Patent GB-1199516-A (GB)
Title: Automatic Welding System.
Inventor: FRIEDMAN ROBERT
IPC: G05B19/12
Filed: 1968-04-04
Abstract: 1,199,516. Programmed electric control: automatic speed control systems. NORTH AMERICAN ROCKWELL CORP. April 4, 1968 [April 5, 1967], No.16335/68. Headings G3N and G3R. Programmed Electric Control, Fig. 3. A programmed control arrangement for welding particularly for pipe welding of the gas or electric type comprises a transparent table 35 supporting a Mylar sheet 40, 41 containing opaque indicia. A carriage containing a plurality of photo-cells is moved across the sheet at a constant speed or a speed synchronized with welding electrode movement. In electric welding the path of a tape 91 would be indicative of arc welding current which is maintained at determined values by a closed loop control circuit controlling a phase controlled thyristor arrangement. The various operations i.e. wire speed electrode movement, and an H.F. arc starting circuit are controlled by other opaque tapes 192-196. In the case of pipe welding the arrangement may control a pre-heating run before the welding proper is commenced, and normally only after this time has elapsed, the carriage is switched over to run synchronously with the electrode movement. Automatic Speed Control Fig.9. In an automatic speed control system wherein a D.C. shunt motor is fed with variable width pulses, the motor current is maintained at its maximum or minimum value during speed deviations to obtain a high restoration rate. A constant current set point signal, which may be derived from a circuit illustrated in Fig.6 (not shown), is applied through terminal 127 to a constant current circuit 122 which charges a capacitor 141, which at a determined voltage fires a unijunction transistor 143 rendering a transistor 142 conductive shunting the emitter of transistor 143 to earth. At the same time capacitor 141 is discharged and applies a negative pulse through a capacitor 146 to momentarily turn off a transistor 147 hence a positive pulse is applied through a capacitor 148 to fire a thyristor 149. This turns on a transistor 151 in series with the motor which is connected to lead 153. Attached to the motor shaft is a wheel having slots admitting light to a photo-sensitive thyristor 160 responsive to either light or a gating current. When no light reaches the thyristor 160 a capacitor 162 is charged through a transistor 161 and a 1K resistor. When light reaches thyristor 160 it is fired which simultaneously discharges capacitor 162 through a diode 165, and renders a transistor 166 conductive which turns off thyristor 149. When capacitor 162 is discharged, a transistor 164 is turned off applying a pulse over lead 167 to an overspeed circuit 124. Under speed control is accomplished by placing a clamp on the emitter of transistor 143 which restricts the voltage to just less than the triggering voltage of this transistor, hence it will not trigger. As soon as thyristor 149 is turned off the clamp is removed hence the capacitor 141 voltage rises and transistor 143 conducts thus turning the motor current on almost instantaneously. Overspeed control transistor 180 when turned on energizes transistor 147 and reduces the voltage on the base 181, which reduces the firing voltage of transistor 143 hence pulses from this will not turn off transistor 147. This prevents firing pulses being passed to the thyristor 149 again until the motor has slowed to its new speed.