Abstract:
A micropump comprising a pump body including a fluid inlet channel, a fluid outlet channel and pumping reservoir, the fluid inlet channel and the fluid outlet channel communicating with the pumping reservoir, a diaphragm covering the pumping reservoir, a piezoelectric strip actuator attached to the diaphragm such that by applying a voltage to the actuator, the diaphragm can be raised or lowered relative to the pumping chamber, a valve on the inlet channel and the outlet channel, the valve opening and closing the inlet and the outlet channel in response to the raising and lowering of the diaphragm.

Description:
BACKGROUND 
     This invention relates to a piezoelectric micropump and to methods and apparatuses for pumping fluid in small volumes and at controlled flow rates using a micropump employing a diaphragm and a piezoelectric strip actuator. 
     Numerous fluidics applications in such areas as medicine, chemistry, and environmental testing exist on a small scale for reasons of sample size, reagent costs, or portability. Cost-effective fluidics including pumps, that are capable and reliable are required for such small scale systems. A number of micropumps are known for delivering small amounts of a fluid to a delivery point. Some of the pumps include piezoelectric actuators. U.S. Pat. No. 4,938,742 to Smits describes a micropump with piezoelectric valves. These valves contain a diaphragm covered by a single layer of piezoelectric material, which limits the control and deflection of the valves. Some of the principles involved in piezoelectric micropumps are described in  Piezoelectric Micropump Based Upon Micromachining of Silicone , Sensors &amp; Actuators, 15, 1988 pp. 153-167. 
     U.S. Pat. No. 4,939,405 to Okuyama et al. discloses a piezoelectric vibrator pump in which a piezoelectric vibrator is mounted in a housing. The vibrator pump does not employ a diaphragm. Instead the vibrator itself is coated with plastic. The pump includes a suction inlet line and a discharge outlet line both of which contain non-return values that alternately open and close in response to the vibration of the vibrator. 
     U.S. Pat. No. 5,611,676 to Ooumi et al. discloses the use of a cantilevered piezoelectric bimorph. A piezoelectric bimorph has two layers of a piezoelectric material separated by a shim. The application of an electric field across the two layers of the bimorph causes one layer to expand while the other contracts. This causes the bimorph to warp more than the length or thickness deformation of the individual layers. 
     Another example of a micropump is described in International Patent Application WO 98/51929 to Fraunhofer. Fraunhofer discloses a piezoelectric micropump that is constructed from two silicone wafers each of which includes a valve flap structure and a valve seat structure. The two wafers are juxtaposed and bonded together such that the flap structure in one wafer overlies the valve structure in the other wafer. The micropump is disclosed as being self-priming and suitable for conveying a compressible media. 
     Commonly assigned U.S. Pat. No. 6,368,079 to Peters describes a micropump which includes a plurality of diaphragm pumping chambers that are actuated by a cantilever mounted piezoelectric strip actuator. 
     The present invention provides a new and improved piezoelectric micropump. 
     SUMMARY OF THE INVENTION 
     In accordance to one aspect of the present invention a micropump for pumping a fluid is disclosed that includes a pump body. The pump body includes a fluid inlet channel and a fluid outlet channel, and a pumping chamber. The fluid inlet channel and the fluid outlet channel directly or indirectly communicate with the pumping chamber. The pumping chamber is formed between a plastic diaphragm and a reservoir in the pump body. A piezoelectric strip actuator is attached to the diaphragm such that by applying a voltage to the actuator, the actuator is deformed and the diaphragm is raised or lowered. In accordance with one embodiment of the invention, a reed valve is provided on the inlet and outlet channel. These reed valves open and close the inlet and outlet channels in response to raising and lowering the diaphragm. In one embodiment of the invention, pressures up to about 20 psi and flow rates up to about 100 μl/sec and more typically up to about 50 μl/sec are achieved. 
     In accordance with the invention, the micropump may include one or more pumping chambers. The term “pumping chamber” as used herein includes any chamber formed between an actuated diaphragm and a reservoir in the pump body. The term includes a chamber that functions as a volume accumulator. 
     In another embodiment of the invention, the micropump includes two or more pumping chambers that may be the same or different volume. In one embodiment, the ratio of the stroke volume of the first pumping chamber to the stroke volume of the second pumping chamber is about 2:1 but the ratio can vary from about 2:1 to 1:1 depending upon the application of the pump. 
     The diaphragm for the second chamber may be attached to the same piezoelectric actuator that actuates the diaphragm for the first chamber or to a different individually or independently operated actuator. Where the same actuator is attached to both diaphragms, the actuator may be double acting, i.e., the pumping chambers operate 180° out of phase with one another. By applying a first voltage to the actuator, the first diaphragm can be raised while the second diaphragm is lowered, and by applying a second voltage (i.e., reversing the polarity of the first voltage), the first diaphragm can be lowered while the second diaphragm is raised. 
     Micropumps can be designed having sequentially actuated diaphragms and used for a variety of different applications or purposes. In one embodiment, the second pumping chamber may function as a volume accumulator. The outlet from the first pumping chamber directly or indirectly communicates with the inlet to the volume accumulator and the volume accumulator includes a second fluid outlet from which fluid is discharged. Micropumps including two pumping chambers connected in series in this manner can be designed to provide more constant fluid output than a micropump which includes a single pumping chamber. With a micropump having a single pumping chamber, the output occurs in pulses when the diaphragm is lowered or compressed but not when it is raised. If the first chamber is larger than the volume accumulator (e.g., twice as large), a unit of discharge can be achieved with each raising and lowering of the second pumping chamber diaphragm thereby providing more constant output and reducing pulsation. 
     In another embodiment of the invention, the micropump may be constructed with two or more pumping chambers that are activated sequentially such that fluid is expelled from one chamber as it is drawn into a second chamber. The second chamber volume can vary but for most applications it will be smaller or equal in volume to the first chamber. 
     In still another embodiment of the invention, the micropump can be constructed with a plurality of pumping chambers having diaphragms that can be actuated individually by dedicated actuators. In accordance with one example of this embodiment of the invention, a micropump can be provided wherein one pumping chamber pumps a liquid composition while the other pumping chamber pumps a gas such as air. The pumped air can be used to purge a line or element in the fluidic flow of the first pumping chamber. In one embodiment, air is used to purge a spray nozzle that is directly or indirectly supplied with liquid from the first pumping chamber. 
     In accordance with one embodiment of the invention, the reed valve is formed by a film of a flexible polymer that may be either low flex modulus or high flex modulus, such as a KAPTON (aromatic polyimide) film (KAPTON is a trademark of the E. I. DuPont Company). Preferably, the reed valve is formed from a low flex modulus film. In one embodiment a cut out defining a flap which functions as the reed valve is cut in the film. In another embodiment, the film may include a first cut out defining a first flexible flap that functions as an inlet valve and a second cut out defining a second flexible flap that functions as the outlet valve. One of the flaps may be located over a valve seat at the mouth of the inlet channel and the other flap may be located over a valve seat at the mouth of the outlet channel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof wherein: 
     FIG. 1 is a perspective view of a piezoelectric micropump having a single pumping chamber. 
     FIG. 2 is a partial cross-section of the micropump of FIG.  1 . 
     FIG. 3 is an exploded view of the micropump of FIG.  1 . 
     FIG. 4 illustrates a reed valve. 
     FIG. 5 illustrates a reed valve construction that provides a higher cracking pressure. 
     FIG. 6 is a cross-section of a micropump having a pumping chamber and a volume accumulator which are operated in series by a single actuator. 
     FIG. 7 is a cross-sectional exploded view of a micropump having a first pumping chamber and a volume accumulator which are individually actuated by dedicated actuators. 
     FIG. 8 is a perspective view of a micropump having independently actuated pumping chambers. 
     FIG. 9 is a cross-section of the micropump of FIG.  8 . 
     FIG. 10 is another cross-section of the micropump of FIG.  8 . 
     FIGS. 11A and 11B illustrate a cupped diaphragm in accordance with one embodiment of the invention 
     FIG. 12 is an exploded view of a micropump actuator mount in which the actuator is pinned on a wire pivot. 
     FIG. 13 is a cross-sectional view of the actuator mount shown in FIG.  12 . 
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings which are provided, FIG. 1 is a perspective view of a micropump  10  in accordance with one embodiment of the invention. The micropump  10  includes a pump body  12 . In this embodiment, the pump body  12  includes a single pumping chamber (internally) that includes a diaphragm  16  on the surface of the pump body. The pump body  12  includes a recessed area  13  in which a group of electrical probes can be mounted as illustrated below in FIG.  8 . The pump body  12  may be made of an injection molded or machined plastic such as DELRIN, an acetal resin available from E. I. DuPont Co. The material forming the pump body is selected to be compatible with the fluid that is pumped through the micropump. 
     An actuator  40  is mounted on the upper surface of the pump body. The actuator is pinned to the pump body near each of its ends by a pair of spacer elements  42  and  44 . The term “pinned” as used herein refers to a relatively flexible mount that permits the ends of the actuator to rock or flex up and down as the actuator vibrates. In one embodiment, the spacer elements  42  and  44  may be formed from the same material as the diaphragm  16 . The actuator may be bonded to the spacers and the diaphragm using an adhesive  45  as described in more detail below. This mount is relatively flexible and permits rocking at the ends of the actuator. A more rigid mount could be used as an alternative mount but it has been found that greater deflection that can be achieved if the ends are able to rock as described herein. In another embodiment of the invention the actuator  40  can be clamped at one end to the pump body  12  to provide a cantilevered mount as shown in commonly assigned U.S. Pat. No. 6,368,079. In still another embodiment the actuator is pinned on a wire as shown in FIGS. 12 and 13. 
     The micropump  10  is shown in more detail in FIGS. 2 and 3. In the illustrated embodiment, the pump  10  includes a modular pump insert  15  that is received into a matching cavity in the pump body  12 . Insert  15  may be retained within the pump body by a press fit. The use of insert  15  simplifies manufacture and assembly of the micropump. The insert  15  has molded or machined within it an inlet channel  20  and an outlet channel  22 . In this embodiment, the micropump also includes a pair of vee-jewels  24  and  25 . A film  29  in which the reed valves  26  and  28  are cut (FIG. 4) is captured between the pump body  12  and the insert  15  as described below. While the micropump may be constructed using insert  15  as illustrated, those skilled in the art will appreciate that the structures of the insert can be molded, microetched or micromachined directly into the pump body using conventional techniques. 
     In one embodiment the pumping chamber may have a stroke volume of about 0.10 to 10 μl and more typically about 0.3 to 0.8 μl. For many applications, it is desirable if the pump is self-priming, i.e., the pump is able to pump gases and liquids. To provide self-priming ability, the dead volume and cracking pressure are minimized. 
     In the embodiment illustrated in FIG. 3, the pumping chamber insert  15  includes a inlet channel  20  and an outlet channel  22 . The inlet channel  20  is widened at its mouth  21  so that it can receive a vee-jewel  24 . The vee-jewel  24  is a highly polished element that includes a channel that runs down its center axis. One face of the vee-jewel  24  includes a frustoconical surface that is designed to seat a ball valve (this surface is not used in this invention) while the opposite face is flat. The vee-jewel  24  is inverted such that its flat face is oriented so that the reed valve  28  seats against the highly polished flat surface of the base of the vee-jewel  24 . To facilitate manufacture the reed valves can be formed in a single film. As shown in FIG. 4, reed valves  26  and  28  are formed by U-shaped cut outs  31  in a flexible polymeric film  29 . The film  29  is captured internally between the insert  15  and the pump body  12 . Outlet reed valve  26  is located over the outlet channel  22  and inlet reed valve  28  is located over the inlet channel  20 . Reed valves  26  and  28  open and close in opposite directions in response to the pressure changes in the reservoir  34 . To prevent the outlet reed valve  26  from closing the outlet channel  22  when the diaphragm  16  is lowered, the mouth  36  of the outlet channel  22  is recessed as shown. 
     The micropump that is illustrated can be assembled by inserting vee-jewel  25  into a cavity in the pump body  12  followed by inserting the reed valve film  29  into the cavity in the pump body  12  oriented such that the valve  26  is aligned with the vee-jewel  25 . Vee-jewel  24  is inserted into the insert  15  and insert  15  is press fit into the pump body  12  thereby capturing the film  29  between the vee-jewels in an orientation such that the reed valves  26  and  28  respectively open and close channels  20  and  22 . The vee-jewels  24  and  25  are aligned with channels  20   a  and  22   a  in the pump body. Channels  20   a  and  22   a  are extensions of the inlet  20  and the outlet  22  and communicate with the reservoir  34  in the pump body  12 . The film  29  may be adhered at its periphery to the pump body  12  if desired but this is not necessary. 
     Those skilled in the art will appreciate that the use of vee-jewels is optional. A seat for the reed valve can be fabricated directly in the pump body using conventional injection molding or microfabrication techniques. Vee-jewels are advantageous because they provide a highly polished surface that the reed valves can seat against without leakage. 
     The film that forms the reed valves can be any material that exhibits the desired flexibility and chemical resistance required in the micropump. While a KAPTON film about 0.0005 inch thick is preferred, other polymeric films having a smooth surface finish could also be used. 
     In some applications, it may be desirable to design the reed valves to provide a higher valve cracking pressure. If the reed valve sits flatly on the seat, the cracking pressure is zero or minimal and is essentially a function of the stiffness of the film. However, by building stress into the reed valve, a higher cracking pressure can be provided. This can be achieved as illustrated in FIG. 5 using a valve seat  70  with a channel  71 . The valve seat  70  is beveled such that when the reed valve is seated, it is under a slight stress produced by the bending in the reed valve from its normal flat position. This causes the film  72  to press against the seat  70  with a small force. This force must be exceeded before fluid can displace the reed from the seat and pass through the valve. 
     The pumping chamber  14  is formed by a diaphragm  16  and a cavity or reservoir  34 . The diaphragm  16  is bonded to the pump body  12  at its periphery such that the diaphragm covers the reservoir  34  of pumping chamber  14 . The diaphragm may be secured to the pump body using an adhesive, but the diaphragm is preferably secured by a non-adhesive bonding technique such as melt fusion or ultrasonic welding. In one embodiment of the invention the diaphragm is manufactured from a laminate of polyethylene terephthalate/aluminum/acrylonitrile. In this embodiment, the aluminum reduces permeability of the diaphragm and the acrylonitrile layer of the laminate can be melted to bond the diaphragm to the surface of the DELRIN pump body without using an adhesive or solvents. Bonding the diaphragm without an adhesive or solvent can be very advantageous. The dimensions of the channels and reservoirs in the pump body are very small and, consequently, small amounts of extraneous material such as adhesive can easily clog the pump. By melt bonding the diaphragm directly to the pump body, problems accompanying the use of these extraneous materials are avoided. Adhesives also tend to be susceptible to chemical or oxidative attack. By omitting their use the pump can be used to process materials that could not be processed if the materials interacted with the adhesives. 
     Important properties to consider in selecting the diaphragm are flexibility, chemical resistance, impermeability, and the ability to bond the diaphragm to the actuator without adhesive. The materials for the diaphragm and the pump body are preferably selected so that an adhesive is not required to bond the diaphragm to the pump body. Diaphragms that require minimal force to deflect such as low modulus films are particularly useful. In this way, the force of the actuator is directed to producing pressure as opposed to deforming the film forming the diaphragm. Less force is required to obtain a given stroke volume than would be required of a higher modulus material formed the diaphragm. The diaphragm may be about 0.005 inch thick in one embodiment of the invention. 
     In some cases the presence of a metal film within the diaphragm can cause electrical interference. The metal film can pick up signals within the pump or cause an electrical short. In this case it is desirable to use a nonconductive impermeable film as the diaphragm. One useful high voltage compatible, non-conductive film is a polychlorotrifluoroethylene (PCTFE)/acrylonitrile laminate sold under the name ACLAR™ by Honeywell Corp. 
     The invention is being illustrated using circular diaphragms but the diaphragm could be a film that is integrated into the micropump as a layer that covers the reservoir or cavity in the pumping chamber. For example, this film could be a continuous layer that is bonded to the surface of the micropump body in the process manufacturing the pump body. 
     In accordance with one embodiment of the invention, the diaphragm is cupped. The diaphragm is formed from a conformable film that tends to deform to form a cup or dish when it is thermally bonded to the pump body at its periphery. This is illustrated in FIG. 11 where FIG. 11A illustrates the circular diaphragm  16  on the surface of the micropump body  12  prior to bonding. This diaphragm includes a meltable thermoplastic (acrylonitrile) film that is positioned against the pump body  12 . Upon heating the circular diaphragm to bond it to the pump body, the diaphragm accumulates in the reservoir  34  and forms a cupped portion  17  as shown in FIG.  11 B. Cupping enhances the pumping action of the diaphragm and more efficient actuator force. Because, the diaphragm is not under tension, the actuator does not have to overcome or compete with latent tension in the diaphragm to drive the pump. An additional way to cup the diaphragm is to preform it into a cupped shape. 
     When the diaphragm is formed from a cupped film as shown in FIG. 11B, the pumping force is a direct function of the width of the actuator. In accordance with a particular embodiment, the pressure generated by the pump is a function of the pumping force which in turn is a direct function of the width of the actuator. The pumping force is not a function of the elasticity of the diaphragm in this embodiment. A direct relationship between pumping force and the width of the actuator facilitates pump design. The flow rate achieved in a pump is a function of the rate and deflection of the diaphragm (i.e., stroke volume) which in turn is a function of the effective length of the actuator and the frequency with which it vibrates. It is usually possible to select a pump actuator that is large enough to provide the desired pressure and flow rate. One advantage of using a strip actuator in the pump is that the remainder of the pump construction is relatively independent (or not directly limited by) the width of the actuator. Different actuator widths can be accommodated in a single pump design. This enables one to provide pumps having different pumping pressure capabilities by using actuators of different widths. 
     The actuator  40  can be made from a commercially available piezoelectric ceramic. The preferred piezoelectric ceramics are lead zirconate titanate, class 5H. Class 5A piezoceramics may also be used, but require higher voltages to achieve similar motion to class 5H piezoceramics. These actuators are usually formed of two layers of a piezo ceramic. In one embodiment, the actuator  40  contains two layers of piezoelectric ceramic (not shown) separated by a layer or shim that may be made of brass or other material. The application of an electric field across the two layers of the piezoelectric ceramic causes one layer of the ceramic to expand while the other layer of the ceramic contracts. This results in a warpage or curvature of the actuator which is greater than the change in the length or thickness of the piezoelectric ceramic itself. The warpage causes the ends of the actuator to bend relative to the middle of the actuator. If the polarity of this voltage is reversed, the opposite effect is achieved and the actuator bends in the opposite direction. 
     A piezoelectric strip actuator useful in providing a pump capable of pumping about 0.4 to 100 microliters per second may have a width of approximately 1 to 3 mm. and an effective length of approximately 5 to 30 mm. The term “effective length” refers to the distance between the points  47  and  48  at which the actuator is pinned to the pump body. Of course, in theory there are only practical limits on the size of the actuator. 
     The actuator  40  can be fixed to the diaphragm  16  by an adhesive  45 . The adhesive may be a pressure sensitive adhesive, a UV curable adhesive, a cyanoacrylate adhesive, or the like. Constructions are also feasible which bond the diaphragm to the actuator without an adhesive, e.g., by inserting the actuator through a sleeve in the diaphragm. In the illustrated embodiment, the ends of the actuator are joined by adhesive to the pump body via spacers  42  and  44 . These spacers may be formed from the same laminate as the diaphragm  16  itself. As previously mentioned, these spacers provide a flexible mount that permits the ends of the actuator to flex or pivot. Other flexible films that permit end flexing may also be used. 
     In another embodiment, the actuator is directly connected to the diaphragm. For example the diaphragm may include a loop of film through which the actuator passes. 
     FIGS. 12 and 13 illustrate another embodiment of the invention in which the actuator is pinned on a small round wire. The end of the actuator  40  is bound to the pump body  12  by an elastic band  50  that is retained in a pair of vertical channels  52  in the pump body  12  by a pair of barbs  54  that are captured within cut outs in the walls of the channels  52 . The actuator is pinned on the wire  60  which is retained on the face of the pump body  12  between two sets of retaining blocks  62 . The wire  60  can vary in diameter. In one embodiment it is about 0.005 inch. 
     In the embodiment shown in FIG. 1 the pump has a single pumping chamber. The application of a voltage to the actuator strip causes the strip to warp in one direction and raise the diaphragm, and application of the opposite polarity voltage causes the strip to warp in the opposite direction and lower the diaphragm. When the diaphragm is raised, a vacuum or reduced pressure is caused in the chamber  14  which opens the reed valve  28  and draws fluid into the pumping chamber  14  through the inlet channel  20 . The reduced pressure on the reed valve  26  draws that reed into contact with the base of the vee-jewel  25 . This temporarily closes the outlet channel  22  as the reservoir  34  is filled. When the diaphragm  16  is lowered, the reed valve  28  is forced into seating contact with the polished base of the vee-jewel  24 , the inlet channel  20  is temporarily closed, and fluid is forced out of the reservoir  34  through the outlet channel  22 . The mouth  36  of the outlet channel  22  is recessed so that the pressure applied to the reed valve  26  when the diaphragm  16  is lowered does not close the outlet channel  22 . Instead the fluid in the reservoir  34  passes around the reed valve  26  and out the outlet channel  22 . In this construction, the pump outputs fluid during one-half of the pumping cycle, namely, when the diaphragm  16  is lowered. 
     The voltage is applied to the actuator by leads which are not shown in FIGS. 1-3. The leads can be attached to the piezoelectric ceramic in a parallel or in a series circuit. In one embodiment, the leads are attached to form an RC circuit. One lead can be attached to each of the layers of ceramic making up the actuator. Alternatively as shown in FIG. 8, a negative lead  256  can be attached to each ceramic layer via a jumper wire  258  and a positive lead  254  can be attached to the shim. The signal that is applied to the ceramic to drive it is preferably applied in a way that reduces noise and vibration. In one case, initially the drive signal rapidly accelerates the actuator and then gradually decreases the vibration frequency. 
     FIG.  6  and FIG. 7 illustrate an embodiment in which a micropump  110  includes a micropump body  112  that has a primary pumping chamber  114 A and a secondary pumping chamber or volume accumulator  114 B. These chambers are each covered by diaphragms  116 A and  116 B, respectively. The primary pumping chamber is associated with an insert  115 , a pair of vee-jewels  124  and  125  and a reed film  129  having reed valves  126  and  128  cut therein. The insert, the vee-jewels and the reed film are assembled with the pump body  112  in the same way as has been disclosed for the embodiment shown in FIGS. 1-3. The second pumping chamber  114 B is a volume accumulator in this embodiment. Consequently the insert and vee-jewels are not required and the channels feeding and emptying the reservoir  134 B can be readily formed directly into the pump body  112 . In this embodiment of the invention the micropump  110  includes one actuator  140  that is secured to both the first and second diaphragm  116 A and  116 B and pinned to the pump body at end  150  by a spacer  142  and a drop of adhesive  143 . With this construction, application of a voltage to the actuator  140  deforms the actuator such that one of diaphragms  116 A and  116 B is raised by the actuator  140  (e.g., the diaphragm located in the middle of the actuator) while the other of the diaphragms is lowered (e.g., the diaphragm located at an end of the actuator). Reversing the polarity of the voltage has the reverse effect, the diaphragm at the end of the actuator may be raised while the diaphragm at the middle of the actuator may be lowered. 
     The micropump  110  can be constructed and used in a manner that provides a more consistent flow than the single chamber micropump  10  of FIG.  1 . In this embodiment the outlet channel  122  from the first chamber  114 A feeds the volume accumulator chamber  134 B by means of vertical channel  127 . Channel  122  is shown extending from chamber  134 A to the end  136  of the pump body  12 . To close access to channel  122  from the vertical channel  132 , channel  132  is lined with a tube member  135 . In the first half of the pumping cycle a voltage is applied to the actuator  140  such that the middle of the actuator moves up, and the ends move down. This movement simultaneously pulls the primary pumping chamber diaphragm  116 A up, and pushes the volume accumulator diaphragm  116 B down. The movement of the primary pumping chamber diaphragm up creates a pressure differential which seals the outlet reed valve  126  against the seat of the vee-jewel  124  and opens the inlet valve  128  and draws the medium in through the inlet reed valve  128  and inlet  120 . The movement of the diaphragm  116 B downward discharges any medium in the chamber  134 B via the outlet tube  135 . 
     In the second half of the pumping cycle the polarity of the voltage applied to the actuator  140  is reversed such that the middle of the actuator  140  moves down, and the ends move up. This movement simultaneously pushes the diaphragm  116 A down and pulls the diaphragm  116 B up. The movement of the diaphragm  116 A down creates a pressure differential which seals the inlet valve  128  against the vee-jewel  124  and opens the outlet valve  126 . This movement also simultaneously forces the medium in the chamber  114 A into the expanding chamber  114 B via the interconnecting passage  122 , while fluid in excess of the volume of the chamber  114 B is discharged to the outlet tube  132 . The flow to the outlet tube  135  is a function of the differential of the volumes of chambers  114 A and  114 B which in this embodiment may be 2:1 but may be varied as a matter of design choice. For example, during the first half of the pumping cycle, two units of fluid may be drawn into the primary pumping chamber  114 A while one unit of fluid is forced from the secondary pumping chamber  114 B. During the second half of the pumping cycle, two units of fluid may be forced from the primary pumping chamber  114 A. One of these two units may fill the secondary pumping chamber  114 B while the other unit may pass through the secondary pumping chamber and be dispensed from the outlet tube  135 . 
     FIGS. 8-10 illustrate another embodiment of the invention where the micropump  210  includes a pump body  212  having a pair of pumping chambers  214 A and  214 B which are formed by a pair of diaphragms  216 A and  216 B. These diaphragms are controlled individually by a pair of actuators  240 A and  240 B. Pins  252  are provided to make electrical connections to the actuators from a controller (not shown). The pumping chambers  214 A and  214 B are otherwise constructed and manufactured in the manner illustrated in FIG.  1 . In one example of this embodiment of the invention, the pumping chamber  214 A is used to pump a liquid fluid such as a pharmaceutical or analytical formulation, and pumping chamber  214 B is used to pump a gas such as air that can be used to purge one or more elements of the liquid pumping fluidics such as a dispenser nozzle. This is illustrated in more detail in FIGS. 9 and 10 which are cross-sections through the micropump of FIG.  8 . In FIG. 9, the liquid pumping module  214 A includes a liquid inlet  220 A in an insert  215 A. Inlet tube  220 A may be a hypodermic needle that draws medicament from a container. In a manner directly analogous to FIG. 1, the micropump is assembled using a pair of vee-jewels  224 A and  225 A and a reed film  229 A having reed valves therein. Actuator  240 A raises and lowers the diaphragm  216 A. When the diaphragm is raised, liquid is drawn into the reservoir  234 A through the inlet  220 A. When the diaphragm is lowered, liquid is expelled through the outlet  222 . Similarly, the micropump shown in FIG. 10, for pumping air, is assembled from an insert  215 B that includes an air filter  261  through which air is drawn into the reservoir  234 B via inlet tube  220 B. Again, a pair of vee-jewels  224 B and  225 B provide seats for the reed valves in the film  229 B. When the diaphragm  216 B is raised, air is drawn into the air inlet  260 . When it is lowered, air is expelled through the outlet  262 . The outlet  262  from the air module and the outlet  222  from the liquid module can feed a three way connection to a spray nozzle (not shown). The three way connection optionally includes a valve to control which branch (air from line  262  or liquid from line  222 ) feeds the nozzle. After spraying liquid, air may be pumped through the spray nozzle to remove any solution that otherwise might leave residue in the nozzle. In an alternative embodiment, the pumping chamber  214 B may be used to pump another purging fluid such as water. 
     The micropump of the present invention is particularly useful in a dosing device in metering solutions or suspensions of a medicament. In one embodiment, it is used in an inhaler where the micropump is used to withdraw a fixed amount of a solution or suspension of a medicament from a supply vessel and pump it to an aerosol sprayer. More particularly, the micropump is useful in metering dosages to EHD (electrohydrodynamic) aerosol sprayers such as the sprayers disclosed in U.S. Pat. No. 6,302,331 to Dvorsky et al. 
     The micropump of the invention can be supplied by a liquid containment system of the type described in commonly assigned U.S. application Ser. No. 10/187,477 filed contemporaneously herewith. In this case the inlet tube  220 A may be a needle that punctures a septum in the container and withdraws liquid medicament as described herein. 
     Having described the invention in detail and by reference to specific embodiments thereof, it will be apparent that numerous modifications and variations are possible without departing from the spirit and scope of the following claims.