Linear actuators are devices that produce mechanical linear motion by converting various forms of energy into mechanical energy. Typically part of motion control systems in automated assembly processes, linear actuators are most often computer-controlled, although simple actuators may be powered mechanically by hand. The various forms of energy which power linear actuators include hydraulic, pneumatic, mechanical, electro-mechanical and piezoelectric. Linear actuators often act as servomechanisms to provide and transmit a precise amount of energy to work another mechanism or equipment part, or the actuator may do the actual work itself. Linear actuator manufacturers assist in robotic processes in a wide range of industries, including automotive, biotechnology, pharmaceuticals, food, packaging and electronics. Different types of processes use various actuator designs, including ball screw actuators, electric linear actuators (or electric cylinders), rotary
actuators, and miniature linear actuators. Piezoelectric and telescopic actuators are employed for specialty applications, with piezoelectric actuators supplying extremely small, precision movement, and telescopic, or spindle actuators providing vertical mechanical motion. Nearly all factory automation processes use linear actuators to push, lift, rotate or transport products or equipment during various manufacturing processes. Some linear actuators and units operate in vacuum, radiation,
cryogenic, corrosive and underwater environments.
Actuators are not only powered by a variety of mechanical, electrical, pneumatic and hydraulic designs, but they also create motion based on several different principles. Many linear actuators use a ballscrew design consisting of a screw rod which rotates in and out of a housing, providing linear motion. Ball screw actuators, also called drive screws, are rotated using either a synchronous timing belt drive, worm gear drive or direct drive. The turning of the screw pushes a drive nut along the screw, which in turn pushes the rod out. Rotating the screw in the opposite direction retracts the rod. A cover tube protects the screw nut from environmental elements and contamination. Radial thrust bearings permit the screw to rotate freely under loaded conditions. Rotary acutators are not linear at all, although, like rotary tables, they serve purposes similar to those of linear actuators in assembly automation applications by providing radial motion. Most miniature linear actuators are electric, although some may use piezoelectric power for highly precise, short movement, while others are pneumatic actuators. Telescopic actuators utilize a fairly new "spindle" technology to provide linear motion; because they are telescopic, the length of the actuator can fit inside a fairly small housing, making telescopic actuators highly space-efficient.
When choosing from linear actuator manufacturers, several factors are important for the success of the actuator within its application, including the speed, stroke length and load rating of the linear actuators. The duty cycle accuracy and programmability requirements must also be measured, as well as desired lifetime of the linear actuator system, particular safety requirements, environmental concerns and space constraints. If the linear actuator system is not battery-run, the size and kind of motor (AC, DC or special) are important considerations. Different available electric motors, which include stepper, brushed DC or brushless servomotors, give different levels of torque and accuracy. Rotary
actuators and linear actuators may be powered electrically, hydraulically or pneumatically. Electric linear actuators are typically powered by DC or stepping motors. Hydraulic actuators have brute strength, essentially no compressibility and excellent power-to-weight ratio. However, they tend to leak, have lower reliability, are higher maintenance, expensive and loud, use flammable fluids and generate heat. Even though pneumatic actuators are inexpensive, have rapid response and are simple and easy to control, they are also loud, and their position is difficult to control.
Electromechanical actuators are quickly replacing pneumatic actuators because they save money by reducing unnecessary energy consumption within plants, have vastly improved control and flexibility, are especially beneficial for multi-positional tasks and provide no health and environmental issues due to high noise levels. However, the tendency of these electrical linear actuators to spark limits their use in hazardous environments, and they have lower power and torque-to-weight ratios. Research has been moving forward on piezoelectric linear actuators and other forms of technology, which use short high voltage bursts to create small-scale movement, but this has been primarily focused on micro-actuators and micro-manipulation.
Linear Actuator – Bishop-Wisecarver Corporation
Linear Actuator – Bishop-Wisecarver Corporation
Linear Actuator – Bishop-Wisecarver Corporation
Linear Actuator – Bishop-Wisecarver Corporation
History of Linear Actuators
Many modern linear actuators don't look substantially different in form or function from their earliest antecedents, though the precision with which they're produced and the power sources generating the motion have changed significantly over the centuries since the production of the first linear actuator.
It's difficult to pin down an exact date for the creation of the earliest linear actuators, but tools resembling those used in modern machine shops probably arose at some point in the years of the Industrial Revolution, alongside the many other machine tools invented and refined during the period. By the 1800s, English and American machinists, manufacturers, and industrialists were working with a number of tools reliant upon linear actuators.
Several basic types of linear actuator and their close antecedents were invented or standardized through the 1800s with the further evolution of machining, hydraulics, and pneumatics.
If we jump forward to late later half of the 20th century, we see Bent Johnson's invention of the first electric linear actuator in order to improve a friend's wheelchair in 1979. Within a few years, the electric actuator had spread to agriculture and other industries, where it served to revolutionize automation in an assortment of fields.
Today, leaps forward in engineering, materials, and physics have allowed the invention of myriad forms of linear actuator, and the further refinement of various technologies used in the production of actuators. Even the simplest micro linear actuator in 2017 carries centuries of advancements in machining, standards, and materials manufacturing in its design.
Actuators—Classification and Applications
In automation processes, actuators are probably the most commonly used components in a wide range of industries. Actuators move or control systems based on the need, using an energy source and a control signal. The control signal can be either a pneumatic or hydraulic pressure, electric voltage or current, or human power, but it is relatively weak. After receiving the control signal, the actuator converts the energy from the energy source into mechanical motion.
Actuators are basically classified on the basis of motion and power source, linear or rotary, and based on power source, hydraulic, electric or pneumatic actuators.
- Linear actuators work in a straight direction that provides push and pull action; whereas rotary actuators have rotational motion.
- In standard electric linear actuator design, a motor drives the motion; the rotation, with the use of power screw or similar device, is converted to linear displacement. Actuators with opposite mechanisms are also available, typically hydraulic actuators.
- To operate control valves remotely, valve actuators are used. Typically, a valve actuator incorporates an electric motor to drive a worm gear, through which the operator stem is turned. Some different types of actuators, like ball screw actuators, have push and pull racks that impart rotary motion. You would have an idea by now that a design of an actuator closely aligns with the design of the valve.
- Actuators have applications where compact designs are required for extra force or where air power is not available to drive cylinders.
- Some designs use chains to drive the valve, and other linear slides make use of belts that are toothed, screws, pinion sets, and rack for achieving push and pull action.
- There are ball screws actuators that combine stepper motors and ball screws to achieve precise controllable positioning.
- Actuators mainly have application in medical equipment, packaging machines, and production machinery, transportation industry, which range from aircraft to rail.
As designs of the actuator follow its application, there a number of other actuators that do specific work. And increasingly with the innovation that number is increasing at a great pace, it is better to contact a supplier to understand the basics of newer models and designs.
Common Types of Actuators and Their Application
In the processing industry, plant engineers and designers work continuously to achieve productive and efficient plant design and processes. In designing a facility, one part of machinery that is used at almost every automation stage for is an actuator. Actuators, which are a type of motor, move and control loads in a system. There are various types of actuators available on the market to meet most individual or plant-wide automation requirements. To make a sound choice regarding actuators, a person must know about the factors that determine the effectiveness of an actuator.
The following paragraphs describe various types of actuators so that you, as a buyer, understand the purpose of a specific actuator.
Electric Linear Actuator
In linear actuators, the mechanical parts include linear guides, motors, and a drive mechanism, which converts the electrical energy into displacement. The actuator is driven by either electro-magnetism, mechanical transmission, or thermal expansion, which provide push and pull motion in a straight line. Electric linear actuators are primarily used as an automation component when machine parts require controlled movement in a straight line, such as locking doors, opening and closing of dampers, and braking machine motions. The most common electromechanical actuators are 12 Volt linear actuators. In these types, an actuator movement is supplemented by many means; however, the most common are ball bearings, lead screws, belts, linear slides and voice coils.
An electric rotary actuator is powered electrically, and it consists of motors and an output shaft that has limited rotary motion. It is used in the automation of gates and valves that require controlled rotational movement. Typically, they have application in quarter-turn valves, robotics and windows. The actuators that are used for valve movement are called valve actuators.
Fluid Power Linear Actuators
Fluid Power Linear Actuators are mechanical devices that include cylinder and piston mechanisms to produce linear displacement. However, unlike electric linear actuators, hydraulic fluid, gas, or differential air pressure is used for motion instead of an electric motor. They are typically used in opening and closing of damper doors, clamping, and welding.
Fluid Power Rotary Actuators
A fluid power rotary actuator incorporates a cylinder and piston mechanism, a gearing system, and output shaft, which has limited rotational travel. It basically works when hydraulic fluid, gas, or differential air pressure, based on the application, is turned into rotational motion. Similar to electric rotary actuators, they can be used to open and close doors, dampers, doors, and clamps.
A form of linear actuator closely related to hydraulic actuators, but using gases instead of liquids to exert pressure on the piston. Accordingly, pneumatic linear actuators typically leverage air compressors. Notably inefficient, loud, and inconvenient for many tasks, but inexpensive and easy to use.
Linear Chain Actuator
The mechanical devices used in linear chain actuators are sprockets and sections of chain, which provide controlled linear motion. They are used when a straight line push or pull motion is required. Available in many sizes and chain styles, they are typically fitted with driving gears that produce the force needed for the motion.
Linear actuators which leverage the property of certain materials to expand with the application of voltage, the piezoelectric effect. You'll see these discussed as ultrasonic actuators and used in the manipulation of fluid films. The relative weakness of the effect make piezoelectric linear actuators a choice for applications requiring highly precise positioning involving short ranges of motion. Repeatability with piezoelectric actuators can also be a concern.
The same basic mechanism seen in various mechanical actuators drives the linear motion of an electro-mechanical actuator, but with the significant difference of using an electric servo motor to generate rotary motion rather than a knob or handle. There are a huge number of variants on the basic electro-mechanical linear actuator, including but not limited to:
- Simplified design
- Standard design
- Compact designs
Manual actuators are operated manually. Depending on the design, rotating screws or hand operated knobs or wheels are installed that work in conjunction with guided linear motion mechanisms and gearboxes. This type of actuator is used when precise positioning matters in manipulation of tools and work pieces. They can either be comprised of lead screws, racks, and pinions, or be belt driven with various load or drive force capability.
A type of motor similar to a rotary electric motor, but which utilizes repeated magnetic field structures across the length of the actuator to produce motion. Doesn't require a lead screw for conversion due to the motion of the motor, but offers a fairly low load capacity due to the limitations of the materials used. Viable in many environments which would be otherwise hostile to motors and linear actuators, and significantly long-lasting by nature.
Telescoping Linear Actuator
Various types of specialized actuator used where space is limited. These include, but are not limited to:
- Telescopic cylinder actuator
- Rigid belt actuator
- Segmented spindle
- Rigid chain actuator
- Helical band actuator
Designing and Engineering Linear Actuators
When determining a design for your linear actuator or actuators, there are countless factors to take into consideration. One of the first things you'll need to determine is the viability of standard linear actuator designs for your project. If standard can't be made to work efficiently, it's time to start looking at custom options.
- Input voltage
- Load speed
- Load capacity in lbs
- IP rate
The specific application and type of linear actuator you're using may require or suggest the use of various additional components, tools, and accessories.
With electro-mechanical linear actuators, for example, you may need to use speed controllers, digital timers, fuses, monitoring tools, and various other electrical accessories to optimize your use and management of your actuator.
Some makers may also offer customized accessories for adjusting standardized actuators to specific tasks, or for simple convenience and ease-of-use. Make sure to ask your manufacturer about any recommended or available accessories for use with your actuators.
Characteristics of Pneumatic and Electric Actuators
While selecting an actuator type, either pneumatic or electric, the first step is to determine power source. Points that need to be considered are: torque at the valve stem, failure mode, power source availability, speed of operation, control accessories, frequency of operation, size of valve, plant environment, system maintenance and system component cost.Pneumatic actuators make use of air pressure supply that ranges from 40 to 120 psi, based on the need. When higher air pressure comes into play, they may not prove quite worthy, as it is difficult to guarantee high pressure. Electromechanical Actuators most commonly use a 110 VAC power supply; however, they are available in a number of varieties, including AC and DC actuators with single phase or three phase motors.
Pneumatic and electric actuators can work in a quite wide temperature range. Pneumatic actuators perform well in –4 to 174 degree F range. However, the range can be extended to –40 to 250 degree F with use of optional bearings, grease and seals. Electric linear actuators work effectively in –40 to 150 degree F range. However, electric actuator if used in outdoors must be sealed from the environment, as moisture can deter functioning.
Depending on the requirement, you can find electric actuator that conforms to National Electrical Manufacturers Association, which makes them cost effective and applicable in wide range of industries. However, pneumatic actuators are considered better when working in explosion sensitive areas.The other factors that you have to consider for selecting an actuator are:
- Performance characteristics
- Duty cycle
- Speed control
- Modulating control
- Torque-to-weight ratio
Research and learn about all these determinants, as you will find all these terms in specification sheet. The key to choose right equipment is to know your need and requirements first, once you know them, it is not hard to find complementary equipment.
What to Buy: Pneumatic or Electric Actuators?
Hydraulic and pneumatic actuators are the workhorse in a wide variety of applications, ranging from packaging to military to aerospace. Their ubiquitous presence can be attributed to the various functions they can perform. From linear actuators to rotational ones, they have been used in automation of many machines and processing facilities.
Actuators can perform the following purposes:
- Actuators are typically used for movement of the valve members, such as ball, disc, or plug, to the specific position based on the need. The actuator is fitted with a mechanism that the closes or open valve members and the appropriate control that directs the movement.
- Valve actuators can hold the valve closure members in the specific position for specific time. For throttling applications where fluids typically create dynamic torque, the present actuators have sufficient stiffness delivered through fluid power or spring to withstand the torque.
- They act as a safety in the event of system failure. Depending on the need, in failure mode, they can be fully opened, closed or remain unchanged. Pneumatic or electro hydraulic units are ideal for this purpose.
- In multi-powered valves, based on the requirements, pneumatic actuators can provide 90° or 180° rotation. However, for rotation greater than 180°, electric actuators are preferred, as their motion is not limited by any mechanical shortcoming.
- They are used to achieve various operating speed. Special types of actuators are needed when high-speed operation is desired, as vibration can deter functioning of many typical actuators.
The Versatility of Linear Actuators
There are several types of linear actuators: mechanical actuators, electro-mechanical actuators, linear motor actuators, piezoelectric actuators, hydraulic actuators, pneumatic actuators, wax motor actuators, segmented spindle actuators, moving coil actuators and moving iron controllable actuators. There are a variety of advantages and disadvantages regarding each type of actuator. Operators will select different actuators based on the application. Some actuators such as piezoelectric actuators are not as commonly utilized due to a number of factors. Piezoelectric actuators require large amounts of voltage which is expensive but the advantage with this unit is it provides very small amounts of expansion which is preferred for some applications. On the flip side, electro-mechanical actuators are widely used due to their high usability and functional properties. These systems are simple to use and the actuation process is easy to repeat.
Linear actuators will typically be designed for either standard or compact construction. Compact linear actuators are usually created with specialized motors to allow for high torque while occupying a small space. Pneumatic and hydraulic actuators are great for applications that require high levels of output. Hydraulic systems utilize fluids and unbalanced pressures to achieve the desired outputs of the mechanism. Pneumatic actuators has a similar process like hydraulic actuators but the difference is these actuators use condensed gas instead of liquids. Regardless of which style of actuator it will successfully provide linear motion for applications ranging from DVD drive openers to opening massive heavy duty doors. Manufacturers will work with users to determine which actuators are best for their application as well as options to ensure the longevity of these devices.
Advantages and Disadvantages of Electric Linear Actuators
Which one to buy, electric or pneumatic actuators? This question is critical for machine design and control systems engineers, as it determines performance and efficiency in different conditions. In many designs and applications, a pneumatic cylinder may work better, as it has proved its efficacy over many years. However, electric linear actuators present many advantages as well. The decision to choose an actuator should be based on the application.
Advantages of Electric Actuators
- Linear actuators can handle complex motions, unlike pneumatic actuators. Sophisticated motion control systems are fitted in electric actuators, which makes electric actuators a preferred choice by many control engineers and machine designer engineers.
- The complexity does not compromise control and accuracy but gives designers space to make the systems more autonomous. The advance actuators can be programmed, adding flexibility in terms of multiple starts and stops and different speeds of valve actuators. For many designers, the programmability is what that distinguishes electric actuator from pneumatic actuators.
- They have high efficiency and consume lower energy, which makes them an environmentally friendly choice. A typical design is a 12 Volt Linear Actuator. The operation cost can be significantly brought down with electric actuators.
- They do not have a rigid design, but add flexibility; an engineer can change speed, part geometry, and start and stop points to meet new requirements.
Disadvantages of Electric Actuators
The electric system has a couple of disadvantages too.
All conventional actuator systems are simple and inexpensive. Moreover, they work well under different sets of challenging conditions and have proved to be reliable over a long period. However, new electric actuators are complex and incorporate a number of components, including motor, controller driver and cables. Not just that, these all parts are needed to be integrated and programmed accordingly, which require depth control knowledge.
Moreover, the cost of the electric actuators can shadow down the advantages at first look. However, efficient operation, new environmental regulations, and flexibility will make up for the investment made upfront.
Using Linear Actuators
Because of the wide variety of applications and the myriad fine details of using linear actuators, it's difficult to offer universal instructions for their implementation and use. Follow manufacturer instructions and the advice of your mechanics and engineers for optimal efficiency, efficacy, and safety.
While all linear actuator installations will be different, there are a few key concepts you'll want to keep in mind regardless of any specifics.
- Know all of your goals and and what to expect in advance.
- Familiarize yourself with instructions before putting anything together.
- Follow all manufacturer instructions for all involved parts and systems.
- Check components individually where possible before starting the system.
- If something looks, feels, or sounds wrong, stop and confirm with the manufacturer.
Caring for Linear Actuators
A linear actuator, like any mechanical component, will last far longer and operate far more efficiently if properly cared for.
A linear actuator should be attended to frequently by someone familiar with the component and its function. As a general rule, if something looks wrong, sounds wrong, or feels wrong in operation, it deserves attention--even if it hasn't become a problem yet.
When a linear actuator goes bad, it can go very bad, with implications for the rest of your system. Take the time to identify and resolve problems with your actuators early and they'll cost you far less time and money in the future.
Different linear actuators in different applications and environments have different requirements for lubrication--so make sure you check with your manufacturer and engineers to figure out the best lubrication type and schedule to keep your actuators operating at peak efficiency. This becomes increasingly important the more precise and finely tuned your system is--and the more critical efficiency may be.
If you're using ball screws, for example, you've invested quite a bit to be able to achieve efficiency of 90% or higher; poor lubrication practices will drop that by as much as 85%, leaving you worse off than you'd have been with a naturally less efficient linear actuator.
Linear actuators should be stored in their factory packaging until you're ready to use or install them, to prevent to buildup of dust and other debris on the surface of the unit. How long it's safe to store your linear actuator, and what adjustments or shifting you should do to keep it in functional condition, will depend on the type of linear actuator you're using. Adjustments every few months to keep oil evenly distributed are recommended in most cases, however.
Check in with Manufacturer
If something strikes you as wrong with your linear actuator, your best bet for identifying the problem and resolving it will be to check back with the manufacturer. The detailed specifications of linear actuators lead to quite a few niche problems that a typical mechanic or engineer may not be able to spot and resolve.
Compliance concerns for linear actuators will be on a case by case basis, with the specific requirements and expectations varying between industries, applications, environments, labor laws, and various other federal, local, and industrial regulations. That said, there will always be 'common sense' considerations you'll want to keep in mind to minimize risk and liability.
Because so many linear actuators end up requiring a fair degree of customization to their role, there are few hard standards to go on in the industry.
Outside of the topics we've already discussed, there are a few specifics to keep in mind when shopping for linear actuators—especially if you're going to need to make additional purchases in the future for maintenance, expansion, or ongoing manufacture.
Choosing a Manufacturer
There are two ways to measure the quality of a linear actuator manufacturer: by their quality as a manufacturer in general, and their quality as a manufacturer for your specific needs. Combining the two will get you the best possible outcome for the foreseeable future.
- Versatile. A good manufacturer works to make the product you need, not shoehorn your requirements into one of their standard offerings regardless of how well it fits. While you can certainly save time and money by working with standardized equipment, it's not always efficient or effective to do so. Make sure you're working with a manufacturer that understands that and knows how to adjust to its customers.
- Reliable. Judging reliability may seem like a difficult thing without committing to a manufacturer, but you can tell quite a bit before you even request an estimate. First, pay close attention to the way support staff communicates with you; do you have to leave a message and wait for someone to get back to you on their own schedule, or do you receive prompt and immediate responses to your inquiries? You should also look at references and look for any complaints against the manufacturer with appropriate groups.
- Experienced. Experience counts for a lot in manufacturing linear actuators and related equipment. Because of the wide variety of applications and order types coming through an actuator manufacturer's hands, you want them to be able to quickly and effectively adjust to make your project as perfectly as possible. It's best to avoid being a learning experience for a manufacturer when possible.
- Transparency. You should always know what you're getting and what you're paying for when working with a manufacturer. This includes a thorough understanding of what you're paying for shipping, a lack of tacked-on costs after your initial estimate, and clear and concise terms on warranties, guarantees, and support agreements. If there's a delay or a problem, you should hear about it as soon as someone has time to call you--not days or weeks later when they realize they can't cover it up.
- Support. A good linear actuator manufacturer should be your first and final stop for information on maintaining and repairing your linear actuator. In a broader sense, you can judge quite a bit about the overall quality of a manufacturer by observing the quality of the support staff managing customers, service requests, and other secondary and tertiary responsibilities. If the customer support isn't adequate, the manufacturing probably lags as well.
- Specific application. A suitable manufacturer for your needs will have familiarity with your specific application, or something similar. At absolute worst, they should have more than passing familiarity with the particular type of linear actuator you need for your project. A manufacturer that understands your needs can help you avoid missteps, waste, and errors in production, installation, and operation of your linear actuator. When looking at references, it's best to look closest at those most closely resembling your own needs and expectations.
- Logistics. Logistical considerations play a major role in procuring components such as actuators. Make sure your expectations for shipping, handling, procurement, and other factors align well with a potential manufacturer.
- Scheduling. Manufacturers don't often have infinite flexibility in their schedules. Make sure their availability generally matches your needs now and in the future, lest you end up put on a backburner while higher priority customers and clients receive their orders.
- Volume. If a manufacturer can't keep up with your volume requirements, they're obviously not going to be a good fit. ON the other hand, some manufacturers may require commitments to higher volumes than you're interested in. While there's some leeway here as you could conceivably buy in bulk just to have replacements handy down the line, it's usually best to work with a manufacturer that operates at the same scale you need.
Linear Actuator Types
- 12 Volt linear actuators provide mechanical linear motion by converting 12 volts of direct current (DC) electrical energy.
- Ball screw actuators are devices that produce mechanical linear motion by converting rotary motion into mechanical energy through the use of ball screw and ball nut combinations.
- DC actuators are devices that produce linear motion through conversion of electrical direct current (DC) energy to mechanical energy.
- Diaphragm pneumatic linear actuators achieve valve
actuation by using a diaphragm in a closed piston to enable control
from a low pressure pneumatic (air) supply, similar to the way air
cylinders work. Coiled springs of diaphragm pneumatic linear actuators
provide quick and dependable valve shutdown that is independent of
flowline pressure, ensuring a fail-safe position.
convert electricity into mechanical energy.
- Electrohydraulic thrusters are linear actuators
that consist of motors and closed-loop hydraulic systems for the driving
and operating of brakes, levers, dampers and safety mechanisms for
a variety of industrial equipment.
- Hydraulic linear actuators utilize some sort of
hydraulic fluid to achieve the positioning movement. Typically, electricity
is used to start the positioning process.
- Linear cylinders are simple cylinders that have
a pin-ended rod connecting to a crank arm, which then rotates the shaft.
A fail-safe linear cylinder is spring-loaded to ensure the return of
the shaft to a safe position.
- Linear thrusters provide cyclical linear motion
via double-acting air or hydraulic cylinders attached to plates and
- Microactuators are microscopic devices, with physical dimensions ranging from submicrometers to millimeters, used to provide mechanical linear motion to another mechanism or part through the conversion of various types of energy.
typically used in small spaces that
require large payloads.
- Planetary linear actuators consist of a piston assembly
and shaft assembly and have planetary rollers on a piston located between
the helical shaft and housing grooves. Piston movement causes the roller
to follow the helical grooves into the housing, forcing piston rotation,
while the rollers follow helical grooves into the shaft, causing shaft
- Rack-and-pinion linear actuators make use of fluid
pressure to move a piston connected to a gear rack, which rotates a
pinion. The output torque of rack-and-pinion linear actuators can be
doubled with two parallel piston-rack units.
- Rod linear actuators are electric
linear actuators that have an output rod which provides linear
motion through a motor-driven ball or ACME screw assembly. The load
of rod linear actuators is typically unsupported but could be attached
to the end of a screw or rod.
- Rodless linear actuators have a barrel of extruded
anodized aluminum and are formed with a longitudinal slot, permitting
a connection between the piston and mounting carriage. A hardened stainless
steel band pneumatically seals the cylinder, while a second stainless
steel band on the exterior closes the slot and avoids contamination
to the interior of the cylinder; a system of slide rails divides the
two bands in the pressure-free zone between the two piston seals, allowing
the mounting carriage to move.
are compact, simple and efficient linear actuators
that rotate an output shaft through a fixed arc to produce oscillating
power. They require limited space and simple mountings and can
produce high instant torque in either direction.
- Servo actuators are used to provide position control, utilizing linear motion in order to maintain proper functioning of another mechanism or equipment part.
- Valve actuators are mechanisms that provide linear movement to valves through the use of various screw assemblies.
Linear Actuator Terms
Accuracy – The difference from the precise value of
the intended velocity or position of electric
ACME Screw – A threaded screw utilizing sliding friction surfaces between
the nut and the screw. These screws are used in linear actuators and are self-locking
and is about 30-40% efficient.
Back Drive – Torque produced by the applied load on a drive resulting
in the reversal of rotation of the nut in many linear actuators.
Backlash – The space between the interactive elements in a drive train
or leadscrew assembly that creates a mechanical “deadband” when shifting directions.
– A screw that operates
on ball bearings. Ball bearing screws (or ball
screws) have a low starting torque, are approximately 90% efficient and can
be back driven.
Bi-directional Repeatability – The divergence in the ending position attained
by moving away and then returning to a regular point from both plus and minus
directions of linear actuators. The error or non-repeatability factor is determined
from the sum of the hysteresis, the backlash of linear actuators system resolution.
Cantilevered Load – Loads or forces that are not symmetrically placed
on the center of the positioner table in rotary
Compression Load – A load that leads toward compressing the positioner in
electric linear actuators.
Continuous Motor Torque – The torque created by the linear actuators motor
at rated constant current.
Cycle – A complete positioner extension and retraction returned to the
beginning point in rotary
Duty Cycle – The amount of time a positioner can run and how much time
it needs to cool. It is on time to cooling time, meaning a duty cycle of 25%
is a cycle in which a positioner of electric
linear actuators operates continually for ten seconds and then must rest
for thirty seconds.
Dynamic Load Rating – Linear actuators design constant used in calculating
the estimated travel life of the roller screw; the dynamic men load is the load
at which this linear actuators device will perform one million revolutions.
– The ratio of input power to
Error – The difference between the actual and the intended condition of
linear actuators. Error typically refers to the position but could refer to velocity
of many linear actuators.
Extension Rate – The speed at which the positioner extends or retracts
in rotary linear actuators. Extension rate differs with the load on DC positioners
but differs very little on AC positioners or linear actuators step-motor positioners.
Force Rating – The linear force created by linear actuators at constant
Hardwired Signals – Electrical signals traveling between two control devices
of linear actuators that are connected with dedicated conductors.
Holding Brake – A brake that works against backdriving to hold the positioner
in place under compression loads or tension of rotary
Hysteresis – The opposing force accumulated in an elastic material or
mechanism after the outside forces acting on it have been changed (e.g. the mechanical
wind-up in the lead-screw assembly of linear actuators).
– Moving or positioning a load in incremental
– The distance the lead screw nut travels
for every rotation of the lead screw.
Limit Switch – Switches found in linear actuators that limit the travel
or motion of rotary actuators in
a specific direction.
Linear Movement – Movement in a straight line as seen by the movement
of linear actuators.
Linear Position Accuracy – The error between the intended shift and real
position attained by a linear positioning component or stage system. The linear
accuracy of components and stage systems, which includes motor accuracy, leadscrew
accuracy, stage accuracy (pitch and yaw) and thermal expansion, varies with complexity
and number of components in linear actuators.
Linear Rate – Rate of movement of linear actuators components.
Load – The amount of force axially put on the positioner in rotary
Max Velocity – The linear velocity that linear
actuators will attain at a given motor rpm in electric
Maximum Static Load – The mechanical load limit of linear actuators
if recirculated oil or other cooling method is used to allow higher than rated
torque from the motor.
Microstepping – The technique of electronically subdividing every complete
step of a stepping motor.
Multiplex System – An electric actuator system that utilizes two lead-screws
in order to actuate several three-piece pump modules, the combination of which
drives the pistons in a linear motion to create displacement. Each electric
actuator system uses a pneumatic rotary actuator to drive its main function.
Optical Encoder – Linear actuators or rotary
actuators element that has alternating opaque and clear spaces. Detectors
calculate the light and dark changes, and the position is determined by counting
the amount of changes.
Pneumatic – Pneumatic actuators are operated or actuated by compressed
air or other gases.
Resolution – The lowest exact positioning movement attainable from a
Stroke Length – The complete movement of rotary
actuators positioning table from complete retraction to full extension.
Thrust – The complete force necessary to move loads of linear actuators,
taking into account friction, acceleration and gravity.
Unidirectional Repeatability – The capability of electric
linear actuators systems to return to an intended position, nearing that
position from a plus and minus direction.