Effects of non-tip external forces and impulses on robot dynamics

The dynamics of robot manipulation with arbitrary forces, torques, and impulses applied to any link in the mechanism are studied. Using the principle of virtual work, and formulating the Lagrangian dynamics with spatial vectors, a modification to a linear-time forward dynamics algorithm can express the equations of motion of a manipulator that has either time-varying or impulsive forces applied anywhere on the manipulator. This permits the efficient simulation of accidental contact, and of multiple contacts that arise naturally in dextrous manipulation. The authors have implemented the equations as part of a computer simulation of robot dynamics, to test the effects of various external loadings. The initial results were derived from the study of free, unpowered planar mechanisms of two and three links subject to gravity