U.S. patent application number 16/893563 was filed with the patent office on 2021-05-13 for plasma torch cutting system.
The applicant listed for this patent is Lincoln Global, Inc.. Invention is credited to Christopher J. Williams.
Application Number | 20210138574 16/893563 |
Document ID | / |
Family ID | 1000004886378 |
Filed Date | 2021-05-13 |
![](/patent/app/20210138574/US20210138574A1-20210513\US20210138574A1-2021051)
United States Patent
Application |
20210138574 |
Kind Code |
A1 |
Williams; Christopher J. |
May 13, 2021 |
PLASMA TORCH CUTTING SYSTEM
Abstract
A plasma cutting system includes a plasma cutting power supply
configured to provide cutting current to a torch. A controllable
gas valve regulates at least one of a flow rate and a pressure
supplied to the torch. A controller is operatively connected to the
power supply to control a current level, and to the gas valve to
adjust a valve position. The controller is configured to receive
real-time torch position information from a motion control system
that controls positioning of the torch. The position information
includes torch positions along a first axis and a second axis that
is perpendicular to the first axis. The controller is configured to
calculate respective derivatives from the torch positions along the
first and second axes, and a real-time velocity magnitude of the
torch from the respective derivatives, and adjust the current level
and the valve position based on the calculated real-time velocity
magnitude.
Inventors: |
Williams; Christopher J.;
(Norham, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Lincoln Global, Inc. |
Santa Fe Springs |
CA |
US |
|
|
Family ID: |
1000004886378 |
Appl. No.: |
16/893563 |
Filed: |
June 5, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62932550 |
Nov 8, 2019 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 10/003 20130101;
B23Q 15/08 20130101; B23Q 15/12 20130101; B23K 10/006 20130101;
B23K 31/10 20130101 |
International
Class: |
B23K 10/00 20060101
B23K010/00; B23K 31/10 20060101 B23K031/10; B23Q 15/12 20060101
B23Q015/12; B23Q 15/08 20060101 B23Q015/08 |
Claims
1. A plasma cutting system, comprising: a plasma cutting power
supply configured to provide a cutting current to a torch to create
a plasma arc; a controllable gas valve for regulating at least one
of a flow rate and a pressure of a plasma gas supplied to the
torch; and a controller operatively connected to the plasma cutting
power supply to control a current level of the cutting current, and
operatively connected to the controllable gas valve to adjust a
valve position of the controllable gas valve, wherein the
controller is configured to: receive real-time torch position
information from a motion control system that controls positioning
of the torch, wherein the real-time torch position information
includes torch positions along a first axis and torch positions
along a second axis that is perpendicular to the first axis,
calculate respective derivatives from the torch positions along the
first axis and the torch positions along the second axis, calculate
a real-time velocity magnitude of the torch from the respective
derivatives, and adjust the current level of the cutting current
and the valve position of the controllable gas valve based on the
calculated real-time velocity magnitude of the torch.
2. The plasma cutting system of claim 1, wherein the current level
of the cutting current is reduced based on a reduction in the
calculated real-time velocity magnitude of the torch.
3. The plasma cutting system of claim 1, wherein the current level
of the cutting current and the flow rate of the plasma gas supplied
to the torch are reduced based on a reduction in the calculated
real-time velocity magnitude of the torch, and increased based on
an increase in the calculated real-time velocity magnitude of the
torch.
4. The plasma cutting system of claim 1, wherein the controller
maintains kerf consistency by reducing the current level of the
cutting current as the torch approaches a corner portion of a part
cut from a workpiece.
5. The plasma cutting system of claim 1, wherein the real-time
torch position information includes torch positions along a third
axis that is perpendicular to the first axis and the second axis,
and the controller is configured to calculate the real-time
velocity magnitude of the torch from a derivative of the torch
positions along the third axis.
6. The plasma cutting system of claim 1, wherein the controller is
further configured to extinguish the plasma arc to end a cutting
operation by reducing the current level of the cutting current
while an arc length of the plasma arc is simultaneously shortened
by movement of the torch toward a workpiece.
7. The plasma cutting system of claim 1, wherein the controller
reduces the current level of the cutting current and the flow rate
of the plasma gas supplied to the torch as the torch approaches a
corner portion of a part cut from a workpiece.
8. The plasma cutting system of claim 7, wherein the controller
increases the current level of the cutting current and the flow
rate of the plasma gas supplied to the torch as the torch departs
from the corner portion of the part cut from the workpiece.
9. A plasma cutting system, comprising: a plasma cutting power
supply configured to provide a cutting current to a torch to create
a plasma arc; a controllable gas valve for regulating at least one
of a flow rate and a pressure of a plasma gas supplied to the
torch; and a controller operatively connected to the plasma cutting
power supply to control a current level of the cutting current, and
operatively connected to the controllable gas valve to adjust a
valve position of the controllable gas valve, wherein the
controller is configured to: receive real-time torch position
information from a motion control system that adjusts velocity of
the torch when cutting a corner portion of a part cut from a
workpiece, calculate first derivatives from the real-time torch
position information and determine real-time velocity magnitudes of
the torch when the corner portion of the part is cut from the
workpiece, and maintain kerf consistency by adjusting, based on the
determined real-time velocity magnitudes of the torch, the current
level of the cutting current and the valve position of the
controllable gas valve as the corner portion of the part is cut
from the workpiece.
10. The plasma cutting system of claim 9, wherein the real-time
torch position information includes torch positions along a first
axis and torch positions along a second axis that is perpendicular
to the first axis, and the controller is configured to calculate
respective first derivatives from the torch positions along the
first axis and the torch positions along the second axis.
11. The plasma cutting system of claim 9, wherein the real-time
torch position information includes torch positions along a first
axis, torch positions along a second axis that is perpendicular to
the first axis, and torch positions along a third axis that is
perpendicular to the first axis and the second axis, and the
controller is configured to calculate respective first derivatives
from the torch positions along the first axis, the torch positions
along the second axis, and the torch positions along the third
axis.
12. The plasma cutting system of claim 9, wherein the current level
of the cutting current and the flow rate of the plasma gas supplied
to the torch are reduced based on a reduction in the real-time
velocity magnitudes of the torch, and increased based on an
increase in the real-time velocity magnitudes of the torch.
13. The plasma cutting system of claim 12, wherein the controller
reduces the current level of the cutting current and the flow rate
of the plasma gas supplied to the torch as the torch approaches the
corner portion of the part cut from the workpiece.
14. The plasma cutting system of claim 13, wherein the controller
increases the current level of the cutting current and the flow
rate of the plasma gas supplied to the torch as the torch departs
from the corner portion of the part cut from the workpiece.
15. A plasma cutting method, comprising the steps of: providing a
plasma cutting system comprising: a plasma cutting power supply
configured to provide a cutting current to a torch to create a
plasma arc; a controllable gas valve for regulating at least one of
a flow rate and a pressure of a plasma gas supplied to the torch;
and a controller operatively connected to the plasma cutting power
supply to control a current level of the cutting current, and
operatively connected to the controllable gas valve to adjust a
valve position of the controllable gas valve; receiving real-time
torch position information from a motion control system that
controls positioning of the torch, wherein the real-time torch
position information includes torch positions along a first axis
and torch positions along a second axis that is perpendicular to
the first axis; calculating, by the controller, respective
derivatives from the torch positions along the first axis and the
torch positions along the second axis; calculating, by the
controller, a real-time velocity magnitude of the torch from the
respective derivatives; and adjusting the current level of the
cutting current and the valve position of the controllable gas
valve based on the calculated real-time velocity magnitude of the
torch.
16. The plasma cutting method of claim 15, wherein the step of
adjusting includes reducing the current level of the cutting
current and the flow rate of the plasma gas supplied to the torch
based on a reduction in the calculated real-time velocity magnitude
of the torch, and increasing the current level of the cutting
current and the flow rate of the plasma gas supplied to the torch
based on an increase in the calculated real-time velocity magnitude
of the torch.
17. The plasma cutting method of claim 15, wherein the controller
maintains kerf consistency by reducing the current level of the
cutting current as the torch approaches a corner portion of a part
cut from a workpiece.
18. The plasma cutting method of claim 15, wherein the real-time
torch position information includes torch positions along a third
axis that is perpendicular to the first axis and the second axis,
and the controller calculates the real-time velocity magnitude of
the torch from a derivative of the torch positions along the third
axis.
19. The plasma cutting method of claim 18, further comprising the
step of extinguishing the plasma arc to end a cutting operation by
reducing the current level of the cutting current while an arc
length of the plasma arc is simultaneously shortened by movement of
the torch toward a workpiece.
20. The plasma cutting system of claim 15, wherein the step of
adjusting includes reducing the current level of the cutting
current and the flow rate of the plasma gas supplied to the torch
as the torch approaches a corner portion of a part cut from a
workpiece.
21. The plasma cutting system of claim 20, wherein the step of
adjusting includes increasing the current level of the cutting
current and the flow rate of the plasma gas supplied to the torch
as the torch departs from the corner portion of the part cut from
the workpiece.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Provisional
Patent Application Ser. No. 62/932,550 filed on Nov. 8, 2019, the
disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention relates to cutting systems that
utilize plasma torches, and to controlling cutting current and/or
gas flow during a cutting operation.
Description of Related Art
[0003] Automated plasma cutting systems have been developed which
use computer numerical control (CNC) technology to control the
movement and process of a plasma cutting operation, including
controlling the movement of the cutting torch. For example, a CNC
controller can move a plasma torch in perpendicular X and Y
directions along a workpiece placed onto a cutting table to cut a
desired shape or part from the workpiece. Workpieces can also be
held by a fixture for cutting by a torch mounted to a robot whose
movements are controlled by a robot controller. A consistent kerf
(e.g., a consistent cut width and bevel angle) is desirable so that
the part cut from the workpiece has generally uniform edges and
correct dimensions. Cutting speed or torch velocity can affect the
kerf, and velocity changes can result in a widening or narrowing of
the kerf. For example, faster cutting speeds provide a narrower
kerf and slower cutting speeds provide a wider kerf.
BRIEF SUMMARY OF THE INVENTION
[0004] The following summary presents a simplified summary in order
to provide a basic understanding of some aspects of the devices,
systems and/or methods discussed herein. This summary is not an
extensive overview of the devices, systems and/or methods discussed
herein. It is not intended to identify critical elements or to
delineate the scope of such devices, systems and/or methods. Its
sole purpose is to present some concepts in a simplified form as a
prelude to the more detailed description that is presented
later.
[0005] In accordance with one aspect of the present invention,
provided is a plasma cutting system. The system includes a plasma
cutting power supply configured to provide a cutting current to a
torch to create a plasma arc. A controllable gas valve regulates at
least one of a flow rate and a pressure of a plasma gas supplied to
the torch. A controller is operatively connected to the plasma
cutting power supply to control a current level of the cutting
current, and is operatively connected to the controllable gas valve
to adjust a valve position of the controllable gas valve. The
controller is configured to receive real-time torch position
information from a motion control system that controls positioning
of the torch. The real-time torch position information includes
torch positions along a first axis and torch positions along a
second axis that is perpendicular to the first axis. The controller
is further configured to calculate respective derivatives from the
torch positions along the first axis and the torch positions along
the second axis. The controller is further configured to calculate
a real-time velocity magnitude of the torch from the respective
derivatives, and adjust the current level of the cutting current
and the valve position of the controllable gas valve based on the
calculated real-time velocity magnitude of the torch.
[0006] In accordance with another aspect of the present invention,
provided is a plasma cutting system. The system includes a plasma
cutting power supply configured to provide a cutting current to a
torch to create a plasma arc. A controllable gas valve regulates at
least one of a flow rate and a pressure of a plasma gas supplied to
the torch. A controller is operatively connected to the plasma
cutting power supply to control a current level of the cutting
current, and operatively connected to the controllable gas valve to
adjust a valve position of the controllable gas valve. The
controller is configured to receive real-time torch position
information from a motion control system that adjusts velocity of
the torch when cutting a corner portion of a part cut from a
workpiece. The controller is further configured to calculate first
derivatives from the real-time torch position information and
determine real-time velocity magnitudes of the torch when the
corner portion is cut from the workpiece. The controller is further
configured to maintain kerf consistency by adjusting, based on the
determined real-time velocity magnitudes of the torch, the current
level of the cutting current and the valve position of the
controllable gas valve as the corner portion of the part is cut
from the workpiece.
[0007] In accordance with another aspect of the present invention,
provided is a plasma cutting method. The method includes providing
a plasma cutting system that includes a plasma cutting power supply
configured to provide a cutting current to a torch to create a
plasma arc, a controllable gas valve for regulating at least one of
a flow rate and a pressure of a plasma gas supplied to the torch,
and a controller operatively connected to the plasma cutting power
supply to control a current level of the cutting current, and
operatively connected to the controllable gas valve to adjust a
valve position of the controllable gas valve. The method further
includes receiving real-time torch position information from a
motion control system that controls positioning of the torch. The
real-time torch position information includes torch positions along
a first axis and torch positions along a second axis that is
perpendicular to the first axis. The method further includes
calculating, by the controller, respective derivatives from the
torch positions along the first axis and the torch positions along
the second axis, and calculating, by the controller, a real-time
velocity magnitude of the torch from the respective derivatives.
The method further includes adjusting the current level of the
cutting current and the valve position of the controllable gas
valve based on the calculated real-time velocity magnitude of the
torch.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The foregoing and other aspects of the invention will become
apparent to those skilled in the art to which the invention relates
upon reading the following description with reference to the
accompanying drawings, in which:
[0009] FIG. 1 is a perspective view of a plasma cutting table;
[0010] FIG. 2 is a schematic representation of an example plasma
cutting system;
[0011] FIG. 3 is a schematic representation of an example plasma
cutting system;
[0012] FIG. 4 shows a plasma cutting operation;
[0013] FIG. 5 shows a plasma cutting operation;
[0014] FIG. 6 shows a plasma cutting operation;
[0015] FIG. 7 shows a plasma cutting operation;
[0016] FIG. 8 shows a plasma cutting operation;
[0017] FIG. 9 is a flow diagram of an example plasma cutting
method; and
[0018] FIG. 10 shows an example controller.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The present invention relates to plasma cutting systems. The
present invention will now be described with reference to the
drawings, wherein like reference numerals are used to refer to like
elements throughout. It is to be appreciated that the various
drawings are not necessarily drawn to scale from one figure to
another nor inside a given figure, and in particular that the size
of the components are arbitrarily drawn for facilitating the
understanding of the drawings. In the following description, for
purposes of explanation, numerous specific details are set forth in
order to provide a thorough understanding of the present invention.
It may be evident, however, that the present invention can be
practiced without these specific details. Additionally, other
embodiments of the invention are possible and the invention is
capable of being practiced and carried out in ways other than as
described. The terminology and phraseology used in describing the
invention is employed for the purpose of promoting an understanding
of the invention and should not be taken as limiting.
[0020] As used herein, "at least one", "one or more", and "and/or"
are open-ended expressions that are both conjunctive and
disjunctive in operation. For example, each of the expressions "at
least one of A, B and C", "at least one of A, B, or C", "one or
more of A, B, and C", "one or more of A, B, or C" and "A, B, and/or
C" means A alone, B alone, C alone, A and B together, A and C
together, B and C together, or A, B and C together. Any disjunctive
word or phrase presenting two or more alternative terms, whether in
the description of embodiments, claims, or drawings, should be
understood to contemplate the possibilities of including one of the
terms, either of the terms, or both terms. For example, the phrase
"A or B" should be understood to include the possibilities of "A"
or "B" or "A and B."
[0021] As used herein, the noun "real time" and the adjective
"real-time" refer to instances of both real time and near-real time
(e.g., within milliseconds or hundreds of milliseconds, such a up
to one second, from actual real time as determined by processing
latency, network latency, and/or other communication latency).
[0022] FIG. 1 shows an example plasma cutting table 102. The plasma
cutting table 102 has a main body 104 upon which a workpiece, such
as a metal sheet or plate, is placed. The plasma cutting table 102
includes a gantry 106 that can move back and forth along the length
of the cutting table's main body 104 in a first direction (e.g., in
a Y direction). The gantry 106 can move on tracks or rails that
extend along the sides of the table 102. A plasma cutting torch 108
is attached to a movable torch carriage 110 that is mounted on the
gantry 106. The torch carriage 110 can move back and forth along
the gantry 106 in a second direction (e.g., in an X direction) that
is perpendicular to the first direction. The plasma cutting table
102 can be programmed to make precise cuts in a workpiece through
controlled movements of the torch carriage 110 and gantry 106 in
the X and Y directions, respectively. In certain embodiments, the
torch carriage 110 can move the plasma cutting torch 108 vertically
toward and away from the workpiece (e.g., in a Z direction), so
that the torch can be moved in three perpendicular directions. In
certain embodiments, the torch carriage 110 can also rotate or tilt
the torch 108 in a plane perpendicular to the plane of the table
(e.g., in the X-Z plane), to make beveled cuts. In further
embodiments, the torch carriage 110 can also rotate the torch 108
about the vertical or Z-axis when cutting a part from a workpiece,
to maintain an angular orientation of the torch or plasma arc with
respect to the kerf cut through the workpiece.
[0023] The plasma cutting table 102 can include a water tray 112
located adjacent the workpiece. During a plasma cutting operation,
the water tray 112 is filled with water, and the water can be
drained to allow the water chamber to be cleaned to remove
accumulated dross and slag. The plasma cutting table 102 can also
include a user interface 114 for setting various operational
parameters of the plasma cutting table and the plasma cutting
operation. The user interface 114 can be operatively connected to a
motion controller, such as a CNC, and/or operatively connected to a
plasma cutting power supply or plasma cutting control system.
[0024] FIG. 2 depicts an exemplary embodiment of a plasma cutting
system 200. The plasma cutting system 200 can include an integrated
plasma cutting control system 116. The plasma cutting control
system 116 can include a power supply electronics module 118 which
functions as a plasma cutting power supply and is used to generate
the cutting current signal that is sent to the torch 108. The power
supply electronics module 118 provides the torch 108 with cutting
current to create a plasma arc for cutting a part from a workpiece
W. All of the power electronics which are used to generate the
cutting current signal can be located within the same housing 120
as a main system controller 122. Alternatively, the plasma cutting
system 200 can include a separate plasma cutting power supply that
is operatively coupled to the control system 116. The main system
controller 122 controls various aspects of the cutting operation,
such as current and gas flow control of plasma and shielding gas.
As shown, the controller 122 communicates with the power generation
components of the power supply module 118 internal to the housing
120 to control operations of the power supply module. Further, the
controller 122 controls the plasma and shielding gas flow and/or
pressure by directly communicating with a gas flow control device
124. The gas flow control device 124 controls the flow of gas from
a gas supply 126 and gas line 128 to the torch 108 via a
controllable gas valve 130 or valves. The controllable gas valve
130 or valves can regulate plasma and shielding gas pressure and/or
flow rate to the torch 108. The main system controller 122 is
operatively connected to the plasma cutting power supply to control
a current level of the cutting current, and operatively connected
to the controllable gas valve 130 to simultaneously adjust a valve
position of the controllable gas valve. The operative connections
may or may not be direct connections. For example, the controller
122 could provide a positioning signal (e.g., 4-20 mA, 0-10 V,
etc.) to the gas flow control device 124 that directly controls the
movement of a proportional valve in the gas flow control device, or
the controller could communicate positioning information to a
further electronic controller in the gas flow control device, and
the further electronic controller would control the gas valve
accordingly. The main system controller 122 can send positioning
signals to the flow control device 124 to control the positions of
the valves and, thus, adjust gas pressure/flow rate. The main
system controller 122 can simultaneously adjust the cutting
amperage applied to the torch 108 by controlling operations of the
power supply electronics module 118. The main system controller 122
can adjust the gas pressure/flow rate and current level of the
cutting current in concert (e.g., one level based on the other)
using, for example, a lookup table, calculation, or other
algorithm. In plasma cutting operations that utilize both a plasma
and shielding gas, the main system controller 122 can control both
gas flows in concert with the current level; however, in plasma
cutting operations that utilize only a plasma gas, the main system
controller 122 will control just the plasma gas flow.
[0025] The main system controller 122 directly communicates with a
motion controller 132. The motion controller 132 controls the
movements of a gantry 106 along the cutting table 102, the
movements of a torch-holding carriage 110 along the gantry, the
vertical positioning the torch 108 on the gantry, and possibly
rotations of the torch along horizontal and/or vertical axes.
Accordingly, the motion controller 132 can control movements of the
torch 108 in X, Y, and Z directions, and certain rotations of the
torch if desired. With further reference to FIG. 1, the Y direction
or axis can extend into and out of the plane of FIG. 2, along the
length of the cutting table 102. The X direction or axis can extend
along the gantry 106. The Z direction or axis can be substantially
vertical, extending toward and away from the cutting table 102. In
addition to controlling the movements of the torch-holding carriage
110 along the gantry 106 in the X direction, and the movements of
the gantry 106 along the table 102 in the Y direction, the motion
controller 132 also controls the height of the torch 108 in the Z
direction during operation of the system 200, and the angling of
the torch 108 for any desired bevel cutting and rotation of the
torch about the Z-axis for cut consistency.
[0026] To the extent the cutting table 102 has any automated or
motion functions, the main system controller 122 can be coupled to
the table to control the table's operations. For example, if the
table 102 is a water table or can move the workpiece, the main
system controller 122 can control these operations. The plasma
cutting control system 116 can have a user interface output device
134 (e.g., a user interface screen), and/or a user interface input
device 135 (e.g., a keyboard) to allow the user to input and review
various operational parameters and characteristics of the plasma
cutting system 200 and the cutting operation.
[0027] The main system controller 122 and/or any other controller
discussed herein (e.g., the motion controller 132) can include an
electronic controller having one or more processors. For example,
the controller 122 can include one or more of a microprocessor, a
microcontroller, a digital signal processor (DSP), an application
specific integrated circuit (ASIC), a field-programmable gate array
(FPGA), discrete logic circuitry, or the like. The main system
controller 122 can further include memory and may store program
instructions that cause the controller to provide the functionality
ascribed to it herein. The memory may include one or more volatile,
non-volatile, magnetic, optical, or electrical media, such as
read-only memory (ROM), random access memory (RAM),
electrically-erasable programmable ROM (EEPROM), flash memory, or
the like. The main system controller 122 can further include one or
more analog-to-digital (A/D) converters for processing various
analog inputs to the controller, and one or more digital-to-analog
(D/A) converters for processing various digital outputs from the
controller.
[0028] FIG. 3 depicts a further exemplary embodiment of a plasma
cutting system 201. The system 201 is similar to the system shown
in FIG. 2 except that the gantry table and motion controller are
replaced with a robot arm 136 and robot controller 138. The robot
controller 138 includes control circuitry 140 for controlling the
movements of the robot arm 136. An example robot arm 136 is a
6-axis robot arm. The end effector of the robot arm 136 is the
plasma torch 108 and the robot arm manipulates the plasma torch to
cut a part from the workpiece W held by a fixture 142. The control
circuitry 140 in the robot controller 138 is operatively connected
to the main system controller 122 in the plasma cutting control
system 116 for bidirectional communications therewith. The robot
controller 138 can include a user interface, such as a teach
pendant 144, to program the movements of the robot arm 136 and
otherwise interact with the robot system and, in certain
embodiments, interact with the plasma cutting control system 116.
As used herein, the terms "motion controller" and "motion control
system" include circuitry for controlling the movements and
positioning of a plasma cutting torch, whether on a cutting table
or robot arm. Thus, "motion controller" and "motion control system"
include the motion controller 132 shown in FIG. 2 and the robot
controller 138 shown in FIG. 3, as well as other known motion
controllers for plasma cutting operations. For ease of explanation,
the motion control system that controls positioning of the torch,
and its interaction with the main system controller 122, is
discussed below in the context of the motion controller 132 shown
in FIG. 2. However, various aspects of the motion control system
are equally applicable to the robot controller 138 and other known
motion controllers for plasma cutting operations, as will be
appreciated by one of ordinary skill in the art.
[0029] FIG. 4 schematically shows an example plasma cutting
operation. The plasma cutting torch 108 generates a plasma jet or
plasma arc 146 that cuts a kerf through the workpiece W. The "kerf"
is the width of material removed during plasma cutting. The plasma
torch 108 contains passages for the plasma gas and optionally a
shielding gas 148. The use of a shielding gas can help constrict
the plasma arc 146 and blow away the dross from the workpiece
W.
[0030] With reference to FIGS. 2 and 3, the motion controller 132
(or robot controller 138) is programmed to move the torch 108
during a cutting operation to cut a part of a desired shape from a
workpiece W located on the cutting table 102 or held by a fixture
142. The main system controller 122 is operatively connected to the
motion controller 132 (or robot controller 138) to receive torch
position feedback information in real time during the cutting
operation. The motion controller 132 (or robot controller 138)
continuously sends, in real time, present torch position
information to the main system controller 122 during cutting. The
main system controller 122 knows the current and past positions of
the torch 108 and can determine, in real time, the torch velocity
and acceleration. The real-time torch position information can
include torch positions along at least a first axis, torch
positions along a first axis and a second axis that is
perpendicular to the first axis, or torch positions along three
axes that are perpendicular to each other (e.g., along the X, Y and
Z axes). The real-time torch position information could also
include a radial distance and an angle or angles (e.g., polar
coordinates, cylindrical coordinates, or spherical
coordinates).
[0031] The main system controller 122 receives the real-time torch
position information and samples the torch position information
periodically (e.g., every 100 ms) and calculates the torch's
real-time velocity magnitude. This is done, for example, by
calculating respective first derivatives or rate of change of the
torch position along the different axes of movement (e.g., X', Y',
Z') and then calculating the magnitude of the velocity. In a
Cartesian coordinate system, the magnitude of velocity can be
calculated as the square root of the sum of the squared derivatives
or {square root over ((X'.sup.2+Y'.sup.2+Z'.sup.2))}. In certain
embodiments, the main system controller 122 only calculates the
velocity magnitude of torch movements in a plane parallel to the
workpiece W (e.g., in the X-Y plane), and, thus, needs only to
calculate the first derivatives of movements in such a plane (e.g.,
X' and Y'). If the main system controller 122 only cares about the
real-time velocity magnitude of torch 108 movements in a plane
parallel to the workpiece W, then the velocity magnitude can be
calculated as {square root over ((X'.sup.2+Y'.sup.2))}. Information
about torch acceleration can be calculated similar to velocity
using the second derivatives of the torch position (e.g., X'', Y'',
Z'').
[0032] The main system controller 122 is configured to adjust the
current level of the cutting current and the valve position of the
controllable gas valve 130 based on the calculated real-time
velocity magnitude of the torch 108. Thus, the main system
controller 122 can adjust plasma (and optionally shielding) gas
pressures and/or flow rates and plasma cutting current level in
real time based on the present velocity of the torch 108. As the
torch velocity changes, the main system controller 122 will adjust
the plasma and shielding gas pressures/flow rates and the cutting
current level accordingly. As noted above, the main system
controller 122 can adjust the gas pressure/flow rate and current
level of the cutting current in concert using, a lookup table,
calculation, or other algorithm. The lookup table, calculation, or
other algorithm can include torch velocity as a parameter for
determining the correct gas pressure/flow rate and cutting current.
For example, the lookup table can relate torch velocity to the
correct gas parameters and current level. Within the plasma cutting
system, it is to be expected that the cutting current will respond
more quickly to set point changes than the gas flow, so adjustments
to the gas valve position based on torch velocity can slightly lead
(in time) changes to the current level.
[0033] When cutting a part from a workpiece, a consistent kerf is
desirable so that the part has generally uniform edges and correct
dimensions. Torch velocity can affect the kerf, and velocity
changes can result in a widening or narrowing of the kerf. For
example, faster cutting speeds provide a narrower kerf and slower
cutting speeds provide a wider kerf. If the cutting current level
is kept constant while the torch velocity changes, the kerf can
widen and narrow and will be inconsistent. However, adjusting the
current level based on torch velocity can help to maintain kerf
consistency. For example, increasing the cutting amperage will
widen the kerf, and decreasing the cutting amperage will narrow the
kerf. Adjustments to the cutting current level can be used to
offset changes in torch velocity to maintain kerf consistency. If
torch velocity decreases, the cutting current level can also be
reduced so that the kerf is not widened due to the slower torch
velocity. If torch velocity increases, the cutting current level
can also be increased so that the kerf is not narrowed due to the
faster torch velocity. The correct plasma and shielding gas
pressure/flow rate will depend on the cutting current level, so
plasma and shielding gas amounts can also be adjusted based on
torch velocity.
[0034] It is common for torch velocity to decrease and then
increase when cutting corner portions of a part. FIGS. 5-8 show an
example plasma cutting operation during which the cutting current
level and gas valve position can be adjusted as torch velocity
changes, to maintain a consistent kerf. The kerf 150 is shown in
solid line in FIGS. 5-8. The remaining uncut portion 152 of the
part 154 to be cut from the workpiece W is shown in dashed lines.
The part 154 is square and the torch 108 is shown cutting the upper
side and upper left corner 156 of the part. Between FIGS. 5 and 6,
the torch velocity will decrease as the torch 108 approaches the
corner 156, and between FIGS. 7 and 8, the torch velocity will
increase as the torch departs from the corner.
[0035] From the torch position information received from the motion
controller 132, the changes in torch velocity can be recognized by
the main system controller 122 in real time. If the cutting current
level is kept constant while the corner 156 is cut, the kerf 150
will widen at the corner due to the slower torch velocity. To avoid
this, the main system controller 122 can determine the torch
velocity magnitude and reduce the current level of the cutting
current, and adjust the valve position of the controllable gas
valve 130, as the torch 108 approaches the corner 156. As the torch
108 slows down near the corner cut, the current level and gas flow
will be reduced by the main system controller 122 to avoid blowing
out too much material in the corner 156. This can make the cut
edges along the workpiece W more consistent (i.e., keep the kerf
150 consistent). As the torch 108 departs from the corner 156 and
speeds up, the main system controller 122 can increase the cutting
current level and increase the gas flow to the torch.
[0036] The main system controller 122 can also weigh the velocity
in certain directions when adjusting gas pressure/flow rate and
current level. For example, the main system controller 122 can take
into account the velocity in the X and Y directions to a greater
degree than velocity in the Z direction. That is, velocity changes
in the Z direction can be less impactful on gas flow and current
level adjustments than velocity changes in the X and Y directions.
The main system controller 122 can also adjust the gas
pressure/flow rate and cutting current level based on a calculated
real-time velocity magnitude in less than the three axial
directions, such as in only one direction or in two directions
(e.g, X and Y directions).
[0037] When cutting of the part 154 is complete, the main system
controller 122 turns off the plasma arc and the arc "snaps off".
Abruptly snapping off the arc when the arc is long and the current
is high causes wear and tear on the electrode and can reduce
consumable life. For example, an excessive amount of hafnium is
pulled from the electrode when the arc snaps off abruptly.
Deterioration of the nozzle orifice in the torch is also
accelerated when the arc abruptly snaps off.
[0038] To reduce the wear on the consumables in the torch 108 due
to the arc snapping, the plasma cutting system drives the torch
toward the workpiece W (e.g., downward or in the Z direction) to
shorten the arc length as the current is reduced by the main system
controller 122 at the end of a cutting operation. The movement of
the torch 108 toward the workpiece W is controlled by the motion
controller 132, or can be controlled by the main system controller
122. By moving the torch 108 toward the workpiece W, the arc is
kept as short as possible but is maintained as the current
approaches 0 amps. The arc then snaps off at a lower current level
than it would if the torch 108 had not been driven toward the
workpiece W. The lower current level as the arc extinguishes
reduces damage to the nozzle orifice and reduces or prevents the
hafnium in the electrode from being pulled away, which leads to
longer and less variable consumable life. In certain embodiments,
the rate of current reduction before the arc snaps off and the
motion of the torch 108 toward the workpiece W can be tied to a
logarithmic gas curve associated with the venting of the gas from
the torch at the end of the plasma cutting operation.
[0039] FIG. 9 provides a flow diagram of an example plasma cutting
method performed by a plasma cutting system. The plasma cutting
system, such as a system described above, is provided in step 170.
Real-time torch position information is received from a motion
control system that controls positioning of a torch (step 172). The
real-time torch position information can include torch positions
along a first axis and torch positions along a second axis that is
perpendicular to the first axis. A controller of the plasma cutting
system calculates respective derivatives from the torch positions
along the first axis and the torch positions along the second axis
(step 174). The controller calculates a real-time velocity
magnitude of the torch from the respective derivatives (step 176).
The controller adjusts the current level of the cutting current and
the valve position of a controllable gas valve based on the
calculated real-time velocity magnitude of the torch (step 178). At
the end of a cutting operation, the controller extinguishes the
plasma arc by reducing the current level of the cutting current
while an arc length of the plasma arc is simultaneously shortened
by movement of the torch toward a workpiece (step 180).
[0040] FIG. 10 illustrates an embodiment of an example controller,
such as the main system controller 122 of the plasma cutting
systems 200, 201 discussed above. The controller 122 includes at
least one processor 814 which communicates with a number of
peripheral devices via bus subsystem 812. These peripheral devices
may include a storage subsystem 824, including, for example, a
memory subsystem 828 and a file storage subsystem 826, user
interface input devices 135, user interface output devices 134, and
a network interface subsystem 816. The input and output devices
allow user interaction with the controller 122. Network interface
subsystem 816 provides an interface to outside networks and is
coupled to corresponding interface devices in other computer
systems.
[0041] User interface input devices 135 may include a keyboard,
pointing devices such as a mouse, trackball, touchpad, or graphics
tablet, a scanner, a touchscreen incorporated into the display,
audio input devices such as voice recognition systems, microphones,
and/or other types of input devices. In general, use of the term
"input device" is intended to include all possible types of devices
and ways to input information into the controller 122 or onto a
communication network.
[0042] User interface output devices 134 may include a display
subsystem, a printer, a fax machine, or non-visual displays such as
audio output devices. The display subsystem may include a cathode
ray tube (CRT), a flat-panel device such as a liquid crystal
display (LCD), a projection device, or some other mechanism for
creating a visible image. The display subsystem may also provide
non-visual display such as via audio output devices. In general,
use of the term "output device" is intended to include all possible
types of devices and ways to output information from the controller
122 to the user or to another machine or computer system.
[0043] Storage subsystem 824 provides a non-transitory,
computer-readable storage medium that stores programming and data
constructs that provide the functionality of some or all of the
modules described herein. For example, the storage subsystem 824
can include stored relationships that correlate torch velocity to
cutting current level, and that correlate torch velocity and/or
cutting current level to plasma or shield gas valve positions,
pressures, flow rates, etc.
[0044] These software modules are generally executed by processor
814 alone or in combination with other processors. Memory 828 used
in the storage subsystem 824 can include a number of memories
including a main random access memory (RAM) 830 for storage of
instructions and data during program execution and a read only
memory (ROM) 832 in which fixed instructions are stored. A file
storage subsystem 826 can provide persistent storage for program
and data files, and may include solid state memory, a hard disk
drive, a floppy disk drive along with associated removable media, a
CD-ROM drive, an optical drive, flash memory, or removable media
cartridges. The modules implementing the functionality of certain
embodiments may be stored by file storage subsystem 826 in the
storage subsystem 824, or in other machines accessible by the
processor(s) 814.
[0045] Bus subsystem 812 provides a mechanism for letting the
various components and subsystems of the controller 122 communicate
with each other as intended. Although bus subsystem 812 is shown
schematically as a single bus, alternative embodiments of the bus
subsystem may use multiple buses.
[0046] The controller 122 can be of varying types including a
workstation, server, computing cluster, blade server, server farm,
or any other data processing system or computing device. Due to the
ever-changing nature of computing devices and networks, the
description of the controller 122 depicted in FIG. 10 is intended
only as a specific example for purposes of illustrating some
embodiments. Many other configurations of the controller 122 are
possible having more or fewer components than the controller
depicted in FIG. 10.
[0047] It should be evident that this disclosure is by way of
example and that various changes may be made by adding, modifying
or eliminating details without departing from the fair scope of the
teaching contained in this disclosure. The invention is therefore
not limited to particular details of this disclosure except to the
extent that the following claims are necessarily so limited.
* * * * *