Shape Sensing of Variable Stiffness Soft Robots using Electrical Impedance Tomography

TL;DR

This paper introduces a novel electrical impedance tomography (EIT) based shape sensing method for variable stiffness soft robots, demonstrating accurate, real-time shape reconstruction in two prototype designs with high repeatability.

Contribution

The paper presents a new FDM-EIT system for soft robot shape sensing, enabling high-resolution, real-time tomographic imaging with a low-cost, compact setup.

Findings

EIT measurements accurately infer shape changes during actuation.

Reconstructed EIT images show distinct patterns for different degrees of freedom.

High measurement repeatability despite some mechanical hysteresis.

Abstract

Soft robotic systems offer benefits over traditional rigid systems through reduced contact trauma with soft tissues and by enabling access through tortuous paths in minimally invasive surgery. However, the inherent deformability of soft robots places both a greater onus on accurate modelling of their shape, and greater challenges in realising intraoperative shape sensing. Herein we present a proprioceptive (self-sensing) soft actuator, with an electrically conductive working fluid. Electrical impedance measurements from up to six electrodes enabled tomographic reconstructions using Electrical Impedance Tomography (EIT). A new Frequency Division Multiplexed (FDM) EIT system was developed capable of measurements of 66 dB SNR with 20 ms temporal resolution. The concept was examined in two two-degree-of-freedom designs: a hydraulic hinged actuator and a pneumatic finger actuator with hydraulic beams. Both cases demonstrated that impedance measurements could be used to infer shape changes, and EIT images reconstructed during actuation showed distinct patterns with respect to each degree of freedom (DOF). Whilst there was some mechanical hysteresis observed, the repeatability of the measurements and resultant images was high. The results show the potential of FDM-EIT as a low-cost, low profile shape sensor in soft robots.