Proposal of Work Posture Evaluation Method Focusing on Assembly Height and Direction for a Large Product

Abstract

In the production field, savings in labor and manpower are being achieved by means of automation and mechanization of processes. However, several operations still partly depend on manual work in assembly, inspection, and equipment maintenance processes. In particular, assembly operations for large products force workers to match their postures to the work positions of the products and equipment. Maintaining and repeating such awkward postures increases the workload and causes lower-back pain and upper-limb disorders. To evaluate work posture in the production field, methods based on observation by analysts are often used. Representative methods include OWAS, RULA, and REBA, all of which are readily available. However, results depend on the analyst's skill level and evaluation of the worker's posture is time-consuming. In this study, we propose a method for easily estimating posture during assembly work. An experiment was conducted to clarify the effects that assembly height and direction have upon work posture, and the evaluation value of the work posture was determined under each condition based on OWAS. Then, a table based on OWAS was constructed incorporating the height of the worker and height and direction of the assembly parts as inputs for estimating work posture. Furthermore, we verified the accuracy of this technique. The correlation coefficient between observation by an analyst and the proposed method was 0.77, and the estimation accuracy was 61.2%. This result indicates that the proposed method is valid.