VDC-Based Admittance Control Of Multi-DOF Manipulators Considering Joint Flexibility Via Hierarchical Control Framework

Multi-degree-of-freedom (Multi-DOF) manipulators have shown a high potential for enhancing the flexibility and performance of robotic manipulations. However, the presence of unknown disturbance, including uncertain dynamics and external forces/torques, makes the control of a multi-DOF manipulator rather complicated, and the stability of the robotic system is hard to be guaranteed. In this paper, a virtual decomposition control (VDC)-based admittance control approach for multi-DOF manipulators has been proposed considering joint flexibility via hierarchical control framework. The joint flexibility is solved by a separate adaptive controller different from the manipulator’s links. The high-level admittance controller is built upon a low-level VDC-based inner control loop, which can deal with the complicated system dynamics (including the joint friction and joint flexibility) and modeling uncertainty. The external force/torque (F/T) is estimated with a generalized momentum-based interaction force estimation technique; thereby avoiding the cost of wrist F/T sensors. The robotic system’s stability has been guaranteed in both free-space motions and constrained motions using the specific features of VDC (proof of each subsystem’s virtual stability). The advantages and effectiveness of the proposed method in tuning the robot-environment dynamic behavior are demonstrated through experiments.