| 摘要 |
PURPOSE:To stabilize the lead-in operation of a servo by changing a coefficient so that a phase margin of an equalizer characteristic may be larger in an intermediate band compared with a prescribed characteristic immediately after loop closing, and the prescribed characteristic may be obtained after a prescribed time with the gradual increase of a gain in the intermediate area according to time passage. CONSTITUTION:A controller 15 makes the characteristic of an equalizer 8 into that having the larger phase margin in the intermediate band at the time of the servo loop closing, namely at the time of a lead-in start, and changes the coefficient to determine the characteristic of the equalizer 8 so that the gain in the intermediate band may gradually increase according to the time passage and may return to the characteristic at the time of normal performance after the passage of a lead-in time. Consequently, since the characteristic having the sufficiently large phase margin in the intermediate band in the initial stage of the lead-in can be obtained, overshooting at the time of the lead-in can be sufficiently suppressed. Thus, the lead-in operation can be stably and surely attained.
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