Abstract:
The invention comprises a power impact torque tool that is torque-limited by a novel torque-timing device that controls the amount of time that the tool motor operates after the operator initiates tool operation. The invention also includes the torque-timing device itself and with other tools. The invention further includes the torque-timing device in the form of a modular, releasably-attachable, user-adjustable control apparatus for tools powered by compressable fluids. The torque-time-limiting device allows the user to adjust a needle valve that controls the filling of a reservoir which, when full, provides the pressure required for actuating a shut-off valve.

Description:
FIELD OF INVENTION  
         [0001]    This invention relates generally to the field of power impact tools and, more particularly, to a modular control apparatus for a power impact tool and more specifically to timing devices.  
         BACKGROUND OF INVENTION  
         [0002]    Power impact tools (e.g., pneumatic, hydraulic, electric, etc.) are well known in the art. Power impact tools produce forces on a workpiece by the repeated impact of a motor-driven hammer on an anvil that is mechanically connected, directly or indirectly, to exert a force on the workpiece. Some power impact tools exert linear forces. Other power impact tools exert torque, which is a twisting force.  
           [0003]    One difficulty in current power impact tools is that power may be applied too long to the workpiece. The accumulation of impacts on any already tightened workpiece may cause damage. Current power impact tools shut off when the operator manually enables shutting off. For example, in a pneumatic hand tool such as a torque wrench, the operator releases the trigger valve to shut off the supply of compressed air to the tool motor. The number of impact forces delivered to the workpiece depends on the reflexes and attentiveness of the tool operator. During any delay, the workpiece may become overtorqued and damaged.  
           [0004]    Accordingly, there is a need in the field of power impact tools for ways to provide more predictable amounts of torque ultimately applied to a workpiece. Additionally, there is a need for a control apparatus that will limit the time that a force of a power impact tool is applied to a workpiece.  
         SUMMARY OF INVENTION  
         [0005]    The present invention provides an apparatus and method for use in controlling power impact tools.  
           [0006]    An first general aspect of the invention provides a modular control apparatus comprising:  
           [0007]    a modular structure;  
           [0008]    at least one control valve; and  
           [0009]    an adjustment mechanism for controlling at least one limit of the control valve.  
           [0010]    A second general aspect of the invention provides a power impact tool comprising:  
           [0011]    a housing;  
           [0012]    an air motor contained within said housing; and  
           [0013]    a modular, releasably-attachable, user-adjustable control apparatus.  
           [0014]    A third general aspect of the invention provides a power impact tool comprising:  
           [0015]    a housing;  
           [0016]    an air motor contained within said housing, wherein said air motor provides a first torque output; and  
           [0017]    a modular, releasably-attachable, user-adjustable control apparatus;  
           [0018]    An fourth general aspect of the invention provides a power impact tool comprising:  
           [0019]    a housing;  
           [0020]    an air motor within said housing;  
           [0021]    a workpiece adapter operatively attached to said air motor; and  
           [0022]    a modular, releasably-attachable, user-adjustable control apparatus.  
           [0023]    The foregoing and other features of the invention will be apparent from the following ore particular description of various embodiments of the invention.  
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0024]    Some of the embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:  
         [0025]    [0025]FIG. 1A depicts a cross-sectional view of an alternative embodiment of a power impact tool adapted to receive a modular, releasably-attachable control apparatus, in accordance with an embodiment of the present invention;  
         [0026]    [0026]FIG. 1B depicts a cross-sectional view of an embodiment of a modular, releasably-attachable, user-adjustable, control apparatus, in accordance with an embodiment of the present invention;  
         [0027]    [0027]FIG. 2 depicts a diagrammatic view of an embodiment of a modular, releasably-attachable, user-adjustable control apparatus, in accordance with an embodiment of the present invention;  
         [0028]    FIGS.  3 A-C depict a cross-sectional view of an embodiment of a poppit valve of an embodiment of a modular, releasably-attachable control apparatus, the valve shown in three different operational positions in accordance with an embodiment of the present invention;  
         [0029]    [0029]FIG. 4A depicts a cross-sectional view of an embodiment of an adapter plate in accordance with an embodiment of the present invention; and  
         [0030]    [0030]FIG. 4B depicts a cross-sectional view of an alternative embodiment of an adapter plate in accordance with an embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]    Although certain embodiments of the present invention will be shown and described in detail, it should be understood that various changes and modifications may be made without departing from the scope of the appended claims. The scope of the present invention will in no way be limited to the number of constituting components, the materials thereof, the shapes thereof, the relative arrangement thereof, etc., and are disclosed simply as an example of an embodiment. Although the drawings are intended to illustrate the present invention, the drawings are not necessarily drawn to scale.  
         [0032]    The modular control apparatus is used with, or as part of, a power impact tool and allows for time-limiting the torque output. Power impact tools can include various power (e.g., pneumatic, hydraulic, electric, etc.) impact tools. This modular control apparatus, when used with a power impact tool, for example with a pneumatic impact tool, provides a fixed duration of torque from the air motor within the tool, to a workpiece, such as a nut or bolt. A motor, as defined and used herein, is any device for converting a first flow of energy into kinetic energy. For example, an air motor converts the energy of a flow of expanding compressed gas into the rotational motion of a mechanical drive shaft. For another example, an electric motor converts a flow of electricity into the rotational motion of a mechanical drive shaft. For yet another example, the drive piston and valves of a jack hammer form a motor to convert the energy of an expanding compressed fluid into linear motion of a mechanical drive shaft. For a final example, a hydraulic motor converts the kinetic energy of a flowing, slightly compressible fluid (hydraulic fluid) into the rotational motion of a mechanical drive shaft. The drive shaft, in each embodiment, is rotated by the motor, and tools, for operating on work pieces (workpiece adapters) are mechanically connected directly or indirectly between the drive shaft and the work piece.  
         [0033]    Referring now to FIG. 1A, an embodiment of a power impact tool  10  is shown in a vertical section through the centerline of the tool  10 . The tool  10  has a handle  12  containing a channel  50  for receiving a compressible fluid through a port  52  at the base of the handle  12 . A channel is a confined path for the flow of a compressible fluid. Channels may be pipes, hoses, bores formed in a block of material, or similar flow constraints.  
         [0034]    A compressible fluid, as defined and used herein, is a fluid with a bulk modulus that is less than the bulk modulus of water. Compressible fluids with low bulk moduli transfer energy by converting the potential energy of their compressed state into the kinetic energy of an expanding fluid and then into the kinetic energy of a motor rotor. Elemental gases, such as helium and nitrogen, and mixed gases such as air, are compressible fluids with low bulk moduli. Slightly compressible fluids have high bulk moduli and are used for force transmission. Hydraulic fluids, for example, typically have higher bulk moduli. Either type of compressible fluid can transfer energy into a motor.  
         [0035]    The port  52  is equipped with a fitting  54  for connecting to a supply of compressed fluid. A supply of compressible fluid may be, for example, a compressed air hose such as is used in an auto repair shop to power pneumatic tools. Within the channel  50  is a manually operated valve  62 , shown in FIG. 1 as a trigger valve  62 , which enables the tool-user to regulate the flow of compressible fluid through the channel  50 . By depressing the trigger  60 , the valve  62  is opened, thereby channeling the compressible fluid toward a motor  14  of the tool  10 . The channel  50  extends to a backplate  70  of the tool where the channel  50  terminates at a port  56  sized and shaped to receive (see FIG. 1B) a corresponding port  250  to a first channel  202  in a modular control apparatus  600 . Thus, the first channel  202  is the input channel.  
         [0036]    A modular control apparatus  600  is a first apparatus that controls at least one function of at least one second apparatus. Furthermore, a modular control apparatus  600  is modular in that it may be manipulated as a single physical unit (a module). The module comprises a generally solid block, or body, within which are formed the mechanisms which implement control functions. The body may be created from a single block or may be built up from a plurality of ub-blocks. The modular control apparatus  600  may be manipulated into a relationship with a second apparatus in which interaction between the modular control apparatus  600  and a second apparatus results in a change in the operation of the second apparatus. For some examples in the field of pneumatics, a modular control apparatus  600  may shut off air flow to a tool  10  (a second apparatus) after a user-selected time, may oscillate the direction of air flow, as in a jack hammer, or may change the pressure of the air entering the second apparatus.  
         [0037]    The modular control apparatus  600  is configured to be releasably attachable to the tool  10 . The apparatus is releasably attachable when the connections between the modular control apparatus  600  and the tool  10  can be opened and closed by the tool user. The connectors may be bolts, clamps, latches, or similar devices known in the art. In an embodiment, the connections can all be opened or all be closed by a single motion of the user&#39;s hand.  
         [0038]    Also located on the backplate  70  is a port  58  sized and shaped to receive the compressed fluid which is discharged from (see FIG. 1B) an output port  252  of a second channel  212  of the modular control apparatus  600 . The second channel is the output channel. The backplate  70  may be, for example, the backplate  70  of a Model 749 pneumatic torque wrench made by Chicago Pneumatic Tool. In an embodiment, the backplate  70  has a cylindrical protrusion  74 , perhaps accommodating a motor bearing within, which is used an alignment mechanism for aligning the modular control apparatus  600  to the tool  10 .  
         [0039]    Referring to FIGS. 1A and 1B, in an embodiment, the modular control apparatus  600  has a structure  80  containing a cavity  78  sized and shaped to slidingly receive the cylindrical protrusion  74  of the backplate  70 . The purpose In an embodiment, the backplate may further comprise an alignment dowel  72  which is sized and shaped to be slidingly received into a cavity  76  in the modular control apparatus  600 . In an alternate embodiment, the cavities  76  and  78  may be in the backplate  70  and the cylindrical protrusion  74  and alignment dowel  72  may be part of the modular control apparatus  600 . In another alternate embodiment, the backplate  70  has at least one alignment mechanism and at least one cavity, with at least one corresponding cavity and at least one corresponding alignment mechanism integrated into the modular control apparatus  600 .  
         [0040]    In alternative embodiments, the backplate  70  may be an adapter  900  which provides an interface between a tool  10  and the modular control apparatus  600 . In such retrofit cases, an adapter  900  may be designed for each uniquely designed tool. On the modular control apparatus-receiving side of the adapter  900 , at least a portion of the adapter may be configured like the backplate  70  of a tool  10  for which the modular control apparatus  600  was originally designed. Remaining portions of the adapter  900  provide two channels for compressible fluids: a first adapter channel  910  between the compressible fluid supply and the input port  250  of the modular control apparatus  600  and a second adapter channel  920  between the discharge port  252  of the modular control apparatus  600  and the tool  10  motor  14 . The adapter  900  also provides sufficient structure  70  and attachment mechanisms  80  for securing the adapter  900  to the tool  10  and to the modular control apparatus  600 .  
         [0041]    [0041]FIG. 2 shows an embodiment of a modular control apparatus  600  in a semi-diagrammatic view. An embodiment of the modular control apparatus  600  contains an  15  automatic shutoff valve  100  that shuts off the flow  214  of compressible fluid to the motor at a user-adjustable time after the beginning of flow of compressible fluid through the modular control apparatus  600 . In the embodiment of FIG. 2, compressible fluid flows through an input port  250  into a first channel  202 , through the biased-open valve  100 , into and through a second channel  212 , and is discharged from port  252  into the inlet  58  (FIG. 1A) of the motor of the tool.  
         [0042]    The valve  100  comprises a valve chamber  120 , a valve body  114 , a biasing mechanism  116 , and seals  110  and  118 . The valve chamber  120  has ports  150 - 158  to a plurality of channels  202 ,  204 ,  208 ,  210 , and  212 . The valve body  114  fits slidingly within the valve chamber  120 . In the embodiment shown in FIG. 2, the valve body  114  has one degree of freedom of translational motion. In this embodiment, the valve body  114  may also have one degree of freedom of rotational motion because the valve body  114  has rotational symmetry about its long axis. The rotational symmetry of the valve body  114  obviates the need for the valve body  114  to maintain a specific rotational orientation within the valve chamber  120  during operation. The degree of freedom of motion which opens and closes the valve  100  is the operational degree of freedom. In alternate embodiments, the valve body  114  and valve chamber  120  may not be rotationally symmetric. In other alternate embodiments, a valve  100  operates by sliding rotationally instead of translationally. Those having skill in the art will realize the advantages of minimizing the mass of the valve body  114  within the other design constraints.  
         [0043]    The biasing mechanism  116  is any mechanism or combination of mechanisms that exerts force on the valve body  114  in one direction aligned to the operational degree of freedom of motion of the valve body  114  and over at least a portion of the range of valve body  114  motion. The biasing mechanism  116  is typically a spring, but may be a compressible fluid or other elastic members.  
         [0044]    In the embodiment of FIG. 2, a first end of the valve body  114  has a poppit portion  108 . The poppit portion  108  is a rotationally symmetric extension of the valve body  114  with a uniform and smaller diameter than the maximum diameter of the valve body  114 . The poppit portion  108  has a predetermined length  112 . When the valve body  114  is in its biased position, the poppit portion  108  is received slidingly into a correspondingly narrowed portion  102  of the valve chamber  120 . The narrowed portion  102  of the valve chamber  120  may made longer than the poppit portion  108  of the valve body  114 , in order to form a chamber  104  for receiving compressible fluid from the reservoir  400 . The reservoir  400  is a cavity for accumulating compressible fluid. The receiving chamber (or actuating chamber)  104  may be considered a further extension of the valve chamber  120 . In an alternate embodiment, the receiving chamber  104  may be wider than the diameter of the poppit portion  108  of the valve body  114 . In another embodiment, the receiving chamber  104  may be an extension of the fifth channel  208  which connects the reservoir  400  to the poppit end, or biased end, of the valve chamber  120 . In yet another embodiment, there is no discrete receiving chamber  104 , as the narrow poppit portion of the valve chamber  120  is a port directly into the reservoir  400 . The end surface  106  of the poppit portion  108  is exposed to the pressure of compressible fluid which may be received in the receiving chamber  104 . The pressure of the fluid in the reservoir  400  exerts a force on the end surface  106  of the poppit portion  108  of the valve body  114  and, thereby, on the valve body  114  itself. The receiving chamber  104  may be regarded as an expandable and contractible chamber having one moveable wall, the moveable wall being the end surface  106  of the poppit portion  108  of the valve body  114 . In an embodiment wherein the valve operates by rotation, the actuating chamber  104  may be completely separate from the main valve chamber.  
         [0045]    The pressure of the compressible fluid at a given time in the reservoir  400  depends, in the first instance, on the rate of flow into the reservoir  400 . The rate of flow is controlled by the setting of a needle valve  300 . The needle valve  300  comprises a needle valve seat  304  within a third channel  206 , a needle valve body  302 , and a user-accessible extension of the needle valve  306 . The needle valve seat  304  comprises a channel portion tapered concentric to the needle valve body  302 , a shaft bearing to hold the shaft of the needle valve body  302 , and a seal to prevent leakage through the shaft bearing. The third channel is the reservoir input channel. In an embodiment, the threaded extension  306  is screwed into a threaded portion  308  of the third channel  206 . In an alternate embodiment, the extension  306  is provided with a locking mechanism, for example: a set screw, to prevent vibrations caused by operating the tool to change the setting. The user selects the amount of time between the introduction of compressible fluid into port  250  (as by squeezing the trigger  60  (FIG. 1A)), and the closing of the poppit valve  100  by adjusting the needle valve  300 . The higher the rate of flow, the faster the reservoir  400  reaches a pressure sufficient to close the valve  100 .  
         [0046]    Referring now to FIGS.  3 A-C, at a point in the operating cycle where the pressure of the compressible fluid in the receiving chamber  104  exerts more force on the valve body  114  than the biasing mechanism  116 , the valve body  114  begins to move against the bias (FIG. 3A). At or near the boundary between the poppit-receiving portion  102  of the valve chamber  120  and the remaining valve chamber  120 , the valve chamber has a seal  110 . The seal  110  prevents pressure leakage from the receiving chamber  104  into the remaining valve chamber  120  while the valve body  114  moves against the bias for the predetermined length  112  of the poppit portion  108 . The valve body  114  moves against the bias by the force exerted on the end surface  106  of the poppit portion  108  by the compressible fluid from the reservoir  400  as it reaches the receiving chamber  104 . AS shown in FIG. 3B, when the valve body  114  moves against the bias more than the predetermined length  112  of the poppit portion  108 , the seal  110  is avoided, exposing the entire area determined by the cross-section of the valve body  114  to the pressure from the reservoir  400  through receiving chamber  104 . The equal pressure on the increased area creates a steep increase in the anti-bias force, thereby slamming the valve body  114  into the anti-biased (closed) position (FIG. 3C). The valve body has a channel through which the compressible fluid flows  214  from the first channel  202  to the second channel  212  when the valve  100  is open (FIG. 3A). This channel is made wider than the valve chamber ports  150  and  158  (FIG. 2) for the first channel  202  and second channel  212  so that flow  214  through the valve  100  is unaffected by the initial anti-bias motion for the predetermined length  112  of the poppit portion  108  (FIGS.  3 A-B). Thus, from the perspective of the fluid flow  214  through the valve  100 , nothing happens until the valve body  114  slams shut (closes) (FIG. 3C).  
         [0047]    When the valve  100  closes (FIG. 3C), two ports  152  and  156  (FIG. 2) are exposed (opened) in the portion of the valve chamber  120  at the biased end of the valve chamber  120 . The biased end of the valve chamber  120  is the end of the valve chamber  120  where the valve body  114  rests when the force exerted by the biasing mechanism  116  predominates, as shown in FIG. 3A. When the valve body  114  was in the biased position, or within a predetermined poppit portion  108  length  112  of the biased position, two ports  152  and  156  (FIG. 2) where closed by surfaces of the valve body  114 . When the valve body  114  moves to the anti-biased position, as shown in FIG. 3C, the two ports  152  and  156  open. One of these ports  152  receives compressible fluid from a fourth channel  204 . The fourth channel  204  connects the first channel  202  (the fluid input channel, FIG. 2) to the valve chamber  120  when the valve body  114  is in the anti-biased position (FIG. 3C). The compressible fluid from the fourth channel  204  provides sufficient pressure to latch the valve  100  in the anti-biased position. The other port  156  in the valve chamber  120  which is opened by the valve body  114  moving to the anti-biased position is a vent port  156 . The vent port  156  discharges  222  and  224  compressed fluid into the sixth channel  210 . The sixth channel  210  leads to open air, in the case of a pneumatic device, or to a return line in the case of compressible fluids not normally released into the atmosphere, such as hydraulic fluid or dry nitrogen. In any embodiment, the sixth channel  210  drains compressible fluid  222  and  224  and its pressure from the valve chamber  120  and reservoir  400  (FIG. 2) through fifth channel  208  and receiving chamber  104 . The sixth channel  210  is sufficiently narrow, as compared with the fourth channel  204  (the latching channel), that the valve  100  will remain latched for as long as compressible fluid is available from the fourth channel  204  by way of the first channel  202 . However, when the supply of compressible fluid is shut off, as by releasing the trigger  60  (FIG. 1A) in the present embodiment, the vent  210  dissipates  222  and  224  the pressure from the valve chamber  120  and reservoir  400 , allowing the biasing force on the valve body  114  to once again predominate and move the valve body  114  back to its biased position (FIG. 3A).  
         [0048]    As shown in FIGS.  3 A-C, the biasing mechanism  116  may be a spring. At the anti-biased end of the valve chamber  120 , a ring seal  118  provides a bumper for the valve body  114  as it closes. In an embodiment, the ring seal  118  may also aid in sealing the junction between a part of the modular control apparatus  600  (FIG. 1B) containing most of the valve chamber  120 , and a second part forming the anti-biased end of the valve chamber  120 . In the embodiment of FIGS.  3 A-C, the anti-biased end of the valve body  114  has a recess for receiving one end of a coil spring  116 . The recess aids in maintaining the alignment of the spring  116  during operation.  
         [0049]    Referring back to FIG. 2, the first channel  202  also has a port  160  into a third channel  206  and another port  162  into a fourth channel  204 . The third channel  206  provides restricted flow of compressible fluid from the first channel  202  to the reservoir  400 . In the embodiment of FIG. 2, the flow restriction is a variable flow restriction wherein the amount of flow restriction is determined by the position of a user-adjustable needle valve  300 . Compressible fluid from the third channel  206  flows through the flow restriction into a reservoir  400 . The reservoir  400  accumulates compressible fluid, increasing the pressure within the reservoir  400 . The reservoir  400  has an outlet through a fifth channel  208  which leads to the receiving chamber  104  portion of the valve chamber  120 . The pressure in the receiving chamber  104  exerts a force on an end surface  106  of the poppit portion  108  of the valve body  114 . The pressure-derived force opposes the biasing force on the valve body  114 .  
         [0050]    The rate at which the reservoir fills with compressible fluid is determined by the flow restriction. The nearer the needle valve  300  is to being closed, the longer it takes for the reservoir  400  to accumulate enough fluid to create enough pressure to exert enough force to overcome the biasing force on the valve body  114 . Thus the needle valve  300  position  15  determines the amount of time between the beginning of fluid inflow (when the operator squeezes the trigger  60  (FIG. 1A) on a pneumatic torque wrench, for example) and the latching of the valve  100 , which shuts off the motor  14  of the tool  10 . In addition to minimizing wasted energy and avoiding over-torque conditions by time-limiting tool operation, the needle valve  300  adjustment can be used to compensate for the inevitable changes in the properties of the valve spring  116  over the life of the tool  10 . Likewise, the needle valve  300  can be adjusted to provide different times for different work situations. For example, tightening an eight-inch-long bolt would take more time than tightening a one-inch-long bolt.  
         [0051]    Referring again to FIGS. 1A and 1B, the valve  100 , needle valve  300 , and channels  203 ,  204 ,  206 ,  208 ,  210 , and  212  are contained within a modular structure  80  designed to be aligned with and releasably attached to a tool  10 . The alignment mechanisms  72 ,  74 ,  76 , and  78  comprise passive means to ensure that the input port  250  and discharge port  252  of the modular control apparatus  600  mate sealingly with the fluid supply port  56  and the motor inlet port  58  of the tool  10 , respectively. In an embodiment, the backplate  70  of-the tool  10  has a cylindrical extension  74  that fits into a corresponding recess  78  in the modular control apparatus  600 . The backplate  70  is further equipped with at least one asymmetrically arranged rod  72  corresponding to at least one hole  76  in the modular control apparatus  600 . The rods  72  are arranged asymmetrically so that there is only one orientation of the modular control apparatus  600  that will allow the apparatus  600  to be received onto the tool  10 . That orientation is the orientation at which the ports of the apparatus  250  and  252  and the tool will line up properly. The attachment mechanism may be as simple as a bolt through the modular control apparatus into a threaded hole in the tool. Those skilled in the art of tool manufacture will be aware of many different ways of making the attachment. The requirements for the attachment mechanism are that it create a seal against leakage of the compressible fluid and that it be reusable.  
         [0052]    In a particular embodiment, a modular control apparatus  600  is integrated with a handle  12  comprising a trigger valve  62  and  60  and associated channel  50 , port  52 , and fitting  54 . In this embodiment, the motor  14  and elements of a drive train from a drive shaft of the motor  14  to an output fitting are modular and releasably attach to the integrated handle  12  and modular control apparatus  600 . The advantage of this embodiment is that all of the elements controlling the flow of energy to the motor  14  are in one module.  
         [0053]    Referring to FIG. 1C, the body of the an embodiment of modular control apparatus  600  may be manufactured from two or more blocks (also called parts or sub-blocks)  82  and  84 . In an embodiment, the first block  84  is machined to contain the valve chamber  120  (FIG. 2), reservoir  400 , the alignment holes  76  and  78 , attachment mechanisms, the input and discharge ports  250  and  252 , and all channels except the third channel  206 ,. All of the features of the first block  84  can be formed by drilling and machining. The second block  82  contains the third channel  206  and the needle valve  300 . The third channel  206  may be formed by drilling and machining. In assembly, the spring  116  and bumper seal  118  are inserted before the valve body  114 , and an annular chamber end  180  with the poppit seal  110  after the valve body  114 . Annular chamber end  180  forms the receiving chamber  104  and the valve chamber extension  102 . Installation of the needle valve  300  requires at least one seal (not shown). Assembling the two blocks  82  and  84  together closes the valve chamber  120  and reservoir  400 . The blocks  82  and  84  may be bolted together or affixed by permanent means, such as welding. A releasable assembly (bolts) is generally preferred, as it enables maintenance and refurbishment of the valve  100 .  
         [0054]    While this invention has been described in conjunction with the specific embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the embodiments of the invention as set forth above are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.