US3313139A - Precision centrifuge - Google Patents

Description

April 11, 1967 Y. CAUMARTIN ETAL PRECI SION CENTRIFUGE Filed Oct. 27, 1964 3 Sheets-Sheet l ww MW wfx Apl'il 11, 1967 y, CAUMARTIN ETAL 3,313,139

PRECISION CENTRIFUGE Filed 001;. 27, 1964 3 Sheets-$heet 2 Fig.4.-

April 11, 1967 CAUMARTIN ETAL 3,313,139

PRECISION CENTRIFUGE Filed Oct. 27, 1964 3 Sheet$-$heet 3 Fig. 3.

I r v E T 1 United. States Patent 3,313,139 PRECISION CENTRIFUGE Yves Caumartin and Helmut Habermann, Vernon,

France, assignors to Etat Francais (French State) represented by the Minister of Armed Forces, Ministerial Delegation of Armament, Direction of Researches and Manufacture of Armament, Laboratory of Ballistic and Aerodynamic Researches, Vernon, France Filed Oct. 27, 1964, Ser. No. 406,833 Claims priority, application France, Nov. 21, 1963,

954,564, Patent 1,391,760

3 Claims. (Cl. 73-1) This invention relates in general to centrifuges and has specific reference to a precision centrifuge.

In modern technique it is current practice to use apparatus requiring prior to their actual operation elaborate tests in order to ascertain their behaviour as a function of the accelerations to which they are subjected.

It is the essential object of this invention to provide a centrifuge capable of subjecting various apparatus, notably accelerometers, to a plurality of acceleration values ranging from 0 to several tens times g, or the acceleration due to gravity, the various relationships between these accelerations as well as their direction being thus known with a high degree of precision.

To this end the precision centrifuge according to this invention comprising a vertical shaft rotatably driven by an electromotor is characterized in that this shaft has its lower end supported by a hydraulic footstep bearing having a very low friction torque and its upper portion mounted in an air-bearing having practically zero friction torque, and that the rotary members of the centrifuge are housed inside a fairing or casing of revolution rigid with said shaft.

The precision centrifuge according to this invention is advantageous in that the variations in reaction torque are practically eliminated so that a predetermined velocity of rotation may be obtained with a high degree of precision. On the other band, due to the fairing of the rotary members the centrifuge may be operated in a conventional closed room.

In order to afford a clearer understanding of the present invention and of the manner in which the same may be carried out in practice, reference will now be made to the accompanying drawings illustrating diagrammatically by way of example a typical form of embodiment of the invention. In the drawings:

FIGURE 1 is a vertical section showing the general structure of the precision centrifuge of this invention;

FIGURE 2 is a longitudinal section showing on a larger scale the hydraulic footstep bearing of the vertical shaft of the precision centrifuge;

FIGURE 3 is a longitudinal section showing the airbearing provided at the upper end of the centrifuge;

FIGURE 4 is a longitudinal section showing a component element of the rotary electric collector ring;

FIGURE 5 is a block diagram showing the system for controlling the centrifuge.

Referring first to FIGURE 1, the precision centrifuge according to this invention comprises essentially a vertical shaft 1 carrying two opposite radial arms 2, 3. One of these arms, for instance 2, carries on its outer end a measuring plate on which the apparatus A to be tested is secured. In this example the apparatus being tested is an accelerometer. The opposite arm 3 carries on its outer end a balance weight B.

The shaft 1 has its lower end supported by a hydraulic footstep or like bearing designated in general by the reference numeral 4, and its upper end mounted in an air bearing 5. The shaft 1 of the centrifuge illustrated is coupled in line with the armature 6 of an electromotor 7. This motor 7 and the air bearing 5 are supported by 3,313,139 Patented Apr. 11, 1967 ice a base plate 8 mounted on the upper portion of a triangular frame structure 9 isolate-d from external vibration. On the other hand, the hydraulic footstep or like bearing 4 is supported by a concrete slab 11 isolated from external vibration likely to be transmitted through the soil.

The shaft 1 is balanced by means of weight 12 which are eight in number in this example and slidably mounted respectively on radial rods 13 rigid with shaft 1 and locked in adequate positions along said rods. These radial rods 13 are disposed in two separate horizontal planes containing each four rods.

To avoid constant losses due to the frictional contact of air with the revolving surfaces the assembly comprising the two lateral arms 2, 3 and rods 13 carrying the balance Weights 12 is housed inside a casing or fairing of revolution 14 comprising a cylindrical central portion having an upper extension and a lower extension in the form of conical shells. Thus, the centrifuge according to this invention may be operated simply in a conventional closed room.

To adjust with the highest possible degree of precision the shaft 1 in its vertical position, a first rough adjustment is effected by simply moving the air bearing 5 relative to its support 8 by'using a micrometric screw 15.v

Thus a first degree of precision is obtained in the shaft adjustment. To improve this adjustment, tensioning devices 16 provided on bracing rods or cables 17 are acted upon, these bracing rods or cables 17 being fastened on the surrounding walls 18 of the room through adequate tension springs 19. These bracing rods or cables 17 may be three or more in number. producing an elastic deformation of the frame structure 9, whereby a precision of the order of 1:100,000 radians may be obtained as far as the verticality of shaft 1 is concerned.

In the foregoing, the shaft 1 is disclosed as having its lower end supported by a hydraulic footstep bearing or like device 4. This hearing will now be described more in detail with specific reference to FIGURE 2. The lower portion of shaft 1 is formed with a central blind bore 1a engaged by a cylindrical central upstanding flanged pintle 21 carried by a base plate 22 of very hard material, a ball 23 being interposed between these members 21 and 22. The cylindrical intermediate pintle 21 has a longitudinal passage or duct 24 formed therein which communicates at its lower end with a radial duct 25 connected to a source ofoil under pressure 26 (FIG- URE 1). The longitudinal duct 24 opens at its upper end into the bottom of said blind bore 1a and is provided with a pair of spaced branch radial ducts 27 opening in turn into the lateral surface of the cylindrical pintle 21. On the other hand, the cylindrical skirt 1b formed at the lower end of shaft 1 by the blind bore 1a has at least one longitudinal bore 20 formed therein which opens into the lower end face of the shaft 1 and communicates with said blind bore 1a through a small orifice 28 at its upper end and also through one or more intermediate transverse ducts 29. I

During the operation of the centrifuge the shaft 1 is supported by the upper face of pintle 21 through the medium of an oil film. On the other hand, another oil film is interposed laterally between said pintle 21 and the skirt 1b of shaft 1.

frictional contacts is extremely low.

Now reference will be made to FIGURE 3 to de scribe in detail the air bearing designated in general by the reference numeral 5 in FIGURE 1. This air bear ing consists of two annular members 31, 32 assembled by means of screws 33 and receiving the shaft l ther ethrough. Formed between these members is an annular Their tension is used for.

Under these conditions, the shaft 1 is properly centered and the resistance caused by" 3 chamber 34 connected through a pipe 35 to a source of compressed air shown at 36 in FIGURE 1. The chamber 34 communicates through an annular slot 37 with a narrow, sleeve-like space left between shaft 1 and,

members 31, 3-2; The compressed air introduced into this space escapes along the path shown by the arrows in FIGURE 2. This space communicates on the other hand through a pipe 38 with a pressure gauge 39 (FIG- UR-E l) for checking the air pressure.

The air bearing permits like-wise of minimizing friction losses.

T-he circuits of the electrical apparatus A rigid with the arm 2 of the centrifuge are connected to a rotary, mercury-type electric collector shown at 41 in FIGURE 1. This collector consists of a plurality of superposed elements of which one is shown in detail in FIGURE 4. This elementary collector comprises a stationary annul'ar trough 42 filled with mercury 43 and disposed coaxially to the shaft 1. Partially immersed in the mercury 43 is thev cylindrical depending skirt of a conducting inverted cup 44 solid with shaft 1, an insulating sleeve or socket 45 being interposed between the cup 44 and shaft 1. The mercury 43 is electrically connected through a conduct-or 46 with fixed control apparatus and the conducting cup 44 is connected through another conductor 47 passing through the interior of shaft 1 to the apparatus A being tested. a V The collector illustrated in FIGURE 4 is advantageous in that it introduces a very low coefficient of friction in the operation of the centrifuge and has similarly a very moderate contact resistance while being practically free of eddy current.

Now reference will be made to FIGURE 5 to describe the centrifuge rotor control means according to this invention. To this end the fairing or casing 14 surrounding the rotary members of the centrifuge carries a transverse annular disc 51 in which a number of spaced holes 52 are formed along its periphery. During the rotation of the centrifuge these holes move past an optical detector comprising a light source 53 and a photo-electric cell 54 disposed above and under the disc 51, as shown. Thus, when the centrifuge has attained a velocity of rotation approximating the value consistent with the required acceleration, the photocell 54 delivers electric pulses used for adjusting the velocity of rotation. To this end the photocell 54 is connected to the inlet of a frequency divider 55 having its output connected to the input of a phase discriminator 56. On the other hand,

a reference pulse generator 57 monitored by a therrno'-.

statically controlled quartz is delivered to a frequency divider 58 having its output connected to another input of said phase discriminator 56. This phase discriminator 56 of any known and suitable type is used to compare the phases of the signals fed to its two inputs and delivers at its output end square signals of which the average value is proportional to the relative phase of the measure and reference signals.

Since the centrifuge correction is of the phase type or, in other words a position correction, this correction is stabilized by means of a phase-lead network 59 of which the output signal is fed to an amplifier modulator 60.

A potentiometer 61 also connected to the output of the phase-lead network 59 permits of modifying at will the average torque.

The output signal of modulator 60 is fed to a power amplifier 63 supplying the, torque motor 7 driving the centrifuge. The signal necessary for operating the motor 7 by supplying the fixed phase is delivered by the quartz generator 57. The square-waveform output signals issuing from the generator 57 are converted into sine waves by a selective amplifier 62 similar to amplifier 63 before feeding the fixed phase of motor 7.

The phase corrector device described herein-above is suitable for providing a mean speed precision.

Now various means for controlling the operation of the centrifuge will be described by way of example of the order of 1:100,000.

Firstly, some means must be provided for checking the variations in length of the arm 2 carrying the apparatus A to be tested, these variations resulting either from changes in the room temperature or in the centrifugal force. The variation in the length of arm 2 is calculated through a capacimetric method. The capacitor of the control system consists, on the'one hand, of a metal disc 71 (FIGURE 1) rigid with the measuring plate 10 and projecting outside the fairing 1'4, and on the other hand of a pair of electrically insulated metal plates 72, 73 rigid with a support 74 carried by a stationary bracket 75.

In the inoperative condition and for a given position of the centrifuge rotor the disc 71 registers with the pair of metal plates 72, 73. A microfaradmeter 76 delivers a voltage proportional to the relative spacing between disc 71 and plates 72, 73. This voltage is read on the screen .of an oscillograph 77.

The device is calibrated through a known displacement of support 74, this displacement producing a variation in the voltage read on the screen of the oscillograph.

Whenthe centrifuge is rotating pulses are delivered to the oscillograph 77 and the amplitude of these pulses permits of calculating the variation in length of arm 2.

Means for checking the degree of balance of the centrifuge rotor are also provided. If the rotor is in a state of unbalance, vibrations occur in the frame structure 9. The amplitude of these vibrations is evidenced :by measuring same at a point where it attains a peak value. This measurement may be carried out by means of a C- meter or capacitance method similar to that set forth hereinabove in connection with the determination of variations in length of the arm 2.

The balance is restored by shifting and locking the weights 12.

Now a device for checking the inclination of the measuring plate 10 will de described. This. plate, on which the accelerometer or other apparatus A to be measured is secured, carries in addition a flat mirror 81. Besides, a self-collimating sight 8 2 is mounted on a fixed support 83 sealed in the lateral wall 18 of the room. The light source consists of the discharge of a capacitor in a spark-gap 84.

In the inoperative condition the mirror 81 is brought in alignment with the sight 82 and the light beam reflected by this mirror 81 into the sight causes a luminous cross to appear in the eyepiece and the centering of the haircross is adjusted thereon.

During the operation, instead of observing through the eyepiece, a photograph is taken by means of a camera 85. A flash from the light source 84 is produced when the mirror 81 moves past the sight 82. On this photograph the relative shift between the luminous cross and the reference hair-cross indicates the possible inclination of the measuring plate 10.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the in vention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims. I

What we claim is:

1. A precision centrifuge comprising a fixed frame structure, a vertical shaft carrying the objects subjected to the action 'of the centrifugal force, an electromotor rotatably driving said vertical shaft, a hydraulic, low-frictional torque footstep bearing carrying the lower end of said vertical shaft, an air bearing of practically zero frictional torque mounted on said frame structure and receiving the upper portion of said vertical shaft, an external casing of revolution rigid with said shaft and enclosing the rotary component elements of the centrifuge, an upper base plate rigid with said frame structure, supporting said air bearing and receiving said vertical shaft therethrough, a plurality of micrometric screws for adjusting the position of said air bearing on said base plate, and bracing wires, tensioning devices and springs attached together between said base plate and a plurality of fixed points surrounding the centrifuge, said tensioning devices permitting of adjusting the verticality of said vertical shaft by the elastic deformation of said frame structure.

2. Precision centrifuge as set forth in claim 1, comprising a radial arm rigid with said vertical shaft, a measuring plate secured on the end 'of said radial arm and carrying the object subjected to the action of the centrifugal force, and means for measuring the variation in length of said arm, said means comprising a metal element rigid with said measuring plate, a support adjustably mounted on said frame structure, a pair of metal plates carried by said support at the level of said metal element rigid with said measuring plate so that said element will move past said pair of metal plates during the operation of the centrifuge, and a faradmeter for measuring the variation in capacitance, during the rotation of the centrifuge, of the capacitor consisting on the one hand of said metal element carried by said measuring plate and on the other hand of said pair of metal plates carried by said support.

3. Precision centrifuge as set forth in claim 1, comprising a radial arm rigid with said shaft, a measuring plate mounted on the end of said radial arm and carrying the object to be subjected to the action of the centrifugal fonce, and means for controlling the inclination of said measuring plate, said means comprising a fiat mirror rigid with said measuring plate, a fixed support rigid with said frame structure, a self-collimating sight mounted on said fixed support and so positioned that said flat mirror moves past said sight during the rotation of said arm, a fixed flight source, means for switching on said light source as the mirror moves past said self-collimating sight, whereby said mirror will reflect the light beam issuing from said light source towards said sight to permit the checking of the variation in the inclination of said measuring plate.

References Cited by the Examiner UNITED STATES PATENTS 2,683,636 6/1954 Wilcox 3089 2,769,949 11/ 1956 Stratton 318-3 18 2,924,092 2/1960 Bourns et al 731 3,067,620 12/1962 Holloway et al 731 3,205,696 9/1965 Froomkin 73-1 FOREIGN PATENTS 149,372 8/ 1920 Great Britain.

LOUIS R. PRINCE, Primary Examiner. S. C. SWISHER, Assistant Examiner;

Claims (1)

1. A PRECISION CENTRIFUGE COMPRISING A FIXED FRAME STRUCTURE, A VERTICAL SHAFT CARRYING THE OBJECTS SUBJECTED TO THE ACTION OF THE CENTRIFUGAL FORCE, AN ELECTROMOTOR ROTATABLY DRIVING SAID VERTICAL SHAFT, A HYDRAULIC, LOW-FRICTIONAL TORQUE FOOTSTEP BEARING CARRYING THE LOWER END OF SAID VERTICAL SHAFT, AN AIR BEARING OF PRACTICALLY ZERO FRICTIONAL TORQUE MOUNTED ON SAID FRAME STRUCTURE AND RECEIVING THE UPPER PORTION OF SAID VERTICAL SHAFT, AN EXTERNAL CASING OF REVOLUTION RIGID WITH SAID SHAFT AND ENCLOSING THE ROTARY COMPONENT ELEMENTS OF THE CENTRIFUGE, AN UPPER BASE PLATE RIGID WITH SAID FRAME STRUCTURE, SUPPORTING SAID AIR BEARING AND RECEIVING SAID VERTICAL SHAFT THERETHROUGH, A

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