IMU-based Transparency Control of Exoskeletons Driven by Series Elastic Actuator

Wearable devices such as rehabilitation robots, power augmentation exoskeletons, and haptic manipulators feature operation modes that need to mirror the user's action as naturally as possible. By tracking such motions, the human-robot physical interaction is minimized, or, in other words, the device displays effusive mechanical transparency. The present work applies a transparency control framework based on inertial measurement units fixed on the user to a series elastic exoskeleton joint. This approach guarantees the robot's transparent behavior without explicitly relying on force or human-robot interaction sensors. Instead, we used a state estimator to provide the human-related quantities needed for feedforward and feedback control. The proposed controller considers the dynamics of the series elastic actuator for two motor driver configurations: torque-based and velocity-based low-level control. Using a novel definition of the human-robot transparency impedance, we designed and experimentally evaluated the performance of both controllers.