JPH02274476A - Bolt fastening device - Google Patents

Abstract

PURPOSE:To control the fastening force of a bolt so that the axial tension of plural bolts in the same kind become a desired uniform axial tension in the case of fastening them by constructing a fastening device so as to directly detect the propagation time of the ultrasonic wave made incident on the bolt of the axial tension of the bolt under fastening through measuring it. CONSTITUTION:A probe 7 is brought into contact with one end face in the axial direction of the bolt 6 under fastening, the bolts 6a, 6b head end faces, for instance, and when an ultrasonic wave pulse is made incident by the pulse impression by a transmitting circuit 8 toward the screw side end face relative to the end face from the end face, the incident wave is reflected on the screw side end face to reciprocate the bolt whole length and the reflection wave signal fed from the screw side end face is received to the probe 7. This received reflection wave signal is transmitted to a route detection circuit 12 and the propagation time of one or optional reciprocation number is measured. This measured propagation time is compared by a comparison circuit 14 with the propagation time for the specific known axial tension of the bolt in the same kind and the axial tension of the bolt 6 is directly detected based on this comparison result.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a bolt tightening device that uses a driving device to tighten a bolt, and in particular, relates to a bolt tightening device that uses an ultrasonic propagation time. The present invention relates to a device suitable for directly detecting the axial force of a bolt during tightening and controlling the bolt tightening force so that the axial force of a plurality of bolts becomes a desired uniform axial force.

[Conventional technology]

FIG. 3 is a block diagram showing an example of the configuration of a conventional bolt tightening device in which a bolt is tightened using a driving device. In the figure, 1 is a strain detector that detects a signal due to strain generated in the axial direction of the bolt due to torque when tightening the bolt, 2 is an amplifier circuit that amplifies the signal due to the strain detected by the strain detector 1, 3 is a setting circuit for setting a strain signal based on a predetermined known tightening torque, and the value of the set strain signal becomes a threshold value.

4 is a comparison circuit that compares the output value of the amplifier circuit 2 with the threshold value set in the setting circuit 3, and shuts down when the output value of the amplifier circuit 2 reaches or even slightly exceeds the threshold value. The attachment is configured to output a drive stop signal to the drive device 5 to stop the drive.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, it is possible to measure the torque of tightening that generates strain that has a correlation with the axial force of the bolt with fairly high accuracy, but the torque value of the measured tightening is Since the value does not necessarily represent the true axial force of the bolt corresponding to the value, even if the torque measurement accuracy of tightening is good, it does not mean that the axial force of the bolt is accurately measured. This is because the frictional force between the bolt seating surface and the fastened member during bolt fastening affects the tightening torque, and the roughness and shape of the fastening surface.

In addition to hardness, presence or absence of oil and fat adhesion, etc., the tilt of the bottom seat surface,
This is because there are variations depending on various conditions such as the eccentricity of the bolt head and whether or not a washer is used. When the frictional force is large, the axial force of the bolt is small; on the other hand, when the frictional force is small, the axial force of the bolt may become excessive. In this way, the frictional force is directly related to the torque when tightening a bolt, so if the frictional force at the fastened part decreases due to break-in after fastening, it will cause the bolt to loosen. If you tighten the door to a degree equivalent to the case where the friction force is too low, if the friction force is small, the axial force of the bolt may be excessive and even cause damage, so take the effort to counter the strain on the bolt. Even if a torque threshold is set for tightening, the threshold value will have a variable correlation between strain and tightening torque, and the bolt will not reach the desired uniform bolt axial force generation state. The problem with tightening was that the force could not be controlled.

In view of the above-mentioned problems of the prior art, the present invention directly detects the axial force of the bolts inside using the propagation time of ultrasonic waves, and uses the measured propagation time to tighten the axial force of the bolts of the same type. It is an object of the present invention to provide a bolt tightening device capable of controlling the bolt tightening force so that the force becomes a desired uniform axial force.

[Means to solve the problem]

In order to achieve the above object, the bolt tightening device of the present invention is configured such that when the correlation value of the axial force of the port in the bolt reaches a certain value, the bolt tightening device of the present invention is tightened by the drive device. In the device, bolt tightening is controlled to stop the drive.
a probe that injects an ultrasonic pulse from one end surface in the axial direction of the bolt toward the other end surface opposite to the one end surface by applying a pulse by a transmitting circuit, and sends a reflected wave signal from the other end surface to a receiving circuit; a path detection circuit that measures the propagation time of the reflected signal sent from the receiving circuit via the detection circuit; A setting circuit that sets a threshold value of The present invention is configured to include a comparison circuit that stops the drive of the drive device when tightening the bolt in response to a signal.

[Effect]

To tighten, a probe is brought into contact with one end surface in the axial direction of the bolt inside, for example, the end surface of the bolt head, and an ultrasonic pulse is applied by a transmitting circuit from this end surface toward the end surface on the screw side opposite to the end surface. When incident, the incident wave is reflected at the threaded end face and reciprocates along the entire length of the bolt, and a reflected wave signal from the threaded end face is received by the probe. The received reflected wave signal is amplified by the receiving circuit and then sent to the path detection circuit via the detection circuit, and the path detection circuit measures the propagation time for one or any number of round trips. This measured propagation time is measured in advance by the path detection circuit, and compared by the comparison circuit with the propagation time for a predetermined known axial force of the bolt of the same kind, which is set in the setting circuit as a threshold value. be done. The propagation time compared here is the propagation speed of the ultrasonic wave, which changes with the internal stress of the bolt due to the increase in the axial force of the bolt, and
It changes in correlation with the bolt's overall length, which changes with axial elongation, and is not affected by the frictional force between the bolt seating surface and the fastened member, so the bolt axis changes through the measured propagation time. It becomes possible to directly detect force.

The propagation time comparison signal output from the comparison circuit is sent to the drive device for bolt tightening, and the bolt is tightened when the measured value of the bolt reaches or even slightly exceeds the threshold value. acts to stop the driving of the drive device,
The tightening force of bolts can be controlled so that the axial force of bolts of the same type is uniform.

〔Example〕

One embodiment of the present invention will be described with reference to FIGS. 1 and 2. In the figure, 6 indicates the inner bolt to be tightened, 6a indicates one end surface of the bolt 6 in the axial direction (the head end surface in the embodiment), and 6b indicates the other end surface opposite to the end surface 6a (the end surface on the thread side in the embodiment).
, 7 is a probe that is brought into contact with the end surface 6a and injects an ultrasonic pulse toward the end surface 6b by applying a pulse from the transmitting circuit 8, and the probe 7 receives the reflected wave from the end surface 6b. The reflected wave signal is output to the receiving circuit 9. The receiving circuit 9 includes a path detection circuit 1 that amplifies the reflected wave signal and measures the propagation time from incidence to reception of the reflected signal via the detection circuit 10.
Send to 2. Reference numeral 11 denotes a control circuit that outputs a clock signal and sends the cough clock signal to the transmitting circuit 8, the receiving circuit 9, and the detection circuit 10 to control the timing of transmitting and receiving signals. 1
Reference numeral 3 denotes a setting circuit in which a propagation time for a predetermined known axial force of the same type of bolt, which has been measured in advance by the path detection circuit 12, is set as a threshold value. Second
Figure (a) shows the procedure for setting the threshold value. First, the travel time t in a state where the bolt 6 is not yet tightened and the axial force is zero is determined by the path detection circuit 12, and the travel time t
0 is input to the setting circuit 13. Next, the propagation time t in a state where the bolt 6 is tightened and the axial force is known is determined. The propagation time t1 is also input to the setting circuit 13 in the same way as t0. The propagation time t is the state in which the entire length from the end face 6a to 6b of the bolt 6 when the axial force is zero is extended in the axial direction due to the action of the axial force X, and is due to the internal stress in that case. It changes in correlation with the propagation speed of the ultrasonic wave and the overall length of the bolt 6. The change in the total length of the bolt 6, that is, the elongation in the axial direction and the propagation speed of the ultrasonic wave within the bolt 6, change in correlation with the magnitude of the axial force, so the propagation time tl correlates with the magnitude of the bolt axial force. It can also be said that it changes. Now, for the specified tightening of the bolt 6, the target axial force is
Then, the propagation time T which should be the threshold value for the axial force X is expressed by the following equation.

T=to +kX Here ni=-shi2''-.

Input the axial force
is calculated, and the calculated value is manually input to the setting circuit 13 to complete the setting of the threshold value. Reference numeral 14 denotes a comparison circuit, which compares the threshold propagation time T set by the setting circuit 13 with the propagation time t measured by the travel distance detection circuit 12 of the actually tightened bolt with unknown axial force. The comparison signal is output. The comparison signal is sent to the drive device I5 for tightening the bolt 6, and when the comparison signal is t<T, tightening is continued, and when t≧T, the drive device 5 stops driving and tightening is performed. Terminate it.

When the process is finished, it is indicated by, for example, a lamp or a buzzer.

In Figure 2 (c), tightening is continued based on the above comparison signal.

This shows the flow of stopping.

The measured value of the propagation time compared by the comparison circuit 14 changes due to the change in the propagation speed of the ultrasonic wave due to the change in internal stress and the change in the overall length of the bolt 6 as described above. Since the change in the overall length of the bolt 6 is caused by the change in the axial force applied to the bolt 6, the comparison of propagation time can be said to be a method of directly detecting the axial force of the bolt and comparing the detected axial force. I can say that. This means that conventional tightening is no longer affected by the frictional force between the bolt seating surface and the fastened member, as is the case with torque comparisons. Therefore, when tightening multiple bolts of the same type, the The tightening force can be controlled so that the axial force of the bolt becomes the desired uniform axial force. In addition, the above propagation time may be the one when the entire length of the incident region 2 volt 6 is made to reciprocate once, but if the propagation time is made to make the entire length of the incident region 2 volt 6 back and forth multiple times within the range of attenuation where the level of the reflected wave signal can be measured, , the difference between the propagation time and the threshold value is accumulated according to the number of round trips, and when compared with the threshold value, the difference between the two becomes clearly visible. Therefore, measurement accuracy can be improved,
In particular, even when measuring short bolts, it becomes possible to measure them with high precision.

The ultrasonic waves propagating inside the bolt 6 are reflected from various places depending on the shape of the bolt 6, and reflected wave signals from these places are received, but in such a case, the desired reflected wave signal from the end face 6b and It is desirable to extract the gate signal separately from other unnecessary signals, and the gate signal for this purpose is sent from the control circuit 11 to the receiving circuit 9. It is preferable to output it to a detection circuit IO or the like as necessary. Furthermore, the configuration of the setting circuit 13 and the comparison circuit 14 may include a memory, a comparator, etc., or a microcomputer may be used to perform storage, calculation, setting, comparison, etc.

〔Effect of the invention〕

Since the present invention is configured as described above, tightening can be directly detected by measuring the propagation time of the ultrasonic wave incident on the bolt. Therefore, when tightening a plurality of bolts of the same type, it becomes possible to control the tightening force of the bolts so that their axial forces become a desired uniform axial force. By being able to control this, it is possible to prevent bolts from loosening due to under-tightening, or from being damaged due to over-tightening.
Conventional tightening is expensive as it eliminates the need to use high-strength and expensive bolts that are used to withstand excessive amounts.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing one embodiment of a bolt tightening device according to the present invention, Fig. 2(a) is a flow explanatory diagram for setting a propagation time threshold value, and Fig. 2(b) is a block diagram showing an embodiment of a bolt tightening device according to the present invention. It is a flow explanatory diagram of continuing and stopping tightening based on a comparison signal with a value. FIG. 3 is a block diagram showing an example of the configuration of a conventional bolt tightening device. 5... Tighten the drive device, 6... Bolts, 5a, 6b
... End face of bolt, 7... Probe, 8... Transmission circuit, 9... Receiving circuit, 10... Detection circuit, 12...
- Path detection circuit, 13...setting circuit, 14...comparison circuit.

Claims (1)

[Claims] 1. In a bolt tightening device that is controlled to stop driving the tightening drive device tightening the bolt when the correlation value of the axial force of the bolt during tightening reaches a certain value, A probe that injects an ultrasonic pulse from one end surface toward another end surface opposite the one end surface by applying a pulse by a transmitting circuit, and sends a reflected wave signal from the other end surface to a receiving circuit, and a probe that detects a wave signal from the receiving circuit. a path detection circuit that measures the propagation time of the reflected wave signal sent through the circuit; and a path detection circuit that measures the propagation time in advance for a predetermined known axial force of the bolt to determine a threshold value of the propagation time. The setting circuit to be set compares the set threshold with the propagation time for the bolt with unknown axial force measured by the path detection circuit, outputs a comparison signal, and tightens the bolt based on the comparison signal. A bolt tightening device comprising: a comparison circuit for stopping the drive of a drive device.