Patent GB-564722-A (GB)
Title: Improvements relating to apparatus for causing a controlled appliance to follow the movements of a controlling device
IPC: G05D3/12
Filed: 1943-06-17
Abstract: 564,722. Electric follow-up systems. EVERSHED & VIGNOLES, Ltd., and MARCHMENT, W.T. June 17, 1943, Nos. 9769/43 and 3670/44. [Class 40 (i)] [Also in Group XXXVII] In a follow-up system employing a direct-current servomotor, in the position of correspondence direct currents resulting from half-wave rectification of an A.C. supply are fed over parallel circuits by way of the opposite armature terminals to the field winding, thus giving an electrodynamic braking effect, whereas when a controlling movement takes place the armature is included in one of the circuits. In Fig. 1, direct current is supplied from a centre-tapped transformer 11 (or separate transformers) and rectifiers 14, 15 to circuits 16, 17, both of which are connected to the field winding 10 of the motor 4 when a contact arm 8 engages both conductive sectors 1, 2 of a disc 3. The disc 3 may be carried on a ship or other structure subject to rocking movements, while the arm 8 is stabilized by a gyroscope or otherwise. When the arm 8 engages only one of the sectors 1, 2, one of the circuits 16, 17 includes the armature of the motor 4 which therefore rotates to drive the disc 3 into the position of correspondence. In Fig. 2, the controlling member operates through a selsyn system comprising a toroidal resistance 20 interconnected with a toroidal inductance 21, the latter having a rotor 24 which is driven by the motor 4. When the brushes 22 which are supplied with A.C. are moved over the resistance 20, the voltage induced in the rotor 24 is applied over a transformer 25 to parallel circuits including rectifiers 30, 31 leading to thermionic relays 18, 19 which are of low impedance and are biassed so that normally they just pass current. The motor 4 is connected to the A.C. supply in the same way as in Fig. 1, and the result of the applied voltage is to render one of the relays 18, 19 conducting and the other non-conducting, so that the motor receives current through its armature in the appropriate direction to drive the rotor 24 into a fresh null position. In order to provide for electrodynamic braking, each of the relays 18, 19 is bridged by a rectifier 41, 42 to provide a path for the back E.M.F. when the motor comes to rest. Fig. 3 shows a somewhat similar arrangement for the control of a recorder 48 by a delicate instrument, such as a voltmeter or ammeter, which moves a light coil 24 in the field of a toroidal inductance 21, while the motor 4 drives the brushes 22 of a resistance like 20, Fig. 2, but developed in linear form. The output of the coil 24, which has no iron core, is amplified by a pair of pushpull valves 46, 47. The brushes 22 may be made to execute their full travel over the resistance 49, 50 for any desired deflection of the coil 24 by a suitable choice of tapping points and by the addition, if necessary, of sections of dead resistance, such as 53, 54, which are not traversed by the brushes. The connections shown in Fig. 3 give full travel of the brushes 22 and recording pen 48 for a deflection of 90 degrees of the coil 24, while those shown in Fig. 4 give full travel for a deflection of 180 degrees.