1. Field of the Invention
The present invention relates to a rotation correcting apparatus and an optical disk apparatus that is used to record or reproduce data from an optical disk.
2. Related Art
In recent years, along the increase in rotation speed such as a CD-R/RW or a DVD-Drive, a drive unit that rotates a disk at near a limit rotation number of a disk motor and a pickup mechanism is being developed progressively. For example, techniques of increasing the data reading performance of a wobbling disk or an eccentric disk during a high-speed rotation and improving the accuracy of track jump and layer jump in a DVD double-layer disk is proposed (see Japanese Patent Application Laid-open Publication No. 2003-263760).
According to the technique described in the above document, a signal that follows the eccentricity or wobbling of the optical disk is A/D converted, and is stored in the memory. Based on the data stored in this memory, a pickup or a feed motor that shifts the pickup to a radial direction of the optical disk is controlled.
According to the above document, both a tracking servo system and a feed motor control system are subjected to eccentricity correction. However, the output from a feed motor control circuit that controls the feed motor makes no change irrespective presence or absence of eccentricity correction. A phase of a control signal from the feed motor control system is delayed from that of a control signal of the tracking servo system due to a phase delay in the feed motor control circuit. Therefore, when eccentricity correction is carried out in both the tracking servo system and the feed motor control system, the operation of the feed motor becomes unstable, because the actual eccentricity of the optical disk and the operation of the feed motor are not in the same phase. As a result, the servo control of the tracking servo system is not convergent.