Patent GB-776086-A (GB)
Title: Improvements in or relating to arrangements for use in indicating the direction of rotation of shafts
IPC: B66B3/00
Filed: 1955-01-04
Abstract: 776,086. Photo-electric apparatus. BULL, R. A., COATES, C., and HUNTRISS, H. C. Jan. 4, 1955, No. 206/55. Class 40 (3). An arrangement for use in indicating direction of rotation of a shaft comprises a circular member mounted on and rotating with the shaft and an element fixed adjacent the member so that it attempts to follow rotation of the latter but has restricted movement, the element carrying means for intercepting a light beam so that the condition of the latter differs with the direction of rotation. In the embodiment the shaft forms part of a colliery winding gear and the element is a magnet 13 (Fig. 2), in contact with circular iron member 10, its movement being restricted by adjustable stops 14. The magnet carries an apertured screen 20 which blocks the beam from lamp 16 when the magnet engages one stop but allows it to reach photo-cell 19 in the other extreme position of the magnet. A further beam is directed by prisms 27, 28 across the path of a series of apertures 24 in the plate 23 on member 10 to a second photo-cell 29. The output of photo-cell 19 is amplified at 40 (Fig. 3), and fed to single stroke multivibrator 41 which provides two opposite outputs reversing on change of input which are applied to gates 42 and 43 for 5 kc/s and 6 kc/s signals from Hartley oscillators 44, 45, respectively. The gates are arranged to be closed when negatively biased by the multivibrators. The disposition and shape of apertures 24 is such that photo-cell 29 gives a sine wave output of frequency proportional to angular velocity which is converted to square waveform at 50 and then rectified at 51 to provide a bias for multivibrator 59. A negative output is obtained from the latter when the input is zero and a zero output otherwise and is applied to gating circuit 46 to block the 5 or 6 kc/s signal only when negative. Thus a 5 or 6 kc/s signal, according to the direction of rotation is passed to push-pull modulator 52 where it is modulated by the square waves from 50 to give pulses of carrier wave of length dependent on speed which are passed through low-pass filter 54 to recording head 34 with a 45 kc/s bias voltage. Instructions in the form of bell signals in response to which the winding gear is operated are picked up by microphone 60, amplified at 61, and fed through the filter to the recording head. In practice, two tape recorders are used alternately with a short period of overlap, and when switching between the respective recording heads is effected H.T. is applied to oscillator 62 to give an audio signal which is recorded on the tapes. A check of the operation of the winding gear against bell signal instructions given to the winding men may be made by playing back the recording in the apparatus of Fig. 5. Signals from reproducing head 70 after amplification at 71 are fed through low-pass filter 72 and audio amplifier 73 to loudspeaker 74 which reproduces the bell and tape changing signals. The output of 71 is also fed through high-pass filter 75 and amplifier 76 to a detector 77 which removes the carrier-wave to give D.C. pulses which are shaped into square pulses at 78 and applied to differentiator 80 which gives positive and negative pips. Either the positive or negative pips are eliminated by diode 81 and the others fed to integrating condenser 82 the voltage on which is measured by a valve voltmeter to give a speed indication. The pips may also be counted in a pulse counter to indicate distance travelled. The signal from filter 75 is also fed to amplifiers 85 and 86 having anode circuits tuned to select 5 and 6 kc/s signals respectively and eliminate the envelope. The continuous 5 kc/s signal from 85, e.g. after amplification at 89 is rectified at 91 and fed to flip-flop circuit 93 which provides operating current for the switch 95 for one of the direction indicating lamps 97. Similarly, lamp 98 is lit in response to 6 kc/s signals from the tape. A circuit is described (see Fig. 4, not shown) for varying the gain of amplifier 50 in response to fluctuations in supply voltage of lamp 16 to give a constant amplitude output.