Asymmetric Velocity Moderation: a Reactive Strategy for Human Safety

As Human-Robot Interaction becomes closer, it is necessary to seek human safety so that the robot does not harm the human when the human ventures into the robot's workspace. Therefore, we propose a reactive strategy for human safety called Asymmetric Velocity Moderation. Our proposed method restricts the velocity of the end-effector according to the distance between human and robot. Moreover, our method considers the displacement vector which is the vector formed by the closest points between human and robot. Therefore, we do not consider only the distance but also the direction. The reason to consider the direction is that even though the velocity directed towards the human should be firmly restricted if the distance is short, we can relax the restriction of the velocity directed away from the human even if the distance is short. Thus, by introducing the angle between the displacement vector and the end-effector velocity vector we can improve the trade-off between safety and efficiency. We carried out experiments with a human-size humanoid robot and a human subject standing next to each other, and made them perform independent tasks. Through these experiments, we verified that our method not only provides human safety but also copes with the trade-off between human safety and the efficiency of the robot when performing a task.