This Article takes an In-depth look at Linear Actuators
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A linear actuator, sometimes referred to as a ram, piston, or activator, facilitates movement in a straight line to initiate or complete a particular task. These devices are prevalent in everyday appliances and work environments, playing key roles in things like computer disk drives and printers. Essentially, a linear actuator provides straight-line force. Historically, a common battlefield strategy involved using a hefty tree trunk as a battering ram against doors, illustrating rudimentary linear motion.
The primary types of linear actuators include screw-driven, wheel and handle, and cam varieties. In screw types, movement is guided by the winding or unwinding of a screw. Wheel and handle actuators derive motion through a belt's force or chain linked to a shaft. Cam-based actuators rely on an eccentric circle to drive shaft motion.
Each industry may define a linear actuator differently, but the most accepted definition is a device converting rotational force into linear movement. This original force might be from a manual crank or an electric motor, which is then channeled to a linear mechanism or device.
Linear actuators deliver motion in a safe, clean, and quiet manner, with excellent control precision. Their durable construction, low maintenance needs, and energy efficiency make them invaluable in manufacturing settings. With customizable designs for diverse conditions, these actuators are vital across numerous applications and products.
Linear actuators emerged during the Industrial Revolution to manage increasingly complex machines. They were key components in hydraulic and pneumatic systems in steam engines, using pistons to convert steam power into energy.
The modern electric actuator arose in 1979 when Danish entrepreneur Brent Jensen developed it to aid a friend's wheelchair. The actuator allowed for height adjustment of the chair, enhancing user convenience. Jensen extended the application of this concept beyond the initial invention, leading to the first electric actuator.
Prior to Jensen's breakthrough, electric motors were limited to rotational actions. His innovation opened up the potential uses for electric motors, vastly expanding their application possibilities. The mechanism designed for his friend's wheelchair unveiled a multitude of new applications, significantly widening the practical uses of electric motors.
With Jensen's company providing innovations in the agricultural sector, they refined his system for their equipment, improving the functionality of forage harvesters with linear actuators to efficiently load silage into silos. Once proven beneficial in agriculture, linear actuators spread across many sectors as a dependable, efficient solution.
Building on Jensen’s original design, a diverse range of actuators has been developed. The concept of the first electrical linear actuator has been adapted to suit various types of equipment and production methods. The most common types of linear actuators include mechanical or electromechanical, hydraulic, pneumatic, and piezoelectric actuators.
Mechanical or electro mechanical linear actuators do the basic function of converting rotary motion to linear. They do the conversion by using one of the types normally found in linear actuators – screw, wheel and handle, or cam. Mechanical linear actuators get their energy from an AC or DC motor.
The screw-type mechanical linear actuator uses a ball screw, roller screw, or similar screw design. In this system, a rotating screw shaft is driven in a linear motion. A stator assembly rotates the shaft to achieve the desired direction of movement.
The wheel and handle version uses a belt, chain, rack, or cable that is attached to the shaft. This form of linear actuator uses several different types of guide mechanisms, which include plain bearing, cam roller guide, and recirculating bearings. Since they operate at high speeds and have long strokes, they are normally enclosed in a housing.
The cam-type linear actuator employs an eccentrically shaped wheel that rotates to generate linear motion. This rotational movement creates thrust that drives a shaft. Cam-based linear motion systems are commonly used in automotive applications.
Electric cylinders provide greater accuracy, efficiency, and ease of installation compared to pneumatic or hydraulic linear actuators. They offer precise fluid motion control and accurate positioning, making them ideal for applications that require close tolerances and long service life.
The energy and cost efficiency of electric cylinder linear actuators allows them to have improved controls, flexibility, and the ability to perform multi-positional functions. Their valves are opened and closed by a sliding rod. Pinch, angle, diaphragm, gate, and globe type valves are used with a screw assembly drive of ball, lead, or ACME.
The types of drives used by electric cylinder linear actuators include direct, geared, or belt. The motor can be connected to either the top of the guide cylinder with a screw assembly or to the side of the housing. The variety of motors can be brushed DC, stepper, or brushless servomotors.
DC actuators create linear motion by converting electrical direct current (DC) energy into mechanical energy. DC energy is one of the two primary types of electrical energy flow, the other being alternating current (AC) energy. Unlike AC, which oscillates electrical flow back and forth at specific frequencies, DC provides a unidirectional flow of electricity. DC is a simpler energy source, commonly used in low-voltage applications, and can be derived from AC sources or converted into AC through an inverter or motor-generator set.
The main parts of DC actuators are a DC motor, a screw rod and a housing, made from metals such as aluminum, zinc or steel. The DC motor can be brushed or brushless. A brushed DC motor consists of a permanent magnet stator and a wound iron-core armature, as well as a commutator with mechanical brushes. While the brushes serve to connect the power source to the armature, or a rotating coil that induces voltage from motion through a magnetic field, the brushes also cause decreased service life due to wear and tear.
Electric actuators generate linear motion by converting electrical energy into mechanical energy. These actuators are often connected to valves, which move in response to an external power source. The required power is supplied by either single-phase or three-phase AC motors or DC motors, along with various gear mechanisms.
Electric actuators are divided into two different types: rotary and linear. When selecting an electric rotary actuator, important factors to consider include actuator torque and range of motion. Important factors to consider when selecting include the number of turns, actuating force, and the length of the valve stem stroke.
Electric linear actuators produce linear motion by converting electrical energy into mechanical energy. These actuators are commonly used with valves powered by an external source. Typically, they employ single-phase or three-phase AC motors or DC motors as their actuation mechanisms.
Most electric linear actuators are composed of the same basic components. These components include an electric motor, a screw, a nut and gears in many cases. In an electric actuator, the nut makes possible the transformation of electrical energy to mechanical energy when it rotates along the screw. Using butterfly, ball, and plug valves, electric rotary actuators rotate from open to close.
A rack and pinion actuator features two gears: a circular gear known as the pinion and one or two linear gears called racks. The actuator utilizes a piston connected to the linear rack gear. As the actuator operates, the pinion, piston, and rack collaborate to produce linear motion.
When pressurized air is introduced to a rack and pinion actuator, the piston moves linearly, which the pinion gear then converts into rotational motion. This rotation drives a valve stem to either open or close. Once the air pressure is released, the piston returns to its original position, reversing the pinion gear's motion.
Rack and pinion actuators are ideal for controlling quarter-turn ball, butterfly, and ball valves. Their compact design facilitates easy installation and maintenance-free operation, making them efficient and reliable for both single and multiple cycles per day. Known for their durability and low cost, rack and pinion actuators can produce linear motion in either clockwise or counterclockwise directions, depending on the application requirements.
Compact linear actuators are engineered for applications with limited space. Despite their slim, streamlined design, these actuators deliver the same load capacity as larger models, with a push force of up to 3500 N and a pull force of 2000 N. Their low noise levels make them particularly desirable for environments where space is restricted. They are robust enough to handle high static pull forces, regardless of their compact size and shape.
These actuators are commonly used in harsh, challenging environments, offering both high speed and substantial force. They are tightly sealed to ensure durability and long life under tough conditions. Their compact size makes them versatile, suitable for a range of applications in industrial, medical, and research fields. Additionally, their small size allows for stacking, enabling multiple actuators to work together efficiently.
Weighing approximately 6 g and with a thickness of 6 mm, compact linear actuators achieve speeds of up to 1000 mm/s and a stroke frequency of 50 Hz. Their rod travel length ranges from 5 mm to 300 mm, making them adaptable for various uses. Their precision and compact dimensions make them ideal for applications such as wheelchairs, treatment chairs, and medical lifts.
Hydraulic linear actuators have the common elements of a hydraulic motor with a cylinder, piston, and incompressible liquid, which applies unbalanced pressure on the piston. When a large amount of force is necessary, hydraulic actuators are the normal choice.
Hydraulic linear actuators are designed to provide maximum mechanical energy for applications requiring substantial force. These actuators are commonly found in machinery that lifts heavy materials, such as cranes and excavators. Whenever significant lifting or movement of large objects is needed, hydraulic linear actuators are likely involved in the equipment's lifting mechanism.
The fluid in a hydraulic linear actuator is how it gets its power. By changing the amount of fluid, the movement of the actuator can be controlled. Various forms of oils have been designed for this function.
Hydraulic linear actuators offer exceptional accuracy and reliability, similar to other types of linear actuators. Their agility and adaptability allow them to be engineered to replicate arm-like movements, enabling precise pushing and pulling actions for various machine appendages.
Rotary actuators are compact and efficient devices that generate oscillating power by rotating an output shaft through a fixed arc. They are space-efficient and easy to mount, delivering high instantaneous torque in both directions. These actuators are commonly employed for various movements, including lifting, lowering, opening, closing, indexing, and transferring.
The various forms of energy that run rotary actuators include hydraulic, pneumatic, and electrical. Hydraulic rotary actuators are often used for steering or as an alternative to hydraulic cylinders or motors. Pneumatic rotary actuators are commonly used for material handling, product assembly, testing and quality control, packing, welding, and machine loading and unloading applications. Lastly, for electric rotary actuators, there is a wide range of applications including automotive power lock systems, fertilizer spreaders for farming and wind turbine construction.
12-volt linear actuators use 12 volts of direct current to create slow linear mechanical motion. The advantages of a 12-volt actuator include high power levels, durability, and reliability. New designs have made them space efficient and include more advanced hardware.
A 12-volt linear actuator rotates a lead screw with a helical thread, similar to a common bolt. The lead screw is threaded to a lead nut, which does not rotate with the lead screw. As the lead screw rotates, the nut is driven along its threads. The direction of the rotation of the nut is dependent on the rotation of the lead screw. The linkages connected to the nut converts the motion to linear displacement.
Most 12-volt linear actuators are built as heavy duty, high rate of rotation mechanisms, or include both functions. They are built for accuracy and movement resolution rather than force or a high rotation rate. Most are mounted on butterfly valves or dampers.
Ball screw actuators, or drive screws, produce mechanical linear motion by converting rotary motion into mechanical energy through the use of a ball screw and ball nut combination. They are very accurate and precise due to their tight manufacturing tolerances and lack of compressibility in the ball bearings.
Highly durable, ball screw actuators can have a lifetime of 5,000 km if operated at low loads and speeds or lifetimes of 3,000 km at high loads and speeds. The actuator's speed is determined by its pitch. The screw lead is the screw pitch multiplied by the number of threads, which determines the linear travel of the ball nut per rotation of the screw. Ball screw actuators with a higher screw pitch provide higher axial movement to a nut faster per given screw rpm, while those with a lower screw lead produce greater linear thrust.
Ball screw linear actuators consist of a ball screw, a train of recirculating ball bearings, a ball nut and a cover tube or housing that attaches to the load, which is attached to the end of the ball screw and unsupported. The ball bearings travel in opposed, hardened rod tracks or grooves that are cut out inside of the axially translating ball nut at a particular helix angle using a belt, direct, or worm gear drive.
Ball screw linear actuators are employed in industries such as aviation, missile production, and medical equipment. They are commonly used in blood separation devices and dialysis machines. These actuators convert a motor's torque into linear thrust and are capable of handling higher dynamic loads efficiently.
Miniature, micro, or mini linear actuators are integral to motion control systems and are typically computer-controlled. They feature a compact design with sizes ranging from 150 mm (5 in) to 1500 mm (59 in) in stroke length, making them easy to install in tight spaces.
The stroke of a miniature linear actuator is less than one in. or 10 mm to 59 in or 1500 mm. Though those are standard sizes, custom versions can be manufactured for special applications. The 10 mm version has been used for the manufacture of toys.
The load thrust of a miniature linear actuator varies between 10 Newtons or 2.25 lb. to 6000 Newtons or 1349 lb. The industrial version can go as high 15,000 Newtons or 3,372 lb. The motor drives three gears and begins with a small gear that drives a middle gear that drives a bigger gear to push the shaft. There are also pneumatic and hydraulic versions.
Miniature linear actuators are utilized in control systems to move or regulate objects. They can be designed with electrical, mechanical, pneumatic, or hydraulic mechanisms. These actuators find applications across various industries, including robotics, medical fields, automotive, and aerospace.
When selecting a miniature linear actuator, several key factors must be considered. These include duty cycle, accuracy, programmability, safety requirements, environmental conditions, and space constraints. Their compact size enables installation in extremely confined spaces.
A piezoelectric actuator converts an electrical signal into a physical displacement. Piezoelectric materials change dimensions when a force such as voltage is applied making these actuators useful for applications that need precise positioning. Since they give off very little heat and no power, they are ideal for precision scientific instruments and ultrasonic machines.
Applying pressure to a crystal can generate electricity, and conversely, applying electricity to a crystal can cause it to exert pressure. Technically, when a voltage is applied to a crystal, it undergoes electrical stress, transforming it into a type of battery. In piezoelectric actuators, this principle is utilized as the crystal produces electrical pressure in response to material deformation, causing the material to adjust and change shape.
The minimal moving parts, simple design, no need for lubrication, and high reliability makes piezoelectric actuators perfect for precision movements of camera lens, microphones, and ultrasound equipment. They can operate innumerable times without experiencing any wear or deterioration. Their time of response is only limited by the inertia of the object being moved and the output of the electronic driver.
Pneumatic linear actuators operate on the same principles as hydraulic ones but use air pressure instead of a fluid to move a piston. In the case of a pneumatic linear actuator, the piston is contained in a cylinder and is large enough to form a tight seal against the walls of the cylinder. When compressed air enters the cylinder housing, the piston is forced to move upward.
The force generated by a pneumatic linear actuator is determined by the piston size and the pressure of the compressed gas. Increasing the pressure applied to the piston enhances the actuator's strength. This process is clean, straightforward, and completed efficiently and quickly.
Pneumatic linear actuators are ideal for applications in microchip and electrical component production as they are not affected by magnetic forces. They can endure extreme temperature fluctuations, operating effectively in a range from -40°F to 250°F. Additionally, their lack of magnetic interference means they pose no risk of explosion or flammability.
A servo linear actuator is equipped with a servo controller that continuously monitors the actuator's performance by comparing the desired outcomes to the actual results. When discrepancies are detected, the actuator is adjusted to rectify them. These actuators are commonly used in remote control and automated systems.
Servo linear actuators complete tasks controlling an actuator that flips a switch or changes the positioning and focus of a lens. The adjustments can be very minute in fractions of an inch to moving tons of material. A servo linear actuator operates by information it receives, which determines its output. The controller compares the data received to the desired ideal conditions. A variety of instruments provides the input data that include various forms of sensors.
Servo linear actuators are ideal for a range of sophisticated applications, including advanced automation, robotic control, beam steering, remote-controlled vehicles, marine equipment, and aerospace manufacturing. As manufacturing technologies continue to evolve, these actuators are increasingly essential in various fields.
Valve linear actuators are designed to open and close valves. While valves, in the past, required a person to open and close them, by using a linear actuator, the same operation can be performed remotely using either a pneumatic, hydraulic, or electric linear actuator system. Actuators react quicker and can regulate flow rates to automatically close or open a valve.
Linear valves come in several types similar to those used in other systems, such as globe, gate, and pinch valves. A globe valve features a disk that presses against an opening to control flow; removing the disk allows flow, while closing it stops flow. A gate valve operates like a lift gate: when the gate is raised, flow is allowed; when lowered, flow is halted. A pinch valve controls flow by constricting the pipe through which the medium passes.
Lead screw actuators convert rotational movement from a rotary motor into linear motion. Their thread profile and rolled thread structure provide exceptional strength and efficiency. The actuator's nut is made from low-friction materials or lubricated metal, ensuring smooth operation. The actuator relies on the screw shaft and nut moving against each other to minimize energy loss due to friction, resulting in quiet, vibration-free performance.
The key components of a lead screw actuator include a screw shaft and a nut, both of which are threaded to facilitate the conversion of rotational motion into linear motion. The screw shaft is a cylindrical rod with helical grooves running along its length, known as external threads. The nut has internal threads that mesh with the external threads of the shaft.
Lead screw actuators operate in two main ways. In one scenario, the shaft remains stationary while power is applied to the nut, moving it along the shaft's axis. In the other scenario, the shaft rotates and drives the nut along its axis, transforming rotational motion into linear motion through applied torque.
Lead screw actuators are often used with stepper motors for open-loop control, and when paired with Brushless DC motors, they offer high speed efficiency at a low cost. They are available in various sizes to suit different applications.
Linear ball slides, known for their low friction coefficient, are often referred to as non-magnetic linear actuators. Their central components include a ball bearing slide and guide rail, which contribute to their exceptionally low friction. The friction coefficient of linear ball slides is about 1/50th that of the rail, and the gap between dynamic and static friction is minimal, ensuring stable and smooth movement.
These slides are commonly used in automated applications such as bending machines and laser welders. They are highly valued in mechanical structures requiring high precision and are ideal for linear reciprocating motion applications. The robust structure of a linear ball slide allows it to endure a certain amount of torque.
Due to their low friction, linear ball slides produce minimal heat even when operating at high speeds.
Recirculating slide guides are an excellent choice for applications requiring long travel and exceptional accuracy. These guides feature a carriage and guide rail set on a grooved path, with the carriage incorporating two tracks to ensure smooth and even ball motion. Despite their lightweight and compact design, recirculating slide guides can carry loads of over 1500 lbs (700 kg).
The balls in a recirculating slide guide make contact at four points, enabling the load and movement to be distributed in all directions. The steel rolling ball elements produce extremely low resistance, ensuring stability and very smooth motion. The simplicity of the design makes recirculating slide guides both affordable and compact, making them ideal for high-speed linear applications.
Rod linear actuators produce motion by extending or retracting a rod within its housing. The load is either attached to the rod, or the rod moves the load through pushing and pulling actions. These actuators are ideal for pressing or inserting applications and are capable of high-speed operation, significant force, and precise end-to-end positioning.
Choosing rod linear actuators eliminates the need for hoses, filters, valves, and oil and air management equipment. Their housing and mounting sizes can be customized to meet various industrial standards, making them versatile and adaptable. Rod linear actuators are often excellent replacements for traditional fluid power systems.
Underwater linear actuators are built to withstand constant exposure to water and must meet very high standards, including a high ingress protection (IP) rating. These actuators can be permanently submerged and are coated with a salt spray-resistant layer to prevent corrosion.
They are used in various applications, such as boat hatch actuators, which feature long stroke lengths to accommodate different hatch sizes and include quick-release mechanisms for critical system safety. The precision of underwater linear actuators, combined with their high IP rating, allows them to endure harsh maritime conditions while delivering reliable performance.
A belt-driven linear actuator converts rotary motion into linear motion using a timing belt connected between pulleys at each end of the drive. The belt is crafted from highly durable materials: a reinforced elastomer fiber for light-duty applications and a steel-reinforced polyurethane for heavy-duty applications.
The belt features teeth that mesh precisely with the pulleys, ensuring efficient torque transfer and preventing slippage. A notable advantage of belt-driven actuators is their ability to cover long distances, making them more cost-effective compared to other actuator types.
This design is particularly suited for applications requiring low loads, high speed, and extended stroke lengths.
The types of linear actuators mentioned here represent just a subset of the many available varieties. Each industry may use specific terminology to classify and describe their actuators, with some industries recognizing only a few types, while others have numerous varieties, ranging from ten to fifteen.
When selecting a linear actuator, there are several considerations that apply universally across all types and forms. Below are a few key factors to consider.
The speed of a linear actuator refers to how quickly it can extend and retract. Certain applications require the actuator to move rapidly while maintaining precise motion control.
The stroke length of a linear actuator determines how far it can extend from its starting position. Smaller tasks may require a short stroke, while larger applications necessitate a longer stroke.
The load rate refers to the amount of weight that a linear actuator can move.
Linear actuators are used for performing automated tasks and typically require some level of programming.
The lifespan of a linear actuator is influenced by the materials being moved, the environment, and the manufacturing process. Durable and high-quality actuators tend to last longer and operate more efficiently.
The type of power an actuator uses is crucial to its performance. Common options include electrical, hydraulic, and pneumatic motors. The choice of motor depends on the actuator's intended function.
Larger actuators deliver more power but require more space and weigh more. In contrast, smaller actuators offer greater precision and flexibility in placement.
This is a brief discussion of actuators and their function. More detailed information can be provided by actuator manufacturers who can design a tool to fit your needs. ISO certified producers have the staff and expertise to explain actuators and their versatile use.
A linear actuator is a device that transforms rotational motion into push or pull linear motion, which can then be used to lift, lower, slide, or tilt machinery or materials. They offer effective, maintenance-free motion control...
Electric actuators are devices capable of creating motion of a load, or an action that requires a force like clamping, making use of an electric motor to create the force that is necessary...
A linear actuator is a means for converting rotational motion into push or pull linear motion, which can be used for lifting, dropping, sliding, or tilting of machines or materials. They provide safe and clean...
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A lead screw is a kind of mechanical linear actuator that converts rotational motion into linear motion. Its operation relies on the sliding of the screw shaft and the nut threads with no ball bearings between them. The screw shaft and the nut are directly moving against each other on...
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