JP2004169706A - Fluid transport system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid transport system capable of preventing deterioration of characteristics. <P>SOLUTION: In this fluid transport system, chambers 20s and 20t of a plurality of micropumps are serially disposed. In each micropump, the chamber of the micropump has first opening parts 24s, 22t, and 24x, and second opening parts 22s, 22t, and 22x. When pressure in the chambers 20s and 20t is increased, passage resistance change ratio of the first opening parts 24s and 24x is larger than passage resistance change ratio of the second opening parts 22s and 22x. Between the micropumps adjoining each other, they are communicated with each other by the first opening part 24x that is common, with the second opening parts 22s and 22t positioned on the opposite side respectively. Otherwise, they are communicated with each other by the second opening part 22x that is common, with the first opening parts 24s and 24t positioned on the opposite side respectively. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a fluid transport system, and more particularly, to a fluid transport system that sends a very small amount of fluid with high precision using a micropump.

  Conventionally, various micro pumps for feeding a very small amount of liquid have been proposed. These micropumps are incorporated in a fluid transport system that performs chemical analysis or the like using a very small amount of liquid.

For example, Japanese Patent Laying-Open No. 2001-322099 (Patent Document 1) discloses a micropump in which a chamber is connected to an external flow path via an opening. Also, two micropumps are arranged in parallel in "AN IMPROVED VALVE-LESS PUMP FABRICATED USING DEEP REACTIVE ION ETCHING" (Anders Olsson et al., MEMS '96 (IEEE) pp. 479-484) and the phase difference is set. It is disclosed that by driving with, the influence of each other is canceled.
JP 2001-322099 A

  By the way, depending on the configuration of the fluid transport system, the characteristics may be deteriorated due to the influence of the external flow path. For example, depending on the length and shape of the flow path, the pressure compression wave generated by the vibration accompanying the driving of the micropump is reflected and interferes with the original wave, so that desired characteristics may not be obtained.

  Therefore, a technical problem to be solved by the present invention is to provide a fluid transport system capable of preventing deterioration of characteristics. Another object of the present invention is to provide a new and useful fluid transport system in which the pressure generated by the system is increased and the characteristics are improved by utilizing the pressure waves of a plurality of micropumps.

  The present invention provides a fluid transport system having the following configuration in order to solve the above technical problems.

According to a first aspect of the present invention, in a fluid transport system in which a plurality of micropump chambers are arranged in series,
Each micropump is provided with a first opening and a second opening in a chamber of the micropump, and when the pressure in the chamber is raised or lowered, the change rate of the flow path resistance of the first opening is the same as the above. It is configured to be larger than the change rate of the flow path resistance of the second opening,
Between adjacent micropumps, the second openings are located on opposite sides of the first opening communicating with each other, or the first openings are located on the opposite sides of each other communicating with the second opening common. A fluid transport system in which the part is located.

  In the above configuration, the fluid transport system is configured such that the change rate of the flow path resistance of one opening is smaller than the change rate of the flow path resistance of the other opening, so that the pressure in the chamber increases and decreases. Fluid is transported using the fact that the ratio of the fluid passing through each opening is different.

  In the above configuration, the plurality of micropumps communicate with each other at a common first opening, and the second openings are located on opposite sides of each of the micropumps. If the fluid transport system is configured so that the openings are located, it is possible to prevent interference between the micropumps, and to improve the characteristics by utilizing the pressure waves of each other, so that stable and high characteristics can be achieved. Is obtained.

  According to a second aspect of the present invention, there is provided the fluid transport system according to the first aspect, wherein chambers of two adjacent micropumps are driven with different driving waveforms or with a phase difference.

  In the above configuration, the adjacent chambers are driven with different drive waveforms or with a phase difference, so that pressure compression waves generated by driving the respective micropumps appropriately interfere with each other, so that the liquid sending characteristics are improved. It can be used positively for improvement.

  According to the third aspect of the present invention, with respect to two adjacent micropump chambers, the first micropump chamber is inverted with the first drive waveform and the second micropump chamber is inverted with the first drive waveform. The fluid transport system according to the first aspect, wherein the fluid transport system is driven by each of the second drive waveforms.

  In the above configuration, the adjacent chambers are driven by different driving waveforms inverted from each other, so that the pressure compression waves generated by driving the respective micro pumps are appropriately interfered with each other, thereby positively improving the liquid sending characteristics. It is possible to use it.

  According to a fourth aspect of the present invention, the first opening and the second opening each have a uniform cross-sectional shape, and the length of the first opening is longer than the length of the second opening. A fluid transport system according to the first aspect, which is also short.

  According to a fifth aspect of the present invention, there is provided the fluid transport according to the first aspect, wherein a flow path is connected to the outermost two micropump chambers of the plurality of micropumps via the openings. Provide system.

  According to a sixth aspect of the present invention, there is provided the fluid according to the first aspect, wherein the pressure absorbing portions are connected to the chambers of the two outermost micropumps through the openings, respectively. Provide a transportation system.

  Hereinafter, examples will be described with reference to FIGS. 1 to 19 as embodiments of the present invention. In the drawings, the same reference numerals are used for the same components.

  First, a fluid transport system according to a first embodiment will be described with reference to FIGS. 1 to 5 and FIGS.

  FIG. 1 is a sectional view of a micropump 10 used in a fluid transport system. FIG. 2 is a plan view of the fluid transportation system.

  In the fluid transport system, the substrate 12 and the thin plate 14 are joined. The substrate 12 is formed with a dent that becomes the chamber 20 and the fluid reservoir 30, and a slit that becomes the first and second openings 22, 24 and the flow path 34, on which the thin plate 14 that becomes the diaphragm is joined. Is done. The thin plate 14 is formed with a through hole 32 for supplying a liquid, and communicates with the fluid reservoir 30. On the upper surface of the thin plate 14, a piezoelectric element 16 is fixed to a portion facing the chamber 20. A voltage is applied to the piezoelectric element 16 from the drive circuit 18 so as to bend and deform.

  The chamber 20 is connected to the fluid reservoir 30 via the first opening 22 and to the flow path 34 via the second opening 24. The fluid reservoir 30 is wider and has a larger volume than the chamber 20 and the flow path 34. The first opening 22 is formed such that the rate at which the flow path resistance changes in accordance with the differential pressure is larger than that of the second opening 24.

  Note that the first opening 22 and the second opening 24 do not need to be formed of one narrow channel, respectively. For example, as in the micropump 10a of the modified example of FIG. May be constituted by the flow paths 24a and 24b. Similarly, the first opening may be constituted by a plurality of flow paths.

  The micropump 10 increases or decreases the volume of the chamber 20 and pressurizes the fluid in the chamber 20 by utilizing the thin plate 14 and the piezoelectric element 16 that bend in a unimorph mode. At this time, the fluid is transported using the fact that the rate of change in the flow path resistance between the first opening 22 and the second opening 24 is different between when the pressure is increased and when the pressure is decreased.

  That is, the fluid in the chamber 20 is pushed out through the first and second openings 22 and 24 due to the decrease in the volume of the chamber 20. When the volume of the chamber 20 returns to the original state, the fluid is sucked into the chamber 20 through the first and second openings 22 and 24. By repeating this, the fluid can be transported in a desired direction as described below.

The amount of fluid flowing out of the chamber 20 through the first and second openings 22 and 24 is V ₁₁ and V ₂₁ , and the amount of fluid flowing into the chamber 20 through the first and second openings 22 and 24, respectively. Let V ₁₂ and V ₂₂ be the inflows of
V ₁₁ + V ₂₁ = V ₁₂ + V ₂₂ (1)
It becomes.

  Here, as described above, the first opening 22 is formed such that the rate of change in the flow path resistance according to the differential pressure is larger than that of the second opening 24.

Therefore, for example, when the differential pressure is relatively increased by rapidly reducing the volume of the chamber 20, and the differential pressure is relatively decreased by gradually returning the volume of the chamber 20,
V ₁₁ <V ₁₂ (2)
It becomes.
From equations (1) and (2),
V ₂₁ > V ₂₂ (3)
It becomes.
That is, as can be seen from Equations (2) and (3), as a whole, fluid is transported in the positive direction in FIG.

  Conversely, when the volume of the chamber 20 is gradually reduced to make the differential pressure relatively small, and when the volume of the chamber 20 is rapidly returned to make the differential pressure relatively large, the fluid is transported in the negative direction in FIG. Is done.

  As one specific example, a photosensitive glass having a thickness of 500 μm is used for the substrate 12, the depressions of the chamber 20 and the fluid reservoir 30, the first and second openings 22, 24, and so on until the depth reaches 100 μm. The slit of the channel 34 is formed by etching. The first opening 22 has a depth of 100 μm, a width of 25 μm, and a length of 20 μm. The second opening 24 has a depth of 100 μm, a width of 25 μm, and a length of 150 μm. The main part of the fluid reservoir 30 is a rectangular parallelepiped, having a depth of 100 μm, a width of 1.2 mm, and a length of 4.0 mm. The fluid reservoir 30 is formed such that the flow path expands from the first opening 22 at an angle of 45 degrees left and right. The channel 34 has a depth of 100 μm, a width of 150 μm, and a length of about 15 mm. The thin plate 14 is a glass plate having a thickness of 50 μm, and a piezoelectric element 16 of PZT (lead zirconate titanate) ceramics having a thickness of 50 μm is adhered to the upper surface thereof with an adhesive. When a voltage of 30 V was applied to the piezoelectric element 16, the displacement amount (maximum depression amount) was 80 nm, and a pressure of 0.4 MPa was generated in the water filled in the chamber 20.

  Next, a driving voltage waveform applied to the piezoelectric element 16 of the micro pump 10 will be described.

  The micropump 10 has a displacement speed of vibration of an actuator unit 15 (a portion of the thin plate 14 facing the chamber 20 and the piezoelectric element 16 fixed to the portion, as shown in FIG. 1) for increasing or decreasing the volume of the chamber 20. However, it is necessary to drive the chamber 20 differently when increasing the volume and when decreasing the volume.

  Regarding the vibration of the actuator section 15, the vibration mode of vibration (hereinafter, referred to as “natural vibration”) in which the vibration of the actuator section 15 and the flow of the fluid resonate is a major factor that determines the vibration behavior. When a voltage is applied to the piezoelectric element 16 to cause the actuator section 15 to vibrate, the driving can be efficiently performed by focusing on the period of the natural vibration and adding a drive voltage waveform having a desired vibration behavior.

The period of the natural vibration here can be represented by using the following four acoustic element components.
(A) Acoustic capacitance of the actuator unit 15: Cp
(B) Acoustic capacitance of liquid in chamber 20: Ca
(C) Inertance of the first opening 22: Mi
(D) Inertance of the second opening 24: Mo

Here, the “acoustic capacitance” corresponds to a compression (or deformation) volume per unit pressure. Regarding (a), the deformation of the substrate 12 can be ignored, and can be calculated by obtaining only the deformation volume of the actuator section 15 when a unit pressure is applied to the inner surface of the chamber 20. (B) can be calculated from the amount of volume decrease when a unit pressure is applied to the entire liquid in the chamber 20. Alternatively, assuming that the density of the liquid is ρ, the velocity of sound in the liquid is v, and the volume of the chamber 20 is W,
Ca = W / (ρv ² ) (4)
Is required.
However, if the substrate 12 is an elastic body such as a resin, it should be added including the deformation when calculating (a).

“Inertance” corresponds to an inertia coefficient when the liquid in the flow path is to be extruded at a unit pressure. Inertance: M is obtained from pressure: acceleration with respect to P: α,
M = P / α (5)
Can be calculated.
Alternatively, assuming that the mass of the liquid in the flow path is m and the cross-sectional area of the flow path is S,
M = m / S ² (6)
Can be calculated. For a flow path having a non-uniform flow path cross-sectional area, this may be integrated by a distance in the longitudinal direction.

  In the case where the first opening 22 or the second opening 24 is constituted by a plurality of flow paths, the inertance in which the flow paths are combined as a parallel flow path should be used for this calculation. . For example, when there are two flow paths 24a and 24b corresponding to the second opening as shown in FIG. 3, since the flow paths 24a and 24b are in a parallel relationship, the reciprocal of the inertance of each flow path 24a and 24b alone is The reciprocal of the sum is the inertance of the entire second opening.

The period of the natural vibration: T is calculated by using the acoustic capacitances Cp and Ca and the inertances Mi and Mo.
T = 2π ((Cp + Ca) · Mo · Mi / (Mo + Mi)) (7)
It is expressed as

  However, the value of the cycle T of the natural vibration of the vibration mode may be shifted due to the influence of the flow path system connected to the micropump 10 or the influence of the mass component of the actuator 16. The actual value may shift in the range of about 0.5 to 2 times the value calculated by the above equation (8).

  In addition, there are natural vibrations in a general sense due to a mode in which the actuator section 15 vibrates alone, and a vibration mode due to an interaction between the micropump 10 and an external flow path system connected to the micropump 10. Here, the drive voltage waveform is determined by focusing only on the vibration in which the vibration of the actuator section 15 and the flow of the fluid resonate.

  Next, FIGS. 17 to 19 show examples of drive voltage waveforms for causing the actuator section 15 to have a desired vibration behavior. The following is merely an example, and any waveform other than these may be used as long as the vibration speed differs between when the volume of the chamber 20 increases and when the volume decreases. For example, one cycle of increasing and decreasing the volume of the chamber 20 may be realized by a combination of a plurality of drive voltage waveforms. Further, the case where the piezoelectric element 16 is used to deform the chamber 20 is illustrated, but other driving means (for example, an electrostatic actuator, a magnetostrictive element, a shape memory alloy, or the like) may be used.

17, rise time: _{T R} and fall time: shows _{T F} is different driving voltage waveforms 91a, and 91b, the waveform 90a of the displacement behavior of the piezoelectric element 16 (the amount of deflection) corresponding thereto, the 90b. Driving voltage waveforms 91a, 91b is at the time of forward driving _T R _{<T F,} at the time of reverse driving _T R> is _{T F.}

Rise time: T _R and fall time: at least one of T _F is the natural vibration cycle: it is preferable that the T or more. When the voltage applied to the piezoelectric element 16 changes over a longer period than the period of the natural vibration, the vibration behavior of the actuator unit 15 is less affected by the natural vibration, and thus easily follows the voltage waveform. This is because the vibration behavior of the unit 15 can be easily controlled.

  Although the drive voltage waveforms 91a and 91b are trapezoidal, the upper flat portions 92a and 92b are not necessarily required.

The drive voltage waveforms 95a and 95b of FIG. 18 and the corresponding waveforms 94a and 94b of the displacement behavior of the piezoelectric element 16 are represented by the drive voltage waveforms 95a and 95b according to the time constants τ ₁ and τ ₂ due to the capacitance and electric resistance. Shows a case where is dulled. For example, the time constants τ ₁ and τ ₂ are made different by making the wiring resistance of the switching circuit different between charging and discharging, and the charging time is made by incorporating a rectifying element such as a diode or a non-linear element in the driving circuit or wiring. And the discharge time are made different. Further, if an electrostatic actuator whose capacitance changes with respect to voltage is used, the time constants τ ₁ and τ ₂ change with time, and as a result, such drive voltage waveforms 95 a and 95 b realizable.

FIG. 19 shows drive voltage waveforms 97a and 97b using pulse waves 98a and 98b such as rectangular waves, and waveforms 96a and 96b of the displacement behavior of the piezoelectric element 16. Driving voltage waveforms 97a, 97b of the drive cycle: _{T 2} is the natural vibration period: shifting slightly from T. Drive cycle: the range of T ₂ is the natural vibration period: if much 1/2 to 2 times T, then this method is effective. This driving method utilizes the fact that the length of the rise time and the fall time of the displacement of the piezoelectric element 16 changes when the duty ratio (T ₁ / T ₂ ) of the drive pulses 98a and 98b is changed. By utilizing the fact that the relationship between the rise time and the fall time is reversed at a duty ratio of 50%, bidirectional liquid transfer can be realized.

  The pulse waves 98a, 98b need not be rectangular waves, but may be triangular waves, trapezoidal waves, or the like.

  Next, absorption of pressure by pulsation of the micropump will be described.

  As shown in FIG. 1, the upper wall of the fluid reservoir 30 is also formed of the thin plate 14. Thereby, the pulsation of the fluid pressure ejected from the first opening 22 to the outside of the chamber 20 can be reduced, and stable characteristics can be obtained.

  In order to discuss the pressure absorption characteristics numerically, it is preferable to use the concept of “(acoustic) capacitance: C” = “deformation (compression) volume per unit pressure” as described above. It is considered that the larger this value is, the more the instantaneous pressure change is absorbed by deformation (compression), so that the relaxation pressure absorption is higher. This capacitance should be evaluated by the sum of two components, one related to the compressibility of the liquid (Cw) and the other due to the deformation of the thin plate 14 on the upper wall (Cd).

Here, assuming that the density of the liquid is ρ, the velocity of sound in the liquid (propagation velocity of the plane pressure wave) is v, and the volume is X,
Cw = X / (ρ × c ² ) (8)
Can be represented by

Further, regarding the deformation of the thin plate 14 on the upper wall, a well-known equation of “fixed four-sided fixed pressure distortion of a plate having a constant thickness” can be used. When the plate thickness is t, the width is w, the length is L, and the Young's modulus of the plate is E,
Cd = α × L × w ⁵ / (2 × E × t ³ ) (9)
Can be obtained by Here, α is a dimensionless constant, and approximately α ≒ 0.028 when the ratio of the width to the length is 2 or more.

  Specifically, when the sum of the absolute values of the capacitance: C of the fluid reservoir 30 is larger than that of the chamber 20, the fluid reservoir 30 serves as a pressure absorbing unit. Since the pressure compression wave is generated by the deformation of the wall surface in the chamber 20, the deformation volume under the pressure is less than the volume vibration generated in the chamber 20 in the harder portion (that is, the capacitance is small). This is because it is not suitable as a pressure absorbing portion.

  For the above example, the fluid reservoir 30 is at least three times larger in volume than the chamber 20, so Cw is three times or more. Also, the width of the fluid reservoir 30 portion of the thin plate 14 is 2.4 times wider than that of the chamber 20 and there is nothing to prevent the displacement of the thin plate 14, so that Cd is about 80 times or more. Therefore, since the total capacitance of the fluid reservoir 30 is sufficiently larger than the capacitance of the chamber 20, a sufficient effect can be expected.

  In the present embodiment, the pressure absorbing section (fluid reservoir 30) is provided immediately near the outlet of the first opening 22, but there is an effect even if the position and the number are different. Further, a pressure absorbing section may be provided in the flow path 34 on the second opening 24 side.

  In addition, if it is limited to the micropump 10 of the type shown in FIGS. 1 and 2, it is very significant that the fluid reservoir 30 which is the pressure absorbing portion is located very close to the outlet of the first opening 22. .

  This is because the micropump 10 of this type utilizes the characteristic that the flow resistance of the first opening 22 increases at high pressure due to the turbulence effect generated near the first opening 22. It is necessary to control the value of the differential pressure between the two ends as intended and accurately. Therefore, the pressure immediately near the outlet of the first opening 22 (the fluid reservoir 30) must always be kept sufficiently lower than the internal pressure peak of the chamber 20.

  In other words, this type of micropump 10 is driven by utilizing the fact that the flow path resistance greatly changes depending on the presence or absence of turbulence generated near the first opening 22. Desired turbulence may not be generated due to the influence of pulsation when the micropump 10 is driven. However, if the fluid reservoir 30 is configured to function as a pressure absorbing unit and the influence of pulsation is eliminated, the desired turbulence may be reduced. A flow can be generated, and the characteristics can be improved and stabilized.

  Incidentally, the upper wall of the flow path 34 is also formed of the thin plate 14. Since the width of the flow path 34 is smaller than that of the fluid reservoir 30, the flow path 34 does not exhibit the pressure absorption characteristics as large as the fluid reservoir 30, but has the following effects.

  That is, when the flow path 34 is long, the movement of the fluid in the second opening 24 is directly affected by the inertial force of the liquid in the flow path 34, so that the vibration in response to the driving cycle of the pump 10 It can be expected that this will be prevented beforehand for the problem that it is hindered and normal liquid feeding cannot be performed.

  More specifically, the inertial force of the flow path is proportional to inertance (acoustic inertia coefficient): M. Inertance: M is proportional to the length of the flow path and inversely proportional to the square of the cross-sectional area, as described with respect to equation (7). Therefore, the smaller the cross-sectional area of the flow path, such as a shallow flow path and a narrow width, and the longer the flow path, the more easily the flow path is affected by inertia. However, the inertial force is also proportional to the acceleration. Therefore, a constant pressure is applied to the entire flow path with respect to a uniform flow in the entire flow path, so that the flow path length remains effective. However, for the propagation of high-frequency vibration, a half of the wavelength is used. Only one length of inertia works. This is because, regarding the propagation of the high-frequency vibration, a portion in which the fluid moves forward and a portion in which the fluid moves backward alternately exist by the length of 波長 wavelength within the length of the wavelength.

The wavelength at which the high-frequency vibration propagates through the flow path can be represented by the above-described acoustic capacitance: C and inertance: M. Here, assuming that the capacitance per unit length is Ca and the inertance per unit length is Ma, the vibration period: the length of a half wavelength with respect to the vibration of T: Lh is:
Lh = T / √ (Ma × Ca) (10)
become.

  As can be seen from the equation (10), when the capacitance per unit length: Ca is increased, the length: Lh at which the inertance is effective effectively with respect to the high-frequency vibration is reduced (that is, the effective inertance is reduced). Let it do). In other words, the above effect can be expected by increasing the capacitance by increasing the width of the flow path 34 or reducing the thickness of the thin plate 14 on the upper wall so as to achieve the “pressure absorption configuration”. In addition to this purpose, this method is an effective means for designing a system with good responsiveness even in a configuration having a long flow path, or when dare to transmit pulsating vibration to a distant place.

  The effect of the present embodiment is not limited to the micro pump 10 of the type shown in FIG. 1, but is effective for all micro pumps accompanied by pulsation at the time of liquid supply.

  For example, as shown in the top view of FIG. 4, a micropump of a type called a "nozzle / diffuser system" that has divergent entrances and exits 42 and 44 as openings and utilizes the fact that the flow path resistance in the divergent direction is always large. It is particularly effective for a micropump having no valve, such as 40. The micropump 40 of FIG. 4 drives the piezoelectric element 48 with an alternating current, for example, like the micropump 30 shown in FIGS.

  Further, as shown in the cross-sectional view of FIG. 5, for example, in a micropump 50 of a type in which liquid is supplied with opening and closing valves 52 and 54 which are on-off valves, the higher the driving speed, the larger the amount of liquid supply per cycle. The effect is considered to be effective because it is expected to be easily affected by the pulsation. The micropump 50 in FIG. 5 drives the piezoelectric elements 52a and 54a that open and close the valves 52 and 54 at a predetermined timing in synchronization with the driving of the piezoelectric element 56a facing the chamber 56. For example, as shown in FIG. 5A, with the valve 52 closed, the chamber 56 is deformed and pressurized as shown by an arrow 56s, and the liquid flows from the chamber 56 to the flow path 34 as shown by an arrow 50a. Extrude. Next, as shown in FIG. 5 (b), with the valve 54 closed, the chamber 56 is returned to its original position as shown by the arrow 56t to reduce the pressure, and the liquid is sucked from the fluid reservoir 30 as shown by the arrow 50b. . Repeat this.

  Next, a second embodiment will be described with reference to FIGS.

  The fluid transport system shown in FIG. 6 is configured substantially in the same manner as the first embodiment of FIGS. 1 and 2, but differs from the first embodiment in that the flow path 34 connected to the second opening 24 is A pressure absorbing section 60 is provided on the way. The upper wall of the pressure absorbing section 60 is formed of the thin plate 14 as in the first embodiment. Since the pressure absorbing portion 60 is wider than the flow path 34, the thin plate 14 at that portion is easily bent and deformed by pressure. Since the capacitance (Cd) of the pressure absorbing portion 60 due to the deformation of the thin plate 14 is proportional to the fifth power of the width w as shown in Expression (9), the value is increased only by, for example, increasing the width by about 20%. About 2.5 times. Actually, it should be evaluated by the sum of the capacitance (Cw) due to the compression of the liquid, but even if the width is increased to this extent, it may function sufficiently as the pressure absorbing portion.

  The pressure absorbing portion 60 not only exhibits a pressure absorbing effect but also has a characteristic of reflecting a high-frequency pressure compression wave. Specifically, reflection occurs where the effective acoustic impedance changes, such as at the interfaces 61a and 61b between the flow path 34 and the pressure absorbing section 60. This reflection can occur not only at the portion where the acoustic impedance increases but also at the interface where the acoustic impedance decreases.

Assuming that the acoustic impedance before the reflecting portion 61a (the portion of La) is Za and the acoustic impedance at the front of the reflecting portion 61a (the portion of Lb) is Zb, the reflectance K of the pressure at the reflecting portion 61a is:
K = (Zb−Za) / (Za + Zb) (11)
Can be represented by

The value of the acoustic impedance at each part: Z is
Z = √ (M × C) (12)
Is required. Here, M and C are the effective values of the inertance: M and the acoustic capacitance: C, respectively.

  In this configuration, only high-frequency vibrations higher than a certain level can be reflected. As a daily limit of the lower frequency limit, when a wave propagates in the pressure absorbing section 60, it should be a frequency at which about half or more of the wavelength can exist in the region. In other words, a wave having a wavelength at which a wave propagates in the pressure absorbing section 60 twice or more the length of the pressure propagating through the pressure absorbing section 60 (ie, Lb) is not reflected. Only waves are reflected.

  That is, the high-frequency component having a frequency equal to or higher than the predetermined frequency is less likely to propagate to the front of the pressure absorbing portion, so that the flow of the fluid ahead of this portion can be made a smooth flow without pulsation. As a result, even if there is a part of a complicated flow path shape such as a sharply bent part or a connector part with an external flow path in the flow path on the other side, or even if there is an uncertain element such as mixing of bubbles, in that part, By preventing reflection of waves that are difficult to control, it is possible to help stabilize the liquid sending characteristics.

  The reflected wave reflected by the pressure absorbing unit 60 may return to the second opening 24 of the micropump 20 to affect the characteristics of the micropump 20 in some cases. Generally, this effect often leads to characteristic deterioration. However, by designing in consideration of the position of the wave front, on the contrary, it is also possible to increase the efficiency by actively using the reflected wave. In particular, this effect is great for the micropump 10 of the type shown in FIGS.

  That is, in the micropump 10 of the type described above, since it is required that the value of the flow path resistance does not change even if the pressure changes in the second opening 24, the pressure fluctuation between both ends of the second opening 24 should be as small as possible. It is desirable that there be few. Therefore, by using the above-mentioned reflected wave to cause the reflected wave having a phase difference with respect to the pressure oscillation periodic waveform to interfere with the second opening 24, the pressure fluctuation at the second opening 24 is suppressed, It is possible to obtain better characteristics.

  For this purpose, for the distance La from the second opening 24 to the pressure reflecting portion 61a, the wave of the driving cycle of the micropump 10 is N times (波長 = 1, 2, 3) the wavelength that propagates through the flow path. , ...) Avoid the length in the vicinity and find the optimal distance. However, as N increases, the attenuation of the reflected wave increases accordingly, and the effect of suppressing the pressure fluctuation by the reflected wave decreases. Furthermore, if the wavelength changes due to a slight design error, disturbance, or the like, the phase of the reflected wave shifts, which may result in a completely different result from the target. Therefore, preferably, the distance La from the second opening 24 to the pressure reflecting portion 61a is shorter than の of the wavelength of the driving cycle of the micropump 10, and the pressure La is adjusted to a position where the phase of the reflected wave becomes optimal. The reflection part 61a is arranged.

Note that the length of a half wavelength with respect to the driving cycle of the micropump 10: Tp is calculated as in the above-described equation (11).
Lh = Tp / √ (M × C) (13)
It becomes.

  Therefore, the position of the pressure reflecting portion 61a (that is, the length of La) is optimized with respect to Lh, or the capacitance: C and the inertance: M of the pressure propagation channel portion (La portion) are changed. What is necessary is just to optimize Lh with respect to the position of the pressure reflection part 61a.

  Next, a modification of the second embodiment will be described.

  In the fluid transport system in FIG. 7, the pressure absorbing units 60, 62, and 64 are arranged at intervals at a plurality of locations of one flow path. Thereby, the propagation of the high frequency component can be more strongly prevented. When the plurality of pressure absorbing portions 60, 62, 64 are arranged in this way, the reflection at the interfaces 61a, 61b; 63a, 63b; 65a, 65b may not be as strong as in the case of FIG. It is possible to reduce high-frequency components propagating before the pressure absorbing portion 64 while reducing components reflected back to the opening 24 and returning.

  The pressure absorbing section may have a configuration other than those shown in FIGS. 6 and 7 as long as there is a boundary where the acoustic impedance: Z is discontinuous.

  Furthermore, regardless of the value of the acoustic impedance, such a reflection phenomenon can occur in a part where the flow path is sharply bent, such as a part that obstructs the straightness of the pressure wave, so it can be used for the same purpose. it can.

  For example, in the fluid transport system of FIG. 8, a plurality of bent portions 34k are provided in the front 34s of the flow path 34, and each of the bent portions 34k can reflect a part of the high-frequency wave.

  Next, a third embodiment will be described with reference to FIGS.

  By arranging a plurality of micropumps as in the first and second embodiments and connecting them to form a system, the durability of the system can be improved as compared with the case where one micropump is used alone. . In such a usage, as described below, it is possible to prevent the influence of the pulsation between the micropumps or to use the mutual pulsation to further improve the performance.

  In the fluid transport system shown in FIG. 9, micro pumps 10a and 10b connected to fluid chambers 30a and 30b, respectively, are connected in parallel to increase the flow rate of the system. At this time, the micropumps 10a and 10b are prevented from inadvertently malfunctioning due to the pulsation of the micropumps 10a and 10b, and the flow characteristics of the flow path 36 are prevented from fluctuating in the flow path 36 after the merging. Pressure absorbers 60a, 60b are provided in the middle of each flow path 34a, 34b connected to 10b.

  In the fluid transport system of FIGS. 10 and 11, a plurality of micropumps 10c and 10d are connected in series between the fluid chamber 30 and the flow path 38, so as to increase the pressure generated as a system. At this time, it is expected that interference of pressure waves occurs between the micro pumps 10c and 10d due to the influence of the pulsation of the micro pumps 10c and 10d, and desired characteristics cannot be obtained. In order to prevent this, in the fluid transport system of FIG. 10, a pressure absorbing section 60 is provided in the flow path 34 connecting between the chambers of the micro pumps 10c and 10d. In the fluid transport system of FIG. 11, only the pressure absorbing section 60 is provided between the micro pumps 10c and 10d, and the flow path is eliminated. This method can be used not only for the micropump of the type shown in FIG. 1 but also for general micropumps including pulsation.

  When a plurality of micropumps are connected in series, besides a method of alleviating the pulsating pressure, there is also a method of improving the characteristics by utilizing each other's pressure waves. The following is an example.

  In the fluid transport system of FIG. 12, the chambers of a plurality of micro pumps 40a, 40b, 40c are connected in series between the flow paths 31, 35 (there is no problem if they are connected via the flow paths), and the adjacent micro pumps 40a, 40b are connected. , 40c with a phase difference (or by shifting the timing of the drive voltage).

  FIG. 13A shows a common first opening 22x between chambers 20s and 20t of two micropumps 10s and 10t of the type shown in FIGS. 1 and 2, and a second opening 24s on the opposite side. , 24t through a fluid transport system having a configuration for communicating with flow paths 31, 35. The micro pumps 10s and 10t are appropriately driven so that the behaviors of the actuators have a phase difference with each other (or that the positive and negative of the deformation direction are opposite). For example, FIG. 13B shows an example of drive voltage waveforms 80 and 82 applied to actuators (not shown) of these micropumps 10s and 10t, respectively. In the drive voltage waveforms 80 and 82, the sharp rise 80a or fall 82a and the gentle fall 80b or rise 82b are synchronized, and the phases are shifted by 180 degrees.

  FIG. 14 (a) communicates between the chambers 20s and 20t of the micropumps 10s and 10t of the type shown in FIG. 1 through a common second opening 24x, and the first openings 22s and 22t on the opposite sides are pressure-absorbed. The fluid transport system has a configuration in which the fluid transport system communicates with a flow path (not shown) via the units 60s and 60t. In this case, it is desirable to provide the pressure absorbing portions 60 s and 60 t from the viewpoint of stability of characteristics.

  FIG. 14B shows an example of drive voltage waveforms 84 and 86 applied to actuators (not shown) of these micropumps 10s and 10t. The actuators of the micro pumps 10s and 10t have different rise times (lengths of 84a and 86a) and fall times (lengths of 84b and 86b), and either one of the rise time and the fall time is different. When the displacement speed of one actuator is the fastest, the deformation direction of one actuator coincides with the displacement direction of the other actuator.

In the fluid transport system in FIG. 15, a plurality of micropumps 40s and 40t are connected in series between flow paths 31 and 35 via a flow path 33 that is a connection part. By setting the length L ₀ of the flow path 33 to an appropriate length, pulsations generated by the micro pumps 40 s and 40 t can be mutually used with respect to the wavelength of the pressure compression wave transmitted through the flow path 33. .

As described above, the length L ₀ of the flow path 33 is set so as to avoid the vicinity of N times (N = 1, 2,...) Of 波長 of the wavelength of the pressure compression wave, and from one micro pump to the other micro pump. What is necessary is just to make the pressure compression wave which advances toward and the reflected wave reflected cancel each other. If the length L ₀ of the flow path 33 is equal to or less than の of the wavelength of the pressure compression wave, the attenuation of the reflected wave is small, so that the effect of canceling out becomes large. To achieve the same result.

However, if the flow path 33 is too short, not only this effect cannot be obtained, but also the adverse effect may be caused. For a sine wave, which is the most common pressure compression wave, the length from the peak of the pressure to the point where the pressure becomes zero corresponds to a quarter of its wavelength, and less than that. Not only is the effect not expected, but it can also have an adverse effect. Therefore, it is desirable that the length L ₀ of the flow path 33 be equal to or more than １ ／ of the wavelength of the vibration of the driving frequency.

  By arbitrarily combining the various devices described above, a fluid transfer system with higher performance can be constructed.

  For example, the fluid transport system in FIG. 16 includes three series-connected micropumps 10u, 10v, and 10w, flow paths 34u, 34v, and 34w including pressure absorbing units 60u, 60v, and 60w, micropumps 10x, 10y, and 10z. The flow paths 34x, 34y, and 34z are connected in parallel between the fluid reservoir 30x and the pressure absorbing unit 60x. In this way, by connecting those connected in series and arranging them further in parallel and joining them, it is possible to increase both the flow rate and the generated pressure in the flow path 36 after the joining.

  As described above, the fluid transport system can prevent the deterioration of the characteristics by providing the pressure absorbing unit and the reflecting unit.

  It should be noted that the present invention is not limited to the above embodiments, but can be implemented in various other modes.

  For example, the invention is not limited to the case where two flow paths communicate with the chamber of the micropump, and three or more independent flow paths may communicate with each other. Moreover, the fluid circulation system may be configured by connecting the flow paths connected to the chamber of the micropump.

  Further, the present invention is not limited to liquids, but is applicable to all fluids including gases.

It is sectional drawing of a micro pump. It is a top view of the fluid transportation system of a 1st example of the present invention. It is a top view of the fluid transport system of the modification of FIG. It is a top view of the fluid transportation system of other modification. It is sectional drawing of the micro pump of another modification. It is a top view of the fluid transportation system of a 2nd example of the present invention. It is a top view of the fluid transport system of the modification of FIG. It is a top view of the fluid transportation system of other modification. It is a top view of the fluid transportation system of a 3rd example of the present invention. It is a top view of the fluid transport system of the modification of FIG. It is a top view of the fluid transportation system of other modification. It is a top view of the fluid transportation system of another modification. It is the (a) top view and (b) drive voltage waveform diagram of the fluid transportation system of another modification. It is the (a) top view and (b) drive voltage waveform diagram of the fluid transportation system of another modification. It is a top view of the fluid transportation system of another modification. It is a top view of the fluid transportation system of another modification. 2 is a graph of a displacement behavior and a drive voltage of the micropump of FIG. 1. It is a graph of other displacement behavior and drive voltage. It is a graph of another displacement behavior and drive voltage.

Explanation of reference numerals

10, 10a, 10b, 10c, 10d, 10s, 10t, 10u, 10v, 10w, 10x, 10y, 10z Micropump 14 Thin plate (wall)
20, 20s, 20t Chamber 22, 22s, 22t, 22x First opening 24, 24s, 24t, 24x Second opening 24a, 24b Flow path (opening)
30, 30a, 30b, 30x Fluid reservoir 31 Flow path 33 Flow path (connection part)
34, 34a, 34b, 34u, 34v, 34w, 34x, 34y, 34z Channel 34k Bent portion (reflection portion)
35, 36, 38 Channels 40, 40a, 40b, 40c, 40s, 40t Micropumps 42, 44 Entrance (opening)
46 chamber 50 micropump 52, 54 valve (open / close valve)
56 chambers 60, 60a, 60b, 60s, 60t, 60u, 60v, 60w, 60x Pressure absorbing parts 61a, 61b Interface (reflection part)
62 Pressure absorption section 63a, 63b Interface (reflection section)
64 Pressure absorption section 65a, 65b Interface (reflection section)

Claims (6)

In a fluid transport system in which a plurality of micropump chambers are arranged in series,
Each micropump is provided with a first opening and a second opening in a chamber of the micropump, and when the pressure in the chamber is raised or lowered, the change rate of the flow path resistance of the first opening is the same as the above. It is configured to be larger than the change rate of the flow path resistance of the second opening,
Between adjacent micropumps, the second openings are located on opposite sides of the first opening communicating with each other, or the first openings are located on the opposite sides of each other communicating with the second opening common. A fluid transport system, wherein the part is located.   The fluid transport system according to claim 1, wherein chambers of two adjacent micropumps are driven with different drive waveforms or with a phase difference.   For the two adjacent micropump chambers, the first micropump chamber is driven by a first drive waveform and the second micropump chamber is driven by a second drive waveform obtained by inverting the first drive waveform. The fluid transportation system according to claim 1, wherein:   The first opening and the second opening each have a uniform cross-sectional shape, and a length of the first opening is shorter than a length of the second opening. 2. The fluid transportation system according to 1.   The fluid transport system according to claim 1, wherein a flow path is connected to each of the chambers of two outermost micro pumps among the plurality of micro pumps through the openings. The fluid transport system according to claim 1, wherein a pressure absorbing unit is connected to the chambers of two outermost micro pumps of the plurality of micro pumps via the openings. .

Images