Dispensing – Processes of dispensing – Molten metal
Reexamination Certificate
1999-02-19
2001-07-17
Kastler, Scott (Department: 1742)
Dispensing
Processes of dispensing
Molten metal
C222S594000, C075S331000
Reexamination Certificate
active
06260741
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable
REFERENCE TO MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
This invention relates to a method of and apparatus for dispensing fluids and, more particularly, to a method of and apparatus for producing droplets on demand.
Methods of forming and dispensing of droplets of liquids have been used in many applications including ink-jet printing and the precision dispensing of chemicals and pharmaceuticals. More recently, the basic technology has been utilized to provide accurate placement of solder on printed circuit boards (PCBs) and electronic components. For example, U.S. Pat. No. 5,415,679 to Wallace, describes an ejection device which includes an electrostrictive transducer which, when activated by a particular waveform, can be used to produce and apply droplets of solder to a substrate. The particular waveform described by Wallace is shown in FIG.
1
. This waveform is characterized by a first rise time RT
1
, followed by a first dwell time DT
1
, followed by a fall time FT, followed by a second dwell time DT
2
and a final rise time RT
2
back to the nominal position.
The process by which a droplet is generated when the prior art waveform drives the transducer is well known. An expansion wave is generated during the first rise time RT
1
and this wave splits into two waves which travel in opposite directions back and forth along the axis of the ejector. Each time a wave hits a tube end, a pressure inversion occurs (i.e. an expansion becomes a compression, and vise versa). A stable droplet is generated only if the compression wave generated during the fall time FT is synchronized with the passage of a compression wave traveling towards the orifice. This implies that the first dwell time DT
1
of the waveform shown in
FIG. 1
is critical to the formation of a droplet. Similarly, the expansion wave generated during the final rise time RT
2
has to be synchronized by tuning the second dwell time DT
2
. In principle, the purpose for this expansion is to minimize or even cancel any residual pressure waves in the tube after a droplet is generated.
Developing practical droplet forming systems using the waveform shown in
FIG. 1
has been difficult because determining the right dwell times DT
1
and DT
2
is difficult and typically requires continuous tuning which involves significant intervention of a trained operator. In addition, the jetting parameters necessary to achieve a stable system, Pressure, DT
1
, DT
2
, and Voltage, can vary from device to device making automatic tuning difficult.
Accordingly, it is an object of this invention to provide an improved method of and apparatus for producing droplets.
It is another object of this invention to provide an improved method of and apparatus for producing droplets which utilize a simplified waveform.
SUMMARY OF THE INVENTION
The present invention is directed to an apparatus for dispensing a fluid in droplets. The dispensing apparatus includes a dispensing chamber having a nominal volume for holding a volume of the fluid, a dispensing orifice coupled to the chamber to permit the fluid to be ejected from the chamber, a transducer coupled to the chamber and adapted for changing the volume of the chamber. A controller is connected to the transducer and is adapted for transmitting a signal to the transducer to selectively change the volume of the chamber. The signal generated by the controller and transmitted to the transducer includes three components: 1) an initial rise time during which the signal controls the transducer to gradually increase the volume of the chamber; 2) a fall time during which the signal controls the transducer to decrease the volume of the chamber; and 3) a final rise time during which the signal controls the transducer to gradually increase the volume of the chamber. In accordance with the present invention, the fall time is substantially smaller than the initial rise time and the final rise time. The voltage signal applied to the transducer gradually increases from a first voltage during the initial rise time to a second voltage, decreases during the fall time to a third voltage, and gradually increases from a third voltage during the initial rise time to a fourth voltage. The first voltage can be the same as the fourth voltage which is the nominal voltage of the signal.
The present invention also includes a method of producing a droplet in a dispensing apparatus which includes a dispensing chamber with an adjustable volume and a substantially constant pressure. The method includes the steps of: 1) gradually increasing the volume in the dispensing chamber over a first period of time, RT
1
; 2) decreasing the volume in the chamber over a second period of time, FT; and 3) gradually increasing the volume in the dispensing chamber over a third period of time, RT
2
; wherein said second period of time, FT is substantially smaller than the first period of time, RT
1
and the third period of time, RT
2
.
The present invention further includes a method of producing a droplet in a dispensing apparatus which includes a dispensing chamber with substantially constant volume and an adjustable pressure. The method includes the steps of: 1) applying a substantially constant, decreased pressure to the dispensing chamber for a first period of time, RT
1
; 2) applying a substantially constant, increased pressure to the chamber for a second period of time, FT; and 3) applying a substantially constant, decreased pressure to the dispensing chamber for a third period of time, RT
2
; wherein the second period of time, FT is substantially smaller than the first period of time, RT
1
and said third period of time, RT
2
.
The transducer can include a piezoelectric transducer that is bonded to the dispensing chamber or is integral with and forms a portion of the dispensing chamber. The piezoelectric transducer receives a voltage modulated signal that causes the transducer to change shape and causes the volume of the dispensing chamber to increase or decrease as a function of the voltage amplitude. The initial rise time, RT
1
and final rise time, RT
2
can each be on the order of 500 to 2000 microseconds and the fall time, FT can be on the order of approximately 0 microseconds.
REFERENCES:
patent: 5415679 (1995-05-01), Wallace
patent: 5643353 (1997-07-01), Wallace et al.
patent: 6029896 (2000-02-01), Self et al.
Andres Magdalena
Pham-Van-Diep Gerald C.
Crosby David E.
Kastler Scott
Mintz Levin Cohn Ferris Glovsky & Popeo, P.C
MPM Corporation
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