Uniformity in manikin posturing: A comparison between posture prediction and manual joint manipulation

Journal article, 2008

This paper presents the results of a comparison of manikin posturing within and between simulation engineers. Five simulation engineers were asked to simulate and visualize four manual assembly cases. They repeated each task six times, three times with a posture prediction tool and three times with manual adjustment of the body angles. The results show that the posture prediction tool was not used in an optimal manner. Although the prediction tool was quick at suggesting a likely posture, the simulation engineers were reluctant to consider a simulation task completed until the manikin’s posture was realistic in all aspects, not only in the configurations for the major body joints postures but also for fingers, wrists and feet. This fine tuning of fingers is performed with manual manipulation of joints and cancels out the time gained with the posture prediction tool. The fine tuning does not affect the results in objective evaluation methods. Therefore, a lower acceptance level of correctness among managers, simulation engineers and ergonomic specialists is desired, or a shift from visualization to simulation is necessary. Manikin postures differ between simulation engineers. A posture variation exists and this variation in working behaviour should be accepted and simulated. However, simulation engineers also need more extensive knowledge of how workers actually behave on the assembly line; study visits are thus recommended. A shift is also recommended from simulations and visualizations of normal working behaviours to that of ergonomically correct behaviours. This comparison of manikin posturing within and between simulation engineers is an attempt to understand the use of the tool in a practical sense. The comparison indicates that if a posture prediction tool is to be beneficial for the whole organisation, all disciplines involved in the use of manikins must accept simulation results with postures containing some non-cosmetic elements. It is not until such an acceptance is achieved that the successful use of a posture prediction tool will become a reality.