Displacement Control Method of Hydraulic Servomotor Based on Swashplate Moment Disturbance Compensation

Hydraulic servomotor is a common energy-saving hydraulic power component that can switch between pump and motor operating conditions. Precise displacement control of hydraulic servomotors is crucial for minimizing throttling losses and enhancing overall efficiency. Nonetheless, the accuracy of hydraulic servomotor displacement control is negatively impacted by high-frequency uncertainty disturbances in swashplate moment. Traditional adaptive robust control methods have overlooked this factor, resulting in suboptimal displacement control effectiveness. To address this issue, a swashplate disturbance compensation robust control approach is introduced in this article, aiming to enhance the control accuracy of hydraulic servomotor displacement under high-frequency uncertainty disturbances. In the article, a mathematical model for the servomotor displacement adjustment system is formulated, and an average disturbance model for the moment of a swashplate is developed to account for periodic disturbances and uncertainties. Comparing experimental results of sine commands at different frequencies reveals that the proposed method achieves a substantial enhancement in displacement control accuracy. Specifically, the proposed method demonstrates a maximum improvement of 39.2% and 27.4% in displacement control accuracy compared to the PID method and traditional adaptive robust control, respectively. Note to Practitioners - The motivation of this article is to solve the displacement control problem of axial piston hydraulic servo motors, but it is applicable to other axial piston variable pumps and variable motors. There is a high frequency of pressure pulsation during the operation of variable hydraulic pumps and variable motors, which significantly affects the accuracy of the displacement control. However, traditional displacement control methods do not account for the pulsation inside the casing, leading to lower control accuracy. To address this issue, this article proposes a new control method aimed at enhancing the accuracy of displacement control in hydraulic servo motors. The proposed method involves modeling the disturbance torque experienced during the swashplate movement of hydraulic servo motors, analyzing the variable mechanism, and incorporating compensation for this disturbance into the control signal. This approach ensures precise displacement control during the operation of hydraulic servo motors and enhances the operational efficiency. The newly proposed control method has undergone rigorous stability testing, and initial experiments have demonstrated its feasibility. In comparison to traditional control methods, the accuracy of displacement control has been enhanced by approximately 10% to 40%. However, a limitation of the proposed control method lies in the restricted number of sensors located on the housing of the hydraulic servo motor. As a result, the method lacks full sensor information and can only make use of estimated values from the state observer in place of actual measurements. In future studies, efforts will be directed towards resolving the sensor acquisition challenge to further augment the accuracy of displacement control.