Abstract:
A pusher is disposed to drive material out of a dispensing outlet and extends into a first chamber that is configured to contain a hydraulic fluid disposed to drive the pusher. A second chamber is configured to exchange hydraulic fluid with the first chamber. A fluid control mechanism is disposed between the first chamber and the second chamber. Air under pressure is applied to urge a rapidly transforming material to flow toward one portion of a bifurcated chamber from another portion of the bifurcated chamber. The driven rapidly transforming material is allowed to drive a material from a dispensing outlet. At least a portion of the rapidly transforming material is caused to physically transform to a form that is more resistant to flowing. The dispensing outlet is caused to change position. At least a portion of the rapidly transforming material is caused to physically transform away from the form that is more resistant to flowing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Serial No. 60/146,199 entitled “DISPENSING APPARATUS AND METHOD” filed on Jul. 29, 1999, incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This application relates to dispensing. 
     Many applications call for an automatic mechanism that dispenses a desired amount of a material. For example, in an automatic assembly line used in producing semiconductor-based electronic circuits, when an electronic part such as a chip resistor, a capacitor, or a packaged integrated circuit (“IC”) is to be mounted onto a substrate having a circuit pattern formed thereon, creamy solder is deposited in a selected position on the substrate by use of a dispenser and then the electronic part is automatically mounted in the selected position by use of a chip mounter. 
     The dispenser typically includes a tube needle fixed at a bottom end of the dispenser, a syringe that stores the creamy solder above the tube needle, and a plunger housed within the syringe above the creamy solder in an upwardly and downwardly movable manner for discharging the creamy solder by a downward displacement of the plunger towards the tube needle. The downward displacement of the plunger pushes the creamy solder down within the syringe and discharges the creamy solder from a bottom end of the tube needle. 
     Typically, the plunger is driven down towards the tube needle by air under pressure. However, air under pressure compresses readily and can escape around the plunger into a space below the plunger. As a result, as air is added under pressure, the plunger may not reliably move downward as desired and creamy solder may not be dispensed in a desired amount. 
     A desired amount of material may be dispensed by a device that employs an auger or screw that is rotated to cause dispensing. In the device, the rotative force is converted to linear, outward force that drives the material being dispensed. 
     SUMMARY OF THE INVENTION 
     Apparatus is provided that includes a dispensing outlet and a pusher disposed above the dispensing outlet. The apparatus further includes a first chamber into which the pusher extends. The first chamber is configured to contain a variable amount of a hydraulic fluid above the pusher. The apparatus further includes a second chamber configured to exchange hydraulic fluid with the first chamber, and a fluid control mechanism disposed between the first chamber and the second chamber. Accordingly, material can be dispensed by the pusher under careful control, to help prevent the material from being dispensed in undesired quantities or at undesired times. In particular, a solder dispensing mechanism can be provided that delivers, from a solder syringe, highly controlled quantities of solder at specified locations in rapid succession. 
     Other features and advantages will become apparent from the following description, including the drawings, and from the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram of dispensing apparatus. 
     FIGS. 2,  4 , and  5 A are side views of dispensing apparatus. 
     FIG. 3 is a top view of a portion of dispensing apparatus. 
     FIG. 5B is a side view of a fluid control mechanism. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a block diagram of a dispensing system  10  in which a rapidly transforming (“RT”) material  12  such as a magneto-rheological (“MR”) material helps to control the amount of outgoing material  14  that is dispensed. Under typical conditions, the RT material is effectively a liquid or other substantially uncompressible fluid. In a hydraulic fashion, in response to a force emanating from a direction A, the RT material flows from a first part  16  to a second part  18  of a bifurcated chamber  20  through a passage  22 , causing a transfer mechanism  24  to drive the outgoing material in direction B. 
     When an activator  26  is toggled, the RT material in the passage undergoes a physical transformation to become effectively a solid and thereby blocks RT material from flowing through the passage. As a result, the force emanating from direction A does not reach the outgoing material, which is therefore no longer driven in direction B. 
     When the activator is toggled again, the RT material in the passage undergoes a reverting physical transformation, allowing RT material to resume flowing through the passage to drive the outgoing material further in direction B. 
     FIG. 2 (side view) and FIG. 3 (top view) illustrate an embodiment  30  of the dispensing system  10  (FIG. 1) in which the outgoing material  14  (FIG. 1) is or includes creamy solder  32  provided in a syringe  34  (e.g., a 10 cc syringe) having a tube needle  36 , the RT material  12  flows in response to air under pressure  38  such as air under a pressure of at least 50 psi, and the activator  26  (FIG. 1) includes a magnet actuating mechanism  40 . (In a typical embodiment, the air under pressure is under a pressure ten to twenty times greater than the air pressure in a conventional mechanism for dispensing solder from a syringe.) Embodiment  30  may have a diameter of approximately one inch. In embodiment  30 , outer and inner concentric chambers  42 ,  44  (FIGS. 2-3) serve as first and second parts  16 ,  18  of bifurcated chamber  20  (FIG.  1 ), transfer mechanism  24  (FIG. 1) includes piston  46  and spring  48 , and passage  22  (FIG. 1) includes passages  50 ,  52  and may have an overall width of approximately two to four times the thickness of a human hair. A piston ring  54  is disposed within outer chamber  42 . The air under pressure causes the piston ring to drive the RT material through the passages into the inner chamber. The RT material driven into the inner chamber forces piston  46  to move outward of the inner chamber (i.e., downward in FIG.  2 ), which drives creamy solder out the tube needle. In at least some cases, it is advantageous for the starting positions of the piston  46  and the piston ring  54  and the relative sizes of the outer and inner concentric chambers to be arranged complimentarily and commensurately so that the outer chamber holds most or all of the RT material when the syringe is effectively full and the inner chamber holds most or all of the RT material when the syringe is effectively spent. In a typical embodiment, the amount of RT material used is at least sufficient to effectively fill the inner chamber inward of the piston  46  when the syringe is effectively spent. Stop pins shown as posts in FIG. 2 may be used to block piston  54  from moving beyond a functional point. 
     The magnet actuating mechanism is able to removably impose a strong magnetic field within the passages so that at least some RT material in the passages undergoes a physical transformation to an effective solid and thereby blocks the flow of RT material through the passages. When the strong magnetic field is so imposed, RT material is blocked from entering the inner chamber, and the piston  46  no longer drives creamy solder out of the tube needle. When the strong magnetic field is removed, the transformed RT material in the passages undergoes a reverting physical transformation, once again allowing RT material to flow from the outer chamber through the passages to the inner chamber, which causes piston  46  to resume driving creamy solder out of the tube needle. 
     Thus, controlled, noncontinuous outward motion of piston  46  can be derived from air under continuous pressure, because the magnet actuating mechanism can turn the flow of RT material on and off. As a result, creamy solder can be driven out of the tube needle in controlled, desired portions at selected times. For example, a large amount of solder can be dispensed from the syringe at a particular spot by positioning the tube needle over the spot and letting the RT material flow through the passages for a commensurately long period of time. 
     The magnet actuating mechanism may operate by physically moving a magnet such as a natural magnet or an electromagnet to a position near the passages to impose the strong magnetic field and by physically moving the magnet to another position away from the passages to remove the strong magnetic field. The natural magnet may be or include a rare earth magnet of any size, e.g., a magnet having a diameter up to 2 inches in diameter, such as {fraction (1/16)} inch, {fraction (3/32)} inch, ⅛ inch, 0.25 inch, 0.5 inch, 0.75 inch, 1 inch, 1.25 inch, 1.5 inch, 1.75 inch, or 2 inches. Where the magnet is or includes an electromagnet, the strong magnetic field may be imposed by running a high electrical current through the electromagnet and the strong magnetic field may be removed by removing the high electrical current. 
     It may be desirable for the strong magnetic field to be imposed to block the flow of RT material when the dispensing system is turned off or unexpectedly loses all electrical power, such as in a general or local power failure. In such a case, the magnet actuating mechanism may include a natural magnet and may be arranged so that a force such as gravity or the force of a spring causes the no-power default position of the natural magnet to be near the passages to impose the strong magnetic field. Thus, if a malfunction causes the magnet actuating mechanism to lose electrical power but does not cause the air under pressure to cease pushing on the RT material, the RT material does not continue to flow through the passages, because the natural magnet assumes the no-power default position near the passages to impose the strong magnetic field, which physically transforms the RT material in the passages and thereby blocks the flow. Alternatively or in addition, an electrical sensor may be used to block the flow of RT material when the dispensing system is turned off or unexpectedly loses electrical power. 
     Piston  46  may have airtight seals both in the inner chamber and in the syringe so that air does not leak past the piston, to help prevent air from disrupting the transfer of force from the air under pressure to the outgoing material. 
     The dispensing mechanism may also include a direction sensitive mechanism such as a check valve or one-way valve to allow RT material that is in the second part of the bifurcated chamber to be returned quickly to the first part when the dispensing mechanism is to be reset, perhaps after most or all of the outgoing material has been driven as desired. For example, a check valve that effectively provides a small opening for flow in one direction and a large opening for flow in the opposite direction may be used. In such a case, the small opening serves as the passage for the flow of RT material that causes the outgoing material to be driven by the piston, and the large opening serves to allow the RT material to be returned, in a reset procedure, to the first part of the bifurcated chamber faster than the RT material originally flowed out of the first part. For example, as a result, RT material that takes two hours to flow from the first part to the second part can be returned to the first part in much less than two hours. 
     Depending on the nature of the direction sensitive mechanism used, the direction sensitive mechanism may be largely or entirely self-cleaning, because RT material or other material that becomes undesirably stuck in the walls of the passage and that is not dislodged by the flow of RT material in one direction is highly likely to be dislodged by the flow of RT material in the opposite direction. 
     Spring  48  may be used in the resetting of the dispensing system. For example, the dispensing system may have two operational states and a resetting state. In the first operational state, the strong magnetic field is not imposed, so the RT material flows through the passage from the first part to the second part of the bifurcated chamber, compressing and thereby storing energy in the spring while driving the outgoing material. In the second operational state, the strong magnetic field is imposed, so the RT material in the passage is effectively solid and therefore blocks the RT material from flowing in either direction despite the air under pressure and the energy stored in the compressed spring. In the resetting state, the strong magnetic field is not imposed and the air under pressure is removed or its pressure is reduced, so the spring de-compresses, releasing its stored energy by driving the RT material back into the first part of the bifurcated chamber, perhaps through a direction sensitive mechanism as described above. 
     The dispensing system may be used in a reworking application in which a circuit board having one or more missing solder connections is reworked to add the missing solder connections. In the reworking application, the location of a missing solder connection may be determined by a machine vision system, the dispensing system may be aimed at the location, and the activator may cause a controlled amount of creamy solder to be deposited at the location. 
     The RT material may have the consistency of heavy oil and may be or include MR Fluid by Lord Corporation. MR Fluid is responsive to an NdFeB magnet or an electromagnet. When the passage containing the MR Fluid is near or in contact with the NdFeB or electromagnet, flow through the passage is retarded or stopped within approximately 10 milliseconds. 
     The dispensing system may be arranged to allow an unused syringe containing creamy solder to be attached to the dispensing system by screwing on and to allow a spent syringe to be removed by unscrewing. In such a case, a half-turn may be sufficient in each screwing direction. 
     In the passage, the RT material effectively serves as its own switch or valve to turn on and off the flow of RT material from the first part of the bifurcated chamber to the second part. Thus, in a typical embodiment, the passage is much like a section of a water pipe or hose in that the passage has no moving mechanical parts and is sealed off and isolated from the outside without a physical or mechanical connection through the passage wall to an external switch control. In the typical embodiment, the influence of the activator penetrates the passage wall magnetically, not physically or mechanically. As a result, the dispensing system has substantial reliability and maintenance advantages, especially where the passage has a small width. 
     In another embodiment, the dispensing system may have another physical configuration. For example, embodiment  100  shown in FIG. 4 has a bifurcated chamber  102  that has first and second parts  104 ,  106  that are disposed side by side. 
     FIG. 5A illustrates another embodiment  200  in which the first part  202  is narrow and long and the second part  204  is wide and short. In part  202 , piston  206  is driven downward by air that is pumped into part  202  from above. Accordingly, RT material  208  that is disposed below piston  206  is driven through a passage  210  into part  204 , thereby driving piston  212  upward. As in the cases described above, a magnetic actuating mechanism  213  is used to control the flow of RT material through the passage. As illustrated in FIG. 5B, a ball check valve  214  including a ball  216  having a narrow passage  218  and being biased by a spring  220  may be used. In such a case, when piston  206  is being driven downward (assuming the magnetic actuating mechanism is set to allow RT material to flow), the RT material can pass through the narrow passage from first part  202  to second part  204 , and when piston  206  is being driven back up in a reset procedure after a syringe is spent, the RT material can flow in the opposite direction significantly faster because the ball is moved out of the way by the flow. 
     Under the same principle of moving a liquid or liquid-like material from one part to another (i.e., from one chamber to another), a fluid material such as hydraulic oil or de-ionized water could be used in place of the RT material. In such a case, a miniature solenoid valve or another switching mechanism such as a pneumatically driven valve or a shuttle valve may be used to control the flow of the fluid material. Such an arrangement might be advantageous in a situation in which the introduction of a magnetic field is undesirable, such as where the magnetic field would adversely affect the material being dispensed. The de-ionized water might be used where an oil leak through the valve or elsewhere would be particularly disadvantageous, in which case surfaces that come in contact with the de-ionized water may be made of or include stainless steel, aluminum, plastic, or other material that is resistant to rust and corrosion from water. 
     Other embodiments are within the scope of the following claims. For example, the dispensing apparatus may include multiple pistons, perhaps driven by different air supplies, for enhanced flexibility or control or safety. The dispensing apparatus include cascaded pistons or pistons connected in parallel or serial formation. The piston may be driven by electric power or by gravity or by an engine. The chambers may be spaced apart by a substantial distance. The dispensing apparatus may be oriented to dispense material upwards, or horizontally.