A Look Into Rotary Actuators And Their Different Power Sources

By Author: Reshma Lemos
Total Articles: 3
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Rotary Actuators
The rotary actuators produce torque or rotary motion. Earlier, mechanical actuators were used. The mechanical ones had a liner motion in one single direction and gave rise to rotation. Now-a-days, electrical actuators are more used. Some actuators are also powered by hydraulic or pneumatic power, and some use energy that they have in their springs.

The electric actuators have the electric motors and these provide for continuous rotation or for movement at a fixed angular position (as in steeper motors and servomotors). There is also a torque motor, which does not produce any rotation, but generates a torque that can cause rotation.

Power Sources of Different Kinds of Actuators

Electric Actuators
Electric actuators include the steeper motors, servomotors and other kinds of actuators.

Stepper Motors
The steeper motors consist of an electric motor that moves in defined and discrete steps. The motor provides for continuous rotation at a given and controlled speed. The motor also provides for a well-controlled angular movement. The stepper ...
... can be combined with a position encoder or a datum sensor, and can work as a rotary actuator this way, moving the motor to any defined angular position.

Servo Motors
A servomotor is made up of components like an electric motor (sometimes fluid motors are also used), a gear-train for reducing the great number of motor rotations to a higher and greater torque rotation, a position-encoder that can identify the output shaft’s position and a comprehensive in-built control system. The input-control signal that reaches the servomotor indicates the desired position of the output. If there is a difference between the encoder’s position and the position that is commanded, an error signal is created. When the error occurs, the gear train and the motor rotate, until the motor’s encoder can reflect the desired and commanded position.

Other Kinds of Electric Rotary Actuators
The more recent actuators use memory wire, and the built of these actuators is ultra light. With the current application, the wire gets heated above the transition temperature and hence has a shape change. The shape-change gives rise to a torque which gets applied to the system’s output shaft. The wire gets coiled when power is removed, and achieves its earlier shape.

The Fluid Power Actuators
Pneumatic and hydraulic power may also be used for powering an actuator, and the more powerful and larger actuators are powered this way. The pneumatic rotary actuators and the hydraulic ones have a similar kind of internal construction, and hence both are considered under the category of fluid-power actuators. The fluid-power actuators may have 2 kinds of forms. One kind consists of linear piston-and-cylinder mechanism, and the system is geared for producing rotation. The other kind has rotating and asymmetrical vane, which swings with-in a cylinder that has 2 differing radii. As there is a differential pressure gradient between 2 sides of the asymmetrical vane, a torque gets produced. This torque maneuvers the output shaft. Vane actuators have a great number of in-built sliding seals, which are often the cause of leakage. The piston-and-cylinder type of actuators does not suffer from leakages.

Vaccum Actuators
Sometimes pneumatic power may not be available, but there is an availability of a vaccum. In these cases vaccum actuators are used. The cars of the 1960s had these vaccum-actuator run windscreen wipers. The vaccum of the petrol engine was used for running the quarter-turn vane actuator, which oscillated to provide the functionality.

Applications of Rotary Actuators
The pneumatic rotary actuators and other actuators are used in a wide variety of industrial and other processes and have tremendous application scenarios. Actuators of different power sources, sizes and operating speeds are used to suit the different industrial processes. The display devices, like the air core gauges (commonly used in the automotive indicator-instrument clusters) use the zero-power actuators. The valve actuators are used in the process valves and in pipelines in pharmaceutical, chemical and pharmaceutical industries, in dams and in other areas. The socket weld ball valves are combined with the actuators to provide the best flexibility and great stress resistance.