Comments on "On the robust control of robot manipulators by M.W. Spong

In the above-title paper (ibid., vol.37, no.11, pp.1782-1786, Nov. 1992) a simple robust control is given for guaranteeing uniform ultimate boundedness of tracking errors for n-link robot manipulators. It is pointed out here that an equally simple control law, which is also continuous in nature, can guarantee global exponential stability of tracking errors under the same set of conditions.>