964, 526. Shaft position digitisers. K. ZUSE. June 16, 1961 [June 18, 1960], No. 21761/61. Heading G4H. The position of a shaft is represented, in one embodiment, by a thirteen bit signal which is obtained from a coded scale having only three tracks each of which consist of a single series of binary code elements. Part of the scale is shown in Fig. 3 in which the units track SK 0 is read five bits at a time by a reading window F 1 , the pattern of code elements repeating after every twenty bits, so that each of digits 0-9 is represented by two different five bit signals sensed by photo-cells 1-5, Fig. 4a and applied to a decoding matrix Wp 0 , Fig. 4 which marks the corresponding lead 0, 0SP1/SP-9, 9SP1/SP. The tens and hundreds digits are represented by binary-coded blocks of four code elements selected from tracks SK 1 and SK 2 as shown in Fig. 3. The five-bit units digit determines whether the first or the last two blocks of four code elements are to be read from tracks SK 1 , SK 2 within window F 1 , and which of the two blocks is to be assigned as the tens digit and which as the hundreds digit, by controlling the selection of photo-cells 6-15 and their connection to decoding matrices Wp 1 and SP"/SP Wp 2 . If the units digit is odd S 1 operates to select photo-cells 7-10 and 12-15, otherwise cells 6-9 and 11-14 are selected. The output of OR gate S1 2 is connected to an upper row of gates of which successive pairs are respectively normally open, closed, open, closed and to a lower row of gates of which successive pairs are normally closed, open, closed, open, a "1" output from gate S1 2 altering the conditions of the pairs of gates. Since, when the units digit is 7, 8 or 9, the tens and hundreds digits may be read from the part of the scale associated with the following decade, provision is made for reducing the tens and hundreds digits by one when this situation arises. Relay S 2 is operated to reduce the tens digit by one if lead 7SP1/SP, 8SP1/SP or 9SP1/SP of Wp 0 is marked, but relay S 3 is only operated to reduce the hundreds digit by one if lead 7SP1/SP, 8SP1/SP or 9SP1/SP of Wp 0 is marked and gate K1 is opened by theoutput of Wp 1 , i.e. when the tens digit is 9. In another embodiment, the shaft is fixed to a first scale, Fig. 6, and is coupled to a second scale, Fig. 5, through 2000:1 reduction gearing. One revolution of the shaft is divided into 400 g (centigrades) = 4 x 10SP4/SPc (centi minutes) = 4 x 10SP6/SP cc (centi seconds). Each scale produces a 4-digit number, each digit being in a 2-out-of-5 code. In Fig. 5, (the coarse scale), the least significant track d repeats every five code elements and represents increments of 20 c. The value of the 20 c digit determines which five of the nine positions in the window F 2 are read for tracks a, b, c. In Fig. 6, (the fine scale) the least significant track d (representing increments of 1 cc also repeats every five code elements and the value read determines which five of the nine positions are read for tracks a, b, c, but a given S-bit group from this track takes one of two values in dependence on the first two bits read from track a. Since the 10 c digit from track a is only required to take the values 0, 1 i.e. 00011, 00110, the first two bits read from track a, which are either both 0 or both 1, are ignored by the circuitry associated with the 10 c digit and are used solely to determine which value is to be taken by the 1 cc digit. For example, the group 01100 read from track d is interpreted as 2 if the first two bits from track a are both 0, or as 7 if these two bits are both 1. In this way the digits 0-9 may be obtained from track d using only 5 distinct code groups. Other arrangements of scales are illustrated in Figs 7-10 (not shown).
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