Closed Loop Control for Cementitious Robotic Additive Manufacturing

Abstract

Additive manufacturing of cementitious materials is a growing field with major applications in construction. Research on cementitious extrusion processes and their products is necessary for advancement in the field in order to refine the technology and prepare it for widespread adoption. However, the additive manufacturing process is highly volatile with many factors affecting the final product including the environmental conditions, the material’s properties–including time dependent properties and imperfect homogeneity–and extrusion rates. This project focuses on improving the quality of the research on the products of cementitious additive manufacturing by incorporating real-time feedback. In particular, this project is an early endeavor into simultaneous control over two variables, filament width and height between the nozzle and filament, during the pressure-driven extrusion process on a SCARA (Selective Compliance Articulated Robotic Arm). This will serve to monitor the immediate results and adapt to minimize and mitigate defects in the finished product. This project required designing an assembly to be attached to the SCARA which allows an optical and depth camera to track the motions of the nozzle while always remaining downstream to the current filament extrusion. This system was implemented into the existing infrastructure for the SCARA machine for automatic operation. A computer vision algorithm was designed for this particular system to deliver the observation parameters to the PID controllers. Ultimately, the preliminary data from the system shows promise for reducing the impact poorly designed code, however the inherent system delays and trouble recognizing all frames has limited the current performance. With more development, two variable control might have the potential to outperform single variable control systems for cementitious 3D printing.