Patent ID: 7518967

Claim:
A position control method for controlling a position of an object lens in a direction perpendicular to a tangential direction of a spiral track or of concentric tracks formed on a recording surface of a recording medium without a guide groove, said position control method comprising: a first step of trying to read a predetermined data recorded on the recording medium; a second step of determining whether or not the predetermined data is readable; and a third step of, according to whether or not the predetermined data is readable, switching a criterion for controlling the position of the object lens based on a tracking error signal, wherein the first step is performed when determining a type of the recording medium, wherein the predetermined data includes an address data, wherein: a first light source is used when the recording medium is determined to be of a first type, and a second light source is used when the recording medium is determined to be of a second type, wherein the third step comprises a step of, if the predetermined data is not readable, switching to a criterion that includes shifting an on-track determination position in the tracking error signal by a predetermined amount and controlling the position of the object lens with the tracking error signal, said on-track determination position of the tracking error signal being a position at which it is determined that on-track occurs, and wherein the predetermined amount equals half of a wavelength of a waveform of the tracking error signal.