JPH04224081A - Electrically-driven press type resistance welder - Google Patents

Abstract

PURPOSE:To automatically manage the welding quality by setting the bearing part and the elastic body having the high precise moving performance whose frictional force is made low on the pressurizing force transmitting route. CONSTITUTION:The resistance welder applys the pressurizing force and sends the electric current which are required for welding the matter to be welded through the electrode 9 to execute press-welding. And the motor 19 is used as the pressurizing source of the electrode 9. The rotary motion of the motor 15 is changed to the linear movement through the ball screw 3 and the ball nut 20. The bearing part 40, having the moving function of high precision, for transmitting the linear movement required to detect the displacement due to expansion of the nugget generated in the course of forming nugget to the sensor 50 is provided at the pressurizing force transmitting route such as between the motor 15 and the ball screw 3 and/or the ball screw 3 and the electrode holders 7. The elastic body which absorbs the bent at the time of electrode pressurizing is provided at the bearing part 40. Therefore, the variable pressurization control can be executed automatically with the expantion monitor.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a resistance welding machine including a spot welding gun, and more specifically, it monitors the amount of nugget expansion that occurs during nugget formation at a spot weld, and feeds this back to an electric motor. The present invention relates to an electric pressure resistance welding machine that maintains and improves welding quality by variable control of electrode pressure.

0002

[Prior Art] As a method of controlling the quality of spot welding, the phenomenon in which the welded part expands thermally due to heating and softening due to temperature rise during the nugget formation process is utilized, and the nugget expansion force pushes up the electrode and its displacement. Expansion monitors for controlling welding quality by monitoring quantity are known.

However, this method has not been put into practical use in most production lines. The reason for this is that the spot welding gun uses an air cylinder as the electrode pressure source, which makes it difficult to make a soft landing on the workpiece.
The shock from pressurization becomes vibration and remains in the gun arm, making it difficult to accurately measure the amount of nugget expansion in a short period of time. Also, if the amount of nugget expansion is insufficient, in order to generate a large nugget, the current must be increased and the pressurizing force must be quickly lowered. This method takes time, and therefore the electrode has poor responsiveness, making it difficult to vary the pressing force depending on the nugget formation conditions.

0004

[Problems to be Solved by the Invention] The present invention is necessary because it has been difficult to accurately measure the amount of nuggets in a short time and to increase or decrease the pressing force in a short time on conventional production lines. The problem is that a quick electrode pressure response could not be obtained.

[0005]

[Means for Solving the Problems] Therefore, the present invention has taken the following technical measures to solve the above problems. That is, it is a resistance welding machine that applies pressure and current necessary for welding to a workpiece through an electrode, and uses an electric motor as a pressure source for the electrode, and rotates the rotational movement of the electric motor using a ball screw and a In an electric pressurizing device that converts linear motion through a ball nut, during the nugget generation process, a pressurizing force transmission path such as between the electric motor and the ball screw and/or between the ball screw and the electrode holder is This electrically pressurized resistor is equipped with a bearing section that transmits linear motion to the sensor to detect the amount of displacement due to the nugget expansion that occurs in the sensor, and an elastic body that absorbs the deflection when the electrode is pressurized in this bearing section. Provide welding machines.

[0006]

[Embodiment] Fig. 1 is a sectional view of a main part of a C-type spot welding gun according to an embodiment of the present invention, in which 1 is a C-shaped gun arm made of a cast metal with good conductivity. It is. A pressure device 2 is integrally fixed to the gun arm 1. 3 is a ball screw that passes through the inside of the casing 4 of the pressurizing device. 6 is an electrode holder inserted into the opening at the tip of the gun arm 1, and 7 is an electrode holder inserted into the tip of the ball screw. 10 is an equalization mechanism that supports the entire gun, and a guide rod 12 fixed to the robot support bracket 11 passes through bearings 13 provided on both sides of the gun arm, allowing the entire gun to freely float in the left and right direction. It makes it possible. 14 is a balance spring, which connects the electrode part 8 on the arm side to the electrode part 9 on the movable side.
This is to bring the workpiece into contact with the workpiece in advance. Reference numeral 15 denotes an electric motor constituting the pressurizing device, and a servo motor is fixed to the casing side.

Next, FIG. 2 shows a sectional view of the main parts of the electric pressurizing device. An angular contact ball bearing 17 is mounted inside a casing 4 fixed to the gun arm 1 via an insulating bush 16, and an inner ring 18 of the angular contact ball bearing and a ball nut 20 are fixed to each other. rotates together with the inner ring via a bearing 21 installed between the inner ring 18 and the outer ring 19. The ball screw 3 passes through an angular contact ball bearing 17 in the casing, is incorporated into a screw hole of a ball nut 20, and is supported by passing through bearings 22 and 23 attached to the front and rear parts of the casing 4. has been done. Further, a rotation stopper 5 is provided to prevent the ball screw itself from rotating.

A spline shaft 24 is attached to the tip of the ball screw 3.
The electrode holder 7 to which the electrode portion 9 is attached is slidably connected to the spline shaft 24 via a ball bearing. The tip of the spline shaft 24 has the amount of electrode displacement due to nugget expansion during welding, and is effective as an elastic material that absorbs deflection to release abnormal pressure so that no more than necessary electrode pressure is applied to the welding area. A disc spring 25 is inserted. In particular, the movable part of the ball screw 3 has less deflection compared to the movable part of the air cylinder, so
This spring 25 functions as an electrode follow-up when immediate electrode response during welding is required, such as in nut projection welding.

A belt gear 26 is provided on the outer periphery of the ball nut 20, and power is transmitted between this gear 26 and a belt gear 27 provided on the output shaft of the motor via a toothed belt 28. ing. Therefore, the linear movement of the ball screw 3 causes the ball nut 20 to be driven by the toothed belt 28 from the motor output shaft.

The positioning air cylinder 29 is provided to position the entire gun when the electrode is opened, the cylinder case 30 is provided integrally with the pressurizing device, and the cylinder rod 31 is connected to the external member 32. It is fixed at

33 is a detector for detecting strokes. In other words, in the case of electric pressurization, one electric motor 15 simultaneously moves both the electrode portion 9 on the large stroke side, that is, the ball screw side, and the electrode portion 8 on the small stroke side, that is, the gun arm side. Since it cannot be controlled, the electrode part 8 on the gun arm side is brought into contact with the object to be welded using the balance cylinder 14, and the speed of the electrode part 9 on the large stroke side, that is, on the ball screw side is reduced. Contacts the workpiece without shock.

That is, the rotation speed of the ball nut 20 on the large stroke side is detected by a position detector 33 such as an encoder provided behind the output shaft of the electric motor 15 to control the motor rotation. It is something. In other words, when detecting the above rotation angle, the movement pulse on the small stroke side is approximately constant, so this pulse is subtracted from the total number of output pulses from the time the rotation torque starts until it stops. I will do it.

Note that the detector 33 is installed behind the electric motor 15.
Another method is to directly connect large and small strokes at the same time.
It is also possible to operate the electrodes after determining the movement order of the electrodes using a regulating means without moving the electrodes. In this case, for example, after detecting that one electrode section has come into contact with the workpiece using L/S or the like, the other electrode section is started.

Next, in the embodiment shown in FIG. 3, the electrode holder 7 and the board are
This is a detailed cross-sectional view of the bearing part 40 that connects the bearing part 40 to the screw 3, which is suitable for obtaining high-precision motion performance at a position where a quick reaction is required to detect the amount of displacement due to nugget expansion that occurs during the nugget production process. A structural example is shown.

In this case, an outer cylinder of a ball bearing is fixed inside the electrode holder 7 via an insulating material. A spline shaft 24 inserted into this outer cylinder is connected to the tip of the ball screw 3, and balls 0 arranged on both sides of a protruding raceway surface formed on the outer periphery of this spline shaft 24 roll. The movement allows smooth linear movement between the electrode holder 7 and the spline shaft 24.

Therefore, when the electrode part 9 is pushed up due to the expansion of the nugget during welding, this upward movement sensitively reacts to the electrode holder of this bearing part, and at the same time, the electrode part 9 inserted between the spline shaft 24 and the electrode holder 7 The disk spring 25 contracts in accordance with the amount of expansion, and the dog 51 connected to the electrode holder 7 operates the sensor section 50 of the spot welding gun body to measure this movement as the amount of nugget expansion.

Next, FIG. 4 shows an example in which the apparatus of the present invention is implemented in an X-type spot welding gun as another embodiment. The gun arms 34 and 35 are attached to a support member 37 fixed to a welding transformer 36 via a rotating shaft 38 so as to be openable and closable. Support member 39 integrated with one gun arm 34
An electric motor 15 is supported by the motor 15, and a ball screw 3 is connected to the output shaft of the electric motor 15 via a bearing portion 40. This ball screw 3 is attached to a ball nut 4 attached to the other gun arm 35 via a fixed support member 41.
It is combined and connected to the two screw holes. Therefore, the rotational motion of the output shaft of the electric motor is converted into the direction (linear motion) of opening and closing the electrode tips 43, 44 fixed to the tips of the gun arms 34, 35 by the ball screw 3 and ball nut 42.

FIG. 5 is a detailed cross-sectional view of the bearing portion 40 connecting the output shaft 45 of the electric motor 15 and the ball screw 3. It basically has the same structure as FIG. A cylindrical portion 46 is integrally formed at the tip of the spline shaft 24, and the spline shaft 24 is fixed to the ball screw 3. Due to the rolling motion of the balls 0 arranged on both sides of the protruding raceway surface formed on the outer periphery of the spline shaft 24, the bearing portion between the cylindrical portion 46 and the spline shaft 24 responds to rotational motion and the amount of electrode displacement. Transmits smooth linear motion.

As a result, when the electrode of the gun arm rises due to nugget expansion during welding, the ball nut 42 returns the ball screw 3 by the amount of movement, compressing the disc spring 25. By this operation, the dog 51 connected to the ball nut 42 operates the sensor section 50 fixed to the cylindrical section 46, and measures the amount of expansion of the nugget.

Next, the operation of the present invention will be explained based on FIGS. 1 to 3. When the start button is pressed, a welding start command is input to the control device of the electric motor 15, and the motor starts rotating. When the output shaft of the electric motor is rotated and the toothed belt 28 rotates,
The ball nut 20 rotates, causing the ball screw 3 to move in a straight line and lowering the electrode section 9. When this electrode part 9 comes into contact with the workpiece, the gun arm 1 on the small stroke side moves ahead of the gun arm side electrode part 9 on the large stroke side due to the biasing force of the balance spring 14. - contact with the block.

In this case, the movement of the ball screw 3 is controlled to operate at high speed at first, and to reduce the speed just before it is touched, in order to soften the impact of the electrode portion on the workpiece. This is done by an encoder 33 directly connected to the rear of the output shaft of the motor, which decelerates the motor rotation when the ball nut 20 on the large stroke side rotates to a preset rotation speed. The electric motor 15 switches from speed control to torque control when a certain angle is reached, or when the output torque increases rapidly, or when this is detected using L/S together.

In this state, when the upper and lower electrode sections begin to pressurize the workpiece, the rotational torque of the electric motor increases rapidly and the pressurizing force rises smoothly. When the output torque reaches a predetermined value, this is detected, and welding current flows from the welding transformer to the spot welding gun in response to an energization command from the welding control device, and pressure welding of the workpiece is started.

[0023] Thus, the welded part is heated and softened to form a nugget, which gradually expands thermally. The electrode is pushed up by this nugget expansion force, and this movement is transmitted to the electrode holder 7 as the amount of electrode displacement during the growth process of the nugget, which is detected point by point by the sensor section 50, and the detected value corresponds to the set value. When the electric motor 1 is exceeded or when it is not exceeded.
By sending a signal to the control device 5 and controlling the torque and rotation speed of the electric motor according to the command, the electrode pressurizing force is controlled according to the size of the nugget during the nugget production process.

After welding is completed, the electric motor 15 is reversed, the electrode portion 9 of the ball screw 3 on the large stroke side is opened, and the air in the positioning air cylinder is switched to supply air to the working chamber. supply and move the entire gun to the left to position it.

[0025]

As explained above, according to the present invention, an electric motor is used as a pressurizing source for the electrode, and an electric motor is used to convert rotational motion of the motor into linear motion via a ball screw and a ball nut. In the pressure device, a bearing portion and a bearing portion having high precision movement performance with reduced mechanical friction force are provided in the pressure transmission path between the electric motor and the ball screw and/or between the ball screw and the electrode holder. Because the elastic body is provided, the amount of nugget expansion can be quickly reacted at this connection part, and the true amount of nugget expansion can be detected in a short time.In addition, the rising action when pressurizing the electrode is faster, which is different from conventional production lines. Pressure force variable control and welding quality control using the expansion monitor, which was almost impossible to touch, can be performed automatically.

[0026]

[Brief explanation of the drawing]

FIG. 1 is a front view showing an embodiment in which the device of the present invention is used in a C-type spot welding gun.

FIG. 2 is a detailed sectional view of the device of the present invention.

FIG. 3 is a detailed cross-sectional view of a bearing section connecting an electrode holder and a ball screw of the device of the present invention.

FIG. 4 is a front view showing an embodiment in which the device of the present invention is used in an X-type spot welding gun.

FIG. 5 is a detailed cross-sectional view of a bearing section connecting an output shaft and a ball screw of the device of the present invention.

FIG. 6 is a view taken along the line A-A in FIG. 3;

[0027]

[Explanation of symbols]

3 Ball screw 7 Electrode holder 8 Electrode part 9 Electrode part 15 Electric motor 20 Ball nut 24 Spline shaft 25 Elastic body 33 Position detector 40 Bearing part 50 Sensor part 51 Dog

Claims (4)

[Claims] 1. A resistance welding machine that applies pressure and current necessary for welding to a workpiece through an electrode, and has an electric motor as a pressure source for the electrode, and the rotational movement of the electric motor In an electric pressurizing device that converts motion into linear motion via a ball screw and a ball nut, a pressurizing force transmission path such as between the electric motor and the ball screw and/or between the ball screw and the electrode holder, etc. A bearing part is provided that transmits linear motion to the sensor to detect the amount of displacement due to nugget expansion that occurs during the nugget generation process, and an elastic body is provided in this bearing part to absorb deflection when the electrode is pressurized. Electric pressure resistance welding machine. 2. The electric pressurized resistance welding machine according to claim 1, wherein said electric motor is provided with a detector that feeds back torque and rotational speed for controlling electrode pressing force and electrode moving speed. 3. The electric pressurized resistance welding machine according to claim 1, wherein the bearing portion is formed by arranging and combining balls around the outer circumference of a spline shaft fixed to a ball screw. 4. The electric pressure resistance welding machine according to claim 1, wherein the sensor is disposed before and after the elastic body in which the sensor portion and the dog are movable relative to each other.