Control

Stiffness Control

Stiffness control is the regulation of a robot's apparent elastic behavior, commanding the relationship between end-effector (or joint) displacement and restoring force so the robot behaves like a programmable spring about an equilibrium pose. It is the static special case of impedance control, which additionally shapes apparent damping and inertia. Stiffness can be rendered actively through torque control or provided physically by variable stiffness actuators.

Why it matters for physical AI

Tasks from peg insertion to polishing succeed by being soft in some directions and stiff in others; commanding stiffness, not just position, is fundamental to contact-rich manipulation.