AT398848B - MICROTOM, IN PARTICULAR ULTRAMICROTOM - Google Patents

Description

AT 398 848 B

The invention relates to a microtome, in particular an ultramicrotome, with a device base, with a specimen carrier rod pivotably mounted in a bearing arrangement and with a micrometer spindle provided for displacing a knife carrier or knife, the bearing arrangement for the specimen carrier rod and essentially below the knife carrier or knife horizontal bearings for the micrometer spindle are connected to the device base.

With a view to reducing weight without reducing torsional stiffness, models were developed based on the ultramicrotome developed by Porter and Blum in 1953 (see KR Porter and J. Blum, A study in microtomy for electron microscopy, Anatomical Record, volume .117, Sn . 685 - 710, 1953) from 1953, most of the ultramicrotomes were made entirely of aluminum alloys (including Sorvall-Dupont-RMC ultramicrotomes MT1 and MT2, Reichert ultramicrotomes OmU2 and OmU3). However, it was soon recognized that, in addition to the advantage of high torsional rigidity and comparatively low weight, aluminum constructions have the disadvantage of a very high coefficient of thermal expansion and very high heat conductivity. These disadvantages mean that changes in temperature in the room or incidence of heat radiation (for example solar radiation, heat radiation from the operator) result in length changes which are in the um range and thus far above the thickness range of ultra-thin cuts, which is normally between about 0.02 and 0, 2 µm. It is therefore difficult to reproducibly obtain uniform slice thicknesses in the minimum thickness range around 0.02 μm with such aluminum structures. The phenomenon is so pronounced in cutting preparation at a reduced temperature (" kyro-ultramicrotomy " in the temperature range between about -80 ° C and -190 ° C) that aluminum structures are hardly suitable for this work (cf. H. Sitte and K. Neumann, ultramicrotomes and equipment for ultramicrotomy, in: G. Schimmel and W. Vogell, collection of methods of electron microscopy, Wissenschaftliche Verlags GmbH Stuttgart 1983, delivery 11, sn. 69 - 91, in particular page 85). From 1958 onwards, LKB offered the ultramicrotome LKB-Ultrotome, again devices in steel construction, and partly high-alloy steels with extremely low thermal expansion (e.g. high-alloy nickel steels such as " Invar " from Krupp or similar products) were used to change the length of the decisive construction elements ( e.g. specimen carrier rod, knife and specimen holder) or at least to a limited extent (devices with steel construction including LKB-Ultrotome l / lll / IV / V as well as LKB-Nova and LKB-SuperNova, Reichert-Jung ULTRACUT and ULTRACUT-E and Sorvall -Dupont-RMC MT5000 and MT6000). All of the devices made of steel are extremely heavy. In addition, for price reasons, it is not possible to design the device base, which is particularly heavy with regard to the required torsional rigidity, from special steels with minimal thermal expansion (e.g. " Invar with 35.5% Ni).

It is therefore an object of the present invention to implement a microtome, in particular an ultramicrotome, of the type mentioned at the beginning, in which a simple device base, as a carrier for all elements of the device, is light, inexpensive to manufacture and shipping, and advantageous in terms of manipulation and torsion-resistant Precision mechanics of the knife and object holder can be used without the disadvantages of a large thermal expansion or a high thermal conductivity.

An additional object within the scope of an embodiment of this invention is to keep the temperature fluctuations of the device base and the precision parts articulated thereon as low as possible in order to further increase the precision of the ultramicrotome in the border area by means of these simple additional measures.

According to the invention, this is achieved in that an extension rod known per se, arranged in the axial extension of the micrometer spindle and connected in the axial direction without play to the micrometer spindle, is provided, which extends to a geometrical location which is substantially vertical under the bearing arrangement of the specimen carrier rod lies, and that the extension rod is at the geometric location mentioned in the axial direction without play with the device base or a device base fixed component in connection.

With such a design, changes in length of the device base caused by temperature fluctuations do not interfere with the relative position between the knife and the preparation. Rather, in the case of temperature fluctuations, essentially only the thermally induced longitudinal expansion of the extension rod in relation to that of the specimen carrier rod goes into the relative position between the knife and the free specimen carrier rod end. A spindle extended to approximately below the bearing of the specimen carrier rod is already known from DE-PS 1 117 900. However, the description and the figure of the mentioned German patent do not provide any information about the exact function of this spindle. In any case, the spur gear, which converts the rotary movement on the knob 65 into a rotary movement of the spindle, is not a play-free connection, as is essential for the subject matter of the invention. By turning the knob 65 in one direction of rotation, one can cause the part 66 of the second

AT 398 848 B known microtome moved forward (i.e. away from the spur gear), pulling the part 66 towards the spur gear is no longer possible with the device shown, because then the spur gear attached to the extension of the spindle would simply lift off the other spur gear . It should also be noted that the spindle of the aforementioned German patent 1117900 is not axially displaceably mounted in a device-base bearing below the knife, as is the case with the subject matter of the invention. Also, the spur gear connected to the rotary knob 65 is not a component that is fixed to the device base.

Due to the structural differences from the subject matter of the invention, the known microtome is unable to achieve the object of the invention, in particular to keep the effects of temperature fluctuations as low as possible. The teaching according to the invention, practically unavoidable temperature-related changes in length due to the " play-free extension " To make the micrometer spindle ineffective, so that the decisive relative position between the knife and the free end of the specimen carrier rod does not change due to temperature, is neither disclosed nor suggested in DE-PS 1117900. On the contrary, the teaching in the aforementioned DE-PS is to intentionally bend the base by means of an electroma grinder in order to cause the knife to withdraw.

The design according to the invention makes it possible to use much lighter materials for the device base, which enable cost-effective production and reduce the shipping costs. Torsionally rigid bases can preferably consist of aluminum or an aluminum alloy.

In this simple way, not only can the thermal expansion of the device base (aluminum base) 20 be switched off, but for example when using high-alloy nickel steels (e.g. " Invar ", " Indilatans ", " Dilatherm " or other commercially available alloys as material for the Extension rod an effect can be achieved without higher costs, which corresponds to the formation of the entire base from such a special alloy, which is impossible for reasons of price, it being particularly advantageous for the specimen carrier rod and the extension rod arranged underneath it to be between the micrometer spindle and the device base made of the same material, in particular from a material of extremely low thermal expansion (less than 2.10-SK-1, preferably less than 0.5.10-6 K-1), so that both elements react to temperature changes in the same direction and with the same length changes. In addition to high-alloy nickel steels, quartz and glass ceramic are particularly suitable as such materials.

The micrometer spindle thus remains rotatable about its longitudinal axis by at least one articulated connection with at least one degree of freedom of rotation. The above-mentioned articulated connection between the micrometer spindle and the extension rod and / or the extension rod and the device base can preferably be kept free of play at all times by a spring preload acting in the axial direction. The above-mentioned articulated connection between the micrometer spindle and the device base and / or the extension rod of the device base can, according to the invention, be effected in various ways either by a tip bearing or by a highly polished, sufficiently hard bearing ball (e.g. ball bearing steel ball or quartz ball), which either is in contact with the two adjacent parts by circular line contact (as known per se, for example from AT-PS 199903) or by spherical surfaces of the same radii ("calottes").

In order to eliminate undesirable constraining forces on the sensitive micrometer spindle, the aforementioned 40 extension rod can be provided on both sides with such articulated connections that allow twisting around the rod axis, but no axial displacements, or on one side as a spring rod or spring cardan and only on the other side with one be articulated connection.

Embodiments of the invention relate to further measures for reducing thermally induced undesired relative movements between the preparation and the knife edge as a result of a change in the room temperature or an incident heat radiation.

A further reduction in the temperature sensitivity of such systems can be achieved within the scope of an embodiment of the invention in that the specimen carrier rod and the extension rod located underneath are covered with a cover made of thermally insulating material (e.g. polystyrene, polyurethane 50-han foam or foam rubber), which Switch off rapid temperature changes caused by air currents. Similar effects can be achieved in that the above-mentioned cylindrical elements are surrounded by cylindrical sleeves, which create an air gap of the order of at least 1 mm between the inside of the sleeve and the metallic surfaces of the specimen carrier rod or the extension rod, and possibly additionally by a reflecting heat radiation, and preventing the rapid exchange of heat between the room atmosphere and the specimen carrier or extension rod through the air gap in the same way as insulating glass. 3rd

AT 398 848 B

Further advantages and features of the invention, as well as its configurations, result from the following description of preferred exemplary embodiments of the system according to the invention in comparison to a system according to the prior art with reference to the accompanying drawings. Throughout these drawings, a side view shows:

Fig. 1: a schematic partial section through an ultramicrotome according to the prior art

Technology;

Fig. 2: a schematic partial section through preferred embodiments of the inven tion system according to the invention with device base (aluminum base), and the

3 to 5: special embodiments of the extension rod according to the invention for extending the micrometer spindle to shift the knife support.

The structure of the ultramicrotome shown schematically in FIG. 1 and partly in section is conventional. On a stable, as torsionally rigid metal base 1 there is support for the knife carrier 2 with the knife 3 at the front (left) and the bearing block 4 at the rear (right) with the main bearing 5, the intermediate lever 6 articulated on the main bearing and the specimen carrier rod 8 in turn articulated on this intermediate lever 6 with the specimen 9. The entire mechanism for advancing and moving the specimen is protected by a cover 10. This mechanism essentially includes the eccentric 11 drive shaft 12, which is rotated with a bearing system, not shown, handwheel and / or motor drive in the direction of the arrow and thereby the oscillating up and down movement of the specimen carrier rod 8 via the intermediate member 13 Camp 7 causes. The preparation 9 only touches when the " cutting path " to take a cut, the cutting edge of the knife 3. After reaching the lowest position, the specimen carrier rod 8 is withdrawn by lifting the bolt 14 'of the lifting magnet 14, so that the specimen 9 is returned to its starting position above the knife 3 off (behind) the knife edge (" Single Pass-Movement ", see also H.Sitte and K. Neumann, lc1983, Sn 37-43, as well as H.Sitte, Ultramikrotomie, mta-Joumal Extra No. 10, Umschau-Verlag Breidenstein GmbH, 1985 , Sn. 1-8, especially Fig. 9 on page 7). The feed of the preparation 9 against the knife 3 takes place between two successive cutting passes, for example by means of the micrometer spindle 17 rotated with discrete preselectable amounts with a stepper motor 15 in a known manner via a coupling 16. The tightly fitting, play-free contact between the end of the micrometer spindle 17 and the extension 6 'of the intermediate lever 6 ensures a spring element 18 during the removal of the cut.

According to FIG. 1, the support for the knife 3 in its holder 2 is usually provided as a cross support for moving the knife 3 against the specimen 9 (" north-south displacement "), and for transversely displacing the knife 3 relative to the specimen ("; East-west shift ”; not shown in the diagram of FIG. 1). The north-south shift takes place in a known manner by means of a micrometer spindle 19, the spindle nut 20 of which is rigidly connected to the support plate 21 and therefore moves the spindle 19 back and forth according to the rotation of the spindle 19 about its longitudinal axis 22/22 ', this rotation of the Spindle 19 is preferably carried out by means of a handwheel 23.

1, apart from a precise function of the feed, drive and bearing elements as well as the single-pass retraction, an optimal function of this conventional system according to FIG. 1 is dependent on all elements located between the cutting edge of the knife 3 and the front surface of the preparation 9 , these are in particular the elements 2, 21, 20, 19, 4 and 8, exactly maintaining their length in the north-south direction or changing their lengths in the same direction, to the same extent and synchronously in the event of a change in length. Since it is not possible to keep the air temperature in the work area constant and to completely shield the device from heat radiation, this requirement cannot be met in practice. A particularly disadvantageous effect here is the night-time lowering of modern heating systems, the heat radiation of the operator, which changes constantly during normal work processes, as well as air currents in connection with the fact that the main mass of the device is contained in the base 1 and, in contrast, for example, the mass of the specimen carrier rod 8 in The comparison is extremely small: A fluctuation in the room temperature, heat radiation or drafts therefore primarily affect the specimen carrier rod 8 in the thermodynamic sequence, while the heavier stand base 1 only reacts with a delay. The length section L of the solid device base 1 will therefore change much more slowly than the length section I between the bearing 7 and the front surface of the specimen 9, since the specimen carrier rod 8, as far as possible, for reasons of the load on the bearing system 7/5 and the sensitivity to vibrations is easily trained. The above-mentioned thermodynamically determined differences in length (L-1), which cause an irregular cutting sequence, will become more disruptive the greater the difference between the (linear) thermal expansion coefficients and the thermal conductivity values of the materials used for the base 1 and the specimen carrier rod 8. As already mentioned at the beginning, irregularities are therefore around 4 when using aluminum alloys

AT 398 848 B is many times larger than when using iron alloys, whereby among the iron alloys, the alloys already mentioned with a high nickel content have an extremely small expansion coefficient and extremely poor heat conduction and therefore offer the best conditions for optimum reproducibility of the cutting thicknesses. As already explained, therefore, despite the higher costs and the disadvantageously high weight of the devices, ultramicrotomes were made exclusively from iron alloys.

With reference to Fig. 2 it is shown that despite the use of a light device base 1 'made of a torsionally rigid aluminum alloy with the arrangement according to the invention is technically simple, thermodynamic changes in length, which lead to an irregular cut sequence, not only on the usual for steel components Keeping order of magnitude, but even reducing it below this magnitude. In the context of a particularly simple embodiment of this invention, the micrometer spindle 19 ′ is connected directly behind the support base plate 24 to an extension rod 25 made of an alloy of minimal thermal expansion, for example an alloy with a high nickel content (for example " Invar "), which is underneath the specimen carrier rod 8 runs and is connected below the bearing 7 via a tip bearing 26 directly or via rigid intermediate members (eg bearing block 4 ') to the aluminum base 1'.

The rigidly attached to the micrometer spindle 19 'rod 25 is pressed by a spring element, preferably by the illustrated plate springs 27 between the disc 28 and the rear boundary of the support base plate 24 in the direction of the arrow against the tip bearing 26, so that the tip bearing 26 always has a backlash Contact between the two bearing halves results. If there is no other determination of the position of the micrometer spindle 19 ', for example by means of a spindle lock of a known type, the respective position of the spindle nut 20 is therefore not determined by the length section L of the aluminum base 1', but exclusively by the length section L 'of the extension rod 25 or of it subsequent section of the spindle 19 'also made of steel in the present exemplary embodiment, wherein it is advantageous that when manufacturing from the same high-alloy stainless steels, the thermal expansion as well as the heat capacity and, consequently, the thermodynamic behavior of the elements 8 and 19' and 25 differ very little from each other. In this arrangement according to FIG. 2, the pulley 28 can be designed as a pulley for a toothed belt transmission 29 which, via a stepper motor 30, causes the knife support with the knife 3 to be gradually advanced or withdrawn in a technically known manner.

An embodiment of this compensation arrangement according to Fig. 3 consists in that instead of a single point bearing 26 at each end of the rod 25 ', a bearing is provided, which is formed by a ball 31 (e.g. bearing ball made of hardened steel), the corresponding ones Surfaces at the end of the micrometer spindle 19 'or at the ends of the rod 25' are designed either as conical surfaces K or as edges of bores B (cf. also receiving cylinder 32). In both cases there is a circular line contact which, with appropriate lubrication, in particular with the addition of a friction or. Stick-slip-inhibiting additives (e.g. molybdenum disulfide " Molykote ") ensure reliable storage. The advantage of this arrangement is that an exact alignment of the axes 22/22 'of the micrometer spindle 19' and the rod 25 (see FIG. 2) is no longer necessary. 4, a tip bearing 33 with a " spring bearing " 34 can be combined, the " spring bearing " in the simplest way by a section of greatly reduced diameter corresponds to the shaft 35/35 'corresponding to the extension rod 25/25'. Instead of such a " spring bearing " 34 a " spring gimbal " 36 can be provided between the sections 35 and 35 'of the shaft, with cross-cut millings on the sides of the shaft forming a joint with two limited freedom of rotation. Finally, according to FIG. 5 for articulated connections similar to the joints 19731/25 'or 25731/32 (supports K and B according to FIG. 3), or 19733/35 or 35/34/35' (FIG. 4), or 35/36/35 '(FIG. 5) joints can also be provided with a ball 31 which is received on both sides in the manner shown by hollow spheres (“spherical caps”), the radii of which correspond to the radius of the ball 31.

A further embodiment of the system according to the invention can be according to FIGS. 2 and 5 consist in that the specimen carrier rod 8 and the extension rod 35 are surrounded by a foam insulation 38/38 '(e.g. styrofoam, polyurethane foam, moltoprene foam), which enables rapid heat transfer between the metallic elements 8, 10 or 35 and the surrounding air, in particular in the case of a draft, prevented by this being delayed and therefore having less of an effect on the individual cut for a predetermined duration of a cutting cycle. The same can be achieved in a different embodiment of the invention in that according to FIGS. 2 and 4 covers the cylindrical metallic elements 8 and 35 with concentrically arranged metallic sleeves 40 and 40 ', an air gap of the order of magnitude between the inner wall of the sleeves 40/40' and the metallic surfaces of the cylindrical elements 8 and 35 at least 1 mm remains, the 5th

Claims (17)

AT 398 848 B prevents the rapid transfer of heat through thermal convection in the way an insulating glazing works. The present invention can be implemented in different embodiments without losing the character of the invention. In particular, the invention can be used in different and from the 5 FIGS. 1 and 2 different arrangements of the feed and retraction mechanism can be implemented in a corresponding modification. The selection and combination of the joint types on the extension rod 25, 25 'or 35, which are listed under numbers 26, 31K, 31B, 33, 34 and 36 in FIGS. 2 to 5, as well as under the numbers 19731/35 in Fig. 5 and described above. 1. Microtome, in particular ultramicrotome, with a device base, with a specimen carrier rod which is pivotably mounted in a bearing arrangement and with a micrometer spindle provided for displacing a knife carrier or 75 knives, the bearing arrangement for the specimen carrier rod and essentially below the knife carrier or Knife-lying storage for the micrometer spindle are connected to the device base, characterized in that the micrometer spindle is rotatably and axially displaceably mounted in its bearing, that a known, arranged in the axial extension of the micrometer spindle (19 ') and in the axial direction Extension rod (25, 25 ', 35) connected to the 20 micrometer spindle (19') without play is provided, which extends to a geometrical location which is substantially vertically below the bearing arrangement (7) of the specimen carrier rod (8), and that the extension rod ( 25, 25, 35) is connected to the device base (Γ) or a component (4 ') which is fixed to the device base in the axial direction without play in the axial direction. 25th 2. Microtome according to claim 1, characterized in that the device base (1 ') in a manner known per se made of aluminum or an aluminum alloy, in particular a duralumin alloy of low elasticity. 3. Microtome according to claim 1 or claim 2, characterized in that the materials from which the extension rod (25, 25 ', 35) and the specimen carrier rod (8) are made have a similar or the same linear coefficient of thermal expansion. 4. Microtome according to claim 3, characterized in that the linear thermal expansion coefficient-35 cient of the material of the specimen carrier rod (8) and the extension rod (25, 25 ', 35) is less than 2.10-5K-1, preferably less than 0.5.10 Is -6K_1. 5. Microtome according to claim 3 or 4, characterized in that the specimen carrier rod (8) and the extension rod (25, 25 ', 35) are made of the same material. 40 6. Microtome according to one of claims 1 to 5, characterized in that the material for the specimen carrier rod (8) and / or the extension rod (25, 25 ', 35) is a high-alloy nickel steel, quartz or glass ceramic. 7. Microtome according to one of claims 1 to 6, characterized in that the extension rod (25, 25 ') below the bearing arrangement (7) of the specimen carrier rod (8) is rotatable, but in the axial direction without play on the device base (1') or a device base-fixed Component (4 ') is stored. 8. Microtome according to one of claims 1 to 7, characterized in that the micrometer spindle 50 (19 ') and the extension rod (25', 35) can be rotated with respect to one another about their common longitudinal axis (22-22 '), but without play in the axial direction keep in touch. 9. Microtome according to claim 8, characterized in that the extension rod (35) is non-rotatably, preferably via an articulated spring bearing that allows pivoting of the extension rod, 55 with the device base (1 ') or a device base-fixed component (4') . 10. Microtome according to one of claims 1 to 9, characterized in that as a bearing element between the extension rod (25 ', 35) and micrometer spindle (19') and / or between extension 6 AT 398 848 B rod (25.25 ') and Device base or a device base-fixed component (4 ', 32) is arranged in a manner known per se, a ball (31), preferably a hardened and highly polished bearing ball made of steel or a bearing ball made of quartz. 11. Microtome according to claim 10, characterized in that the ball (31) - as known per se - rests on both sides in bearing seats, the ball and a bearing seat touching each other along a circular line. 12. Microtome according to claim 10, characterized in that the ball (31) rests on both sides in hollow spherical surfaces (" calottes) of the bearing receptacles, the radius of the hollow spherical surfaces corresponding to the spherical radius 13. Microtome according to one of claims 1 to 9, characterized in that as a bearing element between extension rod (25 ', 35) and micrometer spindle (19') and / or between extension rod 75 (25, 25 ') and device base or one component base-fixed component (4 ', 32) a tip bearing (26, 33) is provided, which consists of a conical tip and a cone receiving this tip, the opening angle of which exceeds that of the tip. 14. Microtome according to one of claims 1 to 13, characterized in that on the micrometer spin-20 del (19 ') a toothed belt pulley (28) is attached, which is connected via a toothed belt (29) to a stepper motor (30), the Rotation causes the knife (3) to advance or retract relative to the specimen (9). 15. Microtome according to one of claims 1 to 14, characterized in that the on the micrometer 25 spindle (19 ') attached or hinged to it extension rod (25, 25', 35) and / or the specimen carrier rod (8) by thermal insulating sleeves (38, 38 ') are surrounded, these sleeves preferably being formed from a plastic foam. 16. Microtome according to claim 15, characterized in that as thermal insulation for the 30 micrometer spindle (19 ') attached or articulated to it cylindrical extension rod (25, 25', 35) and / or for the likewise cylindrical specimen carrier rod (8) cylindrical metallic sleeves (40, 40 ') are provided, there being a distance of the order of magnitude of at least 1 mm between the inner wall of the sleeves (40, 40') and the metallic surfaces of these elements (8, 25, 25 ', 35). 35 17. Microtome according to claim 14 or claim 15, characterized in that the outer metallic surfaces of the metal foils (39,39 ') or the sleeves (40,40') are polished to a high gloss. Including 2 sheets of drawings 40 45 50 7 55