This paper applies a combined precision stage to fabricate micro-structures by two-photon polymerization (TPP). The combined stage consists of PZT and stepper-motor stages to achieve precision positioning in long displacements. First, we derive the models of the stages by identification experiments. Second, we apply robust loop-shaping techniques to improve the positioning performance of the stages. Third, we integrate the stages and develop a multi-loop control structure to provide long-stroke and high precision. In addition, we propose coordinate transformation and anti-locking functions for further improvement of the system performance. Last, we apply the combined stage to a TPP system for fabricating micro-structures, and define performance indexes based on image processing and optical qualities. The obtained performance criteria can be used to adjust controller design to improve precision manufacturing.

Abstract:We report on high precision high speed micromachining of Al2O3 and AlN using pulsed near infrared fiber laser. Ablation thresholds are determined to be 30 J/cm 2 for alumina and 18 J/cm 2 for aluminum nitride. The factors influencing the efficiency and quality of 3D micromachining, namely the surface roughness, the material removal rate and the ablation depth accuracy are determined as a function of laser repetition rate and pulse overlap. Using a fluence of 64 J/cm², we achieve a material removal rate of up to 94 mm³/h in Al2O3 and 135 mm³/h in AlN for high pulse overlaps (89% and 84%). A minimum roughness of 1.5 μm for alumina and 1.65 μm for aluminum nitride can be accomplished for medium pulse overlaps (42% to 56%). In addition, ablation depth deviation of the micromachining process of smaller than 8% for alumina and 2% for aluminum nitride are achieved. Based on these results, by structuring exemplarily 3D structures we demonstrate the potential of high quality and efficient 3D micromachining using pulsed fiber laser.