According to the theory of phononic crystals, the hydraulic pipeline is designed to be a periodic structure composed of steel pipes and hoses to suppress the vibration of the hydraulic system with band gaps. We present theoretical and experimental investigations into the flexural vibration transfer properties of a high-pressure periodic pipe with the force on the inner pipe wall by oil pressure taken into consideration. The results show that the vibration attenuation of periodic pipe decreases along with the elevation of working pressure for the hydraulic system, and the band gaps in low frequency ranges move towards high frequency ranges. The periodic pipe has good vibration attenuation performance in the frequency range below 1000 Hz and the vibration of the hydraulic system is effectively suppressed. All the results are validated by experiment. The experimental results show a good agreement with the numerical calculations, thus the flexural vibration transfer properties of the highpressure periodic pipe can be precisely calculated by taking the fluid structure interaction between the pipe and oil into consideration. This study provides an effective way for the vibration control of the hydraulic system.

Using high-speed on-off valves (HSVs) with small size, low cost, and high switching accuracy instead of expensive proportional/servo valves, and researching high-performance vacuum servo system can further enhance the competitiveness of vacuum servo technology. However, due to the delay characteristics of high-speed on-off valve (HSV), the average gas mass flow rate of the output has dead zone, saturated zone and nonlinear zone. A linear compensation method for flow output is designed, so that the average gas mass flow rate of the output is approximately positively correlated with the duty cycle of the pulse width modulation (PWM) signal. Furthermore, because of the air compression and the leakage of the system, there exist parametric uncertainties, unmodeled dynamics and disturbances in the vacuum servo system. An adaptive backstepping control (ABC) strategy based on discontinuous projection mapping is designed. The adaptive backstepping control strategy inhibit the influence of system's parametric uncertainties through on-line update of the uncertain parameters, and uses its own robustness to eliminate the effects of unmodeled dynamics and disturbances. Compared with the sliding mode control (SMC) strategy, the experimental results show that when the tracking frequency reaches 3-4Hz, the adaptive backstepping control strategy can ensure good tracking performance. INDEX TERMS Adaptive backstepping control, High-speed on-off valves, Pulse width modulation, Vacuum servo system.

A new robust nonlinear controller is proposed to improve the performance of the atmospheric pressure simulator that has some special characteristics such as asymmetry and nonlinearity. The three major components in such systems, the chamber, the servo valve and the vacuum pump, are studied to develop a full nonlinear model which encompasses all the major nonlinearities. Based on the model expressed in the controllability canonical form, a feedback linearization controller is developed to handle the strong asymmetry and nonlinearity of the atmospheric pressure simulator. Considering the parametric uncertainties and un-modeled dynamics existing in the atmospheric pressure simulator, a self-tuning fuzzy proportional integral derivative controller integrating with feedback linearization is introduced to improve the performance of the atmospheric pressure simulator at high-altitude simulations. Simulations and experiments indicate that the proposed controller can effectively raise the dynamic response performance, and in the meantime stability can be ensured.

A vacuum pressure tracking system with high-speed on-off valves is a discontinuous system due to the discrete nature of high-speed on-off valves. Chamber pressure changes in the system are determined by the mass flow rates during the processes of charging and discharging. Here, a sliding mode controller with an asymmetric compensator based on average mass flow rate is designed for accurate vacuum pressure tracking. The controller output signal is converted into the duty cycles of the high-speed on-off valves via a pulse width modulation pulsing scheme. Owing to the extreme asymmetry of the processes, an asymmetric structure comprising one high-speed on-off valve in the charging unit and three high-speed on-off valves in the discharging unit is applied to weaken the impact of asymmetry. In addition, an asymmetric compensator is also designed to modify the pulse width modulation pulsing scheme to further eliminate the asymmetry. Experimental results indicate that the proposed controller achieves better performance in pressure tracking with the asymmetric compensator overcoming process asymmetry and enhancing system robustness.

No abstract