Oscillation Compensation in On-The-Fly Laser Processing via Optical Tracking Sensors

In today’s industrial solar cell production, laserprocessing is a standard technology and will remain important for future developments, such as silver-free solar cell concepts. High throughput laser processing of more than 10.000 wafers per hour with a high precision of 10 to 100 μm is required. Current laser systems use complex automation and transport systems for accurate positioning. However, these systems are costly, large, and have limited throughput. On-the-fly laser processing, with wafers processed on a conveyor belt, offers a compact and cost-effective high-throughput approach. However, its accuracy is limited by transport imprecision.
To achieve both high throughput and accuracy, we propose a novel system concept that uses real-time measurement of speed fluctuations to adjust the beam position in feed-forward control of the laser scanner. An FPGA-based array of optical tracking sensors was developed and used in an on-the-fly demonstrator setup. The sensor’s accuracy is characterized and demonstrated in a one-dimensional oscillation compensation. Structural deviations of the laser markings are reduced from 82.2 to 13.2 μm (1 σ), a six-fold improvement. Thereby, sampling delay limits the control bandwidth. Offline analysis shows that Kalman filtering could compensate for this, and still reduce the estimation uncertainty by 23%.
Note to practitioners: We demonstrate a compact and robust laser processing system for solar cells in motion, compatible with high-speed beam delivery. Instead of depending on highprecision transport systems, our approach actively controls the beam position to offset speed fluctuations. A prototype was created using an array of optical tracking sensors that measure the workpiece’s speed on its surface. This setup generates an encoder signal for the laser scanner, which adjusts the laser beam’s position in real time. Advantageous are the high sampling rate of the sensors and low latency, achieved through parallel sampling via an FPGA. This approach could also be adapted for other applications involving high throughput laser processing.