Pneumatic position servo control considering the proportional valve zero point

With the improvement of the performance and the reduction in the cost of the pneumatic proportional valve, the simple structure pneumatic position servo system is widely applied in various fields. However, the high accuracy tracking control is still a challenge, because the accurate parameters of the pneumatic system are unavailable. The situation becomes even worse, when the zero point of proportional valve is unknown. The impact of the inaccurate valve zero point will be accumulated due to the integration property of the valve, which degrades the tracking performance. To deal with this problem, an adaptive backstepping sliding mode control method is proposed in this paper. The zero point of the proportional valve is treated as an uncertain parameter and estimated online. The proposed controller is proved to be stable, thus the tracking error asymptotically converges to zero by using Lyapunov theorem. The experimental results demonstrate the effectiveness and superiority of the proposed approach, as compared with the method without considering the valve zero point.