| There are two kinds of electro hydraulic servo system, namely, pump-controlled system and valve-controlled system. Compared with the latter, pump-controlled system has the advantages of saving energy, protecting environment having low failure rate, being convenient to fix and having the low installed cost. Meanwhile it also has the disadvantages of having slow response and low control accuracy. But because of the energy shortage, the pump-controlled system is definitely the result of the development of hydraulic control technology. The object of study is differential cylinder system controlled by pump in this paper, which focuses on how to reduce speed and motion stability and how to reduce the vibratory shock and noise in the system thus to realize the final research goal-to speed the practicality of pump-controlled system.Based on the different actuator, pump-controlled system can be devided into pump-controlled hydraulic motor and pump-controlled hydraulic cylinder, among which the latter can be further devided into pump-controlled symmetrical hydraulic cylinder and pump-controlled differential cylinder. As for the hydraulic motor and symmetrical cylinder, the volumes in the two cavities are equal, so they can be controlled by variable speed. Benefiting from the development of motor control technology, these two systems have bean widely used in many fields. On the other hand, as for the widely-used differential hydraulic cylinder, it has the different volumes in the two cavities and asymmetric flow. So in order to control the differential cylinder directly by pump, two problems-asymmetric flow and pre-pressure in the two cavities have to be handled firstly. To solve these problems, most studies adopts the compensation through hydraulic check valve by auxiliary pump and accumulator. A type of hydraulic pump with three outlets is introduced in this paper. Two of the outlets are connected with the two cavities of differential cylinder, and the third port is connected with tank. The flow through three ports can be distributed according to the volume ratio of the two cavities in differential cylinder, thus to balance the asymmetric flow and realize the purpose of directly controlling differential cylinder by hydraulic pump.The core component of pump-controlled hydraulic cylinder system is servo pump with variable displacement. This paper begin with the study of variable displacement hydraulic pump. The first is theoretical analysis of the kinematics and dynamics of swash-plate axial piston pump, and establish its mathematical equation. The simulation model of the axial piston pump is established in the Simulation X, through which the variable displacement and flow characteristics of the axial piston pump are studied. Next the simulation study of flow and pressure pulsation in the axial piston pump with three outlets in series is conducted in this paper. In order to reduce pulsating quantity, the damping structure of port plate is optimum designed,thus to fix the best parameter of triangular damping groove, reduce the pulsating quantity and provide vibration and noise reduction in axial piston pump with data support.At present, most servo variable pump have auxiliary pump in series, so it is a good choice that auxiliary pump can be used to balance the asymmetric flow in differential cylinder. According to the being-used control scheme, the pump-controlled different cylinders can be devided into dylinder with constant speed and variable displacement, cylinder with variable speed and constant displacement, and cylinder with variable speed and displacement. Due to the mature technology of speed adjustment in motor, the system of pum-controlled differential cylinder with variable speed and constant displacement develop most quickly. The three types of differential cylinder systems are elaborated in this paper, which focuses on the theoretical analysis, modeling and simulation and experimental research at two types of pump-controlled different cylinders—constant speed and variable displacement, and variable speed and displacement. Pump-controlled differential cylinder system, in fact, is the controlling of flow in variable pump. The pump flow equals to the product of pump speed and displacement. The controlling of variable speed and displacement is realized at the same time, which has the better control performance than the other two types of systems because of one more controlling degree of freedom. But meanwhile the complexity of this controlling system is enhanced, for such system becomes into nonlinear system in nature, which bring great difficulties in controlling system and dynamic analysis. In order to simplify the problem, the controlling way of taking variable displacement as main methods and variable speed as supplement is adopted. The control threshold of minimum speed is set up and displacement control signal is added up to the motor speed-control signal, thus to realize the compound control of displacement and speed, and improve the dynamic response speed. In this paper, the simulation models of pump-controlled differential cylinders with constant speed and variable displacement and with variable speed and displacement are established, which are used to study the dynamic features. The simulation result shows that the dynamic response speed of the differential cylinder with variable speed and displacement is faster obviously than that of the cylinder with constant speed and variable displacement.On the aspect of control strategies, the control mechanism of position servo, speed servo and pressure servo widely used in electro-hydraulic servo control are analyzed, position and speed hybrid control with load compensation is proposed in the system of pump-controlled differential cylinder. The force load compensation formula model is obtained through experiments and data fitting, then added the model up to position servo control signal, with this method can solve the disturbance by force load. The undisturbed switching of the speed feed-forward control and the position feed-back control is realized by designed the speed feed-forward control model and switch parameters.In order to verify the theoretic research, physical test stand is build to test the dynamic features of two types of pump-controlled differential cylinders afore mentioned. Meanwhile the speed and position curves of system when the differential position and speed make the compound servo in the differential cylinder with two types mentioned before are tested, which show that this type of compound servo strategy can control piston rod’s smooth running and accurate position. The testing result verifies the accuracy of theory and simulation study and provide is spread and application of pump-controlled differential cylinder with certain basis.In order to replace the valve-controlled system with pump-controlled system, the phenomenon of hydraulic shock in valve-controlled system is analyzed. In this paper, the hydraulic system of slipping arm of cinder scraper in blast furnace is the studying subject. The common passive buffering technique is analyzed and active variable damping methods is proposed. According to the simulation analysis and field measurement, the active variable damping method can reduce the hydraulic shock effectively. |
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