FIELD: physics.
SUBSTANCE: optical data storage medium is illuminated with a laser beam and the data medium is rotated via a constant linear velocity control method, taking into account the radial position where the laser beam forms a spot on the data medium. The rotation speed is varied according to the radial position on the data medium between two linear velocities. A focusing error signal and/or tracking error signal is generated. Focusing control and/or tracking control is performed over a laser beam which illuminates the data medium based on the focusing error signal and/or tracking error signal. Separate output signals of control loops for the focusing error signal and/or tracking error signal pass through predetermined types of frequency band-stop filters for the focusing error signal and/or tracking error signal in order to obtain residual errors of the focus and/or tracking error signal and compare the residual errors with predetermined reference values.
EFFECT: high accuracy of measuring residual errors caused by mechanical properties of the medium.
2 cl, 14 dwg, 3 tbl
