What is a linear actuator?
A linear actuator is a device that is used to control the position or movement of an object, mechanism or system. Linear actuators work by converting rotary motion to produce linear motion, thus creating movement in a straight line.
The straight line movement itself can vary. It can be a pull force, for example with a belt drive, or a push movement. They’re engineered to suit the application, with a force of less than a pound for a small actuator with limited power up to and beyond 2000 pounds for larger actuators.
Linear actuators in their many guises, from mechanical linear actuators through to electric linear actuators, pneumatic and hydraulic actuators, are used throughout industry, anywhere linear motion is needed. They can push, pull, lift, or lower a load, operating within plant and equipment, machine tools, computer peripherals, valves, hoists, and belt drives.
What are linear actuators used for?
A linear actuator is essentially a simple tool for a simple operation, which is why they are chosen for integration into a wide range of everyday products, from electrically and hydraulically operated hospital beds to critical plant like electric valve actuators in the nuclear industry.
Easy to install and operate, linear actuators are found all around us, in every corner of industry, including manufacturing, and aerospace. There is a limitless number of applications for these high-performance maintenance-free devices, in manufacture, aerospace, power generation, water treatment, and office equipment.
A range of actuation methods is available, from hydraulic and pneumatic to electric, electromechanical and even piezoelectric. Different actuators are suited to particular applications, based on aspects like load-carrying capacity, harsh environments, cost efficiency, and linear displacement.
Mechanical linear actuators or electromechanical linear actuators
Mechanical linear actuators use a combination of gears, rails, pulleys and chains to complete a movement by converting rotary motion to linear motion. Examples of the mechanical linear actuator in use include crankshafts, and rack and pinion arrangements.
Electromechanical actuators or electric actuators work in a similar way but are equipped with an electric motor whose rotary motion is converted to linear movement.
Hydraulic linear actuators
The hydraulic linear actuator operates using a piston in a hollow cylinder. Pressure is applied to the piston using pressurized hydraulic fluid to generate the movement. Hydraulic linear actuators can be used for high-force, high-load applications like clamping, welding, and pressing.
Pneumatic linear actuators
Pneumatic linear actuators use compressed air to generate force, typically operating at lower pressures and higher speeds than hydraulic alternatives. Pneumatic actuators are accurate and affordable, available in many different styles and mountings, but do require an air compressor in use. They are often used in pneumatic systems like rock drills, paint sprayers, and blast cleaners.
Typically used in high-precision electromechanical applications, piezoelectric actuators generate a small displacement when a voltage is applied. They offer high accuracy and can be used to achieve very precise positioning of mechanical devices but have a short range of motion.
Types of Linear Actuators
There are many types of linear actuators on the market today, working in a variety of ways with differing designs and applications.
Lead Screw Actuators
Lead screw types of compact linear actuators feature a rotating nut located inside a cylinder to convert rotary motion. The motor is fixed, it is the rotating nut that initiates the movement. Lead screw-type actuators have very few moving parts and are simple and economical in use. Lead screws are ideal for cost-driven applications; the trade-off is that the screw shaft is subject to frictional wear and tear.
This type of linear actuator can be subdivided into other categories including ball screws, and planetary roller screw types. Ball screw actuators incorporate ball bearings which reduce the friction over the life cycle of the actuator, but are more expensive and often noisier in use.
Planetary roller screw actuators feature threaded rollers in a planetary arrangement around the shaft. They are high performance, low maintenance, and extremely efficient, but balanced by a far greater cost than other options.
Belt-driven actuators are typically specified where speed of operation is an important consideration. They are usually used in horizontal applications. Based on polyurethane steel belts, they offer a long stroke length at high speed. The belts do stretch and will require regular tensioning.
Rod Type and Rodless Actuators
Rod-style actuators involve movement created by the rod emerging from the actuator tube. Rodless actuators feature an actuator housing that encases the moving element.
The two are quite different. A rod-style actuator is best for a thrust application, producing more force, while rodless actuators are specified for applications where the load requires support.
Rod-style actuators can lead to compromised rigidity and increased wear of the bearing elements. Rodless actuators generally occupy a smaller footprint, which can be a benefit in certain applications.
How to choose and specify a linear actuator
It’s vital to have an in-depth understanding of the application when choosing types of linear actuators, be they hydraulic actuators, pneumatic actuators, or electromechanical actuators. The required stroke, force, and leverage are important considerations.
- Understand the weight of the object or load you need to move to determine the amount of force required
- How far do you need to move this? This is known as the stroke length
- Is it a fast movement or a slow, measured movement in terms of inches per second? Force and speed will be a trade-off to achieve the desired end result
At BE Power Transmission, we supply a range of high-performance electric linear motion actuators produced by Swedish specialists Ewellix, designed and built to provide power, performance, and extremely fine positioning for a wide range of applications. Electric actuators are typically more accurate than hydraulic and pneumatic actuators. They’re efficient, provide advanced levels of reliability, and are virtually maintenance-free.
Talk to our specialists for advice on specifying and installing linear actuators.