In complex systems like aircraft engines and oil refinery machines, pipeline inspection is an essential task for ensuring safety. Here, we proposed a type of smart material–driven pipeline inspection robot (weight, 2.2 grams; length, 47 millimeters; diameter, <10 millimeters) that could fit into pipes with sub-centimeter diameters and different curvatures. We adopted high–power density, long-life dielectric elastomer actuators as artificial muscles and smart composite microstructure–based, high-efficiency anchoring units as transmissions. Fast assembling of components using magnets with an adjustable number of units was used to fit varying pipeline geometries. We analyzed the dynamic characteristics of the robots by considering soft material’s unique properties like viscoelasticity and dynamic vibrations and tuned the activation voltage’s frequency and phase accordingly. Powered by tethered cables from outside the pipe, our peristaltic pipeline robot achieved rapid motions horizontally and vertically (horizontal: 1.19 body lengths per second, vertical: 1.08 body lengths per second) in a subcentimeter-sized pipe (diameter, 9.8 millimeters). Besides, it was capable of moving in pipes with varying geometries (diameter-changing pipe, L-shaped pipe, S-shaped pipe, or spiral-shaped pipe), filled media (air or oil), and materials (glass, metal, or carbon fiber). To demonstrate its capability for pipeline inspection, we installed a miniature camera on its front and controlled the robot manually from outside. The robot successfully finished an inspection task at different speeds.

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Soft actuators with high safety, adaptivity, and energy-to-weight ratio have the potential to be used in developing more adaptive legged robots. In this work, we incorporate soft actuators into rigid parallel mechanisms and develop multi-degree-of-freedom (multi-DOF) soft-rigid hybrid joints that can actively achieve 1, 2, and 3 DOFs actuated by 2, 4, and 8 bellows-type fluidic elastomer actuators (FEAs), respectively. The FEAs exhibit large axial strain (ϵ e max = 176%, ϵ c max = 25%), small radial expansion (ϵ r max = 12%) at 70 kPa, and are light weight, and the rigid parallel mechanisms constrain motions of the joints to the desired DOFs. We characterize the proposed joints’ kinematic and static performances by measuring their range of motion and blocked torque upon actuation. Results show that these joints successfully achieve all desired DOFs and are of high torque to weight ratio (4.07 N·m·kg−1). A bucking prediction model is established to evaluate the critical buckling pressure. As a demonstration for legged robots, we use the proposed joints and develop two types of multi-DOF legs based on inspirations from the DOF configuration of legged mammals’ musculoskeletal systems. Preliminary results demonstrate that FEAs-based multi-DOF legs can perform fundamental biomimetic movements (e.g. leg swing) through pressure adjustment, and high-speed tasks (e.g. ball kicking and jumping) through high-pressure and short-pulse actuation.