JPS6171976A - Bolt tightening method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a bolt tightening method for correctly tightening a bolt with a target axial force.

(Prior art) Conventional bolt tightening methods include the torque method, one rotation angle method,
There are yield point method, axial force method, etc. The problem with the torque method is that variations in the torque coefficient directly result in variations in the axial force, resulting in low tightening accuracy.

In the rotation angle method, the rotation angle is measured from the position where the washer is in close contact with the washer, but the detection accuracy at the start of measuring one rotation angle is poor, and highly accurate tightening is still difficult. With the yield point method, it is difficult to detect the yield point with high precision, and with the axial force method, it is difficult to measure the axial force of a bolt during tightening and is not practical.

(Problems to be Solved by the Invention) As described above, each of the conventional tightening methods has its limitations, making it difficult to accurately manage the axial force.

This invention was made in view of these circumstances,
To provide a bolt tightening method that allows tightening with accurate axial force at all times as long as the bolts are of the same type.

(Means for Solving the Problems) In order to achieve this object, the present invention aims to reduce the torque difference between the tightening torque and the return torque when tightening with a constant axial force to the friction coefficient of the screw or bearing surface. Taking advantage of the fact that it is a constant value regardless of the type of bolt.

In tightening, the tightening torque at the target axial force is calculated from the torque difference during the process, the torque difference at the target axial force, and the torque difference at the target axial force (target value of the torque difference). That is, in this invention, the target value of the torque difference between the tightening torque and the return torque at the target axial force is determined in advance, and the torque difference between the tightening torque and the return torque at an appropriate position during tightening of the same type of bolt is determined in advance. The difference is detected, the tightening torque at the target axial force is calculated using the target value of the torque difference and the detected torque difference, and the tightening is completely completed with this calculated tightening torque. be.

(Function) Now, it is known that if the tightening torque of the bolt is Tf and the return torque is Tt, these 'r, 'r, etc. are expressed by the following equation within the elastic range.

Tf-2Ff(dp(1,,15μs+tanβ)+d
. μ. )-(1)Tt-TFf(dp(1,1,5μ8
tanβ)+d(,μ.) ・−(2) However.

Ff: Axial force generated in the bolt d, : Effective diameter of male thread β : Lead angle μ of screw, : Friction coefficient μ on thread surface, : Friction coefficient d on seating surface (,: Equivalent diameter at 0 points on nut seating surface (1),
(2) Find the difference between equations.

T4 Tz-Ff-dp ・tanβ ・(3) In other words, the difference between the tightening torque Tf and the return torque Tt at a predetermined axial force Ff is determined by the type of bolt and the shaft, regardless of the friction coefficient on the threaded surface or bearing surface. It is determined by the force Ff. Therefore, this torque difference Tf-T is proportional to the axial force Ff.

FIG. 3 is a diagram showing changes in tightening torque Tf and return torque Tt with respect to axial force Ff. These tightening torques Tf
Since the return torque and the return torque are proportional to the axial force Ff within the elastic range, these Tf and Tl are straight lines. In addition, Tf□ in the figure
, Tzl is Tf2. Tf2. ■ indicates the tightening torque and return torque when the friction coefficient μ is large.

Torque generated during tightening, for example, 40~ of target axial force
At the tightening torque Tfo corresponding to 80%, the tightening is reduced to medium and slightly returned, and the return torque Tt (or Ttz) at the axial force F1 (or F2) at this time is detected. Both torques T at this axial force Fl (or F2)
Difference between fo and Tt□ (or Tf2).

That is, Tfo 'I'11. (or Tfo=exposure). Considering the case where μ is small in Fig. 3, ΔA
, OB and ΔCOD are similar, and ΔEOB and ΔF
``OD is also similar.

Here, Ts is the difference between the tightening torque Tf and the return torque Tt at the target axial force Ff, that is, the target value of the torque difference.As shown in equation (3) above, Ts is determined only by the type of screw, and is determined by the friction coefficient. Impact of? 0, which is a constant that does not receive this result.

The delivery torque T required to obtain the target axial force Ff is
f is calculated from this equation (4). Therefore, if the tightening is stopped when the tightening torque Tf reaches this Tf, it becomes possible to tighten with the target axial force Ff.

When bolts of the same type have different friction coefficients 1 For example, if μ is large, tighten to Tf2 in FIG. 3 in exactly the same way to obtain target axial force Ff'? i: Can be obtained.

In the above description, the relationship between the axial force Ff and the tightening torque Tf has been explained as being proportional. However, by determining the target torque from this reference value and tightening to that target torque,
Can be tightened to target axial force.

(Embodiment) FIG. 1 is a block diagram of an embodiment of a device for tightening according to the method of the present invention, and FIG. 2 is a flowchart of its operation.

In FIG. 1, reference numeral 2 denotes a motor that can rotate in forward and reverse directions.

The motor 2 tightens and tassels the bolts. 4
a and 4b are forward/reverse selector switches for motor 2.

6 is a thyristor, 8 is a current detection resistor, 10 is an AC power source, and 12 is a switch, which form a closed circuit with the motor 2. 14 is a gate circuit.

Controls the thyristor 6 on and off in synchronization with the power supply 10,
Controls the N1 flow flowing to the motor 2.

When the switch 12 is turned on, the changeover switch -f4 a.

4b is on the normal rotation side, motor 2 rotates in the normal direction and bolts are tightened f=
J is performed (see step 100 in FIG. 2).

The tightening torque T is detected by a resistor 8.

16 is a comparator, and tightening is done by applying an appropriate tightening torque T during the tightening process.
It is determined that fo has been reached (FIG. 2, step 102
). 18 is a resistor for setting this torque Tfo. When the tightening torque Tf reaches Tfo, the torque Tfo is stored in the memo IJ 20 based on the output of the comparator 16 (FIG. 2, step 104).

Also, the timer 22 is activated.

The timer 22 first sends a signal to the gate circuit 14 to once stop the motor 2, while the changeover switch 4a+4
b is switched to the reverse side, and the gate circuit 14 is operated again to reverse the motor 2 (FIG. 2, step 106).

The timer 22 reverses the motor 2 for a very short time and stores the return torque η at that time in the memory 24 (FIG. 2, step 108).

Reference numeral 26 denotes a computing unit, which stores in advance in the memory 28 the target value Ts of the torque difference (FIG. 2, step 1.10).
.

The above equation (4) is calculated using the tightening torque Tfo and the return torque η stored in the memory 20.24 (second
Figure, step 1.1.2). On the other hand, the timer 22 is
After a short period of reverse rotation, the changeover switches 4a+4b and gate circuit 14 are switched to perform forward rotation 2 (FIG. 2, step 114).

The comparator 30 determines that the tightening torque T of the motor 2, which has started rotating forward again, has reached the final tightening torque Tf determined by the calculator 26, and outputs a stop signal to the gate circuit 14. Stop motor 2P (Fig. 2, step 116)
).

(Effects of the Invention) As mentioned above, in the present invention, when tightening with a constant axial force, the torque difference between the tightening torque Tf and the return torque T6 is not affected by the coefficient of friction, and moreover, it is independent of changes in the axial force. Using the points that change with a certain relationship, the tightening torque at the target axial force is calculated using the target torque difference Ts at the target axial force and the torque difference at an appropriate position during tightening. Since tightening is performed up to the tightening torque, it is possible to always tighten with the correct axial force without being affected by variations in the friction coefficient of the threaded surface or bearing surface. Moreover, there is no need to make any special modifications to the bolts themselves to measure the axial force, and if the bolts are of the same type, they are always tightened with the same axial force, resulting in good workability. Furthermore, when changing the type of bolt, the target value of torque difference Ts should be changed. It is convenient and can be handled by simply changing it.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a tightening device according to the method of the present invention, and FIG. 2 is an operation flowchart. FIG. 3 is a diagram explaining the principle. Patent Applicant Shibaura Seisakusho Co., Ltd. Agent Patent Attorney Yama 1) Written by Yudai 3 Gensuke Tori Tsui fO ■ ■ ■ ■ ■ 7-7' °\ /: F2' ■

Claims (2)

[Claims] (1) Obtain the target value of the torque difference between the tightening torque and the return torque at the target axial force in advance, and calculate the torque difference between the tightening torque and the return torque at an appropriate position during tightening of the same type of bolt. A bolt tightening method characterized in that a tightening torque at a target axial force is calculated using the detected torque difference and a target value of the torque difference, and tightening is completed with the calculated tightening torque. (2) The tightening torque and return torque at appropriate positions during tightening are respectively T_f_0 and T_l, and the target value of the torque difference is T_s, and the tightening torque T at the target axial force
_f, Formula: T_f=T_f_0・T_s/(T_f_0−T_
1) The bolt tightening method according to claim 1, wherein the bolt tightening method is calculated according to (l).