Coiled Shape Memory Alloy (CSMA) Actuators and Conductive Filament for the Realization of 3D Printed Robots
Soft robots and humanoids need actuators with low proﬁle, lightweight, high strain and relatively high frequency. Coiled shape memory alloy (CSMA) actuators satisfy these requirements, as SMAs are high-energy density actuators. There are a number of variables that aﬀect the performance of the CSMA actuators. We present the manufacturing, characterization and simulation of the NiTi based CSMA actuators mainly focusing on the geometry and performance relationships. The manufacturing technique resulted in 80% strain with respect to loaded length and greater than 1000% with respect to original length, when actuated with an input voltage of 3.4 V, 0.66 A, and 6 MPa load. The strain response at different frequency was determined experimentally and these actuators can be used in many soft robots. To improve actuation speed, a novel 2-step hot-cold water-cooling was implemented. One of the requirements of fully functional 3D printed robots is electrical connections in some part of the printed structure. To this eﬀort, we present composite materials consisting of conductive carbon nanoparticles, thermoplastics, and solvents to create ﬁlaments for 3D printing. The mechanical and electrical properties of ﬁlaments were investigated using a concentration of 0 − 15% weight of carbon nanoparticles (NC) in polylactide (PLA) using dichloromethane (DCM) solvent and subsequently, the DCM is evaporated by drying. The electrical conductivity of the composite ﬁlament is compared with commercial and academia counterparts. To demonstrate the application of CSMA, three devices /systems are presented in this study. The ﬁrst one is the actuation of an artiﬁcial musculoskeletal (MS) system that can be used as a building block for bioinspired soft robots. The second one is a soft robotic pump inspired by the pumping action of a biological heart. The soft artiﬁcial heart can be used in a humanoid robot with facial expressions and can simulate someone blushing or angry by circulating a blood-like ﬂuid. Diﬀerent designs and their characterization are presented both experimentally and via simulations. The third application is a coronary artery stent. In this work, we performed a case study on the double helix coiled SMA for use as a stent to overcome the mechanical failure due to stress concentration in existing stents. Simulation and experiments were conducted using hyperelastic silicone rubber that mimics the human coronary arteries.