Focus control apparatus in multi-layered disk reading apparatus utilizing acceleration, deceleration and focus error signals to switch between layers of the disk

摘要

Focus control apparatus in a reading apparatus for reading a multi- layered disk having information recorded on a plurality of recording surfaces thereof. The focus control apparatus includes a signal generating system for generating an acceleration signal for forcing the objective lens to move in the optical axis direction of the light beam and a deceleration signal for braking the objective lens which has been forced to move. The apparatus further includes control circuit for supplying a lens driving system with the acceleration signal and the deceleration signal as the driving signal in response to a switching instruction for switching a recording surface from which information is to be read, and for supplying the driving system with the focus error signal as the driving signal after the generation of the deceleration signal, to focus the light beam on a target recording surface. The deceleration signal has a parameter which is a function of distance between the recording surface which has been read before the switching instruction is issued and the target recording surface. Preferably, either of the acceleration signal and the deceleration signal is a signal which is compensated for the influence of gravity acting on the objective lens.