Image-Based Iterative Active Error Compensation for Polygon Mirror-Based Scanning Systems

This article deals with the correction of cross-scan errors in polygon mirror (PM)-based laser scanning systems by active error compensation (AEC) using a fast-steering mirror (FSM). However, AEC is susceptible to sensor noncollocation errors since the FSM is typically controlled via an internal angular sensor. This sensor error can be evaluated by position measurements of the scanning laser, but these measurements are not always feasible due to the inherent duty cycle of PM-based scanning systems. Image-based iterative AEC (II-AEC) is proposed to use partial measurements to address the sensor noncollocation error, thereby improving the precision of PM-based scanning systems. II-AEC consists of a cascade structure where the inner loop employs iterative learning control for the FSM using the internal sensor, and the outer loop iterates the inner loop reference based on the laser positions measured by a complementary metal–oxide–semiconductor (CMOS) sensor. II-AEC has been implemented and evaluated on a PM-based stereolithography apparatus, resulting in a 40-fold printing precision improvement compared to the uncompensated apparatus.