Real-time interferometric monitoring and measuring of photopolymerization based stereolithographic additive manufacturing process: sensor model and algorithm

Abstract

As additive manufacturing is poised for growth and innovations, it faces barriers of lack of in-process metrology and control to advance into wider industry applications. The exposure controlled projection lithography (ECPL) is a layerless mask-projection stereolithographic additive manufacturing process, in which parts are fabricated from photopolymers on a stationary transparent substrate. To improve the process accuracy with closed-loop control for ECPL, this paper develops an interferometric curing monitoring and measuring (ICM&M) method which addresses the sensor modeling and algorithms issues. A physical sensor model for ICM&M is derived based on interference optics utilizing the concept of instantaneous frequency. The associated calibration procedure is outlined for ICM&M measurement accuracy. To solve the sensor model, particularly in real time, an online evolutionary parameter estimation algorithm is developed adopting moving horizon exponentially weighted Fourier curve fitting and numerical integration. As a preliminary validation, simulated real-time measurement by offline analysis of a video of interferograms acquired in the ECPL process is presented. The agreement between the cured height estimated by ICM&M and that measured by microscope indicates that the measurement principle is promising as real-time metrology for global measurement and control of the ECPL process.

A feasibility study on process monitoring and control in vat photopolymerization of ceramics

“…Zhao improved the ICM system by moving from an implicit model relating measured phase angle to cured height empirically to a parameter estimation based method using an elaborated optics model [111]. The ICM system potentially enables real-time, full-field part shape measurements for the layerless process [112].…”

Emerging scientific and industrial applications of digital holography: an overview

“…DHI methods have been used for dimensional metrology, surface topography, roughness and form measurements [18-20, 27-30, 137-142]. Application of these methods is also demonstrated for machine tools testing [47,48], photo-polymerization process [143], monitoring of fibers drawn using electrospinning process [144], as potential candidate for onsite studies. With technological advances and development of new manufacturing processes such as additive manufacturing and rapid prototyping, improved quality control and precision measurement methods are required.…”

Review on residual stress in selective laser melting additive manufacturing of alloy parts

“…This system could capture the detailed distortion characteristic of the Ti-6Al-4V single-wall parts. Compared with the method of synchrotron radiation, the technique of image analysis is more easily to be implemented as real-time feedback in a closed-loop control system [139]. A similar sensor-based real-time monitoring system can also be found in the similar work [135].…”

“…3, the means of infrared imaging, high-speed X-ray imaging, micro-diffraction and other optical detecting aided with appropriate image computation algorithms could realize on-site thermal state monitoring of the molten pool, powder layer, deposited layer, temperature field as well as the hot spot or incomplete fusion during melting and solidification. These techniques bring exciting expectations for homogenizing the surface temperature field, reducing thermal gradient and then adjusting residual stress through closed-loop feedback control of input laser energy [136,138,139,[164][165][166][167][168][169].…”