Electronic welding current generator for pulsed-arc welding

The invention relates to an electronic welding current Generator for the pulse arc welding, with a by electrical control variables controllable power supply, which can be preset on electronic circuit, in pulsed operation respectively during the pulse phases t_P on higher generator pulse current I_p or a higher generator Pulse voltage U_p and respectively during the base phase t_G on lower generator base current I_G or a lower Generator-ground voltage U_G can be generated, wherein during the basic phases t_G the base current I_G is regulated.

From US-PS 4,758,707 is already such a electronic welding current generator known. The regulation electronic welding current described therein Generator has the aim that, at each current pulse, only a single drop of welding material is detached. To is a correct relationship between the pulse rate and the feeding of the welding wire sought. Therefore, in a time interval immediately prior to the insertion of a Current pulse, the minimum applied voltage is detected, the proportional to the current across the arc voltage applied is. This measurement is used to control the pulse frequency used, with the aim of ultimately the voltage of the Arc in good approximation at a predetermined value to keep. Here, the duration of the current pulse, and the amplitude of the current pulse and the base current while the entire Schweißpprozesses kept constant, which means that, when the welding current described therein Generator called I_p-I_GModulation (pulsed current Basic current modulation) is used.

An electronic welding current generator in accordance with this However, the art is in practice in itself problematic, since in the I_p-I_GModulation no "inner Scheme "for the process stability effect, the process so must be controlled in each case from the outside. namely, the current flowing through the arc current at a constant held wire feed speed is constant, derailed the process without additional regulatory action within a short time:For example, if the distance between the wire and Workpiece increases for some reason, is the resistance of the arc whereby higher at, constant current, the voltage increases. However, this has with the result that the introduced power, and thus the Melting rate of the wire is increased; thereby increasing the distance between the wire and workpiece, so that Arc length, even more - the process derailed. The same thing applies if the distance and thus the resistance decreased between the welding wire and the workpiece. In this case lowers the applied voltage, the power and thus the melting rate of the welding wire decreases and the arc length even further shrinks.

In the electronic known from US-PS 4,758,707 Welding current generator is therefore the pulse rate means an elaborate control electronics continuously adapted to the necessary process stability at constant to ensure wire feed speed.

In electronic welding current generators, which in the Pulse phase not the current, but the voltage constant hold (U_p-I_GModulation instead I_p-I_GModulation) and thus constant pulse rate without complex Control electronics work, however arising various, significant problems: By heating and Wear increases the contact resistance between the contact tip and the wire material, as well as the Line resistance gradually in the welding cables. Now is during the pulse phase t_p the resistance of the arc extremely small so that the voltage drop across Contact resistance during the pulse phase a significant represents share of the total voltage. Most arc However, no electric tap possible, so that the real Arc voltage for the purpose of regulating the pulse voltage can not be detected as an actual value. Thus decreases available on the arc voltage over time unnoticed, the arc is shorter and spatter increases to until the complete derailment of the process. A for Avoid these consequences any possible visual inspection the arc length, connected with a manual Readjusting the Solllwerts of the pulse voltage U_p overwhelmed the operator and ruled out for reasons of cost and lack of quality assurance of itself. A precautionary replacement of the contact nozzle to a small number of welding cycles results in a high die consumption and in frequent downtime and thus leading to avoidable high cost.

The invention is therefore based on the object, a electronic welding current generator for the pulse Arc welding of the aforementioned type so to design that the welding process is an "internal Control "subject and also automatically, via several welding cycles gradually rising, Tendency to arc shortening or extension counteracts.

This object is achieved in that during the pulse periods t_p the pulse voltage U_p controlled is wherein: During basic phases t_G the basic voltage U_G is measured time-selectively,the measured value E, the real acting length of LL is arc directly proportional, stored and after every pulse period T is updated,the updated, the length LL of the arc reproduced measurement E for higher control of Welding process with an adjustable setpoint for SWLL the length LL of the electric arc is compared and because of the resultant control deviation ± X_w of the set target value of the pulse voltage U_p readjusted becomes.

Flowing from the updated measured value E and the target value SWLL, SWU_LL resulting deviation ± X_w is a abandoned downstream PI controller and the manipulated variable Y ± increasingly, the manipulated variable Y ± incrementally or decrementing the target value of the pulse voltage U_p and optionally in addition to the target value for the duration of Pulse phase t_p and / or the setpoint for the duration of the Base phase t_G acts. The level of intervention (control factor) is adjustable or fixed rigidly.

Further advantageous embodiments of the invention are in in the sub-claims.

By the invention it is thus possible to extremely advantageous self-control effect, the "internal control" the U_p-I_GModulation, in a generic to use electronic welding current generator, whereby to respect shorter time intervals, a Process stability without other interventions results: The constant feed rate of the material is wire, if at constant tension from any Reasons temporarily a smaller current should flow, the distance between the wire and workpiece - the Arc length - downsize, which by the smaller product of current and voltage a smaller Power is introduced and thus the Drahtabtragsrate verrringert. By arc shortening is due to the decrease of the ohmic resistance of However, increasing power vigorously, whereby the introduced Power increases, thus increasing the Drahtabtragsrate becomes; the distance between the wire and workpiece - the Arc length - is self-regulating larger again. Also a current fluctuation in other direction is accordingly balanced.

It has however been recognized according to the invention that the Length of the arc over several welding cycles only then can be kept constant if the set value of the Pulse voltage U_p is nachgeregeltl kontuinierlich to the Voltage drops across the welding cables and the contact nozzle compensate. The invention furthermore recognized been that the contact resistance in a time interval the order of a welding cycle to be constant can be approximated. Due to the negative differential resistance of the arc, however, the Arc resistance in the base current phase t_G several Orders of magnitude greater than in the pulse phase t_pSo that over the inventive measurement of the fundamental voltage U_G while the base phase t_G a directly proportional access to the gradual change of the contact resistance, and thus the possibility to compensate for these changes continuously, given is.

The invention has the salient advantage that through the Arc-length control the pulse arc welding in both directions Process stability increased significantly reduces the contact nozzle usage and Still downtimes are decreases. In a practical experimental arrangement was the Contact die life when using the invention on 5 times of welding cycles increase. such as commuting, also remains with manual welding, in a fillet weld the Arc length stable; additionally spatter is greatly reduced. Des wide Ren is the influence of the welding cable resistance increase in the heating of the Welding cable now without influence on the welding process.

The core of the invention lies in the detection of a measured value, which is directly proportional to for real acting arc length behaves, wherein advantageously the principle of pulse technique with U_p-I_GModulation is used. During the pulse period t_p is the pulse voltage U_p regulated during the base phase t_G however, the base current I_G, Becomes during the base phase t_G time selectively measured the generator voltage, stored and updated after each pulse period, then an in this way the Arc length proportional measured value obtained for the outstanding manner in a the arc length-preserving, overriding control is available.

This actual "arc length" is an adjustable setpoint "arc length" compared, and the resulting control deviation ± X_w through a downstream PI controller amplifies the control value ± Y. The setpoint follows the relationship U_LL= U_O+ M · U_IG; the meanings are:

U_LL= Setpoint arc lengthU_O= Fundamental voltage (adjustable z. B. potentiometer between 13-20Vm = slope factor with adjuster, adjustable (z. B. on board) 0.02-0.05U_IG= Control voltage for the base current I_G,

Thus a process all influences can advantageously be considered characteristic Set which can be obtained similarly rigid VDE characteristic.

With the controller output variable ± Y may in many ways to the pulse technique required process parameters such as setpoints U_p, t_p or t_G, Incrementing or decrementing be interfered with, the level of intervention, the control factor, adjustable can be designed or rigidly fixed.

To illustrate the principle of the invention are the following Rule Types serve:

Control type "pulse voltage increase in tendency to arc shortening":Effective setpoint U_p= Set setpoint U_p+ .DELTA.U_p, Where: U_p= Α · (+ Y); the value of Y is suppressedα = level of intervention (control factor).

Control type "pulse voltage increase and pulse time increase in tendency to Arc shortening ":

Effective setpoint U_p= Set setpoint U_p+ .DELTA.U_pEffective setpoint U_tp= Set setpoint U_tp+ .DELTA.U_tp; where:.DELTA.U_p= Α · (+ Y); the value of Y is suppressed.DELTA.U_tp= Α1 · (+ Y)

These two control modes are preferably suitable for automatic Welding and here in particular to increase the contact nozzle service life and Eliminating the effects of the supply cable.

Control type "pulse voltage increase in tendency to arc shortening and Basic time increase in tendency to arc extension ":

Effective setpoint U_p= Set setpoint U_p+ .DELTA.U_pEffective setpoint U_tG= Set setpoint U_tG+ .DELTA.U_tG; where:.DELTA.U_p= Α · (+ Y); the value of Y is suppressed.DELTA.U_tG= Α2 · (Y); the value Y + is suppressed.

This U_p-t_G-Regelart Is preferably suitable for manual welding.

Depending on the application, one of the three above-mentioned control modes specified or are switched on. This requires an optimally adjusted welding process, wherein an existing Regelartschalter must be "balance" in the position. The nominal value of the voltage "arc length" SWU_LL is set during ongoing process so, to the control value ± Y = 0. For this purpose, the manipulated variable to a difference display be connected in any design, eg. as a zero instrument or LED row Ad od. Ä., To detect positive and negative deviations from zero. In this Compensating position affects the PI controller only as a P-controller with a defined gain and thus function as a display amplifier. After the adjustment can then click the desired control mode are switched; then the process parameters should not be adjusted. If this is required, for example in another welding job, is a unique first readjustment necessary. This adjustment can also designed automatically be (Autom. Zero adjustment).

The regulation control variable ± Y may be associated with a limit monitor which users signals when the increased service life is reached. As input receives the Limit monitor preferably the arithmetic mean of the manipulated variable, whereby rapid manipulated variable rashes are suppressed.

Preferably, the limit indicator in the balance position and during the Ignition phase of a welding process blocked to avoid false positives; he is thus released delayed. The limit value can with an associated potentiometer for setting the threshold voltage U_GW be adjusted.

Short description of the drawing in which shows

<b>Fig.</b> 1The block diagram of the electronic welding current generator,

<b>Fig.</b> 2, the detection of the base voltage by sample-and-hold and

<b>Fig.</b> 3, showing the relationship between the control factor, the effective Voltage setpoint U_p the pulse phase t_G at the U_p-t_G-Regulation.

Preferred embodiments of the invention

A period T of the welding voltage <b>1</b> is the block diagram <b>Fig.</b> 1 of the electronic Welding current generator shown. In pulsed operation, during the pulse phases t_p a higher generator pulse voltage U_p and during the basic phase t_G a lower generator basic voltage U_G generated, wherein preferably the basic phases t_G last longer in time than the pulse periods t_p, The welding voltage signal is a matching network <b>2</b> given where appropriate to adjust the Measured value and / or for normalization and possibly for electrical isolation. The Output of the network <b>2</b> is the time-selective detection of the straight branch the base voltage U_G the welding voltage signal of a sample and hold <b>3</b> fed; simultaneously, the output signal from the network<b>2</b> to parallel a block <b>4</b> for the selection and definition of the basic phase t_G given up. This building block <b>4</b> serves with decreasing measurement voltage the sample signal to delay, with rising test voltage, however, immediately turn off, thus actually only the horizontal branch of the fundamental voltage U_G is detected. This thus obtained Measured value E is directly proportional to real acting length LL of the arc. Of the Measured value e is updated by each period T of the welding voltage, so that always an updated measured value E is proportional to the arc length at the output of LL Sample and hold <b>3</b> is available; this measured value E thus is the actual value the base voltage U_G again, the directly proportional to the real acting arc length LL is.

Now the comparison is this measured value E (U value_G with an adjustable setpoint for the arc length SWLL, which is preferably a voltage value SWU_LL is, wherein the target value SWU_LL from a block <b>6</b> is won. The nominal value of the voltage SWU_LL follows the relationship: SWU_LL= U_O+ M · U_IGWherein the slope factor m using a potentiometer <b>18</b> is set, the supplied with the control voltage U_IG the base current is multiplied. A potentiometer<b>19</b> the block <b>6</b> is the fundamental voltage U_O set. In this way, at the input of PI controller <b>5</b> won the deviation ± X, which the PI controller <b>5</b> is supplied.

This equation allows a process all influences can be considered characteristic Setting similar to the rigid VDE characteristic. The deviation ± X_w is the PI controller <b>5</b> strengthened for the command value ± Y, which represents the control output. With usually output ± Y can now in many species to the pulse technique required process parameters such as setpoints, pulse voltage U_p, Pulse phase t_p or Base phase t_G be encroached incrementally or in descending order. The Of intervention, which is the control factor α can be adjusted designed or rigidly defined will.

In the block diagram of <b>Fig.</b> 1 is to the manipulated variable Y ± parallel through a diode <b>7</b> in Forward to a switch <b>9</b> for the control mode "pulse voltage increase at Tendency to arc shortening "abandoned, ie with decreasing arc length is in this type of control the pulse voltage increased until the original Arc length is reached again. This type of control optimized in particular the Welding process.

Simultaneously, the control value ± Y is a forward-biased diode <b>7 '</b> on a switch <b>9 '</b> for the control mode "pulse voltage increase and pulse time increase in Tendency to arc shortening "abandoned, ie with decreasing arc length the pulse voltage while the pulse width is increased until the original arc length is reached again.

Simultaneously, the control value ± Y is a reverse biased diode <b>8th</b> a switch <b>9 ''</b> abandoned for generating the control mode "pulse voltage increase at Tendency to arc shortening and basic time increase in tendency to Arc extension ", ie the type of control is used for pulse voltage increase at declining arc length and the basic time increase with increasing arc voltage and is mainly used in manual welding.

The switches <b>9, 9 ', 9' '</b> are used to set or choice of control mode. Before each block<b>11, 11 ', 11' '</b> is ever a potentiometer <b>10, 10 ', 10' '</b> arranged to the control factor α or α<b>1</b> or α<b>2</b> adjust. The blocks<b>11, 11</b>'and <b>11 ''</b> consist of active Adding networks, in which by adding the corresponding control voltage plus the differential of this control voltage the corresponding setpoint SW is generated, which is preferably a voltage, namely, one of the target values:

SWU_p= U_p+ dU_p for the block <b>11</b>SWU_tp= U_tp+ dU_tp for the block <b>11 '</b> orSWU_tG= U_tG+ dU_tG for the block <b>11 ''</b>,

This particular reference can now in a suitable power unit as control variable be used.

The manipulated variable Y is ± equal, preferably via an RC network <b>15</b>, to Averaging a limit indicator <b>12</b> and in parallel, a block <b>16</b> to abandoned display adjustment, the output signal to a display instrument <b>17</b> is given, which is a deviation ± zero display capable. The limit monitor<b>12</b> indicates to the user when the by the overriding control of the above Rule Types increased service life is reached. By arithmetic averaging the manipulated variable to suppress rapid manipulated variable rashes. The limit monitor<b>12</b> by means of a switch <b>14</b> in the balance position and during the Ignition phase of a welding process blocked to avoid false positives; he is released delayed. The threshold voltage U_GW can via a potentiometer <b>13</b> the limit monitors <b>12</b> be specified.

In <b>Fig.</b> 2, the detection of the base voltage by the sample-and-hold circuit <b>3</b> shown. The sample-and-hold signal is only during the base phase t_G to the Measuring voltage down, when in fact the basic voltage U_G is achieved, that is to Thus, only the horizontal branch of the measurement voltage is detected. The basic tension is saved and is in the hold phase and preferably positive feedback signal for the subsequent nominal with actual value available.

The target value comparison is done at the input of the PI controller <b>5</b>Whose PI behavior can be provided in a variable manner.

<b>Fig.</b> 3 shows the relationship between the control factor and the base phase t_G and of the control voltage U_tG, In this case, it is seen that at small t_GTimes of the controller action is weakened, because in this case the so-called "internal control" more is effective, that is, the t_pPhase is relatively large compared to the period T. In big t_G-times, Approximately from 15 ms, the controller action so that the pulse rate is gradually decreased, is not too low.

List of reference numerals

<b> 1</b> Period of the welding voltage<b> 2</b> Measured value matching network<b> 3</b> Sample and hold<b> 4</b> Module for the selection of the basic phase<b> 5</b> PI controller<b> 6</b> Block to generate the voltage command value of the Arc length<b> 7, 7 ', 8</b> diodes<b> 9, 9 ', 9''1</b> switch<b>10, 10 ', 10' '</b> potentiometer<b>11, 11 ', 11' '</b> active Addiernetzwerke or addition circuits<b>12</b> limit monitor<b>13</b> potentiometer<b>14</b> limit switches<b>15</b> RC network<b>16</b> Module to display adjustment<b>17</b> Gauge<b>18, 19</b> potentiometerU_O basic tensionU_p pulse voltageI_p pulse currentt_p pulse phaseU_G Basic voltage actual valueI_G Basic current valuet_G basic phaseT pulse periodU_IG Control voltage of the bias currentU_tp Voltage with respect to the pulse phaseU_tG Voltage relative to the base periodLL arc length SWU_LL Voltage setpoint of the arc lengthGW limitU_GW threshold voltagem slope factor± Y controlled variable± X deviationα, α<b>1</b>, α<b>2</b> Control factors (of intervention)SWU_p Set value of the pulse voltageSWU_tp Voltage command value with respect to the pulse phaseSWU_tG Voltage setpoint relative to the base period