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Self-Sustained And Coordinated Rhythmic Deformations With SMA For Controller-Free Locomotion

Ziyang Zhou, Suyi Li

TL;DR

The paper tackles the challenge of onboard actuation and control for shape memory alloy (SMA)–based soft robots by introducing a fully mechanical, electronics-free design. A mono-stable curved beam provides a nonlinear bias that amplifies the SMA coil’s stroke through snap-through buckling, and a slider-based circuit autonomously sequences heating and cooling to generate self-sustained rhythmic deformation. Extending this idea, the authors combine a bistable-switch–driven module connector with a shared power source to synchronize two modules in opposite phase, enabling faster crawling than a single module. The results demonstrate both single-module crawling and improved two-module locomotion with a single DC supply, highlighting a path toward autonomous, lightweight, and scalable SMA soft robots without onboard electronics. This approach has potential for broader locomotion tasks and multi-module coordination in centimeter-scale soft robots.

Abstract

This study presents a modular, electronics-free, and fully onboard control and actuation approach for SMA-based soft robots to achieve locomotion tasks. This approach exploits the nonlinear mechanics of compliant curved beams and carefully designed mechanical control circuits to create and synchronize rhythmic deformation cycles, mimicking the central pattern generators (CPG) prevalent in animal locomotions. More specifically, the study elucidates a new strategy to amplify the actuation performance of the shape memory coil actuator by coupling it to a carefully designed, mono-stable curve beam with a snap-through buckling behavior. Such SMA-curved beam assembly is integrated with an entirely mechanical circuit featuring a slider mechanism. This circuit can automatically cut off and supply current to the SMA according to its deformation status, generating a self-sustained rhythmic deformation cycle using a simple DC power supply. Finally, this study presents a new strategy to coordinate (synchronize) two rhythmic deformation cycles from two robotic modules to achieve efficient crawling locomotion but still use a single DC power. This work represents a significant step towards fully autonomous, electronics-free SMA-based locomotion robots with fully onboard actuation and control.

Self-Sustained And Coordinated Rhythmic Deformations With SMA For Controller-Free Locomotion

TL;DR

The paper tackles the challenge of onboard actuation and control for shape memory alloy (SMA)–based soft robots by introducing a fully mechanical, electronics-free design. A mono-stable curved beam provides a nonlinear bias that amplifies the SMA coil’s stroke through snap-through buckling, and a slider-based circuit autonomously sequences heating and cooling to generate self-sustained rhythmic deformation. Extending this idea, the authors combine a bistable-switch–driven module connector with a shared power source to synchronize two modules in opposite phase, enabling faster crawling than a single module. The results demonstrate both single-module crawling and improved two-module locomotion with a single DC supply, highlighting a path toward autonomous, lightweight, and scalable SMA soft robots without onboard electronics. This approach has potential for broader locomotion tasks and multi-module coordination in centimeter-scale soft robots.

Abstract

This study presents a modular, electronics-free, and fully onboard control and actuation approach for SMA-based soft robots to achieve locomotion tasks. This approach exploits the nonlinear mechanics of compliant curved beams and carefully designed mechanical control circuits to create and synchronize rhythmic deformation cycles, mimicking the central pattern generators (CPG) prevalent in animal locomotions. More specifically, the study elucidates a new strategy to amplify the actuation performance of the shape memory coil actuator by coupling it to a carefully designed, mono-stable curve beam with a snap-through buckling behavior. Such SMA-curved beam assembly is integrated with an entirely mechanical circuit featuring a slider mechanism. This circuit can automatically cut off and supply current to the SMA according to its deformation status, generating a self-sustained rhythmic deformation cycle using a simple DC power supply. Finally, this study presents a new strategy to coordinate (synchronize) two rhythmic deformation cycles from two robotic modules to achieve efficient crawling locomotion but still use a single DC power. This work represents a significant step towards fully autonomous, electronics-free SMA-based locomotion robots with fully onboard actuation and control.
Paper Structure (14 sections, 4 figures)

This paper contains 14 sections, 4 figures.

Table of Contents

  1. Introduction
  2. Result
  3. Actuation Mechanism Design
  4. Selecting the SMA Coil Actuator
  5. Designing the Curved Beam and its Snap-Through Response
  6. Integrating SMA and Curved Beam
  7. Rhythmic Deformation from a Single Module
  8. Working Principle of a Single Module
  9. Single-Module Robotic Locomotion
  10. Synchronizing Rhythmic Deformations from Two Modules
  11. Bistable Switch and New Slider Design
  12. Working Principle of Modular Synchronization/Coordination
  13. Two-module Robotic Locomotion
  14. Discussion

Figures (4)

  • Figure 1: The overall concept of the modular robots in this study. (a) A comparison between the walking pattern of the Chinese grasshopper and our two-module robot reveals many similarities in their gait coordination. (b) Key features of the modular robot platform.(c) An exploded view of a single robotic module; key components are labeled, and each module is 66 mm in length.
  • Figure 2: Design, test, and integration of SMA coil actuator and curved snap-through beam. (a): A comparative study of SMA actuators with different coil numbers ($n$), showing the relationship between heating time and output force. (b) Output force and temperature correlation of the $n=5$ SMA coil. (c) The theoretically predicted and measured force-deformation curve of the curved beam.(The solid line is the averaged test data from 4 load cycles, and the shaded region is the standard deviation). The infrared images below show the deformation of the SMA-curved beam assembly at different deformation stages.
  • Figure 3: The working principle of the rhythmic deformation from on a single robotic module and the corresponding crawling locomotion (a) Exploded view of the "mechanical control circuit" (Fig. \ref{['fig:bigpic']}c). (b) The mechanical slider can move out of (or into) the circuit frame's slots, thus stopping (or starting) the electric current. (c ,d) The schematic diagram and experiment photos show the four phases of a rhythmic deformation cycle. (e) The experimentally measured rhythmic deformation, the inconsistency between different cycles is probably due to the unpredictable sliding friction contact between the slider and circuit frame. (f) A single module, equipped with 3D-printed claws, completed 12 deformation cycles and traveled 50mm, all using a simple DC power supply.
  • Figure 4: Rhythmic deformation coordination with two robotic modules and improved crawling locomotion. (a) Exploded View of a dual-module robot, highlighting the module connector's design. (b) Schematic diagram and experiment video to show the working principle of the module connector. (c,d) Overall working principle of the dual-module robot and its four phases of deformation synchronization: Schematic diagrams are at the top, and experiment photos are below. (e) The dual-module robot completes 5 coordinated deformation cycles and travels 50mm.