GB542940A - Improvements in or relating to calculating devices - Google Patents

Abstract

542,940. Catculating-apparatus. WILLENS, R. A. A. Aug. 2, 1940, No. 12506. [Class 106 (i)] An apparatus for facilitating the selection of at least three values each from a range of a finite number of distinct values to provide a given function of the values selected which shall approximate most closely to a desired value lying in a finite and continuous range, comprises two scales marked in accordance with every possible value of two sub-functions of the variables to be selected and means for moving the scales independently and together to bring the desired values into juxtaposition according to the given ratio. In one form of apparatus, as described for facilitating the selection of a set of at least two pairs of gears from a range of gears, to give a compound gear ratio approximating to a desired ratio, the scale members are constituted by film strips 3, 4, Fig. 1, carried by reels 5, 6 and 7, 8 and sprocket wheels 13, 14 and 15, 16 on a conventional type of film viewer 1 provided with a screen 9 and hinged masking flaps 10, 11. The shafts 19 ... 22 of the sprocket wheels are adapted to be driven in either direction by pairs of bevel gears 23, 24 and 23, 26, Fig. 2, working independently or in geared relationship. The bevel gears 24, 26 are mounted on shafts 25, 27 with gears 28, 29 engaging a gear 30 driven by a hand crank 31. The gear 29 is free on the shaft 27 but may be secured thereto by means of a clutch 32 operated by a hand wheel 33. A hand wheel 34 is provided by means of which the shaft 27 may be driven independently. Spring belts 35 drive the reels through friction clutches. The scales shown in Figs. 4 and 5 are designed to facilitate the selection of four gears from a range of seventy-one gears having every possible number of teeth from twenty to ninety. Each film carries two scales 42, 43 ; the scale 42 is a simple logarithmic scale and the scale 43 is formed of transparent wedgeshaped marks on a black ground a mark being provided for every possible product of any two gears in the range. The mark that represents the product of two gears of twenty teeth is opposite the unit mark of the scale 42. The marks are identified by numbers and tables of the numbers and products are used to determine the products. In operation the unity mark on one scale 42 is adjusted opposite the desired transmission ratio on the other scale and then the scales are coupled to move together until two of the transparent marks, one on each film, coincide. The numbers are noted and the tables give the products. The sensitivity of the device may be adjusted by laterally moving one of the film strips by the action of wing nuts 50 against springs on the spindles. In a modification, Fig. 6 (not shown), the scales are marked in a helical manner on nested cylinders. The upper half of each cylinder carries a scale corresponding to the scales 43. A logarithmic scale corresponding to the scale 42 is marked on the lower half of the inner cylinder and co-operates with an index finger at the lower end of the outer cylinder.