FLOW METERING FOR DISPENSE MONITORING AND CONTROL

Abstract

Methods and systems of accurately dispensing a viscous fluid onto a substrate. In an embodiment, a method includes using an electronic flow meter device to produce electrical flow meter output signals and performing a responsive control function in a closed loop manner by adjusting at least one dispensing parameter to correct for a difference between an output data set and a reference data set. In another embodiment, a system includes a control operatively coupled to a gas flow meter device and to a weigh scale allowing for a density of an amount of viscous material to be determined. In another embodiment, a method includes using a control coupled to both a gas flow meter device and a weigh scale and performing a responsive control function in a closed loop manner by adjusting at least one dispensing parameter using gas flow meter output signals and weigh scale output signals.

Claims

1. A method of controlling a non-contact jetting dispensing system to accurately dispense a viscous fluid onto a substrate, the method comprising: directing the viscous fluid from a viscous fluid supply into a non-contact jetting dispenser having an inlet and an outlet; discharging the viscous fluid through the outlet of the non-contact jetting dispenser, the non-contact jetting dispenser being operable to start and stop flow of the viscous fluid through the outlet onto the substrate; using an electronic flow meter device operatively coupled to the viscous fluid supply or the outlet of the non-contact jetting dispenser to produce electrical flow meter output signals corresponding to the flow rate of the viscous fluid through a flow path between the viscous fluid supply and the outlet of the non-contact jetting dispenser, the electrical flow meter output signals forming an output data set; comparing the output data set to a reference data set stored in a controller; and performing a responsive control function in a closed loop manner by adjusting at least one dispensing parameter to correct for a difference between the output data set and the reference data set.

2. The method of claim 1, wherein performing the responsive control function further comprises adjusting the flow rate of the viscous fluid flowing through and being dispensed through the outlet of the non-contact jetting dispenser.

3. The method of claim 2, wherein adjusting the flow rate further comprises adjusting the viscosity of the viscous fluid.

4. The method of claim 1, wherein performing the responsive control function further comprises adjusting the dispensing time.

5. The method of claim 1, wherein performing the responsive control function further comprises adjusting the frequency at which viscous fluid is dispensed through the outlet onto the substrate.

6. The method of claim 1, wherein: the viscous fluid supply further comprises a pressurized supply using pressurized air flowing through a pneumatic input of the viscous fluid supply, the electronic flow meter device further is operatively coupled to the pneumatic input to produce electrical flow meter output signals corresponding to the flow rate of the pressurized air flowing through the pneumatic input, and adjusting the at least one dispensing parameter further comprises adjusting the pressure of the pressurized supply.

7. The method of claim 1, wherein: discharging the viscous fluid through the outlet further comprises discharging the viscous fluid through the outlet during relative motion between the non-contact jetting dispenser and the substrate; and performing the responsive control function further comprises adjusting the speed of the relative motion between the non-contact jetting dispenser and the substrate.

8. The method of claim 1, wherein: comparing the output data set to the reference data set further comprises using the output data set to determine a speed of relative motion between the non-contact jetting dispenser and the substrate which results in a target amount of viscous fluid being discharged onto the substrate, wherein determining the speed of relative motion comprises: determining amount of viscous fluid in the form of a total number of dots required to substantially equal the target amount by determining an average per dot volume of the output data set; determining a distance between each of the total number of dots required to distribute the dots; and determining a rate at which the total number of dots is to be dispensed from the non-contact jetting dispenser; and using the rate at which the total number of dots is to be dispensed and the distance between each of the dots in the total number of dots; and performing the responsive control function further comprises adjusting the speed of the relative motion between the non-contact jetting dispenser and the substrate to discharge the target amount of viscous fluid onto the substrate.

9. The method of claim 1, wherein comparing the output data set to the reference data set stored in the controller further comprises integrating the output data set to determine a volume of the output data set.

10. The method of claim 9, wherein: comparing the output data set to the reference data set further comprises comparing the volume of the output data set to a reference volume of the reference data set; and performing the responsive control function further comprises performing the responsive control function in the closed loop manner by adjusting the at least one dispensing parameter to correct for the difference between the volume of the output data set and the reference volume of the reference data set.

11. The method of claim 1, wherein performing the responsive control function further comprises detecting an air bubble in the viscous fluid flowing through the non-contact jetting dispenser.

12. A method of controlling a viscous fluid dispensing system to accurately dispense a viscous fluid onto a substrate, the method comprising: directing a first amount of viscous fluid from a viscous fluid supply into a viscous fluid dispenser, the viscous fluid dispenser being operable to start and stop flow of the viscous fluid through an outlet of the viscous fluid dispenser onto a substrate; using a gas flow meter device operatively coupled to the viscous fluid supply to produce gas flow meter output signals corresponding to the flow rate of the first amount; discharging the first amount from the outlet onto a weigh scale coupled to a controller, the weigh scale producing weigh scale output signals proportional to the mass of the first amount; and performing a responsive control function in a closed loop manner by adjusting at least one dispensing parameter using the gas flow meter output signals and the weigh scale output signals.

13. The method of claim 12, wherein performing the responsive control function further comprises adjusting a flow rate of the viscous fluid being dispensed through the outlet using specific gravity of the first amount.

14. The method of claim 12, wherein performing the responsive control function further comprises adjusting the dispensing time using specific gravity of the first amount.

15. The method of claim 12, further comprising: determining the mass of the first amount using the weigh scale output signals; and determining a volume of the first amount using the gas flow meter output signals.

16. The method of claim 15, wherein determining the volume of the first amount further comprises integrating the gas flow meter output signals obtained from the gas flow meter device using the controller.

17. The method of claim 16, wherein performing the responsive control function further comprises: calculating a specific gravity of the first amount using the mass and volume of the first amount; and adjusting the at least one dispensing parameter using the specific gravity of the first amount.

18. The method of claim 16, wherein performing the responsive control function further comprises: calculating a density of the first amount using the mass and the volume of the first amount; and adjusting the at least one dispensing parameter using the density of the first amount.

19. The method of claim 12, wherein the gas flow meter output signals and the weigh scale output signals form an output data set, and performing the responsive control function further comprises adjusting the at least one dispensing parameter using a specific gravity of the first amount calculated using the output data set.

20. The method of claim 12, wherein the gas flow meter output signals and the weigh scale output signals form an output data set, and performing the responsive control function further comprises adjusting the at least one dispensing parameter using a density of the first amount calculated using the output data set.

21. The method of claim 12, wherein the gas flow meter output signals and the weigh scale output signals form an output data set, the method further comprises comparing the output data set to a reference data set stored in the controller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is an elevational view of a viscous fluid dispensing system constructed according to an illustrative embodiment of the invention.

[0015] FIG. 2 is a flow diagram illustrating an embodiment of the steps performed by a control associated with the system shown in FIG. 1.

[0016] FIG. 3 is a flow diagram illustrating another embodiment of the steps performed by a control associated with the system shown in FIG. 1.

[0017] FIG. 4 is an elevational view of a viscous fluid dispensing system constructed according to another illustrative embodiment of the invention.

[0018] FIG. 5 is a flow diagram illustrating an embodiment of the steps performed by a control associated with the system shown in FIG. 4.

DETAILED DESCRIPTION

[0019] FIG. 1 is a schematic illustration of a viscous fluid dispensing system 10 for accurately dispensing viscous fluid and controlling a dispensing operation. The system 10 includes a viscous fluid dispenser 12 with a viscous fluid inlet 14, a dispensing outlet 16 for the viscous fluid and an internal, movable valve 18 for controlling an on/off dispensing operation of viscous fluid 20 onto a substrate 22. The valve 18 is movable between open and closed positions to dispense the viscous fluid 20 through the outlet 16 onto the substrate 22, for example, in discrete volumes. The invention is not limited to this type of method or structure for starting and stopping the flow from a dispenser. For example, other types of dispensers may be used that rely on pressure induced manners of starting and stopping flow. The dispenser 12 may be of any suitable type and configuration, depending on the dispensing application and needs of the user. In general, the dispenser may dispense continuous lines or other patterns of the viscous fluid 20 onto the substrate 22 or may be a jetting type dispenser that rapidly dispenses small, discrete volumes of the viscous fluid in the form of dots or droplets. For example, such jetting dispensers are available from Nordson ASYMTEK, Carlsbad, Calif., under the names DispenseJet® and NexJet™. The dispenser 12 may be operated, for example, pneumatically or electrically. As shown, the dispenser 12 includes, or is coupled with, a solenoid valve 24 that regulates the introduction of pressurized actuation air through a line or conduit 25 in a known manner to move the valve 18 at least to the open position. In a dual air chamber dispenser, pressurized air would be also used to move the valve 18 to the closed position. In other embodiments, a spring may be used to move the valve 18 to the closed position.

[0020] The system 10 further includes a viscous fluid supply container 26 adapted to hold the viscous fluid 20, and coupled in fluid communication with the inlet 14 of the dispenser 12 to establish a flow path for the viscous fluid between the viscous fluid supply container 26 and the outlet 16 of the viscous fluid dispenser 12. In this embodiment, the supply of fluid 20 in the container 26 is pressurized with air from a suitable source 28 regulated by a pressure regulator 30. A liquid flow meter 32a, or flow rate sensor device, is coupled in the flow path to produce electrical flow meter output signals proportional to the flow rate of the fluid 20 flowing through the flow path when the valve 18 is in the open position. The liquid flow meter 32a may be coupled directly in a fluid line or conduit 34 extending from an outlet 36 of the supply container 26 to the inlet 14 of the dispenser 12. In this embodiment, the liquid flow meter 32a is preferably a Sensirion model LG 16-2000 or LG 16-1000 liquid flow sensor, or a model SLQ-QT105 flow sensor, available from Sensirion AG, Switzerland. The specific model of flow meter chosen will typically depend on the flow rates required for the application, and such factors as response time and sensitivity. In other embodiments, the liquid flow meter 32a may be incorporated directly in the dispenser 12, anywhere in the flow path upstream through the outlet 16, as shown in broken lines in FIG. 1. Another alternative, for example, would be locating the liquid flow meter 32a in the nozzle 16. In yet another embodiment, a gas flow meter 32b may be coupled to the pneumatic actuating side of the system. For example, the gas flow meter 32b may be coupled between the pressure regulator 30 and the inlet 38 of the container 26. In this embodiment, the gas flow meter 32b is preferably a Sensirion model SFM 3100 or SFM 4100 gas flow sensor, available from Sensirion AG, Switzerland. A control 40 is operatively coupled to the electronic flow meter, either 32a or 32b, regardless of its position in the system. The control 40 continuously receives and processes the electrical flow meter output signals indicative of either viscous fluid or gas flow rate data points, respectively, from the flow meter 32a or 32b and performs a responsive control function in a closed loop manner, as will be discussed further below. The control 40, for example, may be a PLC or programmable logic controller, or any other suitable computer-based control device capable of processing the signals from the liquid flow meter 32a or 32b and carrying out the functions to be discussed below. The applications for the system 10, as well as the fluid materials to be dispensed may be of any desired type, including those discussed in the background above.

[0021] FIGS. 2 and 3 illustrate different embodiments of general flow diagrams of the software to be implemented and carried out by the control 40 shown in FIG. 1. As shown in a first step 50 of FIG. 2, the flow meter 32a or 32b, pressure regulator 30, and any other control components associated with the dispenser 12, are initialized to start a dispensing operation. In the next step 52, the dispenser 12 begins dispensing the viscous fluid in the desired manner, as programmed and carried out by the control 40, for example, to rapidly dispense multiple dots or droplets, or a line of the fluid 20 onto the substrate 22 (FIG. 1). While the dispensing operation is being carried out, viscous fluid or gas flow data points (signals) are collected by the control 40 from the flow meter 32a or 32b. This data is processed in step 54, in one or more manners, to be discussed further below. For example, the processing in step 54 can involve a comparison of the gathered data set to a stored reference data set or other analysis. At step 56, the control 40 determines whether the flow rate of the viscous fluid is within tolerance. If the flow rate is within tolerance, the process returns to step 52 and continues the dispensing operation. If the flow rate is not within tolerance, the dispense parameters are adjusted accordingly at step 58. The control 40 then continues to carry out the dispensing operation and the control functions in a closed loop manner.

[0022] In order to analyze the data or signals gathered from the flow meter 32a or 32b, the control 40 may, for example, compare the output data from the flow meter 32a or 32b to stored reference data. The output data from the flow meter 32a or 32b, for example, may be a data set. The data set may be plotted graphically as flow rate vs. time. As a result, a curve or wave form may be generated by the control 40. A generally square wave may be created, in which the signal peaks while the dispenser valve 18 is open and then rapidly falls off when the valve is closed. During a jetting operation, the wave or curve generated by the flow signal data output from the flow meter 32a or 32b will resemble a sawtooth pattern along the curve indicating the rapid on and off or open and closed conditions of the valve 18 as the fluid material 20 is rapidly jetted as dots from the dispenser outlet 16. When the valve 18 is maintained in a closed position at the end of the jetting operation, the wave form or curve will fall to zero. In this operation, the analysis performed by the control 40 may compare the wave form generated by data (signals) from the flow meter 32a or 32b to a reference wave form which represents a more ideal flow pattern. If the two wave forms or curves being compared are dissimilar, the control 40 makes adjustments to the system 10. More generally, the control 40 compares a current or real time data set which is based on signals from the flow meter 32a or 32b, and representative of viscous fluid or gas flow, and compares that real time data set to an analogous reference data set of viscous fluid or gas flow. Based on detecting discrepancies between the two data sets that are being compared, the control is programmed to then make adjustments to various process parameters of the system 10. It is not necessary that the data set actually be assembled as a wave form by the control 40. In the case of a continuous dispense operation having a dispense cycle in which the valve 18 is continuously open to dispense, for example, a line of viscous fluid 20, the wave form may be even more square-shaped.

[0023] The analysis performed upon gathering the signals/data from the flow meter 32a or 32b may involve various processes and/or algorithms. One process may involve comparing the average of the peaks in the detected wave form with a reference or ideal wave form stored in the control 40. Another method can involve determining the area underneath the wave form (i.e., integrate under the curve) and comparing that area with reference data.

[0024] In the case of dispensing lines of fluid 20 or jetting dots of fluid 20, a data set representing proper flow during the dispensing, or jetting, can be stored as a reference data set, and then compared to the real time data set from the flow meter 32a or 32b. If the real time data set varies from the reference data set, then corrections can be made to dispensing, or jetting. Alterations to the system may include, for example, changing the air pressure to the syringe or container 26 that supplies the fluid 20, adjusting the time when the dispenser is dispensing viscous fluid 20, the temperature of the dispenser 12, rate of dispensing the viscous fluid 20 (the firing rate), or the number of dots dispensed in a particular pattern. Corrections can be made very quickly, such as within a response time of 40 milliseconds. For example, there is typically on the order of 100 milliseconds between two consecutive dispenses and this time may be used to adjust or correct the amount of viscous fluid 20 dispensed without affecting process time. Consequently, corrections can be made between the end of one dispense or jetting operation and the beginning of the next dispense or jetting operation. This very short response time compares to several minutes which may be required to dispense fluid material 20 on a weigh scale, weigh the fluid material 20, calculate flow, etc. as per prior calibration procedures.

[0025] The system 10 can also be used to detect one or more air bubbles that discharge through the outlet 16. In this case, the flow meter 32a or 32b will detect a momentary increase in the flow rate as the air bubble passes through the dispenser outlet 16. This momentary increase in the flow rate, if detected by the control 40 based on signals from the flow meter 32a or 32b, may be used to indicate the problem to the operator, such as through an alarm, signal light, or other indicator on a control or computer screen. The operator may then inspect the substrates 22 for any quality issues and perform any necessary maintenance of the system 10. The system 10 may also be used to detect a clogged or semi-clogged condition associated with the dispenser 12 and, most likely, associated with the nozzle or outlet 16 of the dispenser 12. In this case, the flow meter 32a or 32b will detect either no flow or significantly reduced flow. If this condition is detected, the signals from the flow meter 32a or 32b may be used by the control 40 to indicate the condition to the operator, such as by use of an alarm sound, light or other indicator such as on a computer or control screen. This will allow the operator to shut the system down for maintenance purposes. Quick shut down of the system 10 due to a problem such as air bubbles or clogged conditions will minimize product waste and increase yield.

[0026] As shown in the first step 60 of FIG. 3, the flow meter 32a or 32b, pressure regulator 30 and any other control components associated with the dispenser 12 are initialized to start a dispensing operation. In the next step 62, the dispenser 12 begins dispensing the viscous fluid 20 in the desired manner, as programmed and carried out by the control 40, for example, to rapidly dispense multiple dots or droplets, or a line of the fluid 20 onto the substrate 22. As previously discussed, while the dispensing operation is being carried out, viscous fluid or gas flow data points are collected by the control 40 from the flow meter 32a or 32b. These signals may include electronic flow meter device signals. This data may be processed in step 64, in one or more manners, to be discussed further below. For example, the processing in step 64 may involve integrating the viscous fluid or gas flow meter data to determine the volume of an amount of viscous fluid 20 passing through the flow meter 32a or 32b. In other words, integrating the flow meter data with respect to time produces the volume of a first amount of viscous fluid 20. The volume of the output data set may then be compared against a reference volume of the reference data set. If desired, the mass of the first amount of viscous fluid 20 may be determined using reference data, where the mass corresponds to a particular volume of a viscous fluid 20 flowing through the flow meter 32a or 32b. These reference values may be stored in the control 40. In step 66, the volume (in the form of data or signals), or the combined mass and volume (in the form of signals or data), may be determined on a per dot basis by dividing the total mass or total volume by the total number of dots. In step 68, the control 40 may determine whether the value (for example, a volume/mass value) is within an acceptable tolerance. If the value is within the acceptable tolerance, the viscous fluid is dispensed and the dispensing process proceeds. Alternatively, if the value is not within the acceptable tolerance, one or more dispensing parameters may be adjusted. Further, the user may be warned, as discussed in more detail below.

[0027] Adjusting the dispensing parameters may include, for example, adjusting the flow rate of the viscous fluid 20 flowing through and being dispensed through the outlet 16 of the dispenser 12, adjusting the dispensing time to be either shorter or longer, adjusting the frequency at which viscous fluid is dispensed through the outlet onto the substrate by increasing the number of dispensing operations over a given period of time, adjusting the number of discrete dots or droplets using multiple doses of viscous fluid 20, and adjusting the speed of the relative motion between the dispenser 12 and the substrate. Each of these dispensing parameters may be adjusted singularly or in combination with the other dispensing parameters to correct for the difference between the output data set and the reference data set. Adjusting the flow rate flowing through and being dispensed through the outlet 16 of the dispenser 12 may include, for example, adjusting the viscosity of the fluid 20 by adjusting the temperature of the viscous fluid 20. The temperature of the viscous fluid 20 may be adjusted using a heater (not shown). The heater may be configured to increase and decrease the temperature of the viscous fluid 20 being dispensed by dispenser 12. Further, the heater may be electrically coupled with the control 40, with the control 40 being configured to manipulate the heater. However, other methods of adjusting the flow rate of fluid 20 being dispensed from outlet 16 are also envisioned.

[0028] Adjusting the speed of the relative motion between the dispenser 12 and the substrate may be performed in the following manner. The system 10 may permit the relative speed between the nozzle 48 and the substrate 22 to be automatically optimized as a function of the viscous fluid dispensing characteristics and a specified total volume of material to be used on the substrate 22. In addition, the system 10 may optimize the positions at which respective dots are to be dispensed as a function of the relative speed between the outlet 16 of the dispenser 12 and the substrate 22. Specifically, comparing the output data set to a reference data set may include using the output data set to determine a speed of relative motion between the dispenser 12 and the substrate 22 which results in a target amount of viscous fluid 20 being discharged onto the substrate 22.

[0029] The speed of relative motion may be determined by first determining the amount of viscous fluid 20 in the form of a total number of dots required to substantially equal the target amount is determined. This may be determined by computing an average per dot volume of the output data set. Additionally, the distance between each of the total number of dots required to distribute the dots or droplets is determined. Additionally, a rate at which the total number of dots or droplets are to be dispensed from the dispenser 12 is determined. This is the rate at which the total number of dots or droplets are to be dispensed and the distance between each of the dots in the total number of dots or droplets. This rate may then be utilized to adjust the speed of the relative motion between the dispenser 12 and the substrate 22 to discharge a target amount of viscous fluid 20 onto the substrate 22. Further details are shown and described by the Applicant in application Ser. No. 13/079,300, entitled “Viscous Material Non-Contact Jetting System”, now issued as U.S. Pat. No. 8,257,779, the disclosure of which is hereby incorporated by reference.

[0030] FIG. 4 is a schematic illustration of a viscous fluid dispensing system 100 for accurately dispensing viscous fluid 20 and controlling a dispensing operation. The system 100 of FIG. 4 is similar to the system 10 of FIG. 1, but additionally includes a weigh scale 72 electrically coupled to the control 40. The weigh scale 72 may include a calibration surface 73 for receiving viscous fluid 20. The weigh scale 72 is configured to receive and weigh an amount of the viscous fluid 20 deposited on the calibration surface 73 and to produce weigh scale output signals proportional to the mass of the amount of viscous fluid 20. The weigh scale 72 enables small amounts of viscous fluids 20 in various forms such as dots or droplets, or lines to be accurately weighed. The viscous fluid 20 may be deposited or jetted depending on the desired application. In addition to the control 40 being operatively coupled to the weigh scale 72, the control 40 is also operatively coupled to either a liquid flow meter 32a or a gas flow meter 32b. As will be discussed in further detail below, using a weigh scale 72 and a gas flow meter 32b provides different benefits than using a weigh scale 72 and a liquid flow meter 32a.

[0031] Using both a weigh scale 72 and a gas flow meter 32b allow for the density of the viscous fluid 20 to be determined, which solves the problems associated with only using either a weigh scale 72 or a gas flow meter 32b coupled to the control 40. For example, using only a weigh scale 72 allows the mass to be determined, however, to obtain the mass from the weigh scale 72, the dispensing operation stops. This decreases the throughput of the viscous fluid dispenser 12, which of course is undesirable. As used herein, “mass” is intended to include any measurement of mass including, for example, mass, mass flow rate, and weight as discussed below. Mass flow rate is a measure of the mass of the viscous fluid 20 flowing through the outlet 16 of the dispenser 12 for a given time unit, and is customarily measured in pounds per second or kilograms per second. Weight is related to mass using the formula W=m×g, where weight (W) equals mass (m) multiplied by gravitational acceleration (g). Alternatively, since the temperature and pressure of the gas flowing through the gas flow meter 32b are known, this allows for the volume of the gas to be determined. As one skilled in the art would appreciate, this allows the volume of the viscous fluid 20 to be determined. As used herein, “volume” is intended to include any measurement of volume including, for example, volume and volume flow rate (also known as volumetric flow rate). Volume flow rate is a measure of the volume of the viscous fluid 20 flowing through the outlet 16 of the dispenser 12 for a given time unit. However, volume does not provide information regarding the mass of the viscous fluid 20.

[0032] As a result, using the weigh scale 72 as a “setup tool” along with a gas flow meter 32b prior to commencing full-scale dispensing allows the density and specific gravity to be determined for an amount of viscous fluid 20. Specifically, the gas flow meter 32b produces gas flow meter output signals proportional to the flow rate of a second amount of the viscous fluid flowing through the flow path and dispensed through the outlet 36. This allows the control 40 to use the density of the first amount and the volume of the second amount to estimate the mass of the second amount. This allows for more accurate dispensing of the viscous fluid 20. Using the historic data regarding the first and second amounts allows the system 10 to adjust dispensing parameters in real time.

[0033] FIG. 5 illustrates a general flow diagram of the software to be implemented and carried out by the control 40. FIG. 5 may utilize both a weigh scale 72 and a gas flow meter 32b to obtain the density or specific gravity of the dispensed fluid. In the first step 74, the gas flow meter 32b, pressure regulator 30 and any other control components associated with the dispenser 12 are initialized to start a dispensing operation. In the next step 76, dispenser 12 begins dispensing the viscous fluid 20 in the desired manner. This includes a first amount of the viscous fluid 20 being dispensed into weigh scale 72, gathering the gas flow meter output data and gathering the weigh scale output data. As a result, the mass of the first amount may be determined using the weigh scale output signals. Likewise, the volume of the first amount may be determined, potentially simultaneously, using the gas flow meter output signals. This data may be processed in step 78, in one or more manners, to be discussed further below. For example, the processing in step 78 may involve integrating the gas flow meter data to determine the volume of a first amount of viscous fluid 20 passing through the gas flow meter 32b. Integrating the viscous fluid or gas flow meter data with respect to time produces the volume of a first amount of viscous fluid 20.

[0034] In the next step 80, the density (equaling mass divided by volume) may be determined by generally dividing the mass obtained using the weigh scale 72 by the volume obtained using the gas flow meter 32b. Specific gravity may also be determined using density. Specific gravity is the ratio of the density of the viscous fluid 20 (as discussed above) to the density of a reference substance, generally water, at a particular temperature. If desired, the mass and volume of the first amount of viscous fluid 20 may be determined on a per dot, per droplet, or per line basis. In other words, the density may be determined using multiple dots or droplets, or lines of viscous fluid 20, or alternatively, the density may be determined using a single dot, a single droplet, or a single line of viscous fluid 20. At step 82, the control 40 determines whether the density of the viscous fluid 20 is within an acceptable tolerance of predetermined values. If the density is within the acceptable tolerance, the process may utilize a conversion factor (such as inverse density equaling volume/mass) to ensure greater operational precision. The acceptable tolerance may be determined using a reference data set stored in the control 40 or by other acceptable methods. If the density is not within an acceptable tolerance, the user is warned. For example, the control 40 may provide a suitable indication to an operator, such as an alarm sound or light indicator, or an indication on a screen or monitor associated with the control. In addition to or in place of an indication to an operator, at least one dispensing parameter may be adjusted as previously discussed. While density is shown and described in relation to FIG. 5, specific gravity may also be determined and adjusted as desired.

[0035] After the control 40 receives and processes the gas flow meter output signals and the weigh scale output signals to determine a density of the first amount, the control 40 may use the density of the first amount and the volume of the second amount to determine an estimated mass of the second amount. Having an estimated mass of the second amount, the control 40 can adjust one or more dispensing parameters, as discussed above, for further amounts of the viscous fluid dispensed through the outlet. As a result, the viscous fluid dispensing system 10 can continually use the density and volume of previous amounts to estimate the mass and continually improve the dispensing operation. This allows all volume measurements to be taken using the gas flow meter, while obtaining the density from the gas flow meter 32b and the weigh scale 72 to compute the mass without stopping production and to make adjustments to the process.

[0036] In another illustrative embodiment of system 100, the control may be operatively coupled to both the weigh scale 72 and the liquid flow meter 32a. In this embodiment, using both a weigh scale 72 and a liquid flow meter 32a allows for the liquid flow meter 32a to be quickly and precisely calibrated. While the weigh scale 72 is first quickly and precisely calibrated by placing an object of a known weight on the calibration surface 73 of the weigh scale 72, the process to calibrate a liquid flow meter 32a is much more difficult. However, dispensing an amount of viscous fluid 20 through the liquid flow meter 32a and onto the calibration surface 73 of the weigh scale 72, allows for a quick and precise calibration of the liquid flow meter 32a. As a result, incorporating both a weigh scale 72 and a liquid flow meter 32a effectively allows for weigh scale 72 to calibrate the liquid flow meter 32a.

[0037] It will be appreciated that the system 10, 100 may be used for on-the-fly adjustments to the dispense parameters and on-the-fly detection purposes as discussed above, while a manufacturing process involving the dispense operation is underway. That is, the routine depicted in FIGS. 2, 3, and 5 may be in continuous use during the manufacturing process such that dispense parameters are adjusted during manufacturing to increase productivity. The routine of FIG. 5 includes determining density prior to full-scale dispensing as discussed above. The systems 10, 100 may also be used with a calibration station in which the dispenser 12 is taken off-line to a calibration station and the routine shown in FIGS. 2, 3, and 5 is performed at the calibration station as opposed to being performed on-the-fly during the manufacturing process. Even this use of the systems 10, 100 at a calibration station have advantages. For example, less fluid material 20 will be used than in typical calibration stations using weigh scales and the calibration and adjustment process will be faster and potentially more accurate. Certain fluid materials, such as flux, are volatile and the solvents associated with these fluids will evaporate when exposed at atmosphere. Thus, if a weigh scale process takes enough time to allow evaporation, the results will be less accurate. With the system 10 of this invention, the flow data is collected by the control 40 in an amount of time that approaches real time. Evaporation of solvents associated with the fluid is not a factor in this metrology. Also envisioned as off-line is where dispenser 12, still coupled to the system 10, 100, dispenses viscous fluid 20 onto a calibration surface 73 of a weigh scale 72 located adjacent or otherwise near the substrate.

[0038] While the present invention has been illustrated by a description of several embodiments, and while such embodiments have been described in considerable detail, there is no intention 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. Therefore, the invention in its broadest aspects is not limited to the specific details shown and described. The various features disclosed herein may be used in any combination necessary or desired for a particular application. Consequently, departures may be made from the details described herein without departing from the spirit and scope of the claims which follow.