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

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

Assessing effects of exoskeleton misalignment on knee joint load during swing using an instrumented leg simulator

Background: Exoskeletons are working in parallel to the human body and can support human movement by exerting forces through cuffs or straps. They are prone to misalignments caused by simplified joint mechanics and incorrect fit or positioning. Those misalignments are a common safety concern as they can cause undesired interaction forces. However, the exact mechanisms and effects of misalignments on the joint load are not yet known. The aim of this study was therefore to investigate the influence of different directions and magnitudes of exoskeleton misalignment on the internal knee joint forces and torques of an artificial leg. Methods: An instrumented leg simulator was used to quantify the changes in knee joint load during the swing phase caused by misalignments of a passive knee brace being manually flexed. This was achieved by an experimenter pulling on a rope attached to the distal end of the knee brace to create a flexion torque. The extension was not actuated but achieved through the weight of the instrumented leg simulator. The investigated types of misalignments are a rotation of the brace around the vertical axis and a translation in anteroposterior as well as proximal/distal direction. Results: The amount of misalignment had a significant effect on several directions of knee joint load in the instrumented leg simulator. In general, load on the knee joint increased with increasing misalignment. Specifically, stronger rotational misalignment led to higher forces in mediolateral direction in the knee joint as well as higher ab-/adduction, flexion and internal/external rotation torques. Stronger anteroposterior translational misalignment led to higher mediolateral knee forces as well as higher abduction and flexion/extension torques. Stronger proximal/distal translational misalignment led to higher posterior and tension/compression forces. Conclusions: Misalignments of a lower leg exoskeleton can increase internal knee forces and torques during swing to a multiple of those experienced in a well-aligned situation. Despite only taking swing into account, this is supporting the need for carefully considering hazards associated with not only translational but also rotational misalignments during wearable robot development and use. Also, this warrants investigation of misalignment effects in stance, as a target of many exoskeleton applications

COVR Toolkit: Supporting safety of interactive robotics applications

International audienceCollaborative robots (cobots) are increasingly finding use beyond the traditional domain of manufacturing, in areas such as healthcare, rehabilitation, agriculture and logistics. This development greatly increases the size and variations in the level of expertise of cobot stakeholders. This becomes particularly critical considering the role of human safety for collaborative robotics applications. In order to support the wide range of cobot stakeholders, the EU-funded project COVR Being safe around collaborative and versatile robots in shared spaces has developed a freely available, web-based Toolkit that offers support to understand how to consider the safety of cobot applications. This paper describes the state of the art for ensuring safety across various life cycle phases in the development and implementation of collaborative robotics applications and highlights how the Toolkit provides practical support during these tasks. The Toolkit aims to be the most comprehensive resource for supporting cobot stakeholders in ensuring the safety of their applications

An Online Toolkit for Applications Featuring Collaborative Robots Across Different Domains

Saenz J, Bessler-Etten J, Valori M, et al. An Online Toolkit for Applications Featuring Collaborative Robots Across Different Domains. IEEE Transactions on Human-Machine Systems. Submitted