Abstract:
A pivot has identical first and second members partially engaged in each other and mobile in rotation relative to each other about a common axis, against the action of at least two return leaf springs each having first and second ends anchored in the first and second parts, respectively, by being wedged inside them.

Description:
[0001]    This application is a continuation of International PCT Application N o  PCT/FR00/02407 filed on Aug. 31, 2000, which designated the United States.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a pivot with leaf springs. The pivot includes identical first and second members partially engaged in each other and rotatable relative to each other about a common axis, against the action of a return leaf spring which has first and second ends anchored in said first and second members, respectively.  
           [0004]    2. Description of the Prior Art  
           [0005]    Pivots of the above type are used in many applications where a device or member is mounted so that it can rotate through a small angle against a return force. Examples of such devices or members include measuring instrument pointers, oscillating mirrors, the platforms of scales, etc.  
           [0006]    French patent No. 2 199 370 discloses a pivot of the above kind including two identical and axially aligned sleeves; each sleeve has an extension designed to be accommodated in a recessed portion of the other sleeve. Two crossed leaf springs elastically couple the two sleeves, which can turn relative to each other through a small angle and against the action of return forces exerted on the sleeves by the leaf springs. The leaf springs are anchored in axial grooves formed in the two sleeves.  
           [0007]    The leaf springs can be welded into the grooves if the leaf springs and the sleeves are made of metal. However, the heating of the leaf springs during welding degrades their mechanical characteristics uncontrollably, especially when they are very thin, as is the case when the pivot is used to mount a delicate mechanical member such as a pointer, for example. This can falsify the equilibrium or rest position of the supported member and degrade the reliability of the assembly.  
           [0008]    An adhesive can also be used to fix the leaf springs in the grooves. The physical and chemical characteristics of the adhesives unfortunately deteriorate over time or because of the environment (vacuum, extreme temperatures), especially in space.  
           [0009]    A specific object of the present invention is to provide a pivot with flexible connections of the type described in the preamble to this description that is free of drawbacks referred to hereinabove.  
         SUMMARY OF THE INVENTION  
         [0010]    The above object of the invention and others that will become apparent on reading the following description are achieved by a pivot with flexible connections including identical first and second members partly engaged in each other and rotatable relative to each other about a common axis against the action of a return leaf spring having first and second ends anchored in the first and second members, respectively.  
           [0011]    In one embodiment of the invention, each of the ends of the leaf spring is wedged in an axial housing provided in one of the members, between a wall portion of the housing and a pair of superposed wedges gripped between another wall portion of the housing and the leaf spring.  
           [0012]    In another embodiment of the present invention each of said leaf spring ends is shaped as a loop designed to be received in an axial housing of complementary shape in one of said members and a conical pin is forced inside said loop to expand it and wedge it in the housing.  
           [0013]    An axially split cylindrical ring is advantageously slid into said looped end, between it and said conical pin.  
           [0014]    Other features and advantages of the present invention will become apparent on reading the following description and examining the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a perspective view of a first embodiment of a pivot according to the invention with two leaf springs.  
         [0016]    [0016]FIG. 2 is a partly cut-away view of the pivot shown in FIG. 1, revealing its internal structure.  
         [0017]    [0017]FIG. 3 is an exploded view of a second embodiment of the present invention with three leaf springs.  
         [0018]    [0018]FIG. 4 is an exploded view of a third embodiment of the invention.  
         [0019]    [0019]FIG. 5 is a partly cut-away view of the FIG. 4 embodiment when assembled.  
         [0020]    [0020]FIG. 6 shows a detail of the embodiment shown in FIGS. 4 and 5. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    The embodiment of a pivot in accordance with the invention shown in FIG. 1 includes identical first and second members  1 ,  2  that are partly slid inside each other so that together they form a substantially circularly cylindrical pivot allowing one of the two members to rotate relative to the other about the axis X of the pivot.  
         [0022]    The member  1  is formed of two parts  1   a,    1   b  aligned with each other along the axis X. The portion  1   a  has a circularly cylindrical outside surface and a substantially semicylindrical recess. The portion  1   b  takes the form of a foot with a substantially semicylindrical outside shape.  
         [0023]    The member  2  is formed of portions  2   a,    2   b  with exactly the same geometry as the respective portions  1   a,    1   b  of the member  1 .  
         [0024]    As shown in FIG. 1, the members  1  and  2  are slid axially inside each other so that the foot  1   b,    2   b  of one of them is accommodated in the substantially semicylindrical recess in the respective portion  2   a,    1   a  of the other.  
         [0025]    As can also be seen in FIG. 1, the foot  1   b  of the member  1  has a circularly cylindrical surface  3  whose radius is slightly less than that of the recess in the member  2   a  and two flat axial surfaces  4 ,  5  parallel to the axis X over the full height of the foot  1   b.  The surfaces  4 ,  5  are designed to cooperate with similar surfaces  6 ,  7  in the recess in the portion  2   a  to serve as abutments defining the maximum relative angular movement of the members  1 ,  2  relative to each other.  
         [0026]    Pivots with leaf springs are essentially used to support members which rotate through a small angle, such as an oscillating mirror for sweeping a light beam over a surface, for example. The abutment surfaces  4 ,  5 ,  6 ,  7  define the limits of such rotation accurately.  
         [0027]    As indicated above, the foot  1   b  of the member  1  and the recess in the portion  2   a  of the member  2  are substantially semicylindrical, rather than strictly semicylindrical, because the surfaces  4 ,  5 , on the one hand, and the surfaces  6 ,  7 , on the other hand, are not able to lie in a common plane passing through the axis X; their inclination relative to each other defines the permitted amplitude of their relative rotation.  
         [0028]    Of course, the foot  2   b  of the member  2  is shaped like the foot  1   b  of the member  1 . Likewise the portions  2   a  and  1   a  of the members  2  and  1 , respectively.  
         [0029]    Two leaf springs  8  and  9 , seen more completely in the partly cut-away view of FIG. 2, couple the members  1  and  2 . Thus the leaf spring  8  is mounted between the foot  1   b  of the member  1  and the portion  2   a  of the member  2  and the leaf spring  9  is mounted between the foot  2   b  of the member  2  and the portion  1   a  of the member  1 . The planes of the leaf springs  8  and  9  are axial and crossed; they are preferably perpendicular to each other.  
         [0030]    In accordance with the present invention, the leaf springs  8  and  9  have ends in the form of respective open loops  8   1 ,  8   2  and  9   1 ,  9   2  so that they can be inserted in complementary axial cylindrical housings in the members that they couple. Accordingly, as shown in FIG. 2, the looped ends  8   1 ,  8   2  of the leaf spring  8  are slid into the housings  10 ,  11  in the portion  2   a  of the member  2  and in the foot  1   b  of the member  1 , respectively. The leaf spring  9  is similarly disposed with one of its ends in the axial housing  10 ′ and the other in the axial housing  11 ′. Note, incidentally, that the axial housings  10 ,  11  and  10 ′,  11 ′ extend from one end of the pivot to the other; this is to facilitate fabrication of the members  1 ,  2 .  
         [0031]    Clearly rotation of one of the members  1 ,  2  relative to the other flexes the leaf springs  8 ,  9 , which then apply to the members to which they are fastened a return torque toward an angular rest position in which the leaf springs are not subject to any flexing force.  
         [0032]    Although in principle the pivot could include only one leaf spring, it is preferable to use an arrangement with two leaf springs to compensate any drift that could affect the stiffness of the leaf springs in the long term, so improving axial guidance by the more balanced radial stiffness obtained with this kind of arrangement.  
         [0033]    According to one important feature of the present invention, the looped ends of the leaf springs  8 ,  9  are anchored into the members that they couple by wedging them into the latter. As is more clearly apparent in FIG. 2, in the partly cut-away view of the looped end  9   1  of the leaf spring  9 , the wedging effect is obtained by means of a split cylindrical ring  12  and a conical pin  13  slid successively into the looped end after installing the latter in the axial housing provided to receive it in the member  2 .  
         [0034]    The diameter of the split ring  12  is chosen to allow it to be inserted into the looped end  9   1 . The ring  12  has a conical interior matching the conical shape of the pin  13 .  
         [0035]    Inserting the conical pin  13  into the ring  12  expands the ring, which then wedges the looped end  9   1  in the housing that receives it, to immobilize it there.  
         [0036]    The conical internal shape of the ring  12  improves the wedging effect because it distributes uniformly the clamping forces needed to obtain the wedging effect from one end to the other of the looped end portion.  
         [0037]    When assembling the pivot, the ring  12  also isolates the leaf spring from the conical pin  13  with respect to axial forces that only the latter could transmit to it. Axial forces could shift, deform or prestress the leaf spring, to the detriment of reproducible performance of the pivot.  
         [0038]    The four looped end portions of the leaf springs  8  and  9  can therefore be fixed into the pivot according to the invention.  
         [0039]    [0039]FIG. 3 shows a second embodiment of the invention constituting a variant of the pivot shown in FIG. 2. In this figure and the subsequent figures, reference numbers identical to those used in the previous figures, possibly with an appended′ or ″, indicate identical or similar elements or members. The FIG. 3 pivot differs from the FIG. 2 pivot essentially in that the members  1  and  2  are coupled by three leaf springs  8 ′,  9 ′ and  14 , rather than by only two leaf springs. In the FIG. 3 exploded view, it can be seen that a central leaf spring  14  whose axial width is substantially twice that of the end leaf springs  8  and  9  is slid into the pivot between the latter, whose flat portions are substantially coplanar and at 90° to that of the central leaf spring  14 . The ends of the leaf springs are all fixed by wedging them using rings like the ring  12  and pins like the pin  13 , which are not shown in order to simplify the figure. The central leaf spring  14  then straddles the middle part of the pivot and increases its resistance to radial forces.  
         [0040]    A third embodiment of a pivot according to the invention is described next with reference to FIGS.  4  to  6 . In the FIG. 4 exploded view it can be seen that this embodiment, like that of FIG. 3, includes three leaf springs or groups of leaf springs  8 ″, ( 14 ′ 1 ,  14 ′ 2 ) and  9 ″.  
         [0041]    In the FIG. 5 view of the assembled pivot, in which the member  2  is cut away, it can be seen that the two central leaf springs  14 ′ 1 ,  14 ′ 2  are adjacent and in contact. They are therefore equivalent to a single leaf spring with a width equal to the sum of those of the leaf springs  14 ′ 1 ,  14 ′ 2 . Dividing the single leaf spring into two portions can facilitate its fabrication.  
         [0042]    The leaf springs  8 ″ ( 14 ′ 1 ,  14 ′ 2 ) and  9 ″ are perfectly flat and thus differ from those of the embodiments shown in FIGS.  1  to  3  in the absence of loops at the ends.  
         [0043]    They further differ in terms of the means used to immobilize their edges by wedging them in the axial housings of the members  1  and  2  that receive them. Those means are shown in more detail in FIG. 6, which shows by way of example the wedging of one end  8 ″ 1 , of the leaf spring  8 ″ into one of the two axial housings  15 ,  15 ′ of the member  1 , here the housing  15   1 .  
         [0044]    In this figure it can be seen that the axial housing  15  has a wall consisting of a cylindrical portion  15   1  and a flat portion  15   2  on which the end  8 ″, of the leaf spring  8 ″ bears.  
         [0045]    To immobilize the end of this leaf spring against this flat portion, the invention uses superposed first and second wedges  16  and  17  which are conformed to co-operate to clamp the leaf spring with a “wedging effect”.  
         [0046]    To this end the wedge  16  has a cylindrical lateral portion  16   1  that substantially conforms to the cylindrical portion  15   1  of the housing  15  and a flat surface  16   2  inclined to the axis of its cylindrical lateral surface.  
         [0047]    The wedge  17  generally conforms to the wedge  16  but further includes a second flat surface  17   1  parallel to the axis of its cylindrical surface. The second flat surface is adapted to be pressed against the leaf spring  8 ″, as shown in FIG. 6.  
         [0048]    To assemble the various components of the pivot shown in FIG. 4, first of all the members  1  and  2  are nested one inside the other, with their respective axial housings aligned. The leaf springs  14 ′ 1    14 ′ 2  are then slid into the latter, with two thin washers  18   1 ,  18   2  between them to prevent their adjacent edges rubbing. As an alternative to this, as mentioned above, the two leaf springs  14 ′ 1 ,  14 ′ 2  could be replaced by a single leaf spring of twice the width.  
         [0049]    Cylindrical keys  19   1 ,  19   2  are then slid into the axial housings to receive the ends of the leaf springs  8 ″ and  9 ″, as explained later, to fix the wedges.  
         [0050]    The leaf springs  8 ″and  9 ″are then inserted in the axial housings, followed by the respective pairs of wedges  16 ,  17 , the wedges of each pair bearing on each other through their flat faces inclined to the axes of their cylindrical surfaces. The length of the keys  19   1 ,  19   2  is adjusted so that, after the leaf springs  8 ″,  9 ″and the wedges  17  have been abutted against the keys, the wedges  16 ,  17  are substantially flush with the outlets of the axial housings  15 ,  15 ′.  
         [0051]    Hitting a wedge  16  in the direction of the arrow F (see FIG. 6) with the corresponding wedge at the other end of the axial housing  15  held in place by an abutment in that housing causes the wedge  16  to slide over the wedge  17  until the cylindrical surface  16   1  of the wedge  16  is stopped by the cylindrical surface  15   1  of the axial housing. Note that the flat surfaces of the wedges  16 ,  17  in contact are then inclined to the axis of the housing.  
         [0052]    The wedging effect due to the sliding on each other of the flat surfaces of the wedges  16 ,  17  then immobilizes the end  8 ′ 1  of the leaf spring  8 ″ in the axial housing  15  by clamping that end against the flat part  15   2  of the housing. The other ends of the leaf springs  8 ″ and  9 ″ and the leaf springs  14 ′ 1 ,  14 ′ 2  are immobilized the same way. For the latter two leaf springs, however, percussion tools must be used of a size that can enter deeply into the axial housings that receive the leaf springs.  
         [0053]    The pivot shown in FIGS.  4  to  6  has various advantages. First of all, it includes flat leaf springs, which are easier to fabricate than the leaf springs with looped ends of the pivots shown in FIGS.  1  to  3 , and less likely to be damaged by the heat treatment that they must undergo. Above all, the dimensional tolerances in respect of these leaf springs can be less strict, because the bearing surface  17   1  of the wedge  17  on the leaf spring is away from the end of the leaf spring, so that the length of the latter can therefore vary somewhat without affecting its immobilization. All these features mean that the pivots shown in FIGS.  4  to  6  can be fabricated at low cost.  
         [0054]    Various fabrication techniques, such as molding or spark erosion, for example, can be used to fabricate the members  1  and  2  of the pivot according to the invention, those techniques being able to produce members of this kind with relatively complex shapes.  
         [0055]    It is now apparent that the invention achieves the stated object. Fixing the leaf springs by wedging them does not degrade the mechanical characteristics of the leaf springs, unlike fixing by welding, and is insensitive to aging and to environmental constraints encountered in space, unlike fixing by gluing. Thus reliable pivots with well-defined and stable performance are produced. Simulating the behavior of this kind of pivot is then easier, so that its performance can be controlled more closely and more reliably. The embodiment shown in FIGS.  4  to  6  is also particularly economical to fabricate.