A discrete-time learning control for robotic manipulators is studied u
sing its pulse transfer function. Firstly, the discrete-time learning
stability condition which is applicable to single-input two-outputs sy
stems is derived. Secondly, the stability of the learning algorithm wi
th a position signal is studied. In this case, when the sampling perio
d is small, the algorithm is not stable because of an unstable zero of
the system. Thirdly, the stability of the algorithm with position and
velocity signals is studied. In this case, we can stabilize the learn
ing control system which is unstable in the case of learning with only
the position signal. Finally, simulation results on the trajectory co
ntrol of robotic manipulators using the discrete-time learning control
are shown. The simulation results agree well with the analytical resu
lts.