Globally, lower back pain is a serious problem. For workers, it not only causes health problems but also has social and economic influences. Lower back pain could be attributed to burden on people’s waists when they handle heavy objects. Ministry of Health, Labour and Welfare in Japan recommends squat lifting, a method of lifting objects with a smaller burden on waist. On the other hand, squat lifting is not commonly used because it requires deep bending of knees to lift an object, leading to a larger work load. Therefore, a leaf-spring type power assist suit for legs has been developed in order to assist squat lifting. However, if the fixing performance of a preceding machine was enhanced, a leaf spring could impede the bending of knee joints during gait motion. In the present study, we developed a power assist suit for legs using a slide mechanism. A leaf spring was chosen so as to meet a target assist torque determined by a motion analysis for lifting objects. In addition, we made a prototype machine with slide mechanism. EMG measurement of the thigh muscle during lifting actions using the prototype machine showed a decrease of up to 46%. It was also confirmed that a machine with slide mechanism could realize a more natural gait than a machine without it.

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