JPH10249535A - Pressure controlling method of spot welding gun - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the spatter or the tip deposition by controlling the movement of an upper tip so as to apply the prescribed pressure to a work, bringing a lower tip into contact with the work, and holding a gun body at the contact position to unify the pressure of the upper and lower tips. SOLUTION: An upper tip 5 is moved downward by a pressure source 4, a gun body 2 is moved upward by a drive source 6, and a lower tip 3 is moved upward. The speed is controlled from the revolution of the pressure source 4 and the drive source 6, and the upper and lower tips 3, 5 simultaneously arrive at the landing start position. The lower tip 3 is elevated at the set speed smaller than the speed before arriving at the landing start position, while the upper tip 5 is lowered at the relative speed equal to the set speed to the gun body 2. The lower tip 3 is stopped when it is brought into contact with a work W, and held at the contact position. The lower tip 3 is not firmly abutted on the work W by the drive source 6. The pressure of the upper and lower tips 3, 5 becomes equal to each other, and a nugget to agree with the joining surface of the work W can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressurization control method mainly applied to a spot welding gun mounted on a robot and used.

[0002]

2. Description of the Related Art Conventionally, as a spot welding gun of this type, as disclosed in Japanese Patent Application Laid-Open No. 6-328267,
A fixed electrode tip that is immovable with respect to the gun body,
It is known that a fixed electrode tip is provided with a movable electrode tip which is opened and closed by a pressure source, and a gun body is movable with respect to a gun support bracket in a direction opposite to the two electrode tips by a driving source.

In the spot welding gun, a movable electrode tip is brought into contact with a work by a pressurizing source, and a fixed electrode tip is brought into contact with the work by moving a gun body by a driving source. can get.

[0004]

In the above-mentioned spot welding gun, the pressing force of the pressurizing source acts equally on the movable electrode tip and the fixed electrode tip via the gun body, but the fixed electrode tip has a drive source. Is applied. In particular, when the relative position of the work with respect to the spot welding gun is shifted toward the fixed electrode tip due to an error in the set position of the work or a positioning error of the robot, the pressing force applied to the fixed electrode tip is increased, and the fixed electrode tip with respect to the work is increased. The difference between the pressing force and the pressing force of the movable electrode tip increases.

Here, if a difference is made in the pressing force between the two electrode tips, the contact resistance between the electrode tip with a small pressing force and the work becomes larger than the contact resistance between the electrode tip with a large pressing force and the work. The heat generation center of the work shifts to the electrode tip side where the pressure is small. Then, as shown in FIG. 7B, the maximum diameter portion of the nugget N shifts to the electrode tip side (upper side in the figure) where the pressing force is small, the nugget diameter at the joint surface of the work W becomes small, and the shearing of the work W The welding strength decreases. Further, if the contact current is increased so that the nugget diameter at the joint surface of the work W becomes a required value, the work W on the upper side is excessively melted, causing problems such as spattering and welding of the electrode tip.

In view of the above, the present invention makes it possible to equalize the pressing force of the fixed electrode tip and the pressing force of the movable electrode tip so that high quality welding can be performed without spattering or chip welding. The challenge is to

[0007]

In order to solve the above-mentioned problems, according to the present invention, a fixed electrode tip which is immovable with respect to the gun body and a movable electrode which is opened and closed by a pressurizing source with respect to the gun body are provided. In a method for controlling the pressure of the spot welding gun, wherein the gun body is movable with respect to the gun support bracket in a direction opposite to the two electrode tips by a drive source, the movable electrode tip is moved from the open position by the pressure source. The workpiece is brought into contact with the workpiece by moving it in the closing direction to approach the workpiece.Then, the pressurizing source is controlled so that a predetermined pressure is applied to the workpiece, and the fixed electrode tip is moved from the open position to the workpiece by moving the gun body by the driving source. The gun body is moved in the approaching closing direction and brought into contact with the workpiece, the point of contact of the fixed electrode tip with the workpiece is detected, and the gun body is held at the position of this point of contact. And controls the drive source so that.

According to the present invention, since the fixed electrode tip is held at the position at the time of contact with the work, the contact pressure of the fixed electrode tip with respect to the work by the driving source is extremely small. Therefore, the pressing force of the fixed electrode tip on the work is only the pressing reaction force of the movable electrode tip acting on the work via the gun body, and the pressing force of both electrode tips on the work becomes uniform. Therefore, the contact resistance of the two electrode tips to the work is also equal, and the center of heat generation during energization coincides with the work joining surface. As a result, a nugget is formed so as to have a maximum diameter at the work joining surface, high-quality welding with shear welding strength can be performed, and spatter and chip welding are less likely to occur.

In order to detect the point in time at which the fixed electrode tip comes into contact with the work, the upper limit of the driving force of the drive source is set so that the movement of the gun body is stopped when the fixed electrode tip comes into light contact with the work. Value, the moving speed of the gun body is detected, and the time when this moving speed becomes zero is detected as the time when the fixed electrode tip comes into contact with the work, or the driving load of the driving source is detected, The time when the load increases may be detected as the time when the fixed electrode tip comes into contact with the work.

A landing start position is set for each of the fixed electrode tip and the movable electrode tip at a predetermined distance from the work, and the fixed electrode tip and the movable electrode tip are moved from their respective open positions in the closing direction. After the electrode tips reach their respective landing start positions, the fixed electrode tips are moved in the closing direction at a predetermined set speed lower than the moving speed before reaching the landing start position, and the movable electrode tips are moved relative to the gun body. It is desirable to move in the closing direction at a relative speed equal to the set speed.

Here, the moving speed of the movable electrode tip with respect to the workpiece is a speed obtained by subtracting the moving speed of the gun body, that is, the fixed electrode tip, from the moving speed of the movable electrode tip with respect to the gun body. Therefore, if the speed is controlled as described above, the movable electrode tip does not move from its landing start position until the fixed electrode tip comes into contact with the work and its movement is stopped, and after the fixed electrode tip comes into contact with the work. The movable electrode tip moves with respect to the work at the set speed and contacts the work. As described above, since the movable electrode tip comes into contact with the work after the fixed electrode tip comes into contact with the work, it is possible to reliably prevent the work from being deformed due to the impact of the movable electrode tip. Further, by performing the closing operation of each chip to the landing start position at a relatively high speed, the time required for pressurization control can be reduced, and the efficiency of the welding operation can be improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, R is a robot for welding a workpiece W, and a spot welding gun G is attached to a wrist Ra at the operating end of the robot R.

The spot welding gun G is, as shown in FIG.
A gun body 2 is supported by a gun support bracket 1 fixed to the wrist Ra so as to be vertically movable. A C-shaped yoke 2a extending downward is attached to the gun body 2.
A lower tip 3, which is a fixed electrode tip, is attached to a lower end of the C-shaped yoke 2a. A pressurizing source 4 composed of a servomotor is mounted on the upper surface of the gun body 2, and a rod 4 a vertically moved by the pressurizing source 4 via a ball screw mechanism (not shown) in the gun body 2 is connected to the gun body 2. 2 project below,
An upper tip 5, which is a movable electrode tip, is attached to the lower end of the rod 4a so as to face the lower tip 3, thereby forming a C-shaped spot welding gun.

As shown in FIG. 3, the gun body 2 is slidably supported by a pair of vertically extending guide bars 1a fixed to the gun support bracket 1. A drive source 6 composed of a servomotor is provided on the upper surface of the gun support bracket 1.
And a vertically long ball screw 6a connected thereto is screwed into a nut 6b fixed to the gun body 2, so that the driving source 6 moves the gun body 2 up and down via a ball screw mechanism. I have to. In addition, this ball screw mechanism
The weight of the gun body 2 is changed to the ball screw 6a via the nut 6b.
Is configured to act as a reverse rotation torque.

The pressurizing source 4 and the driving source 6 are controlled by a gun controller 7. When the spot welding gun G reaches a predetermined hitting position of the workpiece W by the operation of the robot R, the gun controller 7 receives the pressurizing command from the robot controller 8 and controls the pressurization of the spot welding gun G.

The pressurization control is performed as shown in FIG.
The details will be described below. At the time of teaching, each of the lower chip 3 and the upper chip 5
In order to prevent interference with the work W when the gun moves, an open position that is more distant from the work W than the landing start position is set. It is stored in the controller 7.

When a pressurizing command is received (S1), the upper tip 5 is moved downward from its open position in the closing direction by the pressurizing source 4 and the gun body 2 is moved upward by the driving source 6 to lower the lower tip. 3 is moved upward from its open position in the closing direction (S2). Then, speed control is performed based on the positions of the upper and lower chips 3 and 5 calculated from the rotation amounts of the pressurizing source 4 and the driving source 6 (S3), and the lower chip 3 and the upper chip 5
And simultaneously reach the respective landing start positions.

Here, the lowering speed of the upper chip 5 with respect to the work W is a value obtained by subtracting the raising speed of the gun body 2, that is, the lower chip 3, from the lowering speed of the upper chip 5 with respect to the gun body 2. Therefore, when the distance between the open position and the landing start position is equal between the lower chip 3 and the upper chip 5,
The lowering speed of the upper tip 5 with respect to the gun body 2 is
The lower chip 3 and the upper chip 5
And can simultaneously reach the respective landing start positions.

When both chips 3 and 5 reach the landing start position (S4), a predetermined set speed VS lower than the speed before the lower chip 3 reaches the landing start position.
And lowers the upper chip 5 with respect to the gun body 2 at a relative speed equal to the set speed VS (S
5). Then, when the lower chip 3 comes into contact with the work W (S6), the gun body 2, that is, the lower chip 3 is stopped, and the lower chip 3 is held at the position at the time of contact with the work W (S6).
7).

The detection of the point of contact of the lower chip 3 with the workpiece W can be performed as follows. For example, the driving source 6
The upper limit of the driving force (torque) is set to a value at which the upward movement of the gun body 2 is stopped when the fixed electrode tip 3 comes into light contact with the work W (for example, a contact pressure of 5 kgf), that is, the weight of the gun body 2 Is set to a value obtained by adding a little torque to the holding torque necessary and sufficient to support the gun, the rising speed of the gun body 2 is detected, and the time when this becomes zero is regarded as the time when the lower tip 3 contacts the work W. Can be detected. Although the holding torque changes depending on the position of the welding gun G, the holding torque corresponding to the position can be determined by the driving load of the drive source 6.

Even if the upper limit of the driving torque of the driving source 6 is not set as described above, the driving load (motor current) of the driving source 6 can be increased.
Is detected, the point in time when the lower chip 3 contacts the work W can be detected. That is, when the lower chip 3 comes into contact with the work W, the driving load increases, and the time point of the increase can be detected as the contact time point. In this case, the driving torque is reduced to the holding torque after the contact is detected, and the lower chip 3 is stopped in a state where the contact pressure of the lower chip 3 with the work W is substantially zero. Even when the upper limit of the driving torque is set as described above, it is desirable to reduce the driving torque to the holding torque after the contact is detected.

By the way, until the lower chip 3 comes into contact with the workpiece W, since the lowering speed of the upper chip 5 with respect to the gun body 2 and the rising speed of the gun body 2 are equal, the upper chip 5 stops at its landing start position. When the lower chip 3 contacts the work W and the gun body 3 is stopped, the upper chip 5 descends from the landing start position at the set speed VS and contacts the work W. After the contact, the pressing force of the pressure source 4 acts on the upper chip 5 and the lower chip 3 via the gun body 2 equally. Here, the driving torque of the pressure source 4 is
Although it increases as the driving load increases due to the contact of the upper chip 5 with the workpiece W, the limiter value is set according to the required pressing force, and the driving torque of the pressurizing source 4 increases to the limiter value. At this time (S8), the process proceeds to the energization process.

Changes in the moving speed and position of each of the chips 3 and 5 by the above control method are as shown in FIGS. 5A and 5B. The moving speed of the upper chip 5 in FIG. 5A is a relative speed with respect to the gun body 2.

According to the above control method, since the lower chip 3 is held at the position at the time of contact with the work W, the lower chip 3 does not come into strong contact with the work W by the drive source 6, and Pressure of tip 3 and upper tip 5
Is substantially zero.

The workpiece W is located between the landing start position of the lower chip 3 and the landing start position of the upper chip 5.
As long as is present, the pressing force of the two chips 3 and 5 becomes uniform by the same operation as described above, and it is possible to cope with the displacement of the work W with respect to the welding gun G due to the setting error of the work W and the positioning error of the robot R.

When the pressures of the chips 3 and 5 are equalized as described above, the contact resistance of the chips 3 and 5 to the work W also becomes equal, and the center of heat generation during energization matches the joint surface of the work W. As shown in FIG.
The nugget N is formed so as to conform to the joining surface of not only, the shear welding strength is improved, but also spatter and chip welding hardly occur.

In the above embodiment, the spot welding gun G is constituted by a C-shaped gun, but may be constituted by an X-shaped gun as shown in FIG. The main differences between the X-shaped gun and the C-shaped gun are that a lower gun arm 9 is attached to the gun body 2 in the front-rear direction and the lower tip 3 is attached to the tip, and the upper tip 5 is attached to the tip. A longitudinally upper gun arm 10 is provided in the front-rear direction, and the arm 10 is pivotally supported on the gun main body 2 via a pivot 11 so as to be vertically swingable. The other point is that the base end of the upper gun arm 10 is connected via the small link 4b and the arm 10 is swung up and down. Are given the same reference numerals as above, and description thereof is omitted.

Also in this X-type gun, the pressurizing source 4 and the driving source 6 are controlled by the gun controller 7 in the same manner as described above, so that the pressing forces of the chips 3 and 5 can be equalized.

In FIGS. 2 and 6, the pressurizing source 4 and the driving source 6 are constituted by servo motors. However, the present invention can be similarly applied to the case where these are constituted by servo cylinders. .

[Brief description of the drawings]

FIG. 1 is a side view of a robot equipped with a spot welding gun equipped with the apparatus of the present invention.

FIG. 2 is an enlarged side view of a spot welding gun.

FIG. 3 is a sectional view taken along line III-III of FIG. 2;

FIG. 4 is a flowchart showing an example of pressurization control;

FIG. 5A is a graph showing a change in speed of each chip;
(B) Graph showing position change of each chip

FIG. 6 is a side view showing another example of the spot welding gun.

7A is a diagram showing a nugget formed when there is no pressure difference between both chips, and FIG. 7B is a diagram showing a nugget formed when a pressure difference is generated.

[Description of Signs] 1 Gun support bracket 2 Gun body 3 Lower tip (fixed electrode tip) 4 Pressurizing source 5 Upper tip (movable electrode tip) 6 Drive source 7 Gun controller

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Koji Oda 1-10-1 Shinsayama, Sayama-shi, Saitama Honda Engineering Co., Ltd.

Claims (4)

[Claims] A gun body is provided with a fixed electrode tip that is immovable with respect to the gun body and a movable electrode tip that is opened and closed by a pressure source with respect to the fixed electrode tip. In the method of controlling the pressure of a spot welding gun that can be moved by a drive source in a direction opposite to the electrode tip, the movable electrode tip is moved from the open position to the work by approaching the work from the open position by the pressure source, and then brought into contact with the work. The pressurizing source is controlled so as to obtain a predetermined pressure on the work, and the fixed electrode tip is moved from the open position to the work in the closing direction to approach the work by moving the gun body by the driving source, and is brought into contact with the work. Detecting the point of contact of the tip with the workpiece and controlling the drive source so that the gun body is held at the position of the point of contact. Control method for pressurizing the welding gun. 2. An upper limit value of the driving force of the driving source is set to a value such that the movement of the gun body is stopped when the fixed electrode tip comes into light contact with the work, and the moving speed of the gun body is detected. 2. The pressure control method for a spot welding gun according to claim 1, wherein the time when the moving speed becomes zero is detected as the time when the fixed electrode tip comes into contact with the workpiece. 3. The pressure of the spot welding gun according to claim 1, wherein a driving load of the driving source is detected, and a time point when the driving load increases is detected as a time point when the fixed electrode tip comes into contact with the workpiece. Control method. 4. A landing start position is set for each of the fixed electrode tip and the movable electrode tip at a predetermined distance from the workpiece, and the fixed electrode tip and the movable electrode tip are moved from their respective open positions in the closing direction. After the electrode tips reach their respective landing start positions, the fixed electrode tips are moved in the closing direction at a predetermined set speed lower than the moving speed before reaching the landing start position, and the movable electrode tips are moved relative to the gun body. The pressurizing control method for a spot welding gun according to any one of claims 1 to 3, wherein the spot welding gun is moved in a closing direction at a relative speed equal to a set speed.