Rotary actuators enable rotary movements and have long been part of modern automation technology and industrial robotics. Depending on the requirements, they are equipped with different drives. In addition to their high precision, their advantages for factory automation are their enormous performance and drive diversity.
Rotary actuators, formerly also called part-turn motors or rotary motors, are devices that produce a rotary motion from an energy source. The simplest type of these drives uses a linear motion in only one direction to produce a rotation. Electric rotary drives, on the other hand, make use of an electrical energy source, such as an electric motor. The last type is the most common.
Other drives use the hydraulic energy of pneumatic tubes or the mechanical energy of springs. Thus, pneumatic rotary actuators are units powered by compressed air, which generate a rotary motion via a shaft. In this way, they control the rotation and speed of the connected devices. They are used, among other things, in industrial applications for conveying and transferring parts and for positioning and controlling control valves.
Hydraulic rotary actuators, on the other hand, translate a linear movement of the pistons into a rotary movement of the output shaft. In this way, they generate high torques through hydraulic pressure. These components are used wherever rotation and swiveling, rotary acceleration, braking and holding are required. Despite their performance, they are easy to control and can be found in almost every application in mobile hydraulics. They are also used in mowing machines, for example, so that sloping surfaces can also be worked.
If electric rotary actuators have a typical electric motor as power supply, they are able to generate continuous rotation. Also possible is a fixed movement in the direction of a specific position. In this case, the power source is a stepper or servo motor. This electric motor travels a fixed distance, so that, for example, a continuous movement with a fixed speed is created. In addition, rotation to any angular position is possible. One or more reference sensors with a position encoder are used for this purpose.
The so-called torque motor is similar to the stepper motor. However, this produces a very specific torque. An exception to this is only possible if an opposite torque is used that balances the first one.
Electric as well as hydraulic and pneumatic rotary actuators are used in factory automation. A wide range of industries take advantage of the many benefits of the multi-turn actuator – wherever it is necessary to rotate and swivel, accelerate precisely, decelerate, position and hold. The compact units are thus mainly used where high-torque rotations and reversals of direction are required and where large loads have to be tilted.
There are different versions of rotary actuators for the various fields of application. These should always be adapted to the respective application conditions in the best possible way. For example, rotary actuators are used for mixing processes of certain substances, opening and closing valves, butterfly valves or other industrial valves.
Rotary or part-turn actuators are generally extremely durable. To ensure a long service life, however, the type of rotary actuator should be optimally matched to the respective project. This is because different drive principles are implemented depending on the installation space requirements and the torque requirements.
The following two are used most frequently:
With a steep thread drive, intermediate rotation angles of all sizes can be realized, approached and held. Compared to other drive types, they have the advantage of being the most flexible in terms of their external dimensions. In this way, even limited installation space requirements can be met. In addition, options such as angular adjustment, damping and the attachment of sensor technology allow them to meet various requirements for rotary motion with high torques.
The design is based on a multi-start, counter-rotating steep thread. Here, the linear motion of the piston is transferred via the thread into a summed rotation. This means that the longer the linear travel of the piston, the greater the rotary motion.
This is therefore a very simple drive principle. Nevertheless, special precision is required in the manufacture of the actuators in order to make them not only functional, but also reliable and durable.
Rotary actuators based on the steep thread principle are used, among other things, in construction and machine tools (for example, in aerial work platforms or tunnel boring machines) and in vehicle construction (for example, in refuse collection vehicles, side and rear loaders).
So-called rack-and-pinion drives meet even the highest torque requirements. They allow large swivel ranges in the axial direction, even with limited installation space.
Just as with the steep thread principle, the additional options are diverse. Compared to a rotary vane motor, a rack-and-pinion drive requires much larger dimensions to transmit two equal torques. The pinion-equipped drive journal is arranged transversely to a pinion rack and pinion piston, over which generation and transmission pass. Depending on the design, the transverse forces generated by this gearing and acting on the back of the piston are balanced hydraulically.
The rack-and-pinion drive has proven to be particularly suitable for high torques. Drives operating on this principle are used, for example, in cement plants, in the steel and tire industry, in power plants and in ship rudder adjustment.
Swing cylinders are particularly easy to operate and control with high precision. Despite their high performance and reliability, they require only a small installation space. Because they are self-contained systems, the inside of the rotary actuator is protected at all times from external influences such as dirt, dust and moisture.
Compared to other types of actuators, electric rotary actuators in particular perform well. Due to their design, they are not subject to stroke limitations – for example, compared to pneumatic actuators.
The advantages of rotary actuators at a glance:
Rotary actuators achieve a high level of reliability when it comes to use in industries such as mechanical and vehicle engineering or construction machinery technology. They are also regularly used in power plants, in the onshore and offshore sector and in the manufacture of industrial spare parts.
