Flexible Electromagnetic Actuators with Kresling-Origami Housing for Modular Soft Robots

Flexible Electromagnetic Actuators (FEMAs) operate at low driving voltages and respond rapidly. However, they require a bulky external permanent magnet, which is challenging to integrate into a small system. This paper presents small-scale, flexible electromagnetic actuators with bidirectional stability. This actuator integrates two multilayer planner spiral coils with a silicone-encapsulated NdFeB magnet, combined with Kresling-origami PET housings. Origami structures provide compliance and snap-through bistability, enabling large strokes while being lightweight and modular. We also develop a design and modeling framework, which includes the calculation of the discretized Biot-Savart law for multilayer spiral coils and the estimation of time-dependent thermal diffusion in water, revealing a trade-off between magnetic field and heat dissipation. The developed actuators produce surface magnetic fields of 9.93 mT, which is consistent with the simulation results. In the compressed state, it shows a maximum net force of 0.51 N and achieves a stroke length of 18.5 mm with a maximum velocity of 12.5 mm s −1 and acceleration of 0.98 m s −2 underwater. The full open-close cycles are noticed at a frequency of 3.5 Hz, with decreasing amplitude up to 40 Hz. Finally, we demonstrate the FEMAs utilized as a continuum manipulation stage and underwater robots.