| With the development of mobile machinery and digital hydraulics, the combination of intelligent control with digital hydraulic component will become the focus of research in the near future. Because of the complicated structure and no on-line feedbacks of the existing directional control valve for mobile machinery, it is difficult to implement digital control. The usage of a single spool to adjust inlet and outlet throttling area also leads to a high energy consumption. In this thesis, an independent metering control programmable valve (IMCPV) has been developed to replace directional control valve. The IMCPV integrates the digital signal control and independent metering control technology, which has the advantages of increasing hydraulic control flexibility and reducing load backpressure. Meanwhile, since the IMCPV has simple structure, it is convenient to carry out modular production of hydraulic components. The aim of this thesis is to propose new design of IMCPV with its pressure and flow characteristics and also its application in excavator.An IMCPV was consisted of two high-speed switching valves as pilot stage to control the main stage. The inlet and outlet of a hydraulic actuator (hydraulic cylinder, hydraulic motor)were controlled by two IMCPVs separately. For improving the control precision, there were pressure sensors, displacement sensors and CAN BUS interface configured in IMCPV to supply on-line measurement and feedbacks of pressure and flow. The mathematical and simulation models of IMCPV, which have two types of pilot stage (high speed switching valve and proportional valve), were established respectively. The effects of the frequency and the output pressure of high speed switching valve on main stage were discussed. The higher the frequency of high-speed switching valve was, the faster the pilot flow was adjusted, hence the smaller the pressure in pilot chamber changed. As a result, the main spool movement and output flow were much more stable. When the pilot pressure output by high speed switching valve was appropriately raised, the control force on main stage was increased at the same time. Thereupon,the movement of main stage can be accelerated. The dynamic and steady state of two types of IMCPVs were compared with simulated and experimental results. On one hand, it was indicated in the steady state that the IMCPV with high speed switching pilot stage was not sensitive to dead zone and had higher flow gain. Whereas, the IMCPV with proportional pilot stage was much better at linearity and steady state. On the other hand, it was shown in the dynamic state that the response frequency of the IMCPV with high speed switching pilot stage was 20% higher than that of proportional pilot stage.The pressure and flow decoupling dual-level controller was designed based upon the feedbacks which were the pressure in both chambers of hydraulic actuator and the velocity of the hydraulic load. The first-level pressure controller of IMCPV was used to keep the backpressure of cylinder steady at IMPa. The second-level controller was used to control the pressure and flow of the IMCPV hydraulic system. The input of the second-level controller was the pressure in both chambers of hydraulic actuator and velocity of the hydraulic load and its output was the control signals of IMCPV, In this thesis, the simulated and experimental results of hydraulic cylinder with the step signals of 20mm/s and 100mm/s were compared. It was shown in the results that the adjustment time of velocity of hydraulic cylinder was 0.2s,the adjustment time of flow was 0.25s, and the steady-state error was less than 2.5%, when the input step signal was at 20mm/s. When the input step signal was at 100mm/s, the adjustment time of velocity was 0.5s,the adjustment time of flow was 0.55s, and the hydraulic cylinder had steady-state error of 5%.The control accuracy of displacements and velocities with multi-actuators were studied based upon the characteristics of independent metering control hydraulic system. It was shown in experimental results that the accuracy of displacement control was less than ±2mm when the input displacement was 1Hz, ±10mm and the accuracy of displacement control was better than that of velocity control.Furthermore,a new hydraulic system was developed for excavator equipped with IMCPV.By reprogramming the function of IMCPV,the typical hydraulic functions of excavator such as the positive flow control,traveling,slewing,flow priority and flow regeneration were carried out.The new hydraulic system was significantly simplified by replacing shuttle valvesand handlehydraulic signals with electrical signals. In order to achieve automatic control of excavator, the trajectory planning of the excavator bucket teeth was proposed using a time optimal method.This excavator can be used to dig straight trajectory automatically within 18.4s and the operational efficiency was improved by 15.64%.The thesis was outlined as follows:In Chapter 1, the motivation and significance of the research were pointed out. The research background and development status of IMCPV at home and abroad were presented. According to technical characteristics, the intelligent control system and trajectory planning of the excavator were classified. The research content and difficulties were discussed.In Chapter 2,the models of IMCPVs with high speed switching pilot valves and proportional pilot valve were established through theoretical analysis and dynamic simulation. As to IMCPV with high speed switching pilot valves, the effects of different parameters of high speed switching valves on main stage were studied. The test also compared the dynamic and static state between two kinds of IMCPVs. Besides, the IMCPV comprehensive experimental test bed was also built in this chapter.In Chapter 3, a new hydraulic system for excavator equipped with IMCPV was proposed. By reprogramming the function of IMCPV, the typical hydraulic circuits, such as the positive flow control, traveling, slewing, the flow priority and flow regeneration, can be realized. The IMCPV had the same structures and the functions changed according to different programs.In Chapter 4, firstly, the hydraulic model of IMCPV system was built. The digital pressure compensator was designed to guarantee the pressure drop of IMCPV. The flow feedback was calculated by using pressure sensors and LVDTs. Then, the pressure and flow decoupling dual-level controller was designed. The first-level was pressure controller to decouple pressure in two chambers of cylinder. The second-level distributed the pressure and flow of the hydraulic system. Through simulation and experiment, the adjustment time and steady-state characteristics of hydraulic cylinder working at low speed and high speed were studied respectively. Finally, the application of the controller with multi-actuators and errors of displacements and velocities were discussed.In Chapter 5, the virtual simulation platform and kinematics model of excavator with IMCPV excavator system were established. The forward & inverse kinematics solutions of the excavator operation device were studied to find out the relationship between spatial position of bucket teeth and hydraulic actuators' drive space. The trajectory of the bucket teeth was planned using the time optimal method. The displacements, velocities and accelerations of boom, arm,bucket and slewing can be derived.In Chapter 6, the results and conclusions were summarized and the future research prospective were proposed. |
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