Nonlinear Control Method Of Hydraulic Press Based On Fault-tolerant Allocation Strategy

With the continuous improvement of China’s industrial strength,multi-cylinder hydraulic press has been widely used in industrial production.Because it is driven by multiple hydraulic cylinders at the same time,it has a very high requirement for the operation stability of the multi-cylinder hydraulic press.In order to ensure the safety of operation and maintain the operation accuracy of the system,it is extremely important to design fault-tolerant control schemes so that the multi-cylinder hydraulic press can still run stably in the event of actuator failure and maintain high control accuracy.In this paper,two kinds of fault-tolerant control methods for multi-cylinder hydraulic press are proposed,which are sliding mode fault-tolerant control method based on adaptive strategy and sliding mode fault-tolerant dynamic allocation method based on disturbance observer.For the sliding mode fault tolerant control method based on adaptive method,the actuator fault model which can describe many kinds of faults is introduced into the mathematical model of multi-cylinder hydraulic press,and the unknown external disturbance and fault information are estimated on-line by adaptive mechanism,so that the multi-cylinder hydraulic press still has high-precision position tracking and leveling ability when many kinds of faults occur.The control strategy does not need to rely on the fault information detection module(FDI),to avoid the adverse effects of the misstatement or failing to report of the system.For the sliding mode fault-tolerant dynamic allocation method based on disturbance observer,the mathematical model of multi-cylinder hydraulic press is refined into a more universal general model.The controller design is separated into three parts: virtual fault-tolerant control law design based on disturbance observer,dynamic control allocation design and actuator control law design.First of all,the actuator fault and external disturbance are regarded as lumped disturbance,and the disturbance observer is used to observe and compensate it.Using the sliding mode design method,a virtual fault tolerant control law based on disturbance observer is designed.Then,using the dynamic optimization method,a control allocation scheme is designed for the virtual fault-tolerant control law based on disturbance observer,so that the virtual control input can be allocated to each actuator efficiently.The allocation scheme can take into account many performance requirements,such as actuator constraints,output energy,allocation error and so on,and there is no need for iterative solution in the allocation process,so the calculation efficiency is higher and the real-time performance is better.Thirdly,the output force which come from the allocation result is taken as the expected output force,and the actuator control law is designed.Finally,the overall stability of the system is proved.In this paper,the problem of fault-tolerant allocation of multi-cylinder hydraulic press is studied,and the fault-tolerant ability of multi-cylinder hydraulic press with many kinds of faults is realized for the first time.At the same time,it improves the usual deficiency that the physical constraints of actuators are not considered in the fault-tolerant control of multi-cylinder hydraulic press.The problems of large amount of calculation and poor real-time performance of control allocation algorithm for multi-cylinder hydraulic press are also solved.