This paper studies high performance robust motion control of linear motors that have a negligible electrical dynamics. A discontinuous projection based adaptive robust controller (ARC) is constructed. Since only output signal is available for measurement, an observer is designed to provide exponentially convergent estimates of the unmeasurable states. This observer has an extended filter structure so that online parameter adaptation can be utilized to reduce the effect of the possible large nominal disturbance. Estimation errors that come from initial state estimates and uncompensated disturbances are effectively dealt with via certain robust feedback at each step of the ARC backstepping design. Theoretically the resulting controller achieves a guaranteed transient performance and a prescribed final tracking accuracy. In the presence of parametric uncertainties only, asymptotic output tracking is also achieved. This scheme is implemented on an epoxy core linear motor. Extensive experimental results are presented to illustrate the effectiveness and the achievable control performance of the proposed scheme.