This paper describes a collision avoidance method for a biped robot with an upper body. We propose a method wherein the robot stops in front of an obstacle by generating arm force. When the robot detects the obstacle by the arm tip, it should stop short of the obstacle to avoid crash. Hence, we propose trajectory planning in consideration of the pushing force of the arm. The arm force is controlled to be generated as a function of the distance from the robot body to the obstacle. The closer the robot approaches the obstacle, the larger the arm force becomes. As a result, the robot can stop by utilizing the arm force. In case the obstacle is unmovable, the robot can stop by exerting arm force. If it is movable, the robot can continue walking by pushing it. In this paper, the linear inverted pendulum mode (LIPM) and the idea of orbital energy are introduced, and then, we extend LIPM and orbital energy in consideration of the dynamics of the arm force. The extended orbital energy is utilized to discriminate whether the robot can stop or not and to modify the trajectory of the robot to avoid collision.
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