Abstract
There are structural challenges in increasing the softness of conventional soft tactile sensors because rigid electrical elements have to be installed around the sensing areas, which should be compressive, stretchable, and durable. To solve these issues, we propose an inductive tactile sensor whose silicone-rubber body has only two liquid-metal reservoirs connected by an elongated flow channel. When one reservoir is placed around the sensing area, another one can be placed at a non-sensing area. Furthermore, in this structure, touch can be detected by monitoring the inflow and outflow of the liquid-metal in the latter reservoir by using a separately placed coil circuit based on the eddy-current effect. The proposed method requires no direct electrical connections with liquid metal in the reservoirs or flow channels. This means that the sensor body has no inhibitor that reduces its compressibility and stretchability, and that deteriorates its durability. The experimental results demonstrated that larger reservoir diameters provided larger sensitivity and higher signal-to-noise ratio of approximately 65 dB. Additionally, we observed that the bending of the body does not affect the sensor response as much as gravity. Therefore, we conclude that our sensor has structural advantages for tactile-sensor installation, especially in soft actuators, because our completely soft sensor does not experience reduction or deterioration in its functionality owing to its softness.
Highlights
T HE soft structure in a soft robot [1]–[4] makes rich contact with physical environment, allowing completely effective and safe interactions to be achieved
This study proposed a soft inductive tactile sensor that can estimate the applied normal force on the basis of the inductance change caused by the displacement of liquid metal enclosed in a flow channel
The results suggest that the effect of bending on sensor responses is relatively small compared to the response range
Summary
T HE soft structure in a soft robot [1]–[4] makes rich contact with physical environment, allowing completely effective and safe interactions to be achieved. Sensors required for soft robots include tactile sensors, which obtain information from physical interactions with the environment, i.e., a deformation of soft materials and the contact information. Ignorable technical issues have arisen when embedding or adhering tactile sensor elements in a soft-material sensor body. As discussed in [10], the following issues need to be solved: 1) embedding fragile sensor elements, e.g., electric elements and wires, into soft materials deteriorates the sensor durability; 2) embedding rigid materials into soft materials reduces the softness of the sensor body; and 3) adhering rigid sensor elements with soft materials introduces an unavoidable stress concentration and a weak interface
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