This article studies the cavitation performance and preventing method of the hydromechanical pressure compensation independent metering system (HPCIMS). Compared with the conventional load sensing system (CLSS), the meter-in and meter-out orifices of HPCIMS can be regulated independently. A quasi-static behavior analysis of cavitation performance was applied to the HPCIMS and CLSS. The meter-in pressure equation of HPCIMS showed that keeping the ratio of the meter-in and meter-out orifices greater than the minimum value can avoid the cavitation phenomenon. Systems parameters were then kept as constant, and the key parameters related to cavitation performance of the two systems were compared by varying external force. Comparison results show that the cavitation phenomenon in the meter-in chamber of CLSS with the external active load is inevitable, but in HPCIMS, it can prevent the cavitation phenomenon by changing the ratio of the meter-in and meter-out orifices, so the HPCIMS has the cavitation prevention potential.

Hydraulic drive unit (HDU) is a typical actuator, but the characteristic of input delay hinders the application of many advanced control methods in HDU. First, in this paper, a mathematical model of HDU with input delay is established and the parameters are identified. Then, aiming at the input delay problem in HDU, a Smith estimated compensation model predictive control (SECMPC) strategy is proposed. On the one hand, the input delay state equation is employed to be a mathematical pattern for the state observation and predictive model. However, the combination between model predictive control (MPC) and Smith estimated compensation (SEC) is realized, the system state at k + d (d is the time delay coefficient) time is estimated in advance at k time to compensate the delay of the state. And then the prediction model based on input delay state equation is used for model prediction and rolling optimization. Thus, the delay system which is unstable is promoted to a stable system without delay. The effectiveness of SECMPC is proved with the HDU experiment and simulation; the maximum experimental displacement error of traditional MPC control is 15 mm, while that of SECMPC control is 8 mm. The SECMPC have some guiding significance for the control of systems with input delay.

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The electrohydraulic leveling system of the hydraulic press can realize automatic leveling control function. In order to eliminate the eccentric load force accurately, an electrohydraulic leveling system with independent metering is designed. Quasi-static behavior analysis of the leveling cylinders output forces performance is applied to the electrohydraulic leveling system with independent metering. The angle and force hybrid control method is proposed, and then the AMESim/Simulink cosimulation model is built. The HSIC controller and PID controller are used in the simulation, respectively. Simulation results show that both of the leveling angle control and leveling cylinders output forces control can be realized, simultaneously, and the HSIC controller has higher rapidity and smaller overshoot than the PID controller.

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