Abstract:
A system for controlling dispensation of multiple component reactant mixtures. A mixing chamber is positioned adjacent to a part. A metering ram is actuated to pressurize at least two reactant components. The metering ram is stopped if a measured pressure value exceeds a predetermined pressure value. At least one flow meter measures a volume of a reactant component passing through the system.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. provisional application Ser. No. 60/410,756, filed Sep. 13, 2002. 
     
    
     BACKGROUND OF INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a system for controlling dispensation of multiple component reactant mixtures.  
         [0004]     2. Background Art  
         [0005]     Multiple component reactant mixtures are used to form polymeric compositions. Examples of polymers formed by reactant mixtures include epoxies, polyurethanes, and silicone compositions. For example, a silicone seal may be formed by combining a two-part reactant mixture including a catalyst component and a base component that may be mixed and injected to form the silicone seal in situ in an assembly.  
         [0006]     Reactant mixtures are normally mixed in a mixing chamber of a gun injector that dispenses the mixture through a nozzle. The reactant components are provided under pressure to the mixing chamber via separate conduits. These separate conduits may include a flexible conduit portion. For example, the flexible conduit portion may be a hose. When a reactant component is provided under pressure into a flexible conduit portion, the flexible conduit portion may expand. As a result, the volume of a reactant component that is actually dispensed through the flexible conduit portion into the mixing chamber is not known. In addition, changes in temperature can affect the rate of expansion of the conduits, making it difficult to predict the volume of a reactant component that will be dispensed into the mixing chamber at any given time. Injecting an incorrect volume of a reactant component can result in an improper chemical reaction. For example, if an insufficient amount of the base component is provided, the chemical reaction may occur too fast. As a result, the reactant mixture may react and cure inside the nozzle before dispensing is complete, thereby necessitating replacement of the nozzle.  
         [0007]     Before applicant&#39;s invention, there was a need for a system to control dispensation of reactant components and mixtures in order to dispense the desired amounts of the reactant components and the resultant reactant mixture. Problems associated with the prior art as noted above and other problems are addressed by applicant&#39;s invention as summarized below.  
       SUMMARY OF INVENTION  
       [0008]     According to the present invention, a reactant material dispensing system is provided in which at least two components are combined in a dispenser having a nozzle. The system includes a mixing chamber that receives two components under pressure from two separate sources. The two components are maintained separately before they are combined in the mixing chamber. A metering ram pressurizes the two components. A flow meter is provided to measure the volume of each component that passes through the system. Conduits are provided to fluidly connect the metering ram, flow meter, and mixing chamber.  
         [0009]     Other aspects of the invention as it relates to the reactant material dispensing system are that the two components may be a catalyst and a base that are used to form a seal, in situ, in an article of manufacture. The mixing chamber may be connected to a robot arm that positions the mixing chamber and the nozzle adjacent to a part.  
         [0010]     According to other aspects of the invention, a catalyst supply and a base supply may be connected in fluid flow communication to the metering ram. The metering ram pressurizes the reactant components. Alternately, individual metering rams may be used to pressurize each reactant component. Pressure may be monitored using a pressure sensor. The pressure sensor may be located between the metering ram and the mixing chamber. Shutoff valves may be located in a catalyst supply conduit that connects the catalyst supply to the metering ram, or in a base supply conduit that connects the base supply to the metering ram. Alternatively, shutoff valves may be provided in both the catalyst supply conduit and the base supply conduit.  
         [0011]     According to another aspect of the invention, a catalyst conduit and a base conduit may be provided to connect the metering ram to the mixing head. A flow meter may be located in the catalyst conduit, in the base conduit, or in both the catalyst conduit and the base conduit. A catalyst gun valve may be located in the catalyst conduit. A base gun valve may be located in the base conduit.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0012]      FIG. 1  is a top plan view of a robot station for injecting a reactant mixture into a part on a conveyor.  
         [0013]      FIG. 2  is a schematic front elevation view of a reactant mixture injection system.  
         [0014]      FIG. 3  is a flowchart illustrating the method of controlling the reactant mixture injection system. 
     
    
     DETAILED DESCRIPTION  
       [0015]     Referring now to  FIG. 1 , a multi-reactant injection system  10  is illustrated that may be used to inject a silicone sealant mixture on a production line. The system  10  uses a robot  12  to which a mixing chamber  14  is attached. A multiple component reactant mixture is injected through the mixing chamber  14  into a part  16  as it is moved by a conveyor  18 .  
         [0016]     Referring now to  FIG. 2 , the multi-reactant injection system  10  is shown in greater detail. A catalyst supply  40  provides a catalyst to a metering ram  38  through a catalyst supply conduit  60 . A catalyst shutoff valve  52  may be located in the catalyst supply conduit  60  between the catalyst supply  40  and the metering ram  38 . The catalyst shutoff valve  52  can be used to control the flow of catalyst to the metering ram  38  and to prevent catalyst from flowing back into the catalyst supply  40 . Similarly, a base supply  42  provides a base to the metering ram  38  through a base supply conduit  62 . A base shutoff valve  54  may be located in the base supply conduit  62  between the base supply  42  and the metering ram  38 . The base shutoff valve  54  can be used to control the flow of the base to the metering ram  38  and to prevent the base from flowing back into the base supply  42 .  
         [0017]     The metering ram  38  injects the catalyst under pressure into a catalyst conduit  64  and injects the base under pressure into a base conduit  66 . Optionally, individual metering rams could be used to pressurize the reactant components. For example, a first metering ram could be used to pressurize the base and a second metering ram could be used to pressurize the catalyst. The catalyst conduit  64  and the base conduit  66  can be made of a flexible material, such as rubber. Optionally, a portion of the catalyst conduit  64  or the base conduit  66  can be made of a flexible material while the remainder is made of a more rigid material such as steel or aluminum tubing.  
         [0018]     The catalyst conduit  64  and the base conduit  66  fluidly connect the metering ram  38  to a catalyst flow meter  56  and a base flow meter  58 , respectively. A typical flow meter contains sensors (not shown) that measure flow rate, density, temperature, and the volume of a reactant component that passes through the flow meter. Alternately, a single flow meter may be used in the multi-reactant injection system  10  to measure the volume of a reactant component.  
         [0019]     The catalyst and the base are provided to the mixing chamber  14  by a catalyst junction conduit  76  and a base junction conduit  78 . The catalyst junction conduit  76  connects the catalyst flow meter  56  to the mixing chamber  14 . Similarly, the base junction conduit  78  connects the base flow meter  58  to the mixing chamber  14 . The catalyst j unction conduit  76  may contain a catalyst gun valve  68  that controls the flow of the catalyst. Likewise, the base junction conduit  78  may contain a base gun valve  70  that controls the flow of the base. The catalyst gun valve  68  and the base gun valve  70  can be placed in close proximity to the mixing chamber  14  to reduce the possibility of reactant mixture entering the catalyst junction conduit  76  and the base junction conduit  78 , respectively.  
         [0020]     A catalyst pressure sensor  72  and a base pressure sensor  74  can be used to detect pressure in the multi-reactant injection system  10 . The catalyst pressure sensor  72  can be located between the mixing chamber  14  and the metering ram  38 . For example, the catalyst pressure sensor  72  could be located in the catalyst junction conduit  76 , the catalyst gun valve  68 , or the catalyst conduit  64 . Likewise, the base pressure sensor  74  can be located between the metering chamber  14  and the metering ram  38  in locations such as the base junction conduit  78 , the base gun valve  70 , or the base conduit  66 . Alternately, a single catalyst pressure sensor  72  or a single base pressure sensor  74  may be used to monitor pressure.  
         [0021]     One embodiment of the process of the present invention is described with reference to  FIG. 3 . The process begins in the first step  80  with a robot  12  positioning the mixing chamber  14  and the nozzle  24  adjacent to the part  16 . The catalyst shutoff valve  52 , the base shutoff valve  54 , the catalyst gun valve  68 , and the base gun valve  70  are opened. Alternately, the catalyst shutoff valve  52 , the base shutoff valve  54 , the catalyst gun valve  68  and the base gun valve  70  can be opened before or at the same time the robot  12  positions the mixing chamber  14  and the nozzle  24  adjacent to the part  16 .  
         [0022]     Next, at  82 , the metering ram  38  is actuated to pressurize the multi-reactant injection system  10  and dispense the reactant mixture through the mixing chamber  14  and the nozzle  24  and into the part  16 . Alternately, the catalyst shutoff valve  52  and the base shutoff valve  54  can be closed before the metering ram is advanced to prevent the reactant components from being pushed back into the catalyst supply  40  and the base supply  42 .  
         [0023]     At  84 , a measured pressure value is compared to a predetermined pressure value. If the measured pressure value is less than the predetermined pressure value, the actuation of the metering ram  38  continues as depicted by the loop returning to  82 . The measured pressure value is provided by the catalyst pressure sensor  72  or the base pressure sensor  74 . Alternately, the measured pressure value can be provided by both the catalyst pressure sensor  72  and the base pressure sensor  74 .  
         [0024]     At  86 , if the measured pressure value is greater than or equal to the predetermined pressure value, the metering ram  38  is stopped. In another embodiment the catalyst gun valve  68  and the base gun valve  70  may be closed before stopping the metering ram  38 . In yet another embodiment, the catalyst shutoff valve  52  and the base shutoff valve  54  may be closed before stopping the metering ram  38 . In still another embodiment the catalyst shutoff valve  52 , the base shutoff valve  54 , the catalyst gun valve  68 , and the base gun valve  70  can be closed before stopping the metering ram  38 .  
         [0025]     In the next step, at  88 , a measured volume value is compared to a predetermined volume range. The measured volume value is the volume of a reactant component that passes through a flow meter. The measured pressure value is provided by a catalyst flow meter  56  or a base flow meter  58 . If the measured volume value is within the predetermined volume range the part is accepted as shown at  90 . If the measured volume value is outside the predetermined volume range, then the part is rejected as shown at  92 . In another embodiment, the measured volume value is provided by both the catalyst flow meter  56  and the base flow meter  58 .  
         [0026]     While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.