JP2002321067A - Electric resistance welding method and controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct the releasing position of an electrode corresponding to the worn quantity thereof without a line stop even when a welding machine, which is pressurized and driven by an electric servomotor, is operated. SOLUTION: In the process where spot welding is continuously spotted, the worn quantity of electrode tips is measured, with a work being pinched between them. Feedback control is carried out based on the measured value so that the position deviation at a movement start point and/or a deceleration start point of the electrode and a pressurization start point thereof are corrected in real time during the movement of the electrode tip. Thus, the improvement of weldability and productivity is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance welding machine in which pressing operation of an electrode tip is performed by an electric servomotor. The present invention relates to a resistance welding method and a control device for obtaining high-quality welds by appropriate pressure control while suppressing changes.

[0002]

2. Description of the Related Art Electrode tips used for resistance spot welding are subjected to continuous spot welding, and as the welding is repeated, the tip end faces are gradually deformed and worn away, becoming shorter and the electrode position being shifted. Generally, in a resistance welding machine in which a pressurizing operation is performed by an electric servomotor, a shock to a gun operator, a robot, and a pressurizing mechanism is relieved, and an indentation of a workpiece (workpiece), that is, a depression in a welded portion. In order to reduce the pressure, decelerate immediately before the welding pressure point and perform soft touch.

However, when the tip of the electrode tip is worn and shortened, the deceleration start position is far from the work to be welded from the position of the worn electrode tip, even if the pressurizing shaft is correctly controlled by the servomotor. Has become. If the deceleration operation is performed in this state, the section during the constant speed becomes longer, and the pressurizing movement time becomes longer.

Further, when the electrode tip reaches the welding pressurizing position, the electrode tip is pressed against the workpiece by torque control at that position, and then when current is started, the welded portion starts thermal expansion due to Joule heat and then contracts. Therefore, the electrode tip is not stationary even during the torque control welding. Therefore, it is necessary to set the creep speed even during welding and follow the electrode tip by the thermal expansion. Therefore, if the setting of the welding pressurizing position is inappropriate, there is a problem that the following control cannot be optimally performed.

In order to solve this problem, in a conventional electric servo spot welding method, for example, a wear amount of an electrode tip is automatically detected by an encoder value, and when the detected wear amount reaches a limit value, an electrode is worn. A method has been proposed in which a tip dress signal or an electrode tip exchange signal is issued, or the movement start position of the electrode tip is shifted by the amount of wear (Japanese Patent Application Laid-Open No. Hei 9-150278).

However, in this type of conventional method, it is necessary to periodically detect the amount of wear at the number of hit points where the amount of wear of the electrode tip does not significantly advance. Pressing has forced the production line to stop, causing a problem of delay in production tact.

[0007]

According to the present invention, instead of periodically stopping the operating line and detecting the wear amount of the electrode tip as in the prior art, during the process of continuous spot welding, spot welding is performed. At the end of welding or immediately before the start of energization, the amount of wear of the electrode tip is measured with the electrode tip sandwiching the work, and feedback control is performed based on the measured value to start the electrode movement and / or decelerate during electrode tip movement. The displacement between the start point and the electrode press start point is corrected in real time,
The main feature of this is to improve weldability and productivity.

Another invention has been developed to solve the above-mentioned conventional problem, and has taken the following technical means. That is, in a resistance spot welding machine in which the electrode tip is pressed by an electric servomotor, the electrode is pressed by an electric servomotor, and the work sandwiched between the electrodes is pressed and energized to perform welding. The electrode position at the end of the welding is detected by reading with an encoder built in the servomotor, and the detected value is compared with a reference value when the electrode tip is new to calculate the amount of electrode wear. The main feature is that the deceleration start position and the welding pressure position are corrected just before the next welding point by an amount corresponding to the electrode wear amount.

When the servomotor is applied to the pressurizing operation of a welding machine, the rotation operation is usually converted into a linear operation by a ball screw or the like. At this time, the position and speed of the movable electrode tip are controlled by the servomotor. This is performed by detecting a signal of an encoder which is installed on the same axis, generally on the same axis as the rotating shaft on the side opposite to the movable electrode tip.

In the present invention, with a new electrode tip attached, for the purpose of the test, the object to be welded is inserted, but air pressure is applied without power for testing. At this time, the contact point between the electrode tip and the workpiece is stored as a reference level of the welding pressurized position.

[0011] Thereafter, in a normal welding operation, the electrode position when welding is completed for each welding point is detected by measuring the number of pulses oscillated from an encoder built in the servomotor in real time, The detected value is compared with a preset reference value of the welding press position when the electrode tip is in a new state to calculate the amount of electrode wear, and the displacement of the electrode stroke is fed back to obtain the next stroke position. The amount of positional deviation such as the electrode movement start point, deceleration start point, and welding pressure point is corrected in real time.

In this way, the optimum deceleration start position is always maintained, so that the low-speed movement distance from the deceleration start point to the welding pressurizing point does not increase, and the welding is performed by the optimum welding pressurizing position. Therefore, high-quality welding pressure control can be performed.

[0013]

FIG. 1 shows an embodiment in which the present invention is applied to a servo spot welding gun for a robot. Reference numeral 1 denotes a servo spot welding gun for a robot. Reference numeral 2 denotes a guide case of a drive unit that houses the ball screw 3. Reference numeral 4 denotes a servo motor connected to the case. Reference numeral 5 denotes a gun arm fixed to the case via a base 12. Reference numeral 6 denotes a fixed-side electrode tip fixed to the tip of the gun arm. Reference numeral 7 denotes a sleeve having a screw nut concentrically incorporated with the ball screw and moving through the rod side of the unit. Reference numeral 8 denotes a movable-side electrode tip fixed to the tip of the sleeve, and moves opposite to the fixed-side electrode tip 6. 9 is a bracket connected to the guide case. Reference numeral 10 denotes an encoder built in the servomotor. Reference numeral 11 denotes a welding transformer fixed to the bracket side.

The servo motor 4 drives the movable electrode tip 8 via a ball screw, presses the electrode tip 8 against an object to be welded, and obtains a pressing force required for welding with the fixed electrode tip 6. Generate torque. The encoder 10 converts the number of rotations of the rotary shaft of the servomotor 4 into pulses, counts the number of pulses with a counter, and the counted value matches the set number of pulses of the movable electrode tip 8, that is, the number of pulses corresponding to the moving distance. The movement distance is detected at the timing.

FIG. 2 shows a point A at which the movable electrode tip 8 of the servo spot welding machine moves and a point B at which the deceleration starts.
FIG. 8 is a flowchart of the operation when the electrode tip is new, when the electrode tips 6 and 8 are worn out, and after the electrode tip 8 is corrected, when the point and the pressure start position are set to point C.

First, a point A at which the movable electrode tip 8 starts to move when the electrode tip is new, a point B at which the electrode tip decelerates, and a point C at which the pressing is started by the ball screw by the servo motor 4. The rotating motion of 3 advances the sleeve 7 in the axial direction with a screw nut, and the movable electrode tip 8 held at the tip of the sleeve is opened and closed with the fixed electrode tip 6. While the movable electrode tip 8 is moving, the encoder 10 built in the motor 4 counts pulses, reads the electrode moving distance, and inputs and stores three reference point points.

A high-speed moving section in which the movable electrode tip 8 approaches the workpiece at a high speed between the points A and B in FIG. The moving distance a from the point B to the point C in the drawing is a low-speed moving section of the electrode tip in which the movable electrode tip 8 is decelerated immediately before coming into contact with the workpiece and is soft-touched to start pressurizing. L is the moving distance of the movable electrode tip 8 and indicates an opening stroke. The curve in the figure shows the moving speed curve of the movable-side electrode tip 8.

The tip surfaces of the two new electrode tips 6 and 8 are repeatedly heated by spot welding as the continuous lapping point progresses, and gradually collapsed or become dirty or alloyed by the surface film (various plating layers) of the workpiece. The outer shape collapses into an umbrella shape and the dimensions are short and deformed. In such a case, since the weldability is adversely affected, the work of dressing the electrode end face with a tip dresser (cutting tool) and returning it to its original shape is frequently repeated. This cutting work promotes the degree of wear of the electrode tip and promotes shortening.

As shown in the figure, the electrode consumption amount is, for example, tm.
m, the dimensions of the movable-side and fixed-side electrode tips 6, 8 are reduced by about 2 tmm. Naturally, the initially set movement start point of the movable-side electrode tip 8 is shifted from the line A to tmm. This displacement is caused by the deceleration start point B
It will be shifted upward by tmm from the line. The fixed-side electrode tip 6 is also shifted downward by about tmm from the C line at the pressurization start point, and the deceleration distance in the BC section is a + 2tmm.
Optimum pressurizing conditions cannot be obtained.

Therefore, according to the present invention, during operation, the position where the movable electrode tip 8 abuts on the workpiece is detected by the encoder 10, and the detected value and a set reference value are calculated to calculate the actual amount of wear ( tmm) is calculated.

The movable electrode tip 8 is fed back to the controller of the servo motor 4 and the robot controller based on the detected value, and the movable electrode tip 8 is moved downward and corrected by the amount corresponding to the wear amount (2 tmm) at both the points A and B. Thus, both the moving distance L and the deceleration distance a are always kept constant. On the other hand, the fixed-side electrode tip 6 is slightly separated from the pressure start point C by tmm, but the entire welding gun is preliminarily operated by the robot controller while maintaining the deceleration distance of a.
Alternatively, the stationary electrode tip 6 is made to coincide with the pressure start position of the point C by the floating operation of the equalizing device of the gun body. Thereby, the positioning control of the deceleration start position between the movable electrode tip 8 and the fixed electrode tip 6 can be accurately performed. When moving the work side to the stationary welding machine and setting it on the fixed-side electrode tip 6, or when a human being holds the hand like a portable gun and operates the welding machine side to the welding point, the robot described above is used. Alternatively, it is not necessary to perform a scooping operation of the fixed-side electrode chip 6 by the equalizing device.

In this embodiment, the case where the electrode position is corrected at two positions of the electrode movement start position (A line) and the deceleration start position (B line) when the wear of the electrode tip is detected has been described. It goes without saying that correcting only the deceleration start position is also included in the scope of the technical idea of the present invention. Further, although the embodiment of the present invention has been described as representative of the C type welding gun, it can be easily applied to various X type welding guns or various resistance welding machines.

[0023]

As described above, the first aspect of the present invention is as follows.
According to the present invention, the constant electrode opening position, the optimal deceleration start position, and the electrode pressurization start position can be corrected in real time at the end of spot welding or immediately before the start of welding power supply. Since the low-speed travel distance to the welding pressure point is kept constant at each welding point, compared to the conventional technology, there is no need to stop the line for detecting the amount of wear of the electrode tip periodically and extend the welding cycle time. And shortens production tact time, and performs welding at the optimal welding pressure position, enabling high-quality welding pressure control.

According to a second aspect of the present invention, in the electric servo spot welding machine, the amount of wear of the electrode tip is detected each time welding is completed when spot welding is continuously performed, and the amount of wear is detected immediately before the next welding. The control unit has a simple structure and the tact time can be reduced simply by adding a feedback function that can correct the electrode movement start position, deceleration start position, and welding pressure start position of the electrode tip in real time according to the amount of wear. It is possible to improve the production efficiency and to perform high-quality welding pressure control.

[Brief description of the drawings]

FIG. 1 is a schematic view of an entire apparatus showing an example of a case where the method of the present invention is applied to a resistance welding machine that performs electrode pressurization by an electric servomotor.

FIGS. 2A and 2B are flowcharts showing, in each operation flow, electrode positions in a new state, electrode positions before correction when consumed, and electrode positions after correction of each of the electrode tips on the movable side and the fixed side of the device of the present invention.

[Explanation of symbols]

1 is a servo spot welding gun, 2 is a guide case, 3 is a ball screw, 4 is a servomotor, 5 is a gun arm, 6 is a fixed electrode tip, 7 is a sleeve, 8 is a movable electrode tip, 9 is a bracket, and 10 encoders. , 11 are welding transformers

Claims (2)

[Claims] 1. The method according to claim 1, wherein the spot welding is performed continuously.
At the end of welding or immediately before the start of energization, the amount of electrode wear is measured while the electrode tip is sandwiching the workpiece, and feedback control is performed based on the measured value to perform the starting point and / or the deceleration start point of the electrode tip and the electrode application. An electric resistance welding method, which corrects a displacement of a pressure start point in real time. 2. A resistance spot welding machine in which an electrode tip is pressurized by a servomotor to press and energize and weld a work sandwiched between the electrode tips to weld the electrode position at the end of the welding in the servomotor. The amount of electrode wear is calculated by comparing the detected value with the reference value when the electrode tip is new, and the deceleration start position and welding pressure are applied just before the next welding point. A control device for an electric resistance welding machine, wherein the position is corrected by an amount corresponding to the electrode wear amount.