Evaluation of an Exoskeleton-based Bimanual Teleoperation Architecture with Independently Passivated Slave Devices

Search and rescue robotics is becoming a relevant topic in the last years and the growing number of robotic platforms and dedicated projects is the evidence of the interest in this area. In this context, the possibility to drive a remote robot with an exoskeleton is a promising strategy to enhance dexterity, reduce operator effort and save time. However, the use of haptic feedback (bilateral teleoperation) may lead to instability in the presence of communication delay and more complex is the case of bimanual teleoperation where the two arms can exchange energy. In this work, we present a bimanual teleoperation system based on an exoskeletal master, where multi-degrees of freedom (multi-DoFs) and kinematically different devices are involved. In the implemented architecture the two slaves are managed in parallel and independently passivated using the Time Domain Passivity Approach (TDPA) extended for multi-DoFs devices. To investigate the stability of the architecture we designed two tasks highly related to real disaster scenarios: the first one was useful to verify the system behavior in case of small movements and constrained configurations, whereas the second experiment was designed to involve larger contact forces and movements. Moreover, we compared the effect of both delay and low control loop frequency on the stability of the system when TDPA was applied. From the results, it was evident that the overall system exhibited a stable behavior with the use of the TDPA, even passivating the two slaves independently, under simulated time delay and in presence of a low control loop frequency

Gait Phases Blended Control for Enhancing Transparency on Lower-Limb Exoskeletons

A major challenge in the design and control of exoskeletons is the preservation of the user.s natural behavior when interacting with these machines. From this point of view, one of the most important features is the transparency of the exoskeleton. An ideally transparent exoskeleton follows the user's movements without interaction forces. This is the goal of many control algorithms proposed in the literature. Traditional algorithms are based on finite state machines and are affected by assistive torque discontinuity problems in the transitions between phases. State-of-the-art methods approach this problem by imposing a smooth transition that does not account for variable walking speed. In this work, the authors propose an innovative control algorithm for a lower-limb exoskeleton. The proposed control aims at solving the torque discontinuity problem, without requiring a smooth transitions strategy. The proposed control algorithm continuously blends the output of two independent single stance dynamic models, by weighting the contribution of each stance model to the total assistance based on the gait phase. A linear regressor is used to produce the weights, and it requires a brief user-specific calibration. Results showed a significant reduction of interaction forces, and a longer stride length when compared to two finite-state-machine-based controls at two speeds on the treadmill and one self-selected-speed in an overground walk