Abstract:
A pump for use with a dispensing unit of a liquid hot melt adhesive system, dispensing units including the pump, and a method of operating a pump for pumping a liquid like liquid hot melt adhesive. The pump has a piston movable within a pumping chamber for transferring liquid from an inlet to an outlet. A valve body, which is resiliently biased relative to the piston, is moved out of contact with the inlet when the piston moves in a first direction and into contact with the inlet when the piston moves in a second direction. When the piston is moved in the first direction, the resilient biasing actively lifts the valve body out of contact with the inlet for overcoming any attractive adhesive force acting between the valve body and inlet.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application No. 60/562,145, filed Apr. 14, 2004, which is hereby incorporated by reference herein in its entirety. 

   FIELD OF THE INVENTION 
   The present invention pertains to dispensing systems for dispensing flowable materials, and more particularly to piston pumps for such dispensing systems. 
   BACKGROUND OF THE INVENTION 
   Hot melt adhesive dispensing systems generally include a dispenser coupled with one or more dispensing guns, heated hoses fluidly connected to the dispensing guns, and a dispensing unit for melting and supplying heated liquid adhesive to the guns through the heated hoses. The dispensing units of conventional hot melt adhesive systems feature a heated tank for melting and heating adhesive material received into the tank in solid or semi-solid form, a pump, a pump manifold for pumping the molten hot melt adhesive from the tank to outlet ports coupled with the heated hoses, and a controller. Among other system operations, the controller regulates the power supplied to the tank heater and heated hoses to maintain the liquid adhesive at an appropriate viscosity and temperature, depending on the application. 
   Traditional hot melt adhesives are thermoplastic adhesives that are widely used in industry for adhesively bonding many diverse types of products. Such traditional thermoplastic adhesives are solid at room temperature and must be heated to cause a phase transition to a liquid or semi-solid state for promoting flowability and dispensability. In contrast to traditional thermoplastic adhesives, liquid hot melt adhesives have been recently developed that exist in a flowable form at room or ambient temperature without heating to precipitate a phase transition. 
   Liquid hot melt adhesives are characterized by properties that differ significantly from the properties of traditional hot melt materials. Traditional hot melt materials are converted from a room temperature solid to a flowable form in a heated melter and subsequently pumped through a heated hose to a heated manifold and applicator or gun. In contrast, liquid hot melt adhesives are flowable and have a relatively low viscosity at ambient or room temperatures and pressures, form a highly viscous material with adhesive properties similar to traditional hot melt materials when activated by, for example, exposure to elevated temperatures and/or pressures, and solidify upon cooling after being applied to a substrate. The activated and solidified material behaves like a traditional thermoplastic hot melt adhesive and possesses similar bonding characteristics. An exemplary liquid hot melt adhesive, which is disclosed in U.S. Patent Application Publication No. 2004/0029980, consists of discrete particle components dispersed in a carrier fluid and is heat activated. 
   Liquid hot melt adhesives may be activated by, for example, heating shortly before being dispensed from the dispensing gun(s) onto a substrate. The activation may occur at or near the dispensing gun. Alternatively, the activation may occur at any location between the tank and dispensing gun sufficiently close to the dispensing gun so that the viscosity of the activated liquid hot melt adhesive remains low enough to permit flow from the activation site to the dispensing gun. Although liquid hot melt adhesive is not heated at the tank as are traditional thermoplastic adhesives, adhesive dispensing systems nonetheless require a pump, such as a piston pump, for pumping the liquid hot melt adhesive in a nonactivated state from the tank to the dispensing guns. 
   One difficulty observed when pumping liquid hot melt adhesives and, for that matter, when pumping other traditional thermoplastic adhesives, is that these materials tend to coagulate and form a solid tacky coating on moving components located in the liquid path inside the pump. The residual coating may adversely affect the operation of these moving components and, hence, pump operation. The balls of pump check valves are one type of moving component particularly affected by the formation of these coatings. A coated check valve ball may tend to adhere and stick to its seat, which makes pumping inefficient. Eventually, the presence of the coating may result in a total pump failure that may be remedied only by completely disassembling and cleaning the pump to remove the coating. 
   A need therefore exists for a dispensing unit of a hot melt adhesive dispensing system having a pump equipped with moving components resistant to the adverse effects of coating by coagulated liquid hot melt adhesive as described above. 
   SUMMARY OF THE INVENTION 
   The present invention provides a device for use in dispensing a liquid, such as a liquid hot melt adhesive. The device includes a pump housing having an inlet, an outlet, and a pumping chamber between the inlet and outlet. A piston is slidably disposed within the pump housing for movement in a first direction for admitting an amount of the liquid into the pumping chamber through the inlet. Moving the piston in a second direction pumps the amount of the adhesive from the pumping chamber through the outlet. A valve body is coupled with the piston for closing the inlet when the piston is moved in the second direction. The valve body is disengaged from the inlet to open the inlet for admitting the amount of liquid into the pumping chamber when the piston is moved in the first direction. The valve body is engaged with the inlet to close the inlet when the piston is moved in the second direction. 
   In another embodiment of the present invention, a device for use in dispensing a liquid, such as a liquid hot melt adhesive, includes a pump housing having first and second inlets, first and second outlets, a first pumping chamber between the first inlet and the first outlet, and a second pumping chamber between the second inlet and the second outlet. A piston is slidably disposed within the pump housing between the first and second pumping chambers. The piston is movable in a first direction for admitting a first amount of the liquid into the first pumping chamber through the first inlet and pumping a second amount of the liquid from the second pumping chamber from the second outlet. The piston is movable in a second direction for pumping the first amount of the liquid in the first pumping chamber from the first outlet and admitting the second amount of the liquid into the second pumping chamber. First and second valve bodies are coupled with the piston. The first valve body is disengaged from the first inlet to open the first inlet for admitting the amount of liquid into the first pumping chamber when the piston is moved in the first direction and being engaged with the first inlet to close the first inlet when the piston is moved in the second direction. The second valve body is disengaged from the second inlet to open the second inlet for admitting the amount of liquid into the second pumping chamber when the piston is moved in the second direction and is engaged with the second inlet to close the second inlet when the piston is moved in the first direction. 
   In another aspect, a method of operating a pump for dispensing a liquid includes moving a piston in a first direction to admit an amount of the liquid into a pumping chamber through an inlet to the pumping chamber. The method further includes resiliently biasing a valve body relative to the piston to disengage the valve body from the inlet as the piston moves in the first direction and thereby open the inlet for admission of the amount of the liquid. The method may further include moving the piston in a second direction to discharge the amount of the liquid from an outlet of the pumping chamber and applying a biasing force between the piston and a valve body to engage the valve body with the inlet as the piston moves in the second direction. 
   These and other features, advantages and objectives of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the details of the preferred embodiments. 
       FIG. 1  is a schematic drawing of an adhesive dispensing system, including a dispensing unit having a pump according to the present invention; 
       FIG. 2  is a diagrammatic sectional view of the pump manifold and pump of  FIG. 1 , partially fragmented and taken along line  2 - 2  of  FIG. 1 . to illustrate details of the pump during an upstroke portion of a dispensing cycle; and 
       FIG. 3  is a view similar to  FIG. 2  depicting the pump during a downstroke portion of the dispensing cycle. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , an adhesive dispensing system  10  includes a pair of guns  12 ,  14 , a dispensing unit  16  for supplying liquid hot melt adhesive  18  to the guns  12 ,  14 , and hoses  20  connecting the dispensing unit  16  to the guns  12 ,  14 . The dispensing unit  16  includes a reservoir, such as tank  22 , holding a volume of liquid hot melt adhesive  18 , a manifold  24  in fluid communication with the tank  22 , a pump  26  constructed according to the principles of the present invention and coupled to the manifold  24 , and a controller  28 . The tank  22  comprises side walls  30  joined by a base  32  that collectively define the reservoir holding the adhesive  18 . A tank outlet  36  proximate the base  32  is coupled to a passage  38  that connects to an inlet  40  of the manifold  24 . 
   The manifold  24  may optionally include a manifold heater  42  operationally controlled by controller  28  for heating the liquid hot melt adhesive  18  while resident inside manifold  24 . The tank  22  may optionally include a tank heater (not shown) controlled by controller  28  for raising the temperature of the liquid hot melt adhesive  18  while resident in the tank  22 . Optionally, hoses  20  may be configured to be heated and cord sets  21 , also operationally controlled by controller  28 , may be used for heating and controlling the temperature of hoses  20  in a known manner. 
   Pump  26 , which is coupled to the manifold  24 , pumps liquid hot melt adhesive  18  from the tank  22  into the manifold  24 . Manifold  24  divides the adhesive  18  into separate flows and directs the distinct flows to a plurality of outlet ports  48 . The outlet ports  48  are configured to be coupled to the hoses  20  whereby the liquid adhesive  18  is supplied through hoses  20  to the guns  12 ,  14 . The guns  12 ,  14 , which may be mounted to a frame  50 , include one or more modules  52  that apply the adhesive  18  to a desired product (not shown). Modules  52  may be coupled to their own individual manifolds  54  for supplying liquid hot melt adhesive  18 , actuating air, and process air thereto. Although system  10  illustrates two gun manifolds  54 , additional hoses (not shown) identical to hose  20  may transfer liquid hot melt adhesive  18  to additional gun manifolds (not shown) identical to manifold  54  that are located respectively behind manifolds  54 . Other systems  10  may have a single gun, or may have other guns, like guns  12 ,  14  and, furthermore, the guns  12 ,  14  may take on many different configurations, according to the particular adhesive dispensing requirements, without departing from the spirit and scope of the invention. The guns  12 ,  14  and/or the gun manifolds  54  may each incorporate heat exchanger/mixers and heaters (not shown) for blending and/or elevating the temperature of the liquid hot melt adhesive  18 . 
   With reference to  FIG. 2 , pump  26  includes a pump housing  56  enclosing a pumping chamber  58 , an inlet  60  coupling the tank  22  in fluid communication with the pumping chamber  58 , and outlet ports  48  each in fluid communication with a corresponding one of the guns  12 ,  14 . Pump  26  may include additional outlet ports  48  each coupled with gun  12 , gun  14 , or another gun (not shown). Generally, pump  26  moves liquid hot melt adhesive  18  from the inlet  60  to the outlet ports  48 . An upper section  64  of housing  56  houses the pneumatic components of the pump  26  and a lower section  66  of housing  56  houses the hydraulic components of the pump  26 . 
   The upper section  64  of the housing  56  includes an air cylinder  68 , an air piston  70  disposed inside the air cylinder  68 , and a pump shaft  72  extending from the air piston  70  to connect with a piston or plunger  76  positioned inside the pumping chamber  58 . An air logic valve  74  regulates the air pressure supplied to the air cylinder  68  by alternatively filling and emptying air chambers  68   a,b  defined inside the air cylinder  68  on opposite sides of the air piston  70  for reciprocating the air piston  70  relative to the air cylinder  68 . Air chamber  68   a  communicates with an air port  78  and, in a like manner, air chamber  68   b  communicates with an air port  80 . Suitable fittings are used to connect ports  78 ,  80  with the air logic valve  74  having appropriate internal valving for supplying pressurized air to air chambers  68   a,b  to move air piston  70  and pump shaft  72 . 
   Engaged with a blind threaded hole  75  defined in the plunger  76  is a threaded tip  73  of pump shaft  72 . The threaded hole  75  is offset laterally from the center of plunger  76 , although the present invention is not so limited. The present invention contemplates that the pump shaft  72  and plunger  76  may be coupled together in alternative fashions known to persons of ordinary skill in the art and is not limited to the illustrated threaded engagement. 
   Piston pump  26  pumps liquid hot melt adhesive  18  to the guns  12 ,  14  on both the upstroke and the downstroke. Reciprocation of the air piston  70  by cyclically filling and draining air chambers  68   a,b  moves the plunger  76  inside pumping chamber  58  for pumping successive volumes of the liquid hot melt adhesive  18  from the inlet  60  to the outlet ports  48 , as detailed below. To that end, the periphery of plunger  76  has a close fit and tight clearance with an interior wall  77  of pumping chamber  58 . Although the piston pump  26  is illustrated in  FIG. 2  as bi-directional, the invention is not so limited. In particular, the piston pump  26  may be uni-directional and incorporate a return spring for shifting the air piston  70  on the downstroke. Other suitable actuation methods apparent to persons of ordinary skill in the art are contemplated by the invention. 
   Pump shaft  72  is positioned in a bore  83  with a clearance sufficient to permit reciprocating movement thereof. A seal  82  prevents pressurized air from leaking downwardly out of air cylinder  68  into the bore  83 . Another seal  84 , which is mounted within lower housing section  66 , prevents pressurized liquid from escaping from the pumping chamber  58  of housing section  66  into bore  83 . In effect, the seals  82 ,  84  isolate the pneumatic and hydraulic portions of the pump  26 . 
   Movement of the air piston  70  and pump shaft  72  causes the plunger  76  to cyclically vary the volume of an upper section  58   a  and a lower section  58   b  of pumping chamber  58 . Plunger  76  defines a barrier that segregates amounts of liquid hot melt adhesive  18  in the two sections  58   a ,  58   b . Coupling the outlet ports  48  with upper and lower outlet passageways  88 ,  90  defined in the lower section  66  of housing  56  is an intermediate passageway  86  defined partially in lower housing  66  and partially in manifold  24 . The outlet passageways  88 ,  90  converge at the intermediate passageway  86 . 
   Positioned in outlet passageway  88  is a check valve  92  and, similarly, a check valve  94  is located in outlet passageway  90 . Check valve  94  prevents back flow from outlet passageway  90  into the lower section  58   b  of pumping chamber  58  during the upward stroke or upstroke of plunger  76 , as shown in  FIG. 2 . Similarly, check valve  92  prevents back flow from outlet passageway  88  into the pumping chamber  58  during the downward stroke or downstroke of plunger  76 , as shown in  FIG. 3 . 
   Check valves  92 ,  94  may be any suitable check valve that closes by fluid pressure to prevent return flow and that opens at a characteristic cracking pressure to permit forward flow in a desired direction. In the illustrated embodiment, each of the check valves  92 ,  94  is characterized by a valve seat and a compression spring that biases a valve body or ball against the valve seat. The pressure inside the upper and lower sections  58   a ,  58   b  of the pumping chamber  58  varies as the plunger  76  is reciprocated therein, which regulates the opening and closing of check valves  92 ,  94 . Exemplary check valves  92 ,  94  suitable for use in the invention are available commercially from The Lee Company (Westbrook, Conn.). As an alternative to the check valve configuration detailed herein, other varieties of check valves may be utilized in the outlet passageways  88 ,  90  without affecting the operation principles of the piston pump  26 . 
   Extending from the inlet  60  of pump housing  56  through the lower section  66  to the upper section  58   a  of the pumping chamber  58  is an inlet passageway  96 . Branching from the inlet passageway  96  is another inlet passageway  98  that communicates with the lower section  58   b  of the pumping chamber  58 . Successive volumes of liquid hot melt adhesive  18  are supplied from tank  22  through the inlet passageways  96 ,  98  to the pumping chamber  58  as the pump  26  operates. 
   The plunger  76  includes a throughbore  100  and a shaft  102  slidingly received in the throughbore  100  with a clearance sufficient to permit free vertical movement of shaft  102  within throughbore  100 . The throughbore  100  is offset from the threaded opening  75  in plunger  76  by a distance sufficient to accommodate coupling pump shaft  72  with plunger  76  while simultaneously allowing unhindered vertical movement of shaft  102 . 
   Affixed to, or otherwise associated for movement with, one free end of the shaft  102  is a ball or valve body  104 . The alignment of shaft  102  for axial movement along its length within throughbore  100  and the positioning of valve body  104  on shaft  102  cooperate for engaging valve body  104  with a valve seat  106 , which is defined at the intersection of inlet passageway  96  with the pumping chamber  58 . The valve seat  106  coincides with the outlet from the inlet passageway  96 . 
   Affixed to, or otherwise associated for movement with, the opposite free end of the shaft  102  is another ball or valve body  108  which is positioned on shaft  102  for engaging a valve seat  110 . The valve seat  110  is defined at the intersection of the inlet passageway  98  with the pumping chamber  58  and coincides with the outlet from the inlet passageway  98 . The valve seats  106 ,  110  may be located at other positions within the corresponding inlet passageways  96 ,  98 , such as recessed within the passageways  96 ,  98  at the intersection with pumping chamber  58 . 
   Compressed between the valve body  104  and an upper surface  76   a  of the plunger  76  is a biasing element, in the form of compression spring  112  having coils helical wrapped about a length of the shaft  102 , that applies an upward resilient bias force to the shaft  102  and valve body  104  at least during a portion of the upstroke when valve body  104  is in contact with valve seat  106 . Similarly, another biasing element, in the form of compression spring  114  having coils helical wrapped about another length of the shaft  102 , compressed between the valve body  108  and a lower surface  76   b  of the plunger  76  applies a downward resilient bias force to the shaft  102  and valve body  108  at least during a portion of the downstroke when valve body  108  is in contact with valve seat  110 . 
   Valve body  104  and spring  112  are positioned inside the upper section  58   a  of the pumping chamber  58 . Valve body  108  and spring  114  are positioned inside the lower section  58   b  of the pumping chamber  58  and on an opposite side of plunger  76  from valve body  104  and spring  112 . The shaft  102  extends through the space circumscribed by inside the helically-wound coils of the springs  112 ,  114 , which prevents buckling or lateral deflection of the springs  112 ,  114  when compressed. The shaft  102 , valve bodies  104 ,  108 , valve seats  106 ,  110 , and springs  112 ,  114  effectively replace conventional check valves found in the inlet passageways  96 ,  98  of conventional pumps used for pumping traditional hot melt adhesives. 
   The length of the shaft  102 , the characteristics (e.g., length and spring constant) of springs  112 ,  114 , and the range of motion of the plunger  76  are collectively chosen such that the valve body  104  has adequate clearance relative to valve seat  106  for entry of liquid hot melt adhesive  18  through inlet passageway  96  during the downward stroke of plunger  76  and valve body  108  has adequate clearance relative to valve seat  110  for entry of liquid hot melt adhesive  18  through inlet passageway  98  during the upward stroke of plunger  76 . The length of shaft  102 , the characteristics of springs  112 ,  114 , and the range of motion of plunger  76  are also selected such that the valve bodies  104 ,  108  are engaged with the corresponding valve seats  106 ,  110  during the upward and downward strokes of plunger  76 , respectively. 
   In operation and with reference to  FIGS. 1-3 , pump  26  of dispensing unit  16  continuously pumps liquid hot melt adhesive  18  from the inlet  60  to outlet ports  48  by orchestrated movements of plunger  76  caused by operation of the air logic valve  74  alternatingly filling and exhausting the air chambers  68   a ,  68   b . This action moves the air piston  70  and pump shaft  72  at a rate suitable for causing the pump  26  to pump the liquid hot melt adhesive  18  from tank  22  to guns  12 ,  14 . 
   At the bottom of the downstroke of plunger  76  as shown in  FIG. 3 , valve body  108  contacts valve seat  110  and is urged against the valve seat  110  by the biasing force applied by spring  114 , which is compressed between the plunger  76  and valve body  108 . The upper section  58   a  of pumping chamber  58  is occupied by an amount of liquid hot melt adhesive  18 . The pump shaft  72  is poised to move upwardly, and both of the check valves  92 ,  94  are momentarily closed. 
   Pump shaft  72  moves upward when pressurized air is introduced into air chamber  68   b  under the control of air logic valve  74  and pressurized air is simultaneously exhausted from air chamber  68   a . During this upward stroke or upstroke, as shown in  FIG. 2 , valve body  108  eventually lifts from contact with valve seat  110  as the biasing force applied by spring  114  to valve body  108  is gradually removed and the fluid pressure increases in inlet passageway  98  as the volume of lower section  58   b  expands. A gradual increase in the biasing force applied by spring  112  to valve body  104  may also contribute to lifting valve body  108  from contact with valve seat  110 . This supplies additional force for lifting the valve body  108  from the valve seat  110 . After valve body  108  is separated from valve seat  110 , a fresh amount of liquid hot melt adhesive  18  flows through inlet  60  and through the inlet passageway  98  into the lower section  58   b  of pumping chamber  58 . 
   The ball of check valve  92  is moved by the increasing fluid pressure in upper section  58   a  of pumping chamber  58  away from its seat to permit flow from the upper section  58   a  into the outlet passageway  88 . Thus, an amount of liquid hot melt adhesive  18  inside the upper section  58   a  of pumping chamber  58  is forced into outlet passageway  88  as the volume of upper section  58   a  is reduced by upward movement of plunger  76 . The amount of liquid hot melt adhesive  18  expelled from pumping chamber  58  is transferred through passageways  86 ,  88  to outlet ports  48 , which in turn direct the pumped amount of liquid hot melt adhesive  18  to the guns  12 ,  14  through lines  20 . The top of the plunger  76  at the conclusion of the upward stroke is preferably at a level at, or below, an inlet  88   a  to outlet passageway  88 . Hence, the amount of liquid hot melt adhesive  18  pumped in the upstroke is substantially equal to the change in volume of the upper section  58   a  during the upstroke. 
   During the upward stroke of plunger  76 , the ball of outlet check valve  94  is forced onto its seat by its spring and by the increased fluid pressure in outlet passageway  90 . This blocks back flow from outlet passageway  90  into the lower section  58   b  of pumping chamber  58 . Spring  112  is incrementally compressed between the plunger  76  and the valve body  104  as the plunger  76  moves upward. 
   At the top of the upward stroke, valve body  104  contacts valve seat  106  and is urged against the valve seat  106  by the biasing force applied by spring  112 , which is compressed between the plunger  76  and the valve body  104 . The lower section  58   b  of pumping chamber  58  is occupied by a fresh amount of liquid hot melt adhesive  18 . The pump shaft  72  is poised to move downwardly, and both of the check valves  92 ,  94  are again momentarily closed. 
   As shown in  FIG. 3  and as a continuation of the dispensing cycle, pump shaft  72  moves downward when pressurized air is simultaneously introduced into air chamber  68   a  and exhausted from air chamber  68   b . During this downward stroke or downstroke, valve body  104  lifts from valve seat  106  due to the gradual removal of the biasing force applied to valve body  104  by spring  112 , as spring  112  decompresses, in conjunction with the increased fluid pressure in inlet passageway  96  as the volume of upper section  58   a  expands. A gradual increase in the biasing force applied by spring  114  to valve body  108 , as spring  114  is incrementally compressed between plunger  76  and valve body  108 , may also contribute to lifting valve body  104  from contact with valve seat  106 . This assists in lifting the valve body  104  from valve seat  106 . After valve body  104  is separated from valve seat  106 , a fresh amount of liquid hot melt adhesive  18  flows through inlet  60  and inlet passageway  96  into the upper section  58   a  of pumping chamber  58 . 
   During the downstroke of plunger  76 , the ball of check valve  92  is forced onto its seat by its spring and by the increased fluid pressure in outlet passageway  88 . This prevents back flow from outlet passageway  88  into the lower section  58   b  of pumping chamber  58 . Concurrently, the ball of outlet check valve  94  is moved by the increasing fluid pressure in upper section  58   a  of pumping chamber  58  away from its seat to permit flow from the lower section  58   b  into the outlet passageway  90 . Thus, an amount of liquid hot melt adhesive  18  inside the lower section  58   b  of pumping chamber  58  is forced into outlet passageway  90  as the volume of lower section  58   b  is reduced by movement of plunger  76 . 
   At the conclusion of the downward stroke, the bottom of the plunger  76  is preferably at a level at, or above, an inlet  90   a  to outlet passageway  90 . Hence, the amount of liquid hot melt adhesive  18  pumped in the downstroke is substantially equal to the change in volume of the lower section  58   b  during the downstroke. The liquid hot melt adhesive  18  expelled from pumping chamber  58  is transferred through passageways  86 ,  90  to outlet ports  48 , just as described above with respect to the upward stroke. 
   In this manner, successive fresh amounts of liquid hot melt adhesive  18  filling pumping chamber  58  are pumped by each dispensing cycle of pump  26 , which consists of a single upward stroke of plunger  76  and a single downward stroke of plunger  76 , to the guns  12 ,  14 . 
   While the present invention has been illustrated by the description of various embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of Applicant&#39;s general inventive concept.