Qadralimb: embedded TCP actuators in silicone for grasping tasks and underwater soft robots

Abstract In the past few years, significant advancements have been made in soft robotics using various actuators. One notable development is the emergence of Twisted and Coiled Polymers (TCP) and the integration of TCP actuators in silicone. TCP artificial muscles have several advantages: they are quiet, inexpensive, exhibit low hysteresis, operate at low voltage and can be tailored for desired shapes. This research focuses on characterization of the 2-ply TCP actuators embedded in silicone and their application for a swimming robot and grasping application. Initially, the actuators were characterized for static and dynamic behaviors, considering critical parameters such as applied voltage, actuation frequency, pre-tension, resistance of the muscles, geometry and the material composition. Out of these, the first three parameters can be controlled during operation. The study determined the optimum ranges for these controllable parameters, specifically for a swimming and grasping applications. For swimming, a low-profile robotic structure with four limbs (each measuring 140 × 60 × 5 mm 3 ) was developed that was able to swim a vertical displacement of 343 mm in 640 s. Limb actuation conditions were also optimized for grasping, demonstrating successful grasping in air and in water against gravity using a single or combined limbs. The 2-ply TCP actuators provided a strain of 12.5% at a 300 g (2.9 N) optimum load and a blocking force of 1.7 kg (16.7 N) when supplied with 225 J of electrical input energy (20 V, 0.75 A current and 15 s heating time). Notably, this soft structure with embedded TCP actuators has not been demonstrated in an underwater environment, and hence this study adds new knowledge in this area. Furthermore, FEM simulation results on a single limb under the effect of gravity was performed using ANSYS to compare with experimental results. This research has potential applications in underwater exploration and manipulation in hazardous environments.