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KWD accelerates its welding process with 3D vision

28 September 2011

With great speed and an almost playful ease, the robots move between the sheet steel parts. They check, pick up, and place sheet steel in the welding station, then pick it up again and place it for additional testing. The welding system of KWD Automobiltechnik GmbH in Wolfsburg, a subsidiary of Schnellecke Group AG & Co. KG, is breaking new ground in parts production. This is due to a combination of intelligent VisionPro® 3D image processing from Cognex, modern robotics from Kuka, and sophisticated machine building from W-Plan. Under the leadership of KWD, this parts production project was implemented and Cognex has proved to be the ideal partner.

The vision-guided pick-and-place process performs both the transport and the quality control of raw materials and finished parts on the production line. The 3D vision system using VisionPro® 3D vision software from Cognex recognizes the part position and possible distortions of the side panels in the supply rack and forwards the data to the robot controller. The robot controller adapts the gripper movement to the actual position of the parts in real time. The result is increased product quality compared with controlling quality control using the human eye. Now, the working capacity of the machine operator is focused on the smooth control of the system rather than the correct loading and unloading of parts.

Precisely synchronized
The entire production and quality management process for car side panels is under the critical eye of the 3D vision system. Depending on the requirements of the job step, individual or stereo cameras record the relevant image sectors. The Cognex VisionPro 3D software delivers 3D position data in real time. The intelligent vision system is used for geometrical pattern comparison of different 2D tool sets from the comprehensive VisionPro tool library, such as PatMax®. Accurate calibration tools optimize optical distortions and synchronize the cameras with the flowing movements of the highly complex robot grippers.

In the first work step, one robot positions itself with the gripper and integrated vision system in front of the component magazine in which the small parts are arranged horizontally in a stack. It measures the position of the parts and grabs the individual parts in the correct position. The gripping is done in two steps. First, the parts are suctioned by a vacuum, whereupon pins pass into fits and secure the sheets. Meanwhile, a second robot positions itself with its two-sided gripping system and integrated 3D vision technology in front of the transport rack, in which it finds the large parts arranged in a vertical stack. The second robot checks the position of the transport lock, measures the position of the parts, and picks up the components in the correct position. Subsequently, both robots move to the loading station, a turntable, and put down the parts in the correct position and in the logical sequence.

Complete traceability
After the welding process is completed by the spot welding robot, the first and second robots perform an optical spot weld inspection. The number and location accuracy of the spot welds are inspected. The 3D vision system checks whether the welds were placed in the predefined fields. Based on the parameters of the welding control, the system examines whether the roots of the weld points are correct. The data obtained from the testing is archived and images are assigned to the associated parameters. In this way, KWD Automobiltechnik achieves complete traceability and a securely documented verification of quality.

In the final work step, the second robot removes the finished welded component and places it in the transport frame for finished parts. If the required number of finished parts is stacked in the transport frame, the signal is sent to transport logistics, which collects the full transport rack and delivers a new empty rack.

Complete checking
In addition to product control, an important service provided by the new system with Cognex VisionPro 3D is the checking of predefined sections of the system. In addition to the product itself, the 3D vision system inspects a number of initiators and end positions, such as the tensioning levers of the welding station. The transport pawls of the containers are also checked to see whether they are open or closed. Even under full load, the system achieves a marked increase in efficiency.

One of the biggest challenges in the implementation of the 3D vision system was the lighting. The individual components of the side panels do not have a defined position in the transport racks and can be twisted or tilted in a certain area. This results in constantly changing reflection behavior of the bare metal of the car’s sheet metal plates. The solution is the construction of an enclosure with white interior walls, through which white light is dispersed evenly on the metal parts with the greatest possible angle of incidence.

After a nine-month development and commissioning period, the new plant is running in three-shift operation at full speed. However, KWD Automobiltechnik is already thinking one step further. In future systems, 3D vision systems will contribute to a significant reduction in the number of initiators. This increases cost efficiency and minimizes potential sources of error.

For details, visit Cognex on-line at http://www.cognex.com
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