U.S. patent application number 11/760531 was filed with the patent office on 2008-01-31 for method and apparatus for automatically controlling gas pressure for a plasma cutter.
Invention is credited to Anthony V. Salsich, Joseph C. Schneider, James F. Ulrich.
Application Number | 20080023449 11/760531 |
Document ID | / |
Family ID | 38683596 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080023449 |
Kind Code |
A1 |
Salsich; Anthony V. ; et
al. |
January 31, 2008 |
METHOD AND APPARATUS FOR AUTOMATICALLY CONTROLLING GAS PRESSURE FOR
A PLASMA CUTTER
Abstract
A system for providing a dynamically controlled plasma cutting
system includes a plasma cutting system having a proportional valve
and a sensing device arrangement and a controller connected to this
arrangement. The system is configured to dynamically control gas
flow in a plasma torch. The system measures gas pressure at a
proportional valve and makes necessary gas pressure adjustments in
the system by way of controlling a drive signal sent to the
proportional valve to control gas flow.
Inventors: |
Salsich; Anthony V.;
(Appleton, WI) ; Schneider; Joseph C.; (Menasha,
WI) ; Ulrich; James F.; (Grayslake, IL) |
Correspondence
Address: |
ZIOLKOWSKI PATENT SOLUTIONS GROUP, SC (ITW)
136 S WISCONSIN ST
PORT WASHINGTON
WI
53074
US
|
Family ID: |
38683596 |
Appl. No.: |
11/760531 |
Filed: |
June 8, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11460446 |
Jul 27, 2006 |
|
|
|
11760531 |
|
|
|
|
Current U.S.
Class: |
219/121.44 ;
219/121.39 |
Current CPC
Class: |
H05H 1/34 20130101; B23K
10/006 20130101; H05H 1/36 20130101 |
Class at
Publication: |
219/121.44 ;
219/121.39 |
International
Class: |
B23K 9/013 20060101
B23K009/013; B23K 9/095 20060101 B23K009/095 |
Claims
1-24. (canceled)
25. A method for extending the life of a torch consumable
comprising: providing a first fluid line for supplying a plasma gas
to the torch; positioning a programmable control valve in the first
fluid line adjacent the torch to control a flow of the plasma gas;
and manipulating the programmable control valve thereby a)
controlling the flow of the plasma gas to the torch during
operation of the torch; and b) compensating for a volume in the
first fluid line between the proportional solenoid control valve
and the torch.
26. The method of claim 25 wherein a control output from a digital
signal processor is used to adjust the programmable control valve
to perform at least one of the controlling and the compensating
steps.
27. The method of claim 25 wherein the programmable control valve
is a proportional solenoid control valve.
28. The method of claim 26 further comprising a sensor disposed
between the torch and the programmable control valve, such that the
digital signal processor uses a signal from the sensor to adjust
the control output to the programmable control valve.
29. The method of claim 28 wherein the sensor is at least one of a
pressure sensor or a flow sensor.
30. The method of claim 25 further comprising the steps of:
positioning a sensor in the first fluid line between the
programmable control valve and the torch; sensing a parameter in
the first fluid line; and using the sensed parameter to adjust the
programmable control valve during the controlling step.
31. A method for control of a gas flow to a plasma arc torch
including a plasma chamber disposed within a torch body comprising:
providing a first fluid line for supplying a first gas to the
torch; positioning a programmable control valve in the first fluid
line adjacent the torch to control a flow of the first gas; and
manipulating the programmable control valve thereby a) controlling
the flow of the first gas to the torch during operation of the
torch; and b) compensating for a volume in the first fluid line
between the programmable control valve and the torch.
32. The method of claim 31 wherein the programmable control valve
is a proportional solenoid control valve.
33. The method of claim 31 wherein the first gas is a plasma gas
that supplies the plasma chamber.
34. The method of claim 31 wherein a control output from a digital
signal processor is used to adjust the programmable control valve
to perform at least one of the controlling and the compensating
steps.
35. The method of claim 34 further comprising a sensor disposed
between the torch and the programmable control valve, such that the
digital signal processor uses a signal from the sensor to adjust
the control output to the programmable control valve.
36. A plasma arc torch for cutting a workpiece, the plasma torch
having a plasma gas source to supply a plasma chamber such that an
electrical current passing between an electrode and a nozzle
produces a plasma arc that exits the torch through a nozzle exit
orifice, the plasma torch comprising: a means for sensing a
parameter in a first fluid line that supplies a plasma gas from the
plasma gas source; and a means for controlling a flow of the plasma
gas to the plasma chamber based on the sensed parameter using a
programmable control valve disposed in the first fluid line
adjacent the plasma torch.
37. The plasma arc torch of claim 36 wherein the programmable
control valve is a proportional solenoid control valve.
38. The plasma torch of claim 36 wherein the sensed parameter is a
pressure or a flow of the plasma gas.
39. The plasma torch of claim 36 wherein a control output from a
digital signal processor is used to manipulate the programmable
control valve.
40. A plasma cutting system comprising: a power supply; and a
plasma arc torch for cutting a workpiece, the plasma torch having a
plasma gas source to supply a plasma chamber such that an
electrical current passing between an electrode and a nozzle
produces a plasma arc that exits the torch through a nozzle exit
orifice, the plasma torch comprising: a means for sensing a
parameter in a first fluid line that supplies a plasma gas from the
plasma gas source; and a means for controlling a flow of the plasma
gas to the plasma chamber based on the sensed parameter using a
programmable control valve disposed in the first fluid line
adjacent the plasma torch.
41. The plasma cutting system of claim 40 wherein the programmable
control valve is a proportional solenoid control valve.
42. A plasma arc torch for cutting a workpiece, the plasma torch
having a plasma gas source to supply a plasma chamber and a shield
gas source to supply a shield gas to pass through a space between a
nozzle and a shield, such that an electrical current passing
between an electrode and a nozzle produces a plasma arc that exits
the torch through a nozzle exit orifice, the plasma torch
comprising: a means for sensing a parameter in a first fluid line
that supplies at least one of a plasma gas from the plasma gas
source or a shield gas from the shield gas source; and a means for
controlling a flow of the first gas based on the sensed parameter
using a programmable control valve disposed in the first fluid line
adjacent the plasma torch.
43. The plasma arc torch of claim 42 wherein the programmable
control valve is directly coupled to the plasma arc torch.
44. A method for control of a gas flow to a plasma arc torch
including a plasma chamber disposed within a torch body comprising:
providing a first fluid line for supplying a first gas to the
torch; positioning a programmable control valve in the first fluid
line adjacent the torch to control a flow of the first gas; and
manipulating the programmable control valve thereby a) controlling
the flow of the first gas to the torch during operation of the
torch; and b) compensating for a volume in the first fluid line
between the programmable control valve and the torch.
45. The method of claim 44 wherein the programmable control valve
is directly coupled to a torch body of the plasma arc torch.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is a continuation of and claims
priority to U.S. Ser. No. 11/460,446 filed Jul. 27, 2006, the
disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to plasma cutting
systems and, more particularly, to a method and apparatus for
automatically controlling gas pressure for a plasma cutter.
[0003] Plasma cutting is a process in which an electric arc and
plasma gas are used to cut or gouge a workpiece. Plasma cutters
typically include a power source, a gas supply, such as compressed
air, and a torch. The torch is constructed to create and maintain
the plasma arc. To generate the plasma cutting power, a power
source receives an input voltage from a transmission power
receptacle or generator and provides output power to a pair of
output terminals. One of the output terminals is connected to an
electrode and the other is connected to the workpiece. An air
supply is used with most plasma cutters to carry and propel the arc
to the workpiece and assist in cooling the torch.
[0004] In order to operate properly, the plasma torch requires
consistent, and preferably controllable air flow. Typically, this
is provided by a system consisting of a pressure regulator; a
downstream pressure gauge; a downstream, solenoid operated gas
valve; and a downstream pressure limit switch. Using such a
configuration, the operator is able to start and stop the gas flow
as necessary, as well as access and adjust gas pressure settings to
configure the plasma cutting system for a different cutting
operation. While control of air pressure settings in this manner
provides an operator with a great deal of control, such a
construction is not without its drawbacks.
[0005] One drawback associated with existing gas pressure
regulation systems, such as the one described above, is the
imprecision associated with the use of mechanical regulators. An
operator is required to manually check gas pressure and make
adjustments by means of the pressure gauge and pressure regulator.
Therefore, it would be preferable if a system were available that
could dynamically control pressure regulation by an electronic
means. Use of a control loop to control gas pressure, for example,
could result in a more precisely tuned system and also allow for
better accuracy and control of gas pressure. Such a system would
also permit a faster transient response, or even allow for the gas
pressure to be continuously altered, if need be.
[0006] Another drawback of existing systems is the inefficiency
associated with the operator's need to adjust gas pressure
settings. In a dynamic work environment, an operator may be
required to perform gouging and cutting operations in a relatively
continuous or alternating manner. The operator may be required to
sequentially mix a plurality of cutting processes and a plurality
of gouging processes. Suspending one process in order for the
operator to check a pressure gauge and adjust the pressure setting
for another operation is time consuming and results in overall
process inefficiency. Therefore, it would be preferable if a system
were available that would allow multiple pressure levels to be
automatically and repeatedly set by means of multiple, selectable
electrical switch positions, thus obviating the need for the user
to make pressure adjustments.
[0007] It would, therefore, be desirable to design a plasma cutting
system with simplified construction, operation, and control to
ensure optimal pressure in the plasma torch and maximize efficiency
and longevity in the plasma cutting system.
BRIEF DESCRIPTION OF THE INVENTION
[0008] The present invention provides a dynamically controlled
plasma cutting system that overcomes the aforementioned drawbacks.
The plasma cutting system includes a proportional valve and
pressure sensor arrangement and a controller connected to this
arrangement. The proportional valve and pressure sensor are
configured to dynamically control gas flow in a plasma torch and
the controller is configured to adjust the drive signal sent to the
proportional valve.
[0009] Therefore, in accordance with one aspect of the present
invention, a plasma cutting system is disclosed. The plasma cutting
system includes a housing, a power source disposed within the
housing, a plasma torch, and a gas flow system. The system also
includes a proportional valve with an adjustable orifice to control
gas flow, a sensing device, and a controller configured to receive
a signal from the sensing device and regulate operation of the
proportional valve.
[0010] According to another aspect of the present invention, a
plasma cutting system is disclosed. The plasma cutting system
includes a plasma torch, a gas flow system constructed to receive
pressurized gas, a proportional valve having a control to regulate
gas flow, a sensing device, and a controller configured to receive
a reading from the sensing device and regulate operation of the
proportional valve control.
[0011] According to a further aspect of the invention, a method of
controlling gas pressure in a plasma cutting system is disclosed.
The method includes the steps of selecting a desired cutting
operation to be performed, determining a desired gas pressure set
point for the cutting operation, detecting one of an output gas
pressure and an input gas pressure upon initiation of the cutting
operation, determining a drive signal necessary to achieve the
desired gas pressure in response to the detected one of the output
gas pressure and input gas pressure, and adjusting gas pressure in
the plasma cutting system based on the drive signal in order to
bring the actual output gas pressure or input gas pressure toward
the gas pressure set point.
[0012] Various other features and advantages of the present
invention will be made apparent from the following detailed
description and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The drawings illustrate one preferred embodiment presently
contemplated for carrying out the invention.
[0014] In the drawings:
[0015] FIG. 1 is a perspective view of a plasma cutting system
according to the present invention.
[0016] FIG. 2 is a schematic representation of the plasma cutting
system shown in FIG. 1.
[0017] FIG. 3 is a partial schematic view of the plasma torch of
the plasma cutting system shown in FIG. 1.
[0018] FIG. 4 is a cross sectional view of the proportional valve
in the plasma cutting system of FIG. 1.
[0019] FIG. 5 is a flow chart showing a detailed description of the
operation of the proportional valve and the plasma cutting
system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0020] FIG. 1 shows a plasma cutting system 10 according to the
present invention. Plasma cutting system 10 is a high voltage
system with open circuit output voltages that typically range from
approximately 230 Volts Direct Current (VDC) to over 300 VDC.
Plasma cutting system 10 includes a power source 12 to condition
raw power and generate a power signal suitable for plasma cutting
applications. Power source 12 includes a controller 13 that
receives operational feedback and monitors the operation of a
plasma cutting system 10. Power source 12 includes a handle 14 to
effectuate transportation from one site to another. Connected to
power source 12 is a torch 16 via a cable 18. Cable 18 provides
torch 16 with power and compressed air or gas, and also serves as a
communications link between torch 16 and power source 12. Torch 16
includes a handle portion 29, or torch body, having a trigger 31
thereon and work tip 32 extending therefrom. Although shown as
attached to torch 16, it is understood and within the scope of the
claims that trigger 31 could be connected to power source 12 or
otherwise remotely positioned relative to actuating torch 16.
[0021] Also connected to power source 12 is a work clamp 20, which
is designed to connect to a workpiece (not shown) to be cut and
provide a grounding or return path. Connecting work clamp 20 to
power source 12 is a cable 22 designed to provide the return path,
or grounding path, for the cutting current from torch 16 through
the workpiece and work clamp 20. Power source 12 includes a
plurality of inputs such as an ON/OFF switch 30 and may also
include amperage controls and indicator lights 36. Power source 12
can include an operating mode selector 37 connected to controller
13, which allows an operator to select a desired mode of operation
of the plasma cutting system 10. That is, an operator can manually
configure the plasma cutting system 10 to operate in a cutting or
gouging mode if the system is so equipped.
[0022] To effectuate cutting, torch 16 is placed in close proximity
to the workpiece connected to clamp 20. A user then activates
trigger 31 on torch 16 to deliver electrical power and compressed
air to work tip 32 of torch 16 to initiate a pilot arc and plasma
jet. Shortly thereafter, a cutting arc is generated as the user
moves the torch to the workpiece. The arc transfers from the
electrode to the workpiece through the tip. The user may then
perform the desired plasma effectuated processing of the workpiece
by moving torch 16 across the workpiece. The user may adjust the
speed of the cut to reduce spark spatter and provide a
more-penetrating cut by adjusting amperage and/or air pressure. Gas
is supplied to torch 16 from a pressurized gas source 33, from an
internal air compressor 39, or an air compressor (not shown)
external to power source 12.
[0023] As shown in FIG. 2, in one embodiment, controller 13A is
disposed within power source 12. Controller 13A is connected to an
operating mode selector 37. Operating mode selector 37 is used to
select a desired mode of operation of the plasma cutting system 10.
Each mode of operation corresponds to a specific set of gas
pressure and gas flow set points. The set points will exemplify
ideal operating conditions for the plasma cutting system 10 for
each mode of operation. Controller 13A is configured to store
information regarding the gas pressure and gas flow set points for
each desired mode of operation.
[0024] Controller 13A is additionally operatively connected to
plasma torch 16 and trigger 31, as well as to sensing device 60A.
Sensing device 60A is configured to communicate to controller 13A
one of an outlet or inlet gas pressure and/or a gas flow. In one
embodiment, the sensing device 60A is a pressure sensor used to
measure output gas pressure. The pressure sensor can be a
piezo-resistive pressure sensor or any other similar sensor capable
of measuring gas pressure in a welding-type environment. A detected
output gas pressure at proportional valve 58A is measured by
pressure sensor 60A and communicated to controller 13A. The
detected output pressure provides controller 13A with the
information necessary to calculate a drive signal to be sent to
proportional valve 58A, wherein the drive signal can be either of a
current or a voltage. The drive signal sent to proportional valve
58A by the controller 13A thus regulates the gas pressure used in
the cutting operation for the plasma cutting system 10.
[0025] Controller 13A is further configured to determine an input
gas pressure in the plasma cutting system 10 as a function of
output pressure and the drive signal. In one embodiment, a look-up
table is used to set forth an input pressure and an output pressure
associated with each of a number of cutting operations selected by
way of the operating mode selector 37. Inconsistencies in the input
gas pressure can then be detected by comparing an expected drive
signal current or voltage to be sent to the proportional valve 58A,
58B, which is given in the look-up table for a corresponding given
input and output gas pressure, to a drive signal that is actually
necessary to achieve the desired output gas pressure in the plasma
cutting system for the selected cutting operation. Once the trigger
31 of the plasma torch 16 is actuated, the expected drive signal
and the actual necessary drive signal can be compared to determine
if the actual input pressure in the plasma cutting system differs
from the input pressure given in the look-up table. Controller 13A,
is also configured to notify the operator that there is an
out-of-spec input pressure via an indicator light 36 (shown in FIG.
1) located on face of the power supply housing 12 or through some
other acceptable means.
[0026] In addition, controller 13A, is also configured to make gas
pressure adjustments when the plasma cutting system 10 is set-up as
having the sensing device 60A located within the power source
housing 12. Controller 13A calculates a necessary gas pressure
correction for a given length of torch cable 18 (shown in FIG. 1)
by measuring a gas pressure fall time after the proportional valve
58A is completely closed.
[0027] Referring now to FIG. 3, a plasma torch 16 is shown in cross
section, which shows another embodiment of the current invention.
As shown, plasma torch 16 houses a proportional valve 58B,
controller 13B, and sensing device 60B. Proportional valve 58B is a
solenoid-type valve that is connected to the controller 13B.
Controller 13B, in turn, is connected to sensing device 60B. Such a
construction allows the proportional valve 58B to be dynamically
controlled by feedback communicated thereto from the controller
13B, in response to output or input gas pressure readings in the
plasma cutting system 10 as measured by sensing device 60B. The
proportional valve 58B then controls gas flow to the torch head
nozzle 48. As shown in FIG. 4, the proportional valve 58A, 58B has
an adjustable orifice 59 whose size is determined by the amount of
electric current or voltage in the drive signal and running through
control 61 in the proportional valve. Control 61 can be a coil, as
shown in the embodiment of FIG. 4. As gas pressure fluctuates
during a plasma cutting process, the controller 13B is able to
adjust the amount of current or voltage in the drive signal sent to
the control 61 in the proportional valve 58B and increase or
decrease the size of the orifice 59, thus incrementally regulating
the gas pressure in the plasma cutting system 10. When there is no
current or voltage (i.e., no drive signal) being sent through the
valve control 61, the gas flow through the orifice 59 is cut
off.
[0028] In FIG. 5, a more detailed description of the operation of
one embodiment of the plasma cutting system and proportional valve
is set forth. The process begins with operator initialization of
the power source 76. Operator then selects a desired cutting
operation to be performed 80 by the plasma cutting system. Upon
selection of the cutting operation, the process determines a gas
pressure set point 84 for the specified operation. Once the trigger
of the plasma torch is pulled 71, the process is allowed to
continue. Upon actuation of the trigger, a pilot arc is activated
along with an inverter to power the plasma cutting system to enable
an operator to begin a cutting process 72. The proportional valve
is also activated by way of a drive signal so as to begin
regulation of the gas flow in the plasma cutting system 73. The
output gas pressure level at the proportional valve is then
measured to determine whether the pressure level matches with the
desired gas pressure set point associated with the cutting
operation being performed 74. If the gas pressure in the valve
corresponds to the desired gas pressure, no adjustments to the gas
pressure level are made at that time and the drive signal to the
valve remains the same 75. If the pressure level is greater than
that desired, the drive signal sent to a control in the
proportional valve will be decreased so as to decrease valve drive
and thereby reduce the output gas pressure down to the desired
level 77. If the pressure level at the proportional valve is less
than the desired pressure, the drive signal sent to a control in
the proportional valve will be increased so as to increase valve
drive and thereby raise the output gas pressure up to the desired
level 78. After any necessary adjustments to the gas pressure have
been made to bring pressure to the desired gas pressure set point,
the valve drive limit is monitored to determine whether a minimum
or maximum valve drive limit has been reached 79. If the minimum or
maximum valve drive limit has been reached, a "set over" pressure
flag or "set under" pressure flag is respectively set 82, 83. Upon
one of the above flags being set, an alarm is activated in the
plasma cutting system to notify the operator 85. The operator is
thus able to stop the cutting process if required and necessary
adjustments to the plasma cutting system can be made. If the valve
drive limit has not been reached, the plasma cutting system
continues to operate and the cycle is repeated wherein the output
gas pressure level at the proportional valve is measured to
determine whether it equals the gas pressure set point and whether
any additional adjustments are required to reach the desired gas
pressure set point 81.
[0029] Additionally, the process set forth in FIG. 5 can determine
input gas pressure as a function of output gas pressure and drive
signal. After it has been determined that the drive signal has not
exceeded a max or min limit 79, the actual drive signal sent to the
proportional valve can be compared to an expected drive signal
(associated with the selected cutting process). In one embodiment,
a look-up table is used to look-up the expected drive signal range
88 associated with a given input and output gas pressure. The
actual drive signal sent to the proportional valve is then compared
to the expected drive signal to determine if the actual drive
signal matches expected pre-determined critical values 92. Thus, by
looking at the actual and expected drive signals, it can be
determined if the actual input gas pressure corresponds to the
predicted pressure. If the drive signal values match, no action is
taken and the cycle is repeated wherein the output gas pressure
level at the proportional valve is measured to determine whether it
equals the gas pressure set point and whether any additional
adjustments are required to reach the desired gas pressure set
point 81. If the drive signal values do not match, the user is
notified of an out-of-spec input pressure, or alternatively, the
plasma cutting system makes the necessary adjustments 96. As an
example, if the input pressure is too low, then the drive signal
required to meet the desired output pressure will exceed the
expected value. The user can then be notified of such error or the
system can dynamically adjust itself to address the problem.
[0030] The method shown in FIG. 5 can also be modified to control
gas flow in a plasma cutting system rather than gas pressure. A gas
flow set point and gas flow readings would be used rather than gas
pressure in such a method. Additionally, input gas pressure can be
detected rather than output gas pressure.
[0031] It should be noted that the valve identified as a
"proportional valve" in the above description, is not limited to a
valve whose flow rate or pressure is directly proportional to
voltage or current applied to its control. Rather, it is meant to
imply a valve whose output changes incrementally with applied
voltage or current and is not an "on-off" type valve. Voltage or
current can be used to determine the valve limits, as can an
auxiliary position indicator in communication with the moving part
of the solenoid in the valve. There may also be other additional
ways to determine valve position or the limits of its
operation.
[0032] Therefore, one embodiment of the present invention includes
a plasma cutting system having a housing, a power source disposed
within the housing, a plasma torch, and a gas flow system. The
system also includes a proportional valve to control gas flow, and
a sensing device. A controller is also included in the system,
which is configured to receive a signal from the sensing device and
regulate a drive signal to the proportional valve.
[0033] Another embodiment of the present invention includes a
plasma cutting system having a plasma torch actuated by a trigger
and a gas flow system constructed to receive pressurized gas. A
proportional valve having a control is used to regulate the gas
flow, and a sensing device measures gas pressure or gas flow. The
system also includes a controller configured to receive a signal
from the sensing device and regulate a drive signal sent to the
proportional valve. An adjustable operating mode selector is also
included for selecting a desired cutting operation to be performed
by the plasma cutting system, wherein each cutting operation has a
predetermined gas flow and gas pressure set point associated with
it.
[0034] A further embodiment of the present invention includes a
method of controlling gas pressure in a plasma cutting system which
includes the steps of selecting a desired cutting operation to be
performed, determining a desired gas pressure set point for the
cutting operation, detecting one of an output gas pressure and an
input gas pressure upon initiation of the cutting operation,
determining a drive signal necessary to achieve the desired gas
pressure in response to the detected output gas pressure or input
gas pressure, and adjusting gas pressure in the plasma cutting
system based on the drive signal in order to bring the actual
output gas pressure or input gas pressure toward the gas pressure
set point.
[0035] As one skilled in the art will fully appreciate, the
heretofore description of a plasma cutting system is one example of
a plasma cutting system according to the present invention. The
description of the present invention is merely exemplary in nature
and, thus, variations that do not depart from the substance of the
invention are intended to be within the scope of the invention.
Such variations are not to be regarded as a departure from the
spirit and scope of the appending claims.
* * * * *