MICROPUMPS

MICROPOMPES

English Abstract

ABSTRACT
A micropump for delivering metered doses of liquid comprises
a capillary cylinder in which is movably mounted a piston. The cylinder
is mounted in a plastics block with a spool valve slidably movable between
first and second positions. In the first position an inlet line communicates
with the cylinder chamber and upward movement of the piston causes a column
of air and a column of liquid to be drawn in. The valve is then moved to
its other position whereby downward movement of the piston expels the
metered dose of liquid out through an outlet.

Claims

THE EMBODIMENT OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A micropump for metering small quantities of liquid comprising a
capillary cylinder, a gas tight piston disposed in the cylinder for movement
between top and bottom dead centre positions, a two-way valve adapted to
communicate the cylinder chamber to an inlet and an outlet respectively, and
control means adapted to coordinate the piston movements and valve operation
such that in the suction stroke first air and second a regulated quantity of
liquid are drawn into the cylinder chamber, on reverse movement of the piston
to the bottom dead centre position said liquid being delivered through said
outlet and said outlet being blown clear in a residue-free manner by the air
first drawn into the cylinder chamber.
2. A micropump according to claim 1 in which the valve is a spool valve
mounted in a block mounting the cylinder.
3. A micropump according to claim 2 in which the valve block is formed
of a suitable synthetic plastics material.
4. A micropump according to claim 1, 2 or 3 in which the cylinder chamber
is of such a diameter that owing to capillarity the air column between piston
head and liquid is maintained during changes of position of the pump.
5. A micropump according to claim 1, 2 or 3 in which the direction of
movement of the valve is substantially perpendicular to that of the piston.

Description

~5~37~3
This invention relates to micropumps which may be used for the
residue-free metering of very small quantities oE liquid. Such pumps may be
used, for example, for supplying a regulated quantity of medicinal substance
to the atomiser plate of a piezo-electric atomiser. (See for example German
Offenlegungsschrift (DE Al) No. 25 37 765, filed August 25, 1975 (Germany),
published March 3, 1977, applicant Siemens AG, Berlin, inventor W.-D. Drews).
According to the invention there is provided a micropump for metering
small quantities of liquid comprising a capillary cylinder, a gas tight piston
disposed in the cylinder for movement between top and bottom dead centre
positions, a two-way valve adapted to communicate the cylinder chamber to an
inlet and an outlet respectively, and control means adapted to coordinate the
piston movements and valve operation such that in the suction stroke first air
and second a regulated quantity of liquid are drawn into the cylinder chamber,
on reverse movement of the piston to the bottom dead centre position said
liquid being delivered through said outlet and said outlet being blown clear
in a residue-free manner by the air Eirst drawn into the cylinder chamber.
The valve is preferably a spool valve mounted in a block mounting the
cylinder. In a preferred embodiment the cylinder chamber is of such a diameter
that ow~ing to capillarity the air column between piston head and liquid is
maintained during changes of positlon of the pump.
In order that the -lnvention may be readily understood, an embodiment
thereoE will now be described by way of example with reference to the
accompanying drawing in which:-
Figure 1 is a vertical sectional view of a micropump in accordance with
the invention,
- 1 - ~
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Figure 2 is a view similar to Figure 1 showing the pump
at a later stage in its cycle o~ operation; and
Figure 3 is a vertical part section taken along the line
III-III in Figure 1.
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~5Z379
Thc pump comprises a piston 1, preferably of high-grado stecl,
movably mounted in a very narrow capillary cylinder 2 which can be made
for example of glass or metal. The cylinder 2 terminates in a valve block
~ made for example of a suitable synthetic plastics material such as
polytetra1uorethylene, ln which valve spool 5~ made preferably of high-
grade steel, can be moved between the stops 6 and 7. The position of the
necked portion 8 of the valve slide 5 in relation to the lnlet 9 and out-
let 10, respectively, results in a communication between the inlet and
outlet, respectively, and the chamb0r ll of the cylinder.
The piston 1 is in its bottom dead centre position when the
piston grip 12 abuts the cylinder, as shown in Figure 1. The metered dose
is determined by the product of the interior cross sectional area of the
cylinder and the stroke between marks a and c.
The movement of the piston l and valve slide 5 is controlled so
that the following cycle of action takes place:
ta) With the outlet opened tstop 7 lies a~ainst the valve block)
the piston moves out of the position shown in Figure 1 in the direction A
until a certain quantity of air is drawn into the cylinder tthe end face of
the piston i5 at mark ~ .
~b) In the second step, communication is made between the inlet
9 ~and consequently the supply vessel) and the cylinder by displacin~ the
valve slide in the direction D to the stop 6.
tc) The piston l is moved further in the direction A until the
volume of liquid fixed by the stroke and cylinder cross s0ction is drawn
in ~final position shown in Figure 2). The end face of the piston is at
mark c
~d) The valve slide 5 ls returned in the direction C to the stop
7 so that communication is made between the cylinder 2 and outlet 10.

~S~79
~ e) The piston 1 moves to the bottom dead centro ~position shown
in Figure 1). In so doing, first the liquid and khen the air are driven out
of the cylinder 2 and expelled through the outlet line. The air is used
to blow free the valve and the outlet line. After this emptying operation
the initial position is resumed.
The micro-pump according to the invention serves preerably for
metering quantities of liquid in the range rom 10 to 50 ~1, but can also
be designed for larger or smaller volumes by changing the dimensions. The
use of a sufficiently narrow cylinder ensures that owing to the capillarity
the air column between the piston and liquid is maintained even in the case
of changes of position of the filled pump.
Mechanical or electrical means known per se serve to control
the above-described cycle of action. However, operation o:E the pump can
also be controlled by hand. A simple device for the purpose of control
consists of a combination of gear wheels, racks and levers composed as
follows:
Four gear wheels are arranged next to one another and connected
rigidly to one another. The periphe~y of the gear wheels is occupied only
par~ly with teeth in such a way that substantially only one gear wheel
becomes effective at a certain point in time. Thus, while, for example,
the first gear wheel causes the action ~a) via a rack and lever, the other
three run freely un~il the desired quantity of air has entered the cylinder.
The second gear wheel then ensures the adjustment of the valve slide,
while the first gear wheel simultaneously moves the piston to the top dead
centre position. Thenceforward, the third gear wheel brings the valve
slide into the outlet position. The fourth gear wheel together with the
associated transmission elements thereafter moves ~he piston to the bottom
dead centre position. The control mechanism is such that after the gear
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52;:179
wheels have turned through 360 all the elements arc again situated in the
initial position.
In another embodiment of the control device the turning movement
is replaced by an ~p-and-down movem~nt. For thls purpose, it may be ad-
vantageous to arrange the cylinder and valve so that the directions o
movement of ~h~ piston and valve slide run parallel.
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