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Machine Design

Self-Adjusting Pneumatic Cushions Handle Changing Loads and Speeds

Self-adjusting pneumatic cushions handle changing loads and speeds.

Festo Corp.,

Festo Corp., Hauppauge, N.Y., has developed a self-adjusting pneumatic-cushioning system for the its widely used DSNU Series round-cylinder pneumatic actuators. The cushion relies on specially engineered air channels to vent the cushioning air, letting the cushions adapt their characteristics should cylinder loads and speeds change.

The cushion, designated PPS, provides dynamic but gentle damping as the load nears the end of the cylinder without the need for manual adjustment. Until now, users had to manually adjust end-position cushioning on cylinders. However, tuning by hand often means actuators are less than perfectly adjusted. Underdamping results in excessive impacts, more noise, and increased wear; overdamping risks slow cycle times.

The self-adjusting PPS cushions provide just the right damping even if parameters such as friction and pressure change, says Festo. They also reduce acceleration forces on mating components and workpieces. This cuts down wear and minimizes shock and vibration. And compared to shock absorbers, self-adjusting cushions are less expensive and more durable, according to the company.

DSNU round cylinders with the new cushions span diameters from 16 to 63 mm, with stroke lengths to 500 mm. The DSNU actuators already offer users a choice of polymer or manually adjustable pneumatic end-position cushioning for applications involving low and high impact-energy levels, respectively. Self-adjusting PPS cushions are primarily intended for medium impact-energy applications involving loads to about 5 kg and speeds to approximately 1 m/sec.

Because the exhaust flow from the cushioning chamber changes over the damping stroke, Festo’s PPS cushions work with most commonly permissible speed and mass combinations, making them suitable for a wide range of applications. According to Festo Product Manager Steve Sands, about 80% of applications that use DSNU cylinders with manually adjusted cushions would benefit from self-adjusting cushioning. Plus, the PPS system costs less than Festo’s manually adjustable technology, says Sands.

Self-adjusting cushions also hold considerable advantages in terms of machine setup and commissioning. Manually adjusting the end-position damping of linear actuators is time consuming, and can only be done effectively with the actuator installed and operating under load conditions. It also frequently involves two people — one operating the appropriate pneumatic valve, the other adjusting the actuator’s damping characteristics.

Festo estimates that on average, PPS self-adjusting end-position cushions will help users shave 5 min off a cylinder’s installation and setup time. For a typical application, such as a package-sorting system with 60 cylinder-driven routing stations, this would save 5 man-hours.

Festo’s PPS cushions have no settings to change, are tamperproof, and should provide long, maintenance-free service life. And PPS-equipped DSNU pneumatic cylinders are fully interchangeable with the company’s manually adjustable models.


PPS cushioning is also available on the company’s CRDSNU corrosion-resistant stainless-steel round-line cylinders. Because there is no external cushioning-adjustment screw, this eliminates any potential for dirt entrapment around the screw for a cleaner surface with better wash-down characteristics.

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