TABLE OF CONTENTS Two parameters of a cylinder are usually known: the piston or bore diameter and the maximum stroke. For standardised cylinders the diameter of the piston rod and the most relevant mounting dimensions are given in the particular standard. But there is typically no information available about the parameters and characteristics needed for mathematical modelling, e.g. friction, leakage or heat transfer.
When selecting or modelling a cylinder, the delivered force at the rod has to be known. It is given by the diameters of the piston and the rod, the pressures in both chambers and friction forces of the piston and rod seals. The geometrical data is usually given in the data sheet and the nominal pressure specified during the design of the drive. Unknown are the friction forces. They occur because a sliding piston seal has to push outwards against the sliding surface with enough force to prevent compressed air from escaping from the cylinder.
In a number of cases, friction forces of the cylinder seals are much smaller than the forces required to move the load or the force generated by the back pressure of a fast moving piston when the resistance at the exhaust port is high. In those cases it is more important to calculate the opposing forces carefully than to spend much time on determining the friction forces.
But there are also situations when the friction forces have to be taken into account because they dominate the response (Bowns and...
