Research On Electro-hydraulic Proportional Control Systems Of The Major-Motion Mechanisms For Forging Manipulator

With the development of the technology and economic of our country, the demand for large forgings is increasing deeply, thus the heavy load and automation are the main direction of the forging equipment. Forging manipulator, whose dexterity under heavy load increases the efficiency of the forging, is large ancillary equipment for the forging press in a free forging center. As auxiliary equipment, the manipulator has to cooperate with the movement of the forging press closely, so the control performance of the manipulator is very important. In a forging manipulator, all the movements are controlled by the electro-hydraulic system and its control performance has an impact on the property of the manipulator, thus the design and control of the electro-hydraulic system is one of the key technologies for the forging manipulator. Extreme environment, complex working condition and heavy load bring challenges to the control of the systems, especially the electro-hydraulic systems of the major-motion mechanisms, including front and rear lifting systems, pitching system and buffering system, as they are coupling together. In this condition, how to get precise control under heavy load and good buffering performance during the corporation work is the main problem for the electro-hydraulic systems of the forging manipulator.In this dissertation, the electro-hydraulic systems of the major-motion mechanism for a heavy duty forging manipulator are designed and mathematic models are built accordingly. The plastic deformation and elastic deformation models of the forging, and the kinematics and dynamics of the major-motion mechanism are built in the dissertation, combined with the mathematic models of the electro-hydraulic systems, the co-simulation model of the major-motion mechanism is built in MATLAB/Simulink. With the co-simulation model, the characteristic of the loads for the hydraulic systems is studied, and the control characteristic of the lifting system is analyzed. In order to improve the control performance of the lifting system, the influence of heavy load and hose of the system are studied, then spool displacement compensation is designed based on the characteristics of the proportional valve and hose compensation is designed based on the mathematical model of the rubber hose. Both simulation and experiment results show that the compensation strategies are effective in improving the displacement tracking precision of the lifting system. With the digital prototype, the coupling characteristic of the major-motion mechanism is analyzed and control strategy for the pose of the clamp is designed. In order to improve the buffering performance of the clamp, a stretching process of a flat-tool is simulated and it is shown that the vertical buffering performance of the clamp will be improved by increasing the tracking precision of the lifting system and the horizontal buffering performance of the clamp will be improved by arranging well-adjusted accumulators to the buffering system.The main contents of the dissertation are presented as follows:In chapter1, the working principle and the developing history of the forging manipulator in our country and abroad were outlined, the drive and control technology of the electro-hydraulic system and the common structure of the forging manipulator were summarized, the researching background and significance were also analyzed and the main contents of the subject were introduced.In chapter2, the characteristic of major-motion mechanism was analyzed according to a heavy duty forging manipulator and the schematic diagram of the lifting systems, the pitching system and the buffering system were designed. Simulation models of the hydraulic systems were built in MATLAB/Simulink based on the mathematic models of the components in the hydraulic circuits. Aiming at the fundamental motion, the control performance of the lifting system and the buffering performance of the buffering system were preliminarily studied.In chapter3, one new type heavy load forging manipulator was introduced and the loads of the hydraulic systems, including the plastic deformation and elastic deformation of the work piece and the dynamic model of the major-motion mechanisms. The co-simulation model of the work piece, the mechanism and the hydraulic system was built. Then equivalent gravity loads and equivalent inertia loads of the hydraulic systems were calculated with the co-simulation model, the characteristic of the load was analyzed.In chapter4, the lifting system of the forging manipulator was studied, and it was shown that the rubber hose connected from the control valve to the cylinder, the dead zone and low natural frequency of the proportional valve make it difficult to get good tracking precision. Aiming at these disadvantages of the lifting system, spool displacement compensation and hose compensation strategies were designed based on the mathematical model of the system.In chapter5, simulation model of the lifting system was built in the environment of AMESim and the compensation strategies were tested in comparing with traditional PID control. Displacement tracking test rig of the lifting system was built according to the lifting system of the forging manipulator. Comparative experiments were carried out between the optimal traditional PID control and P control with the compensation strategies. Besides, the simulation model of the lifting system was linearized in AMESim, and the stability was studied and results showed that it is independent of the compensation strategies.In chapter6, the coupling characteristic of the major-motion mechanism and the motion control property of the clamp were analyzed, the motion control strategy of the clamp was designed, and the quick forging mode of the manipulator was studied with the control strategy. Aiming at the stretching process of a plat-tool, the buffering behavior of the clamp was simulated with the co-simulation model. The effect of the displacement tracking performance and the accumulator were studied based on the optimization of the lifting and the buffering systems.In chapter7, the main results and conclusions were summarized, the achievements were concluded, and suggestions were provided for the future work.