Found in every piece of machinery, an actuator is a machine part that triggers movement by getting feedback from a control signal. This signal could be as simple as pulling a rope in a pulley, or could be made to include more complex technology like the pneumatics used to control the brake in a car. Other examples of actuators include electric motors, stepper motors, and hydraulic cylinders. Actuators can be separated by the types of power sources they use and the movement they produce. Below is a short overview of the major types and their applications.
Types of Actuators
Linear actuators produce movement along a straight path. They can be mechanical or electrical but are mostly seen in hydraulic or pneumatic devices. Linear actuators are made up of three major parts: a nut, cover, and sliding tube. Whereas the sliding tube provides space for motion, the nut and cover provide the interlocking movement necessary to keep the actuator moving in a straight path.
Rotary actuators also live up to their name, generating rotational movement. These actuators are often used for turning a machine and many are electrically powered. Some examples include windshield wipers, and manufacturing machines that transfer an object from one place to another.
By Source of Energy:
Hydraulic actuators are powered by hydraulic fluid pressure created from a piston suspended in the center of a fluid-filled cylinder. When the piston is submerged, it raises the pressure exerted by the fluid which can then be used for thrust. Hydraulic actuators usually produce linear movement and are often found in car transport carriers and steppers.
Pneumatic actuators use pressurized gasses to produce mechanical movement. The control of a flow of gas can be stopped or started very abruptly to exert a specific level of pressure. This level of control allows for very precise movements which make it especially useful for starting and stopping. Bus brakes, exercise machines, and pneumatic mail systems are common examples of these actuators in use.
Electric actuators require electricity to initiate certain motions. Electric cars, manufacturing machinery, and robotics equipment often use electric actuators for their ability to produce precise motion from an electrical current. There are two major types of electric actuators: electro-mechanical and electro-hydraulic. Electro-mechanical actuators convert electric signals into rotary or linear movement (or both) whereas electro-hydraulic actuators give movement to a hydraulic accumulator by moving the piston.
Thermal actuators usually depend on a shape memory alloy which will be deformed when cold and revert back to its original shape when heated. Motion in these actuators often come from the Joule Effect which is the name given to the process by which a conductor will heat up when a current is passed through it.
Magnetic Actuators have a similar effect to thermal actuators but rather than deforming with temperature change, the moveable component is usually a coil which is influenced by a magnetic field. The magnetic field surrounding a coil is initiated by an electrical current sent by the control source.
Mechanical Actuators are solely controlled by mechanical movement in which a force like pulling or pushing triggers a motion elsewhere. Some examples are pulley, rack, and pinion systems. In systems like these, you could simply turn a gear interlocked with several others and cause movement further down the line.
Supercoiled Polymer Actuators are a relatively recent innovation used in robotics and prosthetic limbs. By using a coil which contracts and expands when heated or cooled, engineers have been able to replicate the motion of human muscle. They are created by coiling high-strength polymer fibers like fishing line into a spring-like shape. These polymer fibers can stretch at normal temperatures and then contract back into their normal state when subjected to heat.
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