Patent GB-587342-A (GB)
Title: Improvements in or relating to variable-ratio gear mechanism
IPC: G07F15/06
Filed: 1945-01-05
Abstract: 587,342. Prepayment mechanism for meters. SANGAMO WESTON, Ltd., and WESTON, G. E. Jan. 5, 1945, No. 533. [Class 27] [Also in Group XXIV] Variable-ratio ratchet gearing for driving the fixed charge collecting mechanism of a prepayment gas or electricity meter, or for other purposes, comprises a ratchet-wheel 51 secured to a final driven shaft 52, Figs. 3 and 4, and driven by a pawl 50 pivoted on an arm 44, which is oscillated continuously by a cam 46 on a driving shaft 14, which latter also operates adjustable means for lifting the pawl out of engagement with the ratchet-wheel during an adjustable part of a complete cycle, comprising a predetermined number of oscillations, to vary the total number of steps imparted to the ratchet-wheel 51 by the driving shaft 14 during the said cycle, the remaining oscillations being ineffective. The ratio of effective to idle pawl-strokes per cycle is controlled by the adjustable coaction of one member, a setting shaft 13, Fig. 2, which is rotated continuously by the driving shaft 14 and another member, a shaft 24, which is reciprocated continuously thereby. A complete cycle occupies one day, during which time a continuously gear-driven cam 30 makes one revolution and reciprocates the shaft 24 one stroke from the right (shown) to the left of Fig. 2, whereupon the shaft is released and a spring 25 snaps it rapidly back to the position shown: During this time the driving shaft 14 makes 528 revolutions and the pawl 50 an equal number of strokes, whilst the setting-shaft 13 makes eleven revolutions. At the commencement of a cycle (position shown), a radial arm 55, Figs. 2 and 3, the pawlset arm, fast on the rotating shaft 13, strikes the periphery of a six-toothed star-wheel 54 fast on the shaft 24, advancing it one tooth so that a three-lobed cam 42, Figs. 3 and 4, turning with the shaft 24, .releases a pin 49 on the tail 47 of the pawl 50 and allows a spring, not shown, to move. the pawl into engagement with the driven ratchet-wheel 51 whereby future pawl-strokes become effective. At some point during the leftward travel of the shaft 24, determined by the setting adjustment, the star-wheel 54 secured to it comes into the plane of rotation of a second arm 56, Figs. 2 and 3, the pawlrelease arm, adjustably secured to the rotating shaft 13, which arm, in timed relation, strikes the star-wheel 24 advancing it one tooth further, thereby again turning the three-lobed cam 42, Figs. 3 and 4, which lifts the pawl 50 off the ratchet-wheel 51 so that the latter remains stationary during the remainder of the cycle until the shaft 24 and star-wheel 54 are returned to the commencing point, shown, of the next cycle. Blade-springs 43, Fig 4, bear on a second sixtoothed star-wheel 41 to retain the shaft 24 at circumferential intervals of one-sixth of a revolution. To vary the point in the cycle at which the pawl-release arm 56 strikes the star-wheel 54, the arm is secured to a sleeve 59, Fig. 2 which is screw adjustable along a thread on the shaft 13, the gear-ratios, thread-pitch and thickness of the arm being so selected that the star-wheel 54 advances axially one thread-pitch whilst the setting shaft 13 rotates once, and the arm 56 can strike the star-wheel 54 only once during its axial reciprocation. The axial and radial setting of the pawl-release arm 56 is adjusted by using a tool to turn a pinion 64, meshing a toothed disc 62, secured to the threaded sleeve 59, each complete revolution of adjustment corresponding to a variation of one shilling per week in the meter charge. Turning with the shaft 13 by means of a square 70 is a scaleplate 72 graduated with 48 divisions, each of which thus corresponds to a change of “ penny per week, which is the value of one tooth of the final driven ratchet wheel 51. The scale 72, Fig. 2, co-operates with an index-mark 78 carried by the disc 62, and a spring-loaded ball 82 on the scale-plate 72 engages one of a series of 48 holes 80 in the adjusting disc 62 to retain the disc and plate in their relative positions of adjustment. Complete revolutions of the disc 62 are indicated by a small scale-plate 87 carried by a twelve-toothed star-wheel 83 on the scaleplate 72, which is stepped forward one tooth for each complete revolution of the adjusting disc 62 by a pin 85 on that disc, the scale-plate 87 being marked in shillings per week. In order to avoid confusion with the shillings digit at prices separated by, say, only penny per week from the nearest shilling value, a blade-spring 86, acting on the scale star-wheel 83, is so arranged that, at the exact shilling-value, as shown, the spring presses on the top of a tooth, thus retaining the actual shilling digit, e.g., 8, opposite the index pointer 90, whilst at other settings, the blade spring 86 falls into a notch of the star-wheel 83, so that the index-pointer 90 lies midway between the next higher and lower shillings digit for all intermediate portions of the pence scale 72. The adjustment-range extends from a minimum of a halfpenny per week, with the pawl set and release arms 55, 56 coplanar, to a maximum of ten shillings per week. To check for correct functioning, the driving shaft 14 can be manually turned by an external knob 91, a slip coupling 23 in the normal synchronous-motor drive permitting this. A scale-plate 92 on the final driven shaft 52 indicates if the charge is correct over the cycle. An additional indicator plate 95 is driven by the motor to show that it is operating. An arm may be provided to lift the driving pawl 50 off the ratchet-wheel 51 when the coinstorage capacity of the meter is exhausted.