JPS5810194B2 - Boruto Shimetsuke Hohou - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a bolt tightening method using the torque-angle method in which the bolt is tightened by switching from high-speed rotation to low-speed rotation midway through the tightening process, and tightening with the final bolt axial force is not possible due to the force. The purpose is to improve accuracy.

Conventionally, the torque method and the nut rotation angle method are generally known for tightening bolts.

The former torque method is based on the premise that the bolt axial force is proportional to the torque value, that is, the torque value required to rotate the bolt, and is a method that detects this torque value every moment and then controls and manages the tightening using the bolt axial force. be.

However, the proportional relationship between bolt axial force and torque changes considerably due to factors other than the bolt, such as temperature and equipment characteristics, as well as variations in the coefficient of friction with the bolt being tightened due to rust on the bolt. It is difficult to obtain stable bolt axial force due to variations in bolt axial force.

An improved version of this torque method is the nut rotation angle method, which takes advantage of the fact that the elongation of a bolt is mechanically proportional to its rotation angle. This is a method of reducing variations in bolt axial force, which is proportional to bolt elongation, by rotating and tightening the bolt (nut) by a predetermined angle from the so-called seating point.

In this case, it is very difficult to confirm whether the nut has accurately contacted the seat surface of the member to be tightened, so
The moment when a certain amount of torque is reached is detected as the snug point, and rotation at a certain angle is controlled from that point on.

This is called the torque-angle method.

By the way, in the above-mentioned torque method and rotation angle method, in order to further shorten the tightening time, bolts are usually tightened using high-speed rotation by a motor.

However, even if a motor stop signal is issued when the bolt has completed tightening at high speed, there is a risk that the bolt will be tightened further due to the inertia of the motor shaft.

Furthermore, if a stop signal is output in anticipation of additional tightening due to inertial force, variations in the tightening torque and bolt axial force will occur due to changes in the frictional resistance of the seat surface, fluctuations in the motor rotation speed, etc.

In view of these problems, the present applicant has previously proposed a device to solve this problem.

That is, the device temporarily tightens the bolt at high speed until the bolt is seated, then switches to low speed rotation after the bolt is seated, and rotates the bolt up to a certain angle from the time the bolt is seated.

For example, if the principle of operation is shown in Fig. 1, the graph a in Fig. 1 is
shows the relationship between bolt torque T and time t, where point A in graph a is the seating point, and up to this point the rate of increase in torque T is slow;
After passing point A, torque T increases in a functional manner until point B.

The bolt axial force is desirable up to the vicinity of this point B, and if it exceeds point B, it will be over tightened and problems such as thread breakage will occur.

Therefore, ideally, if the bolt is rotated through a certain angle from point A to point B at low speed, the accuracy of the bolt axial force can be improved.

To do this, first detect the predetermined torque value T0 at point A, where the motor can rotate at high speed, take out a pulse as shown in the waveform in Figure 1 at this point, and use this as a trigger to reduce the motor to low speed rotation. (see waveform c) and start the angle detector.

That is, the rotation angle from point A is sequentially counted using a rotation angle detector such as a magnet steel or an optical encoder, for example, using the pulse counting method shown in waveform a in Figure 1. When a certain number of counts is reached, the rotation angle from the point A is Outputs a motor stop signal to stop rotation.

Then the bolt will be completed at point B.

However, as a practical matter, it is difficult to detect a high-speed snug point with high accuracy, and even if it is detected accurately, the angle from the snug point to point B is 30 degrees.
Therefore, there was a problem that the inertia of the motor rotor could cause the motor to exceed point B, making control difficult.

This invention further improves the torque-rotation angle method and provides a method that completely eliminates the trouble caused by the overrun.

The present invention will be described below with reference to the drawings.

In contrast to the conventional bolt rotation direction which was always constant, the key point of the present invention is to temporarily add reverse rotation to the bolt rotation direction. Do it between.

That is, first, the bolt is temporarily tightened at high speed until it is seated, then the rotation is stopped, and then the bolt is rotated slightly in the opposite direction to loosen the torque, and then the bolt is rotated at low speed in the forward direction to detect the snagging point. This is a method of rotating a fixed angle from a starting point.

Hereinafter, the present invention will be explained with reference to the drawings.

Figure 2 graph e shows bolt tightening torque T and time t.
This shows the relationship between section m during high-speed rotation, section n during low-speed rotation, and section p during reverse rotation, and A1 of graph e.
The point is when the seat is seated, and point A2 is the snagging point, which is the first point.
This corresponds to point A in the figure.

The operation of the present invention based on this graph e is as follows.

That is, in the high-speed rotation section m, the torque T increases with a curve similar to the conventional one, and reaches a seating point A1 at a predetermined torque T0.

Then, the signal for detecting this predetermined torque T0 becomes, for example, a second signal.
A pulse output with a waveform f-1 in the figure is generated, which first stops the high-speed rotation of the motor.

However, at this time, the high-speed rotation does not stop instantaneously (see waveform g-1 in FIG. 2), so the torque T overruns by a small amount from point A1.

Then rotate the motor slightly in the opposite direction.

For example, as shown in waveform g-2 in FIG. 2, the rotation is slightly reversed at low speed.

Then the overrun bolt loosens and its torque T
is weaker than the torque T0 when the driver is seated.

This reverse rotation is performed until the torque T becomes slightly weaker than the predetermined torque T0, and then stopped, and at the same time, the bolt is rotated again in the forward direction (tightening direction) at a low speed (see waveform g-3 in Figure 2). ).

Then, the torque T starts to increase again and reaches the snug point A2, which is the snug torque T1.

This point A2 is detected using a signal such as a pulse of waveform f-2 in FIG. 2, and this signal is input to the rotation angle detector as a trigger.

At this time, since the bolt rotates at a low speed, there is no worry of torque T overrun, and the rotation angle is accurately counted from point A2 (see waveforms in Figure 2).

Then, when the rotation is made by a certain angle from point A2, it is sufficient to instantaneously stop the low-speed rotation, and instantaneous stopping is possible at low speed.

In addition, the time during reverse rotation can be set in advance using a timer, or the amount of overrun can be detected with an angle detector, and the molecule α
Alternatively, the reverse rotation may be stopped by detecting the point in time when the torque T becomes slightly lower than the predetermined torque T0 using a torque detector.

As explained above, this invention stops the rotation of the bolt using a detection signal when the bolt is seated from high-speed rotation,
After that, I rotated the bolt a little in the opposite direction, then returned the bolt to low-speed forward rotation to detect the snug point, and from this second detection signal, the bolt was further rotated by a certain angle.
Counting constant rotation angles using the rotation angle method can eliminate uncertain and unstable factors such as starting from the snug point when the bolt rotates at low speed and detecting the snug torque at high speed rotation.As a result, the torque-angle method The tightening becomes reliable, and the accuracy of the tightening can be improved.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the relationship between each output characteristic with respect to time in bolt tightening using the conventional torque-rotation angle method, and Fig. 2 shows each output with respect to time showing an example of the bolt tightening method according to the present invention. FIG. 3 is an explanatory diagram of the relationship between characteristics.

Claims (1)

[Claims] 1. Tightening using the torque-rotation angle method, in which the bolt is temporarily tightened by high-speed rotation until it is seated, then switched to low-speed rotation and tightened by a certain rotation angle, is a method that detects the bolt from the high-speed rotation when the bolt is seated. The bolt stops rotating in response to a signal, then rotates a little in the opposite direction, then returns to low-speed forward rotation to detect the snug point, and from this second detection signal, the bolt is further rotated by a certain angle. A bolt tightening method using the torque-angle method.