US3077806A - Ultramicrotome with return stroke motion separating means - Google Patents

Description

Feb. 19," 1 963 B. 'r. HELLSTROM 3,077,806

ULTRAMICROTOME WITH RETURN STROKE MOTION SEPARATING MEANS 3 Sheets-Sheet 1 Fig.1

Filed Sept. 8, 1959 jllllllilllll Feb. 19, 1963 B. 'r. HELLSTRGM 3,

ULTRAMICROTOME WITH RETURN STROKE MOTION SEPARATING MEANS 3 Sheets-Sheet 2 Filed Sept. 8, 1959 Fig.5

Feb. 19, 1963 B. T. HELLSTROM ULTRAUICROTOME WITH RETURN STROKE MOTION SEPARATING MEANS 5 Sheets-Sheet 3 Filed Sept. 8, 1959 3 871 ,5996 ULTRAMECRQTGMEZ WHTH RETURN STRQKE Mt'iiifil l SEPARATHQQ MEANS Biirie Thorstensson Hellstriim, Bromine, Sweden, assignor to Liid-Produhter Fahriksahtieholag, Stockholm, Sweden, a company of Sweden Filed Sept. 5, 1959, Ser. No. 838,516 Claims priority, application Sweden Sept. 10, 1958 17 Claims. (til. 83--411) The present invention relates to microtomes of the kind wherein the specimen block is secured to the end of a bar which is moved periodically up and down with a suitable speed and frequency, the cutting operation taking place when the end of the bar moves downwards and the specimen block strikes a knife-edge. The sections are then collected on the surface of a liquid contiguous to the knifeedge.

Experience has shown that it is necessary to withdraw the knife-edge laterally from the specimen block when the moving bar returns to its initial position, and it has been found in practice that an appreciably greater clearance between the knife-edge and the specimen block is required than that which theoretical calculation would suggest if the sections just cut are not to be caught again on the specimen block and be destroyed. The reason for this is that the tip of the specimen block becomes moistened by the liquid surface at the knife-edge upon which surface the sections of the specimen block are collected, or that the sections twist a little after they are released so that a corner projects beyond the knife-edge. In either case there is a risk of the sections being caught when the specimen block moves upwards.

The object of the invention is to provide a reliable and accurately-operating, but nevertheless inexpensive, microtome of the kind described. in particular the invention aims at enabling an adequate withdrawal of the knife-edge.

The microtome according to the invention is chiefly characterized by the mounting of the bar carrying the specimen block and the knife-edge on a common base, the withdrawing devices being designed to cause such an elastic deformation of the base by applying a mechanical force to said base that the knife-edge is brought away from the path of motion of the specimen block when the bar moves upwards to its initial position. in an especially useful embodiment of the invention said mechanical force is produced by means of a magnetic device.

The invention will be described below in greater detail With reference to the accompanying drawings in which:

PEG. 1 shows a microtome according to the invention partly in elevation and partly in vertical section;

FIG. 2 shows a detail of the microtome according to FIG. 1;

FIG. 3 is a plan view corresponding to FIG. 1;

FIG. 4 shows the microtome according to FIGS. 1 and 3 partly in front elevation and partly in section;

FIG. 5 is a graph showing the torque from the driving device for the moving bar as a function of the position of the specimen; and

FIG. 6 is a block diagram of the microtome and its control devices.

The microtome comprises a base l9, upon which are arranged an oscillating specimen bar ill, a driving device 12 therefor and a knife holder 13.

The specimen block 14 is mounted on a specimen holder 15 and thereby attached to the front end of the specimen bar it, which in this case is cylindrical. The bar 11 is provided at its rear end with a cross piece 16 and is secured to the base It) by means of a short and wide Bfil'lfidh Patented Feb. 19, 1963 ice leaf spring 17. On the rear end of the bar 11 there is disposed a heating coil 18, which is supplied through flexible leads (not shown in FIGS. 1-5), from an adjustable current source, the current corresponding to the desired elongation and thus also to the feed. The heating coil 18 is bifilar in order to avoid magnetostrictive effects which might introduce difiiculties when the spec men bar 11, as in this case, consists of a ferromagnetic material. It will be appreciated that by dimensioning the specimen bar 11 properly or, alternatively, by feeding the heating, coil 18 in a suitable way, it will be possible to make the elongation curve of the bar approximately linear for a fairly long period, e.g. 20 minutes or more. At a cutting frequency of 25 cuts per min. the elongation may be, for instance, 0.00075 millimetre per minute, which corresponds to a section thickness of 0.00003 mm.

In order to attain a satisfactory linearity of feeding, the heat conduction outwards must be negligible while the heat conduction along the specimen bar 11 must be such that at the end of the heating period there is still a portion of the bar which has not increased observably in temperature. As long as the losses are negligible and the temperature gradient along the bar is constant, a linear elongation of the bar is obtained.

It has been found that a still better linearity of feeding may be obtained with a modified type of heating device. The specimen bar is suspended on two supports which are secured to the specimen bar near its rear end. Each of said supports is secured to the base of the apparatus by means of a leaf spring. An electric winding is provided on each support, close to the specimen bar. A third winding, the main winding, is provided on the rear portion of the specimen bar, which is extended beyond the supports.

in order to cool the bar after a cutting period, the bar is provided with a central passage 19 with branches 20 opening radially outwards. The bar is surrounded by a cylindrical jacket 21, which is secured to the bar at its extreme front and rear points. Through a flexible hose 2% cooling air is sucked into the iuterspace 22 between the jacket 2-1 and the bar 11 and thence through the branches El) and passage 19. During the cutting period the air gap 22 has an insulating eiiect which, as mentioned before, is advantageous from the point of linearity. The jacket 21 consists of a material having low heat conducting capacity, and it is provided with a heat reflecting surface in order to reduce heat losses.

The specimen holder 15 is such that the specimen block 14 may be clamped between a pair of nib-like jaws, one of which extends rearwardly in the form of a cylindrical pin 24. This pin is inserted into a radial bore in an arcuate rod 25 and locked thereto by means of a set screw, not shown. The centre of curvature of the arcuate rod 25 is assumed to coincide with the tip of the specimen block M. In trimming the specimen block for cutting, material is cut away so that the desired portion of the specimen lies at or adjacent the tip of a four-sided pyramid, and this pyramid is then orientated so that its axis is parallel and, if possible, coincident, with the axis of the bar ill, if this axis is envisaged as extending forwards. in addition, the pyramid is suitably arranged with one base-edge parallel with the knife-edge so that in cutting the knife acts simultaneously along the entire side of the pyramid and with no appreciable lateral forces. To permit this orientation the arcuate rod 25 is slidable in a block 26, which in turn can pivot about a stud 27 at the end of the bar 11. Great possibilities are thus available for orienting the specimen in the best possible way. The rod 25 and the block 26 are lockable by means of set screws 28 and 29, respectively. Moreover (though this feature is not shown in detail) the front portion of the bar 11 is shaped as a hinge,

O which may be locked by means of a set screw and which when unlocked permits a certain turning about a horizontal axis, thus providing a further possibility of adjustment. However, this hinge is intended primarily to permit a quick removal of the specimen block-holder, e.g. for re-trimming or the like.

The knife member 31 consists, as is usual, of a piece of glass having a sharp and fairly straight edge pro duced by breaking. The knife 31 is clamped in the knife holder 13 by means of a clamping screw 32. In order that lateral movements, if any, of the specimen bar 11' shall affect the thickness of the section as little as possible, the part of the knife which is utilizedfor cutting should be perpendicular to the axis of the speci men bar 11. As it is difiicult to ensure accurate alignment of the edge of a glass-knife, the microtome is arranged in such away that the knife holder 13 is adjustable about a vertical axis through the cutting point of the knife edge. As shown in FIG. 3, the knife holderv 13 is slidable alongan arcuate rod 33, whose centre of curvature is on the knife edge. It may be mentioned, as an example of the importance of this adjustment, that if the knife-edge is inclined 3 in relationship to the ideal position, a lateral movement of the specimen bar. 11 of only 0.0001 mm. is required for the thickness variation.

of the section to be of the order of 50 AU, that is, 3.0- 50% of the normal thickness of a section.

The knife holder 13is arranged to be locked in de sired position on the arcuate rod'33 by means of asetscrew 34. The rod 33 is secured to a slide 35 which by means of a screw 36, is slidable parallel to the axis of the specimen bar on, a guide rack 37. The guide rack is attached to a stud 38 which is rotatable about a horizontal axis by means of a screw 39, this axis being perpendicular to the specimen bar 11 andcoinciding with the knife-edge. By virtue of these adjustments a suit, able cutting angle may be set. The stud 3.8.is carried in a block 40 which is. rotatable about a vertical axis (not shown here) and lock-able in desired position by means of an eccentric locking mechanism having an operating handle 41. The knife holder 13 may thus be swung away from the specimen bar 11. so that the knife 31, and the sections of the specimen collected thereat, become readily accessible.

Movement of the specimen bar 11. is controlledby the force transmitted from the driving device 12'tl1rough a lifting cord 42. Essentially, the driving device comprises a moving coil assembly with a stationary inner bipolar permanent magnet 43 and a cylindrical. stator 44 with, in this case, indefinite poles. The mass of the coil 45 is rather small and the torque is of such an order of magnitude that, substantially, the nature of the external load, i.e. the mass and movement of inertia of the bar 11 and the clamping forces, will determine the character of the movement.

The coil 45, is rather wide in relation to the core magnet 4-3, and has an evenly distributed winding which is connected by flexible supply leads to the control device described hereinafter, said leads being taken out through a coaxial hole in one end of the shaft.

Due to the fact that the width of the coil 45 appreciably exceeds the width of the magnet poles, there are always the same number of winding turns in the magnetic flux independently of the turning angle, which is -35. On account of the propagation of the leakage flux laterally of the magnet poles, an increment is obtained of the interaction between the coil and the magnetic field, but this increment becomes smaller in the end positions of the coil due to the fact that only about half the leakage flux may be utilized there. For this reason the curve of the torque plotted against the turning angle, when a constant current flows through the coil, will take the form shown in FIG. 5. The coil 45 is. suitably wound on a frame of brass or the like with slotted faces in order to reduce to a proper extent the damping caused by eddy currents.

FIG. 6 shows a block diagram of the units essential for the electronic operation of the microtome. These units are: a transformer and rectifying unit 45, connected to the mains, for the power supply of the control device; a multivibrator 4-7 for automatically repeated cutting; an impulse unit 48 for manual release of individual cutting movements; a switch 49 for selective switching between automatic and manual cutting; a univibrator 50 arranged for both automatic and manual cutting; a pulse former 51 arranged for control of cutting speed i.e. the rate of downward movement of the bar 11; a univibrator 52 arranged for withdrawing of the knife; and power stages 53, 54 with corresponding driving stages 55, 56, arranged for the cutting movement and the withdrawing movement, respectively. In addition, there is shown diagrammatically a device57 for fan cooling and the device 18 for the thermal feed. In FIG. 6 the microtome is merely indicated diagrammatically. The knife 31' with its adjustment devices is mounted on a plate 16 A, which. may be bent down under the action of an electromagnet 58. The specimen block is clamped to the bar 11, which is raised and lowered periodically by means ofthe flexible cord 42 which is attached to the pulley 59 of the motor 12.

In its idle position the bar 11 is held up by the torque of the rotor coil 45 which then is fed with a high current' from the power stage 53. When cutting is to take place, the rotor current is decreased so that the bar 11 starts to fall. The current reduction is controlled by the pulse forming stage 51 so as to take place more or less rapidly according to the desired cutting speed. When.

the specimen block has passed the cutting position the current in the coil is increased and the falling motion of the bar is gently checked by applying a suitably formed current curve.

The possibility of changing the cutting speed in a simple way is very valuable because specimen blocks thathave different hardness must be cut with different cutting speeds to obtain sections of acceptable quality. The time between the cutting moments is maintained constant by impulses emitted from the multivibrator 47, which is connected through the univibrator 50 to the pulse former 5]. Normally the frequency of the multivibrator 47 and thus the cutting frequency is maintained constant so that, for instance, 25 cuts per minute are obtained. It is possible to change the cutting frequency within a wide range, but with thermal feed it is of advantage to keep the frequency constant since direct proportionality is then established between the thickness of the section and the feeding current. If individual cutting movements are desired, e.g. in connection with a manual feed as described below, the switch 49 is set in such a way that the univibrator 50 can receive starting impulses from the impulse unit 48 only, the latter taking the form, for instance, of a push button. In this case the movement will be exactly like that obtained during a period of the automatically repeated process, and thus it will be independent of the manner in .which the process is initiated.

In the present case the necessary withdrawing movement is provided by the feature that the plate 10A, upon which the knife 31 and its adjusting mechanism are situated, is bent downwards (the knife moving downwardly and outwardly) under the action of the electromagnet 58. This is normally not energised, but it is supplied with a short current surge from the power stage 54 a certain time after the bar has left its initial position. This time delay must be adjusted to the speed at which the bar 11 is set to fall, and theadjustment is preferably automatic by reason of the selector switch (not shown), which is included in the pulse former 51 and which controls the speed of fall, being coupled. also to those circuits in the univibrator 50 which determine the moment for the withdrawing to begin. It should be mentioned that the electronic control device contains transistors as active elements, transistors being especially useful as the loads are of the low impedance type and rather slow D.C. variations occur.

in FIG. 6 curves are depicted showing the approximate appearance of the impulses generated. In these curves the instant of starting of the cutting movement is marked a and withdrawing starts at b. Cutting takes place at c with a speed depending on the slope of the current curve. The amplitude of the withdrawing motion may vary strongly with no inconvenience provided only that a certain minimum limit of a few hundredths of a mm. is exceeded. On the other hand, an extremely high accuracy is required concerning the reproducibility of the idle position in which the knife stops after the withdrawing movement, and for this reason an elastic deformation is utilized which resides in the bending of the front and upper part of the base, that is, the plate 10A upon which the knife holder is secured. As long as the bending is carried out within the linearity range of the respective materials, in this case so called nodular iron, very good reproducibility of the starting position is obtained which allows an even thickness of section to be achieved.

The plate 10A, upon which the knife holder 13 is disposed, forms a direct extension of the base 10 on which the specimen bar 11 is mounted. Under the motion imposed upon it the knife 31 will move in a curve-which is directed outwards and downwards and whose radius depends on the distance between the knife-edge and the centre of deilexion. The curvature of the movement is of secondary importance, the vital point being that the defiexion of the plane is combined with a suflicient movement directed away from the specimen block.

In lieu of an electromagnetic force, hydraulic or purely mechanical forces may be utilized for providing the bending necessary for withdrawal of the knife. The advantage of the electromagnetic driving device is, firstly, that no extra mechanical details for applying the driving force are required and, secondly, that the magnitude and the timedependence of the force may be varied within wide limits and thereby be easily adjusted to the electrodynamic device 12 which is used for moving the specimen bar.

In certain cases it is desirable, before a series of ultrathin sections of a specimen is cut, to be able to cut appreciably thicker sections--of the order 0.0001 to 0.001 mm. or even more-in order to find out by means of an ordinary lightmicroscope if the specimen is properly orientated or otherwise of such a character that an electronmicroscopic investigation may be of interest. For this purpose the microtome is provided with a device enabling a linear mechanical feed of 0.015 mm. in all. This feed is performed manually by setting a wheel 69 which egg. is turned one revolution for a feeding movement of 0.001

By means of the switch 4% the automatic repetition of the cutting movements is interrupted and the bar 11 stops in its idle position ready for cutting. However, and as already mentioned, an individual cutting movement may be initiated by actuation of the impulse unit 43. After a number of thick sections have been cut manually in this manner, automatic cutting and thermal feed may immediately be resumed when desired.

The feed just mentioned is provided as a superimposition upon the withdrawing motion in such a way that a force is applied from below, by means of a lever til mounted on a shaft 60, upon the plate 10A on which the knife holder is mounted, this force linearly increasing with a screw-motion. The linear force is achieved by a coil spring 62 which bears against one arm of the lever 61. and is compressed by means of a screw 63 connected through a suitable gearing 64- with the wheel 69. The latter cooperates with a graduated scale. By means of a suitable choice of lever 61, spring 62 and gearing 64, the gear ratio may be adjusted such that a knife movement of 0.001 mm, say, is obtained by one turn of wheel 69. In this way a feed of some 0.01 to 0.02 mm. may be conveniently arranged.

When larger longitudinal movements are in question, e.g. when mounting the specimen block and knife, a screw operated conventionally arranged slide movement is used giving a knife displacement of 0.5 mm. per revolution. The operating wheel 65 for this movement is located adjacent the above mentioned fine feed wheel 69' on one side of the microtome. The coupling between the operating member 65 and the slide 66 that carries the knife holder is adjusted in such a way that only a turning movement is transmitted, whereby to avoid setting up forces which might interfere with the withdrawal of the knife during the operation of the microtome.

The horizontal longitudinal displacement of the knife 31 may be carried out by means of an adjusting screw of the same general type as is used in micrometers.

- In order to reduce as far as possible the disturbing effect of shocks and vibrations which may reach the microtome by Way of the base, it is necessary to position the microtome on a very massive foundation. By means of resilient and damping inserts the foundation is given as low a natural frequency as possible while at the same time a good sound damping effect is obtained.

The foundation for the microtome is formed as a plate upon which a microscope for watching the cutting action is placed. In order to avoid the microtome being subjected to vibrations and bending stresses caused by forces from the microscope when this is used, the microtome is supported on damping inserts in such a way that the risk of disturbing forces being transmitted is a minimum. However, in this case a compromise is necessary as it is not possible to have too flexible a coupling between the microscope and the microtome because it would then be very difiicult to work with the microscope as the image would easily be set into oscillation. Usually the microscope is of the binocular type having a magnifying power which may be varied between 15 and 100.

Modifications and changes of details may be undertaken within the scope of the invention.

What is claimed is:

1. A microtome comprising an elastically deformable base, a bar flexibly mounted at one end thereof to one location on said base, means for moving the other end of said bar upwardly and downwardly with respect to said base, means for mounting a specimen block on said other end of said bar to be movable therewith, a knife member including a knife edge rigidly mounted at another location on said base, said knife edge being so positioned as to engage said specimen block upon the downward movement thereof, and means for removing said knife edge from the path of said specimen block during the upward movement thereof, said means comprising means for effecting elastic deformation of said base during said upward movement.

2. A microtome as defined in claim 1 in which said means for effecting elastic deformation of said base is electromagnetic.

3. A microtome as defined in claim 1 in which the means for moving said other end of said bar upwardly and downwardly is electrodynamic.

4. A microtome as defined in claim 1 in which said means for moving said other end of said bar upwardly and downwardly is electrodynamic and said means for effecting elastic deformation of said base is electromagnetic and said two means are interconnected through control means.

5. A microtome as defined in claim 1 in which the means for moving said other end of said bar upwardly and downwardly comprises a stator rigidly connected to said base, a movable coil positioned within said stator, a core magnet associated with said coil and means for supplying electric current to said coil, said core magnet being mechanically connected to said bar.

6. A microtome as defined in claim 5 in which the coil is wider thanthe width of the poles of the magnet.

7. A microtome as defined in claim 1 comprising means for heating said bar to cause elongation thereof.

8. A microtome as defined in claim 7 in which said means for heating is a bifilar heating coil.

9. A microtome as defined in claim 7 in which said bar is provided with an axial passageway and'means for passing a fluid through said passageway.

10. A microtome as defined in claim 7 in which said bar is provided with a jacket and an axial passageway connected to the space between said bar and said jacket,

and means for sucking air through said space and passage a horizontal plane and having a center of curvature at the edge of said knife member.

13. A microtome as defined in claim 12 in which said arcuate bar is carried by a slide mounted on said base,.

said slide being movable. parallel to the axis of said bar.

bar is mounted to said base by means of a leaf spring.

of said lever bearing against a spring mounted in said' base, and means for varying the tension on said spring. 16. A microtome as defined in claim 1 comprising a holder for said knife member, a slide on said base supporting said member holder and means for adjusting said slide in the direction parallel to the axis of said bar.

17; A microtome as defined in claim 1 in which said References Cited in the file ofthis patent UNITED STATES PATENTS Richards Aug; 11, 1942 Drouin May 2, 1950 Kahler Sept. 8, 1953 Haanstra Mar. 8,

OTHER REFERENCES PhilipsTechnical Review, volume 17, No. 6, December 1955. (Pages 179-181 relied on.) (Copy in Division 57;).

Claims (1)

1. A MICROTOME COMPRISING AN ELASTICALLY DEFORMABLE BASE, A BAR FLEXIBLY MOUNTED AT ONE END THEREOF TO ONE LOCATION ON SAID BASE, MEANS FOR MOVING THE OTHER END OF SAID BAR UPWARDLY AND DOWNWARDLY WITH RESPECT TO SAID BASE, MEANS FOR MOUNTING A SPECIMEN BLOCK ON SAID OTHER END OF SAID BAR TO BE MOVABLE THEREWITH, A KNIFE MEMBER INCLUDING A KNIFE EDGE RIGIDLY MOUNTED AT ANOTHER LOCATION ON SAID BASE, SAID KNIFE EDGE BEING SO POSITIONED AS TO ENGAGE SAID SPECIMEN BLOCK UPON THE DOWNWARD MOVEMENT THEREOF, AND MEANS FOR REMOVING SAID KNIFE EDGE FROM THE PATH OF SAID SPECIMEN BLOCK DURING THE UPWARD MOVEMENT THEREOF, SAID MEANS COMPRISING MEANS FOR EFFECTING ELASTIC DEFORMATION OF SAID BASE DURING SAID UPWARD MOVEMENT.

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