Patent GB-583835-A (GB)
Title: Improvements in electric follow-up control systems
IPC: G05D3/14
Filed: 1939-01-24
Abstract: 583,835. Control of D.C. motors. TUSTIN, A., and METROPOLITAN-VICKERS ELECTRICAL CO., Ltd. Jan. 24, 1939, Nos. 2503 and 17764. [Class 38 (iii)] [Also in Group XXXVIII] In follow-up control systems for guns, rudders, fluid valves moved by hydraulic, electric or other power, the torque applied to the load is differentially controlled in accordance with the displacement of the load relatively to the controlling member and the velocity of approach of the load to the position corresponding with the control member. The invention is described with reference to an electric control system. The follow-up control mechanism is carried in a casing 1-4 mounted in bearings in fixed plates 5, 6 and rotated through gearing 7 by the motor. which drives the load. The control shaft 10 operated as shown by handle 9 or by a receiving selsyn carries the planet wheels 14, 15 of a differential 11, 12 through which torque is transmitted through shaft 31 and disc 39 to the outer end of a spiral spring 36 and through a sleeve 20 carrying a contact member 21 adapted progressively to engage one or other of two banks 16, 17 of contact springs controlling the torque of the driving motor. The contact springs may form continuous variable resistance circuits or may control tapped resistances. The inner end of spring 36 is connected to the casing by a device to be described later, and considering first the effect of a small control movement the torque applied by the control shaft is divided between springs 36 and the spring contact bank which therefore has its resistance determined by the relative displacement of the controi shaft. The resistance of shaft 31 and sun wheel 11 due to spring 36 is opposed by a factor dependent on the relative follow-up velocity of the casing 1 so that the contact device 21 driven by sun wheel 12 is positioned according to the difference between these factors. When the velocity has been increased and the relative displacement reduced to such extent that the two factors equalize, the contact member 21 thereafter engages the other contact spring bank and causes the driving motor to apply a reverse torque. The factor dependent on relative velocity may be applied electrically by windings 34 on the casing and a laminated rotor 33 with squirrel cage windings on the shaft 31 or by a coupling in the form of a D.C. machine with brushes rotating with the field system and connected through a resistance. These arrangements produce a factor proportional to the velocity but by arranging an auxiliary self exciting winding on the D.C. machine, or by using a hydraulic coupling the factor may be made proportional to the square of the velocity which is the ideal condition. In order that the reactive torque applied to the control shaft 10 shall not increase proportionately throughout the range of large relative displacements, the spring 36 is connected to the casing in the following manner. The inner end of the spring is anchored to a pinion 40 loose on shaft 31 and geared to an internally toothed ring 42 carried by a U-shaped member 43 also loose on the shaft. The bar of this member and a bar 47 on the casing engage between the ends of a pair of spiral springs 37, 38 anchored to a loose sleeve 45. The stiffness of the springs 37, 38 is much less than that of spring 36 so that this spring is stressed only to the point at which it overcomes the stress of springs 37, 38. This has the effect of limiting the maximum speed of the casing without limiting the acceleration to this speed. The inertia of the rotating mass associated with shaft 31 introduces a factor dependent on the acceleration of the control shaft 10 to compensate for the inertia of the gun and a brake 48 operating on shaft 31 may be used to introduce a controlling factor commensurate with the friction in the gun mounting. The circuits of the driving and controlling equipment are shown in Fig. 3. The gun 60 and casing 1-4 represented at 71 are driven by a D.C. motor 62 supplied with constant current from a metadyne transformer 63 maintained at constant speed by regulator 65. The follow-up regulating resistances 16, 17 control field windings 69, 70 of a further metadyne 67 having its primary brushes short-circuited and its secondary winding connected to the field winding of the D.C. motor 62. In a modification, Fig. 6 (not shown), the differential gear 11, 12 is replaced by a receiving selsyn. In another modification of Fig. 1 the spring device is arranged between the contact element 21 and sun wheel 12, sun wheel 11 being subjected only to the torque of the coupling between shaft 31 and the casing.