TESCLA: A Fully Soft Electromagnetic Linear Actuator With Continuous Bending Enabled by Liquid-Metal Solenoids

Linear actuators are widely employed in robots and wearable devices due to their capability of directly generating linear motion. Although soft actuators and flexible linear actuators have been developed to enable effective operation in various configurations, they are still constrained by a limited actuation range and a discrete bending, which restricts their achievable workspace and curvatures. Here, we propose a tubular electromagnetic soft conformal linear actuator (TESCLA) exerting thrust force over a large actuation stroke with continuous bending. The actuator operates under both a straight configuration and a conformal deformation to the surrounding environment, leveraging the softness of liquid-metal solenoids (soft stator) and compliant magnetic composites (soft mover). The synchronous actuation strategy allows the actuator to produce controllable bidirectional electromagnetic thrust by applying an electric current to the soft stator. In addition, the step position is estimated by measuring inductance variance of the soft solenoids resulting from the displacement of the soft mover. The design of the actuator components is evaluated through numerical simulations to determine an effective configuration, considering performance characteristics such as thrust force, minimum step size, and sensing resolution. By utilizing the functionalities of the proposed actuator, biomimetic robotic applications and a wearable haptic device were demonstrated.