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What is a Rotary Actuator?

This article will explain what a rotary actuator is, how it works and how to select one.


What is a Rotary Actuator?


A rotary actuator is a pneumatic cylinder used to provide a turning or angular movement, allowing a stroke in an oscillating motion through a defined angle. They are durable and give a relatively high force (torque) for size. Rotary actuators simplify a design and can reduce maintenance issues.


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How does a rotary actuator work?


- A rotary actuator operates by applying force at a distance from the axis of rotation, inducing a turning motion. There are two primary types: rotary vane actuators and rack and pinion actuators, each functioning as follows:


- In a rotary vane actuator, compressed air propels against a vane connected to a central spindle, causing it to rotate. The air 'behind' the vane is then released through a port. Upon reaching a predetermined angle of rotation, the airflow reverses, prompting the spindle to return to its original position, ready to repeat the process. Rotary vane actuators are typically utilized for lighter loads due to their limited rotation and torque capacity.


- Contrarily, rack and pinion actuators offer a broader torque range and rotation capability compared to rotary vane actuators, and they tend to be more robust and durable. In this design, the rack forms part of the piston rod within a double-acting linear cylinder. A pinion gear engages with the rack, rotating a spindle as the piston moves under pressure. The spindle, positioned perpendicular to the piston, rotates clockwise and then counterclockwise as the linear cylinder undergoes its double action. Rack and pinion rotary actuators are favored for applications requiring higher speed and reduced wear.


How to Choose a Rotary Actuator


Before selecting a rotary actuator, consider the specific requirements of your application. Here are some factors to consider:


1. Rotation: Determine the angle of rotation needed for your application.


2. Torque: The torque, or turning moment, relies on the force applied, its direction, and the distance from the point of application to the pivot. Imagine a simple bar pivoted at one end. When force is exerted on this bar, the greatest turning moment (or torque) happens when the force is applied at the farthest point from the pivot and perpendicular to the bar.


3. Package size: For confined spaces, a vane rotary actuator is preferable. However, depending on torque requirements, rotation angle, available shaft options, and mechanical efficiency, a rack and pinion actuator might be more suitable.


Types of Rotary Actuators


The Norgren range comprises both rotary vane and rack and pinion actuators, both of which are double acting. While rotary vane actuators can rotate to an angle of 270 degrees, rack and pinion actuators can achieve a full 360 degrees of rotation.


Typical Applications of Rotary Actuators


Rotary actuators find common use in industrial applications for tasks such as clamping, positioning, and transferring parts.


Additional Components Required for Rotary Actuators


To integrate a rotary actuator into a pneumatic system, fittings and tubing are necessary. Additionally, for proper operation of a compressed air system, clean and filtered air is essential.


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