An Untethered Brittle Star-Inspired Soft Robot for Closed-Loop Underwater Locomotion

Patterson, Zach J.; Sabelhaus, Andrew P.; Chin, Keene; Hellebrekers, Tess; Majidi, Carmel

doi:10.1109/iros45743.2020.9341008

Cited by 38 publications

(41 citation statements)

References 33 publications

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“…For the kinematic design of a poly-limb underwater crawling robot, spiders are natural sources of inspiration, both for their iconic tetra- to octo-pod body structure and gaits, and for their wide range of habitats covering both on land and in water ( Wang and Wang, 2020 ; Ballesteros et al, 2021 ). The hexapod/octopod gaits of spiders with benthic-facing tarsus/metatarsus segments ( Figure 1A ) could provide excellent traction on the sediment-filled sea floor ( Zentner, 2013 ), but soft actuators with continuum flexible bodies could not reproduce such gaits, only sweeping across a spherical surface ( Patterson et al, 2020 ) rather than following a linear path ( Figure 1B ). The continuum soft body of soft actuators also makes them inherently prone to external force exertions, causing undesired deformations on non-actuating directions, as well as hindering the force output capability.…”

Section: Design Concept Of the Crawling Robot With H 2 Sa Legs And Soft Jointsmentioning

confidence: 99%

“…Soft robotics is a top-trending area, inspiring paradigm changes in robotic design and actuation, with soft-material bodies of inherent compliance being used both as structural components and as actuators ( Rus and Tolley, 2015 ; Wang et al, 2015 ; Liu et al, 2021 ). There have been many notable attempts in developing underwater soft robots, but mostly focused on the manipulation and sampling end of operations, ranging from underwater soft actuators ( Ku et al, 2009 ; Yim et al, 2007 ), wrist joint ( Kurumaya et al, 2018 ), manipulator arms ( Phillips et al, 2018 ; Gong et al, 2019 ; Shen et al, 2020 ), and underwater exploration platforms ( Patterson et al, 2020 ). These underwater soft robot designs showcased their advantages for the underwater environment: soft manipulators or grippers composed of simple structural design and modular variants could achieve both a high degree of dexterity and flexibility ( Phillips et al, 2018 ; Gong et al, 2019 ; Shen et al, 2020 ).…”

Section: Introductionmentioning

confidence: 99%

“…However, despite their success as manipulators and sampling grippers, existing underwater soft robotic limbs still require conventional robotic vehicles as mounting platforms ( Phillips et al, 2018 ; Gong et al, 2019 ; Shen et al, 2020 ), while existing soft underwater vehicles or robotic platforms are highly scarce, with highly limited payload or locomotion capabilities ( Ishida et al, 2019 ; Patterson et al, 2020 ), insufficient for carrying soft manipulators. The key bottle neck of soft robots for payload-and-precision demanding tasks such as marine benthic crawling lies in the soft actuators.…”

Section: Introductionmentioning

confidence: 99%

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Underwater Crawling Robot With Hydraulic Soft Actuators

et al. 2021

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Benthic operation plays a vital role in underwater applications, where crawling robots have advantages compared with turbine-based underwater vehicles, in locomotion accuracy, actuation efficiency, current resistance, and in carrying more payloads. On the other hand, soft robots are quickly trending in underwater robotic design, with their naturally sealed body structure and intrinsic compliance both desirable for the highly unstructured and corrosive underwater environment. However, the limitations resulting directly from the inherent compliance, in structural rigidity, actuation precision, and limited force exertion capability, have also restricted soft robots in underwater applications. To date soft robots are adopted mainly as grippers and manipulators for atraumatic sampling, rather than as locomotion platforms. In this work, we present a soft-robotic approach to designing underwater crawling robots, with three main innovations: 1) using rigid structural components to strategically reinforce the otherwise omni-directionally flexible soft actuators, drastically increasing their loading capability and actuation precision; 2) proposing a rigid–soft hybrid multi-joint leg design, with quasi-linear motion range and force exertion, while maintaining excellent passive impact compliance by exploiting the inherent flexibility of soft actuators; 3) developing a novel valve-free hydraulic actuation system with peristaltic pumps, achieving a compact, lightweight, and untethered underwater crawling robot prototype with a 5:1 payload-to-weight ratio and multi-gait capability. The prototype was tested for design verification and showcasing the advantages of the proposed hybrid mechanism and actuation approach.

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Section: Design Concept Of the Crawling Robot With H 2 Sa Legs And Soft Jointsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Underwater Crawling Robot With Hydraulic Soft Actuators

et al. 2021

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“…This approach allows for a reversible transition between compliance with its surroundings when unactuated to stiff and load-bearing when actuated [19,20]. Although SMA actuators have only been utilized in a limited number of untethered soft robots, their applicability is promising as shown by examples of bio-inspired robots that mimic aquatic [15,[21][22][23] and land-based [15,[24][25][26][27] biological organisms. However, they have two large drawbacks that serve as key bottlenecks for their use.…”

Section: Introductionmentioning

confidence: 99%

Characterization and Analysis of a Flexural Shape Memory Alloy Actuator

2021

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Shape memory alloys (SMAs) are popular as actuators for use in soft robots due to their high work density and compatibility with miniaturized on-board batteries and power electronics. However, because SMA actuators are activated through electrical Joule heating, they exhibit poor energy efficiency and low actuator frequencies that arise from long cool-down times. Moreover, in the case of SMA wires that are subject to flexural loading, their load capacity and mechanical work output decrease exponentially with decreasing cross-sectional area. In this study, we perform analytic and numerical analyses to examine the thermal and structural design space around a particular class of flexural SMA wire actuators with the intention of increasing actuator operating frequency and actuation forces. Measurements obtained through experimental testing are consistent with theoretical studies of actuator force output and provide additional insight into the efficiency of electrical-to-mechanical energy conversion. Together, the theoretical and experimental studies provide insights that have the potential to inform SMA wire design and usage in soft robotic applications.

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“…Therefore, most modeling of SMA and other electrothermal actuators occurs in artificial test setups with extensive sensing capabilities [10], [11], [13]. Bringing these electrothermal actuators into practical application, such as untethered soft robotics [14], will require accurate models that can operate within significant design and sensing constraints. rohanmeh, asabelha, cmajidi@andrew.cmu.edu Fig.…”

Section: Introductionmentioning

confidence: 99%

In-Situ Sensing and Dynamics Predictions for Electrothermally-Actuated Soft Robot Limbs

Sabelhaus,

Mehta,

Wertz

et al. 2021

Preprint

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Modeling the dynamics of soft robot limbs with electrothermal actuators is generally challenging due to thermal and mechanical hysteresis and the complex physical interactions that can arise during robot operation. This article proposes a neural network based on long short-term memory (LSTM) to address these challenges in actuator modeling. A planar soft limb, actuated by a pair of shape memory alloy (SMA) coils and containing embedded sensors for temperature and angular deflection, is used as a test platform. Data from this robot are used to train LSTM neural networks, using different combinations of sensor data, to model both unidirectional (one SMA) and bidirectional (both SMAs) motion. Open-loop rollout results show that the learned model is able to predict motions over extraordinarily long open-loop timescales (10 minutes) with little drift. Prediction errors are on the order of the soft deflection sensor's accuracy, even when using only the actuator's pulse width modulation inputs for learning. These LSTM models can be used in-situ, without extensive sensing, helping to bring soft electrothermally-actuated robots into practical application.

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An Untethered Brittle Star-Inspired Soft Robot for Closed-Loop Underwater Locomotion

Cited by 38 publications

References 33 publications

Underwater Crawling Robot With Hydraulic Soft Actuators

Underwater Crawling Robot With Hydraulic Soft Actuators

Characterization and Analysis of a Flexural Shape Memory Alloy Actuator

In-Situ Sensing and Dynamics Predictions for Electrothermally-Actuated Soft Robot Limbs

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