Highly Sensitive Iontronic-Based Aquatic Triaxis Force Sensor with Hybrid Microstructures for Delicate Force Sensing in Underwater Robots.

Reliable robotic manipulation in aquatic environments requires flexible triaxis force sensors capable of precise contact force detection, while well-sealed force sensors generally suffer from high hydrostatic pressure preloading that occupies the sensing range and compromises the sensitivity. Herein, we develop a novel and highly sensitive iontronic-based aquatic triaxis force sensor. It features an open-architecture design to compensate for hydraulic pressure changes caused by water depth. Additionally, it incorporates hybrid sensitive microstructures with distinct elastic moduli to improve sensitivity for force sensing while maintaining a sufficient sensing range. To achieve precise shear and normal force sensing, a mathematical model for triaxis force sensing is established by using the differential capacitance changes. Characterization tests demonstrated our aquatic triaxis force sensor has high normal force sensitivity of 0.32 N-1 at normal force sensing range of 0-18.5 N, along with a high shear force sensitivity of 0.761 N-1 for the x-axis and 0.758 N-1 for the y-axis within the range of 0-4.2 N. Notably, the sensor achieves a high normal force resolution of 0.02 N and a shear force resolution of 0.01 N. Moreover, the sensor generally maintains consistent sensing performance across varying aquatic environments. Finally, successful demonstrations in different object grasping tasks and underwater pipeline docking applications for three-axis force sensing validate the promising potential of our developed triaxis force sensor for delicate three-axis force measurement in aquatic environments.