US3430852A - Rotor stabilizer - Google Patents

Description

March 4, 1969 A. LENKEY ETAL ROTOR STAB ILI ZER Filed June 8, 1967 Sheet of4 JAMES B. GRAESER JR. BY ANDREW LENKEY ATTORNEY M r 4. 1969 A. LENKEY I ETAL Q 3,430,852

ROTOR STABILIZER Filed June a, 19s? Sheet 2 of 4.

\ 1N/VEN'IORS:

22 JAMES B. GRAESER JR.

BY ANDREW LENKEY ATTORNEY March 4, 1969 A. LENKEY ETAL ROTOR STABILIZER Sheet Filed June 8, 1967 FIG. 2 a

INVENTORSI JAMES B. GRAESER JR. ANDREW LENKEY ATTORNEY March 4, 1969 A. LENKEY ETAL 3,430,852

' ROTOR STABILIZER Filed June a, 1967 Sheet 4 of 4 (\1 i so s4 FIG. 3

FIG. 30.

INVENTORS BY ANDREW LENKEY ATTORNEY United States Patent 9 Claims ABSTRACT OF THE DISCLOSURE Apparatus for stabilizing a spinning rotor below a predetermined speed of rotation which apparatus is completely removable from the centrifuge and in which a tractive electromagnet actuates a stabilizing member into engagement with the rotor below said speed.

Cross-references to related applications Copending application Ser. No. 273,166, filed Apr. 15, 1963, now Patent No. 3,322,338 entitled Centrifuge Stabilizing Assembly With Heat Probe and assigned to the assignee of the present invention, relates to the same general subject matter.

The present invention relates generally to rotor stabilizing apparatus and particularly to improved apparatus for stabilizing centrifuge rotors below a predetermined speed.

In high speed centrifuges employing relatively heavy rotors mounted upon and driven by small diameter, flexible spindles, instability or wobbling of the rotor usually occurs below a certain speed. This wobbling action, if permitted a wide excursion, has various adverse effects among which are the creation of high stresses and the remixing of sample components separated during the high speed portion of the centrifuge run.

Apparatus for stabilizing centrifuge rotors during low speed operation are known in which a rotor-stabilizing member is automatically moved to engage the rotor and prevent wobbling when the rotor speed drops below a predetermined level. Actuation of the stabilizing member has been accomplished in various ways, as for example, by a solenoid. The apparatus of the prior art, however, has proven deficient in a number of Ways. For example, they utilize complex structures limiting access to the interior of the rotor chamber, tend to chatter during operation thereby creating an objectionable noise level (especially when energized by an A.C. power supply) and provide no Way of limiting the force with which the stabilizing member engages the rotor. This latter characteristic not only results in excessive component wear but may have the effect of disturbing and remixing the separated components or sediment as a consequence of the rotor being jarred during deceleration after a run.

Accordingly, the overall object of the present invention is to provide an improved apparatus for stabilizing centrifuge rotors so as to overcome the aforedescribed problems.

More specifically, it is an object of this invention to provide a simplified centrifuge rotor stabilizing apparatus, which is completely removable from the centrifuge to permit complete access to the centrifuge chamber interior.

It is another object of the present invention to provide a centrifuge rotor stabilizing assembly which is substantially chatter and noise free.

Yet another object of this invention is to provide apparatus for actuating a centrifuge rotor stabilizing member in which the engagement force of the stabilizing member is limited so as to reduce and minimize component wear and jarring of the rotor.

With these and other objects in view, the present in- 3,439,852 Patented Mar. 4, 1969 vention will be clearly understood in connection with the accompanying drawings in which:

FIG. 1 is a plan view of a portion of a centrifuge machine including a rotor stabilizing assembly embodying the present invention;

FIG. 2 is an elevation View, in section, of the apparatus of FIG. 1 taken along the plane 2-2 showing the rotor stabilizer in the retracted or rotor-released position;

FIG. 2a is an elevation view, in section, similar to FIG. 2 showing the rotor stabilizer in the advanced or rotorengaging position; and

FIGS. 3 and 3a are elevation views, in section, of a portion of the rotor stabilizing apparatus showing in greater detail the geometry and relative positions of the components in the rotor-released and rotor-engaging positions.

Referring to the drawings, the reference numeral 10 designates a centrifuge rotor mounted for rotation on a small diameter, relatively flexible spindle 12. Mounted on the top of the rotor coaxially therewith, is a sleeve 14 which provides a convenient handle for manipulating the rotor. The lower end of the resilient spindle 12 is rotatably driven through suitable gearing by an electric motor (not shown) located beneath the rotor. The rotor 10 spins within a chamber 16 defined by a cylindrical steel housing 18 which concurrently functions as a guard should the rotor explode under the strain created by the relatively high rotational velocity at which it is operated. A liner 19 is mounted inside the chamber 16 proximate the interior surface of the housing 18. The chamber interior is refrigerated by means (not shown) including evaporator coils surrounding the liner which serves to control the chamber temperature.

A stabilizing assembly, designated generally by the refence numeral 20, is mounted across the open top of the chamber 16. The assembly 20, which is removable as a unit, is supported with respect to the centrifuge machine frame by means of three brackets 22, 24 and 26 secured to the housing 18.

The stabilizing assembly includes a generally triangle-shaped base or support plate 28 which extends across the chamber 16. Suitably fastened to the plate 28 proximate the extremities of the wider end, are fixed support pins 31 and 32. The pins and 32 are adapted to be received by detents 34 and 36 formed in the brackets 22 and 24, respectively. A block 38 is mounted at the small end of the plate 28 for carrying a movable support pin 40. The pin 40 has an enlarged, pointed end 42 adapted to be received by detents 44 in the bracket 26. The block 38 is provided with a stepped longitudinal bore 46 having a shoulder 48, the end 42 of the pin 40 being slidably'received in the bore 46. The pin 40 is biased outwardly by means of a coil spring 50 compressed within the bore 46 between the shoulder 48 and the pin end 42. The inner end of the pin 40 is grooved to receive a snap ring 52 which limits the outward movement of the pin.

To permit the stabilizing assembly 20 to be adjustably positioned up or down within the chamber 16 in order to accommodate rotors of various heights, several vertically spaced detents are formed in each of the brackets 22, 24

and 26. To position the assembly 20 at any selected level within the chamber 16, the fixed pins 30 and 32 are inserted in the detents 34 and 36 at the appropriate level and pin 40 is manually retracted and inserted in the corresponding detent 44 in bracket 26. It will be appreciated that the insertion and removal of the assembly 20 is thereby made exceedingly simple and the operation can be performed with one hand.

The support plate 28 is provided with a circular opening for receiving a stabilizer support assembly 62 which carries a stabilizing member 64 and an electromagnetic actuating device for advancing the member 64 into contact with the sleeve 14 on the rotor 10. The assembly 62 is suspended from the plate 28 by a support bracket 66 which extends across the opening 60. The bracket 66 has a centrally located hole 68 having a vertical axis positioned substantially coincident with the geometric or figure axis of the rotor and spindle 12.

The following description relates to the stationary portion of the assembly 62. A fixed, outer housing 70 made of a suitable non-magnetizable material such as aluminum and having an upright, cylindrical flange 72 projecting upwardly through the hole 68, is held in place and suspended from the bracket 66 by means of a retaining ring 74 mounted in a groove formed in the flange 72. The outer housing 70 further has a depending flange portion 76 provided with an annular step 78. Mounted within the step 78 is a circular plate 80 made of a suitably magnetizable material. The plate 80 has a central, upwardly extending annular lip 82 provided with a bore 84 coaxial with the cylindrical flange 72. The lip 82 functions as an electromagnet pole piece as will be described in greater detail later. The upper end of the pole piece 82 i dished out or cut away to form an inwardly sloping or tapered surface 86. A sleeve 88, made of a non-magnetic material such as brass, is press fit within the bore 84. The sleeve 88 has an upper rim 90 projecting upwardly a short distance from the inner, lower edge of the tapered surface 86. The rim 90 serves as a stop means as will be described below. Another non-magnetizable sleeve 92, which may also be made of brass or the like, is press fit about the outer surface of the pole piece 82 and within the bore defined by the flange 72. Carried within the outer housing 70 and disposed about the sleeve 92 is a donut shaped electromagnet 94. A pair of electrical leads 96 extend through an opening 98 in the housing 70 for connection with external circuitry for energization of the electromagnet 94. A cylindrical radiation shield 100 is suitably secured to the undersurface of the plate 80 by rivets 102, for example, for the purpose of minimizing radiant energy exchange between the stabilizer member 64 and assembly 62 on the one hand and the chamber 16 on the other.

The following is a description of the movable components, actuated by the electromagnet 94, for advancing the stabilizing member 64 into contact with the sleeve 14. Slidably mounted within the sleeve 92 is a generally cylindrical magnetizable armature 104 having an annular step or undercut 106 formed therein in the bottom portion. The downwardly projecting flange 108 defined thereby is provided with a beveled lower surface 110, the slope of which is substantially the same as that of the tapered surface 86 of the pole piece 82. The use of tapered surfaces on coacting magnetic elements such as the pole piece 82 and armature 104, is well known in the art for providing larger forces for a given amount of linear travel and for minimizing chatter and noise. A narrow, ringlike flat surface 112 is retained at the lower edge of the armature 104 for making contact with the upper edge of the sleeve 88 when the armature is advanced to the rotorengaging position. By inspection of the geometry of the armature 104, it will be appreciated that the depth of the undercut 106 determines the surface area of the conical surface 110.

The upper portion of a tube 114, made of non-magnetic material such as brass, is press fit within the bore of the armature 104. The lower portion of the tube 114 slides freely within the sleeve 88. A bearing assembly exterior housing 116 is aifixed to the tube 114 so as to move up and down therewith. Specifically the housing 116 has an upright cylindrical portion 118 about which the tube 114 is press fit. The housing 116 further includes a lower, depending cylindrical flange 120 which defines an interior well 122. The flange 120 carries a ring-like, interior bearing housing 124 having a generally T-shaped crosssection with an upper, horizontal leg 126 and a vertical 4 leg 127. The interior housing 124 is supported within the well 122 by means of a retaining ring 128 and a washer 130 interposed between the ring 128 and the horizontal leg 126 of the housing 124. The outer diameter of the interior housing 124 is substantially less than the inside diameter of the well 122. In this way, the interior housing 124 is free to slide, within limits, transversely of the axis of rotation of the rotor 10. The exterior housing 116 is made of a nonmagnetic material such as aluminum and the interior housing 124 is preferably fabricated of a selflubricating plastic material such as the acetal resin material sold under the trademark Delrin manufactured by E. I. du Pont de Nemours & Company. This material is characterized by the radical [(OCH Thus, the housing 124 moves within the well 122 with its upper surface in frictional engagement with the undersurface of the horizontal portion of the exterior housing 116.

The stabilizing member 64, also made of Delrin or other suitable self-lubricating plastic, is carried by the inner race of a ball-bearing 142 and locked in place between a snap ring 144 and a shoulder 146 formed in the exterior surface of the member 64. The outer race 148 of the bearing 142 is similarly carried within the vertical leg 127 of the housing 124 and is held in place by a retaining ring 150.

The movable portion of the stabilizer assembly is biased to the retracted or rotor-released position by a helical coil spring 152 compressed between the horizontal surface of the undercut 106 on the armature 104 and the upper horizontal face of the pole piece 82. It will be seen that in the advanced position of the stabilizer, as depicted in FIG. 2a, the lower surface of the stabilizing member 64 comes into contact with the upper edge of the sleeve 14. To facilitate engagement of these elements should there be misalignment due to rotor eccentricity, the lower surface of the member 64 may be tapered or rounded as shown. The downward travel of the armature, and hence that of the stabilizing member64 is limited by the rim 90 of the sleeve 88 which eventually will be engaged by the surface 112 on the armature. It should be pointed out that since the motor and transmission of the centrifuge machine are shock-mounted, some downward, vertical displacement of the rotor and spindle is possible. Thus, as the stabilizing member 64 is moved into engagement with the sleeve 14, there may be some slight downward movement of the rotor 10.

One aspect of the present invention which will now be described, tends to limit the force with which the stabilizing member 64 engages the sleeve 14 thereby minimizing the jarring or disturbance of the rotor 10 which might otherwise tend to remix the sediment within the sample containers carried by the rotor. Referring specifically to FIGS. 3 and 3a, the former shows the armature in the retracted or rotor-released position while the latter shows the armature at its limit of travel in the other direction corresponding to the rotor-engaging position. It will be seen that because of the undercut 106 on the armature 104, substantially all lines of flux emanating from the face of the armature intercept the face of the pole piece irrespective of the air gap between the elements within the limits of travel of the armature. In other words, the cross-sectional area defined by the lines of magnetic flux between the faces remains substantially constant throughout the entire range of travel of the armature. It will also be appreciated that the pole piece may be undercut instead of the armature so that the pole piece will have the smaller surface area. As a further obvious alternative, the surfaces may be made to slope outwardly instead of inwardly toward the axis of rotation as depicted in the drawings.

With the cross-sectional area of the magnetic lines of flux being held substantially constant, the only remaining variable which will affect the attractive force on the armature is the air gap between the armature and the pole piece. By providing the stop means 90 to limit the downward travel of the armature, and thereby retain an air gap between the elements, the device may be operated within a range in which force is approximately linearly related to distance between the armature and pole piece. The residual air gap which is provided by the stop means also functions to prevent jamming of the elements due to inexact machining and prevents residual magnetism from holding the elements together after de-energization of the electromagnet.

Means serving to energize the electromagnet 94 below a predetermined speed of rotation of the rotor to advance the member 64 includes the circuitry shown schematically in FIG. 2. A speed transducer 160 is mounted to detect the rotational speed of the spindle 12. Transducer 160 feeds a signal to a speed control circuit 162 having an output coupled via the connection 164 to appropriate contacts (not shown) within the detent 44 on the bracket 26. Corresponding contacts (not shown) on the pin head 42 of pin 40 serve to complete the connection between the speed sensor 160 and the leads 96 through a connector plug 166. Where the output signal from the circuit 162 is A.C., a diode 168 may be included to rectify the signal and provide the electromagnet with DC.

Operation of the foregoing apparatus is as follows:

With a selected rotor mounted upon the spindle 12 the stabilizing assembly 20 is brought down into the chamber 16 to an appropriate level. At the selected level, fixed pins 30 and 32 are inserted into the corresponding detents in brackets 22 and 24, respectively, pin 40 is pushed into the bore 46 and the narrow end of the assembly 20 is lowered into the chamber into position. The pin 40 is then permitted to enter the appropriate detent 44 in the bracket 26. It will be noted that the assembly 20 is a completely self-contained, removable unit requiring no external wiring and when removed permits complete access into the chamber 16 for installation or removal of a rotor. Inasmuch as the rotor is not yet operating, the electromagnet 94 will be energized thereby attracting the armature 104 and moving it along with the exterior housing 116 downwardly until the stabilizing member 64 engages the sleeve 14. The rotor is now started. It should be noted that the elastic axis on which the rotor rests is never quite straight and consequently the equilibrium positions of the rotor at rest and while spinning at high speed are not identical. A transition of the equilibrium position of the rotor therefore occurs, accompanied by wobbling, usually at lower speeds of several thousand revolutions per minute. The lateral displacement or wobbling of the rotor during the transition range is minimized by frictional damping provided by the stabilizing member 64 and the interior housing 124 in cooperation with the exterior housing 116. While the member 64 spins with the rotor 10 within the ball bearing 142, it describes, along with the interior housing 124, an orbiting path about the common axis of the non-rotating components of the assembly 62. The limiting amount of lateral displacement of the combination of the interior housing 124 and stabilizing member 64 is determined by the clearance between the periphery of the interior housing 124 and the interior wall of the flange 120.

After the rotor 10 has passed through its transition speed and has begun to rotate steadily about an axis (which, of course, will vary with the rotor and the particular sample loading), the speed control circuit 162 deenergizes the electromagnet 94. The coil spring 152 moves the armature upwardly to retract the stabilizing member 64. The rounded lower surface of the member 64 tends to coaxially align the member with the axis of rotation of the rotor 10 established above the transition speed so that the member 64 will already be properly oriented when it is lowered once again for engagement with the sleeve 14.

Following completion of the centrifuge run, the rotor 10 is gradually decelerated. As it approaches the transition speed at which wobbling might be expected to occur, a signal from the speed sensor 160 causes an output signal to appear on the connecting line 164 to once again energize the electromagnet 94. The armature 104 thereby moves downwardly against the force of the helical spring 152 until contact is made by the member 64 against the sleeve 14, the travel of the armature 104 being limited by the rim 90.

It will be obvious to those skilled in the art that various modifications may be made to the specific exemplary embodiments of the invention described. While particular embodiments have been discussed, it will be understood that the invention is not limited thereto and that it is contemplated to cover in the appended claims any such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a centrifuge rotor stabilizer in which a stabilizing member and a bearing assembly in which said member is rotatably mounted, are advanced from a rotor-released position to a rotor-engaging position below a predetermined rotor speed, the improvement in which a movable, magnetizable element is secured to said bearing assembly;

a stationary, magnetizable element is mounted proximate said movable element and separated therefrom by an air gap for attracting said movable element when said stationary element is magnetically energized so as to move said bearing assembly and the stabilizing member to said rotor-engaging position;

an electromagnet surrounds said stationary element for magnetically energizing said stationary element when said rotor speed is below said predetermined level; and

resilient means is interposed between said movable and said stationary elements urging said elements apart.

2. Apparatus as defined in claim 1 in which said movable and stationary elements have opposing,

tapered, parallel faces, the face on one of said elements having a smaller area than the face on the other of said elements, the cross-sectional area defined by the lines of magnetic flux between said faces remaining substantially constant throughout the entire range of travel of said movable element.

3. Apparatus as defined in claim 1 in which said movable and stationary elements have opposing parallel sloping faces, the face of one of said elements having a smaller area than the face of the other of said elements, the geometric projection of the face of smaller area normal to said face falling on the face of the other element within the limits of travel of the elements relative to one another.

4. Apparatus as defined in claim 1 in which a stop means is disposed between said elements for limiting the travel of said movable element thereby leaving an air gap between said elements when said bearing assembly and stabilizing member are in said rotor-engaging position.

5. In an apparatus for stabilizing a centrifuge rotor about its axis of rotation within a predetermined speed range, said apparatus including a stabilizer member rotatably mounted within a bearing assembly and means operatively associated with said assembly for advancing the combination of said assembly and said stabilizer member whereby said member is brought into engagement with said rotor when said rotor speed falls within said predetermined speed range, the improvement in which said advancing means comprises a substantially cylindrical, stationary pole piece mounted coaxially of the geometric axis of said rotor;

an electromagnet disposed about said pole piece for magnetically energizing said piece when said rotor speed is within said predetermined range; and

a generally cylindrical armature connected to said bearing assembly and positioned coaxially of said pole piece and proximate thereto so as to be attracted by said pole piece upon energization thereof.

6. Apparatus as defined in claim in which said armature and said pole piece have opposed, sloping, substantially parallel faces; and

the outer cylindrical surface of said armature is undercut to reduce the area of said sloping face of said armature, the depth of said undercut being such that substantially all magnetic lines of flux emanating from said sloping armature face intercept said sloping face of said pole piece irrespective of the position of said armature Within its range of travel.

7. Apparatus as defined in claim 6 which includes stop means secured to said pole piece and projecting therefrom to be engaged by said armature to limit its range of travel and maintain an air gap between said armature and pole piece when said armature is in its most advanced position.

8. Apparatus for stabilizing a centrifuge rotor about its axis of rotation during low speed operation, said apparatus including a stabilizer member movable between rotor engaging and rotor released positions, said rotor being mounted for rotation within a chamber defined by a cylindrical housing, said housing including a plurality of brackets having detents for receiving pins mounted on said apparatus for supporting same, including a base plate for carrying a stabilizer member support assembly;

a pair of spaced, fixed support pins attached to one WILLIAM I. PRICE, Primary Examiner.

end of said base plate and adapted to be received by a corresponding pair of said brackets; and

a retractable, spring-biased support pin attached to the opposite end of said base plate and adapted to be received by a third of said brackets, said apparatus being supported solely by said pins when in place in said chamber.

9. Apparatus as defined in claim 8 in which said base plate supports electromagnetic means for actuating said stabilizer member toward said rotor for engagement therewith below a predetermined speed;

said apparatus including means responsive to the rotational speed of said rotor for energizing said electromagnet below said prede-' termined speed; and

means interconnecting said electromagnet and said speed-responsive means including contact means on said spring-biased pin and on said third bracket for completing the circuit to said electromagnet.

References Cited UNITED STATES PATENTS 7/1934 Krauss 210144 5/1967 Stallman et a1 233-23 US. Cl. X.R.

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