A. J. Czmerk

Position keeping properties of actuators depend highly on their stiffness. The low stiffness of pneumatic systems is well known, which is disadvantageous during positioning and when a position has to be kept. It is one of the reasons why hydraulic systems have advantages over pneumatic systems when it comes to positioning tasks. This paper deals with the analysis of the passive stiffness of a double-acting cylinder. The stiffness of pneumatic cylinders is derived as a function of chamber pressures determined by the bulk modulus of pneumatic systems. The stiffness of a passive system of the chambers is written by the pressure change through small displacement of the piston and as a result of the restoring force. In case of the passive system the effect of the valve actuation is neglected. From the deduction it is clear that the stiffness of a cylinder changes along the stroke, dead volumes at the end positions play a relatively important role. The results are compared with the restoring forces of the piston seals and other sealing elements in the stiction region. The restoring effects of the elastic elements were determined by measurements.

Keywords: pneumatic system, stiffness, friction, stiction

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