Overview

While the most often used actuators for pneumatic drives are cylinders for translational movements, there are many applications that require a turning or twisting movement of up to 360 degrees. Examples are turning components over in a drilling jig, providing a wrist action on a pick-and-place device or operating process valves. For these applications semi-rotary actuators can be used. There are different designs available. Many are based on cylinders that use a rack and a pinion or a skotch yoke to convert the linear movement to rotation, see Figs. 10.1 and 10.2. Larger actuators of this type are often used in the process industry to operate quarter turn valves. For smaller loads, rotary vane designs are used, as shown in Fig. 10.4, or helical shafts to convert the linear piston movement to rotation. While the skotch yoke types are limited to 90 degrees rotation and the vane types to 270 degrees, rack-and-pinion actuators are available for several complete revolutions. A comparison of different designs is given by French and Ramirez (1996).

Figure 10.1: Cut-away view of a semi-rotary drive with rack-and-pinion

Manufacturers typically specify maximum velocities for semi-rotary actuators. In our laboratory experiments we found that throttling of the exhaust port is necessary to stay within these limits.

These drives usually operate from one fixed stop to the other. For high precision rotatory positioning for handling devices, Schillings (1993, 2000) describes a belt cylinder drive that works on the basis of a band cylinder without piston rods and uses...