Patent GB-583836-A (GB)
Title: Improvements in or relating to electric follow-up systems
IPC: G05D3/14
Filed: 1939-06-06
Abstract: 583,836. Follow - up systems. TUSTIN, A., and METROPOLITAN - VICKERS ELECTRICAL CO., Ltd. June 6, 1939, Nos. 16634, 17765 and 19012. [Class 40 (i)] In an electrically-controlled follow -up system for guns, rudders, fluid valves, &c., a supplementary rotary member is caused to follow the movements of the controlling member by means which are responsive to the resist - ance to rotation of the supplementary member and which govern the energization of a control circuit for the motive equipment driving the load so as to vary the torque thereof in accordance with said resistance to rotation, the supplementary member being loaded in accordance with one or more of the following factors : (a) misalignment of the controlling member and the load, (b) relative velocity of controlling member and load, (c) acceloration of the controlling member, (d) frictional resistance of the load. As described, the motive equipment is electric, but it may use hydraulic or other sources of power. As shown in Fig. 1, the controlling shaft 3 rotates a shaft 19a though a variable electric motor control resistance device mounted in fixed casing 1, and shaft 10a is connected to a supplementary shaft 10 having an electric coupling 27, 28 and a spring coupling 35 with drum 5 rotating with the shaft 4 driven by a motor (not shown) which drives the load. The spring coupling comprises a main spring 31 and auxiliary, initially stressed but weaker springs 38, substantially the same as the spring coupling- described in Specification 583,835 and opposes displacement of the shaft 10 relatively to the controlling shaft 3, whereas the electric coupling which is of the eddy current type, applies a torque to the shaft in the opposite direction to the spring coupling which increases with the velocity of the driven shaft 4 in following up the controlling shaft. The resistance to the movement of shaft 10 by the controlling shaft 3 is increased by the inertia of the rotor 28 of the electric coupling in dependence on the acceleration of the controlling shaft, and by a friction brake 40, 41 which introduces a component adjusted in accordance with the frictional resistance of the load. The motor control resistance comprises a cage 13 driven by the controlling shaft 3 and carrying two sets of resistance elements 22, 23, Fig. 2, each connected in series, the points of connection being connected to two sets of pivoted spring-controlled contact fingers 16, 17 which are normally out of contact with a tapered conducting member 19a, Fig. 2a fixed on shaft 10a. The fingers have counterweights at their lower ends to prevent vibration of cage 13 about shaft 10a from affecting the amount of resistance in circuit. The resistances control the excitation of windings of a metadyne controlled reversible load-driving motor in a manner similar to that described in the above mentioned Specification, electrical connections from the control resistance being taken from slip rings on shafts 3 and 10a. When the controlling shaft is turned one way or the other, the resistance to rotation of shaft 10 causes one or other set of fingers 16, 17 to come into action to cut out resistance in the motor circuit. When the speed of the load has reached a value such that the torque due to the electric coupling exceeds the opposed torque due to the spring coupling, the other set of fingers comes into action to cause a reverse drive. The eddy current coupling device may be replaced by other forms of electric coupling or a hydraulic coupling as described in the above-mentioned Specification which may produce a torque proportional to the square of the velocity. Alternatively, instead of producing velocity loading on shaft 10, a D.C. generator controlled by the shaft 10 and drum 5 may supply an auxiliary exciter winding on the motor which drives the load. Reducing the torque required to be applied to shaft 3, Fig. 6 (not shown): This is particularly necessary when shaft 3 is controlled by the receiver of a Selsyn transmission system. The motor control resistances are arranged in a bridge circuit which, in addition to controlling the single exciter winding of a-load motor, also control an auxiliary follow-up motor which causes shaft 10 to follow shaft 3. The circuits shown in this Figure also include the D.C. generator, previously referred to, replacing the electric, coupling for introducing the velocity component. In a modification, Fig. 7 (not shown), of this arrangement, the auxiliary follow-up motor is also used to introduce the velocity component with acceleration and friction components if required. The field winding of the auxiliary motor is supplied from a constant voltage source and carried by the rotary drum 5 so that the armature which is carried by shaft 10, in order to follow up the movement of the controlling shaft, must be supplied by the variable control resistance with current to overcome the back E.M.F. due to the rotary field (dependent on velocity) in addition to the normal follow up current which is dependent on displacement and also on acceleration and friction as follows from previous explanations. The current supplied to the armature is supplied to the exciting winding of the load motor. Modifications utilizing Selsyn transmission systems. In the system shown in Fig. 8, a transmitting Selsyn 120 and a Selsyn 123 controlling the shaft 10 are connected to a differential Selsyn 126, the rotor of which controls the motor control resistances 71. When selsyns 120, 122 are not in correspondence, the bridge circuit including the resistances 71 supplies current to field winding 103 of a motor which drives shaft 10 to correspond with the transmitting Selsyn. The voltage appearing across winding 103 is dependent on the relative displacement of the transmitter and shaft 10 and of any acceleration and, friction components applied to shaft 10, and is used to control the load motor over conductors 106a, 107a. Previously described arrangements comprising a D.C. generator 29, 110 for introducing a velocity component or using the motor 103, 129 for this purpose are also employed. The motor 103, 129 may be dispensed with, shaft 10 being caused to follow up by the torque of Selsyn 123. The generator 110 may have an adjustable shunt 129a serving to damp the shaft 10. Selsyn control, with coarse and fine adjustment, Fig. 9. Coarse adjustment of the load shaft 4 in correspondence with the controlling shaft.3 is. effected by differential Selsyn. 142 connected .to transmitting and receiving Selsyns 140, 141, whereas fine adjustment is effected by differential Selsyn 145 and Selsyns 143, 144 geared to Selsyns 140, 141. The rotor of the fine adjustment Selsyn 144 also applies to supplementary shaft 10, by means of an electric or other coupling 27, 28 previously described, a torque dependent on the relative velocity, shaft 10 being moved in correspondence with the controlling shaft by means of Selsyns 143, 148 and differential Selsyn 147. Assuming a large displacement of shaft 3, differential Selsyn 142 rotates the controller 19 of control resistances 22, 23 and operates relay &c. 155 which connects up said control resistances and disconnects corresponding resistances 22, 23 of the fine differential Selsyn 145. Current depending on the displacement in direction and magnitude is therefore supplied to winding 159 of polarized relay 160 also controlling a variable resistance device 19a, 16a, 17a, whereby winding 167 of a metadyne controlling the load motor is correspondingly excited. Differential Selsyn 147 also operates its controller in accordance with misalignment between supplementary shaft Selsyn 148 and Selsyn .143, whereupon field winding 152 of D.C. motor 150 is correspondingly excited to rotate shaft 10 subject to the torque component due to the relative velocity between 4 and 10. At the same time, the controller of Selsyn 147 applies to an opposing winding 165 of the polarized relay 160 a current dependent on this component thereby modifying the excitation of metadyne winding 167. When approximate correspondence between shafts 4 and 3 has been attained, the controller of Selsyn 142 is normal and relay OC155 releases to connect up the fine differential Selsyn 145 and its controller. Fine adjustment takes place in the same way as the coarse adjustment, but as the controlling Selsyns are moving at higher speed, resistance 164 in the controlling circuit of the follow-up motor 150 is, short-circuited. The shaft 10 may also introduce acceleration and friction components, but it may be advantageous to reduce the inertia of shaft 10 and therefore the acceleration component. Modification, Fig. 10, in which the displacement and velocity components are introduced by means other than the supplementary shaft 10. The controlling shaft 3 rotates the shaft 10 through a controller 19 as previously described, but the shaft 10 introduces only the acceleration and friction components due to fly-wheel 218 and brake 219. The displacement and velocity components are derived from a Selsyn 203 on the shaft 3 and a Selsyn receiver (not shown) on the controller shaft. These Selsyns control equipment to produce in known manner output voltages in magnitude and phase dependent on the displacement and' its direction and in which a relative velocity component is introduced, these voltages being used to control the equipment for driving the load in conjunction with voltages derived from the controller 19. In a further modification, Fig. 11 (not shown), shafts 3 and 10 are coupled by a spring so that shaft 10 lags behind shaft 3 and furnishes a displacement component by means of a Selsyn connected to a Selsyn on shaft 3 which may be the same Selsyn that is used to furnish a velocity component.