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Industrial actuators require careful analysis of application requirements before choosing the right actuator for the application.
An actuator is a mechanical or electro-mechanical device that converts energy from a control signal into mechanical motion. In simpler terms, an actuator is a device that allows controlled movement or positioning.
Actuators need a control signal and a source of energy to bring about mechanical motion. Actuators use an energy source – such as electrical, compressed air, or hydraulic pressure – and a control signal that can be manual, an automatic electronic system, a fixed mechanical system, a software-run system or a robotic control system.
From regulating the flow of fuel to a gas turbine, to operating valves and hydraulic cylinders in industrial plants, actuators serve the general purpose of controlling movement, and are a key component in several industrial valve control applications.
What are different types of actuators? Actuators are classified according to the type of motion they produce and the type of power or source of energy they use to control the application.
Actuators can create two main types of motions – linear and rotary.
Linear and rotary actuators may be used together in instances where a mechanism necessitates operation in two planes of motion, requiring both rotational movements, clockwise and counterclockwise, as well as linear movement up and down.
The different types of actuators classified according to the source of energy are given below
Pneumatic actuators: Pneumatic actuators use a vacuum or pressurized gas to act as a piston inside a cylinder to create mechanical movement.
There are single-acting cylinders that have one port where pressurized gas enters in one direction. The compressed air forces the piston to move in one direction compressing a spring which is fitted to the piston. Double-acting cylinders extend and retract without a spring and have two ports where air can enter in and out.
Pneumatic-powered actuators are preferred because they are safe, generally fast, cost-effective and can produce large amounts of torque with small pressure changes. Due to the high pressure involved to power a pneumatic actuator, these valves respond quickly, and are the preferred choices in applications where you need to stop and start the main controls immediately.
Among many other uses, pneumatic actuators are often employed on valves used to control cooling water flow in power plants.
Electric actuators: Electrical actuators require electrical energy to enable movement. Being driven by an easily available energy source, electric actuators are considered to be more energy-efficient and clean.
The largest issue with electrical actuators is they can overheat if there are extreme changes in duty cycle. Slower speeds due to inertia also make it less popular in certain applications. Some of the commonly used applications are in the opening and closing of butterfly or ball valves. Electrical actuators are further divided into electromechanical actuators and electrohydraulic actuators.
Electromechanical actuators: These actuators convert electric signals into rotary movements, linear movements, or a combination of the two. Electromechanical actuators are accurate, have a longer lifespan and require low maintenance.
Electrohydraulic actuators: These actuators are powered electrically, but give movement to a hydraulic accumulator, which in turn provides the force for the movement. When these actuators are used, there is no need for a separate hydraulic pump; this lowers the cost, and enhances reliability and safety.
Hydraulic actuators: Hydraulic actuators have a cylinder, or a fluid motor with a piston, that uses hydraulic power to generate mechanical motion. The mechanical motion in turn is converted to linear, rotatory, or oscillatory motion as per the application.
Liquids are almost incompressible; the density changes caused by pressure and temperature are negligible. For this reason, the amount of torque generated from a hydraulic actuator valve is high, making it very powerful. There are single-acting hydraulic actuator valves that apply pressure on one side of the pistons, moving it in the opposite direction. A spring would be necessary for the reverse motion. On the other hand, double-acting hydraulic actuators apply pressure on both sides of the piston for a movement from both sides.
Some applications where hydraulic actuators are used are in the main stop and control valves for high-pressure steam turbine piping.
Magnetic actuators: Magnetic actuators make use of magnetic effects to generate mechanical force, a rotary or linear motion, continuous or limited motion. Magnetic actuators are found in a wide range of HVAC applications to shut off or mix fluids and steam.
Thermal actuators: A thermal actuator generates linear motion in response to temperature changes, using a piston and a thermal sensitive material.
Thermal actuators are widely used in applications where fluid mixing and diverting is necessary, and in safety shut-off processes where it is required to open or close a valve based on a temperature set point.
Thermal valve actuators can function even if there is a power failure and are reliable and safe as they are not subjected to short circuits.
Every actuator has a unique purpose and energy requirement. It is important to understand how each actuator works to choose the right valve actuator.
Take a look at the following points to select the right actuator:
The most common NEMA ratings are NEMA 4, 4x, and 7.
For instance, operating an electrical actuator close to a water source, without protective sheaths and other safety measures, may be dangerous.
Actuated valves, like other industrial plant equipment, are subjected to hazardous environments, wear and tear. All valve actuators should undergo preventive maintenance to:
The following points need to be considered when maintaining an actuator:
Actuators are used widely in many industrial and other applications. Careful analysis of the requirements must be done before choosing the right fit for the actuator application’s purpose.
Gilbert Welsford Jr. is the founder of ValveMan. Edited by Mark T. Hoske, content manager, Control Engineering, CFE Media and Technologies, mhoske@cfemedia.com.
KEYWORDS: Actuators, actuator selection
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Nov 26, 2020 By Team YoungWonks *
What is an actuator? You may have often heard those working with hardware or electronics talk about valves and actuators. And while our last blog talked about valves, this one is about actuators, often used with valves. So this blog shall share a simple introduction to the actuator; we shall also look at the different types of actuators being used today.
Actuators are mechanical or electro-mechanical devices that, upon being operated electrically, manually, or by various fluids, allow controlled and sometimes limited movements or positioning. They refer to that component of a machine that helps carry out the moving and controlling of a mechanism or system; take for instance opening a valve. To put it simply, they can be called movers.
Actuators basically need a control signal and a source of energy. Upon receiving a control signal, the actuator uses energy from the source to bring about a mechanical motion. The control system can be a human, a fixed mechanical or electronic system, or even software-based, say a printer driver, or a robot control system.
Examples of actuators include electric motors, stepper motors, electroactive polymers, screw jacks, servomechanism, solenoids and hydraulic cylinders.
Actuator types also vary depending on motions, power configurations, styles and sizes depending on the application.
Mechanical actuators create movement by converting one kind of motion, such as rotary motion, into another kind, such as linear motion. Say for instance, a rack and a pinion. Another example is that of a chain block hoisting weight where the mechanical motion of the chain is used to lift a load.The functioning of mechanical actuators relies on the combinations of their structural components, such as gears and rails, or pulleys and chains. High reliability, simplicity of utilisation, easier maintenance and greater precision of positioning are some of the advantages. They can be categorised into hydraulic, pneumatic and electric actuators.
Hydraulic actuators have a cylinder or fluid motor that uses hydraulic power to generate mechanical motion, which in turn leads to linear, rotatory or oscillatory motion. Given the fact that liquids are nearly impossible to compress, a hydraulic actuator can exert a large force. When the fluid enters the lower chamber of the actuator’s hydraulic cylinder, pressure inside increases and exerts a force on the bottom of the piston, also inside the cylinder. The pressure causes the sliding piston to move in a direction opposite to the force caused by the spring in the upper chamber, making the piston move upward and opening the valve. The downside with these actuators is the need for many complementary parts and possibility of fluid leakage.
Pneumatic actuators convert energy in the form of compressed air into mechanical motion. Here pressurised gas or compressed air enters a chamber thus building up the pressure inside. Once this pressure goes above the required pressure levels in contrast to the atmospheric pressure outside the chamber, it makes the piston or gear move kinetically in a controlled manner, thus leading to a straight or circular mechanical motion. Examples include pneumatic cylinders, air cylinders, and air actuators. Cheaper and often more powerful than other actuators, they can quickly start or stop as no power source has to be stored in reserve for operation. Often used with valves to control the flow of air through the valve, these actuators generate considerable force through relatively small pressure changes.
Examples of maker projects using pneumatic actuators include lifting devices and humanoid robots with arms and limbs, typically used for lifting.
Now let us look at the electrical actuators, those that run on electricity.
Taking off from the two basic motions of linear and rotary, actuators can be classified into these two categories: linear and rotary. Electric linear actuators take electrical energy and turn it into straight line motions, usually for positioning applications, and they have a push and pull function. They convert energy from the power source into linear motion using mechanical transmission, electro-magnetism, or thermal expansion; they are typically used whenever tilting, lifting, pulling and pushing are needed. They are also known for offering precision and smooth motion control; this is why they are used in industrial machinery, in computer peripherals such as disk drives and printers, opening and closing dampers, locking doors and for braking machine motions. They are also used in
3d printers and for controlling valves. Some of them are unpowered and manually operated with a rotating knob or handwheel. Electric linear actuators
Consisting of motors and output shaft mechanisms with limited rotary travel, electric rotary actuators convert electrical energy into rotary motion. Used in a wide range of industries where positioning is needed, and driven by various motor types, voice coils, these actuators work as per specifications such as the intended application, drive method, number of positions, output configuration, mounting configuration, physical dimensions and electrical characteristics. A common use is for controlling valves such as ball or butterfly valves. Other applications include automation applications where a gate, door or valve needs controlled movement to certain rotational positions.
Electromechanical actuators are mechanical actuators where there’s an electric motor in place of the control knob or handle. The rotary motion of the motor leads to linear displacement. The inclined plane concept is what drives most electromechanical actuators; the lead screw’s threads work like a ramp converting the small rotational force by magnifying it over a long distance, thus allowing a big load to be moved over a small distance. While there are many design variations among electromechanical actuators available today, most have the lead screw and the nut incorporated into the motion. The biggest advantages are their greater accuracy in relation to pneumatics, their longer lifecycle and low maintenance effort required. On the other hand, they do not boast the highest speed.
Instead of hydraulic systems, electrohydraulic actuators have self-contained actuators functioning solely on electrical power. They are basically used to actuate equipment such as multi-turn valves, or electric-powered construction and excavation equipment. In case of controlling the flow of fluid through a valve, a brake is typically installed above the motor to prevent the fluid pressure from forcing open the valve. The main advantage here is that these actuators help do away with the need for separate hydraulic pumps and tubing, simplifying system architectures and enhancing reliability and safety. Originally developed for the aerospace industry, today they are found in many other industries where hydraulic power is used.
A thermal actuator is a non-electric motor that generates linear motion in response to temperature changes. Its main components are a piston and a thermal sensitive material. When there is a rise in temperature, the thermal-sensitive materials begin to expand in response, driving the piston out of the actuator. Similarly, upon detecting a drop in the temperature, the thermal-sensitive materials inside contract, making the piston retract. Thus these actuators can be used for carrying out tasks such as releasing latches, working switches and opening or closing valves. They have many applications, particularly in the aerospace, automotive, agricultural and solar industries.
Magnetic actuators are those that use magnetic effects to produce motion of a part in the actuator. They usually come in the following categories: moving coil actuator, moving magnet actuator, moving iron actuator and electromagnetic actuator.
In case of the first kind (moving coil actuator), a mobile coil driven by a current is placed in a static magnetic field, where it is subject to the Lorentz force. This force is proportional to the applied current.
Moving magnet actuators work differently; here mobile permanent magnet is placed between two magnet poles and is switched from one pole to the other using coils. Such actuators can generate high forces but are not easily controlled.
In moving iron actuators, a soft magnetic part placed into a coil system moves in a fashion that keeps the system magnetic energy to a minimum.
Lastly, electromagnetic actuators are the ones comprising electric motors such as Brushless DC motors (BLDC) and stepper motors. These magnetic actuators are used for various purposes such as valve control, pump and compressor actuation, locking mechanisms,aerospace engineering, vibration generation, fast positioning etc. Advantages include reduced system cost, improved robustness, and reduced control complexity.
Actuators play a pivotal role in the world of robotics and IoT. These components transform an input signal, usually electrical, into motion or some form of mechanical action. From linear to rotary, hydraulic to pneumatic, the variety in types of actuators is vast, each serving a unique purpose in engineering designs. As the world of robotics continues to advance, understanding the intricacies of these actuators becomes increasingly essential. For young enthusiasts eager to dive into the realm of robotics and IoT, starting early can give them a head start. Programs like YoungWonks, which offer coding classes for kids, often use tools like the Raspberry Pi to explore such intriguing topics, providing hands-on experience with actual components, including actuators.
*Contributors: Written by Vidya Prabhu; Lead image by: Leonel Cruz
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