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. •A hierarchical control framework is proposed for multi-DOF manipulators.•A VDC-based adaptive controller is provided for joint flexibility to solve system dynamics.•An admittance control based on low-level VDC is presented to achieve compliance with high control bandwidth.•Rigid stability proof and motion/force convergence proof are presented.•Experimental demonstration is provided to verify the proposed approach.