Joint Design for 3-D Printing Non-Assembly Mechanisms

Abstract

The layer-based additive manufacturing (AM) processes can directly fabricate sub-systems with multiple components during the building process. Novel applications in robotics and many others have been demonstrated by removing the need of component assembly. However, the AM processes also have inferior accuracy compared to the Computer Numerical Control (CNC) machining process. Hence the joint clearance that can be achieved in a 3D-printed mechanism is large. This would significantly limit the use of AM in directly building movable sub-systems without further assembly operations after the building process. To reduce the joint clearance, we present a novel joint design by considering the fabrication limitation of AM processes. A novel marker structure is developed for various types of joints including cylindrical pin joints. The relation of the marker design and the rotation performance of the 3D-printed joint is modeled. Test cases based on the Stereolithography Apparatus (SLA) process have been performed to verify the effectiveness of the developed joint design. Compared to the traditional pin joint design, the new design can achieve a smaller clearance during rotation while still be able to be fabricated by the SLA process. Consequently its rotation performance can be improved.