Patent GB-773967-A (GB)
Title: Method and apparatus for making magnetic recordings
IPC: G06K19/06
Filed: 1955-04-14
Abstract: 773,967. Statistical apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. April 14, 1955 [April 16, 1954], No. 10752/55. Class 106 (1). Magnetic record marks representing different values are made on magnetizable record cards by moving the record cards past a recording head, applying an increasing A.C. voltage to the recording head during part of this movement and selectively determining the rate of voltage increase according to the value to be recorded. The rate of voltage increase is determined in accordance with the discharge of a condenser of predetermined capacity, condensers of different capacities being selected in correspondence with the value to be recorded. As shown in Fig. 4, the cards are separated one at a time from a stack and fed by two pairs of feed rollers under erasing heads 654 and recording heads 656, one for each card column, and the finished card is passed to a receiving tray. The initial movement required to advance a card to the first recording position is 3¢ in. and the card is divided into twelve horizontal rows (see Fig. 12), each having a depth of  in. so that the card feed corresponding to each recording operation will be  in. To enable the feed rollers to advance the card these two different steps they are driven through a differential gear mechanism from either of two driving shafts. The desired card advance is obtained by coupling the corresponding one of these two shafts by the energization of electromagnets controlling onerevolution clutches. The electromagnets are shown in the circuit of Fig. 9, coil 34, when energized, serving to advance the card 3¢ in. and coil 36 serving to advance it  in. The intensity of magnetization of each mark increases at a rate according to the value to be recorded, this being determined by the rate of increase of voltage applied to the recording head. The voltages corresponding to different digital values are shown in Fig. 11. As is shown the recording period is somewhat less than the  in. which the card is advanced for the recording operation on each row. The higher the digital value to be recorded, the greater the rate of increase of recording voltage to the maximum. A condenser 688, Fig. 9, determining the rate of increase of recording voltage is selected for each recording head by the depression of one of a column of ten keys 44, Fig. 4. The keys are mechanically interlocked so that only one can be depressed at once and a " no-entry " bar is arranged to be displaced by the depression of any key to open a contact 686, Fig. 9. The keyboard also carries a motor bar 54, Fig. 4, which is depressed to start the recording cycle when the keys have been set. A latch holds the motor bar depressed until the end of the recording cycle at which time a solenoid 56 is energized to release it. This solenoid also releases all the keys which have been set ready for setting up the following row. In the control circuit, Fig. 9, of the machine, switch SWL supplies power to the motor M, the heater transformer, and the D.C. power unit which has positive line 74, earth line 76 and negative line 78. When the motor bar 54 is pressed condenser 602 is charged through contacts 604, the pulse of current causing coil 34 to be momentarily energized so that the record card is fed into position for the first recording operation. The recording heads 656 are supplied with a recording voltage at 5 kc. and a high frequency bias voltage at 50 kc. This high frequency voltage is also fed to the erase heads to remove any previous magnetic markings. When a key is depressed to select any desired digit, e.g. 7 the contacts 48-9 of the " 7 " key close and contacts 686 open. One side of the condenser 688 is then connected to earth line 76 and the other side is connected via wire 692 through a low value current limiting resistance 710 to the cathode anode junction 694 of triode 698 and pentode 706. The grid 696 of 698 is connected through resistor 700 and contacts 608 to the positive line 74 so that the cathode of triode 698 is also made positive and charges the condenser 688. Pentode 706 is a constant current discharge device for discharging the selected condenser during the recording period at a constant rate. The rate of discharge is proportional to the capacitance of the condenser because the rate of discharge is always constant. When all desired keys are depressed, the " card-feed " key 62 is pressed and the recording operation begins. Key 62 closes contacts 612 picking relay R3. Coil 36 is then energized through contacts R3B. A switch 63 (Fig. 4) is closed by the presence of a card so that relay R2 picks when cam contacts Cl close. As soon as relay R2 picks, contacts R2C open thereby disconnecting grid 696 from positive line 74 so that the voltage of point 694 begins to fall at a rate determined by the condenser selected. Point 694 is connected to grid of triode 704 controlling the output of a cathode follower 712 the grid of which is connected to the 5 kc. oscillator. The output from cathode follower 712 modulated by triode 704 appears across cathode load 714 (see Fig. 10, not shown), and is connected to the grid of a pentode acting as a linear amplifier. The anode of the pentode is connected to the recording head 656. The pentode is arranged to cut off the voltage at a predetermined maximum level to prevent distortion of the voltage wave pattern due to non- linearity of the constant current discharge. Towards the end of the recording operation a second cam contact C2 opens to de-energize relay R2 which causes relay R4 to be picked and, through contacts R4A, energizes solenoid 56 releasing motor bar 54 and all keys. When twelve rows have been recorded the card passes beyond the switch 63 so that relat R1y is de-energized and a third cam contact C3 picks up relay R6. Contacts R6A energize clutch coil 34 to cause the next card automatically to be fed into recording position. Specification 773,966 is referred to.