ROTARY MICROTOME DRIVE

Abstract: Novel rotary microtome. In order to avoid the sticking and friction inherent in conventional slide mounts for the sample table, the invention provides a construction in which the sample table (4) is advanced by means of a parallogram linkage (1, 6, 8, 9). Retraction of the sample table (4) is effected without disturbing the leadscrew assembly (17, 18) by means of a lost-motion arrangement (9a, 9b).

Description: ROTARYMICROTOMEDRIVE This invention relates to rotary microtomes, by which is meant microtomes in which relative incremental advance movement between a specimen table and a relatively recip- rocable knife, and the reciprocating .movement itself are both derived from a single rota able drive member. The typical increment of the advance movement is some 4 microns in the case of specimens embedded in paraffin wax, and some 0.5 - 1.0 microns in the case of samples embedded in synthetic resin. Conventional rotary microtomes provide the advance move¬ ment by means of a leadscrew which acts on a linear dovetail slide carrying the specimen table. This provides a robust mechanism v/hich is well able to withstand the cutting forces involved, but in practical use, the arrangement is lively to suffer from friction and sticking and attendant vibration, which interfere with the accuracy of the advance movement. This is particularly the case in rotary microtomes designed for specimens embedded in synthetic resin, since in these it is necessary to provide for specimen retraction between successive cutting strokes, in order to prevent the last-cut section from re-adhering to the sample under the effects of static electricity during the return stroke. This retrac- tion is conventionally of some 0 microns or so, and re-setting of the specimen advance after such a retraction is rendered unreliable, particularly where, in addition to the friction and sticking effects associated Y.iτh the dovetail slide referred to above, the leadscrew itself is moved bodily to permit the retraction. The present invention is concerned to provide a specimen table advance mechanism for a rotary microtome in which the effects of friction and sticking and vibration are largely eliminated, in which the cutting forces involved are well catered for and which can be adapted for both paraffin- embedded and synthetic resin-embedded specimens without substantial re-design of the basic arrangement. Basically the present invention provides a rotary microtome in which the advance movement of the specimen table relative to the cutting member is provided "oy a parallelogram linkage. As will be readily understood from the subsequent description of a specific embodiment of the invention, the parallelogram linkage may itself also act as the support for the specimen table. To eliminate friction and sticking entirely from the points of articulation of the parallelogram linkage, they may be constituted by strip hinges. The invention will now be described with reference to the accompanying drawing, whose single Figure is a diagram¬ matic side view of the specimen table support and advance mechanism of a rotary microtome for synthetic resin- embedded specimens. The mechanism in the Figure is supported on the massive base 1 of the microtome, v/hich bass is apertured at la and lb for the passage of parts of the mechanism. A knife 2 is fixed to the base by conventional means (not shown in the Figure) and a specimen 3 is shown as mounted on a specimen support 4 which is carried for reciprocating movement relative to the knife (as shown by the arrow 4a) on a dove¬ tail guide 5 which together with the specimen support 4 constitutes the specimen table of the microtome. The guide 5 is rigidly fixed to a bracket 6 which forms an upper limb of a parallelogram linkage whose lower limb is constituted by a pedestal structure secured fast to the base 1. The other sides of the parallelogram are formed on the one hand by a link 8 adjacent the dovetail guide 5 and on the other hand by a member generally indicated at 9 through which both* advance and retraction of the specimen table are effected. Articulation of the parallelogram linkage is provided by four paired sets of crossed strip hinges indicated at 10a. - d_, each set having a horizontal strip 10' and a vertical strip 10" arranged orthogonally to define a unique hinge line. It will be understood that for mechan¬ ical stability and balance the pair of sets of hinges at each articulation point lie one on either side of the median plane of the mechanism on which the Figure is based. For reasons of clarity, the clamping blocks and screws which secure the strip hinges to the various members of the parallelogram linkage have been omitted from the Figure. From a general inspection of the Figure, it will be appreciated that the articulation of the parallelogram linkage will permit movement of the specimen accurately parallel to the base 1 of the microtome. The movement is provided by e^ns of the member 9 v/hich, as can be seen in the Figure, is constructed in two parts. The first part, 9a., is articulated at 10b_ and lOd to the brackets 6 and pedestal structure 7 respectively, and its rotation about the articulation point lOd. is used to cause the advance and retraction movements of the specimen table. The second part, 9b_, of the member 9 is secured to the first part a. in such a manner as to permit lost motion between the two. The two parts articulate about a pair of ball pivots 11 located in corresponding V-notches 11a, lib in the respec- tive parts, and are held normally in the relative positions shown in the Figure by means of a tension spring 12 v/hich is accommodated within* aligned bores 13a_ 13b_ in the parts 9a* and 9b_, and whose ends 12a., 12b_ engage corresponding abut¬ ment members 14a., 14b_ by which the tension in the spring is transmitted to the parts 9a. and 9b , . The precise normal alignment between the parts 9a and 9b_ is defined by a stop 15 on the part 9b , and an anvil 16 on the part 9a.. The normal orientation of the composite member 9 is defined by means of a trunnion nut 17 on a leadscrew 18 which is joumalled in the base 1 and is driven in standard manner by the rotary drive of the microtome to provide the necessary advance movement of the specimen table. It will be appreciated that the tv/o-part member 9 could be replaced by a corresponding unitary member for a microtome in which no retraction is required. However, in the present embodi¬ ment, the microtome driving train includes a cam 19 which is rotated by the microtome drive as indicated ' oy the arrow 19a to cause rocking movement of a lever 20 pivoted at one end to the base of the machine at 21. A link 22 is con¬ nected via ball and socket joints 23, 24 betv/een the other end of the lever 20 and the end of the second part 9b_ of the member 9« The high region of the cam 19 causes the lever 20 to pivot in an anti-clockwise direction during the return stroke of the specimen past the knife blade 2, this movement being transmitted to the part 9b_ of member 9- Consequently, this latter part rotates anti-clockwise about the trunnion nut 17, whose circular surface allows a rock- ing movement. As the part 9b. rotates in this way, the part 9a. is constrained by its articulations respectively to the part 9b_ and the base 1 to pivot i -a clockwise direction about the fixed articulation point 10d_, the force to cause this movement being transmitted from the part 9b , via the spring 12 as the two parts 9a and 9b , pivot apart about the ball pivots 11. When the cam 19 again presents its low region to the lever 20, the parts 9a. and b regain their earlier relative alignments, • with the stop 15 and anvil 16 in contact, and the normal advance sex by the leadscrew is accurately maintained. The dimensions of the cam 19 on the one hand, and the linkage formed by the lever 20, link 22 and part 9b_ of member 9 are selected τ.o cause a retraction of some 0 microns. I e use of the parallelogram linkage will be understood to enable the production of a very accurate advance motion without the problems of friction and sticking and vibration inherent in the conventional linear dovetail slide arrange¬ ment. 3y the use of strip hinges of a suitable material, such as the beryllium-cooper alloy used in the illustrated embodiment, these causes of difficulty and error are completely eliminated, even in a rotary microtome as here¬ inbefore defined. More significantly, the parallelogram linkage permits the manufacture of two patterns of rotary microtome, one with retraction and one without, on the basis of a single specimen table support and advance mech¬ anism. This allows considerable economy by reducing the overall amount of tooling necessary to produce the two patterns. With reference to the retraction mechanism in the illustrated embodiment, this operates without movement either of the leadscrew or of its nut, so that the accuracy with which the advance movement is set is unaffacted by the retraction. In addition to the elimination of sticking and friction and the attendant vibration, the use of strip hinges in the present embodiment also achieves a consider¬ able reduction in the amount of maintenance which is necessary during the life of the microtome.

Claims: CLA-D-S 1. A* otary microtome of the type in which both the relative incremental advance movement between a specimen table and a relatively reciprocable knife and also the rec¬ iprocating movement itself are derived from a single rotatable drive member characterised by the provision of a parallelogram linkage whose articulation provides the relative incremental advance movement. 2. A rotary microtome according to Claim 1 characterised in that the parallelogram linkage supports the specimen table. 3. A rotary microtome according to Claim 1 characterised in that the articulation points of the parallelogram link- age comprise strip hinges. 4. A rotary microtome according to Claim 3 characterised in that each of the articulation points comprises crossed strip hinges. 5. A rotary microtome according to Claim 1 characterised in that advance .rovement LH transmitted to the parallelo¬ gram linkage from a leadscrew via a transmission mechanism. 6. k rotary microtome according to Claim 5 characterised in that the transmission mec- " ..aniεm incorpora .: lost-motion me ns. 7. A rotary microtome according to Claim 6 characterised in that the transmission mechanism is a lever. 8. A rotary microtome according to Claim 6 or Claim 7 wherein retraction means cx upon said lost motion means. 9. A rotary microtome of the type in which both the relative incremental advance movement between a specimen table and a relatively reciprocable knife and also the reciprocating movement itself are derived from a single rotatable drive member, characterised in that the advance movement is transmitted from an incremental drive mechanism via a transmission mechanism which incorporates lost motion to provide relative retraction between the specimen table and the rrnife without any corresponding reverse movement of the incremental drive mechanism. 10. A rotary microtome according to Claim 9 characterised in that the incremental drive mechanism is a leadscrew and nut.

Inventors: JACKSON B, PARKER P
Applicants: JACKSON B, PARKER P
Application year: 1981
Main classification: G01N1
IPC codes: G01N1