JPH0430975A - Screw driving method - Google Patents

Abstract

PURPOSE:To fasten a work to a board with the specific fastening force, by measuring the torque of the returning time of a screw with its loosening, after measuring the torque of the fastening time with the work being fastened to a base material by a screw and operating the necessary fastening torque for the specific fastening force based on the difference in both torques. CONSTITUTION:The torque To' of the returning time of a screw is measured with its loosening, after measuring by a sensor 10 the torque To of the fastening time of a work with its being fastened to a base material by the screw. The necessary fastening torque T for the specific fastening force is operated by a control circuit 12 based on the difference(To-To') in both torques and the thread fastening of the specific fastening force P is performed by this fastening torque T.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a screw tightening method, and more particularly to a screw tightening method Q in which a tightening torque corresponding to a predetermined tightening force is determined and the tightening torque is used.

The tightening torque when tightening a workpiece to a base material using a conventional screw is divided into two factors: the torque consumed by friction on the screw shaft (thread surface torque), and the torque required to apply axial tension to the screw (shaft It is known that the torque consists of the torque (force torque) and the torque consumed by the screw head and the workpiece seating surface (seat surface torque). Each of these torques is obtained by multiplying the respective coefficients by the nominal diameter of the screw used and the tightening force at that time.The axial force torque is constant depending on the screw used, but the thread surface torque and seat surface torque varies depending on the workpiece and cannot be quantitatively known in advance.

Therefore, conventionally, by keeping the tightening torque constant,
Efforts are made to stabilize the tightening force.

In addition, the actual tightening force is obtained by measuring the distortion of the workpiece being tightened, the elongation of the screw shaft, etc., and the tightening torque necessary to obtain the desired tightening force is determined.

Problem to be Solved by the Invention However, in the conventional example described above, the thread surface torque and bearing surface torque vary depending on the individual workpieces, so even if the tightening torque is constant, the tightening force becomes uneven and unstable. There is.

Therefore, in order to obtain the desired tightening force, it is necessary to set a large tightening torque or use a large number of screws, resulting in a problem that a lot of waste is generated in the screw tightening work.

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, it is an object of the present invention to provide a screw tightening method that can tighten with a stable tightening force and can suppress wasteful screw tightening work.

Means for Solving the Problems In order to achieve the above object, the present invention tightens a workpiece to a base material with a screw, measures the tightening torque, and then loosens the screw and measures the torque when returning. , the tightening torque required for a predetermined tightening force is calculated based on the difference between both torques, and the screw is tightened with the predetermined tightening force using this tightening torque.

It has already been mentioned that the tightening torque when tightening the workpiece to the base material by the action screw consists of the thread surface torque, the axial force torque, and the seat surface torque. On the other hand, when loosening this screw, the returning torque just before the screw head separates from the workpiece seating surface is still related to the above three torques, but in this case, the axial force torque has a negative effect.

Therefore, by taking the difference between the torque during tightening and the torque during return, the value of the axial force torque can be determined, and the value of the sum of the thread surface torque and the seat surface torque can be calculated.

This allows the relationship between the tightening torque and the tightening force to be known for each screw tightening, so it is possible to obtain the tightening torque for obtaining the desired tightening force.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 to 4.

As shown in FIG. 3, a screw tightening machine as shown in FIG. 4 is used in this embodiment to fasten a plate-shaped workpiece 2 to a base material 3 with a screw 1. As shown in FIG. The screw tightening head 4 is connected to the guide member 5
It is supported so that it can be raised and lowered. Also, screw tightening head 4
is configured to be movable up and down by a feed screw 7 which is rotationally driven by a moving motor 6. A drive motor 9 is attached to the screw tightening head 4 for rotationally driving the screw tightening bit 8 and applying torque to the screw 1.

A torque detector IO is attached to the screw tightener 8. The moving motor 6 consists of a servo motor, and an encoder 11 for detecting its rotational position is attached.

Torque detector 10 and encoder 11 are connected to control circuit 12 . On the other hand, based on the control signal output from the control circuit 12, the drive motor 9 and the movement motor 6 are controlled via the respective drive circuits I3.14. Data such as the pitch and shaft length of the screw 1 to be used are input into the control circuit 12 in advance.

In the above configuration, as shown in FIG. 2, the tightening is performed at the maximum torque T just before seating. is detected by the torque detector 10. This tightening torque To and the tightening force P at that time.

The relationship with is expressed by the following equation (1). This is detailed in, for example, "Screw Handbook" (published by Nikkan Kogyo Shimbun, first edition on May 20, 1939, pages 603 to 606).

T o−P o (d (k + + k 2 +
k 3) d: Nominal diameter of screw 1 1: Thread surface torque coefficient 2: Axial force torque coefficient 3: Seat torque coefficient 1, and the maximum return torque T01 at that time
Detect. This return torque T o' and the tightening force Pa
The relationship with is expressed by the following equation (2).

To'=Po (d (k+ kz+ k3)l
-(2) 2 Subtract equation (2) from (1) to obtain the following equation (3).

T.

T,'=Pθ　(2d　k21 In formula (3), Each torque T.

T.

Nominal name of screw 1 Atsukata P. Compute the value of.

By adding equation (2) to equation (1), the following equation (4) is obtained.

To+To'=Po (2d (k++ k3)) In equation (4), each torque T. , To', tightening force P. , the nominal diameter d of the screw 1, and calculate the value of 1 for the thread surface torque coefficient, which is an unknown quantity, and 3 for the bearing surface torque coefficient.

Substitute the value of 3 for +, the nominal diameter d of the screw 1, and 2 for the axial force torque obtained by this into the following general formula (5).

P −T/ I d (k++ k2+ k3)
) - (5) This makes it possible to obtain the tightening torque T corresponding to the predetermined tightening force P. By tightening the screws with this tightening torque T, the workpiece 2 can be tightened onto the board with the predetermined tightening force P. It can be tightened to 3.

Effects of the Invention Since the present invention has the above configuration and operation, the torque corresponding to the predetermined tightening force can be known in advance, and as a result, the workpiece can be tightened to the substrate with the predetermined tightening force.

[Brief explanation of the drawing]

Fig. 1 is a flowchart of the embodiment of the present invention, Fig. 2 is a diagram showing the torque during tightening and returning, Fig. 3 is a schematic diagram of the screw tightening state, and Fig. 4 is a diagram showing the torque used in this embodiment. It is a schematic block diagram of a screw tightening machine. Maximum torque when tightening screw work base material Maximum torque when returning Tightening torque Tightening force

Claims (2)

[Claims] (1) After tightening the workpiece to the base material with a screw and measuring the tightening torque, loosen the screw and measure the torque when returning it, and then calculate the required tightening force based on the difference between both torques. A screw tightening method characterized by calculating a tightening torque and tightening the screw with a predetermined tightening force using this tightening torque. (2) Based on the general formula for tightening torque, which is expressed by multiplying the sum of the thread surface torque coefficient and seat surface torque coefficient by the axial force torque coefficient by the nominal diameter of the screw and the tightening force, By taking the difference between the torque at tightening and the torque at return, which is expressed by multiplying the value obtained by subtracting the axial force torque coefficient from the sum by the nominal diameter and tightening force, the unknown The value of the tightening force is calculated by deleting a certain screw surface torque coefficient and the bearing surface torque coefficient, and substituting the known value of the axial force torque coefficient therein, and then calculating the value of the tightening force and the axial force. By substituting the value of the torque coefficient into the above general formula, a relational expression between tightening force and tightening torque is obtained, and based on this relational expression, the tightening torque required for a predetermined tightening force is calculated. 2. The screw tightening method according to claim 1, wherein the screw is tightened with a predetermined tightening force using an applied torque.