Actuator Speed Control Using Digital Hydraulics

Abstract

In the last few years, the energetic efficiency of hydraulic systems has been widely discussed. One approach that has a particular potential is digital hydraulics. According to recent research, digital hydraulics has several potential advantages when compared with traditional technology, such as improved energy efficiency and the simplicity and robustness of its components. In this context, the main objective of this paper is to discuss the speed control of symmetrical actuators using digital hydraulic principles. It is proposed a hydraulic circuit configuration based on use of several fixed displacement units instead of one pump, on/off directional valves replacing flow control valves, and a specific control strategy. An energy management device is also proposed. This device allows the digital hydraulic system to operate in motor mode as well as store energy, therefore, improving the efficiency. The modelling of the hydraulic system is carried out by AMESim software and the control is implemented in the MATLAB software. The simulations were carried out using a co-simulation technique. Initially, the speed behaviour of the digital hydraulic system, using different delay times applied to on/off valves, is analyzed. The cases where the smallest power loss and the best dynamic behaviour take place are identified. Based on this, the actuator speed behavior, flow rate on the on/off valves and actuators and the pressure in the fixed displacement units for different speed steps are studied. The preliminary results showed a small power loss in the digital hydraulic system when compared with the average efficiency of other hydraulic systems. The speed transitions had small oscillations and adequate dynamic behavior.