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We propose a self collision avoidance system for humanoid robots designed for interacting with the real world. It protects not only the humanoid robots' hardware but also expands its working range while keeping smooth motions. It runs in real-time in order to handle unpredictable reactive tasks such as reaching to moving targets tracked by vision during dynamic motions like e.g. biped walking.

The collision avoidance is composed of two important elements. The first element is reactive self collision avoidance which controls critical segments in only one direction — as opposed to other methods which use 3D position control. The virtual force for the collision avoidance is applied to this direction and therefore the system has more redundant degrees of freedom which can be used for other criteria. The other second element is a dynamic task prioritization scheme which blends the priority between target reaching and collision avoidance motions in a simple way. The priority between the two controllers is changed depending on current risk.

We test the algorithm on our humanoid robot ASIMO and works while the robot is standing and walking. Reaching motions from the front to the side of the body without the arm colliding with the body are possible. Even if the target is inside the body, the arm stops at the closest point to the target outside the body. The collision avoidance is working as one module of a hierarchical reactive system and realizes reactive motions. The proposed scheme can be used for other applications: We also apply it to realizing a body schema and occlusion avoidance.