A Nonlinear Model-Based Variable Input Control for the Position Control System of HDU

During the motion process of a hydraulic drive legged robot, the hydraulic drive unit (HDU) of each robotic joint generally adopts an outer loop impedance control method based on a hydraulic control inner loop. The hydraulic control inner loop can be generally divided into two parts: position closed-loop control and force closed-loop control. When the position closed-loop control is adopted, the performance of the position control directly determines the performance of the outer loop impedance control. Therefore, it is important to design a high-accuracy position control method aimed at HDU. Based on the ideas above, this paper introduces the position control system. Through an HDU performance test platform, the deficiency of the position control system is studied, using different typical input signals and gait trotting input signals. Then, a model-based variable input controller (MVIC) is proposed and designed. This controller contains the hydraulic system’s built-in nonlinear and load characteristics. Finally, the control performance of the MVIC is proved experimentally under different working conditions. The experiment’s results indicate that the MVIC can improve the HDU position control performance significantly. These results can provide important guidance and lay the experimental foundation for control strategy for hydraulic inner loops with position-based impedance control.