公开(公告)号：JPH03214473A

公开(公告)日：1991-09-19

申请号：JP910390

申请日：1990-01-18

Applicant: SONY CORP

Inventor： MUTO TAKAYASU ,  HAMAMOTO HISASHI

IPC: G11B21/08

Abstract: PURPOSE:To prevent the runaway of a head travel means occurring by interrupting the travel of a head by controlling a servo device when the fact that no track detecting output is obtained appropriately is detected with an abnormality detecting means. CONSTITUTION:A reticle 9 and a scale 10 are provided with slits of prescribed interval, respectively, and light quantity made incident on a photodetector 11 in accordance with the turn of a heat arm 2 is varied, and the detecting output DET1-DET4 are outputted, and they are converted to differentiation signals, and the travel speed of the heads 4A-4D are detected. A multiplex circuit 15 receives the detecting output, and outputs a position detection signal Sp. A control circuit 40, when detecting the fact that no voltage in which a prescribed voltage is converted with an A/D conversion circuit 55 is obtained from a reference voltage source 54 after a speed control signal is generated, or the fact that no pulse generating at every traverse of a track is obtained from a comparator 21, interrupts the generation of the speed control signal. In such a way, it is possible to prevent the runaway of an arm 2 occurring, and to evade the damage of a magnetic disk and that of the heads 4A-4D.