Abstract:
A compact, high capacity pump for pumping fluid. A first one-way valve is between an inlet port and the pump&#39;s fluid chamber. A second one-way valve is between the pump&#39;s fluid chamber and an outlet port. A diaphragm separates a piezoelectric stack from the fluid chamber. A power source provides power to the piezoelectric stack causing it to expand and contract. The expansion and contraction of the piezoelectric stack causes fluid to be pumped from the inlet port to the fluid chamber through the first one-way valve and causes fluid to be pumped from the fluid chamber to the outlet port through the second one-way valve. In one preferred embodiment, both one-way valves are disc valves. In another preferred embodiment both one-way valves are MEMS valves.

Description:
[0001]    This application is a continuation of Ser. No. 10/833,838 filed Apr. 28, 2004, which is incorporated herein by reference. 
     
    
       [0002]    The present invention relates to pumps, and in particular, to small sized high capacity piezoelectric fluid pumps. This invention was made with Government support under contract DAAH01-01-C-R046 awarded by DARPA. The Government has certain rights in this invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    Conventional fluid pumps are well known. Although conventional fluid pumps are readily available in both low and high capacity designs, a common feature is that they have many moving parts that create noise and vibration. Also, there are reliability and lifetime limitations due to normal wear phenomena. Furthermore, because conventional pumps have multiple parts, they tend to be large, heavy and expensive. 
         [0004]    Micropumps, also known as miniature pumps, are pumps that are fabricated on a microchip utilizing micromachining processes. For small capacity requirements, micropumps provide improved reliability with fewer parts. For example, micropumps utilizing electroactive transducers have emerged for biomedical and metering applications where small pressures and flow rates are required and where conventional pumps are somewhat impractical. The typical capacity of a micropump may be in the range of a few nano liters per second to a few micro liters per second. Since the total fluid power output of these devices is very small, efficiency is not highly important and is generally low. The relatively low efficiency of the micropump makes massive parallel arraying of many micropumps unattractive as a way of competing with larger conventional pumps. Scaling up the size and pressure of such electroactively driven devices does not improve the efficiency and is difficult due to on-chip fabrication techniques. This class of pump is therefore not able to compete directly with larger conventional pump designs for large fluid output. 
         [0005]    Micro Electro Mechanical System (MEMS) microvalve arrays are known and are utilized to achieve precision fluid flow control. In a microvalve array, multiple diaphragms cover multiple ports to restrict and control fluid flow. In some designs, heaters can be activated to warm and expand a closed fluid volume that in turn moves diaphragms to close and open the individual ports to achieve a desired flow. This arrangement permits precise flow rate control but is slow to respond due to thermal conduction to and from the closed fluid volume. Other activation methods, such as piezoelectric activation, can provide faster opening and closing of the ports. 
         [0006]    What is needed is a compact, high capacity pump that has minimal moving parts, is able to handle a relatively large fluid output, and has improved operating efficiency and reliability as well as reduced weight, size and cost. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a compact, high capacity pump for pumping fluid. A first one-way valve is between an inlet port and the pump&#39;s fluid chamber. A second one-way valve is between the pump&#39;s fluid chamber and an outlet port. A diaphragm separates a piezoelectric stack from the fluid chamber. A power source provides power to the piezoelectric stack causing it to expand and contract. The expansion and contraction of the piezoelectric stack causes fluid to be pumped from the inlet port to the fluid chamber through the first one-way valve and causes fluid to be pumped from the fluid chamber to the outlet port through the second one-way valve. In one preferred embodiment, both one-way valves are disc valves. In another preferred embodiment both one-way valves are MEMS valves. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a first preferred embodiment of the present invention. 
           [0009]      FIG. 1A  shows a preferred passive disc. 
           [0010]      FIGS. 2A-3B  illustrate the operation of the first preferred embodiment. 
           [0011]      FIG. 4A  shows a second preferred embodiment of the present invention. 
           [0012]      FIGS. 4B-4I  illustrate the operation of the second preferred embodiment. 
           [0013]      FIGS. 5A-5F  show a third preferred embodiment of the present invention. 
           [0014]      FIGS. 6A-6C  show a fourth preferred embodiment of the present invention. 
           [0015]      FIG. 7  is a graph of Output Pressure/E Field vs Frequency. 
           [0016]      FIG. 8  presents an example of a utilization of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]      FIGS. 1-3B  disclose a first preferred embodiment of the present invention. As shown in  FIG. 1 , AC power source  1  provides power to piezoelectric stack  4  of piezoelectric fluid pump  5 . In the preferred embodiment, pump  5  is approximately 3 inches tall, 1.5 inches diameter and weights approximately 200 grams. Frequency modulator  2  and amplitude modulator  3  are connected in series as shown and can be adjusted to vary the frequency and amplitude of the signal reaching piezoelectric stack  4 . Diaphragm  6  is bonded to the top of stack  4  and separates stack  4  from fluid chamber  7 . Inlet 1-way passive disc valve  10  controls the flow of fluid through inlet port  8  into fluid chamber  7 . Likewise, outlet 1-way passive disc valve  11  controls the flow of fluid leaving fluid chamber  7  through outlet port  9 . 
       Preferred Passive Disc Valve 
       [0018]      FIG. 1A  shows a top view of a preferred passive 1-way disc valves  10  (part no. J378062) and  11  (part no. _J378067), both available from Kinetic Ceramics, Inc. with offices in Hayward, Calif. Passive 1-way disc valves are preferably fabricated from metal and are approximately 0.02 inches thick 
       Operation of the First Preferred Embodiment 
       [0019]    As voltage is applied to stack  4  via AC power source  1 , stack  4  will expand and contract in response to the AC signal, causing diaphragm  6  to bend up and down in a piston-like fashion. 
         [0020]      FIG. 2B  shows a plot from t=0-½T of the sine wave of the AC signal generated by AC power source  1 . From t=0-½T, stack  4  has contracted (i.e., decreased in length), see  FIG. 2A . This has caused diaphragm to bend downward, thereby expanding the size of fluid chamber  7 . The expanding of the size of fluid chamber  7  causes a corresponding drop in pressure inside fluid chamber  7 . When the pressure inside fluid chamber  7  becomes less than the pressure inside fluid inlet port  8 , 1-way passive disc valve  10  will open permitting the flow of fluid into fluid chamber  7 . When the pressure inside fluid chamber  7  becomes less than the pressure inside fluid outlet port  9 , 1-way passive disc valve  11  will close preventing a back flow of fluid from outlet port  9  into fluid chamber  7 . 
         [0021]    From t=½T-T (see  FIG. 3B ), stack  4  has expanded (i.e., increased in length), as shown in  FIG. 3A . This has caused diaphragm to bend upward, thereby decreasing the size of fluid chamber  7 . The decreasing of the size of fluid chamber  7  causes a corresponding increase in pressure inside fluid chamber  7 . When the pressure inside fluid chamber  7  becomes greater than the pressure inside fluid outlet port  9 , 1-way passive disc valve  11  will open permitting the flow of fluid into fluid chamber  7 . When the pressure inside fluid chamber  7  becomes greater than the pressure inside fluid inlet port  8 , 1-way passive disc valve  10  will close preventing a back flow of fluid from fluid chamber  7  into inlet port  8 . 
         [0022]    In this fashion, piezoelectric fluid pump  5  will continue to pump fluid from inlet port  8  to outlet port  9  until AC power source  1  is removed. 
         [0023]    Applicant built and tested a prototype of the first preferred embodiment and achieved an output power of approximately 0.1 horsepower. In comparison it is estimated that a conventional pump capable of operating at the same or similar capacity would have many more parts and would weigh 2 to 4 Kg. 
       Second Preferred Embodiment 
       [0024]    A second preferred embodiment is disclosed by reference to  FIGS. 4A-4E . In the second preferred embodiment, 1-way active disc valves  15  and  16  have replaced 1-way passive disc valves  10  and  11  of the first preferred embodiment. I-way active disc valves  15  and  16  are electrically connected to AC power sources  12  and  13  as to open and close based on electrical signals. 
       Preferred Active Disc Valves 
       [0025]      FIG. 4F  shows a top view of active disc valve  15  and  FIG. 4G  shows a perspective ¼ cutout section of active disc valve  15 . Piezoelectric actuator  15   a  is bonded to the top of metal disc valve  15   b . Piezoelectric actuator  15   a  utilizes the d 31  piezoelectric mode of operation (d 31  describes the strain perpendicular to the polarization vector of the ceramics). 
       Operation of Active Disc Valves 
       [0026]      FIGS. 4H and 4I  illustrate the operation of the preferred active disc valve. In  FIG. 4H  no electricity has been applied to the piezoelectric actuator  15   a  and metal disc valve  15   b  is sealing flow inlet port  8 . In  FIG. 4I , electricity has been applied to piezoelectric actuator and it has contracted causing metal disc valve  15   b  to bend thereby breaking the seal over inlet port  8 . Fluid can now flow through the valve. 
       Operation of the Second Preferred Embodiment 
       [0027]    In  FIG. 4A , t=0 (FIG.  4 E 1 ) and the voltage output of AC power source  1  is at a maximum. 1-way active disc valve  16  is closing in response to power source  12  and 1-way active disc valve  15  is opening in response to power source  13 . 
         [0028]    In  FIG. 4B , 0&lt;t&lt;½ T (FIG.  4 E 1 ) and the voltage output of AC power source  1  is a negative going sine function. Voltage from AC power source  1  has caused stack  4  to contract bending diaphragm  6  downward resulting in a pressure drop in fluid chamber  7 . Pressure sensor  19  has sensed a decrease in pressure inside pumping chamber  7  and has sent a signal to microprocessor  18 . Microprocessor  18  has sent a control signal to power sources  12  and  13  causing them to transmit control voltages to 1-way active disc valves  16  and  15 , respectively. The positive voltage from AC power source  13  (FIG.  4 D 2 ) has caused 1-way active disc valve  15  to open and the negative voltage from power source  12  (FIG.  4 D 1 ) has caused 1-way active disc valve  16  to remain closed. Fluid from inlet port  8  has entered pumping chamber  7 . 
         [0029]    In  FIG. 4C , ½T&lt;t&lt;T, the voltage output of AC power source  1  is a positive going sine function (FIG.  4 E 1 ), causing stack  4  to expand bending diaphragm  6  upward and resulting in a pressure increase in fluid chamber  7 . Pressure sensor  19  has sensed a decrease in pressure inside pumping chamber  7  and has sent a signal to microprocessor  18 . Microprocessor  18  has sent control signals to power sources  12  and  13  causing them to transmit control voltages to 1-way active disc valves  16  and  15 , respectively. The negative voltage from AC power source  13  has caused 1-way active disc valve  15  to close and the positive voltage from AC power source  12  has caused 1-way active disc valve  16  to open. Fluid from pumping chamber  7  has entered outlet port  9 . 
         [0030]    At time t=T (FIG.  4 E 1 ), the voltage output of AC power source  1  is again at a maximum and stack  4  is at a fully expanded condition, as shown in  FIG. 4A . 1-way active disc valve  15  is opening in response to power source  13  and 1-way active disc valve  16  is closing in response to power source  12  preventing fluid from flowing back to fluid chamber  7  through 1-way active disc valve  16 . In this fashion, piezoelectric fluid pump  5  will continue to pump fluid from inlet port  8  to outlet port  9  until AC power sources  1 ,  12 , and  13  are removed. 
         [0031]    In this fashion, piezoelectric fluid pump  5  will continue to pump fluid from inlet port  8  to outlet port  9  until AC power source  1  is removed. 
         [0032]    Due to the fast response of the piezoelectric active disc valve, the pump actuator can be cycled faster than it could with the passive disc valve. This will allow for more pump strokes per second and an increase in pump output. 
       Third Preferred Embodiment 
     MEMS Valves 
       [0033]    A third preferred embodiment is disclosed by reference to  FIGS. 5A-5F . The third preferred embodiment utilizes two passive MEMS valve arrays. 
         [0034]    In the third preferred embodiment, pump  30  is similar to pump  5  shown in  FIG. 1 , with an exception being that disc valves  10  and  11  of pump  5  have been replaced with 1-way passive microvalve arrays  31  and  32 , as shown in  FIG. 5A . Preferably, microvalve arrays  31  and  32  are two micromachined MEMS valves. 
         [0035]      FIG. 5B  shows an enlarged side view of microvalve array  31 . Microvalve array  31  is fabricated from silicon, silicone nitride or nickel and includes an array of fluid flow ports  31   a  approximately 200 microns in diameter. The array of fluid flow ports  31   a  is covered by diaphragm layer  31   b .  FIG. 5C  shows an enlarged top view of a cutout portion of microvalve array  31 . Microvalve array  31  has a plurality of diaphragms  31   c  covering each fluid flow port  31   a.    
       Operation of a Microvalve Array 
       [0036]    Microvalve arrays  31  and  32  function in a fashion similar to passive disc valves  10  and  11 . In  FIG. 5E , the pressure pressing downward on diaphragm  31   c  is greater than the pressure of fluid inside fluid flow port  31   a . Therefore, diaphragm  31   c  seals fluid flow port  31   a . Conversely, in  FIG. 5F , the pressure pressing downward on diaphragm  31   c  is less than the pressure of fluid inside fluid flow port  31   a . Therefore, diaphragm  31   c  is forced open and fluid flows through fluid flow port  31   a.    
         [0037]    Applying this principle to the third preferred embodiment, when the pressure inside fluid chamber  7  becomes less than the pressure inside fluid inlet port  8 , individual valves within the multitude of microvalves in microvalve array  31  will open permitting the flow of fluid into fluid chamber  7 . When the pressure inside fluid chamber  7  becomes less than the pressure inside fluid outlet port  9 , the individual valves within the multitude of micro valves in the microvalve array  32  will close preventing a back flow of fluid from outlet port  9  into fluid chamber  7 . 
         [0038]    Likewise, when the pressure inside fluid chamber  7  becomes greater than the pressure inside fluid outlet port  9 , the individual valves within the multitude of micro valves in microvalve array  32  will open permitting the flow of fluid into outlet port  9 . When the pressure inside fluid chamber  7  becomes greater than the pressure inside fluid inlet port  8 , the individual valves within the multitude of micro valves in microvalve array  31  will close preventing a back flow of fluid from fluid chamber  7  into inlet port  8 . 
         [0039]    Due to its small size and low inertia, the microvalve array can respond quickly to pressure changes. Therefore, pump output is increased because it can cycle faster than it could with a more massive valve 
       Fourth Preferred Embodiment 
     Active MEMS Valve Operation 
       [0040]    A fourth preferred embodiment is similar to the second preferred embodiment described above in reference to  FIGS. 4A-4E , with the exception that active disc valves  15  and  16  ( FIG. 4A ) are replaced with active microvalve arrays  41  and  42  ( FIG. 6A ). 
         [0041]      FIG. 6B  shows an enlarged side view of microvalve array  41 . Microvalve array  41  is fabricated from silicon and includes an array of “Y” shaped fluid flow ports  41   a  approximately 200 microns in diameter. Preferably, microvalve array  42  is identical to microvalve array  41 . Below the junction of each “Y” are heaters  41   b . Heaters  41   b  for microvalve array  41  are electrically connected to power source  51  and heaters  41   b  for microvalve array  42  are electrically connected to power source  52 . Pressure sensor  19  senses the pressure inside fluid chamber  7  and sends a corresponding signal to microprocessor  18 . Microprocessor  18  is configured to send control signals to power sources  51  and  52 . 
       Operation of an Active Microvalve Array 
       [0042]    Microvalve arrays  41  and  42  function in a fashion similar to active disc valves  15  and  16 . For example, in  FIG. 6B  active microvalve array  41  is open. Fluid is able to flow freely through fluid flow ports  41   a . In  FIG. 6C , microvalve array  41  is closed. Power source  51  has sent voltage to heaters  41   b  of microvalve array  41 . Heaters  41   b  have heated the adjacent fluid causing a phase change to a vapor phase and the formation of high pressure bubbles  41   c . High pressure bubbles  41   c  block fluid flow ports  41   a  for a short time closing microvalve array  41 . The lack of mass or inertia due to there being no valve diaphragm permits very fast response which enables the valves to open and close at high a frequency beyond 100 kHz. 
         [0043]    Applying this principle to the third preferred embodiment, when piezoelectric stack  4  contracts and the pressure inside fluid chamber  7  becomes less than the pressure inside fluid inlet port  8 , pressure sensor  19  will send a corresponding signal to microprocessor  18 . Microprocessor  18  will then send a control signal to power sources  51  and  52 . Consequently, individual valves within the multitude of microvalves in microvalve array  41  will open permitting the flow of fluid into fluid chamber  7  ( FIG. 6B ). Also, individual valves within the multitude of micro valves in the microvalve array  42  will close ( FIG. 6C ) preventing a back flow of fluid from outlet port  9  into fluid chamber  7 . 
         [0044]    Likewise, when piezoelectric stack  4  expands and the pressure inside fluid chamber  7  becomes greater than the pressure inside fluid outlet port  9 , pressure sensor  19  will send a corresponding signal to microprocessor  18 . Microprocessor  18  will then send control signals to power sources  51  and  52 . Consequently, the individual valves within the multitude of micro valves in microvalve array  42  will open permitting the flow of fluid into outlet port  9 . Also, the individual valves within the multitude of micro valves in microvalve array  41  will close preventing a back flow of fluid from fluid chamber  7  into inlet port  8 . 
         [0045]    Due to its ability to anticipate the need to open and close, the active microvalve array can respond very quickly. Hence, the pump can cycle faster and pump output is increased. 
       Fifth Preferred Embodiment 
     Resonant Operation 
       [0046]    The fifth preferred embodiment recognizes that at certain frequencies generated by AC source  1 , stack  4  will resonate. As stack  4  resonates, the amount of electrical energy required to displace stack  4  by a given amount will decrease. Therefore, the efficiency of the piezoelectric pump will be increased. 
         [0047]    Any electromechanical spring/mass system (including piezoelectric stack  4 ) will resonate at certain frequencies. The “primary” or “first harmonic” frequency is the preferred frequency. In the fifth preferred embodiment, AC power source  1  an electrical drive signal to the piezoelectric stack  4  at or near the primary resonant frequency. That frequency is calculated by using the mass and modulus of elasticity for the piezoelectric stack: f=sqrt(k/m) where m is the mass of the resonant system and k is the spring rate (derived from the modulus of elasticity). When in resonance, the amplitude of the motion will increase by a factor of 4 or 5. Thus for a given pump stroke, the drive voltage and electrical input power can be reduced by a similar factor. 
         [0048]    For example,  FIG. 7  shows a graph of output pressure versus frequency for two pump configurations: A pump having a piezoelectric stack with a length of 3.2 inches, and a pump having a piezoelectric stack with a length of 0.8 inches. As can be seen by the graph, when the pump is operated so that the piezoelectric stack resonates, it is possible to achieve approximately a 300% increase in efficiency. 
       UTILIZATION OF THE PRESENT INVENTION 
       [0049]    The present invention can be utilized for a variety of purposes. One preferred purpose is illustrated in  FIG. 8 . In  FIG. 8 , pump  5  is utilized to pump hydraulic fluid to hydraulic actuators  91 - 99 . The hydraulic actuators are utilized for the primary flight control system for a remotely piloted vehicle. In the preferred embodiment shown in  FIG. 8 , piezoelectric pump  5  pumps hydraulic fluid to hydraulic actuators  91 - 99  at a flow rate of up to 60 cc/second. The high hydraulic power output permits fast aircraft control surface adjustments. The combination of high power and light weight materials permits fast aircraft maneuvering that would otherwise not be feasible. 
         [0050]    Although the above-preferred embodiments have been described with specificity, persons skilled in this art will recognize that many changes to the specific embodiments disclosed above could be made without departing from the spirit of the invention. Therefore, the attached claims and their legal equivalents should determine the scope of the invention.