Work piece condition detection using flame electrical characteristics in oxy-fuel thermal processing equipment

An automated oxy-fuel thermal processing system including an oxy-fuel torch, an automated machine tool operatively coupled to the torch for moving the torch relative to a work piece, and a circuit including a voltage source or a current electrically connected to the torch and configured to be electrically connected to the work piece. The automated oxy-fuel thermal processing system may further include a processor that is operatively connected to the torch, the automated machine tool, the circuit, and the voltage source or current source, wherein the processor is configured to control the operation of the torch, the automated machine tool and the voltage source or current source, and to monitor a current or voltage in the circuit in a predefined manner.

FIELD OF THE DISCLOSURE

Embodiments of the present invention relate generally to the field of oxy fuel thermal processing equipment, and more particularly to system that can obtain parameters associated with a thermal cutting or welding process using electrical characteristics of the torch flame an oxy fuel thermal processing equipment.

BACKGROUND OF THE DISCLOSURE

Modern automated gas cutting torches are commonly equipped with features such as automatic ignition, automatic standoff control, kindling temperature detection, ignition and blowout detection, and neutral flame detection. Each of these features can be implemented using actuation and sensing mechanisms that should be reliable, economical, and resistant to the harsh operating environments created when cutting is performed (e.g. high heat, abrasive debris, particulate deposition etc.).

Kindling temperature detection has been successfully achieved using optical infrared (IR) sensors directed toward a work piece. While optical sensors are generally effective for such an application, they are extremely sensitive to abrasion and particulate deposition, and are therefore commonly mounted within a torch and directed down the torch's cutting oxygen orifice. One problem with this approach is that it cannot be implemented in cases where the diameter of a torch's cutting oxygen bore is too small to accommodate an optical sensor.

Automatic ignition in gas cutting torches has been achieved by temporarily re-routing a torch's fuel-oxygen mixture through the torch's cutting bore for a period of time sufficient to allow a flame, ignited internally, to propagate to the tip of the torch, where it is allowed to stabilize. This solution requires solenoids to be operatively mounted within the torch for adjustably routing the fuel-oxygen mixture.

Various techniques for automatic standoff control are known, each of which is associated with particular shortcomings. For example, capacitive standoff control techniques, such as those described in U.S. Pat. No. 6,251,336, rely on the assumption that a work piece (e.g. a steel plate) is a quasi-infinite surface. Such techniques therefore perform inconsistently when a cutting torch nears the edges of a work piece. Inductive standoff control techniques rely on perturbations in an induced, oscillating magnetic field around a work piece, and are therefore susceptible to undesirable cross-interference when two torches are operated near one another. Optical standoff control methods require sensors that must be mounted on the exterior of a torch, and are therefore susceptible to being obscured, scratched or otherwise damaged by debris during cutting. Mechanical standoff control methods that use whiskers or rider plates require large radii in which to operate. Such methods may therefore yield inconsistent results when performed adjacent a work piece's edges or near areas where two cuts meet.

It is apparent that current approaches for implementing certain advantageous features of modern gas cutting torches suffer from various inconsistencies of operation. Moreover, such approaches require additional electronics and hardware to be mounted on or inside of a gas cutting torch, which can substantially increase the cost of an automated torch system while diminishing the reliability of a system. It would therefore be advantageous to provide an automated gas cutting torch system that provides features such as kindling temperature detection, automatic ignition, and automatic standoff control, wherein such system is reliable, economical, and robust.

SUMMARY OF THE DISCLOSURE

Various embodiments of the present disclosure are generally directed to an automated oxy-fuel thermal processing system and a method of operating the same. In some embodiments the system is an oxy-fuel cutting system. In other embodiments the system is an oxy-fuel welding system.

An oxy-fuel thermal processing system is disclosed. The system includes a driver coupled between first and second surfaces for driving a current between the first and second surfaces, the first and second surfaces exposed to a flame of a torch associated with the oxy-fuel processing system. A voltage sensor may be coupled between the first and second surfaces for sensing a voltage response to the driven current. A microprocessor is in communication with the current driver and the voltage sensor for receiving driven current and sensed voltage response information, the microprocessor configured to calculate a first parameter associated with a thermal process based on said received current and voltage response information, to determine if the first parameter is within a predetermined range, and when the first parameter is outside the predetermined range to instruct adjustment of a second parameter associated with the thermal process.

An oxy-fuel thermal processing system is disclosed. The system includes a voltage source coupled between first and second surfaces for applying a voltage between the first and second surfaces, the first and second surfaces exposed to a flame of a torch associated with the oxy-fuel thermal processing system. A current sensor may be coupled between the first and second surfaces for sensing a current response to the applied voltage. A microprocessor is in communication with the voltage source and the current sensor for receiving applied voltage and sensed current response information. The microprocessor may be configured to calculate a first parameter associated with a thermal process based on said applied voltage and sensed current response information, to determine if the first parameter is within a predetermined range, and when the first parameter is outside the predetermined range to instruct adjustment of a second parameter associated with the thermal process.

A method is disclosed for controlling an oxy-fuel thermal processing process, comprising: applying a voltage between first and second surfaces while the first and second surfaces are exposed to a flame of a torch; sensing a current generated in response to the applied voltage; and determining a first parameter associated with a thermal processing process based on the applied voltage and the sensed current; determining whether the first parameter is within a predetermined range, and when the first parameter is outside the predetermined range adjusting a second parameter associated with the thermal processing process.

A method is disclosed for controlling an oxy-fuel thermal processing process, comprising: driving a current between first and second surfaces while the first and second surfaces are exposed to a flame of a torch; sensing a voltage between the first and second surfaces in response to the driven current; and determining a first parameter associated with a thermal process based on said driven current and sensed voltage; determining whether the first parameter is within a predetermined range, and when the first parameter is outside the predetermined range adjusting a second parameter associated with the thermal process.

In some embodiments the disclosed system may include a cutting torch, an automated machine tool operatively coupled to the cutting torch for moving the cutting torch relative to a work piece, and a sensing circuit including a voltage source electrically connected to the torch and configured to be electrically connected to the work piece. The sensing circuit further includes a processor that is in communication with the cutting torch, the automated machine tool, the circuit, and the voltage source. The processor may be configured to control the operation of the cutting torch, the automated machine tool, and the voltage source and to monitor a current in the circuit in a predefined manner.

A method for operating a cutting torch system is also disclosed. In some embodiments the method may include outputting a voltage from a voltage source that is electrically connected in series with a cutting torch and a work piece being cut by the cutting torch, lowering the cutting torch toward the work piece until current flows between a tip of the gas cutting torch and the work piece, indicating that a tip of the cutting torch has reached a zero height at which the tip is in contact with the work piece.

DETAILED DESCRIPTION

The oxy-fuel cutting process is used to cut material that reacts with oxygen by heating the material to a kindling temperature, and then burning the material away in an oxygen-rich atmosphere. To achieve this, as shown inFIG. 1an oxy-fuel cutting torch1can comprise a long cylinder2with internal passages4,6configured to deliver gaseous fuel (e.g., acetylene, propane, or the like) and oxygen, respectively, to a nozzle8, mounted at the cylinder's bottom. The nozzle8can issue a premixed combustible mixture from an array of ports10arranged around a central port12from which pure oxygen is issued.

To begin a cut, the torch1is positioned a distance above a work piece14. The torch1may be operating with a stable flame16(FIG. 2) oriented downward at the work piece14. At this point oxygen is not supplied through the central port12. Rather, the flame16may be used to heat the work piece14until it is hot enough that the material will burn in an oxygen atmosphere. The critical temperature needed for a cut to successfully begin is referred to as the “kindling temperature.” When the work piece14reaches its kindling temperature, oxygen is supplied via the central port12. If the work piece14is sufficiently hot, it will ignite and the flow of oxygen will pierce the work piece. If the work piece14is too cool, however, the flow of oxygen will only serve to further cool the material and the heating process will have to be repeated before cutting can be performed. As will be appreciated, in order to obtain an efficient process, it is important to accurately determine when the work piece is ready for cutting (i.e., when the material of the work piece has reached its kindling temperature).

Once piercing of the work piece14is accomplished, the torch1can then be moved along a desired cut path to cut the work piece into a desired shape. Generally speaking, as the flame16advances through the work piece, the material in front of the flame is relatively cool, and thus it must be brought up to the kindling temperature in order to enable it to be cut by the flame. The process relies on the preheat flame, but particularly relies on the heat released from the cut itself. As will be appreciated, if the torch1is advanced too quickly the heat released from the cut may not have sufficient time to conduct into the surrounding plate, and the temperature of the surface inside the advancing cut will fall. If the temperature drops too low then combustion may stop, and the preheat process will need to be repeated to restart the cut.

There are a number of practical issues that arise when attempting to automate an oxy-fuel cutting process. Before the process is begun, the torch1is ignited and the flow of fuel and oxygen brought into desired proportions. The torch1is then brought to a predetermined height above the work piece and allowed to bring the material to its kindling temperature. The specific height and the timing of the process can be important to the successful initiation of a cut.

To accomplish these functions, cutting systems often include automated and/or manual adjustment mechanisms for moving the torch1in two horizontal axes (x-y) in order to generate a cut path on a work piece such as a flat plate. The adjustment mechanism may also be configured for adjusting the height of the torch1relative to the work piece. Such adjustment mechanisms are known in the art, and thus will not be described in detail herein. It will be appreciated that the disclosed system not limited to use with such mechanisms, there are many potential embodiments that include them.

As described, the oxy-fuel cutting process can include a series of operations including a number of steps that rely on feedback, either from a human operator or from an appropriately robust suite of sensors and controls. For example, feedback can be desirable to facilitate adjusting the torch's fuel-oxygen mixture to achieve a desired “neutral flame.” During the preheat operation, if sensor feedback indicates the work piece14temperature is not determinable (e.g., due to sensor error), the operator must visually observe the glow of the work piece, or an automated system must be programmed to wait for an additional period of time to ensure that the work piece has achieved its kindling temperature so that cutting will successfully start. In another example, a standoff distance “SD” between the torch1and the work piece14depends on feedback control since the standoff can be on the order of an inch or less, and the torch may be positioned many feet from the operator making visual observation difficult or inconvenient.

While a desired level of feedback can be obtained by mounting sensors on or around the torch, the volatile environment of the oxy-fuel cutting system necessitates sensors that are hardened against electrical noise, thermal stresses, abrasion and impact. As a result such sensors are often either very vulnerable to damage and/or are very expensive.

In the context of a torch flame16, an electrical potential applied between two surfaces that are otherwise electrically isolated (e.g., the torch1and the work piece14) will result in a flow of current through the torch flame. This relationship can be measured using an arrangement such as that shown inFIG. 2, illustrating the torch1, the torch flame16, a voltage source18and a shunt resistor20. It will be appreciated that the voltage source18and shunt resistor20are but one possible embodiment, and that other arrangements can also be used. In addition, although the description will proceed in relation to the use of two surfaces under test (e.g., the torch1and the work piece14), other sensing surface configurations can also be used, and thus the disclosure is not so limited.

The relationship between voltage and current can be divided into three regimes, shown inFIG. 3. In the central, “linear regime” (II), current through the torch flame is limited by the electrical resistance of the torch flame which separates the two surfaces1,14. As such, the slope of the characteristic curve in this linear regime (II) is constant. However, as the magnitude of current through the torch flame16approaches either extreme, it eventually enters a “saturation regime” (I, III). In the saturation regime (I, III), current through the torch flame16is limited by the cathode (i.e., negative) surface's capacity to emit electrons.

In the linear regime, the characteristic relationship between current and voltage (I-V) can, but need not, pass through the origin. For embodiments in which the two surfaces1,14are made from different materials, or are at different temperatures, they will have a different affinity for electrons. As a result, if the circuit represented byFIG. 3is opened, charge will accumulate until the surfaces1,14reach a steady-state “floating potential.” This “floating potential” is the potential between two surfaces1,14that is necessary to achieve zero current.

The slope in the linear regime (II) is influenced by a number of characteristics including the flame temperature, the gas composition, and especially the distance between the surfaces. The slope of the I-V curve is an implicit measurement of the torch flame's electrical resistance in the path between the two surfaces1,14. As the surfaces1,14approach each other (e.g., as the torch nozzle8is moved toward the work piece14), or as the concentration of free radicals increases in the torch flame16, the resistance of the torch flame drops detectably.

The floating potential, on the other hand, is influenced by the surface materials and temperature. Thus, for a given pair of surfaces1,14if the temperature of one surface is known, then the floating potential can be assumed to be an indicator of the temperature of the other surface.

The disclosed system and method exploits the electrical conductivity of the torch flame16to detect parameters important to the cutting process (e.g., torch offset, work piece temperature), while minimizing and/or eliminating the need for physical sensors and/or probes. By imposing an “electrical action,” measuring a resulting “electrical response,” and interpreting the results, it is possible to extract a great deal of information on the oxy-fuel process.

In some embodiments the electrical action can take the form of either an applied voltage or a driven current, with the resultant measurement being a measured current or measured voltage, respectively.FIG. 4Ashows one exemplary non-limiting embodiment of a system22in which a voltage source24applies the electrical action, a current sensor26such as a shunt measures the current response, and a processor28collects a series of measurements and computes various parameters. A non-limiting exemplary list of directly measured parameters includes linear slope, floating potential, upper/lower saturation current, upper/lower saturation voltage and upper/lower saturation slope. A non-limiting exemplary list of derived parameters includes standoff distance “SD,” standoff error, flame mixture quality, cut speed error, imminent cut loss, successful ignition, and work piece temperature. These parameters may be communicated to one or more dependent systems29. A non-limiting exemplary listing of such dependent systems29includes a torch height controller, motors for positioning the torch vertically with respect to the work piece, motors for moving the torch in the x-y axis with respect to the work piece, a cut speed controller, a gas flow controller, valves regulating the flow of gases, an operator display and a master CNC responsible for control of any or all of the aforementioned systems.FIG. 4Billustrates an alternate embodiment of the disclosed system30in which current is driven in lieu of voltage. In this embodiment a current source32applies the electrical action, a voltage sensor34measures the voltage response, and a processor36collects a series of measurements and computes various parameters, which have been previously identified. In both examples, the imposition of an electrical action and measurement of an electrical response is used to interrogate the system's I-V characteristic, as will be described below, to obtain information about the operation of the system.

There are two fundamental measurements that are used to derive most of the measurements offered by the present disclosure: (1) floating potential, and (2) linear slope. Others are also possible, such as saturation threshold current, saturation threshold voltage, and the slope in the saturation regions, but the inventor has found that the linear regime characteristics appear to be the most reliable.

One non-limiting exemplary method for measuring the floating potential is to force the current flow between the surfaces1,14to zero. Once the voltage between the two surfaces1,14stabilizes, it is taken as the floating potential. When driving voltage in lieu of current, the mean voltage signal can be adjusted until the mean current is zero. The mean voltage at zero mean current is then taken as the floating potential.

One non-limiting exemplary method for measuring slope is by calculation, using two points in the linear regime. For accuracy, it may be desirable that the two points be as different in value as possible while remaining in the system's linear regime. Operation in the linear regime can be reasonably ensured if the two measurements are made near the floating potential.

One non-limiting exemplary method for measuring floating potential and slope simultaneously is to apply an oscillating signal of some definite amplitude, such that the average current is zero. The average voltage will be the floating potential, and the ratio of the signal amplitudes will be the slope.

As previously noted, the standoff height separating the torch1from the work piece14can be an important parameter in controlling an oxy-fuel cutting process. Prior to the preheat process, the exact location of the work piece surface may not necessarily known. One non-limiting exemplary embodiment that enables the location of the work piece surface to be determined, and a specific height to be maintained, is shown inFIG. 5. The torch1and the work piece14may constitute the two surfaces under test, (i.e., as shown inFIGS. 4A and 4B), eliminating the need for additional probes or sensors. It will be appreciated that any of a variety of surfaces of the torch1may be used as one of the surfaces under test, including the torch nozzle. A dedicated probe mounting surface (not shown) could also be mounted near the nozzle. In addition, a surface other than the work piece14could constitute the other surface under test. For example, any electrically conductive component positioned near the flame16could be used. In the illustrated embodiment, the torch1can be moved toward the work piece14in small predetermined increments. At each increment, a slope measurement can be recorded using the system22,30ofFIG. 4A or 4B. In one embodiment these compiled slope values are stored in memory (not shown) associated with the processor28,36. For example, the compiled slope values may be stored in a look up table in the memory.

In the aggregate, and as shown inFIG. 5, these measurements can form a trend tending to zero resistance for some position of the torch1with respect to the work piece14. That extrapolated location may represent the position of the torch1where the tip of the nozzle8is touching the work piece14. During operation of the system (e.g., preheating or cutting), when a particular flame resistance measurement is encountered, that value can be used to determine the position of the work piece14, or more particularly it can be correlated to a specific standoff distance “SD” (FIG. 1) between the torch1and the work piece14. This can be performed using a lookup table, or a predetermined standard value could be used. The system may make this determination continuously or periodically during cutting operations to confirm a desired standoff distance “SD” is maintained. In other embodiments, a pre-existing compilation of expected values for reference slope may be stored for given conditions.

Adjustments in standoff distance “SD” can be made during a cut to compensate for curvature in the work piece14and/or to compensate for differences in level between the work piece surface and the cutting machine path. When cutting is initiated, the standoff distance “SD” between the torch1and the work piece14can be “trusted.” As such, a slope determination (using one of the previously described techniques) at the beginning of a cut can establish a reference value. After that, as the cut progresses, subsequent periodic slope determinations (again, using one of the previously described techniques) can be compared with the reference value and used to generate an error signal and/or an alarm condition if the determined slope departs from the reference value by a predetermined amount. In this way, the slope determination can act as a continuous measurement of errors in height.

The disclosed system and method can also be used to assess the gas mixture of the associated torch1. As the gas mixture is adjusted, a variety of techniques may be used to assess its appropriateness for cutting. In some embodiments the flow of oxygen and fuel can be actively adjusted to maximize the heat flux into the work piece14.

In one exemplary embodiment, the torch1can brought into position above the work piece14, and the gas mixture can be adjusted while performing slope determinations in the manner previously described. With this method, the torch1and the work piece14are the surfaces under test (i.e., as shown inFIGS. 4A and 4B). The mixture at which the slope is extreme (i.e., a minimum or maximum value) can be used as the point at which the flame temperature is highest (since the most desirable condition may be the condition in which heat flux into the work piece14is at a maximum).

In an alternative embodiment, illustrated inFIG. 6, two identical probes38,40may be placed symmetrically in the torch flame16at a height in the flame similar to where a work piece would be positioned during operation. In one embodiment, the probes38,40may be a pair of tungsten rods extending into the torch flame16from either side. Alternatively the probes38,40could be a pair of air or water cooled copper or stainless steel tube members. In one non-limiting exemplary embodiment the probes may be built into the torch1. Due to the symmetrical nature of the test, the floating potential between the probes38,40is very small, making the measurement simpler. The gas mixture at which the slope is extreme can be used as an approximation for the point at which the flame temperature is highest. In this embodiment, it is desirable that the measurement be performed at a location in the torch flame16that is representative of where the work piece14will ultimately be positioned. It will be appreciated that changes in gas mixtures and flow rates can make the flame grow and shrink drastically. As such, changes that actually cool the flame can register more extreme slopes if the hottest part of the flame has moved to the proximity of the probes.

Measured and/or calculated values of slope measurement and fuel-oxygen mixture can be used by the processor28,36to determine an optimum fuel-oxygen mixture setting, as shown in the graph ofFIG. 6.

The disclosed system and method can, in some embodiments, be used to measure the temperature of a work piece14. Thus, the torch nozzle8and the work piece14may be used as the measurement surfaces (i.e., surfaces1,14shown inFIGS. 4A and 4B). During preheating of the work piece14, the nozzle8on the torch1is already at its steady state temperature. Meanwhile the temperature of the work piece will be rising. Since all other factors that influence the floating potential are held constant, the floating potential can be used as an indicator for the work piece temperature during preheat. In fact, as the work piece14heats up, the floating potential can actually be observed to stabilize for a brief period as the work piece surface becomes molten. When the floating potential crosses a certain threshold appropriate to the material, the nozzle, and the gas composition, cutting can begin. In some embodiments the threshold value or values (kindling temperature, floating potential) will be predetermined and stored in memory.

It has been established how the disclosed system and method may be used to monitor the standoff distance “SD” between the torch1and work piece14during a cutting process. In some embodiments the system and method can, in addition or alternatively, be used to diagnose the “health” of the cutting process. As the material in the cutting oxygen stream cools, the floating potential will decline. If the floating potential drops below a threshold appropriate to the nozzle, gas composition and flow rate, it can be used as an indicator that the cutting process is proceeding too fast, and should be slowed in order to maintain appropriate cutting parameters. In some embodiments the threshold value or values (kindling temperature, floating potential) will be predetermined and stored in memory.

Some embodiments of the disclosed system and method may be used to detect cutting flame ignition. When lighting a torch flame, regardless of the ignition process, it is not always clear whether a stable flame has been struck. A spark may have failed to be struck, or the flame may have blown off of the tip, or any number of other problems may prevent a first attempt from yielding a stable flame. As a result, it is desirable to check that ignition was successful. With the disclosed system and method, any two conductive surfaces in the vicinity of where a stable flame should be can be monitored. Failure to detect conduction in the presence of a potential substantially higher than a reasonable floating potential (e.g., 10 V) indicates that ignition has failed. In one embodiment the two conductive surfaces could be the torch1and the work piece14.

FIG. 7Ais a flow diagram illustrating an exemplary method according to the disclosure. At step100, a voltage is applied between first and second surfaces associated with an oxy-fuel cutting system. In some embodiments the first and second surfaces are a torch surface and a work piece, respectively. The first and second surfaces may be exposed to the flame of an oxy-fuel torch during operation. At step110, a current generated in response to the applied voltage is sensed. At step120, a first parameter associated with a cutting process is determined based on the applied voltage and the sensed current. At step130, a determination is made about whether the first parameter is within a predetermined range. At step140, if it is determined that the first parameter is outside the predetermined range, a second parameter associated with the cutting process is adjusted.

FIG. 7Bis a flow diagram illustrating an exemplary method according to the disclosure. At step150, a current is driven between first and second surfaces associated with an oxy-fuel cutting system. In some embodiments the first and second surfaces are a torch surface and a work piece, respectively. The first and second surfaces may be exposed to the flame of an oxy-fuel torch during operation. At step160, a voltage generated in response to the driven current is sensed. At step170, a first parameter associated with a cutting process is determined based on the driven current and the sensed voltage. At step180, a determination is made about whether the first parameter is within a predetermined range. At step190, if it is determined that the first parameter is outside the predetermined range, a second parameter associated with the cutting process is adjusted.

Referring now toFIG. 8shows a non-limiting exemplary automated oxy-fuel cutting torch system50(hereinafter “cutting system50”) in accordance with the present disclosure. The torch system50may include a gas cutting torch52(hereinafter “the torch52”) that is operatively mounted to a computer numerical control (CNC) machine54or other automated machine tool that is capable of moving the torch52along a predefined path, such as may be specified in a software file. The torch52is shown generically connected to the CNC machine14, but it will be appreciated that in practical application the torch52will be mounted to the CNC machine54in a manner that facilitates 2-dimensional or 3-dimensional movement of the torch52as further described below. The torch52may be any type of gas cutting torch, including, but not limited to, an oxy-fuel torch, a propane torch, a propylene torch, a butane torch, or a mixed-fuel torch.

The cutting system50may also include a controller56, which in one embodiment comprises a microprocessor. The controller56may include a circuit58including an electrical power source60connected electrically in series with a resistor62or other current or voltage measurement device. The power source20may be a voltage source or a current source. For the sake of convenience, the following description of the cutting system50and the accompanying method shall assume that the power source60is a voltage source, in which case a current may be induced and measured in the circuit58as further described below. However, it will be understood that the power source60may alternatively be a current source, in which case a voltage may be induced and measured between the torch52and a work piece66(described below).

During operation of the cutting system50, one side of the circuit58may be electrically connected to the torch52, such as by a first conductor70, and the other side of the circuit58may be electrically connected to a work piece66that is to be cut by the torch52, such as by a second conductor68. The circuit58may further include a switch70for connecting the torch52to ground when the cutting system50it is not in operation, thereby preventing the buildup of static electricity in the circuit58. The circuit58may include additional switches (as shown inFIGS. 10-12) for placing the torch in and out of electrical communication with circuits for ignition as further described below.

The controller56may further include a processor72that is capable of executing a number of predefined instructions. The processor72may be operatively connected to the power source60for regulating an amount of voltage output therefrom as further described below, and may also be electrically coupled the circuit58, such as at points A and B, for measuring an amount of current flowing in the circuit58. The processor72may further be operatively connected to the CNC machine54and to the torch52for controlling/modifying the operation thereof as described in greater detail below. The processor72may further be operatively connected to the switch70for controlling the operation thereof, such as for selectively moving switch between a closed position, wherein the torch52is connected to the circuit58(e.g. when the cutting system50is in use), and an open position, wherein the torch52is connected to ground (e.g. when the cutting system50is not in use). A non-volatile memory (not shown) may be associated with the processor72for storing software instructions executed by the processor72and/or for storing data collected from the circuit58.

Referring toFIG. 9, a flow diagram illustrating an exemplary method of operating the cutting system50in accordance with the present disclosure is shown. Generally, the method exploits the electrically conductive nature of the torch's flame to determine the state of the work piece66being cut before and during cutting. Particularly, the high-temperature gases present in the torch's flame are sufficiently dissociated so that if a voltage is applied between the torch52and the work piece66a current will flow through the flame. This principle will be described in greater detail below in the context of the exemplary method.

At a first step200of the exemplary method, the work piece66may be manually or automatically positioned below the unlit torch52and connected to the circuit58, such as by the conductor68. For example, the conductor68may be connected to the work piece through the table, such as by an alligator clip or some similar means of electrically conductive attachment. The nozzle74of the torch may initially be disposed well above the surface of the work piece66, such as at a standoff distance “SD” of 6-12 inches, for example. If the switch70is in the open position, the processor72may direct the switch to move to the closed position, thereby placing the torch in electrical communication with the circuit58.

At step210of the method, the processor72may command the power source60to output a relatively low voltage, a non-limiting example of which is 12V. The processor72may then command the CNC machine54to slowly lower the unlit torch52until the processor72detects current flowing in the circuit58between connection points “A” and “B”, indicating that the nozzle74of the torch52has been brought into contact with the work piece66to complete the circuit58. The processor72may then record the height of the torch52in this position as a “zero height” (i.e. the height of the upper surface of the work piece66). This height may be stored in volatile or non-volatile memory associated with the processor.

At step220of the method, the processor may command the CNC machine54to elevate the torch52away from the work piece66. The processor72may simultaneously direct the power source60to charge an energy storage device (described below) that is electrically connected within the circuit58. For example, referring toFIG. 10, the energy storage device may be a capacitor bank78, in which case one or more capacitors in electrical communication with the torch52and some other surface (e.g. the work piece66) may be charged in advance to a predetermined voltage and discharged when the CNC machine54moves the torch52into contact with said surface. Alternatively, referring toFIG. 11, the energy storage device may be an inductor80that is in electrical communication with the torch52, in which case a switch82may be closed to induce a current in an inductor80, wherein the energy stored in the inductor80is discharged once the torch52is moved into the proximity of the work piece66or other surface and the switch82is opened.

In either case (i.e. either a capacitive or inductive energy storage device), if the processor72has commanded activation of a flow of gas from the torch52(e.g. by actuation of appropriate solenoid valves), and has properly positioned the torch52in advance, then the above-described discharge of electrical energy may create an ignition site in the gap between the torch52and the work piece66or other surface, thereby igniting the stream of gas flowing therethrough. This process may be enhanced by imposing some combination of oscillating voltages or high voltages to increase the gap distances over which ignition can occur, as shown inFIG. 12.

At step230of the method, the processor72may detect successful ignition of the gas by directing the voltage source to output a relatively low voltage, a non-limiting example of which is 24V, after discharge of the capacitors. If the fuel gas was successfully ignited by the discharge, a small current will flow through the flame76and will be detected by the processor72between points “A” and “B” in the circuit58. If, by contrast, ignition was not successful, there will be no flame76and therefore no detectable current in the circuit58. In the case of ignition failure, the processor72may repeat the entire ignition process (i.e. step220of the method) until successful ignition is detected.

At step240of the method, the processor72may direct the CNC machine54to raise the torch52until the nozzle74reaches a predefined standoff distance “SD” relative to the known zero height (i.e. the surface of the work piece66). The processor72may then direct the power source60to output a low voltage, a non-limiting example of which is 12V. At such a low voltage, the current in the circuit58will be determined by the resistance of the path between the torch52and the work piece66or some other surface. Such resistance is highly sensitive to variations in the quality of the flame76. Thus, the gas mixture in the torch52(e.g. the ratio of fuel gas to oxygen) may be adjusted until a desired current value in circuit58, as determined by the processor72, is achieved at the predefined standoff distance “SD”, where this desired current value is indicative of a desired quality of flame76. In one non-limiting exemplary embodiment, the desired current value may be indicative of a flame76that is suited for preheating the work piece66prior to cutting.

At step250of the method, the processor72may command the CNC machine54to move the torch52to a designated location along the surface of the work piece66where cutting is to begin. The processor72may then adjust the voltage in the circuit58to maintain a constant current, such as may be achieved by directing the CNC machine54to adjust the standoff distance “SD.” That is, when the standoff distance “SD” is increased, the voltage in the circuit58increases and the current in the circuit58decreases. Conversely, when the standoff distance “SD” is decreased, the voltage in the circuit58decreases and the current in the circuit58increases. The processor72may in this way utilize the measured current in the circuit58to maintain a consistent standoff distance “SD” relative to the work piece regardless of variations in the surface of the work piece66. This principle is described in U.S. Pat. Nos. 4,328,049 and 3,823,928, the disclosures of which are incorporated herein by reference.

At step260of the method, the processor72may command the power source60to increase its output voltage to a predefined maximum value at which the current in the circuit58is guaranteed to be limited by electron evaporation from the work piece66. This predefined maximum value may be determined from the geometry and flow rate of the torch52, for example. Such parameters may be known in advance, and an operator may consult a schedule of voltages or currents that are known to be important. Other embodiments of the present method may include looking for current-voltage sensitivities (i.e. the relationship between a change in current relative to a change in voltage).

With the voltage set at the predefined maximum value, the current in the circuit58will increase coherently with the temperature of the work piece66. It will be appreciated by those of skill in the art that when a material, particularly metal, is sufficiently heated, the increased kinetic energy exhibited by the electrons of the material may allow the electrons to momentarily escape from the material's boundaries. If an anode that is charged with a sufficiently large voltage is placed in the vicinity of the material, the electrons that escape from the material will be pulled away by the charged anode at exactly the same rate at which they evaporate from the material. This rate of evaporation is known to be a function of the temperature of the material.

The current in the circuit58, as affected by the above-described electron evaporation from the work piece66and as detected by the processor72, may be used to reliably determine the temperature of the work piece66. When the measured current reaches a predefined level, such as a level indicative of a kindling temperature in the work piece66, preheating of the work piece66is complete and cutting can begin. As will be appreciated by those of ordinary skill in the art, cutting the preheated work piece66may be achieved by activating the flow of cutting oxygen.

At step270of the method, the CNC machine54may move the torch52along the work piece66in accordance with a predefined cutting path at an appropriate speed for maintaining the quality of the cut. As the cut is made, the desired standoff distance “SD” may be maintained by continuously performing the torch height adjustment as described in step250above.

It should be appreciated that certain steps of the above-described exemplary method may be hindered by inconsistencies and imperfections in the surfaces of work pieces being cut. For example, oxidation on the surface of a work piece may form a barrier that resists current flow for contact sensing (as described in step210above) and/or that resists electrical arcing for torch gas ignition (as described in step220above). U.S. Pat. No. 7,087,856, which is incorporated herein by reference, describes a method for detecting contact through oxidation layers on a work piece in a manner that is safe to humans (i.e. that does not involve the application of high voltage or high frequency energy for an appreciable amount of time). It is contemplated that such a method may be similarly implemented in the context of the present disclosure for contact sensing and/or for torch gas ignition.

Additionally, the effect of oxidation or surface irregularities may be compensated for by taking initial calibration measurements when the work piece is in a known condition. A non-limiting example of this would be positioning the ignited torch52above a plate known to be at or near ambient temperature, and applying sufficient voltage so as to drive a current limited by thermionic emission from the plate. This calibration current sensed at this condition is an indication of the plate condition. The kindling temperature can then be recognized by when the measured current increases by some pre-determined amount relative to the calibration current.

In view of the forgoing, it will be appreciated that the cutting system50and accompanying method of the present disclosure provide a number of important advantages relative to existing automated cutting torch systems. Particularly, the system and method facilitate features such as automatic standoff control, automatic ignition, ignition detection, flame quality detection, and kindling temperature detection without requiring many of the moving parts, on-board electronics, and sensors associated with existing torch systems. The cutting system50of the present disclosure is therefore far more economical, reliable, and robust than existing systems.

It will be appreciated that although the foregoing description related to the specific implementation of the disclosed system and method in relation to an oxy-fuel cutting apparatus, that the disclosed system and method can be implemented in any of a variety of oxy-fuel thermal processing apparatus. In one non-limiting example, the disclosed system and method can be implemented in an oxy-fuel welding apparatus.

Based on the foregoing information, it will be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those specifically described herein, as well as many variations, modifications, and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing descriptions thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for the purpose of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended to be construed to limit the present invention or otherwise exclude any such other embodiments, adaptations, variations, modifications or equivalent arrangements; the present invention being limited only by the claims appended hereto and the equivalents thereof. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for the purpose of limitation.