Abstract:
In a microtome ( 1 ) for producing thin sections for histology, there is a danger of collisions between the sample ( 9 ) and the cutting edge ( 7 ) in setup mode for coarse feed. It is an object of the invention to limit the collision force of such a collision so that it lies within an admissible range and, therefore, damage is avoided, and the microtome ( 1 ) is thereby inherently safe in setup mode. It is also an object of the invention, using the same means, to make available methods that resolve collisions and permit automatic approximation between sample ( 9 ) and cutting edge ( 7 ). The support force of the associated advancing means ( 18 ) acting in the advancing device ( 12 ) is limited since the otherwise customary screwing of the associated advancing means ( 18 ) on the advancing device ( 12 ) is replaced, for example, by a spring mounting or by a connection acting with magnetic force. Thus, when the support force is exceeded in the event of a collision, the associated advancing means ( 18 ) lift away from their contact face and experience a displacement ( 30 ). The collision force is thus limited to the support force. An additional switching off of the electromotive advancing drive and an associated process for resolving a collision via the electrical control ( 11 ) forms the basis of a further method for automatic approximation between sample ( 9 ) and cutting edge ( 7 ), which is likewise inherently safe by using the same means. The microtome ( 1 ) according

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority of the PCT application PCT/DE2015/000161 based on German application DE 10 2014 005 445 having a priority date of Apr. 11, 2014, the entire content of which is herewith incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Technical Field 
         [0003]    The invention describes a microtome with an electromotive feed system which has means incorporated for enhanced user safety and prevention of damage by limiting the applied forces at uncontrolled collisons between specimen and knife edge and thus making the microtome inherently save. Further the invention exhibits means which cause in addition a deactivation of the electromotive drive in a case of a collision and is providing with the same means a method for a thereof derived automated approach between specimen and knife edge. 
         [0004]    Microtomes are sectioning instruments with primary use in histology, biology, medical research but also in materials science and quality assurance for producing thin sections of specimen. These sections are then used in microscopic, mainly light microscopic examination methods 
         [0005]    Background Art 
         [0006]    With all types of microtomes the production of thin sections in the sectioning process is performed by a relative movement of a clamped specimen and the cutting edge of a sectioning tool along a linear or curved sectioning path. Thereby the section thickness of the resulting section is basically the amount of feed which is carried out in a previous step as a relative movement to each other between specimen and sectioning tool. This feed movement is typically, but not necessarily, in a vertical direction to the sectioning movement. The feed can either be carried out as feed of the specimen by the specimen holder or as feed of the sectioning tool by the knife carrier. 
         [0007]    Common microtomes differ in their type of construction as there are rocking microtomes with knife carrier feed system, sledge microtomes with knife carrier or specimen feed systems, disk microtomes with knife carrier feed system and rotary microtomes with knife carrier or specimen feed systems. Microtomes used in microtome-cryostats to produce frozen sections are called cryostat-microtomes. Fundamentally they also differ as to the named types of construction and types of feed system. It should be noted, that in general each type of microtome can be represented either with knife carrier feed system or with specimen feed system. 
         [0008]    State of the art microtomes of all named types have at their feed system a guidance body which is either firmly connected to a main body of the respective microtome or to a support body which moves directed along the sectioning path of the microtome. Thereby it is depending on the type of microtome and depending whether there is a knife carrier feed system or a specimen feed system to determine to which of the named parts the feed system is connected. The connection of the guidance body with either the main body or the support body can be arranged by fastening with screws, by glueing together or by other fastening techniques but also by being one piece together with the main body or the support body respectively. 
         [0009]    The feed system thereby always consists of the guidance body, a thereon or therein moveable guiding element and interconnected feed means. The interconnected feed means for example may consist of a spindle with nut, a spindle bearing with bearing elements, a bearing housing and a driving element for the feed movement. Other forms of interconnected feed means for example can contain rack and pinion drives, worm gear arrangements or rope pull system components. Common to all arrangements of interconnected feed means in the state of the art is, that at least one functional part of these interconnected feed means is fixedly connected with the guidance body, for example by screw connection or is in one piece with it and that at least one further functional part of these interconnected feed means drives the moveable guiding element when the driving element is initiated. 
         [0010]    When starting sectioning a specimen and producing successive thin sections of it, there is to overcome initially the difficulty to minimize the unknown distance between a specimen of variable size and the knife edge. That procedure in the set-up phase of sectioning is called approach and is typically performed 80-120 times during a work day in a routine lab. Thereby ideally the middle of the specimen is positioned at about same height as the knife edge of the sectioning tool opposite to it in a certain distance. Then a so called coarse feed movement is carried out with the feed system of the microtome to minimize the distance between specimen and knife edge in order to enable the following first cuts, the so called trim-sections of the specimen, in a secure and appropriate manner. 
         [0011]    It should be mentioned, that with most microtomes, whether they have knife carrier feed system or specimen feed system, it is possible for example, to loosen the knife carrier from its base by unlocking clamping levers and manually shift it towards the specimen until touching and then lock the clamping levers again. The same procedure is also feasible with specimen clamps, if they would be equipped with clamping mechanisms to unlock. This type of an approach between specimen and knife edge is outermost non-ergonomic and will be not followed up further. 
         [0012]    It is state of the art with mechanically acting feed mechanisms to have safety mechanisms to avoid demolitions on microtome parts during feed movements. WO 95/14 219 A1 is describing a purely mechanical working microtome where the manually operated coarse feed system is secured with a slip clutch when reaching the limit stop and where the mechanically working micrometer mechanism has a safeguard against inner disruption when reaching the limit stop. 
         [0013]    WO 2004/ 029 587 A1 is also describing a mechanically feeding microtome with a manual coarse feed, where the coarse feed handwheel is equipped with a slip clutch to avoid demolitions in case of a blockage between coarse feed mechanism and feeding spindle. 
         [0014]    The state of the art is also including solutions for spindle based feed systems, which offer the desired zero backlash of the feed systems by using spring assemblies. DE 34 04 098 C2 is describing a microtome with mechanical feed system with a spindle and with a mechanically acting retraction mechanism, which interferes with a spring loaded spindle bearing. 
         [0015]    In DE 37 27 975 C2 is the description of a microtome with mechanical feed system based on a spindle, which incorporates spring assemblies between the spindle and divided nuts and at the spindle and nut bearings respectively in order to avoid backlash. 
         [0016]    DE 34 04 097 C1 describes a microtome with an electromotive coarse feed system in superimposition of a purely mechanical fine feed system. DE 29612938U1 describes a microtome which applies preferably a stepping motor to operate coarse and fine feed. It is generally state of the art with all construction types of microtomes to use stepping motors for feed systems. 
         [0017]    With such microtomes the above said coarse feed movement, for minimizing the distance between the specimen and the knife edge before starting with trim sections, is carried out by a corresponding operational command with a switch or with a keypad by simultaneously careful observation of the shrinking distance between specimen and knife edge. Thereby the difficulty is on the one hand to approach under visual control as close as possible between specimen and knife edge, but on the other hand to avoid a collision between specimen and knife edge as this may lead to damages of the knife edge but also the specimen as well. The necessity to approach as close as possible comes from the fact that the required section thickness of trim-sections is typically below 30 μm. Thus right away first sections will only be produced after such an approach, if the remaining distance between specimen and knife edge is already in that range. For a better visual control of the gap between specimen surface and knife edge it is also common to use optical accessories like stereomicroscopes or magnifying glasses, which may also be equipped with additional illumination devices. 
         [0018]    This is cumbersome and non-ergonomic and does not guarantee securely to prevent a collision, because the blank specimen surface also has unevenness. Moreover there is always the risk of operating error with respective damages at the specimen and/or the knife edge. With gross operating errors or with a first failure of a technical means there is also to a certain degree the danger of injury, for example bruises at the fingers of the operator. 
         [0019]    In order to avoid the erroneous and time consuming specimen approach under manual control of the coarse feed automatic approach systems were implemented. A microtome is known from DE 42 05 256 C2, that has an electromotive feed system for coarse and fine feed and an automatic approach system. With that device, which is mounted on the rear side of the knife carrier and where the specimen is positioned at the end of the sectioning path, the danger and the difficulty which is associated with a manually operated approach under visual control can be avoided. However in practical use, there was found a significant impairment of the functionality by soiling of sectioning debris, because the device is positioned in the area of generating sections. This leads to malfunctions and respective efforts to reinstall the correct function. 
         [0020]    DE10258553B4 is describing a device for automatic approach by using a light barrier. The location for this device is again in the area between knife carrier and specimen holder and therefore exposed to functional limitations due to soiling. 
         [0021]    DE19911173C2 describes an automatic approach system based on a pressure sensor which is positioned in determined reference to the knife edge. The location of the sensor is again in the area of potential soiling between knife carrier and specimen holder with the respective disadvantages for precision and functional efficiency of the device. 
         [0022]    In DE102007023457B4 a method is proposed for an automatic approach based on a light barrier with a light band and generating a reference value in respect to the knife edge. But again the location of the optical means is in the gap between knife carrier and specimen holder and therefore afflicted with the same disadvantages mentioned above. 
         [0023]    EP 2 503 315 A2 finally describes a microtome with an electromotive feed system and a thereto connected measurement of the specimen orientation and out of it a correction procedure of the specimen orientation and subsequent automatic approach. However the location of the system is again at the rear side of the knife carrier and is therefore essentially exposed to the same soiling problems from sectioning debris at sectioning, although there is a specific mechanical protection device in place, which then makes the whole system expensive. 
         [0024]    DE 195 281 80 C2 is describing a method for an automatic approach system with measurement of the conductivity, when specimen and knife edge are touching each other. This however requires a usable minimum conductivity of the specimen media and embedding media. Those requirements however are only available with frozen section in microtome-cryostats. For practical use, the valuation of the conductivity measurement and herewith related criteria for feed stop will be aligned with temperature tables in order to achieve functionality as secure as possible. For specimen with paraffin embedding media or plastic embedding media this method cannot be used due to missing the minimum of conductivity needed. 
         [0025]    All named methods and devices for an approach between specimen and knife edge, those with manual operation as well as those with automatic approach, have in common the disadvantage of lacking functionality and missing inherent safety. This involves that in case of malfunction, caused by an operator as well as in a case of first failure of the utilized technical means, an uncontrolled collision can happen between the specimen and an opposite contact point. This is particularly harmful, because the driving electromotive force of the feed system is acting further until, either by manual intervention or by damaging a technical component, the process comes to an end. The thereby acting forces can be substantial, especially if, as mostly in use, the feed system is working with an electromotive drive together with a spindle and respective nut with fine thread pitch. The ordinary operating parameters of the microtome are then considerably exceeded. 
         [0026]    Thereby risk of damage of specimen and/or the knife edge is given to a large extent. Further there is risk of damage of components of the microtome. 
         [0027]    With gross operating errors or with a first failure of a technical means, there is in addition to a certain extent the risk of injury, for example bruises at the fingers of the operator. 
       BRIEF SUMMARY OF THE INVENTION 
       [0028]    It is an objective of the invention to describe a microtome with an electromotive operated feed system and a method for operating such a microtome with that feed system, which, at a high level of functionality, allows manually operated as well as automated feed movements for an approach between specimen and knife edge at set-up procedures and thereby has inherent safety, as with exceeding of a determined collision force between the specimen and an opposite collision point, means will be activated, which will limit the collision force. 
         [0029]    Although there are means acting which give inherent safety when exceeding a determined collision force, it is a further objective of the invention, to cause in addition a deactivation of the acting electromotive drive in case of collision and thereto connect procedure steps which lead to an adjustment of the collision situation, in order to enable at a further undisturbed operation a fast and ergonomic functionality of approach between specimen and knife edge. 
         [0030]    It is in addition an objective of the invention to develop further the procedure steps in order to realize an automatic approach system between specimen and knife edge while using the identical means. 
         [0031]    These objectives are accomplished according to the present invention by a microtome with the characteristics of claim  1 . Claims  2  to  9  are describing forms of the microtome according to claim  1 . Claims  10  and  11  are describing methods for operating a microtome according to claim  1 . 
         [0032]    The solution of the problem is based on an analysis of the acting forces and their directions at a sectioning process. In a modification of the force diagram for chipping procedures as described in the so called Orthogonal-Process from Merchant (Zerspantechnik: Prozesse, Werkzeuge, Technologien von Eberhard Paucksch et al.), can be showed, and can be substantiated by practical measurements, that with standard sectioning conditions there is a thrust in opposite to the feed direction, which is caused by shearing and grinding processes at the formation of the section. In the state of the art, this thrust is countered by a zero-backlash bearing of the feed means and in particular a fixed connection, in general a screw connection of, for example, the bearing housing of the feed means with the guidance body of the feed system. Only with a zero-backlash arrangement and a specific rigidity it will be possible at all to generate sectioning results in the thickness range of microns. 
         [0033]    That fixed connection, which is applied in the state of the art, between at least one functional part of the interconnected feed means and the guidance body, which is immobile in direction of the feed axis, absorbs the brace force, which is the REACTIO of the mentioned thrust. Thereby it is avoided that by applying thrust at the sectioning process the interconnected feed means may give way and the fed section thickness can be carried out reliably. 
         [0034]    The sufficient brace force in order to achieve good sectioning results is however by no means high in respect to the applied sectioning force. Measurements have shown, that the values of brace force acting against the feed direction are in the range of 10-40% of the applied sectioning force, depending on the type of utilized sectioning tool and the type of specimen and specimen embedding media. As result of this analysis follows, that a brace force in feed direction of about 50% of the applied sectioning force is sufficient for normal sectioning applications in order to achieve still confident and good sectioning results. Naturally exempt of this are increased brace forces as they may occur with inadmissible operating parameters at sectioning, for example with collisions in the sectioning path at the sectioning process. The sufficient brace force in feed direction also has to include the REACTIO of friction forces from the feed movement, for example of the linear guidance of the guidance element inside the guidance body. 
         [0035]    The solution of this invention is, that the fixed connection of the state of the art instruments which is typically a screw connection between the guidance body of the feed system, which is immobile in feed direction, and the interconnected feed means, now is replaced by a connection which acts only up to a defined limit value of the brace force as a rigid connection with two contact surfaces lying on top of each other and which offers in case of exceedance of that limit value a flexibility opposite to the feed direction. 
         [0036]    This now offers the possibility to determine a limit value of brace force in feed direction for the force which may occur at set-up procedures between a specimen and an opposite area of the knife carrier. According to the invention this is solved by having at the guidance body as well as at least at one functional part of the interconnected feed means each a contact surface, whereby the contact surfaces are loaded with a defined force, which is of same absolute value but of opposite direction as the determined limit value for a tolerated force occurring at a collision between the specimen and the knife edge, or a collision point at the knife carrier. 
         [0037]    Thereby it is ensured, that with an ongoing feed drive after an occurring collision, for example caused by operation error or by malfunction of technical means of the deactivation circuits, and an exceedance of the determined limit value of the brace force, the interconnected feed means detach from the contact surface at the guidance body. With a further ongoing feed drive at a further existing collision a shift of the interconnected feed means will take place in opposite direction to the feed direction. 
         [0038]    When determining the limit value it should be observed, that, depending on the installation position of the feed system, the weight of the interconnected feed means has to be taken in account in addition. As a consequence, for a vertical installation position of the feed system with a vertically directed feed axis, an addition of the weight force of the interconnected feed means has to take place if the feed direction is upwards and a subtraction of the weight force of the interconnected feed means has to take place if the feed direction is downwards. With installation positions of the feed system which are neither horizontal nor vertical, a respective prorated weight force of the interconnected feed means has to be taken in account by trigonometric calculations. 
         [0039]    The procedure of shifting of the interconnected feed means will be limited by a self-activating decoupling of reasonable sized and configured components which are relevant in that moving procedure, for example by undo the end of a spindle from the respective feed nut and therefore is limiting the shifting range. 
         [0040]    A microtome of that embodiment is inherent safe in relation to occurring collision forces, as with an occurring collision and exceedance of the limit value of the brace force there is no further increase of the collision force in feed direction above the force which is relevant in the shifting range of the interconnected feed means. 
         [0041]    An advanced embodiment is, to equip the microtome according to the invention with two switchable limit values of the brace force. This solution takes in account, that the above mentioned thrust, opposite to the feed direction, is only active directly while sectioning. However, if the microtome is in set-up procedure this thrust is not applied and hence there is no need to take it in account when determining the limit value of the brace force. For that operating condition it is sufficient to have a limit value which is above the reaction forces resulting from the friction of coarse feed movements. 
         [0042]    This by far lower limit value of the brace force enables a more gently and less risky approach between specimen and knife edge at set-up mode. However, there is a need for the possibility to switch to a higher limit value of the brace force for the sectioning mode, because then there is to take additionally in account the thrust generated at sectioning mode as a counterforce. Otherwise there would be no reliable sectioning process, because the generated thrust would be in the range of the brace force. And therefore it could happen at sectioning, that the contact surfaces of the interconnected feed means and the guidance body would detach from each other. For switching the limit values there are numerous possibilities given. This depends mostly with the technical means used to create the brace force. For example with purely mechanical solutions by a mechanical lever, or with purely electrical solutions by activating of actuators thru the electronic control, or with pneumatic or hydraulic solutions by direct operation of valves, or with more complex solutions by electrical activation of electrically controlled pneumatic or hydraulic valves by the electronic control. 
         [0043]    For example, the brace force between guidance body and a thereto attached functional part of the interconnected feed means and the force which is relevant in the shifting range can be created by compression springs or tension springs, whereby one point of force is at the guidance body and one point of force at the opposite functional part of the interconnected feed means. The use of compression springs and tension springs as force generating means is of relative disadvantage, because the force in the shifting range is not constant but increasing up to the disengaging point, even when using very long springs. Thereby it should be remarked, that when selecting the technical design, it should be taken in account, that the finale force at the end of the shifting range should still represent an acceptable collision force in terms of avoiding damages to the specimen or the knife edge. 
         [0044]    Therefore it is advantageous, to generate the brace force at the contact surfaces by magnetic force of permanent magnets or electromagnets as force generating means. Thereby also one point of force is at the guidance body and one point of force at the opposite functional part of the interconnected feed means. Conditioned by the decrease of magnetic force with increasing distance between a magnet and a ferromagnetic anchor, or also between two magnets, consequently the force, which is also the collision force, will decrease after exceedance of the limit value with mounting shift as soon as a shift takes place. At this a changeover of the limit values of the brace force can be carried out, for example, by positioning the ferromagnetic anchors at two different distances from the magnets by an actuator. 
         [0045]    Respectively other analogue arrangements are possible; the changeover over the distance positions can take place at the part which is related to the guidance body or at the part which is related to the functional part of the interconnected feed means, whereby the single parts can be all magnets or magnets combined with ferromagnetic anchors or other appropriate anchor materials. If the magnets are accomplished as electromagnets, the simplest changeover of the limit values of the brace force is by electrical switching of the coil current. 
         [0046]    Further embodiments of force generating means can be, for example, small pneumatic or hydraulic actuators, most common pneumatic or hydraulic cylinders, whereby also there one point of force has to be at the guidance body and one point of force at the opposite functional part of the interconnected feed means. A changeover of the limit values of the brace force, for example, can be performed by switching the applied pressure of the utilized pneumatic or hydraulic actuators. A constant force within the shifting range can be achieved, for example, by using relief valves which are adjusted for a respective pressure 
         [0047]    The multitude of possibilities to use as force generating means for the brace force and possibilities for changeover of the limit values of the brace force and to achieve a constant, or falling, or increasing brace force, but only to the extent that the collision force, which is equally strong, does not cause any damage within the shift range, is not yet exhausted with the above named force generating means. The invention includes also those further possibilities as much as they meet the named criteria and the generated force has one point of force at the guidance body and one point of force at the opposite functional part of the interconnected feed means. 
         [0048]    When exceeding the applicable limit value of the brace force and with a then beginning shift, the interconnected feed means may tend to a twisting around the feed axis caused by friction forces, especially if there are rotational acting feed means utilized, for example spindle and feed nut. In order to bear and guide the interconnected feed means on the feed axis while shifting it is also with non-rotational acting feed means necessary to take measures, which, especially in regard of the installation position of the respective feed system, can compensate force components, for example, of gravitation force, which are not acting in feed direction or feed counter direction. This is indispensable in regard of a continued functionality after a collision took place and an afterwards reversed collision situation. 
         [0049]    A shifting range guidance is therefore generally in place, according to the invention, for all embodiments of interconnected feed means, which guides the interconnected feed means while shifting and protects them against twisting. This can be achieved, for example, for rotational acting feed means by a fixedly connected guiding pin as twist protection, which is mounted at the guidance body parallel to the feed axis in a certain distance. This guiding pin being movable in a drill hole of a functional part of the interconnected feed means in feed direction and feed counter direction, as, for example, a spindle arranged in feed axis ensures that the interconnected feed means together move on the feed axis. 
         [0050]    For the shifting range guidance of non-rotational acting interconnected feed means there is, for example, a need of a minimum of two guiding pins in order to achieve the effect or other known guiding elements can be used for achieving a linear guidance and a twist protection as well. When utilizing pneumatic or hydraulic cylinders as force generating means, they could serve for an integrated form of shifting range guidance, because they already include guidance despite their force generating function. 
         [0051]    A further embodiment of the microtome consists to that effect, that the condition after an occurred collision and a therefore resulting detachment of the contact surfaces between the guidance body and the interconnected feed means will be detected by switching means and that a deactivation of the electric motor which is driving the feed system will be caused via the electronic control. 
         [0052]    Thereby it is of importance, that on the one hand a most immediate detection of the detachment of the contact surfaces takes place and that on the other hand this is carried out with a high reproducibility, because the respective switch-off position is relevant for the accuracy of the method of the further procedure steps. At that it is an aim to achieve a reproducibility of the respective switch-off position with a variation of clearly less than the typical sectioning thickness at first trim sections, for example 30 μm. Simplest, the detecting switching means can be realized by a microswitch, which will be triggered by a mechanical flag. This solution, however, is comparatively inaccurate. The utilization of light barriers, foil pressure sensors, strain gauges or piezo transducers are alternatives as detecting switching means, which, depending on their fineness and the respective application, will satisfy the challenged fast response as well as the wanted high reproducibility 
         [0053]    However, the surfaces of, for example, foil pressure sensors or strain gauges cannot directly be used as contact surfaces at the guidance body or at the interconnected feed means, because they do not exhibit the adequate stiffness and therefore section thickness variations would result at sectioning processes with varying thrust under load. With piezo transducers, especially from crystalline material, the given stiffness of, for example 1 μm elongation at 20N brace force of a selected product, will be sufficient for forming directly with the two active areas for one part a contact surface between guidance body and interconnected feed means and for the other part, with the opposite surface, being connected either at the guidance body or at a functional part of the interconnected feed means and herewith fulfill the function of a detecting switching means. 
         [0054]    A further and more economic version of detecting switching means is consisting by using essential functional parts of the fitting and constituting them as switching means simply by selection of material and configuration. Thereto the contact surfaces lying on each other of on one hand the guidance body and the other hand a functional part of the interconnected feed means, for example, could be thought of as two electrical contacts lying on each other, which would separate at a collision and followed commencing shift and therefore send a signal to the electronic control. However, thereto it is mandatory, that the two contact surfaces can embrace different electrical potentials after separation. This, for example, can be achieved by a guidance body, or a part of the guidance body, being made of electrically non-conducting material and a therein inserted conducting ring or one or several conducting pins to provide an electrical and mechanical contact surface. 
         [0055]    The same possibility is consisting naturally in reverse by choosing a non-conducting material for that functional part of the interconnected feed means designated as surface contact and to insert into that material a conducting ring or one or several conducting pins to provide an electrical and mechanical contact surface. There is a necessity to choose non-conducting material for one of the two of the carrier parts of the contact surfaces, because commonly all further parts of the feed system consist of metals and therefore would existing an electrical connection via linking guidance, joints or bearings even after a commencing shift and separation of the contact surfaces. 
         [0056]    The further solution of the problem according to the invention is achieved by a method for operating a microtome by a sequence of procedural steps, which are actuated by the electronic control. For this purpose, the feed position, which is accumulated in respect of an initialisation position at power up of the microtome, will be determined and stored at the moment of deactivation of the electric motor caused by the detecting switching means. Immediately after this the electric motor will be activated again, but in reverse direction, and conducts a movement which is laid down in the electronic control and leads to a safe rectification of the collision. 
         [0057]    The solution of the problem consists herewith in realizing an automatic approach between specimen and knife edge by using further procedural steps based on the so far mentioned partial solution steps. To do so, the electronic control is verifying if an automatic approach was initiated via the control panel. In a next step the electronic control is checking the position of the support body. The therefore necessary information is commonly available at the electronic control, because information about start of the sectioning path and end of the sectioning path is needed also for regular application mode. If the support body, which can be moved by the sectioning drive, is positioned at the end of the sectioning path, a feed movement will be conducted which continues up to an intended collision between the specimen and the knife carrier body beyond the knife edge. Expediently a flat surface is located at the knife carrier body, which is oriented vertical in regard to the feed direction and which is offset in regard to the knife edge by a certain distance. 
         [0058]    With a then occurring collision a deactivation of the electric motor takes place via the mentioned means. The distance in feed direction between the collision surface at the knife carrier body and the knife edge is set as knife carrier reference value and this value is stored in the electronic control. In addition at the electronic control is stored a value for safety retraction. Both values must be added and the resulting value for movement will be carried out in opposite direction to the feed direction by activation of the electric motor. With that the collision is dissolved and the specimen is located within the distance of the safety retraction ahead of the knife edge. The procedure of automatic approach will be finished as soon as the electronic control will detect the position of the support body, which can be moved by the sectioning drive, in the start position of the sectioning path. Then the electric-motor will be activated in feed direction for a movement which is of same magnitude as the safety retraction and therefore is neutralizing the safety retraction. Now the specimen is in trim position in regard to the feed position as well as in regard to the sectioning path. 
         [0059]    The described solution for a configuration of the feed system of a microtome and the thereto matching procedural steps of a method to operate a microtome can be applied to all types of microtomes mentioned at the beginning, likewise in cryostat microtome versions, whether the respective type of microtome in regards to the feed system is configured with knife carrier feed system or specimen feed system at that. As electric motors for driving the feed system all types of motors can be utilized which are permitting to reverse the direction by the control, especially also linear motors. At that, depending on the type of motor, an additional position measurement device for measuring the respective feed position, being connected to the electronic control, will be mandatory for applying the described method. The utilization of stepping motors is facilitating an economically advantageous solution, as with that a position feedback control is not needed 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0060]    Further advantages and embodiments of the microtome according to the invention as well as the methods for operation of such a microtome ensue from the following figures and their descriptions. 
           [0061]    In particular  FIG. 1 a    up to  FIG. 5 b    shows microtomes according the state of the art, always without housing, in different embodiments but with feed systems of generally the same kind.  FIG. 6 a    and  FIG. 6 b    shows graphics of force effects in sectioning mode and with collision in set-up mode. The  FIGS. 7 a    up to  9   c  show embodiments of the microtome according to the invention and  FIGS. 10 a    up to  11   k  outline the methods for operation according to the invention of the microtome according to the invention. For components which are connected to each other the representation of the respective fasteners was spared for reasons of clarity, to the extent the type of connection is irrelevant for the invention. 
           [0062]    The drawings illustrate in 
           [0063]      FIG. 1 a    a rocking microtome with knife carrier feed system according the state of the art 
           [0064]      FIG. 1 b    a longitudinal section thru a rocking microtome with knife carrier feed system according the state of the art 
           [0065]      FIG. 2  a sledge microtome with specimen feed system according the state of the art 
           [0066]      FIG. 3  a disk microtome with knife carrier feed system according the state of the art 
           [0067]      FIG. 4 a    a rotary microtome with knife carrier feed system according the state of the art 
           [0068]      FIG. 4 b    a longitudinal section thru a rotary microtome with knife carrier feed system according the state of the art 
           [0069]      FIG. 5 a    a rotary microtome with specimen feed system according the state of the art 
           [0070]      FIG. 5 b    a longitudinal section thru a rotary microtome with specimen feed system according the state of the art 
           [0071]      FIG. 6 a    a schematic depiction of force effects in sectioning mode 
           [0072]      FIG. 6 b    a schematic depiction of force effects in the case of collision between knife edge and specimen with a microtome according to the invention 
           [0073]      FIG. 7 a    a microtome with specimen feed system according to the invention 
           [0074]      FIG. 7 b    a microtome with specimen feed system according to the invention after an occurred collision 
           [0075]      FIG. 7 c    an exploded view of a feed system of a microtome according to the invention with springs for generating the brace force 
           [0076]      FIG. 7 d    an exploded view of a feed system of a microtome according to the invention with magnets for generating the brace force 
           [0077]      FIG. 7 e    a longitudinal section thru a microtome according to the invention with magnets for generating the brace force 
           [0078]      FIG. 7 f    a longitudinal section thru a microtome according to the invention after an occurred collision with magnets for generating the brace force 
           [0079]      FIG. 7 g    an exploded view of a feed system of a microtome according to the invention with magnets for generating the brace force and with changeover of the limits of the brace force 
           [0080]      FIG. 7 h    a rear view of a feed system of a microtome according to the invention with magnets for generating the brace force and with changeover of the limits of the brace force, in a first position of the changeover means 
           [0081]      FIG. 7 i    a longitudinal section thru a feed system of a microtome according to the invention with magnets for generating the brace force and with changeover of the limit values of the brace force, in a first position of the changeover means 
           [0082]      FIG. 7 j    a rear view of a feed system of a microtome according to the invention with magnets for generating the brace force and with changeover of the limits of the brace force, in a second position of the changeover means 
           [0083]      FIG. 7 k    a longitudinal section thru a feed system of a microtome according to the invention with magnets for generating the brace force and with changeover of the limit values of the brace force, in a second position of the changeover means 
           [0084]      FIG. 8 a    a longitudinal section thru a microtome according to the invention with magnets for generating the brace force and with a piezo transducer as detecting switching means 
           [0085]      FIG. 8 b    a magnified detail of a longitudinal section thru a feed system of a microtome according to the invention with magnets for generating the brace force and with a piezo transducer as detecting switching means 
           [0086]      FIG. 9 a    a longitudinal section thru a microtome according to the invention with magnets for generating the brace force and with integrated detecting switching means 
           [0087]      FIG. 9 b    an exploded view of a feed system of a microtome according to the invention with magnets for generating the brace force and with integrated detecting switching means 
           [0088]      FIG. 9 c    a magnified detail of a longitudinal section thru a feed system of a microtome according to the invention with magnets for generating the brace force and with integrated detecting switching means 
           [0089]      FIG. 10 a    a flow chart of a routine in the electronic control of the microtome according to the invention for controlling the switch-off function at a beginning shift after a collision and for rectification of a collision 
           [0090]      FIG. 10 b    a microtome according to the invention previous to a set-up procedure 
           [0091]      FIG. 10 c    a microtome according to the invention with an occurred collision at a set-up procedure 
           [0092]      FIG. 10 d    a magnified detail of knife edge and specimen with an occurred collision 
           [0093]      FIG. 10 e    a microtome according to the invention after a rectification of a collision 
           [0094]      FIG. 10 f    a magnified detail of knife edge and specimen after a rectification of a collision 
           [0095]      FIG. 11 a    a flow chart of a routine in the electronic control of the microtome according to the invention for executing an automatic approach between knife edge and specimen 
           [0096]      FIG. 11 b    a microtome according to the invention positioned at the end of the sectioning path before starting an automatic approach between knife edge and specimen 
           [0097]      FIG. 11 c    a magnified detail of knife edge and specimen previous to starting an automatic approach procedure 
           [0098]      FIG. 11 d    a microtome according to the invention positioned at the end of the sectioning path at an automatic approach procedure between knife edge and specimen at the collision with the knife carrier reference surface 
           [0099]      FIG. 11 e    a magnified detail of knife edge and specimen at an automatic approach procedure in the state of collision with the knife carrier reference surface 
           [0100]      FIG. 11 f    a microtome according to the invention positioned at the end of the sectioning path at an automatic approach procedure between knife edge and specimen after rectification of the collision with the knife carrier reference surface 
           [0101]      FIG. 11 g    a magnified detail of knife edge and specimen at an automatic approach procedure after rectification of the collision with the knife carrier reference surface 
           [0102]      FIG. 11 h    a microtome according to the invention positioned at the start of the sectioning path at an automatic approach procedure between knife edge and specimen in the state of safety retraction 
           [0103]      FIG. 11 i    a magnified detail of knife edge and specimen at an automatic approach procedure in the state of safety retraction 
           [0104]      FIG. 11 j    a microtome according to the invention positioned at the start of the sectioning path past finalizing an automatic approach procedure between knife edge and specimen 
           [0105]      FIG. 11 k    a magnified detail of knife edge and specimen past finalizing an automatic approach procedure between knife edge and specimen 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0106]      FIG. 1 a    shows a perspective view of a rocking microtome with knife carrier feed system according to the state of the art. The main body  2  of the microtome  1  bears the support body  4 , which is serving as rocking arm and is pivoted in the rocking arm bearing  3   c . The sectioning tool  6  is connected to the knife carrier  5 . To simplify the illustration the embodiment of a so-called magnetic knife carrier is shown here, as with all further depictions, whereby the sectioning tool  6  is fixed in its position by flush-mounted permanent magnets, not illustrated here. The knife carrier  5  is shown here, and with all further depictions, as being of one piece for simplification. Practically in use are knife carriers which, for example, are consisting of a support part, a knife carrier base part with the option for positioning and a knife carrier top part with the option for clearance angle adjustment. Since these characteristics are not affecting the invention they are neglected and the knife carrier  5  is depicted simplified. Opposite to the knife edge  7  of the sectioning tool  6  is located the specimen holder  8  with a thereto connected specimen  9  and together fixed to the support body  4 . The specimen holder  8  is here also, as with all further depictions, illustrated as being of one piece for simplification. Practically in use are specimen holders which, for example, include adjustment means for specimen orientation and for the attachment of in-between devices to enable best fitting regarding specimen shape and specimen size. Since these characteristics are not affecting the invention they are neglected and the specimen holder  8  is depicted simplified. The sectioning drive  10  serves for the production of sections of the microtome  1 . The feed system  12 , which can move the knife carrier  5  in direction of double arrow feed movement  14  forward and backward, serves for approach between specimen  9  and knife edge  7 . 
         [0107]      FIG. 1 b    shows a longitudinal section thru the rocking microtome which is shown in  FIG. 1 a   . A feed system  12  according to the state of the art is here illustrated with its main components. In this example, the guidance body  15  is firmly connected with the main body  2 . Inside the guidance body  15  the guidance element  16  can move along the linear guidance  13  and is, in this example, firmly connected to the knife carrier  5 . The interconnected feed means  18  are firmly connected to the guidance body  15  by one of their functional parts. Thereby that firm connection may be effected via fastening screws  25 , as illustrated here, or to implement the functional part as one piece with the guidance body  15 . The interconnected feed means  18  which are shown here comprise a spindle, a spindle bearing with its individual parts and a coupling to the electric motor, as well as the electric motor  18   a  itself and its fastening parts. Further embodiments of feed means may be present in the form of rack and pinion drives, lever arrangements or wire rope hoist assemblies. 
         [0108]    Common to all embodiments is the existence of a functional part, which, for example, is serving as fitting, mounting or bearing housing of the other interconnected feed means  18  and which exhibits a firm connection to the guidance body  15 . 
         [0109]      FIG. 1 b    also illustrates how the sectioning drive  10  is moving the support body  4  and with it the specimen holder  8  and the specimen  9  on a segment of a circular orbit around the rocking arm bearing  3   c.  This is indicated by double arrow  3 , which is describing the sectioning path. 
         [0110]    The sectioning drive of the microtome is shown here in a generic way. With all further depictions of other types of microtomes the illustration of the sectioning drive will be neglected, since it is of no importance for the object of the invention. Solely the sectioning path will be depicted respectively. 
         [0111]    The electronic control  11  with the control panel  31  is at least connected to the electric motor  18   a.  That electrical connection is not illustrated here. With an activation of the electric motor  18   a  in feed direction by the electronic control  11 , the further interconnected feed means  18  are effecting a movement of the knife carrier  5  which is connected to the guidance element  16  and herewith a movement of the knife edge  7  towards the specimen  9 . If a deactivation in due time does not take place, caused by an operation error or by a first failure of a technical means, an uncontrolled collision will occur between knife edge  7  and specimen  9  with consequences of damage. 
         [0112]      FIG. 2  shows a sledge microtome with specimen feed system according to the state of the art in a perspective view. Connected to the main body  2  of the microtome  1  is the guidance of sectioning path  3   b.  The support body  4  can be moved on the sectioning path in direction of double arrow  3  along the guidance of sectioning path  3   b.  Connected to the support body  4  is the knife carrier  5 , to which the sectioning tool  6  is attached which exhibits the knife edge  7 . In this example, the feed system  12  is connected via the guidance body  15  laterally to the main body  2 . The moveable guidance element  16  of the feed system  12  can accomplish the feed movement in direction of double arrow  14 . Connected to the upper ending of the guidance element  16  is the specimen holder  8 , which holds the specimen  9 . 
         [0113]    The electronic control  11  with the control panel  31  is at least connected to the electric-motor  18   a.  This electrical connection is not illustrated here. 
         [0114]    With an activation of the electric motor  18   a  in feed direction by the electronic control  11 , the further interconnected feed means  18  are effecting a movement of the specimen holder  8  which is connected to the guidance element  16  and herewith a movement of the specimen  9  towards the knife edge  7 . If a deactivation in due time does not take place, caused by an operation error or by a first failure of a technical means, an uncontrolled collision will occur between knife edge  7  and specimen  9  with consequences of damage. 
         [0115]      FIG. 3  shows in a perspective view a disk microtome with knife carrier feed system according to the state of the art. Connected to the main body  2  of the microtome  1  is the disk bearing  3   a.  Around that, the guidance body  4 , which has here the shape of a disk, can move on a circular sectioning path in direction of double arrow  3 . Connected to the support body  4  is the specimen holder  8 , which holds the specimen  9 . In this example, the feed system  12  is connected via the guidance body  15  laterally to the main body  2 . The moveable guidance element  16  of the feed system  12  can accomplish the feed movement in direction of double arrow  14 . Connected to the upper ending of the guidance element  16  is the knife carrier  5 , to which the sectioning tool  6  is attached which exhibits the knife edge  7 . 
         [0116]    The electronic control  11  with the control panel  31  is at least connected to the electric motor  18   a.  That electrical connection is not illustrated here. 
         [0117]    With an activation of the electric motor  18   a  in feed direction by the electronic control  11 , the further interconnected feed means  18  are effecting a movement of the knife carrier  5  which is connected to the guidance element  16  and herewith a movement of the knife edge  7  towards the specimen  9 . If a deactivation in due time does not take place, caused by an operation error or by a first failure of a technical means, an uncontrolled collision will occur between knife edge  7  and specimen  9  with consequences of damage. 
         [0118]      FIG. 4 a    shows a perspective view of a rotary microtome with knife carrier feed system according to the state of the art. Connected to the main body  2  of the microtome  1  is the guidance of sectioning path  3   b  in which the support body  4  is moveable along the sectioning path, indicated with double arrow  3 . The support body  4  carries the specimen holder  8  with the thereto attached specimen  9 . The knife carrier  5  is connected to the feed system  12 . Connected to the knife carrier  5  is the sectioning tool  6 , which exhibits the knife edge  7 . The feed system  12 , which can move the knife carrier  5  forward and backward in direction of double arrow for feed movement  14 , serves for approach between the specimen  9  and the knife edge  7 . The electronic control  11  with the control panel  31  is electrically connected with the feed system  12 . This electrical connection is not shown here for simplicity. 
         [0119]      FIG. 4 b    shows a longitudinal section thru the rotary microtome of  FIG. 4 a   . Depicted is a feed system  12  with its main components according to the state of the art. In this example, the guidance body  15  is firmly connected to the main body  2 . Inside the guidance body  15 , the guidance element  16 , which is firmly connected to the knife carrier  5 , is moveable along the linear guidance  13 . The interconnected feed means  18  are firmly connected to the guidance body  15  with one of their functional parts. Thereby this firm connection can take place via fastening screws  25 , as shown here, or by accomplishing the respective functional part in one piece with the guidance body  15 . 
         [0120]    The interconnected feed means  18  which are shown here comprise a spindle, a spindle bearing with its individual parts and a coupling to the electric motor  18   a,  as well as the electric motor  18   a  itself and its fastening parts. Further embodiments of feed means may be present in the form of rack and pinion drives, lever arrangements or wire rope hoist assemblies. 
         [0121]    Common to all embodiments is the existence of a functional part, which, for example, is serving as fitting, mounting or bearing housing of the other interconnected feed means  18  and which exhibits a firm connection to the guidance body  15 . 
         [0122]    The electronic control  11  with the control panel  31  is at least connected to the electric motor  18   a.  That electrical connection is not illustrated here. 
         [0123]    With an activation of the electric motor  18   a  in feed direction by the electronic control  11 , the further interconnected feed means  18  are effecting a movement of the knife carrier  5  which is connected to the guidance element  16  and herewith a movement of the knife edge  7  towards the specimen  9 . 
         [0124]    If a deactivation in due time does not take place, caused by an operation error or by a first failure of a technical means, an uncontrolled collision will occur between knife edge  7  and specimen  9  with consequences of damage. 
         [0125]      FIG. 5 a    shows a perspective view of a rotary microtome with specimen feed system according to the state of the art. Connected to the main body  2  of the microtome  1  is the guidance of sectioning path  3   b  in which the support body  4  is moveable along the sectioning path, indicated with double arrow  3 . The knife carrier  5  is firmly connected to the main body  2 . Attached to the knife carrier  5  is the sectioning tool  6 , which exhibits the knife edge  7 . The support body  4  carries the feed system  12 , which supports at the front end the specimen holder  8  with the thereto attached specimen  9 . The feed system  12 , which can move the specimen holder  8  with attached specimen  9  forward and backward in direction of double arrow for feed movement  14 , serves for approach between the specimen  9  and the knife edge  7 . The electronic control  11  with the control panel  31  is electrically connected with the feed system  12 . This electrical connection is not shown here for simplicity. 
         [0126]      FIG. 5 b    shows a longitudinal section thru the rotary microtome of  FIG. 5 a   . Depicted is a feed system  12  with its main components according to the state of the art. In this example, the guidance body  15  is firmly connected to the support body  4  which is moveable along the sectioning path indicated by double arrow  3 . Inside the guidance body  15 , the guidance element  16 , which is firmly connected to the specimen holder  8  with attached specimen  9 , is moveable along the linear guidance  13 . The interconnected feed means  18  are firmly connected to the guidance body  15  with one of their functional parts, which is in the example the spindle bearing  21 . Thereby this firm connection can take place via fastening screws  25 , as shown here, or by accomplishing the respective functional part, here the spindle bearing  21 , in one piece with the guidance body  15 . 
         [0127]    The interconnected feed means  18  which are shown here comprise a spindle  19  with a spindle flange  20 , a spindle bearing  21 , a bearing disk  22 , a spindle bearing nut  23  and a shaft coupling  24  to the electric motor  18   a,  as well as the electric motor  18   a  itself and its mounting rods  26 . Further embodiments of feed means may be present in the form of rack and pinion drives, lever arrangements or wire rope hoist assemblies. 
         [0128]    Common to all embodiments is the existence of a functional part, which, for example, is serving as fitting, mounting or bearing housing of the other interconnected feed means  18  and which exhibits a firm connection to the guidance body  15 . 
         [0129]    The electronic control  11  with the control panel  31  is at least connected to the electric motor  18   a.  That electrical connection is not illustrated here. 
         [0130]    With an activation of the electric motor  18   a  in feed direction by the electronic control  11 , the further interconnected feed means  18  are effecting a movement of the specimen holder  8  with attached specimen  9  which is connected to the guidance element towards the knife edge  7 . 
         [0131]    If a deactivation in due time does not take place, caused by an operation error or by a first failure of a technical means, an uncontrolled collision will occur between knife edge  7  and specimen  9  with consequences of damage. 
         [0132]      FIG. 6 a    shows a schematic diagram of the force effects at a sectioning process, which is derived from the Orthogonal Process by Merchant (Orthogonalprozess nach Merchant) which is known in literature for cutting processes. It is illustrated how the sectioning tool penetrates into the specimen material with its wedge angle b, keeping a clearance angle a, and with a feed thickness h, and how thereby a section with the cutting thickness i is sliding on the rear of the sectioning tool under a cutting angle c. Relevant for the difference in thickness between feed thickness h and the effective cutting thickness i are compressions by shear forces and friction forces at the section formation, which are characterized in the partition of forces by shear angle d and friction angle e. The active force F a , acting on the specimen material, has to overcome the shear forces as well as the friction forces. In detail is F d  the shear force in the shear plane and F dN  the shear normal force, which is perpendicular thereto. F R  is the cutting plane friction force and F N  is the normal force perpendicular thereto. The active force F a  is partitioned into the components, which is the cutting force F c  opposite to the sectioning direction and thereto perpendicular the thrust F s  opposite to the feed direction. At a minimum it is necessary to brace this thrust F s  in order to avoid an evasion of the section material opposite to the feed direction at the sectioning process, or by inversion of the conditions, to avoid an evasion of the sectioning tool. That is the precondition for an application-based section formation process. 
         [0133]      FIG. 6 b    shows a schematic diagram of the force effects in set-up mode with an occurred collision between knife edge  7  and specimen  9  without switching off the electric motor  18   a  and therefore, according to the invention, resulting shift  30  of the interconnected feed means  18  in feed axis  17  along the guidance of the shifting range  47 . Thereby is the absolute value of the collision force F K  of same amount as the limit value of the brace force F G , however of opposite direction. At that the force F G  is chosen, that it is on one hand admittedly stronger than the thrust F s  from  FIG. 6 a   , which occurs in sectioning mode, in order to enable an application-based sectioning process, but on the other hand to be weak enough to limit the collision force F K  to values, which would as much as possible avoid to provoke any damages. For example, F G  can be chosen as F G =1,5×F s . 
         [0134]    In case of a switchable limit value of the brace force F G  and depending on whether sectioning mode or set-up mode is present, the thrust F s  from  FIG. 6 a    can be neglected, as it is only occurring in sectioning mode. Therefore a very small value for F G  can be determined in set-up mode, which must be merely larger than the sum of the inner friction forces of the interconnected feed means  18  between themselves and the friction force of the guidance between guidance body  15  and guidance element  16 . The diagram shows that the absolute value of F K  is limited to F G  and therefore inherent safe in regard of avoidance of a collision force F K  which would be above the determined limit value of the brace force F G . 
         [0135]      FIG. 7 a    shows in a perspective view a microtome  1  according to the invention, —without housing parts—, with specimen feed system in sectioning mode or in set-up mode. Connected to the main body  2  is the guidance of sectioning path  3   b  along which the support body  4  is moveable in direction of double arrow sectioning path  3 . The knife carrier  5  is connected to the main body  2  and carries the sectioning tool  6  with knife edge  7 . The feed system  12  is firmly connected with the support body  4  via its guidance body  15 . The specimen holder  8  with attached specimen  9  is connected to the guidance element  16 , which can perform the feed movement of the feed system  12 , indicated with double arrow  14 . The interconnected feed means  18  fit close to the guidance body  15  with a defined force. The electronic control  11  with the control panel  31  is connected to the feed system  12  via the motor cable  46  to the electric motor  18   a,  which is part of the interconnected feed means  18 . 
         [0136]      FIG. 7 b    shows in a slightly rotated view the microtome  1  of  FIG. 7 a    with an occurred collision in set-up mode. An uncontrolled feed movement  14  caused by an operation error or by a first failure of technical means leads to a collision between specimen  9  and knife edge  7 . With continued operation of the electrical motor  18   a  a shift  30  of the interconnected feed means  18  is commencing at the exceedance of the limit value of the brace force. This shift is leading away from the guidance body  15  along the guidance of the shifting range  47 . 
         [0137]      FIG. 7 c    shows an exploded view of a feed system  12  of a microtome according to the invention with springs  28  as part of the force generating means  32  for generating the brace force. 
         [0138]    The parts of the feed system  12  are: the guidance element  16 , the guidance body  15 , the guidance shifting range  47 , the force generating means  32  and the interconnected feed means  18 , which themselves, in this embodiment consist of: the electrical motor  18   a,  the spindle  19 , the spindle bearing  21 , the bearing disk  22 , the spindle bearing nut  23 , the shaft coupling  24  and the mounting rods  26 . In this example, the force generating means  32  are the springs  28 , the spring sleeves  27  and the spring rods  29 . In assembled condition the spring rods  29  are screwed-in to the guidance body  15  and therefore stationary at a shift. The springs  28  are supported on one side at the head of the spring rods  29  and on the other side at the bottom of the blind holes at the spindle bearing  21 . With that the spindle bearing  21  is pressed with the force of the pre-stressed springs  28  against the guidance body  15 . The spring sleeves  27  are simply serving for a better duct of the springs  28  and are connected to the spindle bearing  21 . 
         [0139]      FIG. 7 d    shows an exploded view of a feed system  12  of a microtome according to the invention with magnets  34 , which are shown here as permanent magnets, as part of the force generating means  32  for generating the brace force. 
         [0140]    The parts of the feed system  12  are: the guidance element  16 , the guidance body  15 , the guidance shifting range  47 , the force generating means  32  and the interconnected feed means  18 , which themselves, in this embodiment consist of: the electrical motor  18   a,  the spindle  19 , the spindle bearing  21 , the bearing disk  22 , the spindle bearing nut  23 , the shaft coupling  24  and the mounting rods  26 . In this example, the force generating means  32  are the magnets  34  with the ferromagnetic anchor plates  33  and the positioning screws  48 . 
         [0141]    In assembled condition the magnets  34  are connected at the guidance body  15 , for example by gluing together, and therefore they are stationary at a shift. The ferromagnetic anchor plates  33  are hold in position in the spindle bearing  21  by the positioning screws  48 . Caused by the magnetic force which is acting between the magnets  34  and the ferromagnetic anchor plates  33 , the spindle bearing  21  is pressed against the guidance body  15  by a defined force. 
         [0142]      FIG. 7 e    shows a longitudinal section thru a microtome  1 , in sectioning mode or in set-up mode, according to the invention with magnets  34  as part of the force generating means  32  for generating the brace force. The main body  2  is firmly connected to the guidance of sectioning path  3   b  along which the support body  4  is moveable in direction of double arrow sectioning path  3 . Likewise connected to the main body  2  is the knife carrier  5  which carries the sectioning tool  6  with the knife edge  7 . The feed system  12 , which corresponds to the embodiment shown in  FIG. 7 d   , is firmly connected via the guidance body  15  to the support body  4 . The specimen holder  8  with attached specimen  9  is connected to the guidance element  16 , which can perform the feed movement of the feed system  12 , indicated with double arrow  14 . The interconnected feed means  18 , consisting of the spindle  19 , the spindle flange  20 , the spindle bearing  21 , the bearing disk  22 , the spindle bearing nut  23 , the shaft coupling  24 , the mounting rods  26  and the electrical motor  18   a  are pressed with the brace force via the spindle bearing  21  against the guidance body  15 . The force generating means  32 , consisting of the magnets  34 , the ferromagnetic anchor plates  33  and the positioning screws  48 , determine by their characteristics and adjustments the value of the brace force. The guidance of the shifting range  47  is shown in this operating state as unmoved, because the interconnected feed means  18  are pressed against the guidance body  15  with the brace force of the force generating means  32 . With activation of the electrical motor  18   a  by the electronic control  11  and the control panel  31  via the motor cable  46 , the feed movement  14  will be carried out by the spindle  19  acting on the nut thread at the guiding element  16 . 
         [0143]      FIG. 7 f    shows a longitudinal section thru a microtome  1 , in set-up mode, according to the invention, at an occurred collision and with magnets  34  as part of the force generating means  32  for generating the brace force. The main body  2  is firmly connected to the guidance of sectioning path  3   b  along which the support body  4  is moveable in direction of double arrow sectioning path  3 . Likewise connected to the main body  2  is the knife carrier  5  which carries the sectioning tool  6  with the knife edge  7 . The feed system  12  is firmly connected via the guidance body  15  to the support body  4 . The specimen holder  8  with attached specimen  9  is connected to the guidance element  16 , which can perform the feed movement along the linear guidance  13 , indicated with double arrow  14 . This depiction illustrates a collision situation where the specimen  9  is in contact with the knife edge  7 . With the depicted operating state, the interconnected feed means  18 , consisting of the spindle  19 , the spindle flange  20 , the spindle bearing  21 , the bearing disk  22 , the spindle bearing nut  23 , the shaft coupling  24 , the mounting rods  26  and the electric motor  18   a,  are shifted by the shift indicated with arrow  30  along the guidance of the shifting range  47 . The force generating means  32 , consisting of the magnets  34 , the ferromagnetic anchor plates  33  and the positioning screws  48 , determine with their characteristics and their adjustments also the existing force between guidance body  15  and interconnected feed means  18  on the shifting path while a shift  30  takes place and thus the collision force acting on the shifting path. Thereby the magnets are located stationary at the guidance body  15 , while the ferromagnetic anchor plates  33 , which are hold by the positioning screws  48  at the spindle bearing  21 , are moving with the shift  30 . With continued activation of the electrical motor  18   a  by the electronic control  11  and the control panel  31  via the motor cable  46 , the shift  30  goes on thru spindle  19  and the nut thread at the guidance element  16  at an existing collision between specimen and knife edge. Thereby the interconnected feed means  18  are further moving along the guidance of the shifting range  47  until, for example, the spindle ending disengages from the nut thread at the guidance element  16  and therefore the movement comes to an end. In this example, is the magnetic force between guidance body  15  and the interconnected feed means  18  steady decreasing and therefore also the collision force on the shifting path while a shift  30  takes place. 
         [0144]      FIG. 7 g    shows an exploded view of a feed system  12  of a microtome according to the invention with magnets  34 , which are depicted here as permanent magnets, as part of the force generating means  32  for generating the brace force and additionally with changeover means  49  for changeover of the brace force. The components of the feed system  12  are: the guidance element  16 , the guidance body  15 , the guidance shifting range  47 , the force generating means  32  and the interconnected feed means  18 , which themselves in this embodiment consist of: the electrical-motor  18   a,  the spindle  19 , the spindle bearing  21 , the bearing disk  22 , the spindle bearing nut  23 , the shaft coupling  24  and the mounting rods  26 . In this example, the force generating means are the magnets  34  with the ferromagnetic anchor plates  33  and the positioning screws  48 . In assembled condition the magnets  34  are connected at the guidance body  15 , for example by gluing together, and therefore they are stationary at a shift. The ferromagnetic anchor plates  33  are hold in position in the spindle bearing  21  by the positioning screws  48 , whereby the positioning screws  48  brace themselves at the segment ring  51 , which itself fits closely to the spindle bearing  21 . Caused by the magnetic force which is acting between the magnets  34  and the ferromagnetic anchor plates  33 , the spindle bearing  21  is pressed against the guidance body  15  by a defined force. In this example, the segment ring  51  has 3 segments of 120° each, which have each on one side a helicoidal thickening whereas the other side is a flat contact surface. The mentioned three segments are punctuated by slots, thru which, in a functional and assembled condition, the positioning screws  48 , which hold the ferromagnetic anchor plates  33 , protrude and brace themselves with their head at the helicoidal segment areas. By rotating the segment ring  51 , the ferromagnetic anchor plates  33  are moved axially back and forth corresponding to the thickening or tapering at the position where the positioning screws are protruding thru the slots, and therefore the acting magnetic force between the guidance body  15  and the interconnected feed means  18 , which acts as brace force, is changed. In this same depicted example, the segment ring  51  is rotatable by a pinion  52 , which is actuated by an actuator  53 , and thus effect a changeover of the brace force. 
         [0145]      FIG. 7 h    shows, referring to the depiction in  FIG. 7   g,  a rear view of a feed system  12  of a microtome according to the invention with changeover of the limit values of the brace force in the status of a first changeover position. The actuating means  50 , consisting of the segment ring  51  and the pinion  52 , are in engagement with each other. The positioning screws  48  protrude thru the slots at the segment ring  51  and brace themselves with their head at the thinner zone of each of the helicoidal thickening segments. 
         [0146]      FIG. 7 i    shows, referring to the depiction in  FIG. 7   g,  a longitudinal section thru a feed system  12  of a microtome according to the invention with magnets  34 , ferromagnetic anchor plates  33  and positioning screws  48 , for generating the brace force between the guidance body  15  and the spindle bearing  21 , and with a changeover of the limit values of the brace force in the status of a first changeover position. The head of the positioning screw  48  is thereby in contact with the thinner zone of the respective segment of the segment ring  51 , whereby the air gap between the magnet  34  and the ferromagnetic anchor plate  33  has a small value denoting this changeover position, and which represents an increased brace force. 
         [0147]      FIG. 7 j    referring to the depiction in  FIG. 7   g,  a rear view of a feed system  12  of a microtome according to the invention with changeover of the limit values of the brace force in the status of a second changeover position. The actuating means  50 , consisting of the segment ring  51  and the pinion  52 , are in engagement with each other. In reference to the depiction in  FIG. 7 h   , the pinion  52  is rotated by  45 ° in clockwise direction. Therefore, with the depicted gearing the segment ring  51  is rotated as well by 45°, but in counter-clockwise direction. The positioning screws  48  protrude thru the slots at the segment ring  51  and brace themselves with their head now at the thicker zone of each of the helicoidal thickening segments. 
         [0148]      FIG. 7 k    shows, referring to the depiction in  FIG. 7   g,  a longitudinal section thru a feed system  12  of a microtome according to the invention with magnets  34 , ferromagnetic anchor plates  33  and positioning screws  48 , for generating the brace force between the guidance body  15  and the spindle bearing  21 , and with a changeover of the limit values of the brace force in the status of a second changeover position. The head of the positioning screw  48  is thereby in contact with the thicker zone of the respective segment of the segment ring  51 , whereby the air gap between the magnet  34  and the ferromagnetic anchor plate  33  has a higher value denoting this changeover position, and which represents a decreased brace force. 
         [0149]      FIG. 8 a    shows a longitudinal section thru a microtome  1 , in sectioning mode or in set-up mode, according to the invention with magnets  34  as part of the force generating means  32  for generating the brace force and with a piezo sensor  36  as detecting switching means  35 . The main body  2  is firmly connected to the guidance of sectioning path  3   b  along which the support body  4  is moveable in direction of double arrow sectioning path  3 . Likewise connected to the main body  2  is the knife carrier  5  which carries the sectioning tool  6  with the knife edge  7 . The feed system  12 , which is based on the embodiment illustrated in  FIG. 7 d   , is firmly connected via the guidance body  15  to the support body  4 . The specimen holder  8  with attached specimen  9  is connected to the guidance element  16 , which can perform the feed movement along the linear guidance  13 , indicated with double arrow  14 . The interconnected feed means  18  are pressed with the brace force against the guidance body  15 . The force generating means  32  determine by their characteristics and adjustments the value of the brace force. The guidance of the shifting range  47  is shown in this operating state as unmoved, because the interconnected feed means  18  are pressed against the guidance body  15  with the brace force of the force generating means  32 . With activation of the electrical motor  18   a  by the electronic control  11  and the control panel  31  via the motor cable  46 , the feed movement  14  will be carried out.  FIG. 8 b    shows the embodiment in detail. 
         [0150]      FIG. 8 b    shows a magnified detail thru a longitudinal section of a microtome  1 , in sectioning mode or in set-up mode, according to the invention with magnets  34  as part of the force generating means  32  for generating the brace force and with a piezo sensor  36  as detecting switching means  35 . The feed system  12 , which is based on the embodiment illustrated in  FIG. 7 d   , is firmly connected via the guidance body  15  to the support body  4 . The interconnected feed means  18 , consisting of the spindle  19 , the spindle flange  20 , the spindle bearing  21 , the bearing disk  22 , the spindle bearing nut  23 , the shaft coupling  24 , the mounting rods  26  and the electrical motor  18   a  are pressed via the piezo sensor  36 , which is part of the detecting switching means  35 , and which is fixed with one of its active surfaces to the spindle bearing  21 , with its opposite active surface against the guidance body  15 . The force generating means  32 , consisting of the magnets  34 , the ferromagnetic anchor plates  33  and the positioning screws  48 , determine by their characteristics and adjustments the value of the brace force. The guidance of the shifting range  47  is shown in this operating state as unmoved, because the interconnected feed means  18  are pressed against the guidance body  15  with the brace force of the force generating means  32 . With activation of the electrical motor  18   a  by the electronic control  11  and the control panel  31  via the motor cable  46 , the feed movement  14  will be carried out by the spindle  19  acting on the nut thread at the guiding element  16 . In case of a collision and following exceedance of the brace force, the interconnected feed means  18  are together shifted along the guidance of the shifting range  47 . That commencing shift will, nevertheless there is given inherent safety at assumed undisturbed functionality, be detected, in this example, by the piezo sensor  36  and signaled to the electronic control  11  by the sensor cable  37 , which also belongs to the detecting switching means  35 . Subsequently the electronic control  11  is switching off the electric-motor  18   a.    
         [0151]      FIG. 9 a    shows a longitudinal section thru a microtome  1 , in sectioning mode or in set-up mode, according to the invention with magnets  34  as part of the force generating means  32  for generating the brace force and with integrated detecting switching means  35 . The main body  2  is firmly connected to the guidance of sectioning path  3   b  along which the support body  4  is moveable in direction of double arrow sectioning path  3 . Likewise connected to the main body  2  is the knife carrier  5  which carries the sectioning tool  6  with the knife edge  7 . The feed system  12 , which is based on the embodiment illustrated in  FIG. 7 d   , is firmly connected via the guidance body  15 , which consists of the guidance body main part  15   a  and the guidance body isolated part  15   b,  to the support body  4 . The specimen holder  8  with attached specimen  9  is connected to the guidance element  16 , which can perform the feed movement along the linear guidance  13 , indicated with double arrow  14 . The interconnected feed means  18  are pressed with the brace force against the isolated part of the guidance body  15   b.  The force generating means  32  determine by their characteristics and adjustments the value of the brace force. The guidance of the shifting range  47  is shown in this operating state as unmoved, because the interconnected feed means  18  are pressed against the guidance body  15  with the brace force of the force generating means  32 . With activation of the electrical motor  18   a  by the electronic control  11  and the control panel  31  via the motor cable  46 , the feed movement  14  will be carried out. For a better understanding  FIG. 9 b    shows an exploded view and  FIG. 9 c    a magnified detail of this feed system  12 . 
         [0152]      FIG. 9 b    shows an exploded view of a feed system  12  of a microtome according to the invention with magnets  34 , which are shown here as permanent magnets, as part of the force generating means  32  for generating the brace force and with integrated detecting switching means  35 . The parts of the feed system  12  are: the guidance element  16 , the guidance body  15 , which consists of the guidance body main part  15   a  and the guidance body isolation part  15   b,  the guidance shifting range  47 , the force generating means  32  and the interconnected feed means  18 , which themselves, in this embodiment consist of: the electrical motor  18   a,  the spindle  19 , the spindle bearing  21 , the bearing disk  22 , the spindle bearing nut  23 , the shaft coupling  24  and the mounting rods  26 . In this example, the force generating means  32  are the magnets  34  with the ferromagnetic anchor plates  33  and the positioning screws  48 . The detecting switching means  35 , in this example, consist of the contact ring  39 , the contact screw F  54  and the contact screw Z  55 , as well as the electrical connections between the contact screws to the electronic control, which are not shown in this depiction. In assembled condition the magnets  34  are connected at the guidance body  15 , in this example at the guidance body isolation part  15   b,  for example by gluing together, and therefore they are stationary at a shift. The ferromagnetic anchor plates  33  are hold in position in the spindle bearing  21  by the positioning screws  48 . Caused by the magnetic force which is acting between the magnets  34  and the ferromagnetic anchor plates  33 , the spindle bearing  21  is pressed against the guidance body  15 , in this example against the contact ring  39 , which is inserted into the guidance body isolation part  15   b,  by a defined force. The guidance body isolation part  15   b  consists of an electrically non-conductive material of high rigidity, for example, a suitable plastic material in this regard or technical ceramics. The contact ring  39  consists of copper or brass or another suitable contact material. In order to effect the electrical connection to the electronic control, which is not shown here, serve the contact screw F  54  to connect with the contact ring  39  via a connection thread and the contact screw Z  55  to connect with the conductive spindle bearing  21 , also via a connection thread there. The double function of the contact ring  39  and the spindle bearing  21  to serve on one hand as contact surface for the brace force and on the other hand as an electrical contact surface for detection of a commencing shift of the interconnected feed means  18 , is illustrated in  FIG. 9   c.    
         [0153]      FIG. 9 c    shows a magnified detail of a longitudinal section thru a feed system  12  of a microtome according to the invention with magnets  34  as part of the force generating means  32  for generating the brace force and with integrated detecting switching means  35 . The feed system  12 , which is based on the embodiment illustrated in  FIG. 7 d   , is firmly connected via the guidance body isolated part  15   b,  to the support body  4 . 
         [0154]    Both parts, as well as the guidance element  16 , are only partly visible in the magnified detail shown here. The interconnected feed means  18 , consisting of the spindle  19 , the spindle flange  20 , the spindle bearing  21 , the bearing disk  22 , the spindle bearing nut  23 , the shaft coupling  24 , the mounting rods  26  and the electrical motor  18   a  are pressed with the brace force via the spindle bearing  21  against the contact ring  39 , which is part of the detecting switching means  35 , and which is inserted into the guidance body isolated part  15   b.  The force generating means  32 , consisting of the magnets  34 , the ferromagnetic anchor plates  33  and the positioning screws  48 , determine by their characteristics and adjustments the value of the brace force. The guidance of the shifting range  47  is shown in this operating state as unmoved, because the interconnected feed means  18  are pressed against the guidance body  15  with the brace force of the force generating means  32 . With activation of the electrical-motor  18   a  by the electronic control  11  and the control panel  31  via the motor cable  46 , the feed movement will be carried out by the spindle  19  in conjunction with the nut thread at the guidance element  16 . In case of a collision and following exceedance of the brace force, the interconnected feed means  18  are together shifted along the guidance of the shifting range  47 . That commencing shift will, nevertheless there is given inherent safety at assumed undisturbed functionality, be immediately detected, in this example, by the integrated detecting switching means  35 . In this example the detecting switching means consist of the contact ring  39 , the therein screwed-in contact screw F  54 , the contact screw Z  55 , which is in contact with the spindle bearing  21 , which is made from electrically conductive material, and the two electrical connections  45  which serve for connection between the contact screws  54  and  55  and the electronic control  11 . With a commencing shift, caused by an exceedance of the brace force, the spindle bearing  21  is lifting its contact surface from the contact surface at the contact ring  39 . Thus, for example, opens an existing electrical detection circuit, which is fed by the electronic control, and the contact ring  39  and the spindle bearing  21  adopt different electrical potentials, which will be interpreted as signal for the commencing shift. Following this signal, the electronic control is switching off the electric-motor  18   a  via the motor cable  46 . 
         [0155]      FIG. 10 a    shows a flow chart of a routine in the electronic control  11  of a microtome  1 , according to the invention, for monitoring the switching-off function at a commencing shift  30  after a collision took place and for an afterwards rectification of the collision. The monitoring is permanent during the entire operation of the microtome  1 . In step S 1  of the flow chart it is questioned whether the detecting switching means  35  are signaling a shift  30  of the interconnected feed means  18  after an occurred collision. If a shift was reported, the driving electric-motor  18   a  of the feed system  12  will be switched off in step S 2 . In order to rectify a further continuing collision situation and to bring back the microtome  1  again in a usable state of operation step S 3  takes place. In this step the electric-motor  18   a  will be actuated in counter direction to the feed direction  14   a  in order to drive with the feed system  12  the distance which represents the value of safety retraction  42 . Herewith the specimen is located at a distance represented by the safety retraction  42  in front of the knife edge  7  and the microtome  1  is again ready for ordinary use. 
         [0156]      FIG. 10 b    shows the microtome  1  according to the invention without automatic approach function in a certain distance between knife edge  7  and specimen  9 . 
         [0157]      FIG. 10 c    shows the microtome  1  according to the invention at an occurred collision in set-up mode, for example, caused by an operation error or by a first failure of a technical means. The depiction shows the situation after switching off the driving electric-motor  18   a  as result of a signal of the detecting switching means  35  and represents the situation after steps S 1  and S 2  in the flow chart of  FIG. 10 a   . 
         [0158]      FIG. 10 d    shows a magnified detail of the knife edge  7  and the specimen  9  at an occurred collision according to  FIG. 10 c   . Obviously the knife edge  7  is in contact with the specimen  9 . 
         [0159]      FIG. 10 e    shows the microtome  1  according to the invention after a rectification of a collision, representing step S 3  of the flow chart in  FIG. 10   a.    
         [0160]      FIG. 10 f    shows a magnified detail of the knife edge  7  and the specimen  9  after a rectified collision and execution of the safety retraction  42  opposite to the feed direction  14   a.    
         [0161]      FIG. 11 a    shows a flow chart of a routine in the electronic control  11  of the microtome  1  according to the invention for execution of an automatic approach between the knife edge  7  and the specimen  9 . After beginning of an automatic approach via the control panel  31  of the electronic control  11 , it is questioned in step S 4  of the flow chart, whether the specimen  9 , or with embodiments with moveable knife carrier, the knife carrier  5 , is positioned at end position sectioning path  43 . This is the precondition, that the specimen  9  and the knife carrier reference surface  41  are located opposite to each other in a certain distance. Then, in step S 5 , the electric-motor  18   a  is actuated until the specimen  9  is colliding with the knife carrier reference surface  41  and the therefore commencing shift  30  being immediately signaled by the detecting switching means  35  to the electronic control  11 . Consequently the electric-motor  18   a  will be switched off in step S 7 . In step S 8  the electronic control determines the added value of the safety retraction  42  and the reference distance knife carrier  38 , whereby the reference distance knife carrier  38  represents the gap by which the knife carrier reference surface  41  is backed away from the knife edge  7  in feed direction  14   a.  In step S 9  now the electric motor  18   a  will be actuated and the added value will be carried out in counter direction to the feed direction  14   a.  Herewith the specimen  9  is located by the value of the safety retraction  42  in front of the knife edge  7 . In step S 10  the electric-motor  18   a  will be stopped after that execution took place. Now, the specimen  9 , or with embodiments with moveable knife carrier, the knife carrier  5 , must be moved to the start position sectioning path  44 . For microtomes with a manual sectioning drive this has certainly to be performed by hand. For microtomes with a motorized sectioning drive, a respective sequence can be incorporated as branch operation to the flow chart for the electronic control. In step S 11  of the actual flow chart is solely tested, that the microtome  1  should be now in its start position sectioning path  44 . If true, the electric-motor  18   a  will be actuated again in step S 12 , in order to carry out the value of the safety retraction  42  in feed direction  14   a.  This means that the safety retraction  42  will be abrogated. After execution, the electric-motor  18   a  will be stopped again in step S 13 . Now the specimen  9  is in trim-position, that means it is located in feed direction  14   a  in the same position as the knife edge  7  and in sectioning direction above the knife edge  7 . Herewith, the automatic approach function is completed. 
         [0162]      FIG. 11 b    shows a microtome  1  according to the invention in end position sectioning path  43  previous to the beginning of an automatic approach between knife edge  7  and specimen  9 . 
         [0163]      FIG. 11 c    shows a magnified detail of the knife edge  7  and the specimen  9  previous to the beginning of an automatic approach according to  FIG. 11   b.  Thereby the knife carrier reference surface  41  is located opposite to the specimen  9  in a certain distance. This is regardless of, whether it is, as in the depicted example, about a specimen feed system, or a knife carrier feed system and it is also regardless of whether, as in the depicted example, the specimen  9  is moved along the sectioning path  3  or the knife carrier  5  with the sectioning tool  6 . 
         [0164]      FIG. 11 d    shows a microtome  1  according to the invention in end position sectioning path  43  at an automatic approach between knife edge  7  and specimen  9  with collision with the knife carrier reference surface  41 . 
         [0165]      FIG. 11 e    shows a magnified detail of  FIG. 11 d    with knife edge  7  and specimen  9  at an automatic approach in the state of collision with the knife carrier reference surface  41  and with, according to the invention, switched-off electric-motor  18   a  after the collision took place and the commencing shift  30  was immediately detected by the detecting switching means  35 . In this state the specimen  9  is in contact with the knife carrier reference surface  41 . 
         [0166]      FIG. 11 f    shows a microtome  1  according to the invention in end position sectioning path  43  at an automatic approach between knife edge  7  and specimen  9  after rectification of a collision with the knife carrier reference surface  41   FIG. 11 g    shows a magnified detail of  FIG. 11 f    with knife edge  7  and specimen  9  at an automatic approach after rectification of the collision with the knife carrier reference surface  41 . Thereby illustrated is the reference distance knife carrier  38  between knife carrier reference surface  41  and knife edge  7 , as well as the safety retraction  42 , which represents a safety distance between the specimen  9  and the knife edge  7 . At rectification of a previously existing collision, specimen  9 , or with other embodiments, the knife edge  7 , will be moved in opposite direction to the feed direction  14   a  by the sum of the reference distance knife carrier  38  and the safety retraction  42 . 
         [0167]      FIG. 11 h    shows a microtome  1  according to the invention, which is now representing the next step of the automatic approach sequence. The microtome  1  is depicted in start position sectioning path  44 . The safety retraction  42  between the specimen  9  and the knife edge  7  still exists. 
         [0168]      FIG. 11 i    shows a magnified detail of  FIG. 11 h    with knife edge  7  and specimen  9  at an automatic approach procedure in a state with safety retraction  42 . 
         [0169]      FIG. 11 j    shows a microtome  1  according to the invention in start position sectioning path  44 , after completion of an automatic approach procedure between the knife edge  7  and the specimen  9  and with abrogated safety retraction  42 . 
         [0170]      FIG. 11 k    shows a magnified detail of  FIG. 11 j    with knife edge  7  and specimen  9  after completion of an automatic approach procedure between the knife edge  7  and the specimen  9 , whereby, in this example, specimen  9  is positioned in start position sectioning path  44  and with regard to the feed direction  14   a,  in the same plane as the knife edge  7 , and herewith in trim-position. 
         [0171]    The microtome according to the invention and the herewith feasible methods according to the invention are considerably increasing the safety at the set-up mode of microtomes as well as in versions of cryostat-microtomes. The inherent safety in regard to inadmissible collision forces prevents damages to specimen and sectioning tools and reduces danger of injury at operation errors. The supplementary switching-off of the feed drive at a detected collision, nevertheless the given inherent safety, enables at a technically undisturbed operation an efficient work process and provides the basis for the thereof resting method of an automatic approach. The automatic approach function is to a large extent free from problems with debris in the area between knife carrier and specimen, as simply the recessed knife carrier reference surface needs to be free from soiling, and as there is no need for additional moveable or optical means. Moreover, in case of malfunction the automatic approach is certainly inherent safe as well. 
       LIST OF COMPONENT PARTS 
       [0172]      1  microtome 
         [0173]      2  main body 
         [0174]      3  double arrow sectioning path 
         [0175]      3   a  disk bearing 
         [0176]      3   b  guidance of sectioning path 
         [0177]      3   c  rocking arm bearing 
         [0178]      4  support body 
         [0179]      5  knife carrier 
         [0180]      6  sectioning tool 
         [0181]      7  knife edge 
         [0182]      8  specimen holder 
         [0183]      9  specimen 
         [0184]      10  sectioning drive 
         [0185]      11  electronic control 
         [0186]      12  feed system 
         [0187]      13  linear guidance 
         [0188]      14  double arrow feed movement 
         [0189]      14   a  arrow feed direction 
         [0190]      15  guidance body 
         [0191]      15   a  main part guidance body 
         [0192]      15   b  isolated part guidance body 
         [0193]      16  guidance element 
         [0194]      17  feed axis 
         [0195]      18  interconnected feed means 
         [0196]      18   a  electric motor 
         [0197]      19  spindle 
         [0198]      20  spindle flange 
         [0199]      21  spindle bearing 
         [0200]      22  bearing disk 
         [0201]      23  spindle bearing nut 
         [0202]      24  shaft coupling 
         [0203]      25  fastening screw 
         [0204]      26  mounting rod 
         [0205]      27  spring sleeve 
         [0206]      28  spring 
         [0207]      29  spring rod 
         [0208]      30  arrow shift 
         [0209]      31  control panel 
         [0210]      32  force generating means 
         [0211]      33  ferromagnetic anchor plate 
         [0212]      34  magnet 
         [0213]      35  detecting switching means 
         [0214]      36  piezo sensor 
         [0215]      37  sensor cable 
         [0216]      38  reference distance knife carrier 
         [0217]      39  contact ring 
         [0218]      41  knife carrier reference surface 
         [0219]      42  safety retraction 
         [0220]      43  end position sectioning path 
         [0221]      44  start position sectioning path 
         [0222]      45  electrical connection 
         [0223]      46  motor cable 
         [0224]      47  guidance shifting range 
         [0225]      48  positioning screws 
         [0226]      49  changeover means 
         [0227]      50  actuating means 
         [0228]      51  segment ring 
         [0229]      52  pinion 
         [0230]      53  actuator 
         [0231]      54  contact screw F 
         [0232]      55  contact screw Z 
         [0233]      56  connection isolated part 
         [0234]    a clearance angle 
         [0235]    b wedge angle 
         [0236]    c cutting angle 
         [0237]    d shear angle 
         [0238]    e friction angle 
         [0239]    h feed thickness 
         [0240]    i cutting thickness 
         [0241]    F a  active force 
         [0242]    F d  shear force 
         [0243]    F dN  shear normal force 
         [0244]    F R  cutting plane friction force 
         [0245]    F N  normal force 
         [0246]    F c  cutting force 
         [0247]    F s  thrust 
         [0248]    F K  collision force 
         [0249]    F G  limit value of brace force 
         [0250]    S 1 -S 13  steps of flow charts