Messtechnisch unterstützte Quantifizierung der Repetitionsbelastung des Hand-Arm-Systems bei manuellen Arbeitsprozessen an modernen Montagearbeitsplätzen und deren Bewertung

Abstract

Measurement-based evaluation of the repetitive strain on the hand-arm system during manual work processes at modern assembly workplaces Objective: On both modern assembly lines and U-shaped lines, the workplaces comprise multiple workstations or work processes with differing requirements. This presents difficulties for recognition and assessment of the repetitive nature of the activity as a whole. This paper presents the measurement of repetitive strains on the upper extremities on real-case U-shaped assembly line systems. Methods: In a field study, a total of 24 workers in six plants in the metalworking and electrical engineering sectors were analysed at 18 different U-shaped assembly line workplaces. Movements of the hand-arm system and muscular activity of the hand flexor muscles (M. carpi ulnaris) and the trapezius muscles were recorded at each workplace over a period of between 1 and 2 hours by means of the CUELA measurement system and surface electromyography (EMG). Results: The medians of the angular velocities of the wrist varied between the different workplaces from a low of 2.4 °/s to a high of 20.5 °/s. Correspondingly, the average movement frequencies of the wrist lay between 0.23 and 0.43 Hz. Conversely, the micropause components (angular velocity < 1 °/s for Δt > 0.5 s) reached values between 13.5 % and 1.6 % of the working time. Without any evident relation to the kinematics, the surface EMG of the forearm flexors exhibited on average a dynamic (P90) load of around 20 % of the individual maximal voluntary EMG activity (MVE). At half of the workplaces however, the micro pauses (time component EMGRMS < 0.5 % MVE) totalled only 10 % or less of the recorded working time. Conclusions: Repetitive strains on the hand-arm system were also quantified in the field at workplaces differing in their degree of automation and with alternating workstations. Although the dynamic forces that must be applied at modern assembly lines are generally quite moderate, the associated repetitive strains are often high. This must be taken into particular consideration when planning job rotation on assembly lines. Keywords: assembly line – manual work processes – U-shaped assembly line – repetitive strain – workload analysis based on measured data