Peristaltic micropump

0001The present invention relates to a micropump, and in particular to a micropump that operates on a peristaltic pumping principle.

0002Micropumps that operate on a peristaltic pumping principle are known from the prior art. So the article deals "<nplcit id="ncit0001" npl-type="s"><text>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</text></nplcit>, with a peristaltic micropump, which has an inlet, three pumping chambers, three silicon membranes, three normally closed active valves, three piezo stack actuators made of PZT, microchannels between the pumping chambers and an outlet. The three pumping chambers are of the same size and are etched into a silicon wafer.

0003From the <patcit id="pcit0001" dnum="WO8707218A"><text>WO 87/07218</text></patcit> a peristaltic micropump is also known which has three membrane regions in a continuous substrate surface. A pump channel, which is connected to a fluid supply, is formed in a carrier layer which carries the substrate and an associated support layer. A transverse rib is formed in the pump channel in the area of ​​an inlet valve and an outlet valve, on which an associated membrane section rests in the unactuated state in order to close the inlet valve and the outlet valve in the unactuated state. The third membrane area, which can also be operated separately, is arranged between the separately operable membrane areas assigned to the inlet valve and the outlet valve. By actuating the third membrane area, the chamber volume between the two valve areas is increased. A peristaltic pumping action between the inlet valve and the outlet valve can thus be achieved by correspondingly timed activation of the three membrane regions. According to the<patcit id="pcit0002" dnum="WO8707218A"><text>WO 87/07218</text></patcit> the actuator element consists of a three-way composite made of metal membrane, continuous ceramic layer and segmented electrode arrangement. The ceramic layer must be polarized in segments, which is technically difficult. Such a segmented piezo bending element is therefore complex and allows only small stroke volumes, so that such a pump cannot work in a bubble-tolerant and self-priming manner.

0004From the <patcit id="pcit0003" dnum="DE19719862A1"><text>DE 19719862 A1</text></patcit> is known a micromembrane pump that does not operate on the peristaltic principle, in which a pump membrane adjacent to a pump chamber can be actuated by a piezo actuator. A fluid inlet and a fluid outlet of the pump chamber are each provided with passive check valves. According to this document, the compression ratio of the micropump, ie the ratio of the stroke volume of the pump diaphragm to the total pump chamber volume is dependent on the maximum pressure value, which is dependent on the valve geometry and the valve wetting and is necessary to open the valves, in order to enable bubble-tolerant, self-priming operation of the micromembrane pump there.

0005In addition to the above-mentioned piezo actuators, it would also be possible to implement micropumps using electrostatic actuators, but electrostatic actuators only allow very small strokes. Alternatively, it would also be possible to implement pneumatic drives, which, however, requires a high level of effort with regard to external pneumatics and the switching valves required for this. Pneumatic drives thus represent complex, expensive and space-intensive processes to implement a membrane deflection.

0006The object of the present invention is to provide a peristaltic micromembrane pump which can be constructed in a simple manner and which enables bubble-tolerant, self-priming operation.

0007According to the invention, this object is achieved by a peristaltic micropump according to claim 1.

0008The present invention thus provides a peristaltic micropump in which the first and second valves are open when unactuated, and in which the first and second valves can be closed by moving the membrane towards the pump body while the volume of the pumping chamber is closed Movement of the second membrane area can also be reduced toward the pump body.

0009With this construction, the peristaltic micropump according to the invention enables the realization of bubble-tolerant, self-priming pumps, even when piezo elements arranged on a membrane are used as the piezo actuator. Alternatively, so-called piezo-stacks (piezo-stacks) can also be used according to the invention, which are disadvantageous compared to piezo-diaphragm converters in that they are large and expensive, problems with the connection technology between the stack and the membrane and problems with the adjustment of the stack deliver and are therefore associated with a higher effort.

0010In order to ensure that the peristaltic micropump according to the invention can work in a bubble-tolerant and self-priming manner, 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 stroke volume being the volume displaceable by the pump membrane, the dead volume the volume remaining between the inlet opening and outlet opening of the micropump, when the pump 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 the pressure required in the fluid chamber region of the micropump, ie in the pressure chamber to create a liquid / gas interface at a location that is a flow restriction in the microperistaltic pump, ie between the pumping chamber and the passage opening of the first or second valve, including this passage opening.

0011If the ratio of stroke volume to dead volume, which can be referred to as the compression ratio, satisfies the above condition, it is ensured that the peristaltic micropump works in a bubble-tolerant and self-priming manner. This applies both when using the peristaltic micropump for conveying liquids when a gas bubble, usually an air bubble, gets into the fluid area of ​​the pump, and when using the micropump according to the invention as a gas pump, when moisture inadvertently condenses from the gas to be conveyed and thus a gas / liquid interface can occur in the fluid area of ​​the pump.

0012Compression ratios that meet the above condition can be achieved according to the invention, for example, by making the volume of the pump chamber larger than that of valve chambers formed between the respective valve membrane regions and opposite pump body sections. In preferred exemplary embodiments, this can be achieved in that the distance between the membrane and the surface and the pump body surface is greater in the region of the pump chamber than in the region of the valve chambers.

0013A further increase in the compression ratio of a peristaltic micropump according to the invention can be achieved by adapting the contour of a pump chamber structured in the pump body to the bending line of the pump membrane, ie the curved contour thereof in the actuated state, so that the pump membrane in the actuated state essentially that can displace the entire volume of the pump chamber. Furthermore, the contours of valve chambers formed in the pump body can also be adapted accordingly to the bending line of the opposite membrane sections, so that, in the optimal case, the actuated membrane area displaces essentially the entire valve chamber volume when closed.

0014Preferred exemplary embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. Show it:<dl id="dl0001"><dt>Fig. 1</dt><dd>a schematic cross-sectional view of an embodiment of a peristaltic micropump according to the invention in a fluid system;</dd><dt>2a to 2f</dt><dd>schematic representations for explaining a piezo diaphragm transducer;</dd><dt>3a to 3c</dt><dd>schematic cross-sectional views to explain the terms stroke volume and dead volume;</dd><dt>Fig. 4</dt><dd>a schematic diagram showing the volume / pressure tension levels during a pumping cycle;</dd><dt>5a to 5c</dt><dd>schematic representations to explain the term delivery pressure;</dd><dt>6a to 6c</dt><dd>schematic views of an alternative embodiment of a micropump according to the invention;</dd><dt>Fig. 7</dt><dd>an enlarged view of a range of <figref idref="f0005">Fig. 6b</figref>;</dd><dt>Fig. 8</dt><dd>an enlarged schematic cross-sectional view of a modified area of <figref idref="f0006">Fig. 7</figref>;</dd><dt>9a, 9b and 9c</dt><dd>schematic representations of possible pump chamber designs;</dd><dt>10a and 10b</dt><dd>schematic representations of an alternative embodiment of a micropump according to the invention;</dd><dt>11 to 13</dt><dd>schematic cross-sectional views of enlarged areas of modifications of the in the <figref idref="f0008">10a and 10b</figref> example shown;</dd><dt>Fig. 14</dt><dd>is a schematic cross-sectional view of a further alternative embodiment of a micropump according to the invention;</dd><dt>Fig. 15</dt><dd>a schematic representation of a multiple micropump according to the invention; and</dd><dt>Fig. 16</dt><dd>is a schematic representation of an alternative embodiment of a micropump according to the invention.</dd></dl>

0015A first exemplary embodiment of a peristaltic micropump according to the invention, which is integrated in a fluid system, is shown in <figref idref="f0001">Fig. 1</figref> shown. The micromembrane 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 and together with the same forms a piezo membrane transducer. The piezo elements 22, 24, 26 can be glued to the respective membrane sections or can be formed on the membrane by screen printing or other thick-film techniques.

0016The outer surface of the membrane element is joined to a pump body 30 so that there is a fluid-tight connection between them. Two fluid passages 32 and 34 are formed in the pump body 30, one of which, depending on the pumping direction, represents a fluid inlet and the other a fluid outlet. At the in<figref idref="f0001">Fig. 1</figref> In the exemplary embodiment shown, the fluid passages 32, 34 are each surrounded by a sealing lip 36.

0017Furthermore, in the <figref idref="f0001">Fig. 1</figref> In the embodiment shown, the underside of the membrane element 10 and the upper side of the pump body 30 are structured in order to define a fluid chamber 40 between them.

0018In the exemplary 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 to one another, for example by silicon fusion bonding. How<figref idref="f0001">Fig. 1</figref> can be seen, the membrane element 10 has three recesses in the upper side thereof and one recess in the lower side thereof, in order to define the three membrane regions 12, 14 and 16.

0019The diaphragm sections 12, 14 and 16 can each be actuated in the direction of the pump body 30 by the piezo elements or piezoceramics 22, 24 and 26, so that the diaphragm section 12 together with the fluid passage 32 constitutes an inlet valve 62 which can be actuated by actuating the diaphragm section 12 can be locked. In the same way, the membrane section 16 and the fluid passage 34 together constitute an outlet valve 64, which can be closed by actuating the membrane section 16 by means of the piezo element 26. Finally, the volume of the pump chamber region 42 arranged between the valves can be reduced by actuating the piezo element 24.

0020Before working on the in <figref idref="f0001">Fig. 1</figref> Peristaltic micropump shown is first briefly the fluid system environment into which the micropump according <figref idref="f0001">Fig. 1</figref> is installed. The pump is glued to a carrier block 50 with the pump body 30, optionally as in FIG<figref idref="f0001">Fig. 1</figref> is shown, grooves 52 may be provided in the carrier block 50 to receive excess adhesive. The grooves 52 can, for example, be provided surrounding the fluid channels 54 and 56 formed in the carrier block 50 in order to absorb excess adhesive and to prevent it from getting into the fluid channels 54, 56 or the fluid passages 32, 34. The pump body 30 is glued to the support block or added that the fluid passage 32 is in fluid communication with the fluid channel 54 and that the fluid passage is in fluid communication with the fluid channel 56. A further channel 58 can be provided in the carrier block 50 between the fluid channels 54 and 56 as a transverse leak protection. At the outer ends of the fluid channels 54, 56, connectors 60 are provided, for example for attaching hose lines to the in<figref idref="f0001">Fig. 1</figref> fluid system shown can serve. Furthermore, in<figref idref="f0001">Fig. 1</figref> schematically shown a housing 61, which is joined to the support block 50, for example using an adhesive connection, in order to provide protection for the micropump and to seal the piezo elements moisture-tight.

0021To describe a peristaltic pump cycle of the in <figref idref="f0001">Fig. 1</figref> The pump shown is initially assumed to be in an initial state in which the inlet valve 62 is closed, the pump membrane corresponding to the second membrane section 14 is in the unactuated state and the outlet valve 64 is open. Starting from this state, the pump diaphragm 14 is moved downward by actuating the piezo element 24, which corresponds to the pressure stroke, as a result of which the stroke volume is conveyed through the open outlet valve into the outlet, ie the fluid channel 56. The compression of the pump chamber 42 during the pressure stroke by the stroke volume leads to an overpressure in the pump chamber, which is reduced by the fluid movement through the outlet valve.

0022Starting from this state, the outlet valve 64 is closed and the inlet valve 62 is opened. The pump membrane 14 is then moved upward by stopping the actuation of the piezo element 24. The thereby expanding pump chamber leads to a negative pressure in the pump chamber, which in turn results in a suction of fluid through the opened inlet valve 62. Then the inlet valve 62 is closed and the outlet valve 64 is opened so that the above-mentioned initial state is reached again. The described pump cycle would thus pump a fluid volume, which essentially corresponds to the stroke volume of the membrane section 14, from the fluid channel 54 to the fluid channel 56.

0023According to the invention, piezo membrane transducers or piezo bending transducers are preferably used as piezo actuators. Such a bending transducer achieves an optimal stroke if the lateral dimensions of the piezoceramic correspond to approximately 80% of the membrane underneath. 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 strokes and thus volume strokes in the range from 0.1 µl to 10 µl can be achieved. Preferred exemplary embodiments of the present invention have volume strokes at least in such a range, since bubble-tolerant peristaltic pumps can advantageously be realized with such a volume stroke.

0024It should be noted in the case of piezo diaphragm converters that they only allow an effective stroke downwards, ie towards the pump body. In this regard, the schematic representations of the<figref idref="f0002">2a to 2f</figref> referred. <figref idref="f0002">Fig. 2a</figref> shows a piezoceramic 100 which is provided with metallizations 102 on both surfaces thereof. The piezoceramic preferably has a large d31 coefficient and is in the direction of arrow 104 in<figref idref="f0002">Fig. 2a</figref> polarized. According to<figref idref="f0002">Fig. 2a</figref> there is no voltage on the piezoceramic.

0025To generate a piezo diaphragm converter, the in <figref idref="f0002">Fig. 2a</figref> Piezoceramic 100 shown firmly mounted on a membrane 106, for example glued, as in <figref idref="f0002">Fig. 2b</figref> is shown. The membrane shown is a silicon membrane, but the membrane can 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 made conductive by a two-component injection molding.

0026If a positive voltage, ie a voltage in the polarization direction, U> 0, is now applied to the piezoceramic, the piezoceramic contracts, see <figref idref="f0002">Fig. 2c</figref>. Due to the firm connection of the piezoceramic 100 to the membrane 106, the membrane 106 is deflected downward by this contraction, as by arrows in FIG<figref idref="f0002">Fig. 2d</figref> is made clear.

0027In order to cause the membrane to move upward, a negative voltage, ie a voltage against the polarization direction, would have to be applied to the piezoceramic, as in <figref idref="f0002">Fig. 2e</figref> is shown. However, this leads to depolarization of the piezoceramic even at low field strengths in the opposite direction, as in FIG<figref idref="f0002">Fig. 2e</figref> 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, cannot be realized, as in FIG<figref idref="f0002">Fig. 2f</figref> is indicated.

0028Despite this disadvantage in that, due to the asymmetrical nature of the piezo effect, only an active downward movement, ie in the direction towards the pump body, can be realized with the two-layer silicon-piezo bending transducer, ie the piezo diaphragm transducer of such a bending transducer is a preferred embodiment of the present invention, since this form of transducer has numerous advantages. On the one hand, they have a fast response behavior, on the order of approximately 1 millisecond with low energy consumption. Furthermore, scaling with dimensions of piezoceramic and membrane over large areas is possible, so that a large stroke (10 .... 200 µm) and a large force (switching pressures 10⁴ Pa to 10⁶ Pa) are possible, with a larger stroke the achievable force decreases and vice versa. Furthermore, the medium to be switched is separated from the piezoceramic by the membrane.

0029If the peristaltic micropumps according to the invention are to be used in applications in which bubble-tolerant, self-priming behavior is required, the microperistaltic pumps must be designed in order to comply with a design rule with regard to the compression ratio, which defines the ratio of stroke volume to dead volume. To define the terms displacement volume ΔV and dead volume V₀ first be on the <figref idref="f0003">3a to 3b</figref> referred.

0030<figref idref="f0003">Fig. 3a</figref> schematically shows a pump body 200 with an upper surface thereof, in which a pump chamber 202 is structured. A diaphragm 204 is schematically shown above the pump body 200 and is provided with an inlet valve piezo actuator 206, a pump chamber piezo actuator 208 and an outlet valve piezo actuator 210. Piezoactuators 206, 208 and 210 allow respective areas of membrane 204 to move downward, ie toward the pump body 200, as indicated by arrows in <figref idref="f0003">Fig. 3a</figref> is shown. By line 212 is in<figref idref="f0003">Fig. 3a</figref> furthermore, the section of the membrane 204 opposite the pump chamber 200, ie the pump membrane, is shown in its deflected state, ie actuated by the pump chamber piezo actuator 208. The difference in the pump 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 pump membrane.

0031According to <figref idref="f0003">Fig. 3a</figref> The channel regions 214 and 216 arranged under the inlet valve piezo actuator 206 and under the outlet valve piezo actuator 210 can be closed by actuating the corresponding piezo actuator in each case by the respective membrane regions resting on the regions of the pump body lying underneath. Here are the<figref idref="f0003">Figures 3a to 3c</figref> only rough schematic representations, the respective elements being designed in such a way that the respective valve openings can be closed. Thus, an inlet valve 62 and an outlet valve 64 are again formed.

0032In <figref idref="f0003">Fig. 3b</figref> A situation is shown in which the volume of the pump chamber 202 is reduced by actuating the pump chamber piezo actuator 208 and in which the inlet valve 62 is closed. In the<figref idref="f0003">Fig. 3b</figref> The situation shown thus represents the state after a quantity of fluid has been expelled from the outlet valve 64, the volume of the fluid region remaining between the closed inlet valve 62 and the passage opening of the open outlet valve 64 being the dead volume V₀ with respect to the pressure stroke as shown by the hatched area in <figref idref="f0003">Fig. 3b</figref> is shown. The dead volume with respect to a suction stroke at which the inlet valve 62 is opened and the outlet valve 64 is closed is defined by the volume of the fluid region remaining between the closed outlet valve 64 and the passage opening of the opened inlet valve 62, as in FIG<figref idref="f0003">Fig. 3c</figref> is shown by the hatched area.

0033At this point it should be noted that the respective dead volume is defined from the respectively closed valve to the passage opening, at which a significant pressure drop takes place at the moment of a respective volume change of the pumping chamber. With a symmetrical construction of the inlet valve and outlet valve, as is preferred for a bidirectional pump, the dead volumes V₀ identical for the pressure stroke and the suction stroke. If there are different dead volumes due to an asymmetry for a pressure stroke and a suction stroke, then in the sense of a worst-case scenario it is assumed below that the larger of the two dead volumes is used to determine the respective compression ratio.

0034The compression ratio of the microperistaltic pump is calculated from the stroke volume ΔV and the dead volume V₀ as follows: <maths id="math0001" num="Gl.1"><math display="block"><mi mathvariant="normal">ϵ</mi><mo>=</mo><mi mathvariant="normal">ΔV</mi><mo>/</mo><msub><mi mathvariant="normal">V</mi><mn>0</mn></msub></math><img file="EP1458977B2_D0001.tif" /></maths>

0035In the following , a worst-case analysis is assumed in which the entire pump area is filled with a compressible fluid (gas). The volume / pressure conditions occurring in the peristaltic pump during a peristaltic pump cycle as described above are shown in the diagram of<figref idref="f0004">Fig. 4</figref> shown. Here are in<figref idref="f0004">Fig. 4</figref> Both the isothermal volume / pressure characteristic curves and the adiabatic volume / pressure characteristic curves are shown, whereby in the sense of a worst-case analysis, isothermal conditions as they occur with slow state changes are assumed below.

0036At the beginning of a pressure stroke, a pressure p prevails in the fluid region existing between the inlet valve and the outlet valve₀while this area is a volume V₀ + ΔV. Starting from this state, the pressure membrane moves down by the stroke volume ΔV during the pressure stroke, as a result of which an overpressure p_Ü in the fluid area, ie the pump chamber, so that at a volume of V₀ a pressure of p₀ + p_Ü prevails. The overpressure in the pumping chamber is reduced by conveying the air volume ΔV through the outlet until pressure equalization has taken place. This outflow of fluid from the outlet corresponds to in<figref idref="f0004">Fig. 4</figref> the jump from the upper curve to the lower curve. At the end of the pressure equalization, there is a state p₀, V₀that 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 stroke volume ΔV. Thus, the in<figref idref="f0004">Fig. 4</figref> state referred to as "suction stroke after expansion" p₀ - p_u, V₀ + ΔV changed. Due to the prevailing negative pressure, a fluid volume ΔV is sucked in through the inlet opening until pressure equalization has taken place. The inflow of fluid into the pumping chamber corresponds to in<figref idref="f0004">Fig. 4</figref> the jump from the lower curve to the upper curve. After pressure equalization, the state p therefore prevails₀, V₀ + ΔV, which in turn corresponds to the starting point of a pressure stroke.

0037In the above general state considerations, which serve to explain the invention in general, the volume displacements of the inlet valve and outlet valve between the respective suction strokes and pressure strokes were neglected.

0038In order to achieve a bladder tolerance, the overpressure p_Ü in the pressure stroke, or the negative pressure p_U for the suction stroke, exceed a minimum value for the pressure stroke or fall short for the suction stroke. In other words, the pressure amount during the pressure stroke and the suction stroke must have a minimum value, which is the delivery pressure p_F can be referred to, exceed. This delivery pressure is the pressure in the pressure chamber which must at least prevail to move a liquid / gas interface at a point which is a flow restriction between the pump chamber and the passage opening of the first or second valve, including this passage opening. This delivery pressure can be determined as follows depending on the size of this river constriction.

0039Capillary forces have to be overcome if free surfaces, for example in the form of gas bubbles (for example 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 r₁ and the minimum radius of curvature r₂ of the meniscus of this interface:<maths id="math0002" num="Gl.2"><math display="block"><mi mathvariant="normal">Δp</mi><mo>=</mo><mi mathvariant="normal">σ</mi><mo>⁢</mo><mfenced separators=""><mfrac><mn>1</mn><msub><mi mathvariant="normal">r</mi><mn>1</mn></msub></mfrac><mo>+</mo><mfrac><mn>12</mn><msub><mi mathvariant="normal">r</mi><mn>2</mn></msub></mfrac></mfenced></math><img file="EP1458977B2_D0002.tif" /></maths>

0040The delivery pressure to be generated is defined by equation 2, specifically at the point within the flow path of the microperistaltic pump at which the sum of the inverse radii of curvature r₁ and r₂ a liquid / gas interface with a given surface tension is maximum. This point corresponds to the river constriction.

0041For example, a channel 220 (<figref idref="f0003">Fig. 5a</figref>) considered with a width d, the height of the channel also being d. The channel 220 has a change in cross section at both channel ends 222, for example below the valve membrane or the pump membrane. In<figref idref="f0003">Fig. 5a</figref> the channel is completely filled with a liquid 224 which flows in the direction of arrow 226.

0042According to <figref idref="f0003">Fig. 5b</figref> An air bubble 228 now strikes the change in cross-section at the entrance to the channel 220. A wetting angle θ occurs in the process. The wetting angle θ defines a maximum radius of curvature r₁ and a minimum radius of curvature r₂ a meniscus 230 to be moved through the channel 220, with r₁ = r₂ applies. In<figref idref="f0003">Fig. 5c</figref> the situation is shown when the air bubble or the meniscus 230 reaches the cross-sectional change 222 at the end of the channel 220.

0043If such a channel represents the area of ​​a fluid system where the greatest capillary force has to be overcome, the pressure required in this special case is r₁ = r₂ = r = d / 2:<maths id="math0003" num="Gl.3"><math display="block"><mi mathvariant="normal">Δp</mi><mo>=</mo><mi mathvariant="normal">σ</mi><mo>⁢</mo><mfrac><mn>2</mn><mi mathvariant="normal">r</mi></mfrac><mo>=</mo><mi mathvariant="normal">σ</mi><mo>⁢</mo><mfrac><mn>4</mn><mi mathvariant="normal">d</mi></mfrac></math><img file="EP1458977B2_D0003.tif" /></maths>

0044This pressure barrier is not to be neglected in microperistaltic pumps of the type according to the invention due to the small geometrical dimensions if such a channel represents the constriction of the pump. With a line diameter of, for example, d = 50 µm and an air / water surface tension of σ_wa = 0.075 N / m is the pressure barrier Δp_b = 60 hPa, while with a duct diameter d = 25 µm the pressure barrier Δp_b = 120 hPa.

0045In the case of microperistaltic pumps of the type according to the invention, however, the mentioned constriction will generally be defined by the distance between the valve membrane and the opposite area of ​​the pump body (for example a sealing lip) when the valve is open. This constriction represents a gap that is infinitely wide compared to the height, ie r₁ = r and r₂ = infinite.

0046For such a channel, the following results from equation 2:<maths id="math0004" num="Gl.4"><math display="block"><mi mathvariant="normal">Δp</mi><mo>=</mo><mi mathvariant="normal">σ</mi><mo>⁢</mo><mfrac><mn>1</mn><mi mathvariant="normal">r</mi></mfrac></math><img file="EP1458977B2_D0004.tif" /></maths>

0047In general, the relationship between the smallest radius of curvature and the smallest wall distance d is given by the following relationship:<maths id="math0005" num="Gl.5"><math display="block"><mi mathvariant="normal">r</mi><mo>=</mo><mfrac><mi mathvariant="normal">d</mi><mrow><mn>2</mn><mo>⋅</mo><mi>sin</mi><mfenced separators=""><mn>90</mn><mo>⁢</mo><mi mathvariant="normal">°</mi><mo>+</mo><mi mathvariant="normal">Γ</mi><mo>-</mo><mi mathvariant="normal">Θ</mi></mfenced></mrow></mfrac></math><img file="EP1458977B2_D0005.tif" /></maths> where Θ represents the wetting angle and Γ the tilt between the two walls.

0048The worst-case scenario, ie the smallest radius of curvature regardless of the tilt angle and wetting angle, is given when the sine function becomes maximum, ie sin (90 ° + Γ-Θ) = 1. This occurs, for example, when there are abrupt changes in cross-section, as shown in the<figref idref="f0003">5a to 5c</figref> are shown, or in combinations of tilt angle Γ and wetting angle Θ. In the worst case scenario:<maths id="math0006" num="Gl.6"><math display="block"><mi mathvariant="normal">r</mi><mo>=</mo><mfrac><mi mathvariant="normal">d</mi><mn>2</mn></mfrac></math><img file="EP1458977B2_D0006.tif" /></maths>

0049The smallest occurring radius of curvature can therefore be considered as independent of the tilt angle Wand, wetting angle Θ or abrupt changes in cross-section, half of the smallest emerging wall distance.

0050In a peristaltic pump, on the one hand, there are fluid connections between the chambers with a given channel geometry and a constriction that defines the smallest flow dimension d. The following applies to such a channel:<maths id="math0007" num="Gl.7"><math display="block"><mi mathvariant="normal">Δp</mi><mo>=</mo><mi mathvariant="normal">σ</mi><mo>⁢</mo><mfrac><mn>4</mn><mi mathvariant="normal">d</mi></mfrac></math><img file="EP1458977B2_D0007.tif" /></maths>

0051On 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 stroke d. The following applies to these:<maths id="math0008" num="Gl.8."><math display="block"><mi mathvariant="normal">Δp</mi><mo>=</mo><mi mathvariant="normal">σ</mi><mo>⁢</mo><mfrac><mn>2</mn><mi mathvariant="normal">d</mi></mfrac></math><img file="EP1458977B2_D0008.tif" /></maths>

0052The respective constriction (channel constriction or valve constriction in the open state) at which larger capillary forces have to be overcome can be regarded as the flow constriction of the microperistaltic pump.

0053In preferred exemplary embodiments of the present invention, connecting channels within the peristaltic pump are therefore designed in such a way that the diameter of the channel exceeds at least twice the valve constriction, ie the distance between the diaphragm and the pump body when the valve is open. In such a case, the valve gap represents the flow restriction of the microperistaltic pump. For example, with a valve stroke of 20 µm, connecting channels with a smallest dimension, ie, a narrow point, of 50 µm can be provided. The upper limit of the channel diameter is determined by the dead volume of the channel.

0054The 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 is, for example, approximately 0.475 N / m. A peristaltic pump that is designed to overcome the capillary force at a surface tension of 0.1 N / m is therefore suitable for pumping almost all known liquids and gases in a bubble-tolerant and self-priming manner. Alternatively, the compression ratio of a microperistaltic pump according to the invention can be made correspondingly higher in order to enable such a pumping for mercury, for example.

0055The design rules discussed in the following apply to the conveyance of gases and incompressible liquids. When conveying liquids, it must be assumed that, in the worst-case scenario, air bubbles fill the entire pump chamber volume. When pumping gases, it must be expected that liquid can get into the pump due to condensation. In the following it is assumed that the piezo actuator is designed in such a way that all required negative and positive pressures can be achieved.

0056First, 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 air bubble.<maths id="math0009" num="Gl.9"><math display="block"><msub><mi mathvariant="normal">p</mi><mn>0</mn></msub><mo>⁢</mo><msup><mfenced separators=""><msub><mi mathvariant="normal">V</mi><mn>0</mn></msub><mo>+</mo><mi mathvariant="normal">ΔV</mi></mfenced><msub><mi mathvariant="normal">γ</mi><mi mathvariant="normal">A</mi></msub></msup><mo>=</mo><mfenced separators=""><msub><mi mathvariant="normal">p</mi><mn>0</mn></msub><mo>+</mo><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">Ü</mi></msub></mfenced><mo>⁢</mo><msup><mfenced><msub><mi mathvariant="normal">V</mi><mn>0</mn></msub></mfenced><msub><mi mathvariant="normal">γ</mi><mi mathvariant="normal">A</mi></msub></msup></math><img file="EP1458977B2_D0009.tif" /></maths> The variables p₀, V₀, ΔV and p_ü were referring to above <figref idref="f0004">Fig. 4</figref> explained. γ_A represents the adiabatic coefficient of the gas, ie 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 the pressure stroke is greater than the positive delivery pressure p_F be:<maths id="math0010" num="Gl.10"><math display="block"><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">Ü</mi></msub><mo>></mo><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">F</mi></msub></math><img file="EP1458977B2_D0010.tif" /></maths>

0057Now consider a suction stroke. The suction stroke differs in the initial position of the volumes. After the expansion, the negative pressure p_U in the pumping chamber, ie p_U is negative:<maths id="math0011" num="Gl.11"><math display="block"><msub><mi mathvariant="normal">p</mi><mn>0</mn></msub><mo>⁢</mo><msup><msub><mi mathvariant="normal">V</mi><mn>0</mn></msub><msub><mi mathvariant="normal">γ</mi><mi mathvariant="normal">A</mi></msub></msup><mo>=</mo><mfenced separators=""><msub><mi mathvariant="normal">p</mi><mn>0</mn></msub><mo>+</mo><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">U</mi></msub></mfenced><mo>⁢</mo><msup><mfenced separators=""><msub><mi mathvariant="normal">V</mi><mn>0</mn></msub><mo>+</mo><mi mathvariant="normal">ΔV</mi></mfenced><msub><mi mathvariant="normal">γ</mi><mi mathvariant="normal">A</mi></msub></msup></math><img file="EP1458977B2_D0011.tif" /></maths>

0058The left side of equation 11 represents the state before expansion, while the right side represents the state after expansion. The negative pressure p_U the pressure stroke must be less than the necessary negative delivery pressure p_F. It should be noted that the delivery pressure p_F when considering the pressure stroke, the amount is positive, when the suction stroke is considered, it is negative. It follows:<maths id="math0012" num="Gl.12"><math display="block"><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">U</mi></msub><mo>></mo><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">F</mi></msub></math><img file="EP1458977B2_D0012.tif" /></maths>

0059For the minimum necessary compression ratio of bubble-tolerant microperistaltic pumps for the pressure stroke, the following equations result:<maths id="math0013" num="Gl.13"><math display="block"><mi mathvariant="normal">ϵ</mi><mo>></mo><msup><mfenced><mfrac><msub><mi mathvariant="normal">p</mi><mn>0</mn></msub><mrow><msub><mi mathvariant="normal">p</mi><mn>0</mn></msub><mo>+</mo><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">F</mi></msub></mrow></mfrac></mfenced><mfrac><mn>1</mn><msub><mi mathvariant="normal">γ</mi><mi mathvariant="normal">A</mi></msub></mfrac></msup><mo>-</mo><mn>1</mn></math><img file="EP1458977B2_D0013.tif" /></maths>

0060The following compression ratio results for the suction stroke: <maths id="math0014" num="Gl.14"><math display="block"><mi mathvariant="normal">ϵ</mi><mo>></mo><msup><mfenced><mfrac><msub><mi mathvariant="normal">p</mi><mn>0</mn></msub><mrow><msub><mi mathvariant="normal">p</mi><mn>0</mn></msub><mo>+</mo><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">F</mi></msub></mrow></mfrac></mfenced><mfrac><mn>1</mn><msub><mi mathvariant="normal">γ</mi><mi mathvariant="normal">A</mi></msub></mfrac></msup><mo>-</mo><mn>1</mn></math><img file="EP1458977B2_D0014.tif" /></maths>

0061Is the delivery pressure p_F small compared to atmospheric pressure p₀, the previous equations can be simplified as follows, which means linearization around point p₀, V₀ corresponds to:<ul id="ul0001" list-style="none"><li>Pressure stroke:<maths id="math0015" num="Gl.15"><math display="block"><mi mathvariant="normal">ϵ</mi><mo>></mo><mfrac><mn>1</mn><msub><mi mathvariant="normal">γ</mi><mi mathvariant="normal">A</mi></msub></mfrac><mo>⁢</mo><mfrac><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">F</mi></msub><msub><mi mathvariant="normal">p</mi><mn>0</mn></msub></mfrac></math><img file="EP1458977B2_D0015.tif" /></maths></li><li>Suction stroke:<maths id="math0016" num="Gl.16"><math display="block"><mi mathvariant="normal">ϵ</mi><mo>></mo><mo>-</mo><mfrac><mn>1</mn><msub><mi mathvariant="normal">γ</mi><mi mathvariant="normal">A</mi></msub></mfrac><mo>⁢</mo><mfrac><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">F</mi></msub><msub><mi mathvariant="normal">p</mi><mn>0</mn></msub></mfrac></math><img file="EP1458977B2_D0016.tif" /></maths></li></ul>

0062The valid equation for the suction stroke and the pressure stroke is:<maths id="math0017" num="Gl.17"><math display="block"><mi mathvariant="normal">ϵ</mi><mo>></mo><mfrac><mn>1</mn><msub><mi mathvariant="normal">γ</mi><mi mathvariant="normal">A</mi></msub></mfrac><mo>⁢</mo><mfrac><mfenced open="|" close="|"><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">F</mi></msub></mfenced><msub><mi mathvariant="normal">p</mi><mn>0</mn></msub></mfrac></math><img file="EP1458977B2_D0017.tif" /></maths>

0063In the case of rapid changes in state, the conditions are adiabatic, ie γ_A = 1.4 for air. In the case of slow changes in state, the conditions are isothermal, ie γ_A = 1. With a consistent application of the worst case assumption, the criterion with γ_A = 1 used. Thus, as a design rule for the necessary compression ratio of bubble-tolerant microperistaltic pumps, it can be stated that the compression ratio must be greater than the ratio of the delivery pressure to the atmospheric pressure, ie:<maths id="math0018" num="Gl.18"><math display="block"><mi mathvariant="normal">ϵ</mi><mo>></mo><mfrac><mfenced open="|" close="|"><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">F</mi></msub></mfenced><msub><mi mathvariant="normal">p</mi><mn>0</mn></msub></mfrac></math><img file="EP1458977B2_D0018.tif" /></maths>

0064Or with the volumes mentioned: <maths id="math0019" num="Gl.19"><math display="block"><mfrac><mi mathvariant="normal">ΔV</mi><msub><mi mathvariant="normal">V</mi><mn>0</mn></msub></mfrac><mo>></mo><mfrac><mfenced open="|" close="|"><msub><mi mathvariant="normal">p</mi><mi mathvariant="normal">F</mi></msub></mfenced><msub><mi mathvariant="normal">p</mi><mn>0</mn></msub></mfrac></math><img file="EP1458977B2_D0019.tif" /></maths>

0065The simple linear design rule given above corresponds to the tangent to the isothermal equation of state <figref idref="f0004">Fig. 4</figref> in point p₀, V₀.

0066Preferred exemplary embodiments of microperistaltic pumps according to the invention are thus designed in such a way that the compression ratio satisfies the above condition, the minimum necessary delivery pressure corresponding to the pressure defined in equation 8 if the narrow passages 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 can correspond to the pressure defined in equation 3 or equation 7 if the flow restriction of the microperistaltic pump is not defined by a gap but by a channel.

0067Should a microperistaltic pump according to the invention be used if pressure boundary conditions of a negative pressure p₁ at the inlet or a back pressure p₂ prevail at the outlet, the compression ratio of a microperistaltic pump must be correspondingly larger in order to enable 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, the excess pressure p_Ü, or negative pressure p_U at least reach this back pressure so that a pumping effect occurs. For example, the height difference of a possible inlet vessel or outlet vessel of 50 cm in water alone leads to back pressures of 50 hPa.

0068The desired delivery rate also represents a boundary condition that places additional requirements. For a given stroke volume ΔV, the delivery rate Q is defined by the operating frequency f of the repeating peristaltic cycle: Q = ΔV · f. Both the suction stroke and the pressure stroke of the peristaltic pump must be performed within the period T = 1 / f, in particular the stroke volume ΔV must be converted. The available time is therefore a maximum of T / 2 for suction stroke and pressure stroke. The time required to convey the stroke volume through the pump chamber supply line and the valve constriction now depends on the one hand on the flow resistance and on the other hand on the pressure amplitude in the pump chamber.

0069If foam-like substances are to be pumped with a microperistaltic pump according to the invention, it may be necessary to overcome a plurality of capillary forces, as described above, since several corresponding liquid / gas interfaces occur. In such a case, the microperistaltic pump must be designed to have a compression ratio in order to be able to generate correspondingly higher delivery pressures.

0070In summary, it can be stated that the compression ratio of a microperistaltic pump according to the invention must be chosen correspondingly higher if the delivery pressure p required in the microperistaltic pump_F In addition to the capillary forces mentioned, it also depends on the boundary conditions of the application. It should be noted that here the delivery pressure is considered relative to atmospheric pressure, ie a positive delivery pressure p in the pressure stroke_F is assumed, while a negative delivery pressure p_F Is accepted. An amount of the delivery pressure of at least p. Can therefore be a technically sensible value for robust operation for a suction stroke and a pressure stroke_F = 100 hPa can be assumed.

0071If one considers a back pressure of, for example, 3000 hPa at the pump outlet, against which it is necessary to pump, then a compression ratio of ε> 3 results according to equation 13 above, an atmospheric pressure of 1013 hPa being assumed.

0072If the microperistaltic pump has to prime against a large negative pressure, for example a negative pressure of -900 hPa, then a compression ratio of ε> 9 must be maintained according to equation 14 above in order to enable pumping against such a negative pressure.

0073Examples of peristaltic micropumps that enable the realization of such compression ratios are explained in more detail below.

0074<figref idref="f0005">Fig. 6b</figref> shows a schematic cross-sectional view of a peristaltic micropump with membrane element 300 and pump body 302 along the line bb of FIG <figref idref="f0005">6a and 6c</figref>, while <figref idref="f0005">Fig. 6a</figref> a schematic plan view of the membrane element 300 and <figref idref="f0005">Fig. 6c</figref> shows a schematic top view of the pump body 302. The membrane element 300 in turn has three membrane sections 12, 14 and 16, which are each provided with piezo actuators 22, 24 and 26. In turn, an inlet opening 32 and an outlet opening 34 are formed in the pump body 302, such that the inlet opening 32 defines an inlet valve together with the membrane region 12, while the outlet opening 34 defines an outlet valve with the membrane region 16. A pump chamber 304 is formed in the pump body 302 below the membrane section 14. Furthermore, fluid channels 306 are formed in the pump body 302, which are fluidly connected to the valve chambers 308 and 310 assigned to the membrane regions 12 and 16. In the exemplary embodiment shown, the valve chambers 308 and 310 are formed by recesses in the membrane element 300, a recess 312 contributing to the pump chamber 304 also being formed in the membrane element 300.

0075In the in the <figref idref="f0005">6a to 6c</figref> In the exemplary embodiment shown, the pump chamber volume 304 is larger than the volume of the valve chambers 308 and 310. In the exemplary embodiment shown, this is achieved by a pump chamber lowering in which a structuring in the form of a pump chamber lowering is formed in the pump body 302. The stroke of the pump membrane 14 is preferably designed so that it can largely displace the volume of the pump chamber 304.

0076A further increase in the pump chamber volume compared to the valve chamber volume is in the in the <figref idref="f0005">6a to 6c</figref> The embodiment shown here is achieved by making the pump chamber membrane 14 larger in area (in the plane of the membrane element 300 or the pump body 302) than the valve chamber membranes, as best shown in FIG <figref idref="f0005">Fig. 6a</figref> you can see. This results in a pump chamber that is larger in area compared to the valve chambers.

0077In order to reduce the flow resistance between the valve chambers 308 and 310 and the pump chamber 304, the supply channels 306 are structured in the surface of the pump body 302. These fluid channels 306 provide reduced flow resistance without significantly degrading the compression ratio of the peristaltic micropump.

0078Alternatively to that in the <figref idref="f0005">6a to 6c</figref> In the embodiment shown, the surface of the pump body 302 could be implemented with three-stage depressions in order to implement the pumping chamber of increased depth (compared to the valve chambers), while the upper chip is a substantially unstructured membrane. Such two-stage reductions are technologically somewhat more difficult to achieve than in the<figref idref="f0005">6a to 6c</figref> shown embodiment.

0079Exemplary dimensions of the in the <figref idref="f0005">6a to 6c</figref> The exemplary embodiment of a peristaltic micropump shown is as follows:<ul id="ul0002" list-style="none" compact="compact"><li>Dimensions of the valve diaphragm 12, 16: 7.3 x 5.6 mm;</li><li>Dimension of the pump membrane 14: 7.3 x 7.3 mm;</li><li>Membrane thickness: 40 µm;</li><li>Diameter of the inlet and outlet nozzle 32, 34: at least 50 pm;</li><li>Valve chamber height: 8 µm;</li><li>Pump chamber height: 30 µm;</li><li>Valve sealing lip width d_DL: 10 µm;</li><li>realizable overall size: 8 x 21 mm;</li><li>Dimensions of the piezo elements: area: 0.8 times the membrane dimension, thickness: 2.5 times the membrane thickness;</li><li>Piezo element thickness: 100µm; and</li><li>Opening cross-section of the openings 32, 34: 100 µm x 100 µm.</li></ul>

0080An enlarged view of the left part of the in <figref idref="f0005">Fig. 6b</figref> The cross-sectional view shown is in <figref idref="f0006">Fig. 7</figref> shown, wherein in <figref idref="f0006">Fig. 7</figref> the height H of the pumping chamber 304 is indicated. Although according to the representation of<figref idref="f0006">Fig. 7</figref> Since the structures in the pump body 302 and in the membrane element 300 forming the pump chamber 304 have the same depths, it is preferred to design the structures in the pump body 302 with a greater depth than that in the membrane element in order to provide the flow channel 306 with a sufficient flow cross section without unduly affecting the compression ratio. For example, the structures in the pump body 302 that contribute to the fluid channel 306 and the pump chamber 304 can have a depth of 22 μm, while the structures in the membrane element 300 that define the valve chambers 308 or contribute to the pressure chamber 304 have a depth of 8 µm.

0081<figref idref="f0006">Fig. 8</figref> FIG. 3 shows a schematic cross-sectional view of an enlargement of section A of FIG <figref idref="f0006">Fig. 7</figref> , but in a modified form. According to<figref idref="f0006">Fig. 8</figref> the web is spaced from the opening 32 towards the channel 206. As a result, assembly tolerances can be taken into account in double-sided lithography. Furthermore, it can be prevented that wafer thickness fluctuations, which can result in valve openings with different cross-sectional sizes, have no negative effects. As in<figref idref="f0006">Fig. 8</figref> As can be seen, the distance x to the membrane 12 defines the flow constriction between the pump chamber and the valve passage opening when the valve position is open.

0082As stated above, in the areas of the fluid system where a pumping action is required by forming a pumping chamber volume of a peristaltic pump, the compression ratio of the peristaltic pump must be chosen large in order to ensure self-filling behavior and robust operation with regard to a bladder tolerance. In order to achieve this, it is preferred to keep the dead volumes small, which can be supported by the contour or Shape of the pump chamber is adapted to the bending line of the pump membrane in the deflected state.

0083A first possibility of realizing such an adaptation is to implement a round pump chamber, ie a pump chamber, the circumferential shape of which is adapted to the deflection of the pump membrane. A schematic plan view of the pump chamber and fluid channel section of a pump body with such a pump chamber is shown in FIG<figref idref="f0007">Fig. 9a</figref> shown. The round pump chamber 330, in turn, is comparable to the representation of FIG<figref idref="f0005">Fig. 6c</figref> the fluid channels 306, which establish a fluid connection to valve chambers, which in turn can be structured in a membrane element, for example.

0084In order to be able to achieve a further reduction in the dead volume and thus a further increase in the compression ratio, the pumping chamber under the pumping membrane can be designed such that its contour facing the pumping membrane follows the bending line of the pumping membrane with a precise fit. Such a contour of the pump chamber can be achieved, for example, by an appropriately shaped injection molding tool or by an embossing stamp. A schematic plan view of a pump body 340, in which such a fluid chamber 342 is structured following the bending line of the actuator membrane, is shown in FIG <figref idref="f0007">Fig. 9b</figref> shown. Furthermore, in<figref idref="f0007">Fig. 9b</figref> Structured fluid channels 344 are shown in the pump body, which lead to and away from the fluid chamber 342. A schematic cross-sectional view along the line cc of<figref idref="f0007">Fig. 9b</figref> is in <figref idref="f0007">Fig. 9c</figref> shown, wherein in <figref idref="f0007">Fig. 9c</figref> a membrane 346 with the piezo actuator 348 assigned to it is also shown. A flow through the fluid channels 344 is shown in FIG<figref idref="f0007">Fig. 9c</figref> indicated by arrows 350. Furthermore, in<figref idref="f0007">Fig. 9c</figref> to recognize the contour 352 of the fluid chamber or pump chamber 342 which faces the membrane 346 and which is adapted to the bending line of the membrane (in the actuated state). This shape of the fluid chamber 352 enables the entire volume of the fluid chamber 342 to be displaced when the membrane 346 is actuated by the piezo actuator 348, as a result of which a high compression ratio can be achieved.

0085An embodiment of a peristaltic micropump, in which both the pump chamber 342 and valve chambers 360 are adapted to the bending lines of the respectively assigned membrane sections 12, 14 and 16, is shown in FIGS <figref idref="f0008">10a and 10b</figref> shown where <figref idref="f0008">Fig. 10b</figref> shows a schematic top view of the pump body 340 while <figref idref="f0008">Fig. 10a</figref> is a schematic cross-sectional view taken along line aa of <figref idref="f0008">Fig. 10b</figref> shows. Like that<figref idref="f0008">10a and 10b</figref> It can be seen that the shape and contour of the valve chamber 360 and 362, as explained above with reference to the pump chamber 342, are adapted to the bending line of the respectively assigned membrane section 12 or 16. As further best in<figref idref="f0008">Fig. 10b</figref> As can be seen, fluid channels 344a, 344b, 344c and 344d are again formed in the pump body 340. Fluid channel 344a represents an input fluid channel, fluid channel 344b connects valve chamber 360 to pump chamber 342, fluid channel 344 connects pump chamber 342 to valve chamber 362, and fluid channel 344d represents an output channel.

0086As further in <figref idref="f0008">Fig. 10a</figref> is shown, the diaphragm element 380 in this exemplary embodiment is an unstructured diaphragm element which is introduced into a recess provided in the pump body 340 in order to define the valve chambers and the pump chamber together with the fluid regions formed in the pump body 340.

0087The connecting channels 344b and 344c between the actuator chambers are switched in such a way that they contain a small dead volume compared to the stroke volume. At the same time, these fluid channels significantly reduce the flow resistance between the actuator chambers, so that also higher pumping frequencies and thus larger delivery flows, such a flow again using arrows 350 in<figref idref="f0008">Fig. 10a</figref> is displayed. In the area of ​​the valve chambers 360 and 362, the fluid channels 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 channels 344a and 344b or between the fluid channels 344c and 344d. The contour of the valve chambers must be adapted exactly to the bending line of the respective membrane sections in order to achieve a tight fluid separation. Alternatively, as in <figref idref="f0009">Fig. 11</figref> is shown, a web 390 can be provided in the respective valve chamber in the region of the largest stroke of the membrane section 12, which is shaped accordingly so that it can be completely sealed by the bending of the membrane section 12. More specifically, the web bends upwards towards the edges of the valve chamber, in accordance with the shape of the valve chamber adapted to the bending line. This web can protrude into the respective valve chamber, alternatively as in<figref idref="f0009">Fig. 11</figref> is shown, the depth of the connecting channels 344 can be greater than the stroke y of the diaphragm section 12, at which the diaphragm section lies against the pump body, so that the web 390 is sunk, so to speak. If the depth of the connecting channels is greater than the maximum stroke, this is at the expense of the compression ratio, but enables low flow resistances between the actuator chambers.

0088An alternative embodiment of a valve chamber 360 is shown in FIG <figref idref="f0009">Fig. 12</figref> shown, where the depth of the connecting channels 344 is smaller than the maximum stroke y of the diaphragm section 12, and thus as the depth of the valve chamber 360 adapted to the bending line of the diaphragm section 12 in the region of the greatest stroke of the diaphragm section 12 closed state of the valve can be reached.

0089In order to achieve a valve seal in the closed state that meets the specified pressure requirements, it may be preferred to provide a web 390a in the valve chamber 360, which does not simulate the maximum possible bending line of the actuator element, i.e. the membrane section 12 together with the piezo actuator 22, such as in <figref idref="f0009">Fig. 13</figref> is shown. The maximum possible bending line of the membrane section 12 is in<figref idref="f0009">Fig. 13</figref> shown by a dashed line 400, while line 410 corresponds to the maximum possible deflection of membrane section 12 due to the provision of web 390a. Thus, in the fully deflected state, when the web 390 is sealed, the membrane 12 rests on the web 390a with a residual force, which residual force can be dimensioned in order to meet pressure requirements which the seal has to withstand.

0090In practical implementations, the bending line of the membrane will often not be perfectly concentric to the center of the membrane, for example due to assembly tolerances of the piezoceramics and due to inhomogeneities in the adhesive application by which the piezoceramics are attached to the membranes. The area of ​​the web seal can therefore be slightly increased, for example by approx. 5 up to 20 µm, depending on the stroke of the actuator, compared to the rest of the fluid chamber, in order to ensure a safe contact of the membrane with the web and thus a secure seal. This also corresponds to that in<figref idref="f0009">Fig. 13</figref> shown situation. It should be noted, however, that this increases the dead volume and reduces the compression ratio.

0091As an alternative to the options mentioned, a plastically deformable material, for example silicone, can be used as the fluid chamber material, at least in the area under the movable membrane. Inhomogeneities can then be compensated for by appropriately large actuator forces. In such a case, there is no longer a hard-hard seal, so that there is a certain tolerance against particles and deposits.

0092The following is a brief example of a dimensioning of a peristaltic pump, as shown in the <figref idref="f0008">10a and 10b</figref> is shown. The thickness of the membrane sections 12, 14 and 16 and thus the thickness of the membrane element 380 can be 40 μm, for example, while the thickness of the piezo actuators can be 100 μm, for example. A PZT ceramic with a large d31 coefficient can be used as the piezoceramic. The side length of the membranes can be, for example, 10 mm, while the side length of the piezo actuators can be, for example, 8 mm. The voltage swing for actuating the actuators in the actuator geometry mentioned 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 membrane of approximately 2 to 4 μl.

0093By 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 is eliminated, so that only the connecting channels that connect the valve chambers to the pump chamber remain. If connecting channels with a depth of 100 µm, a width of 100 µm and a length of 10 mm each, so that the overall length for the fluid channels 344b and 344c is 20 mm, this results in a pump chamber dead volume of 0.2 µl. A compression ratio ε = ΔV / V = ​​4 µl / 0.2 µl = 20 can be determined from this.

0094With such a large compression ratio of up to 20, such fluid modules are bubble-tolerant and self-priming and can convey both liquids and gases. Such fluid pumps can also build up in principle several bar pressure for compressible and liquid media, depending on the design of the piezo actuator. In such a micropump, the maximum pressure that can be generated is no longer limited by the compression ratio, but is defined by the maximum force of the drive element and the tightness of the valves. Despite these properties, a suitable channel dimensioning with a low flow resistance can deliver several ml / min.

0095In the exemplary embodiment described above, all of the fluid channels, ie also the inlet fluid channel 344a and the outlet fluid channel 344d, were guided laterally, ie the fluid channels run in the same plane as the fluid chambers. As stated above, sealing the channels can be difficult with such a course. An advantage of the lateral course of the fluid channels, however, is that the entire fluid system, including reservoirs connected to the inlet channel 344a and / or the outlet channel 344d, can be molded in one manufacturing step, for example by injection molding or embossing.

0096In <figref idref="f0008">Fig. 14</figref> An embodiment of a microperistaltic pump according to the invention is shown, in which the inlet fluid channel 412 and the outlet fluid channel 414 are vertically sunk in the pump body 340. The fluid channels 412 and 414 have an essentially vertical section 412a and 414a, each of which opens essentially centrally under the assigned membrane sections 12 and 16 into the valve chambers 360 and 362, respectively. The advantage of in<figref idref="f0008">Fig. 14</figref> Embodiment of the fluid channels shown is that the fluid channels can be sealed in a defined manner. However, it is disadvantageous that such vertically recessed fluid channels are difficult to manufacture in terms of production technology.

0097The peristaltic micropumps according to the invention are preferably controlled in that the membrane, for example the metal membrane or the semiconductor membrane, is at a ground potential, while the piezoceramics are moved through a typical peristaltic cycle, in each case by applying corresponding voltages to the piezoceramics.

0098In addition to the microperistaltic pump described above using three fluid chambers 342, 360 and 362, a peristaltic micropump according to the invention can have further fluid chambers, for example another fluid chamber 420, which is connected to the pump chamber 342 via a fluid channel 422. Such a structure is in<figref idref="f0010">Fig. 15</figref> schematically shown, 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.

0099A structure with four fluid chambers as in <figref idref="f0010">Fig. 15</figref> is shown, for example, can form a branching structure or a mixer in which the mixed streams can be actively promoted. The expansion to four fluid chambers with four assigned fluid actuators enables, for example, in<figref idref="f0010">Fig. 15</figref> is shown, the realization of three peristaltic pumps, each pump direction between all reservoirs 424, 426 and 430 can be realized in both directions. It is possible for a single membrane element to cover all fluid chambers and reservoir containers, a separate piezo actuator being provided for each fluid chamber. The entire fluid system can thus be made very flat, the functional, fluid structures including fluid chambers, channels, membranes, piezo actuators and support structures having a total height of the order of 200 to 400 μm. Systems are therefore conceivable that can be integrated into chip cards. Flexible fluidic systems are also conceivable.

0100In addition to the exemplary embodiments shown, fluid chambers can be connected as desired in one plane. For example, different reservoirs. B. each be assigned a microperistaltic pump, which then, for example, supply reagents to a chemical reaction (for example in a fuel cell), or perform a calibration sequence for an analysis system, for example in a water analysis.

0101To produce a piezo membrane transducer, the piezoceramics can be glued to the respective membrane sections, for example. Alternatively, the piezoceramics, for example PZT, can be applied directly in thick-film technology, for example by screen printing with suitable intermediate layers.

0102An alternative embodiment of a microperistaltic pump according to the invention with a sunk inlet fluid channel 412 and a sunk outlet fluid channel 414 is shown in FIG <figref idref="f0010">Fig. 16</figref> shown. The inlet flow channel 412 in turn opens substantially centrally below the membrane section 12 into a valve chamber 442, while the outlet fluid channel 414 opens substantially centrally below the membrane section 16 into a valve chamber 444. The respective mouth openings of the inlet channel 412 and the outlet channel 414 are provided with a sealing lip 450. Furthermore, a pump chamber 452 is formed in the pump body 440, which is fluidly connected to the valve chambers 442 and 444 by fluid channels in walls 454. According to the in<figref idref="f0010">Fig. 16</figref> In the exemplary embodiment shown, the three membrane sections 12, 14 and 16 in turn form a membrane element 456. In this exemplary 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 are used using suitable housing parts 470 and 472, which are shown in<figref idref="f0010">Fig. 16</figref> shown removed from the pump body and the membrane element are used.

0103Piezo stack actuators are advantageous in that they do not have to be firmly connected to the membrane element, so that they enable a modular structure. In the case of such piezo stack actuators which are not firmly connected, the actuators do not actively retract a membrane section when actuation thereof is ended. Rather, the membrane section can only be moved back by the restoring force of the elastic membrane itself.

0104The peristaltic micropumps according to the invention can be manufactured using a wide variety of manufacturing materials and manufacturing techniques. The pump body can be made of silicon, for example, can be made of plastic by injection molding or can be machined using precision engineering. The membrane element, which forms the drive membrane for the two valves and the pump 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 two-component injection molding technology and provided with conductive coatings, or can be realized by an elastomer membrane.

0105The connection between the diaphragm element and the pump body is an important point because high shear forces can occur at this connection during operation of the peristaltic pump. The following requirements apply to this connection:<ul id="ul0003" list-style="dash" compact="compact"><li>tight;</li><li>thin joint layer (&lt;10 µm), since the pump chamber height is a critical design parameter that influences the dead volume;</li><li>mechanical resistance; and</li><li>chemically resistant to media to be pumped.</li></ul>

0106In the case of silicon as the basic structure and membrane element, silicon fusion bonding without a joining layer can be carried out. In the case of a silicon-glass combination, anodic bonding can preferably be used. Other options are eutectic wafer bonding or wafer bonding.

0107If the basic structure is made of plastic and the membrane element is a metal foil, lamination can be carried out if an adhesion promoter is used between the membrane element and the basic structure. Alternatively, gluing with an adhesive with high shear strength can take place, in which case capillary stop trenches are then preferably formed in the basic structure in order to prevent glue from penetrating into the fluid structure.

0108If both the diaphragm element and the pump body are made of plastic, ultrasonic welding can be used to connect them. If one of the two structures is optically transparent, laser welding can alternatively take place. In the case of an elastomeric membrane, the sealing properties of the membrane can also be used to ensure sealing by clamping.

0109The following briefly explains how a possible attachment of the membrane to the pump body can take place in a microperistaltic pump according to the invention. If the membrane of the micropump according to the invention is glued to the pump body, it should be noted that the metering of joining layer materials (e.g. Adhesive) is critical, since on the one hand the membrane must be completely sealed (that is, sufficient adhesive must be applied) and, on the other hand, penetration of excess adhesive into the fluid chambers must be avoided.

0110The joining layer material, which can be an adhesive or an adhesive, is applied to the joining layer, for example by dispensing or by means of a suitably shaped stamp. After the application of the joining layer material, the membrane is placed on the base body. Possible ridges, for example can be at the edge of the membrane when separated, there is space in a corresponding receptacle for the burr, so that a defined position of the membrane is ensured, especially in the direction perpendicular to the surface thereof, which is important with regard to the dead volume and the tightness.

0111Then a stamp is pressed onto the pump body so that the adhesive layer remains as thin and defined as possible. In order to absorb excess adhesive, a capillary stop trench can be provided, which surrounds the fluid areas formed in the pump body. Thus, such excess glue cannot get into the fluid chambers. Under these conditions, the adhesive can harden and thin. Curing can take place at room temperature or accelerated in the oven or by UV radiation when using UV-curing adhesives.

0112As an alternative to the adhesive technique described, the base body or pump body can be loosened by suitable solvents as a joining technique and a plastic membrane can be joined to the base body.