Patent GB-1446255-A (GB)
Title: Data storage medium transducer controlling apparatus
IPC: G11B5/55
Filed: 1974-01-28
Abstract: 1446255 Transducer controlling apparatus INTERNATIONAL BUSINESS MACHINES CORP 28 Jan 1974 [27 Feb 1973] 03860/74 Heading G5R [Also in Division G3] Apparatus for controlling the operation of a transducer 10 for performing data writing operations on tracks on a relatively moving record medium 15 is operative to automatically move the transducer into a first position in which it extends over any selected track and beyond one edge of said track and to subsequently automatically move the transducer into a second position in which it extends over the selected track and beyond the other edge of that track the apparatus placing the transducer in an erase mode when in said first position and in a write mode when in said second position. The data tracks are concentric annuli on a magnetic disc 15. The start of each track is marked by an index mark (17), Fig. 1 (not shown), detected by index transducers, and each track is divided into sectors each having a sector identification, ID, (19), at the start. A circuit 72, Fig. 2b, causes head 10 to be always in a read or a write mode, the head performing a D.C. erase operation in the write mode when there is no data input on line 66. To write in a particular track, a control 60, Fig. 2a, enters the desired track number over line 65 into register 32. A circuit 33 compares the contents of register 32 with those of a counter 31 indicating the current position of the head 10 and if the head is not at the selected track, circuit 33 gives an output on a COUNT UP line or on a COUNT DOWN line to AND circuits 34 or 35, respectively, whereby a latch 36 or 37, respectively, is set and controls a counter 51 via OR circuit 48 or 49, respectively, to add or subtract pulses passed to OR circuit 50 from a track access oscillator 42 via AND circuit 45 enabled by a SEEK TRACK signal on line 61 from control 60. The four outputs of counter 51 sequentially energize the four windings 20a, 20b, 20c, 20d of a stepping motor 20, the particular sequence determining whether motor 20 drives head 10, via lead-screw 21, towards or away from the centre of disc 15. Ten pulses from oscillator 42 are required to move head 10 by one track, i.e. by 0À01 inch, and at the tenth pulse counter 43 gives an output to reset latches 36, 37 via one-shot 44 and to update counter 31 via AND 40 and delay 38 or via AND 41 and delay 39. If the head 10 is still not at the selected track the sequence is repeated until the head is centred at the nominal position of the selected track resulting in a signal to control 60 on line 58 via OR 56 and inverter 57, control 60 then firing single-shot 46 twice to step head 10 inwards by two steps, i.e. 0À002 inch, offset inwards from the nominal track position. When in this position the head 10 reads the sector ID (19) of the required sector, control 60 over line 64 puts the head in the write mode whereby it performs a D.C. erase operation over the selected sector, whereafter control 60 fires single-shot 47 four times to step head 10 outwards by four steps, i.e. 0À002 inch offset outwards from the nominal track position. When in this position head 10 reads the sector ID again, the head is again put in the write mode but simultaneously with data supply on line 66, such data thereby being recorded on the chosen sector of the selected track. Head 10 is then stepped inwards by two steps so that it is centred on the nominal track position and thereafter reads such recorded data for verification. The head 10 has a gap width of 0À006 inch, whereby the apparatus effectively provides read tracks of 0À006 inch width with guard bands of width 0À002 inch on either side. In modifications, the inward and outward offset of the head may be only 0À001 inch, or the inward offset may be greater or smaller than the outward offset.