A method and apparatus position a beam spot on a recording medium. The
positioning includes (a) observing a first center error in a first closed
loop control during tracking mode, the first center error including a
repeatable run out (RRO) error, (b) estimating a center error (CE)-RRO
from the first center error, the CE-RRO being part of the first center
error caused by the RRO, (c) observing a second center error in a second
closed loop control during a rough seek, (d) subtracting the CE-RRO from
the second center error, (e) controlling the beam spot based on the
second center error less the CE-RRO during the rough seek, and (f) adding
an open loop control to the second closed loop control during the rough
seek, the added open loop control inducing a motion of the lens relative
to an optical center of the OPU during the rough seek.