Patent Publication Number: US-2018043388-A1

Title: Pneumatically-driven jetting valves with variable drive pin velocity, improved jetting systems and improved jetting methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. 13/219,070, also filed Aug. 26, 2011, and published as U.S. Patent App. Pun. No. 2013/0052359 on Feb. 28, 2013, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     The invention relates generally to the jetting of fluid materials and, in particular, to electro-pneumatic jetting valves, jetting systems and improved jetting methods. 
     Jetting valves are used in the electronic packaging assembly to jet minute dots of a fluid material onto a substrate. Numerous applications exist for jetting valves that jet fluid materials such as underfill materials, encapsulation materials, surface mount adhesives, solder pastes, conductive adhesives, and solder mask materials, fluxes, and thermal compounds. As the type of fluid material changes, the jetting valve must be adapted to match the fluid material change. A “jetting valve” or “jetting device” is a device which ejects, or “jets”, a droplet of material from the dispenser to land on a substrate, wherein the droplet disengages from the dispenser nozzle before making contact with the substrate. Thus, in a jetting type dispenser, the droplet dispensed is “in-flight” between the dispenser and the substrate, and not in contact with either the dispenser or the substrate, for at least a part of the distance between the dispenser and the substrate. 
     Materials that can be jetted by means of jetting valves can have different characteristics, such as viscosity, elasticity, etc. As the characteristics change, different needle velocities are required to promote proper jetting from the jetting valve. Needle velocity affects key characteristics of the jetted fluid material, such as proper break-off, dot velocity, and satellite generation. In general, thicker, higher viscosity materials require a higher needle velocity to be jetted than thinner, lower viscosity materials. 
     Jetting valves may be electro-pneumatically actuated using a pneumatic piston that moves a needle used to jet the fluid material as the needle strikes a valve seat. In conventional designs for electro-pneumatic jetting valves, a single solenoid valve is used to port air pressure to the pneumatic piston to open the jetting valve and a return spring is used to close the jetting valve at a fast enough speed to jet a droplet of material. As a result, the velocity of the needle, or drive pin, is not highly variable and generally remains within a relatively narrow range. Given that the needle velocity is limited to a relatively narrow range, the range of material viscosities that can be jetted is likewise limited in such jetting devices. 
     While conventional jetting valves have proven adequate for certain applications, improved jetting valves are needed with a higher capability for adapting to different fluid material characteristics. 
     SUMMARY OF THE INVENTION 
     Pneumatic Jetting Valve with Overlap Period Controlling Drive Pin Speed 
     In one embodiment, a jetting valve is provided for use with a supply of fluid material and a supply of air pressure. The jetting valve includes a pneumatic actuator having a pneumatic piston and a drive pin extending from the pneumatic piston. The jetting valve further includes a housing having a first chamber and a second chamber. The pneumatic piston is enclosed between the first and second chambers, and the drive pin is moved by the pneumatic piston. First and second solenoid valves are connected to the supply of air pressure. The first solenoid valve has a first state in which air pressure is supplied to the first chamber to apply a first force to the pneumatic piston for moving the pneumatic piston and drive pin in a first direction. The first solenoid valve has a second state in which the first air chamber is vented to ambient pressure. The second solenoid valve has a first state in which air pressure is supplied to the second chamber to apply a second force to the pneumatic piston for moving the pneumatic piston and drive pin in a second direction. The second solenoid valve has a second state in which the second air chamber is vented to ambient pressure. 
     The jetting valve may further include a fluid chamber and a nozzle. The fluid chamber may enclose a valve seat and a valve element. The nozzle has a dispense orifice and a flow passage in fluid communication with the valve seat. The valve element is movable to a position in contact with the valve seat to jet a droplet of material from the dispense orifice. 
     A controller of the jetting valve is operable to hold the first solenoid valve in the first state for a first time period and the second solenoid valve in the first state for a second time period, where the beginning of the second time period follows the beginning of the first time period. The drive pin is moved towards the valve seat during the second time period, and the movement of the drive pin during the second time period causes the valve element to move into contact with the valve seat to jet a droplet of material. The controller maintains a predetermined overlap period between said first time period and said second time period. The overlap period is used to control the speed of the drive pin as the drive pin is moved towards the valve seat during the second time period, which in turn, controls the speed of the valve element as it contact with the valve seat. The faster the drive pin is moved, the faster the valve element moves. 
     The jetting valve may further include a fluid module containing the fluid chamber. The movement of the drive pin during the second time period causes the drive pin to contact the fluid module, and the contact of the drive pin with the fluid module causes the valve element to move into contact with the valve seat. The jetting valve may further include a resilient member in the fluid module, the resilient member configured to bias the valve element away from the valve seat. 
     The housing of the jetting valve may include a spring that exerts a spring bias on the pneumatic piston. The spring may be compressed when the pneumatic piston is moved in the first direction by compressed air supplied to the first chamber, and the spring may be expanded when the pneumatic piston is moved in the second direction by compressed air supplied to the second chamber. 
     Each movement of the valve element jetting valve into contact with the valve seat may operate to jet a droplet of material through the nozzle orifice. 
     Systems Having User Interface to Control Valve Speed of a Pneumatic Jetting Device 
     In another embodiment, a system for jetting is provided that includes a jetting device having a pneumatic piston that causes movement of a valve element that contacts a valve seat to jet a droplet of material and a controller having a user interface that enables the user to vary the speed of the valve element. 
     The jetting device can have upper and lower piston chambers on opposite sides of the piston that are controlled by independent solenoid valves, wherein the speed of the valve element is controlled by the control of the solenoids. 
     In another embodiment, the solenoids can be controlled to provide a desired overlap time period during which compressed air is supplied to both the upper and lower piston chambers at the same time to control the speed of the valve element. 
     Methods for Jetting from a Pneumatically Actuated Jetting Device Having a Valve Speed User Interface 
     In one method, the jetting device has pneumatically driven piston that causes a valve element to move into contact with a valve seat to jet a droplet of material, and a user interface is provided that the user can use to input information that is used by the controller to vary the speed of the valve element. 
     The jetting device can have upper and lower piston chambers on opposite sides of the piston that are controlled by independent solenoid valves, wherein the speed of the valve element is controlled by the control of the solenoids. 
     Various other methods are described below that will not be reiterated here to avoid unnecessary duplication. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and, together with a general description of embodiments of the invention given above, and the detailed description given below, serve to explain the principles of the embodiments of the invention. 
         FIG. 1A  is a perspective view of a jetting valve in accordance with an embodiment of the invention. 
         FIG. 1B  is a perspective view similar to  FIG. 1A  in which an outer housing of the modular jetting device has been removed for purposes of description. 
         FIG. 2  is a cross-sectional view taken generally along line  2 - 2  in  FIG. 1B , but showing only the heater, fluid module and piston housing, and functional blocks representing the components for supplying compressed air to the piston chambers. 
         FIG. 3  is a diagrammatic view of the hydraulic circuit of the jetting valve of  FIGS. 1 and 2 . 
         FIG. 4  is a diagrammatic view of the control signals for the solenoid valves used to operate the electro-pneumatic jetting valve of  FIGS. 1-3  in accordance with an embodiment of the invention. 
         FIG. 5  is a diagrammatic view similar to  FIG. 4  in which the timing of the control signals for the solenoid valves is modified so that the overlap time over which air pressure is applied to the air chambers is reduced in comparison with  FIG. 4 . 
         FIG. 6  is a graph of overlap time versus viscosity. 
     
    
    
     DETAILED DESCRIPTION 
     Subheadings are provided in some sections below to help guide the reader through some of the various embodiments, features and components of the invention. 
     Generally, the embodiments of the invention relate to a jetting valve that uses first and second solenoid valves to operate a pneumatic piston of an electro-pneumatic actuator, which precipitates movement of a valve element for opening and closing the jetting valve. Independent air lines are coupled with top and bottom chambers of the pneumatic piston. The first and second solenoid valves independently control the air pressure supplied to the top and bottom chambers of a pneumatic piston. The first solenoid valve is used to open the jetting valve and the second solenoid valve is used to close the jetting valve. The velocity of the needle that is fixed to the piston to cause the valve to open and close can be varied by changing the amount of time that the action of the second solenoid valve in supplying compressed air to the top piston chamber overlaps with the action of the first solenoid valve in supplying compressed air to the bottom piston chamber. By controlling the amount of overlap in the electric pulses controlling these first and second solenoid valves, the operator can control the needle velocity, and thereby select, or produce, an optimum needle velocity for the fluid material being jetted, based its fluid material characteristics. 
     With reference to  FIGS. 1A-3  and in accordance with an embodiment of the invention, a jetting valve  10  includes a fluid module  12  that has a valve element  14 , an electro-pneumatic actuator  16 , an outer cover  18 , and a fluid interface  20 . The outer cover  18  is composed of thin sheet metal and is fastened to the inner framework of the jetting valve  10  by conventional fasteners. The jetting valve  10  includes a syringe holder  26  mounted as an appendage to the outer cover  18 . A syringe  22  is supported by the syringe holder  26  and the jetting valve  10  is supplied with pressurized fluid material from the syringe  22 . Generally, the fluid material may be any material or substance known by a person having ordinary skill in the art to be amenable to jetting and may include, but is not limited to, solder flux, solder paste, adhesives, solder mask, thermal compounds, oil, encapsulants, potting compounds, inks and silicones. When the fluid material in the syringe  22  is depleted or changed, the syringe  22  is removed from the syringe holder  26  and replaced. 
     The jetting valve  10  may be installed on a robot, for example, in a machine or system (not shown) for intermittently jetting amounts of a fluid material as dots onto a substrate, such as a printed circuit board. The jetting valve  10  may be operated such that a succession of jetted amounts of the fluid material are deposited on the substrate as a line of spaced-apart dots. The substrate targeted by the jetting valve  10  may support various surface mounted components, which necessitates jetting the minute amounts of fluid material rapidly and with accurate placement to deposit fluid material at targeted locations on the substrate. 
     Fluid Module 
     As best visible in  FIG. 2 , the fluid module  12  may include a nozzle  28 , a module body  30 , and a fluid chamber  38  in communication with the fluid connection interface  20 . A first section or portion  40  of the module body  30  includes a fluid passageway  42  that couples the fluid interface  20  in fluid communication with the fluid chamber  38  through passageways  47 ,  47   a  (later described). A fluid conduit  44  ( FIG. 1B ) extends from the syringe  22  to the fluid interface  20  for placing the fluid module  12  in fluid communication with the fluid material contained inside the syringe  22  and for supplying the fluid material under pressure from the syringe  22  to the fluid connection interface  20 . In this embodiment, the fluid conduit  44  is typically a length of tubing directly connecting the outlet of the syringe  22  with the fluid connection interface  20  without any intervening structure. In one embodiment, the fluid connection interface  20  includes a Luer fitting. 
     The syringe  22  may be configured to use pressurized air to direct the fluid material to flow toward the fluid interface  20  and ultimately to the fluid chamber  38  of the fluid module  12 . The pressure of the pressurized air, which is supplied to the head space above the fluid material contained in the syringe  22 , may range from forty (40) psig to sixty (60) psig. Typically, a wiper or plunger (not shown) is disposed between the air pressure in the head space and the fluid material level inside the syringe  22 , and a sealing cap (not shown) is secured to the open end of the syringe barrel for supplying the air pressure. 
     A second portion  45  of the module body  30  is configured to support the nozzle  28 . A valve seat  52  is disposed between the fluid inlet  42  and the fluid chamber  38 . The valve seat  52  has an opening  54  in fluid communication with the fluid outlet  48 . 
     The fluid module  12  may further include a strike plate in the form of a wall  62  of a movable element  60 . A biasing element  68 , which peripherally contacts the movable element  60 , is configured to apply an axial spring force to the movable element  60 . 
     A sealing ring  64  supplies a sealing engagement between an insert  63  and the exterior of the movable element  60 . The part of the moveable element  60  which is below sealing ring, or O-ring,  64  defines a part of the boundary of the fluid chamber  38 . The valve element  14  is attached to moveable element  60  and is located inside the fluid chamber  38  at a location between the wall  62  of the movable element  60  and the valve seat  52 . Alternately, valve element  14  and movable element  60  may be constructed as a single unitary element, rather than two separate elements. 
     A third portion  32  of the module body is attached to the top of insert  63  by a friction fit. The second portion  45  of the module body is attached by a friction fit to the first portion  40  of the module body to enclose all the other components of the fluid module. Namely, once first portion  40  and second portion  45  are pressed together they enclose these parts of the fluid module: nozzle  28 , valve seat  52 , valve element  14 , movable element  60 , sealing ring  64 , biasing element  68 , insert  63  and third portion  32  of the module body. Thus, in the preferred embodiment, the fluid module is comprised of elements  45 ,  40 ,  28 ,  52 ,  14 ,  60 ,  64 ,  68 ,  63  and  32 . As an alternative to using friction fits, threaded connections could be used to allow these components to be more easily disassembled. 
     In the assembled position described above and shown in  FIG. 2 , the passageways  47  and  47   a  that couple the fluid passage  42  in fluid communication with the fluid chamber  38  are provided as follows. Annular passageway  47   a  is created by a space provided between first portion  40  and third portion  32  of module body  30 . Passageway  47  is provided by grooves or channels formed on the outside of insert  63 . When insert  63  is press fit into second portion  45  of the module body  30 , the grooves on the exterior of insert  63  and the interior surface of second portion form passageways  47 . If insert  63  were threaded into second portion  45 , instead of being press fit into it, a fluid passageway could be drilled through the insert  63  provide a flow path from fluid passage  42  to fluid chamber  38 . 
     Syringe 
     As described above, a fluid conduit  44  ( FIG. 1 ) extends from the syringe  22  to the fluid interface  20  for placing the fluid module  12  in fluid communication with the fluid contained inside the syringe  22  and for supplying the fluid material under pressure from the syringe  22  to the fluid interface  20 . The fluid conduit  44  may be a length of tubing directly connecting the syringe  22  and fluid interface  20  without any intervening structure. Fluid material is fed through the passageway  42  to the fluid chamber  38  and, as fluid material is dispensed by the jetting valve  10 , the arriving fluid material from the syringe  22  replenishes the fluid material volume in the fluid chamber  38 . 
     The syringe  22  is configured to use pressurized air to direct the fluid material to the passageway  42  and ultimately through a passageway  47  in the fluid module  12  to the fluid chamber  38 . The pressurized air, which is confined by a wiper or plunger (not shown) in a headspace above the fluid material contained in the syringe  22 , may range from five (5) psig to sixty (60) psig. 
     Drive Pin 
     A drive pin  36  is indirectly coupled with the valve element  14  to jointly cooperate with fluid module  12  to jet fluid material from the jetting valve  10 . The tip  34  of the drive pin  36  operates in a hammer-like manner to transfer its momentum in an impulse to the wall  62  of the movable element  60 . The valve element  14  is disposed inside the fluid chamber  38  on the opposite side of the wall  62  of the movable element  60  from the tip  34  of the drive pin  36 . The impact of the tip  34  of the actuated drive pin  36  with the wall  62  of the movable element  60  causes the valve element  14  to impact the valve seat  52  and jet fluid material from the fluid chamber  38 . The faster the drive pin  36  is moving when it strikes the wall  62 , the faster the valve element  14  will move to impact the valve seat  52  and jet a droplet of material. Consequently, by controlling the speed of the drive pin  36  in the manner described below, the speed of the valve element  14  is also controlled. As described above, biasing element  68  is in contact with the movable element  60  to apply an axial spring force to the movable element  60 . When the drive pin  36  is not pushing down on the wall  62 , the valve element  14  and movable element  60  are moved away from the valve seat  52  by the axial spring force applied by the biasing element  68 . As mentioned above, the movable element  60  and the valve element  14  may be constructed as a single, unitary component, rather than as two separate components. 
     Heater 
     A heater  76 , which has a body  80  that operates as a heat transfer member, at least partially surrounds the fluid module  12 . The heater  76  may include a conventional heating element (not shown), such as a cartridge-style resistance heating element residing in a bore defined in the body  80 . The heater  76  may also be equipped with a conventional temperature sensor (not shown), such as a resistive thermal device (RTD), a thermistor, or a thermocouple, providing a feedback signal for use by a temperature controller in regulating the power supplied to the heater  76 . The heater  76  includes spring-loaded pins  79  that contact respective contacts  59  in the piston housing  90  in order to provide signal paths for a temperature sensor and to provide current paths for transferring electrical power to the heating element and temperature sensor. 
     As best seen in  FIG. 2 , the fluid module  12  sits within the heater  76 . With reference to  FIG. 1B , arms  91   a  and  91   b  include lower ends that are received within the holes  78  of heater  76  and are releasably secured within the heater  76  by spring biased clips  77  that are received within slots (not shown) in the arms  91   a ,  91   b . As the knob  250  is rotated, the bolt  260  that is fixed to knob  250  rotates within a threaded collar  270  that is fixed to the arms  91   a  and  91   b . Thus, knob  250  is rotated until the heater  76  and fluid module  12  are brought up into compressive contact with the piston body  90 . 
     To remove the fluid module  12  and heater  76 , the knob  250  is rotated in the reverse direction to lower the fluid module  12  and heater  76  away from piston body  90 . The spring biased clips  77  are then depressed to withdraw the clips from the slots in arms  91   a ,  91   b , so that the fluid module  12  and heater  76  can be detached from the jetting valve  10 . To reattach fluid module  12  and heater  76 , the lower ends of arms  91   a ,  91   b  are inserted into the holes  78  in heater  76  until the latches  77  snap into the slots in the arms  91   a ,  91   b . The knob  250  is then rotated until heater  76  and fluid module  12  are brought into contact with piston body  90 . 
     Opposing Piston Air Chambers with Independent Solenoids 
     With reference to  FIGS. 2 and 3 , the electro-pneumatic actuator  16  of the jetting valve  10  includes the drive pin  36  and a pneumatic piston  80  affixed to one end of the drive pin  36 . A pair of air piston chambers  92 ,  96  are defined inside a piston housing  90  of the jetting valve  10  and separated from each other by the pneumatic piston  80 . The volume of each of the air chambers  92 ,  96  can vary according to the position of the pneumatic piston  80 . A compression spring  86  is captured between a spring retainer  118  and the pneumatic piston  80 . The force applied by the compression spring  86  operates as a closure force that acts on the pneumatic piston  80  and drive pin  36  to bias the drive pin  36  toward the wall  62  of the movable element  60 . Thus, when both piston chambers  92 ,  96  are vented to atmosphere, the spring  86  bias drive pin  36  against the wall  62 , which in turn, biases the valve element  14  against the valve seat  52 , to maintain the jetting valve  10  in the normally closed position. 
     The jetting valve  10  includes solenoid valves  82 ,  84 , which are electro-mechanical devices used to control the flow of air pressure from an air supply  93  to the air chambers  92 ,  96 . Air chamber  92  is disposed on one side of the pneumatic piston  80  and air chamber  96  is disposed on the opposite side of the pneumatic piston  80  from air chamber  92 . As the pneumatic piston  80  moves in response to selective pressurization of the air chambers  92 ,  96 , the volume of each of the air chambers  92 ,  96  will change. 
     The first solenoid valve  82  is coupled by a first passageway  88  penetrating the housing  90  of the jetting valve  10  with the air chamber  92  on one side of the pneumatic piston  80 . As shown in  FIG. 3 , the first solenoid valve  82  includes a mechanical valve  55  with an air inlet port  56 , an air exhaust port  58 , and a flow path  57  that can be switched to be coupled with either the air inlet port  56  or the air exhaust port  58 . The first solenoid valve  82  is configured to either port air pressure from the air supply  93  through the air inlet port  56  and first passageway  88  to the air chamber  92  or to exhaust air pressure from the air chamber  92  through the first passageway  88  and air exhaust port  58 . The air pressure pressurizing air chamber  92  acts on the surface area of the pneumatic piston  80  sharing a boundary with the air chamber  92  to apply a force to the pneumatic piston  80  and the drive pin  36  connected to the pneumatic piston  80  to move drive pin  36  in a direction away from the fluid module  12 . 
     The second solenoid valve  84  is coupled by a second passageway  94  penetrating the housing  90  of the jetting valve  10  with the air chamber  96 . The second solenoid valve  84  includes a mechanical valve  69  with an air inlet port  70 , an air exhaust port  72 , and a flow path  71  that can be switched to be coupled with either the air inlet port  70  or the air exhaust port  72 . The second solenoid valve  84  is configured to either port air pressure from the air supply  93  through the air inlet port  70  and second passageway  94  to the air chamber  96  or to exhaust air pressure from the air chamber  96  through the second passageway  94  and air exhaust port  72 . The air pressure pressurizing air chamber  96  acts on the surface area of the pneumatic piston  80  sharing a boundary with the air chamber  96  to apply a force to the pneumatic piston  80  and the drive pin  36  connected to the pneumatic piston  80 , that is opposite in direction to the force applied by air pressure inside air chamber  92 , to move drive pin  36  in a direction towards fluid module  12 . 
     The exhaust of solenoid valve  82  is fitted with a silencer  120  and the exhaust of solenoid valve  84  is also fitted with a silencer  122 . The silencers  120 ,  122  reduce the level of noise produced by the exhaust of pressurized air from the solenoid valves  82 ,  84 . The pressure of the compressed air from the air supply  93  is regulated by a regulator  124  before being supplied to the solenoid valves  82 ,  84 . An air line  128  branches to supply regulated air pressure from the regulator  124  to the air inlet ports  56 ,  70  on the inlet side of the solenoid valves  82 ,  84 . The regulator  124  is used to set the air pressure on the inlet side of the solenoid valves  82 ,  84 . The pressure at the outlet of the regulator  124  and on the inlet side of the solenoid valves  82 ,  84  is displayed on a pneumatic pressure gauge  126 . 
     The solenoid valves  82 ,  84  also include respective solenoids  101 ,  103  with coils that are electrically actuated by respective driver circuits  100 ,  102 . The driver circuits  100 ,  102  are coupled in communication with a controller  104 , which provides independent supervisory control over the driver circuits  100 ,  102 . The driver circuits  100 ,  102  are of a known design with a power switching circuit providing electrical signals to the solenoids  101 ,  103 , respectively. 
     Controller 
     The controller  104  can cause the driver circuit  100  to supply an electrical signal as a current pulse of a given duration to the solenoid  101  of solenoid valve  82 . In response to the electrical signal, the current flowing through the coil of the solenoid  101  generates a magnetic field that causes the displacement of an actuator mechanically linked to the mechanical valve  55  of solenoid valve  82 . The mechanical valve  55  then changes state by opening the flow path  57  so that the first passageway  88  is coupled by the air inlet port  56  and flow path  57  with the air supply  93 . Pressurized air flows from the air supply  93  through the first passageway  88  into the air chamber  92 , which is a closed variable volume that is pressurized by the arriving air pressure, to put an upward pressure on the piston  80  in  FIG. 2 . 
     When the electrical signal to the coil of solenoid  101  is discontinued, a spring (not shown) is used to return the actuator and mechanical valve  55  back to an idle state. In the idle state, the solenoid valve  82  switches the flow path  57  of the mechanical valve  55  so that the air exhaust port  58  of solenoid valve  82  is coupled with the first passageway  88 . Air pressure is exhausted or vented from air chamber  92  through the first passageway  88 , flow path  57 , and air exhaust port  58 . Thus, solenoid  101 , unless energized, is set to vent the chamber  92 . If the pneumatic piston  80  is moved downwardly in  FIG. 2  to reduce the open volume of air chamber  92 , air in air chamber  92  can vent through the air exhaust port  58 . The air chamber  92  may be de-pressurized by the venting process and/or may be maintained at or near atmospheric pressure (i.e., ambient pressure) by the venting process. 
     Similarly, the controller  104  can cause the driver circuit  102  to supply an electrical signal as a current pulse of a given duration to the solenoid  103  of solenoid valve  84 . In response to the electrical signal, the current flowing through the coil of the solenoid  103  generates a magnetic field that causes the displacement of an actuator mechanically linked to the mechanical valve  69  of solenoid valve  84 . The mechanical valve  69  then changes state by opening the flow path  71  so that the second passageway  94  is coupled by the air inlet port  70  and flow path  71  with the air supply  93 . Pressurized air flows from the air supply  93  through the second passageway  94  into the air chamber  96 , which is another closed variable volume that is pressurized by the arriving air pressure, to put a downward pressure on the piston  80  in  FIG. 2 . 
     When the electrical signal to the coil of solenoid  103  is discontinued, a spring (not shown) is used to return the actuator and mechanical valve  69  back to an idle state. In the idle state, the solenoid valve  84  switches the flow path  71  of the mechanical valve  69  so that the air exhaust port  72  of solenoid valve  84  is coupled with the second passageway  94 . Air pressure is exhausted or vented from air chamber  96  through the second passageway  94 , flow path  71 , and air exhaust port  72 . Thus, solenoid  103 , unless energized, is set to vent the chamber  92 . If the pneumatic piston  80  is moved upwardly in  FIG. 2  to reduce the open volume of air chamber  96 , air in air chamber  96  can vent through the air exhaust port  72 . The air chamber  96  may be de-pressurized by the venting process and/or may be maintained at or near atmospheric pressure (i.e., ambient pressure) by the venting process. 
     The operation of the solenoid valves  82 ,  84  to open and close the mechanical valves  55 ,  69  may be coordinated to open and close the jetting valve  10  for controlling the jetting fluid material from the fluid module  12 . Specifically, motion of the pneumatic piston  80  caused by the selective pressurization of air chambers  92 ,  96  moves the tip  34  of the drive pin  36  relative to the wall  62  of the movable element  60  of fluid module  12  to move the valve element  14  towards and away from valve seat  52  to jet droplets of material. 
     The controller  104  may send one control signal to the driver circuit  100  associated with solenoid valve  82  to cause air chamber  92  to be pressurized and another separate control signal to the driver circuit  102  associated with solenoid valve  84  to cause air chamber  96  to be pressurized. As described below, the timing of the control signals may be selected to control the speed of the drive pin  36 , and in turn, the speed at which valve element  14  drives valve seat  52  to jet a droplet of material. 
     The controller  104  may comprise any electrical control apparatus configured to control one or more variables based upon one or more user inputs. Those user inputs can be provided by the user through a user interface  105  that can be a key board, mouse and display, or touch screen, for example. The controller  104  can be implemented using at least one processor  106  selected from microprocessors, micro-controllers, microcomputers, digital signal processors, central processing units, field programmable gate arrays, programmable logic devices, state machines, logic circuits, analog circuits, digital circuits, and/or any other devices that manipulate signals (analog and/or digital) based on operational instructions that are stored in a memory  108 . The memory  108  may be a single memory device or a plurality of memory devices including but not limited to random access memory (RAM), volatile memory, non-volatile memory, static random access memory (SRAM), dynamic random access memory (DRAM), flash memory, cache memory, and/or any other device capable of storing digital information. The controller  104  has a mass storage device  110  that may include one or more hard disk drives, floppy or other removable disk drives, direct access storage devices (DASD), optical drives (e.g., a CD drive, a DVD drive, etc.), and/or tape drives, among others. 
     The processor  106  of the controller  104  operates under the control of an operating system  112 , and executes or otherwise relies upon computer program code embodied in various computer software applications, components, programs, objects, modules, data structures, etc. The computer program code residing in memory  108  and stored in the mass storage device  110  also includes control program code  114  that, when executing on the processor  106 , provides control signals as current pulses to the driver circuits  100 ,  102  for driving the solenoid valves  82 ,  84 . The computer program code typically comprises one or more instructions, whether implemented as part of an operating system or a specific application, component, program, object, module or sequence of operations, that are resident at various times in memory  108 , and that, when read and executed by the processor  106 , causes the controller  104  to perform the steps necessary to execute steps or elements embodying the various embodiments and aspects of the invention. The routines executed to implement the embodiments of the invention executed by one or more specific or general purpose controllers of the control system will be referred to herein as “computer program code” or simply “program code.” 
     Various program code described herein may be identified based upon the application within which it is implemented in a specific embodiment of the invention. However, it should be appreciated that any particular program nomenclature that follows is used merely for convenience, and thus the invention should not be limited to use solely in any specific application identified and/or implied by such nomenclature. Furthermore, given the typically endless number of manners in which computer programs may be organized into routines, procedures, methods, modules, objects, and the like, as well as the various manners in which program functionality may be allocated among various software layers that are resident within a typical computer (e.g., operating systems, libraries, API&#39;s, applications, applets, etc.), it should be appreciated that the invention is not limited to the specific organization and allocation of program functionality described herein. 
     As will be appreciated by one skilled in the art, the embodiments of the invention may also be embodied in a computer program product embodied in at least one computer readable storage medium having non-transitory computer readable program code embodied thereon. The computer readable storage medium may be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination thereof, that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. Exemplary computer readable storage medium include, but are not limited to, a hard disk, a floppy disk, a random access memory, a read-only memory, an erasable programmable read-only memory, a flash memory, a portable compact disc read-only memory, an optical storage device, a magnetic storage device, or any suitable combination thereof. Computer program code containing instructions for directing a processor to function in a particular manner to carry out operations for the embodiments of the present invention may be written in one or more object oriented and procedural programming languages. The computer program code may supplied from the computer readable storage medium to the processor of any type of computer, such as the processor  106  of the controller  104 , to produce a machine with a processor that executes the instructions to implement the functions/acts of a computer implemented process for sensor data collection specified herein. 
     Control of Overlap Time 
       FIGS. 4 and 5  show electric pulse signals supplied as drive currents to the respective solenoids  101 ,  103  of solenoid valves  82 ,  84  to open the solenoid valves  82 ,  84  and supply pressurized air to the air chambers  92 ,  96 . When the solenoid  101  of solenoid valve  82  is in an energized condition, solenoid valve  82  supplies air pressure to the air chamber  92 . When the solenoid  101  of solenoid valve  82  is not in an energized condition, solenoid valve  82  vents the air chamber  92  toward ambient pressure through the exhaust port  58  or maintains the air chamber  92  at ambient pressure as the volume changes due to motion of the pneumatic piston  80 . When the solenoid  103  of solenoid valve  84  is in an energized condition, solenoid valve  84  supplies air pressure to the air chamber  96 . When the solenoid  103  of solenoid valve  84  is not in an energized condition, solenoid valve  84  vents the air chamber  96  toward ambient pressure through the exhaust port  72 . 
     As shown in  FIG. 4 , to open the jetting valve  10 , an electric pulse signal  140  is supplied to the coil of the solenoid  101  of solenoid valve  82  at time t 1 . While energized in this first state by the electric pulse signal  140 , the mechanical valve  55  of solenoid valve  82  is switched so that air pressure can be supplied to the air chamber  92  at the pressure established by regulator  124 . The pressurization of air chamber  92  generates a force that moves or lifts the drive pin  36  and pneumatic piston  80  in a first direction away from the fluid module  12 . As described below, when this happens, the spring, or biasing element,  68  causes the valve element  14  to retract away from valve seat  52 . As the pneumatic piston  80  is lifted in the first direction, the solenoid  103  of solenoid valve  84  remains in an unenergized condition and the air chamber  96  is coupled with the exhaust port  72  of solenoid valve  84 . In this second state, the solenoid valve  84  vents the air pressure from the air chamber  96  created by the motion of the pneumatic piston  80  in the first direction. 
     When the drive pin  36  has been raised by a desired distance, or for desired duration, an electric pulse signal  150  is supplied at time t 2  to the solenoid  103  of solenoid valve  84  to open the mechanical valve  69  of solenoid valve  84  and to supply compressed air from the air supply  93  to air chamber  96 . The force applied by the pressurization of air chamber  96  to pneumatic piston  80  and the force of the compression spring  86  cooperate to cause the drive pin  36  to begin moving downwardly toward the fluid module  12 . However, the pressurized air at the pressure established by regulator  124  remains in air chamber  92  because the solenoid  101  of solenoid valve  82  is still energized. At time t 3 , the electric pulse signal  140  is discontinued to the solenoid  101  of solenoid valve  82 . In the non-energized state, the mechanical valve  55  of solenoid valve  82  is switched to vent the air pressure from air chamber  92  through the exhaust port  58  and to return air chamber  92  to ambient pressure. This causes drive pin  36  to move more rapidly towards the fluid module  12  and impact the fluid module  12  to jet a droplet of material. At time t 4 , the electric pulse signal  150  is discontinued to the solenoid  103  of solenoid valve  84 . In the non-energized state of its solenoid  103 , the mechanical valve  69  of solenoid valve  84  is switched to vent the air pressure from air chamber  96  through the exhaust port  72  and to return air chamber  96  to ambient pressure. With both chambers  92 ,  96  at ambient pressure, the spring  86  holds down piston  80  and drive pin  36  in  FIG. 2  to maintain the valve element  14  against valve seat  52  in the normally closed position. 
     The electric pulse signals  140 ,  150  are timed to be overlapping so that, over a portion but not all of each cycle, the air chambers  92 ,  96  are concurrently pressurized. An overlap period for the pressurization of the air chambers  92 ,  96  is determined by the temporal coincidence between the electric pulse signals  140 ,  150 . The overlap period can be controlled by adjusting the onset time, t 1 , and the end time t 3  for pulse  140  and by adjusting the onset time, t 2 , and the end time, t 4 , for pulse  150 . The onset time, t 1 , for pulse  140  will precede the onset time, t 2 , for pulse  150 . The end time, t 3 , for pulse  140  will precede the end time, t 4 , for pulse  150 . The onset time, t 2 , for pulse  150  is sequenced to occur between the onset time, t 1 , for pulse  140  and the end time, t 3 , for pulse  140 . Similarly, the end time, t 3 , for pulse  140  is sequenced to occur between onset time, t 2 , for pulse  150  and the end time, t 4 , for pulse  150 . These timings, particularly the timing of t 2  and t 3 , which are controlled by the controller  104 , produce the overlap in the pulses  140 ,  150 . 
     While not apparent in  FIGS. 4 and 5 , the pulses  140 ,  150  are idealized and are understood to have rise and fall times as understood by a person having ordinary skill in the art. In addition, the times t 1 -t 4  represent either the moments that the pulses  140 ,  150  are dispatched from the controller  104  and almost instantaneously received by the solenoid valves  92 ,  94 . The mechanical valve  55  of solenoid valve  82  and the mechanical valve  69  of solenoid valve  84  will each have a response time for actuation to switch the respective one of the flow paths  57 ,  71 . 
       FIG. 4  shows an overlap period denoted as Overlap Time  1  for the electric pulse signals  140 ,  150 , which is measured between time t 2  and time t 3 , that is a comparatively long overlap time. Given the relatively lengthy duration of Overlap Time  1 , a pressurized condition exists in the air chamber  96  over a relatively large fraction of the time that the pneumatic piston  80  is moving downwardly to close the jetting valve  10 . The air pressure in air chamber  92  opposes the downward motion of the pneumatic piston  80  and, in turn, causes the drive pin  36  to move at a relatively slow velocity. Generally, the rate of motion of pneumatic piston  80  is proportional to the temporal overlap between the electric pulse signals  140 ,  150 . The shorter the overlap, the faster the piston  80  will move downwardly in  FIG. 2 , and the longer the overlap, the slower piston will move downwardly. 
     The controller  104  is operable to hold the first solenoid valve  82  in a first state for a first time period. The solenoid valve  82  is held in the first state, in which air pressure is supplied to air chamber  92 , for a period of time approximately equal to the duration of the electric pulse signal  140 . The duration of the electric pulse signal  140  and, hence, the first time period are defined by the time period between times t 1  and t 3 . The controller  104  is operable to hold the second solenoid valve  84  in the first state, in which air pressure is supplied to air chamber  96 , for a second time period approximately equal to the duration of the electric pulse signal  140 . The duration of the electric pulse signal  150  and, hence, the second time period are defined by the time period between times t 2  and t 4 . 
     The controller  104  maintains a predetermined overlap period between the first time period (i.e., the duration of electric pulse signal  140 ) and the second time period (i.e., the duration of electric pulse signal  150 ). The drive pin  36  moves towards the valve seat  52  during the second time period. The overlap period is used to control the speed of the drive pin  36  as the drive pin  36  is moved towards the valve seat  52  during the second time period. The movement of the drive pin  36  during the second time period causes the valve element  14  to move into contact with the valve seat  52  to jet a droplet of material. 
     In the preferred embodiment described herein, the movement of the drive pin  36  during the second time period causes the drive pin  36  to contact the fluid module  12 . Specifically, the contact is with the wall  62  of the movable element  60  as described hereinabove. The contact of the drive pin  36  with the fluid module  12  causes the valve element  14  to move into contact with the valve seat  52  to jet a droplet of material. 
     For the next cycle of the jetting valve  10  shown in  FIG. 4 , pulse signals  142 ,  152  similar to pulse signals  140 ,  150  and with Overlap Time  1  are supplied to the solenoids  101 ,  103  of solenoid valves  82 ,  84 . Successive cycles are generated by successive electrical pulse pairs (not shown) with the same Overlap Time  1  as pulse signals  140 ,  150  and pulse signals  142 ,  152  to sequentially jet droplets of material. 
       FIG. 5  shows an overlap period given by an Overlap Time  2  for the pulse signals  140 ,  150  between time t 2  and time t 3  that is shorter in duration than the overlap period given by Overlap Time  1  ( FIG. 4 ). In  FIG. 5 , the drive pin  36  will move at a higher velocity than in  FIG. 4  because the pneumatic piston  80  will move downwardly against a pressurized condition in the air chamber  92  for shorter period of time. This is because in  FIG. 5 , the air chamber  92  is vented more quickly toward atmospheric pressure after the solenoid  103  of solenoid valve  84  has been energized than is the case in  FIG. 4 . 
     Thus, the overlap time between the pulses powering the solenoid valves  82 ,  84  can be used to control the speed of the drive pin  36  and valve element  14 . A shorter overlap period (e.g., Overlap Time  2 ) may be utilized for relatively thick materials that require the drive pin  36  to be moving faster to jet the material. For thinner materials, the drive pin  36  needs to be moved at a slower speed, so as not to cause splashing of the material when it is jetted, and thus a longer overlap period (e.g., Overlap Time  1 ) may be utilized. 
       FIG. 6  shows two sample points to illustrate the correlation between overlap time and viscosity. The material for Point A is a viscosity of 12,500 centipoise (at 25° C.) and for that material it has been empirically determined that an overlap time of 1 millisecond provides good jetting of droplets. The material for Point B is a higher viscosity material having a viscosity of 60,000 centipoise (at 25° C.). For that material, it has been empirically determined that an overlap time of 0.25 milliseconds provides good jetting. This type of information, which may be obtained for numerous materials, may be stored in a lookup table that would be available via the user interface. Additionally, this data can be used to generate a line, a curve or mathematical formula that automatically produces an overlap time for a given viscosity value. This is described in more detail below. 
     Note that although viscosities of materials are typically given by manufacturers at 25° C. which is approximately room temperature, it is common to heat materials to a jetting temperature to reduce their viscosity before they are jetted. Thus, if desired, the system may be set up to utilize viscosities at jetting temperatures rather than 25° C. room temperature viscosities, with appropriate adjustments made. 
     User Interface for Drive Pin Speed Control 
     Given this description of the invention, and how overlap time can be controlled, controller  104  may include a keyboard, mouse and display, for example, that allows the user to input information that can be used by the controller  104  to control the speed of movement of the pneumatic piston  80 , and thereby, the speed at which the valve element  14  is moved by the movement of the piston  80  as valve element  14  contacts the valve seat  52  to jet a droplet of material. 
     For example, the user may input a viscosity value for the material to be jetted. In response to that input, a lookup table within the controller  104  may be used to correlate an empirically-determined overlap time value with the viscosity value. That overlap time value may then be used by controller  104  to control the solenoids  82 ,  84  to produce a drive pin velocity or speed that provides good jetting for the material. As an alternative to a look-up table and as mentioned above, if the empirical data follows a curve, curve fitting tools may be used to determine a mathematical equation that correlates overlap time with viscosity and that formula may be utilized by the controller to generate the overlap time that corresponds to the viscosity value input by the user. 
     As another example, controller  104  may utilize a control panel, or touch screen, with a series of buttons or pads representing a range of viscosity materials, such as a range for high viscosity values, a range for medium viscosity materials and a range for low viscosity materials. If the user will be jetting a material in the medium viscosity range, the user can push the medium viscosity button. In response to this input, the controller  104  selects the overlap time that has been empirically determined to produce good jetting with medium viscosity materials. The controller  104  would then use that overlap time value to control the solenoids  82 ,  84  to produce the desired drive pin speed. 
     As yet another example, controller  104  may include a database of different materials that are jetted by the user. Each material may typically be supplied by a jetting material manufacturer and given a product name by the manufacturer, such as Product A. In that instance, if the user is using Product A, the user may go to an appropriate screen in the interface provided by controller  104 , and using a drop-down list, for example, select Product A. In response to that selection, controller  104  may use a lookup table to find the numerically determined overlap time value for that material and use that overlap time value to control the solenoids  82 ,  84  to achieve the desired drive pin speed for that material. 
     As still another example, controller  104  may include an interface with a slide bar. When the user moves the slide bar in one direction, the controller reduces the overlap time to speed up the drive pin velocity. When the user moves the slide bar in the opposite direction, the controller  104  increases the overlap time to speed up the drive pin velocity. During jetting tests, the user may use the slide bar to speed up and slow down the drive pin speed of the jetting valve and observe the results of the jetting tests. Based on those results, the operator may empirically determine which overlap time produces the best results for the material being jetted and use that overlap time in the manufacturing operation. The user may also build up its own look up table in this way by empirically determining an optimal overlap time for each material that the user jets in its manufacturing operation. In another variation, the user may use the high viscosity, medium viscosity and low viscosity buttons, or pads on a touch screen, to initially set the position of the slide bar. Then, if the material does not jet properly but instead accumulates on the nozzle, the user may adjust the sliding scale to reduce the overlap time and increase the drive pin speed until proper jetting is achieved. Conversely, if the initial position of the slide bar caused splattering of material to occur on the substrate, and/or the production of small satellite droplets of material, then the sidebar may be used to increase the overlap time and reduce drive pin speed until proper jetting is achieved. The overlap time reading for good jetting may then be recorded, stored in memory and used for the manufacturing operation. 
     In yet another embodiment, overlap time, and thereby drive pin speed, may be changed “on the fly” while the jetting valve is moved by a robot across a substrate to jet a droplet of material with one overlap time/drive pin speed used at one location on the substrate and to jet a droplet of material with a different overlap time/drive pin speed used at a different location on the substrate to jet another droplet of material. 
     Give the above description of how this invention operates, a number of inventive systems and methods can be employed to practice these invention. 
     Systems Having User Interface to Control Valve Speed of a Pneumatic Jetting Device 
     In one system for jetting materials according to the invention, the jetting device has a pneumatic piston that causes movement of a valve element that contacts a valve seat to jet a droplet of material and the controller has a user interface that enables the user to vary the speed of the valve element. 
     In another system the jetting device has upper and lower piston chambers on opposite sides of the piston that are controlled by independent solenoid valves, and the speed of the valve element is controlled by the control of the solenoids. 
     In another system, the solenoids are controlled to provide a desired overlap time period during which compressed air is supplied to both the upper and lower piston chambers at the same time. 
     Methods for Jetting from a Pneumatically Actuated Jetting Device Having a Valve Speed User Interface 
     In one method for jetting materials according to the invention, the jetting device has a pneumatically-driven piston that causes a valve element to move into contact with a valve seat to jet a droplet of material, and a user interface is provided that the user can use to input information that is used by the controller to vary the speed of the valve element. 
     In another method, the user input relates to the material that is to be jetted from the jetting device. 
     In another method, the user input relates to the viscosity of the material. 
     In another method, the jetting device is pneumatically actuated and has a drive pin fixed to a piston that is reciprocated by compressed air supplied to chambers on opposite sides of the piston, wherein movement of the drive pin moves a valve element into contact with a valve seat in a fluid chamber to jet a droplet of material through a nozzle orifice that is in fluid communication with the fluid chamber, and wherein: the valve is first maintained in a closed position with the valve element forced against the valve seat; then at a time T 1  the chamber on one side of the piston is connected to a supply of compressed air to retract the piston, drive pin and valve element away from the valve seat and allow fluid material to flow into the valve seat; at a time T 2  that is after T 1 , the chamber on the opposite side of the piston is connected to a supply of compressed air, to move the piston, drive pin and valve element towards the valve seat; at a time T 3  that is after T 2 , the first chamber is disconnected from the supply of compressed to allow pressure in the first chamber to be vented; and at a time T 4  that is after T 3 , the second chamber is disconnected from the supply of compressed air to allow pressure in the second chamber to be vented; wherein the time period between T 2  and T 3  comprises an overlap period during which both the first chamber and the second chamber are connected to a supply of compressed air; and wherein the duration of the overlap period is selected to control the velocity of the drive pin while it moves towards the valve seat. 
     In another method, a shorter duration overlap period is utilized to jet materials having a first viscosity and a longer duration overlap period is utilized to jet materials having a second viscosity, wherein said first viscosity is less than said second viscosity. 
     In another method, a user interface is provided that the user can use to input information to a controller and the controller utilizes the information input by the user to generate the overlap period that controls the drive pin velocity. 
     In another method, the user inputs information relating to the material and the controller utilizes the information input by the user to generate the overlap period that controls the drive pin velocity. 
     In another method, the user inputs information relating to the material viscosity and the controller utilizes the information input by the user to generate the overlap period that controls the drive pin velocity. 
     In another method, data correlating overlap period duration with material viscosity is stored and the controller utilizes the information input by the user and the stored data to generate the overlap period that controls the drive pin velocity. 
     In another method, a mathematical formula correlating information of the type input from the user at the user interface with overlap time period information is stored in the controller and that formula is utilized by the controller in response to the information input by the user to provide the desired overlap time period. 
     In another method, a slide bar is provided on a user interface that allows the user to reduce overlap time, and thereby, increase drive pin speed, or increase overlap time, and thereby reduce drive pin speed. 
     In another method, buttons, or touch pads, on a user interface are provided that correspond to material characteristics such as viscosity ranges. The user then uses the button or touch pad to select the range most appropriate for the material to be jetted and the controller retrieves from memory the overlap time that has been empirically determined to work best with that viscosity range and uses that overlap time to jet materials. 
     In another method, the user then uses the button or touch pad to select the range most appropriate for the material to be jetted and the controller retrieves from memory the overlap time that has been empirically determined to work best with that viscosity range and presets the slide bar to use that overlap time to jet materials. The user then uses the slide bar to hunt for a more optimal overlap time by speeding up and slowing down drive pin velocity and recording the drive pin speed/overlap time that produces the best jetting for the material. That drive pin speed/overlap time valve is then used in the manufacturing operation. 
     References herein to terms such as “vertical”, “horizontal”, etc. are made by way of example, and not by way of limitation, to establish a frame of reference. It is understood by persons of ordinary skill in the art that various other frames of reference may be equivalently employed for purposes of describing the embodiments of the present invention. 
     It will be understood that when an element is described as being “attached”, “connected”, or “coupled” to or with another element, it can be directly connected or coupled to the other element or, instead, one or more intervening elements may be present. In contrast, when an element is described as being “directly attached”, “directly connected”, or “directly coupled” to another element, there are no intervening elements present. When an element is described as being “indirectly attached”, “indirectly connected”, or “indirectly coupled” to another element, there is at least one intervening element present. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Furthermore, to the extent that the terms “includes”, “having”, “has”, “with”, “composing”, or variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the open-ended term “comprising.” 
     While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Thus, the invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants&#39; general inventive concept.