| 摘要 |
<p>According to the invention, the actual position of a servo head is calculated by converting servo signals (PosN, PosQ) read out from a servo head (31) to digital signals every predetermined time and by making a digital operation circuit (50) operate on the basis of converted digital values. The method of calculating a predicted position of a servo head which is necessary for calculating the actual position of the servo head, is charaterized in that the moving speed of the servo head is calculated from the previous position and the current one, and a predicted next position of the servo head is calculated from the calculated moving speed and the time interval until the next time of calculating. Also, this invention is characterized in that when the actual position of the servo head calculated from its predicted position and the digital-converted servo signals is largely different from the predicted position used as the calculating basis, noise in the servo signals is considered as the cause and the predicted position is assumed to be the actual position leaving as it is, without using the calculated values as the actual position. Further, this invention is characterized in that the period of the servo signal read out from the servo head is measured in a state in which the servo head is moved at a predetermined speed by feeding a predetermined driving current to a motor after the power supply for driving a disc is switched on, and that the moving speed of the servo head is calculated from the measured period and the known distance corresponding to the period of the servo signal. <IMAGE></p> |
