Adaptive hot melt feed

An adaptive hot melt feed system includes a melt system, a feed system, a gas control device, a sensor, and a controller. The melt system includes a heated vessel. The feed system is configured to deliver a solid material to the vessel of the melt system for melting. The gas control device is configured to control a supply of gas provided to the feed system to drive the solid material from the feed system to the melt system. The sensor can be configured to detect an amount of material in the vessel of the melt system. The controller is in electronic communication with the gas control device and is programmed to signal the gas control device to vary the supply of gas to the feed system based on a fill metric determined by the controller.

FIELD OF INVENTION

The present invention relates generally to hot melt feed and dispenser systems and more particularly to an adaptive hot melt feed system.

BACKGROUND

Hot melt systems are commonly used in manufacturing assembly lines to apply an adhesive for the construction or closure of packaging materials, such as boxes, cartons, and the like. Conventional hot melt dispensing systems can include a material feed system and a hot melt dispenser system. The material feed system can deliver hot melt adhesive pellets to the hot melt dispenser system, which, in turn, heats and melts the adhesive pellets to produce a liquid adhesive. When a volume of melt material in the hot melt dispenser system reaches a minimum value, additional adhesive pellets can be delivered from the feed system to the hot melt dispenser system. In some systems, compressed gas can be used to drive the adhesive pellets from the feed system to the hot melt dispenser system using a venturi vacuum. The amount of adhesive pellets and the time required to deliver the adhesive pellets to the hot melt system can be critical for ensuring proper operation. For instance, a long delivery time can reduce the dwell time of the adhesive pellets in the hot melt system, which can prevent the adhesive pellets from reaching a melting temperature before being dispensed. Conversely, too much material delivered too fast can cause the melt chamber to overflow. In conventional hot melt systems, the pellet flow rate is controlled by an operator performing various calibration actions such as adjusting the pressure of the compressed gas to the venturi vacuum. This can typically take several fill cycles and guesswork to optimize. Once optimized, the operator must continue to monitor adhesive pellet delivery and adjust gas pressure to the venturi vacuum as multiple factors, including clogged air filters, low feed supply, and high ambient temperature or humidity, can cause a change in the adhesive pellet flow.

SUMMARY

An adaptive hot melt feed system includes a melt system, a feed system, a gas control device, a sensor, and a controller. The melt system includes a heated vessel. The feed system is configured to deliver a solid material to the vessel of the melt system for melting. The gas control device is configured to control a supply of gas provided to the feed system to drive the solid material from the feed system to the melt system. The sensor can be configured to detect an amount of material in the vessel of the melt system. The controller is in electronic communication with the gas control device and is programmed to signal the gas control device to vary the supply of gas to the feed system based on a fill metric determined by the controller.

A method of supplying a solid hot melt material to a melt system includes supplying a gas to a feed system to drive the solid material to the melt system, determining fill metrics, and signaling a gas control device to increase, decrease, or maintain the gas supplied to the feed system. Fill metrics are automatically determined by a controller, which signals the gas control device.

While the above-identified figures set forth embodiments of the present invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the invention. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features, steps and/or components not specifically shown in the drawings.

DETAILED DESCRIPTION

The present invention is directed to an adaptive hot melt feed system that can automatically adjust a flow rate of solid hot melt material (e.g., adhesive pellets) from a feed system to a melt system for melting. The hot melt feed system can adapt to changing conditions (e.g., air supply, volume of feed material in a hopper, size of feed material, clumping of material due to increased temperature or humidity, etc.) that increase or decrease the flow of solid hot melt material from the feed system to the melt system. In this manner, the adaptive hot melt feed system can continuously optimize the time it takes to deliver the solid hot melt material to the melt system to ensure the solid hot melt material has a sufficient dwell time in the melt system to allow the solid material to melt prior to being dispensed. Prior art methods required an operator to routinely monitor the delivery of the solid hot melt material and optimize flow the solid hot material by manually increasing or decreasing a pressure of compressed gas supplied to a venturi vacuum used to drive the solid hot melt material to the melt system. The present invention automatically adapts to changing conditions and removes the need for a manually operated gas pressure regulator and operator calibration.

FIG. 1is a schematic view of one embodiment of adaptive hot melt feed system10. Adaptive hot melt feed system10includes feed system12, melt system14, gas control device16, and controller18. Feed system12is configured to deliver solid hot melt material20from solid material vessel22to melt system14. Feed system12includes venturi vacuum24connected to feed line26for delivering solid hot melt material20to melt system14. Compressed gas28is delivered to feed system12to drive venturi vacuum24. A supply of compressed gas28is controlled by gas control device16. Solid hot melt material20is delivered to melt system14for melting and dispensing. Melt system14includes melt vessel30for heating hot melt material20and pump32for dispensing melted hot melt material20. One or more sensors34a,34bcan be used to provide fill metrics data36to controller18, which can include a duration of the feed interval and/or an amount of solid hot melt material20delivered in a feed interval or an amount of melted hot melt material20dispensed between feed intervals. Fill metric data36can be collected during each fill cycle and sent to controller18. Based on fill metric data36, controller18can cause gas control device16to adjust the supply of compressed gas28delivered to feed system12in the next fill cycle to increase or decrease the duration of the feed interval (i.e., the time it takes to deliver solid hot melt material20to melt system14) and the power level at which the feed system operates.

Feed system12can be configured to deliver solid hot melt material20to melt system14. Solid hot melt material20may be an adhesive material, including, for example, a thermoplastic polymer glue such as ethylene vinyl acetate (EVA) or metallocene, or other adhesive material as known in the art. Solid hot melt material20can be in the form of pellets of varying size and shape. The terms “solid hot melt material” and “solid material” are used interchangeably hereinafter to clearly distinguish the solid hot melt material from melted hot melt material dispensed from melt system14. Likewise, the terms “melted hot melt material” and “melted material” are used interchangeably. Solid material20and melted material20are the same material in different forms (solid and liquid). Hot melt material20can exist in both solid and liquid form in melt system14and is, therefore, simply referred to as “hot melt material20” when present in both forms.

Feed system12can be connected to solid material vessel22. Solid material vessel22can be a cylindrical drum or bucket, hopper, or other suitable structure for containing a quantity of solid material20. In some embodiments, solid material vessel22can include a mechanical agitator or other mechanism (e.g., compressed gas supply) for breaking up clumps of solid material20and/or assisting with delivery of solid material20into venturi vacuum24. Venturi vacuum24can be positioned in solid material vessel22or at an outlet of solid material vessel22. Venturi vacuum24can be positioned in a lower portion of solid material vessel22such that a flow of solid material20into venturi vacuum can be gravity-assisted. It will be understood by one of ordinary skill in the art that the structure of solid material vessel22and positioning of venturi vacuum24can be varied according to the application and that the present invention is not limited to the configuration disclosed.

Compressed gas28can be delivered from compressed gas source38to venturi vacuum24to create a vacuum, which can induce a flow of solid material20from solid material vessel22, through feed line26, and into melt system14. Compressed gas source38can be compressed air or other gas suitable for the application delivered through a conduit suitable for transporting compressed gas. Feed line26can be a hose or passage having a diameter substantially larger than a diameter of solid material20to allow solid material20to freely flow through feed line26. Feed line26can be of varying length depending on operator setup. Generally, a melt system configuration can have a feed line between 2 meters and 20 meters long, although lengths outside of this range are possible. The length of feed line26is generally limited by the capability of venturi vacuum24as driven by gas source38. If feed line26is too long, venturi vacuum24may not be able to induce flow of solid material20through the full length of feed line26to melt system14. Feed line26can connect to venturi vacuum24at one end and melt system14at an opposite end. Generally, feed line26can be oriented with respect to melt system14in a manner that allows gravity to partially drive the flow of solid material20, without allowing a large quantity of solid material20to enter melt system14after venturi vacuum has stopped flow. As will be discussed further, supply of compressed gas28to venturi vacuum24can be shut off when a volume of hot melt material20in melt system14has reached a pre-defined fill capacity level. If a significant length of feed line26extends generally downward into melt system14, solid material20that has entered feed line26before venturi vacuum24has been shut off, but is located in the downward extending portion of feed line26, can enter melt system14, causing the volume of hot melt material20in melt system14to exceed the fill capacity level. To avoid over-filling of melt vessel30, feed line26can be oriented to allow at least some solid material20to remain in feed line26after gas supply to venturi vacuum24has been shut off.

Melt system14can include melt vessel30and one or more heating elements (not shown) for melting solid material20to form melted (liquid) material20. Melt system14can also include pump32and a dispenser (not shown) for dispensing melted material20from melt system14. Melt system14can be sized to hold a relatively small total material20volume (e.g., 0.5 liters) and can be configured to melt solid material20in a relatively short period of time (e.g., in continuous operation, the comparatively small volume of new solid material20added per fill may be melted and heated in a matter of seconds). Solid material20can be dispensed from feed line26into an inlet at the top of melt vessel30, such that solid material20forms a surface layer of hot melt material20in melt vessel30. In some embodiments, melt system14can include an air filter to remove dust and other particulates present with solid material20in feed line26. Pump32can be configured to pump melted hot melt material20from melt vessel30to the dispenser (not shown) configured to selectively discharge melted material20. Pump32can be a reciprocating pump in which a piston or plunger displaces a known volume of material, or can be any other type of positive displacement pump as known in the art.

Melt system14can be equipped with one or more sensors34aconfigured to detect a volume level or height of hot melt material20present in melt vessel30. Sensor34acan be an ultrasonic sensor or other sensor (e.g., capacitive sensor, float sensor, etc.), as known in the art, suitable for detecting a height within melt vessel30to which hot melt material20extends (e.g., along an inner wall of melt vessel30or at a highest surface point of hot melt material20). Sensor34acan be configured to signal controller18when the level of hot melt material has reached a minimum height, indicating a need to resupply melt system14with solid material20, and when the level of hot melt material has reached a maximum height, indicating a need to cease supply of solid material20so as to not exceed the capacity of melt vessel30. The minimum and maximum values can be set based on the volume of melt vessel30, the time required for melting solid material20, and a discharge rate of melted hot melt material20from melt system14. Controller18can be programmed to adjust the minimum value based on the dispensing rate. For example, during continuous use, the minimum level can be adjusted upward such that, the time between feed intervals may be significantly reduced. Due to the relatively small volume of melt system melt vessel30, it is necessary that solid material20be delivered to melt system14in a time period of sufficiently short duration to ensure solid material20can be melted prior to being dispensed. The flow rate of solid material20from feed system12to melt system14can be adjusted by varying the supply of compressed gas28to venturi vacuum24using gas control device16.

Gas control device16is located between compressed gas source38and feed system12. Gas control device16can be located within hot melt system14, on feed system12, or elsewhere. In one embodiment, gas control device16can be a voltage to pressure (V to P) or current to pressure (A to P) electronic pressure regulator, in which the pressure of compressed gas28can be increased or decreased to increase or decrease, respectively, a velocity of solid material20through feed line26. In an alternative embodiment, gas control device can be a solenoid, which can deliver compressed gas28to venturi vacuum24as a pulsed or pulse width modulated gas flow at a constant pressure to obtain a desired flow of solid material20. A duration or width of pulses can be increased or decreased to increase or decrease, respectively, the velocity of solid material20through feed line26. If a gas pressure supplied by operator-supplied compressed gas source38is too high, a duty cycle (proportion of time gas is on during a feed interval) can be decreased (e.g., pulse width decreased). If gas pressure is near a lower limit for optimal transfer of solid material20, the duty cycle may need to be maximized such that the duration of time the gas is off is negligible (e.g., pulse width maximized). In such case, solenoid gas control device16functions similarly to a constant flow regulator. In both embodiments, gas control device16can be adjusted by controller18without operator input.

Controller18can be a processor capable of receiving, transmitting, and processing data. Controller18can include display40to provide the operator with fill metrics36provided by melt system14(e.g., sensors34a,34b) and/or determined by controller18for each fill cycle. As used herein, a “fill cycle” encompasses a period of time beginning with the supply of gas28to venturi vacuum24to fill melt system melt vessel30and ending with the next time sensor34asignals controller18to refill melt vessel30. Controller18can determine a duration of time it takes to fill melt system14with solid material20during a feed interval. As used herein, “feed interval” refers to the time from which the supply of gas28to venturi vacuum is turned on to the time the fill capacity level is detected and the supply of gas28to venturi vacuum is turned off. In some embodiments, sensor34acan provide controller18with information needed to determine the amount of solid material20delivered to melt system14during a feed interval. Additional sensors34b, such as a piston position sensor, can provide controller18with information needed to determine an amount of melted material20dispensed by melt system14between feed intervals. As used herein, the duration between feed intervals refers to the time from when controller18is signaled to stop filling melt vessel30to the time controller18is signaled to refill melt vessel30or the time from when the supply of gas28to venturi vacuum is turned off to cease the supply of solid material20to the time the supply of gas28to venturi vacuum is turned on to refill melt system14. Controller18can signal gas control device to increase, decrease, or maintain the supply of gas28(i.e., increase/decrease gas pressure or duty cycle) to feed system12within the present feed interval or during the next feed interval to optimize feed performance. All data, including feed interval duration, duty cycle and/or gas pressure, and amount of solid material20delivered and/or melted material20dispensed can be collected and/or determined by controller18and is collectively referred to herein as fill metrics or fill metric data36.

FIG. 2shows a method100of supplying solid material20to hot melt system14. In step102, compressed gas28is supplied to feed system12via compressed gas source38and gas control device16to operate venturi vacuum24. In step104, solid material20is delivered to melt system14in a feed interval. As previously discussed, sensor34acan be used to determine when a volume of hot melt material20in melt vessel30reaches the preset minimum level. This event can be transmitted to controller18, which can then signal gas control device16to supply gas28to feed system12. The same or additional sensor34acan detect when enough solid material20has been delivered to melt vessel30of melt system14to reach the preset maximum fill level. This event can be transmitted to controller18, which can then signal gas control device16to cease the supply of gas28to feed system12. Any solid material20remaining in feed line26at the time gas28is shut off can remain in feed line26, can be gravity-fed back to feed system12, or can be gravity-fed or delivered by momentum to melt system14, depending on the orientation of feed line26and velocity of solid material20. Any solid material20that is delivered to melt system14after gas28has been shut off (after melt vessel30has reached the maximum fill level) contributes to the amount of solid material20delivered to melt system14during that feed interval.

In steps106and108, controller18can determine a cumulative duration of a current feed interval in progress (i.e., how long it is taking to fill melt vessel30) and signal gas control device16to increase or maintain the supply of gas28to feed system12. If the cumulative duration is exceeding a maximum value (delivery is taking too long), controller18can signal gas control device16to increase gas pressure to feed system12or increase the duty cycle (i.e., amount of time gas flow is on in a pulse width modulated gas flow) to increase the velocity of solid material20through feed line26and thereby increase the feed rate. Increasing the velocity and feed rate of solid material20reduces the feed interval duration.

After a fill is complete, controller18determines, in step110, the duration of the feed interval as defined from time at which gas28is supplied to feed system12to operate venturi vacuum to the time at which enough solid material20has been delivered to melt system14to reach a maximum fill level and the supply of gas28to feed system12has been shut off. An optimal feed interval for the disclosed embodiments having a 0.5 liter melt volume can be around five seconds; however, it will be understood by one of ordinary skill in the art that the feed interval duration can vary depending on the size of melt vessel30, time it takes to melt solid material20, and a discharge rate of melted material20from melt system14. Although the efficiency of hot melt system10can be improved by delivering solid material20in discrete feed intervals, in alternative embodiments, system10may be configured to provide a continuous feed of solid material20, in which case, a small amount of solid material20is continuously delivered to melt system14with a feed rate being continuously optimized by controller18based on fill metrics36.

In step112, controller18determines the amount of solid material20delivered to melt system14during the feed interval. The amount of solid material20delivered to melt system14can be determined by measuring a change in volume or level of hot melt material20(including both solid and melted material20) in melt vessel30. Alternatively, the amount of solid material20delivered can be calculated based on a number of piston strokes made to discharge melted material20between feed intervals. Although one or both methods can be used, the combination of the two provides greater accuracy. Level measurements can over- or under-quantify the amount of solid material20delivered depending on how solid material20enters melt vessel30and when and where measurements are taken. While some solid material20will sink into melted material20already in melt vessel30, some may collect in solid form at the surface of the melted material20. In this case, sensor34amay detect a maximum fill level as indicated by the level of solid material20, but the level of material in melt vessel30will decrease, independent of dispensing, as solid material20melts and air gaps between pellets of solid material20are removed. In some cases, solid material20can form a mound on the top center of the hot melt material in melt vessel30, which will cause a variation in the level across the surface of hot melt material20and which can affect readings of sensor34a. Additionally, some solid material20may enter melt vessel30after the maximum level has been detected and may not be included in the measurement depending on when the measurement is made. In contrast to melt vessel30, a cylinder of pump32contains a known volume of melted material20, which can be dispensed from melt system14. As melted material20is dispensed, the level of hot melt material20in melt vessel30goes down until reaching the present minimum level, at which point, a new feed interval begins. The number of piston strokes (number of times the cylinder has been emptied) and/or partial piston strokes from the end of one feed interval to the beginning of the next feed interval can be used to calculate the total volume of hot melt material20delivered to melt system14. In this case, overfilling or underfilling of melt vessel30is less likely to impact the accuracy of the measurement as both are accounted for in the measurement. In the disclosed embodiments, an optimal amount of solid material20delivered to melt system14can equate to about 100 milliliters of melted hot melt material20although this value can vary depending on use.

Several variables can affect the delivery of solid material20. For example, a restricted air filter on melt system14, an excessively long feed line26, a long upward vertical extension of feed line26, a low volume of solid material in container20, and clumping of solid material20due to increased temperature or humidity can slow the feed rate of solid material20. In contrast, an excessively short feed line26or long downward vertical extension of feed line26can increase the feed rate of solid material20. A long duration feed interval can reduce the dwell time or amount of time solid material20has to melt in melt vessel30before being dispensed. A short duration feed interval can increase the potential for overfilling as a high velocity of solid material20typically associated with a short duration feed interval can cause additional solid material20to be delivered to melt system14after supply of gas28has been shut off. Based on the determined feed interval duration and amount of solid material20delivered in the feed interval, controller18can determine if the duration of the feed interval needs to be increased, decreased, or maintained to ensure optimal dwell time and complete melting of solid material20. In step114, controller18can signal gas control device16to increase, decrease, or maintain the supply of gas28to feed system12. Controller18can signal gas control device16to increase gas pressure to feed system12or increase the duty cycle (i.e., amount of time gas flow is on in a pulse width modulated gas flow) to increase the velocity of solid material20through feed line26and thereby increase the feed rate. Increasing the velocity and feed rate of solid material20reduces the feed interval duration. Controller18can signal gas control device16to decrease gas pressure to feed system12or reduce the duty cycle to reduce the velocity of solid material20through feed line26and thereby reduce the feed rate. Reducing the velocity and feed rate of solid material20increases the feed interval duration.

Steps102through114are repeated for each fill cycle. Controller18can use fill metrics36from previous fill cycles to adaptively determine how to proceed with future fill cycles. Generally, controller18can be programmed to make gradual adjustments to gas supply28such that optimization occurs over several fill cycles instead of a single fill cycle. The gradual optimization can reduce the impact single, outlying, events can have on optimization. For example, if the operator, for any reason, manually increases the pressure of gas supply28for one fill cycle to an undesirable level, and thereby undesirably reduces the feed interval duration, controller18will only moderately adjust the supply of gas28during the next fill cycle based on the detected reduced feed interval duration. If the feed interval duration continues to be undesirably fast, controller18can make further and potentially greater adjustment to the supply of gas28in the following fill cycle. If, alternatively, the operator has manually reduced the pressure of the supply of gas28, the gradual adjustment made by controller18prevents overcompensation. In this case, gradual adjustment prevents increasing the supply of gas28to a level that results in over-filling melt melt vessel30.

All fill metrics data36, including feed interval duration, duty cycle and/or gas pressure, and amount of solid material20delivered and/or piston strokes between feed intervals can be provided to the operator in display40. Additionally, controller18can provide alerts to the operator through display40when the algorithm used to optimize fill metrics36indicates a need for operator action. For instance, controller18may be unable to optimize the feed of solid material20if feed line26, pump32, or the air filter in melt system14is clogged or if solid material vessel22is nearing empty, etc. In such cases, the operator may need to fix the problem preventing optimization before adaptive hot melt feed system10can be effectively operated. Such problems are not unique to adaptive hot melt feed system10, but can be mitigated by the continuous display of fill metrics data36and alerts provided by controller18.

Adaptive hot melt feed system10can largely eliminate the need for operator intervention in fill optimization. Because controller18can determine fill metrics36for each fill cycle and adapt to changing variables that affect the delivery of solid material20to melt system14, it is not necessary for the operator to monitor delivery of solid material20and manually adjust the supply of gas28to feed system12. No manual calibration or calculation is required to operate adaptive hot melt feed system10.

SUMMATION

Any relative terms or terms of degree used herein, such as “substantially”, “essentially”, “generally”, “approximately” and the like, should be interpreted in accordance with and subject to any applicable definitions or limits expressly stated herein. In all instances, any relative terms or terms of degree used herein should be interpreted to broadly encompass any relevant disclosed embodiments as well as such ranges or variations as would be understood by a person of ordinary skill in the art in view of the entirety of the present disclosure, such as to encompass ordinary manufacturing tolerance variations, incidental alignment variations, transient alignment or shape variations induced by thermal, rotational or vibrational operational conditions, and the like. Moreover, any relative terms or terms of degree used herein should be interpreted to encompass a range that expressly includes the designated quality, characteristic, parameter or value, without variation, as if no qualifying relative term or term of degree were utilized in the given disclosure or recitation.