Patent GB-952341-A (GB)
Title: Improvements in or relating to the determination of the instantaneous angular position of a rotatable shaft
IPC: G05D3/20
Filed: 1960-06-20
Abstract: 952,341. Electric selective signalling systems. CONTINENTAL ELEKTROINDUSTRIE A. G., [trading as CONTINENTAL ELEKTROINDUSTRIES A.G. ASKANIA WERKE]. June 20, 1960 [June 19,1959; Aug. 15, 1959], No. 21617/60. Heading G4H. In a system for producing digital signals reresentative of the angular position of a shaft by producing first a signal representing by its phase the angular position of the shaft and then digitising this phase signal when it is desired to produce digital signals, inaccuracies caused by the fact that the shaft might move during the finite time taken by the digitising process are compensated for by performing a second digitising process immediately after the first digitising process. As described the shaft forms part of a kinetheodolite and the phase significant signal is produced by capacitatively coupled stator 12' and rotor 13 discs Fig. 5, the stator being fed with four-phase 1 kc/s A.C. as shown. The phase significant signal is amplified and shaped 57, 59, as also is the zero-phase reference signal. The shaped reference and data signals appear on leads 60 and 65. When it is desired to effect a digitising of the data signal a pulse appears at a terminal 71 to thereby opening a gate 69. This allows the next shaped reference pulse on lead 65 to open a gate 66 which then allows 1 mc/s clock pulses to pass to a counter 68 until the gate 66 is closed by the next data pulse on lead 60. Gate 69 closes itself after a short time by feedback through a delay 73. Thus the presence of a pulse at terminal 71 initiates a digitising of the phase significant data signal and the result appears in the counter 68. If however during the digitising process the shaft moves then the pulse that closes gate 66 may arrive either to early or too late in which case the count reached will not correspond to the position of the shaft at the instant that the digitising process was initiated. According to the Specification a measure of this error can be determined by performing a second digitising operation immediately after the first. This operation is initiated a predetermined time after the first operation by a pulse from a counter 80 which is reset by the gate closing pulse that passes via delay 73 and which counts four of the cycles of the zero-phase reference signal on lead 63. The result of this count is also registered in counter 68 from where the two results can either be transferred to punched record cards for subsequent processing or direct to an electronic computer. In a second embodiment (Fig. 6 not shown), the second counting process described above which measures the time between a reference pulse and a data pulse is replaced by a counting process which measures the time between two successive data pulses. If the shaft is stationary then the time between two data pulses will be equal to that between two-reference pulses: if, however, the shaft is moving then it will differ from this value and the difference can be used to effect a correction of the first count. Specification 946,772 is referred to.