A method to improve the motion trajectory tracking accuracy of pneumatic servo system—by exciting longitudinal resonance

The compressibility of the air and the friction characteristics of the pneumatic cylinder are the main reasons for the unstable motion and poor control accuracy of the pneumatic cylinder, which have been restricting the development of high-precision motion control for pneumatic cylinders. For this reason, it is very important to ameliorate the friction characteristics of pneumatic cylinder to improve motion servo control accuracy of pneumatic systems. Reducing friction is a common method to improve the friction characteristics of pneumatic cylinder. In this paper, the longitudinal vibration mode of the cylinder block caused by the high-frequency vibration of the piezoelectric stacks was selected for research. Based on the inverse piezoelectric effect and the principle of vibration friction reduction, a pneumatic cylinder with longitudinal resonance was configured by means of modal analysis, impedance test and vibration amplitude test. Subsequently, the influence of pressure in pneumatic cylinder on friction was studied and mathematical models of friction in the case of resonance and non-vibration were established. Furthermore, a model-based integral sliding mode controller was constructed for the pneumatic system to track some reference motion trajectories. The test results show that longitudinal high-frequency resonance can not only reduce the friction of pneumatic cylinder to a certain extent, but also improve motion trajectory tracking precision.