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Tendon-Driven Reciprocating and Non-Reciprocating Motion via Snapping Metabeams

Mohsen Jafarpour, Ayberk Yüksek, Shahab Eshghi, Stanislav Gorb, Edoardo Milana

Abstract

Snapping beams enable rapid geometric transitions through nonlinear instability, offering an efficient means of generating motion in soft robotic systems. In this study, a tendon-driven mechanism consisting of spiral-based metabeams was developed to exploit this principle for producing both reciprocating and non-reciprocating motion. The snapping structures were fabricated using fused deposition modeling with polylactic acid (PLA) and experimentally tested under different boundary conditions to analyze their nonlinear behavior. The results show that the mechanical characteristics, including critical forces and stability, can be tuned solely by adjusting the boundary constraints. The spiral geometry allows large reversible deformation even when made from a relatively stiff material such as PLA, providing a straightforward design concept for controllable snapping behavior. The developed mechanism was further integrated into a swimming robot, where tendon-driven fins exhibited two distinct actuation modes: reciprocating and non-reciprocating motion. The latter enabled efficient propulsion, producing a forward displacement of about 32 mm per 0.4 s cycle ($\approx$ 81 mm/s, equivalent to 0.4 body lengths per second). This study highlights the potential of geometry-driven snapping structures for efficient and programmable actuation in soft robotic systems.

Tendon-Driven Reciprocating and Non-Reciprocating Motion via Snapping Metabeams

Abstract

Snapping beams enable rapid geometric transitions through nonlinear instability, offering an efficient means of generating motion in soft robotic systems. In this study, a tendon-driven mechanism consisting of spiral-based metabeams was developed to exploit this principle for producing both reciprocating and non-reciprocating motion. The snapping structures were fabricated using fused deposition modeling with polylactic acid (PLA) and experimentally tested under different boundary conditions to analyze their nonlinear behavior. The results show that the mechanical characteristics, including critical forces and stability, can be tuned solely by adjusting the boundary constraints. The spiral geometry allows large reversible deformation even when made from a relatively stiff material such as PLA, providing a straightforward design concept for controllable snapping behavior. The developed mechanism was further integrated into a swimming robot, where tendon-driven fins exhibited two distinct actuation modes: reciprocating and non-reciprocating motion. The latter enabled efficient propulsion, producing a forward displacement of about 32 mm per 0.4 s cycle ( 81 mm/s, equivalent to 0.4 body lengths per second). This study highlights the potential of geometry-driven snapping structures for efficient and programmable actuation in soft robotic systems.
Paper Structure (7 sections, 4 figures)

This paper contains 7 sections, 4 figures.

Table of Contents

  1. INTRODUCTION
  2. Methods
  3. Design and Fabrication
  4. Mechanical Testing
  5. Swimming Robot
  6. Results and Discussion
  7. CONCLUSIONS

Figures (4)

  • Figure 1: Design and configurations of the snapping structure. The spiral-based metabeam, consisting of interconnected double-spiral unit cells, forms the snapping structure shown under the tested boundary conditions (fixed and pinned) and loading types (symmetric and asymmetric).
  • Figure 2: Representative force–displacement curves of the PLA metabeam under fixed–fixed and pinned–pinned boundary conditions, showing distinct snapping behavior. The photos illustrate the metabeams before loading and at the maximum applied displacement.
  • Figure 3: Mechanical behavior of the snapping structure under asymmetric tensile loading and varying boundary conditions. Representative force–displacement curves for (a) fixed–fixed, (b) pinned–pinned, and (c, d) fixed–pinned configurations with asymmetric loading applied on the fixed and pinned sides, respectively. The insets show the deformed structure at the maximum displacement (55 mm) and its tip trajectory during loading and unloading.
  • Figure 4: Swimming robot driven by tendon-actuated snapping structures. The top view shows the two identical snapping mechanisms arranged symmetrically on the sides of a rigid body. Sequential snapshots demonstrate the robot’s motion underwater during five actuation cycles with two asymmetric loading configurations: fixed–pinned (fix) and fixed–pinned (pin).