Fluid transportation system

Abstract

A fluid transportation system includes: a micropump provided with a chamber and a diaphragm driven by an actuator; fluid communication sections communicating with both ends of the chamber of the micropump; a pressure absorbing section that is provided at least one of the fluid communication sections so as to absorb or reduce a fluid vibration pressure; and a narrow section that is provided at a position further than the pressure absorbing section from the chamber so as to narrow a flow path cross-section, wherein, when R represents a flow path resistance value of the narrow section and C represents an acoustic capacitance value of the pressure absorbing section, a value obtained by multiplication between R and C is not smaller than a driving cycle period value of the micropump.

Description

This application is based on Japanese Patent Applications No. 2005-253219 filed on Sep. 1, 2005 and No. 2006-157492 filed on Jun. 6, 2006 in Japan Patent Office, the entire content of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a fluid transportation system, and particularly relates to a fluid transportation system that transports a tiny amount of fluid, using a micropump.

BACKGROUND OF THE INVENTION

In recent years, there have been developed and offered various micropumps that are incorporated in a fluid transportation system for biological tests, chemical analysis, drug discovery, etc. and transport a tiny amount of liquid in high accuracy. Such a micropump is structured such that a flow path and fluid reservoir that communicate with a respective one of the both ends of a chamber provided with a diaphragm driven by a piezoelectric element, through a narrow flow path portion or open-and-close valve.

Japanese Patent No. 3629405 discloses this type of a micropump in which a diaphragm is driven by a piezoelectric element and thus regularly deformed so as to transport fluid in one direction through a chamber. However, this type of micropump has a problem that a pressure vibration wave, which is generated in the chamber due to driving of a piezoelectric element, is transferred to the upstream side and downstream side through the inlet and outlet.

In this situation, Japanese Patent No. 3569267 and Japanese Non-examined Patent Publication No. 2000-265963 disclose providing a pressure-absorbing section at the inlet and outlet so as to absorb or reduce a vibration pressure. However, such a pressure-absorbing section is not always complete, leaving a problem that vibration that leaks from the pressure-absorbing section affects sections where the vibration is applied in a case where an active component such as a pump or movable valve is not provided at the upstream side or downstream side of the pressure-absorbing section.

With this background, an object of the present invention is to provide a fluid transportation system capable of inhibiting a vibration pressure generated in a chamber from leaking out from a pressure absorbing section further to the upstream side and/or downstream side.

SUMMARY OF THE INVENTION

In a first aspect of the invention, there is provided a fluid transportation system, including:

a micropump provided with a chamber and a diaphragm driven by an actuator;

fluid communication sections communicating with both ends of the chamber of the micropump;

a pressure absorbing section that is provided at least one of the fluid communication sections so as to absorb or reduce a fluid vibration pressure; and

a narrow section that is provided at a position further than the pressure absorbing section from the chamber so as to narrow a flow path cross-section,

wherein,

when R represents a flow path resistance value of the narrow section and C represents an acoustic capacitance value of the pressure absorbing section, a value obtained by multiplication between R and C is not smaller than a driving cycle period value of the micropump.

In a second aspect of the invention, there is provided a fluid transportation system, including:

a micropump provided with a chamber and a diaphragm driven by an actuator;

fluid communication sections communicating with both ends of the chamber of the micropump;

a pressure absorbing section that is provided at least one of the fluid communication sections so as to absorb or reduce a fluid vibration pressure; and

a filtering section having a plurality of micro flow paths, the filtering section being provided at a position further than the pressure absorbing section from the chamber,

wherein,

when R represents a flow path resistance value of the filtering section and C represents an acoustic capacitance value of the pressure absorbing section, a value obtained by multiplication between R and C is not smaller than a driving cycle period value of the micropump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a schematic structure of a fluid transportation system in a first embodiment in accordance with the invention, wherein (A) is a plan view of a thin etched plate and (B) is a cross-sectional view;

FIGS. 2A to 2C are diagrams showing the operation (forward liquid feeding) of a micropump of a fluid transportation system; and

FIGS. 3A to 3C are diagrams showing (backward liquid feeding) of the micropump;

FIG. 4 is a plan view showing a schematic structure of a fluid transportation system in a second embodiment in accordance with the invention;

FIG. 5 is a plan view showing a schematic structure of a fluid transportation system in a third embodiment in accordance with the invention;

FIG. 6 is a plan view showing a schematic structure of a fluid transportation system in a fourth embodiment in accordance with the invention;

FIG. 7 is a plan view showing a schematic structure of a fluid transportation system in a fifth embodiment in accordance with the invention;

FIG. 8 is a plan view showing a schematic structure of a fluid transportation system in a sixth embodiment in accordance with the invention;

FIG. 9 is a plan view showing a schematic structure of a fluid transportation system in a seventh embodiment in accordance with the invention;

FIG. 10 is a plan view showing a schematic structure of a fluid transportation system in an eighth embodiment in accordance with the invention;

FIG. 11 is a plan view showing a schematic structure of a fluid transportation system in a ninth embodiment in accordance with the invention.

PREFERRED EMBODIMENTS OF THE INVENTION

The invention includes the following structures.

(Item 1)

A fluid transportation system including:

a micropump provided with a chamber and a diaphragm driven by an actuator;

fluid communication sections communicating with both ends of the chamber of the micropump;

a pressure-absorbing section that is provided at least one of the fluid communication sections so as to absorb or reduce a fluid vibration pressure; and

a narrow section that is provided at a position further than the pressure absorbing section from the chamber so as to narrow a flow path cross-section,

wherein,

when R represents a flow path resistance value of the narrow section and C represents an acoustic capacitance value of the pressure absorbing section, a value obtained by multiplication between R and C is not smaller than a driving cycle period value of the micropump.

(Item 2)

A fluid transportation system including:

a micropump provided with a chamber and a diaphragm driven by an actuator;

fluid communication sections communicating with both ends of the chamber of the micropump;

a pressure-absorbing section that is provided at least one of the fluid communication sections so as to absorb or reduce a fluid vibration pressure; and

a filtering section having a plurality of micro flow paths, the filtering section being provided at a position further than the pressure absorbing section from the chamber,

wherein,

when R represents a flow path resistance value of the filtering section and C represents an acoustic capacitance value of the pressure absorbing section, a value obtained by multiplication between R and C is not smaller than a driving cycle period value of the micropump.

In the fluid transportation systems according to the above Items 1 and 2, since a narrow section or a filtering section having a plurality of micro flow paths that is provided at a position further than the pressure absorbing section from the chamber, a vibration pressure generated in the chamber by driving the actuator is absorbed in two steps at the pressure absorbing section, and the narrow section or filtering section. Thus, it is possible to inhibit the vibration pressure generated in the chamber from leaking out from the pressure absorbing section further to the upstream side and downstream side.

Further, when R represents the flow path resistance value of the narrow section or the filtering section, and C represents the acoustic capacitance value of the pressure absorbing section, the value obtained by multiplication between R and C is preferably larger than or equal to a driving cycle period value of the micropump. Thus, after a vibration of the pressure absorbing section ceases, a subsequent vibration is started by the actuator, and thereby fluid is smoothly transported. Herein, in order that the value obtained by multiplication between R and C does not become too large, the flow path resistance value of the narrow section or the filtering section is smaller than the effective inner flow path resistance value of the micropump.

Particularly, in the fluid transportation system of Item 2, the filtering section eliminates foreign matters having been mixed in the fluid. Accordingly, the filtering section is preferably disposed on upstream side, in the transportation direction, of the chamber.

In the fluid transportation system of Items 1 and 2, since the vibration pressure is effectively absorbed, the value of the acoustic capacitance of the pressure absorbing section is preferably larger than that of the acoustic capacitance of the chamber. In order to obtain the same effect, preferably, at least one wall surface of the pressure absorbing section is a thin plate deformable by a fluid pressure and the width of the thin plate is larger than the width of the chamber.

Further, it is possible to achieve fluid transportation in high accuracy by the use of a micropump that includes a first throttle flow path and a second throttle flow path at the both ends of the chamber of which respective flow path resistances change corresponding to a differential pressure, wherein the changing rate of the flow path resistance of the first throttle flow path is larger than that of the second throttle flow path; the actuator transport fluid from the first throttle flow path toward the second flow path, by repeatedly increasing and decreasing the pressure of fluid in the chamber in a first pattern where the time of increasing the pressure is shorter than the time of decreasing the pressure; and the actuator transports fluid from the second throttle flow path toward the first flow path, by repeatedly increasing and decreasing the pressure of fluid in the chamber in a second pattern where the time of increasing the pressure is longer than the time of decreasing the pressure.

Now, an embodiment of a fluid transportation system in accordance with the invention will be described, referring to the attached drawings. Herein, common symbols are given to the same members and components common in the figures showing the respective embodiments, and overlapping descriptions are omitted.

(Schematic structure in a first embodiment, referring to FIGS. 1A and 1B)

A fluid transportation system 10A in accordance with a first embodiment includes, as shown in FIG. 1B, a joint of a glass substrate 11 and thin plate 20. The glass substrate 11 is formed with an inlet 12 and outlet 13. Further, the thin plate 20 is made of a SI-based substrate that is formed by etching with a chamber 21, throttle flow paths 22 and 23, fluid reservoir 24, filtering section 25, flow path 26, pressure absorbing section 27, and narrow section 28, these communicating with each other. Further, a piezoelectric element 30 as an actuator is stuck on the outer surface of the chamber 21, and the membrane portion of the chamber 21 functions as a diaphragm.

Taking an example of concrete dimensions, the thin plate 20 is 200 μm thick; the membrane diaphragm or the like of the chamber 21 is 30 μm thick; and the throttle flow paths 22 and 23 are 25 μm deep.

The fluid reservoir 24 is formed with a larger width and capacity than the chamber 21 and functions as the pressure absorbing section on the inlet side. The filtering section 25 includes a coarser first filtering section 25a and a finer second filter 25b, and is located at a position further than the chamber 21 from the fluid reservoir 24. Further, one end of the fluid reservoir 24 communicates with the inlet 12 of the glass substrate 11 through the filtering section 25.

One end of the narrow section 28 communicates with the pressure absorbing section 27 and is located at a position further from the chamber 21, narrowing the flow path cross-section, while the other end communicates with the outlet 13 of the glass substrate 11. The absorbing section 27 is formed with a larger width and capacity than the chamber 21.

(Operation of micropump, referring to FIGS. 2A to 2C and 3A to 3C)

In the fluid transportation system 10A, the micropump 31 includes the chamber 21, throttle flow paths 22 and 23, and piezoelectric element 30. Now, the operation of the micropump 31 will be described.

Conceptually, the micropump 31 includes throttle flow paths 22 and 33 at the both ends of the chamber 21 of which respective flow path resistances change corresponding to a differential pressure, wherein, the changing rate of the flow path resistance of the throttle flow path 22 is larger than that of the throttle flow path 23; fluid is transported from the throttle flow path 22 toward the throttle flow path 23, by repeatedly increasing and decreasing a pressure of fluid in the chamber by the piezoelectric element 30 in a first pattern where the time of increasing the pressure is shorter than the time of decreasing the pressure (refer to FIGS. 2A to 2C); and fluid is transported from the throttle flow path 23 toward the throttle flow path 22, by repeatedly increasing and decreasing the pressure of fluid in the chamber by the piezoelectric element 30 in a second pattern where the time of increasing the pressure is longer than the time of decreasing the pressure (backward liquid feeding, refer to FIGS. 3A to 3C).

Concretely, FIGS. 2A to 2C show the liquid feeding state in the forward direction (the first pattern), wherein when a voltage in the wave form shown in FIG. 2A is applied to the piezoelectric element 30 to quickly increase the pressure of fluid in the chamber 21, a turbulent flow occurs and the flow path resistance becomes larger in the throttle flow path 22, and thus the fluid is exhausted from the chamber 21 through the throttle flow path 23. When the pressure of fluid in the chamber 21 is slowly decreased, fluid is introduced into the chamber 21 through the throttle flow path 22 with a small flow path resistance. In the present first embodiment and also in other embodiments, description will be given with an assumption that fluid is transported in the first pattern.

FIGS. 3A to 3C show the liquid feeding state in the backward direction (the second pattern), wherein when a voltage in the wave form shown in FIG. 3A is applied to the piezoelectric element 30 to slowly increase the pressure of fluid in the chamber 21, fluid is exhausted from the chamber 21 through the throttle flow path 22 with a small flow path resistance. When the pressure of fluid in the chamber 21 is quickly decreased, a turbulent flow occurs in the throttle flow path 22 to increase the flow path resistance, and thus fluid is introduced into the chamber 21 through the throttle flow path 23.

(Function of Filtering Section and Narrow Section)

When the micropump 31 is driven in the first pattern, fluid is transported with high accuracy to the outlet 13 through the inlet 12, filtering section 25, fluid reservoir 24, throttle flow path 22, chamber 21, throttle flow path 23, flow path 26, pressure absorbing section 27, and narrow section 28.

In the transportation process described above, by driving the piezoelectric element 30, a pressure vibration wave generated in the chamber 21 is transmitted to the inlet and outlet sides through fluid. The fluid reservoir 24 and pressure absorbing section 27 absorb or reduce the vibration pressure, by the elasticity of the membrane portion thereof, and prevents the vibration pressure from being transmitted to the inlet and outlet sides. However, it is impossible to completely absorb transmission of the vibration pressure.

With regard to the fluid reservoir, region Y (refer to FIG. 1A) excluding the region formed with the filtering section 25 functions as a pressure absorbing section.

Since the filtering section 25 and narrow section 28 have a large flow path resistance, a remaining vibration pressure having not been absorbed by the fluid reservoir 24 nor the pressure absorbing section 27 can be absorbed substantially completely, which prevents the vibration pressure from leaking from the inlet 12 and outlet 13 to the upstream and downstream sides. Particularly, the filtering section 25 can eliminate foreign matters mixed in the fluid.

(Schematic Structure in a Second Embodiment, Refer to FIG. 4)

A fluid transportation system 10B in a second embodiment is constructed basically, as show in FIG. 4, by connecting, in parallel, two fluid transportation systems each including a micropump 31, described in the first embodiment, and merges transported fluids at a merging section 29a which joints flow paths 29, 29 provided on the downstream side of narrow sections 28, 28.

When plural micropumps fluid-communicate with each other through a flow path, a vibration generated by one micropump affects the operation of another micropump and tends to cause characteristic variation. However, as in the present second embodiment, when micropumps 31, 31 are connected in parallel, micropumps 31, 31 do not affect each other.

(Schematic Structure in a Third Embodiment, Refer to FIG. 5)

A fluid transportation system 10C in a third embodiment is constructed, as shown in FIG. 5, basically by connecting, in parallel, two fluid transportation systems each including a micropump 31, similarly to the second embodiment, and merges transported fluids at a merging section 29a which joints flow paths 29, 29 communicating with the downstream side of pressure absorbing sections 27. In the present third embodiment, instead of the narrow section 28 described in the first and second embodiment, filtering sections 25 (each including a first filtering section 25a and second filtering section 25b) are provided. Herein, the downstream side of the fluid reservoirs 24 and the upstream side of the pressure absorbing sections 27 have a circular shape in a top view.

The effects of the present third embodiment are the same as those in the first embodiment, and the effects by the parallel connection of the two micropumps 31 are the same as in the second embodiment.

(Schematic Structure of a Fourth Embodiment, Refer to FIG. 6)

A fluid transportation system 10D in a fourth embodiment has, as shown in FIG. 6, the same basic structure as in the first embodiment, and further includes a flow path 41 on the upstream side of the filtering section 25 and a flow path 42 on the downstream side of the narrow section 28.

(Schematic Structure of a Fifth Embodiment, Refer to FIG. 7)

A fluid transportation system 10E in a fifth embodiment has, as shown in FIG. 7, is provided with a filtering section 25 (including a first filtering section 25a and second filtering section 25b) in the pressure absorbing section 27 instead of a narrow flow path 28, other structures being the same as in the first embodiment).

The effects of the present fifth embodiment are the same as in the first embodiment, and further it is possible to prevent foreign matters from mixing into the chamber 21 by the filtering section 25. Particularly, it is effective when an actuator capable of transporting fluid in both directions, with an example of a micropump 31.

(Schematic Structure of a Sixth Embodiment, Refer to FIG. 8)

A fluid transportation system 10F in a sixth embodiment is, as shown in FIG. 8, the structure on the upstream side is the same as in the first embodiment, while a throttle flow path 23, flow path 26, and outlet 13 are provided on the downstream side of the micropump 31, wherein the pressure absorbing section 27, shown in the first embodiment, is omitted.

In the sixth embodiment, the flow path 26 on the downstream side is sufficiently long, and reaches the outlet 13 (atmospheric air opening) without communicating with another micropump. Such a structure is used for a purpose, for example, of exhausting waste liquid remaining on the upstream side than the inlet 12 to a separated place. With regard to the downstream side, since the system is affected little by a pressure vibration, it is necessary to provide a pressure absorbing section (fluid reservoir 24) and filtering section 25 only on the upstream side. Thus, a small sized fluid transportation system 10F can be achieved with a simple structure.

(Schematic Structure of a Seventh Embodiment, Refer to FIG. 9)

A fluid transportation system 10G in a seventh embodiment has, as shown in FIG. 9, the same structure on the upstream side of a micropump 31 as in the first embodiment, and is provided with a throttle flow path 23, flow path 26, pressure absorbing section 27, and outlet 13 on the downstream side of the micropump 31, wherein the narrow section 28, described in the first embodiment, is omitted.

In the present seventh embodiment, a filtering section 25 is provided only on the upstream side which is affected much by a pressure vibration, and the narrow section 28 on the downstream side is omitted for a smaller size.

(Schematic Structure of an Eighth Embodiment, Refer to FIG. 10)

In a fluid transportation system 10H in an eight embodiment, as shown in FIG. 10, the flow path described in the first embodiment is omitted, and a narrow section 28 communicates with an outlet 13. Other structures are the same as in the first embodiment. It is also possible to achieve a small size by omitting a flow path 26.

(Schematic Structure of a Ninth Embodiment, Refer to FIG. 11)

In a fluid transportation system 10I in a ninth embodiment is structured, as shown in FIG. 11, the upstream side of a micropump 31 is constructed, same as the downstream side, with a pressure absorbing section 27 and a narrow section 28, wherein an inlet 12 is provided on the upstream side of the narrow section 28. In the case of a transportation system into which foreign matters hardly be mixed, for example, in the case of a transportation system in a sealed state isolated from outside, since trapping of foreign matters by a filtering section 25 is unnecessary, it is not necessary to provide a filtering section 25 on the upstream side of the micropump 31. As a filtering section 25 is omitted, the manufacturing process of a fluid transportation system 10I is simplified.

(Absorption Vibration Pressure)

Now, absorption of the vibration pressure due to pulsation of the micropump 31 will be described in detail. In order to absorb the vibration pressure, it is necessary to take the acoustic capacitance into account. The acoustic capacitance corresponds to the compression (or deformation) volume for a unit pressure. With regard to the acoustic capacitances of the chamber 21, fluid reservoir 24, and pressure absorbing section 27, deformation of the glass substrate 11 can be neglected, and the acoustic capacitances can be calculated by just obtaining the deformed volumes of the membrane portions at the time of applying a unit pressure to inside the chamber 21, fluid reservoir 24, and pressure absorbing section 27 respectively.

With regard to the acoustic capacitances of fluid in the chamber 21, fluid reservoir 24, and pressure absorbing section 27, the acoustic capacitances can be calculated from the decrease in volume at the time of applying a unit pressure to the entire inside fluid. Alternatively, the acoustic capacitances can also be obtained from the density of fluid, the acoustic velocity in the fluid, and the inner volumes of the chamber 21, fluid reservoir 24, and pressure absorbing section 27.

An acoustic capacitance has two components. They are a component of deformation, caused by a pressure, of a part of a housing which stores fluid inside, and a component of compression, caused by a pressure, of the fluid itself inside the housing. The value of an acoustic capacitance in a practical fluid transportation system is to be determined with the sum of these two components. However, as in the case of the first embodiment, if the former component is larger than the latter component by several orders, sometimes, only the former component is practically taken into account.

In the fluid transportation system, the acoustic capacitances of the fluid reservoir 24 (concretely, region Y) and the pressure absorbing section 27 are preferably larger than that of the chamber 21. It is possible to effectively absorb the vibration pressure in the chamber caused by driving the micropump 31 (piezoelectric element 30).

In order to make the acoustic capacitances of the fluid reservoir 24 and pressure absorbing section 27, the reservoir 24 and pressure absorbing section 27 are preferably formed of a membrane section. Concretely, in the first embodiment, the reservoir 24 and pressure absorbing section 27 are formed of a membrane section which is obtained by etching a thin plate (for example, a membrane with a thickness of approximately 30 μm obtained by etching a thin plate with a thickness of 200 μm by about 170 μm) to have a width larger than that of the chamber 21.

Taking an example of dimensions, region Y in the fluid reservoir 24 and the pressure absorbing section 27 have approximately the same dimension, that is, a width of 1.5 mm and a length of 3.0 mm. The both acoustic capacitances of these are approximately 90×10⁻¹⁸ (m³/Pa).

Taking an example of the dimensions of the filtering section 25, the first filtering section 25a is constructed with 10 micro grooves with an opening width of 40 μm, length of 200 μm, and depth of 25 μm. The second filtering section 25b is constructed with 17 micro grooves with an opening width of 20 μm, length of 60 μm, and depth of 25 μm.

The filtering section 25 has a role to prevent entrance of foreign matters into the chamber 21, and has a function to damp a pressure vibration because of a high flow path resistance value R as well as the narrow section 28. A liquid with a viscosity of 1 cp (corresponding to water at 20° C.) has a resistance value R of approximately 2.0×10¹² (N·s/m⁵).

If the filtering section 25 is arranged to have these functions, just in case that a part of the filtering section 25 is clogged with foreign matters, fluid can flow to the rest of the filtering section, which gives an advantage of a structure with a higher security compared to the case where only a single narrow section 28 is disposed.

Taking an example of the dimensions of the narrow section 28, the opening width is 40 μm, length is 0.50 mm, and depth is 170 μm. A liquid with a viscosity of 1 cp has a resistance value R of approximately 1.2×10¹² (N·s/m⁵).

In such a manner, by making the opening cross-sectional area of the narrow section 28 sufficiently smaller (not greater than a half, and preferably not greater than 1/10) than the cross-sectional area of the flow path before and after the narrow section 28, a required flow path resistance value R can be secured even if the flow path is comparatively short.

Further, by making the narrow section 28 sufficiently narrow, substantially no pressure distribution and no velocity distribution of the fluid inside the narrow section 28 are generated. Therefore, stable pressure damping characteristics can always be obtained, independently from the driving voltage wave form, frequency, or disturbance conditions.

Herein, the filtering section 25 or narrow section 28 is preferably disposed adjacent to the pressure absorbing section (including the fluid reservoir 24 and pressure absorbing section 27). Thus, it can be avoided that the characteristics become unstable in such a way that a vibration wave having not been absorbed by the pressure absorbing section interferes between the pressure absorbing section and the filtering section 25 or between the pressure absorbing section and the narrow section 28.

On the other hand, on the upstream side of the chamber 21, it is preferable to provide a filtering section 25. Thus, when a foreign matter comes flowing from the upstream side, it is prevented that the foreign matter is mixed into the chamber 21.

On the downstream side of the chamber 21, it is preferable to provide not a filtering section 25 but a narrow section 28. Thus, just in the case that a foreign matter is mixed into the chamber 21, the foreign matter is expected to flow out to the downstream side. In this case, the cross-sectional area of the narrow section 28 is preferably larger than the cross-sectional area of a stitch of the filtering section 25.

Further, in the fluid transportation system, when R represents the flow path resistance value of the narrow section 28 or the filtering section 25, and C represents the acoustic capacitance value of the fluid reservoir 24 or the pressure absorbing section 27, the value obtained by multiplication between R and C is preferably not smaller than a driving cycle period value of the micropump 31 (piezoelectric element 30). Thus, after the vibration of the fluid reservoir 24 or the pressure absorbing section 27 ceases, a subsequent vibration is started by the piezoelectric element, and thereby fluid is smoothly transported. Herein, if the value obtained by multiplication between R and C is too large, the response after a start of driving the micropump 31 becomes low, and it is too long before a desired flow velocity is attained, which is not preferable. Accordingly, the value of obtained by multiplication between R and C is preferably set to be not longer than a preferable response time in a practical embodiment.

In a case of a structure, for example, as in the second embodiment shown in FIG. 4, that has two micropumps 31, 31 in the same shape and disposed in parallel and merges liquids having been respectively transported at the merging section 29a, if the timing when the liquids fed out from the respective micropumps 31, 31 reach the merging section 29a deviates, problems occurs, for example, gas bubbles collect in the merging section 29a.

Accordingly, deviation of the reach timing of the liquids transported from the micro pumps 31, 31 is permitted only for a time not longer than the time for transportation of liquid from one micropump 31 for the amount to fill the inner volume of the merging section 29a (the region shown by dashed lines). In the case of the second embodiment, since the merging section 29a is 200 μm wide and the flow rate by the micropumps 31, 31 is approximately 400 nL/sec, deviation of the reach timing is permitted only for about 20 milli sec. Therefore, the upper limit value obtained by multiplication between R and C in the second embodiment is needed to be set to about 20 milli sec. Further, taking into account that it is after a time which is about three times the time constant when the transportation speed becomes stable, the upper limit value obtained by multiplication between R and C is preferably about 6 milli sec which is approximately ⅓ of the above described value.

Herein, the flow path resistance value R corresponds to the coefficient of pressure loss at the time when fluid flows in the flow path, and can be obtained by R=ΔP/Q, Q representing the flow rate per unit time and ΔP representing the pressure loss.

Setting the resistance value R too large is not preferable because the flow of liquid transported by the micropump 31 is inhibited and the flow velocity is lowered. Accordingly, the resistance value R of the filtering section 25 or the narrow section 28 is preferably smaller than the effective inner flow path resistance value of the micropump 31.

The micropump 31 in the first embodiment achieves preferable pump characteristics (The flow rate and generation pressure are high.) with the driving cycle period in the vicinity of 90 μsec. On the other hand, the value obtained by multiplication between R and C at the portion of the fluid reservoir 24 and the adjacent filtering section 25 is 180 μsec, and the value obtained by multiplication between R and C at the portion of the pressure absorbing section 27 and the adjacent narrow section 28 is 108 μsec. Since these values obtained by multiplication between R and C are greater than the driving cycle period (90 μsec) of the micropump 31, transportation of liquid becomes smooth by the above described effect, and characteristics variation becomes smaller.

As an example, as the second embodiment shown in FIG. 4, with a structure in which a pair of transportation systems, in the same shape, including the respective micropumps 31, 31 were disposed in parallel and liquids having been respectively transported were merged in a merging section 29a, the respective liquid feeding amounts were measured. The two liquids were colored with respective dyes; the flow rate ratio between the two liquids was determined by the ratio between the widths of the laminar flows of the two liquids on the downstream side of the merging section 29a; and the total flow rate of the two liquids at a velocity at which the meniscus on the downstream side of the merging section 29a moves was measured. In the case where no narrow section 28 was provided, the variation in the liquid feeding amounts of the two liquids was approximately ±20%, wherein the liquid feeding ratio varied each time of liquid feeding. However, by providing narrow sections 28, the variation in the liquid feeding amounts of the two liquids was lowered approximately to +5% or lower, and the results stopped varying each time of liquid feeding.

On the other hand, when the length of the narrow sections 28 were changed from 0.50 mm to 0.35 mm, the variation in the liquid feeding amounts of the two liquids increased approximately to ±10%. Herein, the resistance value R of the narrow sections 28 was approximately 0.8×10¹² (N·s/m⁵) and the value obtained by multiplication between R and C was 72 μsec, which is a smaller value than the driving cycle period (90 μsec) of the micropumps 31. From this point, it is understood that the effect of the narrow sections 28 is little, and the effect becomes significant when the value obtained by multiplication between R and C becomes the driving cycle period or larger.

As another example, as the third embodiment shown in FIG. 5, with a structure in which a pair of transportation systems, in the same shape, including the respective micropumps 31, 31 were disposed in parallel, liquids having been respectively transported were merged in a merging section 29a, and filtering sections 25 were provided at the pressure absorbing sections 27, the respective liquid feeding amounts were measured in the same manner as described above.

The micropumps 31, 31 used here had a driving cycle period of 250 μsec. The two filtering sections 25 on the downstream side have the same shape and dimensions. The first filtering sections 25a have a structure having 9 micro grooves with an opening width of 130 μm, length of 450 μm, and depth of 80 μm. The second filtering sections 25b have a structure having 20 microgrooves with an opening width of 60 μm, length of 180 μm, and depth of 80 μm. A liquid with a viscosity of 1.5 cp has a resistance value R of approximately 0.18×10¹² (N·s/m⁵). The two pressure absorbing sections 27 has the same shape and dimensions, wherein the upstream side is in a substantially circular shape with a diameter of 5.6 mm, and the values of the acoustic capacitances C are both approximately 1700×10⁻¹⁸ (m³/Pa). A test of feeding liquid by merging the two liquids in these conditions was performed, resulting in the variation in the liquid feeding amounts of approximately ±3% or lower.

On the other hand, as a result of comparison tests for a case where the length of the respective filtering sections 25 was shortened to be approximately 0.7 times the above described value, and for a case where filtering sections 25 were not provided, variation in the respective liquid feeding amounts was approximately ±10% in the former case, and ±20% in the latter case. With these tests also, it proved that the effects become significant when the value obtained by multiplication between R and C is larger or equal to the driving frequency of the micropumps 31.

Now, the cause of the significant effects obtained with the value obtained by multiplication between R and C larger than the value of the driving frequency of the micropumps 31 will be described. If a driving voltage in a pulse form is applied to the micropumps 31 by adding one pulse to generate a differential pressure, the value of the generated differential pressure is represented by P₀, and the value of the differential pressure after an elapsed time of t from the generation of the differential pressure is represented by P(t), then the relation is P(t)=P₀·exp(−t/R·C). This drop in the differential pressure is caused by a flow of liquid in a narrow section 28 or a filtering section 25. When Q(t) represents the flow rate of a liquid flowing in the narrow section 28 or filtering section 25 after the elapsed time of t, Q(t) is expressed by Q(t)=P₀·exp(−t/R·C)/R.

As understood from the above expression, even if a momentary differential pressure is generated by a driving voltage in a pulse form, a time delay is caused on the flow of the liquid in a narrow section 28 or filtering section 25, and the liquid does not flow until a certain time elapses. In other words, even if the differential pressure P generated by driving the micropump 31 changes suddenly, in respect of the flow rate Q of the liquid flowing in the narrow section 28 or filtering section 25, the liquid tends to flow gradually, taking an elapse time t, at shortest, exceeding the value obtained by multiplication between R and C.

Accordingly, since the change in the flow rate Q cannot sufficiently follow a phenomenon that sequentially changes in a shorter time than the value obtained by multiplication between R and C, as a result, a fluid vibration with a period shorter than the value obtained by multiplication between R and C is damped without a leakage to outside the narrow section 28 or filtering section 25, which realizes stable liquid feeding with a steady flow almost free from superimposed pulsating vibrations.

Further, the fluid reservoir 24 or the pressure absorbing section 27 preferably not only have a function to absorb or reduce vibration pressure, but also have a characteristic to reflect a compressional pressure wave of a high frequency wave. By reflecting the high frequency component to the side of chamber 21, the high frequency component is inhibited from being transmitted to either the inlet side or outlet side, which allows the flow of the fluid to be smooth and free from pulsation.

(Other Embodiments)

A fluid transportation system in accordance with the invention is not limited to the above described embodiment, and can be variously changed without departing from the spirit of the invention.

For example, a fluid transportation system may be constructed with a glass substrate 11 formed with structures including the chamber 21, throttle flow paths 22 and 23, fluid reservoir 24, and pressure absorbing section 27. The flow path 26 may be a plurality of flow paths disposed in parallel between the throttle flow path 23 and pressure absorbing section 27.

Still further, active valves may be provided facing the throttle flow paths disposed at the both ends of the chamber 21. For this kind of an active valve, a piezoelectric element is provided at a membrane portion facing a throttle flow path and driven so as to transport fluid in one direction by forcefully opening and closing the throttle flow path. Even when active valves are provided, a time lag with respect to increasing and decreasing the pressure occurs between the active valves and the chamber 21, which transmits the vibration pressure toward outside the chamber 21. Therefore, as in the present embodiment, it is advantageous to provide a fluid reservoir 24 and pressure absorbing section 27, and provide a filtering section 25 and narrow section 28 so as to prevent the vibration pressure from leaking outside.

Either a filtering section 25 or narrow section 28 is preferably disposed at both the upstream side and downstream side of a micropump 31 so that vibration transmission is completely isolated from outside. Herein, any one of a combination of filtering sections 25, a combination of a filtering section 25 and a narrow section 28, and a combination of narrow sections 28 can be applied. In a case where either the upstream side or downstream side is affected little by vibration, and particularly in such a case where the flow path 26 communicates with an outlet 13 (atmospheric air opening) without fluid-communication with another micropump, as in the sixth embodiment (refer to FIG. 8), the narrow section 28 or filtering section 25 may be omitted on the downstream side of the micropump 31. Likewise, the pressure absorbing section 27 or fluid reservoir 24 is not always needed to be disposed on both the upstream side and downstream side of the micro pump 31, and may be disposed on only one of the upstream side and downstream side.

Claims

1. A fluid transportation system, comprising: a micropump provided with a chamber and a diaphragm driven by an actuator; fluid communication sections communicating with both ends of the chamber of the micropump; a pressure absorbing section that is provided at least one of the fluid communication sections so as to absorb or reduce a fluid vibration pressure; and a narrow section that is provided at a position further than the pressure absorbing section from the chamber so as to narrow a flow path cross-section, wherein, when R represents a flow path resistance value of the narrow section and C represents an acoustic capacitance value of the pressure absorbing section, a value obtained by multiplication between R and C is not smaller than a driving cycle period value of the micropump.

2. The fluid transportation system of claim 1, wherein the narrow section is disposed on the downstream side, along a transportation direction, of the chamber.

3. The fluid transportation system of claim 1, wherein the micropump transports fluid by repeatedly deforming the diaphragm; and an acoustic capacitance of the pressure absorbing section has a larger value than an acoustic capacitance of the chamber.

4. The fluid transportation system of claim 1, wherein at least one wall surface of the pressure absorbing section comprises a thin plate deformable by a fluid pressure; and a width of the thin plate is larger than a width of the chamber.

5. The fluid transportation system of claim 1, wherein a flow path resistance value of the narrow section is smaller than an effective inner flow path resistance value of the micropump.

6. The fluid transportation system of claim 1, comprising a first throttle flow path and a second throttle flow path at the both ends of the chamber, of which respective flow path resistances change corresponding to a differential pressure, wherein, a changing rate of the flow path resistance of the first throttle flow path is larger than that of the second throttle flow path; the actuator transports fluid from the first throttle flow path toward the second throttle flow path, by repeatedly increasing and decreasing a pressure of fluid in the chamber in a first pattern where a time of increasing the pressure is shorter than a time of decreasing the pressure; and the actuator transports fluid from the second throttle flow path toward the first throttle flow path, by repeatedly increasing and decreasing the pressure of fluid in the chamber in a second pattern where the time of increasing the pressure is longer than the time of decreasing the pressure.

7. A fluid transportation system, comprising: a micropump provided with a chamber and a diaphragm driven by an actuator; fluid communication sections communicating with both ends of the chamber of the micropump; a pressure absorbing section that is provided at least one of the fluid communication sections so as to absorb or reduce a fluid vibration pressure; and a filtering section having a plurality of micro flow paths, the filtering section being provided at a position further than the pressure absorbing section from the chamber, wherein, when R represents a flow path resistance value of the filtering section and C represents an acoustic capacitance value of the pressure absorbing section, a value obtained by multiplication between R and C is not smaller than a driving cycle period value of the micropump.

8. The fluid transportation system of claim 7, wherein the filtering section is disposed on the upstream side, along a transportation direction, of the chamber.

9. The fluid transportation system of claim 7, wherein the micropump transports fluid by repeatedly deforming the diaphragm; and an acoustic capacitance of the pressure absorbing section has a larger value than an acoustic capacitance of the chamber.

10. The fluid transportation system of claim 7, wherein at least one wall surface of the pressure absorbing section comprises a thin plate deformable by a fluid pressure; and a width of the thin plate is larger than a width of the chamber.

11. The fluid transportation system of claim 7, wherein a flow path resistance value of the filtering section is smaller than an effective inner flow path resistance value of the micropump.

12. The fluid transportation system of claim 7, comprising a first throttle flow path and a second throttle flow path at the both ends of the chamber, of which respective flow path resistances change corresponding to a differential pressure, wherein, a changing rate of the flow path resistance of the first throttle flow path is larger than that of the second throttle flow path; the actuator transports fluid from the first throttle flow path toward the second throttle flow path, by repeatedly increasing and decreasing a pressure of fluid in the chamber in a first pattern where a time of increasing the pressure is shorter than a time of decreasing the pressure; and the actuator transports fluid from the second throttle flow path toward the first throttle flow path, by repeatedly increasing and decreasing the pressure of fluid in the chamber in a second pattern where the time of increasing the pressure is longer than the time of decreasing the pressure.

13. A fluid transportation system, comprising: a micropump provided with a chamber and a diaphragm driven by an actuator; fluid communication sections communicating with both ends of the chamber of the micropump; a first pressure absorbing section that is provided at one of the fluid communication sections so as to absorb or reduce a fluid vibration pressure; a narrow section that is provided at a position further than the first pressure absorbing section from the chamber so as to narrow a flow path cross-section, a second pressure absorbing section that is provided at another one of the fluid communication sections so as to absorb or reduce a fluid vibration pressure; a filtering section having a plurality of micro flow paths, the filtering section being provided at a position further than the second pressure absorbing section from the chamber, wherein, when R represents a flow path resistance value of the narrow section and C represents an acoustic capacitance value of the first pressure absorbing section, a value obtained by multiplication between R and C is not smaller than a driving cycle period value of the micropump; and when R′ represents a flow path resistance value of the filtering section and C′ represents an acoustic capacitance value of the second pressure absorbing section, a value obtained by multiplication between R′ and C′ is not smaller than the driving cycle period value of the micropump.

14. The fluid transportation system of claim 13, wherein the narrow section is disposed on the downstream side, along a transportation direction, of the chamber; and the filtering section is disposed on the upstream side, along the transportation direction, of the chamber.

15. The fluid transportation system of claim 13, wherein the micropump transports fluid by repeatedly deforming the diaphragm; and acoustic capacitances of the first and second pressure absorbing sections have larger values than an acoustic capacitance of the chamber.

16. The fluid transportation system of claim 13, wherein at least one wall surface of each of the first and second pressure absorbing sections comprises a thin plate deformable by a fluid pressure; and a width of each thin plate is larger than a width of the chamber.

17. The fluid transportation system of claim 13, wherein flow path resistance values of the narrow section and the filtering section are smaller than an effective inner flow path resistance value of the micropump.

18. The fluid transportation system of claim 13, comprising a first throttle flow path and a second throttle flow path at the both ends of the chamber, of which respective flow path resistances change corresponding to a differential pressure, wherein, a changing rate of the flow path resistance of the first throttle flow path is larger than that of the second throttle flow path; the actuator transports fluid from the first throttle flow path toward the second throttle flow path, by repeatedly increasing and decreasing a pressure of fluid in the chamber in a first pattern where a time of increasing the pressure is shorter than a time of the pressure; and the actuator transports fluid from the second throttle flow path toward the first throttle flow path, by repeatedly increasing and decreasing the pressure of fluid in the chamber in a second pattern where the time of increasing the pressure is longer than the time of decreasing the pressure.