Implementation and evaluation of a soft tactile sensor using electrical impedance tomography

Compliant tactile sensing has received increasing interests in human-robot interactions and soft robotic sensing. However, it is still challenging to achieve high sensing performance over an area with low wiring complexity. This paper is to implement and evaluate a soft, distributed sensor that is enabled by the technique of electrical impedance tomography (EIT), which allows areal sensing using only boundary measurements. To achieve mechanical compliance of the sensor, a functional natural rubber composites filled with exfoliated graphite (EG/NR) is fabricated by spray coating. Long-term stability of the sensing material is evaluated under cyclic tests, and a high gauge factor of 6.25 is obtained, which can be explained from the evolution of the micromorphology under strain. A continuous sensing area with a diameter of 12 cm is prepared, and 16 electrodes are attached along the periphery to implement distributed sensing. The performance of the sensor is characterized under indentation tests. Results show that the intensity sensitivity monotonically decreases with the distance to the boundary, and consistent response is obtained along all the radial directions, providing predictable performance over the sensing area.