TABLE OF CONTENTS Pneumatic cylinders are very well suited to rapidly accelerate a mass to a high speed, e.g. 1 m/s. At the end of the cylinder stroke this mass has to be decelerated gently to prevent damage from the load and the machine, and avoid excessive noise. Due to the tendency to use lightweight aluminium profiles even for extended assembly lines, the permissible impact at stroke end has become smaller than in the past when heavy iron beams were used. Small light duty cylinders have little mass in their components and load and therefore fixed cushioning with shock absorbing pads set into the end covers is in many cases adequate to solve the problem. For larger cylinders with more mass industrial shock absorbers are often used. A recent alternative is the use of electronic control (anon. 2003).
For some applications adjustable cushioned cylinders are suited that contain a pneumatic damping system [1]. As shown below, this system can only work if the load and the velocity during the final part of the stroke remain the same during the complete service life because a change of these parameters puts the system out of tune. An adjustment requires thorough understanding of the dynamic effects and requires suitable measurement equipment, e.g. an acceleration sensor.
There are several cushion designs, but the principle of operation is the same. Figure 8.3 shows a type with the cushion seals placed in the end covers. The operation is as follows: the piston is moving...
