Hardware
Series Elastic Actuator (SEA)
A series elastic actuator (SEA) is an actuator that deliberately places a compliant element, typically a spring, between the motor's gear train and the load, introduced by Pratt and Williamson at MIT in 1995. Measuring spring deflection turns force control into a position measurement problem, yielding accurate force output, shock tolerance, and low mechanical output impedance. SEAs have been used in legged robots, exoskeletons, and collaborative arms such as Rethink's Baxter.
Why it matters for physical AI
Compliant actuation makes sustained, safe physical contact tractable, which is why SEA-style designs recur wherever robots must touch people or absorb impacts rather than track trajectories rigidly.
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