| In this dissertation, load-sensing hydraulic system of forestry felling & cultivation machine executive mechanism was studied based on China Key Projects in the National Science & Technology Pillar Program during the Eleventh Five-year Plan Period:Research and development on key technology and equipment for Multi-function Forestry Felling & Cultivation Machine (2006BAD11A15). The operation & control property of the executive mechanism trajectory planning and hydraulic system pump with load match were investigated with the object of forestry felling &cultivation machine executive mechanism. The main works are listed as follew:The major action of executive mechanism were analyzed in this dissertation, which include boom lift, jib deploying and retracting, telescopic expansion, harvester head working, working arm rotation and other secondary action. The specialty demand of executive mechanism kinetics, compound action demand as well as the main technical parameters such as freedom, positioning accuracy, working area, maximum operating speed and hydraulic parameters were determined. The arm's motion driving force was calculated according to the analysis of operating condition. The executive mechanism is a type of special construction machinery with multi-degree of freedom. For the frequently start, brake, reverse, and dramatically change of external load, and much more shock and vibration for the mechanism, thus, the hydraulic system had to meet higher request. The power loss during the flowing of part hydraulic oil was analyzed in the open hydraulic system (open center valve system and close center valve system) and closed hydraulic system, the result showed that the load-sensing hydraulic system could be fit for the multi-actuator mechanism. Both of single hydraulic cylinder and two parallel hydraulic cylinders were introduced to analyze arm luffing mechanism. Luffing speed and luffing force (torque) were considered as the main parameters for the arm luffing mechanism. The expansion rate of luffing cylinder was calculated by geometrical method, and the force of luffing cylinder was determined by statics method. The hydraulic system parameters could be verified as the luffing cylinder parameters were calculated by the former parameters. The executive mechanism basic loops are the working arm loop and the harvester head loop. Control block are blocks of sandwich plate design assembly varied functions. According to the high-pressure variable displacement pump, the executive mechanism hydraulic control blocks selected the high pressure load-Sensing control block of sandwich plate design. The variable displacement load-sensing pump in the entire hydraulic system provides pressure oil for each device.Hydraulic model was established, which included the model of load-sensing pump, adjustable throttle, load-sensing pipe and actuator (load) etc. It can be indicated from the study of the hydraulic model that the actuator of the hydraulic system is a nonlinear time-varying system. The hydraulic system was simulated, while considerable attentions had been paid on the factors of the volume characteristics and the hydrodynamic force etc. in the entire manifold. The functional plot of load to pressure and load to flow can be obtained by the verification of the characteristics of load-sensing hydraulic system via simulation. It can be indicated that the flow output of load-sensing system just depend on the load-sensing valve opening degree and has no relation with the external load.The dissertation establishes the three-degree-of-freedom kinetic equation of the operating arm system, deduces the maximum operating speed equation, and analyses the impact of degree of freedom. From the analysis of the join force and position control used to solve the effective driving force and the joint driving torque, a 6-order control equation is obtained is found. In order to verify the hydraulic system, the paper had performed a motion simulation on actuator, and dipped out the relation between velocity and acceleration rate of the actuator end (the harvester head). The load-sensing hydraulic system of the executive mechanism possessed controllability and stability.The hydraulic mathematical models are derived for the electro-hydraulic proportional position control system and electro-hydraulic proportional velocity control system respectively in toolbox Simulink of Matlab. The simulation results are analyzed and the boom plant model of the electro-hydraulic proportional position control system and electro-hydraulic proportional velocity control system are given. The control parameters of executive mechanism the electro-hydraulic system were determined. The control pattern of executive mechanism the electro-hydraulic system based on CAN-Bus were designed.For verifying the energy saving effectand handling characteristics of the load-sensing system, experimental analysison which were made based on the physical prototype which was established for the experiment on the load-sensing hydraulic system of forestry felling &cultivation machine executive mechanism as a result. |
PDF Full Text Request