Patent GB-1006768-A (GB)
Title: Thermal selective printer
IPC: B41J2/32
Filed: 1964-06-12
Abstract: 1,006,768. Selective signalling. NATIONAL CASH REGISTER CO. June 12, 1964 [July 2, 1963], No. 24544/64. Heading G4H. [Also in Division B6] Matrix-head thermal printers.- A thermal printer comprises two print heads 26, 27, Fig. 2, alternately selected for printing and each including a matrix of resistive elements 15 (Fig. 5, not shown) selected sets of which are energizable to produce selected characters on a thermally sensitive record tape 30 held in cooperative relationship with the heads by a platen 51. The printer further comprises a matrix 90 (Fig. 9, not shown) of magnetic cores C1A ... C5G, respectively corresponding to said resistive elements and each having a respective sense wire 341 (Fig. 11, not shown) coupled thereto and which is adapted to control a drive circuit 313, Fig. 8A for energizing the corresponding resistive element. The matrix 90 further includes a plurality of read-in wires 350 (Fig. 10, not shown) one for each different character to be printed and each coupled to that set of cores C1A C5G, corresponding to the set of resistive elements, which when energized produce the selected character and means for energizing any selected one of said readin wires 350 to switch the cores coupled thereto from a first to a second state of magnetization the switched cores being restored to said first state by a readout wire 340 coupled to all the cores. Printing operation; selective electric signalling.-On depression of a single character key, e.g. A an associated switch 80, Fig. 8A, closes thereby completing a circuit from line 103 to line 104 or completing a circuit from line 103 to lines 104 and 105 for dual character keys, e.g. 8/I. Concomitantly with the depression of the key a beam between lamp 406 and photocell 404 is interrupted and the output from the photo-cell is amplified by an amplifier 400 and applied to a trigger circuit 360, whose output pulse is applied to first inputs of two AND gates 424, 425 controlled by the outputs of a character selection flip-flop 380. The latter is settable by two operation keys LTR and FIG to cause letters or digits to be printed. Depending on which of the two keys has been depressed the pulse from the trigger circuit 360 will be passed by one or the other of the gates 424 and 425 to one or the other of two single-shot circuits 381 and 382. The output pulses from one or the other single-shot circuits are fed via an OR gate 392 and a clipping circuit 495, to a single shot circuit 470. The latter stretches the input pulse to a 15 m.sec. output pulse which is fed via an amplifier 490 to a delayed pulse forming circuit 515, producing a read-out pulse which is applied to the read-out wire 340 to reset those cores which were set by the energized read-in wire 350. Each core has its own sense wire (Fig. 11, not shown) respectively coupled to drive circuits 313 which are in turn respectively coupled to the resistive elements of each of the two print heads 26 and 27. Since only one head is active at any time the heads are selected alternately by a flip-flop 480 changing its state with each pulse thereby selecting one or the other of pulse forming circuits 333, 332. Letter-spacing arrangements.-The tape 30 is advanced in letter-spacing direction after every second character is printed and the pulses from the circuit 333 are used also as tape advancing pulses. These are applied via clipping circuit 536, Fig. 8B, and an OR gate 107 to a singleshot circuit 107 whose output pulses are fed via an amplifier 150 to a control circuit 165 of a servomotor 42 and also to a pulse stretching single shot circuit 197 whose output pulse is fed to a platen solenoid 50, Fig. 2, to retract the platen 51 from contacting the heads 26 and 27 during the tape advance. Continuous tape feed key actives.-To advance the tape continuously a tape feed key TF is depressed thereby rendering operative a freerunning multivibrator 112 the output signals from which are fed via a clipping circuit 137 to the OR gate 109. Each output pulse from the multivibrator 112 will cause the servomotor 42 to step and the tape 30 will be fed continuously while the key TF is depressed. Tape feeding, guiding and tensioning arrangements.-The thermally sensitive tape 30, Fig. 2, is advanced from a reel 29 mounted on a spindle 31 over idler rollers 36, 38, 40 past the printing heads 26, 27 and around a capstan 41 of the servomotor 42 from which it is directed by a guide member 43. A pinch roller 44 forcing the tape firmly against the capstan 41 is provided to permit the capstan to draw the tape past the print heads. As the torque of the servomotor is very low and may not be able to overcome the inertia of the reel 29 during the short time between steps of advancing of the tape 30 the idler roller 38 is mounted on a spring 39 which is flexed during rotation of the motor to allow the capstan 41 to draw the tape the requisite amount the restoring force of the spring 39 then unwinding the reel 29 and the proper tensioning of the tape being maintained by a pressure spring 37 and the idler roller 36. Platen construction.-To ensure that the tape 30 is held against the print heads 26, 27 during the printing operation a platen solenoid 50, Fig. 2, is provided whereby the tape is threaded between the print heads and platen 51, spanning two character widths, and mounted on the end of the armature of the solenoid 50. The platen is retracted during tape advance by energizing the solenoid 50 the platen 51 being normally spring-biased to force the tape into contact with the print heads. Keys.-The keys, Fig. 3, are of the type having a stem of a D cross-section and to prevent rotation of the keys small tabs 57, 58, 59 of a soft material, e.g. aluminium, being placed in each key bore and located to engage the flat portion of the D-section of the stems. The end of each stem is notched to accommodate parts 74, 75, 76 of associated key lever arms 71, 72, 73. Also associated with each key indirectly is a leaf spring electrical switch 80 whose spring contact 82 rests on a shoulder 83 of the respective key lever arm 73 the switch 80 being closed on depression of the key to complete an electrical circuit which effects the printing of the character corresponding to the depressed key Specification 973,200 is referred to.