Positive displacement shuttle pump

A positive displacement shuttle pump having a cylinder with axially displaced and mutually isolated inlet and outlet portions; a shuttle piston having a reservoir for accepting pressurized feed from the inlet port in the feed cycle and for dispensing feed to the outlet port in the dispensing cycle; a displacement piston extending longitudinally in the shuttle piston and communicating with the reservoir; an actuator for extending the displacement piston into the reservoir to pressurize the feed and urge the feed through the outlet port during the dispensing cycle; the displacement piston is responsive to the pressurized feed in the reservoir for retracting during the feed cycle; the displacement piston driving the shuttle piston through the feed and dispensing cycles.

FIELD OF INVENTION 
This invention relates to a positive displacement shuttle pump for 
dispensing fluids, and more particularly to such a pump which uses the 
motion of the pump to automatically operate an internal metering piston to 
measure out and dispense the proper quantity of a fluid. 
BACKGROUND OF INVENTION 
Current fabrication techniques in the electronics industry require 
extremely precise, repeatable dispensing of very small amounts of adhesive 
or solder paste. For example, in surface mount technology drops of solder 
paste earlier applied to leads of 0.06 inch width and spacing of 0.100 mil 
now must be deposited to mount leads of 0.007 mil on spacings of 0.020 
inch. 
With such small, closely spaced leads a number of problems are aggravated. 
The amount of solder paste or adhesive deposited must be small and 
consistent in volume from lead to lead or the leads might be bent or 
encounter different attachment resistance. In addition, bridging can occur 
between the leads. Such attachment shortcomings are even more 
problematical when the surface mount chips which must be delicately 
removed, replaced and re-soldered have a value of up to $2000-3000. There 
are a number of pumps presently available for dispensing fluids but all 
have serious shortcomings. 
Conventional syringe pumps, typically air pressure driven, operate (pulse) 
at high speeds, e.g., three times a second, which vibrates the paste and 
causes the solids to settle out and clog the pump. Further, the separation 
distorts the proper proportions of each of the elements--lead, tin, flux 
and solvent in the solder paste or constituents in other mixtures, so that 
an improper mixture of paste or adhesive is being deposited. Further, as 
the pumping action depletes the solder paste supply in the syringe, the 
empty space is filled by more and more air. Air is compressible; 
therefore, once the depletion begins there is no way to know just how much 
time and pressure should be applied on each stroke in order to keep the 
output volume consistent. Syringe pumps also are very difficult to control 
for small volumes. A typical syringe pump cylinder would have to move only 
micro-inches to dispense 10.sup.-6 cubic inches of material. 
Systolic pumps squeeze the feed material. If the feed material is solder, 
then the flakes of tin and lead are pressed against the tube and their 
abrasive quality tends quickly to wear out the tube. Gear pumps suffer 
from the fact that the gear meshing action tends to squeeze the solder 
flakes or other feed material between the gear teeth. In the case of 
solder flakes, the lead or tin begins to coat the gear teeth. This 
eventually packs the teeth and jams the gears while removing lead and tin 
from the solder paste so that the paste dispensed does not contain its 
constituents in the proper proportions, and eventually jams the gears 
together. 
In order to avoid this problem, gear teeth are typically designed with 
sufficient clearances so that the feed mixtures don't get crushed between 
the moving gear teeth. With these larger clearances the volumetric 
uncertainties are large with respect to the small volumes that these pumps 
are required to measure and dispense. In addition, the gear teeth 
characteristic dimensions must be larger than the clearances required. 
Thus with a reasonable tooth size, the amount of feed mixture dispensed 
requires only a small rotation of the gears, which is not easily 
controlled to give precise metering. 
In conventional piston pumps, the feed pressure necessary to introduce the 
mixture to the pump can add unpredictable amounts to the volume being 
dispensed and the piston retraction can draw back the feed material, such 
as solder paste, from the nozzle, which further detracts from the 
predictability of the dispensing volume. It is necessary to vary the feed 
pressure in piston pumps to accommodate for differences in the viscosity 
of the feed material, but this introduces additional problems: increased 
pressure of the piston pump results in increased pressure tending to drive 
out the feed material, even when the piston is in the retracted position, 
so that leakage and inconsistency become even more of a problem. 
SUMMARY OF INVENTION: I 
It is therefore an object of this invention to provide a simple, compact 
and reliable positive displacement pump for metering a fluid. 
It is a further object of this invention to provide such a pump which is 
extremely accurate in dispensing a fluid and consistent in its accuracy. 
It is a further object of this invention to provide such a pump which 
eliminates unpredictable cross-feeding from the input to the output. 
It is a further object of this invention to provide such a pump which 
eliminates drawback which sucks back fluid from the dispensing nozzle or 
port. 
It is a further object of this invention to provide such a pump which 
requires no valves or complex controls. 
It is a further object of this invention to provide such a pump which can 
operate at a high rate of speed. 
It is a further object of this invention to provide such a pump which 
functions without causing settling or separation of the feed mixture. 
It is a further object of this invention to provide such a pump which 
precisely delivers minute quantities of fluids with great repeatability. 
It is a further object of this invention to provide such a pump which 
develops high pressure during the dispensing cycle, forcing liquid through 
very small nozzles. 
It is a further object of this invention to provide such a pump which is 
small, lightweight and easy to operate. 
It is a further object of this invention to provide such a pump which is 
easy to construct and has few moving parts. 
It is a further object of this invention to provide such a pump which can 
be operated by any of a wide variety of actuators. 
The invention results from the realization that a truly accurate, 
consistent pump for metering very small quantities of a fluid of various 
viscosities can be effected by using a shuttle piston to move a feed 
reservoir between the feed inlet and dispensing outlet and dispensing feed 
from that reservoir using a metering piston disposed in the shuttle piston 
and automatically actuated by the operation of the shuttle piston. 
This invention features a positive displacement shuttle pump having a 
cylinder with axially displaced and mutually isolated inlet and outlet 
ports. The shuttle piston has a reservoir for accepting pressurized feed 
from the inlet port in the feed cycle and for dispensing feed to the 
outlet port in the dispensing cycle. A displacement piston extends 
longitudinally in the shuttle piston which communicates with the 
reservoir. An actuator extends the displacement piston into the reservoir 
to pressurize the feed and urge the feed through the outlet port during 
the dispensing cycle; the displacement piston is responsive to the 
pressurized feed in the reservoir for retracting during the feed cycle. 
There are means for driving the shuttle piston through the feed and 
dispensing cycles. 
In a preferred embodiment, the cylinder and the shuttle piston are of 
circular cross section. The ports may be on opposite sides of the 
cylinder. The reservoir may include a cross bore in the shuttle piston. 
The displacement piston may be coaxial with the shuttle piston and 
circular in cross section. There may be stop means to limit the retraction 
of the displacement piston in the feed cycle. The reservoir may include a 
chamber proximate the displacement piston for exposing the displacement 
piston to feed pressure during the feed cycle to retract the displacement 
piston. The actuator may include adjustment means for setting the amount 
of feed dispensed by the displacement piston. The means for driving may 
include a connecting rod or simply a handle. 
DISCLOSURE OF PREFERRED EMBODIMENT 
Other objects, features and advantages will occur to those skilled in the 
art from the following description of a preferred embodiment and the 
accompanying drawings, in which:

The invention may be accomplished with a displacement shuttle pump which 
has a cylinder with axially displaced and mutually isolated inlet and 
outlet ports: that is, the ports in normal operation are totally unable to 
communicate with each other, thereby preventing any drawback or crossover 
of the feed which would cause leakage of unpredictable or unmeasurable 
volume. Slidably received in the cylinder is a shuttle piston which has a 
reservoir for accepting pressurized feed from the inlet port during the 
feed cycle and for dispensing feed to the outlet port during the 
dispensing cycle. Typically the cylinder and the piston may be circular in 
cross section, but not necessarily. The cylinder may be of any other 
suitable cross section. The shuttle piston may be driven to and from in 
the cylinder by any number of linear devices or rotary devices with a 
linear converter: for example, air or electrical solenoids, cranks, or the 
like. The reservoir may be a peripheral or annular chamber on the shuttle 
piston, or may be a cross bore through the shuttle piston. Whatever its 
shape, the reservoir aligns with the inlet port during the feed cycle to 
receive fresh feed, and then aligns with the outlet port during the 
dispensing cycle in order to dispense some precisely measured minute 
portion of feed. But the reservoir never communicates simultaneously with 
both: they are mutually isolated. Dispensing is accomplished by a 
displacement piston which acts to meter the amount of feed dispensed from 
the reservoir. The displacement piston extends longitudinally in the 
shuttle piston. The head of the displacement piston communicates with the 
reservoir and the displacement piston contains a stop element for limiting 
its retraction during the feed cycle. 
There is an actuator for extending the displacement piston into the 
reservoir to pressurize the feed and urge the feed through the outlet port 
during the dispensing cycle, and the displacement piston is directly 
responsive to the pressurized feed in the reservoir for retracting during 
the feed cycle. In operation, when the shuttle piston is in the feed 
cycle, the pressure of the feed drives the displacement piston to retract 
up to the limit of its stop. When the shuttle piston reciprocates to its 
dispensing cycle, the dispensing piston encounters the stationary, 
passive, actuator, which accommodates the movement of the shuttle piston 
but prevents the further movement of the displacement piston, thereby 
actually causing relative motion between the shuttle piston and the 
displacement piston which it carries, so that the displacement piston 
protrudes at least partway through the reservoir, which has now been 
disconnected from the feed inlet. This intrusion of the displacement 
piston into the reservoir pressurizes the feed in the reservoir and causes 
it to be driven out of the outlet port which the reservoir encounters in 
the dispensing cycle. The inlet and outlet ports may be on opposite sides 
of the cylinder. If the cylinder is circular, the ports may be 
diametrically opposed, but they need not be. They could be side by side. 
They are mutually isolated by virtue of the fact that they are axially 
displaced and so the reservoir cannot align with both of them at the same 
time. 
The reservoir may include an ancillary chamber proximate the displacement 
piston for exposing the displacement piston to feed pressure during the 
feed cycle and assisting in the retraction of the displacement piston. 
There is a recess proximate the head of the displacement piston, so that 
even when it is extended there is sufficient room above its head so that 
the feed pressure being introduced into the reservoir during the feed 
cycle can sufficiently access the head of the piston to drive it back and 
retract it. The actuator may include an adjustment device in order to 
control the position of the actuator and thereby control the extent of 
travel or intrusion of the displacement piston into the reservoir during 
the dispensing cycle. 
There is shown in FIG. 1 a positive displacement shuttle pump 10 according 
to this invention which includes a housing cylinder 12 which may be 
circular in cross section and a shuttle piston 14 which will have the same 
cross section as cylinder housing 12. Shuttle piston 14 may be driven 
reciprocally to the left and right in FIG. 1 by means of a simple handle 
16 that can be hand operated. There is a reservoir 18 in piston 14 which 
as shown in FIG. 1 constitutes a cross bore, but it may as well be a 
peripheral or annular space or a space of any other suitable 
configuration. In the feed cycle, as pictured in FIG. 1, reservoir 18 
aligns with inlet port 20 which provides a means for introducing feed to 
reservoir 18 in the dispensing cycle. When piston 14 slid to the left, 
reservoir 18 aligns with outlet port 22 through which the feed is 
dispensed in repeatably precise, minute quantities. Metering or dispensing 
piston 24 is slidably reciprocally received in shuttle piston 14 and as 
shown is coaxially disposed with shuttle 14. The head 26 of piston 24 
communicates with reservoir 18. 
Piston 24 is slidably mounted in bearing 28 in bore 30 of piston 14. Piston 
24 carries a stop element 32 which is slidably received in enlarged bore 
33, and is fixed to piston 24. Stop element 32 engages with a limiting 
element 34 on shuttle piston 14 to limit the extent of retraction; that 
is, movement to the left in FIG. 1 of piston 24. There is an actuator 
member 36 mounted in the end plate 38 of cylinder 12. Actuator 36 includes 
rod 40 and a threaded knurled adjustment nut 42. When piston 14 is driven 
to the left in the dispensing cycle, the end 44 of metering piston 24 is 
brought into contact with the end 46 of rod 40. Since rod 40 is stationary 
by means of the threaded engagement as shown at 48 with end plate 38, the 
movement to the left of metering piston 24 is arrested while the movement 
to the left of shuttle piston 14 is permitted to continue because of the 
enlarged hole 50 in limit plate 34, which permits rod 40 to penetrate into 
shuttle piston 14. Thus as shuttle piston 14 continues to move to the left 
and the like movement of metering piston is halted, the metering piston 
begins to protrude into reservoir 18 to the extent allowed to by the 
adjustment controlled by nut 42. Port 55 is provided in cylinder 12 to 
vent volume 57 during the reciprocal movement of piston 14 and may be 
connected to a source of pressure and vacuum for driving shuttle piston 
14. 
An ancillary chamber 52 is provided in shuttle piston 14 so that even if 
the head of dispenser piston 26 is fully extended there is still a portion 
of head 26 which would be exposed to the pressurized feed in reservoir 18 
through chamber 52 to enable piston 24 to be driven to the left or 
retracted during the feed cycle. 
This can be seen more readily in the dispensing cycle, as shown in FIG. 2, 
where head 26 is protruding into reservoir 18 and the additional volume 
provided by chamber 52 is operating advantageously to impose the feed 
pressure. Also shown more clearly in FIG. 2 is the condition of shuttle 
piston 14 during the dispensing cycle. There the end 46 of rod 40 of 
actuator 36 has been received in bore 50 of limit plate 34, where it bumps 
up against the left end 44 of reciprocating piston 24 and drives it to the 
right relative to shuttle piston 14, which has moved to the left, thereby 
causing the head 26 of dispensing piston 24 to enter reservoir 18 and 
pressurize the feed fluid. Since reservoir 18 is no longer aligned with 
inlet 20 but is aligned with outlet 22, the precise and repeatable minute 
amount of feed is dispensed through outlet port 22. Piston 14 is limited 
in its rightward motion in the feed cycle by limit plate 54, and in its 
leftward motion in the dispensing cycle by a stop shoulder 17 on handle 
16. 
Piston 14 has a diameter of 0.500 mil and a length of 0.3 inch and has a 
slip fit 0.0500 inch engagement with cylinder 12. Metering or dispensing 
piston 24 has a length of 0.500 inches, a diameter of 0.00010, and has a 
0.0500 slip fit with bearing 28. Cross bore reservoir 18 is 0.5 inch long, 
0.05 inch in diameter, and contains a volume of 0.001 cubic inch. 
Ancillary chamber 52 is approximately 0.1 inch in diameter, 0.5 inch long 
and contains a volume of 0.004 cubic inch. 
Although in FIGS. 1 and 2 piston 14 is shown as capable of being driven to 
and fro by handle 16, this is not a necessary limitation of the invention. 
Any suitable means including all available automatic devices may be used 
to operate shuttle piston 14. For example, in FIG. 3, handle 16 has been 
replaced by a simple connecting rod 60 which acts as a means for operating 
piston 14. That rod 60 is driven by a pneumatic solenoid 62, which 
includes a piston 64 fixed to rod 60 and slidably received in bore 66 
within housing 68. A source of pneumatic pressure 70 provides pneumatic 
pressure through valve 72, first to inlet 74 which drives piston 64 to the 
right, and shuttle piston 14 to the feed cycle, and second inlet 76, which 
introduces pneumatic pressure to drive piston 64 to the left and shuttle 
piston 14 to the dispensing cycle. 
Although specific features of the invention are shown in some drawings and 
not others, this is for convenience only as each feature may be combined 
with any or all of the other features in accordance with the invention. 
Other embodiments will occur to those skilled in the art and are within the 
following claims: