Patent GB-1080041-A (GB)
Title: Improvements in or relating to position responsive switching systems
Inventor: HARBOUR JOHN
IPC: G05B19/35
Filed: 1965-03-19
Abstract: 1,080,041. Electric selective signalling. IMPERIAL CHEMICAL INDUSTRIES Ltd. March 16, 1966 [March 19, 1965], No. 11656/65. Heading G4H. A system for providing at least one output signal when a movable member (e.g. a shaft) is in a predetermined position or range of positions comprises a cyclically operable number generating means having a range corresponding to the total range of movement, means for generating in each cycle of the number generating means a differentially timed pulse indicative of the position of the movable member and gating means enabled by the presence of preselected number signals for passing a position indicating pulse only if the movable member is in the preselected position or range of positions. In the form of Fig. 1 a clock pulse generator 10 feeds pulses to a three-decade counter 16, 18, 20 counting repeatedly up to 1000. Certain ones of the decimal output leads are gated and used to switch a current to a transformer, the current having a stepped waveform approximating to a sine-wave. This waveform is smoothed to provide sine and cosine waves for application to the stator windings of a resolver 82, the rotor of which is connected to the movable shaft 118. A circuit is provided to ensure that the supply waveform to the resolver has exactly the correct phase. For this purpose one of the waveforms is applied to a zero-crossing detector and the zero-crossing detector signals are compared with the timing of the counts 250 and 750 produced by gates 98 and 100. A flip-flop 96 compares the timing of the two sets of pulses and applies a signal to a thermistor 70 which with a capacitor 72 acts as a variable delay to adjust the phase of the output waveforms from the transformer 66. Zero-crossing signals from the other waveform are similarly compared with signals at counts 000 and 500 and the frequency of the clock generator 10 is adjusted to maintain these signals at the correct counts. The outputs of the quadrature windings of the resolver are applied to zero-crossing detectors 120, 122 producing outputs for both positive- and negative-going crossings. These are applied to a circuit 160 controlled by two gates 136, 138 responsive to predetermined counts, signals being taken from the wires complement terminals on a selecting panel connected to the counters. The outputs from the gates set and reset a flipflop which, accordingly, is set for a range of numbers, e.g. 600-700. The positive going zero-crossing pulse from detector 120 is applied to a pulse generator 134. All four pulses from both detectors are applied to a similar generator 132. The outputs from either generator S1 or S4 may be applied to circuit 160. If the signal S1 is applied, it passes through gates 142 or 144 according to which is open to set or reset a flip-flop 150. If the signal appears during the predetermined number range the flip-flop 150 is set to give an output. Otherwise there is no output which indicates that the shaft position is outside the range specified by the input numbers to the gates 136 and 138. Delays 146, 148 are designed to provide an effect equivalent to mechanical backlash preventing the system dithering when the shaft oscillates slightly on the edge of the preselected range There may be a number of circuits 160 each producing a signal when the shaft lies in a preselected position range. The binary counters 16, 18, 20 may be replaced by decade rings, ten-step approximations to sinewaves being derived from the outputs. Instead of the resolver a coded disc may be used, sensed optically, magnetically, electrostatically or by contacts.