Ergonomic Posture Analysis of Automobile Assembly Jobs based on Multi-Year Observation Data

Abstract

Posture is represented as a composite of the positions of all human joints, and human naturally takes posture at any moment whether it is good or bad. Good posture is a necessary condition for healthy life. Now, the importance of good posture becomes a universal truth. On the contrary to this, bad postures induce various illnesses or disorders, in particular, musculoskeletal disorders. Musculoskeletal disorders bring pains or agonies in musculoskeletal systems, and can be exacerbated to some kinds of cumulative disorders. In the industrialization era, repetitive works become main jobs for workers, so that the workers have to specialize in the repetitive works. Consequently, the prevalence of musculoskeletal disorders, which are work-related disorders, has been growing higher. Plenty of researches have been conducted to prevent or deal with the work-related musculoskeletal disorders. The researchers have focused on grasping risk factors for work-related musculoskeletal disorders so far. The results clearly reveal that awkward posture, excessive force, and repetition during work are the most influential factors. Among these factors, the working posture is the one mostly referred to. Nonetheless, dissimilar to the work-related musculoskeletal disorders, contributing factors for working posture have not been investigated enough. Previously, it was mainly concerned how a working posture varies when a worker takes a specific posture, for example reaching, in a particular context. There is no single study on the understanding the contributing factors for the working posture among various factors in a work site. This dissertation starts with this motivation, and aims to resolve this research question: which factors are the contributing factors for working postures, and how much are they influential? It is practically impossible to consider every variable to resolve this question, so the study should be preceded by selecting a candidate set of expected contributing factors. To get the candidate set, we primarily referred to literature on this issue. Unfortunately, there was little researches on this subject, so we additionally paid attention to the studies on the risk factors for the work-related musculoskeletal disorders. The first part of this dissertation is an overview study of existing systematic reviews. Through the overview study, risk factors for work-related musculoskeletal disorders were collected, and the terminologies were standardized. Moreover, associations between the risk factors and work-related musculoskeletal disorders were analyzed for each body part. Based on the result of the analysis, the candidate set was drawn. The candidate set was composed of individual and physical exposure factors. For the drawn candidate set, the factors were measured through field researches. A series of field research had been conducted in an automobile assembly plant for seven years. The gathered data contained the two factors mentioned above and the working posture. Through statistical analyses of the data, the contributing factors were finally determined. Then, their influence was analyzed as well. Existing ergonomic assessment methods normally deliver a risk level and an action level. However, the results are not differential, and the basis is not very concrete. Moreover, these existing methods do not consider from job satisfaction and job stress viewpoints. To this end, at first, comparisons among the existing methods were carried out. Then, job satisfaction was estimated using the assessment methods. Finally, quantitative models for job satisfaction and job stress were suggested using statistical analysis and machine learning techniques. While pooling the data from the work site, we attempted to find ergonomic problems in the work site and to resolve the problems. It is so much important to clear up ergonomic problems from ergonomic and working postural perspectives. Hence, in this dissertation, the ergonomic problems in an automobile assembly plant were figured out. Then, appropriate interventions were suggested. After that, through a follow-up study, the effectiveness of the implemented interventions was analyzed by comparing before and after the interventions regarding the working postures and the results of ergonomic assessment methods. Lastly, to manage musculoskeletal disorders in the work site effectively, it is required to manage numerous information efficiently. The efficiency of information management is determined by ease of data input and retrieval. From this perspective, a database system is the most proper system for monitoring the information on musculoskeletal disorders. Thus, we constructed a database system appropriate to the work site. The database system was built on a web-based platform to increase the accessibility. Additionally, software for postural analysis was developed for more reliable and accurate analysis of the working posture. The two systems suggested in this study are expected to help both academic researchers and practitioner in the real field.