Frequency and stability enhancement of high-speed on-off valve for water hydraulic manipulator joint based on multistage voltage and sliding mode control

Water hydraulic manipulators are becoming indispensable heavy-duty tools in nuclear facilities due to their zero-pollution advantage. Due to the limited reliability and lifespan of hydraulic valves using water as the working medium, water hydraulic high-speed on-off valves (WHSVs), capable of delivering discrete flow rates, are commonly employed as control components for water hydraulic manipulators. However, low-frequency flow output of the WHSV can cause vibrations in the manipulator joint and even damage the structure. To improve the operating frequency of the WHSV and enhance the stability of the manipulator, a multistage voltage and sliding mode control (MVSMC) algorithm is proposed to regulate WHSV operation. The sliding mode controller is employed to control the pre-opening current and holding current of the WHSV, which significantly reduces the switching time and increases the maximum switching frequency (MSF) of the WHSV. The dynamic characteristics and MSF of the WHSV driven by double-voltage control (DVC) and MVSMC are measured. Compared to DVC, the opening time of the WHSV driven by MVSMC is reduced by 46.5 %, and the closing time is reduced by 24.6 %. The WHSV driven by MVSMC achieves an MSF of 253 Hz, which is 25.9 % higher than that achieved with the DVC method. An experimental platform with a WHSV-controlled cylinder is constructed to test the manipulator joint. Experimental results demonstrate that MVSMC reduces the vibration amplitude of the manipulator joint by 15.9 % and improves system stability. The proposed MVSMC provides an effective control approach to achieve high-frequency operation in water hydraulic manipulators.