Abstract:
Systems and methods related to dispensing fluid and controlling a dispensing operation. The system includes a fluid dispenser including an inlet and an outlet, the dispenser being operable to start and stop the flow of the fluid from the outlet onto a substrate. The system also includes a fluid supply reservoir adapted to hold the fluid, and having an outlet coupled in fluid communication with the inlet of the fluid dispenser to establish a flow path for the fluid between the fluid supply reservoir and the outlet of the fluid dispenser. The fluid supply reservoir further includes a pneumatic input coupled to an air flow path adapted to receive pressurized air for forcing the fluid from the outlet of the reservoir. An electronic air flow meter device is operatively coupled to the air flow path to produce electrical output signals.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. patent application Ser. No. 14/591,300, filed Jan. 7, 2015, and published as U.S. Patent application. Pub. No. 2016/0193619 on Jul. 7, 2016, which is incorporated by reference herein in its entirety. 
       TECHNICAL FIELD 
       [0002]    The present invention relates generally to the field of fluid dispensers that accurately dispense small amounts of fluids in various forms such as dots or droplets, or lines. 
       BACKGROUND 
       [0003]    In the manufacture of various items, such as printed circuit (“PC”) boards, it is frequently necessary to apply small amounts of fluid materials. Such materials include, by way of example and not by limitation, general purpose adhesives, solder paste, solder flux, solder mask, grease, oil, encapsulants, potting compounds, epoxies, die attach pastes, silicones, RTV and cyanoacrylates. While examples are given herein related generally to PC board manufacturing processes, it will be appreciated that the invention is applicable to many other fluid dispensing processes that would benefit from improved flow control. 
         [0004]    As one example, a fabrication process known as flip chip technology has developed, which has multiple processes that require fluid dispensing. For example, a semiconductor die or flip chip is first attached to a PC board via solder balls or pads, and in this process, a viscous solder flux is applied between the flip chip and the PC board. Next, a viscous liquid epoxy is dispensed and allowed to flow and completely cover the underside of the chip. This underfill operation requires that a precise amount of the liquid epoxy be deposited along at least one side edge of the semiconductor chip. As the volume of the epoxy decreases during the curing process, a pseudo-hydrostatic state of stress will be imposed on the solder balls or pads, and this will provide resistance to deformation of the solder balls or pads, and therefore resistance to fracture. The liquid epoxy flows under the chip as a result of capillary action due to the small gap between the underside of the chip and the upper surface of the PC board. Once the underfill operation is complete, it is desirable that enough liquid epoxy be deposited to encapsulate all of the electrical interconnections, so that a fillet is formed along the side edges of the chip. A properly formed fillet ensures that enough epoxy has been deposited to provide maximum mechanical strength of the bond between the chip and the PC board. It is critical to the quality of the underfilling process that the exact amount of epoxy is deposited at exactly the right location. Too little epoxy can result in corrosion and excessive thermal stresses. Too much epoxy can flow beyond the underside of the chip and interfere with other semiconductor devices and interconnections. These parameters must be accurately controlled in the context of manufacturing environments that require high speed productivity. 
         [0005]    In another application, a chip is bonded to a PC board. In this application, a pattern of adhesive is deposited on the PC board; and the chip is placed over the adhesive with a downward pressure. The adhesive pattern is designed so that the adhesive flows evenly between the bottom of the chip and the PC board and does not flow out from beneath the chip. Again, in this application, it is important that a precise amount of adhesive be deposited at exact locations on the PC board. 
         [0006]    The PC board is often being carried by a conveyor past a fluid dispenser that is mounted for movement above the PC board. The moving dispenser is often of the type capable of depositing small dots or droplets of fluid material at desired locations on the PC board. This type of dispenser is commonly referred to as a non-contact jetting dispenser. There are several variables that are often controlled in order to provide a high quality fluid dispensing process. First, the weight or size of each of the dots is controlled. Known fluid dispensers have closed loop controls that are designed to hold the dot size constant during the material dispensing process. It is known to control the dispensed weight or dot size by varying the supply pressure of the fluid, the on-time of a dispensing valve within the dispenser and the stroke length of a valve member of the jetting dispenser. Known control loops have advantages and disadvantages depending on the design of a particular dispenser and the fluid being dispensed. However, known techniques often require additional components and mechanical structure, such as weigh scales, thereby introducing additional cost, time and reliability issues. Further, known methods often involve the use of calibration procedures, separate from the manufacturing process, which reduces productivity. Therefore, there is a continuing need to provide faster and simpler means for controlling parameters such as dot size, and dispensed fluid volume or weight. 
         [0007]    Another important variable that may be controlled in the dispensing process is the total amount or volume of fluid to be dispensed in a particular cycle. Often the designer of a chip packaging specifies the total amount or volume of fluid, for example, epoxy in underfilling, or adhesive in bonding, that is to be used in order to provide a desired underfilling or bonding process. In jetting, for example, for a given dot size and dispenser velocity, it is known to program a dispenser control so that the dispenser dispenses a proper number of dots to dispense a specified amount of the fluid in a desired line or pattern at the desired location. Such a system is reasonably effective when the dispensing parameters remain constant. However, such parameters are constantly changing, albeit, often only slightly over the short term. The cumulative effect of such changes can result in an undesirable change in the volume of fluid being dispensed by the dispenser. Therefore, there is also a need for a control system that can determine dispensed weight and/or volume in an accurate but easy manner. In addition, there is a need for the real time detection of process excursions such as clog detection, leak detection, and air bubble detection. 
         [0008]    Generally, there is a need for an improved computer controlled fluid dispensing system that addresses these and other challenges of accurately dispensing small amounts of fluid in high productivity manufacturing processes and the like. 
       SUMMARY 
       [0009]    In a first illustrative embodiment, the invention provides a fluid dispensing system for accurately dispensing fluid and controlling a dispensing operation. The system includes a fluid dispenser with an inlet and an outlet, the dispenser being operable to start and stop the flow of the fluid from the outlet onto a substrate. A fluid supply reservoir is adapted to hold the fluid, and has an outlet coupled in fluid communication with the inlet of the fluid dispenser to establish a flow path for the fluid between the fluid supply reservoir and the outlet of the fluid dispenser. The fluid supply reservoir further includes a pneumatic input coupled to an air flow path adapted to receive pressurized air for forcing the fluid from the outlet of the reservoir. An electronic air mass flow meter device is operatively coupled to the air flow path to produce electrical output signals proportional to the mass flow rate of the air flowing through the pneumatic input. A pressure regulator is operatively coupled to the air flow path. A pressure low pass filter is coupled downstream of the pressure regulator and upstream of the pneumatic input in the air flow path. The pressure low pass filter comprises one or more components that attenuate high frequency changes in pressure without impeding low frequency changes in pressure A control is operatively coupled to the electronic flow meter for receiving and processing the electrical output signals. 
         [0010]    The pressure low pass filter further may take various forms such as air flow restrictor devices which may be passive or adjustable and at least one air expansion tank. 
         [0011]    In other aspects, the system may include an electronic temperature detector operatively coupled to the air flow path to produce electrical output signals proportional to the temperature of the air flowing through the pneumatic input. The temperature detector is operatively coupled to the control for providing a compensation factor used during processing of the electrical output signals from the electronic air mass flow meter device. Other factors that may be compensated for include pressure and/or humidity of the air in the system. As further discussed below, when pressure low pass filters are used, together with one or more compensation factors directed to temperature, pressure and humidity of the air used to drive the fluid in the system, the readings from a sensitive mass air flow meter, designed to measure very low rates of air flow, will be most accurate. 
         [0012]    The control is configured to calculate an actual volume of the fluid in the fluid supply reservoir using the electrical output signals from the electronic air mass flow meter and, for example, one or more of the compensating factors of temperature, pressure and humidity of the air being directed through the mass air flow meter device. Once the actual volume of the fluid is determined, a running total of fluid dispensed may be calculated, for example, by having the control keep track of the volume dispensed during each dispense cycle and subtracting those amounts from the initial total volume measurement. In this way, the real time volume of the fluid remaining in the reservoir or syringe may be tracked and, for example, an operator may be alerted to a low volume condition that requires replacement or refilling of the reservoir or syringe. In addition, an excursion from a nominal range can be detected and the operator may be alerted to take action to correct a problem. 
         [0013]    In another illustrative aspect of the invention, a method of controlling a fluid dispensing system to accurately dispense fluid includes directing pressurized air in a flow path. The pressure of the air is regulated with a pressure regulator in the air flow path. The air is directed through a pressure low pass filter coupled to the air path at a location downstream of the pressure regulator. A fluid is directed from a fluid supply into a dispenser using pneumatic pressure in the flow path on an input side of the dispenser. The fluid is directed from an outlet of the dispenser. An electronic air mass flow meter device is operatively coupled to the air flow path to produce electrical output signals proportional to the flow rate of the air flowing through the flow path. The electrical output signals from the electronic flow meter device are processed to perform a control function, such as a volume measurement or other function such as disclosed herein. The method may include any of the additional steps involving, for example, a pressure low pass filter discussed herein, or one or more of the temperature, pressure or humidity compensation methods discussed herein. 
         [0014]    In another method, the air may not be directed through a pressure low pass filter, however, the method will involve the step of using at least one of an electronic temperature detector operatively coupled to the air flow path, an electronic pressure detector operatively coupled to the air flow path, or an electronic humidity detector operatively coupled to the air flow path for providing a compensation factor used during processing of the electrical output signals from the electronic air mass flow meter device. As with other methods disclosed herein, calculating an actual volume of the fluid in the fluid supply reservoir is accomplished using the electrical output signals from the electronic air mass flow meter, as well as any compensating factor determined from pressure, temperature and/or humidity measurements taken of the air flow. 
         [0015]    In another method, a volume of fluid in a fluid supply reservoir of a fluid dispensing system is determined in an efficient manner. The method includes directing pressurized air in a closed air flow path leading to the fluid supply reservoir. The pressure of the air is regulated with a pressure regulator in the closed air flow path to a first pressure. The pressure of the air is changed with the pressure regulator to a second pressure different from the first pressure. An electronic air mass flow meter device operatively coupled to the air flow path is used to produce electrical output signals proportional to the flow rate of the air flowing through the flow path during the change between the first and second pressures. The electrical output signals from the electronic flow meter device are then processed to determine the actual volume of fluid in the fluid supply reservoir using the electrical output signals. 
         [0016]    In another method, the stroke length of a valve having a fluid inlet is set in an efficient manner. This method generally comprises directing pressurized air to the fluid inlet of the valve. The valve is then adjusted to a closed position. The closed position is detected using an electronic air flow meter to indicate when air flow through the fluid inlet has reached a set point. The valve is then adjusted from the set point to a desired open position defined by the stroke length. 
         [0017]    These and other objects and advantages of the invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a schematic illustration of a first embodiment of a system constructed in accordance with the invention. 
           [0019]      FIG. 2  is a basic flow chart describing a general method that may be carried out by the control shown in  FIG. 1 . 
           [0020]      FIG. 3  is a schematic illustration, similar to  FIG. 1 , but illustrating another illustrative embodiment of a system constructed in accordance with the invention. 
           [0021]      FIG. 4  is a schematic illustration of a dispense system for purposes of describing another embodiment of a method carried out by the control. 
           [0022]      FIG. 5  is a schematic illustration, similar to  FIG. 1 , but illustrating a method of setting a zero point of a dispenser valve. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Generally, the present invention is embodied in various systems and methods that utilize the characteristics of air flow to determine fluid dispense characteristics during a dispense process. In these systems, a fluid supply container or reservoir, such as a syringe, relies on pressurized air to force the fluid from the supply container to a dispense valve, such as a jetting type dispenser that dispenses discrete dots or droplets of the fluid onto the desired substrate. For example, in various dispense systems the air drives a piston or plunger in a syringe which, in turn, forces the fluid into the dispense valve. Complicating factors for this type of process include the fact that the air is compressible and its density changes with changes in temperature, pressure, and humidity. Another complicating factor is that the flow of the fluid from the syringe or other fluid supply container is not constant. For example, when using a jetting dispenser or valve, the changes in fluid flow are sudden and often bidirectional because the jetting dispenser tends to displace fluid back into the syringe at one point of the dispense cycle. Because the fluid flow rate changes quickly, the pressurized air flow used to force the fluid into the dispenser can experience similar abrupt flow rate changes, which are also bidirectional. A third complicating factor is that the air temperature in the syringe can change during the measurement period. The syringe is moving around within a robot, for example, that may be heated or cooled and there can be heat transfer between the air and the syringe and the surrounding environment. The same is true for the air supply tube leading to the syringe. A change in temperature changes the air density and thus changes the measured volume of air. A fourth complicating factor relates to the air potential instability of the pressurized supply. Typically, the air supply to the syringe or fluid supply container is regulated with either a pulse width modulated device or a mechanical air regulator or valve. As the air pressure in the syringe drops, the regulator supplies more air. A mass flow meter used in this supply line is very sensitive and the changes in air supply create flow that is seen as noise to this sensor. 
         [0024]      FIG. 1  illustrates a first embodiment of a jetting dispense system  10 . The system  10  includes a jetting dispenser, such as a valve  12  coupled with a fluid supply, in the illustrative form of a piston operated syringe  14  schematically illustrated, as shown. It will be appreciated that components of the system  10  may take on many optional forms or types. For example, the valve  12  may be an on/off valve that dispenses various types of fluid patterns, or it may be a jetting valve, a pump or any other type of dispenser depending on the application needs. In the exemplary or illustrative embodiments disclosed, the syringe  14  includes a syringe body  16  with an outlet  18  and a reservoir portion  20 , as well as a plunger or piston  22  that is movable through the force of pressurized air directed through an air input  24 . The pressurized air is supplied by an air supply  25 , which may be simply shop or house air, for example, at about 100 psi. The air is supplied into an air line  26 , which may be suitable flexible tubing, such as polyurethane tubing. The fluid outlet  18  is connected to a line  27  leading to a fluid inlet  28  of valve  12 . The air line  26  leads into a pressure regulator  30  that reduces the shop or house air to suitable system pressure, such as 30 psi. The pressure regulator  30  therefore serves as a first manner of providing low pressure stability to the pneumatic side of the system  10 . A pressurized air supply  32  is also provided for the actuating section of the valve  12 . Thus, an air line  34  leads to an inlet  36 . It will be appreciated that the valve  12  may be actuated in other manners instead, such as electric. 
         [0025]    As additional methods or means for providing stability, and reducing transients or peaks and valleys in the air pressure, a pressure low pass filter is placed between the pressure regulator  30  and an air flow meter  120 . The air flow meter  120  may have various levels of sophistication depending on the circumstances, as will be described herein. An air mass flow sensor  40  ( FIG. 3 ) is described herein and is generally a device that provides a raw signal that is a function of the mass of air that flows through the sensor. The air flow meter  120  is generally a combination of the sensor  40  and other sensors that are used to accurately measure volumetric flow. For purposes of providing the pressure low pass filter, for example, one or more tanks  50  for the air are coupled in the supply air path or line  26  between the pressure regulator  30  and the air flow meter  120 . To further mitigate the problem of transient air flow, a long length of small diameter tubing  26   a  (such as 20 to 40 feet of tubing) is coupled between the pressure regulator  30  and tanks  50  creating flow resistance for the air. In similar manner, a length of tubing  26   b  may be coupled downstream of the flow meter  120 . This allows the flow meter  120  to be sized so that its dynamic range of measurement can be compressed to give high resolution over the range of flow desired. The length of tubing and resistance will be determined by the specific performance of the dispenser  12 . The pressure low pass “filters  26   b , will average out the air flow to and from the reservoir or syringe  14  and, therefore, the air flow meter  120  is measuring the average air flow that takes place over a given period of time (t). As will be described in regard to subsequent embodiments, the flow restriction or filter provided by the long length of tubing  26   a  may instead or in addition be another type of flow restriction device, which may or may not be adjustable. All signals are sent to a control  70  are processed in accordance with the general methods as discussed further below. It will be appreciated that the “control”  70  may include one or more components, as are generally conventional in digital processing, for controlling not only the specific components as described herein, but also other operational components such as those associated with the valve  12 . In this regard, the valve  12  may have one or more temperature sensors, one or more heaters, and electric actuators such as solenoids for controlling its actuation, as well as other operational components. 
         [0026]      FIG. 2  illustrates a general flow diagram of the software to be implemented and carried out by the control  70  of  FIG. 1 . In a first step  80 , the pressure regulator  30 , flow meter  120  and any other control components associated with the dispenser  12  are initialized to start a dispensing operation. In the next step  82  the dispenser  12  begins dispensing the fluid in the desired manner, as programmed and carried out by the control  70 , for example, to rapidly dispense multiple dots or droplets, or a line of the fluid  84  onto the substrate  86  ( FIG. 1 ). While the dispensing operation is being carried out, air flow data points (signals) are collected by the control  70  from the flow meter  120 . This data is processed in step  88 , in one or more manners, to be discussed further below. In step  90 , the collected data is processed, such as for purposes of calculating the volume of fluid  84  in the syringe  14 . A control function  92  is then performed by the control  70  based on the calculation, such as informing the operator of a low volume condition in the syringe  14 . 
         [0027]      FIG. 3  illustrates another embodiment of a system  100 , similar to that shown in  FIG. 1 . The components of the system  100  that are the same as described above with regard to  FIG. 1  are denoted with the same reference numerals and have the same function. Therefore, these components need no further description here.  FIG. 3  shows a single tank  50 , however, as with the previous embodiment this may instead be multiple air tanks  50 . As mentioned above in connection with  FIG. 1 , the long length of tubing  26   a  which serves as one form of pressure low pass filter has been replaced in the system  100  of FIG.  3  by a proportional valve  102  used as a restrictor device downstream of the pressure regulator  30 . This proportional valve  102  is adjustable and is set so that if the air pressure is changed at the pressure regulator  30 , it will take a desired period of time for the pressure at the air flow meter  120  to change to the new, adjusted pressure. For example, this time period may be designed to be 90 seconds. This flow restrictor  102  helps to reduce or essentially eliminate transients or abrupt changes in the air flow through the pneumatic portion of the dispense system. As air takes the place of the fluid material  84  in the reservoir or syringe  14 , the electronic pressure regulator  30  will adjust or turn on and off in order to maintain system air pressure constant at the desired set point pressure. Therefore, this action will tend to create transient characteristics in the pneumatic portion of the system, or in other words abrupt air pressure changes. The proportional valve or restrictor  102 , and the air expansion tank  50 , will help ensure that the air flow meter  120  does not experience fast occurring transients or changes in air pressure. The air mass flow sensor  40  is chosen to be extremely sensitive because the fluid dispensing that is occurring with the system  100  involves very small amounts of fluid, such as on the order of 20 microliters. Therefore, the amount of fluid dispensed while the air mass flow meter  120  is actually taking an air flow measurement and sending the data to the control  70  is a fraction of that fluid amount. With this system  100 , and as an one of many possible examples, significant pressure transients (that is, abrupt and brief upward and downward changes in the air pressure) are averaged out over a desired time period such as 90 seconds. This helps ensure that these abrupt pressure changes do not negatively affect the measurements taken by the air flow meter  120 . The signals produced by both the pressure regulator  30 , the proportional valve  102  and the air flow meter  120  are sent bi-directionally to the control  70 . 
         [0028]      FIG. 3  illustrates a more sophisticated and accurate volumetric air flow meter  120  including the air mass flow sensor  40 , as previously described. All other components that are denoted with the same reference numerals as shown and described with respect to  FIG. 3  need no further description here, except as discussed below. An analog to digital converter  122  takes the analog signal produced by the air mass flow sensor  40  and converts it to a digital signal which is used by a microprocessor  124  communicating with the main control  70  or computer. The microprocessor  124  gathers the information from not only the air mass flow sensor  40 , but also from a humidity sensor  126 , as well as a pressure and temperature sensor  128   a ,  128   b . In practice, a temperature sensor  128   b  is located in the flow meter  120  and another temperature sensor (not shown) is located as close as possible to the air section  14   a  of the reservoir or syringe  14  so that the temperature measured is as accurate as possible. In some environments, the temperature of the reservoir or syringe  14  is different than the temperature of the flow meter  120 . In these situations, the temperature of the reservoir or syringe  14  is used in the calculations. If the temperatures are the same, then to reduce complexity, the system can include only the temperature sensor in the flow meter  120 . These measurements are sent back to the main control  70 , such as a computer, and air mass, temperature, humidity, and pressure are measured as a function of time (t) during a specified measurement time period. These measured values are sent to the main control  70  which then uses the equation as discussed below, based on the Gas Law, to compute the air volume associated with the fluid material reservoir, and thereby subsequently compute the fluid material volume in the syringe  14 . This function may also be integrated in the microprocessor  124  in  FIG. 3  if the processing power is sufficient. Stated generally another way, the volumetric air flow meter  120  measures the flow rate of the air during a specified time period, or the change in air volume as a function of time (t). Then, the control  70  integrates that result over the time period of the measurement to convert it to the total volume of air change over that period of time (t). The control  70  will integrate the amount of air flowing past the air flow meter in both directions, because the air mass flow sensor  40  is bidirectional. This negates the effects of various transient flow characteristics, because the air will travel in the air line  26  in both directions due to various occurrences, such as movement of the valve  12  by a robot, which squeezes and moves the flexible air line  26 , as well as due to on and off operation of the valve  12 . The syringe  14 , as well as the air line  26   b  leading to the syringe  14  are thermally insulated in a manner sufficient to prevent temperature change of the air in the syringe  14 . This is important, again, to reduce transient temperature swings that may affect the measurements taken by the sensitive air mass flow sensor  40 . Thus, it will be understood that both upstream and downstream components provide stability to the air flow leading to the syringe  14  thereby ensuring that the measurements taken by the air mass flow sensor  40  and the subsequent calculations and determinations are as accurate as possible. 
         [0029]      FIG. 4  illustrates a highly simplified version of a system  100 ′ as previously described in connection with  FIGS. 1 and 3 , for purposes of understanding another embodiment of a method that may be carried out by the control  70 . Generally, the goal of this method is to allow the actual volume in the fluid reservoir or syringe  14  to be determined or measured as needed on the fly to essentially re-zero the control system  70  with regard to the volume or amount of fluid  84  in the reservoir  14 . As needed or desired, the dispensing operation may be stopped and a discrete pressure change in the pneumatic side of the system  100 ′ may be used to determine the actual volume of fluid  84  in the reservoir  14 . This will be described in more detail with reference to the flow chart shown in  FIG. 5 . However, generally, the air pressure is changed from, for example, 30 psi to 35 psi using the pressure regulator  30 . This will cause an amount of air to flow through the air mass flow sensor  40  shown in  FIG. 4 , or, for example, the volumetric air flow meter  120  shown in  FIG. 3 . During this pressure change, the jetting dispensing valve  12  is closed. The air flow will stop once the pressure reaches the new set point of 35 psi. Using the equation as described below, determining the actual fluid volume in the syringe  14  is possible because new values are measured during a pressure change from 30 psi to 35 psi. This gives a measurement of fluid volume that is actually present in the reservoir or syringe  14  at that time. In this manner, the control  70  and operator essentially can clear the accumulated errors in the control  70  by taking a new measurement. One may periodically perform this operation, as desired, and as set in the control  70 . As shown below, the equation is used to solve for volume in the case in which air pressure is changed, e.g., from 30 psi to 35 psi. 
         [0030]    Flow Meter Measurements Processing 
         [0031]    The air mass flow sensor  40  measures the mass flow of air referenced to “normal” conditions Pn, Tn and RHn which are chosen and set by the manufacturer of the air mass flow sensor  40 . The following equation is used to determine volumetric flow rate (V) from mass flow rate (M) under actual conditions: 
         [0000]    
       
         
           
             V 
             = 
             
               M 
                
               
                 
                   
                     Pn 
                     - 
                     
                       ( 
                       
                         RHn 
                         · 
                         PVn 
                       
                       ) 
                     
                   
                   
                     Pa 
                     - 
                     
                       ( 
                       
                         RHa 
                         · 
                         PVa 
                       
                       ) 
                     
                   
                 
                 · 
                 
                   Ta 
                   Tn 
                 
               
             
           
         
       
     
       Where: 
       [0032]    Pn—Normal absolute pressure (PSIA)
 
Pa—Actual absolute pressure (PSIA)
 
RHn—Normal relative humidity (%)
 
RHa—Actual relative humidity (%)
 
PVn—Saturated water vapor pressure at normal temperature (PSIA)
 
PVa—Saturated water vapor pressure at actual temperature (PSIA)
 
Tn—Normal temperature (° R) Note: ° R=° F.+460=9/5.(° C.-+273.15)
 
Ta—Actual temperature (° R)
 
         [0000]    
       
         
           
             
               
                 
                   
                       
                   
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         [0033]    The following equations and algorithm define the process of using the mass flow meter  120  to determine the fluid level in the syringe  14 . 
         [0034]    The goal of this example is to measure the volume of fluid  84  in the syringe  14 . 
         [0035]    The bulk modulus of the fluid  84  in the syringe  14  is many orders of magnitude higher than the air that is flowing into the syringe  14 . 
         [0036]    It is possible to measure the temperature (Ta), pressure (Pa), and relative humidity (RHa) of the air in the syringe  14 . 
         [0037]    The equations below will not include compensation for relative humidity (RHa), but will assume the use of dry air. The purpose is to describe the general algorithm here. Humidity compensation is added as described above, to achieve further accuracy. 
       DEFINITIONS 
       [0038]    Vse—volume of an empty syringe  14 . 
         [0039]    Vsys—volume of the air path between the mass flow sensor  40  and the syringe  14 +the volume of the empty syringe  14  (including associated air lines, fittings, etc.) 
         [0040]    Vf—volume of the fluid  84  in the syringe  14 . 
         [0041]    Va—volume of the air path between the mass flow sensor and syringe  14 +the volume of the syringe with fluid in it. (Vf=Vsys−Va) 
         [0042]    Px—Absolute Air Pressure time× 
         [0043]    Tx—absolute temperature at time x 
         [0044]    n—moles of gas 
         [0045]    Mx—molar mass of gas (Ma for air) 
         [0046]    DeltaM—mass of air measured between time x and y 
         [0047]    R—universal gas constant value of 0.08206 (atm—L)/(mol.K). 
         [0048]    Universal gas Law: PV=nRT 
         [0049]    Conversion of mass to moles: n=m/M 
         [0050]    Substituting conversion into the universal gas law: 
         [0000]    
       
         
           
             PV 
             = 
             
               
                 m 
                 · 
                 R 
                 · 
                 T 
               
               M 
             
           
         
       
     
         [0051]    Solving for mass: 
         [0000]    
       
         
           
             m 
             = 
             
               
                 P 
                 · 
                 V 
                 · 
                 M 
               
               
                 R 
                 · 
                 T 
               
             
           
         
       
     
         [0052]    In accordance with this method the air pressure is changed from time  1  to time  2 , and the change in air mass is calculated. Temperatures and Pressures are measured at time  1  and  2 . 
         [0000]    
       
         
           
             
               
                 m 
                 2 
               
               - 
               
                 m 
                 1 
               
             
             = 
             
               
                 
                   
                     P 
                     2 
                   
                   · 
                   
                     V 
                     2 
                   
                   · 
                   M 
                 
                 
                   R 
                   · 
                   
                     T 
                     2 
                   
                 
               
               - 
               
                 
                   
                     P 
                     1 
                   
                   · 
                   
                     V 
                     1 
                   
                   · 
                   M 
                 
                 
                   R 
                   · 
                   
                     T 
                     1 
                   
                 
               
             
           
         
       
     
         [0053]    Since the volume has not changed: 
         [0000]    
       
      
       V 
       2 
       =V 
       1  
      
     
         [0054]    Solving for V: 
         [0000]    
       
         
           
             V 
             = 
             
               
                 ( 
                 
                   
                     m 
                     2 
                   
                   - 
                   
                     m 
                     1 
                   
                 
                 ) 
               
                
               
                 R 
                 M 
               
                
               
                 
                   ( 
                   
                     
                       
                         P 
                         2 
                       
                       
                         T 
                         2 
                       
                     
                     - 
                     
                       
                         P 
                         1 
                       
                       
                         T 
                         1 
                       
                     
                   
                   ) 
                 
                 
                   - 
                   1 
                 
               
             
           
         
       
       
         
           
             Or 
              
             
               : 
             
           
         
       
       
         
           
             
               V 
               X 
             
             = 
             
               Δ 
                
               
                   
               
                
               
                 
                   m 
                   x 
                 
                 · 
                 
                   R 
                   M 
                 
               
                
               
                 
                   ( 
                   
                     
                       
                         P 
                         2 
                       
                       
                         T 
                         2 
                       
                     
                     - 
                     
                       
                         P 
                         1 
                       
                       
                         T 
                         1 
                       
                     
                   
                   ) 
                 
                 
                   - 
                   1 
                 
               
             
           
         
       
     
         [0055]    Where “v x ” could be “V sys ” or “V A ”, depending on process step. With this formula, the closed volume can be measured. Process: 
         [0056]    1) Install an empty syringe  14 . 
         [0057]    2) Set the air pressure with the regulator  30  and allow it to stabilize. 
         [0058]    3) Measure air pressure and temperature with sensors  128   a ,  128   b.    
         [0059]    4) Change the air pressure with regulator  30  and allow it to stabilize 
         [0060]    5) Measure the air mass change, temperature, and pressure, and this is m sys . 
         [0061]    6) Calculate the volume, V sys . 
         [0062]    7) Install syringe  14  with fluid  84  in it. 
         [0063]    8) Repeat steps  2  through  6  to obtain V A . This is now V sys -V f  (the fluid  84  displaces air in the syringe  14 ). 
         [0064]    9) V f ═V sys -V A . 
         [0065]    V f , or the volume of the fluid  84  in the syringe  14 , can be updated by measuring the dispensed volume of fluid from the flow meter measurements and subtracting it from the previous value of V f . 
         [0066]    Since there will be some accumulated error from the dispensed volume measurements, it is possible to re-set V f  by repeating the process steps  8  and  9  at times that it are deemed necessary. Note that it will not be necessary to re-measure V sys  unless the type of fluid reservoir is changed 
         [0067]    Example calculations: 
         [0000]    
       
         
           
             
               := 
               
                 8.3144 
                  
                 
                     
                 
                  
                 
                   m 
                   3 
                 
                  
                 
                   Pa 
                   · 
                   
                     K 
                     
                       - 
                       1 
                     
                   
                   · 
                   
                     mol 
                     
                       - 
                       1 
                     
                   
                 
                  
                 
                     
                 
                  
                 Universal 
                  
                 
                     
                 
                  
                 gas 
                  
                 
                     
                 
                  
                 constant 
                  
                 
                     
                 
                  
                 in 
                  
                 
                     
                 
                  
                 SI 
                  
                 
                     
                 
                  
                 units 
               
             
              
             
                 
             
           
         
       
       
         
           
             
                 
             
              
             
               Ma 
               := 
               
                 28.956 
                  
                 
                   gm 
                   mol 
                 
               
             
           
         
       
       
         
           
             Ma 
             = 
             
               0.029 
                
               
                 kg 
                 mol 
               
                
               
                   
               
                
               Conversion 
                
               
                   
               
                
               of 
                
               
                   
               
                
               mole 
                
               
                   
               
                
               to 
                
               
                   
               
                
               kg 
                
               
                   
               
                
               for 
                
               
                   
               
                
               dry 
                
               
                   
               
                
               atmospheric 
                
               
                 
                     
                 
                  
                 
                     
                 
               
                
               air 
             
           
         
       
     
         [0068]    T1:=(25+273.15)K Measured temperature is 25 C, need to convert to absolute temperature in K.
       T1:=298.15K   T2:=(28+273.15)K   P1:=25psi (note: absolute pressure)   P1=1.724×10 5  Pa   P2:=45psi (note: absolute pressure)   P2=3.103×10 5  Pa   Δmsys:=100 mg   Δmsys=1×10 −4  kg       
 
         [0000]    
       
         
           
             Vsys 
             := 
             
               Δ 
                
               
                   
               
                
               
                 msys 
                 · 
                 
                   R 
                   
                     Ma 
                     · 
                     
                       ( 
                       
                         
                           
                             P 
                              
                             
                                 
                             
                              
                             2 
                           
                           
                             T 
                              
                             
                                 
                             
                              
                             2 
                           
                         
                         - 
                         
                           
                             P 
                              
                             
                                 
                             
                              
                             1 
                           
                           
                             T 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                       ) 
                     
                   
                 
               
             
           
         
       
       
         
           
             Vsys=0.064L 
           
         
       
     
         [0078]    It will be appreciated that, using the calculations and parameters set forth herein, volume values associated with the fluid may be calculated and used in various manners. For example, the volume value may be the actual volume of fluid in the fluid supply reservoir. The volume value may instead, or in addition, be the volume of fluid dispensed by the fluid dispenser in a single dispense operation or in multiple, successive dispense operations. For example, an initial volume in the fluid supply reservoir or syringe may be calculated. Then, successive volumes of the fluid may be dispensed from the fluid dispenser. Then, these volume values are subtracted from the initial, actual volume calculated in the fluid supply reservoir. This will yield a result equaling the remaining volume of fluid in the fluid supply reservoir. In order to eliminate any accumulated error in this calculation, the method described above may be used to calculate the actual volume of fluid in the fluid supply reservoir. 
         [0079]    Various additional actions may be taken based on the volume values calculated by the control. For example, in response to calculating the fluid volume in the supply reservoir using a method disclosed herein, an electrical alarm may be activated indicating a low fluid level in the fluid supply reservoir. Comparing a first calculated actual volume to a second calculated actual volume after a fluid dispensing operation will yield the dispensed volume of fluid resulting from that dispensing operation. The dispensed volume of fluid may be compared by the control to a target volume and the process can further include changing at least one of: the pressure of the air in the flow path, a relative speed of movement between the fluid dispenser and a substrate being dispensed on, or a fluid pattern being dispensed by the fluid dispenser. This change can be used to match or at least more closely associate the dispensed volume of fluid to the target volume of fluid. In addition, or in the alternative, a discrepancy between the dispensed volume of fluid and the target volume of fluid may be determined and the control activates an electrical alarm indicating the presence of a discrepancy between the dispensed volume and the target volume. Also, if the density of the fluid is known, it may be used to calculate the mass of the dispensed volume calculated by the control. Alternatively, or in addition, the mass of the dispensed volume of fluid may be determined, such as by using a weigh scale, and the calculated dispensed volume may be used with the determined mass to calculate the density of the dispensed volume (v=m/d). This may be useful in those situations where the density of the fluid may change over time, such as the settling of a particulate material within a fluid. In this case, if the density is out of range, corrective measures may be taken to replace the fluid, better mix the fluid, etc. If the calculated density is out of range with respect to a target density, a comparison of these two figures may be used to allow the control to activate an electrical alarm to an operator. 
         [0080]    Referring now to  FIG. 5 , the systems described herein may also be used to determine when the zero point of the jetting valve or dispenser is reached during setup. When a new or initial jetting dispenser or valve  12  is installed to the system  10 ,  100 ,  100 ′, there is a need to adjust the closed position of the valve  12 , generally referred to as the zero point, and then to set the stroke length of the valve  12 . The stroke length of the valve  12  refers to the distance that the valve stem moves from its fully open position to its fully closed position. In several different types of jetting dispensers or valves  12 , such as the DJ9000 available from Nordson Corporation, Asymtek Division, this setting is made by an operator by tactile feel and has set up-to-set up variability based on this fact, as well as component wear, general condition, and cleanliness. In accordance with another method of the present invention, any of the systems disclosed herein may be used to determine when the jetting valve zero point is reached during setup. That is, the measurement of the air flow mass as described above may be used for this purpose. With reference to  FIG. 5 , a clean and fully assembled jetting dispenser or valve  12  is installed in the system but without any fluid material in the system and without a supply syringe  14  installed. The air line  34  is connected to enable driving the valve stem associated with the valve  12 . The system air line  26   b  in communication with the mass air flow sensor  40  is directly coupled to the fluid material inlet  28 , instead of connecting the reservoir or syringe  14  to the fluid material inlet  28 . A jetting cartridge or valve setup routine may be programmed into the control  70  and activated. The valve  12  will be actuated to the operating state, in a open condition. Thus, system air will be flowing through the fluid material inlet  28  and out from the dispensing outlet of the valve  12  at a flow rate. Air pressure, at the required test pressure, will be supplied to the system air line  26 ,  26   b . The mass air flow sensor  40  will measure the air flow rate and the operator will be instructed to adjust the valve micrometer  140  to increase or decrease the air flow rate as required. The operator will continue adjusting the micrometer  140  at the top of the jetting dispense valve  12  so as to close the valve stem and shut off the valve  12  and when the air flow rate reaches a set point, or is reduced below a set value, the operator is signaled that the zero point is set. For example, a green light or other indicator may be used on the control  70  to indicate that the zero point or closed position of the valve stem (not shown) associated with the jetting dispense valve  12 , has been reached. The operator will then be instructed to set the micrometer  140  to the appropriate open value in increments, such as tactile clicks or another setting method which may be manual or automatic. In this regard, the micrometer  140  is typically turned in an opposite direction to that used to reach the set point in the previously described step. The set up is then finished and the air pressure in the system lines  26 ,  26   b , as well as air pressure to the valve actuator inlet  36  are turned off. The set up flow values are logged for process verification and tracking. Then, in order to operate the system as previously described, the operator removes the system air connection from the fluid material inlet  28  and connects the reservoir or syringe  14  as previously described and shown in, for example,  FIGS. 1 and 3 . 
         [0081]    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.