What is the repercussions of the introduction of a cobot on productivity and biomechanical constraints on operators in a collaborative task?
Authors: Bouillet Kévin , Lemonnier Sophie , Clanche Fabien , Gauchard Gérome 
Published: June 2023

Collaborative robots, or cobots, are robots designed to closely collaborate with a human in a shared workplace. Introducing a cobot in a collaborative work situation aims to preserve productivity without impair the operator’s health, even improve them. Musculoskeletal disorders (MSDs), main occupation diseases in Industry, are pathologies of multifactorial origin, as biomechanical solicitations are one of them (e.g., posture, repetitiveness).This paper evaluates the repercussions of the introduction of a cobot in a collaborative task with two studies: first to compare a task in collaboration with a cobot or a human co-worker and second to analyze the impact of pace (i.e., rhythm and leader); both on productivity, quality of interactions, operator’s posture and attentional demand.Thirty-four participants in Study 1 and twenty in Study 2 performed a collaborative task inspired by assembly lines in factories, in collaboration with a co-worker. In Study 1, this co-worker was either a human or a YuMi cobot, participants were always the leader; in Study 2, the co-worker was always the YuMi cobot; the leader was either the participants or the cobot, and in this last case, different paces were imposed. Productivity was measured with the number of products manufactured, quality interactions with the rate of idleness and activity of participant and co-worker and interactions rate between them, participant’s posture with joints angles and RULA evaluation and attentional demand with performance at a second task.In Study 1, productivity was less important with the cobot than with a human, with less interactions and with higher attentional demand. However, posture was less risky with the cobot for operator health in terms of MSDs. In Study 2, productivity and attentional demand increased with the pace until a threshold at the mean-imposed pace. Posture was riskier for operator health in terms of MSDs only for the fastest imposed pace.In Study 1, deterioration of productivity and quality of the interactions with the cobot co-worker was mainly due to the limited capabilities of the cobot. Results about posture were also linked with pace, but differences were also observed during operator’s activity with less biomechanical solicitations working with the cobot than with the human for the same actions. Leading or following the pace seemed to not influence these variables in Study 2. Thus, the results of Study 2 seemed to indicate that the differences between human-human and human-cobot interactions observed in Study 1 were mainly due to the slower pace due to the cobot, except for the better posture which could be linked with the introduction of the cobot.Even though the experiment took place in a laboratory, the task was strongly inspired by the field and the results are consistent with those in the literature. These results therefore allow us to establish solid hypotheses that can be generalized to real situations in a factory, especially concerning the improvement of the posture when the operator is facing a cobot.