If sensors are the eyes of an automation system, actuators are its muscles. Actuators convert electrical, pneumatic, or hydraulic energy into physical motion, enabling PLCs to control real-world processes. Understanding actuator technologies is essential for any automation engineer.
Electric Actuators
Electric actuators use electric motors to produce linear or rotary motion.
AC Motors are the workhorses of industrial automation:
- Induction motors: Most common, reliable, low maintenance. Controlled by VFDs for variable speed applications
- Synchronous motors: Higher efficiency at constant speed, used in compressors and large pumps
- Servo motors: Precise position and speed control, used in motion control applications
DC Motors are less common in new installations but still found in legacy systems:
- Brushed DC motors: Simple speed control via voltage variation
- Brushless DC motors: Higher efficiency, used in precision applications
Stepper motors provide precise positioning without feedback:
- Open-loop control with defined step angles
- Ideal for positioning in packaging, 3D printing, and laboratory equipment
Pneumatic Actuators
Pneumatic systems use compressed air to produce motion. They are widely used in factory automation for their speed and simplicity.
Pneumatic cylinders:
- Single-acting: Air extends the piston, a spring returns it. Used for clamping and pressing
- Double-acting: Air extends and retracts the piston. Most common type
- Rodless cylinders: Linear motion without a protruding rod, ideal for long strokes in confined spaces
Pneumatic valves:
- Directional control valves: 3/2-way, 5/2-way, and 5/3-way configurations for controlling cylinder motion
- Proportional valves: Variable air flow for speed and position control
- Solenoid valves: Electrically operated by PLC digital outputs
Hydraulic Actuators
Hydraulic systems use pressurised oil to produce high-force motion. They are used where pneumatic systems cannot provide sufficient force.
- Hydraulic cylinders: Forces from kilonewtons to meganewtons for heavy presses, injection moulding, and steel mills
- Hydraulic motors: High torque at low speed for winches, conveyors, and mobile equipment
Integration with PLCs
Modern actuators integrate with PLCs through various interfaces:
- Digital outputs: Simple on/off control for contactors, solenoid valves, and indicator lights
- Analogue outputs: 4-20 mA or 0-10 V signals for proportional control of valves, drives, and positioners
- Fieldbus communication: PROFINET, IO-Link, or AS-Interface for intelligent actuators with diagnostics
- Motion control: Pulse train (PTO) or fieldbus-based servo control for precise positioning
Actuator Selection Criteria
When selecting an actuator, consider:
- Force or torque requirements for the application
- Speed and acceleration profiles needed
- Precision and repeatability requirements
- Environmental conditions including temperature, humidity, and explosive atmospheres
- Maintenance requirements and lifecycle costs
EDWartens UK courses provide hands-on experience with electric, pneumatic, and hydraulic actuators integrated with Siemens PLC systems, giving students practical skills for real-world automation projects.