Assessing ergonomics on cobot for an optimized integrated solution in early phase of product and process design

The design goal for Human-Robot collaboration is combining the repeatability and productivity of automated systems with the flexibility of the operators [1]. One main interest is for cobots to take over complex and physically demanding assembly tasks, reducing the biomechanical workload on workers and increasing product quality. However, as reported by several authors [1-3], the introduction of cobots is not straightforward and should be thoroughly investigated and planned to avoid higher mental stress on workers and a decrease in efficiency. In this respect, Digital Human Modelling can support the integration of robots in design or evaluation of hybrid cells, anticipating process and interaction criticalities.One key aspect of hybrid cells is task allocation between worker and cobot. Recently, Authors in [4] proposed an optimization procedure that looks into productivity and ergonomics. However, the proposed approach is rather complex to apply and does not allow for evaluations of the what-if type, which are particularly useful in the development of new hybrid cells.The paper proposes a new methodology, which has the advantage of being simple and allowing for a visualization of shared operations through a simulator, and for a heuristic evaluation during the design phase of the hybrid workstation, and, finally, permitting a “what-if” analysis. The work is part of the research project D-HUMMER (Digital HUMan Model for ERgonomic workplace) funded by EIT Manufacturing (project number 22294).The simulation tools are the IPS IMMA and IPS Robotics that integrate in the same scenario the evaluation of the biomechanical load on different anthropometries of workers with the performance of the robot working cycle. The advantage of a full digital approach allows frontloading in Concept Phase the workstations’ layout and sequence, even considering different variants, before any production line is established.In the presented methodology, each working job scenario is represented by a state-machine (fig. 1), where each state defines a single atomic task (i.e. a single state) that may be fulfil by either the robot or the human operator, depending on the choice of the workplace designer. Each atomic task is characterized by several parameters (e.g. human strains, time of execution, etc.). In each of the simulator runs, a performance index I_k is computed:I_k = sum_(i=1, to n) alpha_i,k * t_i,k + beta_i,k * s_i,kwhere:k : is the index of each scenario, each represented by a state machine.i : is the index of each state in the state machine.t_i,k : is the time required for each atomic tasks_i,k : is the human strain required for each atomic taskalpha and beta are appropriate weights for each parameter.The paper presents the methodology through a real industrial use case of the Whirlpool microwave assembly. In the current workstation (fig.2) the operator assembles a heavy component (transformer), given by a robot that places it on a table. The worker has therefore the full weight of the component in hands. The optimized solution (fig.3) improves the robot usage, resetting the weight for the worker, and achieving better safety and ergonomics conditions.The methodology has been applied to an already-existing industrial solution. However, its application in early stage may mark a paradigm shift in the workstation design layout for manufacturing companies.