Inchworm-Inspired Soft Robot with Groove-Guided Locomotion

Abstract

Soft robots require directional control to navigate complex terrains. However, achieving such control often requires multiple actuators, which increases mechanical complexity, complicates control systems, and raises energy consumption. Here, we introduce an inchworm-inspired soft robot whose locomotion direction is controlled passively by patterned substrates. The robot employs a single rolled dielectric elastomer actuator, while groove patterns on a 3D-printed substrate guide its alignment and trajectory. Through systematic experiments, we demonstrate that varying groove angles enables precise control of locomotion direction without the need for complex actuation strategies. This groove-guided approach reduces energy consumption, simplifies robot design, and expands the applicability of bio-inspired soft robots in fields such as search and rescue, pipe inspection, and planetary exploration.

Figures (9)

• Figure 1: Geometry, actuation cycle, and groove-guided orientation of the inchworm-inspired soft robot. ( a) Photograph of the soft robot, consisting of a multilayer rolled dielectric elastomer actuator (RDEA) integrated with a flexible PET sheet. ( b) Actuation cycle during locomotion: the robot contracts at 0 V with a minimum length $l_{\min}=25$ mm and maximum height $h_{\max}$; upon applying 1.9 kV, the actuator extends to $l_{\max}=27$ mm with reduced height $h_{\min}$; returning to 0 V restores the contracted state (see Supplementary Movie S1). This contraction--extension cycle drives the robot forward along the substrate. ( c) Schematic of the robot on 3D-printed grooved substrates at different groove orientations ($\theta_{\rm s}=0^\circ,\,5^\circ,\,15^\circ,\,30^\circ$). The groove angles bias frictional engagement, passively steering the robot and aligning its direction of motion with the groove orientation.
• Figure 2: Fabrication process of the rolled dielectric elastomer actuator (RDEA). ( a) Step-by-step illustration of the fabrication workflow. The Ecoflex/Elastosil blend is first deposited onto a PMMA substrate and uniformly spin coated. The coated film is thermally cured at 60° C. A PET mask is then aligned on the cured layer to define the electrode regions, and compliant electrodes are deposited using an airbrush. The sample is subsequently baked at 60° C to remove excess solvent (post-transfer baking). These steps (spin coating, curing, mask placement, electrode transfer, and baking) are repeated to build a multilayer actuator. ( b) Layer-by-layer breakdown of the final 5-layer RDEA structure. Alternating elastomer layers and electrode masks (left and right configurations) are stacked to ensure electrical connectivity to opposite terminals.
• Figure 3: Inchworm soft robot fabrication. ( a) Using a laser cutter, a flexible polyethylene terephthalate (PET) sheet was used to fabricate the body of the soft robot. ( b) The PET was bent at the edges to form an arc. ( c) The RDEA was placed in between the arc and was secured using conductive epoxy.
• Figure 4: Temporal evolution of the robot’s orientation angle on a 0° grooved substrate. The robot's orientation remains nearly constant, indicating that without directional surface cues the robot follows a straight trajectory with no reorientation.
• Figure 5: Temporal evolution of the robot’s orientation angle on a 5° grooved substrate. The robot exhibits small, but systematic angular deviations, demonstrating that shallow surface cues effectively guide locomotion and induce gradual reorientation consistent with the groove angle.