2018 年 84 巻 864 号 p. 18-00055
In this study, we measured and analyzed the degree of posture discomfort with respect to the coordinated range of motion (ROM) of the thumb. For ergonomic assessment of a product CAD model using a digital hand model, such joint properties are necessary to be clarified when estimating possible natural postures to use the product. We concentrated on the thumb, which plays an important part to form various grasps by opposition. To model range of motion considering coordination among joint variables, each subject's hand during a given set of exercises was captured by an optical mocap system. A posture of the carpometacarpal (CM) joint of the thumb was expressed with spherical coordinates to integrate different subjects' ROM easily. The result was shown some characteristics of the thumb such as coordination among joint variables or collision between thumb and other parts of the hand. The posture discomfort data was collected through the experiments for four adults with healthy hand. To control variety of the postures, each subject was asked to reproduce about 45 displayed postures and to answer whether the subject felt discomfort or not in terms of keeping that posture for 10 seconds. The discomfort experiment results were combined into a discomfort possibility map with respect to joint postures. This map can assist product design, for example considering interface layout.