GB980144A - Automatic tracking control for magnetic reading head - Google Patents

Abstract

980,144. Automatic alignment control systems. SPERRY RAND CORPORATION. Jan. 24, 1963 [Feb. 5,1962], No. 2988/63. Heading G3R. [Also in Division G5] A method for correcting non-alignment of a sensing head with respect to a magnetic information recording track, wherein a plurality of guidance signal sequences are recorded in individual tracks near the information track, comprises sensing the signals in the guidance tracks, comparing the signals, and adjusting the position of the head in accordance with the relative characteristics of the guidance signals. The recording surface 100 shown in Fig. 1 comprises four information tracks 102,104,106 and 108 and five guidance tracks 110, 112, 114, 116, 118. The tracks 110, 114, and 118 comprise a pattern of dots, e.g. bursts of 10 cycles of a 1.4 mc/s frequency, whilst tracks 112 and 116 comprise a pattern of dashes, e.g. bursts of 30 cycles of the same 1. 4 mc/s frequency. The output from the head HD1 passes to a filter 133 which separates the information signal and passes the guidance signal through an amplifier to a transformer 134. The secondary of transformer 134 is connected to a full wave rectifier, a filter, a D.C. restorer unit 160, and a filter, the output of which passes to a differential servo 122 which controls the lateral position of the head. If the head is central, the input to transformer 134 will be a sine wave of constant amplitude and the output on line 190 will be zero. If the head deviates to one side the sine wave input to transformer 134 will be modulated in amplitude, being larger during the dot intervals or the dash intervals according to the sense of the deviation; the output on line 190 is then a positive or negative voltage depending on the sense of the deviation. A unit 126, which may be an instruction register, provides a voltage to servo 122 to select the desired information channel and connects line 190 to terminal 192 or 194 according to whether the channel is odd or even, since the guidance tracks are oppositely orientated for odd and even channels. In a modification, Fig. 3 (not shown), the recording surface comprises a pair of adjacent guidance tracks on one side of a group of five information channels, then a further pair of guidance tracks and a further group of information channels. The head assembly includes a track sensing head and five information sensing heads, the output of the track sensing head being fed directly to amplifier 131. The track sensing head may be a single head reading both guidance tracks or may be a pair of heads each reading one guidance track.