Control and performance of upper- and lower extremity SEA-based exoskeletons

In the last years compliant actuators have become extremely popular in the field of wearable robotics, due to their ability to realize safe human-robot interfaces. One of the most well-known example of a compliant actuator is the series elastic actuator (SEA), consisting of an elastic element (e.g. a spring) in series with a stiff actuator; such actuation architecture is considered to be the simplest design solution to realize compliant, compact, and light-weight actuators for wearable robots; in addition, from the control perspective, SEA architecture allows for simple force or torque control in addition to position control. In this chapter, three wearable robots for upper- and lower-limb rehabilitation and assistance, developed at The BioRobotics Institute of Scuola Superiore Sant’Anna, are described. The three devices have similar SEA-based actuation units, integrating commercial electromagnetic motors and custom torsional springs, with constant stiffness and linear torque-deformation characteristics. Closed-loop torque control performance show that the systems can be highly transparent when controlled under zero-torque modality, i.e. the interaction with the human is minimal and the actuators do not hinder the user’s movement, and bandwidths and output torques are compatible with the human movements to be assisted.