Abstract:
A planetary roll system, in particular for a device for extending bones. The system comprises two elements that can be displaced in opposition to one another and that are interconnected by at least one drive element. A hosing is designed to receive at least one planetary roll which comprises at least one radial cavity.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a planetary roller system, in particular for a device for extending bones, with two elements that can be moved in relation to one another and that are interconnected via at least one drive element. 
     Devices of this kind are known and commonly available on the market in a wide variety of formats and designs. They are used in particular also as a drive means for devices for extending bones. They can be inserted into a bone cavity or a medullary space of a bone, and distraction can take place after the bone has been cut through. 
     A disadvantage is that conventional planetary roller systems for distraction devices cannot take up or generate very high forces and cannot be exactly and precisely manufactured in miniature format. In addition, they must be able to be easily taken apart for cleaning, and, particularly when used in medical instruments, they must be able to be fitted very quickly and simply. 
     Specifically in the design of distraction devices having a very small cross section, planetary roller systems are used as drive systems whose cross sections have to have a very small diameter. In order to very high forces during distraction or movement of one element in relation to the other element, conventional planetary roller systems are not suitable as drive elements or drive units. 
     JP 2001 330087 A discloses a differential gear for a vehicle, in which three planetary rollers are mounted securely in a planetary roller cage. 
     A similar mounting of planetary rollers in planet carriers or cages is disclosed in DE 44 21 428 C1 and WO 01/81787 A. 
     The object of the present invention is to make available a planetary roller system, in particular for a device for extending bones, which overcomes the stated disadvantages and with which straightforward assembly and disassembly is possible in a simple, inexpensive and precise manner, and with which very high forces can be transmitted, the aim being for the planetary roller system to have very small diameters. 
     SUMMARY OF THE INVENTION 
     This object is achieved by the fact that a housing for receiving at least one planetary roller has at least one radial recess, and a receiving pocket is formed in each case at the front in the area of the recesses, said receiving pocket being arranged approximately centrally with respect to the recess in the circumferential surface and opening inwardly. 
     In the present invention, a housing for receiving the individual planetary rollers is formed which preferably has three radial recesses spaced apart from one another. The recesses are provided in a circumferential surface of a housing, corresponding receiving pockets being formed at the end of the respective recesses for the purpose of receiving shaft ends of planetary rollers for suitable bearing. 
     Three recesses are preferably provided at an angle of approximately 120° from one another in the circumferential surface of the housing. However, the scope of the present invention is also intended to cover the case where, for example, two opposite recesses or several recesses can be provided in the housing for the purpose of receiving planetary rollers. It is also conceivable for four radial recesses to be provided in the circumferential surface of the housing for the purpose of receiving the planetary rollers. 
     It is important in the present invention that the housing ensures that the individual planetary rollers are optimally mounted inside the recesses and inside the receiving pockets, and that simple assembly is therefore made possible by means of the housing. In this way, very high forces can be transmitted in a planetary roller system of this kind with the housing. In this way, the overall diameter of the planetary roller system can be made very small. This is also aided by the fact that the corresponding bridges are formed at an obtuse angle and thus enlarge the recesses, in particular in the inner area, such that the corresponding planetary rollers with greater diameter can be fitted. This likewise serves for optimal higher force transmission with reduction of the overall cross-sectional diameter of the planetary roller system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages, features and particulars of the invention will become evident from the following description of a preferred illustrative embodiment and from the drawing, in which: 
         FIG. 1  shows a schematic and partial longitudinal section through the first element in the end area of a device for extending bones, with a planetary roller system; 
         FIG. 2  shows a schematic plan view of an essential part of the planetary roller system; 
         FIG. 3  shows a schematic cross section through a housing of the planetary roller system along line III-III in  FIG. 2 ; 
         FIG. 4  shows a schematic cross section through the housing of the planetary roller system, with indicated planetary rollers, sun wheel and crown wheel. 
     
    
    
     DETAILED DESCRIPTION 
     According to  FIG. 1 , a device R according to the invention comprises a first element  1 , and a second element  2  that is guided linearly and axially in said first element  1 . 
     Integrated in the first element  1 , particularly in the end area, there is an energy and/or data transmission element  3  which delivers the required energy and ensures energy transmission and bidirectional and contactless exchange of data. In the end area  19  of the element  1 , there are also at least two radial locking bores  4  which serve to fix the device R for example in a bone that is to be extended. At the same time, the element  1  is secured against radial torsion relative to the bone during fixing. 
     The element  1  is preferably designed as a receiving sleeve  5  that comprises an electronics unit  6  (only symbolically indicated here) connected to the energy and/or data transmission element  3  and also to a drive element  7 . 
     The drive element  7  comprises an electric motor  8  which sets a drive shaft  10  in a rotary movement via bearings  9  (only symbolically indicated here). Adjoining one end of the drive shaft  10  there is a planetary roller system  11  in which a plurality of planetary rollers  24  (symbolically indicated in  FIG. 4 ) drive the individual planetary rollers  24  in rotation via the drive shaft  10 , preferably configured as sun wheel  25 . The planetary rollers  24  are fitted into corresponding recesses  12 , which are described in more detail with reference to  FIGS. 2 ,  3  and  4 . 
     The electric motor  8  is preferably adjoined by a force sensor  13  for determining the axial forces of the shaft and also the torques, which force sensor  13  is in turn connected to the electronics unit  6 . 
     Between the electric motor  8  and an end area  14  of the first element  1 , the latter has a guide area  15  in its inside, said guide area  15  preferably having a cylindrical configuration. 
     In the end area  14 , a guide element  16  is fitted on the element  1 , this guide element  16  having an inner cross section  17  that corresponds approximately to an outer cross section  18  of the second element  2 . 
     Inner cross section and outer cross section are preferably of polygonal configuration in cross section. In this way it is possible to avoid radial torsion of the element  2  guided in the guide area  15  of the element  1 . It is able to move axially to and fro along a center axis M, but it cannot twist radially. 
     The element  2  is preferably configured almost completely as a polygonal profile with regard to its outer cross section. 
     However, in its end area  19 , its cross section can have another outer contour  20  approximately corresponding to the guide area  15  of the first element  1 . 
     The inside of the element  2 , which is preferably configured as a crown wheel  26  (see  FIG. 4 ), is preferably configured as rotary thread which interacts with the planetary roller system  11 , in particular with the planetary rollers  24 . 
     By means of suitable driving of the drive shaft  10  and sun wheel  25 , the element  2  can move out of the element  1  in the direction of the double arrow X, along a center axis M indicated in  FIG. 1 . 
     The element  2  can be moved axially out of the element  1  until the end area  19  of the element  2  abuts internally against the guide element  16 . 
     In this way it is possible to ensure a very substantial travel of the element  2  relative to the element  1 . 
     In the present invention it is important that the substantial travel can also be achieved by the fact that the element  2  can be moved out axially in relation to the element  1  with absolute precision under very high forces via the planetary roller system  11 , the element  2  being guided via the guide element  16  such that it cannot twist radially relative to the element  1 . 
     However, the scope of the present invention is intended also to cover the case where the element  2  for example is not guided inside the element  1 , but instead engages as an outer sleeve over the latter and receives the element  1  inside it and guides it in a manner secure against torsion. In this case, for example, the planet carrier  12  can lie outside the end area  14  of the element  1  and mesh with a corresponding inner thread  21  of the element  2 . 
     The scope of the present invention is also intended to cover the case where, for example, the cross section of the end area  19  of the element  2  has a round, polygonal, many-cornered or other configuration in cross section, in order to ensure axial and radial guiding relative to the element  1 , in which case a securing against torsion is not absolutely essential, because said securing against radial torsion can be ensured via the guide element  16  between elements  1  and  2 . 
     Between the end area  19  and the guide element  16 , a receiving space  23  for accommodating sensors, force sensors, displacement sensors or the like can be provided inside the guide area  15 . 
     In the illustrative embodiment according to  FIG. 2 , a housing  27  is shown which has an approximately cylindrical configuration and has a plurality of radial recesses  12  in a circumferential surface  28 . 
     Between the individual radial recesses, individual bridge elements  29  are formed from the circumferential surface  28  and enclose an obtuse angle β, and a bridge apex  30  is oriented toward the center axis M. 
     As is indicated in  FIGS. 3 and 4 , the respective bridge apices  30  and the bridge elements  29  enclose an angle γ of approximately 120° relative to one another. 
     A recess  12  is formed in each case between the respective bridges  29 , and the individual recesses  12  in end areas in the circumferential surface  28  of the housing  27  have receiving pockets  31 , as is indicated in particular in  FIG. 2 . Inside walls  32  of the receiving pockets  31  can be oriented parallel to one another, or, as is indicated in particular in  FIG. 3 , they can be configured widening conically inward toward the center axis M, thus serving to support a shaft end  33  of the planetary roller  24 . In this way, the planetary roller  24  can bear inside the receiving pockets  31 . 
     However, the scope of the invention is also intended to cover the embodiment in which the inside walls  32  can be oriented parallel to one another. 
     The respective recesses  12  and receiving pockets  31  are arranged or spaced apart relative to one another at an angle α preferably of approximately 120° in relation to the center axis M. 
     When three planetary rollers  24  are fitted into the respective recesses  12  and receiving pockets  31 , they are able to be engaged centrally by the drive shaft  20  or a sun wheel  25  and interact with a crown wheel  26  in order to move the two elements  1  and  2  linearly in relation to one another.