Did you know that pneumatic rotary actuators are a durable and simple way to convert compressed air pressure in rotary movement? Capable of operating in hazardous environments and when utilized to their full potential, rotary actuators deliver a high force for their size. Here, we outline three ways to ensure you are magnifying the return on investment from your rotary actuators.
Many engineers don’t realize that due to their integrated bearings, rotary actuators can adequately support a working load, this means engineers may not need to include additional bearings into their mechanical design. This is especially true of rack and pinion actuators which utilize large bearings.
A key point to understand is that rotary actuators should typically be sized based on their ability to stop a load rather than their ability to move the load. That’s because the kinetic energy of a rotating mass is exponential as the load moves further away from the rotation point. A component of the equation for mass moment of inertia is k2, meaning that the load gets exponentially worse the farther away it is from the shaft.
For example, let’s say a 2-inch/50mm vane rotary actuator at 100 psi/6 bar has an output rating of 65 lb-in/7.4Nm of torque. In a typical application, this little actuator is easily able to get the load moving over 270° quickly. However, stopping the load via the internal vane against the stator is an instant stop, very much like a hammer to a hard surface. Further, be conscious of over-center loads where gravity can greatly add to the rotational velocity.
Imagine a small child pushing an adult on a playground swing; the child has the ability to start moving an adult in a full swing, but it would take many large adults to stop the swinging person in a short distance. Similarly, once the actuator gets to the end of the stroke, we must consider the kinetic energy absorption ability of the actuator.
In high speed and load applications, the critical specification is not torque output but rather the kinetic energy rating. It is common to learn that the application requires a larger actuator because the larger unit will have more capacity to stop a load. If the designer sizes the actuator based on torque output alone—on starting the load—then external stops will likely be required to stop the load. Basic rule: Consider both the demand torque and the kinetic energy absorption rating.
All manufacturers of rotary actuators provide torque output and kinetic energy absorption ratings. Some units have optional pneumatic cushions and internal hydraulic shock absorbers, which greatly enhance the stopping ability of the actuator.
With many models, options are available to adjust the rotational angle of travel. Most manufacturers provide adjustable stops as an option providing an additional level of control over the application. This feature greatly simplifies set-up time.
Article contributed by Kevin Hill, European product manager pneumatic actuators, Pneumatic Division Europe, Parker Hannifin Corporation.