On singular time-optimal control along specified paths

This paper presents a general necessary condition for singular time optimal control of robotic manipulation moving along specified paths. Early work [l], [7] ignored the issue of singular control, assuming bang-bang acceleration along the path. Recent work [6] has shown that the time optimal control can be singular if one of the equations of motion reduces to a velocity constraint. This paper derives a more general necessary condition for singular control. It is also proven that singular control cannot exist if the set of admissible controls is strictly convex, as is demonstrated for a two-link planar manipulator with elliptical actuator constraints.