U.S. patent application number 15/184005 was filed with the patent office on 2018-02-08 for welding system with arc control.
This patent application is currently assigned to Illinois Tool Works Inc.. The applicant listed for this patent is Illinois Tool Works Inc.. Invention is credited to Adam E. Anders, Richard M. Hutchison, Shuang Liu, Erik D. Miller, James T. Olejniczak, Quinn W. Schartner.
Application Number | 20180036822 15/184005 |
Document ID | / |
Family ID | 56204066 |
Filed Date | 2018-02-08 |
United States Patent
Application |
20180036822 |
Kind Code |
A1 |
Schartner; Quinn W. ; et
al. |
February 8, 2018 |
WELDING SYSTEM WITH ARC CONTROL
Abstract
A method and apparatus for controlling arc/short between a wire
and a work piece is described. A current path parallel to the
wire/work is provided. The voltage drop across the parallel path
can be preset, to limit the wire/work voltage, or it can be
controlled to a desired level. The control can be in response to
feedback.
Inventors: |
Schartner; Quinn W.;
(Kaukauna, WI) ; Olejniczak; James T.; (Appleton,
WI) ; Hutchison; Richard M.; (Iola, WI) ;
Miller; Erik D.; (Verona, WI) ; Liu; Shuang;
(Dangtu, CN) ; Anders; Adam E.; (Osh Kosh,
WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Illinois Tool Works Inc. |
Glenview |
IL |
US |
|
|
Assignee: |
Illinois Tool Works Inc.
Glenview
IL
|
Family ID: |
56204066 |
Appl. No.: |
15/184005 |
Filed: |
June 16, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14743405 |
Jun 18, 2015 |
|
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15184005 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 9/1062 20130101;
B23K 9/091 20130101; B23K 9/0956 20130101; B23K 9/0671 20130101;
B23K 9/095 20130101; B23K 9/0953 20130101; B23K 9/1056 20130101;
B23K 9/1043 20130101 |
International
Class: |
B23K 9/10 20060101
B23K009/10; B23K 9/067 20060101 B23K009/067; B23K 9/095 20060101
B23K009/095 |
Claims
1. A welding-type system, comprising: a power circuit disposed to
provide welding-type power on a first electrode and a second
electrode, wherein the power circuit has at least one control
input; an arc clamp module, electrically coupled to the first
electrode and the second electrode; and a controller, having a
power circuit control output connected to the at least one control
input.
2. The welding-type system of claim 1, wherein the arc clamp module
is an active arc clamp module and has an arc clamp control input,
and wherein the controller has an arc clamp control module having
an arc clamp control output connected to the arc clamp control
input.
3. The welding-type system of claim 2, further comprising a
feedback circuit electrically coupled to at least one of the first
electrode, second electrode, and arc clamp module, wherein the
feedback circuit is disposed to provide a feedback signal to the
controller, wherein the arc clamp control output is responsive to
the feedback signal.
4. The welding-type system of claim 3, wherein the feedback circuit
includes a current sensor, and wherein the arc clamp control output
is responsive to the current sensor.
5. The welding-type system of claim 4, wherein the feedback circuit
includes a voltage sensor, and wherein the arc clamp control output
is responsive to the voltage sensor.
6. The welding-type system of claim 3, wherein the feedback circuit
includes a voltage sensor, and wherein the arc clamp control output
is responsive to the voltage sensor.
7. The welding-type system of claim 2, wherein the arc clamp
control module is at least partially implemented using
hardware.
8. The welding-type system of claim 2, wherein the arc clamp
control module is at least partially implemented using
software.
9. The welding-type system of claim 2, further comprising a wire
feeder electrically coupled to at least one of the first electrode
and second electrode.
10. The welding-type system of claim 9, wherein the arc clamp
module is electrically coupled to at least one of an output of the
wire feeder and an input of the wire feeder.
11. The welding-type system of claim 1, wherein the arc clamp
module comprises at least one of a transient voltage suppressor, a
diode, and a plurality of diodes, arranged such that a voltage drop
across the arc clamp module limits the current in the arc for the
voltage drop across the arc clamp module.
12. The welding-type system of claim 11, wherein the arc clamp
module comprises the plurality of diodes, and wherein the arc clamp
module further comprises a plurality of voltage taps, each disposed
between at least two of the plurality of diodes, and wherein each
voltage tap is also electrically connectable to the second
electrode.
13. The welding-type system of claim 12, wherein each of the
plurality of voltage taps is electrically connectable to the second
electrode by at least one of a manual switch and a electronically
controlled switch.
14. The welding-type system of claim 11, wherein the arc clamp
module further comprises at least one transistor disposed to
control the voltage across the arc clamp module.
15. The welding-type system of claim 1, wherein the arc clamp
module comprises at least one transistor disposed to control the
voltage across the arc clamp module.
16. A method of controlling welding-type power, comprising:
providing welding-type power on a first electrode and a second
electrode, wherein a working current path is between the first
electrode and the second electrode; and controlling at least one of
current through the working path and voltage across the working
current path by providing a bypass current path.
17. The method of claim 16, further comprising providing feedback
from the working current path and controlling the bypass current
path in response to the feedback from the working current path.
18. The method of claim 17, wherein the feedback is responsive to
at least one of current in the working current path and voltage
across the working current path.
19. A welding-type system, comprising: means for providing
welding-type power on a first electrode and a second electrode,
wherein a working current path is between the first electrode and
the second electrode; means for controlling the means for providing
welding type power, connected to the means for providing welding
type power, wherein the means for controlling receives feedback
from the working current path; and means for current to bypass the
working current path.
20. The system of claim 16, wherein the means for current to bypass
includes controllable devices, and the controllable devices are
connected to the means for controlling.
Description
FIELD OF THE INVENTION
[0001] The present disclosure relates generally to the art of
welding type systems. More specifically, it relates to welding type
systems that provide arc control.
BACKGROUND OF THE INVENTION
[0002] Generally, electric arc welding entails providing current
through a welding arc. The heat of the arc melts metal that fuses
together. When welding with a wire feeder, the arc is formed
between the tip of the wire and the workpiece. If the wire touches
the workpiece a short circuit forms, and the arc is
extinguished.
[0003] Some welding processes are performed best when there is not
short circuits, others intentionally alternate between short
circuits and arcs (short arc welding, e.g.), and others are
performed best remaining in a short circuit (laser cladding
welding, e.g.). Generally, short circuits result in less heating of
the workpiece, but the transition from a short to an arc results in
spatter.
[0004] The prior art has attempted to reduce spatter by reducing
the current during, or just before, the transition from short to
arc. Because the transition occurs quickly, simply commanding the
current to a lower level can result in spatter because the current
isn't lowered quickly enough due to system inductance and the
system response time. Early attempts included changing the
resistance using a switch in the current path. (See. e.g., patent
5001326). These attempts were largely unsuccessful because they
still were not fast enough to reduce the current before the arc
formed. A significant improvement was predicting when the arc would
form, based on the rate of change of output power (dp/dt). This
prediction provided enough advance time to overcome the lag time in
the current command, thus the current was reduced before the arc
formed. This greatly reduced spatter. The predictive technique is
described in U.S. Pat. No. 6,087,626, which is hereby incorporated
by reference. While the predictive control works well, it is a
sophisticated control scheme, and not necessarily consistent with
low cost welders.
[0005] Another improvement was using mechanical control of the wire
to create the arc. The arc is formed when the wire is retracted (or
the advance is slowed). Thus, the transition to the arc occurs at a
known time and the current is lowered prior to that time.
Alternatively, the current is lowered, and then the wire is
retracted. Because the current is low when the arc is formed,
spatter is reduced. This sort of system is described in U.S. Pat.
No. 6,984,806, hereby incorporated by reference. While this system
performs well it requires a wire feed motor close to the arc.
[0006] Also, the prior art is limited by the system response time.
Whether the command is to change the current or to retract the wire
it takes time for that command to be carried out. In the event of
an unexpected arc, or an unexpected change in arc length, the
response time for the wire to retract or the current to be reduced
can be too long, resulting in spatter.
[0007] Welding processes that are best performed avoiding short
circuits occasionally do have short circuits. It is desirable to
transition back to an arc without excess spatter. The ways to
control spatter in short circuit welding can be used in non-short
circuit welding, but add to the cost and complexity. It is not
practical to pay for the cost of a reversible wire feed for the
occasional short circuit, in most arc welding applications.
Likewise, it is often not practical to use the predictive control
when shorts occur only occasionally.
[0008] Another welding process is laser cladding welding. Laser
welding can be performed as a hybrid process where the laser
provides the heat and wire is fed into the molten pool. The wire is
preferably resistively preheated. A welding-type device can be used
for this, where the output is intentionally short circuited to the
workpiece (often called hot-wire applications). However, if an
inadvertent arc forms, it can create spatter or cause too much iron
to become part of the weld (by melting too much wire). Arcs can be
avoided by lowering the output power, but the system response time
limits the usefulness of this to avoid arcs and spatter.
[0009] In all three of the above processes (desired all arc and no
short, desired repeated arc-short-arc-short transitions, and
desired all short and no arc) it is desirable to control the arc
and the arc formation in such a way as to avoid spatter and to
maintain the desired state (whether it be arc or short). The
control should be simple and fast, so that it can be used on a wide
variety of type of welding type systems. Accordingly, a welding
type system is desired that provides arc control, preferably by
rapidly changing the current level in the arc, using simple and
effective circuitry
SUMMARY OF THE PRESENT INVENTION
[0010] According to a first aspect of the disclosure a welding-type
system includes a power circuit, an arc clamp module, and a
controller. The power circuit is connected to provide welding-type
power on a first electrode and a second electrode, and the power
circuit has at least one control input. The arc clamp module is
electrically coupled to the first electrode and the second
electrode. The controller has a power circuit control output that
is connected to the control input on the power circuit.
[0011] Welding-type system, as used herein, includes any device
capable of supplying welding type power, including ancillary
devices such as a wire feeder, robot, etc. A welding-type power
supply can be located within a single housing or distributed
amongst multiple housings. Welding-type power, as used herein,
refers to welding, plasma, induction heating power, or hot wire
welding/preheating (including laser welding).
[0012] According to a second aspect of the disclosure a method or
controlling welding-type power includes providing welding-type
power on a first electrode and a second electrode. There is a
working current path is between the first electrode and the second
electrode. At least one of current through or voltage across the
working current path is controlled by providing a bypass current
path that is in parallel with the working current path. Working
current, as used herein, refers to the arc, resistive or process
current that is used to heat (or otherwise perform a desired
function). Bypass current, as used herein, refers to current
shunted from the working current path that is used to control or
suppress the arc. Output current, as used herein, is the current
provided by the power circuit, and includes the working current and
the bypass current.
[0013] Arc clamp module, as used herein, refers to a module that
limits the output voltage of a welding-type power supply by
providing a current path alternative to the arc so that an arc is
extinguished, prevented from forming, or controlled. An arc clamp
module can be passive, wherein it operates without control, or
active, wherein it operates in response to one or more control
signals. Controller, as used herein, refers to digital and analog
circuitry, discrete or integrated circuitry, microprocessors, DSPs,
etc., and software, hardware and firmware, located on one or more
boards, used to control a device or module such as a power circuit
or arc clamp module. Electrically connected, as used herein, means
an electric signal can pass between two or more components, either
directly or through intermediate components.
[0014] The arc clamp module is passive in one embodiment, and is an
active arc clamp module in another embodiment. The active arc clamp
modules have an arc clamp control input, and the controller has an
arc clamp control module with an arc clamp control output connected
to the arc clamp control input.
[0015] A feedback circuit connected to one or both of the
electrodes and/or to the arc clamp module, provides feedback to the
controller, and the controller controls the arc clamp control
output in response thereto in another alternative.
[0016] The feedback circuit includes a current and/or voltage
sensor and the arc clamp module is controlled in response to
current and/or voltage in various embodiments. Controlling in
response to current, as used herein, includes controlling in
response to functions thereof and controlling in response to
voltage, as used herein, includes controlling in response to
functions thereof.
[0017] The arc clamp control module is at least partially
implemented using hardware and/or at least partially implemented
using software in various embodiments.
[0018] The welding-type system includes a wire feeder connected to
the first electrode in one embodiment.
[0019] The arc clamp module is electrically coupled to an output of
the wire feeder and/or an input of the wire feeder in various
embodiments.
[0020] The arc clamp module includes a TVS and/or a plurality of
diodes, arranged such that the voltage drop across the arc clamp
module limits the current in the arc at a desired voltage across
the arc clamp module in one embodiment. TVS, or transient voltage
suppressor, as used herein, includes modules or devices that are
designed to react to sudden or momentary over voltage
conditions.
[0021] The arc clamp module includes a plurality of diodes and a
plurality of voltage taps, with each tap between at least two of
the plurality of diodes, and with each tap also electrically
connectable (such as by a switch) to the second electrode in
another embodiment.
[0022] The arc clamp module includes at least one transistor that
controls the voltage across the arc clamp module in one
embodiment.
[0023] Other principal features and advantages of will become
apparent to those skilled in the art upon review of the following
drawings, the detailed description and the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a circuit diagram of a welding-type power
supply;
[0025] FIG. 2 is a circuit diagram of an arc clamp module;
[0026] FIG. 3 is a circuit diagram of an arc clamp module;
[0027] FIG. 4 is a circuit diagram of an arc clamp module;
[0028] FIG. 5 is a circuit diagram of an arc clamp module;
[0029] FIG. 6 is a circuit diagram of an arc clamp module;
[0030] FIG. 7 is a circuit diagram of an arc clamp module;
[0031] FIG. 8 is a circuit diagram of an arc clamp module;
[0032] FIG. 9 is a circuit diagram of an arc clamp module;
[0033] FIG. 10 is a circuit diagram of an arc clamp module;
[0034] FIG. 11 is a circuit diagram of an arc clamp module;
[0035] FIG. 12 is a circuit diagram of an arc clamp control
module;
[0036] FIG. 13 is a circuit diagram of an arc clamp module; and
[0037] FIG. 14 is a circuit diagram of an arc clamp control
module.
[0038] Before explaining at least one embodiment in detail it is to
be understood that the invention is not limited in its application
to the details of construction and the arrangement of the
components set forth in the following description or illustrated in
the drawings. The invention is capable of other embodiments or of
being practiced or carried out in various ways. Also, it is to be
understood that the phraseology and terminology employed herein is
for the purpose of description and should not be regarded as
limiting. Like reference numerals are used to indicate like
components.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0039] While the present disclosure will be illustrated with
reference to particular circuits and control schemes used in
particular welding type systems performing particular welding type
processes, it should be understood at the outset that the invention
can also be implemented with other welding type systems and other
circuitry and control schemes, and to perform other welding type
processes.
[0040] Embodiments of the present invention will be described in
the context of laser welding, and in the context of short circuit
and pulse welding. Laser welding (or hot wire) is performed with
the welding wire short circuited to the workpiece. The welding
power supply preheats the wire and the laser provides the energy to
melt the wire. Because the welding power supply is used only for
preheating, arcs are typically avoided.
[0041] Generally, the embodiment of the invention described with
respect to laser welding uses a typical welding-type power supply
used in a typical fashion for laser welding, with the addition of
an arc suppression circuit in parallel with the wire/work current
path. The embodiment of the invention described with respect to
short circuit and pulse welding uses a typical welding-type power
supply used in a typical fashion, with the addition of an arc
control circuit in parallel with the wire/work current path. Both
the arc suppression circuit and the arc control circuit are arc
clamp modules.
[0042] Welding-type power supply, as used herein, includes any
device capable of supplying welding, plasma cutting, and/or
induction heating power, as well as control circuitry and other
ancillary circuitry and devices such as a wire feeder associated
therewith. A welding-type power supply can be located within a
single housing or distributed amongst multiple housings.
[0043] The output of the welding-type power supply is provided to
the welding wire and short circuit, and the arc suppression circuit
includes an alternative current path for the output current. When
an arc begins to form the output voltage rises, and the alternative
current path clamps the voltage to level that prevents the arc from
forming (or controls the arc). One embodiment provides for a
passive clamping circuit, and another provides for a controlled
current path. Preferably, in either case, the controller for the
output is commanded to reduce the output. The clamp can quickly
suppress the arc during the time it takes for the output to respond
to the command. After the output has been reduced, the clamp
becomes inactive until the next time it is needed.
[0044] Referring now to FIG. 1, a welding-type power supply 100
includes a power circuit 102, a wire feeder 104, a contact tip 106,
an arc current sensor 110, an arc clamp module 112 and a clamp
current sensor 114 that cooperate to preheat a welding wire 107
that is used in laser welding on work piece 108. Welding power
circuit 102 may operate as a prior art welding power circuit, and
is preferable implemented using a Miller Auto-Axcess.RTM. or
Axcess.RTM. welding power supply. Wire feeder 104 receives power
from power circuit 102, and is preferably implemented using a
Miller Axcess Wire Feeder.RTM..
[0045] Arc clamp module 112 is provided to clamp the output and
prevent arcs from forming between wire 107 and workpiece 108 (in
hot wire applications). Arc clamp module 112 provides an
alternative output current path in parallel with wire cladding 107.
The parallel current path shunts current from wire cladding 107 (or
welding wire 107 in an arc welding process) and provides control of
the power available to the process.
[0046] Arc clamp module 112 is shown as an external module in FIG.
1, but can be integral to power circuit 102 and/or wire feeder 104.
Arc clamp module 112 is preferably located such that the loop
formed by the parallel current paths is minimized to reduce the
circuit inductance, thus allowing current to transition between the
two paths with minimal delay. In many welding applications, the
power source and wire feeder are packaged in separate boxes
allowing the power source to be remotely located away from the work
area, and the wire feed drive assembly is also located remote from
the local user interface, in some applications. In such cases, the
output weld cables between the power source and wire feeder add to
the total output inductance in the output circuit. Connecting arc
clamp module 112 across the contact tip, with a separate work lead
connection keeps the loop as short as possible. However, in
practice, it is might be easier to terminate one side of the arc
clamp module 112 at wire feeder 104. It might also be convenient to
terminate the arc clamp module 112 to the work at power circuit
102.
[0047] Arc clamp module 112 can be an active module, where the
output current or voltage is sensed and the alternative current
path is opened in response to the sensing, or it can be passive,
such as implemented by a series of diodes (described more fully
below). Arc clamp module 112 is shown in FIG. 1 as being actively
controlled, and arc current sensor 110 and/or a clamp current
sensor 114 provide feedback to an arc clamp control module arc
clamp control module 116 that is part of a welding-type power
supply controller 103. Arc clamp control module 116 is shown
integral to system controller 103, but it can be distributed and/or
located in wire feeder 104, in an external module, or a combination
thereof.
[0048] System 100 includes three main current paths: arc clamp
module 112; the arc/short wire--workpiece, and the output of power
circuit 102. Prior art welding-type power supplies typically have
an output current sensor integral to power circuit 102 (or wire
feeder 104) source which measures the total output current. Thus,
clamp current sensor 114 measures the current in the arc clamp
module 112, and arc current sensor 110 measures the current in the
arc/short circuit. Preferably, the number of current sensors in the
system is minimized without compromising critical performance
attributes. Therefore, alternate current sensing arrangements are
possible for the clamp and arc current sensing. For example, the
clamp circuit current could be mathematically derived as the
difference between a sensed total output current and a sensed arc
current. Similarly, the arc current could be mathematically derived
as the difference between a sensed total output current and a
sensed clamp current.
[0049] In operation arc clamp module 112 controls the voltage
across the arc and/or controls the current through the arc by
providing an alternative current path. The control can be to
prevent the voltage or current from rising above a given magnitude,
or to control it based on IN feedback, to maintain an arc or short
state between wire 107 and work 108 as desired.
[0050] Alternatives include connecting arc clamp module 112 to
power circuit 102, to the output of wire feeder 104, to a node
within wire feeder 104, or at or closer to contact tip 106. Also,
clamp current sensor 114 could be located between arc clamp module
112 and work 108.
[0051] The above arrangements can be used to implement alternatives
that prevent arcs, or control transitions, depending on the
implementation of arc clamp module 112 and arc clamp control module
116. Various embodiments of arc clamp module 112 are shown in FIGS.
2-9. Each could be arranged in the location shown in FIG. 1, or any
other location where an alternative current path to the wire/work
current path.
[0052] An embodiment of arc clamp module 112 that is passive is
shown in FIG. 2, and includes an overcorrect protection circuit
202, diodes 204-208, "n" diodes 210. A voltage tap exists between
each of diodes 204-208 and each of the "n" diodes. The operation
will be described with respect to diodes 204-208, and operates in a
similar manner with the "n" diodes shown as a block, where "n" is
chosen to give the desired clamp magnitude.
[0053] Diodes 204-208 are in series (but for the voltage taps) and
form a passive arc clamp. Diodes 204-208 do not conduct current
when the circuit voltage is below the total forward voltage drop of
the series diode connection. Conversely, the diodes begin to
conduct current when the circuit voltage exceeds the total forward
voltage drop. Because diodes 204-208 current conduction is
independent of any additional controls, this embodiment is a
passive arc clamp module.
[0054] One embodiment of the invention is using arc clamp module
112 as an add-on to an existing welding-type power supply, and
because diodes 204-208 conduct current from anode to cathode, arc
clamp module 112 should be connected to the weld or cladding
circuit in the proper polarity for the circuit to function.
Alternatively, a parallel branch of series diodes could be added
that conduct in the opposite polarity, thereby making connection of
arc clamp module 112 polarity insensitive.
[0055] Each diode has a forward drop Vf. Preferably, all of the
diodes in series are the same size or rating so Vf is similar for
each diode, and the arc clamp module 112 set point can be more
easily predicted. The total number of diodes sets the maximum clamp
voltage at zero current to n*Vf. As current increases in the
diodes, the voltage drop across the Arc Voltage Clamp can be
approximated by the following equation: Vclamp=n*Vf+Iclamp*Rd,
where Rd is a the slope resistance of the diode.
[0056] The clamp set point can adjusted to clamp at a lower voltage
by manually connecting the work to one of several tap connections
between the diodes, as shown. Alternatives include providing one
set point, or set points for less than between every diode pair (a
tap after every other diode, e.g.). This embodiment of arc clamp
module 112 is particularly well suited for hot-wire laser cladding
systems.
[0057] Overcorrect protection 202 is an optional means to protect
the diodes from failure due to thermal overstress condition, and
can be implemented using fuses, thermistors, etc.
[0058] FIG. 3 is an embodiment of arc clamp module 112 where the
voltage taps therein are implemented with manual switches 304-308.
Switches 304-308 can be set by the user, either on the system front
panel, by an input on arc clamp module 112, or other means. This
embodiment operates in a manner similar to the embodiment of FIG.
2, but does not require a tool to change the clamp voltage set
point. This embodiment is suitable for hot-wire cladding system.
Overcorrect protection is shown as combined with switch, and could
be implemented using fuses or circuit breakers, or could be
omitted.
[0059] FIG. 4 is an embodiment of arc clamp module 112 where the
voltage taps therein are implemented with relays 404-408.
Electromechanical devices 404-408 can be automatically controlled
by the controller arc clamp control module 116 based on the
application or program selected by the user. This embodiment is
suitable for hot-wire cladding. Automatic control of the wire/work
voltage set by arc clamp module 112 is implemented with hardware,
software, or both. The control logic to switch the set point could
be based on user input, built in program and application data,
current and voltage feedback, temperature feedback, or combination
thereof. Overcorrect protection is not shown in this embodiment,
although it could be added (and it could be added or omitted from
any embodiment). When overcorrect protection is not used with this
embodiment current through arc clamp module 112 can be interrupted
by automatic switching of relays 404-408, effectively disabling the
clamp. Control logic to disable the clamp circuit could be based on
clamp current feedback, clamp temperature feedback, duty cycle or a
combination thereof.
[0060] FIG. 5 is a circuit diagram of an embodiment of arc clamp
module 112 including a transistor 502, a gate drive circuit 504,
and includes clamp (or wire/work) voltage feedback. Transistor 502
shunts a percentage of the arc current into arc clamp module 112
when a desired clamp voltage is reached. This embodiment can
effectively operate as a programmable zener diode. Closed loop
control (using the V feedback) can be implemented to achieve the
desired clamp voltage. An error signal can be derived from the
actual clamp voltage (Vclamp feedback) and the target clamp voltage
(Vref), such that as Vclamp feedback exceeds Vref the error signal
drives a gate voltage increase. Conversely, as Vclamp feedback
falls below Vref the error signal drives a gate voltage decrease.
In this way, the control system uses gate voltage to operate the
transistor in a linear region to shunt more or less current in the
Arc Voltage Clamp thereby achieving the desired clamp voltage. This
embodiment could be used in hot-wire cladding systems and arc
welding systems. It offers the benefit of using closed loop control
to regulate the clamp voltage, with the ability to adjust the
target clamp voltage to the optimum value for a given application.
Transistor 502 should be sized to dissipate large amounts of power
as it conducts current at the clamp voltage. Alternatively, more
transistors could be combined in parallel to reduce the component
size and spread the heat dissipation. Closed loop control of the
voltage across arc clamp module 112 could be implemented with
hardware, software, or a combination thereof. Control logic to
adjust the clamp voltage set point could be based on user input,
built in program and application data, current and voltage
feedback, temperature feedback, or a combination thereof. The clamp
voltage set point could also be dynamically adjusted in response to
user input, sensor feedback, or combination thereof. Overcorrect
protection is not shown (but could be added) because current
through arc clamp module 112 can be interrupted by turning the
transistor off. Control logic to turn off the transistor could be
based on clamp current feedback, clamp temperature feedback, duty
cycle or a combination thereof.
[0061] FIG. 6 is a circuit diagram of an embodiment of arc clamp
module 112 similar to FIG. 5, including transistor 502, gate drive
circuit 504, clamp (or wire/work) voltage feedback, along with a
diode block 602. Operation is similar to the embodiment of FIG. 5,
and uses closed loop control and gate voltage of transistor 502 to
regulate the voltage and current in arc clamp module 112. However,
the clamp voltage drop and total power dissipation is now spread
across diodes 602 and transistor 502, with a smaller percentage of
the total clamp voltage falling across the transistor. This should
provide advantages in thermal management and control. Additional
transistors can be added at different tap connections to provide a
desired range of operation and control resolution for a wide
variety of applications and power levels. This embodiment is
suitable for both hot-wire cladding systems and arc welding
systems. It offers the benefit of using closed loop control to
regulate the clamp voltage, with the ability to adjust the target
clamp voltage to the optimum value for a given application. The
clamp voltage set point can be dynamically adjusted as described
above.
[0062] When arc clamp module 112 is used in arc welding
applications it can help improve starts. During an arc strike, the
clamp can initially be disabled with the transistor off. Upon
current and/or voltage threshold detection, the clamp could be
enabled and used to control the energy available to the welding arc
as the arc is initiated.
[0063] Similarly, arc clamp module 112 could be enabled
periodically during the process to control the arc energy available
following a short circuit, similar to or as an improvement to
controlled short circuit welding processes like RMD, STT and CMT.
Arc clamp module 112 is controlled such that the arc current and
voltage are regulated to set point values for a desired period of
time following a short circuit event, as the arc re-ignites. By
controlling the power in the short circuit, spatter is reduced as
the process transitions to an arc state. The output command can be
the same as systems without arc clamp module 112, wherein module
112 acts until the output responds to the command, and module 112
is no longer needed to control the output. Alternatively, the
output command can be controlled using a scheme specifically
designed to take advantage of the very fast response of the arc
clamp module 112.
[0064] Arc clamp module 112 can help respond to inadvertent short
circuits in MIG, spray, hybrid pulse/short welding, and other
processes where undesired shorts occur. By diverting power from the
wire/work when a short forms or is about to clear, spatter can be
reduced.
[0065] FIG. 7 is a circuit diagram of an active arc clamp module
112 similar to that of FIG. 6, and includes diode block 702, switch
704, current sensor 114 and a voltage sensor 706. Diode block 702
includes "n" diodes, where "n" is chosen based on the smallest
desired voltage a cross arc clamp module 112. Switch 704 can be
used to enable or disable arc clamp module 112 on and off, or to
control the voltage drop across arc clamp module 112 in response to
sensed voltage. When switch 704 is used to control the voltage
across arc clamp module 112 (and thus the wire/work voltage, it is
preferably implemented using one or more transistors operated in
the linear range.
[0066] FIG. 8 is a circuit diagram of another embodiment of arc
clamp module 112, which includes diode block 702, a diode block
802, current sensor 114 voltage sensor 706, and a plurality of taps
804, and operates in a manner similar to the embodiment of FIG. 2.
However, in this embodiment diode block 702 sets the minimum
wire/work clamp voltage, and diode block 704 along with taps 804
control the actual clamp voltage. The tap used can be user set,
such as on the front panel, or can be set by controller arc clamp
control module 116 based on feedback form the process. When it is
set by controller 116 switches such as IGBTs or transistors can
enable or disable taps.
[0067] FIG. 9 is a circuit diagram of an embodiment of a passive
arc clamp module 112, and includes diode block 702, and operates in
a manner similar to the embodiment of FIG. 2. However, in this
embodiment diode block 702 sets the wire/work clamp voltage, and
there are no taps. The number of diodes is chosen to give the
desired clamp voltage.
[0068] FIG. 10 is a circuit diagram of an embodiment of arc clamp
module 112 similar to FIG. 6, including transistor 502, gate drive
circuit 504, clamp (or wire/work) voltage feedback, diode block 602
along with a rectifier comprised of diodes 1001-1004 and a second
switch 1006. Operation is similar to the embodiment of FIG. 6, with
the addition of diode bridge 1001-1004, which rectifies the signal
from the feeder/work. This makes clamp module 112 able to be
connected without regard to polarity.
[0069] The clamp of FIG. 10 may be used in welding for low spatter
short clearing. Initially transistors 502 and 1006 are off during
an arc phase in a welding process. Transistor 502 is turned on when
a short is detected. The forward voltage drop of diode block 602 is
such that no current initially flows because the short circuit is a
lower voltage path. As the short begins to separate, voltage
increases until the forward drop is reached and transistor 502 and
diode block 602 begin to conduct. Current through transistor 502
and diode block 602 is used to detect onset of an arc condition. At
this time the transistor 502 is turned off and transistor 1006 is
modulated to reduce the current in the arc to a desired level for a
desired period of time. When the desired time expires, both
transistors are turned off and the process repeats with the arc
phase.
[0070] Alternatives include a different control scheme, and using
the rectifier with other clamp topologies.
[0071] When using arc clamp module 112 in a laser cladding
applications complete arc suppression should provide less spatter
and loss of material. Less spatter will also prolong the life on
the laser optics. However, sometimes, small arcs are a benefit to
mixing the weld puddle. Arc clamp module 112 can be used to allow
arcs at certain times, to reduce spatter when the arc is formed,
and to control the frequency of the arcs using controller 116.
Spatter controlled arcs at a regular frequency can be used to mix
the weld puddle in a desired fashion, such that dilution is at a
desired level. In such operation arc clamp module 112 prevents arcs
from forming most of the time. When a small arc is desired, arc
clamp module 112 is controlled to allow the voltage to rise
slightly, thus allowing the arc to form. The magnitude to which the
voltage is allowed to rise is preferably chosen to provide little
spatter. Then, arc clamp module 112 is controlled to limit the
voltage, thus ending the arc and returning to the short state. The
frequency of the arcs could be user set, factory set, or responsive
to the process feedback. The arcs can be at a set frequency, or at
varying times.
[0072] FIG. 11 is a circuit diagram of an embodiment of arc clamp
module 112 similar to FIG. 6, including transistor 502, gate drive
circuit 504, clamp (or wire/work) voltage feedback, along with a
diode block 602. Operation is similar to the embodiment of FIG. 6,
and uses closed loop control and gate voltage of transistor 502 to
regulate the voltage and current in arc clamp module 112. The clamp
voltage drop and total power dissipation is spread across diodes
602 and transistor 502. However, the embodiment of FIG. 11 adds an
additional controlled switch 1102 (and gate drive 1104). Switch
1102 is a mosfet in this embodiment, but it could be other types of
semiconductor switches. Switch 1104 bypasses the string of "n"
diodes 602 so that current can be shunted away from the weld faster
by reducing the voltage at the clamp. The rate of current increase
in the clamp (the current decrease in the weld) is primarily
determined by V=L*di/dt where L is the cable inductance and V is
the voltage difference between the weld and the clamp. For a given
inductance in the cabling between the clamp and the weld, a higher
voltage differential between the weld and the clamp will increase
the di/dt in the clamp. A diode 1110, a capacitor 1112, and a
voltage control 1114 disposed between diodes 602 and the work, and
across switch 502 helps protect switch 502 from overvoltage
transients when it turns off. Voltage control 1114 could consist
simply of a resistor, a diode, a Zener diode, or it could be an
active circuit. A resistor with an appropriate time constant to
sufficiently discharge capacitor 1112 to a desired low level before
the next clamping event is used in the preferred embodiment. Shunt
current feedback sensor 1106 and weld current sensor 1108 are used
to provide current feedback as described with respect to other
embodiments
[0073] During an arc phase of the weld process, both switches 502
and 1102 are off, and the capacitor is discharging (or discharged).
When the circuit detects that the weld process enters a short,
switch 502 is turned on. The voltage across diodes 602 is higher
than the voltage of the weld during the short, and little to no
current will flow in the clamp during the short. When the short
begins to clear, the weld voltage begins to rise, forward biasing
the diodes, and drawing current into the clamp circuit. Upon
detecting rising voltage or current in (or across) diodes 602, arc
clamp module arc clamp control module 116 in controller 103 turns
on switch 1102. This reduces the voltage drop in the clamp to just
the drop of the two switches, thereby increasing the voltage
driving the current up, and thus increasing di/dt in the clamp.
Switch 502 can be controlled using pwm to maintain a desired
minimum current in the weld to prevent arc outages (when 502 is
off, all current goes into the weld, when switch 502 is on, some
current is diverted from the weld into the clamp). After a desired
amount of time, or until some process parameter is reached, both
switches 502 and 1102 turn off, and the cycle starts again.
[0074] The embodiment of FIG. 11 is well suited for hot-wire
cladding systems and arc welding systems. It provides closed loop
control to regulate the clamp voltage, with the ability to adjust
the target clamp voltage to the optimum value for a given
application. The clamp voltage set point can be adjusted as
described above, for example by selecting the number of diodes 602
that are used. The embodiment of FIG. 11 can be used in the way
other embodiments described herein are used.
[0075] An embodiment shown in FIG. 13 is similar to FIG. 11, but
without diodes 602, switch 1102 and gate drive 1104. Instead of
using the forward voltage drop of diodes 602 to set the voltage for
the initial clamping, diode 1110 and capacitor 1112 are used. The
voltage on capacitor 1112 can be actively controlled by voltage
control 1114 to set the initial clamping level. This provides more
flexibility for setting the initial clamping voltage than diodes
602 provided, and the initial clamping voltage is infinitely
adjustable. The voltage may be set and controlled dynamically with
software without having to change any hardware.
[0076] During the arc phase of the process, switch 502 is turned
off, and the voltage on capacitor 1112 drops to a level near the
arc voltage. When the circuit detects that the weld process is in a
short, the capacitor voltage may be further reduced to the desired
clamping level. This can be done by dissipating energy from the
capacitor, or potentially returning it to the weld process. Once
the short begins clearing, the voltage begins to rise, forward
biasing diode 1110, drawing current into the clamp circuit and
charging capacitor 1112. Upon detecting the rising voltage or
current in the clamp, arc clamp module arc clamp control module 116
in controller 103 turns on switch 502. This provides an alternate
current path (with respect to the current path of diode 1110 and
capacitor 1112) with a lower voltage drop, thereby increasing the
di/dt into the clamp. Switch 502 can be PWMed to maintain a desired
minimum current in the weld to prevent arc outages. After a desired
amount of time, or until some process parameter is reached, the
switch turns off, and the cycle starts again.
[0077] FIGS. 12 and 14 illustrate an embodiment of arc clamp module
arc clamp control module 116 in controller 103 that controls the
switches in the arc clamp. FIG. 12 is a flow chart to control the
embodiment of FIG. 11. The process begins at step 1201. Then, at
decision point 1203 it is determined if the process is in a short.
If it is not a short, the process returns to monitor the arc/short
state, or monitors and adjusts the voltage on capacitor 1112 in an
alternative.
[0078] If the process is in a short, switch 502 is turned on at
step 1207. Then, an optional step 1209 monitors and adjusts the
voltage on capacitor 1112. Next, at decision point 1211, the
control monitors for when the short begins to clear. If the short
is not beginning to clear the control returns to optional step 1209
(or decision point 1211 if step 1209 is omitted).
[0079] If the short is beginning to clear the control proceeds to
steps 1213 and 1215 where switch 1102 is turned on and the weld
current is regulated and the clearing current is sampled. Next, at
decision point 1217 the control monitors whether the clamping is
completed. This embodiment relies on a timer or process feedback to
end the clamping. If the clamping isn't completed the control
returns to step 1215, and if the clamping is completed the control
returns to decision point 1203.
[0080] FIG. 14 is a flow chart to control the embodiment of FIG.
13. The process begins at step 1401. Then, at decision point 1203
it is determined if the process is in a short. If it is not a
short, the process returns to monitor the arc/short state, or
monitors and adjusts the voltage on capacitor 1112 in an
alternative.
[0081] If the process is in a short, step 1209 calls for monitoring
and adjusting the voltage on capacitor 1112. Next, at decision
point 1211, the control monitors for when the short begins to
clear. If the short is not beginning to clear the control returns
to step 1209. If the short is beginning to clear the control
proceeds to step 1403 and 1215 where switch 502 is turned on and
the weld current is regulated and the clearing current is sampled.
Next, at decision point 1217 the control monitors whether the
clamping is completed. This embodiment relies on a timer or process
feedback to end the clamping. If the clamping isn't completed the
control returns to step 1215, and if the clamping is completed the
control returns to decision point 1203.
[0082] The implementations of arc clamp control module 116 shown in
FIGS. 12 and 14 are exemplary. There are many alternatives to
control the timing of the switches and the voltage on capacitor
1112 to clear the short at a desired current. The physics of the
system put limits on how quickly current can be diverted from the
weld into the clamp. Therefore, the decision as to when to start
clamping should be made with the physical limitations in mind.
[0083] The decision of when to start clamping includes, in various
embodiments, feedback indicative of current in the clamp circuit,
weld process voltage, and/or capacitor voltage. Current in clamp
circuit is used by detect when current starts to flow into diodes
602 or capacitor 1112. This could be compared to a threshold a
current level that is fixed or process dependent, or di/dt or dp/dt
or other functions could be calculated and compared to a threshold.
The weld process voltage could be used to set when the short begins
to clear because the weld voltage begins rising. The weld process
voltage could be compared to a threshold (fixed or process
dependent) or dv/dt or other function could be calculated and
compared to thresholds. The voltage on capacitor 1112 could be by
detecting when the voltage rises in response to current flowing in
the clamp. The voltage on capacitor 1112 could be compared to a
threshold, or dv/dt or some other function could be calculated and
compared to a threshold.
[0084] When a feedback parameter is used to control the turning on
and off of the clamp switches, the threshold for the measured
parameter could be set in a variety of ways. A closed loop control
could adjust the thresholds automatically to achieve a the desired
result, such as a given clearing current. The control could start
with an initial threshold, and measure the clear current at each
clearing event. The controller could include a loop such as a PID
loop, and adjust the threshold to reduce the error between the
desired clear current and the actual clear current. This could be
done dynamically throughout the weld so that it could adapt even if
the weld is changing.
[0085] An alternative has a control loop that regulates based on
the clamping time before the clearing event. For example, the loop
could control such that the weld current tends to a target value 50
usec before the clearing is detected. The control loop varies the
threshold to achieve that target. Other alternatives include the
welding power supply providing thresholds based on process
parameters or pretested values, and/or an operator setting one or
more of these parameters, and making adjustments as necessary.
[0086] The embodiments of FIGS. 12 and 14 use process feedback or
communication with the welding power supply to initiate clamping a
given time after entering the short. The time can be processed
based, empirically determined, user set, etc. Another alternative
uses a model to predict when the short is about to clear, and begin
clamping at that time. This does not initially seem ideal because
it does not account for process variability easily.
[0087] The performance of the clamp and the behavior of the weld
can be affected by the amount of current left in the weld (desired
clear current), and the duration of the clamping. Reducing the
current in the weld below a certain point (dependent on material,
wire, wire feed speed, gas, etc.), can produce arc outages and
other undesired behavior. Thus, the desired clear current should be
as low as desired without causing excess negative side effects.
[0088] Also, the current in the weld is preferably lowered to the
desired clear current before the short clears. However, clamping
too early before the clearing event may remove too much power from
the weld, and increase the dissipation in the clamp circuit.
Therefore, one alternative begins the clamping as close to the
clearing event as possible, while still being able to reduce the
current to the set point before the clear. After the clearing
event, the clamp is preferably turned off, otherwise the arc could
be extinguished. However, turning the clamp off too soon could
increase spatter. Therefore, an appropriate amount of post-clearing
clamp time needs to be established. The controls discussed here
could be analog or digital, or a combination thereof.
[0089] Another application of the clamp is in a pulse process to
rapidly reduce current at the start of a short, whether the short
is intentionally part of the process or inadvertent. Rapidly
reducing current at the start of the short helps the process
quickly return to the background current.
[0090] Yet another application is using the clamp to snub the
voltage spike on a rogue cathode (also called an anomalous
cathode). A rogue cathode adversely affects process, and snubbing
the voltage helps the process perform better.
[0091] Numerous modifications may be made to the present disclosure
which still fall within the intended scope hereof. Thus, it should
be apparent that there has been provided a method and apparatus for
controlling an arc between a wire and a work piece that fully
satisfies the objectives and advantages set forth above. Although
the disclosure has been described specific embodiments thereof, it
is evident that many alternatives, modifications and variations
will be apparent to those skilled in the art. Accordingly, the
invention is intended to embrace all such alternatives,
modifications and variations that fall within the spirit and broad
scope of the appended claims.
* * * * *