Self-Collision Detection and Prevention for Humonoid Robots Paper by James Kuffner et al. Jinwhan Kim

Introduction  Efficient geometric approach to detecting link interference for articulated robots  Fast, feature-based minimum distance determination  Full-body trajectories are checked in advance for potentially self-colliding posture prior to being executed

Collision Detection in Robotics  Mobile robots Collision with environmental obstacles or other robots  Articulated robots Self-collision also needs to be checked e.g.) Serial-chain manipulators, Humanoid robots

Humanoid Robots  The robot consists of a tree of connected links  A set of five serial chains 2 arms + 2 legs + 1 neck- head chain

# of Pairs to be checked  Assume that joints limits prevents collision between a given link and its parent link

H7 Humonoid Robot  A total of 31 links : N=31  Eliminate unnecessary pairs which cannot collide each other Full (435 pairs) Pruned (76 pairs)

Interference Detection  Trajectory sampling Binary collision results 1) Swept volumes Computations are difficult and expensive 2) Trajectory discretization Preferred due to its simplicity, but collisions may not be detected

 Bounds and collision-free guarantees A conservative measure of the minimum distance can guarantee a collision-free motion Maximum joint velocities are bounded

 Protective Hulls Convex protective hulls of each link as conservative approximation provide a safety margin

 Minimum Distance Determination The convex nature of the protective hulls allows fast minimum distance determination Voronoi-clip(V-clip) Threshold distances considering errors in modeling and control

Self Collision in Walking

Collision-free Trajectory Generation

Control System for Safe Walking

Conclusion  Detecting self-collision for humanoid robots for generating collision-free full-body trajectories  Efficient minimum distance determination methods using conservative convex protective hull models  Implementation of online Joystick control

Future Work  Reduce the number of pairs to be checked by calculating active pairs for given joint angle ranges  Investigating alternative minimum distance determination method which is applicable to non-convex hulls