Abstract:
Systems and methods for applying liquid coating materials to a substrate, such as an electronic component or circuit board. A control system ( 18, 24, 26 ) of a coating system ( 10 ) controls an applicator ( 16 ) and a robot ( 14 ) moving the applicator ( 16 ) to apply the liquid coating material to the substrate ( 12 ) in accordance with the information contained in a coating program. The control system ( 18, 24, 26 ) determines a volume of liquid coating material actually dispensed onto the substrate ( 12 ) during the coating program, and compares the dispensed volume to a desired dispensed volume of liquid coating material to produce an error signal representing the difference between the calculated and desired volume values. The control system ( 18, 24, 26 ) uses the error signal to change the dispensed volume of liquid coating material on a subsequent substrate by a future coating program.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/806,024, filed Jun. 28, 2006, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]    The present invention relates generally to dispensing liquid coating materials and, more particularly, to a system and method for applying liquid coating material, such as a conformal coating material, to a substrate, such as a circuit board. 
       BACKGROUND OF THE INVENTION  
       [0003]    Many industrial applications require the use of discrete, well-defined and uniform coatings applied to predetermined areas. Such coatings are very useful in varied processes, such as conformal coatings on non-uniform or irregular substrates like electronic circuit boards. In the production of discrete coatings for application to discrete substrate areas, for example, it is desirable to obtain broad, uniform coatings in a non-contact application process with sharp, square, cut-on and cut-off edges with no stringing of material. In particular, conformal coating material is used to protect selected components of a circuit board from moisture, dirt, etc. 
         [0004]    When such coatings are dispensed, the volume of coating material dispensed onto the substrate may be controlled so that substantially the same amount of coating material is dispensed onto successive substrates during production. In one conventional coating material dispensing system, a flow meter is supplied in the line coupling the fluid supply with the dispensing valve. When the dispensing valve is opened, the volume of material dispensed is read using the encoder counts of the flow meter. The time interval during which the measured volume of material was dispensed is also determined and a volumetric flow rate is calculated. This calculated flow rate is compared to a set point representing a desired flow rate and, if necessary, a correction is made to adjust the actual flow rate towards the desired flow rate. 
         [0005]    Conventional coating material dispensing systems may be inaccurate if used for applying conformal coating selectively to components or areas of a circuit board because the dispensing valve will only be opened for a very short time interval, perhaps as short as a few milliseconds. During the time interval that the dispensing valve is open, only a very small amount of coating material will be dispensed. The flow meter senses the small dispensed amount as a relatively small number of encoder counts. 
         [0006]    Either the time interval, the number of encoder counts, or both, may be characterized by significant inaccuracies, which will result in an inaccurate calculation of flow rate. The system then compares the inaccurate calculated flow rate to the set point to produce an “error.”f Because of the inaccuracy, the error from the comparison may result in a correction of the wrong magnitude or even a correction in the wrong direction. Either result may cause an improper amount of coating material to be dispensed the next time the dispensing valve is opened. The result could easily be that the system produces so much inaccuracy it is of little practical value to the user. 
         [0007]    Therefore, an improved apparatus and method of coating materials are needed that are not susceptible to such inaccuracies in the dispensed amount of coating material. 
       SUMMARY OF THE INVENTION  
       [0008]    In one embodiment, a system is provided for applying a liquid coating material to a substrate, such as a circuit board, as determined by a coating program. The system may comprise an applicator configured to receive the liquid coating material from a reservoir and configured to dispense the liquid coating material onto the substrate. A regulator is configured to regulate a flow of the liquid coating material to the applicator. A meter is configured to generate volume signals representing the volumes of liquid coating material flowing to the applicator, The system includes a robot configured to move the applicator relative to the substrate and a control system configured to access the coating program. The control system is configured to control the robot and the applicator to apply the liquid coating material to the substrate in accordance with information in the coating program. At completion of the coating program, the control system is configured to utilize one or more volume signals from the meter to determine a dispensed volume of the liquid coating material applied to the substrate during the coating program. The control system is further configured to compare the dispensed volume to a desired dispensed volume of the liquid coating material for the coating program and to produce an error signal representing the difference between the dispensed volume and the desired dispensed volume. The control system is configured to reduce the difference between the dispensed volume of the liquid coating material on a subsequent substrate and the desired dispensed volume based on the error signal. 
         [0009]    In another embodiment, a method is provided for applying liquid coating material to a substrate as determined by a coating program. The method comprises dispensing the liquid coating material from an applicator to the substrate as directed by the coating program, determining a dispensed volume of the liquid coating material applied to the substrate after the coating program concludes, comparing the dispensed volume to a desired dispensed volume of the liquid coating material for the coating program, and producing an error signal representing the difference between the dispensed volume and the desired dispensed volume. The method further includes changing the dispensed volume of the liquid coating material applied to a subsequent substrate based upon the error signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0010]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and, together with a general description of embodiments of the invention given above, and the detailed description given below, serve to explain the principles of the embodiments of the invention. 
           [0011]    The FIGURE is a schematic view of a computer-controlled coating system in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION  
       [0012]    With reference to the FIGURE, a coating system  10  may be used to apply a liquid coating material, such as a conformal coating material, to a series of substrates, such as the representative substrate  12 . Although the operation of a representative coating system  10  will be described herein, those skilled in the art will appreciate that a wide variety of other coating systems may be used to complete the method described below. The coating system  10  may be, for example, a Model SC-105, SC-205, or SC-400 conformal coating applicator commercially available from Asymtek (Carlsbad, Calif.). 
         [0013]    In the representative embodiment, the coating system  10  includes a multi-axis electro-mechanical positioner or robot  14  and a conformal coating applicator  16  coupled with the robot  14 . For example, the applicator  16  may be suspended from the robot  14  above the substrates  12 . In one embodiment, the robot  14  is adapted to move the applicator  16  in directions defined within an X-Y-Z Cartesian coordinate frame to supply three degrees of freedom. The robot  14  includes a drive coupled to independently controllable motors (not shown) in a known manner. The applicator  16  is manipulated by robot  14  relative to the substrate  12  for applying amounts of liquid coating material to selected areas of the substrate  12 . 
         [0014]    A programmable controller  18  coordinates the movements and actuations of the coating system  10 . The controller  18  may be a programmable logic controller (PLC), a microprocessor based controller, personal computer, or another conventional control device capable of carrying out the functions described herein as understood by a person having ordinary skill in the art. A human machine interface (HMI) device  19  is operatively connected to the controller  18  in a known manner. The HMI device  19  may include input devices and controls, such as a keypad, pushbuttons, control knobs, a touch screen, etc., and output devices, such as displays and other visual indicators, that are used by an operator to control the operation of the controller  18  and, thereby, control the operation of the coating system  10 . 
         [0015]    Substrates  12 , for example, printed circuit boards with attached semiconductor die and other components, are supported in an operative relationship with the applicator  16  in a known manner and liquid coating material is applied from the applicator  16  onto selected areas on each substrate  12 . Depending on the dispensing application, a series of substrates  12  as may be coated in a batch mode. Alternatively, the substrates  12  may be continuously transported past the applicator  16  on an automatic conveyor  20 . The conveyor  20  has a conventional design and, furthermore, may have a width that can be adjusted to accommodate substrates  12  of different dimensions. The conveyor  20 , which may also include pneumatically operated lift and lock mechanisms (not shown), receives command signals from a conveyor controller  22 . 
         [0016]    The applicator  16  is electrically coupled with an applicator controller  24 , which supplies command signals that control the operation of the applicator  16 . A motion controller  26  is electrically coupled by a communication link  21  with the robot  14 . The solenoid  34  is electrically coupled by a communication link  23  with the motion controller  26 . The conveyor controller  22  and motion controller  26  are also electrically coupled with controller  18  over respective communication links  25 ,  27 . The motion controller  26  is electrically coupled over a communication link  29  with the conveyor controller  22 . Thus, a programmable control system for coating system  10  includes the controller  18 , the applicator controller  24 , the motion controller  26 , and the optional conveyor controller  22  as interconnected components that communicate with each other. 
         [0017]    The motion controller  26  supplies command signals to the robot  14  over the communication link  21 . The command signals are used by the robot  14  to control the position and/or velocity of the applicator  16 . Generally, the robot  14  includes electric motors, such as servo motors or stepper motors, that drive the motion of the different axes of the robot  14 . 
         [0018]    Applicator  16  includes a body  30  suspended from the robot  14 , a nozzle  31  mounted to one end of the body  30 , and a flow control mechanism (not shown) disposed inside the body  30 . The flow control mechanism inside body  30  may comprise an air-actuated needle, an air piston, and a valve seat that cooperate to form a dispensing valve (not shown) operative to control a flow of conformal coating material dispensed from the applicator  16 . A pressurized fluid supply  32  and a solenoid  34  cooperate to supply pressurized fluid in a known manner to regulate the actuation of the dispensing valve inside the body  30 . Specifically, the solenoid  34  controls air pressure in a conduit  33  connecting the pressurized fluid supply  32  with the applicator  16  so as to move the air piston and, thereby, move the needle relative to the valve seat to provide an opened position for the dispensing valve in which liquid coating material is dispensed from the applicator  16  onto the substrate  12 . The solenoid  34  may vent the air pressure acting on the air piston to permit the needle to return to a closed position in which the needle contacts the valve seat to discontinue the dispensing. 
         [0019]    The coating system  10  includes a pressurized liquid supply  38  that operates in a known manner under the command of controller  18  to generate a continuous stream or supply of the pressurized liquid coating material. For example, the pressurized liquid supply  38  may include a diaphragm or piston pump that siphons amounts of liquid coating material from a reservoir and then pumps the stream of liquid coating material under pressure from the reservoir through a fluid path to the applicator  16 . The pressurized liquid supply  38  is electrically connected by a communication link  39  with the controller  18 , which can regulate operating parameters such as the temperature and pressure of a liquid coating material by communicating appropriate control signals to the pressurized liquid supply  38  over communication link  39 . 
         [0020]    The pressurized liquid supply  38  is optionally configured with one or more conventional heating elements  38 a that are electrically coupled with a conventional temperature controller  60  that is electrically coupled with the controller  18 . The construction and operation of conventional heating elements, such as heater elements  38 a, and temperature controllers, such as temperature controller  60 , are understood by a person having ordinary skill in the art. In an alternative embodiment, the applicator  16  may include heating element (not shown) or a heating element (not shown) may be disposed in the one of the conduits  51 ,  53 ,  55 . Regardless of the specific location of the heating element in the flow path between the pressurized liquid supply  38  and the nozzle  31 , the liquid coating material may be heated in this flow path before being applied to the substrate  12 . 
         [0021]    The applicator  16  includes a liquid inlet  36  that is coupled in fluid communication with a pressurized liquid supply  38 . The liquid coating material is supplied from the pressurized liquid supply  38  to the applicator  16  through the liquid inlet  36  for regulated dispensing out of a dispensing orifice (not shown) in the nozzle  31 . The body  30  has a fluid inlet  40  coupled with pressurized fluid supply  32  and internal passageways (not shown) that direct the pressurized fluid to outlets in the vicinity of the dispensing orifice in nozzle  31 , where the pressurized fluid is discharged to interact with and manipulate the stream  42  of liquid coating material that is sprayed from the applicator  16 . A fluid regulator  43 , which communicates over communication link  45  with motion controller  26 , controls the flow of pressurized fluid from the pressurized fluid supply  32  to the fluid inlet  40 . A representative applicator similar to applicator  16  is described in U.S. Pat. No. 7,028,867, the disclosure of which is hereby incorporated by reference herein in its entirety. 
         [0022]    The system  10  is operated as instructed by a library of operational cycles or sequences that are stored in a memory  44  associated with the controller  18  and/or stored in other computers. The operational sequences are recalled and placed in a particular operational program, as desired, executing on the controller  18 . The operational sequences can be adjusted to accommodate different environmental conditions, different types of substrates  12 , or different types of conformal coating material. During operation, the controller  18  can transfer an entire operational program as electrical signals over communication link  25  to the motion controller  26  for execution at the motion controller  26 . Alternatively, the controller  18  can transfer one or more instructions as electrical signals over communication link  25  in a batch of instructions and data to the motion controller  26  for subsequent execution. The operator may enter parameters, such as the type of substrate  12 , the type of liquid coating material, the liquid pressure, the assist air pressure, the velocity of the applicator  16 , the distance between the substrate  12  and applicator  16 , etc., at the HMI device  19 . The entered parameters are stored in the memory  44  of controller  18  for future use in an operational sequence. Each substrate  12  is matched by the controller  18  with a coating program that determines which specific components and areas of the substrate  12  are to be coated with liquid coating material. Typically, the liquid coating material is applied to only selected areas and/or components on the substrate  12 . 
         [0023]    With continued reference to the FIGURE, an “air over fluid” (A/F) regulator  50  and a flow meter  52  are situated in the flow path for the liquid coating material from the pressurized liquid supply  38  to the liquid inlet  36  of the applicator  16 . As a result, the liquid coating material is constrained to flow through the A/F regulator  50  and flow meter  52  in transit from the pressurized liquid supply  38  to the applicator  16 . A liquid input of the A/F regulator  50  is coupled by a conduit  51  with a liquid outlet of the pressurized liquid supply  38 . Similarly, the A/P regulator  50  has a liquid outlet coupled by a conduit  53  with a liquid input of the flow meter  52 , which in turn has a liquid outlet coupled by a conduit  55  with the liquid inlet  36  of the applicator  16 . 
         [0024]    The A/F regulator  50  controls the fluid pressure of the pressurized liquid material in transit in the fluid path to the applicator  16 . The controller  18  is electrically coupled by a communication link  57  with a) regulator  54 . In one embodiment, the regulator  54  may be a “voltage over pressure” (E/P) regulator that receives a control voltage from the motion controller  26  and includes a transducer that converts the control voltage to a fluid pressure. Alternatively, the regulator  54  may receive a control current or a serial communications signal, instead of a control voltage, for conversion to a fluid pressure. The regulator  54  delivers pressurized fluid to the A/F regulator  50  for use in controlling the fluid pressure of the liquid coating material flowing through the A/F regulator  50 . 
         [0025]    The A/F regulator  50  is positioned in a conduit  35  defining a fluid path between the pressurized liquid supply  38  and the flow meter  52 . In an alternative embodiment, the flow meter  52  may be positioned in the fluid path between the pressurized liquid supply  38  and the A/F regulator  50  so that the flow meter  52  is upstream from the A/F regulator  50 . With this alternative arrangement, the flow meter  52  would alter the pressure of the liquid coating material after the liquid coating material has flowed through the A/F regulator  50 . 
         [0026]    The controller  18  is electrically coupled by a communication link  59  with the flow meter  52 . In response to the flow of liquid coating material from conduit  53  to conduit  55 , the flow meter  52  generates a string of counts or electrical pulses each representing a fixed volume of liquid coating material flowing through or past the flow meter  52 . Alternatively, the string of electrical pulses from the flow meter  52  may be communicated from the flow meter to the motion controller  26  and then relayed from the motion controller  26  to the controller  18 . In one embodiment, the flow meter  52  may comprise a gear meter that rotates in response to flow through the gear meter and, for a fixed amount of rotation representing a known volume, generates an electrical pulse with an encoder that is transmitted as an electrical signal in a signal stream to the controller  18 . For example, the gear meter may generate a pulse for every 0.04 cubic centimeters of liquid coating material flowing through the flow meter  52 . 
         [0027]    In use and with reference to the FIGURE, the controller  18  obtains a coating program for the substrate  12  when substrate  12  is properly positioned relative to the applicator  16 . The coating program determines which components and/or areas of the substrate  12  are to be coated with liquid coating material, which is usually applied in strips. For example, possibly twenty-five separate components or areas of a substrate  12  may be coated with strips of the liquid coating material. The controller  18  retrieves an operational sequence from the memory  44  of controller  18  and, in turn, communicates control signals to the motion controller  26  over communication link  25  representing the operational sequence. The motion controller  26  sends command signals to the robot  14  over communication link  21  that instruct the robot  14  to move the applicator  16  at specified velocities to desired locations with respect to the substrate  12 . The motion controller  26  controls the movements of the robot  14  to move the applicator  16  in a plane (e.g., X and Y directions) across the substrate  12 , opening and closing the dispensing valve in the applicator  16  as necessary during this movement to apply the liquid coating material to the desired components and areas of the substrate  12 . 
         [0028]    Specifically, at any particular location on substrate  12 , the motion controller  26  also provides a command signal to the solenoid  34  to cause it to change state to open the dispensing valve causing discharge of liquid coating material from nozzle  31 . Concurrently, the motion controller  26  provides command signals to the robot  14  to initiate motion of applicator  16  relative to the substrate  12 . The stream  42  of liquid coating material may be optionally manipulated by an assist fluid, such as air, that affects the shaping of the stream  42  discharged from the applicator  16 . After a predetermined time lapses, the motion controller  26  subsequently changes the state of the valve command signal to return the solenoid  34  back to its original state. This action closes the dispensing valve to discontinue the discharge of liquid coating material from the nozzle  31  of the applicator  16 . The motion controller  26  may cause the dispensing valve of the applicator  16  to open and close the dispensing valve multiple times (e.g., twenty-five times) during the extent of the coating program so that multiple components and areas of the substrate  12  receive an amount of liquid coating material. 
         [0029]    During the coating program or in preparation for the execution of the coating program, the controller  18  provides electrical signals to the motion controller  26 , which prompt the motion controller  26  to provide command signals to the regulator  54 , The regulator  54  controls an air pressure supplied to the A/F regulator  50  to selecting a liquid pressure for the pressurized liquid coating material flowing from the pressurized liquid supply  38  to the applicator  16 . The selected value of liquid pressure, which is dispensing application dependent, may further depend on the desired flow rate of the liquid coating material. The flow rate for the liquid coating material is influenced, among other factors, by the liquid pressure, the diameter of the discharge orifice in the dispensing nozzle  31 , the material viscosity, etc. 
         [0030]    Coating system  10  is significantly more accurate than conventional conformal coating systems because system  10  determines the volume of coating material dispensed over an entire substrate  12 , which can be calculated relatively accurately, compares that calculated value to a set point, and makes a correction, if needed, based on this relatively accurate calculation. 
         [0031]    At the start of each coating program for substrate  12 , the controller  18  obtains an “encoder count” from the flow meter  52 . For example, the controller  18  may consider the initial encoder count to be zero. During the coating program that applies the liquid coating material to the areas and components on substrate  12 , the controller  18  receives the string of pulses from the flow meter  52  and incrementally accumulates a total number of pulses as the liquid coating material flows to the applicator  16 . At the conclusion of the coating program for each substrate  12 , the pulse string from the flow meter  52  ends. The controller  18  includes an accumulator that contains the total number of pulses communicated from the flow meter  52  during the coating program. 
         [0032]    Based upon a known calibration of the amount of liquid coating material represented by each pulse generated by the flow meter  52 , the controller  18  converts the total number of pulses to a total volume of liquid coating material dispensed onto the substrate  12 , The controller  18  compares the total dispensed volume with a desired total dispensed volume and produces an error signal representing the difference between the calculated and desired dispensed volumes. As necessary and based upon the error signal, the controller  18  communicates a control signal to the motion controller  26 , which supplies a control current, a control potential, or a control signal to the regulator  54  to manipulate the flow constriction represented by the A/F regulator  50  in order to compensate for the difference between the calculated and desired dispensed volumes of liquid coating material. Generally, the fluid pressure is set in proportion to the input current, potential, or control signal to the regulator  54 . 
         [0033]    If the total dispensed volume is too low, the control signal communicated from the controller  18  to the motion controller  26  causes the motion controller  26  to react by increasing the control potential applied to the E/P transducer  54 . This action opens the A/F regulator  50  wider to increase the flow of liquid coating material to the applicator  16 . If the total dispensed volume is too high, the control signal communicated from the controller  18  to the motion controller  26  causes the motion controller  26  to react by decreasing the control potential applied to the E/P transducer  54 . This action causes the EP transducer  54  to react by closing the A/F regulator  50  to reduce the flow of liquid coating material to the applicator  16 . 
         [0034]    For subsequent substrates  12  that are coated by system  10  according to the coating program, the correction is in a direction that is predicted to reduce the error signal. As a result, the discrepancy between the total dispensed volume and desired total dispensed volume for subsequent substrates  12  should be reduced. If the error signal is not adequately compensated, additional corrections can be made as the calculated total dispensed volume is compared with the desired total dispensed volume. Each substrate  12  that is processed according to the coating program typically receives an identical total dispensed volume of liquid coating material on the areas and components. 
         [0035]    The correction to the flow of liquid coating material under the closed loop control may be implemented by use of control windows in the software code executing on the controller  18 . The inner control window represents the maximum permissible deviation from the desired total volume, either above or below the desired total volume, that if exceeded will initiate a responsive action by the controller  18 . The outer control window represents the maximum permissible deviation from the desired total volume, either above or below the desired total volume, that if exceeded will initiate a response by the controller  18  that causes a drastic reaction, such as stopping the system  10  and/or sounding an alarm. 
         [0036]    If the calculated total volume dispensed during the coating program is within a first percentage (e.g., ±1%) of the desired total dispensed volume, the controller  18  makes no correction within this inner control window. If the calculated total volume dispensed during the control program is more than a second percentage (e.g., ±10%) of the desired total dispensed volume, the controller  18  may stop the system  10  and/or sound an alarm outside of this outer control window as determined by the user&#39;s preference. The substrate  12  being coated when the coating operation deviates outside of the outer control window is flagged as having an out of tolerance conformal coating applied to it. If the calculated total volume dispensed during the coating program is between the inner and outer control windows, the controller  18  may correct the flow of liquid coating material to the applicator  16  within this intermediate control window without sounding an alarm. The correction, which is executed as described above, is of a magnitude and sense to counteract the out of tolerance condition. For example, the corrective action may be taken if the total dispensed volume is greater ±5% of the desired total dispensed volume. 
         [0037]    In this way, any trends affecting total dispensed volume during a coating program are detected contemporaneously with their occurrence and responsive corrections are made as automatic intervention to offset the trend. Unless the control falls outside of the outer control window, the responsive corrections are implemented without operator intervention. For example, a change in the viscosity of the liquid coating material may cause the total dispensed volume to shift away from the desired total dispensed volume. The viscosity change is detected as a change in the total dispensed volume and, subsequently, is corrected by an action executed by the controller  18 . System  10  assists the customer in maintaining a high quality liquid material coating operation by utilizing a relatively accurate dispensed volume calculation compared to conventional systems, while ensuring that the customer does not waste liquid coating material by applying more material than is necessary. 
         [0038]    The controller  18  of the system  10  does not track or otherwise monitor the time interval required to dispense the liquid coating material onto the substrate  12  during the execution of the coating program. As such, the controller  18  does not calculate a volume flow rate for the liquid coating material dispensed onto each substrate  12  during the coating program. 
         [0039]    In an alternative embodiment, the controller  18  may adjust the velocity of the robot  14  as a control parameter to adjust the total dispensed volume of coating material dispensed from the applicator  16  onto the substrate  12 . For example, if the controller  18  determines that the total dispensed volume is less than the desired volume, then the controller  18  could reduce the velocity of the robot  14  by an amount effective to compensate for the discrepancy that effectively increases the total amount of liquid coating material dispensed onto the areas or components of the substrate  12 . Conversely, if the controller  18  determines that the total dispensed volume is greater than the desired volume, then the controller  18  could increase the velocity of the robot  14  by an amount effective to compensate for the discrepancy that effectively decreases the total amount of liquid coating material dispensed onto the areas or components of the substrate  12 . 
         [0040]    In another alternative embodiment, the controller  18  may adjust the temperature of the liquid coating material as a control parameter to adjust the total dispensed volume. To that end, the controller  18  would communicate electrical signals to the pressurized liquid supply  38  that command the pressurized liquid supply  38  to heat or to cool the liquid coating material. As known to a person having ordinary skill in the art, changing the temperature of the liquid coating material changes its viscosity. For example, if the total dispensed volume dispensed from the applicator  16  onto the substrate  12  is too low, the temperature of the liquid coating material is increased to decrease its viscosity and, thereby, create a higher flow of liquid coating material to the applicator  16 . This will operate to increase the amount of liquid coating material dispensed onto the areas or components of the substrate  12  during the coating program. Conversely, if the total dispensed volume dispensed from the applicator  16  onto the substrate  12  is too high, the temperature of the liquid coating material is decreased to increase its viscosity and, thereby, reduce the flow of liquid coating material to the applicator  16 . This will operate to decrease the amount of liquid coating material dispensed onto the areas or components of the substrate  12  during the coating program. 
         [0041]    Robot velocity and coating material temperature are variables that are independent of the fluid pressure of the liquid coating material. Therefore, a separate control loop could utilize fluid pressure from the pressurized fluid supply  32  to, for example, manipulate the stream  42  to achieve a desired fan width of a spray pattern from the applicator  16  while, concurrently, the volume of liquid coating material being dispensed onto the substrate  12  is maintained near the desired set point by varying robot velocity or coating material temperature. 
         [0042]    While the invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. 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 Applicants&#39; general inventive concept.