Many industrial applications require linear motion during their operating sequence. One of the simplest and most cost effective ways to accomplish this is with a pneumatic actuator, often referred to as an air cylinder. An actuator is a device that translates a source of static power into a useful output motion. It can also be used to apply a force. Actuators are typically mechanical devices that take energy and convert it into some kind of motion.
Pneumatic actuators are mechanical devices that use compressed air acting on a piston inside a cylinder to move a load along a linear path. Unlike their hydraulic alternatives, the operating fluid in a pneumatic actuator is simply air, so leakage doesn’t drip and contaminate surrounding areas.
When selecting an air cylinder, it’s important to properly match the cylinder to the application, particularly in terms of required force. The theoretical force available in the actuator is the piston surface area multiplied by the supplied air pressure. Spring force must be subtracted from this value for single acting cylinders. The actual force applied to the load will be 3 to 20% less due to pressure losses in the system.
When the required piston surface area (A) is known, the bore diameter (d) can be found by the formula.
Stroke length is determined by the required travel of the machine element driven by the actuator. The final selection criterion is the cylinder mounting arrangement, and the resulting configuration.
There are many different configurations available from various manufacturers. The more common ones include rigid nose or tail mount, trunnion mount, rear pivot mount and foot mount. Once the basic actuator size and configuration are known, other options such as end-of-stroke cushions or special seals should be considered. In some applications, position detection switches are required, typically accomplished with a magnetic piston and switches.
There are many factors such as system contamination, corrosion, minor leaks and wear that will affect the available air pressure and flow used to drive the actuator. An actuator and fluid power system should be sized correctly so as not to waste energy, with a margin added to account for minor reductions in pressure and flow due to the factors listed above.
Filed Under: Motion Control Tips