Actuators: Definition and Types

An actuator is a device that makes something move or operate. Actuators initiate the movement of machine parts when they receive part of the input energy as a feedback control signal. In other words, actuators convert energy into physical or mechanical motion. The main purpose of an actuator is to control movement within a machine.

According to the movement of the mechanical part, actuators can be divided into the following two categories:

If an actuator tends to move objects in a straight line, such an actuator is called a linear actuator. A simple linear actuator usually consists of a nut, a cover and a sliding tube. The sliding tube transmits motion to the object, while the nut and cover combination holds the actuator in place.

A rotary actuator helps an object or part of a machine attached to it rotate around its axis, or simply make it move in a circular motion. It utilizes an air cylinder to provide the torque required to periodically turn or rotate the mechanical parts of a machine. 

Rotary vane actuator

Rotary vane actuators consist of vanes attached to a central main shaft. Compressed air tends to push the blades, which in turn causes the main shaft to rotate. Air behind the blades is released through ports. When the vanes reach their pre-calibrated angle of rotation, the airflow reverses, causing the main shaft to move back to its original position. The process is then repeated again and again after regular intervals. Compared to rack and pinion actuators, rotary vane actuators generate less torque and can therefore rotate a limited distance. These types of rotary actuators are typically used for lighter loads.

Rack and pinion actuators

The rack and pinion actuator consist of two cylinders and two pistons, which are connected to each other with the help of a rack. There is a pinion in contact with the rack. When there is a pressure difference between the ports where the actuator is provided, the rack is able to move back and forth, causing the pinion to rotate accordingly. When the rack moves all the way to one side, the pinion rotates clockwise. As the rack moves back to its original position, the pinion tends to rotate counterclockwise. Rack and pinion actuators provide greater torque compared to rotary vane actuators. They are best suited for applications that require higher speed and less wear, such as automation, the pharmaceutical industry, etc.

There are eight types of actuators depending on the energy used to drive the actuators:

Electric actuators operate using electrical energy. The signal transmission rate of electric actuators is quite high. Furthermore, they are easy to operate and offer high precision and sensitivity. Electric actuators are divided into two categories, namely electromechanical actuators, and Electrohydraulic actuators.

Electromechanical actuator

Electromechanical actuators convert input electrical energy into linear or rotary motion. In some cases, electromechanical actuators are also used to exhibit a combination of linear and rotational motion in mechanical components. 

Electro-hydraulic actuator

Electro-hydraulic actuators are driven by electrical energy. The output of the electro-hydraulic actuator is fed to a hydraulic accumulator. The accumulator then generates the force used to move the object.

Hydraulic actuators are driven by various liquids or fluids. They use a liquid-filled cylinder with a piston suspended in the center. Hydraulic actuators typically help objects move in a straight line and exhibit linear motion.

Pneumatic actuators operate using compressed air. Pneumatic actuators are very reliable and accurate. The use of pressurized gas to induce mechanical motion is often preferred because it increases precision and allows objects to exhibit fine motion. Even small changes in pressure can create enormous power. Pneumatic actuators are used in applications that need to start or stop machines quickly.

Thermal actuators convert thermal energy into kinetic energy. These types of actuators contain a temperature-sensitive element that expands and contracts in response to changes in ambient temperature. The expansion and contraction of the temperature-sensitive element cause the piston to move. Thermal actuators are reliable and best suited for hazardous locations. Thermal actuators are used in applications such as temperature control, freeze protection, and more.

Mechanical actuators are one of the most commonly used actuators in daily life. For example, pulley systems, gears, rack and pinion systems, etc. are prominent examples of mechanical actuators. Muscle force is applied to the input of the mechanical actuator, the actuator then provides a lot of leverage to the applied force, and finally, the desired motion of the object is achieved. 

Supercoiled polymer actuators are mainly used in robotics and medical fields to manufacturing prosthetics. They use pressure to induce motion using coils that contract and expand when heated or cooled.

The working principle of the magnetic actuator is based on the principle of magnetic actuation based on the Lorentz force equation. The force required to displace a machine part from its original position with the help of a magnetic actuator is generated by placing the current-carrying conductor in a static magnetic field. The magnetic field generated around the current-carrying conductor interacts with the static magnetic field and generates a large force.

Piezoelectric actuators are actuators that use electronic signals as input to control the mechanical movement of equipment. Instead of using rails and pistons to transfer energy, piezoelectric actuators use pressure changes caused by the compression and expansion of materials such as ceramics to generate high-frequency strokes. These types of actuators have a high-frequency responses and higher displacement resolution.

The above briefly introduces the types of actuators. If you want to buy actuators, please contact us.

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