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

In today’s industrial solar cell production, laser processing 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 overcome this, we propose a novel system using real-time measurement of speed fluctuations to adjust the beam position via feed-forward control to achieve both high throughput and accuracy. 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. Oscillatory 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%.