| Hydraulic transmission,the key technology for the operation control of large-scale machine,is widely used in aerospace,military,industry,agriculture and other fields.The efficiency and movement performance of a hydraulic system are directly determined by the hydraulic valve,which is the critical component for motion control.Although the conventional hydraulic valve is assembled with a single spool and easy to control,this kind of structure has some shortcomings,such as low control degrees,high energy consumption,poor sensing ability and single function.These problems can be overcome by developing a new valve structure and a multi-function controller.In this thesis,an innovative design of hydraulic valve was proposed,and its programmable control technology was investigated to expand the functions of the valve and to improve its performance,so as to optimize the energy saving characteristics,and to improve the motion performance of the machine.In this thesis,a proportional pilot programmable valve was developed.This valve had a symmetrical twin spool structure to independently control the metering in and metering out of the load,allowing system efficiency and actuator moving performance to be improved.The main stage of the valve was integrated with thin film sputtering pressure sensors and embedded displacement sensors to realize accurate state sensing capabilities.The controller and monitoring system of this valve were developed to achieve multi-hydraulic functions,for instance,displacement control,pressure control and flow control.Self-adaptive switching and optimization between working modes and operating parameters were also achieved to enable functions beyond conventional hydraulic valves.A fuzzy controller for spool displacement was proposed to obtain rapid and precise movement of the spool.A switching time of the proportional pilot programmable valve of 35ms was reached,which was as good as the performance of the Bosch Rexroth valve of the same diameter.The presented valve could be used to track 5Hz and 10Hz sinusoidal signals effectively,and the errors could be controlled within 20?m and 60?m,respectively.In order to overcome the problem that the motion characteristics of the main valve of digital hydraulic pilot programmable valve were affected by the dynamic performance of the pilot High Speed on/off Valve(HSV),a multi-voltage adaptive driving method for the HSV was proposed.The non-contact measurement of the HSV working state was realized by using current feedback decision,and the adaptive driving with different equivalent voltages was also achieved to improve the dynamic performance of the HSV,and to reduce its coil temperature and energy consumption.Compared with the mature dual-voltage industry driving method,the opening time was shortened by 1.0ms(19.6%),the closing time was shortened by 2.6ms(49,1%),and the total switching time was shortened by 3.8ms(34.6%).The coil temperature was reduced from 95? to 26?,and energy consumption was reduced from 23.44W to 2.62W.An advanced algorithm was proposed to preserve the dynamic characteristics of the HSV under a variable supply pressure while improving its dynamic performance.By this method,the critical switching currents of the HSV under the current working conditions were calculated,and the corresponding current trigger values were updated,so that the influence of the supply pressure on the dynamic performance of the HSV could be reduced.It was shown in the experimental results that the variation range of total switching time of the HSV was controlled to within 0.3ms(7.4%)under varying pressures from 4 MPa to 20 MPa.A digital hydraulic pilot programmable valve was developed,and its dynamic performance was improved with combination of digital hydraulic technology,independent metering control technology and programmable control technology.A programmable controller for this valve was modified to adaptively switch the working modes and optimize the operating parameters.A spool displacement controller of the digital hydraulic pilot programmable valve was proposed,and the spool characteristics under high-frequency discrete fluid was analyzed.It was demonstrated that the digital hydraulic pilot programmable valve had much better dynamic characteristics compared to conventional valves.The higher the operation frequency of the pilot HSVs,the smaller the main spool vibration range.The spool movement errors of the proposed valve could be controlled to within 20?m.The larger the supply pressure of the pilot stage,the better the dynamic characteristics of the main spool,but the more intense the spool vibrating.The measured stability times of 25%,50%,and 75%stroke step response were less than 35ms.It was indicated that the digital hydraulic pilot programmable valve had better dynamic characteristics when compared with the proportional pilot programmable valve.A two-level closed-loop fuzzy pressure controller was developed,whose outer loop was a pressure closed loop and inner loop was a displacement closed loop.It was shown in the experimental results that this pressure controller had much better dynamic and static characteristics compared to traditional controllers,as the pressure step stability time could be controlled to within 120ms.The strong robustness and self-adaptive abilities were obtained by the pressure controller,as the pressure adjusting time reached 70ms under a variable load.Because the displacement controller of existing advanced hydraulic valve is usually a closed system,it is difficult to communicate between the displacement controller and the pressure controller.Therefore,the control voltage of the hydraulic valve is often used as a stand-in for the corresponding spool displacement in flow calculations.However,the accuracy of flow calculation results will be negatively affect by this method.In this thesis,a flow feedback calculation algorithm was proposed,and a fast dynamic performance was achieved by the flow controller based on this algorithm.The stability time of the flow step response could be controlled to within 100ms.When the flow controller was applied to the proportional pilot programmable valve and digital hydraulic pilot programmable valve,their steady-state errors of the flow rate were 0.4L/min and 0.7L/min,respectively.The thesis is outlined as follows:In Chapter 1,the achievements and challenges of current state-of-the-art programmable valve technology and digital hydraulic technology were reviewed,and their development trends were presented.The significance and background of this research were explored,and the contents and challenges of this research were discussed.In Chapter 2,a valve control unit with a twin spool configuration was presented,its proportional pilot control method based on voice coil motors(VCMs)was proposed.The integrated sensing system,embedded controller and programmable monitoring system based on CAN bus were developed.A fuzzy spool controller was developed,and the dynamic and static performance of proportional pilot programmable valve were studied by theoretical analysis,simulations and experiments.In Chapter 3,the influence of the control algorithm on the dynamic performance of HSV was analyzed theoretically.A multi-voltage adaptive driving method for HSV was proposed and verified by simulations and experiments.Based on this,a dynamic characteristics preservation method for HSV to adapt to changing supply pressure was discussed,and the performance of this method and traditional single-voltage control method in achieving good dynamic characteristics and robustness in HSV were analyzed.In Chapter 4,a valve control unit using HSVs for pilot control was designed based on the twin spool structure.A programmable control system based on FPGA technology was developed,and its spool displacement controller was proposed.The effects of supply pressure and operation frequency of the pilot stage on the dynamic and static performance of the main spool were studied by simulations and experiments.In Chapter 5,a comprehensive experimental test bench for programmable valves was proposed.A fuzzy pressure controller and fuzzy flow controller of programmable valves were proposed,and a flow feedback calculation method based on spool displacement and orifice pressure difference was presented.The pressure control,flow control and compound control performance of proportional pilot programmable valve and digital hydraulic pilot programmable valve were verified by experiments.In Chapter 6,the results and conclusions were summarized,and a future research prospective was proposed. |
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