Abstract:
A closed-loop piezoelectric pump is disclosed for use in a fluid delivery system. The pump housing includes a movable diaphragm that defines a pumping chamber within the pump housing, the pumping chamber having an inlet for admitting fluid and an outlet for emitting fluid. A piezoelectric transducer is coupled to the moveable diaphragm and operates to produce a pumping action by varying the volume of the pumping chamber. The piezoelectric transducer may be used to generate an acoustic pressure pulse within the fluid delivery system and to sense reflections of the acoustic pressure pulse caused by impedance changes downstream of the pump. Properties of the fluid path downstream of pump may be determined from the characteristics of the sensed reflections.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is related to the following co-pending U.S. Patent Applications, being identified by the below enumerated identifiers and arranged in alphanumerical order, which have the same ownership as the present application and to that extent are related to the present application and which are hereby incorporated by reference:  
         [0002]    Application Ser. No. 10010448-1, titled “Piezoelectrically Actuated Liquid Metal Switch”, filed May 2, 2002 and identified by Ser. No. 10/137,691;  
         [0003]    Application Ser. No. 10010529-1, “Bending Mode Latching Relay”, and having the same filing date as the present application;  
         [0004]    Application Ser. No. 10010531-1, “High Frequency Bending Mode Latching Relay”, and having the same filing date as the present application;  
         [0005]    Application Ser. No. 10010570-1, titled “Piezoelectrically Actuated Liquid Metal Switch”, filed May 2, 2002 and identified by Ser. No. 10/142,076;  
         [0006]    Application Ser. No. 10010571-1, “High-frequency, Liquid Metal, Latching Relay with Face Contact”, and having the same filing date as the present application;  
         [0007]    Application Ser. No. 10010572-1, “Liquid Metal, Latching Relay with Face Contact”, and having the same filing date as the present application;  
         [0008]    Application Ser. No. 10010573-1, “Insertion Type Liquid Metal Latching Relay”, and having the same filing date as the present application;  
         [0009]    Application Ser. No. 10010617-1, “High-frequency, Liquid Metal, Latching Relay Array”, and having the same filing date as the present application;  
         [0010]    Application Ser. No. 10010618-1, “Insertion Type Liquid Metal Latching Relay Array”, and having the same filing date as the present application;  
         [0011]    Application Ser. No. 10010634-1, “Liquid Metal Optical Relay”, and having the same filing date as the present application;  
         [0012]    Application Ser. No. 10010640-1, titled “A Longitudinal Piezoelectric Optical Latching Relay”, filed Oct. 31, 2001 and identified by Ser. No. 09/999,590;  
         [0013]    Application Ser. No. 10010643-1, “Shear Mode Liquid Metal Switch”, and having the same filing date as the present application;  
         [0014]    Application Ser. No. 10010644-1, “Bending Mode Liquid Metal Switch”, and having the same filing date as the present application;  
         [0015]    Application Ser. No. 10010656-1, titled “A Longitudinal Mode Optical Latching Relay”, and having the same filing date as the present application;  
         [0016]    Application Ser. No. 10010663-1, “Method and Structure for a Pusher-Mode Piezoelectrically Actuated Liquid Metal Switch”, and having the same filing date as the present application;  
         [0017]    Application Ser. No. 10010664-1, “Method and Structure for a Pusher-Mode Piezoelectrically Actuated Liquid Metal Optical Switch”, and having the same filing date as the present application;  
         [0018]    Application Ser. No. 10010790-1, titled “Switch and Production Thereof”, filed Dec. 12, 2002 and identified by Ser. No. 10/317,597;  
         [0019]    Application Ser. No. 10011055-1, “High Frequency Latching Relay with Bending Switch Bar”, and having the same filing date as the present application;  
         [0020]    Application Ser. No. 10011056-1, “Latching Relay with Switch Bar”, and having the same filing date as the present application;  
         [0021]    Application Ser. No. 10011064-1, “High Frequency Push-mode Latching Relay”, and having the same filing date as the present application;  
         [0022]    Application Ser. No. 10011065-1, “Push-mode Latching Relay”, and having the same filing date as the present application;  
         [0023]    Application Ser. No. 10011329-1, titled “Solid Slug Longitudinal Piezoelectric Latching Relay”, filed May 2, 2002 and identified by Ser. No. 10/137,692;  
         [0024]    Application Ser. No. 10011344-1, “Method and Structure for a Slug Pusher-Mode Piezoelectrically Actuated Liquid Metal Switch”, and having the same filing date as the present application;  
         [0025]    Application Ser. No. 10011345-1, “Method and Structure for a Slug Assisted Longitudinal Piezoelectrically Actuated Liquid Metal Optical Switch”, and having the same filing date as the present application;  
         [0026]    Application Ser. No. 10011397-1, “Method and Structure for a Slug Assisted Pusher-Mode Piezoelectrically Actuated Liquid Metal Optical Switch”, and having the same filing date as the present application;  
         [0027]    Application Ser. No. 10011398-1, “Polymeric Liquid Metal Switch”, and having the same filing date as the present application;  
         [0028]    Application Ser. No. 10011410-1, “Polymeric Liquid Metal Optical Switch”, and having the same filing date as the present application;  
         [0029]    Application Ser. No. 10011436-1, “Longitudinal Electromagnetic Latching Optical Relay”, and having the same filing date as the present application;  
         [0030]    Application Ser. No. 10011437-1, “Longitudinal Electromagnetic Latching Relay”, and having the same filing date as the present application;  
         [0031]    Application Ser. No. 10011458-1, “Damped Longitudinal Mode Optical Latching Relay”, and having the same filing date as the present application;  
         [0032]    Application Ser. No. 10011459-1, “Damped Longitudinal Mode Latching Relay”, and having the same filing date as the present application;  
         [0033]    Application Ser. No. 10020013-1, titled “Switch and Method for Producing the Same”, filed Dec. 12, 2002 and identified by Ser. No. 10/317,963;  
         [0034]    Application Ser. No. 10020027-1, titled “Piezoelectric Optical Relay”, filed Mar. 28, 2002 and identified by Ser. No. 10/109,309;  
         [0035]    Application Ser. No. 10020071-1, titled “Electrically Isolated Liquid Metal Micro-Switches for Integrally Shielded Microcircuits”, filed Oct. 8, 2002 and identified by Ser. No. 10/266,872;  
         [0036]    Application Ser. No. 10020073-1, titled “Piezoelectric Optical Demultiplexing Switch”, filed Apr. 10, 2002 and identified by Ser. No. 10/119,503;  
         [0037]    Application Ser. No. 10020162-1, titled “Volume Adjustment Apparatus and Method for Use”, filed Dec. 12, 2002 and identified by Ser. No. 10/317,293;  
         [0038]    Application Ser. No. 10020241-1, “Method and Apparatus for Maintaining a Liquid Metal Switch in a Ready-to-Switch Condition”, and having the same filing date as the present application;  
         [0039]    Application Ser. No. 10020242-1, titled “A Longitudinal Mode Solid Slug Optical Latching Relay”, and having the same filing date as the present application;  
         [0040]    Application Ser. No. 10020473-1, titled “Reflecting Wedge Optical Wavelength Multiplexer/Demultiplexer”, and having the same filing date as the present application;  
         [0041]    Application Ser. No. 10020540-1, “Method and Structure for a Solid Slug Caterpillar Piezoelectric Relay”, and having the same filing date as the present application;  
         [0042]    Application Ser. No. 10020541-1, titled “Method and Structure for a Solid Slug Caterpillar Piezoelectric Optical Relay”, and having the same filing date as the present application;  
         [0043]    Application Ser. No. 10030438-1, “Inserting-finger Liquid Metal Relay”, and having the same filing date as the present application;  
         [0044]    Application Ser. No. 10030440-1, “Wetting Finger Liquid Metal Latching Relay”, and having the same filing date as the present application;  
         [0045]    Application Ser. No. 10030521-1, “Pressure Actuated Optical Latching Relay”, and having the same filing date as the present application;  
         [0046]    Application Ser. No. 10030522-1, “Pressure Actuated Solid Slug Optical Latching Relay”, and having the same filing date as the present application; and  
         [0047]    Application Ser. No. 10030546-1, “Method and Structure for a Slug Caterpillar Piezoelectric Reflective Optical Relay”, and having the same filing date as the present application. 
     
    
     
       FIELD OF THE INVENTION  
         [0048]    This invention relates generally to the field of fluid pumping. More particularly, this invention relates to methods and apparatus for using a piezoelectric pump with integrated sensing to provide a controlled delivery of fluid.  
         BACKGROUND  
         [0049]    Fluid pumps are used extensively in many areas. In some areas, such as chemistry, medicine and biotechnology, relatively low fluid volumes and controlled flow rates are required. An example is the delivery of a pharmaceutical solution or suspension from a container to a delivery point. A number of piezoelectric pumps, including micro-pumps, have been developed. The amount of fluid pumped by a piezoelectric pump typically relates to the driving voltage and pulse width of the electrical signal used to energize the piezoelectric element. This provides an “open-loop” method for controlling the pump. The “open-loop” method does not provide sufficient accuracy for all applications.  
         SUMMARY  
         [0050]    A closed-loop piezoelectric pump is disclosed for use in a fluid delivery system. A piezoelectric transducer in the pump operates to produce a pumping action by varying the volume of the pumping chamber. The piezoelectric transducer may be used to generate an acoustic pressure pulse within the fluid delivery system and to sense reflections of the acoustic pressure pulse caused by impedance changes downstream of the pump. Properties of the fluid path downstream of pump may be determined from the characteristics of the sensed reflections.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0051]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as the preferred mode of use, and further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawing(s), wherein:  
         [0052]    [0052]FIG. 1 is a diagrammatic representation of a piezoelectric pump in accordance with certain aspects of the present invention.  
         [0053]    [0053]FIG. 2 is a sectional view of a piezoelectric pump utilizing a piezoelectric element in an extension mode in accordance with certain aspects of the present invention.  
         [0054]    [0054]FIG. 3 is a sectional view of a piezoelectric pump utilizing a piezoelectric element in a bending mode in accordance with certain aspects of the present invention.  
         [0055]    [0055]FIG. 4 is a diagrammatic representation of a piezoelectric pump utilizing a piezoelectric element in a shearing mode in accordance with certain aspects of the present invention.  
         [0056]    [0056]FIG. 5 is a sectional view of a piezoelectric pump utilizing a piezoelectric element in a shearing mode in accordance with certain aspects of the present invention.  
         [0057]    [0057]FIG. 6 is a further sectional view of a piezoelectric pump in accordance with certain aspects of the present invention utilizing a piezoelectric element in a shearing mode and showing an expanded pumping chamber.  
         [0058]    [0058]FIG. 7 is a further sectional view of a piezoelectric pump in accordance with certain aspects of the present invention utilizing a piezoelectric element in a shearing mode and showing a contracted pumping chamber.  
         [0059]    [0059]FIG. 8 is a diagrammatic representation of a fluid mixing system incorporating a piezoelectric pump of the present invention.  
         [0060]    [0060]FIG. 9-14 depict the operation of a piezoelectric pump with integrated sensing, in accordance with certain aspects of the present invention.  
         [0061]    [0061]FIG. 15 is a diagrammatic representation of a fluid delivery system incorporating a piezoelectric pump of the present invention.  
         [0062]    [0062]FIG. 16 is a further diagrammatic representation of a fluid delivery system incorporating a piezoelectric pump of the present invention.  
         [0063]    [0063]FIG. 17 is a diagrammatic representation of a closed-loop piezoelectric pump system in accordance with certain aspects of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0064]    While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail one or more specific embodiments, with the understanding that the present disclosure is to be considered as exemplary of the principles of the invention and not intended to limit the invention to the specific embodiments shown and described. In the description below, like reference numerals are used to describe the same, similar or corresponding parts in the several views of the drawings.  
         [0065]    One aspect of the present invention is a closed loop, piezoelectric pump. The closed-loop pump includes a sensing element that may be used, for example, to measure the amount of chemical dispensed or the concentration of chemical in a mixing tank. More generally, information can be obtained about impedance changes in the fluid path downstream of the pump. In medical applications, for example, this means that blockage in blood vessels can be measured and the type of blockage characterized at locations remote from the location where the catheter is inserted into the blood vessel. This information can be used to “close the loop” for treatment. In one application, the breakup of a thrombosis in an anticoagulent dispensing application is sensed. In another application, the hardness and removal of plaque in blood vessels during removal by laser surgery is monitored, so that the appropriate laser power and number of pulses are used.  
         [0066]    A diagrammatic representation of a first embodiment of a piezoelectric pump of the present invention is shown in FIG. 1. Referring to FIG. 1, the piezoelectric pump  100  comprises a substantially rigid pump housing  102 . Fluid enters the pump through inlet port  112  and exits the pump through outlet port  114 . The outlet  114  may also comprise a membrane  116  which is permeable to sound and acts as a flow restrictor.  
         [0067]    [0067]FIG. 2 is a sectional view through the section  2 - 2  of the pump shown in FIG. 1. Referring to FIG. 2, the piezoelectric pump  100  comprises a substantially rigid pump housing  102 . The pump housing  102  is separated into a first chamber  104  and a second chamber  106  by a flexible diaphragm  108 . The second chamber is referred to as the pumping chamber. One surface of a piezoelectric transducer  110  is coupled to the flexible diaphragm  108 , while the other is coupled to the pump housing  102 . One or more piezoelectric transducers may be used, and may be located in the first chamber or the second chamber or in both chambers. The piezoelectric transducer may be formed from any of a number of piezoelectric materials, including PZT and PZWT100. The pumping chamber has an input port or inlet  112 , through which fluid is drawn into the pumping chamber, and an output port or outlet  114 , through which fluid is expelled from the pumping chamber. The outlet  114  may also comprise a membrane  116  which acts as a flow restrictor and is permeable to sound. Other flow restriction devices may be used in place of the sound-permeable membrane, including devices such as diffusers/nozzles and valvular conduits. In operation, an electric voltage is applied across the piezoelectric transducer  110 , which causes the piezoelectric transducer to move in the directions of the arrow  118 , that is, in a direction substantially perpendicular to the surface of the diaphragm  108 . In turn, the flexible diaphragm  108  is moved, either increasing or decreasing the volume of the pumping chamber  106 . There are many ways to build the piezoelectric actuator portion of the pump. In addition to the extension element described above, other piezoelectric elements, such as bending and shearing elements may be used.  
         [0068]    A sectional view of a second embodiment of a piezoelectric pump of the present invention is shown in FIG. 3. Referring to FIG. 3, the piezoelectric pump  100  comprises a substantially rigid pump housing  102 . The pump housing  102  is separated into a first chamber  104  and a pumping chamber  106  by a flexible diaphragm  108 . One surface of a piezoelectric transducer  110  is coupled to the flexible diaphragm. One or more piezoelectric transducers may be used, and may be located in the first chamber or the pumping chamber or both. For example, a second piezoelectric transducer may be placed in the pumping chamber on the opposite side of the diaphragm from the transducer  110 . The second piezoelectric transducer would be operated out-of-phase with the first piezoelectric transducer. The pumping chamber has an inlet  112 , through which fluid is drawn into the pumping chamber, and an outlet  114 , through which fluid is expelled from the pumping chamber. The outlet  114  may also comprise a membrane  116  that is permeable to sound. In operation an electric voltage is applied across the piezoelectric transducer  110 , which causes the piezoelectric transducer to move in the directions of the arrows  120 , that is, in a direction substantially parallel to the surface of the diaphragm  108 . This, in turn, causes the flexible diaphragm  108  to bend, either increasing or decreasing the volume of the pumping chamber  106 .  
         [0069]    A diagrammatic representation of a further embodiment of a piezoelectric pump of the present invention is shown in FIG. 4. Referring to FIG. 4, the piezoelectric pump  100  comprises a substantially rigid pump housing  102 . The pump housing  102  is separated into a first chamber  104  and a pumping chamber  106  by piezoelectric elements  110 . The piezoelectric elements  110  provide a self-actuated diaphragm. The pumping chamber has an inlet  112 , through which fluid is drawn into the pumping chamber, and an outlet  114 , through which fluid is expelled from the pumping chamber. The outlet  114  may also comprise a membrane  116  that is permeable.  
         [0070]    [0070]FIG. 5 shows a sectional view of the piezoelectric pump shown in FIG. 4, the section denoted by  5 - 5  in FIG. 4. In operation, an electric voltage is applied across the piezoelectric transducer  110 , which causes the piezoelectric transducer to deflect in a shear mode. When the voltage is applied in one direction, the volume of the pumping chamber  106  is increased, as shown in FIG. 6. This causes fluid to be drawn into the pump through the inlet. When the voltage is applied in the opposite direction, the volume of the pumping chamber is decreased, as shown in FIG. 7. This causes fluid to be expelled from the pump through the outlet  114 .  
         [0071]    [0071]FIG. 8 is a diagrammatic representation of a fluid pumping system incorporating a piezoelectric pump. For clarity, the various components of the system are drawn to different scales. The piezoelectric pump  100  has been described above. In this application, the pump  100  draws fluid through inlet tube  202  from a fluid reservoir  204  containing a first fluid  206 . The inlet tube  202  is coupled to the inlet  112  of the pump through check valve  208 . The check valve  208  prevents fluid from re-entering the fluid reservoir when the volume of the second pump chamber  106  is decreased. Other flow restriction devices may be used, including passive devices such as diffusers/nozzles, flaps and valvular conduits, and active devices such as piezoelectric valves. During the pumping operation, the actuator increases the volume of the pump relatively quickly, drawing fluid from the reservoir through the valve  208 . The pump outlet is connected via delivery tube  212  and opening  214  to mixing tank  216  that contains a second fluid  218 . Relatively little fluid is drawn into the pumping chamber through the flow restrictor due to its fluid drag effects. In this application, fluid  206  from the fluid reservoir  204  is mixed with fluid  218 . A stirrer  220  may be positioned in the mixing tank to facilitate mixing of the fluids.  
         [0072]    In accordance with one aspect of the present invention, it is recognized that the motion of the piezoelectric transducer generates a pressure fluctuation in the fluid and may be used as SONAR transducer. In prior systems, this pressure fluctuation is generally confined to the working chamber of the pump. However, in accordance with the present invention, the pressure fluctuation is allowed to propagate, as a sound wave in the fluid, through the outlet of the pump and into the delivery tube. This is shown schematically in FIGS. 8-13 for a particular embodiment. Referring to FIG. 9, in operation, the piezoelectric element  110  of pump  100  is activated, causing diaphragm  108  to move and generate a pressure pulse  302  in the pumping chamber of the pump. The flow restrictor in the outlet is chosen so as to have an acoustic impedance that is closely matched to the acoustic impedance of the fluid. As a consequence, a substantial portion of pressure pulse is transmitted through the flow restrictor with little distortion and enters the delivery tube  212 , as shown in FIG. 10. Preferably, the direction of the pump displacement is oriented towards the output port of the pump. As shown in FIG. 11, the pressure pulse propagates along the delivery tube until it reaches the interface  214  between the delivery tube  212  and the mixing tank  216 . Because of the mismatch in the acoustic impedance between the tube and the tank, a portion  304  of the pressure pulse is reflected and propagates back along the tube towards the pump. The remainder of the pressure pulse  302  propagates into the mixing tank. Referring to FIG. 12, the reflected pressure pulse  304  passes back through the flow restrictor and reaches the pump diaphragm  108 . The force applied on the pump diaphragm is transmitted to the piezoelectric element and induces an electrical voltage across the element. In this manner, the piezoelectric element acts as an acoustic pressure sensor, where the electrical voltage is the sensed signal. A signal analyzer may be electrically connected to the piezoelectric element (via suitable signal conditioning circuitry), and the sensed signal may be analyzed to infer properties of the pump, the delivery tube, and the fluid in the delivery tube and the mixing tank.  
         [0073]    Referring to FIG. 13, the pressure pulse ( 302  in FIG. 12) is reflected from the far wall of the mixing tank  216  and propagates back towards the tube/tank interface as reflected pressure pulse  306 . A portion of the pressure pulse will reenter the delivery tube  212  and propagate back to the pump. As shown in FIG. 14, the reflected pressure pulse finally reaches the diaphragm  108  and is sensed by the piezoelectric element  110  as described above. The characteristics of the sensed signal provide more information from which the properties of the fluid in the mixing tank can be inferred.  
         [0074]    The initial pressure pulse may the pulse generated by normal pumping motion, or it may be specially generated as a test signal. Preferably the pulse should have short duration to allow time separation of the reflected pulses. Such short duration pulses have a broad frequency spectrum. An example of such a pulse is a square wave.  
         [0075]    In a further embodiment of the present invention, the pump is operated in a closed-loop mode. In this mode of operation, the properties of the sensed signal are used to adjust the pumping action of the pump. In this manner, desired fluid properties may be obtained with high accuracy.  
         [0076]    In a further embodiment of the present invention, depicted in FIG. 15 and FIG. 16, a generated pressure pulse is used to determine the length of a slug of pumped fluid in a delivery tube. Referring to FIG. 15, a piezoelectric pump  100  is coupled to a delivery tube  212 . A pressure pulse  302  is generated by piezoelectric transducer  110  acting on the moveable diaphragm  108 . The pressure passes through flow restrictor  116  with little loss of energy. The fluid slug occupies the pumping chamber  106  and the interior of the delivery tube  212 . The end of the slug is denoted by the surface  402 . Referring now to FIG. 16, when the pressure pulse encounters the acoustic impedance discontinuity at the end  402  of the slug, a reflected pulse  404  is generated which propagates back up the delivery tube to the pump. The reflected pulse passes through the flow restrictor and is sensed by the piezoelectric transducer  110 . The resulting response signal is then analyzed. In one embodiment, the propagation time of the pulse and the sound speed in the fluid are used to determine the length of the fluid slug. Additionally, if the area of the fluid delivery tube is known, the volume of fluid in the slug can be calculated. This provides a measure of the volume of fluid that has been dispensed. In a further embodiment, a relief line is provided to ensure that the delivery tube empties between pumping cycles. The relief line relieves the pressure in the delivery tube up-stream of the fluid slug in the delivery tube.  
         [0077]    An overview of a system incorporating a closed-loop piezoelectric pump is shown in FIG. 17. Referring to FIG. 17, a pulse generator  502  is provided to generate signals for controlling the piezoelectric pump  100 . An analyzer  504  is provided to receive signals from the piezoelectric pump  100 . The pulse generator  502  and analyzer  504  realized by a general purpose computer  506  or an equivalent device such as a microprocessor based computer, digital signal processor, micro-controller, dedicated processor, custom circuit, ASICS and/or dedicated hard wired logic device. The pulse generator  502  and analyzer  504  are coupled to the piezoelectric pump via signal conditioner  508 . The analyzer may utilize such characteristics as the time elapsed between the generation of the pulse and the sensing of the reflected pulses or the transfer function between the sensed signals and the generated signal. In one embodiment, the analyzer is calibrated by using a system with known acoustical properties. The analyzer and pulse generator are coupled to provide a closed-loop control system by which the flow of fluid dispensed by the pump can be controlled. The piezoelectric pump  100  draws fluid in though the input tube  202  and fluidic valve  208  and dispenses it through delivery tube  212 . A flow restrictor  116  is provided to restrict flow of fluid back into the pump and allow passage of sound pulses generated by the piezoelectric transducer in the pump and by reflections of those sound pulses. If only monitoring is required (i.e. no pumping action) the flow restrictor may not be required.  
         [0078]    Those of ordinary skill in the art will recognize that the present invention has been described in terms of exemplary embodiments based upon use of a piezoelectric transducer. However, the invention should not be so limited, since the present invention could be implemented using equivalent structural arrangements.  
         [0079]    While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those of ordinary skill in the art in light of the foregoing description. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.