Abstract:
A method for rapidly and uniformly mixing solutions within a biochemical analyzer by rapidly and repeatedly moving a sampling probe in a two-dimensional boomerang-curved pattern within the solution.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method and apparatus for uniformly mixing liquid samples, reagents, or other solutions in a container. In particular, the present invention provides a method for rapidly and uniformly mixing a liquid solution by repeatedly moving a sampling probe needle in a two-dimensional curved pattern within the solution.  
       BACKGROUND OF THE INVENTION  
       [0002]     Various types of analytical tests related to patient diagnosis and therapy can be performed by analysis of a liquid sample taken from a patient&#39;s infections, bodily fluids or abscesses. These assays are typically conducted with automated clinical analyzers onto which tubes or vials containing patient samples have been loaded. The analyzer extracts liquid sample from the vial and combines the sample with various reagents in special reaction cuvettes or tubes. Usually the sample-reagent solution is incubated or otherwise processed before being analyzed. Analytical measurements are often performed using a beam of interrogating radiation interacting with the sample-reagent combination, for example turbidimetric, fluorometric, absorption readings or the like. The measurements allow determination of end-point or rate values from which an amount of analyte related to the health of the patient may be determined using well-known calibration techniques.  
         [0003]     Clinical analyzers employ many different processes to identify analytes and throughout these processes, patient liquid samples, and samples in combination with various other liquids like reagents or diluents or re-hydrated compositions, are frequently required to be mixed to a high degree of uniformity. Due to increasing pressures on clinical laboratories to increase analytical sensitivity, there continues to be a need for improvements in the overall processing efficiency of clinical analyzers. In particular, sample analysis continuously needs to be more effective in terms of increasing assay throughput, producing a demand for sample-reagent mixers that mix a liquid solution to a high degree of uniformity at very high speed, without unduly increasing analyzer cost or requiring a disproportional amount of space.  
         [0004]     Various methods have historically been implemented to provide a uniform sample solution mixture, including agitation, mixing, ball milling, etc. One popular approach involves using a pipette to alternately aspirate and release a portion of liquid solution within a liquid container. Magnetic mixing, in which a vortex mixing action is introduced into a solution of liquid sample and liquid or non-dissolving reagents has also been particularly useful in clinical and laboratory devices. Typical of such mixing is disclosed in U.S. Pat. No. 6,382,827 wherein a liquid solution in a liquid container is mixed by causing a freely disposed, spherical mixing member to rapidly oscillate within the solution in a generally circular pattern within the container. The spherical mixing member is caused to rapidly move within the solution by revolving a magnetic field at high speed in a generally circular pattern in proximity to the liquid container. Magnetic forces acting upon the magnetic mixing member cause it to generate a mixing motion within the liquid solution.  
         [0005]     Ultrasonic mixing techniques like described in U.S. Pat. No. 4,720,374 employ ultrasonic energy applied from the exterior of the package and coupled into a reaction compartment so that a solid tablet of material within the compartment is dissolved or so that liquids contained therein are uniformly mixed. The container may include an array of sonication-improving projections mounted therein and spaced from each other to provide recirculating channels which communicate with both the tablet-receiving recess and the remainder of the volume of the container such that, in use, the projections act to confine a tableted material within a relatively high ultrasonic energy zone and simultaneously permit a flow of hydrating liquid from the high energy zone through the channels thereby to rapidly effect the dissolution of the tableted material.  
         [0006]     U.S. Pat. No. 6,382,827 discloses a method for mixing a liquid solution contained in a liquid container by causing a freely disposed, spherical mixing member to rapidly oscillate within the solution in a generally circular pattern within the container. The spherical mixing member is caused to rapidly move within the solution by revolving a magnetic field at high speed in a generally circular pattern in proximity to the liquid container. Magnetic forces acting upon the magnetic mixing member cause it to generate a mixing motion within the liquid solution.  
         [0007]     U.S. Pat. No. 5,824,276 discloses a method for cleaning contact lens by applying a solution flow in an oscillatory fashion, so that the lens moves up and down within a container but does not contact the container for an extended time period. The method includes suspending the article in a solution within a container such that the article does not experience substantial or extended contact with the container interior. A predetermined flow of solution is passed into the container, thereby providing an upward force which, in conjunction with the buoyancy force, overcomes the downward gravitational force on the article, when the article is more dense than the solution. Alternatively, if the article has a lower density than the treatment solution, the flow is generated at the top of the container, to produce a substantially steady state effect.  
         [0008]     Accordingly, from a study of the different approaches taken in the prior art to the problems encountered with quickly mixing small volume solutions taken with the challenges of minimizing the cost and physical size of a mixer, there is a need for an improved approach to the design of a simplified, space-efficient liquid sample and or sample-reagent mixer. In particular, there is a continuing need for improved sample-reagent solution mixer which provides high speed and uniform mixing of solutions contained in tubes. There is an even further need for a method for uniform high-speed mixing having a mixing motion that is provided by the same probe that is used to aspirate and dispense reagent into the solution.  
       SUMMARY OF THE INVENTION  
       [0009]     The principal object of the invention is to provide an improved mixing device for rapidly and uniformly mixing solutions within a biochemical analyzer by rapidly and repeatedly moving a sampling probe needle in a two-dimensional generally parabolic pattern within the solution. The sampling probe needle is attached to a moveable arm and the mixer reciprocates the moveable arm in a first direction and also reciprocates the arm in a second direction perpendicular to the first direction, so that the probe needle is moved in a generally parabolic pattern. In an exemplary embodiment, the probe needle is attached to a moveable arm having a protruding foot with a vertical roller pin in contact with a roller bearing. The moveable arm is vibrated by an alternating electromagnet in a first direction causing the roller pin to roll along the circumference of the roller bearing and the arm to move side-to-side in a in a second direction, generally perpendicular to the first direction. Varying the magnitude of movement of the moveable arm, in combination with adjusting the diameters of roller pin and roller bearing, produces a generally parabolic or generally “boomerang-shaped” generally ellipsoidal mixing pattern of the probe needle that has been found to be surprisingly efficient in time and effective in mixing uniformity. In one embodiment, the generally “boomerang-shaped” mixing pattern has a first dimension in said first direction and a second dimension in said second direction wherein the first dimension is about one-half as large as the second dimension.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The invention will be more fully understood from the following detailed description thereof taken in connection with the accompanying drawings which form a part of this application and in which:  
         [0011]      FIG. 1  is a schematic plan view of an automated analyzer adapted to perform the present invention;  
         [0012]      FIG. 2  is an enlarged schematic plan view of a portion of the analyzer of  FIG. 1 ;  
         [0013]      FIG. 2A  is perspective view of a reaction cuvette useful in operating the analyzer of  FIG. 1 ;  
         [0014]      FIG. 3  is perspective view of an aliquot vessel array useful in the analyzer of  FIG. 1 ;  
         [0015]      FIG. 4  is a perspective view of an aliquot vessel array storage and handling unit of the analyzer of  FIG. 1 ;  
         [0016]      FIG. 5  is perspective view of a reagent cartridge useful in operating the analyzer of  FIG. 1 ;  
         [0017]      FIG. 6  is a top plan view of a reagent cartridge management system useful in operating the analyzer of  FIG. 1 ;  
         [0018]      FIG. 7  is perspective view of a reagent cartridge useful in the reagent cartridge management system of  FIG. 6 ;  
         [0019]      FIG. 8  is a schematic view of a liquid aspiration and dispensing system useful in the analyzer of  FIG. 1 ;  
         [0020]      FIG. 9  is a schematic view of the liquid aspiration and dispensing system of  FIG. 8  aspirating reagent from the reagent cartridge of  FIG. 6 ;  
         [0021]      FIG. 10  is a schematic view of the liquid aspiration and dispensing system of  FIG. 8  dispensing reagent into the reaction cuvette of  FIG. 2A ;  
         [0022]      FIG. 11  is an enlarged diagram illustrating a first mixing pattern of motion generated by the roller mixing assembly exemplary of the present invention;  
         [0023]      FIG. 11A  is an enlarged diagram illustrating a second mixing pattern of motion generated by the roller mixing assembly exemplary of the present invention;  
         [0024]      FIG. 12  is a side elevation view of the roller mixing assembly exemplary of the present invention;  
         [0025]      FIG. 13  is a front view of the roller mixing assembly exemplary of the present invention exemplary of the present invention;  
         [0026]      FIG. 14  is a top view of the roller mixing assembly exemplary of the present invention exemplary of the present invention;  
         [0027]      FIG. 15  is a chart illustrating the mixing effectiveness of a popular prior art mixing patterns; and,  
         [0028]      FIG. 16  is a first chart illustrating the mixing effectiveness of the roller mixing assembly exemplary of the present invention.  
         [0029]      FIG. 17  is a second chart illustrating the mixing effectiveness of the roller mixing assembly exemplary of the present invention.  
         [0030]      FIG. 18  is a chart illustrating a characteristic of the roller mixing assembly exemplary of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]      FIG. 1 , taken with  FIG. 2 , shows schematically the elements of an automatic chemical analyzer  10  in which the present invention may be advantageously practiced, analyzer  10  comprising a reaction carousel  12  supporting an outer carousel  14  having cuvette ports  20  formed therein and an inner carousel  16  having vessel ports  22  formed therein, the outer carousel  14  and inner carousel  16  being separated by a open groove  18 . Cuvette ports  20  are adapted to receive a plurality of reaction cuvettes  24 , like seen in  FIG. 2A , that contain various reagents and sample liquids for conventional clinical and immunoassay assays while vessel ports  22  are adapted to receive a plurality of reaction vessels  25  that contain specialized reagents for ultra-high sensitivity luminescent immunoassays. Reaction carousel  12  is rotatable using stepwise movements in a constant direction, the stepwise movements being separated by a constant dwell time during which reaction carousel  12  is maintained stationary and computer controlled assay operational devices  13 , such as sensors, reagent add stations, mixing stations and the like, operate as needed on an assay mixture contained within a cuvette  24 .  
         [0032]     Analyzer  10  is controlled by software executed by the computer  15  based on computer programs written in a machine language like that used on the Dimension® clinical chemistry analyzer sold by Dade Behring Inc, of Deerfield, Ill., and widely used by those skilled in the art of computer-based electromechanical control programming. Computer  15  also executes application software programs for performing assays conducted by various analyzing means  17  within analyzer  10 .  
         [0033]     As seen in  FIG. 1 , a bidirectional incoming and outgoing sample fluid tube transport system  34  comprises a mechanism for transporting sample fluid tube racks  38  containing open or closed sample fluid containers such as sample fluid tubes  40  from a rack input load position at a first end of the input lane  35  to the second end of input lane  35  as indicated by open arrow  35 A. Liquid specimens contained in sample tubes  40  are identified by reading bar coded indicia placed thereon using a conventional bar code reader to determine, among other items, a patient&#39;s identity, tests to be performed, if a sample aliquot is to be retained within analyzer  10  and if so, for what period of time. It is also common practice to place bar coded indicia on sample tube racks  38  and employ a large number of bar code readers installed throughout analyzer  10  to ascertain, control and track the location of sample tubes  40  and sample tube racks  38 .  
         [0034]     A conventional liquid sampling probe  42  is located proximate the second end of the input lane  35  and is operable to aspirate aliquot portions of sample fluid from sample fluid tubes  40  and to dispense an aliquot portion of the sample fluid into one or more of a plurality of vessels  52 V in aliquot vessel array  44 , seen in  FIG. 3 , depending on the quantity of sample fluid required to perform the requisite assays and to provide for a sample fluid aliquot to be retained by analyzer  10  within an environmental chamber  48 . After sample fluid is aspirated from all sample fluid tubes  40  on a rack  38  and dispensed into aliquot vessels  52 V maintained in an aliquot vessel array storage and transport system  50  seen in  FIG. 4 , rack  38  may be moved, as indicated by open arrow  36 A, to a front area of analyzer  10  accessible to an operator so that racks  38  may be unloaded from analyzer  10 .  
         [0035]     Aliquot vessel array transport system  50  comprises an aliquot vessel array storage and dispensing module  56  and a number of linear drive motors  58  adapted to bi-directionally translate aliquot vessel arrays  52  within a number of aliquot vessel array tracks  57  below a sample aspiration needle probe  54  and roller mixing assembly  55 , described hereinafter and exemplary of the present invention, located proximate reaction carousel  12 . Sample aspiration probe  54  is controlled by computer  15  and is adapted to aspirate a controlled amount of sample from individual vessels  52 V positioned at a sampling location within a track  57  and is then shuttled to a dispensing location where an appropriate amount of aspirated sample is dispensed into one or more cuvettes  24  for testing by analyzer  10  for one or more analytes. After sample has been dispensed into reaction cuvettes  24 , conventional transfer means move aliquot vessel arrays  52  as required between aliquot vessel array transport system  50 , environmental chamber  48  and a disposal area, not shown.  
         [0036]     Temperature-controlled storage areas or servers  26 ,  27  and  28  inventory a plurality of multi-compartment elongate reagent cartridges  30 , like that illustrated in  FIG. 5  and described in co-pending application Ser. No. 09/949,132 assigned to the assignee of the present invention, containing reagents in wells  32  as necessary to perform a number of different assays. As described later in conjunction with  FIG. 6 , server  26  comprises a first carousel  26 A in which reagent cartridges  30  may be inventoried until translated to a second carousel  26 B for access by a reagent aspiration probe  60  and roller mixing assembly  55  exemplary of the present invention.  FIG. 6  shows an advantageous embodiment in which carousel  26 A and carousel  26 B are circular and concentric, the first carousel  26 A being inwards of the second carousel  26 B. Reagent containers  30  may be loaded by placing such containers  30  into a loading tray  29  adapted to automatically translate containers  30  to a shuttling position described later.  
         [0037]     Additional reagent aspiration needle probe  62  is also associated with a roller mixing assembly  55  like that associated with aspiration probe  60  are independently mounted and translatable between servers  27  and  28 , respectively and outer cuvette carousel  14 . Probe  62  comprises conventional mechanisms for aspirating reagents required to conduct specified assays at a reagenting location from wells  32  in appropriate reagent cartridges  30 , probe  62  subsequently being shuttled to a dispensing location where reagents are dispensed into cuvettes  24 .  
         [0038]      FIG. 6 , taken with  FIG. 7 , illustrates a single, bidirectional carrier shuttle  72  adapted to remove reagent cartridges  30  from loading tray  29  having a motorized rake  73  that automatically locates reagent cartridges  30  at a shuttling position beneath shuttle  72 . Cartridges  30  are identified by the type of reagent solution contained therein using conventional barcode-like indicia and a bar-code-reader  41  proximate loading tray  29 . Computer  15  is programmed to track the location of each and every reagent cartridge  30  within analyzer  10 . Shuttle  72  is further adapted to dispose a reagent container  30  into slots in at least one slotted reagent container tray  27 T or  28 T within at least one reagent storage area  27  or  28 , respectively. In a similar fashion, shuttle  72  is further adapted to remove reagent containers  30  from reagent container trays  27 T and  28 T and to dispose such reagent containers  30  into either of two concentric reagent carousels  26 A and  26 B within reagent storage area  26 . Shuttle  72  is also adapted to move reagent containers  30  between the two concentric reagent carousels  26 A and  26 B. As indicated by the double-headed arc-shaped arrows, reagent carousel  26 A may be rotated in both directions so as to place any particular one of the reagent containers  30  disposed thereon beneath reagent aspiration probe  60 . Any one of the reagent containers  30  disposed in reagent container trays  27 T and  28 T may be located at a loading position beneath reagent container shuttle  72  or at a reagent aspiration location beneath aspiration and dispensing probe  62 , respectively, by reagent container shuttles  27 S and  28 S within reagent storage areas  27  and  28 , respectively. Reagent container shuttles  27 S and  28 S are similar in design to reagent container shuttle  72  seen in FIG.  7 . Reaction cuvettes  24  supported in outer carousel  14  and reaction vessels  25  supported in inner carousel  16  are shown in dashed lines to indicate that they are positioned below the surface of carousel  26 .  
         [0039]     Carrier shuttle  72  seen in  FIG. 7  is adapted to automatically compensate for unknown changes in length of a belt  72 B driven by motor  72 M by an automated tensioner  72 T like described in co-pending U.S. patent Ser. No. 10/623,311 and assigned to the assignee of the present invention, and adapted to maintain a constant tension on the belt  72 B regardless of rapid changes in its driving direction so that reagent containers  30  attached thereto by clamps  72 C may be accurately positioned along the direction of belt  72 B, as indicated by the double-ended arrow, and disposed at their shuttling location beneath reagent container shuttle  72  or within storage areas  26 ,  27  or  28  as belt  72 B wears. Reagent container shuttles  27 S and  28 S are similar in design to one another and include a reagent container tray  28 T secured to one leg of a belt so that tray  28 T is free to be driven to and from along the direction of by the double-ended arrow. Consequently, reagent containers  30  within slots in tray  28 T may be automatically positioned at a shuttling location beneath container shuttle  72 .  
         [0040]     Aspiration probe  60  useful in performing the present invention may be seen in  FIG. 8  as comprising a Horizontal Drive component  60 H, a Vertical Drive component  60 V, a Wash Module component  60 W, a Pump Module component  60 P, an aspiration and dispensing probe needle  60 N, and a Wash Manifold component  60 M having the primary functions described in Table 1. Components of the Wash Module component  60 W and Pump Module component  60 P unidentified in  FIG. 9  will be described later. Horizontal Drive component  60 H and Vertical Drive component  60 V are typically computer controlled stepper motors or linear actuators and are controlled by computer  15  for providing precisely controlled movements of the Horizontal Drive component  60 H and Vertical Drive component  60 V.  
                   TABLE 1                       Module   Primary Functions                   Horizontal   Position the Vertical Drive 60V over reagent cartridges       Drive 60H   30 containing reagent liquids and carried in a vial rack           30A and over cuvettes 24 carried in ports 20.       Vertical   Drive probe 60N through the covering of a reagent       Drive 60V   cartridge 30.       Wash Module   Remove contamination from needle 60N with liquid       60W   cleansing solutions.       Wash Manifold   Connect needle 60N to Pump Module 60P       60M       Pump Module   Pump reagent liquids and sample fluids.       60P       Needle 60N   Aspirate and dispense reagent liquids and sample fluids.                  
 
         [0041]      FIG. 9  shows Pump Module  60 P connected to conventional hollow, liquid-carrying probe-like needle  60 N having conventionally defined interior and exterior surfaces and supported by Wash Manifold  60 M, the Wash Manifold  60 M being connected by a hollow air tube  70  to a three-way valve  71 . Probe needle  60 N preferably has a tapered point designed to reduce friction when inserted through the covering of reagent cartridge  30  and may be connected to Wash Manifold  60 M using any of several screw-like connectors, not shown, or alternately, permanently welded thereto. Valve  71  is operable to optionally connect air tube  70  to (1) a vent valve  73  connected to an atmospheric vent tube  74  or to (2) a piston-type syringe pump  76  by a hollow air tube  77 . A conventional air pressure measuring transducer  78  is connected to air tube  77  between pump  76  and valve  71  by a hollow air tube  79 .  
         [0042]      FIG. 9  also illustrates probe needle  60 N having punctured the covering of a reagent carrier  30  and positioned within a reagent liquid contained therein. Level sensing means, for example using well known capacitive signals, are may be advantageously employed in order to ensure that probe needle  60 N is in fluid communication with the liquid. Piston  76  is activated and the distance it is moved is controlled by computer  15  so that a controlled volume of reagent liquid is withdrawn or aspirated into probe needle  60 N. During this process, valve  71  is closed to vent tube  72 , but is open to air tube  77  and air tube  70 . Valve  71  is operable to optionally connect air tube  70  to a vent valve  73  connected to an atmospheric vent tube  74 .  FIG. 9  also shows Wash Manifold  60 W as comprising a flush valve  82  connected to Wash Manifold  60 W by a hollow liquid carrying tube  81 . Flush valve  82  is operable to connect liquid carrying tube  81  to a pressurized rinse water source  84  by a hollow liquid tube  83 . After aspiration of calibration or quality control liquid from reagent carrier  30  is completed, Wash Manifold  60 M is raised by Vertical Drive  60 V and positioned by Horizontal Drive  60 H so that probe  60  may dispense calibration or quality control liquid into a cuvette  24  carried in port  20  in carousel  14  as illustrated in  FIG. 10 .  
         [0043]     During operation of analyzer  10  using the devices illustrated in  FIGS. 2-9 , there are several instances when it is critical that liquids or solutions of one or more liquids be quickly and uniformly mixed producing a demand for a mixing device that mixes a liquid or liquid solution to a high degree of uniformity at very high speed, without unduly increasing analyzer cost or requiring a disproportional amount of space or a specialized mixing-only device. High speed mixing to obtain a uniformly dispersed solution might be required, for example: 
        1. After sample aspiration needle probe  60  extracts a first reagent from a first reagent cartridge  30  and dispenses reagent into a reaction cuvette  24 , roller mixing assembly  55  may be operated to cause needle  60 N to mix reagent and an optional chase or probe cleaning liquid;     2. Before sample aspiration needle probe  54  extracts sample from a vessel  52 V in aliquot vessel array  44  and dispenses sample into a reaction cuvette  24 , roller mixing assembly  55  may be operated to cause needle  54 N to mix sample that has been retained in vessel  52 V for an extended period of time waiting re-testing or additional testing;     3. Before sample aspiration needle probe  54  extracts sample from a vessel  52 V in aliquot vessel array  44  and dispenses sample into a reaction cuvette  24 , roller mixing assembly  55  may be operated to cause needle  60 N to mix sample that has been diluted in vessel  52 V; and,     4. After sample aspiration needle probe  54  extracts a second reagent from a first reagent cartridge  30  and dispenses reagent into reaction cuvette  24 , roller mixing assembly  55  may be operated to cause needle  60 N to mix reagent and an optional chase or probe cleaning liquid.     5. After sample aspiration needle probe  54  extracts sample from a vessel  52 V in aliquot vessel array  44  and dispenses sample into a reaction cuvette  24 , roller mixing assembly  55  may be operated to cause needle  60 N to mix the sample with the reagent in the reaction cuvette  24 .        
 
         [0049]     A key feature of the present invention is the discovery that an unexpectedly high degree of mixing uniformity may be achieved by using roller mixing assembly  55  to rapidly move probe needles  54 N,  60 N or  62 N in a “boomerang-shaped” pattern within either the reagents in wells  32  prior to the reagent aspiration process illustrated in  FIG. 9  or within sample retained in vessels  52 V in aliquot vessel array  44 , or within sample-reagent mixture in cuvette  24  after the dispensing process illustrated in  FIG. 10 .  
         [0050]     The mixing action provided by the roller mixing assembly  55  exemplary of the present invention cycles probe needle  60 N in a first mixing generally parabolic pattern like seen in  FIG. 11  or in a second generally “boomerang-shaped” like seen in  FIG. 11A  in which needle probe  60 N is moved along a path beginning at the tail of arrow  11 A and following arrow  11 A to it&#39;s point; at the point of arrow  11 A, the movement of needle probe  60 N is reversed and needle probe  60 N is moved along a path beginning at the tail of arrow  11 B and following arrow  11 B to it&#39;s point. The tail of arrow  11 A and the point of arrow  11 B coincide and the point of arrow  11 A the tail of arrow  11 B coincide. Probe needle  60 N is continuously moved in either the generally ellipsoidal pattern or in the “boomerang-shaped” pattern using roller mixing assembly  55  comprising a first means to provide reciprocating left-to-right movement and a second means to provide front-to-back reciprocating movement of the probe needle  60 N, thereby producing a generally parabolic,  FIG. 11 , or “boomerang-shaped” mixing pattern,  FIG. 11A . Conventional wisdom might employ two electromagnets to provide the two means for reciprocating needle  60 N, it has been found to be much more cost effective to employ only one electromagnet coupled with a curved surface and with needle probe  60 N as illustrated in  FIGS. 12-14  to produce a generally ellipsoidal mixing pattern. In addition, a key advantage of the roller mixing assembly  55  over other mixing device design is the lack of motors and the use of a simple on-off signal, as opposed to a control system to maintain a motor speed), thereby reducing manufacturing cost and at the same time, producing a more reliable and durable mixing design. As discussed later, by changing the operating conditions of the mixer such as frequency and duty cycle, the boomerang pattern can be altered as shown in  FIG. 11  and  FIG. 11A . Clearly, probe needles  54 N and  62 N may also be moved in the same “boomerang-shaped” pattern by roller mixing assembly  55  in order to achieve high efficiency mixing.  
         [0051]      FIG. 12  shows a front view of needle probe  60 N depending from a protruding foot  87  of a moveable arm  85  of roller mixing assembly  55 . The protruding foot  87  has a roller pin  86  extending vertically upwards and in contact with a curved surface provided by a roller bearing  88  mounted to a stationary block  89  using a pin  90 . The needle probe  60 N is attached to a moveable arm  85  having a protruding foot  87  with a vertical roller pin  86  in contact with a roller bearing  88 . Roller bearing  88  is advantageously employed to provide a curved surface to provide side-to-side movement because such a bearing reduces friction and wear. However, any similar curved surface, for example a stationary pin or semi-circular surface with a circumference would suffice in providing the desired motion. The moveable arm  85  is vibrated by a conventional alternating electromagnet  92  and a ferromagnetic plate  91  in a first direction causing roller pin  86  to roll along the circumference of roller bearing  88  and arm  86  to move side-to-side in a in a second direction, perpendicular to the first direction. Varying the magnitude of movement of the moveable arm  86 , in combination with adjusting the diameters of roller pin  86  and roller bearing  88 , produces a “boomerang-shaped” mixing pattern of needle probe  60 N that has been found to be surprisingly efficient in time and effective in mixing uniformity. In an exemplary embodiment, the “boomerang-shaped” mixing pattern has a first dimension in the first direction and a second dimension in the second direction wherein the first dimension is about one-half as large as the second dimension.  
         [0052]     Moveable arm  85  is biased so that left-to-right movement a first distance, indicated in  FIG. 12  by arrow  12 A, forces roller pin  86  to roll along the outer circumference of roller bearing  88 , thereby causing arm  85  to also move a second distance in a direction perpendicular to the plane of  FIG. 12 . This movement in the second direction of arm  85 , perpendicular to the first direction is illustrated by arrow  13 A in  FIG. 13 , a right side view of roller mixing assembly  55 , in which a ferromagnetic plate  91  is shown attached to arm  85 . Plate  91  is caused to vibrate perpendicularly to the plane of  FIG. 13  by an alternating electromagnet  92 , seen in  FIG. 14 . Varying the phase of alternating electric current supplied to electromagnet  92  causes plate  91  and arm  85  to oscillate in a direction perpendicular to the plane of  FIG. 13 , forcing roller pin  86  to roll along the outer circumference of roller bearing  88 , thereby causing arm  85  to move sidewise in the direction of double-headed arrow  13 A. The dimension of movement in the second direction is generally larger than the dimension of movement in the first direction, and in an exemplary embodiment is generally twice as large as the dimension of movement in the first direction. A close examination of  FIGS. 12-14  reveals how needle probe  60 N may be continuously moved in the “boomerang-shaped” pattern of  FIG. 11  using roller mixing assembly  55 . It is clear that varying the magnitude of movement of plate  91  and arm  85 , in combination with modifying the diameters of roller pin  86  and roller bearing  88 , can alter the dimensions of the generally ellipsoidal patter seen in  FIG. 11  or the “boomerang-shaped” pattern seen in  FIG. 11A , however the overall shape of such a pattern will remain approximately similar.  
         [0053]     The dimension of movement in the second direction is generally twice as large as the dimension of movement in the first direction. A close examination of  FIGS. 12-14  reveals how needle probe  60 N may be continuously moved in the “boomerang-shaped” pattern of  FIG. 11  using roller mixing assembly  55 . It is clear that varying the magnitude of movement of plate  91  and arm  85 , in combination with modifying the diameters of roller pin  86  and roller bearing  88 , can alter the dimensions of the generally ellipsoidal patter seen in  FIG. 11  or the “boomerang-shaped” pattern seen in  FIG. 11A , however the overall shape of such a pattern will remain approximately similar.  
         [0054]     The significant increase in mixing efficiency that is achieved may be seen by measuring the variation in optical absorption of a dye mixture in water before and at the end of a given time interval, say 2-3 seconds, for different mixing methods. If the mixing method is highly effective, the variation or difference in absorption will be close to zero in less than 1 second because the water-dye solution will have essentially the same uniformity and the optical absorption will be unchanged. The amount of time required to reduce the variation in absorption to zero is thus an indication of the efficiency of the mixing method.  FIG. 15  shows the difference in absorption of a water-dye solution for a prior art mixing technique in which a mixing probe is vibrated back-and-forth in a single linear direction. The difference is absorption does not begin to be close to zero until after one second of mixing, or approximately 150 “back-and-forth” mixing cycles where the probe sweeps through the entire length of the vessel. A roller mixing assembly  55  like seen in  FIG. 14  and constructed with the electromagnet air gap  14 G adjusted to achieve approximately ½ the stroke of the prior art mixing technique, in combination with adjusting the diameters of roller pin  86  and roller bearing  88  to achieve a generally parabolic or “boomerang-shaped” pattern,  FIGS. 11 and 11 A, has a significantly increased mixing efficiency as illustrated in  FIG. 16 . In contrast to the prior art, the roller mixing assembly  55  exemplary of the present invention is significantly more efficient, achieving close to zero difference in absorption in approximately 0.3 second, or 75 “boomerang-shaped” mixing cycles. The shorter required stroke of the roller mixing assembly provides the advantage of a reduced chance of the probe tip from striking the vessel wall, which has been shown to be a leading cause of the creation of bubbles and foaming while mixing.  
         [0055]      FIG. 17  illustrates another mixing parameter that affects the efficiency of roller mixing assembly  55 . Depending upon a number of system parameters including the viscosity of liquid being mixed and the frequency at which roller mixing assembly  55  is operated which affects the displacement of the tip of needle probe  60 N, foam may be generated within reaction cuvette  24 . The frequency at which the tip of needle probes  54 N,  60 N and  62 N is vibrated within this range is determined by the rate at which electromagnet  92  is “turned on and off”. The presence of foam may be determined by measuring the variation in intensity of a 700 nanometer wavelength interrogating signal passing through reaction cuvette  24 , the greater the variation being indicative of foam generated by the mixing action of roller mixing assembly  55 . In  FIG. 17 , the adverse presence of foam is seen appearing as a large increase in signal at an operating frequency near the left one-third side of the chart.  
         [0056]     Optimally, the design parameters of roller mixing assembly  55  are selected so that a “good” mix is achieved in 0.5 seconds or less and foam is not generated, a “good” mix defined as having signal variation less than 2% deviation from a zero baseline as seen in  FIG. 16 . What has been discovered is that, depending upon the stiffness of the probe to be used, the air gap  14 G distance between electromagnet  92  and plate  91  must be adjusted to fall within a range that produces a displacement of the tip of needle probes  54 N,  60 N and  62 N in a range from about 0.6 to about 1.2 mm. It has also been discovered that, depending upon the viscosity of the liquid to be mixed, the electromagnet  92  may be operated at different “on-off” frequencies in order to vary the mixing pattern and maximize the mixing efficiency of roller mixing assembly  55 .  
         [0057]     In a typical embodiment, before sample is delivered to a reaction cuvette  24 , a first reagent with a first viscosity is delivered to an empty reaction cuvette  24  and may be mixed before and/or after delivery, sample is then delivered to the reaction cuvette  24  containing first reagent and may be mixed before and/or after delivery, finally a second reagent may be delivered to reaction cuvette  24  already containing mixed sample and reagent and may be mixed before and/or after delivery. All of these liquids and mixtures generally will all have different viscosities and different volumes. Thus, the optimum design parameters and/or operating conditions will be different for the roller mixing assembly  55  associated with needle  54 N to mix sample that has been retained in vessel  52 V prior to delivery to a reaction cuvette and the roller mixing assembly  55  associated with needle  60 N to delivery first reagent to an empty reaction cuvette and the roller mixing assembly  55  associated with needle  62 N to add a second reagent and mix with an existing sample-first reagent mixture. This relationship may be seen in  FIG. 18  illustrating three different air gap  14 G distance ranges between electromagnet  92  and plate  91  required to maintain the displacement of the tip of probe needles  54 N,  60 N and  62 N within about 0.6 to about 1.2 mm. Due to the inverse square nature of magnetic forces involved, if less force is required to achieve the 0.6-1.2 mm stroke, then a larger gap can be used, with an accompanying larger permissible variation in that gap, so that increased robustness and manufacturing tolerances are obtained. An artesian will appreciate that these values will change depending upon other design parameters, including the material of construction of, the length of, the diameter of, and the flexibility of probe needles  54 N,  60 N and  62 . Irrespective of these variations, however, the use of a mixing assembly like roller mixing assembly  55  having a moveable arm  85  vibrated in a first direction so that roller pin  86  rolls along the circumference of roller bearing  88  and causes arm  86  to move side-to-side in a in a second direction, perpendicular to the first direction produces a “boomerang-shaped” mixing pattern of needle probe  60 N that has been found to be surprisingly efficient in time and effective in mixing uniformity.  
         [0058]     Table 1 below summarizes an exemplary set of operating conditions for an instance in which the sample probe  54  generally delivers body fluids like serum, first reagent probe  60  delivers reagents to a reaction cuvette  24  before sample is added thereto, and reagent probe  62  delivers reagents to a reaction cuvette  24  already having sample and reagent added and mixed therein.  
                               TABLE 1                           ELECTROMAGNET       DUTY           PROBE   ON-OFF CYCLE   FREQUENCY   CYCLE   TIME                   Probe 54   2 ms on, 2 ms off   250 Hz   50%   0.5 sec       Probe 60   6 ms on, 3 ms off   111 Hz   67%   0.5 sec       Probe 62   3 ms on, 1 ms off   250 Hz   75%   0.5 sec                  
 
         [0059]     It should be readily appreciated by those persons skilled in the art that the present invention is susceptible of a broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications and equivalent arrangements will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to specific embodiments, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements, the present invention being limited only by the claims appended hereto and the equivalents thereof.