Motion analysis system for the ergonomic assessment of manufacturing and assembly manual activities

The environment of manufacturing and assembly manual activities radically evolved in the last decades. First, the western world workforce is alarmingly aging. In the last 15 years the percentage of European employees older than 50 years rose from 21.6% to 30.4%. Furthermore, the latest developments in legislations (EU Machinery directive, 2006/42/EC, 89/391/EEC, Occupational Safety and Health act) force the companies to assess, monitor and safeguard the health of their operators. Finally, an increasing pressure from the civil society and the stakeholders pretends safe working conditions in manufacturing and assembly processes. This paper tackles these issues proposing an original Motion Analysis System (MAS) for the ergonomic assessment of human operators involved in industrial processes. This research exploits different motion capture (MOCAP) technologies, e.g. optical, inertial and miscellaneous, to register the static postures and the dynamic movements of an operator during manufacturing or assembly activities. The information provided by the MOCAP technologies about the evolution over time of the position and orientation of the skeleton segments are processed by the MAS. This system calculates for each monitored frame the angle values of all the relevant joints of the human body accurately reproducing the operator movements. Furthermore, the MAS assesses the risk of musculoskeletal disorders of the performed manufacturing and assembly activities with the automatic evaluation of three ergonomic indices considering the features of the products and tools which the operator pick and handle. Along with the calculation of REBA and OWAS indices, an original one is developed and proposed based on the ISO 11226:2000 norm. The MAS is tested and validated with the industrial case study of a gearbox assembly process comparing the novel ergonomic index with the traditional ones. The results suggest that the proposed index accurately evaluates the ergonomic risk of specific assembly tasks compared to the classical approaches.