Patent ID: 7460455

Claim:
A method used in an optical storage device comprising a pickup head, wherein the pickup head comprises an object lens, a first light source, and a second light source, the object lens focuses laser light generated by the first light source onto a first focal point or focuses laser light generated by the second light source onto a second focal point, the first focal point is a predetermined distance from the second focal point, a driving control effort is used to change a location of the object lens, and the method is used to determine a relationship between the difference of the object lens location and the driving control effort, the method comprising: (a) turning on the first light source; (b) providing the driving control effort to move the object lens; (c) measuring a first parameter when the first focal point passes through a predetermined layer of an optical disc; (d) turning off the first light source and turning on the second light source; (e) measuring a second parameter when the second focal point passes through the predetermined layer of the optical disc; and (f) determining the relationship between the difference of the object lens location and the driving control effort according to the predetermined distance, the first parameter, and the second parameter.