Agonist-Antagonist Pouch Motors: Bidirectional Soft Actuators Enhanced by Thermally Responsive Peltier Elements

TL;DR

The paper addresses durability and actuation bandwidth limitations of silicone-based, phase-change soft actuators by introducing Mylar-based pouch motors filled with Novec 7000 and driven by flexible Peltier junctions to realize agonist–antagonist muscle-like actuation. A series-pouch motor design with multiple cavities and narrow interconnections enables controlled buckling and smooth curvature, while a geometric model governs cavity and channel volumes under vapor-pressure phase-change, coupled with bidirectional thermal control for rapid actuation. Fabrication and experimental evaluation include temperature measurements across multiple power levels, a detailed manufacturing workflow, and an inverter switch to alternate heating and cooling. Three bio-inspired applications—artificial muscle, gripper, and locomotion—demonstrate the ability to achieve flexion/extension, grip lightweight irregular objects, and crawl on textured substrates, illustrating a versatile and potentially more durable soft-robotic platform. Overall, the work advances soft robotics by delivering a durable, energy-efficient actuation strategy that supports complex, reconfigurable, agonist–antagonist tasks.

Abstract

In this study, we introduce a novel Mylar-based pouch motor design that leverages the reversible actuation capabilities of Peltier junctions to enable agonist-antagonist muscle mimicry in soft robotics. Addressing the limitations of traditional silicone-based materials, such as leakage and phase-change fluid degradation, our pouch motors filled with Novec 7000 provide a durable and leak-proof solution for geometric modeling. The integration of flexible Peltier junctions offers a significant advantage over conventional Joule heating methods by allowing active and reversible heating and cooling cycles. This innovation not only enhances the reliability and longevity of soft robotic applications but also broadens the scope of design possibilities, including the development of agonist-antagonist artificial muscles, grippers with can manipulate through flexion and extension, and an anchor-slip style simple crawler design. Our findings indicate that this approach could lead to more efficient, versatile, and durable robotic systems, marking a significant advancement in the field of soft robotics.

Figures (9)

• Figure 1: a) Cutaway of a typical Peltier and b) operation principle of Peltier with one p-type and one n-type thermoelement.c) TEGWay Peltier Tegway showing size (40x40mm) and flexibility. d) Singular mylar pouch motor filled with Novec 7000 for phase-change expansion. e) Series pouch motors attached to flexible Peltier for reversible flexion and extension. f) Agonist-antagonist configuration of muscle, showing flexion and extension based on heating direction, gripper showing capabilities of reversible flexion and extension, and crawler demonstrating locomotion.
• Figure 2: Geometric model for the Agonist-Antagonist pouch motors
• Figure 3: Experimental setup for collecting Peltier and Mylar temperature values. In the case of flexible polyimide heater, the Peltier is substituted.
• Figure 4: For the creation of the pouch motors, mylar films are cut to size, and then boundaries are sealed using an impulse heater. Thin (width: 2 mm; thickness: 150 $\mu$m) Nichrome ribbon wire was placed into the pouch to create areas that are thermally resistant according to designed internal cavity geometry. Once placed, sealing will only occur where wire is absent. After sealing, wire is removed and corresponding Novec 7000 volume is injected using a 22 gauge needle, and injection port is sealed.
• Figure 5: Temperature of inner side of mylar and surface of Peltier collected with the setup from Fig. \ref{['fig:tempsetup']}