DOI: 10.25442/hku.29533820.v1
title: Supporting data for "Soft Actuation and Variable-Stiffness Mechanisms for Humanoid Robots"

description: Humanoid robots achieve a wide range of motions through rigid and high-performance motors. Soft robots, on the other hand, leverage material compliance and structural adaptability to achieve similar mobility while improving safety.Soft actuators have limitations. Pneumatic soft actuators are poorly integrated, typically only realize a single deformation, and rely on bulky air pumps. In practical applications, humanoid robots are highly integrated, and it remains a challenge to embed soft actuators into humanoid robots that can not only enhance interaction safety but also maintain overall performance. Therefore, the development of soft actuators, as well as variable stiffness mechanisms, for humanoid robots that strike a balance between functionality and safety, has become a research priority in the field of soft robotics.Focusing on improving the safety of human-robot interaction, this research aims to develop lightweight and variable-stiffness soft actuators suitable for robotic hands and robotic arms, as well as anti-falling variable-stiffness mechanisms for humanoid robots.First, a series of elastomer-constrained flat tube actuators (EFTAs) are proposed to realize structural preprogramming and elastic constraints by embedding folded flat tubes into a silicone rubber matrix. By adjusting the folding pattern and rubber stiffness, the EFTAs can achieve five basic motions: extension, bending, helix, twisting, and contraction. This single-material system has multimodal output capabilities, making it suitable for integration into volume- and mass-sensitive lightweight platforms such as robotic hands.Secondly, a pumpless drive mechanism is introduced where motors are used to control bellows compression and extension through cables. The bellows contract linearly along a guide bar under cable control, pushing gas into a flat tube actuator for bending motion. This mechanism effectively eliminates bulky pneumatic control and supply systems. It complements EFTAs at the structural and drive levels, thereby facilitating the application of pneumatic soft actuators in the design of compact end-effectors of humanoid robots.Thirdly, a modular antagonistic variable stiffness continuum modular robot (AVSBCR) has been proposed and prototyped using Multi Jet Fusion. Cables pass through the circumferential holes of the corrugated segment and are fixed at the end. Multiple cable combinations allow for multi-degree-of-freedom deformation. When tightening all cables simultaneously, it enhances the stiffness of the modular robot. The AVSBCR has a significant motion range, which makes it suitable for robotic arm applications that require a balance between flexibility, accuracy, and load capacity.Finally, an anti-falling mechanism is proposed for wheeled humanoid robots. The particle bag is soft under normal pressure, which allows it to absorb sudden impact effectively. When a collision or fall occurs, the deformation caused by external compression first dissipates part of the energy, and a vacuum power instantly stiffens the particle bag, generating a large conforming surface to form a support. This mechanism only requires 16% of the total robot mass, significantly reducing the falling resistance, thus improving safety.The thesis also showcases two prototyping case studies: Soft Aloha, a wheeled inflatable humanoid robot with anti-falling capabilities, and MSCRLS, a modular soft continuum robot with a lattice structure that has demonstrated versatility in robotic arms and dexterous hands.