What is an Actuator

An actuator is responsible for moving and controlling a mechanism or system by converting energy into motion, such as rotating a motor or opening a valve. When an actuator receives a controlling signal, it converts the source energy into mechanical motion. In mechatronics systems or CNC machines, actuators enable various automated actions. Actuators can be categorized into two main types: linear actuators, which move in a straight path, and rotary actuators, which provide rotating motion. Actuators are further classified based on the type of energy they convert into motion: electrically operated, hydraulically operated, and pneumatically operated. The chart below shows the categorization of different actuators.

  

With the help of an actuator, the state or physical position of a machine part can be changed, creating an electrical signal from an output module of a PLC. Actuators are typically directly connected to a PLC output module, either periodically or sometimes via a relay unit. A common example of an actuator is a solenoid-controlled valve used in hydraulic or pneumatic circuits of a CNC machine to divert or control the pressure line as required. Different actuators with various voltage ratings are regularly used with CNC machines to perform a range of tasks.

Usually, an actuator has two conditions: ON or OFF, which represent it is activated and deactivated events. In a PLC, the ON condition or actuator activation is referred to as "Logic-1" or "Logic high," while the OFF state is referred to as "Logic-0" or "Logic low." To activate an actuator, the PLC output status needs to be Logic-1 and a 24V DC voltage is supplied to the corresponding actuator from the PLC output module. Similarly, if the PLC output status becomes Logic-0, no voltage will be present at the PLC output module terminal, and the corresponding actuator will be deactivated. Actuators used in CNC machines can have different voltage ratings, such as 24V DC, 110V AC, and 220V AC. Since a 24V DC voltage is delivered from the PLC's output module terminal, the required operating voltage of an actuator is switched through a relay unit.

How an actuator is connected to the PLC output module:

Actuators are connected to the PLC output module in two different ways. Lower current rating actuators are sometimes directly connected to the PLC, while higher current or voltage rating actuators are supplied through a relay unit. The following picture shows how actuators are connected to a PLC output module. 

In the picture above, the PLC's output terminals represent different output addresses where actuators with two distinct voltage ratings are connected to the PLC output module. The "Solenoid-1" is directly coupled with the PLC output address "Q 0.6," and the "Motor" is connected to "Q 0.0" through a relay unit. Solenoid-1 is a low current rating 24V DC operated valve, while the Motor is a higher current rating and operates with 220V AC. The status of the corresponding output address "Logic 1" indicates that the actuator will be energized or activated, while a status of "Logic 0" signifies that the actuator is in a de-energized state. LEDs are used with each output terminal to indicate the status of the corresponding actuator from the outside. A glowing LED represents an energized actuator, while an off LED indicates a de-energized actuator. In this case, the output addresses Q0.0 and Q0.6 are in Logic-0 state, which means the LEDs are not glowing, and the corresponding actuators are also deactivated. Only the Q0.3 LED is glowing, indicating that the "Lamp" actuator is in the activated state. PLC output modules can have different types based on factors such as the number of actuators they can handle, voltage, current rating, etc. Generally, most PLCs are operated with 24V DC, and higher voltage or current rating actuators are managed through a relay unit.