Automatic piezo stroke adjustment

A method of calibrating the jetting profile includes applying voltage to a piezoelectric actuator to move a valve closure structure between non-impact and impact positions, sensing the position of the valve closure structure, establishing a reference point using voltage and position data, and using the reference point to adjust the voltage applied. Another method uses a mechanical stop to calibrate a jetting system. This method includes applying voltage to the piezoelectric actuator to move the valve closure structure between non-impact and impact calibration positions, sensing the position of the valve closure structure, generating voltage and position calibration data, establishing a master reference point using this data, and using the master reference point to determine wear of at least one of: the piezoelectric actuator and the valve closure structure. Another method of operating a jetting system includes the user inputting information into a control component. Another method involves using voltage data and the position data relating to a piezoelectric actuator for preventative maintenance of one or more components of the jetting valve.

TECHNICAL FIELD

The present invention generally relates to non-contact, jetting dispensers for depositing small droplets of a viscous fluid onto a substrate, and more specifically, to dispensers of this type that are actuated by one or more piezoelectric elements.

BACKGROUND

Non-contact viscous material dispensers are often used to apply minute amounts of viscous materials, i.e. those with a viscosity exceeding fifty centipoise, onto substrates. As used herein, “non-contact” means where the jetting dispenser does not contact the substrate during the dispensing process. For example, non-contact jetting dispensers are used to apply various viscous materials onto electronic substrates like printed circuit boards. Viscous materials applied to electronic substrates include, by way of example and not by limitation, general purpose adhesives, solder paste, solder flux, solder mask, thermal grease, lid sealant, oil, encapsulants, potting compounds, epoxies, die attach fluids, silicones, RTV, and cyanoacrylates.

Specific applications abound for dispensing viscous materials from a non-contact dispenser onto a substrate. In semiconductor package assembly, applications exist for underfilling, solder ball reinforcement in ball grid arrays, dam and fill operations, chip encapsulation, underfilling chip scale packages, cavity fill dispensing, die attach dispensing, lid seal dispensing, no flow underfilling, flux jetting, and dispensing thermal compounds, among other uses. For surface-mount technology (SMT) printed circuit board (PCB) production, surface mount adhesives, solder paste, conductive adhesives, and solder mask materials may be dispensed from non-contact dispensers, as well as selective flux jetting.

Jetting dispensers generally contain either pneumatic or electric actuators for moving a shaft or tappet repeatedly toward a seat while jetting a droplet of viscous material from an outlet orifice of the dispenser. The electrically actuated jetting dispensers can, more specifically, use a piezoelectric actuator. Precisely jetting fluids using a valve closure structure contacting a valve seat requires that the shaft be brought into contact with the valve seat using a prescribed stroke (displacement) and velocity to effectively eject a dot of fluid material from the outlet of the nozzle. The displacement and velocity curve collectively form the motion profile. The stroke, velocity, and sealing force are best controlled when the point of impact between the valve closure structure and the valve seat is precisely known and measured. There must be sufficient force after the impact of the shaft with the valve seat to create a seal to prevent leakage of the fluid material. However, too much force will result in excess wear, or even damage, to the components.

Changes of only a few micrometers affect the performance of the fluid dispenser. Typically, these adjustments are performed manually by a user through mechanical means, such as adjusting a screw. This manual process takes multiple iterations yet still fails to precisely adjust the motion profile for the desired performance. Therefore, there exists a continuing need to determine the position of the valve closure structure relative to the valve seat to optimize performance and settings of the fluid dispenser, and adjust the motion profile of the fluid dispenser accordingly.

For at least these reasons, it would be desirable to provide a jetting system and method that addresses these and other issues.

SUMMARY

In one embodiment, a method of calibrating the jetting profile of a jetted fluid material for a jetting system is disclosed. The jetting system includes a jetting dispenser and a control component operatively coupled to the jetting dispenser. The jetting dispenser includes a valve seat, a valve closure structure, and a piezoelectric actuator. The method includes applying voltage to the piezoelectric actuator to move the valve closure structure between a non-impact position where the valve closure structure is not impacting the valve seat and an impact position where at least a portion of the valve closure structure is impacting the valve seat. The method also includes generating voltage data as the valve closure structure is moved. The method also includes sensing the position of the valve closure structure as the valve closure structure is moved using a sensing device. The method also includes generating position data as the valve closure structure is moved. The method also includes establishing a reference point using the voltage and position data. The method also includes using the reference point to adjust the voltage applied to the piezoelectric actuator.

In another embodiment, a method of calibrating the jetting profile of a jetted fluid material for a jetting system is disclosed. The jetting system includes a jetting dispenser and a control component operatively coupled to the jetting dispenser. The jetting dispenser includes a piezoelectric actuator, a valve seat, a valve closure structure, and a mechanical stop positioned at a predetermined distance away from the valve closure structure in a non-impact calibration position. The method includes applying voltage to the piezoelectric actuator to move the valve closure structure between the non-impact calibration position where the valve closure structure is not impacting the mechanical stop and an impact calibration position where at least a portion of the valve closure structure is impacting the mechanical stop. The method also includes generating voltage calibration data as the valve closure structure is moved. The method also includes sensing the position of the valve closure structure as the valve closure structure is moved using a sensing device. The method also includes generating position calibration data as the valve closure structure is moved. The method also includes establishing a master reference point using the voltage and position calibration data. The method also includes using the master reference point to determine wear of at least one of: the piezoelectric actuator, the valve closure structure, and the valve seat.

In yet another embodiment, a method of calibrating the jetting profile of a jetted fluid material for a jetting system is disclosed. The jetting system includes a jetting dispenser and a control component operatively coupled to the jetting dispenser. The jetting dispenser includes a valve seat, a valve closure structure, a piezoelectric actuator, and a mechanical stop positioned at a predetermined distance away from the valve closure structure in a non-impact calibration position. The method includes applying voltage to the piezoelectric actuator to move the valve closure structure between a non-impact position where the valve closure structure is not impacting the valve seat and an impact position where at least a portion of the valve closure structure is impacting the valve seat. The method also includes generating voltage data as the valve closure structure is moved. The method also includes sensing the position of the valve closure structure as the valve closure structure is moved using a sensing device. The method also includes generating position data as the valve closure structure is moved. The method also includes establishing a reference point using the voltage and position data. The method also includes applying voltage to the piezoelectric actuator to move the valve closure structure between the non-impact calibration position where the valve closure structure is not impacting the mechanical stop and an impact calibration position where at least a portion of the valve closure structure is impacting the mechanical stop. The method also includes generating voltage calibration data as the valve closure structure is moved. The method also includes sensing the position of the valve closure structure as the valve closure structure is moved using the sensing device. The method also includes generating position calibration data as the valve closure structure is moved. The method also includes establishing a master reference point using the voltage and position calibration data. The method also includes comparing the reference point to the master reference point to determine wear of the valve seat.

In yet another embodiment, a method of operating a jetting system by a user is disclosed. The jetting system includes a jetting dispenser and a control component operatively coupled to the jetting dispenser. The jetting dispenser includes a piezoelectric actuator, a valve seat, a valve closure structure, and a mechanical stop positioned at a predetermined distance away from the valve closure structure in a non-impact calibration position. The method includes inputting the fluid type into the control component by the user. The method also includes inputting the jetting frequency into the control component by the user. The method also includes inputting the droplet size into the control component by the user. The method also includes determining a master calibration profile by applying voltage to the piezoelectric actuator to move the valve closure structure between the non-impact calibration position where the valve closure structure is not impacting the mechanical stop and an impact calibration position where at least a portion of the valve closure structure is impacting the mechanical stop. The method also includes applying the master calibration profile to the jetting system using the control component. The method also includes determining a calibrated jetting profile by applying voltage to the piezoelectric actuator to move the valve closure structure between a non-impact calibration position where the valve closure structure is not impacting the valve seat and an impact calibration position where at least a portion of the valve closure structure is impacting the valve seat. The method also includes applying the calibrated jetting profile to the jetting system.

In yet another embodiment, a method of doing maintenance in a jetting system is disclosed. The jetting system includes a jetting dispenser and a control component operatively coupled to the jetting dispenser. The jetting dispenser includes a piezoelectric actuator and a valve closure structure. The method includes applying voltage to the piezoelectric actuator to move the valve closure structure between a first position and a second position. Voltage data is generated as the valve closure structure is moved. The position of the valve closure structure is sensed using a sensing device as the valve closure structure is moved. Position data is generated as the valve closure structure is moved. The voltage data and the position data are used for preventative maintenance.

In yet another embodiment, a method of calibrating the jetting profile of a jetting fluid material for a jetting system is disclosed. The jetting system includes a jetting dispenser and a control component operatively coupled to the jetting dispenser. The jetting dispenser includes a valve seat, a valve closure structure, and a piezoelectric actuation mechanism having a piezoelectric actuator. The method includes receiving input from a user of a desired stroke length of the valve closure structure. Voltage is applied to the piezoelectric actuator to move the valve closure structure between a non-impact position where the valve closure structure is not impacting the valve seat and an impact position where at least a portion of the valve closure structure is impacting the valve seat. Voltage data is generated as the valve closure structure is moved. The position of the valve closure structure is sensed using a sensing device as the valve closure structure is moved. Position data is generated as the valve closure structure is moved. Based, at least in part, on the voltage data and the position data, a reference point is determined. The method further includes, based, at least in part, on the voltage data and the position data, determining a top voltage corresponding to the position of the valve closure structure resulting in the desired stroke length of the valve closure structure. The reference point and the top voltage are used to adjust a voltage applied to the piezoelectric actuator.

A method of calibrating the jetting profile of a jetted fluid material for a jetting system is disclosed. The jetting system including a jetting dispenser and a control component operatively coupled to the jetting dispenser. The jetting dispenser includes a piezoelectric actuation mechanism having a piezoelectric actuator, a valve closure structure, and a mechanical stop positioned at a predetermined distance away from the valve closure structure in a non-impact calibration position. The method includes applying voltage to the piezoelectric actuator to move the valve closure structure between the non-impact calibration position where the valve closure structure is not impacting the mechanical stop and an impact calibration position where at least a portion of the valve closure structure is impacting the mechanical stop. Voltage calibration data is generated as the valve closure structure is moved. The position of the valve closure structure is sensed using a sensing device as the valve closure structure is moved. Position calibration data is generated as the valve closure structure is moved. The method further includes, based, at least in part, on the voltage calibration data and the position calibration data, determining a reference gain indicative of a ratio of the displacement of the valve close structure to the voltage applied to the piezoelectric actuator. Based, at least in part, on the reference gain, a wear characteristic is determined for at least one of: the piezoelectric actuation mechanism and the valve closure structure.

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

DETAILED DESCRIPTION

Referring toFIGS. 1, 1A, and 2, a jetting system10in accordance with an embodiment of the invention generally includes a jetting dispenser12communicatively coupled with a control component14. The jetting dispenser12includes a piezoelectric actuation mechanism16, a valve closure structure18, and a nozzle hub20including a valve seat22. Specifically, the valve closure structure18includes a drive pin24and a poppet26. The jetting dispenser12receives fluid material38under pressure from a suitable fluid supply30through a fluid supply conduit32. The drive pin24is driven by action of the piezoelectric actuation mechanism16to move a tip70of the poppet26towards the valve seat22and cause a quantity of the fluid material38to be dispensed.

The piezoelectric actuation mechanism16includes a piezoelectric actuator34having piezoelectric stacks91a,91b(hereinafter referred to collectively as the piezoelectric stack91), a plunger99, and an asymmetrical flexure94. The flexure94is an integral part of an actuator body98, within which the piezoelectric actuation mechanism16is generally disposed, and includes a coupling element97that connects the flexure94to the plunger99. A spring102within the piezoelectric actuator34applies a spring force to the plunger99and piezoelectric stack91to keep them in compression.

Using the piezoelectric actuator34, including the piezoelectric stack91, allows the jetting dispenser12to have very specific positional control of the valve closure structure18because the voltage applied to the piezoelectric actuator34is proportional to the force generated by the piezoelectric actuator34. Specifically, when a voltage is applied to the piezoelectric stack91, the piezoelectric actuator34expands or lengthens, with the change in length being proportional to the amount of voltage applied. Due to this proportionality, the jetting system10is capable of finely controlling the motion profile of the fluid material38dispensed through the outlet40. Pneumatic actuators do not exhibit such proportionality.

The plunger99functions as a mechanical interface connecting the piezoelectric stack91with the asymmetrical flexure94. The spring102is compressed in the assembly such that the spring force generated by the spring102applies a constant load on the piezoelectric stack91, which preloads the piezoelectric stack91. The asymmetrical flexure94, which may be comprised of a metal material, has an arm100that is physically secured with an end of the drive pin24opposite to the downward tip of the drive pin24. The asymmetrical flexure94functions as a mechanical amplifier that converts the relatively small displacement of the piezoelectric stack91into a useful displacement for the drive pin24that is significantly larger than the displacement of the piezoelectric stack91.

The piezoelectric stack91of the piezoelectric actuator34is a laminate comprised of layers of a piezoelectric ceramic that alternate with layers of a conductor as is conventional in the art. The spring force from the spring102maintains the laminated layers of the piezoelectric stack91in a steady state of compression. The conductors in the piezoelectric stack91are electrically coupled with a driver circuit associated with the control component14, which supplies current-limited output signals, in a manner well known in the art, with pulse width modulation, frequency modulation, or a combination thereof. When power is periodically supplied from the driver circuit, electric fields are established that change the dimensions of the piezoelectric ceramic layers in the piezoelectric stack91.

The dimensional changes experienced by the piezoelectric stack91, which are mechanically amplified by the asymmetrical flexure94, move the drive pin24linearly in a direction parallel to its longitudinal axis. When the piezoelectric ceramic layers of the piezoelectric stack91expand, the spring102is compressed by the force of the expansion and the asymmetrical flexure94pivots about a fixed pivot axis to cause movement of the drive pin24upward and away from the poppet26. This allows a biasing element39to move the poppet26away from valve seat22. The drive pin24is guided using a drive pin guide50. When the actuation force is removed and the piezoelectric ceramic layers of the piezoelectric stack91are permitted to contract, the spring102expands and the asymmetrical flexure94pivots to move the drive pin24downward into contact with the poppet26, causing the poppet26to contact the valve seat22and jet a droplet of material. Thus, in the de-energized state, the piezoelectric actuator34maintains the valve in a normally closed position. In operation, the asymmetrical flexure94intermittently rocks in opposite directions about a fixed pivot axis as the piezoelectric stack91is energized and de-energized to move the drive pin24into and out of contact with the poppet26to jet droplets of material at a rapid rate.

It will be appreciated that the piezoelectric actuation mechanism16, and the dispenser12in general, may be alternatively configured in some embodiments such that when the piezoelectric stack91expands, the drive pin24is moved downward and into contact with the poppet26to cause a quantity of material to be dispensed from the outlet40. Conversely, when an applied voltage is removed from the piezoelectric stack91to allow the piezoelectric stack91to contract, the drive pin24is moved upward and away from the poppet26. Thus, in such an embodiment, the voltage applied to the piezoelectric stack91of the piezoelectric actuator34corresponds with the downward movement of the drive pin24toward the poppet26.

A sensing device48senses the position of the valve closure structure18(including a component thereof, such as the drive pin24and/or the poppet26) as it is moved by the piezoelectric actuation mechanism16. In some aspects, the sensing device48may be attached directly or indirectly to the valve closure structure18. A target (not shown) may be placed on the valve closure structure18so that the sensing device48reads the position of the target relative to the sensing device48. For example,FIG. 1shows the sensing device48being a linear encoder that reads position and motion using lines (not shown) placed on the drive pin24. Thus, the sensing device48allows the position and velocity of the valve closure structure18to be determined as the valve closure structure18is moved. In other embodiments, the sensing device48may additionally or alternatively sense the position and velocity of the poppet26. Further, the position and velocity of the valve closure structure18may be measured using a variety of other types of position feedback devices such as eddy current sensors or optical proximity sensors.

FIG. 2shows a detailed view of the jetting dispenser12in a closed position. As shown, the fluid cartridge56is attached to the jetting dispenser12and includes a cartridge body57and a portion of the valve closure structure18, specifically shown as the poppet26. WhileFIGS. 1 and 2show the jetting dispenser12having a fluid cartridge56, a fluid cartridge56is not required and may be replaced by other suitable structure. Further details may be seen in Applicant's co-pending U.S. patent application Ser. No. 14/730,522, filed Jun. 4, 2015, entitled “Jet Cartridges for Jetting Fluid Material, and Related Methods”, which is hereby incorporated by reference.

FIG. 3depicts a chart of a voltage applied to the piezoelectric actuator34(i.e., voltage data76) and plotted over a period of time making up one dispensing cycle of a dispenser. It will be noted that the chart shown inFIG. 3contemplates the alternative dispenser12configuration described above in which a voltage applied to the piezoelectric actuator34(and the consequent expansion thereof) causes the drive pin24to move downward and into contact with the poppet26. Conversely, the removal or reduction of voltage to the piezoelectric actuator34(and the consequent contraction thereof) in this alternative configuration causes the drive pin24to move upward and away from the poppet26, allowing the poppet26to disengage with the valve seat22.

Before describing illustrative methods of adjusting the original jetting profile58to obtain a calibrated jetting profile60, it is beneficial to first describe aspects of the original jetting profile58and the calibrated jetting profile60. As used herein, “profile” refers to the range of voltages applied to the piezoelectric actuator34over a period of time (e.g., the period of time corresponding to a single complete up-down reciprocation of the valve closure structure18), which may be repeated multiple times to effectuate a complete dispensing operation. The original jetting profile58generally refers to an initial operational profile before one or more of the methods described herein are employed to calibrate the jetting system10and/or ascertain a degree of wear of the jetting system10. The calibrated jetting profile60generally refers to an operational profile that is determined after one or more of the aforementioned methods are performed and, preferably, represents an improved operation of the jetting system10, such as in respect to an optimal sealing engagement of the poppet26with the valve seat22.

The original jetting profile58consists of an opening profile62, an on time64, and a closing profile66, and may be created in a variety of different manners. For example, using a graphic user interface (not shown) associated with the control component14, a user defines the opening profile62by selecting a starting voltage36, an ending voltage68, the amount of time to go from the starting voltage36to the ending voltage68, and the transition time. The transition time is the amount of time used at the beginning and end of the opening profile62. The closing profile66may be defined in much the same manner. The ending voltage68of the closing profile66is typically the same as the starting voltage36of the opening profile62. The user may also provide a sealing offset voltage (Vso), which will be discussed in greater detail below. Once the opening profile62and closing profile66have been created, the opening profile62and closing profile66are stored in a library of original jetting profiles58. The opening profile62and the closing profile66may be stored together in a single file. The user may select the on time64after selecting the profile which, as used herein, refers to the time from the beginning of the opening profile62to the beginning of closing profile66. Further, the on time64is greater than the time associated with the opening profile62.

With the original jetting profile58discussed above, it is beneficial to provide an illustrative example. With continued reference toFIG. 3, at rest, a maximum jetting profile voltage is applied to the piezoelectric actuator34to hold the valve closure structure18in the closed position. As shown, the opening profile62starts at 45 Volts when in the closed position. The opening profile62then drops to 5 Volts in 200 microseconds to move the poppet26away from the valve seat22, with 75 microseconds of transition time at each end. Regarding the closing profile66, for example, the valve closure structure18is separated from the valve seat22in the open position at 5 Volts and then increases to 45 Volts in 100 microseconds to move the poppet26towards the valve seat22, with 25 microseconds of transition time at each end.

With the original jetting profile58discussed above, relevant voltage measurements are now discussed with continued reference toFIG. 3. Various illustrative methods may be used to determine a closed voltage (Vc) in the calibrated jetting profile60based on the original jetting profile58. The closed voltage (Vc) is the voltage at which the tip70of the valve closure structure18first impacts the valve seat22, preferably with a desired force and velocity. The sealing offset voltage (Vso) is the additional voltage applied to the closed voltage (Vc) to achieve a sealed voltage (Vs) at which there is sufficient force applied to the tip70of the valve closure structure18to close without leakage. The sealing offset voltage (Vso) is dependent at least upon the type of fluid material38being dispensed and the pressure of the fluid material38, and generally ranges from about 5 Volts to 30 Volts. As mentioned above, the sealing offset voltage (Vso) is typically a known constant throughout the methods described herein, and may be initially input into the control component14by the user. The closed voltage (Vc), the sealing offset voltage (Vso), and the sealed voltage (Vs) are related using the formula Vs=Vc+Vso. It will be noted that the sealing offset voltage (Vso) may be a negative value in some embodiments, such as with the configuration of the dispenser12depicted inFIGS. 1 and 1Ain which the downward movement of the drive pin24and poppet26corresponds to a reduction in voltage applied to the piezoelectric actuator34.

Illustrative methods of determining the closed voltage (Vc) are now considered. In one illustrative embodiment, when the sensing device48indicates one or more consecutive non-changing positions of the valve closure structure18(e.g., the drive pin24or the poppet26), the voltage measurement corresponding to the first of these positions is considered the closed voltage (Vc). In another illustrative embodiment, as depicted inFIG. 5and discussed in greater detail below, the closed voltage (Vc) is determined by ascertaining the intersection of a first trendline72with a second trendline74in a graph of applied voltage plotted against a corresponding measured position of the valve closure structure18. Using either illustrative method of determining the closed voltage (Vc), a reference point (RP) may accordingly be determined. The reference point (RP) reflects the closed voltage (Vc) and the position of the valve closure structure18(e.g., the poppet26) corresponding to the closed voltage (Vc). In the illustrative method400(FIG. 4) discussed below, the original jetting profile58is calibrated to obtain the calibrated jetting profile60based at least in part on the closed voltage (Vc) and/or the reference point (RP).

FIG. 4shows an illustrative method400of adjusting or calibrating the original jetting profile58of the jetting system10. At step402, voltage is applied to the piezoelectric actuator34to move the valve closure structure18(e.g., the poppet26) between a non-impact position52and an impact position54. As used herein, the impact position54refers to where at least a portion of the valve closure structure18is physically impacting the valve seat22, while the non-impact position52refers to where no portion of the valve closure structure18is impacting the valve seat22. It does not matter whether the valve closure structure18starts at a non-impact position52and moves into an impact position54, or starts at an impact position54and moves into a non-impact position52. Both arrangements are suitable.

At step404, the sensing device48senses the position of the valve closure structure18as the valve closure structure18is moved relative to the sensing device48. At step406, the control component14, for example, generates position data78(FIG. 5 or 6) and voltage data76(FIG. 5 or 6) using signals obtained from the sensing device48and based on the known voltage applied to the piezoelectric actuator34, respectively. Additionally, velocity data (not shown) may be generated as the valve closure structure18is moved relative to the sensing device48, which enables the reference point (RP) and/or closed voltage (Vc) to be established using voltage data76, position data78, and velocity data.

At step408, the reference point (RP) is determined, such as by the control component14, based on an analysis of the voltage data76and the position data78. The reference point (RP) may be determined using a variety of methods, such as by plotting the voltage data76versus the position data78. The position data78includes non-impact and impact position data.

At step410, the control component14, for example, determines the closed voltage (Vc) based, at least in part, on the reference point (RP) determined in step408. For instance, since the reference point (RP) includes both a positional component and a voltage component, the closed voltage (Vc) may be thus ascertained from the voltage component.

At step411, the sealed voltage (Vs) is determined based, at least in part, on the closed voltage (Vc). For example, the sealed voltage (Vs) may be determined using the closed voltage (Vc) and the sealing offset voltage (Vso) according to the formula Vs=Vc+Vso. It will be appreciated that in some aspects, the sealing offset voltage (Vso) may not be used to effectuate the dispensing operation. In such an aspect, the sealed voltage (Vs) is equal to the closed voltage (Vc) since the sealing offset voltage (Vso) is effectively zero.

At step412, the sealed voltage (Vc) is used to determine the calibrated jetting profile60. In particular, the original jetting profile58is shifted to the calibrated jetting profile60based, at least in part, on the sealed voltage (Vs). For example, the original jetting profile58is shifted to the calibrated jetting profile60such that the calibrated jetting profile60includes a starting voltage36and/or ending voltage68equal to the sealed voltage (Vs).

FIG. 5provides an illustrative example of using the intersection of the first trendline72and the second trendline74to calibrate an original jetting profile58. It will be noted that the chart shown inFIG. 5contemplates a dispenser in which application of voltage to the piezoelectric actuator34causes the upward movement of the valve closure structure18away from the valve seat22and the removal or reduction in applied voltage results in the downward movement of the valve closure structure18towards the valve seat22, as is the case with the dispenser12shown inFIGS. 1 and 1A. The chart shows the position of the valve closure structure18versus the voltage applied to the piezoelectric actuator34. UnlikeFIG. 3, where the sealed voltage (Vs) is the maximum jetting profile voltage, inFIG. 5the the sealed voltage (Vs) is the minimum jetting profile voltage. Here, the starting voltage36is 0 Volts. The valve closure structure18is separated from the valve seat22at a predetermined position using a voltage relative to the impact voltage. As shown, in the impact position54, the valve closure structure18moves only a few microns in the voltage range from 0 to 60 volts. Sealing takes place in this voltage range, with lower voltages corresponding to higher sealing forces. In non-impact position52, the valve closure structure18moves away from the valve seat22as the voltage increases in the 70 to 110 volt range. In the 60 to 70 volt range, there is a transition from sealing to motion. With this arrangement where the sealed voltage (Vs) is the minimum voltage, the closed voltage (Vc) is the voltage where the tip70of the valve closure structure18last impacts the valve seat22. The control component14, for example, generates the first trendline72, preferably a linear trendline, from a substantially linear portion of the impact position data. The control component14, for example, also generates a second trendline74, preferably a linear trendline, from a substantially linear portion of the non-impact position data. Specifically,FIG. 5has a first linear trendline of y=0.1x+997 microns, and a second linear trendline of y=3.24x+799.4 microns. While trendlines using linear equations are shown and described, the trendlines may alternatively use higher order or piecewise equations.

With continued reference toFIG. 5, the control component14, for example, determines the intersection of the first trendline72with the second trendline74. This intersection is considered the reference point (RP) having a closed voltage (Vc). The reference point (RP) (and/or the closed voltage (Vc) embodied therein) is used to determine calibrated jetting profile60. Specifically, the reference point (RP) ofFIG. 5occurs at 1003.3 microns and 62.9 volts. As a result, the original jetting profile58is shifted to the calibrated jetting profile60, such that the calibrated jetting profile60includes a maximum voltage (or minimum voltage, depending on the particular dispenser12configuration) corresponding to the closed voltage (Vc) plus the sealing offset voltage (Vso) (i.e., the sealed voltage (Vs)). As previously discussed, for the jetting system contemplated with respect toFIG. 5, the sealing offset voltage (Vso) is a negative value, since the sealed voltage (Vs) is less than the closed voltage (Vc).

FIG. 6shows another illustrative example of an implementation of at least part of the method400. Specifically,FIG. 6shows a chart plotting the measured position of the valve closure structure18(i.e., the position data78) against the voltage applied to the piezoelectric actuator34(i.e., the voltage data76). It will be noted that the chart shown inFIG. 6contemplates the alternative dispenser12configuration described above in which a voltage applied to the piezoelectric actuator34(and the consequent expansion thereof) causes the drive pin24to move downward and into contact with the poppet26.

InFIG. 6, the voltage increases from 20 Volts to 110 Volts in 100 incremental steps. This results in each step increasing the voltage by 0.9 Volts (100 steps/(110 Volts-20 Volts)). The tip70of the valve closure structure18impacts the valve seat22at the closed voltage (Vc). Specifically, as the position data78is analyzed, one or more consecutive non-changing positions indicate the reference point (RP) (and thus also the closed voltage (Vc)) occurred at the first of these positions. The number of consecutive non-changing positions may be selected by the user using a graphic user interface (GUI). This first position is the reference point (RP) having a closed voltage (Vc) of approx. 55 volts. While four non-changing positions have been found to be appropriate, more or less non-changing positions may be desired. As discussed above, the original jetting profile58is then shifted to the calibrated jetting profile60based at least in part on the determined closed voltage (Vc).

This method400of calibrating a jetting profile provides many benefits. First, this method provides more consistent jetting results across jetting systems10, and can be widely applied to a variety of jetting systems10. On a given set of hardware components, the impact position varies up to about 40 micrometers, which corresponds to approximately 20 Volts for the jetting system10ofFIG. 1. This is especially problematic when attempting to define a jetting profile for multiple jetting systems10using a single jetting profile. Instead, this method allows for the peak voltage and the impact voltage to be adjusted for each individual jetting system10and for each particular arrangement of hardware components within the jetting system10. Likewise, by calibrating the individual components together, the tolerance requirements of the components can be lessened, which in turn, reduces the manufacturing costs associated with the hardware components.

This method may reduce the wear and the associated replacement costs on hardware components, such as the valve seat22, the valve closure structure18, and the piezoelectric actuation mechanism16. Further, by using this method periodically as part of a preventative maintenance routine, the method400provides more consistent jetting over the life of the jetting system10, because wear of the hardware components change the relative positioning and closed voltage (Vc). This is important because the distance that the valve closure structure18travels from the valve seat22during opening, the amount of time the valve closure structure remains separated from the valve seat, and the speed at which the valve closure structure18contacts the valve seat22on closing strongly influence the volume and consistency of the jetting process. By calibrating the jetting profile relative to the closed voltage (Vc), this improves the consistency of the performance within the life of the jetting system10. Further, since the valve seat22typically wears out more quickly due to the repeated contact with the valve closure structure18, the valve seat22often needs to be replaced before the other components, such as, for example, the piezoelectric actuation mechanism16or the valve closure structure18.

This method400allows the original jetting profile58to be calibrated to account for specific material properties of the fluid material38being dispensed. For example, it is desirable with low-viscosity fluid materials to reduce the impact velocity while increasing the sealing force. This is because the velocity required to sufficiently eject the fluid material38from the outlet40is reduced. Further, for low viscosity fluid materials, it is desirable to increase the sealing force, to prevent unintended leakage of fluid material38through the outlet40. As used herein, a low-viscosity fluid material generally has a viscosity of less than about 100 centipoise. Conversely, for high-viscosity fluid materials, it is desirable to increase the impact velocity while decreasing the sealing force. As used herein, a high-viscosity fluid material generally has a viscosity of greater than about 1000 centipoise.

FIGS. 7-9show another illustrative embodiment, where the jetting system10incorporates a reference cartridge80. Specifically,FIGS. 7 and 8show the reference cartridge80including a cylinder82, a mechanical stop84, and a holder86. The reference cartridge80is preferably positioned at the same location as a brand new fluid cartridge56. As shown, the mechanical stop84is a block of known dimensions that is preferably manufactured with a high degree of precision.

Incorporating the reference cartridge80into the jetting system10provides a “master calibration” to determine the relative wear between the fluid cartridge56and the rest of the jetting dispenser12. The reference cartridge80may also be used to determine the wear of other components of the system10, such as the valve closure structure18and/or the piezoelectric actuation mechanism16. WhileFIG. 9shows the valve closure structure18as a drive pin24, the valve closure structure18may include any suitable combination of elements known to one skilled in the art such as, for example, poppets, needles, plungers and/or balls.

FIG. 10shows an illustrative method1000for calibrating a jetting system10using a reference cartridge80having a mechanical stop84positioned at a predetermined distance away from the valve closure structure18in a non-impact calibration position. At step1002, the fluid cartridge56including a portion of the valve closure structure18, specifically shown inFIG. 1as a poppet26, are removed from the jetting system10, while the reference cartridge80is inserted into the jetting system10as shown inFIG. 9. Removing these components and replacing them with the reference cartridge80reduces the variability imparting by the fluid cartridge56(e.g., the valve seat22) and allows for a more precise calibration due to fewer components. At step1004, voltage is applied to the piezoelectric actuator34to move the valve closure structure18between a non-impact calibration position and an impact calibration position. As used herein, an impact calibration position is where at least a portion of the valve closure structure18is impacting the mechanical stop84, while a non-impact calibration position is where no portion of the valve closure structure18is impacting the mechanical stop84. It does not matter whether the valve closure structure18starts at a non-impact calibration position and move into an impact calibration position, or starts at an impact calibration position and moves into a non-impact calibration position. Specifically,FIG. 9shows the drive pin24of the valve closure structure18contacting the mechanical stop84instead of the poppet26of the valve closure structure18contacting the valve seat22as shown inFIG. 1.

At step1006, the sensing device48senses the position of the valve closure structure18, either directly or indirectly, while the valve closure structure18is actuated by virtue of the applied voltage of step1004. For example, the sensing device48may sense the position of the valve closure structure18, such as the drive pin24. At step1008, voltage calibration data is generated based on the known voltages applied to the piezoelectric actuator34in step1004and position calibration data is generated based on the sensed positions of the valve closure structure18. This generation of voltage calibration data and position calibration data may occur simultaneously with or after measuring the movement of the valve closure structure18.

At step1010, the control component14, for example, establishes a master reference point (MRP) using the voltage calibration data and position calibration data. The method for determining the master reference point (MRP) may be performed in an analogous manner as the methods for determining the reference point (RP) discussed above in relation to the method400. While both seek to determine the closed voltage (Vc), in this illustrative method, the closed voltage (Vc) is determined when at least a portion of the valve closure structure18first or last impacts (depending on the arrangement of components) the mechanical stop84.

At step1012, the control component14uses the master reference point (MRP) to determine one or more wear characteristics of the jetting system10by comparing the master reference point with historic data as discussed below. Further, method1000may include alerting the user when a wear characteristic of a component is outside of an acceptable tolerance or a component is in need of preventive maintenance. For example, the user may be alerted via the graphic user interface associated with the control component14. The method may also include tracking the number of cycles the valve closure structure18impacts the mechanical stop84, determining a useful life of the components, and determining preventative maintenance schedules and routines using voltage and position calibration data and the number of cycles.

Using the reference cartridge80to calibrate the jetting system10aids in determining whether the hardware components are at or near the end of their useable life. This master calibration determines the overall wear in the jetting dispenser12, but does not determine the relative wear between the piezoelectric actuation mechanism16and the valve closure structure18. However, storing the closed voltage (Vc) associated with the reference cartridge80from when the reference cartridge80was new, and at various other times, allows for tracking of wear and enhanced preventative maintenance. For example, a master reference point (MRP) may be determined multiple times over a period of time and stored. A contemporary master reference point (MRP) may be presently determined and compared against one or more of the stored master reference points (MRP). If a difference in the contemporary master reference point (MRP) and the one or more stored reference points (MRP) is observed, this may be indicative of wear of one or more components of the dispenser12.

Further, comparing the closed voltage (Vc) corresponding to the fluid cartridge56and/or the replaced components of the valve closure structure18to the closed voltage (Vc) corresponding to the reference cartridge80tracks the wear of the fluid cartridge56and/or the replaced components of the valve closure structure18, including the wear of the valve seat22. For example, if the reference cartridge80was configured such that the relative positioning of the mechanical stop84(with respect to the drive pin24) matched that of the poppet26in a non-worn state, a difference between the closed voltage (Vc) corresponding to the reference cartridge80and a previously-recorded closed voltage (Vc) corresponding to the present poppet26may reveal wear in the replaced poppet26and/or the replaced valve seat22. Similarly, such a difference may also reveal wear in the piezoelectric actuation mechanism16(or component thereof) since, for example, more voltage may now be required to expand the now-worn piezoelectric actuator34over the same distance.

In another illustrative embodiment, a method of a user operating a jetting system10including a mechanical stop84positioned at a predetermined distance away from the valve closure structure18in a non-impact calibration position is also disclosed. In this embodiment, the user inputs various parameters into the control component14using a graphic user interface (not shown) electronically connected to the control component14. By way of example and not by limitation, the user enters the fluid type, the jetting frequency, and/or the droplet size. Based at least in part on the parameter(s) provided by the user, the control component14then determines a calibrated jetting profile60by applying voltage to the piezoelectric actuator34of the piezoelectric actuation mechanism16to move the valve closure structure18between a non-impact calibration position and an impact calibration position. In this embodiment, the impact calibration position occurs where the valve closure structure18impacts or leaves contact with the mechanical stop84, according to the particular configuration of the jetting system10. The method includes applying the calibration profile to the jetting system10using the control component14. The method includes determining a jetting profile by applying voltage to the piezoelectric actuator34to move the valve closure structure18between a non-impact calibration position where the valve closure structure18is not impacting the valve seat22and an impact position54where the valve closure structure18is impacting the valve seat22. The method includes applying the calibrated jetting profile60to the jetting system10. A warning on the graphic user interface or an auditory sound may be produced by the control component14to warn the user when wear is beyond a recommended level or preventative maintenance is requested.

FIG. 11depicts an exemplary method1100of calibrating the jetting system10and/or determining wear of the jetting system10using a stroke length of the valve closure structure18specified by a user. The method1100may be used, for example, to account for variations in the piezoelectric actuation mechanism16, the valve closure structure18, and/or other component of the jetting system10. For instance, due to repeated use or simply slight variations in manufacture, the “gain” of the system may vary. That is, the displacement caused by the piezoelectric actuation mechanism16per unit of applied voltage may vary from particular system to system.

At step1102, a desired stroke length of the valve closure structure18is received from a user. The desired stroke length, for example, may specify the desired stroke length of the poppet26from its upper-most non-impact position to its impact position with the valve seat22. In some aspects, the user may further input the sealing offset voltage (Vso) or other parameters relating to the operation of the jetting system10. Step1102, as well as the other steps of the method1100, may be effectuated via the control component14.

At step1104, voltage is applied to the piezoelectric actuator34to move the valve closure structure18(e.g., the poppet26) between non-impact and impact positions (or vice versa). At step1106, the position(s) of the valve closure structure18are sensed by the sensing device48as the valve closure structure18is moved between non-impact and impact positions (or vice versa). At step1108, based on the known voltage applied to the piezoelectric actuator34in step1104and the sensed position(s) in step1106, the voltage and position data are generated.

At step1110, the reference point (RP) is determined based on an analysis of the voltage and position data. The reference point (RP) may be determined in a similar manner as described above with respect to the method400shown inFIG. 4and the illustrative examples ofFIGS. 5 and 6. Based on the reference point (RP), the closed voltage (Vc) may additionally be determined. For example, the voltage component of the reference point (RP) may indicate the closed voltage (Vc).

At step1112, the voltage and position data are analyzed to determine a top voltage (Vt). The top voltage (Vt) is the voltage that, when applied to the piezoelectric actuator34, provides the desired stroke length received from the user in step1102. More particularly, the top voltage (Vt) is the voltage that provides the maximum upward travel of the valve closure structure (e.g., the poppet26) relative to valve seat22, hence the term “top” voltage. As such, the top voltage (Vt) may be the maximum voltage applied in a jetting profile for a dispenser12in which voltage applied to the piezoelectric actuator34causes the valve closure structure18to move away from the valve seat22, such as the dispenser12depicted inFIGS. 1 and 1A. Conversely, the top voltage (Vt) may be the minimum voltage applied in a jetting profile for a dispenser12in which voltage applied to the piezoelectric actuator34causes the valve closure structure18to move towards the valve seat22.

At step1114, the closed voltage (Vc) and/or the reference point (RP) is used to shift the original jetting profile58to a first calibrated jetting profile60a. The determination of the first calibrated jetting profile60amay be performed in a manner similar to the determination of the calibrated jetting profile60described in step412of the method400and the illustrative examples provided inFIGS. 3, 5 and 6. For example, the first calibrated jetting profile60amay be determined such that the first calibrated jetting profile60ahas a starting voltage and/or an ending voltage equal to the closed voltage (Vc) or equal to the sealed voltage (Vs) in the event that the sealing offset voltage (Vso) was provided or otherwise accessible.

At step1116, the top voltage (Vt) is used to determine a second calibrated jetting profile60b. Specifically, the first calibrated jetting profile60ais stretched or compacted, relative to the closed voltage (Vc) (or the sealed voltage (Vs), as the case may be), to form the second calibrated jetting profile60bsuch that the minimum voltage (in a dispenser12where applied voltage causes downward movement of the valve closure structure18towards the valve seat22) or the maximum voltage (in a dispenser12where applied voltage causes upward movement of the valve closure structure18away from the valve seat22) of the second calibrated jetting profile60bequals the top voltage (Vt). It will be noted that step1114and step1116may be performed in a reverse order than depicted inFIG. 11. For example, the original jetting profile58may first be stretched or shrunk based on the top voltage (Vt) and the resulting profile may then be shifted according to the closed voltage (Vc) and/or the sealed voltage (Vs). Similarly, step1114and step1116may be performed concurrently.

With reference toFIGS. 12 and 13, an illustrative example of the method1100will now be provided.FIG. 12is similar in many respects toFIG. 3and depicts the original jetting profile58, as well as the first calibrated jetting profile60aand the second calibrated jetting profile60b.FIG. 13is similar in many respects toFIG. 6and includes a chart of measured position data78plotted against voltage data76. The chart ofFIG. 13includes data during the non-impact position52(i.e., the valve closure structure18is moving towards the valve seat22) and during the impact position54. The gradient of the charted line during the non-impact position may be considered the displacement versus voltage “gain” of this particular dispenser12.

Initially, a user provides an input, such as via the control component14, of 50 micrometers for the desired stroke length1302of the valve closure structure18, as well as a sealed voltage offset (Vso) of approx. 5 volts. Voltage is applied to the piezoelectric actuator34, the position(s) of the valve closure structure18is sensed by the sensing device48, and the position data78and voltage data76are generated accordingly. Using methodologies described above in greater detail, the voltage data76and position data78are analyzed to determine the reference point (RP) shown inFIG. 13, here corresponding to approx. 55 volts and a displacement of approx. 1145 micrometers.

Based on the closed voltage (Vc) (55 volts) of the reference point (RP), the first calibrated jetting profile60ais determined. The first calibrated jetting profile60ais determined by shifting the original jetting profile58such that the maximum voltage of the first calibrated jetting profile60aequals the sealed voltage (Vs), which is the closed voltage (Vc) plus the sealing offset voltage (Vso). In the present example, the maximum voltage of the first calibrated jetting profile60ais 60 volts (55 volts+5 volts).

The second calibrated jetting profile60bis determined based at least in part on the top voltage (Vt). In particular, the second calibrated jetting profile60bis determined by stretching or compacting the first calibrated jetting profile60aso that the minimum voltage of the second calibrated jetting profile60bequals the top voltage (Vt). The top voltage (Vt) may be determined by an analysis of the charted data inFIG. 13. For example, with the reference point (RP) already determined, the desired stroke length1302(i.e., the change in position of the valve closure structure18) may be subtracted from the position of the reference point (RP). Here, this would result in a position of 1095 micrometers (1145 μm−50 μm=1095 μm). The position of 1095 micrometers may be cross-referenced in the data line in the chart to determine that the position of 1095 micrometers corresponds to the top voltage (Vt) of approx. 37 volts.

As another technique for determining the top voltage (Vt),FIG. 13's charted data during the non-impact position52may be extrapolated to a trend line. The trend line may be expressed in the form of a y=mx+c equation, wherein y equals the measured position, x equals the voltage, m equals the gradient of the line, and c equals some constant. The top voltage (Vt) may be determined by setting y in the aforementioned equation to 1095 micrometers (i.e, the difference between the position of the reference point (RP) and the specified desired stroke length1302), and solving for x, which will yield the top voltage (Vt). It will be appreciated that these and other techniques for determining the top voltage (Vt) may be implemented via software, which may be executed by the control component14.

With the top voltage (Vt) determined to be 37 volts, the first calibrated jetting profile60amay be compacted into the second calibrated jetting profile60bsuch that the minimum voltage of the second calibrated jetting profile60bis equal to 37 volts, as can be seen inFIG. 12.

FIG. 14depicts an illustrative method1400of calibrating a jetting system10and/or determining a wear characteristic (including electrical degradation) of the jetting system10using a reference cartridge80having a mechanical stop84positioned at a predetermined distance away from the valve closure structure18in a non-impact calibration position, as shown inFIGS. 7-9.

At step1402, the fluid cartridge56is removed from the jetting system10and replaced with the reference cartridge80. At step1404, voltage is applied to the piezoelectric actuator34to move the valve closure structure18between a non-impact calibration position and an impact calibration position. As used herein, an impact calibration position is where at least a portion of the valve closure structure18is impacting the mechanical stop84, while a non-impact calibration position is where no portion of the valve closure structure18is impacting the mechanical stop84. For example, the drive pin24may contact the mechanical stop84in the impact position instead of the poppet26contacting the valve seat22in the configuration shown inFIG. 1.

At step1406, the sensing device48senses the position of the valve closure structure18, either directly or indirectly, while the valve closure structure18is actuated by virtue of the applied voltage of step1404. At step1408, voltage calibration data is generated based on the known voltages applied to the piezoelectric actuator34in step1404and position calibration data is generated based on the sensed positions of the valve closure structure18. This generation of voltage calibration data and position calibration data may occur simultaneously with or after measuring the movement of the valve closure structure18.

At step1410, a reference “gain” is determined, wherein the reference gain reflects the ratio of the displacement of the valve closure structure18to the voltage applied to the piezoelectric actuator34. For example, since calibration position and voltage data may be plotted against one another in the same manner as the position data78and the voltage data76shown inFIG. 6 or 13, the data line in such a chart corresponding to the non-impact calibration position may be analyzed to determine a trendline. The gradient of the trendline may accordingly represent the reference gain. The reference gain may be stored for later use, such as in a comparison of a current reference gain with one or more stored reference gains.

At step1412, the reference gain is used to determine a wear characteristic (including electrical degradation) of the dispenser12or component thereof, including the valve seat22, the valve closure structure18, or the piezoelectric actuation mechanism16. For example, the reference gain may be compared against a pre-determined range of gains reflecting “normal” gains. If the reference gain is outside of the pre-determined range of gains, this may indicate that the dispenser12or component thereof has suffered detrimental wear and may require maintenance or replacement. As another example, the current reference gain may be compared against a past reference gain for the same dispenser12. If the difference between the current reference gain and the past reference gain is greater than a pre-determined threshold, this may also be indicative of wear. Upon a determination of the wear characteristic, the user may be notified, such as via a graphic user interface associated with the control component14or an auditory signal.

As referred to herein, that control component14may be any type of processing (or computing) device having one or more processors. For example, the control component14can be an individual processor, workstation, mobile device, computer, cluster of computers, set-top box, game console or other device having at least one processor. In an embodiment, more than one control component14may be implemented on the same processing device. Such a processing device may include software, firmware, hardware, or a combination thereof. Software may include one or more applications and an operating system. Hardware can include, but may not be limited to, a processor, memory, and/or graphical user display. The control component14may be disposed as part of the dispenser12and/or as a separate component from the dispenser12.

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