| 摘要 |
PURPOSE:To realize accurate positioning of head on the track, by embedding an odd number of optical fibers in the magnetic head at odd-number times intervals of the track width of concentric circle form, projecting light from the central fiber, receiving light with the fibers at both ends, and findig the output difference. CONSTITUTION:An odd number of optical fibers 2a to 2c are embedded in a head 1 at intervals of black and white track width (2W+1), namely light reflecting property and light absorbing property of a magnetic disc 3. The central fiber 2a is used for light projection, and the both side ones 2b, 2c are used for light reception. Individually, light source such as LED, and photo detector such as photo diode are arrayed in the terminal part. The outputs of photo diodes 11, 12 arranged at the terminals of these 2b, 2c are passed through preamplifiers 13, 14 and variable gain amplifiers 15, 16, and the difference or sum of the both outputs is determined in circuit 17, 18. At a comparater 19, the output of a second circuit 18 is compared with the reference value Vr, and the gain of amplifiers 15, 16 is so controlled that the result of such comparison may be found within the setting range in the vicinity of the reference value. The differential output of thus controlled amplifiers 15, 16 is used as a position signal for servo mechanism. |
