More about Rotary Actuators

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Rotary actuators convert energy into controlled rotational force, and are often used in systems where cylinder mountings are not a viable solution. There are a wide range of rotary actuator designs available, including rack and pinion, piston chain, helical spine, Scotch yoke, bladder and vane rotary actuators, each suited to a specific group of applications.

The rack and pinion rotary actuator is perhaps one of the most familiar, as its design lends its name to certain automotive steering systems. Generally in a rack and pinion actuator, pressurized fluid propels a piston inside a hydraulic cylinder, and the piston drives a toothed rack. The teeth of the rack interlock with those of a rotating pinion, which is turned as the piston drives the rack. The pinion is typically affixed to a shaft, and thereby provides the system with rotational power as it turns.

A helical spline rotary actuator, also known as a sliding spline actuator, consists of a cylindrical housing, a shaft, and a piston sleeve. Both the inside of the piston sleeve and the shaft (where it meets the piston) are splined with matching teeth. The device is hydraulically sealed so that the application of pressure to a port will drive the piston sleeve. This pressure also causes the sleeve to rotate as it moves, thereby turning the shaft.

A typical bladder rotary actuator uses expandable bladders to drive a specialized arm, which is attached to the rotating shaft. When significant pressure is applied to a bladder, it expands and moves the accompanying arm; the movement of the arm turns the output shaft. Vane actuators work by a similar means, but use fluid filled chambers to drive a vane attached a drive shaft.

Among the many applications for rotary actuators are positioning, switching, opening/closing and feeding tasks. Because they are relatively simple and durable devices, they can be used in a wide range of marine, material handling and industrial operations with minimal risk of failure.