Proposal of a complexity model for human-robot collaboration assembly processes

Assembly complexity in manual processes has been widely addressed over the years in manufacturing-related literature. The concept of complexity indeed is linked to the cognitive and physical effort required on behalf of the human operator in completing the assembly process and is directly linked to the occurrence of process failures and inefficiencies. In the light of the introduction of novel technologies such as collaborative robotics such paradigm should be revised. This paper presents a proposal for a complexity model, i.e., "C-HRC model", for Human-Robot Collaboration assembly processes. C-HRC model provides a multidimensional framework and a practical tool for analysing the complexity of collaborative assembly processes performed by humans supported by collaborative robots. In this situation, the collaboration with the robot may require an additional effort from the human operator, resulting in a more complex activity and thus more error prone. In this regard, the C-HRC model integrates insights from multiple disciplines to provide an overview of collaborative assembly complexity based on four layers: product complexity, assembly complexity, interaction complexity and collaboration complexity. The conceptual foundation of the C-HRC model is thoroughly detailed and supported by a review of the relevant literature. Hence, the paper uses the complexity formulation proposed by Samy and ElMaraghy as a basis to provide a quantitative approach. The model is then applied to practical case studies to demonstrate its application and illustrate how it can enhance the understanding of effective human-robot collaboration. This provides process designers with a practical tool to support design and improve collaborative assembly processes.