This article details steps in creating low-power artificial muscles using 3D printing. It describes a manufacturing system that can be used to fabricate seamless tubular dielectric elastomer actuators (DEA), for eventual use in biorobotic devices. The focus is on producing passive elastomeric components of DEA and the dimensional changes that occur after printing is complete. A four-axis printing system is described, capable of spray depositing multilayer tubular silicone membranes onto an air-permeable mandrel. Mechanical strain was imparted in the membranes by means of inflation. A laser measurement system was constructed to act as a 3D scanner, which measured the shape of the inflated “balloon.” The surface shape was reconstructed in software using the parametric modeling tool Grasshopper. Seamless auxetic tessellations were calculated across the entire surface, and then converted to CNC GCode. These toolpaths were then physically extruded over the surface of the balloon, stacked five layers high. When the extruded silicone structure was completely cured, the pneumatic strain was released, allowing the structure to collapse evenly. The compression in the printed structure was balanced by the tension in the stretched membranes, thus producing a minimum energy structure.

This article is the second in a two-part series describing a process for conformal 3D printing onto inflated substrates. The article describes the design and build of a custom-built four-axis 3D printer with the ability to measure the shape of any uneven substrate, and to then accurately extrude a thixotropic silicone onto the substrate by using Direct Ink Writing techniques. Details of strategies for 3D scanning a double-curved tubular inflated substrate using an industrial triangulation laser measurement device are given. Methods to import scan data and create a digital representation of the surface within the parametric design software Grasshopper 3D are explained. Geodesic print paths are created over the surface of the computed substrate, and these are the basis for calculating 3D printer toolpaths. A constant surface linear velocity strategy is developed, allowing the printer to move the print nozzle at a varying speed over the substrate surface. The change in speed is correlated with changes in the surface linear velocity of a fourth axis rotation of the variable radius balloon substrate. This ensures that the extruded bead maintains a constant thickness, even while using a constant flow rate deposition. The process is achieved by adapting cartographic techniques to re-project to the desired print paths. The efficacy of this technique is analyzed by 3D scanning a printed patterned balloon, then measuring and comparing multiple cross-sections of the extruded beading.