Stability-Guaranteed Impedance Control of Hydraulic Robotic Manipulators

In challenging robotic tasks, high-bandwidth closed-loop control performance of the system is required for successful task completion. One of the most critical factors inhibiting the wide-spread use of closed-loop contact control applications has been the control system stability problems. To prevent unstable system behavior, the need for rigorously addressed manipulator dynamics is substantial. This is because the contact dynamics between a manipulator and its environment can be drastic. In this paper, a novel Cartesian space impedance control method is proposed for hydraulic robotic manipulators. To address the highly nonlinear dynamic behavior of the hydraulic manipulator, the system control is designed according to the subsystem-dynamics-based virtual decomposition control (VDC) approach. The unique features of VDC (virtual power flow and virtual stability) are used to analyze the interaction dynamics between the manipulator and the environment. Based on the desired impedance parameters and stability analysis, an explicit method to design the control gains for the proposed impedance control law is developed. The L2 and L8 stability is guaranteed in both free-space motions and constrained motions. Experimental results demonstrate that the hydraulic robotic manipulator is capable of adjusting its dynamic behavior accurately in relation to the imposed target impedance behavior. This provides compliant system behavior, which is needed in many dynamically challenging robotic tasks.