summarized in Table 1.

〔Example〕

As shown in FIG. 1, a hole 2 passing through a structural member 1
An acceleration sensor 6 is attached to the head 4 of the bolt 3 inserted into the bolt 3, or to one surface 4a or 5a of the hexagonal part of the nut 5 tightened to the bolt 3. The moving state is detected as acceleration A. Then, the surface 5b or 4b opposite to the surface 5a or 4a on which the acceleration sensor 6 is attached is struck with the hammer 7. On the other hand, a force sensor 8 made of a piezoelectric element, a strain gauge, etc. is attached to the striking surface of the hammer 7, and when the hammer 7 strikes one surface 5b of the nut 5 or one surface 4b of the head 4 of the bolt 3, a force is generated. A signal A is obtained which is related to the force F by the sensor 8 and the acceleration A of the nut 5 or bolt 4 itself. The hammer 7 hits the structural member 1 (in this example, a plate) fastened with the bolt 3 in the direction of extension of the plate, so the rigidity is very high and the nut 5 is sufficiently tightened. If the nut 5 and the washer 9 are in the same position, no slipping occurs between the nut 5 and the washer 9, and signals A and F are generated from the acceleration sensor 6 and the force sensor 8 based on the stiffness. On the other hand, if the bolt 3 is loose, the washer 9 will slip slightly due to the impact of the hammer 7 in the shearing direction. Therefore, even if the hammer 7 and the surface of the nut 5 are hit at the same initial speed, the force F is small when the hammer is loose, and when it is tight, there is no slipping and the repulsive force is large. As a result, the force F obtained by the force sensor 8 provided on the hammer 7 becomes large. The force F and acceleration A thus detected are amplified by amplifiers 20 and 21 using their peak values as signals, as shown in FIG.
2 and 23 capture the peak value, and calculate this by the calculation unit 24.
and here the ratio of both, i.e. A/F or F/
A is calculated and displayed on the display section 25 made of a cathode tube, liquid crystal display, etc., numerically or, if necessary, graphically or in color. Further, the A/F or F/A calculated by the calculation unit 24 may be output as is by an LED or the like.
Furthermore, as shown in FIG. 4, the reference value B is input into the comparator 26 in advance, and compared with A/F or F/A from the calculation section 24, and displayed on the display section 25 or output from the LED 27. or loudspeaker 2
It is also possible to issue an alarm from 8 onwards. [Experimental Example] Next, an experimental example will be shown. The axial force (tightening force) of the bolt 3 with a diameter of 22 mm was changed, and the weight was adjusted to 260 g.
The force F and acceleration A when hitting b were investigated. Representative examples of the results are shown in FIGS. 5a to 5c. Figure 5 shows that when the axial force is 1 ton, the force F at the time of impact is a-1, and the acceleration A is a-2.
Similarly, when the axial force is 4 tons, the force F is b-
1, the acceleration is shown in b-2, the force Fc-2 shows the acceleration when the axial force is 22.5 tons, and the acceleration c-2 shows the acceleration. Table 2 summarizes the force F and acceleration A for each of these.

[Table] [Effects of the Invention] The bolt loosening detection method according to the present invention includes attaching an acceleration sensor to the head of a bolt fastened to a structure or one hexagonal surface of a nut, and attaching a force sensor to a hammer. Hit the head of the bolt or the hexagonal surface of the nut corresponding to the mounting surface of the acceleration sensor, and calculate the ratio of the signal of the acceleration sensor and the signal of the force sensor obtained by this hitting. The fastening state of the bolt is determined by comparing the ratio of the signal from the acceleration sensor and the signal from the force sensor when the bolt is in a predetermined fastening state. Therefore, the force F of the force sensor installed on the hammer side and the acceleration A of the acceleration sensor installed on the head of the bolt or the nut side can be detected from the state where the hammer is repelled and the bolt is slightly misaligned. Even when the mass is small or the diameter of the bolt is large, it is possible to obtain an appropriate signal and accurately detect the loosening of the bolt. In addition, the axial force generated in a bolt can be estimated by simply striking the bolt in a direction perpendicular to its axis, so it is used in the assembly of large structures such as large towers and bridges. The tightness of a large number of bolts can be detected non-destructively and efficiently.

[Brief explanation of drawings]

FIG. 1 is a side sectional view showing the concept of the bolt loosening detection method according to the present invention, and FIG. 2 is a front view thereof.
3 and 4 are block diagrams of a signal processing device, and FIGS. 5a to 5c are graphs of data obtained by said device. 1... Structural material, 2... Hole, 3... Bolt, 4... Head,
4a...plane, 5...nut, 5a...plane, 6...acceleration sensor, 7...hammer, 8-point force sensor, 20,
21... Amplification section, 22, 23... Peak detector, 24
...Arithmetic section, 25...Display section, 26...Comparator, 27...
LED, 28... Loudspeaker.

Claims (1)

[Claims] 1 Attach an acceleration sensor to one side of the hexagonal surface of the head of a bolt or nut fastened to a structure, and attach a force sensor to a hammer, and use the hammer to detect the acceleration of the head of the bolt or the hexagonal surface of the nut. one surface corresponding to the sensor mounting surface is struck, and the ratio of the signal of the acceleration sensor and the signal of the force sensor obtained by this striking;
A method for detecting loosening of a bolt, characterized in that the fastening state of the bolt is determined by comparing the ratio of a signal from an acceleration sensor with a signal from a force sensor when the bolt is in a predetermined fastening state.