This includes everything you need to know about linear actuators.
You will learn:
A linear actuator transforms rotary motion into straight-line movement, permitting the lifting, lowering, sliding, or tilting of equipment or materials. They provide efficient, clean, and maintenance-free motion control solutions.
Electric linear actuators utilize either a DC or AC motor coupled with a gear assembly and lead screw system to extend or retract the primary rod shaft. The motor size differentiates various actuators, with options ranging from 12V DC to 48V DC.
Key considerations for linear actuators include their static and dynamic load capacities. Dynamic load capacity indicates the force it can handle while in operation, whereas static load capacity pertains to the force it can support when stationary and maintaining a load.
The adhesive applicator depicted in the diagram employs an actuator to automate the adhesive application process, a task formerly performed manually.
Actuators are essential for automating tasks such as opening automatic doors, adjusting car seats, and controlling computer disk drive mechanisms. Essentially, a linear actuator operates on the principle of an inclined plane, where the lead screw utilizes minimal rotational force to move up or down the ramp.
Linear actuators are available in various configurations to suit any application, environment, setting, or industry. They are categorized based on their mechanical drive mechanism, guide, and housing. Below are explanations of some common types.
Mechanical actuators are the simplest form of actuators that convert rotary motion into linear motion. Types of mechanical actuators include ball screws, leadscrews, rack and pinion, belt-driven, and cam actuators. Below are examples of mechanical actuators from Venture Mfg. Co. in Dayton, Ohio.
Hydraulic actuators are hydraulic cylinders equipped with a piston that uses an incompressible liquid to generate unbalanced pressure, resulting in linear displacement.
In the pictured hydraulic actuator, fluid under pressure enters through the port on the left side of the chamber and pushes against the face of the piston. When the pressure on the fluid is released, the piston moves back to the left.
Pneumatic actuators rapidly generate low to medium force and are used as servo devices. Pneumatic linear actuators utilize compressed air to convert energy into mechanical motion. They consist of a piston, cylinder, and valve or port, enabling them to produce either linear or rotary mechanical motion.
Piezoelectric actuators use the piezoelectric effect, where electricity is generated by pressure and latent heat, creating an electromechanical interaction between mechanical and electrical states. These actuators consist of multiple layers of piezo elements, such as ceramics, which combine the expansion effects of each element to produce movement.
The diagram below shows a stacked piezoelectric actuator used to open or close a valve.
Coiled actuators use magnets to generate a magnetic field, which induces a current to move a coil and create motion in a shaft or shuttle. The force of the motion is proportional to the number of turns in the coil, the magnetic flux, and the current. Increasing the current enhances the force.
Electro-mechanical actuators are programmable, allowing the force and motion profile to be adjusted via a computer. Although electro-mechanical actuators share similarities with mechanical actuators, they differ significantly by using various motors, such as DC brushless, stepper, or servo types, to generate rotary motion. They come in different designs, including simplified, standard, and compact options.
Telescoping actuators are designed for applications with limited space and come in various forms, including rigid belt, segmented spindle, rigid chain, and helical band. A common type features tubes of equal length that extend and retract within each other, similar to a handheld telescope. The range of motion for a telescoping actuator is greater than its unextended length.
Ball-guided positioning linear slides offer precision accuracy and stiffness, providing low friction and smooth, accurate motion for various loading configurations. Balls run on a pair of tracks without generating friction, wear, or skidding due to preload. These slides are non-magnetic, making them ideal for applications where magnetic interference must be avoided.
A linear actuator moves in a straight line, as opposed to rotational motion. While the basic function of an actuator remains the same, various methods are used to achieve this motion. Linear actuators have diverse applications, ranging from wheelchair ramps and toys to advanced technological instruments used in spacecraft.
The operation of an actuator is fairly straightforward. A screw, such as a lead screw, ball screw, or roller screw, is used depending on the required performance. The screw turns clockwise or counterclockwise, causing a nut to move and create linear motion. Ball screws are ideal for fast, dynamic applications requiring precise positioning, while roller screws are best suited for applications involving high forces.
The motion of the screw in a linear actuator is illustrated in this diagram. The motor, positioned above the actuator, provides the energy needed to turn the screw.
The power supply for a linear actuator comes from a DC or AC motor. Typical motors operate within a voltage range of 12V DC to 48V DC, although other voltages are also available. Brush DC actuators feature a switch to reverse the motor's polarity, altering the actuator's motion. Servo motors and stepper motors require control electronics to electrically commutate the motor, with rotor feedback essential for commutation of BLDC and servo motors via a hall effect sensor or encoder. The control electronics for an actuator may be either externally available or integrated into the system.
The speed and force of an actuator are influenced by its gearbox. Generally, the amount of force is inversely related to the actuator’s speed. A gearbox that reduces the actuator’s speed will provide greater force, due to the correlation between speed and force.
One of the fundamental differences between actuators is their stroke length, which is determined by the length of the screw and shaft. The speed of the actuator is influenced by the gears that connect the motor to the screw.
The mechanisms used to stop the stroke of an actuator include limit switches, micro switches, encoders, linear potentiometers, and LVDTs. A micro switch, shown in the image below, is positioned at the top and bottom of the shaft and is activated by the up and down movement of the screw.
This AC or DC motor provides the energy necessary to drive the actuator. While electricity is the most common energy source, air and fluid energy are also used in some applications.
The power converter delivers power from the source to the actuator based on measurements from the controller. Examples of industrial power converters include hydraulic proportional valves and electrical inverters.
The Actuator is the actual device.
The load driven by the actuator is determined by a mathematical formula or a load capacity chart. Loads are calculated for vertical and horizontal configurations, as well as for movement along the X and Y axes. An actuator experiences two types of loads: static and dynamic. Static load refers to the force when the actuator is stopped, while dynamic load refers to the force when the actuator is in motion. Each type of load has its own capacity range.
The controller ensures proper system function by allowing an operator to input quantities and setpoints.
A recent advancement in actuator sensor control is the Phase Index sensor. This digital, high-speed, high-resolution, and non-contact positioning sensor is designed for electromechanical actuators. It is resistant to vibrations, shocks, particulate debris, and moisture. As a self-calibrating sensor, it does not need backup power to maintain the actuator’s position when powered off, ensuring that the actuator is immediately available upon reactivation.
The Power Index Sensor calculates positioning by using the phase relationship between two cyclic signals with different periods. Its major benefits include remarkable accuracy and the ability to operate effectively in harsh and stressful climatic conditions, thanks to its patented mechanism.
Linear actuators are designed for efficiency and ease of use. Their design is based on the inclined plane principle, starting with a threaded lead screw that acts as a ramp. This setup produces force over a greater distance to move the load effectively.
The purpose of any linear actuator design is to provide push or pull motion. This motion can be powered either manually or through an external energy source, such as air, electricity, or fluid.
Power is the primary consideration when designing a linear actuator. To achieve mechanical power output, an input power source is required. The amount of mechanical power output is defined by the force or load that needs to be moved. Manufacturers provide data on performance graphs and charts, detailing factors such as force (F), speed (V), and current draw (I), which indicate the load capacity of the actuator.
The duty cycle refers to how often the actuator operates and the duration of its operation. It is influenced by the actuator's temperature during use, as power loss occurs through heat. Adhering to duty cycle guidelines helps prevent overheating of the motor and protects the actuator's components from damage.
Since not all actuators are identical, their duty cycles can vary. Factors affecting the duty cycle include the load, especially for DC motors, as well as ambient temperature, loading characteristics, and the age of the actuator.
Understanding the efficiency of an actuator is crucial for assessing its performance in operation. For a ball screw actuator, its efficiency will indicate whether holding brakes are necessary. Efficiency is calculated by dividing the mechanical power produced by the electrical power supplied. The resulting ratio is expressed as a percentage, representing the actuator's efficiency rating.
Several factors influence the lifespan of an actuator. Proper care and maintenance, similar to other industrial tools, play a significant role in extending its longevity. Some factors that can help extend the life of an actuator include:
Staying within the rated duty cycle – The duty cycle represents a balance between usability and lifespan. The chart below, provided by Actuonix Motor Devices, illustrates a typical duty cycle example.
Minimize side load – Actuators are designed for push and pull motions, and side loading can significantly reduce their effectiveness. Internal friction caused by side loading can quickly wear out the actuator’s components. If side loads are unavoidable, using a slide rail with the actuator can help extend its lifespan.
Staying within the recommended voltage – Applying more voltage than recommended may cause the actuator to run faster temporarily, but it will lead to quicker wear and reduced lifespan.
Force – Each actuator has a defined load capacity, such as 20 pounds. Operating it below its maximum rated capacity will help extend its lifespan.
Extreme environments – While most actuators are designed for industrial settings, it is best to avoid exposing them to extreme heat, cold, dirt, dust, or moisture. For moist conditions, there are actuators specifically designed to operate underwater. The actuator below, from Ultramotion, is engineered for underwater use.
Linear actuators can be used for tension, compression, or both, to generate pushing or pulling forces. The load capacity of a linear actuator is measured in two ways: dynamic and static. Dynamic load capacity refers to the actuator's performance while it is in motion, whereas static load capacity refers to its ability to hold a load in a fixed position without movement.
The load capacity of a linear actuator is determined by its ability to move and hold a load. Loading refers to the forces applied to the actuator, including both compressive forces that push towards it and tensile forces that pull away from it.
Dynamic load capacity is a test that measures the number of revolutions of linear motion a linear actuator can achieve before experiencing fatigue, which is identified by flaking on rolling elements and the rated life of these elements. The International Organization for Standardization (ISO) standard 14728-1:2017 outlines the guidelines for assessing load fatigue in linear actuators.
The dynamic, working, or lifting load capacity refers to the force applied to the linear actuator while it is in motion. This capacity determines the actuator's ability to move an object and is the load it will handle while powered, extending, or retracting. It indicates how much force the actuator can push or pull during operation.
When a load is in a static position, it is fixed or stationary and not moving. Static load capacity measures how much weight an actuator can safely support without back driving or sustaining damage.
Modern linear actuators resemble their early designs but have benefited greatly from technological advances. These improvements have enhanced production precision and power sources.
Advancements in engineering, materials, technology, and physics have expanded the use of linear actuators into a wide range of industries and applications. Though they often go unnoticed, linear actuators are present in many everyday environments, including stores, offices, and schools. They have become integral to technological advancements and development.
In space exploration, every component of the vehicle must be optimized for maximum utility while minimizing weight. Micro linear actuators are crucial in this regard, saving space and performing essential tasks. They are employed for operating robotics, opening and closing valves, tracking, securing locking systems, and moving robotic arms.
One of the most common applications of linear actuators in cars is for powered tailgates. Self-opening and closing tailgates have become highly popular and convenient. Additionally, linear actuators are used for opening and closing side doors and activating air brakes.
Linear actuators are integral to advanced medical equipment. They play a crucial role in healthcare by facilitating patient lifting and positioning. For example, linear actuators in beds and chair recliners allow healthcare personnel to easily adjust the height of the bed for patient treatment. Additionally, monitoring equipment, such as ventilators and temperature control devices, often uses linear actuators to adjust their height and positioning.
One common issue with operating a snowblower is the need to frequently adjust the direction of the chute. Since operating a snowblower requires both hands, reaching to change the chute's position can be challenging. A recent advancement in linear actuator technology addresses this by incorporating a switch that allows the chute's position to be adjusted with a simple thumb press. The snowblower pictured below features a linear actuator on its side for convenient and easy repositioning of the chute.
The automotive industry leverages robotics to enhance production quality and accuracy while managing production costs. Electric linear actuators play a key role by controlling and repeating precise movements, regulating acceleration and deceleration rates, and managing the required force.
In bar feeders, actuators combined with controllers are used to insert rods into the machine and adjust their height for optimal positioning. Rodless actuators are also utilized to move pallets and position lumber for cutting and packaging.
Although there are many types of linear actuators available, selecting the right one for your application is crucial. When purchasing an actuator, it's important to understand the specific requirements of your situation. Below are some key considerations to help you choose the most suitable actuator for your needs.
When evaluating where the actuator will be installed, it's crucial to determine the type of motion required. For instance, the motion needed to open and close a door or valve differs from that required to activate a process on a machine. Actuators are designed to produce either straight-line or circular motion. Assessing the type of motion and how it integrates into your process is essential for selecting the right actuator.
Electrical actuators have been refined and optimized for a wide range of applications, making them the most popular and commonly used type. However, they may not be suitable for all conditions. In cases where power is limited or unavailable, it may be necessary to consider pneumatic or hydraulic actuators as alternatives.
An actuator designed for use in outer space, where precision and accuracy are paramount, may not be suitable for heavy-duty applications in a factory setting. The choice of actuator often depends on the size and nature of the work. Small, delicate operations require actuators capable of precise movements, whereas tasks such as stacking pallets or managing a valve may not demand the same level of precision.
A primary function of an actuator is to deliver force to perform work, such as lifting, tilting, moving, activating, and sliding objects and materials. The extent of work an actuator can perform depends on the force required to move a load, which is defined by its load capacity. Manufacturers provide detailed information on their products' load capacities, and this data should be carefully reviewed to ensure that the actuator meets the requirements of the job.
Actuators are available with various motors and stroke lengths. The stroke length is determined by the length of the shaft or lead screw. Before purchasing an actuator, it is important to assess the required amount of movement for the job to ensure the actuator meets those needs.
While speed is an important factor when selecting an actuator, it is also crucial to consider the weight that needs to be moved. When a substantial amount of force is required, the actuator will move more slowly. Speed is typically measured in distance per second. Calculating the necessary duty cycle can provide valuable data to help choose an actuator with the appropriate speed and performance to meet the work conditions.
Most actuators do not perform well in dirty, wet, moist, or dusty environments. While some models are designed to work underwater, most require protection in the form of enclosures or shelters to function effectively in unclean, rugged, or rough conditions.
Each actuator features a distinct mounting style. For example, a dual pivoting mount positions the actuator on either side of the mounting point, allowing it to pivot. In contrast, a stationary mount enables the actuator to produce push or pull motions from a fixed position. Proper mounting is crucial for ensuring optimal performance and efficiency, and it should be carefully considered during the purchasing process.
Side loading occurs when force is applied radially to the actuator, which can lead to issues such as offset loads, inadequate fixed mounting, or loads pushing against the actuator. Problems associated with side loading include extension tubes pushing against the cover, rough ball nut operation, damage to gears, and actuator binding.
If the space where an actuator is needed seems restrictive and confined, you might worry that an actuator won’t fit due to its size or length. However, there are actuators specifically designed for such conditions. Several manufacturers offer various types of telescoping actuators that are built to operate effectively in compact spaces.
Pin-to-pin mounting, with spherical bearings on both sides, provides maximum tolerance for misalignment. Higher-quality designs often include features that restrict roll around the actuation axis by limiting one of the spherical bearings to only two degrees of freedom, enhancing stability and precision.
Using spherical bearings on both sides allows for maximum tolerance of misalignment. Higher-quality designs often feature constraints that limit roll around the actuation axis by restricting one of the spherical bearings to only two degrees of freedom.
The use of actuators began immediately after World War II, initially involving motors to create rotary motion, which was then converted into linear motion using ball screws. The modern version of linear actuators was introduced in the 1980s, featuring high-strength samarium and neodymium magnets. Today’s models include coils that work with these magnets to move the assembly.
Each year, new and innovative methods for utilizing linear actuators continue to emerge. These advancements enable the automation of industrial machines, provide precise control, and facilitate the positioning of heavy loads. The applications of linear actuators are vast and continually expanding.
Linear actuators offer a safer alternative compared to other energy conversion methods. They stand out for their effectiveness, boasting a high success rate while minimizing risk to people, machines, and products. In contrast, other processes often demand more time, are less efficient, and carry higher risks. By utilizing a linear actuator, machines can operate autonomously with reduced risk of interference or danger.
When evaluating the use of linear actuators, a key consideration is their return on investment. Although the initial cost may be higher than other methods, the long-term benefits and efficiency make linear actuators a superior choice. Their straightforward design and durability ensure they deliver exceptional value over time, making them a worthwhile investment.
Linear actuators are compact and straightforward, making their installation both quick and easy. With just a few wire and cable connections, they can be set up and ready for use with minimal effort, delivering impressive accuracy right away.
Most linear actuators operate quietly, with the amount of noise they generate largely dependent on their quality and usage. Key factors influencing noise levels include the manufacturer's standards and the quality of materials used. Generally, linear actuators produce noise levels of less than 55 decibels (dB).
A linear actuator can perform over 200 million cycles before requiring replacement. Throughout this extensive lifespan, it typically needs no repairs, adjustments, or maintenance, consistently delivering exceptional accuracy and efficiency.
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