Patent Publication Number: US-2010108256-A1

Title: Closed loop control of adhesive dot characteristics

Description:
BACKGROUND 
     Automatic adhesive dispensing systems are used in a variety of industries to efficiently join parts in a manufacturing assembly line. Typically, an adhesive dispenser is used to apply adhesive onto a part moving relative to the adhesive dispenser (e.g., on a conveyor). The adhesive may be dispensed under pressure applied by a piston or a motor driven pump to form an adhesive dot on the part. 
     In such manufacturing environments, it is often necessary to accurately dispense the adhesive to form an adhesive dot having a desired size and shape at a precise location. However, the accuracy of the adhesive dispensing process may be adversely impacted by a variety of variables, including: general environmental conditions, the physical state of the adhesive being dispensed, the physical condition of the adhesive dispenser, the stability of electrical and other system parameters, etc. Changes in these variables can cause the adhesive dot formed by the adhesive dispensing system to vary from desired target values. 
     In the magnetic disk drive manufacturing environment, automated adhesive dispensing systems are often used to attach sliders to disk drive suspensions. As schematically illustrated in  FIG. 1 , in a typical process, an adhesive dot  1   00  may be dispensed onto a disk drive suspension  102 , and a slider  104  may be picked up and then attached to the disk drive suspension  102 . If a size of the adhesive dot  100  is not within a serviceable range of values, however, the slider  104  may not adequately adhere to the disk drive suspension  102 , or adhesive material may be exposed beyond the slider  104 . Such failures in the adhesive dispensing process may significantly impact disk drive suspension yield and thus increase the ultimate manufacturing cost for magnetic disk drives. 
     There is therefore a need in the art for an improved adhesive dispensing process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view illustrating a slider above a disk drive suspension carrying an adhesive dot. 
         FIG. 2  is a schematic view illustrating an example adhesive dispensing system, according to one illustrated embodiment. 
         FIG. 3  is a schematic view illustrating the example adhesive dispensing system of  FIG. 2  in greater detail, according to one illustrated embodiment. 
         FIG. 4  is a flow chart illustrating one method of operating a feedback system for an adhesive dispenser, according to one illustrated embodiment. 
         FIG. 5  is a flow chart illustrating one method of manufacturing disk drives, according to one illustrated embodiment. 
         FIGS. 6A and 6B  show a flow chart illustrating one method of operating a feedback system for an adhesive dispenser in greater detail, according to one illustrated embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 2 , in one embodiment, an adhesive dispensing system  200  includes an adhesive dispenser  202  configured to dispense adhesive dots  203  onto disk drive suspensions  204 , an adhesive monitoring device  206  positioned downstream from the adhesive dispenser  202  and configured to measure a characteristic for each of the adhesive dots  203 , and a feedback system  208 . In one embodiment, as described in greater detail below, the feedback system  208  is operable to: receive information from the adhesive monitoring device  206  indicative of the measured characteristics of the adhesive dots  203 ; determine an average for the measured characteristics of the adhesive dots  203 ; determine a statistical dispersion for the measured characteristics of the adhesive dots  203 ; compare the average to a function of a reference characteristic value and the statistical dispersion; and modify a control variable associated with the adhesive dispenser  202  based at least in part on the comparison. 
     In the illustrated embodiment, the adhesive dispensing system  200  dispenses adhesive dots  203  onto disk drive suspensions  204 . However, in other embodiments, similarly configured adhesive dispensing systems may dispense adhesive in a variety of different manufacturing environments. For example, an adhesive dispensing system may dispense adhesive in a microelectronic manufacturing environment, or in a manufacturing environment for plastics. The adhesive dispensing systems and processes described herein may thus be implemented in any of these manufacturing environments. 
     The adhesive dispensed by the adhesive dispensing system  200  may comprise any of a variety of adhesives depending upon the manufacturing environment. In one embodiment, the adhesive may comprise UV123HGA glue produced by the Norland Company. This adhesive may be quickly cured by exposure to ultraviolet light. 
     The adhesive dispenser  202  may have a variety of different configurations. In one embodiment, the adhesive dispenser  202  includes an adhesive dispensing nozzle  210 . The adhesive dispensing nozzle  210  may be communicatively coupled to a source of adhesive within a body  212  of the adhesive dispenser  202 . In one embodiment, the source of adhesive may comprise an adhesive tank within the body  212 , and a source of compressed air may be coupled to the adhesive tank in order to pneumatically force adhesive out via the adhesive dispensing nozzle  210 . In other embodiments, other mechanisms for dispensing adhesive may be used. For example, a mechanically driven piston may be positioned within the adhesive tank in order to drive the adhesive out through the nozzle  210 . 
     As illustrated, the adhesive dispenser  202  may be positioned above a conveyor belt  213 , which moves the disk drive suspensions  204  from left to right in  FIG. 2 . In one embodiment, the conveyor belt  213  may be automatically controlled to stop periodically such that each disk drive suspension  204  is briefly positioned underneath the adhesive dispenser  202  at an appropriate location to receive an adhesive dot  203 . In such an embodiment, the adhesive dispenser  202  may be configured to stay absolutely motionless. In other embodiments, the adhesive dispenser  202  may be configured to move, and the disk drive suspensions  204  may remain motionless as the adhesive dispenser  202  moves from one to the other, dispensing the adhesive dots  203 . In still other embodiments, the conveyor belt  213  may move the disk drive suspensions  204  to an approximate location under the adhesive dispenser  202 , and the adhesive dispenser  202  may then be moved to achieve a finer control over the placement of the adhesive dots  203 . For example, the adhesive dispenser  202  may incorporate a machine vision system to accurately place the adhesive dots  203 . 
     The adhesive monitoring device  206  may be configured to measure any of a variety of characteristics of the adhesive dots  203 . In one embodiment, the adhesive monitoring device  206  may be configured to measure a size for each of the adhesive dots  203 . For example, the adhesive monitoring device  206  may be configured to measure at least one of a diameter, a height or a weight of the adhesive dots  203 . In another embodiment, the adhesive monitoring device  206  may be configured to measure a dispensed location for each of the adhesive dots  203 . Such a location measurement may be taken relative to an absolute coordinate system, or may be taken relative to some other component or feature. 
     The adhesive monitoring device  206  may also comprise any of a variety of devices for taking such measurements or otherwise determining the characteristics. In one embodiment, the adhesive monitoring device  206  may comprise a machine vision system. The machine vision system may be configured, for example, to measure a diameter for each of the adhesive dots  203 . The machine vision system may also or alternatively be configured to measure the location of each of the adhesive dots  203 . In other embodiments, the adhesive monitoring device  206  may comprise one or more scales for measuring an approximate weight of the adhesive dots  203 . For example, for each of the disk drive suspensions  204 , before and after weight measurements may be taken along the conveyor belt  213  in order to determine an approximate weight of the adhesive dots  203 . 
     The adhesive monitoring device  206  may be positioned at a variety of locations downstream from the adhesive dispenser  202 . As used herein, it may be understood that the term “downstream” is used as a general term to indicate that the adhesive monitoring device  206  is positioned so as to measure characteristics for the adhesive dots  203  after the adhesive dispenser  202  has dispensed the adhesive dots  203 . In one embodiment, as illustrated, the adhesive monitoring device  206  may be positioned downstream from the adhesive dispenser  202  along the conveyor belt  213 . In another embodiment, the adhesive dispenser  202  may be moved relative to the disk drive suspensions  204 , and the adhesive monitoring device  206  may be configured to move relative to the disk drive suspensions  204  as well, taking measurements of the adhesive dots  203  after the adhesive dispenser  202  has deposited them. In still another embodiment, the adhesive monitoring device  206  may be substantially co-located with the adhesive dispenser  202 , and the disk drive suspension  204  may remain motionless as the adhesive dispenser  202  first dispenses an adhesive dot  203 , and the adhesive monitoring device  206  then measures a characteristic of the adhesive dot  203 . 
     The feedback system  208  may comprise any of a variety of systems communicatively coupled to and configured to receive information from the adhesive monitoring device  206 . The feedback system  208  may be further configured to analyze such information, and modify a control variable associated with the adhesive dispenser  202 . In one embodiment, the feedback system  208  may comprise a computing device including at least one interface communicatively coupled to the adhesive monitoring device  206 , and at least one interface communicatively coupled to the adhesive dispenser  202 . In another embodiment, the feedback system  208  may comprise a hard-wired electronic device, such as an application specific integrated circuit (“ASIC”). 
     The feedback system  208  may be located proximate the adhesive dispenser  202  and the adhesive monitoring device  206 , as illustrated, or the feedback system  208  may be remotely located. In one embodiment, the feedback system  208  may be located remotely and shared among a variety of different adhesive dispensers  202  and adhesive monitoring devices  206 . In another embodiment, the feedback system  208  may be incorporated into the body of the adhesive dispenser  202  or the adhesive monitoring device  206   
     In  FIG. 3 , the feedback system  208  and the adhesive dispenser  202  are illustrated in greater detail. In one embodiment, the feedback system  208  may comprise a computing device including a controller  214  and a memory  216 . The controller  214  may be operable to execute instructions, and the memory  216  may have computer-readable instructions stored thereon that are executable by the controller  214  in order to cause the controller  214  to process information indicative of characteristics of a plurality of adhesive dots  203  dispensed by the adhesive dispenser  202 . The controller  214  may comprise any of a variety of processing units operable to execute instructions, and the memory  216  may comprise any computer-readable memory, such as a hard disk drive, optical disk drive, solid state memory device, etc. 
     In one embodiment, the memory  216  may have instructions stored thereon that enable the feedback system  208  to perform the acts described above. In another embodiment, the memory  216  may have instructions stored thereon to cause the controller  214  to: determine an average for the characteristics of the plurality of adhesive dots  203 ; determine a statistical dispersion for the characteristics of the plurality of adhesive dots  203 ; compare the average to a function of a reference characteristic value and the statistical dispersion; and modify a control variable associated with the adhesive dispenser  202  based at least in part on the comparison. In different embodiments, the memory  216  may include other instructions for controlling the feedback system  208  and other components of the adhesive dispensing system  200 . 
     As illustrated in  FIG. 3 , the adhesive dispenser  202  may include a pressure regulator  218  coupled to a source of compressed air  220 . The adhesive dispensing nozzle  210  may in turn be coupled to an adhesive tank (not shown) communicatively coupled to the source of compressed air  220  via the pressure regulator  218 . Thus, the pressure applied to the adhesive within the adhesive tank may be controlled using the pressure regulator  218 . 
     In one embodiment, the pressure regulator  218  may comprise an electronic pressure regulator communicatively coupled to the feedback system  208 . By changing the settings of the pressure regulator  218 , the feedback system  208  may modify a control variable associated with the adhesive dispenser  202  and thereby control the size of the adhesive dots  203 . For example, the feedback system  208  may signal the pressure regulator  218  to allow greater pressure to be applied to the adhesive in the adhesive tank, resulting in larger adhesive dots  203 . 
     In different embodiments, the adhesive dispensing system  200  may incorporate a variety of other devices and feedback mechanisms. For example, in one embodiment, the adhesive dispensing system  200  may include an actuator for moving the adhesive dispenser  202  relative to the disk drive suspensions  204 . In such an embodiment, the feedback system  208  may provide feedback for controlling this actuator in order to improve location accuracy for the dispensed adhesive dots  203 . 
       FIG. 4  illustrates a flow diagram for a method  400  of operating a feedback system for an adhesive dispenser, according to one embodiment. The method  400  will be discussed in the context of the adhesive dispensing system  200  illustrated in  FIG. 3 . However, the acts disclosed herein may be executed in a variety of different manufacturing environments with different adhesive dispensing systems, in accordance with the described method. 
     As described herein, all of the acts comprising the method  400  may be orchestrated by the controller  214  based at least in part on execution of computer-readable instructions stored in the memory  216 . In other embodiments, a hardware implementation of all or some of the acts of method  400  may be used. 
     At act  402 , an average for characteristics of a plurality of adhesive dots  203  is determined. As described above, these characteristics may comprise size characteristics (e.g., a diameter, height, weight, and/or circumference), location characteristics (e.g., absolute or relative positioning information), or other physical characteristics of the plurality of adhesive dots  203 . 
     In one embodiment, the adhesive dispensing system  200  may include an adhesive monitoring device  206  configured to measure or otherwise determine the characteristics for each of the plurality of adhesive dots  203 . The adhesive monitoring device  206  may then send information indicative of the measured characteristics of the adhesive dots  203  to the feedback system  208  for analysis. In one embodiment, the information indicative of the measured characteristics may be sent one data point at a time from the adhesive monitoring device  206  to the feedback system  208 . For example, upon the completion of each measurement, information indicative of that measurement may be sent to the feedback system  208 . In other embodiments, the adhesive monitoring device  206  may buffer the information before sending it on to the feedback system  208 . 
     The plurality of adhesive dots  203  for which the average is determined at act  402  may comprise any quantity of adhesive dots  203 . In one embodiment, the plurality of adhesive dots  203  may comprise approximately  50  adhesive dots  203 . Such a sample size may provide a statistically significant snapshot of the adhesive dots  203 , while allowing relatively rapid intervention if the adhesive dispensing system  200  begins to malfunction. In other embodiments, more or fewer adhesive dots may be used in act  402  based upon the particular needs of the adhesive dispensing system. For example, a sample size including fewer adhesive dots  203  may be used in order to increase the reaction time of the feedback system  208 . Meanwhile, a sample size including more adhesive dots  203  may be used in order to prevent unnecessary corrections to the adhesive dispenser  202 . 
     The feedback system  208  may determine any of a variety of averages for the measured characteristics. In one embodiment, the average comprises a mean of the characteristics of the plurality of adhesive dots  203 . In other embodiments, the average may comprise a median, a geometric median, a truncated mean, a weighted mean, a mode, etc. 
     At act  404 , a statistical dispersion for the characteristics of the plurality of adhesive dots  203  is determined. The feedback system  208  may determine any of a variety of measures of statistical dispersion. In one embodiment, the statistical dispersion may comprise a standard deviation of the characteristics of the plurality of adhesive dots  203 . In other embodiments, the statistical dispersion may comprise a range, an interquartile range, a mean difference, a median absolute deviation, an average absolute deviation, a coefficient of variation, a quartile coefficient of dispersion, a relative mean difference, a variance, a variance to mean ratio, etc. In different embodiments, particular measures of the statistical dispersion may be preferable. 
     At act  406 , the average is compared to a function of a reference characteristic value and the statistical dispersion. As used in act  406 , the term “function” refers to a mathematical function, which in act  406  takes both the reference characteristic value and the statistical dispersion as variables. 
     In one embodiment, the reference characteristic value comprises a target value for the characteristics of the adhesive dots  203 . For example, if the characteristic comprises a diameter of the adhesive dots  203 , then the reference characteristic value may comprise a target diameter. That is, the reference characteristic value may comprise a nominal value for the diameter. In other embodiments, the reference characteristic value may comprise one of a plurality of acceptable values for the diameter. 
     Thus, the average of the characteristics of the plurality of adhesive dots  203  may be compared against a mathematical function of the reference characteristic value and the statistical dispersion. In one embodiment, this comparison may be indicative of the extent to which the average of the measured characteristics varies from the reference characteristic value as a function of the statistical dispersion of the measured characteristics. For example, if the statistical dispersion comprises a standard deviation, the comparison may indicate that the average is more than one standard deviation away from a target value for the measured characteristic. As another example, the comparison may indicate that the average is more than two standard deviations away from the target value for the measured characteristic. 
     In some embodiments, such a comparison may yield better information for determining whether or not the adhesive dispensing process should be adjusted than a simple comparison between the average and the reference characteristic value, since the comparison of act  406  also yields information regarding the variability (i.e., the statistical dispersion) of the data. That is, in some instances, the average of the characteristics may vary significantly from the reference characteristic value, but the measured characteristics may have such a large statistical dispersion that it is not efficient to adjust the adhesive dispensing process based on this set of characteristics. On the other hand, the average of the characteristics may only vary slightly from the reference characteristic value, but the measured characteristics may have such a tight statistical dispersion that it is efficient to adjust the adhesive dispensing process to bring the average even closer to the reference characteristic value. 
     At act  408 , a control variable associated with the adhesive dispenser  202  is modified based at least in part on the comparison. In one embodiment, the feedback system  208  may send electrical signals to a component of the adhesive dispenser  202  in order to modify the control variable associated with the adhesive dispenser  202 . In another embodiment, the feedback system  208  may send electrical signals to some other component of the adhesive dispensing system  200  in order to modify the control variable associated with the adhesive dispenser  202 . In still other embodiments, other mechanisms for modifying the control variable may be used. 
     The control variable may comprise any of a variety of control variables associated with the adhesive dispenser  202 . For example, in one embodiment, the control variable may represent a pressure setting of the pressure regulator  218 . In another embodiment, the control variable may correspond to a time interval during which the adhesive dispenser  202  dispenses adhesive dots  203 . In such an embodiment, the feedback system  208  may cause a controller (not shown) of the adhesive dispenser  202  to dispense adhesive for a longer or shorter time interval. In yet another embodiment, the control variable may correspond to a location metric for positioning the adhesive dispenser  202  relative to the disk drive suspensions  204 . In such an embodiment, the feedback system  208  may cause the adhesive dispenser  202  itself to be positioned differently, or may instead cause the conveyor belt  213  to stop at different locations. 
     In one embodiment, as described in greater detail below, the control variable may be modified in order to cause the characteristics of the plurality of adhesive dots  203  to more closely approximate the reference characteristic value. For example, if the average of the characteristics of the plurality of adhesive dots  203  is below the function of the reference characteristic value and the statistical dispersion, then the control variable may be varied in order to cause the characteristic to increase. Of course, despite this modification to the control variable, the individual characteristics of subsequently dispensed adhesive dots may vary from the reference characteristic value by more or less than the average determined at act  402 , based at least in part on the statistical variation of the adhesive dispensing process. 
     The control variable may also be modified by different amounts in different embodiments. In some embodiments, the control variable may be modified by a single increment or decrement. For example, the control variable may be modified by a tolerance value, which is indicative of a minimum increment by which the control variable may be modified. The tolerance value may, in such an embodiment, reflect a minimum resolution for the control variable. In other embodiments, the control variable may be modified by different values depending upon how far the average has varied from the reference characteristic value. For example, the control variable may be modified by a first value if the average varies by a single standard deviation from the reference characteristic value, and by a second, larger value if the average varies by two standard deviations from the reference characteristic value. One particular algorithm for modifying the control variable is described in greater detail with respect to  FIGS. 6A and 6B . 
     Although act  408  refers to a single control variable, it may be understood that multiple control variables associated with the adhesive dispenser  202  may be modified based at least in part on the comparison. In some embodiments, multiple characteristics may be measured, and multiple control variables may be modified substantially simultaneously. In other embodiments, multiple control variables may be modified in order to achieve changes in a single characteristic of the adhesive dots  203 . In addition, as described in greater detail below with respect to  FIGS. 6A and 6B , the control variable may be modified based on a plurality of comparisons and other tests. 
       FIG. 5  illustrates a flow diagram for a method  500  of manufacturing disk drives, according to one embodiment. The method  500  will be discussed in the context of the adhesive dispensing system  200  illustrated in  FIG. 3 . However, the acts disclosed herein may be executed in a variety of different manufacturing environments with different adhesive dispensing equipment, in accordance with the described method. 
     As described herein, all of the acts comprising the method  500  may be orchestrated by the controller  214  based at least in part on execution of computer-readable instructions stored in the memory  216 . In other embodiments, a hardware implementation of all or some of the acts of method  500  may be used. 
     At act  502 , a plurality of adhesive dots  203  are dispensed onto a plurality of disk drive suspensions  204 . As described above, this plurality of adhesive dots  203  may comprise any quantity of adhesive dots  204 . In one embodiment, the plurality of adhesive dots  203  may comprise approximately  50  adhesive dots  203 . Such a sample size may provide a statistically significant snapshot of the dispensed adhesive dots  203 , while allowing relatively rapid intervention if the adhesive dispensing system  200  begins to malfunction. 
     The plurality of adhesive dots  203  may be dispensed onto the disk drive suspensions  204  in a variety of ways. In one embodiment, the conveyor belt  213  may be automatically controlled to stop periodically such that each disk drive suspension  204  is briefly positioned underneath the adhesive dispenser  202  at an appropriate location to receive an adhesive dot  203 . In other embodiments, the adhesive dispenser  202  may be configured to move, and the disk drive suspensions  204  may remain motionless as the adhesive dispenser  202  moves from one to the other, dispensing the plurality of adhesive dots  203 . In still other embodiments, the conveyor belt  213  may move the disk drive suspensions  204  to an approximate location under the adhesive dispenser  202 , and the adhesive dispenser  202  may then be moved to achieve a finer control over the placement of the adhesive dots  203 . 
     At act  504 , a characteristic for each of the plurality of adhesive dots  203  is measured. As described above, these measured characteristic may comprise size characteristics (e.g., a diameter, height, weight, and/or circumference), location characteristics (e.g., absolute or relative positioning information), or other physical characteristics. In some embodiments, multiple characteristics may be measured. 
     In addition, a variety of devices may be used to measure these characteristics. In one embodiment, the adhesive monitoring device  206  may be configured to measure the characteristics for each of the plurality of adhesive dots  203 . The adhesive monitoring device  206  may then send information indicative of the measured characteristics for each of the adhesive dots  203  back to the feedback system  208  for analysis. 
     At act  506 , an average for the measured characteristics of the plurality of adhesive dots  203  is determined. This average may be determined in a manner similar to that described with reference to act  402  above. 
     At act  508 , a statistical dispersion for the measured characteristics of the plurality of adhesive dots  203  is determined. This statistical dispersion may be determined in a manner similar to that described with reference to act  404  above. 
     At act  510 , the average is compared to a function of a reference characteristic value and the statistical dispersion. This comparison may be performed in a manner similar to that described with reference to act  406  above. 
     At act  512 , a change to be made to a physical parameter of a subsequent adhesive dot is determined based at least in part on the comparison. The physical parameter may comprise any of a variety of physical parameters related to the measured characteristics. For example, in one embodiment, a physical parameter of the subsequent adhesive dot may comprise a size of the adhesive dot, and the measured characteristic may comprise a diameter, weight, height or other size-related characteristic of the adhesive dots  203 . In another embodiment, the physical parameter may comprise a location of the adhesive dot, and the measured characteristic may comprise a relative or absolute location of the previously dispensed adhesive dots  203 . In still another embodiment, the physical parameter may comprise the measured characteristic itself. 
     In one embodiment, the change to be made to the physical parameter may be determined such that the characteristic of the subsequent adhesive dot more closely approximates the reference characteristic value. For example, if the average of the measured characteristics of the plurality of adhesive dots  203  is below the function of the reference characteristic value and the statistical dispersion, then it may be determined that a size of a subsequent adhesive dot should be increased. 
     In one embodiment, the change may simply be indicative of an increase or decrease of the physical parameter, without assigning any value to the change. In other embodiments, it may be determined that the physical parameter should be changed by a quantifiable amount. For example, it may be determined that the width of the subsequent adhesive dot should be decreased by 5 μm. This quantifiable change may be variable or fixed in different embodiments. 
     At act  514 , the subsequent adhesive dot is dispensed onto a subsequent disk drive suspension  204  based at least in part on the change. In one embodiment, the feedback system  208  may communicate with any of a number of components of the adhesive dispensing system  200  in order to modify a control variable associated with the adhesive dispenser  202  based at least in part on the change. 
     In one embodiment, the subsequent adhesive dot may be dispensed using control variables that make it more likely that the characteristic of the subsequent adhesive dot will more closely approximate the reference characteristic value. For example, if the average of the characteristics of the plurality of adhesive dots  203  is below the function of the reference characteristic value, then the subsequent adhesive dot may be dispensed using control variables that have been varied to cause the characteristic to increase. Of course, as described above, it may be understood that the individual characteristics of the subsequent adhesive dot may vary from the reference characteristic value by more or less than the average determined at act  506 , based at least in part on the statistical variation of the adhesive dispensing process. 
       FIGS. 6A and 6B  illustrate a flow chart for a method  600  of operating a feedback system for an adhesive dispenser in greater detail, according to one embodiment. The method  600  will be discussed in the context of the adhesive dispensing system  200  illustrated in  FIG. 3 . However, the acts disclosed herein may be executed in a variety of different manufacturing environments with different adhesive dispensing equipment, in accordance with the described method. 
     As described herein, all of the acts comprising the method  600  may be orchestrated by the controller  214  based at least in part on execution of computer-readable instructions stored in the memory  216 . In other embodiments, a hardware implementation of all or some of the acts of method  600  may be used. 
     At act  602 , an average for measured characteristics of a plurality of adhesive dots  203  is determined. The characteristics may be measured and the average determined in a manner similar to that described above with reference to acts  504  and  402  above. 
     At act  604 , a standard deviation for the measured characteristics of the plurality of adhesive dots is determined. The standard deviation may be determined in a manner similar to that described above with reference to act  404  above. 
     At act  606 , a number of comparisons are made in order to determine whether or not a pressure applied to form subsequent adhesive dots should be decreased at act  608 . In different embodiments, more or fewer comparisons/tests may be used in order to determine whether or not to adjust a control variable, such as the pressure. For example, in some embodiments, the pressure applied at the pressure regulator  218  may be decreased at act  608  based solely on whether or not the first one or two of the comparisons listed in act  606  have been satisfied. 
     In one embodiment, the average is compared to a first sum of the reference characteristic value added to the standard deviation (i.e., the “Std”) multiplied by a first factor. As illustrated in act  606 , the first factor may comprise  0 . 5 , although different factors may be used in other implementations. If it is determined that the average is larger than the first sum, then it may be further determined that a size of a subsequent adhesive dot should be reduced by a first decrement based at least in part on this determination. In one embodiment, the first decrement may correspond to a minimum increment by which the size of the adhesive dots can be changed. In one embodiment, for example, a minimum unit by which the pressure of the pressure regulator  218  may be adjusted may correspond to an approximate change of 5 μm in a diameter of a subsequent adhesive dot. Thus, in one embodiment, it may be determined that the size of the subsequent adhesive dot should be reduced by 5 μm based at least in part on the determination that the average is larger than the first sum. 
     In one embodiment, the standard deviation is also compared to a maximum standard deviation (“MaxStd”). The maximum standard deviation may comprise a standard deviation value selected in order to ensure that the set of measured characteristics is not too variable. That is, it may be used to determine whether or not the determined average is reliable enough for basing decisions on whether or not to modify the adhesive dispensing process. In one embodiment, the maximum standard deviation may comprise 30 μm, where a normal standard deviation for the adhesive dispenser  202  may be between 8 and 20 μm. If it is determined that the standard deviation is not larger than the maximum standard deviation, then it may be further determined that the size of the subsequent adhesive dot should be reduced by the first decrement based at least in part on this additional determination. 
     In one embodiment, the average may be further compared to the reference characteristic value added to a tolerance value. As described above, the tolerance value may correspond to a minimum increment by which the size of the adhesive dots  203  can be changed. Thus, in one embodiment, this comparison may be used to prevent overshoot by ensuring that the average is greater than the reference characteristic value by at least a minimum increment by which the size of a subsequent adhesive dot may be changed. If it is determined that the average is larger than the reference characteristic value added to the tolerance value, then it may be further determined that the size of the subsequent adhesive dot should be reduced by the first decrement based at least in part on this additional determination. 
     In some embodiments, the current average is compared to an old average. The old average may correspond to a previous average of measured characteristics associated with a previous plurality of adhesive dots  203 . In some embodiments, if the current average is equal to the old average, this may indicate that the adhesive dispensing process is proceeding abnormally. For example, it may indicate that the adhesive monitoring device  206  is taking inaccurate measurements. 
     In some embodiments, the average may be further compared to zero. If the average equals zero, it may indicate that the adhesive dispenser  202  has failed to deposit the adhesive dots, or that the adhesive monitoring device  206  has failed to properly detect the adhesive dots. In either case, the adhesive dispensing system  200  may be stopped, and diagnostics may be executed to determine why the average equals zero. 
     At act  608 , if all of the comparisons of act  606  have been satisfied, a pressure applied during the adhesive dispensing process may be decreased. In one embodiment, the feedback system  208  may send an electrical signal to adjust a pressure setting of the pressure regulator  218 . Thus, in one embodiment, an average size of subsequently dispensed adhesive dots may be reduced. Of course, in other embodiments, different control variables for a variety of components within the adhesive dispensing system  200  may be varied in order to decrease the size of subsequently dispensed adhesive dots. 
     In one embodiment, the pressure may be decreased by a minimum increment corresponding to a minimum resolution of a control variable associated with the pressure. However, in some embodiments, the average may have diverged widely from the reference characteristic value, and it may be desirable to further decrease the pressure. In such an embodiment, acts  610  through  616  provide a mechanism for accelerating the change in the size of subsequently dispensed adhesive dots when the average varies further from the reference characteristic value. 
     At act  610 , a number of comparisons are again made in order to determine whether or not the pressure applied to form subsequent adhesive dots should be further decreased at act  612 . In different embodiments, more or fewer comparisons/tests may be used in order to determine whether or not to further adjust the pressure. For example, in some embodiments, the pressure applied at the pressure regulator  218  may be decreased at act  612  based solely on whether or not the first comparison listed in act  610  has been satisfied. 
     In one embodiment, the average is compared to a second sum of the reference characteristic value added to the standard deviation multiplied by a second factor, the second factor being greater than the first factor described above with reference to act  606 . As illustrated in act  610 , the second factor may comprise two, although different factors may be used in other implementations. If it is determined that the average is larger than the second sum, then it may be further determined that the size of the subsequent adhesive dot should be reduced by a second decrement larger than the first decrement based at least in part on this determination. In one embodiment, the second decrement may simply correspond to two times the first decrement, which may correspond to a minimum increment by which the size of the adhesive dots can be changed. In other embodiments, the second decrement may correspond to some other multiple of the first decrement. 
     In one embodiment, the standard deviation is also multiplied by a differential standard deviation (“DiffStd”), and this result is compared with the tolerance value. In one embodiment, the differential standard deviation may comprise a statistical measure of the detectability of the standard deviation. Thus, this comparison may comprise another verification of the trustworthiness of the measured characteristics. In one embodiment, the differential standard deviation may equal  0 . 5 , although different values may be used in other implementations. If it is determined that the standard deviation multiplied by the differential standard deviation is larger than the tolerance value, then it may be further determined that the size of the subsequent adhesive dot should be reduced by the second decrement based at least in part on this determination. 
     At act  612 , if both of the comparisons of act  610  have been satisfied, a pressure applied during the adhesive dispensing process may be further decreased. In one embodiment, the feedback system  208  may send an electrical signal to further adjust a pressure setting of the pressure regulator  218 . Thus, in one embodiment, an average size of subsequently dispensed adhesive dots may be further reduced. Of course, in other embodiments, different control variables for a variety of components within the adhesive dispensing system  200  may be varied in order to decrease the size of subsequently dispensed adhesive dots. 
     At act  614 , a number of comparisons are again made in order to determine whether or not the pressure applied to form subsequent adhesive dots should be still further decreased at act  616 . In different embodiments, more or fewer comparisons/tests may be used in order to determine whether or not to further adjust the pressure. For example, in some embodiments, the pressure applied at the pressure regulator  218  may be decreased at act  616  based solely on whether or not the first comparison listed in act  614  has been satisfied. 
     In one embodiment, the average is compared to a third sum of the reference characteristic value added to the standard deviation multiplied by a third factor, the third factor being greater than the second factor described above with reference to act  610 . As illustrated in act  614 , the third factor may comprise three, although different factors may be used in other implementations. If it is determined that the average is larger than the third sum, then it may be further determined that the size of the subsequent adhesive dot should be reduced by a third decrement larger than the second decrement based at least in part on this determination. In one embodiment, the third decrement may simply correspond to three times the first decrement, which may correspond to a minimum increment by which the size of the adhesive dots can be changed. In other embodiments, the third decrement may correspond to some other multiple of the first decrement. 
     In one embodiment, a result of the standard deviation multiplied by the differential standard deviation is again compared with the tolerance value, in a manner similar to that described above with respect to act  610 . If it is determined that the standard deviation multiplied by the differential standard deviation is larger than the tolerance value, then it may be further determined that the size of the subsequent adhesive dot should be reduced by the third decrement based at least in part on this determination. 
     At act  616 , if both of the comparisons of act  614  have been satisfied, a pressure applied during the adhesive dispensing process may be further decreased. In one embodiment, the feedback system  208  may send an electrical signal to further adjust a pressure setting of the pressure regulator  218 . Thus, in one embodiment, an average size of subsequently dispensed adhesive dots may be further reduced. Of course, in other embodiments, different control variables for a variety of components within the adhesive dispensing system  200  may be varied in order to decrease the size of subsequently dispensed adhesive dots. 
     Acts  618  through  628  are similar to acts  606  through  616  described at length above, except that the comparisons are changed where appropriate to ensure that the average is lower than respective mathematical functions of the reference characteristic value. For example, at act  618 , the average is compared to a first result of the standard deviation multiplied by a first factor subtracted from the reference characteristic value. If it is determined that the average is smaller than the first result, then it may be determined that a size of a subsequent adhesive dot should be increased by a first increment based at least in part on this determination. At act  618 , the average may also be compared to a result of the tolerance value subtracted from the reference characteristic value. If it is determined that the average is larger than the tolerance value subtracted from the reference characteristic value, then it may be further determined that the size of the subsequent adhesive dot should be increased by the first increment based at least in part on this additional determination. 
     Similarly, at act  622 , the average is compared to a second result of the standard deviation multiplied by a second factor subtracted from the reference characteristic value, the second factor being greater than the first factor. If it is determined that the average is smaller than the second result, then it may be determined that a size of a subsequent adhesive dot should be further increased by a second increment larger than the first increment based at least in part on this determination. At act  626 , the average is compared to a third result of the standard deviation multiplied by a third factor subtracted from the reference characteristic value, the third factor being greater than the second factor. If it is determined that the average is smaller than the third result, then it may be determined that a size of a subsequent adhesive dot should be further increased by a third increment larger than the second increment based at least in part on this determination. 
     As illustrated in  FIG. 6B , upon completing the acts  602  through  628 , the method  600  may return to the beginning, and another average may be calculated for another plurality of adhesive dots. Thus, in one embodiment, the adhesive dispensing system  200  may be constantly monitored and may constantly respond to feedback based on a previously dispensed plurality of adhesive dots. 
     The foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams, schematics, and examples. Insofar as such block diagrams, schematics, and examples contain one or more functions and/or operations, each function and/or operation within such block diagrams, flowcharts, or examples can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In one embodiment, the present subject matter may be implemented via Application Specific Integrated Circuits (ASICs). However, the embodiments disclosed herein, in whole or in part, can be equivalently implemented in integrated circuits, as one or more programs executed by one or more processors, as one or more programs executed by one or more controllers (e.g., microcontrollers), as firmware, or as virtually any combination thereof.