US2482853A

US2482853A - Microtome with rotating cutter and specimen feed mechanism supported therewith

Info

Publication number: US2482853A
Application number: US646120A
Authority: US
Inventors: William A Ladd
Original assignee: Columbian Carbon Co
Current assignee: Columbian Carbon Co
Priority date: 1946-02-07
Filing date: 1946-02-07
Publication date: 1949-09-27
Anticipated expiration: 1966-09-27

Description

Sept. 27', 1949. w A. LADD 2,482,853

MICROTOME WITH ROTATING CUTTER AND SPECIMEN FEED-MECHANISM SUPPORTED THEREWITH Filed Feb. 7, 1946 3 Sheets-Sheet 3 49a 50 3 E 0 5 54a 52 /8 24, f 3/'-"o v I 6 Z 3m 55 Z INVENTOR. W/LL/AM A. LA 00 BY MMM+6M ATTORNEYS Patented Sept. 27, 1949 I M FENT' M B T MEW THR TING UT ER ND smerMnw-Fmn Eonnnasln'sperq p mn rHER wI-Tn" William m l a, Brooklyn, n. x4.

Amman fl b i JCQmpan acorporatjon ofllel'aware AnplicationlFebnuary' 7, IMGySerial Nt'o. 516,120

.e nmi ble Jimmie-fi w rk h fiel -Pf nat ra i0, li i tac ha rre l n ion 9 l 'c rubbe M le w. t evn n "in md m j eqerih eebl k nd w eni i n Due to the extremely small particle size ofllcarbeen mac ie insfiw nit ha ee .i nn h at seth electron .nfi s q pe f u .g no However previog slyknown mi- ;ci'etgmes, have been iou'ncl inadequate for 1 the mg oi ryhherv specimens of v slufimient thinp ess; pn satis faetoxpik election, mierqsoope examin tiee anfei iont to adapt the. high speed cuttin pgsin qiple, to, the, .progluctlon pf ,su1ficient1y thin WQW$-QQEPSWW w l a ru b n l' av it -nee esgary tqn se materially greater outwe ds th fihq re i ron- 56 For .in an9e l 1av fel e e uenrl dd i t emplgo ,a lgnife gpeed of the order ,gfj 200-300 miles lpenhour and to. use. a. knife-carrying, mechanisni having high momentum. Even under sueh .perience dni ob ainin $1 5? More hspteq x ens.

JnQwen tovalttaei su cu tin spee s t' wa found'necessary to mount the cuttin edge onfa wheele e mula fld e hhay n 91 idere 'm m t znen iede l'fi ex emely rap yolu- .Wit wum r ee e enfi. a ldit n i vd f r e CPQPEQEGJ h i l ifl axi m w elwll e jy wd sa-na r fn hen-cut in gle ,lp qese enewe it ew ro e hee e .i th position. 9 the eu tine v ed e wi q 1 9 .t e .m an resu ted in Wide: fillc tiens eet 'iqknes ethe eeetienee d f l l-ties ha e n en unterefl Q- lie-ed th .s e ime time the path of 0. e fidge ate uei rmsn d and t leve midsiulfin of he (mi in ed -fin 59 inlfih o e t??? of WFh ultnaf n. bim wimen Th ere en inv ntion bro de ,am m qve n {My-pr nat o wil .he' .d c ib d with m erencm t e e c empan n drawin s which Ion is a.horizontal sectionz along the line13'-.3

speclirnenl holder of ,a micnometerfeeding mech- ;F 1.g Q6. 1shahonizor 1ta1z section of the specimen holdenjalong the linezfi -fieofiEig. 4; and

.Eigfl i'sa secti'ona-Lvievwof the knife-holder,

Referring more particularly to Fig. 1, theknizfe or, cutting; edge; is. indicated by the reference numenazlii I: and; isesupponted by. the flywheel 2, fabricated: fwomlah heavymetaliso as tohave momentum. I-Ihe;;flywhee1= is. supported and adapted. ,fimJgxe .drivemby sha jt 3, and is: positioned within chamber 4', -fformed by E bQWI' ShaDGd elementi and acover plate-6 the cover plate being Securely 3 tion of shaft 3, and is supported at its lower end by the thrust bearing M.

The bearing H rests upon a rubber cushion l5 and is vertically, though non-rigidly, supported by a cushion bushing or sleeve iii of rubber or other resilient material mounted in the upper end of the base stand 9.

A rigid circular disc ll, advantageously of wood or other light material of consequently relatively low momentum, for supporting a micrometer feed mechanism, and of suflicient thickness for rigidity, is rigidly supported by th upper end of bearing I l by means of the collar I8 and set screws I9. The diameter of the disc I! is slightly less than that of the bowl so as to provide a small clearance, say about inch.

The specimen is supported by the specimen holder and micrometer feed mechanism 2 I which in turn is rigidly supported by the disc I! by means of the flange 22 and screws 23.

As shown more clearly in Figs. 4 and 5, the specimen 20 is embedded, as shown, in wax 24, such as conventionally used for this purpose. This specimen is preferably positioned off-center, as shown, for the reasons to be subsequently stated.

The wax supporting the specimen is contained in the thimble 25, and is prevented from turning within the thimble by means of the screws 26 which project into the wax. The thimble is adapted to fit snugly, though removably, into a recession in the upper end of the micrometer feed mechanism shaft 21, and is securely held therein by means of the screw cap 28 and threads 29.

The shaft 21 extends vertically through sleeve 28a, which in turn is supported by the housing 39, rigidly fastened to the disc H, as previously described. The lower end of housing 39 supports bracket 3|, which in turn supports a gear train. This gear train in the particular apparatus 11- lustrated is designed to give a reduction ratio of 1667:1 and consists of a 100-tooth gear wheel 32 securely fastened to the lower end of the shaft 21. Gear 32 enmeshes with a 6-tooth pinion gear 33, attached at its lower end to a 100-tooth gear wheel 34, which in turn enmeshes with the worm 35. Worm 35 is directly connected to pulley 39, which is driven by motor 31 through belt 39, ratio control mechanism 39, belt 40, pulley 4|, and belt 42. 43 and 44 represent belt tighteners. In the particular apparatus her illustrated, the motor 31 and the series of pulleys and belts connecting said motor with the worm 35 are such as to vary the speed of the worm from 100 to 1600 R. P. M.

The shaft 2'! is threaded into the sleeve 28a, the threads being cut 52 per inch, so that the shaft 21 is fed upwardly, when rotated in the advancing direction, at the rate of 488 microns per revolution. The sleeve 29a is provided with split, tapered threads at 45 and 46 whereby any play may be taken up by the tightening of the threaded adjusting rings 41 and 48.

Because of the extremely rapid rotation of the flywheel carrying the knife I, it is essential that the knife be securely and rigidly fastened to the flywheel. This is accomplished by means of the knife holder 49, positioned within the flywheel, and projecting through an opening in the circumference of the flywheel. The outer edge of the knife holder is flush with the circumference of the flywheel and is prevented from moving beyond this point by means of shoulders 50. The knife blade is securely held between two half-cylinders 5i, held together by bolt 52. The halfcylinders holding the knife blade between them 4 are rotatably and removably mounted within the cylindrical housing of the holder 49 and are therein secured in the desired position by means of the set screws 53.

As special precaution against the knifes becoming loosened, I have in the apparatus illustrated provided the bolt 52 extending through a hole in the knife blade, and further have provided the half-cylinders 5| with flanges at their inner end to avoid all possibility of their bein thrown out through the opening in the holder 49 by the terrific centrifugal force.

An adjustable counter weight 54 is placed diametrically opposite the knife so as to balance the flywheel. The under portion of the fly wheel is shown enclosed by members 55, removably fastened to the flywheel by any convenient means, as by screws 56. The cylindrical housing of the knife holder 49 and the counter weight 54 are fastened to the flywheel by

screws

49a and 54a, respectively, passing through the flange thereof as shown in Fig. 3. A cross-sectional view of the knife holder showing the set screws 53 is represented by Fig. 7 of the drawings.

Because of the hazards involved in the operation of an apparatus of this sort at the required speeds, it is advisable that the bowl 5 and the cover 6 be fabricated of steel of sufficient strength to afford protection to the operator in the event of any part breaking or coming loose during operation. It is also desirable that lock nuts be used throughout the apparatus.

For the purpose of collecting the minute sections of the specimen cut by the operation, the apparatus is provided with duct 51, as more clear- 1y shown in Figs. 2 and 3 of the drawings, leading from the chamber 4 through a glass or other transparent tube 58 to a suction device 59, such as a blower, With means, such as a screen, provided in the lower end of the transparent tube for supporting a layer 60 of fine fibers such as cotton, through which the current of air carrying the specimens may be drawn from the chamber 4, the specimens contained in said air stream be ing retained on the cotton. By this means the specimens are readily collected and during the collection may be observed for the purpose of determining whether the microtome is functioning properly.

In the specific apparatus illustarated, the cutting edge describes a circle of about 15 /2 inches in diameter so that when the fly wheel is turning at a speed of 5000 R. P. M. the cutting speed is about 230 miles per hour. Under such circumstances it is diflicult to maintain a true cutting edge. In the present apparatus this difficulty is alleviated by positioning the specimen off-center in the wax, as previously described, and by rigidly fastening the specimen to the revolving shaft 21 so that as said shaft revolves, feeding the specimen into the path of the cutting edge, the portion of the cutting edge which strikes the specimen is continually shifting, thus extending the useful life of the cutting edge between resharpenings.

Further, by rotatably mounting the half-cylinders which hold the knife blade, the cutting angle of the knife may be adjusted to any desired angle.

Microtome knives currently available have in general been found too soft for the high speed cutting of specimens, such as rubber, herein described. For use in my present apparatus I prefer to use a blade of highly tempered steel.

In the operation of the apparatus herein described, it is desirable to bring the flywheel to speed and then gradually feed the specimen into the path of the knife. In discontinuing the operation, the specimen should be lowered before reducing the speed of the flywheel, for the reason that in operation there is a tendency for the head or flywheel to ride at a higher level at top speed than at rest or at lower speeds. I

A further advantage in the mounting of the specimen off-center is that by so doing one ootains the effect of direct and oblique cutting at all angles with respect to any grain in the sample.

It will be understood from the foregoing description of the apparatus that the specimen is held relatively stationary except for its rotation and slow advancement into the path of the knife. The flywheel carrying the knife is, as previously described, designed to operate at very high speeds. At these high speeds, very slight inaccuracies in balancing the flywheel will result in the axis of rotation precessing, similar to a spinning top. Any attempt to stop this precessing by rigidly holding the upper end of the shaft 3 by an additional bearing, or by fastening bearings I! and I4 rigidly to the base stand 9 would set up terrific stresses sufficient to bend or break the shaft. In the apparatus shown, axial precession is permitted by the resilient bushing and, by reason of my novel arrangement for rigidly supporting the specimen by the bearing l I, any precession of the flywheel is accompanied by a corresponding movement of the specimen so that no relative movement of the specimen with respect to the cutting edge is occasioned by axial precession.

By reason of this arrangement, specimens of satisfactory thinness for electron microscopy may be cut, the actual thickness being controlled by speed of the knife, the rate at which the specimen is fed into the path of the cutting edge, the thickness of that cutting edge, and the elimination of relative motion of cutting edge and specimen caused by precession of the high speed rotating knife or cutting-edge carrier.

I claim:

1. A microtome comprising a shaft rotatably mounted in a bearing, with at least one end thereof projecting beyond one end of the bearing, a cutting edge supported by and rigidly connected with a projecting end of said shaft, means for rotating said shaft within the bearing, a micrometer feed mechanism rigidly supported by said bearing and adapted to hold a, specimen to be cut and feed said specimen into the path of the cutting edge, said feed mechanism comprising a shaft adapted to rotate slowly as it moves toward the path of said cutting edge, and means for rigidly mounting the specimen on that end of the last said shaft toward the path of the cutting edge, so that the specimen is slowly rotated as it is moved into the path of the cutting edge.

2. A microtome comprising a shaft rotatably mounted in a bearing, with at least one end thereof projecting beyond one end of the bearing, a cutting edge supported by and rigidly connected with a projecting end of said shaft, means for rotating said shaft within the bearing, a micrometer feed-mechanism rigidly supported by said bearing and adapted to hold a specimen to be cut and feed said specimen into the path of the cutting edge, said feed mechanism comprising a shaft adapted to rotate slowly as it moves toward the path of said cutting edge, and means for rigidly mounting said specimen on that end of the last said shaft toward the path of the cutting edge in a, position eccentric to the axis of the last said shaft, so that the specimen is slowly rotated as it moves into the path of the cutting edge, at the same time moving across the cutting edge.

3. A microtome comprising a housing, a resilient bushing extending through a wall of said housing and supported thereby, a bearing extending through the bushing and housing and'into the chamber within said housing, a shaft extending through said bearing and supported thereby and projecting from the inner end of said bearing into the chamber, a flywheel mounted on the inner end of said shaft, a cutting edge supported by and rigidly connected to said fly wheel, means for rotating said shaft and flywheel within said chamber, a micrometer feed-mechanism adapted to hold a specimen to be cut and feed it into the path of the cutting edge, said feed-mechanism being rigidly supported by the inner end of said bearing and otherwise independently of the housmg.

WILLIAM A. LADD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 198,346 Cairns Dec. 18, 1877 305,225 Pumphrey Sept. 16, 1884 474,389 Lafferty May 10, 1892 1,728,843 Trunz Sept. 17, 1929 1,797,694 Ott May 24, 1931 1,825,421 Roesch Sept. 29, 1931 2,047,400 Walter July 14, 1936 2,107,208 Nankivell Feb. 1, 1938