Actuator is a device that starts or stops mechanical equipment with the help of hydraulic fluid, electric current or other sources. They are usually used in automation to control the motion of a moving member in any machine. Depending on the source of power, actuators can be categorized into four main types:-
Hydraulic Actuators: These actuators utilize hydraulic energy for automation. Such actuators can produce rotary, linear or oscillatory motion. They have high force capabilities and are preferred in conditions where heavy equipments are to be moved. These actuators can generate a large output force for very small input force, and are also able to maintain their mechanical stiffness. However, the major drawback of such actuators is that it takes some time to compress the liquid before it can multiply the force. A typical hydraulic actuator consists of a hollow cylinder and piston arrangement. The piston can execute reciprocating motion by pressurizing and de-pressurizing the cylinder, to move the mechanical system.
Electric Actuators: They are generally powered by electric source. Such actuators are commonly used in control systems, because they can be easily interfaced with controlling equipments. Also unlike fluids used in pneumatic systems, electric energy is far easier to control and use. Also, electric supply is readily available in today's world. This supply is used to power motors, which then delivers mechanical torque. Moreover, since they are no leakage issues with these actuators, one do not need to worry about cleaning the spilled fluids. The major drawback of such actuators is that electrical short circuiting can cause fire accidents. Also their power to weight ratio is very less as compared to the hydraulic actuators.
Pneumatic Actuators: These actuators convert energy of compressed air at high pressure to impart motion to the moving member. Such motion can either rotary or linear. Similar to hydraulic actuators, pneumatic actuators also contain a piston cylinder arrangement, but they also have valves or ports to control the inflow and outflow of air to increase or decrease the pressure. The size of these valves greatly determines the power delivery capacity of pneumatic actuators. Often several pneumatic actuator manufacturers use large diameter butterfly valves in high power pneumatic actuators to deliver more power. Such actuators have the advantage that they can be used in areas where energy cannot be stored to power the actuator. In addition to valves, such actuators also consist of a diaphragm to separate the piston from the compressed air. As the air inside the cylinder is compressed or de-compressed, the diaphragm moves which in turn moves the piston to cause motion in the moving member. The major disadvantage of such actuators is that proper sealing is necessary to avoid any leakage.
Mechanical actuators: They generally convert rotary motion into straight line motion, with the help of gears, pulleys or chains. The most common example of large diameter butterfly valves actuator in a car jack. The main advantage of these actuators is that small input force can produce very large output force.
