JPH0198705A - Looseness detecting method of bolt - Google Patents

Abstract

PURPOSE: To detect bolt looseness in an ensured and nondestructive way by arranging an acceleration sensor on the object to be stricken and a force sensor or the acceleration sensor on the striking object respectively, and determining bolt looseness by the signal obtained from the acceleration sensor and the signal obtained from the force sensor. CONSTITUTION: When the head 4 of a bolt 3 or the surface 4b or 5b of a nut 5 is stricken by a hammer 7, no slide occurs between the nut 5 and a washer 9 if the nut 5 is tightly fastened, hence signals A, F in correspondence with the rigidity are generated by an acceleration sensor 6 and a force sensor 8 due to the rigidity. On the other hand, if the bolt 3 is loosen, a slight slide takes place on the part of the washer 9, the force F acting between the hammer 7 and the surface of the nut 5 is smaller in such a case. In the case of being fastened, the counter force is larger, and the force F obtained by the force sensor 8 is larger. The peak values of the detected force F and acceleration A are introduced to a calculating section 24, the ratio of the two values is calculated and displayed by a display section 25.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a bolt loosening detection method, and more specifically, a method for detecting the loosening of a bolt by hitting the bolt in a shearing direction, and non-destructively determining the loosening of the bolt by the force and acceleration generated by this hitting. The present invention relates to a bolt loosening detection method that detects bolt loosening.

[Traditional technique]

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 the judgment is made by a human based on the sound and vibration of the strike. However, this method is highly dependent on people's ``sensibilities'', and as a result, there are large individual differences, and not only can only an expert make an accurate judgment, but when there is little slack, only a highly skilled person can make a judgment at all. The problem is that it is not possible.

For this reason, a sensor is attached to one side of the nut screwed into the bolt, and the opposite side of the nut is hit with a hammer, and the acceleration of the bolt caused by this hit is detected and sent to a signal analyzer to detect loosening of the bolt. A detection method has been proposed. However, this method has the problem that a sufficient signal cannot be obtained when the mass of the hammer is small or when the diameter of the bolt is large, resulting in errors in detection.

[Purpose of the invention]

The present invention was obtained in order to eliminate the drawbacks of the prior art, and is capable of accurately loosening bolts without being influenced by conditions such as the size and stiffness of the bolt or the mass of the hammer. It also provides a non-destructive detection method.

[Summary of the invention]

To achieve the above object, the present invention has an acceleration sensor attached to one side of the hexagonal surface of the head of the bolt or the side of the nut, and a force sensor or Hit with a hammer equipped with an acceleration sensor.

Note that the output of the acceleration sensor attached to the hammer is a signal with the same waveform that is proportional to the output of the force sensor attached to the tip, so the following explanation will be based on the force sensor.

Processes both the acceleration A obtained by the acceleration sensor and the force F obtained by the force sensor when struck with a hammer,
For example, the loose state of the bolt is detected by calculating the ratio of both signals or by performing mathematical processing using both signals as variables.

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 hitting the hexagonal surface of a nut (or bolt head), we can see that even if the hammer is hit at the same initial speed, if the nut is slack, the repulsive force will be smaller. Therefore, the force F acting on the hammer
becomes smaller. However, when the nut is tightly tightened to the bolt, there is no slippage at the washer, and therefore a large repulsive force is generated on the hammer, and the force F obtained by the acceleration sensor becomes 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 or not. It is.

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.

Table 1 The present invention detects such a phenomenon, that is, detects the force F generated in the hammer and the acceleration A, and calculates the ratio to detect the loosening of the bolt.

〔Example〕

As shown in FIG. 1, an acceleration sensor is mounted on the head 4 of a bolt 3 inserted into a hole 2 passing through a structural member 1, or on one surface 4a or 5a of a hexagonal part of a nut 5 tightened on this bolt 3. 6 is installed, and the moving state of the head 4 of the nut 5 or bolt 3 is detected as acceleration A. Then, the surface 4b or 5b on the opposite side to the surface 5a or 4a on which the acceleration sensor 6 is attached is pressed with a hammer 7.
Hit with.

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 the hammer 7 strikes one surface 5b of the nut 5.

Alternatively, when one side 4b of the head 4 of the bolt 3 is struck, signals F and A related to the force F from the force sensor 8 and the acceleration A of the nut 5 or the bolt 4 itself are obtained.

The hammer 7 hits the structural member 1 (a plate in this embodiment) that is fastened with the bolt 3 in the direction of extension of the plate, so the rigidity is very high and the nut 6 is sufficiently tightened. If the nut 5 and the washer 9 are in the same state, no slipping occurs between the nut 5 and the washer 9, and the acceleration sensor 6 and the force sensor 8 generate a signal A corresponding to the stiffness.

F occurs.

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, if the hammer is loose, the force F will be small, but if the hammer is tight, there will be no slippage, and the repulsive force will be large. The force F obtained by the force sensor 8 provided at 7 becomes large.

The force F and acceleration A thus detected are sent to an amplifier 20, using their peak values as signals, as shown in FIG.
21, the peak value is captured by peak detectors 22 and 23, and introduced into the calculation unit 24, where the ratio of the two, that is, A/F or F/A, is calculated, and this is calculated numerically or as required. The information is displayed on the display section 25 made of a cathode tube, liquid crystal display, etc., using figures and colors according to the information.

Further, A/F or F/^ calculated by the calculation unit 24 may be outputted as is by an LED or the like, or furthermore, as shown in FIG. Compare with A/F or F/A from the calculation unit 24,
Display on the display unit 25, output from the LED 27,
Alternatively, the alarm may be emitted from the loudspeaker 28.

[Example of practical experience]

Next, an experimental example will be shown.

The axial force (tightening force) of the bolt 3 with a diameter of 22 mm was varied, and the force F and acceleration A when one side of the nut 5 was hit with a hammer 7 weighing 1260 g were investigated. A representative example of the results is shown in Section 5.
Shown in Figures (a) to (C).

Figure 5 shows the force F at the time of impact when the axial force is 1 ton (a-1), the acceleration A is (a-2), and the force F when the axial force is 4 tons ( (b-1) shows the acceleration, (b-2) shows the force F when the axial force is 22.5 tons, (c-1) shows the acceleration, and (c-2) shows the acceleration.

Table 2 shows the answer F and acceleration A for these questions.

Note to Table 2: Axial force = tons, acceleration = m/see'' (G), car kgf [Effects of the invention] As explained above, the present invention provides an acceleration sensor on the object to be hit, and a force sensor on the object to be hit. The system uses the acceleration and force signals obtained from both sensors to calculate the signal ratio and detect bolt loosening. However, an appropriate signal can be obtained even if the bolt is loose, and as a result, there is no detection error and the loosening of the bolt can be accurately detected.

Furthermore, when tightening a nut against a bolt, it is possible to inspect the tightness of that part by simply hitting that part.

Since the axial force of the bolt can be confirmed by simply applying a striking force perpendicular to the axis of the bolt, that is, by striking in the shearing direction, it is possible to non-destructively check the looseness of bolts of various structural members.

[Brief explanation of the drawing]

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. Figures 3 and 4
The figure is a block diagram of a signal processing device, and Figures 5(a) to (C)
) is a graph of data obtained by the device. 1... Structural material, 2... Hole, 3... Bolt, 4...
・Head, 4a...plane, 5...Nand, 5a...plane, 6...acceleration sensor, 7...hammer, 8...
Force sensor, 20, 21... Amplifying section, 22, 23...
- Peak detector, 24... Arithmetic unit, 25... Display unit, 26... Comparator, 27... LED, 28... Loudspeaker. Agent Patent Attorney Nobuo Ogawa −

Claims (1)

[Claims] The object to be hit is provided with an acceleration sensor, and the object to be hit is provided with a force sensor or an acceleration sensor, and the loosened state of the bolt is determined from the signal A obtained from the acceleration sensor and the signal F obtained from the force sensor. How to detect loose bolts.