Improving transparency of powered exoskeletons using force/torque sensors on the supporting cuffs

Most of the control strategies embedded in recent robotic exoskeletons for rehabilitation and assistance are specific implementations of the well-known "assistance as needed" paradigm. A key point in the design of these systems is the requirement for the robot to exert negligible interaction forces to the wearer if he/she is performing well. Optimizing transparency of a device is a challenging task: various strategies have been proposed to achieve this goal, involving both the mechanical structure of the robot and the control algorithms. In this work, we propose a simple yet effective approach that requires minimal redesign efforts in the robotic structure and in the controller to be implemented on existing devices. We experimentally validate the method by comparing kinematic, kinetic and electromyo-graphic data collected from 3 healthy subjects as they walked in three different conditions: free treadmill walking, walking in a robotic trainer with a traditional zero-impedance configuration and walking in the same robot with the new zero-impedance configuration. Results show that the novel configuration was capable of effectively reducing the interaction forces and, as a consequence, it affected subjects' natural gait less than the traditional one did.