Wrench Estimation of Modular Manipulator with External Actuation and Joint Locking

This paper proposes an external wrench estimation method for modular manipulators, where each link module is driven with external actuation (e.g., rotors, thrusters) and inter-module joints can be locked to increase end-effector stiffness or workforce of the manipulator. For such systems, the commonly-used momentum-based observer (MBO [1]) is not suitable due to the presence of unknown joint locking (JL) torque and also the degeneracy of Jacobian transpose relation with the system degree-of-freedom (DOF) becoming less than six with the joint locking. To overcome this, we propose two novel external wrench estimation algorithms: a distributed algorithm based on recursive Newton-Euler dynamics and a centralized algorithm based on D'Alembert's principle, both using an F/T (force/torque) sensor at the base. Experiments are conducted to demonstrate the effectiveness of the proposed algorithms.