In a lightweight planar parallel robot, unwanted linkage vibrations are induced during high-speed motion. The transfer functions from motor inputs to linkage vibrations are dependent on the robot configuration. In this work, we experimentally identify linkage vibrations by performing experimental modal analysis using lead zirconate titanate transducers. Then, the contributions of linkage modes are separated from configuration-dependent transfer functions. Through redefinition of vibration inputs, the flexible linkage dynamics is approximated by a linear dynamic model with variations of natural frequencies. Based on this simplification, a modal controller is designed to control two linkage modes. Experimental control results, yielding more than 50% reduction of vibration amplitudes of these two modes, validate the effectiveness of the proposed control strategy.