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1. Prediction of the behavior of a pneumatic soft robot based on Koopman operator theory

   https://doi.org/10.23919/MIPRO48935.2020.9245155  

   Kamenar, E.; Crnjaric-Zic, N.; Haggerty, D.; Zelenika, S.; Hawkes, E. W.; Mezic, I. (September 2020, MIPRO)

   null (Ed.)

   Thanks to their flexibility, soft robotic devices offer critical advantages over rigid robots, allowing adaptation to uncertainties in the environment. As such, soft robots enable various intriguing applications, including human-safe interaction devices, soft active rehabilitation devices, and soft grippers for pick-and-place tasks in industrial environments. In most cases, soft robots use pneumatic actuation to inflate the channels in a compliant material to obtain the movement of the structure. However, due to their flexibility and nonlinear behavior, as well as the compressibility of air, controlled movements of the soft robotic structure are difficult to attain. Obtaining physically-based mathematical models, which would enable the development of suitable control approaches for soft robots, constitutes thus a critical challenge in the field. The aim of this work is, therefore, to predict the movement of a pneumatic soft robot by using a data-driven approach based on the Koopman operator framework. The Koopman operator allows simplifying a nonlinear system by“lifting” its dynamics into a higher dimensional space, where its behavior can be accurately approximated by a linear model, thus allowing a significant reduction of the complexity of the design of the resulting controllers. 

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2. 3D Knitting for Pneumatic Soft Robotics

   https://doi.org/10.1002/adfm.202212541  

   Sanchez, Vanessa; Mahadevan, Kausalya; Ohlson, Gabrielle; Graule, Moritz_A; Yuen, Michelle_C; Teeple, Clark_B; Weaver, James_C; McCann, James; Bertoldi, Katia; Wood, Robert_J (April 2023, Advanced Functional Materials)

   Abstract Soft robots adapt passively to complex environments due to their inherent compliance, allowing them to interact safely with fragile or irregular objects and traverse uneven terrain. The vast tunability and ubiquity of textiles has enabled new soft robotic capabilities, especially in the field of wearable robots, but existing textile processing techniques (e.g., cut‐and‐sew, thermal bonding) are limited in terms of rapid, additive, accessible, and waste‐free manufacturing. While 3D knitting has the potential to address these limitations, an incomplete understanding of the impact of structure and material on knit‐scale mechanical properties and macro‐scale device performance has precluded the widespread adoption of knitted robots. In this work, the roles of knit structure and yarn material properties on textile mechanics spanning three regimes–unfolding, geometric rearrangement, and yarn stretching–are elucidated and shown to be tailorable across unique knit architectures and yarn materials. Based on this understanding, 3D knit soft actuators for extension, contraction, and bending are constructed. Combining these actuation primitives enables the monolithic fabrication of entire soft grippers and robots in a single‐step additive manufacturing procedure suitable for a variety of applications. This approach represents a first step in seamlessly “printing” conformal, low‐cost, customizable textile‐based soft robots on‐demand. 

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3. Recent advances in biomimetic soft robotics: fabrication approaches, driven strategies and applications

   https://doi.org/10.1039/D2SM01067D  

   Dong, Xiaoxiao; Luo, Xiaohang; Zhao, Hong; Qiao, Chenyu; Li, Jiapeng; Yi, Jianhong; Yang, Li; Oropeza, Francisco J.; Hu, Travis Shihao; Xu, Quan; et al (October 2022, Soft Matter)

   Compared to traditional rigid-bodied robots, soft robots are constructed using physically flexible/elastic bodies and electronics to mimic nature and enable novel applications in industry, healthcare, aviation, military, etc. Recently, the fabrication of robots on soft matter with great flexibility and compliance has enabled smooth and sophisticated ‘multi-degree-of-freedom’ 3D actuation to seamlessly interact with humans, other organisms and non-idealized environments in a highly complex and controllable manner. Herein, we summarize the fabrication approaches, driving strategies, novel applications, and future trends of soft robots. Firstly, we introduce the different fabrication approaches to prepare soft robots and compare and systematically discuss their advantages and disadvantages. Then, we present the actuator-based and material-based driving strategies of soft robotics and their characteristics. The representative applications of soft robotics in artificial intelligence, medicine, sensors, and engineering are summarized. Also, some remaining challenges and future perspectives in soft robotics are provided. This work highlights the recent advances of soft robotics in terms of functional material selection, structure design, control strategies and biomimicry, providing useful insights into the development of next-generation functional soft robotics. 

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4. Characterization of Compliant Parallelogram Links for 3D-Printed Delta Manipulators

   https://doi.org/10.1007/978-3-030-71151-1_7  

   Mannam, P.; Kroemer, O.; Temel, F. Z. (March 2021, International Symposium on Experimental Robotics)

   Siciliano, B.; Laschi, C.; Khatib, O. (Ed.)

   We design a compliant delta manipulator using 3D-printing and soft materials. Our design is different from the traditionally rigid delta robots as it is more accessible through low-cost 3D-printing, and can interact safely with its surroundings due to compliance. This work focuses on parallelogram links which are a key component of the delta robot design. We characterize these links over twelve dimensional parameters, such as beam and hinge thickness, and two material stiffness settings by displacing them, and observing the resulting forces and rotation angles. The parallelogram links are then integrated into a delta robot structure to test for delta mechanism behavior, which keeps the end-effector parallel to the base of the robot. We observed that using compliant hinges resulted in near-delta behavior, laying the groundwork for fabricating and utilizing 3D-printed compliant delta manipulators. 

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5. Biodegradable, Sustainable Hydrogel Actuators with Shape and Stiffness Morphing Capabilities via Embedded 3D Printing

   https://doi.org/10.1002/adfm.202303659  

   Sun, Wenhuan; Williamson, Avery_S; Sukhnandan, Ravesh; Majidi, Carmel; Yao, Lining; Feinberg, Adam_W; Webster‐Wood, Victoria_A (June 2023, Advanced Functional Materials)

   Abstract Despite the impressive performance of recent marine robots, many of their components are non‐biodegradable or even toxic and may negatively impact sensitive ecosystems. To overcome these limitations, biologically‐sourced hydrogels are a candidate material for marine robotics. Recent advances in embedded 3D printing have expanded the design freedom of hydrogel additive manufacturing. However, 3D printing small‐scale hydrogel‐based actuators remains challenging. In this study, Free form reversible embedding of suspended hydrogels (FRESH) printing is applied to fabricate small‐scale biologically‐derived, marine‐sourced hydraulic actuators by printing thin‐wall structures that are water‐tight and pressurizable. Calcium‐alginate hydrogels are used, a sustainable biomaterial sourced from brown seaweed. This process allows actuators to have complex shapes and internal cavities that are difficult to achieve with traditional fabrication techniques. Furthermore, it demonstrates that fabricated components are biodegradable, safely edible, and digestible by marine organisms. Finally, a reversible chelation‐crosslinking mechanism is implemented to dynamically modify alginate actuators' structural stiffness and morphology. This study expands the possible design space for biodegradable marine robots by improving the manufacturability of complex soft devices using biologically‐sourced materials. 

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