Patent GB-1375786-A (GB)
IPC: B41J7/52
Filed: 1972-03-30
Abstract: 1375786 Control of printers HONEYWELL INFORMATION SYSTEMS Inc 30 March 1972 [21 June 1971] 15188/72 Heading G4H A positional control system for the print head of a serial printer includes logic 50, 100, Fig. 3, for determining the minimum displacements 52, 54, 102, 104 in each of two directions 46, 48 needed to move the print head to a new position, coarse positioning systems 56, 70, 76, 90, 92 and 106, 118, 124, 138, 140 which use these displacements to move the print head in each direction at a number of different velocity levels 60-64, 108-112, and fine positioning systems 82, 86, 88, 94 and 130, 134, 136, 142 that are switched on when the final velocity approaches 64, 112 to the new print positions have been completed. The print head 20, Fig. 2c is divided axially into eight bands and, circumferentially into twelve sectors; the location of a selected character is fed in USASC11 code to a TIMING CONTROL 40 (together with a signal 32), wherein it is separated into a band code B 3 B 2 B 1  and a sector code B 4 B 5 B 6 B 7 . These codes are fed to band and sector channels 46 and 48, while time delays in 40 Fig. 11, (not shown), are actuated by signal 32 to produce control signals 58, 59. Band channel 46.-Band code 42 is fed to a circuit 50, Fig. 6 (not shown), wherein it is compared with the stored code of the present band position of the print head: difference signals 52, 54 are gated into a BAND SERVO CONTROL 56, Fig. 10 by signal 58, where they set a counter 332. The output of counter 332 is fed to a range decoder 358 whose outputs are grouped to provide a velocity high, medium or low signal 60-64 to command motor 76 in the coarse positioning system; as the bands (Fig. 2c) are traversed pulses 90 or 92 (depending on whether movement is up or down) are used to decrement the counter, so that its output at any time indicates the number of bands still to be crossed. If no motion is needed, signal 59 causes a flip-flop 402 to send a signal 98 back to control 40, otherwise a COUNT=0 signal 362 from counter 332 causes a VELOCITY MODE SIGNAL 368 to allow signals 60, 62 or 64 and 66 or 68 to pass to a BAND FUNCTION GENERATOR 70. When the COUNT = 0, a signal 364 (together with signals 96 from 70 denoting transitions between velocity levels 60, 62 and 64) causes flip-flop 366 to switch from signal 368 to a POSITION MODE signal 94, which is also transmitted to GENERATOR 70. Generator 70, Fig. 12, comprises a circuit 430 which produces a step signal 428 in response to signals 60- 64, a circuit 434 which produces a ramp signal 432 in response to signal 428, and switching circuits 436, 438, 500. Signal 432 is gated by FET 492 or 494 on to line 514 or 516 (depending on signals 66, 68) and is fed, with a TACH VELOCITY feedback signal 80, to a differential amplifier 518, the resulting error signal 72 serving to control motor 76. When the velocity signals 60-64 fall to zero, POSITION MODE signal 94 gates an ANALOG POSITION signal 88 to amplifier 518; this signal effects the fine positioning, the TACH VELOCITY signal 80 being negligible by this time. Signal 88 and signals 90, 92 are obtained from a position transducer 82 which comprises a pair of magnetic resistors sensing gear teeth on a disk coupled to the motor shaft Fig. 15 (not shown). A sense amplifier 86 produces a sinusoidal signal 88 and two pulse trains 90, 92; the timing is such that the operative pulse train decrements the counter by one when it is still half a band away from the corresponding boundary. Thus the velocity output 60-64 becomes zero with half a band still to be traversed, and it is this half band which is controlled by the analogue signal 88. Meanwhile, under the influence of counter 332, a BAND READY signal is sent by flip-flop 402 (Fig. 10) back to CONTROL 40. Simultaneous reception of BAND READY and SECTOR READY signals 98, 146 causes delay circuits in 40 to produce a signal which actuates the printing mechanism, followed by signals 147 (to reset flip-flop 402) and 148 which loads the newly selected printing position into the store (150) in circuit 50 (and similarly in SECTOR CHANNEL 48) so that the entire process may begin again. Sector channel 48.-This is basically the same as channel 46, with the exception of circuit 100. This includes comparison logic Figs. 7-9 (not shown), which ensure that the shortest path between any two sections is chosen: rotation of the print head is clockwise if  NEW POSITION >< OLD POSITION and if #NEW POSITION-OLD POSITION # <> 6; otherwise, rotation is anticlockwise (Fig. 2A).