GB723366A - Apparatus for checking electric spot-welding operations - Google Patents

Abstract

723,366. Electric indicating systems. OFFICE NATIONAL D'ETUDES ET DE RECHERCHES AERONAUTIQUES. June 5, 1952 [June 6, 1951], No. 14248/52. Class 40 (1) [Also in Group XXII] For supervising spot welding, the pressure exerted by the electrodes on the work, and the welding current, are indicated simultaneously against a time base on a cathode ray tube. The pressure is preferably measured by strain-gauges, and potentials proportional to both variables are applied alternately through a multivibrator-controlled gating circuit to the Y plates of the C.R.T., the time base X of which is controlled so that the whole welding " operation " may be indicated or, on a " spread " scale, only that portion when the welding current flows. Welding current circuit Fig. 1. The workpieces 46-47 to be welded are held between pressure electrodes 44, 45, the pressure between the workpieces being determined by the fluid pressure in a cylinder 52 cyclically controlled in known manner by an electrically actuated controller 58 started in operation by the operator depressing a pedal. This actuation of the pedal also closes a contact 41 to energize a winding 27 which closes a main switch 24 to connect a direct current supply, obtained e.g. by rectification at 22 from the A.C. supply 21, to the primary of a transformer 20 in series with the winding 37 of a switch 34. When the primary current has risen to the operating value of the winding 37, the switch 34 opens to de-energize winding 27 and open the main switch 24, the weld being effected by the current surge in the secondary 42 as the primary circuit breaks. Pressure measuring circuit, Fig. 4. Strain gauges 100-103 secured to one of the electrodes 44, 45-two on the cylindrical surface and the other two in a transverse section of the electrode -are connected in a bridge circuit 104 fed from a frequency stabilized oscillator 108. The bridge output, which varies in magnitude and sense with the electrode pressure variations from a predetermined value, is applied through a phase sense detector 120, push-pull amplifier 123 and low pass filter 126 to push-pull connected tubes 145, 146, the anodes of which are connected to the plates 191-192 of a C.R.T. 202 through a further amplifier 190. Welding current measuring circuit, Fig. 4. A potential proportional to the welding current is taken from spaced points along the electrode 45, amplified at 164, and applied through tubes 160-161 to the C.R.T. plates 191-192 in parallel with the outputs from the tubes 145-146. C.R.T. control circuit, Fig. 4. A free-running multivibrator 184 applies through a clipper and shaper 183 rectangular voltage pulses V, V<SP>1</SP> in antiphase to lines 181, 182, to block the tube pairs 145-146, 160-161 alternately, so that amplified potentials proportional to electrodes pressure and welding current are applied alternately to the Y plates 191-192 of the C.R.T. 202. The time base potentials applied to the X plates 194, 195 are derived from a scanning generator 196, the frequency of which is adjustable at 197-198. Normally with a switch 200 engaging contact S1 scanning is effected in dependence on the setting of members 197-198 and the pressure and current curves during the whole spot welding operation are continuously indicated. By moving the switch 200 to contact S2 the time base is controlled by a device 201. By moving the switch 391 therein to position I a single stroke indication is given of the whole of each welding operation, Fig. 3 (not shown). In positions II of switch 391 a single stroke " spread out" indication is given; only that portion of the cycle commencing with the breaking of the main switch 24 is indicated, Fig. 7 (not shown). The scanning is in both cases controlled by relay circuits, Fig. 5 (not shown), made and broken by contacts 302-303, 312-313, Fig. 1, actuated by the pedal and main switch 24 respectively.