Abstract
This paper presents a novel hydraulic system featuring a hydraulic differential cylinder directly connected to two fixed-displacement hydraulic pumps driven by independent electric servo motors. By controlling the velocities of these two electric servo motors, precise control over the motion of the hydraulic cylinder is achieved. This innovative system is referred to as a two-motor-two-pump (2M2P) motor-controlled hydraulic cylinder (MCC). Unlike valve-controlled cylinders, the absence of valve throttling in a 2M2P MCC significantly enhances the system’s energy efficiency. However, the load-holding function in four-quadrant operation enforced by legislation for hydraulic cylinders used for, for example, lifting crane booms, is difficult to implement in a 2M2P MCC. This paper introduces a novel 2M2P MCC capable of achieving passive load-holding functionality via minimum cylinder pressure control. A non-linear model of the system is developed in MATLAB/Simulink and validated experimentally. The degree of state coupling is analyzed through model linearization and the relative gain array method. A multi-input-multi-output control algorithm with a state decoupling function is designed and experimentally verified on a laboratory single-boom crane. The experimental results demonstrate the effectiveness of the proposed system and control algorithm under given operating conditions.
