Linear Actuators: Types, Processes, Applications and Advantages

What is a Linear Actuator?

A linear actuator is a device that converts rotary motion into a straight-line movement for lifting, lowering, sliding, or tilting materials or equipment. Linear actuators are efficient, clean, and have no maintenance-free motion control options.

Electric linear actuators are typically powered by either a DC or AC motor and are integrated with a gear assembly and lead screw system that extends and retracts the primary rod shaft.

The motor size differentiates the types of actuators. It generally refers to the motor voltage that powers the actuator, which can range from 12V DC to 48V DC.

There are two important load capacities for linear actuators to consider. Dynamic load capacity describes the force that the actuator can carry in motion (under operational conditions), while static load capacity relates to how much force can be applied to the actuator while in a stationary state and is applying a load.

The adhesive applicator demonstrated in the sketch uses an actuator for the purpose of automating the application of an adhesive previously done manually.

Actuators perform automation tasks that utilize actuators such as adjustments for automatic doors, movement for seat adjustments in a car, and traversing for a disk drive in computers.

Simply put, a linear actuator is based on an inclined plane motion where as a lead screw requires less rotational force when the actuator is ramped up or down.

How Does a Linear Actuator Work?

A linear actuator operates in a straight line as opposed to rotating. The function of the actuator remains constant, but several methods accomplish this.

Linear actuators have several applications, from wheelchair ramps and toys to high-tech instruments used within spacecraft.

The act of an actuator is not too complicated. It will use a screw (lead screw, ball screw, or roller screw), depending on performance needs. The screw will spin clockwise or counter-clockwise turning the screw which moves the nut producing linear motion.

To develop quickly, and position accurately use ball screws, while roller screws are suited to higher forces.

The motion of screw in a linear actuator is depicted in this illustration. The motor is situated above the actuator, which uses energy to turn the screw.

A linear actuator powered with a DC or AC motor. The standard motor voltage ranges are 12V DC to 48V DC. Don’t worry, there are other voltages too. Brush DC actuators have a switch that can reverse the polarity of the motor to affect the motion of the actuator.

Servo motors and stepper motors must have control electronics that commutate the motor electrically. The rotor feedback is required and is typically measured using a Hall effect sensor or encoder for BLDC motors and servo motors.

The control electronics for an actuator may be available from an external control source or are usually incorporated into the assembly.

The speed and amount of force an actuator is capable of producing are influenced by the gearbox of the actuator. Generally, the amount of force is proportional to the speed of the actuator.

A gearbox that increases the speed of the actuator will result in less force, due in large part to the inverse relationship between force and speed.

One of the major differences between actuators is stroke length. Stroke length is defined as the length of the screw and shaft. The speed of the actuator is affected by the gears used to connect the motor to the screw.

Stopping stroke mechanisms can include limit switches, micro switches, encoders, linear potentiometers, and LVDTs (linear variable differential transformers).

The micro switch is positioned at both the top and bottom of the shaft, which is activated when the screw moves it in the up or down direction.

Parts of a Linear Actuator

Power Source

This is the AC or DC motor that provides the energy to actuate the actuator. While electricity is a common power source there are some applications that use air or fluid to provide energy.

Power Converter

The power converter is the device that transmits power from the source to the actuator as directed from the measurements of the controller. Examples of industrial power converters include hydraulic proportional valves and electrical inverters.

Actuator

The Actuator is the real device.

Mechanical Load

The load driven by the actuator is either based on a mathematical formula or a load capacity chart. loads are calculated in vertical and horizontal, plus movement in the x and y axes. An actuator works with two types of loads: static and dynamic.

Static load is the force when the actuator is stopped; the dynamic load is the force when the actuator is moving. Each type of load generates its own capacity range.

Controller

The controller allows an operator to input quantities and setpoints, and allows the system to function properly.

Phase Index™ Sensor

One of the latest innovations in actuator sensor control is known as the Phase Index sensor. It is a digital, high-speed, high-resolution, and non-contact positioning sensor for electromechanical actuators.

It is resistant to vibrations, shocks, particulate debris, and moisture. It is a self-calibrating sensor, therefore there is no need for backup power to keep the actuator’s position when power is lost; it will have the actuator immediately available on power reactivation.

The Power Index Sensor derives positioning from the phase relationship between two cyclic signals of differing periods. The major advantages of the sensor is it is exceedingly accurate over different environments, and can work easily in extreme and harrowing climatic conditions because of its patented means of operation.

Types of Linear Actuators

Linear actuators come in different designs for use in any application, environment, surrounding and industry. Their classification is based on the mechanical drive mechanism, guide and housing. Below are descriptions of a few of the typical types.

Mechanical Actuators

Mechanical actuators are the basic version of actuators that convert rotary motion to linear motion. Types of the mechanical actuators include ball screws, leadscrews, rack and pinion, belt-driven, and cam actuators. The following are examples of mechanical actuators from Venture Mfg. Co. in Dayton, Ohio.

Hydraulic Actuators

Hydraulic actuators are hydraulic cylinders with a piston that applies an incompressible liquid to provide a unbalanced pressure that creates linear displacement. 

The hydraulic actuator shown in the image has fluid under pressure applied through the port shown on the left side of the chamber, applying pressure on the face of the piston. Once the pressure on the fluid is released, the piston moves back to the left.

Pneumatic Actuators

Pneumatic actuators can produce low to medium force quickly and they can function as a servo device. Pneumatic linear actuators are capable of conversion of compressed air to movement or mechanical motion.

Pneumatic actuators also incorporate use with a piston, cylinder and valve or port to produce either linear or rotary mechanical motion.

Piezoelectric Actuators

Piezoelectric actuators are actuators that employ the piezoelectric effect which is generating electricity by the application of pressure and latent heat, thus producing an electromechanical effect by coupling the mechanical state and electrical state.

Piezoelectric actuators are made up of multiple layers of piezo elements, for example ceramics, that in a stacked fashion take advantage of the effect of expansion for each individual element to create movement.

The following figure displays a stacked piezo actuator using the motion to either enter a valve (open) or exit a valve (close).

Coiled Actuators

The coiled actuator utilizes magnets to generate a magnetic field and while inducing current to move the coil leading to motion of a connecting shaft or shuttle. The force of this motion can be defined by motion speed, number of turns in a coil, magnetic flux, and current where the current can be increased for greater force.

Electro-mechanical Actuators

Electro-mechanical actuators are digital devices allowing one to program the force and motion profile using a PC. Like also applying a mechanical actuator, electric actuators are similar, as this type of actuator will induce rotary motion through electrical means in a motor.

Available motor types include DC brushless, stepper, or servo. These actuators can also be used in more than one application or multiple operations and standard, and compact versions may exist.

Telescoping Actuators

Telescoping actuators are excellent for your applications where you may have established or compact ranges of motion, but typically have small flanges! Types of telescoping actuators can vary (e.g., rigid belt, segmented spindle, rigid chain, and helical band).

One way to conceptualize a commonly used version of a telescoping actuator is the tube (every tube) is large, equal in length, and can move in length proportions at 360 degrees (like your little hand-held telescope in a small). The amount of motion to extend fully or retract a telescoping actuator can be greater than its un-extended length.

Ball Slide

Ball guided positioning linear slides provide accuracy and stiffness specifically designed to have low friction and smooth, exact motion for all loading configurations. Ball slides have balls moving across two tracks in an airway, which makes this product have no friction, wear or skidding due to a preload.

Ball slides can also be both non-magnetic and magnetic which are beneficial. In terms of non-magnetic, this is advantageous for applications where a magnetic influence must occur.

Design of Linear Actuators

Linear actuators are designed for convenience and efficiency. They are based on the principle of the inclined plane. The mechanical linear actuator begins with a lead screw threaded as a ramp, therefore creating force through greater distance to move a load.

The primary purpose of any linear actuator design is to provide push or pull motion. The motion can occur by manual application or some energy source such as air, electricity, or fluid.

Power

Power is the most important consideration when designing a linear actuator. To obtain mechanical power output, a power input source must be obtained. The mechanical power output amount is determined by the load or force that must be moved.

The manufacturer provides information on performance graphs and charts that indicate values of performance/data such as force (F), speed (V) or current draw (I) that concur with the load capacity of the actuator.

Duty Cycle

The duty cycle is how often the actuator operates and how long it operates. The duty cycle is affected by how hot the actuator gets acting as when power is used, ultimately results in power loss through heat.

Following the duties cycle limitations will prevent the motor from entering a point of overheating and possibly damaging other components of the actuator.

Not all actuators are the same and duty cycles may or may not be the same. The duty cycle can change based on conditions, the load (particularly for DC motors), ambient temperature, loading characteristics, and the age of the actuator.

Efficiency

Understanding the efficiency of an actuator is key to understanding its performance in operation. For a ball screw actuator, its efficiency will determine whether holding brakes are necessary.

Efficiency is determined by taking the mechanical power produced and dividing it by the electrical power supplied. The resulting ratio will be expressed as a percent of the actuator’s efficiency rating.

Actuator Life

There are a number of factors that determine the life of an actuator. Proper care and maintenance, like other industrial tools, play an important role in maximizing the life of the actuator. Below are a few things that may extend the life of an actuator:

1. Staying within the stated duty cycle – The duty cycle provides a proper balance between operating the actuator and the life of the actuator. The example chart provided by Actuonix Motor Devices below, is a typical example of a duty cycle.
2. Minimize side load – Actuators are designed for push and pull operations. Side loading can compromise the effectiveness of the actuator and can cause internal friction that will wear down the internal components very quickly. If side loads cannot be avoided, use a slide rail with the actuator to help extend its life.
3. Staying within the specified voltage – Supplying more voltage than specified may speed up the actuator but will also significantly shorten your actuator life.
4. Force – Every actuator has a rated load capacity, for example, a 20 pound actuator. If you expose it to less than maximum rated, it can help extend the life.
5. Extreme environments – Most actuators are made for industrial service, but make sure to avoid extreme heat, extreme cold, dust, dirt and moisture.There are actuators manufactured for wet environments and even underwater applications. The actuator below is from Ultramotion, and it is designed for underwater properties.

Load Capacity

Linear actuators can provide tension, compression, or both to provide a pushing or pulling force. The load capacity for a linear actuator can be measured in two ways dynamic load capacity and static load capacity.

The dynamic load capacity is the operation performed by the linear actuator while in motion, while the static load capacity is the actuator’s ability to hold a load when stationary and not in motion.

The load capacity of a linear actuator is based on movement and holding of the load. Load capacity refers to all forces applied to the linear actuator, meaning compressive forces pushing toward the actuator and tensile forces pulling away from the actuator.

The dynamic load capacity is a measurement that will determine the number of revolutions of linear motion that a linear actuator can perform before fatigue occurs (fatigue occurs when the rolling elements start to flake and at the rated life of rolling elements).

The International Organization for Standardization (ISO) lays out the guidelines for determining load fatigue for linear actuators, ISO Standard 14728-1:2017.

Dynamic load capacity, working load capacity, and lifting load capacity refer to the force placed on the linear actuator under dynamic conditions.

The loading capacity of an actuator dictates its capability to move an object and the load it can carry during basic function while extended or retracted, which indicates how much force the actuator can push or pull while working.

Static load occurs when an object is in a static position, either fixed or stationary – it is not moving.  The static load capacity of an actuator means how much weight the actuator can withstand safely without back driving or damaging the actuator.

Uses of Linear Actuators

While modern linear actuators resemble their predecessors in form, they have many more technological improvements. There are improvements in production accuracy and improvements in power sources.

Micro linear actuators have benefited from many advancements in engineering, materials, technology, and physics, opening up into additional industries and applications. 

Linear actuators are prevalent in many environments and although they tend to be part of the landscape often don’t go noticed e.g., retail stores, offices, or schools.  Linear actuators have become part of the development and evolution of technology.

Space

In space, however, each one of the components of the vehicle must be engineered for maximum functionality and feasibility, while generally optimizing the weight of all components.

In space very small items and components greatly matter, Micro linear actuators are very valuable in this sense.

The Micro linear actuator can or will save space and or execute the most important functions that it has been tasked to do i.e. operate robotic features, open and close valves, track then secure locking systems and mobile robotic arms.

Automobiles

One of the most common uses for linear actuators in your car will be the powered tailgate.  The self opening and closing powered tailgate has proven to be very popular and convenient. Linear actuators have made a strong impact with regards opening and closing side doors, and even deploying and retracting air brakes.

Medicine

Linear actuators can been found in the world of advanced medical equipment. They are a vital component of health care services in patient lifting and positioning.

Linear actuators in a bed or chair recliner allows health care personnel to make height adjustments for patient treatment with ease.

Other devices, if there is monitoring equipment, ventilators and temp controllers include linear actuators to allow for height and location adjustments made.

Snowblower

With a snowblower, one of the most common challenges to operating is the constant need to adjust the chute direction. Since operating a snowblower requires both of your hands, to modify the chute position can be an inconvenience to do so with the reach.

A recent development in linear actuator technology was to take the notion of making the chute position adjustable with a thumb press that is affixed by way of a switch.

The snowblower shows below utilizes linear actuator on the outer side to allow for the easy change in direction of the chute.

Robotics

The automotive industry has transitioned to robotics to improve on the quality and precision of production while managing production costs. Electric linear actuators assist through controlled and then repeatability of movement and with respect to controlling acceleration and deceleration, and force requirements.

In bar feeders, actuators combined with controllers, will insert bars into to the machine and to adjust lift heights when multiple rods are fed to be optimally at the same height position. Rodless actuators are also being used to move pallets around and position lumber for cutting and packaging.

Choosing a linear actuator

There are many kinds of linear actuators available, but it’s important to choose the right one for your application. When buying an actuator, it is important to know the specifics of what is needed in your situation. Here are a few important items to look at to help you choose the right actuator for your needs.

Evaluation

When evaluating where the actuator would be installed, it is very important to know the kind of motion needed. For example, the motion to open and close a door or valve would not be the same as to actuate a process on a machine.

Actuators are designed to give either straight-line motion or rotary motion. It is important to evaluate what type of motion is needed and how it will integrate into your process to decide the appropriate actuator.

Power Source

Electrical actuators have become refined and optimized for many applications and are the most common and widely used actuator.

However, not all circumstances are suitable for electrical. Occasionally, it will be necessary to discuss pneumatic or hydraulic actuators based on the power supply available.

Level of Accuracy

An actuator that has been built for outer space where precision and accuracy have great importance will typically not be suited to heavy-duty tasks in a factory setting. The specification of the actuator typically relates to the size and type of work.

Small and delicate tasks may require the need for actuators that would do accurate movements, while stacking a pallet or operating a valve may not require the same accuracy.

Force

One of the primary functions of an actuator is to exert force to do work including, lifting, tilting, moving, activating, and sliding objects and materials.

The amount of work an actuator can do depends on the amount of force necessary to move the load, also known as its load capacity.

Manufacturers have specific load capacities on their product documentation, this information should be carefully reviewed to ensure an actuator can be used for the job.

Movement

Actuators come in several different motor and stroke lengths. Length of stroke is determined by the length of the lead screw or shaft. Before purchasing an actuator, it is important to assess how much movement the job requires so that an actuator will meet the needed distance.

Speed

Speed is also an important factor when selecting an actuator; however, it is an important factor only up to the weight of the load that must be moved. In other words, if a lot of force must be exerted, the actuator will move more slowly.

Speed is usually measured in distance per second. Calculating the required duty cycle is an excellent way of collecting this kind of data to help select an appropriate actuator with a speed and performance to do the work required.

Environment

Most actuators do not perform well, if at all, in dirty, wet, moist, or dusty environments. While some models are made to use underwater, most actuators require some form of protection from unclean, rugged, and rough conditions by either enclosures or shelter.

Mounting

For example, a dual pivoting mount will permit the actuator to pivot when the actuator is mounted on both sides of the mounting point. Conversely, a stationary mount would allow the actuator to push or pull in a fixed position.

Properly mounting an actuator has a significant impact on its performance and efficiency, and should be considered carefully during the purchasing process.

Side Loading occurs when force is applied radially to the actuator. Side Loading can cause offset loads (what it is not designed for), not fixed mounted properly, or loads are pushing against the actuator.

Each side loading issue can create the following problems: extension tubes pushing on the cover, rough turning with ball nut, damage to gears, and binding with actuator.

Space

If the area where you need an actuator appears small and confined, you may be concerned that the actuator won’t fit within spatial constraints because of its size or length.

However, some actuators are purposely designed for these situations. Many manufacturers produce different types of telescoping actuators that are designed to work in small spaces.

Pin-to-pin mounting with spherical bearings on both ends allows for maximum amount of tolerance for misalignment.

Many higher quality designs will have additional features that limit the roll around the actuation axis by limiting one of the spherical bearings down to two degrees of freedom, giving it stability and precision.

Pin-To-Pin mounting

By used a spherical bearing on each end, it will allow for maximum tolerance for misalignment. Higher-end designs will impose limits looking to limit roll around the actuation axis by restricting one of the spherical bearings to two degrees of freedom.

Advantages of Linear Actuators 

Actuator usage began right after World War II, with initial action taken in the form of motors to create rotary motion, where ball screws would create a linear motion.

The modern linear actuator was initiated in the 1980’s, finalized to incorporate samarium and neodymium magnets of the onset. Current linear actuator designs include coils operating with these magnets for assembly movement. 

Every year there are new and different ways to use linear actuators, which allow for more automation of industrial machines, provide better control of movement, and position heavy loads accurately. It is clear how wide-ranging, and ever-growing, the opportunities of linear actuators can be.

Safety of Actuators

Operating around linear actuators is safer than other energy conversion methods. Linear actuators typically have a better effectiveness rate with much less risk associated to humans, machines and products.

The alternative processes usually require time, are inefficient and involve higher risk. Nevertheless, with linear actuators, machines will act with less risk of interference, and danger when acting independently.

The Cost of a Linear Actuator

When looking at the cost to utilize linear actuators, you may want to compare the return on investment. While initially, coupling them into a process may cost more than alternatives, the long term gains and efficiency will elevate its effectiveness over competitors.

Linear actuator designs are uncomplicated and reliable, enabling design accumulation which will freely give benefits for the long term. Therefore, a linear actuator would be worth the cost.

Linear Actuator Installation

Linear actuators are compact and straight-forward; it is easy to install linear actuators very quickly for use, because it requires very little attaching of wires and cables, for immediate use with a high degree of accuracy.

Silence

Most linear actuators will operate with only background noise, with the ultimate noise dependent on the manufacturer, and how the linear actuator is used.

The main constraints on noise will be the manufacturer’s warranty and the parts they assemble off the shelf. On most occasions, a linear actuator will not reach noise levels above 55 decibels (dB).

Durability of an Actuator

A linear actuator can perform over 200 million cycles and then be replaced. Do not expect to have to perform repairs, adjustments or maintenance at any time during the period. Throughout the life of the actuator, you will have accuracy and efficiency – lots of it.