Self-Collision Detection and Prevention for Humonoid Robots

Paper by James Kuffner et al.

Presented by David Camarillo

Introduction Efficient geometric approach to detecting

link interference for articulated robots Fast, feature-based minimum distance

determination Full-body trajectories are checked prior to

execution for potentially self-collisions

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

Torso is the root with five serial chain branches 2 arms + 2 legs + 1 neck-

head chain

Number of Pairs to be checked Assume that joints limits prevents collision

between a given link and its parent link

2

2322

1

NNiP

N

i

H7 Humonoid Robot A total of 31 links : N=31 Eliminate unnecessary pairs which cannot

collide each other Heuristic or exhaustive search approach

Full(435 pairs)

Pruned(76 pairs)

Collision-free Trajectory Generation

User Desired Trajectory

CollisionDetector

Online TrajectoryManager

Pre-CalculatedWalking Patterns

Collision-freeTrajectory

Interference Detection

Trajectory sampling Binary collision results1) Swept volumes

Computations are difficult and expensive

2) Trajectory discretizationPreferred due to its simplicity, but collisions

may not be detected

Interference Detection cont.

Bounds and collision-free guarantees A conservative measure of the minimum

distance can guarantee a collision-free motion

Maximum joint velocities are bounded

maxqq

qqJx )( minmax ),,,( dtqqqx

Interference Detection cont.

Protective Hulls Convex protective hulls of each link as

conservative approximation provide for safety margin, and efficient computation

Interference Detection cont.

Minimum Distance Determination Voronoi-clip(V-clip)

No hierarchical bounding volumes Execution time dependent on model

geometry, and velocity, not distance “Almost constant time”

User can add padding to account for errors in modeling and control

Self-Collision in Walking

Control System for Safe Walking

Could incorporate with balancing scheme

More Practical to detect before hand

Experiments with joystick controlled 3-step trajectory

Future Work Dynamic pruning by considering joint

angles during trajectory simulation Investigating alternative methods which

could work with non-convex hulls