Abstract:
A membrane actuated fluid dispensing head apparatus and method for dispensing fluids. The dispenser housing has a top plate, a bottom plate, and a fluid distribution plate disposed between the top and bottom plates. The top plate has fluid inlet means therethrough for admitting pressurized fluid over the distribution plate, the bottom plate having a plurality of elongated hollow pipettes thereon extending away from the top plate and in fluid communication with the fluid distribution plate. A first resilient membrane is disposed between the fluid distribution plate and the bottom plate, the bottom plate having a plurality of spaced cavities thereon having outer peripheries and in fluid communication with the pipettes. A second resilient membrane is disposed between the top plate and the distribution plate having an opening therethrough. The fluid distribution plate has a plurality of spaced apertured members having outer peripheries, some of the outer peripheries of the members substantially coinciding with some of the outer peripheries of the cavities whereby, when a pressurized source of fluid is injected into the dispenser housing via the inlet means, the fluid flows under pressure over the fluid distribution plate, out of the apertures in the members and against the membrane forcing portions of the membrane down into the cavities and out the pipettes.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to fluid dispensing apparatus and method for dispensing liquids; and, more particularly, to a membrane actuated fluid dispenser for delivering the fluid through a plurality of pipettes. 
     2. Related Art 
     Dispensing apparatuses capable of simultaneously delivering fluid through a plurality of pipettes are well known in the art. One such example is shown in U.S. Pat. No. 3,572,552, to Guinn and No. 3,807,235 to Lefkovits. Both patents use vacuum or pressure only which does not address the diaphragm (membrane) sag problem. When an elastic membrane is clamped down, it attempts to squeeze into available voids. The cavities are available voids and the excess membrane material bunches up in the cavity and sometimes wrinkles and sags into the cavity. This adversely affects the accuracy of the dispensed volume. 
     In addition, diaphragm blockage of holes is a problem with certain cavity shapes and hole locations. These patents that use a flat surface immediately above or below the cavity are subject to this. When the diaphragm wrinkles or sags, then vacuum or pressure is applied, if the diaphragm has a sag or wrinkle near the hole then the wrinkle or sag gets forced over the hole, thus blocking its operation. 
     There is an uneven sealing towards the center of the array of cavities that results when a membrane is peripherally clamped between two large flat plates. It is difficult to seal such an arrangement because the large forces required will bend the plates and they will actually lift up in the center, thus unsealing the center cavities. 
     Membranes that conform to the shape of the chamber as in these prior art patents forego the possibility of variable volume dispensing. 
     The use of fixed dispensing needles makes cleaning and contamination control much more difficult. 
     such prior art devices allows the dispensed fluid to enter the cavity. This makes it difficult to clean and control contamination. 
     There is thus a need for a fluid dispenser which dispenses a liquid through one or more pipettes in a controlled manner. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide an improved apparatus and method for dispensing liquid out of at least one pipette. 
     It is a further object of this invention to utilize fluid under pressure to flex a membrane against apertured cavities in a plate deforming the membrane into the cavities and out apertures in the cavities into hollow pipettes aligned with the cavities. 
     It is an object of this invention to carry out the foregoing object by reversing the pumping of fluid thereby drawing liquid into which the pipettes may be disposed up into the pipettes wherein reversing the air pressure ejects the drawn-up liquid out of the pipettes. 
     These and other objects are preferably accomplished by providing a membrane actuated fluid dispensing head having a dispenser housing with a top plate, a bottom plate, and a fluid distribution plate disposed between the top and bottom plates. The top plate has fluid inlet means therethrough for admitting pressurized fluid over the distribution plate, the bottom plate having a plurality of elongated hollow pipettes mounted thereon extending away from the top plate and in fluid communication with the fluid distribution plate. 
     A first resilient membrane is disposed between the fluid distribution plate and the bottom plate, the bottom plate having a plurality of spaced cavities thereon having outer peripheries and in fluid communication with the pipettes. A second resilient membrane is disposed between the top plate and the distribution plate having an opening therethrough. The distribution plate has a plurality of spaced apertured members having outer peripheries, some of the outer peripheries of the members substantially coinciding with some of the outer peripheries of the cavities whereby, when a pressurized source of fluid is injected into the dispenser housing via the inlet means, the fluid flows under pressure over through the opening in the second membrane over the distribution plate, out of the apertures in the members and against the membrane forcing portions of the membrane down into the cavities and out the pipettes. 
     The injection of pressurized fluid can be used to pump fluid out the pipettes, then reversed to draw liquid up into the pipettes (when dipped into a liquid), then reversed again to eject the liquid out the pipettes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is an assembled perspective view of the membrane dispensing head apparatus of the invention; 
     FIG. 2 is an exploded view of a portion of the apparatus of FIG. 1; 
     FIG. 3 is a view taken along line  3 - 3  of FIG. 5 but illustrating the opposite side of plate  31 ; 
     FIG. 4 is a view taken along line  4 - 4  of FIG. 2; 
     FIG. 5 is a view taken along line  5 - 5  of FIG. 2; and 
     FIG. 6 is a top plan view of the plate  39  alone of FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1 of the drawing, a membrane dispensing head apparatus  10  is shown having an injector in the form of a syringe  11  coupled to top plate  12  of apparatus  10  by flexible tubing  13 . Syringe  11  includes the usual plunger  14  and an internal spring  15  for delivering a fluid, such as air or oil, under pressure, upon actuation of plunger  14 , through tubing  13  to the inlet  16  coupled to top plate  12 , as by threading into a threaded hole therein, as is well known in the art. Inlet  16  is in fluid communication with both sides of top plate  12 . 
     As seen in FIG. 2, the various components of apparatus  10 , excluding syringe  11  and tubing  13 , is shown in exploded view. Thus, top plate  12  has a plurality of nonthreaded corner through-holes  17  about its periphery for received threaded bolts  18  therethrough for reasons to be discussed. One or more quick release knobs, such as two threaded knobs  19 ,  20 , having knurled enlarged heads  21 ,  22 , respectively, may be provided adapted to extend into side holes  23  (the hole in plate  12  associated with knob  19  is not visible) to provide a quick, release. That is, each knob  19 ,  20  has a smooth upper shaft portion  19 ′,  20 ′, respectively, and a lower integral threaded shaft portion (only  20 ″ visible in FIG. 1) so that the upper shaft portions extend through non-threaded holes  17  (and aligned holes to be discussed), the threaded portions exiting out of the assembled plates in FIG. 1 whereby the latter may be threaded to suitable apparatus (not shown) in which apparatus  10  is to be used. Knobs  21 ,  22  may be rotated to quickly and easily secure apparatus  10  in position or release the same. A plurality of spacers and washers, such as washer  24  and spacers  25 ,  26 , may be provided with each knob. 
     Oppositely spaced unthreaded holes  117  and  118  are also provided through plate  12  for receiving a pair of spaced alignment pegs therethrough, as will be discussed. 
     Top plate  12  is adapted to abut against flexible inner overlay  27 , which is configured similarly to plate  12 , having an elongated slot  28  therethrough close to one edge of plate  31  for reasons to be discussed. A plurality of corner peripheral holes  29  extend through overlay  27  aligned with holes  17 . Like side holes  30  are also provided aligned with holes  23 . Holes  29 ′,  29 ″ are aligned with holes  117 ,  118 , respectively. 
     A fluid distribution plate  31  is provided sandwiched between a lower overlay  32 , also of a resilient material, and first overlay  27 . Plate  31  has a plurality of spaced grooves  200  aligned with holes  35  (see FIG. 3) as will be discussed. 
     Distribution plate  31  is configured similarly to plate  17  and overlays  27 ,  32  and has a plurality of elongated spaced circular ridges  33  (see FIG. 3) extending transversely across plate  31  and facing plate  39 . Plate  31  has a plurality of rows of spaced concave depressions  34  concentrically disposed within each of the circular raised ridges  33 , each depression  34  having one or more apertures  35 , preferably two adjacent each side of the circular ridge, therethrough for reasons to be discussed. Peripheral corner holes  35 ′ through plate  31  are aligned with aforementioned holes  29 ,  17 . Like side holes  36  are aligned with aforementioned holes  23 ,  30 , hole  100  is aligned with holes  29 ′,  117  and hole  101  is aligned with holes  29 ″,  118 . 
     The lower overlay  32  also has peripheral corner holes  37  aligned with holes  35 ′,  29  and  17  and side holes  38  aligned with holes  36 ,  30  and  23 . Overlay  32  is of a flexible material and abuts against a pipette plate  39 . Overlap  32  also has a hole  103  aligned with holes  101 ,  29 ″ and  118 , and a hole  102  aligned with holes  100 ,  29 ′ and  117 . Pipette plate  39  is of a rigid material and has a plurality of comer peripheral threaded holes  40  aligned with holes  37 ,  35 ′,  29  and  17 . Plate  39  also has spaced side holes  41  aligned with holes  38 ,  36 ,  30  and  23 . Upstanding pegs  104 ,  105  are fixedly mounted on plate  39  extending toward plate  12 . 
     A plurality of spaced rows of concave depressions  42  are provided in bottom plate  39 . As seen in FIG. 4, each depression  42  has a central hole  43  (FIG. 6) and is aligned at its center or bottom area  44  with an elongated needle or pipette  45 . Each pipette  45  is hollow and its interior opens into fluid contact with the interior of each depression  42  via holes  43 . Circular ridges  33  are able 0.010″ high and in width and serve a double function. Without raised ridges  34 , thousands of pounds of pressure would be needed to compress the membrane  32  enough so that it will seal. When this much pressure is applied at the periphery of the housing, the entire plate warps and the membrane would., not seal the cavities toward the center of the housing. The circular ridges  33  provide an individual seal through pressure on the membrane around each depression  34  and around each cavity  42  that requires just one or two pounds to seal each cavity in pipette plate  39 . Now, only a couple of hundred pounds are needed to seal the membrane  32  and the top and bottom plates  12 ,  39  do not bend enough to create any leakage. 
     When vacuum is applied to aspirate (suck up) the dispensed medium, if the membrane  32  was allowed to cover the small holes  35  in the fluid distribution plate  31 , then the membrane  32  would not be drawn up tight against the distribution plate  31  because the vacuum would be cut off by the membrane  31  covering the holes  35 . By putting the small holes  35  immediately adjacent to the inside wall of the circular ridges  33 , the membrane  32  is unable to stretch enough to conform to the sharp vertical walls of the ridge  33  and cover the holes  35 . 
     Although two holes  35  adjacent each side of cavities  34  are disclosed, this number can vary. More holes allows for the use of a more viscous fluid than air. Larger/smaller holes could be used for faster/slower delivery or aspiration. 
     In assembly of the parts in FIG. 2, overlay  32  may be placed against plate  39 , pegs  104 ,  105  entering holes  102 ,  103 , respectively (pegs  104 ,  105  may be off-center from each other along with their respective holes forming alignment means for the assembled parts). 
     Plate  31 , with depressions  34  facing overlay  32 , is now mounted on top of overlay  32 , peg  104 , entering aligned holes  102 ,  100  and peg  105  entering aligned holes  103 ,  101 . Overlay  27  is now mounted against plate  31 , slot  28  transversely crossing the ends of the spaced grooves  200  adjacent the edge of plate  31 . Peg  105  extends through and aligns with holes  103 ,  101  and  29 ″. Peg  104  extends through and aligns with holes  102 ,  100  and  29 ′. 
     Finally, top plate  12  is mounted against overlay  27 , peg  105  entering hole  118  and peg  104  entering hole  117  thus aligning the assembled parts. Screws  18  are now extended through the non-threaded end peripheral aligned holes in overlays  27 ,  32  and plate  31  and threaded into threaded end peripheral holes  46  in plate  39 . 
     Knobs  21 ,  22  may be extended through the aligned side peripheral holes with the threaded portions  20 ″ extending on the outside of plate  39  whereby the entire apparatus may be secured to its intended application. Tubing  13  is inserted into inlet  16  and secured therein in any suitable manner. 
     In operation, pressurized pumping fluid is supplied to inlet  16  (illustrated by the syringe  11  being actuated downwardly), to force the pumping fluid under pressure through tubing  13  and through slot  28  of overlay  27 . This fluid, under pressure, is distributed across manifold plate  27  into one end of the grooves  200 , along grooves  200 , and through holes  35  and about depressions  34  on the opposite side of manifold plate  31 . The depressions  34  are aligned with depressions  42  in plate  39  (separated by flexible overlay  32  which is the elastic membrane). 
     Thus, fluid pressure against the inner overlay  32  distends overlay  32  forcing the portions of overlay  32  overlying depressions  42  against and down into the same, thus, in effect, pumping fluid out of holes  43  through the aligned pipettes  43  and dispensing whatever liquid may be in the pipettes. The pipettes  43  at this stage may be disposed in a suitable liquid. 
     Plunger  14  of syringe  11  is now released and, under spring pressure, returns to the FIG. 1 position drawing the membrane  32  back up to plate  31  and also drawing liquid up through the pipettes. Syringe  11  is now reactivated, thus again applying fluid pressure ejecting the drawn-up liquid out of the pipettes. 
     Any suitable materials and dimensions may be used. For example, overlays  27  and  32  may be made of silicon rubber. Plate  31  may be of stainless steel. DELRIN® plastic may also be used. Plates  12  and  39  may be of stainless steel along with pipette  45  or nipple for disposable tips secured thereto in any suitable manner. 
     Although a particular number of ridges  33  and aligned grooves  200  are disclosed, any suitable number may be used. Any suitable number of depressions  34 ,  42  may also be used along with any suitable number or placement of holes  35 ,  43 . For example, the outer peripheral rows of depressions in both plates  31 ,  39  may not be apertured if desired. 
     Any suitable rigid non-porous material may be used with strategically placed openings where the fluid can exit and be forced against membrane overlay  32  to flex the same down into cavities or depressions  42 . 
     Although a conventional syringe  11  is disclosed for delivering fluid under pressure, obviously more sophisticated conventional pressure regulated pressurized fluid apparatus may be used. Thus, both pressure and vacuum may be used. 
     Instead of fixed stainless steel pipettes, nipples with disposable tips may be mounted on the pipettes and removed therefrom. Although the term pipette has been used to refer to the spaced apertured members, spaced nipples may be used receiving the disposable types thereon. The spaced nipples broadly act as pipettes receiving the removable nipples therefrom. 
     The apparatus disclosed herein may be used as a fluid dispensing head in other suitable apparatus. For example, such other apparatus may provide for the dispensing head apparatus of the invention to fill pipette  45  at one position, then dispense the sucked in liquid at another. Such other apparatus could also provide regulated pressurized fluid (where the pressure can be positive, negative or both) to the apparatus  10  without the syringe  11 ). This other apparatus can be made integral to the apparatus or can be a separate module connected with appropriate tubes and/or wires for control. The head movement apparatus can be simply a provision for handheld movement or at the other extreme it can be attached to a fully automated robotic device. Alternatively, the head can remain in one location and the reservoir and item the liquid is being dispensed to can move to the head. The movement apparatus and the pressurized fluid source may be any suitable apparatus well known in the art. 
     Thus, the apparatus  10  may be a handheld low priced device that could possibly have the pressure pump and electrical control elements combined in a single unit attached to the apparatus. The other extreme would have the apparatus attached to a robotic arm and the pressure pump and electrical controls remotely located and controlled by a computer. In between the two extremes other configurations may occur to one skilled in the art. 
     Any suitable dimensions may be used. For example, overlays  27  and  32  may be about 0.030″ thick. Slot  28  may be about {fraction (31/2)} inches long and ⅛-inch wide. Plates  12  and  39  may be about 0.5″ thick. Manifold plate  31  may be about 0.025″ thick. Apparatus  10 , without syringe  11 , may be a portable handheld device. Depressions  34  and  42  may be about 0.2″ in diameter. Holes  43  may be about 0.027″ in diameter. Holes  35  may be about 0.01″ in diameter. Pipettes  45  may have openings about 0.027″ in inner diameter and about 0.040″ on the outer diameter. 
     By using vacuum and pressure in my invention, wrinkles and sags are taken up by forcing the membrane into contact with the lower surface of the pumping fluid distribution plate. 
     The small holes placed immediately next to the inside wall of the “circular ridges” avoids this problem in the prior art. 
     The “circular ridges” provide sealing even though low clamping forces are used. The invention can easily be adapted to the use of disposable commercially available dispensing tips. 
     By using a regulated an calibrated fluid pressure source, such as an air pump and a vacuum pump working through an adjustable regulator, complete control is provided over the dispensing mechanism up to the limits of the volume range that it was designed for. None of the prior art patents addresses the problem of dispensing the small amount that would remain in the needle or dispensing tip due to capillary action. The invention herein allows for a small extra mount of delivery pressure to dispense this small amount. 
     The size of the pipettes or needles disposable tips may be adjusted so that the dispensed fluid never enters the cavities. The volume within the needles or tip is sufficient to hold the entire dispensed volume. 
     Advantages of my invention are as follows: 
     1. Low membrane clamping pressure (because of the circular ridges) on the membrane allows use of molded plastic parts for high volume production; 
     2. No possibility of blockage of holes by the membrane; 
     3. Variable volume because of the use of an adjustable and regulated source of pumping fluid pressure. By arranging for a small increase in the delivery pressure, the small remaining volume in the tip can be dispensed if desired; 
     4. Easily cleaned if adapted to use commercially available disposable tips; and 
     5. Much lower cost than using individual syringes. 
     Membranes  32  may be made of metal or other elastic material. 
     Changing the overall height of the circular ridges can provide increased volume. 
     Prior art devices do not address contamination or cleaning. The dispensed volume of my invention is intended to remain within the needle or disposable tip. Thus, only the needle needs to be cleaned and the membrane and chamber never contact the dispensed fluid. If disposable tips are used, the tips are changed to eliminate cleaning and contamination. 
     An extra shot of dispensing air pressure to expel portion retained by capillary action can easily be accomplished with my invention while it is not easily accomplished with those inventions that use excess pressure or vacuum to force the membrane to conform to the shape of the cavity. Forcing conformance also puts a concentrated stress point on the membrane at the opening where the vacuum or pressure tries to force the membrane through the hole. 
     Use of regulated and calibrated vacuum and pressure to vary the volume within a volume range specific for the materials and dimensions of the particular dispensing head allows for easy varying of the dispensed volume. 
     Although a particular embodiment of the invention is disclosed, variations thereof may occur to an artisan and the scope of the invention should only be limited by the scope of the appended claims.