Toward a Human-Machine Interface Based on Electrical Impedance Tomography for Robotic Manipulator Control

In this study, we proposed a novel human-machine interface (HMI) for robotic manipulator control. The specific target was to adjust the impedance coefficients of the robot controller in real time by measuring the human forearm muscle contractions. We firstly designed a HMI system. Different from the frequently used sEMG technologies, the interface in our study could detect muscle morphological changes within the skin by the electrical impedance tomography (EIT). The sensing front-end was a soft elastic fabric band which was compatible to different arm shapes. With the specific designed sensing hardware and the re-construction algorithms, EIT images indicating forearm muscle shapes were obtained. We then designed a hybrid positon/impedance controller on a UR5 with the impedance coefficients being tuned in real time by the grasp force estimation. A sigmoid regression algorithm was used to map the EIT images to the grasp forces. After implementation of the whole system, two experiments were carried out. The first experiment was the off-line grasp force estimation. With the 1:1 cross validation, an average R2 of $0.83 \pm 0.04$ and an average of the relative root mean square error (RRMSE) of $0.31 \pm 0.10$ across 5 subjects were yielded. The second experiment was the real-time robot control. Trajectory tracking task with dynamic uncertainties were investigated and grasp forces were estimated in real-time. With higher muscle contraction levels, smaller position errors were observed and shorter time was needed to return to the expected trajectory when there were external disturbances. The results proved the feasibility of the new approach on human-robot interaction tasks. Future endeavours will be made to get more promising results.