Abstract:The human motion capture system based on inertial sensors usually needs to perform specific standard actions to complete the alignment before performing motion capture to obtain the attitude of the inertial measurement unit (IMU) coordinate system relative to the limb coordinate system. Users with limited motion (such as hemiplegic patients) cannot complete some standard actions. For users with normal motion, there is no guarantee that they can perform standard actions correctly, resulting in human motion capture errors. In order to overcome the shortcomings of the existing methods, this paper studies a method of human upper limb motion capture based on inertial sensors without alignment action. The method does not need to perform specific alignment action and can directly perform motion capture after wearing IMU. By comparing with the ‘T-Pose’ static alignment scheme, the effectiveness of the alignment-free action method is verified, and the upper limb motion capture experiment is carried out based on the OpenGL virtual human model. Experiments indicate that the proposed method is simple and effective, and it still has a good human motion capture effect without performing standard alignment actions, which is suitable for users with limited movement such as hemiplegic patients