Soft capacitive tactile sensor using displacement of air–water interface

We propose a soft capacitive tactile sensor using the displacement of an air–water interface. This soft tactile sensor is composed of a soft contact part with a chamber and channel filled with water and a clip-shaped sensing part to detect the position of the interface. This tactile sensor changes the displacement of the air–water interface in the channel when a contact force is applied. The change in displacement is detected as a change in the capacitance at the sensing part. This sensor structure does not require stiff electrical elements to be embedded in the soft silicone rubber body, which improves the flexibility and durability of the sensor. Therefore, the proposed tactile sensor exhibits high flexibility and durability against bending and external stresses. Additionally, the proposed tactile sensor can detect not only press force but also pull force. This results in the detection of a press or pinch in a robot skin. The experimental results show that the proposed sensor can successfully detect both press and pull static forces. The sensitivity of the proposed sensor was 0.169 pF/N for an applied force in the press direction and −0.152 pF/N for a force in the pull direction based on the results of an evaluation of the static sensor characteristics. Furthermore, an evaluation of the dynamic sensor characteristics revealed that the proposed tactile sensor has high repeatability and a quick response to an external force. Additionally, the hysteresis of the proposed tactile sensor is small, especially in the press direction.