Objective lens unit and method of assembling objective lens unit

An objective lens unit comprising:

• a base frame having a supporting shaft provided uprightly on a center thereof;
• a lens holder having a boss portion formed in a center thereof and fitted to the supporting shaft so as to be slidable along a direction of an axis of the supporting shaft and to be capable of oscillating about the axis;
• a focusing coil externally fitted on the boss portion;
• a pair of tracking coils respectively disposed on both side surfaces of the lens holder;
• a pair of magnets respectively disposed on both side portions of the base frame with the lens holder interposed therebetween;
• and
• reinforcing frame portions formed along an outer peripheral surface of each of the tracking coils by applying an adhesive to portions between the lens holder and the outer peripheral surface of each of the tracking coils.

A method of assembling an objective lens unit, the method comprising:

• providing an objective lens unit including a base frame having a supporting shaft provided uprightly on a center thereof, a lens holder having a boss portion formed in a center thereof and fitted to the supporting shaft so as to be slidable along a direction of an axis of the supporting shaft and to be capable of oscillating about the axis, a focusing coil externally fitted on the boss portion, a pair of tracking coils respectively disposed on both side surfaces of the lens holder, and a pair of magnets respectively disposed on both side portions of the base frame with the lens holder interposed therebetween;
• applying a thermosetting adhesive to portions between the lens holder and an outer peripheral surface of each of the tracking coils;
• filling the thermosetting adhesive into a central hole of each of the tracking coils;
• filling the thermosetting adhesive into a gap defined by the lens holder, each of the tracking coils, and the focusing coil;
• and
• curing the thermosetting adhesive by heating, thereby forming reinforcing frame portions along the outer peripheral surface of each of the tracking coils, forming reinforcing core portions in the central hole of each of the tracking coils, and forming a reinforcing connecting portion in the gap defined by the lens holder, each of the tracking coils, and focusing coil.