Patent GB-979788-A (GB)
Title: Improvements in or relating to electrical position-encoding apparatus
IPC: G01D5/20
Filed: 1961-02-01
Abstract: 979,788. Shaft position digitizers. GENERAL ELECTRIC CO. Ltd., and C. J. WAYMAN. Feb. 1, 1962 [Feb. 1,1961], No. 3905/61. Heading G4H. General: Two relatively movable toothed ferromagnetic cores 1, 2 Fig. 1 have different tooth pitches so that for a multiplicity of consecutive ranges of movement of shaft 10, the variation in the coupling between a primary winding 5 and a plurality of secondary windings 6, 7, 8, undergoes a multiplicity of cycles, and the signals induced in the secondary windings by excitation of the primary winding are used to derive a digital representation of the relative positions of the cores in each of the ranges. Details of operation: In the example shown, stator 1 has 18 teeth and rotor 2 has 16 teeth so that one revolution of shaft 10 produces 16 cycles of variation in the coupling between winding 1 and windings 6, 7, 8. During each rotation of shaft 10 through 22. 5 degrees the voltages induced in windings 6, 7, 8 have amplitudes which are proportional to Sin 16#, Sin (16# +#) and Sin (16# + 2#) where # = 2#/3 and ##22. 5 degrees is the angular position of shaft 10 in any of the 16 ranges. Windings 6, 7, 8 supply two Scott-connected transformers 12,13, Fig. 2, the ratio of the number of the turns in primary windings 14, 15 being 2: #3 so that the effective voltages supplied thereto have amplitudes which are proportional to Sin 16# and Cos 16# respectively. Amplitude comparators 24, 25, 50, 71 and 72 produce a reflected binary coded output at terminals 31, 31<SP>1</SP>, 61, 61<SP>1</SP>, 79 (in descending order of significance) in response to interrogation signals applied at 45. Each comparator includes an output pulse transformer e.g. 41, the direction of the current in the primary winding of which is determined by which of the two input signals to the comparator is the larger, a change in the output signal occurring when the two input signals pass through equality. The output at 31 thus changes when 16# = 11. 25 degrees and that at 31<SP>1</SP> changes when 16# = 5. 625 degrees and 16. 875 degrees. The voltage appearing at 48 depends on the total currents in the emitter circuit of transistors 37, 38 and is zero when 16# = 0, #, 2#, whereas the voltage at 48<SP>1</SP> is zero when 16# = #/2, 3#/2, and a change in the output at 61 thus occurs at four different values of 16#, i.e. when the curves representing the voltages at 48 and 48<SP>1</SP> intersect. A further comparator 64 has inputs from transformers 12, 13 which are proportional to Sin (16# + #/4) and Cos (16# + #/4) and provides a suitably varying voltage at 70 for comparison with the voltage at 62 in comparator 71. The least significant digit is obtained as a result of the comparison of the voltage at 62<SP>1</SP> with a constant D.C. voltage applied to comparator 72 from 76. The interrogating signals may be either pulses or an alternating voltage, the output signals in in the former case being of either polarity, and in the latter case alternating voltages which are either in phase or in anti-phase with the interrogating voltage. Since the code pattern repeats every 22. 5 degrees rotation of shaft 10, the digitizer may be used to represent the "fine" position of an input shaft coupled directly to shaft 10. In a further embodiment, Figs. 5, 6 (not shown) the stator and rotor have 12 and 10 teeth respectively, thus dividing one revolution of shaft 10 into ranges of 36 degrees. Only two secondary windings are provided on the stator, giving outputs proportional to Sin 10# and Cos 10# so that ordinary, separate transformers are used to provide the two input signals to the coding circuit. In this embodiment each 36 degrees range is divided into 20 sections, each represented by a five digit binary number in a cyclic permuting code. The coding circuit is similar to that of Fig. 2 but includes voltage dividing circuits in the interconnections of some of the comparators in order to produce voltage cross-overs at the desired angular positions of the shaft 10. Specification 979,789 is referred to.