Patent ID: 6490234
Filing Date: 2002-12-03
Classification: G11B

Abstract:
An optical disk reproducing device including a focus servo mechanism in which in response to reception of reflection beams from an optical disk by a photo detector, a received optical beam amount detection signal corresponding to the received optical beam amount and a position error detection signal with respect to a focusing position error are generated, and in response to the level of the detection signal of the received optical beam amount a focus servo controller is changed over to an automatic focus loop and through a control in a direction eliminating the position error depending on the detection signal of the position error, laser beams from a laser beam optical source are automatically focused with respect to the optical disk, characterized in that the focus servo mechanism comprises: a signal generation circuit which generates a signal for advancing or backing a focusing position of the laser beams with respect to the optical disk; a maximum value detection circuit which detects the maximum value of the detection signal of the received optical beam amount; and a level holding circuit which holds the level of the detection signal of the position error at the moment in response to the detection signal from the maximum value detection circuit, wherein the focus servo controller drives the signal generation circuit and causes to detect the maximum value through the maximum value detection circuit without changing over to the automatic focus loop, and thereafter performs a control of changing over to the automatic focus control, and by synthesizing the level of the detecting signal of the position error held in the level holding circuit and the level of the current detection signal of the position error, an automatic focusing is performed in the automatic focus control.