SWINGING BUCKET CENTRIFUGE ROTOR

Abstract: A swinging bucket centrifuge rotor (10) comprises a body (12) that has a reference plane (10R) that extends generally perpendicular to a vertically extending axis of rotation (10A). The body (12) has at least one pair of confronting planar sidewalls (24A, 24B) each of which has a trunnion pin (30) mounted thereon. Each trunnion pin (30) has an axis (30A) therethrough that extends generally perpendicularly to the planar sidewall (24A, 24B) on which the pin (30) is mounted. Each sidewall (24A, 24B) further has a generally cylindrical swinging bucket support surface (40) thereon. Each cylindrical support surface (40) has an axis of generation (40A) that lies in the reference plane (10R) in parallel relationship to the axis (30A) of the trunnion pin (30). Thus, a portion of each cylindrical support surface (40) lies above and below the reference plane (10R).

Description: SWINGING BUCKET CENTRIFUGE ROTOR Background of Invention Field of Invention The present invention relates to a swinging bucket centrifuge rotor. Cross Reference To Related Application Subject matter disclosed herein is disclosed and claimed in contemporaneously filed copending application S. N. , titled "Bucket For Use In A Swinging Bucket Centrifuge Rotor". Description of Prior Art Swinging bucket rotors are well known in the centrifuge art. In the particular class of very high speed (i. e., "ultra"- class) rotor, the rotor usually comprises a rotor body having an array of cavities located on the undersurface thereof. These cavities are adapted to receive a bucket which when installed hangs from the undersurface ofthe rotor body. When the rotor is accelerated to high speed the bucket swings from its rest position to a horizontal position, usually with some surface of the bucket coming to rest against a support surface on the underside ofthe body. This support surface is contoured to receive the bucket, thus transferring some ofthe load from the bucket hanger to the rotor body. United States Patent 3,997,105 (Hayden et al.) is believed a representative example of such a rotor construction. Rotors of this type usually incorporate a spring mechanism in the hanger that allows a pin on the bucket to deflect when the bucket rotates to the horizontal position. This deflection allows the bucket to rest against the support surface ofthe rotor body. This traditional type of swinging bucket rotor can sometimes cause difficulties for the clinician. Since the bucket hangs from the undersurface ofthe body the clinician must reach under the rotor to insert the bucket onto the rotor. This action is rendered even more difficult if the rotor is mounted to on the shaft installed in a centrifuge instrument. It is not uncommon for a bucket to be improperly installed. During operation improper installation of a bucket can cause damage to the rotor and/or, the instrument, or worse, a rotor disruption. A different type of swinging bucket rotor developed to improve the bucket installation is disclosed in United States Patent 3,997,105 (Chulay et al.). This type of swinging bucket rotor is known as a "top loader", owing to the fact that the buckets are installed from the top, usually by dropping onto a pin or a hanger. One problem with both the traditional and the "top-loader" rotor is the fact that, when the bucket is in the horizontal position, the support surface on the rotor body typically only supports the portion ofthe bucket lying above a generally horizontal reference plane. Due to unequal support a large bending moment is applied to the rotor body support surface. The rotor body must thus be designed to accommodate this load, resulting in considerably larger and more expensive rotor. United States Patent 4,585,434 (Cole et al.) discloses a rotor in which the bottom surface ofthe bucket acts as the support surface, with the bucket resting on the structure that is usually considered the rotor windshield. However the requirement of a windshield also adds size and cost to the rotor. In view ofthe foregoing it is believed advantageous to provide a top loading swinging bucket rotor that provides support for both the portion of the bucket that lies both above and below a predetermined plane, thus reducing the bending moment applied to the rotor body. SUMMARY QF INVENTION In a first aspect the present invention is directed toward a swinging bucket centrifuge rotor for use in a centrifuge instrument that comprises a body adapted for rotation about an axis of rotation extending vertically through the body. The body has a reference plane that extends through the body generally perpendicular to the axis of rotation. The body has at least one pair of confronting planar sidewalls which are circumferentially spaced apart to define a generally axially extending slot sized to receive a swinging bucket therein. Each planar sidewall has a trunnion pin mounted thereon, with each trunnion pin having an axis therethrough. Each trunnion pin is disposed a first predetermined radial distance from the axis of rotation The axis of each trunnion pin extends generally perpendicularly to the planar sidewall on which it is mounted. Each sidewall further has a generally cylindrical swinging bucket support surface thereon, the cylindrical support surface being disposed on each sidewall a second, greater, radial distance from the vertical axis. Each cylindrical support surface has an axis of generation that lies in the reference plane. Thus, a portion of each cylindrical support surface lies above and below the reference plane. The axis of generation of each cylindrical support surface may be parallel to or collinear with the axis of a trunnion pin. In another aspect the present invention also relates to a bucket for use in a swinging bucket centrifuge rotor. The bucket in accordance with this aspect ofthe invention comprises a cylindrical body having a reference axis extending therethrough with a pair of planar abutments formed on the body. The abutments are diametrically disposed on the body with respect to the axis thereof. Each planar abutment surface has a planar side surface and a bottom support surface thereon. A slot is formed between a portion of each abutment and the body ofthe bucket. Each planar side surface has a first groove that extends generally parallel to the axis ofthe body and a second groove that extends generally peφendicular to the axis ofthe body. The first and second grooves communicate with the slot. The first and second grooves together with the slot cooperate to define a resilient spring element on each abutment. The bottom support surface on each abutment is generally cylindrical in shape and has an axis of generation that lies along the axis ofthe body, whereby a portion of each bottom support surface lies on opposite sides ofthe axis ofthe body. BRIEF DESCRIPTION OF D A INGS The invention will be more fully understood from the following detailed description, taken in connection with the accompanying drawings, in which; Figures IA and IB are, respectively, plan and side sectional views of a swinging bucket centrifuge rotor in accordance with a first aspect ofthe present invention; Figures 2A, and 2B are, respectively, a plan and a side elevational view, partially in section, and Figure 2C is a sectional view of a bucket for use in the swinging bucket rotor of Figure IA and IB; Figures 3 A through 3D are side sectional views ofthe bucket shown in Figures 2A through 2C in use with a rotor as shown in Figures IA and IB. DETAILED DESCRIPTION OF INVENTION Throughout the following detailed description similar reference characters refer to similar elements in all Figures ofthe drawings. With reference to Figures IA and IB, respectively shown are a plan view and a side elevational view, partially in section, of a swinging bucket centrifuge rotor generally indicated by the reference character 10 in accordance with the present invention. The rotor 10 is a relatively massive member formed from a strong, light weight, material, such as titanium or aluminum, by either casting, forging, or machining from solid bar stock The various surfaces to be described herein are imparted to the rotor 10 by suitable machining operations, as should be understood by those skilled in the art. The rotor 10 is adapted for rotational motion within a centrifuge instrument about a vertical axis of rotation 10A extending therethrough. The rotor 10 includes a body portion 12 having a central hub region 14 from which emanates a plurality of generally radially extending arms. The arms are generally indicated by the reference character 16. Although six arms 16A through 16F are illustrated, it should be understood that any predetermined convenient number of arms may radiate from the hub 14. The rotor 10 has an upper planar surface 18 and a lower surface 20 thereon. A mounting recess 22 extends through the hub 14 from the upper surface 18 to the lower surface 20. The lower portion ofthe mounting recess 22 is frustoconical in shape (Figure IB) to receive the correspondingly tapered upper end ofa drive shaft (not shown) of a centrifuge instrument whereby the rotor 10 may be coupled to a source of motive force. When mounted to the shaft the axis ofthe shaft ofthe instrument aligns with the axis of rotation 10A ofthe rotor 10. As is best illustrated in Figure IB the body 10 has a reference plane 10R that extends therethrough in generally peφendicular relationship to the axis of rotation 10 A. That is to say, in the conventional usage, the reference plane 10R is oriented generally horizontally when the rotor 10 is mounted for rotation about a generally vertically disposed axis of rotation 10 A. Each arm 16A through 16F carries thereon a pair of generally parallel, planar sidewalls 24A, 24B, respectively. The sidewall 24A on a given one ofthe arms 16A through 16F is confrontationally disposed with respect to the sidewall 24B on the next-circumferentially adjacent arm thereby to define a circumferential array of slots 26 A through 26F. Each slot extends generally axially through the rotor, (i. e., substantially parallel to the axis of rotation 10A). The paired sidewalls 24 A, 24B on respective circumferentially adjacent arms 16 are circumferentially spaced apart sufficiently to accommodate a swinging bucket sample container 100 that will be described more fully herein. The radially inner ends ofthe paired sidewalls 24A, 24B are joined by a scalloped contoured surface 28A through 28F which affords sufficient head space to accept the head ofthe bucket 100 to be described when the same swings from its rest toward its operating position. Each planar sidewall 24A, 24B in each confronting pair of sidewalls has a trunnion pin 30 mounted thereon. Each trunnion pin 30 itself has an axis 30 A therethrough. The axis 30A of each trunnion pin 30 extends generally peφendicularly to the planar sidewall 24A, 24B, as the case may be, on which it is mounted. The axes 30 A ofthe trunnion pins disposed on circumferentially adjacent arms lie on a common line 36A through 36F, as shown in Figure 1 A. As will be developed and discussed herein (Figures 3A through 3D) these lines 36A through 36F align with a swing axis 100S on which a bucket 100 depending from the paired trunnion pins 30 swings as the bucket 100 displaces from its first, rest, position (Figure 3 A) to its second, operating position (Figure 3D). The trunnion pin 30 on each arm is located a predetermined radial distance 30R (Figure IB) from the axis of rotation 10 A. The axis 30 A of each of trunnion pin 30 preferably lies on the reference plane 1 OR (Figure IB). The radially outer end of each arm 16A through 16F has a generally circumferentially extending finger 38 A, 38B thereon. The finger 38 A on a given one ofthe arms 16A through 16F is confrontationally disposed with respect to the finger 38B on the next-circumferentially adjacent arm. The paired confronting fingers 38A, 38B on respective circumferentially adjacent arms 16 partially close the slots 26A through 26F defined by the sidewalls on which the fingers are disposed. However, the ends ofthe fingers 38 A, 38B are circumferentially spaced apart sufficiently to permit the main cylindrical portion ofthe body ofa swinging bucket sample container 100 to swing outwardly as the bucket moves toward its operating position. Each finger 38A, 38B has a generally cylindrical swinging bucket support surface thereon 40 thereon. Each support surface 40 has a predetermined radius of curvature associated therewith. The support surfaces 40 are disposed on each sidewall 24A, 24B (as the case may be) a second, greater, radial distance 40R from the vertical axis 10A (Figure IB). As is made clear in Figure IB each cylindrical support surface 40 has an axis of generation 40A that lies in the reference plane 10R. The axis of generation 40A may be disposed in parallel relationship to the axis 30A ofthe trunnion pin 30 that extends from the sidewall on which the support surface is mounted. In the most preferred instance the axis 30A of each trunnion pin lies in the reference plane 10R in collinear relationship with the axes of generation 40A ofthe support surfaces 40. As is apparent from Figure IB the above-described relationship between the axis of generation 40A of each cylindrical support surface 40 and the reference plane 10R ofthe rotor 10 thereby subdivides the surface 40 into a portion 40T that lies axially above the reference plane 10R and a portion 40B that lies axially below the reference plane (both with respect to the axis of rotation 10A). The advantage afforded by this disposition ofthe support surfaces 40 will become more clear herein. -o-O-o- In another aspect the present invention is directed toward a bucket generally indicated by the reference character 100 for use in a swinging bucket centrifuge rotor. The bucket is illustrated in Figures 2A through 2C herein. In accordance with the present invention the bucket 100 comprises a generally cylindrical body portion 104 through which a longitudinal reference axis 100A ofthe bucket 100 extends. The open top 104T ofthe body 104 defines the upper, or top, end ofthe bucket 100. The closed lower end 104E ofthe body 104 may be spherical, conical, or otherwise configured. The bucket 100 also has a predetermined swing axis 100S defined therethrough. The swing axis 100S is that axis about which the bucket 100 swings as it moves from its first, rest, position (Figure 3 A) to its second, operating, position (Figure 3D). Preferably, the swing axis 100S peφendicularly intersects the longitudinal axis 100 A ofthe bucket 100. The body 104 is hollow to define a central, sample container-receiving cavity 106 therein. The mouth 108 ofthe cavity 106 may be threaded (if desired) to receive a cap 110 (Figure 2C). The cavity 106 may be otherwise closed in any suitable manner. The swinging bucket 100 includes a pair of ear-like abutments 114A, 114B formed on the body portion 104. As is best seen in Figures 2A and 2C a slot 118A, 118B each serves respectively to separate the axially upper portion of each ofthe abutments 114 A, 114B from the main body ofthe bucket 100. The purpose ofthe slots 118 A, 1 I8B shall become more clear hereafter. Each abutment 114 A, 114B has a planar exterior lateral surface 122 and a generally cylindrical bottom support surface 124 thereon. The planar exterior lateral surface 122 is arranged to lie peφendicular to the swing axis 100S. The cylindrical bottom support surface 124 has a radius of curvature that is equal to the radius of curvature ofthe support surface 40. As is best seen in Figure 2B the planar exterior lateral surface 122 of each abutment has a first groove 126 and a second, intersecting, groove 128 formed therein. The first groove 126 extends generally parallel to the longitudinal axis 100 A ofthe bucket 100 while the second groove 128 extends generally peφendicularly to that axis. The lower portion ofthe first groove 126 has tapered lead-in surfaces 126T thereon. The upper portion ofthe first groove 126 and the entirety of the second groove 128 communicate with the slot 118 lying adjacent to the abutment 114A, 114B in which the grooves are formed, as the case may be. As such, the first and second grooves 126, 128, together with the slot 118, cooperate to define in each abutment 114 A, 114B a resilient spring element 132. The axis of generation 124A of the generally cylindrical bottom support surface 124 on each abutment 114A, 1 14B lies along the longitudinal axis 100A ofthe ofthe bucket 100 in peφendicular relationship with respect thereto. Accordingly, the cylindrical bottom support surface 124 is subdivided into portions 124T, 124B (Figure 2B) that lie on respective sides ofthe axis 100 A ofthe bucket 100. As viewed in Figure 2B the portion 124T ofthe surface 124 is illustrated as lying to the right ofthe longitudinal axis 100A ofthe bucket 100, while the portion 124B ofthe surface 124 is illustrated as lying on the left ofthe longitudinal axis 100 A. The advantage afforded by this configuration ofthe support surface 124 will also become more clear herein. The axis of generation 124A may be disposed parallel to or collinear with the swing axis 100S. Based upon considerations which are more fully discussed herein the axis of generation 124A may be disposed either "above" the swing axis 100S, in which case the axis of generation 124A lies closer to the top end 104T of the bucket 100 than does the swing axis 100S. Alternatively, the axis of generation 124A may be disposed "below" the swing axis 100S, in which case the swing axis 100S lies closer to the top end 104T ofthe bucket 100 than does the axis of generation 124A . -o-O-o- Having described the structural details of both the rotor 10 and the swinging bucket 100 for use therein, the manner in which these members are used together may be understood from Figures 3 A to 3D. In Figure 3 A the rotor 10 and the bucket 100 are shown while at rest. The rotor is assumed to be mounted to the shaft ofa centrifuge instrument (not shown) such that the axis 10A ofthe rotor 10 is disposed in a generally vertical disposition with respect to an external datum. The bucket 100 is installed on the rotor 10 in the position shown by lowering the bucket 100 into one ofthe slots 26 such that the trunnion pin 30 on each ofthe confronting sidewalls 24A, 24B that define the slot 26 is received within a groove 126 defined on an abutment 114 A, 114B ofthe bucket 100. The bucket 100 is lowered until the undersurface ofthe resilient element 132 rest against corresponding trunnion pin 30. The tapered lead-in surfaces 126T assist in this installation. The bucket 100 is thus supported in a depending relationship from the paired trunnion pins 30 by the resilient elements 132 on each abutment 114A, 114B. When in the rest position the longitudinal axis 100A ofthe bucket 100 lies peφendicular to the reference plane 10R ofthe rotor 10. The swing axis 100S ofthe bucket 100 aligns with the line 36 and the collinear axes 30A. Figure 3B illustrates the relationship between the rotor 10 and the bucket 100 as the rotor accelerates to a relatively low rotational speed. Since the center of gravity CG ofthe bucket 100 (and any liquid sample carried therein) lies below the swing axis 100S the bucket 100 starts to swing (about the swing axis 100S) from its rest position (Figure 3 A) toward its operating position (Figure 3D). As rotor speed increases the longitudinal axis 100 A ofthe bucket 100 approaches the horizontal reference plane 10R (Figure 3C). Due to the centrifugal loading ofthe bucket 100 (and any liquid sample carried therein) the spring element 132 on each abutment 114A, 114B begins to deform. As a result the G (Figure 3C) between the support surface 124 on each ofthe abutments 114A, 114B ofthe bucket and the support surface 40 on each sidewall 24 A, 24B begins to radially narrow. The disposition ofthe bucket 100 with respect to the rotor 10 when the bucket 100 has reached its operating speed is illustrated in Figure 3D. At operating speed the longitudinal axis 100 A ofthe bucket 100 lies substantially on the horizontal reference plane 10R ofthe rotor 10. The deflection ofthe spring element 132 on each abutment 114 A, 114B deforms to an extent such that the support surface 124 on each abutment 114 A, 114B contacts against the support surface 40. In particular, the portion 124T of each of support surface 124 that lies above the reference plane 10R rests against and is supported by the corresponding portion 40T ofthe support surface 40. In addition, in accordance with the present invention, the portion 124B of each of support surface 124 that lies below the reference plane 10R is also supported by a corresponding portion 40B of the support surface 40. When supported by the surface 40 a substantial portion ofthe centrifugal load generated by the bucket 100 (and any liquid sample carried therein) is transferred from the trunnion pins 30 to the corresponding arms 16 of the rotor 10. However, since the bucket 100 is supported substantially equally both above and below the reference plane 10R no bending moments are generated in the transference ofthe load. This reduces the amount of material in the rotor 10 which is needed to support the load. The relative position among the axis of generation 124A and the swing axis 100S (on the bucket 100) and the axis of generation 40 A and and the line 36 (on the rotor 10) serves to define the gap G between the support surfaces 124 and 40 (Figure 3C). In the preferred instance the axis of generation 40A and the line 36 are collinear in the plane 10R. Accordingly, the axis of generation 124 A on the bucket 100 is located along the longitudinal axis 100 A above the swing axis 100S. The distance between the swing axis 100S and the axis of generation 124A is usually on the order of 0.010 inch to 0.015 inch. (This distance is exaggerated in the figures for clarity of illustration.) If it is desired to have the axis of generation 124 A be located along the longitudinal 100 A below the swing axis 100S, then the axis of generation 40A must lie parallel to and radially outward from the line 36 in the plane 10R. -o-O-o- Those skilled in the art, having the benefit of the teachings ofthe present invention as hereinbefore set forth, may impart modifications thereto. Such modifications are to be construed as lying within the contemplation ofthe present invention, as defined by the appended claims.

Claims: What is claimed is: 1. A swinging bucket centrifuge rotor for use in a centrifuge instrument, the rotor comprising: a body adapted for rotation about an axis of rotation extending vertically through the body, the body having a reference plane extending therethrough, the reference plane extending generally peφendicular to the axis of rotation, the body having at least one pair of confronting planar sidewalls, the planar sidewalls being circumferentially spaced apart to define a generally axially extending slot sized to receive a swinging bucket therein, each planar sidewall having a trunnion pin mounted thereon, each trunnion pin having an axis therethrough, the axis of each trunnion pin extending generally peφendicular to the planar sidewall on which it is mounted, the trunnion pins each being disposed a first predetermined radial distance from the axis of rotation, each sidewall further having a generally cylindrical swinging bucket support surface thereon, the cylindrical support surface being disposed on each sidewall a second, greater, radial distance from the vertical axis, each cylindrical support surface having an axis of generation that lies in the reference plane, whereby a portion of each cylindrical swinging bucket support surface lies above and below the reference plane. 2. The rotor of claim 1 wherein the axis of generation of each support surface lies in parallel relationship to the axes ofthe trunnion pins. 3. The rotor of claim 2 wherein the axes ofthe trunnion pins line in the reference plane. 4. The rotor of claim 1 wherein the axis of generation of each support surface is collinear with the axes ofthe trunnion pins.

Inventors: ROMANAUSKAS WILLIAM A, ROMANAUSKAS, WILLIAM, A.
Applicants: SORVALL PRODUCTS LP, SORVALL PRODUCTS, L.P.
Application year: 1996
Main classification: B04B5
IPC codes: B04B5