PATENT ABSTRACT
A medical instrument includes a hermetically tight sheath, a heat source, a surface area thermally coupled to the heat source, a rotor arranged outside the hermetically tight sheath and serving to generate a flow of fluid at the surface, a magnet at the rotor, and means for generating a variable magnetic field in order to move the rotor. The means for generating a variable magnetic field is arranged inside the hermetically tight sheath.

PATENT DESCRIPTION
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an exoscope, an endoscope or another medical instrument, and in particular to the cooling of the medical instrument. 
       BACKGROUND OF THE INVENTION 
       [0002]    Exoscopes, endoscopes and other medical instruments can contain image sensors, processors and other circuitry for processing image data and other data, power electronics, light-emitting diodes or other light sources and other heat sources. Normally, the thermal output generated by these heat sources is carried off mainly by natural convection, which is driven by the heating of the air surrounding the medical instrument. The continuing process of miniaturization of electronic components, their increasing performance and their availability at ever lower costs cause that medical instruments contain an increasing number of electronic components with increasing thermal output. Heat dissipation by means of natural convection is therefore no longer sufficient in all cases. A conventional fan or compressor, for forcing convection or a cooling flow of fluid, cannot readily be cleaned and autoclaved and is therefore not considered for use at many medical instruments. 
       SUMMARY OF THE INVENTION 
       [0003]    It is an object of the present invention to make available an improved medical instrument which in particular is better cooled and at the same time can be easily cleaned and preferably autoclaved. 
         [0004]    This object is achieved by the subjects of the independent claims. 
         [0005]    Developments are set forth in the dependent claims. 
         [0006]    A medical instrument comprises a liquid-tight sheath, a heat source, a surface area thermally coupled to the heat source, a rotor arranged outside the hermetically tight sheath and serving to generate a flow of fluid at the surface, a magnet at the rotor, and means for generating a variable magnetic field in order to move the rotor. 
         [0007]    A medical instrument comprises a fluid-tight or at least liquid-tight sheath, a heat source, a surface area thermally coupled to the heat source, a rotor arranged outside the sheath and serving to generate a flow of fluid at the surface, a magnet at the rotor, and means for generating a variable magnetic field in order to move the rotor, the means being arranged inside the fluid-tight sheath. 
         [0008]    In particular, the medical instrument is an exoscope or an endoscope. 
         [0009]    An exoscope is a device provided and designed for extracorporeal use, for visual inspection or observation of objects in medicine, in particular of objects at or near outer surfaces of a human or animal body. In contrast to an endoscope, an exoscope is not designed to be inserted through a small natural or artificial opening into a natural or artificial cavity. Instead, an exoscope is designed for observation of an object which is visible from outside, at least during observation, in particular during an operation. Accordingly, during its intended use, the exoscope is located entirely outside the human or animal body and, in contrast to the endoscope, does not necessarily have a long thin shaft. 
         [0010]    An exoscope can have one or more cameras or light-sensitive image sensors for two-dimensional or three-dimensional capturing and displaying, for example on a screen. Alternatively, an exoscope is monocular or binocular for direct observation with the human eye. An exoscope is generally designed or optimized for an object distance in the range of a few centimeters or a few decimeters. An exoscope can have a high magnification, facilitating a resolution not attainable with the naked eye, and it can thus have properties of a magnifier or stereo magnifier or of a microscope or stereo microscope. The exoscope generally differs from the microscope or stereo microscope in having a greater object distance. 
         [0011]    The sheath is in particular hermetically tight. The hermetically tight sheath in particular encloses the observation beam path. Moreover, the hermetically tight sheath can enclose the illumination beam path and/or other parts of the medical instrument. All the components and structural parts of the medical instrument arranged inside the hermetically tight sheath are protected there, in particular from water vapor and other damaging fluids. All the components and structural parts of the medical instrument arranged inside the hermetically tight sheath cannot become soiled and therefore also do not have to be cleaned. In particular, the outer surface of the hermetically tight sheath is as far as possible substantially smooth and convex, in order to make cleaning easier. 
         [0012]    The heat source comprises in particular an image sensor, a processor or another circuit for preparing or processing image data and/or other data, a light-emitting diode or another lighting means and/or power electronics for supplying electrical power to a lighting means, a processor or a circuit. The heat source is in particular arranged in a handle or grip at the proximal end of the medical instrument and/or at the distal end of the medical instrument. The heat source is in particular arranged inside the hermetically tight sheath. The exoscope can comprise a plurality of the heat sources described. 
         [0013]    The surface area thermally coupled to the heat source is in particular an area of the outer surface of the hermetically tight sheath. The surface area is coupled to the one or more heat sources of the medical instrument in particular by heat conduction, radiation and/or convection inside the hermetically tight sheath. 
         [0014]    The rotor is in particular designed to generate a flow of ambient air or a flow of carbon dioxide, water or another surrounding medium of the medical instrument. The rotor can generate a flow of fluid at the surface thermally coupled to the heat source, by conveying ambient air toward the surface area and/or by conveying ambient air away from the surface area. The rotor comprises in particular a plurality of permanent magnets with alternately oriented polarity. 
         [0015]    The means for generating a variable magnetic field is in particular designed to generate a rotating or substantially rotating magnetic field. The means comprises in particular a plurality of rigidly arranged electromagnets or coils. The means for generating a variable magnetic field and the rotor act in particular like the stator and rotor of a synchronous or asynchronous polyphase motor. 
         [0016]    Means for powering the electromagnets and in particular for generating currents with different phases in the electromagnets can in particular be provided inside the hermetically tight sheath. Alternatively, alternating currents for the electromagnets can be provided by a separate device and can be transmitted to the medical instrument by means of electrical lines. 
         [0017]    Alternatively, the means for generating a variable magnetic field comprises one or more permanent magnets which are rotatable about an axis and are coupled to an electric motor, an ultrasonic motor or another drive. 
         [0018]    The rotor can be provided with a smooth surface which can be easily cleaned, or it can be designed as a disposable product that is discarded after one use and is replaced by a new and sterile rotor. The means for generating a variable magnetic field is protected inside the hermetically tight sheath from soiling and from the effect of water vapor and other damaging fluids. Thus, by arranging only the rotor outside the sheath, and arranging the means for generating a variable magnetic field inside the hermetically tight sheath, it is possible to simplify, or indeed actually permit, the cleaning of the medical instrument. 
         [0019]    By means of a flow of fluid being generated at the surface area thermally coupled to the heat source, the rotor facilitates effective removal of the thermal output generated by the heat source. Therefore, the medical instrument can have, for example, a greater number of circuits, and more complex circuits, for preparing and processing image data, a stronger light source or a brighter lighting means and/or other functions that generate waste heat. 
         [0020]    In a medical instrument as described herein, the means for generating a variable magnetic field is provided and designed in particular to generate a rotating magnetic field. 
         [0021]    The means for generating a variable magnetic field comprises in particular at least three electromagnets, which are provided such that alternating currents with a mutual phase difference of 120 degrees flow in them. 
         [0022]    In a medical instrument as described herein, the means for generating a variable magnetic field is in particular also designed for magnetically bearing the rotor. 
         [0023]    By virtue of a magnetic and therefore contactless bearing of the rotor, deterioration and wear can be avoided, friction can be reduced or entirely avoided, and therefore the required drive power can be reduced and low-noise operation can be facilitated. An additional emergency bearing can be provided in order to avoid, in the event of an unforeseen external action or a failure of the means for generating a variable magnetic field, a collision between the rotor and other parts of the medical instrument, abrasion, damage or destruction of the rotor, and contamination of a patient with abrasion particles. The emergency bearing comprises, for example, a structural part in the shape of a bearing shell made of polytetrafluoroethylene (PTFE; also known under the brand name Teflon) or another tough material that facilitates low friction. 
         [0024]    In a medical instrument as described herein, the rotor is provided and designed in particular to generate a flow of fluid in a direction from proximal to distal. 
         [0025]    A medical instrument as described herein is designed in particular to generate a flow of fluid at the distal end of the medical instrument. 
         [0026]    For this purpose, the rotor and optionally one or more means for guiding a flow of fluid generated by the rotor can be arranged at or near the proximal end of the medical instrument and designed in order to generate a flow of fluid from proximal to distal. 
         [0027]    In a medical instrument as described herein, the rotor is arranged in particular at or near the distal end of the medical instrument. 
         [0028]    In a medical instrument as described herein, the rotor is in particular designed to generate a flow of fluid in a direction from distal to proximal. For this purpose, the rotor is in particular arranged at or near the distal end of the medical instrument. 
         [0029]    In a medical instrument as described herein, the rotor is in particular movable in a direction parallel to a longitudinal axis of the medical instrument. 
         [0030]    The mobility of the rotor in a direction parallel to the longitudinal axis of the medical instrument can simplify, or indeed actually permit, complete cleaning and sterilization of the medical instrument. The rotor is movable in particular between two or more positions, in each of which it is held and can be driven magnetically. The rotor can be movable between these positions manually, magnetically or by some other drive means. 
         [0031]    In a medical instrument as described herein, the rotor can in particular be separated from other parts of the medical instrument in a non-destructive and reversible manner. 
         [0032]    The rotor can in particular be separated from other parts or the rest of the medical instrument by being moved in the distal direction and past the distal end of the medical instrument. Alternatively, the rotor can be separated by a movement in the proximal direction and past the proximal end of the medical instrument. The removability of the rotor can simplify the cleaning of the medical instrument and allow the rotor to be exchanged in the event of damage or destruction. 
         [0033]    In a medical instrument as described herein, at least one of the means for generating a variable magnetic field is movable between several positions and several devices for generating a variable magnetic field are provided, so as to be able to drive the rotor at several positions. 
         [0034]    The in particular manual or magnetic mobility of the rotor, between at least two positions where the rotor can be rotated, can facilitate different cooling modes. In particular, the rotor can be arranged alternately at or near the proximal end of the medical instrument or at or near the distal end of the medical instrument, in order to particularly cool different areas of the medical instrument. By providing means for generating a variable magnetic field at each position where the rotor is intended to be held and rotated, a rigid and therefore particularly robust configuration of these means for generating variable magnetic fields can be facilitated. In particular, a mobility of means for generating a variable magnetic field can facilitate a positioning and driving or operation of the rotor at any desired or almost any desired location along the path on which the means for generating a variable magnetic field is movable. 
         [0035]    A medical instrument as described herein further comprises in particular a controller for controlling the means for generating a variable magnetic field, wherein the controller is designed to control at least one of the rotational direction and the rotational speed of the rotor. 
         [0036]    A controller for controlling the means for generating a variable magnetic field can, in particular by controlling the rotational speed, facilitate an adjustment or variation of the cooling power and/or, by controlling or switching the rotational direction, can facilitate a movement of the area of maximum cooling at the medical instrument. 
         [0037]    A medical instrument as described herein further comprises in particular means for detecting a temperature of the heat source, wherein the controller is coupled to the means for detecting the temperature and is designed to control at least one of the rotational direction and the rotational speed of the rotor depending on the temperature of the heat source. 
         [0038]    The means for detecting a temperature of the heat source comprises in particular a sensor for direct or indirect detection of the temperature of the heat source, which sensor is arranged at or in the heat source. Alternatively, the means for detecting the temperature of the heat source comprises a signal input for receiving a sensor signal from a sensor for direct or indirect detection of the temperature of the heat source. The temperature of the heat source can, for example, be detected by measuring the voltage at a thermocouple, the voltage at, the current in or the resistance of an element with temperature-dependent resistance, a current consumption of the heat source, a supply voltage at the heat source and/or one or more other parameters. 
         [0039]    A medical instrument as described herein further comprises in particular two means for detecting respectively the temperature of one of two heat sources, wherein the controller is connected to the two devices for detecting the temperatures of the heat sources and is designed to control the rotational direction of the rotor depending on the temperatures of the heat sources. 
         [0040]    In particular, the medical instrument comprises a first heat source (for example a light source or image sensor) at the distal end and a second heat source (for example a processor or another circuit for processing or preparing image data) at the proximal end. The controller is designed to control a first rotational direction of the rotor and a flow of fluid in the distal direction when the first heat source requires more cooling than the second heat source, and to control a second rotational direction of the rotor and a flow of fluid in the proximal direction when the second heat source requires more cooling. 
         [0041]    A medical instrument as described herein is in particular an endoscope, an exoscope or a surgical microscope. 
         [0042]    A medical instrument as described herein also comprises in particular a guiding means for guiding or diverting a flow of fluid generated by the rotor. 
         [0043]    The guiding means comprises in particular a jacket for keeping the flow of fluid at the surface portion thermally coupled to the heat source or for guiding the flow of air to the surface portion thermally coupled to the heat source. 
         [0044]    Alternatively or in addition, the guiding means can comprise one or more guide grates and/or one or more guide blades for guiding the flow of fluid in a desired direction and/or for shaping a flow of fluid to a desired cross section or a desired speed profile. 
         [0045]    In a medical instrument as described herein, in particular at least one of the rotor and the guiding means is designed to generate a flow of fluid which extends, at least in part, helically around a shaft of the medical instrument. 
         [0046]    For this purpose, the guiding means in particular comprises helically curved or helically wound guide blades and/or a jacket by which a flow of fluid already generated helically by the rotor is guided to the shaft. A flow of fluid extending helically around the shaft can be laminar to a particularly long portion of the shaft and can thus, for example, extend the cooling action of the flow of fluid particularly far in the distal direction from the rotor arranged at the proximal end. 
         [0047]    A medical instrument as described herein further comprises in particular means for converting a laminar flow to a turbulent flow. 
         [0048]    The means for converting a laminar flow to a turbulent flow comprises in particular one or more turbulators, or turbulence or vortex generators, as are known in particular from aeronautics. The means for converting a laminar flow to a turbulent flow is in particular arranged upstream from the surface portion thermally coupled to the heat source. By means of laminar flow up to or almost up to the surface portion thermally coupled to the heat source, it is possible for the flow of fluid, with comparatively small losses, to reach as far as the surface portion thermally coupled to the heat source. By means of a turbulent flow at the surface portion thermally coupled to the heat source, the heat transfer between the surface and the flow of fluid can be improved, and therefore also the cooling performance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0049]    Embodiments are explained in more detail below with reference to the attached figures, where: 
           [0050]      FIG. 1  shows a schematic view of an exoscope; 
           [0051]      FIG. 2  shows a further schematic view of the exoscope from  FIG. 1 ; 
           [0052]      FIG. 3  shows a schematic view of an endoscope; 
           [0053]      FIG. 4  shows a further schematic view of the endoscope from  FIG. 3 ; 
           [0054]      FIG. 5  shows a schematic view of a further exoscope; 
           [0055]      FIG. 6  shows a schematic view of a further exoscope; 
           [0056]      FIG. 7  shows a further schematic view of the exoscope from  FIG. 6 ; 
           [0057]      FIG. 8  shows a schematic view of a further exoscope; 
           [0058]      FIG. 9  shows a schematic axonometric view of a further exoscope; 
           [0059]      FIG. 10  shows a schematic axonometric cross-sectional view of the exoscope from  FIG. 9 ; 
           [0060]      FIG. 11  shows a further schematic axonometric view of the exoscope from  FIGS. 9 and 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0061]      FIG. 1  shows a schematic view of an exoscope  10  with a proximal end  12  and a distal end  14 . The exoscope  10  comprises a shaft  13 , which in particular has a circular cylindrical or substantially circular cylindrical outer shape with an axis of symmetry  18 . This axis of symmetry  18  is also referred to hereinbelow as the longitudinal axis of the exoscope  10 . The exoscope  10  further comprises a handle  15  at the proximal end  12 . 
         [0062]    The view of the exoscope  10  in  FIG. 1  is similar to a cross-sectional view. In contrast to a true cross-sectional view, a number of components and structural parts of the exoscope  10  are each indicated in plan view and section surfaces are not hatched. 
         [0063]    The exoscope  10  comprises a hermetically tight sheath  20 , which in particular is composed of a plurality of parts cohesively or coalescently joined to one another. Arranged inside the hermetically tight sheath  20  are optical fibers  22 , by means of which illumination light generated by a light source  30  at the proximal end  12  of the exoscope  10  is transmitted to the distal end  14 . Moreover, a beam path  24  for observation light is provided inside the hermetically tight sheath  20  and in particular in the area of the shaft  13 . The beam path  24  is provided such that light emanating from an object to be viewed is transmitted to an image sensor  72  arranged in the handle  15 . The light source  30  comprises in particular one or more light-emitting diodes  32  and a lens  34  or other devices which ensure that as much as possible of the light generated by the light-emitting diode  32  is coupled into the optical fibers  22 . 
         [0064]    The light source  30 , the optical fibers  22 , the image sensor  72  and devices (not shown in  FIG. 1 ) for preparing and processing an image signal generated by the image sensor  72  and/or for controlling the light source  30  are examples of heat sources inside the hermetically tight sheath  20 . Since no substance exchange takes place between the inside of the hermetically tight sheath  20  and the environment of the exoscope  10 , all of the heat generated by the heat sources has to be released to the environment of the exoscope  10  via the hermetically tight sheath  20 . 
         [0065]    In the area of the handle  15  of the exoscope  10 , an axial compressor or a rotor  50  is arranged which, in particular, is rotatable about the longitudinal axis  18  of the exoscope  10 . The rotor  50  comprises a ring  52 , at the outer circumference of which blades  54  are arranged substantially in a radial direction. Proximal guide blades  84  are arranged proximally from the rotor  50 , in particular proximally from the blades  54  of the rotor  50 . Distal guide blades  86  are arranged distally from the rotor  50 . An annular jacket  82  connects the radially outer ends of the proximal and distal guide blades  84 ,  86  and encloses the rotor  50 . The blades  54  of the rotor  50  are designed in such a way that a rotation of the rotor  50  in a predetermined rotational direction about the longitudinal axis  18  of the exoscope  10  generates a proximal to distal air flow  57  in the annular space between the hermetically tight sheath  20  and the jacket  82 . The air flow  57  generated by the rotating rotor  50  is substantially parallel to the longitudinal axis  18  of the exoscope  10 . 
         [0066]    A magnetic flux conductor  62 , several conductor coils  64  at the magnetic flux conductor  62 , and a controller  68  coupled to the conductor coils  64  are arranged inside the hermetically tight sheath  20 . The controller  68  comprises several power sources for generating alternating currents in the conductor coils  64 . The magnetic flux conductor  62 , the conductor coils  64  and the controller  68  form means for generating a variable magnetic field. The controller  68  is designed to generate alternating currents of identical frequency and of differing phase position in the magnetic flux conductors  62 , such that the conductor coils  64  generate corresponding magnetic alternating fields. The controller  68  is in particular designed to generate, by means of the conductor coils  64 , a substantially rotating magnetic field for moving or driving the rotor  50 . To ensure that the rotor  50  can be driven by the rotating magnetic field generated by the controller  68  via the conductor coils  64 , the ring  52  and/or the blades  54  of the rotor  50  are magnetizable or magnetized. Alternatively or in addition, the rotor  50  can be designed to be electrically conductive, in order to facilitate an induction of eddy currents in the rotor  50  by a rotating magnetic field. 
         [0067]    The controller  68  is coupled to one or more temperature sensors  36  at the light source  30  and/or at one or more other heat sources inside the hermetically tight sheath  20 . Alternatively or in addition, the controller  68  can have one or more signal inputs for detecting currents, voltages, resistances or other parameters, from which it is possible to calculate or estimate the temperature or the temperatures of one or more heat sources. The controller  68  is designed to control currents in the conductor coils  64  in accordance with the one or more temperatures. In particular, the controller  68  is designed to drive the rotor  50  only when a predetermined temperature threshold is exceeded, or to drive the rotor  50  more quickly when a detected temperature has a higher value and more slowly when the detected temperature has a lower value. Moreover, the controller  68  can be designed to reverse the rotational direction of the rotor  50 , particularly in accordance with several detected temperatures. 
         [0068]    The controller  68  can furthermore be designed to control currents in the conductor coils  64  in such a way that the rotor  50  does not touch the hermetically tight sheath  20 , the jacket  82  or any other parts of the exoscope  10  but instead rotates with magnetic support in a manner free of contact and therefore free of wear. 
         [0069]    The light source  30  and, if appropriate, further heat sources inside the hermetically tight sheath  20  are coupled to said hermetically tight sheath  20 , in particular to an outer surface area  40  of the hermetically tight sheath  20 , by heat radiation, heat conduction in a medium filling the inside of the hermetically tight sheath  20 , by convection in this medium and/or by a heat conductor not shown in  FIG. 1 . The heat generated by the heat source  30 ,  72  is carried off, by an airflow  57  generated by the rotating rotor  50 , along the surface  40  coupled to the heat source  30 ,  72 . 
         [0070]      FIG. 2  shows a further schematic view of the exoscope  10  from  FIG. 1 . The plane of the drawing of  FIG. 2  is orthogonal to the plane of the drawing of  FIG. 1  and orthogonal to the longitudinal axis  18  of the exoscope  10 .  FIG. 2  shows the exoscope  10  cut open along a surface orthogonal to the longitudinal axis  18  and close to the magnetic flux conductor  62 , the conductor coils  64  and the rotor  50 . Just as in  FIG. 1 , section surfaces are not hatched in  FIG. 2 , in contrast to many cross-sectional views. 
         [0071]    The magnetic flux conductor  62  has approximately the shape of a star whose radial portions are each surrounded by a conductor coil  64 . Moreover, the magnetic flux conductor  62  has a central through-opening  63  in which the optical fibers  22  are arranged. The radially outer end faces of the radial portions of the magnetic flux conductor  62  abut on the inner surface of the hermetically tight sheath  20 . The ring  52  and the blades  54  of the rotor  50  are arranged concentrically with respect to the circular cylindrical hermetically tight sheath  20  and radially spaced apart therefrom in the area shown. The rotor  50  is surrounded by the annular jacket  82 . The jacket  82  is spaced apart from the radially outer ends of the blades  54  of the rotor  50 . 
         [0072]      FIG. 3  shows a schematic view of an endoscope  11 . The manner in which the endoscope  11  is shown in  FIG. 3  corresponds to the manner in which the exoscope is shown in  FIG. 1 . 
         [0073]    The endoscope  11  is similar, in some features and properties, to the exoscope  10  shown in  FIGS. 1 and 2 . Features and properties of the endoscope  11  are set out below which distinguish the latter from the exoscope shown in  FIGS. 1 and 2 . 
         [0074]    The endoscope  11  shown in  FIG. 3  has a long shaft  13 , which is represented in a shortened form in  FIG. 3 . The shaft  13  accommodates optical fibers  22  which transmit illumination light and which are coupled to a plurality of light sources  30  inside the handle  15  at the proximal end  12  of the endoscope  11 . Each individual light source  30  is in particular similar to the light source shown in  FIG. 1 . The shaft  13  moreover accommodates a beam path  24  for observation light, which emanates from an object to be observed. The beam path  24  comprises in particular a series of rod lenses indicated in  FIG. 3 . The beam path  24  extends as far as an eyepiece  16  at the proximal end of the endoscope  11 . In order to screen off surrounding light, and optionally to couple a camera to the endoscope  11 , an eyepiece cup  17  is provided at the eyepiece  16 . 
         [0075]    The light sources  30  are coupled to the hermetically tight sheath  20  and in particular to the surface area  40  by means of a heat conductor  42  made of copper, aluminum or another material with high thermal conductivity. The heat conductor  42  is in particular ring-shaped or substantially ring-shaped such that the heat generated by the light sources  30  is carried off via an annular surface area  40  and such that particularly efficient use is made of the annular air flow  57  generated by the rotor  50 . 
         [0076]    The rotor  50 , the jacket  82 , the proximal and distal guide blades  84 ,  86 , the magnetic flux conductor  62 , the conductor coils  64  and the controller  68  correspond to or are substantially similar to those shown in  FIGS. 1 and 2 . 
         [0077]    In contrast to the view in  FIG. 3 , one or more temperature sensors at the light sources  30  and/or at other heat sources inside the hermetically tight sheath  20  can be coupled to the controller  68 , similarly to the exoscope shown in  FIGS. 1 and 2 . 
         [0078]      FIG. 4  shows a further schematic view of the endoscope  11  from  FIG. 3 . The nature of the view in  FIG. 4  corresponds to the nature of the view in  FIG. 2 . In particular, the plane of the drawing of  FIG. 4  is orthogonal to the longitudinal axis  18  of the endoscope  11  and to the plane of the drawing of  FIG. 3 , wherein a cross section is shown along a surface near the rotor  50 , the magnetic flux conductor  62  and the conductor coils  64 . The beam path  24  for observation light is arranged in the central through-opening  63  of the magnetic flux conductor  62 . 
         [0079]      FIG. 5  shows a schematic view of a further exoscope  10  which, in some features and properties, is similar to the exoscope shown in  FIGS. 1 and 2 . As in  FIGS. 1 to 4 , a cross section through the exoscope is indicated, wherein section surfaces are not hatched. The plane of the drawing or sectional plane of  FIG. 5  corresponds to the planes of the drawings or sectional planes of  FIGS. 1 and 3 . Features and properties of the exoscope  10  are set out below which differ from those of the exoscope shown in  FIGS. 1 and 2 . 
         [0080]    The exoscope  10  has a proximal end  12 , a distal end  14 , a shaft  13 , which extends to the distal end  14 , and a handle  15  near the proximal end  12 . The exoscope  10  comprises a hermetically tight sheath  20 , inside which an image sensor  72  or a camera is arranged near the distal end  14  of the exoscope  10 . The image sensor  72  constitutes a heat source, of which the heat has to be carried away. Moreover, the exoscope can have further heat sources not shown in  FIG. 5 , for example inside the handle  15 . These heat sources not shown in  FIG. 5  can include devices for preparing or processing an image signal from the image sensor  72  and power electronics for providing electrical power for these devices, for the image sensor  72 , for a light source or for other consumers. 
         [0081]    Moreover, means  60  for generating a variable magnetic field is arranged inside the hermetically tight sheath  20  and in particular occupies a substantially annular installation space symmetrical to the longitudinal axis  18  of the exoscope  10 . Near the means  60  for generating a variable magnetic field, a rotor  50  is arranged outside the hermetically tight sheath, which rotor  50  can rotate about the longitudinal axis  18  of the exoscope  10 . The rotor  50  has a ring  52  with magnets  53  embedded therein, blades  54  protruding radially outward from the ring  52 , and an annular jacket  55  which connects the radially outer ends of the blades  54  to one another in a ring shape and mechanically supports them. By means of a variable and in particular rotating magnetic field, generated by the means  60 , interacting with the magnets  53  in the ring  52  of the rotor  50 , the rotor is driven like a rotor of a synchronous three-phase motor and rotates about the longitudinal axis  18  of the exoscope  10 . Moreover, the means  60  for generating a variable magnetic field can be designed to support the rotor magnetically or hold it free of contact in a predetermined position. 
         [0082]    The rotor  50  and in particular its blades  54  are designed to generate an airflow  57  during rotation about the longitudinal axis  18  of the exoscope  10 . The air flow  57  generated by the rotor  50  continues along the shaft  13  in the form of a laminar air flow  58  that helically encloses the shaft  13 . Proximally from the surface  40  thermally coupled to the heat source  72 , turbulators  88  are arranged at the outer surface of the hermetically tight sheath  20  and cause a transfer from a laminar stream in the air flow  58  to a turbulent stream in the air flow  59  at the surface  40 . The turbulent air flow  59  at the surface  40  improves the heat transfer from the surface  40  to the air flow  59  and thereby improves the cooling action. 
         [0083]    The rotor  50  rotating in a predetermined rotational direction sucks in ambient air near the outer surface of the hermetically tight sheath  20  in the area of the handle  15 . In this way, also in the area of the handle, the rotating rotor  50  generates an air flow that carries off heat from heat sources (not shown in  FIG. 5 ) arranged inside the handle  15 . 
         [0084]      FIG. 6  shows a schematic view of a further exoscope  10  which, in some features and properties, is similar to the exoscopes shown in  FIGS. 1 and 5 , in particular to the exoscope shown in  FIG. 5 . The nature of the view corresponds to that of  FIG. 5 . Features and properties of the exoscope  10  are described below which distinguish the latter from the exoscope shown in  FIG. 5 . 
         [0085]    The exoscope shown in  FIG. 6  differs from the exoscope shown in  FIG. 5  particularly in that no turbulators  88  are provided. Moreover, the hermetically tight sheath  20 , particularly in the area of the rotor  50  and of the shaft  13 , is designed such that the rotor  50  can be moved in the distal direction starting from the position shown in  FIG. 6 . The means  60  for generating a variable magnetic field is designed to magnetically support the rotor  50 , i.e. to hold the rotor  50  at the intended position shown in  FIG. 6 , even during rotation, similarly to what is described above with reference to  FIGS. 1 and 5 . 
         [0086]      FIG. 7  shows a further schematic view of the exoscope from  FIG. 6 . The nature of the view in  FIG. 7 , in particular the plane of the drawing, corresponds to those of  FIG. 6 .  FIG. 7  shows the exoscope  10  in a further configuration. In relation to the position intended for the use of the exoscope  10 , which position is shown in  FIG. 6  and is also indicated by broken lines in  FIG. 7 , the rotor  50  has been moved in a direction  51  parallel to the longitudinal axis  18  of the exoscope  10  and beyond the distal end  14  of the exoscope  10 . The rotor  50  is thus geometrically and mechanically separated from the rest of the exoscope  10  and can be cleaned and autoclaved independently and, in the event of damage, can be easily replaced. 
         [0087]      FIG. 8  shows a schematic view of a further exoscope  10  which, in some features and properties, is similar to the exoscopes shown in  FIGS. 1 ,  2  and  5  to  7 , in particular to the exoscope shown in  FIGS. 6 and 7 . The nature of the view in  FIG. 8  and, in particular, the section surface shown correspond to those of  FIGS. 1 ,  3  and  5  to  7 . Features and properties of the exoscope  10  are described below which distinguish the latter from the exoscope shown in  FIGS. 6 and 7 . 
         [0088]    The exoscope shown in  FIG. 8  comprises a first means  60  for generating a variable magnetic field near the handle  15  and a second means  61  for generating a variable magnetic field near the distal end  14  of the exoscope  10 . Like the devices shown in  FIGS. 1 to 7  for generating variable magnetic fields, each of the two devices  60 ,  61  is similarly provided and designed to generate a substantially rotating magnetic field and by this means to drive the rotor and set it in rotation. Moreover, both devices  60 ,  61  for generating variable magnetic fields are in particular provided and designed to support the rotor  50  and to hold it in a predetermined position during the rotation. The rotor  50  can thus be operated alternatively in two different positions at the exoscope  10 . In  FIG. 8 , the rotor  50  is shown in each of the two positions. 
         [0089]    When the rotor  50  is operated in the distal position, shown on the left-hand side in  FIG. 8 , the heat source  72  at the distal end  14  of the exoscope  10  is cooled particularly intensively. When the rotor  50  is operated in the proximal position, shown on the right-hand side in  FIG. 8 , and when the rotational direction is reversed in order to generate an air flow  57  in the opposite direction, the handle  15  is cooled particularly intensively. The exoscope  10  can comprise a controller (not shown in  FIG. 8 ) which, by measuring several temperatures, in particular by measuring the temperatures of several heat sources inside the hermetically tight sheath  20 , makes it possible to determine which heat source is most in need of cooling. Depending on the measured temperatures, the controller can then operate the rotor in different positions and/or with different running directions, in order in particular to cool the heat source that has the greatest need of cooling. A movement of the rotor  50  in direction  51  parallel to the longitudinal axis  18  of the exoscope  10 , between the two positions shown in  FIG. 8  and/or further positions, can take place magnetically or manually, after a prompt generated by the controller  68 , at a user interface or some other way. 
         [0090]    In a departure from the view shown in  FIG. 8 , three or more devices for generating variable magnetic fields can be provided. Alternatively, one means for generating a variable magnetic field can be movable inside the hermetically tight sheath  20  (in particular by means of an ultrasonic motor or an electrical drive) in order to operate the rotor  50  at two or more different positions. 
         [0091]      FIG. 9  shows a schematic axonometric view of a further exoscope  10  which, in some features and properties, is similar to the exoscopes shown above in  FIGS. 1 ,  2  and  5  to  8 . In particular, the exoscope has heat sources that require cooling. 
         [0092]    The exoscope  10  has a handle  15  at the proximal end  12  and a camera housing  73  at the distal end  14 . The handle  15  and the camera housing  73  are connected to each other by a rigid and straight shaft  13  with a substantially circular cylindrical circumferential surface. The viewing direction of a camera in the camera housing  73  is orthogonal to the longitudinal axis of the shaft  13 . 
         [0093]    In the transition area between the handle  15  and the shaft  13 , a jacket  82  and guide blades  86  are arranged in a monolithic or substantially monolithic structural part. The jacket  82  surrounds a rotor for generating a substantially laminar air flow  58 , guided and shaped by the jacket  82  and the guide blades  86 , along the shaft  13  to the camera housing  73 . As it continues on its way, the air flow  58  washes round the camera housing  73  and thus increases the heat removal from the surface of the latter. 
         [0094]      FIG. 10  shows a further schematic axonometric view of the exoscope  10  from  FIG. 9 . The exoscope  10  in  FIG. 10  is shown cut open along a plane that contains the axis of symmetry of the outer surface of the shaft  13  and the optical axis of a camera  72  in the camera housing  73 . The cross section shown in  FIG. 10  reveals the rotor  50  surrounded by the jacket  82 , means  60  for generating a variable magnetic field for driving the rotor  50  in the transition area between handle  15  and shaft  13 , and an installation space  76  in the handle  15  for a processor or other circuitry  74  for preparing or processing an image signal or for other heat sources. Moreover, the figure shows a bundle of optical fibers  22  provided in the shaft  13 , for carrying illumination light from a light source in the installation space  76  in the handle  15  to the distal end  14  of the exoscope  10 , and also a camera  72  in the camera housing  73 . 
         [0095]      FIG. 11  shows a further schematic axonometric view of the exoscope from  FIGS. 9 and 10 . The nature of the view in  FIG. 11  is similar to that in  FIG. 9 . In contrast to  FIGS. 9 and 10 , the exoscope  10  in  FIG. 11  is shown in a configuration which is suitable not for operating or using the exoscope  10  but instead for cleaning it. The jacket  82  with guide blades  86  and the rotor  50  have been moved in the distal direction starting from their positions intended for operation or use of the exoscope  10  in the transition area between handle  15  and shaft  13 . In this way, the surfaces of the rotor  50 , and surfaces in the area of the jacket and of the guide blades  86 , are accessible for cleaning. The remaining outer surfaces of the exoscope  10  are in particular formed by several surface components that are joined to one another free of seams, in particular by cohesive bonding, in order to facilitate simple and complete cleaning.