Patent GB-1190845-A (GB)
Title: Analog-to-Digital Converter
Inventor: SCHUMAN RALPH HENRY
IPC: H03M1/14
Filed: 1967-04-14
Abstract: 1,190,845. Shaft encoders. WARNER & SWASEY CO. 14 April, 1967 [6 June, 1966], No. 17341/67. Heading G4H. A shaft encoder for indicating the angle of a shaft in a decimal code comprises a coded disc having tracks for activating photo-electric sensers to generate first logic signals in a cyclic code having a unique representation for each of 20 increments of angle, each increment having an extent equal to a units digit value of the decimal number, the value of the units digit being defined thereby, together with the 1 bit of the binary coded decimal digit of the next higher denomination. The coded disc and the photo-electric reading means produces a code as shown in Fig. 5. In Fig. 4, apertures in the disc are shown by black areas and the disc is divided into 2000 steps. In track 3 the apertures occupy 2 steps and are separated by 2 steps. The disc co-operates with a slitted mask and there are 4 groups of 3 slits for track 3, there being one photo-cell for each group. The group G+ and Group G - are complementary, as are groups F+ and F - . The G and F signals overlap, Fig. 5, so that for odd numbers they are either both present ("1") or both absent("0"). In even numbers G and F are different. Signals A-E are derived from track 1, the slits being placed to provide a series of overlapping signals which, with the F and G signals, define 20 positions allowing a tolerance of up to 1 step in the positions of the A-E signals. Complementary signals (A-, B-, C-, D- and E - ) are obtained from track 2. Binary-coded representations of the numbers in each decade are obtained from combinations of the signals A-G and their complements. A further signal I is obtained representing 10 which is used as the lowest digit in the next higher decade. The other digits 2, 4 and 8 are obtained from tracks 4, 5 and 6. Each track has lead or lag slits 20d, 20g &c., there being a photo-cell behind each slit. One of each pair of outputs is taken in accordance with the signal I representing 1 in this decade. A further signal valued 10, to be used as the lowest digit in the next decade, is derived from tracks 7 and 8, one of which has a lead slit 100d and the other a lag slit 100g. Two tracks are used to economize on the circumferential distance to be covered by the slitted mask. The lead or lag slit is selected under the control of the I signal. The 2, 4 and 8 digits of the third decade are produced from slits sensing tracks 9, 10 and 11 and a "10" digit is obtained from track 12. Lead or lag slits are selected by the value of the 1 digit. The innermost track 12 produces a "1" digit from the next higher decade. The other digits of the fourth decade are derived from a second disc driven through a 100-1 reduction gear. The disc moves in the opposite direction and the coded numbers are arranged to increase in the clockwise, instead of the anti-clockwise direction. Otherwise the discs are similar and for shaft movement in the reverse direction they are removed and interchanged. This disc also produces three binary-coded decades. A cam-shaft driven through a further 10-1 reduction carries four cams each with lead and lag switches. Outputs are selected by the "10" digit from the second disc. The cam switches give the seventh binary-coded decade.