Abstract:
Disclosed is a fluid dispenser, comprising a main body having an elongate bore formed therethrough; a dispensing rod having a tip, the dispensing rod being extendably movable along an axis of the elongate bore to dispense fluid; and a nozzle assembly comprising a nozzle having a contact surface that includes an exit orifice for dispensing the fluid from the elongate bore, and a nozzle holder for holding the nozzle. The nozzle is received by the main body to define a transverse gap that allows the nozzle to be movable transversely within the nozzle holder and with respect to the axis of the elongate bore to align the exit orifice with the dispensing rod, upon the tip of the dispensing rod being urged against the contact surface of the nozzle. Also disclosed is a nozzle assembly for a fluid dispenser, as well as a method of assembling a fluid dispenser.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to a fluid dispenser with a self-aligning nozzle, and a method of assembling the fluid dispenser. 
       BACKGROUND 
       [0002]    Fluid dispensers are widely used in industry, especially in the electronics manufacturing field, for dispensing viscous materials, such as solder fluxes, epoxy, silicon and so on. These dispensers can be classed according to their respective dispensing principles, such as time-pressure dispensing, rotary-screw dispensing, positive displacement dispensing, and jet dispensing. 
         [0003]    In a dispensing system, the dispenser is typically mounted on a movable platform which provides automatic and accurate motion for the dispenser in three dimensions relative to the substrate to which material is to be applied. Alternatively, the motion can be realized by combining the movements of the platform and the substrate. 
         [0004]    The choice of dispenser is mostly determined by the application requirements of the electronic manufacturing process. These might include the viscosity of the dispensed material, desired dispense pattern on the substrate, dispensed dot dimension, quantity of dispensed units per hour, selected dispensable area and so on. In some applications, each component on the substrate to which fluid is to be dispensed has a specific area, and is not permitted to contact the dispenser tip. In these applications, the dispenser must dispense droplets in a controlled manner at a certain non-contact distance from the substrate. Dispensers with such a capability are usually called jet dispensers, dot jetting machines, or jet pumps. 
         [0005]    Normally, a jet dispenser comprises an actuator, a fluid chamber, a nozzle, a nozzle holder, a piston, a syringe and several seals. The actuator provides reciprocating movement to the piston by connecting or coupling with the piston. Presently, several kinds of actuators are known, such as pneumatic, piezo-electrical, and linear solenoid valve actuators. The fluid chamber is connected with the syringe, where the fluid is pressurized by compressed air so as to have a constant flow rate to supply viscous fluid to the nozzle through the fluid path between the syringe and the fluid chamber. The nozzle may be removable, and is typically held or pressed by the nozzle holder by screwing or clamping to contact the fluid chamber tightly. Alternatively, if the nozzle is not removable, it may be integrated into one part with the nozzle holder. During a dispensing operation, the actuator moves the piston and imparts sufficient momentum to the fluid in the fluid chamber to force droplets through the exit orifice of the nozzle, while the viscous fluid is supplied into the fluid chamber continuously from the syringe. 
         [0006]    One of the critical performance criteria for jet dispensers is repeatability. This refers to the droplet variation under the same dispensing parameters after re-assembling the nozzle or fluid chamber. Re-assembly is typically required periodically due to cleaning of the dispenser. The variation of the alignment between the piston and the nozzle after each disassembly and re-assembly may influence the repeatability. Such variation can also have a significant effect on the jetting capability. 
         [0007]    Currently known jet dispensers usually adopt special positioning parts, such as linear bearings, plastic guides, or static seals in order to precisely align the piston and nozzle. The alignment is realized by very fine machining and assembly tolerances or by using special tools. Fine tolerances need precise machinery and very skilled technicians, which increases the machining complexity. Also, complex machining processes may also cause operating parameters of the dispensing process to depart from desired parameters. Additionally, the positioning parts will inevitably be subject to abrasion since they are in constant contact with the piston during its reciprocating movement. Once the abrasion reaches a certain threshold, the positioning parts will cease to be effective. 
         [0008]    The present invention seeks to at least partly overcome one or more of the above problems. 
       SUMMARY 
       [0009]    Certain embodiments of the invention relate to a fluid dispenser, comprising:
       a main body having an elongate bore formed therethrough;   a dispensing rod having a tip, the dispensing rod being extendably movable along an axis of the elongate bore to dispense fluid; and   a nozzle assembly comprising a nozzle having a contact surface that includes an exit orifice for dispensing the fluid from the elongate bore, and a nozzle holder for holding the nozzle, the nozzle being received by the main body to define a transverse gap that allows the nozzle to be movable transversely within the nozzle holder and with respect to the axis of the elongate bore to align the exit orifice with the dispensing rod, upon the tip of the dispensing rod being urged against the contact surface of the nozzle.       
 
         [0013]    Other embodiments relate to a nozzle assembly for a fluid dispenser, the fluid dispenser comprising a main body having an elongate bore formed therethrough, a dispensing rod having a tip, the dispensing rod being extendably movable along an axis of the elongate bore to dispense fluid, and a nozzle coupling section, the nozzle assembly comprising:
       a nozzle having a contact surface that includes an exit orifice; and   a nozzle holder for holding the nozzle,   wherein the nozzle is receivable in the nozzle coupling section to define a transverse gap that allows the nozzle to be movable transversely with respect to the axis of the elongate bore to align the exit orifice of the nozzle with the dispensing rod, upon the tip of the dispensing rod being urged against the contact surface of the nozzle.       
 
         [0017]    Further embodiments relate to a method of assembling a fluid dispenser, the method comprising the steps of:
       providing a dispenser body having an elongate bore formed therethrough, a dispensing rod having a tip, the dispensing rod being extendably movable along an axis of the elongate bore to dispense fluid, and a nozzle coupling section;   providing a nozzle assembly which comprises a nozzle having a contact surface that includes an exit orifice, and a nozzle holder for holding the nozzle;   partially retracting the tip of the dispensing rod;   coupling the nozzle holder to the nozzle coupling section to define a transverse gap that allows the nozzle to be movable transversely with respect to the axis of the elongate bore to align the exit orifice of the nozzle with the dispensing rod, upon the tip of the dispensing rod being urged against the contact surface of the nozzle;   restricting movement of the nozzle along the axis of the elongate bore;   extending the tip of the dispensing rod to contact the contact surface of the nozzle, thereby moving the nozzle transversely within the nozzle holder and with respect to the axis of the elongate bore; and   repeatedly retracting and extending the tip until the exit orifice of the nozzle is aligned with the axis of the dispensing rod.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Embodiments of the invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings in which: 
           [0026]      FIG. 1  is a cross-sectional view through a fluid dispensing apparatus according to certain embodiments of the invention; 
           [0027]      FIG. 2  is a close-up view of part of the apparatus of  FIG. 1 ; and 
           [0028]      FIG. 3  is a flow diagram of a process for assembling a fluid dispensing apparatus. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Referring to  FIG. 1 , there is shown an embodiment of a fluid dispenser (in this embodiment, a jet dispenser)  10 . The fluid dispenser  10  has a main body comprising a support frame or upper chamber  11  and a fluid chamber  19  coupled to the support frame  11 . The fluid chamber  19  stores and provides fluid. 
         [0030]    Interposed between the support frame  11  and fluid chamber  19  is a layer or block of thermally insulating material  21 . The insulation block  21  advantageously prevents or substantially reduces transfer of heat from the support frame  11  to the fluid chamber  19 , thus preventing fluid in the fluid chamber  19  from being heated, which might otherwise affect its physical properties and thus add variability to droplets of fluid dispensed from the fluid dispenser  10 . 
         [0031]    Housed within the support frame  11  is an actuator  13  for providing up-and-down reciprocating movement of a movable piston rod (also referred to herein as a dispensing rod)  14  within an elongate bore  30  which terminates at a fluid dispensing end  31 . The piston rod  14  moves along an axis (not shown) of the elongate bore  30 . The actuator  13  may be any suitable actuator known in the art, for example a piezoelectric actuator, a pneumatic actuator or a linear solenoid valve actuator. Operation of the actuator  13  may be controlled by a programmable microcontroller (not shown) of known design. 
         [0032]    On either side of the insulation block  21 , and surrounding the piston rod  14 , are seals  15  and  25  for preventing ingress of fluid into the upper chamber  11 . 
         [0033]    The fluid chamber  19  comprises a fluid inlet channel  16  which is in fluid communication with the elongate bore  30 . The fluid inlet channel  16  is inclined with respect to the horizontal. Fluid from a syringe  12  (which may store solder flux, adhesive or other viscous liquids) continuously flows into the fluid inlet channel  16  and down the incline of the fluid inlet channel  16 , and, when the piston rod  14  is retracted, flows into the elongate bore  30  and is available for dispensing on a down-stroke of the piston rod  14 . An end seal  18  is arranged at an end of the fluid inlet channel  16  that is opposite to the elongate bore  30  to prevent egress of the fluid from the fluid inlet channel  16 . 
         [0034]    Coupled to the lower end of fluid chamber  19  is a nozzle assembly, including a nozzle holder  22  and a nozzle  24  which is housed within an internal space defined between the nozzle holder  22  and the fluid chamber  19 , with nozzle  24  abutting against a contact surface  20  of the fluid chamber  19 . The nozzle holder  22  is preferably attached to the fluid chamber  19  by a nozzle coupling section (shown as a threaded neck  38  connection). 
         [0035]    As shown in  FIG. 2 , the nozzle  24  comprises a circular collar  48  having a curved surface portion  33 , a protruding section  36  extending from the circular collar  48  and an orifice  28 . The orifice  28  is located at the centre of the curved surface portion  33  of the circular collar  48 . The nozzle holder  22 , on the other hand, comprises an aperture  35  through which the protruding section  36  of the nozzle  24  is fitted. As the diameter of the circular collar  48  is larger than the width of the aperture  35 , a contact surface  58  of the nozzle holder  22  abuts against the circular collar  48  to prevent the nozzle  24  from sliding through the aperture  35 . Moreover, when the nozzle holder  22  and the nozzle  24  are in place on the lower end of the fluid chamber  19 , a transverse gap  26  is defined between an outer perimeter of the nozzle  24  and an inner surface of the fluid chamber  19 . This is because the width of the internal space (as defined by the nozzle holder  22  and the fluid chamber  19 ) is larger than the diameter of the circular collar  48  of the nozzle  24 . Likewise, an additional transverse gap  27  is formed between the protruding section  36  and the aperture  35 , because the width of the aperture  35  is larger than the diameter of the protruding section  36  of the nozzle  24 . In consequence, the nozzle  24  is movable laterally within the defined internal space, to the extent allowed by transverse gaps  26 ,  27 , for self-alignment of the orifice  28  with the piston rod  14 . Each gap  26 ,  27  is preferably larger than about 20 um. 
         [0036]    The curved surface portion  33  is a concave indentation formed in the nozzle  24 , and has a shape which is complementary to the curved shape of the tip  29  of the piston rod  14 . Due to the presence of transverse gap  26  (between the nozzle  24  and the fluid chamber  19 ) and the transverse gap  27  (between the nozzle holder  22  and the nozzle  24 ), the nozzle  24  is movable in lateral directions within the nozzle holder  22  such that a downward extension of the piston rod  14  along the elongate bore  30  urges the surface portion  33  of the nozzle  22  transversely (i.e. orthogonal to the bore axis) to align the orifice  28  with the piston rod  14 . As such, the mating curved surfaces  33  and  29  together provide a self-alignment feature for the nozzle  24 , to ensure that the orifice  28  is substantially aligned with the piston rod  14 , and thereby ensuring greater consistency of droplet ejection during operation of the fluid dispenser  10  or between disassembly and re-assembly of the fluid dispenser  10 . 
         [0037]    As shown in  FIG. 1  and  FIG. 2 , the contact surface  33  may be a truncated sphere or truncated spheroid. The curved surface  33  may also have alternative shapes, such as a conical shape, e.g., an inverted cone with its apex located at the entry to the exit orifice  28 . 
         [0038]    It will be appreciated that the curved surface  33  need not be concave, and in fact in some embodiments may be convex. In such embodiments, the tip  29  of the piston rod  14  may have the opposite curvature than that shown in  FIG. 1  and  FIG. 2  (i.e., be concave) in order to mate with the convex curved surface  33  and provide the self-alignment feature. 
         [0039]    Referring now to  FIG. 3 , there is shown an embodiment of a method  40  of assembling the fluid dispenser  10 . 
         [0040]    The method  40  begins with the nozzle holder  22  detached from the remainder of the fluid dispenser  10  (i.e., detached from the fluid chamber  19 ). At step  41 , the actuator  13  of the fluid dispenser  10  retracts the piston rod  14  such that it is at a distance above the intended position of the curved surface  33  (i.e., the position of the curved surface  33  when the nozzle holder  22  is attached), and holds the piston rod  14  at that position. Preferably, the piston rod  14  is retracted until its tip  29  is retracted beyond the contact surface  20  of the fluid chamber  19 . 
         [0041]    At step  42 , the nozzle  24  is placed adjacent to the fluid chamber  19  and the nozzle holder  22  is placed on the threaded neck  38 , and screwed onto the neck  38  until the circular collar  48  of the nozzle  24  is lightly secured against the contact surface  20  of the fluid chamber  19 , as well and against the contact surface  58  of the nozzle holder  22 , with a small torque (e.g. 2 kgf.cm -3.5 kgf.cm). The tightening torque applied by nozzle holder  22  is preferably increased until it reaches a desired threshold (e.g. 2 kgf.cm-3.5 kgf.cm). 
         [0042]    At step  43  the actuator  13  extends the piston rod  14  such that the tip  29  of piston rod  14  contacts the curved surface  33  of the nozzle  24 . Then, at step  44 , jetting operation parameters (such as stroke and open/close time) of the fluid dispenser  10  are set (for example, by programming the microcontroller), and the fluid dispenser  10  commences a number of consecutive jetting operations, for example, 100 times or 5 0  times. If there is any misalignment between the exit orifice  28  of the nozzle  24  and the axis of the elongate bore  30  of the fluid dispenser  10 , the repeated impact of the tip  29  of the piston rod  14  on the curved surface  33  during the consecutive jetting operations will tend to move the nozzle  24  laterally within the gap  26  (since the nozzle  24  is only lightly held between the nozzle holder  22  and contact surface  20 ), as previously described, thus aligning the exit orifice  28  with the piston rod  14 . 
         [0043]    At step  45  the microcontroller of fluid dispenser  10  instructs the actuator  13  to retract the piston rod  14  again, for example to its earlier retracted position, and to hold it at that position. At this point the nozzle holder  22  can be tightened with a relatively larger torque (e.g. 22 kgf.cm-32 kgf.cm) so as to securely hold the nozzle  24  against the contact surface  20  (step  46 ). Then, at step  47 , the actuator  13  can be instructed to extend the piston  14  again. At this point the alignment procedure of the exit orifice  28  of the nozzle  24  and the piston rod  14  is finished and the fluid dispenser  10  is ready for dispensing operations (step  48 ). 
         [0044]    Embodiments of the invention can self-align the nozzle  24  with the piston rod  14  very precisely during assembly as well as during dispensing. Moreover, due to the complementary shapes of the nozzle surface and the piston rod tip, the variation of the aligned position after respective re-assemblies is very small, which improves the repeatability of the fluid dispenser  10 . The alignment can be realised in a very easy and convenient manner. In addition, the center positions of the piston rod  14  and the nozzle  24  can be aligned automatically, without the use of special measurement tools to perform alignment calibration, and without requiring fine tolerances and special guiding parts. The nozzle holder  22 , the nozzle  24  and the piston rod  14  can be manufactured very easily and with coarse tolerances. By avoiding fine tolerances it is possible to eliminate precise positioning parts which continually contact and have abrasion with the piston rod  14 . Thus, embodiments of the invention reduce the cost and increase the abrasion lifetime of the piston. 
         [0045]    Although particular embodiments of the invention have been described in detail, many modifications and variations are possible within the scope of the invention, as will be clear to a skilled reader.