Classification and Review of Pump-Controlled Differential Cylinder Drives

Pump-controlled hydraulic cylinder drives may offer improved energy efficiency, compactness, and plug-and-play installation compared to conventional valve-controlled hydraulic systems and thus have the potential of replacing conventional hydraulic systems as well as electro-mechanical alternatives. Since the late 1980s, research into how to configure the hydraulic circuit of pump-controlled cylinder drives has been ongoing, especially in terms of compensating the uneven flow requirements required by a differential cylinder. Recently, research has also focused on other aspects such as replacing a vented oil tank with a small-volume pressurized accumulator including the consequences of this in terms of thermal behavior. Numerous references describe the advantages and shortcomings of pump-controlled cylinder drives compared to conventional hydraulic systems or electro-mechanical drives. This paper presents a throughout literature review starting from the earliest concepts based on variable-displacement hydraulic pumps and vented reservoirs to newer concepts based on variable-speed electric drives and sealed reservoirs. By classifying these drives into several proposed classes it is found that the architectures considered in the literature reduce to a few basic layouts. Finally, the paper compares the advantages and shortcomings of each drive class and seek to predict future research tasks related to pump-controlled cylinder drives.

Design and Application of Improved PDF Controller in Higher-Order System

This article focuses on improving PDF (Pseudo Derivative Feedback) controller and employing it in electro-hydraulic position servo system of pump-controlled cylinder. Based on PDF theory, the derivative controller has been improved according to zero-placement theory. System’s stability has been analyzed. Moreover, the improved PDF is compared to 1DF PID and traditional PDF through simulation using an approximated dynamic system model of a higher-order hydraulic system, which consists of PLC, digital valve, hydraulic cylinder and optical sensor. The results show that the improved PDF controller provides satisfactory control performance on contrast with 1DF PID control strategy and traditional PDF controller in hydraulic system.