| 摘要 |
PURPOSE:To attain the accurate servo control with an optical memory device by forming a servo system so as to obtain zero from addition and subtraction carried out between the signal corresponding to the replacement of a focusing lens and the difference signal of an optical detector. CONSTITUTION:When a light spot is shifted from the center of a track, the reflected light quantity is varied to produce a difference between the photocurrents flowing through photodiodes 9a and 9b. An error signal Ed undergoes a subtraction with the signal voltage Et corresponding to the displacement of a focusing lens through an adder/subtractor circuit 15. In this case, a drive current is flowed to an actuator coil 6 to shift the focusing lens. Thus the difference between the signal Ed and the voltage Et is set at zero. The signal Ed contains a component which is approximately proportional to the displacement of the focusing lens. While the voltage Et is proportional to the displacement of the focusing lens. Therefore a proportion constant is selected and an addition/subtraction is carried out with no effect of the displacement of the focusing lens given to an error signal Em. Then the signal Em is defined as a tracking error signal component. Then a light spot can be fixed on a track regardless of the position of the focusing lens by constituting a servo system so that the signal Em is set at zero. |
