| 摘要 |
1,241,417. Control of D.C. motors. LINCOLN ELECTRIC CO. Ltd. 1 Aug., 1968 [7 Aug., 1967], No. 36210/67. Heading H2J. [Also in Division G3] In a welding apparatus (not described) a wire electrode is advanced by a D.C. electric motor 12 with a shunt field winding 12c, the motor having an automatic speed control. The motor may be compound wound; its armature 12d is energized through a thyristor 13 from an unsmoothed rectified A.C. supply provided by avalanche diodes D 8 -D 11 . A speed setting voltage derived from RV 1 ; a voltage across R A proportional to armature current and the armature voltage are compared at the base of a transistor T& 3 , a resultant speed error voltage appears across a capacitor C 6 . A transistor TR 1 is arranged to conduct when the armature voltage falls to remove the speed setting voltage and similarly a transistor TR 4 shorts the capacitor 6 so that the voltage on capacitor 6 varies periodically with the half waves of the A.C. supply. When, in each half cycle, the voltage rises above that on the base of a transistor TR 5 this regeneratively switches to its conducting state applying a pulse to transformer W 1=2=3 to fire the thyristor; transistor TR 5 is reset by transistor TR 4 becoming conducting. |
