Abstract:
An apparatus for converting a rotary motion into an axial motion, is used as overload protection; the force transmitting elements of the conversion apparatus, in the form of a threaded spindle, a nut and/or the intervening planetary rollers and roller bodies, are made with different contours of deformable, preferably elastically deformable material.

Description:
FIELD OF THE INVENTION 
     The invention relates to a use of an apparatus for converting a rotary motion into an axial motion or vice versa. 
     DESCRIPTION OF THE RELATED ART 
     FIGS. 1 a  and  1   b  show, in section and plan view respectively, a spindle  1 , which by way of example may be the end of a drive motor shaft. Provided on the spindle  1  is preferably a simplex fine thread  10 , which in turn has a pitch S of 0.3 to 0.25 mm or less. 
     Also, a number of rollers or roller bodies  3   a-   3   f , for instance six, which are shown in FIG. 1 a  in section and in FIG. 1 b  in plan view, are disposed in the mounted state of the spindle arrangement in planetlike fashion between the spindle  1  and a nut  2 . A correspondingly finely embodied groove contour  31 , comprising grooves of a certain spacing extending next to one another and parallel, is also provided on predetermined segments on the rollers or roller bodies  3   a-   3   f . The groove contour  31  facing toward the spindle  1  that will hereinafter be called the spindle-side contour. Because of this constant groove spacing and the groove depth, an exact engagement with the thread  10  of small pitch on the spindle  1  is assured. 
     Between the segments formed on the individual rollers or roller bodies  3   a-   3   f , coarse guide grooves  32  of V-shaped cross section are also formed, which will hereinafter be called the nut-side contour. The spacing of the guide grooves  32  is exactly the same as that of guide grooves  20 , which are formed in the interior of the spindle nut  2 . The guide grooves  20  are also of V-shaped cross section, and mate with the guide grooves  32  of the roller or roller bodies  3  (i.e.,  3   a-   3   f ). 
     In order that all the rollers or roller bodies  3  will mesh exactly and reliably both with the nut-side groove contour of a certain spacing in the interior of the nut  2  and with the spindle  1  of small thread pitch, the spindle-side groove contour  31  on each of the planetary rollers is disposed with a specific pitch offset that is constant from roller to roller and is fixed as a function of the total pitch to be attained. 
     In this way the rollers or roller bodies  3   a-   3   f  in the intended intermediate segments each has a different pitch offset, with respect to the fine contour  31 . The rollers  3  must therefore be disposed in a very specific order, to which end a suitable identification is provided on individual rollers  3 , for instance on the face end. 
     When the pitch of the fine thread on the spindle  1  is 0.3, for instance and with a corresponding spacing of the groove pitch, this would mean a pitch offset or displacement of 0.05 mm from one roller to another, or expressed in degrees, 60° of angle between each pair of the six illustrated rollers  3   a-   3   f . Or expressed in another way, when counting begins at a certain roller, the pitch offset of the contour  31  of the nth roller is equal to the product of the (number of the particular roller of interest −1)×360°/total number of rollers. 
     In an alternate, second embodiment, the planetary rollers are provided with a thread of positive or negative pitch and the spindle is analogously provided with grooves. The nut-side guide grooves of the rollers and the corresponding guide grooves of the nut remain as described above. However, in the second embodiment a cage is necessary that keeps the planetary rollers spaced apart angularly from one another. 
     Such an apparatus for converting a rotary motion into an axial motion is described in U.S. Pat. No. 4,926,708, the contents of which are incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     According to the invention, such an apparatus for converting a rotary motion into an axial motion and vice versa is used for overload protection. 
     In accordance with an advantageous further feature of the invention, the apparatus used for converting a rotary motion into an axial motion is further embodied such that the force transmitting elements, namely the threaded spindle, the nut and/or the rollers or roller bodies having the various contours are made from deformable, preferably elastically deformable material. The elastically deformable material of the force transmitting elements is preferably polymer material or suitable deformable or elastically deformable materials. 
     Thus if in the known apparatus for converting a rotary motion into an axial motion the force transmitting elements, especially the rollers or roller bodies with the different contours, are made of deformable or elastically deformable material, such as a polymer and the like, a system pitch change dependent on the load is obtained that can be used and exploited as overload protection. Such a system pitch change can also be established not only as a function of load but also via the rpm and the prestressing of the entire spindle system. This in turn means that if there is major prestressing in the low rpm, a greater force transmission results, with attendant major protection against overload. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other objects and the nature and advantages of the present invention will become more apparent from the following detailed description of an embodiment [s] taken in conjunction with drawings, wherein: 
     Shown in the drawings are: 
     FIG. 1 a , sectional views of the essential elements of an embodiment of an apparatus for converting a rotary motion into an axial motion; 
     FIG. 1 b , partly in plan view and partly in the form of a sectional view, the same elements of the embodiment shown in FIG. 1 a ; and 
     FIG. 2, a diagram in which changes in pitch for various thread pitches of the rollers are shown. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the apparatus for converting a rotary into an axial motion the spindle  1  is rotated counter to the nut  2 , then its thread  10  rolls along inside the threads of the rollers  3   a , which in turn with their peripheral grooves  32  roll along the lands of the nut  2 . The contouring of the spindle and the rollers creates a forward thrust, whose magnitude depends on the characteristic geometry of the roller spindle drive. 
     In order to be able to use the apparatus as overload protection, one or more elastic transmission elements are used in the present invention. Then, because of load-dictated elastic deformation, the rolling geometry of the spindle  1 , rollers  3  and/or nut  2  varies. The thus-varied geometrical data (or, geometry) directly affect the total pitch of the roller spindle drive, as can be clearly seen from the pitch change in FIG. 2, which will later be described in detail. 
     The spindle-side contour  31  of the rollers or roller bodies  3  that are disposed in planetary fashion around the spindle  1  will vary with the axial force between the spindle  1  and the nut  2  (overloading force). This variation can be embodied either in the form of a thread pitch (S P =S S ; S P =−S S ) or as a groove contour (S P =0, without pitch) where S S  designates the spindle pitch and S P  designates the pitch of the planetary roller bodies. 
     For example, if the rollers  3  are of elastic polymer, then axial stress will deform each of them, causing each groove contour  31  adjacent to the nut  2  to be displaced axially, or offset, relative to the axial position of the same groove contour  31  on the opposite side of the roller  3 , where that groove contour  31  engages the thread  10  of the spindle  1 . This offset tilts each contour groove  31 , creating a virtual pitch S P . 
     The total pitch S ges  is dependent on the rolling circle diameters D M  of the nut  2  and D S  of the spindle S, on the spindle-side rolling circle diameters D PS  of the rollers or roller bodies, on the nut-side rolling circle diameters D PM  of the rollers or roller bodies, and on the pitches S S  and S P , and can be expressed as follows:          S   ges     =             D   PS       D   S            S   S       +     S   P             D   PM       D   M       +       D   PS       D   S                                  
     Especially in an embodiment in which the pitches of the spindle and of the rollers or roller bodies are the same, that is, S P =S S , the overload protection becomes pronounced, as can also be seen from the diagrams in FIG.  2 . Letting D P =(D M −D S )/2, if D P /D S =1 (one), the total pitch of the apparatus for converting a rotary into an axial motion is zero (0). However, this also applies for all the other three possible embodiments of the apparatus for converting rotary into axial motion with an arbitrary total pitch. 
     In the diagram in FIG. 2, on the ordinate, the total pitch S ges  is plotted over the pitch S S , and plotted on the abscissa is the quotient of the rolling circle diameters D P  and D S , that is, D P /D S . A zero line is also shown as a heavy solid line, at the point on the ordinate marked 0.00. The graph beginning approximately at the ordinate value of 4.00, with rectangles entered at regular intervals, indicates a pitch ratio S ges /S S  if S P =S S . The graph beginning below the ordinate value of 1.00, with triangles entered at regular intervals, applies to a pitch ratio S ges /S S  at which the pitch S P  of the planetary rollers or roller bodies  3  is zero (0), or in other words S P =0. 
     The graph beginning in the diagram at the ordinate value above −3.00, with diamonds plotted at regular intervals, applies to a pitch ratio at which the spindle pitch −S S  is equal to the planetary roller pitch S P ; that is, S P =−S S . 
     In the diagram of FIG. 2, the above-described graphs with the diamonds entered at regular intervals describe a variable, load-dependent system pitch change, since the lower graph (with the diamonds plotted at regular intervals), beginning at a negative drive (beginning at the ordinate value −3.00), intersects the zero line of the ordinate at an abscissa value of one and then changes over to a positive drive. 
     Under a relatively heavy load, this variable load-dependent system pitch change thus means a zero pitch (that is, a standstill in terms of drive) and after that a reversal of direction. 
     The pitch of the spindle system is accordingly zero if the two rolling diameters are of equal magnitude (D P /D S =1) as a result of an excessive increase in load. This operating principle is designated in the application as overload protection.