A Motion Similarity Measurement Method of Two Mobile Devices for Safety Hook Fastening State Recognition

Fall from height (FFH) is an accident that leads to fatalities in construction workers, and a major cause of FFH is due to the improper fastening of a safety hook of a safety harness to a temporary structure. In this study, we propose a new approach for recognizing the fastening state of the safety hook based on the similarity of motion between the motion of the hook and the body. We first assume that the similarity of motion between a hook and a body will be more similar when a hook is fastened to a part of a body than when the hook is fastened to a temporary structure. Under this assumption, we propose a new method that measures the similarity of motion of a hook and a body. In the proposing method, motions are represented through acceleration and rotations of the hook and the body. The magnitude of acceleration is represented as an ordinal variable and the magnitude of acceleration is jointly represented with rotations in a spherical coordinate system for effective similarity measurement of both motions. The effectiveness of our approach is verified by our newly collected task-related human activity dataset comprising the motion data of the hook and the body from inertial measurement unit (IMU) embedded mobile devices. Our proposed method confirmed that representing the magnitude of acceleration as an ordinal variable shows improved performance of 82.95% in terms of Youden's index. Moreover, it further verified that jointly representing the magnitude of acceleration and the rotation in the spherical coordinate system shows improved performance of 90.64% in terms of Youden's index.