Designing a tool to assess design-related drivers of cognitive workload in collaborative assembly systems: a Delphi study

Collaborative assembly systems introduce new cognitive demands for operators due to dynamic human-robot interaction, making cognitive workload (CWL) assessment important for safety, performance, and well-being. Existing CWL assessment methods are often poorly suited to industrial practice, as they are retrospective, intrusive, or insufficiently focused on designable system characteristics. This study presents HERALD (Human-centric Evaluation of Robotics and Assembly cognitive LoaD), a practical indicator-based method for assessing designable sources of potential CWL in collaborative assembly workstations. A two-round Delphi study with experts in human factors, ergonomics, industrial engineering, and robotics was conducted to identify, refine, and evaluate the content relevance and practical usability of key CWL determinants. The resulting tool comprises 11 factors organised into task-related, workstation-related, and robot/interaction-related domains, operationalised through observable indicators. HERALD supports systematic evaluation and design by generating a factor-level diagnostic profile of workload-related design conditions, rather than directly measuring operators' momentary workload in collaborative assembly settings.