Rotary Actuator

旋转执行器Common

An actuator whose output is rotation, the power unit behind a robot's rotating joints.

A rotary actuator is a drive unit whose output is rotation about an axis, as opposed to a linear actuator, whose output is straight-line motion. In humanoids and robot arms, it's usually packaged as an all-in-one joint module: a motor plus a reducer, plus an encoder and a driver, sometimes also a torque sensor and a brake — mount it and you have a working rotary joint. Selecting one mainly comes down to peak/rated torque, speed, weight, and backdrivability (whether it can be pushed from the output side by an external force). Most of a humanoid's shoulder, elbow, hip, and knee joints are rotary actuators, while linear actuators are commonly used at the shin and ankle, where a push-pull motion is needed — balancing the two is a basic trade-off in whole-robot design.

Also called: Rotary Joint Module
Related: Actuator · Joint Actuator Module · Linear Actuator (Electric Cylinder) · Speed Reducer / Gearbox · Revolute Joint · Peak Torque
Sources: Rotary actuator - Wikipedia