Stretchable tri-axis force sensor using conductive liquid

• We propose a stretchable tactile sensor which can measure tri-axis forces and stretches simultaneously by integrating two types of sensor units: tri-axis force sensor units and stretch sensor units.
• The force sensor unit is composed of 4-capacitors using paired liquid electrodes and can detect the applied forces by measuring the capacitance changes of each capacitor.
• The stretch sensor units composed of a conductive liquid channel, whose impedance changes by the elongation of the channel.
• By using this sensor, we evaluated that the sensor can measure the 0- to 0.25-N normal forces, −0.15- to 0.15-N shear forces, and 0- to 0.2-strain stretches.

This paper reports on a stretchable tri-axial tactile sensor using an electro-conductive liquid encapsulated inside channels composed of an elastomer. The sensor was constructed by integrating two types of sensor units: tri-axial force sensor units composed of 4-capacitors with paired conductive liquid electrodes and stretch sensor units composed of a conductive liquid channel. The capacitances between the paired liquid electrodes of the force sensor unit change to the applied tri-axis forces. And the resistance of the liquid channel consisted in the stretch sensor unit increases to the stretch. Thus the tri-axial forces and stretches can be detected by measuring capacitance changes of the force sensor unit and resistance changes of stretch sensor unit. The sensor was 35 mm × 35 mm in area and 2.1 mm thick. To evaluate the sensitivity, we measured 0- to 0.25-N normal forces, −0.15- to 0.15-N shear forces, and 0- to 0.2-strain stretches with the sensor. The average sensitivities of the force sensor units were 0.0074 N−1, 0.0032 N−1, and 0.0046 N−1 for the normal, X-axis, and Y-axis shear forces. The stretch sensor units exhibited 3.2-strain sensitivity to stretching. Using the arrayed force sensor units, we demonstrated the sensor responsivity to the normal force distribution.