Fig. 2

General control system diagram. The signals from the Human–Exoskeleton—e.g., human–robot interaction forces, limbs’ kinematics, and/or recorded human muscle or brain activity—are processed sequentially by three different blocks—each corresponding to High-, Mid- and Low-level control, to generate the actuation command. High-Level Control: the Control Aim defines the role of the exoskeleton in the overall performance of the human-exoskeleton system, i.e., enhance or hinder task completion. The Human–Robot Synchronization block generates an estimation of the actual state and is used by the Mid-level control, together with the control aim, to provide reference values—e.g., desired position or force—to the Low-level control. The Low-level Control then transforms that reference into actual assistive/resistive force/motion and sends the actuation command to the exoskeleton hardware