U.S. patent application number 11/061262 was filed with the patent office on 2005-09-08 for pipetting means and method of operating a pipetting means.
Invention is credited to Bigus, Hans-Jurgen, Debusmann, Ralph, Richter, Martin, Wackerle, Martin.
Application Number | 20050196304 11/061262 |
Document ID | / |
Family ID | 31501857 |
Filed Date | 2005-09-08 |
United States Patent
Application |
20050196304 |
Kind Code |
A1 |
Richter, Martin ; et
al. |
September 8, 2005 |
Pipetting means and method of operating a pipetting means
Abstract
A pipetting means includes a micropump comprising a pump chamber
with a first opening and a second opening. Furthermore, the
micropump includes means for changing the volume of the pump
chamber. A first active valve is provided to perform opening and
closing the first opening. Furthermore, a second active valve is
used to perform opening and closing the second opening.
Furthermore, the pipetting means comprises a pipette tip connected
to the first or second opening via a pipette channel.
Inventors: |
Richter, Martin; (Munchen,
DE) ; Wackerle, Martin; (Tegernau, DE) ;
Bigus, Hans-Jurgen; (Pliezhausen, DE) ; Debusmann,
Ralph; (Munchen, DE) |
Correspondence
Address: |
GLENN PATENT GROUP
3475 EDISON WAY, SUITE L
MENLO PARK
CA
94025
US
|
Family ID: |
31501857 |
Appl. No.: |
11/061262 |
Filed: |
February 17, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11061262 |
Feb 17, 2005 |
|
|
|
PCT/EP03/06389 |
Jun 17, 2003 |
|
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Current U.S.
Class: |
417/413.2 ;
417/410.1; 417/412; 417/413.3 |
Current CPC
Class: |
B01L 3/02 20130101; B01L
2300/0681 20130101; B01L 2400/0439 20130101; B01L 2400/0638
20130101; F04B 43/046 20130101; B01L 2400/0622 20130101 |
Class at
Publication: |
417/413.2 ;
417/410.1; 417/412; 417/413.3 |
International
Class: |
F04B 017/00; F04B
035/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 22, 2002 |
DE |
102 38 564.5 |
Claims
What is claimed is:
1. A pipetting apparatus, comprising: a micropump having a pump
chamber with a first opening and a second opening; an actor for
changing the volume of the pump chamber; a first active valve for
opening and closing the first opening; a second active valve for
opening and closing the second opening; and a pipette tip connected
to the first or second opening via the pipette channel.
2. The pipetting apparatus of claim 1, wherein the active valves of
the micropump include piezoelectric valves.
3. The pipetting apparatus of claim 1, wherein the actor for
changing the volume of the pump chamber includes a membrane and a
piezoelectric actuator for actuating the membrane.
4. The pipetting apparatus of claim 3, wherein the membrane is
arranged between holding elements.
5. The pipetting apparatus of claim 1, further including a pump
body including a first disc-shaped body element and a second
disc-shaped body element arranged thereupon.
6. The pipetting apparatus of claim 1, wherein a pump body
comprises a semiconductor material.
7. The pipetting apparatus of claim 1, wherein the pump chamber
further comprises at least one further opening; and wherein the
micropump further comprises at least another active valve for
opening and closing the at least one further opening.
8. The pipetting apparatus of claim 1, further comprising a filter
for filtering a working medium of the micropump.
9. A method of operating a pipetting apparatus, comprising: a
micropump having a pump chamber with a first opening and a second
opening; an actor for changing the volume of the pump chamber; a
first active valve for opening and closing the first opening; a
second active valve for opening and closing the second opening; and
a pipette tip connected to the first or second opening via the
pipette channel; the method comprising the steps of: actively
closing the first or second opening, whereby an environment is
disconnected from the pump chamber; actively opening the second or
first opening, whereby the pump chamber is connected to the pipette
channel; enlarging the volume of the pump chamber for sucking
dosing fluid through the pipette tip; and reducing the volume of
the pump chamber for expelling dosing fluid through the pipette
tip.
10. The pipetting apparatus of claim 9, wherein the pipetting
apparatus is used as an air cushion pipetting apparatus.
11. The pipetting apparatus of claim 9, wherein the pipetting
apparatus is used as a direct displacement pipetting apparatus.
12. The pipetting apparatus of claim 9, wherein the pipetting
apparatus is used as a micro-titer pipetting apparatus.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of co-pending
International Application No. PCT/EP 03/06389, filed Jun. 17, 2003,
which designated the United States and was not published in English
and is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to pipetting means and more
specifically to pipetting means with micropumps.
[0004] 2. Description of the Related Art
[0005] With increasing enhancement of the manufacture of
micromechanical structures, today various devices may be realized
as microstructure devices. Such a microstructure device, for
example, includes a micropipetting means with a micropump.
[0006] FIG. 1 shows a known pipetting means having first and second
micropumps 110a and 110b each constructed of three pump body
sections 110, 112 and 114 arranged on top of each other. The pump
body sections 110, 112 and 114 each include a flat disc or wafer
with microstructures created by means of suitable etching methods.
Typically, the pump body sections 110, 112 and 114 in such a known
micropump comprise semiconductor material, such as silicon. Each of
the micropumps 110a and 110b includes a pump chamber 116 formed by
boundaries of the pump body sections 110-114. The pump chamber 116
comprises an inlet opening 118 formed in the lower pump body
section 110. Above the inlet opening 118, a first flapper valve
formed as passive check valve is arranged. The flapper valve 120 is
formed in the center pump body section 112 and comprises an
elongated flexible flapper 120a extending across the inlet opening
118.
[0007] The pump chamber 116 further comprises an outlet opening
122, which can be closed and opened by a second passive flapper
valve 124 arranged in the pump body section 110. The second flapper
valve 124 comprises a flapper 124a with a longitudinal flexible
shape, corresponding to the first flapper valve 120.
[0008] Furthermore, the micropumps 100a and 100b comprise a
piezoelectric actuation element 126 for changing the volume of the
pump chamber. The piezoelectric actuation element 126 is arranged
as a piezoelectric ceramics layer in large area manner on a thinly
formed membrane 128 flexibly arranged between holding elements. On
applying a suitable voltage to the piezoelectric actuation element
126, the membrane 128 deforms and causes, depending on the polarity
of voltage, enlarging or reducing the volume of the pump chamber
116.
[0009] In a suction process, a voltage deforming the membrane 128
such that an enlargement of the volume of the pump chamber 116
results is applied to the piezoelectric actuation element 126.
Here, in the pump chamber 116, negative pressure is generated,
which causes the valve 120 to transition from a closed state to an
open state, whereas the valve 124 comprises a closed state by the
negative pressure. Thereby, fluid is sucked through the opening 118
into the pump chamber 116.
[0010] In a pumping process, the pump chamber volume is decreased
by applying an electric voltage to the piezoelectric actuation
element 116. The positive pressure developing here causes a force
moving the flapper valve 124 downward to be applied to the flapper
valve 124. Thereby, the opening 122 is opened, whereas the inlet
opening 118 is closed by the valve 120. By the positive pressure in
the pump chamber 116, the fluid is expelled from the pump chamber
116 through the opening 122.
[0011] The micropumps 100a and 100b are arranged in the pipetting
means such that the micropump 100a is connected to a pipette
channel 132 of a pipette tip 134 on the suction side, i.e. with the
inlet opening 118, and to an environment on the pressure side, i.e.
with the outlet opening 122. But the micropump 100b is connected in
opposite direction relative to the micropump so that it is
connected to the pipette channel on the pressure side and to the
environment on the suction side.
[0012] When sucking a medium to be dosed, the micropump 100a
attached to the pipette channel on the suction side is actuated so
that the volume of the pump chamber increases and air from the
pipette channel is sucked into the pump chamber. Here, an air
cushion 136 in the pipette tip 134 is reduced and a dosing medium
138 is sucked into the pipette tip 134. The second micropump 100b
in connection to the pipette channel on the pressure side remains
switched off here.
[0013] Conversely, when dosing the sucked medium, the micropump
100b is actuated by decreasing the volume of the pump chamber
thereof, whereas the micropump 100a remains switched off. The
micropump 100b connected to the pipette channel on the pressure
side here generates a positive pressure in the pipette channel
causing build-up of the aircushion 136 and expulsion of the dosing
medium.
[0014] The above-described micropumps 100a and 100b distinguish
themselves by simple control, since in the pumping and suction
processes only the piezoelectric actuation element 126 has to be
actuated as single active element. Furthermore, an advantage of the
micropumps 100a and 100b is that they can be manufactured in
compact manner in that, on a chip on which the micropumps are
arranged, only little area is consumed. Moreover, there is
long-year experience for such known micropumps with flapper valves,
so that the structures of the micropump can be created with high
accuracy.
[0015] The use of passive check valves in the micropumps 100a and
100b, which open or close with positive and negative pressures,
respectively, however have the disadvantage that holding the liquid
is not always guaranteed. Already small positive pressure at the
inlet opening 118 may cause the passive check valve to open
slightly, whereby fluid may flow into the pump chamber or flow
out.
[0016] In the employment of the micropumps 100a and 100b in the
above-described pipetting means, due to the above-described
insufficient holding of the dosing liquids, therefore leaking rates
already occur with small pressure differences in opening direction.
Particularly holding large amounts of liquids is only possible in
limited manner due to the hydrostatic pressure and the leaking
rates connected thereto.
[0017] A substantial disadvantage of the micropumps 100a and 100b
further consists in that, at high pressure pulses, a so-called
fluidic short may occur. If the micropump 100a is actuated during
sucking the dosing fluid, a pressure p2 smaller than a pressure p1
of the environment in connection with the outlet opening of the
micropump 100a develops in the pipette channel 132. Since, however,
the pipette channel is in connection with the outlet opening of the
micropump 100d and also the environment with the inlet opening of
the micropump 100b, the pressure difference causes the valves of
the micropump 100b to maybe open due to the pressure difference, so
that a fluidic short occurs through the micropump 100b.
Furthermore, a fluidic short may also occur in expelling the dosing
fluid. In this case a pressure p2 greater than the pressure p1 of
the environment in connection with the inlet opening of the
micropump 100b is generated in the pipette channel by actuating the
micropump 100b. By the pressure difference between the environment
and the pipette channel, the valves of the micropump 100a may open,
so that a fluidic short through the micropump 100a may occur in a
dosing process.
[0018] As it is known, the danger of the fluidic short may be
reduced by suitably controlling the piezoelectric element 126, in
which short-term high pressure pulses are avoided. Controlling the
piezoelectric element 126 may for example take place by means of a
sinusoidal waveform. Generating the sine form, however, requires
incremental circuitry by having to provide additional devices and
circuit components.
[0019] A further disadvantage of the above-described known
pipetting means is that the manufacture thereof is expensive. The
micropumps 100a and 100b are formed of three wafers arranged on top
of each other after structuring. Arranging the wafers requires high
precision so that the structures of the various wafers each
arranged on top of each other are accurately positioned at the
intended position. Here, the effort increases with each additional
wafer.
[0020] Furthermore, with the known micropumps 100a and 100b, the
center pump body section 112 has to be formed thinly, in order to
keep an overall height of the pump chamber 116 small, so that high
compression capability is achieved. Thinning the wafer is performed
by means of grinding, as it is known. By the grinding, however,
mechanical stresses occur, which may lead to damage of the
sensitive microstructures or the breaking of the wafer.
[0021] Alternatively, in the manufacture of the center pump body
section, also a thin wafer may be used as starting wafer. In order
to suitably transport and store the thin wafers during the
manufacturing process, however, expensive handling devices
specially adapted to the thin wafers are required. Furthermore,
when handling thin wafers, there is the danger of breakage of the
wafer, whereby in mass production the rejection rate is increased
and the production costs rise.
[0022] A further disadvantage resulting by the use of passive check
valves in the micropumps 100a and 100b is that simple fluid
guidance is not possible, because the fluid stream is impeded in
flowing in and out by the flappers. In particular, the opening
degree of the flappers depends on the positive or negative pressure
in the pump chamber, so that, depending on the present pressure,
different courses of the fluid result when letting in or streaming
out. This has to be taken into account in a design of the
micropump.
[0023] Furthermore, for forming the outlet flapper valve 124 an
outlet channel 130 in the pump body section 110 has to have a large
diameter due to the elongated shape of the valve flap 124a.
Thereby, an outer area of the pump body section 110 reduces,
whereby mounting the micropump is made more difficult.
[0024] Moreover, a substantial disadvantage of the pipetting means
according to FIG. 1 is that two micropumps 100a and 100b have to be
used to achieve sucking and dosing, because the micropumps 100a and
100b can only be operated with one pumping direction. This requires
great effort in the manufacture and additional consumption of
space.
[0025] A pipetting means including two micropumps with passive
flapper valves, corresponding to the pipetting means described with
reference to FIG. 1, is described for example in DE 198 47 869
A1.
[0026] WO 99/10 099 A1 discloses a micro dosing system including a
micro membrane pump and an open-jet dosing device or doser. The
micro membrane pump is connected to a reservoir by means of an
input and further comprises an output connected to an input of the
open-jet doser by means of a conduit. At the input and output of
the micro membrane pump, passive check valves are provided, so that
a liquid can be pumped from the reservoir to the open-jet doser.
The open-jet doser further includes a pressure chamber with two
openings each forming an input and output of the open-jet doser,
respectively. The micro membrane pump and the open-jet doser
further include a membrane each, to change the volume of the
pressure chamber.
[0027] DE 197 06 513 A1 shows a micro dosing device comprising a
pressure chamber connected to a media reservoir via an inlet, and
further comprising an outlet for expelling fluid. The device
includes a membrane with an actor in order to change the volume of
the pressure chamber. For preventing a backflow through the channel
connected to the media reservoir, a valve is arranged between the
pressure chamber and the media reservoir. The valve is operable by
means of a piezoelectric drive actuating a moveable membrane for
closing.
[0028] EP 0 725 267 A2 discloses an electrically controllable
micropipette including a microinjection pump. The microinjection
pump includes a chamber with a chamber valve controllable by means
of an electrically controllable actuator device. In operation, the
pumping chamber of the microinjection pump is filled with fluid
from a supply and then given off via discharge capillary.
[0029] EP 0 568 902 A2 shows a micropump with a pumping chamber
comprising an inlet and an outlet each comprising a valve to close
them. The pumping chamber further comprises a membrane that can be
activated by means of a micro-actuation device. In operation,
bending the membrane is performed, whereby the pressure in the
pumping chamber is reduced, so that liquid enters the pumping
chamber through the inlet when the inlet valve is raised from its
seat, while the outlet valve remains in a closed position, and is
then expelled via the opened outlet valve.
SUMMARY OF THE INVENTION
[0030] It is an object of the present invention to provide a
pipetting means and a method of operating a pipetting means, which
enable secure and stable dosing of a dosing fluid.
[0031] In accordance with a first aspect, the present invention
provides a pipetting apparatus, having a micropump having a pump
chamber with a first opening and a second opening; an actor for
changing the volume of the pump chamber; a first active valve for
opening and closing the first opening; a second active valve for
opening and closing the second opening; and a pipette tip connected
to the first or second opening via the pipette channel.
[0032] In accordance with a second aspect, the present invention
provides a method of operating a pipetting apparatus, having a
micropump having a pump chamber with a first opening and a second
opening; an actor for changing the volume of the pump chamber; a
first active valve for opening and closing the first opening; a
second active valve for opening and closing the second opening; and
a pipette tip connected to the first or second opening via the
pipette channel; the method having the steps of actively closing
the first or second opening, whereby an environment is disconnected
from the pump chamber; actively opening the second or first
opening, whereby the pump chamber is connected to the pipette
channel; enlarging the volume of the pump chamber for sucking
dosing fluid through the pipette tip; and reducing the volume of
the pump chamber for expelling dosing fluid through the pipette
tip.
[0033] The present invention is based on the finding that a
pipetting means with a micropump with stable and secure dosing
behavior can be realized by refraining from using a micropump with
passive valves for opening or closing openings of a pump chamber.
According to the present invention, in the inventive pipetting
means, a micropump with active valves is used for opening and
closing the pump chamber openings.
[0034] Thereby, the openings of the pump chamber can be closed
securely even when backpressures occur. This prevents a fluidic
short at high pressure pulses and avoids the occurrence of leaking
rates.
[0035] The inventive use of a micropump with active valves enables
operating in two pumping directions, so that only one micropump is
required for sucking and dosing.
[0036] By providing active valves, also a simple fluid guidance is
achieved, because a course of the fluid flowing in or out is not
impeded by the flappers, in contrast to the known micropumps with
flapper valves. Thereby, also simple fluid guidance results in
inlet and outlet channels connected to the openings. Furthermore,
the openings may be formed with simple and symmetric shape. This
simplifies structuring the openings in the manufacture of the
micropump.
[0037] Moreover, in the inventive pipetting means, a production
process is kept simple, because the critical creating of thin
flexible flappers is not required.
[0038] In contrast to the known pipetting means with a micropump
with passive flapper valves, in the inventive pipetting means it is
not required to arrange an elongated valve flap in a largely
dimensioned outlet channel of a pump body. Thereby, an outer
surface of the pump body may comprise a large mounting area for
mounting the micropump to a support, so that simple and secure
mounting of the micropump is possible.
[0039] A preferred embodiment of the present invention includes a
pipetting means with a micropump, in which the active valves
include piezoelectric valves. Furthermore, the means for changing
the volume of the pump chamber preferably comprises a pump membrane
actuatable with a piezoelectric actuation means for changing the
volume. The piezoelectric actuation means preferably includes a
thin piezo-active layer applied on an outer side of the pump
membrane.
[0040] The pump membrane is preferably arranged between holding
elements enabling bending of the membrane, without having to accept
disadvantageous effects on the active valves.
[0041] The micropump is preferably formed with a layer structure of
two structured flat discs arranged on top of each other. Thereby,
the manufacture of the micropump is kept simple and inexpensive.
Preferably, semiconductor material, and particularly preferably,
silicon material is used as material of the discs.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] These and other objects and features of the present
invention will become clear from the following description taken in
conjunction with the accompanying drawing, in which:
[0043] FIG. 1 is a cross-sectional illustration of a known
pipetting means comprising two micropumps with passive flapper
valves;
[0044] FIG. 2 is a schematic cross-sectional illustration of an
embodiment of a micropump used in a pipetting means according to
the present invention; and
[0045] FIG. 3 is a schematic cross-sectional illustration of an
embodiment of a pipetting means with a micropump according to the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] In the following, with reference to FIG. 2, a micropump 200
is explained, which is employed in one embodiment of the present
invention.
[0047] According to FIG. 2, the micropump 200 comprises a pump body
210 preferably formed of a disc-shaped first pump body section 212
and a disc-shaped second pump body section 214. The pump body
sections 212 and 214 are arranged on top of each other in vertical
direction (y axis) and connected to each other at peripheral
regions thereof via connection structures. The pump body sections
212 and 214 preferably include discs of a semiconductor material,
and particularly preferably of silicon. The pump body 210 may
however, in other embodiments, comprise any other
micro-structurable material. The disc-shaped pump body sections 212
and 214 are preferably structured by means of known lithography and
etching techniques and connected by means of known connection
techniques for forming the pump body 210.
[0048] A longitudinally formed pump chamber 216 is formed in the
micropump 200 by a recess 218 in the lower pump body section 212
and a well-shaped recess 220 in the upper pump body section 214.
The recesses 218 and 220 facing in direction of the pump body are
preferably arranged in centered manner in horizontal direction (x
axis) to achieve a symmetrical structure. Preferably, the pump
chamber is formed with small height to achieve a high compression
ratio.
[0049] The micropump further comprises two openings 222 and 224
letting fluid into the pump chamber 116 or letting it out, which
are each formed on opposite sides of the pump chamber 216 in the
lower pump body section 212. The openings 222 and 224 each extend
in the shape of a truncated cone from a surface facing outward with
respect to the pump body 210 to a surface of the lower pump body
section 212 facing inward. The openings may, however, also be
formed with other shapes, such as a cylinder shape. Preferably, the
openings 222 and 224 have a symmetrical shape to simplify
manufacture thereof.
[0050] Above the opening 222, a first active valve 226 for closing
and opening the opening 222 is arranged. The first active valve 226
includes a closing element 228 formed on an inner surface with
respect to the pump body 210 of the second pump body section 214.
The closing element 228 is formed such that it is spaced in
vertical direction from the opening 222 in an opened state of the
first active valve 226.
[0051] The closing element 228 comprises a flat closing surface
extending in horizontal direction across valve seat structures 222a
and 222b arranged lateral to the opening 222, so that the opening
222 is completely closed by the closing element 228 in a closed
state of the valve 226. The valve seat structures 222a and 222b are
preferably formed such that, when closing the valve 226, the rest
area of the closing element 228 is kept small. The small rest area
causes secure closing by the closing element 228, because the
danger of leaky closing, for example by uneven places in the valve
seat structures 222a and 222b, is minimized with decreasing rest
area.
[0052] The closing element 228 is connected to holding elements 232
and 234 each laterally by thin ridges. Thereby, the closing element
228 is arranged flexibly with reference to the holding elements 232
and 234 and can be brought from an opened state to a closed state,
in which the closing element 228 rests on the valve seat structures
222a and 222b with a closing surface and closes the opening
222.
[0053] In order to cause the opening and closing of the first
active valve, a first piezoelectric actuation element 230 is
arranged on a surface of the closing element 228 opposite the
closing surface. The first piezoelectric actuation element 230
preferably includes a thin layer of piezoelectric material, such as
quartz.
[0054] The first piezoelectric actuation element 230 can be
connected to a control means (not shown) via electric terminals
(not shown), in order to achieve, by applying an electric voltage,
a contraction or expansion of the first piezoelectric actuation
element 230, each causing vertical displacements of the closing
element 228.
[0055] Above the opening 224, also a second active valve 236 is
formed, which is preferably formed correspondingly to the first
valve 226. More specifically, the second active valve 236 comprises
a closing element 238 arranged above the opening 224, which is
connected to holding elements 242 and 244 via laterally arranged
ridges. The second active valve 236 also includes a second
piezoelectric actuation element 240 for enabling the vertical
movement of the closing element 238. Furthermore, corresponding to
the first valve, valve seat structures 224a and 224b are each
formed laterally to the opening 222.
[0056] As will be explained in greater detail later on, the
piezoelectric elements 230 and 240, by applying a corresponding
electric voltage, cause opening and closing the openings 222 and
224, respectively, so that the pump chamber 216 for letting in or
letting out a pumping medium through the openings 222 and 224,
respectively, may be closed or opened.
[0057] For changing the volume of the pump chamber, the pump
chamber 216 comprises a thin membrane 246 arranged between the
holding elements 234 and 244. Thereby, the thin membrane 246 is
bendable between the holding elements 234 and 244 in flexible
manner, so that by actuating the membrane the volume of the pump
chamber 216 can be changed. The massively formed holding elements
234 and 244 prevent movement from transferring to the closing
elements 228 and 238 in an actuation of the membrane 246, so that a
disadvantageous influence on the active valve by the movement of
the membrane 246, which may for example lead to opening a closed
valve, is prevented. Furthermore, the holding elements 234 and 244
also serve as mounting means enabling mounting the micropump 200 to
a support.
[0058] On a side of the membrane 246 facing away from the pump body
210, also a piezoelectric membrane actuation element 250 for
activating the membrane 246 is arranged. The piezoelectric membrane
actuation element 250, like the piezoelectric actuation elements
230 and 240, preferably comprises a thin layer of piezoelectric
material. Furthermore, the piezoelectric membrane actuation element
250 can be connected to a control means via electrical terminals
(not shown) to enable applying an electric voltage.
[0059] The pump 200 is a pump according to the peristalsis
principle, in which the actuation elements 230, 240, and 250 are
actuated successively in predetermined orders.
[0060] Operating the micropump 200 according to this principle is
subsequently explained in greater detail.
[0061] In the following, at first a first pumping direction is
explained, in which fluid is pumped from the opening 222 to the
opening 224.
[0062] In a suction process, at first the second valve 236 is
actuated to close the opening 224. Actuating the second valve 226
takes place by applying an electric voltage to the second
piezoelectric element 240, which causes the closing element 238 to
be moved downward in horizontal direction for closing the opening
224. Then the first piezoelectric element 230 is actuated to open
the opening 222.
[0063] Subsequently, a voltage is applied to the piezoelectric
membrane actuation element 250 to cause deformation of the membrane
246, so that the volume of the pump chamber 216 increases. Thereby,
negative pressure develops in the pump chamber 216, whereby fluid
from the opening 222 is sucked into the pump chamber 216. After
terminating the suction process, the first valve 226 is closed.
[0064] For pumping out the fluid stored in the enlarged pump
chamber 216, the second valve 236 is then actuated by applying an
electric voltage to the second piezoelectric actuation element 240
to open the opening 224. After opening, a voltage causing the
volume of the pump chamber 216 to reduce is applied to the
piezoelectric membrane actuation element 250. This causes the fluid
to be pressed out of the pump chamber 216 and through the opening
224.
[0065] Preferably, the opening 222 is in connection with a first
fluid reservoir in the operation of the micropump 200, whereas the
opening 224 is in connection to a second fluid reservoir. This
causes fluid to be pumped from the first fluid reservoir into the
second fluid reservoir in the above-described pumping process. The
first and second fluid reservoirs may for example be ambient air or
a container with liquid or gas.
[0066] After performing the above-described pumping clock, the
pumping process may be repeated once or several times in order to
pump a desired amount of fluid from the first reservoir to the
second reservoir.
[0067] For pumping the micropump 200 with a second pumping
direction, in which fluid from the opening 224 is pumped to the
opening 222, the active valves 226 and 236 are operated in
correspondingly interchanged manner with reference to the above
explanations.
[0068] More specifically, in the second pumping direction, at first
the first valve 226 is closed, the second valve 236 is opened, and
then the membrane is actuated for enlarging the pump chamber
volume, in a suction process. Thereby, fluid is sucked from the
opening 224 into the pump chamber 216. Then the second valve 236
closes the opening 224, whereas the first valve 226 opens the
opening 222. Subsequently, the membrane 246 is actuated for
reducing the pump chamber volume, whereby the fluid in the pump
chamber 216 is expelled through the opening 222.
[0069] In the following, with reference to FIG. 3, an embodiment of
a pipetting means 252 is explained, in which the micropump 200
explained with reference to FIG. 2 is used for dosing the dosing
medium.
[0070] According to FIG. 3, the micropump 200 is arranged on a
support element 254 in the pipetting means 252, wherein a pipette
channel 256 formed in the support element 254 is connected to the
opening 224 of the micropump.
[0071] The pipetting means 252 further comprises a pipette tip 258
comprising, at a front-side end, an opening for sucking and
expelling dosing liquid. At a rear-side end, the pipette tip 258
comprises a connection element 260 formed to connect the pipette
channel 256 to the interior of the pipette tip 258. Preferably, the
connection element 260 is introduced into the pipette channel 256
in releasable manner to enable exchanging the pipette tip 258.
[0072] The support element 254 further includes a channel 262
connected, at a first end thereof, to the opening 222 of the
micropump 200. A second end of the channel 262, which is arranged
laterally at the support element, is in contact with an
environment, which for example comprises air.
[0073] The pipetting means 252, as it is shown in FIG. 3, may
comprise a filter 264 connected to the channel 262 via a connection
element 266a, between the second end of the channel 262 and the
environment connected to the channel.
[0074] Typically, the environment includes air as medium, so that
the filter is preferably formed as an air filter. The filter 264
may include all known filter types, such as particle filters,
chemically selectively absorbing filters or electrostatic
filters.
[0075] Filtering the air prevents contamination of the dosing
medium by particles or chemical impurities of the air. Furthermore,
impurities, which may prevent densely closing the openings, are
prevented from depositing at the active valves. The filter 264 may
further comprise an outer connector element 266b to enable a
connection to a suction line disposed outside the support element
252.
[0076] In the following, now an operation of the pipetting means
252 is explained in greater detail.
[0077] For sucking a dosing medium preferably including a liquid,
the micropump 200 is at first operated with a pumping direction, in
which a working medium, which is for example air or another gaseous
medium, is sucked through the opening 224 from the pipette channel
256, pumped into the pump chamber 216 and into an environment
connected to the channel 262 via the opening 222. This pumping
direction corresponds to the second pumping direction explained
with reference to FIG. 2, so that an illustration of the associated
processes of the micropumps can be taken from the corresponding
above explanations.
[0078] The pumping process for sucking causes negative pressure to
develop inside the pipette tip 258, whereby the dosing medium is
sucked inside the pipette tip 258. The pumping process for sucking
the dosing medium 268 can be repeated until the desired amount of
the dosing medium 268 is sucked into the pipette tip 258. During
the suction process, the working medium residing in the pipette tip
258 as a gaseous cushion 270 is increasingly displaced by the
dosing medium 268. The gaseous cushion 270 causes the pipette
channel not to come into contact with the dosing medium. This
prevents the dosing medium from being soiled by dosing medium
remains of the previous dosing medium present in the channel in an
exchange of the pipette tip 258 for dosing another dosing
medium.
[0079] After the desired dosing medium amount has been sucked, the
valve is actuated for closing to achieve holding the dosing medium
in the pipette tip 258.
[0080] In an ensuing dosing process, the micropump 200 is operated
with the reverse pumping direction, in which the working medium of
the micropump 200 is sucked from the environment via the opening
222 and pumped into the pipette channel 256 via the opening
224.
[0081] This pumping direction corresponds to the first pumping
direction explained with reference to FIG. 2, so that it is
referred to the corresponding explanations with regard to an exact
description of the pumping processes.
[0082] Pumping the working medium from the environment into the
pipette channel 256 generates positive pressure in the pipette
channel 256 and in the gaseous cushion 270, so that the dosing
medium 264 is forced out of the pipette tip 258 by the expanding
aircushion. The pumping process may be repeated until a desired
dosing medium amount has been brought out of the pipette tip
258.
[0083] As already mentioned previously, tight closing independent
of occurring counterpressure is achieved by the active valves 226
and 236. This has an advantageous effect in the pipetting means
252, because a fluidic short, as can occur in known micropumps with
flapper valves, is prevented. The pipetting means 252 thus achieves
high dosing accuracy.
[0084] Likewise, unwanted release of the dosing medium when holding
it in the pipette tip is prevented by the small leaking rates of
the active valves.
[0085] Although the active valves of the micropump 200 are formed
as piezoelectric valves in the described embodiments, other
embodiments of the present invention may include other actively
actuatable valve types, such as mechanically actuatable valves,
electrostatic valves, or electromagnetic valves.
[0086] For actuating the membrane, instead of the described
piezoelectric actuation means, any other known actuation means for
actuating the membrane may be used, such as an electrostatic
actuation means.
[0087] Furthermore, in other embodiments, any known means may be
used, which enables changing the pump chamber volume. Such means
may for example include rotatable elements for compressing and
decompressing a fluid in the pump chamber.
[0088] Although the pump chamber only comprises two openings in the
described embodiment, it may also comprise more than two openings
with correspondingly associated active valves in alternative
embodiments. This enables selective pumping, in which for example
various fluids may be pumped alternatingly into the pump chamber
from various reservoirs and then be pumped into predetermined other
reservoirs via selectively selected openings. In this embodiment,
selective mixing of various fluids may be performed in the pump
chamber, wherein a mixing ratio is adjustable by controlling the
active valves. The use of the pump chamber as "mixing reactor"
achieved thereby further has the advantage of good mixing being
achieved by the high pressures in the pump chamber.
[0089] Furthermore, the pipetting means with a micropump according
to the present invention is not limited to the shown embodiment of
an aircushion pipetting means. Other embodiments may for example
include a pipetting means according to the direct displacement
principle or a micro-titer pipetting means, in each of which the
inventive micropump for dosing the dosing medium is used.
[0090] While this invention has been described in terms of several
preferred embodiments, there are alterations, permutations, and
equivalents which fall within the scope of this invention. It
should also be noted that there are many alternative ways of
implementing the methods and compositions of the present invention.
It is therefore intended that the following appended claims be
interpreted as including all such alterations, permutations, and
equivalents as fall within the true spirit and scope of the present
invention.
* * * * *