The Research On Control Strategy Of Pump Controlled Differential Cylinder

Fluid power technology has been widely used in construction and agricultural machinery with the advantages of large power-density ratio, continuous variable transmission ratio and so on. However, economic and environmental factors make energy efficiency became a big concern of many research institutions in the recent years. Much progress has been made to improve fluid power energy efficiency from many aspects. Among these approaches, using a displacement controlled (DC) system to replace a traditional valve-controlled system showed eminent energy reduction. For this issue, this thesis studies pump displacement controlled actuators from the view of controls background.The thesis will focus on the control strategy design of pump displacement control and actuator displacement control of closed loop displacement controlled (DC) differential cylinder. The control and hydraulic co-simulation model for DC differential cylinder is built with AMESim and Matlab.In order to design control strategy, nonlinear models are derived for variable displacement pump and pilot-operated check valve and linear actuator. Reduced pump model are used in the design of sliding mode control (SMC) for pump displacement control. SMC law is robust in controlling pump displacement in spite of uncertain control pressure and swash plate moment. Four-Quadrant operation of DC differential cylinder is defined depending on the direction of load and velocity.This thesis presents the first time formulation of an adaptive robust control (ARC) for pump controlled differential cylinder. The proposed control scheme, ARC, ensures system stability and robustness for a wide range of motion. Furthermore, changes in plant behavior are estimated by online parameter adaption. In chapter five, the ARC results are compared to conventional PI plus velocity feedforward (PI+FF). Results show that the advantage of online parameter adaption of ARC leads to a dramatic increase in actuator position accuracy.The proposed novel control strategy, SMC and ARC, are simple and easy to implement, which are benefit of industrial implementation for pump controlled differential cylinder.