Patent GB-1174446-A (GB)
Title: Improved Magnetic Film Unit Adapted to be Connected to an Ordinator.
IPC: G11B15/20
Filed: 1967-06-16
Abstract: 1,174,446. Magnetic data storage. SOC. INDUSTRIELLE BULL-GENERAL ELECTRIC. 16 June, 1967 [28 June, 1966], No. 27996/67. Headings G4C and G5R. [Also in Division H1] A magnetic film unit comprises equal numbers of angularly and axially staggered write heads and read heads mounted on a rotatable support to scan transverse tracks on a sprocket-holed magnetic film while the film is stationary, the film being driven stepwise by a device associated with a cycling shaft driven at half the speed of the head support and the assembly being controlled such that a transducing operation may be performed during either of two equal phases into which one rotation (cycle) of the shaft is divided and a subsequent single step advance of the film can only be performed during the course of the second phase of that or the following cycle. A number of such units (e.g. 3, 5 or 7) may form an input-output element connected to a data processor or ordinator, being allocated even and odd numbers and being subservient to a master unit allocated an odd number. Record details (Fig. 1).-Double-sprocketed, 35 mm. magnetically coated, cellulose acetate film 12 is scanned by four write and read heads axially spaced a distance D equal to threequarters of a film advance step P so that the four tracks forming a block are interlaced with the tracks of other blocks. Each track consists of a preparatory zone ZP containing a series of recorded binary O's followed by a locating 1, an operational zone ZE in which 12 characters, each of 8 bit, 1 parity, are recorded, and a terminal zone ZT containing binary O's. Head support (Fig. 3A).-The four read and write heads are respectively connected in series and coupled to the circuitry by transformers 38 (see Division H1) and the head support 28 is belt-driven via pulley 33 and a synchronous motor. A flanged drum 37, fixed to the support 28, is notched to pulse photo-cells CIE and CIL (not visible), corresponding respectively to the write and read heads, when each head reaches the locating binary 1 in the zone ZP. A further notch (ILS, Fig. 3b, not shown) in the disc 37 is located just before the end of a phase to avoid "losing" a phase during recording. The film 12 is guided by an electromagnetically-operated presser 21 and may be spaced from the heads by a spacer (not shown). Advance mechanism (Fig. 4B).-The film is advanced one sprocket hole at a time by clawed arms 59 horizontally reciprocated by cam 57 on a cycling shaft 52 connected through a 2:1 reduction gear to a pulley 51 belt-driven from the same motor as drives the head support. Energization of an electromagnet (80, Fig. 4A, not shown) releases a latch arm (81), fixed to shaft 70, to allow a spring (83) to rotate the arm (81) and thereby the shaft 70 to raise member 84 and engage the claws 69 with the film. When the film is thus advanced, a cam 58 engages roller 79 to retract the claws and re-engage the latch (81). An indexing disc (88, Fig. 4E, not shown) rotates with the shaft 52 to mask an ADVANCE photo-cell (CA) for “ of each cycle. In addition, the master unit has a second indexing disc (92) with two masking portions (93) to pulse a clock photo-cell (CH) for use in synchronizing the operation of a number of film units. A check advance (CVA) photo-cell (22, Fig. 2, not shown) on the deck plate of each unit senses the film sprocket holes to provide pulses indicating whether the film advance is correct or faulty. Input-output element (Figs. 6A, 6B).-Information to be transferred between a data processor 103 and transmit and receive film units is stored in a buffer register 99 including a series-parallel converter. Instructions, in the form of a 3-bit film unit code and 2-bit function, are fed from the data processor 103 to register 108 and via delay 106 to validation unit 115 which requires an incident detection logic circuit 97 to indicate whether the film unit addressed via the register 108 and decoder 109 is available or not. The circuit 97 receives signals from an advance control 96 supplied with signals from the advance mechanism indexing photo-cell CA and the check advance photo-cell CVA. The circuit 97 also indicates non-availability if the addressed unit is undergoing rewind, being synchronized with another unit or if the film presser 21 is faulty. READ instructions in register 108 are decoded at 111 and a read authorizing voltage fed to AND-gates 120 and 128. Pulses from the write head indexing photo-cell CIE are fed to register 117 which controls AND-gate 120 to open AND-gate 121, via OR-gate 118 and authorization register 119, when the read heads L1-L4 are appropriately positioned. If pulses from CIE reach AND-gate 120 before the read authorization voltage is set up at AND-gate 121, reading cannot commence until the succeeding phase. Character and word counters 100, 101 operate via the AND-gate 128 to provide a film advance signal when a block has been read. Operation of the read network 123 causes a timing pulse generator 112 to operate in sync. with the signals read instead of applying sync. pulses via R1 to terminal r 1  of the validation unit 115. WRITE instructions in register 108 are decoded at 110 to open AND-gate 130 when a pulse from the read head indexing photo-cell CIL passes through register 131 to thereby authorize a group of writing power amplifiers 134. Timing pulses R 1 , R 2  occurring respectively at the boundaries and centrally of the binary cells in each record track, are used by the digital modulator 136 to record the series of binary O's at the zones ZP and ZT of each track. As soon as the first write head indexing pulse from photo-cell CIE is stored in register 117, the latter returns-to-zero the buffer 99 and counters 100, 101, instructs transfer of the first character from the data processor 103 to the buffer 99 and causes recording of the locating 1 in the zone ZP. The characters are recorded until an end-of-block signal from counter 101 authorizes register 119 to initiate a check read which is conducted as a normal read operation and is subsequently followed by a film advance step. Synchronization of film units.-The optimum working relation between associated even and odd units and a data processor is when the units are in antiphase, whereby a transducing operation in one unit is accompanied by a film advance in the other. To ensure such relation, signals from the clock pulse photo-cell CH and the advance photo-cell CA of the master unit are employed by logic circuits (139, 98, Figs. 10, 11, not shown) to actuate a brake 95 on the motor shaft of the phase-faulty unit(s). If braking lasts longer than 4 secs., a warning lamp is lit.