Patent Publication Number: US-2016221171-A1

Title: Hydraulic hammer having dual valve acceleration control system

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to a hydraulic hammer, and more particularly, to a hydraulic hammer having a dual valve acceleration control system. 
     BACKGROUND 
     Hydraulic hammers for milling stone, concrete, and other materials may be mounted to various machines (e.g., excavators, backhoes, tool carriers, and other types of machines). For example, a hydraulic hammer may be mounted to a boom of a machine and connected to the machine&#39;s hydraulic system. High pressure fluid in the hydraulic system may be supplied to the hammer to drive a piston of the hammer in a reciprocating manner. The piston may, in turn, drive a work tool in a reciprocating manner, causing the work tool to mill material it contacts. 
     An exemplary hydraulic hammer is disclosed in U.S. Patent Application Publication No. 2009/0321100 by Anderson, published Dec. 31, 2009 (“the &#39;100 publication”). Specifically, the &#39;100 publication discloses a fluid operated percussive device having a piston that slides in a cylinder room. The percussive device also has a main valve and an auxiliary valve for controlling the movement of the piston. The main valve is adapted to transmit pressure fluid to a driving chamber for the percussive piston. The auxiliary valve is adapted to switch the main valve. 
     Although the percussive device of the &#39;100 publication may be suitable for some applications, it may be less than optimal for others. For example, for a large hydraulic hammer (e.g., one weighing more than 1000 kg), which has a correspondingly large piston, the main valve must be very large in size to allow sufficient fluid transfer to move the piston without increasing the fluid supply pressure. For a large hammer it becomes impractical to locate the main valve around the piston as is commonly done for smaller hammers because of the size and weight of the large main valve. Often a separate housing is utilized to house the large main valve, but this too is less than optimal because of the increased cost and complexity associated with the additional housing. The disclosed embodiments may help solve these and/or other problems known in the art. 
     SUMMARY OF THE INVENTION 
     One disclosed embodiment is related to a hydraulic hammer, which may include a housing and a piston configured to reciprocate within the housing. The hydraulic hammer may also include an acceleration channel formed within the housing. The acceleration channel may be configured to receive a pressurized fluid for accelerating the piston in a first direction. The hydraulic hammer may further include a first valve in communication with the acceleration channel. The first valve may be configured to selectively supply a first portion of the pressurized fluid to the acceleration channel. The hydraulic hammer may also include a second valve in communication with the acceleration channel. The second valve may be configured to selectively supply a second portion of the pressurized fluid to the acceleration channel. 
     Another disclosed embodiment is related to a valve control system for a piston associated with an acceleration channel. The valve system may include a first valve in communication with the acceleration channel. The first valve may be configured to selectively supply a first portion of a pressurized fluid to the acceleration channel. The valve system may also include a second valve in communication with the acceleration channel. The second valve may be configured to selectively supply a second portion of the pressurized fluid to the acceleration channel only after the first valve begins to supply the first portion of the pressurized fluid. 
     Yet another disclosed embodiment is related to a valve control system for a piston associated with an acceleration channel. The valve system may include a first valve in communication with the acceleration channel. The first valve may be configured to selectively supply a first portion of a pressurized fluid to the acceleration channel. The valve system may also include a second valve in communication with the acceleration channel. The second valve may be configured to selectively supply a second portion of the pressurized fluid to the acceleration channel. The first valve and the second valve may be configured to supply the first portion and the second portion of the pressurized fluid independently of each other and based on a position of the piston. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an exemplary disclosed machine; 
         FIG. 2  is a schematic view of a portion of an exemplary disclosed hydraulic hammer of the machine of  FIG. 1 ; 
         FIG. 3  is a top view of a portion of the exemplary disclosed hydraulic hammer of  FIG. 2 ; 
         FIG. 4  is a schematic illustration of a first embodiment of an exemplary disclosed dual valve acceleration control system of the hydraulic hammer of  FIG. 2 ; 
         FIG. 5  is a schematic illustration of a second embodiment of an exemplary disclosed dual valve acceleration control system of the hydraulic hammer of  FIG. 2  in a first state of operation; 
         FIG. 6  is a schematic illustration of the dual valve acceleration control system of  FIG. 5  in a second state of operation; and 
         FIG. 7  is a schematic illustration of the dual valve acceleration control system of  FIG. 5  in a third state of operation. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an exemplary disclosed machine  10  having a hydraulic hammer  12 . Machine  10  may be configured to perform work associated with a particular industry such as, for example, mining or construction. Machine  10  may be a backhoe loader (shown in  FIG. 1 ), an excavator, tool carrier, a skid steer loader, or any other type of machine. Hammer  12  may be pivotally connected to machine  10  through a boom  14  and a stick  16 . Alternatively, hammer  12  may be connected to machine  10  in another way. 
     Machine  10  may include a hydraulic supply system (not shown in  FIG. 1 ) for moving and powering hammer  12 . For example, machine  10  may include a pump  66  (see  FIGS. 4-7 ) connected through one or more hydraulic supply lines (see  FIGS. 4-7 ) to hydraulic cylinders  18  associated with boom  14  and stick  16 , and to hammer  12 . The hydraulic supply system may supply pressurized fluid, for example oil, from the pump to the hydraulic cylinders  18  and hammer  12 . Hydraulic cylinders  18  may raise, lower, and/or swing boom  14  and stick  16  to correspondingly raise, lower, and/or swing hammer  12 . Operator controls for movement of hydraulic cylinders  18  and/or hammer  12  may be located within a cabin  20  of machine  10 . 
     As shown in  FIG. 1 , hammer  12  may include a housing  22 , which may be connected to stick  16 . A work tool  24  may be operatively connected to an end of housing  22  opposite stick  16 . It is contemplated that work tool  24  may include any tool capable of interacting with hammer  12 . For example, work tool  24  may include a chisel bit, moil point, percussion buster, blunt tool, ramming tool, tamping plate, cutter, or other bit. 
     As shown in  FIG. 2 , hammer  12  may have a piston  46  and a cylinder  26  within housing  22 . Piston  46  may be configured to move back and forth within cylinder  26  to impact work tool  24 . Hammer  12  may also include a dual valve acceleration control system  70  to control the movement of piston  46 . System  70  may do so by controlling the flow of pressurized fluid from pump  66  (see  FIGS. 4-7 ) of machine  10  to an acceleration channel  76 . As pressurized fluid flows to acceleration channel  76 , it imparts a force on piston  46  and may drive piston  46  toward work tool  24 . 
     Still referring to  FIG. 2 , housing  22  may include, among other things, a frame  40  and a head  42 . Frame  40  may be a generally hollow body having one or more flanges or steps along its axial length. Head  42  may cap off one end of frame  40 . Specifically, one or more flanges on head  42  may couple with one or more flanges on frame  40  to provide a sealing engagement. One or more fasteners (not shown) may rigidly attach head  42  to frame  40 . For example, the fasteners may include screws, nuts, bolts, tie rods, or any other fastener(s) capable of securing the two components. Additionally, cylinder  26  may include holes to receive the fasteners (e.g., holes  44 , shown in  FIG. 3 ) which may correspond with holes in head  42 . 
     Hammer  12  may also include a back buffer  28 , a front buffer  30 , and isolation sliding plates  38 , all within housing  22 . As shown in  FIG. 2 , front buffer  30  may be positioned within frame  40  between cylinder  26  and frame  40 . Back buffer  28  may be positioned within frame  40  between head  42  and cylinder  26 . Isolation sliding plates  38  may be positioned between frame  40  and cylinder  26 , and may be configured to extend along an inner wall of frame  40  from front buffer  30  toward back buffer  28 . As shown in  FIG. 2 , isolation sliding plates  38  may extend up to and beyond cylinder  26 . Isolation sliding plates  38  may be configured to absorb noise and vibration and to work as sliding and wearing plates, which enable small axial movements of cylinder  26  when milling material. 
     As shown in  FIGS. 4-7 , piston  46  may comprise varying diameter sections along its length, for example one or more narrow diameter sections disposed between wider diameter sections. Piston  46  may include three narrow diameter sections  54 ,  56 ,  58 , separated by two wide diameter sections  60 ,  62 . Narrow diameter sections  54 ,  56 ,  58  may cooperate with the inner wall of cylinder  26  to selectively open and close fluid pathways (e.g., passages  101 ,  102 , and  103 ) of dual valve acceleration control system  70 . 
     As shown in  FIGS. 4-7 , dual valve acceleration control system  70  may include an annular lift channel  68 , an annular switch channel  72 , an annular tank channel  74 , an acceleration channel  76 , a first valve  82 , a second valve  84 , and numerous fluid passages (e.g., passages  101 - 109 ) interconnecting the components.  FIG. 4  shows a first embodiment of dual valve acceleration control system  70  and  FIG. 5  shows a second embodiment of dual valve acceleration control system. The difference between the first embodiment shown in  FIG. 4  and the second embodiment shown in  FIGS. 5  is the addition of a check valve  86 , an orifice  88 , and a passage  110  to the second embodiment. These three elements of the second embodiment are associated with second valve  84  and affect how movement of second valve  84  is triggered. All other elements of dual valve acceleration control system  70  may be the same for both embodiments. Accordingly,  FIGS. 5, 6, and 7 , which show different states of operation for the second embodiment, are equally applicable to the first embodiment of  FIG. 4  for all of the same components. In both the first embodiment and the second embodiment, dual valve acceleration control system  70  may be fluidly connected to pump  66 , an operator valve  78 , and a tank  80 , which may be housed in machine  10 . 
     As shown in  FIGS. 4 and 5 , pump  66  may be configured to draw fluid from tank  80  and discharge a pressurized fluid. The pressurized fluid from pump  66  may be selectively directed through operator valve  78  to lift channel  68  via passage  104 , first valve  82  via passage  107 , and second valve  84  via passage  105 . Lift channel  68  may be configured to direct the pressurized fluid to contact a shoulder  61  at wide diameter section  60  in order to force piston  46  in an upward second direction  92 . Switch channel  72  may be configured to fluidly communicate via passage  102  with first valve  82  to move the valve position of first valve  82 . As shown in  FIGS. 4 and 5 , tank channel  74  via passage  103  may be configured to drain pressurized fluid to tank  80 . Pressurized fluid may also drain to tank  80  from acceleration channel  76  through first valve  82  via passages  108  and  109 . As shown in  FIGS. 4 and 5 , only first valve  82  is configured to selectively drain the pressurized fluid from acceleration channel  76  to tank  80 . Lift channel  68 , switch channel  72 , tank channel  74 , and acceleration channel  76  may all protrude from cylinder  26  defining passages surrounding piston  46 . Movement of piston  46  (i.e., of narrow diameter sections  54 ,  56 ,  58  and wide diameter sections  60 ,  62 ) caused by the pressurized fluid may selectively open or close the channels along cylinder  26 . 
     For the first and second embodiments, as shown in  FIGS. 4-7 , first valve  82  may be disposed between pump  66  and tank  80 , and may be configured to control movements (e.g., acceleration) of piston  46 . In particular, first valve  82  may control when piston  46  transitions between upward and downward movements. First valve  82  may include a valve element movable between at least two distinct positions, and may be configured to selectively supply a first portion of pressurized fluid to acceleration channel  76 . As shown in  FIGS. 4-7 , first valve may include three distinct positions; thus, first valve  82  may be characterized as a three position, three port valve. When the valve element of first valve  82  is in the first position (upper-most position) as shown in  FIGS. 4 and 5 , acceleration channel  76  may be fluidly connected to tank  80 . When the valve element of first valve  82  is in the second position (middle position), acceleration channel  76  may be fluidly disconnected from both pump  66  and tank  80 . When the valve element of first valve  82  is in the third position (lower-most position) as shown in  FIGS. 6 and 7 , acceleration channel  76  may be fluidly connected to pump  66  via passages  107  and  109  and oriented to supply the first portion of pressurized fluid to acceleration channel  76 . The valve element may move between the first, second, and third positions depending on a pressure level at switch channel  72 . Specifically, when the pressure level at switch channel  72  is below a threshold value, the valve element of first valve  82  may be forced to the first position. Alternatively, when the pressure level within the switch channel  72  is greater than the threshold value, the valve element of first valve  82  may be forced to the third position. When first valve  82  transitions from the first position to the third position or the third position to the first position, it will transition by way of the second position. The second position may momentarily block all flow through first valve  82 , which may reduce the amount of internal leakage when transitioning between positions. 
     In another embodiment (not shown), first valve  82  may be a two position, three port valve, which comprises just the first position and the third position as described above, thereby eliminating the second position in which all flow through first valve  82  is blocked. It is also contemplated that additional embodiments for first valve  82  may be utilized having greater or lesser numbers of positions and ports. 
     For the first and second embodiments, as shown in  FIGS. 4-7 , second valve  84  may be configured to selectively supply a second portion of pressurized fluid to acceleration channel  76 . Second valve  84  may be disposed between passages  105  and  106 , fluidly connecting acceleration channel  76  and lift channel  68 . Second valve  84  may include a valve element movable between two distinct positions; thus, second valve  84  may be characterized as a two position, two port valve. When the valve element is in the first position (upper-most position) as shown in  FIGS. 4 and 5 , a check valve  85  may prevent flow of pressurized fluid from lift channel  68  via passage  105 , through second valve  84 , into acceleration channel  76 . However, check valve  85  may allow flow of pressurized fluid from acceleration channel  76  back through second valve  84  to lift channel  68  if the pressure differential is such that flow in that direction through check valve  85  may occur. When the valve element of second valve  84  is in the second position (lower-most position) as shown in  FIGS. 6 and 7 , acceleration channel  76  may be fluidly connected with lift channel  68  via passages  105  and  106 , thereby supplying the second portion of pressurized fluid to acceleration channel  76 . 
     It is contemplated that other configurations for second valve  84  may be utilized. For example, second valve may be a pilot operated check valve, which can be opened by an external pilot pressure at the pilot channel. The pilot channel of the pilot check valve may be configured to connect to passages  101  or  110 . 
     First valve  82  and second valve  84  may be positioned on opposite sides of piston  46  within cylinder  26 , as shown in  FIG. 3 . Positioning first valve  82  and second valve  84  in this way may be advantageous for several reasons. First, the pressurized fluid flow to acceleration channel  76  may be more balanced, thereby reducing the side loading on piston  46 . Second, a separate valve housing or enlarged cylinder  26  may not be required. As a result, design and construction of housing  22  may be simplified, and isolation sliding plates  38  may extend further along housing  22 , thereby covering a bigger portion of cylinder  26 . And third, cylinder  26  may be slimmer and lighter than it would be if only a single larger valve was utilized. Cylinder  26  being slimmer and light may also increase the overall power of hammer  12  when compared to traditional hydraulic hammers of equivalent weight. 
     Movement of second valve  84  from the first position to the second position may be triggered in a variety of ways. The first embodiment, as shown in  FIG. 4 , provides a first example of how movement of second valve  84  may be triggered. According to the first embodiment, second valve  84  may be in fluid communication with switch channel  72  via passage  101 . The valve element of second valve  84  may move between the first and second positions depending on a pressure level within switch channel  72 . Specifically, when the pressure level within switch channel  72  is below a threshold value, the valve element may be forced to move to the first position (upper-most position). Alternatively, when the pressure level within the switch channel  72  is greater than the threshold value, the valve element may be forced to move to the second position (lower-most position). Because both first valve  82  and second valve  84  are in fluid communication with switch channel  72 , first valve  82  and second valve  84  may be configured to move positions at about the same time if the threshold pressure values for moving first valve  82  and second valve  84  are the same. Alternatively, if the threshold pressure values are different, then first valve  82  and second valve  84  may be configured to move positions independently at different times. For example, first valve  82  may be configured to move position at a lower threshold pressure value, while second valve  84  may be configured to move position at a higher threshold pressure value. 
     The second embodiment, as shown in  FIGS. 5-7 , provides a second example of how movement of second valve  84  may be triggered. According to the second embodiment, check valve  86  may be disposed in passage  101  fluidly disconnecting second valve  84  with switch channel  72 , thereby preventing the fluid pressure of the switch channel  72  from triggering the movement of second valve  84 . Instead, second valve  84  may be in fluid communication with acceleration channel  76  via passage  106  and  110 . Therefore, according to the second embodiment, second valve  84  may be configured to move positions based on the pressure level in acceleration channel  76  rather than the pressure level in switch channel  72  as is the case for the first embodiment. As shown in  FIGS. 5-7 , according to the second embodiment, orifice  88  may be disposed in passage  110  between second valve  84  and acceleration channel  76  to limit the flow rate of pressurized fluid to second valve  84 . 
     It is contemplated that additional methods for triggering the movement of second valve  84  between the first position and the second position may also be utilized. For example, passage  110  may be directly connected to first valve  82  in addition to acceleration channel  76 . Therefore, second valve  84  movement may be dependent not only on the pressure in acceleration channel  76 , but also directly dependent on the position of first valve  82 . As a result, first valve  82  may open and close this connection. By first valve  82  opening and closing this connection, check valve  86  and orifice  88  may be eliminated. 
     It is also contemplated that hammer  12  may include other orifices, valves, channels, and/or other components in addition to those included in dual valve acceleration control system  70  as described in reference to the first embodiment ( FIG. 4 ) and second embodiment ( FIGS. 5-7 ). For example, according to other embodiments, dual valve acceleration control system  70  may include additional valves besides first valve  82  and second valve  84 . One or more additional valves may be used to supplement operation of first valve  82  and/or second valve  84 . For example, one or more additional valves (e.g., 1, 2, 3, 4, 5, or more) may be used in conjunction with second valve  84 . The one or more additional valves may be connected in parallel with second valve  84  and thus the operation may be the same as second valve  84 . In yet another example, one or more additional valves may be used in conjunction with first valve  82 . The one or more additional valves may be connected in parallel with first valve  82  and thus the operation may be the same as first valve  82 . Utilizing additional valves may enable the size of the hammer and piston to get larger or valve sizes to be reduced further. When utilizing additional valves, first valve  82 , second valve  84 , and the one or more additional valves may be spaced evenly around piston  46 . 
     INDUSTRIAL APPLICABILITY 
     The disclosed dual valve acceleration control system may be used in any hydraulic hammer, including large hydraulic hammers (e.g., those weighing more than 1000 kg), which traditionally require large control valves to allow sufficient fluid transfer to move their large pistons without increasing fluid pressure. By using a first valve and a second valve, fluid transfer can be divided (e.g., evenly or non-evenly) between the two valves, thereby allowing each valve to be of smaller size than when a single larger control valve is utilized for an equivalent size hydraulic hammer. The reduced size of the first and second valves can enable the valves to be positioned within the piston housing and thereby eliminate the need for a separate valve housing as is often used for larger hydraulic hammers. Utilizing first and second valves as described herein may allow the first valve to be about half the size than the larger single valve for an equivalent size hammer. Operation of hammer  12  will now be described primarily with reference to  FIGS. 5, 6, and 7  (i.e., the second embodiment); however, the operation description is equally applicable to the first embodiment of  FIG. 4 .  FIG. 4  will be referenced when explaining the difference in operation of the first and second embodiments. 
     Referring to  FIG. 5 , an operator request may be made to begin operation of hammer  12  via, for example, an operator valve  78 . After the request is made, pump  66  may direct pressurized fluid, for example oil, into lift channel  68  via passage  104 . Pressurized fluid supplied to lift channel  68  may apply a pressure on piston  46 . Specifically, the pressurized fluid within lift channel  68  may apply a pressure to shoulder  61  of wide diameter section  60  and bias piston  46  upward in second direction  92 . During this operation, the valve element of first valve  82  may be in the first position such that acceleration channel  76  is in fluid communication with tank  80 . Therefore, as piston  46  slides upward in second direction  92  as a result of the pressure in lift channel  68 , fluid within acceleration channel  76  can drain to tank  80  as the volume of acceleration channel  76  decreases as a result of the approaching wide diameter section  62 . Also during this operation, the valve element of second valve  84  may be in the first position, thereby check valve  85  may prevent flow of pressurized fluid from lift channel  68  into acceleration channel  76 . 
     As shown in  FIG. 6 , movement of piston  46  in second direction  92  may open switch channel  72 . Specifically, movement of piston  46  upward in second direction  92  may correspondingly move narrow diameter section  54  to a location adjacent to switch channel  72 . While switch channel  72  is uncovered, pressurized fluid may flow from lift channel  68  along narrow diameter section  54  into switch channel  72 , thereby increasing the pressure level at switch channel  72  and causing first valve  82  to be moved from the first position (upper-most position) to the third position (lower-most position). As shown in  FIG. 6 , for the second embodiment, check valve  86  will prevent the pressure at switch channel  72  from reaching and thereby moving second valve  84 . Instead, movement of second valve  84  from the first position to the second position may be driven by (e.g., dependent on) first valve  82  first supplying a first portion of pressurized fluid to acceleration channel  76 . Acceleration channel  76  may be in fluid communication with the second valve  84  via passages  106  and  110 . As a result, the first portion of pressurized fluid may supply pressure fluid to second valve  84 , thereby causing second valve  84  to move from first position (upper-most position) to the second position (lower-most position). In other words, second valve  84  may be configured to supply the second portion of the pressurized fluid only after first valve  82  begins to supply the first portion of the pressurized fluid. 
     For the first embodiment shown in  FIG. 4 , when the pressure level at switch channel  72  is increased as a result of pressurized fluid flowing up from lift channel  68 , second valve  84  may move from the first position to the second position because of the direct supply of pressurized fluid to second valve  84  via passage  101 . For this embodiment, although first valve  82  and second valve  84  both move positions based on pressure at switch channel  72 , their movement may be independent of one another. For example, as described above, the pressure threshold value at which each valve moves may be different. 
     When both first valve  82  and second valve  84  have moved their valve element positions, as shown in  FIG. 6 , the first portion of pressurized fluid from pump  66  may flow through first valve  82  into acceleration channel  76 , and the second portion of pressurized fluid from lift channel  68  may flow through second valve  84  into acceleration channel  76 . The first portion of pressurized fluid may have a volume less than, equal to, or greater than the second portion of pressurized fluid. According to one embodiment, when first valve  82  is larger (i.e., has a greater flow capacity) than second valve  84 , the first portion of pressurized fluid supplied to acceleration channel  76  may have a greater volume than the second portion of pressurized fluid. In another embodiment, when first valve  82  and second valve  84  are the same size (i.e., have the same flow capacity), the first portion of pressurized fluid supplied to acceleration channel  76  may have a greater volume because first valve  82  may move position before second valve  84 . 
     As a result of pressurized fluid (e.g., first portion and second portion) flowing through first valve  82  and second valve  84  into acceleration channel  76 , piston  46  will switch the direction of movement from second direction  92  to first direction  90 , as shown in  FIG. 6 . Piston  46  may then be accelerated downward in first direction  90  to impact work tool  24  due to the flow of pressurized fluid (e.g., first portion and second portion) into acceleration channel  76 . It is also contemplated that dual valve acceleration control system  70  may be configured such that piston  46  may switch direction based on flow of just the first portion of pressurized fluid through first valve  82  and then the second portion of pressurized fluid through second valve  84  may be supplied to acceleration channel  76  to acceleration piston  46  in first direction  90 . 
     As shown in  FIG. 6 , the acceleration of piston  46  in first direction  90  will cause wide diameter section  60  to move toward lift channel  68 , thereby displacing the fluid within lift channel  68 . Displacing fluid from lift channel  68  may facilitate an additional flow of pressurized fluid to acceleration channel  76  via, for example, second valve  84 . Upon piston  46  reaching an impacting position (as shown in  FIG. 7 ), switch channel  72  may become fluidly connected with tank channel  74  by way of the annular space around narrow diameter section  56 . Fluidly connecting switch channel  72  and tank channel  74  may allow fluid within the channels to drain back to tank  80 , thereby lowering the pressure level at switch channel  72 . Lowering the pressure at switch channel  72  causes first valve  82  and second valve  84  to move back to their first positions as originally shown in  FIG. 5 . The impact of work tool  24  with the material (not shown) may cause piston  46  to recoil. Following impact and the switching of first valve  82  and second valve  84  back to their first position, the process may automatically restart so long as operator valve  78  remains open. 
     There may be pressure peaks within acceleration channel  76  when piston  46  shifts movement from second direction  92  to first direction  90  and vice versa. Pressure peaks can cause untimely direction switching of piston  46 , as well as untimely position switching of at least first valve  82 . To reduce the magnitude of pressure peaks in acceleration channel  76 , pressurized fluid may flow back to high pressure lines (e.g., lift channel  68 ) through second valve  84  when in either the first position or the second position. Reducing the magnitude of the pressure peaks can help maintain proper timing of first valve  82  with piston  46  movements, thereby enabling a more efficient operation. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed systems. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed systems. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.