Velocity-dependent real-time screw extrusion control for the speed-adaptive robot-assisted additive manufacturing

The incessant pursuit of the large-scale, complex-geometry components catalyses the emergence of the new additive manufacturing process. The robotic-arm assisted screw-extrusion additive manufacturing (SEAM) process has been considered an ideal solution for meeting those ever-increasing demands. However, due to the lack of an integral controller, such a process faces a unique challenge to synchronise the extrusion flow with the motion. To tackle this challenge, this study proposes a velocity-dependent feedforward extrusion controller to tune the extrusion volume in real-time. This study shows that the extrusion volume of the custom-built screw-extrusion system is linearly dependent on the rotation velocity of the screw, which can be tuned by the external DC voltage signal. By extracting the velocity signal from the robotic system, the proposed extrusion controller can effectively tune the extrusion volume without accessing the robotics’ motion controller. Further micro-scale characterisation reveals that the proposed controller can significantly reduce the undesired overflow and underflow, leading to more refined surface finish and consistent wall thickness. The findings of this study not only provide a systematic and practical guideline for flow manipulation in robotic SEAM systems but also contribute to the broader field of motion-synchronised extrusion control for six-axis robotic arms.