Toward a bio-inspired rehabilitation aid: sEMG-CPG approach for online generation of jaw trajectories for a chewing robot

The purpose of this study was to develop a bio-inspired masticatory robot that generates real-time trajectories, using surface electromyography signals (sEMG). We employed the central pattern generator (CPG) concept to generate smooth transitions from one chewing pattern to another during an exercise. Online changes in the recreated chewing patterns were provided based on the features extracted from the sEMG of the masticatory muscles of a tele-operator. The proposed method employed several concepts, including kinematics, sEMG feature extraction and selection, classification, and robotic control. First, chewing patterns were recognized by a multiclass support vector machine based on time-domain features extracted from sEMG signals. Next, CPG neurons generated a suitable trajectory for the robot actuators to reproduce the corresponding chewing pattern in the jaw (supposedly mounted on the moving platform of a 6RSS robot). The performance of the proposed approach was examined using a semi-real life chewing scenario. The average recognition rate for all the chewing classes, time windows, trials, and subjects was 86.36% +/- 5.2%. Despite the sudden changes in the chewing patterns throughout the experiment, variations in actuator angles during transitions were smooth due to the limit cycle property of the CPG. The proposed method provided a solution for some inherent problems in generating a smooth and continuous trajectory in applications related to rehabilitation robots. This would make the proposed system and methodology feasible for a rehabilitation robot in real life exercise therapy. (C) 2019 Elsevier Ltd. All rights reserved.