Rigid versus soft exoskeletons: Interaction strategies for upper limb assistive technology

Compliant and soft materials are increasingly being used to design wearable robotic devices, with significant implications for the choice of the device’s control strategy. What was once a field dominated by rigid robots, now includes systems with different compliance, number of degrees of freedom (DOF), and mode of delivering forces to the human body. In this chapter we provide a simple taxonomy for assistive wearable exoskeletons for the upper limbs, based on their material and number of DOF, and comment on the implications of these features for the choice of an interaction controller. Finally, we compare two upper limb devices, with opposing hardware (rigid vs soft) and control characteristics, in an assistive task on healthy subjects. The chapter highlights the major differences of soft versus rigid exoskeletons and serves as a tutorial for the design of an appropriate interaction control strategy.