Safety-driven optimisation of human–robot collaborative assembly line balancing

In the dynamic field of advanced manufacturing, integrating collaborative robots (cobots) into assembly lines has emerged as a transformative approach to improve efficiency and human job quality. This paper addresses the safety challenge of human–robot collaboration (HRC) in the context of an assembly line balancing problem (ALBP) aimed at minimising cycle time. A constraint programming (CP)-based model optimally assigns cobots to workstations, allocates assembly tasks between humans and cobots, and sequence them on a single-model line. The CP model includes a novel workstation zoning policy to eliminate the medium and high-risk parallel tasks in a collaborative workstation. Numerical examples illustrate the impact of the proposed policy. Comparing the optimal results in the presence and absence of zone constraints in HRC-ALBP reveals improved safety at the cost of a minor increase in cycle time. This contributes to bridging the gap between HRC safety and operational goal. With minor modifications, a second version of the model minimises the number of cobots used, providing further insight into the optimisation of cobot integration. By considering different objective functions, safety-oriented constraints, and managerial insights, this work contributes to the creation of a decision-support tool that aligns with the human-cantered principles of Industry 5.0.