An energy-centric perspective on safety for physical human-robot interaction under ISO guidelines

The International Organization for Standardization (ISO) defines safety as the ability of a robotic system to operate within limits that reduce risks to humans to an acceptable level. However, ISO standards (such as ISO/TS 15066 and ISO 10218–2) contain ambiguities that may lead to inconsistent risk assessments or hazard underestimation. This Perspective Article presents an energy-centric viewpoint on safety in physical human-robot interaction (pHRI). Building on our previous critical review of pHRI safety constraints, the article isolates and explicates one central theme emerging from that analysis: the role of mechanical energy in interpreting ISO/TS 15066 transient-contact limits. Specifically, we discuss how pain-related force limits can be mapped to admissible elastic energy stored in tissue deformation, why the instant of maximum deformation is central for transient-contact assessment, how this interpretation changes under free-recoil and potential-clamp conditions, and why energy-based metrics remain insufficient as standalone descriptors of pain perception or sustained-contact risk. We conclude by outlining open challenges and future research directions for leveraging energy-centered metrics toward safe and effective human-robot interaction.