Rotary Cylinders
Automotive, building, construction, food processing and packaging, metal working, mining, construction, textile production and forestry industries employ rotary cylinders alone or in conjunction with tangential models. Because these apparatus use only compressed air, they provide an economic and environmentally friendly solution to many mechanical operations such as machine loading, material handling, product assembly, welding and packing. Single and double acting cylinder configurations allow both the unidirectional and bidirectional capabilities needed for many of these applications. While some rotary cylinders offer adjustable degrees of rotation, others have a fixed range of motion. As precision is important in either case, engineers are often involved in the design and specific settings of a given cylinder, though charts and guidance can be available from the manufacturer as well. Further considerations to be explored include linear stroke, operating temperature, pressure range, maximum torque and load capacity.
There are two methods employed in the provision of rotary motion. Both rotate a protruding shaft to which the arm and necessary load or tooling are attached. In the vane or internal vane model, compressed air flows into one of two ports located in opposite compartments of the main cylinder. The air moves from high pressure to low pressure and in so doing rotates the internal vane, which is attached to the external shaft. This type of cylinder is usually bi-directional with inlets and exhausts located on both sides of the internal barrier used to build pressure. As vane actuators can be limited in torque and degrees of rotation, many industries employ rack-and-pinion style rotary cylinders. These are designed more similarly to traditional air cylinders. The body is a circular or rectangular cylinder with an air valve, for inlet and exhaust, located at each end. This component houses two pistons. A toothed rack and pinion are located between the pistons. When air is introduced into either end of the closed cylinder, the corresponding piston pushes the rack in the opposite direction. The pinion rolls along the rack creating rotation. This movement is transferred from the pinion to a connected shaft that, similar to vane construction, protrudes from the shaft and connects to the tooling or load. The number of teeth and length of the rack determine the range of rotation possible with this design.
