Abstract:
In order to provide a universal joint suitable as a small diameter joint capable of transmitting a large torque and having a high rotational precision and a high durability at a low cost, the universal joint is a kind of spring ring joints coupling a driven shaft with a driving shaft, for which an angle formed by their axis lines is not great, constructed so as to deal with deviations of the axis lines with respect to each other, owing to the fact that thin bending plates made of glass fiber reinforced polyimide bend. Linking boss portions supporting the bending plates and an intermediate disk are made of a high duty aluminium alloy for elongation having a high tenacity by die cast. A part of the linking boss portions and the intermediate disk is formed as protruding arbors for caulking and the bending plates are jointed directly therewith by caulking.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a joint having a small diameter and in particular to a universal joint having a high durability, which couples two dynamic force transmitting shafts deviated slightly in an angular direction from each other. 
     DESCRIPTION OF THE PRIOR ART 
     FIGS.  7 ( a ) and  7 ( b ) show a bending joint  700  made of a light alloy by mechanical processing in one body, having a small diameter and suitable for dynamic force transmission; FIG.  7 ( a ) being a side view shown in a direction perpendicular to an axis line, FIG.  7 ( b ) being a side view shown parallelly to the axis line. A first slit  702  is formed, which traverses an axis line S in a cylinder cutting direction perpendicular to the axis line S, starting from a cylindrical surface  701 , leaving a part exterior to a chord C forming a center angle of about 90° C. Then a second slit  703  is formed similarly and parallelly to the first slit  702  in a reverse direction at a position separated from the first slit  702  by a small distance d along the axis line S, the slits forming a pair. 
     Further a third and a fourth slit  704  and  705  forming another pair are formed in an orthogonal direction with respect to the pair formed by the first and the second slit  702  and  703  at a position separated from the second slit  703  by the same distance d similarly to the pair formed by the first and the second slit  702  and  703 . Still further a pattern of the first slit  702  to the fourth slit  705  is repeated with the same separation distance d from the fourth slit  705 . By forming such slits  702  to  705  in series, even if a mounting axis line Se of a driven shaft  712  is deviated with respect to a driving shaft  710 , deviation can be absorbed by variations of widths δof the slits  702  to  705  and it is possible to deal therewith flexibly for transmitting rotation between the different axis lines. 
     Such a bending joint  700  is less flexible than a bending joint, in which a slit is formed in spiral and it has a smaller region of angular deviation between axis lines to be connected. However, since it can deal therewith for either rotational direction, forward or reverse, it has a high mechanical strength, and rotation transmission precision increases with increasing dynamic force transmitting torque, it is excellent in safety, reliability and durability. 
     However formation of the first slit  702  to the fourth slit  705  includes a number of fabrication steps and it is difficult to expect so as to have a high processing precision. Even if the processing is automated, since one cannot help relying on mechanical cutting processing, equipment investigation and production cost cannot be reduced. Further, since it is formed in one body, it is poor in adaptability, in case where dynamic force transmitting shafts having different diameters should be coupled. Further, since the different slits  702  to  705  traverse the axis line S of the bending joint  700 , transmitted torque is absorbed by center displacement due to twisting deformation of linking parts  706  and according to measurements a relationship between rotation angle and torque cannot be represented not by a smooth curve but by a waveform. This is a problem, to which attention should be paid, particularly when it is applied to a mechanism such as an encoder, etc., to which precise angle transmission is necessary. 
     Moreover a universal joint disclosed in Japanese Utility Model Publication No. Hei 7-52428(B) solves the problem and contributes to not expensive supply thereof, because mass- production is possible therefor. However external shape thereof is somewhat complicated and one cannot help relying on manual work for linkage of two members by means of screws at mounting. Moreover, since throughholes required for making; screws pass through are formed in the neighborhood of a hole for the dynamic force transmitting shafts, thickness of parts linked by means of screws, to which load to be transmitted is applied, is reduced, which causes decrease in mechanical strength, and durability decreases due to variations in stress during rotation given repeatedly to the throughholes. Since a certain thickness remaining after formation of the throughholes is necessary, down-sizing for the purpose of space saving is limited even at the sacrifice of mechanical strength and it is unsuitable for a universal joint having an outer diameter smaller than 20 mm. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a universal joint at a low cost, which can deal with a great torque to be transmitted not at the sacrifice of strength and suitable for a coupling having a small diameter producing no errors of rotational angle transmission and having a high precision as well as a high durability. 
     In order to achieve the above object a universal joint according to the present invention having a bending coupling structure comprises a pair of thin bending plates, each of which has a basic shape of a ring; a pair of linking boss portions, each of which supports deformably one of the thin bending plates at two points in the neighborhood of two extremities of a diameter on a one-side surface thereof; and an intermediate disk supporting the thin bending plates similarly at two points on each surface in the neighborhood of two extremities of a straight line orthogonal to the diameter. 
     The linking boss portions and the intermediate disk are made of a high duty aluminium alloy for elongation having a high tenacity or other equivalent materials by die cast and a round plain arbor for caulking protruding from the center of each of supports holding the thin bending plates, which secures directly one of the bending plates, is formed in one body therewith. 
     The high duty aluminium alloy is an Al-Mg-Cr alloy (hydronarium or hydro) and each of the bending plates is a thin plate, whose thickness is smaller than 0.6 mm, made of glass fiber reinforced polyimide or another equivalent synthetic resin. Further the bending plate may be a thin plate made of carbon fiber reinforced epoxy resin or another equivalent resin, whose thickness is smaller than 0.8 mm. 
     Moreover it is preferable to form the bending plate by superposing a stainless steel thin plate having a same shape, whose thickness is smaller than 0.4 mm, on the synthetic resin thin plate. In addition, the round plain protruding arbor for caulking may be constructed in one body by insert formation using another suitable member at the die cast formation of each of the linking boss portions and the intermediate disk. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view showing an embodiment of the universal joint according to the present invention; 
     FIG.  2 ( a ) is a side view of a mounted universal joint in the embodiment indicated in FIG. 1, viewed in a direction perpendicular to an axis line, indicated partly in cross section; 
     FIG.  2 ( b ) is a side view of the mounted universal joint, viewed along the axis line; 
     FIG.  3 ( a ) is a side view of the intermediate disk in a second embodiment of the universal joint according to the present invention, indicated partly in cross-section; 
     FIG.  3 ( b ) is a side view of the universal joint having a linking member different from that indicated in FIG.  3 ( a ); 
     FIG. 4 is an exploded perspective view similar to FIG. 1 for explaining the intermediate disk in a third embodiment of the universal joint according to the present invention; 
     FIG.  5 ( a ) is a cross-sectional view in a plane passing through the axis line, showing means for fixing a linking boss portion in a fourth embodiment of the universal joint according to the present invention; 
     FIG.  5 ( b ) is a side view thereof viewed in an axial direction; 
     FIG.  6 ( a ) is a side view showing means for fixing a linking boss portion in a fifth embodiment of the universal joint according to the present invention, viewed in a direction perpendicular to the axis line; 
     FIG.  6 ( b ) is a cross-sectional view thereof, cut along a line B—B in FIG.  6 ( a ); 
     FIG.  7 (a) is a side view showing a prior art universal joint, viewed in a direction perpendicular to the axis line; and 
     FIG.  7 ( b ) is a side view thereof, viewed along the axis line. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinbelow several embodiments of the universal joint according to the present invention will be explained, referring to the drawings, in which FIG. 1 is an exploded perspective view showing an embodiment of the universal joint  10  according to the present invention; FIG.  2 ( a ) is a side view of a mounted universal joint, viewed in a direction perpendicular to an axis line, indicated partly in cross section; and FIG.  2 ( b ) is a side view thereof, viewed along the axis line. For convenience&#39;s sake the right side in the figures is a driving side, while the left side is a driven side. 
     In FIGS. 1,  2 ( a ) and  2 ( b ), reference numeral  11  is a linking boss portion, in which a hole  13 , into which a driving shaft  12  is inserted, is formed, while  14  is a linking boss portion, in which a hole  16 , into which a driven shaft  15  is inserted, is formed. It is fabricated always with a same shape and size except for the diameter of the shaft.  17  is a ring-shaped intermediate disk. A central throughhole  18  is formed therein so that the inner diameter d 1  thereof is equal to or greater than the diameter d 2  of the driven shaft  12  and the driving shaft  15 . 
     The driving shaft linking boss portion  11 , the driven shaft linking boss portion  14  and the intermediate disk  17  are made of a hydronarium die cast product (HD-3) (hydro or hydra), which is an Al-Mg-Cr high duty aluminium alloy, or another equivalent material. Supports  19 ,  20  are disposed protrudingly in the axial direction at the neighborhood of two extremities of straight lines on one surface  11   a ,  14   a  of each of the linking boss portions  11  and  14  and both surfaces  17   a  and  17   b  of the intermediate disk  17 . Further round plain arbors for caulking  21  and  22  extend respectively from supporting surfaces  30  and  33  of the supports  19  and  20  by a predetermined length.  23  represents a bending plate having a basic shape of a ring. The inner diameter d 3  of a central opening  24  is so determined that the remaining annular outer peripheral portion can flexibly deal with bending while maintaining a certain strength capable of transmitting a required torque and that it can bear repeated deformation. In the present embodiment, 4 chords, outside of which every 2 arch portions opposite to each other or both the sides of the central opening  24  are cut away, define a square. Caulking holes  28  and  29  are formed in the neighborhood of extremities of diameters  26  and  27  corresponding to the two diagonals of this square at positions corresponding to the protruding arbors for caulking  21  and  22 , which are engaged respectively with the caulking holes  28  and  29 . 
     The bending plate  23  is a polyimide thin plate, a glass fiber reinforced polyimide thin plate, a carbon fiber reinforced epoxy thin plate or another equivalent synthetic resin thin plate. A thickness of the plate is selected between 0.2 and 0.6 mm, depending on the torque to be transmitted or an environment, in which it is used, or a stainless steel thin plate having the same shape as the thin plate (not shown) is superposed thereon to be used in order to take measures to meet severe conditions. 
     Now mounting of the universal joint according to the present embodiment will be explained. The respective protruding arbors for caulking  21  of the driving shaft linking boss portion  11  and the driven shaft linking boss portion  14  are inserted into the corresponding caulking holes  28  with a washer  31  for each of them. Thereafter extremities of the protruding arbors for caulking  21  are deformed by press to form caulking heads  21   a . Each of the bending plates  23  is secured to the supporting surface  30  of the supporter  19  by joining by press and at the linking boss portion  11 ,  14  it is supported deformably around the supporting surface  30  as a fulcrum owing to a space formed by a step between each of the one-side surfaces  11   a ,  14   a  and the supporting surface  30  of each of the supports  19 . 
     Then the bending plates  23 , which are supported by the driving shaft linking boss portion  11  and the driven shaft linking boss portion  14 , respectively, are set opposite to each other and the intermediate disk  17  is put therebetween. That is, for each of the bending plates  23 , the corresponding protruding arbors for caulking  22  on the intermediate disk  17  are inserted into the remaining holes  29  on the diameter  27  orthogonal to the diameter  26 , on which the caulking holes  28  are fixed to the two linking boss portions  11  and  14 , with washers  31  and thereafter extremities of the protruding arbors for caulking  22  are deformed by press to form caulking heads  22   a . 
     Access holes  32 , which are at positions in both the linking boss portions  11  and  14 , corresponding to the caulking holes  29  in the bending plates  23 , are extra holes used only for inserting a caulking tool (not indicated in the figures) for caulking work, but it has effects to lighten the universal joint  10  itself, independently from strength and to reduce rotational inertia. Each of the bending plates  23  is secured to the supporting surface  33  of the support  20  by joining by press. Each of the bending plates  23  is supported deformably around a surface contacting with the supporting surface  33  as a fulcrum owing to a space formed by a step between each of the surfaces  17   a  and  17   b  of the intermediate disk  17  and the supporting surface  33  of each of the supports  20 . 
     As described above, it is possible to deal with deviation in the axis line between the driving shaft and the driven shaft owing to the fact that the two annular thin bending plates  23  supported deformably between the linking boss portions  11  and  14  opposite to each other on both the sides of the intermediate disk  17 . Consequently, e.g. within a high precision apparatus, it is possible to transmit precisely movement with a same rotational speed (angle) from the driving shaft to the driven shaft, whose axis line is approximately in accordance with the axis line of the former. Further polyimide resin, of which the bending plates  23  are made, has a high heat resistance and it can endure satisfactorily a high temperature environment (about 400° C.), including self heat production due to repeated deformation during high speed rotation. 
     In the embodiment described above, since a material having a high elongating property and a high tenacity, for which caulking processing is possible, is used for both the linking boss portions  11  and  14  as well as the intermediate disk  17 , the protruding arbors for caulking  21  and  22  are formed by making the same material as both the linking boss portions  11  and  14  as well as the intermediate disk  17  extend therefrom. On the contrary, as indicated in FIGS.  3 ( a ) and  3 ( b ) in a second embodiment, separate members  221  and  222  may be buried by insert formation in intermediate disks  171  and  172  as linking members for the bending plate  23 . In the embodiment described below, same reference numerals are used for the members corresponding to those indicated in the preceding embodiment. 
     Suitable rivet members  221  are buried by insert formation in the intermediate disk  171  indicated in FIG.  3 ( a ) and used for caulking similarly to the preceding embodiment. In the intermediate disk  172  indicated in FIG.  3 ( b ) headless bolts  222  are buried by insert formation. The bending plates  23  are fixed by means of nuts  124  and adhesive product  125  is used in order to prevent loosening thereof. In the second embodiment, although explanation has been made for the intermediate disk  17 , linking members for the bending plates  23  may be buried by insert formation also in the linking boss portions  11  and  14 . 
     In the embodiment described above axis lines of the protruding arbors  22  extending from the intermediate disk  17  on both the sides are aligned one a same line. On the contrary, in a third embodiment, in an intermediate disk  13  of a universal joint  101  illustrated as an example in a perspective view in FIG. 4, round plain protruding arbors  22  for caulking are disposed on diameters orthogonal to each other together with supports  20  on linking surfaces  173   a  and  173   b  of the bending plates  23  so that the bending plates  23  are supported with a phase difference of 90° on both the sides. 
     Although the embodiment described above is so constructed that screw holes  34  are tapped and setscrews (not shown) are used as linking means between the linking boss portions  11 ,  14  and the driving shaft  12  as well as the driven shaft  15 , in the universal joint  10  according to the present invention, linking means described below are possible by using a high tenacity material for forming both the linking boss portions  11  and  14 . The linking means are common for the driving shaft  12  and the driven shaft  15  and linking boss portions  311  (fourth embodiment) and  411  (fifth embodiment) for a dynamic force transmitting shaft  120  will be explained together. 
     FIG.  5 ( a ) is a cross-sectional view of the linking boss portion  311  in the fourth embodiment viewed in a direction perpendicular to the axis line and FIG.  5 ( b ) is a side view thereof viewed along the axis line, indicated partially in cross section. In the linking boss portion  311 , a slit  313  debouches in a base plate  312  forming an angle with respect to the axis line L 1  from a surface  311   a  of a peripheral wall  314  of the boss portion on the side, where the bending plate  23  is mounted, towards another surface  311   b  opposite thereto with a small distance S 1 , and traverses a shaft hole  315  along a diameter. The extremity of the base plate  312  arrives at the neighborhood of the peripheral wall  316  on the opposite side. 
     A bolt hole  317  is formed in the peripheral wall  314  of the boss portion on the side of the opening in a direction perpendicular to the surface of the slit  313 . That is, a bolt throughhole  318  is formed in one of the wall surface portions opposite to each other of the slit  313 , around which a hollow  321  is disposed for sinking a head of a bolt, while a female screw  322  is formed on the other thereof. A bolt not indicated in the figure is inserted into the bolt throughhole and fastened in a direction for reducing the width of the slit  313 . In this way linkage of the linking boss portion  311  with the dynamic force transmitting shaft  120  is achieved by fixing a surface  323  of the dynamic force transmitting shaft engaged with the shaft hole  315  with a small play to the inner peripheral surface  324  thereof by press. 
     FIG.  6 ( a ) is a side view of a linking boss portion  411  in the fifth embodiment and FIG.  6 ( b ) is a cross-sectional view thereof along a line B—B in FIG.  6 ( a ). A slit  413  having a base plane  412  perpendicular to the axis line L 2  is formed in the linking boss portion  411  so that it debouches at a small distance S 2  from one surface  411   a  of the linking boss portion  411  on the side, where the bending plate  23  is mounted, towards the surface  411   b  opposite thereto and traverses the linking boss portion  411  along a diameter. 
     Bolt holes  417  are formed in a direction perpendicular to the slit  413  on each of the sides of the linking boss portion  411 , putting the shaft hole  415  therebetween. That is, a bolt throughhole  418  is formed in one of the wall surface portions opposite to each other of the slit  413 , around which a hollow  421  is disposed for sinking a head of a bolt, while a female screw  422  is formed on the other thereof. 
     Bolts (not shown) are inserted in bolt throughholes and fastened in a direction for reducing the width of the slit  413 . In this way linkage of the linking boss portion  411  with the dynamic force transmitting shaft  410  is achieved by fixing a surface  423  of the dynamic force transmitting shaft engaged with the shaft hole  415  with a small play to the inner peripheral surface  424  thereof by press. 
     Although several preferred embodiments of the present invention have been explained, referring to the drawings, the embodiments do not restrict the present invention. It is a matter of course that it is possible to combine various constructions and embodiments within an extent defined by the claims. 
     As clearly seen from the above explanation, by using the universal joint according to the present invention, since arbors for caulking are formed protrudingly on each of the linking boss portions and intermediate disk themselves by die cast formation, it is possible to reduce the size necessary for fixing the bending plates to the limit without damaging strength and to deal with down-sizing for outer diameters smaller than 20 mm and durability while maintaining a satisfactory precision. In addition, by mass-production by die cast and mechanization of caulking work it is easy to realize cost reduction.