Abstract:
A system for controlling the operation of pneumatic tools includes a controller for controlling the delivery of compressed air to the tool. The controller includes a first flow path that is associated with operation of the pneumatic tool at a first flow rate and a second flow path that is associated with operation of the pneumatic tool at a second flow rate. The controller is configured to automatically configure the system for operation of the pneumatic tool via a flow of air from one of the first flow path or the second flow path. In painting environments, such a system enhances control of the operation of the pump in accommodating a generally stable pump reciprocation rate as fluid viscosities change.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to controllers for controlling operation of pneumatic flows, and in particular, to an air flow controller for use in industrial compressed air systems, such as in automated paint systems, where it is commonly required to move materials having different viscosities. 
       BACKGROUND OF THE RELATED ART 
       [0002]    In spray paint operations, a paint fluid, commonly in the form of a liquid or a relatively fine powder, is mixed with compressed air to atomize the paint particles and transfer the atomized paint particles onto the surface of an item being painted. Frequently, a paint gun is fluidly connected to a paint source and an air source and mixes the two materials proximate a paint location. Alternatively, many paint guns include a paint container that is physically supported by the paint gun. During most painting operations, it is very important to maintain a clean paint supply in order to ensure a quality finish. The paint fluid is frequently formed from a mixture of resins and colored particulates or flakes. The paint fluid is generally delivered to a mixing point through a series of pipes, tubes, or hoses. Preferably, this fluid path is relatively smooth or free of steps of discontinuities where the resin or color particulates may collect and form an undesirable particulate or resin ball. Understandably, any collection of particulates or resin, whether solid or pliable, introduced into the fluid paint flow can detrimentally affect operation of the paint gun or quality of the paint finish. 
         [0003]    One commonly used spray paint gun, commonly referred to as a high volume low pressure (HVLP) spray gun, generates high volumes of low-pressure air which transfers the paint particles to the surface of the article being painted with relatively low velocity. The high volume low velocity transfer of paint to the work piece reduces overspray generated during the painting process and thereby improves the paint to part transfer ratio. In such systems, a fluid regulator regulates the flow of fluid between a high-pressure port and a low-pressure port of the paint gun. Understandably, operation of such systems requires the periodic cleaning of the fluid transfer lines. This cleaning process generally includes passing a fluid having a different viscosity than the paint, such as air, a cleaning agent, or solvent through a pump to remove residual paint from the pump and the fluid paths of the spray system. Solvents are also passed through the pump when it is desired to change the color being applied to a part. 
         [0004]    The fluid properties of paint being sprayed and the cleaning agent or other fluids passed through the pump are generally not the same. It is readily appreciated that fluid paints, even paints that have been somewhat thinned for spray application, are generally more viscous than air or cleaning agents. Commonly, when the spray system is to be cleaned for non-use or a color change, the supply of paint is replaced with a supply of cleaning agent that is then run through the system in a manner similar to the paint. Passing solvent through a system configured to deliver a spray of atomized paint undesirably alters the operation of the delivery system. 
         [0005]    The introduction of another fluid, such as solvent, a source of air, or an air vacuum condition, to the pump substantially increases the pump reciprocation rate if the air flow is provided at a flow rate associated with moving the thicker paint through the pump. Commonly, after the initial introduction of the second fluid to the fluid system, the pump must be maintained at a paint delivery operating pressure. If the pump operating pressure is prematurely reduced, the pump may have occasion to stall thereby delaying the cleaning process. Conversely, if the pump operating pressure is maintained at a paint delivery pressure after the less viscous fluid overtakes the fluid path of the pump, operation of the pump increases to a level that detrimentally affects pump performance and/or longevity. 
         [0006]    Accordingly, it would be desirable to provide a pneumatic tool control system that automatically alters a compressed air flow based on real-time operating characteristics of the pneumatic tool. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention is directed to a system for controlling the operation of pneumatically powered tools that solves the aforementioned problems. A system includes a controller for controlling the delivery of compressed air to the tool. The controller includes a number of flow paths wherein each flow path is associated with an operational condition of the pneumatic tool. Preferably, the system includes a controller configured to provide a first flow path and a second flow path that are each associated with an operating condition of the pneumatic tool. In painting environments, the control system is configured to provide a flow that is tailored to controlled operation of a pneumatic device such as a pump or the like. 
         [0008]    Therefore, in accordance with one aspect of the present invention, a method for controlling the delivery of compressed air to a tool includes the steps of (a) receiving compressed air from a source; (b) determining a compressed air flow rate; and (c) allowing the compressed air to flow at a selected rate sufficient to maintain a selected operating pressure when the determined compressed air flow rate is equal to or less than a flow rate set with an air flow control valve. The method further includes a step (d) that includes automatically reducing the compressed air flow rate to maintain a preset air flow rate at a pressure below the selected operating pressure when the determined compressed air flow rate exceeds the selected flow rate. Such a method delivers a compressed air flow that is responsive to the operating condition of the controlled tool. 
         [0009]    According to another aspect of the present invention, a system for controlling operation of a pneumatic tool that is powered by compressed air is disclosed. The system includes an inlet, an outlet, and at least two flow paths between the inlet and the outlet. The inlet is configured to be connected to a source of compressed air and the outlet is configured for communicating an air flow to the pneumatic tool. The system includes an air flow controller that is constructed to 1) allow flow along a first flow path when a flow rate at the outlet approximates a desired flow rate as determined by a pressure regulator and 2) allow flow along a second flow path when the flow rate at the outlet exceeds a threshold associated with the desired flow rate to maintain a desired operation of a pneumatic tool. Such a system provides for operation of a pneumatic tool at various flow rates that are determined, in part, based on the operating condition of the tool. 
         [0010]    Another aspect of the present invention discloses a pneumatic system that comprises a tool powered by a flow of compressed air, an air flow control valve for providing a desired flow rate, and a controller connected to the air flow control valve. The controller is configured to 1) allow the flow to the tool at the desired flow rate when the flow is not more than the desired flow rate; and 2) allow the flow to the tool at another rate independent of the desired flow rate if the flow exceeds the desired flow rate. Such a system provides for automatic control of operation of the tool in response to the operating environment. 
         [0011]    Various other features, aspects, and advantages of the present invention will be made apparent from the following detailed description and the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The drawings illustrate one preferred embodiment presently contemplated for carrying out the invention and in the drawings: 
           [0013]      FIG. 1  is a schematic representation of a pneumatic system according to the present invention; and 
           [0014]      FIG. 2  is a flow chart showing operation of the pneumatic system shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    Referring to  FIGS. 1 and 2 , the invention disclosed herein relates to a method and apparatus for controlling the air flow rate of compressed air, sometimes referred to as either pressurized air or as atomization air, to a tool. The system and method are particularly useful in connection with a spray paint operation, in which the compressed air is mixed with a volume of liquid or powdered paint in order to atomize the paint fluid into minute particles and transfer the paint particles onto the surface of an item being painted. The present invention is particularly useful in controlling operation of pneumatic pumps whose operating speed may alter depending on the viscosity of the fluid passed through the pump. The invention disclosed herein is also adaptable for use with other types of pneumatically powered tools in which the optimal operation of the tool is dependent upon receiving more than one predetermined or desired flow rate of compressed air. 
         [0016]      FIG. 1  is a schematic representation of a pneumatic system  10  according to the present invention. Pneumatic system  10  includes a controller or control system  12  that is fluidly connected between a source  14  of compressed air and a tool  16 . System  12  includes an inlet passage  18  that extends between source  14  and a solenoid or switch  20  and an outlet passage  22  that extends to tool  16 . Control system  12  includes a processor  24  that controls operation of switch  20 . Downstream of switch  20 , control system  12  includes a first air flow path  26  and a second air flow path  28 . First air flow path  26  includes a pressure regulator  30  having a pressure gauge  32  and a solenoid or valve  34  that are positioned between switch  20  and outlet passage  22 . A connection  36  extends between valve  34  and processor  24  to electro-mechanically control airflow  38  along first air flow path  26 . 
         [0017]    System  12  includes a second air flow path  28  that has an airflow control  50  that is connected to processor  24  via a converter such as a voltage pneumatic converter  52 . Airflow control  50  includes an air chamber  54  that is separated into a first sub-chamber  56  and a second sub-chamber  58  by a diaphragm  60 . A needle  62  extends from diaphragm  60  and engages a lateral opening or orifice  64  formed in second air flow path  28 . A spring  66  is disposed in second sub-chamber  58  between diaphragm  60  and a wall  68  of airflow control  50 . 
         [0018]    An airflow meter  70  is fluidly connected to first air flow path  26  and second air flow path  28  downstream of valve  34  and airflow control  50 , respectively. Airflow meter  70  includes a first pressure transducer  72  and a second pressure transducer  74 . Second pressure transducer  74  is offset from first pressure transducer  72 . A constriction  76  is provided between first pressure transducer  72  and second pressure transducer  74 . A connection  78  extends between each pressure transducer  72 ,  74  and processor  24 . Transducers  72 ,  74  and constriction  76  are associated such that processor  24  can assess the flow through second air flow path  28  as a function of a pressure differential detected at airflow meter  70 . Alternatively, airflow meter  70  could be provided as a turbine flow meter or as a heat flow meter. Regardless of the specific configuration of meter  70 , altering the interference of needle  62  with orifice  64  automatically alters the flow provided at outlet passage  22  to tool  16 . Such a construction allows airflow control system  12  to operate tool  16  at either of first airflow  38  or a second airflow  80 . Each airflow  38 ,  80  can be adjusted to respond to real-time changes associated with the operating state of tool  16 . 
         [0019]    Control system  12  as described above is exemplary of one control system configured to provide the desired pneumatic control of tool  16 . Although control system  12  includes a number of mechanical, electrical, and electromechanical flow manipulating devices, these specific devices and orientation of devices are merely exemplary. Other devices and arrangement of such devices are envisioned and within the scope of the claims. Variations of such flow control system components and the configuration of components are disclosed in the applicants U.S. Pat. Nos. 6,516,707 and 6,223,645. The disclosures of these documents are incorporated by reference. Unlike the systems of these references, the present invention is directed to controlling the operation of a tool through providing variable flow rates that are provided generally independent of the static or dynamic nature of the flow. That is, control system  12  is configured to provide at least two different flows in response to changes in the operating condition of tool  16 . 
         [0020]      FIG. 2  graphically shows the operation of flow control system  12 . Referring to  FIGS. 1 and 2 , at system start  100 , tool  16  has yet to be triggered, and system  10  achieves a ready state  102  in that the lines of system  10  are pressurized and maintained at a generally static ready state. System  10  is maintained  104 ,  106  in ready state  102  until tool  16  is triggered. When tool  16  is initially triggered  108 , valve  34  of system  12  is opened such that the air flow at outlet passage  22  is provided to maintain an initial air flow  110  at a desired pressure associated with regulator  30 . After initial air flow  110 , air flow switch  20  proximate air inlet passage  18  is activated and initiates an instruction at processor  24  to close valve  34  thereby directing flow only along second air flow path  28  such that system  10  operates in flow mode control  112 . 
         [0021]    During flow mode control  112 , as air flows through the pressure differential flow meter  70 , first and second transducers  72  and  74  generate an electronic pressure differential signal which is sent to processor  24 . The electronic pressure differential signal is compared to a desired signal to assess if a desired flow  114  is being achieved. If a desired flow is provided  116 , system  10  maintains the configuration of the respective valves of system  10  in flow mode control  112 . Commonly, depending on the type of tool  16  connected to system  10 , desired flow  114  relates to an operating speed of the tool under an intended load. If the desired flow is not being provided  118 , and the trigger of tool  16  remains activated,  120 ,  122 , system  10  alters the configuration of airflow control  50  until the desired flow is achieved  126 . 
         [0022]    Depending upon the difference in value between a measured signal and a value associated with the desired flow attained at flow meter  70 , processor  24  directs a signal to the pneumatic converter to produce and transmit a pneumatic signal which is sent to airflow control  50  to alter the flow  124 . The pneumatic signal sent to the airflow control  50  deflects diaphragm  60  to either open the flow control valve to permit a greater flow of pressurized air through the system, or close the air control valve in order to restrict the amount of air flowing through the system. 
         [0023]    In a paint pump application, when a paint pump is initially provided with an air flow during pumping of paint, the reciprocation rate of the pump is affected by the viscosity of the material being pumped. If the air flow rate measured at meter  70  is lower than the desired level associated with the airflow control  50 , system  12  operates at the predetermined pressure associated with regulator  30  as needle  62  will be maintained in a fully open position or a position wherein needle  62  does not interfere with orifice  64 . Transducers  72  and  74  provide signals with which processor  24  can determine a desired operating flow rate. If the viscosity of the material passed through the pump changes, such as by introducing an air fluid, a fluid experiencing a vacuum condition, or a solvent through the pump, the lower viscosity of the alternate fluid allows the pump to reciprocate faster when air is supplied at the desired pressure that is associated with operation of the pump to move paint. 
         [0024]    The faster reciprocation of the pump is indicative of a higher air flow rate through system  12 . When system  12  experiences a higher air flow rate at a desired operating pressure, processor  24  generates an instruction to introduce needle  62  into orifice  64  thereby restricting second air flow path  28 . The introduction of needle  62  into orifice  64  reduces the operating pressure provided to the pump by maintaining a desired air flow rate that correlates to an air flow rate associated with moving paint. Such a configuration provides controlled operation of a pneumatically operated pump independent of the viscosity of the material passed through the pump. By controlling the operation of the pump by the air flow rate delivered to the pump, unnecessary racing of the pump can be avoided. 
         [0025]    Such real-time and dynamic control of pneumatic tool  16  continues until the trigger of tool  16  is deactivated  128 . When the tool  16  is triggered off, air flow through the pressure differential flow meter  70  is suspended. When there is no air flow through the pressure differential flow meter  70 , the electronic signal produced by the first and second transducers  72  and  74  is equal, processor  24  generates an instruction to open valve  34  in air flow path  26 , and thereby revert the system back to pressure regulation status. 
         [0026]    It is to be understood that the embodiments disclosed above are merely exemplary of the invention which may be embodied in various forms. Changes maybe made in the details of construction, arrangement and operation of various elements of the invention without departing from the spirit of the invention. For example, the flow rate control of system  12  might be activated by any of an electronic, pneumatic, electromechanical, or any combination thereof, signal received from the tool rather than just a pneumatic signal. Therefore, specific structural and functional details disclosed above are not to be interpreted as limiting the scope of the invention. 
         [0027]    As one skilled in the art will fully appreciate, the heretofore description of an air flow control system has applications beyond the disclosed paint sprayer application. It is appreciated that the present invention is equivalently applicable with any device that requires more than one controlled air flow and/or those systems wherein it may be beneficial to alter the operating paradigm that is used to configure the operation of the pneumatic device. The description of a paint sprayer illustrates just one embodiment in which the present invention may be implemented. The present invention has been described in terms of the preferred embodiment, and it is recognized that equivalents, alternatives, and modifications, aside from those expressly stated, are possible and within the scope of the appending claims.