Pumps – Processes
Reexamination Certificate
1999-11-10
2001-07-17
Walberg, Teresa (Department: 3742)
Pumps
Processes
C417S413100
Reexamination Certificate
active
06261066
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a micromembrane pump and, in particular, to a micromembrane pump comprising a pump membrane, a pump body and inlet and outlet openings provided with passive non-return valves.
2. Description of Prior Art
According to the prior art a large number of different micromembrane pumps exists, the drive concepts used being predominantly electromagnetic, thermal and piezoelectric driving principles. Electromagnetic driving principles are described e.g. in E. Quandt, K. Seemann, Magnetostrictive Thin Film Microflow Devices, Micro System Technologies 96, pp. 451-456, VDE-Verlag GmbH, 1996. Thermal drive concepts are explained e.g. in B. Büstgens et al, Micromembrane Pump Manufactured by Molding, Proc. Actuator 94; Bremen 1994, pp. 86-90. EP-A-0134614 and H. T. G. Van Lintel et al, A Piezoelectric Micropump Based on Micrmachining of Silicon, Sensors & Actuators, 15, 1988, pp. 153-167, explain piezoelectric driving principles.
Piezoelectric drives are based on the use of piezoceramics causing a movement of the pump membrane and producing therefore a pumping effect in combination with a valve unit and a connection unit, respectively. There are several variations of piezoelectrically driven micromembrane pumps operating with active valves, with passive non-return valves or also with valveless fluidic connections. Such valveless fluidic connections are disclosed e.g. in A. Olsson et al: The First Valve-less Diffuser Gas Pump, Proceedings MEMS 97, pp. 108-113, Nagoya, Japan, 1997.
EP-A-0134614 describes a peristaltic pump making use of three piezomembranes, one piezomembrane being positioned at the inlet, the other one at the outlet and a further one between these two. On the basis of the periodic movement of the piezomembrane at the inlet and the movements of the piezomembranes at the outlet and in the middle, which are displaced in phase relative to the first-mentioned periodic movement, a pumping movement of the medium to be pumped is accomplished in the final analysis.
In addition, piezoelectric bending transducers, which are fixedly held on one side thereof, are known, the pump membrane being secured to a free end of these bending transducers. Such drive units are combined with a valve unit consisting of passive non-return valves.
Like the above-mentioned peristaltic pumps, the afore-mentioned valveless piezomembrane pumps make use of a piezomembrane as a drive unit, a fluidic connection unit being used, which consists of conically tapering channels with different flow resistances. By means of these pyramidal diffusers a direction-dependent flow resistance is defined, which produces a pumping effect in one direction. Like the other micropumps, also such a micropump including a valveless connection unit can build up a counterpressure during operation; this counterpressure can, however, no longer be maintained when the drive unit is switched off.
A known micromembrane pump which has an electrostatic drive is described in R. Zengerle: Mikromembranpumpen als Komponenten für Mikro-Fluidsysteme; Verlag Shaker; Aachen 1994; ISBN 3-8265-0216-7, and shown in DE 41 43 343 A1. Such a micropump is shown in FIG.
1
.
The micropump shown in
FIG. 1
consists of four silicon chips, two of these chips defining the electrostatic actor consisting of a flexible pump membrane
10
and a counter-electrode
12
which is provided with an insulating layer
14
. The two other silicon chips
16
and
18
define a pump body having flap valves
20
and
22
arranged therein. A pump chamber
24
is formed between the pump body, which is defined by the silicon chips
16
and
18
, and the flexible pump membrane
10
, which is connected to the pump body along the circumference thereof. A spacer layer
28
is arranged between the suspension devices
26
of the flexible pump membrane
10
and the counterelectrode.
When an electric voltage is applied to the electrostatic actor, the elastic pump membrane
10
is electrostatically attracted to the rigid counterelectrode
12
, whereby a negative pressure is generated in the pump chamber
24
, this negative pressure having the effect that the pump medium flows in via the inlet flap valve
22
, cf. arrow
30
. When the voltage has been switched off and the charge has been balanced by short-circuiting the electrodes, the pump membrane will relax and displace the pump medium from the pump chamber via the outlet flap valve
20
.
In contrast to the above-described electrostatic drives, the pump membrane of a piezoelectrically operated micropump is moved by piezoelectric forces, a piezoelectric crystal being connected to the pump membrane. The application of an electric voltage to the piezoelectric crystal causes a contraction or an elongation of the crystal and therefore a bending deformation of the membrane, which, together with a valve unit of the type shown e.g. in
FIG. 1
, finally produces a pumping effect. With the exception of the different drive means, also a piezoelectrically driven micropump could have the structural design described in FIG.
1
.
The above-described electrostatically driven micromembrane pumps have a plurality of disadvantages when used in the form shown e.g. in FIG.
1
.
Due to the small stroke of the electrostatic actor, typically 5 &mgr;m, and the comparatively large pump chamber volume, the height of the pump chamber being typically 450 &mgr;m, such a known pump has a very small compression ratio. The term compression ratio stands for the ratio of the displaced pumping volume to the total pump chamber volume. Due to this small compression ratio, it is impossible to convey compressible media, such as gases, since the compressibility of such media normally exceeds the compression ratio of the pump.
Furthermore, the pump chamber of the known pumps described has a geometry which is disadvantageous as regards fluid dynamics and which is, moreover, not bubble tolerant. Inclusions of air in a fluid pump medium accumulate in the pump chamber and, due to their comparatively high compressibility, they cause a substantial deterioration of the pumping characteristics. In addition, a self-priming behaviour cannot be achieved due to the poor compression behaviour. Due to the production process used, the pump membrane of the known micropumps is, in addition, in electrical contact with the medium conveyed. Since voltages in the order of 200 V occur at the actor during operation, substantial electric potentials may exist in the pump medium in the case of failure, and, depending on the respective case of use, these electric potentials may cause a malfunction of external components. In addition, known micro-pumps are mounted by glueing individual chips according to the prior art known at present, this kind of mounting being incapable of satisfying the requirements which have to be fulfilled for an efficient production.
Also existing piezoelectric micromembrane pumps show most of the above-mentioned disadvantages. Fundamentally, a substantial advantage of the piezoelectric micropump in comparison with the electrostatic micropump is to be seen in the possibility of driving the actor also by voltages which are lower than 200 V. Hence, the pumping rate can be adjusted via the frequency as well as via the driving voltage, a circumstance which may result in substantial simplifications as far as the driving electronics is concerned.
DE 195 46 570 C1 shows a micromembrane pump defined by a structured silicon plate and a glass sheet connected thereto, non-return valves being formed in the structured silicon plate. DE 694 01 250 T2 shows a fluid pump without passive non-return valves. The pump disclosed in this publication has a small pump chamber so that the pump can be filled due to capillary forces alone.
It is the object of the present invention to provide a micromembrane pump which eliminates the above-mentioned disadvantages of the prior art, which permits compressible media to be conveyed, and which shows a self-priming behaviour and is bubble-tolerant. It is a further object of the pr
Kluge Stefan
Linnemann Reinhard
Richter Martin
Woias Peter
Beyer Weaver & Thomas LLP
Fastovsky Leonid
Fraunhofer-Gesellschaft Zur Forderung der Angewandten Forschung
Walberg Teresa
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