Patent Abstract:
A welding system is provided that includes a wearable wire feeder having a wire drive motor that is responsive to a control signal received directly from a power unit. Another welding system is provided that includes a wearable wire feeder that is configured to couple to a constant voltage power unit and does not include a voltage sensor. Another welding system is provided that includes a power unit, a wearable wire feeder separate from the power unit, a cable extending directly from the power unit to the wearable wire feeder and a welding torch coupled to and separate from the wire feeder. A method is provided that includes receiving a control signal from a power unit at a wearable wire feeder and driving a welding wire from the wearable wire feeder to a welding torch in response to the control signal, wherein the wearable wire feeder is separate from the torch.

Full Description:
BACKGROUND 
     The invention relates generally to portable welding systems. More specifically, embodiments of the invention relate to a wearable wire feeder having various components integrally mounted inside a wearable unit. 
     Portable welding systems may be used in field applications where it is not practical or convenient to send a work piece to a welding shop for repair or fabrication. These welding systems find applications in the farming and ranching industry and in a variety of other settings. To provide the welding functionality, a welding wire feeder may be used to feed a welding wire through a torch to a molten weld location in front of the tip of the torch. In many applications, it may be desirable to move the wire feeder to a remote location or to a different location in a work area. Otherwise, the wire feeder may be required to drive the wire over an unnecessarily long run of conduit to the particular location. As a result, the wire feeder may require a more robust and expensive drive mechanism. 
     Unfortunately, conventional wire feeders are designed as stationary devices intended to remain within a particular work area. Additionally, conventional portable wire feeders can be difficult or impossible to carry in areas requiring one or both hands of the user. Some wire feeders may be integrated into the welding torch, such as “push-pull” or “self-contained” wire feed torches. However, these wire feeders and torches may result in a bulky and heavy torch that is difficult to hold, maneuver, and weld in certain locations, and the wire feeder torches may be up to 10 to 15 feet in length. Some wire feeders may include control circuitry to provide control of the various parameters of the wire feeder and the torch, such as weld power, wire feed speed, etc. The wire feed mechanisms and control circuitry in these wire feeders may also add cost and manufacturing complexities. 
     Additionally, wire welders, conventional portable wire feeders, or the torch and wire feeder units, may be too heavy or bulky to move effectively. For example, if the user attempts to move along stairs, ladders, steep inclines, or across a farm or other unpaved surface, then the user may need to grab the welding equipment with both hands, hold on to a rail or other support, or seek assistance to move the unit. Wire welders may also require an additional cart or a long extension cord to reach some locations. 
     BRIEF DESCRIPTION 
     In one embodiment, a welding system is provided that includes a portable wire feeder. The feeder includes a support for a spool of welding wire, and a wire feed drive motor for driving the spool in response to a control signal received from wire feed control circuitry in a power unit. A welding torch is coupled to the wire feeder by a cable. The torch is controllable to generate a signal for the control circuitry to cause the control circuitry to drive the motor and thereby to feed welding wire to the torch for a welding operation. 
     The system may also include a welding power supply. The power supply may include the control circuitry for the portable wire feeder. Moreover, the power supply may itself include a wire feeder, such as an integrated wire feeder. Both the integrated wire feeder and the portable wire feeder may be driven by the same control circuitry. In such arrangements, a switch may be provided for switching between provision of the control signals to the integrated wire feeder and the portable wire. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a perspective view of a wearable wire feeder coupled to a portable engine-driven welding system in accordance with an embodiment of the present invention; 
         FIG. 2  is a perspective view of the wearable wire feeder of  FIG. 1  in accordance with an embodiment of the present invention; 
         FIG. 3  is a cut-away side view of the wearable wire feeder of  FIGS. 1 and 2  in accordance with an embodiment of the present invention; 
         FIG. 4  is a block diagram of a wearable wire feeder coupled to a portable engine-driven welding system in accordance with an embodiment of the present invention; and 
         FIG. 5  illustrates a process for operating the wearable wire feeder coupled to a portable engine-driven welding system in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of a portable engine-driven welding system  10  coupled to a wearable wire feeder  12  in accordance with an embodiment of the present invention. The illustrated system  10  is a metal inert gas (MIG) welding system, although other welding systems may utilize the wearable wire feeder  12  discussed below. As illustrated in  FIG. 1 , welding system  10  may include a cart or other portable assembly, as indicated generally by reference numeral  14 . In the illustrated embodiment, the cart  14  has a tubular frame  16  with wheels  18  for easily moving the cart  14  from place to place. The components described in  FIG. 1  and discussed below are generally mounted in an enclosure  20  comprising a number of panels  22  which can be removed or displaced to access the components within the cart  14 . A front panel  24  includes various controls and cable connections. The front panel  24  includes a control panel  26  where the various adjustments can be made for setting the regime of the control circuitry, where provided, as well as various welding settings. Moreover, as illustrated in  FIG. 1 , the front panel  24  includes a number of receptacles  28 , shown covered by optional covers in the figure, which allow for plug-in connection of power tools, lights, and other devices. In a presently contemplated embodiment, electrical service is provided in the front panel at 60 Hz, 120V, and 240V. 
     In general, the system can provides welding resources to a power/control cable  30  and to a ground cable  32 . The ground cable  32  is coupled to a ground clamp  33  which may be attached to a work piece. The power/control cable  30  is coupled to the wearable wire feeder  12 , which in turn is coupled to a welding torch  34  (e.g., the welding gun) having a torch cable  35 . In one embodiment, the power/control cable  30  may be about 15 to about 50 feet, and the welding torch  34  and cable  35  may be about 3 to about 5 ft. Thus, the cable  35  is relatively short as compared to a conventional wire feeder. In operation, a welding operator contacts an electrode in the welding torch  34  with the work piece to complete an electrical circuit, and thereby creating an arc used to melt metal and perform the welding operation. 
     The close proximity of the wearable wire feeder  12  to the operator (i.e., mounted on operator), the torch  34 , and the weld location enables the operator more freedom to weld at remote locations. The short distance between the wire feeder  12  and torch  34  also enables use of smaller welding wire, a smaller wire feed drive, and so forth. The short distance of the cable  35  reduces the weight associated with the cable  35 . Further, there is less weight in the power/control cable  30  because it does not include welding wire. Additionally, the welding operation is not limited to the position of the wire feeder  12 , because the wire feeder  12  is always with the operator. 
     While reference will be made in the present discussion to MIG welding torches and to MIG welding in general, it should be borne in mind that the welding system  10 , while including a wire feeder  12  for performing MIG welding operations, is not necessarily limited to such operations. In certain embodiments, the power supply and power control circuitry described below may be designed for constant voltage power control regimes only. However, other embodiments may not be limited to constant voltage operation. 
     The system  10  illustrated in  FIG. 1  has an engine-driven power supply that generally includes an engine and a generator, as discussed below with reference to  FIG. 4 . In the illustrated embodiment, the system  10  having the engine and generator set form a compact and portable unit having a small footprint that occupies little space at the welding location, and can be transported by a single operator. In one embodiment, the system  10  uses a single-cylinder gasoline engine, such as a 10-40 HP engine running at a nominal speed of 1800 or 3600 RPM. However, the system  10  may utilize a variety of spark ignition engines or compression ignition (e.g., diesel) engines having one or more cylinders. The system  10  may also include an appropriate fuel tank for supplying necessary fuel for running the engine. In certain embodiments, the engine may include an air-cooling system, a liquid-cooling system, or both. The engine directly drives a generator which, in one embodiment, has a rated power output of either 4500 Watts peak, 4000 Watts continuous, or 6000 Watts peak, 5500 Watts continuous power output. As with the engine, however, other suitable generators and power ratings may be used in the system  10 . Alternatively, the system  10  may be coupled to a power outlet by a power cord  36  and plug  37 . 
     As mentioned above, the wearable wire feeder  12  is coupled to the welding system  10  by a power/control cable  30 . As described in more detail with reference to  FIG. 4 , the power/control cable  30  may supply power, control signals, and gas to the wearable wire feeder  12 , and control circuitry in the welding system  10  may send control of the wire feed and other welding parameters to the wire feeder  12 . In certain embodiments, the power/control cable  30  provides a direct connection for the system  10  to the wire feeder  12 . Thus, in such an embodiment, the power/control cable  30  does not include any intermediate control circuitry or the like. In this embodiment, the wire feeder  12  may not contain any voltage-sensing boards or circuits, as the welding system  10  may provide a constant voltage for welding via power/control cable  30 . The system  10  may also be coupled to a gas source, such as gas cylinder  39  to provide shielding gas for the welding operation. Thus, the wire feeder  12  also may include features, such as gas conduit, regulators, valves, and controls, for routing the gas to the welding torch  34 . 
     Advantageously, to facilitate portable welding in small locations, a user may wear the wearable wire feeder  12  as a fanny pack, a shoulder pack, etc., thus freeing both of the user&#39;s hands. The wire feeder  12  may be mounted to a user&#39;s belt, thigh, shoulder, or any other location by straps, loops, clasps, or any suitable mounting mechanism  13 . For example, as a shoulder pack, the wire feeder  12  may include a strap  13  that mounts over the user&#39;s shoulder. The engine-driven welding system  10  may also be moved on wheels  18  to a suitable location, allowing a user to reach welds in remote or difficult to reach areas. 
     Turning now in more detail to the wire feeder  12 ,  FIG. 2  depicts a perspective view of the wire feeder  12  having a panel  40  that is open to expose a wire spool  42 . The panel  40  may be hinged or otherwise removable to allow insertion and removal of the wire spool  42 . In one embodiment, the wire feeder  12  may be configured to receive up to about a 2 lb wire spool. The top panel  40  may be secured to the housing  44  of the wire feed  12  by a mechanical or magnetic clasp, a lock, or any suitable mechanism. In one embodiment, the housing  44  may be manufactured from molded plastic. In other embodiments, the housing  44  may be manufactured from a composite or any other suitable material. For example, in an embodiment the housing  44  may be made entirely or consist essentially of plastic, composite, carbon fiber, fiberglass, other non-metallic materials. In other embodiments, the housing  44  may consist essentially of a combination of materials, such as plastic and composites, plastic and other nonmetallic materials, etc. 
     The housing  44  of the wire feeder  12  may also include one or more user inputs, such as controls and/or dials  46 , which may enable a user to control the rate of adjustment of the wire feed speed or other suitable parameters of the wire feeder  12 . For example, the dials  46  may include wire speed, gas flow rate, welding voltage/current, and so forth. In addition to the dials  46 , the wire feeder  12  may include other control features, such as switches, keypads, and displays. The displays may include digital and/or analog displays of wire speed, gas flow rate, welding current, and so forth. As mentioned above, the wire feeder  12  receives power and control signals from the system  10  via the power/control cable  30 . Thus, in some embodiments, the wire feeder  12  may have only limited or no control features. The front of the wire feeder may also include one or more connections  48  to the welding torch  34 . The wire feeder  12  may also include a connection  52  for to the power/control cable  30  that couples the wire feeder  12  to the welding system  10 . In some embodiments, the connection  52  may be unique so that only a specific welding system may be used with the wearable wire feeder  12 . 
       FIG. 3  is a cutaway view of the wire feeder  12  illustrating various internal components. As mentioned above, the wire feeder  12  may include controls such as controls  46 , the connections  48  to the welding torch, and the connection  52  to the welding system  10  via power/control cable  30 . The connections  48  may include a power plug  54  and a multi-pin connector  55 . The wire feeder  12  may include a wire spool mount  56 , such as a rotating shaft, nut, lock ring, other suitable mount, or any combination thereof. To supply wire to the torch  34 , the wire feeder  12  may include a wire drive  58  that feeds the wire out to the torch  34 . In the illustrated embodiment, the wire drive  58  includes a pair of facing drive wheels  58 A and  58 B, which compressively fit about and drive the welding wire in response to rotation provided by a motor. As discussed further below, the wire drive  58  may be controlled in response to a control signal received from the welding system  10  through the power/control cable  30 . Additionally, the wire drive  58  receives power from the welding system  10  through power/control cable  30 . Thus, in certain embodiments, no control circuits or other control of the wire drive motor  58  or other welding parameters are included in the wire feeder  12 . Advantageously, eliminating the control circuitry, interface, or control elements from the wire feeder  12  reduces the size, cost, and weight of the wire feeder, thus allowing greater portability. Moreover, as discussed above, the short length of the cable  35  (see  FIG. 1 ) due to the close proximity of the feeder  12  (i.e., worn by the user) enables use of smaller, less powerful, more lightweight, and less expensive components of the wire drive  58 . 
     The wire feeder  12  also could include a potentiometer  59 , which is connected to one of the controls  46  so a user can adjust the motor speed  59 . In one embodiment, the potentiometer  46  may be used to change the rate of adjustment of the wire feed speed. For example, the potentiometer  59 , and thus the adjustment of the wire feed speed, may be set so that a user-selected target arc length and heat input is maintained at the weld. 
       FIG. 4  is a block diagram illustrating an embodiment of the welding system  10  and the wire feeder  12 . Various internal components of the welding system are further illustrated, such as a power supply  60  that includes an engine  62  and generator  63 , a controller circuit  64 , an operator interface  66 , a cart electric service  68 , and a gas supply  70 . The controller circuit  64  may include a contactor control  72 , a transformer  74 , and a switch  76 . The components may be included in a system of the type illustrated in  FIG. 1  and described above. That is, the system may include a wire feeder (with any associated spool, motor drive, gearing and so forth) in a base unit and power supply. A system of this type is available commercially from Miller Electric Mfg. of Appleton, Wis., under the commercial designation Renegade. The presence of a wire feed control circuit, discussed above, in such systems permits very straightforward interfacing of the remote wire feeder without the need for duplication of control circuitry. That is, the same circuitry used to power and control the in-unit wire feeder may provide power and feed speed control signals to the remote wire feeder. At the same time, it should be recognized that other systems may be provided in which control circuitry is provided in a power supply without an integrated wire feeder, and even without other welding support equipment other than the power supply and wire feeder control circuitry. Such systems may provide, for example, a DC power source and wire feed control signals for the remote unit. Moreover, such systems need not be engine driven, but may be driven by connections to the power grid or by batteries. 
     It should also be noted that, when a power supply is used that does include a separate or integrated wire feeder, and the same control circuitry is to be used for regulating operation of the remote wire feeder, one or more switches may be provided for effecting the transition from use of one wire feeder to another. For example, a switch may deactivate the internal or integrated wire feeder and allow control signals to be provided to the remote wire feeder. Such switching devices may be manual or automatic. Thus, for example, where a user desires to plug the remote wire feeder into the power supply, the power supply may recognize that the remote wire feeder is present and operative, and send signals to the remote wire feeder rather than the internal or integrated wire feeder. Here again, such control may be simply mechanical or electromechanical in nature (e.g., a toggle switch), or may be based upon a digital control algorithm (e.g., sensing presence of the remote wire feeder and altering application of wire feed control signals appropriately). 
     The wire feeder  12  may be coupled to the welding system  10  by the power/control cable  30 , as discussed above, thus coupling the wire feeder  12  to the controller circuit  64 . The wire feeder  12  may receive power and a control signal from the controller circuit  64 . The wire feeder  12  may include a controller  78 , such as the potentiometer  59 , for regulating the rate of adjustment of the wire feed speed received from controller circuit  64 . For example, the controller  78  may allow for operator control of the feed speed of the wire electrode, or the speed may be regulated as a function of other process variables controlled by the control circuitry  64 . Such variables may include, for example, the current applied to the welding torch by the contactor control  72 . In one embodiment, a user may adjust the controller  78  via one of the controls  46  on the housing of the wire feeder  12 . The controller  78  may respond to the change in resistance of the potentiometer  59  and control the wire feed speed based on the change. 
     The switch  76  may be coupled to an output from the generator  63  to enable the controller circuit  64  and the welding system  10  in general to operate alternatively from grid power or another external power supply. Thus, the power cable  36  may also be routed to the switch  76 . Operation of the switch  76  may then reconnect the controller circuit  64 , wire feeder  12 , and in general the system  10  from the power supply  60  to a power grid or external power via the power cable  36 . In certain configurations, arrangements other than an integrated cable or cord may be made for providing power to the system, such as plug receptacles that receive a separate power cord plug. 
     The controller circuit  64  may also include the transformer  72  to aid in adjusting the voltage supplied to various components. For example, the transformer  72  may adjust the voltage received from the power supply before output to the cart electrical service  68  and the receptacles  28  on the front of the system  10 , so that power tools or other accessories may be coupled to the system  10  and use auxiliary power. 
     Power from generator  63  may be conditioned by the controller circuit  64  and the contactor control  72 . In general, the controller circuit  64  may include a converter which smoothes and conditions the power output by the generator, and may transform power to one or more output levels. In certain embodiments, the converter includes a center tap coil that enables 120V and 240V service output for lamps, power tools, and so forth. Other conversion techniques may, of course, be provided for auxiliary power. In some embodiments, the controller circuit  64  allows for operation both from the grid as well as by output of the engine-drive generator  63 . For example, an operator may perform welding operations while coupled to the power grid via power cable  36 , while running engine  62  for providing output power service locally, such as for lights or power tools. Alternatively, the controller circuit  64  may permit either grid power or engine-generated power solely. 
     The generator  63  may convert the power output (e.g., mechanical energy) of the engine  62  to an electrical power. Generally, the generator  63  includes a device configured to convert a rotating magnetic field into an electrical current (e.g., AC generator). The generator  63  includes a rotor (rotating portion of the generator) and a stator (the stationary portion of the generator). For example, the rotor of the generator  63  may include a rotating drive shaft disposed in a single stator configured to create an electrical current (e.g., welding current) from the rotation of the magnetic field. In an embodiment, the generator  63  may include a four-pole rotor and three-phase weld output configured to provide beneficial welding characteristics. Further, the generator  63  may include a plurality of independent winding sections in the rotors and/or stators, such that the generator  63  is configured to output multiple electrical outputs having different characteristics. For example, the generator  63  may include a first section configured to drive a welding current to a welder, and a second section configured to power auxiliary devices. 
     Within the control circuitry, the electrical output of the generator may be provided to a rectifier, which produces rectified DC power. The rectified DC power is provided to controller circuit  64 , which may include, as in a presently contemplated embodiment, at least one energy storage device such as a capacitor for smoothing the ripple in the rectified signal to provide a DC bus. An alternative embodiment may use a DC generator instead of AC generator and rectifier, or the rectifier may be part of the generator, or between the generator and the converter. 
     Controller circuit  64  may also include an inverter and rectifier that convert the smoothed and rectified DC signal to a welding output (having an appropriate current and voltage). For example, controller circuit  64  may provide welding current selectable by the operator. Various control functions including a hot start and a protection system may also be provided. 
     The welding system  10  illustrated in  FIG. 4  may also include the operator interface  66 , which may provide for the control panel  26  having switches and dials or knobs for setting the various operational parameters of the system. For example, the operator interface  66  may allow for setting the type of welding operation to be performed (e.g., MIG), as well as currents or voltages desired, wire feed speed, and other welding operating parameters. Where the feed speed of wire electrode is not automatically controlled by controller circuit  64 , the operator interface may also permit manual setting of the electrode feed speed. 
     As discussed above, the wire feeder  12  may include the wire drive  58  that drives the wire spool  42  to advance welding wire to the torch  34 . The welding wire, for MIG welding, is fed into the torch  34  along with one of two power conductors coupled to the contactor control. Another of the conductors is coupled to the ground cable  32  to complete the electrical circuit through a work piece  80 . The system  10  may also be provided with the optional gas supply  70 , such as gas cylinder  39 , to provide an inert gas used for shielding of the weld. Where a flux core wire electrode is used in MIG welding, such gas supplies may not be required. The gas supply  70  may be controlled by the controller circuit  64 , and may include various control mechanisms, such as gas solenoids, valves, etc. For example, in one embodiment, the gas solenoid may be controlled by the controller circuit  64  via a remote switch on the welding torch  34 . In an alternative embodiment, a gas purge switch may be provided on the on the feeder  12 . 
     In some embodiments, the welding system  10  may include an on-board wire feeder  82  integrated into the unit so that no additional wire feeder is needed for welding. In such an embodiment, the welding system  10  may include a switch  83  to disable or enable the on-board wire feeder  82  of the system  10  so that an external wire feeder, such as the wearable wire feeder  12 , may be used. 
     The power/control cable  30  may provide various functions including a multi-conductor control cable, a heavy weld cable, and a shielding gas line. For example, in one embodiment, the power/control cable  30  may include a gas line, a weld power line, two contactor closure wires for weld power and gas, and two drive motor power wires. The power/control cable  30  may also include or consist essentially of a 4-wire control cable that includes two wire feed control wires and two voltage control wires. In one embodiment, for a power/control cable of about 50 feet, the weld power line may be 3 gauge wire. In another embodiment, for a power/control cable of about 30 feet, the weld power line may be 4 gauge wire. Additionally, in some embodiments, the power/control cable  30  may include a work lead. It should be noted, however, that the length of cable is generally only limited by the voltage drop for welding power. In many practical applications, such as for maintenance, repair, shipyard work, welding while on man lifts, and similar tasks, the power supply may be positionable sufficiently close to the application such that the run length of the power cable may be kept reasonably short (e.g., within 50 feet). 
     Advantageously, as discussed above, by locating the controller circuit  64  on the welding system  10 , the wearable wire feeder  12  may be lighter, smaller, less bulky, and less expensive to manufacture. Further, the portability of the welding system  10  and the length of power/control cable  30  may increase the range of the welding system  10  and provide for welding in locations away from a power grid or in hard to reach areas. The short distance between the worn wire feeder  12  and the torch  34  may provide the ability to reach welds in difficult or small areas and may permit aluminum welding. 
     Referring now to  FIG. 5 , a process  100  for operating the welding system  10  and wearable wire feeder  12  is shown. Beginning with block  102 , a user may first connect the wearable wire feeder  12  to the welding system  10 , such as by power/control cable  30 , and may connect the welding torch  34  to the wearable wire feeder  12 . The user may also connect the ground clamp  33  to the material to be welded. 
     To generate power, the user may plug the welding system  10  into an electrical outlet using power cable  36 , or if greater portability or range is desired, may alternatively or additionally activate the engine  63  and generator  62  of the system  10  (block  104 ). The user may then secure the wearable wire feeder  12  to the user&#39;s body to allow hands-free use of the wire feeder (block  106 ). It may be advantageous for the user to wear the wire feeder  12 , such as by strapping  13  the wire feeder  12  around the user&#39;s waist as a fanny pack or wearing the wire feeder  12  over the user&#39;s shoulder. 
     After power is available, either from the grid or generated by the power supply  60 , the user may then turn on and select the various operating parameters of the welding system  10 , such as voltage, gas, wire feed, etc (block  108 ). As stated above, selection of such parameters enables the controller circuit  64  to pass the control signals to the wire feeder  12  and control the wire feed, gas supply, and welding power to the torch  34 . 
     The user may select an appropriate wire feed speed adjustment and/or voltage using the controls  46  on the wearing wire feeder  12  (block  110 ), thus allowing the user to be remote from the welding system  10  when initiating or adjusting the welding process. For example, the rate of adjustment of the wire feed speed may be based on a setup parameter chart so that to maintain a selected target arc length and heat input at the weld. Further, by wearing the wire feeder  12  and freeing up both hands, the user may be able to use hands for support, movement, and adjustment of the wire feeder  12  and operation of the torch  34 . Once all adjustments have been made to the user&#39;s preferences, the user may operate the torch  34  by depressing a trigger or other switch on the torch  34  and then perform the welding operation (block  112 ). 
     In summary, the system described above allows for a base unit, containing a power supply, to be easily coupled to welding components, including a remote wire feeder, a welding torch, and a short run of cable between the wire feeder and welding torch. The remote wire feeder is coupled to the power supply by a longer run of cable that provides welding power and wire feed signals for the wire feeder. Control circuitry for generating the wire feed signals is provided in the power supply and need not be duplicated in the remote wire feeder. The remote wire feeder may be a simple as a motor, any needed drive linkages, and a spool of welding wire. A trigger on the welding torch causes a signal to be sent to the control circuitry that, in turn, causes the wire feeder to drive wire to the torch. On the other hand, certain controls, such as wire feed speed, voltage, and so forth, may be provided on the remote wire feeder. These may be controlled by the user via dials, knobs, buttons or any other control input interface. In many or most applications, the wire feeder will be designed to be worn such that the welder may conveniently work without the need to more, carry, or drag the wire feeder between welding locations. 
     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.

Technology Classification (CPC): 1