Research On Electro-hydraulic Servo System Of Lifting Mechanism For Snubbing Unit

The lifting mechanism is the key part of the snubbing unit,and is generally driven synchronously by two hydraulic cylinder systems,the performance of the hydraulic system is essential for the whole snubbing unit.This thesis analyzes and studies the lifting electro-hydraulic servo system of the snubbing unit.According to the characteristics of the hydraulic system of long stroke, heavy load range, the nonlinear mathematical model of single asymmetric hydraulic cylinder with asymmetric valve control is established; on this basis, with consideration of the coupling of double system, this thesis establishs the double-system model.The hydraulic system is required to run stably in a large range. Based on the analysis of single system model, in this thesis feedback linearization theory based on differential geometry is adopted to transform the nonlinear system into a completely controllable linear system, the high-order nonlinear term of the system is reserved, a large range linear system is achieved and this thesis analyzes the zero dynamic stability of the system. In this paper, the controller is designed by the bounded tracking principle for the controllable system after being linearized for a large range. The disturbance observer is designed to suppress the influence of the load disturbance to the system. For different working conditions, the feedback linearization controller and PID controller are simulated, the simulation results show that the PID is better when the system works near the steady point; however, when the system is far from the steady point, the feedback linearization controller is more effective than PID.This thesis analyzes the unsynchronized factors of the double system for subbing unit, and designs the master-slave approach, the synchronized master command approach and the cross- coupled approach. For different working conditions, the feedback linearization controller is adopted to control the single system, this thesis simulates the three schemes of synchronization.Comparing the synchronization error of different control schemes, we find that and the cross-coupled approach control scheme has the highest precision, synchronized master command approach takes the second place and master-slave approach followed. Therefore, the system uses the cross coupling control method.Using the x PC Target module the author build the single and dual system’s control model,and experiment to verify the proposed control strategies for electro-hydraulic servo system of lifting mechanism for subbing unit. Because the asymmetric valve controlled asymmetric cylinder has the same characteristics as symmetrical valve control cylinder, therefore, based on the existing equipment, this experiment uses symmetrical valve controlled symmetrical cylinder. The experimental results show that the feedback linearization control is effective and the cross-coupled approach control scheme has the minimum synchronization error.