Integrating ergonomic risks evaluation through OCRA index and balancing/sequencing decisions for mixed model stochastic asynchronous assembly lines

In the paper we proposed and tested on a real industrial case, related to a company in the segment of Agricultural Equipment, an approach to design asynchronous assembly lines in compliance with ergonomic legislation. We considered the OCRA index as method for ergonomic risk assessment, as it is the preferred method indicated in international norms for detailed risk assessment related to handling of low loads at high frequency. A genetic algorithm approach able to integrate the ergonomic risks evaluation and balancing/sequencing is proposed. The approach allow designing line configurations taking into account many characteristics of the complex scenario of real industrial cases: mixed models assembly lines, stochastic task times, precedence constraints among tasks, equipment and line feeding duplication costs associated to parallel workstations. Thanks to the integration of a discrete event simulator, it is also possible to consider the effect of blocking and starvation phenomena on the effective cycle time and on worker's ergonomic load. The respect of ergonomic norms is often view by companies as an onerous obligation, being often associated to the increase of required manpower. Results show that, using the proposed approach, extra costs due to the compliance with ergonomic legislation can be very limited. This should encourage companies to adopt design methodologies able at the same time to comply with ergonomic norms and to defend their profitability.