Abstract:
A rotor and specimen holder assembly for producing a relatively low power, low audible level, cool running centrifuge. The centrifuge rotor assembly is designed to enable a specimen holder to retract into the body of the rotor during centrifugation to produce aerodynamic features.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to U.S. Provisional Patent Application No. 60/706,935 filed Aug. 10, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a centrifuge rotor and tube holder design, and more particularly, to a rotor assembly for producing a relatively low power, low audible level, cool running centrifuge.  
         [0004]     2. Background Art  
         [0005]     Centrifuges are commonly used in medical and biological research for separating and purifying materials of differing densities such as viruses, bacteria, cells, proteins, and other compositions. A centrifuge normally includes a motor, a rotor, and specimen holders capable of spinning up to tens of thousands of revolutions per minute. Specimen holders include, for example, test tubes, test tube holders, or any other means that is suitable for retaining a specimen.  
         [0006]     A preparative centrifuge rotor has some means for accepting specimen holders or “buckets” containing the samples to be centrifuged. Preparative rotors are commonly classified according to the orientation of the sample tubes or buckets. Vertical tube rotors carry the sample tubes or buckets in a vertical orientation, parallel to the vertical rotor axis. Fixed-angle rotors carry the sample tubes or buckets at an angle inclined with respect to the rotor axis, with the bottoms of the sample tubes being inclined away from the rotor axis so that centrifugal force during centrifugation forces the sample toward the bottom of the sample tube or buckets. Swinging bucket rotors have pivoting tube carriers that are not horizontal when the rotor is stopped and that pivot the bottoms of the tubes outward under centrifugal force.  
         [0007]     With current swinging bucket rotor designs, the centrifuge buckets are primarily left uncovered by the rotor and generate considerable aerodynamic drag. This drag increases as the non-aerodynamic features move further away from the axis of rotation. Although these aerodynamic features significantly impact upon rotor operations at speeds lower than 3,000 RPM, they can be an even more significant factor at higher RPMs. Because many newer laboratory and forensic protocols require much higher rotational speed during centrifugation, including up to, and well exceeding, 4,000 RPM, identifying efficient and cost effective means of reducing aerodynamic drag is desirable. With current rotor technology, the curved shape of the centrifuge buckets prevents the buckets from retracting into the rotor housing to completely seal the voids therein. Thus, significant aerodynamic drag is generated during centrifugation due to air entering the rotor through these voids.  
         [0008]     Centrifugation generally involves rotating a sample solution at high speed about an axis to create a high centrifugal force to separate the sample into its components based upon their relative specific gravity. The sample is carried in a rotor which is placed in a centrifuge chamber in a centrifuge instrument. The rotor is driven to rotate at high speed by a motor beneath the centrifuge chamber. At high speed operations, aerodynamic drag on the rotor becomes increasingly significant. Significantly more power is required to overcome the aerodynamic drag at high speed. In addition, cooling means must be provided to offset the heat generated by aerodynamic friction. Some centrifuges are provided with means for drawing a vacuum or partial vacuum in the centrifuge chamber in an effort to reduce the aerodynamic drag; however, cooling can still be necessary.  
         [0009]     In the past, cooling of the centrifuge chamber has been accomplished by attaching refrigerant coils to the outside of the centrifuge chamber (see, e.g., U.S. Pat. No. 5,477,704 to Wright). In such a configuration, a space must be provided between adjacent passages to allow for welding (e.g. at 19 and 20), which reduces the available surface area for efficient heat transfer from the chamber. Significant drawbacks of this design are that cooling or refrigerating the chamber is expensive and prone to malfunction. Accordingly, there is a need for a simple, cost effective means of reducing aerodynamic drag and resulting friction heat with certain swinging bucket rotor designs.  
       SUMMARY OF THE INVENTION  
       [0010]     It is an object of the present invention to overcome the shortcomings of the prior art by providing a rotor and specimen holder assembly comprised of a centrifuge rotor assembly and a plurality of specimen holders. The rotor assembly is specifically designed to enable the specimen holders to retract into the body of the rotor during centrifugation to produce aerodynamic features. Slotted openings along the periphery of the rotor house the specimen holders. The specimen holders are designed to fill or plug these peripheral voids in the rotor as the rotor begins to rotate and the holders move into the retracted position.  
         [0011]     Once the specimen holders are in the retracted position, the subjacent surface of each holder forms an uninterrupted interface about its slot which prevents circulating air from entering the rotor and tube holder assembly. This produces a continuous surface and an aerodynamic assembly that approaches the drag characteristics of a spinning disk. This interface also protects samples from the warmer circulating air and aids in keeping the samples at or near ambient temperatures. Voids near the center of the rotor may optionally be left open, as these locations&#39; overall effect on drag is minimal.  
         [0012]     The above and still further features and advantages of the present invention will become apparent upon consideration of the following detailed description of specific embodiments thereof, particularly when taken in conjunction with the accompanying drawings, wherein like reference numerals in the various figures are utilized to designate like components. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a perspective view of a rotor and specimen holder assembly shown in the rotational position according to the present invention.  
         [0014]      FIG. 2  is a cross-sectional view of a rotor and tube holder assembly shown in the rotational position according to the present invention.  
         [0015]      FIG. 3  is a bottom perspective view of a rotor and tube holder assembly shown at rest according to the present invention.  
         [0016]      FIG. 4  is a cross-sectional view of a rotor and tube holder assembly shown at rest according to the present invention.  
         [0017]      FIG. 5  is a cross-sectional view of a centrifuge assembly with the rotor shown at rest according to the present invention.  
         [0018]      FIG. 6  is a perspective view of a specimen holder according to the present invention.  
         [0019]      FIG. 7  is a cross-sectional view of a rotor featuring a specimen holder interface according to the present invention. Subsequent airflow about the rotor is also depicted.  
         [0020]      FIG. 8  is a cross-sectional view of a rotor shown without a specimen holder interface. Circulating air flows into the rotor through openings positioned along the rotor periphery. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Referring now to  FIGS. 1-8 , the present invention comprises a novel design for a fully retractable specimen holder and rotor assembly for use in existing and new centrifuges  14  that are employed, for example, in medical, industrial, and laboratory settings.  
         [0022]     The specimen holder  10  can either hold a specimen or some type of container, such as a test tube, test tube holder, or “bucket” containing a sample to be centrifuged. The rotor  12  and specimen holder assembly of the present invention may incorporate the use of specimen holders  10  having an extended collar  16 , rotation pins, or other pivot mechanisms that enable the specimen holder  10  to swing from a resting position to a rotational position. Pivot mechanisms may include, for example, mounting holes, rivets, bolts, trunnions, springs, hinges, and the like.  
         [0023]     The rotor  12  allows for the vertical or near vertical insertion of the specimen holder  10  and its contents. The extended collar  16 , rotation pins, or other pivot mechanisms on the specimen holder prevent the specimen holder from falling through the rotor  12 . In a preferred embodiment, the specimen holder  10  is primarily rectilinear in its cross-sectional geometry or includes at least one lower flat surface that forms a continuous, uninterrupted planar surface with the rotor bottom  18  to produce a more perfect aerodynamic feature. The present invention also enables the full retraction, inside the lower planar surface of the rotor, of round or multifaceted specimen holder configurations, significantly improving aerodynamic performance of the rotor assembly.  
         [0024]     The rotor comprises a ribbed disc that supports and protects the specimen holders  10 . The lower planar surface of the disc forms the rotor bottom  18  to which the ribs are attached. As an option, an outer rib  20  may extend about the outside circumference of the rotor bottom  18 . The outer rib extends upward from the rotor bottom to form an exterior wall of the rotor  12  about the area containing the specimen holder. The outer rib  20  provides an aerodynamic shape to reduce air drag, protects the distal tip of the specimen holder  10 , and provides radial support to the rotor  12 . At the center of the rotor bottom  18  is a rotor hub  22  that extends upward from the rotor bottom. The rotor hub  22  has an open center to fit over a drive shaft of a centrifuge motor, which rotates the rotor. The rotor hub  22  acts as a bearing surface for the rotor  12 .  
         [0025]     As shown in  FIGS. 3 and 4 , a series of elongated support channels  24  extend upward from the lower surface  18  of the rotor. The rotor  12  of the present invention may also employ fewer or more support channels  24 , as appropriate for a particular application. Each channel  24  includes a pair of side ribs  26 ,  28  that support the specimen holder  10  and its contents during centrifugation. The bottom of the side rib  26  abuts the rotor bottom  18 , and the top of the side rib  26  is parallel thereto. The interior or proximal section of the side rib  26  is positioned towards the rotor hub  22 . The distal section of the side rib  26  extends towards the outer rib  20 . The proximal section forms a ninety degree (90°) angle with, abuts against and supports the collar  16 , rotation pins, and/or other pivot mechanisms of the specimen holder  10 . The side ribs  26 ,  28  prevent movement of the specimen holder  10  beyond the horizontal position during rotation and also provide radial strength to the rotor  12 .  
         [0026]     In a preferred embodiment of the invention, the specimen holder  10  is ensconced within the support channel  24  so that, in the rotational position, no more than the outer tip (distant from the rotor hub  22 ) of the specimen holder extends beyond the distal edge of the side ribs  26 ,  28 . In use, there is minimal to no protrusion of the specimen holder  10  into the centrifugal air stream about the rotor  12 . In a preferred embodiment, the dimensions of the side ribs  26 ,  28  are commensurate to the proportions of the specimen holder  10  so that there is no protrusion of the specimen holder  10  beyond the support channel  24  (and into the centrifugal air stream).  
         [0027]     Because the geometry and dimensions of the specimen holder  10  generally correspond to those of the support channel  24 , the specimen holder  10  is able to nest or retract upward into, and horizontally align with, the support channel  24  during rotation of the rotor  12 . Once the specimen holder  10  is in the retracted position, the subjacent surface of the holder is flush with the bottom  18  of the rotor so as to form a continuous planar surface. This uniform surface or interface  34  forms a barrier that severs access from the support channel  24  to a clearance slot  30  in the bottom surface  18  of the rotor. As a result, circulating air is prevented from entering the rotor and tube holder assembly, significantly decreasing aerodynamic drag on the rotor  12 .  
         [0028]     As depicted in  FIGS. 1 and 4 , each support channel  24  also includes a clearance slot  30  about the bottom  18  of the rotor to receive the specimen holder  10 . Each clearance slot  30  has an interior end near the rotor hub  22 . As shown, a side rib  26  extends upward from the rotor bottom  18  on each side of the clearance slot. The clearance slot  30 , which may be predominantly square in its cross section geometry, allows the specimen holder  10  to swing from a generally vertical, resting position into a horizontal position during rotation of the rotor  12 . During centrifugation, the specimen holder  10  remains recessed within the channel  24  and supported by the side ribs  26 ,  28 . The clearance slot  30  is preferably wider than the main body of the specimen holder  10 , but smaller than the diameter of the collar  16  of the specimen holder. Each side rib  26 ,  28  is shown flush with the clearance slot  30 ; however this arrangement is merely illustrative. The dimensions of the rotor  12 , and clearance slot  30  may be configured to accommodate various specimen holder and pivot designs.  
         [0029]     As shown in  FIGS. 1 and 2 , the specimen holders  10  are designed to be contiguous with the clearance slots  30  as the rotor  12  begins to rotate and the holders move into the retracted position. Once the specimen holders  10  are in the retracted position within the body of the rotor  12 , the lower or subjacent surface of each holder forms a substantially continuous and uninterrupted surface with the rotor bottom  18 , which is preferably planar. As a result of this relative seal or interface  34  about the clearance slot  30 , circulating air is prevented from entering the rotor and tube holder assembly. There is, therefore, no interruption in the flow of air (drag) about the rotor  12 , and the specimen holder  10  itself is not subjected to the friction of air resistance during centrifugation. This produces an aerodynamic assembly that approaches the drag characteristics of a spinning disk. The continuous interface  34  also protects samples from the warmer circulating air and aids in keeping the samples at or near ambient temperatures. Voids near the center of the rotor  12  may optionally be left open, as these locations&#39; overall effect on drag is minimal.  
         [0030]     Extending from the side ribs  26 ,  28  of each channel  24  and towards the rotor hub  22  is an inner rib  32  that extends upward from the rotor bottom  18 . The inner rib provides radial strength to the rotor  12 . The distance between the inner ribs  32  on each side of the clearance slot  30  is preferably slightly wider than the width of the clearance slot, but smaller than the diameter of the extended collar  16  or other pivot mechanism of the specimen holder  10 . A top surface of the inner ribs  32  is shown parallel to the rotor bottom  18  and intersects the proximal surface of the side ribs  26 ,  28  at a ninety degree (90°) angle.  
         [0031]      FIGS. 4-5  show the specimen holder  10  positioned in a near vertical position due to the design of the rotor  12 . As shown, the distance between the proximal surface of the side rib  26  and the interior end of the clearance slot  30  is less than the diameter of the main body of the specimen holder. The specimen holder  10  pivot mechanism rests against the proximal surface of both side ribs  26 ,  28  and the top surface of the inner rib  32  on each side of the clearance slot  30 .  
         [0032]     In one embodiment of the invention, a flat cover (not shown) may be fitted over the top of the rotor  12  to protect the insides of the rotor. The cover can also be used to provide a more aerodynamic air flow over the rotor. The cover includes a center hole to allow insertion of one or more specimen holders  10  when the rotor is at rest.  
         [0033]     The rotor  12  is utilized by being mounted to a drive system of the motor of the centrifuge  14 . The specimen holder  10  can either hold a specimen or some type of container, such as a test tube or bucket containing a sample to be centrifuged. In a preferred embodiment, the specimen holder  10  is primarily square in its cross section geometry and/or includes at least one substantially planar or flat side. As such, the specimen holder  10  can be placed into a clearance slot  30  of the centrifuge  12  in any orientation. It will be appreciated that the geometry of the specimen holders  10  may be varied in accordance with the needs of a particular application or user preference. Similarly, any number and size of specimen holders  10  can be accommodated, dependent only on the size of the rotor  12 .  
         [0034]     When in place, the extended collar  16  or other pivot mechanism of the specimen holder rests against the inner ribs  32  associated with each clearance slot  30 , whereby the collar supports the specimen holder  10  in a vertical or near vertical position in the rotor  12 . The optional cover may already be in place during insertion of the specimen holder  10 . Any additional components of the centrifuge  14  are properly positioned. The rotor  12  is rotated by the motor. The centrifugal force of rotation causes the specimen holder  10  to rotate upward from a rest or a near vertical position to a retracted position, as shown in  FIGS. 1 and 2 . When the specimen holder  10  is in the retracted position, the lower surface of the collar  16  of the specimen holder rests against the proximal surface of the side ribs  26 ,  28 , and the support channel  24  protects the specimen holder within the rotor  12 . While the specimen holder  10  is retracted within the rotor body during centrifugation, the inferior or subjacent surface of the specimen holder  10  is generally flush with the lower plane or bottom  18  of the centrifuge rotor.  
         [0035]     As depicted in  FIG. 2 , during rotation of the rotor  12 , the specimen holder  10  is retracts upward and nests within the support channel  24 . In the retracted position, the specimen holder  10  is horizontally aligned with the support channel  24 . Also, because the preferably planar subjacent surface of the holder is flush with the bottom surface  18  of the rotor, the holder surface and rotor bottom  18  comprise a single and uninterrupted interface. This continuous interface  34  traverses the clearance slot  30  in the bottom surface  18  of the rotor and serves as a barrier that severs access from the support channel  24  to the clearance slot  30 . By substantially sealing the clearance slot  30  of the rotor  12 , circulating air generated during rotation of the rotor  12  is prevented from entering the rotor body and tube holder assembly by way of the clearance slot  30 . Moreover, the specimen holder  10  is not entirely subjected to the friction of air resistance during rotation and does not heat up due to the friction.  
         [0036]     In the present invention, the specimen holder  10  fully, or at least substantially, occupies the support channel  24 , and simultaneously overlays the clearance slot  30  such that there is generally no exposed area within the channel  24  and no protrusion of the specimen holder  10  into the centrifugal air stream about the rotor  12 . As a result of this continuous interface  34 , the clearance slot  30  is impervious to centrifugal air flow. Moreover, because there is no protrusion of the specimen holder  10  beyond the support channel  24  (and into the centrifugal air stream), the specimen holder contents are able to achieve a fully retracted position during rotation. This, in turn, allows for high-quality straight-line separation of fluids of varying densities, or fluids and suspended solids within the specimen holder  10 .  
         [0037]     When rotation of the rotor  12  is terminated, that is, when the centrifuge  14  stops spinning, the specimen holder  10  returns to its original, at rest position, due to gravity.  
         [0038]     There are several advantages provided by the novel specimen holder design of the present invention. Because the specimen holder  10  will retract into a vertical position at relatively low RPM (less than 250 or 500 RPM), the specimen holder design impacts upon the aerodynamics of the rotor  12  operation even at relatively low RPM. At higher RPM, the design significantly impacts upon power consumption of the centrifuge  14 , and substantially decreases the noise generated by aerodynamic drag. Moreover, the decrease in aerodynamic resistance results in less heat from friction.  
         [0039]     Because the relationship between increased RPM and necessary horsepower is logarithmic, decreasing aerodynamic drag of the rotor  12  can have a considerable impact on the horsepower requirements for high speed operations. Moreover, since many modern centrifuges  14  use low temperature samples, this reduction in heat from friction is a tremendous benefit of the rotor specimen holder design of the present invention. Although the geometry of the specimen holder  10  (round, cylindrical, rectangular, etc.) may be varied in accordance with the needs of a particular application or user preference, it is preferable for the specimen holder  10  to be designed with at least one substantially planar surface, such as the design depicted in  FIGS. 1 and 2 . It is advantageous, in a preferred embodiment of the invention, that the cross section of the specimen holder be rectilinear and, preferably, square. The increased aerodynamic performance of the present rotor  12  and specimen holder  10  assembly decreases load on the centrifuge motor, and permits motors of smaller horsepower to be used to achieve a desired separation speed.  
         [0040]     It will be appreciated that a representative use of the present invention involves the separation of platelets from plasma. Because this is more easily accomplished at RPMs in excess of 4,000, use of the present invention with the general rotor  12  design depicted in  FIG. 5  allows the centrifuge  14  to achieve the required RPM with up to fifty percent (50%) less power than conventional means.  
                                                   TABLE 1                           Rotor/Specimen Holder Seal vs. Conventional Centrifuge Rotors                        ROTOR/           CONVENTIONAL   CONVENTIONAL   SPECIMEN       SPECIFICATIONS   ROTOR A   ROTOR B   HOLDER SEAL                    Maximum RPM   1700   2400   3300       Time to Maximum RPM (sec)   120   90   60       Sample Degradation Above Ambient   11   9   7       After 5 Minutes (F)       Sample Degradation Above Ambient   26   17   9       After 10 minutes (F)       Sample Degradation Above Ambient   53   20   10       After 60 minutes (F)       Sample Processing Time for   15   12   7       Chemistries (min)       Sample Processing Time for   25   20   15       Coagulation Studies (min)       Operating Power Consumption   231   120   92       (Watts)                  
 
         [0041]     Referring now to Table 1, there is shown a comparison of the improved operating speeds, sample quality and integrity, sample processing times, and power consumption of the rotor and specimen holder seal of the present invention versus conventional rotors. The data was collected at 115 VAC using a 1/30 th  horsepower permanent split capacitor motor. Results were reproduced to ensure accuracy. Testing was conducted at QBC Diagnostics, Inc., State College, Pa. and at The Drucker Company, Inc., Philipsburg, Pa.  
         [0042]     The foregoing data demonstrate that as compared to conventional centrifuge rotors, the specimen holder seal and rotor assembly of the present invention is able to: (a) reach desirable operating speeds in less time, (b) reach higher operating speeds without increasing power consumption, (c) reduce sample processing time, (d) improve sample quality due to the higher G forces, and (e) maintain sample integrity by minimizing the sample temperature rise above ambient.  
         [0043]     While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various alterations in form and detail may be made therein without departing from the spirit and scope of the invention.