GB1509957A - Servo arrangement for adjusting the position of a transducer relative to a movable magnetic recording medium - Google Patents

Abstract

1509957 Automatic position control BASF AG 15 Aug 1975 [17 Aug 1974] 34019/75 Heading G3R [Also in Division G5] In a transducer position servo arrangement, a magnetic recording medium has an information signal track and an adjacent reference track formed by a single line transition between differently magnetized regions. The transducer head has at least one air-gap and is moved in an alternating manner relative to the reference track to produce a voltage signal indicating misalignment which is used for correcting the transducer position. A magnetic recording medium 1, which may be a rigid disc or a flexible coated foil disc, carries data tracks 2 and reference tracks 3 extending parallel to the data tracks and defined by line transitions between regions of differential magnetisation. These lines 3 are used for servo positioning of a magnetic data head and may be formed alongside, within, or in a layer beneath the data tracks. The data and reference tracks may be read by a flux sensitive Hall transducer or a flux variation induction sensor oscillated transversely to the tracks. The transducer may have two air gaps, or a single gap sensing both tracks and producing a composite signal which is separated into data and servo components by a filter circuit. One embodiment of the transducer, Fig. 9, has an air gap 43 for reading the data tracks 2, and a perpendicular gap 46 for reading reference tracks 3. Data signals are derived from a coil 47 associated with a magnetic circuit formed by pole pieces 40, 41, 42, airgap 43, and staggered yoke portions 44, 45. Servo positioning information is provided by a coil 48 which is wound on the yoke portion 45 only, and has a magnetic circuit comprising pole pieces 41, 42, gap 46 and yoke portions 44, 45. Both gaps may operate on the flux proportional or flux variation proportional principle. In the case of an oscillating servo track reading gap, following a path d with respect to a reference track 3, Fig. 10a, pulses are produced each time the track is crossed, Fig. 10b. The pulses are shaped to constant duration form, Fig. 10c, and used to control the charging and discharging at constant rate of an integrating capacitor, Fig. 10d. The magnitude of the capacitor voltage at alternate transition times to, t 2 , t 4 is stored as a step voltage function, Fig. 10e, which represents the direction and magnitude of the deviation of the transducer from the track 3 and is used as a servo signal to correct the transducer position. A further embodiment of the transducer is described with reference to Figs. 6, 7 and 8 (not shown).