Distributed system for controlling application of molten thermoplastic material

Abstract: A distributed system for controlling application of molten thermoplastic material includes a system controller including a network for transmitting information between the controller and a plurality of distributed control modules along a shared bus; at least one applicator for applying the material; and a melter for supplying molten material to the at least one applicator; the melter including a plurality of melter control modules for controlling delivery of the material to the at least one applicator, with each of the melter control modules being coupled to the network; the applicator comprising at least one applicator control module, the applicator control module being coupled to the network; wherein the system controller transmits instructions to a selectable number of the control modules across the network based on a selectable application of the material, and receives across the network information from each control module used in the selected application.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to systems for melting and applying molten thermoplastic material to a product. More particularly, the invention relates to a distributed control system for controlling application of such material using a number of applicators. 2. Description of the Prior Art A conventional apparatus for applying molten thermoplastic material, such as an adhesive, for example, includes as the basic components a melter, one or more applicators and a control system. A melter typically includes a tank having a hopper that holds the solid unmelted material, a heating grid for applying heat to the material at the bottom of the hopper, and a reservoir for holding the molten material. The molten material is then pumped from the reservoir to an applicator or dispenser through a hydraulic system of supply hoses, pumps, valves and so on. The applicator or dispenser is an apparatus that applies the molten material to a product, such as, for example, a disposable diaper. Applicators are typically pressure fed or metered and include temperature devices such as heaters and sensors, and solenoids, and in the case of metered applicators, motor, pump and related pressure devices such as transducers. US patent 4,545,504 discloses an apparatus for dispensing a hot melt thermoplastic which consists of a hopper containing granular thermoplastic, an extruder for melting the molten thermoplastic and delivering it to a manifold and then to an applicator for dispensing the molten thermoplastic. The apparatus comprises a control system for the extruder applicator and an extruder-accumulator-applicator. The control system includes a number of circuits comprising relay controls and relays, respectively. Energizing a particular relay control may cause corresponding relays to close such that power is provided through a particular one of the circuits. Thus various components of the applicator, such as an applicator valve, are controlled. Control systems used heretofore for controlling a melter and associated applicators are limited in several respects. In a typical system, system control is centralized and installed in or integral with the melter control system, and each applicator is individually cabled up to the control system and melter hydraulics (such as, for example, a manifold arrangement attached to the reservoir). This involves substantial numbers and lengths of individual or dedicated power and control lines from the melter system controller to each applicator, perhaps on the order of forty to sixty wires for a metered applicator. A pressure fed applicator may require, for example, twelve to twenty four wires. Thus, when a melter is used for supplying material to a plurality of applicators, a significant wiring layout must be accomplished along with the usual installation and troubleshooting problems associated therewith. The use of dedicated hardwired direct connections from each applicator individually back to the melter/system controller also substantially reduces flexibility of the system for making configuration changes and for expandability. For example, upgrading an existing system may be limited by the number of control channels available and the power handling capacity of the melter system. Of course, melters can be designed with excess capacity based on a projected long term need, but this results in idle control and unused system power capacity until such capacity is needed, which can involve a substantial waste of up front design cost and effort. Although known melter systems can accommodate system modifications, such as, for example, changing over an application from pressure fed to metered, such changes heretofore are cumbersome and costly because they involve having to reconfigure not only the application end of the line, but also the melter system control. In the example of changing an application from pressure fed to metered, the melter system control may need to have a motor control and or temperature control added to accommodate the metered applicator. Sometimes, entire additional melters must be provided to accomplish application changes. Stand-alone controllers are frequently required. Additionally, the number of melters required to accomplish all applications must be increased due to power and control capacity limitations of the melters. Expandability of known systems frequently is limited by electrical power capacity of the melter control system. The delivery of additional material to added on applicators often is a straightforward modification of the manifold and pump delivery system. However, shop power to operate the additional applications is typically part of the individual cabling from the melter to each application. Therefore, the number of applications that can be connected to a melter system may be limited by the electrical power limitations in the melter, unless an entire switch gear and wiring is to be replaced, which can be a very expensive operation. Thus, the expandability of the control system tends to be substantially more limited than the hydraulic system architecture could otherwise accommodate. Overdesigning the melter initially to have sufficient electrical power for expanding the system results in excess capacity and may needlessly increase the size, cost and complexity of the melter. In other cases, additional stand-alone melters are necessary to provide the necessary control and power capacity. Typical control systems heretofore have not been particularly user friendly, in the sense that they typically require the operator to know which control channels are connected to which applicator hardware because each applicator system is separately configured to the central controller, along with having to interpret and recall the various control system designations rather than simply being able to rely on common terminology to group the various elements together according to each application. The objectives exist, therefore, to provide a better system control design for applying molten thermoplastic material. Such a system should be flexible to accommodate configuration changes in an existing system without substantial modification of the melter, accommodate expansion of an existing system without involving a substantial modification of the melter control system, provide for expandability and flexibility to more closely match the expandability and flexibility of the hydraulic architecture, and provide a more user friendly interface during system configuration and operation. SUMMARY OF THE INVENTION The present invention contemplates a significant departure from conventional centralized control systems for applying molten thermoplastic material by providing in one embodiment, a distributed system for controlling application of molten thermoplastic material to include a system controller and a network for transmitting information between the controller and a plurality of distributed control modules along the network comprising a shared bus; at least one applicator for applying the material; and a melter for supplying molten material to the at least one applicator; the melter including a plurality of melter control modules for controlling delivery of the material to the at least one applicator, with each of the melter control modules being coupled to the network; the applicator comprising at least one applicator control module, the applicator control module being coupled to the network; wherein the system controller transmits instructions to a selectable number of the control modules across the network based on a selectable application of the material, and receives across the network information from each control module used in the selected application. These and other aspects and advantages of the present invention will be readily understood and appreciated by those skilled in the art from the following detailed description of the preferred embodiments with the best mode contemplated for practicing the invention in view of the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified schematic diagram of a distributed control system for applying molten thermoplastic material in accordance with the invention. FIG. 2 is a functional block diagram for a control system architecture suitable for use with the present invention. FIG. 3 is another schematic diagram for an expanded application system as shown in FIG. 1 . FIG. 4 is a functional block diagram of the logical relationships for a distributed application control system in accordance with the invention. FIG. 5 is a detailed functional block diagram of control function and device relationships for a typical distributed control system for applying molten material such as in FIG. 4 . FIGS. 6 A- 6 D illustrate exemplary a graphical user interface for configuring a distributed control system in accordance with the invention. FIG. 7 illustrates a prior art configuration for a system for applying molten thermoplastic material. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to FIG. 7 , a conventional molten thermoplastic material application system includes a melter 1, a pressure fed applicator 2 and a metered applicator 3. Molten material is fed to the applicators 2 and 3 by respective supply hoses 4 a and return hoses 4b. Shop power, such as a 230 VAC supply 5 is connected to the melter and supplied to the applicators as part of a respective wiring cable arrangement 6. The metered applicator cable 6 could contain upwards of forty to sixty wires, while a typical wiring cable for the pressure fed applicator 2 may contain twelve to twenty-four wires. It is readily apparent that as the number of additional applicators at a manufacturing site is increased, wiring will quickly become a burden both for installation and troubleshooting and maintenance. Additionally, the centralized melter 10 control system will need to be reconfigured and perhaps significantly modified to accommodate expansion, upgrading or applicator changeover. With reference to FIG. 1 , an embodiment of the invention is illustrated in simplified schematic form for purposes of describing the basic concepts of the invention. Although the descriptions that follow herein include reference to specific subsystems such as pressure fed applicators, metered applicators, microprocessor based control systems and so on, these details of the described embodiments are intended to be exemplary and should not be construed in a limiting sense. Those skilled in the art will readily appreciate that the benefits and improvements achieved with the present invention can be realized in a variety of different configurations, particularly as to the selected hardware for implementing the distributed control system. The invention is further applicable to application control of different types of material using different types of applicators. In the basic configuration of FIG. 1, a melter 10 is provided along with a pressure fed applicator 12 and a metered applicator 14. Although not shown in FIG. 1 for clarity, the applicators 12 and 14 are connected to the melter 10 by supply and return hoses in a manner similar to that explained with reference to FIG. 7 . A distributed control system 20 for controlling application of the molten thermoplastic material including control of the melter 10 and a number of applicators (in the present example, two) is provided and includes a system controller 22 which for convenience can be physically located with the melter 10 . The flexibility of the system 20 , however, easily accommodates locating the controller 22 at some other location, even a remote location, if such is desired for a particular application of the invention. The control system 20 further includes a number of applicator control modules 24, preferably there being a control module for each of the applicators or each type of applicator. Thus, in FIG. 1 there is a control module 24 a for the metered applicator 14 and a control module 24 b for the pressure fed applicator 12. There is no physical limitation as to a particular module being used to control more than one applicator other than the control module having to contain, or being expandable to contain, an adequate control hardware and software configuration for the desired control functions. Hereinafter it is assumed that each control module controls a single applicator unless otherwise indicated, it being understood that such description is merely exemplary and not a limitation on the use of the invention. Each control module 24 contains a suitable control module including a control circuit for controlling operation of its respective applicator. In an environment involving control of applicators such as pressure fed and metered applicators, it is expected that the applicator control modules will each contain an internal processor, such as, for example, a microprocessor based system, for carrying out the control functions, as will be described hereinafter in greater detail. Such functions include monitoring and control of temperature, pressure, solenoids, motors and so on. In all the various embodiments, circuits, systems and subsystems described herein, those skilled in the art will appreciate that the electronic functions and circuits can be realized in many different ways. In addition to microprocessor based technologies, other available examples include microcontrollers, microcomputers, digital signal processing, analog processing, discrete digital logic circuits and so on. The system will, however, generally require a microprocessor or other communications processor, as is known in the art. The distributed control system 20 further includes a network bus 26 , which in this example is a simple two- to twelve-wire bus. The number of wires in the network bus will be determined by the communications needs between the system controller 22 and the distributed applicator control modules. An important aspect of the invention resides in noting that the network bus 26 is shared by the various applicators 12 and 14 and that from a wiring standpoint, the shared bus is substantially the only electrical interconnection among the various electronic components of the application system. The bus 26 provides a communications link between the system controller 22 within the melter electrical box 21 and each of the applicator control modules 24. The system controller 22 and each of the applicator control module 24 include the appropriate hardware and software for implementing the communications network across the bus 26 . In some cases, a simple twisted wire pair can be used for the bus 26 . A suitable communications network protocol commercially available is LonWorks™ LonTalk™ protocol available from ECHELON®. This network conveniently is compatible with conventional microprocessor operating systems such as WINDOWS®. The network bus 26 is used to transmit instructions and data between the system controller 22 and the applicator control modules 24 . Those skilled in the art will readily appreciate that the exemplary description of a hardwired network is for explanation only. Other communication links can be used if so desired for a specific application, such as optical networks, RF or microwave transmission, and so on. The use of a simple hardwired connection, however, in many cases will simplify the interface between the network components and the system control hardware/software. The distributed control system 20 is used preferably in conjunction with a distributed power system, in which shop power 28 is provided at the melter (28 a ) and at each of the applicator sites (28 b ). This can significantly reduce the size and cost of the switch gear associated with the melter 10, because the supply 28 a can be sized for the melter independent of how many applicators are hydraulically connected thereto. With reference to FIG. 2 , an architecture suitable for realizing the control system 20 is shown in functional block diagram form. In this embodiment, the system controller 22 is realized in the form of an operator interface 40 and an industrial computer 41 , such as an INTEL® 486 microprocessor platform running a software application under, for example, a WINDOWS® operating system 42 . Other hardware systems and operating software systems commercially available can readily be utilized, modified or custom designed if so desired, as will be appreciated by those skilled in the art. The melter is conveniently provided with its own "control module" section 44 which includes a temperature control module 48 , a motor control module 50, an input/output (I/O) module 52 and a level control module 53 . The temperature control module 48 may include heater controls and temperature sensor (RTD) controls, and is used, for example, to control temperature of the grid at the bottom of the hopper to melt the solid thermoplastic material. The motor control module 50 is used, for example, to control the motor driving the pump which transfers the molten material to the applicators 12 and 14. As indicated in FIG. 2, this can include a pressure control 54, particularly for supplying the pressure fed applicator 12 . The I/O module 52 can be used for discrete data transfer between the system controller 22 and any number of sensors and other control circuits associated with the melter 10 or with the manufacturing facility that employ the applicators. The level control module 53 is used, for example, to monitor the level of the solid thermoplastic material in the supply hopper of the melter, and may provide a signal indicating that the hopper needs to be filed and an alarm indicating that the hopper is almost empty and the system should be shutdown. As illustrated in FIG. 2 , each of the control modules 48, 50, 52 and 53 are connected to the shared network bus 26. The system controller 22 is also linked by the bus 26 to each applicator control module 24 , of which one is shown in FIG. 2 . The control module 24 for an applicator typically will include a temperature control module 56, which could be the same structurally as the melter temperature control module 48 , but need not be. In the case of a control module for a metered applicator, a motor control module 58 is provided to control metered application of the molten thermoplastic material. The hardware and software implementations of the functional boxes in FIG. 2 will depend on the particular application involved, but for convenience can be based on control and sensor circuits known to those skilled in the art and therefore need not be described in detail herein to fully understand and practice the invention. An important aspect in conjunction with the modular design of the applicator control modules 24 is the use of the communications network between each control module 24 and the system controller 22. With reference next to FIG. 3 , another example of the distributed control system 20 is shown including added applicator devices. In this embodiment, a single control module 24 c is connected to control two pressure fed applicators 12 a and 12 b . Furthermore, two control modules 24 d and 24 e are connected to respective metered applicators 14 a and 14 b . The applicator control modules in FIG. 3 can be realized, for example, with the exemplary architecture illustrated in FIG. 2. It will be noted from FIG. 3 that the applicator control modules are linked along the shared network bus 26 back to the system controller 22 which, in this case, is at the melter 10 . The simple communication link between the system controller 22 and each of the applicator control modules 24 makes expansion, upgrading and reconfiguration of the system 20 highly flexible and convenient. Applicators can be added within the capability of the melter 10 hydraulic system architecture, rather than being limited as in the prior art by system power constraints at the melter or controller limitations such as, for example, the number of available control channels. Furthermore, reconfiguration is greatly simplified compared to prior systems. For example, if an application is to be changed from a pressure fed applicator to a metered applicator, the melter control section need not be reconfigured. The pressure fed control module is simply replaced with a metered applicator control module, and all configuration data and control instructions can be input by the operator into the system controller 20 and communicated to the application site along the network bus 26 . As shown in FIG. 3 , the applicators are connected to the melter 10 via the supply and return hoses 4a and 4 b. In the example shown, a jumper hose 8 connects the return port of the first metered applicator 14 b to the input port of the second metered applicator 14 a . Although not used in the embodiment shown here, this daisy chain configuration of the hydraulic architecture can also be used with the pressure fed applicators 12 a and 12 b if so desired. Note that in FIG. 3, functional modular blocks are included for each control module which correspond to the functional blocks previously described herein with respect to FIG. 2 . Thus, Smart Box A in FIG. 3 is a control module for a pressure fed applicator, and includes the temperature control module 48 . Smart Box 2 and Smart Box 3 are for metered applicators and thus include the temperature control module 56 and the motor control module 58. Also shown in FIG. 3 are some of the various sensor readings taken at the melter and applicators, which data can be transmitted back to the system controller 22 on the shared bus 26. These sensors can include, for example, material temperature sensors (in the example of FIG. 3 , the molten material is an adhesive applied to disposable diapers and hence abbreviated "adh."), heated pattern air temperature in the applicator, motor control signals for the metered applicators and so on. Further note that the melter control box 44 ("Box D") for the melter 10 is also indicated with the included functional circuits as described with reference to FIG. 2 herein. With reference next to FIG. 4 , use of the distributed control system 20 facilitates organization and control of an entire distributed application system. FIG. 4 illustrates the logical relationships for the various control aspects of an exemplary distributed system. In this embodiment, a high level host system 70 , such as an industrial personal computer or PLC, is used to interconnect, control, monitor or otherwise interface with a number of melter systems, in this case three such systems. The system 70 can be located, for example, apart from the main production area where the melters and applicators are utilized. The system 70 can provide a centralized display to provide information on all the melter systems. Each melter system 72 can include a single enclosure for a plurality of tank groups 74. Each tank group 74 comprises the main melting section and may consist, for example, of a hopper, grid and reservoir. A dual tank group may consist of a single hopper, two grids and two reservoirs, for example, with each reservoir feeding two hydraulic groups 76 . In the discussion herein with regard to FIG. 4 , it will be appreciated that the particular arrangements are exemplary in nature, and in practice will be selected based on the particular application needed by the designer. Each hydraulic group 76 includes a melter manifold and the associated devices for supplying molten material for each application 78 connected to the system. These devices may include, for example, a motor, pump, manifold, hoses and the applicators. The logical relationships illustrated in FIG. 4 can be repeated as needed. FIG. 5 illustrates in functional block form a more detailed summary of the actual physical devices that make up a typical distributed system such as shown in FIG. 4 . This detail is shown for one of the melter systems 72. As shown, the melter 72 includes the melter electrical (control) box 44 with the previously described control modules and functions including the circuits 48, 50 and 52 . Also shown is a control module 62 corresponding to the control module 53 , for control of the level of the material in the melter hopper. The shared bus 26 of the network provides a communication link between the system controller 22 and each of the control modules 24 associated with the applicators 12 and 14. The logical arrangement of the various system groups are included in FIG. 5 , showing a single tank group 74 (including the associated hopper temperature, grid temperature, reservoir temperature and level control sensor data) for a first hydraulic group 76 a and a second hydraulic group 76 b . The first hydraulic group 76 a includes a manifold assembly including various monitoring and control functions for the manifold temperature, motor, pump and pressure. These manifold controls are directly connected to the melter box 44 since they are physically within the melter 72 enclosure. A supply hose 4a feeds the molten material to a first metered applicator 14 a , daisy chained by a jumper hose 8 to a second metered applicator 14 b , and connected back to the manifold by a return hose 4b. The associated control module 24 a controls the first metered applicator 14 a and a second control module 24 b controls the second metered applicator 14 b , both control modules operating based on instructions and data exchanged with the system controller 22 along the shared bus 26. The second hydraulic group 76 b similarly includes a manifold assembly 82 which feeds two pressure fed applicators 12 a and 12 b , both of which are controlled via a third control module 24 c also connected to the shared bus 26. Thus, from FIG. 5 it is apparent that the distributed power and control system for the application system, including the use of the communications network for electronic access to the distributed control module, greatly enhances the ability to expand the system and reconfigure the distributed applicators that can be remote from the melter 70 , with substantially reduced impact on having to reconfigure or modify the melter itself. With reference next to FIGS. 6 A- 6 D, the distributed system 20 described herein is particularly well suited for use with commercially available operating systems, such as a WINDOWS graphical user interface. FIG. 6 A shows a typical tank configuration window in which the system controller 22 allows the operator to select the tank configuration. In the example of FIGS. 6 A- 6 D, the specific application is for applying adhesive to disposable diapers, so that the operator can simply enter tank name 82 , select the pump configuration, and name them. In FIG. 6 C the operator can select the applicator configuration and name specific hoses and applicators associated with each pump. In the example of FIG. 6 C, the waist/cuff pump and applicators are being configured. In FIG. 6 D, the configuration process is completed by assigning individual control channels to specific hoses and applicators. The example given is for a cuff elastic applicator connected to the waist/cuff pump (configured in FIG. 6 B). The effect of a control system as configured using a graphical user interface, such as the examples of FIGS. 6 A- 6 D, is to provide a true logical to physical mapping which substantially simplifies the overall system complexity presented to an operator by the system controller. First, application specific grouping of independent control channels allows the channels to be collectively controlled for simplified operation. Second, the operator can easily view both the physical device and the logical names to facilitate service on the system. Other variations and modifications of the specific embodiments herein shown and described will be apparent to those skilled in the art, all within the intended spirit and scope of the invention. While the invention has been shown and described with respect to particular embodiments thereof, these are for the purpose of illustration rather than limitation. Accordingly, the patent is not to be limited in scope and effect to the specific embodiments herein shown and described nor in any other way that is inconsistent with the extent to which the progress in the art has been advanced by the invention.

Claims: A distributed system for controlling application of molten thermoplastic material comprising: at least one applicator for applying the material; and a melter (10) for supplying molten material to set at least one applicator (12, 14); characterized by a system controller (22) including a network for transmitting information between said controller (22) and a plurality of distributed control modules (24) along a shared bus (26); said melter (10) including a plurality of melter control modules (48, 50, 52, 53) for controlling delivery of the material to said at least one applicator (12, 14), with each of said melter control modules (48, 50, 52, 53) being coupled to said network; said applicator (12, 14) comprising at least one applicator control module (24), said applicator control module (24) being coupled to said network; wherein said system controller (22) transmits instructions to a selectable number of said control modules (24, 48, 50, 52, 53) across said network based on a selectable application of the material, and receives across said network information from each control module (24, 48, 50, 52, 53) used in the selected application. The system of claim 1, wherein said melter (10) controls temperature, pressure and delivery of molten material from the melter (10) to a first plurality of said applicators (12, 14) based on instructions received from said system controller (22) to said melter control modules (48, 50, 52, 53), and wherein each of said first plurality of applicators (12, 14) controls temperature and delivery of the material based on instructions received from said system controller (22) to said applicator control modules (24). The system of claim 2, wherein said melter (10) comprises a first manifold assembly (80) for distributing the material to said first plurality of applicators (14), wherein said system controller (22) logically groups and independently controls said first plurality of applicators (14) and said first manifold assembly (80) as a hydraulic group (76). The system of claim 3, wherein said system controller (22) logically controls a tank group (74) that supplies material to said first hydraulic group (76a) and a second hydraulic group (76b), said second hydraulic group (76b) comprising a second manifold assembly (82) in said melter (10) for distributing the material to a second plurality of applicators (12). The system of claim 4, wherein said system controller (22) logically controls a plurality of said melters (10), each of said plurality of said melters (10) comprising at least one tank group (74) and at least one hydraulic group (76) having a plurality of applicators (12, 14). The system of claim 2, wherein each of said plurality of applicators (12, 14) are selected from the group comprising pressure fed applicator (12) and metered applicator (14). The system of claim 2, wherein said plurality of applicators (12, 14) comprises a plurality of metered applicators (14) hydraulically connected in a daisychain configuration and at least one pressure fed applicator (12). The system of claim 1, wherein said applicator control modules (24) are contained in an applicator control box (A, B, C) at their associated applicator (12, 14), the system further comprising a distributed power system whereby each applicator control box (A, B, C) receives system power (28) for operating its associated applicator (12, 14). The system of claim 1, wherein said system controller (22) comprises control software (42) that receives input instructions from an operator to configure said melter (10) and said applicator (12, 14) for a selected application (78), and further to group and name logical control functions together for the selected application (78), allowing collective control of independent devices. The system of claim 9, wherein said control software (42) comprises a graphical user interface program for inputting configuration and logical grouping data to said system controller (22).

Inventors: CRAWFORD KAREN J, LYNCH MICHAEL S, MEANS SCOTT B, CRAWFORD, KAREN J., LYNCH, MICHAEL S., MEANS, SCOTT B.
Applicants: NORDSON CORP, NORDSON CORPORATION
Application year: 1996
Main classification: G05B19
IPC codes: B05C11, G05B19, B29B13