Abstract:
A rotary dispenser that provides for airlessly applying a fluidic coating material to a target surface. The rotary dispenser of the present invention includes an angled fluidic passage therein, a fluid control body and a motor driven shaft to which the rotary dispenser is operationally attached. The rotary dispenser, with its angled fluid passage, provides a flow conduit which produces a series of overlapping circular spray patterns. The resulting spray patterns can be controlled to provide a narrow line spray pattern with clearly defined edges. Another embodiment of the present invention provides a spray pattern for coating the interior surface of hollow objects. A method of using the rotary dispenser in various coating applications is also disclosed.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to systems for depositing a material onto a surface, and more particularly, to spraying devices for spraying coatings onto production articles, such as circuit boards, in the conformal coating industry. Coating spraying devices are as well used for coating the interior surfaces of hollow objects.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field  
           [0003]    Uniform thickness coatings are often applied over sections of circuit boards. The coatings prevent water vapor, gases, or fluids from corroding the electrical connections on a circuit board. The coatings may comprise a wide variety of materials such as ultraviolet (UV) acrylic gels, moisture and thermal cure silicones, and the like.  
           [0004]    2. Related Art  
           [0005]    Coatings are typically applied to a circuit board using devices such as spray guns or spray nozzles. Such devices generally include a liquid spray material that is atomized by compressed air and is then directed toward the surface to be coated. The spraying devices are commonly attached to an apparatus, such as a multi-degree of freedom robotic positioning apparatus, that provides accurate positional displacement relative to the article being coated.  
           [0006]    As electronic components mounted on circuit boards become smaller, and more compactly spaced, known large diameter spray nozzles can no longer provide the edge control necessary to provide accurate coating deposition in particular areas of circuit boards. The edge of the conformal coating must be accurately maintained over large areas of the circuit board, while simultaneously the degree of spattering or erroneous deposition of coating material must be minimized.  
           [0007]    Furthermore, there is now an increasingly common requirement for providing a small diameter spray pattern with clearly defined edges to provide the accuracy and precision required to produce the spray in the narrowly defined space created by closely spaced electronic components.  
         SUMMARY OF THE INVENTION  
         [0008]    In order to overcome the above deficiencies, the present invention provides a rotary dispenser that produces a circular spray pattern whose edge can be precisely controlled, by using a fluid dispensing conduit which extends at an oblique angle with respect to the axis of rotation of the rotary dispenser. The fluid dispensing conduit extends from an outer, planar surface of the rotary dispenser, to the central interior of the rotary dispenser.  
           [0009]    For generating a round spray pattern, the rotary dispenser is rotated about its longitudinal axis while a coating material is forced through the rotary dispenser, producing a spray pattern such as round. This round spray pattern is then projected onto a surface, such as, inter alia, a circuit board surface. The rotary dispenser can then be moved laterally, while continuously dispensing coating material, to produce a band of coating material having clearly defined edges.  
           [0010]    In a first general aspect, the present invention provides apparatus which includes a drive motor; a rotary shaft, having a first end and a second end, said first end operationally coupled to said drive motor; at least one fluid dispensing conduit, within said rotary shaft, having a first centerline and a second centerline, and an outlet positioned at said second end of said rotary shaft; and wherein an angle exists between said first centerline and said second centerline, said angle being an oblique angle.  
           [0011]    In a second general aspect, the present invention provides a coating application system comprising: a supply of fluidic coating material; a fluidic coating material control system for supplying said fluidic coating material to a material discharge system; a coating material supply system in communication with said material discharge system; a rotary dispenser operationally coupled to said material discharge system; an in-line drive system, for supplying motive power to move said rotary dispenser in a rotary direction and in a lateral direction, said drive system operationally coupled to said rotary dispenser; and a fluid passage extending through said rotary dispenser, said fluid passage having a first end in communication with said material discharge system and a second end in communication with an outlet opening, wherein said fluid passage forms an oblique angle between said first end and said second end.  
           [0012]    In a third general aspect, the present invention provides a method for applying a coating material, said method comprising the steps of: providing a rotary dispenser having a coating material supply chamber therein, and a fluid dispensing conduit therein, wherein said fluid dispensing conduit is operationally coupled to said coating material supply chamber, and wherein the fluid dispensing conduit is positioned at an oblique angle to said coating material supply chamber; providing a supply of coating material to said rotary dispenser; coupling said dispenser to a drive motor; rotating said rotary dispenser; and projecting the coating material toward a surface to form a pattern.  
           [0013]    In a fourth general aspect, the present invention provides an apparatus comprising: a robotic precision controller; a drive motor; a rotary shaft, having a first end and a second end, said first end operationally coupled to said drive motor; at least one fluid dispensing conduit, within said rotary shaft, having a first centerline and a second centerline, and an outlet positioned at said second end of said rotary shaft; and wherein an angle exists between said first centerline and said second centerline, said angle being an oblique angle.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The features of the present invention will best be understood from a detailed description of the invention and an embodiment thereof selected for the purposes of illustration and shown in the accompanying drawings in which:  
         [0015]    [0015]FIG. 1 is a front view of a rotary dispenser in accordance with an embodiment of the present invention;  
         [0016]    [0016]FIG. 2 is a bottom view of a rotary dispenser in accordance with an embodiment of the present invention;  
         [0017]    [0017]FIG. 3 is a cross-sectional side view of the rotary dispenser of FIG. 2;  
         [0018]    [0018]FIG. 4 is a top view of a representative coating pattern as deposited by the rotary dispenser of the present invention;  
         [0019]    [0019]FIG. 5 is a perspective view of a coating application apparatus including a rotary dispenser of the present invention;  
         [0020]    [0020]FIG. 6 is a front view of a robotic precision controller having a rotary dispenser of the present invention; and  
         [0021]    [0021]FIG. 7 is a top view of a robotic precision controller having a rotary dispenser of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    Although certain preferred embodiments of the present invention will be shown and described in detail, it should be understood that various changes and modifications may be made without departing from the scope of the appended claims. The scope of the present invention will in no way be limited to the number of constituting components, the materials thereof, the shapes thereof, the relative arrangement thereof, etc., and are disclosed simply as an example of an embodiment. The features and advantages of the present invention are illustrated in detail in the accompanying drawings, wherein like reference numerals refer to like elements throughout the drawings.  
         [0023]    Referring to FIG. 1, there is illustrated a front view of a rotary dispenser  10  in accordance with an embodiment of the present invention. The rotary dispenser  10  includes a coating material supply chamber  20  extending through a first section  50 , a second section  60  and a third section  70 . The rotary dispenser  10  also includes a fluid dispensing conduit  30 , which extends from the coating material supply chamber  20  to an outer face  40  of the rotary dispenser  10 .  
         [0024]    The size and shapes of first section  50 , a second section  60  and a third section  70  are shown in exemplary forms. The sizes and shapes can be adjusted to accommodate existing coating machinery wherein a known dispenser could be replaced with the novel rotary dispenser of the present invention. The rotary dispenser  10  is shaped to apply coating material to the interior of devices having geometries closely approximating the exterior of the rotary dispenser  10  such as, inter alia, test tubes, bottles, containers, etc. In an exemplary embodiment the rotary dispenser  10  is useful for printed circuit board coating applications, the overall height of the rotary dispenser  10  may be, inter alia, 0.300 inches, with the first section height being 0.15 inches, the second section height being 0.050 inches, and the third section height being 0.100 inches. The diameter of the coating material supply chamber  20  may be, inter alia, 0.047 inches to a depth of 0.227 inches. The diameter of the fluid dispensing conduit  30  may be, inter alia, 0.0156 inches.  
         [0025]    Alternative embodiments of the rotary dispenser  10  may include more than one coating material supply chamber  20 , or more than one fluid dispensing conduit  30 .  
         [0026]    [0026]FIG. 2 illustrates a bottom view of the rotary dispenser  10 . Opening  65  represents the outer terminus of fluid dispensing conduit  30 . As shown in FIG. 2, the fluid dispensing conduit  30  extends at an oblique angle from the coating material supply chamber  20  through the third section  70  of the rotary dispenser  10 . In an advantageous embodiment, the distance from the center of the coating material supply chamber  20  to the center of the opening  65  may be about 0.087 inches.  
         [0027]    [0027]FIG. 3 is a cross-sectional side view of the rotary dispenser  10 . The rotary dispenser  10  is free to rotate about longitudinal axis  35 , which may, but need not, coincide with the centerline of coating material supply chamber  20 . Fluid dispensing conduit  30  extends at an oblique angle from the coating material supply chamber  20  through the third section  70  of the rotary dispenser  10 . Centerline  45  of the fluid dispensing conduit  30  defines the angle θ between the fluid dispensing conduit  30  extends at an oblique angle from the coating material supply chamber  20  through the third section  70  of the rotary dispenser  10 . The angle θ may be such that the fluid dispensing conduit  30  extends to outer planar surface  40  or to outer peripheral surface  85  of the rotary dispenser  10 . In one advantageous embodiment, as illustrated in FIG. 3, an angle θ of 45 degrees is utilized.  
         [0028]    The rotary dispenser is commonly attached to an apparatus, such as a multi-degree of freedom robotic positioning apparatus, that provides accurate positional displacement relative to the article being coated. Therefore, when the rotary dispenser is moved in a horizontal direction relative to a surface, the rotary dispenser can create a round spray which produces a line narrower than about ⅛ inch.  
         [0029]    In operation, fluid coating material (not shown) is supplied under pressure to the coating material supply chamber  20 , and is then forced through the fluid dispensing conduit  30 . At the same time, the rotary dispenser  10  is rotated about longitudinal axis  35 , at some desired height above a target surface upon which the coating is to be deposited. The fluid coating material which issues from the outer face  40  will produce a round or circular spray pattern on the target surface. The pattern formed by the resultant deposited coating material will have a clearly defined edge. Also, the amount of spattering, or extraneous coating material deposited outside the circular pattern, is minimized or eliminated.  
         [0030]    The entire rotary dispenser  10  can simultaneously be moved in a lateral direction so that the spray pattern forms a continuous, elongated pattern on the target surface. Again, this elongated pattern will have a clearly defined edge, and spattering is minimized.  
         [0031]    [0031]FIG. 4 is a top view illustrating a representative coating pattern  75  as deposited by the rotary dispenser  10  of the present invention. Rotary dispenser  10  is positioned over upper surface  74  of target substrate  70 , and an initial circular pattern  71  (shown partially in phantom) is produced by the application of a coating material via rotary dispenser  10 . As the rotary dispenser  10  is moved in direction  73 , coating pattern  75  is produced, which has characteristically well-defined edges  72 .  
         [0032]    [0032]FIG. 5 is a perspective view of a coating application system  51  including a rotary dispenser  10  of the present invention. Coating application apparatus  51  includes a supply of fluidic coating material  52 , and a fluidic coating material control system  53  which controls the flow of the fluidic coating material  52  in the coating application system  51 . A coating material supply system  56  is operationally coupled to the fluidic coating material control system  53  and to a material discharge system  54 . The material discharge system  54  includes a rotary dispenser  10  of the present invention. A drive system  55  is operationally coupled to the rotary dispenser  10 . The drive system  10  provides motive force and controls the movement of the rotary dispenser  10  in its rotational movement, as well as the lateral movement of the rotary dispenser  10 .  
         [0033]    As used herein, the term “coating applicator” refers to a portion of a conformal coating system from which the conformal coating is dispensed, such as, for example, a dispensing valve or a spray valve. As used herein, the term “end effector” refers to any device(s) attached to an x, y, z, or other axis of movement to perform various applications, such as, for example, dispensing, pick and place, routing, etc.  
         [0034]    [0034]FIG. 6 is a front view of the conformal coating system  100  also shown in FIG. 7. As shown in FIG. 3, attached to end effector  126  is rotary dispenser  10  of coating valve  132 . Coating valve  132  uses conformal coating to dispense a pattern, such as, for example, a round spray pattern.  
         [0035]    [0035]FIG. 7 is a top view of an exemplary precision robotic controller or conformal coating system  100  according to the present invention. System  100 , according to the present invention, comprises frame  121 , Y axis ball screw slide  122 , X axis ball screw slide  124  and end effector  126 . End effector  126  is capable of rotation about the φ axis  118 . End effector  126  moves left and right along the Y axis by sliding along Y axis ball screw slide  122 . Similarly, end effector  126  moves back and forth along with frame members  128  and  130  and Y axis ball screw slide  122 , along X axis ball screw slide  124 .  
         [0036]    The embodiments described above are directed toward the coating of substantially planar articles, such as, inter alia, circuit boards. However, in an alternative application, the rotary dispenser  10  of the present invention could be utilized to coat the interior of hollow articles, such as, inter alia, syringes. In this embodiment, the rotary dispenser  10 , or a plurality thereof, could be operationally mounted to an automated machine. The automated machine would provide positioning of the rotary dispenser  10  in the syringe, so that the entire interior surface of the syringe could be coated.  
         [0037]    The foregoing description of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed or to the materials in which the form may be embodied, and many modifications and variations are possible in light of the above teaching. For instance, the rotary dispenser of the present invention may be embodied of inter alia, 300 series stainless steel, for use in a printed circuit board coating application. Further, the rotary dispenser of the present invention is not limited to applying ultraviolet (UV) acrylic gels, and moisture and thermal cure silicones to circuit boards, but also can used to spray other materials such as paints, oils, inks, etc. The rotary dispenser can also be used to spray materials onto other surfaces besides circuit boards. The rotary dispenser of the present invention can spray materials with viscosities in the range from about 0 centipoise to about 50,000 centipoise. Such modifications and variations that may be apparent to a person skilled in the art are intended to be included within the scope of this invention as defined by the accompanying claims.