Diaphragm actuators and bellows drives can be used in a variety of ways as drive systems or pneumatic spring actuators. In the world of pneumatics, they form a class of their own with special properties – in particular, they have no annoying stick-slip effect. The stick-slip effect refers to the jerky sliding of solid bodies moving against one another. This phenomenon occurs when a body is moved whose static friction is significantly greater than the sliding friction. This is often the case with pneumatic cylinders.
Bellows cylinders function both as driving and pneumatic spring systems and fall under the category of diaphragm actuators. Bellows cylinders function as a driving component by providing supply and exhaust functions. 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 an attached rubber bellows. There are no sealing components and no moving mechanical parts. Bellows cylinders are single-acting drives that do not require spring returns, as the reset is achieved by the application of external force.
A major advantage of bellows cylinders is their particularly low installation height compared to conventional cylinders and their ease of movement. This means that larger axis offsets and angular rotations of up to 20° are also possible. The stick-slip effect, which is often a problem with conventional cylinders, also does not occur with bellow cylinders. Double bellows are intended for larger strokes. They can be used with various media such as compressed air, gases, and liquids if the properties of the rubber are taken into account.
Pneumatic muscles are diaphragm actuators, more precisely diaphragm contraction actuators, which are also referred to as tension actuators. They were developed based on the model of a biological muscle. It consists 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 power transmission. When internal pressure is applied, the tubular sheath extends in circumferential direction. This generates a tractive force and a contraction movement in the longitudinal direction. 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 power/weight ratio, works particularly powerfully, quickly and without any stick-slip effect, with an initial force that is 10 times higher than comparable pneumatic cylinders.