Patent Description:
Document <CIT> (describing the preamble of claims <NUM> and <NUM>) discloses a plasma cutting system including a plasma cutting table. A gantry is movable along the plasma cutting table in a first direction. A torch carriage is movable along the gantry in a second direction that is perpendicular to the first direction. A torch holder is attached to the torch carriage and includes a motor having a hollow shaft rotor. A plasma cutting torch is attached to the hollow shaft rotor for <NUM>-degree rotation by the hollow shaft rotor around an axis of the plasma cutting torch.

Plasma arc torches are used to cut parts from workpieces and to cut openings or holes in parts and workpieces. When making perpendicular cuts through a workpiece, the cut edge of the part or hole would ideally be perpendicular to the surface of the workpiece. However, plasma arcs will often leave a slight bevel along the cut edge. For example, the width of the plasma arc at the top of the workpiece can differ slightly from the width of the plasma arc at the bottom of the workpiece. The plasma cutting system may focus the arc vertically in the center or middle of the workpiece, and the width of the plasma arc at the top of the workpiece may be slightly larger than the width of the arc at the bottom of the workpiece. Such an arc will cut a kerf through the workpiece that is wider at the top of the workpiece than the bottom, resulting in a slight bevel along the cut edges. The beveled edge can be removed with additional labor and/or machining, which is undesirable, or be left on the part, which is also undesirable. Thus, minimizing the beveled edge on a plasma-cut surface would be beneficial.

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.

In accordance with a first aspect of the present invention, a plasma cutting system according to claim <NUM> is provided. The system includes a plasma cutting power supply that simultaneously outputs both of a first plasma cutting current and a second plasma cutting current. A plasma arc torch is operatively connected to the plasma cutting power supply. The plasma arc torch includes a first cathode that receives the first plasma cutting current, a first electrode electrically connected to the first cathode, a first swirl ring around the first electrode, a second cathode that receives the second plasma cutting current, a second electrode electrically connected to the second cathode and radially offset from the first electrode, and a second swirl ring around the second electrode. The plasma arc torch simultaneously generates a first plasma arc from the first electrode and a second plasma arc from the second electrode during a plasma cutting operation. A gas controller is configured to separately control a flow of a first plasma gas to the first swirl ring and a flow of a second plasma gas flow to the second swirl ring. A torch actuator moves the plasma arc torch during a plasma cutting operation. The torch actuator is configured to rotate the plasma arc torch during the plasma cutting operation. The rotation of the plasma arc torch during the plasma cutting operation is to control an angular orientation of the plasma arc torch with respect to a kerf cut through a workpiece. A motion controller is operatively connected to the torch actuator to control movements of the plasma arc torch during the plasma cutting operation.

Further preferred embodiments of the first aspect of the present invention are defined in dependent claims <NUM> to <NUM>. second swirl ring. A torch actuator moves the plasma arc torch during a plasma cutting operation. The torch actuator comprises a motor having a hollow shaft rotor for rotating the plasma arc torch during the plasma cutting operation. A motion controller is operatively connected to the torch actuator to control movements of the plasma arc torch during the plasma cutting operation.

In accordance with a second aspect of the present invention, a plasma cutting method according to claim <NUM> is provided. The method includes providing a plasma arc torch. The plasma arc torch comprises a first input power connection, a second input power connection, an axially extending torch body, a first cathode electrically connected to the first input power connection, a first electrode electrically connected to the first cathode, a first swirl ring around the first electrode, a second cathode electrically connected to the second input power connection, a second electrode electrically connected to the second cathode and radially offset from the first electrode, and a second swirl ring around the second electrode. The method further includes providing a plasma cutting power supply having a first plasma cutting current output operatively connected to the first input power connection, and a second plasma cutting current output operatively connected to the second input power connection. A first plasma arc is generated from the first electrode and a second plasma arc is generated from the second electrode. A kerf is cut through a workpiece by the first plasma arc to create a cut edge. At least a portion of the cut edge is removed by the second plasma arc while cutting the kerf through the workpiece by the first plasma arc.

Further preferred embodiments of the second aspect of the present invention are defined in dependent claims <NUM> to <NUM>.

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:.

The present invention relates to plasma cutting systems and methods and to plasma arc torches for cutting workpieces using a plasma arc while minimizing any undesired beveling along cut edges, so that the cut edges are substantially smooth and flat. 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.

As used herein, "at least one", "one or more", and "and/or" are open-ended expressions that are both conjunctive and disjunctive in operation. 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.

Discussed herein are plasma arc torches that can have, among other things, fluid and electrical connections and a handle portion at an upstream end of the torch, and a nozzle, swirl rings and electrodes at a downstream or cutting end of the torch. The term "proximal" as used herein refers to the upstream direction of the torch, toward the end of the torch having the handle portion and any fluid and electrical connections. The term "distal" as used herein refers to the downstream direction of the torch, toward the cutting end of the torch.

Embodiments of the present invention described herein are discussed in the context of a plasma cutting system, and in particular a plasma cutting table. However, other embodiments are not limited to plasma cutting tables. For example, embodiments can be utilized with a plasma cutting robot, such as a robotic arm, and the plasma arc torch and torch holder described herein can be incorporated into an end effector or end of arm tooling for a robot.

<FIG> shows an example plasma cutting system. The plasma cutting system includes a plasma cutting table <NUM>. The plasma cutting table <NUM> has a main body <NUM> upon which a workpiece, such as a metal sheet or plate, is placed. The plasma cutting table <NUM> includes a gantry <NUM> that can move back and forth along the length of the cutting table's main body <NUM> in a first direction (e.g., in a Y direction). The gantry <NUM> can move on tracks or rails that extend along the sides of the table. A plasma arc torch <NUM> is attached to a movable torch carriage <NUM> that is mounted on the gantry <NUM>. The torch carriage <NUM> can move back and forth along the gantry <NUM> in a second direction (e.g., in an X direction) that is perpendicular to the first direction. The plasma cutting table <NUM> can be programmed to make precise cuts in a workpiece through controlled movements of the torch carriage <NUM> and gantry <NUM> in the X and Y directions, respectively. In certain embodiments, the torch carriage <NUM> can move the plasma cutting torch <NUM> 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 <NUM> can also rotate or tilt the torch <NUM> in a plane perpendicular to the plane of the table (e.g., in the X-Z plane), to make beveled cuts.

As is known in the art, the plasma cutting table <NUM> includes a water tray <NUM> located adjacent the workpiece. During a plasma cutting operation, the water tray <NUM> is filled with water, and the water can be drained to allow the water chamber to be cleaned to remove accumulated dross and slag.

<FIG> schematically shows various components of an example plasma cutting system <NUM>. The plasma cutting system <NUM> includes the plasma cutting table <NUM> and plasma arc torch <NUM>. The plasma cutting table <NUM> includes a torch actuator, such as the gantry <NUM> and torch carriage <NUM>, that moves the torch during a cutting operation. The system <NUM> can include a torch height controller <NUM> which can be mounted to the gantry <NUM>. The system <NUM> can also include a drive system <NUM> which is used to provide motion to the torch <NUM> relative to a workpiece W positioned on the table <NUM>. A plasma cutting power supply <NUM> is coupled to the torch <NUM> to provide first and second plasma cutting currents used to create two plasma arcs during a plasma cutting operation. The plasma cutting power supply <NUM> has a first plasma cutting current output and a second plasma cutting current output that are operatively connected to respective input power connections on the plasma arc torch <NUM> to generate the two plasma arcs. The system <NUM> can also include a gas console or gas controller <NUM> that can separately control gas flow rates and/or pressures of two plasma gasses and a shield gas used during the cutting operation. The gas console <NUM> can also be used to select different gases depending in the cutting operation that is being performed. That is, certain gases may be used for some cutting operations, but would not be used for others. Various gasses can be used for the two plasma gasses and the shield gas, such as air, nitrogen, oxygen, etc..

The plasma cutting system <NUM> can also include a computer numeric controller (CNC) <NUM>, which can include a user input/display screen or user interface <NUM>. The user interface <NUM> and controller <NUM> are used by a user to input and read cutting operational parameters and data, and allow the system <NUM> to be operated as an automated, programmable cutting system. Various input parameters can be input by the user into the controller <NUM>, via the user interface <NUM> (or other means) including: torch current, material type, material thickness, cutting speed, torch height, plasma and shield gas composition, etc. The table <NUM> can also include a user interface <NUM> that is operatively connected to the CNC and/or the plasma cutting power supply <NUM>. In embodiments employing a robotic arm as the torch actuator rather than a gantry and torch carriage, the CNC can be a robot controller that controls the movements of the robotic arm. The plasma cutting system <NUM> can have many different configurations, and embodiments are not limited to that shown in <FIG>, which is intended to be exemplary.

The motion controller <NUM>, gas controller <NUM>, or plasma cutting power supply <NUM> can utilize an electronic controller and can include one or more processors. For example, the controllers 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 controllers 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 controllers can further include one or more analog-to-digital (A/D) converters for processing various analog inputs to the controller. The program instructions for the motion controller <NUM> can include cut charts or nesting software. Such instructions typically include cutting information including instructions for the system <NUM> when cutting various holes or contours, taking into account the sizes and shapes of the holes/contours and the material being cut. As is generally understood the controllers can allow a user to cut numerous successive holes, contours or a combination of holes and contours in a workpiece without stopping between cuts. For example, the operator can select a cutting program that includes both hole and contour cutting instructions, and the motion controller <NUM> will determine the order and positioning of the cuts, as well as the various parameters of the cuts based on the user input information.

The controllers can operate in a networked environment using logical and/or physical connections to one or more remote computers. Examples of the remote computers include workstations, server computers, routers, personal computers, and the like. The networked environment can include local area networks (LAN) and/or wide area networks (WAN). Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets and the Internet. When used in a LAN networking environment, the controllers are connected to the local network through a network interface or adapter. When used in a WAN networking environment, the controllers typically include a modem or network interface, or are connected to a communications server on the LAN, or have other means for establishing communications over the WAN, such as the Internet. In a networked environment, program modules implemented by the controllers, or portions thereof, may be stored in a remote memory storage device. It will be appreciated that network connections described herein are exemplary and other means of establishing communications links between devices may be used.

<FIG> shows the plasma cutting torch <NUM> and torch carriage <NUM> in more detail. The plasma cutting torch <NUM> of the present invention is rotated when changing cutting directions, to maintain a constant angular orientation of the torch with respect to the cut edge and the kerf cut through the workpiece. According to the present invention, the torch <NUM> uses a primary, higher-power arc to cut the kerf through the workpiece, and a trailing secondary, lower-power arc to remove at least a portion of the cut edge created by the primary arc (e.g., remove material such as a bevel from the cut edge). The purpose of the secondary, lower-power arc is to trail the primary arc and square and refine the cut edge created by the primary arc; this can be accomplished by removing a portion of the cut edge or slicing a new cut edge just inside of the cut edge created by the primary arc. The torch <NUM> is rotated during the cutting operation to maintain the position of the secondary arc along the cut edge. The CNC is programmed to control the movements of the torch <NUM> in the X and Y directions when cutting a curved portion or otherwise changing directions of the cut, while simultaneously rotating the torch about a longitudinal axis <NUM> of the torch. The torch <NUM> is rotated according to the direction of the cut to control the angular orientation of the torch to the kerf and the cut edge, which results in maintaining common orientations and "arc cutting edges" along the cut edge of the workpiece of the two plasma arcs generated by the torch <NUM>.

The torch carriage <NUM> includes torch holder <NUM> to which the torch <NUM> is secured. The torch holder <NUM> is attached to the torch carriage <NUM> and is capable of rotating the torch <NUM> during plasma cutting. In the example embodiment shown, the torch holder <NUM> includes a motor <NUM> that rotates the torch <NUM>. In certain embodiments, the motor <NUM> can rotate the torch <NUM> through at least <NUM>°, so that the torch can be completely rotated during cutting. The motor <NUM> can have a hollow shaft rotor <NUM> to which the torch <NUM> is attached. In certain embodiments, the torch <NUM> is mounted within the hollow shaft rotor <NUM>, coaxially with the rotor, so that the rotor rotates with the torch around the axis <NUM> of the torch. Example motors <NUM> for rotating the torch <NUM> include permanent magnet, hollow shaft torque motors, hollow shaft servo motors, hollow shaft stepper motors, and the like. The CNC can control the rotational angle of the torch <NUM> as desired during plasma cutting via the motor <NUM>. In particular, the CNC can control the rotational angle of the motor <NUM> and torch <NUM> so that the angular orientation of the torch with respect to the kerf and cut edges of the workpiece W remains substantially constant during cutting. The motor <NUM> can include a positional feedback device, such as an encoder, that transmits angular positional data to the CNC. The torch holder <NUM> can include a bracket that is cantilevered from the torch carriage <NUM>, and a stator of the motor <NUM> can be secured to an upper surface of the bracket. In other embodiments, the stator itself is cantilevered from the torch carriage <NUM>, and the motor <NUM> functions as the torch holder. The hollow shaft rotor <NUM> and/or the torch <NUM> can include clamping devices or fasteners that secure and axially align the torch within the rotor.

In certain embodiments, the torch <NUM> can include rotary connectors <NUM> (<FIG>) to connect the torch to the power supply, gas console, etc., so that the torch can be rotated without twisting its supply cables and/or hoses. Rotary connectors can be particularly useful if torch rotations exceeding <NUM>° are desired.

<FIG> is a schematic view of an example plasma arc torch <NUM> that is capable of generating two plasma arcs simultaneously. The torch <NUM> has first <NUM> and second <NUM> input power connections for receiving a first plasma cutting current and a second plasma cutting current, respectively, from the plasma cutting power supply. The torch <NUM> generates a primary plasma arc <NUM> and a secondary plasma arc <NUM>. The current level of the first plasma cutting current is greater than the current level of the second plasma cutting current, and the energy level of the primary plasma arc <NUM> is greater than the energy level of the secondary plasma arc <NUM>. For example, the first plasma cutting current can be more than twice or more than three times greater than the second cutting current. Example current levels for the first plasma cutting current and the second plasma cutting current are 300A and 80A, respectively. However, various current levels for the first and second plasma cutting currents could be used within the scope of the present invention.

It can be seen that the torch has an axially extending torch body. Radially inward of the torch body, the torch <NUM> includes a first cathode <NUM> that receives the first plasma cutting current. A first electrode <NUM> is electrically connected the first cathode <NUM> and is used to generate the primary plasma arc <NUM>. The torch <NUM> also has a second cathode <NUM> that receives the second plasma cutting current. A second electrode <NUM> is electrically connected to the second cathode <NUM> to generate the secondary plasma arc <NUM>. The second cathode <NUM> and second electrode <NUM> are radially offset from the first cathode <NUM> and first electrode <NUM>. In the embodiment shown, the first cathode <NUM> and first electrode <NUM> are centered on and extend along the axis <NUM> of the torch. In other example embodiments, the first cathode <NUM> and first electrode <NUM> and the second cathode <NUM> and second electrode <NUM> are all radially offset from the axis <NUM> of the torch. Alternatively, the second cathode <NUM> and second electrode <NUM> can be centered on and extend along the axis <NUM>. In certain embodiments, the first cathode <NUM> and first electrode <NUM> are parallel with the second cathode <NUM> and second electrode <NUM>.

The torch further includes a first swirl ring <NUM> around the first electrode <NUM>, and a second swirl ring <NUM> around the second electrode <NUM>. The swirl rings <NUM>, <NUM> swirl respective plasma gas flows <NUM>, <NUM> for generating the plasma arcs <NUM>, <NUM>. The gas controller in the plasma cutting system can separately or individually control the flow rate and/or pressure of the first plasma gas provided to the first swirl ring <NUM> and the second plasma gas provided to the second swirl ring <NUM>. The composition of the first plasma gas can be the same as the second plasma gas, or the gasses can be different from each other. In an example embodiment, the first plasma gas is nitrogen and the second plasma gas is oxygen. The use of nitrogen for the first plasma gas will extend the life of the first electrode <NUM> given there is little to no oxidization. Extending the life of the first electrode <NUM> will put its usable life closer to that of the second electrode <NUM>, which will last longer given its lower amperage.

<FIG> shows an example plasma cutting operation. The purpose of the primary plasma arc <NUM> is to cut the kerf through the workpiece W. The primary plasma arc <NUM> is used for mass material removal. The secondary plasma arc <NUM> trails the primary plasma arc <NUM> during the cutting operation and removes at least a portion of the cut edge created by the primary plasma arc. The secondary plasma arc <NUM> refines the cut made by the primary plasma arc <NUM>. The primary plasma arc <NUM> is focused on the vertical center of the workpiece W and can leave a beveled edge when cutting the kerf. The secondary plasma arc <NUM> is focused below the center of the workpiece W to square the cut edge by shaving off the bevel and polish the cut surface made by the primary plasma arc <NUM>. As can be seen in <FIG>, the primary plasma arc <NUM> has a first focus depth D1 distal of the first electrode <NUM>, and the secondary plasma arc <NUM> has a second focus depth D2 distal of the second electrode <NUM>. The distance between the second focus depth D2 and the second electrode <NUM> is greater than the distance between the first focus depth D1 and the first electrode <NUM>. The first focus depth D1 is typically at the vertical center of the workpiece and the second focus depth D2 is just below the vertical center of the workpiece. The focus depths D1, D2 of the plasma arcs <NUM>, <NUM> can be adjusted by the plasma gas flow rates.

During a plasma cutting operation, the torch actuator rotates the plasma arc torch <NUM> such that the second electrode <NUM> and the secondary plasma arc <NUM> trail the first electrode <NUM> and primary plasma arc <NUM> while cutting a part contour or hole. With respect to the cutting direction (e.g., the X-Y direction of torch movement), the secondary plasma arc <NUM> tracks slightly behind and to the side of the primary plasma arc <NUM>. The degree to which the secondary arc <NUM> tracks to the side of the primary arc <NUM> is controlled by rotating the torch <NUM> via the hollow shaft rotor. Whether the secondary plasma arc <NUM> tracks on the left or right side of the primary arc will depend on the direction of torch movement (e.g., clockwise or counterclockwise in the X-Y plane) and whether a part contour or hole is being cut. In certain embodiments, the plasma cutting system cuts part contours and holes through parts in a particular direction (e.g., clockwise or counterclockwise) of X-Y torch movement. Using counterclockwise X-Y torch movements as an example, when cutting a part contour, the secondary, trailing arc <NUM> will track to the left of the primary, leading arc <NUM> when two arcs are viewed from the trailing arc toward the primary arc as can be seen in <FIG>. This allows the secondary arc <NUM> to remove the bevel from the outer edge of the part contour as the torch <NUM> is moved in a counterclockwise direction in the X-Y plane. When cutting a hole through a part, the torch <NUM> will be rotated slightly counterclockwise about the torch axis by the torch holder, so that the secondary, trailing arc <NUM> will track to the right of the primary, leading arc <NUM>. This allows the secondary arc <NUM> to remove a bevel from the edge of the hole as the torch <NUM> is moved counterclockwise in the X-Y plane to cut the hole.

<FIG> show an example plasma cutting operation during which the torch <NUM> is rotated to maintain the angular orientation of the torch with respect to a kerf <NUM> cut through the workpiece W. The kerf <NUM> is shown in solid line in <FIG>. The remaining uncut portion <NUM> of the part <NUM> to be cut from the workpiece W is shown in dashed lines. The torch <NUM> includes an orientation mark near the kerf <NUM> to help illustrate how the angular orientation of the torch changes along the cutting path. It can be seen in <FIG> that as the torch <NUM> transitions from cutting a straight portion of the part <NUM> to a curved portion of the part, the torch is rotated in a first direction (e.g., counterclockwise). Between <FIG> and <FIG>, the torch <NUM> is rotated in a second direction (e.g., clockwise) to cut another curved portion of the part <NUM>. As the torch <NUM> moves along the contour of the part <NUM>, the orientation mark on the torch <NUM> remains adjacent the kerf <NUM> due to the torch being rotated by the hollow shaft rotor on the torch holder. The torch <NUM> can be rotated clockwise and counterclockwise as needed, based on the shape of the cut to be made, and based on whether a part or hole is being cut. Rotating the torch <NUM> during the plasma cutting operation maintains the proper tracking of the secondary plasma arc with respect to the primary plasma arc along the trajectory of the cut. The torch <NUM> is rotated to keep both arcs tangential with the direction of cut. The motion controller can base trajectory planning on the secondary arc but also use the primary arc for checking against potential interferences.

Claim 1:
A plasma cutting system (<NUM>), comprising:
a plasma cutting power supply (<NUM>) configured to output a first plasma cutting current;
a plasma arc torch (<NUM>), for cutting a kerf through a workpiece, operatively connected to the plasma cutting power supply (<NUM>), wherein the plasma arc torch (<NUM>) comprises:
a first cathode (<NUM>) for receiving the first plasma cutting current;
a first electrode (<NUM>) electrically connected to the first cathode (<NUM>);
a first swirl ring (<NUM>) around the first electrode (<NUM>);
wherein the plasma arc torch (<NUM>) is configured to generate a first plasma arc (<NUM>) from the first electrode (<NUM>) during a plasma cutting operation;
a gas controller (<NUM>) configured to separately control a flow of a first plasma gas to the first swirl ring (<NUM>);
a torch actuator for moving the plasma arc torch (<NUM>) during a plasma cutting operation, wherein the torch actuator is configured to rotate the plasma arc torch (<NUM>) during the plasma cutting operation;
a motion controller (<NUM>) operatively connected to the torch actuator and configured to control movements of the plasma arc torch (<NUM>) during the plasma cutting operation; and wherein the plasma cutting system (<NUM>) is characterized by:
the plasma cutting power supply (<NUM>) being further configured to simultaneously output a second plasma cutting current;
in that the plasma arc torch (<NUM>) further comprises:
a second cathode (<NUM>) for receiving the second plasma cutting current;
a second electrode (<NUM>) electrically connected to the second cathode (<NUM>) and being radially offset from the first electrode (<NUM>); and
a second swirl ring (<NUM>) around the second electrode (<NUM>),
wherein the plasma arc torch (<NUM>) is configured to simultaneously generate a second plasma arc (<NUM>) from the second electrode (<NUM>) during the plasma cutting operation;
wherein the gas controller (<NUM>) is further configured to separately control a flow of a second plasma gas to the second swirl ring (<NUM>);
wherein the plasma cutting system is configured such that the torch (<NUM>) uses a primary, higher-power arc to cut the kerf through the workpiece, and a trailing secondary, lower-power arc to remove at least a portion of a cut edge created by the primary arc.