Diaphragm actuators and bellows actuators can be used in a variety of applications as drive or pneumatic spring systems. They form a class of their own in the world of pneumatics thanks to their special properties – a particular benefit is that they have no annoying stick-slip effect. The stick-slip effect is the jerky sliding motion when solid bodies move against each other. This phenomenon occurs when a body, whose static friction is significantly greater than the sliding friction, is moved. This often happens with pneumatic cylinders.
Bellows cylinder are both drive and pneumatic spring systems and fall into the category of diaphragm actuators. When provided with pressurisation and exhaust functions, bellows cylinders can be operated as a drive component. As the stroke increases, the force generated is reduced in relation to the contractional force of the bellows. When bellows cylinders are supplied with permanent pressure, they act as a cushioning component. The simple design consists of two metal connecting plates with a rubber bellows attached to them. There are no sealing components and no moving mechanical parts. Bellows cylinders are single-acting drives that do not require a spring return, as they are reset by the application of external force.
A major advantage of bellows cylinders is the particularly low installation height compared to conventional cylinders as well as their ease of movement. This means that larger axis offsets and angular rotations of up to 20° are also possible. And the bellow cylinders are not prone to the stick-slip effect, which is often a problem with conventional cylinders. Double bellows can be used for large strokes. They can be used with different media, such as compressed air, gas and liquids, as long as the properties of the rubber are taken into account.
Pneumatic muscles are diaphragm actuators, or more precisely diaphragm-contraction actuators, also known as pull actuators. They were developed according to the model of a biological muscle and consist of contractible tubing and appropriate connectors. The contractible tubing is made up of a rubber sheath with a non-crimped fabric made of aramid fibres on the inside. The diaphragm hermetically seals the operating medium. The fibres provide reinforcement and transmit power. When internal pressure is applied, the diaphragm extends in circumferential direction. This creates a tensile force and contracts the tubing lengthwise. The maximum usable tensile force is available at the start of the contraction and then decreases with the stroke. The advantages: The diaphragm actuator has an outstanding force-to-weight ratio and is powerful in operation. It is also free of stick-slip effects and its initial force is 10 times higher than comparable pneumatic cylinders.