Patent Publication Number: US-6902405-B2

Title: Simulator apparatus with at least two degrees of freedom of movement for an instrument

Description:
CROSS-REFERENCE TO PENDING APPLICATIONS 
   The present application is a continuation of pending International patent application PCT/EP01/12649 filed on Oct. 31, 2001 which designates the U.S., and which claims priority of German patent application DE 100 55 292.7 filed on Nov. 3, 2000. 

   BACKGROUND OF THE INVENTION 
   The invention relates to a simulator apparatus with at least two degrees of freedom of movement for an instrument that has an elongated shaft comprising a holding device for the instrument, the holding device being designed such that the instrument has at least a first degree of freedom of a swivelling movement about a first swivel axis and at least a second degree of freedom of swivelling movement about a second swivel axis, running perpendicular to the first swivel axis. 
   Such a simulator apparatus is known for example from U.S. Pat. No. 6,024,576. 
   In general, such a simulator apparatus is used as interface between an operator and an instrument in simulators. A specific use, to which the following description relates without limiting the present invention thereto, is the integration of a simulator apparatus mentioned at the beginning in a simulator for simulating a minimally invasive surgical intervention in a human or animal body. 
   The term “instrument” is to be understood generally in the sense of the present invention, and in the case of a medical simulation, it can be an endoscope, a tool such as scissors, forceps, a dissector, clamp applicator etc. 
   In recent years, minimally invasive surgery has gained clearly in importance by comparison with open surgery. In minimally invasive surgery, a viewing system, for example an endoscope, and one or more instruments such as forceps, scissors, HF instruments, clamp applicators, etc. are introduced into the body by minimal incisions. The minimally invasive surgical operation is carried out with video assistance with the aid of the abovementioned instruments in combination with peripheral devices. 
   At present, minimally invasive surgery is used, for example, for removing a gall bladder, the appendix and for handling herniotomies. Further fields of use are being opened up. 
   However, “minimally invasive” surgery covers as a term not only surgical interventions, but also interventions such as, for example, the introduction of substances into the body, or biopsies where use is made of the minimally invasive technique. 
   By contrast with open surgery, the advantage of the minimally invasive technique resides in the mode of procedure, which spares the patient and entails less surgical trauma, shorter times of stay in hospitals and a shorter incapability for work. 
   By contrast with open surgery, however, the handling of the instruments during a surgical intervention is substantially more complicated, firstly because the freedom of movement of the instrument inserted through the incision is restricted because of the only small incision, and secondly because the surgeon does not himself have a clear dimensional view of the working tip of the instrument located in the body, nor of the operating site, but instead only a two-dimensional visual monitoring is possible via the video monitor. It goes without saying that the coordination of the guidance and operation of the instrument or instruments are thereby rendered more difficult. 
   There is thus a greater need for training in the new techniques of minimally invasive surgery. Various alternatives currently exist for training in surgical procedures of minimally invasive surgery. 
   One alternative consists in carrying out training operations in vivo on animals, specifically on pigs. However, such training is cost intensive, time consuming to prepare and, moreover, ethically dubious. 
   In the case of a further alternative, physicians are trained on in vitro organs in a training box into which the instruments can be appropriately introduced. The organs arranged in the training box are certainly biological organs, but training in the case of this alternative is likewise time consuming to prepare and cannot be regarded as realistic. 
   Finally, training in minimal invasive surgery is currently being carried out on model organs or training objects in a training box. However, such model organs are not sufficiently realistic for training for an entire operation. Moreover, the preparation of the model organs and training objects requires a not inconsiderable preparatory outlay, since the models are for the most part destroyed during the operation and initially require to be prepared again for further training sessions. 
   Because of the disadvantages of the training systems used to date, there was already a need very early for so called virtual simulators that can be used to overcome the disadvantages of the previous training systems. 
   The actual operating site is generated exclusively via a computer in the case of virtual simulation. Realistic simulation requires a model database that fixes the geometric shapes and physical properties of the tissues, organs and vessels, as well as the geometry and kinematics of the instrument or instruments. In the journal “Biomedical Journal”, Volume No. 51, April 1998, U. Kühnapfel describes a “Virtual-Reality-Trainingssystem für die Laparoskopie” [“Virtual reality laparoscopy training system”] that has an input box which exhibits from the outside the customary instrument grips and a virtual endoscope. In the housing, the minimally invasive instruments are guided in a mechanical guide system that further permits the detection of the deflection of the instruments and actuators. In addition, various foot switches are present that can be used to activate surgical and general functions. Via angle encoders, for example, a PC-based sensor data acquisition process measures the positions of the joints of the operating instruments and transmits these continuously to a graphics workstation. A “virtual” image of the endoscope view is calculated there from in real time. The consistency of the tissue to be treated is fed back to the operator realistically as force feedback by inherently calculated “virtual” reactive forces between organs and instruments. 
   Consequently, in the case of virtual simulation of minimally invasive interventions, no use is made of physically present organs—instead the spatial and physiological structures of such organs are present as data in a computer. The simulator apparatus mentioned at the beginning in this case forms the interface between the operator and the instrument to be handled and the simulation computer system. The operator to be trained handles the instrument accommodated in the mechatronic simulator apparatus, the data stored in the computer, for the spatial and physiological structure of the virtual organ being transmitted as force feedback by the simulator apparatus to the instrument while the latter is being handled, as a result of which the operator is afforded a realistic feel. 
   The previous developments in this field have concentrated primarily on the creation of the simulation software, while so far available holding systems capable of localization have been used as mechatronic simulator apparatus. In the interests of realistic simulation, the simulator apparatus should take account of all degrees of freedom that are present for a minimally invasive surgical instrument, specifically a tilting of the instrument about the surface of the body, a movement in the direction of the shaft and a rotary movement about the longitudinal axis of the shaft. However, a problem in this is the mechanical implementation of these many degrees of freedom in the holding device of the simulator apparatus for the instrument. 
   For example, the simulator apparatus known from U.S. Pat. No. 6,024,576 cited above comprises a complicated mechanical lever system whose disadvantage resides particularly in the fact that the simulator apparatus is very large overall. It is therefore impossible using such a simulator apparatus for two or more apparatuses to bring a plurality of instruments so close together that the instrument tips can touch. Because of the many levers used in this known simulator apparatus, undesirable moments of inertia and torques occur when this simulator apparatus is being used and must be compensated in a complicated way in order to permit a realistic force feedback. 
   WO 96/30885 discloses a virtual surgical system for simulating surgical interventions on the basis of image data. It is possible thereby to simulate a surgical procedure by using the image data of a patient, it being possible to simulate the instruments used by a surgeon in carrying out an actual procedure. This known apparatus makes use as input apparatus of a mouse, a three-dimensional mouse, a joystick or a seven-dimensional joystick. The joystick provided in the known apparatus is designed in the form of a lever at whose lower end a ball is arranged that can be rotated in various directions of solid angle in a ball cup. However, a mouse or a joystick does not correspond to the application of an actual surgical instrument. 
   Further, EP-0 970 662 A1 discloses a simulator apparatus for simulating the insertion of a catheter into blood vessels. The simulated catheter has only degrees of freedom of rotation about the longitudinal axis of the catheter, and of translatory movement in the direction of the longitudinal axis of the catheter. Provided for the purpose of achieving a force feedback is a gear arrangement that has, inter alia, a differential gear which, however, is arranged with reference to the longitudinal central axis of the catheter in a fashion laterally apart and aside from the latter, and which is connected to the catheter via various stands and holding devices. 
   It is therefore the object of the invention to specify a simulator apparatus of the type mentioned at the beginning that has a compact design and mechanics of low torque. 
   SUMMARY OF THE INVENTION 
   According to the invention, a simulator apparatus with at least two degrees of freedom of movement for an instrument that has an elongated shaft, is provided, comprising: 
   a holding device for holding said instrument, said holding device being designed such that said instrument has at least a first degree of freedom of swivelling movement about a first swivel axis and at least a second degree of freedom of swivelling movement about a second swivel axis, said second swivel axis running perpendicular to said first swivel axis, 
   said holding device having a cardanic suspension, said cardanic suspension having a spherical element in which said shaft of said instrument is partly received, said spherical element being suspended such that it can rotate about said first swivel axis and about said second swivel axis. 
   The simulator apparatus according to the invention therefore has a cardanic suspension for the instrument that has the advantage of the particularly low-torque guidance of the instrument in the holding device. The cardanic suspension permits the superimposition of the swivelling movements of the instrument both about the first swivel axis and about the second swivel axis. While in the case of a real intervention an operating instrument can usually be swivelled about the plane of the body surface about two axes that are perpendicular to one another and intersect in the incision, the simulator apparatus according to the invention permits a realistic simulation of such manipulations of an instrument. 
   In a preferred refinement, the cardanic suspension is formed by a bow-shaped element that can be swivelled about the first swivel axis, and an annular element, connected to the spherical element, that can swivel about the second swivel axis, the instrument being guided on the bow-shaped element. 
   This refinement implements a cardanic suspension that is of particularly simple design and has the further advantage that in the case when, as provided in a further preferred refinement, the simulator apparatus is provided with a first feedback for the first and second degrees of freedom, the corresponding actuators for the force feedback can be provided in a fixed fashion on the apparatus and therefore need not be moved as well, as a result of which particularly low-torque mechanics of the simulator apparatus can be achieved. 
   In a further preferred refinement, there are fastened on the annular element two mutually opposite seats, arranged offset by approximately 90° with reference to the second swivel axis, for the spherical element, the spherical element in the seats being held such that it can rotate relative to the seats about an axis of rotation passing through both seats, and such that it is immobile with reference to the seats perpendicular to this axis of rotation. 
   By means of this measure the advantage is achieved that the instrument itself need be guided only at the bow-shaped element with reference to a swivelling movement about the first swivel axis, while the guiding of the instrument with reference to the swivelling movement about the second swivel axis is accomplished via the spherical element, the seats and, via these, the annular element. 
   As already mentioned, the first degree of freedom and the second degree of freedom are provided with a force feedback, there being provided in a further preferred refinement for the force feedback for the first and second degrees of freedom in each case at least one actuator, that acts on the bow-shaped element and the annular element. 
   Actuators also moved can advantageously be avoided by the previously described refinement. 
   In a further preferred refinement, the holding device is designed such that the instrument has a third degree of freedom of rotating movement about the longitudinal axis of the shaft, and a fourth degree of freedom of translatory movement in the direction of the shaft. 
   Due to the abovementioned refinement, the simulator apparatus according to the invention advantageously also permits, in a realistic fashion, movements of an instrument in the direction of the longitudinal axis and rotary movements about the longitudinal axis of the shaft. The simulator apparatus according to the invention thus permits at least four degrees of freedom of movement for the instrument. 
   It is preferred in this case if the holding device has for the third and fourth degrees of freedom a gear arrangement that has a first bevel gear, which is connected to the shaft and co-rotates with the latter about the longitudinal axis thereof, and has a second and a third bevel gear which are arranged on either side of the first bevel gear and are in rolling engagement therewith. 
   The simulator apparatus according to the invention therefore has, for the third and fourth degree of freedom, a gear arrangement that resembles a differential gear and has the advantage that it can be arranged around the shaft of the instrument and is of particularly small overall size, and in particular large radii of movement of the moving parts such as in the case of the known lever arrangements are avoided. Guiding of the instrument in the holding device with particularly low torque is thereby also achieved. As stated in a further preferred refinement, the gear arrangement can be used both to implement the degree of freedom of the rotary movement about the longitudinal axis of the shaft and the degree of freedom of the translatory movement in the direction of the shaft with a force feedback, and also a superimposition of the two movements is rendered possible with low torque by the gear arrangement provided according to the invention. Moreover, the gear arrangement with three bevel gears has the advantage that the actuators, for example electric motors, possibly present for a force feedback, can be arranged immovably in the simulator apparatus, the result being to avoid further moments of inertia and torque, and to avoid a greater space requirement for the movement of such motors. 
   In a further preferred refinement, the first bevel gear is in rolling engagement with the shaft via one or more pinions with the aid of a tooth system extending along the shaft. 
   A translatory movement of the shaft along its longitudinal axis onto the first bevel gear is effected with particularly low torque by means of this measure. In the case of such a longitudinal movement of the shaft, the first bevel gear is set rotating about its longitudinal axis, and this thereby sets the second and the third bevel gears in rotary movements of mutually opposite direction. Force feedback to the degree of freedom of the rotary movement about the shaft can therefore be implemented with particular ease by providing the second and third bevel gears, which are retarded by one or more actuators, as in a further preferred refinement. In order to achieve force feedback to the degree of freedom of the translatory movement, the second and the third bevel gears are then driven in opposite directions with the same torque and at the same speed. 
   However, the same actuators can also be used to achieve force feedback to the degree of freedom of the rotary movement of the shaft about its longitudinal axis. Specifically, as already mentioned when the instrument is being rotated about its longitudinal axis the first bevel gear is also corotated about the longitudinal axis of the shaft and, in the process, this sets the second and the third bevel gears in rotary movements in the same direction. In order to achieve force feedback to the degree of freedom of the rotary movement of the shaft about its longitudinal axis, the actuators must therefore retard the second and the third bevel gears in the same direction and with the same torque. 
   In a further preferred refinement, the second and the third bevel gears are arranged concentrically with the shaft. 
   This arrangement of the second and third bevel gears results in a particularly space-saving design, of small overall size, of the gear arrangement and of the overall arrangement of shaft and gear arrangement. 
   In a further preferred refinement, the gear arrangement is arranged in the spherical element. 
   A particularly space-saving design of the overall simulator apparatus is achieved by this measure despite the at least four possible degrees of freedom of the movement of the instrument. Because of its arrangement in the spherical element, the gear arrangement executes the swivelling movements about the first and second swivel axes together with the instrument. The gear arrangement is therefore suspended in a cardanic fashion in a particularly space-saving way. 
   In a further preferred refinement, in each case one-position detection sensor is provided for determining the position of the instrument for at least one degree of freedom, preferably for all degrees of freedom. 
   The instantaneous values of all degrees of freedom of the instrument which are rendered possible by the simulator apparatus according to the invention can be detected in real time with the aid of such position detection sensors, and can be used, in turn, to generate signals for the force feedback in real time in a computer by appropriate signal processing. 
   In a further preferred refinement, the instrument has a moveable operating device and the moveable operating device is equipped with force feedback. 
   Particularly when the instrument is not an endoscope, but a surgical instrument such as forceps or scissors, this measure has the advantage that the simulator apparatus according to the invention can also simulate the force resistances occurring during the real preparation, for example cutting or grasping, of tissue. In the simplest case, it is possible to attach to the moveable operating device a Bowden cable that is connected to an actuator which, in turn, receives control signals from the simulation computer system. With the refinement mentioned previously, the simulator apparatus according to the invention even has five degrees of freedom for the simulation. 
   In a preferred use of the simulator apparatus, the latter is used to simulate a minimally invasive operation on the human or animal body. 
   Further features and advantages emerge from the following description and the attached drawing. 
   It goes without saying that the features mentioned above and those still to be explained below can be used not only in the respectively specified combination, but also in other combinations or on their own, without departing from the scope of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of the invention is illustrated in the drawings and will be described in more detail hereafter with reference thereto. In the drawings: 
       FIG. 1  shows an overall perspective illustration of a mechatronic simulation apparatus for simulating at least two degrees of freedom of movement of an instrument with force feedback; 
       FIG. 2  shows the simulator arrangement in  FIG. 1  in an operating position changed from  FIG. 1 ; 
       FIG. 3  shows the simulator apparatus in  FIGS. 1 and 2  in a further operating position changed from  FIGS. 1 and 2 ; 
       FIG. 4  shows a side view of the simulator apparatus in  FIGS. 1  to  3  with partial omissions and partly in section; 
       FIG. 5  shows a further side view of the simulator apparatus in  FIGS. 1  to  4 , the side view being rotated by approximately 90° by comparison with  FIG. 4 ; 
       FIG. 6  shows a gear arrangement, present in the simulator apparatus in  FIGS. 1  to  5 , in perspective illustration to an enlarged scale; 
       FIG. 7  shows a detail of the simulator apparatus in  FIGS. 1  to  5  in a longitudinal section to an enlarged scale; and 
       FIG. 8  shows a section along the line VIII—VIII in FIG.  7 . 
   

   DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
   A simulator apparatus, provided With the general reference  10 , for simulating at least two degrees of freedom or movement of an instrument  12  is illustrated in  FIGS. 1  to  5 . 
   The simulator apparatus  10  is used, in particular, to simulate minimally invasive surgical operations on the human or animal body for the purpose of training physicians. 
   The instrument  12  is a pair of preparation forceps for cutting tissue in the exemplary embodiment shown. Instead of such preparation forceps, it is also possible, however, for an endoscope to be inserted as instrument  12  into the simulator apparatus  10 , or it is possible to insert other tools such as clamp applicators, suction and irrigation instruments and the like into the simulator apparatus  10 . The instrument  12  can be removed from the simulator apparatus for the purpose of changing instruments. 
   The instrument  12  has, in general, an elongated shaft  14  that is passed through the simulator apparatus  10  or is accommodated therein, a tool  16  at the distal end of the shaft which, in the present exemplary embodiment, has two jaw parts, for example provided with cutting edges, and a grip  18  at the proximal end of the shaft  14 . An operating device  18  has a moveable grip part  20  and an immovable grip part  22 . 
   The simulator apparatus  10  has a holding device  24 , which will be explained in more detail below. 
   The holding device  24  has a cardanic suspension  25 . The cardanic suspension  25  permits the simulation of a degree of freedom of swivelling movement of the instrument  12  about a first swivel axis  26 , as well as of a further degree of freedom of swivelling movement of the instrument  12  about a second swivel axis  28 , running perpendicular to the first swivel axis  26 . With the aid of these two degrees of freedom, it is possible to simulate any desired tilted positions of the instrument  12  with reference to a surface  30 , which simulates the body surface of a patient in the case of a use of the simulator apparatus  10  to simulate minimally invasive operations on the human or animal body. The point of intersection between the swivel axes  26  and  28 , which lies at a point on the longitudinal axis of the shaft  14 , constitutes the invariant point of the swivelling movements of the instrument  12 . Since in the case of real minimally invasive surgery the instrument is guided through an incision in the body surface, and the invariant point lies approximately in the incision, the arrangement of the swivel axes  26  and  28  is made in the case of the simulator apparatus  10  such that the point of intersection lies approximately at the level of the surface  30  or slightly there below. 
   In order to implement the swivel axis  26  of the cardanic suspension  25 , the cardanic suspension  25  has a bow-shaped element  32  that is designed approximately in a shape of a semicircle. The bow-shaped element  32  is mounted swivelably about the swivel axis  26  on a mounting frame  34  ( FIGS. 4 and 5 ) which is itself immovable. 
   In order to implement the swivel axis  28 , the cardanic suspension  25  has an annular element  36  that is arranged inside the bow-shaped element  32 . The annular element  36  is suspended about the second swivel axis  28  by means of mounting angles  38  and  40 . 
   Furthermore, there are fastened to the annular element  36  two mutually opposite seats  42  and  44  that are arranged offset by approximately 90° with reference to the second swivel axis  28 . The seats  42  and  44  are designed as spherical shell segments and accommodate a spherical element  46 . 
   The shaft  14  of the instrument  12  is accommodated in the spherical element  46  and goes through the latter, as will be explained in more detail later. 
   The spherical element  46  is mounted in the seats  42  and  44  by means of two pins  48  and  50  (indicated by broken lines) that engage in corresponding bores in the spherical element  46 . The spherical element  46  can thus be rotated relative to the seats  42  and  44  about an axis of rotation  52  defined by the pins  48  and  50 , but is immovable with reference to the seats  42  and  44  at right angles to this axis of rotation  52 . Overall, the spherical element  46  can be moved relative to the bow-shaped element  32 , and also relative to the annular element  36 . 
   The shaft of the instrument  14  is guided only in the bow-shaped element  32 , but not in the annular element  36 . For this purpose, the shaft  14  is guided in the bow-shaped element  32  via a sleeve  52  that projects through an elongated hole  54  formed in the bow-shaped element  32 . The shaft  14  can move together with the sleeve  52  in the longitudinal direction of the elongated hole  54  when the instrument  12  is swivelled about the second swivel axis  28 . 
   Both the degree of freedom of the swivelling movement about the first swivel axis  26  and the degree of freedom of the swivelling movement about the second swivel axis  28  are provided in each case with force feedback. 
   An actuator, for example a DC motor for force feedback to the bow-shaped element  32 , is arranged for the bow-shaped element  32 , which elements  32  can be swivelled about the first swivel axis  26 . A position detection sensor  58 , for example in the form of a potentiometer or an incremental rotary encoder, is arranged opposite the actuator  52  for the purpose of detecting position, that is to say for determining the angle of the angular position of the bow-shaped element  32 . 
   Correspondingly, as force feedback for the degree of freedom of the swivelling movement about the second swivel axis  28  a further actuator  60  is connected to the annular element  36  via the mounting angle  40 , and a position detection sensor  62  is connected via the mounting angle  38 . 
   The mode of operation of the cardanic suspension  25  without and with force feedback is therefore as follows. An operator, for example a physician to be trained, takes hold of the operating device  18  of the instrument  12  in one hand. By moving the operating device  18 , the instrument  12  can now be tilted in arbitrary solid angle directions about the plane  30  about the invariant point formed by the point of intersection of the first swivel axis  26  with the second swivel axis  28 . This is illustrated by way of example in  FIGS. 1  to  3  with the aid of various tilted positions. 
   From the tilted position in  FIG. 1 , the instrument  12  was tilted about the second swivel axis  28 , while the swivel position remains unchanged with reference to the first swivel axis  26 . In the event of this movement, the annular element  36  has been tilted correspondingly about the second swivel axis  28 , while the spherical element  46  has changed its position relative to the bow-shaped element  32 , but not relative to the annular element  36 . In the drawing, the sleeve  52  with the shaft  14  has been moved correspondingly to the right in the elongated hole  54  of the bow-shaped element  32 . 
   Starting from  FIG. 2 , the tilted position illustrated in  FIG. 3  is reached by having swivelled the instrument  12  in a direction into the plane of the drawing about the first swivel axis  26 . In this case, the annular element  36  has not been moved, but the spherical element  48  has moved relative to the annular element  36 . 
   In order in the case of the above described movements of the instrument  12  to simulate a force resistance that is to be overcome, for example, by the elasticity, stiffness of a simulated tissue when handling the instrument  12 , the above mentioned movements can be counteracted by a software-aided computer-controlled drive of the actuators  56  and  60 , such that the operator feels a “real” force resistance as if he is carrying out the same actions on a patient. 
   The position detection sensors  58  and  62  continuously detect in real time the current angular positions of the instrument  12  about the first swivel axis  26  and second swivel axis  28 , and the actuators  56  and  60  are driven for force feedback in real time on the basis of these data and the tissue data stored in the computer. 
   It goes without saying that the instrument  12  can be swivelled not only sequentially about the first swivel axis  26  and the second swivel axis  28 , but also simultaneously in any desired solid angle directions about both swivel axes  26  and  28 . 
   It follows from the above that the actuators  56  and  60 , as well as the position detection sensors  58  and  62  were not also moved during the movements of the instrument  12  and the movements, associated therewith, of the annular element  36 , the bow-shaped element  32  and the spherical element  46 , and so the holding device  24  is of very low torque and the cardanic suspension  25  constitutes a very compact design for implementing the previously named degrees of freedom. 
   In accordance with a further aspect, the simulator apparatus  10  has a gear arrangement  70 , which will be described in more detail below with reference to  FIGS. 6  to  8 . 
   The gear arrangement  70  is a component of the holding device  24  for the instrument  12 , it being possible to use the gear arrangement  70  to simulate further degrees of freedom of movement for the instrument  12  with force feedback. These further degrees of freedom are a degree of freedom of rotary movement of the instrument  12  about the longitudinal axis of the shaft  14 , and a further degree of freedom of translatory movement of the instrument  12  in a direction of the shaft  14 . 
   As emerges from  FIGS. 7 and 8 , the gear arrangement  70  provided for simulating the two above named degrees of freedom with force feedback is arranged as a whole in the spherical element  46  of the cardanic suspension  25 . The gear arrangement  70  is illustrated in perspective in  FIG. 6  to a large scale without the spherical element  46 . 
   Firstly, the gear arrangement  70  has a first bevel gear  72 . The first bevel gear  72  can be rotated about an axis of rotation  74  running transverse to the shaft  14 . The first bevel gear  72  has a tooth system (not illustrated in  FIG. 6 ) on a frustoconical circumferential surface  76 . The frustoconical surface  76  can also be designed as a friction surface instead of a tooth system. 
   The gear arrangement  70  further has a second bevel gear  78  and a third bevel gear  80 , the second bevel gear  78  and the third bevel gear  80  being arranged on either side of the first bevel gear  72 . The second bevel gear  78  and the third bevel gear  80  are arranged around the shaft  14  of the instrument  12  in a fashion coaxial therewith. The bevel gears  78  and  80  can therefore be rotated about the longitudinal axis of the shaft  14 . The axes of rotation of the bevel gears  78  and  80  run perpendicular to the axis of rotation of the bevel gear  72 . 
   The second bevel gear  78  has a frustoconical surface  82 , and the third bevel gear  84  has a frustoconical surface  84 , the frustoconical surfaces  82  and  84  being in rolling engagement with the frustoconical surface  76  of the first bevel gear  72 . The frustoconical surfaces  82  and  84  correspondingly have tooth systems, or are constructed as friction surfaces. 
   While the second bevel gear  78  and the third bevel gear  80  are not connected to the shaft  14 , the first bevel gear  72  is connected to the shaft  14  via a pinion arrangement that has a first pinion  86  and a second pinion  88 . The first pinion  86  is connected securely in terms of rotation to the second pinion  88  via a shank  90 . An axis of rotation of the arrangement composed of the first pinion  86 , the shank  90  and the second pinion  88  runs parallel to the axis of rotation  74  of the first bevel gear  72 . 
   The first bevel gear  72  has a spur gear  92  that engages with the first pinion  86  in a meshing fashion. 
   By contrast, the second pinion  88  engages with a tooth system  94  extending along the shaft  14 . 
   The spur gear  92  can be constructed as one piece with the first bevel gear  72 , or be connected securely in terms of rotation to the latter as a separate part. 
   In accordance with  FIGS. 7 and 8 , the gear arrangement  70  is arranged inside the spherical element  46  in a cutout  96 . 
   The shaft  14  of the instrument  12  is guided by cylindrical sleeves  98  and  100  through the gear arrangement  70 . Because of the tooth system  94  provided on the shaft  14 , the shaft  14  has a key-like profile in cross section, the gear arrangement having a keyhole-like passage  102  ( FIG. 8 ) which is complementary correspondingly thereto. The first bevel gear  72  is connected in this way to the shaft  14  securely in terms of rotation via the pinions  86  and  88 , that is to say given a rotation of the shaft  14  about its longitudinal axis the first bevel gear  72  in the spherical element  48  is rotated about the longitudinal axis of the shaft  14  in accordance with a double arrow  104 , depending on the direction of rotation of the shaft. 
   The second bevel gear  78  is connected securely in terms of rotation to an annular flange  106 . The third bevel gear  80  is connected securely in terms of rotation to a cylindrically constructed box  108  that, in turn, is connected securely in terms of rotation to a further annular flange  110 . The annular flange  106 , which is connected securely in terms of rotation to the second bevel gear  78 , has on its outer circumference a tooth system that meshes with a pinion  112  that is connected to the output shank of an actuator  114 , for example a DC motor. 
   The annular flange  110 , which is connected securely in terms of rotation to the third bevel gear  80  via the box  108 , likewise has on its outer circumference a tooth system that meshes with a pinion  114  that is connected on the output side to an actuator  118 . 
   The actuators  114  and  118  serve as force feedback for the degree of freedom of the translatory movement in direction of the shaft, and as force feedback for the degree of freedom of the rotary movement of the instrument  12  about the shaft  14 , as will be described in yet more detail hereafter. 
   The mode of operation of the gear arrangement  70  is as follows, the mode of operation firstly being described without force feedback. 
   If the instrument  12  is rotated about the longitudinal axis of the shaft  14 , because of the keyhole-like connection to the keyhole-like passage  102  the shaft  14  corotates the pinions  88  and  86 , and thus the first bevel gear  72  in the direction of rotation of the shaft  14 . The first bevel gear  72  is mounted in a floating fashion inside the box  108 . In the event of this rotation of the first bevel gear  72  about the longitudinal axis of the shaft  14 , the first bevel gear  72  does not rotate about its axis of rotation  74 . By contrast, the bevel gear  72  rotating about the longitudinal axis of the shaft  14  sets the second bevel gear  78  and the third bevel gear  80  rotating in mutually identical directions. 
   If the instrument  12  is displaced along the direction of the shaft  14  in the holding device  24 , the tooth system  94  sets the pinion  88  and thus the pinion  86  in a rotation that causes a corresponding rotation of the bevel gear  72  about the axis of rotation  74  without, as previously described, the bevel gear  72  rotating about the longitudinal axis of the shaft  14 . Because of the rotation of the first bevel gear  72  about the axis of rotation  74 , the second bevel gear  78  and the third bevel gear  80  are now set rotating in mutually opposite directions. 
   In order now to bring about a force feedback to the degree of freedom of the rotation of the instrument  12  about the longitudinal axis of the shaft  14 , the actuators  114  and  118  must retard the second bevel gear  78  and the third bevel gear  80  in the same direction of rotation relative to one another with the same torque. 
   In order to bring about a force feedback to the degree of freedom of the translatory movement of the instrument  12  in the direction of the shaft  14 , because of the oppositely directed rotary movement of the second bevel gear  78  relative to the third bevel gear  80  the actuators  118  and  114  must correspondingly retard the bevel gears  78  and  80  in opposite directions, as far as possible with the same torques, in order thereby to oppose this degree of freedom with a force feedback. 
   The gear arrangement  70  has rendered it possible not to require the actuators  114  and  118  also to be moved. This results in an implementation also of these two degrees of freedom of the instrument  12  that is of particularly low torque, and in a particularly compact design, since it is necessary, as far as moving parts are concerned, only for the bevel gears  72 ,  78  and  80  and smaller pinions to be moved. 
   It goes without saying that movements of the instrument  12  in the direction of the shaft  14  and movements of the instrument  12  about the longitudinal axis of the shaft  14  can be performed in a fashion superimposed on one another simultaneously. 
   Furthermore, position detection sensors (not illustrated individually), for example in the form of angle encoders, are provided for the degrees of freedom of the rotary movement about the longitudinal axis of the shaft  14  and the translatory movement in the direction of the shaft  14  in order to be able to carry out computer-aided simulation with the aid of appropriate software. 
   It follows from the above description that the simulator apparatus  10  renders possible a simulation of four degrees of freedom of movement of the instrument  12 , all the degrees of freedom being provided with force feedback. 
   A fifth degree of freedom of movement consists in the case of the instrument  12  in the movement of the moveable grip part  20 . Force feedback can also be provided for this degree of freedom of movement, for example by connecting at the moveable grip part a Bowden cable (not illustrated) that is connected to an actuator (not illustrated) in the form of a DC motor. Appropriate position detection sensors detect the current position of the moveable grip part for the purpose of real time calculation of the force feedback. 
   The compact design of the simulator apparatus  10  renders it possible to use three such apparatuses in close proximity, one simulator apparatus, for example an endoscope, and two further apparatuses respectively accommodating a tool. The compact design of the simulator apparatus  10  even renders it possible in this case for the instrument tips to be able to touch one another, as is the case with real surgical operations. 
   Via a measured data acquisition and control card the simulator apparatus  10  is connected (in a way not illustrated) in a unit to a central processor. Stored in a program in the measured data acquisition and control card are the kinematics for determining the position of the instrument tip, of the tool  16  in the case of the instrument  12 , and the inverse kinemetics for the distribution of the force and torque components at the instrument tip, as well as a software for the control. 
   The previously described actuators are to be understood only by way of example, it also being possible to implement such motors by means of hollow-shank motors. Moreover, instead of one axial hollow-shank motor acting coaxially, it is possible for a plurality of motors to act coaxially on the bevel gears  78  and  80 .