Objective lens driving system in a optical pick-up and method of modulating the resonance frequency of its lens holder

摘要

An objective lens driving system in an optical pick-up comprises a lens holder which has a shaft hole and holds an objective lens, a fixed member which has a journal inserted into the shaft hole, a magnet and a driving coil which are arranged opposite each other so as to generate a magnetic force for driving the lens holder along the journal and a magnetic piece which is arranged opposite the magnet to hold the lens holder at a predetermined neutral position using the magnetic force generated between the magnet and the driving coil while the driving coil is not excited and is magnetized until it is saturated by emf from the magnetic field generated by the magnet. Each of the magnet and magnetic piece has an associated magnetic flux density; the magnetic flux density generated by the magnet is larger than the saturation flux density around the magnetic piece.