Abstract:
A spray gun, in one embodiment, is provided with a sensor configured to monitor distance between the spray gun and a target object, and a drive responsive to the sensor, wherein the drive is configured to control a fluid valve of the spray gun based on the distance. A retrofit kit, in another embodiment, is provided with a feedback-controlled system configured to change fluid flow of a spray gun in response to one or more sensed parameters indicative of condition of a target object, a relationship between the spray gun and the target object, or a combination thereof. A spray controller, in a further embodiment, is provided with a control configured to terminate or decrease fluid flow of a spray in response to a first spray stroke away from a target object, and configured to start, continue, or increase fluid flow of the spray in response to a second spray stroke toward the target object. In yet another embodiment, a method of operation is provided for controlling fluid flow in response to feedback associated with a target object. In addition, a tangible medium is provided with instructions stored on the tangible medium, wherein the instructions comprise code configured to terminate or decrease fluid flow of a spray if the spray is not directed toward a target object, and code configured to start, continue, or increase fluid flow of the spray if the spray is directed toward the target object.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to spray devices and, more particularly, to the transfer efficiency of spray guns. 
       BACKGROUND 
       [0002]    This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
         [0003]    The objective when spraying paint is to maximize the amount of coating material that is deposited on the substrate and minimize the amount that goes into the atmosphere. High volume low pressure (HVLP) and high transfer efficiency (HTE) spray guns have been designed and mandated in many jurisdictions to limit the amount of overspray due to the paint bouncing back off the substrate. However, there is another major reason for overspray that has not been addressed. This is overspray created when the spray gun is triggered, but not pointed at the substrate. This is a common occurrence in the automotive refinishing business. For example, if a painter is painting the hood of a car, the painter should trigger the fluid off at the end of the stroke and trigger the fluid back on for the return stroke. This avoids spraying paint into the air at the end of each stroke. However, the painters find it easier to hold the trigger fully open as they reach the end of the stroke and reverse directions. This practice can lead to significantly higher material costs and significantly higher volatile organic compound (VOC) emissions into the atmosphere. 
       BRIEF DESCRIPTION 
       [0004]    A spray gun, in one embodiment, is provided with a sensor configured to monitor distance between the spray gun and a target object, and a drive responsive to the sensor, wherein the drive is configured to control a fluid valve of the spray gun based on the distance. A retrofit kit, in another embodiment, is provided with a feedback-controlled system configured to change fluid flow of a spray gun in response to one or more sensed parameters indicative of condition of a target object, a relationship between the spray gun and the target object, or a combination thereof. A spray controller, in a further embodiment, is provided with a control configured to terminate or decrease fluid flow of a spray in response to a first spray stroke away from a target object, and configured to start, continue, or increase fluid flow of the spray in response to a second spray stroke toward the target object. In yet another embodiment, a method of operation is provided for controlling fluid flow in response to feedback associated with a target object. In addition, a tangible medium is provided with instructions stored on the tangible medium, wherein the instructions comprise code configured to terminate or decrease fluid flow of a spray if the spray is not directed toward a target object, and code configured to start, continue, or increase fluid flow of the spray if the spray is directed toward the target object. 
     
    
     
       DRAWINGS 
         [0005]    These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0006]      FIG. 1  is a diagram illustrating an embodiment of a spray coating system; 
           [0007]      FIG. 2  is a flow chart illustrating an embodiment of a spray coating process; and 
           [0008]      FIGS. 3 and 4  are cross-sectional side views of different embodiments of a spray coating device used in the spray coating system and method of  FIGS. 1 and 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
         [0010]      FIG. 1  is a flow chart illustrating an exemplary spray coating system  10 , which includes a spray coating gun  12  for applying a desired coating to a target object  14 . In certain embodiments, the spray coating gun  12  may include an air atomizer, a rotary atomizer, an electrostatic atomizer, or any other suitable spray formation mechanism. As discussed in detail below, the spray coating gun  12  includes one or more sensors (S)  13  coupled to one or more valves (V)  15 , such that the spray coating gun  12  automatically controls fluid flow through the valves  15  in response to sensor feedback from the sensors  13 . As discussed in detail below, the sensor  13  may monitor distance, presence and absence, stroke direction, stroke velocity, or a combination thereof, of the target object  14  relative to the spray coating gun  12 . In response, the valve  15  automatically closes when the spray coating gun  12  is pointed away from the target object  14  (e.g., into air) and automatically opens when the spray coating gun  12  is pointed at the target object  14 . The valve  15  also may increase fluid flow in response to sensor  13  feedback indicative of a distance increase, an optimal or improving spray angle, an optimal or improving surface (e.g., flat), an optimal or increasing temperature, and so forth. On the other hand, the valve  15  may decrease fluid flow in response to sensor  13  feedback indicative of a distance decrease, a poor or worsening spray angle, a poor or worsening surface (e.g., multiple angles, corner, etc.), a poor or decreasing temperature, and so forth. 
         [0011]    The spray coating gun  12  may be coupled to a variety of supply and control systems, such as the fluid supply  16 , an air supply  18 , and a control system  20 . The control system  20  facilitates control of the fluid and air supplies  16  and  18  and ensures that the spray coating gun  12  provides an acceptable quality spray coating on the target object  14 . For example, the control system  20  may include an automation system  22 , a positioning system  24 , a fluid supply controller  26 , an air supply controller  28 , a computer system  30 , and a user interface  32 . The control system  20  also may be coupled to a positioning system  34 , which facilitates movement of the target object  14  relative to the spray coating gun  12 . Accordingly, the spray coating system  10  may provide a computer-controlled mixture of coating fluid, fluid and air flow rates, and spray pattern. Moreover, the positioning system  34  may include a robotic arm controlled by the control system  20 , such that the spray coating gun  12  covers the entire surface of the target object  14  in a uniform and efficient manner. 
         [0012]      FIG. 2  is a flow chart of an embodiment of a spray coating process  100  for applying a desired spray coating to the target object  14 . As illustrated, the process  100  proceeds by identifying a target object  14 , selecting a desired fluid for application to a spray surface of the target object  14 , and configuring a spray coating gun  12  for the identified target object  14  and selected fluid (block  102 ). In the illustrated embodiment, the process  100  then queries for an engagement state of the spray coating gun  12  (block  104 ). For example, the process  100  may monitor whether or not a user manually pulls a trigger, button, or other actuator intended to initiate a spray from the spray coating gun  12 . At block  104 , if the process  100  determines that the gun  12  (e.g., trigger) is not engaged, then the process  100  may proceed to turn off (or maintain an off state of) valves that control fluid flow through the spray coating gun  12  (block  106 ). Otherwise, if the process  100  determines that the gun  12  (e.g., trigger) is engaged, then the process  100  may proceed to sense (e.g., monitor) one or more parameters of the target object  14  relative to the spray coating gun  12  (block  108 ). For example, the sensed parameters may include the presence or absence of the target object  14  within a field of view (e.g., spray direction and/or area), a distance between the target object  14  and the spray coating gun  12 , a stroke velocity and/or acceleration of the spray coating gun  12  relative to the target object  14 , a stroke direction of the spray coating gun  12  relative to target object  14 , an angle of the spray coating gun  12  relative to the target object  14 , a surface wetness of the target object  14 , a surface morphology of the target object  14 , a surface temperature of the target object  14 , and so forth. The sensing block  108  may include laser, infrared, photoelectric, optical, fiber optic, electromagnetic or electrostatic, microwave, capacitive, piezoelectric, or ultrasonic sensing, or any combination thereof. As discussed further below, the sensor feedback may be used by the process  100  to control fluid flow through the spray coating gun  12  to improve transfer efficiency, improve uniformity of the spray coating, reduce waste, and so forth. 
         [0013]    Based on the sensed parameters  108 , the illustrated process  100  proceeds to evaluate whether or not the target object  14  is present within the field of view of the spray coating gun  12  (block  110 ). If the target  14  is not present (e.g., out of the field of view), then the process  100  responds by turning off (or maintaining an off position of) the valves that control fluid flow through the spray coating gun  12  (block  106 ). If the target  14  is present (e.g., within the field of view), then the process  100  continues by evaluating whether or not the target object  14  is within an acceptable range (e.g., distance) relative to the spray coating gun  12  (block  112 ). If the range is not acceptable at block  112 , then the process  100  responds by turning off (or maintaining an off position of) the valves that control fluid flow through the spray coating gun  12  (block  106 ). For example, if the target object  14  is at a distance greater than a maximum distance or less than a minimum distance relative to the spray coating gun  12 , then the process  100  does not form a spray coating. In some embodiments, the process  100  may respond by setting off an alarm (e.g., audio and/or visual) to alert the user without terminating the spray. 
         [0014]    If the range is acceptable at block  112 , then the process  100  responds by turning on (or maintaining an on position of) the valves to create a spray downstream from the spray coating gun  12  (block  114 ). In turn, the process  100  may adjust the valves and various other controllable features of the spray coating gun  12  based on the sensed parameters (block  116 ). For example, the process  100  may increase the fluid flow and spray density as the distance increases between the spray coating gun  12  and the target object  14 . Similarly, the process  100  may decrease the fluid flow and spray density as the distance decreases between the spray coating gun  12  and the target object  14 . The process  100  may vary the liquid flow rate of the coating fluid and also features that control the atomization and shaping of the spray downstream from the spray coating gun  12 . For example, the process  100  may adjust the air flow rate to an atomization orifice surrounding a central liquid exit, a plurality air shaping orifices, a pneumatically controlled valve, and so forth. In some embodiments, the process  100  may increase the liquid flow rate in response to a greater stroke velocity of the spray coating gun  12  relative to the target object  14 , and decrease the liquid flow rate in response to a lesser stroke velocity of the spray coating gun  12  relative to the target object  14 . 
         [0015]    The process  100  continues to sense the parameters and control the fluid flow as indicated by blocks  104 - 116  until the gun is disengaged (block  118 ). If the spray coating gun  12  is not disengaged at block  118 , then the process  100  continues in a closed loop by returning to block  104 . Otherwise, if the spray coating gun  12  is disengaged at block  118 , then the process  100  proceeds to cure/dry the coating applied over the desired surface (block  120 ). If an additional coating (e.g., same or different coating) is desired by the user at query block  122 , then process  100  proceeds through blocks  104 - 120  to provide another coating of fluid. If the user does not desire an additional coating at query block  122 , then process  100  is finished at block  124 . 
         [0016]      FIG. 3  is a cross-sectional side view illustrating an exemplary embodiment of the spray coating gun  12 . As illustrated, the spray coating gun  12  includes a spray tip assembly  200  coupled to a body  202 . The spray tip assembly  200  includes a fluid delivery tip assembly  204 , which may be removably inserted into a receptacle  206  of the body  202 . For example, a plurality of different types of spray coating devices may be configured to receive and use the fluid delivery tip assembly  204 . The spray tip assembly  200  also includes a spray formation assembly  208  coupled to the fluid delivery tip assembly  204 . The spray formation assembly  208  may include a variety of spray formation mechanisms, such as air, rotary, and electrostatic atomization mechanisms. However, the illustrated spray formation assembly  208  comprises an air atomization cap  210 , which is removably secured to the body  202  via a retaining nut  212 . The air atomization cap  210  includes a variety of air atomization orifices, such as a central atomization orifice  214  disposed about a fluid tip exit  216  from the fluid delivery tip assembly  204 . The air atomization cap  210  also may have one or more spray shaping orifices, such as spray shaping orifices  218 ,  220 ,  222 , and  224 , which force the spray to form a desired spray pattern (e.g., a flat spray). The spray formation assembly  208  also may comprise a variety of other atomization mechanisms to provide a desired spray pattern and droplet distribution. 
         [0017]    The body  202  of the spray coating gun  12  includes a variety of controls and supply mechanisms for the spray tip assembly  200 . As illustrated, the body  202  includes a fluid delivery assembly  226  having a fluid passage  228  extending from a fluid inlet coupling  230  to the fluid delivery tip assembly  204 . The fluid delivery assembly  226  also comprises a fluid valve assembly  232  to control fluid flow through the fluid passage  228  and to the fluid delivery tip assembly  204 . The illustrated fluid valve assembly  232  has a needle valve  234  extending movably through the body  202  between the fluid delivery tip assembly  204  and a fluid valve adjuster  236 . The fluid valve adjuster  236  is rotatably adjustable against a spring  238  disposed between a rear section  240  of the needle valve  234  and an internal portion  242  of the fluid valve adjuster  236 . The needle valve  234  is also coupled to a trigger  244 , such that the needle valve  234  may be moved inwardly away from the fluid delivery tip assembly  204  as the trigger  244  is rotated counter clockwise about a pivot joint  246 . However, any suitable inwardly or outwardly openable valve assembly may be used within the scope of the present technique. The fluid valve assembly  232  also may include a variety of packing and seal assemblies, such as packing assembly  248 , disposed between the needle valve  234  and the body  202 . 
         [0018]    An air supply assembly  250  is also disposed in the body  202  to facilitate atomization at the spray formation assembly  208 . The illustrated air supply assembly  250  extends from an air inlet coupling  252  to the air atomization cap  210  via air passages  254  and  256 . The air supply assembly  250  also includes a variety of seal assemblies, air valve assemblies, and air valve adjusters to maintain and regulate the air pressure and flow through the spray coating gun  12 . For example, the illustrated air supply assembly  250  includes an air valve assembly  258  coupled to the trigger  244 , such that rotation of the trigger  244  about the pivot joint  246  opens the air valve assembly  258  to allow air flow from the air passage  254  to the air passage  256 . The air supply assembly  250  also includes an air valve adjustor  260  coupled to a needle  262 , such that the needle  262  is movable via rotation of the air valve adjustor  260  to regulate the air flow to the air atomization cap  210 . As illustrated, the trigger  244  is coupled to both the fluid valve assembly  232  and the air valve assembly  258 , such that fluid and air simultaneously flow to the spray tip assembly  200  as the trigger  244  is pulled toward a handle  264  of the body  202 . Once engaged, the spray coating gun  12  produces an atomized spray with a desired spray pattern and droplet distribution. As further illustrated, an air conduit  266  is coupled to the air inlet coupling  252  and a fluid conduit  268  is coupled to the fluid inlet coupling  230 . 
         [0019]    In this particular embodiment, the rate of fluid flow delivered from the fluid delivery assembly  226  may be adjusted based on one or more sensed parameters (e.g., distance, velocity, acceleration, angle, direction, etc.) between the spray coating gun  12  and the target object  14 . The parameters between the spray coating gun  12  and the target object  14  may be determined by way of a sensor  280  attached to the spray coating gun  12  directly behind the spray tip assembly  200  and on the body  202  of the spray coating gun  12 . The position of the sensor  280  behind the spray tip assembly  200  and on the body  202  of the spray coating gun  12  enables removal of the spray tip assembly  200  without disturbing the placement of the sensor  280 . The sensor  280  may be capable of sensing the presence or absence of the target object  14 . More specifically, the sensor  280  may be configured to monitor distance, velocity, acceleration, angle, direction, or a combination thereof, between the spray coating gun  12  and the target object  14 . The sensor  280  may be of any type including, but not limited to, laser, infrared, photoelectric, optical, fiber optic, electromagnetic or electrostatic, microwave, capacitive, piezoelectric, and ultrasonic sensors. 
         [0020]    For example, once the distance between the spray coating gun  12  and the target object  14  is determined, the sensor  280  may communicate this distance to a programmable logic controller (PLC) or other automated input/output arrangement. The logic controller  282  may reside either on the spray coating gun  12  or at a remote location to the spray coating gun  12 . The logic controller  282  may determine, based on the distance between the spray coating gun  12  and the target object  14 , whether the fluid flow rate delivered from the fluid delivery assembly  226  should be adjusted. For instance, if the distance between the spray coating gun  12  and the target object  14  cannot be determined (e.g., no presence detected), the fluid flow rate delivered from the fluid delivery assembly  226  may be stopped until such time that the distance between the spray coating gun  12  and target object  14  can be determined. In addition, the fluid flow rate delivered from the fluid delivery assembly  226  may be varied based on the distance between the spray coating gun  12  and the target object  14 . For instance, if the distance between the spray coating gun  12  and the target object  14  decreases, the fluid flow rate delivered from the fluid delivery assembly  226  may be decreased. Similarly, if the distance between the spray coating gun  12  and the target object  14  increases (e.g., within a suitable range while the target object  14  is within a field of view of the spray coating gun  12 ), the fluid flow rate delivered from the fluid delivery assembly  226  may be increased. In either case, the automatic flow control may be subject to limits, e.g., upper and lower, in both the flow rates and distances for outputting a spray. In other words, if the spray coating gun  12  is either too close or too distant from the target object  14 , then the sensor  280  feedback may trigger an automatic shutoff, an alarm, a delayed shutoff, or another suitable corrective action in response. 
         [0021]    The fluid flow rate delivered from the fluid delivery assembly  226  may be varied by communicating with a drive  284  located within the internal portion  242  of the fluid valve adjuster  236 . The drive  284  may be actuated to counteract the inward movement of the needle valve  234  away from the fluid delivery tip assembly  204 . In addition, it may be desirable to actuate the drive  284  without disturbing the position of the trigger  244 . In one embodiment, the needle valve  234  and the drive  284  may be configured such that the drive  284  causes the fluid valve assembly  232  to move toward the fluid delivery tip assembly  204  without moving the needle valve  234 . For example, the needle valve  234  may be configured to allow the drive  284  to slide coaxially through the needle valve  234  when the drive  284  is actuated. This could be accomplished using a mechanism within the needle valve  234  which allows an inner portion of the needle valve  234  to separate from an outer portion of the needle valve  234 . The outer portion of the needle valve  234  would stay in position while the inner portion of the needle valve  234  moves coaxially with the drive  284 . In such an embodiment, the trigger  244  would not experience the force exerted by the drive  284 . Therefore, the user would not be aware when the drive  284  overrides the user&#39;s depression of the trigger  244 . It should be noted that this particular embodiment for actuating the drive  284  and for maintaining the position of the trigger  244  while actuating the drive  284  is merely illustrative and should not be construed as limiting. Other embodiments for carrying out these general objectives may be implemented. It should also be noted that the drive  284  may be an electronic drive, pneumatic drive, hydraulic drive, or any combination thereof. 
         [0022]      FIG. 4  is a cross-sectional side view illustrating an alternative embodiment of the spray coating gun  12 . As illustrated, the spray coating gun  12  includes a spray tip assembly  300  coupled to a body  302 . The spray tip assembly  300  includes a fluid delivery tip assembly  304 , which may be removably inserted into a receptacle  306  of the body  302 . For example, a plurality of different types of spray coating devices may be configured to receive and use the fluid delivery tip assembly  304 . The spray tip assembly  300  also includes a spray formation assembly  308  coupled to the fluid delivery tip assembly  304 . The spray formation assembly  308  may include a variety of spray formation mechanisms, such as air, rotary, and electrostatic atomization mechanisms. However, the illustrated spray formation assembly  308  comprises an air atomization cap  310 , which is removably secured to the body  302  via a retaining nut  312 . The air atomization cap  310  includes a variety of air atomization orifices, such as a central atomization orifice  314  disposed about a fluid tip exit  316  from the fluid delivery tip assembly  304 . The air atomization cap  310  also may have one or more spray shaping orifices, such as spray shaping orifices  318 , which force the spray to form a desired spray pattern (e.g., a flat spray). The spray formation assembly  308  also may comprise a variety of other atomization mechanisms to provide a desired spray pattern and droplet distribution. 
         [0023]    The body  302  of the spray coating gun  12  includes a variety of controls and supply mechanisms for the spray tip assembly  300 . As illustrated, the body  302  includes a fluid delivery assembly  326  having a fluid passage  328  extending from a fluid inlet coupling  330  to the fluid delivery tip assembly  304 . The fluid delivery assembly  326  also comprises a fluid valve assembly  332  to control fluid flow through the fluid passage  328  and to the fluid delivery tip assembly  304 . The illustrated fluid valve assembly  332  has a needle valve  334  extending movably through the body  302  between the fluid delivery tip assembly  304  and a fluid valve adjuster  336 . The fluid valve adjuster  336  is rotatably adjustable against a spring  338  disposed between a rear section  340  of the needle valve  334  and an internal portion  342  of the fluid valve adjuster  336 . The needle valve  334  is also coupled to a trigger  344 , such that the needle valve  334  may be moved inwardly away from the fluid delivery tip assembly  304  as the trigger  344  is rotated counter clockwise about a pivot joint  346 . However, any suitable inwardly or outwardly openable valve assembly may be used within the scope of the present technique. The fluid valve assembly  332  also may include a variety of packing and seal assemblies, such as packing assembly  348 , disposed between the needle valve  334  and the body  302 . 
         [0024]    An air supply assembly  350  is also disposed in the body  302  to facilitate atomization at the spray formation assembly  308 . The illustrated air supply assembly  350  extends from an air inlet coupling  352  to the air atomization cap  310  via air passages  354  and  356 . The air supply assembly  350  also includes a variety of seal assemblies, air valve assemblies, and air valve adjusters to maintain and regulate the air pressure and flow through the spray coating gun  12 . For example, the illustrated air supply assembly  350  includes an air valve assembly  358  coupled to the trigger  344 , such that rotation of the trigger  344  about the pivot joint  346  opens the air valve assembly  358  to allow air flow from the air passage  354  to the air passage  356 . The air supply assembly  350  also includes an air valve adjustor  360  to regulate the air flow to the air atomization cap  310 . As illustrated, the trigger  344  is coupled to both the fluid valve assembly  332  and the air valve assembly  358 , such that fluid and air simultaneously flow to the spray tip assembly  300  as the trigger  344  is pulled toward a handle  364  of the body  302 . Once engaged, the spray coating gun  12  produces an atomized spray with a desired spray pattern and droplet distribution. 
         [0025]    In the illustrated embodiment of  FIG. 4 , the air supply  18  is coupled to the air inlet coupling  352  via air conduit  366 . Again, embodiments of the air supply  18  may include an air compressor, a compressed air tank, a compressed inert gas tank, or a combination thereof. In contrast to the embodiment of  FIG. 3 , the illustrated embodiment of  FIG. 4  has the fluid supply  16  directly mounted to the spray coating gun  12 . In other words, the fluid supply  16  is arranged in an on-gun configuration, such that the user can add the fluid mixture without putting down the gun  12  and/or without substantially delaying the spray process. The illustrated fluid supply  16  includes a gravity feed canister or cup  368  coupled to the fluid inlet coupling  330  on a top side of the body  302 . The fluid supply  16  may be described as a top-mounted on-gun configuration. The cup  368  has a tapered portion  370 , which leads to an outlet connector  372  coupled to the fluid inlet coupling  330 . The fluid supply  16  may include a filtered vent, a collapsible wall portion, an air supply, or a pressure balancer to facilitate the gravity feed. 
         [0026]    Similar to the embodiment of  FIG. 3 , the rate of fluid flow delivered from the fluid delivery assembly  326  may be adjusted based on one or more sensed parameters (e.g., distance, velocity, acceleration, angle, direction, etc.) between the spray coating gun  12  and the target object  14 . The parameters between the spray coating gun  12  and the target object  14  may be determined by way of a sensor  380  attached to the spray coating gun  12  directly behind the spray tip assembly  300  and on the body  302  of the spray coating gun  12 . The position of the sensor  380  behind the spray tip assembly  300  and on the body  302  of the spray coating gun  12  enables removal of the spray tip assembly  300  without disturbing the placement of the sensor  380 . The sensor  380  may be capable of sensing the presence or absence of the target object  14 . More specifically, the sensor  380  may be configured to monitor distance, velocity, acceleration, angle, direction, or a combination thereof, between the spray coating gun  12  and the target object  14 . The sensor  380  may be of any type including, but not limited to, laser, infrared, photoelectric, optical, fiber optic, electromagnetic or electrostatic, microwave, capacitive, piezoelectric, and ultrasonic sensors. 
         [0027]    For example, once the distance between the spray coating gun  12  and the target object  14  is determined, the sensor  380  may communicate this distance to a programmable logic controller (PLC) or other automated input/output arrangement. The logic controller  382  may reside either on the spray coating gun  12  or at a remote location to the spray coating gun  12 . The logic controller  382  may determine, based on the distance between the spray coating gun  12  and the target object  14 , whether the fluid flow rate delivered from the fluid delivery assembly  326  should be adjusted. For instance, if the distance between the spray coating gun  12  and the target object  14  cannot be determined (e.g., no presence detected), the fluid flow rate delivered from the fluid delivery assembly  326  may be stopped until such time that the distance between the spray coating gun  12  and target object  14  can be determined. In addition, the fluid flow rate delivered from the fluid delivery assembly  326  may be varied based on the distance between the spray coating gun  12  and the target object  14 . For instance, if the distance between the spray coating gun  12  and the target object  14  decreases, the fluid flow rate delivered from the fluid delivery assembly  326  may be decreased. Similarly, if the distance between the spray coating gun  12  and the target object  14  increases (e.g., within a suitable range while the target object  14  is within a field of view of the spray coating gun  12 ), the fluid flow rate delivered from the fluid delivery assembly  326  may be increased. In either case, the automatic flow control may be subject to limits, e.g., upper and lower, in both the flow rates and distances for outputting a spray. In other words, if the spray coating gun  12  is either too close or too distant from the target object  14 , then the sensor  380  feedback may trigger an automatic shutoff, an alarm, a delayed shutoff, or another suitable corrective action in response. 
         [0028]    The fluid flow rate delivered from the fluid delivery assembly  326  may be varied by communicating with a drive  384  located within the internal portion  342  of the fluid valve adjuster  336 . The drive  384  may be actuated to counteract the inward movement of the needle valve  334  away from the fluid delivery tip assembly  304 . In addition, it may be desirable to actuate the drive  384  without disturbing the position of the trigger  344 . In one embodiment, the needle valve  334  and the drive  384  may be configured such that the drive  384  causes the fluid valve assembly  332  to move toward the fluid delivery tip assembly  304  without moving the needle valve  334 . For example, the needle valve  334  may be configured to allow the drive  384  to slide coaxially through the needle valve  334  when the drive  384  is actuated. This could be accomplished using a mechanism within the needle valve  334  which allows an inner portion of the needle valve  334  to separate from an outer portion of the needle valve  334 . The outer portion of the needle valve  334  would stay in position while the inner portion of the needle valve  334  moves coaxially with the drive  384 . In such an embodiment, the trigger  344  would not experience the force exerted by the drive  384 . Therefore, the user would not be aware when the drive  384  overrides the user&#39;s depression of the trigger  344 . It should be noted that this particular embodiment for actuating the drive  384  and for maintaining the position of the trigger  344  while actuating the drive  384  is merely illustrative and should not be construed as limiting. Other embodiments for carrying out these general objectives may be implemented. It should also be noted that the drive  384  may be an electronic drive, pneumatic drive, hydraulic drive, or any combination thereof. 
         [0029]    In certain embodiments, the sensor  280 , drive  284 , and associated logic controller  282  of  FIG. 3  may be supplied as a retrofit kit option for existing spray coating guns. In addition, the sensor  280  and drive  284  may communicate through the logic controller  282  via wireless communication technology, such as microwave, radio frequency, and infrared. Similarly, the sensor  380 , drive  384 , and associated logic controller  382  of  FIG. 4  may be supplied as a retrofit kit option for existing spray coating guns. Again, the sensor  380  and drive  384  may communicate through the logic controller  382  via wireless communication technology, such as microwave, radio frequency, and infrared. These retrofit kits may be configured to mount to any existing spray coating gun. 
         [0030]    In some embodiments, one or more sensors may be mounted to the head, body, handle, hoses, or a combination thereof, of the spray gun. For example, these sensors may be mounted via clamps, Velcro, adhesives, epoxy, screws, ties, or a combination thereof. Again, these sensors may be wired sensors, wireless sensors, or a combination thereof. Furthermore, the sensors may be configured to sense position, distance, velocity, acceleration, angle, surface temperature, surface morphology, surface wetness, or a combination thereof, of the target object relative to the spray gun. These sensed parameters may be used by an on-board controller to adjust operation of the spray gun. The on-board controller may include a processor, memory, and code disposed on the processor. The on-board controller alternatively may include a programmable logic controller (PLC) or another suitable controller. Similar to the sensors, the on-board controller may be mounted to the head, body, handle, hoses, or a combination thereof, of the spray gun. For example, the on-board controller may be mounted via clamps, Velcro, adhesives, epoxy, screws, ties, or a combination thereof. The controller, in turn, is configured to control operation of one or more valves (e.g., liquid valve, air valve, or both) to adjust an operational state (e.g., on or off), flow rate, or a combination thereof, of the spray gun. Again, the valves may include a pneumatic valve, a hydraulic valve, a motorized valve, a solenoid type valve, or another suitable feedback controllable valve. In each of the disclosed embodiments, the closed loop control provided by the sensors and controlled valves enables more efficient transfer of a coating fluid onto a target object, thereby reducing waste (e.g., into the air) and improving the quality of the coating applied to the target object. 
         [0031]    While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.