Patent GB-503023-A (GB)
Title: Improvements in or relating to control apparatus employing electric discharge devices for producing electric current impulses
IPC: B23K11/24
Filed: 1937-09-29
Abstract: 503,023. Control systems for resistance welding. SIEMENS-SCHUCKERTWERKE AKT,.GES. Sept. 29, 1937, Nos. 26409 and 26410. Convention dates, Sept. 29, 1936 and Sept. 9, 1937. [Class 38 (iv)] In control apparatus for producing electric current impulses preferably for spot welding apparatus in which the welding circuit is connected to A.C. mains for not more than one half-wave through a single anode grid-controlled main discharge vessel, the grid circuit of the main discharge vessel includes an impedance through which a circuit is closed, for the purpose of varying the grid potential, by an auxiliary discharge vessel supplied with a uni-directional potential and serving to cause or to prevent ignition of the main discharge vessel by an ignition control potential of peaked wave form. In the arrangement shown in Fig. 1, the grid circuit of the main discharge vessel 2 includes resistances 4, 5, 9, 10. Negative grid bias is imparted, to the vessel'2 2 by rectified A.C. applied across the resistances 4, 5 and obtained through a transformer and a rectifier 6. A positive potential of peaked form is applied across the resistance 9 from a transformer 11 supplied from an A.C. source 12 having a definite phase relationship to the power source 3. The. transformer circuit includes a choke 14 and the transformer has a highly saturated core and an exciting winding 111 fed with D.C. through a regulating resistance 27. In parallel with resistance 10 is connected the auxiliary discharge vessel 16, a choke 20, a source of D.C. from rectifiers 17, and a condenser 21. Discharge vessel 16 is rendered conductive during the interval needed to charge condenser 21 which may be short-circuited by switch 23 connected with main switch 26 so as to close alternately therewith. When switch 26 is closed, switch 23 is opened and positive potential from transformer 25 is applied to the grid of the auxiliary discharge vessel 16 overcoming the negative bias due to the potential across resistance 5. The vessel 16 is rendered conductive until the condenser 21 is charged and a positive potential impulse is thereby applied across resistance 10 to the grid of the main valve 2. The positive potential impulses across resistances 9 and 10 are so related in phase and intensity that they together overcome the negative potential across resistances 4, 5 and so ignite the main discharge vessel at a point in the half-wave determined by the adjustment of resistance 27, the arc being extinguished at the end of the half-wave. When switch 26 is opened, switch 23 closes and discharges condenser 21 in readiness for a repetition of the weld. The resistance 9, Fig. 3 (not shown), and its associated transformer may be omitted, the positive voltage peak across resistance 10 then being sufficient to overcome the negative voltage across resistance 4, 5. The resistance 10 may be connected in the grid circuit of the main valve 2 by inductive coupling by means of transformer having its primary and secondary winding in the grid circuit of the main valve 2 and the anode circuit of the auxiliary valve 16 respectively. In the modification shown in Fig. 4, a negative blocking potential is applied to the grid of the main valve 2 by resistances 30, 31, 35 connected to an A.C. source 33 through a rectifier 32. The positive peak potential is produced by a transformer 34 with phase adjusting means as in Fig. 1. The mains valve 2 is rendered conducting by the first voltage peak due to transformer 34 after the negative potential applied to its grid is reduced by short-circuiting the resistance 35. This is effected, when the switch 37 is closed, by the ignition of the auxiliary discharge vessel 36. Switch 37 when closed causes condenser 38 to short-circuit resistance 31, thus reducing the negative potential on the grid of the valve 36. At the same time an auxiliary circuit is closed through the cathode-grid circuit of the main discharge vessel 2 and condenser 39, whereby the discharge of condenser 39 extinguishes valve 36. In a modification, Fig. 5 (not shown), the auxiliary discharge vessel 36 is extinguished by an auxiliary potential derived from the main circuit through the discharge vessel 2 by means of a current transformer across resistance 42. In a modification of this arrangement, Fig. 6 (not shown), the grid circuit of the main discharge vessel 2 includes a resistance 50 in circuit with a switch 60 and with the secondary of the transformer 57. When this switch and a switch 61 in the anode circuit of the auxiliary discharge vessel are closed, the main vessel 2 is ignited by the peak potential generated by transformer 57. At the same time, the auxiliary vessel is ignited by a voltage transformer 59 arranged across the welding circuit mains, or a current transformer, thereby short-circuiting a resistance 52 which results in increase of current through series resistances 50, 53 whereby the potential increase across one of these resistances 50 blocks the main discharge vessel. In the modification shown in Fig. 7, the anode potential for the auxiliary discharge vessel 70 is supplied from a condenser 71 which is not charged until the switch 72 is closed by a connection to the welding pedal switch, so that there is a short interval before the welding impulse is applied. The grid-cathode circuits of both the main discharge valve 63 and the auxiliary valve 70 are connected across condenser 66 to which is applied negative bias from transformer 69 and rectifier 68 as long as switch 72 is in the inoperative position shown. When switch 72 is operated, contact 172 connects condensers 66, 71 through resistance 80. As the charge on condenser 71 increases, the blocking potential across resistance so decreases until the peak potential obtained through transformer 76 is sufficient to ignite auxiliary discharge vessel 70. Condenser 71 is then discharged through the anode circuit of discharge vessel 70, this circuit including the primary of transformer 67, the secondary of which thereby supplies a potential impulse to the grid circuit of the main discharge vessel 63 thus igniting it. The auxiliary vessel 70 charges condenser 74 and is therefore blocked after an interval depending upon the capacity of the condenser which may be adjustable.