Development of a Motion Recording System Using a Combination of Head Direction and Thigh Direction for WRMSDs Risk Evaluation

摘要

Posture and motion analysis during working time are very important to evaluate the risk of work related musculoskeletal disorders (WRMSDs). During the working hour, the worker will assume many types of postures and motions. The risk level of WRMSDs may be related to the accumulative effect of workload that is induced by working postures and motion during daily working life. Accumulative effects may be from both the total amount of physical workload and the loading patterns. Recording of working posture and motion during the entire working time is needed to evaluate the accumulative effect of workload in an individual's job. There are many methods for evaluating of working posture and motion such as the Ovako Working Analysis System in addition to various motion recording systems. However, it is difficult to collect working posture and motion data for the entire working day. Almost all working posture-evaluating methods should be completed manually by observers, and the working space is restricted due to the limitation of image sensor as angle of view and the obstacles in workplace. The development of a new motion recording system specific for the occupational health field is needed to evaluate the accumulative effect of posture and motion. So, the aim of this study is to develop the new motion recording system that is specific to evaluating the risk of WRMSDs. The required functions for a new motion recording system are as follows. 1) Portable and stand alone system to cover all areas in the workplace; 2) Compact size and lightweight to prevent obstructions of work tasks; 3) Long battery life to record during whole working time. To realize these functions, following two important problems should be solved. 1) Body motion has to be detected by motion sensors that are put on worker's body and not an image sensor like a camera in order to be portable; 2) The whole body motion needs to be detected from the movement of a few body parts to decrease number of sensors and increase recording time. The idea presented in this paper is that the working posture and motion might be estimated by the combination of the triaxial direction of the head and triaxial direction of the thigh. We believe that the human body motion during working is not as complicated as compared to the motion during that occurs during sports and dance, and that high precision measurements will not be required to estimate the risk level of WRMSDs. In this paper the relationship between human body motion and the change of each body parts direction will be discussed. Additionally, results from the trial using the prototype of the new motion recording system will be presented.