Building Linkage Models of Human Arms

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In this project, we have developed a systematic method to build a personal link model of human upper arms through their motion measurements. A3D position sensor and flexible joint angle sensors are utilized in the measurements of upper arm motion and wrist motion.First, we have introduced a 2-link 1-DOF mechanism into the link model of a upper arm to describe human shoulder motion. It is required to estimate personal model parameters involved in the link model so that the model can be applied into individual persons. Thus, we have established a method to identify model parameters through the measurements of simple motions performed in advance. Model parameters including the location of shoulder joint center, length of two links and the relationship between two joint angles in the introduced 2-link 1-DOF mechanism, the location of elbow joint center, and length of forearm can be identified through the measurements. Traditional 1-link 1-DOF models cannot describe the position and the orientation of human hand simultaneously while the proposed mode is capable of describing them in a simple manner. In addition, difference among individual persons can be taken into the link model easily as well as the difference of sensor locations can be eliminated through the identification of model parameters. Second, we have developed flexible joint angle sensors to measure human wrist motion. Since the range of wrist motion is narrow, we have found that the 3D sensor is inappropriate to the measurements of wrist motion. Thus, we have prototyped angle sensors using strain gauges and have found that they have sufficient accuracy as long as the wrist angle is under 50 degrees. As mentioned above, we have found that the proposed method is effective to build a personal model of human upper arms. Building wrist models is an open issue.