What is an actuator?
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.
Types of Actuators
Depending on the kind of movement they make, and the source of energy used to function, actuators can be classified into different types. 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. How electric linear actuators work 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.
Applications of electric linear actuatorsThe uses of electric linear 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 actuators to achieve movement in a straight line. 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 electric linear 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.
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.Electric rotary actuators can be made by combining standard motors, gearboxes, and rotary switches or with customized components. Customized designs are often seen in low torque units while higher torque units tend to stick to standard components. 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. Hydraulic rotary actuators come in three major designs, piston, gear, and vane type. Piston-type hydraulic rotary actuators use pressurized fluid to move a piston and generate rotational movement. Swashplate motors are a common example of this. In gear-type, the fluid is used to move meshed gears, which then rotate the central shaft. Vane-type of hydraulic actuators use fluid to rotate the vane that in turn rotates the central shaft. Hydraulic rotary actuators are simple in design and are able to provide low speeds and high torque. 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 redacting a piston or, more rarely, using a carriage that runs on a driveway or a cylindrical tube. The redaction of the piston is either done with a spring or by supplying fluid from the other end. Pneumatic linear actuators have been used in engines for decades as they are fast up and powerful up to 40,000 lbs behind a single stroke. Their simplicity makes it easier for operators to adjust these parameters by making changes to the air pressure, size of the bore, and valve. 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. Quite frankly though, it’s the low cost that attracts many customers to pneumatic linear actuators or their electric and hydraulic counterparts. But this could prove to be a mistake in the long run as pneumatic linear actuators are often ridden with high maintenance and operational expenses. The compressible nature of air and pressure losses make them inefficient as well. 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. Scotch yoke design works in a similar manner, with a piston that moves linearly when pressure is applied. The rotary shaft is connected to the piston through a pin and slot system. When pressure is applied, the piston causes the shaft to rotate through a cam system, which in turn will open or close the valve. In the vane configuration actuator, a vane is fixed on a central shaft that is placed inside a cylindrical chamber. When pressure is applied through compressed air, the vane begins to rotate till the end of the stroke. At this stage, air pressure is applied from the opposite end causing the vane to rotate the shaft in the reverse direction. 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.
Actuator working principles
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.
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.
How an actuator works
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.
How to mount a linear actuator
Choosing an actuator and connecting it properly is only half the job done. Equally important is mounting the actuator in a method that is right for your application. Below are two common methods that are used to mount an electric linear actuator.
Dual pivot mounting allows the actuator to pivot on either side with a mounting point that is free to pivot.
Dual pivot mounting
This method involves fixing an actuator on both sides with a mounting point that is free to pivot, which usually consists of a mounting pin or a clevis. Dual pivot mounting allows the actuator to pivot on either side as it extends and redacts, allowing the application to achieve a fixed path motion with two free pivot points. One of the most useful applications of this method is to open and close doors. When the actuator extends, the dual fixed points enable the door to swing open. The action of the door closing and opening causes changes in angle, but the pivot provides ample space for the two mounting points to rotate. While using this method, make sure that there is enough room for the actuator to extend, without any obstacles on its way.
In this method, the actuator is mounted in a stationary position with a shaft mounting bracket fixing it to the shaft. Common uses of this kind of mounting are to achieve action similar to pushing something head-on. For instance, this form of mounting is ideal for switching a button on or off. When deciding on this method, ensure that the mounting apparatus can handle the load of the actuator.