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J R Soc Interface ; 17(168): 20200070, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32693743


The inherent force-velocity trade-off of muscles and motors can be overcome by instead loading and releasing energy in springs to power extreme movements. A key component of this paradigm is the latch that mediates the release of spring energy to power the motion. Latches have traditionally been considered as switches; they maintain spring compression in one state and allow the spring to release energy without constraint in the other. Using a mathematical model of a simplified contact latch, we reproduce this instantaneous release behaviour and also demonstrate that changing latch parameters (latch release velocity and radius) can reduce and delay the energy released by the spring. We identify a critical threshold between instantaneous and delayed release that depends on the latch, spring, and mass of the system. Systems with stiff springs and small mass can attain a wide range of output performance, including instantaneous behaviour, by changing latch release velocity. We validate this model in both a physical experiment as well as with data from the Dracula ant, Mystrium camillae, and propose that latch release velocity can be used in both engineering and biological systems to control energy output.

Bioinspir Biomim ; 15(5): 055005, 2020 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-32580172


Gram-scale insects, such as cockroaches, take advantage of the mechanical properties of the musculoskeletal system to enable rapid and robust running. Engineering gram-scale robots, much like their biological counterparts, comes with inherent constraints on resources due to their small sizes. Resource-constrained robots are generally limited in their computational complexity, making controlled, high-speed locomotion a challenge, especially in unstructured environments. In this paper we show that embedding control into the leg mechanics of robots, similarly to cockroaches, results in predictable dynamics from an open-loop control strategy that can be modified through material choice. Tuning the mechanical properties of gram-scale robot legs promotes high-speed, stable running, reducing the need for active control. We utilize a torque-driven damped spring-loaded inverted pendulum model to explore the behavior and the design space of a spring-damper leg at this scale. The resulting design maps show the trade-offs in performance goals, such as speed and efficiency, with stability, as well as the sensitivity in performance to the leg properties and the control input. Finally, we demonstrate experimental results with magnetically actuated quadrupedal gram-scale robots, incorporating viscoelastic legs and demonstrating speeds up to 11.7 body lengths per second.

Soft Robot ; 7(1): 59-67, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-31460833


Multimaterial mechanisms are seen throughout natural organisms across all length scales. The different materials in their bodies, from rigid, structural materials to soft, elastic materials, enable mobility in complex environments. As robots leave the lab and begin to move in real environments, including a range of materials in 3D robotics mechanisms can help robots handle uncertainty and lessen control requirements. For the smallest robots, soft materials combined with rigid materials can facilitate large motions in compact spaces due to the increased compliance. However, integrating various material components in 3D at the microscale is a challenge. We present an approach for 3D microscale multimaterial fabrication using two-photon polymerization. Two materials with three orders of magnitude difference in Young's moduli are printed in consecutive cycles. Integrating a soft elastic material that is capable of more than 200% strain along with a rigid material has enabled the formation of hybrid elements, strongly adhered together, with layer accuracy below 3-µm resolution. We demonstrate a multilink multimaterial mechanism showing large deformation, and a 3D-printed 2-mm wingspan flapping wing mechanism, showing rapid prototyping of complex designs. This fabrication strategy can be extended to other materials, thus enhancing the functionality and complexity of small-scale robots.

Science ; 360(6387)2018 04 27.
Artigo em Inglês | MEDLINE | ID: mdl-29700237


Mechanical power limitations emerge from the physical trade-off between force and velocity. Many biological systems incorporate power-enhancing mechanisms enabling extraordinary accelerations at small sizes. We establish how power enhancement emerges through the dynamic coupling of motors, springs, and latches and reveal how each displays its own force-velocity behavior. We mathematically demonstrate a tunable performance space for spring-actuated movement that is applicable to biological and synthetic systems. Incorporating nonideal spring behavior and parameterizing latch dynamics allows the identification of critical transitions in mass and trade-offs in spring scaling, both of which offer explanations for long-observed scaling patterns in biological systems. This analysis defines the cascading challenges of power enhancement, explores their emergent effects in biological and engineered systems, and charts a pathway for higher-level analysis and synthesis of power-amplified systems.

Fenômenos Biomecânicos , Modelos Teóricos
Nano Lett ; 17(7): 4497-4501, 2017 07 12.
Artigo em Inglês | MEDLINE | ID: mdl-28617606


Additive manufacturing processes enable fabrication of complex and functional three-dimensional (3D) objects ranging from engine parts to artificial organs. Photopolymerization, which is the most versatile technology enabling such processes through 3D printing, utilizes photoinitiators that break into radicals upon light absorption. We report on a new family of photoinitiators for 3D printing based on hybrid semiconductor-metal nanoparticles. Unlike conventional photoinitiators that are consumed upon irradiation, these particles form radicals through a photocatalytic process. Light absorption by the semiconductor nanorod is followed by charge separation and electron transfer to the metal tip, enabling redox reactions to form radicals in aerobic conditions. In particular, we demonstrate their use in 3D printing in water, where they simultaneously form hydroxyl radicals for the polymerization and consume dissolved oxygen that is a known inhibitor. We also demonstrate their potential for two-photon polymerization due to their giant two-photon absorption cross section.