An Engineer’s Primer on the Actuator Component

What You’ll Learn:

What an actuator is, and what the difference is between linear and rotary
The three main energy types—electric, pneumatic and hydraulic—plus thermal, magnetic and piezoelectric
What to keep in mind when choosing an actuator

With ever advancing automation, actuators play an increasingly critical role in machine design to enable mechanical movement. These components are used in countless applications, from household appliances and electronics to the automotive and aerospace industries.

In simple terms, an actuator converts energy into motion. Actuators can be categorized by their energy source—most commonly electric, hydraulic or pneumatic—or by their movement: linear or rotary.

Linear vs. Rotary

A linear actuator extends or retracts along a set line and distance, providing a controlled back-and-forth motion such as lifting, lowering, pushing, pulling or positioning objects. A typical linear actuator couples a motor with a mechanism such as a belt and pulley, rack and pinion, or ball screw. Designs vary to offer long travel lengths, high speed, high positioning accuracy or a combination of all three.

Linear actuators can be designed compactly, are easily mounted and integrated with little to no maintenance, and can be built to withstand poor conditions. Their design is limited by stroke length and force input.

A rotary actuator, as the name suggests, is designed to turn something, such as rotating objects continuously or opening and closing valves. More versatile than its linear counterpart, rotary actuators enable a range of motions such as dumping, turning over, opening and closing, mixing, positioning, and so on. They can be designed for any degree of rotation, including constant rotation, and they offer higher torque while running at lower speeds compared to linear actuators.

Typically, the mechanism on a rotary actuator—e.g. gears, cams, or belts—directly creates a rotational motion. While the actuator itself can be a simple, compact design, factoring in rotation angle can complicate mounting and integration.

Actuator Types

Electric: Powered by electricity, these actuators can be further categorized by motor type: DC, stepper or servo motors. Known for their precision, electric actuators generally have higher accuracy and repeatability, along with simpler maintenance requirements compared to other systems. However, they can overheat under heavy loads and have a limited force output compared to fluid-powered options (hydraulic and pneumatic). While initial costs run higher than other systems, electric actuators are a quieter, cleaner and more customizable option.

Pneumatic: Using compressed air or gas to create motion is ideal where the application requires rapid movements and high repeatability, such as assembly lines. Installing pneumatic actuators is somewhat cumbersome, requiring a tank, high-pressure pump and flow control valve. That being said, once in place they are maintenance-free, barring any leaks.

While pneumatic movements are fast, they are imprecise and can lag as the air compresses first before it creates motion. Pneumatic systems are generally cheaper and hardier than their counterparts, but are seen as an inefficient use of energy. They are also typically built for a specific job, which complicates upgrades.

Hydraulic: These actuators function similarly to pneumatic, but rather than air or gas they use a non-compressible liquid: hydraulic fluid. Since the fluid does not compress, hydraulic actuators are capable of using high pressures to move very high forces with immediate response times at moderate speeds, which make them ideal for heavy machinery.

Hydraulic systems are generally expensive, noisy and, similar to pneumatic versions, imprecise. However, they can generate forces up to 25 times more than pneumatic counterparts.

Piezoelectric: Used for extreme precision, piezoelectric actuators produce motion using the piezoelectric effect—i.e., converting electrical energy directly into linear motion. Piezoelectric actuators create minimal heat and use very little power, making them ideal across industries for precise, high-speed positioning of mechanical devices.

Thermal: Using thermal energy to produce mechanical motion, these actuators comprise a heating element, such as a resistor or bimetallic strip, and a mechanism to convert thermal expansion and retraction into movement. Wax motors are a common thermal actuator. When the wax melts, it expands and generates a force that extends a piston.

Magnetic: These actuators use magnetic effects to create motion. A control system and a source of energy are required to create movement from electric currents. Magnetic actuators are typically categorized as moving magnets, moving coil and moving iron.

Choosing an Actuator

Beyond the type of motion needed and the available energy source, designers should consider priorities such as force, speed, response time, range of motion, environment and precision and control.

Naturally, the heavier the object the more load or torque capacity is needed, and each type of actuator has its limit. Hydraulic options are a natural choice for extremely heavy jobs and immediate response times. If speed is a top priority, electric and pneumatic options are ideal. Electric and piezoelectric lend themselves to extreme precision applications.

The operating environment will also narrow down options; some actuators will not hold up in extreme temperatures, or in moist, dusty or corrosive environments. Similarly, space constraints can rule out larger systems or complex mounting arrangements.

And while initial costs vary considerably among actuator types, consider long-term operating costs including consumables (hydraulic fluid, compressed air, electricity); maintenance and repair downtimes; and expected lifespans.

Standards

Standards and certifications for actuators are specific to industries, applications and locations. Each application should be thoroughly researched to ensure a chosen actuator complies with all needed requirements.