ABSTRACT
Actuator is the device that mechanically drives a mechatronic 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 process control applications in particular, actuators are often used to operate controller components (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 operation of the process (i.e., to drive the process according to a desired response) are termed
servoactuators
. 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, are termed
servomotors
. One broad classification of actuators separates them into the two types:
incremental-drive actuators
and
continuous-drive actuators
. Stepper motors, which are driven in fixed angular steps, represent the class of incremental-drive actuators. They can be considered as digital actuators, which are pulse-driven devices. Each pulse received at the driver of a digital actuator causes the actuator to move by a predetermined, fixed increment of displacement. Stepper motors were studied in Chapter 8. Most actuators used in mechatronic applications are continuous-drive devices. Examples are dc torque motors, induction motors, hydraulic and pneumatic motors, and piston-cylinder drives (rams). Microactuators are actuators that are able to generate very small (microscale) actuating forces/torques and motions. In general, they can be neither developed nor analyzed as scaled-down versions of regular actuators. Separate and more innovative procedures of design, construction, and analysis are necessary for
microactuators
. Micromachined, millimeter-size micromotors with submicron accuracy are useful in modern information storage systems. Distributed or multilayer actuators constructed using piezoelectric, electrostrictive, magnetostrictive, or photostrictive materials are used in advanced and complex applications such as adaptive structures and various microelectromechanical systems (MEMS).
