Stable Impedance Control of a Single Leg of Hydraulic Legged Robot Based on Virtual Decomposition Control

Even though the nonlinear model-based control method can solve the problem of compliant contact force for robot, it increases the complexity of highly nonlinear dynamics model-based control of the complex robot. As thus, a stable impedance control method based on virtual decomposition control (VDC) is proposed for a single leg of hydraulic legged robot. Firstly, the mathematical preliminaries of VDC is given out. Then, the single leg of hydraulic legged robot is linked with a massless virtual manipulator to be a combined manipulator. The combined manipulator is decomposed into the subsystems consisting of links and joint objects using the VDC approach. The virtual power flow and virtual stability features of VDC are utilized to analyze the kinematics, dynamics, control and virtual stability of the subsystems and the massless virtual manipulator. Meanwhile, the dynamics stability of the combined manipulator in the environment interaction is analyzed. Besides, the system control gain which can guarantee the system stability and ideal impedance performance is given out. Finally, the experimental results on a single leg system of hydraulic legged robot show that the proposed control method can not only reduce the robot contact force but also track the target impedance.