Series Elastic Actuator (SEA)

串联弹性驱动器SEACommon

An actuator with a spring deliberately placed between the motor and the load, sensing force from spring deflection.

A series elastic actuator deliberately places an elastic element (a spring) between the motor (plus reducer) and the output, an idea proposed by MIT's Gill Pratt and Matthew Williamson in 1995. Measuring how much the spring deflects gives an accurate estimate of output torque, enabling precise force control; the spring also cushions impacts and protects the reducer, making the robot safer to be around when it contacts a person. The trade-off is lower stiffness and lower bandwidth, which makes precise position control harder. SEAs are common in legged robots, exoskeletons, and collaborative robots that need compliance. The contrasting approach is quasi-direct drive, which skips the spring and estimates torque directly from motor current through a low gear ratio.

ExampleThe joints of Rethink Robotics' Baxter dual-arm robot use series elastic actuators, so the arm yields and gets pushed aside rather than colliding rigidly with a person.

Also called: Series Elastic Drive
Related: Actuator · Compliance · Torque Control · Quasi-Direct Drive · Variable Stiffness Actuator (VSA) · Backdrivability
Sources: Series elastic actuator - Wikipedia