Patent GB-683185-A (GB)
Title: Improvements in or relating to calculating instruments
IPC: G06G1/00
Filed: 1951-02-07
Abstract: 683,185. Optical projection apparatus. METTLER, E., (trading as METTLER, FABRIK FUR ANALYSENWAAGEN, E.). Feb. 7, 1951 [July 19, 1950], No. 2967/51. Class 97 (i). [Also in Group XIX] A calculating instrument comprises a plurality of rotatable scale carriers with one or more fine scales thereon, an illuminating device and a magnifying optical system by means of which a small section of the fine scales is depicted in enlarged scale on a projection screen and, for each said rotatable scale carrier a further rotatable scale carrier on which is or are located the same scale or scales in coarser graduation and which over a large section of their length can be made directly visible and read, each of said rotatable scale carriers provided with the fine scales being mechanically coupled with its associated rotatable scale carrier provided with the corresponding coarse scales. An annular glass disc 9, Fig. 1, bearing the appropriate fine scales is fixed to a carrier 7 rotatably mounted on a bearing pillar 6 secured to the instrument base 3. A second annular disc 11, bearing the appropriate scales for cooperation with the scales on the disc 9, is fixed to a carrier 10 rotatably mounted coaxially with the carrier 7 on a conical bearing 12 of a plate 13 supported by columns 14, 15, 16 and 17 extending from the base 3, Fig. 2. An area of the scales on the disc 11 is projected on to a screen 19, Fig. 1, by an optical system comprising a lamp 20, Figs. 1, 2 and 3, lenses 21, 22, Fig. 3, a mirror 23, a lens 24, a prism 25 and mirrors 26, 27 and 28. An area of the scales on the disc 9 is also projected on to the screen 19 by a similar optical system comprising a lamp 30, lenses 31, 32, a mirror 33, a lens 34, a prism 35 and mirrors 36, 37, 38. The two projected areas are side by side on the screen 19, Fig. 1, on which a cursor line is marked. Colour filters 54, 55, Fig. 3, in the projecting systems cause the images of the scales on the discs 11 and 9 to be red and green respectively. The screen 19 is formed by an opaque disc supported by brackets 47, 48, Figs. 1 and 2, and viewable through a window 51, Fig. 1, in the instrument housing 4. The carriers 7 and 10 each have a ring of gear teeth 63 and 71 respectively. Two cylindrical rollers or drums 44, 45, Fig. 2, are mounted on a horizontal shaft 46 supported by the brackets 47, 48. The drums 44, 45 each have a series of circular scales corresponding and similar to the scales on the discs 9 and 11 respectively, but not so accurately graduated. The drum 44 is connected through the gears 56, 58, 59, 60, 62 and 63, Figs. 1 and 2, to the carrier 7 and the drum 45 is connected through the gears 64, 65, 67, 68, 70 and 71 to the carrier 10. A cursor 50, Fig. 2, is extended over the drums 44, 45 beneath a viewing window 52, Fig. 1. Between the windows 51, 52 there is a plate 53, Figs. 1 and 2, bearing indicia in line with and denoting the scales on the drums 44, 45. The discs 9 and 11 and their associated drums 44, 45 may be rotated in individual pairs or together by external manually-operated means (see Group XIX).