US2556715A - Phase shift heat control for welders - Google Patents

Description

June 12, 1951 s. G. VIGARS PHASE SHIFT HEAT CONTROL FOR WELDERS 2 Sheets-Sheet 1 Filed Feb. 9, 1950 lnventor B5 I I l W (Ittorneg June 12, 1951 s. G. VIGARS 2,556,715

PHASE SHIFT HEAT CONTROL FOR WELDERS Filed Feb. 9, 1950 2 Sheets-Sheet 2 62777 60072904 v I J FIJI-770? 6a Bnventor Patented June 12, 1951 PHASE SHIFT HEAT CONTROL FOR WELDERS Sterling G. Vigars, Royal Oak, Mich., assignor to General Motors Corporation, Detroit, Mich, a

corporation of Delaware Application February 9, 1950, Serial No. 143,17

8 Claims. 1

This invention relates to welding control means andzmore specifically to adjustable control means for sequentially operating groups of welding heads in sequence. In many installations it is necessary to fire a plurality of spot welders at one instant and immediately follow that by a second or third group to, in a relatively short time, secure together desired parts. These parts may be of different thicknesses and difierent contours at spaced positions and it, therefore, may be necessary to apply different total heats to the different groups of spot welds.

It is therefore an object of m invention to provide a control system for sequentially energizing different groups of electrodes for weldin and to separately adjust the proportionate amount of heat available to the individual groups.

It is a further object of my invention to provide sequential group weld control means in which any one group may be adjusted to provide the desired heat without in any way affecting any of the other groups.

With these and other objects in view which will become apparent as the specification proceeds, my invention will be best understood by reference to the following specification and claims and the illustrations in the accompanying drawings, in which: 4

Figure 1 is a circuit diagram embodying a system including my invention.

Figure 2 is a group of curves of the voltages and currents appearing on the control tubes.

Figure 3 is a similar group of voltage and current curves illustrating the effect of varying the phase by the means disclosed.

Referring now more specifically to Figure 1, there is shown therein a main pair of power input lines 2 and 4 controlled by main switches 6 and 8 respectively, switch 6 being connected by line H) to a pair of normally open contacts W1 and thence through line I2 to one side of the primaries l4 and I6 of two welding transformers. It might be mentioned at this point that while two welding transformers are shown, an number can be used with this system, and two is merely illustrative. It is desired to point out also that the relay coils are referred to by letters and that the contacts operated by each relay coil are likewise referred to by the same letters as the coil and with a following sub-number to differentiate the different contacts, but to identify them with their control relay. To further assist in tieing the operated contacts back into its operating relay, we have shown in dotted arrow lines the direction of the control relay from the contacts. The second main switch contact 8 is connected through line l8 to a second normally open pair of contacts W2, and thence through line 20 to lines 22 and 24, extending itself to a mercury pool electrode 26 in ignitron, 28. Tap line 24 likewise extends from line 20 to the mercury pool electrode 30 in ignitron 32 and tap line 22 extends from main line 20 to line 34.

A second set of control power input lines 36 and 38 are connected to the control panel power and extend to two manually operated switches 40 and 42, the movable terminal of switch 40 being connected through line 44 to one side of a plurality of control relay coils RI, Tl, R, R2 and T2. Line 36 is connected through tap line 46 to a pair of normall closed contacts R1, which are operated by main relay R. The opposite side of this pair of contacts is connected through line 48 to a manually operated switch 50 and thence through line 52 to one side of a control relay coil W. The opposite side of relay coil W is connected through line 54 to a second manually controlled switch 56 and thence through line 58 to one side of a second pair of normally closed contacts R2, likewise controlled by control relay R and then finally through line 60 to the opposite control line 38. A relay coil 62 is connected between lines 48 and 58 and controls the hydraulic control pressure.

One side of control relay coil BI is connected through line 64 to one side of a normally closed pair of contacts Tli, the opposite side of which is connected through line 66 to tie line 68 extending between relay TI and a selector switch 10. Selector switch 10 is connected also by line 12 with line 14, the latter extending between a control pressure switch 16 and one side of a pair of normally open contacts T22. Pressure switch 16 is also connected directly to manually controlled switch 42. One terminal of relay R. is connected through line 18 to stationary contact of selector switch 82 and also to the other side of normally open contacts T22. A second stationary contact 84 on selector switch 82 is connected through line 86 to stationary contact 88 of selector switch Ill and also through tie line 90 with one side of normally open contacts T12. Relay R2 is connected through normally closed contacts T21 to arm 82.

That portion of the system so far described initiates the cycle and likewise proceeds to, in timed relation, sequentially provide energy for the different groups controlled by the welding transformers, and is outlined in dot and dash lines as will be noted.

The second section shown immediately below and also outlined in dot and dash lines may be referred to as the phase shift control portion of the system. This consists of the main control transformer primary TP, one side of which is connected through tie line 92 to main line I2, the opposite side being connected through lines 3 3 and 22 to main line 20. It is, therefore, energized at all times when relay coil W is energized to close its contacts W1 and W2. Transformer primary TP is center tapped and to the center is connected a windin TPA, the opposite end of which is connected to one end of a Variable resistor 24 and also through condenser 96 to line 92. The adjustable tap 98 on resistor 94 is connected through line I to adjustable tap I62 on a second variable resistor I04, and also to adjustable tap I06 on a third adjustable resistor I98. Resistance I04 is likewise connected to a pair of normally open contacts Rili operated by relay RI, the opposite side of which is connected directly to line 34. In like manner resistor Hi8 is connected to a pair of normally open contacts R21, also connected to line 34. By

, adjusting the position of adjustable taps I02 and I65, the phase of the control may be shifted to provide different amounts of heating, as will appear in the following more detailed discussion.

The third dash and dot outlined section of I my control system contains the thyratron controls which are commonly used with each group of following ignitron contactors, the latter, of course, being the actual firing means. This section consists, therefore, of two control thyratrons Hi3 and H2, each capable of controlling Opposite half cycles, two secondary transformer coils TS and T81, both inductively coupled to the primary TP, and two secondary coils TSA and TSA1 inductively coupled to primary coil TPA.

The connections of these various parts will now be more described in detail.

One end of transformer coil TS is connected through line I I4 to a resistance I IS, in turn connected to control grid H8 of tube H2. A condenser IZU is directly connected across resistance H6. The opposite end of transformer coil TS is connected directly to one terminal of the secondary coil TSA and that in turn is connected through line I22 to the plate I24 of tube Hi! and to the cathode iZfi of the tube H2. The same type of connections exist on the opposite side for controlling the other half cycle in that transformer T81 is connected directly through resistor I28 to control grid I30 of tube H0 and has condenser I32 connected directly across said resistor. Transformer secondary T81 is also connected to transformer secondary TSAi and thence through lines I34 and I36 to plate I38 of tube H2, and also to the cathode I46 of tube H0. These tubes will alternately conduct on opposite half cycles at predetermined positions in their energizable time, depending upon the control set forth above. When these conduct, they cause the ignitrons controlled thereby at that particular instant to fire and weldin current through the transformers results.

The last and final section to be described is that enclosed in dot and dash lines at the bottom of Figure 1, and this consists generally of a pair of ignitron tubes and a weldin transformer for each group of spot welders which it is desired to control, and as mentioned previously we are here concerned illustratively with only two, although the number could be as large as desired. In this instance control line I42 extends from cathode I26 of tube H2 down to a pair of normally open contacts BIZ and thence through a normally closed thermo switch I44 and a fuse ILIIS to one side of a half wave rectifier I48 and also to the opposite side of a half wave rectifier IEIE, the direction of current flow being indicated. The opposite side of rectifier M8 is connected to the igniting electrode I52 of the tube 32 and the opposite side of the rectifier [Eli is connected through line I54 to the mercury electrode 3d of the tube 32 and also to the spaced or plate electrode I56 of a second ignitron tube I58. In like manner the spaced plate electrode Hit of the tube 32 is connected through line I62 to the mercury electrode $4 of the tube I58. Line Hi l, which proceeds downwardly from thyratron lid, is connected through a normally open pair of contacts Biz and thence to two half wave rectifiers I66 and IE8 connected respectively to the igniting electrode III} and the mercury electrode I64 respectively. Line I12 interconnects the mercury electrode of tube I58 with one terminal of the welding transformer primary I4, which has connected thereacross a surge resistance I'M. Thus the two thyratrons H2 and III} alternate-- 1y control the firing of the ignitrons 32 and I58 to provide alternately half cycles of welding power to transformer I4.

Afterthe welding by transformer I4 is accomplished, ignitrons 32 and I58 are switched out of the circuit and are replaced by ignitrons 28 and H6. Line I42 also extends down to and is connected to a pair of normally open contacts R22 and thence through a thermo overload switch IlIl and fuse ISO to two half wave rectifiers I82 and I85, rectifier I82 being connected to igniting electrode I86 of tube 28. Plate I88 of tube 28 is connected through line I913 with a mercury electrode I92 of tube I16 and likewise to one side of the transformer primary I 6 of the second welding transformer. Half wave rectifier I84 is also connected to the mercury electrode 26 of tube 28 and through line I94 to the spaced electrode or plate I96 of tube IIB. Line I34, extending from thyratron III is also connected to one side of a pair of normally open contacts R23 which are in turn connected to two rectifiers I98 and 26B, rectifier I98 being connected to igniting electrode 2E2 of tube H6.

The operation of this system, as indicated above, provides a series of sequential groups of welds; that is, several spot welds will be performed by the firing of the tubes 32 and I58 to energize transformer primary I4 and the amount of heat provided in each weld will be controlled by the settings on resistors 94 and H34 in series. Then next in sequence, another plurality of spot welds will be performed by the energization of tubes 28 and I I6 and the amount of heat developed in this plurality of welds will be determined by the adjustable settings on resistors 94 and IE8 in series.

The heat control is provided basically by the resistive-reactive network enclosed in the dash and dotted outline at the upper center of the system. The secondaries of the peaking transformer TS and T31 are connected to the grid circuit of the associated heat control thyratrons so that the voltage of these secondaries will lag the plate voltage applied to these tubes. The amount of this lag is determined by the amount of resistance in the phase shift control circuit including primaries TP and TPA and indicated as variable resistances 94, I04, and I03, With zero resistance or with each of these rheostats moved to a position to cut out the resistance involved, the la is zero degrees and with the resistance portion of the circuit open or infinite resistance the lag is 180.

The resistance portion of this phase shift circuit consists of what might be termed a heat control resistor for each of the groups of welders which are to be fired. Resistor I04 acts as the heat control resistor for the first group of ignitrons 32 and I58. In like manner resistor I08 acts as the heat control resistor for the second band of ignitrons 28 and I16. Associated with each of the heat control resistors when it is in circuit is what might be termed a power factor adjustment resistor 94 which is common to all of the circuits and is set initially. For example, with all the resistance of resistor I04 cut out, the power factor adjustment resistor 94 is adjusted to compensate for the normal power factor of the load. This brings the peaking voltage in phase with the load current. This peaking voltage overcomes the negative bias supplied by TSA or TSA1, as the case may be, and causes the thyratron tube to fire at the beginning of the cycle. When this occurs the result is 105% heat or all that can be obtained from a single cycle and is the calibration of any indicator on resistor I04 or I08 when set for nominal zero resistance.

Increasing the resistance of either M4 or H18 in the circuit will decrease the amount of heat obtained per cycle, since it causes the peaking voltage to lag in an amount dependent upon its setting. Resistor I04, or rather tap I02 thereon, can be adjusted to vary the percent of heat or current over practically a full range. Indicating means on the adjustment of resistor I64 can be calibrated as a measure of percentage heat derived. This can be further described by reference to the showings of Figure 2 and Figure 3 of the drawings in which various voltage and current curves are shown.

Referring specifically to Figure 2, there is shown therein a curve labeled E which is the normal voltage applied to one of the thyratrons H2 or II!) from the main line. A second curve of smaller height designated IL, or load current, discloses the phase difference in the voltage applied to the thyratron and the current at the load when full heat is applied. Eco indicates the voltage on the grid bias and Es, the peaking voltage. The dotted line indicates the critical grid voltage curve. A study of these curves will dicate their time phase differences and it will be seen by shifting the peak voltage Es along the time base by a variation in the phase control resistance that the triggering of the thyratron may be varied in time relation, that is, later or earlier in the main voltage cycle, to cause more or less total current to fiow per half cycle.

This is perhaps better illustrated by further reference to Figure 3 in which there is illustrated the movement of the peaking voltage along the time base. E in this instance still indicates the voltage from the line applied to the thyratron plate and IL is now shown in dotted lines, since we do not obtain the full current. The peaking voltage Es has been moved along the time axis and now triggers the tube at a later instant in the cycle and IL indicates the total current at reduced heat. The distance between the starting instant of the voltage curve Ep and the starting instant of the dotted line indicating IL at full heat is determined by the setting on resistor 94,

which has previously been referred to as the power factor resistor, and this is a constant distance or delay being preset for given load conditions. The second horizontal distance, that is, between the beginning of the dotted line curve IL at full heat and the beginning of the curve II. at reduced heat, is controlled by the setting on resistor I04 or [08 as the case may be, and is adjustable, depending upon the desires of the operator.

In the operation of this system, therefore, the operator would first adjust and set adjustable tap 98 on resistance at to compensate for the power factor of the load. He then would adjust the various taps I52 on resistor I04, and tap I05 on resistor I68, and any further adjustable resistors if more than two banks or welders were to be fired for the heat setting which was desired on each bank. With the system then ready to be operated, main switches 3, 3 and 40, 42 are closed. At this time relay W is energized through an obvious circuit to close contactors W1 and W2. The pressure switch I6 will then be closed by an increase in pressure on the welding machine, and when this closes, timer relay TI starts to time out, and relay R! is energized, since TI and RI are in parallel circuit relation across the main power lines 36 and 33 at this point. When RI is energized, it closes its contacts Rh, Biz, and Biz. The closure of contacts Rh completes the energizing circuit through the phase shift control circuit as follows: from main line 20 through line 22, line 34, transformer primary TP and line $2 to opposite main line I2, and at the same time a parallel circuit from line 22 through line 3 5, contacts Rh, resistor I64, tap Hi2, line I69, tap 58, resistor Q4, condenser 36 and line 92. Biasing transformer primary winding TPA is, of course, included in this circuit.

At this time power is also supplied in alternate half cycles to the cathodes and plates of the heat control thyratrons HE and H2, but they will not fire until the bias voltage applied to the control grids permits the same. The energizing circuits for the thyratrons on alternate half cycles when the plate becomes positive are, of course, practically identical and only one of these energizing circuits will be specifically traced, it being assumed that the other will be clear therefrom. Full line voltage appears across the plate and cathode of thyratron lll through the following circuit: supply line 25, line 24, rectifier I50, fuse Mt, normally closed thermally actuated safety contacts M l, contacts R52, when closed, as just described, line M2, line E22 to plate I24, then from the cathode I45 through line 234, contacts Rlx, which have just been closed, rectifier I66, igniting electrode its of ignitron 558, line Iil, primary winding i l of the welding transformer to main line I2.

However, since the thyratron H8 is biased to cut off, no current can flow until a sufiicient voltage is applied to the biasing grid This is accomplished by the voltages supplied by the transformer secondaries TSA1 and TS1, which apply said voltage through resistor I23 to the control grid I30 in such phased relation as indicated by the setting E532 on resistor ltd. When this peaking voltage Es is applied to the grid its thyratron Ilil conducts, which completes the energizing circuit through the ignitron as just traced, and welding current is supplied to the transformer primary I4, whose value from maxi mum to minimum is determined by the setting I92. In the other half cycle tube H2 triggers ignitron' 32 in' exactly the same manner as tube Hi! triggers tube [58 and exactly the same amount of heat or current is supplied to the transformer primary 14' in the next half cycle and it is determined as well by the setting in on the resistor I64. This action continues as long as relay RI remains energized, which is, of course, for a predetermined number of cycles, which time is determined by timer relay TI, and when that has timed out, it is energized, being the type of relay which is time delay actuated to close and it then opens its contacts Til and relay RI is deenergized.

When this occurs, contacts Rh are opened to deenergize phase control resistor IE4, contacts Rlz are opened to open the circuit to ignitron 32, and relay contacts Rls are likewise opened to open the circuit to ignitron i533. Therefore, all of the first set of ignitrons and the first welding transformer are now excluded from the system. When timer relay TI is energized to deenergize relay RI, it also completes or closes a circuit for the energization of timer T2 by closing normally opened contacts Tl2. Upon the energization of timer T2, relay R2, likewise in parallel relationship therewith, will be energized through normally closed contacts T21 which do not pick up until T2 times out. With the energization of relay R2, switches R21, R22, and R23 are closed. These switches complete circuits to phase shift resistor H38, ignitron 28 and ignitron lit in exactly the same manner as relay R5 did in the first instance, and as soon as this occurs line voltage is again applied. to thyratrons Hi and I [2, which now control the firing periods of ignitrons 28 and H6 and the energized cycles of welding transformer Hi. It is not believed necessary to specifically trace circuits in this regard, as they are similar to. those of'ignitrons 32 and IE8. When timer T2 has now timed out, it will open its contacts T21, deenergizing relay R2' and in turn deenergizing the control system for welding transformer I6. It will be obvious. that as many different control circuits may be supplied as banks of transformers desired, and when the last timer has timed out, it will complete a circuit through relay R by closing its contacts such as T22, the energization of relay R opening the hydraulic solenoid valve 62 and when pressure is thus removed the pressure switch 76 drops out and the control system is deenergized.

I claim:

1. In a welder control system for energizing a plurality of welding transformers in sequence; electronic means connected to the primaries. of each of the transformers to control the conductive periods thereof, a common electronic control means, a first switching means connecting said common electronic means with any one of the first named electronic means, a phase shifting network connected to the common electronic means, said phase shifting network including a plurality of parallel paths ofsimilar components of adjustable value, said plurality of paths being equal to the number of transformers to be controlled, a second switching means in each path, a source of power, and sequentially actuated timer relay means connected to the source and to both switching means to simultaneously switch the parallel paths and the first named electronic means for a given transformer.

2. In a welder control system for energizing a plurality of welding transformers in sequence, electronic means connected to the primaries of each of the transformers tocontrol the conduc- Cir tive periods thereof, a common electronic" means of the grid bias type, a first switching means connecting said coimnon electronic means to any one of the first named electronic means, a resistance-reactance network inductively coupled to the biasing means of the common electronic means, said network including a plurality of parallel paths and adjustable resistances in each path, the number of paths being equal to the number of transformers to be actuated, a second switching: means in' each path, a source of power, a plurality of time controlled sequentially operated relays connected to the source of power and relay means controlled by the time controlled relays and actuating. both the first and second switching means to sequentially energize one path in the network and one of the first named electronic means at a' time to control the heating effect of a given transformer.

3. In a welder control system for energizing a plurality of welding transformers in sequence, electron tube means connected to the primary of each transformer to determine its inductive periods, a second electron tube means, biasing means for said second electron tube means, a resistance-reactance network inductively coupled to said biasing means, a plurality of parallel paths each having a variable resistor therein in said network to control the phase of the biasing voltage, switching means for connecting the second and sequentially the first electron tube means and in the parallel paths of the network to include one path for each first electron tube so that one transformer is energized at a time in order and its heating effect is determined by the setting on the variable resistor then in circuit.

4. In a welding control system, a plurality of welding transformers which it is desired to energize sequentially, electron tube control means connected to each transformer, common multi-electrode tube means, switching means for connecting said common tube means to each of the first named tube control means, a source of power connected to the switching means so that when the switching means are closed and the first named electron tube control means is fired by a control pulse from the common multi-element tube means, the associated welding transformer will be energized, biasing means for the multi-electrode tube means, and a resistive-reactive network including parallel adjustable resistance paths inductively coupled to the biasing means and to the power sourceto control the firing pulse initiation.

5. In a welding control system, a plurality of welding transformers which it is desired to energize sequentially, electron tube control means connected to each transformer, common multielectrode tube means, switching means for connecting said common tube means to each of the first named tube control means, a source of power connected to the switching means so that when the switching means are closed and the first named electron tube control means is fired by a control pulse from the common multi-element tube means, the associated welding transformer will be energized, biasing means for the multielectrodev t'ube means, said biasing means including a plurality of phased inductive windings in series connected to one of the elements, a resistive-reactive network including a plurality of parallel adjustable resistance paths connected to inductive means mounted in juxtaposition to the inductive means of the biasing circuit, switching means in the parallel paths so that only one may be used at a time and means to connect the network to the power source so that voltage flowing therein may be dephased and applied to the biasing means to control energization of the multi-element tube means.

6. In a welding control system, a plurality of welding transformers which it is desired to energize sequentially, electron tube control means connected to each transformer, common multielectrode tube means, switching means for connecting said common tube means to each of the first named tube control means, a source of power connected to the switching means so that when the switching means are closed and the first named electron tube control means is fired by a control pulse from the common multi-element tube means, the associated welding transformer will be energized, biasing means for the multielectrode tube means, said biasing means including a plurality of phased inductive windings in series connected to one of the elements, a resistive-reactive network including inductive means coupled to said windings in the biasing circuit, a common adjustable resistance connected to said inductive means and a plurality of adjustable resistors connected to the source and to the common resistance, the common resistance,adjustment compensating for the load and each of the parallel resistors adjusting the phase of the trigger pulse applied to the biasing circuit, switching means in the parallel resistance circuits so that only one variable resistance at a time will be in circuit and common relay means to actuate both the first and second named switching means.

7. In a control system for energizing a plurality of transformers in sequence for energization for differing cyclic intervals to obtain different amounts of energization from each, a multi-element electronic control means, a source of power, a plurality of adjustable phase shift networks, a first switching means to connect each phase shift network separately between the control elements of the electronic control means and the source of power, a second switching means to connect the electronic control means separately to each transformer, a common timed sequence switch actuating means to operate one element of the first switching means and one of the second switching means simultaneously as a pair, and the pairs in sequence to provide each transformer with one of the phase shifting networks to control the energization thereof.

8. In a welder control system for energizing a plurality of welding transformers in sequence for differing cyclic intervals to obtain different amounts of heating from each, a source of power, a multi-electrode electronic control means, a plurality of adjustable phase shift networks connected to said source, switching means to connect each separately to the control electrodes of the electronic control means, a second switching means to connect the electronic control means to each transformer, and a common timed sequence switch actuating means to operate one element of the first switching means and one of the second simultaneously and the pairs in sequence to provide each transformer with one of the adjustable phase shifting networks to control the energization thereof.

STERLING G. VIGARS.

No references cited.

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