NEW APPROACHES TO SOFT MULTIDIMENSIONAL ACTUATION BY HARNESSING PROGRAMMED POROSITY

In the last decade, soft machines have rapidly reached a sufficient degree of maturity, due to their undeniable usefulness and effectiveness in robotic applications. They outperform conventional rigid-body robots in terms of compliance, deformability, versatility, or adaptability. At the heart of this success is the strong potential of exploring a plethora of new bioinspired designs, much like living organisms, which strongly engage in rapid adaptation to unexpected environments and real-world operations. Indeed, the proboscis, consisting of a robust muscular hydrostat with extremely high flexibility and a nearly infinite degrees of freedom, represents a remarkable example of a boneless continuum arm capable of unprecedented dexterity and versatility. It can passively reduce the transverse deflections, while transmitting the stress (force) to desired regimes and controlling its shape by limiting or resisting deformations. This compliant, yet strong, multifunctional organ introduces new challenges for soft continuum robots. Among them, one main challenge consists in accomplishing continuity in actuated soft bodies with no sharp distinction or edges among components or regions of different stiffness. This thesis addresses this open challenge by investigating inherent characteristics of constitutive materials, fabrication technologies (polylithic versus monolithic constructions), and new design principles. The work focuses on porous matter enabling compressible strain via equivalent stiffness in parallel and/or series. First, by exploiting low-cost moulding and casting fabrication, a polyurethane-based open-cell foam is employed to develop ultralight hybrid pneumatic artificial muscles (UH-PAMs). Then, inductive sensing is embedded, and proprioceptive sensory feedback is demonstrated. In contrast to such polyurethane foam capable of uniaxial (compressive) strain, soft 3D architected materials (also called metamaterials) have a strong potential due to aperiodically or periodically arranged unit air cells allowing for either enhanced or programmed deformations in continuum soft bodies. Innovative design strategies for programmable and optimized deformation, while retaining continuity in an architecture, are presented. The designs are implemented in devices through a collaborative work with the Hebrew University of Jerusalem (Prof. Shlomo Magdassi) since cutting-edge 3D printing technology (i.e., Digital Light Processing) is applied by using the designs developed in this work. Finally, soft continuum actuators capable of programmed deformations based on materials that have high deformability in extension (523%) and compression (80%) by both, intrinsic characteristics (i.e., material microporosity), and design (i.e., unit grid tessellation), are presented. We build actuated monolithic continuum architectures with stiffness gradients and demonstrate their performance in a three-fingered soft gripper. The first continuum multidimensional actuator, encoding in the same structure axial and bending movements with just one actuation source, is demonstrated.