Liquid dispensing module

A liquid dispensing module includes a dispenser body assembly, a flexible seal, a needle, and an actuator. The dispenser body assembly includes a liquid inlet, a discharge outlet, and a flow channel including a valve seat between the inlet and outlet. The flexible seal engages the dispenser body assembly and includes a downstream end. The needle includes an enlarged portion engaging and retaining the downstream end of the flexible seal to place the flexible seal in lengthwise compression between the enlarged portion and the dispenser body assembly. The needle also includes a valve element that moves between open and closed positions. The flexible seal prevents liquid from leaking out of the flow channel.

FIELD OF THE INVENTION

This invention generally relates to liquid dispensing devices used for a variety of purposes, but particularly for dispensing viscous liquids such as hot melt adhesives.

BACKGROUND OF THE INVENTION

A typical dispensing device for supplying liquid, such as hot melt adhesive, generally includes a body including a needle having a valve element that opens and closes a dispensing orifice. The needle is usually actuated in at least one direction by pressurized air to dispense discrete amounts of pressurized liquid. A spring mechanism and/or pressurized air is used to move the valve element in an opposite direction against a valve seat, which stops the flow of liquid from the dispensing orifice.

More specifically, liquid dispensing modules include a flow channel adjacent the dispensing orifice and an actuator chamber at an opposite end of the device. The actuator chamber contains a portion of the needle which is typically connected with a piston member and which may also be connected with a spring return mechanism as discussed above. Under air pressure applied on one side of the piston member sufficient to overcome the spring return mechanism, the valve element on the needle is moved in a direction away from the valve seat to discharge liquid. When the air pressure is removed, the spring return mechanism will automatically actuate the needle towards a closed position where the valve element engages the valve seat.

A dynamic seal is typically placed generally between the dispenser body and the moving needle to prevent liquid from the flow channel from leaking into the actuator chamber. Dynamic seals are understood to be seals between two surfaces that move relative to one another. These dynamic seals may press tightly against the needle and cause friction and seal wear. The higher friction may place greater demands on the requirements for pressurized air to move the needle. Even with reduced friction, the dynamic seal will wear over time and lose its ability to seal properly. This inadequate sealing will allow the liquid to enter the actuator chamber to bind the piston and will also allow pressurized air to enter into the flow channel, causing undesired dispensing discontinuities.

One alternative to a dynamic seal is a flexible bellows seal as described in U.S. Patent Application Publication No. 2006/0097015 to Riney. The flexible seal includes one end coupled to the needle and another end coupled to the dispenser body. The ends of the flexible seal can move relative to each other such that there is no frictional engagement between the seal and either of the needle and the dispenser body. It would be desirable to provide a liquid dispensing module that improves on the flexible bellows seal and further addresses the problems with using dynamic seals in a flow channel.

SUMMARY OF THE INVENTION

In one illustrative embodiment, a liquid dispensing module includes a dispenser body assembly, a needle, a flexible seal, and an actuator. The dispenser body assembly includes a liquid inlet, a discharge outlet, and a flow channel that directs a flow of liquid from the liquid inlet to the discharge outlet. The flow channel includes a valve seat between the liquid inlet and the discharge outlet. The flexible seal includes an upstream end sealingly engaging the dispenser body assembly and includes a downstream end. The flexible seal is adapted to seal the flow channel from the actuator. The needle includes a valve element adapted for reciprocating movement in the dispenser body assembly between an open position where the valve element is disengaged from the valve seat and a closed position where the valve element is engaged with the valve seat. Liquid flow through the discharge outlet is allowed in the open position and prevented in the closed position. The needle also includes an enlarged portion engaging and retaining the downstream end of the flexible seal to place the flexible seal in lengthwise compression to promote the sealing function. The downstream end is adapted to move with the needle. The actuator reciprocates the needle between the open and closed positions to selectively dispense liquid from the discharge outlet.

In some embodiments of the liquid dispensing module, the upstream end of the seal is engaged and retained by a recess having a transverse surface formed in the dispenser body assembly to place the flexible seal into lengthwise compression. In the illustrative embodiments, this recess is in a needle guide. The flexible seal may include a central portion between the upstream and downstream ends and flared away from the needle to define an interior cavity. The interior cavity may be pressurized with air from the actuator chamber to prevent the central portion from collapsing onto the needle. The dispenser body assembly can further or alternatively include a needle guide adjustably positioned within the dispenser body assembly to preload the flexible seal with lengthwise compression.

In some embodiments of the liquid dispensing module, the liquid dispensing module includes at least one of an annular groove or an annular recess. In a liquid dispensing module with an annular groove, the annular groove is formed in the enlarged portion of the needle and receives and retains the downstream end of the flexible seal to facilitate placing the seal in lengthwise compression. In a liquid dispensing module with an annular recess, the annular recess is formed in the dispenser body assembly and, more preferably, in the needle guide, and the recess receives and retains the upstream end of the flexible seal to facilitate placing the seal in lengthwise compression. The annular groove or annular recess can include a converging portion. The upstream or downstream end of the flexible seal is wedged into the converging portion to further promote sealing of the flow channel relative to the air actuator portion of the module.

In another aspect, assemblies are provided for use in a liquid dispensing module including the needle guide, needle and seal with any one or more of the features discussed herein.

DETAILED DESCRIPTION

With reference toFIG. 1, one embodiment of a liquid dispensing module10is illustrated. The exterior appearance of the dispensing module10includes a dispenser body assembly12, a dispensing nozzle14from which adhesive or other liquid is dispensed, and fasteners16such as bolts for connecting the dispensing module10to a gun manifold, or body (not shown).FIGS. 2 and 3provide a sectional view of the dispensing module10and more clearly shows the internal components of or within the dispenser body assembly12that operate to dispense liquid from the dispensing nozzle14in a controlled manner.

As shown in the illustrative embodiment ofFIGS. 2 and 3, the dispenser body assembly12has a liquid inlet18in the dispenser body assembly12, a discharge outlet20in the dispensing nozzle14, and a flow channel22between the liquid inlet18and the discharge outlet20capable of directing a flow of the liquid. The liquid inlet18includes an inlet seal19disposed around the liquid inlet18in the dispenser body assembly12. The dispensing module10further includes a nozzle cap21coupling the dispensing nozzle14with the dispenser body assembly12. The nozzle cap21defines a portion of the flow channel22and includes a static seal23such as an O-ring between the nozzle cap21and the dispenser body assembly12. The flow channel22includes a valve seat24adjacent to the discharge outlet20. The dispensing module10further includes a needle28, a needle guide30, and a flexible seal32.

The needle28is positioned within the dispenser body assembly12and undergoes reciprocating motion. The needle28includes a valve element34that cooperates with valve seat24to selectively dispense liquid from module10. While the embodiment ofFIGS. 2 and 3includes a needle tip as the valve element34, alternative forms of valve element34such as a ball are possible and within the scope of this invention. The needle28reciprocates between an open position and a closed position. In the open position, valve element34is disengaged from the valve seat24so that a gap is formed between the valve element34and the valve seat24. This gap allows liquid to be dispensed from discharge outlet20. In the closed position (shown inFIG. 2), valve element34is engaged with the valve seat24so as to prevent any liquid from being dispensed from the discharge outlet20. Movement of the needle28between the open and closed positions therefore controls the dispensing of liquid from module10.

The needle28further includes an enlarged portion36disposed within the flow channel22. The enlarged portion36is adapted to engage and retain one end of the flexible seal32to seal the flow channel22as discussed in detail below. The enlarged portion36may be integrally formed with the needle28or, alternatively, may be separately formed and coupled to the needle28. The enlarged portion36defines a second surface37transverse to the direction of the needle movement. In the embodiment ofFIGS. 2 and 3, the enlarged portion36is a flared portion defining an annular groove38facing away from the discharge outlet20and an opposing fillet radius40. The annular groove38includes the second surface37. In the illustrated embodiment, the annular groove38includes a converging portion41. The converging portion41allows the flexible seal32to be wedged into sealable engagement with the annular groove38. The converging portion41may be defined by a first side42in the non-enlarged portion of the needle28and a second side44in the enlarged portion36. The second side44is inwardly tapered towards the first side42. Alternatively, the first side42could be tapered inwardly in alternative embodiments. The second surface37and the annular groove38are adapted to engage the flexible seal32.

The dispenser body assembly12further includes a needle guide30disposed above the flow channel22. The needle guide30may be mounted with a threadable engagement, by interference fit, or by other known methods of coupling two mechanical elements. As will be discussed further below, threadable engagement of the needle guide can be used to facilitate adjustment in the position of the needle guide resulting in an adjustable, lengthwise compression applied to the seal32. The needle guide30maintains the needle28vertically aligned within the dispenser body assembly12so that, for example, the valve element34and valve seat24properly engage in the closed position. The needle guide30includes a main body portion46having a first end48oriented towards the discharge outlet20and a second end50. The main body portion46has the shape of a cartridge with cylindrical end portions52,54adjacent to the first and second ends48,50, respectively, and a narrow central portion56. The narrow central portion56provides space for the aforementioned bolts or fasteners16to pass through the dispenser body assembly12. The cylindrical portion52adjacent to the first end48includes a static seal58such as an O-ring.

The needle guide30includes an extension portion60projecting below the first end48of the main body portion46. The extension portion60is generally cylindrical and may include a slightly tapered end62as most clearly shown inFIG. 3. The main body portion46and the extension portion60include a needle passageway64having a length and adapted to receive a portion of the needle28. The needle28moves relative to the needle guide30in the needle passageway64as the needle28reciprocates between the open and closed positions. The narrow central portion56may also include a weep hole57in fluid communication with the needle passageway64and another corresponding weep hole59in the dispenser body assembly12. If the liquid in the flow channel22leaks into the needle passageway64, the liquid will seep through the weep holes57,59and out of the front of the liquid dispensing module10. The weep holes57,59allow an operator to know if the flexible seal32has failed.

The dispenser body assembly12further defines a first surface65transverse to the direction of needle movement within an annular recess66. In the illustrated embodiment, the first surface65and the recess66are formed in the needle guide30. The recess66is adapted to engage and retain one end of the flexible seal32to seal the flow channel22as discussed in detail below. The annular recess66includes a converging portion67includes a first side68in the extension portion60of the needle guide30and a second side70. The second side70is inwardly tapered towards the first side68. The first side68could also or alternatively be tapered to assist with wedging the seal32into a sealed condition as will be discussed below. The slightly tapered end62of the extension portion60allows the flexible seal32to readily slide onto the extension portion60and into the annular recess66.

Liquid in the flow channel22is typically under pressure and will undesirably migrate, or leak, out of the flow channel22unless a seal is provided. Thus, the illustrative embodiment of the liquid dispensing module10includes the flexible seal32as shown inFIGS. 2 and 3. The flexible seal32includes an upstream end74, a downstream end76, and a central portion78between the upstream and downstream ends74,76. The central portion78is generally thicker in cross-section than the upstream and downstream ends74,76. The upstream and downstream ends74,76have respective openings80,82, and the flexible seal32includes a passageway84extending between the first and second openings80,82. The passageway84is adapted to allow the needle28and the extension portion60of the needle guide30to be disposed partially within the flexible seal32. The passageway84is configured to have a slightly smaller diameter than the corresponding diameters of the needle28and the extension portion60, thereby forming a frictional or interference fit between the flexible seal32and the needle28and needle guide30. This interference fit helps seal the flow channel22from liquid leaks. The flexible seal32is generally arch-shaped. More specifically, the central portion78of the flexible seal32generally flares radially outward away from the needle28. Accordingly, an annular interior cavity88is formed between the central portion78of the flexible seal32and the needle28. The central portion78may also be described as bulbous, or the flexible seal32may be described as having only one convolution at the central portion78. The flexible seal32has a profile as shown inFIG. 3. The upstream end74includes a generally cylindrical portion85. The downstream end76also includes a generally cylindrical portion87adjacent to the central portion78of the flexible seal32. On the opposite side of the generally cylindrical portion87, the downstream end76includes an angled tapered portion86.

The flexible seal32is mounted within the liquid dispensing module10such that the upstream end74is engaged and retained by the needle guide30and the downstream end76is engaged and retained by the enlarged portion36of the needle28. These engagements of the upstream and downstream ends74,76of the flexible seal32places the flexible seal32into lengthwise compression. The lengthwise compression allows the flexible seal32to effectively seal the flow channel22from liquid leaks past the engagement points of the upstream and downstream ends74,76. The flexible seal32is mounted within the liquid dispensing module10such that the upstream end74engages the first surface65and the downstream end76engages the second surface37.

The upstream end74of the flexible seal32is wedged into the converging portion67between the first and second sides68,70of the annular recess66and is held in position because of the converging portion67. In a similar fashion, the downstream end76of the flexible seal32is wedged into and retained in the annular groove38between the first and second sides42,44and is retained by this converging portion41. Thus, the flexible seal32is placed into lengthwise compression between the annular groove38and the annular recess66. Preferably, this lengthwise compression preload is present when the needle28is in the open and closed position.

Accordingly, the flexible seal32seals the flow channel22from the air actuator section of the module10, as will be discussed further below. As the needle28moves between the open and closed positions, the downstream end76of the flexible seal32moves with the needle28so that there is no relative motion between the flexible seal32and the needle28where these elements are engaged. The flexible seal32is therefore not a dynamic seal in that the needle28does not move against the seal32. Consequently, the flexible seal32of the current embodiment does not suffer from the drawbacks associated with conventional dynamic seals used for reciprocating needles, such as frictional wearing of the seal against the needle.

The pressure of the liquid in the flow channel22acts upon the flexible seal32, but the arch-shape of the flexible seal32transmits the majority of this liquid pressure force onto the upstream and downstream ends74,76to help ensure sealing engagement of the seal ends74,76within the annular recess66and the annular groove38. The transmission of this liquid pressure force onto the upstream and downstream ends74,76also helps prevent the central portion78from collapsing the interior cavity88and from coming into contact with the needle28, which would undermine the benefits of replacing a dynamic seal with the flexible seal32. The liquid dispensing module10may only include one of the annular groove38or the annular recess66for engagement with the flexible seal32in alternative embodiments. In these alternative embodiments, other techniques such as chemical bonding or adhesives can be used to provide sealing engagement of the other seal end74or76. Furthermore, the interference fit between the passageway84of the flexible seal32and each of the needle28and the extension portion60of the needle guide30also ensures the sealing engagement of the flexible seal32with the needle28and the needle guide30.

The flexible seal32may be formed from any of a variety of available elastomeric materials or rubbers, such as, for example, the fluoroelastomer marketed as Viton®. When the elastomeric material forming the seal is Viton®, the elastomeric material may have a hardness or durometer in the range of 40-90. In the exemplary embodiment illustrated, the elastomeric material has a durometer of about 65. This durometer is high enough to provide resistance to hydraulic pressure in the flow channel22and prevent the central portion78of the flexible seal32from collapsing onto the needle28, which undermines the benefits of replacing a dynamic seal with the flexible seal32. The durometer is also low enough to prevent damping of the needle28by the flexible seal32as the needle28reciprocates from the open position to the closed position. Thus, a durometer in the range of 40-90 for the flexible seal32allows the flexible seal32to resist a wide range of hydraulic pressures in the flow channel22while also not adversely impacting the movements of the needle28and the dispensing of liquid from the liquid dispensing module10.

Additionally, the needle guide30may be adjustably positioned within the dispenser body assembly12such that the flexible seal32is slightly preloaded with compression when the needle28is in the closed position. This compression ensures that the upstream and downstream ends74,76of the flexible seal32remain respectively engaged with the first surface65and the second surface37transverse to the movement of the needle. In the illustrated embodiment ofFIGS. 2 and 3, the compression ensures that the upstream and downstream ends74,76of the flexible seal32stay wedged within the annular recess66and the annular groove38, respectively. As the needle28moves toward the open position, the upstream and downstream ends74,76of the flexible seal32move toward each other thereby further compressing the central portion78of the flexible seal32. As the needle returns to the closed position, the upstream and downstream ends74,76of the flexible seal32move away from each other thereby “stretching” or reducing compression in the central portion78of the flexible seal32. However, the central portion78of the flexible seal32preferably remains in compression between the needle guide30and the needle28because of the compression preloading previously described. The flexible seal32could also be preloaded with compression in other embodiments by adjusting the position of the enlarged portion36on the needle28, modifying the length of the flexible seal32or otherwise making structural modifications that result in the seal32being under a preload compression.

The flexible seal32provides an additional benefit as well. When the needle28is moved to the open position, a gap forms between the valve element34and the valve seat24near the discharge outlet20. The pressurized liquid then exerts an upward force on the valve element34of the needle28. Advantageously, the flexible seal32is compressed along central portion78when the needle28is moved to the open position. This compression provides a downward restoring force on the needle28to counteract the upward force from the pressurized liquid, thereby hydraulically balancing the needle28. As noted previously, the durometer of the flexible seal32is chosen to not dampen the movement of the needle28as well. The hydraulic balancing of forces allows for quicker response when opening and closing the dispensing module, i.e., engaging/disengaging the valve element34from valve seat24during dispensing operations, which leads to more accurate dispensing of liquid from the dispensing module10.

The liquid dispensing module10ofFIG. 2includes an actuator90operatively coupled to the needle28and adapted to actuate the needle28between the open and closed positions. The actuator90is disposed within an actuation chamber92disposed above the second end50of the needle guide30. The actuator90of this embodiment includes a piston assembly94coupled to a top portion96of the needle28. The piston assembly94divides the actuation chamber92into a lower portion92aand an upper portion92b. Piston assembly94generally includes a piston seal98positioned between a lower piston element100and an upper piston element102. The lower piston element100is coupled with the piston seal98and the upper piston element102and defines a piston passageway104through the piston assembly94. The piston passageway104includes an annular projection106adapted to mate with a corresponding annular notch108formed in the top portion96of the needle28. Additionally, a crimping ring member110may be disposed around the top portion96of the needle28above the piston assembly94. The piston assembly94is held onto the needle28by the combination of the crimping ring member110and the engagement of the annular projection106and annular notch108. The piston assembly94could alternatively be coupled to the needle28with alternate fastening means, such as a threaded fastener.

The lower portion92aof the actuation chamber92defines a pressurized air chamber inFIG. 2. The needle guide30may further include a dynamic seal112disposed around the needle28at the second end50of the needle guide30. The dynamic seal112is a pneumatic seal that prevents pressurized air from the lower portion92aof the actuation chamber92from leaking into the flow channel22and the needle passageway64in the needle guide30. A pressurized air inlet port114is connected to the lower portion92aof the actuation chamber92and includes an air inlet seal116at the dispenser body assembly12. When the lower portion92aof the actuation chamber92is pressurized with air from the air inlet port114, the air exerts a force on the lower piston element100that moves the piston assembly94and needle28upwards to the open position, thereby disengaging the valve element34from the valve seat24.

The actuator90may further include a spring-return mechanism118coupled to the needle28that urges the needle downwards to the closed position where the valve element34is engaged with the valve seat24. The spring return mechanism118includes a piston cap120and a spring122. The piston cap120is threadably coupled with the dispenser body assembly12as shown inFIG. 2and includes a static seal124such as an O-ring between the piston cap120and the dispenser body assembly12. The spring122is a compression spring extending between the upper piston element102and the piston cap120. Thus, when the lower portion92aof the actuation chamber92is depressurized, the spring-return mechanism118applies a downward force to the piston assembly94that causes the valve element34to engage with the valve seat24. The piston cap120can be threadably moved along the dispenser body assembly12to adjust the amount of spring return force that is provided by the compression spring122to oppose movement of the piston assembly94. Other configurations for the actuator90are possible, such as a double acting piston with air chambers on both sides of the piston assembly94in the upper portion92band the lower portion92aof the actuation chamber92, may be used in alternative embodiments of the dispensing module10. Furthermore, electrical actuators may be used to selectively move the needle between the open and closed positions.

Referring toFIG. 4, an alternative embodiment of the liquid dispensing module210is shown. This embodiment of the dispensing module includes many of the same elements as the previous embodiment, and like reference numerals are used to indicate the same elements described above. The valve element212of this embodiment is a ball instead of a needle, and the dispensing nozzle214has been modified to include a valve seat216appropriate for engaging the ball valve element212. The nozzle cap218is also modified from the previous embodiment, but the nozzle cap218still engages the dispensing nozzle214and the dispenser body assembly12as described above. The piston cap120of the previous embodiment has also been replaced with a dispenser cap220. The dispenser cap220is press fit or otherwise engaged with the dispenser body assembly12with a static seal124such as an O-ring held between these elements. The dispenser cap220includes a central aperture222holding an adjustment element224and a cap seal226. The adjustment element224is a threaded member in the illustrated embodiment. The adjustment element224is adapted to engage the top portion96of the needle28to block further upward movement of the needle28when the lower portion92aof the actuation chamber92is pressurized. The adjustment element224may be moved up and down with respect to the dispenser cap220in order to modify the stroke of the needle28, or how far the needle28may travel upwardly before the adjustment element224blocks further upward movement of the needle28. The cap seal226prevents any pressurized air in the upper portion92bof actuation chamber92from escaping the liquid dispensing module210through the central aperture222of the dispenser cap220. In each other aspect, the dispensing module210includes the elements of the previous embodiment's dispensing module10, including the flexible seal32engaged with a first surface65in the needle guide30and a second surface37in the needle28.

Referring toFIG. 5, another alternative embodiment of the liquid dispensing module310is illustrated. This embodiment of the dispensing module includes many of the same elements as the previous embodiments, and like reference numerals are used to indicate the same elements described above. In this embodiment the needle guide30has been removed and integrally formed as a needle guide portion312of the dispenser body assembly12. The needle guide portion312does include a first end48facing the flow channel22and including an annular recess66and an extension portion60, as well as a second end50facing the actuation chamber92and including a dynamic seal112for engaging the needle28. In this embodiment, rather than preloading the flexible seal32with compression by moving the needle guide30, the first end49of the needle guide portion312and the enlarged portion36of the needle28are located such that the flexible seal32is in compression when the needle28is in the closed position.

Referring toFIG. 6, another alternative embodiment of the liquid dispensing module410is shown. This embodiment of a dispensing module410is substantially identical to the module210ofFIG. 4, but the pneumatic dynamic seal112has been removed from the needle guide30. Thus, pressurized air is allowed to escape along the needle passageway64and pressurize the interior cavity88of the flexible seal32. The weep holes57,59of previous embodiments have also been removed to prevent the pressurized air from leaking directly from the needle passageway64outside the liquid dispensing module10. The pressurized interior cavity88will further resist collapse of the flexible seal32onto the needle28caused by the hydraulic pressure in the flow channel22, which would undermine the benefits of replacing a dynamic seal with the flexible seal32. Nevertheless, the upstream and downstream ends74,76of the flexible seal32remain sealably engaged in the annular recess66and the annular groove38, respectively, because of the lengthwise compression in the flexible seal32.

Referring toFIG. 7, another alternative embodiment of the liquid dispensing module510is illustrated. This embodiment of a dispensing module510is substantially identical to the module310ofFIG. 5, but the pneumatic dynamic seal112has been removed from the needle guide portion112. Thus, pressurized air is allowed to escape along the needle passageway64and pressurize the interior cavity88of the flexible seal32. The weep holes57,59of previous embodiments have also been removed to prevent the pressurized air from leaking directly from the needle passageway64outside the liquid dispensing module10. The pressurized interior cavity88will further resist collapse of the flexible seal32onto the needle28caused by the hydraulic pressure in the flow channel22, which would undermine the benefits of replacing a dynamic seal with the flexible seal32. Nevertheless, the upstream and downstream ends74,76of the flexible seal32remain sealably engaged in the annular recess66and the annular groove38, respectively, because of the lengthwise compression in the flexible seal32.

While the present invention has been illustrated by a description of various preferred embodiments and while these embodiments have been described in some detail, it is not the intention of the Applicants 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. For example, the needle valve element34ofFIG. 2could be used in combination with the modules410,510having no dynamic seal112at the needle guide. The various features of the invention may be used alone or in numerous combinations depending on the needs and preferences of the user.