Experimental validation and characterization of a real-time metrology system for photopolymerization-based stereolithographic additive manufacturing process

Abstract

Exposure Controlled Projection Lithography (ECPL) is a stereolithography-based additive manufacturing process, curing photopolymer parts on a stationary substrate. To improve the process accuracy with a closed-loop control, an in situ interferometric curing monitoring and measurement (ICM&M) system was developed to infer the output of cured height. The authors have previously reported an ICM&M method which consists of a sensor model for the ICM&M system and online parameter estimation algorithms based on instantaneous frequency. In this paper, to validate the ICM&M method, an application program was created in MATLAB to integrate the ECPL and ICM&M systems and to acquire and analyze interferograms online. Given the limited computing power, the ECPL process interferograms were acquired real time and analyzed off-line. A series of experiments was performed curing square samples by varying exposure time and intensity. Results show that the ICM&M can provide a cost-effective measurement for cured heights with excellent accuracy and reliability, and possess decent capability of estimating lateral dimensions. The off-line ICM&M is a convincing demonstration and benchmark for the real-time ICM&M metrology, providing a comprehensive evaluation of the ICM&M system’s measurement characteristics as well as its utilities in modeling and control of the additive manufacturing process dynamics.