A pair of underdamped ratchets, coupled via a perturbed asymmetric potential, is shown to make a transition to a fully synchronized state wherein stable controlled transport is achieved when the coupling strength exceeds a threshold at which the collective dynamics is attained. This transition to collective transport is connected to a chaos-periodic/quasiperiodic bifurcation in which current reversal is completely eliminated. Based on the Lyapunov stability theory and linear matrix inequalities, we give some necessary and sufficient criteria for stable controlled transport and obtain an exact analytic estimate of the threshold (kth) for the onset of stable controlled current.