A Miniaturized Five-Axis Isotropic Tactile Sensor for Robotic Manipulation

Miniaturized multi-axis (force & torque) tactile sensors are paramount for the robot system to interact safely with the external environment, especially for the controlled adhesive robots. However, there exists a drawback——measurement anisotropy, which prevents sensors from performing equally well in all the directions and the high degree of integration. Based on the plate capacitive mechanism, this paper introduces a miniaturized 5-axis tactile sensing method with a novel double-layer sensitive structure. Practically, shear force is detected by measuring the change of overlap area in the upper-layer-sensing cell, while the normal force and moment can be obtained by the variable space between two plates arranged in a ${2} \times {2}$ -grid in the lower-layer-sensing cell. Moreover, in order to achieve the measurement isotropy, the relationship between the force/torque and the capacitance is clarified to facilitate the independent adjustment of the sensitivity of each axis. Based on the methodology, a miniature 5-axis flat tactile sensor is manufactured. The experimental results show that the shear sensitivity of the prepared sensor is over 0.2557pF/N within 7 N, reaching the same magnitude as normal force (0.2859pF/N over 3N range). The sensitivities of torque are over 1.8406 $({N}\cdot {m})^{-{1}}$ with a full-scale range of $0.04~{N}\cdot {m}$ . The results demonstrate that the miniaturized tactile sensor is capable of isotropic measurement among 5-axis for robotic manipulation.