Novel Soft-Rigid Hybrid Robotics Approach Enabled via Multilayered Bellow-type Soft Pneumatic Actuator

Abstract

Soft robotics is an emerging field characterized by compliant and adaptable structures, presents unique challenges and opportunities for technological advancements. The thesis provided herein aimed to explore various soft robotic actuators and address critical limitations by proposing a novel Soft-Rigid Hybrid (SRH) approach. The study encompassed ideation, conceptualization, investigation, and the sharing of a multi-staged development of SRH robotics approach.

Following an extensive literature review and analysis of various soft actuators, multilayered bellow-shaped soft pneumatic actuators (MBSPAs) were selected as a basis for investigation, for their for their potential compatibility with the SRH approach. The first stage of development involved a thorough examination of the working principles and fabrication methods for layered soft pneumatic actuators, leading to the creation of the Thermoplastic Polyurethane Multilayered Bellow-shaped Soft Pneumatic Actuator (TPU-MBSPA). The TPU-MBSPA demonstrated highly efficient displacement motion, with key design variables and fabrication details documented in the thesis and submitted as a journal article to contribute to the expanding field of soft robotics. To further advance our understanding of the TPU-MBSPA and facilitate numerical simulations, extensive material characterization was conducted. Uniaxial tensile tests and additional investigations were employed to validate simplifications, isotropicity, and temperature independence. A numerical simulation model, based on experimentally obtained material data, accurately predicted the expansion performance of the TPU-MBSPA. Additional exploration of an alternative application as a displacement sensor showcased the versatility and potential applications of the TPU-MBSPA beyond its primary function.

With the TPU-MBSPA as the foundation, the study progressed to address limitations in the state-of-the-art soft grippers by introducing SRH Revolute Joint Actuator (SRH-RJA) and SRH Prismatic Joint Actuator (SRH-PJA). Detailed philosophies, designs, and constructions of these joint actuators were presented. Through iterative designs, the occurrence of radial bulging in SRH-RJA was mitigated using bio-inspired armadillo-casing and embedded casing methods, leading to significant improvements in force output. The choice of materials for the rigid components was justified based on practicality. The novelty, efficiency, and superiority of the proposed joint actuators were extensively evaluated through quasi-static displacement characterization, blocked-force output analysis, and variable joint-stiffness assessments. These key characteristics were compared with other soft-rigid hybrid robots in the literature. Additional tests, including frequency-based displacement characteristics, durability assessments with life cycle testing up to 25,000 cycles, force output, stiffness, and power density, further validated the performance of the joint actuators. Furthermore, a proof-of-concept 3-point SRH Gripper (SRHG) demonstrated the manipulative capabilities, varied joint stiffness, and compliance when handling objects of diverse sizes, weights, and stiffness.

Leveraging the modular capability of the SRH joint actuators, a naturally compliant dexterous anthropomorphic hand was designed using the Modular SRH (MSRH) approach. By capitalizing on each SRH-RJA's active degrees of freedom (DOF), the MSRH hand offered up to 21 actively controlled DOF, making it highly adaptable and suitable for physical human-robot interaction (pHRI) while maintaining structural rigidity with the usage of rigid skeletons. The design, fabrication, and evaluation of the first MSRH prototype were presented, highlighting its lightweight and low manufacturing costs. The pneumatic soft robotic actuators provided flexibility in choosing the number of controlled DOF and joint coupling, enabling innovative solutions to spatial constraints in robotic hand design.

Finally, a preliminary pneumatic control strategy was investigated to pave the way for practical applications of the SRH approach in future fully automated systems. Adaptive control methods were studied for a 1-DOF SRH-RJA, demonstrating their potential for accurately tracking desired angular displacements of the soft-rigid hybrid actuator.

Overall, this thesis successfully provided valuable insights, demonstrations, and promising results for the proposed SRH approach in soft robotics. The comprehensive study not only established a precedent for the development of SRH robots but also contributed novel methods and procedures to expand knowledge in this emerging research field. The SRH approach holds significant potential for a wide range of applications, including delicate object handling in industries like agriculture, encouraging safe and efficient automated harvesting.