The Effects Of The Delay To Electro-hydraulic Digital Servo System And The Research Of Compensation Method

When Network communication technology was introduced into the electro hydraulic control system, there are presenting the phenomena in the process of real-time data transmission such as network latency, packet loss, and timing disorder and so on, in which, the maximum affect for the system is delay. Delay mainly determined by the characteristics of variability, randomness and uncertainty showed by the latency of network control system, which has a serious impact on the accuracy, dynamic performance and stability of the electro-hydraulic control system.This paper focused on the closed-loop transmission delay of electro-hydraulic control system based on the network, the system composition and distribution of transmission delay between the intelligent nodes, and the randomness and variability characteristics of the transmission delay, and established the discrete mathematical model of power hydraulic control system with the delay. From the network transport protocols, the drive ways of intelligent nodes such as electro-hydraulic controllers and sensors, and the select of the sampling period, the factors impacting on the size of the delay of the electro-hydraulic control system. The specific case study is the electro-hydraulic position system of Sauer-Danfoss construction machinery vehicles. Under the conditions of the CAN-bus network communication, the12smart nodes were set, in which high-priority nodes were six, then calculated the delay parameters of the system of CAN bus control. Using MATLAB/TrueTime Toolbox, the simulation model was established, and the impact of fixed delay and random delay on the electro-hydraulic control system were researched by the simulation.Focused on the adverse effects of the delay for the accuracy and stability of the electro-hydraulic control system, when the traditional Smith predictor is applied to electro-hydraulic control system, the changing parameters of delay and the exact model of the electro-hydraulic system are needed to be accurately estimated. But variability and randomness of the delay are just changing the working status of electro-hydraulic control system in real time, it is very difficult to accurately estimate delay parameters and the exact model. This paper designed a fuzzy control compensation scheme based on Smith predictor to optimize the Smith Predictor strategy. This paper introduced the fuzzy control technology into Smith predictive control technology, and then directly applied on the electro-hydraulic control system based on network, which improved the characteristics of delay parameters changes insensitive that Smith predictive control to the electro-hydraulic control system, and can trace the real parameters changes well.Finally, through the instance simulation of electro-hydraulic position control system of Sauer-Danfoss construction machinery vehicles based on the CAN-bus, in the electro-hydraulic control system based on network controlled, when the delay increased, the overshoot of the system significantly increased and regulation time is longer; when the delay increased to11ms, electro-hydraulic control system presented an unstable state; and in the case that the total delay is certain, when the proportion of the delay is greater that electro-hydraulic controller to actuator, the damage to the electro-hydraulic control system is more serious. This paper verified the effectiveness and feasibility of Smith estimated fuzzy control methods. Simulation results showed that the fuzzy control scheme based on Smith’s estimates have a very good compensation effect for the fixed delay and random delay of the electro-hydraulic control system based on network controlled.