ABSTRACT
An actuator is a device that mechanically drives a control system. There are many classifications of actuators. Those that directly operate a process (load, plant) are termed process actuators. Joint motors in a robotic manipulator are good examples of process actuators. In applications of process control in particular, actuators are often used to operate controller components (called final control elements), such as servovalves, as well. Actuators in this category are termed control actuators. Actuators that automatically use response error signals from a process in feedback to correct the time-varying behavior of the process (i.e., to drive the process according to a desired response trajectory) are termed servo actuators. In particular, the motors that use position, speed, and perhaps load torque measurements and armature current or field current in feedback, to drive a load according to a specified motion trajectory, are termed servomotors.
