Actuators - What are they - Different types - Uses and applicatons

Actuators - What are they - Different types - Uses and applicatons

In the world of machinery and automation, actuators play a pivotal role as the "muscles" of various systems, silently powering the movement that brings machines to life. An actuator is essentially a device that takes an energy source — be it electrical, pneumatic, or hydraulic — and converts it into physical motion. This motion can be linear or rotary, and it can be used to control a system or mechanism. Actuators are the key components that enable precise control in both complex and simle equipment, from the delicate positioning of optical lenses to a home Automation system to lift a TV out of a cabinet.


  1. Linear Actuators:
    • Electric Linear Actuators
    • Pneumatic Linear Actuators
    • Hydraulic Linear Actuators
    • Mechanical Actuators (like screw jacks)
    • Piezoelectric Actuators
    • Electro-mechanical Actuators
  2. Rotary Actuators:
    • Electric Rotary Actuators
    • Pneumatic Rotary Actuators
    • Hydraulic Rotary Actuators
  3. Solenoid Actuators:
    • Linear Solenoids
    • Rotary Solenoids
  4. Micro Actuators:
    • Micro Piezo Actuators
    • Shape Memory Alloy Actuators
    • Electroactive Polymer Actuators
  5. Electrohydraulic Actuators:
    • Servo Valves
    • Proportional Valves
  6. Pneumatic Actuators:
    • Diaphragm Actuators
    • Rack and Pinion Actuators
    • Scotch Yoke Actuators
  7. Thermal and Magnetic Actuators:
    • Bimetallic Strips (thermal)
    • Thermally Expandable Materials (wax actuators)
    • Magnetostrictive (Magnetostrictive) Actuators
  8. Smart Material Actuators:
    • Piezoelectric Actuators
    • Electrostrictive Actuators
    • Magnetostrictive Actuators
    • Shape Memory Alloys
  9. Muscle Wire Actuators:
    • Also known as Nitinol or shape-memory actuators, which contract when heated.
  10. Servo Actuators:
    • Typically integrated with a servo mechanism for precise control.
  11. Stepper Actuators:
    • Stepper Motor-based, which can provide precise positioning through rotational steps.

Above is  a list of all the different types of actuators in service today, now lets go into more depth about each one.

1. Linear Actuators

Mode of Operation: Linear actuators are devices that create motion in a straight line as opposed to the rotary motion of a conventional motor. They come in various modes of operation:

  1. Electric Linear Actuators: These are powered by electric motors that drive a mechanism, such as a lead screw or a belt drive, to convert the motor’s rotary motion into linear motion.

    • Example Application: They are widely used in industrial machinery for precision control of positioning, such as in CNC machines, or in consumer products like adjustable desks.
  2. Pneumatic Linear Actuators: These actuators use compressed air to drive a piston within a cylinder, producing linear motion. The force produced by these can be quite high, and speeds can be fast, however because air is compressible it can be very hard to have any level os precision, with pneumatic Actuators. For this reason, they tend to be used just for point-to-point applications. 

    • Example Application: Pneumatic linear actuators are commonly used for applications requiring a low to medium force over a relatively short distance, such as in material handling or clamping operations.
  3. Hydraulic Linear Actuators: Hydraulic actuators also use a piston mechanism, but they are powered by pressurized hydraulic fluid. Because hydraulic fluid is a non-compressible material, it means Hydrailics are used for very high force applications. They do tend to be slow but make up for it in force. These types of systems are also builky and expensive because they require the system to use a high pressure hydraulic fluid pump to build the pressure, and a resevoir tank to hold the fluid. 

    • Example Application: These actuators are suitable for very high force applications, such as in construction equipment like excavators and in industrial presses.
  4. Mechanical Actuators: Mechanical linear actuators convert rotary motion into linear motion mechanically, often using screws or gears and are usually manually driven, so they would typically have a handle to wind and convert that rotary motion into linear motion.

    • Example Application: Mechanical actuators, like screw jacks, are used in lifting platforms and in automotive jacks.
  5. Piezoelectric Actuators: These actuators employ the piezoelectric effect to convert electrical energy into precise linear motion on a minute scale. Applying a voltage accross a Piezo stack as they are called in the industry makes the material expand and contract on a micro scale but with high force and high precision. 
    • Example Application: Due to their high precision, piezoelectric actuators are used in most fuel injectors in vehicles. The Piezo stack will be used to open and close the fuel line in the injectors to devliver the right amount of fuel to each cylinder depenind on the throttle position. {iexo actuator are extremely fast to operate, making them ideal for applications like this. 

Each type of linear actuator comes with its own set of capabilities, control methodologies, and suitable applications, often determined by the force required, the precision of movement, the speed of operation, and environmental considerations like temperature, cleanliness, and space constraints.

 Rotary and Linear Actuators

2. Rotary Actuators

Mode of Operation: Rotary actuators convert energy into rotational motion. They are typically used when a component needs to be rotated to a specific angle or position. Here are the main types:

  1. Electric Rotary Actuators: These actuators use electric motors to provide rotary motion and can be controlled very precisely. They often incorporate gearboxes to increase torque output.

    • Example Application: Electric rotary actuators are frequently used in robotics, for articulation of joints, or in satellite dish positioning where precise control is essential.
  2. Pneumatic Rotary Actuators: Pneumatic rotary actuators rely on compressed air to turn a shaft in a circular motion and are used when high speed or a high number of cycles are required.

    • Example Application: These actuators are commonly used in automation for material handling, clamping, and conveyor system applications where quick and repetitive movement is needed.
  3. Hydraulic Rotary Actuators: These actuators use pressurized hydraulic fluid to create rotation. They provide a very high torque and can hold a load steady without the need for additional energy.

    • Example Application: Hydraulic rotary actuators are suitable for heavy-duty applications such as steering mechanisms in construction vehicles or for industrial applications where large loads need to be rotated.

Kind of Motion Produced: Rotary actuators produce rotational or angular motion around a fixed axis. This is typically measured in degrees of rotation and can range from subtle adjustments to multiple full rotations.

Materials and Technologies Employed:

  • Gears, such as spur, helical, or worm gears, are often used to increase torque and adjust the speed of rotation.
  • For pneumatic and hydraulic rotary actuators, vane or rack-and-pinion designs are common.
  • Materials can include various grades of steel and aluminum for structural parts, with specialized seals for fluid containment in hydraulic and pneumatic systems.

Specialized Rotary Actuators:

  • Servo Actuators: Servo actuators are a type of electric rotary actuator that incorporates a servo mechanism to provide highly accurate control of angular position, velocity, and acceleration.

    • Example Application: Servo actuators are integral in precision applications such as CNC machining, robotics, and camera tracking systems where tight control is required.
  • Stepper Actuators: Stepper motor actuators are electric rotary actuators that rotate in fixed increments or steps, allowing precise control without the need for feedback systems.

    • Example Application: They are used in 3D printers, automated assembly lines, and any application where precise incremental movement and positioning are critical.

Rotary actuators are chosen based on the required rotation angle, torque, speed, and control accuracy. Their selection is also influenced by the environment they will operate in and the expected duty cycle. Electric actuators are often preferred for precision and ease of control, whereas pneumatic and hydraulic actuators are selected for their speed and force, respectively.


3. Solenoid Actuators

Mode of Operation: Solenoid actuators are devices that convert electrical energy into mechanical work through electromagnetic force. When an electric current passes through a coil, it creates a magnetic field, which then moves a ferromagnetic plunger or armature within the solenoid, creating linear or rotary motion.

  1. Linear Solenoids: These are the most common type, wherein the magnetic field directly pulls or pushes the armature in a straight line.

    • Example Application: Linear solenoids are used in applications such as door locks, vending machines, and hydraulic valves where short, quick, linear motion is required.
  2. Rotary Solenoids: Rotary solenoids convert the linear motion of the solenoid into rotary motion, often through a mechanism inside the solenoid casing.

    • Example Application: Rotary solenoids are used in applications like paper feed mechanisms in printers or for actuating the latch in industrial machinery.

Kind of Motion Produced:

  • Linear solenoids produce a push or pull action.
  • Rotary solenoids produce rotational movement over a limited angle, typically less than 180 degrees.

Materials and Technologies Employed:

  • Coils of wire, which can be wound in various ways to optimize magnetic field strength and efficiency.
  • Ferromagnetic materials for the plunger, which is designed to move in response to the magnetic field.
  • A casing, often made from metal, to provide a return path for the magnetic field and protect the internal components.

Example Application: Solenoid valves, an application of linear solenoids, are widely used in fluid control systems to open and close valves, typically in HVAC systems, irrigation systems, and industrial process controls. Rotary solenoids find their application in various electromechanical devices that require a fast-acting rotational movement for a short period, such as in pinball machines or automatic door openers.

The selection of a solenoid actuator typically depends on the application's power requirements, the necessary force or torque, the stroke or rotation angle needed, and the duty cycle. Solenoids are favored for their simplicity, reliability, and fast response times. However, they are usually not intended for long strokes or continuous motion due to heat build-up from the coil, which can limit their duty cycle.

actuator types

4. Micro Actuators

Mode of Operation: Micro actuators are small-scale devices designed to produce motion or force at a micro level. They are essential in applications where precise, minimal movements are necessary, such as in micro-electromechanical systems (MEMS).

  1. Micro Piezo Actuators: These actuators use piezoelectric materials which deform when an electric field is applied, allowing for very precise control down to the nanometer scale.

    • Example Application: Micro piezo actuators are used in optical equipment for lens adjustment, in precision machining for tool positioning, and in medical devices such as miniature pumps or dispensing systems.
  2. Shape Memory Alloy Actuators: Shape memory alloys (SMAs) are materials that can return to a pre-deformed shape when heated. As actuators, they can convert thermal energy into mechanical energy.

    • Example Application: SMA micro actuators are found in medical devices, such as stents that expand at body temperature, and in aerospace applications for the precise control of small valves or dampers.
  3. Electroactive Polymer Actuators: Electroactive polymers (EAPs) change shape or size when stimulated by an electric field. They are often referred to as artificial muscles due to their muscle-like flexibility.

    • Example Application: EAPs are used in haptic feedback devices for virtual reality systems, as well as in robotics to create soft, flexible joints or grippers.

Kind of Motion Produced: Micro actuators typically produce linear or bending motion, although rotary motion can also be achieved through the arrangement of several micro actuators in a specific configuration. The motion is characterized by very small displacements and high precision.

Materials and Technologies Employed:

  • Piezoelectric ceramics or polymers are used in micro piezo actuators.
  • Nickel-titanium alloys are common in shape memory alloy actuators.
  • Polymers that can respond to electrical stimulation are used for electroactive polymer actuators.

Example Application: In the field of microfluidics, micro piezo actuators are often used to control the flow of fluids through tiny channels. Their precision and speed enable them to handle the delicate and precise operations necessary in this application. Electroactive polymers are explored for use in the development of more lifelike prosthetics, providing nuanced movement that mimics natural muscle motion.

Micro actuators are an area of active research and development, offering potential breakthroughs in various fields, including medical devices, biotechnology, and nanotechnology. They are chosen for applications where space is at a premium and precise control is required. Advances in materials science and microfabrication technology continue to enhance the capabilities and applications of micro actuators.

5. Electrohydraulic Actuators

Electrohydraulic actuators combine the best of electrical and hydraulic systems to deliver controlled and powerful actuation. They typically include servo valves and proportional valves, which are used to regulate the flow and pressure of hydraulic fluid in response to electrical control signals. These actuators are highly prized in applications requiring robust force, high-speed response, and precise control.

Servo Valves

Servo valves are a critical component in an electrohydraulic actuator system. They are high-performance devices that control fluid flow and direction in response to an electrical input. Here’s how they contribute to the functionality of the actuators:

  • Operation: Servo valves are typically used in closed-loop control systems and receive electrical signals from a controller. These signals modulate the valve position, controlling the flow and direction of hydraulic fluid.

  • Precision: They offer high precision and responsiveness, which are crucial for applications requiring very exact motion control.

  • Applications: These valves are common in flight simulators, fatigue testing of materials, and precision machine tools, where the response time and accuracy of the actuation are paramount.

Proportional Valves

Proportional valves are less complex than servo valves and are used when the precision of servo valves is not required, or the cost needs to be minimized. They provide variable control over the hydraulic flow and pressure based on the electrical input.

  • Operation: Proportional valves control the hydraulic circuit in proportion to an electrical command signal. Unlike servo valves, they do not typically have feedback loops.

  • Versatility: They are versatile and can be used in open-loop systems or systems that do not require the high dynamic performance of a closed-loop system.

  • Applications: These valves are often employed in applications such as mobile equipment, including excavators and cranes, industrial machinery, and process control where fine tuning of the hydraulic actuation is needed but the extreme precision of a servo valve is not critical.

Electrohydraulic actuators, through the use of servo and proportional valves, allow for a wide range of control in many industrial and mobile applications. They bridge the gap between the need for high-power actuation and the desire for control and precision, which is not always possible with purely electrical or purely hydraulic systems. The choice between a servo valve and a proportional valve in an electrohydraulic actuator system often comes down to the application's requirements for precision, response speed, and cost.

6. Pneumatic Actuators

Pneumatic actuators are devices that use compressed air to produce mechanical motion. The efficiency and cleanliness of air as a power source make these actuators popular in a wide range of applications, particularly where the safety and cleanliness of the workplace are paramount, such as in the food and pharmaceutical industries. They are available in various designs, with the most common being diaphragm actuators, rack and pinion actuators, and scotch yoke actuators.

Diaphragm Actuators

Diaphragm actuators harness the force of air pressure against a flexible diaphragm to create motion.

  • Operation: When air pressure increases, the diaphragm moves, which in turn can either open or close a valve or move a linear positioner.

  • Advantages: Diaphragm actuators provide a smooth actuating mechanism and are ideal for applications requiring a fail-safe mechanism because they can be designed to revert to a 'safe' position if the air supply fails.

  • Applications: They are typically used in valve actuation for process control where precise flow regulation is needed, such as in HVAC systems or wastewater treatment plants.

Rack and Pinion Actuators

Rack and pinion actuators convert linear piston motion into rotational motion through the interaction of gears.

  • Operation: Compressed air drives a piston back and forth, and the piston is connected to a rack gear that meshes with a pinion gear, resulting in rotational motion.

  • Versatility: These actuators can be used to drive rotary valves, dampers, or any other rotating mechanism and are known for their durability and reliability.

  • Applications: Common applications include automation systems, material handling, and robotics.

Scotch Yoke Actuators

The scotch yoke is a mechanism for converting the linear motion of a slider into rotational motion or vice versa.

  • Operation: The linear motion of a piston inside a cylinder is converted into rotation by the scotch yoke mechanism. This is accomplished by the piston's connection to a yoke with a rotating slot that engages a pin on the rotating part.

  • Benefits: The scotch yoke design is known for its ability to generate high torque at specific points in the rotation, making it well-suited for operating quarter-turn valves.

  • Applications: These actuators are widely used in heavy-duty valve operations, such as in the oil and gas industry, where large valves require a significant amount of torque to open and close.

Each of these pneumatic actuator types offers distinct advantages and are chosen based on the requirements of the application, such as the need for linear versus rotary motion, the required torque, and the precision of movement. Pneumatic systems are especially beneficial in explosive or flammable atmospheres due to the inherent safety of compressed air compared to electric or hydraulic systems.

7. Thermal and Magnetic Actuators

Thermal Actuators

Mode of Operation: Thermal actuators utilize temperature changes to create movement. They typically work by expanding and contracting materials or by exploiting the phase change in materials in response to heat or cooling.

  1. Shape Memory Alloy (SMA) Actuators: SMAs return to a pre-set shape when heated. These actuators can be 'programmed' to change shape at specific temperatures, making use of the shape-memory effect.

    • Example Application: SMA actuators are used in automotive applications, such as in self-adjusting radiator louvers that open or close depending on the temperature, and in medical devices like stents and braces.
  2. Bimetallic Actuators: Bimetallic strips consist of two metals with different expansion coefficients bonded together. When heated or cooled, the difference in expansion causes the strip to bend.

    • Example Application: Bimetallic actuators are commonly used in thermostats and household irons for temperature control, acting as simple, self-regulating switches.

Kind of Motion Produced:

  • SMAs typically produce linear motion as they contract upon heating and extend when cooled.
  • Bimetallic strips create bending or twisting motion in response to temperature changes.

Materials and Technologies Employed:

  • Shape Memory Alloys, like Nickel-Titanium (Nitinol), are known for their superelasticity and shape memory properties.
  • Bimetallic actuators use layers of metals like steel and copper or brass, chosen for their differing thermal expansion rates.

Magnetic Actuators

Mode of Operation: Magnetic actuators use magnetic fields to generate motion. The actuation can be based on the attraction and repulsion between magnetic fields, the movement of ferrofluids, or the deformation of magnetostrictive materials.

  1. Electromagnetic Actuators: Similar to solenoids, these actuators use magnetic fields generated by electric currents to create motion, but they can also be designed for more complex movements.

    • Example Application: They are used in electrically adjustable car mirrors, where a small electromagnetic actuator adjusts the angle of the mirror.
  2. Magnetostrictive Actuators: These actuators use materials that change shape or dimensions in the presence of a magnetic field, a phenomenon known as magnetostriction.

    • Example Application: Magnetostrictive actuators are used in high-precision industrial positioning systems and vibration control applications.

Kind of Motion Produced:

  • Electromagnetic actuators can produce linear or rotary motion, often in a controlled and precise manner.
  • Magnetostrictive actuators typically produce linear motion or vibrations.

Materials and Technologies Employed:

  • Electromagnets, soft magnetic materials, and sometimes permanent magnets are integral parts of electromagnetic actuators.
  • Magnetostrictive materials, like Terfenol-D, a compound of terbium, iron, and dysprosium, are used for their property to expand or contract in a magnetic field.

Thermal and magnetic actuators offer unique advantages in applications requiring responsiveness to environmental changes or where the precise application of force is needed without direct electrical connections. Thermal actuators are valued for their simplicity and reliability in temperature-sensitive applications, while magnetic actuators are appreciated for their precision and controllability. Both types have found niches in various fields ranging from aerospace to biotechnology, where their specific properties can be harnessed effectively.

Piezoelectric (Magnetostrictive) Actuators

Mode of Operation: Piezoelectric actuators convert electrical energy into mechanical displacement through the piezoelectric effect, where certain materials produce an electric charge when mechanically stressed and conversely change shape when an electric field is applied.

Kind of Motion Produced:

  • Piezoelectric actuators typically produce linear motion, but they can also be designed to create rotary motion through the arrangement of multiple piezo elements.
  • The displacement is usually very small (in the range of micrometers), but it can be highly precise.

Materials and Technologies Employed:

  • Piezoelectric ceramics, such as Lead Zirconate Titanate (PZT), are the most commonly used materials for these actuators.
  • Piezo actuators are often used in stacks or benders, where multiple piezo elements are stacked to increase the output displacement or arranged to produce bending motion.
  • Precision machining and sophisticated control electronics are crucial to maximize the efficiency and accuracy of piezoelectric actuators.

Example Application:

  • In micro-positioning applications such as optical alignment or semiconductor wafer handling, piezoelectric actuators provide extremely precise control over movements.
  • They are also used in fuel injectors for modern internal combustion engines, where the fast and precise operation of piezo actuators allows for better control over fuel delivery and atomization.
  • In the field of medicine, piezoelectric actuators are utilized in surgical instruments for ultrasonic cutting or in drug delivery systems for controlled release.

Piezoelectric actuators are selected for their high-speed response and precision, making them ideal for applications requiring fine adjustment. They are inherently low-power and can maintain their position when the power is off, which is beneficial for power-sensitive applications. Due to their small size and the ability to create force directly from electrical energy without the need for moving parts, they have high reliability and a long operational life. However, they are not suited for applications requiring large displacements or high force without the use of mechanical amplification mechanisms.


8. Smart Material Actuators

Piezoelectric Actuators:

  • Operation: Utilize the piezoelectric effect in certain materials that deform when an electric voltage is applied.
  • Motion: Highly precise linear or angular displacement.
  • Materials: Piezoelectric ceramics like PZT.
  • Applications: Precision engineering, medical devices, inkjet printers.

Electrostrictive Actuators:

  • Operation: Similar to piezoelectric actuators, but the strain produced is proportional to the square of the electric field.
  • Motion: Precision linear motion, less hysteresis than piezo.
  • Materials: Electrostrictive polymers or ceramics.
  • Applications: Precision optics, adaptive structures.

Magnetostrictive Actuators:

  • Operation: Materials change size or shape in the presence of a magnetic field.
  • Motion: Linear motion, or small precise vibrations.
  • Materials: Alloys like Terfenol-D.
  • Applications: Sonar systems, precision machining.

Shape Memory Alloys:

  • Operation: Alloys that "remember" their original form and return to it when heated.
  • Motion: Linear contraction upon heating.
  • Materials: Alloys like Nitinol.
  • Applications: Medical devices, adaptive and responsive systems.

9. Muscle Wire Actuators

  • Operation: Contract when electrically heated due to the shape memory effect.
  • Motion: Short, linear contraction.
  • Materials: Nickel-titanium alloy (Nitinol).
  • Applications: Robotic systems, active textiles.

10. Servo Actuators

  • Operation: Combine motors with a feedback sensor for precise control of angular or linear position, velocity, and acceleration.
  • Motion: Controlled motion as determined by the servo system.
  • Materials: Motors, gears, control electronics.
  • Applications: Radio-controlled devices, robotics, camera focus mechanisms.

11. Stepper Actuators

  • Operation: Driven by stepper motors that move in discrete steps, allowing precise control of angle and speed.
  • Motion: Incremental rotary or linear motion.
  • Materials: Stepper motors, rotors, gears.
  • Applications: 3D printers, CNC machines, camera platforms.

These various actuators enable sophisticated motion control in numerous applications, leveraging the unique benefits of electrical, pneumatic, hydraulic, and smart materials technologies. They provide tailored solutions where complex motions, high precision, or adaptive responses are required. Smart material actuators, in particular, open new possibilities in the realms of miniaturization and efficiency, being key in the development of innovative products from medical implants to advanced aerospace components.


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