WO2013066687A1

WO2013066687A1 - Liquid dispensing apparatus with a multiple stage snuff back module

Info

Publication number: WO2013066687A1
Application number: PCT/US2012/061633
Authority: WO
Inventors: Kai Luebbecke; Mathias ANDRÉ
Original assignee: Nordson Corporation
Priority date: 2011-10-31
Filing date: 2012-10-24
Publication date: 2013-05-10

Abstract

A liquid dispensing apparatus (10) includes a dispenser module (20) having a distribution passage (22) and an outlet aperture (32) configured to dispense pressurized liquid. The liquid dispensing apparatus (10) also includes a snuff back module (12) including a snuff back shaft (36) extending into fluid communication with the distribution passage (22). At the end of a dispensing cycle, an actuating mechanism (60) of the snuff back module (12) actuates movement of the snuff back shaft (36) from an extended position to a first and/or second withdrawn position, thereby pulling pressurized liquid back from the outlet aperture (32) to cleanly cut off liquid flow. A controller (106) operates the actuating mechanism (60) to move the snuff back shaft (36) between the extended position, the first withdrawn position, and the second withdrawn position, which enables different liquid volumes to be pulled back depending on the size of the outlet aperture (32).

Description

LIQUID DISPENSING APPARATUS WITH A MULTIPLE STAGE SNUFF BACK MODULE

Cross-Reference to Related Application

[0001] This application claims the priority of Application Serial No.

61 /553,630, filed October 31 , 201 1 (pending), the disclosure of which is hereby incorporated by reference herein.

Field of the Invention

[0002] The present invention generally relates to a liquid dispensing apparatus for applying a liquid to a substrate and more particularly, to a liquid dispensing apparatus including a snuff back module for drawing back liquid flow after a dispensing cycle

Background

[0003] Many industrial applications require the dispensing and application of liquid coatings onto substrates by a liquid dispensing apparatus. Two examples of such coatings are a liquid moisture-proof insulator film applied to printed circuit boards and an adhesive coating applied to spine areas of a book to bond the spine areas to an outer cover. In many of these applications, discrete areas of the substrate with sharp cut-off edges must be coated with liquid. As a result, so-called snuff back modules have been developed for improving the cut-off of liquid dispensing at the end of a liquid dispensing cycle. The snuff back module may be incorporated into the dispenser valve controlling liquid flow through the liquid dispensing apparatus, or the snuff back module may include separate structure added to the liquid dispensing apparatus. Each type of snuff back module functions to draw liquid back from an outlet aperture of the liquid dispensing apparatus when the dispenser valve closes, thereby forming a clean cut-off of liquid at the outlet aperture.

[0004] One example of a snuff back module including independent structure from the dispenser valve is described in U.S. Patent No. 5,733,597 to Schmitkons et al., the entire disclosure of which is hereby incorporated by reference herein. As shown in that reference, the snuff back module includes a snuff back shaft in operative communication with the outlet passages of a liquid dispensing apparatus downstream of a dispenser valve. The snuff back module is located in an extended position during dispensing of liquid from the liquid dispensing apparatus, and then moves to a withdrawn position at the end of a dispensing cycle. The movement of the snuff back shaft effectively causes a vacuum force to be applied to the liquid remaining in the outlet passages, which forces liquid to be pulled back into the liquid dispensing apparatus from the outlet aperture. The stroke length of the snuff back shaft is set to withdraw the same volume of liquid from the outlet aperture during each actuation of the snuff back shaft.

[0005] However, some liquid dispensing apparatuses include one or more outlet apertures having an adjustable size. For example, a slot-shaped outlet aperture of a bookbinding adhesive dispensing apparatus may be modified in width to accommodate differently sized books, as described in U.S. Patent No. 6,960,261 to Westermann, the entire disclosure of which is hereby incorporated by reference herein. Thus, the total area of the outlet aperture may vary significantly from one dispensing cycle to another dispensing cycle. As a result, the set volume of liquid that the conventional snuff back module pulls back into the liquid dispensing apparatus may not be optimized for all sizes of the outlet aperture. In this regard, when the snuff back module is configured to withdraw enough liquid to cause a clean cut-off at a larger outlet aperture size, too much air may be drawn into the liquid dispensing apparatus when a smaller aperture size is used.

[0006] There is a need, therefore, for a liquid dispensing apparatus with a snuff back module that addresses one or more of these deficiencies in the field of dispensing apparatuses and enables clean cut-off of dispensed liquid for varying sizes of outlet apertures.

Summary of the Invention

[0007] According to one embodiment of the invention, a snuff back module draws a pressurized liquid back from an outlet aperture of a dispensing apparatus. The snuff back module includes a snuff back shaft configured to extend into fluid communication with the outlet aperture of the dispensing apparatus. The snuff back shaft is moveable between an extended position and a withdrawn position to draw the pressurized liquid back from the outlet aperture. The snuff back module also includes an actuating mechanism that withdraws the snuff back shaft from the extended position. The actuating mechanism is configured to stop the movement of the snuff back shaft at a first withdrawn position and is configured to stop the movement of the snuff back shaft at a second withdrawn position farther from the extended position than the first withdrawn position. The snuff back module also includes a controller operating the actuating mechanism to selectively move the snuff back shaft from the extended position to the first withdrawn position, from the extended position to the second withdrawn position, and from the first withdrawn position to the second withdrawn position.

[0008] In one aspect, the outlet aperture of the dispensing apparatus is a slot-shaped outlet aperture having an adjustable size. The controller is configured to decide whether the snuff back shaft is withdrawn to the first or second withdrawn positions based on the width of the slot-shaped outlet aperture. The controller operated the actuating mechanism to stop the snuff back shaft at the first withdrawn position temporarily when moving the snuff back shaft between the second withdrawn position and the extended position.

[0009] In another aspect, the actuating mechanism includes a first actuator configured to move the snuff back shaft to the first withdrawn position and a second actuator configured to move the snuff back shaft to the second withdrawn position. The first actuator is a pneumatically-driven first piston operatively coupled to the snuff back shaft and configured to move with the snuff back shaft through a first stroke length. The second actuator is a pneumatically-driven second piston operatively coupled to the snuff back shaft and configured to move with the snuff back shaft through a second stroke length. The actuating mechanism further includes a valve mechanism that selectively directs pressurized air to the lower side of the first piston or the upper or lower side of the second piston to move the snuff back shaft. The actuating mechanism also includes an air throttle configured to throttle exhaust flow from the lower side of the first piston to limit the speed of the snuff back shaft as it moves from the first withdrawn position to the extended position.

[0010] In another embodiment of the invention, a liquid dispensing apparatus includes a dispenser module and a snuff back module. The dispenser module includes a distribution passage, an outlet passage communicating with the distribution passage, an outlet aperture communicating with the outlet passage, and a dispenser valve moveable between open and closed positions to control flow of pressurized liquid into the distribution passage. The snuff back module includes a snuff back shaft extending into fluid communication with the distribution passage. The snuff back shaft is moveable between an extended position and a withdrawn position to draw the pressurized liquid back from the outlet aperture. The snuff back module also includes an actuating mechanism that withdraws the snuff back shaft from the extended position. The actuating mechanism is configured to stop the movement of the snuff back shaft at a first withdrawn position and is configured to stop the movement of the snuff back shaft at a second withdrawn position farther from the extended position than the first withdrawn position. The snuff back module also includes a controller operating the actuating mechanism to selectively move the snuff back shaft from the extended position to the first withdrawn position, from the extended position to the second withdrawn position, and from the first withdrawn position to the second withdrawn position.

[0011] In one aspect, the dispenser module includes a snuff back passage communicating with the distribution passage and receiving the snuff back shaft. The snuff back module further includes a snuff back module housing coupled to the dispensing module when the snuff back shaft extends into the snuff back passage. Alternatively, the snuff back module may be incorporated as a part of the dispenser module.

[0012] According to another embodiment of the invention, a method of dispensing a pressurized liquid from a liquid dispensing apparatus including a dispenser valve, an outlet aperture, and a snuff back module includes opening the dispenser valve to actuate flow of the pressurized liquid to the outlet aperture. The method also includes closing the dispenser valve to stop flow of the pressurized liquid to the outlet aperture. The snuff back shaft is moved from an extended position to a first withdrawn position to draw a first volume of pressurized liquid back from the outlet aperture. The snuff back shaft is moved from the extended position to a second withdrawn position to draw a second volume of pressurized liquid larger than the first volume back from the outlet aperture. The method also includes stopping the snuff back shaft at the first withdrawn position temporarily when the snuff back shaft moves between the second withdrawn position and the extended position.

[0013] In one aspect, the outlet aperture is a slot-shaped outlet aperture with an adjustable width, and the method further includes determining whether the snuff back module is moved from the extended position to the first withdrawn position or to the second withdrawn position based on the width of the outlet aperture. In another aspect, the snuff back shaft is operatively coupled to a first piston operable to move the snuff back shaft to the first withdrawn position and a second piston operable to move the snuff back shaft to the second withdrawn position. The method further includes directing pressurized air to at least one side of one or both of the first and second pistons to move the snuff back shaft.

[0014] In yet another embodiment of the invention, a method of dispensing a pressurized liquid from a liquid dispensing apparatus including a dispenser valve, an outlet aperture, and a snuff back module includes opening the dispenser valve to actuate flow of the pressurized liquid to the outlet aperture. The method also includes closing the dispenser valve to stop flow of the pressurized liquid to the outlet aperture. The snuff back shaft is moved from an extended position to a first withdrawn position by a first actuator to draw a first volume of pressurized liquid back from the outlet aperture. The snuff back shaft is moved from the extended position to a second withdrawn position by a second actuator to draw a second volume of pressurized liquid larger than the first volume back from the outlet aperture.

[0015] Various additional features and advantages of the invention will become more apparent to those of ordinary skill in the art upon review of the following detailed description of the illustrative embodiments taken in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0016] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention.

[0017] FIG. 1 A is a schematic side view of a liquid dispensing apparatus according to one embodiment of the invention, with the outlet aperture of the apparatus defining a first width.

[0018] FIG. 1 B is a schematic side view of the liquid dispensing apparatus of FIG. 1 A, with the outlet aperture defining a second width. [0019] FIG. 2 is a cross-sectional front view of the liquid dispensing apparatus of FIG. 1 A.

[0020] FIG. 3 is a perspective view of the snuff back module of the liquid dispensing apparatus of FIG. 2.

[0021] FIG. 4 is a cross-sectional side view of the snuff back module of FIG. 3 taken along line 4-4.

[0022] FIG. 5 is a schematic cross-sectional side view of the snuff back module of FIG. 4 with a first embodiment of a valve mechanism in a first operating state to move the snuff back shaft to the extended position.

[0023] FIG. 6 is a schematic cross-sectional side view of the snuff back module of FIG. 5 with the valve mechanism in a second operating state to move the snuff back shaft to the first withdrawn position.

[0024] FIG. 7 is a schematic cross-sectional side view of the snuff back module of FIG. 6 with the valve mechanism in a third operating state to move the snuff back shaft to the second withdrawn position.

[0025] FIG. 8 is a schematic cross-sectional side view of the snuff back module of FIG. 4 with a second embodiment of a valve mechanism in a first operating state to move the snuff back shaft to the extended position.

[0026] FIG. 9 is a schematic cross-sectional side view of the snuff back module of FIG. 8 with the valve mechanism in a second operating state to move the snuff back shaft to the first withdrawn position.

[0027] FIG. 10 is a schematic cross-sectional side view of the snuff back module of FIG. 9 with the valve mechanism in a third operating state to move the snuff back shaft to the second withdrawn position.

[0028] FIG. 1 1 is a schematic cross-sectional side view of the snuff back module of FIG. 10 with the valve mechanism in a fourth operating state to move the snuff back shaft to the first withdrawn position.

Detailed Description of the Illustrative Embodiments

[0029] An exemplary embodiment of a liquid dispensing apparatus 10 including a snuff back module 1 2 is shown in FIGS. 1 A-4. With specific reference to the schematic views of FIGS. 1 A and 1 B, the liquid dispensing apparatus 10 is an adhesive dispenser configured to apply a coating of hot melt adhesive 14 to a book 16 along an inner spine surface 18. To this end, the liquid dispensing apparatus 10 includes a dispenser module 20 having a distribution passage 22 extending from a dispenser valve 24 to an outlet passage 26. The outlet passage 26 is bounded by a cover plate 28 including a moveable slider 30. Thus, the cover plate 28 and slider 30 define a slot-shaped outlet aperture 32 communicating with the outlet passage 26. When the dispenser valve 24 is in an open position, the hot melt adhesive 14 flows through the distribution passage 22 and the outlet passage 26 to be extruded from the outlet aperture 32. The spine surface 1 8 of the book 16 is coated with the adhesive 14 at the outlet aperture 32 as the book 16 moves in a direction into or out of the view of FIGS. 1 A and 1 B. The book 16 is held in alignment with the outlet aperture 32 by lateral guides 34 connected to the cover plate 28 and the slider 30.

[0030] As shown in FIG. 1 A, the snuff back module 12 includes a snuff back shaft 36 that communicates with the distribution passage 22. As described in further detail below, the snuff back shaft 36 is moveable between an extended position and at least one withdrawn position to pull adhesive 14 back from the outlet aperture 32 into the outlet passage 26 when the dispenser valve 24 closes at the end of a book 16. When the slider 30 and the lateral guides 34 move to accommodate a larger book 38 as shown in FIG. 1 B, the outlet aperture 32 defines a larger width W than shown in FIG. 1 A.

Consequently, the snuff back shaft 36 must be withdrawn farther from the extended position to pull the adhesive 14 back from the wider outlet aperture 32. The snuff back module 1 2 of the current invention advantageously includes multiple stages of withdrawing the snuff back shaft 36 to adjust for different sizes of the outlet aperture 32.

[0031] With reference to FIG. 2, the dispenser module 20 includes a module housing 40 and a nozzle block 42 clamped into engagement with the module housing by a nozzle retainer 44. The nozzle retainer 44 is locked in position against the nozzle block 42 by tightening a fastener 46 into the module housing 40. Although not shown in FIG. 2, the dispenser module 20 includes the dispenser valve 24 for controlling flow of pressurized adhesive 14 from a liquid inlet (not shown) into the distribution passage 22. The distribution passage 22 delivers the adhesive 14 into the outlet passage 26, which is defined between the nozzle block 42 and the module housing 40. The adhesive 14 then flows out of the outlet aperture 32 onto a book (not shown) moving past the outlet aperture 32 towards a downstream tray 48 coupled to the module housing 40. As described above, the width W of the outlet aperture 32 is adjustable to accommodate books 1 6, 38 of varying sizes. It will be understood that the nozzle block 42 and nozzle retainer 44 may be formed as integral portions of the module housing 40 in other embodiments within the scope of the invention, such that the outlet passage 26 and the outlet aperture 32 are formed in the module housing 40.

[0032] The module housing 40 also includes a snuff back passage 50 extending from the distribution passage 22 to a receptacle slot 52 configured to receive the snuff back module 12. To this end, the snuff back module 12 includes a pneumatic housing 54 extending into the receptacle slot 52 and the snuff back shaft 36, which extends into the snuff back passage 50. The pneumatic housing 54 is retained in the receptacle slot 52 by fasteners (not shown), by a frictional fit, or by another known coupling method. In the extended position of the snuff back shaft 36 shown in FIG. 2, the snuff back shaft 36 is located partially in the distribution passage 22 as close as possible to the outlet passage 26. This proximate positioning of the snuff back shaft 36 to the outlet passage 26 improves the immediate effect of drawing back adhesive 14 from the outlet aperture 32 when the snuff back shaft 36 begins to withdraw from the extended position. It will be understood that the snuff back module 12 may be integrally incorporated into the dispenser module 20 rather than including a separate pneumatic housing 54 inserted into the receptacle slot 52 in other embodiments within the scope of the invention.

[0033] With reference to FIGS. 2-4, the snuff back module 1 2 includes an actuating mechanism 60 coupled to the snuff back shaft 36 and configured to move the snuff back shaft 36 between the extended position and a plurality of withdrawn positions. To this end, the actuating mechanism 60 of the illustrated embodiment includes a first actuator 62 and a second actuator 64 configured to move the snuff back shaft 36. More particularly, the first actuator 62 includes a pneumatically-actuated first piston 66 operatively coupled to the snuff back shaft 36 and a collar 68 fixedly coupled to the snuff back shaft 36. The first piston 66 and the collar 68 are mounted on the snuff back shaft 36 within a first piston chamber 70 defined by the pneumatic housing 54. The first piston chamber 70 includes a primary chamber portion 70a sized to closely receive the first piston 66 and a narrowed chamber portion 70b smaller in cross section than the primary chamber portion 70a and extending above the primary chamber portion 70a. In this regard, the first piston chamber 70 includes an intermediate shoulder 70c formed at the junction of the primary chamber portion 70a and the narrowed chamber portion 70b. The first piston 66 includes an upper side 66a facing the collar 68, a lower side 66b, and a peripheral side 66c extending between the upper and lower sides 66a, 66b. The peripheral side 66c of the first piston 66 carries an O-ring seal 66d configured to fluidically isolate the space above the upper side 66a from the space below the lower side 66b.

[0034] The first piston 66 is freely slidable with respect to the snuff back shaft 36, but the selective engagement of the first piston 66 and the collar 68 enables the first piston 66 to move the snuff back shaft 36 when pressurized air is supplied to the lower side 66b of the first piston 66. As shown most clearly in FIG. 4, the narrowed chamber portion 70b communicates with at least one vent passage 70d formed in the pneumatic housing 54. Consequently, the upper side 66a of the first piston 66 cannot be forced downwardly by pressurized air in the exemplary embodiment. It will be understood that the snuff back module 12 may be modified to enable pressurization of this upper side 66a of the first piston 66 in other embodiments within the scope of the invention. When the lower side 66b of the first piston 66 is pressurized, the upper side 66a forces the collar 68 and therefore also the snuff back shaft 36 to move upwardly through a first stroke length until the upper side 66a abuts the shoulder 70c at a first withdrawn position (described in further detail with reference to FIG. 6 below). As will also be described in further detail below, the collar 68 is smaller in cross section than the narrowed chamber portion 70b such that the collar 68 and the snuff back shaft 36 can continue to move upwardly when actuated by the second actuator 64.

[0035] Similarly, the second actuator 64 includes a pneumatically- actuated second piston 72 fixedly coupled to the snuff back shaft 36 adjacent a rear end 36a of the snuff back shaft 36. The second piston 72 is mounted on the snuff back shaft 36 within a second piston chamber 74 defined by the pneumatic housing 54. The second piston chamber 74 includes a primary chamber portion 74a sized to closely receive the second piston 72 and a narrowed chamber portion 74b smaller in cross section than the primary chamber portion 74a and extending above the primary chamber portion 74a. In this regard, the second piston chamber 74 includes an intermediate shoulder 74c formed at the junction of the primary chamber portion 74a and the narrowed chamber portion 74b. The second piston 72 includes an upper side 72a, a lower side 72b, and a peripheral side 72c extending between the upper and lower sides 72a, 72b. The peripheral side 72c of the second piston 72 carries an O-ring seal 72d configured to fluidically isolate the space above the upper side 72a from the space below the lower side 72b.

[0036] The second piston 72 moves with the snuff back shaft 36, and thus can force the snuff back shaft 36 to move when pressurized air is supplied to either the upper side 72a or the lower side 72b of the second piston 72. When the lower side 72b of the second piston 72 is pressurized, the second piston 72 forces the snuff back shaft 36 to move upwardly through a second stroke length SL₂ until the upper side 72a abuts the shoulder 74c at a second withdrawn position (described in further detail with reference to FIG. 7 below). The narrowed chamber portion 74b of the second piston chamber 74 is configured to receive the top end 36a of the snuff back shaft 36 when the second piston 72 abuts the shoulder 74c. When the upper side 72a of the second piston 72 is pressurized, the second piston 72 forces the snuff back shaft 36 to move downwardly to the extended position shown in FIGS. 2 and 4. Thus, the first and second actuators 62, 64 are operable to act as first and second stages of a multi-stage snuff back or withdrawal movement of the snuff back shaft 36, as described in further detail below.

[0037] To facilitate assembly of the snuff back module 12, the pneumatic housing 54 includes a plurality of housing portions 54a, 54b, 54c, 54d coupled to each other with a plurality of seals 76 between adjacent housing portions 54a, 54b, 54c, 54d. More particularly, a first housing portion 54a is sized to fit inside the receptacle slot 52; a second housing portion 54b is coupled to the first housing portion 54a and defines a portion of the first piston chamber 70; a third housing portion 54c is coupled to the second housing portion 54b and defines portions of the first and second piston chambers 70, 74; and a fourth housing portion 54d is coupled to the third housing portion 54c and defines a portion of the second piston chamber 74. It will be understood that the pneumatic housing 54 may be formed from more or fewer portions in other embodiments of the invention.

[0038] In order to operate the first and second actuators 62, 64 of the exemplary embodiment, the actuating mechanism 60 further includes a valve mechanism 80 for controlling the flow of pressurized air into the first and second piston chambers 70, 74. The valve mechanism 80 includes a first solenoid valve 82 including five ports 86a, 86b, 86c, 86d, 86e and a second solenoid valve 84 including four ports (not shown). The pneumatic housing 54 includes a plurality of passages configured to communicate with ports of the first and second valves 82, 84 as described in further detail below. More particularly, the pneumatic housing 54 includes an air inlet passage 88 communicating with an air inlet port 90, which is connected to a source of pressurized air 92 as schematically shown in FIG. 2. The air inlet passage 88 delivers the

pressurized air into an inlet port 86a of the first solenoid valve 82 as shown in FIG. 4. A first outlet port 86b of the first solenoid valve 82 communicates with the upper side 72a of the second piston 72 in the second piston chamber 74 via a first pressure passage 94 in the pneumatic housing 54. A second outlet port 86c of the first solenoid valve 82 communicates with a second pressure passage 96 in the pneumatic housing 54, which leads to the inlet port (not shown) of the second solenoid valve 84. First and second exhaust ports 86d, 86e of the first solenoid valve 82 communicate with corresponding air outlet passages 98a, 98b in the pneumatic housing 54. One or both of the air outlet passages 98a, 98b may include an air throttle 100, which limits the flow rate of pressurized air exhausting from one or both of the piston chambers 70, 74.

[0039] As described above, the second solenoid valve 84 includes four ports (not shown). The inlet port of the second solenoid valve 84

communicates with the first solenoid valve 82 via the second pressure passage 96. A first outlet port of the second solenoid valve 84 communicates with the lower side 72b of the second piston 72 via a third pressure passage 102 in the pneumatic housing 54. A second outlet port of the second solenoid valve 84 communicates with the lower side 66b of the first piston 66 via a fourth pressure passage 104 in the pneumatic housing 54. The second solenoid valve 84 also includes an exhaust port (not shown) selectively exhausting pressurized air to the ambient surroundings.

[0040] Consequently, the first solenoid valve 82 is operable to control whether pressurized air is delivered to the upper side 72a of the second piston 72. The second solenoid valve 74 is operable to control whether pressurized air from the first solenoid valve 82 is delivered to either the lower side 66b of the first piston 66 or the lower side 72b of the second piston 72. The first and second solenoid valves 82, 84 are operatively connected to a power supply (not shown) and a controller 106 via corresponding electrical connector ports 108. As described in further detail below, the controller 1 06 operates the valve mechanism 80 to cause the actuating mechanism 60 to move the snuff back shaft 36 between the extended position, the first withdrawn position, and the second withdrawn position.

[0041] Turning to FIGS. 5-7, a first embodiment of the valve mechanism 80 is shown in various operating states. In this first embodiment, the first solenoid valve 82 is a 5/2 way valve and the second solenoid valve 84 is a 4/2 way valve. Each of these valves 82, 84 may be conventional 5/2 way and 4/2 way solenoids commercially available from various suppliers. The pressurized air source 92 and the first and second valves 82, 84 are shown schematically in FIGS. 5-7 to more clearly illustrate the operation of the snuff back module 12. The pressurized air source 92 may include a pressure gage 92a that is configured to provide feedback to an operator or the controller 106 that indicates the operating pressure of air entering the solenoid valves 82, 84.

[0042] Beginning with the first operating state shown in FIG. 5, the first solenoid valve 82 is in a first state such that the pressurized air source 92 delivers air to the upper side 72a of the second piston 72 via the first pressure passage 94. In this first state of the first solenoid valve 82, the inlet port of the second solenoid valve 84 communicates with the air throttle 100 in one of the air outlet passages 98a. The second solenoid valve 84 is also in a first state in which the lower side 72b of the second piston 72 communicates with the exhaust port via the third pressure passage 102. Meanwhile, the lower side 66b of the first piston 66 communicates with the inlet port (and thus the air throttle 1 00 exhaust) via the fourth pressure passage 104. In this regard, the upper side 72a of the second piston 72 is pressurized while the lower sides 66b, 72b of the first and second pistons 66, 72 are not pressurized (exhausted). The second piston 72 forces the snuff back shaft 36 downwardly to the extended position shown in FIG. 5. The air throttle 1 00 slows the speed of the snuff back shaft 36 as it approaches the extended position, which

advantageously prevents a quick ejection of adhesive material from the outlet aperture 32 at the beginning of a new dispensing cycle (e.g., when the snuff back shaft 36 would be moved to the extended position). [0043] Turning to the second operating state shown in FIG. 6, the first solenoid valve 82 moves to the second state such that the pressurized air source 92 delivers air to the inlet port of the second solenoid valve 84. Also in the second state of the first solenoid valve 82, the upper side 72a of the second piston 72 communicates with the air outlet passage 98b not including an air throttle 1 00. The second solenoid valve 84 remains in its first state in this second operating state. Thus, the pressurized air from the first solenoid valve 82 is delivered to the lower side 66b of the first piston 66, while the lower side 72b of the second piston 72 communicates with the exhaust port of the second solenoid valve 84. To this end, the lower side 66b of the first piston 66 is pressurized while the upper and lower sides 72a, 72b of the second piston 72 are not pressurized. The first piston 66 forces the collar 68 and the snuff back shaft 36 upwardly to the first withdrawn position shown in FIG. 6, in which the first piston 66 engages the shoulder 70c of the first piston chamber 70.

[0044] Now referring to FIG. 7, a third operating state is shown. In this third operating state, the first solenoid valve 82 remains in the second state such that the pressurized air source 92 delivers air to the inlet port of the second solenoid valve 84. Also in the second state of the first solenoid valve 82, the upper side 72a of the second piston 72 communicates with the air outlet passage 98b not including an air throttle 1 00. The second solenoid valve 84 moves to a second state, in which the pressurized air from the first solenoid valve 82 is delivered to the lower side 72b of the second piston 72, while the lower side 66b of the first piston 66 communicates with the exhaust port of the second solenoid valve 84. As a result, the lower side 72b of the second piston 72 is pressurized while the upper side 72a of the second piston 72 and the lower side 66b of the first piston 66 are not pressurized. The second piston 72 forces the snuff back shaft 36 upwardly to the second withdrawn position shown in FIG. 7, in which the second piston 72 engages the shoulder 74c of the second piston chamber 74. The valve mechanism 80 may then be moved back to the first operating state to move the snuff back shaft 36 back to the extended position from the second withdrawn position, beginning another operational cycle. As readily understood from FIGS. 5-7, the stroke length SL_{1 ;} SL₂ of the movement of the snuff back shaft 36 and the corresponding volume of adhesive pulled back from the outlet aperture 32 may be modified between at least two stages. [0045] Turning to FIGS. 8-1 1 , a second embodiment of the valve mechanism 80 is shown in various operating states. In this second

embodiment, the first solenoid valve 82 is a 5/3 way valve and the second solenoid valve 84 is a 4/2 way valve. Each of these valves 82, 84 may be conventional 5/3 way and 4/2 way solenoids commercially available from various suppliers. The pressurized air source 92 and the first and second valves 82, 84 are shown schematically in FIGS. 8-1 1 to more clearly illustrate the operation of the snuff back module 12.

[0046] Beginning with the first operating state shown in FIG. 8, the first solenoid valve 82 is in a first state such that the pressurized air source 92 delivers air to the upper side 72a of the second piston 72 via the first pressure passage 94. In this first state of the first solenoid valve 82, the inlet port of the second solenoid valve 84 communicates with the air throttle 100 in one of the air outlet passages 98a. The second solenoid valve 84 is also in a first state in which the lower side 72b of the second piston 72 communicates with the exhaust port via the third pressure passage 102. Meanwhile, the lower side 66b of the first piston 66 communicates with the inlet port (and thus the air throttle 1 00 exhaust) via the fourth pressure passage 104. In this regard, the upper side 72a of the second piston 72 is pressurized while the lower sides 66b, 72b of the first and second pistons 66, 72 are not pressurized (exhausted). The second piston 72 forces the snuff back shaft 36 downwardly to the extended position shown in FIG. 8. The air throttle 1 00 slows the speed of the snuff back shaft 36 as it approaches the extended position, which

advantageously prevents a quick ejection of adhesive material from the outlet aperture 32 at the beginning of a new dispensing cycle.

[0047] Turning to the second operating state shown in FIG. 9, the first solenoid valve 82 moves to the second state such that the pressurized air source 92 delivers air to the inlet port of the second solenoid valve 84. Also in the second state of the first solenoid valve 82, the upper side 72a of the second piston 72 communicates with the air outlet passage 98b not including an air throttle 1 00. The second solenoid valve 84 remains in its first state in this second operating state. Thus, the pressurized air from the first solenoid valve 82 is delivered to the lower side 66b of the first piston 66, while the lower side 72b of the second piston 72 communicates with the exhaust port of the second solenoid valve 84. To this end, the lower side 66b of the first piston 66 is pressurized while the upper and lower sides 72a, 72b of the second piston 72 are not pressurized. The first piston 66 forces the collar 68 and the snuff back shaft 36 upwardly to the first withdrawn position shown in FIG. 9, in which the first piston 66 engages the shoulder 70c of the first piston chamber 70.

[0048] Now referring to FIG. 1 0, a third operating state is shown. In this third operating state, the first solenoid valve 82 remains in the second state such that the pressurized air source 92 delivers air to the inlet port of the second solenoid valve 84. Also in the second state of the first solenoid valve 82, the upper side 72a of the second piston 72 communicates with the air outlet passage 98b not including an air throttle 1 00. The second solenoid valve 84 moves to a second state, in which the pressurized air from the first solenoid valve 82 is delivered to the lower side 72b of the second piston 72, while the lower side 66b of the first piston 66 communicates with the exhaust port of the second solenoid valve 84. As a result, the lower side 72b of the second piston 72 is pressurized while the upper side 72a of the second piston 72 and the lower side 66b of the first piston 66 are not pressurized. The second piston 72 forces the snuff back shaft 36 upwardly to the second withdrawn position shown in FIG. 10, in which the second piston 72 engages the shoulder 74c of the second piston chamber 74.

[0049] Turning to the fourth operating state shown in FIG. 1 1 , the first solenoid valve 82 moves to a third state such that the pressurized air source 92 delivers air to the upper side 72a of the second piston 72 via the first pressure passage 94 and also to the inlet port of the second solenoid valve 84. The second solenoid valve 84 returns to its first state in this fourth operating state. In this regard, the pressurized air from the first solenoid valve 82 is delivered to the lower side 66b of the first piston 66a, while the lower side 72b of the second piston 72 communicates with the exhaust port of the second solenoid valve 84. To this end, the lower side 66b of the first piston 66 and the upper side 72a of the second piston 72 are pressurized while the lower side 72b of the second piston 72 is not pressurized. The second piston 72 forces the snuff back shaft 36 and the collar 68 downwardly until the collar 68 is blocked by the first piston 66, which abuts the shoulder 70c of the first piston chamber 70. Thus, the first and second pistons 66, 72 force the snuff back shaft 36 downwardly to the first withdrawn position shown in FIG. 1 1 . The valve mechanism 80 may then be moved back to the first operating state to move the snuff back shaft 36 back to the extended position from the first withdrawn position, beginning another operational cycle. As readily understood from FIGS. 5-7, the stroke length SL_{1 ;} SL₂ of the movement of the snuff back shaft 36 and the corresponding volume of adhesive pulled back from the outlet aperture 32 may be modified between at least two stages.

[0050] It will be understood that the actuating mechanism 60 may be modified in various ways consistent with the scope of the invention. For example, the actuating mechanism 60 includes two separate actuators 62, 64 for moving the snuff back shaft 36 to two withdrawn positions, but these separate actuators 62, 64 could be replaced by a single actuator in another embodiment. Furthermore, the actuators 62, 64 may be modified to non pneumatic actuators such as electromagnetically controlled movement actuators in other embodiments. In another example, the actuating mechanism 60 may be configured to move the snuff back shaft 36 to more than two distinct withdrawn positions to increase the number of stages that the multi-stage snuff back module 12 can operate through. In sum, the two pneumatic pistons 66, 72 shown in the exemplary embodiment of FIGS. 1 -1 1 is but one way to practice the currently described invention, and other modifications within the scope of the following claims are also envisioned.

[0051] Returning to the exemplary embodiment, the snuff back module 12 may be advantageously controlled to selectively draw different volumes of adhesive 14 back from the outlet aperture 32 of the dispenser module 20 depending on the size of the outlet aperture 32. For example, in the

bookbinding liquid dispensing apparatus shown in FIGS. 1 A-2, the outlet aperture 32 may have a width W within a first range of widths such as 1 -15 millimeters, or within a second range of widths such as 16-30 millimeters.

When the outlet aperture 32 has a width within the first range of widths, the snuff back module 12 may move the snuff back shaft 36 through the first stroke length SU of 4 millimeters to the first withdrawn position. When the outlet aperture 32 has a width within the second range of widths, the snuff back module 12 may move the snuff back shaft 36 through the second stroke length SL₂ of 12 millimeters to the second withdrawn position, thereby drawing more adhesive 14 back from the wider outlet aperture 32. Thus, the second stroke length SL₂ and the volume snuffed back by the snuff back module 12 are more than twice as large as the first stroke length SU and the corresponding volume snuffed back. In this regard, the snuff back module 12 advantageously draws back more fluid when the outlet aperture is wider 32 and less fluid when the outlet aperture 32 is narrower. This adjustment may be automatically controlled by the controller 106, which may receive information on the size of the outlet aperture 32 so as to operate the snuff back module 12 most effectively. The snuff back module 12 therefore enables clean cut-off and start-up of liquid dispensing over numerous dispensing cycles of the liquid dispensing apparatus 10.

[0052] While the present invention has been illustrated by the description of specific embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. The various features discussed herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of the general inventive concept. What is claimed is:

Claims

1 . A snuff back module for drawing a pressurized liquid back from an outlet aperture of a liquid dispensing apparatus, the snuff back module comprising: a snuff back shaft configured to extend into fluid communication with the outlet aperture of the dispensing apparatus, said snuff back shaft moveable between an extended position and a withdrawn position to draw the pressurized liquid back from the outlet aperture;

an actuating mechanism coupled to said snuff back shaft for withdrawing said snuff back shaft from the extended position, said actuating mechanism configured to stop the movement of said snuff back shaft at a first withdrawn position and configured to stop the movement of said snuff back shaft at a second withdrawn position farther from the extended position than the first withdrawn position; and

a controller operating said actuating mechanism to selectively move said snuff back shaft from the extended position to the first withdrawn position, from the extended position to the second withdrawn position, and from the first withdrawn position to the second withdrawn position.

2. The snuff back module of claim 1 , wherein the outlet aperture of the dispensing apparatus is a slot-shaped outlet aperture having an adjustable width, and said controller is configured to decide whether said snuff back shaft is withdrawn to the first withdrawn position or the second withdrawn position based on the width of the slot-shaped outlet aperture.

3. The snuff back module of claim 1 , wherein said controller operates said actuating mechanism to stop said snuff back shaft temporarily at the first withdrawn position when said actuating mechanism moves said snuff back shaft between the second withdrawn position and the extended position.

4. The snuff back module of claim 1 , wherein said actuating mechanism includes a first actuator configured to move said snuff back shaft to the first withdrawn position and a second actuator configured to move said snuff back shaft to the second withdrawn position.

5. The snuff back module of claim 4, wherein said first actuator includes a pneumatically-driven first piston operatively coupled to said snuff back shaft and configured to move with said snuff back shaft through a first stroke length, and said second actuator includes a pneumatically-driven second piston operatively coupled to said snuff back shaft and configured to move with said snuff back shaft through a second stroke length longer than said first stroke length.

6. The snuff back module of claim 5, wherein said first piston includes upper and lower sides, said second piston includes upper and lower sides, and said actuating mechanism further includes a valve mechanism for selectively directing pressurized air to said lower side of said first piston, said lower side of said second piston, and/or said upper side of said second piston to move said first and second pistons.

7. The snuff back module of claim 6, wherein said valve mechanism includes a first valve and a second valve, said first valve operable to direct pressurized air to said upper side of said second piston and/or to said second valve, and said second valve operable to direct pressurized air to said lower side of said first piston or to said lower side of said second piston.

8. The snuff back module of claim 6, wherein said actuating mechanism further includes an air throttle configured to throttle exhaust flow from said lower side of said first piston, thereby limiting the speed of said snuff back shaft during movement from the first withdrawn position to the extended position.

9. A liquid dispensing apparatus, comprising:

a dispenser module including a distribution passage, an outlet passage communicating with said distribution passage, an outlet aperture

communicating with said outlet passage, and a dispenser valve moveable between open and closed positions to control flow of pressurized liquid into said distribution passage; and

a snuff back module comprising:

a snuff back shaft extending into fluid communication with said distribution passage, said snuff back shaft moveable between an extended position and a withdrawn position to draw the pressurized liquid back from said outlet aperture;

10. The liquid dispensing apparatus of claim 9, wherein said dispenser module further includes a snuff back passage communicating with said distribution passage, said snuff back shaft extending into said snuff back passage.

1 1 . The liquid dispensing apparatus of claim 10, wherein said snuff back module further comprises a snuff back module housing coupled to said dispensing module when said snuff back shaft extends into said snuff back passage.

12. The liquid dispensing apparatus of claim 9, wherein said outlet aperture of said dispenser module is a slot-shaped outlet aperture having an adjustable width, and said controller is configured to decide whether said snuff back shaft is withdrawn to the first withdrawn position or the second withdrawn position based on said width of said slot-shaped outlet aperture.

13. The liquid dispensing apparatus of claim 9, wherein said actuating mechanism includes a first actuator configured to move said snuff back shaft to the first withdrawn position and a second actuator configured to move said snuff back shaft to the second withdrawn position.

14. The liquid dispensing apparatus of claim 13, wherein said first actuator includes a pneumatically-driven first piston operatively coupled to said snuff back shaft and configured to move with said snuff back shaft through a first stroke length, and said second actuator includes a pneumatically-driven second piston operatively coupled to said snuff back shaft and configured to move with said snuff back shaft through a second stroke length longer than said first stroke length.

15. The liquid dispensing apparatus of claim 14, wherein said first piston includes upper and lower sides, said second piston includes upper and lower sides, and said actuating mechanism further includes a valve mechanism for selectively directing pressurized air to said lower side of said first piston, said lower side of said second piston, and/or said upper side of said second piston to move said first and second pistons.

16. The liquid dispensing apparatus of claim 15, wherein said actuating mechanism further includes an air throttle configured to throttle exhaust flow from said lower side of said first piston, thereby limiting the speed of said snuff back shaft during movement from the first withdrawn position to the extended position.

17. A method of dispensing a pressurized liquid from a liquid dispensing apparatus including a dispenser valve, an outlet aperture, and a snuff back shaft, the method comprising:

opening the dispenser valve to actuate flow of the pressurized liquid to the outlet aperture;

closing the dispenser valve to stop flow of the pressurized liquid to the outlet aperture;

moving the snuff back shaft from an extended position to a first withdrawn position to draw a first volume of pressurized liquid back from the outlet aperture;

moving the snuff back shaft from the extended position to a second withdrawn position to draw a second volume of pressurized liquid larger than the first volume of pressurized liquid back from the outlet aperture; and stopping the snuff back shaft at the first withdrawn position temporarily when the snuff back shaft moves between the second withdrawn position and the extended position.

18. The method of claim 17, wherein the outlet aperture is a slot-shaped outlet aperture having an adjustable width, and the method further comprises: determining whether the snuff back shaft is moved from the extended position to the first withdrawn position or to the second withdrawn position based on the width of the outlet aperture.

19. The method of claim 17, wherein the snuff back shaft is operatively coupled to a first piston operable to move the snuff back shaft to the first withdrawn position and to a second piston operable to move the snuff back shaft to the second withdrawn position, and moving the snuff back shaft further comprises:

directing pressurized air to at least one side of one or both of the first and second pistons to move the snuff back shaft.

20. The method of claim 19, wherein the first piston includes a lower side, the second piston includes a lower side, and moving the snuff back shaft further comprises:

throttling exhaust flow of pressurized air from the lower side of the first and/or second pistons to limit a speed of the snuff back shaft during movement from the second withdrawn position to the extended position.

21 . A method of dispensing a pressurized liquid from a liquid dispensing apparatus including a dispenser valve, an outlet aperture, and a snuff back shaft, the method comprising:

moving the snuff back shaft from an extended position to a first withdrawn position with a first actuator to draw a first volume of pressurized liquid back from the outlet aperture; moving the snuff back shaft from the extended position to a second withdrawn position with a second actuator to draw a second volume of pressurized liquid larger than the first volume of pressurized liquid back from the outlet aperture.

22. The method of claim 21 , wherein the outlet aperture is a slot-shaped outlet aperture having an adjustable width, and the method further comprises: determining whether the snuff back shaft is moved from the extended position to the first withdrawn position or to the second withdrawn position based on the width of the outlet aperture.

23. The method of claim 21 , wherein the first actuator includes a first piston operable to move the snuff back shaft to the first withdrawn position, the second actuator includes a second piston operable to move the snuff back shaft to the second withdrawn position, and moving the snuff back shaft further comprises: directing pressurized air to at least one side of one or both of the first and second pistons to move the snuff back shaft.