Manipulation

Contact Mode

A contact mode is a discrete classification of the contact state between bodies, specifying which contacts are active and whether each is sticking, sliding, or separating. Manipulation tasks traverse sequences of contact modes, and each mode imposes different dynamics and constraints, making the overall system hybrid. Contact-implicit trajectory optimization and mode-enumeration planners reason over these discrete switches, whose combinatorial explosion is a core difficulty of dexterous manipulation.

Why it matters for physical AI

Learned policies implicitly discover contact mode sequences that model-based planners must enumerate explicitly, and understanding mode structure explains why contact-rich tasks are so much harder than free-space motion.