Patent Publication Number: US-11033926-B2

Title: Adhesive dispensing system and method with melt on demand at point of dispensing

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. patent application Ser. No. 15/218,065, filed Jul. 24, 2016, and published as U.S. Patent App. Pub. No. 2016/0332187 on Nov. 17, 2016, which is a continuation of U.S. patent application Ser. No. 13/790,118, filed Mar. 8, 2013, and issued as U.S. Pat. No. 9,427,768 on Aug. 30, 2016, which claims the benefit of U.S. Provisional Patent App. No. 61/718,976, filed Oct. 26, 2012, the disclosures of which are incorporated by reference herein in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to an adhesive dispensing system, and more particularly, to adhesive dispensing systems and methods using a receiving device for melting adhesive at the point of dispensing. 
     BACKGROUND 
     A conventional system for dispensing heated adhesive (i.e., a hot-melt adhesive dispensing system) generally includes a melter having a tank or reservoir for receiving adhesive materials in solid or liquid form, a heater grid for heating and/or melting the adhesive materials in the tank or reservoir, and a pump in communication with the heater grid and the tank or reservoir for driving and controlling the dispensation of the heated adhesive from the melter to downstream dispensing guns or modules. One or more hoses may also be connected to the melter to direct the dispensation of heated adhesive to the adhesive dispensing guns or modules located downstream from the pump. Furthermore, conventional dispensing systems generally include a controller (e.g., a processor and a memory) and input controls electrically connected to the controller to provide a user interface with the dispensing system and to control the various components of the dispensing system. 
     Conventional hot-melt adhesive dispensing systems typically operate at ranges of temperatures sufficient to melt the received adhesive and heat the adhesive to an elevated application temperature prior to dispensing the heated adhesive. As adhesive throughput requirements increase (e.g., up to 20 lb/hour or more), adhesive dispensing systems have traditionally increased the size of the tank or reservoir used with the melter to ensure that the maximum desired flow of molten adhesive can be supplied. However, large tanks and reservoirs result in a large amount of hot-melt adhesive being held at the elevated application temperature within the adhesive dispensing system. During periods of operation when the adhesive dispensing system is not operating at a maximum throughput, large amounts of hot-melt adhesive may be held at the elevated application temperature within the tank or reservoir for significant lengths of time, which can lead to degradation and/or charring of the adhesive, negative effects on the bonding characteristics of the adhesive, clogging of the adhesive dispensing system, and/or additional downtime. Furthermore, the provision of heated hoses extending from the melter to the dispensing modules further increases the complexity and expense of the adhesive dispensing system, while also further increasing the time that the adhesive is held at the elevated application temperature. 
     In several other conventional adhesive dispensing systems, the tank or reservoir of the melter has been reduced in size or nearly eliminated by providing a different type of melter configured to melt adhesive on demand when required by the dispensing modules (referred to as “melt on demand”). By using melt on demand, some of the problems associated with holding the adhesive at the elevated application temperature for long periods of time are reduced in significance, including but not limited to, charring and degradation. One example of such a melt on demand process is described in U.S. Pat. No. 6,230,936 to Lasko. Although systems such as the one shown in the Lasko patent melt adhesive on an as-needed basis, these systems continue to suffer from re-solidification of adhesive when used during periods of low throughput. It is highly impractical or impossible to expel clogs of re-solidified adhesive from the system when these clogs occur. In addition, the conversion efficiency of the energy applied to the adhesive is lowered by the problems experienced with these systems. 
     For reasons such as these, an improved hot-melt adhesive dispensing system that maximizes energy conversion efficiency while using melt on demand would be desirable. 
     SUMMARY OF THE INVENTION 
     According to one embodiment of the current invention, an adhesive dispensing system is provided for melting adhesive on demand and dispensing the adhesive. The dispensing system includes a dispensing applicator having a manifold with a manifold passage and a dispensing module coupled to the manifold passage. The dispensing system also includes a receiving device positioned proximate to the dispensing applicator. The receiving device includes a receiving chamber for receiving a small amount of solid adhesive at the location of the dispensing applicator. The receiving device also includes an outlet positioned to deliver melted adhesive into the manifold immediately after melting. A first heating device is positioned proximate to the manifold and to the receiving device, and the first heating device rapidly melts the adhesive on demand. A second heating device positioned within the manifold applies heat energy to maintain the adhesive as a liquid in the manifold passage. The operation of the first and second heating devices prevents re-solidification of the melted adhesive. 
     In one aspect, the first heating device may include an induction coil and a susceptor that is actuated electromagnetically by the induction coil to heat up and thereby apply heat energy to rapidly melt the adhesive. Alternatively, the first heating device may include a heater unit in the form of a heater grid defining a plurality of openings and including a heating element that heats the adhesive moving through the plurality of openings. In another embodiment, the manifold includes a cartridge receptacle and the receiving device is a cartridge filled with solid adhesive. The cartridge is inserted into the cartridge receptacle so that the solid adhesive may be melted by the first heating device. In each of these alternatives, as well as other arrangements for the first heating device, the adhesive is melted and then discharged immediately into the manifold for use by the dispensing applicator. For example, the receiving device may nest at least partially into the manifold such that the outlet is positioned within the manifold. In another example, the receiving device may be coupled to the manifold such that the outlet is positioned to feed directly into the manifold passage. 
     The first heating device may be located in various different locations within the adhesive dispensing system. For example, the first heating device is located within the manifold in some embodiments. In other embodiments, the first heating device is located within the receiving device. Alternatively, the first heating device may be divided into a first portion in the receiving device and a second portion in the manifold. In the example including an induction coil and a susceptor discussed above, the susceptor would be located within the receiving device and the induction coil would be located within the manifold. Regardless of where the first heating device is located, the first heating device remains positioned to rapidly heat and melt the solid adhesive in the receiving device so that the melted adhesive flows into the dispensing applicator. 
     In another aspect, the second heating device may include a heater cartridge extending through the manifold and heating the manifold and the manifold passage. The second heating device may also include etched resistance heaters located adjacent to the manifold passage. More particularly, the etched resistance heaters may define at least a portion of the sidewall of the manifold passage so that adhesive flows past the etched resistance heaters to receive heat energy. The dispensing applicator may include any type of dispensing module for discharging the melted adhesive onto a substrate. To this end, the dispensing applicator may include a jetting module that operates to rapidly jet minute droplets of melted adhesive onto the substrate. In another example, the dispensing applicator may include a metering pump that feeds one or more dispensing modules. Consequently, the melted adhesive does not solidify downstream from the first heating device, and purging of solid material from the dispensing applicator is rendered unnecessary. 
     In another embodiment according to the invention, a method for dispensing an adhesive uses an adhesive dispensing system having a dispensing applicator with a manifold including a manifold passage and also having a receiving device. Solid adhesive is supplied to the receiving device and rapidly heated with a first heating device. As a result, the adhesive is melted rapidly on demand when needed for dispensing. The method also includes delivering the melted adhesive directly from the receiving device into the manifold. A second heating device applies heat energy to maintain the adhesive as a liquid within the manifold. The dispensing applicator then dispenses the melted adhesive. The method provides melting of adhesive on demand while avoiding the problems of charring or solidification. 
     These and other objects and advantages of the invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein. 
    
    
     
       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 of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is a schematic view of an exemplary embodiment of an adhesive dispensing system with melt on demand according to the current invention. 
         FIG. 2  is a schematic front view of the adhesive dispensing system of  FIG. 1 , the system including multiple dispensing modules supplied by a receiving device. 
         FIG. 3  is a cross-sectional front view of the receiving device and the manifold of the adhesive dispensing system of  FIG. 2 . 
         FIG. 4  is a cross-sectional front view of an alternative receiving device including a heater unit and manifold according to another embodiment of the adhesive dispensing system. 
         FIG. 5  is a cross-sectional front view of an alternative embodiment of the receiving device and the manifold, similar to the adhesive dispensing system of  FIG. 3 . 
         FIG. 6  is a cross-sectional front view of an alternative receiving device in the form of a cartridge and a manifold according to another embodiment of the adhesive dispensing system. 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS 
     Referring to  FIGS. 1 through 3 , an adhesive dispensing system  10  in accordance with one exemplary embodiment of the invention is shown. The adhesive dispensing system  10  is configured to improve the dispensing operation by using a melt on demand process at the point of dispensing to melt solid adhesive material rapidly when that material is needed for dispensing. To this end, the storage of molten hot melt adhesive at elevated temperatures in reservoirs, tanks, and/or heated hoses located remote from the point of dispensing is substantially eliminated from the adhesive dispensing system  10 , and the likelihood for degradation and/or charring of the adhesive is reduced significantly as a result. Moreover, the adhesive does not require transport or pumping over lengthy distances between the point of melting and the point of dispensing because the melting occurs at the point of dispensing. In other words, a receiving device  12  of the adhesive dispensing system  10  is located at the same location as a dispensing applicator  14 . The adhesive is advantageously melted by a first heating device  16  located proximate to the receiving device  12  and then kept in the liquid state by a second heating device  18  included within the dispensing applicator  14 . As a result, the adhesive is rapidly melted on demand when needed for dispensing and kept at an elevated temperature in a liquid state downstream from the receiving device  12  to prevent re-solidification of the adhesive. Therefore, the adhesive dispensing system  10  reduces or eliminates problems with re-solidification of adhesive while also being more energy efficient as a result of the melt on demand process. 
     With reference to  FIG. 1 , a schematic layout of the exemplary embodiment of the adhesive dispensing system  10  is illustrated. To this end, the dispensing system  10  includes the dispensing applicator  14  and receiving device  12  previously described, as well as a fill system  20  configured to supply solid adhesive to the receiving device  12 . The fill system  20  can take any number of known forms, but the fill system  20  of the exemplary embodiment in  FIG. 1  includes a hopper  22  with a solids pump  24  and a hose  26  extending from the hopper  22  to the receiving device  12 . The hopper  22  may include a large storage tote configured to store solid particulate adhesive such as pelletized adhesive for periodic delivery to the receiving device  12 . The solids pump  24  may include a pneumatic pump having an eductor and/or a venturi (not shown) to move solid adhesive from the hopper  22  with pressurized air through the hose  26  to the receiving device  12 . It will be understood that the solids pump  24  may include other types of feeding mechanisms, including non-pneumatic forms of feeding such as a mechanical agitator, in other embodiments consistent with the scope of the invention. The hopper  22  may be repositioned adjacent to the receiving device  12  as well in other embodiments. 
     As shown in  FIGS. 1 and 2 , the fill system delivers the solid adhesive material to the receiving device  12 , which is located adjacent to the dispensing applicator  14  so that the receiving device  12  can store a small amount of solid adhesive for melting on demand, such as needed for dispensing. The first heating device  16  is schematically shown within the receiving device  12 , but it will be understood that the first heating device  16  may be located within the dispensing applicator  14  or be divided into portions in each of the receiving device  12  and the dispensing applicator  14  in other embodiments. The dispensing applicator  14  of the exemplary embodiment includes a manifold  30  and a plurality of dispensing modules  32  coupled to the manifold  30 . The manifold  30  is configured to receive melted adhesive material from the receiving device  12  and supply that melted adhesive to the dispensing modules  32 . To this end, the manifold  30  may include a manifold passage  34  that extends internally through the manifold  30  between the receiving device  12  and the dispensing modules  32 . The manifold passage  34  may be heated by the second heating device  18  to maintain the adhesive in the manifold  30  in the molten liquid state at the elevated temperature, thereby preventing solidification of the adhesive. It will be understood that the dispensing applicator  14  may be modified in other embodiments. For example, the manifold  30  may be incorporated into one or more dispensing modules  32 , or the manifold  30  may be omitted in other embodiments depending on the particular type of dispensing applicator  14  required for dispensing the adhesive. 
     As well understood, the dispensing modules  32  include flow valves configured to actuate selective control over the dispensing of the adhesive. The dispensing modules  32  may include any known type of dispensing module  32  used to dispense various types of adhesive materials onto substrates. In one example, the dispensing modules  32  include the jetting module described in co-pending U.S. Patent Publication No. 2011/0300295 to Clark et al., which is co-owned by the assignee of the current application, and the disclosure of which is hereby incorporated by reference in its entirety herein. To this end, the dispensing module  32  operates to rapidly open and close a valve member against a valve seat (not shown) to repeatedly permit flow of the adhesive towards a dispensing outlet and then force minute droplets  36  of the adhesive from the dispensing outlet and onto a substrate  38  as shown schematically in  FIG. 1 . Therefore, the dispensing modules  32  may operate to rapidly jet minute droplets of the adhesive from the dispensing applicator  14 . It will be appreciated that other types of dispensing applicators, including similar and different types of contact or non-contact nozzles/modules, may be used without departing from the scope of the invention. 
     The adhesive dispensing system  10  may also include a controller  40  configured to operate the various components of the receiving device  12  and the dispensing applicator  14 . To this end, the controller  40  operates the first and second heating devices  16 ,  18  to provide melt on demand to the dispensing modules  32 . In one example, the controller  40  receives input corresponding to an actuation of dispensing at one or more of the dispensing modules  32  and then actuates the first heating device  16  to rapidly melt and supply more molten adhesive to the manifold  30 . As shown schematically in  FIG. 3 , this input to the controller  40  may be module actuation signals sent directly from the dispensing modules  32 , but this input could also include other alternatives such as a level sensor detecting removal of adhesive from at least some portion of the manifold passage  34 . As a result, whenever the dispensing modules  32  operate to dispense adhesive material supplied from the manifold  30 , the controller  40  operates the first and second heating devices  16 ,  18  to melt more adhesive and maintain a small supply of adhesive at the elevated temperature within the manifold passage  34  for use by the dispensing modules  32 . It will be understood that the controller  40  may be connected to additional components such as the fill system  20  and may also operate to control additional operational features of the adhesive dispensing system  10 , including but not limited to: refill of the receiving device  12  with the fill system  20 , and actuation of the dispensing modules  32  to dispense molten adhesive. In this regard, the arrangement of components of the adhesive dispensing system  10  and the operation of the controller  40  and the first and second heating devices  16 ,  18  collectively minimizes the heat energy applied to enable dispensing of adhesive at an elevated temperature. 
     With particular reference to  FIG. 3 , further details of the receiving device  12  and the manifold  30  of the exemplary embodiment are shown. More specifically, the receiving device  12  of this embodiment includes the first heating device  16  for rapidly heating and melting the adhesive to an elevated temperature. One example of such a first heating device  16  could include an inductor/susceptor-type of heating device for rapidly melting the adhesive on demand for the dispensing applicator  14 . Continuing with this example, the receiving device  12  may include many of the components described in U.S. Pat. No. 6,230,936 to Lasko, the disclosure of which is hereby incorporated by reference in its entirety herein. To this end, the receiving device  12  may include a body  42  including a distal end  44  connected to a nose assembly  46  and a proximal end  48  defining an inlet  50  ( FIG. 2 ) for receiving the adhesive  52  in the form of beads, pellets, or other solid or semi-solid particulate from the hose  26 . The body  42  therefore defines an internal receiving chamber  54  extending from the inlet  50  to the nose assembly  46  such that a small supply of solid adhesive  52  can be held in the receiving chamber  54  and fed towards the first heating device  16 . A feed screw or auger  56  may be mounted on a screw barrel  58  located within the receiving chamber  54  and configured to actuate movement of adhesive  52  towards the nose assembly  46 . In this regard, the feed screw  56  is driven by a motor (not shown) to rotate and force movement of the solid adhesive  52  downwardly in the orientation shown in  FIG. 3 . As described in further detail below, the driving movement of the feed screw  56  is controlled to correspond to the demands for adhesive  52  at the dispensing applicator  14 , thereby causing the receiving device  12  to provide the desired amounts of molten adhesive  52  to the dispensing modules  32 . Alternatively, it will be understood that the feed screw  56  and screw barrel  58  may be omitted in other embodiments such that the solid adhesive  52  is gravity-fed to the bottom of the receiving chamber  54  and into the nose assembly  46  for melting by the first heating device  16 . Other types of agitators for moving the solid adhesive  52  may also be used without departing from the scope of the invention. 
     With continued reference to  FIG. 3 , the nose assembly  46  includes a conical housing cone  60  having a central orifice  62 . The conical housing cone  60  may be coupled to the distal end  44  of the body  42  with a threaded collar  64  or a similar connection mechanism. It will be appreciated that the nose assembly  46  may alternatively be integrally formed with the body  42  (e.g., as the bottom end of the body  42 ) or may be reshaped in other ways (e.g., non-tapered) in other embodiments of the receiving device  12 . The nose assembly  46  also includes a conical inductor  66  received within the conical housing cone  60 . The conical inductor  66  is an induction coil of wire that may be supplied with electrical current to electromagnetically induce heating of a conical susceptor  68  received within the conical inductor  66 . The conical susceptor  68  may be corrugated or bent to increase the effective surface area facing the adhesive  52  in the conical housing cone  60 . The conical susceptor  68  also includes a central orifice  70  aligned with the central orifice  62  in the conical housing cone  60  such that melted adhesive can flow through an outlet  74  of the receiving device  12  defined at the central orifice  62  of the conical housing cone  60 . A stationary inner cone  76  is also located within the conical housing cone  60  and is connected at a sliding joint  78  to the end of the screw barrel  58  at the distal end  44  of the body  42 . Therefore, the conical housing cone  60  defines a melting passage  80  defined between the conical susceptor  68  and the stationary inner cone  76  and extending from the receiving chamber  54  of the body  42  to the outlet  74 . The melting passage  80  receives adhesive  52  driven out of the receiving chamber  54  by the feed screw  56  or otherwise fed by gravity or other agitators out of the receiving chamber  54 , and the susceptor  68  rapidly melts the solid adhesive  52  into a molten state within the melting passage  80  before the adhesive  52  passes through the outlet  74  and into the manifold  30 . 
     The receiving device  12  of this embodiment is positioned such that the nose assembly  46  nests at least partially into the manifold  30  of the dispensing applicator  14 . As a result, the outlet  74  is located within the manifold  30  such that the outlet  74  discharges molten adhesive  52  directly and immediately into the manifold passage  34  after melting of the adhesive  52  within the melting passage  80 . As described in further detail below, the manifold  30  may also be heated such that the nesting of the nose assembly  46  into the heated manifold  30  provides additional heat energy at the nose assembly  46  for melting the adhesive  52 . To this end, at least a portion of the first melting device  16  may be located within the manifold  30  instead of within the receiving device  12 . Alternatively, the nose assembly  46  may be reconfigured without a tapered shape or without the amount of nesting into the manifold  30  that is illustrated in  FIG. 3 , as long as the outlet  74  continues to discharge molten adhesive directly and immediately into the manifold passage  34  after melting. One example of such a non-tapered, non-nesting arrangement is described in further detail below with reference to the embodiment shown in  FIG. 4 . In another alternative example, a heater grid (not shown) may be formed from a plurality of susceptors arranged in a grid structure and induced by one or more inductors. 
     In operation, whenever the dispensing modules  32  require more adhesive  52  for dispensing as determined at the controller  40 , the feed screw  56  is rotated to force solid adhesive  52  into the melting passage  80  for melting using heat energy generated by the electromagnetic inducement of the susceptor  68  with the induction coil  66 . Additionally, the controller  40  may turn on or actuate heating at the susceptor  68  in response to the dispensing modules  32  requiring more adhesive  52  if the first heating device  16  had been previously turned off or placed into a standby mode. The heat energy applied by the susceptor  68  is tailored to rapidly melt the adhesive  52 , but with gentle enough heating to avoid charring and degradation of the adhesive  52 . When the dispensing modules  32  stop requesting more adhesive (e.g., dispensing operations are stopped), the feed screw  56  may be driven in reverse a short amount to remove the pressure that forces adhesive  52  into and through the melting passage  80 . This reversal of flow may not be required in all embodiments of the invention, including other embodiments with gravity-fed solid adhesive  52  held in a receiving chamber  54  without a feed screw  56 . It will be understood that the feed screw  56  may be driven with different speeds to provide various levels of molten adhesive throughput, depending on the requirements at the dispensing modules  32 . 
     Advantageously, by locating the receiving device  12  at the dispensing applicator  14  and by optionally nesting the nose assembly  46  into the manifold  30 , the adhesive  52  may be melted on demand and delivered to the dispensing modules  32  simply by flowing directly from the outlet  74  of the receiving device  12  into the manifold passage  34 . Thus, no heated hoses or other conduits are required between the receiving device  12  and the dispensing applicator  14 . Moreover, the melt on demand process enables molten adhesive  52  to be supplied to the dispensing modules  32  without necessitating the holding of a reservoir or tank full of adhesive at the elevated temperature at a location remote from the dispensing applicator  14 . Consequently, the melt on demand process in the exemplary embodiment is energy efficient (e.g., a maximized percentage of the energy supplied to the dispensing system  10  is realized in the adhesive  52  dispensed from the applicator  14 ) and requires fewer components than other dispensing systems having hoses extending between separated melters and applicators. In addition, the elimination of a large reservoir or tank for holding molten adhesive at a location remote from the dispensing applicator  14  reduces the likelihood of charring or solidification of the adhesive. 
     Additionally, the manifold  30  is also configured to reduce the likelihood of charring or solidification of the adhesive. To this end, the manifold  30  includes the second heating device  18  described briefly above. The second heating device  18  may include one or more types of heating elements located within the manifold  30  and operable to maintain the temperature of the adhesive  52  flowing through the manifold passage  34 . In the exemplary embodiment shown in  FIG. 3 , the second heating device  18  includes an etched resistance heater  86  positioned adjacent to the manifold passage  34 . The etched resistance heater  86  may receive electrical current to generate and apply heat energy to the manifold passage  34  and any adhesive  52  located in the manifold passage  34 . The etched resistance heater  86  may be positioned within the manifold  30  so that the etched resistance heater  86  defines at least a portion of the sidewalls defining the manifold passage  34 . However, it will be understood that the etched resistance heater  86  may be repositioned in other embodiments, as long as the heat energy generated is delivered to the manifold passage  34 . 
     The manifold  30  shown in  FIG. 3  includes an optional metering pump  88  that meters the supply of molten adhesive  52  in the manifold passage  34  to the dispensing modules  32 . To this end, the manifold passage  34  may branch into separate passage portions downstream from the optional metering pump  88  to divide the flow of adhesive  52  and supply each of the dispensing modules  32  associated with the dispensing applicator  14 . This arrangement of the manifold passage  34  advantageously enables the receiving device  12  to supply multiple dispensing modules  32  with molten adhesive while using melt on demand. Although the etched resistance heater  86  is shown as positioned at a collection portion  89  of the manifold passage  34  located upstream from the pump  88 , it will be appreciated that the etched resistance heater  86  may also be repositioned to directly heat the portions of the manifold passage  34  that branch off downstream from the pump  88  in other embodiments of the invention. It will be understood that the collection portion  89  is located upstream from the optional pump  88  (when included in the manifold  30 ) and upstream from the dispensing modules  32  to provide a small volume of molten adhesive from which the dispensing modules  32  can draw in order to conduct dispensing operations. 
     The second heating device  18  also includes a heater cartridge  90  in the exemplary embodiment shown in  FIG. 3 . The heater cartridge  90  extends through the manifold  30  and may include multiple passes running between the branches of the manifold passage  34  downstream from the metering pump  88 . The heater cartridge  90  is inserted or cast into position within the manifold  30  and operates to heat the entire manifold  30  (or a substantial portion thereof), which then applies heat energy to the adhesive  52  in the manifold passage  34  to maintain the adhesive  52  at the elevated temperature. It will be understood that the etched resistance heater  86  or the heater cartridge  90  may be used alone rather than in combination in other embodiments of the dispensing system  10 , and additional types of heaters may also be used in the second heating device  18  without departing from the scope of the invention. The application of heat energy to the adhesive  52  in the manifold  30  prevents re-solidification of the adhesive  52  downstream from the receiving device  12  during periods of low throughput or between dispensing cycles. Thus, the use of the second heating device  18 , in combination with the first heating device  14 , advantageously enables a melt on demand process configured to supply multiple dispensing modules  32  during periods of both high and low throughput. The problems of conventional dispensing systems with solidification of the adhesive are reduced or eliminated when using the adhesive dispensing system  10  of the current invention. The operation of the adhesive dispensing system  10  is therefore optimized for energy efficiency (e.g., a minimized amount of heat energy is applied to enable dispensing of adhesive  52  at the elevated temperature) and improved for melting at the point of demand. 
     In another exemplary embodiment of the adhesive dispensing system  110  shown in  FIG. 4 , an alternative arrangement of a receiving device  112  and a dispensing applicator  114  are provided. Several of the components of this embodiment of the adhesive dispensing system  110  are identical or substantially similar to the components described above, and these components (for example, the manifold  30 ) have been marked with the same reference numbers in this embodiment without additional explanation below. In this embodiment, the receiving device  112  includes a first heating device  116  defined by a heater unit  118  in the form of a heater grid  118 . Many of the components of the receiving device  112  of this embodiment are also described in U.S. Patent Application No. 61/703,454 to Clark et al., entitled “Adhesive Dispensing Device having Melt Subassembly with Optimized Reservoir and Capacitive Level Sensor” (Our Ref.: NOR-1496P), the disclosure of which is hereby incorporated by reference in its entirety herein. The receiving device  112  of this embodiment operates to store a small amount of solid adhesive  52  and provide molten adhesive  52  using melt on demand at the location of dispensing in a similar manner as described with reference to the embodiment of  FIGS. 1 through 3 . 
     To this end, the receiving device  112  includes the heater grid  118 , a receiving chamber  120  located above the heater grid  118  and configured to supply solid particulate adhesive  52  into the heater grid  118 , and an optional cyclonic separator unit  122  located above the receiving chamber  120  and configured to deliver the adhesive  52  from the fill system  20  and hose  26  into the receiving chamber  120 . As described in further detail in the Clark application, the receiving chamber  120  may also include a level sensor  124  configured to sense the level of adhesive  52  within the receiving chamber  120  to ensure that the fill system  20  continually provides refills of solid adhesive  52  into the receiving device  112  as the adhesive  52  is dispensed by the dispensing applicator  114 . The heater grid  118  includes a peripheral wall  126  and a plurality of partitions  128  extending across the space between the receiving chamber  120  and the manifold  30 . The heater grid  118  therefore defines a plurality of openings  129  through the heater grid  118  and between the partitions  128  for flow of the adhesive  52 . It will be understood that the plurality of openings  129  may be defined by different structure than grid-like partitions in other embodiments of the heater unit  118 , including, but not limited to, fin-like structures extending from the peripheral wall  126 , without departing from the scope of the invention. In this regard, the “heater unit”  118  may include a non grid-like structure for heating the adhesive  52  in other embodiments. The heater unit  118  (shown as heater grid  118  in this embodiment) can include any structure, as long as at least one opening  129  is provided for adhesive flow through the adhesive dispensing system  110 . 
     The peripheral wall  126  is configured to receive a heater cartridge  130  or another equivalent heating element, which may be inserted or cast into the heater grid  118 . The heater cartridge  130  applies heat energy to the heater grid  118 , which is conducted through the peripheral wall  126  and the partitions  128  to transfer heat energy to the adhesive  52  flowing within the plurality of openings  129  and thereby rapidly melt the adhesive  52  on demand. The operation of the heater cartridge  130  and the heater grid  118  may be controlled by the controller  40  to melt adhesive  52  when required by dispensing operations at the dispensing applicator  114 . Therefore, a minimized amount of heat energy is applied to enable dispensing of adhesive  52  at the elevated temperature. Similar to the previous embodiment, the controller  40  is coupled to one or more inputs such as the dispensing modules  32  as described in detail above. The receiving device  112  also defines an open bottom outlet  132  at the lower end of the openings  129  in the heater grid  118 . The receiving device  112  is coupled to the manifold  30  of the dispensing applicator  114  (such as by threaded fasteners  134  or other similar connectors) so that this outlet  132  communicates directly with the manifold passage  34  (and more particularly, with the collection portion  89  of the manifold passage  34 ). Therefore, similar to the previous embodiment, the receiving device  112  includes an outlet  132  that immediately feeds adhesive  52  directly from the openings  129  in the heater grid  118  into the manifold passage  34  after melting at the heater grid  118 . 
     The heater grid  118  and receiving chamber  120  are sized to be relatively small such that a minimal volume of adhesive  52  is held at an elevated temperature before use in the dispensing applicator  114 . In this regard, there is no reservoir or tank of molten adhesive positioned remote from the receiving device  112  and dispensing applicator  114 . As a result, the problems of adhesive charring are reduced or eliminated in this adhesive dispensing system  110 . Similar to the previously described embodiment, the manifold  30  again includes a second heating device  18  that operates to apply heat energy to the melted adhesive  52  to maintain the melted adhesive  52  at the elevated temperature and in the liquid state downstream from the receiving device  112 , thereby preventing re-solidification of the adhesive  52 . The second heating device  18  may again include various types of heating elements, including, but not limited to, the etched resistance heater  86  (now shown within the manifold  30  adjacent to the manifold passage  34 ) and/or the heater cartridge  90  for heating the entire manifold  30 . Therefore, the adhesive dispensing system  110  of this embodiment also enables the energy-efficient melt on demand operation with an advantageous reduction or elimination of charring and solidification of the adhesive  52 . 
     An alternative embodiment of the adhesive dispensing system  210  is shown in  FIG. 5 . Many of the components of this embodiment of the adhesive dispensing system  210  are identical or substantially similar to the components described above with reference to the embodiment shown in  FIG. 3 , and these components have been marked with the same reference numbers in this embodiment without additional explanation below. To this end, the adhesive dispensing system  210  includes the same receiving device  12  and dispensing applicator  14  as the first embodiment described above, but the manifold  230  and the nose assembly  246  have been modified in this embodiment to divide the first heating device  16  into a first portion within the manifold  230  and a second portion within the nose assembly  246 . More specifically, the conical inductor  266  is moved to a location within the manifold  230  but still proximate to the conical susceptor  68 , which remains in the nose assembly  246 . As discussed above, the conical inductor  266  is an induction coil of wire that may be supplied with electrical current by the controller  40  to electromagnetically induce rapid heating of the conical susceptor  68  and the adhesive  52  within the susceptor  68 . Although a first portion (inductor  266 ) is located within the manifold  230  and a second portion (susceptor  68 ) is located within the nose assembly  246 , the first heating device  16  continues to operate in the same manner to rapidly melt adhesive  52  on demand, just like in the embodiments discussed above. 
     It will be understood that the first heating device  16  may include additional heating elements such as heater cartridges or other types of heating elements located in the manifold  230  to assist with the rapid and gentle melting of the adhesive  52  in other embodiments not illustrated. In still other embodiments consistent with the scope of this invention, the inductor  266  and susceptor  68  may be switched in position, or both located within the manifold  230 . Regardless of the chosen layout of the first heating device  16 , the first heating device  16  remains proximate to both the receiving device  12  and to the dispensing applicator  14  so that the adhesive  52  is melted at the point of application and on demand, thereby limiting the likelihood of charring or degradation of the adhesive  52 . 
     With reference to  FIG. 6 , an alternative embodiment of an adhesive dispensing system  310  including the latter type of arrangement discussed above is shown. More specifically, the first heating device  16  includes a conical inductor  366  in the form of an induction coil and a conical susceptor  368  each located within the manifold  330  near the entrance to the manifold passage. The adhesive dispensing system  310  contains many components that are identical or substantially similar to the components described above with reference to the other embodiments, and these components have been marked with the same reference numbers in this embodiment without additional explanation below. 
     In this embodiment, the manifold  330  is modified to include the first heating device  16 , as described above, and a cartridge receptacle  394  formed adjacent to the conical inductor  366  and conical susceptor  368 . It will be understood that other types of heating elements may be used for the first heating device  16  in other similar embodiments. For example, the inductor  366  and susceptor  368  may be divided with one in the cartridge  312  and one in the manifold  330  similar to  FIG. 5 , or with both elements  366 ,  368  in the cartridge  312  similar to  FIG. 3 , without departing from the scope of the current invention. The cartridge receptacle  394  communicates with the manifold passage  34  and is sized to closely receive a cartridge  312 , which is the receiving device  12  in this embodiment. To this end, the cartridge  312  includes a hollow chamber (defining the receiving chamber  54 ) that is filled with solid adhesive  52  and generally gravity-feeds this solid adhesive  52  into a portion of the cartridge  312  that is nested within the cartridge receptacle  394  and located adjacent to the conical susceptor  368  in the manifold  330 . Thus, the first heating device  16  is operable to rapidly heat the solid adhesive  52  located in the cartridge  312  at the cartridge receptacle  394  to melt that adhesive and supply it into the manifold passage  34  on demand. This melting operation is substantially identical (rapid and gentle) to the other melting operations described in detail above for the other embodiments. Similar to the previous embodiments, the manifold  330  continues to include the second heating device  18 , which applies heat energy to keep the adhesive  52  in the liquid state within the manifold  330 . As a result, this embodiment of the adhesive dispensing system  310  continues to achieve energy-efficient melt on demand operation with an advantageous reduction or elimination of charring and re-solidification of the adhesive  52 . 
     The combination of a melt on demand process at the point of application using a first heating device  16  to rapidly melt the adhesive  52  and a second heating device  18  for maintaining the temperature of adhesive  52  located downstream from the receiving device  12  may be used in other embodiments with different sets of components other than those shown in the exemplary embodiments. For example, the dispensing applicator  14  may include some or all of the components described in the apparatus of U.S. Pat. No. 8,201,717 to Varga et al., which is co-owned by the assignee of the current application and the disclosure of which is hereby incorporated by reference in its entirety herein. Regardless of the particular structures used to define the receiving device  12  and the dispensing applicator  14 , the melt on demand process enabled by the adhesive dispensing systems of the current invention advantageously addresses many of the drawbacks with conventional dispensing systems. The adhesive dispensing system maximizes the useful conversion of heat energy applied to the adhesive  52  while avoiding problems caused by solidification and charring of adhesive within a dispensing applicator. 
     While the present invention has been illustrated by a description of several embodiments, and while those embodiments have been described in considerable detail, there is no intention 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. Therefore, the invention in its broadest aspects is not limited to the specific details shown and described. The various features disclosed herein may be used in any combination necessary or desired for a particular application. Consequently, departures may be made from the details described herein without departing from the spirit and scope of the claims which follow.