Flexible three-dimensional force sensor of high sensing stability with bonding and supporting composite structure for smart devices

Characteristics, such as large measurement range, good repeatability and stability, are the guarantee for a wide application of flexible three-dimensional force sensors in robots and other smart devices. In this research, a flexible three-dimensional force sensor is presented, whose structure includes force-sensitive cells, fixed under the bump and a support layer, filled around the force-sensitive cells. This setup allows the sensor to quickly recover, after the force is released, to ensure its excellent performance. The production method is very simple and has the advantage of large-scale and low-cost manufacturing. The sensor exhibited good repeatability and stability, after 25 000 cycles of loading and releasing, under 8 N force. Meanwhile, it has a large measuring range, which is 0–15 N in the direction of normal force and 0–5.5 N in the direction of shear force. The sensitivity of the sensor in the x, y, and z directions is 1.5321 V−1 N−1, 1.501 29 V−1 N−1, and 0.936 87 V−1 N−1, respectively. The load response time of the sensor is 33 ms and the unload recovery time of 18 ms. Regarding practical applications, the sensor shows good prospects. For example, the sensor and its array can be installed on the manipulator to sense the magnitude and location of the three-dimensional force; in the case of the flexible smart keyboard, the presented sensor array can save space significantly and recognize multiple specific input features, in order to enhance information security; while as a car controller, it is multi-functional integrated and portable, thus showing great potential as replacement to the traditional operating methods.