A pneumatic rotary actuator is a device that facilitates the rotary motion of the connected application, which is usually seen on the energy transmission of the pneumatic rotary table on a lathe. The pneumatic rotary actuators are not one-size-fits-all products. Instead, depending on the requirements of the applications, they are capable of transmitting the rotary motion with different forms of mechanisms, which determine the different types of these actuators.
An actuator is commonly seen as a cylinder, is a component in the transmission system of a machine, and offers the kinetic energy that is transformed by the compatible power source, which can be electric, hydraulic, or pneumatic forces to the mechanism of its application. In other words, this device is necessary when there is the need to drive the mechanism on a machine.
Here we would focus more on the rotary actuators that are driven by the pneumatic forces, which can be the compressed air or gas. With the interrelation between the delivering of the pneumatic forces and the operation of the mechanism inside the actuator, the durability and contamination-resistance of this type of actuator can be ensured when the machine is in operation.
The actuators are able to transmit either linear or rotary motion based on the requirement of the connected machines. For the transmission of the linear motion, the components of the actuators are usually set in linear arrangement. As for that of the rotary motion, there are several kinds of constructions, including the rack-and-pinion, the scotch yoke, and the vane types of actuators.
The pneumatic rotary actuators may come in three main types, which differ in the constructions of mechanism, the working principles, and the compatible applications, including the rack-and-pinion, the rotary vane, and the Scotch Yoke actuators.
The rack-and-pinion actuator is a cylinder when being seen on the exterior. On the interior, a circular gear acts as the pin, and a linear gear, which is set perpendicular to the circular gear, acts as the rack. Depending on whether the actuator is single-acting or double-acting, it may consist of either one piston on the one side, or two pistons on both sides.
For the single-acting form, the piston is controlled by a mechanical spring. The spring, which is set on the piston side of the cylinder, can either close or open the inlet of the chamber, and allow the compressed air or gas to be released or fed into the chamber.
As for the double-acting actuator, there is no spring inside the cylinder. Instead, it utilizes the variation between the degree of the pressure, to cause the pistons on both sides to open or close the cylinder relatively to each other.
● Rotary vane
The rotary vane, as the name implies, is equipped with a movable vane. In addition to the vane, there is also a shaft that would rotate along with the vane as the compressed air is fed in through the port of the vane.
Similar to the rack-and-pinion type, the rotary vane may also come in either single-acting or double-acting form. This determines whether there is a one or two vanes in the mechanism, which thus influences the oscillating range of the actuator. Besides, this type of actuator is more suitable for the applications with relatively lighter weight.
● Scotch Yoke
Regarded as the counterpart of the rotary vane type of actuator, the Scotch Yoke type enables the rotary motion of more heavy duty applications. The Scotch Yoke drives the piston on the shaft by a pin and a slot. When the shaft moves linearly, it would lead to the rotary motion of the pin, which makes the transmission of the rotary motion.
Now that we have learned the various types of pneumatic rotary actuators there are, to choose the right one that is suitable for the specific application is what needs to be taken into serious consideration, since one pneumatic rotary actuator cannot fit for every application. To make the proper choice for the related application, there are some parameters to follow, including the required load, the oscillating range, and the space.
● The required load
As the above introduction has mentioned, the rotary vane and the Scotch Yoke actuators have their own compatible applications with different loads. The former is suitable for lighter loads, while the latter is applied when the loads are relatively heavier.
● The oscillating range
The oscillating range determines the rotation angle of the rotary motion. Comparing these three types, the rack-and-pinion is provided for restricted rotation angle, and the rotary vane is able to offer up to 280° of rotation angle.
● The space
Since the configuration of these three types of actuators are designed differently, in addition to the above parameters, whether the shape of the actuator can fit for the space of the required mechanism is another thing to consider.
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