Movement variability highlighted during an assembly activity

Movement variability is often neglected when analysing work situations. It is also practically ignored when designing work situations, designers being focused on the aim of defining standard procedures that minimize production cycle times. In this context, the aim of this laboratory study was to characterize the variability of the movement involved in performing an assembly task, and more particularly the influence of the age of the operator and of the pace of work on the coordination of the upper limbs.
65 subjects belonging to 3 age groups (30-35, 45-50, 60-65 years) assembled parts at two paces of work: comfortable and rapid. The task was to assemble together a handle and a support by means of two nuts. For each pace, each assembly required from 12 to 15 seconds, the task being repeated for 20 minutes. The analysis of the assembly process focused on coordination of the upper limbs and was conducted on the basis of video recordings, using an observation table specifically developed for the task.
This analysis made it possible to identify 44 types of coordination for assembling the parts, 3 of which corresponded to 78% of the assemblies made. According to the preliminary statistical analyses, neither the age of the subject nor the pace of work significantly changed the number of types of coordination used.
Although, for the task studied, neither age nor pace seem to be influencing factors, these findings show that wide variability can exist in performing an assembly task. Neglecting movement variability as of design of a work situation could result in the future activity of the operators being understood only partially, leading to the risks not being fully assessed.