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ABSTRACT Small organisms use propulsive springs rather than muscles to repeatedly actuate high acceleration movements, even when constrained to tiny displacements and limited by inertial forces. Through integration of a large kinematic dataset, measurements of elastic recoil, energetic math modeling and dynamic math modeling, we tested how trap-jaw ants (Odontomachus brunneus) utilize multiple elastic structures to develop ultrafast and precise mandible rotations at small scales. We found that O. brunneus develops torque on each mandible using an intriguing configuration of two springs: their elastic head capsule recoils to push and the recoiling muscle–apodeme unit tugs on each mandible. Mandibles achieved precise, planar, circular trajectories up to 49,100 rad s−1 (470,000 rpm) when powered by spring propulsion. Once spring propulsion ended, the mandibles moved with unconstrained and oscillatory rotation. We term this mechanism a ‘dual spring force couple’, meaning that two springs deliver energy at two locations to develop torque. Dynamic modeling revealed that dual spring force couples reduce the need for joint constraints and thereby reduce dissipative joint losses, which is essential to the repeated use of ultrafast, small systems. Dual spring force couples enable multifunctionality: trap-jaw ants use the same mechanical system to produce ultrafast, planar strikes driven by propulsive springs and for generating slow, multi-degrees of freedom mandible manipulations using muscles, rather than springs, to directly actuate the movement. Dual spring force couples are found in other systems and are likely widespread in biology. These principles can be incorporated into microrobotics to improve multifunctionality, precision and longevity of ultrafast systems.
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Dynamics and energetics of dual spring force couples in torque reversal systems
Abstract Latch-mediated spring actuation (LaMSA) systems leverage the interplay of springs and latches to rapidly accelerate a load. In biological systems, elastic energy is often distributed across multiple structures, resulting in forces applied from multiple springs. Here, we specifically examine dual spring force couples in torque reversal systems. A dual spring force couple applies forces from recoiling springs at two locations to generate torque. Torque reversal systems transition from spring loading to spring actuation through a change in torque direction. We develop a mathematical model of a dual spring force couple in a torque reversal system, where one spring is attached to the pivot point of the rigid body. During spring loading, this spring compresses to store elastic energy; during spring actuation, it recoils, driving pivot translation and contributing to rotation. We experimentally validate the model using a physical model. We then vary geometric parameters and the energy partition between the two springs to examine how these factors shape system dynamics. We show how variations in geometry and energy partition influence the rotational, translational, and coupling terms in the mathematical model. Finally, we demonstrate that the energetics of these systems must be carefully accounted for to accurately capture how potential energy is transformed into kinetic energy. We hypothesize that dual spring force couples in torque reversal systems may be prevalent in biological organisms, and that insights from this work can guide the design of spring-actuated mechanisms in robotics.
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- Award ID(s):
- 2153327
- PAR ID:
- 10645124
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Bioinspiration & Biomimetics
- ISSN:
- 1748-3182
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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