Patent GB-1311821-A (GB)
Title: Electromagnetic positioning apparatus
IPC: H02P25/08
Filed: 1971-05-27
Abstract: 1311821 Letter sorting NATIONAL CASH REGISTER CO 27 May 1971 [27 Aug 1970] 17392/71 Heading B8A [Also in Divisions H1 and H3] In a diverter gate for, e.g. a postal conveyer a vane (Figs. 1, 2, not shown) is pivotally supported by a vertical shaft passing through a horizontal table to divert, e.g. envelopes to either the upper or lower side of the table, under which is carried a motor coupled to the shaft in which a rotor is magnetically movable from one defined position to another without oscillation or overshoot in response to external switching. In the motor (Fig. 4) a laminated stator 31 of magnetic material having twelve inwardly projecting polepieces 30a to 30b spacedly embraces a laminated rotor 36 of magnetic material having eight outwardly projecting polepieces 38a to 38h, which is coupled to the vertical shaft 29. Each stator pole has a winding, and the latter are series connected in groups of four; surrounding 30a, 30d, 30g 30j; 30b, 30e, 30h, 30k; 30c, 30f, 30i, 301; in respective phases I, II, III. In one index position, phase I is continuously energized and phase III is selectively energized so that rotor poles 38b, 38d, 38f, 38h are attracted to stator poles 30d, 30g, 30j, a while rotor poles 38a, 38c, 38e, 38g are counterattracted to stator poles 30c, 30f, 30i, 30l to establish the position shown in which the rotor poles are symmetrically disposed relatively to the stator poles. On de-energization of phase III, the rotor poles 38h, 38b, 38d, 38f align themselves with corresponding stator poles to effect 7¢ degrees counterclockwise solution and phase II is simultaneously pulsed to increase the kinetic energy of the rotor. After 15 degrees counterclockwise rotation phase II is again energized to counterbalance phase I and arrest the movement of the rotor in its second index position. On de-energization of a phase winding, the energy of its collapsing field is diverted into the phase I winding whose energization is momentarily strengthened to add kinetic energy to the rotor. For energization, phase I is continuously energized from source 42 (Fig. 5) through diode 46, while phases II, III are alternatively energized under control of flip-flop circuit 56 in response to vane position change pulses derived, e.g. from an address reader. Flip-flop 56 alternatively produces logic 1 on output 58, logic 0 on output 60, and vice versa; the respective outputs being sensed by differentiators 62, 63 firing Schmitt trigger 68 on changeover of the flip-flop to trigger oneshot multivibrator 70 delivering a logic 1 pulse for 6ms., which on cessation triggers oneshot multivibrator 76 delivering a logic 0 pulse for 6 ms. This output is supplied to transistorized AND gates 92, 114 and 108, 129 together with, respectively, the outputs 58 and 60 of flip-flop 56; transistors 148 or 206 being driven conductive when the appropriate gates receive + ve voltages at both their inputs, whereby Darling- ton pairs 170, 176; or 224, 230 are driven conductive so that phase II or III windings are mutually exclusively excited. De-energization of either develops a back EMF as the field collapses, which discharges through diode 248 or 250 and the phase I winding. Fig. 6 shows operating impulses of the circuit and energization of the respective change of state of flip-flops 56 develops opposed signals at 58, 60, the AND gate 92, 114 is enabled to excite phase II, and the differentiators 2 develop opposed pulses at 64, 68. A short pulse appears at 67 and on cessation generates a 6 ms. pulse at 22. On cessation of this an opposed 6 ms. pulse appears at 78 to disable the AND gate and de-energize phase II for that interval, after which it is re-energized. Phase III is necessarily de-energized when phase II is energized and vice versa, so that the rotor is impelled to change its position during the 6 ms. phase II pulse, swings under inertia during the subsequent 6 ms. interval, and on phase II reenergization is stepped into its final position displaced 15 degrees from its initial position without overshoot, in which it is held indefinitely by combined phase I and phase II oscillation until a further changeover of flipflop 56 initiates a similar return cycle.