Electric heating – Metal heating – By arc
Patent
1990-10-17
1992-12-22
Shaw, Clifford C.
Electric heating
Metal heating
By arc
901 42, B23K 912
Patent
active
051735920
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method and apparatus for multi-layer welding using a welding robot.
BACKGROUND OF THE INVENTION
Welding robots now come into wide use since they fulfill objectives such as labor saving, quality-enhancement or improvements in environmental conditions of welding work or the like, in place of conventional welding work relying upon experiences or intuition of an operator. Among welding operations performed by the welding robot, multi-layer welding is a very important operation for reasons such as securing a strength of a welded portion but robots have many technical difficulties.
Japanese Patent Application Laid-Open (Kokai) No. 58(1983)-188572 (corresponding to U.S. Pat. No. 4,508,953) discloses a multi-layer welding operation, generally, the first layer is welded according to the tracking function, and therefore, a deviation occurs between a teaching path and an actual welding path. Even if a teaching path is used as a reference path for determining paths for the second and succeeding layers, the tracking function is necessary for the second and succeeding layers similar to the first layer. However, in the second and succeeding layers, the first layer is already filled with a bead, and therefore, a current variation cannot be obtained. Accordingly, groove position information is not known.
For this reason, a method which uses no tracking function for the second and succeeding layers stores an actual welding path when the first layer is welded and determine paths for the second and succeeding layers on the basis of the stored path. In this method, there is a method for corresponding the locus when the first layer is welded to instructed points of the teaching path to store it as a point having passed during the actual welding and generating an actual welding path at the stored point, as proposed in the aforesaid Japanese Patent Application Laid-Open (Kokai) No. 58(1983)-188572.
However, when generally, the tracking function is used, a welding torch follows an actual welding line with unevenness under the tracking conditions, and therefore, in the aforesaid method, case where the actual welding path is defined merely on the basis of the point having passed during actual welding, that is, in the case where the instructed points are defined by two passed point, said unevenness becomes included in data of the passed points, and as a result, an error occurs between original welding lines.
More specifically, as shown in FIG. 1, an error occurs in the obtained actual welding path (indicated at the broken line between x and x) irrespective of the presence or absence of a positional deviation between the instructed path and the actual welding line (a curve indicated by the solid line). Accordingly, if the actual welding path is defined by the conventional method to determine paths of the second and succeeding layers using the actual welding path as a reference, an error in the first layer becomes included in the final layer.
As the way for obtaining an operational locus of the second and succeeding layers, Japanese Patent Application Laid-Open (Kokai) No. 58(1983)-187270 discloses a method for storing the operational locus of the first layer in a memory of a robot control device, providing a shift width .DELTA.S as a parameter in an arithmetic processor of the robot control device to obtain the shift direction of the second and succeeding layers from the stored data of the first layer, and obtaining the operational locus of the second and succeeding layers from said shift width to carry out the multi-layer welding.
The aforesaid method is a method comprising teaching within an X-Y plane and having a restriction of setting of a shift amount which is accurate and only in one direction.
However, actually, in the welding operation by the robot, there are present three-dimensional errors due to reasons such as occurrences of an error in work setting, a thermal strain during welding, an error in temporary welding and the like, and therefore, the welding locus can
REFERENCES:
patent: 4508953 (1985-04-01), Murakami et al.
patent: 4979127 (1990-12-01), Mizuno et al.
Nakazato Tatsumi
Okumura Shinji
Takaoka Keiichi
Kabushiki Kaisha Yaskawa Denki Seisakusho
Shaw Clifford C.
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