Thermal imaging & vision systems
of “21700 cells”, but not at this speed, adaptability, and with these high precision requirements. Our engineers found a solution to the first challenge. We have a lot of experience with global laser processes. We knew that the entire system, including the laser welding and the fast, adaptable clamping had to be considered as a single system. For the second challenge, precise and fast work, we rely on machine vision technology and MVTec’s HALCON machine vision software. The soft- ware works at top speed, is very precise and allow us to get close to our 100 per cent detection goal,” explains Keven Tremblay, product line manager at Laserax.
FOUR ROBOTS OPTIMISE WELDING OF THE CURRENT COLLECTOR TO THE MODULE But how does the interaction of laser-welding and robotic clamping in cooperation with machine vision enable such a process improvement? In the first step of the workflow, a module is delivered to the system and fed into the “Battery Welding Machine” through an opening on the side. There are four robots that carry out the busbar clamping and one gantry-mounted laser head with larger field of view to perform the laser welding. Two cameras are attached to the side of the laser scan head to allow 3D stereoscopic vision. In the first step, the two cameras take high-resolution images of the battery module on a 400 x 400 mm area from above. The HALCON machine vision software then calculates the X-Y-Z positions of all the cells by merging the images from the two cameras. The coor- dinates determined in this way are transmitted to the clamping robots and the laser system. The precise posi- tion of each spot to be welded on the cells is found and
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determined with an accuracy that allows global weld position to cell of +/-100µm.
The robots clamp the current collectors onto the cells, while the laser welds the clamped compo- nents one after the other. The machine works with four robots in order to maximise the operating time of the laser. This is where the robots demon- strate their specific strength in this laser welding machine, as they allow to weld each cell in less than 100ms. Weld quality monitoring is performed in real time during the welding process using a dedicated sensor for this purpose that capture the emitted light form the process.
THE TASK FOR MACHINE VISION: COMMUNICATING THE WELDING POINTS TO THE ROBOTS QUICKLY AND PRECISELY The task of the machine vision software is to find the position of the welding points and transform the corresponding points into the coordinate system of the four robots. This is not so easy in this case, as Tremblay explains: “The workspace of 400 x 400 mm is quite large, therefore determining the individual positions in the µm range is technologically extremely challenging.” In the first step, the HALCON machine vision software is used to detect objects with an accu- racy that can reach the sub-pixel level. This enables the “Battery Welding Machine” to find the areas to be welded precisely, robustly, and very quickly and determine the positions. Based on that, a coordinate system can be created for the robot using hand-eye calibration. This must be done in advance to ensure that the robots hit the relevant points precisely during
operation. During hand-eye calibration, a calibration plate is used initially to calibrate the machine in real- life measurement. The calibrated camera images are then used to calibrate the robots. The machine uses the clamping tools attached to the robot’s gripper arm and placed in the camera’s field of view to perform the robot calibration. Several images with different posi- tions of the robot are then taken and offset against the robot’s axis positions. The result is a “common” coordinate system of camera and robot. In this way, the robot hits the exact positions that were previously detected by the camera.
LASER WELDING BASED ON MACHINE VISION: MORE ENERGY FOR BATTERY PRODUCTION
“The “Battery Welding Machine” is now being used by our customers. The feedback we have received has been consistently positive. Above all, our customers appreciate the fact that they can now produce much faster and maintain quality and versatility. This means that our solution has hit the nail on the head,” says a delighted Tremblay at Laserax. The company is already planning its next developments based on laser welding and machine vision. “In particular, 3D vision and reliable pattern recognition will be explored further. We are looking for a highly reli- able and consistent localisation option for specific features. This in turn is the basis for our high-precision laser processes,” explains Tremblay.
MVTec Software
www.mvtec.com
November 2024 Instrumentation Monthly
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