Abstract:
A multi-axis waterjet cutting system is disclosed which eliminates high-pressure tubing coils in the area adjacent the waterjet system&#39;s cutting head and isolates critical system components from the backsplash of the cutting process. A high-pressure swivel is combined with an on/off valve arrangement in such a way that these components are closely adjacent the cutting head and rotate therewith, and are substantially shielded from waterjet back-splash. The cutting head and the swivel/valve combination are rotated about the cutting head&#39;s final axis of rotation (e.g., the A-axis) by a drive mechanism substantially shielded by the structure which rotates the cutting head associated with a prior axis of rotation (e.g., the C-axis). 
     By eliminating high pressure tubing coils, the disclosed system reduces the clearance needed for manipulation of the cutting head around the workpiece.

Description:
BACKGROUND 
       [0001]    The use of high velocity, liquid jets and abrasive-laden liquid jets to precisely cut a variety of materials is well known. Briefly, a high velocity liquid jet is first formed by compressing the liquid (typically water) to an operating pressure of 50,000-90,000 psi or more), and forcing the compressed liquid through an orifice having a diameter approximating that of a human hair; namely, 0.003 to 0.040 inches. The material defining the jet-forming orifice is typically a hard jewel such sapphire, ruby or diamond. 
         [0002]    The resulting highly coherent waterjet is discharged from the orifice against a workpiece via a generally tubular cutting nozzle at a velocity which approaches or exceeds the speed of sound. Those skilled in the art will recognize, however, that numerous other liquids can be used without departing from the scope of the invention, and the recitation of the jet as comprising water should not be interpreted as a limitation. Accordingly, the term “waterjet” and “water” as used herein shall include any liquid suitable for cutting a workpiece in the manner described herein. 
         [0003]    To enhance the cutting power of the waterjet, abrasive materials have been added to the jet stream to produce an abrasive-laden waterjet, typically called an “abrasivejet”. The abrasivejet is used to effectively cut a wide variety of materials from exceptionally hard materials (such as tool steel, aluminum, cast iron armor plate, certain ceramics and bullet-proof glass) to soft materials (such as lead). Typical abrasive materials include garnet, silica, and aluminum oxide having grit sizes of #36 through #200. 
         [0004]    To produce the abrasivejet, the waterjet passes through a “mixing region” wherein a quantity of abrasive is enhanced with kinetic energy from the high speed waterjet, thus enabling abrasive removal of most materials through abrasion. The abrasive material, which is under atmospheric pressure in an external hopper, is drawn into the mixing region by the lower pressure region via a conduit (referred to as the “abrasive feed tube”) that communicates at one end with the interior of the hopper, and at the other end with the mixing region via an abrasive inlet hole formed in the cutting head housing that houses the jet-forming orifice jewel and mixing region. 
         [0005]    The resulting abrasive-laden waterjet (or “abrasivejet”) is then discharged against a workpiece through an abrasivejet nozzle that is supported closely adjacent the workpiece. The spent abrasive-laden water is drained away from the workpiece in any of a number of known ways, and collected in a collection tank for recycling of the abrasive and/or proper disposal. 
         [0006]    As used hereinafter in this specification and in the claims, and as recognized by those of ordinary skill in the art, the term “waterjet cutting systems” includes abrasivejet cutting systems, the term “waterjet” includes “abrasivejet” within its scope when referring to the jet that is discharged towards the workpiece, and the term “cutting head” refers to a unit comprising a housing that has a high pressure water inlet (and an abrasive inlet if an abrasivejet cutting head), and encloses the orifice member, a mixing region if an abrasivejet cutting head, fluid paths therebetween and required seals in the positions and spatial relationships needed for efficient cutting. The cutting head may also include an on/off actuator that controls the flow of water within the cutting head. As also known to those of ordinary skill the art, The cutting head directs the waterjet/abrasivejet to the workpiece through a discharge nozzle. 
         [0007]    To appropriately and precisely position the cutting head with respect to a workpiece, a growing number of waterjet cutting system applications provide translation and/or rotation of the cutting head nozzle (usually referred to as the “cutting tool” or simply the “nozzle”) along and about a plurality of axes to so that the workpiece can be approached from multiple directions. 
         [0008]    Those of ordinary skill in the art recognize that the commonly used axes are the “X”, “Y”, “Z”, “A”, “B” and “C” axes. The first three are linear axes; i.e., the cutting head and nozzle are moved linearly in the directions of the X, Y and Z axes. The X and Y axes may correspond, for example, to the length and width of a cutting table underlying the cutting nozzle, while the Z axis corresponds to the height of the cutting nozzle above the cutting table. The A, B, and C axes are axis of rotation; i.e., the cutting head and nozzle rotate about the A, B and C axes. By convention, the C axis is parallel to the Z axis and perpendicular to the X-Y plane. The A axis is perpendicular to the C axis, with its centerline parallel to the X-axis when the C-axis position is zero. The B axis is also perpendicular to the C axis, with its centerline passing through the centerline of the C axis, but orthogonal to the A-axis; in other words, the A axis is parallel to the X-axis, and the B-axis is parallel to the Y-axis when the C-axis position is zero. 
         [0009]    This specification will discuss the invention in terms of these standard and commonly used nomenclatures; however, it should be recognized that the invention is not limited by the use of this nomenclature, and that other axes and axis relationships can be used without departing from the scope of the invention. 
         [0010]    Existing waterjet cutting systems employ swivels and coils to supply the high pressure cutting liquid to the nozzle. The mechanisms utilized to accommodate the rotational axes of movement have been bulky, and have restricted the positioning of the nozzle vis-à-vis the workpiece, thus limiting the application of waterjet cutting, particularly where multiple axes of rotation are employed. The use of coils that allow movement about these axes is expensive and poses a possible safety hazard due to the common fatigue failure of the coils which, as previously described, are the conduits for up to 50,000 psi or more of pressurized water. In addition, such coils reduce clearance around the cutting head of the system, limiting the orientation of the cutting tool around the workpiece at times. 
         [0011]    Swivels are safer but, to limit the size which can add to the bulky size of the mechanism, most manufactures use small ¼-inch high pressure swivels, which have a short mean time between failure as compared to the larger ⅜-inch high-pressure swivels. 
       SUMMARY 
       [0012]    A waterjet cutting system constructed in accordance with the invention herein eliminates high-pressure tubing coils in the area adjacent the waterjet system&#39;s cutting head and isolates critical system components from the backsplash of the cutting process. Preferably, a high-pressure swivel is combined with an on/off valve arrangement in such a way that these components are closely adjacent the cutting head but substantially shielded from waterjet back-splash, minimizing the mechanism&#39;s size while increasing waterjet back-splash safety and mean time before failure. The cutting head and the swivel/valve combination are rotated about the cutting head&#39;s final axis of rotation (described below) by a drive mechanism substantially shielded by structure associated with a prior axis of rotation . . . preferably, the cutting head&#39;s prior axis of rotation. 
         [0013]    As used in this specification, the term “final axis of rotation” refers to the axis of rotation about which the cutting head is rotated without such rotation moving the position of another rotational axis. As used in this specification, a “prior axis rotation” refers to the axis of rotation about which the cutting head is rotated prior to its rotation about its final axis of rotation. Where the cutting head has both “A” and “B” axes of rotation, the “final axis of rotation” is whichever of the two is moved last. 
         [0014]    By eliminating high pressure tubing coils, and thereby reducing the clearance needed to manipulate the cutting head around the workpiece, the preferred system constructed in accordance with the invention also simplifies the kinematics of the multi-axis system, making it easier to be programmed for accurate CNC control while protecting critical components from back-splash to thereby increase mean time to failure. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a side elevation view in schematic of a cutting head assembly and its preferred rotatable support structure constructed in accordance with the invention for use in a 5-axis waterjet cutting system; 
           [0016]      FIG. 2  is a fragmentary top plan view in schematic of the cutting head assembly and support structure of  FIG. 1 , including a mount bearing that permits it to rotate about the “A” axis; 
           [0017]      FIG. 3  is a front elevation view, in schematic, of a preferred cutting head assembly constructed in accordance with the invention, wherein certain internal water paths and bearing assemblies are illustrated in dotted or hidden lines for ease of discussion; 
           [0018]      FIGS. 4-6  are each a right side elevation view, in schematic, of a cutting head assembly and an alternative “A”-axis drive assembly constructed in accordance with the invention; and 
           [0019]      FIG. 7  is a front elevation view, in schematic, of a cutting head assembly and “z”-axis carriage to which it is mounted, illustrating the preferred internal water-conducting conduit in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]      FIG. 1  is a side elevation view in schematic of a cutting head assembly and its preferred rotatable support structure constructed in accordance with the invention for use in a 5-axis waterjet cutting system.  FIG. 1  illustrates a preferred example of a shielded swivel/valve combination that rotates with the cutting head about a final axis of rotation, plus a driving mechanism for same shielded within a prior axis&#39; structure. A 5-axis system is described because it is believed to currently be the most widely used of the waterjet cutting systems employing linear and rotational axes, and not by way of limitation. As stated earlier, the term “waterjet” as used herein includes “abrasivejet” within its scope when referring to the cutting system or the jet that is discharged towards the workpiece. 
         [0021]    The five exemplary axes employed by the illustrated cutting system are the “X”, “Y”, “Z”, “A” and “C” axes. The illustrated combination in  FIG. 1  includes a cutting nozzle  10  that has been rotated about its A-axis into the illustrated 9 o&#39;clock position. Those skilled in the art will recognize that the cutting nozzle  10  moves linearly along the X, Y and Z axes, and rotates about the A and C axes to approach a workpiece from multiple directions. The “X” and “Y” axes may correspond, for example, to the length and width of a cutting table underlying the cutting nozzle, while the Z-axis corresponds to the height of the cutting nozzle above the cutting table. 
         [0022]    As illustrated in  FIG. 1 , the C-axis is perpendicular to the X-Y plane and parallel to the Z-axis, while the A-axis is positioned with its centerline perpendicular to the C-axis. The cutting nozzle  10  is mounted within a cutting head  26  that is, in turn, mounted to a C-axis structure  16 . The C-axis structure, in turn, is mounted to a carriage structure (not shown) which can travel along the Z-axis to position the cutting head at the desired height above the cutting table as the cutting process proceeds. 
         [0023]    As will be apparent, rotation about the C-axis is not limited by a high pressure water conduit. In  FIG. 1 , the C-axis structure  16  is schematically illustrated as comprising a generally tubular member  16  which houses an A-axis drive mechanism  14 , and also carries a high-pressure water conduit  72  ( FIG. 7 ) that conducts the high pressure water from the swivel  12  at its upstream end to a swivel  18  ( FIGS. 1 and 3 ) at its downstream end that is coupled to the cutting head&#39;s high pressure water inlet. The C-axis structure  16  is mounted on the Z-axis carriage (not illustrated) for movement along the Z-axis to position the cutting head  26  at the desired height above the cutting table. The C-axis structure is securely affixed to the Z-axis carriage by a pair of collar-like bearing assemblies  16   a,    16   b  which permit the structure  16  to rotate within the collars without movement vis-à-vis the carriage in the Z-axis direction. As will be appreciated, the C-axis structure  16  thereby supports cutting head  26  and rotates it about the C-axis. The swivel  12  at the top of the C-axis structure is axially aligned with the C-axis and preferably has no restrictions on its the total angle of rotation, permitting the C-axis structure  16  and the cutting head  26  to be rotated about the C-axis without restriction. The swivel  12  is preferably far from the waterjet back-splash region, does not interfere with the cutting area 
         [0024]    As the C-axis structure rotates, thereby rotating the cutting head, the internal conduit  72  ( FIG. 7 ) rotates about the C-axis as well, its coupling to the cutting head&#39;s inlet swivel  18  ( FIGS. 1 and 3 ) rotates with the cutting head and C-axis structure  16  and is thereby maintained without the need for coils. The rotating C-axis structure  16  and its carried high pressure water conduit  72  serve in the elimination of high pressure coils and/or the conventional light weight ¼-inch high-pressure water swivel at the cutting head, and the swivel  18  permits the cutting head to be rotated about the A-axis while remaining coupled to the downstream end of the high pressure line  72 . 
         [0025]    As illustrated in  FIG. 1 , the cutting head&#39;s A-axis is positioned with its centerline perpendicular to the C-axis. The drive  14  for A-axis rotation, is placed within the C-axis structure  16 , and is thereby protected from waterjet splash-back, despite its proximity to the cutting head. This minimizes the size of the cutting head&#39;s mechanical components at or near the cutting head. By limiting the size of the mechanical components, the cutting head is able to reach into confines smaller than any other 5-axis waterjet head presently for sale or in use. In practice, it has been found that cutting systems employing the illustrated configuration require a clearance of approximately 9 inches in diameter when the cutting head is rotated compared with the clearance of approximately 18 inches required by known 5-axis systems. 
         [0026]    As described below, the preferred A-axis swivel  18  is preferably included within a common housing  23  with a high pressure on/off valve  22 . The high pressure valve/swivel combination within the common housing  23  results in the use of larger swivel within less space, permitting use of the relatively larger long-life swivel components without impinging on the positioning constraints that would be imposed by such swivels if used in known 5-axis waterjet cutting systems. This allows for long periods of operation without failure, readily available components and safety without the need of high pressure coils. 
         [0027]    Thus, the preferred configuration provides:
       1. the inclusion of both a high pressure water swivel and on/off valve in a common body;   2. a mechanical control system designed such that the critical components are positioned to be free of the back-splash of the waterjet cutting process;   3. the elimination of any high pressure tubing coils used to allow rotation of an axis; and   4. the positioning of the A-axis perpendicular to the C-axis thus simplifying the kinematics of the 5 axis system, making it easier to program.       
 
         [0032]      FIG. 2  is a fragmentary top plan view in schematic of the cutting head assembly and support structure of  FIG. 1 , including a mount bearing that permits it to rotate about the “A” axis. Those of ordinary skill in the art know that the nozzle  10  is mounted in a cutting head  26  that is typically coupled to a source of high pressure water via an internal passage in an extension tube  28 . The extension tube sealingly engages the internal water passage in the on/off valve  22  employing actuator  30  that is pneumatically driven to selectively block or permit the egress of high pressure water into the upstream end of the extension tube. Waterjet and abrasivejet nozzles, cutting heads, extension tubes and on/off actuators, per se, are each well known in the art, and a description of any specific configuration thereof is accordingly omitted for the sake of brevity; this invention is not limited to any specific configuration of same. 
         [0033]      FIG. 3  is a front elevation view, in schematic, of a preferred cutting head assembly constructed in accordance with the invention, wherein certain internal water paths and bearing assemblies are illustrated in dotted or hidden lines for ease of discussion. The actuator  30  is illustrated attached to the common housing  23  for visual clarity. Common housing  23 , containing the on/off valve  22  and swivel  18 , is coupled between on/off actuator  30  and extension tube  28  to permit the passage of hi-pressure water from a water inlet line to the cutting nozzle, the on/off valve  22  and swivel  18  being interconnected via an internal conduit within the common housing. The water inlet line (not shown) is fastened onto the generally tubular shaft  32  of the swivel  18  which is affixed to the common housing. The internal passage of the generally tubular shaft  32  feeds the high pressure water into the on/off valve  22  within the common housing  23 . The on/off valve  22  has an inlet passage  35  sealingly coupled to the swivel shaft  32  for that purpose, and an outlet passage  36  sealingly coupled to the inlet passage of the generally tubular extension tube  28 . 
         [0034]    The on/off valve  22  within the common housing is preferably a needle valve actuated by the on/off actuator  30 . The preferred actuator comprises a pneumatically responsive needle (not shown) that selectively blocks fluid communication between the on/off valve&#39;s inlet  35  and the valve&#39;s outlet  36  in response to a signal from a CNC or other control unit or switch, to activate and deactivate the waterjet/abrasivejet. 
         [0035]    The internal passage of the extension tube  28  conducts high pressure water from the on/off valve outlet  36  to the cutting head  26  for discharge as a waterjet or abrasivejet at the downstream end of the cutting nozzle  10 . Accordingly, the entire path taken by the high-pressure water exiting from the conduit  72  is internal to the common housing  23 , extension tube  28  and cutting head  26  and, therefore, within the portion of the cutting system that rotates about the A-axis (as further described below). 
         [0036]    The common housing  23  is preferably supported by the Z-axis carriage structure for movement along the Z-axis in such a way that the actuator  30 , extension tube  28  and cutting head  26  are also supported by the carriage structure for movement along the Z-axis. The preferred structure by which this support is provided is schematically illustrated in  FIGS. 4-7  as strut arm  38 . 
         [0037]    In accordance with the preferred embodiment of the invention, the system&#39;s A-axis drive  14  is housed within the C-axis structure  16 , as illustrated in  FIGS. 1 and 4-6 . It may be noted that in this embodiment of a 5-axis cutting system, the C-axis is the “prior axis” referred to earlier in this specification, and it may be further noted that the movement of the cutting head about the C-axis only moves the A-axis. 
         [0038]      FIGS. 4-6  show examples of A-axis drive mechanisms housed within the C-drive structure, but those of ordinary skill in the art will recognize that the invention is not limited to any particular A-axis drive mechanism, and that other drive mechanisms can be used within the scope of the invention. Turning initially to  FIG. 4 , the schematically illustrated A-drive mechanism comprises an electric stepping motor  40  which drives a pair of tie rods  44 ,  46  via a gearbox  42  that is coupled to the proximal ends of the tie rods via a crank arm  43 . The tie rods extend generally parallel to the C-axis. The distal ends of the tie rods are coupled to the cutting head  26 , preferably via affixation to the exterior of the common housing  23 . In operation, the stepping motor is activated under CNC control (or by a control signal from an alternative source) to precisely rotate the cutting head  26  about the A-axis to the desired angular position, acting through the crank arm  43  and tie rods  44 ,  46 . 
         [0039]    In accordance with the invention, the A-drive mechanism is substantially enclosed within the C-axis structure and thereby substantially shielded from back-splash from the waterjet cutting process. 
         [0040]    The alternative drive mechanism schematically illustrated in  FIG. 5  comprises a helically-threaded shaft  50  which is controllably rotated by the stepping motor  40 , and a coupling block  52  which engages the threaded shaft to move linearly in a path generally parallel to the C-axis and thereby cause rotation of the cutting head about the A-axis via a set of linkages  54 ,  56  coupled to the exterior of the common housing  23 . 
         [0041]    In  FIG. 6 , a belt and pulley system is utilized to rotate the cutting head about the A-axis. A split belt  60  is coupled at one end to a first coupling block  62 , and extends upward therefrom, around an idler pulley  66  and then downward towards and around a driven pulley  67  to a second coupling block  64 , to which the belt&#39;s other end is affixed. The coupling blocks, in turn, are mounted on (or integral with) a carriage  68  that engages a threaded shaft controllably rotated by a stepping motor  40  to move the carriage  68  linearly in a path generally parallel to the C-axis and thereby cause rotation of the cutting head about the A-axis via belt  60  and the driven pulley  67 , which is coupled to the exterior of the common housing  23  and whose axis of rotation is preferably co-axially aligned with the A-axis. The driven pulley  67  is mounted at  76  ( FIG. 3 ) about an arm  78  of the common body  23  for that purpose. 
         [0042]    As described earlier, the common housing  23  is preferably supported by the Z-axis carriage structure for movement along the Z-axis in such a way that the actuator  30 , extension tube  28  and cutting head  26  are also supported by the carriage structure for movement along the Z-axis. More precisely, and as further described above, the common housing, actuator, extension tube and cutting head affixed to the C-axis structure which, in turn, is supported by the Z-axis carriage. The common housing  23  is preferably supported by the strut arm  38  of the C-axis structure  16  ( FIGS. 4, 5 ) via a high angular contact bearing unit  24   a  ( FIG. 3 ) coupled to the arm  78  of the common body. The bearing unit  24   a  allows rotation of the cutting head about the A-axis, and prevents longitudinal motion along the A-axis. Those of ordinary skill in the art will recognize that the common housing can alternatively be an integral part of the cutting head, with the resulting cutting head housing being configured to shield the swivel  18  and on/off valve  22  from waterjet backsplash. 
         [0043]    While the foregoing embodiment is, for the reasons stated above, a 5-axis configuration, those skilled in the art will recognize that the invention herein is not so limited and may be applied to any number of axis having any number of orientations and relationships. Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention, which is defined by the appended claims.