JPS5815267B2 - Bolt tightening method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention is a method of properly tightening bolts that tighten members, etc., in a state where axial force (stress x bolt cross-sectional area) is accurately generated. The appendix relates to the method and apparatus thereof.

In machines, equipment, etc., it is important for the strength of the structure that the bolts be properly tightened so that axial force is generated inside them. The rotation angle of tightening and tightening are related to axial force, such as torque, and the tightening point at which the appropriate axial force is generated is determined using characteristic values that are relatively easy to measure, and the bolt is removed at that point. Various methods have been tried to tighten bolts by indirect determination of the axial force, but due to the complexity of the correlation and the high accuracy of characteristic value measurement, tightening is performed at the end of the work. The axial force generated within the bolt in the bolt is highly variable, and the drawback is that it is generally unreliable.

This invention attempts to eliminate the above-mentioned drawbacks of the conventional technology, and uses an ultrasonic axial force meter that can continuously detect the axial force of bolts using ultrasonic waves to control the tightening mechanism. The method and device for highly accurate bolt tightening are such that the point at which a preset appropriate axial force is generated in the bolt is determined by the detected value of the axial force and the tightening work is completed. The purpose is to provide

An embodiment of the present invention will be described below.

In Fig. 1, a nut runner 1 has a DC servo motor 2 at the upper part of the main body, a socket part 3 is rotatably protruded at an eccentric position at the lower part, and a speed reduction mechanism connecting the two is built into the main body. .

A hexagonal hole 4 is opened at the axial center position of the lower end of the socket portion 3, and is fitted into the head of a bolt 6 for tightening members 5, 5' in a machine or the like.

An ultrasonic sensor 7 is installed in the inner cavity of the socket portion 3 following the hexagonal hole 4.
is inserted so that it can slide only up and down, and its top surface is
Pressed by the coil spring 3 housed in the EA
The tip is placed in close contact with the head of bolt 6.

A coaxial cable 9 connected to the ultrasonic sensor γ passes through the axis of the socket part 3 and is connected to a rotatable side terminal in a signal transmitter 10 disposed coaxially with the socket part 3 in a part of the nut runner 1. has been done.

The simplest signal transmitter 10 is a slip ring type, and the fixed side terminal C is connected to the signal transmitter 10.

The simplest signal transmitter 10 is a slip ring type, and a coaxial cable 11 connected to its fixed side terminal exits outside the device and is connected to an axial force meter 12.

This axial force meter 12 is based on the principle that when an ultrasonic wave is transmitted through a metal, its propagation speed decreases with the stress applied to the metal, and t- is a direct correspondence between the two. In principle, instead of directly measuring the propagation velocity considering accuracy and stability in practical use, the ultrasonic propagation distance is proportional to the propagation velocity and inside the object to be measured - in this case, the length inside the bolt. By measuring the natural vibration of the object to be measured, which is inversely proportional to the distance of one reciprocation in the direction, the axial force within the object to be measured is detected.

Furthermore, this tightening apparatus includes a servo controller 14 which is connected to an axial force gauge 12 through a signal wiring 13, and this servo controller 14 is connected to the DC servo motor 2 of the nut runner 1 through a signal wiring 15.

Here, the servo controller 14 memorizes a preset target value of axial force for proper tightening of the bolt 6, and compares this value with the actual axial force value continuously detected by the axial force meter 12 to determine the proper tightening of the bolt 6. This is to judge the progress of the bolt 6 tightening work of No. 1 and control the rotation and stop of the servo motor 20.

Next, the bolt tightening method of the present invention, which is carried out using the above-mentioned apparatus, will be specifically explained.

In addition, FIG. 2 is a dimensional explanatory diagram showing an example of the state of change in the axial force during the tightening process.

The bolt 6 is inserted through the members 5, 5' to be fastened, and the nut 16 is held by the bolt 6 so as not to rotate.

Here, an ultrasonic wave is oscillated from the ultrasonic sensor 7, and this ultrasonic wave is propagated into the bolt 6 from the contact surface between the sensor 7 and the head of the bolt 6.

The axial force meter 12 continuously changes the oscillation frequency by its own oscillation circuit, and at the oscillation frequency at which the length of the bolt 6 and the wavelength of the ultrasonic wave in the bolt 6 resonate, the axial force meter 12 changes the oscillation frequency before the bolt 6 is tightened, that is, when there is no load. natural frequency f in the state
.

Catfish detection~, remember this. Next is Natsutranna 1
rotates its socket part 3 at a relatively high speed, and the nut 16 is seated on the member 5 (point A → point B in Figure 2), and the bolt 6
Axial force begins to occur inside.

From here, the rotational speed of the socket portion 3 is reduced to, for example, about 5 rpm, the bolt 6 is carefully tightened by the nut runner 1, and the axial force is gradually increased.

During this time, ultrasonic waves are constantly emitted from the sensor 7 into the bolt 6, and the axial force meter 12 measures the changing natural frequency fN of the bolt 6 while the axial force is increasing. Frequency f.

and the harmonic order n and the rate of change of the natural frequency fN-f.

2.fo is determined, and the axial force that correlates to the rate of change is continuously calculated and detected using a conversion factor determined in advance for the same type of bolt.

Note that carrier waves are transmitted between the fixed axial force meter 11 and the sensor 7 that rotates together with the socket portion 3 via coaxial cables 9 and 11 and a signal transmitter 10 that connects them with a slip ring mechanism. It will be done.

The detected value of the axial force is converted into an electrical variation amount by a converter in the axial force meter 12 and sent to the servo controller 14 via the signal wiring 13.

The servo controller 14 compares the pre-stored target value of the appropriate axial force for the bolt 6 with the detected value of the sent axial force, and determines the progress state of the bolt tightening work based on the difference. Then, the servo motor 2 is continued to rotate depending on the degree of rotation.

The oscillation and propagation of ultrasonic waves and the transmission of signals between each device continue with the tightening of the bolt 6 by the socket portion 3 as the work continues.

In this example, in order to improve the final precision of the action,
When the detected value of the axial force reaches, for example, about 90% of the appropriate axial force target value, the servo motor 2 is automatically decelerated by a command from the servo controller 14, and the rotational speed of the socket part 30 is set to about 2 rpm (second Figure point C).

While the bolt 6 is finally tightened by the nut runner 1 under such slow rotation, the axial force gauge 12
When the detected value of axial force matches the target value of appropriate axial force,
Since the servo controller 14 immediately stops the servo motor 2, the tightening work of the bolt 6 by the nut runner 1 is automatically completed.

(Second test point) Inside the hook bolt 6, an axial force is generated and maintained with high precision for proper tightening set as a target.

The tightening device is removed from the bolt 6 and the next bolt is used in the operation with the same sequence as described above.

As described above, since the present invention is a bolt tightening method and its apparatus having the features described in the claims, the bolt tightening according to the present invention is carried out in accordance with the proper setting in advance during work. It is now possible to automatically complete the tightening work while generating axial force inside the bolt with much higher precision than with conventional methods and devices.
The tightening state of the member by the bolt tightened in this manner is rational, and the tightening is extremely reliable in terms of strength.

Thus, the method and apparatus of the present invention are particularly applicable to various assembly processes using bolt tightening, and the bolt tightening process improves the accuracy of the work, and has the advantage of automation and labor saving.

Note that there are some axial force meters that use ultrasonic waves that detect axial force using a method that is slightly different from that of the above embodiment, but they can be used in the present invention.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 shows a cross-sectional side view of the main parts and a block diagram. Tightening is an explanatory diagram of the device, and FIG. 2 shows the axial force change during the tightening process. It is an explanatory diagram showing correlation with time. 1... Nut runner, 2... Servo motor, 3...
・Socket part, 6... Bolt, 7... Ultrasonic sensor, 8... Coil spring, 10... Signal transmitter, 12.
...Ultrasonic axial force meter, 14...Servo controller.

Claims (1)

[Claims] 1. Ultrasonic waves are propagated into the inside of the bolt from one end in the axial direction of the bolt, and the bolt is tightened, and the tightening is performed by transmitting information about the natural frequency of the bolt, which changes as the action progresses, to the ultrasonic axis. The force is transmitted to a force meter to continuously detect the axial force generated in the bolt, and when the detected value of the axial force matches the target value of the appropriate axial force preset for the Pol IC, the force is applied to the bolt. A bolt tightening method characterized in that tightening ends the work. 2. A nut runner, which has a built-in socket part that can be partially fitted into a bolt head or a nut and is rotatable by a servo motor, and which is an ultrasonic sensor that is brought into close contact with one end of the bolt by the pressing force of an elastic member; A signal transmitter that is disposed in a part of the nut runner and transmits signals between the rotating part and the fixed part; An ultrasonic axial force meter that continuously detects the axial force generated in the bolt by receiving a carrier wave of information about the natural frequency, and the detected value of the axial force given by the axial force meter and the appropriate axial force memorized in advance. A bolt tightening device comprising: a servo controller that controls the servo motor by comparing and determining a target value.