Research On Active Control Of Load Port Independent Control System Based On Hydraulic Pressure Difference Compensation

Hydraulic systems are widely used in aerospace,shipbuilding,engineering machinery,steel metallurgy and other fields because of their small size,light weight,high rigidity,high precision and fast response.The traditional valve control hydraulic system uses a single spool to control the meter-in and meter-out circuits of the hydraulic actuator.The operation is simple,but the throttling loss is large.Therefore,two or more spools are used to control the meter-in and meter-out oil way of the hydraulic actuator.The load port of the meter-out circuit has an independent metering system,thus avoiding repeated throttling losses and reducing energy consumption.Independent metering system is the same as the traditional hydraulic system.According to the load force direction of the hydraulic actuator,it is divided into active load conditions and passive load conditions.Hydraulic actuators are prone to cavitation in active load conditions,which will cause pressure fluctuations,Abrupt flow rate,cavitation and other problems.Independent metering system with mechanical hydraulic pressure compensation was taken as the a research object in this paper.In order to prevent cavitation phenomenon,the throttle characteristics of the meter-in and meter-out were analyzed,and the minimum ratio?of meter-in and meter-out orifice was obtained.The anti-cavitation control strategy under active load conditions of independent metering system was designed,simulation and experimental research were carried out.The research content mainly includes:(1)The static characteristics of the piston rod extension and retraction conditions of the load sensing system and the independent metering system were analyzed respectively,and the influence of different throttling area ratio?on the system pressure and flow characteristics was finally obtained.Finally,the minimum value of the throttling area ratio?of the inlet and outlet valves to prevent cavitation from the load port independent control system under active load conditions was obtained.(2)The simulation models of independent metering system and load sensing system were built by the hydraulic system simulation software AMESim,the control method of meter-in and meter-out valves under active load conditions of load port independent control system was proposed.Independent metering system and load-sensing system active load condition simulation were analyzed,The simulation results showed that in the load sensing system,the pressure of the inlet chamber falls below 0 with the increasing of the load force F,which is called cavitation phenomenon;in the independent metering system,the inlet chamber pressure can be kept as the target pressure P_mby changing the ratio?of metering in orifice and metering out orifice,as a result that the cavitation phenomenon can be prevented.(3)The active load conditions and passive load conditions of independent metering system were analyzed respectively,and the active load conditions anti-cavitation control strategy and passive load conditions movement based on expert PID were designed,hydraulic system simulation software AMESim and control system simulation software MATLAB/Simulink were used to establish a joint simulation model of the load port independent metering system,and the active load and passive load compound conditions was simulated and analyzed.The simulation results showed that:under the active load condition,while completing the motion control,the pressure of the meter-in cavity was effectively controlled to prevent the occurrence of cavitation;under the passive load condition,the motion control was better completed.The load port independent control system model was established in the AMESim system,and the control model was established in Simulink.Through the two kinds of co-simulations,the pressure of the hydraulic actuator's meter-in cavity was relatively stable.(4)Based on the proposed active load condition and passive load condition control strategies of the load port independent control system,the active and passive control test bench of the independent metering system was taken as the research object,the electronic control system scheme was designed and BODAS was used to compile a control program,and experimental research on active load conditions and passive load control was carried out.The experimental results showed that:under active load conditions,the speed of the piston rod of the hydraulic cylinder was effectively controlled,and the meter-in pressure keep stable at the target value of about 0.5MPa;under passive load conditions,the speed of the piston rod of the hydraulic cylinder was effectively controlled.