Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1997-04-10
1998-10-06
Font, Frank G.
Optics: measuring and testing
By polarized light examination
With light attenuation
21912434, G01B 1124, B23K 912
Patent
active
058185950
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to butt welding in which the end surfaces of two workpieces are brought into contact with each other and welded by laser beams, and particularly to a workpiece butt position detecting method preferable for butt welding of workpieces cut by shears, presses, and the like.
BACKGROUND ART
Laser welding is the art of welding by narrowing laser beams down to fine beams, and is particularly suitable for welding thin plates, having plate thickness of 2 mm or less with high accuracy. However, in the case of using laser beams for plates of thickness of 1.6 mm or less, a tolerance limit of the deviation of the position of the laser beams from the butt position is in the range of -0.2 mm to +0.2 mm; therefore, any amount of the deviation of the beams greater than the above causes poor welding. As countermeasures against the above, various kinds of methods for detecting a workpiece butt position are proposed.
First, there is a method for detecting a butt position, that is, the position of a weld line, by spraying compressed gas from the back surface of a butt portion and by detecting the gas passing the butt portion on the front surface side (for example, Japanese Patent Application Laid-open No. 59-150685). Then, there is a method for detecting a butt position by irradiating light to the butt portion by a light emitting device positioned at the back side of the workpieces and by detecting the light passing the butt portion on the front surface side (for example, Japanese Patent Application Laid-open No. 61-123494).
However, by the above-described method using compressed gas or light, a butt position cannot be detected when a gap does not exist at a butt portion (a clearance between the workpieces butted against each other). In many cases, thin plates to be welded by laser are cut by a shear or a press, and when the workpieces cut by a shear or a press are butted against each other, a butt gap is not normally produced; therefore, a method for passing compressed gas or light is not applicable.
There is a method for detecting a butt position and a butt gap by taking an image of a butt portion with a CCD camera and by conducting image processing of the light and darkness (for example, Japanese Patent Application Publication No. 3-50635, Japanese Patent Application Laid-open No. 1-99791). In this method, a weld line is extracted by processing an image taken by a CCD camera and by discriminating, from the density, a weld line forming a butt portion from the other portion.
However, when workpieces have sags at the end portions, like the workpieces cut by a shear and a press, the portions of the sags form darkness; and therefore it is extremely difficult to detect, with an accuracy within .+-.0.2 mm, an actual weld line from a dark portion having a certain width. Further, the detection of a butt portion by image processing often causes misjudgment when a flaw is on the surface of a workpiece, and has a disadvantage of a long cycle time since the processing speed is slow.
Further, there is a method for detecting the position of a butt portion by generating an eddy current at the butt portion and by detecting the eddy current with the use of a magnetic force line type of sensor, or a method for detecting a butt position from the variation of current contact resistance (for example, Japanese Patent Application Laid-open No. 59-101295, Japanese Patent Application Laid-open No. 59-150686).
However, in the above-described methods, it is difficult to detect the butt position with the above-described accuracy, and there is a disadvantage of the detecting systems being expensive.
SUMMARY OF THE INVENTION
The present invention is made to eliminate the above-described disadvantages of the conventional art, and its object is to provide a workpiece butt position detecting method for butt welding by which the butt position of workpieces having chamfered edges or sags at the ends thereof can be detected with high accuracy.
The workpiece butt position detecting method for butt welding rela
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Adachi Kaoru
Ono Kazuhiko
Font Frank G.
Komatsu Ltd.
Smith Zandra V.
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