An actuator is a part of a device or machine that helps it to achieve physical movements by converting energy, often electrical, air, or hydraulic, into mechanical force. Simply put, it is the component in any machine that enables movement.
Sometimes, to answer the question of what does an actuator do, the process is compared to the functioning of a human body. Like muscles in a body that enable energy to be converted to some form of motion like the movement of arms or legs, actuators work in a machine to perform a mechanical action.
Actuators are present in almost every machine around us, from simple electronic access control systems, the vibrator on your mobile phone and household appliances to vehicles, industrial devices, and robots. Common examples of actuators include electric motors, stepper motors, jackscrews, electric muscular stimulators in robots, etc.
How does Linear Actuator work?
Defined simply, an actuator is a device that converts energy, which may be electric, hydraulic, pneumatic, etc., to mechanical in such a way that it can be controlled. The quantity and the nature of input depend on the kind of energy to be converted and the function of the actuator. Electric and piezoelectric actuators, for instance, work on the input of electric current or voltage, for hydraulic actuators, its incompressible liquid, and for pneumatic actuators, the input is air. The output is always mechanical energy.
Actuators are not something you would read about every day in media, unlike artificial intelligence and machine learning. But the reality is that it plays a critical role in the modern world almost like no other device ever invented.
In the industrial mechatronics systems, for instance, they are solely responsible for ensuring a device such as a robotic arm is able to move when electric input is provided. Your car uses actuators in the engine control system to regulate air flaps for torque and optimization of power, idle speed, and fuel management for ideal combustion.
Actuators are not something you would read about every day in media, unlike artificial intelligence and machine learning. But the reality is that it plays a critical role in the modern world almost like no other device ever invented.
They are not just seen in large applications. At home, actuators are the critical devices that help you to set up consoles or cabinets that could hold televisions and can be opened at the touch of a button. They are also seen in TV and table lifts which users can adjust through electric switches or buttons at their convenience.
Fancy a recliner to watch the TV? In all likelihood, it has a movable head or footrest that uses an actuator too. Home automation systems that can intuitively close window blinds depending on the amount of light streaming in are also dependent on actuators. In short, their use is endless because any mechanical movement requires them, and most devices require some form of mechanical movement.
Following are the usual components that are part of the functioning of an actuator:
- Power source: This provides the energy input that is necessary to drive the actuator. These are often electric or fluid in nature in the industrial sectors.
- Power converter: The role of the power converter is to supply power from the source to the actuator in accordance with the measurements set by the controller. Hydraulic proportional valves and electrical inverters are examples of power converters in industrial systems.
- Actuator: The actual device that converts the supplied energy to mechanical force.
- Mechanical load: The energy converted by the actuator is usually used to make a mechanical device function. The mechanical load refers to this mechanical system that is being driven by the actuator.
- Controller: A controller ensures that the system functions seamlessly with the appropriate input quantities and other setpoints decided by an operator.
Types of Linear Actuators
Depending on the kind of movement they make, and the source of energy used to function, there are different types of actuators. Here is a list of the various types of actuators:
Electric Linear Actuator
As the name implies, electric linear actuators use electrical energy to enable movements in a straight line. They work by moving a piston back and forth based on electrical signals and are mostly used for movements such as pulling, pushing, blocking, lifting, ejecting, clamping, or descending.
Linear actuators function with a motor that generates high-speed rotational motion and a gearbox that slows down its impact. This will, in turn, increase the torque that would be used to turn a lead screw, which results in linear motion of a shaft or drive nut. Often, a 12V DC motor is used in linear actuators but those with other voltages are can also be used. Switching the polarity of the connection from motor to the battery would make the motor rotate in the reverse direction.
Manufacturers offer linear actuators in different strokes, which is done by increasing or decreasing the length of the shaft. With different gears, different speeds can also be achieved. Generally speaking, the more the speed of the screw turn, the less the force. A switch within the main actuator shaft at the top and lower end stop the screw as it reaches the end of its movement or stroke. As the shaft reaches its end, the switch cuts off power to the motor.
Electric Rotary Actuator
Electric rotary actuators use electrical energy to achieve rotational movement. This movement can either be continuous or be towards a fixed angle as seen in servo and stepper motors. Typically speaking, an electric rotary actuator consists of a combination of an electric motor, limit switch, and a multiple stage helical gearbox.
In simple terms, this actuator’s operations can be defined like this: when a conductor that carries current is brought within a magnetic field, it will experience a force that is relative to the field’s flux density, the current that is flowing through it, and its dimensions. Rotation and torque are generated due to the force and back electromotive force (EMF) that ensues.
Hydraulic Linear Actuator
The purpose of a hydraulic linear actuator is the same as that of an electric linear actuator – to generate a mechanical movement in a straight line. The difference is that hydraulic linear actuators achieve this with an unbalanced pressure that is applied with hydraulic fluid on a piston in a hollow cylinder that can lead to torque strong enough to move an external object.
The main advantage of a hydraulic linear actuator is the massive amount of torque it can generate. This is because liquids are almost incompressible. Single-acting hydraulic actuators have pistons that can move in just one direction and a spring is needed for reverse motion. A double-acting hydraulic actuator applies pressure at both ends to facilitate similar movement from both sides.
Hydraulic Rotary Actuator
Hydraulic rotary actuators make use of incompressible, pressurized fluid to rotate mechanical parts of a device. They mostly come two kinds of rotational components, circular shafts that have keyway and tables that have a bolt pattern which can be used to mount other components.
They are available with single and double shafts. The shaft is rotated when the helical spline teeth on it connect to the corresponding splines on the piston, effectively converting linear movement to rotational motion. When pressure is applied through fluids, the piston moves within the housing prompting the splines to make the shaft rotate. The shaft can be locked in place when a control valve is shut and fluid is held inside the housing.
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Pneumatic Linear Actuator
Pneumatic actuators are often considered to be the most cost-effective and simplest of all actuators. Pneumatic linear actuators function using compressed air to create movement, either by extending and retracting a piston or, more rarely, using a carriage that runs on a driveway or a cylindrical tube. The retraction of the piston is either done with a spring or by supplying fluid from the other end.
Pneumatic linear actuators are best suited to achieve high speed and torque on a relatively small footprint. Quick, point-to-point motion is their strength and they don’t easy get damaged by hard stops. This rugged nature makes them popular in devices that need to be explosion-proof or resistant to hard conditions like high temperature.
Pneumatic Rotary Actuator
Pneumatic rotary actuators use compressed air to produce oscillatory motion. As with pneumatic linear actuators, these are also simple in their design, durable and suitable for work in hazardous environments.
Three of the most common configurations in pneumatic rotary actuators are Rack & pinion, scotch yoke, and vane design. In rack & pinion configuration, the compressed air pushes a piston and rack in linear motion, which in turn causes rotary movements in a pinion gear and output shaft. These could come in single, double or multiple racks.
Piezoelectric Actuators
Piezo materials are a group of solids like ceramic that reacts to electrical charge by expanding or contracting and generate energy when mechanical force is applied. Piezoelectric actuators take advantage of the movement caused by electric signals to create short high-frequency and fast-response strokes. The movement that piezoelectric actuators produce is often parallel to the electric field. However, in some cases, where the device is set to work on the transverse piezoelectric effect, the movement is orthogonal to the electric field.
Selecting a Linear actuator
As we have seen already, actuators have myriad applications in different fields. But this doesn’t mean that all actuators are made equal. When purchasing an actuator, you should be able to know which suits your requirements best. Here is a comprehensive guide on how to choose the right actuator for your needs.
Step 1. Assess the movement required:
Does the object you need to move in your project require linear or rotary movement? Linear actuators are useful in exerting a mechanical force that would move an object in a straight line while rotary actuators, as the name suggests, generate circular motion.
Step 2: Consider the energy input:
Electrical actuators are becoming more and more popular due to their increasing sophistication and flexibility in handling various kinds of operations. But that doesn’t mean it's suited for every work out there. Consider hydraulic or pneumatic actuators if your work does not include electrical voltage input.
Step 3: Assess the precision level required:
Some actuators are ideal for heavy-duty work in rough environments, but they may not work well when it comes to handling smaller work like packaging which requires precision and the ability to repeat the same action hundreds or thousands of times.
Step 4 : Find out how much force you need:
The purpose of an actuator is to move or lift an object. Find out, in your case, how much this object weighs. The load capacity of an actuator decides how much it can lift, and although many actuators may look similar, their load capacity will vary. Before you buy an actuator, make sure the weight of your object matches the capacity of the actuator.
Step 5: Find out how far you need the object moved:
Distance, or stroke length as it is technically known, matters here. The stroke length decides how far your object can be moved. Manufacturers often sell actuators of varying stroke length.
Step 6: How fast do you want the movement to be:
The speed of the actuator is often an important factor for most people, depending on their project. Usually, projects that require actuators to exert high force would move slower than those that generate low force. Speed of an actuator is measured in distance per second.
Step 7: Consider the operating environment:
Does the actuator need to work in a rugged or rough environment, where dust or humidity is a concern? If this is the case, you would want to choose a product with higher protection rating.
Step 8: Decide on the mounting style:
Actuators in the market come in different mounting styles and understanding their benefits is necessary before buying an actuator. For instance, a dual-pivot mounting method in a linear electric actuator allows the device to pivot on both sides while extending and retracting. With this, the application gets to have two free pivot points while moving on a fixed path.
Conversely, stationary mounting, which secures the actuator to an object along the shaft, is useful for actions such as pushing a button. At this stage, you should be able to narrow down your options to a significantly smaller pool from where you started. From here, you will need to narrow down further. For instance, linear actuators come in different styles for different kinds of functions. Rod-style, for instance, is the most common and simple among them, with a shaft that expands and retracts. Track style, which does not change its overall length or size during operations are more suited when space constraints are an issue. There are also column lifts and other actuators that would be ideal for setting up TV and table lifts. Factors such as operating voltage and motor type may also be worth considering.
Capabilities of a Linear Actuator
Performance metrics are quantifiable outputs that help you evaluate the quality of a particular product. Actuators can be considered under several performance metrics. Traditionally, most common among them have been torque, speed, and durability. These days, energy efficiency is also considered equally important. Other factors that may be considered include volume, mass, operating conditions, etc.
Torque or force
Naturally, torque is one of the most important aspects to consider in the performance of an actuator. A key factor here is to note that there are two kinds of torque metric to consider, static and dynamic load. Static load torque or force refers to the actuator’s capacity when it is at rest. The dynamic metric refers to the device’s torque capacity when it is in motion.
Speed
Speed of an actuator differs depending on the weight of the load it is supposed to carry. Usually, the higher the weight, the lower the speed. Hence the speed metric should first be looked at when the actuator is not carrying any load.
Durability
The type of actuator and the manufacturer’s design decides the durability of an actuator. Although those such as hydraulic actuators are considered more durable and rugged compared to electric actuators, the detail specs on the quality of the material used will be up to the manufacturer.
Energy efficiency
With increasing concerns on energy conservation and its direct impact on operational costs, energy efficiency is becoming more and more a decisive metric in all kinds of machinery. Here the lesser the quantity of energy required for an actuator to achieve its goal, the better.
Linear Actuator Applications & Capabilities
The uses of linear electric actuators are virtually endless. Manufacturing plants use them in material handling. Cutting equipment that moves up and down and valves that control flow of raw materials are examples of this. Robots and robotic arms within and outside the manufacturing industry also make use of linear actuator systems to achieve movement in a straight line.
As automation trends become increasingly popular, customers are always looking for ways to implement linear actuators into their applications.
With home automation systems becoming popular, electric linear actuators have become useful in the function of automated window shades. Home appliances like TV can be placed at optimum height without hassle using TV lifts that make use of linear electric actuators. There are also table lifts which use actuators to adjust the height to the needs of users.
In the solar power industry, they help in moving the panels to the direction of the sunlight. Even in industries like agriculture, where heavy machinery that uses hydraulic actuators are more common, electric linear actuators are used for fine and delicate movements.