JPH0343160A - Constant speed fastening method for bolt-unit - Google Patents

Abstract

PURPOSE:To remarkably reduce the dispersion of an axial tension and to perform a screw fastening work of good accuracy by fastening with the maintenance of the rotation speed of a nut runner at a constant speed irrespective of the fluctuation in a fastening load. CONSTITUTION:A set rotation number set on a speed setter 1 is fed out to a nut runner driving motor 5 via a comparator 2, speed deviation amplifier 3 and servoamplifier 4. A pulse signal corresponding to the actual rotation number of the nut runner is then transmitted from a pulse generator 6 and fed out to the comparator 2 via a feedback circuit 7. The pulse signal is compared with the set rotation number of the speed setter 1 by the comparator 2 and based on the comparison arithmetic result the converting signal of the voltage or current for correcting the rotation number is fed out to the control circuit 5A of the motor 5. By maintaining the rotation number of the nut runner at a constant speed irrespective of the fluctuation in the fastening load, the effect of the dispersion of a friction coefficient on a screw face and seating face is eliminated and the fluctuation range of the axial tension can be reduced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a constant-speed tightening method for bolts and nuts, and more specifically, to a method for controlling axial force fluctuations during bolt and nut tightening work using a nut runner. It concerns preventive measures.

[Conventional technology]

BACKGROUND OF THE INVENTION Automatic tightening of bolts and nuts using a Su7 runner is carried out in the automobile engine assembly process. As a means for bolting engine components, such as a cylinder head and a cylinder block, with a predetermined tightening torque,
A method (torque method) in which the final tightening torque is set in advance on the nut runner, the actual torque during bolt tightening is detected, and the bolt tightening operation by the nut runner is terminated when the final tightening torque and the actual torque match. As shown in Figure 4, the nut runner is set in advance with a snug torque of approximately H of the final tightening torque, and after passing the snug point, the nut runner is rotated by a certain angle and then stopped (torque - angle). law is used.

[Problem to be solved by the invention]

The above torque method attempts to provide a predetermined tightening strength to the bolts and nuts by grasping the tightening force of the bolts and nuts using the tightening torque of a nut runner and controlling this. However, the tightening strength of bolts and nuts is actually the axial force transmitted to the bolts and nuts (hereinafter referred to as axial force).
The tightening torque and the axial force are often not the same value because this axial force changes depending on the friction coefficient of the threaded surface and the seating surface. As shown in the figure, even if the tightening torque is controlled to be constant, the axial force may vary by as much as 100%. To explain it more quantitatively, the tightening torque (
The relationship T-KDF□■ [where (D) is the diameter of the bolt and (K) is the torque coefficient] is established between T) and the axial force (F). Here, the torque coefficient (
The coefficient of friction (μ)°, which is the main element of K), not only varies greatly depending on the characteristics of the bolt seating surface and threaded surface, but is also affected by the rotational speed when tightening the bolt/naft.

That is, as shown in Fig. 6, the friction coefficient is large in the static friction region where the rotation speed of the nut runner is low (usually 3 PPM or less), and the friction coefficient is small in the dynamic friction region where the rotation speed of the nut runner is high.From this viewpoint, the axial force (F ), it is preferable to tighten bolts and nuts with a naph runner at a constant speed in the dynamic friction region where the friction coefficient (μ) has little effect.・The nut tightening method simply sets the final tightening torque (T) while ignoring the relationship between the above-mentioned axial force (F) and friction coefficient (μ), so the bolt may not be tightened past the snug point. At the end of the process, the rotational speed decreased gradually and reached the final tightening torque. To explain in detail,
In the conventional system, the drive motor of the nut runner is driven with a constant voltage and the speed is not particularly controlled, so as the actual tightening torque increases, the number of rotations of the nut runner gradually decreases.

This is the series-wound characteristic of a DC motor, and all motors whose speed is not controlled by a series-wound motor or a commutator motor exhibit this kind of characteristic.Natsurunners, which do not control the rotational speed in this way, do not change the rotational speed. This change in rotational speed affects the coefficient of friction and causes variations in the axial force. As shown in Fig. 6, when the rotational speed of the naph runner strays near the boundary between the dynamic friction region and the static friction region, the change in the friction coefficient (μ) suddenly increases, resulting in large variations in the axial force (F). occurs.

Furthermore, in the torque-angle method, since the snug point is set by torque, there is a problem similar to the above.

[Means to solve the problem]

As a means for solving the above problems, the present invention provides a nap runner that sets the final tightening state of bolts and nuts using tightening torque, and maintains the rotation speed of the nut runner at a constant speed regardless of fluctuations in the tightening load. The present invention provides a constant speed tightening method for bolts and nuts.

[Effect]

By maintaining the rotational speed of the naph runner at a constant speed and tightening, the influence of variations in the friction coefficient is reduced, and the range of variation in axial force is significantly reduced compared to the conventional method.

〔Example〕

FIG. 1 is a tightening torque/time diagram and a rotational speed/time diagram showing an embodiment of the present invention.

Further, FIG. 2 is a block diagram showing a specific example of a constant speed drive device for a nut runner. As illustrated in Fig. 2, the constant speed drive device of the Natsu runner consists of a speed setter (1), a comparator (2), a speed deviation amplifier (3), and a servo amplifier (4).
), nut runner drive motor (5), and pulse generator (6) are connected in series, and the pulse generator (6) and comparator (2) are connected in series.
) by providing a feedback circuit (7>) between them.

The rotation speed of the nut runner (not shown) is set in the speed setting device (1), and this set rotation speed is applied to the nut runner drive motor (not shown) via the comparator (2), speed deviation amplifier (3), and servo amplifier (4). 5). A pulse signal corresponding to the actual rotation speed of the nut runner is transmitted from the pulse generator (6), and this pulse signal is sent to the comparator (2>) via the feedback circuit (7).
2) Set the speed of the pulse signal! (1) is compared with the set rotation speed sent from A voltage or current conversion signal is sent to correct the number.The rotation speed of the nut runner set in the speed setting device (1) can be set within the range where the final tightening torque can be transmitted to the bolts and nuts in the dynamic friction region. As low as possible (e.g. around 10 rpm)
The rotation speed of the nut runner can be maintained at a constant value from the beginning of bolt/nut tightening to the end of tightening, as shown in Fig. The overall time required for tightening can be shortened by connecting and tightening in a constant speed rotation state until the end of tightening. In short, the present invention maintains the rotational speed of the nut runner at a constant speed regardless of fluctuations in the tightening load, thereby eliminating the influence of variations in the coefficient of friction on the threaded surfaces and seating surfaces, thereby eliminating fluctuations in axial force. This ensures bolt and nut tightening conditions with less friction.

〔Effect of the invention〕

If the present invention is applied to a nut runner that tightens bolts and nuts using the torque method, variations in axial force will be significantly reduced compared to conventional methods, and screw tightening work can be performed with high precision.

[Brief explanation of drawings]

Fig. 1 is a tightening torque/time diagram and a rotational speed/time diagram showing an embodiment of the present invention, and Fig. 2 is a block diagram showing a specific example of a constant speed drive device for a Lotus 7 runner. . Third
The figures are a tightening torque/time diagram and a rotational speed/time diagram for the conventional method, and FIG. 4 is a torque/angle diagram for the torque-angle method. Moreover, FIG. 5 is an axial force/tightening torque diagram in the conventional method, and FIG. 6 is a friction coefficient/rotational speed diagram. (1) -Speed setter, (2) -Comparator, (3)
-Speed deviation amplifier, (4)--Servo amplifier, (5)--Nandrar runner drive motor, (5A)--Control circuit, (6)--Pulse generator, (7)--Feedback circuit. Patent Applicant Sanyo Kiko Co., Ltd. Agent Shogo Ebara No. 5 The key is shown in Figure 4.

Claims (1)

[Claims] (1) In a nutrunner that sets the final tightening state of bolts and nuts using tightening torque, bolts are tightened while maintaining the rotational speed of the nutrunner at a constant speed regardless of fluctuations in the tightening load.・Constant speed tightening method of nuts.