Single layered soft skin actuated with twisted and mandrel coiled actuators for soft robotics

Abstract Soft silicone‐based artificial skin is essential in soft robotics because of high elongation, safe human interaction, low energy requirements and ease of manufacturing. Inspired by nature, several attempts have been made to fabricate morphing structures using synthetic soft skin. In this study, a novel elastomeric skin is demonstrated featuring embedded actuators and micro‐fluidic channels, that is capable of grasping objects. The actuators are twisted, and mandrel coiled nylon artificial muscles, with nichrome heaters that overcome key challenges in developing synthetic soft skin. The desired properties of a morphing skin are being low‐cost, lightweight, highly deformable, compact size, silent cyclic actuation, fast response, and long life. The actuators are fabricated from 160 μm diameter resistance wires wrapped on twisted nylon 6 fishing line precursor fibers of 800 μm diameter. The wrapped nichrome (0.42 mm pitch) along with the twisted precursor fibers are coiled on a 1.4 mm diameter mandrel rod to obtain high strain. This muscle termed twisted, and mandrel coiled polymer fishing line muscle with nichrome is embedded in soft skin samples and tested. Characterization results on the actuators (3.2 mm in diameter) showed remarkable tensile actuation of ~36% strain from loaded length at 0.99 MPa for an input power of 4.9 W, a blocked stress of 1.27 MPa, an actuation frequency of 0.04 Hz, and a lifecycle >22,000 cycles. These actuators, when embedded in the soft skin of 4 mm thick, showed ~50% bending strain within 10s and a cyclic behavior with active water cooling. A soft gripper fabricated with embedded soft skin is integrated to our child‐sized humanoid robot (HBS Robot) demonstrating its potential in grasping unconventional and deformable objects, hence advancing the progress in soft robotics.