Patent GB-609296-A (GB)
Title: Improvements in and relating to follow-up control systems
IPC: G05D3/12
Filed: 1941-10-01
Abstract: 609,296. Automatic voltage control systems. TUSTIN, A., MORRIS, D. G. O., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Oct. 1, 1941, Nos. 4390/41 and 15438/42. [Class 38 (iv)] Also in Groups XXXVII and XXXVIII] In a system for controlling the magnitude of a quantity or displacement of an object either automatically on departure from or want of correspondence with a particular or desired value, and in which control is effected by a main sequence of actions each producing a dependent quantity, e.g. departure from value producing an A.C. quantity, rectification, a D.C. quantity, amplification, adjustment of value, the tendency of the system to produce oscillation about a desired value due to time lags in the transmission of sinusoidal components of varying values is suppressed by a subsidiary sequence derived from one of the dependent quantities and including means resonant to frequency components in said quantity in the neighbourhood of the oscillation frequency and producing a control effect in opposition to the oscillatory variations in value. Resonance may be effected by mechanical or electrical means or a combination thereof. When a lagging response of the subsidiary sequence is utilized, it is applied to the main sequence in aiding relationship and when a leading response is utilized, in opposed relationship. In the diagrammatic representation of such a system shown in Fig. 1, the arrow A represents the controlled quantity and variation thereof operating through means a effects control of a dependent quantity B and so on through the main chain b, C ... g, H, whereupon h exercises the desired control on A. The subsidiary sequence may be for example, A, p, G, g, H, h, A; or A, g, B, b ... A; or a sequence containing a reactive link C, r, C. Positional control systems. The system shown in Fig. 3 (Comp.) provides for control of shaft 5 in correspondence with the position of control handle 6. A selsyn system 9, 10 provides an A.C. output voltage, dependent in amplitude and phase (8 degrees or 180 degrees) upon the amount of misalignment and the direction thereof, which is rectified at 14 and applied across resistance 22 to control differentially the outputs of a pair of valves 16, 17 which are applied to corresponding amplifying valves 27, 28 supplying a variator winding 15 of metadyne 2, the resultant effect in winding 15 being dependent in amplitude and direction on the misalignment. H.T. supply for the valves is taken from conductors 23, 24. According to the invention, the variable components of armature voltage of the motor 1, which drives shaft 5 under control of the metadyne, are applied over transformer primary 34 to secondaries 35, 36 which are tuned to the desired frequency by condensers 21 and effect a corresponding subsidiary response of valves 16, 17. The rectifying device 14 may be that described in Specification 609,305. The two parts of variator winding 15 may be shunted by non-linear resistances 33 so that limitation of response may be effected while providing large response for small misalignment. Fig. 10 (Comp.) (not shown) indicates an alternative resonant circuit. In modification, Fig. 8 (15438/42) (not shown), the subsidiary sequence is initiated by armature current instead of voltage, whereas in Figs. 4 and 9 (15438/42) (both not shown) armature voltage and current are used to excite electro-mechanical resonance devices. In Fig. 5 (Comp.), progressive contact controllers operated by moving coil relays are used both in the main and the subsidiary sequence for providing the main and subsidiary controlling quantities. The selsyn system 7, 8 provides an output voltage which controls the moving coil 84a of a relay polarized by coil 86 and operating a contact controller having resistances 82, 83 connected to opposed variator windings 80, 81 of metadyne 2 which supplies the driving motor 1. The common points of the resistances and variator windings are connected across a D.C. source. This comprises the main sequence. The subsidiary sequence comprises a centretapped resistance 87 between the variator windings and supplying the moving coil 89 of a feed-back relay 88 (see Group XXXVII) which has a spring-controlled shaft loaded with a mass 93 to constitute the resonant system and controls resistances 91, 92 connected across a centre-tapped resistance 85 in series with the main moving coil 84a. The centre tap of 85 and the common point of resistances 91, 92 are connected across the D.C. source so that the subsidiary sequence produces a voltage across 85 which exerts a subsidiary control on the main relay. The shaft of the subsidiary relay may be damped by a disc 96 and magnet 95. The arrangement shown in Fig. 5 (Comp.) may be modified as in Fig. 9 (Comp.) (not shown) by feeding back the D.C. voltage across resistance 87 to a winding on the main moving coil relay 84 which in this case is a D.C. relay controlled by rectified selsyn output and is polarized by a D.C. winding, the feed-back relay 88 being dispensed with. The feed-back circuit is made resonant to the required frequency by a series inductance and a shunt condenser to provide a lagging component. In another modification, Fig. 11 (15438/42), the resonance in the subsidiary sequence is provided by an auxiliary metadyne 144 and associated circuit elements. The main sequence, which is shown in part, includes a metadyne 140 or other dynamo-electric machine or a relay controlled by winding 142 in accordance with the misalignment of the system. A winding 143 in series with 142 serves as a variator winding for metadyne 144 having its secondary brushes connected to a further variator winding 145 of metadyne 140. Metadyne 144 has its primary brushes short-circuited through a winding 147 producing an aiding flux along the primary commutation axis, and a further secondary winding 146 which opposes armature reactors. Metadyne 144 and winding 145 are arranged to give a resonant response at the desired frequency and the fluxes produced by windings 142, 145 are in opposition. The system described in Specification 609,304 and employing phase-advancing arrangements may be modified by introducing resonance. Automatic control system, Fig. 12 (15438/42). The back E.M.F. of motor 130 is applied to a circuit including a resonant network 133-135 and a winding 132 which controls a carbon pile resistance 121 in series with the field winding 131 of the motor.  The first Provisional Specification also refers to rectifying arrangements described in Specifications 527,768, [Group XXXVIII], and 604,185'and to various phase-advancing arrangements including the phase-advancing metadyne system described in Specification 592,209.