JP2000117652A - Method of detecting failure in fastening of screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an accident by judging the loosening of a bolt caused by the crackings or the like of the bolt or a work in the case where a torque value is lowered to a predetermined detection level or lower. SOLUTION: Whether a held torque value (Tof) is more than a predetermined torque value (Tz) or not is judged, and it is judged that the fastening is normally executed when the value is more, and a normal state judgement output is sent. When the value is less as the result of the judgement, it is judged that the fracture caused by the generation of cracking or the like on a bolt 2 and a work 5, or the loosening immediately after the fastening, is generated, and the abnormal state judgement output is sent. When the bolt is fastened to a form and keeps its axial force, the reaction force by the residual fastening force is detected by a torque sensor 15 while rotating the bolt, and a low value close to a target value is indicated, so that whether the state is normal or not is judged on the basis of the value. In a case of the cracking on the bolt 2 and the work 5, the bolt 5 is only rotated by the reaction torque, and the torque sensor 15 does not detect its reaction force, so that the generation of cracking is judged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic bolt tightening device for a nut runner or the like, in which when a bolt is tightened to a work (substrate), the bolt or the work is cracked and normal tightening cannot be performed. The present invention relates to an inexpensive screw tightening failure detection method for detecting the problem.

[0002]

2. Description of the Related Art Conventionally, when a bolt is fastened to a work by using an automatic bolt tightening device such as a nut runner, the rotation speed of the nut runner is controlled based on a preset curve, and the tightening time is reduced. Is constantly monitored, and the tightening is terminated when the torque reaches a preset target value.

[0003] If the bolt or the work breaks due to any cause during the tightening, the monitored torque value drops sharply, and the bolt or the work breaks. Can be detected.

[0004]

If the bolt or the work breaks during the screw tightening, it can be immediately known from the fact that the tightening torque is constantly detected as described above. The occurrence of a serious accident can be prevented by means such as emission.

However, if the torque value has reached the target value and the torque value has reached the target value, it is determined that the torque value is normal. However, there was a problem in that a warning could not be issued even when the vehicle was in use, which could cause a serious accident.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide a particularly expensive method for preventing damage due to a crack in a bolt or a work immediately after tightening the bolt, which has been difficult to find in the past. It is an object of the present invention to provide a method of detecting a screw tightening failure that can reliably detect without adding a device and prevent an accident due to breakage of a bolt or a work.

[0007]

The object of the present invention is to provide a method of detecting a screw tightening failure, which comprises a nut runner or the like when a bolt reaches a target torque value when tightening a bolt. A command of zero speed is given to the motor of the tightening tool, and when the torque value after a certain period of time after the command is lower than a preset torque detection level, the bolt or the work becomes loose due to cracks or the like. Is determined to have occurred.

[0008] Further, a first torque detection level close to a target value and a second torque detection level close to zero torque are provided, and the torque values detected after a predetermined time from the command are the first and second torque detection levels. The second detection level is determined to be a simple loosening of the bolt, and the lower level is determined to be lower than the first detection level to determine that a crack has occurred in the bolt or the work.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of an apparatus for carrying out a screw tightening failure detecting method according to the present invention will be described with reference to FIG. Reference numeral 1 denotes a nut runner, which is a servo drive motor 11 driven by an output from a servo amplifier described later.
And a reduction gear 12 with a bendable rotation from the motor 11.
An output shank 13 connected to the output shaft of the reduction gear 12, a socket 14 for rotating the bolt 2 by the rotational force of the output shank 13, and a reaction torque sensor 15 for detecting the rotational torque of the output shank 13. It is composed of Note that a servo amplifier may be housed in the housing part of the motor 11.

FIG. 2 shows a control circuit 3 for controlling the nut runner 1 described above. Reference numeral 31 denotes a CPU which is a central processing unit; 32, a servo amplifier for driving the motor 11 of the nut runner 1; The servo amplifier 3
2 outputs an output for driving the motor 11 at a rotation speed of a predetermined curve, and outputs the torque sensor 15
Is a ROM which sends out an output of zero speed when a predetermined target value is detected.

Next, the operation will be described with reference to the characteristic diagram of FIG. 3 and the flowchart of FIG. FIG.
As shown in FIG.
When the nut runner 1 is attached to the nut runner 1, the head 21 of the bolt 2 is fitted into the socket 14 of the nut runner 1, and an output according to the curve shown in the characteristic diagram of FIG. The motor 11 via the servo amplifier 32
Is rotated to start the tightening by rotating the bolt 2 (step S1). In addition, 6 is a washer.

Simultaneously with the tightening by the motor 11, the torque sensor 15 samples a torque, which is a reaction force accompanying the tightening, at regular time intervals, and monitors whether the torque substantially matches a preset torque curve. If the torque value at each time point is abnormally large with respect to the torque curve, the fastening is determined to be a fastening abnormality such as burn-in and the fastening is stopped.

If the abnormality does not occur, it is determined whether the torque value due to the tightening has reached between a preset upper limit value and a lower limit value, that is, whether the torque value has reached a target value. It is monitored whether or not it is (step S2).

If the CPU 31 determines that the torque value has reached the target value, the CPU 31 issues a command of zero speed to the servo amplifier 32 (a function of keeping only the torque at a constant value and not issuing a rotation command; (Stall function) to bring the motor 11 into the braking state. Conventionally, when it is determined that the target value has been reached, the servo amplifier 32 is turned off to terminate the tightening operation.

When the servo amplifier 32 sends out the output of zero speed, the nut can be continuously tightened by the reaction force of the residual torsional stress of the power transmission system in the nut runner 1, that is, the nut has a function of residual torsion. The runner 1 maintains a low tightening force close to the target value.

In this state, it is determined whether or not a preset time T ₁ has been reached (step S4), and the time T _{1 is determined.}
Holds the torque value at the time when it reaches (Step S5)
At the same time, the output of the servo amplifier 32 is turned off (step S6).

Then, the held torque value Tof
It is determined whether or not the torque value is greater than a preset torque value Tz (step S7). If it is determined that the torque value is greater than the preset torque value Tz, a normality determination output is sent (step S8).

On the other hand, when it is determined that the bolt 2 or the work 5 is small in the above-mentioned determination, it is determined that the bolt 2 or the work 5 is broken due to a crack or the like or loosened immediately after tightening (step S9), and an abnormal condition is determined. The judgment output is transmitted (step S10).

That is, if the bolt 2 is tightened in a shape and maintains its axial force, the torque sensor 15 detects the reaction force due to the residual tightening force while rotating the bolt, so that a low value close to the target value is obtained. (Value greater than torque value Tz)
Thus, whether the value is normal or not can be determined based on the magnitude of this value.

When a crack occurs in the bolt 2 or the work 5 (a crack occurs in the bolt 2 at a portion 23 between the head 21 and the screw 22 of the bolt 2 shown in FIG. 5), Since the torque sensor 15 does not detect the reaction force only by rotating the bolt 2 with the reaction force torque, it can be determined that a crack has occurred.

Further, even if cracks do not occur and the bolts are loosened immediately after tightening, the bolts 2 are not affected by the reaction torque.
Is rotated, the residual torque reaction force decreases and falls below the torque value Tz. In this case, too, it is determined that abnormal tightening has occurred.

In the above-described embodiment, the method of changing the rotation speed as a method of tightening the bolts has been described. However, it is needless to say that the present invention can be applied to a fixed angle rotation method or a yield point detection method. is there. That is, when the tightening torque reaches the target value, by monitoring the torque value after a certain time in the state of zero speed, it is possible to determine whether or not abnormal tightening is performed as in the above-described embodiment. it can.

Further, in the above-described embodiment, although only one of the torque detection levels Tz is used as a criterion for judging whether or not the tightening is abnormal, the torque detection level is set to the first value close to the target value. A torque detection level Tz and a first torque detection level Tz 'close to zero torque are provided. If the detection level detected after a certain period of time from the speed zero is between the first and the second, the bolt is simply loosened. Judge that there is,
Further, when the voltage is equal to or lower than the second detection level, it may be determined that a crack has occurred in the bolt 2 or the work 5.

3

As described above, according to the present invention, when the tightening torque reaches the target value, the torque value after a certain period of time in the state of zero speed is monitored, and the torque value is set to the preset torque detection level. If it is smaller than this, an abnormality determination output indicating that the screw has become loose is sent, so that an accident due to the loose bolt can be prevented from occurring.

Further, the torque detection level is set between a first torque detection level close to the target torque and a second torque detection level close to zero torque.
When the detected torque value is between the first and second torque detection levels, it is determined that the bolt is loose, and when the detected torque value is smaller than the second torque detection level, Since it is determined that a crack has occurred in a bolt or a work, it is possible to determine whether the same bolt is loose due to a crack or an improper tightening method.

[Brief description of the drawings]

FIG. 1 is a front view of a nut runner used in a screw tightening failure detection method according to the present invention.

FIG. 2 is a circuit block diagram for controlling the above.

FIG. 3 is a characteristic diagram of screw tightening.

FIG. 4 is a flowchart illustrating an operation.

FIG. 5 is a cross-sectional view showing a state where bolts are fastened to a work.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nut runner 11 Motor 15 Torque sensor 2 Bolt 3 Control circuit 31 CPU 32 Servo amplifier 33 ROM 4 Workpiece 5 Workpiece

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[Procedure amendment]

[Submission date] December 11, 1998 (1998.12.
11)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Fig. 4

[Correction method] Change

[Correction contents]

FIG. 4

Claims (2)

[Claims] When a bolt reaches a target torque value when tightening a bolt, a command of zero speed (stall function) is given to a motor of a tightening tool such as a nut runner, and a torque value after a predetermined time from the command is given. However, when the torque detection level is lower than a preset torque detection level, it is determined that the bolt is loosened due to a crack or the like in the bolt or the work. A first torque detection level close to a target value and a second torque detection level close to zero torque, wherein the torque values detected after a predetermined time from the command are first and second torque detection levels. The second detection level is determined to be a simple loosening of the bolt, and the lower level is determined to be lower than the first detection level to determine that a crack has occurred in the bolt or the work. Item 7. The screw tightening detection method according to Item 1.