EP1458977B2 - Peristaltic micropump - Google Patents

Description

The present invention relates to a micropump, and more particularly to a micropump operating on a peristaltic pumping principle.

Micropumps operating on a peristaltic pumping principle are known in the art. So is the article " Design and simulation of an implantable medical drug delivery system using microelectromechanical systems technology ", by Li Cao et al., Sensors and Actuators, A94 (2001), pages 117 to 125 , comprising a peristaltic micropump having an inlet, three pumping chambers, three silicon diaphragms, three normally-closed active valves, three PZT piezo stack actuators, microchannels between the pumping chambers, and an outlet. The three pumping chambers are of equal size and are etched into a silicon wafer.

From the WO 87/07218 Also, a peristaltic micropump is known which has three membrane regions in a continuous substrate surface. In a carrier layer, which carries the substrate and an associated support layer, a pump channel is formed which communicates with a fluid reservoir. In the pumping channel in each case a transverse rib is formed in the region of an inlet valve and an outlet valve, on which an associated membrane portion rests in the unactuated state to close the inlet valve and the outlet valve in the unactuated state. Between the inlet valve and the outlet valve associated separately operable membrane areas of the third membrane region, which is also actuated separately, arranged. By actuating the third diaphragm area, the chamber volume between the two valve areas is increased. Thus, by a corresponding timed control of the three membrane areas a peristaltic pumping action between the inlet valve and the outlet valve can be achieved. According to the WO 87/07218 the actuator element consists of a threefold composite of metal membrane, continuous ceramic layer and segmented electrode arrangement. The ceramic layer must be segmented polarized, which is technically difficult. Such a segmented piezo-bending element is thus expensive and only allows low stroke volumes, so that such a pump can not work bladeless tolerant and self-priming.

From the DE 19719862 A1 is known, not working on the peristaltic principle, micro-diaphragm pump, in which a pumping chamber adjacent to a pumping membrane is actuated by a piezoelectric actuator. A fluid inlet and a fluid outlet of the pumping chamber are each provided with passive check valves. According to this document, the compression ratio of the micropump, ie the ratio of stroke volume of the pumping membrane to total pumping chamber volume depending on the maximum valve geometry and valve wetting dependent pressure required to open the valves, is set to provide a bubble tolerant self-priming operation to allow local micromembrane pump.

In addition to the above-mentioned piezoelectric actuators, it would also be possible to realize micropumps using electrostatic actuators, but electrostatic actuators allow only very small strokes. Alternatively, the realization of pneumatic actuators would be possible, but this makes a lot of effort in terms of external pneumatic and the required switching valves necessary. Pneumatic drives thus represent complex, expensive and space-consuming procedures to implement a diaphragm deflection.

The object of the present invention is to provide a peristaltic micromembrane pump which can be easily assembled and which enables a bubble-tolerant, self-priming operation.

According to the invention, this object is achieved by a peristaltic micropump according to claim 1.

The present invention thus provides a peristaltic micropump in which the first and second valves are open in the unactuated state and in which the first and second valves are moved by moving the membrane can be closed to the pump body, while the volume of the pumping chamber can also be reduced by moving the second membrane area towards the pump body.

With this construction, the peristaltic micropump according to the invention makes it possible to realize bubble-tolerant, self-priming pumps, even if piezoelements arranged on a membrane are used as piezo actuators. Alternatively, according to the invention as piezo actuators also so-called piezo-stacks (piezo stacks) can be used, which are disadvantageous to piezo membrane transducers in that they are large and expensive, problems with the connection technique between stack and membrane and problems in adjusting the stack supply and thus are associated with a higher total effort.

To ensure that the inventive peristaltic micropump can work bubble-tolerant and self-priming, it is preferably dimensioned such that the ratio of stroke volume and dead volume is greater than a ratio of delivery pressure and atmospheric pressure, the displacement being the volume displaceable by the pump membrane, the dead volume the volume remaining between the inlet port and the outlet port of the micropump, when the pumping diaphragm is actuated and one of the valves is closed and one is open, the atmospheric pressure is at most about 1050 hPa (worst case consideration), and the delivery pressure is that in the fluid chamber region Micropump, d. H. in the pressure chamber, necessary pressure is to maintain a liquid / gas interface at a location which is a flow restriction in the microperistaltic pump, i. between the pumping chamber and the passage opening of the first or second valve, including this passage opening, to move past.

If the ratio of stroke volume and dead volume, which can be called the compression ratio, satisfies the above condition, it is ensured that the peristaltic micropump works bubble-tolerant and self-priming. This applies both when using the peristaltic micropump for conveying liquids, when a gas bubble, usually an air bubble, enters the fluid region of the pump, as well as when using the micropump according to the invention as a gas pump when accidentally condensed moisture from the gas to be pumped and Thus, a gas / liquid interface may occur in the fluid region of the pump.

Compression ratios satisfying the above condition can be realized in the present invention, for example, by making the volume of the pump chamber larger than that of the valve chambers formed between the respective valve diaphragm portions and opposite pump body portions. In preferred embodiments, this can be realized by the distance between the membrane and surface and pump body surface in the pump chamber is greater than in the region of the valve chambers.

A further increase in the compression ratio of a peristaltic micropump according to the invention can be achieved by moving the contour of a pumping chamber structured in the pump body to the bending line of the pumping membrane, i. H. the curved contour of the same in the actuated state, adapted so that the pumping membrane in the actuated state can displace substantially the entire volume of the pumping chamber. Furthermore, the contours of valve chambers formed in the pump body can be adapted accordingly to the bending line of the respective opposite membrane sections, so that in the optimal case in the closed state, the actuated membrane region displaces substantially the entire valve chamber volume.

Fig. 1

eine schematische Querschnittansicht eines Ausführungsbeispiels einer erfindungsgemäßen peristaltischen Mikropumpe in einem Fluidsystem;

Fig. 2a bis 2f

schematische Darstellungen zur Erläuterung eines Piezo-Membranwandlers;

Fig. 3a bis 3c

schematische Querschnittdarstellungen zur Erläuterung der Begriffe Hubvolumen und Totvolumen;

Fig. 4

ein schematisches Diagramm, das die Volumen/Druck-Zugstände während eines Pumpzyklusses zeigt;

Fig. 5a bis 5c

schematische Darstellungen zur Erläuterung des Begriffs Förderdruck;

Fig. 6a bis 6c

schematische Ansichten eines alternativen Ausführungsbeispiels einer erfindungsgemäßen Mikropumpe;

Fig. 7

eine vergrößerte Darstellung eines Bereichs von Fig. 6b;

Fig. 8

eine vergrößerte schematische Querschnittdarstellung eines modifizierten Bereichs von Fig. 7;

Fig. 9a, 9b und 9c

schematische Darstellungen möglicher Pumpkammergestaltungen;

Fig. 10a und 10b

schematische Darstellungen eines alternativen Ausführungsbeispiels einer erfindungsgemäßen Mikropumpe;

Fig. 11 bis 13

schematische Querschnittansichten vergrößerter Bereiche von Modifikationen des in den Fig. 10a und 10b gezeigten Beispiels;

Fig. 14

eine schematische Querschnittansicht eines weiteren alternativen Ausführungsbeispiels einer erfindungsgemäßen Mikropumpe;

Fig. 15

eine schematische Darstellung einer erfindungsgemäßen Mehrfach-Mikropumpe; und

Fig. 16

eine schematische Darstellung eines alternativen Ausführungsbeispiels einer erfindungsgemäßen Mikropumpe.

Preferred embodiments of the present invention will be explained below with reference to the accompanying drawings. Show it:

Fig. 1

a schematic cross-sectional view of an embodiment of a peristaltic micropump according to the invention in a fluid system;

Fig. 2a to 2f

schematic representations for explaining a piezo-membrane converter;

Fig. 3a to 3c

schematic cross-sectional views to explain the terms stroke volume and dead volume;

Fig. 4

a schematic diagram showing the volume / pressure Zugstände during a pumping cycle;

Fig. 5a to 5c

schematic representations to explain the term delivery pressure;

Fig. 6a to 6c

schematic views of an alternative embodiment of a micropump according to the invention;

Fig. 7

an enlarged view of a range of Fig. 6b ;

Fig. 8

an enlarged schematic cross-sectional view of a modified region of Fig. 7 ;

Fig. 9a, 9b and 9c

schematic representations of possible pump chamber designs;

10a and 10b

schematic representations of an alternative embodiment of a micropump according to the invention;

Fig. 11 to 13

schematic cross-sectional views of enlarged areas of modifications of the in the 10a and 10b shown example;

Fig. 14

a schematic cross-sectional view of another alternative embodiment of a micropump according to the invention;

Fig. 15

a schematic representation of a multi-micropump according to the invention; and

Fig. 16

a schematic representation of an alternative embodiment of a micropump according to the invention.

A first embodiment of a peristaltic micropump according to the invention, which is integrated in a fluid system, is disclosed in US Pat Fig. 1 shown. The micro-diaphragm pump comprises a membrane element 10 which has three membrane sections 12, 14 and 16. Each of the membrane sections 12, 14 and 16 is provided with a piezo element 22, 24 and 26, respectively, and forms together with the same a piezo membrane transducer. The piezo elements 22, 24, 26 may be glued to the respective membrane sections or may be formed by screen printing or other thick film techniques on the membrane.

The membrane element is circumferentially joined to a pump body 30 at outer portions thereof, so that there is a fluid-tight connection therebetween. In the pump body 30, two fluid passages 32 and 34 are formed, one of which, depending on the pumping direction, a fluid inlet and the other represents a fluid outlet. At the in Fig. 1 In the embodiment shown, the fluid passages 32, 34 are each surrounded by a sealing lip 36.

Furthermore, in the in Fig. 1 In the embodiment shown, the underside of the membrane element 10 and the top of the pump body 30 are structured to define a fluid chamber 40 therebetween.

In the embodiment shown, both the membrane element 10 and the pump body 30 are implemented in a respective silicon wafer, so that they can be joined together, for example, by silicon fusion bonding. As Fig. 1 can be seen, the membrane element 10 in the upper side of the same three recesses and in the bottom thereof has a recess to define the three membrane regions 12, 14 and 16.

By the piezoelectric elements or piezoceramics 22, 24 and 26, the diaphragm sections 12, 14 and 16 respectively in the direction of the pump body 30 to be actuated, so that the diaphragm portion 12 together with the fluid passage 32 is an inlet valve 62, which by actuation of the membrane portion 12th can be closed. In the same way, the diaphragm section 16 and the fluid passage 34 together constitute an outlet valve 64 which can be closed by actuating the diaphragm section 16 by means of the piezoelectric element 26. Finally, by actuating the piezoelectric element 24, the volume of the pumping chamber region 42 arranged between the valves can be reduced.

Before looking at how the in Fig. 1 The peristaltic micropump shown will first be briefly the fluid system environment in which the micropump according to Fig. 1 is installed described. The pump is glued to the pump body 30 on a support block 50, optionally, as in Fig. 1 shown grooves 52 may be provided in the support block 50 to receive excess adhesive. The grooves 52 may be provided, for example, surrounding the fluid channels 54 and 56 formed in the support block 50 to receive excess adhesive and prevent it from entering the fluid channels 54, 56 and the fluid passages 32, 34, respectively. The pump body 30 is bonded to the support block such that the fluid passage 32 is in fluid communication with the fluid passage 54 and that the fluid passage is in fluid communication with the fluid passage 56. Between the fluid channels 54 and 56, a further channel 58 may be provided as a cross leak protection in the support block 50. At the outer ends of the fluid channels 54, 56 connecting pieces 60 are provided, for example, for attaching hoses to the in Fig. 1 can serve shown fluid system. Furthermore, in Fig. 1 schematically shown a housing 61 which is joined, for example using an adhesive bond to the support block 50 to provide protection for the micropump and terminate the piezoelectric elements moisture-proof.

For the description of a peristaltic pump cycle the in Fig. 1 shown pump is initially assumed from an initial state in which the inlet valve 62 is closed, the pump diaphragm corresponding to the second diaphragm portion 14 is in the unactuated state and the exhaust valve 64 is open. Starting from this state, the pumping membrane 14 is moved downward by actuation of the piezoelectric element 24, which corresponds to the pressure stroke, whereby the stroke volume through the open outlet valve in the outlet, that is, the fluid channel 56 is promoted. The compression of the pumping chamber 42 during the pressure stroke by the stroke volume leads to an overpressure in the pumping chamber, which degrades by the fluid movement through the outlet valve.

From this state, the exhaust valve 64 is closed and the inlet valve 62 is opened. Subsequently, the pumping membrane 14 is moved upward by the actuation of the piezoelectric element 24 is terminated. The thereby expanding pumping chamber leads to a negative pressure in the pumping chamber, which in turn has an intake of fluid through the open inlet valve 62 result. Subsequently, the inlet valve 62 is closed and the exhaust valve 64 is opened, so that again the above-mentioned initial state is reached. As a result of the pumping cycle described, a fluid volume which essentially corresponds to the displacement volume of the membrane section 14 would thus be pumped from the fluid channel 54 to the fluid channel 56.

Piezoelectric converters or piezoelectric bending converters are preferably used according to the invention as piezo actuators. Such a bending transducer performs an optimum stroke when the lateral dimensions of the piezoceramic correspond to approximately 80% of the underlying membrane. Depending on the lateral dimensions of the membrane, which can typically have side lengths of 4 mm to 12 mm, deflections of several 10 μm stroke and thus volume strokes in the range from 0.1 μl to 10 μl can thus be achieved. Preferred embodiments of the present invention have volume strokes at least in such a range, since in such a volume stroke advantageous bubble tolerant peristaltic pumps can be realized.

It should be noted with piezo membrane transducers that they allow an effective stroke only downwards, ie towards the pump body. In this regard, reference is made to the schematic representations of Fig. 2a to 2f directed. Fig. 2a shows a piezoceramic 100, which is provided on both surfaces thereof with metallizations 102. The piezoceramic preferably has a large d31 coefficient and is in the direction of arrow 104 in FIG Fig. 2a polarized. According to Fig. 2a no voltage is applied to the piezoceramic.

To produce a piezo-membrane transducer is now in Fig. 2a shown piezoceramic 100 fixedly mounted on a membrane 106, for example glued, as in Fig. 2b is shown. The membrane shown is a silicon membrane, but the membrane may be formed by any other materials as long as it can be electrically contacted, for example, as a metallized silicon membrane, as a metal foil, or as a plastic membrane rendered conductive by a two-component injection molding.

If a positive voltage, ie a voltage in the polarization direction, U> 0, is applied to the piezoceramic, then the piezoceramic contracts, see Fig. 2c , Due to the firm connection of the piezoceramic 100 to the membrane 106, the membrane 106 is deflected downwards by this contraction, as indicated by arrows in FIG Fig. 2d is clarified.

In order to bring about a movement of the membrane upwards, a negative voltage, ie a voltage opposite to the direction of polarization, would have to be applied to the piezoceramic, as in FIG Fig. 2e is shown. However, this leads to a depolarization of the piezoceramic even at low field strengths in the opposite direction, as in Fig. 2e is indicated by an arrow 108. Typical depolarization field strengths of lead zirconate titanate ceramics (PZT ceramics) are, for example, -4000 V / cm. Thus, a movement of the membrane upwards, ie in the direction of the piezoceramic, not be realized, as in Fig. 2f is indicated.

Despite this drawback to the effect that due to the asymmetrical nature of the piezoelectric effect with the two-layer silicon piezoelectric bending transducer, ie the piezo diaphragm transducer, only an active downward movement, ie toward the pump body out, can be realized, is the use Such a bending transducer is a preferred embodiment of the present invention, since this form of transducer has numerous advantages. First, they have a fast response, on the order of about 1 millisecond with low power consumption. Furthermore, a scaling with dimensions of piezoceramic and membrane over large areas is possible, so that a large stroke (10 .... 200 microns) and a large force (switching pressures 10 ⁴ Pa to 10 ⁶ Pa) are possible, with a larger Hub decreases the achievable force and vice versa. Furthermore, the medium to be switched is separated from the piezoceramic by the membrane.

If the peristaltic micropumps of the invention are to be used in applications where bubble-tolerant, self-priming behavior is required, the micro-peristaltic pumps must be designed to comply with a compression ratio design rule that defines the ratio of stroke volume to dead volume. To define the terms displacement volume .DELTA.V and dead volume V ₀ is first on the Fig. 3a to 3b directed.

Fig. 3a schematically shows a pump body 200 having an upper surface thereof, in which a pumping chamber 202 is structured. Above the pump body 200, a diaphragm 204 is schematically shown, which is provided with an inlet valve piezoactuator 206, a pumping chamber piezoactuator 208 and an outlet valve piezoactuator 210. By means of the piezoactuators 206, 208 and 210, respective regions of the membrane 204 can be moved downwards, ie in the direction of the pump body 200, as indicated by arrows in FIG Fig. 3a is shown. Through the line 212 is in Fig. 3a Further, the pump chamber 200 opposite portion of the diaphragm 204, ie the pumping membrane, in its deflected, that is actuated by the pumping chamber piezoelectric actuator 208, shown state. The difference of the pumping chamber volume between the undeflected state of the membrane 204 and the deflected state 212 of the membrane 204 represents the stroke volume ΔV of the pumping membrane.

According to Fig. 3a For example, the channel regions 214 and 216 disposed below the inlet valve piezoactuator 206 and below the outlet valve piezoactuator 210 may be closed by a respective actuation of the corresponding piezoelectric actuator by resting the respective membrane regions on the underlying regions of the pump body. Here are the FIGS. 3a to 3c merely rough schematic representations, wherein the respective elements are designed so that a closing of respective valve openings is possible. Thus, in turn, an intake valve 62 and an exhaust valve 64 are formed.

In Fig. 3b a situation is shown in which the volume of the pumping chamber 202 is reduced by operating the pumping chamber piezoactuator 208 and in which the inlet valve 62 is closed. In the Fig. 3b The situation shown thus represents the state after ejection of a fluid amount from the exhaust valve 64, wherein the volume of the remaining between the closed inlet valve 62 and the passage opening of the open exhaust valve 64 fluid area represents the dead volume V ₀ with respect to the pressure stroke, as indicated by the hatched area in Fig. 3b is shown. The dead volume with respect to a suction stroke in which the inlet valve 62 is opened and the outlet valve 64 is closed is defined by the volume of the fluid area remaining between the closed outlet valve 64 and the passage opening of the open inlet valve 62, as in FIG Fig. 3c is shown by the hatched area.

It should be noted at this point that the respective dead volume is defined by the respective closed valve up to the passage opening at which a significant pressure drop occurs at the moment of a respective change in volume of the pumping chamber. With a symmetrical construction of inlet valve and outlet valve, as is preferred for a bidirectional pump, the dead volumes V ₀ for the pressure stroke and the suction stroke are identical. If different dead volumes occur due to an asymmetry for a pressure stroke and a suction stroke, then, in the sense of a worst-case analysis, it is assumed in the following that the larger of the two dead volumes is used to determine the respective compression ratio.

The compression ratio of the micro-peristaltic pump is calculated from the stroke volume ΔV and the dead volume V ₀ as follows: $$\mathrm{\epsilon }=\mathrm{.DELTA.V}/{\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="imgf0002.png"\; state="\{\{state\}\}">V</figure-callout>}}_0$$

In the following, a worst-case view is assumed in which the entire pump area is filled with a compressible fluid (gas). The volume / pressure conditions occurring in the peristaltic pump in a peristaltic pumping cycle as described above are shown in the graph of FIG Fig. 4 shown. Here are in Fig. 4 in each case both the isothermal volume / pressure characteristics and the adiabatic volume / pressure characteristics are shown, wherein in the sense of a worst-case consideration in the following of isothermal conditions, as they occur in slow state changes, is assumed.

At the beginning of a pressure stroke, there is a pressure p ₀ in the fluid area existing between the inlet valve and the outlet valve, while this area has a volume V ₀ + ΔV. Starting from this state, the pressure membrane moves during the pressure stroke to the stroke volume .DELTA.V down, creating an overpressure p _Ü in the fluid region, ie the pumping chamber forms, so that at a volume of V _0, a pressure of p ₀ + p _Ü prevails. The overpressure in the pumping chamber degrades by the air volume .DELTA.V is conveyed through the outlet until a pressure equalization has taken place. This outflow of fluid from the outlet corresponds to Fig. 4 the jump from the upper curve to the lower curve. At the end of the pressure equalization there is therefore a state p ₀ , V ₀ , which corresponds to the starting point of a suction stroke. Starting from this state, the membrane is moved away from the pump body, ie the volume of the pressure chamber expands by the displacement volume .DELTA.V. Thus, the in Fig. 4 as "suction stroke after expansion" designated state p ₀ - p _u , V ₀ + ΔV changed. Due to the prevailing negative pressure, a fluid volume .DELTA.V is sucked through the inlet port until a pressure equalization has taken place. The inflow of fluid into the pumping chamber corresponds to Fig. 4 the jump from the lower curve to the upper curve. After pressure equalization, the state p ₀ , V ₀ + ΔV prevails, which in turn corresponds to the starting point of a pressure stroke.

In the above general state considerations, which serve to illustrate the invention in general, the volume displacements of the intake valve and the exhaust valve between the respective suction strokes and pressure strokes were neglected.

In order to achieve a bubble tolerance, the overpressure p _Ü during the pressure stroke, and the negative pressure p _U during the suction stroke, exceed a minimum value during the compression stroke or during the intake stroke must fall below. In other words, the pressure amount during the compression stroke and the suction stroke must exceed a minimum value, which may be referred to as delivery pressure p _F. This delivery pressure is the pressure in the pressure chamber which must at least prevail to bypass a liquid / gas interface at a location which is a flow point between the pumping chamber and the passageway of the first or second valve, including this passageway move. This delivery pressure can be determined as follows, depending on the size of this flow point.

Capillary forces must be overcome if free surfaces, for example in the form of gas bubbles (eg air bubbles), are moved in the fluid areas within the pump. The pressure that must be applied to overcome such capillary forces depends on the surface tension of the liquid at the liquid / gas interface and the maximum radius of curvature r ₁ and the minimum radius of curvature r _{2 of} the meniscus of that interface: $$\mathrm{Ap}=\mathrm{\sigma }\left(\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="imgf0010.png"\; state="\{\{state\}\}">r</figure-callout>}}_1}+\frac{12}{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="imgf0010.png"\; state="\{\{state\}\}">r</figure-callout>}}_2}\right)$$

The delivery pressure to be provided is defined by Equation 2 at the location within the flow path of the microperistaltic pump where the sum of the inverse radii of curvature r ₁ and r _{2 of} a liquid / gas interface having a given surface tension is at a maximum. This point corresponds to the Flußengstelle.

For example, to illustrate, a channel 220 (FIG. Fig. 5a ) with a width d, where the height of the channel is also d. The channel 220 has a cross-sectional change at both channel ends 222, for example below the valve membrane or the pumping membrane. In Fig. 5a the channel is completely filled with a liquid 224 flowing in the direction of the arrow 226.

According to Fig. 5b An air bubble 228 now encounters the change in cross section at the entrance of the channel 220. In this case, a wetting angle θ occurs. The wetting angle θ defines a maximum radius of curvature r ₁ and a minimum radius of curvature r _{2 of} a meniscus 230 to be moved through the channel 220, with r ₁ = r ₂ for the same height and width of the channel. In Fig. 5c the situation is illustrated when the air bubble or meniscus 230 reaches the cross-sectional change 222 at the end of the channel 220.

If such a channel represents the area of a fluid system at which the greatest capillary force must be overcome, the required pressure in this special case is r ₁ = r ₂ = r = d / 2: $$\mathrm{Ap}=\mathrm{\sigma }\frac{2}{\mathrm{r}}=\mathrm{\sigma }\frac{4}{\mathrm{d}}$$

This pressure barrier is not negligible in microperistaltic pumps of the type according to the invention due to the small dimensions of geometry, if such a channel represents the bottleneck of the pump. With a line diameter of for example d = 50 μm and a surface tension air / water of σ _wa = 0.075 N / m, the pressure barrier Δp _b = 60 hPa, while with a channel diameter d = 25 μm the pressure barrier Δp _b = 120 hPa.

In the case of microperistaltic pumps of the type according to the invention, however, the mentioned constriction is generally defined by the distance between the valve membrane and the opposite region of the pump body (for example a sealing lip) when the valve is open. This bottleneck represents a gap having an infinite width compared to the height, ie r ₁ = r and r ₂ = infinity.

For such a channel it follows from equation 2 above: $$\mathrm{Ap}=\mathrm{\sigma }\frac{1}{\mathrm{r}}$$

wobei Θ den Benetzungswinkel darstellt und Γ die Verkippung zwischen den beiden Wänden.In general, the relationship between the smallest radius of curvature and the smallest wall distance d is given by the following relationship: $$\mathrm{r}=\frac{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0010.png"\; state="\{\{state\}\}">d</figure-callout>}}{2\cdot \sin \left(90\mathrm{°}+\mathrm{\Gamma }-\mathrm{\Theta }\right)}$$

where Θ represents the wetting angle and Γ the tilt between the two walls.

The worst-case case, ie the smallest radius of curvature independent of the tilt angle and wetting angle, is given if the sine function is maximal, ie sin (90 ° + Γ-Θ) = 1. This occurs, for example, in abrupt cross-sectional changes, as in the Fig. 5a to 5c shown, or combinations of tilt angles Ben and wetting angle Θ. In the worst case case: $$\mathrm{r}=\frac{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0010.png"\; state="\{\{state\}\}">d</figure-callout>}}{2}$$

As the smallest occurring radius of curvature, therefore, half of the smallest ascending wall distance can be considered independently of the tilt angle Γ, wetting angle Θ or abrupt changes in cross section.

In a peristaltic pump, fluid connections exist between the chambers with a given channel geometry and a constriction defining a minimum flow dimension d. For such a channel: $$\mathrm{Ap}=\mathrm{\sigma }\frac{4}{\mathrm{d}}$$

On the other hand, the peristaltic pump has a constriction at the inlet or outlet valve, which is defined by the gap geometry dependent on the valve lift d. For these applies: $$\mathrm{Ap}=\mathrm{\sigma }\frac{2}{\mathrm{d}}$$

The respective constriction (channel constriction or valve constriction in the open state), at which larger capillary forces must be overcome, can be regarded as a flow point of the microperistaltic pump.

In preferred embodiments of the present invention, therefore, communication channels within the peristaltic pump are designed such that the diameter of the channel is at least twice that of the valve throat, i. the distance between diaphragm and pump body in the open valve state, exceeds. In such a case, the valve gap represents the flow point of the microperistaltic pump. For example, with a valve lift of 20μm, communication channels having a smallest dimension, i. Bottleneck, be provided by 50μm. The upper limit of the channel diameter is determined by the dead volume of the channel.

The capillary force to be overcome depends on the surface tension at the liquid / gas interface. This surface tension in turn depends on the partners involved. For a water / air interface, the surface tension is about 0.075 N / m and varies slightly with temperature. Organic solvents generally have a significantly lower surface tension, while the surface tension at a mercury / air interface, for example, about 0.475 N / m. A peristaltic pump designed to overcome the capillary force at a surface tension of 0.1 N / m is thus suitable for pumping virtually all known liquids and gases in a bubble-tolerant and self-priming manner. Alternatively, the compression ratio of a micro-peristaltic pump according to the invention can be made correspondingly higher in order to enable such pumping, for example, also for mercury.

The design rules discussed below apply to the pumping of gases and incompressible liquids, and in the case of liquids, it must be assumed that in the worst case, air bubbles fill the entire pumping chamber volume. In the promotion of gases must be expected that can get into the pump due to a Auskondensierung liquid. In the following it is assumed that the piezoelectric actuator is designed so that all required negative pressures and pressures can be achieved.

Die Variablen p₀, V₀, ΔV und p_ü wurden oben bezugnehmend auf Fig. 4 erläutert. γ_A stellt den Adiabatenkoeffizient des Gases, d.h. der Luft, dar. Die linke Seite der obigen Gleichung stellt den Zustand vor der Kompression dar, während die rechte Seite den Zustand nach der Kompression darstellt. Weiterhin muß der Überdruck p_Ü beim Druckhub größer als der positive Förderdruck p_F sein: $${\mathrm{p}}_{\mathrm{Ü}}>{\mathrm{p}}_{\mathrm{F}}$$

First, consider a pressure stroke. During the ejection process, the actuator membrane compresses the gas volume or air volume. The maximum overpressure in the pump chamber p _Ü is then determined by the pressure in the air bubble. It is calculated from the equation of state of the bubble. $${\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_0{\left({\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="imgf0002.png"\; state="\{\{state\}\}">V</figure-callout>}}_0+\mathrm{.DELTA.V}\right)}^{{\mathrm{\gamma }}_{\mathrm{A}}}=\left({\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_0+{\mathrm{p}}_{\mathrm{<figure-callout\; id="0"\; label="Ü\; \; V"\; filenames="imgf0002.png"\; state="\{\{state\}\}">Ü\; </figure-callout>}}\right){\left({\mathrm{V}}_{}\right)}^{}{\left({\mathrm{}}_0\right)}^{{\mathrm{\gamma }}_{\mathrm{A}}}$$

The variables p ₀ , V ₀ , ΔV and p _ü were discussed above with reference to FIG Fig. 4 explained. γ _A represents the adiabatic coefficient of the gas, ie the air. The left side of the above equation represents the state before compression, while the right side represents the state after compression. Furthermore, the overpressure p _Ü must be greater than the positive delivery pressure p _F during the pressure stroke: $${\mathrm{p}}_{\mathrm{Ü}}>{\mathrm{p}}_{\mathrm{F}}$$

Now consider a suction stroke. The suction stroke differs by the initial position of the volumes. After expansion, the negative pressure p _U arises in the pumping chamber, ie p _U is negative: $${\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_0{{\mathrm{<figure-callout\; id="0"\; label="V"\; filenames="imgf0002.png"\; state="\{\{state\}\}">V</figure-callout>}}_0}^{{\mathrm{\gamma }}_{\mathrm{A}}}=\left({\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_0+{\mathrm{p}}_{\mathrm{<figure-callout\; id="0"\; label="U\; \; V"\; filenames="imgf0002.png"\; state="\{\{state\}\}">U\; </figure-callout>}}\right){\left({\mathrm{V}}_{}\right)}^{}{\left({\mathrm{}}_0+\mathrm{.DELTA.V}\right)}^{{\mathrm{\gamma }}_{\mathrm{A}}}$$

The left side of Equation 11 represents the state before expansion, while the right side represents the state after expansion. The negative pressure p _U during the pressure stroke must be smaller than the necessary negative delivery pressure p _F. It should be noted that the discharge pressure p _F in terms of absolute value in the consideration of the pressure stroke, in terms of absolute value in the consideration of the suction stroke. It follows: $${\mathrm{p}}_{\mathrm{U}}>{\mathrm{p}}_{\mathrm{F}}$$

From the above equations results for the minimum required compression ratio of bubble-tolerant microperistaltic pumps for the pressure stroke: $$\mathrm{\epsilon }>{\left(\frac{{\mathrm{p}}_0}{{\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_0+{\mathrm{<figure-callout\; id="1"\; label="p\; F"\; filenames="imgf0010.png"\; state="\{\{state\}\}">p\; </figure-callout>}}_{\mathrm{F}}}\right)}^{\frac{1}{{\mathrm{\gamma }}_{\mathrm{A}}}}-1$$

For the suction stroke the following compression ratio results: $$\mathrm{\epsilon }>{\left(\frac{{\mathrm{p}}_0}{{\mathrm{<figure-callout\; id="0"\; label="p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_0+{\mathrm{<figure-callout\; id="1"\; label="p\; F"\; filenames="imgf0010.png"\; state="\{\{state\}\}">p\; </figure-callout>}}_{\mathrm{F}}}\right)}^{\frac{1}{{\mathrm{\gamma }}_{\mathrm{A}}}}-1$$

• Druckhub: $$\mathrm{ϵ}>\frac{1}{{\mathrm{\gamma }}_{\mathrm{A}}}\frac{{\mathrm{<figure-callout\; id="0"\; label="p\; F\; p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_{\mathrm{F}}}{{\mathrm{p}}_{}}$$
  
• Saughub: $$\mathrm{ϵ}>-\frac{1}{{\mathrm{\gamma }}_{\mathrm{A}}}\frac{{\mathrm{<figure-callout\; id="0"\; label="p\; F\; p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_{\mathrm{F}}}{{\mathrm{p}}_{}}$$
  

If the delivery pressure p _{F is} small compared to the atmospheric pressure p ₀ , the preceding equations can be simplified as follows, which corresponds to a linearization around the point p ₀ , V ₀ :

• compression stroke: $$\mathrm{\epsilon }>\frac{1}{{\mathrm{\gamma }}_{\mathrm{A}}}\frac{{\mathrm{<figure-callout\; id="0"\; label="p\; F\; p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p\; </figure-callout>}}_{\mathrm{F}}}{{\mathrm{p}}_{}}$$
  
• suction stroke: $$\mathrm{\epsilon }>-\frac{1}{{\mathrm{\gamma }}_{\mathrm{A}}}\frac{{\mathrm{<figure-callout\; id="0"\; label="p\; F\; p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p\; </figure-callout>}}_{\mathrm{F}}}{{\mathrm{p}}_{}}$$
  

As a valid equation for the suction stroke and the pressure stroke results: $$\mathrm{\epsilon }>\frac{1}{{\mathrm{\gamma }}_{\mathrm{A}}}\frac{\left|{\mathrm{<figure-callout\; id="0"\; label="p\; F\; p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p\; </figure-callout>}}_{\mathrm{F}},\right|}{{\mathrm{p}}_{}}$$

For fast state changes, the ratios are adiabatic, ie γ _A = 1.4 for air. For slow state changes, the ratios are isothermal, ie γ _A = 1. With a consistent application of the worst-case assumption, the criterion with γ _A = 1 is used below. Thus, as a design rule for the necessary compression ratio of bubble-tolerant micro-peristaltic pumps, it can be stated that the compression ratio must be greater than the ratio of the delivery pressure to the atmospheric pressure, ie: $$\mathrm{\epsilon }>\frac{\left|{\mathrm{<figure-callout\; id="0"\; label="p\; F\; p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p\; </figure-callout>}}_{\mathrm{F}},\right|}{{\mathrm{p}}_{}}$$

Or with the mentioned volumes: $$\frac{\mathrm{.<figure-callout\; id="0"\; label="DELTA.V\; V"\; filenames="imgf0002.png"\; state="\{\{state\}\}">DELTA.V\; </figure-callout>}}{{\mathrm{V}}_{}}>\frac{\left|{\mathrm{<figure-callout\; id="0"\; label="p\; F\; p"\; filenames="imgf0002.png"\; state="\{\{state\}\}">p\; </figure-callout>}}_{\mathrm{F}},\right|}{{\mathrm{p}}_{}}$$

The simple linear design rule given above corresponds to the tangent to the isothermal equation of state of Fig. 4 at the point p ₀ , V ₀ .

Preferred embodiments of microperistaltic pumps according to the invention are thus designed such that the compression ratio satisfies the above condition, wherein the minimum necessary delivery pressure corresponds to the pressure defined in equation 8 if channel narrows occurring in the peristaltic pump have minimum dimensions which are at least twice as large as the valve gap. Alternatively, the minimum required delivery pressure may correspond to the pressure defined in Equation 3 or Equation 7 if the flow location of the microperistaltic pump is not defined by a gap but a channel.

If a microperistaltic pump according to the invention is to be used when pressure boundary conditions of a negative pressure p ₁ at the inlet or a counterpressure p ₂ prevail at the outlet, the compression ratio of a microperistaltic pump must be correspondingly greater in order to allow pumping against these inlet pressures or outlet pressures. The pressure boundary conditions are defined by the intended application of the microperistaltic pump and can range from a few hPa to several 1000 hPa. For such cases occurring in the pumping chamber pressure p _T, or negative pressure p _U must achieve these back pressures at least, so that a pumping action occurs. For example, only the height difference of a possible inlet vessel or outlet vessel of 50 cm in water leads to counter pressures of 50 hPa.

Further, the desired delivery rate is a constraint that places additional demands. For a given swept volume ΔV, the delivery rate Q is defined by the repetitive peristaltic cycle operating frequency f: Q = ΔV · f. Within the period T = 1 / f both the suction stroke and the pressure stroke of the peristaltic pump must be performed, in particular the displacement .DELTA.V must be implemented. The available time is therefore maximum T / 2 for suction stroke and pressure stroke. The time required to promote the stroke volume through the pumping chamber inlet and the valve throat now depends on the one hand on the flow resistance, on the other hand on the pressure amplitude in the pumping chamber.

If foam-like substances are to be pumped with a microperistaltic pump according to the invention, it may be necessary for a plurality of capillary forces, as described above, to be overcome since a plurality of corresponding liquid / gas interfaces occur. In such a case, the micro-peristaltic pump must be designed to have a compression ratio in order to be able to produce correspondingly higher delivery pressures.

In summary, it can be determined that the compression ratio of a microperistaltic invention must be appropriately higher when necessary in the microperistaltic delivery pressure p _F in addition to the aforementioned capillary forces also depends on the boundary conditions of the application. It should be noted that here the delivery pressure is considered relative to the atmospheric pressure, that is, a positive delivery pressure p _{F is} assumed in the pressure stroke, while a negative delivery pressure p _{F is} assumed in the intake stroke. As a technically meaningful value for a robust operation, therefore, an amount of the delivery pressure of at least p _F = 100 hPa can be assumed for a suction stroke and a pressure stroke.

Considering a back pressure of, for example, 3000 hPa at the pump outlet, against which must be pumped, then results from the above equation 13, a compression ratio of ε> 3, assuming an atmospheric pressure of 1013 hPa.

If the microperistaltic pump must suck against a large negative pressure, for example a negative pressure of -900 hPa, a compression ratio of ε> 9 must be maintained according to Equation 14 above in order to allow pumping against such negative pressure.

Examples of peristaltic micropumps that enable the realization of such compression ratios are explained in more detail below.

Fig. 6b shows a schematic cross-sectional view of a peristaltic micropump with membrane element 300 and pump body 302 along the line BB of Fig. 6a and Fig. 6c , while Fig. 6a a schematic plan view of the membrane element 300 and Fig. 6c a schematic plan view of the pump body 302 shows. The membrane element 300 in turn has three membrane sections 12, 14 and 16 which are each provided with piezoactuators 22, 24 and 26. In the pump body 302, in turn, an inlet opening 32 and an outlet opening 34 is formed, such that the inlet port 32 defines an inlet valve together with the diaphragm portion 12, while the outlet port 34 defines an outlet valve with the diaphragm portion 16. Below the diaphragm portion 14, a pumping chamber 304 is formed in the pump body 302. Furthermore, fluid channels 306 are formed in the pump body 302, which are fluidly connected to the diaphragm areas 12 and 16 associated valve chamber 308 and 310. The valve chambers 308 and 310 are formed in the embodiment shown by recesses in the membrane element 300, wherein in the membrane element 300 further to the pumping chamber 304 contributing recess 312 is formed.

In the in the Fig. 6a to 6c In the embodiment shown, the pumping chamber volume 304 is made larger than the volumes of the valve chambers 308 and 310. This is achieved in the illustrated embodiment by forming a pumping chamber depression in which a structuring in the form of a pumping chamber depression is formed in the pump body 302. The stroke of the pump diaphragm 14 is preferably designed so that it can largely displace the volume of the pumping chamber 304.

A further increase of the pumping chamber volume compared to the valve chamber volume is in the in the Fig. 6a to 6c shown embodiment in that the pumping chamber membrane 14 in terms of area (in the plane of the diaphragm member 300 and the pump body 302) is made larger than the valve chamber membranes, as best in Fig. 6a you can see. This results in a larger in terms of area compared with the valve chambers pump chamber.

In order to reduce the flow resistance between the valve chambers 308 and 310 and the pumping chamber 304, the supply channels 306 in the surface of the pump body 302 are structured. These fluid channels 306 provide reduced flow resistance without significantly degrading the compression ratio of the peristaltic micropump.

Alternatively to that in the Fig. 6a to 6c In the embodiment shown, the surface of the pump body 302 could be realized with three stage depressions to implement the pumping chamber of increased depth (compared to the valve chambers), while the top chip is a substantially unstructured membrane. Such two-stage subsidence are technologically more difficult to implement than that in the Fig. 6a to 6c shown embodiment.

• Abmessung der Ventilmembrane 12, 16: 7,3 x 5,6 mm;
• Abmessung der Pumpmembran 14: 7,3 x 7,3 mm;
• Membrandicke: 40 µm;
• Durchmesser der Einlaß- bzw. Auslaßdüse 32, 34: mindestens 50 pm;
• Ventilkammerhöhe: 8 µm;
• Höhe der Pumpkammer: 30 µm;
• Breite der Ventil-Dichtlippen d_DL: 10µm;
• realisierbare Gesamtgröße: 8 x 21 mm;
• Abmessungen der Piezoelemente: Fläche: 0,8 mal Membranabmessung, Dicke: 2,5 mal Membrandicke;
• Dicke der Piezoelemente: 100µm; und
• Öffnungsquerschnitt der Öffnungen 32, 34: 100µm x 100µm.

Exemplary dimensions of the in Fig. 6a to 6c shown embodiment of a peristaltic micropump are as follows:

• Valve diaphragm dimensions 12, 16: 7.3 x 5.6 mm;
• Measurement of the pumping membrane 14: 7.3 x 7.3 mm;
• Membrane thickness: 40 μm;
• Diameter of the inlet or outlet nozzle 32, 34: at least 50 pm;
• Valve chamber height: 8 μm;
• Height of the pumping chamber: 30 μm;
• Width of the valve sealing lips d _DL : 10μm;
• Total realized size: 8 x 21 mm;
• Dimensions of the piezo elements: Area: 0.8 times membrane dimension, thickness: 2.5 times membrane thickness;
• Thickness of the piezo elements: 100μm; and
• Opening cross-section of the openings 32, 34: 100μm x 100μm.

An enlarged view of the left part of the in Fig. 6b shown cross-sectional view is in Fig. 7 shown in FIG Fig. 7 the height H of the pumping chamber 304 is displayed. Although according to the presentation of Fig. 7 For example, as the patterns forming the pumping chamber 304 in the pump body 302 and in the membrane member 300 have equal depths, it is preferable to make the patterns in the pump body 302 deeper in depth than those in the membrane member to provide the flow channel 306 with a sufficient flow area without unduly compromising the compression ratio. For example, the patterns in the pump body 302 that contribute to the fluid channel 306 and the pumping chamber 304 may have a depth of 22 μm, while the patterns in the membrane element 300 that define the valve chambers 308 and the pressure chamber 304, respectively, have a depth of 8 microns may have.

Fig. 8 FIG. 12 is a schematic cross-sectional view of an enlargement of the section A of FIG Fig. 7 but in a modified form. According to Fig. 8 the web is spaced from the opening 32 in the direction of the channel 206. As a result, mounting tolerances can be taken into account in a double-sided lithography. Furthermore, it can be prevented that wafer thickness variations that may result in valve openings with different cross-sectional sizes, have no negative impact. As in Fig. 8 can be seen, defines the distance x to the diaphragm 12, the Flußengstelle between the pumping chamber and valve port with the valve open.

As stated above, in the areas of the fluid system in which a pumping action is required by forming a pump chamber volume of a peristaltic pump, the compression ratio of the peristaltic pump is made large to ensure self-filling behavior and robust operation with respect to bladder tolerance. In order to achieve this, it is preferable to keep the dead volumes small, which can be assisted by adapting the contour or shape of the pumping chamber to the bending line of the pumping membrane in the deflected state.

A first possibility to realize such an adaptation is to implement a round pumping chamber, ie a pumping chamber whose circumferential shape is adapted to the deflection of the pumping membrane. A schematic plan view of the pumping chamber and fluid channel section of a pump body having such a pumping chamber is shown in FIG Fig. 9a shown. In turn, round pumping chamber 330 open similar to the representation of Fig. 6c the fluid channels 306, which produce a fluid connection to valve chambers, which in turn may be structured, for example, in a membrane element.

In order to achieve a further reduction of the dead volume and thus a further increase in the compression ratio, the pumping chamber can be configured under the pumping membrane so that its contour facing the pumping membrane follows in a precise fit the bending line of the pumping membrane. Such a contour of the pumping chamber can be achieved for example by a correspondingly shaped injection molding tool or by an embossing punch. A schematic plan view of a pump body 340, in which such a bending line of the actuator membrane following fluid chamber 342 is structured, is in Fig. 9b shown. Furthermore, in Fig. 9b illustrated in the pump body structured fluid channels 344 which lead to the fluid chamber 342 and away from the same. A schematic cross-sectional view along the line cc of Fig. 9b is in Fig. 9c shown in FIG Fig. 9c Furthermore, a membrane 346 with the same associated piezoelectric actuator 348 shown. A flow through the fluid channels 344 is in Fig. 9c indicated by arrows 350. Furthermore, in Fig. 9c the membrane 346 facing to the bending line of the membrane (in the actuated state) adapted contour 352 of the fluid chamber or pumping chamber 342 to recognize. This shape of the fluid chamber 352 allows substantially all the volume of the fluid chamber 342 to be displaced upon actuation of the diaphragm 346 by the piezoactuator 348, whereby a high compression ratio can be achieved.

An embodiment of a peristaltic micropump, in which both the pumping chamber 342 and valve chambers 360 are adapted to the bending lines of the respective associated membrane sections 12, 14 and 16, is in the 10a and 10b shown, where Fig. 10b a schematic plan view of the pump body 340 shows while Fig. 10a a schematic cross-sectional view taken along the line aa of Fig. 10b shows. Like that 10a and 10b can be seen, the shape and contour of the valve chamber 360 and 362 as explained above with reference to the pumping chamber 342, adapted to the bending line of the respective associated membrane portion 12 and 16 respectively. Furthermore, as best in Fig. 10b In turn, fluid channels 344a, 344b, 344c, and 344d are formed in the pump body 340. The fluid channel 344a constitutes an input fluid channel, the fluid channel 344b connects the valve chamber 360 to the pumping chamber 342, the fluid channel 344 connects the pumping chamber 342 to the valve chamber 362, and the fluid channel 344d constitutes an outlet channel.

As further in Fig. 10a 11, the membrane element 380 in this embodiment is an unstructured membrane element which is inserted into a recess provided in the pump body 340 to define the valve chambers and the pump chamber together with the fluid regions formed in the pump body 340.

The connection channels 344b and 344c between the actuator chambers are connected so that they contain a small dead volume compared to the stroke volume. At the same time, these fluid channels reduce the flow resistance between the actuator chambers significantly, so that even larger pumice frequencies and thus larger flow rates, such a stream in turn by arrows 350 in Fig. 10a is displayed, become possible. In the area of the valve chambers 360 and 362, the fluid passages are separated by actuating the membrane sections 12 and 16, respectively, through the fully deflected membrane sections so that fluid separation occurs between the fluid passages 344a and 344b and between the fluid passages 344c and 344d, respectively. The contour of the valve chambers must be exactly adapted to the bending line of the respective membrane sections in order to achieve a dense fluid separation. Alternatively, as in Fig. 11 is shown, a web 390 may be provided in the respective valve chamber in the region of the largest stroke of the diaphragm portion 12, which is shaped accordingly, so that it can be completely sealed by the bending of the diaphragm portion 12. More specifically, the web bends up to the edges of the valve chamber, according to the shape of the valve chamber adapted to the bending line. This web can protrude into the respective valve chamber, wherein alternatively, as in Fig. 11 1, the depth of the connection channels 344 may be greater than the stroke y of the membrane portion 12, in which the membrane portion abuts against the pump body, so that the web 390 is sunk, so to speak. If the depth of the connection channels is greater than the maximum stroke, this results in the cost of the compression ratio, but allows low flow resistance between the actuator chambers.

An alternative embodiment of a valve chamber 360 is shown in FIG Fig. 12 shown where the depth of the connecting channels 344 is smaller than the maximum stroke y of the diaphragm portion 12, and thus as the depth of the the bending line of the diaphragm portion 12 adapted valve chamber 360 in the region of the largest stroke of the diaphragm portion 12. This allows a secure seal in the closed state of the valve can be achieved.

In order to achieve a valve seal in the closed state that meets predetermined pressure requirements, it may be preferable to provide a web 390a in the valve chamber 360 which does not simulate the maximum possible bending line of the actuator element, ie the membrane section 12 together with the piezoactuator 22 in Fig. 13 is shown. The maximum possible bending line of the membrane section 12 is in Fig. 13 shown by a dashed line 400, while the line 410 corresponds to the maximum possible deflection of the diaphragm portion 12 due to the provision of the web 390a. Thus, in the fully deflected condition, when the web 390 is sealed, the membrane 12 seats with a residual force on the land 390a, which residual force can be dimensioned to meet pressure requirements that the gasket must endure.

In practical implementations, the bending line of the membrane will often not be perfectly concentric with the membrane center, for example due to assembly tolerances of the piezoceramics and due to inhomogeneities in the application of adhesive, by which the piezoceramics are attached to the membranes. Therefore, the area of the land seal can be slightly increased, for example, by about 5 to 20 μm, depending on the stroke of the actuator, relative to the rest of the fluid chamber in order to ensure reliable contact of the membrane with the web and thus a secure seal. This also corresponds to the in Fig. 13 shown situation. It should be noted, however, that this increases the dead volume and the compression ratio is reduced.

As an alternative to the abovementioned possibilities, a plastically deformable material, for example silicone, can be used as the fluid chamber material at least in the region below the movable membrane. By correspondingly large-sized actuator forces, inhomogeneities can then be compensated. In such a case, there is no hard-hard seal, so that a certain tolerance against particles and deposits exists.

In the following is a brief example of a sizing of a peristaltic pump, as in the 10a and 10b shown. The thickness of the membrane sections 12, 14 and 16 and thus the thickness of the membrane element 380 can be, for example, 40 μm, while the thickness of the piezoactuators can be, for example, 100 μm. As a piezoceramic, a PZT ceramic with a large d31 coefficient can be used. The side length of the membranes may for example be 10 mm, while the side length of the piezoelectric actuators may be 8 mm, for example. The voltage swing for actuating the actuators in the aforementioned actuator geometry can be, for example, 140 V, which results in a maximum stroke of approximately 100 to 200 μm with a stroke volume of the pump diaphragm of approximately 2 to 4 μl.

By adapting the fluid chamber design to the bending line of the membrane, the dead volume of the three fluid chambers required for the peristaltic pump drops, so that only the connection channels connecting the valve chambers to the pumping chamber remain. Connecting channels with a depth of 100 microns, a width of 100 microns and a length of 10 mm, so that there is a total length for the fluid channels 344b and 344c of 20 mm, resulting in a pumping chamber dead volume of 0.2 ul. From this a compression ratio ε = ΔV / V = 4 μl / 0.2 μl = 20 can be determined.

With such a high compression ratio of up to 20, such fluid modules are bubble tolerant and self-priming and can deliver both liquids and gases. Furthermore, such fluid pumps can in principle build up several bar pressure for compressible and liquid media, depending on the design of the piezoelectric actuator. In such a micropump, the maximum pressure that can be generated is no longer limited by the compression ratio, but defined by the maximum force of the drive element and by the tightness of the valves. Despite these properties, several ml / min can be delivered by a suitable channel dimensioning with a low flow resistance.

In the embodiment described above, all the fluid channels, i. H. Also, the inlet fluid passage 344a and the outlet fluid passage 344d are guided laterally, d. H. the fluid channels are in the same plane as the fluid chambers. As stated above, in such a course, the sealing of the channels may be difficult. However, it is advantageous in the lateral course of the fluid channels that the entire fluid system, including reservoirs connected to the inlet channel 344a and / or the outlet channel 344d, can be formed with a manufacturing step, such as injection molding or stamping.

In Fig. 14 an embodiment of a micro-peristaltic pump according to the invention is shown in which the inlet fluid channel 412 and the outlet fluid channel 414 are vertically recessed in the pump body 340. The fluid channels 412 and 414 have a substantially vertical portion 412a and 414a, each of which opens into the valve chambers 360 and 362 substantially centrally below the associated membrane portions 12 and 16, respectively. The advantage of in Fig. 14 shown embodiment of the fluid channels is that the fluid channels can be sealed sealed. The disadvantage, however, is that such vertical sunken fluid channels are difficult to produce manufacturing technology.

The peristaltic micropumps according to the invention are preferably activated by the membrane, for example the metal membrane or the semiconductor membrane, being at a ground potential, while the piezoceramics are moved through a typical peristaltic cycle by respectively corresponding voltages be applied to the piezoceramics.

In addition to the above-described microperistaltic pump using three fluid chambers 342, 360 and 362, a peristaltic micropump according to the invention can have further fluid chambers, for example a further fluid chamber 420, which is connected to the pumping chamber 342 via a fluid channel 422. Such a structure is in Fig. 15 1, wherein a first reservoir 424 is connected to the valve chamber 360 via the fluid channel 344a, a second reservoir 426 is connected to the valve chamber 420 via a fluid channel 428, and a third reservoir 430 is connected to the valve chamber 362 via the fluid channel 344d.

A structure with four fluid chambers, as in Fig. 15 is shown, for example, form a branching structure or a mixer, in which the mixed streams can be actively promoted. The extension to four fluid chambers with four associated fluid actuators, such as in Fig. 15 the realization of three peristaltic pumps, wherein each pumping direction between all reservoirs 424, 426 and 430 can be realized in both directions. It is possible that a single membrane element covers all fluid chambers and reservoir container, wherein a separate piezoelectric actuator is provided for each fluid chamber. Thus, the entire fluidics can be made very flat, wherein the functional fluidic structures including fluid chambers, channels, membranes, piezo actuators and support structures can have an overall height in the order of 200 to 400 microns. Thus, systems are conceivable that can be integrated into smart cards. Furthermore, even flexible fluidic systems are conceivable.

In addition to the exemplary embodiments shown, fluid chambers can be connected as desired in one plane. For example, different reservoirs z. B. are each assigned a Mikroperistaltikpumpe, which then, for example, reagents perform a chemical reaction (for example, in a fuel cell), or perform a calibration sequence for an analysis system, for example in a water analysis.

To produce a piezo-membrane converter, the piezoceramics can be glued, for example, to the respective membrane sections. Alternatively, the piezoceramics, for example PZT, can be applied directly in thick film technology, for example by screen printing processes with suitable intermediate layers.

An alternative embodiment of a microperistaltic pump of the invention with recessed inlet fluid passage 412 and recessed outlet fluid passage 414 is shown in FIG Fig. 16 shown. The inlet flow channel 412 in turn opens substantially centrally below the membrane portion 12 in a valve chamber 442, while the Auslaßfluidkanal 414 opens substantially centrally below the diaphragm portion 16 in a valve chamber 444. The respective orifices of the inlet channel 412 and the outlet channel 414 are provided with a sealing lip 450. Further, a pumping chamber 452 is formed in the pump body 440 which is fluidly connected to the valve chambers 442 and 444 by fluid passages in walls 454. According to the in Fig. 16 The three membrane sections 12, 14 and 16 in turn form a membrane element 456. In this embodiment, however, the membrane sections are driven by piezo stack actuators 460, 462 and 464, which can be placed on the corresponding membrane sections. For this purpose, the piezo stack actuators using suitable housing parts 470 and 472, the in Fig. 16 remote from the pump body and the membrane element are used.

Piezostapelaktoren are advantageous in that they need not be firmly connected to the membrane element, so that they allow a modular structure. In such non-fixed piezo stack actuators, the actuators do not actively retract a diaphragm section when an actuation thereof is terminated. Rather, a return movement of the membrane portion can be done only by the restoring force of the elastic membrane itself.

The peristaltic micropumps of the present invention can be made using a variety of materials of manufacture and manufacturing techniques. The pump body may for example be made of silicon, be made of plastic by injection molding or manufactured by machining technically. The membrane element which forms the drive diaphragm for the two valves and the pumping chamber can be made of silicon, can be formed by a metal foil, for example stainless steel or titanium, can be formed by a plastic membrane provided with conductive coatings in two-component injection molding technique. or may be realized by an elastomeric membrane.

• dicht;
• dünne Fügeschicht (< 10 µm), da die Pumpkammerhöhe ein kritischer Designparameter ist, der das Totvolumen beeinflußt;
• mechanische Beständigkeit; und
• chemisch beständig gegen zu fördernde Medien.

The connection between the membrane element and the pump body is an important point since high shear forces can occur at this connection during operation of the peristaltic pump. The following requirements apply to this connection:

• thick;
• thin bonding layer (<10 μm), since the pump chamber height is a critical design parameter that affects the dead volume;
• mechanical resistance; and
• chemically resistant to media to be conveyed.

In the case of silicon as the basic structure and membrane element, a non-silicone Silicon Fusion Bonding can take place. In the case of a silicon-glass combination, anodic bonding may preferably be used. Other possibilities are a eutectic wafer bonding or a wafer life.

If the basic structure is made of plastic and the membrane element is a metal foil, lamination can be performed if a bonding agent is used between the membrane element and the basic structure. Alternatively, bonding may be carried out with a high shear adhesive, in which case capillary stop trenches are preferably formed in the base structure in order to avoid penetration of adhesive into the fluid structure.

If both membrane element and pump body are made of plastic, ultrasonic welding can be used to connect them. If one of the two structures is optically transparent, a laser welding can alternatively take place. In the case of an elastomeric membrane, the sealing properties of the membrane may also be used to provide a seal by clamping.

The following briefly explains how a possible attachment of the membrane to the pump body can take place in a micro-peristaltic pump according to the invention. If in the micropump of the invention, the membrane is glued to the pump body, it should be noted that the dosage of Fügeschichtmaterialien (eg adhesive) is critical, since on the one hand, the membrane must be tight (so sufficient adhesive must be applied), and on the other hand, penetration must be avoided by excess adhesive in the fluid chambers.

The bonding layer material, which may be an adhesive or an adhesive, is used e.g. dispensed by dispensing or by a suitably shaped stamp on the joining layer. After the application of the bonding layer material, the membrane is fitted onto the base body. Possible burrs, e.g. can be at the edge of the membrane, find in a corresponding receptacle for the burr place, so that a defined position of the membrane is ensured especially in the direction perpendicular to the surface thereof, which is important in terms of dead volume and tightness.

Then press with a stamp on the pump body, so that the adhesive layer remains as thin and defined. To accommodate excess adhesive, a capillary stop trench may be provided surrounding the fluid areas formed in the pump body. Thus, such excess adhesive can not get into the fluid chambers. Under these conditions, the adhesive can be defined and cured thin. Curing may be at room temperature or accelerated in the oven or by UV irradiation using UV-curable adhesives.

As an alternative to the adhesive bonding technique described, the base body or pump body can be dissolved by suitable solvents and a plastic membrane can be bonded to the base body as a joining technique.

Claims (17)

1. Peristaltic micropump comprising:

   a first membrane region (12) with a first piezo-actor (22; 460) for actuating the first membrane region;

   a second membrane region (14) with a second piezo-actor (24; 462) for actuating the second membrane region;

   a third membrane region (16) with a third piezo-actor (26; 464) for actuating the third membrane region; and

   a pump body (30; 302; 340; 440),

   wherein the pump body forms, together with the first membrane region (12), a first valve (62) whose passage opening (32) is open in the non-actuated state of the first membrane region and whose passage opening may be closed by actuating the first membrane region,
   wherein the pump body forms, together with the second membrane region (14), a pumping chamber (42; 304; 330; 342; 452) whose volume may be decreased by actuating the second membrane region, and
   wherein the pump body forms, together with the third membrane region (16), a second valve (64) whose passage opening (34) is open in the non-actuated state of the third membrane region and whose passage opening may be closed by actuating the third membrane region,
   wherein the first and second valves (62, 64) are fluidically connected to the pumping chamber,
   wherein between a stroke volume ΔV, a dead volume V₀, a delivery pressure P_F, and the atmospheric pressure P₀ the following relationship applies: $$\mathrm{\Delta V}/{\mathrm{V}}_0>{\mathrm{P}}_{\mathrm{F}}/{\mathrm{P}}_0,$$

   

   
   wherein the stroke volume ΔV is a volume displaced by an actuation of the second membrane region (14), wherein the dead volume V₀ is a volume present between the opened passage opening (32; 34) of one of the valves (62, 64) and the closed passage opening (32, 34) of the other of the valves (62, 64) in the actuated state of the second membrane region (14), and wherein the delivery pressure p_F is the pressure necessary in the pumping chamber (42; 304; 330; 342; 452) to move a liquid/gas interface past a bottleneck in the peristaltic micropump.
2. Peristaltic micropump of claim 1, wherein between the first membrane region (12) and the pump body (302; 340; 440) a first valve chamber (308; 360; 442) is formed, and wherein between the third membrane region (16) and the pump body (302; 340; 440) a second valve chamber (310; 362; 444) is formed, wherein the valve chambers are fluidically connected to the pumping chamber (42; 304; 330; 342; 452).
3. Peristaltic micropump of claim 2, wherein the volume of the pumping chamber (304) is greater than the volume of the first or second valve chamber (308, 310).
4. Peristaltic micropump of claim 3, wherein a distance between membrane surface and pump body surface in the region of the pumping chamber (304) is greater than in the region of the valve chamber (308, 310).
5. Peristaltic micropump of claim 3 or 4, wherein the second membrane region (14) and the pumping chamber are greater in area than the first or third membrane region (12, 16) and the associated valve chambers.
6. Peristaltic micropump of one of claims 2 to 5, wherein the membrane regions (12, 14, 16) are formed in a membrane element (10; 300; 380; 456), wherein the valve chamber (308, 310; 360, 362; 442, 444), the pumping chamber (42; 304; 330; 342; 452), and fluid channels (306; 344) are formed between the valve chambers and the pumping chamber by structures in the pump body and/or the membrane element.
7. Peristaltic micropump of one of claims 1 to 6, wherein the pumping chamber (330; 342) has a structure in the pump body (340), wherein the contour of the structure is adapted to the arched contour of the second membrane section (14) in the actuated state.
8. Peristaltic micropump of one of claims 2 to 6, wherein the pumping chamber (342) and the valve chambers (360, 362) have structures in the pump body (340), wherein the contours of the structures are adapted to the respective arched contour of the corresponding membrane section (12, 14, 16) in the actuated state.
9. Peristaltic micropump of one of claims 1 to 8, wherein the first and the third membrane region (12, 16) and the piezo-actors (22, 26; 460, 464) thereof are designed such that they push on a counter-element (390; 390a) with a predetermined force in the actuated state to close the respective valve.
10. Peristaltic micropump of claim 8, comprising lateral fluid feed lines (344a, 344b) to the valve chambers (360, 362) formed in the pump body (340), which are closed by actuating the corresponding membrane section.
11. Peristaltic micropump of claim 10, wherein, in the region of a valve chamber (360, 362), a ridge (390; 390a) is provided against which the corresponding actuated membrane section abuts to close the corresponding lateral fluid line.
12. Peristaltic micropump of claim 10, wherein the valve chambers comprise, opposite the corresponding membrane section, a plastically deformable material against which the corresponding membrane section abuts in the actuated state.
13. Peristaltic micropump of one of claims 1 to 12, further comprising at least one further membrane region with a further piezo-actor for actuating the further membrane region, the further membrane region forming, together with the pump body, a further valve whose passage opening is open in the non-actuated state of the further membrane region and whose passage opening may be closed by actuating the further membrane region, the further valve being fluidically connected to the pumping chamber.
14. Peristaltic micropump of one of claims 1 to 13, wherein the piezo-actors are piezo-membrane converters formed by respective piezo-elements applied onto a membrane region.
15. Peristaltic micropump of claim 14, wherein the piezo-elements are glued onto the respective membrane region or formed on the respective membrane region in thick film technique.
16. Peristaltic micropump of one of claims 1 to 13, wherein the piezo-actors are formed by respective piezo-stacks.
17. Fluid system with a plurality of peristaltic micropumps of one of claims 1 to 16 and a plurality of reservoirs fluidically connected to the peristaltic micropumps.

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