How to Choose the Right Actuator for Your Robot

When building a robot, component choices can have a major impact on the eventual performance you can achieve. Actuator choice can have an especially significant effect on how well a robot performs.

Both the specifications of the component and the type of actuator you choose can help create a more efficient, more predictable, and more effective system for the tasks you need to automate.

Some actuators will also be impractical due to size, power, or how they convert energy into motion. Knowing which actuators to choose and which should be avoided will help you choose the best actuator for a new robot.

Types of Actuators

All actuators create one or both of two types of motion: linear and rotary. How they create that motion can vary significantly. These are the types of actuators that most robot designers will use when building a new system.

Hydraulic Actuators

Hydraulic actuators use pressure and hydraulic fluid to create motion. Hydraulics are commonly used in applications where a great deal of force and speed is required. Construction equipment — like diggers and earthmovers, for example — often have visible hydraulic actuators.

Some modern robotics also use hydraulics. Boston Dynamics, for example, uses hydraulic systems to create robots that are highly agile.

These actuators are often expensive, however, and prone to failure without proper maintenance. Choice of fluid type can also have a major impact on system performance. The incorrect fluid may reduce actuator performance or render it unusable.

Many common, petroleum-based hydraulic fluids can also cause serious environmental damage — killing plant life and contaminating soil — if they leak from an actuator. While environmentally-friendly hydraulic fluids exist, they can attack urethane seals and may require specialized hydraulic system components.

Pneumatic Actuators

Along with electric actuators, pneumatic actuators are some of the most commonly used actuators in manufacturing and automation system design. These actuators are similar to hydraulic actuators, but use compressed air in place of hydraulic fluid.

Quarter-turn pneumatic actuators, which are used to open or close valves, operate in two different modes — double-acting and spring-return.

Doubling-acting actuators use a piston driven by compressed air to open and close a valve. Spring-return actuators drive pistons in a single direction and use a spring to return pistons to their original position to either open or close a valve.

The benefits of pneumatic actuators include high force and speed, low unit cost, and a small working footprint. Only hydraulic actuators can provide more speed and force per unit size. The actuator’s force and speed are also typically easy to adjust.

For this reason, it’s not uncommon to see pneumatic actuators used when space is at a premium. Collaborative robots (cobots), which are increasingly popular among manufacturers, are typically designed to be lightweight and take up minimal space. It’s not uncommon for robot designers to use pneumatic actuators for cobots with grippers.

Pneumatic actuators tend to be much noisier than comparable actuators, however and may be more sensitive to vibrations.

Electric Actuators

Electrical actuators use electricity to create motion. Like pneumatic actuators, they can create extremely precise and consistent movements, due to the steady flow of energy that an electrical current provides. Electric actuators are commonly used in electric vehicles, industrial robots, and industrial machinery.

There are two main types of electrical actuators:

• Electromechanical actuators convert electrical signals into rotary or linear motion. Some actuators may be capable of just linear or rotary motion, while a few may be able to create both.
• Electrohydraulic actuators use electric power to activate a hydraulic accumulator. The accumulator then provides the force needed for motion. Like hydraulic actuators, electrohydraulic actuators are often used in industrial equipment that requires a great deal of force and speed.

Initial costs for electric actuators tend to be expensive, though maintenance and operating costs may be lower. Some electric actuators may also be unsuitable for certain environments.

Actuators used in the field, for example, may require weather-proofing. If not sealed from the environment, moisture buildup can cause serious damage to the actuator.

Manual Actuators

Manual actuators use manual input to drive motion. Typically, this manual input is converted by using levers, gears and gearboxes, or wheels to facilitate movement.

Manual actuators have been mostly displaced by other actuator types, as they require a human operator to function.

These actuators are typically used only under very specific circumstances — often when input power requirements are low, uses of the actuator will be infrequent, the operating environment is safe enough for a human operator, or operating speed is not critical.

If potential risks to operators are minimal and the machine powered by the actuator isn’t too essential, these actuators can sometimes be an acceptable, low-cost alternative to more effective and conventional actuators.

Manual actuators are almost always impractical for robots or autonomous systems that need to run continuously. In some specific circumstances, however, they can still provide a low-cost alternative to other actuator types.

Weighing Actuator Choices for a Robot

The power and functionality that your robot needs will determine which actuator will be best.

If you need an actuator that can deliver a serious amount of force, for example, a hydraulic actuator may be necessary. If you need precision, electric and pneumatic actuators may be a better choice.

When the speed of actuator cycle times is a concern, pneumatic actuators tend to be the best option.

Cost may also be a major factor in your decision. In terms of component costs, hydraulic actuators tend to be some of the most expensive. Electric actuators will typically be cheaper, but still may be costly compared to pneumatic operations.

In terms of maintenance costs, electric actuators tend to be cheap to both operate and maintain. Pneumatic actuators may be slightly more expensive, while hydraulic actuators will likely be the most expensive to maintain.

If you are willing to pay high upfront initial costs for savings down the line, electric actuators may be the best option. Otherwise, pneumatic actuators may be a better choice.

Some designers also consider the environmental impact of their actuators. Electric actuators can be extremely clean if the power they use is drawn from a renewable source of energy. Hydraulic actuators can pose a serious risk to the local environment if the petroleum-based hydraulic fluid they use begins to leak.