FEATURE: BEAM CONTROL


“The main challenge is to divide printing trajectories in a smart way, so that all lasers are used as much as possible”


gstream to the stage and the other part to the scanner. ‘We rely on the fact that third order-


limited motion will be followed exactly by the stage and the scanner,’ Schlüter explained. There is a feedback loop inside the scanner and the stage, but the feedback loop from the scanner to the stage isn’t closed: the system relies on the fact that the scanner and stage can follow the motion perfectly. ‘We have tested this capability and found that the overall accuracy of the system is determined by the accuracy of the scanner and the accuracy of the stage,’ Schlüter added. ‘There is no additional tracking error or additional control error introduced by the combined motion.’ Scanlab doesn’t provide a graphical user


interface with its software, but ACS Motion Control distributes a GUI for XL Scan. Users can program the system graphically with mark and jump commands. The XL Scan and similar products are


all complex control systems, Schlüter remarked. They require programming knowledge on the side of the user, but this is because there are numerous variables to be considered with the synchronised motion. ‘We are requested to make these scanner


systems simpler, but the problem is that we have a cycle time of 10µs, and therefore rely on programming the system in mark and jump commands that are directly sent to the trajectory control or to the RTC, depending on the system,’ Schlüter said. ‘However, we are discussing new ways of programming the RTC card, to make programming the scanner simpler.’ Scanner control is usually a key internal


knowhow of the integrator. They have software specialists that know how to program the RTC card. ‘We have requests from our Chinese


customers to provide simpler interfaces,’ Schlüter said. ‘But, the simpler the interface, the less powerful they are. One of the advantages of the RTC card is that it has almost 1,000 commands, which gives a lot of power over controlling how the beam is steered.’ An example of one of these commands


18 LASER SYSTEMS EUROPE SPRING 2020 Aerotech has recently released a five-axis laser scanner, the AGV5D, for micromachining


is the auto-laser control function, which maintains the spacing of the spots at a constant distance, regardless of the speed of the scanner. The control command works with an


ultrashort pulse-on-demand laser. ‘This increases throughput efficiency,’ said Schlüter, ‘because you can now use the laser while the scanner is accelerating or decelerating.’ XL Scan can achieve accuracy of 10µm


under certain conditions, Schlüter explained – with a focal length for the optics of 100mm and a field of view of 50 x 50mm, for example. This is limited to the size of the field of the scanner, because the focal length magnifies any error.


Scanner syncing Kildušis, at Direct Machining Control, said that the next challenge for beam control software, will be synchronising multiple scanners and multiple beams. This is already a trend in additive


manufacturing, he said, where there is a


push to print larger parts and increase printing speed. Therefore multiple galvo scanners are used at the same time to print a single part. ‘For software, the main challenge is to divide printing trajectories in a smart way, so that all lasers are used as much as possible,’ Kildušis said, making sure that the different galvos operating in the build chamber produce a uniform part. Another challenge for the beam control


software used in additive machines will be to handle the large amounts of data generated when building complex parts, Kildušis noted, for instance when lattice structures are sliced and filled with hatching lines. Scanlab has also recently introduced an open interface extension for its scan control systems, which combines process data, such as the signal of a pyrometer, with the co-ordinates of the scanner. The software gives the user a map of the temperature of a part. ‘That is something we think is useful for additive manufacturing,’ Schlüter said. l


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Five-axis machining is able to create tiny holes in materials such as silicon nitride


Aerotech


Aerotech


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