A Soft Wearable Elbow Skeleton for Safe Motion Assistance by Variable Stiffness

Abstract Wearable robots could provide external physical assist, contributing to the well-being of elderly or disabled users in accomplishing tasks or therapeutic procedures. However, closely integrating robot dynamics into human activity demands for safety, pleasance and effectiveness simultaneously, requiring both strength and compliance. Soft robotics is generally regarded as a suitable alternative to rigid motor-based actuators for their light weight and passive compliance. However, existing approaches either have predetermined and/or limited passive compliance, or have moderate payload or motion range. While proven very successful in hand actuation in terms of various robotic gloves, their fundamental limitations restrict further expansion to driving other human body parts with higher demands in payload and speed. Previously we have developed an origami soft robotic joint with high torque, customizable dimensions and motion range. In this paper, we report the most recent results on controller development and wearable system integration of the proposed soft actuator in achieving excellent variable-stiffness compliant performance with inherent safety. Using the newly proposed controller, we demonstrate that a higher stiffness leads to quicker passive recovery than human’s normal reaction, suitable in stabilizing common object; while a more submissive configuration, represented by a lower stiffness, could delay the submissive interaction time allowing for a more delicate control of the dynamics of the interaction port with further involvement of human commands, suitable for objects requiring smoother dynamics like preventing a cup of coffee from sloshing. The proposed control strategy and framework has been implemented in a 3D-scanned, 3D-printed wearable robot with elbow actuation, to demonstrate the advantages and new features through experimental results.