Patent ID: 6055219
Filing Date: 2000-04-25
Classification: G11B

Abstract:
A method for switching the read operation of an optical disc drive between the CLV mode and the CAV mode in response to the current radial position of a pickup head of the optical disc drive, the optical disc drive including a spindle motor for rotating an optical disc during the read operation, said method comprising the steps of:setting a selected radial position P.sub.s of the pickup head as a switching point, a period C.sub.T, a first constant C.sub.1, and a second constant C.sub.2 ;obtaining a first reference signal Vckrt1 of a frequency f.sub.Vckrt1 ;obtaining a signal Fgrt of a frequency f.sub.Fgrt which indicates the current speed of the spindle motor;moving the pickup head to the innermost radial position on the optical disc;counting the number T.sub.n of pulses in Vckrt1 that appear during one half period of Fgrt, and then obtain a position error signal n, where n=T.sub.n -C.sub.T ;obtaining a line speed ratio F.sub..beta. ;counting for the number T.sub.n1 of pulses in Vckrt1 that appear during one half period of Fgrt when the pickup head is located at a first new radial position P.sub.r, to thereby obtain a position error signal x, where x=T.sub.n1 -C.sub.T ;obtaining the radial position P.sub.r of the pickup head in accordance with ##EQU17## obtaining a second reference signal Vckrt2 of a frequency f.sub.Vckrt2 when the pickup head is located at the switching point P.sub.s, where ##EQU18## and switching the mode of operation from the CLV mode to the CAV mode, and changing the reference signal for the CAV mode to Vckrt2.