When selecting which type of rotary actuator is best for your application, the main design considerations are mechanical efficiency, package size, shaft options, max rotation and cost. Beyond that, you must also consider characteristics such as backlash, ability to stop a load, and ability to handle axial and radial loads on the shaft.
There are two main types of pneumatic rotary actuators. Here’s a breakdown of the advantages and disadvantages of each to help you make the right choice for your application.
Rack and pinion rotary actuators
Ideal for: High-speed production applications and situations where low wear and long life are important, Our PTR Series of rack and pinion rotary actuators are one example of this type of actuator.
- Widest ranges of torque and rotation and deliver excellent mechanical efficiency, often as high as 90-95%
- Designed with a profile that simplifies mounting options
- Hollow pinion gears offer flexibility, allowing the machine’s shaft to mount through the pinion gear of the actuator, thus eliminating the need for a coupling
- Accommodate large loads, unlike air cylinders, which provide force but do not support a load
- Same roller bearing assembly that supports the pinion gear can also support axial loads
- Potential for backlash, caused by a very small gap between the gears – typically not an issue for most applications as the “play” is only about one degree
- Wear on the gears is common, which can cause the backlash to increase slightly over time; for precise positioning a double rack version can be used, which completely eliminates backlash by imposing a counter force on the pinion gear
Ideal for: Applications where space is limited due to their compact size; often used to clamp, transfer, or position light loads in medium-speed applications. Our PV Series vane actuators provide the maximum amount of output torque from the smaller possible envelope size.
- Fair mechanical efficiency at 75-85% due to the friction of the vane seals and shaft bearings
- Very small amount of bypass leakage over the vane seals (it is virtually impossible to design a vane type rotary actuator with bubble-tight vane seals)
- No backlash, so positioning is precise
- Less expensive so great choice for light to medium duty pneumatic applications
- Limited rotation and torque range compared to rack and pinion actuators, typically up to 280° maximum for a single vane model – so best suited to light loads in medium-speed applications
- Can only accommodate light loads as the shaft uses small bushing-type bearings
- Minimal shock capability compared to other types – external stops are typically required in higher speed applications
Whatever your application requirements, our range of pneumatic rotary actuators are designed to help you optimize performance and maximize results. You can find out more about pneumatic technology by exploring other articles in our Know Your Pneumatics series.
Article contributed by Kevin Hill, European product manager, pneumatic actuators, Pneumatic Division Europe, Parker Hannifin Corporation.