EP4617491A1

EP4617491A1 - Micropump with improved valves

Info

Publication number: EP4617491A1
Application number: EP24163759.4A
Authority: EP
Inventors: Florian Siemenroth; Nicole Bartek
Original assignee: Bartels Mikrotechnik GmbH
Current assignee: Bartels Mikrotechnik GmbH
Priority date: 2024-03-15
Filing date: 2024-03-15
Publication date: 2025-09-17

Abstract

The present invention relates to the field of micropumps. In particular, the invention relates to a micropump with improved flap valves.

The micropump comprises a structured polymer foil (1) which is placed between two members (5, 6), each member (5, 6) against which the moveable portion of the valve is designed to rest in order to provide a tight seal provides a groove (15) along the regions of the aforesaid circumference (16), such that a possible bulge (14) along said circumference (16) can entirely plunge into said groove (15) when the valve is in its closed position, so that an area of the moveable portion of the valve which is intended to mechanically contact the member (5, 6) in said closed position can lie flat against said member (5, 6), providing a best possible fluid seal.

The invention also relates to a method for fabricating a micropump with improved valves.

Description

Introduction

The invention relates to the field of micropumps. In particular, the invention relates to a micropump with improved flap valves.

Prior art and disadvantages

The present invention is directed towards an improvement of a micropump, and towards an improvement of manufacturing the same.
Micropumps are widely used to deliver a liquid or a gas for various purposes. A micropump is characterized by a volume flow which ranges from the femtolitre- to the millilitre-per-minute. In such small regions, specific aspects of microfluidics such as surface tension, capillarity effects, and the formation of interfaces between different media become highly relevant when a gas bubble is contained in a liquid.
Micropumps that are able to handle such situations are known e.g. from EP 2 222 959 B1 or US 8 043 073 B2 , which originate from the same applicant as the present invention, the content of which is incorporated by reference herein. US 8 043 073 B2 shows the general concept on how to handle the described situation by a cost effective and reliable pump system. A stacked structure of two distinct members is proposed that further contains certain microstructures which form a fluidic channel. Inside this channel, the stream can, depending on the design of the channel, move from the one member to the other, or along a gap between both members which forms the channel. In order to generate the flow, firstly, a fluidic connection exists in the fluid channel that leads into a pump chamber. Said chamber has one flexible wall (typically the capping) which is formed by an elastic membrane and covered by an often disc shaped actuator. By changing its geometry as a result of driving the actuator with an AC voltage, portions of the flexible wall move back and forth, alternately increasing and decreasing the internal volume of the pump chamber.
An important element of such a micropump is the flow rectification. This is achieved by special valves, often realised as flat flap valves. Such a valve is obtained by structuring a semi-finished polymer foil with certain slits.
In the following, Figs. 1 - 6 show examples from the prior art in order to illustrate the functioning of a micropump and the underlying problem of the present invention.
Figure 1 and Figure 2 show schematic drawings of such a foil 1, both of which are taken from the US patent 8 043 073 B2 . The lying-"U"-shaped slits 2 (not all with reference numerals) allow for movement of the flap part 3 of the foil 1 (moveable portion of the valve) which is connected to the surrounding material only via one elastic "hinge" 4. The shapes of the different flaps 3 in Fig. 2 can vary, depending on the specific design of the channel 10, in order to handle different sealing positions or opening directions. The centre of foil 1 is covered with an optional sieve structure, which is, however, not shown in subsequent figures.
Figure 3 and Figure 4 each show a schematic cross section through a micropump with an upper and lower member 5, 6, a channel 10 in between, and a disc shaped actuator 7 on a flexible membrane 8 forming the capping of the pump chamber 9. Both constructions vary mainly in the directions into which the flap valves are moveable.
The foil 1 is positioned between both members 5, 6, providing the flat flap valves. The material surrounding the actual valves stays clamped between the upper and the lower member 5, 6, holding the valves in place. In these Figures, for visualization purposes, all valves are shown in an intermediate (half-open) position.
When the actuator 7 moves up and down, fluid (not shown) is sucked into the pump chamber 9 and expelled therefrom alternatingly. When the fluid is sucked in, the pressure in channel 10 drops, resulting in opening the valves that are upstream (left) of the fluidic connection 11 in the middle of channel 10. At the same time, the other valves downstream (right) of the fluidic connection 11 close themselves.
When the filled pump chamber 9 is emptied by moving the actuator 7 downwards, the pressure rises. Thus, the upstream valves are closed, and the downstream valves become open. As a result, during one such cycle, the fluid is transported from an left-hand inlet 12 through the channel 10, and out of a right-hand outlet 13.
It is clear that the quality of the micropump, and in particular, the safety against undesired backflow, as well as the efficiency (e.g. transported volume/stroke cycle) depends, amongst others, on the tightness of the flap valves when in the closed position. Thus, it is preferred to have flap valves that are as leak tight as possible when closed.
Figure 5 shows a (not-to-scale) schematic cross section perpendicular to the axis of the fluid channel 10, in a section which is covered by a flap 3 of a valve consisting of foil 1. Note that for reasons of clearness, only the said moveable portion, i.e. flap part 3, of the valve is shown, and not the material surrounding the same. Ideally, when closed, the surface of the flap valve lies flat against the surface in which the channel 10 is embedded, providing a large contact area and thus, a best possible seal.
However, as shown in Figure 6 , due to a common production process being used due to its cost efficiency, namely stamping or laser cutting, the border areas of the slits 2 (see Figs. 1 and 2) are not flat, but provide a bulge 14, resulting either from mechanical forces in the case of stamping, or thermal melting in the case of laser cutting. This poor edge quality results in small "spacers" that allow, even when the valve is in the closed position as shown, a significant amount of fluid to pass the closed valve due to the reduced contact area. Also important, although not shown in the Figure, is that the bulge 14 is not necessarily even along its length, but might consist of alternating bumps and recesses, so that a large number of bypasses is formed that reduce tightness even more. Another effect of such flaws can be an altered, and usually increased, stiffness of the originally softer polymer along the circumference. While the percental amount of the bulge height typically ranges from 5% to 20% of the total thickness of the foil 1 (having a typical thickness of 1 µm to 500 pm, e.g. between 5 µm to 30 pm), the loss of performance (pressure and/or volume rate) due to such bulge formation can range from 5% up to 50%. In fact, the negative effect described is even present when the bulge thickness is in the one-digit µm range.
One solution to this problem provided in the art is using a femtosecond laser for the cutting process. Because such a laser does not use thermal heat to melt the polymer, but instead molecularises it directly, it can be described as a "cold" process that does not use mechanical energy for ablation. However, such a process is time consuming, and the laser system itself is costly, resulting in significantly higher cost for the production of the flap valve foils.

Object of the invention

The object of the present invention is providing a micropump with improved flap valves that still can be cost effectively produced.
The object is solved by a micropump according to claim 1, and a method of producing such a micropump according to claim 4. Advantageous embodiments can be found in the respective dependent subclaims, the following description and the figures.

Description

The invention is directed towards a micropump of the abovementioned type, i.e. for the delivery of fluids, and in particular liquids that can contain gaseous bubbles. The micropump comprises a multitude of flap valves provided by a structured polymer foil which is placed between two members, the members providing a channel in-between with an inlet and an outlet, and an actuator provided for alternating the volume of a pump chamber which has a fluidic connection to the channel.
By increasing the volume of the pump chamber, an under pressure can be generated in said pump chamber, propagating through the fluidic connection into the channel, such that valves located in the channel between inlet and fluidic connection can be opened, and valves located in the channel between fluidic connection and outlet can be closed, and so that by decreasing the volume of the pump chamber, an over pressure can be generated in said pump chamber, propagating through the fluidic connection into the channel, such that valves located in the channel between inlet and fluidic connection can be closed, and valves located in the channel between fluidic connection and outlet can be opened. In this way, a fluid flow can be generated, and fluid can be conveyed through the micropump.
The aforementioned foil is structured such that flap valves are provided that each comprise an elastic hinge as a connection to the surrounding material of the foil and that further comprise a circumference that is disconnected from said surrounding material by a slit, providing a moveable portion, such that the flap part of the valve is moveable around its hinge at least in one direction perpendicular to the surface of the foil. It is also possible that the flap part of the valve is moveable in both directions perpendicular to the surface of the foil (i.e. above and/or below the surface of the member against which the foil is placed).
The micropump is characterized in that each member against which the moveable portion of the valve is designed to rest in order to provide a tight seal (this can be the upper and/or the lower member, depending on the specific construction) provides a groove along the regions of the aforesaid circumference, such that a possible bulge along said circumference, resulting from the fabrication process such as stamping or thermal laser cutting, can entirely plunge into said groove when the valve is in its closed position (i.e. resting against the member surface that forms the valve seat). It is clear that the width of said groove must be at least minimally larger than the area that is intended to be touched by the circumference.
As a result, the area of the moveable portion of the valve which is intended to mechanically contact the member in said closed position, i.e. the circumference, can lie flat against said member, providing a best possible fluid seal.
The invention thus avoids the disadvantages known from the prior art. The valve foil can be produced using a cost efficient fabrication process such as stamping or laser cutting which produces flaws such as bulges and the like along the circumference of the moveable part of the flap valve. Nevertheless, such flaws become irrelevant with regard to the tightness of the seal provided by the valve when in the closed position, because the initially problematic areas do not determine the quality of the seal anymore; rather, the quality is determined by such areas of the flap valve that are not affected by the fabrication process, but only by the initial (and unimpeded) surface quality and characteristics.
Various embodiments of the invention are described in more detail below by aid of Figures 7 and 8.
As can be seen in Figure 7 which shows a cross section through the channel 10 in lower member 6 almost identical to the one in Figs. 5 and 6, a groove 15 is present in lower member 6. The groove 15 extends along the region above which the circumference 16 of the foil 1 would rest against the surface of member 6 (portion of the sealing surface) if no groove 15 would be present (such as it is the case in Fig. 5 and Fig. 6). Accordingly, the bulge 14 that runs along said circumference 16 does not come into mechanical contact with the sealing surface at any time. Thus, these regions cannot result in a reduction of the quality of the seal when the valve is closed, neither due to the presence of the bulges themselves, acting like "spacers", nor due to the fact that these regions might have less favourable mechanical properties stemming from the production process (see above).
It is clear that the width W of the grooves, in a side or top view, should be selected so that the borders of the groove extend beyond all circumferences of all valves in both directions, i.e. away from the centre of the flap, as well as towards the centre of the flap. A distance of 5 pm, 10 pm, 20 pm, 50 pm, 100 pm, 200 pm, 500 pm, or 1000 pm, in one or both directions is preferred.
According to an preferred embodiment, the depth D of the groove 16 is larger than the height of a bulge 14 that is formed when the foil 1 is stamped or thermally laser cut in order to form the circumference 16 of the moveable portion of the valve. In this way it is made sure that the bulge does not impede proper closing of the valve when its flap rests against the sealing surface.
According to another embodiment, the according member 5, 6 contains further an outer border groove 17 that is positioned such that also the outer border of the foil 1 containing the valves is located above such an according outer border groove. In other words, not only the moveable portions of the flap valves, but also the edges of the entire foil 1 itself can be negatively influenced to the production process. For illustration, Figure 8 shows a schematic bottom view onto upper member 5. The circle represents the contour of the pump chamber 9. Although not being directly responsible for the sealing quality of the valves, bulges along the outer border of the (not depicted) foil can result in delamination problems when assembling the housing of the micropump. The outer border groove 17 is located along the outer border of the foil. Thus, elimination of the influence of these problematic areas is a further advantage of the present invention.
Fig. 8 also indicates an example on the position of grooves 15 intended to receive the bulges of the moveable parts of the valves (not depicted). The dotted lines indicate the positions of the openings where channel 10 enters member 5. These openings are to be covered by the valves when the foil is later placed between both members. The circumference of the moveable portion of each valve is designed to rest in an according groove 15.
The invention is also directed towards a method for the fabrication of a micropump according to the general type as described above, i.e. a micropump with a valve foil which is clampable between two members, a pump chamber, and a channel. The structuring of the foil forming the valves is achieved by means of a process which produces bulges along a circumference of the moveable parts of the valves, such as stamping or thermal laser cutting, as mentioned above. According to the invention, prior to placing (or clamping) said foil between the lower and upper member that form the housing containing the channel and the pump chamber, grooves are fabricated in all regions of the surface of each member against which the circumference of the flap part of each valve would rest in its closed position (when no grooves would be present, which is the case in the prior art). The grooves are dimensioned such that the bulges which are usually formed due to the foil's structuring can be entirely received within said grooves, so that the aforementioned advantages arise.
According to a preferred embodiment, also an outer border groove 17, said groove 17 being positioned such that also the outer border of the foil containing the valves is located above said outer border groove, is fabricated in the according regions of the member such that the aforementioned advantages arise.
Typically, the members, and therefore, the grooves as well, are fabricated by injection moulding, and the foil is structured using laser ablation or stamping. According to another embodiment, the grooves are fabricated by the same process as the foil's structuring. Thus, the grooves can be fabricated via stamping, or via thermal laser ablation. Since the bottom and side walls of the grooves do not come into contact with the flap part of the valve, said wall surface quality is of minor importance. In particular, when using stamping, due to the mechanical forces, the upper edges of the grooves will tend to be pushed into the surrounding material and not stand up which would result in a poorer sealing quality.
Also, a combination of grooves pre-produced by injection moulding together with the member(s) with a post-processing using another fabrication process such as laser ablation or stamping is possible, depending of the specific requirements of the finished product.

List of reference numerals

1: foil
2: slit
3: flap part, flap
4: hinge
5: upper member, member
6: lower member, member
7: actuator
8: membrane
9: pump chamber
10: channel
11: fluidic connection
12: inlet
13: outlet
14: bulge
15: groove
16: circumference
17: outer border groove, groove

W: width
D: depth

Claims

Micropump for the delivery of fluids, comprising a multitude of flap valves provided by a structured polymer foil (1) which is placed between two members (5, 6), the members (5, 6) providing a channel (10) in-between with an inlet (12) and an outlet (13), and with an actuator (7) provided for alternating the volume of a pump chamber (9) which has a fluidic connection (11) to the channel (10), so that by increasing the volume of the pump chamber (9), an under pressure can be generated in said pump chamber (9), propagating through the fluidic connection (11) into the channel (10), such that valves located in the channel (10) between inlet (12) and fluidic connection (11) can be opened, and valves located in the channel (10) between fluidic connection (11) and outlet (13) can be closed, and so that by decreasing the volume of the pump chamber (9), an over pressure can be generated in said pump chamber (9), propagating through the fluidic connection (11) into the channel (10), such that valves located in the channel (10) between inlet (12) and fluidic connection (11) can be closed, and valves located in the channel (10) between fluidic connection (11) and outlet (13) can be opened, so that a fluid flow can be generated and fluid can be conveyed through the micropump, wherein the foil (1) is structured such that flap valves are provided that each comprise an elastic hinge (4) as a connection to the surrounding material of the foil (1) and a circumference (16) that is disconnected from said surrounding material by a slit (2), providing a moveable portion, such that the flap part (3) is moveable around its hinge (4) at least in one direction perpendicular to the surface of the foil (1), characterized in that each member (5, 6) against which the moveable portion of the valve is designed to rest in order to provide a tight seal provides a groove (15) along the regions of the aforesaid circumference (16), such that a possible bulge (14) along said circumference (16) can entirely plunge into said groove (15) when the valve is in its closed position, so that an area of the moveable portion of the valve which is intended to mechanically contact the member (5, 6) in said closed position can lie flat against said member (5, 6), providing a best possible fluid seal.
Micropump according to claim 1, wherein the depth (D) of the groove (15) is larger than the height of a bulge (14) that is formed when the foil (1) is stamped or thermally laser cut in order to form the circumference (16) of the moveable portion of the valve.
Micropump according to claim 1 or 2, wherein the according member (5, 6) contains further an outer border groove (17) that is positioned such that also the outer border of the foil (1) containing the valves is located above said outer border groove (17) .
Method for the fabrication of a micropump according to the preamble of claim 1, wherein the structuring of the foil (1) is achieved by means of a process which produces bulges (14) along a circumference (16) of the moveable parts of the valves, and wherein, prior to placing said foil (1) between lower and upper member (5, 6), grooves (15) are fabricated in all regions of the surface of each member (5, 6) against which the circumference (16) of the flap part (3) of each valve would rest in its closed position, wherein said grooves (15) are dimensioned such that said bulges (14) forming due to the foil's (1) structuring can be received within said grooves (15) .
Method according to claim 4, wherein also an outer border groove (17), said groove (17) being positioned such that also the outer border of the foil (1) containing the valves is located above said outer border groove (17), is fabricated in the according regions of the member (5, 6).
Method according to claim 4 or 5, wherein the grooves (15, 17) are fabricated by the same process as the foil's (1) structuring.