A recent study published in Engineering presents a significant advancement in robotic tactile sensing technology. Researchers have developed a novel soft tactile unit named the F³T sensor, which can mathematically decouple three-dimensional (3D) force and temperature measurements.

Human skin can accurately perceive contact forces and environmental temperatures, but existing soft tactile sensors face challenges in precisely decoupling these signals. This limitation restricts robots’ ability to perform advanced tasks. The newly developed F³T sensor is inspired by the structure and function of human skin. It features a four-layer design that integrates multiple materials and sensing principles.

The top-most layer is an ion gel-based temperature-sensing film. When the temperature changes, the distance between polymer chains in the gel varies, leading to a change in resistance, which enables independent temperature measurement. The second layer is a circular coaxial magnetic film with a floating mount multilayer capacitor. This design facilitates the physical decoupling of normal and tangential forces in all directions. The third layer, a floating capacitor, is sensitive only to normal force, effectively eliminating the influence of tangential force. The fourth is the hard PCB layer for supporting and signal processing. The inner silicone elastomer in the sensor is similar to the hypodermis of human skin, which helps connect components and buffer impact forces.

The F³T sensor can accurately decouple temperature, normal force, and all-directional tangent force. When in contact with an object, the composite signal received by the sensor is separated. The ion gel layer first decouples and measures the temperature. Then, through structural design and material regulation, the floating capacitor accurately measures the normal force, and the magnetic film measures the tangential force.

Characterization tests show that the sensor has high performance. The relationship between contact temperature and current in the gel is calibrated, and the temperature measurement is hardly affected by external forces. The normal force measurement has high accuracy, and the tangential force measurement can precisely detect both magnitude and direction. The sensor also has a fast dynamic response.

The performance of the F³T sensor was evaluated under static and dynamic conditions. In static tests, it accurately detected 3D forces and temperature with low errors, outperforming traditional sensors. In dynamic tests, when integrated into a robotic gripper, it enabled the gripper to adaptively respond to external disturbances and perform stable grasping.

The F³T sensor was also demonstrated in an automated chemical reaction procedure and human-robot cooperation scenarios. In the preparation of a polyvinyl alcohol (PVA) solution, it helped maintain precise control over the heating and shaking process. In the “tea delivery” task, it enabled the robot to detect human intent and complete a smooth handover.

Although the F³T sensor shows great potential, there are still areas for improvement, such as enhancing inter-layer adhesion, ensuring performance consistency, and reducing temperature measurement delay. Overall, this new sensor technology is expected to promote the development of more adaptable robotic systems in various applications.

The paper “A Soft Tactile Unit with Three-Dimensional Force and Temperature Mathematical Decoupling Ability for Robots,” is authored by Xiong Yang, Hao Ren, Dong Guo, Zhengrong Ling, Tieshan Zhang, Gen Li, Yifeng Tang, Haoxiang Zhao, Jiale Wang, Hongyuan Chang, Gao Tsz Ki, Jia Dong, Wu Ningxin, Yajing Shen. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.02.008. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.