Patent GB-648851-A (GB)
Title: Preselector
IPC: G05D3/12
Filed: 1948-02-28
Abstract: 648,851. Electric selective signalling. GUARDIAN ELECTRIC MANUFACTURING CO. Feb. 28, 1948, No. 6333. Convention date, Aug. 9, 1943. [Class 40 (i)] The preselector of Specification 648,867 is modified in that the main switch controlling the motor circuit is actuated through an axially slidable rod mounted outside the peripheries of the selector and stepper gears, the rod being movable axially inwards to close the switch either by depression of the control knob or through a manually-operated pivoted lever, and being releasably held in each of its axial positions by detents. Transmitter, construction. As shown, the control knob 50, Fig. 1, is secured by a transparent disc 45 to an annular indicator 46 fixed to a cup-shaped member 43 which with a selector gear 64 is fixed to a rotatable sleeve 20. The knob is normally held against rotation by a locking-pin 66 engaging in one of the circumferentially-arranged holes 67, Fig. 7, in the gear 64, the holes corresponding in number to the gear teeth. Pushing the knob inwardly (i.e. axially) releases the selector gear 64 from the locking-pin 66, after which the knob is rotated in either direction to a desired setting, and then released, whereupon it is returned axially by leaf-springs 62 to its original axial position where it is again locked by the pin 66, the new setting being indicated by a fixed index mark 38c, Fig. 5, against the annular dial 46. A stepper gear-wheel 68, identical with the selector gear 64 is mounted concentrically therewith, and is rotated with the selector gear during setting thereof, the stepper gear being locked to the selector gear by a pin 72 on the latter engaging one of the holes 71, Fig. 7, in the stepper gear. The stepper gear is freed from the selector gear when the latter is retracted axially upon release of the control knob 50. The inward axial movement of the control knob 50 also closes through a push-rod 122 a main switch 120 if this has not previously been closed by pulling forward the lever 124, Figs. 1, 5, the main switch being held in its actuated position by a spring detent 130 engaging in grooves in the push-rod 122. In addition, snap-action switches 58, 60 of known construction are closed in the depressed position only of the control knob by means of a rod 55 nested within the tubular shaft 21 carrying the stepper gear which is precluded from axial movement. Rotation of the control knob is limited by a cam 112 rigid with shaft 21 coacting with spring-pressed stops 114, Fig. 8 (not shown) to slightly less than 180 degrees on either side of the neutral position. A further cam 110 on shaft 21, Fig. 10 (not shown), causes closure of one of switch pairs 96, 97 or 98, 99, Fig. 2 (not shown), according to the direction of setting of the control knob, the actuated switch pair opening when the shaft returns to the neutral position. After a setting operation the shaft 21 is returned to the neutral position by one of two stepper magnets 86, 87 acting through armatures 87c on the stepper gear 68, the rotary position of which is indicated by a dial 37 carried by shaft 21 and visible through the disc 45. The selector and stepper gears coact with spring-biassed roller detents 75, Fig. 7, to ensure precise positioning of these wheels. Any lack of alignment may, however, be corrected by adjusting the stepper gear by means of a tool inserted through one of the holes 45a, Fig. 5, in the dial 46 into a hole 37d in the dial 37. The whole control mechanism is encased as at 150 and arranged for mounting on a panel 11. Circuit arrangements, Fig. 11. When the control knob 50 is released after being rotated to a new setting the motor armature 140 is energized in the appropriate sense over the switches 97, 99, one of which has been actuated to off-normal as above described. The motor drives the controlled member and also a cam 161 which pulses the appropriate stepping magnet 86 or 87 over the actuated switch 96 or 99 until the stepper gear has returned to neutral when the actuated switch pair 96, 97 or 98, 99 is returned to normal to break the motor circuit. A relay 135, Figs. 1, 11 is provided to prevent inaccurate operation of the stepper gear in the event of the motor coming to rest with the cam operated contacts 160 closed. The relay is in this case actuated upon depression of the control knob to prevent immediate energization of the stepping magnet 86 or 87. Limit switches 162, 163 are also provided to ensure the normal range of movement is not exceeded.