Rotary actuators come in the following types in terms of position: - two positions, fixed or adjustable - three positions, fixed or adjustable Rotation is alternating in all the types.  There also exist rotary actuators that always rotate in the same direction, with 4, 6, or more positions. Rotary actuator with single rack: A pinion is keyed on to the rotating part and is rotated by means of a rack.   The rack is driven by two pneumatic pistons, one on either side.  As there is no play take-up-system, it's not suitable for applications requiring accurate positioning.  But there is a version with outer adjustable mechanical stops that stop the rotating part and also take up play.   Rotary actuator with double rack. The pinion keyed onto the rotating element is turned by two opposing racks, each driven by  pneumatic piston.  The system has automatic play take-up, which means it is suitable for applications requiring accurate positioning.  The parallelepiped shape of the design makes them ideal for use on mechanical arms.   Blade-type rotary actuator The rotating element is connected to one or two blades inside a cylindrical chamber.  The air pressure on one of the sides of the blade rotates the element.   These are compact cylindrical actuators designed for manipulation where particularly accuracy and high loads are not required.   Chain-type rotary actuator A chain that is stretched at either end by a pneumatic piston winds round and rotates a pinion.  This type of actuator is not included in our catalog.