JPH0573551B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a screw fastening method that can control the tightening force of a bolt with high precision.

(Prior art) Conventionally, when tightening a bolt, in order to control the tightening force (axial force) to a constant value, the tightening torque and rotation angle of tightening are generally detected, and these torques and rotation angles are set to preset values. However, in the former case, it is strongly affected by the roughness of the seat surface and frictional resistance, and in the latter case, it is difficult to decide where to set the initial setting. It was difficult to control the axial force at a constant level.

Recently, attempts have been made to control the axial force by directly measuring the elongation of the bolt. For example, in Japanese Patent Application Laid-open No. 130100/1987, an ultrasonic sensor is used to detect the elongation of the bolt while tightening the bolt. A screw fastening method is described in which tightening is terminated when the detected value matches a preset target value.

However, according to the method described in the above-mentioned publication, the S/N ratio of the ultrasonic signal of the ultrasonic sensor is disturbed by disturbances such as the surface roughness of the object to be fastened or the presence of burrs or foreign objects, and the S/N ratio of the ultrasonic signal of the ultrasonic sensor is disturbed. It becomes difficult to detect elongation, and in some cases elongation (axial force) occurs midway through.
There was a risk that the tightening work would be stopped mid-way due to the large amount of damage. Furthermore, since no special measures were taken against abnormal elongation due to uneven contact or eccentric tightening of the threaded portion, there was a risk that this abnormal elongation would be detected and tightening would be terminated, thereby overlooking poor tightening.

(Objective of the Invention) The object of the present invention is to eliminate the disturbance factors of the S/N ratio of the ultrasonic signal, accurately grasp the abnormal elongation, and accurately detect the true elongation of the bolt. The object of the present invention is to provide a screw fastening method that can keep the force constant.

(Structure and operation of the invention) The purpose is to tighten the bolt while detecting the tightening torque with a torque sensor until the torque value reaches a value near the yield point of the bolt, and then use an ultrasonic sensor to tighten the bolt. Tighten until the elongation reaches a predetermined value within the permanent deformation region of the bolt while detecting the rotation angle, and at this time, while detecting the rotation angle of the bolt with a rotation angle sensor, the correlation between the rotation angle and the bolt elongation is This is achieved by a screw fastening method that monitors and determines that there is an abnormality when the rotation angle of the bolt is out of a predetermined range.

According to the present invention configured in this manner, since the tightening torque method is first used to tighten to near the yield point, the ultrasonic wave of the ultrasonic sensor is The S/N ratio of the signal is no longer disturbed, and the correlation between the bolt rotation angle and bolt elongation is monitored, and if the bolt rotation angle is outside a predetermined range, it is determined to be abnormal. Therefore, abnormal elongation due to uneven contact or eccentric tightening of the threaded portion can be accurately grasped.

(Example) Hereinafter, an example of the present invention will be described based on the accompanying drawings.

FIG. 1 shows an example of an apparatus for carrying out the screw fastening method according to the present invention. In the same figure, 1
2 is a first bolt fastener that operates by tightening torque control, and 2 is a second bolt fastener that operates by bolt extension and rotation angle control, and both are installed adjacent to each other on the fastened object conveyance line 3. be done. A pallet 4 is placed on the conveyance line 3 for objects to be fastened, and a first object 5 and a second object 6 are separately set on top of the pallet 4, from left to right in the figure. It is transported in the direction shown by arrow A. A bolt 7 is temporarily fastened to the first and second fastened objects 5 and 6 in advance, and the bolt 7 is first attached to the first bolt fastener 1.
The bolts are tightened by a predetermined amount, which will be described later, and then moved in the direction of arrow A and finally tightened by the second bolt fastener 2, which will be described later.

Thus, the first bolt fastener 1 is provided with an air motor 9 and a speed reduction mechanism 10 on a support plate 8, and an output shaft 11 of these is extended downward from the support plate 8 to a tip of the output shaft 11. It has a socket 12 attached thereto, and can be raised and lowered arbitrarily as indicated by arrow B in the figure by a lifting means (not shown). The air motor 9 is operated by air supplied from an air source (not shown) through an air pipe 13.
A torque sensor 15 is also installed on the output shaft 11, and these are connected to a separately provided tightening control device 16 by cables 17, 17. As a result, the first bolt fastener 1 is driven and controlled by the tightening control device 16 while monitoring the torque value, and tightens the bolt 7 by a predetermined amount.

On the other hand, the second bolt fastener 2 is equipped with a direct current (DC) motor 18 as a drive source, and a socket 19 with an ultrasonic sensor for detecting the elongation of the bolt and a rotation angle sensor 20.
DC motor 18, socket with ultrasonic sensor 19,
The rotation angle sensor 20 is connected to the tightening control device 16 by cables 21, 21, 21, respectively.
As a result, the second bolt fastener 2 is driven and controlled by the tightening control device 16 while monitoring the elongation and rotation angle of the bolt, and performs the final tightening of the bolt 7 at a low speed. In addition,
Components that are the same as those of the first bolt fastener are given the same reference numerals, and their explanations are omitted.

Here, the socket 19 with the ultrasonic sensor is connected to the second
It has an assembly structure as shown in the figure. In FIG. 2, 30 is a socket body, and an ultrasonic sensor 31 is installed in the lower inner diameter portion of the socket body. The ultrasonic sensor 31 includes a movable ring 33 that also serves as a damper, which is biased downward by a coil spring 34, inside a case 32, and a vibrator 35 and its protection plate 36 attached to the lower end of the movable ring 33. ,
A lead wire 39 is connected to a positive electrode plate 37 and a negative electrode 37' on the vibrator 35 from a connector 38.

As a result, when the second bolt fastener 2 (FIG. 1) is lowered and the socket 19 is engaged with the head of the bolt 7, the vibrator 3 of the ultrasonic sensor 31
5 comes into contact with the head of the bolt 7 via the protective plate 36 (the state shown in FIG. 2), and under this state, an ultrasonic wave is generated to detect the elongation of the bolt 7 when it is tightened. At this time, since the movable ring 33 and therefore the vibrator 35 are supported in a floating state, fluctuations in the S/N ratio of the ultrasonic signal are caused by disturbances caused by vibrations acting between the socket 19 and the bolt 7 during tightening. This can be prevented, and the ultrasonic sensor 31 can be maintained with high accuracy.

Hereinafter, a screw fastening method using the device configured as described above will be explained.

FIG. 3 shows a control diagram for executing the present screw fastening method. The figure shows the correlation between the bolt tightening time t and the torque value T in diagram A, and since it is within the elastic region, it shows how the torque value T increases linearly with the tightening time t. Diagram B shows the correlation between the rotation angle θ and the elongation ε of the bolt, and shows how the elongation ε slightly lurks around the yield point and then increases linearly in the plastic region.

Therefore, in this method, the bolt is first tightened along line diagram A to point P1 near the yield point of the bolt, and then,
Final tightening should be carried out along line B up to point P2 within the plastic region of the bolt.

Specifically, first, the first bolt fastener 1 is activated and the bolt 7 is started to be tightened to the first and second fastened objects 5 and 6 while the torque sensor 15 detects the torque value T. do. Then, the torque value T is
Stop tightening when Tx corresponding to point P1 is reached,
Release the first bolt fastener 1. Next, the pallet 4 is moved under the second bolt fastener 2, and the second bolt fastener 2 is operated to detect the elongation of the bolt 7 with the ultrasonic sensor 31 (Fig. 2). After that, tightening is performed, and when the elongation ε reaches εx corresponding to the P2 point, the tightening is stopped and the second fastener 2 is released.

At this time, the rotation angle sensor 20 detects the bolt 7.
The rotation angle θ is also detected, and the rotation angle θ ₁ until the bolt begins to elongate permanently and the angle θx until the elongation ε reaches εx are compared with the upper and lower limit settings for each rotation angle to determine if any abnormalities are detected. It is becoming detected. In addition, as for the elongation ε of the bolt, just before starting the tightening operation by the second bolt fastener 2, an ultrasonic signal (pulse) is emitted to reduce the elongation ε of the bolt to relative zero in a very short time. Assuming ε ₀ , the elongation ε after that is measured.

Therefore, each of the above-mentioned controls is collectively performed by the tightening control device 16, and this tightening control device 16 has a basic structure as shown in FIG. 4.

That is, the tightening control device 16
The measurement control section 40A includes a torque amplifier circuit 41 which is a signal receiving section from the torque sensor 15, and a sequence control section 40B.
The A-D conversion circuit 42, the ultrasonic receiving circuit 43 which is a signal receiving section from the ultrasonic sensor 31, the pulse counting circuit 44 proportional to the bolt length, the pulse oscillation circuit 45, and the rotation angle sensor 20. In addition to the angle pulse calculation circuit 46 which is the signal receiving section of , and a signal output circuit 51 that outputs NG signals.

In the above embodiment, the first and second bolt fasteners 1 and 2 were installed together and each was operated by a separate control system, but the cable processing of the ultrasonic sensor socket 19 was eliminated and this If the socket 19 can be rotated multiple times by making it wireless or by using a rotary joint, it is possible to provide both control functions to one fastener.

(Effects of the Invention) As explained above in detail, according to the screw fastening method according to the present invention, the S/N of the ultrasonic signal is first tightened to near the yield point using the tightening torque method.
In addition to eliminating factors that disturb the ratio, during subsequent tightening, the correlation between the rotation angle of the bolt and the bolt elongation is monitored to accurately identify abnormal elongation due to uneven thread contact or eccentric tightening. The true elongation can be accurately detected and the axial force can be kept constant, which has great utility value.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an example of a device for carrying out the screw fastening method according to the present invention, Fig. 2 is a sectional view showing the structure of a similar socket with an ultrasonic sensor, and Fig. 3 is a screw fastening method according to the present invention. Control diagram FIG. 4 is a block diagram showing the structure of the tightening control device. 1, 2... Bolt fastener, 15... Torque sensor, 20... Rotation angle sensor, 31... Ultrasonic sensor.

Claims (1)

[Claims] 1. Tighten the bolt while detecting the tightening torque with a torque sensor until the torque value reaches a value near the yield point of the bolt, and then detect the elongation of the bolt with an ultrasonic sensor. Tighten the bolt until it reaches a predetermined value within the permanent deformation region of the bolt. At this time, the rotation angle sensor detects the rotation angle of the bolt and monitors the correlation between the rotation angle and the elongation of the bolt. A screw fastening method characterized in that an abnormality is determined when the angle deviates from a predetermined range. 2. The length of the bolt at the time when the bolt is tightened until the torque value reaches a value near the yield point of the bolt is set as a reference value, and the elongation of the bolt from this reference value is detected. screw fastening method. 3 Use the rotation angle sensor to determine the rotation angle until the bolt begins to permanently elongate and the rotation angle until the bolt rotation angle reaches a predetermined value, and compare these rotation angles with the upper and lower limit values to determine if there is an abnormality. A screw fastening method according to claim 1, characterized in that: