Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
1999-08-09
2001-03-13
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S086610
Reexamination Certificate
active
06201206
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of detecting wear amount of welding gun electrodes and a welding method in a welding robot having a welding gun attached to an end of its robot arm for holding an object to be welded with a fixed-side electrode and a moving-side electrode opposite to the fixed-side electrode and moving driven by a servomotor or an air cylinder to hold with pressure the object to be welded.
BACKGROUND ART
Conventionally, in a welding robot having a resistance welding gun attached to an end of its robot arm, a moving-side electrode is moved by a driving source such as an air cylinder or a servomotor (gun axis servomotor) to hold an object to be welded together with a fixed-side electrode which forms a pair, the object is held with pressure, and a high-current is passed for performing welding. Since both of the paired electrodes are gradually worn due to pressure and welding heat at welding, it has been necessary to detect amounts of wear of the electrodes during operation of the robot to correct positions of the electrodes.
As a method for correcting positions of the electrodes, an equalizing mechanism (mechanism which is usually fixed, but the fixation is released at the application of pressure to move a welding gun supported by a spring to an optimal position) is provided, or a method described in JP-A-7-284957 is employed.
However, the equalizing mechanism has a disadvantage of being expensive. Additionally, the method in JP-A-7-284957 has a problem that distribution of a wear amount is previously determined, or a wear amount of a fixed-side electrode is obtained by subtracting a wear amount of a moving-side electrode from an entire wear amount (fixed-side electrode plus moving-side electrode), in which the former method is not of high accuracy and the latter method is complicated since it involves a two-step procedure.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a method of detecting wear amount of welding gun electrodes that simply detects wear amounts of electrodes without requiring an equalizing mechanism.
It is another object of the present invention to provide a welding method which eliminates the need for an equalizing mechanism.
The wearing detecting method according to the present invention comprises the steps of:
fixing a plate-shaped jig between the fixed-side electrode and the moving-side electrode;
controlling, before either of the electrodes is worn,the robot such that the end of the arm moves by an external force only in the direction the moving-side electrode moves, then moving the moving-side electrode toward the jig, and after the moving-side electrode comes into contact with the jig, pressing the moving-side electrode against the jig with a constant force such that the end of the arm moves in a direction opposite to the direction in which the moving-side electrode moves with a counterforce;
acquiring a position of the robot and a position of the gun-axis servomotor in a predetermined coordinate system as reference positions respectively when the jig is held between the moving-side electrode and the fixed-side electrode;
acquiring thereafter a position of the robot and a position of the gun-axis servomotor in the coordinate system in a similar manner; and
calculating a wear amount of the fixed-side electrode and a wear amount of the moving-side electrode from a difference between the present position of the robot and the reference position of the robot and a difference between the present position of the gun-axis servomotor and the reference position of the gun-axis servomotor, respectively.
The use of a fixed jig with actually pressurized between the moving-side electrode and the fixed-side electrode to detect wear amounts of the electrodes, makes it possible to detect wear amounts with a simple procedure and at a higher accuracy.
A welding method according to the present invention comprises the steps of:
fixing a workpiece between the fixed-side electrode and the moving-side electrode;
controlling the robot such that the end of the arm moves by an external force only in the direction the moving-side electrode moves, then moving the moving-side electrode toward the workpiece, and after the moving-side electrode comes into contact with the workpiece, pressing the moving-side electrode against the workpiece with a constant force such that the end of the arm moves in the direction opposite to the direction in which the moving-side electrode moves with a counterforce;
causing the workpiece to be held between the moving-side electrode and the fixed-side electrode and performing welding; and
releasing the holding with pressure for the workpiece to return the moving-side electrode to its original position.
In short, in the method of detecting wear amount of welding gun electrodes, the use of a workpiece as a jig and performing operations except for wear amount detection (position detection) at a higher speed, realizes an equalizing operation. The equalizing operation by a robot eliminates a need of a fixed-side chip to be abutted on a workpiece for teaching, even in a gun having no equalizing mechanism, thus realizing teaching similarly to a gun with an equalizing mechanism. This substantially facilitates teaching and eliminates the need for wear correction. In this case, a driving source for the moving-side electrode may be a gun axis servomotor or an air cylinder.
REFERENCES:
patent: 4352971 (1982-10-01), Slade
patent: 4841113 (1989-06-01), Hamada et al.
patent: 4912294 (1990-03-01), Tsujii
patent: 4999475 (1991-03-01), Yasuge
patent: 5340960 (1994-08-01), Takasaki et al.
patent: 7-284957 (1995-10-01), None
patent: 9-150278 (1997-06-01), None
patent: 10-99973 (1998-04-01), None
patent: 10-156546 (1998-06-01), None
Kabushiki Kaisha Yaskawa Denki
Oblon, Spivak, McClelland & Neustadt, P.C.
Shaw Clifford C.
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