Adaptive Backstepping Control of Vacuum Servo System Using High-Speed on-off Valves

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.