Beyond Physical Safety in Human–Robot Collaboration: Investigating Speed and Proximity Effects in Mental Workload
DOI: 10.54941/ahfe1007393
archive: archived pipeline: cataloged verified
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Summary
This study addresses the gap in human–robot collaboration (HRC) safety standards, which currently prioritize physical risks while neglecting cognitive factors like mental workload. The authors investigate how collaborative robot (cobot) speed and human–robot proximity influence operators’ mental workload during shared tasks. Motivated by the need to understand cognitive demands in dynamic industrial environments, the research tests three hypotheses: that cobot speed, proximity, and their interaction significantly modulate mental workload. The experiment employed a within-subject design with 25 participants (21 included in final analysis) performing a shelf-replenishment task with a Sawyer cobot. The task involved verifying product expiration dates and sequencing items, requiring coordination and temporal monitoring. Two variables were manipulated: robot speed at three levels (0.3 m/s, 0.5 m/s, and 0.9 m/s) and proximity at two levels (near, corresponding to elbow reach; far, corresponding to full arm extension), resulting in six experimental conditions. Mental workload was assessed using a multimodal approach: subjective ratings via the Subjective Workload Assessment Technique (SWAT), performance metrics (error rates), and physiological data from functional near-infrared spectroscopy (fNIRS) measuring pre-frontal cortical activity. Results indicated that robot speed was the primary determinant of mental workload. High speed (0.9 m/s) significantly increased perceived mental demand, stress, and error rates compared to lower speeds. Proximity alone did not produce significant global effects on workload; however, it acted as an amplifying factor, with the combination of high speed and near proximity yielding the highest workload scores and greatest variability. Performance data mirrored subjective findings, showing increased error rates and behavioral dispersion at higher speeds. Physiological measures confirmed pre-frontal engagement during task execution relative to baseline, but differentiation among specific experimental conditions was modest. The fNIRS data showed increased inter-individual variability in hemodynamic responses under high-demand conditions rather than uniform amplitude shifts, suggesting that escalating workload manifests as reduced regulatory stability before producing strong neural amplitude differences. The study concludes that regulating robot speed is a critical mechanism for maintaining mental workload within functional limits in HRC settings. While proximity alone has limited impact, it exacerbates cognitive demand when combined with high operational intensity. The findings suggest that excessive speed compromises performance stability and increases cognitive load, potentially leading to errors. The integration of subjective, performance, and physiological indicators provides a comprehensive neuroergonomic assessment framework. The authors recommend that adaptive control systems dynamically adjust robot speed based on operator workload to optimize safety and efficiency, moving beyond physical safety standards to include cognitive ergonomics in HRC design.
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| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
| discover | success | Crossref | — | — | 1 | 2026-08-09 |
| archive | success | canonical_url | — | — | 1 | 2026-08-09 |
| extract | success | cached | — | — | 3 | 2026-08-10 |
| clean | success | clean | — | — | 1 | 2026-08-09 |
| chunk | success | chunk | — | — | 1 | 2026-08-09 |
| embed | success | embed | Qwen/Qwen3-Embedding-8B | — | 1 | 2026-08-09 |
| promote | success | — | — | — | 1 | 2026-08-09 |
| summarize | success | llm | qwen3.6-27b-nvidia | summ-v5 | 2 | 2026-08-10 |
| tag | success | vector_similarity | — | — | 11 | 2026-08-11 |
| verify | success | — | — | — | 2 | 2026-08-10 |
Summary generated by qwen3.6-27b-nvidia on 2026-08-10; verification: verified.
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- Empirical Findings: physiological data