[Paper Review] Process Monitoring of Extrusion Based 3D Printing via Laser Scanning

Matthias G.R. Faes, Frederik Vogeler+5 more|arXiv (Cornell University)|Jan 1, 2014

Additive Manufacturing and 3D Printing Technologies5 references32 citations

TL;DR

This paper proposes a real-time process monitoring system for extrusion-based 3D printing using a 2D laser triangulation scanner to detect geometric deviations during printing. The system measures extruded track width and height with ~10 µm accuracy, enabling online feedback to correct layer thickness errors and support a zero-defect manufacturing strategy.

ABSTRACT

Extrusion based 3D Printing (E3DP) is an Additive Manufacturing (AM) technique that extrudes thermoplastic polymer in order to build up components using a layerwise approach. Hereby, AM typically requires long production times in comparison to mass production processes such as Injection Molding. Failures during the AM process are often only noticed after build completion and frequently lead to part rejection because of dimensional inaccuracy or lack of mechanical performance, resulting in an important loss of time and material. A solution to improve the accuracy and robustness of a manufacturing technology is the integration of sensors to monitor and control process state-variables online. In this way, errors can be rapidly detected and possibly compensated at an early stage. To achieve this, we integrated a modular 2D laser triangulation scanner into an E3DP machine and analyzed feedback signals. A 2D laser triangulation scanner was selected here owing to the very compact size, achievable accuracy and the possibility of capturing geometrical 3D data. Thus, our implemented system is able to provide both quantitative and qualitative information. Also, in this work, first steps towards the development of a quality control loop for E3DP processes are presented and opportunities are discussed.

Motivation & Objective

• To develop a real-time monitoring system for extrusion-based 3D printing to detect geometric deviations during layer deposition.
• To integrate a compact 2D laser triangulation sensor into an FDM 3D printer for online measurement of track geometry.
• To enable closed-loop feedback control by using measured deviations to adjust layer thickness or re-slice the CAD model dynamically.
• To support the Zero Defect Additive Manufacturing vision by detecting and correcting errors early in the build process.
• To validate the feasibility of online process control using laser-based geometric sensing in FDM printing.

Proposed method

• A modular 2D laser triangulation scanner was integrated into an extrusion-based 3D printer to capture real-time 3D profile data of deposited thermoplastic tracks.
• Laser line profiles were extracted from images and fitted to ellipses to determine track width and height with sub-micron precision.
• Measurement errors were analyzed across different thermoplastic materials (PLA, ABS) to assess material-dependent light diffusion effects.
• The system was tested on various materials, with error analysis showing average deviations of 8.55 µm, peaking at 13.86 µm for translucent white ABS.
• Feedback strategies were proposed, including dynamic layer thickness adjustment via feed rate or movement speed control, and real-time re-slicing of the CAD model.
• The approach supports both compensation (feedback mode) and prediction (forward mode) for quality control in additive manufacturing.

Experimental results

Research questions

• RQ1 Can a 2D laser triangulation system detect geometric deviations in extruded thermoplastic tracks with sufficient accuracy for real-time process control in FDM?
• RQ2 How do material properties such as color and translucency affect laser measurement accuracy due to light diffusion?
• RQ3 What are the most effective feedback strategies to correct z-direction errors during layer-by-layer 3D printing?
• RQ4 Can online monitoring enable a closed-loop control system that reduces dimensional inaccuracy and prevents part rejection?
• RQ5 How can laser-based geometric sensing be integrated into existing FDM systems to support zero-defect manufacturing?

Key findings

• The laser triangulation system achieved a measurement accuracy of approximately 10 µm, with average error across materials at 8.55 µm.
• The gray ABS material showed the most favorable measurement performance (6.15 µm average error), while translucent materials like white ABS exhibited higher errors (13.86 µm) due to light diffusion.
• The system successfully captured real-time 3D profiles of extruded tracks and enabled detection of geometric deviations during printing.
• The highest measurement error was observed on translucent materials, indicating that material optical properties significantly affect sensor accuracy.
• Proposed feedback strategies include dynamic adjustment of layer thickness via feed rate or movement speed, and real-time re-slicing of the CAD model to correct deviations.
• The study demonstrates the feasibility of integrating laser-based geometric sensing into FDM systems to enable real-time quality control and support zero-defect manufacturing.