U.S. patent number RE37,608 [Application Number 08/352,389] was granted by the patent office on 2002-03-26 for plasma torch electronic pulsing circuit.
This patent grant is currently assigned to Thermal Dynamics Corporation. Invention is credited to Dennis J. Solley, David A. Tatham.
United States Patent |
RE37,608 |
Solley , et al. |
March 26, 2002 |
Plasma torch electronic pulsing circuit
Abstract
A plasma arc torch having new electronic circuit concepts
wherein main current regulated power means regulates the pilot
current prior to main arc transfer. Further, the circuit may
contain two inductors to which DC current initially flows but is
interrupted upon main arc transfer such that one inductor maintains
the pilot arc while the current in the second inductor forces the
establishment of the transferred arc. Also, advantages are
presented in pulsing the cutting arc as well as pulsing the pilot
arc.
Inventors: |
Solley; Dennis J. (Tucson,
AZ), Tatham; David A. (Enfield, NH) |
Assignee: |
Thermal Dynamics Corporation
(St. Louis, MO)
|
Family
ID: |
46202530 |
Appl.
No.: |
08/352,389 |
Filed: |
December 8, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
682727 |
Apr 8, 1991 |
5189277 |
|
|
Reissue of: |
762852 |
Sep 18, 1991 |
05170030 |
Dec 8, 1992 |
|
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Current U.S.
Class: |
219/121.54;
219/121.48; 219/121.57 |
Current CPC
Class: |
H05K
5/0021 (20130101); B23K 10/006 (20130101); H05H
1/36 (20130101) |
Current International
Class: |
B23K
10/00 (20060101); H05H 1/36 (20060101); H05H
1/26 (20060101); H05K 5/00 (20060101); B23K
009/00 () |
Field of
Search: |
;219/124.02,121.54,121.57,121.5,121.56,74,75,121.48 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Paschall; Mark H.
Attorney, Agent or Firm: Senniger, Powers, Leavitt &
Roedel
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
The subject matter of this application is related to and comprises
a continuation-in-part of the patent application having Ser. No.
07/682,727, filed on Apr. 8, 1991 .[.pending.]. .Iadd.now U.S. Pat.
No. 5,189,277.Iaddend., which application is owned by a common
assignee.
Claims
Having thus described the invention what is claimed and desired to
be secured by Letters Patent is:
1. A plasma torch unit of the type having a torch assembly adapted
to operate on a work member and having a torch electrode, a pilot
electrode, and means for providing an ionized gas
therebetween.Iadd., .Iaddend.a current regulated power means
electrically connected between said electrodes and work member to
supply regulated .[.charge.]. .Iadd.current .Iaddend.to the
.[.electrode.]. .Iadd.electrodes .Iaddend.and work member during
torch usage, pilot arc control means for controlling an electric
arc between said electrodes and pulsing the same during torch
usage, said pilot arc control means electrically connected between
said current regulated power means, the electrodes, and the work
member, first circuitry of the electrical connection provided
between the power means and the work member, second circuitry of
the electrical connection provided between the power means and the
torch electrode, and third circuitry provided between the power
means, pilot arc control means, and the pilot electrode, disconnect
means in said .[.second.]. .Iadd.third .Iaddend.circuitry between
the power means and said pilot electrode, current sensing means for
sensing current in said first circuitry and generating a signal in
response to torch usage, and an inductor means in series with said
disconnect means and the said pilot electrode, said current sensing
means operating said disconnect means with a feedback signal to
pulse the generated electric arc between the electrodes, and diode
means connecting between said second and third circuitry to
.[.regulate.]. .Iadd.provide a path for .Iaddend.the conduct of
current to the pilot electrode.
2. The torch unit of claim 1 and wherein said diode means providing
for conduct of current from the current regulated power means only
towards the first inductor means .Iadd.to temporarily sustain the
pilot current when said disconnect means is open.Iaddend..
3. The torch unit of claim 2 and further including resistor means
connected between said first and second circuitry and generating a
voltage drop related to the pilot demand .[.and generated pulse
duration.]. .Iadd.then increasing the electrode to workpiece
voltage to increase the transfer height.Iaddend..
4. The torch unit of claim 1 and wherein a second inductor means
provided within the power means and responsive to the current
detected by the current sensing means to provide .[.a pulsing of
the generated main arc between the torch electrode and the metal
work during torch usage.]. .Iadd.high frequency filtering of the
power means.Iaddend..
5. The torch unit of claim 4 and wherein said current sensing means
generating a signal to the .[.second inductor.]. .Iadd.comparator
.Iaddend.to regulate the current generated by said power means and
sustaining of the pulsing of the arc between the torch electrode
and the work member.
6. The torch unit of claim 5 and wherein the current generated of
the current regulated power means also being pulsed .[.by the
second inductor.]. .
7. The torch unit of claim 6 and wherein said current sensing means
operating to provide a pulsed pilot arc.
8. The torch unit of claim 6 and wherein said current sensing means
operating to provide a pulsed main arc..Iadd.
9. A plasma torch unit of the type having a torch assembly adapted
to operate on a workpiece, and having a torch electrode, a pilot
electrode, and means for providing an ionized gas therebetween, the
torch unit characterized by: a current regulated power supply
electrically connected between the electrodes and the workpiece to
supply regulated current to the torch electrode and the pilot
electrode for the pilot arc, and to the torch electrode and the
workpiece for the main arc; a pilot arc control circuit connected
between said power supply and the pilot electrode and including a
first pilot inductor and a diode that temporarily maintains pilot
current when said pilot arc control circuit is open circuited; a
second inductor connected between said power supply and said torch
electrode; and a disconnect circuit selectively connected between
said power supply and said pilot inductor and said diode for
pulsing the generated electric arc between the electrodes such that
when said disconnect circuit is open circuited said pilot inductor
and said diode remain connected between the torch electrode and the
pilot electrode temporarily supplying pilot current, said
disconnect circuit connected to said pilot arc control circuit and
operable to open circuit said pilot arc control circuit to generate
an induced voltage in the second inductor which is greater than the
open circuit voltage thereby forcing current to flow between the
workpiece and the torch electrode to help initiate the transfer of
the pilot arc into the main arc; wherein said regulated current for
the pilot arc is pulsed. .Iaddend..Iadd.
10. A plasma torch unit of the type having a torch assembly adapted
to operate on a work member and having a torch electrode a pilot
electrode, and means for providing an ionized gas therebetween; a
current regulated power means for supplying regulated current to
the work member and torch electrode during torch usage, said
current regulated power means electrically connected to the work
member by first circuitry provided between the power means and the
work member and electrically connected to the torch electrode by
second circuitry provided between the power means and the torch
electrode; pilot arc control means for controlling an electric arc
between the torch electrode and the pilot electrode, said pilot arc
control means electrically connected between the power means and
the pilot electrode and electrically connected to the pilot
electrode by third circuitry provided between the control means and
the pilot electrode, said pilot arc control means including
disconnect means between the power means and the pilot electrode;
current sensing means for sensing current in said first circuitry
and generating a feedback signal in response to torch usage; and
diode means connecting between said second and third circuitry to
provide a path for the conduct of current to the pilot electrode;
the unit characterized by: first inductor means coupled to said
pilot arc control means for temporarily sustaining the pilot
current when said disconnect means is open; second inductor means
provided within the power means for forcing the establishment of
the transferred arc by way of an induced voltage greater than the
open circuit voltage when the disconnect means is opened thereby
forcing current to flow between the workpiece and the torch
electrode; and an interconnect means between the current sensing
means and the disconnect means so that said current sensing means
operates said disconnect means with the feedback signal.
.Iaddend..Iadd.
11. The torch unit of claim 10 wherein said diode means provides
conduct of current from the current regulated power means only
towards the inductor means to temporarily sustain the pilot current
when said disconnect means is open. .Iaddend..Iadd.
12. The torch unit of claim 11 further including resistor means
electrically connected between said first circuitry and the
disconnect means generating a voltage drop related to the pilot
demand then increasing the electrode to work member voltage to
increase the transfer height. .Iaddend..Iadd.
13. The torch unit of claim 10 wherein the second inductor means
provided within the power means is responsive to the current
detected by the current sensing means to provide high frequency
filtering of the power means. .Iaddend..Iadd.
14. The torch unit of claim 10 wherein said current sensing means
generates a signal to a comparator to regulate the current
generated by said power means. .Iaddend..Iadd.
15. The torch unit of claim 10 wherein the current generated by the
current regulated power means is being pulsed. .Iaddend..Iadd.
16. The torch unit of claim 10 wherein said current sensing means
operates to provide a pulsed pilot arc. .Iaddend..Iadd.
17. The torch unit of claim 10 wherein said current sensing means
operates to provide a pulsed main arc. .Iaddend..Iadd.
18. The torch unit of claim 10 wherein: the current regulated power
means is electrically coupled between the electrodes and the work
member to supply regulated current to the torch electrode and the
pilot electrode for the pilot arc, and to the torch electrode and
the work member for the main arc; and the disconnect means
comprises a disconnect circuit coupled to said pilot arc control
circuit and operable to open circuit said pilot arc control circuit
to generate an induced voltage which is greater than the open
circuit voltage in a second inductor means coupled between said
power means and said torch electrode to help initiate the transfer
of the pilot arc into the main arc. .Iaddend..Iadd.
19. The plasma torch unit of claim 18, wherein said pilot arc
control circuit includes the inductor means for temporarily
maintaining pilot current when said disconnect circuit is open.
.Iaddend..Iadd.
20. The plasma torch unit of claim 18 wherein the current sensing
means is characterized by a current sensor coupled to the work
member and to said disconnect circuit, said current sensor
generating a signal in response to current flowing in the work
member to actuate said disconnect circuit. .Iaddend..Iadd.
21. The plasma torch unit of claim 18 wherein said regulated
current for the pilot arc is pulsed. .Iaddend..Iadd.
22. The plasma torch unit of claim 18, further characterized by: a
pulsing circuit coupled to said power means for pulsing the pilot
arc current. .Iaddend..Iadd.
23. The plasma torch unit of claim 22 wherein said pulsing circuit
pulses the main arc current. .Iaddend..Iadd.
24. The plasma torch unit of claim 10 wherein: the current
regulated power means coupled between the electrodes and the work
member supplies regulated current to the torch electrode and the
pilot electrode for the pilot arc, and to the torch electrode and
the work member for the main arc; and further characterized by a
pulsing circuit coupled to the power means and operable to pulse
the current for the pilot arc. .Iaddend..Iadd.
25. The plasma torch unit of claim 24 wherein said pulsing circuit
is operable to pulse the current for the main arc.
.Iaddend..Iadd.
26. A plasma torch unit of the type having a torch assembly adapted
to operate on a work member and having a torch electrode a pilot
electrode, and means for providing an ionized gas therebetween; a
current regulated power means for supplying regulated current to
the work member and torch electrode during torch usage, said
current regulated power means electrically connected to the work
member by first circuitry provided between the power means and the
work member and electrically connected to the torch electrode by
second circuitry provided between the power means and the torch
electrode; pilot arc control means for controlling an electric arc
between the torch electrode and the pilot electrode, said pilot arc
control means electrically connected between the power means and
the pilot electrode and electrically connected to the pilot
electrode by third circuitry provided between the control means and
the pilot electrode, said pilot arc control means including
disconnect means between the power means and the pilot electrode;
current sensing means for sensing current in said first circuitry
and generating a feedback signal in response to torch usage; and
diode means connecting between said second and third circuitry to
provide a path for the conduct of current to the pilot electrode;
the unit characterized by: first inductor means coupled to said
pilot arc control means for temporarily sustaining the pilot
current when said disconnect means is open; second inductor means
provided within the power means for forcing the establishment of
the transferred arc; and an interconnect means between the current
sensing means and the disconnect means so that said current sensing
means operates said disconnect means with the feedback signal.
.Iaddend..Iadd.
27. The plasma torch unit of claim 26 wherein the disconnect
circuit is connected to said pilot arc control circuit and operable
to open circuit said pilot arc control circuit to generate an
induced voltage in the second inductor which is greater than the
open circuit voltage thereby forcing current to flow between the
workpiece and the torch electrode to help initiate the transfer of
the pilot arc into the main arc. .Iaddend..Iadd.
28. The plasma torch unit of claim 26, further characterized by: a
current sensor connected to the workpiece and to said disconnect
circuit, said current sensor generating a signal in response to
current flowing in the workpiece to actuate said disconnect
circuit. .Iaddend..Iadd.
29. The plasma torch unit of claim 27, further characterized by: a
pulsing circuit connected to said power supply for pulsing the
pilot arc current. .Iaddend..Iadd.
30. The plasma torch unit of claim 29, wherein said pulsing circuit
pulses the main arc current. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention is in the field of plasma torches and in
particular is directed to a plasma torch having an improved pilot
and main arc generating circuit.
Plasma torches, otherwise known as electric arc torches, are known
in the art for performing operations, such as cutting, welding, etc
, on workpieces, and operate by directing a plasma consisting of
ionized gas particles towards a workpiece. An example of the
conventional single gas plasma torch is illustrated in Hatch, U.S.
Pat. No. 3,813,510, assigned to the assignee herein Other patents
disclosing such torches are U.S. Pat. Nos. 4,225,769; 4,663,512;
and 4,663,515. The disclosures of all of the above-mentioned
patents are incorporated herein by reference thereto. As these
patents illustrate, a gas to be ionized, such as nitrogen, is fed
through channels in the torch mechanism in such a manner as to
swirl in front of the end of a negatively charged electrode. The
welding tip which is adjacent the end of the electrode has a
sufficiently high voltage applied thereto to cause a spark gap to
jump between the electrode and the welding tip, thereby heating the
gas and causing it to ionize. A pilot DC voltage between the
electrode and the welding tip maintains the pilot arc. The
iononized gas in the gap appears as a flame and extends externally
of the tip where it can be seen by the operator. The extension of
the pilot arc and the flame, which for practical purposes, may be
considered as being co-extensive depends upon the power in the
gap--i.e., the arc current--as well as the pressure of the gas
forced into the gap and out of the torch. The pilot arc provides a
source of light which enables the operator to see the proper
position for the torch before starting the welding or cutting
operation. In actual practice, when the pilot arc is on, a
loop-shaped arc extending out of the torch can be seen. As the
torch head is brought down towards the workpiece, the pilot arc
jumps from the electrode to the workpiece due to the fact that the
impedance of the workpiece current path is lower than the impedance
of the welding tip current path.
Conventional single gas plasma torches include pilot arc circuits
which provide a 20-40 amp. pilot arc current at 100-200 volts
across the electrode-tip gap, resulting in an extension of the arc
about 1/4-1/2 inch past the welding tip. As a consequence, the
torch must be brought to within about 1/4-1/2 inch of the workpiece
before the transfer arc jumps to the workpiece. This creates
difficulties in the starting of cutting or welding operations.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a plasma arc torch
circuit which is more efficient than prior art circuits and which
regulate the power source in response to sensing of the torch
.[.arch.]. .Iadd.arc .Iaddend.transferring .Iadd.from
.Iaddend.between the pilot electrode .Iadd.and the torch electrode,
to torch electrode .Iaddend.and the work member.Iadd..
.Iaddend.
It is another object of the invention to optimize the power
regulator design with respect to semiconductor switch and diode
stresses, transformer and inductor design and overall component
count.
It is still a further object to provide a plasma arc torch with
smoother on-plate transfer dynamics
Briefly stated, the present invention comprises new electronic
circuit concepts for a plasma arc torch wherein main current
regulated power means regulates the pilot current prior to main
arch transfer Further, the circuit may contain two inductors to
which DC current initially flows but is interrupted upon main arc
transfer such that one inductor maintains the pilot arc while the
current in the second inductor forces the establishment of the
transferred arc. Also, advantages are presented in pulsing the
cutting arc as well as pulsing the pilot arc.
These, as well as other objects and advantages will become more
apparent upon a reading of a detailed description of the preferred
embodiment in conjunction with the drawings, wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic wiring diagram of one prior art plasma arc
torch operating circuit;
FIG. 2 is schematic wiring diagram of another prior art plasma arc
torch operating circuit;
FIG. 2A is a schematic wiring diagram of a prior art pilot arc
regulating circuit as used within FIG. 2;
FIG. 2B is a schematic wiring diagram of another prior art pilot
arc regulating circuit as used within FIG. 2;
FIG. 3 is a schematic wiring diagram depicting a plasma arc torch
operating circuit according to the principles of the present
invention;
FIG. 4 is a schematic wiring diagram of a modified embodiment of
the present invention as it would be configured within the circuit
of FIG. 3; and
FIGS. 5A and B, in combination, are a more detailed schematic
wiring diagram of the present invention
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to the drawings, and FIG. 1 in particular, there is
shown a schematic wiring diagram for one prior art plasma arc
torch, generally referred to by the reference numeral 10. Torch 10
includes torch tip electrode 12 .Iadd.or torch electrode as is
known in the art .Iaddend.and annular torch pilot electrode 14
.Iadd.or tip as is known in the art .Iaddend.spaced from .[.tip.].
.Iadd.torch .Iaddend.electrode 12. An electronic pilot circuit P
connected between .[.tip.]. .Iadd.torch .Iaddend.electrode 12 and
pilot electrode 14 provides an electric potential between
electrodes 12 and 14 to create a pilot arc which heats a supplied
gas such as nitrogen causing it to ionize as is well known in the
art. FIG. 1 shows prior art circuit C which uses a resistively
regulated pilot arc having a current regulated power means 16 and a
pilot regulator means 18 including a disconnect means 20 in series
with a resistor 22. A high frequenty pilot initiation means 24 is
positioned in series with pilot regulator means 18 and may be
inserted in the circuit adjacent either electrode 12 or electrode
14 as shown in FIG. 1 to initiate .[.investigation.].
.Iadd.ionization .Iaddend.of plasma gas to commence pilot
operations.
A current sensing means 26 is connected in .[.parallel with pilot
regulator means 18 and connects with the metal to be worked at.].
.Iadd.series with work .Iaddend.28 in main circuit M. When
.[.tip.]. .Iadd.torch .Iaddend.electrode 12 is placed sufficiently
close to the metal work 28 the arc will transfer to the work 28
causing current to flow through main circuit M and current sensing
means 26 will sense the current differential and act to disconnect
pilot regulator means 18 by opening pilot regulator means 18 by
opening its disconnect means 20.
One problem associate with the prior art circuit 10 of FIG. 1 is
that the circuit voltage of current regulated power means 16 must
be large compared with the torch piloting voltage between .[.tip.].
.Iadd.torch .Iaddend.electrode 12 and pilot electrode 14 to allow
the pilot regulator means 18 to perform the function of a current
source during pilot opration. This causes circuit 10 to be
inefficient, power being dissipated as heat in pilot regulator
means 18.
FIG. 2 shows another prior art circuit 10' similar to that of FIG.
1 in that it also contains electronically controlled pilot
regulator means 18' in pilot circuit P' and a parallel main circuit
M'. The circuit 10' of FIG. 2 also includes similar current
operated power means 16', .[.tip.]. .Iadd.torch .Iaddend.electrode
12', pilot electrode 14', current sensing means 26', pilot
initiation means 24' (alternatively positioned as shown) and work
piece or member 28'. The difference between circuit 10' of FIG. 2
and circuit 10 of FIG. 1 is the provision .[.of circuit connection
on the opposite side of power means 16 from current means 26'
connected to pilot regulator means 18' in order to provide a second
current regulated control loop, one for pilot arc operation and one
for transferred main arc cutting.]. .Iadd.that FIG. 2 uses an
active loop with feedback, either linear .Iaddend.(.Iadd.FIG.
2a.Iaddend.) .Iadd.or switching .Iaddend.(.Iadd.FIG. 2b.Iaddend.)
.Iadd.regulator, while FIG. 1 uses a passive current limiting means
.Iaddend.(.Iadd.resistor.Iaddend.).
FIG. 2A shows one prior art pilot regulating circuit 18'a wherein
the pilot is linearly regulated; that is, the pilot current is
regulated against a set demand means 3d by varying the conductance
of a linear element 3a.
FIG. 2B shows another prior art pilot regulating 18'b wherein the
pilot is switch regulated. That is, the pilot is regulated against
a set demand 3d' to vary the duty cycle of a switching element 3g
within a feedback loop. Either scheme can tightly regulate the
pilot arc against AC line variations and against plasma gas in use,
however, both add parts count and cost to the torch and are
relatively inefficient.
FIG. 3 shows the preferred plasma torch circuit 100 in accordance
with the principles of the present invention. Circuit 100 includes
torch .[.tip.]. electrode 112, pilot electrode 114, current
regulated power means 116, pilot regulator means 118, alternatively
positionable pilot initiation means 124, current sensing means 126,
and metal work 128. Pilot regulator means 118 comprises an
electronic disconnect 120 in series with a current smoothing and
energy storage inductor 130, and a free-wheeling diode 132
connected in parallel with disconnect 120 and in series with
inductor 130.
According to the invention, current sensing means 126 not only
controls disconnect 120 through line 134, but also sends a current
signal to comparator 136 through line 138 which controls the output
of power means 116.
During torch piloting, disconnect means 120 is "on" and is in its
saturated state. The voltage seen between the metal work piece 128
and torch .[.tip.]. electrode 112 is essentially the voltage at
which the torch maintains the pilot arc determined by torch
geometry and the plasma gas used. This voltage is considerably
lower than the open circuit voltage used in prior art torch
circuits. When the torch is brought sufficiently close to metal
work piece 128, ionization current is detected by current sensing
means 126. In response to sensing the working current, sensing
means 126 acts through line 134 to force disconnect means 120 to
its "off" or high impedance state. At the moment of arc trnasfer to
work piece 128, the pilot arc is maintained by current flowing
through energy storage inductor means 130 and the free-wheeling
diode means 132. At the same instant, the current flowing in
through the smoothing inductor means 140 of power regulator 116 is
forced to flow between the workpiece 128 and torch .[.tip.].
electrode 112.[.,.]. .Iadd.. At the moment of disconnect,
disconnect 120 open circuits the inductor means 140 to generate a
transient voltage between the torch electrode and the workpiece
using the stored energy in the inductor means 140, greatly in
excess of the pilot voltage, that initiates and initially supports
the transfer to the main arc, .Iaddend.thereby maintaining the
transferred plasma arc. When the energy is dissipated in the
storage inductor means 130, the pilot arc between torch .[.tip.].
electrode 112 and pilot electrode 114 self extinguishes. When
transfer is detected in current sensing means 126 the pilot demand
means 1e is changed and the power means 116 changes the power to
that demanded for the torch operation on work piece 128.
A further embodiment of the present invention resides in
additionally pulsing the pilot current.
Instead of maintaining a constant pilot demand means (1e), the
demand may be pulsed between two (or more levels) at various
frequencies and duty cycles. During this pulsing the pilot arc is
maintained throughout and no high frequency arc initiation means
124 is required, as would be the case for a `blown-out` pilot.
This pulsing feature offers several advantages. First, higher
standoff instances between the work metal 128 and torch .[.tip.].
electrode 112 at the moment of transfer. Second, a tip cleaning
action is observed i.e. during plasma cutting molten metal is blown
onto the tip face where it adheres in particulate form. At the same
time, electrode material is removed from the torch electrode and
adheres to the inside tip. Both forms of contamination can cause
the tip orifice to become distorted. When the pilot arc is pulsed
following each cut significantly more power is dissipated in the
.[.tip.]. .Iadd.torch .Iaddend.electrode 112 for the pulse
duration. This thermal modulation is believed to be responsible for
dislodging metal particles from the inner and outer tip
surfaces.
With reference to FIG. 4, there is shown an alternative circuit
wherein a small resistor 142 is added in series with the pilot
means 118. This modification can further improve the obtainable
standoff on some plasma torch designs. The pilot current (Ip) flows
through resistor 142 to generate a voltage drop (Ip.times.R) which
is in series with the pilot voltage measured between torch
.[.tip.]. .Iadd.electrode .Iaddend.112 and pilot electrode 114.
Thus the open circuit voltage between the metal work piece means
128 and the pilot electrode means 114 is increased, assisting the
standoff at transfer. The power dissipated in this resistor is then
a function of the pilot demand and pulse duration.
A further alternative circuit provides a pulsing cutting or main
arc. From the invention pulsing the pilot arc before transfer it is
clear that it is possible to pulse the means 1e, after the arc has
transferred and while the transferred plasma arc is cutting the
work metal means 128. This provision of pulsing the main arc offers
several potential advantages. First, by selecting the appropriate
pulse rate and duty cycle in relation to the cutting variables, it
will offer a proportionally greater arc cutting
capacity/penetration for a small increase in power consumption.
Second, it allows the tip orifice size to be reduced in comparison
to a conventional plasma cutting system operating in response to a
DC demand level. This will, allow, a smaller focussed plasma column
and result in smaller kerf widths. Plasma arc stability may also
improve as a result of pulsing.
FIGS. 5A and B are a more specific electronic circuit schematic
diagram embodying some of the concepts of the invention as
enumerated above. Like reference numerals appearing in FIG. 5 refer
to like circuit components or group of components as appear in
FIGS. 3 and 4. Reference numberal 120c depicts the control circuity
for disconnecting means 120. The power supply means is not shown in
FIG. 5.
It can therefore be seen that the novel circuity shown in FIGS. 3
through 5 fulfills the objects and provides the advantages set
forth above. Inasmuch as numerous changes could be made to the
circitry without departying from the spirit and scope of this
invention, the scope of the invention is to be determined solely by
the language of the following claims as interpreted by the patent
laws and in particular the doctrine of equivalents.
* * * * *