Abstract:
A needle cleaning system, for use with a liquid dispensing system that dispenses a quantity of material through a dispensing needle or transfer pin, includes a vacuuming device coupled with a residual material collection device, wherein the collection device includes at least one appropriately shaped orifice for receiving an end of the dispensing needle or pin. The liquid dispensing system further includes control means for periodically positioning the dispensing needle or pin relative the orifice in the collection device. The vacuuming device creates an airflow, which passes around the exterior of the needle or pin and into the collection device, thereby removing residual material from the exterior of the dispensing needle or pin without contact.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is directed generally to liquid dispensing systems having controllably movable cartridges and more specifically to liquid dispensing systems that utilize liquid dispensing needles or transfer pins and a system and method for the self-cleaning thereof.  
         BACKGROUND OF THE INVENTION  
         [0002]    Several types of prior art dispensing systems are used for dispensing metered amounts of liquid or paste for a variety of applications. One such application is in the assembly of printed circuit boards and integrated circuit chips. Dispensing systems are used in this application for the process of encapsulating the integrated circuits with an encapsulate material and in the process of under filling flip integrated circuit chips with an encapsulant. Prior art dispensing systems are also used for dispensing dots or balls of liquid epoxy or solder onto circuit boards and integrated circuits. The liquid epoxy and solder is primarily used to connect components within an integrated circuit.  
           [0003]    In a typical dispensing system, a pump and dispenser assembly is mounted to a moving assembly, such as a gantry, for moving the pump and dispenser assembly along three mutually orthogonal axes (x, y, z), by servomotors or other similar devices that are controlled by a computer system or controller. To dispense a volume of liquid on a circuit board or some other substrate at a desired location, the pump and dispenser assembly, which normally includes a nozzle coupled with a dispensing needle, is moved along the horizontal x and y axes until it is located over the desired location. The pump and dispenser assembly is then lowered along the vertical z-axis until the dispensing needle is at an appropriate height over the substrate, where it dispenses a metered volume of liquid through the needle. The pump and dispenser assembly is then raised along the z-axis, moved along the x and y axes to a next desired location and then lowered along the vertical z-axis to dispense a metered volume of liquid at the next location.  
           [0004]    In dispensing applications such as those described above, the accuracy of the volume of liquid dispensed by the system is an important feature of the system. These dispensing systems are effective in dispensing precise amounts of metered material onto a substrate, however, over time small an amount of residual or other material tends to build up on the exterior surface of the dispensing needle or pin. The build up of excess material leads to unwanted material drops, material splatter and or line/dot width variation.  
           [0005]    It is therefore desirable to have a dispensing system that is capable of periodically cleaning residual material from the exterior surface of the dispensing needle or transfer pin.  
         SUMMARY OF THE INVENTION  
         [0006]    In one aspect, the present invention is directed to a needle cleaning system for removing an amount of residual material from a liquid dispensing needle or pin. The system includes a container assembly having at least one orifice, a vacuum source operatively connected to the container assembly wherein the vacuum source creates an airflow through the at least one orifice into the container assembly and a control system that positions the liquid dispensing needle or pin relative to the at least one orifice in the container assembly wherein the residual material is removed from the dispensing needle or pin by the airflow.  
           [0007]    The system may be constructed and arranged such that the residual material is removed from the liquid dispensing needle or pin without contact occurring between the dispensing needle or pin and the container assembly. The system may include a disposable cup for collecting an amount of removed residual material. The system may include a tube for directing the airflow towards the bottom of the disposable cup. The container assembly may include a plurality of various diameter orifices to accommodate a variety of various gauge dispensing needles or pins. The vacuum source may be coupled with one or more of the plurality of different diameter orifices whereby an airflow is created through the one or more of the plurality of different diameter orifices into the container assembly.  
           [0008]    Another aspect of the invention is directed to a needle cleaning system for removing an amount of residual material from a liquid dispensing needle or pin where the system includes a container assembly having an iris-type shutter having a variable diameter opening, a vacuum source operatively connected to the iris-type shutter wherein the vacuum source creates an airflow through the variable diameter opening and into the container assembly and a control system that positions the liquid dispensing needle or pin relative to the iris-type shutter such that the airflow through the variable diameter opening causes the removal of the residual material from the dispensing needle or pin.  
           [0009]    The system may be constructed and arranged such that the diameter of the variable diameter opening of the iris-type shutter may be increased or decreased to accommodate a variety of different gauge dispensing needles or pins. The control system may be constructed and arranged to operatively control the diameter of the variable diameter opening of the iris-type shutter. The container assembly may further include a disposable cup for collecting an amount of removed residual material.  
           [0010]    Another aspect of the invention is directed to a self-cleaning liquid dispensing system. The system includes means for receiving a liquid from a liquid source, means for dispensing the liquid through a needle or pin onto a medium and means for removing an amount of residual material from an exterior portion of the needle or pin without contacting the needle or pin.  
           [0011]    The system may be constructed and arranged such that the means for removing residual material includes a needle cleaning system that includes a container assembly having at least one orifice, a vacuum source operatively connected to the container assembly wherein the vacuum source creates an airflow through at least one orifice into the container assembly and means for operatively positioning the liquid dispensing needle or pin relative to the at least one orifice wherein the residual material is removed from the dispensing needle or pin without contact between the dispensing needle or pin and the orifice. The system may be constructed and arranged such that the means for operatively positioning the liquid dispensing needle or pin relative to the orifice includes a computer control system.  
           [0012]    Another aspect of the invention is directed to a self-cleaning liquid dispensing system. The system includes at least one dispensing needle or pin, a needle cleaning system that includes at least one vacuum source for operatively removing residual material from the at least one dispensing needle or pin and means for operatively positioning one or more dispensing needles or pins relative to a vacuum source. The system may be constructed and arranged such that the needle cleaning system may include at least one container assembly. The container assembly may be constructed and arranged to include at least one orifice for receiving an end of a dispensing needle or pin. The container assembly may be constructed and arranged to include a plurality of various diameter orifices. The container assembly may be constructed and arranged to include at least one adjustable diameter orifice. The system may be constructed and arranged to include at least one vacuum source that may be coupled with the container assembly such that the vacuum source causes a stream of air to flow through an orifice and into the container assembly.  
           [0013]    Another aspect of the invention is directed to a method for cleaning residual material from a dispensing needle or pin in a liquid dispensing system. The method includes steps of supplying at least one container assembly having at least one orifice, positioning the needle or pin relative to the at least one orifice and supplying a vacuum source for creating an airflow through the orifice and into the container assembly wherein the airflow causes residual material to be pulled from the dispensing needle or pin. The method may further include the step of removing the residual material from the dispensing needle or pin without having contact between the dispensing needle or pin and the orifice. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    For a better understanding of the present invention, reference is made to the drawings, which are incorporated herein by reference, and in which:  
         [0015]    [0015]FIG. 1 is a part cross-sectional, part side view of a prior art liquid dispensing system;  
         [0016]    [0016]FIG. 2 is a block diagram illustrating a control system of the prior art liquid dispensing system of FIG. 1;  
         [0017]    [0017]FIG. 3 is a part cross-sectional, part side view of a liquid dispensing system incorporating a needle cleaning system according to a first embodiment of the invention;  
         [0018]    [0018]FIG. 4 is a top view of the needle cleaning system of FIG. 3;  
         [0019]    [0019]FIG. 5 is a block diagram illustrating a control system of the liquid dispensing system of FIGS. 3 and 4;  
         [0020]    [0020]FIG. 6A illustrates a partial broken away view of the needle cleaning system of FIGS. 3 and 4;  
         [0021]    [0021]FIG. 6B illustrates an enlarged view of the needle cleaning system of FIGS. 3, 4 and  6 A;  
         [0022]    [0022]FIG. 7 is a top view of a needle cleaning system having an adjustable diameter orifice according to a second embodiment of the present invention; and  
         [0023]    [0023]FIG. 8 is a block diagram illustrating a control system of a liquid dispensing system incorporating the needle cleaning system of FIG. 7. 
     
    
     DETAILED DESCRIPTION  
       [0024]    For purpose of illustration, the present invention will now be described with reference to a needle cleaning system for use with a controllable liquid dispensing system that uses a needle type device to dispense viscous materials onto a substrate, such as a printed circuit board. One skilled in the art will appreciate, however, that embodiments of the present invention are not limited to such dispensing systems, and may be used in other applications requiring dispensing of a controlled amount of material from a container through a needle, a transfer pin or other similar device,  
         [0025]    Referring to FIG. 1, a prior art controllable liquid dispensing system  10 , which includes a liquid pump and dispenser assembly  18  and a conveyor assembly  20  is shown. Liquid pump and dispenser assembly  18  can be one of a number of known systems, such as one of the different models of liquid dispenser systems sold by Speedline Technologies, Inc., Haverhill, Mass., under the trademark CAMALOT™ In the present example, the pump and dispenser assembly  18  includes a displacement pump  22  that receives liquid under pressure from a syringe  24 , and dispenses the liquid through a dispensing needle  26 . Displacement pump  22  is shown mounted to lead screws  30  for computer controlled movement along mutually orthogonal axes (x, y, z).  
         [0026]    The conveyor assembly  20  can be any one of a number of different positioning systems for transporting and aligning a workpiece with respect to the liquid pump and dispenser assembly  18 . In the present example, the conveyor assembly  20  has a pair of elongated parallel rails  40 ,  42  and a pair of elongated conveyors  44 ,  46  that extend along and next to the rails for supporting and transporting a workpiece  50 , such as a circuit board, along a direction of travel  52 . Motors (not shown) are mounted to the rails  40 ,  42  for driving the conveyors  44 ,  46 .  
         [0027]    As the workpiece  50  is transported into the liquid dispensing system  10 , a detector, such as a vision inspection system (not shown), detects when the workpiece  50  is in proper position for processing. With the workpiece  50  properly aligned, the liquid pump and dispenser assembly  18  controllably dispenses material onto the workpiece  50  for one of a number of different purposes as noted above. Additional conveyors or positioning systems (not shown) are typically employed for transporting the workpiece  50  to and from the conveyor assembly  20  during pre-processing and post-processing stages.  
         [0028]    For most applications, it is desirable that the dispenser assembly  18  be a precise distance above a substrate. For these applications, a height sensing device, such as a touch probe, can be used to measure the distance of the from the tip of dispensing needle  26  to the substrate to aid in proper positioning of the dispensing unit prior to dispensing. In the present example, a height-sensing device  54  is shown mounted to the displacement pump  22 . The height-sensing device  54  is responsible for determining the height of the dispensing needle  26  above the workpiece  50  and may operate as a mechanical touch probe or other similar device such as a laser sensor (not shown). One example of a height sensing device is described in U.S. Pat. No. 6,093,251, which is assigned to Speedline Technologies, Inc., Franklin, Mass., and which is incorporated herein by reference, although other height sensing devices are contemplated.  
         [0029]    Referring now to FIG. 2, a computer control system  56  for controlling different functions of the liquid dispensing system  10  of FIG. 1 is shown. The computer control system  56  is typically configured such that when a new type of workpiece  50  is provided to the liquid dispensing system  10  (e.g., a new type of printed circuit board), the locations, sizes and amounts of material that need to be dispensed by the liquid dispensing system  10  can be adjusted. The computer control system  56  is operatively connected to a pump and dispenser control system  58 , which is coupled to the liquid pump and dispenser assembly  18 . The pump and dispenser control system  58  is a standard control system as is known in the art and selectively determines the volume of material to be dispensed by liquid pump and dispenser assembly  18  onto workpiece  50 .  
         [0030]    The computer control system  56  is shown operatively connected to a drive mechanism  48 , which is connected to the lead screws  30 . By connecting the drive mechanism  48  to a standard power control system, such as a servomotor, the positioning of the liquid pump and dispenser assembly  18 , along mutually orthogonal axes (x, y, z), can be controlled. Height information generated by the height-sensing device  54  is used by the computer control system  56  and drive mechanism  48  to accurately position the dispensing needle  26  at a desired height. The computer control system  56  may also be used to control the operation of the conveyor assembly  20 .  
         [0031]    Referring now to FIGS. 3 through 6B, a needle cleaning system  60 , in accordance with certain embodiments of the present invention, is shown mechanically attached to rail  42 . In alternative embodiments, the needle cleaning system  60  may be attached to other parts of liquid dispensing system  10  or it may be a freestanding unit. The needle cleaning system  60  uses an orifice connected with a vacuum supply to create a high-speed stream of air for periodically suctioning residual or other material from the dispensing needle  26  as described below.  
         [0032]    In the present example, the needle cleaning system  60  includes a container assembly  62  for suctioning and collecting the residual material from dispensing needle  26 . The needle cleaning system  60  includes a pair of rotary dials  66 ,  68 , wherein each dial includes a plurality of cleaning orifices  70 . The rotary dials  66 ,  68  are rotationally mounted to a pair of platforms  72 ,  74 , which are in turn mounted to container assembly  62 . The platforms  72 ,  74  each have an opening that will allow an airflow  84  to pass through a chosen cleaning orifice  70  through a venturi tube  76  and into the container assembly  62 . The cleaning orifices  70  have a variety of different diameters, which allows the needle cleaning system  60  to accommodate different gauge dispensing needles  26 . A total of ten orifices  70  are shown, however, additional or fewer orifices may be employed as required. Prior to operation, an appropriate cleaning orifice  70  is chosen, whose dimensions correspond to the dimensions of the dispensing needle  26 .  
         [0033]    The container assembly  62  is operatively connected to a vacuum source  64  by a vacuum hose  82 . When the vacuum source  64  is initiated, it causes the airflow  84  to stream into the container assembly  62  through an orifice  70 . A set of cleaning parameters for the dispensing needle  26 , such as needle gauge, needle length and frequency of cleaning can be input into computer control system  56 . The cleaning parameters may be stored on magnetic media either internal or external to the computer control system  56  and loaded into the computer control system  56  using an appropriate magnetic reading apparatus as needed. Alternatively, an operator of the liquid dispensing system  10  may manually enter the cleaning parameters into the computer control system  56 . The cleaning parameters may also include the coordinates of the cleaning orifice  70  in relation to the dispensing needle  26 , the distance above the cleaning orifice  70  at which the needle  26  should be positioned at the beginning of the cleaning process, the distance into the cleaning orifice  70  that dispensing needle  26  should be inserted during cleaning, the rate at which the dispensing needle  26  should be advanced and the amount of vacuum pressure needed from vacuum source  64  for proper cleaning of the dispensing needle  26 .  
         [0034]    In the present embodiment, an appropriately dimensioned orifice  70  (i.e., an orifice whose diameter corresponds to the gauge of the dispensing needle being cleaned) may be selected or dialed by the computer control system  56  or may be manually selected by a user. In certain embodiments, different orifices may accommodate more than one gauge needle. For example, an orifice having a diameter of approximately 0.025 inches may appropriately accommodate needles having a range of outer diameters of approximately 0.014-0.009 inches. As described, only one orifice  70  is in operation at any given time, however, additional of the orifices  70  may be connected to the vacuum source  64  or to alternate vacuum sources and used concurrently.  
         [0035]    As illustrated, the computer control system  56  is operatively connected to the vacuum source  64 . Once the needle  26  is properly positioned over a cleaning orifice  70  in rotary dial  66 , as shown in FIG. 6, or just prior thereto, the computer control system  56  signals the vacuum source  64  to turn on. In alternative embodiments, a photocell or a group of photocells (not shown) or a proximity type sensing device may be positioned to detect the presence of a dispensing needle  26  to be cleaned. The photocells may be reflective photocells and may include LED&#39;s coupled with CCD arrays (not shown) that detect the presence of and or the distance an object (e.g., a dispensing needle  26 ) is to the rotary dials  66 ,  68 . Upon detection of a dispensing needle  26 , the photocell(s) will trigger the cleaning process by turning the vacuum source  64  on. After cleaning, as the dispensing needle is withdrawn from the cleaning system  60 , the photocells will trigger the vacuum source  64  to turn off. In this embodiment, the photocells help reduce the amount of circuitry needed, such as timers, to operate the needle cleaning system.  
         [0036]    In the present embodiment, when the vacuum source  64  is activated, it creates a suction force in vacuum hose  82 , which causes an airflow  84  to flow past the end of the dispensing needle  26 , through the selected orifice  70 , through the venturi tube  76  and into the container assembly  62 . After the airflow  84  exits the venturi tube  76  it experiences a first airflow reversal  86  at the bottom of container  90  and a second airflow reversal  88  again at the top of container  90 . The airflow reversals  86 ,  88  cause sufficient flow disruption so as to separate the liquid residue  92  from the airflow. The removed liquid residue  92  contacts the container bottom with sufficient momentum as to cause it to adhere to the bottom of the container.  
         [0037]    With the vacuum source  64  initiated, the computer control system  56  directs the drive mechanism  48  to lower the dispensing needle  26  into the selected orifice  70  an appropriate distance, preferably using the height information acquired from the height sensor  54 . The rate of movement of dispensing needle  26  in the z-axis may be governed by the computer control system  56  and may also be calibrated with regard to the gauge of the needle and the material being dispensed so as to minimize the time required to efficiently clean the dispensing needle  26  and return it to its primary function of dispensing liquid. Alternatively, the dispensing needle may be controlled at a preset speed wherein the needle cleaning system adapts to the presence of dispensing needle.  
         [0038]    In operation, as the dispensing needle  26  meets the airflow  84  created by the vacuum source  64 , the airflow  84  will pull any residual material from the exterior surface of the dispensing needle  26 . In the present embodiment, once the residual material is removed from the dispensing needle  26 , it will flow along with the rapidly moving airstream through venturi tube  76  and into a disposable contain  90 , as above-described.  
         [0039]    Alternatively, the vacuum source  64  may be connected directly to a selected orifice  70 , such that the residual material removed from dispensing needle  26  passes directly into the vacuum hose  82 , rather than into the disposable cup  90 . As described, the vacuum source  64  is controlled by the computer control system  56 , however, the vacuum source  64  may be manually controlled or left continuously running during operation of the liquid dispensing system  10 . Prior to the cleaning operation as described above, the computer control system  56  will preferably shut off the liquid pump and dispenser assembly  18 , so that additional liquid will not be removed from within dispensing needle  26  during cleaning.  
         [0040]    For illustration purposes, a single pump and dispenser assembly  18  is shown. In other embodiments, the needle cleaning system  60  may be employed by various other liquid dispensing systems, such as the systems described in U.S. Pat. No. 6,082,289, which is assigned to Speedline Technologies, Inc., Haverhill, Mass., and which is incorporated herein by reference. These liquid dispensing systems may employ multiple cartridges and therefore multiple dispensing needles, which may vary in size and shape. The needle cleaning system  60  may accommodate dispensing systems using multiple dispensing needles by individually or simultaneously introducing each dispensing needle to a properly dimensioned cleaning orifice  70 . To accommodate these dispensing systems, multiple orifices  70  may be controllably selected by an operator or by the computer control system  56  during cleaning. In an alternative embodiment, a single cleaning system having multiple various diameter cleaning orifices, each attached to a vacuum source, may be used.  
         [0041]    Also for illustration, a single conveyor assembly is shown, however, it is contemplated that multiple conveyors may be simultaneously employed by dispensing system  10 .  
         [0042]    Referring now to FIGS. 7 and 8, an alternative embodiment of the present invention is contemplated, wherein the needle cleaning system  10  incorporates an adjustable diameter orifice  100  for accommodating multiple or various gauge dispensing needles  26 . The adjustable diameter orifice  100  is shown having an iris shutter arrangement, although other types of adjustable diameter orifices are contemplated, wherein the diameter of the orifice  100  may be controlled by computer control system  56  or may be manually adjusted by a user. This embodiment of the present invention may be programmed to accommodate all of the types of dispensing systems discussed above including dispensing systems employing single or multiple dispensing needles and single or multiple conveyor systems.  
         [0043]    Having thus described at least one illustrative embodiment of the invention, various alterations, modifications and improvements will readily occur to those skilled in the art. Such alterations, modifications and improvements are intended to be within the scope and spirit of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention&#39;s limit is defined only in the following claims and the equivalents thereto.