Patent Application
20100171054
The present invention relates to miniaturised valve systems, and in particular to integrated valve systems, which commonly are fabricated using silicon micromachining.
Microsystems technology (MST) or microelectromechanical systems (MEMS) can be regarded as a spin-off from the microelectronics. In miniaturised systems from this technology field, integrated circuits may be combined with e.g. mechanical, fluid, chemical, or biological systems in an integrated system. Commonly the choice of design, materials and processing is made on the basis of the vast knowledge from microelectronic processing, but as the field of MEMS has developed and found new application areas the technology have been acknowledged as a stand-alone technology and the development of design and processing is rapidly improving.
One important application area of MEMS is microfluidics. Microfluidics deals with the behavior, precise control and manipulation of small volumes of fluids. By using MEMS-technologies highly miniaturised fluidic system can be accomplished. The complexity of such systems may be very high and virtually any functionality can be incorporated. Microfluidics is mostly used for development of biotechnical systems such as e.g. lab-on-a-chip devices or bioassays, but other application areas begin to benefit from the superior properties of microfluidics. One important application area is micropropulsion, which may be used in for example space technology for e.g. altitude control. By using microfluidic MEMS-structures the overall size and mass of e.g. a propulsion system becomes drastically decreased and consequently the size and mass of a satellite to be launched becomes substantially reduced. Moreover the reliability of an integrated micropropulsion system is potentially higher than for a conventional system.
As in microelectronics the microfluidic MEMS-structures are mainly fabricated using silicon wafers as substrates, but e.g. other semiconducting materials, polymers, ceramics and glass are emerging.
Valves in fluidic systems usually have fast response times to properly control flow rates in the system. In fluidic systems that handles high pressures and high flow rates such valves may cause detrimental pressure gradients or shockwaves. This is a problem for conventional valves and in particular for miniaturised valves due to their inherently fast response times.
In many fluidic systems it is desirable to have parallel fluid branches, each controlled by at least one valve having an individual turn-on and turn-off response time. One such fluidic system is found in bi-propellant rocket engines, wherein the control of the turn-on and turn-off of different fluid branches is very important. Another application may be in chemical analysis, wherein a plurality of reactants is to be added in a pre-determined sequence. Conventionally a single valve, controlled by e.g. an electrical motor or a linear actuating device, is used to obtain the above described feature. The linear acting device may be a pneumatic or a hydraulic device. However, such conventional valve control devices are relatively heavy and bulky.
Obviously the prior art has drawbacks with regards to being able to provide valve system having small size and weight and permitting high flow rates and a pre-determined response time.
The object of the present invention is to overcome the drawbacks of the prior art. This is achieved by the device as defined in the independent claim.
In a first aspect the present invention provides an integrated microvalve system comprising at least a first fluid branch and a microvalve being controlled by a control pressure in a control channel. The microvalve is adapted to control a fluid flow in the first fluid branch. A flow restrictor arrangement is located between a control port and the control channel to give a pre-determined turn-on and turn-off response characteristics of the microvalve. Preferably, the flow restrictor arrangement comprises at least a first flow restrictor.
In one embodiment the flow restrictor arrangement comprises a deflate channel and an inflate channel arranged in parallel, and of which at least one of the inflate/deflate channel comprises a check valve adjacent to the control port. The first flow restrictor is integrated in the deflate channel, and a second flow restrictor is integrated in the inflate channel. Preferably, the deflate channel comprises a turn-on check valve adjacent to the control port and the inflate channel comprises a turn-off check valve adjacent to the control port. The flow restrictors may have different flow restriction to give different turn-on and turn-off response characteristics for the microvalve.
The integrated microvalve system may comprises two or more parallel fluid branches, wherein the microvalve/microvalves of each fluid branch is connected to a separate flow restrictor arrangement, preferably adapted to give different turn-on and turn-off response characteristic for said two or more parallel fluid branches.
In a second aspect the present invention provides an integrated microvalve system comprising a pressure controlled microvalve, which comprises at least a first flexible membrane acting against a first valve seat. The maximum deflection of the flexible membrane is preferably limited and the flexible membrane is further preferably provided with damping means.
Thanks to the invention it is possible to provide an integrated microvalve system having a high pressure capability and a controlled response time.
It is a further advantage of the invention to provide an integrated microvalve system that has a large cross-sectional flow area permitting a high flow rate in one or several parallel branches. The microvalve system may comprise several parallel fluid branches, each having different pre-defined response times.
It is yet a further advantage of the invention to provide an integrated microvalve system with low power consumption.
It is yet another advantage of the invention to provide a microvalve that comprises a protection for catastrophic failure due to exposure to high pressure.
Embodiments of the invention are defined in the dependent claims. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings and claims.
Preferred embodiments of the invention will now be described with reference to the accompanying drawings, wherein
a is a schematic block diagram of an integrated microvalve system comprising two flow restrictors and one check valve integrated in the deflate channel according to the present invention,
b is a schematic block diagram of an integrated microvalve system comprising two flow restrictors and one check valve integrated in the inflate channel according to the present invention,
a is a schematic block diagram of an integrated microvalve system comprising a flow restrictor arrangement according to the present invention,
b is a schematic block diagram of an integrated microvalve system comprising two parallel fluid branches according to the present invention,
a-c are schematic diagrams illustrating the relative microvalve position of a) the first fluid branch, b) the second fluid branch and c) the control pressure in the control port of an integrated microvalve system according to the present invention,
a-b illustrate cross sectional views of a microvalve in a) closed and b) open position according to the present invention,
a-b illustrate cross sectional views of a gas suspension means of a microvalve according to the present invention.
The basis of the present invention is control of the turn-on and/or turn-off response times of at least one microvalve in an integrated microvalve system. The integrated microvalve system is preferably designed and manufactured using methods, materials and technologies of the field of Microsystem Technology (MST) or Microelectromechanical Systems (MEMS).
Commonly microsystems for fluidics are built using silicon micromachining, which may comprise shaping, typically using photolithography and etching, and bonding of silicon wafers. The present invention is however not limited to silicon micromachining. By way of example other semiconductor materials, polymers and ceramics may be used. Neither is the present invention limited to systems built using photolithography and etching, for example may high precision machining, laser machining, injection moulding, etc. be used. Micromachined wafers may be joined using other methods than bonding, such as welding, soldering, gluing, etc.
Referring to
In one embodiment of the present invention the flow restrictor arrangement 21 comprises at least a first flow restrictor 24.
Referring to
Referring to
The microvalve 2 of the fluid branch 8 is controlled by a pressure difference between an inlet pressure in an inlet 11 of the fluid branch 8 and a control pressure in the control channel 17. In principle, the microvalve 2 is closed if the pressure difference between the inlet pressure in the inlet 11 and the control pressure in the control channel 17 is less than a critical pressure difference and open when the pressure difference is exceeding the critical pressure difference. However, unlike conventional pressure controlled microvalves 2 the response times of the microvalve 2 of the present invention are given by the flow restrictor arrangement 21.
One example of the operation of the integrated microvalve system 1 of
The flow restrictors 24, 25 may be formed by conventional micromachining. By way of example the flow restrictors 24, 25 may comprise e.g. crossed grooves of adjacent silicon wafers.
One embodiment of the present invention comprises a filter 28, which protects the check valves 34, 35 from particle contamination. The flow restriction provided by the filter 28 adds flow restriction to the flow restriction caused by the flow restrictor arrangement 21.
Referring to
One embodiment of an integrated microvalve system 1 according to the present invention comprises two or more parallel fluid branches 8, 9. Each fluid branch 8, 9 is connected to separate flow restrictor arrangement 21, 22, each comprising a deflate channel 30 and an inflate channel 31 arranged in parallel. Each deflate channel 30 comprise at least a first flow restrictor 24 and each inflate channel 31 comprises at least a second flow restrictor 25. The flow restrictor arrangements 21, 22 have independent pre-determined turn-on and/or turn-off response characteristics for the different fluid branches 8, 9 due to different flow restriction of the first and second flow restrictors 24, 25 of the different flow restrictor arrangements 21, 22. Preferably, however not limited to this, the fluid branches 8, 9 have common turn-on and turn-off check valves 34, 35 and a common control port 19. Further a filter 28 may be arranged at the control port 19 to protect the turn-on and turn-off check valves 34, 35 from particle contamination.
In one embodiment of an integrated microvalve system according to the present invention each fluid branch 8, 9 comprises two or more microvalves 2 arranged in parallel and connected to a common flow restrictor arrangement 21, 22.
The fluid branches 8, 9 of an integrated microvalve system 1 according to the present invention may be totally separated and can have significant different flow rate capacity.
a-c schematically illustrate the turn-on/turn-off sequence of an integrated valve system 1 comprising two parallel fluid branches 8, 9, each comprising at least one microvalve 2. A microvalve 2 position 61 of a first fluid branch 8 versus time 62 and a microvalve 2 position 61 of a second fluid branch 9 are illustrated in
Referring to
When the microvalve 2 is closed the fluid pressure in the fluid cavity 40 is low and the contact pressure acting on the valve seat 44 depends on the relation between inlet channel area at the valve seat 44 multiplied with the fluid pressure at the inlet 11 and the area of the flexible membrane 42 multiplied with the control pressure together with the pretension of the flexible membrane 11 on the valve seat. As long as the first force is smaller the second force the sum of pretension and membrane internal pressure times the membrane area the valve is closed.
In another embodiment also a second flexible membrane 43 is located on the opposite wall of the control cavity 41. The second flexile membrane 43 is acting against a second valve seat 45, which preferably is connected to the same inlet 11 as the first valve seat 44.
Each flexible membrane may have a central embossment 48, 49. The flat outer surfaces of the embossments 48, 49 act against the first and the second valve seat 44, 45, respectively. From the fluid inlet 11 the fluid is distributed to two fluid cavities 40 located adjacent each valve seat 44, 45. The cavities 40 and the valve seats 44, 45 are formed in a third and fourth silicon wafer 57, 58. Optionally, a valve seat membrane 47 suspends the valve seat 44, 45 giving some flexibility to prevent wear and tension of the valve seat 44, 45. A fifth silicon wafer 59 comprises the input 11 and a sixth silicon wafer 60 comprises an outlet 12 of the microvalve 2.
The sixth wafer 60 may comprise a control port 19, which is connected to the control cavity 41, and preferably a flow restrictor arrangement 21 according to the present invention is arranged in between the control port 19 and the control cavity 41. The flow restrictor arrangement 21 may be located in any of the silicon wafers 55, 56,57, 58, 59, for example in the interface between the first and the second silicon wafer 55, 56 as shown in
When the control pressure is decreased the control cavity 41 deflates and both flexible membranes 42, 43 deflect inwards and the microvalve 2 opens. The fluid outlet through both valve seats 44, 45 is collected to a common outlet 12. When the outlet pressure builds up or if the control pressure is further reduced the gap between the embossments becomes zero and the microvalve 2 is open to its maximum. One or both flexible membranes 42, 43 may comprise an anti-stiction means 51, such as an anti-stiction coating, a surface modification and a microstructured surface, to prevent sticking when in contact with each other.
A potential problem with the design of a pressure controlled microvalve is the risk for an avalanche effect when the microvalve 2 opens. When the microvalve 2 opens and fluid starts to flow through the microvalve 2, the outlet pressure will increase as soon as the fluid reaches the next flow restriction down the line. This means that the pressure in the fluid cavity 40 rapidly increases, which will further deflate the control cavity 41 yielding an inward deflection of the flexible membranes 42, 43. In order to prevent a harmful shock when the first and second flexible membranes 48, 49 meets the flexible membranes may comprise damping means 50, e.g. a thick and soft anti-stiction coating located on the embossments 48, 49, which acts as a cushion when the flexible membranes hits each other.
Referring to
In a damping means 50 as described above it is important that both etch depths in the embossments 48, 49 are equal in order to minimize the dead volume when the structure is closed. Both the vertical clearance 78 between the two embossments 48, 49 outside the contact area 78 and the lateral clearance 79 between the protrusions 52 and the recesses 53 should be kept to a minimum. By making the central grooves a little narrower the primary contact point automatically can be located to the center, as a groove with higher aspect ratio is etched a little slower than a wider groove. It shall be noted the etch depths of the embossments 48, 49 must be twice what required for flat milled embossments for a given stroke length.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, on the contrary, is intended to cover various modifications and equivalent arrangements within the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0602523-3 | Nov 2006 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2007/050912 | 11/28/2007 | WO | 00 | 1/12/2010 |
