In order to record or reproduce information on/from a target track on an eccentric disk by using a head, a disk device must drive the head make the head follow the target track whose distance from the center of rotation continuously varies due to eccentricity. Hereinafter, an HDD (Hard Disk Drive) will be described as an example.
FIG. 8 is a block diagram illustrating a conventional HDD. As shown in FIG. 8, the conventional HDD is provided with a magnetic head 819 for recording or reproducing information on/from a magnetic disk 815 to output a head position signal 806; an actuator mechanism for operating the magnetic head 819 on the basis of a magnetic head control amount signal 809; a phase learning unit 801 for learning a phase shift amount which is a phase difference between variations in the servo information number that are read by the magnetic head 819 and variations in the amount of eccentricity of the magnetic disk 815, and outputting a phase shift amount signal 812; a sinusoidal wave generator 802 for outputting an eccentricity sync sinusoidal signal 813 having the phase shift amount that is learned by the phase learning unit 801, at a frequency synchronized with the rotation frequency of the magnetic disk 815; an eccentricity control amount calculator 803 for multiplying the sinusoidal signal by a weight factor to obtain an eccentricity control amount, and performing learning of eccentricity amount and updation of weight factor to output an eccentricity control amount signal 804; a positioning controller 808 for adding the eccentricity control amount to an ordinary feedback control amount to calculate a magnetic head control amount for compensating the eccentricity of the magnetic disk 815 and making the magnetic disk 819 follow a target track, and outputting a magnetic head control amount signal 809; a subtracter 820 for subtracting the head position signal 806 from a target position signal 805 that is externally input, and outputting a positional error signal 807 as a result of subtraction; and a learning switch 811 for selecting whether learning of eccentricity amount and updation of weight factor are to be carried out or not.
When performing seeking of the magnetic head 819, the learning switch 811 is turned off, whereby the eccentricity control amount calculator 803 temporarily stops learning of eccentricity amount and updation of weight factor. After the operation of the disk device changes from seeking to settling, calculation of an eccentricity control amount is carried out using a weight factor that has been calculated just before the stop, and the learning switch 811 is turned on to resume learning of eccentricity amount and updation of weight factor when the magnetic head 819 enters in a predetermined positioning range, thereby preventing degradation of controllability during settling.
Further, when the magnetic head 819 is unintentionally moved due to an impact or the like applied from the outside and thereby the positioning error of the magnetic head 819 exceeds the predetermined value, the learning switch 811 is turned off to stop learning of eccentricity amount and updation of weight factor. When the magnetic head 819 enters in the predetermined positioning range, the learning switch 811 is turned on to resume learning of eccentricity amount and updation of weight factor, thereby preventing degradation of controllability.
In the conventional disk device described above, when performing seeking, calculation of eccentricity control amount, learning of eccentricity amount, and updation of weight factor are temporarily stopped. After the operation of the disk device changes from seeking to settling, calculation of an eccentricity control amount is carried out using a weight factor that is calculated just before the stop, and learning of eccentricity amount and updation of weight factor are resumed when the magnetic head enters in the predetermined positioning range. However, since the value of weight factor varies depending on the target track on which the magnetic head should be positioned, convergence of weight factor takes time, resulting in an increase in seek time.
Further, even when an impact or the like is applied from the outside, since learning of eccentricity amount and updation of weight factor are carried out until the positioning error of the magnetic head exceeds the predetermined value, there may occur cases where the eccentricity control amount is not correctly calculated, resulting in degradation of controllability.
The present invention is made to solve the above-described problems and has for its object to provide a disk device, a disk eccentricity control method, and a recording medium, which can reduce seek time, and stabilize positioning of head.