RESUMO
OCRA (OCcupational Repetitive Action) is currently one of the most widespread procedures for assessing biomechanical risks related to upper limb repetitive movements. Frequency factor of the technical actions represents one of the OCRA elements. Actually, the frequency factor computation is based on workcycle video analysis, which is time-consuming and may lead to up to 30% of intra-operator variability. This paper aims at proposing an innovative procedure for the automatic counting of dynamic technical actions on the basis of inertial data. More specifically, a threshold-based algorithm was tested in four industrial case studies, involving a cohort of 20 workers. Nine combinations of the algorithm were tested by varying threshold values related to time and amplitude. The computation of frequency factor showed an average relative error lower than 5.7% in all industrial-based case studies after the appropriate selection of the time and amplitude threshold values. These findings open the possibility to use the threshold-based algorithm proposed here for the automatic computation of OCRA frequency factor, avoiding the time efforts in video analysis.
RESUMO
Professional drivers have been found to be at a high risk of developing low back pain due to prolonged sitting and vehicle vibration. In a previous survey carried out on 1,155 tractor drivers, tractor vibration and/or incorrect posture while driving were found to cause low back disorders in more than 80% of the interviewed drivers. In this context, the present research introduces a new evaluation protocol to assess the ergonomic characteristics of agricultural tractor seats through the use of pressure sensors, taking into account both static and dynamic conditions. The degree of comfort was defined by analyzing the pressure distribution exerted by a sample of 12 drivers sitting on two seats in five different operating conditions. The pressure distribution values thus obtained were compared with the corresponding pressures recorded with the 12 drivers sitting on a reference seat (rigid seat, backrest, and suspension) designed for the purpose. From the comparison, it was possible to define a comfort index (CI) that allowed an objective assessment of the two seats. Statistical analysis showed that the CIs of the two seats were significantly different in all five operating conditions. Moreover, the two seats showed different CIs as a function of the operating condition. Although less comfortable, one seat showed almost constant CI values in all five operating conditions. Conversely, the other seat showed a progressively decreasing CI from the static condition to the uneven ground condition.