Design and Experimental Evaluation of an Origami-inspired Robotic Arm with Octopus-like Functionalities

Abstract

Conventional articulated robot arms excel on structured production lines but remain unsafe and ineffective in cluttered, dynamic settings, while existing soft-robotic manipulators sacrifice load-bearing capacity and positional repeatability for safety and adaptability, origami-robots improve this trade-off. The octopus arm, a muscular hydrostat, is a biological example of overcoming this trade-off by uniting shape morphing, distributed actuation and tunable stiffness. This thesis introduces a fold-flat, modular origami structure that co-locates distributed magnetic actuation and thermally tunable stiffness inside each unit module, thereby matching the octopus arm’s three biological features, shape morphing (1), distributed actuation (2) and tunable stiffness (3). A four-legged water-bomb module was created by mapping biologically derived requirements onto an additively manufactured construction that integrates paired NdFeB permanent magnets, a central pancake electromagnet, and a Joule-heated conductive-PLA crease. Physical prototypes and finite-element analysis predicted ±20 ° biaxial bending, 100 % axial extension, and a 50% stiffness reduction. A proof-of-concept prototype verified these predictions, except that the bending was up to 10°. Single-leg or single-hinge tests revealed a steep modulus drop between 45 °C and 60°C, yielding up to 90 % stiffness reduction under 34 V excitation. At module level the actuator stack produced 10 mm axial stroke, ±10 ° bending and peak push/pull forces of 0.8 N/1.0 N while maintaining repeatable 3-DoF motion. Eight of the ten primary requirements were met; sustained horizontal self-support and whole-arm 90 ° curvature were limited by cable weight and hinge play. The study identified two bottlenecks: high coil currents that drive the PLA above its glass transition, and asymmetric flux coupling when the coil drifts toward one magnet. Improvement strategies include closed-loop thermal control, heat-resistant substrate polymers, and improved electromagnet positioning. By uniting shape morphing, distributed actuation, and tunable stiffness in a centimetre-scale, magnetically actuated origami cell, this work realises an octopus-like robotic arm with power-off stiffening, planar manufacturability, and modularity. The results establish a viable route toward deployable continuum arms for confined-space inspection, human-robot collaboration, and search-and-rescue operations.