Collision Reaction

The strategy a robot follows after detecting a collision — deciding whether to stop, go soft, or yield.

Collision reaction is the last step in a robot's collision-handling pipeline. A 2017 survey by Haddadin, De Luca, et al. places it at the end of a chain: first detect whether a collision has happened, then localize which link was hit and estimate the force's magnitude and direction, judge whether it was accidental or intentional contact, and only then decide how to react. Common reactions include: stopping immediately (a protective stop); switching to a torque mode that only compensates gravity, making the arm soft and easy to push away; actively yielding in the direction of the collision force; or switching to impedance or admittance control to continue compliantly. De Luca et al. (2006) demonstrated collision detection on the DLR-III lightweight arm using a generalized-momentum-based method that relies only on the robot's own sensors, and that also gives the direction of the collision for use by different reaction strategies. If a person is pinned between the robot and a table, simply stopping doesn't relieve the pressure, which is why yielding and going soft matter especially in collaborative settings.

ExampleFranka arms let you use setCollisionBehavior to set separate ‘contact’ and ‘collision’ thresholds for each joint and each end-effector direction: a force between the two thresholds is just logged as contact, while exceeding the collision threshold stops the robot immediately, requiring a call to automaticErrorRecovery to reset before it can continue.

Also called

Post-Collision Response Strategy, Collision Reflex

Related

Collision Detection (Robot Safety) · Generalized Momentum Observer · Protective Stop · Power and Force Limiting · Damping Mode · Physical Human-Robot Interaction

Sources

Haddadin, De Luca, Albu-Schäffer. Robot Collisions: A Survey on Detection, Isolation, and Identification. IEEE T-RO, 2017
De Luca et al. Collision Detection and Safe Reaction with the DLR-III Lightweight Manipulator Arm. IROS 2006
libfranka robot.h（setCollisionBehavior / automaticErrorRecovery）