The influence of machine speed on human performance for simple and highly repetitive work processes.

Partially automated processing of horticultural products often contains simple and highly repetitive manual work processes. The handling of susceptible products, especially the feeding of conveying units, is difficult to mechanise. The machine capacities continuously increase and in consequence a higher material input is necessary. This is commonly realised by boosting the speed of material transport, but in practice a full capacity is rarely achieved. The manual material input is a shortcoming that needs to be optimised, taking into account that there are motivating aspects for the worker like a belt speed increase, but also risk factors resulting from the work task itself. Highly repetitive work can cause work related disorders. Job satisfaction is generally low in this work environment, offering no substantial task variation, with stress commonly present due to high production speeds. There should be a balance between task demands and worker's motivation and abilities. The purpose of this pilot study is to introduce a motion-based approach for assessing the effects of machine speed on worker's performance in a simple repetitive task. A conveyor belt and wooden sticks are used to simulate a simple and highly repetitive process of placing products on a moving belt. The influences of increasing machine speeds on the human performance and motion are investigated in this study. A 3-D-motion analysis system collects objective data (Jakob, 2005). Active infrared light emissive diodes are attached to the upper extremities of the subjects to record the motions. Three different machine capacities are run from 7300 pieces up to 10300 pieces per hour. The speed of the moving belt respectively rises from 0.19 m/s to 0.3 m/s. To decide on the optimal speed, knowledge about the product and the complexity of product placement is also essential. Within the experiments it was possible to determine major influence factors on the human performance, which is again influenced by many internal factors like abilities, health status or motivation and external factors like work technique and process organisation. Two different work techniques were identified. A synchronous work style proved to be more efficient, but at the same time caused more body movement as an asynchronous work style. Although the experimental work task was very simple, large variations in the human capacities were noticed. The operation breakdown limits the maximum human capacity and needs to be optimised first. The synchronous work style showed a greater potential for a performance increase induced by the machine speed but also by large variations in the individual performance-rate. To explain these variations the precise analysis of the motion tracks revealed more differences in the efficiency of individual job performance.