Patent GB-609705-A (GB)
Title: Improvements in and relating to electrical position-indicating apparatus
IPC: G05D3/14
Filed: 1941-05-19
Abstract: 609,705. Electric indicating and position controlling systems. TUSTIN, A., MORRIS, D. G. O., and METROPOLITAN - VICKERS ELECTRICAL CO., Ltd. May 19, 1941, No. 6445. [Class 40 (i)] In indicating apparatus comprising a rotary system which, provides in response to energy directly received from a distant object, an electrical quantity dependent on the angular deviation between the position of the rotary system and the direction of the remote object, and in which the rotary system is maintained within the limits of deviation providing response to the energy corresponding to the deviation, an indicator of the required direction with reference to a fixed datum is set by taking the algebraic sum of two control quantities dependent respectively on the aforesaid deviation and on the actual position of the rotary system with reference to a fixed datum. The arrangements described include automatic and manual means for driving the rotary system. In the arrangement shown in Fig. 1, the shaft 1 comprises the rotary system and the actual direction of the distant object is shown by an indicator connected to phase wires 14. The position which the shaft occupies is shown roughly on a selsyn indicator 65 controlled by a selsyn 60 driven by shaft 1. This shaft also drives, through step-up gearing, the rotor of a selsyn 4 the stator of which is connected by phase wires 7 to the rotor of selsyn 8 moved, as will be explained later, through an angle dependent on the deviation of the actual position of shaft 1 from the required direction. The angular position of the rotor field of 8 transmitted over phase wires 14 is therefore the algebraic sum of the deviation and the actual direction, transmitted by selsyn 4, with reference to a datum. The deviation is transmitted from shaft 1 in a manner not described in the form of two voltages, between 15 and 16, and between 17 and 16, which are equal when there is no deviation but vary in opposite senses when deviation occurs. These voltages are applied to potentiometers 18, 19 from the arms 20, 21 of which voltage is taken to operate a deviation indicator 22 which registers zero when there is no deviation arm and the arms 20, 21 are central. Manual control. When deviation occurs in one direction or the other as shown on indicator 22, shaft 10 carrying the arms 20, 21 is rotated from the central position in the direction to zeroize the indicator and the constants of the circuits and gear ratios are arranged so that the angular movement of the rotor of selsyn 8 driven from shaft 10 corresponds to the deviation, and the indication provided on wires 14 represents the actual direction of the distant object. Manual control is intended for approximate control on large deviations, the indicator being subsequently controlled automatically as described below. The manner in which the shaft 1 is driven, in the case of manual or automatic control of the indicator, to maintain it in a position of approximate correspondence with the direction of the distant object is described in a subsequent paragraph. When the shaft 1 is driven in conjunction with manual control of the indicator, the control may be used to pick-up one of a number of distant objects. Automatic control of indicator. The armature 12 of a D.C. motor is connected over switch 53 to a source 55. Deviation voltages taken from the potentiometers over leads 47, 16a and 48, 16a and after amplification at 49 are applied in opposition to the field windings 44, 45, whereupon shaft 10 is driven in a direction to equalize the voltages. Hunting of the driving motor due to time lag is reduced by providing phase advancing circuits 51, 52 in the amplifier or by reverse feed-back of alternating lag components in the output. Automatic control of rotary shaft 1. During manual and automatic control of shaft 10, potentiometer 40 is operated to provide from D.C. source 41, 42 voltages dependent on the deviation which are applied over wires 37, 38 to the input circuit of amplifier 29 supplying the variator windings 27, 28 of metadyne 25 supplying armature current to motor 2 which drives shaft 1 at a speed dependent on the displacement of shaft 10 and in a direction to reduce the deviation of shaft 1 from the required position. The potentiometer 40 is graded so that for large deviations the shaft 1 is driven at considerably higher speeds. The secondary voltage of the metadyne is also applied over conductors 36 and resistance capacity network 35 to the input of amplifier 29 in a sense opposing the input from the deviation conductors 37, 38, whereby the secondary voltage is maintained constant for a particular deviation as determined by displacement of shaft 10 and hunting is prevented. During automatic operation of shaft 10, hunting by motor 2 due to lag in the operation of shaft 10 in response to deviation voltages on conductors 47, 48 may be avoided by closing switch 58, whereby voltages dependent on the deviation are applied over 56, 57 to amplifier 29. An additional component of torque is thus applied to shaft 1 to reduce the deviation. The conductors 56, 57 may be connected to the output of amplifier 49. The arrangement is such that if the deviation voltages supplied over conductors 15-17 are subject to interruption, the shaft 1 continues to be driven at the same speed during an interruption as before so that when the voltages reappear shaft 1 is still approximately positioned provided that the change of direction of distant object has continued at approximately the same speed. Modifications. Fig. 2 (not shown), comprises a single potentiometer replacing potentiometers 18, 19 when the deviation is transmitted in the form of current variations. Back-lash or resilience in the drive between motor 2 and shaft 1 is compensated by a voltage applied to amplifier 29 and derived from a selsyn system which compares the actual positions of the motor armature and shaft 1 as described with reference to Fig. 3 (not shown). The compensating voltages may be derived over a rectifying system such as that described in Specifications 592,208 or 609,297. The potentiometer 40 may be replaced by a dynamometer controller such as that described in Specifications 583,835 or 583,836. The Provisional Specification describes the use of a Ward-Leonard driving system.