Development of a Real-Time Geometric Quality Monitoring System for Extruded Filaments of 3D Concrete Printing Construction

Extrusion-based 3D concrete printing (3DCP) is an additive manufacturing (AM) technology in the construction field and is gaining significant attention as an emerging construction method for the future. The variability in concrete composite material properties in this field poses a challenge in maintaining consistent printing quality. Furthermore, the economic and environmental costs of discarding large structures in case of printing failures are significantly higher compared to other AM technologies. These inherent characteristics highlight the critical need for real-time, in-situ quality monitoring of printed filaments during the 3DCP process. Existing studies on geometric quality monitoring techniques provide only partial information on the extruded concrete filaments, such as width or height, and some studies are limited to linear paths. Moreover, the requirements of 3DCP, such as cost, weight, installation space, minimum object distance (MOD), field of view (FOV), and maintenance, make it challenging to find suitable commercial 2D laser profile sensors. Therefore, this paper presents the design of a 2D profile sensing system tailored to meet the requirements of 3DCP and proposes an algorithm that can compute comprehensive cross-sectional information, including the width, thickness, and area of the extruded concrete filament during 3D printing. Notably, the proposed sensing system is integrated with an infinitely rotatable nozzle device on the end effector of a 3D printer robot arm, enabling continuous monitoring of extrusion in all directions along the printing path. Comprehensive experimental results from static, motion, and concrete 3D printing tests validate that the developed 2D profile sensing system is capable of performing real-time, in-situ quality monitoring in 3DCP by accurately computing filament cross-sectional shape information. Furthermore, this paper provides a comprehensive solution that includes practical calibration method along with design, offering a crucial technology for detecting defects and failures, ultimately contributing to the high-quality and safe construction of structures in 3DCP.