Development of a computer vision based real-time feedback system for closed-loop control in 3D concrete printing

Sammanfattning: With 3D concrete printing (3DCP) starting to go beyond small scale novelty projects and the aim to disrupt the construction industry, more development is needed to overcome remaining challenges and improve the processes. Quality assurance and control can be important concerns to gain the confidence of early adopters. To this point only few projects have worked on developing a feedback system that allows for real-time print result monitoring and closed-loop control. This project has set out and is focussed at moving the 3DCP technology one step closer in this direction. More specifically, closed-loop control of the extruded bead width was chosen as a target. Currently, the print result is only visually observed and manually controlled by the operator. Most print results show bead width inconsistencies that can be attributed to various external influences. A central aspect in this thesis is on using computer vision for closed-loop extrusion control. Chosen as the vision system was a laser profile scanner. The idea is to replace the visual inspection of the operator by an automated process and increase bead width consistency. The results have shown that controlling the concrete extrusion is more challenging than anticipated. While the laser profile scanner has proven as a suitable tool for bead width measurement, several limiting factors resulted in unsuccessful control approaches. Most notably, the system in combination with materials used for this project showed unstable and hard to control behaviour. In addition, a several second delay between pump speed changes and differences in extruded width plus the lack of full tangential control affected the results.  Despite the failure to effectively control the system, a number of findings were made and deeper understanding for the challenges gained. The system was not found to be uncontrollable. Instead, more dedicated control approaches in both, software and modification of hardware are suggested. The overall approach could be continued and with further time invested lead to success. The background, implementation details and findings are presented in the following report. Everything is followed and summed up by a discussion of the outcome and a conclusion on the project.