US Patent 7990824 Method for distinguishing unbalanced disc

A method for distinguishing unbalanced disc in an optical disc reproducing/recording apparatus, comprising following steps: moving an optical pickup head to a first position of an optical disc; rotating the optical disc to a predetermined rotating speed; transferring a focus error signal produced by the optical pickup head to a focus control voltage signal; controlling the optical pickup head by the focus control voltage signal to maintain a focus light spot produced by the optical pickup head on the optical disc; and distinguishing if the optical disc is an unbalanced disc according to the focus control voltage signal.