Two-stage dispensing unit

Abstract

To provide a dispenser, a dispensing unit, and a method of operating the dispenser.SOLUTION: A dispensing unit includes: a main housing having a main chamber; a reciprocating piston; a nozzle; and an adjuster assembly. The adjuster assembly further includes an actuator disposed in an adjuster chamber and axially movable within the adjuster chamber. The actuator is configured to engage a reciprocating piston assembly and to drive downward movement of the reciprocating piston assembly. The reciprocating piston assembly includes: a first piston portion having a lower end configured to pressurize a fluid within an orifice of the nozzle; and a second piston portion that is separately formed from the first piston portion and having an upper end configured to engage the actuator. The first piston portion is configured to move a first distance and the second piston portion is configured to move a second distance.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to devices and methods for dispensing viscous materials onto substrates, such as printed circuit boards. [Background technology]

[0002] Viscous material dispensers having dispensing units for dispensing electronic assembly materials operate in a variety of ways. Some known dispensing units use a servomotor to drive a rotary auger, while some use a linear servomotor to drive a piston. Other dispensing units do not use an electric servomotor but instead rely on other actuation means. One such dispensing unit includes a dispensing valve or unit that operates by using air pressure to move a piston away from a valve seat, thereby compressing a spring, and then releasing the air pressure, allowing the spring to accelerate the piston and push it back until it abuts the valve seat. This dispensing unit forces a droplet of material through an orifice in the valve seat when the piston contacts the valve seat. Such dispensing units typically use a solenoid valve to control the flow of air (or other gas) into and out of the piston chamber.

[0003] FIG. 1 illustrates one such dispensing unit 1. As shown, the dispensing unit 1 includes a main housing 2 that includes an elongated cylindrical chamber 3 formed within the housing. The dispensing unit further includes a nozzle assembly 4 secured to a lower end of the housing 2 and an elongated piston 5 disposed within the chamber 3. The piston 5 is configured to move up and down within the chamber 3. A lower end of the piston 5 engages a valve seat 6 associated with the nozzle assembly 4. The chamber 3 defines a dispensing cavity that is in fluid communication with a material supply pipe 7 adapted to receive material from a material supply assembly. The material supply pipe 7 introduces viscous material into the chamber 3 through an inlet. The viscous material is forced under pressure into a small dispensing cavity within the chamber.

[0004] The reciprocating piston 5 is actuated by an actuator, and its lower end is configured to engage a valve seat 6. The amount of material dispensed by the dispensing unit 1 is controlled by the dispensing unit's air lift distance 8 (FIG. 2A) and fluid intake lift distance 9 (FIG. 2B). Specifically, the air lift distance 8 affects the velocity of the piston 5, thereby affecting the ejected dot size. A larger air lift distance 8 increases the piston's impact velocity against the valve seat 6, imparting a higher level of kinetic energy and improving the ability to eject smaller dots. In addition, the fluid intake lift distance 9 also affects the ejected dot size. A smaller fluid intake lift distance 9 of the piston 5 reduces the amount of fluid intake, resulting in a smaller ejected dot. Summary of the Invention

[0005] In order to eject smaller dots of material, in the dispensing unit 1 shown in Figure 1, the dispensing unit does not allow for independent adjustment of the air lift distance 8 and the fluid suction lift distance 9. As shown in Figures 2A and 2B, an increase in the air lift distance 8 results in a corresponding linear increase in the fluid suction lift distance 9, and conversely, a decrease in the air lift distance 8 results in a corresponding linear decrease in the fluid suction lift distance 9. The structure of the piston 5 prevents independent adjustment of these two elements.

[0006] One aspect of the present disclosure relates to a dispenser configured to dispense a material onto a substrate. In one embodiment, the dispenser includes a frame, a support coupled to the frame and configured to receive a substrate, a gantry coupled to the frame, and a dispensing unit supported by the gantry and configured to dispense the material onto the substrate. The dispensing unit includes a main housing having a main chamber, a reciprocating piston assembly disposed within the main chamber and axially movable within the main chamber, and a nozzle coupled to the main housing. The nozzle has an orifice coaxial with the main chamber of the housing. The dispensing unit further includes an assembly coupled to the dispensing unit and configured to drive up and down movement of the reciprocating piston assembly. The assembly includes a housing coupled to the main housing. The housing has a chamber coaxial with the main chamber. The assembly further includes an actuator disposed within the chamber and axially movable within the chamber. The actuator is configured to engage the reciprocating piston assembly and drive downward movement of the reciprocating piston assembly. The reciprocating piston assembly includes a first piston portion having a lower end configured to pressurize the fluid in the orifice of the nozzle, and a second piston portion separate from the first piston portion and having an upper end configured to engage the actuator, the first piston portion configured to move a first distance, and the second piston portion configured to move a second distance.

[0007] This embodiment of the dispenser may further include a housing threadably coupled to the main housing to adjust the second distance of the second piston portion. The dispensing unit may further include a spring disposed within the chamber and configured to engage with the actuator. The spring may be configured to bias the actuator downward. The dispensing unit may further include an air lift piston body secured to the second piston portion. The air lift piston body may be configured to drive upward movement of the second piston portion and the actuator when pressurized air is delivered to a portion of the chamber below the air lift piston body. The actuator may include a flange disposed on an end of the actuator. The flange may be configured to engage with the housing when moving the second distance. The dispensing unit may further include a fluid lift regulator secured to the main housing. The fluid lift regulator may be configured to limit movement of the first piston portion a first distance. The first piston portion may include a collar configured to engage the fluid lift regulator to limit the first distance of movement of the first piston portion.

[0008] Another aspect of the present disclosure relates to a dispensing unit of a dispenser configured to dispense a material onto a substrate. In one embodiment, the dispensing unit includes a main housing having a main chamber, a reciprocating piston assembly disposed within the main chamber and axially movable within the main chamber, and a nozzle coupled to the main housing. The nozzle has an orifice coaxial with the main chamber of the housing. The dispensing unit further includes an assembly coupled to the dispensing unit and configured to drive up and down movement of the reciprocating piston assembly. The assembly includes a housing coupled to the main housing. The housing has a chamber coaxial with the main chamber. The assembly further includes an actuator disposed within the chamber and axially movable within the chamber. The actuator is configured to engage with the reciprocating piston assembly and drive downward movement of the reciprocating piston assembly. The reciprocating piston assembly includes a first piston portion having a lower end configured to pressurize a fluid within the orifice of the nozzle and a second piston portion separate from the first piston portion and having an upper end configured to engage with the actuator. The first piston portion is configured to move a first distance and the second piston portion is configured to move a second distance.

[0009] This embodiment of the dispensing unit may further include a housing threadably coupled to the main housing to adjust the second distance of the second piston portion. The dispensing unit may further include a spring disposed within the chamber and configured to engage with the actuator. The spring may be configured to bias the actuator downward. The dispensing unit may further include an air lift piston body secured to the second piston portion. The air lift piston body may be configured to drive upward movement of the second piston portion and the actuator when pressurized air is delivered to a portion of the main chamber below the air lift piston body. The actuator may include a flange disposed on an end of the actuator. The flange may be configured to engage with the housing when moving the second distance. The dispensing unit may further include a fluid lift adjuster secured to the main housing. The fluid lift adjuster may be configured to limit movement of the first piston portion a first distance. The first piston portion may include a collar configured to engage the fluid lift adjuster to limit the first distance of movement of the first piston portion.

[0010] Yet another aspect of the present disclosure is a method of operating a dispenser to dispense material onto a substrate. The dispenser includes a main housing having a main chamber, a reciprocating piston assembly disposed within the main chamber and axially movable within the main chamber, and a nozzle coupled to the main housing. The nozzle has an orifice coaxial with the main chamber of the housing. The dispenser further includes an assembly coupled to the dispensing unit and configured to drive the up and down movement of the reciprocating piston assembly. The reciprocating piston assembly includes a first piston portion and a second piston portion. In one embodiment, the method includes moving the first piston portion of the reciprocating piston assembly a first distance and moving the second piston portion of the reciprocating piston assembly a second distance, the second distance being greater than the first distance.

[0011] An embodiment of the method may further include adjusting a second distance of the second piston portion. The method may further include biasing an actuator coupled to the second piston portion downward. The method may further include driving upward movement of the second piston portion and the actuator when pressurized air is delivered to a portion of the main chamber below the air lift piston body. The actuator may include a flange disposed on an end of the actuator. The flange may be configured to engage with the housing when moving the second distance. The method may further include limiting a first distance of movement of the first piston portion using a fluid lift adjuster secured to the second piston portion.

[0012] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in various figures is represented by a like reference numeral. For clarity, not every component may be labeled in every drawing. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view of a known dispensing unit; [Figure 2A] 2 is an enlarged cross-sectional view of a portion showing an air lift distance of the discharge unit shown in FIG. 1. FIG. [Figure 2B] 1. FIG. 4 is an enlarged cross-sectional view of another portion of the discharge unit shown in FIG. 1, illustrating the fluid suction lift distance. [Figure 3] FIG. 1 is a schematic diagram of a dispenser according to one embodiment of the present disclosure. [Figure 4] FIG. 2 is a cross-sectional view of a dispensing unit according to an embodiment of the present disclosure. [Figure 5] FIG. 5 is a perspective cross-sectional view of the discharge unit shown in FIG. [Figure 6] 5 is an enlarged cross-sectional view of a portion showing a two-stage actuator of the discharge unit shown in FIG. 4. FIG. [Figure 7A]5 is an enlarged cross-sectional view of a portion showing an air lift distance of the discharge unit shown in FIG. 4. FIG. [Figure 7B] 5 is an enlarged cross-sectional view of another portion of the discharge unit shown in FIG. 4, illustrating the fluid suction lift distance. [Figure 8] FIG. 10 is a cross-sectional view of a dispensing unit according to another embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0014] For purposes of illustration only, and not for purposes of limitation of generality, the present disclosure will now be described in detail with reference to the accompanying figures. The present disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The principles presented in this disclosure are capable of other embodiments and of being practiced or carried out in various ways. Furthermore, the phraseology and terminology used herein (the description) are for purposes of description and should not be regarded as limiting. The use of "including," "comprising," "having," "containing," "involving," and variations thereof herein is intended to encompass the items previously listed and equivalents thereof, as well as additional items.

[0015] Various embodiments of the present disclosure relate to a viscous material dispensing system, an apparatus including the dispensing system, and a technique for dispensing material onto an electronic board by a dispensing unit configured to control a desired level of current through a coil of a pneumatic solenoid valve.

[0016] FIG. 3 schematically illustrates a dispenser, generally designated 10, according to one embodiment of the present disclosure. The dispenser 10 is used to dispense viscous materials (e.g., adhesives, encapsulants, epoxies, solder pastes, underfill materials, etc.) or semi-viscous materials (e.g., solder flux, etc.) onto an electronic substrate 12, such as a printed circuit board or semiconductor wafer. The dispenser 10 may alternatively be used for other applications, such as applying automotive gasket materials, in certain medical applications, or for applying conductive inks. It should be understood that references to viscous or semi-viscous materials, as used herein, are intended to be exemplary and non-limiting. The dispenser 10 generally includes first and second dispensing units, generally designated 14 and 16, respectively, and a controller 18 that controls operation of the dispenser. It should be understood that the dispensing units may also be referred to herein as dispensing pumps and / or dispensing heads. Although two dispensing units are shown, it should be understood that one or more dispensing units may be provided.

[0017] The dispenser 10 may also include a frame 20 having a base or support 22 for supporting the substrate 12, a dispensing unit gantry 24 movably coupled to the frame 20 for supporting and moving the dispensing units 14, 16, and a weight measuring device or scale 26 for weighing the dispensed amount of viscous material and providing weight data to the controller 18, e.g., as part of a calibration procedure. Other transport mechanisms, such as a conveyor system (not shown) or walking beam, may be used in the dispenser 10 to control the loading and unloading of substrates into and from the dispenser. The gantry 24 may be moved using a motor under the control of the controller 18 to position the dispensing units 14, 16 at predetermined locations above the substrate. The dispenser 10 may include a display unit 28 connected to the controller 18 for displaying various information to an operator. An optional second controller may be present for controlling the dispensing units. Each dispensing unit 14, 16 may also be configured using a z-axis sensor to detect the height at which the dispensing unit is positioned above the electronic board 12 or above features mounted on the electronic board. The z-axis sensor is coupled to the controller 18 and relays information obtained by the sensor to the controller.

[0018] As mentioned above, before performing a dispensing operation, a substrate, such as a printed circuit board, must be aligned or otherwise positioned with the dispenser of the dispensing system. The dispenser further includes a vision system 30, which in one embodiment is coupled to a vision system gantry 32 movably coupled to the frame 20 for supporting and moving the vision system. This embodiment is also shown in FIG. 3. In another embodiment, the vision system 30 may be located on the dispensing unit gantry 24. As mentioned above, the vision system 30 is employed to locate landmarks, or components, known as fiducials, on the substrate. Once the location is determined, a controller can be programmed to manipulate the movement of one or more of the dispensing units 14, 16 to dispense material onto the electronic board.

[0019] The systems and methods of the present disclosure relate to dispensing material onto a substrate, such as a circuit board. The system and method descriptions provided herein refer to an exemplary electronic board 12 (e.g., a printed circuit board) supported on a support 22 of a dispenser 10. In one embodiment, the dispensing operation is controlled by a controller 18, which may include a computer system configured to control the material dispenser. In another embodiment, the controller 18 may be operated by an operator. The controller 18 is configured to manipulate the movement of the vision system gantry 32 to move the vision system to acquire one or more images of the electronic board 12. The controller 18 is further configured to manipulate the movement of the dispensing unit gantry 24 to move the dispensing units 14, 16 to perform the dispensing operation.

[0020] Embodiments of the present disclosure relate to dispensing units, such as dispensing units 14, 16, each configured to independently adjust and control air lift distance and fluid intake lift distance. In some embodiments, the air lift distance can be ten times (10X) greater than the fluid intake lift distance. In one embodiment, a two-piece reciprocating piston of an embodiment of the present disclosure can be employed on a dispensing platform, such as the NuJet™ dispensing unit offered by ITW EAE, Inc., Hopkinton, Massachusetts.

[0021] 4 and 5, in one embodiment, a dispensing unit, generally designated 40, according to an embodiment of the present disclosure, is configured to dispense dots of assembly material, such as underfill. The dispensing unit 40 may be provided in the dispenser 10 shown in FIG. 3. The dispensing unit 40 includes a main housing 42 and a nozzle assembly, generally designated 44, releasably secured to the main housing. Specifically, the main housing 42 is configured to define an elongated chamber 46 that receives the viscous material for dispensing. A reciprocating piston assembly, generally designated 50, is disposed within the elongated chamber 46. The elongated chamber 46 defines a dispensing cavity in fluid communication with a material supply conduit 52 adapted to receive the assembly material from a material supply assembly (cartridge). The material supply conduit 52 introduces the viscous material into the elongated chamber 46 through an inlet 54. The viscous material is delivered to the elongated chamber 46 and delivered under pressure to a small dispensing cavity 56 within the elongated chamber. The reciprocating piston assembly 50 is a two-piece structure including a fluid piston 60 and an air lift piston 62 that is separate from the fluid piston. As used herein, the fluid piston 60 may be referred to as the first piston portion, and the air lift piston 62 may be referred to as the second piston portion. As shown, the fluid piston 60 is positioned below the air lift piston 62, with the fluid piston 60 biased upward and the air lift piston 62 biased downward. The fluid piston 60 and air lift piston 62 of the reciprocating piston assembly 50 are configured to be received within the elongated chamber 46 and to slidably move therewith.

[0022] Continuing with reference to FIG. 6 , the fluid piston 60 of the reciprocating piston assembly 50 of the dispensing unit 40 is prominently shown. As shown, the dispensing unit 40 includes a fluid housing 64 that defines a dispensing cavity 56 within the elongated chamber 46. The nozzle assembly 44 includes a valve seat 66 positioned at the lower end of the fluid housing 64. A nozzle nut (not shown for clarity) is threadably secured to the main housing 42 and is provided to secure the valve seat 66 in position relative to the fluid housing 64 and the main housing 42. The valve seat 66 includes a generally cylindrical member having a conical surface and a small diameter bore formed therein. In one embodiment, the valve seat 66 may be fabricated from a hard material such as carbide or a ceramic material. A diaphragm seal 68 is supported by the fluid housing 64 and is provided to seal against the fluid piston 60 of the reciprocating piston assembly 50 to maintain the viscous material within the dispensing cavity 56 of the elongated chamber 46 above the valve seat 66. This arrangement allows the viscous material to be expelled from the small diameter bore in the valve seat 66 onto a substrate, such as the circuit board 12, when the reciprocating piston assembly 50 engages the valve seat.

[0023] In one embodiment, the nozzle assembly 44 may be provided to the end user of the dispenser as a complete assembly to facilitate cleaning of the nozzle assembly. Specifically, a used nozzle assembly may be completely removed from the main housing 42 of the dispensing unit 40 by unscrewing the nozzle nut and replaced with a new (clean) nozzle assembly.

[0024] In one embodiment, a nozzle heater 70 is secured to the lower end of the main housing 42 to control the temperature of the assembly material within the dispensing cavity 56. The nozzle heater 70 includes a heater element 72 that provides controlled heat to the nozzle assembly 44. The viscosity of the assembly material affects the dispensing of the material through the small diameter bore in the valve seat 66 of the nozzle assembly 44. The nozzle heater 70 is provided to help control the viscosity of the assembly material to optimize dispensing performance.

[0025] In operation, the fluid piston 60 of the reciprocating piston assembly 50 is movable between an upper position and a lower position within the elongated chamber 46 of the main housing 42. A dispensing medium, e.g., underfill, is introduced under pressure into the dispensing cavity 56 of the elongated chamber 46 through the inlet 54, and the dispensing material flows through the fluid housing 64 to an open space above the valve seat 66. In the lower position, the fluid piston 60 seats against the valve seat 66, and in the upper position, the fluid piston is elevated a predetermined distance above the valve seat of the nozzle assembly. As described in more detail below, an actuator assembly is provided to drive the reciprocating motion of the fluid piston 60 and air lift piston 62 of the reciprocating piston assembly 50 within the elongated chamber 46 to dispense the viscous material. In some embodiments, the actuator assembly can include one of a pneumatic valve assembly, a piezoelectric actuator, a voice coil motor, or other suitable actuator that controls the movement of the reciprocating piston assembly 50, and operation of the actuator assembly moves the fluid piston 60 of the reciprocating piston assembly 50 between the upper and lower positions. When the fluid piston 60 moves to a lowered position against the valve seat 66, a small droplet of material is expelled through a small diameter bore in the valve seat.

[0026] The dispensing unit 40 provides pressurized air to a source of dispensing material to introduce the material into the elongated chamber 46 of the dispensing unit's main housing 42 via a material supply line 52. The specific pressure provided can be selected based on the material being used, the amount of material being dispensed, and the operating mode of the dispensing unit 40. During dispenser operation, a user defines a dispensing area on a circuit board through a user interface for the dispensing platform. The dispensing unit 40 can be used to dispense dots and lines of material. The dispensing unit 40 is used to dispense a line of material formed through multiple dispensing cycles of the dispenser, and is used to dispense material to selected locations on a circuit board or other substrate using individual dispensing cycles. For a line of material, the user defines the start and stop positions of the line, and the dispensing platform can move the dispensing unit to place material along the line. Once all dispensing areas on the circuit board are defined and dispensing parameters are set using the dispensing unit's control panel, the dispenser can receive the circuit board for processing. After moving the circuit board to the dispensing location, the dispenser controls the gantry system to position the dispensing unit 40 over the dispensing location. In another embodiment, the circuit board may be moved under a stationary dispensing unit. Dispensing for a particular board continues until material has been dispensed at all locations on that board. The board is then removed from the system and a new board can be loaded into the system.

[0027] 4 and 5, the dispensing unit 40 further includes an air lift regulator assembly, generally designated 80. The air lift regulator assembly 80 is configured to provide downward movement to the reciprocating piston assembly 50. As shown, the air lift regulator assembly 80 includes an upper regulator housing 82 and a lower regulator housing 84 coupled to and positioned below the upper regulator housing. The lower regulator housing 84 is threadably secured to the main housing 42 of the dispensing unit 40. The upper and lower regulator housings 82 and 84 are each configured to have an elongated chamber, designated 86, that is coaxial with the elongated chamber 46 of the main housing 42 along a common axis. The air lift regulator assembly 80 further includes an actuator 88 disposed within the elongated chamber 86. A portion of the lower regulator housing 84 guides the up and down movement of the actuator 88 within the lower and upper regulator housings 82 and 82.

[0028] A lower end of actuator 88 includes a flange 90 that a spring 92 engages to bias the actuator downward within elongated chamber 86 of lower regulator housing 84. As shown, spring 92 engages a portion of lower regulator housing 84 and flange 90 to bias actuator 88 downward. The lower end of actuator 88 is configured to engage an upper end of air lift piston 62 of reciprocating piston assembly 50, such that movement of actuator 88 causes movement of the air lift piston of reciprocating piston assembly 50.

[0029] The amount of up and down adjustment of actuator 88 is controlled by rotating upper regulator housing 82, which in turn rotates lower regulator housing 84, to adjust the distance between flange 90 and bushing 94 provided within the lower regulator housing. The greater the distance between flange 90 and bushing 94, the greater the movement of actuator 88 and, therefore, the greater the velocity the actuator will achieve when driving downward movement of reciprocating piston assembly 50. Engagement of flange 90 with bushing 94 limits the upward movement of actuator 88.

[0030] The amount of up and down movement of actuator 88 is further affected by an air lift piston assembly that is configured to move the actuator upward against the bias of spring 92. As shown, the air lift piston assembly includes a disk-shaped air lift body 96 that is secured to air lift piston 62 of reciprocating piston assembly 50 at a location where the upper end of the air lift piston extends beyond the disk-shaped body. With this arrangement, pressurized air introduced by air line 98 into the portion of elongated chamber 46 below air lift body 96 causes upward movement of actuator 88 against the bias of spring 92. As mentioned above, the axial distance between flange 90 and bushing 94 of lower regulator housing 84 can be adjusted by rotating upper regulator housing 82 (and therefore lower regulator housing 84) relative to main housing 42 to create an air gap between the flange and bushing. This air gap allows for a greater distance between the actuator 88 and the upper end of the air lift piston 62 of the reciprocating piston assembly 50, thereby increasing the working distance and therefore the speed of the actuator when dispensing material.

[0031] The larger the air gap distance, the greater the distance traveled by the actuator and reciprocating piston assembly. Conversely, the smaller the air gap distance, the smaller the distance traveled by the actuator and piston. As noted above, the greater the distance, the greater the velocity of the piston impact by the fluid piston 60 of the reciprocating piston assembly 50 against the valve seat 66, imparting a higher level of kinetic energy and therefore improving the ability to eject smaller dot sizes. Figure 7A shows the air lift distance 100.

[0032] The dispensing unit 40 further includes a fluid lift adjuster assembly that adjusts the fluid intake lift distance. As shown, the fluid lift adjuster assembly includes a fluid lift adjuster 102 coupled to the air lift piston 62 of the reciprocating piston assembly 50 and disposed within the elongated chamber 46 of the main housing 42. The fluid lift adjuster 102 includes a cup seal 104 that contains pressurized air below the air lift body 96. A fluid lift collar 106 is secured to the upper end of the fluid piston 60 of the reciprocating piston assembly 50. A spring 108 is disposed between the fluid lift collar 106 and the main housing 42 to bias the fluid lift collar upward. The fluid lift adjuster 102 is secured to the main housing 42 with precision threads and configured to guide the reciprocating piston assembly 50 and engage the fluid lift collar 106. The axial position of the fluid lift adjuster 102 determines the fluid intake lift distance of the fluid piston 60 of the reciprocating piston assembly 50. FIG. 7B shows the fluid intake lift distance 110.

[0033] Because the air lift piston 62 of the reciprocating piston assembly 50 is separate from the fluid piston 60 of the reciprocating piston assembly, the air lift distance 100 can be controlled independently of the fluid intake lift distance 110. If it is desired to minimize the impact of the fluid piston 60 against the valve seat 66, the air lift distance 100 is minimized. If it is desired to maximize the impact of the fluid piston 60 against the valve seat 66, the air lift distance 100 is maximized. As a result, the fluid piston 60 is configured to move a first distance and the air lift piston 62 is configured to move a second distance, where the second distance can be greater than the first distance. In some embodiments, the second distance achieved by the air lift piston 62 is ten times greater than the first distance achieved by the fluid piston 60. It should be understood that the first distance can be configured to be greater than the second distance, if desired. The movement of the fluid piston 60 can be configured to be the same as or different from the movement of the air lift piston 62.

[0034] As mentioned above, to produce smaller dots of material, it is desirable to optimize the air lift distance 100 and the fluid suction lift distance 110. In one example, the air lift distance 100 is 250 microns and the fluid suction lift distance 110 is 100 microns. Other optimized distances can be provided depending on the material being dispensed.

[0035] The fluid intake lift distance 110 is minimized when it is desired to minimize the amount of material introduced into the elongated chamber 46 of the main housing 42. The fluid intake lift distance 110 is maximized when it is desired to maximize the amount of material introduced into the elongated chamber 46 of the main housing 42. As discussed above, to produce smaller dots of material, it is desirable to minimize the amount of material delivered to the discharge cavity 56 of the elongated chamber 46 of the main housing 42, and therefore minimize the fluid intake lift distance 110.

[0036] It should be noted that the air lift distance 100 and the fluid suction lift distance 110 can be adjusted independently of one another. The air lift distance 100 is achieved by adjusting the upper regulator housing 82 as described above. The fluid lift distance 110 is achieved by adjusting the fluid lift regulator 102 as described above. The independent adjustments allow for optimization of the control over the size of the dots dispensed by the dispensing unit 40.

[0037] In one embodiment, an air valve assembly, generally designated 120, provides the reciprocating axial movement of the reciprocating piston assembly. Specifically, during operation of the dispensing unit 40, the air valve assembly 120, in conjunction with the air lift regulator assembly, drives the up and down movement of the reciprocating piston assembly 50. In one particular embodiment, the air valve assembly 120 directs pressurized air through the air line 98 beneath the disk-shaped air lift body 96 and into the elongated chamber 46 of the main housing 42. The air valve assembly 120 can be configured to supply pressurized air to drive the upward movement of the air lift body and actuator against the bias of the spring 108. A vent 122 is provided to exhaust air from the elongated chamber 46 of the main housing 42. The air valve assembly 120 supplies and then exhausts the pressurized air through the air line 98. This allows the air lift piston 62 and fluid piston 60 of the reciprocating piston assembly 50 to dispense dots of material through the small diameter bore in the valve seat 66. In one embodiment, the air valve assembly 120 operates at a rate of 300 cycles per second (300 Hertz). The air valve assembly 120 can be configured to operate at any desired rate.

[0038] Because the fluid piston 60 is separated from the air lift piston 62 of the reciprocating piston assembly 50, the fluid piston is able to maintain a relatively small fluid intake distance 110. Thus, when the air valve assembly 120 circulates pressurized air into the elongated chamber 46 of the main housing 42, the air lift body 96 and air lift piston 62 can move away from the fluid piston 60, thereby allowing for a larger air lift distance 100 for the air lift piston. The actuator 88 and air lift piston 62 can achieve a larger travel distance, thereby achieving a higher velocity for the fluid piston 60 to produce a smaller dot of material.

[0039] In another embodiment, the air valve assembly 120 can be replaced by a piezoelectric actuator assembly coupled to the air lift regulator assembly to achieve rapid up and down movement of the reciprocating piston assembly 50. The piezoelectric actuator assembly can operate at speeds up to 1000 Hz. A sensor assembly can be included to detect the movement of the piezoelectric actuator assembly in a closed loop. The sensor assembly can be used as part of a control system to provide feedforward control of the reciprocating piston movement. An adaptive routine can be provided that can vary the drive signal used to drive the actuator assembly to ensure the desired motion profile is achieved despite changes in operating parameters such as viscosity. For example, the viscosity of a material can change over time and temperature. This change in viscosity can change the load on the actuator assembly, which can alter the actual motion achieved. By detecting this change in the motion profile, subsequent drive signals can be adjusted as needed to maintain the desired motion profile. Because these operating parameters tend to change gradually over time and temperature, the feedforward adaptive routine can track these changes in real time. This is distinct from a feedback control system, which varies the drive signal in real time across the full bandwidth of the system. A feedforward control system only needs to adapt at a rate faster than the variations it is trying to compensate for. The overwhelming advantage of feedforward control systems is that, unlike feedback control systems, they can be designed to be unconditionally stable.

[0040] In another embodiment, a voice coil motor actuator assembly may be provided for operating the dispensing unit. Voice coil motor actuator assemblies are known in the art and may be suitably coupled to the dispensing unit to drive movement of the piston.

[0041] In operation, the dispensing unit is positioned at a nominal clearance height above a substrate, such as a circuit board 12. While variations in the height of the circuit board or irregularities in the flatness of the top surface of the circuit board can cause the clearance height to vary without adversely affecting the dispensing of the viscous material, this clearance height is maintained at a relatively consistent height above the circuit board throughout the entire dispensing operation. Specifically, the dispensing unit is not required to lift the nozzle in the z-axis direction off the circuit board at the end of each dispensing operation. However, to accommodate variations in the height of the circuit board and irregularities in the flatness of the circuit board (or even to avoid obstacles), the dispenser can be configured to achieve z-axis movement. In certain embodiments, a laser detection system can be used to determine the height of the dispenser.

[0042] In another embodiment, the two-piece reciprocating piston can be employed in another platform, such as the SmartStream™ dispensing unit offered by ITW EAE. For example, referring to FIG. 8 , in another embodiment, a dispensing unit is generally designated 130. Similar to dispensing unit 40, dispensing unit 130 is configured to dispense dots of assembly material, such as underfill, onto a substrate. Dispensing unit 130 can be incorporated into dispenser 10 shown in FIG. 3 . The primary difference between dispensing unit 130 and dispensing unit 40 is that dispensing unit 130 dispenses a viscous material, such as underfill material, by pressure generated by a reciprocating piston assembly through a valve within a dispensing cavity. In other words, dispensing unit 130 operates by generating pressure to dispense the viscous material rather than by piston impact against a valve seat. As shown, dispensing unit 130 includes a two-piece reciprocating piston assembly 132 having a fluid piston 134 and a separate air lift piston 136. The operation of reciprocating piston assembly 132 is similar to the operation of reciprocating piston assembly 50 .

[0043] Various controllers, such as controller 18, can perform the various operations described above. Using data stored in associated memory and / or storage devices, controller 18 also executes one or more instructions stored on one or more non-transitory computer-readable media that controller 18 may include and / or couple to, resulting in manipulated data. In some examples, controller 18 can include one or more processors or other types of controllers. In one example, controller 18 is or includes at least one processor. In another example, controller 18 performs at least some of the operations described above using application-specific integrated circuits tailored to perform particular operations in addition to or instead of a general-purpose processor. As illustrated by these examples, examples according to the present disclosure can perform the operations described herein using many specific combinations of hardware and software, and the disclosure is not limited to any particular combination of hardware and software components. Examples of the present disclosure can include computer program products configured to perform the methods, processes, and / or operations described above. The computer program product can be or include one or more controllers and / or processors configured to execute instructions to perform the methods, processes, and / or operations described above.

[0044] Having thus described several aspects of at least one embodiment of this disclosure, it will be understood that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

Claims

1. 1. A dispenser configured to dispense a material onto a substrate, comprising: The frame and a support coupled to the frame and configured to receive the substrate; a gantry coupled to the frame; a dispensing unit supported by the gantry and configured to dispense material onto the substrate, a main housing having a main chamber; a reciprocating piston assembly disposed within the main chamber and axially movable within the main chamber; a nozzle connected to the main housing, the nozzle having an orifice coaxial with the main chamber of the housing; an assembly coupled to the dispensing unit and configured to drive the up and down movement of the reciprocating piston assembly, a housing coupled to the main housing, the housing having a chamber coaxial with the main chamber; an actuator disposed within the chamber and axially movable within the chamber, the actuator configured to engage the reciprocating piston assembly and drive downward movement of the reciprocating piston assembly; an assembly having a discharge unit comprising: Equipped with the reciprocating piston assembly comprises a first piston portion having a lower end configured to pressurize fluid in the orifice of the nozzle, and a second piston portion spaced from the first piston portion and having an upper end configured to engage the actuator; the first piston portion is configured to move a first distance and the second piston portion is configured to move a second distance; dispenser.

2. 10. The dispenser of claim 1, wherein the housing is threadably coupled to the main housing to adjust the second distance of the second piston portion.

3. 3. The dispenser of claim 2, wherein the dispensing unit further comprises a spring disposed within the chamber and configured to engage the actuator, the spring configured to bias the actuator downward.

4. 4. The dispenser of claim 3, wherein the dispensing unit further comprises an air lift piston body secured to the second piston portion, the air lift piston body configured to drive upward movement of the second piston portion and the actuator when pressurized air is delivered to a portion of the main chamber below the air lift piston body.

5. The dispenser of claim 2 , wherein the actuator includes a flange on an end of the actuator, the flange configured to engage the housing when moved the second distance.

6. 2. The dispenser of claim 1, wherein the dispensing unit further includes a fluid lift regulator secured to the main housing, the fluid lift regulator configured to limit movement of the first piston portion the first distance.

7. 7. The dispenser of claim 6, wherein the first piston portion includes a collar configured to engage the fluid lift regulator to limit the first distance of travel of the first piston portion.

8. 1. A dispensing unit of a dispenser configured to dispense a material onto a substrate, comprising: a main housing having a main chamber; a reciprocating piston assembly disposed within the main chamber and axially movable within the main chamber; a nozzle connected to the main housing, the nozzle having an orifice coaxial with the main chamber of the housing; an assembly coupled to the dispensing unit and configured to drive the up and down movement of the reciprocating piston assembly, a housing coupled to the main housing, the housing having a chamber coaxial with the main chamber; an actuator disposed within the chamber and axially movable within the regulator chamber, the actuator configured to engage the reciprocating piston assembly and drive downward movement of the reciprocating piston assembly; and an assembly having Equipped with the reciprocating piston assembly comprises a first piston portion having a lower end configured to pressurize fluid in the orifice of the nozzle, and a second piston portion spaced from the first piston portion and having an upper end configured to engage the actuator; the first piston portion is configured to move a first distance and the second piston portion is configured to move a second distance; Discharge unit.

9. 9. The dispensing unit of claim 8, wherein the housing is threadably connected to the main housing to adjust the second distance of the second piston portion.

10. 10. The dispensing unit of claim 9, further comprising a spring disposed within the chamber and configured to engage the actuator, the spring configured to bias the actuator in a downward direction.

11. 11. The dispensing unit of claim 10, further comprising an air lift piston body secured to the second piston portion, the air lift piston body configured to drive upward movement of the second piston portion and the actuator when pressurized air is delivered to a portion of the main chamber below the air lift piston body.

12. 10. The dispensing unit of claim 9, wherein the actuator comprises a flange on an end of the actuator, the flange configured to engage the housing when moved the second distance.

13. 9. The dispensing unit of claim 8, further comprising a fluid lift adjuster secured to the main housing, the fluid lift adjuster configured to limit travel of the first piston portion the first distance.

14. 14. The dispensing unit of claim 13, wherein the first piston portion comprises a collar configured to engage the fluid lift regulator to limit the first distance of travel of the first piston portion.

15. 1. A method of operating a dispenser to dispense material onto a substrate, the dispenser comprising: a main housing having a main chamber; a reciprocating piston assembly disposed within the main chamber and axially movable within the main chamber; a nozzle coupled to the main housing, the nozzle having an orifice coaxial with the main chamber of the housing; and an assembly coupled to the dispensing unit, the assembly configured to drive up and down movement of the reciprocating piston assembly, the reciprocating piston assembly comprising a first piston portion and a second piston portion, the method comprising: moving the first piston portion of the reciprocating piston assembly a first distance; moving the second piston portion of the reciprocating piston assembly a second distance; Including, the second distance is greater than the first distance; method.

16. The method of claim 15 further comprising adjusting the second distance of the second piston portion.

17. The method of claim 15 further comprising biasing an actuator coupled to the second piston portion downward.

18. 18. The method of claim 17, further comprising driving upward movement of the second piston portion and the actuator when pressurized air is delivered to a portion of the main chamber below an air lift piston body of the second piston portion.

19. 18. The method of claim 17, wherein the actuator includes a flange on an end of the actuator, the flange configured to engage the housing when moved the second distance.

20. 16. The method of claim 15, further comprising limiting the first distance of travel of the first piston portion with a fluid lift adjuster fixed to the second piston portion.

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