A Force Decoupling Method for Simultaneously Measuring Vertical and Shear Force

Wearable device-based shear force sensing has been a challenging problem, whereas shear-force sensing plays a crucial role in motion measurement and robot manipulation. This paper presents a three-dimensional (3-D) flexible force sensor for measuring uniaxial vertical (i.e., normal) and 2-D shear forces. The proposed sensor is fabricated with silica gel and force-sensitive resistors (FSRs). A novel force decoupling method based on the hemispherical structure has been developed, which only requires calibration from the vertical direction, i.e., Z-axis. Experiments were carried out with a triaxial linear motion stage and a 3-D force sensor. Results show that the sensing module could measure Z-axis force ranging from 0 to 10 N with RE (relative error) of 3.2%, and shear forces (X- and Y-axes) ranging from 0 to 1.6 N with an RE of 5.5% and 5.9%, respectively. The proposed sensing module can be employed in application scenarios that require measuring interfacial stress.