Hardware

Variable Stiffness Actuator (VSA)

A variable stiffness actuator (VSA) is an actuator whose mechanical compliance can be adjusted independently of its output position, typically by using a second motor to reconfigure internal elastic elements. Unlike a series elastic actuator with a fixed spring, a VSA can stiffen for precise positioning and soften for impact absorption or safe human contact within the same task, storing and releasing elastic energy for explosive motions.

Why it matters for physical AI

Physical compliance that is tunable in hardware absorbs impacts faster than any control loop can react, which matters for robots working in contact-rich, human-populated environments where collisions are inevitable.