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.
How does a rotary actuator work?
In a rotary actuator the force is applied a distance away from the axis of rotation, causing a turning movement. There are two basic constructions of a rotary actuator; rotary vane actuators, and rack and pinion actuators, which operate as follows:
In a rotary vane actuator, compressed air pushes against a vane, which is attached to a central spindle. This acts to turn the spindle, with the air 'behind' the vane released through a port. When the vane reaches a stop at the specified angle of rotation, the air flow is reversed and the spindle rotates back to its original position for the process to repeat. Rotary vane actuators are more limited in rotation and in torque than the rack and pinion version, and are therefore more commonly used for lighter loads.
A rack and pinion actuator offers greater torque range and range of rotation than its rotary vane counterpart, and are generally bigger and longer lasting. In a rack and pinion actuator, the rack is machined as part of the piston rod of a double acting linear cylinder. A pinion gear meshes with the rack and turns a spindle as the piston moves due to an applied pressure. The spindle sits at right angles to the piston and rotates clockwise, then anti-clockwise as the linear cylinder completes its double action. Rack and pinion rotary actuators are useful for applications requiring more speed and less wear.
How do I select a rotary actuator?
Consider your application before choosing your rotary actuator. Here are some of the things to look for:
- Rotation: What angle of rotation do you require?
- Torque: The torque or turning moment is dependent on the force applied, its direction and the distance between that force and a pivot point, for example the pivot of the spindle. Envisage a plain bar, pivoted at one end and then imagine a force being applied to this bar. The largest turning moment (or torque) will occur when the force is applied at the furthest end of the bar from the pivot and at right angles to the bar.
- Package size: A vane rotary actuator is better for limited spaces. Depending on torque and the angle of rotation required, associated shaft options and mechanical efficiency, then a rack and pinion actuator will work better.
Types of rotary actuators
The IMI Norgren range includes both rotary vane and rack and pinion actuators as double acting. Whereas rotary vane actuators can turn to an angle of 270 degrees, rack and pinion actuators can achieve a full 360 degrees.
Typical applications of rotary actuators
Rotary actuators are used in industrial applications for clamping, positioning and transferring parts.
Do I need anything else to make rotary actuators work?
In order to connect the rotary actuator into a pneumatics system, fittings and tubing is required. For a compressed air system to function properly, clean, filtered air is also necessary.