Patent GB-721213-A (GB)
Title: Improvements in or relating to electric arc lamps
IPC: H05B31/30
Filed: 1951-07-11
Abstract: 721,213. Arc lamps. GENERAL ELECTRIC CO., Ltd., BATCHELOR, G. D., and FIELDER, N. C. July 11, 1952 [July 11, 1951], No. 16445/51. Class 39 (1) An arc lamp includes mechanism for striking the arc comprising a manual control for moving the electrodes into contact to initiate the arc and means responsive to the initiation of the arc for. rendering the manual control ineffective for as long as the arc is maintained and for causing the electrodes to separate to an appropriate extent. The holder for the negative electrode 11 is mounted on a carriage 18 slidable along a pair of parallel guides 19 and having a threaded nut engaging a lead screw 20 which can be rotated by a gear train for advancing the negative electrode 11 progressively towards the positive electrode 10 as the electrodes burn away. The carriage 18 is slidable along the guides 19, to make the negative electrode 11 touch the positive electrode 10, by a linkage comprising two slider members 30 and 31 moving in alignment in guides in a frame member 32 The slider member 30 is pin-jointed at 33 to one arm of a bell crank 34 pivoted at 35 to the member 32, the other arm of the bell crank 34 carrying a manual control knob 36. The bell crank 34 is arranged to actuate a switch controlling the current supply to the electrodes and has coupled to it a rod 37 actuating a lock. The slider member 31 has a slot 40 engaged by a pin so as to couple the member 31 to a crank member 41 pivoted at 42 to a part fixed to the frame member 32 and having a forked end which embraces the lead screw 20 so that when the slider members 30 and 31 are moved in the direction of the arrow X the lead screw 20, carriage 18 and negative electrode 11 are moved so as to make the negative electrode approach the positive electrode 10. The slider members 30 and 31 are connected. by a pair of links 43 and 44 pivoted together at 45 and pivoted to the members 30 and 31 at 46 and 47. When in the aligned position the links 43 and 44 provide a rigid connection between the slider members 30 and 31 so that movement of the bell crank 34 is transmitted to the negative electrode 11 to bring it into contact with the positive electrode 10. A solenoid 48 having a plunger 49 is arranged adjacent the position which the pivot 45 occupies when the manual control knob 36 has been operated to move the electrodes 10 and 11 into contact. The winding of the solenoid 48 is arranged to carry the whole or a fraction of the current passing between the electrodes so that the plunger 49 is moved to move the pivot 45 in the direction Y thereby moving the links 43 and' 44 out of alignment and rendering the manual control inoperative, the carriage 18 returning along its guides 19 to separate the electrodes to an appropriate extent. Thereafter the movement of the electrode 11 is controlled by an electric motor driving the shaft 25 and gear train shown. A catch, operated mechanically or by a solenoid, may be provided to prevent the bell crank 34 returning to its original position during operation of the lamp. The linkage arrangement described can be replaced by an electromagnetic clutch or by a mechanical clutch operated electromagnetically, e.g. by a solenoid, the clutch being engaged, when the electrodes are separated and no current is flowing between them, to transmit drive to move the electrodes into contact, and being thrown out of engagement when current flows between the electrodes.