We present a modified recursive Newton-Euler method for computing some dynamic expressions that arise in two problems of fault detection and control of serial robot manipulators, and which cannot be evaluated numerically using the standard method. The two motivating problems are: i) the computation of the residual vector that allows accurate detection of actuator faults or unexpected collisions using only robot proprioceptive measurements, and ii) the evaluation of a passivity-based trajectory tracking control law. The modified Newton-Euler algorithm generates factorization matrices of the Coriolis and centrifugal terms that satisfy the skew-symmetric property. The computational advantages with respect to numerical evaluation of symbolically obtained dynamic expressions is illustrated on a 7R DLR lightweight manipulator.

We present a method that allows automatic reaction of a robot to physical collisions, while preserving as much as possible the execution of a Cartesian task for which the robot is kinematically redundant. The work is motivated by human-robot interaction scenarios, where ensuring safety is of primary concern whereas preserving task performance is an appealing secondary goal. Unexpected collisions may occur anywhere along the manipulator structure. Their fast detection is realized using our previous momentum-based method, which does not require any external sensing. The reaction torque applied to the joints reduces the effective robot inertia seen at the contact and lets the robot safely move away from the collision area. If we wish, however, to continue the execution of a Cartesian trajectory, robot redundancy can be exploited by projecting the reaction torque into the null space of a dynamic task matrix so as not to affect the original end-effector motion. This leads to the use of the so-called dynamically consistent approach to redundancy resolution, which is further elaborated in the paper. A partial task relaxation strategy can also be devised, with the objective of keeping contact forces below a user-defined safety threshold. Simulation results are reported for the 7R KUKA/DLR lightweight robot arm.