Open-looped pressure and volume control of multi-degree-of-freedom hydraulic systems

Although hydraulic systems are powerful, they are notorious for their power inefficiency and the requirement of multiple components, such as a large hydraulic supply unit and control valves. In this study, we aimed to simplify the hydraulic components of a centralized multi-degree-of-freedom hydraulic system by adopting on-off valves and synchronizing them with a servo pump. To achieve individual actuator pressure control, we proposed two control algorithms: the multichannel electrohydraulic actuator (MEHA) and the open-looped alternating pressure control system (APCS-OL). In the MEHA approach, the servo pump switches between the reference signal of each actuator by periodically opening or closing the valves. On the other hand, the APCS-OL system utilizes a servo pump that supplies a periodic source pressure, such as a triangular wave, and the valves operate by comparing the source pressure with the reference signal. Furthermore, we introduced two algorithms for volume control: the periodic switching mode and the hysteresis switching mode. In the periodic switching mode, the controller cyclically switches between the actuators. In the hysteresis switching mode, the controller triggers a switch if the estimated volume exceeds the error band by a specific threshold. The experimental results demonstrated successful control of both the pressure and volume of all actuators using the proposed algorithms in the multi-degree-of-freedom hydraulic system.