serieelastict

Series elastic actuators (SEAs), or seriële elastische actuators in Dutch, are actuators in which a compliant element such as a torsional or linear spring is placed in series with the motor and drive train. The spring’s deflection provides a built-in measure of output force and shapes the actuator’s dynamic response. By placing the spring in series, the actuator gains controlled compliance, which is advantageous for safe interaction with humans and for precise force control.

Construction and operation typically involve a motor (DC or brushless), a gear reducer, a spring, and sensors that measure spring deflection and motor position. The output is connected after the spring, so the load experiences the spring-mediated motion. Control loops use the deflection of the spring to estimate output torque and regulate either force or impedance.

Advantages of SEAs include improved force control bandwidth, inherent compliance that enhances safety in human-robot interaction, and the ability to store and release energy during dynamic tasks. They facilitate impedance control and low impedance behavior, which is beneficial for manipulation, grasping, and locomotion.

Common applications are in humanoid and service robots, robotic grippers, prosthetic limbs, exoskeletons, rehabilitation devices, and legged robots, where accurate force control and safe contact with humans or delicate objects are important.

Design considerations include selecting an appropriate spring stiffness, accounting for nonlinearities and hysteresis in the spring, temperature effects, damping and friction, backdrivability, and long-term durability. Designers trade off stiffness, control bandwidth, size, and weight, and SEAs are often discussed alongside parallel elastic actuators and variable stiffness Actuators.