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

Gang Yang,Yong Wu,Lei Lei,Peng Jiang,Jingmin Du,Baoren Li

doi:10.1109/access.2020.3007208

Abstract

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.

Highlights

Pneumatic system has been widely used in robots, medical equipments and other industries because of its low maintenance cost, high power-weight ratio, cleanness and simple structure [1]–[4]
The use of high-speed on-off valves (HSVs) instead of proportional/servo valve can effectively avoid the problems of temperature drift, zero drift and hysteresis caused by the existence of analog circuit in the control loop
This paper proposes a higher frequency range of dynamic vacuum pressure tracking control, expanding the pneumatic pressure frequency from 1-2Hz to 1-4Hz, and use the HSVs as the control elements of the vacuum servo system

Summary

INTRODUCTION

Pneumatic system has been widely used in robots, medical equipments and other industries because of its low maintenance cost, high power-weight ratio, cleanness and simple structure [1]–[4]. The gas mass flow rate into and out of the chamber is changed by controlling the opening and closing state of the HSVs of the charging and discharging unit, and the change of chamber pressure is realized. An ABC strategy is designed uses its own robustness to eliminate uncertain nonlinearities of the system in this paper, and on-line update of the uncertain parameters in real time to eliminate the influence of the system’s parametric uncertainties, ensuring the control performance of the system. For the principle sketch of vacuum servo system shown in Fig., this paper designs a charging/discharging cooperative working mode, which realizes the pressure control of the chamber by controlling the difference between the gas mass flow of the input and output of the chamber.

MASS FLOW LINEAR COMPENSATION

CONCLUSION