Abstract:
An apparatus for dispensing an amount of fluid is disclosed where the amount of fluid and the pressure thereof is controlled by the height of the fluid relative to the spray mechanism that can dispense the fluid. A reservoir is positioned above the spray mechanism such that a column of fluid constitutes the reservoir of fluid. The height of the fluid reduces upon actuation of the spray mechanism. A controller detects the initial height of fluid and the height of the fluid after the dispensing operation to determine the amount of fluid dispensed. The controller is programmed with a parameter for the amount of fluid to be dispensed. If the determined amount of fluid dispensed is not within the parameters, the controller operates an iterative process to refill the reservoir to an amount such that during subsequent spraying operations, the amount dispensed approaches the parameter amount of fluid.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates in general to a method and apparatus for controlling a fluid for a discrete/pulse dispensing application. 
     The present invention relates to an interior panel for a vehicle, and in particular to a headliner. A headliner typically consists of various layers or plies, such as a stiffening and silencing layer. Such layers can be formed, at least, of a rigid carrier layer which is integrated into the vehicle interior panel. Moreover, the interior panel typically further consists of at least one decorative layer and an intermediate shock-absorbing layer. Such an interior panel with an integrated stiffening and silencing layer may, in particular, be designed as an acoustic headliner when used as a roof liner. The interior panel is typically prefabricated and is mounted at a corresponding place of the vehicle, such as the interior of the vehicle roof. However, such a special construction of the roof liner is not needed according to the invention. 
     The process of forming a vehicle or automotive headliner typically includes cutting a thin sheet of polyurethane foam and coating the foam with a reactive component in a liquid state which polymerizes to form a polyurethane which stiffens the substrate. Multiple layers (or plies) may be so coated and pressed together to provide a desired stiffness. Another method includes a liquid or multiple reactive components in liquid form being sprayed onto a sheet of material as it passes on a conveyor. Still another method is roll coating, wherein sheet material is fed between rolls which are coated with a liquid which transfers the coating onto the workpiece. Roll coating is not necessarily a separate method, but can be used in conjunction with a spraying apparatus. For example, roll coating applies one of the chemical agents and spraying applies a second agent. 
     In the manufacture of automotive headliners using a spray coating method, there has been a need to control the “catalyst” that is applied to the manufacturing process. The term “catalyst” is generically used to describe the polyurethane catalyst that is used in conjunction with polyurethane adhesives to collectively form a bond between the various plies of an automotive headliner. Controlling the amount and spray pattern of catalyst has been a difficult task. Typically, the catalyst application process requires very low pressures for very short time intervals. For example, a catalyst could be dispensed at about 5 p.s.i. for a relatively short period of time (on the order of seconds), and then the apparatus would be turned off for a relatively longer period of time (on the order of about one minute). It would be typical for an on/off cycle to comprise a total of one minute, with the “ON” time equaling a few seconds and the “OFF” time equaling the remaining time. 
     Historically, the dispensing pressure of a fluid in a dispensing apparatus has been controlled by a mechanical (spring and diaphragm) pressure regulator. Such regulators have shortcomings when used for controlling pulse fluid applications. For example, regulators “creep”, which means that during periods of inactivity (such as the exemplary relatively long “OFF” time) there is a tendency for the regulator to pass fluid and build downstream pressure. This is because regulators are best equipped to operate in a continuous flow situation. Regulators can also be unreliable at the low operating pressures required for intermittent spraying operations because regulators have an inherent quality of operating with a fluctuating pressure. Thus, an apparatus that is more precise at low pressure would be advantageous for the application of a catalyst. Regulators can also have a slow response time to an actuation signal. Additionally, when flow amount is based only on pressure and flow opening, the actual amount of material dispensed is not measured. Thus, a more accurate apparatus for determining and controlling an amount of catalyst/fluid dispensed would be beneficial. Regulators also eventually wear out after prolonged use. Finally, traditional regulators offer no vent for bubbles or gases entrained in the fluid to escape. 
     Therefore, for in order to limit the shortcomings of using regulators in a catalyst dispensing system, and to obtain the advantages described above, it would be beneficial to implement a novel method and apparatus for dispensing a catalyst/fluid. 
     SUMMARY OF THE INVENTION 
     This invention relates to an apparatus for dispensing an amount of fluid where the amount of fluid and the pressure thereof is controlled by the height of the fluid relative to the spray mechanism that can dispense the fluid. A reservoir is positioned above the spray mechanism such that a column of fluid constitutes the reservoir of fluid. The height of the fluid reduces upon actuation of the spray mechanism. A controller detects the initial height of fluid and the height of the fluid after the dispensing operation to determine the amount of fluid dispensed. The controller is programmed with parameters for the amount of fluid to be dispensed. If the determined amount of fluid dispensed is not within the parameters, the controller operates, in an iterative process, to refill the reservoir to an amount such that during subsequent spraying operations, the amount dispensed approaches the desired parameter amount of fluid. 
     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a fluid dispensing apparatus according to a first embodiment of the invention. 
         FIG. 2  is a perspective view of a fluid dispensing apparatus according to a second embodiment of the invention. 
         FIG. 3  is a flow diagram of the operating process according to the fluid dispensing apparatus of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, there is illustrated in  FIG. 1  a diagram of the first embodiment of the fluid dispensing apparatus, indicated generally at  10 , according to the invention. A conveyor line  12  is used with the apparatus  10  to move a workpiece  14  into contact with the apparatus  10 . The conveyor  12  can also be used to move multiple workpieces  14  (or a continuous generally elongated workpiece) into contact with the apparatus  10  for mass production of workpieces  14 . The apparatus  10  includes a reservoir  16  that contains a volume of fluid  18 . The reservoir  16  has a supply line  28  connected to a source of fluid (not shown, but can be embodied as a supply tank, for example) that is adapted to replenish the reservoir  16  with fluid  18  based on the desired parameters of the dispensing operation (described below). The reservoir  16  is also connected by a feed line  20  to at least one spray mechanism  22 . The spray mechanism  22  can be a spray gun, nozzle or any other type of dispensing apparatus. Preferably, and in order to cover a larger area of a workpiece  14 , there are a plurality of spray mechanisms  22  connected to the feed line  20 . The feed line  20  is preferably also connected to a generally straight spray pipe  26  that is positioned over the conveyor  12 . The spray mechanism  22  is preferably positioned along the spray pipe  26  such that the feed line  20  supplies the fluid  18  through the pipe  26 . The pipe  26 , and thus the spray mechanism  22 , is preferably positioned over the conveyor  12  and a workpiece  14  such that when the apparatus  10  is activated, the spray mechanism  22  dispenses the fluid onto a workpiece  14 . Located at one end of the pipe  26  is an optional low pressure gauge  24  for monitoring the pressure at the discharge end of the spray mechanism  22 . 
     The operation of the apparatus  10  for dispensing a fluid will be described next. The reservoir  16  is initially filled with a volume of fluid  18 . In this embodiment, the reservoir  16  is open to the atmosphere and thus, is subject to atmospheric pressure. An advantage of having the reservoir  16  open to the atmosphere is that any entrained bubbles in the fluid  18  can be vented out. With the fluid reservoir  16  elevated, the height of the reservoir  16  (and fluid  18 ) will cause the pressure felt at the spray mechanism  22  (and pressure gauge  24 ) to vary with the fluid height. It is anticipated that the spray mechanism  22  will be opened only for a given period of time. The period of time the apparatus  10  is dispensing fluid will vary depending upon the application the fluid dispensing apparatus  10  is being used for. In the illustrated example, a plurality of workpieces  14  pass by the spray mechanism  22  on the conveyor  12 . The spray mechanism  22  will dispense fluid  18  for the period of time that the workpiece  14  is passing under the spray mechanism  22  and will then shut-off when the workpiece  14  has passed by the mechanism  22 . Therefore, it is preferred that the spray of fluid  18  will only be on when the workpiece  14  is under the spray mechanism  22  so that the fluid  18  is dispensed only onto the workpiece  14  and not onto the conveyor  12 . The apparatus  10  can be activated manually when a workpiece  14  is properly aligned under the spray mechanism  22 , or can be automated and include the use of an infrared or other type of triggering system to indicate proper alignment of the workpiece  14 . The period when the mechanism  10  is active versus inactive will be a function of at least the physical characteristics of the fluid  18  being used, the size of the material being used as a workpiece  14 , the height of fluid in the feed line  20 , as well as any other factor that is desired to be used in conjunction with the apparatus  10 . 
     An alternate embodiment of the invention is illustrated in  FIG. 2 . In the alternate embodiment, the reservoir is implemented as a vertical tube  32  instead of the large suspended reservoir tank  14 . Since the horizontal cross-section of the vertical tube  32  is less than that of the reservoir  16 , it is anticipated that the measurement of the fluid height can be more accurately quantified and controlled. As described below, the fluid height can be measured before (H 1 ) and after (H 2 ) a dispensing operation. However, it can be appreciated that this step would only take place if refilling is deferred until after H 2  is measured. Alternatively, refilling could be continuous and a controller  34  could activate the dispensing mechanism when it detects that H 1  is met. The difference in the fluid heights is then used to determine the volume of fluid  18  dispensed during the dispensing operation. Depending on whether the amount of fluid  18  dispensed was within the design parameters, the vertical tube  32  could be refilled to a greater or lesser height H 1  to account for the dispensed amount variation (described below). It is preferred that the vertical tube  32  also be connected to a fluid supply line  28  for refilling the tube  32 . A solenoid valve  30  is preferably positioned between the tube  32  and the fluid supply source (not shown) to control the amount of refilling. The fluid supply line  28  can be connected to the base of the vertical tube  32  or at any point along the vertical tube  32 . Unlike the elevated reservoir  14 , the supply source that feeds the supply line  28  would not have to be positioned at the same or higher elevation. The solenoid valve  30  can then be operated in conjunction with a controller  34  to monitor and control the amount of fluid  18  used to replenish the vertical tube  32 . The spraying operation of the alternate embodiment of the invention is substantially the same as that described in conjunction with the first alternate embodiment. However, it can be appreciated that the supply line  28  could continuously feed either the reservoir  16  or tube  32  rather than as an intermittent refilling step. 
     The amount of fluid  18  dispensed will vary with the starting height H 1  of the fluid  18  in the feed tube  20  or reservoir  16 . The pressure applied to the fluid  18  at the spray mechanism  22  is proportional to the density of the fluid  18 , the height H 1  of the fluid column and the pull of gravity. When the spray mechanism  22  is activated for a fixed period of time, a certain amount of fluid  18  will be dispensed based on those conditions, as well as the orifice size of the spray mechanism  22 . Thus, the amount of fluid  18  dispensed can be calculated based on the fluid drop in the reservoir  16  or tube  32 . For example, the height difference (H 1 −H 2 ) in the reservoir  16  or tube  32  from an initial (pre-spray) state to a secondary (post-spray) state multiplied by the cross-sectional area of the reservoir  16  or tube  32  (area—A) will give the amount of fluid used per cycle. Thus:
 
(( H   1 − H   2 )× A )/# of cycles=Average fluid consumption per cycle of operation
 
Since the cross section of the tube  32  is considerably less than that of the reservoir  16 , calculations that are performed using the tube configuration  10 ′ as opposed to the reservoir configuration  10  will generally yield more accurate results using fewer number of machine cycles in the calculation for average fluid consumption per cycle of operation. Alternatively stated, the value of H 1 −H 2  will be larger for smaller cross-sectional areas (the fluid drop will be greater in the tube  32  than in the reservoir  16  for the same volume of fluid consumption). If the height of the fluid reservoir  16  or tube  32  is fixed, the elevation of the spray mechanism  22  is fixed, and if the level H 1  of fluid  18  in the reservoir is maintained, then the distance from the spray mechanism  22  to the top of the fluid (column height—H 1 ) is also a constant. Since the pull of gravity is constant, the fluid pressure applied to the spray mechanism  22  will also be constant. Having a generally constant and generally consistent pressure at the spray mechanism  22  addresses some of the limitations with the prior art methods of fluid dispensing.
 
     Additionally, measuring the amount of fluid  18  dispensed per cycle will allow the user to determine whether the proper amount of fluid  18  is being used for the application the mechanism  10  is being used for. In the preferred embodiment, the fluid  18  is a catalyst as described above. For certain applications, controlling the amount of fluid  18  dispensed is important to the process of forming a interior panel for a vehicle. By controlling the amount of catalyst applied to a workpiece  14 , the more consistently a product can be produced. 
     A controller  34  can also be used in conjunction with the apparatus  10  and  10 ′ according to the invention. The controller  34  could be programmed to monitor and control operational parameters, such as fluid pressure or fluid dispensed per cycle. Implementing a controller  34  with the apparatus  10  and  10 ′, could allow the apparatus  10  and  10 ′ to correct the output of the apparatus should a measured quantity be outside of the design parameters. Design parameters could be a specific pressure, a range of pressures, a specific amount of fluid used, a range of amounts of fluid used, as well as any other quantification for measuring the fluid consumption during operation of the apparatus. If the measured quantity is outside design parameters, the controller can adapt the operation of the system. For example, if the downstream pressure of the fluid  18  is lower than desired, the starting height H 1  of the fluid  18  could be increased to raise the output pressure of the fluid  18 . If the pressure is too high, the starting height H 1  of the fluid  18  in the reservoir  16  or tube  32  could be lowered by refilling the reservoir  16  or tube  32  to a lower height than the previous starting fluid height H 1 . This process can be repeated through several operational cycles with the controller  34  allowing a higher or lower amount of fluid  18  to be used to refill the reservoir  16  or tube  32  until a fluid pressure (or amount of fluid dispensed) is within design limits. To control the amount of fluid  18  that is used to replenish the reservoir  16  or tube  32 , it is preferred that the controller  34  be adapted to control a (normally closed) solenoid valve  30 . The solenoid valve  30  is preferably connected between the fluid supply line  28  and the reservoir  16  or tube  32 . The controller  34  can then operate the solenoid  30  for a period of time to allow the proper amount of fluid  18  to be replaced in the reservoir  16  or tube  32 . The controller  34  is also preferably connected to a sensor  36  in the reservoir  16  or tube  32  that allows the controller  34  to detect the height of the fluid therein. The fluid height sensor  36  can be a float switch, level sensor, infrared eye, or any other suitable sensing mechanism. Also, the fluid height sensor  36  could be used to alert users if the fluid exceeds a certain amount such that the reservoir  16  or tube  32  is nearing an overflow state. Thus, the controller  34  can control refilling of the reservoir  16  or tube  32  by the amount of time the fluid supply line  28  is open, the height of the fluid  18 , or the pressure at the spray mechanism  22 . Alternatively, the pressure and height of fluid could be varied by positioning the reservoir  16  on a movable slide device such that the controller  34  (or manual operation) could reposition the reservoir  16  to achieve the desired fluid pressure. This alternate embodiment could also be used without a per-cycle refilling step and adjusting the reservoir height would be used to control the fluid pressure. It is preferred that the tube  32  be fixed and the pressure control be accomplished by varying the height of the fluid within the tube  32 . 
     In a preferred pressure detection scheme, a low pressure transducer  40  can be mounted at the bottom of the vertical tube  32 . It is further preferred that the transducer  40  be positioned at substantially the same elevation as the spray mechanism  22 . The controller  34  could be used to take readings from the transducer  40  prior to and after each period of fluid dispensing. Although the transducer  40  is shown at two locations, it is preferred that a single transducer is used. The transducer  40  could be positioned at either indicated location and is also preferably connected to the controller  34 . The solenoid valve  30  would be used, preferably after all the readings and measurements were taken and calculated, to replenish the vertical tube  32  (or reservoir  16 ). Additionally, the transducer  40  could also be used to take continuous measurements so that the controller  34  can make continuous calculations to the amount of fluid  18  being consumed during the dispensing process. It is preferred that continuous readings are taken during the refilling process such that the controller  34  can shut off the valve  30  when the appropriate fluid amount (H 1 ) is reached. In a preferred embodiment, the controller  34  can also control the speed of the conveyor  12  in conjunction with controlling the spray mechanism  22  to allow the proper spray distribution to be applied to the workpieces  14  while simultaneously controlling the amount of fluid  18  being dispensed. 
     The controller  34  operating program can also include an algorithm programmed to monitor the fluid consumption and other design parameters. It is preferred that the controller algorithm be implemented in conjunction with the components described above. However, it can be appreciated that the embodiments of the invention can be practiced with a greater or lesser amount of components to dispense fluid  18  onto a workpiece. The algorithm is preferably programmed with a value or range of values for the amount of fluid  18  dispensed per cycle of operation of the apparatus  10  and  10 ′. Using the various measuring devices to provide feedback, the controller  34  can adapt the system to provide the workpiece  14  with the desired amount of fluid  18 . After a number of cycles, the controller  34  would eventually converge upon the optimal filling height H 1  of the reservoir  16  or tube  32  in order to dispense an amount of fluid  18  that is within the design range of the apparatus  10  and  10 ′. It is preferred that the feedback system continue to operate even after the optimal starting fill height H 1  has been determined in order to maintain the proper level of fluid height in the reservoir  16  or tube  32 . Particularly, this could be important if a downstream change occurs. For example, if the spray mechanism  22  orifices clog with the fluid  18 , the controller  34  can detect that not enough fluid  18  is reaching the workpiece  14  and will increase the amount of fluid  18  in the reservoir  16  or tube  32  so that the desired amount of fluid  18  is dispensed. Alternatively, the controller  34  could be programmed to alert operating personnel if the fluid pressure falls outside design parameters too frequently or at too high or low a value. 
     Illustrated in  FIG. 3  is a flow diagram of the operating process according to the present invention. In a first step  100 , a conveyor for moving workpieces into contact with a dispensing apparatus is activated. In a second step  102 , a provided reservoir is filled with fluid to an initial height. In a third step  104 , at least one of a first fluid pressure at the spray mechanism and first fluid height is measured. In a fourth step,  106 , the dispensing mechanism is operated to dispense an amount of the fluid. In a fifth step  108 , at least one of a second fluid pressure at the spray mechanism and second fluid height is measured. In a sixth step  110 , the amount of fluid dispensed is calculated using any of the methods described above. In a seventh step  112 , it is determined whether the amount of fluid dispensed is within the design parameters, is greater than the design parameters, or is less than the design parameters. If the amount of fluid dispensed is within design parameters, then the fluid is refilled to the initial height according to step  102 . If the amount of fluid dispensed is greater than desired, then in an eighth step  114 , the reservoir is refilled a lesser amount. In the reservoir and fluid height system, the reservoir is refilled to a lesser height. If the amount of fluid dispensed is less than desired, then in a ninth step  116 , the reservoir is refilled to a greater amount. In the reservoir and fluid height system, the reservoir is refilled to a greater height. Regardless of whether the eighth step  114  or ninth step  116  is taken, the pressure or height of the fluid is measured according to the third step  104 . It is preferred that the process is repeated until it is desired that the operation be stopped and no further workpieces receive the fluid according to the dispensing operation. 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.