GB1086724A - Improvements in or relating to apparatus for controlling the movement of a moveable member - Google Patents

Abstract

1,086,724. Selective signalling. ELECTRICAL & MUSICAL INDUSTRIES Ltd. May 28, 1964 [May 28, 1963; Aug. 21, 1963], Nos. 21345/63 and 33020/63. Heading G4H. [Also in Division H4] A system for determining the direction of movement of a movable member comprises a conductor situated along the route to be taken by the movable member, means for feeding oscillations of adjustable phase to the conductor, sensing means associated with the movable member for sensing the oscillations in the conductor, and means for comparing the phase of the said oscillations with the phase of reference oscillations to provide a signal controlling the movement of the member in a direction dependent on the sense of the phase difference. As shown in Fig. 1, conductors 1, 2 extend along a route to be traversed by a vehicle 3 which may be guided by signals from a pair of inductive pick-up coils in the manner described in Specification 935,751. The conductor 1 is fed with an A.C. signal of reference phase from a generator 8 and the conductor 2 is fed with an A.C. signal from generator 9 which may be adjusted at 10 to be either in phase or antiphase with the reference signal on conductor 1. A pair of sensing coils 4, 5 on the vehicle co-operate with the conductors 1, 2 respectively, and supply signals to a phasecomparator 6 which via apparatus 7 controls the vehicle driving means to drive the vehicle forward or in reverse in accordance with the phase relationship of the two signals. When both conductors are de-energized the control apparatus 7 stops the vehicle. In a modification, Fig. 2 (not shown), the two ends C, D of the conductor 2 are both connected to the same terminal of the generator 9 and the other terminal is connected by a selector switch to one of a plurality of tapping points between the ends C, D. Thus the signal at the selected tapping point divides and flows in opposite phase along the two portions of the conductor CD and when conductors 1 and 2 are energized by outputs from the generators 8, 9 in the same phase, a vehicle automatically homes on to the selected tapping point. The Figure accompanying Provisional Specification 33020/63 shows the application of the arrangement to control the vertical movement of a lifting platform 3 in a mobile crane 1. Conductors A to I are arranged vertically one above the other on the crane frame and the platform 3 is provided with an arm 4 carrying a pick-up device P1 co-operating with the conductors A to I. A pair of conductors L1, L2 are situated along the route of the crane and energized by signals from a reference phase oscillator J1 and an adjustable phase oscillator J2 respectively. The reference signal is supplied by a pick-up P2 to amplifier and phase-shifter stages 5 to 13 which are arranged so that conductor A is provided with a signal of reference phase, and the phase of the signals applied to the remaining conductors progressively increases by 22¢ degrees at each stage. The generator J2 is adjusted to provide a signal having a phase shift which is proportional to the mean phase of the signals applied to two adjacent conductors A, B &c. and defines a required one of the gaps between adjacent conductors. This signal is supplied via pick-up P3 to a phase discriminator 19 receiving as its other input the signal from pick-up P1, the output from the discriminator having a polarity determined by whether the control signal supplied by pick-up P3 leads or lags the signal supplied by P1. The discriminator output controls via unit 20 a motor MV, which drives the lifting platform, so that it is de-energized when the platform reaches the required position. A servo system 18 controls the horizontal movement of the crane via a control unit 21 which controls the motor MH. The units 20, 21 are interconnected so that the platform 3 may only be moved when the crane has reached the required position. A further small movement of the platform 3 may be provided by a further pick-up coil mounted a few inches above or below the pick-up P1 which is connected to the phase discriminator in place of P1.