| 摘要 |
PURPOSE:To attain an correct tracking and to simplify assembly adjustment by detecting the position of an objective lens from the difference between an offset signal and a position signal supplied from a detection element. CONSTITUTION:An objective lens 1 is constructed of an aperture plate 2 integrally formed with an opening part 2a, an LED 3 to be used as a light source and a semiconductor position detection element 4 sensing the light of the LED 3 through the opening part 2a, and grasps displacement in the direction perpendicular to the track of the objective lens 1. A subtractor 20 obtains a difference (I-1)-(I-2) between optical currents, while a subtractor 21 obtains the difference between said difference signal and the offset signal set by a bias correction circuit 22. The output of the subtractor 21 is taken out as an objective lens position signal, and the bias correction circuit 22 corrects the position with the position signal of a PSD 4 at the time of initial assembly as an offset amount. Thus merely the offset signal is adjusted in accordance with the misalignment of the objective lens at the time of assembly to make the mechanical position adjustment of the objective lens unnecessary, whereby the assembly adjustment is extremely easy. |
