Welding head and method for joining a workpiece

Abstract

A method for joining a workpiece by means of a welding head, in which at least one line of light is generated on a workpiece, which crosses a joint line at a site to be joined and a joint seam generated at a joined site after processing. The lines of light are imaged at the site to be joined and at the joined site in order to generate reference data relating to the geometry of the site to be joined and measurement data relating to the geometry of the joined sites. The reference data and the measurement data are then compared at one and the same workpiece site before and after processing, in order to determine the geometry of the joint seam independently of the geometry of the site to be joined.

1 . A welding head for joining a workpiece, comprising:
 a welding device which is adapted to weld a joint site of the workpiece to be processed inside a working region,   a light section device which is attached to the welding device and has at least one light source for generating at least one line of light inside the working region on the workpiece, which crosses a joint line at a site to be joined and a joint seam generated at a joined site after processing by the welding device,   at least one camera for observing the working region of the workpiece to be processed, which images the line of light at the site to be joined and the line of light at the joined site at regular time intervals, in order to generate reference data (DataR(t)) relating to the geometry of the site to be joined and measurement data (DataM(t)) relating to the geometry of the joined site with a joint seam, and   a processing unit for receiving the reference data (DataR(t)) and measurement data (DataM(t)) from the at least one camera and for comparing the reference data (DataR(t)) and measurement data (DataM(t)) respectively at the same workpiece site before and after processing by the welding device, so that the geometry of the joint seam can be determined independently of the geometry of the site to be joined.   
     
     
         2 . The welding head as claimed in  claim 1 , wherein the welding device is a metal shielding gas welding device. 
     
     
         3 . The welding head as claimed in  claim 2 , wherein the at least one camera is attached to an outer side of the welding device. 
     
     
         4 . The welding head as claimed in  claim 1 , wherein the welding device comprises a housing, through which a beam path for a laser beam is formed and which has focusing optics for focusing the laser beam onto the joint site of the workpiece to be processed inside the working region. 
     
     
         5 . The welding head as claimed  claim 1 , wherein the processing unit comprises the following:
 a buffer memory for temporarily storing the received reference data;   a comparator for comparing the measurement data (DataM(t)) at a respective first instant (t 1 ) with the reference data (DataR(t)) at a respective second instant (t 2 ), the respective first (t 1 ) and second (t 2 ) instants respectively having a predetermined time difference (Δt); and   an integrator for determining the respective predetermined time difference (Δt) by means of integration of the joining speed (v(t)) with respect to time and comparing the calculated joining displacement with the predetermined distance (d) between the line of light sections.   
     
     
         6 . The welding head as claimed in  claim 1 , wherein the light section device comprises a first light fan device having a first light source for generating a straight line of light, which crosses the joint line at the site to be joined, and a second light fan device having a second light source for generating a straight line of light on the workpiece, which crosses the joint seam at the joined site. 
     
     
         7 . The welding head as claimed in  claim 6 , wherein the straight lines of light of the first and second light fan devices, which are generated on the workpiece, extend mutually parallel. 
     
     
         8 . The welding head as claimed in  claim 6 , wherein the first and second light fan devices are arranged with respect to one another so that the light fan of the first light source and the light fan of the second light source respectively strike the workpiece to be processed obliquely with respect to the optical axis (L) of the laser beam, so that a distance between the welding device and the workpiece can be determined by means of triangulation. 
     
     
         9 . The welding head as claimed in  claim 8 , wherein the light fans of the first light source and of the second light source are arranged with respect to one another so that they converge with one another starting from the respective light sources. 
     
     
         10 . The welding head as claimed in  claim 7 , further comprising a control unit which regulates the distance between the welding device and the workpiece to a constant value by determining the distance (d) between the mutually parallel lines of light of the first and second light fan devices. 
     
     
         11 . The welding head as claimed in  claim 1 , wherein the at least one camera is a CMOS camera. 
     
     
         12 . The welding head as claimed in  claim 4 , having a beam splitter by which an observation beam path of the camera can be coupled coaxially into the laser beam path. 
     
     
         13 . The welding head as claimed in  claim 6 , wherein the first and second light sources are lasers, in particular semiconductor lasers. 
     
     
         14 . The welding head as claimed in  claim 6 , wherein an optical bandpass filter, which is tuned to the wavelengths of the first and second light sources, is arranged in front of the at least one camera. 
     
     
         15 . A method for joining a workpiece by means of a welding head as claimed in  claim 1 , having the steps:
 generating at least one line of light inside a working region of the workpiece, which crosses a joint line at a site to be joined and a joint seam generated at a joined site after processing by means of the welding device at a predetermined distance (d),   imaging the lines of light at the site to be joined and at the joined site at regular time intervals by means of at least one camera, in order to generate reference data (DataR(t)) relating to the geometry of the site to be joined and measurement data (DataM(t)) relating to the geometry of the joined sites, and   processing the reference data (DataR(t)) and measurement data (DataM(t)) generated by the at least one camera by means of a processing unit, the processing comprising the comparison of the reference data (DataR(t)) and measurement data (DataM(t)) respectively at one and the same workpiece site before and after processing by the laser beam, in order to determine the geometry of the joint seam independently of the geometry of the site to be joined.   
     
     
         16 . The method as claimed in  claim 15 , the processing step further comprising:
 temporary storage of the received reference data (DataR(t));   comparison of the measurement data (DataM(t)) at a respective first instant (t 1 ) with the reference data (DataR(t)) at a respective second instant (t 2 ), the respective first (t 1 ) and second (t 2 ) instants respectively having a predetermined time difference (Δt); and   determining the respective predetermined time difference (Δt) by means of integration of the joining speed (v(t)) with respect to time and comparison of the calculated joining displacement with the predetermined distance (d) between the line of light sections.   
     
     
         17 . The method as claimed in  claim 15 , further comprising the step of regulating the distance between the welding device and the workpiece by means of triangulation.