US2666572A - Centrifuge apparatus - Google Patents

Description

Jan. 19, 1954 c s I 2,666,572

' CENTRIFUGE APPARATUS Filed May 9, 1950 INVENTOR. fawara 6. /cl e/s 344d wiw I. Patented Jan. 19, 1954 Y I 2,666,572 GENTRfFUGE APPARATUS Edward G. Pickels, Palo Alto, Calif., assignor to v Specialized Instruments Corporation, Belmont, Calif., a corporation of California Application May 9, 1950, Serial No. 160,888

This invention relates generally to centrifuge apparatus, and particularly to ultra centrifuges which utilize high rotative speeds of the order of from 5,000 to 40,000 R.'P. M. or more.

Because of the high rotative speeds employed in ultra centrifuge equipment it is not possible to design the'rotors with a factor of safety as high as might normally be considered'good engineer ing practice, and therefore it 'is necessary to guard against excessive rotative speeds. For example if a rotor is designed to operate at a maximum speed of 20,000 R. P. M., excessive speed of the order of 30,000 R. P. M. may cause bursting of the rotor, with resulting damage to other parts of the equipment, and possible injury to the attendant.

Ultra centrifuges are generally intended for laboratory use, and the rotor drive is arranged to make available any one of many possible speeds of rotation, and to govern or regulate the speed to that selected. Several sizes and types of rotors are generally supplied to accommodate for various types of work and different rotative speeds. Thus one rotor may be adapted for one type'of separating work and designed for speeds ranging up to 20,000 R. P. M., and another designed for higher speeds which may for example range up to 40,000 R. P. M. There is always the possibility that an attendant may apply the wrong rotor for the speed of operation selected, with the result that the safe speed of operation for a particular rotor is exceeded. In addition the electrical speed control means employed may fail to function properly and thereby cause the rotor to be driven at an excessive speed.

'It isa general object of the present invention to provide'improved centrifuge apparatus having means whereby when the safe speed of operation of a rotor is exceeded, the driving torque to the rotor is interrupted.

Another object of the invention is to provide improved means of the above character which is relatively simple in construction, and which is operated responsive to the magnitude of centrifugal force applied to a member carried by the rotor.

Another object of the invention is to provide a simplified assembly unit adapted to be mounted directly upon a centrifuge rotor, and which will cause a member to be automatically extended in a radial direction to perform a safety control operation, when the speed of the rotor exceeds a predetermined value.

Additional objects and features of the invention will appear from the following description 1 Claim. (Cl. 233-24) iii) surfaces.

in which the preferred embodiment of the invention has been set forth in detail in conjunction with the accompanying drawing.

Referring to the drawing- Figure 1 is a side elevational view in section, illustrating centrifuge apparatus incorporating the present invention.

Figure 2 is a cross-sectional detail taken along the line 2-2 of Figure 1.

Figure 3 is a cross-sectional detail on an enlarged scale taken along the line 33 of Figure 1.

Figure 4 is a schematic view illustrating circuit means for the driving motor.

The apparatus illustrated in Figure 1 includes a centrifuge rotor l0 having sample receiving pockets ii. A vertically extending stud shaft I2 is carried by the journal mounting l3, and is adapted to be driven by an electric motor, through suitable gearing. The lower end of the rotor has a socket opening Hi which accommodates the upper end of the shaft E2. The shaft also carries an eccentric driving pin it, adapted to extend into driving relation with a pin H which is fixed to the rotor. The rotor may be enclosed within the refrigerated liner of a suit able vacuum chamber, the top of which is removable to'facilitate access. The lower wall E8 of the liner can be secured to the lower wall it of the vacuum chamber by the collar 2!. A vacuum sealing member 22, formed of rubber or like resilient material, extends between wall it and the journal mounting i3, and is expanded by compression spring 20 to hold its end faces in sealing engagement with the cooperating metal The driving motor and gearing .are carried by cushion mounting means whereby the shaft I 2 is permitted a substantial amount of lateral displacement. This makes possible selfbalancing action of the rotor. V

The safety control means which I employ makes use of a centrifugally operated, unit 2%, which is removably mounted in the lower portion of the rotor body. This unit (see Figure 3) includes a fitting 20, which is externally threaded for engaging the threaded bore 2'! in the rotor body. A pin 20 is slidably disposed in the fitting 26, and is stepped to provide the annular shoulder 29. The bore 3! which accommodates the pin is likewise of stepped diameter to provide a shoulder 32, which is engaged by shoulder 20 when the pin is projected.

A shear pin 03 serves to normally lock the pin 28 in retracted position within the fitting 26. Pin 33 extends through registering openings in the pin and fitting, as illustrated in Figure 3. When the pin 28 is forced outwardly with sufficient centrifugal force, shear forces are applied to'th'e pin 33 at two points. The shear strength of the pin 33 is selected so that for a predetermined outward force applied to pin 28, the pin 33 will shear to permit pin 2% to move to the projected position illustrated in dotted lines in Figure 3. It will be evident that the unit it is roadie ly removable for replacement of a sheared pin 33.

Adjacent to the path of movement of the unit 24, there is an electrical conductor B t (Figure i) in the form of a vertically extending wire or knock-out pin. The upper end of the-pin 36 shown pressing against a springnetalstrip 31. This strip is bent to extend inwardly beneath the annular plate 38, for electrical connection with the upper end of the terminal bolt 33. The lower end of pin (it is attached to the upper end of a bolt 41, which in turn is electrically connected by strip 52 with the terminal bolt 3. The lower ends of the terminal bolts as and 43 are available for electrical connection to a circuit serving to control energization of the driving motorv As illustrated in Figure 3, pin 3% is disposed in the path of movement of the pin 22, when the pin is in its extended limiting positionillustrated in dotted lines. Therefore it will be evident that when pin 23 is extended during high speed operation of the rotor, it immediately strikes and breaks or knocks out the con: ctor pin 36.

The actual connections betu eon the knock-out pin 36. and the driving motor n vary in practice, but should be such that or ge oi the, pin either discontinues current supply to the motor in entirety, or modifies operation of the motor or drive through the speed control means employed to reduce the driving torque and the speed of operation. One suitable arrangement is illustrated schematically in Figure 4. In this instance the variable speed electric driving motor 46 is shown driving the rotor it through the speed multiplying gearing ll. The customary magnetic starter box 33 connects between the motor and the current supply lines as. The starting box at has a control circuit 5i which when opened, causes the motor it to be de en ergized. The conductor is is connected in series with the circuit 3!, so that when the conductor 36 is broken, the circuit is opened to deenergize the motor 46. Y

It will be evident that my apparatus provides positive means to protect ultra centrifuge rotors from being subjected to excessive speeds of ro tation. The unit 24 can be factory installed in the rotor and constructed to provide protection against excessive speeds for that particular piece of equipment. Therefore when several difierent rotors are being used with the same equipment, but designed for different speeds of rotation, protection is automatically provided in accordance with the rotor design. The protection is positive and dependable in its action and it can be made to operate within relatively close limits. After the prescribed speed of operation has been exceeded and pin 28 has been projected to interrupt driving of the motor, it is a relatively simple matter to remove the entire unit 24, after which the broken shear pin is replaced and the unit reinstalled in the rotor. The knock-out pin 36 canlikewise be readily replaced to restore the machine to normal operating condition.

I claim:

'In high speed centrifuge apparatus, a horizontal mounting Wall, a vertical drive shaft havingan upper end portion extending through said tor coupling to a rotor, a centrifuge rotor adapted to carry samples to be centrifuged and adapted to be reinovably socketed upon the upper end portion of the shaft whereby th rotor is driven when the shaft is rotated, the rotor having a lower annular portion, a fitting mounted in said annular portion, a weighted pin slidably carried by the fitting and movable between generally radially extended and retracted limiting positions relative to the outer peripheral surface of said annular portion, said pin when in extended position projecting beyond the contour of said outer periphery, a, shear pin serving to normally lock said first named pin to said fitting and in retracted position said shear pin being broken by centrifugal force acting upon said first named pin when the speed of rotation of the rotor exccedsa predetermined value, driving means for the shaft including an electrical circuit adapted to be opened to reduce application of driving torque to the shaft, and a knock-out electrical conductor included in se ies with said circuit and mounted on said wall in spaced proximity with the outer periphery of said annular portion when the rotor is seated upon the shaft, said weighted pin serving to knock out said conductor when in its extended position.

EDWARD G. PICKELS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,04%,287 turges Nov. 12, 1912 1,296,138 Taylor Mar. i l, 1919 1,824,722 Jones Sept. 22, 1931 2,242,194 Reisch May 13, 1941 2,281,797 Potter May 5, 1942 2,456,347 Vogel- Dec. 1-4, 1943 OTHER REFERENCES Skarstrom et; al'.: The Electrically Driven Magnetically Supported Vacuum. Type Tetracentrifuge, Review of Scientific Instruments, vol. 11, pages 3.98-lii3. (Copyin Scientific Library.)

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