Patent Application
20050279742
The present invention relates to the art of electric arc welding and more particularly to a novel output stage for an electric welder to boost the OCV of the power source, especially for AC welding, such as AC TIG, AC MIG and AC submerged arc. The invention can be used in DC welding also.
The present invention is primarily directed to the output stage of an AC power source for an electric arc welder for performing an AC welding process, such as an AC TIG welding process or an AC MIG welding process and AC submerged arc welding. Power sources used for this type of welder have output stages that often involved a center tapped choke with alternating polarity switches on opposite sides of the choke where the electrode of the welding process is connected to the center tap of the choke. Prior patents showing this type of configuration are Stava U.S. Pat. No. 4,947,021; Bodewigs U.S. Pat. No. 5,340,963; Corrigall U.S. Pat. No. 5,513,093, and Holverson U.S. Pat. No. 6,723,957. These output stages using center tapped chokes are well known in the welding field and are incorporated by reference herein as background information relating to an AC welder of the type to which the present invention is particularly applicable. The output stage of a power source as described in the patents mentioned above is sometimes modified to place the choke in the common line between the center tap and the electrode. Both the positive and negative currents flow in opposite direction through the same choke, instead of flowing in only designated sections of a center tapped choke. The use of a common choke is shown in Stava U.S. Pat. No. 6,365,874, which patent also describes the relationship between a common choke and a center tapped choke in several embodiments of AC output stages. This Stava patent is also incorporated herein as background information relating to relevant AC output stages for a generic inverter type power source. The invention involves the selective actuation of a positive and negative boost circuit to increase the open circuit voltage (OCV) at least when a polarity change occurs. This is especially helpful at low current welding. A relevant background patent to this general concept, is Bilczo U.S. Pat. No. 4,897,522 illustrating a center tapped choke together with a common choke and having a continuously operated boost winding in the output stage of a DC welder. This patent is incorporated by reference herein as background information although, it is limited to a DC welder instead of an AC welder constituting the primary use of the invention.
Increasing the circuit voltage of a power source used for arc welding greatly improves the welding performance and arc stability of the process. This is especially true for AC welding operations where output circuit is commanded to switch between positive and negative polarity. In this situation, it is important to reestablish the arc immediately upon polarity reversal, both positive and negative to positive, in order to maintain arc stability in the AC welding process whether it is AC TIG or AC MIG. This is also true in AC submerged arc welding. As described in prior patents, the background technology for AC welding often involves an output stage having a center tapped choke. The purpose of this choke is well known and operates well under most applications. The choke arrangement utilizes the stored energy in the core of the choke to maintain current flow in the same direction in both sections of the center tapped choke irrespective of the actual welding polarity. In theory, the center tapped choke develops whatever voltage is required to maintain the current flow in either the positive or negative direction. The limitation of this design is the amount of stored energy available to reignite the welding arc at the moment of polarity reversal. The stored energy is proportional to the square of the current through the sections of the center tapped choke multiplied by ½ the inductance of the choke. In most AC welding applications, this energy is more than adequate to reignite or reestablish the welding arc when there is a change in polarity. However, there are conditions where there is not enough energy to consistently reignite the arc; therefore, the center tapped choke must be quite large to accomplish more energy storage. Larger chokes are more costly and they also impede the welding performance of AC welding. In some instances, when the choke is on the common leg of the output circuit, energy must be dissipated during each polarity cycle of the AC welding process. In this situation, there is not enough energy to reestablish consistently the arc at polarity reversals. Thus, there is a need for an output stage or circuit to assure sufficient open circuit voltage to reignite the arc in opposite directions during polarity reversal and AC welding process without merely increasing the capacity of the power source during the output circuit.
The main welding output of a standard power source used for electric arc welding (this phrase includes plasma arc cutting) usually develops an open circuit voltage of less than about 80 volts. The typical arc voltage is usually less than 30 volts. Thus, at reversal of polarity, there is only about 50 volts open circuit voltage to reestablish the arc. In addition to this 50 volts would be the voltage produced by the output choke. This total voltage, however, is sometimes insufficient to reestablish the welding arc. This is especially true at low current welding operations, such as welding at less than 10 amperes as is common in AC TIG welding. Low open circuit voltage for the power source creates high efficiency; however, the power source has difficulty maintaining the welding arc especially at longer arc lengths. For instance, in short arc welding, a low open circuit voltage is generally not enough to reignite consistently the arc at polarity reversals. Consequently, the output voltage for a power source, especially for AC MIG welding, must be high enough to maintain the arc during times of long arc lengths. Furthermore, higher voltage output from the power source inverter reduces the efficiency of the inverter. However, there is a need for a higher open circuit voltage, especially at polarity reversal in AC welding process. A solution would be to increase the open circuit voltage of the main output circuit of the power source. This is expensive and drastically reduces the efficiency of the power source. Consequently, the need for a high open circuit voltage for a standard AC welding presents a dilemma. Furthermore, a high open circuit voltage should not be available at the output terminals of the inverter used as the power source when the inverter is not driving a welding operation. There is a need for a circuit to provide high open circuit voltage for an AC welding process when high open circuit voltage for the power source itself is not sufficient. These needs are solved efficiently by the present invention relating to a novel output stage or output circuit for the power source of an electric arc welder capable of AC welding.
In accordance with the invention, there is provided additional boost windings with rectifiers and current limiting resistors together with control switches that are enabled or activated as needed to increase the open circuit voltage at particular instances in the welding process. The term “enable” or “activated” means that the switches can be operated in accordance with commands to the main switches in the AC output circuit of the power source or are merely closed. A separate positive and negative auxiliary boost voltage source is selectively switched to be added to the main positive or main negative voltage of the power source. A resistor in the separate auxiliary boost voltage sources limit the current in the separate sources to less than 20 amperes and preferably less than about 5 amperes. The voltage of the auxiliary separate boost voltage sources is in the general range of at least 100 volts. Consequently, whenever the separate voltage sources are switched into the output circuit of the main power source the open circuit voltage is high; however, very little current is provided at the high voltage. The high open circuit voltage merely assures reignition of the arc at polarity reversals in an AC welding process. The added voltage is a factor in the process; but, the added current is insignificant. Of course, an auxiliary open circuit voltage boost is advantageous in a number of welding processes; therefore, the control switches in the auxiliary separate positive and negative voltage sources are enabled, i.e. activated, to be operated whenever it is necessary to have a higher or open circuit voltage than is available as the main output voltage terminals of the power source used for driving the welder. Consequently, the invention relates to a positive and negative auxiliary boost voltage source having a current limiting resistor and a switch which is enabled or activated for operation at the times when there is a need for higher open circuit voltage.
In accordance with the present invention there is provided a converter or output stage for an electric arc welder used to weld at a gap between an electrode and a workpiece when a trigger switch is closed. This output stage has a first input terminal connected to an output terminal of a power source, with a positive voltage having a magnitude and a first amperage range. A second input terminal is connected to an output terminal of the power source, with a negative voltage having a second magnitude and a second amperage range. An auxiliary positive voltage supply with a positive voltage substantially greater than the main positive voltage and a positive current drastically less than the first amperage range, an auxiliary negative voltage supply with a negative voltage substantially greater than the main negative voltage and a negative current drastically less than the second amperage range, a first switch connecting the main positive voltage across the gap, a second switch for connecting the main negative voltage across a gap, and a polarity control device for alternately operating the first and second switches to produce an AC welding current across the gap. A third switch adds the auxiliary positive voltage to the main positive voltage. A fourth switch adds the auxiliary negative voltage to the main negative voltage. Then, a switch control device is activated to selectively enable the third and fourth switches for operation in unison with the first and second switches, respectively. The “enable” function can be actual closing of the third and fourth switches or merely conditioning the switches to be operated in unison with the first and second switches during AC the welding process. In one aspect of the invention, the switch control device is activated when the trigger switch is closed. In other words, when the welder is to be operated, the switch control device is enabled so that these third and fourth switches can be operated in unison with the first and second switches. In accordance with another aspect of the invention, there is a delay between the closing of the trigger switch and activation of the switch control device. This delay allows operation of the welder for a few cycles prior to activating the switch control device to allow operation of the auxiliary switches by themselves or in conjunction with the main switches. The term “enable” means that the switches can be or are operated. Indeed, in some instances when the switch control device is enabled the switches themselves are closed to apply the auxiliary voltage directly to the main switches of the output circuit or converter of the electric arc welder.
In accordance with an aspect of the invention, a resistor in series with the auxiliary boost voltage supplies limit the current to a level substantially less than 20 amperes and preferably less than about 5 amperes. The auxiliary voltage supplies have a voltage greater than 100 volts to increase the open circuit voltage to a level 100 volts higher than the open circuit voltage of the main output terminals of the power source. By providing low current in the auxiliary boost voltage circuits, the open circuit voltage is increased, but the current is low.
In accordance with another aspect of the invention, the two main positive and negative voltages are provided by secondary windings on the output transformer of a standard power source. The auxiliary voltage sources are preferably additional secondary windings or a secondary winding on the output transformer of the power source; however, the auxiliary voltages can be provided by separate transformers or even by an appropriate battery stack. The invention is primarily applicable to AC welding, such as AC TIG, AC MIG or AC submerged arc; however, the open circuit voltage increase obtainable by using the present invention is applicable to some welding operations where DC positive or DC negative is used by operating only the positive or the negative switches of an output stage.
In accordance with another aspect of the present invention, the output converter or output stage of the present invention has an output center tapped choke with a first switch in series with one section of the choke and a second switch in series with the other, second section of the choke. Of course, a single common choke can be used in combination with a center tapped choke or as the only energy storing component in the output stage of the present invention.
In accordance with another aspect of the present invention, there is provided a circuit to boost the OCV of the power source for an electric arc welder for welding across a gap between an electrode and a workpiece, when a trigger switch is activated, i.e. closed. The welder has a positive open circuit voltage of a first magnitude and a negative open circuit voltage of a second magnitude. The circuit includes an auxiliary voltage source of a third magnitude with a selectively operated switch to connect the auxiliary voltage source in series with one of the open circuit voltages. A switch control device operates the selectively operable switch. In accordance with this aspect of the invention, there is a second auxiliary voltage source with a fourth given magnitude. The selectively operated switch includes a second switch to connect the second auxiliary source in series with another of the open circuit voltages. In accordance with this aspect of the invention, the OCV of the main positive and negative voltage of another power source are increased by adding the auxiliary boost voltage to one or both of the main voltage sources.
In accordance with another aspect of the present invention there is provided an output stage for power source of an electric arc welder for performing a welding process between an electrode and a workpiece when a trigger switch is closed. The output stage comprising a first polarity circuit in series with the electrode and workpiece, the first circuit includes a first main power source with a first voltage and a first main switch operated by a first switch signal. A second polarity circuit is provided in series with the electrode and the workpiece and includes a second main power supply with a second main voltage and a second main switch operated by a second switch signal. An AC controller alternately creates the first and second switch signals to perform an AC welding process between the electrode and workpiece. An auxiliary first polarity circuit includes a first auxiliary voltage source additive to the first main supply and a first auxiliary switch in series with the first main switch and operated by a first boost signal. A second polarity circuit is provided including a second auxiliary voltage source additive to the second main supply and a second auxiliary switch in series with the second main switch and operable by a second boost signal. A boost controller is used for selectively creating the first boost signal during operation of the first switch signal and the second boost signal during operation of the second switch signal. These boost signals may be used to enable the switches or to actually close the switches in accordance with various implementations of the present invention.
Still a further aspect of the invention is the provision of a method of AC arc welding including applying a main positive voltage across an electrode and workpiece, applying a main negative voltage across the electrode and workpiece and alternating the positive and negative voltages across the electrode and workpiece. The method then applies a positive high voltage across the electrode and workpiece concurrently with the main positive voltage and an auxiliary high negative voltage across the electrode and workpiece concurrent with the main negative voltage. In accordance with this method, the current of the auxiliary voltages is less than about 20 amperes. The auxiliary voltages are substantially greater, than the main voltages and the current of the auxiliary power sources is drastically less than the main voltages.
In accordance with another aspect of the present invention there is provided an auxiliary OCV boost circuit for the output circuit of an electric arc welder to perform a welding process between an electrode and a workpiece. The power source has a main voltage output with a first voltage and a main negative voltage output with the second voltage. The boost circuit comprises a source of positive voltage substantially greater than the first voltage, a first switch to add the positive boost voltage to the main positive voltage, a source of negative voltage substantially greater than the second voltage, a second switch to add the negative boost voltage to the main negative voltage and a switch control device to selectively enable the first and second switches. Again, the term “enable” is broadly used to operate and/or condition the operation of the first and second switches.
The primary object of the present invention is the provision of an output converter or output stage for a power source used in an electric arc welder, which converter or output stage selectively increases the open circuit voltage of the power source in both the positive and negative directions, especially for the purpose of reigniting an arc during the polarity reversal in an AC welding process. The invention can also be used in DC welding.
Yet another object of the present invention is the provision of a converter or output stage, as defined above, which converter and output stage allows the use of a substantially smaller choke and can be used in various output circuits of an electric arc welder.
Still another object of the present invention is the provision of a converter or output stage, as defined above, which converter or output stage increases the open circuit voltage of the power source selectively when required by the welding process being performed.
A further object of the present invention is the provision of a method for electric arc welding, which method adds a voltage to the positive main voltage of a power source and adds a negative voltage to the main negative output voltage of the power source with switches for the purposes of adding the voltages at selected times during the welding process.
These and other objects and advantages will become apparent from the following description taken together with the accompanying drawings.
The present invention is an improvement in an electric arc welder of the type normally used in AC TIG welding and AC MIG welding. Such a welder A is shown as welder A in
In accordance with the present invention converter or output stage B includes a positive and negative auxiliary OCV boost circuit for both the positive voltage terminal 40 and the negative voltage terminal 50. Positive auxiliary boost circuit 200 includes a high voltage source illustrated in the preferred embodiment as two additional sections 210, 212 of transformer 20. These windings have a greater number of turns to give an increased voltage and are reduced in size since a low current is provided by these windings. Windings 210, 212 are directed to a full wave rectifier section 214 connected to the positive terminal of capacitor 220 so that the voltage on capacitor 220 is a high voltage generally above 100 volts. Lead 216 is at a voltage substantially greater than the main power source voltage on terminal 40. The auxiliary boost voltage is determined by the output of the full wave rectifier driven by windings 210, 212. Of course, these two windings are shown as separate windings; however, they could be a single winding for driving circuit 200. The term secondary winding for providing a high voltage power source includes one or more secondary winding sections of transformer 20. The voltage across grounded capacitor 220 is added to the voltage at terminal 40 by an auxiliary boost switch 240 having a gate 240a created as the output of operating logic device 242, shown as an AND gate. The logic device has two inputs which must be a logic one or true to create a signal in gate 240a. Thus, one of the input leads 244 is considered to be an enable lead and the other lead 246 is an operating lead. These functions could be reversed. Of course, there could be a single operating lead that would more enable or cause an output logic device 242. Operating input 246 is the output of controller 90 which is logic one or true when positive switch 80 is gated by a signal on line 80a. The logic on lines 80a and 246 are the same in this embodiment of the invention. To limit the current in auxiliary boost circuit 200 to a level less than 200 amperes and preferably less than about 5 amperes, there is a resistor 250 in series with auxiliary boost switch 240. When device 242 is enabled by a signal on line 244, switches 80, 240 operate in series and in unison to add the high voltage on grounded capacitor 220 with the relatively low voltage on the main output terminal 40. Thus, when there is a signal on line 244 enabling device 242, a signal on line 246 closes auxiliary boost switch 240 for adding a high boost voltage to the normal low voltage from the power source.
Negative auxiliary OCV boost circuit 202 is essentially the same as circuit 200. An high negative voltage, low current is created by a winding on transformer 20 indicated to be two sections 210, 212 in the preferred embodiment. These winding sections provide a high voltage, low current that is a voltage at terminal 50 that is negative as controlled by rectifier section 258. Thus, a high negative voltage is applied across capacitor 260 between terminal 50 and lead 262. The voltage on grounded capacitor 260 is essentially the same as the voltage on grounded capacitor 220, as previously described. Thus, auxiliary boost switch 270 is closed by a gating signal in line 270a from operating logic device 272 having an enabling input 274 and an operating input 276. This operating input is coordinated with the signal on gate line 82a of main negative switch 82. Gate leads 80a and 246 are normally the same logic and are activated when circuit B is in positive polarity. In a like manner, lines 82a and 276 are essentially the same lead and are operative when circuit B is shifted to negative polarity. Resistor 280 in circuit 202 limits the already low current in circuit 202 to a level less than 20 amperes and preferably less than about 5 amperes. Winding sections 210, 212 produce high voltage and low current. Resistors 250, 280 limit the low current to even a reduced controlled level.
Circuit B can operate with boost switches 240, 270 operated at all times so that there is always an added open circuit voltage during a welding process. However, in accordance with the preferred embodiment of the invention, switches 240, 270 are employed to assure that an arc is reignited at polarity reversals. Thus, if there is current flow through shunt 100 there is an arc and, in the preferred embodiment, there is no need for closing auxiliary boost switches 240, 270. To effect this operating scheme, logic inverter 290 has an input 292 that determines when there is a certain level of current in shunt 100. This level is near or at zero. When there is no current flow or little current flow, there is no arc and switches 240, 270 are activated or closed. The logic on line 292 is inverted to an opposite logic on line 294. A signal on line 294 indicates that there is no arc. Thus, a logic on line 294 enables lines 244, 274 to show there is no arc across electrode E and workpiece W. The preferred embodiment of the present invention causes lines 244, 272 to enable devices 242, 272 when there is no arc. This event applies a high voltage from grounded capacitors 220, 260 in series with the relatively low welding voltage at terminals 40, 50. The arc is relit. The arc is stabilized, even during low current operation.
The invention is the concept of selectively adding a high voltage, low current boost during the positive and/or negative polarity portion of a welding operation by the main power source.
The embodiment of the invention illustrated in
Turning now to the detail logic scheme in
The invention of adding an open circuit voltage auxiliary boost circuit to an AC output stage has universal application. To illustrate the fact, reference is made to Stava U.S. Pat. No. 6,365,874 wherein the AC output circuits shown in
As can be appreciated when considering the showings of
Yet another slight modification of the invention is illustrated in
The invention is broadly the addition of a voltage boost, schematically represented as auxiliary source 600 in
The various modifications can be combined in a variety of architectures to employ the invention in many environments obvious from the general description of the invention. The control and controllers are normally digital and software operated with the controllers being generally microprocessor based. Other analog and digital control and controller technology can be used.
