Patent Publication Number: US-6659740-B2

Title: Vibrating membrane fluid circulator

Description:
This is a continuation in part of application Ser. No. 09/745,405 filed on Dec. 26, 2000 which is a continuation application of application Ser. No. 09/117,982 filed Aug. 11, 1998, now abandoned. 
    
    
     The present invention relates to a vibrating membrane fluid circulator. 
     Numerous types of pump are known both in industrial and in biomedical fields. The following can be mentioned: 
     reciprocating positive displacement pumps whose main elements are pistons or membranes associated with admission and delivery valves. Their main drawback lies in the cyclical aspect of their motion and in the presence of the valves; 
     so-called “peristaltic” positive displacement pumps in which continuously moving wheels deform and compress a flexible tubular pump body. The compression can be damaging for certain liquids to be pumped that include sensitive elements (e.g. blood); 
     “impeller” pumps such as centrifugal pumps based on a vaned rotor or a vortex. Their drawback lies in the high speed of rotation which generates shear in the fluid streams, friction, and cavitation, all of which phenomena can be damaging to fragile fluids; and 
     axial turbine pumps in which fragile fluids suffer likewise from the same drawbacks as in the preceding pumps. 
     Also known is a vibrating-membrane fluid propulsion device, as described in document FR-A-2 650 862. That device provides a technical solution which is not always suitable for obtaining the hydraulic performance required by most industrial and biomedical applications, 
     The vibrating membrane fluid circulator of the invention proposes solutions whereby the fields of application of the circulator are enlarged, the hydraulic performance thereof is improved, the circulator is more compact, and finally the pump body can he for a single use only, which is advantageous in the biomedical field. 
     To this end, the fluid circulator of the invention comprises an internal hydraulic circuit made up in succession of an admission orifice, a pump body and a delivery orifice, the pump body having two rigid walls defining therebetween a pumping chamber for the fluid extending from said admission orifice to said delivery orifice with a deformable membrane located in said pumping chamber and having two external surfaces facing respectively said walls, at least one of said membrane surfaces and at least one said walls defining in said pumping chamber a circulation space for the fluid, said deformable membrane being maintained under a tension parallel to the fluid circulation direction from said admission orifice to said delivery orifice, said membrane having one edge located near said admission orifice and provided with means for coupling to a motor member generating a periodic excitation force substantially normal to the external faces of said membrane, said circulation space having a cross section perpendicular to the fluid circulation direction the size of which measured in the periodic force direction being progressively decreasing from said admission orifice to said delivery orifice. 
     Means to keep the membrane under tension enable it to constitute a medium for waves travelling from the edge of the membrane subjected to the excitation force towards its opposite edge. Displacement of these waves is accompanied by forced damping due to the shape of the rigid walls, which results in a reduction of the width (thickness) of the cross section of the circulation space along the circulation direction, so that mechanical energy is transferred from the membrane to the fluid, with this appearing in the form of a pressure gradient and of a fluid flow. The characteristics of the pressure gradient and of the fluid flow are related to the dimensions of the pump body, to the dimensions of the membrane, to the shape and the spacing of the rigid walls, to the mechanical characteristics and the tension state of the membrane, and to the parameters of the excitation applied thereto. 
     The periodic excitation of the membrane is implemented at frequencies which are associated with the mechanical characteristics of the membrane and with its tension state. The excitation frequency should be kept down to low values of the order of 40 Hz to 80 Hz so as to avoid localized pressure effects and shear effects between fluid streams. 
     In one embodiment of the invention, said pumping chamber is a flat tubular chamber and the membrane is a flat membrane tapered towards the edge thereof located near said delivery orifice. 
     In another embodiment of the invention, said pumping chamber is an annular tubular chamber and the membrane is shaped as a sleeve with a larger thickness at its edge near said admission orifice than at its edge near said delivery orifice. 
     Other characteristics and advantages appear from the description given below of various embodiments of the invention. 
    
    
     Reference is made to the accompanying drawings, in which: 
     FIG. 1 is a longitudinal section view through a tubular pump body for a longitudinal type fluid circulator, said view being fragmentary and diagrammatic; 
     FIG. 2 is a longitudinal section view through a pump body of a cylindrical type fluid circulator; 
     FIG. 3 is a diagrammatic longitudinal section view of FIG. 1 with one embodiment of motor means; 
     FIG. 4 is a section view of the invention like FIG. 3 with another embodiments of motor means and membrane; 
     FIG. 5 is a section view of a variant of FIG. 4 with other motor means; 
     FIGS. 6 and 7 are two orthogonal section views of a sleeve shaped membrane; 
     FIGS. 8 and 9 are orthogonal section views of an embodiment of the tubular pump as diagrammatically illustrated by FIG. 2; 
     FIG. 10 is a functional sketch of the motor means of FIGS.  8  and  9 . 
    
    
     The device of the invention shown in FIG. 1 comprises a hydraulic circuit made up in succession of an admission orifice  1 , a pump body  2 , and a delivery orifice  3 . The pump body  2  is a flat tube of varying section which defines a pumping chamber  4  by rigid walls  5 ,  6 ,  7 , and  8 . In the chamber  4  there is housed a deformable propulsion membrane  9  which is in the form of a flexible elastomer strip of width equal to the distance between the walls  7  and  8 . Motor means (not shown) generates a periodic excitation force  10  which is applied to coupling means at the edge  11  of said membrane  9  adjacent to the admission orifice  1 , said force being regularly distributed over the edge of the membrane and having a direction that is normal to the external faces  9   a  and  9   b  of the membrane  9 . The membrane  9  is maintained under tension by members (not shown) developing forces  12  and  13  in opposite directions and applied to the membrane at the edge  11  and at the edge  14  which is near the delivery orifice  3 . The membrane  9  defines in the pumping chamber  4  either one or two circulation spaces  4   a  and  4   b  for the fluid. These spaces may be either tightly separated (if the membrane is laterally joined with flexible diaphragm with walls  7  and  8 ) or in communication along these lateral walls and through apertures made in the membrane at its edge near the admission orifice. When excited, the membrane is thus a medium for waves travelling from the edge  11  which is subjected to the excitation towards the other edge  14  which is situated adjacent the delivery orifice. Wave displacement is accompanied by forced damping due to the shape and to the spacing of the rigid walls  5  and  6 , resulting in a progressive decreasing of the thickness of the circulation spaces  4   a  and  4   b  from the admission orifice towards the delivery orifice. 
     The damping causes energy to be transferred from the membrane  9  to the fluid, with this being in the form of a pressure gradient and a flow of fluid. 
     Overall the circulator constitutes an energy transducer, successively transferring energy from the excitation motor to the membrane and then from the membrane to the fluid. The energy delivered by the exciter depends on various parameters such as the excitation force, the excitation frequency, and the amplitude of excitation which is itself associated with the excitation frequency and the force. It is thus possible to modulate the energy delivered by the exciter by acting on the various parameters that have an effect on the energy delivered to the membrane. 
     The mechanical energy in the membrane  9  must essentially behave as a flow of mechanical energy propagating by means of the membrane from the excitation edge  11  where energy is transferred from the exciter to the membrane, towards the other edge of the membrane. This energy comprises a kinetic energy fraction and a deformation energy fraction, and there are physical limits on such operation. The transfer of energy from the membrane to the fluid takes place progressively along the length of the membrane with the waves simultaneously propagating and being damped. 
     The hydraulic energy of the fluid is expressed as the hydraulic power delivered by the circulator, i.e. the product of the flow rate multiplied by the pressure gradient, with the relationship between flow rate and pressure depending mainly on the dimensions of the pump body and of the membrane, and on the spacing and the shape of the rigid walls  5  and  6 , this also taking into account the internal headlosses of the system. 
     A variant of the device is shown in FIG. 2, where the hydraulic circuit is cylindrical and comprises an admission orifice  15 , a pump body  16 , and a delivery orifice  17 , the pump body defining a pumping chamber  18  between walls  19  and  20  that are rigid, circularly symmetrical, and coaxial. The chamber  18  is of annular cross section with a radial thickness which decreases from the admission orifice  15  to the delivery orifice  17 . A deformable tubular membrane  21  is housed in the tubular space  18  and is made of silicone elastomer, for example. This tubular or sleeve shaped membrane  21  defines in the pumping chamber  18  one or two circulation spaces  18   a  and  18   b  which can be either totally separated or in communication. An excitation motor member (not shown) generates a radial and regular distribution of periodic excitation forces  22 , said distribution of forces being applied by means of a coupling to the edge  23  of the tubular membrane  21  adjacent to the admission orifice. The membrane is held under axial tension between the edges respectively near the admission and the delivery orifices by means (not shown) generating an axial regular distribution of tension forces  24  and  25  in opposite directions applied to the edges  23  and  26  of the membrane. 
     The membrane  9  shown FIG. 3 has an edge  11  near the admission orifice  1  thicker than the edge  14  near the delivery orifice  3 . This edge  14  includes means  30  (a terminal rib for example) clamped into fixation means  31  of the pump body  2 , having a transverse grove for the rib  30  and longitudinal slits for the fluid output. 
     A permanent magnet  32  is secured the thicker edge  11  of the membrane in front of a pole piece  33 . The poles of the magnet are spaced from each other in a direction perpendicular to the membrane and the pole piece  33  has poles  33   a ,  33   b  and  33   c  which can change depending on the direction of the current in a coil  34 . The pole piece and the coil constitute a variable magnetic field generator which moves the magnet  32  up and down generating waves in the membrane  9 . The magnet or the securing structure thereof with the membrane may be guided in guide means not shown provided on the pump body  2 . These guide means cooperate with fixation means  31  to put and maintain the membrane under longitudinal tension with a possible adjustment thereof. 
     FIG. 4 shows a variant embodiment of FIG. 3 in which the pump body  2  has a lateral admission orifice  1  and is closed near the thickest edge of the membrane  9  by flexible lips  35  tightly joined to the pump body  2 . Membrane  9  is coupled beyond the lips to a magnetic motor  36  having a movable core  37  secured to the membrane  9  and a pole piece  38  with a coil  39  for periodically attracting the core into the air gap of the pole piece by a control current supplied to the coil. A blade spring  40  generates the necessary return force for having an oscillating vertical movement of the thickest edge of the membrane. Tension forces are created and maintained between the spring  40  and the fixation means  31 . 
     In FIG. 5 motor means are embodied as a piezoelectric displacement generator  41 . 
     FIG.  6  and FIG. 7 show a tubular or sleeve shaped membrane  21  for the circulator of FIG.  2 . This membrane has a thick edge  23  and a thin edge  26 , the edge  26  being extended by a diaphragm sleeve  42  used to apply longitudinal tensile force to the sleeve. This diaphragm sleeve may be made of a material different from the membrane  21  and is provided with a terminal rib  43  for fixation into the pump body. The transversal section of FIG. 7 shows that the membrane  21  is made of a plurality of longitudinal lugs  44  laterally linked each other by a flexible diaphragm portion  45 . In the illustrated case the diaphragm portion joints obliquely two adjacent lugs, extending from the internal face of one lug to the external face of the adjacent one. This structure allows an ability to a radial expansion and contraction of the tubular membrane under minimal radial forces. 
     FIGS. 8 to  10  show a circulator with a sleeve shaped membrane  21  located in a pump body  16  secured with its thin edge to this body in the same manner as the flat membrane is secured to the flat tubular body (FIG. 3) and coupled by its thick edge to a radial periodic forces generator  46 . This generator includes permanent magnets  47  secured to the thick edge  23  of the membrane and extending along radial directions which are regularly distributed around the membrane. These magnets are maintained (or guided) in individual pockets  48  of the pump body. Between these pockets are located ferromagnetic cores  49  with coils  50  defining a plurality of electromagnets. The opposite poles of each magnet are radially spaced each from the other. For two consecutive permanent magnets, the north and south poles are inverted. In the rest state of the membrane, the average line  51  of the poles of the electromagnet is located between the poles of the permanent magnets  47 . By supplying the coils  50  with an alternative current, the sign of the poles on the line  51  changes periodically and generates successive attraction of each pole of the permanent magnets along their radial alignment, thus generating periodic expansions and contractions of the membrane  21 . 
     In each embodiment of the invention, the membrane excitation means are constituted by an electromagnetic motor whose feed circuit for receiving excitation alternating current includes a power amplifier circuit and a circuit for generating an excitation signal so as to provide the possibilities of modulating amplitude, of programming, of storage, and of generating complex excitation signals, enabling the circulator of the invention to comply with numerous applications.