Patent ID: 7548493

Claim:
Device for scanning a track on a record carrier via a beam of radiation, the track comprising marks representing information, the device comprising a head ( 22 ) for providing the beam and generating at least one sensor signal, the head comprising a focusing element, a focusing unit ( 25 ) for controlling the focusing element ( 34 ) to maintain an in-focus position for generating a focused spot on the track in dependence on a displacement signal based on the sensor signal, the displacement signal being indicative of a displacement of the focusing element with respect to an in-focus position, the sensor signal having overlapping ranges of sensor signal values for different ranges of the displacement, wherein a multitude of piecewise converters ( 42 , 43 , 44 ), each converter converting a range of the sensor signal values into a first, second and third position signal, and selection means ( 46 ) for comparing the first, second and third position signals with an estimated displacement signal and for selecting one of the first, second or third position signals as the displacement signal based on an estimated displacement.