Internal array electrodes improve the spatial resolution of soft tactile sensors based on electrical resistance tomography

Robots operating in unstructured environments would benefit from soft whole-body tactile sensors, but implementing such systems typically requires complex electrical wiring to a large number of sensing elements. The reconstruction method called electrical resistance tomography (ERT) has shown promising results (good coverage, manufacturability, and robustness) using electrodes located only along the boundary of the sensing region. However, relatively poor spatial resolution in the sensor's central region is a major drawback of the ERT approach. This paper introduces a new scheme of internal array electrodes to improve spatial resolution. We also systematically derive the optimal pairwise current injection patterns from a mathematical formulation of the ERT system. By highlighting the importance of each electrode pair, this approach enabled us to reduce the number of current injection patterns. Simulation of the standard and proposed sensor designs revealed that the internal array electrodes greatly improve distinguishability in the central region. For validation, a fabric-based soft tactile sensor made of multiple conductive fabrics was developed, including electronics that enable sampling at 200 Hz. During a 225-point localization test conducted without sensor-specific calibration, the constructed sensor showed average localization errors of 2.85 cm ± 1.02 cm. This result is notable because only 16 point electrodes were used to achieve this performance.