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This includes everything you need to know about linear actuators.
You will learn:
What is a Linear Actuator?
Types of Linear Actuators
How Does a Linear Actuator Work?
Linear Actuator Design
And much more…
Chapter One – What is a Linear Actuator?
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 motion control that is efficient and maintenance free.
Electric linear actuators use a DC or AC motor with a series of gears and a lead screw to push the main rod shaft. The difference between actuators is determined by the size of the motor, which can range from 12v DC to 48v DC.
Static and dynamic are the load capacity variables for a linear actuators. Dynamic load capacity is the amount of force being applied when the actuator is in motion. Static load capacity is when the actuator is motionless and holding a load in place.
This adhesive applicator in the diagram is using an actuator to repeatedly apply an adhesive, what used to be a manual operation.
Actuators open automatic doors, move car seats forwards and back, and open and close computer disk drives. The basic principle behind a linear actuator is the concept of an inclined plane, where the lead screw of the actuator continues along a ramp of small rotational force.
Chapter Two – Types of Linear Actuators
Linear actuators come in several configurations to fit any possible application, environment, setting, or industry. They are categorized by their mechanical drive mechanism, guide, and housing. Below explains some of the common types.
Types of Linear Actuators
Mechanical Actuators is the simplest form of actuator that converts rotary motion into linear motion. Ball screw, leadscrew, rack and pinion, belt driven, and cam actuators are categorized as mechanical. Below are mechanical actuators from Venture Mfg. Co. in Dayton, Ohio.
Hydraulic Actuators are hydraulic cylinders with a piston that uses an incompressible liquid to produce unbalanced pressure on the piston to create linear displacement.
In the pictured hydraulic actuator, the fluid, under pressure, enters through the port to the left 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 produce low to medium force and are used as servo devices. Pneumatic linear actuators use compressed air to convert energy into mechanical motion. They consist of a piston, cylinder, and valve or port, which can produce linear or rotary mechanical motion.
Piezoelectric Actuators use the piezoelectric effect, which is electricity created by pressure and latent heat resulting in an electromechanical interaction between mechanical and electrical states. Piezo actuators have multiple layers of piezo elements, such as ceramics, which combine the effect of each element‘s expansion to create movement.
The diagram below is of a stacked piezoelectric actuator that opens or closes a valve.
Coiled Actuators have magnets that generate a magnetic field, which produces current to move a coil to create motion in a shaft or shuttle. The force of the motion is proportional to the turns of the coil and the magnetic flux as well as the current. Increasing current increases the force.
Electro-Mechanical Actuators are programmable so the force and motion profile can be changed using a computer. Though electro-mechanical actuators are similar to mechanical actuators, they are significantly different because they use a variety of motors such as DC brushless, stepper, or servo types to generate rotary motion. Some of the different aspects of an electro-mechanical actuator are simplified, standard, and compact designs.
Telescoping Actuators are used where space is limited and come in several forms, which include rigid belt, segmented spindle, rigid chain, and helical band. A common form of telescoping linear actuator has tubes that are equal in length that extend and retract inside each other, much like a handheld telescopic. The range of motion of a telescoping actuator is greater than its unextended length.
Ball-guided positioning linear slides have precision accuracy and stiffness. They have low friction and smooth, accurate motion for a wide range of loading configurations. Balls run on a pair of tracks without creating friction, wear, or skidding at preload. They are non-magnetic making them perfect for applications that need to avoid magnetic interference.
A linear actuator actuates, or moves, in a linear straight line. Though the basic function of an actuator is the same, there are different ways that motion is achieved. The uses of linear actuators include wheelchair ramps to toys and technological instruments for spacecraft.
The operation of an actuator is fairly simple. A screw, such as a lead screw, ball screw, or roller screw, is used, depending on the required performance, and creates motion by turning clockwise or counter clockwise, which causes a nut on the screw to move to create linear motion. Ball screws are ideal for fast and dynamic applications that need precise positioning while roller screws are best for high forces.
The motion of the screw of a linear actuator can be seen in this diagram. The motor, above the actuator, supplies the energy to turn the screw.
The power supply is from a DC or AC motor. The typical motor has a voltage range from 12v DC to 48v DC, with other voltages available. Brush DC actuators have a switch to reverse the polarity of the motor, which makes the actuator change its motion. Servo motors and stepper motors require control electronics to electrically commutate the motor with rotor feedback needed for commutation of BLDC and servo motors using a hall effect sensor or encoder. The control electronics for an actuator can be available externally or built in.
The speed and force of an actuator depends on its gearbox. The amount of force depends on the actuator‘s speed. A gearbox that lowers the actuator’s speed supplies greater force, since there is a correlation between speed and force.
One of the basic differences between actuators is their stroke, which is defined by the length of the screw and shaft. Speed depends on the gears that connect the motor to the screw.
The mechanism to stop the stroke of an actuator include a limit or micro switches, encoders, linear potentiometers, and LVDT. A microswitch can be seen in the image below. Microswitches are located at the top and bottom of the shaft and are triggered by the up and down movement of the screw.
Components of a Linear Actuator:
This is the AC or DC motor that provides the energy necessary to drive the actuator. Though electricity is the most common source of energy, air and fluid energy is also used.
The power converter supplies power from the source to the actuator using the measurements from the controller. Examples of industrial power converters are hydraulic proportional valves and electrical inverters.
The Actuator is the actual device.
The load driven by the actuator. The load capacity is determined by a mathematical formula or a load capacity chart. Loads are calculated for vertical and horizontal configurations as well as movement along the X and Y axes. An actuator has two forms of loads – static and dynamic. Static is when the actuator is stopped, while dynamic is when it is in motion. Each form of load has a capacity range.
The Controller ensures proper system function. It allows an operator to input quantities and setpoints.
Phase IndexTM Sensor
A new development in actuator sensor control is the Phase Index sensor, which is a positioning sensor for electromechanical actuators. It is a digital, high speed, high resolution, and non-contact position sensor that is resistant to vibrations, shock, particulate debris, and moisture. As a self calibrating sensor, it does not require backup power to keep the actuator’s position when powered off, which makes the actuator immediately available when powered up.
The Power Index Sensor uses the phase relationship between two cyclic signals with different periods to calculate positioning. The major benefit of this patented mechanism, aside from its astounding accuracy, is its ability to function in the harshest and most stressful of climatic conditions.
Chapter Four – Linear Actuator Design
Linear actuators are designed for efficiency and ease of use. The basis of a linear actuators design is the inclined plane and begins with a threaded lead screw, which serves as a ramp to produce force that acts along a larger distance to move the load.
The purpose of any linear actuator design is to provide push or pull motion. The energy to supply that motion can be manual or an energy source, such as air, electricity, or fluid.
Linear Actuator Design
Power is the first consideration when designing a linear actuator. To get mechanical power out, it is necessary to have power in. The amount of mechanical power out is defined by the force or load to be moved. Manufacturers supply data regarding these factors on performance graphs and charts that include force (F), speed (V), and current draw (I), which determine what load the actuator will be able to move.
The duty cycle is how often the actuator will operate and the amount of time it will take. The temperature of the actuator while in motion determines the duty cycle since power is lost through heat. Following the duty cycle guidelines helps ensure that the actuator does not overheat the motor and damage the actuator‘s components.
Since not all actuators are the same, there is a variation in their duty cycles. Another factor is the load, which is especially true of DC motors. Other factors that can determine the duty cycle are ambient temperature, loading characteristics, and age.
Knowing the efficiency of an actuator helps to understand how it will perform when in operation. For a ball screw actuator, its efficiency will determine whether there is a need for holding brakes. The efficiency of an actuator is found by dividing mechanical power produced by electrical power. The resulting answer is its efficiency rating as a percentage.
There are various factors that affect the life of an actuator. As with any industrial tool, the care of an actuator can have a great deal to do with its longevity. Some factors that can extend the life of an actuator are:
Staying within the rated duty cycle – The duty cycle is a balance between usability and lifespan. The chart below, from Actuonix Motor Devices, provides an example of a typical duty cycle.
Minimize side load – Since actuators are designed to push and pull, side loading significantly reduces how they will be useful. The internal friction caused by side loading rapidly wears out its components. If a side load is necessary, using a slide rail with the actuator will extend its life span.
Staying within the recommended voltage – By applying more voltage than is recommended, the actuator will run faster for a short time but will wear out quicker.
Force – Actuator has a defined load capacity, such as 20 pounds. Operating it below its designed maximum capacity will extend its life.
Extreme environments – Though most actuators are designed to operate in industrial environments, it is best to avoid extreme heat, cold, dirt or dust, and moisture. There are actuators that are designed to operate underwater and may be a choice for moist conditions. The actuator below, from Ultramotion, is designed for underwater use.
Chapter Five – Load Capacity
Linear actuators can be used for tension, compression, or both to produce pushing or pulling forces. The two measurements for a linear actuator load capacity are dynamic and static. When a linear actuator is in the dynamic position, it is in motion or moving. In the static position, it is not moving and is holding a load in a set position.
The load capacity of a linear actuator is determined by its ability to move and hold a load. Loading refers to the forces that push towards or compress the actuator as well as the forces that pull away from it.
Dynamic load capacity is a test that determines the number of revolutions of linear motion that a linear actuator can achieve before fatigue, which is determined by the presence of flaking on rolling elements and the rated life of a rolling element. The International Organization of Standards (ISO) standard 14728-1:2017 describes the load fatigue for linear actuators.
The dynamic, working, or lifting load capacity is the force that will be applied to the linear actuator when it is in motion and is what is needed for it to move something. It is the load the actuator will see when it is powered, extending or retracting, and how much it will push or pull.
When a load is in static position, it is fixed or stationary and not moving. Static load capacity is determined by how much an actuator can safely hold without back driving or being damaged.
Chapter Six – Uses for Linear Actuators
Modern linear actuators look much the same as they did when they were first introduced. Technological advances have significantly improved the precision of their production and the source of their power.
Engineering, materials, technology, and physics has seen the expansion of the use of linear actuators into a wide and diverse array of industries and applications. Though many of us do not notice them, we have contact with linear actuators at stores, the office, and schools. They have become the backbone of technological advancements and development.
Uses for Linear Actuators
In space exploration, every part of the vehicle has to be put to maximum use; while keeping weight down. Micro linear actuators save room and are useful for operating robotics and doing minor tasks. They are used to open and close valves, tracking, securing locking systems, and moving robotic arms.
One of the most common uses for linear actuators in cars is powered tailgates. Self opening and closing tailgates have become extremely popular and convenient. Linear actuators are also used for opening and closing side doors and activating air brakes.
Linear actuators are a part of the most advanced medical equipment. A critical function for health care personnel is lifting patients, which is made easier with linear actuators on beds and chair recliners. Nurses can easily adjust the height of the bed for a patient‘s treatment. Monitoring equipment such as ventilators and temperature control devices have their height adjusted using linear actuators.
One of the problems with operating a snowblower is constantly changing the direction of the chute. Since operating a snowblower requires the use of both hands, reaching to change the position of the chute is difficult. A recent development in linear actuator technology is a switch that changes the position of the chute by pressing a thumb against an activation switch. The chute on the snowblower pictured below has a linear actuator on its side for easy repositioning.
The automotive industry is using robotics to improve production quality and accuracy, while controlling the cost of production. Electric linear actuators control and repeat precise movements, control rates of acceleration and deceleration, and control the amount of required force.
In bar feeders, actuators, with controllers, insert rods into the machine and adjust the optimum height. Rodless actuators are able to move pallets and position lumber for cutting and packaging.
Chapter Seven – How to Choose a Linear Actuator
Though there are multiple and varied types of linear actuators, when making the decision to purchase one, it is important to select the right actuator for the job. When purchasing an actuator, it is important to know the requirements that best suits your situation. Below are some considerations regarding how to choose the right actuator for the job.
When examining where the actuator will be placed, it is important to determine the type of motion that is required. Opening and closing a door or valve is different from activating a process on a machine. Actuators are designed to move objects in a straight line or produce circular motion. Assessing these motions and how they fit into your process is essential.
Electrical actuators have been perfected and improved to fit any application. Though they are the most popular and widely used of the actuators, does not mean that they fit all conditions. It may be necessary to consider a pneumatic or hydraulic actuator when power is limited or unavailable.
Level of Precision:
An actuator that is activating equipment in outer space may not be ideal for heavy duty use in a factory since aerospace equipment requires precise precision and accuracy. In many cases, the size of the work determines the type of actuator. Small delicate operations involve precise movements, while the stacking of pallets or managing a valve does not have to be that precise.
A main function of an actuator is to deliver force in the form of work. Actuators lift, tilt, move, activate, and slide objects and materials. The amount of work an actuator will perform will depend on the required force to move a weight, which is determined by its load capacity. Manufacturers provide information and data on the load capacity of their products, which should be studied to determine if the provided capacity fits the job.
Actuators come with different motors and stroke lengths. The stroke length is determined by the length of the shaft or lead screw. Prior to purchasing an actuator, it is necessary to determine how much movement will be required by the job.
Though speed is an important factor when considering an actuator, it is important to consider the weight that has to be moved. When a great deal of force is required to move a weight, an actuator will move slower. The measurement of speed in an actuator is in distance per second. Calculating the necessary duty cycle can provide data to help in purchasing the right actuator at the speed to meet the work conditions.
Most actuators do not perform well in dirty, wet, moist, or dusty environments. Though there are models that are designed to work underwater, most have to have some form of shelter or enclosure to be able to perform in unclean, rugged, or rough conditions.
Every actuator has a different mounting style. A dual pivoting mounting places the actuator on the two sides of the mounting point, which allows it to pivot. The common stationary mounting allows the actuator to produce push or pull motions from a set position. Proper mounting ensures optimum performance and efficiency from an actuator. It should be carefully decided during the purchasing process.
Side loading is when force is applied to the actuator radially and can create offset load, insufficient fixed mounting, or having loads pushed against the actuator. The problems of a side load include extension tubes pushing against the cover, rough ball nut riding, damage to gears, and the actuator binding.
If the space where an actuator is needed seems restrictive and confined, you may think that you won‘t be able to install an actuator because of the size or length of the actuator. There are actuators that are designed to operate in confined spaces. Several manufacturers offer different forms of telescoping actuators that can fit into any size environment.
Pin-to-pin mounting, with spherical bearings on both sides, allows for maximum misalignment tolerance. Higher quality designs include features to constrain roll about the actuation axis by limiting one of the spherical bearings to only two degrees of freedom
With spherical bearings on both sides, allows for maximum misalignment tolerance. Higher quality designs include features to constrain roll about the actuation axis by limiting one of the spherical bearings to only two degrees of freedom.
Chapter Eight - Benefits of Linear Actuators
The implementation of the actuator began immediately after World War II and involved the use of a motor to create rotary motion that was converted into linear motion using ball screws. The modern version of linear actuators was introduced during the 1980s and used high strength samarium and neodymium magnets. The news models have coils to move the assembly with magnets.
Every year, new and innovative methods have been developed for the use of linear actuators, which can automate industrial machines, provide precise control, and enable positioning of heavy loads. Their uses are endless and ever growing.
Linear Actuator Benefits
Linear actuators are safe to use compared to other methods for converting energy. They are the most effective tools and have an exceptional success rate with less risk to people, machines, and products. Other processes require more time, have less efficiency, and can be dangerous. A linear actuator allows a machine to work on its own without unnecessary interference or potential danger.
Linear Actuator Cost
A major factor in determining the use of linear actuators is their return on investment. The initial cost may be higher compared to other processes but when examined over time and work completed, linear actuators far exceed other methods. Their simple design and length of service make them an ideal investment.
Since linear actuators are not a huge tool with multiple facets, their installation can be quick and easy. By connecting a few wires and cables, they can be immediately put to work with little effort but provide great accuracy.
Lack of Noise
The majority of linear actuators work quietly and noiselessly. Their quality and how they are used determines the amount of noise they produce. An essential component of a linear actuators noise level is its manufacturer and the quality of the materials used to produce the actuator. The typical noise level of a linear actuator is less than 55 decibels (dB).
A linear actuator can operate for more than 200 million cycles before needing to be replaced. During those millions of cycles, it will not need to be repaired, adjusted, or have any form of maintenance with applications completed with exceptional accuracy and efficiency.
Linear actuators convert rotational motion into push or pull linear motion, which can be used for lifting, dropping, sliding, or tilting machines or materials.
Though the function of all linear actuators is the same, there are several different ways the motion is achieved.
The basis for a linear actuator‘s design is an inclined plane.
Linear actuators come in several configurations to fit any possible application, environment, setting, or industry.
Modern linear actuators look much the same as they did when they were first introduced.
Static and dynamic are the two load capacity variables of a linear actuator.
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...
Linear Motion Products
High-precision, linear motion goods are essential components at the core of several items which are generally used in machine tools and equipment for manufacturing semiconductors. These items are utilized...
Types of Linear Actuators
A linear actuator actuates, moves, in a linear, straight, line to complete or start a process. There are a variety of terms used to describe a linear actuator such as ram, piston, or activator. They are very common in...
Ball screws are mechanical linear actuators that consist of a screw shaft and a nut that contain a ball that rolls between their matching helical grooves. The primary function of ball screws is to convert rotational motion to linear motion. Ball nuts are used in...
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...
Linear bearings are a type of bearing that "bear" or support the load of the carriage during its single-axis linear movement and provide a low friction sliding surface for the guide rails. In a linear guide, the carriage is the component that travels in a straight line, back and forth, along the length of the guide rail...
Linear Rails are ideal for moving items through a production process with great precision and as little friction as possible if creating, packing, and distributing products. Linear Rail is a type of gadget that...
A roller table is a small, stiff, limited linear guide device with an integrated cross-roller guide. Electrical or mechanical drive systems are frequently used to move a roller table, making it easy to transfer heavy loads...
Linear slides, also referred to as linear guides or linear-motion bearings, are types of bearings that allow smooth and near-frictionless motion in a single axis. Machine tools, robots, actuators, sensors, and other...