Patent GB-712751-A (GB)
Abstract: 712,751. Calculating-apparatus. FELT & TARRANT MANUFACTURING CO. Jan. 31, 1951, No. 2420/51. Class 106 (1) . In order to ensure full key-strokes in a keydriven calculating machine, alternatively engaging full-stroke pawls co-operate with a rack carried by the usual totalizer-actuating sector gear 43, and the down-stroke pawl actuates ordinal lock levers to lock all the keys upon release of a partially depressed key. The operator must then complete the key stroke and operate a release key before resuming operation. The keys are also released by operation of the totalizer clearing lever. Each ordinal column of keys 24 is adapted to rock the sector 43 through lever mechanism 48, 52 described in Specification 712,749; this mechanism is also adapted to enter the true or complementary values of the keys, in the manner described in Specification 712,750, and includes positive and negative stop-bars 71, 72 alternatively connected by a link 70' with the sector 43. Secured to the sector 43 is a rack 80 with reversely-directed ratchet teeth 81 and 83, the former engaged by a spring-actuated pawl 84 during the down-stroke of a key and the latter by a pawl 82 on the upstroke. Selective control of the pawls is effected by a masking plate 88, mounted on the sector 43 by means of pins and cam-slots, and connected by a link 95 with a lever 71a through which the stop-bar link 70<SP>1</SP> is connected with the sector 43. The lever 71a is pivoted on the spindle 44 independently of the sector, but has a lost-motion coupling 102, 103 with the sector. Normally the pawl 84 engages the rack 80 to prevent reverse movement of the sector 43 until the down-stroke of a key is complete, whereupon the lever 71a and masking plate 88 are arrested whilst the sector movement continues until the lost-motion coupling 102, 103 is taken up. During this small continued movement, the cam-slots force the masking plate 88 outwardly to disengage the pawl 84 and engage the pawl 82 which prevents reverse key movement during the up-stroke. A latch 100 retains the masking plate 88 in its outward position against a return spring until the up-stroke is complete, whereupon the latch 100 is tripped by contact with a fixed bar 105, and the released mask 88 restores the disengage pawl 82 and re-engages the pawl in preparation for the next key action. If a full key stroke is not made, the pawl 84 remains engaged with the rack 80 whilst the sector 43 is still under the action of its return spring 64: this pulls a bar 111 carrying the pawl to the right, and rocks a transordinal shaft 116 clockwise. A second transordinal shaft 121 has pins 122 engaging under arms 125 of a series of ordinal locking levers 123, and a catch (not shown) normally locks the shaft 121 to hold the locking levers 123 against their springs 124. The clockwise movement of shaft 116 trips the catch to release the shaft 121 and the locking levers 123 which engage under ears 126 on the levers 52 to prevent further key action except in the order in which incomplete key action has occurred. The operator thereupon completes the key-stroke and then depresses a release key (not shown) which returns the shaft 121 into engagement with its now restored catch, and disengages the locking levers 123 from the levers 52 so that operation of the machine can continue. Operation of the machine clearing lever also returns the shaft 121 to release the machine for further operation.