Safety first in rehabilitation robots! Investigating how safety-related physical human-robot interaction ca be assessed

Abstract

In recent years, various robotic devices have been developed to be used in rehabilitation, assist patients, compensate for or alleviate disabilities. Those rehabilitation robots interact very closely with humans and transfer energy to their body to fulfil their purpose. This naturally introduces risks which have to be assessed carefully as rehabilitation robot use should be safe for patients and healthcare professionals. The main aim of this thesis was to gain more insight into safety challenges in rehabilitation robotics and to take first steps towards addressing those challenges.We found that excessive loads on the soft tissue and musculoskeletal tissue can be considered the most relevant hazards in physical interaction between rehabilitation robots and their users. The nature of interaction in rehabilitation robotics, characterized by continuous contacts, cyclic loading, vulnerable users, and sometimes uncontrolled environments, makes safety considerations complex. Even relatively small forces can lead to hazardous situations when they are e.g. applied for long durations, to impaired body structures, in interfaces with peak stresses or unfavorable microclimates. Safety validation experiments can be a useful approach to test physical human-robot interaction, preferably without a human in the loop, and develop mitigation strategies to reduce (peak) stresses and loads. Misalignments are a prominent issue in exoskeleton use. We have shown that misalignments can affect knee joint loads significantly in a dummy during swing. Another study revealed that discomfort increases over time when repetitive loads are applied through an exoskeleton cuff-like interface and that perception of comfort varies considerably between subjects. Future research should extend current knowledge by focusing on accurate measurement methods for the force interplay at the human-robot interface; investigating the effects of misalignments in weight bearing situations; and researching changes in discomfort over time in extended (patient) populations. The research in this thesis provided insights into current safety issues and research gaps regarding rehabilitation robot safety. It is a first step towards building a knowledge base which can support the development and market entrance of safer rehabilitation robots though comprehensive guidelines.